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July 6

Household LED lighting

Some LED lights for household use to replace incandescents have a similar frosted, globular appearance, and a similar size, to the bulbs they are replacing. An LED drawing about 12 watts is intended to replace an incandandescent 60-watt light bulb or thereabouts. My question is, how many individual light-emitting diodes are inside that LED "bulb"? Or more generally, what are the specifications of the largest single LEDs now in common use? --98.158.139.69 (talk) 07:54, 6 July 2014 (UTC)

There are a large number of incandescent replacements of various quality and using a large variety of LEDs types and brands so I don't know if your first question can meaningfully be answered.

As for the second, do you really mean largest? Or brightest?

One of the brightest single die LED is the latest version of Cree XM-L [1]. However although it can be powerful enough to beat a 60W incandescent, it isn't really intended for the purpose you describe and isn't used much for it. (Note that despite the similar name, the XM-L Easywhite isn't that similar as it's a multidie LED.) See e.g. Cree's own incandescent replacements which definitely don't use an XM-L or even a single LED of any type [2] by any resonable definition.

Then there's stuff like the SST-90/CST-90 etc which are single die and can be brighter than the XM-L although with a much larger surface area [3] [4] [5]. But again, although it can be brighter than a 100W incandescent, isn't really intended or well suited for incandescent replacements and so isn't used much for that purpose.

Of course you can also get massive LED arrays. E.g. BridgeLux make one that can output up to 16k lumens [6] [7] (probably some more details [8] on the test) [9] which is a lot more than any 60W incandescent (probably closer to a 750W halogen). I mean at that level, the LED itself is likely consuming well over 100W. (If you're really interested in size, the Vero 29 LED array is I believe ~29mm in diameter hence the name.)

I doubt this is the most powerful (or largest), many manufacturers have their own arrays, particularly the so called "chip-on-board" [10]. And depending on the quantity required, they may be able to produce something more if really needed.

Chinese manufacturers in particular seem quite willing to do that, even for relatively small quantities, although I'm not sure that the output will necessarily be much better than from a reputable manufacturer, or that it will last long or that it will be very uniform. But see e.g. these "500W" LED www.aliexpress.com/item/500W-Lamp-LED-chip-LED-chip-size-Taiwan-Epistar-45x45mil-47000-5000LM-FREE-SHIPPING/1401410645.html www.aliexpress.com/item/Free-shipping-500w-led-chip-white-color-8-4A-72-82V-3-years-warranty-high-brightness/1421216136.html www.aliexpress.com/item/500W-Cool-Cold-White-6000K-10000K-14000K-20000K-High-Power-LED-Light-45Mil-Chip/1253392737.html (which are ~ 47.6x47.6mm). Closest video I could find is this 200W [11] (running at 170W) but I don't know whether it's a Chinese LED and at 200W it probably isn't that different from the Bridgelux Vero 29 anyway.

In other words, the answer to your second question depends a lot on stuff like, what do you mean by "single LED", "common use", "largest"/"brightest".

If you're imagining use in household lighting, one of the obvious complicating factors is it's not necessarily meaningful to simply think of these in isolation. As shown by the incandescent replacement cases, using a single LED may actually be far more difficult given the specific light pattern requirement. Also it tends to complicate heat management. Of course using too many LEDs may similarly make it complicated to achieve your desired light pattern and otherwise complicate design. On the other hand, as particularly obvious in the flashlight arena, having a bright single LED (whether multiedie or single die) may sometimes be less important than having a surface brightness (i.e. the light output is spread out over a small area), one of the reasons why stuff like the SST-90 is much less popular than the XM-L. (The other is efficiency which of course related to both battery life and heat output and is particularly important in a flashlight.)

Besides all that, I don't believe most household lighting is really that well designed. For starters, until very recently the sort of lights available were very limiting, even more so if you only wanted incandescents or halogens. This and other factors means many people have a small number of bright lights which doesn't give that uniform lighting, when they'd probably be better served by more smaller lights. In other words, what's commonly used for incandescent replacements (or other replacements) may not necessarily be what would be well suited and commonly used if you can actually afford a professional lighting designer.

Nil Einne (talk) 16:42, 6 July 2014 (UTC)

Thanks for that! You asked "what do I mean by single LED". I have here at hand a flashlight that uses 4.5 volts and has a clearly visible array of 16 LEDs. When I look at LED turn signals on cars (presumably using 12 volts) or LED traffic lights (presumably using 120 volts or more), each light similarly displays an array of LEDs, but those LEDs are obviously larger than the ones in the flashlight. So I was presuming that the LED "light bulb" I talked about would contain a similar array of LEDs, using 120 volts, and I wondered how many were likely to be in there. (Yes, I realize that the voltage to the individual LEDs may be lower if they are wired in groups in series; I just mention the voltage incidentally.) Your second link refers to 80 LEDs in a "bulb" of similar style and size, so that's an answer.

As to the second question, I didn't have any specific interpretation in mind, but yours (or something less detailed) is the sort of answer I was expecting. Thanks again. --50.100.189.160 (talk) 05:38, 7 July 2014 (UTC)

You said "incindentally", but it's worth pointing out that LEDs must run at specific (low) voltages which correspond to the photon energy (and thus vary by color). --Tardis (talk) 06:11, 7 July 2014 (UTC)

I tend to think that a single bright light source, pointing in all directions, suspended from the center of the ceiling, is the most efficient placement of lighting, regardless of the light source (LED, CFL, incandescent, halogen, etc.). You want two things with your light, for it to spread everywhere in the room, as evenly as possible, but also to reflect only once before you see it, to limit absorption. Those two goals tend to be in opposition, though. For example, placing lights in corners tends to light the room more evenly, but then you get more reflections off walls and thus more absorption and lower efficiency. If you have white walls the absorption is a less of a factor, than, say, dark wood paneling.

