Wikipedia:Reference desk/Archives/Science/2013 March 1

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March 1

Error correction for analog signals

Is there a way to use error correction for analog signals to remove noise? i.e. is it possible to trade bandwidth for noise, like you can with digital error correcting codes.

I am aware of Dolby noise reduction for audio tapes, and spread spectrum, but neither one removes noise completely.

Or in other words, given a specific level of environmental noise, with analog is it possible to have zero noise in the final signal like you can with digital? Ariel. (talk) 02:34, 1 March 2013 (UTC)

Unlike a digital signal, analog signals are not quantized. If we define the noise as the error between the desired signal and the received signal - then the analog domain means that you can produce an arbitrarily-small but still-measurable noise-signal; for any sufficiently-small noise, a sufficiently-more-sensitive measurement can detect it. Contrast this to the the digital domain; the minimum error for any given sample is exactly one bit; anything smaller than exactly one bit is defined as zero. So, it's easier to have a "perfect reconstruction" for a digital signal; you can't make your measurement more accurate than the actual signal.

Now that this definition is cleared up, we can answer your first question. Analog signal processing is full of tricks to reduce noise: this is summarized in the power/gain/bandwidth product. If you spend more power, you can achieve lower noise. If you use more bandwidth, you can achieve lower noise.

Some tricks that analog signal processors use: you can double the amount of signal by creating a differential pair. This adds the benefit of redundancy and also takes advantage of the electromagnetic propagation properties of coupled differential elements.

You can double the bandwidth; compare single side band, which uses less bandwidth, to dual side-band, where redundant information can be used to improve signal-to-noise ratio. In principle, an arbitrary amount of redundancy can be added to a transmission by modulating at multiple frequencies, and constructing a special radio-receiver that down-mixes and combines each signal. This is rarely done in practice; there are better ways to make use of available spectrum. Frequency modulation in the analog domain is one such technique; an arbitrarily-large frequency spectrum can be used to frequency-modulate a signal of a given input bandwidth; here, SNR is traded against spectrum availability.

Typically, the best way to reduce noise in the analog domain is to prevent it in the first place. Modulate a signal so that it operates in the best regime that your actual devices work at: this is the premise for the superheterodyne and the multiple intermediate frequency stages on some complex radios. Select better parts: lower noise amplifiers are made out of higher-quality semiconductor. Better tolerances on passive components, and more stringent filtering of parasitics, all make for a better analog signal. Nimur (talk) 05:38, 1 March 2013 (UTC)

Thank you. I was trying to understand what makes digital immune to noise, and now I see the unavoidable noise is in the quantization, and thus digital is not in fact immune to noise, you just see it elsewhere. How do you do the resolved checkbox? 17:04, 1 March 2013 (UTC)

I know nothing about this subject and first learned electronics a few hours ago, so this is just speculation: but can't we say that analog signals certainly are quantized in one respect: no electrons passing means exactly no electrons passing, not an arbitrarily small amount. Thus a completely open circuit, or a capacitor that is charging, might literally let nothing through. The question did not say that what ISN'T noise has no added tolerance due to the noise reduction - so if you include something like a capacitor on the circuit, it might still qualify as. Therefore, it seems to me quite likely that if you know something about the characteristics of what the signal is supposed to be, you can indeed reduce noise. For example, imagine a microphone that changes voltage between 1-5 volts depending on the sound(totally arbitrary and probably wrong numbers). Well, if you know that a voltage of 1-2 represents physical hertz that do NOT exist in your environment, you are guaranteeing that there is no signal there. You can then "trade" that extra bandwidth for lower noise by dropping it to 0. Let's go further: if you know half of your bandwidth is empty, can't you broadcast twice in analog, reverse one of the waves, and then filter the noise that is outside of the "0" of combining the waves? If they are in sync aren't tricks like this possible totally in analogue? This seems to me certainly to be bandwidth-for-noise: you can trade half your bandwidth (one of two lines for example) to broadcast twice and get a better signal? As I said I know nothing about this subject and first learned any electronics a few hours ago. 91.120.48.242 (talk) 07:56, 1 March 2013 (UTC)

Re: "can't we say that analog signals certainly are quantized in one respect: no electrons passing means exactly no electrons passing, not an arbitrarily small amount", that's not how it works. An analog electrical signal in a wire doesn't just have 0 or 1 electrons. It can have 0.9999999 or 1.0000001 electrons per unit of time. Of course, being a statistical property, it takes time to gather enough samples to tell those two apart. This too breaks down when you get to the point where the quantum nature of time matters. --Guy Macon (talk) 08:36, 1 March 2013 (UTC)

Can you really say that about a completely open circuit though? This is akin to saying that RAM is not really digital, because in fact the bit can be flipped by cosmic rays before it's read - so it really doesn't have a value of "1" but more like 0.99999999999999995487 to 0.999999999999999999871 and it doesn't really have a "0" so much as 0.00000000000000000442 - 0.00000000000000079325. I think that's a pretty thin/ridiculous argument though. An open circuit really is a digital 0, and a bit really is a digital 0 or 1. It's not analogue by any stretch of the imagination. 91.120.48.242 (talk) 14:48, 1 March 2013 (UTC)

Voltage is not quantized. A circuit doesn't work just from the number of electrons moving, but also from how "hard" they move (voltage). Ariel. (talk) 17:04, 1 March 2013 (UTC)

Again, except for no amps. A circuit is open from no amps through it and it doesn't make sense to talk about how hard the electrons AREN'T moving across it. 86.101.32.82 (talk) 19:27, 1 March 2013 (UTC)

Sure you can. That's what voltage IS! It's the potential difference in an open circuit. You can't measure voltage in a closed circuit - the voltage difference across a wire is zero (ignoring the tiny resistance in the wire). You can only measure voltage when there is resistance to current, and an open circuit is the ultimate resistance. Ariel. (talk) 19:36, 1 March 2013 (UTC)

See Johnson noise, incidentally. To completely remove _any_ analogue noise, you'd need to cool the device to absolute zero. Tevildo (talk) 20:55, 1 March 2013 (UTC)

Re: Re: "can't we say that analog signals certainly are quantized in one respect: no electrons passing means exactly no electrons passing, not an arbitrarily small amount". See shot noise, the quantized nature of current does actually produce noticeable noise in some amplifiers when very low-level signals are being processed. Re "digital is immune to noise". This is, in fact, not correct. Random noise, even at very low levels, has a small, but finite, probability of causing a digital error. Over a short message with low noise on the channel and/or good error correction there is a good chance that the message will be received uncorrupted. However, over a long enough message (or many short messages) there will eventually be a sufficient number of errors to overwhelm the error correction and part of the message will be lost. This is because there will always be a finite limit to the number of bits it is possible for the error correction algorithm to deal with. An analogous process to digital error correction can indeed be achieved with analog signals. One simple way of doing this is to send multiple copies of the same message (either in space over different routes or in time over the same route). In the presence of random noise the copies will add together according to N, but the noise will add only according logN (because it adds or subtracts randomly) and hence the signal to noise ratio increases according to N/logN. SpinningSpark 21:28, 1 March 2013 (UTC)

On the other hand, the Shannon limit establishes that however noisy the digital channel is, there will still be a data rate that you can push through it with vanishingly small error probability, if you use sufficient error correction. See also channel capacity for a worked example, and Shannon–Hartley theorem. Jheald (talk) 21:40, 1 March 2013 (UTC)

When dimensional analysis fails

Can someone give an example of a dimensional analysis/order of magnitude estimate gives a very wrong answer?

