Wikipedia:Reference desk/Archives/Science/2015 March 3

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March 3

Rapidly turning on and off an LED lamp

I remember as a kid I was always told not to turn the lights on and off rapidly because it would make the bulb burn out faster. Is the same true for LED lamps or is it safe to rapidly turn them on and off without any adverse effects? ScienceApe (talk) 00:41, 3 March 2015 (UTC)

The answer is not appreciably. In fact one the very things that make LEDs so useful is their ability to turn on and off very rapidly, such as in fiber optics or optocoupler. Also, since an LED is either on or off, you can't reliably make it "half as bright" like a lightbulb by giving it less current, the way you typically controll an LEDs brightness is by using Pulse-width_modulation which also turns the led on and off typically in the KHz range, which surprisingly is not mentioned in the article, but does not appreciably reduce the life of the LED.. Vespine (talk) 04:15, 3 March 2015 (UTC)

Not true. LED brightness is almost linearly related to drive current. There's lots of discussion (some of it wrong) on the web, but this gives some graphs. Typically, LEDs are run at high current with low duty cycle to give them a high perceived brightness. However, they could also be run at 100% duty cycle and variable current to provide varying brightness.--Phil Holmes (talk) 10:46, 3 March 2015 (UTC)

Ok, I did get that one fact wrong, but it doesn't invalidate my response to the OP. It is true that typically, LED brightness is adjusted using PWM, especially in applications where the LED brightness needs to vary, i.e. is not fixed. LED drivers for displays use PWM, not varying current. Vespine (talk) 22:52, 3 March 2015 (UTC)

I just read Phil's user page :) Let me just add, I'd trust him more than me on this subject. :) Is the rest of my response "roughly right" Phil? I'm actually a big fan of LEDs and I have made a few LED projects, one I'm particularly proud of but it's a far cry from making lasers and pin diodes in a professional capacity ;) Vespine (talk) 22:58, 3 March 2015 (UTC)

It's certainly true that a key feature of LEDs is their ability to be switched on and off quickly. It's made optical communications (and therefore telecommunications/the internet) what it is today. I would say that, as a general rule, LEDs are used as being either on or off: it's not common to modulate their intensity. However, given that they are almost always pulsed in use, then using pulse width modulation would certainly be an option if you wanted to do this.--Phil Holmes (talk) 10:36, 4 March 2015 (UTC)

Reading your question again, my reply specifically refers to the diode part, however an "LED LAMP", especially one you can stick into a domestic light socket is typically far more than just "a lighe emitting diode" or two. It's usually a bunch of components, resistors, capacitors, rectifiers, if it's fancy even some sort of control IC. These components might very well be far less forgiving to fast switching and fail far sooner than the actualy LED part of the lamp. Vespine (talk) 04:21, 3 March 2015 (UTC)

I agree that you might hypothetically be right - but LED's are DC devices and we're feeding them with AC current - so there must be some circuitry to take care of that - which probably slows down switching transients to the point where they're not a problem. At any rate, if there is a problem, it is entirely negligible compared to the issues of rapidly switching incandescent lamps. SteveBaker (talk) 04:03, 4 March 2015 (UTC)

Basic science: Switching incandescent bulbs off and on stresses the glass-to-metal seal, thus, leading to an early lose of vacuum.--Aspro (talk) 00:25, 4 March 2015 (UTC)

I'm gonna call [citation needed] there (it's possible, but I can envision other possibilities too). There are lots of mechanical details that could potentially fail, and possibly due to changing thermal stresses. It seems like it would be easy to determine which one is most common. DMacks (talk) 18:18, 4 March 2015 (UTC)

Why didn't this hurt? (Not medical advice)

So here's a question I've had for a while and I don't think it qualifies as medical advice as it's something fully In the past that no longer affects me in any way (except that I do have a fantastic scar). Anyway, at the start of last summer, I managed to cut open the radial artery in my right hand whilst in Israel. For those who want to survey the damage to give a better answer/like seeing this kind of thing, here's a lovely picture of it popping up to say hi to everyone. After six hours and losing a litre of blood, the doctors (who spent most of the time bickering with each other as Israeli doctors are known to do) finally managed to get the artery cauterised and the wound stitched up. I was prescribed beer (to drink only with my left hand), and sent back to my friends' house without painkillers or any supplies.

Now an odd thing about this particular injury is that I never felt pain from it any point. Not when it was cut open (though there was a feeling of warm liquid on my hand and something draining out of me at times), not when I had it wrapped in paper towels and a hand towel, not when the doctors ran it under water for no good reason, nor when they unwrapped my bandage and had me hold my hand over a sink so they could argue with each other while I watched my life fountain out of my hand into the drain and nearly passed out from blood-loss, etc. In fact, the only time I felt anything was the searing intense pain when the doctor cauterising the artery—which really does smell like chicken—accidentally touched a bone.

I could attribute this to shock (as the whole time I was making morbid jokes and feeling loopy), but even the next day I felt no pain (remember there were no painkillers), and not any time after. There was no nerve damage, and there was still glass in my hand (as evidenced by the glass I pulled out a week later even though my hand had been x-rayed twice). Occasionally if tried working with my bandaged hand in the first week of digging (which started three days after the incident) to pick up a pickaxe or use a handpick, it would hurt from the vibrations, but otherwise nothing.