Oh, and also you want to avoid blindingly bright light. This is less of a problem if it's on the ceiling, as you don't normally look in that direction, whereas light sources placed lower in the room need to be pointed towards a wall to reduce this problem, but this again increases absorption. Here technologies that spread the light out over a larger area, like traditional fluorescent tubes, might have the advantage. If they won't blind you, then you don't have to point them towards walls or add a frosted cover to spread the light out (which also decreases efficiency). I think ultimately we may have true LED TVs (as opposed to those sold as LED TVs which are just LCD TVs with an LED back-light) that can be left on white (or whatever color we prefer) when not in use, to light our rooms. StuRat (talk) 14:13, 9 July 2014 (UTC)

People who are immune to addiction

For understanding any biological process it is invaluable to look for mutants that fail to undergo it. It would seem like the same should be true for addiction. Simply doing an online search, I see people who claim to be able to stop smoking cigarettes whenever they wish ( [12] [13]). But I'm having trouble finding the inspiration to think of a way of phrasing the search to pull out serious research papers, indeed if any exist. Has anyone tried to find these people and look for a genetic basis? Wnt (talk) 18:03, 6 July 2014 (UTC)

There is some evidence that people who are genetically predisposed to very low levels of novelty seeking (such as myself) also have a low (but not zero) risk of developing addictions, but the evidence is not conclusive. 24.5.122.13 (talk) 22:12, 6 July 2014 (UTC)

Identifying a unique group of people who are (intrinsically rather than situationally) immune to (substance or behavioural) addiction in order to probe what genetic mutation might be responsible for their immunity is a research idea that runs into ethical and practical challenges. Genome-wide association study (GWAS) is in its infancy and needs a massive number of statistical tests to eliminate false-positive results. One problem is that genes identified in GWAS for drug dependence may be involved either in adjusting brain wiring prior to drug experiences, subsequent to them, or both. On-going research into drug, alcohol and tobacco addiction focusses on Dopaminergic pathways of which the Mesolimbic pathway is believed to be a "reward" pathway. The Substance dependence article gives over 100 references in this field. 84.209.89.214 (talk) 00:05, 7 July 2014 (UTC)

You're absolutely right about the difficulty of GWAS even for far more easily diagnosed disease. I was hoping for some sort of gift from the gods here - an old history that carefully analyzed the opium addiction of hundreds of Chinese nobles in a few pedigrees who are now preserved safely in a crypt, or a lucky hit from the reverse genetics of a particular allele of something like dopa decarboxylase. I suppose one of the countries like the UK that DNA test all arrestees might conceivably cross-reference that with blood data on addictive drugs and then see which required treatment for or showed some visible sign of withdrawal, but as you say that is an ethical line I'm not at all eager to see crossed. Wnt (talk) 14:28, 7 July 2014 (UTC)

There are certainly people who aren't prone to specific addictions, but not being prone to any addictions would be quite rare, if it exists at all. You might have better luck looking at meds which cause a wide range of addictions as a side effect. See Dopamine receptor agonist#Side-effects for an example. If we can figure out what it's doing, that should help us to develop meds which do the opposite. StuRat (talk) 04:09, 7 July 2014 (UTC)

This is a good lead. Searching d3 agonist addiction pulls out some less than compelling information about buspirone being used to prevent reinstatement in rats,^[14] slightly better evidence for effectiveness of an ingredient in Chinese herbal medicine (levo-tetrahydropalmatine),^[15] and various other mysterious effects.^[16][17] But I find these studies frustrating - you're seldom sure what protein is really being targeted, the authors end up trying to explain why certain doses have a small effect and larger doses have none. Numbers are small, error bars overlap, etc. No doubt there is something to it but I can't shake the impression that they're looking at something like the correlation between whacking a mouse with a rolled-up newspaper and how long it takes to solve a maze afterwards. Wnt (talk) 14:59, 7 July 2014 (UTC)

It's not even clear that the current use of the term "addiction" lends itself to such distinctions. During the period when cigarette smoking was still being studied as being carcinogenic, there was a distinction between habit-forming and physiological addictions. Cigarette smoking fell into the habit-forming arena whereas opiates were physiological. Heroin metabolism changes liver function, for example, and could cause death if withdrawn. Nicotine did not. To elevate the dangers of cigarette smoking, there was a campaign to change the definition of addiction. It's current form is something along the lines of "any voluntary behavior that a person chooses to do despite negative social or physical impacts" (paraphrased). So alcohol drinking that doesn't damage social relationships or health would not be considered "addiction" but smoking would if it continues despite the person knowing the risk of lung disease (this redefinition was the objective sought to combat smoking and elevate treatment options). A person with end stage cancer that is on Fentanyl and would suffer severe withdrawal symptoms and possibly death if Fentanyl were withdrawn is not considered "addicted" though they would be classified as "physically dependent." Since the definition is so entwined with political correctness and human behavior, it would be difficult to create an ethical and scientifically meaningful experiment. Gambling, sex, heroin, methamphetamine and tobacco are all potentially clinical addictions with very different mechanisms on behavior. A confounding question like "can someone be addicted to second-hand smoke?" or "why is the cancer patient using 200mg of Oxy a day not addicted, but the 40mg recreational user an addict?" These are political-social constructs of the definition and not a scientific distinction. --DHeyward (talk) 10:29, 7 July 2014 (UTC)

And knowing that behavior is ultimately driven by brain chemistry means that all addiction could be described as physical addiction, such as to the dopamine released by engaging in that behavior. Therefore, the distinction of whether they will suffer measurable physical harm if they go "cold turkey" seems like a more meaningful one, to me. StuRat (talk) 14:49, 8 July 2014 (UTC)

Geomagnetism

How are the earth's internal currents (that cause its magnetic field) generated? Is there a big battery in there?--109.149.211.41 (talk) 18:27, 6 July 2014 (UTC)

Take a look through Earth's_magnetic_field#Physical_origin and see if it answers your question sufficiently. Mikenorton (talk) 18:32, 6 July 2014 (UTC)

The key is dynamo theory. I believe that I have seen a diagram of a cleverly constructed mechanical dynamo, containing no magnets but only a conductive disk and electromagnets powered by the disk, which I was told would produce electricity and a magnetic field when spun above some velocity. But I haven't seen it in quite some time. Wnt (talk) 18:35, 6 July 2014 (UTC)

Not a battery but a giant magnet in pictorial terms. The Earthcore is believed to be composed primarily of iron aka ferromagnetic material. --Kharon (talk) 22:44, 7 July 2014 (UTC)

