Wikipedia:Reference desk/Archives/Science/2016 November 11

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November 11

Antimicrobial resistance

I read part of Antimicrobial resistance. I'm wondering - since bacteria are evolving to be resistant to antibiotics, is it possible that there can be an entirely new type of treatment that attacks the DNA of the bacteria? Bubba73 ^{You talkin' to me?} 01:05, 11 November 2016 (UTC)

There are indeed antibiotics that attack bacterial DNA, such as furazolidone and nitrofurantoin. There is a particular difficulty in making such a drug specific to bacterial DNA. Nitrofurantoin is able to achieve this specificity by having low toxicity by itself, however bacterial enzymes metabolize the drug into a far more toxic metabolite after it enters the bacterial cell. Now obviously the bacteria can't evolve to not have DNA, but they can evolve resistance to these drugs through other means: The enzyme that activates the drug could be lost or altered; if the drug enters the cell through a transporter, that transporter could be lost or altered; an efflux pump could evolve to force the drug out of the cell; an enzyme could evolve to destroy the toxic metabolites of the drug; a protein could evolve to bind and sequester the drug or its metabolites in a fashion such that it can do no further harm. Someguy1221 (talk) 02:17, 11 November 2016 (UTC)

As mentioned, there already are. The problem is that you have DNA too. We generally want to avoid harming the patient with antibiotic therapy. The utility of most antibiotics comes from the fact that they selectively target bacteria (and sometimes other microbes as well). Usually this is because they target things that differ between prokaryote and eukaryote cells. DNA, however, is pretty much the same among all known life, so anything that affects bacterial DNA will likely affect your DNA as well. We've discovered some antibiotics that attack DNA, but we use them not for their antibiotic effect, but for chemotherapy. In this instance, their nonspecific effect is useful, although, as with many chemotherapeutic drugs, their usefulness is limited by their adverse effects. --47.138.165.200 (talk) 05:28, 11 November 2016 (UTC)

I was trying/failing to remember and hit on a nice little student essay: [1] It mentions mitomycins, bleomycins, imidazoles, nitrofurans, as well as (more indirectly) antibiotics quinolones, coumermycins and novobiocin affecting DNA replication, and rifamycins, streptolidigin and lipiarmycin affecting transcription of DNA. Now any list that long in biology is pretty much bound to be incomplete, and many of these likely do not meet your criteria, but it's a lot more than I could come up with. Wnt (talk) 18:29, 11 November 2016 (UTC)

What's the name of the star?

This evening at 8:00, in the US Central time zone, I noticed (from right to left) (if I have them right) Venus, Mars, and Jupiter in a straight line pointing to a very bright star, which from my point of view was in the northeast. Which one was it? PS: the local weatherman pointed out the conjunction a few nights ago. The question is asked in good faith. --Halcatalyst (talk) 03:57, 11 November 2016 (UTC)

According to software, starting closet to the Sun are Mercury, Saturn, Venus, and Mars, but Mercury it probably too close to the Sun to see. But I don't see them pointing at a bright star. Bright stars Altair and Vega are to the north of Mars. Bubba73 ^{You talkin' to me?} 04:17, 11 November 2016 (UTC)

Not sure you are correctly recognizing planets. The most obvious bright star in the northeast at 8 PM right now is Capella. If you can recognize the Pleiades, Capella will be pretty much directly north of them. Looie496 (talk) 05:12, 11 November 2016 (UTC)

Were those planets right on the horizon? They are indeed in a line at the moment, but that's where you'd see them 8pm in the US right now. From the more northern states, you wouldn't even see Venus and Jupiter if I'm reading these star charts correctly. Someguy1221 (talk) 08:09, 11 November 2016 (UTC)

Your timezone doesn't matter. It's designed to compensate for your longitude. Your lattitude does matter. From where I live, at about 52° north, I can just see Mars in the evening very low in the sky. That is, on the rare nights when it isn't cloudy. Mercury, Saturn and Venus are in the evening sky too and visible if you're far enough south, although I think Mercury is too close to the sun. All of them are in the southwest if you're on the northern hemisphere (northwest if you're on the southern hemisphere). Jupiter only rises in the early morning in the east. In the evening no planets are visible in the northeast.