So, anyway, my question after all of this is this: why the heck didn't I feel any pain from this thing? Again, I don't want any advice on what to do as it's a nice healthy scar that doesn't unthreatening me in any way, shape, or form, and I don't plan on opening up any more arteries as I hate not being able to do heavy work on digs for two week. I just want to know why it never caused me pain even though it was a potentially fatal injury. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 12 Adar 5775 01:51, 3 March 2015 (UTC)

Some parts of the body are less sensitive than others. Consider getting a flu shot or whatever. It's a needle poking into your arm, but it's not particularly painful. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:04, 3 March 2015 (UTC)

When I was 5, I managed to put my arm through a window and slice it open. I had stitches and still have a scar, but, like you, there was no pain. I do recall the stitches itching, though. So my theory was that there was nerve damage. I have full nerve function there now, so, perhaps due to my young age, I was able to regenerate those nerves. StuRat (talk) 04:25, 3 March 2015 (UTC)

This one basically cut through the artery and somehow avoided the radial nerve. I only felt some loss of sensation between the knuckles of my index and middle fingers (which came back after four months–I'm 25, so don't know if that helped). They tested for nerve damage (which felt weird because I had to watch and it felt like something would pop out of the hole in my hand) and found nothing wrong. My stitches also itched a bit (especially as they got covered in sweat). Sounds like a badass scar though, Stu. Maybe it's a sort of prolonged shut-down response (after shock has subsided) so your body doesn't process what should be agonising pain? We're not talking minor pin-pricks in either case, but rather massive damage. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 12 Adar 5775 04:49, 3 March 2015 (UTC)

Oh, come on Sir William Matthew - you may feel like you're only 25, but by my reckoning you're almost 162 years old! Richerman (talk) 10:50, 3 March 2015 (UTC)

Ha, that's what I get for naming my account after Petrie.... Sir William Matthew Flinders Petrie | ^{Say Shalom!} 14 Adar 5775 23:08, 5 March 2015 (UTC)

Have you read Acute stress reaction? How about Nociception#Regulation, or Pain#Theory? Also check out pain tolerance and the distinct pain threshold. I doubt you can get conclusive answers, but food for thought at least. Also I thought at least one person should provide some references, and wanted to congratulate you on your injury :) SemanticMantis (talk) 15:15, 3 March 2015 (UTC)

I'm also wondering now about how 'clean' the wound was. WP:OR: getting sliced by a razor hurts way less then being mauled by a saw, no matter where on the body it occurs... cuts from very sharp objects are generally preferable to those incurred by dull blades, in terms of healing time, scarring, stitches, pain, etc. SemanticMantis (talk) 01:04, 4 March 2015 (UTC)

Oooh, these are useful. Thanks, Semantic! And thank you for the grats. It was a very good object lesson for the noobs about always paying careful attention. One that I shall use for years to come.

I would say not clean at all. It was basically a freshly broken otherwise sturdy section of plate glass that I guess fell against my hand and then on the ground. It also left a nice little piece in my neck that avoided anything carotid-like (also shredded some lovely cotton-linen trousers of mine and cut the sides of my driving loafers, though the latter were at least salvageable after I got the blood out using my trusty saddle soap). It seemed to be fully healed after a week and then the stitches were left in for another week. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 14 Adar 5775 23:08, 5 March 2015 (UTC)

Reference 4 in 'Malnutrition in South Africa'

Hi there,

I am looking for the actual reference for reference 4 in 'Malnutrition in South Africa', as the link is unfortunately invalid. ( http://en.wikipedia.org/wiki/Malnutrition_in_South_Africa#cite_ref-Malnutrition_in_South_Africa_4-1 ) The reference is ""Malnutrition in South Africa". Retrieved10 December 2012." The invalid link is http://myfundi.co.za/e/Malnutrition_in_South_Africa

Thank you very much for your time. I am currently looking into volunteering for Wikipedia myself and really appreciate your help.

OliviaOlivia Beth G (talk) 11:46, 3 March 2015 (UTC)

Hi Olivia, a few things: First, welcome to Wikipedia! Feel free to be WP:BOLD, and if you see a problem, WP:SOFIXIT - WP only exists because people like you want to make it better. If you need help learning how to edit the article, include the citation, etc, you can ask at WP:HELPDESK. You can also try this tutorial/game thing called Wikipedia:The_Wikipedia_Adventure.

Now, for this issue - the best place to post this problem (which is link rot) is on the talk page for that article [1]. But it is also fine to post it here.