Hehe, you're barking up the wrong tree. So far as I know (and I'm no expert either) the Earth's core is vastly hotter than the 1000K Curie temperature of iron, i.e. it's not ferromagnetic. It's a conductor, moving, that has electric currents because it is moving through its own magnetic field, and maintains a magnetic field due to its own electric currents... it is, in short, as fearsome a knot of diffy-q's as you would ever cross paths with. Wnt (talk) 00:29, 8 July 2014 (UTC)

If you think the Earth's magnetic field is complicated, look at stellar magnetic field. StuRat (talk) 14:52, 8 July 2014 (UTC)

July 7

Bird identification

This weekend I was camping in Upstate New York and I saw some birds that I'd like to know more about. I was camping in a hay field and in the mornings there were several birds that were pecking around the field. They weren't there the rest of the day, just the mornings. When I was playing fetch with my dog, and I threw the ball near the birds, the nearest one to my dog would fly near my dog as if trying to scare her away. So, they seem to be at least a little territorial and once I saw that, I stopped throwing it anywhere near the birds.

As far as their appearance goes, they were white and either brown or grey. I didn't want to get very close, so I couldn't be sure about the color. They reminded me a bit of sandpipers in the way they walked. Their beaks were at least an inch long, possibly two. The beak wasn't really long and thin but more triangular. Their backs were brown or grey. The bellies were white. Across the chest coming up from the belly was a horizontal band of the color, then a band of white, and then the neck was colored. And they were larger than sparrows or such but weren't as big as crows.

Any help? Dismas|^(talk) 01:49, 7 July 2014 (UTC)

List of birds of New York may help. --Jayron32 02:01, 7 July 2014 (UTC)

Going through that list, does killdeer work? --Jayron32 02:09, 7 July 2014 (UTC)

Nearly. This image seems to match the color/white/color banding I saw on the chest. Dismas|^(talk) 03:18, 7 July 2014 (UTC)

Note that killdeer are known for diving at animals and people they consider to be a threat, only to veer away at the last moment, in order to drive them away. So, I think that's a match. StuRat (talk) 03:54, 7 July 2014 (UTC)

Thank you, both! Dismas|^(talk) 23:17, 7 July 2014 (UTC)

Dried milk

With the dishwasher temporarily not working, my roommate and I are currently handwashing everything, and sometimes (like now [hangs head]) the dishes pile up for a few days. Of all the dirty dishes that we normally produce, the most difficult to clean are the glasses in which a tiny amount of milk was left to dry out, rather than rinsing it out and leaving a little water behind. Part of this is due to the physical location (it's at the bottom of the glass), but even so, it's far harder to scrape out the dried milk than anything else, as it adheres to the glass with an unusual firmness. Can anyone imagine why? I'm running water into the cup and then using a soap-fortified scouring pad that looks remarkably like this image, if that helps. Nyttend (talk) 02:53, 7 July 2014 (UTC)

When I was very much younger casein glue made from milk was a very effective way to stick things together. That link actually mentions that it is still used in the labelling of bottles, so presumably it works well with glass. Your kitchen may have become a glue factory. HiLo48 (talk) 03:26, 7 July 2014 (UTC)

I don't think it's just milk. Any number of substances that rinse right out with water when wet seem to become well adhered to the cookware once they dry. Consequently, rinsing the dishes immediately saves a heck of a lot of effort later. Also, dishes which lack sharp corners make it easier to wash up. StuRat (talk) 03:49, 7 July 2014 (UTC)

Somewhat OT and I'm not certain this will help in your case but generally speaking if let something which has dried up soak for a while (probably at least 30 minutes) it will be a lot easier to clean up. Re: what StuRat mention, it may not be quite as easy if you hadn't let it dry up, but it's easier than trying to clean it after only a minute or two of soaking. In fact particularly with pots and pans just used for cooking, it may sometimes be easier to clean up after soaking than it is straight away. As for the more general case, beyond just cleaning it up straight away, or at least rinsing out the item, you can always fill it with sufficient water that it's not going to dry up. Nil Einne (talk) 06:13, 7 July 2014 (UTC)

That's my usual approach too. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:22, 7 July 2014 (UTC)

Being rather on the slob side of life, I've found that using very hot water, plenty of soap, and the rough side of a sponge works exceptionally well (even without soaking) - then again, the hot water at my house is very very hot. The simple solution, though, is to rinse out oatmeal, milk, and other things like it ahead of time.Phoenixia1177 (talk) 04:14, 8 July 2014 (UTC)

Is it worth pointing out that the OP actually asked "Why?" HiLo48 (talk) 04:34, 8 July 2014 (UTC)

As in, why does the residue of a liquid cling to the container after the water has evaporated? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:43, 8 July 2014 (UTC)

I'm not sure if that was addressed to me or the discussion thus far, but it's the same reason that any drying adhesive works. Also relevant: the history section of the Adhesive article mentions casein, Casein Glue, and [18].Phoenixia1177 (talk) 18:57, 8 July 2014 (UTC)

In the case of a liquid in the container that includes anything "sticky" (eg, casein, sugar, gelatine), the sticky component becomes more concentrated as water evaporates. This would be part of the reason why. CBHA (talk) 19:02, 8 July 2014 (UTC)

Level of humidity and comfort/discomfort on the human body

Is there a chart somewhere (on Wikipedia or elsewhere) that breaks down the categories of humidity and the relative comfort to humans? I am referring to the humidity level only. I am not referring to a chart that displays humidity levels alongside actual temperatures (such as the charts located at the article for Heat index). I have looked in Wikipedia and in Google searches and can't seem to find anything. Sometimes, on my local news, the weather report of the meteorologist will include a chart that says something like this: Humidity 50 to 59% = Comfortable; 60 to 69% = Mildly Uncomfortable; 70 to 79% = Extremely Uncomfortable; 80 to 89% = Dangerous. (I just made up those numbers, but the chart would look something like that.) Does anyone know where I can find a chart like this? Thanks. Joseph A. Spadaro (talk) 17:42, 7 July 2014 (UTC)

Any such chart would be very subjective. Some people enjoy high humidity. Some hate it. Some adapt to it, or its absence, over time. And temperature is always relevant to comfort too. HiLo48 (talk) 17:46, 7 July 2014 (UTC)

