Wikipedia:Reference desk/Archives/Science/2012 April 17

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April 17[edit]

obviously pseudoscience that ended up completely right?[edit]

are there examples of obvious quakery, obviously fake pseudescience promalgated by complete amateurs or better yet charlatans, completely dismissed as ridiculous pseudoscience that isn't even plausible: but which happens to be the current scientific consensus after all? (anything counts, from germ theory to the existence of plastic, etc etc etc). -- (talk) 07:47, 17 April 2012 (UTC)

See #Pseudo science above. (When it gets archived it will be at Wikipedia:Reference desk/Archives/Science/2012 April 14##Pseudo science). SpinningSpark 08:10, 17 April 2012 (UTC)
I think the OP may have meant things that were fake science when originated, and are still regarded as fake science now, but none the less gave the right result. This is subtly different to what was covered in the previous question, which was about the science, not the result. Trouble is, if it turned out to be right, mostly it will now be regarded as good science. As was posted in the previous question, plate tectonics was originallly regarded as bad science, but is now accepted as good science. In contrast is possibly Ohm's Law
When Ohm announced his findings, it was ridiculed by leading scientists, as it was based on somewhat dubious practical measurements, and not derived mathematically from first principles. This is still a valid criticism. But Ohm was and is never the less correct in his conclusion, as proved by very accurate measurements, and by conduction element field interaction theory.
Another example is the realisation that thalidomide causes birth defects and deformities. The researcher McBride suspected the link but fudged his research data to prove it. So that was bad science and is still bad science. However it has been accepted that he was right, in fact the evidence after some years of thalidomide use by pregnant women became overwelming.
Keit120.145.193.144 (talk) 14:43, 17 April 2012 (UTC)
Samuel Hahnemann, the founder of homeopathy, nevertheless was on to something when he claimed in 1828 that some diseases were due to miasms, which were familial predispositions to certain types of disease. This assertion predated theories of genetic origins of disease. --TammyMoet (talk) 15:29, 17 April 2012 (UTC)
Clearly a case of "even a blind dog can hit a tree once in a while" if I ever seen one. --Jayron32 15:41, 17 April 2012 (UTC)
According to one of the chemistry professors at my alma mater, the Nernst equation was dubbed "Nernst's folly" immediately after its publication. Walther Nernst's work was only later accepted according to this version events for which I can find no references (and "Nernst's folly" returns precisely zero google hits). (talk) 21:14, 17 April 2012 (UTC)
Copernicus advocated a heliocentric model of the solar system. He did this based on the philosophical assumption that planets must move in circles (This was before the laws of gravity were known). We know today that this is completely false, and there was no true scientific basis for it whatsoever. However the heliocentric model has gained near-universal acceptance, because of the scientific work of Newton and Kepler. - Lindert (talk) 20:53, 17 April 2012 (UTC)
The problem is one of a distinction between predictions that are 'correct' phenomenologically – that is, predictions that offer accurate descriptions of real phenomena – versus predictions that offer correct underlying reasoning. Alfred Wegener's initial theory of continental drift, for example, was descriptively correct; continents really did move about on the Earth's surface, and they did form the supercontinent of Pangaea in the past. On the other hand, elements of Wegener's reasoning were quite faulty. Wegener suggested that the driving force for drift might be Polflucht (literally 'flight from the poles'): centrifugal force caused by the rotating Earth, pushing the continents 'outward' towards Earth's equatorial bulge. So the idea of continental drift was correct, but the reasoning behind it was wrong. Lindert's example above of Copernican theory is an even more stark example—planets certainly orbit the sun; planets don't do so because roughly-circular orbits are philosophically ideal. TenOfAllTrades(talk) 21:58, 17 April 2012 (UTC)
Acupuncture may be an example. Theory is a lot of mumbo-jumbo about flows of qi, and meridians. It's quite implausible. However, it seems to mostly work. Ratbone121.221.128.125 (talk) 03:33, 18 April 2012 (UTC)
My physiotherapist justified the acupuncture that she used on me by saying that the foreign body stimulates an immunoresponse which leads to increased blood flow. Since blood flow to tendons is sparse, it is a limiting factor in the rate of healing. That may explain why it helps with injured tendons and other tissues that have poor blood flow, without resorting to concepts like qi, feng shui or Exegesis. (talk) 05:10, 18 April 2012 (UTC)
Democritus's atoms fell out of favor for over a thousand years. Also, see Wright brothers#Trouble establishing legitimacy et seq. (talk) 05:30, 18 April 2012 (UTC)
Nikola Tesla's AC power.Smallman12q (talk) 12:37, 18 April 2012 (UTC)
Or compare the narrative taught about Christopher Columbus (said world was round, everyone laughed at him, proved everyone wrong by sailing around world, although mistook Americas for East Indies) with the reality (everyone knew the world was round, he said the world was half the size it actually is, everyone laughed at him, he got lucky when it turned out there was land roughly where he expected the East Indies to be as otherwise he would have died, gains wealth, fame, and respect). Columbus was wrong, dead wrong, but he discovered land where he said it would be. (talk) 09:25, 19 April 2012 (UTC)
Ah, Lindert just made me think of the classic example: Giordano Bruno#Bruno's cosmology! As explained in the article, Bruno believed that the stars were other suns, and the stars and earth were made of the same elements (even if he thought there were four...), and the Earth revolved around the Sun, and space was infinite. But it was not, so far as I know, based on real observations; it was merely pseudoscience that happened to be right in some key regards. Wnt (talk) 02:43, 20 April 2012 (UTC)

