Wikipedia:Reference desk/Archives/Science/2013 October 5

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

October 5

3D printer that can make a copy of itself

Can a 3D printer be made that can make a copy of itself? 3D printers are rather slow, but even if it takes a week for one printer to make a copy if itself, in a year's time you'll have enough to cover the entire Earth's surface. Count Iblis (talk) 01:12, 5 October 2013 (UTC)

Given that 3D printers incorporate quite a lot of complex electronics etc, not at the moment, no. They can produce many of the mechanical parts though: see RepRap Project. AndyTheGrump (talk) 01:25, 5 October 2013 (UTC)

Not to mention that why would you want it to replicate? It is a very expensive way to make an inferior product as far as many parts go. And if you want a vast number, conventional mass production methods are far cheaper and quicker. 3D printing is good for "feel it in your hand" checking the design of parts, and seeing how a device with many parts goes together - somewhat similar to the use of wooden mockups by aeroplane designers before CAD/CAE visualisation tools became available. 1.122.115.40 (talk) 05:37, 5 October 2013 (UTC)

Lots and lots of people for a long time have thought about building self-replicating machines for various reasons. Certainly not practical with anything like today's 3D printers, but it would be a major first step. Staecker (talk) 12:10, 5 October 2013 (UTC)

One consideration is that you would have to start with a pile of raw materials big enough to cover the entire Earth's surface. 173.62.242.128 (talk) 11:12, 5 October 2013 (UTC)

Thanks, the RepRap Project looks interesting. Perhaps one day you could make self-replicating machines that will eat up entire planets to make Dyson spheres, traveling from one solar system to another until all the stars in the entire galaxy are surrounded by Dyson spheres. Due to the exponential increase in the number of machines, this would not take very long. Count Iblis (talk) 20:05, 5 October 2013 (UTC)

3D printers, in their present developmental stage, are pretty primitive machines. Even if people report having printing this or that, its possibilities are very limited, both regarding the form of the output as well as the plastic used. OsmanRF34 (talk) 22:45, 5 October 2013 (UTC)

• See grey goo. μηδείς (talk) 04:50, 7 October 2013 (UTC)

Neanderthal diets

Is there any estimate for how many calories in the adequate neanderthal diet, and also what kind of food was mostly eaten (what kinds of meats, grains etc.) — Preceding unsigned comment added by 174.88.241.119 (talk) 04:07, 5 October 2013 (UTC)

See Neanderthal behavior#Diet. Seems like we don't know much about that topic, and no doubt it varied hugely according to habitat.--Shantavira|^{feed me} 07:18, 5 October 2013 (UTC)

Brains and muscles burn the most calories, and Neanderthals had bigger brains and were more muscled than us sapienses. μηδείς (talk) 16:30, 5 October 2013 (UTC)

Why does skin feel nicer after a shower?

Given people use moisturizer, I would assume skin would feel nicer without the oil washed off. But it seems, at least to me, to have a nice "just-showered feeling". Can anyone explain this? Thanks. μηδείς (talk) 05:06, 5 October 2013 (UTC)

Hmmmm. I wonder how many people use moisturizer? I don't. HiLo48 (talk) 05:34, 5 October 2013 (UTC)

It's a girly thing. They like to put all sorts of liquids, oils, and greases on their skin. I've never understood why. I always feel better after I have used soap to get all oils etc, whether my skin's natural production, or otherwise (eg oil or grease on my skin from working on machinery), off. Recently my lady had an ECG check. The electrodes would not stick to her skin. The cardiologist then said "this often happens with women, but never with men. Please come without any moisturiser on next time." 1.122.115.40 (talk) 05:44, 5 October 2013 (UTC)

Moisturizer is for dry skin and it is also essential if one wears make-up. Plus dry skin makes people look older. Young people have natural "dewy" skin. I have family and friends who've spent their lives out in the sun of Southwest U.S. and their dry skin looks like leather. Contrast that to people who live in more humid environments (think tropics) where skin isn't so wrinkled. Probably the good feeling you get from showers is the same one gets from exfoliating...you're removing dirt and dead skin cells. But your body needs the oils that your follicles produce. Liz ^{Read! Talk!} 02:31, 7 October 2013 (UTC)

