Wikipedia:Reference desk/Archives/Science/2015 July 7

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July 7

Determining size of screw

What size screw is this?[1]My other car is a cadr (talk) 09:20, 7 July 2015 (UTC)

If it could be an American size, then your diameter measurement (threaded part) places it between number 12 and 1/4 inch. Your measurement of thread pitch, 23 threads per inch, is closer to the 24 threads per inch that is used with number 12 than to the 20 threads per inch used with 1/4 inch. See http://gsi.nist.gov/global/docs/vps/csfiles/cs_24-30.pdf Jc3s5h (talk) 09:57, 7 July 2015 (UTC)

Thanks for the help. I google imaged "1/4 inch screw" and this site[2] shows the same screw I got (at least I hope it's the same screw). My other car is a cadr (talk) 12:29, 7 July 2015 (UTC)

Resolved

My experience with cameras made in America, East Germany, and Japan (all of which were intended for the American marketplace) is the screw that holds them to a tripod is 1/4 inch diameter, 20 threads per inch. If you are in the US, Canada, or the UK, visit a hardware store to check (that's an ironmonger in the UK). Jc3s5h (talk) 12:44, 7 July 2015 (UTC)

Weird pin number setup on QRE1113

I'm trying, and failing, to get a Fairchild QRE1113[3] working here. Embarrassingly enough, I can't even seems to get the pins right. Regarding the second page of the datasheet:

1. Is it just me or is the pin one marker drawn in the "wrong" place? Every other component seems to have it in the upper left corner, but this datasheet drew it in the lower left corner. I said "drawn wrong", because the actual component[4] has the pin one marker in the right place.

2. Is it just me or are the pin numbering completely wrong? What I was taught was this: Dual_in-line_package#Orientation_and_lead_numbering, but the pin numbering from the datasheet completely disregarded convention. My other car is a cadr (talk) 15:19, 7 July 2015 (UTC)

I can't make out the pin marking in the actual pic. Do you have any way to make the device a larger portion of the pic ? StuRat (talk) 15:30, 7 July 2015 (UTC)

Sorry, I don't have have a macro-capable camera so this is best I can do. The component's pretty tiny so it's hard to get a good shot. I highlighted the notch here[5]. My other car is a cadr (talk) 15:47, 7 July 2015 (UTC)

Oops, had a brain fart. If you google image "QRE1113" then you'll get lots of high quality images of the actual device, and by the looks of things, the datasheet was correct. The pin one notch is indeed in a non-conventional spot, and that my device is the "wrong" one here. I'm guessing counterfeiting is to blame here. Funny they managed to copy the actual device but failed to get the pin notch right. My other car is a cadr (talk) 15:54, 7 July 2015 (UTC)

How do you know the device is right ? (You can try hooking it up that way, and let us know if it works, so we can close this Q.) StuRat (talk) 15:59, 7 July 2015 (UTC)

I got it working by brute-forcing all the 12 combinations. My other car is a cadr (talk) 16:11, 7 July 2015 (UTC)

Isn't that 24 combos ? 4 possible spots for first pin × 3 remaining spots for 2nd pin × 2 remaining spots for 3rd pin × 1 remaining spot for last pin. StuRat (talk) 16:16, 7 July 2015 (UTC)

I tried to pin down which one was the infra-red LED first, so that's only two pins; I only needed to brute-force the 1st pin and 2nd pin right (4 * 3 remaining spots), then I know the remaining two pins belonged to the phototransistor.

Resolved

Can a venus fly trap ingest human protein?

Is semen from a human male was regularly placed inside the mouths of a venus fly trap, would it be enough to sustain the plant? 182.253.73.219 (talk) 15:28, 7 July 2015 (UTC)

Venus_flytrap#Carnivory references many detailed scientific papers explaining what is digested and how. Semen#Composition_of_human_semen likewise has relevant information and citations. You can figure out the answer if you're willing to work for it and do the reading. You can ask at WP:REX if you have problems accessing the referenced material. Alternatively you might be able to perform some experiments. SemanticMantis (talk) 17:45, 7 July 2015 (UTC)

