Wikipedia:Reference desk/Archives/Science/2017 May 20

= May 20 =

Defibrillator paddles vs defibrillator pads/ patches
I've read that the defibrillator pads enable a faster defibrillation than defibrillator paddles. What is the explanation for that? and how faster is it? if it significant why is it (paddles) still in use? 93.126.88.30 (talk) 05:19, 20 May 2017 (UTC)
 * Do the sections Defibrillation and Defibrillation answer your questions? Rojomoke (talk) 08:30, 20 May 2017 (UTC)
 * Yes, I think so. Thank you. It took me to totally different explanation from what I thought... "Many hospitals in the United States continue the use of paddles, with disposable gel pads attached in most cases, due to the inherent speed with which these electrodes can be placed and used. This is critical during cardiac arrest, as each second of nonperfusion means tissue loss.". But it's written there that "Paddles offer a few advantages over self-adhesive pads.", and no more details or explanation which or what the advantages are. 93.126.88.30 (talk) 11:59, 20 May 2017 (UTC)
 * Note it also says "In hospital, for cases where cardiac arrest is likely to occur (but has not yet), self-adhesive pads may be placed prophylactically." This would seem to imply that in such cases, the pads are used instead of the paddles. It isn't however stated if the advantage here is that they are faster to use than the paddles, or offer some other advantage (like less room for error), although the fact that paddles are sometimes preferred for speed would suggest that in these cases if attaching the electrodes to the machine is slower than using the paddles, the difference is likely small enough that the other advantages otherweigh the use of paddles. Nil Einne (talk) 12:59, 21 May 2017 (UTC)

Where are the amino-acids / steroids derivatives hormones are made in?
I'v listened to this lecture on Youtube (by KhanAcademy), and mentioned that athat peptides and proteins hormones are made in the RER but he doesn't mention where amino-acids-derivatives hormones and steroids hormones made in, and it just increases my curiosity to know where they are made in... 93.126.88.30 (talk) 11:44, 20 May 2017 (UTC)
 * You read out article about endoplasmic reticulum, that you linked to above, you may discover that they are made in SER. Ruslik_ Zero 12:17, 20 May 2017 (UTC)
 * There must be something very memorable about this particular term; I have a rather naughty lack of interest in biology except where it overlaps chemistry, and yet this particular term has stuck in my head ever since I first heard it in middle school. This is completely irrelevant, but this answer certainly called it back as clearly as it did the first time I heard it. ^_^ Double sharp (talk) 15:16, 20 May 2017 (UTC)
 * Peptide hormones are made in RER because the "rough" is ribosomes, and to be hormones, they generally need to leave the cell at the time of their creation. Note there can be exceptions - some cell surface proteins might be made in RER, but only become "hormones" when cleaved at a much later time, on some other part of the cell surface.
 * Modified amino acids can, in principle, be made just about anywhere. Amino acids are present throughout the cytosol and modifying them (in general) can imply a simple standalone enzyme.
 * Smooth ER should be important for steroid hormones because cholesterol lives in membranes, and SER has a lot of membrane. Wnt (talk) 17:27, 20 May 2017 (UTC)
 * The steroid hormones are mostly made from cholesterol, found in many biological membrane, include the plasma membrane of every cell in the body. A series of enzymes convert the the cholesterol into hormones like cortisol, for which the synthetic pathway is known. The amine hormones, like epinephrine, are made from amino acids; for example, in the case of epinephrine (adrenaline) there are a few enzyme-mediated steps from tyrosine. These reactions take place either in the cytoplasm of cells (tysoine through to dopamine) or inside neurotransmitter vesicles (dopamine to norepinephrine through the action of dopamine beta-hydroxylase). Klbrain (talk) 00:12, 21 May 2017 (UTC)
 * Thank you very much you helped me to study further by your notes! I appreciate it. 93.126.88.30 (talk) 02:48, 21 May 2017 (UTC)

Ladder paradox and electric circuit
In the ladder paradox, if the doors were doubling as electrical switches in series on a circuit, would current be able to flow? It must either flow in the ladder's reference frame with the circuit open, or fail to do so in the garage frame with the circuit closed. If current does flow, is the impedance the same in both frames? Neon Merlin  18:56, 20 May 2017 (UTC)


 * Err. You have lost me here. Is this anything to do with Voltage ladder? Aspro (talk) 19:27, 20 May 2017 (UTC)


 * No, see Ladder paradox. I'm trying to get my brain around the relativity of current flow at the speed of light (or just a fraction slower).  If the ladder is the same length as the garage in the same reference frame, then current should flow for just a fraction of a second as the ladder collides with both doors.  This must also happen with the moving ladder, but how do we explain away the apparent paradox?    D b f i r s   19:45, 20 May 2017 (UTC)


