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July 21

Can sound travel through Mars' atmosphere?

Imagine this situation. Two people at a distance are shouting over the surface of Mars (ignore the habitability). Could they hear sound? --IEditEncyclopedia (talk) 04:35, 21 July 2015 (UTC)[reply]

Here is a webpage from NASA JPL about Mars Polar Lander's acoustic microphone. This 1999 space probe was lost and could not operate its instruments atthe Martian surface. But, you can read what planetary scientists expected to hear!

After the loss, the Planetary Society tried to piggyback their experiment on another spacecraft, the NETLANDER probe. That mission never launched; CNES did not fund it. I don't recollect any more recent serious scientific effort - attached to NASA or any other space exploration agency - to place a microphone on Mars. (Here's the project webpage, hosted at Berkeley's Space Sciences Laboratory: Mars Microphone). "Sound on the surface of Mars is expected to be similar to that on Earth, except much fainter because the atmospheric pressure is much less than on Earth. Martian atmospheric pressure is about 7 millibars (as on Earth, this is altitude-dependent), which is less than 1% of the Earth's."

Even if the Martian atmosphere could transfer sound waves - perhaps at very low amplitude - it is unlikely that any such sound would be audible to unassisted human ears. Human ears don't work very well in extremely low ambient pressure. The technical term is "barotrauma": exposing your ear to such low pressure that is not at equilibrium with the rest of your body can cause temporary or permanent damage, including hearing loss. Here's a recent research article: Predictors of ear barotrauma in aircrews exposed to simulated high altitude. We know from experiments like this (and from terrible accidents) that humans don't deal well with low pressure: high altitude air crews and astronauts on the Martian surface are both, for practical physiological purposes, essentially in total vacuum; they must be provided a safe and controlled pressurized environment. If you're interested in "trying it out for yourself" just to see what it's like to expose your ears to near-vacuum conditions, the FAA and the Air Force work jointly to open up their high altitude physiology and safety training program to civilian members of the public every once in a while. You can find details at American Flyers, a commerical facilitator. A friend of mine flew up to Beale for this course some years ago: the effects of severe low pressure were, in his words, quite unpleasant. In addition to physical discomfort, there are also profound psychological effects.

Nimur (talk) 05:11, 21 July 2015 (UTC)[reply]

Just to be clear, sound clearly exists on Mars. It has an atmosphere, which can transmit vibrations. That's all sound is: matter which vibrates. The Martian atmosphere, though quite thin by Earth standards, is real, and thus can really transmit sound waves. You are correct that it is unlikely humans could hear the sound, for a variety of reasons, but the sound clearly would exist, and be detectable, just not by unaided human ears. --Jayron 32 05:31, 21 July 2015 (UTC)[reply]

Be careful, you'll have the philosophers spouting their "If a tree falls in a forest..." nonsense here before too long!. Entirely correct answer though. Fgf10 (talk) 11:29, 21 July 2015 (UTC)[reply]

Ermmmm...wouldn't they be wearing helmets, so they would not be able to the shouts! Sorry! I think Jayron is correct.DrChrissy ^(talk) 14:15, 21 July 2015 (UTC)[reply]

Let's be clear- there are two distinct definitions for sound - see Sound#Definition. One definition is based on physics, and that works fine on Mars, as per Jayron. However, the second definition requires Auditory sensation evoked by the oscillation - So Nimur's perspective is also valid. To go back to the old saw about trees falling that Fgf10 mentions, the solution is very clear - from a physics perspective, sound is just vibration and energy, and of course the tree makes a sound. From a music theory or audiological perspective, sound needs a hearer, and so there isn't a sound if there's no perceiver. SemanticMantis (talk) 14:33, 21 July 2015 (UTC)[reply]

I don't think, even under that definition, sound needs somebody to actually hear it, but just needs to be something somebody could hear, if they were present. In that way it's similar to other human perceptions. We don't theorize that the forest entirely ceases to exist when nobody is looking at it, after all. (I suppose you could, but both would violate Occam's razor, so you would need to explain exactly why it changes depending on the presence or absence of an observer. We do get some things in quantum mechanics that seem to follow that pattern, but that's very different from macro objects.) StuRat (talk) 15:25, 21 July 2015 (UTC)[reply]

No, that's not how the definition works. It doesn't say "capable in principle of being heard", it says "auditory sensation." Using that definition, it's not a sound if nothing hears it. You don't have to use that definition if you don't want to :) SemanticMantis (talk) 15:57, 21 July 2015 (UTC)[reply]

I think it is clear enough that if you could put your ear to a railroad track on Mars, you would hear the oncoming train about as far as on Earth. So the question is how well the sound travels through the Martian air, complicated by the impedance mismatch at the astronaut's helmet (and perhaps at the source, if the source is, say, another astronaut with a smashed radio screaming at a White Ape). I think that the specifics of the helmet are going to matter a lot. But apart from that, well, the sound can be simulated; it's just, alas, that these bastards seem to be holding out on us. Wnt (talk) 19:40, 21 July 2015 (UTC)[reply]

Quick calculation for viability of camping turbine project

I had an idea to turn such a fan as this into a turbine to charge electronics when camping. It's IP55 waterproof.

I'm trying to calculate whether this is viable. I figured if applying 270 mA at 12 V gives a flow of 89.4 CFM (cubic feet per minute) and the wind speed is 5 m/s then the flow rate through the fan blades is 5 m/s x 60 s/min x pi x (0.014 m)2 = 185 litres which is only 6.5 cubic feet. Even if the wind was 10 m/s which is not unlikely but 8m/s is most likely, it's still not going to be producing much power. Am I right in declaring this idea to not be viable? ----Seans Potato Business 14:03, 21 July 2015 (UTC)[reply]

Another reason why it's impractical is that windmill blades need to be far from the ground or anything else that will slow the wind, so you would need to carry a mast with you while camping, too. Alternatively, I like the idea of a flexible solar panel on the top and back of your backpack, so it can charge your devices (in your backpack) while you walk. StuRat (talk) 14:42, 21 July 2015 (UTC)[reply]

It's Scotland so there's plenty of wind, particularly in the hills but not so much sun! 7-8 m/s is a reasonable expectation on the hills. --Seans Potato Business 15:38, 21 July 2015 (UTC)[reply]

On the ground ? StuRat (talk) 15:44, 21 July 2015 (UTC)[reply]

I've no idea. It gets windy enough to make conversation difficult. --Seans Potato Business 16:33, 21 July 2015 (UTC)[reply]

Another option might be piezoelectrics in your shoes to charge things as you walk. That would involve a wire going up each leg, though, into your backpack. StuRat (talk) 15:46, 21 July 2015 (UTC)[reply]

While we're on a digression, I should add that camping frequently involves the availability of free fuel. I don't know if there is a mini steam engine you can carry with you to recharge your electronics, but searching for "camping thermocouple" I found a few links like [1] which sort of make me think there must be a way to recharge items quietly and easily from a campfire. But I'm a bit shy of finding the genuine article at the moment. Of course, if you don't have fuel available you could always find out where the New Horizons mission control replica is and heist its power supply. :) (Fallout... what's a little fallout?) Wnt (talk) 18:02, 21 July 2015 (UTC)[reply]

Here's a review of that product [2]. Here's a review of several off-the-grid chargers, ranging from hand cranks to solar to various combination devices [3]. SemanticMantis (talk) 18:43, 21 July 2015 (UTC)[reply]

Yeah, the general suckiness of thermocouples and the lack of some solid state gizmo that works as quietly, but with the efficiency of a Carnot engine... that strikes me as one of the most gaping holes in our current technology. In this century there are not supposed to be compressors and combustion chambers and fans everywhere, dang it! Wnt (talk) 19:46, 21 July 2015 (UTC)[reply]

And this appears to be the product you're looking for, although if you're prepared to pay a fortune (for the UK you're looking at £300-£500) the Trinity Wind Turbine is a lot cooler (the whole thing folds down into a neat little cylinder about the size and shape of the cardboard tube from a toilet roll). – iridescent 22:05, 21 July 2015 (UTC)[reply]

This guy demonstrates the concept. I think the most practical idea is to use lightweight foldable solar panels. They'll produce some power even in cloudy Scotland though of course much less than in bright sunshine. You probably won't be able to charge something power-hungry like an iPad but it should be possible to charge a radio or maybe a mobile phone. Here are some reviews. Short Brigade Harvester Boris (talk) 05:08, 22 July 2015 (UTC)[reply]

Do people ever make birth control for male nonhuman animals?

I watched a nature documentary that reported that African elephants were confined to nature conservation parks, which had limited space, because human beings were taking over the land for agriculture or something related to the expansion of human development. The elephants thrived in the park too well, and hunting them was no good, because they bereaved the dead. So, a viable option was to invent birth control for the female elephants. This reminded me of the fate of the North American deer and how birth control was invented for the female deer. Do people always make birth control drugs for female animals and not male animals? Is it ever possible to temporarily make infertile a male animal? 140.254.226.190 (talk) 14:08, 21 July 2015 (UTC)[reply]

At least a handful of places have sterilized male squirrels in an effort to control the squirrel population - Santa Monica here [4], UC Davis here [5], Britain here [6]. Many of them use Gonacon - more on that here [7]. SemanticMantis (talk) 14:15, 21 July 2015 (UTC)[reply]

Oh, Gonacon is just a redirect to Wildlife_contraceptive, and doesn't have good info. From the Telegraph article above, "The vaccine stops ovulation and lactation in female squirrels, while halting testicular development in males." The ecoworld article says " Once injected, the animal in question is sterile for 2-4 years." The same article says it can also be used on Feral hogs, horses, deer, cats, and dogs. So the answer to your question is "yes" - Gonacon only started being deployed in the wild fairly recently, but it works on males and females, and will probably increase in usage over the next decade. SemanticMantis (talk) 14:27, 21 July 2015 (UTC)[reply]

I suspect that the question was directed at non-surgical methods, but let's not forget castration.DrChrissy ^(talk) 14:35, 21 July 2015 (UTC)[reply]

Castration changes the physiology and behaviour of male animals, thus vasectomy is the preferred surgical option.

http://www.biodiversityscience.com/2012/12/11/vasectomy-elephant-longer-term/

Roger (Dodger67) (talk) 15:44, 21 July 2015 (UTC)[reply]

Yes it is common practice in the UK (and probably other countries too) to neuter male cats and dogs. --TammyMoet (talk) 17:59, 21 July 2015 (UTC)[reply]

I'll also add that sterilizing females is more effective than sterilizing males, at least for most species. population biology, sexual selection, and fecundity usually work out for mammals such that the number of viable females is the limit to population growth. If you sterilize say 20% of males, you still might find that 100% of viable females give birth that season. But if you sterilize 20% of females, then only 80% can give birth that season. This is why control of wild populations usually targets females or both sexes, and not just males. SemanticMantis (talk) 18:37, 21 July 2015 (UTC)[reply]

Is the correct answer. One human male produces enough sperm to get every woman in the world pregnant in a few weeks. Elephants tend to live in herds of females, with calves, and bulls either solitary or in small groups. The herds and bulls only normally come together to mate. It would only need on rampant bull elephant to mess up the park's program. I suspect the park would want to control the population at a stable level, and keep genetic diversity and family groups. So putting e.g. half of the cows in each herd on the pill would be the best way to achieve population control, whilst retaining diversity. Martin451 16:38, 22 July 2015 (UTC)[reply]

Wild animal photos

Wikipedia:Help_desk#Wild_animal_photos Can someone identify two animal species if provide the photos?Lbertolotti (talk) 20:30, 21 July 2015 (UTC)[reply]

Without seeing the photos, we have no way of knowing whether the species can be identified. Certainly we succeed in making positive identifications sometimes, but it very much depends on the images, and the amount of other information provided (not least the location where the photos were taken). You should note however that when it comes to insects (like the fly which is one of your subjects), it is sometimes only possible to make a positive identification of a particular species through microscopic examination and/or dissection. AndyTheGrump (talk) 20:39, 21 July 2015 (UTC)[reply]

@AndyTheGrump Ok, do you want me to use the Wikimedia uploader for this?Lbertolotti (talk) 22:17, 21 July 2015 (UTC)[reply]

I've added some other wild animals images, luckily we will identify them all.Lbertolotti (talk) 16:54, 22 July 2015 (UTC) Perhaps we should change the images descriptions now.Lbertolotti (talk) 19:05, 26 July 2015 (UTC)[reply]

Bird

Well here it is.Lbertolotti (talk) 00:34, 22 July 2015 (UTC)[reply]

Hey that's a start! Is this near Anchieta,_Espírito_Santo? I can't find a WP article related to Anchieta Island. SemanticMantis (talk) 01:32, 22 July 2015 (UTC)[reply]

Anchieta Island, in the northern coast of the state of São Paulo, Brazil, famous as the site of a state prison.Lbertolotti (talk) 01:42, 22 July 2015 (UTC)[reply]

The photo is very difficult to make out, but I'm guessing that's a plover of some sort. There are a lot of plovers in South America, and many of them have dark backs and white fronts (which is all the colouration I can make out in that photo). Did the bird resemble any of the ones on that list? Smurrayinchester 08:00, 22 July 2015 (UTC)[reply]

Looks like a plover, but the bird's body proportions are different from those images. Look at the size of his legs compared to his torso.Lbertolotti (talk) 12:56, 22 July 2015 (UTC)[reply]

I was thinking it looked more like one of the stilts or avocets. SemanticMantis (talk) 14:24, 22 July 2015 (UTC)[reply]

Am I seeing things, or does the bird have a plume of feathers from the side/back of the head?DrChrissy ^(talk) 14:56, 22 July 2015 (UTC)[reply]

His head was quite smooth, unfortunately I couldn't get closer or he would have flown away.Lbertolotti (talk) 15:21, 22 July 2015 (UTC)[reply]

But there appears to be something white protruding from the side/back of the bird's head?DrChrissy ^(talk) 15:34, 22 July 2015 (UTC)[reply]

Fly

Looks like one of the Musca sp. but getting the exact species may be difficult, if not impossible. Roger (Dodger67) (talk) 19:07, 22 July 2015 (UTC)[reply]

All Musca sp have 6 legs?Lbertolotti (talk) 00:51, 23 July 2015 (UTC)[reply]

All insects have 6 legs, so, yeah. --Jayron 32 01:41, 23 July 2015 (UTC)[reply]

Fish

The black spot on the tail is usually indicative of a Red drum, aka Channel bass, they're a rather ubiquitous fish. However, this fish doesn't seem quite like a red drum because a) the spot is dead center on this fish, and on a red drum, it's closer to the top and b) this one doesn't look like it has a red tint, whereas the red drum does. That's the best I can figure out though. --Jayron 32 01:48, 23 July 2015 (UTC)[reply]

Looks like a juvenile French grunt to me. As they mature they loose the spot and become more yellow. However, in his Reef Fish Identification, Paul Humann follows his juvenile French grunt description with:

These marking are nearly identical to those of several juveniles and adults in the family, making identification difficult. Similar to pale phase of Cottonwick, H. melanurum, distinguished by lower body stripes that are horizontal. Similar Tomtate, H. aurolineatum, distinguished by lack of yellow markings, especially on the belly.

It may not be possible to distinguish between them with your photo. I don't know about the distribution of the other two, but French grunts are very common in Noronha. -- ToE 14:50, 25 July 2015 (UTC)[reply]

Fish2

Resolved

Hard to say from the angle, but I'm inclined to say some variety of puffer fish. Snow ^{let's rap} 23:27, 22 July 2015 (UTC)[reply]

Possibly of genus Tetraodon or Tetraodontidae? Don't we have a dedicated ichthyologist here at the ref desks? Who is it I'm thinking of? Snow ^{let's rap} 23:37, 22 July 2015 (UTC)[reply]

Ah, ok, remembered that completely wrong, but still, as Obsidian Soul has answered other fishy questions, perhaps he can give an appraisal of my best guess so far, which is that this a variety of (or close relative to) the checkered puffer, as seen in this picture of a specimen off the coast of Belize? Snow ^{let's rap} 05:22, 23 July 2015 (UTC)[reply]

@Obsidian Soul

Not sure who the helpful gnome is who added this, but I'm curious, is the {{u|}} template once again failing to send automated notices? Snow ^{let's rap} 12:14, 25 July 2015 (UTC)[reply]

It's a Scrawled filefish. Here is a side photo of one, also at Noronha. -- ToE 13:05, 25 July 2015 (UTC)[reply]

Ah, man, I didn't even get the order right? Snow ^{let's rap} 00:15, 26 July 2015 (UTC)[reply]

Goose

Here I was thinking about the white ones.Lbertolotti (talk) 16:54, 22 July 2015 (UTC)[reply]

These appear to be Roman Tufted Geese. Be aware that the plural of goose in English is geese, not gooses. (Gooses are rude pinches to the buttock, so the mistake can lead to unintended comedy.)