Relative humidity is very closely tied to air temperature, so you can't have a useful chart without knowing the temperature it was made for. The dew point is a measure of absolute humidity, so it is not related to the air temperature. There is a chart in our dew point article relating the dew point to human comfort. Katie R (talk) 17:54, 7 July 2014 (UTC)

I would speculate your local news was taking a slice through the heat index chart you linked to for the temperature it was expected to be that day. Our heat index chart doesn't break down "mildly uncomfortable" (for 80 degrees all temperatures are in yellow), but I'm sure there are some opinions about that out there. Or, being entertainers, the weather forecasters might just draw the lines ad hoc based on their own preferences. Wnt (talk) 18:47, 7 July 2014 (UTC)

Thanks. Your response confused me. Regarding my local weather report: Why would he do as you suggested? The weather reporter would know the specific local temperature (as you stated), but he would also know the specific local relative humidity as well ... correct? If he knows both values, why would he bother to create that speculative/hypothetical generic chart for other values (that he knows do not even exist today)? That would be akin to him saying something like this: "Today's temperature is 80 degrees F. And today's relative humidity is 52%. Therefore, it will be a relatively comfortable day today. However, if today's relatively humidity was 84% (which it is not), then today would have been very uncomfortable for us" (or something to that effect). Why would he offer hypothetical information like that (via his generic chart), when he knows the exact specific information to offer for the day? Or am I misunderstanding your post? Thanks. Joseph A. Spadaro (talk) 19:33, 7 July 2014 (UTC)

He might have been trying to "educate people about what humidity is". I don't know. It's a TV show for entertainment, there's some creativity involved, and I can't really say what his motivation is. Wnt (talk) 11:32, 8 July 2014 (UTC)

So, if a person knows one statistic (relative humidity) without knowing the other statistic (temperature), there is no general categorization of comfort level? If I saw somewhere that the relative humidity was, say, 75%, that wouldn't tell me anything at all (with regard to comfort level), until and unless I also knew the actual temperature? Is that how this works? Thanks. Joseph A. Spadaro (talk) 19:21, 7 July 2014 (UTC)

Yes, you need both. For me, e.g., 75% humidity at 40F would be chilly, while 75% humidity at 70F would be comfortable, and 75% humidity at 104F would be uncomfortably warm. SemanticMantis (talk) 19:34, 7 July 2014 (UTC)

(edit conflict) Correct. A psychrometric chart can be used to get an idea of the relationship between all the various measures of temperature and humidity, but it can be tough to understand at first. With an air temperature (dry-bulb) of 25 C and 75% RH the chart gives a humidity ratio (measure of absolute humidity) of .015, which a psychometric calculator [19] shows is equivalent to a dewpoint of about 20 C, which out dew point article claims is somewhat uncomfortable for most people. However, with an air temp around 17 or 18 C the ratio is .01 or 14 C dew point, which falls in the comfortable range. Katie R (talk) 19:35, 7 July 2014 (UTC)

Also, notice that the calculator isn't needed - the wet-bulb temperature at 100% RH is the same as the dew point, so that figure can be read right off the chart. It slipped my mind when I first wrote the response. Katie R (talk) 19:42, 7 July 2014 (UTC)

89% here and I'm "mildly uncomfortable" after digging a 3x4x3 foot hole. Three on the UV index. The moon is waxing gibbous. Guess my temperature within three degrees (Celsius) and win a signed copy of "Burnin' Up" by Judas Priest (the only one without a Wiki article). InedibleHulk (talk) 19:54, July 7, 2014 (UTC)

@InedibleHulk:, 25 °C (77 °F). CBWeather, Talk, Seal meat for supper? 01:17, 8 July 2014 (UTC)

Aw, so close! It was 21. Dealer wins. But nobody goes home empty-handed: Here's the never-overplayed "Living After Midnight". InedibleHulk (talk) 01:25, July 8, 2014 (UTC)

Both temperature and wind speed figure into it. As an example, 20 below with low humidity and calm winds can be a lot easier to take than 20 above with high humidity and strong winds. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:36, 7 July 2014 (UTC)

Thanks. So this is the part I am not understanding. I look at my local weather report (or I watch it on the TV news). The weather guy tells me what today's temperature is. The weather guy also tells me what today's relative humidity is. After knowing these two values, I then have to go "dig up" that heat index chart to make sense of what this all means? I can't imagine that the TV weather reporter works on the premise that after he offers his data, his viewers go dig up that heat index chart to make sense of it all. No? Joseph A. Spadaro (talk) 19:43, 7 July 2014 (UTC)

Local weathercasters that I'm familiar with will usually give the heat index as well, especially on a very warm day. As in, "It's 87 but it feels like it's 93." ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:19, 7 July 2014 (UTC)

Is it more likely that the local weather reporter was offering a chart/graphic based on the chart located at the dew point article under the section titled "Relationship to human comfort" (using the second and third columns of that chart)? Maybe the weather reporter was discussing (on his chart) humidity as measured by dew point (in degrees) rather than humidity as measured by relative humidity (in percent). Does that seem more likely? Joseph A. Spadaro (talk) 19:50, 7 July 2014 (UTC)

Yes. I agree with Katie that dew point is a much more useful measure of humidity. I use this site to get the dew point forecast, since my local weather station is similarly useless: [20] (I normally only select the temperature and dew point check boxes). Specifically, I need to know whether to leave my windows open with fans in them at night or not. With a dew point over 70F, forget it, the humidity isn't worth it, I run the A/C all night instead. With a dew point under 60F, it is worth using the fans. Between 60 and 70F, it depends on how hot and humid it is inside.