We're not really here to make people work for it, so I should point out that polyamines are distinctive components of sperm and contain large amounts of nitrogen, so in theory it should be a good source. However -- biology doesn't know theory. For all I know sperm could contain something that poisons the plant. As usual in biology, the only way to know for sure is to do the experiment. Wnt (talk) 10:53, 8 July 2015 (UTC)

Good luck with the Grant Application. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 12:04, 8 July 2015 (UTC)

There are a lot of weird and wonderful things studies at universities, see for example the IG Nobel prizes. Back to the original question, Venus fly traps need to be watered with pure water[6], any impurities above 50ppm will kill a fly trap in weeks or months.[7] They especially don't like minerals and salts. Human semen is well known for its salt levels (300 mg of sodium, and 100mg of potassium per 100ml) , sperm also contains many trace minerals such as calcium, zinc, copper,[8] magnesium and other chemicals including Urea, citrate, lactic acid, sugars. You also have to convince the plant to swallow. When an insect lands on the plant, it gets stuck, and tries to escape. In trying to escape it knocks hairs on the plant, that lets the plant know that an insect has been caught. A dead solid object, or a fluid will not trigger the traps reaction, and the trap will not swallow. But, as Wnt says, the only way is to try yourself. Martin451 17:21, 8 July 2015 (UTC)

@Martin451: The salt content you cite (300 mg/100 ml = 3 g/l) is actually less than the 9 g/l in saline (medicine) which approximates the salt level in human blood. I was doubtful of this but at least [9] says 10.2 mg/3.4 ml, which should be the same. According to [10] the hemolymph of Drosophila is roughly 353 mOsm = 0.3 osmoles. If that were all salt it would be 0.15 M NaCl = 8.7 g/l, I think ... I'm not doing it rigourously, but I think the salt content of fluids in a fly should be close to that of human blood. So I don't expect the plant to suffer salt poisoning from a reasonable dose of semen, given the usual caveats (what if we have some funny ion it isn't used to...?).

Getting a flytrap to "swallow" isn't that complicated, even for the amateur; it just involves touching the hairs with something. Wnt (talk) 18:36, 8 July 2015 (UTC)

As for the grant application, I'm thinking citizen science, DIYbio ... maybe crowdsourcing. Certainly they've funded crazier things by crowdsourcing than this. Though I don't know what you'd spend the money on ... porn, or exotic imported Venus flytraps? Decisions, decisions. Wnt (talk) 18:39, 8 July 2015 (UTC)

FWIW, here's a pitcher plant that feeds on bat feces. Wnt (talk) 19:32, 9 July 2015 (UTC)

How long does it take a droplet of water to evaporate?

I've looked at the article on evaporation, and I can't understand it very well. I know that how long it takes water to evaporate depends on lots of things, but I just want a ball-park figure: suppose I've been in the shower, then go through to my bedroom, where it's not so steamy, and warm enough to be comfortable naked, but not unpleasantly hot. Then how long will it take the water droplets on my skin to evaporate, so I don't have to use a towel? Just a rough answer would be great. Thank you. — Preceding unsigned comment added by 62.56.100.166 (talk) 19:28, 7 July 2015 (UTC)

The amount of time will vary enormously with ambient temperature and humidity. A time range of a minute to an hour would be possible in extreme conditions. In your bedroom it might be five minutes. Why not experiment to find out? Dbfirs 20:59, 7 July 2015 (UTC)

We could pick one of the Standard_conditions_for_temperature_and_pressure. SemanticMantis (talk) 21:52, 7 July 2015 (UTC)

The real issue is how quickly the human body can supply heat to the droplets of water. If you get out the shower, go to your bedroom, and sit down, your heart will slow down, you will begin to get cold, and the veins/capillaries etc. will move from further into your skin to retain heat, evaporation will slow down. If you go to your room, and do sit-ups or press-ups you will generate heat, the capillaries will move close to your skin in an effort to cool down, giving heat to the water droplets, which will evaporate keeping your cool.

The recommended daily intake of calories for a man is 2500, or about 100 an hour, this equates to 420kJ per hour or a sustained power usage of 0.116kW. The heat capacity of water is 4.2kJ(kg^-1)(K^-1) the latent heat of vaporisation is 2260 kJ per kg.

