Wikipedia:Reference desk/Archives/Science/2016 January 16

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

January 16

If a person has an MBA, is it wrong to say he's an economist?

Moved to Wikipedia:Reference_desk/Humanities#If_a_person_has_an_MBA.2C_is_it_wrong_to_say_he.27s_an_economist.3F.

Questions about EM radiation

I've been wondering about some things and I'd appreciate any insight into them.

1) I often see visible light described as electromagnetic radiation. If I have a green light lit and had a radio capable of receiving at 563THz, would I receive anything? I assume that I wouldn't, since a radio deals with electrons and not photons.

2) I expect that in any case where a device is powered entirely from RF energy (e.g. a crystal radio), the current draw of the device must be somehow apparent at the transmitter. If this is true, is any conductive object which is connected to ground also drawing power from the transmitter? Does a powered, tunable radio draw less current from the transmitter when not tuned to the transmitter versus when it is tuned to it? Is the load actually measurable?

3) I recall a time when I was transmitting an AM signal into a dummy load and monitoring it with a handheld receiver. As I moved around, I noticed places in the room where the carrier was strong, but the modulation was weak. I observed the same when transmitting an FM signal using an antenna. If the signal wasn't simply just too strong for the receiver, what would cause this? SphericalShape (talk) 00:16, 16 January 2016 (UTC)

1. A radio that receives at 563 terahertz is a photodetector. You can't build whip-antennas that small; your "receiver" would have to look and act like a photodiode.
2. Yes, everything affects everything else; the electromagnetic impedance as seen by a transmitter is minutely affected by every natural and man-made "receiver" in the environment, all the way out to infinity distance; but the farther away, the smaller the effect; and the farther away, the longer the propagation delay. (The behavior of an object a trillion light-years away has a trillion year propagation delay in effecting any change to the impedance observed at the transmitter). For almost all practical purposes, these effects are so small that they are negligible; the ensemble averages out into the background, which is the impedance of free space. Sometimes, engineers use tuned, matched coils: this is about the only case where the effect of the receiver-antenna's loading is non-negligible: those systems are designed for power transfer. Chances are, the effective load caused by your crystal radio (drawing nanowatts of power) did not register on the VU meter tracking the power loading at the AM station fifty miles away. When you start throwing amplified circuits, and tunable radios, into the mix: well, the formal scientific method to analyze this is electrical engineering. The effective load on an amplifier's output is isolated from the input; but there is still some tiny, tiny effect: when you power on your powered radio, the antenna's impedance gets a slight nudge one way or the other; and just as before, that change propagates all the way back as a difference in the load for the radio transmitter. On the whole: these effects are absolutely tiny. The transmitter sees more load-variance based on the wind blowing molecules of air around, than due to all the cumulative effects of all the radio receivers out to infinity and back - and even that is smaller than the load-variance due to a hundred other effects, like the thermal noise inside the transmitter's power supply.
3. Any number of effects might explain this subjective observation; everything from frequency-dependent tuning, to faulty equipment; but it's futile to speculate based on an anecdote.

Nimur (talk) 01:24, 16 January 2016 (UTC)

I always thought (on an intuitive level, since I don't have any systematic knowledge in the area) that radios didn't load the transmitter at all, that this had something to do with "near" and "far" fields and that it was the chief difference between radio transmission and stuff like transformers, induction chargers and NFC tags. Asmrulz (talk) 05:53, 16 January 2016 (UTC)

This is a matter of practical semantics. If the theoretical effect is so small that even our best measurement equipment can't see it ... does this constitute "no effect"? Well, in the same sense that there is "no chance" that you could win the lottery... we're overloading the meaning of "zero" to mean both "zero and almost zero." The semantic problem is very subtle: there is a practical meaning of "almost zero," and there is an even more rigorously-defined theoretical mathematical defintion of almost zero; and I admit some guilt in conflating both cases with "exactly zero." (This is because the English language is an inapt choice for certain specific kinds of descriptions). This ambiguity of natural language leads to a very common semantic problem and if we aren't very careful with our terminology, it can lead us to believe an incorrect conclusion, or to find a paradox where none really exists.

So, to directly address Asmrulz's concern: receiver-antennas in the far field have almost zero effect on the transmitter. How tiny is that effect? It is so small that we probably can't measure it; but we can surely calculate it by solving for the complete electromagnetic field equations, at all points, and then performing some mental and algebraic gymnastics to mathematically transform the result into something that looks like an impedance.

This is where real radio engineering intuition is needed: if we start from pure theory of physics, it might take us days to perform such a calculation, only to find out at the end that our result can be safely ignored. Instead, if we start from practical experience, we know the approximate result of the difficult calculation, and therefore we don't actually perform it. This intuitive leap - knowing the answer by gut-feel - is a constantly-recurring theme in applied electromagnetics. It is one reason that other engineers call high frequency radio and antenna work a "black art."

