Science desk
< October 16	<< Sep \| October \| Nov >>	October 18 >

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.

October 17

Kilonova and superheavy elements

The kilonova from neutron star merger was just announced on Monday as part of gravitational wave detection. I read the article on astronomy.com and said the kilonova produced Earth masses worth of gold, platinum and uranium, which are superheavy elements. It makes me think if the neutron star merger could also produce transactinide elements or even transoganesson elements like moscovium (element 115) and feynmanium (element 137). Based on the amount of gold being produced in that kilonova at over 10 Earth masses, it could produce asteroid-mass worth of moscovium for example. You will strike me gold if you think so. Planet Star 00:16, 17 October 2017 (UTC)[reply]

Some points:

1) Those huge masses are likely mixed in with even huger masses of "junk" elements, so it's not like there will be solid gold planets spit out. After all, there's enough gold in seawater to pave the streets with gold, but it's diluted by a huge amount of water, etc., and hence useless to us.

2) Isotopes of moscovium lists all half-lives less than a second, so I wouldn't expect any to be left, say, a day after the event.

3) Island of stability might mean there are some stable heavy elements created by such an event. If so, this could be quite interesting. We should look for their atomic spectra in light coming from the event. StuRat (talk) 01:27, 17 October 2017 (UTC)[reply]

There are likely more stable isotopes of moscovium with more neutrons than the ones we know. As for looking for their atomic spectra: this is a bit difficult considering that we do not currently know what they are, though there have been some theoretical calculations, such as this one for copernicium. Double sharp (talk) 10:26, 18 October 2017 (UTC)[reply]

Nucleosynthesis#Explosive nucleosynthesis is a good start for your reading, I would then follow the links from there for more details on various questions you may have. --Jayron 32 01:30, 17 October 2017 (UTC)[reply]

Pretty much anything that can exist, would be expected to be created in some quantity in such events. However, as a general rule the superheavy elements are also very unstable. Many will radioactively decay within very short periods of time, preventing them from being seen or used elsewhere. Dragons flight (talk) 11:16, 17 October 2017 (UTC)[reply]

This article in Sky and Telescope magazine addresses some of these issues. The section Striking gold includes a periodic table coded to show what elements are made in what cosmic events, including merging neutron stars: unfortunately, it doesnt go beyond Uranium. {The poster formerly known as 87.81.230.195} 94.0.129.189 (talk) 10:12, 18 October 2017 (UTC)[reply]

You might want to consider that:

(1) there is a "cycling factor" in the r-process, since if a nucleus doesn't capture enough neutrons after A = 209, it will simply decay back to Pb and Bi; and the same thing happens right after A = 238, with nuclei decaying back to Th and U, so that the shorter-lived superheavies would get depleted;

(2) neutron capture, especially high-energy neutron capture, above A = 209 has a tendency to result in fission instead of continuing up the neutron drip line.

Both of these will cut your yield of superheavies severely. Assuming a generous half-life of about a millennium for the superheavy isotopes produced, the amount you find has been calculated to only about 10⁻¹² times that of the Pb produced. Double sharp (talk) 10:29, 18 October 2017 (UTC)[reply]

Moving from warfarin to heparin + surgery

Why would a surgeon move a patient from heparin from warfarin (which was the usual treatment) pre and post surgery? As far as I know, both would increase bleeding (and also work as blood thinners).--Dikipewia (talk) 00:37, 17 October 2017 (UTC)[reply]

The patient should ask. If the doctor can't give a good reason, it might be good to get a 2nd opinion. I've seen doctors change meds "for no apparent reason" way too often. Any change in medication should be discussed with the patient, and a reason given. I wonder if there's a "patient bill of rights" item somewhere that lists "The patient has the right to be informed of any change in medication, given a reason for the change, and refuse the change, if they so choose".StuRat (talk) 01:19, 17 October 2017 (UTC)[reply]

It's not a real ongoing case. It just appear to be normal praxis, see [[1]]. I just want to know the rationale behind this.--Dikipewia (talk) 01:48, 17 October 2017 (UTC)[reply]

