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September 19

How to choose an expert?

If I want to solve an issue -- settling a dispute about an edit in an article in Wikipedia, deciding whether cell phones provoke cancer or taking homeopathic medication -- are we doomed to appeal to an authority to settle the issue? Wikipedia has a rather dismissive attitutde towards credentials, so, it makes the question even trickier. When we admit that we are not competent in a field, how to decide who is competent, when there's a huge body of knowledge in a science? --Doroletho (talk) 00:35, 19 September 2018 (UTC)

Wikipedia doesn't "choose an expert", it summarises what the majority of experts have published in WP:Reliable sources, giving both sides where there is wide disagreement. Dbfirs 06:15, 19 September 2018 (UTC)

• The leap of faith that Wikipedia makes is that, while it takes an expert to appreciate the validity, limitations etc. of the expert consensus on domain Foo, it does not take one to know what that consensus is. And that is what we describe (alongside significant minority views, public perception yada yada). We proceed exclusively by "appeal to authority". Tigraan^{Click here to contact me} 09:07, 19 September 2018 (UTC)
• I need to make one minor quibble, "dismissive attitutde towards credentials" is 100% wrong. Wikipedia has a strong respect for the writings of experts that have been published in reliable sources. Indeed, ALL of Wikipedia is designed to be referenced to the writings of highly credentialed people who have been scrupulously vetted and who's writings are considered highly reliable. What Wikipedia is (and is rightly so!) dismissive of is a) the claim that because a person in an argument says they have credentials, they should win any disagreement and b) that the existence of credentials (even if valid) in a discussion should override actual, published, reliable sources where the person fronting the argument disagrees with those sources. Wikipedia loves credentials, it just dismisses people who use claims of credentials to win arguments in opposition to what is written in reliable sources. --Jayron32 11:09, 19 September 2018 (UTC)

We have an encyclopedia article: an expert ..."has intense experience through practice and education..." and "is widely recognized as a reliable source."

That lede paragraph summarizes it! Expertise is developed by studying, and is established by peer-review. Whether we are participating in editing or reading Wikipedia, or in any other aspect of our lives, we determine "expertise" by finding many other people who agree with us.

This may seem like an oversimplification; it may seem unstable or hazardous; but it works. Alternatives to this method have been proposed; you can study the theory of knowledge to learn about the meta-problem of trying to establish knowledge (and the related concept, "truth"), from first principles; but in short summary, even though many philosophers have proposed alternatives, Wikipedia is one exemplar of a working system in which all knowledge is established through community consensus - including the specific ouroboric knowledge about which members of our community carry even more knowledge.

Nimur (talk) 16:01, 19 September 2018 (UTC)

Society used to appeal to authorities to settle issues on all matters before the scientific revolution. For 300,000 years humanity has existed we didn't have cell phones, cars, satellites etc. etc., and that changed when the scientific revolution started about 300 years ago. The most important thing that allowed the scientific revolution to succeed was to stop to appeal to authority. Count Iblis (talk) 17:06, 19 September 2018 (UTC)

No, we still appeal to valid scientific authorities: Every individual person (like you, me, everyone else here) does not have enough minutes on earth to do every scientific experiment ever done. While what makes science different from other forms of knowledge-making is that one could re-do each experiment (and also that each experiment has the potential to disprove a hypothesis, what is called falsifiability, the ability of a hypothesis to be disproved by experimentation). What has changed is the type of authority upon which we appeal: the appeal to a scientific authority is still necessary, because we literally cannot expect every citizen to do every experiment themselves; the same applies to authorities in other field: we cannot expect every human to read every historical text ever written; but they should be able to check the sources of reliable historians. We still appeal to the authority of those scientists because they have a reputation of using valid scientific methods to make knowledge and we still appeal to the authority of historians because they have a reputation of using valid historical methods to make knowledge, etc. etc. The reliance on valid authority in knowledge building is necessary because no one human can build all of that knowledge on their own from first principles. At some point, they have to have reasons to trust that someone else is doing it right. --Jayron32 17:20, 19 September 2018 (UTC)

Yes, we do need to put our trust in a system, as even scientists cannot go about verifying everything they need to know for their own research. However, this is then the system involving rigorous reviews and independent reproduction/verification of results, so it's not about trusting the judgment of particular individuals. If it's at all possible to have doubts about some result, then such doubts will be the subject of further research. So, it's far more about the whole process making sure that researchers are not going to leave any stone unturned, that allows people to have trust in the results of scientific research. Count Iblis (talk) 20:33, 20 September 2018 (UTC)

The traditional approach has been a combination of authority, jury, evidence, and democracy. People expect "good papers" and "good journals" to be run by "the right people", based on ad hominem considerations, but then allegedly random researchers (chosen by authority) review papers and decide based on the text, and then we review the papers by doing a literature search and seeing who is mostly believed.

The modern issue is that some trolls might generate more comments than everyone else put together. Papers and whole journals might be the blathering of artificial intelligence. Such mechanisms have the net effect of disrupting communication, so people retreat into "bubbles" by which they trust fewer opinions, even if less competent, to go through the mass of nonsense and try to pick out something that sounds logical and reasonable. But then there's also the issue that while in the past a forged figure might be crudely copied and pasted in multiple papers, now we can picture some entities generating convincing forged video, so certainly a good faked PAGE gel. So long as an honest mind trying to reconcile the logic behind the data can make sense of what is genuine, there might be hope, but how long can that last? After that, all communication is lost and humans are back to where they were before the invention of speech, but with a superior species of machines occupying their former niche. Wnt (talk) 14:08, 20 September 2018 (UTC)

That's the problem of knowledge making in general, and in the end following your train of thought leads only to solipsism, which while logically consistent is not a practical way to live one's life. As soon as one places trust in any concept which cannot be perfectly proven (including, even, what your own senses tell you on a daily basis), one must take some leap of faith that the information one is assuming is real is actually real. At some point, you have to just trust it, and you can set your own criteria for what is likely to be more trustworthy, but to follow perfect logic and demand that all information require perfect truth to be acceptable, ONLY solipsism works. --Jayron32 16:49, 20 September 2018 (UTC)

It depends how much effort you want to put into it. The legal system has a highly-developed way of arriving at the truth. Cases are originally heard in a court of first instance. If there is any doubt you can appeal to a higher court, then a still higher court and so on. At the end of the process you get a well-referenced decision which is very unlikely to be wrong. 92.31.140.53 (talk) 15:08, 20 September 2018 (UTC)

Hmmm, I would have said something more like "fifty-fifty". Wnt (talk) 12:28, 22 September 2018 (UTC)

Regarding trusting experts and science see our article on argument from authority. --Modocc (talk) 16:40, 20 September 2018 (UTC)

type of turbine in a dam

I have a hydroelectric question about two dams in western Washington, both described in Wiki: the Upper Baker Dam and Lower Baker Dam. Are both dams equipped with Pelton impulse turbines? If not, what kind of turbines are in use? Thanks for your help! It's a wonderful service. Rossroderick (talk) 03:17, 19 September 2018 (UTC)

They're 300' dams, so that's enough head for Peltons to make sense. I can't find anything on-line about them to confirm this, although [1] contains this tiny cross-section image of the new 30MW Unit 4 which looks more like a Francis turbine. Andy Dingley (talk) 11:32, 19 September 2018 (UTC)

Are there any bacteria that are hydrophobic?

My understanding is bacteria in general all thrive in wet/moist conditions, so are there any bacteria that don't like water? Then, are there any bacteria that are neutral in water (don't actually thrive more). Otherwise, bacteria is generally 100% hydrophilic right. 12.239.13.143 (talk) 18:58, 19 September 2018 (UTC).

"Hydrophobic" and "hydrophilic" are not typically used to describe organisms. All known cells are bags of water, so in that sense (if you don't consider viruses and prions to be alive) you could describe all life as "hydrophilic", because all life needs water. But not all bacteria are adapted to wet environments. Bacteria or archaea live in every terrestrial environment we've checked, including bone-dry deserts, acid mine drainage, salt lakes, and rock miles underground. Bacteria adapted to those environments will often not do well in others because other bacteria will out-compete them. As you may see, the reason those terms aren't used is they don't have much descriptive power when you try to apply them to organisms. They're too reductive. Plus, it risks confusion with their typical usage in chemistry. --47.146.63.87 (talk) 06:45, 20 September 2018 (UTC)

Lipophilic bacteria may be helpful, although I think that article would benefit from some work. Klbrain (talk) 22:48, 22 September 2018 (UTC)

type of hydroelectric turbine in use

Yesterday I asked this:

I have a hydroelectric question about two dams in Western Washington, both described in Wiki: the Upper Baker Dam and Lower Baker Dam. Are both dams equipped with Pelton impulse turbines?

