Wikipedia:Reference desk/Archives/Science/2008 January 2

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January 2

Cutting the carotid artery

What is the best course of action to take if one cuts his carotid artery by accident, until the emergency teams arrive? -- Leptictidium (mammal talk!) 00:41, 2 January 2008 (UTC)

For most people, the brain can be supplied with blood from one carotid, so I'd suggest compression below the cut, plus trying to block/close the wound might be a good idea. For disclosure, I'm not a doctor, nurse, or paramedic; I'd like to see what one of those people has to say. -- Flyguy649 ^talk 00:49, 2 January 2008 (UTC)

I'm not a doctor or anything, either. Our first aid article does not deal specifically with that injury. A Google search indicates that the first aid treatment for a severed carotid artery is a secret, at least on the internet. I managed to find a quiz for lifeguards that suggests lying down and applying pressure both above and below the cut. The pressure above the cut is to prevent air getting sucked in.

Bear in mind that there are several arteries called "carotid" (common, external, and internal) and that they occur in pairs, one on either side. Also, the common and internal would be hard to cut without cutting a lot of other important stuff, so I would imagine that a simple lacerated one of those would be a freak occurrence. --Milkbreath (talk) 01:43, 2 January 2008 (UTC)

To be clear, I meant that the brain can be supplied with blood by one intact left or right (common or internal) carotid artery. It would likely be the common carotid artery that would be severed, although the external carotid could also be severed; the internal carotid is generally quite deep and there would be a lot more damaged than just that. Even with a cut to the common carotid, there would likely also be damage to the internal jugular vein, if I remember my anatomy right. -- Flyguy649 ^talk 05:07, 2 January 2008 (UTC)

BTW I presume if you do call up an emergency team when this happens, say on a phone, they will be the best one's advice to follow. Obviously this doesn't help you if you don't have a phone and someone else has to go and get the emergency team but anyway...Nil Einne (talk) 06:44, 2 January 2008 (UTC)

Been watching Sweeney Todd (2007 film), eh? :-) —Steve Summit (talk) 02:53, 2 January 2008 (UTC)

Are not the answers here in contravention of giving medical advice and should be removed? SpinningSpark 01:33, 5 January 2008 (UTC)

Discussion about deleting a question should be conducted not on the desk itself but on the talk page. I have started one there about this question. --Milkbreath (talk) 02:52, 5 January 2008 (UTC)

zookeeper physics question

Hey It`s Me THE PHYSICS MAGAZINE GUY.I`ve got some questions for you.

A zookeeper devises a rubber-gun to shoot food to a monkey who is too shy to come down down the trees. If the monkey does not move,should the keeper keeper aim above,at or below the monkey. If the monkey lets go of the branch at the instant the keeper,shoots the food,should the keeper aim above,at,or below the monkey in mid-air. —Preceding unsigned comment added by 71.249.146.168 (talk) 01:26, 2 January 2008 (UTC)

See the Trajectory page to solve what looks very much like a homework question--TreeSmiler (talk) 02:23, 2 January 2008 (UTC)

Assuming the gun is designed properly, you always aim at that target. You adjust the sights for distance, wind, and target movement, then you aim at the target. -- kainaw™ 03:29, 2 January 2008 (UTC)

Only a homework question could be so divorced from reality. Is the monkey supposed to catch the food or what? Surely it's more practical to build a platform in the tree, and put the food on the platform. However, the monkey will come down from the tree when it gets hungry enough. There is no way it is going to sit there and starve when it can just climb down and grab the food.--Shantavira|^{feed me} 13:43, 2 January 2008 (UTC)

If the muzzle velocity is significantly high, the short time of flight will make gravity negligible (this would be a "linear approximation" or "straight line" trajectory model, instead of a more accurate parabola). Since you're surely already neglecting air resistance, why not neglect gravity as well? In such a case, the food might seriously harm the monkey. (Why are we shooting food at monkeys?) A slower muzzle velocity would invalidate this approximate solution, though, since the curvature of the trajectory would be too significant to ignore as the food accelerates (falls) towards the ground. Nimur (talk) 13:50, 2 January 2008 (UTC)

Given that the point of the problem is to illustrate the behavior of falling objects (the primate and the bullet), neglecting gravity would diminish the pedagogical value of the exercise. -- Coneslayer (talk) 18:16, 3 January 2008 (UTC)

The poster has previously asked questions here, asserting that they come from a physics magazine called Physics Weekly. I don't have this magazine to confirm, but I would suggest assuming good faith and taking him at his word that he's not cheating on his homework. It seems plausible to me that the magazine questions would resemble homework problems in their style. -- Coneslayer (talk) 14:12, 2 January 2008 (UTC)