Nimur (talk) 17:10, 16 January 2016 (UTC)

My intuition is that of a hobbyist who loves electronics über alles but struggles with quadratic equations, not to mention PDEs. Perhaps in my next life... Asmrulz (talk) 19:16, 16 January 2016 (UTC)

Does a TV detector van work by this method or Van Eck phreaking (or is it even real?) Wnt (talk) 11:26, 16 January 2016 (UTC)

From the picture it looks to be real. The antenna would be detecting UHF or VHF transmissions from the TV local oscillator. The TV is a Superheterodyne receiver. Graeme Bartlett (talk) 11:32, 16 January 2016 (UTC)

I tend to disbelieve the practical utility or historicity of the TV Detector Van; but these vans are an important part of the common culture and mythos amongst paranoids and tin-foil-hat wearers. Surely, the technology could have existed; and in all seriousness, it probably was used at some time or other. But, proposing that it was, or is, part of an ongoing mass-surveillance effort - well, that's much more tenuous a claim.

Of all the effects one could use to remotely determine if a television set is presently powered, the effect of its antenna would be far from the easiest. There are so many stronger signals, where do we begin enumerating them? The conventional cathode ray tube emits all kinds of characteristic radio energy: the flyback transformer carries a lot of power, and some of that is radiated outward. That signal, or the high voltage generated by the electron gun, is probably the easiest signal to detect. Heck, the time-varying load on the AC power supply mains would be easier to spot.

Obviously, new televisions do not use cathode ray tubes: if there really is a TV detector van, and it really does operate in this century, then it probably uses "some other method." Were I in charge of designing such an invasive technology, I'd simply remark that it is incredibly easy to hide a "bug" on a circuit board these days; a sophisticated integrated circuit in today's technology is so small, it could piggy-back on the back side of the solder-pad of a passive component and nobody would even look for it; or you could hide it inside the software in any of the dozens of independently-programmable computers that can be found on any modern electronic device. Your television's power cable probably has more compute-power than a PDP-11; and it's being built by some third-party vendor of bargain-basement commodity electronics technologies: such commodity vendors might be in a dire financial way and therefore susceptible to outside "funding opportunities." The evil genius at Mass Surveillance, Inc., could simply repurpose the fuel budgets from the surveillance vans, use the funds to pay off the vendor, and presto - every television could be carrying a cooperative surveillance device, broadcasting a tiny unique identifer to self-report its activity via wireless link. The days of being able to detect, let alone counter, such electronic surveillance technologies are long over. If the baddies wanted to surveillance you, they shall do so; and you won't even notice it. When is the last time anybody ran a malware check, or inspected the open-source software, on their TV's power supply controller?

Nimur (talk) 17:47, 16 January 2016 (UTC)

Quibbles with the above are that the high voltage in a CRT televison is not "generated by the electron gun" but instead is rectified via a Voltage multiplier from a pulse winding on the Flyback transformer, and that identifying payment evaders of a decreed TV licence fee is a legitimate part of law enforcement. The article Television licence shows that funding sources in different countries vary between licence fee and advertising. A rhetoric that licence funding is imposed by "evil...baddies" is, at best, ignorant that TV broadcasting always needs to be funded somehow or, at worst, unsourceable covert conspiracy speculation. AllBestFaith (talk) 20:24, 16 January 2016 (UTC)

For what it's worth, I do not believe that the UK's television license fee is evil; it's a complex policy that might actually promote better-quality, less-biased broadcasting, and I have often wondered if that policy could be implemented in the United States. Broadcast economics has always worked very differently on this side of the pond, and our government has a different legal and historical relationship with broadcasters, and with respect to our "free press" in general; so the issue is not simple at all. That's a conversation for another time.

Nor do I actually believe that any government is conducting mass surveillance in the fashion described above - certainly not for the purposes of verifying television-usage. I hope my comments are not construed in that way. To clarify my intended point: if any malicious entity - government or otherwise - wished to conduct mass surveillance, for any purpose, the most efficacious methods in this century probably need not involve driving around in vans.

With respect to your other quibbles - point conceded; I was a bit sloppy in my paraphrased description of the CRT. Interested readers should refer to our article for more details. Nimur (talk) 04:17, 17 January 2016 (UTC)

Every new broadcasting station has to conduct field measurements throughout its coverage area to establish their radiated signal strength and the relative strength of interfering signals. This work is naturally done by engineers in a vehicle in the USA and in the UK a prominently labelled TV detector van.

This explains the basics of field strength calculations.

UK detector vans are typically equipped with panoramic display receivers such as this Eddystone combo on which the internal oscillator of a nearby TV receiver is traceable as a radiation spike at 38.9 MHz below a vision carrier frequency. A number of these vans must be kept in service also for investigating reports of illegal transmitters (including espionage devices) and interference. I can attest that during the British GPO monopoly control of broadcasting my complaint about interference to TV reception was met by visits by an enthusiastic engineer carrying a range of signal tracing and filtering equipment, all covered by the standard licence fee. It is obvious that licence collecting authorities find it cost effective to maximise the public expectation that unlicenced receivers will be traced while seldom actually expending resources on general surveillance. A non-technical lay person in the 1950's Britain might not easily distinguish between a dipole or a ladder on the roof of the ubiquitous telephone service vans and suspect that they were all TV detector vans! On Swedish TV I have seen placards that say "We are inspecting <name of town> with a receiver detector. Thank you for keeping your TV licence renewed."