This was the very good answer:

They’re 300’ dams, so that’s enough head for Peltons to make sense. I can’t find anything on-line about them to confirm this, although [16] contains this tiny cross-section image of the new 30MW Unit 4 which looks more like a Francis turbine. Andy Dingley (talk) 11:32, 19 September 2018 (UTC)

I have since learned that the turbine vanes in at least one of the dams have streams of water directed at them, through nozzles, that are controlled by hydraulics, i.e., by oil under pressure controlling the motion of pistons. The hydraulics are used to determine the direction of the flow and possibly the pressure of the flow.

Would that information tend to indicate Pelton impulse turbines or the Francis turbine?

And a second question: Do you know which dam the new 30MW Unit 4 is installed in: the upper or lower dam?

Thanks very much.

Rossroderick (talk) 03:28, 20 September 2018 (UTC)

Atleast the technology of the last unit 4 turbine is pretty clear because of its unique feature of being "fishfriendly". All conventional hydro turbines are fischkillers and on top allow only one direction since no fish is fast enough to swim up in them.

That it is the newest also gives a clue, because altho it is one of the oldest turbine principles of all, it has only recently become very popular again in modern hydroelectric powerplant constructions.

They are called vortex-, low head- or very low head turbines (VLH-Turbines). Seems they are still so brand new and uncommon (altho i had already read about them (wrongly described) as "new innovation" 4-5 years ago) that we actually still dont have an article about them, nomatter they are definitely worth one. I am a little puzzled with the 2 dams tho because these vortex turbines actually dont need a dam and the mentioned sidenote about the benefit for the fish should mean there are 2 of these or the one in the lower dam somehow circumvents the upper to let the fish pass tru both. --Kharon (talk) 04:43, 20 September 2018 (UTC)

A Gravitation water vortex power plant is one of the types mentioned in the Low head hydro power article. DMacks (talk) 05:16, 20 September 2018 (UTC)

Construction- and engineering-firms still seem in a contest about how to call these. I learned about them under the name vortex hydro turbine. I am pretty sure many more will be build in the future because they are actually very simple and easy to build, yet surprisingly effective and versatile and on top very ecological. So guess some common name will crystallize out in some years. --Kharon (talk) 06:18, 20 September 2018 (UTC)

I'm kind of surprised they need a special turbine to spare fish. I mean, haven't any of these engineers heard of FACS sorting? :) Wnt (talk) 13:57, 20 September 2018 (UTC)

Lots of methods have been tried to reenable natural diadromous fish migration. Unfortunately only with limited success no matter the serious effort and investments. These new old vortex turbines actually promise a very good solution to that which is surprisingly cheap and effective enough for power generation on top. Besides Hydro power is pretty abundant anyway so dependent on POV it may actually look a bit silly to take such huge investments, just to tinker out a few more % efficiency. --Kharon (talk) 18:02, 21 September 2018 (UTC)

September 20

Particles, wood heating & diesel

Hello! The dieselgate has brought to light a fraud involving toxic emissions from diesel vehicles. In the case of fine particles, total pollution includes emissions from industry, transport, individual heating &c. How is each contribution calculated? If transport-related emissions have long been undervalued due to car manufacturers' fakes, what is the adjustment factor and have we not, for example, exaggerated the impact of wood heating? Thanks for your help, --methodood (talk) 10:34, 20 September 2018 (UTC)

Dieselgate redirects to Volkswagen emissions scandal. Is that what you're referring to? Also, where have you been for the last eight years. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:02, 20 September 2018 (UTC)

Hi Bugs! Can you give me the detail of the contributions of each pollutant before and after the revelation of the scandal, how it is calculated (and if the prorata didn't evolve, why ?) Thank you.--methodood (talk) 18:31, 20 September 2018 (UTC)

Dieselgate is only about NO_x emissions. Fine particle emissions were not involved. Ruslik_Zero 20:22, 20 September 2018 (UTC)

These numbers are all estimated (numerically projected) based on a few samples. If you manipulate some samples you of course also manipulate the whole picture and change the relation of all picture elements among each other. That does not mean you change every element and its own impact! --Kharon (talk) 22:54, 20 September 2018 (UTC)

Plants question.

If you bring a plant from the cold arctic, like coniferous trees, and bring it to the tropics, equatorial regions, will it be happy, or worse? Cuz I imagine the other way around is more painful, bringing a tropical plant to the cold arctic. So when you bring a arctic plant to the warm regions, with more sunlight, what would be the answer? If things like different soils play a role, then what about if you bring the same soil and so the only changing variables are temperature and latitude? Thanks. 12.239.13.143 (talk) 21:21, 20 September 2018 (UTC).

Depends. I don't have an answer to your actual question, but will note that the equator is not all happiness and sunshine from every plant's perspective. Heat and high humidity are downright stressful for some of them. Someguy1221 (talk) 21:48, 20 September 2018 (UTC)

Not all but many plants are specialized on specific environments and according conditions. Arctic plants for example tend to have a very slow metabolism that probably cant "deal" with the energy volume of sunlight in warmer regions, just like you cant put a Seacow into the Rapids and expect it to survive and reproduce there. --Kharon (talk) 23:14, 20 September 2018 (UTC)

Do yo mind providing any source to your claim that "Arctic plants for example tend to have a very slow metabolism"? Is that something you can cite or just imagined to be the case?

Indeed, arctic plants very fast development, high rates of metabolism concentrated in a short period of time, when there's sun available.

In contrast, in season-less tropical climates, plants can compensate for low rates of metabolism by having long durations of activity. There's plenty of sun for that.

In any of both cases, the evolutionary adaptation is the lowest temperature at which new cells can be generated.Doroletho (talk) 01:50, 21 September 2018 (UTC)

According to this source "the vegetation of the taiga is vulnerable because of its low rate of metabolism and biological activity due to cold temperatures". Mikenorton (talk) 09:16, 21 September 2018 (UTC)

But there's a question of chicken versus the egg: does their metabolism appear to be slow because of the reduced sunshine for much of the year or is it really slow? It's a question of lack of resources versus internal mechanisms. Anecdotally, northern plants are certainly capable of rapid growth when conditions are ripe (broadly similar to a desert bloom) and the stunted "trees" around the treeline also grow bigger and faster further south. Whether they're genetically tuned to grow differently is really the crux of the question. Matt Deres (talk) 15:10, 21 September 2018 (UTC)

Sunshine seems less important than temperature because you find the very same strategy and adaption for example in Greenland sharks who are even apex predators aka Carnivores in their environment, thus hardly dependent on allot of sunlight, have a even extremely slow metabolism and obviously no interest to leave their very cold environment. --Kharon (talk) 17:11, 21 September 2018 (UTC)

Wait a minute you're comparing plants to animals here?? Plants need sunlight to photosynthesize, animals do not. 67.175.224.138 (talk) 05:57, 22 September 2018 (UTC).

Hence: asking for real sources rather than "I imagine that" is the way to go. --Doroletho (talk) 13:01, 22 September 2018 (UTC)

Okay I asked 2 plant professors this question. 1st 1 said for coniferous trees, yes it can as it is strong enough to live in both environments. But not all Arctic plants. Basically his ultimate answer was "depends on the plant." A 2nd 1 predicted that if you move a plant from the Arctic to the tropics, it will have problems where it loses a lot of water. But I ask what if it were moist, rainfall environment, so he goes on with other factors like being exposed to different kinds of bacteria and fungi. So it seems to me, that placing a plant from a wet environment to a dry environment is a bigger issue - so now my 2nd question is - what happens if you bring a desert plant like cacti into a moist, rainfall environment? I'll later ask around about metabolism. 207.140.218.10 (talk) 17:40, 21 September 2018 (UTC).