To take 1 kg (=1 litre) or water from 40C (body temperature) to 100C, would need 60*4.2kJ=252kJ of energy. To evaporate that water would need 252+2260=2512kJ.

Assuming the body converts all energy into heat to the skin, at is average over 24 hours, then the body could boil 420/2512=0.167 litres an hour.

This makes a lot of assumptions, including boiling the water, ignoring loss of heat from the lungs etc., and the maths will need checking. Martin451 23:14, 7 July 2015 (UTC)

These are really useless answers. "The amount of time will vary enormously with ambient temperature and humidity..." Yes, as I already said, I understand that there are lots of factors involved. "Why not experiment to find out?" Because I just want an answer, and you, "Dbfirs", haven't provided one. And "SemanticMantis" just says "We could pick one of the standard conditions for temperature and pressure", but doesn't actually answer my question. Then "Martin451" goes down the irrelevant track of discussing the energy inputs to the human body, even though we already know body temperature and I've already specified the likely skin temperature on which the water droplets sit (initially normal shower temperature, and later a comfortably warm, dry room). Also, "Martin451", I'm talking about evaporation, not boiling the water, so talking about raising the water temperature to 100 degrees is obviously wrong. Is there anyone here actually capable of answering this question? At least two of the respondents ("Dbfirs" and "SemanticMantis") aren't physicists, and it's a fair bet that neither is "Martin451". This is supposed to be the "Science Reference Desk", but none of you has answered a fairly simple question. Replies have either been useless or irrelevant. Is there a physicist working here who can help, please? Thank you. — Preceding unsigned comment added by 212.225.93.0 (talk) 23:07, 7 July 2015 (UTC)

You're acting like a jerk, so there's no reason anyone should feel motivated to help you. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:17, 8 July 2015 (UTC)

Dear 212.225.93.0 . How did you shift your geographical location so fast. Are you really the OP?--Aspro (talk) 23:23, 7 July 2015 (UTC)

First you have to answer the question 'How long does it take to read a book?' Short Brigade Harvester Boris (talk) 23:28, 7 July 2015 (UTC)

Water has a huge heat capacity and Enthalpy. If you body is wet at 40C, then evaporation will very quickly cool the skin, unless your body supplies more heat to the skin. The key fact, as I said above, is how well your body can supply heat, and keep the body warm. The fact is to evaporate water you need to supply energy to that water, or it will just get cold, and not evaporate. This is not a simple question, there are two many factors involved, the best way of answering is to make approximations, and estimates. The other solution, as mentioned above is to experiment, time yourself, have your bedroom at different temperatures, sit on a chair some days, and do press ups other days. This is the way a lot of physics is done, repeating experiments until you have established all factors involved. Martin451 23:29, 7 July 2015 (UTC)

I haven't shifted geographical location and I'm not sure what the numbers are, and I don't know who "OP" is. What I do know is that none of you is capable of answering my question, probably because you're not physicists. Saying I should do the experiment myself is useless: this is a reference desk, so if you don't know the answer, just don't say anything. However, I've now looked at some of the other questions on the reference desk, and it's pretty obvious what is really going on: the people here are mostly blowhards who get their kicks by pretending to know a lot about lots of different things, but who really don't know much. Lots of the people here try to answer lots of questions that they're obviously not qualified for, and they can't give useful answers. Instead they show off, using long words and making silly jokes to cover for their lack of actual knowledge. If you're not a physicist who can answer the question, please don't reply just to bolster your ego. You should make a list of the physicists, chemists, biologists, mathematicians, historians, economists, linguists (and so on...) who work here, then have a rule that only physicists answer physics questions, only chemists answer chemistry questions, and so on. This would make the reference desk better, and wouldn't leave your users (people like me) irritated. I'm not smart enough to answer my question about evaporation, but I am smart enough to know that it's sufficiently well phrased to describe the problem, and sufficiently clear that a physicist can probably give an approximate answer, which is all that I am asking for. If there's a physicist available here, please would s/he answer me. If you're not a physicist, please don't waste your time and mine. Thank you. — Preceding unsigned comment added by 212.225.93.0 (talk) 23:56, 7 July 2015 (UTC)

If you can waste our time, we can certainly waste yours. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:16, 8 July 2015 (UTC)

Dear 212.225.93.0 . OP means Original Poster that asked the question here. You are posting from London and not from the OP's location. So how did you move from one place to another so quick?--Aspro (talk) 00:03, 8 July 2015 (UTC)

I'm reopening this because although I mostly agree with the closure, there remains an issue important for the wider RD that needs to be clarified.

