Wikipedia:Reference desk/Archives/Science/2018 March 4

= March 4 =

Metronidazole
Is metronidazole effective against Staphylococcus aureus or streptococcus pyogenes?--User777123 (talk) 05:46, 4 March 2018 (UTC)
 * We can't give medical advice but you might try a web search. Better yet, ask your doctor.  Be aware of the widespread existence of MRSA in some environments, so any particular case might be resistant to whatever. 173.228.123.121 (talk) 09:59, 4 March 2018 (UTC)
 * Would MRSA be resistant to malacidins too??? 2601:646:8E01:7E0B:59E2:B6:A6B8:FAC7 (talk) 10:16, 4 March 2018 (UTC)
 * Did you read the article you linked to? It seems to answer the general case, bearing in mind they are very recently discovered. Nil Einne (talk) 10:41, 4 March 2018 (UTC)
 * This was a rhetorical question, in response to the statement that MRSA is "resistant to whatever". 2601:646:8E01:7E0B:59E2:B6:A6B8:FAC7 (talk) 03:42, 5 March 2018 (UTC)
 * But malacidins are not yet a functional antibiotic for humans. Actually they're a long way off it. Staphylococcus aureus and Streptococcus pyogenes probably aren't resistant to to 100000K temperatures either. The relevance of this to either the OP question, or 173's point is unclear even if 100000K is technically 'whatever'. Maybe 'whatever' was poorly expressed, still the point is a relevant one. If you did want to nitpick, a much more relevant issue is that MRSA only describes one type of drug resistance namely to beta-lactam antibiotics of which metronidazole is not. The OP's basic point namely that any particular bacteria could be resistant to Metronidazole, or whatever other antibiotic you throw at them, even if that species of bacteria is normally susceptible is still right. But there's no reason to assume MRSA are going to be. Nil Einne (talk) 08:54, 5 March 2018 (UTC)
 * I wonder about the current state of teixobactin. There were some clinical trials announced a few years ago but a quick web search doesn't turn up any news since then.  The isolation chip was touted as a means of high-volume discovery of lots of new drugs but I haven't heard anything more coming out of that either. 173.228.123.121 (talk) 17:28, 4 March 2018 (UTC)
 * Are you sure? Our article suggests the discovery was only announced in 2015. It seems very unlikely that there would be clinical trials announced 'a few years ago' or frankly even 3 years from now given that. This from 2017 and this also from 2017 [//www.sciencedirect.com/science/article/pii/S0006295216303082] also support that view. The last source BTW has info on antibiotics that are in a late stage of development. The most I find from searching is insanely optimistic predictions of clinical trials in a couple of years when it was announced in 2015, which suggests whoever said either had no idea how drug development works, or was just trying to get headlines and didn't care that what they were saying was nonsense. (Not surprisingly, it still remained 'a couple of years' away in media reports in late 2016 [//www.reuters.com/investigates/special-report/usa-uncounted-drugs/].) Meanwhile in the real world less than a month ago, a company [//www.novobiotic.com/news/] is announcing they got $3 million for 3 years for pre-clinical development. Nil Einne (talk) 08:32, 5 March 2018 (UTC)


 * Metronidazole is not effective against aerobic bacteria like Staphylococcus aureus or streptococcus pyogenes. Ruslik_ Zero 20:41, 4 March 2018 (UTC)

regarding LS coupling vs jj coupling
In very heavy atoms (e.g., Hg), LS coupling dominates over the interactions between Ls & Ss momenta, leading to the change in the way they are summed up to obtain their resultant. Namely, instead of combining individual L & S seperately 1st, followed by combining the total L & total S to get J, we combine each individual pair of L & Ss, and then getting J by combining the respective sums of Ls & Ss. My question is why the way we join up the momentum vectors depends on what interaction takes over, and how. I've some more questions with respect to this issue, subtler ones, but they'll wait to later. בנצי (talk) 12:50, 4 March 2018 (UTC)
 * It depends on the strength of spin-orbit interaction: if it is weak as in light atoms then use LS coupling if it is strong as in heavy atoms then use jj-coupling. Ruslik_ Zero 20:53, 6 March 2018 (UTC)
 * I know that - it shows clearly from the content of my question, with details. What I'm asking is why the domination dictates the way we add together the angular momenta ? In other words, why, e.g., in the case of light atoms, we have to add all the Ls & all the Ss respectively, and then combine the totals of L & S ? It is to do with the the stronger electric interaction between the various Ls & the various Ss respectively, than the magnetic interaction between Ls and Ss. BUT WHAT'S THE REASON THIS ORDER OF SUMMING UP (as an instance) IS RELATED TO STRONGER LS COUPLING ? בנצי (talk) 12:30, 7 March 2018 (UTC)

Objects with their full atom components list
I'm looking for a list of some everyday life things which are solid and visible microscopically (such as stone, sand, etc.) and to know what atoms they are made of. I found a list of salt or glucose or other fluid substances and I'd like to use more common or solid things. 93.126.116.89 (talk) 15:20, 4 March 2018 (UTC)
 * Sucrose. --OuroborosCobra (talk) 16:23, 4 March 2018 (UTC)


 * Most of these things are mixtures, and could be a variety of different substances. Sand is mostly made from quartz, and if you look at that article you will see it is made of silicon and oxygen. Yellow sand often contains feldspar, which is more complicated, with silicon and oxygen, and also aluminium, potassium, sodium, and calcium. But some sand is made from broken coral or shells, and then is calcium carbonate, with ... calcium and carbon and oxygen. So it is quite different. A common theme though is that they contain oxygen. Rocks also contain similar kinds of atoms. Darker rocks like basalt might contain Pyroxene, Amphibole, or olivine which also contain magnesium and iron. You may also be interested in Abundance of the chemical elements which asks the other direction, how much of each kind of atom is there in different things. Graeme Bartlett (talk) 22:29, 4 March 2018 (UTC)


 * At what tolerances? Parts per million?  Parts per billion?  Parts per trillion?  Nothing you run into is scrupulously pure; so you need to say "what is the lower limit where I'm going to consider some impurity insignificant?"  -- Jayron 32 23:43, 4 March 2018 (UTC)

"Neutral" oils
In the first sentence of the oil article, the word "neutral" is used to describe oils in general, as though it was a defining characteristic. What does this mean? Does it have any scientific meaning?

If not, we should take it out. -- The Anome (talk) 15:51, 4 March 2018 (UTC)
 * I think it means that it's not an acid or a base. I.e. the pH is 7 (neutral).  173.228.123.121 (talk) 17:00, 4 March 2018 (UTC)


 * There's no inherent reason that oils need to be pH neutral, their side chains can have varying pKas. Also, it's not very relevant to describe the acid or base neutrality of oils, since that only comes into play if they are in a solution with water. --OuroborosCobra (talk) 17:12, 4 March 2018 (UTC)


 * That's what I thought. I will take the word "neutral" out. -- The Anome (talk) 17:14, 4 March 2018 (UTC)
 * I'd guess maybe neutrally charged? --OuroborosCobra (talk) 00:16, 5 March 2018 (UTC)
 * I also took it to mean neutrally charged. Perhaps this is meant to disclude lipid sulfates and the like. Someguy1221 (talk) 01:51, 5 March 2018 (UTC)
 * Or soaps. --OuroborosCobra (talk) 06:01, 5 March 2018 (UTC)
 * The article also says non-polar though. Nil Einne (talk) 08:06, 5 March 2018 (UTC)
 * The Anome, It sounds like there still might be something to this. I suggest bringing the issue up on the article talk page.  173.228.123.121 (talk) 19:33, 5 March 2018 (UTC)