As for the broken link - we could probably use the wayback machine to find the version of the page that as originally cited, even though the link no longer works. Another alternative is to find other references that say similar things. For instance, here [2] is a journal article that found 27.3% incidence of anemia among 2-year-olds in South Africa. Probably better references can be found (this one is a little old), but that's the first one I got. If you need help accessing the full article (or other similar), you can ask at WP:REX. Good luck, and thank you for helping to make WP better :) SemanticMantis (talk) 16:02, 3 March 2015 (UTC)

I've checked the wayback machine, and unfortuanatly, the page isn't archived by it. I've added a { {deadlink} } to it. This records that the link is broken, and puts it on a list of pages to be fixed, but there is a sizable back log. LongHairedFop (talk) 16:06, 3 March 2015 (UTC)

You can try asking the folks at WT:WikiProject South Africa, we're friendly and some of us have a talent for finding good sources. Roger (Dodger67) (talk) 17:41, 4 March 2015 (UTC)

Great - I will have a look myself but thank you very much anyway.

Why does hyperglycemia not cause necrosis?

The whole question is: why when administrating glucose in the vain and it's going outside the vain (para) it causes to necrosis while hyperglycemia (more than 500 mg/dl) doesn't causes necrosis? (It's about the explanation of this phenomenon. not medical advice). Thanks 11:52, 3 March 2015 (UTC) — Preceding unsigned comment added by 149.78.32.22 (talk)

Intravenous sugar solution is 5% = 5 g/ 100 ml = 5000 mg/dl = 50g/l. Hyperglycemia is dangerous over 300 mg/dl. I think the effect of missing the vein is simple osmotic shock from that very high concentration of solute in the sugar solution, which is required in order that a reasonable volume have an effect on the entire blood supply. Wnt (talk) 14:04, 3 March 2015 (UTC)

When the glucose outside of the cell, which one pumps the other?

When glucose found in high concentration outside the cell, which one pumps the other? Is the cell pumps the glucose (and in this way the cell is going to die) or the high concentration of the glucose pumps the cell's content (and in this way the cell is going out of life). Thanks — Preceding unsigned comment added by 149.78.32.22 (talk) 12:01, 3 March 2015 (UTC)

Read the article titled Glucose transporter. --Jayron32 12:04, 3 March 2015 (UTC)

Your question "which one pumps the other" is unclear. According to the article Jayron32 linked to, the process is facilitated diffusion, not pumping (which would require energy). Glucose enters cells if the concentration is higher on the outside than the inside, which is usually the case for an energy-consuming cell. Glucose doesn't kill cells, as you seem to imply. Cells use glucose as fuel, and some cells additionaly build large glucose polymers (glycogen) for use as energy storage. In diabetes the problem is dysregulation of the facilitated diffusion, resulting in a surplus of glucose on the outside of cells that are starving. The "pumping" or rather "facilitated diffusion" is catalyzed by proteins that sit in the cell membrane. Some cells can synthesize glucose (gluconeogenesis), and release it to the environment for the benefit of other cells. Some cells, especially liver cells, assemble glucose into glycogen when supply is high (after a meal), and break down the glucose and release it between meals, thus keeping the glucose concentration in the blood fairly constant. In the kidneys, glucose is actively reabsorbed from the pre-urine against a concentration gradient (i.e. "pumped", to avoid loss of an important nutrient) in a process that requires energy (see Glucose uptake for the details). --NorwegianBlue ^talk 18:01, 3 March 2015 (UTC)

Can humans live with other apes?

Considering that there’ve been anthropologists who’ve lived with foreign people, has anybody ever attempted to live with non‐human apes in the wild? And while I’m at it, is it possible for chimpanzees and humans to co‐exist pacifically? Sorry if these questions sound weird but considering how similar hominids are, I thought that it might still be at least possible. --66.190.99.112 (talk) 20:43, 3 March 2015 (UTC)

Jane Goodall is a good starting point. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 12 Adar 5775 21:12, 3 March 2015 (UTC)

Yeah, I was going to suggest Goodall and Dian Fossey, but neither actually lived with them, per se. Besides Tarzan I'm not aware of anyone who has. ―Mandruss ☎ 21:18, 3 March 2015 (UTC)

Generally, in the real world, humans are bad for non-human primates and their survival outlook. Habitat loss, poaching, etc. The International_Gorilla_Conservation_Programme will have a lot more info on the anthropogenic threats to gorillas.

A few human people do spend a lot of time with apes, the most famous are probably Jane_Goodall and Dian Fossey. To those that say they didn't "live with" the apes, I'm pretty sure they would have been camping right near by, and all the local troop members would have known them by sight and smell. A colleague of mine spent a whole summer in Africa camping next to Geladas, and I would describe that as basically living with them... Anyway, you can still easily get Fossey and Goodall's books and read their research papers to see how close they got, and Gorillas in the mist was also adapted into a movie. Chimpanzee#Interactions_with_humans has some relevant info, as does Gorilla#Interactions_with_humans.

It's also good to think about what can happen when chimps live with humans. Travis_(chimpanzee) ripped someone's face off, and Oliver_(chimpanzee) made many sexual advances on human females [3]. SemanticMantis (talk) 21:23, 3 March 2015 (UTC)

• The question might better be, "Can humans live with other humans?" The history of animal rights activists in Sub-Saharan Africa is frightful, see the death sections in the Dian Fossey and Joy Adamson articles, as well as that of Adamson's husband. See also Ernest Gibbins and Category:Murdered scientists as well. μηδείς (talk) 03:16, 4 March 2015 (UTC)