This isn't a homework exercise or anything. Someone used an order of magnitude estimate to arrive at a conclusion that I think is totally wrong, and I'd like to substantiate my belief that these kinds of estimates are far from fool-proof. 65.92.4.236 (talk) 05:02, 1 March 2013 (UTC)

I think I gave an example way back: in this March 2009 discussion, I intentionally abused dimensional analysis to show that a 60 mph car is also traveling at 3.99x10^-4 ... (no units). This was intended to illustrate that if you use invalid analysis, you can make a valid equation that is totally meaningless. Surprisingly, another reference-desk regular used a different and purportedly better method of analysis to show that the 60 mph car is in fact moving at 8.947x10^-8 ... evidently, my failure to use the correct universal constant caused my calculation to err by four orders of magnitude... but there's no point in re-opening a four-year-old debate! Nimur (talk) 05:17, 1 March 2013 (UTC)

• Trying to correct Dauto or any one on this one would be maddening, [| since there is always someone wrong on the internet]. OsmanRF34 (talk) 13:36, 1 March 2013 (UTC)

That discussion back in 2009 was not about dimensional analysis. Dauto (talk) 20:14, 1 March 2013 (UTC)

If you re-read that discussion in entirety, you will find that on 4 March 2009, you referenced the Wikipedia article on dimensional analysis to support your point. Regardless of the point, or its merit, do you still believe that the discussion was not about dimensional analysis? Nimur (talk) 23:00, 1 March 2013 (UTC)

Interesting discussion! I side with Dauto, in natural untis you don't throw away any information whatsoever, as the choice of units is completely arbitrary and physically completely irrelevant. In fact you can still do "dimensional analysis" because, as I explained below, this is fundamentally nothing more than using a scaling argument. I also explain this here where I consider the classical limit of special relativity in natural units. Count Iblis (talk) 23:19, 1 March 2013 (UTC)

If you read the past RD discussion you'll see that one thing is to exchange different equivalent units (like meter or inches or miles), and another is to covert from meters to seconds! 00:25, 2 March 2013 (UTC)

Well yes, I can "analyze" the gravitational acceleration on Earth to be 2.1512, by pulling a number out of my ass. That's also an invalid dimensional analysis, and also doesn't count as an example to the OP's question.

I don't know what "very wrong" is supposed to mean, but the power radiated by Hawking radiation has a constant factor of 15360pi, so a dimensional analysis result would be wrong by a factor of 48,000. Is that wrong enough? --140.180.255.158 (talk) 10:24, 1 March 2013 (UTC)

I am not sure that is a really case, there is always an arbitrary constant which could be a lot bigger than that (Avogadro's number for example). No one claims the constants will all be 1. I think dimensional analysis fails in general when a problem depends on any set of variables which of themselves can form a dimensionless group. So choose a problem with two lengths for example, or a length a speed and an acceleration. How much water will flow down a Xm long pipe with a diameter of d and a head of pressure of h? The subtler forms of failure are when you do not spot the additional variable on which the problem depends (viscosity, density, gravity, pressure etc). --BozMo talk 10:44, 1 March 2013 (UTC)

Dimensional analysis is nothing more than using a scaling argument. But most people don't know this, and then they get surprised if it doesn't work. Any dimensionally incorrect equation can be fixed and made to be dimensionally correct as follows. If y = f(x1,x2,x3,...xn) where y, x1, x2, etc. are physical quantitiies wich can have incompatible dimensions, and f is some arbitrary function that computes y from the xj in an illegal way (e.g. by adding up length to time, while y has the dimension of mass, so that it doesn't make any sense whatsoever), then you can fix this problem by dividing all the xi by the Planck units for their units (which is always just a combination of hbar, G and c). This has the effect of making f(x1,x2,...,xn) dimensionless. And then you multiply the function f by the Planck unit for y.

E.g. suppose we postulate the equation:

T = L^2

for the period of a pendulum. To make this dimensionally correct, you have to divide L^2 by the square of the Planck length and multiply by the Planck time, you then get:

T = L^2 sqrt[c/(hbar G)]

Then, obviously , the difference between the "correct equation" and this one is that here c, hbar and G appear. So, the reason why dimensional analysis works is because of the hidden assumption on the appearance of these dimensionful constants. The value these constant take depends on the units you chose, you can interpet changing the values of these constants in terms of rescaling your variables. Taking the limit c to infinity amounts to rescaling toward the nonrelativistic limit. So, if we want a relation between variables that is valid in some scaling limit, e.g. the classical nonreltivistic, non-quantum world then you're seeking an equation between physical variables that remains non-singular if you take the limit of c to infinity and hbar to zero. In that scaling limit, these variables then don't appear at all. Count Iblis (talk) 12:40, 1 March 2013 (UTC)

For example, suppose a clock only has an hour hand - how many times will this hour hand pass an hour marker in 24 hours?

Well the correct answer is 86400. Just consider>

• 86400 seconds = 1440 minutes. No one would argue with that! Likewise
• 1440 minutes = 24 hours. No one would argue with that!
• Well a clock's hour marker by definition passes 1 hour marker per hour.
• So to answer the question of how many times this happens in 24 hours, we simply multiply 1 by 24, yielding 24. But notice! We already have shown that 24 hours = 86400. So the answer to the question is that in 24 hours the hour hand must pass the hour marker 86400 times.

 

How many complete revolutions around the face of a clock is this? Well, clock faces normally don't show 24 hour markers, but only 12. So dividing by 12 (the number of hour markers that fit on the face of a clock) we see that in a twelve-hour period, an hour hand will turn all the way around the face of a normal clock 86400 / 12 = 7200 times. Each of those revolutions are half of a day, so if we wanted to see how many years fly by we could divide by the number of half-days per year, which is (360*2). That's 720. So any fool can see that about ten years fly by during every twelve-hour period. Time really does fly! 91.120.48.242 (talk) 14:35, 1 March 2013 (UTC)

. Getting back to actually helping the Original Poster....