Ha the second scenario is a trick question. The answer is to aim straight at the monkey since the instance the bullet "food" is fired, the monkey start dropping, so both objects will accelerate downwards because of gravity at the same time. So unless the muzzle velocity is slow enough that the "food" will reach the ground due to gravity before it reaches the monkey, it will always hit the target dead on (whether a monkey has such good reflexes though, is a better question). --antilived^{T | C | G} 06:03, 3 January 2008 (UTC)

I still say it is all a trick question. By "aim", it implies that you have sights. Sights are designed so you always aim at the target - not above or below it. It doesn't matter if the target is close, far, moving, or still. You adjust the sights and aim directly at the target. Now, if the question asked "Do you adjust your sights to raise the muzzle or lower the muzzle?" it would be completely different. Then, you can consider the muzzle velocity, movement of the monkey, and ballistic curve (as well as wind resistance). -- kainaw™ 17:52, 3 January 2008 (UTC)

A physicist's gedankengunsight does not have these adjustments; when the gun is "aimed" at the target, the axis of the gun barrel will intersect the target. If real-world firearms do not obey this convention, it is merely because their users are not as adept at physicists at doing real-time mental corrections to the aimpoint.  :-P -- Coneslayer (talk) 18:03, 3 January 2008 (UTC)

For what it's worth, I've never heard of anyone (when using an actual gun) try to adjust the sights for target movement. For longer distances where bullet drop is a concern, sometimes yes, altho it's quite common to just adjust the point of aim instead. Friday (talk) 18:12, 3 January 2008 (UTC)

Then, you've obviously never talked to anyone who went to military training for long distance sniping. The first rule of aiming is that the crosshairs (we actually said 'dot', not 'crosshairs') must be centered on the target. No "Kentucky windage" was allowed - which is what they called aiming away from the target to adjust for wind or movement. -- kainaw™ 18:22, 3 January 2008 (UTC)

I suspect it's a military vs civilian thing. Unless you have a rangefinder and a way to measure the wind between you and the target, trying to make an exact adjustment to the scope is still a matter of guessing. Also, how in the heck do you use sights to compensate for a moving target who may stop or change direction at any time? Seems like it'd be too slow. I've never known a hunter to adjust their sights in the field. Do you always have to reset the sights to some zero position when you're done, to avoid having to remember how you set them last? Seems like a lot of trouble for no real benefit. Friday (talk) 18:28, 3 January 2008 (UTC)

To be brief, since we're off-topic, the sights do zero out easily. I calculated range by seeing how many football fields I'd have to run (since I played football for many years). Wind just took time. There are many hours of training in calculating distance and wind before any real shooting. Movement does change. However, most things that need to be shot at long range do not jump all around. They move in a rather straight line. I think a big difference is the distance. I didn't even get a scope until I was shooting over 500 meters. Then, 800 meters was the normal distance. When I went deer hunting, we were shooting at 20-30 meters. -- kainaw™ 18:40, 3 January 2008 (UTC)

FETs

1. What is the advantage of n-channel JFET? The only reason I can think of is higher electron mobility compared to holes.
2. In MOSFET, the pictures show the Inversion Layer Being pinched of at a distance from the Drain. So how can the device conduct? The inversion layer formation provided carriers for it in the first place right? What happens to the carriers at the pinched end? Do they travel along the surface? —Preceding unsigned comment added by 59.93.32.233 (talk) 05:06, 2 January 2008 (UTC)

Found on JFET article, An electric current flows from one connection, called the source, to a second connection, called the drain. A third connection, the gate, determines how much current flows. By applying an increasing negative (for an n-channel JFET) bias voltage to the gate, the current flow from source to drain can be impeded by pinching off the channel Is it correct? Doesn't majority carriers flow form source to drain? So the paragraph is correct only for p-channel right? 59.93.26.127 (talk) 07:02, 2 January 2008 (UTC)

You might find DIBL helpful for your second question - the drain can induce a strong lateral field and "suck" electrons over the nonconducting "gap." Remember that "conducting" and "nonconducting" are only relative terms. Nimur (talk) 11:31, 2 January 2008 (UTC)

1. n-channel and p-channel indicates how the gate must be biased. One does not have any advantage over the other unless by design/manufacturing.
2. The gate controls the size of the inverstion layer. You can see from the picture that by changing the size of the layer, you change the size of the conducting path thereby changing the conductivity. Electrons flows from the S thru the layer to D.