Try using some planetarium software and see for yourself. Stellarium is good and free/open source. PiusImpavidus (talk) 10:21, 11 November 2016 (UTC)

Timezones do matter. They're about an hour wide. That's the difference between pretty dark and daytime. Sagittarian Milky Way (talk) 17:03, 11 November 2016 (UTC)

The relevant question is not "what time zone are you in" (unless it's a very quick-moving object) but "where are you relative to the reference meridian for whatever time standard you're using". —Tamfang (talk) 01:26, 12 November 2016 (UTC)

It's also possible you saw a satellite reflecting sunlight. See Iridium flare. StuRat (talk)

Those last roughly 10 seconds. Bubba73 ^{You talkin' to me?} 03:43, 12 November 2016 (UTC)

What is the most polluted?

Hi all,

I'm from France and I've lived in several cities there and other countries. I live now in Davao, Philippines. It's also a city but it's surrounded by the sea and the province side (with a huge quantity of trees). The problem is that the city is filled with old diesel vehicles and I really cannot breath normally every time I walk in a street. Local people seem to have get used to it.

My question is: What is the healthiest place? A city (like Europe) which seemed to be not that polluted (but with almost no forests around and many plants, factories and industrial centers within a few kilometers) or a city like Davao located very near the see and surrounded by green (but filled with polluting vehicles)? Thank you very much for your help! Ericdec85 (talk) 04:46, 11 November 2016 (UTC)

I've been in this place a few times, the air here is very clean especially if you move a bit away from the town. Count Iblis (talk) 04:51, 11 November 2016 (UTC)

Not sure if you are referring to the most polluted place in Europe, but worldwide, I would say it would be in Bhutan. The place is a carbon sink, which emits 2.2 million tons of Carbon Dioxide but absorbs 4 million tons a year.[2] JoshMuirWikipedia (talk) 04:54, 11 November 2016 (UTC)

So to clarify, Ericdec85, your question is whether it is healthier to live (1) in an industrialized urban area with little pollution or (2) in a more polluted area with lots of greenery and that is close to the sea. Other things being equal, it is certainly healthier to live where there is less pollution. Air pollution has a marked effect on life expectancy. For example, this study found that a decrease of 10 µg/m3 in the concentration of fine particulate matter (PM2.5) was associated with an increase in mean life expectancy of 0.35 years. In contrast, people living in urban areas with low pollution often are quite healthy. As our list of countries by life expectancy shows, the longest life expectancy in the world is in Japan, much of which is quite urban. John M Baker (talk) 16:04, 11 November 2016 (UTC)

To add to this, while trees can help to remove air pollution, it doesn't make sense to decide that a place with trees must have cleaner air, when we can just measure the air pollution directly. As for psychological benefits of living closer to nature, visiting a park on a regular basis can do quite a bit of good, as can raising plants (and maybe some animals) in your own home. StuRat (talk) 16:13, 11 November 2016 (UTC)

Retinal Scan

My father is 67 years old. Recently he had stored Retinal scan.

If, in future he suffers from cataract, then will the retina scan data be access granted or it will show access denied. — Preceding unsigned comment added by Jonathan T45 (talk • contribs) 09:01, 11 November 2016 (UTC)

Without knowing which country you are in, it is impossible to say what the rule would be - though it usually comes down to whether the person concerned consented to such information being shared. However, it is irrelevant as a retinal scan has absolutely no relevance to cataracts, which are a condition of the lens, not the retina. Wymspen (talk) 09:32, 11 November 2016 (UTC)

I think OP is not interested in who has access to the retinal scan. Rather, I think they are interested in whether a cataract would interfere with use of the retinal scan as a biometric used for access control. Perhaps they can clarify. Here [3] is a slightly related article about how cataracts and cataract surgery affect iris scan technology, I have not found anything comparable for retina scan. SemanticMantis (talk) 15:47, 11 November 2016 (UTC)

"Tumbling in Orbit"

Moved from Wikipedia:Reference desk/Humanities § "Tumbling in Orbit"

 – ―Mandruss ☎ 14:48, 11 November 2016 (UTC)

Back in February of this year, North Korea launched a satellite that was described as 'tumbling in orbit'. I am not a science-kinda-guy, so can anyone more intelligent than me explain: What does a satellite 'tumbling in orbit' mean, and what exactly is that North Korean satellite trying to achieve if it is 'tumbling in orbit'? --PolicyJak (talk) 11:27, 11 November 2016 (UTC)

