Wikipedia:Reference desk/Archives/Science/2014 April 2

= April 2 =

Parallel wires attraction
An electromagnetism question from grade 11 physics: "If two parallel wires are placed beside each other and current is sent down each wire in the same direction, will the wires attract or repel one another?" Based on the right-hand rule for conventional current in a straight wire, both currents would be facing down, so the magnetic fields would be going on the same direction. I'm not sure if others were taught this, but I used the X (X) and dot (.) diagrams to represent the direction of the magnetic field, with (X) being magnetic field in and (.) being out, representing cross sections of the circle; and the arrows being the direction of current in the wires:

(X) |  | (.)   (X) |   | (.) (X) |  | (.) + (X) |   | (.) (X) | | | (.) + (X) | | | (.) (X) | | | (.) + (X) | | | (.) (X) | v | (.)  (X) | v | (.)

Now, using the right hand rule for forces based on direction of current, would not the forces be going in the same direction, towards the right? The answer says they're being attracted. If anyone can shed some light on this, it'd be much appreciated. 64.229.154.240 (talk) 00:57, 2 April 2014 (UTC)

No. for the left wire it is the downward going bit of the magnetic field from the  right  wire, then use [] to experiemce a fore to the right, and not surprisingly the right experiences a force to the left. Incidentally you got the relationship between the current and magnetic field direction correct because you used the right hand grip rule. All very handy. Greglocock (talk) 02:48, 2 April 2014 (UTC)

Basically, between the wires, where I placed the "+", the field lines will cancel out. Because "field lines repel each other" (another rule you can use here), the wires are pushed towards the "+" area without a field, i.e. attracted to each other... or basically, what Greglocock said. The important part is the field lines cancellation betwen the wires, anyway. - ¡Ouch! (hurt me / more pain) 06:33, 2 April 2014 (UTC)


 * Thanks, I was a bit puzzled by something and you've clarified it.Greglocock (talk) 22:59, 2 April 2014 (UTC)

Boiler Design
Does a boiler have a manhole.117.194.229.101 (talk) 03:23, 2 April 2014 (UTC)


 * Does a boiler need cleaning and preventive maintenance of its interior components from time to time? That should answer your question. 24.5.122.13 (talk) 05:20, 2 April 2014 (UTC)


 * Well, you could make one to be disposable. That is, once it became encrusted with scale, you would simply replace it.  Or, you could have a small access hole, not large enough for a person to go inside, but big enough to replace a sacrificial rod, for example. StuRat (talk) 06:34, 2 April 2014 (UTC)


 * What do you mean by 'boiler'?, The construction is dependent on size. Richard Avery (talk) 07:13, 2 April 2014 (UTC)


 * Here is a diagram showing the placement of the manhole. The inspection door at the bottom is often called a mudhole, so called because this is were all the gunk gets flushed out during maintenance and has an  appearance  of light brown mud. They are usually  oval. This is so one can take them out, as they are designed to fit inside on a  tapered edge, so that the internal pressure helps to seat them firmly without risk that they might pop out. --Aspro (talk) 10:05, 2 April 2014 (UTC)


 * Well File:A 1958 Mamod SE2 steam engine.jpg doesn't have a manhole and File:HMS Belfast - Boiler room - Boiler opening.jpg does. So size really does matter. Dmcq (talk) 10:40, 2 April 2014 (UTC)
 * Uhumm! Ah! But you did not see Fantastic Voyage. That Mamod SE2 has a fill hole, plenty big enough for a hypodermic syringe. I saw it in the movies so know it it must be true.--Aspro (talk) 22:36, 3 April 2014 (UTC)


 * See Glossary of boiler terms.-- Auric    talk  14:44, 2 April 2014 (UTC)

Living longer by moving at high speed
The international space station moves pretty fast relative to the earth. I was wondering whether, assuming weightlessness doesn't eventually kill a person, could someone live longer* by staying in such as fast-moving environment?

