Wikipedia:Reference desk/Archives/Science/2016 July 25

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July 25

Glassy carbon

How is glassy carbon made? 2601:646:8E01:7E0B:D013:7C29:7816:F57B (talk) 03:15, 25 July 2016 (UTC)

The Wikipedia article you linked contains links to information on scientific journals and patents which should describe exactly that. --Jayron32 10:23, 25 July 2016 (UTC)

This supplier describes a full range of glassy carbon products, from which you may glean ideas about the processes used to make them. AllBestFaith (talk) 22:16, 25 July 2016 (UTC)

Question about gardasil research

According to here,http://www.cdc.gov/hpv/parents/questions-answers.html,under the the question about why Gardasil is recommended for preteens,it states that the vaccine provides a higher immune response in preteens. Where can I find research which proves this?

And how less effective is the vaccine for those aged 22-26? 30 percent less? 50 percent? — Preceding unsigned comment added by Uncle dan is home (talk • contribs) 04:16, 25 July 2016 (UTC)

(EC) The vaccine most effective by far if the person does not already have the strains of HPV it's effective against. As the strains of HPV are primarily sexual transmitted, once the person has had sex, there is a risk they've already caughtbeen infected by one or more of the strains of HPV the vaccine targets. Effectiveness will depend significantly on whether this has happened which will vary from individual to individual (although by 22 years old, the percentage of people who have not been sexually active in the US seems to be quite low). You could look at this on a population basis and it's possible there are studies which have done so but it's definitely not a simple estimation. There may be a minor advantage due to increase immune response, but this isn't the primary advantage to vaccinating at an early age and the site you linked to seem to reflect that. Nil Einne (talk) 09:14, 25 July 2016 (UTC)

The immune response to the vaccine is about 50% weaker in young adults than in teens, as measured by circulating anti-HPV antibodies[1]. However, it is unknown whether this makes women immunized in young adulthood more vulnerable to HPV infection than women immunized as teens or pre-teens. Someguy1221 (talk) 09:05, 25 July 2016 (UTC)

And in addition, because of Nil Einne's response, this finding hold's true even if the women have no prior exposure to HPV, at least as can be measured. Someguy1221 (talk) 09:20, 25 July 2016 (UTC)

Kingsfoil

What real-life plant (if any) was the stand-in for the Middle-Earth medicinal herb Athelas (kingsfoil) in the movie Lord of the Rings? https://www.youtube.com/watch?v=AwYO_4VFAYU 2601:646:8E01:7E0B:D013:7C29:7816:F57B (talk) 08:30, 25 July 2016 (UTC)

This may help. --Jayron32 10:21, 25 July 2016 (UTC)

I searched the internet far and wide, and came across the same article as Jayron, but it doesn't answer the actual question. That page is asking what actual plant matches the description of Kingsfoil from the books, none of which resemble the plant that was shown on screen in Peter Jackson's film version. The internet doesn't seem to know the answer to the question. Someguy1221 (talk) 10:39, 25 July 2016 (UTC)

I can't help today, but OP can likely get some potential answers by posting that clip (or ideally a few still frames) to the plant ID experts at Reddit's /r/whatsthisplant [2]. 14:01, 25 July 2016 (UTC)

I had a look at the clip - but to be honest it is so dark in that scene,and you get such a brief glimpse of the plant, by torchlight, that it could be almost any low-growing, New Zealand plant (though obviously not a grass). Wymspen (talk) 15:13, 25 July 2016 (UTC)

I could not identify it after looking at the clip. It is not inconsistent with native NZ bush, so Jackson may very well have used what was on hand in a typical bush setting. Akld guy (talk) 23:14, 25 July 2016 (UTC)

• I am not sure why anyone would take Jackson's bastardizations as having anything to do with Tolkien's novel. But basil is an herb known for its aroma (put a teaspoon, even dried, in a small boiling pot to see) and the name comes ultimately from the Greek basileus for king. μηδείς (talk) 01:15, 26 July 2016 (UTC)