Now, as to how relative humidity got to be what is reported on weather forecasts, that's a mystery to me. It's just nowhere near as useful as the dew point. Weathermen do provide all sorts of extraneous info, seemingly designed to prove how smart they are, that has nothing to do with how to plan your day. Telling you what it would feel like if we changed the temperature or humidity by a given amount is just one example. StuRat (talk) 20:01, 7 July 2014 (UTC)

As I understand it, the dew point is about as low as the temperature is going to get until the next air mass moves in. Hence it can feel muggy at 70. In the frozen north, as you may have noticed, when the humidity is reasonable you have to scrape the frost off your car in the morning. When it gets to 20 below, there may be no frost to be scraped off. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:22, 7 July 2014 (UTC)

(ec) Not everything a meteorologist discusses is made for telling people what kind of shirt to wear today, though. A landscaper might awake in the morning and look at the RH, for example; near 100% indicates that there's probably quite a bit of dew on the grass, and he should wait before firing up the lawnmower. He could arrive at a similar conclusion by looking at the current DP and temperature, but that's true of many indices a meteorologist provides. In general the DP is much more useful than RH, but I wouldn't assume your local weatherman shows both to boost self-satisfaction... it's just standard as part of any weather broadcast. – Juliancolton | ^Talk 20:25, 7 July 2014 (UTC)

Here the local TV stations rarely tell us the dew point, but tell us the relative humidity religiously, as if it was somehow important. StuRat (talk) 20:59, 7 July 2014 (UTC)

It is religiously important. Humidity's our proverbial scapegoat. If we blamed the sun directly, we'd anger Him. And nobody wants an Angry Sun. InedibleHulk (talk) 21:04, July 7, 2014 (UTC)

ZrZn₂

What do we call this compound? It exists, since apparently it's been reported as a possible ferromagnetic superconductor, but that's all I know. I didn't realise that it was possible for such metal-on-metal compounds to exist, and the naming isn't mentioned in IUPAC nomenclature of inorganic chemistry. Nyttend (talk) 23:53, 7 July 2014 (UTC)

Is it not a ceramic, in the same fashion as other metal/semimetal compounds from comparable chemical groups, like hafnium diboride, titanium dioxide, and zirconium diboride? ... or is it an alloy with more metallic-like characteristics? It seems to be a unique material that's somewhere in-between. There are a wide variety of research papers [21] [22] [23] that seem to indicate a diffusive equilibrium of zinc-zirconium, with many possible stoichiometric ratios coexisting. That sounds like an alloy almost by definition.

This paper - The Zn-Zr System (Dutkiewicz 1992) appears to be the grandfather-paper that's commonly cited among all the others. It may be the authoritative reference. Nimur (talk) 01:34, 8 July 2014 (UTC)

The typical term for such a compound is an intermetallic. Mr.Z-man 03:19, 8 July 2014 (UTC)

I'm sorry: I meant "what do we call this specific compound", like how we call NaCl "sodium chloride", not simply "a salt". Nyttend (talk) 04:46, 8 July 2014 (UTC)

Zirconium dizincide - there are other dizincides, as shown here (I've found reference to calcium, copper, magnesium, platinum and sodium versions). Mikenorton (talk) 07:11, 8 July 2014 (UTC)

Or just zirconium zincide, as in this US patent (assuming that's not ZrZn). Mikenorton (talk) 19:59, 8 July 2014 (UTC)

July 8

Simple change to laws of Physics to reverse cup anemometer

Is there some simple change to the laws or constants of Physics, that will cause cup anemometers to rotate in the reverse direction?

That is, I want clockwise-rotating anemometers to rotate anticlockwise, and vice versa.

Thanks in advance --RM — Preceding unsigned comment added by 121.247.86.28 (talk) 12:10, 8 July 2014 (UTC)

Probably not without changing the universe in dramatic ways. StuRat (talk) 14:07, 8 July 2014 (UTC)

Turn the anemometer upsidedown? CBHA (talk) 14:53, 8 July 2014 (UTC)

Or the OP could stand on his head while observing it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:40, 8 July 2014 (UTC)

We're discussing changing the universe so presumably the solution would be to turn the universe upside-down, not the anemometer. F=-ma would be interesting but I have a feeling the rest of the universe wouldn't work well enough for your anemometer and wind to continue existing. Katie R (talk) 16:35, 8 July 2014 (UTC)

The most obvious solution is to turn the time vector 180 degrees. To accomplish that, the OP would need to leave a message in God's suggestion box. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:11, 8 July 2014 (UTC)

In the mean time, just put the battery in your analog clock in backwards. Bonus, your sense of "clockwise" also reverses, so the anemometer now is already going backwards in that sense. DMacks (talk) 17:22, 8 July 2014 (UTC)

What we would need to do is arrange things so that the drag coefficient of a concave hemisphere is greater than that of a convex hemisphere. Without attempting to think about the maths, possibly if air were rheopectic, so that the slower air associated with the concave vane would have a lower viscocity than the faster air at the convex vane, and therefore generate less of a drag force? Tevildo (talk) 20:30, 8 July 2014 (UTC)

Thanks Tevildo.

I read up about drag. Pressure drag is the strongest component of drag here, am I right? Assuming that the other components of drag are negligible, is there a simple explanation as to why pressure drag of a concave hemisphere is less than that of a convex hemisphere? And what are the laws/constants that can be altered to invert this? --RM

From what I infer from Anemometer, the actual wind speed is calculated from a combination of the "captured" air in the cups and the partially offsetting drag the wind hitting the back of the cups. That calculation is going to vary depending on the shape of the cups, and the article mentions an optimal construction of the cups. I'm at a loss to comprehend what laws of physics would have to change to make the flow of gasses and liquids behave differently than they do. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:45, 8 July 2014 (UTC)

The answer to 'what are the laws/constants that can be altered to invert this?' is 'None.'

I'm not just being flippant. Not only are the laws of the universe fixed, they're also a matched set. All the laws we see in action are the product of the comsic and quantum scale laws that we have come to regard as fundamental. The behaviour of a human-scale device like an anemometer depends on the laws for the fundamental particles, in ways that are difficult to comprehend. AlexTiefling (talk) 22:55, 8 July 2014 (UTC)

It's certainly possible to imagine a universe with different laws of physics - but the likelyhood of there being anemometers in such places seems exceedingly remote. Even the smallest changes to the laws seems to result in there being no stars, no planets, no atmospheres and no people...which pretty much precludes anemometers. SteveBaker (talk) 03:34, 9 July 2014 (UTC)

If the anemometer had negative mass, it would go the other way.

