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April 17

Fins

Plz tell me for a heat transfer equation of fins,we have different cases 1.convection from tip. 2.insulated tip 3.infinitely long. plz tell conditions to be met to assume fins to have insulated tip.

SD — Preceding unsigned comment added by Sameerdubey.sbp (talk • contribs) 04:54, 17 April 2017 (UTC)[reply]

Please do your own homework.

Welcome to Wikipedia. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.. --Jayron 32 11:01, 17 April 2017 (UTC)[reply]

I'd like to see a penguin, seal, fish or dolphin with infinitely long fins. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:22, 17 April 2017 (UTC)[reply]

I believe the case with insulated tips implies heat leaves the fin through the two side faces of the fin, but not through the tip. Dolphin (t) 11:59, 17 April 2017 (UTC)[reply]

The article Heat sink has a section about fin efficiency that offers values for convection coefficient. Fin efficiency is defined as the actual heat transferred by the fin, divided by the heat transfer were the fin to have infinite thermal conductivity. However the key value to use in selecting a heat sink is its Thermal resistance defined as temperature rise in degrees Celsius per watt (°C/W). This is tabulated by heat sink manufacturers and the the temperature rise of the device over the ambient air can be calculated by multiplying it by the dissipated power in watts. Note that the thermal couplings of a semiconductor die to its case and of the case to the heatsink each represent thermal resistances in series with the heatsink, and in the latter case can be minimised by a thin layer of Thermal grease. SdrawkcaB99 (talk) 15:33, 17 April 2017 (UTC)[reply]

Governments

Why is it that governments don't have many scientists and engineers? They have nearly all policy specialists and supporting lawyers, economists and statisticians. 2A02:C7D:B8FC:9000:B8C7:87EC:A8:3648 (talk) 11:12, 17 April 2017 (UTC)[reply]

Who says they don't? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:20, 17 April 2017 (UTC)[reply]

In the U.K. anyway. I checked their organograms. 2A02:C7D:B8FC:9000:B8C7:87EC:A8:3648 (talk) 12:30, 17 April 2017 (UTC)[reply]

Are you referring to an organization chart? Do such charts list every last employee? And do they include consulting firms? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:33, 17 April 2017 (UTC)[reply]

Because scientists deal in facts, and politicians want to be able to ignore those. The aims of scientists and politicians are often almost diametrically opposed. Having said that there, are/have been scientifically trained heads of state (Angela Merkel, Margeret Thatcher, Elio Di Rupo just in Europe alone), and the current Dutch Interior minister (Ronald Plasterk) was a renowned molecular biologist. Fgf10 (talk) 14:43, 17 April 2017 (UTC)[reply]

There were just 2 scientists in the US Congress, as of 2015: [1]. This is somewhat understandable in the case of Republicans, who often run on an anti-science platform such as denying man-made climate change, supporting teaching "intelligent design" in schools, while opposing teaching evolution, etc. But, in the case of Democrats, more of an explanation is needed (although note that both current scientists are Democrats, as was the one who retired to bring the number down to 2). Running for office often requires the opposite of clear, plain statement of facts. For example, if you tell coal miners their jobs are gone and are never coming back, they won't vote for you. So, scientists tend to avoid politics, or, if they do run, they tend to lose if they try telling voters the truth. StuRat (talk) 14:57, 17 April 2017 (UTC)[reply]

In the U.S., both "pure" science and R&D are mostly contracted to private companies. This includes the companies that run the national labs like ORNL and LLNL, and the scientists and engineers that develop weapons systems. There are two major reasons. First: the political philosophy of "small government" gets translates into "fewer (direct) government employees." Silly. Second: government salaries are controlled via a cumbersome set of rules that make it very difficult to pay scientists and engineers competitively. Contracting to a company avoids this problem. -Arch dude (talk) 15:37, 17 April 2017 (UTC)[reply]

Government run by scientists and engineers is called (broadly) technocracy. Wikipedia's article on technocracy discusses some of the benefits and problems thereof. --Jayron 32 15:39, 17 April 2017 (UTC)[reply]

There are several examples of politicians and cabinet members with science and technology backgrounds. From the technology article linked by Jayron32 above, "...leaders of the Communist Party of China are mostly professional engineers". Margaret Thatcher earned a bachelor's and Angela Merkel a doctorate in physical chemistry, Steven Chu has a Nobel Prize in physics, and Jimmy Carter has a background in submarine nuclear engineering.--Wikimedes (talk) 21:42, 17 April 2017 (UTC)[reply]

not the place to discuss these matters--Jayron 32 17:31, 18 April 2017 (UTC)[reply]

The following discussion has been closed. Please do not modify it.