• Here, by the way, is all the canonical description there is: "... long leaves .... a sweet and pungent fragrance." —Tamfang (talk) 06:24, 26 July 2016 (UTC)

Not basil, then. The fragrance might be right, but basil does not have long leaves. Wymspen (talk) 12:00, 26 July 2016 (UTC)

And eagles are not large enough to carry hobbits, Beren, or Luthien--my suggestion is that the inspiration is obvious, and there are indeed varieties with long, rather than round leaves. μηδείς (talk) 21:56, 26 July 2016 (UTC)

However, every schoolboy knows that dock leaves cure nettle rash. Alansplodge (talk) 20:04, 27 July 2016 (UTC)

Anglican schoolboys, perhaps. No Merickan's ever heard of either 'cept in litrature. μηδείς (talk) 22:21, 27 July 2016 (UTC)

You appear to have used 'Anglican' to mean 'English', but in Britain and its Commonwealth (Australia, New Zealand, possibly Canada, and many others), the term means 'one who is an adherent of the Anglican church'. That's the way I read it, and it didn't make sense until I read the Merickan part :)) Akld guy (talk) 03:02, 28 July 2016 (UTC)

Yes, I was working on the premise that JRR was an Englishman, and would have known what English schoolboys know, since he had been one. Alansplodge (talk) 17:42, 29 July 2016 (UTC)

Nichrome wire heating element calculation

So I'm a building myself a heat press for a fashion project of mine. And right now I'm struggling to find a power supply for a structure I've made. The problem is that I don't know how many Volts I need to put through my Nichrome wire heating element to bright it up to the desired temperature of 300-400C and also how much Watts should the power supply be able withstand.

The heating element is made of ~14meters of 2mm thick Nichrome wire. I understand that it is probably too thick, but I've already fixed it in place so I'd rather make the press work with it instead of having to replace all the wire entirely. I've measured the resistance of the wire and it is 5.7ohms in total.

How do I calculate the current and voltage needed to heat it up to 300-400C? Is it even possible to reach such temperature wit the wire such thick? Stepan Drunks (talk) 11:11, 25 July 2016 (UTC)

Our article on Nichrome has a table suggesting that 2 mm diameter wire needs 15-20 Amps to reach 300-400 C in open air. Looking at the picture, you seem to have the wire wound back and forth, which would somewhat reduce air cooling, and probably means you need to use somewhat less current. 15-20 Amps corresponds to 85-115 V, if your resistance measurement is accurate (it seems plausible for the dimensions given). It may go without saying, but you are talking about dangerous voltages, dangerous currents, and dangerous temperatures. If you aren't familiar with the safe handling of these materials, I would strongly encourage you to find someone with more experience to supervise your work. In particular, it looks like you mounted the wire in a metal frame. This could be very dangerous if the current unexpectedly moves through the frame rather than through the heating element. Dragons flight (talk) 11:44, 25 July 2016 (UTC)

Agreed. You would want ceramic insulators separating the heating wire from the frame. This is both for electrical and thermal insulation. You want to avoid the frame becoming so hot you burn yourself if you brush up against it, and you also want to avoid the heating wire cooling down at the edges, for most applications. Look at electrical resistance space heater designs. The good ones use insulators. StuRat (talk) 14:57, 25 July 2016 (UTC)

• As always, use a spreadsheet model to calculate this, so that you can change the parameters interactively without having to manually recalculate the lot.

You can calculate the power for a nichrome element from standard tables, or from standard tables of its resistance, then $V^{2}/R$. There are online calculators like this http://www.jacobs-online.biz/nichrome/NichromeCalc.html It's not an easy calculation from scratch, as the resistivity of the wire is temperature dependent. This power calculation, and then some estimation based on specific heat capacity, will give you a range limit (but not an estimate!) for the press temperature.

You can also get a triac controller (cheap modules from eBay) and an IR thermometer (again, eBay). Then just do some experimentation, but starting small.