The knob at the base of the upper beak and the colouring matches the Chinese goose. -- Roger (Dodger67) (talk) 19:16, 22 July 2015 (UTC)[reply]

I can't say I really see an orange fleshy knob above the nares. Could be, but the picture is at a bad angle and blurry. μηδείς (talk) 01:39, 23 July 2015 (UTC)[reply]

Sand Dollar

Looks consistent with Mellita quinquiesperforata, which was very commonly found in a survey in a bay a bit farther south [8]. --Amble (talk) 21:38, 22 July 2015 (UTC)[reply]

Can u tell if this one was dead or alive?Lbertolotti (talk) 23:15, 22 July 2015 (UTC)[reply]

It still has spines and a lifelike color, so it's either alive or recently deceased. If it had been long dead, you would just have a bleached hard test. I can't say more than that based on the photo alone. Did you pick the animal up from underwater, or did you find it on the sand at the beach? --Amble (talk) 23:22, 22 July 2015 (UTC)[reply]

That was a long time ago, but I think the waves brought him to the sand.Lbertolotti (talk) 00:48, 23 July 2015 (UTC)[reply]

Bird

Brown booby ? Although yours looks to be grey, not brown, but they do range in color to blacks, especially in juveniles. StuRat (talk) 17:24, 22 July 2015 (UTC)[reply]

Based on that reasoning, mine would be even younger than the ones you showed.Lbertolotti (talk) 17:53, 22 July 2015 (UTC)[reply]

Check out this juvenile Brown Booby: [9]. It has only a very subtle lightening of the color on the bib, which I believe I see in your pic, too (although the bib area is almost entirely hidden in your pic). This one has a brown beak and feet, though, unlike yours. StuRat (talk) 17:58, 22 July 2015 (UTC)[reply]

Sea Urchin

Worm

Worm 2

That looks like a caterpillar (a larval moth or butterfly), not a worm. StuRat (talk) 17:16, 22 July 2015 (UTC)[reply]

(I changed title to add the 2, since sections with identical titles can cause bugs.) StuRat (talk) 17:18, 22 July 2015 (UTC) [reply]

Is there some way of being sure? Lbertolotti (talk) 17:23, 22 July 2015 (UTC)[reply]

The first worm is clearly an (oligochaete) earthworm, given the obvious and diagnostic feature of the clitellum, and the lack of the specializations of a leech. The second creature is a caterpillar, given the obvious diagnostic feature of the six true legs and the parapodia. μηδείς (talk) 19:04, 22 July 2015 (UTC)[reply]

How many times per day does a normal person leave their house?

Assume a democratic western country. Count things like going to work, going to the shops, walking the dog, etc but only if the person returns home between each activity. If the person does all those things but does not return home between each one, then it only counts as having left the house once. — Preceding unsigned comment added by 193.50.192.37 (talk) 19:04, 21 July 2015 (UTC)[reply]

You need to be more specific about what you mean by "normal". ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:16, 21 July 2015 (UTC)[reply]

The dictionary definition will do. — Preceding unsigned comment added by 193.50.192.37 (talk) 19:23, 21 July 2015 (UTC)[reply]

That has 21 separate definitions. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:29, 21 July 2015 (UTC)[reply]

Along with the problems as to what is "normal" and what isn't there are too many variables for there to ever be a definitive answer. House in the city or the country? Weekday or weekend? Single person or family? etc etc. MarnetteD|Talk 19:34, 21 July 2015 (UTC)[reply]

Why is it a problem to define a norm? The question is clearly statistical - in which norms are common. 209.149.113.45 (talk) 19:39, 21 July 2015 (UTC)[reply]

I am normal and I normally leave my house once a day; sometimes I go out again in the evening but not normally.--Shantavira|^{feed me} 19:51, 21 July 2015 (UTC)[reply]

As noted by MarnetteD, one's occupation is likely to drive the answer. Someone who works in a company might well leave home just once or twice a day. Someone who works at home might go in and out of their door many times in one day - or possibly not at all. Someone who's a traveling salesman or a touring performer might go months between stays at home. So the question as it stands can't really be answered. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:07, 21 July 2015 (UTC)[reply]

All of these concerns about what is normal, occupation, etc. could be handled by reporting a mean. Table 2 here [10] presents some data. They come up with 4.3 trips per person per day. (and to everyone else, please at least attempt to do some research or find a reference before challenging the question.) SemanticMantis (talk) 21:02, 21 July 2015 (UTC)[reply]
- It remains to be seen whether that's what the OP really wanted. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:15, 21 July 2015 (UTC)[reply]

That's what they're supposed to be getting, though, this being the reference desk and all. I'm fairly certain they didn't ask for sophistry about their question. Ian.thomson (talk) 21:21, 21 July 2015 (UTC)[reply]

If the question is vague, it's not our fault. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:24, 21 July 2015 (UTC)[reply]

The item linked to is only about how people travel not the number of times one might leave the house in a day so it is only a partial answer to the OPs question. This proves my point about the difficulty in getting a definitive answer. BTW my post was not sophistry. MarnetteD|Talk 22:18, 21 July 2015 (UTC)[reply]

How to reliably kill all transponders on a car

I have seen different, vague, confusing things about how many transponders are put on modern cars. In the light of this story, this is no matter a matter for vague wondering. Of course, a critical security patch is available ... the funny thing about critical security patches is, though, there's always a next one, right up to the end of the supported life of a product, no matter what the product. If a driver, hypothetically, would for some reason prefer not to find his car repeatedly running him over and over under the guidance of its parallel parking feature and rear-view camera on the same unlucky day that the North Koreans cause millions of simultaneous traffic accidents in the space of an hour, it would appear that a no-nonsense Battlestar Galactica approach is needed, and fast.

So can anyone point to resources that a) try to go through all the known types of cars and say where everything with an antenna of any kind may be hidden away at, b) give instructions how to physically destroy them, and c) can you inform whether there are any legal coercive tactics already set up to try to prevent this because of the loss of surveillance data?

P.S. this is not a personal request for advice. I have a car from 1997 and a map. :) Wnt (talk) 20:37, 21 July 2015 (UTC)[reply]

Does Paranoia not have the answers you are looking for? --Jayron 32 21:56, 21 July 2015 (UTC)[reply]

This is a real news story. The vulnerability has been known for nine months, but not that many vehicles even received the patch. Even if you believe there's no other way in and the security is perfect now, that still leaves any good group of hackers with a beautiful opportunity to make Pearl Harbor look like a kid saying boo. Wnt (talk) 22:01, 21 July 2015 (UTC)[reply]

Youtube has a very comprehensive and thorougher instructional video of how to disable, stage-by-stage any unwanted electronic car gadgets in just 4 and 35 seconds. Hope this helps.[11]--Aspro (talk) 23:03, 21 July 2015 (UTC)[reply]

Imagine the following scenario, which I think is actually FAR more likely than the above news story (I actually question how "plausible" some of the claims in the "news story" are, is it even possible to disable a car's brakes from the computer? I don't believe consumer cars have brake-by-wire yet, I know some cars can automatically APPLY the brakes, but I've not heard of a car where the pedal can literally be uncoupled from the brakes, but I'm not any kind of expert so I could be wrong.) SO, imagine you do go in and disable some "transponders" in your car, but you've also inadvertently disabled some safety feature, like Automatic braking for example, and you have an accident, and the insurance company finds out that you've "hacked" the car, I imagine you would be up a proverbial creek, all your warranties would be void and you would possibly be personally liable for any and all damages. Vespine (talk) 23:11, 21 July 2015 (UTC)[reply]

Sorry, this is the link to the real article. Note the citations to at least two other tests where brakes were disabled. Wnt (talk) 00:03, 22 July 2015 (UTC)[reply]

These are quite sensational claims! Is there any evidence that the attack could succeed against an unmodified vehicle? Have there been any independent verifications of the claims?

The story claims that the attackers demonstrated remote attacks that can disable a vehicle as it operated on a public roadway (the article says the motor vehicle was operated on Interstate 64 in Missouri when the brakes were intentionally disabled). It's alarmingly unethical - and very probably illegal - to demonstrate these vehicle failures while operating a vehicle on a public roadway in the state of Missouri.

Nimur (talk) 01:14, 22 July 2015 (UTC)[reply]

Either the main journalist is sexing the story up, and/or all three of them are complete idiots. So far as disabling all transponders goes, it would have to depend on both the model and the options fitted, there is no general solution. Greglocock (talk) 01:29, 22 July 2015 (UTC)[reply]

It seems ludicrous to risk actual harm to uninvolved individuals, when the technical merits of these claims could be equally-well demonstrated on a closed course - or even on a non-moving vehicle! To me, this irresponsibility suggests a serious lack of integrity - and causes me to doubt the veracity of the claims.

Besides, even if we wish to accept the claims exactly at face value... so what are the actual implications? Are we supposed to start panicking because a psychopathic attacker who wishes to destroy vehicles and harm humans can cheaply and anonymously attack a vehicle's brakes? The attacker could throw rocks at cars, or drop caltrops on the freeway, too... there are thousands of ways that a person can wreak harm on unsuspecting soft targets. This particular harm-by-cyberattack is difficult to execute, and depends on specific details in specific incarnations of certain technologies ...so, where is the novelty?

Honestly, I am more worried about enemies and random psychopaths who would drop caltrops on roadways than I am worried about computer-enthusiast miscreants who attempt to "hack" vehicle safety and control electronics. How serious a threat are caltrops? They are so serious that they are listed as Item #1 in the CIA virtual Museum Tour (with photos!). You don't need to use advanced technology to cheaply and effectively execute anonymous attacks on public infrastructure.

So, Wnt, as you harden your security against electromagnetic threats, what preventive defenses are you taking against caltrops? How secure is your car against rock-throwers? ...Vandals who slash tires or cut wires? ... Sugar in the gas tank? ...Snipers emplaced on the roadway? How about the more mundane threat of running our of gas due to an economic denial of service atrack? Why do you choose to fixate only on one specific category of potential threats to your vehicle? In one of our recent discussions on security as it pertains information and technology, I linked to some great resources to help you consider the whole security picture - specifically, the plenum session of the President's Cyber Security summit in January 2015. Again, in a computer security question that came up in March of this year, I linked to the computer security section of the Marine Corps Physical Security manual. Your vehicle's greatest security weakness is probably not its computer system or its wireless radios. If you are so concerned about esoteric computer security threats that you would alter your motor vehicle in an effort to remove radios... perhaps you should hire a guard for your vehicle to protect against other, more perspicuous vulnerabilties.

Nimur (talk) 06:02, 22 July 2015 (UTC)[reply]

I think you're missing the point. This one brand controls (and I mean controls) 470,000 vehicles. The articles suggest others have the same problems. Now yes, two hackers playing with one vehicle is a small threat. But a group like North Korea or the Syrian Electronic Army could line up a botnet with thousands of computers, infect millions of vehicles, and SIMULTANEOUSLY crash a large fraction of them. And guess what -- if there are two hundred thousand traffic accidents on the road, you can hit your Onstar button but the cops ain't comin! Now if North Korea could put sugar in the gas tank of every car in my neighborhood, I'd want to harden against that, sure ... though even if they could, it's less distressing to have your vehicle sabotaged when you're not in it. As for ethics, well, is putting a car in neutral on the highway really that much more unethical than putting half a million cars on the road that can be tracked, spied on, and even crashed remotely? (the article skirted some obvious issues, like whether the hackers could tap into the microphone and listen to the occupants' conversations) Wnt (talk) 10:24, 22 July 2015 (UTC)[reply]

I wonder how much access they had to the target vehicle before the demonstration. Greglocock (talk) 10:38, 22 July 2015 (UTC)[reply]

I doubt that it is chicanery on the part of the Wired author. A bill was introduced yesterday in response to this [12] but the details aren't available yet at that link; from the description it doesn't sound like it goes far enough. I don't want car companies to protect their records of everywhere I've ever driven; I don't want them to have them at all. And I don't want an interface to be "secure", I want it genuinely not to be there at all. Wnt (talk) 10:54, 22 July 2015 (UTC)[reply]

How much access did they have to the vehicle? They own it. They initially connected to the Jeep using the hard-wired technician's connection. Then, they rewrote the firmware of the controller. Then, they called a friend who happened to be a writer and said, "Hey, hop in our Jeep and take it for a ride and see what we can do!" This is in no way equivalent to the headline that I saw today: "Hackers take complete control of a smart car from across the globe!" 209.149.113.45 (talk) 14:52, 22 July 2015 (UTC)[reply]

Source for this additional info? It's interesting since the Wired article seems to imply as Wnt suggested that they were able to take control over it remotely without physical access so either with the default firmware, or with new firmware they can upload without physical access but they won't reveal much more until the Black Hat conference. (However they learnt about the vunerability initially.) I presume that in reality, what they mean is that it can happen remotely, but only with special firmware that can be uploaded by someone with physical access which can then use the cars built in system to accept remote commands. Of course one thought is that as long as this can happen with access to the technician port, you could enable remote control simply by designing a device which can be plugged in and is capable of accepting remote commands. This may cost more since you need a unique device for every vehicel you target (ignoring any you recover for later use) and also has a higher risk of being noticed (although in reality, I suspect someone with sufficient resources could make a device most people are unlikely to notice unless they look very carefully and while I'm not sure where the port is on these cars, I suspect people rarely look at them), but otherwise would be just as effective. Now if the vehicle had a clear indication that the technician port was being used on the dashboard, this may be noticed, but that's presuming it can't be hidden by someone with access to the technician's port. Nil Einne (talk) 16:24, 22 July 2015 (UTC)[reply]

It is actually the lack of a reputable source that causes me to disbelieve the claims in this Wired article. Has there been any independent verification? Is there an entry in the national Common Vulnerabilities and Exposures database? What is the entry number? Which peer-reviewed computer security or automotive engineering journal has published a study of this problem? In this case, all the syndicated re-published news articles in the world are worth less than a single good technical write-up in an industry journal.

Instead we are asked to believe that two independent researchers accomplished an incredible feat. Of course it is possible that they discovered and exploited a serious oversight in production vehicles; but this is unlikely. What we need is independent verification. These researchers purport to favor complete disclosure instead of a silent behind-the-scenes security fix. Ok, great - so why didn't Wired link to a CVE entry and a technical whitepaper? Apparently the researchers do not wish to disclose their methodology or permit outside scrutiny?

This is the difference between sensational journalism that has mass appeal to uninformed users of technology, and actual computer security engineering that can be taken seriously by informed individuals. Nimur (talk) 16:56, 22 July 2015 (UTC)[reply]

This "story" is being heavily exaggerated by the media. This morning, I saw a headline "Hackers take complete of a smart car and smash it into a ditch from across the globe!" So, you have to avoid anything written since July 18, 2015. All you will find is garbage. In the original wired article by Andy Greenberg (who mysteriously becomes a woman in articles I've seen written in the past few days), he clearly states that he was given the car by the hackers and he explains that they messed with the stereo, windshield wipers, and set the transmission into neutral. Then, he went to an empty lot and they did more fun stuff. How? Go back to the previous article that Andy wrote. He explains that they sat in the back seat and were directly wired into the car. They replaced the firmware and were able to control the car. So, who are these hackers? Charlie Miller and Chris Valasek have been "hacking" the firmware of various cars for about five years. They work for IOActive and are trying to PROTECT cars from hackers, not turn the world into a global demolition derby. They are trying to perfect a method of rewriting the firmware so they can remote-control as much of the car as possible, all in an attempt to uncover and fix weaknesses. But, all they can control is what the computer controls. Does the computer control the steering wheel? No. Does the computer control the brake (not the ABS - the physical brake)? No. All of that nonsense is coming from Andy Greenberg, who obviously has a tendency to exaggerate. 209.149.113.45 (talk) 17:09, 22 July 2015 (UTC)[reply]

Trying to trace back the exaggerations...

Claim: Hackers disabled the brakes. Original articles: Hackers turned off the engine. Power brakes went out. It was much harder to stop the car, but it was possible - especially if the driver was smart enough to use the emergency brake.