Humans have existed for more than 200,000 years, politics has existed in some form for all that time and even before (I've seen a documentary about politics in ape societies). So our brains are adapted to use politics as a method to function in society. But science is a recent invention. While today we may think that in the old days the church repressed the people to keep them away from science, this is not the correct way to think about this issue. Our brains are programmed to respect authorities, so the Church had the respect of the people and they would then side with the Church if that authority would be challenged. Now science is all about being skeptical, statements need to be rigorously proven, it should be possible for anyone to question anything, the answer can never be an argument from authority. This is the complete opposite of how our minds have evolved. While science has made more and more inroads into society in the last few centuries, we're still the same old people who think in an extremely anti-scientific way about most things in life. Count Iblis (talk) 21:27, 17 April 2017 (UTC)[reply]

in my experience, people who cry the loudest how we shouldn't trust our puny brains also tend to swear by wheatgrass juice and oil pulling and such things, and to think that Ferguson and Berkeley were the result of active measures by a foreign power, so... Asmrulz (talk) 16:43, 18 April 2017 (UTC)[reply]

Aside from the alcohol, what's the difference between wheatgrass juice and beer? And what foreign powers? The cops? The white supremacists? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:09, 18 April 2017 (UTC)[reply]

Please hold these discussions outside of Wikipedia. This is not the purpose of the reference desks. --Jayron 32 17:31, 18 April 2017 (UTC)[reply]

Injected drugs coming out in the feces

Recently I was reading about an intravenous drug (Vincristine), and was surprised that the primary mode of elimination (~80%) is apparently via feces [2]. I assume that means that the drug is moving from the blood into the bowel as its main mode of elimination. How common is this? I had pretty much assumed that the elimination of injected/intravenous drugs was either in the urine (via the kidneys) or by being broken down chemically (e.g. in the liver). I can't recall having heard of anything that moves from blood to bowel in any significant degree. Are there natural substances produced in the body (i.e. not artificial drugs) that are also excreted by moving into the bowel? In a circumstance like this, does the contents of the bowel then affect the rate of elimination? Dragons flight (talk) 13:48, 17 April 2017 (UTC)[reply]

The breakdown of hemoglobin involves transport into (and sometimes back out of, if I'm reading Urobilinogen correctly) the intestines (see Hemoglobin#Degradation in vertebrate animals). DMacks (talk) 13:58, 17 April 2017 (UTC)[reply]

I found a paper about this: [3]. It credits biliary excretion, and suggests that loss of liver function might lead to higher levels in the patient. We could use more data on this -- I know that bile salts are excreted in ~~gall~~ (I mean bile) to the intestine and tend to take some hydrophobic crap with them. Indeed the gallstone classically forms from cholesterol being dumped via this route, and vincristine is, at a zero-order approximation, another big complicated molecule with a lot of rings like that. But I'd be lying if I said I understood the mechanism in any meaningful degree. Wnt (talk) 12:37, 18 April 2017 (UTC)[reply]

That is helpful. DMacks link also suggested transport via the bile duct. That makes more sense for large molecules than direct transport from the blood. I was unaware that the bile duct could be used for elimination. Dragons flight (talk) 15:01, 18 April 2017 (UTC)[reply]

As others have said, the two most significant means of elimination are urine and gut. Urobilinogen excreted in urine gives urine its yellow color, while urobilinogen in the gut is converted to stercobilin that gives feces its usual coloration. - Nunh-huh 15:09, 18 April 2017 (UTC)[reply]

First let me clarify something. When they say it is eliminated in the feces, they do not mean that it wasn't 'broken down' by the liver. They give a small amount of mildly radioactive drug, and see where the radioactivity comes out, but that doesn't mean it is unchanged and still active. You may be misleading yourself with that term 'broken down': in this context it doesn't mean the same as 'broken up'. Everything in the circulation through the liver, which has enzymes (cytochrome P450s) that alter blood-borne compounds, adding or removing side chains or otherwise modifying the chemical bonding. When this results in a change that renders the drug inactive, it is referred to as having 'broken down' the drug, even though the change is minor. This has the effect of either making the compound more water soluble, more likely to be excreted in the urine, or less water soluble, which targets them to the bile ducts and into the feces. What determines which way it goes depends on which specific P450 is doing the modifying, and that can vary depending on genetics, personal history (alcohol consumption turns some of them up, others down), and how much of the compound the liver is faced with. Agricolae (talk) 20:48, 18 April 2017 (UTC)[reply]