If F is fixed, F = m a implies that if the mass changes sign, so does acceleration. Negative mass comes with its own weirdness; a negative-mass planet could orbit the sun, but it could not have a moon, neither of positive nor negative mass. A negative-mass planet itself wouldn't be stable, either. - ¡Ouch! (^{hurt me} / _{more pain}) 06:03, 9 July 2014 (UTC)

¡No! Nor would a zero-mass anemometer stand still in the wind. Air molecules striking the concave sides are decelerated more than molecules striking the convex sides because the latter can form streamlines around the cup. It is the mass of the air molecules that would have to be negative to allow less force to cause greater deceleration, and that's impossible. 84.209.89.214 (talk) 17:34, 10 July 2014 (UTC)

Astigmatism

Are small astigmatisms of -0.25 or less normally corrected? 82.132.216.31 (talk) 13:48, 8 July 2014 (UTC)

With glasses, it's easy to correct astigmatism, so they might as well. However, since contact lenses are normally free to rotate, it's more of a challenge to correct for astigmatism there. StuRat (talk) 14:04, 8 July 2014 (UTC)

My personal experience is that optometrists only measure and specify prescriptions (for e.g. astigmatism, myopia) in multiplies of 0.25 dioptre, but this might be outdated. Without the need for other associated correction (e.g. myopia), most people would not bother with glasses for such limited astigmatism. If glasses are being prescribed anyway, 0.25 dioptre might be corrected, but not say half of that. With contact lenses, I would expect this not to be corrected – basically exactly what StuRat is saying. —Quondum 18:56, 8 July 2014 (UTC)

I have 0.50/0.75 astigmatism correction on my contact lenses. AFAIK it's not a big deal to fix it in contacts, it's just an engineering problem that has been solved. 88.112.50.121 (talk) 19:08, 8 July 2014 (UTC)

My wife was astigmatic and wore contacts (before she had her eyes lasered!) - and the weighted/rotating contact lenses were a continual pain. The problem is that they get rotated out of position for one reason or another and actually make your vision worse until they move back to the correct position. She'd find that blinking kinda helped - but the ones that rely on gravity to do the job suck when you're driving because every time you take a corner, centrifugal force messes up their position. So I strongly disagree that it's "been solved" - the "solution" is only partially effective. SteveBaker (talk) 20:09, 8 July 2014 (UTC)

AFAIK the gravity-driven solution is old fashioned, first generation kind of stuff. It's now driven by micro serrations on the lens, and as the wearer blinks, the eyelid vs. serration action will orient the lens, gravity has nothing to do with it. Works fine for me, sorry it didn't work for your wife. 88.112.50.121 (talk) 20:32, 8 July 2014 (UTC)

SLEEP STUDY

Can anyone help me find out when (what year) the United States Air Force conducted it's first sleep study for Sleep Apnea? Thank You! B~u~g~g~e~d — Preceding unsigned comment added by 173.171.120.204 (talk) 21:01, 8 July 2014 (UTC)

You can contact the Sleep Lab at the US Air Force Academy here. Perhaps someone there may be able to answer your question. --Jayron32 05:27, 9 July 2014 (UTC)

Biological taxonomy (history of)

Which taxa have not been revised since Carolus Linnaeus introduced his system of biological taxonomy?
—Wavelength (talk) 23:52, 8 July 2014 (UTC)
I have mentioned this discussion at Wikipedia talk:WikiProject Tree of Life.
—Wavelength (talk) 23:57, 8 July 2014 (UTC)

Species like Canis lupus are normally mentioned for the first time in a text or paper with their original identifier. Are you asking us to list all species attributed like this to Linnaeus, or some other question? μηδείς (talk) 00:45, 9 July 2014 (UTC)

I have read of some taxa being split, and other taxa being combined, on the basis of things like genotypes and phenotypes. Which taxa have never been revised?

—Wavelength (talk) 00:49, 9 July 2014 (UTC)

I don't know that there's a specific list anywhere, but many of the articles in Category:Plants described in 1753, Category:Fungi described in 1753, and Category:Animals described in 1758 remain at the same name Linnaeus gave them. Linnaeus' Species Plantarum (1753) was the beginning of binomial nomenclature for plants and fungi; the 10th edition of Systema Naturae (1758-1759) was the beginning of binomial nomenclature for animals. Rkitko ^(talk) 02:11, 9 July 2014 (UTC)

Linnaeus named many thousands of taxa of all levels of hierarchy; many (probably most) still exist as names today (though some may be modified in terms of their membership), it would be beyond the scope of anyone here to list all of them in a reasonable amount of time. It is possible (but unlikely) that you'll find such a list existing. You'd have to go through every taxon Linnaeus himself named and then compare it to the modern list, which has millions upon millions of names on it. Good luck. --Jayron32 05:24, 9 July 2014 (UTC)

• Well, an obvious example that hasn't been revised if one looks synchronically is Homo sapiens. We simply don't have any close enough relatives for there to be any confusion, and racial epithets like Homo sapiens mongolensis were never a matter of settled consensus--and the species level, although as mentioned above as suffering borderline cases really is the only objectively definable taxonomic level. Everything else is a judgment call. μηδείς (talk) 19:41, 9 July 2014 (UTC)

Carl Woese would beg to differ. See Five-kingdom_system#Modern_view and Three-domain_system. The modern systematists almost universally use cladistics these days, and the old school of morphological taxonomy is literally dying off. The modern perspective can be summed up as "the most natural divisions of life are between domains, and between species, everything else is artifice born of convenience." SemanticMantis (talk) 19:55, 9 July 2014 (UTC)

Woese would beg to differ, but as I said, his view is neither established consensus, not objectively definable in the way species is. To quote Nicholas Wade's recent book on race, if races were clearly definable they wouldn't be races, they'd be species. It remains that as a species, there has been no scientific splitting or combining of two existing populations of Homo as species.

There isn't really established consensus on definition of species either, as you likely know. Woese' view is supported in systematics about as much as climate change is supported by climate scientists (i.e. widely). But we're far off topic here, and I have not other references of use to add. SemanticMantis (talk) 20:18, 9 July 2014 (UTC)

Yes, indeed, there is almost total consensus on the definition of a species as it applies to sexual species. What there often isn't consensus upon is how it applies in certain borderline cases. μηδείς (talk) 18:16, 10 July 2014 (UTC)

I was tempted to ignore this, but I don't want any readers to be misinformed. Your link provides ample evidence that there is not total consensus on the definition of species, and how they are to be identified. In case anyone's curious, it says:

“ About two dozen species concepts have been identified or proposed since Mayr's 1942 book, and many articles and several books have been written on the species problem. At some point, it became common for articles to profess to "solve" or "dissolve" the species problem.