Many (but not all) cacti will suffer root rot if they are in a wet environment. I wouldn't even try to grow a cactus where I live with a hundred inches of rain a year. Even Mediterranean plants tend to rot here, but conifers grow well. Here is a Quora answer about cacti. Dbfirs 19:39, 21 September 2018 (UTC)

You could probably grow them indoors as long as you don't overwater. --47.146.63.87 (talk) 06:50, 23 September 2018 (UTC)

Well, yes, I do grow small ones indoors where they seem to thrive on neglect most of the time. Dbfirs 10:20, 23 September 2018 (UTC)

Here in So Cal we tore out our lawn and replaced it with xeriscaping, which cut the water bill by about 60%. With a drip irrigation system you don't even have to think about the plants. Should be mandatory around here if you ask me. --47.146.63.87 (talk) 22:15, 23 September 2018 (UTC)

Not about conifers, but here's some comments from the University of Florida (http://gardeningsolutions.ifas.ufl.edu/plants/edibles/fruits/chill-hours.html) regarding deciduous fruit trees - "In order to bloom in spring, deciduous fruit trees like peaches, plums, and nectarines all must go through the plant equivalent of a long winter's nap. They need a dormancy period with a certain number of chilling hours, when the temperature drops below 45 degrees Fahrenheit. The exact number of chilling hours depends on the fruit tree variety, but it can be anywhere from a hundred to more than a thousand....." So, your peach tree might survive in the tropics, but may not set fruit. HiLo48 (talk) 22:47, 22 September 2018 (UTC)

207.140.218.10 already hit the points I would have emphasized; there's simply too many varieties of flora within the meaning of "arctic plant" to give a very straightforward answer. In generally, shrubs, grasses, bryophtes, and flowering plants from the arctic region tend to be highly adapted to the local ecology and do not adapt well to local conditions in the tropics. The afore-mentioned fungi, bacteria and other pathogens, heat, humidity, soil conditions, difference in light and difference in seasonal variability of all of those factors conspire for an inhospitable environment for many species. However, hardier vascular plants, including most conifers, tend to do quite well. Conifers as a clade, you must remember, are not restricted to the arctic (though a small handful of species are adapted to the arctic circle) but rather extend across nearly the entirety of inhabited terrestrial latitudes, generally thriving in most. As a consequence, and because of their high value as timber resources, and as useful species for arresting soil erosion (particularly after previous deforestation following fire or over-harvesting), conifers (softwood pines in particular) have been imported into many of the few regions on earth where they do not occur naturally, including numerous tropical islands.

Additional reading you may find interesting, regarding the distribution of conifers: [2], [3], [4]), and regarding the success of the clade in tropical climates, one of the better studied ecological test cases is Hawai'i, to which story these sources pertain: [5], [6], [7], [8]; I was actually going to tell a long navel-gazing story about how I became aware of the ecological history of pines in Hawai'i and the interesting contrasts they create when the intermingle with the species of the native arboreal and bamboo forests and scrublands, but the sources are probably more useful to your purposes. Snow ^{let's rap} 06:16, 26 September 2018 (UTC)

September 21

Baker Dam turbines, continued dialog

In response to the dialogue about dams on Baker Lake.

But these are NOT low-head dams. The new low-head turbine technology is simply not required, and there are tradeoffs if it's used unnecessarily. And if you look at satellite photos of Baker lake on Googlemaps, you can clearly see the special nets employed to capture fish and move them around the dam. And you can read about them as well, in Wiki articles.

If the Baker-dam turbines are EITHER Pelton OR Francis, what would they likely be? What’s your best guess, and can you justify making it?

Thanks again!Rossroderick (talk) 00:41, 21 September 2018 (UTC)

Several sources list head ranges from 200 or 500 metres up to 1500 metres for Pelton turbines, and from 20 or 80 metres up to 500 or 750 metres for Francis turbines ( https://www.slideshare.net/BKLR/hydraulic-turbines, http://164.100.133.129:81/econtent/Uploads/16-Hydraulic%20Turbines%20%5BCompatibility%20Mode%5D.pdf and https://www.youtube.com/watch?v=k0BLOKEZ3KU&vl=en ). It would also depend on flow rate, see the "Hydraulic turbine selection" graph at page 40 of the second source. So I would say a Francis turbine. Prevalence 02:28, 21 September 2018 (UTC)

When this query was first posted, I did quite a bit of digging around, but decided not to post with a non-definitive reply. But since you ask for "best guess" (with choice limited to Pelton vs. Francis), here's my evaluation: in 1925, Francis turbines were installed; by 1988 they were Peltons. The latter is supported by your description of the hydraulic piston mechanism. The Pelton impulse-jet uses a synchronization device (perhaps using pistons) which I equate as sort of the inverse of the mechanism developed in WW1 for machine guns on airplanes. On airplanes, the machine guns were synchronized such that the bullets would miss the propeller blades, whereas the Pelton device would synchronize the water-jet impulses such that they would hit the turbine blades -- in just the right spot for maximum efficiency. If need be, I could peruse my internet history and (hopefully) find photos/documents that lead me to this (e.g: archived 1925 photo of newly-installed turbines on one of the Baker dams that were not Pelton, probably Francis and archived government document that evaluated Peltons, noting their installation within the system that includes the Baker dams -- but not specifically those dams). So, my "best guess" is that the current primary turbines are Pelton, augmented by some "fish-friendly" system. —2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 03:38, 21 September 2018 (UTC)

Its very odd that no one, not the owner nor management nor locals made any effort to offer some more detailed documentation.

Additionally, after trying to research about it for some time, it also struck me that homeland security may just now look over my shoulder "virtually live" and ask themselves why the heck i am interested in some power station in the state of Washington. So in conclusion let me forward that! Why the heck are you? --Kharon (talk) 17:28, 21 September 2018 (UTC)

I can't find any sources to support the general idea that the water flow is pulsed in Pelton designs. The flow can be increased or decreased depending on output demand, but everything I've seen is that it's essentially held constant at any given time. Sounds like a possible confusion of the idea of pulse vs impulse (physics)? DMacks (talk) 17:31, 21 September 2018 (UTC)

The transfer of water flow from each bucket to the next one of a Pelton wheel is modelled by design to minimise turbulence which represents wasted energy and vibration; note the shaped leading edges of the buckets here. The idea of externally interrupting the flow between buckets invites causing Water hammer, an extremely dangerous phenomenon at the high levels of kinetic energy involved in hydropower stations; witness the devastation in the 2009 Sayano–Shushenskaya power station accident. DroneB (talk) 17:06, 23 September 2018 (UTC)

• The idea of pulsed flow in water turbines (including Pelton wheels) is nonsense. Andy Dingley (talk) 22:03, 23 September 2018 (UTC)

September 22

Valence Bond theory vs Molecular Orbital theory descriptions of O₂

I am reading this paper on the use of VBT and MOT in teaching chemistry, and I'm having trouble getting past the first paragraph. Specifically, the following excerpt is what I'm struggling with:

"MO theory is often presented as a superior or more advanced theory citing “failures” of VB such as the paramagnetism of O₂ and the explanation of excited electronic states. However, a more in-depth application of VB (1) shows that resonance between two paramagnetic structures with two 3-electron π bonds (Figure 1A) is more stable than resonance between two diamagnetic spin paired structures each with a 2-electron π bond and a 4-electron repulsion (Figure 1B)."

I don't understand several points about this. Firstly, isn't the double bond in dioxygen a sigma bond and and pi bond, not two pi bonds as per the text? I understand that the two bonds are actually equivalent (not one sigma and one pi, but two equivalent bonds of mixed character), but to make that point clear you'd need to invoke hybridization, and in their description and drawing they haven't done so.

