Wikipedia:Reference desk/Archives/Science/2011 January 1

= January 1 =

When beer is left in an open container for a long time
What besides alcohol evaporates? I don't hold drinks well so while it doesn't taste good I wonder if it's better for me. Imagine Reason (talk) 00:21, 1 January 2011 (UTC)


 * Well, the carbonation will be lost, and the water in the beer will begin to evaporate as well. I doubt it would be any better for you to drink flat warm beer. Beeblebrox (talk) 00:26, 1 January 2011 (UTC)


 * Carbonation is bad for your teeth, in that it forms carbonic acid, which can etch the surface and allow cavities to form. So, in a sense, flat beer is healthier. StuRat (talk) 06:22, 1 January 2011 (UTC)


 * (ec) I don't think it loses much alcohol in moderate time, because there isn't that much to start with. (Whiskey, on the other hand, becomes substantially weaker in a few hours, I think.)
 * What beer mainly loses when left open is carbon dioxide, which gives it its fizz. Most people don't like "flat" beer.  --Trovatore (talk) 00:27, 1 January 2011 (UTC)


 * (ec)Not sure what you mean by "better for you". You may be better off with a Soft_drink if you don't like beer, especially if you're driving. What happens to beer depends how long it's left. After a few hours the carbonation will go, as Beeblebrox says. The beer will also warm up to room temperature. Some beers taste better very cold, and are traditionally drunk in this state (US and Australian beers in particular) while others, such as UK "bitter" are more often drunk at room temperature. So some beer will taste nasty, other beer won't. After a few days in an open vessel the sugars in beer will start to grow mould and the sugars will turn to vinegar. How long do you mean by a "long time"? Tonywalton Talk 00:40, 1 January 2011 (UTC)
 * Agree that before much alcohol has evaporated the quality will be affected. By the way, English bitter should be drunk at cellar temperature, i.e. about 9degC. It isn't heavily carbonated like canned beer. Itsmejudith (talk) 17:07, 1 January 2011 (UTC)
 * How about trying low/no-alcohol beer? 86.185.77.168 (talk) 02:52, 2 January 2011 (UTC).

White precipitate
When tin is reacted with copper sulfate, a white precipitate is formed. What is this? --Chemicalinterest (talk) 01:30, 1 January 2011 (UTC)


 * Tin(II) sulfate would be my best guess. -- Jayron  32  02:55, 1 January 2011 (UTC)


 * Strange, the fact that you didn't observe a red or dark orange precipitate, means that copper(2+) was not reduced to copper(0). --Plasmic Physics (talk) 08:56, 1 January 2011 (UTC)


 * Tin(II) sulfate is soluble and, I would presume, is in the (almost) colorless solution above the white precipitate. --Chemicalinterest (talk) 12:36, 1 January 2011 (UTC)


 * Maybe Tin(IV) sulfate then? I can't see anything happening to the sulfate itself, and copper compounds are all usually brightly colored.  -- Jayron  32  15:30, 1 January 2011 (UTC)
 * Depending on the pH, you might have hydrated tin(II) oxide. Physchim62 (talk) 16:27, 1 January 2011 (UTC)
 * It is only as acidic as a dilute solution of copper sulfate is. --Chemicalinterest (talk) 18:11, 1 January 2011 (UTC)
 * Which may actually be pretty acidic; copper(ii) is a pretty decent lewis acid, and in solution readily forms copper hydroxide complexes, leaving hydronium behind. -- Jayron  32  18:27, 1 January 2011 (UTC)

I have just completed some tests on a mixture of the almost colorless solution and the white precipitate. Excess HCl dissolves it to form a light yellow-green solution; dilute hydrogen peroxide has no effect on it; and dilute ammonia solution makes the precipitate somewhat more yellow and precipitates more from the solution part. Hope this helps in some way. --Chemicalinterest (talk) 23:04, 1 January 2011 (UTC)
 * The addition of the HCl likely formed Copper(II) chloride; excess cloride ion forms a yellowish-green solution. That would likely indicate that your precipitate was some sort of copper-containing species.  -- Jayron  32  20:54, 2 January 2011 (UTC)

Complex/Quadrature Sampling
While reading some web pages on Software Defined Radio, I saw a method to get a high sampling rate by using two ADCs of lesser speed. Contrary to intuition, the two ADCs were operated not 180° out of phase but in quadrature. What is the actual name of this technique, and is there a wikipedia page on it? I'm currently reading an external link from the SDR article, but it seems to talk about QAM modulation techniques rather than sampling techniques. —Preceding unsigned comment added by 59.93.16.208 (talk) 06:12, 1 January 2011 (UTC)
 * Depending on the exact arrangement, it might be a phase detector combined with an interpolation algorithm; it might be simply a quadrature sampler; it might be an interferometer (if the Q/I components are compared to a reference signal). There are a wide class of methods that use 90-degree (quadrature) modulation to analyze signals; the exact circuit might help us narrow down the method.  Our quadrature article links to some of the numerous uses and applications of 90-degree phase shift for signal analysis; because of the unique properties of fourier analysis, phasing a signal by 90-degrees (in other words, "multiplication of the signal by i) allows additional information to be inserted or extracted from a waveform, because the quadrature signal is orthogonal to the original signal.  So many related techniques rely on this quadrature orthogonality property, it's difficult to name a specific one without looking at the exact circuit.  Nimur (talk) 08:17, 1 January 2011 (UTC)
 * I was reading the GNU Radio site. This is what they have written about the hardware. They have also given an image in which the input from two ADCs are multiplied with Sin and Cos.
 * The USRP has 4 high-speed analog to digital converters (ADCs), each at 12 bits per sample, 64MSamples/sec. So in principle, we have 4 input and 4 output channels if we use real sampling. However, we can have more flexibility (and bandwidth) if we use complex (IQ) sampling. Then we have to pair them up, so we get 2 complex inputs and 2 complex outputs.
 * Where would the bandwidth advantage come from? 59.93.6.216 (talk) 17:22, 1 January 2011 (UTC)