WTF? I thought we were talking about different countries or something. But in reality for me, the original IP geolocates to Kent, the current IP geolocates to London. The time between posts was over 3h 30 minutes. This was more than enough time to get between the two. After all, some people to commute daily between the 2 [11] [12].

More importantly, geolocation is rarely that precise. London and Kent could easily be the same location simply geolocating differently for whatever reason. Both ranges belong to Demon Internet. Perhaps mostly importantly, there is a good chance there is nothing in between (City of) London and Kent in terms of IP geolocation. In other words, even if the geolocation is precise, you may only have to be in a slightly different place to go from one geolocation to the other. In other words, the OPs responses may be problematic, but the geolocation itself is hardly indicative of anything.

Nil Einne (talk) 03:03, 8 July 2015 (UTC)

Be glad it's within the same country. We get open-proxy users (or more likely just one) who appear from random IP's from all over the world. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:16, 8 July 2015 (UTC)

OK, rough answer = 1 hour. Note that this assumes no wind, which will speed evaporation by blowing the envelope of humid air surrounding your body away. It also assumes no movement during the hour, which would tend to cause drops of water to fall off you. It also assumes you lie down on your back so gravity holds the drops on your chest in place until they evaporate. Now, if you'd like to do that experiment, I'd be interested to see how close my estimate comes. StuRat (talk) 03:44, 8 July 2015 (UTC)

Speaking as a physicist, the question is ill posed. Water wets skin, especially after soap has been used. So the drying may be more like a film of water than a series of discrete droplets. If any droplets do form on the skin, they will have a distribution of sizes and evaporation rates. Hair is hygroscopic and definitely holds lots of water, some of it through capillary action if long enough;hair drying is a completely different physics problem yet still relevant to your comfort. Who knows your skin temperature or what you consider comfortable, or your local humidity, or the length of your hair? How dry is dry enough? What about sweat production? The problem conditions are way too vague to give an honest answer. The physicist in me will tell you to do the experiment. I dry off in less than 10 minutes, even without a towel; my wife's hair can stay wet for hours.

If the question is restricted to what might be a simple, relevant model of evaporative drying, I would probably model you, for the purposes of thermal conductivity, heat capacity, etc., as a bag of water. Then this becomes the problem of water evaporating on an open surface. For this the Penman equation is a reasonable empirical model. If you are instead interested in the physics of droplets, the Mason equation is an approximate expression for the growth and shrinkage of droplets. --Mark viking (talk) 04:04, 8 July 2015 (UTC)

Sorry if my comment duplicates others. The question has far too many variables to answer with any accuracy. The initial water temperature is a factor, briefly, but a droplet on human skin soon achieves a stable temperature slightly below body temperature, unless the ambient air temperature is higher, as in desert conditions or a sauna. In such cases, the temperature will be sightly higher than room temperature. But even more important is the humidity. Evaporation takes place much faster at low humidities than high ones. Wind speed is also a very important factor. Higher speeds facilitate evaporation. Human behavior is also a factor. A high level of evaporative cooling may be perceived as something uncomfortable, and may motivate a person to wipe away or shake off water droplets. Then there are the factors I haven't yet thought about. Reading other answers, they include factors like personal perceptions of what "dry" really means, plus the ever-present hairiness factor. Cullen³²⁸ Let's discuss it 05:37, 8 July 2015 (UTC)

Mark Viking (a proper physicist) mentions yet another variable: the oiliness or greasiness of your skin, and how much fat there is underneath, and we cannot estimate this. I think it is very unlikely that any physicist here has studied evaporation of water from human skin in great detail (but I'm happy to be proved wrong). The best we can do is to make guesses, then do experiments to see how accurate we were. In the unlikely case of 100% humidity and a room temperature greater than that of your skin, the water will never evaporate. (BTW, the OP is correct that I don't claim to be a physicist since I studied the subject only to ordinary degree level and taught it only to A-level. I still think that an experiment is the best way to find out when there are so many unknowns.) Dbfirs 18:13, 8 July 2015 (UTC)