This is true, but at the same time, metabolism of drugs is often pretty minimal chemically speaking, and this seems to be the case with vincristine. [4] One carbon atom somehow goes AWOL out of that immense structure with the help of CYP3A5, and that is sufficient to "break down" the drug (to metabolite M1). The weird part is that this apparently matters a lot - that paper says that African-American children treated for leukemia were 42% more likely to die than Caucasians, due to ethnic differences in the rate of weak CYP3A5 alleles. That said ... the Caucasians were more likely to suffer nerve damage and pain from the drug. Chemotherapy is no picnic whatever happens. So this seems to be a case where personalized medicine to get the exact dose right could pay off. See also [5]; I think there were more along this line. Wnt (talk) 03:26, 19 April 2017 (UTC)[reply]

I guess I didn't make myself entirely clear, because your 'at the same time' is exactly what I was trying to describe. The cytochrome P450, CYP3A5 (and to a much lesser extent CYP3A4), carries out a minor chemical modification, which 'breaks down' the drug, and this is affected by (among other things) genetics (for which racial background is a handy proxy). As to 'one carbon somehow going AWOL', specifically, CYP3A5 (& CYP3A4) carries out oxidative cleavage of a carbon-nitrogen bond in one of vincristine's rings. The product has a distribution of electrons so unstable that another bond spontaneously breaks, releasing an O=C—O—H group.[6] The loss of two oxygens makes the molecule less polar - more lipophilic, and hence more likely to be excreted in the bile, and at the same time, less likely in the urine. Agricolae (talk) 15:20, 19 April 2017 (UTC)[reply]

Mixing oil and water

Is there any oil that would mix well with water, without making an emulsion?--Hofhof (talk) 19:32, 17 April 2017 (UTC)[reply]

By definition, an oil cannot mix with water. Someguy1221 (talk) 20:11, 17 April 2017 (UTC)[reply]

I would say that if something mixes with water well, it is not an oil. Ruslik_Zero 20:14, 17 April 2017 (UTC)[reply]

This may be of interest, however. Brandmeister^talk 20:36, 17 April 2017 (UTC)[reply]

That got my attention. Specifically, "To test his hunch, Pashley removed almost all the gas from a water-oil mixture by repeatedly freezing and thawing it while pumping off the gases as they evaporated out". I have spent many long hours removing dissolved gasses from superpure water, and have always used [A] a vacuum at the surface, and [B] mechanical agitation. Never tried freezing and thawing. What is the theory behind that? --Guy Macon (talk) 21:07, 17 April 2017 (UTC)[reply]

We have an article about Degasification, including freeze–pump–thaw. If a liquid crystallizes, it often leaves solutes (including gases) physically separate, so then you can pump off those now-gas-phase molecules. That method is pretty standard in some labs, as is (and sometimes "as a step before other methods") sparging with an inert and/or less-reactive gas.DMacks (talk) 21:20, 17 April 2017 (UTC)[reply]

Odd to think that oil is hard to dry out once you get it wet. Here is the article reference. This cites it and is readily available. There are some others I didn't run down - just search like Pashley emulsion "phase transfer". I was wondering if the method has applications comparable to phase transfer catalysts, or perhaps other applications in chemical synthesis... Wnt (talk) 03:38, 19 April 2017 (UTC)[reply]

We have an article about Water miscible oil paint. DMacks (talk) 20:45, 17 April 2017 (UTC)[reply]

Depends on what you mean by fat, and what you mean by water. If you use fats in the technical sense, it would include, for example, steroids. These have a low but non-zero solubility water, so they would dissolve rather than forming an emulsion, but only in very small amounts. As to water, solubility it depends on what else is in the water. Soluble substances can be added that would make the resulting solution more lipophilic, resulting in hydrophobic substances (such as oils) becoming more soluble. Detergents and some alcohols have this effect - these are molecules with a hydrophilic head and a hydrophobic tail. The tails surround and coat individual molecules of oil, with their water-loving heads pointing out and interacting with the water. This is what happens when you wash oil off your hands using soap, and is also why many liquid medicines include alcohol. However, it doesn't take very much oil to overwhelm the capacity of the solute. (You can also add compounds to water to make it more lipophobic, which would drive out even the small amount of fat, or add a 'stronger' lipid to attract the dissolved fats away from the water.) Agricolae (talk) 20:18, 18 April 2017 (UTC)[reply]