Science desk
< January 19	<< Dec \| January \| Feb >>	January 21 >

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 20

Some articles are unclear

I cannot understand what is said by the articles: protist and algae. The article protist includes algae int it and says that protists are eukaryotic. But the aticle about algae includes cyanobacterias which are prokaryotic. These articles' facts are opposing each other. The article about cyanobacteria includes the cyanobacteria into bacteria domain. But in the article algae there are sentences like this:

Most algae except cyanobacteria contain chloroplasts

So if algae are protists(as mentioned) and protists are eukaryotes (as mentioned), then cyanobacterias should not be included in algae because they don't have a membrane bounded nucleus. What can we do? --G.Kiruthikan (talk) 04:47, 20 January 2014 (UTC)[reply]

Did you read the lead of the algae article? I think it answers your questions. Basically the answer is that the protist article should have said that they include some types of algae. Looie496 (talk) 05:09, 20 January 2014 (UTC)[reply]

"It depends who you ask, and when," to some degree. Have a look at some of the most common classification schemes in use today. Some articles are surely using different schema. We can even find and cite sources that give contradictory correct answers!

I'm actually much more interested in this problem that Wikipedia articles contradict each other!

When I went to lower-grade school, our text-books used the five-kingdom classification method (bacteria, protists, fungi, plants, and animals). This was mostly consistent with what I "knew" to be correct; I had read, cover-to-cover, my home library copy of the 1967 World Book Encyclopedia, and it used a similar categorization. By the time I went to high-school biology, our text-books had switched to the "2.5 kingdom" (archaea, bacteria, everything-else) schema. Everything seemed wrong! Even the waterbears were in the wrong chapter of my high-school book, and there can be no doubt what they are! I got into a lot of trouble with my teacher by making noise about that issue. (If only more people could get so passionate about these important flaws in school biology textbooks!)

What had happened is that over the years, new scientific research has enabled us to classify the same organisms in many different ways. There is no single canonically-correct way to classify an organism; and if you assume that some microorganism must be either a protist or a cyanobacteria, you'd better be very sure you know exactly how you've defined those classifications. Sometimes, superficial treatments about science portray a level of consistency that doesn't really exist in the research community. Molecular biologists may prefer one classification scheme, while zoologists prefer a different scheme, while ecological conservation policy-makers use a totally different type of taxonomy. Classification schemes for organisms are not "facts;" they are positions that are put forward by prominent researchers. Old-fashioned publications, like paper encyclopedias and schoolbooks, had an editorial board who would convene, and there would be a top-down commandment specifying that one set of "facts" was canonically correct and reflected the current state of scientific knowledge (at least for the purposes of that year's publication). That's not how science works - if anything, Wikipedia is giving you more "correctness" by presenting contradictory information and letting you make the critical judgement.

If you are classifying an organism, you need to know which scheme you're using, and what basis is the standard for determining taxa. You should be aware that different sources and authors may use different schema. Particularly at Wikipedia, we are an encyclopedia edited by many individuals, and with very little coherent editorial oversight; nobody here is "the Chief Editor" who commands top-down that all articles shall use schema X. So, at a superficial inspection, our articles may contradict each other. Nimur (talk) 10:30, 20 January 2014 (UTC)[reply]

In addition to Nimur's good points above, the reason it is hard to reconcile "protist" with "algae" is that neither of these groupings are currently believed to be clades. They are both highly polyphyletic, and so they don't make much sense in relation to each other, or to our more modern systematics. You might also be interested in Phylogenetic_nomenclature#Philosophy. Finally, if you read carefully, I don't think our article protist actually says or even implies that all algae are protists. SemanticMantis (talk) 00:07, 21 January 2014 (UTC)[reply]

I have now understood why there were contradictions. But we should make sure that other readers will not get any of the contradictions. Then all will got complicated. (I don't know the grammer well). Some books say that the classification of protists is not natural but rather it is artificial. They say that protists include organisms with many different evolutionary traits and no very recent evolutionary similarities. So regarding this point I think that there is no way of getting out of this complication. The only thing that matters is that according to Wikipedia's article, all protists are eukaryotic. So I think there is a small possibility of excluding cyanobacterias from protists.--G.Kiruthikan (talk) 02:43, 22 January 2014 (UTC)[reply]

How do resistors suppress RF interference?

Every since I started messing with cars I've heard that automobile spark plugs and their the wires contain resistors. Supposedly this eliminates RF noise from interfering with radio reception. On Wikipedia's Spark Plug page I found this statement:

The central electrode is connected to the terminal through an internal wire and commonly a ceramic series resistance to reduce emission of RF noise from the sparking.