Some have argued that the species problem is too multidimensional to be "solved" by one definition of species or one species concept. Since the 1990s, articles have appeared that make the case that species concepts, particularly those that specify how species should be identified, have not been very helpful in resolving the species problem.

”

(bolding by me, citations removed for clarity) You also mention sexual species, and this is another reason why the domain split is often more objective and natural than species distinctions, because definitions based on sexual reproduction cannot be used for huge chunk of organisms. For example, the archaea/bacteria split is much less arbitrary than the distinction between e.g. Escherichia_coli and Escherichia_fergusonii. Since you asked for it, there it is. This is not to say that species is a useless concept. It is in fact very useful, and the problems are mostly of interest to small subfields of biology. I'm really done here now, but feel free to grab the last word if you like ;) SemanticMantis (talk) 19:57, 10 July 2014 (UTC)

July 9

Pulmonary embolism and COPD

I can see, even with my layman's brain, that COPD can be implicated in cases of PE, but what about the other way round? Is there research to show that a past history of PE without other lung issues (say a non-smoker who had a PE as the result of a DVT) increases the chances of COPD occurring? --86.12.139.50 (talk) 13:47, 9 July 2014 (UTC)

PS Before someone says ask my doctor, I'm not asking about an individual patient, but generalised research/data on patientS. --86.12.139.50 (talk) 13:51, 9 July 2014 (UTC)

Eczema herpeticum

I hear often that herpes is carried by a large majority of the population and I also hear that eczema increases the chances of contracting eczema herpeticum if exposed to the herpes virus. So why don't more people with eczema get eczema herpeticum? — Preceding unsigned comment added by 90.192.127.95 (talk) 14:14, 9 July 2014 (UTC)

• Define "get" there's a difference between carrying the virus and showing the symptoms. All the various herpes viruses are quite common, but may only exhibit symptoms once or never. I was hospitalized for quite some time for major abdominal surgery. At one point I had an itch on my spine like a mosquito bite, which was odd, since I was in one of the most expensive hospitals in the world, on my back, during the winter. Turns out I "had" the shingles (the most mild case in history, from what I have read and seen in other people), even though I felt an itch for a few times on one day. Having an infective agent and manifesting the typical or worst symptoms of that agent are two different things. μηδείς (talk) 19:58, 9 July 2014 (UTC)

"Herpes" is a misleading term. The herpes class of viruses includes the one that causes chicken pox, which many people have been exposed to. The ones which cause the venereal disease are less widespread. StuRat (talk) 23:55, 9 July 2014 (UTC)

Why is everything green through night vision goggles?

I got some answers here but didn't feel there was any clear answer I could add to the appropriate Wikipedia articles. I can't believe the word green isn't even used in those articles.— Vchimpanzee • talk • contributions • 19:36, 9 July 2014 (UTC)

• Night vision goggles detect heat. Heat can be cooler or warmer, i.e., brighter or darker, but it doesn't come in inherently different primary colors of heat. Primary colors exist because we have theree types of cones, not because nature comes in those colors. Night vision goggles could come in red or white or whatever. But it turns out that the single color our eyes react to best is green--tthe brightness component of green is better than that of blue or red, so green is a reasonable choice in their design. — Preceding unsigned comment added by Medeis (talk • contribs)

Sorry, but that is, at best, misleading. Infrared light comes in different wavelengths just like optical light. Astrophotography makes good use of that to produce fantastic images. For black-body radiators, infrared, intensity and wavelength distribution are coupled. But that's a bit besides the point. Most modern night vision systems don't use infrared illumination, but rather work by image intensification, using a photo cathode and/or a photomultiplier. In other words, the incoming photons are not observed directly, but trigger the release of an electron that is accelerated towards a fluorescent screen, where it forms a secondary image. Each photon either has the necessary energy to release an electron, or not. Thus, the difference in colour (wavelengths/energies) is lost. The single colour one sees is the fluorescent colour of the screen. --Stephan Schulz (talk) 20:31, 9 July 2014 (UTC)

Since this is controversial, some sources would be helpful. My objective here is to improve the appropriate Wikipedia article or articles.— Vchimpanzee • talk • contributions • 20:43, 9 July 2014 (UTC)

I thought this had been pretty well covered last time. The mechanism converts the invisible light to kind of a "gray-scale" visible light. Instead of gray they use green. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:10, 9 July 2014 (UTC)

It was, but I didn't get a clear answer I felt I could use on any Wikipedia article.— Vchimpanzee • talk • contributions • 21:18, 9 July 2014 (UTC)

Maybe you could craft an attempt at an answer, here, and various editors here could refine it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:26, 9 July 2014 (UTC)

That's pretty much what I was trying to do, thanks. I'm out of time for today and have to return to the real world.— Vchimpanzee • talk • contributions • 21:29, 9 July 2014 (UTC)

The only special thing about the green is it is a good cheap phosphor commonly used for oscilloscopes and suchlike. See Phosphor#Cathode ray tubes. There shouldn't be anything special about it in the night vision goggles articles unless there is a citation for night vision googles saying it is common or giving a reason for the colour -- i.e. the usual no original research business. Dmcq (talk) 22:44, 9 July 2014 (UTC)

You can't say "only" and then say "good cheap". Green is gooder that R&B because it is more intensely perceived at a given brightness (good). I am sure someone who actually studies this sort of physics can explain that, but green is indeed the brightest of the primary colors. μηδείς (talk) 23:01, 9 July 2014 (UTC)

Night vision goggles are green because way back in the 1950s when they were first invented, and worked entirely with simple analog optoelectronics, they used a green phosphorescent image intensifier screen. Now, everyone expects the images to look this way, so that's how they get built.