* So relative to themselves, they'd live a normal lifespan, but relative to earth-time, they might be more likely to live to see the wonders of year 2114. --129.215.47.59 (talk) 12:02, 2 April 2014 (UTC)


 * Fast by our standards, but not all that fast compared to the speed of light. According to Time dilation, the ISS personnel age .007 seconds less than their earthbound counterparts, every six months. ←Baseball Bugs What's up, Doc? carrots→ 12:14, 2 April 2014 (UTC)


 * (ec) See the figure in Time dilation. As seen from the surface of the Earth, a day on the ISS lasts about 25 microseconds longer than a day on the ground.  The difference amounts to a bit less than 10 milliseconds per year; in an entire lifetime, the relative difference comes out to somewhere on the order of one second. TenOfAllTrades(talk) 12:22, 2 April 2014 (UTC)
 * You might live longer according to others if you went for a while near the speed of light and then came back to Earth. But you wouldn't have gained any time on your own watch. I wouldn't call that living longer, just you've been around longer. Dmcq (talk) 13:08, 2 April 2014 (UTC)


 * In order to get a considerable time dilation factor (say e.g. γ = 2, so time would pass at half the rate on Earth) one would also need enormous amounts of energy. Even if you ignore the weight of the spaceship, to simply accelerate a person weighing 80 kg to the required speed (about 86.6% of the speed of light) requires 7.2 * 1018 Joule, which is twenty times the total current worldwide energy consumption per year. When also considering the mass of the spaceship, fuel/oxygen, food and drink, it quickly becomes apparent that such scenarios will remain outside of humanity's reach for long time, if they will ever become feasible at all. - Lindert (talk) 15:46, 2 April 2014 (UTC)


 * To be completely clear though - moving fast doesn't make you live longer...at least not from your perspective. It makes time in the rest of the universe pass more quickly.  From your perspective, your life is exactly as long as it would have been...all else being equal of course.  Everyone else will believe that you lived longer, you're younger than they'd expect.  But not by your own experience.   SteveBaker (talk) 17:01, 3 April 2014 (UTC)


 * I find I can watch an hour's worth of nightly news in 15-20 minutes by DVRing it and skipping the commercials and segments that bore me. I can also play DVD's and video files a 1.5X playback speed, with no loss of enjoyment.  It's a practical solution applicable to daily life for most people more than travel near lightspeed. μηδείς (talk) 20:05, 3 April 2014 (UTC)
 * I just sleep less. No more than 6 hrs. a night. So Even if I die sooner, I have "experienced" more waking hours of stuff and therefore consider myself wiser as a result.165.212.189.187 (talk) 20:49, 3 April 2014 (UTC)
 * Before you jump to that conclusion, you might want to read about Sleep deprivation. ←Baseball Bugs What's up, Doc? carrots→ 21:38, 3 April 2014 (UTC)
 * before you do...this better describes me as my doctor has already concluded. 68.36.148.100 (talk) 06:12, 4 April 2014 (UTC)
 * The real problem is that these people tend to do well, they become the CEOs and politicians who impose their sleeping habits on the rest of the population. This is why the average hard working person ends up being sleep deprived and as a consequence then doesn't have the energy to exercise, gets obese which then leads to heart disease, cancer, diabetes etc. etc. :( .Count Iblis (talk) 17:20, 4 April 2014 (UTC)

Is this a healthy lunch?

 * 2 soft boiled eggs with pinch of salt.
 * 1 bowl of dry Country Crisp (granola/muesli hybrid)
 * 1 Large apple
 * Handful of green grapes.

I am trying to be healthy. Does the above lunch tick all of the boxes? Thank you. --Niolee! Ay! (talk) 13:17, 2 April 2014 (UTC)


 * Here's a link to the USA federal dietary guidelines . You can look up the nutrition info on your daily/weekly food, and see how it compares to the suggestions given. I'll add that only looking at lunch isn't that useful, you need to look at all the food you eat. SemanticMantis (talk) 14:48, 2 April 2014 (UTC)


 * See also here and here. Count Iblis (talk) 15:11, 2 April 2014 (UTC)


 * The obvious thing that's missing is veggies, particularly green veggies. Try adding a salad (with maybe spinach, tomatoes, peppers, beets, mushrooms, beans, nuts/seeds, onions and a balsamic vinegar and olive oil dressing). You also might want to add some dairy, maybe some yogurt ? And you will need something to drink with all this, how about some herbal tea (no caffeine) ? 2 eggs might be a bit much cholesterol, you might want to cut back to one, and skip the salt (you can also add the egg to the salad). Similarly you only need one fruit, so can skip either the apple or the grapes.  And, if you're eating grapes anyway, you might as well eat blue or red grapes, which have more antioxidants (or better yet, switch to berries). Beware anything like muesli/granola, as it often has way too much added sugar (that can be a problem with some yogurts and salad dressings, too).  Mixing sweet things with not-so sweet things can make them more palatable, like yogurt, fruit and granola. StuRat (talk) 15:16, 2 April 2014 (UTC)


