Wikipedia:Reference desk/Archives/Science/2014 July 20

= July 20 =

Pre-CPR resuscitation
Early- and mid-20th century films sometimes depict a pre-CPR method of resuscitation, in which the body is laid on the back, the arms put at the side, and then moved behind the head before being returned to the side; this is repeated until the person breathes or (thought this isn't often shown in the films) until the resuscitator gives up on the hopeless case. What do we call this method? Nyttend (talk) 03:06, 20 July 2014 (UTC)
 * At History_of_cardiopulmonary_resuscitation I see the idea of lifting the arms, but that sounds like "up in the air" not "along the ground to behind head" as you describe. Anything you find, please add a note to that article. DMacks (talk) 03:25, 20 July 2014 (UTC)
 * There's also a mention at Cardiopulmonary resuscitation. HiLo48 (talk) 03:30, 20 July 2014 (UTC)
 * Yes, I was thinking of the lifting-in-the-air; I wasn't describing moving the arms along the ground. Think vaguely of the motion backstroke swimmers use.  Sorry that I missed the history section in the CPR article; I looked for it and somehow completely failed to find it.  Nyttend (talk) 04:16, 20 July 2014 (UTC)
 * That's because this material belongs in the article on artificial respiration, which came before CPR. Or maybe the two articles should be merged. --50.100.189.160 (talk) 04:45, 20 July 2014 (UTC)
 * I was taught this every time I refreshed my First Aid at Work qualification because it is useful in cases where the patient is believed to have ingested poison per ora or where there is a lot of blood round the oral area and you are worried about oral transmission of disease. --TammyMoet (talk) 08:43, 20 July 2014 (UTC)
 * It's called the Sylvester method. --173.49.18.131 (talk) 05:03, 21 July 2014 (UTC)

Ca and K sorbates?
what does it mean? --84.108.213.48 (talk) 07:27, 20 July 2014 (UTC)
 * I think I had understand : Potassium sorbate + Calcium sorbate, but I need to read it again. thanks --84.108.213.48 (talk) 07:31, 20 July 2014 (UTC)
 * Yes, that's right --50.100.189.160 (talk) 09:49, 20 July 2014 (UTC)

Number of employees at the Russian Federal Space Agency
How many employees does ROSCOSMOS (the Russian Federal Space Agency) have? Thanks. --Schweinchen (talk) 13:47, 20 July 2014 (UTC)

Voltage divider - question about current
Suppose I have a device that draws 1 A at 6 v and I have a 12 v supply so I make a voltage divider with two 1 Mohm resistors. Now I can have 6 v across my device but how could it draw 1 A through that 1 Mohm resistor? This was completely neglected at school (a long time ago). 78.148.105.159 (talk) 15:34, 20 July 2014 (UTC)
 * it can't. whatsmore, any load except very small ones (several megaohms) will upset the divider because of how parallel resistances add. That's why voltage dividers are never used as sources of voltage (except in transistor stages, to provide bias voltage to the base, but then the base only draws microamps (huge base-emitter resistance), so it's OK). if the device draws 1A at 6V, then you could connect it through a 6 Ohm series resistor, which would drop 6 V and dissipate 6 W (!) of power as heat, but that's also "suboptimal." If the voltage is AC, one could use a simple stepdown transformer. DC requires the use of DC-DC converters, such as the 7806, which is a linear regulator (there are other conversion methods, such as when you have an oscillator generate a square wave with an adjustible duty cycle, then smoothen the voltage out with a capacitor, or by generating a sinusoid which is then power-amplified and fed into a transformer etc) Asmrulz (talk) 17:35, 20 July 2014 (UTC)
 * The LM7806 regulator is a good suggestion. It will deliver fixed 6V whether a load (up to 1A) is connected or not and it will tolerate a short circuit. But note that when the device takes 1A, the device and the regulator are each dissipating 6 Watts. Therefore the regulator which comes in a TO-220 package should be bolted to a Heat sink. If you know the thermal resistance of the heat sink, say 3 deg C/W, then in this application the regulator runs at 6 x 3 = 18 degrees above ambient temperature, which is reasonable. Read the application note for other information such as the pin connections and the capacitors that should be soldered close to the regulator to ensure stability see Fig 4. 84.209.89.214 (talk) 21:32, 20 July 2014 (UTC)


 * Don't use a voltage divider as a power supply, because it's inefficient, it's sensitive to imperfections in your (probably non-) ideal voltage source; and even if it works, it loses a lot of energy to resistive heating. Real power supplies that source large currents do not use voltage dividers to set the output voltage.  Nimur (talk) 17:37, 20 July 2014 (UTC)


 * Voltage divider mentions this problem, but I added another mention earlier in the article since it seems rather important. -- BenRG (talk) 17:40, 20 July 2014 (UTC)