I like lotion and moisturizer on occasion, it feels nice and smells good. Skin care is not the exclusive domain of women. On a side note, that there are "girl things" and "boy things" pisses me off a little, women get way better clothing; I'm looking forward to the day I can wear a kick ass antique style dress in public.Phoenixia1177 (talk) 06:09, 5 October 2013 (UTC)

Horses for courses. I like wearing a good business suit. There is great freedom to choose a nice shirt and tie. 1.122.115.40 (talk) 10:54, 5 October 2013 (UTC)

Suits and shaving went pretty much the same for me: they were really awesome, at first, but once I had to doing/wearing it/one everyday, they got boring pretty quickly. As for the dress (I wish I had pictures) I recently played a women that wore one in a small play my friend wrote; with everything done right, it looked absolutely awesome (I don't think I could figure out the hair and makeup though:-( ).Phoenixia1177 (talk) 11:03, 5 October 2013 (UTC)

I'm male and use moisturizer, but I consider it a medical necessity. I use it on my feet, which otherwise get so dried out the skin on the soles cracks and bleeds and would then become infected. Similarly for my lips, where I use lip balm. It was interesting when I shopped for some lip balm in Charlotte, NC. Unlike the North, where we keep it in the pharmacy section, in the South they think it's so "girly", they put it next to lipstick. I'm not sure if this is purely a cultural difference, or partially due to dryer weather in the North in winter, making things like lip balm more of a medical necessity. StuRat (talk) 01:07, 6 October 2013 (UTC)

Looking around on Google, it appears to be a common feeling and common question, but I didn't see any definitive answer. A lot of people seem to think that the heat makes your muscles feel good and that there are various psychological factors. Is it specifically your skin that feels better, or do you just feel better, in general, but notice it in your skin? (that sounds like something a serial killer might ask...I can't think of a better wording though). Personally, mines the former, but there do seem to be certain physical indicators of a feeling of "betterness".Phoenixia1177 (talk) 06:09, 5 October 2013 (UTC)

I've given this some thought and, as it happens, I've had my daily shower. It makes me feel good because 1) the warm water is relaxing; 2) the heat tends to fix muscle stiffness, and 3) getting rid of the oils that naturally accumulate on the skin allows the cooling effect of sweating to work much better with less perceived sweat. I note that in hot climate areas like Australia, people enjoy a shower or bath every day. In cold climates such as England, at least until recent times bathing only every second or third day or even once a week was the norm, driven by the desire to look good and not smell. This tells me that either they were too skinflint to tolerate the cost of water heating, or they don't feel better after bathing lie us folk in warm climates do. 1.122.115.40 (talk) 10:52, 5 October 2013 (UTC)

I live in the UK and in the 1950s and 60s and even into the 70s most people didn't have central heating or showers, no double glazing and poor insulation. There was usually ice on the inside of the windows on cold, damp winter mornings and you got dressed under the blankets. Heating up water for a bath using a coal fired boiler or electric immersion heater was a long and comparatively expensive business and you only got one shot at getting the temperature right. Then once you'd had a bath you had to get dressed in a freezing cold bedroom. Also families were bigger before the contraceptive pill came along. The worse-off people in small terraced houses often had an outside toilet and no bathroom and had to fill up a zinc bath in front of the fire in the living room or use public baths. All-in-all not conducive to bathing more than once a week. I remember talking to one of our South African research students in the 70s and she said that when people in SA told her she wouldn't want to bathe every day in the UK she didn't believe them, but once she got here the cold reality of the British winter was something of a shock and her habits changed. I'm sure this is why the Australians love to make jokes about Pommie immigrants not washing and hiding their money under the soap. Richerman (talk) 15:23, 5 October 2013 (UTC)

The muscle thing is a big one for me; I have tourettes and twitch my neck muscles constantly, and painfully, so after a really warm shower is usually the best that I feel all day. It's also a good place to think, if you aren't quick about it, sometimes mulling over the past day can be relieving. Interesting point about differences and climate; I'm going to see if I can find something on the subject going in that direction later- someone had to write a paper about this somewhere (seriously, there's paper on if you should, shouldn't, leave up toilet seats...)Phoenixia1177 (talk) 11:03, 5 October 2013 (UTC)