 * See http://www.brendawatson.com and http://www.cindysays.com/ask_cindy.aspx and http://www.nutritionwerks.com/atd/index.asp.
 * —Wavelength (talk) 16:12, 2 April 2014 (UTC)


 * That's a horrible lunch for people with high cholesterol, high blood pressure, diabetes, diverticulitis, nut and apple allergies, and a host of other conditions. You need to talk to a licensed nutritionist or dietician or at leas your personal physician, not random people on the internet. μηδείς (talk) 16:47, 2 April 2014 (UTC)


 * Hopefully you don't need to pay a licensed physician to tell you not to eat foods which you are allergic to. "Really, there are peanuts in peanut butter ?  I had no idea !". StuRat (talk) 17:08, 3 April 2014 (UTC)

The Variable Specific Impulse Magnetoplasma Rocket on the ISS

 * In the meantime, Chang Díaz doesn’t need nuclear power to continue the development of his singular engine. “We will deploy VASIMR as a solar-powered rocket that can engage in a number of important near-Earth activities,” he says.


 * VASIMR’s frst test in space is tentatively set for 2016 aboard the International Space Station. Instead of nuclear power, the engine will rely on bursts of power from large battery packs charged by the station’s solar panels. Assuming all goes well, Chang Díaz says, Ad Astra will then pursue multiple near-term applications of VASIMR, such as periodically nudging the space station and other large satellites into stable orbits. -- Discover Magazine, May 2014, p. 41.

How do they install the VASIMR rocket on the ISS?

Which docking are they going to use? The Russian end or the U.S. end?

Will they use the Harmony module's pressurized mating adapter? Can the goose-necked structure withstand the force?-- Toytoy (talk) 13:21, 2 April 2014 (UTC)


 * Note that Progress, ATV, and STS (and I imagine Dragon and HTV) perform(ed) reboost burns to raise the ISS' orbit. A Progress propulsion module delivers 2950N of thrust; presumably the other service vehicles have comparable performance. The VASIMR article suggests the test article they're planning on fitting to it will deliver 5N. With that kind of force, they could attach the VASIMR with a cable tie. -- Finlay McWalterჷTalk 14:18, 2 April 2014 (UTC)
 * A small correction (quoting from the linked article) "For reboosts, Progress uses four or eight of its attitude control thrusters (130N each) pointing to the correct direction. The main propulsion system is generally not used for reboosts as it puts stress on the docking interface between the Space Station and the Progress. " 80.189.158.15 (talk) 17:08, 2 April 2014 (UTC)

Anti - Tan
The internet is loaded with anti - tanning scrubs/creams/lotions etc etc. How do these work ? Tanning is caused by melanin. I am clueless on how these scrubs work ! Looks like a placebo more or less to me ! — Preceding unsigned comment added by 117.193.142.11 (talk) 14:54, 2 April 2014 (UTC)


 * I would guess they either bleach or exfoliate the skin. The exfoliants work by removing the tanned skin and replacing it with new lighter-colored skin.  Obviously you can't remove all your skin at once, so this approach would take many applications.  (If wanting to get rid of a tan seems odd to any readers, in parts of the world, like the Orient, white skin is considered the ideal, supposedly showing a life of luxury lived indoors, much like long fingernails show that the woman can't do any real work.)  StuRat (talk)


 * Thanks for the explanation. It did seem odd! 129.215.47.59 (talk) 16:07, 2 April 2014 (UTC)


 * You're quite welcome. StuRat (talk) 18:50, 4 April 2014 (UTC)


 * Wikipedia has an article titled Skin whitening. It would likely answer your questions more authoritatively (or direct you to more places to look) than Stu's answer.  -- Jayron  32  16:48, 2 April 2014 (UTC)

3D molecular rendering software
What software was used to create these images? I know of a variety of programs but I'm wanting to be able to reproduce that appearance precisely. --129.215.47.59 (talk) 16:14, 2 April 2014 (UTC)