Did you mean "praxis" or "practice" ? StuRat (talk) 02:05, 17 October 2017 (UTC)[reply]

Yes. Indeed.Dikipewia (talk) 15:24, 17 October 2017 (UTC)[reply]

Warfarin is generally discontinued for surgery due to the bleeding risk. There is a lot of literature about "bridging" the period when warfarin is discontinued with heparin or other anticoagulants. One fairly recent study [2] of atrial fibrillation patients was of the opinion it was unnecessary to have any anticoagulant. But this is a big topic and it would really take a lot more effort than I'm willing to give it to see how general and agreed-upon that conclusion actually is. Wnt (talk) 11:39, 17 October 2017 (UTC)[reply]

I know that some doctors are against or don't see the necessity of this bridging treatment.

However if they choose a bridging mechanism, why would another anticoagulant be different? During a surgery, what makes the anticoagulant warfarin unsafe and the anticoagulant heparin safe? Both seem to act in the same way, a blood thinners that reduce coagulation to avoid blood clots. Wouldn't this imply that both increase bleeding risk? Dikipewia (talk) 15:24, 17 October 2017 (UTC)[reply]

Warfarin is a vitamin K antagonist while heparin activates antithrombin on binding. Warfarin's effect should be more long lasting (I think) and heparin's can rapidly be reversed with protamine sulfate. Again, this is an area where a great deal is known but I don't know much at all, but I think this is at least part of the answer. Wnt (talk) 19:58, 17 October 2017 (UTC)[reply]

The actual issue is that heparin acts immediately, and when it is stopped, normal clotting returns quickly. It takes much longer for coumadin's anticoagulant effect to start working (full effect in about 3-7 days) because it acts on the liver to inhibit synthesis of clotting proteins. It therefore has a delayed onset of action (you have to wait for the clotting protein synthesis to decrease before it starts to work) and it also continues to work for a while after you stop taking it, until the proteins are synthesized by the liver again). So if you want to turn off anticoagulation during surgery, and then turn it on quickly after surgery, you would prefer heparin, where you're interfering with existing circulating coagulation proteins rather than decreasing the amount of coagulation proteins. - Nunh-huh 06:48, 19 October 2017 (UTC)[reply]

Clean air in the UK

Is it just a question of cars? Couldn't it be that the air on a really small place is contaminated by a local industry? Could that be more unhealthy than London?--Hofhof (talk) 00:53, 17 October 2017 (UTC)[reply]

See air pollution in the United Kingdom. Unfortunately, that doesn't seem to consider any source other than vehicles. Here's a more even treatment of the source, but alas a bit dated (2001): [3]. Note that vehicles are somewhat unique in that they pollute most where the most people are, whereas factories or power stations can be located where the prevailing winds will blow the smoke clear of the cities. StuRat (talk) 00:55, 17 October 2017 (UTC)[reply]

There are many sources of air pollution. Historically, London had life-threatening pollution ("killer fogs", mostly from coal fires) prior to the advent of automobiles. As otehr sources were addressed, car pollution became relatively more important. Modern monitoring methods do a fairly good job of identifying sources, -Arch dude (talk) 00:58, 17 October 2017 (UTC)[reply]

But the question remains: air pollution monitoring covers things like nitrogen dioxide and ozone. But what if I'm close to a chemical plant. Could this chemical plant contaminate more than anything that you find in London?--Hofhof (talk) 01:07, 17 October 2017 (UTC)[reply]

A UK chemical plant shouldn't release many chemicals into the air normally, due to regulations, but there's always the risk of a Bhopal disaster event. StuRat (talk) 01:17, 17 October 2017 (UTC)[reply]

"Shouldn't" is not an exact synonym for "doesn't", mind you. --Jayron 32 01:27, 17 October 2017 (UTC)[reply]

List of active coal fired power stations in the United Kingdom does show they are rapidly reducing reliance on this dirty energy source. StuRat (talk) 01:17, 17 October 2017 (UTC)[reply]