This thread was deviated into politically charged speculation about malicious survellance hardware but the article Conditional access describes non-covert methods and hardware used to protect broadcast TV content pre-emptively. AllBestFaith (talk) 16:51, 17 January 2016 (UTC)

1) Your assumption that a radio deals in electrons, not photons, is incorrect. There is no dividing line between light and radio waves - they are both types of EM radiation and are both made up of photons. Although, as Nimur said, a standard radio antenna won't pick up light-frequency photons, you could in theory built a nano-scale antenna that would do just that. See the experimental device called the nantenna. It's very inefficient and impractical but in principle it does what you describe. --Heron (talk) 13:25, 16 January 2016 (UTC)

2) In practice, no to all your questions. The transmitter launches radio waves into free space and doesn't know what happens to them afterwards. The rest of the world acts as an almost perfect absorber unless the transmitter has the misfortune of being surrounded by tinfoil. It doesn't matter whether the energy is absorbed by a crystal set, a transistor radio or a tree, the transmitter justs sees its energy disappearing into a bottomless pit. Incidentally, I have to quibble with Nimur's statement that the impedance of free space is an average of the impedances of all the stuff in the universe - it's not, it's the impedance of any piece of empty space. The wave from the antenna immediately sees the impedance of free space when it leaves the antenna, not after it's had time to bounce around the universe and average everything out. --Heron (talk) 13:44, 16 January 2016 (UTC)

In case there was any confusion about my statement: the impedance of free space is not caused by the loading effects of all objects in the far field. Rather, the antenna sees a load, which is a superposition of free space plus any other loading effects. This value averages out to the impedance of free space because the additional loading effects is generally negligible. I apologize that my statement was confusing. Nimur (talk) 15:13, 16 January 2016 (UTC)

Heron is correct to point out that the impedance of free space is a physical constant that is fixed by definition relative to the S.I. base units. It is seen by a transmitting antenna both "immediately" and over prolonged time as radiation propagates away, never to return; I mention exceptions to this scenario in response no. 2. below.

1. 563 THz or 563x10¹² Hz is the frequency of green monochromatic light emitted by a common DPSS laser pointer. Many other frequency distributions that stimulate the medium cones of the retina can give the same perception of green because the eye is not a precise spectroscope. A few specialized radio receivers used in Radio telescopes detect electromagnetic radiations at millimeter and submillimeter wavelength, see [[1]] and [2], but these are far below visible or infrared light frequency. Among the many types of Photodetector that can respond to green light, types such as photoresistors, photovoltaic cells, photomultipliers, photodiodes, phototransistors and others convert incoming photons to electron current, which could constitute a non-tunable receiver.

2. The antenna of a Transmitter is designed to deliver electromagnetic energy into the Impedance of free space (i.e. the wave-impedance of a plane wave in free space) which equals the product of the vacuum permeability or magnetic constant μ₀ and the speed of light in vacuum c₀ i.e. about 376.73 ohms. Theoretically any object with a different impedance that intrudes into the space around the transmitter causes a reflection at the point of mismatch, and therefore a mismatch effect at the input to the transmitter antenna. Usually in broadcasting the powers reflected by receiver antennas are negligible and undetectable in comparison with the power delivered to space. Exceptions include large metal structures near a transmitter that may necessitate adjustment using an SWR meter of the antenna matching circuit, and deliberate analysis of reflected radio waves which is the basis of Radar. The instruments known as Grid dip oscillator and gate dip oscillator may be regarded as small transmitters with inductive antennas that are sensitive to power absorbed in any nearby tuned circuit, and are useful for finding its resonant frequency by trial-and-error tuning. A tuned receiver front-end draws most power from the antenna when its resonant frequency equals the transmitted frequency. The power dissipated in an RLC circuit can be calculated if its Q factor is known.

3. The situation where signal is detected near a dummy load suggests the load is imperfectly matched to the transmitter or imperfectly screened, so the OP detected residual leakage. It is unlikely to have reduced AM though the sound volume from most AM radios decreases when the signal strength is weakened, e.g. by rotating the handheld radio. Most FM is transmitted at wavelengths of 3 m or less, see FM broadcasting, so where there are reflecting conductive surfaces moving a receiver by such a small distance can change the relative phasing of multipath interference which may locally distort, weaken or cancel reception. AllBestFaith (talk) 14:06, 16 January 2016 (UTC)

Just let me add that Near and far field is our article about what Asmrulz mentioned above. – b_jonas 12:52, 18 January 2016 (UTC)