Claim: Hackers took control of the steering wheel. Original articles: Hackers could turn power steering on and off. If that happens while turning, the wheel will jerk as it becomes easier and suddenly harder to turn. This does not give the hackers ability to turn the wheel.

Claim: Hackers disabled the car. Original articles: Hackers were able to shut off the engine. Hackers were able to shift into neutral. That does temporarily disable the car, but you can start the engine back up or shift back into drive.

Claim: Hackers took control of a smart car from an unsuspecting young woman and smashed her expensive SUV into a ditch. Original article: ??? This claim has nothing to do with anything previously written. 209.149.113.45 (talk) 17:44, 22 July 2015 (UTC)[reply]

First I should mention I've read the Wired article more carefully and realise it does actually specifically mention rewriting the firmware. I missed that because I only skimmed through the article and it came in a much later section. My bad. (In some ways it didn't really matter whether it was original firmware, or remotely modified firmware for my main point, but I didn't explain this very well.)

Anyway it sounds like you're conflating two different things. The article Wnt highlighted and you yourself pointed to refers to he latest research and says that the car can be controlled remotely. It specifically mentions the previous research which required physical access, but says it was with not only different cars, but different brands of cars. These cars don't use the Uconnect system they were targetting (well it doesn't directly say that, but it's fairly obvious from what was written and some research).

The article doesn't directly state, but seems to strongly imply that no physical access was ever required as it mentions a security flaw (*1), that they wanted to demonstrate an attack which required no physical access (*2) and in particular where it mentions rewriting the firmware, this comes right after they mention the vunerability. Later it goes on to discuss patching the bug etc. No where does it seem to suggest they needed physical access to enable any part of the attack.

So while we can't rule out journalistic sensationalism, it does seem to me that the article strongly implies this flaw did not require physical access and from the researchers POV, it sounds to me like that's definitely what they were trying to achieve. (And per my earlier point, the previous research is interesting, but if anything suggests this flaw doesn't require physical access rather than suggesting it does.)

I don't know if anyone disagrees that the car belong to the hackers, but this tells us nothing about whether they needed physical access to be able to do all they did. *3 (There are many obvious reasons why they would be using their own car.) It also fairly obvious that the hackers are not intending to do anything harmful, but again, this tells us nothing about whether or not they needed physical access.

The only sign we have of that is they seem to be talking about it openly, but that is also explained, there is already a patch for the flaw *4 and they aren't going to release the part which enabled them to rewrite the firmware. (Which also seems to imply they didn't need physical access to me.

*1 It's possible the security flaw is there should be no connection between the network portion and the control portion regardless of firmware changed by physical access. I don't think that's what's being referring to do for the reasons explained later.

*2 Which could mean no physical access was required at the time of control (rather than ever). However as I pointed out earlier, while less impressive and more expensive, you could easily make your physical access attack in to a remote one by adding a remote control device connected to the technician port which in reality very few people are likely to notice if done well. So it doesn't seem to me an attack which required physical access at some stage is really that much more impressive than an attack which requires constant physical access.

*3 By which I'm only referring to after the've worked out what they can do. They're likely need physical access or access to the source code etc to work out how to carry out the attack in first place. Trying to work it all out remotely would likely be an exercise in frustation

*4 I don't think the fact the patch requires physical access tells us much about whether rewriting the firmware using a vunerability. Using a vunerability to patch a flaw is a very bad idea even for a computer system. The controversy over white angles who've done it demonstrates that. It's surely an even worse idea for a car. "Whoops I BSODed your computer" could easily become "Whoops I caused you to have an accident killing yourself, your children and plenty of other children".

P.S. In response to Nimur, but also to the to some extent IP, remember that the article strongly implies that the researchers are fully willing to disclose the details except for how to rewrite the firmware. They only haven't done so yet because they are waiting for the security conference. AFAIK, this practice is common among respected researchers in many computer science fields. Related practices are common in other fields. They have already disclosed the flaw to the relevant parties 9 months ago such that a patch exists. We may dislike their willingness to work with the journalist, who published this story now before the conference (probably with ther permission) with so little details, but in reality that too is fairly common in the modern world in many different areas of science, like it or not given the various demands.

Nil Einne (talk) 19:30, 22 July 2015 (UTC)[reply]

I agree with you, Wnt, that the risks seem to outweigh the benefits, some of which just seem silly. You can turn up the volume on your car from the Internet now, versus reaching all the way over to the radio ? Sure, that's worth making a car that can be hacked ! Here's a list of the features of the Uconnect system: [13]. Of those, several seem potentially dangerous if hacked or if they just have a bug. Turning the volume to a deafening level could cause an accident (and I had a TV where the remote kept sending the volume up signal, so this even seems possible just as a bug). Turning the heat on max on a hot summer day could be dangerous (hopefully the occupant could still open windows). The autostart feature could be used to run the car out of gas or, if in a garage (particularly attached to a house), create a dangerous build-up of carbon-monoxide. If the car isn't smart enough to check to see if the car is running before trying to start it, then that could cause something bad to happen (not quite sure what). StuRat (talk) 16:33, 22 July 2015 (UTC)[reply]

@209.149.113.45: See [14]. Despite what you say, the computer does appear to be controlling the steering wheel. (I can't say from that video what would happen if the driver and the computer had a dispute, though) Wnt (talk) 19:22, 22 July 2015 (UTC)[reply]

I should add that apparently Hacking Team had a similar opinion in 2008; I found this by searching Wikileaks' trove for 'Onstar': [15] (which is mostly commenting on [16], but they sound like they might know something themselves) Wnt (talk) 23:28, 22 July 2015 (UTC)[reply]

A 60 Minutes report shows a demonstration of a car being remotely hacked, giving the hacker the ability to apply or disable the brakes and control other systems: [17] See starting 6:45 into the video. Edison (talk) 19:54, 24 July 2015 (UTC)[reply]

I believe the ability to control the brakes and steering wheel to be designed for automatic parallel parking. Normally the driver would put the car in reverse, and let the car park itself. However, once the ability exists for those systems to be automatically controlled, then unless there is a mechanical lockout of some type, the potential for the software to be modified to allow brakes and steering to be remotely controlled also exists. Automatic steering could also be present for lane maintenance, and automatic braking could exist for an accident avoidance system or Cruise Control (although CC typically lacks brake control). CC also involves automatic control of the accelerator, but that could be a mechanical system, much more difficult to hack. Just keeping all the various system isolated would also make them safe from hacking. That is, there should be no signal wires connecting any critical system like brakes, acceleration, or steering to any system which allow for remote control. (Power might be shared by systems, but that has less risk.) StuRat (talk) 16:38, 25 July 2015 (UTC)[reply]

I'm glad that a few people think I'm not nuts for asking, but I do regretfully have to note that nothing here has answered if there are instructions how to track down and disable all transponders (aside from the car crush video, which among other things I doubt is all that reliable a method!) Wnt (talk) 18:04, 25 July 2015 (UTC)[reply]

July 22

Adult Growth of Vertebrates

Mammals grow until they are adults and then stop growing, so that humans are the same height for most of their life. Birds grow until they are adults and then stop growing. Some long-lived vertebrates, including some fish and crocodilians, continue to grow. I am assuming that the difference is that mammals and birds are warm-blooded, and that so-called cold-blooded reptiles and fish continue to grow. Is that correct, and is there a reason, such as having to do with energy use in adult warm-blooded vertebrates, why growth stops for warm-blooded vertebrates? Robert McClenon (talk) 02:55, 22 July 2015 (UTC)[reply]

The truth is Robert, there's a slight adjustment to be made in the way you are conceptualizing this issue that will greatly improve your understanding of it. Specifically, most any complex organism's growth (and especially that of metazoans) will eventually plateau - these organisms simply very greatly in the length of time it will take them to reach this point, their liklihood of dying first from predation, disease, or an environmental factor and the exact nature of the interplay between environmental constraints and innate epigenetics. In a sense though, you are correct that certain clades show a preponderance for having higher populations of individuals that have stalled out in their growth; its just that the explanation for this difference is often not entirely explained by the relative difference in any two species' physiologies with regard to just things such a growth factors, cellular differentiation, replication errors, and the like, but rather also the entire sum of their genetic qualities and their environmental context (including such things as diet, space, breeding context and other factors which influence growth through epigenetics, but then also dumb luck with regard to survival). So you will find that phylogenetics only sets you up so much to understand which of these species will have great variety in ultimate sizes of individual specimens and/or what proportion of the population have begun to slow (or even have stopped) in their growth; sometimes two very closely related species will vary drastically in this regard, simply because they have a slightly different ecological niches. All of this is not to say that there aren't clades which have genetic features that allow them to grow more tissue of certain types without stalling out or to avoid cancers and other effects of senescence; it simply means that for most organisms, the situation is a little more complex than just these factors. Of course, it is true, since you specifically cite adulthood, that certain species are more likely to stop growing roughly at sexual maturity. As you observe, this trait is particularly strong in Mammalia, but you'll also find great variation in other kinds of tetrapods. Forgive the lack of citations; super exhausted here; will try to cobble together the sourcing and more complete discussion of these issues tomorrow. Snow ^{let's rap} 07:25, 22 July 2015 (UTC)[reply]

There are some differences in the biology of bone growth (which is usually what we really mean by "growth"; otherwise we find ourselves all too capable of growing in mass throughout adulthood!). I haven't given this paper a tenth the attention it merits, but see [18] which discusses the differences between Actinopterygii and tetrapods. So in modern fish, "Perichondral bone is deposited on the surface of the cartilages and continues to grow centrifugally as periosteal bone" whereas in tetrapods a rod of cartilage is quickly covered by bone, except for growth at the epiphyseal plate, which ultimately fuses to stop any further bone growth. That said, epiphyseal fusion still does not have to happen; that is a sort of choice made by the developmental plan of the organism.

I would speculate that there may be adaptive reasons for the differences. We have all probably seen pictures of human 'giants' who can't stop growing, hobbling around on crutches. It seems like aquatic organisms are less affected by changes in scale than those on land, since they rarely need to support their own weight. But that's purely a guess. Wnt (talk) 12:50, 22 July 2015 (UTC)[reply]

Well, I am unaware of any documented case of a human being continuing to grow for the duration of their life, long after reaching sexual maturity. Even those with gigantism eventually top out or begin to slow, though yes, generally well past a point where their general health has begun to suffer as a result of their atypical biomechanics. Though, to be fair, some have continued to grow at least into their 20's and in the most extreme cases, before modern clinical analsysis and mitigating treatment, they tended to die not long after; if not for the pressure this unconstrained growth put on their systems, its hard to say whether it would have otherwise been boundless, but I suppose it is feasible a pituitary disorder would cause them to continue to grow for years more yet.

But returning the issue of variation amongst species and your guess, I'm doubtful (and have never seen any research or researcher speculation that suggests) that the difference is to any significant extent driven by differences in selective pressures with regard to the ocean vs. land-dwelling; many terrestrial species display "life-long" growth and many aquatic species do not. For that matter, I cannot recall seeing support from a researcher along the lines of Robert's notion that it is determined significantly by differing aspects of the physiology of cold-blooded vs. warm-blooded organisms. Rather it has more to do with the creature's complete ecological niche and A) the practical benefits of being large (and it's cost in resources) vs. the advantages of staying small (including smaller dietary needs) B) sexual selection, C) the nature of its genetics with regard to this sustained growth and whether it is likely to cause abnormalities as a result, and D) epigenetics; note that not all of these creatures are determined to grow large, some will only continue to grow if the conditions are just right. Snow ^{let's rap} 21:47, 22 July 2015 (UTC)[reply]

From a the perspective of evolution and ecology, this is about the trade-offs between allocation of resources to growth vs. reproduction. Lifetime fecundity is one of the main drivers of growth patterns - vertebrate organisms are generally hovering around a local maximum where growth is halted after sexual maturity, unless additional growth will increase lifetime fecundity. A key term is indeterminate growth, though that is used more often for plants. The broad topic would come under Life_history_theory, See e.g. here [19], [20], [21] for (freely accessible) research discussing why indeterminate growth occurs in animals, and how it's tied to resource allocation and impacts of life-history strategies. SemanticMantis (talk) 14:35, 22 July 2015 (UTC)[reply]

Solar system distances vs. gravity

Looking at real-scale models of our solar system, it occurred to me that if the sun was scaled down to a 1 cm wide ball, pluto would be a mere grain of dust at about 40 meters away. Yet the gravitational forces make it rotate around the sun. How can that be, especially with all other planets in between? Gil_mo (talk) 09:55, 22 July 2015 (UTC)[reply]

It goes to show you how strong gravity really is. Bear in mind that in space there is no friction, so your Earthly impressions of gravity don't apply to space. Things clump together in space. If there was no strong force of gravity, there wouldn't be planets.217.158.236.14 (talk) 10:26, 22 July 2015 (UTC)[reply]

Friction exists in outer space. I think what you intend to say is that in a vacuum, there is negligible air resistance... and even though this statement is true, gravity is not in any way reduced by friction. (Perhaps you are conflating the force due to gravity with the total net force on an object, which is computed by summing gravity with any other force that might affect some object). Other forces, including frictional resistance force, may oppose gravity in some cases, reducing the net force; but they don't actually reduce the magnitude of the force of gravity. This is a really important distinction that is usually learned in your first physics courses, and the difference between "net" and "component" forces still matters, even in advanced topics.

In fact, according to our theories that are as accurate as our best we can measurements, force due to gravity is unhindered by anything : there is no way to "shield" the effects of gravity. This means that even our outer planets feel the force of gravity: the effect is not "blocked" by inner planets. In fact, if you apply Gauss's law for gravity, the outer planets actually experience more inward pull, because they are pulled inward by the sun and all the other matter in the solar system! Nimur (talk) 16:16, 22 July 2015 (UTC)[reply]

As for "all the other planets" - the sun makes up an incredible 99.8% of the solar system's mass, and almost all of the rest is Jupiter. Uranus and Neptune do have a small impact on Pluto's orbit - over its history, they've nudged it here and there - but they don't even come close to the sun's effect. The closest Pluto comes to another planet is that it sometimes passes 11 astronomical units (AU) from Uranus, while the furthest it ever comes from the Sun is 49 AU. Even at those extremes, the Sun's pull on Pluto is a thousand times greater than that of Uranus (you can see the sums here and here). Smurrayinchester 10:52, 22 July 2015 (UTC)[reply]

Actually, gravity is the weakest of the fundamental forces, by far. It's astonishingly weak compared to the others. Just think about it: every time you lift anything, you're overcoming the gravitational force of the entire Earth, all 5,972,190,000,000,000,000,000,000 kilograms of it, on that object. The apparent weakness of gravity is a big reason why a lot of physicists like string theory, because it predicts the existence of extra dimensions. If gravity "leaks" into those extra dimensions, that would explain why it appears so weak in the three spatial dimensions that we perceive. The fact that Pluto is still captured by the Sun's gravity despite the great distance between the two is, rather, a testament to how massive the Sun is. Stars are ENORMOUS. The Sun contains over 99% of the entire Solar System's mass. Everything else is a rounding error. An even better illustration of the Sun's massiveness is the Oort Cloud, which is over a thousand times farther from the Sun than Pluto is, yet still bound by the Sun's gravity. But even the Sun is a lightweight compared to some other objects in the universe. Our Sun, along with everything else in the Milky Way, orbits the supermassive black hole at the center of our galaxy. It's 26,000 light-years away from us, yet so massive that it still pulls us along for the ride. And in turn, our galaxy is gravitationally bound up with other galaxies into mindblowingly huge groups and superclusters of galaxies. Just look at something like the Great Attractor, which has a gravitational influence that extends for hundreds of millions of light years, to truly get a sense of the scale of the universe. I'll quickly plug Crash Course Astronomy here for anyone looking for a nicely accessible introduction to space. --108.38.204.15 (talk) 11:36, 22 July 2015 (UTC)[reply]

Gravity is the weakest of the four known fundamental forces as usually measured, but it has two characteristics that compensate for that "weakness". First, unlike the strong and weak forces, and like electromagnetism, it operates at an infinite distance, with an inverse-square law. (The differences between general relativity and the original equations of Newton are not that important.) Second, it has no negatives, so that it is cumulative and pulls everything together. As previous editors have noted, the Sun is enormous compared to the rest of the solar system, which extends out to the Oort cloud. Robert McClenon (talk) 22:12, 22 July 2015 (UTC)[reply]

Ha ha, I know it's a weak force in comparison to the others, but it is capable of being massively strong nonetheless. It's strong enough to form planets and keep the solar system together.217.158.236.14 (talk) 14:10, 22 July 2015 (UTC)[reply]

It is "weak" compared to the nuclear forces, but, unlike the nuclear forces, gravity operates at unlimited distance. It is "weak" compared to electromagnetism, but, because electromagnetism has positive and negative, and like signs repel, there aren't large charges pulling across astronomical distances. Robert McClenon (talk) 22:15, 22 July 2015 (UTC)[reply]

You've scaled the distances down by about 1.4E11, but in doing so you've scaled the masses down by around 2.7E33, since the dependence of mass on length is cubic. Therefore the gravitational force (which depends linearly on mass) has been disproportionally scaled in your thought experiment.--Phil Holmes (talk) 11:09, 22 July 2015 (UTC)[reply]

If you scale down all distances in the solar system and scale down masses in proportion to the cube of distances (i.e. keep the average density of each body the same) *and* scale down velocities too then the orbital periods will be unchanged. So your model Earth will still orbit your model Sun with a period of one year - but it will be moving very slowly. Gandalf61 (talk) 11:46, 22 July 2015 (UTC)[reply]

If you are impressed by Pluto orbiting the Sun, don't forget that our entire solar system is orbiting the Galactic Center which is over 25000 light years away! Vespine (talk) 01:33, 23 July 2015 (UTC)[reply]

This is sort of a fun exercise to get your ducks in a row. Gravitational force is proportional to m1m2/r^2. So if you multiply mass by a factor of K^3, and the radius by a factor of K, the force is now multiplied by K^4 (i.e. K^3*K^3/(K)^2). But F=ma, where a is acceleration, and so that is multiplied by a net K (the preceding K^4, divided by a K^3 mass increase). So the acceleration is slowed to scale with the rest of the scale model, and the orbit continues unabated.