See [4]. The phrase means that the satellite is out of control and cannot function. However, stabilisation is sometimes possible. 80.44.161.39 (talk) 11:50, 11 November 2016 (UTC)

• To be useful, a satellite has to be oriented so its antennas, cameras etc are pointing in the right direction. This is usually done with gyroscopes (Three-axis stabilization) or by spin-stabilisation (spinning the satellite like a rifle bullet). If the stabilization goes wrong, the satellite starts to tumble, and this can be very difficult to correct - it takes extremely precise maneuvering to get it back into position, and it's very hard to actually measure how the satellite is spinning from the ground - plus if it's tumbling, its antennas may not be pointing at yours anyway! Smurrayinchester 16:19, 11 November 2016 (UTC)

A satellite will normally need to have various devices pointed in specific directions. If it has solar panels (as opposed to nuclear power), they need to point towards the Sun. A communications antenna needs to point back to Earth, and, in the case of low-Earth orbit, needs to point towards a specific ground station (a communications satellite will have more such antennas pointed in various directions). They may also have various telescopes in the visible light spectrum or others, which need to be pointed towards the object they are studying, whether on Earth or in space. So, to have all these devices pointed toward their targets, it's critical that the satellite itself be stable, which typically means one rotation per orbit, always leaving one side towards Earth. This minimizes the amount of moving of the various devices, although it's not possible to eliminate all of the movement, with the possible exception of a geosynchronous orbit satellite which uses nuclear power, as then it stays above one spot on the Earth and doesn't have solar panels to move to track the Sun. StuRat (talk) 16:28, 11 November 2016 (UTC)

An actual video of a tumbling satellite (not this one) is here. I should add that I failed to find an illustration of a cylinder tumbling in zero gee aboard the space station. But I remember seeing that if you have an object that has a long axis and is rotating on another axis, sometimes the pattern of tumbling can look really confusing! Wnt (talk) 18:17, 11 November 2016 (UTC)

x-ray or ultrasound

Both technologies produce internal images of the body, however for what purpose do physicians use the one or the other? How are the images different? — Preceding unsigned comment added by 83.49.224.251 (talk) 15:12, 11 November 2016 (UTC)

There are many similarities and many differences, and even an overview of these would take some time to present. X-ray is our article about the physical thing, while medical radiography is about the use of x-rays in medical imaging. Ultrasound is also about the acoustic thing, and medical ultrasound is about the medical imaging. I'd suggest having a look at the articles relevant to medical imaging, and coming back with a more specific question if something there is unclear. SemanticMantis (talk) 15:51, 11 November 2016 (UTC)

X-rays are better suited to view hard objects, like bones, teeth, and many foreign objects, such as bullets and swallowed coins. Ultrasound is better suited to study soft tissue, such as a developing fetus. StuRat (talk) 16:32, 11 November 2016 (UTC)

"[ Medical ultrasound ] images muscle, soft tissue, and bone surfaces very well." Also, angiography is a type of X-ray imaging that is used for soft tissue. SemanticMantis (talk) 20:06, 11 November 2016 (UTC)

The x-ray showed the dime the child had swallowed clearly, and the doctors decided to keep him in the hospital until it "passed naturally". When asked the next day for a status update, the nurse replied "No change yet". :-) StuRat (talk) 16:34, 11 November 2016 (UTC)

Feynman Lectures. Lecture 34. Ch. 34–6 [5]

Feynman writes Lorentz transformation in form ${\begin{aligned}x'&={\frac {x+vt}{\sqrt {1-v^{2}/c^{2}}}},&&\quad x&&={\frac {x'-vt'}{\sqrt {1-v^{2}/c^{2}}}},\\[1ex]t'&={\frac {t+vx/c^{2}}{\sqrt {1-v^{2}/c^{2}}}},&&\quad t&&={\frac {t'-vx'/c^{2}}{\sqrt {1-v^{2}/c^{2}}}}.\end{aligned}}$

Does sign matter? It seems sing inverted as compared with Lecture 16 Lecture 16. Feynman uses this version of sings to derive formula for frequency for man moving toward the source of light. X-axes of both men are directed to the source, aren't they? Username160611000000 (talk) 16:10, 11 November 2016 (UTC)