We have "his and hers" ensuites in our house. That's even better. Mine stays up and hers stays down. 1.122.115.40 (talk) 11:06, 5 October 2013 (UTC)

• The muscle thing is a separate issue. I take hot showers when I have a sore muscle/muscles. But any old shower (assuming I use soap, not just water) will give my skin a distinct "smooth" feeling for a few hours that is very pleasurable. As for moisturizers only being for women, many black men use them too, or they will get "ashy" skin. Whatever the phenomenon is I am looking at, it has to do with the surface of the skin, not the muscles. μηδείς (talk) 16:29, 5 October 2013 (UTC)

Thinking about this further, I wonder if there is also an effect because the hands themselves are cleaner, and better able to feel. μηδείς (talk) 18:47, 5 October 2013 (UTC)

Not everyone likes to shower or take a bath: According to this article: "

King Louis XIV stench came from the fact that his physicians advised him to bathe as infrequently as possible to maintain good health. He also stated he found the act of bathing disturbing. Because of this, he is said to have only bathed twice in his lifetime. Another in this “gruesome two-some” class among the aristocracy was Queen Isabel I of Spain who once confessed that she had taken a bath only twice in her lifetime, when she was first born and when she got married." Count Iblis (talk) 19:46, 5 October 2013 (UTC)

Will Cuppy repeated that story about Isabel, and added a footnote that "They gave her a third one after she died." ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:44, 5 October 2013 (UTC)

Along the same lines, there is the (probably apocryphal) story that the color isabella, a yellowish-brown, was named for the color of her underwear... - Nunh-huh 02:37, 8 October 2013 (UTC)

One thing I've wondered is whether people who bathe infrequently or not at all might have a different bacterial flora that is better adapted to that condition, so that they might smell less than someone who abruptly stops after a lifetime. (By and large the smelly compounds are lipid products like small carboxylic acids, still highly reduced and, in theory, could be oxidized by microbes for energy) But I doubt anybody funds research into this one. :) Wnt (talk) 20:16, 5 October 2013 (UTC)

Did you hear about the masochist who liked taking cold showers? So he had hot ones. HiLo48 (talk) 22:40, 5 October 2013 (UTC)

I am not sure how this got onto the smell of Frenchmen and the sexual proclivities of German nobility. μηδείς (talk) 21:12, 6 October 2013 (UTC)

I think in regard to Liz's suggestion above, the exfoliation question makes sense, the lessening of the thickness and roughness of the skin seems a plausibe answer. I wonder how much skin comes off on average? μηδείς (talk) 03:17, 7 October 2013 (UTC)

Side Effect -vs- Symptom in Psychological Disorders (context = psychopathy)

In some disorders, there are "side effects" that are commonly observed with the disorder, but are caused by it- for example, people who are insensitive to pain, suffer more injuries; autistic people saying inappropriate things in certain situations. People with psychopathic personality disorder have poor impulse control, I was wondering if this could be a side effect of an inability to empathize and experience guilt. I imagine that guilt/empathy would be a strong motivator to dissuade us from many of our impulses. On the same subject: people who are insensitive to pain can learn to not injure themselves (as much), autistic folk can learn to recognize certain social cues intellectually, etc. Even if you can't teach a psychopathic individual to empathize, could you teach them to have better impulse control/less violent behaviour? Most generally, can certain disorders be viewed as a lack of certain psychological senses, and for those that can, is there an analogy to learning to compensate with other "senses"? (in the sense of the example cases given) (psych isn't a subject I actively study, so please be charitable with anything that seems outright stupid, I may be describing this poorly given my ignorance of the subject).Phoenixia1177 (talk) 06:32, 5 October 2013 (UTC)

The essence of what you are saying is well known: Yes, you can teach a person to synthesise whatever aspect iof their psychological makeup is missing. It is quite normal for them to teach themselves if their handicap is not too bad. This is the reason why high performing autistics / asperger's people improve with age. It is also the reason why highly intelligent people with Autism, psychopathy, etc, do much better than others with the same problem but have more ordinary intelligence - something that is well known in psychology and psychiatry.