While detecting gravity in the mundane world is difficult, the Cavendish experiment was done in 1797 with a wooden beam and a wire! It measured a force about the weight of a grain of sand from the attraction of lead balls. A true scale solar system model, held in perfect frictionless vacuum, with two hundred years to measure an effect, is going to be much more sensitive than something you rig up in a barn. Wnt (talk) 13:50, 23 July 2015 (UTC)[reply]

What would the mass of the 1 cm sun be in Gandalf's model? Edison (talk) 19:33, 24 July 2015 (UTC)[reply]

Thanks all for the enlightening replies!Gil_mo (talk) 06:46, 23 July 2015 (UTC)[reply]

How does pregabalin work

Hi. I'm trying to find out exactly how pregabalin works for neuropathic pain and need some help. What I don't understand is how it could "know" to deal with the pain in the painful part of the body and not elsewhere - unless it sort of numbs all sensations everywhere? Thank you for pointers. 184.147.131.217 (talk) 14:09, 22 July 2015 (UTC)[reply]

The keyword you may want is "mechanism." which leads to many publications available at no cost on PubMed, a service of the National Institutes of Health. Here's one such paper, Pharmacology and mechanism of action of pregabalin, (2007), which rapidly drives into the technical details of the biochemistry. Nimur (talk) 16:37, 22 July 2015 (UTC)[reply]

Thank you very much! Can you help a little with the translation? It says subtly reduces the synaptic release of several neurotransmitters and a mechanism that may entail reduction of abnormal neuronal excitability through reduced neurotransmitter release. Is this saying that it does indeed reduce all feeling across all nerves equally, especially those that are reacting to something (eg biting tongue same as the neuropathy)? 184.147.131.217 (talk) 16:50, 22 July 2015 (UTC)[reply]

1) "subtly reduces the synaptic release of several neurotransmitters" sounds like it applies to all nerves.

2) "reduction of abnormal neuronal excitability" sounds like it only applies to nerves which are malfunctioning, such as in neuropathy. StuRat (talk) 16:54, 22 July 2015 (UTC)[reply]

Thanks, but I would like to know what it actually means not just what it sounds like. What I really want to understand is how (or if it actually does) the drug would distinguish between all nerves and malfunctioning nerves. 184.147.131.217 (talk) 17:07, 22 July 2015 (UTC)[reply]

In other words, you would like to know whether there is a method of targeted drug delivery, or if there is some binding affinity or functional selectivity for this drug. I don't know the answers, but these keywords may help your literature survey. Nimur (talk) 17:40, 22 July 2015 (UTC)[reply]

Thank you again Nimur. I'm far from unwilling to do such searches, but all the results I have found are unintelligible to me, being written in scientific shorthand. I mean look at [22]! No clue what any of it means. I think I need to request help finding sources written for the general public, please. 184.147.131.217 (talk) 02:04, 23 July 2015 (UTC)[reply]

There are two factors I would emphasize with regard to explaining how the drug can act selectively to reduce neuropathic pain without numbing parts of the body unassociated with the pain. First, as with many substances that regulate neurotransmitters and general neuronal excitability, the chemical will adjust transmission rates within a certain threshold. Neurotransmitters employ various forms of biofeedback (the details of which are best left vague here if you wish to avoid clinical language - suffice it to say, they self regulate when they have already been firing at abnormally high rate). In neuropathic pain, these nerves are often firing excitably either because of damage the cells themselves or other related physiological causes. Regardless of which, if you manipulate the regulatory mechanism so that these cells will only fire so often in a certain context, you can alleviate the pain, while the functions governed by other similar neurons are not affected if they were already not firing at a particularly excited threshold.

The second factor to consider is that nociception is handled by its own neural pathways that, while somewhat intertwined with those govern tactile sensation and other somatic sensation, it is to some extent separate, and thus there are many analgesics alleviate pain in one manner or another but which do not cause a sensation of numbness (localized or general) with regard to other somatosensory modalities. I hope that helps some; feel free to ping me if I've still not hit the right balance between technical and plain language and I will clarify further. Snow ^{let's rap} 07:14, 23 July 2015 (UTC)[reply]

"The precise mechanisms by which gabapentin produces its analgesic and antiepileptic actions are unknown." RxList. μηδείς (talk) 18:59, 22 July 2015 (UTC)[reply]

Thank you, however I am looking for a drug called pregabalin. 184.147.131.217 (talk) 02:04, 23 July 2015 (UTC)[reply]

I suppose I should have clarified, but they are both similar-acting GABA-analogs prescribed for the same reasons. If you're in the US you can even just call a local pharmacy, ask for the pharmacist, and they will tell you. μηδείς (talk) 21:20, 23 July 2015 (UTC)[reply]

Generic plastic solvent

I have a bunch of rare earth magnets imbedded in plastic in a toy. I would like to dissolve away the plastic to get all the magnets for a different project. Any suggestions on what sort of solvent to start with? The toy in specific is "Geomag" a magnetic stick and ball construction set. Tdjewell (talk) 14:57, 22 July 2015 (UTC)[reply]

Can you get your hands on some dichloromethane? That works on most plastics. 209.149.113.45 (talk) 15:16, 22 July 2015 (UTC)[reply]

There are lots of types of plastic, and at least two very different broad categories - Plastic#Thermoplastics_and_thermosetting_polymers. I looked at the company web page [23], and cannot easily determine what kind of plastic they use. I think knowing the type of plastic will be pretty important. SemanticMantis (talk) 15:19, 22 July 2015 (UTC)[reply]

You might try peppermint oil. It can dissolve some plastics and isn't nearly as toxic as most other solvents (it is toxic in high enough doses, though). Plus it makes everything smell nice. StuRat (talk) 16:49, 22 July 2015 (UTC)[reply]

You can try acetone. It's not very toxic, but quite flammable. Test it (and any solvent you try) first - put some on a napkin and rub the plastic with it, see if it makes it "mushy". The biggest issue you will have is it will evaporate very fast, leaving the plastic behind, in a melted mass. Maybe try a glass canning jar, fill it halfway with acetone, and drop the toy inside. Then use a metal rod to stick to the magnets and pull them out. (Which is why I suggested glass, and not a metal paint can.) All that said, you will probably find it easier to remove the magnet using mechanical means. Ariel. (talk) 00:34, 23 July 2015 (UTC)[reply]

Extra note: You will probably spend more money in supplies for doing this, than the magnets would cost to simply purchase. Sell the geomags, and buy magnets, they are not as expensive as you might imagine. Ariel. (talk) 00:36, 23 July 2015 (UTC)[reply]

If you use acetone, either use it outside or in a well ventilated area, because it can quickly stink up the whole house. StuRat (talk) 02:55, 23 July 2015 (UTC)[reply]

Why do you have to dissolve all the plastic? Have you thought of maybe a hack saw or something like that? --Jayron 32 01:34, 23 July 2015 (UTC)[reply]

I think some of these guesses sound a bit dodgy. I mean, acetone? that's a solvent that is hydrophilic enough to mix with water. Really, there's no guarantee that a plastic will dissolve at all, and it matters a lot what it is, but I'd expect better odds with something pretty nonpolar (dichloromethane falls in that category, though it might be easier to use some gasoline, paint thinner etc.) It's also possible that you might weaken the plastic with solvents, making it easier to peel, by soaking out the plasticizer, which again I'd guess is more likely to be hydrophobic. Wnt (talk) 13:32, 23 July 2015 (UTC)[reply]

We have an article about Geomag (product and its company). DMacks (talk) 20:19, 25 July 2015 (UTC)[reply]

Transporters

Is it true that the transporters in Star Trek actually kill the person and then build an exact copy at the destination out of different atoms? 117.168.207.243 (talk) 16:53, 22 July 2015 (UTC)[reply]

Since it's a fictional device, there is no "truth" except for how the authors claimed it would work. That device supposedly dissembled them into atoms, physically sent those same atoms to the remote location, then reassembled them there. I would call that killing them and bringing them back to life, although whether the result is a "new person" or not is debatable. Now, as for reality, that bit about sending the actual atoms to the target is plain silly. The way a transporter would really work would be to just send the information (pattern), but reassemble the person from different atoms there. However, according to physics, one atom with the same proton, neutron and electron configuration is identical to another, so it would make no difference. This does mean the same technology could possibly be used to clone an individual as many times as wanted, so perhaps that's why they made it use the same atoms in the Star Trek universe, to avoid people from asking why the various parties don't just clone themselves an army using the transporters. StuRat (talk) 17:01, 22 July 2015 (UTC)[reply]

Ship of Theseus paradox is relevant here. shoy (reactions) 18:23, 22 July 2015 (UTC)[reply]

I think I get what you mean, but it could use an explanation. That is, the atoms in a human body are normally replaced over a period of time, so replacing them all instantly isn't much different. In any case, it can be thought of as the same person before and after. StuRat (talk) 18:28, 22 July 2015 (UTC)[reply]

Given Bones describes it as disassembling and reassembling the body's molecules, I'd say yes. Other fictional teleportation devices have the entire body converted to a single large wave-particle, which seems less destructive and more continuous. Also there is the fact that you are maintained as data in the "buffer" and can be lost or replicated due to computer problems. I recommend the short story "Think Like a Dinosaur". μηδείς (talk) 18:55, 22 July 2015 (UTC)[reply]

Yes, that is an excellent (newer) Outer Limits episode which discusses the moral implications in a way Star Trek never did. StuRat (talk) 20:06, 22 July 2015 (UTC)[reply]

Supposedly Roddenberry invented the transporter to avoid the cost of building and filming a shuttlecraft - which they eventually had anyway. Perhaps he was inspired by other sci-fi. Such as, well, let's just hope there were no flies on board the Enterprise. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:19, 22 July 2015 (UTC)[reply]

There's not much supposedly about it - there's a couple of interviews where you get it straight from the horse's mouth, but as I recall it he put the issue in a slightly different way, something to the effect of "we couldn't afford to show the ship landing each week." I find that very interesting, because he didn't (at least at the time) realize that interstellar ships that land are less feasible than those that are constructed in space and spend their entire operational existence there. Or if he did, he still would have shown it if he could, because it would have made for entertaining television and up until that point, every space explorer on TV simply set down their one and only vessel on whatever planet they were visiting. Roddenberry, as a result of television logistics, was forced to create a paradigm that actually more accurately reflected the logistics of genuine spaceflight. And that trend continued for a long time; it's rare than any ship above a certain scale lands in Star Trek or similar shows. Snow ^{let's rap} 23:01, 22 July 2015 (UTC)[reply]

So, it looks like one could call Roddenberry a paradigm-shifter? μηδείς (talk) 01:33, 23 July 2015 (UTC)[reply]

Well, it wouldn't be the first time for him, I dare say. But with regard to this particular facet of representing future technologies, I suspect this change was inevitable. Note that while this was a development for television sci-fi, most literature of the time already represented interstellar craft as constructed in space and mostly used exclusively therein. Snow ^{let's rap} 02:17, 23 July 2015 (UTC)[reply]

Having read most of the ref desk today, I think that Medeis is attempting a bit of cleverness here with respect to an unrelated thread on the Language desk - [24]. Clever, but perhaps a bit WP:POINTY :) SemanticMantis (talk) 03:45, 23 July 2015 (UTC)[reply]

Well, at the risk of validating said off-topic digression into banter by participating in it (something I usually try to avoid here), "clever, but perhaps a bit WP:POINTY" is my basic impression of Medeis. :) Snow ^{let's rap} 06:47, 23 July 2015 (UTC)[reply]

We have an article on that: Transporter (Star Trek). The article quotes Lawrence Krauss, author of the book The Physics of Star Trek: "The Star Trek writers seem never to have got it exactly clear what they want the transporter to do. Does the transporter send the atoms and the bits, or just the bits?" So the transporter definitely disassembles the old you, but they haven't made up their minds whether the new you is put together out of the same atoms, or different ones. If it's the same atoms, you could also ask whether they are put back in the same places. One hydrogen atom is as good as another. --Amble (talk) 20:37, 22 July 2015 (UTC)[reply]

This was going to be my observation even before I saw that you had sourced it. Like most fictional technology that has been utilized over long narrative runs (and most Star Trek technology in particular), consistency of the exact mechanics for the transporter has not been great. It's been many years since I saw the relevant material, but I'm fairly certain that there were precise references to the fact that the transporter beam utilizes the same matter at both ends of the process. On the other hand, there was an episode of Star Trek: The Next Generation in which it was discovered that a transporter accident many years in the past had created a duplicate Commander Riker (or Lt. Riker rather). The accident was explained as such: the transporter beam had gotten a lock on Riker and successfully beamed him aboard ship, but interference from the atmosphere reflected a copy back down to the surface, where another Lt. Riker re-materialized (and was then abandoned on the surface of the planet for years by his oblivious crewmates). This obviously suggests that the transporter technology does (or in a pinch, can) utilize other stores of atoms to re-assemble a person, since there would otherwise be only enough atoms in the process to construct one Riker.

Certainly there are other examples of Star Trek technology that suggests this would be no more complicated than using the original material, including their "replicators" which can use stores of material to create most any object or substance for which they have molecular understanding. And there are numerous examples of an individual not materializing immediately, but their "pattern" is retained in the "transporter buffer", though they never explain if that is mere data or the actual mass plus the information on how to reconstruct it. It does raise the question of why you would ever use a technology that is dependent on the exact same atoms, when this represents an extra element of risk in being able to re-create the person that would not be there if you could use an infinite store of (really exactly identical) atoms. Perhaps the idea is that knowing it was the atoms that they started with at the beginning of the process reduces the existential heebi-jeebies of wondering whether the person who materializes at the other end is you or just a copy. There are examples of notable characters in the Star Trek run that I can recall who disliked or even refused to use transporter technology for just this very reason, or of general fear that the process wouldn't put them back together quite right. They are generally treated as similar to people today who fear airline travel and persist in this fear even when shown that statistically it is quite safe, but I never felt the situations were really analogous, given the philosophical questions involved. Of course, even in mundane pre-23rd century life, we change the mass of our bodies at a rate most people don't appreciate, and are basically a brand new person (in terms of matter) every seven years -- it's the organization of those elements which is most important.