Use an op-amp. You can tie it to the 12V rail, tie one input to the divider at 6V and a 6 ohm resistor at the output. Tie the output to the other input. The opamp will drive the load to keep the inputs difference at 0 volts. So you end up with the opamp driving 6V into any load you like. See Voltage follower. --DHeyward (talk) 07:25, 22 July 2014 (UTC)

A linear regulator, or an op amp or any other active semiconductor solution will be more satisfactory than a simple dropping resistor if the demand of the device varies, since the active device can keep the voltage supplied to the device from varying. But a better approach for high current like 1 amp out at 6 volts is a DC to DC power supply which converts the DC to AC and uses a transformer to drop the voltage before converting it back to DC. That can be far more efficient. These DC to DC power supplies have largely replaced the "old school" solution for high current DC voltage conversion which would have been a motor generator set, with a 12 volt motor driving a 6 volt generator. It could be a rotating machine with one shaft and one field winding. Edison (talk) 17:29, 22 July 2014 (UTC)

What do insect bites do to your skin tissues?
Bites by many insects result in rashes, which may last from hours to few weeks. What do insect bites do to your tissues? For the ones that take a few weeks to completely clear up, what makes recovery take soon long? What's happening when your tissues are recovering from an insect bite?


 * For those which aren't trying to harm you, like a mosquito, it's often a bacterial infection. The mosquito injects a blood thinner so it can avoid clotting while drawing blood, but that's also full of bacteria and viruses.  Having microbes injected directly into the blood vessel is one of the worst places for it, since it can't be ejected by bleeding, as in a normal cut, or killed off by free oxygen, in the case of anaerobic bacteria, or removed/killed by washing and sterilizing the wound.  At that point, it's up to the immune system to counter the infection.


 * For those which are trying to harm you, like venomous spiders (not technically insects), the venom may work by any of a number of methods. In any case, first the venom must be diluted to the point where it no longer causes damage, then the damage must be repaired. StuRat (talk) 16:35, 20 July 2014 (UTC)


 * Even a non-infectious mosquito bite can cause an allergic reaction, which believe it or not is called Skeeter syndrome. ←Baseball Bugs What's up, Doc? carrots→ 17:12, 20 July 2014 (UTC)


 * Good point. Note that many of the same problems I noted above also apply to an allergen injected directly into a blood vessel, such as the inability of bleeding to wash it away. StuRat (talk) 17:23, 20 July 2014 (UTC)


 * Typically there are two types of reaction from blood-sucking flies and mosquitoes. The first and subsequent bites will from a histaminic which will be local swelling, redness and itching due to the response to the direct tissue damage of the bite.  If the body forms antibodies to chemicals in the flies' saliva, in later bites, some minutes after the initial red, pimple-like reaction, the skin will become raised and hardened in the shape of a coin or a pancake.  This is called induration, and is caused by white blood cells responding to the presence of activated antibodies.  Odly we lack an article on induration. μηδείς (talk) 17:36, 20 July 2014 (UTC)


 * Beware those bites shaped like a con. They sound dangerous. :-) StuRat (talk) 19:31, 20 July 2014 (UTC)


 * Unless you're goining to start paying me Stuart, don't expect me to notice things the spelczeck doesn't. μηδείς (talk) 23:01, 20 July 2014 (UTC)


 * Is a spellCzech an Eastern European wizard ? StuRat (talk) 20:28, 21 July 2014 (UTC)


 * An Eastern European editor wizard... 24.5.122.13 (talk) 00:06, 22 July 2014 (UTC)

Salt poisoning
Our hypernatremia article mentions salt poisoning as one possible cause. However, we have no article on that. Is salt poisoning simply consuming so much salt in a short time period that your body is unable to compensate by drinking water and urinating salt, in order to bring the sodium balance back to normal ? If so, how much salt intake causes this ? For example, according to this nutrition menu from Chili's, ordering a full order of Texas Cheese Fries as an appetizer followed by a Margarita Shrimp Bowl for the entree and a Molten Chocolate Cake for dessert will result in about 12 grams of sodium:. So, would this cause salt poisoning, if consumed within an hour, by a 200 pound man ? How about a 100 pound woman ? StuRat (talk) 19:28, 20 July 2014 (UTC)


 * This page has the Center for Disease Control recommendations for sodium intake. At Wikipedia, we cannot diagnose whether or not any action you or someone you know has taken or plans to take would cause a medical problem.  Only a doctor would.  -- Jayron  32  19:42, 20 July 2014 (UTC)


 * That's not particularly helpful, as it deals with chronic excessive sodium intake, and I asked about an acute overdose. And I believe you can state whether a particular level of sodium intake would cause medical problems in a theoretical individual.  For example, is there an LD50 value for sodium ? StuRat (talk) 21:25, 20 July 2014 (UTC)