Your follow up question refers to a JFET which has a depletion layers. This layers prevent electrons from flowing therefore the bigger the layers, the less conductivity between S and D. See Field Effect Transistor for more info. The majority of current does flow between S and D. Compared to this, the current from gate is insignificant. You may also want to see Bipolar Junction Transistor where S, D are similar to E(mitter), C(ollector) and gate is B(ase). Basic operation of any transistor is little current out of gate (or base) controls a larger current from source and drain (or emitter and collector). NYCDA (talk) 22:17, 2 January 2008 (UTC)

Note that "pinchoff" is a technical term, and does not mean "pinched closed." When an FET is operating in the pinchoff region, the channel will dynamically change its geometry to maintain a relatively constant current under changes of Vds. In other words, the channel is still open during "pinchoff," it just starts acting differently than it does when in the "resistive" region at much lower values of Vds. --Wjbeaty (talk) 23:32, 2 January 2008 (UTC)

Yes it seems Bill is correct again! [1]

--TreeSmiler (talk) 23:22, 3 January 2008 (UTC)

high tension lines or transmission lines and archival photos of "galloping" lines

Any archival video or photos of transmission lines or high tension wires "galloping"? sean —Preceding unsigned comment added by 75.73.162.109 (talk) 07:52, 2 January 2008 (UTC)

Video [2]--TreeSmiler (talk) 10:18, 2 January 2008 (UTC)

Resonance has some related video and animation links. Nimur (talk) 11:34, 2 January 2008 (UTC)

Hydrogen ion

I have studied in school that when an atom looses or gains electrons, to obtain the nearest noble gas' configuration, an ion of that element is formed. But in the case of Hydrogen the nearest noble is helium with electronic configuration of He(2) Thus Hydrogen gains one electron to achieve that configuration. Thus the Hydrogen ion becomes negatively charged.

But How is it positively charged????????? —Preceding unsigned comment added by 202.179.79.132 (talk) 15:49, 2 January 2008 (UTC)

What you've described is called hydride (H⁻), and it is one of the two possible ions of hydrogen. The other (perhaps more common) ion of hydrogen, H⁺, is sometimes called a hydron (a word I've actually never heard before; most chemists just say "proton"). A H⁺ ion has no electrons at all; it's just a bare nucleus. The nuclear charge is +1, and there are no electrons to cancel it, so the overall ion charge is also +1. —Keenan Pepper 16:27, 2 January 2008 (UTC)

The explanation that the original questioner mentioned regarding noble gases is a simplification; ions try to obtain a stable electron configuration. Often, the best stable state mimics a nearby noble gas valence shell, but this is not always the case. In the case of H⁺, it is easier to lose a single electron than to attract one. The rules which govern stability of electron configuration are extremely complicated, so a lot of simple versions such as the "octet rule" exist; however these are at best "approximate" and do not always apply. Nimur (talk) 16:31, 2 January 2008 (UTC)

This probably counts as a lie-to-children, but you can think of hydrogen as being halfway between two "noble gases" - helium, and vacuum (not that I've ever seen vacuum classed as a noble gas, but I think it technically would fit at least some of the definition). So it can go either way. Confusing Manifestation(Say hi!) 21:36, 2 January 2008 (UTC)

One could also think of a free neutron as a noble gas with valence 0 (an unstable isotope of the vacuum, natch). Of course, the lack of nuclear charge and surrounding electrons causes the neutron to behave rather differently than "proper" atoms, even of noble gases; in particular, it has no Coulomb barrier to prevent it from fusing with other nuclei. But yes, the whole octet rule is a gross simplification, and breaks down rather badly e.g. with the transition metals, which often can exist as several different types of ions. —Ilmari Karonen (talk) 22:07, 2 January 2008 (UTC)

It's probably worth mentioning that unless you're talking about high-vacuum gas phase conditions, the H⁺ ion really doesn't have an independent existent. While it is energetically favorable for hydrogen atom to give up its electron to form "H⁺", the naked proton is not stable by itself, and rapidly latches on to any available lone pair of electrons. For example, in water, a water molecule can dissociate to form OH^- and H⁺, but the H⁺ immediately latches onto a lone pair from another, adjacent water molecule to form a hydronium ion. The hydrogen ion is thus able to fill its "octet" by borrowing the lone pair electrons from the oxygen. Similar things happen in other solvents, where free H⁺s don't really exist by themselves, but get passed from one lone electron pair to another. -- 128.104.112.236 (talk) 23:08, 6 January 2008 (UTC)