I think the classical case where it fails is the energy of a moving object. It's 1/2 mv^2 - but if you do dimensional analysis you will not know about the 1/2. The other examples you were given where the final answer is unitless are cheating, since you can do anything to the number if it has no units. As far as I know the only errors you will have when doing a normal dimensional analysis are scaling errors - where you need to multiply by a constant, and you don't know you need to. It's also possible to calculate things that have no physical meaning - the analysis is not wrong exactly, but doesn't mean anything useful. Ariel. (talk) 17:01, 1 March 2013 (UTC)

There's two aspects of the question: dimensional analysis, and order of magnitude estimation.

Dimensional analysis is a powerful and effective method to use in two situations: a) making sense of recorded data, and b) checking a derived formula. Often, someone working in a new field is trying to deduce a mathematical formula to fit recorded data. Dimensional analysis will give you a possible formula, but of course if there are constants it won't tell you the constants. But in fitting the curve deduced from the possible formula, either a constant will be required to get it to fit the data, or you won't be able to fit the data regardless of what constant you choose - that means the data or the formula is wrong, so you take action as appropriate. It happens that if you are working in the SI metric system, the constants almost always are simple - 2, 2xPI, 1/2 and the like - that's the beauty of the SI system - it's designed that way. When the constants are not these simple factors, they are generally combinations of the well known fundamental constants of physics. In this use, dimensional analysis is not infallible. But the reason it's not infallible is, almost entirely, because in practice you often do not have enough measured data over a range large enough. The data is the problem, not the dimensional analysis.

Ariel says in his example that diensional analysis will miss the constant (1/2 in his example). That's not the point. The point is, in dimensional analysis, you KNOW you may need a constant, so it is up to you to go find it (by fitting to data or by mathematical reasoning).

In dimensional analysis in use (b), us humans often make errors in deriving formulas from first principles. If dimensional analysis says the formula is wrong, then it IS wrong - you can count on it. If dimensional analysis checks out ok, it could still be wrong. In my experience (>40 years in Engineering), it has never happened that way though - it is in practice a very reliable check. Note that here I am referring to checking a derived formula for some real purpose, not an exercise in trying to prove silly things or prove things with nor physical meaning.

Order of magnitude estimation (i.e., working out the correct power of ten magnitude, assumed to be a task quicker & easier than calculating accurately) is something else. Having done a lot of engineering, and supervised both other Engineers and scientists on contract to do research, It seems to me that order of magnitude estimation is something that physicists like to do. Engineers quickly learn to do all calcs to 3 place accuracy unless there is a specific need to be more accurate, which sometimes is the case.

The risk of stuffing things up with order of magnitude estimation is very high. It might serve the OP best by quoting a famous example:-

When Admiral Rickover and his team had just about got the first nuclear submarine ready, Dr Edward Teller, at that time well known as the father of the hydrogen bopmb and an internationally famous nuclear physicist commanding considerable respect from Presidents down, came close to derailing the whole thing. He claimed that he had shown by order of magnitude estimation of radiation levels that the sub could not be safely refueled in port, and wanted nuclear subs to be refuled/serviced in the midle of the ocean, which of course is simply not practical. He put out a press release. This triggered a debate between Teller, and Rickover's team. It went something like this:- A team member showed engineering calculations that showed radiation would be well within agreed safe limits. Teller said, well I can't see where you made a mistake, but you must have made a mistake, becasue my order of magnitude calcs show a very different magnitude. The team then got Teller to walk them through his calcs. Every now and then, as Teller went thu his calcs line by line, they would say things like "Dr Teller, you left out a π/4 term. Let's put that in". Teller: "Why bother, we only need a rough answer here." "let's put it in anyway, please." A little later: "Dr teller, you assumed a sphere, but radiation into the gound only hurts earthworms. Let's assume a hemisphere of exposure and divide by 2." And so on. At the end of it Teller agreed refueling in port would be safe after all. It had turned out that all his approximations erred in the same direction.

Reference: The Rickover Effect: How Admiral Rickover Built the Nuclear Navy, by Theodore Rockwell, John Wiley 1992, Page 312.

Ratbone 58.164.229.83 (talk) 02:24, 2 March 2013 (UTC)

The right citation for the Rayleigh scattering' equation？

I consulted the wiki website to get one formula" http://en.wikipedia.org/wiki/Rayleigh_scattering ", the Rayleigh scattering. It is as attachment 1, and the given citation is "3 ^Seinfeld and Pandis, Atmospheric Chemistry and Physics, 2nd Edition, John Wiley and Sons, New Jersey 2006, Chapter 15.1.1". However, I turn to the book with none of the formula (shown in attachment 15.1.1). So I want to know the right citation, as I need the original documents.

Rayleigh's equation: I=I0* (1+cosθ^2)* ((n^2-1)/(n^2+2))^2* (2π/λ)^4* (d/2)^6/ 2R^2 （http://pan.baidu.com/share/link?shareid=316021&uk=3590423494）

— Preceding unsigned comment added by Yanyan1992111 (talk • contribs) 07:05, 1 March 2013 (UTC)

The expression most likely is in the Seinfeld and Pandis reference, but that particlular page is not available online. It is given in numerous other books [1][2][3][4] (although the last one seems to have got the sign of the cos² term wrong). Or were you looking for Lord Raleigh's original paper from 1899? SpinningSpark 20:34, 1 March 2013 (UTC)

Thank you for your reply.But I still have something that I puzzled.You say the last one seems to have got the sign of the cos^2 term wrong.

Do you think our equation's sign is right or wrong?

We find the particular page of the Seinfeld and Pandis.http://pan.baidu.com/share/link?shareid=316981&uk=3590423494 Acually there is no this expression in this book.http://pan.baidu.com/share/link?shareid=316983&uk=3590423494 http://pan.baidu.com/share/link?shareid=316985&uk=3590423494 http://pan.baidu.com/share/link?shareid=316986&uk=3590423494

Please tell me the authentic citation of my equation!Thank you! — Preceding unsigned comment added by 218.249.94.132 (talk) 07:31, 2 March 2013 (UTC)

The equation in the article is correct. SpinningSpark 22:08, 2 March 2013 (UTC)

Thank you for your reply.But you still don't tell us the right citation of our equation. Can you help us find the citation,as we don't know how to find the equation's citation?