 * Edit: Nevermind! The answer is RasMol and it states this at the bottom of the page. --129.215.47.59 (talk) 16:30, 2 April 2014 (UTC)


 * Only the bottommost image (ball and stick representation) was created with RasMol which seems to no longer be under active development, although Jmol is still used for web based molecular visualization on sites such as Proteopedia. The more stylistic renderings appear to have actually been generated by David Goodsell. Given the unique and instantly recognizable appearance of his scientific illustrations, he likely has his own molecular rendering software. Although UCSF Chimera and to a lesser extent PyMOL can both generate "Goodsell-like" images with a little bit of tweaking. (+)H3N-Protein\Chemist-CO2(-) 21:49, 2 April 2014 (UTC)
 * Wow, Goodsell's stuff is great, looks like a form of cel shading - thanks! SemanticMantis (talk) 23:05, 2 April 2014 (UTC)

Physiology - respiratory insufficiencies?
Hello, I study medicine and I have to prepare a 20 minutes long presentation on respiratory insufficiencies. I read the chapter about this in Guyton, but my professor suggested finding something new, specific and more interesting, something other students probably wouldn't hear otherwise. He seemed to be very excited about asthma... So I'm asking you to tell me if there are any interesting new researches on asthma or other airways-related diseases? I already searched PubMed but couldn't find anything that would really draw attention. Thank you in advance. — Preceding unsigned comment added by Atacamadesert12 (talk • contribs) 20:01, 2 April 2014 (UTC)


 * I'm very interested in the hygiene hypothesis. Here are three recent papers discussing the current knowledge of athsma with respect to the hygiene hypothesis:  . Of course what's interesting or new is subjective, but I'd like to hear a good 20 minute talk based on those papers :) SemanticMantis (talk) 21:23, 2 April 2014 (UTC)


 * Students might be interested to hear about The Roaring Adventures of Puff (RAP) a Canadian asthma education program, the PACE program to enhance treatment of asthma and the physician-patient partnershipor this study of Orem's Self-Care Deficit Theory of Nursing asthma. You might consider making a Google search for Buteyko's Theory of Asthma (which may find links to the Butekyo Breathing Method claimed to improve asthma which will not be given here under our no medical advice rules.) 84.209.89.214 (talk) 22:36, 2 April 2014 (UTC)
 * (OP is specifically asking for references to research for a school project; you can link any reference you think is appropriate to the request.)  For example, here are two studies that claim to be reporting on clinical trials of Buteyko's breathing method that you mentioned  . One seems to show no/low effect, the other concludes in the abstract that the method "may be effective". SemanticMantis (talk) 23:13, 2 April 2014 (UTC)


 * This is also interesting. Count Iblis (talk) 15:42, 3 April 2014 (UTC)

thrombosis and flight
What is the connection \ the link between the blood clot (thrombosis) and flight? I've heard that people sometimes get thrombosis after they fly, so what is the reason for? 213.57.121.149 (talk) 23:26, 2 April 2014 (UTC)


 * Deep vein thrombosis can be caused by being crammed in too small seat for too long, causing circulation problems. The general advice is to get up and walk around periodically, but in my experience the crew gets nervous and tells you to sit back down when you attempt to do so. StuRat (talk) 23:31, 2 April 2014 (UTC)


 * Really?  I fly quite a bit due to work requirements, and have never had that happen.  Of course you get those idiots who want to go to the toilet when the seatbelt lights are on - they are kin to the idiots who get their phones out when the aircraft is accelerating down the runway - they make life unnecessarily complicated for the cabin crew.  Upon getting up and walking around during the level cruise part of the flight, I've more than once ended up having a gossip with a hostess in one of the kitchens - no problems at all.  Perhaps Stu is very old and the cabin crew worry about him falling over during "air bump" turbulence. He's pretty smart, so he probably had enough sense not to walk around when they've got all the trolleys out issuing the meals.  120.145.97.4 (talk) 00:41, 3 April 2014 (UTC)


 * I have always been worried about flying in a plane that can be brought down by a mobile phone or a DS3, but I guess its no worse than petrol (gas) stations that can be exploded by the same devices. All the best, Rich Farmbrough, 13:52, 6 April 2014 (UTC).


 * I had the misfortune of being at a gas station when some idiot smoked while refilling. I couldn't get out of there quickly enough. StuRat (talk) 20:42, 6 April 2014 (UTC)