Regarding effect of an AC signal on a BJT.[edit]

I learned about DC biasing of BJTs in Analog electronics. So far, the DC biasing seemed understandable. However, a few days back, our class started AC signal analysis of BJTs. This confused me a lot. How can an AC signal and a DC signal be applied on a BJT at the same time? More over, during AC analysis, any capacitors are shorted out, but why?. I just don't understand how this helps. Can anybody please answer. — Preceding unsigned comment added by (talk) 10:34, 17 April 2012 (UTC)

We have an article Bipolar transistor biasing you can read. Capacitors are used in such circuits for coupling or de-coupling AC signals. The impedance of a capacitor varies like 1/f. So for a suitably large enough capacitor its impedance can be considered essentially zero at the frequency of operation of the circuit. This is why one replaces the capacitors with short-circuits in AC analysis. On the other hand, DC does not pass through capacitors at all. The two are mixed in the same circuit by applying the DC through resistors and the AC through capacitors. SpinningSpark 12:06, 17 April 2012 (UTC)
When only an AC signal is present, the instantaneous voltage oscillates either side of zero volts. For a sine wave, for example, the amount of time spent above zero (ie positive) is equal to the amount of time spent below zero (ie negative) and the peak positive voltage is numerically equal to the peak negative voltage. When a small amount of DC is added, it displaces this oscillation away from zero in either the positive direction or the negative direction as the case may be. In BJT small signal operation, the DC bias is much greater in magnitude than the peak to peak magnitude of the AC signal, so the combination is always the same polarity and is a small oscillation about the mean, which is the DC voltage. Keit120.145.193.144 (talk) 14:28, 17 April 2012 (UTC)
SpinningSpark is correct. Another point of view is that analysis that keeps track of actual voltages and currents as they change in the presence of AC input signals is too difficult to do with pencil and paper, so simulation programs such as SPICE or ASTAP must be used. But these programs may be hard to use and not impart much insight to the student. So the DC bias is established; with no AC input the conditions are called the quiescent conditions. It is understood that to find the voltage at a certain node at a certain instant, the voltage from the AC model must be added to the voltage from the quiescent condition; likewise for currents. A simplified AC model is derived that is only valid for small departures from the quiescent conditions. This model is often simple enough to analyze using pencil and paper or a scientific calculator.
Also, simulation programs can have bugs or be set up incorrectly, so pencil-and-paper AC analysis can serve as a check on the simulations. Jc3s5h (talk) 14:53, 17 April 2012 (UTC)
Running a SPICE simulation may give one the numerical answers but it does not aid understanding or help to resolve the questioner's confusion. SpinningSpark 17:50, 18 April 2012 (UTC)

Snow patterns[edit]

How the hell does he do this?--Shantavira|feed me 18:57, 17 April 2012 (UTC)

By making footprints in different orientations. Goodbye Galaxy (talk) 19:09, 17 April 2012 (UTC)
...and is his name Qbert ? You can make out the individual footprints, making it fairly obvious how he does it. I imagine he must need a plan and something like laser pointers to mark the vertexes of each cube, though. StuRat (talk) 19:11, 17 April 2012 (UTC)

He is on Facebook seemingly and you can presumable ask him questions from there. (google Simon Beck snow art it's the top result). He has an FAQ in the 'about' section of his Facebook account (strange though that may seem). The about section is just below his photo at the top of his Facebook page. ny156uk (talk) 19:13, 17 April 2012 (UTC)

