Wikipedia:Reference desk/Archives/Science/2015 October 2

= October 2 =

Overcooked food
Is there a Wikipedia article about overcooking? I could not seem to find it when I want to know what happens when food turns black (and any health risk from consumption). 128.54.128.131 (talk) 06:43, 2 October 2015 (UTC)


 * I found these: Heterocyclic amine formation in meat (for meat) and Acrylamide (for starchy foods). Which seem to be what you're looking for.-- O BSIDIAN  †  S OUL  06:52, 2 October 2015 (UTC)


 * The browning (and sometimes blackening) of both breads and meats takes place via the Maillard_reaction. SemanticMantis (talk) 14:06, 2 October 2015 (UTC)
 * Caramelization is the other of the two major browning reactions related to cooking. Well, there's also the extreme of charring and combustion I guess. DMacks (talk) 21:19, 2 October 2015 (UTC)

Precipitation in US forecasts stated in inches
When the weather reporter says "We're going to get 1" of rain on Thursday," does the meteorologist community have a standard of what that means, like 1" in a graduated cylinder of defined cross-sectional area? 20.137.7.64 (talk) 14:17, 2 October 2015 (UTC)
 * See Rain gauge. According to our article, the National Weather Service uses "a funnel emptying into a graduated cylinder, 2 cm in diameter, which fits inside a larger container which is 20 cm in diameter and 50 cm tall." Tevildo (talk) 14:21, 2 October 2015 (UTC)




 * (ec) Yes. But if you think about it, it doesn't really matter what the cross-sectional area of the container is - the larger it is, the more water is required to fill it up to 1" - but the larger it is, the more raindrops you're capturing...so in the end, it all cancels out and the actual cross-sectional area doesn't matter...only the depth of the water at the end.


 * In practice, they use a wide funnel arrangement to capture the raindrops over a large area (see Rain gauge) - which avoids errors due to sheer luck (because the raindrops arrive randomly) - and then they funnel the water into a tall, narrow vessel for measurement. This allows them to measure the depth of the water to greater precision - and also avoids having a large surface area that the captured water might evaporate from and mess up the reading.  But the calculation involves the cross-sectional area of the funnel divided by the cross-sectional area of the narrow vessel, multiplied by the depth of rain measured in that narrow vessel.  That gives you the depth of water you WOULD have gotten if you'd just had a perfectly cylindrical collector.


 * So, essentially, you're right. "Three inches of rain" means that if you put a bucket out in the open in your back yard, then after the rainstorm has passed, it would have a three inch depth of water inside it.  If you look at the depth of water in your swimming pool - that too would go up three inches. SteveBaker (talk) 14:32, 2 October 2015 (UTC)


 * Exactly! Today, precipitation is usually measured using an Automated Surface Observing System (ASOS).  The Tipping Bucket Rain Gauge is very accurate when measuring rainfall; but accumulations of other precipitation (like sleet, snow, hail, and so on) can introduce errors that are still often measured by a human observer.  Nimur (talk) 14:51, 2 October 2015 (UTC)


 * Actually, not quite right - If you left a bucket out in the rain it would have more than three inches in it after the rainstorm passed as buckets are wider at the top than they are are the bottom. Richerman    (talk) 15:48, 2 October 2015 (UTC)
 * Unless it's a straight sided bucket of course. Alansplodge (talk) 15:52, 2 October 2015 (UTC)
 * Naa - that's a paint can. And it won't collect any rain as it's got a lid on. :-) Richerman    (talk) 18:45, 2 October 2015 (UTC)
 * "Plastic pail" actually. Alansplodge (talk) 22:34, 2 October 2015 (UTC)
 * Ah but! - it's got a lip on the top that makes it slightly smaller than the bottom, so it still wouldn't be accurate :-) On a side note - there's a long discussion here as to whether a bucket and a pail are the same thing. Richerman    (talk) 10:38, 3 October 2015 (UTC)
 * One would have to remove the lid to see if the lip actually reduces the circumference of the aperture, but I take your point. The product is on sale in New Zealand, where they sometimes have a quaint turn of phrase. Alansplodge (talk) 22:30, 3 October 2015 (UTC)
 * Yeah, nah, we do ay. Chur bro. Sweet as! Akld guy (talk) 10:02, 4 October 2015 (UTC)