There was another brilliant short sci-fi story (which I am delighted to find we have a stub for) called Think Like a Dinosaur that explored these themes very well. In it, an advanced extraterrestrial race has made contact with a human species on the brink of extinction after ecological devastation of Earth has come to a head. Amongst the technologies they bring with them is a transporter-like technology which unambiguously does send the information only, to construct a duplicate at the other end of the transmission. The "original person" is encased in a stasis-like substance and then disintegrated once transmission/copying is confirmed; the aliens (a pacifist reptilian species to whom the "dinosaur" part of the title refers) call this "balancing the equation". However, because the stasis process quickly kills the original, it has to be aborted if the transmission cannot be confirmed. This happens to a human traveling via this technology, only for the transmission to be later confirmed. The aliens, who know the social chaos that can be unleashed if multiple people with the same identity begin running around, have a strict ethical code about the technology's usage and insist that the original must be destroyed (though they are not willing to resort to violence to seeing it done, instead threatening to refuse further access to their knowledge and technological aid (which is essential to the survival of countless people still stuck on a near-cataclysmic Earth) should the "redundancy" be allowed to live). This creates a deep morale quandary for the humans involved, interlaced with notions of identity, materialism and consciousness. It's the kind of story I wish I had thought of first! Snow ^{let's rap} 22:27, 22 July 2015 (UTC)[reply]

Yes, both Medeis and I referred to that plot above, although we mentioned the Outer Limits episode, which seems to have accurately portrayed the story. You might want to watch that, if you haven't already, and see if you agree. StuRat (talk) 03:05, 23 July 2015 (UTC) [reply]

Oh, I missed those references entirely! Yes, actually I came to be familiar with that story through the Outer Limits episode first and read the story as a result. The episode, which in my opinion is one of the few from the late 90's Outer Limits revival that really holds up in quality today, very faithfully replicates (pun intended!) the sci-fi aspects of the narrative, though the character dynamics are a little different, as you might imagine. Snow ^{let's rap} 05:19, 23 July 2015 (UTC)[reply]

Yes, it was one of my favorites. There were some other good ones, though, like The Human Operators. StuRat (talk) 15:50, 23 July 2015 (UTC) [reply]

The implications of transportation-by-replication are also part of the plot of The Prestige, an excellent film with more cunning twists than a cunning twisty thing. Gandalf61 (talk) 08:24, 23 July 2015 (UTC)[reply]

I'd forgotten that one, and Nolan is one of my all-time favourite filmmakers; worth noting that The Prestige is also based a book of the same name. Snow ^{let's rap} 08:48, 23 July 2015 (UTC)[reply]

That's a fantastic (and also sort of horrifying) movie. Please see the move/read the book before you spoil yourself reading the wiki article, you'll thank me later. shoy (reactions) 13:41, 23 July 2015 (UTC)[reply]

The way I would answer this is a bit different. I'd start off by saying that really, all people are the same atman, and so the teleported people are 'the same person', provided the copying is accurate enough to produce another sentient human being at all. I won't even get into ka/ba distinctions and parallel universes in the chain of creation this time. :) But as you can tell, this isn't actually science. Wnt (talk) 23:21, 22 July 2015 (UTC)[reply]

Good link. I think it's also worth mentioning that our articles on person, personhood and personal identity together are fairly comprehensive and detailed. SemanticMantis (talk) 00:17, 23 July 2015 (UTC)[reply]

This all reminds me of Thomas M Disch's novel Echo Round His Bones (from about the same time as the original Star Trek series), in which the teleportation machine (unknown to the operators) leaves behind a ghostly, but living, "echo" of the person being transported. AndrewWTaylor (talk) 09:01, 23 July 2015 (UTC)[reply]

Duplication by teleporter is also the subject of Algis Budrys' Rogue Moon (1960) written before Star Trek debuted. Rmhermen (talk) 14:43, 23 July 2015 (UTC)[reply]

Outside of Star Trek, the usual name in SF for a device that reduces people or objects to their consituent atoms is "disintegrator ray". Iapetus (talk) 10:17, 23 July 2015 (UTC)[reply]

I think that's a fairly distinct topic from what is being inquired about here, given the missing and rather crucial step of re-assembling those atoms. Snow ^{let's rap} 13:46, 23 July 2015 (UTC)[reply]

Partially distinct. If you used a disintegrator ray to reduce someone to atoms, I think everyone would accept that you had killed the person. If you then used some other gizmo (or magic) to reassemble those atoms into the original person, I suppose its just a matter of philosophy (or faith) whether you have "built a copy" of the original or "resurected" the original. By analogy, I would say the answer to first part of the original question ("is it true that the transporters actually kill the person?") is "yes", and for the second part ("and then build an exact copy?") is "possibly". Iapetus (talk) 09:08, 24 July 2015 (UTC)[reply]

The Farnsworth novelty disintegrator ray was, in fact, nothing more than a harmless teleporter ray. Hardly a distinct technology! I am Nimur, seer of the tapes, knower of the episodes! Tremble before my encyclopedic knowledge of Star Trek!

The details of the Star Trek transporter technology, and all the other bits of fictional science and engineering, have severe inconsistencies across any one of the series, and it gets worse when you compare different series in the franchise at large. The posting above has already linked to Lawrence Krauss' Physics of Star Trek book; and that's probably the best place to go for information; it's pretty clear that the exact mechanism of the transporter technology varies based on plot need. I'll throw in one more resource that every fan should read: the Writers Guide, in which Gene Roddenberry (creator of Star Trek) specifically told the episode writers not to worry about technical details and to focus on making the story exciting. I linked to that document, and a whole lot of other critical literary reviews of it, the last time this came up on the Science desk, in March of this year.

Nimur (talk) 14:55, 23 July 2015 (UTC)[reply]

I think if you really want to look into it there should be a more interesting quantum mechanics question, which I wouldn't pretend to be able to answer: is it possible to "transport" a person this way and be accurate? I'm not asking whether you can manage the disintegration or reintegration or transport, but whether Heisenberg uncertainty principle limits get in the way. After all, when you do an X-ray crystallography structure, it is often hard to tell where every last hydrogen is located, and you may end up making a few assumptions about who is bound to who to get the model finished. But there are other limits besides the quantum there. Also, if the measurements are too imprecise... what if you put your transporter computer in that neat little box they shipped Schroedinger's Cat in, and destroy the computer after you finish? Will that prevent any "measurement" from taking place, so it's just like moving the object, even if you know it had higher-accuracy measurements inside it for some time while it was in the box...? Wnt (talk) 18:15, 23 July 2015 (UTC)[reply]

You can teleport the complete state, as long as you have previously exchanged enough entangled particles between the two endpoints. However, you can't make multiple copies because of the no-cloning theorem. If the transporter beam is itself a quantum channel, you can directly send the full state through it without making a "measurement". Either way, what you definitely don't want to do is measure the state, i.e. collapse it down to classical information. It's not clear whether the Star Trek implementation conforms to any of these ideas, since they use Heisenberg compensators. Nobody knows exactly how those work, but they stop the scriptwriters from having to worry too much about the uncertainty principle. --Amble (talk) 19:13, 23 July 2015 (UTC)[reply]

I don't think there is any kind of teleportation involved, in the senses that you imply here. That is, my impression from personal observation and the sourcing we have above with regard to how the writers treated this subject was that the beam somehow moves the matter through the intervening space, but does so piecemeal. I've never seen any suggestion of entanglement or quantum effects of any sort. Also, perhaps I'm mistaking your meaning here, but you seem to confusing the semantics of teleportation in the sense being discussed here and what quantum teleportation refers to, which is strictly information. Entanglement can be used to generate sympathetic states in linked particles, but no exchange of mass over distance occurs. If you are suggesting that this could be used to transmit the information over distances instantaneously, that's true, but you'd still need to either transmit the matter somehow, or have an identical store of atoms on the other end which could be used in synthesis, in which case, you would in fact end up with a copy. But these are two separate issue -- the original one discussed here, about whether the transported person is constructed of the same mass, and what you are talking about (transmitting information without an intervening medium). The transporter's exact nature (and the OP's question with regard to it) remain an uncertain factor regardless of whether or not it has an additional mechanism like the one you describe. Snow ^{let's rap} 10:23, 25 July 2015 (UTC)[reply]

I was responding to Wnt's question about what's actually allowed by quantum mechanics, which is of course not the same as what's allowed by Star Trek scriptwriters. --Amble (talk) 18:25, 25 July 2015 (UTC)[reply]

@Amble: Yes, ok, I see; in reviewing the context of your post as an answer to Wnt's specific inquiry, it makes a lot more sense. I should have re-read his post in detail before replying to yours - apologies! Snow ^{let's rap} 22:16, 25 July 2015 (UTC)[reply]

@Snow Rise: No problem. I try to follow Wikipedia:Indentation, but given the variety of styles it's often hard to tell who is responding to what. I guess I should learn to use the Ping template. --Amble (talk) 22:38, 25 July 2015 (UTC)[reply]

July 23

Differences between industrial electricity prices from different sources

According to the Energy Information Administration, Washington state had the lowest industrial electricity prices in 2014[25]. But this site[26], citing the Edison Electric Institute, says differently. I believe both sources are correct, they're simply measuring (slightly) different things. So where is the discrepancy coming from? My other car is a cadr (talk) 14:00, 23 July 2015 (UTC)[reply]

At least one of the sources - EIA - provides more details at no cost: here's the 221 page EIA report, Electric Power Monthly. It has an appendix with algorithms and methodology. Edison Electric Institute sells access to their reports: available products. A subset of analysis and reporte are available on their data and analysis website at no cost. Nimur (talk) 14:30, 23 July 2015 (UTC)[reply]

The Edison report is the 12-month average ending in June 2014. The EIA link shows April 2014 only. Rmhermen (talk) 14:33, 23 July 2015 (UTC)[reply]

Thanks a lot. My other car is a cadr (talk) 03:26, 24 July 2015 (UTC)[reply]

Resolved

Small wind turbine blade design

I'm getting a stepper motor from someone's broken printer and I'm going to use that to generate power from the wind to charge a USB battery. [The wind is a lot more reliable in Scotland than the sun and piezoelectric shoes generate too little power]. I want to buy the blades because I think they'll work better (more accurate shape and balance) than homemade ones. My question is which blades should I buy? There's thin and fat ones. They're not designed with this purpose in mind but I don't think that matters too much. Thin Fat Also fat ----Seans Potato Business 15:46, 23 July 2015 (UTC)[reply]

Considering your application (for camping), I'd think you would want the lightest weight blades you can find, which would mean lower width and thickness). The downside of such blades is that they are more fragile, but if they are protected inside a housing, that won't be as much of a concern. Of course, the housing will add to the bulk and weight considerably. If you have a "naked blade" design in mind, then you will need to be careful to protect the blades. If they are removable, that would allow you to pack them more carefully and compactly. StuRat (talk) 16:09, 23 July 2015 (UTC)[reply]

Wind turbine design might be of interest. In particular it discusses why commercial wind turbines (of which there are many in Scotland) typically use only three blades, whereas one might naively think "the more the better" (from my brief reading it seems that the gain in "drive" from adding blades doesn't compensate for the extra weight and drag). AndrewWTaylor (talk) 16:18, 23 July 2015 (UTC)[reply]

Long thin ones are more efficient. It is to do with the characteristics of the aspect ratio (aerodynamics). Fat blades are popular in domestic applications only because the generate less noise. However the drag/air friction is greater. Hence less efficient. Thats why helicopters have thin blades. Cheaper still would be to place a live haggis in a tread mill. One doesn't then need to rely on the wind. Just show it a gravy-boat of redcurrant-horseradish-and-whisky haggis source and it will brake into a gallop, powering the whole village ;¬)--Aspro (talk) 17:03, 23 July 2015 (UTC)[reply]

It is worth bearing in mind that a blade designed for use in a fan (i.e. to create an airflow as a result of being turned by power) may not be the best shape for use as a turbine (i.e. to generate power from a moving airflow). In particular, if the blades aren't symmetrical in cross section (which they shouldn't be for maximum efficiency - they should be cambered like an aircraft wing aerofoil) they will be 'the wrong way up' if you use a fan blade in a turbine. AndyTheGrump (talk) 17:14, 23 July 2015 (UTC)[reply]

As I said: domestic fans are designed to be quiet. The hurricane blowers used in films to create a hurricane on set are aircraft screws. They make a hell of a racket, which is why the actors lips are always out of sync with their voices which have to be dubbed on in post-production. Whether the screw is driven by shaft power or wind is nether here nor there. The physics aero dynamic doesn’t care. That is not to say a quiet narrow bladed domestic fan can't be made. They would look a bit like the complex-curve blades of a nuclear-sub and high-performance Russian military turbo-prop aircraft. However, that technology is still classified so the OP is unlike to find them on eBay. Also,I don't get the "'the wrong way up'" bit. Just turn it the other way round on the shaft! I still think a nice round plump haggis is the better option--Aspro (talk) 17:54, 23 July 2015 (UTC)[reply]

'Turning it the other way round on the shaft' doesn't work. To appreciate why, think of an aeroplane wing - the top surface is generally more curved than the bottom surface, for maximum efficiency (a symmetrical aerofoil will still give lift but the lift/drag ratio is lower). A propeller has the higher-cambered side of the blade facing forwards into the airstream, whereas a turbine blade will have the higher-cambered side at the back - and you can't simply turn it round as this then results in the (rounded) leading edge becoming the (sharp) trailing edge. AndyTheGrump (talk) 18:29, 23 July 2015 (UTC)[reply]

That would only apply if the OP was going to use it as a motor. He clearly states that he intends to use it as a generator. So by reversing the prop the 'wind' drives it – all be it backwards (and SM will generate regardless). Yet thin long bladed air-screws are nearly all 'pullers' so the OP will probably not have to turn it around anyway. Thats the bit I don't understand and you haven't answered yet. --Aspro (talk) 19:32, 23 July 2015 (UTC)[reply]

I am fully aware of what the OP is trying to do, and your response has no relevance to my comment on the differences between a propeller and a turbine with regards to optimal aerofoil camber. Frankly though, I think the OP might do better to seek advice somewhere else, since nobody here has even bothered to comment on the need to match the characteristics of the turbine to the generator - you can't just stick any old set of blades on an electric motor and expect it to generate useful power. AndyTheGrump (talk) 19:49, 23 July 2015 (UTC)[reply]

You said “they will be 'the wrong way up'” which you haven't explained but instead now give a tangential reply to the OP suggesting every other editor here (save for you) are out of their depth. (COI disclaimer. I am a qualified engineer).--Aspro (talk) 20:21, 23 July 2015 (UTC)[reply]

I have given an explanation - your inability to understand it isn't my problem. And your qualifications, since they self-evidently don't include aerodynamics, aren't relevant. AndyTheGrump (talk) 20:39, 23 July 2015 (UTC)[reply]

Hi Andy. I've got motors from a broken Epson printer. I was hoping they would turn out to be stepper motors because for some reason they're the ones many websites advise to use (possibly because they're slow?). These are regular motors (RS445PA14233R, specifically) but at least I know they're low speed motors. I'll continue to look out for broken printers on Freegle/Freecycle but maybe these will work. Do you know whether the propeller I will want would be a push or pull prop? I figure it should be push (relatively unusual for an aircraft) but figure I should check my logic. ---Seans Potato Business 20:09, 23 July 2015 (UTC)[reply]

Whether the generator is mounted in front of or behind the turbine will only affect the direction the generator is turned - it won't have any other consequences beyond the fact that having the turbine 'downwind' will reduce the airflow, and add turbulence. The direction the turbine revolves is solely dependent on whether it is a 'clockwise' or 'anticlockwise' helix, and reversing the way it faces on the generator shaft doesn't reverse the helix. As I have stated above though , a propeller is designed to generate thrust, and thus may not be optimal for use as a turbine. Not only is the camber likely to be wrong (if it doesn't use a symmetrical aerofoil) but you may find that the pitch is too fine - a very fine pitch may result in the turbine not turning at all under load. As I have stated above though, you might do better to ask questions at a specialist website - this website [27] looks as if it might be useful. AndyTheGrump (talk) 20:52, 23 July 2015 (UTC)[reply]

Okay, thanks. I'll ask for advice at a more specialist site. Before I go, could I ask you to clarify a "fine pitch"? These propellers are defined in the format 16" x 10" or 16" x 8" for example, where the second number is the pitch. Is a greater or smaller number a finer pitch? Thanks again. --Seans Potato Business 21:06, 23 July 2015 (UTC)[reply]

The pitch is the theoretical distance the propeller/turbine would move relative to the air mass per revolution, if there was no slip. A coarse pitch is larger than a fine one. AndyTheGrump (talk) 21:11, 23 July 2015 (UTC)[reply]