I can't figure out how he makes the patterns so precisely over such a large area. Laser pointers, stakes and string are fine for making crop circles, but he would need to disturb the snow to set those up?--Shantavira|feed me 07:44, 18 April 2012 (UTC)
Perhaps he does the setup before it snows, leaving stakes at key points? Pfly (talk) 08:18, 18 April 2012 (UTC)
As was pointed out previously, he has an FAQ on his Facebook page. In it he says that he uses a compass and is an expert at orienteering. Additionally, for some of the circles, he will put a stake in the snow and use a length of rope to pivot round it. Dismas|(talk) 21:21, 18 April 2012 (UTC)

Viruses/disease symptoms[edit]

What exactly do diseases/viruses do that makes us humans and animals suffer symptoms? I'm sure different ones do different things, so I guess just use Rabies and HIV/AIDS as an example. Thanks! (talk) 22:17, 17 April 2012 (UTC)

With most common viral symptom, these are caused but one's own body's Immune system fighting off the infection (high temperature, aching muscles etc.). The Rabies virus also attacks the nervous system and thus courses symptoms associated with that disease – It disrupts the normal functioning of the CNS where as some other viruses attack other tissue. HIV/AIDS attack the immune system itself and so the symptom tend to be those of other opportunistic pathogens that now attack the body due to the low immunity. Thus, there is no simple answer. --Aspro (talk) 22:44, 17 April 2012 (UTC)

Diseases may be caused by many different things. Broadly, the causes of disease fall under four different categories:

There are various types of pathogens that infect people. Each specific pathogen will cause harm to the body's cells in a unique way, but in general the various types of have characteristic mechanisms:

  • Viruses have no cellular structure, and lack any mechanism of self-replication. They reproduce by taking over the internal workings of other cells e.g. the body's cells, and basically turns them into virus factories. The whole cell is either consumed in virus production or bursts at the seams when it becomes full and the new viruses repeat the process with more cells. Different viruses attack different types of cell e.g. HIV attacks the cells that make up the body's immune system.
  • Bacteria have their own cellular structure, but live in the hosts body. They may cause damage in a variety of different ways including; consuming the body's own cells and poisioning the body with the products of its own metabolism. Sometimes they also simply obstruct the physical processes in the body e.g. blocking the flow of blood. There also some eukaryotic microparasites (e.g. plasmodium which causes maleria) which cause disease in pretty much the same general way, but the organisms themselves are not bacteria.
  • Macroparasites also cause disease by feeding on the hosts cells and by producing harmful waste. They include ticks and lice and various types of worms.

There are other types of pathogen that cause illness in other ways such as prions, viroids and fungi, but these are generally either rare (mad cow disease) or not serious (Tinea). (talk) 01:57, 18 April 2012 (UTC)

  • Actually at the very general scale HIV and Rabies are doing the same thing: They are infecting normal cells and hijacking them to become "factories" for more virus proteins. The difference in symptoms is based on which type of cell the virus attacks: in the case of HIV the T-cell and Rabies it is slightly more complicated, it attacks nerve cells but also muscle cells and concentrates in certain areas such as the salivary glands. The cause of all pathogenic disease symptoms is, as the IP above mentioned, either based on the immune response (fever, vomiting) or based on damage to cells (more differentiating symptoms). In fact the vast majority of symptoms fall into one of those two categories. Even those from genetic conditions (either a certain type of cell doesn't function properly or can't make the proper products- E.g. pancreatic beta cells in type-1 diabetes) or something triggers an abnormal immune response (allergies for example are the result of something normally innocuous triggering a massive immune response). Deficiencies as well usually produce symptoms because without the needed nutrient a cell cannot function properly. Without Vitamin K clotting doesn't work properly, for instance. So to answer your question: symptoms are caused either by an immune response, either functional or disfunctional, to an external or internal factor; or by some factor preventing the body's systems from properly doing their job. HominidMachinae (talk) 05:26, 18 April 2012 (UTC)
Bacteria have specific means of injuring the host - see superantigen, Shiga toxin, botulinum toxin, cholera toxin, etc. Superantigens interfere with immune response, while diarrhea from cholera I assume helps spread the disease. I don't know for sure what the botox is for, but note that it is an obligate anaerobe, so it probably finds breath and heartbeat to be most annoying. There are much, much weirder symptoms caused specifically - see toxoplasmosis and Ophiocordyceps. Similarly I think rabies exerts this specific tissue tropism to make those infected go on to scratch other animals; the caveat being that this can't be proved, because technically it is an aesthetic statement - of course, viruses don't evolve for any purpose they are aware of. Wnt (talk) 16:51, 20 April 2012 (UTC)