The range of signal frequencies that can be sampled without alias error is said to be limited at half the sampling frequency, called the Nyquist frequency. Alias error here refers to false readings of signal frequencies above the limit. The sketches below demonstrate that phase errors still occur at the Nyquist limit. In the upper sketch the solid samples are at the Nyquist rate and appear to allow an unambiguous reconstruction of the sinewave signal. However with an unfortunate sampling phase relative to the signal, we get the open samples which are all zero. Simply shifting the signal phase by 90 degrees has made it "invisible" to the sampler. In contrast, the lower sketch shows the 0-90-360 degree sampling described by the OP. Here there is no phase ambiguity. Both I and Q (quadrature) components of the signal can be reconstructed. What has been obtained is not an increase in bandwidth but a removal of (amplitudeXphase) ambiguity.  oo888oo o8888888o 8 o888888 o8888888¤ ¤  ¤¤¤   ¤o ¤           o     ¤              o    ¤                o   ¤ o                  ¤ooo ¤8oo                8¤¤  ¤8                  oo¤¤ ¤o              8   o   8                o¤ ¤   8               ¤o   o o¤                8   ¤ o8                ¤¤ooo¤¤                  8oo ¤¤                       ¤                    o¤¤ ¤                           o                 ¤ o              ¤ o            ¤ o          ¤ ¤ oo888ooo¤ 88888888o 888888888                                 8888888                                    ¤¤¤           ooo 8888888       8¤¤888888        ¤o8888888 o¤¤¤888¤¤ o     o           ¤ o            ¤ o              ¤ o                ¤ o oo¤                   o                        oo 8888                                          8888 88888                  ¤                    88888 8888¤                    ¤                   ¤8888 88¤¤                      o                   ¤¤8o o                  ¤ o                           ¤                o                             ¤              o                              ¤            o                               ¤o         o                                 o      o¤                                  ¤¤ooo¤  Cuddlyable3 (talk) 20:04, 1 January 2011 (UTC)

Black hole
I have read somewhere that if a fragment of a red giant remains during the explosion, the star collaspes into a black hole. Is this true? Also what causes the super giant to become a black hole and not a Neutron star? What's the deciding factor between these? --Tyw7 (☎ Contact me! • Contributions)   Changing the world one edit at a time! 08:10, 1 January 2011 (UTC)
 * The final stage of stellar evolution is either a white dwarf, neutron star or black hole in order of increasing mass; and it is the mass which entirely determines which it is to be.  Sp in ni ng  Spark  10:13, 1 January 2011 (UTC)
 * Also, I think you are confused between red giants, which do not explode and is something that happens to smaller/mid-range stars and supernovae, which do explode and is something that happens to larger stars. There is always a remnant after such explosions.  Sp in ni  ng  Spark  10:20, 1 January 2011 (UTC)


 * Red supergiants and blue supergiants are the stars that can either evolve into a neutron star or black hole. Core remnants almost inevitably remain, except for some Wolf-Rayet stars and select Gamma ray bursts. Also read up on Type Ia supernovas, Type Ib supernovas and Type II supernovas, as the deciding limit between neutron stars and black holes is more uncertain than say, the Chandrasekhar limit but hypernovae if they exist likely become black holes and X-ray sources. ~ A H  1 (TCU) 17:20, 1 January 2011 (UTC)
 * Slight correction: the supernovae are the explosions. The stars that go supernova are called supergiants. --Tango (talk) 00:44, 2 January 2011 (UTC)

Sound
How does a flute work? --75.28.52.27 (talk) 17:59, 1 January 2011 (UTC)
 * See the Wikipedia article flute. -- Jayron  32  18:26, 1 January 2011 (UTC)

This article (http://www.phys.unsw.edu.au/jw/fluteacoustics.html) seems to have what you need ny156uk (talk) 18:27, 1 January 2011 (UTC)


 * A flute doesn't work; it plays. [rimshot] Clarityfiend (talk) 03:04, 2 January 2011 (UTC)
 * Our Flute article's section on acoustics will help; and Acoustic resonance is also helpful; particularly resonance of a tube of air. Nimur (talk) 20:50, 2 January 2011 (UTC)

Dumping snow in the sea
From http://www.bbc.co.uk/news/world-europe-12088442:


 * "Deep snowdrifts have trapped thousands of people in their homes on the Danish island of Bornholm [...] There is so much snow that islanders have started dumping it in the sea - a practice normally forbidden for environmental reasons."

Does anyone have any ideas what these "environmental reasons" could be? Do you think it's just in case the snow is contaminated by oil or something, say from the roads? 86.185.77.168 (talk) 23:00, 1 January 2011 (UTC)


 * Also, you would be diluting the salty sea water.Zzubnik (talk) 12:12, 4 January 2011 (UTC)


 * It looks like Norway had similar problems two winters ago, and when they started dumping the snow into the sea, there were indeed environmental concerns for the reason you stated: contamination from traffic. See this report, for example. ---Sluzzelin talk  23:26, 1 January 2011 (UTC)