Incidentally, you should possibly consider alternatives to a horizontal-axis turbine. As our article shows, there are vertical-axis designs which may better suit your needs - they don't need to be pointed into wind, and might be more practical as a portable device. They aren't generally as efficient (in terms of generating power for a given size and windspeed) but some designs at least look as if they might be more robust. AndyTheGrump (talk) 21:38, 23 July 2015 (UTC)[reply]

Hi. The problem is that VAWT blades don't seem to be cheaply available so I'd have to make one myself to keep the project economical. I was hoping that a manufactured plane propeller would be superior to anything I could make myself even if the specifics were suboptimal for the application. There's also these large plastic garden windmill blades but I wonder if they would be worse than the the RC propellers... --Seans Potato Business 22:00, 23 July 2015 (UTC)[reply]

Good luck. Make sure your USB device isn't driving the motor. You'll probably need a charge pump or switching network based on turbine speed and a regulator. --DHeyward (talk) 21:51, 23 July 2015 (UTC)[reply]

Multiple ring systems around planets

Is it possible for a planet to have multiple ring systems moving in different orbits such as this — Preceding unsigned comment added by Malamockq (talk • contribs) 16:55, 23 July 2015‎

No - or at least, it won't be stable in the long term. The objects in each ring will be gravitationally attracted towards the objects in the other, causing the two rings to gradually drift into a common alignment. It is this tendency for multiple small objects in orbit around a common larger one to align their orbits in a common plane that is responsible for the formation of rings in the first place. AndyTheGrump (talk) 17:25, 23 July 2015 (UTC)[reply]

Maybe, if the two rings have enough distance between them. After all, the solar system is also a "ring system", but not all of objects orbit in exactly the same plane. Then there's the Oort Cloud, where there is no single orbital plane at all at that distance. I agree that eventually everything would theoretically fall into a single plane, but that may very well take longer than the age of the universe to happen. Now, as for planets, the problem with a ring system being far enough out to not interfere with an inner ring system on a short time scale would be that, at those distances, it would come too close to other planets, etc. But, if you had a planet without a solar system, say one that had been ejected from it's own system, then this configuration might be possible, and stable for millions or billions of years. StuRat (talk) 17:45, 23 July 2015 (UTC)[reply]

A single object is not a ring. Can't you find some way to resist giving answers to questions you don't know anything about? Looie496 (talk) 19:43, 23 July 2015 (UTC)[reply]

No, it's not a single object, it's a massive number of single objects. I never stated it was a single object, so I have no idea where that straw man came from. (The solar system being a ring system refers to the asteroid belt, Kuiper belt, etc.) Also note that SemanticMantis' and DHeyward's comments and links below supports my assertion. StuRat (talk) 17:13, 24 July 2015 (UTC)[reply]

Hear hear! Fgf10 (talk) 21:09, 23 July 2015 (UTC)[reply]

The problem with the diagram is not that it shows multiple ring systems in different orbits, but that it shows multiple ring systems in non-coplanar orbits. Saturn can be said to have multiple ring systems in coplanar orbits, depending on what you mean by a ring system as opposed to a ring. I think that an earlier editor is right that the objects in the two rings, due to gravitational attraction, will gradually drift into a common alignment. Has there been any computer simulation of the formation and behavior of rings and ring systems? Robert McClenon (talk) 19:47, 23 July 2015 (UTC)[reply]

If the two rings are made up of very small particles (dust), and are some distance apart, the interaction between them will be negligible. Amount of light reflected by a visible object is proportional to the area (cross-section) of the object, for any object substantially larger than the wavelength of reflected light. The gravitational interaction of the object, on the other hand, is proportional to its mass, which scales with volume rather than area. Thus, for a given total reflective area, the smaller the particles making up the rings are, the weaker the gravitational interaction between the rings will be. Dr Dima (talk) 19:48, 23 July 2015 (UTC)[reply]

I feel like somebody should link Ring_system_(astronomy), and point out that we have articles for many specific systems, like Rings of Saturn. One interesting thing mentioned in the article is the notion of a "shepherd moon". Here is one article I found that addresses stability of ring systems [28]. This work looks at equilibria of a "ring configuration", but I think it may have some application to continuous rings [29] Here's another work on the stability of ring systems [30]. Here's a paper on numeric simulations of planetary rings with focus on collisions [31]. Here's an older (1984) paper about then-current unsolved problems in ring dynamics [32]. I suspect looking at recent citations to that article could be fruitful. SemanticMantis (talk) 21:27, 23 July 2015 (UTC)[reply]

Hey, look what a few minutes with google scholar a can find! Here [33] is an article presenting information on Beta_Pictoris. They say in the abstract "A deconvolved image strongly suggests that the newly detected features arise from a system of four noncoplanar rings", emphasis mine. So at least some researchers think that there are noncoplanar rings around things in space, though they do not comment on long-term stability. SemanticMantis (talk) 21:33, 23 July 2015 (UTC)[reply]

I believe it's Tidal locking related. Are the planes of the rings of Saturn and the orbits of moons in the plane of orbit around the sun or the rotation plane of the planet? I don't see why a small rock vs. large moon would be different with respect to tidal locking other than time. Saturn does have the Phoebe ring which is inclined and retrograde. The Phoebe ring is near the ecliptic plane while the other rings and moons are equatorial with Saturn's rotation. Saturn is inclined similar to earth I believe. See Laplace plane and it seems far away rings could exist in the ecliptic plane and near rings would be equatorial. --DHeyward (talk) 22:01, 23 July 2015 (UTC)[reply]

That optical illusion

We have an article on this but I forget what the name is. There are a bunch of great images at commons that could use a proper category. Thanks for any help you can offer. Anna Frodesiak (talk) 22:10, 23 July 2015 (UTC)[reply]

Moiré pattern. Found it ten minutes after looking and two seconds after posting here. :) Anna Frodesiak (talk) 22:14, 23 July 2015 (UTC)[reply]

Hey, a blast from the past! We discussed something rather similar a few years ago here. At that time, I think you added a section to Moiré pattern as I recall. I wonder if maybe a DAB or redirect for kinegram is warranted. SemanticMantis (talk) 22:33, 23 July 2015 (UTC)[reply]

You have a great memory. I remembered posting somewhere about it, but couldn't figure out where.

Not sure if these all fit Fresnel lens of if they are related to Zone plates . --DHeyward (talk) 22:38, 23 July 2015 (UTC)[reply]

Those seem different. Anna Frodesiak (talk) 22:43, 23 July 2015 (UTC)[reply]

I agree they are different, but part of the problem is that the OP link sort of conflates two things - one of them has to do with Lenticular_printing and lenticular lens (and that's what reminds you of Fresnel), while the other thing with the grid screens is rather different. SemanticMantis (talk) 23:02, 23 July 2015 (UTC)[reply]

Anyhow, check the commonscat now. Not sure if it's sorted out properly. I just added a few images and gave Moire a parent cat and that's it.. Anna Frodesiak (talk) 22:42, 23 July 2015 (UTC)[reply]

Looks good. Someone removed your animation section [34] in april. This is a tricky thing to get WP:RS for. This guy [35] says a kinegram is a combination of Moire pattern and Zoetrope. Last time we discussed it, Steve Baker was adamant that kinegrams were not Moire patterns (though I still disagree), and I also don't think that it's all that similar to a zoetrope - as I pointed out before, each image in zoetrope is a complete image, and then some shuttering mechanism is used to expose them sequentially. Here, there are no "frames" and the image is only formed after the screen is overlaid. Perhaps the best thing to do is to make a stub for kinegram, and include links to zoetrope and moire pattern. You could fill it with refs from this thread and the one I linked above, I'd help if you got it started :) SemanticMantis (talk) 22:57, 23 July 2015 (UTC)[reply]

Now this is extra cool: when I go to your new category commons:Category:Moiré and scroll, I see animation effects on several of the thumbnails as I scroll. (It's probably wicked browser- and screen-dependent, though.) —Steve Summit (talk) 23:15, 23 July 2015 (UTC)[reply]

WP:OR- I saw it too! Only on the simpler geometric ones, not the more complicated animations. It was much more apparent on my iPhone 5. On my larger Apple_Thunderbolt_Display and Firefox, I had to make the browser window and thumbnails both rather large before I got the effect, and it was still less apparent. Do you agree a new stub for 'Kinegram' is warranted, or do you think this notion of using periodic banded screen overlays to produce an animation fits better with 'Moire pattern'? Or perhaps somewhere else? SemanticMantis (talk) 00:26, 24 July 2015 (UTC)[reply]

Hardware assisted anti-aliasing, plus hardware-accelerated scrolling, in WebKit, CoreText, and ... everywhere else! The antialiasing strength can be dynamically scaled to ensure smoother performance. Nimur (talk) 15:59, 24 July 2015 (UTC)[reply]

Okay. I started Kinegram. Now to find some way to get an ogv in there. Thanks all. Oh, and please copy edit it. It is not pretty right now. :) Oh, and one more thing. We need to sort out the Commonscats. Any thoughts on how to do that? I also wish to upload the overlays from here. There's no way they're copyrightable, right? I tried to convert them from pdf to pgn and they came out all skewomp. I could make some more, but I do not know the measurements. Anna Frodesiak (talk) 02:18, 24 July 2015 (UTC)[reply]

"When two grids intersect with a patterned effect — that's a Moiré." {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:10, 24 July 2015 (UTC)[reply]

"When the interference hits your eye, and your brain it does fry, that's a Moiré." StuRat (talk) 16:44, 24 July 2015 (UTC)[reply]

"When the lines of a screen make some lines in between, that's a Moiré." —Tamfang (talk) 06:26, 25 July 2015 (UTC)[reply]

@DHeyward, Scs, SemanticMantis, and Nimur: Thank you all for input. Please, please give it a copy edit. I am terrible at describing such things. And, if you are so inclined, make a short ogv that is better than my bit of rubbish. All the best, Anna Frodesiak (talk) 00:12, 25 July 2015 (UTC)[reply]

July 24

How many megapixels equivalent does our eyes have?

How can you measure the amount of megapixels of a human eye?--YX-1000A (talk) 02:04, 24 July 2015 (UTC)[reply]

I keep hearing the claim "about a megapixel" over the years, and after looking into it again, I still think that's the case. First I should get out of the way the issue of measuring the eyeball's resolution to begin with: the human eye is not like a camera. You didn't ask how the human eye is not like a camera, so I won't get into it, but there are ways to measure things like resolution. For instance, if looking at a grated material, how close do the grates have to be (while viewing from a given distance) to tell them apart. Using techniques like this and citing lots of sources that you may also be interested in, this website does a somewhat detailed derivation of the resolution of human vision. They come to a rather ludicrous value in the hundreds of megapixels, but they asking a rather particular question, "how detailed does an image need to be to recreate what you would see while standing in that scene." Since most of our photoreceptors are located in our fovea centralis, your eye is only focused on a very small region of your field of view at a given time. If you take the angular width of the fovea to be only 3 degrees, the result on that source falls down to 1 megapixel. That is, at any given moment, the image you are seeing in your mind could be represented by a 1 megapixel image. Someguy1221 (talk) 03:09, 24 July 2015 (UTC)[reply]

Modern research places the count of photoactive cells in the retina at over 100 million: Facts and Figures Concerning the Human Retina, published by NIH. The authors have made their entire book available at no cost: WebVision: Anatomy and Physiology or the Retina, from the University of Utah.

Are photoactive retinal cells "equivalent" to pixels? That depends on who you ask!

I work with image sensors as part of my day job (when I'm not too busy reading encyclopedias)... so I know a little bit about "pixels..." To be honest, I still don't know how to count pixels on digital cameras, let alone in biological systems with cognitive perception! Today, reputable sensor-manufacturers sell things called "effective pixels" - what are those!? (Here's how Exmor technology works, at least in cartoon form: there's an "intelligent pixel-by-pixel algorithm" baked right into the silicon! But hey, when I learned about them in school, I don't remember photodiodes running algorithms!) Here's another vendor whose latest and greatest toys will also resample the pixels: 2x2, 3x3... you can get as many pixels as you want from today's camera sensors! And here's another vendor who will reshape your square pixels into half as many rectangles! And all these are consumer toys! If only we could see what pixel weirdness they're surely cooking up in the confidential image sensor technology divisions of BAE or Lockheed - they don't put the details on their websites, because we don't need to see what they can see!

The real answer is, whether you're talking about human eyes or exotic cameras, you should probably stop counting pixels, and start looking at other metrics that meaningfully represent image information content - like the optical transfer function and the signal to noise ratio and the dynamic range.

Nimur (talk) 03:42, 24 July 2015 (UTC)[reply]

The vast majority of those 100+ million cells are rods, which don't contribute to daytime vision. There are only about 6 million cones, according to that page. It's also worth noting that there are only about 1 million axons in the optic nerve. -- BenRG (talk) 07:34, 24 July 2015 (UTC)[reply]

Do you have a reference for rods being inactive in daytime vision? I know that rods are what are responsible for night vision, and that they're almost entirely lacking from the fovea, where sharp-focused vision takes place, but I was unaware that rods didn't contribute to daytime peripheral vision. - By the way, the Fovea centralis article has a little table talking about pixel densities of displays in matching the cone density of the fovea (the whole "retina display" thing), which is another way of looking at the resolution of the eye. -- 160.129.138.186 (talk) 15:42, 25 July 2015 (UTC)[reply]

This contributes some interesting data to the discussion, based on resolving power.--Phil Holmes (talk) 11:42, 24 July 2015 (UTC)[reply]

The question is deeply problematic as phrased as the eye is not designed in any sense to function as a camera. It's doesn't capture an image in the sense that a camera does, and if it did, it wouldn't be very ideal to the manner in which the brain processes and assimilates visual phenomena. I'll get into the actual physiology of the eye tomorrow, and try to make some rough correlates between the biomechanics of the eye and the physics of a camera, but first one has to understand the complexities of what human vision actually is. Intuitively, we tend to assume that the eye is taking a recording that is being projected into the brain, but that's not really what is going on. Rather for visual cognition, the brain creates a narrative (that is disturbingly illusory in many ways) from rather limited data. Well, here, no one explains this kind of stuff better than Susan Blackmore, so... Snow ^{let's rap} 10:38, 25 July 2015 (UTC)[reply]

The references posted by nimur and holmes seem to be valid and address the context of the OP's inquiry. I am dubious of Snow's link... Susan Blackmore seems to be full of New age nonsense like "consciousness is an illusion". The link from Blackmore's video lecture is not scientific, the links posted already are scientific, and I'm border line sure that Blackmore is full of ill-informed, unsubstantiated, unfounded claptrap! Void burn (talk) 16:00, 25 July 2015 (UTC)[reply]

Uh, friend, you need to do your research (or at least watch the video which you are judging) before making such hyperbolic, unsubstaniated statements. Susan Blackmore is a leading scientific authority in these matters. There's nothing that is any sense "new age" about the notion that consciousness is a deeply-problematic concept that has troubled any and every researcher who has tried to quantify it in an empirical manner. This is a well-known issue in cognitive science, known very specifically as the "hard problem of consciousness" and the fact that a certain amount of philosophy inevitably creeps in when we try to tackle such a complex and frustratingly elusive concept of what consciousness really is does not change the scientific rigor with which researchers come at the question. And Blackmore doesn't make any strong or remotely controversial claims in that lecture, she just presents the confusing problems, inconsistencies and logical paradoxes that arise from trying to apply the classical intuitive and/or dualistic notions of a mind or soul, and nothing she says is the least bit new to cognitive science -- these are all conundrums that are decades (or in some cases thousands of years) old in the record of inquiry.

I strongly suspect that what happened here is that you watched a particularly vague thirty seconds of that video and then read our article on Blackmore, saw the word "parapsychology" and decided she was a kook. Quite the opposite in fact; here's the story on her checkered history as a hard-science researchers -- in her youth, Blackmore had an "out of body" experience and was so convinced that it was real that she spent years trying to test notions likes telepathy and astral projection, using hard scientific methods. However, having the outlook of a scientist, she was able to see the writing on the wall and eventually accepted that the evidence was not there for the phenomena she had set out to validate, and then changed course and started studying the mind, and in the decades since has become a respected and leading authority in the field of consciousness studies, even penning the definitive introductory text on the topic, that is now used widely in psychology courses. I admit our article on her does a terrible job of contextualizing the two phases of her activity as a researcher (I've been meaning to put together the sources to fix it for ages), but I think that kind of intellectual honesty should be applauded and her early forays into projection (which she did after-all approach with hard scientific methods, hence the lack of confirmation) should not be held against her. The irony of your comments dismissing her stances on consciousness (aside from the fact that they represent the central, non-controversial territory of this field of inquiry) is that the video in question comes from a talk she was giving to the Skeptics Society, an ideological organization devoted to deconstructing pseudoscientific notions (and her introduction makes clear that she was invited to speak in part because she is a stellar example of a scientist who started out studying dubious phenomena and then moved to topics of real significance).