Thanks everyone! I'll certainly be reading about many of the topics mentioned. SphericalShape (talk) 03:05, 19 January 2016 (UTC)

You can also look for fiber optic communication. A signal is modulated onto the carrier and the algorithms create discrete constellation points that are much lower frequency and can be detected with phase discriminators. As was said earlier, all EM radiation is photons and the FM radio antenna emits photons by accelerating electrons in the metal antenna. Even though FM radio is 100MHz, it's modulated down to 10 MHz for processing (your FM radio has an oscillator that's tunable and is 10 MHz higher than channel). The frequency of the carrier is relevant only to the extent that there exists a way to convert it to baseband frequencies. --DHeyward (talk) 12:47, 20 January 2016 (UTC)

Cartilaginous fish outcompeting bony fish as predators

Bony fish (Osteichthyes) vastly outnumber cartilaginous fish (Chondrichthyes) in terms of both number of species and biomass. But in the ocean, more cartilaginous fish than bony fish are apex predators. Why would cartilaginous fish have outcompeted bony fish in that particular ecological niche? —SeekingAnswers (reply) 03:12, 16 January 2016 (UTC)

You may be cherry picking your data a bit. The apex predators in the sea would have to include whales, but you excluded them by specifying fish. So, once you eliminated whales, then sharks are a fairly large portion of the apex predators that remain, and they happen to be cartilaginous fish. StuRat (talk) 03:33, 16 January 2016 (UTC)

That's not cherry picking, since I never asked about bony or cartilaginous fish vis-à-vis mammals; I asked specifically about bony and cartilaginous fish vis-à-vis each other. The question remains why cartilaginous fish would outcompete bony fish in that niche. —SeekingAnswers (reply) 05:03, 16 January 2016 (UTC)

Predators are typically vastly outnumbered by their prey. If they weren't, the predators would die out. Evolutionary pressure may have favored bony fish for survival of the prey, while sharks were just fine as they were. And are. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:53, 16 January 2016 (UTC)

• Look at r/K selection theory. Sharks have a low reproductive rate with small clutches fertilized internally, while bony fish produce a huge number of eggs, with the newborns often being planktonic. This means that in niches filled by smaller fishes, bony fish will tend to have an advantage. You can see the exact same thing comparing the more primitive conifers, which comprise the tallest and oldest trees with the angiosperms with their advanced systems of pollenization and seed dispersal. If you consider plant succession, angiosperm "weeds" will colonize open land first, but conifers like the Douglas fir will tend to be among the apex species. μηδείς (talk) 17:55, 16 January 2016 (UTC)

@Medeis: Yes r/K may come in to it, as may size at birth. But IMO that alone doesn't really explain the issue (if there even is an issue to explain ;). You might be interested to know that plant succession can go the other way too. E.g. Loblolly pines in the Carolinas come in first after clear cuts or fires, and the climax community has much more hardwood broadleaf species (See e.g. Christensen and Peet, 1984, or most any of the studies on the Piedmont or Duke Forest). The fast growth of many conifers is tied to early successional status, and is also why they are such an important timber source. A professor of forestry once told me that this can be seen as a broad, general, trend: east of the Rockies, conifers tend to be earlier successional, while in the west they tend to be late successional. As to the OP @SeekingAnswers: I think this is a very interesting question, but I do think the premise should be clarified and perhaps challenged a bit. Are you saying that most cartilaginous fish species are top predators? Or that most top predator species are cartilaginous fish? Or are you claiming that, among species, a higher percentage of cartilaginous are top predators, as compared to that figure for bony fish? Some of these might be true, but none of them are obviously true to me, and the hypothetical reasons should differ for each one. I'm fairly busy this week, but if you contact me on my talk page I can send more refs later. SemanticMantis (talk) 16:06, 18 January 2016 (UTC)

Characteristic shape of Juniperus virginiana in old field succession

What I was suggesting (and really to make the point you'd need an essay) is that there was an earlier stage at which most of the existing "fish" niches were occupied by chondrichthyes; i.e., sharks, rays, chimeras, all of which had internal fertilization, and produce relatively large eggs compared to bony fish. (I am not sure about the reproduction habits of the extinct spiny sharks and placoderms.)

When the teleosts arose (comprising the vast majority of bony fishes), they had largely external Teleost#Reproduction_and_lifecycle reproduction with a huge number of strategies for dispersal. While the teleost Mola mola lays up to 300,000,000 eggs, sharks like the great white Great_white_shark#Reproduction have only a few young after a very long gestational period.

True sharks existed in the Silurian period, and animals like the six-foot predator Cladoselache appeared in the Devonian, while teleosts only appeared some 100 million years later, in the Triassic. Sharks already filled K-selected niches at that point, hence the teleosts spread like "weeds" (see my angiosperm analogy above) into many r-selected niches, a great number of which might never before have been occupied.