Secondly, don't bonds involving three electrons imply that at least two electrons would have the same set of quantum numbers and therefore be in violation of the Pauli principle? I've never heard anything about 3 electron bonds before, and I don't understand how they can be made to fit with either VBT or MOT as both are quantum based theories and as such must conform to Pauli. Figures 1A and 1B don't help me much either. Assuming that the solid line between the nuclei indicates a sigma bond, figure 1A seems to show a triple bond between the atoms. The existence of two p orbital on each atom also seems to indicate sp hybridization, whereas O₂ has sp² hybridization. Actually, a VBT description that explains the paramagnetism of O₂ would make more sense to me if they showed 2 sp hybridized O atoms triply bonded (1 sigma bond between the sp orbitals, and two pi bonds between p orbitals) with an unpaired electron in each of the remaining sp orbitals. This would not account for the lone pairs though, and would imply a far shorter bond length. Handschuh-^{talk to me} 09:39, 22 September 2018 (UTC)

"O₂ has sp² hybridization" is either circular reasoning or an unsupported underlying premise:) You are rightly concerned about putting a third electron into a single π molecular orbital, but when you add two p atomic orbitals, you get both a π and a π* and that latter can hold up to two more electrons. If you hybridize two p, which can hold a total of 4, your result can also hold a total of 4. Their diagram 1A represents two p orbitals interacting rather than a single unified π. They casually call it "π", but it's really also π* (which also actually does have π symmetry). So there are two sets of π/π* in addition to the σ, but each bonding π (populated by 2 electrons) is weakened by 1 electron in its associated antibonding π. That means each of the two π/π* has net effect of approximately "half bonding". So "1σ+2[half-π]" rather than "1σ+1π" still gives a net appearance of 4 bonding electrons exactly as "O=O" represents. Our triplet oxygen discusses the MO approach in detail and also links to the idea of three-electron bonds. DMacks (talk) 10:31, 22 September 2018 (UTC)

"when you add two p atomic orbitals, you get both a π and a π* and that latter can hold up to two more electrons"

Except this is supposed to be a VBT description of the bonding. Bonding and anti-bonding orbitals are a MOT concept..aren't they? Handschuh-^{talk to me} 10:50, 22 September 2018 (UTC)

No, at the introductory level we usually gloss over that aspect, but Modern valence bond theory is entirely compatible with MOT, and uses many of the same tools to deduce electronic properties. --Jayron32 23:08, 22 September 2018 (UTC)

Also, as shown in the paper, especially the diagram, it isn't a 3-electron, 1-orbital bond, it's a 3-electron, 2-orbital bond; that is you have 3 electrons distributed (via Resonance between two perpendicular pi-bonds). In the case between VBT and MOT here, the difference is in the explanation of the paramagnetism: VBT explains it via resonance, MOT explains it via bonding/anti-bonding orbitals. Either way, however, Pauli is preserved, look at the diagram on the right: You have two perpendicular p-orbitals, and neither ever has more than 2 electrons in them. Ultimately, however, they are both still useful theories which is why we keep them both: VBT is powerful in explaining geometry (angles, positions, and bond lengths), whereas MOT is useful in such matters as visualizing energy and bond order. Each can kind-of come up with explanations the other is better at (i.e. "resonance", which is still an inelegant kludge that MOT avoids entirely), but the point of the paper is that BOTH theories are valid because even VBT can explain observed behavior. --Jayron32 23:16, 22 September 2018 (UTC)

Well, if VBT can include bonding and anti-bonding orbitals then I don't even understand what the distinction between the two theories is. As I understand VBT, a bond is created by overlapping two atomic orbitals. This allows the electrons to be counted as being in atomic orbitals from both atoms in the bond. In the diagram, no atomic orbital has more than 2 electrons, but two atomic orbitals are indicated to be bonding i.e. overlapping to form a bond with a total occupancy of 3 electrons.

Secondly, if VBT is only able to accurately describe the bonding of dioxygen after we update the theory with concepts borrowed from MOT, then that doesn't say much for the paper's argument that VBT is just a good a description of the phenomenon. Handschuh-^{talk to me} 00:10, 23 September 2018 (UTC)

Whatever this is, it is not the familiar approach. The original cited article is [9] - I have to go, so I haven't looked to see if it's in Sci-Hub. Wnt (talk) 12:48, 22 September 2018 (UTC)

Species identification (Unknown spiders)

2 unknown spiders for Species identification:

Based on uploaders talk page, most probable region is North Eastern US, maybe New York?

(Aside: A photo subject identification refdesk would be useful.) ShakespeareFan00 (talk) 10:30, 22 September 2018 (UTC)

For photo identification the TinEye service, an example of Content-based image retrieval, is useful for checking whether an image is already on the web, though it cannot interpret an image. DroneB (talk) 11:07, 22 September 2018 (UTC)

The lower one looks like a Dolomedes tenebrosus - in fact they may both be. Mikenorton (talk) 12:25, 22 September 2018 (UTC)

Uploader responded to my query about region, Long Island, New York is where one (probably both) of the photos were taken. ShakespeareFan00 (talk) 23:17, 24 September 2018 (UTC)

This link gives a distribution for dolomedes tenebrosus, which is consistent with that location. Mikenorton (talk) 23:48, 24 September 2018 (UTC)

When An Idea appears on your conscious mind

What makes ideas pop up into your conscious mind? Is there a brain mechanism for that? — Preceding unsigned comment added by 37.252.180.177 (talk) 23:11, 22 September 2018 (UTC)

See this for example. Before the idea becomes conscious it is sometimes called preconscious though our article uses that term in a somewhat different way. 173.228.123.166 (talk) 00:59, 23 September 2018 (UTC)

Yes, the word did not pop up into my mind when I wrote the question. But it remains unanswered. There is probably loads of preconscious processing. How come only some become conscious? --31.4.136.202 (talk) 09:52, 23 September 2018 (UTC)

I have had occasions where I would need for some reason to remember some obscure fact, like who was some unsuccessful presidential candidate’s vice president candidate, knowing that I knew the answer at least during the campaign. Hard concentration does not bring the answer to mind, but I can leave the search to the unconscious processes and go on to to some other task. After thirty seconds or so the answer pops up without any conscious effort at all. It is literally like the file search is being done by a separate mental process from conscios awareness or mental effort. Edison (talk) 15:54, 23 September 2018 (UTC)

Related may be Working memory#Relation to attention. I cannot remember the name of another possibly related bias (similar to confirmation bias), although we tend to notice what we expect to see or what we're looking for. We routinely think and remember things that are not considered immediately important and quickly discard, but if such normally mundane event is recently seeked for, we'll tend to focus on it (or finally remember what was "tagged for retrieval"). An example is when we notice we need to buy an item (it may have recently stopped working, or a newly perceived need), then we start noticing it in stores and ads, although we never would normally care about the particular item... But that's of course not explaining the internal details of preconscious processing, a lot of which is still mysterious... —PaleoNeonate – 17:23, 23 September 2018 (UTC)

See subliminal advertising. 92.31.140.53 (talk) 18:12, 23 September 2018 (UTC)

This is not what I was talking about, but the aim here is indeed to influence using the unconscious (interestingly, that article seems to need work, including mention on how some of the methods are pseudoscience)... —PaleoNeonate – 20:24, 23 September 2018 (UTC)

• See also Hard problem of consciousness on why the question is tricky. --Jayron32 15:07, 24 September 2018 (UTC)

• Wouldn't it be a safe guess that there is some sort of filing system used by the mind, and if so, wouldn't thoughts be associated with other thoughts, and if thoughts are associated with other thoughts, wouldn't it be unsurprising that thoughts of no known relevance would always be popping up as mere associates of the thoughts to which we attribute relevance? Bus stop (talk) 16:12, 24 September 2018 (UTC)

• I usually don't respond on this page, but this is an interesting question of a subject that fascinates me and I have studied in great detail. The first thing to understand is that no one really knows what consciousness is or what we even need it for. Next to "what lies outside our universe" this is the biggest unanswered question in science today. There are many theories about the mechanisms of consciousness, with one of the most intriguing being the "single-cell theory of consciousness", but it all is really a mystery. What we do know is that there are many, many levels of consciousness, with the highest level (full, waking consciousness) being the smallest part of the mind. And I mean extremely small (microscopic) compared to all the unconscious things going on. We're basically running on autopilot most of the time. The best idea for why we even have it is that it allows us to solve unsolvable problems by viewing it in some big picture, and using intuition to literally guess the correct answer. (Those stupid captcha letters are an excellent example of this.)

Then you have to distinguish between, consciousness, imagination, memory, and cognition. Our mind operates using two separate languages (similar to computer languages). Freud discovered this and wrote extensively on it. Our conscious language is in words, which we have to learn. The subconscious language is not in words, but in terms of meaning and sensory input. The subconscious language is not learned but instinctual, and is the same for all humans (possibly all mammal or even all animals). Nearly all our thoughts are processed in this subconscious language at incredibly fast speed, right up to the point where it is on the tip of your tongue. It doesn't become conscious until you put it into words, which takes much longer.

Coming up with an idea involves imagination, which is what the brain constructs as being an illusion we call the future. Imagination involves combining known information in new ways, thus involves memory. Memory creates an illusion we call the past. But then there is also cognition, which is the ability to attribute a meaning to a thing or event, and differentiate it from other things and events.