As a wild guess, your wire is too thick. A simple estimate says that on 240V mains voltage that's a 10kW heater. This is too big to supply from a domestic 3kW supply and too big to design and build as a first experiment with the technology. If you run it from a low voltage supply, it's still a very low impedance - that means it's either a difficult high current to manage, or else a very low power. At 12V it's only 25W, at 24V only 100W. These are easy voltages to work with (cheap control modules are available), but I doubt that's enough power to be useful. I'd choose a wire size to make a mains-powered element just powerful enough (allowing scope for control) to achieve the temperature needs. I also don't like the look of all that unsupported wire - nichrome expands a lot when hot, so the elements sag. This takes them away from the press surface and the repeated movement also shortens element life.

You can use constant current supplies for small elements, but not large, hot elements. They're easy to work with, but not once the wire gets hot enough to start changing its own resistance.

I think I'd look at starting again. Calculate the power needed _first_, then design an element to deliver this. The power/temperature relationship depends on the heating time: a fast heat might be dominated by the specific heat capacity of the material being pressed (i.e. heating up a cold item) whilst a long heat becomes dominated by heat losses to the outside, which is all about the insulation.

I'd try phoning a heating element maker, or a wire seller, and asking them for advice from the outset. You might also find a heating blanket or a pre-made flat panel is much easier to work with than bare wire. Andy Dingley (talk) 11:56, 25 July 2016 (UTC)

Construction points:

• Assuming your heating element is mains powered, the frame must be connected to ground.
• The target temperature range 300-400C will melt solder so the electrical connections must be by screws or crimped.
• Ceramic or mica standoff insulators are needed to support the heating wire. The support strips in the photograph look inadequate and possibly conductive(!)
• For testing it's very desirable to use a Variac [3] (see Autotransformer) to adjust the mains supply, gradually increasing the voltage while monitoring both voltage and current to confirm your calculation.
• Wires at more than 10V potential should not be exposed to fingers or moisture.
• For safety, heaters of this kind are usually equipped with a Thermostat, a power "ON" lamp and a fuse and/or Circuit breaker.

The article Electric heating is required reading. AllBestFaith (talk) 22:07, 25 July 2016 (UTC)

I'm sorry but I'm going to repeat what some people above had already said. It appears that you are a fashion student, not an electrical engineering student. I have made many electrical projects and even a few high voltage projects, seeing the box you've made and hearing you are considering plugging it into the mains makes me very nervous. 400c is VERY hot, it's far hotter than a clothes iron and it's even hotter than I ever put my soldering iron on. What do you need that kind of temperature for? Vespine (talk) 22:51, 26 July 2016 (UTC)

Agreed. 400 °C is the sort of temperature where lots of stuff spontaneously catches fire. Projects using high voltage OR high current already require lots and lots of care to do safely, and high-power – i.e. high-voltage AND high-current simultaneously – is the sort of thing you really, really don't want to mess with unless you know exactly what you're doing. With all due respect, if you need help with these calculations, chances are you're not at that point just yet. Please don't get yourself killed! --Link ^(t•c•m) 01:03, 27 July 2016 (UTC)

Efficiency of carbohydrates to fat conversion

Good evening, folks. As you know, the human body can convert excess carbohydrates into fat. What is the average efficiency of this process? Thanks.--90.69.12.160 (talk) 21:22, 25 July 2016 (UTC)

irrelevant criticism
The following discussion has been closed. Please do not modify it.
It's kind of disrespectful to greet readers with "Good evening". At the time you posted, 21:22, it was already 09:22 on Tuesday morning of the 26th here in New Zealand. If you want answers from everywhere, please don't address your post to one set of time zones, otherwise readers in other time zones might get the impression that their contribution isn't wanted. Akld guy (talk) 22:54, 25 July 2016 (UTC)

What kind of efficiency are you looking for ?

1) As far as what proportion of the carbohydrates are destroyed in the process, rather than converted to fat, not counting those which are "burnt" to create energy, I would guess that portion is quite low.