My point with conifers was not to point out that they are only apex-succession flora; they are not. Where I grew up, a sight like that at the left would be typical of a plot 5-10 years after colonization--but eventually the oaks will encroach. I am quite familiar with pine barrens, and the fact that if fires are suppressed in those areas the pines will be replaced by oaks and other late-succession hardwoods. My point is that there are no conifer weeds, just like there is no shark equivalent of duckweed or crabgrass. μηδείς (talk) 18:32, 18 January 2016 (UTC)

There are perhaps a few edge cases, but I agree that there aren't any squarely ruderal conifers today. However, there used to be [3], [4]. SemanticMantis (talk) 19:18, 18 January 2016 (UTC)

Why are women bad at chess?

In chess rankings there's only 1 or 2 women in the top 100 players. Does anybody know why? 2.102.185.25 (talk) 06:07, 16 January 2016 (UTC)

Maybe all but those 1 or 2 simply don't like chess. That doesn't mean that women are inherently "bad" at chess. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:49, 16 January 2016 (UTC)

Maybe the OP's phrasing of women being 'bad' at chess was misleading, but it still begs the question why there are so few elite chess players who are women. Isn't also true that men's brains are generally wired to be more logical than women's brains, or has that theory been debunked now? 95.146.213.181 (talk) 18:59, 16 January 2016 (UTC)

If it was simply a difference in interest, then you would need something like 50 to 100 times as many men interested in chess as women to predict that 1 or 2 out of 100 figure. Is there really this much of a discrepancy ? Somehow I doubt it. StuRat (talk) 22:10, 16 January 2016 (UTC)

This debate is as old as the hills, with many hypotheses and speculations, but there are no definite answers (and I don't expect there will ever be). Here is a Scientific American Article blaming it on the negative effect of stereotypes, while chess Grand master Nigel Short claims girls not to be "hard-wired" in their brains to play chess well (personally having a 3:8 score against Judit Polgar). Personally I'm most sympathetic with the hypothesis that 100% confrontational and 0% cooperative games are far more attractive to men than women: Without a broad base, the pyramid of female chess players will not grow high, so always most of the leading chess players will be men, far beyond the gender ratio in total players. --KnightMove (talk) 08:34, 16 January 2016 (UTC)

It's difficult to disentangle "not interested in" and "not good at". If one group of people are dramatically less interested in some activity than some other group - then, inevitably, they will appear to be less good at it because of the lower probability of the most talented members of the group being involved. On the other hand, if some group is less good at something, they'll be less likely to participate in it. Sorting out which of those it is, is extremely difficult.

This applies in varying degrees to chess, mathematics, physics, computer programming and a range of other activities in which women are severely under-represented. One might argue about correlation and causation here - are they being actively discouraged in some manner - are they being passively left out in some manner - or are they simply less interested in those subjects for some reason of genetic pre-disposition - or are they (perhaps) actually less good at it? It may be a combination of such things.

It's equally possible to find groups where men are under-represented, or you can pick any other social, ethnic or religious group and come up with similar biasses in similar areas of human interest.

SteveBaker (talk) 15:52, 17 January 2016 (UTC)

Actually I play in Union Square, Manhattan a lot where I've met some pretty genius-y women chess players. In fact, I met a nine to ten-year-old girl who has only been training for less than a year and holds around a ~1600 rating. Yanping Nora Soong (talk) 05:03, 18 January 2016 (UTC)

Follicular lymphoma

[it looks like a new user posted this without a heading] Wnt (talk) 13:23, 16 January 2016 (UTC)

§information on follicular lymphoma — Preceding unsigned comment added by 24.210.25.88 (talk) 12:54, 16 January 2016 (UTC)

Well, we have an article on follicular lymphoma. Please say what aspect you're most interested in. Wnt (talk) 13:23, 16 January 2016 (UTC)

Is the “ankle” on both sides of the foot?

A little above of the foot, in both sides there are projections. One is from the inside of the led and the second is from the outside of the leg. My question is if the both sides are called "ankle" or just one of them? 92.249.70.153 (talk) 12:56, 16 January 2016 (UTC)

The ankle is a broad region that includes them both and much more. You're thinking of the medial malleolus (on the inside) and the lateral malleolus (on the outside). Wnt (talk) 13:27, 16 January 2016 (UTC)

Radio tuning by analog-to-digital conversion?

In the "Questions about EM" thread above I was reminded that, as "Superheterodyne receiver" puts it, "Virtually all modern radio receivers use the superheterodyne principle." But nowadays the instructions per second of many computer CPUs are up to 3 GHz, which is the top of the UHF band of the radio spectrum. I assume a system designed specifically for one purpose might even be faster. So is it possible to simply plug some kind of digitizer directly into the antenna feed, using no superheterodyne, and make a complete transcript of the entire radio-spectrum signal out there (well, up to UHF that is) like making a digital recording of sound? This should have some amusing features, can you confirm?

• no TV detector van would work on it, apparently.
• records every frequency at the same time.
• can make custom algorithms to try to recover faint signals out from interference - even testing one after another, trial and error, until you find something to wring a distant TV program out of your record of its airing.