Nothing becomes a memory (thus nothing is cognized) until after it passes through the amygdala to the hippocampus. The amygdala is like a filter, that in computer terms compresses our memories into small, easily-stored packets. When you drive across country, you don't remember every tree or house along the way. Your amygdala changes these into generic "forest" and "neighborhood"s. Only those things which really stand out to you are fully committed to memory, and this is determined by emotional saliency (how hard does it tug at my emotions). Thus, the amygdala is also the emotion center of the brain.

So after barely grazing all of the factors involved, back to the original question. It all depends on these unconscious processes. Imagine your brain is running millions of computer programs, simultaneously, and each are always talking and communicating with each other in a very random and chaotic manner (remind you of any particular encyclopedia out there?). It is only when enough parts of your unconscious mind get together (collaborate) and decide (consensus), "ok, this is emotionally important enough for me to cognate, that the thought begins to take shape in your subconscious. And only after some more debate --if it seems important enough--, it may enter what is known as your stream of consciousness, which is that little voice that blabs on endlessly in our minds, using words but still in random order. Some people talk using their stream of consciousness, but this is really incoherent, so most then take that idea and put it into a coherent form that others can understand, which requires another aspect of processing reality called metaperception. (Figure that consciousness starts developing about the age of two and finishes by four. Metaperception begins forming around the age of four and doesn't finish until you're 25, which is most of the reason kids act the way they do.) Zaereth (talk) 00:25, 27 September 2018 (UTC)

September 23

5 ARIs and erectile issues.

Why do 5 Alpha Reductase inhibitors cause erectile dysfunction and are they reversible for Finasteride and Dutasteride? — Preceding unsigned comment added by 103.15.60.45 (talk) 06:08, 23 September 2018 (UTC)

See 5α-Reductase inhibitor. And if you're concerned, see your doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:22, 23 September 2018 (UTC)

I feel the link given gives a very vague answer. I want a more incisive one. — Preceding unsigned comment added by 103.15.60.45 (talk) 06:28, 23 September 2018 (UTC)

Dihydrotestosterone § 5α-Reductase inhibitors goes into more detail. --47.146.63.87 (talk) 06:49, 23 September 2018 (UTC)

Still not enough to describe the effect on penile muscle contractile issues. — Preceding unsigned comment added by 103.15.60.45 (talk) 07:46, 23 September 2018 (UTC)

If you are asking for a concrete case like "when used for few years and five months respectively" it's difficult to answer, unless for a doctor, who meets the patient in person. --Doroletho (talk) 10:55, 23 September 2018 (UTC)

Ok... please remove that time period. Can the effects be reversible? — Preceding unsigned comment added by 103.15.60.45 (talk) 11:57, 23 September 2018 (UTC)

5α-Reductase inhibitor § Sexual dysfunction: Sexual dysfunction, including erectile dysfunction, loss of libido, and reduced ejaculate, may occur in 3.4 to 15.8% of men treated with finasteride or dutasteride.[19][26] This is linked to lower quality of life and can cause stress in relationships.[27] There is also an association with lowered sexual desire.[28] It has been reported that in a subset of men, these adverse sexual side effects may persist even after discontinuation of finasteride or dutasteride.[28] --47.146.63.87 (talk) 07:11, 24 September 2018 (UTC)

3d screen, made of See-through displays

If you stack transparent LCDs, do you get a 3d screen? It would be a rather expensive toy for consumers, but could this work? Doroletho (talk) 10:53, 23 September 2018 (UTC)

No. --Kharon (talk) 11:29, 23 September 2018 (UTC)

Yes it works but Liquid-crystal displays do not emit light so you would have to arrange adequate illumination of the stacked screens, and LCDs have a limited viewing angle so you cannot achieve a full walk-around stereoscopic effect. Unless you really want to use a big stock of LCDs with all their associated connectors, wires, circuit boards and power supplies, first review the alternatives at the end of the article Stereo display. DroneB (talk) 15:51, 23 September 2018 (UTC)

Several famous projects using layered displays have come out of the MIT Media Lab and have been presented at SIGGRAPH and elsewhere. For example:

• Tensor Displays
• Layered3D
• Kinetic Blocks and related tangible displays
• "HR3D" displays using stacked displays

...and so on.

The ideas are neat but the execution is usually limited by several factors: brightness, spatial resolution, and temporal resolution (and skew) are recurring problems that limit the practical performance of such devices. But most of these kinds of demo projects haven't gone anywhere because they're just not very useful - and once the innovative novelty wears off, even researchers lose interest. It's pretty unlikely that hobbyists or companies that target mass-market audiences are going to build anything better - because as soon as you add the extra constraints of cost, reliability, manufacturability, and compatibility, the technology has no clear net advantage over conventional displays.

Here's a review article: Three-Dimensional Displays: A Review and Applications Analysis (2011), which was featured in IEEE's Transactions on Broadcasting.

Nimur (talk) 17:38, 23 September 2018 (UTC)

September 24

What's happened with the PHYTOME project?

Have there been any new processed meat products with phytochemicals sold in the marketplace ever since the project was finished in 2016? — Preceding unsigned comment added by 184.67.108.46 (talk) 10:45, 24 September 2018 (UTC)

filtering salt out of seawater

"The teenager only had a few days worth of supplies and survived by catching fish, burning wood from his hut to cook them, and sipping seawater through his clothes to minimize his salt intake."[10] Can one filter out salt by sipping seawater through the textile of one's clothes? Bus stop (talk) 14:12, 24 September 2018 (UTC)

No, that will not work - but it doesn't mean he didn't try it (or that the news report was inaccurate).

From a scientific point of view, salt water is a chemical solution - the salt has dissolved into the water and is present as individual ions of sodium and chloride. Many textbooks define a solution as a mixture that cannot be separated by filtration. Cloth isn't even a good filter - so it's not going to have any effect at removing the salt - not even in ideal laboratory conditions.

From a practical, survival point of view: this isn't a standard procedure either. Almost all sources agree: in a survival situation at sea, it's better to drink nothing than to try to drink seawater. For reference, I pulled out the Army Survival Manual, which you can purchase online in reprint. They make it pretty clear: do not drink seawater, unless you have a real desalination kit. "By drinking seawater, you deplete your body's water supply, which can cause death." Nimur (talk) 14:23, 24 September 2018 (UTC)

It's pretty clear this is the way it has to work since seawater has more salt than the body's solutes. (almost 4 times as much in fact) Sagittarian Milky Way (talk) 14:56, 24 September 2018 (UTC)

What about using a funnel, and covering it with a piece of paper, into a bottle. Then constantly pouring the water from a bottle back to the funnel. Well, the easy answer to check is if you see salt piling up in the paper funnel, then you're getting progress. 67.175.224.138 (talk) 02:56, 25 September 2018 (UTC).

I think I read something about getting the fluid from the eyes and spine of fish but no other fluid from them and not eating and that would keep you going for a while. Rather desperate but needs must I guess. Dmcq (talk) 14:37, 24 September 2018 (UTC)

They may be incorrectly describing a solar still. --47.146.63.87 (talk) 21:20, 24 September 2018 (UTC)

In the original language of the article, it says that he squeezed sea spray from his clothes and drank that. He didn't filter the water through his clothing. I'm not claiming that is better. It is just not the same thing. 216.59.42.36 (talk) 18:11, 26 September 2018 (UTC)

Baker Dam

Which Baker Dam, upper of lower, uses Pelton turbines?Rossroderick (talk) 15:02, 24 September 2018 (UTC)

I don't think you need to repeat the same question every other day: You can simply continue an opened thread. From all the posts in the last one ( https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Science#Baker_Dam_turbines,_continued_dialog ) I got the impression that there are no sources stating what kind of turbines are mounted in the Baker Dams, so there is no answer to your question, even if you ask it a fourth and a fifth time. 194.174.73.80 (talk) 13:58, 25 September 2018 (UTC) Marco Pagliero Berlin.

@Rossroderick: If you're in the area, you can try Free tours of Baker River Hydroelectric Project, or try "Contact us. We welcome your questions and comments!" —107.15.157.44 (talk) 15:58, 25 September 2018 (UTC)

I've been reading this discussion for a few days. The link Andy Dingly gave after your first question clearly tells (if anybody had taken the effort of actually reading it...) that the new Lower Baker Unit 4 has a Francis turbine. Lower Baker 1 and 2 no longer exist. It doesn't tell anything about Lower Baker 3, but at the same head and higher flow than Lower Baker 4, it's probably a Francis turbine too. Pelton wheels are more common for high head, low flow. No source has been found for Upper Baker. It has slightly higher head and lower flow than Lower Baker, so it could be either type of turbine.