 * See here section 11. -- Jayron  32  04:00, 21 July 2014 (UTC)


 * Let's see, that lists the LD50 as 3-10g per kg of body weight, and a 200 pound man is around 80kg, so that means it would take 240-800 grams to reach the LD50 for him, and 120-400 grams for the 100 pound woman. That's a lot more than I thought.  Also, what is the minimal acute lethal dose ? StuRat (talk) 16:04, 21 July 2014 (UTC)

I'm also interested in knowing what the minimum sodium intake is. I believe the 1.5-2.3 grams stated in the previous link is the range for maximums. StuRat (talk) 21:29, 20 July 2014 (UTC)


 * It varies. This page notes that only about 180 mg per day are needed for a person who doesn't sweat (that's 0.180 grams), but recommends a minimum of 1500 mg (1.5 grams) for a healthy adult.  this page is a bit older, and recommends a safe minimum of 500 mg per day.  -- Jayron  32  04:00, 21 July 2014 (UTC)


 * From here, it indicates that risk as a function of salt intake appears to follow a "J" shaped curve, they also mention that less than 3g per day is associated with risk - they mention that the current guidelines are from projections based on small samples and short term trials; so there does appear to be some controversy. This appears to indicate that low sodium diets can raise various other levels, not all good; the general conclusion being that low sodium diets aren't necessarily beneficial to those without high blood pressure - though, there main recommendation is further testing. This  mentions that lower sodium excretion is associated with higher CVD mortality. This  concludes that the current guidelines are not supported, but that raising sodium intake is also not supported - in short, recommendation either way does not appera to be supported. This  indicates that sodium restriction can have risks to cardiovascular health. These, may also be of interest: , , , . In short, it does not appear that it is supported that a sodium restricted diet is necessarily healthier, nor necessarily healthy - this is not to say that a high salt diet is safe either. There is some sweet spot somewhere in there, but the current US recommendations may be on the too low side (even if the average American consumes too high on the high side...), at any rate, the issue is controversial, and I don't think there is any clear answer at present.Phoenixia1177 (talk) 06:05, 21 July 2014 (UTC)


 * As for the original question, I couldn't find nearly as much info. These are MSDS for Sodium chloride:, which mentions oral toxicity (search for "ld50"). This  (pdf full article: ) discusses salt toxicity and the case of an accidental deat due to salt poisoning in an adult. Here's a news article on someone in jail for not intervening/causing in a case of salt poisoning (involves her child) . This is for animals, but might be relevant: . At any rate, it would appear that it would take a large amount to actually cause acute poisoning - however, the amount and impact on a large dose of salt in a dehydrated individual would be more pronounced. (This  also has a bunch of info, search "range of toxicity".)Phoenixia1177 (talk) 06:33, 21 July 2014 (UTC)

Thanks. I never expected dietary sodium recommendations to be so controversial.

I've also wondered if people in food eating contests involving salty items might be in danger of salt poisoning. (At the top level, though, most of the food is quickly vomited back out or passes through undigested, so that would hopefully limit the sodium absorption.) StuRat (talk) 16:05, 21 July 2014 (UTC)


 * I have no source, but I believe a major inhibiting factor would be the time it takes to digest food. The cases I read about involved children, a mentally handicapped woman eating jam with large amounts of salt added in place of sugar, and people who were given saline enemas. In those cases, the needed dose is either smaller (children) or was from a source that allowed large amounts to be absorbed quickly. For an eating contest, using hot dogs as an example, you'd need to directly absorb the salt content of 60 hot dogs before reaching significant toxic levels (70kg person) - for someone like Takeru Kobayashi, this may be possible, but the digestion time factor should still put him in a safe zone, even if he didn't vomit any of it back up. Finally, it is possible that such people may intake enough to suffer from limited poisoning, but, again, digestion time would most likely prevent this. In almost any situation involving actual food, it is most likely that the eater would vomit before they could take in enough food - and, again, even if not, with digestion time being a factor, it is likely that the person would never have enough salt at anyone time due to excretion. -- Again, I have no direct source, but I would say that this would be almost impossible to do with standard food items under normal circumstance.Phoenixia1177 (talk) 08:24, 22 July 2014 (UTC)


 * However, some people seem to lack the vomit response. (I wonder what percentage that is.)  Fortunately my vomit response is quite good.  I've never had a hangover, for example, because consuming enough alcohol to cause one would just make me to vomit it back up. StuRat (talk) 12:21, 22 July 2014 (UTC)