Orbital mechanics

My local newspaper's article about Dennis Tito's planned 2018 mission to Mars states that it is "timed to take advantage of the once-in-a-generation close approach of the two planets' orbits". I thought the optimal alignment for a Hohmann transfer orbit to Mars happened once every 18 months or so. Is there something special about this particular one, or is the newspaper wrong as usual? --Carnildo (talk) 10:44, 1 March 2013 (UTC)

Their plan includes a Venus flyby, and the low energy transfers that can do that is rare, there is another opportunity in (of the top of my head) 2036ish. And yes, normal Hohmanns are indeed every 18 months or so.Fgf10 (talk) 11:22, 1 March 2013 (UTC)

Mars' orbit is quite eccentric (Elongated), So it makes a difference whether Earth approaches Mars close to Mars perihelium or not. That approach coincides with the perihilum about once every 15 years. combine that with the desired location for Venus fly by and you get a relatively rare event. By the way, the Hohmann transfer orbit window comes about every 26 Months or so. Dauto (talk) 19:51, 1 March 2013 (UTC)

Where did you and Fgf10 get the idea that there's a Venus flyby? Tito never mentioned it in his press conference, and neither does the paper he got his trajectory from. If you look at the first graph on page 19, you'll see that the lowest time-of-flight trajectory occurs every 15 years, with the next one in 2017 and the last one in 2002. Tito's mission is planned for launch in January 2018. --140.180.255.158 (talk) 22:31, 1 March 2013 (UTC)

Did somebody dust off their Spirograph ? :-) StuRat (talk) 03:58, 2 March 2013 (UTC)

carbol

Would you inform to me, please. The contens of carbol and how make it? Generally poeple put in the toilet. thank you — Preceding unsigned comment added by 114.79.0.170 (talk) 13:00, 1 March 2013 (UTC)

See carbolic acid. --PlanetEditor (talk) 13:03, 1 March 2013 (UTC)

Also carbolic soap. --Jayron32 13:04, 1 March 2013 (UTC)

Most peaceful hominid

I know chimpanzees and humans are the most violent hominids, but I'm wondering which is the most peaceful hominid (bonobo, gorilla, or orangutan)? Previously I thought bonobos are the most peaceful, but studies claim otherwise. --PlanetEditor (talk) 13:54, 1 March 2013 (UTC)

By which means are we to quantify peacefulness? --Jayron32 14:15, 1 March 2013 (UTC)

In the sense that they exhibit the least intra-specific aggressive behavior. --PlanetEditor (talk) 14:21, 1 March 2013 (UTC)

The most peaceful hominids are the dead ones. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:39, 1 March 2013 (UTC)

I would be interested in what the second-most peaceful hominid is, so that I can pretend to be that while hunting the most peaceful one. 91.120.48.242 (talk) —Preceding undated comment added 14:36, 1 March 2013 (UTC)

• A serious, referenced answer in good faith, using the notion of intra-species aggression as a way of defining "peacefulness": Of the extant hominids, I'd go with the Orangs, simply because they are the most solitary, and have the smallest groups when they do aggregate. See Orangutan#Social_life. While I'm sure some aggression occurs, they simply don't bump into each other as often. The preceding is considering aggression generally, e.g. for both sexes, disputes over territory, food, etc. However, all most non-human hominids display some male aggression in coercing females to copulate, orangs included; see this overview "Male Aggression and Sexual Coercion of Females in Nonhuman Primates... " here [5]. SemanticMantis (talk) 15:31, 1 March 2013 (UTC)

  Thank you for the reference. Very interesting article. --PlanetEditor (talk) 15:42, 1 March 2013 (UTC)

You're welcome, glad you like it. After reading it further, I think you'll have to limit the type of aggression to get a simple answer. For instance, if we restrict to sexual aggression, then Bonobos are far more "peaceful" than Orangs... SemanticMantis (talk) 15:49, 1 March 2013 (UTC)

Also, the link posted by the OP is not about intra-species aggression in Bonobos, it is about Bonobos eating monkeys. So that doesn't really make them less peaceful under the working definition. To rigorously compare incidence of intra-species aggression between Bonobos and Orangs would require a careful literature search, and possibly WP:OR. But I'll be interested if anyone turns up some more relevant data on the topic. SemanticMantis (talk) 15:35, 1 March 2013 (UTC)

I think the fundamental cause of aggression is domination instinct, which is seen in chimps, gorillas, and humans. Species which do not want to dominate others lack aggression. This is why bonobos and orangs are peaceful. Orangs exhibit, as you said, sexual violence and male-male competition for access to females. So bonobos are the most peaceful. Not sure whether male-male competition exists among bonobos. --PlanetEditor (talk) 15:58, 1 March 2013 (UTC)

According to this, bonobos exhibit less male-male competition. This makes bonobos the most peaceful hominid. --PlanetEditor (talk) 17:41, 1 March 2013 (UTC)

Are you including humans in that comparison? I'd like to know what data the OP is using to assert that humans and chimpanzees are the most violent hominids. The statement is definitely false for modern humans living under a government, and while archeological evidence suggests 15% of humans died of violent causes in pre-Neolithic times, I haven't found any analogous statistics for other hominids. --140.180.255.158 (talk) 18:36, 1 March 2013 (UTC)

"The statement is definitely false for modern humans living under a government" - that is a joke, right? If you look at the history, you will see human history is history of conflicts and wars. While Paleolithic hunter-gathers had far less violence compared to post-Neolithic humans, the rise of civilization and resulting division of labor (origin of full-time warriors) only strengthened organized violence. Have a look at this list. As I said, humans have domination instinct and it is this domination instinct which make them violent. It is this domination instinct because of which one human can kill millions of individuals of their species. It is because of this domination instinct one human is not willing to give up their dominating power even if thousands of other humans are dying. I agree modern democracies are relatively peaceful, but humans are genetically violent [6]. The fundamental question is human nature. If you want to know more whether humans are instinctively violent or not, I would suggest the book The Murderer Next Door: Why the Mind Is Designed to Kill by University of Texas evolutionary psychologist David Buss. --PlanetEditor (talk) 19:06, 1 March 2013 (UTC)

See also Homicidal ideation. "50-91% of people surveyed on university grounds in various places in the USA admit to having had a homicidal fantasy." Horrible. I lament why I did not born as a bonobo. --PlanetEditor (talk) 19:24, 1 March 2013 (UTC)

While violent behavior does have evolutionary purpose, absolute violence will led to species extinction. So evolution made humans in such a way so that they can suppress their violent instinct. This is why humans developed a unique cognitive faculty called morality. While the concept of morality can reduce violence, it can equally facilitate violence. People construct morality to serve their personal goals and dominate others. The unique feature of human violence, which distinguishes it from Chimpanzee violence, is that humans always use moral excuse before perpetrating violence. The perpetrators of violence always label their victims as immoral. For example, the Nazis labeled the Jews as oppressors, the Communist regimes label their victims as "enemies of the people". --PlanetEditor (talk) 19:36, 1 March 2013 (UTC)

No, that is not a joke. It's the central theme of The Better Angels of Our Nature. This is corroborated by Jane Goodall, who writes openly (for instance in Reason For Hope) about how chimpanzees show intra-species aggression far beyond that of the average modern human. — Sebastian 20:47, 1 March 2013 (UTC)

PlanetEditor, your claims are a classic example of cherry-picking data. You linked to a list of casualties in wars, but you haven't linked to a list of non-casualties in wars (99.7% of the population in Syria, much higher globally), a list of casualties in non-wars (see this World Health Organization report, in which violence only accounts for 0.9% of deaths), or a list of non-casualties in non-wars. The fact remains that 15-20% of people died violently in prehistoric times, whereas that number is currently 0.9% globally and much lower in developed countries. This 20-fold discrepancy is actually too small because it measures the percentage of deaths that are due to violence, not the percentage of the population that dies violently per year. Due to technology, the modern mortality rate itself is lower than its prehistoric counterpart.