Thats why there are so many record high Chimneys in industrial areas! As long as anyone pollutes in a save distance from any detector, nature, livestock or human population, they can "contaminated" almost as much as they want without direct, local consequences. Cars emit right where they are, so there are direct, local consequences. --Kharon (talk) 01:40, 17 October 2017 (UTC)[reply]

"The Government announced in November 2015 that the UK will phase out coal-fired power generation by 2025" UK COAL PLANT CLOSURES - A STRUCTURAL SHIFT AWAY FROM COAL. Alansplodge (talk) 12:53, 17 October 2017 (UTC)[reply]

The mayor of London has recently called for a ban on domestic wood-burning stoves - [4] - and there have been concerns about the amount of methane produced by cows - [5]. Pollution is a highly complex issue, with no easy answers. Wymspen (talk) 10:21, 17 October 2017 (UTC)[reply]

Stand next to a wood burning grill and you are breathing more dangerous particulates than you would ever encounter in normal London air. So, yes, local pollution can be intense. However, humans rarely spend much time near intense pollution sources (e.g. wood fires) but many people breathe city air all the time, so the cumulative effect of the latter is often more important. Beyond a certain scale, all industries have regulations for the quantity and type of pollutants they can legally emit into the air. Often there are inspections to show that they have the right kind of mitigation procedures (e.g. the right type of burners, smokestacks, etc.) to mitigate any expected air pollution. For very large scale industries there is also routine monitoring of local air quality. Power plants and industrial activity are a source of air pollution in the UK. (So is agriculture, for some pollutants like ammonia.) However, cars get a lot of attention in the UK because they are a major source of pollution, and they operate in close proximity to people. The growth of relatively more-polluting small diesel engines (roughly 50% of UK transport) and the relatively less stringent emissions standards (compared to, for example, the US) has made air pollution from the transportation sector a more prominent problem in the UK than in most other developed countries. Dragons flight (talk) 11:09, 17 October 2017 (UTC)[reply]

The Department for Environment, Food and Rural Affairs web page, Causes of air pollution , says that "In all except worst-case situations, industrial and domestic pollutant sources, together with their impact on air quality, tend to be steady or improving over time. However, traffic pollution problems are worsening world-wide". A more detailed breakdown linked from that page is What are the causes of air Pollution. Alansplodge (talk) 12:47, 17 October 2017 (UTC)[reply]

One of the issues to consider here is the difference (in modern terms) between Point source pollution and non-point-source pollution. Point source pollution means "We can identify a single source for where this pollution is coming from". Of course, with zero environmental controls you get runaway pollution regardless (such as with the Great Stink, or modern Beijing). If you want to introduce controls, the easiest target is where it is most concentrated: individual industrial sources and power plants. What remains is all of the small pollution sources which add up to a lot. One "scrubber" can clean a LOT of pollution out of a fossil-fuel smoke stack, where the released pollution can all be captured, but put 10,000 cars on the road for a year and you may end up generating just as much pollution as that one stack used to. Stopping each one of those cars from polluting is a lot harder of a logistical problem, and why in modern, developed countries automobile traffic is considered the biggest issue: the former "large single industrial polluter" problem has largely been solved (for a certain definition of "solved"), but the problem of all those cars continues to be an issue. This page looks at one factor (CO2 emissions) in one place (California), but the issues in any developed country are likely similar: It reports that 58% of pollution comes from road transport. To solve pollution most effectively that is the issue to fix, but to get at that problem is not as simple as "clean up a few power plants" it's "install effective public transportation" and "better city planning" and "get people to buy electric cars". Those are MUCH more daunting problems. --Jayron 32 12:32, 18 October 2017 (UTC)[reply]