But if you don't like to accept the existence of the hard problem and what modern research says about it from her lips, perhaps you will be more receptive to David Chalmers, Daniel Dennett, and Donald Hoffman. How about John Searle [36]? I'm just using youtube as a shorthand here so as not to swamp the thread with a tangential discussion. There's a stack of research on this topic taller than Everest converging with the issues Blackmore raises in that video (and again, I reiterate that she doesn't even make any novel strong claims therein, she just points out how questionable intuitive models of consciousness are, and that doesn't even begin to be controversial in the hard study of the mind). But if you feel that you can prove, beyond a shadow of a doubt, that consciousness is an absolute and quantifiable phenomena and can define it in a clear and scientific fashion, I have great news for you -- you're perhaps the greatest thinker in the entire history of philosophy, and you've revolutionized both cognitive science and our fundamental understanding of reality in ways relevant to every last field of human inquiry. But you really need to share that understating, because the rest of us are really struggling with this topic!

All of which is a massive distraction from the OP's question. I didn't link that original video to discuss the notion of consciousness in general; I linked it for (and a put a time parameter in the link to direct to) Blackmore's discussion of visual cognition and how the mind constructs a visual narrative based on the information it receives from the eye (including some mechanics of how the eye itself operates). That is all deeply and essentially relevant to answering the OP's question. You can't understand the eye's "resolution" until you understand the nature of the phenomena of visual cognition and how the brain processes that stimuli. If you have a specific scientific rejection of something she says about human visual cognition in that segment of the lecture which you think might be relevant to the OP's understanding of this topic, by all means, let's discuss it in more detail. But as I see it, you made an exceedingly vague and knee-jerk assessment of a broader topic that was not being addressed, without saying a single thing to address the specific mechanics of vision which we were discussing. I'll let the OP and others here watch the content I linked and judge the academic and empirical rigor of Blackmore's observations (and their relevance to that actual question we're discussing here) for themselves. But with regard to the red herring you've raised here and referenced as "new age nonsense" (specifically, the possibility that consciousness might not conform to our basic intuitions about its fundamental nature), I have to tell you that this is considered an open and inescapable possibility arising from the hardest science you can find in the study of the nature of the mind; this speculation is nowhere near new and hardly considered fringe thinking in consciousness studies. Point in fact, it the opposite view (consciousness is a definite and undeniable phenomena, the existence of which we can test for and verify experimentally) that is presently considered untenable.

But again, I specifically posted that video (and its time parameter) for the content on how the brain contextualizes visual stimuli -- and there's no subfield of perception studies that has more robust data than that of visual cognition, including for the specific phenomena Blackmore mentions (inattention blindness, the biomechanical limitations of saccades, the mapping of photoreceptors on the retina/fovea), none of which are controversial and all of which are necessary in answering the OP's question with any degree of depth and accuracy. Snow ^{let's rap} 19:50, 25 July 2015 (UTC)[reply]

I agree that counting the retinal cells doesn't get you a good answer. For example, our eyes continually vibrate at around 80Hz in Ocular tremor - which allows each cell to successively sample a small area around the point where it's nominally pointing - this produces an effective resolution that's considerably higher than you'd get by counting the cells. When you get tired, this motion decreases and your vision gets noticeably more blurry as a result. But your eyes don't transmit "pixels" to your brain anyway - they send information about higher level concepts like the orientation and motion of high-contrast edges. The number of rod/cone cells give some kind of a lower bound of a couple of megapixels...but if I take a photo of a page from a book with a two megapixel camera and examine the image it produces, it's very obvious that my eyesight is much better than that. SteveBaker (talk) 18:17, 25 July 2015 (UTC)[reply]

If you post your original vision research here, please tag it as "OR" or something so that people realize that it's not supported by the peer-reviewed literature.

Blurred vision is caused by poor focus, not by a lack of eye motion.

If the eye completely ceases to move, the result is complete loss of vision due to neural adaptation, not blurred vision.

Curcio et al say "Foveal cone spacing is commonly assumed to be the limiting factor of visual resolving power. Resolution of gratings consisting of alternating light and dark bars requires that at least one row of unstimulated cones lie between rows of stimulated cones", so as of 1990 vision researchers had not heard of the idea that resolving power is increased by ocular microtremors.

The resolution of the image on the retina is limited by diffraction and lens aberration, and the cone density at the center of the fovea roughly matches that limit. A higher sampling density would not increase resolving power by much, if at all. -- BenRG (talk) 01:57, 26 July 2015 (UTC)[reply]

Nuclear Fission

What is the equation describes the evolution of the energy (w.r.t time) in nuclear fission? 11:34, 24 July 2015 (UTC) — Preceding unsigned comment added by 5.29.9.245 (talk) 11:34, 24 July 2015‎

At it's most basic, it's an exponential decay, depending on the half-life of the material under question. That will do just fine if you're talking about a simple uncontrolled reaction (eg. in a radioisotope thermoelectric generator as used on spacecraft). More complex reactions (for example, a nuclear chain reaction, or a decay chain with several steps) have more complex equations (although still based on exponential decay). Our article on Nuclear reactor physics has equations showing how neutron production changes over time in a reactor - that's a good proxy to energy (since each fission event releases the same amount of energy), but the variables depend not just on the physical properties of the fuel, but also on the design of the reactor. Smurrayinchester 13:35, 24 July 2015 (UTC)[reply]

Thank you! :) 5.29.9.245 (talk) 14:05, 24 July 2015 (UTC)[reply]

Temperate zones in the Pleistocene

Roughly where were the boundaries of the permafrost regions during the Pleistocene epoch, and did any parts of the world stay warm all the way through? With snow at the equator, surely all the crocodiles would have frozen to death? 213.205.198.236 (talk) 16:49, 24 July 2015 (UTC)[reply]

There's some information in our Pleistocene article. The glaciers pushed as far as the 40th parallel, with the permafrost extending a few hundred kilometres in North America, and several hundred in Eurasia. Rojomoke (talk) 17:01, 24 July 2015 (UTC)[reply]

Here's a paper that dicusses this, with a map (Figure 1) that matches pretty well with Rojomoke's information above. Mikenorton (talk) 19:52, 24 July 2015 (UTC)[reply]

And another that looks at conditions in equatorial parts of Africa and South America, with estimates of about 5°C reduction in average temperatures compared to the present day. Mikenorton (talk) 20:01, 24 July 2015 (UTC)[reply]

5 C would be a larger than typical change for the tropics (though potentially accurate for some locations). Most of the tropics are more typically estimated as having a 2-3 C cooling [37]. We also have articles on Last Glacial Maximum and CLIMAP which may be interesting. To answer the original question, no there was no snow at the sea level equator. The all-time record low at a place like Guayaquil, Ecuador (a coastal equatorial location) is 15 C. [38] It would take much more extreme cooling than hypothesized for the recent sequence of glaciations before it would be cold enough to snow there. Dragons flight (talk) 13:20, 25 July 2015 (UTC)[reply]

One of the most pronounced differences in the tropics is the hypothesized "permanent El Niño" state during much of the Plasticene. But as far as I know the tropics stayed pretty warm overall, albeit cooler than present at least in some places. I'd be curious to know your source for "snow at the equator" (other than at high elevations). Short Brigade Harvester Boris (talk) 03:59, 25 July 2015 (UTC)[reply]

I think you're getting confused - the plasticene era was the time when Wallace and Gromit walked the Earth. Richerman (talk) 08:34, 25 July 2015 (UTC)[reply]

See plasticine to understand the above comment. StuRat (talk) 16:17, 25 July 2015 (UTC) [reply]

July 25

Mountain building before plate tectonics

How did scientists explain mountain building and earthquakes before the theory of plate tectonics became widely accepted?

Plate tectonics is indeed relatively recent. But erosion and Deposition_(geology), sedimentation, etc. were worked out long before that. See Uniformitarianism#18th_century for some background. We also have fairly good articles on history of geology and timeline of geology. SemanticMantis (talk) 06:08, 25 July 2015 (UTC)[reply]

See also Geosyncline. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:09, 25 July 2015 (UTC)[reply]

The emphasis was originally on vertical tectonics - unsurprising considering most geoscientists thought that the continents were fixed. The evidence for lateral shortening, however, in the Alps, the Scottish and Scandinavian Caledonides and the Rockies convinced many that the earth was shrinking as it cooled, causing mountain ranges to rise - see Diastrophism#Historical development of the concept and Timeline of the development of tectonophysics (before 1954) (the latter has issues, but it has some useful information). Mikenorton (talk) 11:31, 25 July 2015 (UTC)[reply]

Mountain building can also be explained by vulcanism. Of course, not all mountains are built that way, but some early geologists might have thought they all were. StuRat (talk) 15:40, 25 July 2015 (UTC)[reply]

That was the argument of the plutonists, such as James Hutton, who explained everything in terms of vertical movement due to magma emplacement, see also here. Mikenorton (talk) 16:18, 25 July 2015 (UTC)[reply]

Has anyone researched levee failure due to earthquake ground motion?

I've tried looking online for scenarios with models that calculate probabilistic levee failure in Vancouver Canada due to earthquake ground motion, without any success. Does anyone know of such scenarios? I found a scenario with a model calculating probabilistic levee failure due to tsunamis, but not one due to earthquake ground motion.Philly underwater (talk) 13:38, 25 July 2015 (UTC)[reply]

If you want people to reply, make the title of the thread more informative - researched what. Oh, and please sign your post.DrChrissy ^(talk) 13:22, 25 July 2015 (UTC)[reply]

University of British Columbia at Vancouver hosts one of the world's top geology, geosciences, and geological engineering programs in the world. Surely there have been hundreds of research projects regarding their local geology and civil infrastructure! Maybe a good place to start is the UBC Geological Engineering program website, and in related departments.

For example, I found Applied Science 170, an introductory undergraduate course they offer (at the Okanagan campus) in case studied of engineered systems failures. Here is their additional bibliography, which includes studies of dam and levee failures in the Pacific coast region. Some of those resources point to American (rather than Canadian) studies. For example, from the Teton Dam article, (whose failure was not due to earthquakes - but spurred a major study of dam failures in the entire Western United States), I found the Pacific Northwest Region Safety of Dams program, an ongoing research program of the United States Bureau of Reclamation - the other major government agency that manages water projects and dams in the U.S. Between this website and the websites of the U.S. Army Corps of Engineers, you can find just massive quantities of research and data on dam and levee safety. Here's an entire book: State of the Art for Assessing Earthquake Hazards in the United States (1995).

Nimur (talk) 14:35, 25 July 2015 (UTC)[reply]

But none for canada24.207.79.50 (talk) 17:22, 25 July 2015 (UTC) I was thinking more of scenarios written by companies that do catastrophe modeling24.207.79.50 (talk) 17:34, 25 July 2015 (UTC)[reply]

I think I should ask again, but in different wording.24.207.79.50 (talk) 21:18, 25 July 2015 (UTC)[reply]

Are Canadian earthquakes really that different from everyone else's tremors? The first half of Nimur's post is all about Canadian sources. Roger (Dodger67) (talk) 09:24, 27 July 2015 (UTC)[reply]

Sphere formation

What is the name for the phenomenon when a celestial body is massive enough so that it becomes a sphere? Th4n3r (talk) 16:07, 25 July 2015 (UTC)[reply]

Hydrostatic equilibrium apparently. Mikenorton (talk) 16:12, 25 July 2015 (UTC)[reply]

Yes, as mentioned in List of gravitationally rounded objects of the Solar System. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:14, 25 July 2015 (UTC)[reply]

1 2 3 Void burn (talk) 16:14, 25 July 2015 (UTC)[reply]

Dextrocycloversion and Laevocycloversion

In answering an earlier question, I was reading Eye movement - where it describes our ability to rotate our eyeballs not just left and right, up and down - but also to rotate them clockwise or anticlockwise about an anterior/posterior axis! (So that the top of your eye moves towards your nose while the bottom moves away from it).

I was totally blown away to discover this because it's not obvious that we can do it...and I can't think of any reason why we'd evolve to be able to do it. But This article shows the pair of muscles on each eye that are responsible for doing rotating our eyes that way (they are the "Superior oblique" and "Inferior oblique" muscles).

The motion is called Dextrocycloversion and Laevocycloversion - but web searches on those terms don't produce anything other than dictionary definitions of those terms that describe (often poorly) what this motion is and what muscles produce it.

Clearly we don't have conscious control over this motion as we do with the left/right and up/down axes. Standing in front of a mirror, tilting my head to one side or the other doesn't seem to result in any such motion. You'd think that doing it would result in the horizon spinning clockwise and anticlockwise in front of you!

I really find it hard to believe that this is true - but the muscles clearly exist - and the name for the motion is in every medical dictionary!

So - the obvious questions:

Am I totally misunderstanding these terms?
Why do we need this kind of motion?
Is there a way to produce the motion so we could observe it happening?
By how many degrees can the eyeball rotate in such circumstances? (I'm guessing it's a tiny number...but who knows?)

SteveBaker (talk) 18:34, 25 July 2015 (UTC)[reply]

The chief function of the two oblique muscles is to rotate the eye on its own principal axis to keep the horizontal level in certain head movements, but since the eyeball is radially symmetrical this movement is not easily observable.

Wendell J. S. Krieg, Functional Neuroanatomy (Philadelphia: Blakiston, 1942),pg. 68.—eric 21:05, 25 July 2015 (UTC)[reply]

Interesting. When walking with a normal video camera, the video is rather painful to watch, as it bounces about (hence the invention of the steadicam). We don't observe this when walking ourselves, though. Presumably the brain does a lot of image stabilization, but, since it's not enough to fix the video, there must also be some other mechanism to keep the image from bobbing about. I suspect that this is where those muscles come in. They might even predict your next step and act accordingly, as you make it, to avoid a delay that would wiggle the image.

Also, I suspect that some birds lack these muscles, since they keep their head steady as they walk, then suddenly move it to a new spot, then hold it steady again. A much cruder way to stabilize the image. StuRat (talk) 21:14, 25 July 2015 (UTC)[reply]

~~:The terminology section in Eye movement and the table in Extraocular muscles look useful.—eric 21:20, 25 July 2015 (UTC)~~ [reply]

~~This abstract may help in answering #4. Cyclotorsion seems the best search term.—eric 21:31, 25 July 2015 (UTC)[reply]~~

~~See the last part of the "Torsion" section of this article for #3 and #4.—eric 22:16, 25 July 2015 (UTC)~~[reply]

Searching for Ocular countertorsion i think answers everything.—eric 01:01, 26 July 2015 (UTC)[reply]

How long does it take for a new habitat to change an organism's DNA?