Here is another relevant statistic: in the Middle Ages, the European homicide rate was 30-100 per 100,000 per year. Currently, only 1 EU member has a rate exceeding 2 per 100,000 per year.

I'm surprised you would call that Scientific American article "scientific", as its author seems to lack an elementary knowledge of statistics. He accuses Pinker of confirmation bias, but gives no evidence or contradictory data. He accuses Pinker of cherry-picking, by pointing out 2 data points (out of hundreds) from Pinker's book that don't support his point (!) He also doesn't understand why percentages are meaningful in social analysis:

"Of greater concern is the assumption on which Pinker's entire case rests: that we look at relative numbers instead of absolute numbers in assessing human violence. But why should we be content with only a relative decrease?"

By this logic, France's citizens are not wealthier than India's because India has a greater GDP. I think both the French and the Indians would beg to differ. Also by this logic, the US is not safer than Mali because the former, due to its much larger population, has more homicide victims. Again, I think Malians would beg to differ.

The author's final point is even more bizarre, to the point of being sophistic: "The biggest problem with the book, though, is its overreliance on history". Wow, Pinker dares to use historical evidence in a book about historical violence rates! How presumptuous! --140.180.255.158 (talk) 03:41, 2 March 2013 (UTC)

I'm not going to argue with you, and the ref desk is not a place for debate. Statistics can never shed a light on human nature. The cause of war, from evolutionary perspective, is more important that the number of individuals killed in a war. There may be one victim, and multiple aggressors. The claim that the number of casualties is decreased does not prove that the number of individuals who may engage in violence is also decreased. War is not the only indicator of humans' violent instinct. Bike rage, Road rage, Bullying, Legislative violence, Torture - all are evidence of the violent nature of the average modern human. Humans are far more violent than chimpanzees because the chimps engage in aggression only during territorial dispute, they don't get pleasure from violence, but modern humans engage in violence to gain pleasure. The main point here is that whether Homo sapiens engage in violence or not, they have the instinct of violence. Some engage in real violence, others engage is virtual violence. Blood sport and gladiator are classic proofs that modern humans gain pleasure from violence. Graphic violence, popular combat sports, and the popularity of WWE are the proof that the average modern humans are preoccupied with violence, they are emotionally attracted to violence. --PlanetEditor (talk) 05:02, 2 March 2013 (UTC)

And don't forget edit wars and endless discussions on Wikipedia! If your point is that modern human still has a lot of violent traits, then I don't think anyone would disagree with you. If your point is to convince everyone else that humans are worse than other hominids, then I feel this is indeed not the task of this page. You are the OP; we're here to answer your question. I think we have done an honest attempt at it, and I don't see any further question, so I suggest to close this discussion. — Sebastian 06:05, 2 March 2013 (UTC)

Yeah fine, actually this post was meant to find the ape with least violent behavior, which was determined to be the bonobos. But the discussion altered its course. --PlanetEditor (talk) 06:13, 2 March 2013 (UTC)

Although this isn't a place for debate, you're the OP, and I feel that the following is relevant to your question. How do you know that chimpanzees don't engage in violence for pleasure? The fact that they can't communicate this pleasure doesn't mean they don't perceive it. It is also not true that chimps only engage in violence for territorial purposes--in addition to competing with males for mates, they also beat and rape females into submission. --140.180.255.158 (talk) 07:35, 2 March 2013 (UTC)

File:Http://upload.wikimedia.org/wikipedia/commons/thumb/2/23/War deaths caused by warfare.svg/600px-War deaths caused by warfare.svg.png

You can't judge a book by its cover. Industrialized war may look extremely violent but it's far less so than ancient and homonid endemic violence. Modern human individuals are less likely to die from inter species violence than any other homonid. The nuclear war and genocide of the 20th century killed barely 2% of the societies involved. According to this source murder is a neglible tiny fraction of one per cent. Compare this to hunter-gatherer societies where more than 60% of males can die from violence. Even gorillas have a much higher level of violence than modern humans.--178.167.236.242 (talk) 23:50, 2 March 2013 (UTC)

Calculating the day of conception

Given that someone already know his/her birthday (month, day, year, and approximate time of the event), is it possible to calculate that person's moment of conception or the day his/her parents presumably had sexual intercourse, assuming that his/her parents did not perform artificial insemination as a route to become pregnant and assuming that the parents only engage in reproductive sexual intercourse (not possible in real life, since parents may engage in recreational sexual intercourse) and assuming that the intercourse was a one-time event? I had to make it simpler by making so many assumptions. It might become too complicated, if I add additional variables. 140.254.226.226 (talk) 15:19, 1 March 2013 (UTC)

No. You can come up with an estimate, but nothing more. For example, the existence of preterm birth completely undermines your premise. Consider also that, in cases of artificial insemination and other known-conception data points, babies aren't universally born on their expected due dates. — Lomn 15:22, 1 March 2013 (UTC)

Oh. Then, is it possible to do a similar sort of thing for non-human animals then, particularly for those species when offspring are usually born during a specific season, and the parents only mate during a particular season? I wonder if a mouse-breeder could calculate the day of conception given only the birth date of the baby mice. 140.254.226.226 (talk) 15:31, 1 March 2013 (UTC)

Most definitely in the case of mice. Although if the timing of conception is important (in developmental experiments) you will work the other was round by doing a timed mating, and checking for a vaginal plug to indicate mating has taken place during the previous night. Fgf10 (talk) 15:41, 1 March 2013 (UTC)

How do you know that mice only mate during night time? I wonder if they mate during the day time, or if daylight/moonlight/time of day has anything to do with the mating habits.140.254.226.226 (talk) 17:29, 1 March 2013 (UTC)

Even for highly inbred (genetically homogeneous) strains of laboratory mice, there's still a variation of about +/- one day in the lengths of their gestation periods [7]; you'll get even more variation in wild mice, or cross-breeding different mouse strains. TenOfAllTrades(talk) 15:52, 1 March 2013 (UTC)

I think the more important thing is whether or not the difference is really significant. If it's a +/- day variability and that value is not enough to significantly affect the results, then there's no need to worry. 140.254.226.226 (talk) 15:55, 1 March 2013 (UTC)

That's not what that paper says at all, for instance it's 462.2 +/- 1 hour (NOT day) for standard Bl/6s. Within a strain it's very reproducible. Of course between strains all bets are off. But like I said, you normally work the other way around anyway. Fgf10 (talk) 15:59, 1 March 2013 (UTC)

I'm assuming that you're looking at figure 2a. The error bars on that plot are for the standard error of the mean, not for the standard deviation. SEM is useful for determining (at a rough glance) which population means are significantly different, whereas SD tells you about the actual breadth of the distribution of values that went into the mean. To calculate the SD from the SEM, you have to multiply the SEM by the square root of the number of gestations measured.