Meta-discussion
The following discussion has been closed. Please do not modify it.
I am going to assume that you are not trolling; if I'm wrong, please stop. Wikipedia's Reference Desk is not an "Ask-an-Expert" site. If it were, responders would be expected to provide credentials in their areas of expertise, and we have no mechanism to do that. What we do here is attempt to find your answer in authoritative sources, summarize it for you, and point you to where you can find more information. I don't think your question is one that can be answered in that manner, so I suggest you try elsewhere on the Web. ―Mandruss ☎ 17:15, 11 November 2016 (UTC) I don't like the harsh response. These Feynman questions *are* a resource; the Feynman Lectures are a great public resource for learning physics and it's worth having some things about them. That said, if you're planning to generate a lot more such questions, it might be better to take a more dedicated approach, i.e. to write a Wikiversity course or a Wikibooks study guide to Feynman, and try to recruit a pool of physics folks to go through systematically. Wnt (talk) 17:32, 11 November 2016 (UTC) @Mandruss: First question was asked in Talk page [6]. Then the advice was gotten: Remove talk page chat per wp:TPG. Place to go is wp:Reference desk/science. (TW)). Besides people, who write articles are competent, because articles contain lot of text without citations of authorities. Username160611000000 (talk) 10:33, 13 November 2016 (UTC) Thank you for the link. I certainly don't blame you for following what I consider to be bad advice. Wnt appears to know what he's talking about on this advanced subject, and he probably does. However, as a matter of policy, I feel it's unwise to assume that a responder knows what he's talking about simply because he sounds convincing. Humans are flawed beings and there is low correlation between confidence and competence. It is very hard to know what one does not know, to know the limits of one's knowledge, so we can be simultaneously certain and wrong, and often are. Also, facts are facts and are not subject to debate and consensus. That's why we either need credentials, which we can't do as I said, or we need to refrain from offering our personal "knowledge" and use only external authoritative sources. This has been a festering issue for many years, and the community has yet to confront it and resolve it once and for all. So disagreements like this one will continue to consume some of our valuable time forever. ―Mandruss ☎ 10:42, 13 November 2016 (UTC) Responders have already helped the OP understand the lectures and they have also referred the OP to other related resources that might be helpful to them too. And since the lectures cover many topics it's not surprising they are back to possibly gain more insights and additional resources. In other words, your condemnation is misplaced and disruptive. --Modocc (talk) 12:58, 13 November 2016 (UTC) @Modocc: Spare me please. You're entitled to your opinion that my "condemnation", as you mischaracterize my good faith comments, is misplaced. I invite you to show exactly how they are "disruptive" to the project. Be careful how you throw around such confrontational pejoratives with an editor who has been around long enough not to be too impressed by that kind of talk. ―Mandruss ☎ 13:11, 13 November 2016 (UTC) You told the OP to look elsewhere. For them and us to go away and not work out such questions because we cannot be credentialed. You are attempting to censor, so the shoe fits. You can lead us to water perhaps, but you cannot make us drink the poison. --Modocc (talk) 13:19, 13 November 2016 (UTC) Incorrect on multiple counts. I did not tell anyone to do anything. I stated an opinion/viewpoint and offered a suggestion, which the OP chose not to take, and that was fine with me. In fact, I was out of this thread until the OP pinged me at 10:33. Kindly point to where I told someone to "go away" or attempted to censor. You are distorting the truth and being hyperbolic and argumentative. I am allowed to state a reasoned and respectful viewpoint here whether you like it or not. If anyone is attempting to suppress something here, it's you, and I'm not buying. ―Mandruss ☎ 13:28, 13 November 2016 (UTC) If you continue to insert your unproductive "advice" which is unrelated to actually answering the OPs questions I will ask that you be censured from disrupting this board again. --Modocc (talk) 13:36, 13 November 2016 (UTC) Well go right ahead and ask. I will continue to state my opinions where I see fit. ―Mandruss ☎ 13:38, 13 November 2016 (UTC) @Mandruss:You stated that "I did not tell anyone to do anything." Really? You said "I am going to assume that you are not trolling; if I'm wrong, please stop." No, you shouldn't be telling the OP to stop, advising them to go elsewhere or stopping whatever you disapprove of with their questions. On the contrary, they should continue posting their questions here if they so choose, thus this nonsense is best hatted. --Modocc (talk) 20:20, 13 November 2016 (UTC)