 * Perhaps, but I imagine very few people lack the vomit response and can fit 60+ hot dogs in their stomach while near dehydration, which is what you would need to even near a risky level through food. On the other hand, if you did lack a vomit response and chugged salt water, or something like it, you might be able to poison yourself, but it certainly would be on purpose or do to weird circumstance and mental handicap. Essentially, if someone gets salt poisoning through ingestion, then it was either purposeful, the result of mental handicap and weird circumstance, or some survival style situation (as in a ship wreck). The only cases I've heard of that may be accidental and involving normal people are in the case of saline enemas; and I'm not sure how common it is that someone receives one, nor what portion of those get poisoned.Phoenixia1177 (talk) 00:46, 23 July 2014 (UTC)


 * I many movies people are shipwrecked, adrift in a lifeboat, and very thirsty. They are cautioned not to drink seawater, but inevitably someone does and promptly dies in agony after one good drink. If a 100 pound woman would have a LD50 of 129 grams minimum, and seawater is 3.5% salt, (roughly 35 grams salt per liter) then her lethal drink would be about 3.4 liters. The real story likely is that the person who starts with say a 250 ml drink of seawater actually winds up more thirsty as a result and more and more seawater drinking as time passes, and a day later is worse off than the person who didn't drink seawater, and dies sooner than that person, but not instantly. Edison (talk) 17:14, 22 July 2014 (UTC)


 * Plus they presumably had a high sodium to water ratio in their body to begin with, due to dehydration. StuRat (talk) 00:06, 23 July 2014 (UTC)

How can we know that electrons cannot be broken down into smaller constituent parts
Just tell me how? OsmanRF34 (talk) 20:58, 20 July 2014 (UTC)


 * We can't know for sure. We can however state that there is no verifiable evidence that they can be. If you want absolute certainty, you won't find it in science... AndyTheGrump (talk) 21:01, 20 July 2014 (UTC)
 * See preon. Wnt (talk) 21:05, 20 July 2014 (UTC)


 * In general, as particle accelerators move to higher and higher energies they probe smaller and smaller structures. Broadly speaking, studying interactions with higher and higher energy particles has allowed us to first discover the nucleus of atoms, and then the constituent nucleons, and then the quarks from which nucleons are made.  Such tests have not revealed any internal structure to the electron, which either implies it doesn't exist (i.e. no smaller parts) or the constituent parts are so tightly bound that they can't be revealed by the energies we have available to probe for them.  Given the lack of evidence for internal structure, it is simpler to assume that no constituent parts exist (e.g. Occam's razor).  Dragons flight (talk) 09:36, 21 July 2014 (UTC)
 * Wouldn't it be more advisable to assume that up to energy level x, there could not be found any particles, but above this, we don't know? That would be the same assumption, but with a reasonable limitation.OsmanRF34 (talk) 10:39, 21 July 2014 (UTC)
 * That's why I linked Occam's razor. The simpler assumption (i.e. less complicated theory) is that there are no constituent parts.  That doesn't make it right, but in the absence of evidence assuming anything else just makes your theories more complicated without explaining anything new.  Of course, some people do make theories about what electron constituent parts might look like (e.g. preons) and what consequences they might have, but until there is some experimental evidence for such theories that can't be explained the traditional way, most scientists are just going to assume electrons have no constituent parts.  Dragons flight (talk) 17:19, 21 July 2014 (UTC)


 * What do you want particle physicists to do that they aren't already doing? Obviously they haven't ignored the possibility of preons, as witnessed by the existence of the word "preon" and the papers on the subject. Preons are just one of many possibilities for beyond-the-Standard-Model physics, and without experimental guidance it's not clear how much time one should spend on that possibility and how much on others.
 * One theoretical argument against preons (which is mentioned in the article) is that they would have to have a much larger mass than an electron in order to be confined in such a small space without violating the uncertainty principle. You might be able to cancel that with a negative binding energy, but it's not clear why the binding energy would be so close to minus the sum of the preon masses. To the extent that physicists disbelieve in preons, I suppose this is why.
 * Also, the fact that the fundamental Standard Model fermions are all massless and chiral seems to me to rule out their being composite, but professional physicists have proposed preon models post-Standard-Model, so I must be wrong about that. The article does say that the discovery of the Higgs boson ruled out many of the models. -- BenRG (talk) 18:46, 21 July 2014 (UTC)

What is the difference between ECG and Monitor?
What are the main differences between ECG and monitor? מוטיבציה (talk) 21:28, 20 July 2014 (UTC)


 * An electrocardiogram can be displayed on a monitor and/or recorded on paper tape. The paper tape version traditionally had the advantage of allowing quicker access to recent data which had scrolled off the monitor.  However, modern systems both electronically record the data and hopefully allow rapid access to recent data, but it's still hard to get quicker than paper tape.  Paper tape does need to be changed periodically, however.  In a third world hospital, where power disruptions are frequent, paper tape records may also be more reliable. StuRat (talk) 21:37, 20 July 2014 (UTC)


 * See also heart monitor. (I'm guessing that's what you mean by "monitor" which is a rather general term.)--Shantavira|feed me 06:04, 21 July 2014 (UTC)