Over time negative reactions and feedback from other people result in them working out what they are doing wrong and they learn to correct for it. The process can take some time, years, both because it may be not so easy for them, and also because it can take a long time for situations in which they react inappropriately to be experienced. For instance, a highly intelligent autistic person may become extremely proficient in electronic engineering, designing many really good products which earn the respect of others. With this level of respect they might move after, say, 10 years at work, into a supervisory role. Then of course they will prove at first to be a none too good boss because of their not so good ability to relate to their team. They are now in a situation requiring interpersonal skills that were not tested before - but with experince they will get better at it.

Being a succesful manager in a highly competitive field can derive benefit for a small degree of psychopathy. Impulsiveness, a degree of not caring so much about employee's feelings, and drive, helps them get their team to perform. But they won't be welll liked - again an intelligent boss will pick this up and learn to modulate how he drives people.

You should not forget that definitions of pschological "problems" like autism, asperger's etc" are partly culturally determined, and what negative impact they have is culturally determined. There is no term for Asperger's Sysndrome in many non-European languages of the world - not only in lay language, but in professional language as well. In a nomadic hunter-gatherer society, an Asperger person would simply be regarded as a highly skilled hunter, or spearhead maker, or some such, and might well become tribe chief on that strength. Perhaps an extreme cultural example is an elderly male who persistently has sex with girls under 14. In Western society, such a person would be regarded as a pervert, sent to gaol, and most likely be diagnosed with something by a government appointed shrink. In traditional Australian Aboriginal society, he would be regarded as normal. (Note: the author, who is male, does not at all think that screwing 14 year olds is a good idea in modern Western society.)

See articles in Scientific American in the last 2 years or so on Asperger's Syndrome and Autism for a more complete explanation of this. SA had an article on the positive aspects of psychopathy about 8 to 12 months ago as I recall. 1.122.115.40 (talk) 10:16, 5 October 2013 (UTC)

Mental illnesses are multidimensional, five are used in the Diagnostic and Statistical Manual of Mental Disorders #Multi-axial system. This relates to the psychological senses that you allude to. --Digrpat (talk) 13:02, 5 October 2013 (UTC)

Is the tricuspid valve identical to the semilunar valve?

Diagram of the human heart

When I learn about the heart valves, I see that the shape of tricuspid valve and semilunar valves are the same in their shape. Both of them has the same shape (and it says that the semilunar valves also may to called as tricuspid, theoretically) Do I understand well? 95.35.222.1 (talk) 11:47, 5 October 2013 (UTC)

All the heart valves have basically the same shape; that doesn't mean anything. There are two semilunar valves, the aortic valve and the pulmonary valve; neither of them is identical to the tricuspid valve, which connects the right atrium with the right ventricle. See our heart valve article for more information. Looie496 (talk) 15:42, 5 October 2013 (UTC)

Apparently it is possible to culture mesenchymal stem cells to produce a "semilunar valve" which, short term, seems to stand in for the natural structure, without taking any particular steps to make it know it's a semilunar valve with transcription factors, etc. [1] So at least in concept it seems like they ought to be relatively interchangeable ... still, I bet if you look closely enough, the cells will turn out to know where and what they are. :) Wnt (talk) 20:27, 5 October 2013 (UTC)

• Isn't the simple answer here that tricuspid valves have three cusps and semilunar valves are shaped like a half moon? μηδείς (talk) 21:11, 6 October 2013 (UTC)

Well, our article points out that they can have 2 or 4 leaflets ... and the number of these may even change during a lifetime (I haven't checked that, but it is certainly an astounding idea that illustrates the true plasticity of the structure). But actually, looking over the article just now, it mentions the lack of chordae tendinae, which I'd forgotten about. Wnt (talk) 23:56, 6 October 2013 (UTC)

That's almost impossible to believe! Two and a half valves won't work. Maybe they split over time? μηδείς (talk) 04:48, 7 October 2013 (UTC)

I can think of a lot of hypotheses, but I don't believe any of them. :) Wnt (talk) 16:21, 8 October 2013 (UTC)

Do batteries exposed to the cold lose their ability to produce power permanently or just temporarily?