2) As far as energy used to do the conversion, that may well be significant (whether that energy comes from carbs, fat, protein, glucose, etc.). Would you measure that energy in proportion with the energy stored in the fat created ? StuRat (talk) 01:56, 26 July 2016 (UTC)

The energy to convert carbs to fat comes from NADPH, which is a byproduct of the conversion of glucose into the precursors to nucleotides and aromatic amino acids. One NADPH per carbon, to be specific, and two NADPH is generated per glucose consumed, so basically it takes three glucose molecules to incorporate one glucose molecule into a fatty acid. It's actually really hard to put an energetic cost and thus efficiency on this, for several reasons. 1) The reactions occur spontaneously; 2) Simply getting to the acyl-CoA precursor to make fatty acids passes through glycolysis, which generates energy; 3) The glucose that was consumed to generate the NADPH needed to be consumed anyway to generate those aforementioned precursors. You could try to ask instead how the energy of the fatty acid compares to the energy of the input glucose. In that case, each gram of fat yields 9kcal, while each gram of sugar yields 4kcal of energy. You might think you actually gained energy by converting to fat, specifically the fatty acid yields about 16% more energy than the glucose used to make it. This is because of all those other glucose molecules that were burned to synthesize it. So in the end, you can look at this a couple of ways. You could think of this as being essentially perfectly efficient since the body is simply making use of waste energy generated by nucleotide/amino-acid synthesis. Or you could ask about opportunity cost, I suppose. What if those NADPH were instead NADH, and shuttled to the mitochondria? That would be about 6 ATP per glucose consumed by nucleotide/amino-acid synthesis, or 18 ATP per glucose that would have been used to make fatty acids. Heck, that's about half the energy you would get from simply consuming one glucose through cellular respiration. So you could say you are taking a 1/6 increase in energy at the cost of a 1/2 increase in energy, so a loss of 22% from the energy you could have had. So ah, I guess in summary, it really depends on how you feel like running the numbers. (Conclusions from this answer were drawn from information at: NADPH, Fatty acid synthesis, Fatty acid metabolism, glucose, glycolysis, NADH, pentose phosphate pathway). Now what I haven't read far enough to figure out yet is how things change if things get unbalanced. Such as, what happens when you are eating so little you require net loss of fatty acids while still making nucleotides and amino acids. Do those NADPH go somewhere else instead? And what about when food intake is so high that NADPH requirements to form fatty acids exceed their production as a byproduct? Is there another method to make them? Does the fatty acid synthesis rate have a ceiling? Does the body just make nucleotides/amino-acids it doesn't need? I guess in both situations your accounting of the efficiency may be altered. Someguy1221 (talk) 02:39, 26 July 2016 (UTC)

So the old adage is true: to keep slim, cut down the carbs and sugar.--86.187.174.194 (talk) 23:17, 26 July 2016 (UTC)

If the goal is weight loss, I'd see an endocrinologist. The one my pharmacist recommended helped me lose 70 lbs, 40 of which my gen prac helped me put on with bad advice. I am cleared as of today for bariatric surgery, which should leave me at ideal weight and totally alleiviate my hyper-glycemia, -lipidemia, and -tension. But this has all been done under MEDICAL advice, and I would not trust anything but a trusted, licensed specialist. If you live in NY or NJ, email me for a reference. Otherwise, shop around in your area. μηδείς (talk) 04:17, 27 July 2016 (UTC)

Diet didn't work for you? Count Iblis (talk) 21:29, 28 July 2016 (UTC)

I am not sure that all people who want to lose weight would need an endocrinologist. It all depends on the amount of fat you want to lose, and how it got there. 10 lbs are not comparable to 70 lbs, and an hormonal unbalance is not comparable to being a potato coach. Hofhof (talk) 22:06, 28 July 2016 (UTC)

"Potato coach"? I like that. Yes, I was assuming that if a person were going to the trouble of posting on line that they were probably then more than 10 pounds overweight. And there are many different sorts of conditions like pre-diabetes and hypothyroidism that may only manifest in moderate obesity. In any case, seeing an endocrinologist who specializes in metabolism rather than relying on adages is a reasonable act if one is concerned with one's metabolism. μηδείς (talk) 03:53, 29 July 2016 (UTC)