As far as I can see, the sign of these equations is swapped by reversing which variable is x and which is x'. And the principle of relativity is that x and x' are both valid perspectives. Or you can be measuring x in the opposite direction. There's not much to see here. Wnt (talk) 17:32, 11 November 2016 (UTC)

Frequency must be greater for man who moves toward the source (it's the fact from an experiment). Suppose x-axis and x'-axis are directed toward the source, in non-primed reference frame the man and the source are at rest, primed reference frame is moving toward the source. Then Lorentz transformation will be $x={\tfrac {x'+vt'}{\sqrt {1-v^{2}/c^{2}}}}...$

Putting them to $\cos \,(\omega t-kx)=...$ we get $\omega '={\tfrac {\omega -kv}{\sqrt {1-v^{2}/c^{2}}}}$. Frequency decreases!

So sign does matter.Username160611000000 (talk) 19:50, 11 November 2016 (UTC)

What happens if I quit taking sertraline in a "cold turkey" way?

Corncaking (talk) 18:26, 11 November 2016 (UTC)

We cannot provide medical advice here. Drugs.com may be an option. General Ization ^Talk 18:30, 11 November 2016 (UTC)

Indeed. Nobody can say what will happen for any individual case. OP should contact the prescribing physician for further information regarding their personal use of any prescriptions drugs.

We can, however, provide references on known withdrawal symptoms of Zoloft/ Sertraline. Our coverage on Wikipedia is at Antidepressant discontinuation syndrome. For additional info, here's one magazine article [7], here are a few relevant scholarly articles that discuss symptoms of withdrawal from sertraline [8] [9]. SemanticMantis (talk) 20:18, 11 November 2016 (UTC)

The effects of going off any medication are going to depend on the severity of the condition and the size of the dosage, among other things. Even if we were allowed to answer medical questions, we couldn't answer yours. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:55, 11 November 2016 (UTC)

I went off my homeopathic treatment totally cold turkey, and did not feel crushed. That's a further advantage of it.--Llaanngg (talk) 00:23, 12 November 2016 (UTC)

I prefer such a small amount of homeopathic treatment that there aren't any molecules of it at all. In other words, I skip it entirely. :-) StuRat (talk) 04:30, 12 November 2016 (UTC)

One good thing about homeopathic remedies is that they don't interact with any medicines. Bubba73 ^{You talkin' to me?} 04:33, 12 November 2016 (UTC)

Placebos can have nontrivial effects "However, in another group of subjects, when sham O(2) was delivered after 2 previous exposures to O(2) (O(2) preconditioning), it decreased fatigue, post-exercise headache, HR, and PGE(2), yet without any increase in SO(2). " Count Iblis (talk) 00:35, 13 November 2016 (UTC)

@Corncaking: This is doubtless a breach of some kind of "ethics" around here, but I'm going to quote NAMI here:

What is the most important information I should know about Sertraline?

Do not stop taking sertraline, even when you feel better. Only your healthcare provider can determine the length of treatment that is right for you.

Missing doses of sertraline may increase your risk for relapse in your symptoms.

Stopping sertraline abruptly may result in one or more of the following withdrawal symptoms: irritability, nausea, feeling dizzy, vomiting, nightmares, headache, and/or paresthesias (prickling, tingling sensation on the skin)...

Wnt (talk) 17:23, 12 November 2016 (UTC)

In short, see a doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:51, 12 November 2016 (UTC)

Testing of water for fecal coliform bacteria

Is there an easy way of testing water (for swimming, not drinking) for the presence of fecal coliform bacteria? Something that you can dip into a water sample, obtained from a lake where you intend to swim, to discover whether it's contaminated? --Hofhof (talk) 18:43, 11 November 2016 (UTC)

Hofhof test kits for coliforms in water are widely available, a google search for coliform test kit will deliver several retailers that sell them in most developed countries and even several developing ones. Roger (Dodger67) (talk) 20:27, 11 November 2016 (UTC)

All lake water is likely to contain some contamination, but the test kit will determine whether there is serious contamination. Dbfirs 20:38, 11 November 2016 (UTC)

It's usually the Escherichia coli bacteria that are tested for, with a typical upper limit for beaches being in the region of 400 to 900 bacteria per litre, though for casual swimming an E-coli count of 2000 or even 4000 per litre can often be considered acceptable. In some countries, people swim in water having a much higher bacterial content. Dbfirs 10:52, 12 November 2016 (UTC)