BTW, the fish-friendliness of Lower Baker 4 is all about fish-friendly management of downstream waterlevel. PiusImpavidus (talk) 17:11, 25 September 2018 (UTC)

Where in the deepest bedrock in the world?

Where is the strongest? (lb/in² before a load slowly placed directly on a leveled part of the top of the bedrock damages it) Sagittarian Milky Way (talk) 15:54, 24 September 2018 (UTC)

I'm not clear on what you're asking - bedrock goes from the base of superficial deposits down 10s of km. The strongest part of the crust is at the brittle–ductile transition zone, beneath which higher temperatures promote crystalplasticity. Mikenorton (talk) 17:18, 24 September 2018 (UTC)

I was asking about the top of the bedrock. Sagittarian Milky Way (talk) 17:31, 24 September 2018 (UTC)

Do you mean "How far down is the deepest from the surface one has to go to reach bedrock?" --Jayron32 17:41, 24 September 2018 (UTC)

If you are this paper seems to have all of the data you need. And then some. --Jayron32 17:45, 24 September 2018 (UTC)

That paper implies that there is a place in the US where the rockhead (that's what the top of bedrock is called) is more than 3 km below the surface. That seems a little high in my view, although I can't see the data that was used to give that value, presumably a borehole record. There are plenty of places globally that have hundreds of metres of superficial deposits however, especially in areas that were once close to the front of ice sheets (during the last glacial maximum), where the mass of sediment coming from the ice sheet infilled any existing topography - valleys, lakes etc. Mikenorton (talk) 19:24, 24 September 2018 (UTC)

Actually, if you read the paper, they actually made your exact point years before you thought to write it. --Jayron32 03:44, 25 September 2018 (UTC)

Three km deep sediments are not rare, for example the Po river delta in Italy and the Brandenburg region in Germany are said to lie on three km of sand. But you don't need a three km depression at the beginning: the weight of few hundred metres of sediments can sometime cause the crust to sink into the mantel, so as to give place for even more sediment to accumulate and so on. 194.174.73.80 (talk) 14:50, 25 September 2018 (UTC) Marco Pagliero Berlin

Is it possible for sediments to break through the crust when it was thinner or in the far future if they accumulate enough? Maybe if the sediments continental drift to a place where 4+km of ice form on top? Sagittarian Milky Way (talk) 15:37, 25 September 2018 (UTC)

Sediments (more properly sedimentary rock) can be pushed under the crust at subduction zones. But no, there's nothing to "break through". It's not like the crust is sitting over nothing, there's dense, plastic solid mantle underneath. --Jayron32 16:04, 25 September 2018 (UTC)

As Jayron says, we're dealing with sedimentary rock, not unconsolidated sediment, as once we have a thick enough accumulation (and therefore high enough temperature and pressure) the process of lithification starts. That's why I balked at 3 km to bedrock, because the bottom of such a sequence would have become lithified and therefore would form part of the bedrock itself (and of course part of the crust). There are a some places where unconsolidated sediments were deposited directly onto exhumed (if somewhat altered) mantle, non-volcanic passive margins, but that's because during continental break-up the crust has been thinned away to nothing before the mantle part of the lithosphere has given way - this has been proved by the Ocean Drilling Program (e.g. hole 637). Mikenorton (talk) 18:38, 25 September 2018 (UTC)

September 25

Global Warming in Mexico

Under the various global warming scenarios, does it seem possible/likely that Mexico will become uninhabitable except for mountainous regions?Rich (talk) 00:55, 25 September 2018 (UTC)

See here: "A 2010 study concluded that under a worst-case scenario for global warming with temperatures 12 °C (22 °F) higher than 2007, the wet-bulb temperature limit for humans could be exceeded around much of the world in future centuries.[10] A 2015 study concluded that parts of the globe could become uninhabitable.[11] An example of the threshold at which the human body is no longer able to cool itself and begins to overheat is a humidity level of 50% and a high heat of 46 °C (115 °F), as this would indicate a wet-bulb temperature of 35 °C (95 °F).[12]". Count Iblis (talk) 04:01, 25 September 2018 (UTC)

However, that's speaking of global effects of a staggering 12 degrees Celsius of warming, which would take centuries even with unabated emissions. In the tropics and subtropics, which includes Mexico, things will start getting dire much earlier. If you believe this analysis, originally published in New Scientist, at 4 degrees of warming much of Mexico would indeed be close to uninhabitable. And depressingly we have a good chance of hitting 4 degrees by the end of the century if we continue with our present policies. If you haven't read "The Uninhabitable Earth", do so, though you won't be upbeat afterward. --47.146.63.87 (talk) 04:31, 25 September 2018 (UTC)

Technology can help adapt to the worst conditions. The Inuit adapted to the extreme cold near the north pole, the Tuareg adapted to the extreme heat of the Sahara desert. Walipinis seem a working technological adaption in South America. --Kharon (talk) 04:50, 25 September 2018 (UTC)

There is a limit. The problem is not just heat but humidity—wet-bulb temperature reflects both. At a wet-bulb temperature of around 35 Celsius, the atmosphere no longer convects heat away from your body, and you quickly cook to death. The tropics are famously humid, as contrasted with dry deserts (including polar deserts). Also there's the minor issue of sustaining a modern agricultural society. The Inuit and Tuareg are historically nomadic, but to keep alive 7.6 billion people and growing, you need to grow food, you need water supplies, and so on. We could debate the exact definition of "uninhabitable", but it's not really important for analyzing the potential future, because people will start evacuating long before the point of "you drop dead if you go outside during the day". --47.146.63.87 (talk) 07:56, 25 September 2018 (UTC)

Not a strictly scientific answer, but an interesting fictional consideration of almost exactly the OP's area of interest is to be found in Paolo Bacigalupi's 2015 science fiction novel The Water Knife. {The poster formerly known as 87.81.230.195} 2.221.81.75 (talk) 08:43, 25 September 2018 (UTC)

Yes, that lethal combination does not exist on Earth - the eastern United States comes closest. 92.31.140.53 (talk) 13:07, 25 September 2018 (UTC)

Really? What about Arabia and the Persian Gulf when the wind comes from the water? The Upper Midwest can actually get surprisingly close, it can reach the mid-110s in Minnesota and all the crops drying out makes the air ~115 and not very dry. Sagittarian Milky Way (talk) 13:39, 25 September 2018 (UTC)

Lunation and tropical year in 5000 BC

Nowadays, around AD 2000, the value of the mean synodic month is about 29.5306 mean solar days, and that of the mean tropical year, 365.2422 mean solar days, where a mean solar day is about 86,400 SI seconds. I was wondering about their variation over the millennia, and what their values would have been around, say, 5000 BC or AD 5000. — 79.113.236.200 (talk) 13:30, 25 September 2018 (UTC)

The Wikipedia article titled year has information on the variation of the length of a year, and even has a handy table which, while it doesn't have 5000 BC listed, does have several different years. There are 4 references just before that table, you perhaps could use those to help you in your research. --Jayron32 13:35, 25 September 2018 (UTC)

Year length varies from year to year. I am interested in an average, for a few centuries around the given date. Is that what the table is supposed to represent, or does it merely show the length of the specific year in question ? — 79.113.236.200 (talk) 18:30, 25 September 2018 (UTC)

Correction: 86,400.002 seconds. Sagittarian Milky Way (talk) 13:43, 25 September 2018 (UTC)

Two milliseconds over the course of a year fits within the allowable parameters of "about". --Jayron32 13:48, 25 September 2018 (UTC)

86,400 seconds is a day but yeah, it's pretty similar. Sagittarian Milky Way (talk) 13:58, 25 September 2018 (UTC)

The Babylonians used a mean synodic month of 29d 12h 44m 03 1/3s. The modern value is 29d 12h 44m 02.87s. Although the moon is slowing down (due to the tides) the increase in the length of the day caused by the tides slightly overcompensates. Thus although the month is getting longer, in terms of mean solar days it is diminishing. The length of the mean tropical year diminishes by about 1/2 second per century - you can't really differentiate between mean solar days and ephemeris days (those are the ones that consist of 86,400 SI seconds). 92.31.140.53 (talk) 14:06, 25 September 2018 (UTC)