So do these things exist, or are they at least possible? Wnt (talk) 13:20, 16 January 2016 (UTC)

Software-defined radio, [5] -- Finlay McWalterᚠTalk 14:29, 16 January 2016 (UTC)

Such things as a radio receiver with untuned front end comprising only an ADC exist, see this Wikibook. What can be received this way is limited by

1. The sampling rate of the ADC

The Nyquist–Shannon sampling theorem sets an absolute limit to the radio frequencies that can be analyzed in the digital record. Higher frequencies contribute only noise (see 3. below) and in practice there must always be some pre-filtering to reduce them. If the ADC samples at 48 ksamples/sec one must not expect to detect frequencies higher than 20-24 kHz which is VLF, and no amount of subsequent high speed digital processing can overcome this limit.

2. The quantising resolution in bits of the ADC

Commonly used ADC resolutions are 12 - 24 bits for audio (48 k sample/sec) and 8 bits for video (20 M samples/sec). An ADC resolution of Q bits imposes a Signal to Quantising Noise Ratio

$\mathrm {SQNR} =20\log _{10}(2^{Q})\approx 6.02\cdot Q\ \mathrm {dB} \,\!$

in the receiver circuit. A wanted signal is receivable only if the ratio of its power to the peak sum of interfering signals is significantly more than the reciprocal of SQNR.

3. Interference and noise

These limit terrestrial radio communication more severely than free-space loss, and must not overdrive the ADC. Modern radios still depend on highly selective analog tuned circuits and for that reason most tunable radio receivers are single- or dual-conversion superheterodyne designs. Advances in instruction rate of CPU's that handle swings of several volts betwen binary 1's and 0's should not be confused with the state of the art of analog-to-digital converters which as yet cannnot compete with the microvolt signal-to-noise performance of an analog radio receiver front end. The OP who is interested in long-distance TV reception may find this article informative, and (legal advice follows) should not let their Television licence lapse. AllBestFaith (talk) 15:38, 16 January 2016 (UTC)

The performance of a wideband receiver is necessarily worse than the performance of a narrow-band receiver: see our article on Gain–bandwidth product. By extension, the performance of an ultra-wideband receiver is "ultra-worse."

In practice, what this means is that signal levels will be either too low or too noisy for your analog-to-digital converter (ADC). If you can spend a lot of money to buy a better ADC, you can improve the situation; but ultimately, there is a theoretical reason that explains why a heterodyned radio built on the same technology will still outperform your wide-band version. Where we stand with today's technology: most of the time, we can get the performance we need by using heterodyned radios with digitally controlled tuners, e.g. phase locked loop circuits built on CMOS integrated circuit technology. That's what you'd find if you took apart your cell phone or computer's WiFi radio circuitry. For unusual frequencies, we still use external tuners and mixers.

Nimur (talk) 17:57, 16 January 2016 (UTC)

how do I add the partition coefficient data to an article?

I would ask on a different forum, but this is really specific science editing stuff -- I have some sourced data on log P values of different compounds like carbidopa, etc., but I can't see any documentation on how to add log P data on a pharmacological compound. I see that chembox has one but I don't want to start a whole new chembox on a pharmacological article just to include its log P data. I think the partition coefficient data would be useful for researchers working on extracting amino acid compounds. Yanping Nora Soong (talk) 14:04, 16 January 2016 (UTC)

{{Infobox drug}} does not have a logP field. But that template (as all templates) has a talkpage where you can discuss possible improvements/additions. DMacks (talk) 19:37, 16 January 2016 (UTC)

If you want to discuss changing chemistry articles, you can talk about this at Wikipedia talk:WikiProject Chemistry. Graeme Bartlett (talk) 20:44, 16 January 2016 (UTC)

How often mentally ill people know they are mentally ill?

Common wisdom might claim that the crazy don't know they are crazy. However, are there serious studies about how common it is being deluded about your mental health, maybe broke up by illness? --Scicurious (talk) 14:16, 16 January 2016 (UTC)

The psychiatrists and neuronormative community like to call this "insight". I have been accused of having very poor insight (on my medical records) during my 71-day in a Beth Israel Medical Center psych ward because I argued I didn't need to be involuntarily held for treatment. After getting my hearing adjourned twice, the judge finally released me. A lot of people in the neurodivergent community have differing views on what having "insight" means. Yanping Nora Soong (talk) 15:03, 16 January 2016 (UTC)

Thanks for the concept, your post is very insightful.--Scicurious (talk) 15:27, 16 January 2016 (UTC)

If you think about it, most people don't think they're crazy -- it's the default assumption. People prefer to believe that they are a sane person -- perhaps even the one sane person -- living in an insane world. Thus people with depression see the world as objectively bleak and horrible, paranoids see the world as full of people plotting against them, and many people with schizophrenia see their intrusive thoughts as being beamed in from the outside, instead of believing that they might be mistaken about the nature of reality. This is similar to people's beliefs about the relationship between their own religious and political views and those of others: leftists and rightists look at one another's beliefs, and think these people must be either evil or insane to believe these things. -- The Anome (talk) 15:15, 16 January 2016 (UTC)