Voltage drop

I am experimenting with conductive ink, which I applied to a strip, at the ends of which I placed terminals (nuts and bolts) and I measure a resistance of about 45 Ω over those terminals. But I also want to measure the voltage drop at different points.
So I stacked two 3 V batteries, resulting in about 6.5 V. When I connect two copper wires to the poles I measure a slightly lower voltage at the other ends of those wires. But then when I connect those ends to the terminals I measure only 0.37 V over the terminals. That is about 1/20 of what it should be.
If I place the leads of the multimeter further in, I get an increasingly lower voltage, which is as expected (the voltage drop), but the initial voltage just can't be right, can it?
To make sure, I measured the resistance over a terminal, but that is 0.2 Ω or less. And the wires are well connected to the terminals (a firm pull doesn't pull the wires out). So what may cause this? DirkvdM (talk) 15:55, 17 October 2017 (UTC)[reply]

This would be much simpler with a diagram, because while I think I understood it (and find it as puzzling as you) I may have missed something; or better yet, a photograph. The best guess I have that matches all the symptoms is that one of the copper wires, or its connection with the battery, has a resistance ~ 10kΩ, but that sounds unlikely (this is too low for a broken cable or faulty connection). You could try measuring the resistance of those.

BTW: if you do any kind of experiment, take a lot of photographs - do not spend time choosing good angles/lighting or sorting them out afterwards, just take tons of crappy shots with your cell phone and dump in into a date-named folder on a hard drive. In this day and age it is pretty much free to do that, and once in a blue moon you will be able to retrieve the one photograph from two years ago that shows a crucial point of the setup that you did not realize was crucial back then. This is of course in addition to keeping a lab book, but the amount of lab-book writing required to capture as much information is just enormous. Tigraan^{Click here to contact me} 16:12, 17 October 2017 (UTC)[reply]

You should check the voltage of the pair of batteries when connected. If it is still 6.5 V, then measure the voltage drop on your power supply wires. There could be a problem in those wires. If the voltage from the battery pair is very low it could mean that the battery is flat, or has a very high internal resistance. Or perhaps they are connected back to front. Graeme Bartlett (talk) 21:11, 17 October 2017 (UTC)[reply]

Ah, I think I found the cause. It appears to indeed be internal resistance.
Yesterday, after I disconnected the wires, the voltage over the battery stack was a lot less than what it was at first, just over 3 V if I remember correctly. So the low resistance of the condcutive ink (45 Ω) was a huge drain on the batteries. But this morning it was 6.12 V. So the batteries had drained a bit overall, but during the experiment the 'surface voltage' (what is that called?) was a lot less.
So I tried it again, and now measured the voltage over the battery stack, and it was about 1 V, although it fluctuated quite a bit. Over the terminals it started at 0.42 V and over half a minute it dropped and then seemed to stabilise at about 0.3 V.
So it seems the batteries (CR2032) just couldn't keep up, so to say (they were meant to power a little LED lamp).
But then there is still the difference between the battery stack (about 1 V) and the terminals (0.42 V dropping to 0.3 V). The resistance over a wire is 0.1 Ω (the multimeter can't go any lower). Times two is 0.2 Ω at most. That is a fraction of the resistance of the conductive ink, so the voltage drop should also be a fraction, right? DirkvdM (talk) 10:58, 18 October 2017 (UTC)[reply]

Refer to the data sheet for lithium battery CR2032. Its capacity rating is for a 15kohm load that draws 0.133 to 0.2 mA. The graphs suggest its capacity and output voltage are halved for a 1kohm load and that the heavy load (45 ohm) that the OP uses cannot be powered more than briefly (15 seconds); the internal resistance of the battery can be estimated about 30 ohm. Blooteuth (talk) 17:00, 18 October 2017 (UTC)[reply]

Flu vaccine and disease prevention (US vs. Europe)

Having lived in both US and Europe, I am acutely aware of their differing policies regarding flu vaccines. The US recommends a flu vaccine for all healthy adults (not otherwise excluded by allergies or other concerns). In Europe, the flu vaccine is only recommended for at risk populations (e.g. children, elderly, etc.) As a consequence, the US vaccinates ~50% of the population each year, while the coverage in European countries is much, much lower. I was wondering if there was any research comparing the effects of these diverging policies in terms of the relative incidence of flu-related disease, lost productivity, death, etc. from the US and Europe. I would be particularly interested to know if the much higher vaccination rates in the US can be shown to have appreciable herd immunity related benefits, or is ~50% not high enough to see benefits in the unvaccinated populations. Dragons flight (talk) 16:01, 17 October 2017 (UTC)[reply]