what are the current impediments in expanding the mandatory vaccine panels to include more vaccines
requesting exhaustive replies. — Preceding unsigned comment added by Mahfuzur rahman shourov (talk • contribs) 16:44, 2 October 2015 (UTC)
 * Wow! That almost sounds like an essay prompt for a homework question!  Can you elaborate on what you're looking for?  Nimur (talk) 16:47, 2 October 2015 (UTC)
 * The answer to your question is going to vary significantly depending on the context. What country are you referring to?  Which group(s) of people within that country?  What do you mean by "mandatory"?  Deli nk (talk) 16:59, 2 October 2015 (UTC)

that is no excuse for not giving reply to a question on RD which does not violate rules.
 * It is very much a reason for not giving an answer. It states quite clearly at the top of the page "We don't do your homework for you..." SpinningSpark 15:11, 3 October 2015 (UTC)

mandatory vaccine panels. around the world, various vaccines are applied mandatorily, no exemptions. question of mine is what are the existing impediments in expanding the panels? — Preceding unsigned comment added by Mahfuzur rahman shourov (talk • contribs)


 * This isn't really a science question, but just off the top of my head: To begin with, mandatory vaccination is a per capita tax that hits the poor very hard, unless government makes the vaccines free.  This is especially true when physicians, as is their wont, make it as troublesome and expensive as reasonably achievable to get the vaccinations done.  Between the doctor's fees and the need of a parent to take off work every time a vaccination is scheduled, there can be social pushback.  Also, even very young infants can feel substantial pain from shots,  and parents don't like that either.  Additionally of course there is anti-vaccination paranoia, mostly unjustified but there's very rare Guillain-Barre, and can you ever really rule out the chance al Qaida has a man in QC?  And of course, all the worst diseases for which vaccines are easily made are already covered - new ones will either be a difficult new vaccine (like HIV) or some shot that is fairly unlikely to be needed in a certain area (like Hepatitis A). Wnt (talk) 22:28, 3 October 2015 (UTC)


 * I would add religious objections to that list. Also note that a vaccine for a rare enough disease may actually carry more risk than benefit.  This is especially true if a herd immunity already exists to the disease in question.


 * And, in the US, which lacks price controls for vaccines, if there is insufficient excess capacity to bring competition into play, you can expect the company that produces such a vaccine to dramatically increase the price, perhaps by 5000%, in order to "maximize shareholder value". StuRat (talk) 18:03, 6 October 2015 (UTC)

push-pull stage+unipolar supply
hello, in this circuit here this (fig. b), the speaker is coupled to the output stage using a capacitor. The text says that this is in order to prevent DC flowing through the load, i.e. it forms a high-pass together with the speaker and the transistors.

In another text (a book) which makes the same point (capacitor required in case of unipolar supply) it says the capacitor is there to store energy for the half-period when the top transistor is in cut-off and the bottom transistor conducts. Because then, the load is connected with both poles to ground and the battery cannot contribute to powering it. Which is correct, or is it two ways of saying the same thing? Thanks in advance, Asmrulz (talk) 17:45, 2 October 2015 (UTC)


 * A capacitor isolates the DC voltage (potential). A capacitor also store energy (power). Voltage (potential) and energy  (power) are related but not the same thing. The output from a real  amplifier may not match the speaker's impedance so a capacitor is required. Also notice that in a  amplifier has a minus voltage rail. Although a speaker has impedance it also has conductance (and inductance) and would drain and mess up the signal  between the two driving transistors. Which I think the main point of the capacitor. I'm sure an other editor will pop up to give even a clearer explanation to mine.--Aspro (talk) 18:28, 2 October 2015 (UTC)


 * They are both more or less correct, it's true that the capacitor prevents DC current through the load, but the second text explains what happens and the reason why it's needed better than the first. The mean voltage over the capacitor will become UB/2 (assuming an input signal without DC component) very quickly, but suppose that power and input are turned on at the same moment, and the input signal first goes negative: during that first half period there will be no output at all because the capacitor hasn't charged yet. That follows logically from the second explanation, not from the first.
 * Also: preventing DC current through the load is not really a necessary requirement for an amplifier: in circuit A there will be DC current through the load when the input signal has a DC offset. So the first explanation doesn't really explain why the capacitor is necessary, imho. Ssscienccce  (talk) 20:57, 2 October 2015 (UTC)