The means and standard errors for the most popular strains (BL/6, and A/J, for instance) are calculated from rather large pools of gestations (139 for the BL/6 mice), which means that the error bar shown is roughly one-twelfth the standard deviation. Given a standard error of one hour, the standard deviation is twelve hours. To catch 95% of gestations – two standard deviations, assuming a roughly normal distribution – one has to open the window to plus-or-minus one full day. TenOfAllTrades(talk) 16:16, 1 March 2013 (UTC)

(ec) If intercourse was really a one-time event, the answer to that part of the question is trivial—ask the couple for the one time that they had sex. Conception (if taken to mean fertilisation) can occur anywhere from roughly 4 hours to roughly 72 hours after intercourse, however: [8]. That three-day window means that even if you have the date of intercourse and the date of birth, you still can't precisely pin down the date of conception. TenOfAllTrades(talk) 15:37, 1 March 2013 (UTC)

Which is probably why it's easier to do experiments on mice than humans. At least they are more predictable. According to the fertilisation article, fertilisation is just another word for conception. 140.254.226.226 (talk) 15:50, 1 March 2013 (UTC)

Room-sealed gas fire in chimney?

Mum is wanting to have a gas fireplace installed in the boarded up fireplace of her ~1920s terraced house to use as an alternative to the central heating. My concern regards the requirement for constant, unobstructed ventilation (about 200 cm^2), regardless whether the fireplace is in use, which I think will negate any improvement in efficiency over heating the whole house via the central heating.

I've read in an old thread on a forum that it may be possible to draw air for combustion via the chimney, in the space surrounding the flue. Has anyone here heard of that? --78.144.199.159 (talk) 16:01, 1 March 2013 (UTC)

I'm not quite clear on your Q, but there are generally two types of fireplace, those which draw the warm air out of the living area for combustion, and send it up the chimney, and those which draw the air for combustion from outside, and are sealed on the inside, which are far more efficient. You could combine this with a flue to keep the outside air from flowing after the gas is shut off. However, with this design, you do need to keep the air intake on the outside of the house clear. Another helpful addition is air intakes from the room, which take the air near the flames, but not exposed to the fumes, and return that heated inside air to the room.

Also, one thing to be aware of is that a gas fireplace can make an annoying hissing noise. I think there's a cure for this, if a device is used to lower the gas pressure before it's released, but they don't all have this. StuRat (talk) 16:23, 1 March 2013 (UTC)

Here's a side view (although the air recirculated to the room typically is on the sides of the fireplace, not the front, as shown, to provide an unobstructed "romantic" view of the fire):

    ^
   |^|
O  |^|
U  |^|     I
T  | +-+ > N
S  | F ||  S
I  | I ||  I
D  | R ||  D
E  > E ||  E
   +---+ <

StuRat (talk) 16:38, 1 March 2013 (UTC)

I'm hoping to avoid the type of fireplace which draws air from the living area because those fires require a certain amount of ventilation to comply with UK building regulations. However, I can't use those fireplaces which are designed to use a balanced flue through an outside wall because the house is terraced (the neighbours would not appreciate it). I think most balanced flues have a limited height. I would like a solution which draws air from the outside, via the chimney. 78.144.199.159 (talk) 16:30, 1 March 2013 (UTC)

So you're looking for this system: [9], where it draws outside air down the outside of the chimney ? StuRat (talk) 16:42, 1 March 2013 (UTC)

Neither of the systems in that picture are what I'd like. The balanced flue system shown has to be fitted on an outside wall. Our house is terraced and the chimney is on the party wall.

N   ^
E  |^|
I  |^|
G  |^|     I
H  | +-+ > N
B  | F ||  S
O  | I ||  I
U  | R ||  D
R  > E ||  E
   +---+ <

78.144.199.159 (talk) 17:08, 1 March 2013 (UTC)

I once renovated a Victorian house and installed a coal effect gas fire in the fireplace of the living room. To do this we had to have a flue put in the old chimney, rather than relying just on the old chimney. Both with that one, and when replacing the gas fire in the current house, I had to have a home visit from the supplier to establish how the gas fire would work and what was needed to meet regulations, and I suggest your mother relies on the supplier for information rather than some random guys on the internet. --TammyMoet (talk) 17:04, 1 March 2013 (UTC)

I'm aware that there are building regulations to be met and the fireplace will be fitted and tested by a qualified person in accordance but I want to find out if there's a supplier of the system I'm looking for rather than risk getting lied to by the supplier because they don't stock what I'm looking for and just want to sell. 78.144.199.159 (talk) 17:13, 1 March 2013 (UTC)

Fireplaces are not usually energy efficient. They are installed for looks, not efficiency. A house from 1920 will probably be leaky enough that you don't need to worry. To check use a Blower door and measure it. But central heating can be 95-98% efficient if you use a condensing unit (and I believe all such units in the UK are required to be condensing). No fireplace can match that. Ariel. (talk) 17:16, 1 March 2013 (UTC)

What fireplaces do offer, though, is the ability to heat only one room. So, if everyone is in that room, you can turn down the house thermostat, and save on gas that way. StuRat (talk) 17:21, 1 March 2013 (UTC)

You can do that with central too, with zone heating (although admittedly that's harder to retrofit into a house). Ariel. (talk) 17:35, 1 March 2013 (UTC)

OK, so we are looking at a design like this, then ?

     |
N  |v|^|
E  |v|^|
I  |v|^|
G  |v|^|       I
H  |v| +---+ > N
B  |v|  F  ||  S
O  |v|  I  ||  I
U  |v|  R  ||  D
R  |    E  ||  E
   +-------+ <

(I only showed the air intake on the back of the fireplace, but it could be a full tube surrounding the chimney exhaust tube.) StuRat (talk) 17:23, 1 March 2013 (UTC)

They sell those, they are called "concentric chimney vent". Usually used for retrofitting condensing units to use the existing chimney. (The units need the source and vent at the same height to avoid wind pressure messing with the heater, so you can't just use the chimney as vent only.) They are usually made out of PVC for condensing units, but you can find metal ones too. If your fireplace is too efficient you will need an insulated type or the flue gases will not stay hot enough to exit the chimney. (Since the gases are cooled by the incoming air.) Ariel. (talk) 17:35, 1 March 2013 (UTC)

Or how about an electric exhaust fan ? StuRat (talk) 17:40, 1 March 2013 (UTC)

If you do that make sure to interlock it with the flame, so a failure of the fan doesn't asphyxiate everyone. (It's not enough just to interlock power, you also have to detect rotation.) They actually do sell those BTW - I've seen them on domestic hot water systems (but they are a bit noisy). Ariel. (talk) 17:50, 1 March 2013 (UTC)

Agreed. Also, if it's properly sealed, then any carbon monoxide (created by a flame deprived of sufficient oxygen) won't make it into the living area. StuRat (talk) 18:29, 1 March 2013 (UTC)

Are these concentric flues rigid or flexible? The problem is that UK building regulations require inspection of all flue joints to be possible which would mean a lot of inspection holes would need to be created along the height of the chimney. 78.144.199.159 (talk) 18:21, 1 March 2013 (UTC)

Couldn't a camera on a flexible tube be sent down it for inspection ? StuRat (talk) 18:26, 1 March 2013 (UTC)

They are usually sold as segments that are locked together and fed into the chimney one at a time. There are flexible ones as well - but most of those are plastic for high efficiency systems. There may be flexible metal ones, I don't know. But I think even the flexible ones are sold as lengths that are joined together (they are intended for chimneys with curves).