9.226 minutes. Justin15w (talk) 16:46, 9 July 2015 (UTC)

Sedatives

Can you please name three over-the-counter medications which are sedatives or sedative-like in a thick lotion, cream or jelly form. Thanks in advance. 84.13.144.160 (talk) 23:42, 7 July 2015 (UTC)

As far as I know all the OTC sedatives are anti-histamines. So check those. Ariel. (talk) 23:58, 7 July 2015 (UTC)

I would agree with Ariel that OTC sedatives tend to be anti-histamines but the OP mentions “thick lotion, cream or jelly” which are topical medications. IE not a route used for sedation. Can the OP explain more fully the reason behind his question? He may have got the nomenclature mixed up and really be asking something else.--Aspro (talk) 00:20, 8 July 2015 (UTC)

I would like to treat various skin conditions I have. I refuse to go to the doctor because the medicines he prescribes never have the intended effect. Therefore i am currently seeking a topical medication that has morphine-like effects. Fingers crossed. 84.13.144.160 (talk) 06:33, 8 July 2015 (UTC)

One of the rules of the reference desk is that we do not provide medical advice, which is pretty clear precisely what you are after here. If you don't want to go to the doctor, just ask the chemist, they will tell you what OTC topical medication is available. Vespine (talk) 06:58, 8 July 2015 (UTC)

One tip we can give though - the word you're looking for is "painkiller" or "analgesic". A "sedative" is something with a primary purpose of putting you to sleep. Many painkillers are also sedatives, and vice versa, but asking for a "sedative cream" is just strange. Smurrayinchester 08:10, 8 July 2015 (UTC)

• I think we have taken this as far as we can considering we don't give medical advice. What I might be able to add however, is a bit of background that you may make sense of. Many skin conditions are hard to tell apart by sight alone, so a GP just attempts to discount anything that may lead to acute death – so that your surviving relatives don't sue him. As most skin conditions resolve themselves in time (the human bodies ability to cure itself is awesome) he can just proscribe anything – without getting sued. This, I think, is your objection to handing him an open check that doesn't bring you relief. So, as Vespine suggests, go your local pharmacist (on day when he is not busy) and ask how would you treat this effectively? Without you posting photographs, I can not even hazard a guess that is might be something like psoriasis which can be mitigated by xxxxx, xxx, xxxx & xxxxx or if your suffering from xxxxxx-xxxxx which only needs short course of xxxxxx. Yet your pharmacist will have seen this all before -many times. Alternatively you could go on vacation to a country which have a free healthcare service. Doctors there can't increase their salary by proscribing ineffective treatments. --Aspro (talk) 15:49, 8 July 2015 (UTC)

Health care in France is a neighbour of the OP's UK although GP visits often aren't entirely free. Nil Einne (talk) 18:23, 8 July 2015 (UTC)

@Aspro: When I go to my local GPs-R-us barn, and whichever doctor I see takes my blood pressure, they proscribe salty food and excessive alcohol. The GP visits are free; (as I'm sure you know) much health care in Australia - including pharmaceuticals - is government subsidised. But not those proscriptions - I have to pay full price for them. Pete AU aka --Shirt58 (talk) 10:36, 9 July 2015 (UTC)

Have you actually gone back to your doctor and told them that the medications they prescribed are not having an effect? They might refer you to a specialist if they are not one. If your condition is not being resolved, it is important to inform the doctors of this, and to continue seeking medical attention, as skin problems can be symptoms of serious medical problems such as autoimmune disorders. --108.38.204.15 (talk) 20:54, 8 July 2015 (UTC)

Sunburn cream and gels with lidocaine is available over the counter. Note that "morphine effects" of sedation will not be over the counter but lidocaine has an analgesic effect and I believe is the pre-numbing solution used prior to a painful injection (i.e. gum injection of novocaine for dental work can be preceded by lidocaine topical application, same with wound care.) . --DHeyward (talk) 00:18, 9 July 2015 (UTC)