September 26

Neutron star cooldown time

According to the article on neutron stars the majority of the examples in our galaxy are already cold (or at least cold enough to not be detectable), but according to the article on white dwarfs, that type of star is not expected to cool down for at least trillions of years. Why do neutron stars cool down so much faster than white dwarfs? 182.0.151.47 (talk) 10:07, 26 September 2018 (UTC)

Maybe because while a white dwarf has radius on the order of 3000 6000 kilometres, a neutron star has a radius on the order of 10 kilometres? 194.174.73.80 (talk) 10:39, 26 September 2018 (UTC) Marco Pagliero Berlin

If anything, shouldn't a larger surface area lead to faster cooling, as you can get a greater heat flux through it? 139.194.67.236 (talk) 10:42, 26 September 2018 (UTC)

Of course not. A drop of molten steel gets cold faster than a ton of molten steel. Can you imagine why? 194.174.73.80 (talk) 11:51, 26 September 2018 (UTC) Marco Pagliero Berlin

Could it have something to do with the ratio between volume and surface area not being linear? 216.59.42.36 (talk) 18:05, 26 September 2018 (UTC)

The reason a droplet of steel cools faster than a ton of steel is because the surface area to mass ratio is greater in the droplet than in the ton due to square cube law. That will only work for comparisons of objects of similar densities. The neutron star (with a mass of about 1.5 solar masses) has far greater thermal energy to fit through its tiny surface area, compared to a white dwarf with its surface area several orders of magnitude greater, but a smaller mass of around 1 solar mass. So, the comparison of the radii doesn't answer the question. It just makes it more puzzling. 114.124.239.108 (talk) 23:29, 26 September 2018 (UTC)

You are right, I didn't think of this and IP139, I beg your pardon. So it can be that heat conduction in a neutron star is much faster and the whole star cools quickly, or in the opposite, conduction is very slow, so the surface cools while the core stays very hot. 194.174.73.80 (talk) 15:07, 27 September 2018 (UTC) Marco Pagliero Berlin

PS Neither nor: neutrino emission from the core cools the neutron star very quickly: https://academic.oup.com/mnras/article/324/3/725/1025405

"After a period of intense accretion the neutron star surface cools on a time scale of years." Source: Thermal and transport properties of neutron star matter.[11]

--Guy Macon (talk) 04:07, 27 September 2018 (UTC)

Manhole cover in space?

Assuming that the shaft steel plate cap of the Pascal-B nuclear test actually survived its launch (it was never found), where would it be now? Is that fast enough to leave the solar system? Be ahead of Voyager? It would be ironic if the first contact an alien race had with humans was to be hit by a giant manhole cover travelling at 150,000 mph. SpinningSpark 17:21, 26 September 2018 (UTC)

So close to a nuclear explosion everything simply gets evaporated in some nanoseconds by the heat. The physical expansion is rather slow in comparison. Little Boy exploded 580 metres (1,900 ft) above the city of Hiroshima and caused temperatures of 6000 C° in a cone beneath it on the ground. The nuclear core is so hot that it starts rising up by heating the air around it so viciously that the resulting Convection airflow takes the core with it up. That is how the typical nuclear mushroom forms. --Kharon (talk) 18:15, 26 September 2018 (UTC)

• No, that's rubbish (as usual for your comments). Andy Dingley (talk) 18:17, 26 September 2018 (UTC)
• No, that's rubbish (as usual for your comments) II. --Doroletho (talk) 10:24, 27 September 2018 (UTC)

• It was definitely faster than Earth escape, definitely slower than Solar escape. However no-one knows how it would survive passing through the atmosphere. If it stayed in one piece, it's probably now in a solar orbit. If it broke in two, it probably broke further and burned up on ascent. Andy Dingley (talk) 18:16, 26 September 2018 (UTC)

Well thanks but no thanks for the flowers Andy. Even a 500 ton Tungsten (wolfram) plate would evaporate faster that the physical blast could reach it. Nuclear cores heat up to 100,000,000 C° in their chain reaction. If you put anything close enough to a chain reaction to theoretically push it to 66 km/s, it wont get pushed but turned to its Plasma (physics) state. --Kharon (talk) 18:32, 26 September 2018 (UTC)

The first frame of the high-speed film taken at the time has the thing airborne (that's how they got the lower bound on the speed) so that kind of makes you, well ... wrong. SpinningSpark 18:41, 26 September 2018 (UTC)

I doubt that but since there is no physical evidence (1 frame is no prove), you believe what you like. All i know is that 100,000,000 C° evaporates everything close to it faster than a 1957 highspeed camera can record. --Kharon (talk) 19:04, 26 September 2018 (UTC)

Wrong. Not even close to being correct. Read the reference that you yourself cited: "Two pulses of thermal radiation emerge from the fireball. The first pulse, which lasts about a tenth of a second, consists of radiation in the ultraviolet region. The second pulse which may last for several seconds, carries about 99 percent of the total thermal radiation energy."

In 1957 high speed cameras were commercially available that took 600 pictures per second, and the fastest cameras took 4.5 million pictures per second.[12]

Last time I checked 1/600 of a second is less than either 1/10 of a second or several seconds.

The force that blew the lid off, on the other hand arrived at the speed of sound. Nobody who understands the physics thinks that the nuke vaporized the lid. The question is whether it was traveling fast enough for atmospheric friction to vaporize it before it exited the atmosphere. If the answer is no, then a manhole cover beat Sputnik into space. --Guy Macon (talk) 20:32, 26 September 2018 (UTC)

Even if vaporization of the object does have time to proceed significantly before the shock wave reaches it, that will kickstart the acceleration of the object due to ablation, so no matter which way you slice it the object starts traveling very fast. 114.124.239.237 (talk) 23:48, 26 September 2018 (UTC)

• If you're that interested, you can read my work (and many others, originally Peter Hagelstein) in the '80s on X-ray lasers and the production of them via irradiation of thin metal foils by either lasers or nuclear devices. See the underground Excalibur tests. And these were thin foils, not manhole covers. So please don't give me this crap about 500 ton tungsten manhole covers turning instantly to plasma without moving. Andy Dingley (talk) 11:34, 27 September 2018 (UTC)

The Escape velocity from Earth's gravity is 11.186 km/s and from the Sun's gravity 617.5 km/s. Designer Dr. Robert Brownlee estimated that the explosion accelerated the plate to six times the former, which would not allow its remains to escape the Solar System. The Voyager space probes had escaped from the Sun's gravity by 1980 after flying past Jupiter, see [13]. DroneB (talk) 19:05, 26 September 2018 (UTC)

Sorry, this is plainly wrong. The velocity necessary to leave the Solar System from the Earth' surface is minimum 16.6 km/s though it depends on direction. This is so called total escape velocity. You need to learn some basic physics before making such claims. Ruslik_Zero 19:42, 26 September 2018 (UTC)

With the initial velocity of 66 km/s the final velocity upon leaving Solar System will be 85 km/s if the initial velocity was in the direction of the Earth's orbital motion. If it was launched in the direction opposite to the Earth's orbital motion, it will now orbit Sun in the retrograde direction somewhere between Earth and Mars. The real situation is more messy, of course. Ruslik_Zero 19:58, 26 September 2018 (UTC)

I am no nuclear physicists so i may have overlooked something in my "vaporizing"-answer. Luckily we have good articles to cite from like Effects of nuclear explosions:

(cite) "Energy from a nuclear explosive is initially released in several forms of penetrating radiation. When there is a surrounding material such as air, rock, or water, this radiation interacts with and rapidly heats it to an equilibrium temperature (i.e. so that the matter is at the same temperature as the atomic bomb's matter). This causes vaporization of surrounding material resulting in its rapid expansion." (cite end). So the "blast" is clearly just a secondary phenomenon of the vaporization, or rapid change to a plasma state, given the just 100 MILLION DEGREES Celsius or Kelvin(273.15° difference doesnt matter anymore at such numbers). The only chance that this "Manhole cover" had is when it was far enough away and shielded from the radiation. I concluded for an impulse from 0 to 55Km/s it must have been very close. --Kharon (talk) 02:45, 27 September 2018 (UTC)