OP, you seem to understand why a capacitor is not needed in fig.a, but I'll explain it for others. In fig.a, it's intended that with no signal, the transistors should be biased on by the resistors so that the voltage at the midpoint with respect to the common supply terminal is zero. This means that there will be zero volts across the speaker. In practice, no matter how much care is taken in setting this quiescent condition, one transistor will conduct a fraction more than the other and there will be a small offset current flowing through the speaker. This effect may worsen over a long period of time as components age. Nevertheless, this is why a capacitor need not be fitted in fig.a; there is no need to block DC from appearing across the speaker providing care is taken in the setting up. In fig.b which uses a single polarity supply, the transistors are biased so that the voltage at their junction is half the supply voltage. There is therefore a need to fit the capacitor to prevent DC appearing across the speaker. DC across a speaker is highly undesirable; it causes the speaker cone to move to a position that is not its natural rest position, and can thus cause distorted audio reproduction. Both explanations cited are correct. The capacitor blocks DC while passing the audio signal. The speaker receives audio signal from the top transistor via the capacitor when the polarity of the input signal causes that transistor to turn on and the bottom one to turn off. When the input signal reverses so that the roles are reversed, the stored energy in the capacitor conducts via the lower transistor and causes audio current to flow through the speaker. Thus on each half cycle of input signal, the speaker gets audio via one or other of the transistors. Akld guy (talk) 21:38, 2 October 2015 (UTC)
 * I should point out also that in fig.a, it's rather fortuitous that a capacitor is not needed. If the biasing is set up correctly in the way I described, there is no voltage at the speaker terminal, and it just so happens that the only type of capacitor suitable at that position would be one that has high capacitance. The only type with adequate capacitance is the electrolytic capacitor, which absolutely requires a polarizing DC voltage in order to function. Such a capacitor would be used in fig.b. Akld guy (talk) 22:48, 2 October 2015 (UTC)


 * Note : 'it's rather fortuitous that a capacitor is not needed' the OP needs to realize that these are examples of 'perfect' circuits to explain the principle . As mentioned above, it is difficult in practice to get two perfectly matched transistors that doesn't  need a capacitor. So in a practical circuit  (in say an amplifier that one would buy) a  would include a capacitor to ensure it worked as advertised. Yet in b a capacitor is  absolutely essential for the perfect circuit to work.  I don't know if we have baffled the OP with science here or whether we have helped. So, in short: the  two diagrams are just explaining the principles in perfect circuits and both explinations are correct in the right context.--Aspro (talk) 11:49, 3 October 2015 (UTC)
 * you have, thanks everyone Asmrulz (talk) 17:23, 3 October 2015 (UTC)
 * You seem to have missed the point about the capacitor in fig.a, which is not simply a diagram for illustration. It's an actual practical circuit. The only capacitor suitable in loudspeaker-driving circuits is the electrolytic capacitor since it is the only type that comes in large enough capacitance versions to drive a low impedance such as the speaker. The electrolytic capacitor by its nature requires a polarizing voltage, which shouldn't exist in fig.a at the point where it would be inserted since the aim is to carefully set the biasing of each transistor (with each one's base resistor) so that the DC output voltage is zero. No capacitor need be fitted, which is just as well since no practicable one can be fitted anyway due to lack of polarizing voltage. Akld guy (talk) 23:24, 3 October 2015 (UTC)

Note, the posted exaple with the DC encouppling capacitor uses a single rail power supply. The circuit without the capacitor requires a symetric power supply with a positive voltage rail and a equal negative one. Note: The exaples no not limit the idle current between the transistors and their base bias. If the upper (to+) transistor is NPN and the lower one (to-) is PNP, you might adjust this idle behavior by bypasing an adjustable resistor parallel to the diodes. This shown setup requires a preamplifier or darlington transistors with furter base bias voltage compensation. -- Hans Haase (有问题吗) 19:11, 4 October 2015 (UTC)

Calculating the required value of the elko: f=1/(2*pi*r*c) or c=1/(2*pi*r*f) f=frequency in Hertz, r is impedance of speaker+transistor c=You capacitor in farads, but they are declared in µF (micro farads), so 1,000,000 µF = 1 F -- Hans Haase (有问题吗) 19:27, 4 October 2015 (UTC)