But, are you sure you need inspection? The flu is inside the chimney after all - the chimney will block any gases from entering into living space, and can realistically be called the flue. Ariel. (talk) 18:39, 1 March 2013 (UTC)

There are catalytic flueless gas fires available but they are quite expensive and I did read a comment on a forum that no gas installer would use one of these as, if anything goes wrong you're dead from carbon monoxide asphixiation. There's a bit of discussion about them here. Richerman (talk) 14:41, 2 March 2013 (UTC)

Longest lived known species of single-celled organism

What species of single-celled organism is #1 on the list of longest lived single celled organisms according to reliable source H. sapiens who keep such records, and how long is that record lifespan? 20.137.2.50 (talk) 16:42, 1 March 2013 (UTC)

Defining a species in an organism which reproduces asexually is particularly problematic, as the normal standard of two individuals which can reproduce together and create fertile offspring doesn't apply. StuRat (talk) 16:46, 1 March 2013 (UTC)

Yes, and even defining life-span in this context is problematic! To wit: when a bacterium splits into two, does the parent die and produce two new offspring? Or does the parent survive, and make one clone? Biologically and philosophically, both interpretations are defensible. If you take the first interpretation, no individual lives very long. If you take the second interpretation, then there is some single bacterium out there that has survived millions of years... See Biological_immortality#Bacteria for some scant coverage. SemanticMantis (talk) 17:01, 1 March 2013 (UTC)

If we define cell division as death of the parent cell, then you and I are mostly dead or mostly recently born, depending on how you look at it. I feel younger just thinking about it! :) --Guy Macon (talk) 20:29, 1 March 2013 (UTC)

Stupid idea about using Kickstarter to fund building a nuclear power station

Maybe this is a silly idea, but I was thinking about the cost of nuclear power and why more nuclear power stations aren't built in the UK. Would it be possible to use Kickstarter to collect an amount of money from each of, say, one million people and then provide electricity to those people at no cost for however many years? My understanding is that most of the cost is in the initial outlay. --78.144.199.159 (talk) 21:59, 1 March 2013 (UTC)

It depends what costs you count. Mention Chernobyl or Fukushima, and other costs become obvious. IMHO, even if a reactor doesn't explode, the costs of managing the nuclear waste "forever" must be factored into its total cost. Others may argue differently, but the fact that anyone feels the way I do tells you that it isn't as simple as you propose. HiLo48 (talk) 22:08, 1 March 2013 (UTC)

Well, the vast majority of reactors ever didn't explode, and those you mention were due to stupid mistakes, besides which coal-fired power stations pollute much more per unit energy generated. Are you suggesting that the reason for lack of new nuclear power stations in the UK is due to public disapproval rather than the cost? 78.144.199.159 (talk) 22:20, 1 March 2013 (UTC)

Hey, it was you who mentioned costs, and I pointed out the cost involves a lot more than building them. And yes, the vast majority of reactors don't explode, and those that did may have been due to stupid mistakes, but do you really trust every government, corporation and individual who will be involved with your proposed reactor for the next fifty years to never make a mistake. And then there's the waste...

Why shouldn't I trust all those organisations? Their counterparts do the job just fine all over the globe, including those already operating in the UK. Also, in the UK, the government has agreed to take care of any waste so that isn't a concern either. 78.144.199.159 (talk) 04:02, 2 March 2013 (UTC)

LOL. The waste is dangerous for 1000 years. And your faith in corporations and government is greater than mine. HiLo48 (talk) 04:30, 2 March 2013 (UTC)

Coal-fired power plants don't just pollute more per unit energy generated. They actually release more radioactive material into the environment. See http://www.physics.ohio-state.edu/~aubrecht/coalvsnucMarcon.pdf and http://www.scientificamerican.com/article.cfm?id=coal-ash-is-more-radioactive-than-nuclear-waste --Guy Macon (talk) 23:18, 1 March 2013 (UTC)

• The cost of building a nuclear plant is in the billions of dollars (or pounds, if you prefer). That means you would need millions of people to give you thousands of dollars each. It doesn't seem plausible to me. Looie496 (talk) 22:25, 1 March 2013 (UTC)

Doesn't seem plausible via Kickstarter. But there are lots of public corporations (in the U.S. English usage of the phrase) that actually do this. For example, Duke Energy has thousands - millions, perhaps - of share-holders who each contribute hundreds - or thousands - of dollars. Instead of using Kickstarter to rally up people and raise funds, they use the New York Stock Exchange. They have a huge team of financial experts who make sure that everything is above-board with the money collection. They have a huge team of lawyers and legal experts who make sure that everything the corporation does is in compliance with lots and lots of applicable rules. And then ... they raise billions of dollars - and build a nuclear power plant or three. When you look at the whole ecosystem of the energy economy, it actually is very much like the original poster asked: except that because so much money and so many people and so many laws and regulations and rules rules are involved, Kickstarter just isn't the right forum to raise the funds. Nimur (talk) 03:50, 2 March 2013 (UTC)

Okay, but what if you consider that the annual household energy bill in the UK is about £1 250. If one million invested £2 500, that'd be £2.5b. Maybe it's not realistic, but I'd invest my money for two or three decades of unlimited (probably "within reason") electricity. Maybe it would be easier to sell to companies consuming large amounts of electricity. — Preceding unsigned comment added by 78.144.199.159 (talk) 22:41, 1 March 2013 (UTC)

Economics of new nuclear power plants explains all the costs. Nope, no idea for Kickstarter. Besides that, the people who populate the site are more ofn the hippie-alternative type, who would get more interested in a wind turbine. OsmanRF34 (talk) 00:30, 2 March 2013 (UTC)

The cost of nuclear power is regulatory, not capital. Build your plant in China. μηδείς (talk) 01:57, 2 March 2013 (UTC)