I'm not sure if my question makes sense. I was wondering if, theoretically speaking; my ancestors and I reside in Norway for the last 300 years or so (light-skinned and blue -eyed) and travelled to a warmer climate like Dominican Republic or Africa, how long and what mechanisms by which a person's DNA is changed to look like the current inhabitants? — Preceding unsigned comment added by 67.142.96.127 (talk • contribs)

How much sex are you having with the natives? --Jayron 32 01:57, 26 July 2015 (UTC)[reply]
The DNA itself doesn't change. What happens is that certain organisms reproduce and others don't, and the recombined DNA of those that reproduce is passed on. Imagine if there's a comet that strikes the earth, and only aquatic creatures and those that live buried in underground dens survive, while those that live above ground are roasted to death. (KT event). Then all the elephants will go extinct in a few days, if not hours. That is a drastic "change" in the organism's DNA. For human evolution, disease (think smallpox in the Americas) is the biggest game changer. Other traits like hair color can change very slowly within a population. What matters is the selection pressure. μηδείς (talk) 02:07, 26 July 2015 (UTC)[reply]

(edit conflict × 2) Assuming no interbreeding with the locals (so, assuming a large number of Norwegians accompany you) and ignoring tanning, the skin changes would be the result of Natural selection. One of your descendents could be born with a genetic mutation (not like sci-fi super powers, but a benign mistake in combining the parents' DNA) that causes them to produce more melanin than their ancestors (or their immediate ancestors at any rate). That descendent would be less likely to develop skin cancer and have more resistance to sunburning, so s/he would lead a healthier life and so be more likely to reproduce. A mutation could also occur to make them produce less melanin, which would make them more prone to sunburning and skin cancer, and so make it harder for them to survive long enough to reproduce as much as the darker-skinned descendent. The darker skinned descendent would have their own children, and some of their descendents could have a similar mutation, increasing melanin and so their chances of survivability. It is theoretically possible (though practically impossible) that the change could happen after a single generation (i.e. you have a kid who blends right in with the Khoisan). What would be more likely is that it'd take many generations. I'd guess that 1,000 years would still be theoretically possibly but practically impossible, 10,000 years as possible but remarkably fast, and that it could definitely happen in about 100,000 years. Of course, this is based on reversing how long it took African colonists in Europe to lose their melanin (giving them more vitamin D), a number that might have been thrown off by interbreeding with neanderthals. Ian.thomson (talk) 02:16, 26 July 2015 (UTC)[reply]

I don't think it took nearly 100,000 years for white skin to develop when Homo Sapiens Sapiens moved to Europe. According to Europe#Prehistory, modern humans appeared there some 40-43 thousand years ago. Not sure if we know how long it took for skin color to lighten after that. Does the earliest European modern human artwork from which color could be determined show black skin ? If so, when did it change ? StuRat (talk) 04:19, 26 July 2015 (UTC)[reply]

Why use artwork when you can use genetics? See Human_skin_color#Light_skin, Light_skin#Evolution. It's also not just time, one hypothesis is that there was relatively little selection towards lighter skin in Europe until about 6-10k years ago, roughly when certain behavioral and agricultural changes occurred. It seems from the research linked there that there were few if any light-skinned Europeans before ~20k years ago. SemanticMantis (talk) 14:19, 26 July 2015 (UTC)[reply]

July 26

Scar and hair biology

If someone has a small scar on the chin that makes a beard clearing... Can he transplant hair on the scar? If there are some Dermatologists that claim that they can transplant hair on this scar with about 60% success, are they talking the truth from a biological perspective? Can hair really grow on scars?... Maybe they mean that only some areas in the scar are living skin? What is your final conclusion on this? Thank you!!! Ben-Yeudith (talk) 04:42, 26 July 2015 (UTC)[reply]

If you are talking about hair transplant in scar area then answer is "yes". but one should have enough blood supply at that particular area..turbo 05:20, 26 July 2015 (UTC)[reply]

Turbo, Could you please elaborate even more? Can you give more details of what of the sub-questions the "yes" applies? Thank you. Ben-Yeudith (talk) 13:31, 26 July 2015 (UTC)[reply]

Can we have speed greater than c ?

In Michelson-Morley experiment, we saw that the speed of light in space is equal in all inertial frames and in relativity, light speed is defined to be the maximum. Is it really impossible to get speed slightly greater but equivalent to light speed such that if we calculate that speed as light speed, we won't be wrong?Sayan19ghosh99 (talk) 07:52, 26 July 2015 (UTC)[reply]

Are you asking how sure we are that nothing travels slightly faster than c? Experimentally I think all we can do is measure approximate masses. The mass of the photon is known to be very close to zero, but I suppose that leaves open the possibility that it's a tiny imaginary number (which would make it a tachyon). Theoretically, in quantum field theory, tachyonic particles make the vacuum unstable, which is a very strong reason to think they don't exist. (See Tachyonic field#Interpretation.) -- BenRG (talk) 08:57, 26 July 2015 (UTC)[reply]

My (non-expert) understanding is that the true c, from the viewpoint of relativity, is the velocity that can be attained only by truly massless particles. If photons had a tiny bit of (non-imaginary) mass, they would necessarily have to travel a bit slower than the relativistic c. However, this would also mean that c_photon, unlike the true c, would no longer be a constant in all frames, which would be quite easy to detect: experiments that measure this are thus experiments which can put the masslessness of the photon to the test.

There are also more sensitive tests available: for more on these, see John Baez' page here, and Photon#Experimental checks on photon mass -- The Anome (talk) 13:38, 26 July 2015 (UTC)[reply]

I might be wrong, but I think the OP is saying something like "What if we accelerate something to light speed, and keep on accelerating it ... even if it is still calculated as moving at the speed of light, couldn't it be going faster?" And the answer there is that it takes an infinite amount of energy to accelerate any object with mass to lightspeed, and it would have infinite relativistic mass; if you could apply two infinities of energy it would have two infinities of relativistic mass, but that doesn't really mean anything, and it doesn't ever happen, because if it happened even once we'd have all been sucked away by the infinite gravity of the object, no matter where it is in the observable universe.

That said, photons experience a phenomenon that is sort of like deceleration, in the red shift that occurs as space expands. After all, a galaxy that is coming at us at a slower speed might seem to decelerate and eventually turn back and move away from us as billions of years pass. The photons can't go slower than light speed, but they do lose energy. You might compare this to the difference in overall energy in them going from 0 * infinity to 0 * infinity / 2 (or whatever the redshift is at their source), but that of course isn't really proper mathematics. Wnt (talk) 14:59, 26 July 2015 (UTC)[reply]

Just to be clear, you CAN have 'speed' grater than C, quite easily depending how you define "speed". What you can't have is information faster than C. Our article Faster-than-light which no one has linked yet, is quite good! Vespine (talk) 22:40, 26 July 2015 (UTC)[reply]

Why in Bohr's stationary orbits an electron completes integer wavelengths?

Why mvr=nh/2π and 2πr=nλ ?Sayan19ghosh99 (talk) 07:53, 26 July 2015 (UTC)[reply]

In the Bohr model it was just assumed to be that way. The only justification for it was that it led to a correct formula for the spectral lines of hydrogen.

In real quantum mechanics with the Schrödinger equation, it's for more or less the same reason that musical instruments have discrete harmonics. -- BenRG (talk) 08:36, 26 July 2015 (UTC)[reply]

To continue a bit with the above, look at the Schrödinger equation article itself, specifically the first time-dependent formula: iħ multiplied by the partial derivative over time of the wave function is equal to the Hamiltonian of the wave function. Solutions to that equation always (???) seem to take the form e^{iħ [phase]}, so the wave function ends up as a three-dimensional loop in space, generally with a positive lobe and a negative lobe, as shown. I'll admit that one of the little mysteries I missed is where the negative end of an 1s orbital is, but I think it must be tucked in there somewhere... anyway, the point is that the wave function has to go "all the way round" in a way that ends up quantizing its angular momentum in units of ħ. Wnt (talk) 10:55, 26 July 2015 (UTC)[reply]

How much can ice reduce the temperature in a room.

If you put two liters of ice in 20 cm3 room, how much degrees will the temperature drop, when the ice melts?--Scicurious (talk) 17:03, 26 July 2015 (UTC)[reply]

20 cm3 is a very small room. You couldn't even fit 2 L of ice in there.

Assuming you meant 20 m3, you can work it out easily. Density of ice is about 0.92 kg/L, latent heat of fusion is about 335 J/kg, density of air under typical conditions is 1.2 kg m-3, specific heat of air is 1004 J/(kg K). The rest is just arithmetic.

If the ice is colder than 0 C you need to take account of the heat absorbed by warming up the ice to the freezing point. Short Brigade Harvester Boris (talk) 17:17, 26 July 2015 (UTC)[reply]

However, the adjustment for the ice being below 0 C is not large, because the latent heat of fusion is large compared to the heat capacity of ice. Robert McClenon (talk) 17:52, 26 July 2015 (UTC)[reply]

Generally true, which gives me the opportunity to correct my units: latent heat of fusion is about 335 J/g, not 335 J/kg. Short Brigade Harvester Boris (talk) 21:53, 26 July 2015 (UTC)[reply]

How did we get images of asteroid 2011 UW 158?

A week or two ago it came screaming by the Earth and the radio telescope in Puerto Rico took some pictures. Cool, radio pictures of screaming asteroids, but how was it done? One report said they used a 20 tw signal. How do you generate 20 tw of anything, much less a microwave? So they generate this signal, and point it at the asteroid, and the signal bounces back, but how do you make an image out of returns? Are they scanning the asteroid, pixel by pixel? Or are they somehow able to focus the return signal and get an image all at once, like a camera? 50.43.33.62 (talk) 19:14, 26 July 2015 (UTC)[reply]

Generating 20TW of (peak) power is actually quite easy: you really only need a very short pulse. When this pulse is scattered its temporal profile and spectrum change. From these you can reconstruct the shape of the surface. Ruslik_Zero 20:07, 26 July 2015 (UTC)[reply]

The technique of synthetic aperture radar is used to image objects. Twenty Terra Watts is not really a lot of energy, since a watt is defined by joules per second. I.E. If one was to release (transmit) one joule in a nano-second that would would equate to a 100,000,000 watts.. should the transmit power last for a full second.--Aspro (talk) 20:48, 26 July 2015 (UTC)[reply]

Easy? Sure it is, but with what? (Watt?) I can imagine all kinds of equipment that could be used for this, like capacitors and batteries and transformers, but what are they actually using? Tin cans? Diesel generators?

I can see how the temporal profile can tell you that some parts are farther away, and spectrum change can tell you if something is moving closer or away, but how do you turn that kind of info into an image? 50.43.33.62 (talk) 02:22, 27 July 2015 (UTC)[reply]

What report quoted twenty terawatts? Are you certain they didn't mean effective radiated power? Power is a complicated parameter for RADAR! Start by reading RADAR signal characteristics.

"The Radio Telescope" mentioned in the original question probably refers to the Arecibo Observatory. Arecibo usually operates passively, but for some experiments it can transmit as a true RADAR, as well: read about how the transmitter works; when it does so, it typically uses about 150 kilowatts of average power - that is how much power the electrical generator is providing. (That website is a bit old, citing an operations manual from year 2001, and there have been many facility upgrades at Arecibo since then - so use all of these numbers with caution)! The transmitter is often used to send a pulsed RADAR signal; so at any given fraction of a second, either zero watts or 2.5 megawatts are being transmitted.

That peak pulse number provides true instantaneous power. To compute peak ERP, you multiply the power with the antenna gain to derive a (fictitious) equivalent as if the energy was transmitted in all directions. This allows us to use simplfications in the RADAR equation. In actual fact, the energy is directed by the RADAR antenna: it is not a spherically-isotropic source. Radio astronomers like ERP because it's the amount of power that an equivalent spherical cow would emit.

In specific, you can read about the high priority NEO survey conducted by Arecibo to image 2011 UW 158: Current NEO surveys from the Solar System Sudies group at Arecibo Observatory. Their nominal operational power was scheduled to operate at 900 kilowatts for the survey.

For big antenna facilities like Arecibo, antenna gain is enormous - so you can get very strange values when you look at "effective" radiated power. The physical quantity of energy per unit time, on average, is still only the amount supplied by the electricity source, and is not "terawatts."

Nimur (talk) 14:29, 27 July 2015 (UTC)[reply]

July 27

What chemical properties make soap useful for cleaning?

Why is soap good at cleaning things? What chemical processes underlie the effectiveness of all soaps and detergents? I remember pondering this question during organic chemistry in college, and I vaguely recall coming up with something about "micelles" being especially good at isolating dirt and making it capable of being scrubbed away by physical force or washed away by water, but I feel like there is more to it than that. Why does soap create useful micelles when other compounds with hydrophobic epitopes don't? Is it perhaps related to the reason why soap makes long-lived bubbles with proper agitation?

Also, how is a soap's effectiveness increased or decreased by time and temperature? Does hot water really make certain soaps and detergents more effective than if they were used with cold water? Is there an ideal amount of time for which a given dirty item should be exposed to soap's chemistry, for maximum cleaning power? Thanks for your help! PJsg1011 (talk) 06:39, 27 July 2015 (UTC)[reply]

Regarding the chemical processes, this is due to the fact that one end of the molecule is hydrophobic, whereas the other is hydrophilic -- so the hydrophobic end sticks to the greasy dirt, whereas the hydrophilic end is attracted to water and pulls the grease away from the surface being cleaned. In effect, this makes the surface of the grease particles hydrophilic as well (by coating it with hydrophilic molecules), which makes them miscible with water when normally they're immiscible. One end hydrophobic, the other hydrophilic -- THAT is the key. And yes, higher temperatures usually increase soap's effectiveness -- but this is due to the normal increase in solubility with temperature. 2601:646:8E01:9089:F88D:DE34:7772:8E5B (talk) 08:58, 27 July 2015 (UTC)[reply]

Surfactants make the water grap nonsolvable stuff. Cheap kitchen cleaners use lactic acid to remove fat and oil. Surfactants are more expensive and some you do not taste or smell them. For that reason such cleaners have added parfume or substances we can detect by smalling them. Whe getting enging oils on your hands and use soap, the oils part is removed by water and soap but your hands feel like sill put into vinegar which is not beeing removed by the soap. Then the soap contains some glycerol which is a part of soap production, the ester can solve in water. For that reason shower gels or shampoo might be more effective aginst engine oil on the hands. Todays full synthetic engine oils are based on hydrcracked substances, some very stable compared to mineral oil are esters. Calcite is being removed by citric acid oder formic acid. This show you the major difference between bath and kitchen cleaners. --Hans Haase (有问题吗) 09:14, 27 July 2015 (UTC)[reply]

ESV

What rescue equipment and capabilities does a modern oilfield ESV (Emergency Support Vessel) like the Iolair have? 2601:646:8E01:9089:F88D:DE34:7772:8E5B (talk) 08:50, 27 July 2015 (UTC)[reply]

End of domino impulse

Is it possible to estimate how many dominoes it would take to completely stop the impulse imparted by finger or hand to the first domino? This states that 3,847,295 dominoes is still insufficient to completely exhaust the impulse, resembling a perpetual motion. By impulse I mean standard force to provide watchable collapse speed, not too strong and not too slow. Brandmeister^talk 14:45, 27 July 2015 (UTC)[reply]

Each domino contains gravitational potential energy. That means that it releases energy when it falls down. That energy goes into knocking down the next domino. You can even have each domino get slightly larger than the previous one, since the gravitational potential energy of the smaller one is more than the force required to tip over the larger one. So, there is no theoretically limit to the number of dominoes that can be knocked down. (There is a practical limit, though, as the more you have the greater the chance of them being knocked down prematurely or being misaligned so they don't all fall down.) StuRat (talk) 15:07, 27 July 2015 (UTC)[reply]

I saw a this video of a chain of dominoes of increasing size just the other day. AndrewWTaylor (talk) 16:34, 27 July 2015 (UTC)[reply]

And there are some even bigger ones here. AndrewWTaylor (talk) 18:13, 27 July 2015 (UTC)[reply]

This is an example of a chain reaction. To achieve perpetual motion, each domino would have to bounce back up into its upright state after it had toppled. You could then create a circle of dominos that repeatedly toppled and bounced back up - but this is, of course, impossible. Gandalf61 (talk) 15:14, 27 July 2015 (UTC)[reply]

Or just have an infinite number of dominoes. That could take a while to set up, though. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:13, 27 July 2015 (UTC)[reply]

Desert chimney

I wonder if this concept has ever been tried. In a desert, where the outside is hot but dry, if you use an inside evaporative cooler, that makes the inside air cool but potentially overly humid. If a chimney was added, wouldn't that let the humidity out of the house, but not the cool air, since cool air sinks ? You would need to arrange the chimney so sand wouldn't blow in and fall down it, and some convolutions would also reduce radiative heating. The flue on the chimney could then be opened or closed, to control the house humidity level. So, is this approach ever used ? (I realize there are also swamp coolers that evaporate outside the house, then circulate the coolant inside the house, but I'm not asking about those.) StuRat (talk) 16:27, 27 July 2015 (UTC)[reply]

See qanat, windcatcher ... there may be more useful terms for this tech, which has been used a very long time in the Middle East. Wnt (talk) 18:52, 27 July 2015 (UTC)[reply]

That's a bit different, in that they use wind to replace the air, while I'm talking about not replacing the air, but only allowing the humidity in it to diffuse away, even without winds. (In fact, in my design, you might want to close the flue when windy, to prevent replacing cool, inside air with hot, outside air.) StuRat (talk) 18:58, 27 July 2015 (UTC)[reply]

Desert termite mounds are humid and cool. They are basically very tall chimneys. The termites make them humid. They don't have swamp coolers in them, but I mention this because they remain humid and cool even though they are of the design you mention. 209.149.113.45 (talk) 19:21, 27 July 2015 (UTC)[reply]