That's great. Why does it work? — Preceding unsigned comment added by 50.43.12.61 (talk) 06:48, 20 January 2014 (UTC)[reply]

Same reason that a shock absorber reduces mechanical vibrations. 67.169.83.209 (talk) 09:52, 20 January 2014 (UTC)[reply]

Schematic showing how a wave flows down a lossless transmission line. Red color indicates high voltage, and blue indicates low voltage. Black dots represent electrons. The line is terminated at an impedance-matched load resistor (box on right), which fully absorbs the wave.

It works via (electro magnectic) transmission line theory. A wave is produced and the wave travels down the transmission line and hits the end of the transmission line and bounces back. Each time it travels down the transmission line it releases RF. It does this trillions of times by bouncing back and forth, back and forth endlessly. To stop this, put a resistor in series with the transmission line. The resistor is tune so that to the wave it looks like an infinite transmission line. As the wave travels down the transmission line, it is absorbed by the resistor and does not bounce backwards because as far as the wave is concerned it is going down an infinite transmission line. 220.239.51.150 (talk) 10:39, 20 January 2014 (UTC)[reply]

I think DHeyward is right about the spark plugs, but on a semi-unrelated note, I don't understand this animation. Is the resistor the whole rectangle of wire, or just the wide part? Either way, how can the electron density in the rectangular part be constant in both position and time? The effect of the resistor should be distributed along its length. I can't see any way of interpreting the image such that it's correct. -- BenRG (talk) 20:34, 21 January 2014 (UTC)[reply]

Just the end. A transmission line has an inherent impedance related to the permittivity and permeability of the dielectric as well as its structure dimensions. Energy is stored and transmitted in the field which is the picture. Waveguides are usually TE modes while coaxial cable and power lines are TEM modes. When wavelengths are short compared to the length of the lines, reflections can occur (I like to think of it as the source and load are unaware of each other at initiation and the speed of propagation in the dielectric means the model is a full power transmitter and the load reflects back what it cannot absorb. - YMMV with that though experiment. Transmission lines are often many wavelengths of the source frequency.) Impedance matching the source to the transmission line to the load minimizes reflected energy back to the source. Smith chart and S-parameters are normally the way transmission line matching is analyzed and corrected using power. Ionizing breakdown is a complex impedance (plasmas in waveguide is similar) that a simple resistor cannot match but can limit. The 5k resistor appears as the source impedance for a short circuit limiting what energy is in the spark. --DHeyward (talk) 04:28, 22 January 2014 (UTC)[reply]

Until the air breakdown voltage is reached, there is no current. When the breakdown voltage is reached and the conductive channel is formed, it's very low resistance. A resistor in series limits the total current and therefore the total energy available for the RF impulse. Resistors of 5k are typical. It has nothing to do with RF line matching. It's function is to produce a spark with the minimum energy necessary and therefore the least RF energy produced. --DHeyward (talk) 08:13, 21 January 2014 (UTC)[reply]

Wavelength of electromagnetic radiations emitted by different excited lead isotopes

Do the different isotopes of lead emit electromagnetic radiations of different wavelengths? or Do all four isotopes emit electromagnetic radiations of same wavelengths when they are decaying? — Preceding unsigned comment added by 27.62.251.166 (talk) 13:11, 20 January 2014 (UTC)[reply]

Yes, different isotopes have slightly different molecular spectra due to a difference in nuclear structure. However, these effects are much larger in lighter elements. In lead, which is the heaviest stable element, it may be hard to measure the difference in wavelength between isotopes, but in principle it should be possible. See this article from Encyclopedia Brittanica. The naturally occuring isotopes of lead are observationally stable (see isotopes of lead), so they do not typically decay, but when you compare e.g. Pb-210 with Pb-211 or Pb-214 the energies associated with the decay process differ significantly. - Lindert (talk) 13:47, 20 January 2014 (UTC)[reply]

I want to know whether it fixed that a particular isotope would emit electromagnetic radiations (EMR) having only a certain specified range of wavelengths (i.e., wavelength of EMR emitted by Pb-210 is different from Pb-211) or the wavelengths of EMR emitted is independent of the isotope used. 106.216.118.149 (talk) 14:45, 20 January 2014 (UTC)[reply]

The gamma rays emitted by the decaying nuclei are all different frequencies. However when lead decays it turns into different isotopes of different elements. So your ²¹⁰Pb gives off gamma rays that belong to Bismuth 210m at an energy of 271.3 keV. In the table in the isotopes of lead article you can see the numbers with m1, m2... after them, these give off the gamma rays listed and are all different energies, and belong to lead.

Food chemistry, eggs, milk, and salt

Hello, I witnessed some curious behavior making breakfast recently, and hope you can help clear it up. I whisked two eggs together in a clear measuring cup, until fairly homogenous. I then added a bit (15-20cc) of whole milk, and did not stir. Both eggs and milk were roughly the same temperature, straight from the fridge. The resulting mixture had a distinctly inhomogenous, marbled look, which is as expected (basically like this [1], but even less mixed, and with less milk. The important part is the borders are very sharp).