I've seen what the effects of cold are on a battery after trying to snap some pictures while skiing with a digital camera. I only got a few before it was spent. My question is, do batteries regain their capacitance, their potential for electric generation, if they are exposed to cold but are later brought up to room temperature. Vranak (talk) 13:12, 5 October 2013 (UTC)

In the cold a battery will discharge faster, but it shouldn't damage it. Batteries generate electricity through a chemical reaction. Lowering the temperature causes chemical reactions to proceed more slowly, so if a battery is used at a low temperature then less current is produced than at a higher temperature. OsmanRF34 (talk) 15:05, 5 October 2013 (UTC)

In fact, many people store batteries in the freezer -- not rechargeable batteries generally, but I don't think those should be harmed either as long as they're brought up to temperature before being used. Looie496 (talk) 15:29, 5 October 2013 (UTC)

I am not sure they last longer if stored in the freezer, but yes, they work again after coming back to the expected working temperature. OsmanRF34 (talk) 15:32, 5 October 2013 (UTC)

Thank you guys. Vranak (talk) 02:31, 6 October 2013 (UTC)

I am interested in the question too, and not enlightened by the answers so far. Sometimes it seems to me that battery-powered gadgets, in the cold, lose power quickly. Is that because the battery is cold, and is the effect permanent (meaning that I have to replace the battery, as I usually do when this happens), or will waiting a while in the warm restore the power? It would be handy if I knew I didn't have to go and grab a fresh battery on these occasions.

What I don't understand in the above: "discharge faster" seems to contradict "reactions proceed more slowly". Then, "discharge" implies a permanent loss of charge, while "less current" implies a temporary loss of ability to power a gadget. Finally, "work again" doesn't say whether they will have lost some of their charge after being cold, or not. 217.169.13.12 (talk) 03:29, 6 October 2013 (UTC)

Temporarily until they warm back to room temperature. See Battery (electricity). Batteries are normally stored in a fridge by suppliers so they don't discharge and rechargeables don't lose their ability to hold a charge so quickly. Dmcq (talk) 11:13, 6 October 2013 (UTC)

I wonder if these is some confusion here? From what I can tell, the OP isn't simply referring to storing batteries at low temperatures but actually using them at low temperatures. In that case, from what I can tell from our article and my limited understanding of this area, I think capacity is actually permanently loss. In other words, if you use a device for 1 hour with the batteries at low temperature, even after it warms up again the capacity remaining will be lower than if you had waited for the batteries to warm up before using the device. (This assumes power draw for the device remains the same which may not be the case.)

Of course if you've stored the batteries at room temperature for 2 years, then use them with a device for 1 hour you may end up with less capacity remaining than if you stored the batteries at a low temperature for 2 years then use them with a device at the low temperature for 1 hour because self discharge etc may mean more capacity was lost during that 2 years, so none of this means you shouldn't store your batteries at a low temperature even if you're sure you won't have time for them to properly warm up.

Now if you use batteries at a low temperature for a while and they can no longer or barely power the device and allow them to warm up, you will likely find they work for a while longer (and not just because leaving them for a while will often mean that) and if you have rechargable batteries then all you have to do is recharge them (the remaining capacity was lost but not the capability of holding a charge) but I'm not sure if that's what's the OP is asking. (And I think we've established that if you store your batteries for 2 years at room temperature before you use them they will be worse than if you store your batteries at low temperatures for 2 years and then allow them to warm up before you use them.)

Nil Einne (talk) 14:11, 6 October 2013 (UTC)

I don't know the answer but my guess would be that when you warm them up quite a bit of the charge will appear again. Some energy would I guess be lost due to greater internal resistance whilst discharging but Idon't think that would be a big effect and I can't see there would be any other energy loss. A good project for some schoolchildren? Dmcq (talk) 15:58, 6 October 2013 (UTC)

While I am not familiar with the battery behaviour itself, if the cold serves to increase the internal resistance of the battery and thus drop the voltage at the terminals while under load, most modern devices will compensate by drawing a higher current to meet the power demand of the device. This would result in the device genuinely discharging faster (exacerbating the voltage drop further). If the voltage drop is enough, the device could decide that the discharge threshold has been reached almost immediately, in any event while the battery is still holding more charge than it normally reaches this threshold at. Thus, if the internal resistance increase at low temperatures is the dominant mechanism, I'd expect both effects: more rapid actual discharge, and cutout with a higher level of charge still present, which would become available if the battery is warmed. None of this suggests that the battery would suffer any damage, or that the life of the battery would be reduced (aside from having to be recharged earlier). — Quondum 05:54, 7 October 2013 (UTC)