Legal costs are very high (more than actual regulation, strictly speaking) for starting new plants in the USA, but the capital costs are pretty high, too. Even in China it costs billions of dollars to construct these things. It is also probably also worth noting that the US nuclear industry has been heavily subsidized by government funding in the past, and that they don't need to fully fund their own insurance against accidents — sometimes regulation makes things cheaper for energy companies, too. The economics of all energy generation is somewhat complicated, but nuclear is especially so because of its combination of high capital costs and high regulatory/legal issues. The result is that it's very hard to be profitable with nuclear except in the very long term. --Mr.98 (talk) 04:10, 2 March 2013 (UTC)

And the high regulatory cost is because they insist on building them above ground, in populated areas, which, when combined with bad design, operator incompetence and regulatory capture, is inherently dangerous. If they would build them at the bottom of abandoned mines, far from population centers, with only the cooling towers above ground, they could leak right and left and only endanger the workers. They could also leave the spent radioactive fuel down in the mine, and just fill it in with concrete when the plant is decommissioned. Sure, transporting electricity a longer distance increases costs, but the reduced objections and subsequent delays from the public would more than make up for this added cost. StuRat (talk) 03:54, 2 March 2013 (UTC)

There are a lot of concerns with siting nuclear reactors. "At the bottom of abandoned mines" doesn't really address them, and introduces entirely prohibitive construction costs. I don't think you realize how physically large a modern nuclear reactor power station is, and how hard it woud be to excavate that amount of space in a safe way deep underground, much less the issues that would come into place in making such a facility safe to operate. It's a silly idea. --Mr.98 (talk) 04:10, 2 March 2013 (UTC)

I don't think you realize how big abandoned mines are. StuRat (talk) 05:05, 2 March 2013 (UTC)

It's an intriguing possibility. You could offer some really interesting rewards (eg $1,000 reward: "Free electricity for life"). But the trouble with Kickstarter is that it's a matter of trust. It's fairly easy to trust someone you've never met to follow through at $1,000 to $10,000 - but beyond that, it gets tougher and tougher. The other problem with large construction projects that take a long time to complete is that such projects tend to overrun costs badly. That's bad enough with conventional venture capital - but if you collect $1000 from a million people and fail to deliver...I don't want to imagine the consequences. Coming back and requesting another $500 to get it finished ten years from now would be astronomically hard.

There is another practical problem. The Kickstarter rules for technology projects seem to kill your idea stone dead. http://www.kickstarter.com/help/guidelines says: "In addition, Design and Technology projects that are developing new hardware or products must show on their project pages a functional prototype — meaning a prototype that currently does the things a creator says it can do". So you need to have a working nuclear reactor before you start!

You don't have to use Kickstarter though - there are MANY other crowd-funding sites out there - and (of course) we have an article on that at Comparison of crowd funding services.

So I agree that this is a bold and intriguing idea - but very, very difficult to execute.

SteveBaker (talk) 04:00, 2 March 2013 (UTC)

Geranium care

I have a gorgeous Pelargonium hortorum that my mother bought and hung in her backyard until Thanksgiving, when she was going to throw it out. I found it at my parents' curb and adopted it, it has bloomed constantly in my south-facing window. The only problem I have run into keeping it inside is that, even though it is quite lush, and definitely not overwatered, it is constantly dropping about half-a-dozen yellow leaves out of maybe 12 dozen total. The leaves are not limp, and they are largely from the bottom edges. Is this just a consequence of the constant growth pattern, or can I address it with some sort of care? The article suggests there are growing societies, but the link didn't seem recent. Thanks. μηδείς (talk) 22:07, 1 March 2013 (UTC)

A few questions: Is there new growth (i.e. small leaves emerging), and is it still blooming? If those are both true, then change nothing. If neither are true, I'd give it more light if at all possible, or possibly a very weak shot of N fertilizer. If only one is true, I'd probably also do nothing differently for a few weeks... Realistically, if it limps along until spring, just be patient and give it a good pruning before you set it out in indirect light in the spring. Even when "healthy" plants are successfully wintered indoors, they usually wane and get a bit sad, unless you have very good light and humidity infrastructure. Remember to change any parameter slowly if possible ;) SemanticMantis (talk) 01:24, 2 March 2013 (UTC)

Yes, there is constant new growth and blooming. It has three nice full red flower heads and three sets of green flower buds, and terminal growth on each branch. It's not limping at all. It has the hardiness of a perennial and the vitality of an annual. If this were outside I would just pluck the yellow leaves. It's the fact that they are constantly dropping (even as it grows overall) that annoys me--as far as I know it did this over the summer as well, but it wasn't kept well watered and tended to wilting then. (Frankly, I think it's happier now than it has ever been except when purchased.) It has great light, and is not dry at all. I have thought of repotting it since it might be twice the volume it was when Mom bought it. Would a dilute fertilizer solution be an alternative to that? I just doubt that crowding is the reason for the leaf dropping, because, as I said, it's been doing this all along. μηδείς (talk) 01:55, 2 March 2013 (UTC)

It might be slightly N (or Fe?) deficient, but I would only use either at very small doses until spring. Putting it in a bigger pot will result in it growing much larger and not blooming for a long time. I would do that next fall, and only if you have the space for a much bigger plant. Otherwise just prune the top (and bottom if it is very tight). They are certainly OK to be a little root bound. Honestly, your plant sounds happy and healthy to me. It is normal for it to shed senescent leaves, and it will translocate nutrients when it does so. Just pick off unsightly leaves and enjoy it! SemanticMantis (talk) 02:31, 2 March 2013 (UTC)

Yes, I actually did (half of) my undergrad work in plant science, and have a greener thumb than my sister who did her doctorate in it, but I worked at the crop science department, and they were all outdoor grown monocots. (Although I did grow some pretty, sticky, nutty, funky dicots in my closet.) The fact that nothing on the plant is wilting is reassuring. I will try the dilute NPK fertilizer. I have had success with it with my rebloomed poinsettias.

One other question. If I prune it, where should I prune it? It has a nice 28"-32" diameter bun-shaped growth habit. μηδείς (talk) 03:18, 2 March 2013 (UTC)

Think thinning, not shearing like a sheep. Cut a few branches down to 2-3" long, then cut 2-3" off of a few other stems, and leave the overall shape the same. Make cuts ~1/4" above the target Node_(botany) on each branch. It's hard to kill a healthy houseplant by pruning, and you can root the cuttings to give to friends or keep as insurance. SemanticMantis (talk) 04:31, 2 March 2013 (UTC)

When I first read this Q, I thought you were asking about germanium. But, never mind, as this comment isn't germane to the topic. StuRat (talk) 03:46, 2 March 2013 (UTC)

because you're a man? μηδείς (talk) 02:42, 3 March 2013 (UTC)

Definately go easy on the fertilizer, both because very little is needed and also if the pot dries out the increased concentration can kill it like salt. Polypipe Wrangler (talk) 22:07, 5 March 2013 (UTC)