Something else you might want to look at is what happens with strains which the vaccinations don't cover. That is, do those strains spread more when vaccinations occur for the other strains, because people who would have contracted another strain and stayed home now go out and catch the unvaccinated strains ? StuRat (talk) 16:10, 17 October 2017 (UTC)[reply]

The thing about herd immunity is that it is an abrupt transition between "everyone infectable will get it" and "herd immunity works" (based on a few more or less realistic assumptions - large population (often an OK assumption), probability that person A will catch the disease from person B if infected more or less the same for all A and B (pretty much never the case) - but still a good first approximation). Our article cites [6] (which I have not checked) and says that the herd immunity threshold (= level of vaccination, basically) to stop influenza from propagating is 33 to 44%, meaning a 50% vaccination rate would indeed provide herd immunity, but that it would not take a large drop in the vaccination rate to lose it. I will note that this press article leaves one with the impression that the threshold for herd immunity for flu would be somewhere in the 80-90% range, but I would rather trust the NCBI source. Tigraan^{Click here to contact me} 16:27, 17 October 2017 (UTC)[reply]

The mathematics of these types of functions are actually fairly well studied; there's math like bifurcation theory or even the famous Mandelbrot set which is based on iterative functions that have two states, a "stable" state that collapses back to a single, small value, and an "unstable" state that runs away to infinity. The Mandlebrot set is just the limit between the stable state of the function and the "runaway" state of the function. Disease immunity follows similar behavior: at some value of vaccination, the infection rate always drops back to a small, stable value, whereas at any vaccination rate below that threshold, the infection rate skyrockets to essentially "everybody". While each disease has its own characteristic function that describes its transition, there's usually some "tipping point" between "herd immunity" and "everyone gets sick". LOTS of natural systems obey this kind of mathematics, such as population dynamics. --Jayron 32 16:40, 17 October 2017 (UTC)[reply]

I have been imagining that within the US there might be enough state-to-state or city-to-city variation in vaccination rates that herd immunity was not necessarily an all-or-nothing proposition for the whole US. Also, with flu, the immunity rate should be higher than the vaccination rate if past exposure to similar strains provides some protection. Which is of course is all a way of saying "it's complicated". Dragons flight (talk) 17:41, 17 October 2017 (UTC)[reply]

The U.S. should be vaccinating more widely than it is, for example with universal free vaccinations. I mean, when you antagonize a country that likely has ready resort to pandemic flu strains, and other fun creative projects, it would be a good idea to practice eradicating flu on a yearly basis. Wnt (talk) 20:03, 17 October 2017 (UTC)[reply]

Yes, that's where we get localized outbreaks ("outbreak" is medical speak for "where the infection-rate function tends towards infinity" in my discussion above) of dieseases where the vaccinate rates are too low. This paper discusses the matter. --Jayron 32 13:33, 18 October 2017 (UTC)[reply]

Note that the U.S. only started recommending universal flu vaccination a few years ago. The statistical effect might not be fully apparent yet. --47.138.160.139 (talk) 21:13, 18 October 2017 (UTC)[reply]

How many grams of food caused each gram of blattella germanica in a someone's home?

No, this is not professional advice. Are periplaneta americana similar? Sagittarian Milky Way (talk) 23:31, 17 October 2017 (UTC)[reply]

Potentially none:

1) They can get their food elsewhere and then come into your home.

2) They can also eat things we don't consider food. See German_cockroach#Diet and American_cockroach#Diet. StuRat (talk) 06:09, 18 October 2017 (UTC)[reply]

Well then how many adult roach body weights of nutritious possibly human food substance does a roach pair have to eat to grow from newborn to their first eggs hatching? Sagittarian Milky Way (talk) 07:03, 18 October 2017 (UTC)[reply]