When I sprinkled a few shakes of salt on top, the veins of milk on the surface started wiggling and writhing, making the previously sharp and stable milk/egg border roil. It really caught my eye, as it reminded me of Diffusion-limited_aggregation or vortex shedding or some other clever pattern formation thing.

What's going on here? Something to do with surface tensions? Ions? Would there be any real "reactions" leading to a reaction-diffusion system? Anyway, I highly suggest you take a look next time you make scrambled eggs. Thanks! SemanticMantis (talk) 18:11, 20 January 2014 (UTC)[reply]

I'm not sure, but I think this may have to do with the changes in osmotic pressure caused by addition of salt. 67.169.83.209 (talk) 02:15, 21 January 2014 (UTC)[reply]

I don't really know about the reaction, but I was always told not to add salt before the eggs are cooked because it can make them rubbery. Hot Stop 04:32, 21 January 2014 (UTC)[reply]

Some sources say this [2], but a number disagree [3] [4] [5]. Nil Einne (talk) 17:43, 21 January 2014 (UTC)[reply]

Foo yung

Are Chinese foo yungs healthy? Clover345 (talk) 22:18, 20 January 2014 (UTC)[reply]

"Yes" and "no". They essentially share ingredients with omelets. Your question has been answered on several sites; e.g.: an authoritative one→[6] ~:71.20.250.51 (talk) 22:46, 20 January 2014 (UTC)[reply]

Rubbing Alcohol

I was talking to my neighbor recently, and he recommended applying Rubbing_alcohol to a sore muscle, and vigorously rubbing it in to provide relief. Thus, the name rubbing alcohol. The article here makes no mention of such a use, or why it is called rubbing alcohol. I have no intention of trying this, but I was curious. Is this a common, safe, or valid use of the product? Cthulhu42 (talk) 22:36, 20 January 2014 (UTC)[reply]

The bottle I have handy has instructions that say exactly that, so I assume it's at least common and/or safe. As to how valid it is, I don't know. When the alcohol evaporates, it will cool your skin, but I don't think much of that effect would even reach your muscles, let alone what benefit it would provide. Matt Deres (talk) 00:29, 21 January 2014 (UTC)[reply]

It says here " According to Medical Dictionary, the name "rubbing alcohol" stems from its use in the past as a medicinal rubdown, although this is not as common of an application now". It also describes the reasons for that usage under the heading 'Liniment for muscle aches'. Richerman (talk) 00:35, 21 January 2014 (UTC)[reply]

That's a placebo, except for the fact that rubbing with an antiseptic is less likely to cause infected skin lesions than rubbing without. Also, for all medical questions, consult a health care professional instead of the reference desks, thanks! 193.138.222.5 (talk) 03:19, 21 January 2014 (UTC)[reply]

Evaporative cooling would be similar to ice, I would think. --DHeyward (talk) 04:04, 21 January 2014 (UTC)[reply]

I believe the "effective" ingredient in 'rubbing alcohol' is the "rubbing". ~:71.20.250.51 (talk) 06:36, 21 January 2014 (UTC)[reply]

If you live in the US, then I think that I think yours neighbors reference to "rubbing alcohol" dates back to the laws of prohibition era. It was the only spirit people could legally bye over the counter. This alcohol was the base for making Liniment. Alcohol on its on is only good for cooling and dehydrating Trench foot conditions, etc. Medicated "rubbing alcohol" was much better for soothing muscle complaints (but dreadful for drinking). However, it is extremely difficult to bye now on the North American continent because no pharmaceutical companies hold patents to make it worth selling.--Aspro (talk) 19:06, 21 January 2014 (UTC)[reply]

Note that skin absorption can lead to toxic doses of isopropanol in extreme cases [7]. If something has the potential to do harm, it may also have the potential to do good, or at least, to feel good. Now I find nothing about peripheral effects when simply looking for articles for "rubbing alcohol" in PubMed, and the physiological effects of alcohols are wide and varied; nonetheless, there are peripheral effects of alcohol [8], and chronic alcoholism even lead to peripheral neuropathy (though I don't know that is a direct mechanism). I have noticed that surprisingly, modern medicine really gives very little consideration to ancient technologies for topical anaesthesia, all but ignoring peripheral receptors for opium, for example, or its history of topical use - it is possible that the state of knowledge about this particular application of rubbing alcohol was more advanced some centuries ago than it is today. This is unfortunate because one would hope peripheral therapies offer a chance to deliver treatment to an area with less burden on internal organs. Still, the potential risks I have mentioned also do not seem to have been well investigated, and merely feeling good would not be all the data I'd want to hear! Wnt (talk) 22:59, 23 January 2014 (UTC)[reply]