The question remains. Many among the mentally ill have ups and downs. A share of them will know they are out of their mind. How big is this share?--Scicurious (talk) 15:27, 16 January 2016 (UTC)

Are you considering diagnosed or undiagnosed mentally ill people, or both? -- The Anome (talk) 15:37, 16 January 2016 (UTC)

There has to be some sort of diagnostic. --Scicurious (talk) 22:13, 16 January 2016 (UTC)

The world is run by people pointing doomsday weapons at each other, people play tourist in space while others starve, there are 30 empty homes for every homeless person and in every single community the police treats them as the criminals to be watched, for the want of mass-printed pieces of paper ... surely everyone is insane, even if only a few of us know it. (Which doesn't mean we're any saner than the rest) Wnt (talk) 02:59, 17 January 2016 (UTC)

Another problem is that many mental health issues, such as depression, anxiety, OCD, etc. come in degrees. Is someone who is perhaps a little bit depressed but remains independently functional, mentally ill? An argument could be made either way. People who may have some difficulties, but can otherwise manage in everyday life, are less likely to consider themselves mentally ill regardless of what a psychiatrist might conclude. On the other hand, people with severe problems that make normal life impossible are more likely to be aware of and acknowledge that a problem exists (provided they are capable of coherent thought and communication at all). So a lot is going to depend on the group of people you are talking about and the severity of the illness. Dragons flight (talk) 15:50, 16 January 2016 (UTC)

There's also a big difference between people who are delusional, and people who are not. Would you consider people who are mentally ill (in the sense of meeting the criteria for a clinically defined disorder), but not delusional, "crazy"? Also: there are lots of people out there who are cranky, bitter, antisocial, unhappy, etc. but don't meet the current criteria for any recognized mental illness: would you count them as being "crazy"? -- The Anome (talk) 16:33, 16 January 2016 (UTC)

It has to depend on the nature of the mental condition - and what you mean by "know". For example - I have Asperger syndrome (a variety of Autism) which is a form of mental "illness" - and as you can clearly tell from the fact that I'm writing this, I'm well aware that I have it - and the limitations it imposes upon me are entirely self-evident to me. The fact that something was "wrong" was entirely obvious to me even before I obtained a diagnosis and had a label attached to it. But that's just one (relatively mild) condition.

So let's consider something much more severe - like paranoid schizophrenia perhaps. John Forbes Nash, Jr.'s story is a classic case: According to our article, initially..."Nash seemed to believe that all men who wore red ties were part of a communist conspiracy against him; Nash mailed letters to embassies in Washington, D.C., declaring that they were establishing a government."...so at the time, he clearly didn't know that he had a problem - he thought he was perfectly sane. However, we're told that later: "Only gradually on his own did he "intellectually reject" some of the "delusionally influenced" and "politically oriented" thinking as a waste of effort. By 1995, however, even though he was "thinking rationally again in the style that is characteristic of scientists," he said he felt more limited." - so by then, he clearly knew he had a problem - he'd quite deliberately stopped taking the medication (because it blurred his ability to think clearly enough to do mathematics) - and yet the problem was still present. His earlier inability to understand that he had a problem is self-evident - his later ability to intellectually reason that some of the things he definitely could see were unreal is a clear demonstration that one can have a very severe mental illness and be fully aware that one has it. In the movie about his life A Beautiful Mind (film), the closing scenes has him working in a university, talking to some students - and he opens the conversation by inquiring which of them are "real". It must be very bizarre to lead an existence where one has to ask such questions and distrust one's own senses to that degree.

Nash's case is a good one - at some point in his life, he was clearly "crazy" (to use a politically-incorrect term) and utterly unaware of it. Later, he was still clearly in the grips of the illness - and refusing treatment - yet was fully aware that some portion of his experience of the world was delusional. I think this demonstrates that the answer to this question is "Maybe".

But there is also a question about what you mean by "knowing". Knowing that something is true because a doctor tells you and you trust their judgement is one thing, but knowing that one has a problem from internal reference alone is quite another. In my case, the latter was clearly the case - but in Nash's case, it's unclear whether he would ever have figured out that he was delusional without being informed of it by people he trusted.

So the answer (as is so often the case) is an ambiguous "it depends..."

SteveBaker (talk) 15:29, 17 January 2016 (UTC)

A confounding factor for any study that would be regarded as useful regarding insight is that with mental illness insight can often vary during a person's lifetime. For instance, lack of insight is perhaps more likely in people that experience a mental health problem such as a psychosis for the first time. Then even once a diagnosis has been established, mental confusion and failure of insight can come and go depending on the person's condition such as with cyclothymia. --Modocc (talk) 15:39, 18 January 2016 (UTC)

what is it the partition coefficient of 1-octanol defined as?