With on object like a manhole cover, the radiation is first incident on the top layer of object, heating it directly and very, very quickly. This causes that layer to immediately vaporize and expand as a cloud of hot gas (a process known as ablation), pushing the remaining non-vaporized portion of the cover in the direction away from the blast. With the top layer of the manhole cover removed, the second layer is now irradiated and vaporized, which accelerates the bulk of the manhole cover further. As the cover moves further from the blast, the degree of radiation it is subject to is reduced very rapidly (due to the inverse square law). This allows the object to be accelerated to a very high speed without the bulk of its matter being heated to vaporization. 202.155.85.18 (talk) 03:27, 27 September 2018 (UTC)

• There are too many factors involved to sum this up in a simple answer. First of all, when talking about heat, we're talking about energy. When talking about vaporization, we're talking about energy transfer. How that energy transfers all depends on the method of transfer and the material it transfers to (ie: absorption and dissipation). The initial release of energy comes in the form of a blast from the detonation charges, followed by an intense radiation (light) wave that outruns the supersonic shockwave. At enough intensities, this light exerts more pressure than heat, and this is especially true for reflective objects like metal. (There are actually laser meters that measuer power by the pressure the beams exerts on the mirror.) In close enough proximity, this light blast will arrive at roughly the same time as the concussion, and, since the metal does not absorb radiation well, nor the thermal heat fast enough, it is conceivable it would absorb most of that energy as kinetic and become airborne.

At mach 2 you can expect to be heated to around 200 degrees F. At mach 5 you're up to about 1325 degrees, hitting 4000 by mach 8. Temperatures of the nose of the Apollo capsules reached up to 19,800 degrees (the temp of a blue star). While it is extremely plausible such a thing could be blasted far from the explosion, that it would survive traveling through the atmosphere for any distance before ablating to death or exploding itself like that meteor over Russia a few years ago, is highly unlikely. (Or that it would retain it's energy long enough, as the atmosphere will dissipate it quickly for such a small object. Remember, skin pressure goes up dramatically once you go supersonic, because the air just can't get out of the way fast enough. Zaereth (talk) 03:25, 27 September 2018 (UTC)

You can clearly see at 1:00 on this video: https://www.youtube.com/watch?v=KQp1ox-SdRIt=60 that the expanding blast wave hits nearby objects first (you can see it expanding at the speed of sound) and that the high temperatures come a fraction of a second later (you can see this when the fireball becomes much brighter). Thus a manhole cover that is blown into space by the blast wave is long gone before the high temperatures you keep SHOUTING ABOUT IN ALL CAPS AS IF WHAT MATTERS IS HOW HOT AND NOT HOW SOON reach the place where the manhole cover used to be. And of course you assumed that "the speed of a 1957 highspeed camera" was much lower than the actual figure of 4,500,000 FRAMES PER SECOND.

The distance between the bomb and the cover was 500 feet.

The camera was recording 1 frame per millisecond.

The blast wave hit the manhole cover 506 milliseconds after the bomb went off. Note that being at the bottom of a shaft magnifies the blast wave compared to a free-air detonation, but does little to concentrate the thermal effects, most of which end up vaporizing a big hole 500 feet down.

The welds held for some short amount of time, allowing the pressure to increase, then the manhole cover was launched at a calculated velocity of 180 feet per millisecond.

By the time the thermal maximum happened, roughly 1000 milliseconds later, the manhole cover is calculated to have been roughly 35 miles up and still climbing, having passed through the stratosphere and into the mesosphere.

The scientist who did that calculation concluded that it was going too fast to burn up before reaching outer space: "I was in the business and did my own missile launches. I realized that that piece of iron didn’t have time to burn".[14] This is easily confirmed by examining nickle-iron meteorites that are considerably smaller and faster than the manhole cover, and arrive on the ground icy cold with zero evidence of surface melting.

All of which is just a long-winded way of saying "Kharon is wrong". Zaereth, on the other hand, is likely to be right. It would be very interesting to see the calculations for a gun attempting to fire a metal projectile into space. We have an article on this: Space gun. --Guy Macon (talk) 04:15, 27 September 2018 (UTC)

Not sure if you're talking to me, but you make a good point. You also have to take into account that air pressure and speed all play a role. Meteors that are traveling fast enough may explode before ever reaching the ground, such as the one in Tunguska, or those that hit Jupiter a few years ago. Those that are small enough may ablate completely. Ablation transfers little to almost no heat to the main body, which is why it is used for cooling space vehicles. These are typically 80,000 mph +, and not every meteor is traveling that fast relative to the Earth. Then there is the physical stress of accelerating that at that rate, which I know from experience can lead to an object completely spalling before traveling more than a few yards. It seems entirely plausible either way, but, like I said, too many factors involved to sum it up so simply. I do agree that vaporization from heat of the blast is the least likely. Zaereth (talk) 04:13, 27 September 2018 (UTC)

For whatever it is worth, my physicist's intuition is that the scenario described would not be capable of reaching orbit, too much atmospheric drag relative to the mass and speed of the projectile. However, when I tried to do a rough estimation of the drag forces involved, my calculation made it seem like a much closer thing than I had expected. For 900 kg disk 1.2 m across and 60 km/s initial velocity, I estimated that it would reach an apex of more than 35 km in altitude, which is rather quite a lot. In my rough calculation, the disk slows from 60 km/s to only 2 km/s by 2 seconds after launch, but has already hit an altitude of 10 km by that point. Though the cover would likely be somewhat ablated by the initial explosion and the subsequent hypersonic drag, if the initial acceleration of the launch doesn't tear the cover apart, I would guess that the cover would remain mostly intact until it returned to the Earth. Dragons flight (talk) 14:14, 27 September 2018 (UTC)

Plant identification help

Unidentified plant

The flower

The leaves

Could anyone please help identify this plant, growing in a Sussex garden in September? The stalk is a distinctive red, matching the colour of the flowers. Shallow, chalky soil, full sun, facing south. This specimen is about 2'6" tall. DuncanHill (talk) 18:34, 26 September 2018 (UTC)

This plant is Leycesteria formosa, known commonly in the UK as Himalayan honeysuckle or Pheasant berry. Richard Avery (talk) 07:10, 27 September 2018 (UTC)

Splendid, thank you. DuncanHill (talk) 14:29, 27 September 2018 (UTC)

Dutasteride and erectile dysfunction

Please consult your doctor or pharmacist -- we don't answer this kind of question here

After how many days of daily Dutasteride 0.5 mg administration will the erectile dysfunction become irreversible? — Preceding unsigned comment added by 2401:FA00:C:702:DC27:9C1A:E16F:22E3 (talk) 21:21, 26 September 2018 (UTC) Didn't you ask that question already? ←Baseball Bugs What's up, Doc? carrots→ 22:38, 26 September 2018 (UTC) This is a different one and the previous question was not answered in a satisfactory manner. — Preceding unsigned comment added by 2401:FA00:C:702:DC27:9C1A:E16F:22E3 (talk) 23:02, 26 September 2018 (UTC) When are you going to see your doctor about this? ←Baseball Bugs What's up, Doc? carrots→ 00:23, 27 September 2018 (UTC)

September 27

Plutonium density

According to the article allotropes of plutonium, the least dense phase is the δ phase, and it has a face centered-cubic structure. But a fcc structure is one of the two most dense packings possible, the other being hexagonal close-packing. How is it that the most dense packing structure gives the least dense allotrope? 202.155.85.18 (talk) 06:39, 27 September 2018 (UTC)

• The article matches the refs, even though it seems extraordinary. (A negative thermal expansion coefficient for a crystal? Come on...) Ref #2 lists (p. 294) your remark as "unusual property" #5 and ascribes it to nonstandard behavior of the 5f electrons (p.296 and following give an explanation but I find it hard to follow); in other terms, the "rigid spheres with a constant atomic radius" model is too wrong to apply it here. Tigraan^{Click here to contact me} 07:18, 27 September 2018 (UTC)

Hmmmm...actually that makes a lot of sense. The Goldschmidt correction for actinide series elements is probably much larger due to the lanthanide contraction, so as the coordination number is increased going to more and more close packed structures, the metallic radius increase is so great it leads to overall lower densities. Thanks! 202.155.85.18 (talk) 07:26, 27 September 2018 (UTC)

I don't know what the bloody hell you two are on about but that was great. It almost made me want to follow the links. (I always found physical chemistry banal). — Preceding unsigned comment added by Greglocock (talk • contribs) 09:56, 27 September 2018 (UTC)