 * The apparent paradox is based on the assumption that that current flow is simultaneous. Current can flow in an open circuit. For a short period of time current can flow though one door/switch whether or not the other door/switch is closed because the opened/closed information cannot propagate to the other door/switch faster than the speed of light. This is a familiar situation in electronics engineering. Take two long coaxial cables, one shorted at the far end and the other open at the far end, and suddenly apply a voltage to one end. The current and voltage at the near end of the two cables will be identical until enough time has passed for light to have traveled to the far end and returned. In real life it takes a bit longer, but that is the absolute minimum time needed to tell of the far end is shorted or open. Also see Relativity of simultaneity. --Guy Macon (talk) 19:51, 20 May 2017 (UTC)


 * Thank you for the clear explanation and for the link. In the case of an observer sitting on the ladder travelling at 0.99c, he sees a short garage so thinks that the current should flow for longer because both ends appear to be in contact for most of the ladder length, but if he measures the flow along the ladder at the centre, it will actually be for a shorter time than for a slower ladder.   D b f i r s   20:49, 20 May 2017 (UTC)


 * I don't think there can really be a paradox here. If two doors can appear to do something simultaneously from some frame of reference, there is a spacelike interval between them, and no circuit flows in a spacelike interval because no electron goes faster than light.  So the circuit is never completed, period.  Now to be sure, you might be looking at different events on either end of the barn - like if the front end of the ladder makes a circuit and the back end makes a circuit.  Then, depending on the placement of the battery and so on, maybe you see some process that involves both; but if so, then this will be a process that could happen whether both ends of the ladder complete circuits "simultaneously" or not.  The comments above apply then.  We're talking about a really short interval anyway for each contact, and the electron doesn't get "intel" about other things going on except via slower than light transmission. Wnt (talk) 01:03, 21 May 2017 (UTC)


 * In case it makes a difference, I'm not talking about the ladder itself being a conductor in contact with the doors, just there being a circuit that runs through the ceiling, floor and doors, so that it is closed when and only when both doors are closed. Guy Macon's answer above -- which seems to indicate that the circuit can be divided into two halves, and that current can flow through one half while the other half is open -- seems to be the most relevant so far. (Another way to think about it might be a DPDT switch, with the fixed terminals connected to the terminals of the power source, the 1P1T and 2P2T terminals connected to opposite ends of the load, and with the 1P2T and 2P1T terminals left open.) Neon  Merlin  05:40, 21 May 2017 (UTC)


 * Apologies for mis-reading the circuit design. I agree that Guy's answer is most relevant.  We haven't answered your question about electrical resistance in the circuit which one would expect to be proportional to the length of wire (assuming the majority runs from front to back of the garage), so one would expect it to appear reduced in the frame of the moving ladder?  Will the current appear proportionally greater to fit Ohm's law?    D b f i r s   06:46, 21 May 2017 (UTC)
 * That's a funny point. We can consider any circuit for this, without worrying about switches - even the light bulb in your room can be considered from a relativistic frame of reference, and the math ought to hold up.  Now it should be clear that the number of charge carriers, and the value of each charge, is invariant under any transformation, so the total number of coulombs passing through a circuit between two recognizable events stays the same.  Time dilation however means that this charge will go around the circuit more slowly.  Since the carriers move, in some directions calculating the exact amount of time dilation could be tricky, but I think we can approximate that the electrons' speed is too slow to matter much.  Given that approximation, note that the current appears slowed (i.e. reduced, a factor of sqrt(1 - v^2/c^2) ) regardless of which way it is moving because the whole object is subject to time dilation; however, the circuit is only shortened in one direction!  By a factor (Lorentz contraction) of sqrt(1 - v^2/c^2).  So when the electrons are moving front to back, the time to make the trip increases as quickly as the length decreases, and so the current is the same.  Yet when they are moving along the front or back of the barn, then the time is longer for the same distance and so the current seems reduced!  Now the current could be flowing in either direction perpendicular to the relativistic velocity, so the potential of left and right can't be altered one relative to another, even if there were a reason for it.  It is possible that there is some aspect of relativistic electromagnetism that I don't understand that can be used to model a different magnetic field that somehow affects the current... but at the moment I'm not thinking of how to explain an apparent increase in resistance from left to right. Wnt (talk) 11:33, 21 May 2017 (UTC)


 * See Multiway switching. The speed of current is the speed of light. The ladder paradox can not apply to a circuit using simple switches. But and wire has a capacity and inductivity when current flows. Turning on a light bulb, the filament needs to be heated up before light is emitted and cooled down to stop the light emission. Speed limits of every computer are the physical properties of the used circuits. A master-slave-flip-flop (electronics) shows how dependent switching speeds are inside a circuit. If the inverter is slower than the NAND gates, the input will rush though the whole circuit at once. -- Hans Haase (有问题吗) 13:10, 21 May 2017 (UTC)