A few months ago, I had the privilege to visit Air Mobility Command (60 AMW) at Travis Air Force Base, and I got to wear a pair of real-life combat night vision goggles that the C-5 Galaxy and C-17 Globemaster pilots wear during certain types of night flight. They're entirely digital. They have a CMOS image sensor and and LCD screen inside of an eyepiece optic, and the entire package was controlled by an image signal processor - it's basically a tiny binocular pair of digital cameras with a live preview and a fixed-length zoom-lens. Compared to the electronics inside my iPhone 5S with the gain manually boosted, the image intensity was about the same (although the night vision devices actually had a much larger f-number because they double as binoculars - and there's a lot more to image quality than luminosity - so it's not a fair comparison). But, I can even render the camera image on my iPhone 5S screen using only green pixels, so that I can make it look cool, too.

The reality is, modern night vision devices do not need to appear green. Many will display the final image in black-and-white. Many people confuse thermal imaging with infrared imaging with near infrared with image intensification. These are each different types of night vision device. Now that the electronics and the screens are all digital and computerized, the output image can be made any color and brightness that the designer wishes. They still make them look green because "it looks cool," and you'll hear a zillion theories about human eye sensitivity, or phosphorescent screens, or handwaving about "infrared," that are essentially incorrect.

Nimur (talk) 23:38, 9 July 2014 (UTC)

Here are some photos from the Travis AFB media page : Night Vision Devices used by ground crews and ground security, but no photos of (or through) the gear the pilots get to use! 60th Air Mobile "owns the night". Nimur (talk) 00:25, 10 July 2014 (UTC)

I would hope that the U.S. military doesn't choose green for its night-vision equipment because "it looks cool". You haven't provided a source for that claim, and if I understand correctly your expertise consists of having once looked through a pair of night-vision goggles.

The article Night vision device doesn't contain the terms CCD or LCD, and leaves me with the impression that modern night-vision devices work the same way that they always have. That makes more sense to me, since a device that worked like your iPhone would have a battery life comparable to your iPhone's. If power consumption were not an issue, they would surely use a false-color display, not a monochrome display of any color. -- BenRG (talk) 17:52, 10 July 2014 (UTC)

They don't use green: they use a digital screen. It can be made to render in any color. While I recognize that my comments above are, at best WP:OR (and at worst, it could be possible that I'm just some loony on the internet - although in actual fact I'd like to hope I'm not!), it isn't hard to find sources to back up my claims. For example: here's a news story about F-16 fighter pilot helmet displays: 177th Fighter Wing receives force multiplier technology. "The pilots can choose color palettes and layouts prior to the mission. Once we find out who's flying, we install the modular HMIT to each pilot's physical specifications..." Nimur (talk) 21:52, 10 July 2014 (UTC)

The phosphor used on the screen (or the electronic display) could be in any color they wanted - but our eyes are more sensitive to green than to most other colors - so that's probably the reason for the choice.

However, our OP remarked that this information is being requested in order that it can be added into a Wikipedia article - and for that, we need to find solid references that say why this particular color was chosen. It's not enough to know the answer - we need references. SteveBaker (talk) 20:32, 10 July 2014 (UTC)

This website gives the answer and seems pretty authoritative - they make the things! "A green phosphor is used in these applications because the human eye can differentiate more shades of green than any other color, allowing for greater differentiation of objects in the picture". Strangely, the website is given as an external link in the Night vision device article but nobody has used it for references.Richerman (talk) 21:27, 10 July 2014 (UTC)

July 10

Pressure drag not symmetric?

This is somewhat related to my question from two days back.

Given an object and an axis, it has pressure drag when moved in air along the axis. It has a different pressure drag when moved in the opposite direction. Is there a decomposition of pressure drag into symmetric and asymmetric components? That is, is there a known component of pressure drag that does not change when the direction is reversed? --RM — Preceding unsigned comment added by 121.247.86.28 (talk) 15:46, 10 July 2014 (UTC)

By applying the Parallelogram of force one can always decompose the drag forces into a component parallel to the given axis and another component. 84.209.89.214 (talk) 17:06, 10 July 2014 (UTC)

To clarify my question: Is there a decomposition of pressure drag into two components, one independent of forward/reverse direction, and another that depends on forward/reverse? --RM — Preceding unsigned comment added by 121.247.86.28 (talk) 17:55, 10 July 2014 (UTC)

Regarding drag as a function of a real variable (the velocity), yes, it always has. The decomposition is into a sum of even and odd functions. —Quondum 19:19, 10 July 2014 (UTC)

Apart from the cases of a planar cutout or a symmetrical object such as a sphere, No. Drag is in general a non-linear function of velocity that depends on viscosity, laminar/turbulent flow and possible shock waves. Reversing the flow direction past a 3-D object does not change the object's cross section but without symmetry the flow behaviours and consequent drags can be very different (as the Anemometer cups demonstrate). See also Aerodynamic drag and Drag equation. 84.209.89.214 (talk) 22:01, 10 July 2014 (UTC)

The relation between diarreah and ear infaction

What is the relation between ear infection to diareah (not from aspect of asking advise, but from the aspect of biology aspect)מוטיבציה (talk) 21:50, 10 July 2014 (UTC)

None that I know of -- the ear and the intestines are not connected except through the circulatory system (and even in terms of circulation they're on different loops), so there's no way for an infection to travel between the two except through the bloodstream. 24.5.122.13 (talk) 21:54, 10 July 2014 (UTC)

Wikipedia spells this condition Diarrhea with an alternative spelling diarrhoea that is chiefly British. The Greeks had the word first: διάρροια from διά dia "through" and ῥέω rheo "flow". Presumably the OP wonders about a relation between diarrhea and an ear infection or Otitis but I know of none. 84.209.89.214 (talk) 22:21, 10 July 2014 (UTC)

Taking antibiotics for the ear infection could cause diarrhoea as they can upset the normal bacteria balance in the gut. Richerman (talk) 22:33, 10 July 2014 (UTC)

yes, but one of the symptoms of ear infection in babies is diarrhea. So what is the relation between the two?

Night vision device

In yesterday's discussion about night vision devices, Nimur said, quote, "Many people confuse thermal imaging with infrared imaging with near infrared with image intensification. These are each different types of night vision device." Which got me thinking: are there any night vision devices out there which combine two or more of these functionalities -- maybe even all four? 24.5.122.13 (talk) 21:50, 10 July 2014 (UTC)