Not a silly question, I hope. For example, cyclohexanol's reported log P is +1.23. Does this mean it is is more hydrophilic or less hydrophilic than 1-octanol? Yanping Nora Soong (talk) 17:10, 16 January 2016 (UTC)

It would help to provide the source, but note that the info box in our article on cyclohexanol says 3.6 g/l dissolve in water, vs. 0.46 g/l for 1-octanol. I'd hazard a guess it is more hydrophilic. Wnt (talk) 17:39, 16 January 2016 (UTC)

You mean you want to know what an octanol-water coefficient really means at a technical/mathematical level? DMacks (talk) 19:34, 16 January 2016 (UTC)

Rather, what is octanol's own octanol-water coefficient? It surely can't be 0? (log P = negative infinity?) Does that make sense? If we define octanol to be miscible in octanol, and note that octanol's "solubility" in octanol is 6.3 M. Then 3.6 g/ L implies an aqueous solubility of 276 millimolar. That means that octanol's own water-octanol log P is -2.36 ?

The solubility of 1-octanol in water can be easily found in the literaure, no need to imply or derive it (and probably cannot be calculated without knowing additional parameters anyway). You might be off by about an order of magnitude. DMacks (talk) 20:59, 17 January 2016 (UTC)

I'm basing it off the infobox data given to me by Wnt. I am talking about the theoretical consideration of the octanol/water partition coefficient of 1-octanol. What is it defined as? What is the log P of 1-octanol? Yanping Nora Soong (talk) 05:00, 18 January 2016 (UTC)

@Yanping Nora Soong: A lot of us haven't been trying hard enough. I typed octanol partition coefficient definition into google.com and got back a list of helpful-looking answers including, at the top in a neat little box, this link, which turned out to be a well-disguised ad but it makes some good points like this is the octanol phase vs. water phase (i.e. each contaminated with the other in a proportion that depends in part on what is being tested); a more proper link is this. So that would mean positive is more in octanol. But, that coefficient is reported as K_OW in these sources, not P -- so again, I'd want to see the source context to know for sure. Note logically though, that if cyclohexanol partitions to octanol, that means that cyclohexanol is more like octanol than cyclohexanol is like water - not that octanol is more like water than cyclohexanol is like water. Wnt (talk) 13:50, 19 January 2016 (UTC)

Alcohol and exercise

Apart from the calories in alcohol, what are the downsides to drinking alcohol after exercise or strenuous work (let's say 4 pints of lager a few hours after)?

I guess that drinking would have an impact on the body's ability to rebuild muscle, tendons etc. Maybe, it would also affect the glycogen stored in muscles, vitamin/mineral supplies and hydration, although I think these are all restored withing a few hours of exercise if you've had an appropriate meal and non-alcholic drinks?

Thanks, Mike — Preceding unsigned comment added by 95.146.213.181 (talk) 18:43, 16 January 2016 (UTC)

Alcohol is quickly metabolized into sugar, therefore I would expect the effects to be similar to eating lots of sugar. So probably not good when sedentary, where that sugar will be converted into fat. On the other hand, exercising after drinking might be a good way to burn off those calories, as long as the exercise can be done safely. StuRat (talk) 22:13, 16 January 2016 (UTC)

@StuRat: Ahem ... try ethanol metabolism. The conversion to acetyl-CoA has more in common with fat catabolism. For diabetics, alcohol is not as bad as glucose. Wnt (talk) 02:53, 17 January 2016 (UTC)

Why do you think alcohol consumption would impact the body's ability to recover from exercise? I'm asking to find out what information you're basing this on. I'm not aware of there being a significant impact. The biggest short-term effect I can think of, aside from the psychoactive effects of alcohol, is dehydration, which you touched on. Alcohol interferes with antidiuretic hormone, increasing urine production (something many drinkers are familiar with). This can lead to dehydration if you don't drink enough water to make up for the loss; dehydration is thought to be one of the things responsible for the effects of hangovers. Now, with all that said, there's a different issue here: four pints of lager a day is borderline excessive drinking. For long-term health, anyone consuming that much alcohol regularly should reduce their consumption. --71.119.131.184 (talk) 07:28, 18 January 2016 (UTC)

I'm not basing the impact on the body's ability to recover on any info, it was an assumption on my part. If the body is working to process the alcohol, isn't it using resources to deal with that rather than recovering from exercise? 95.146.213.181 (talk) 18:03, 18 January 2016 (UTC)

Well, in a sense yes, but unless you have some disorder, metabolizing reasonable amounts of alcohol isn't that big of a deal. It's not going to have any more of an effect than eating a meal. In fact, consuming nutrients (in this context, ethanol is a nutrient, since it can be metabolized for energy) after a workout will get your body started on the process of recovery and rebuilding. Insulin levels go up when you're in the "fed state", and serve as a signal to your body to do the things, like cell growth and repair, that require lots of energy and materials. --71.119.131.184 (talk) 21:21, 18 January 2016 (UTC)