Wikipedia:Reference desk/Archives/Science/2013 May 4

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May 4

Trimmer vs shaver

What is the difference between electric trimmer and electric shaver? --Yoglti (talk) 01:43, 4 May 2013 (UTC)

• About $15. μηδείς (talk) 01:52, 4 May 2013 (UTC)

The shavers are intened to get down to bare skin. The trimmer is intended to leave a short length of hair protruding above the skin ("stubble"). The trimmer likely has an adjustable setting to vary the amount of hair left, whereas the shavers have one setting ("as close to the skin as comfortably possible"). -- 71.35.109.118 (talk) 02:50, 4 May 2013 (UTC)

Just my original research; trimmers operate by a pair of toothed blades that slide past each other as one oscillates back and forth, like a small hedge clipper, while shavers are either a rotary blade that runs underneath a circular grill so that it nips the hairs off that stick through the grill, or a thin rectangular blade with lots of sharp slots which oscillates beneath a grill in similar fashion. the shaver appratus being thinner and thus more precise than the trimmer setup. Gzuckier (talk) 05:10, 5 May 2013 (UTC)

How energetic x-rays (kV) is required to reach above background?

How energetic x-ray photons (kV) is required for them to be stronger than background radiation ..? Electron9 (talk) 02:40, 4 May 2013 (UTC)

Your question does not make sense in the English language. I assume you meant to ask How energetic do X-ray photons (described in terms of the equivalent electron acceleration voltage) need to be to be stronger than the background radiation on Earth's surface? This is not a valid question. Do you mean the natural background radiation, or the averaged exposure due to nuclear fallout from accidents and explosions, medical X-rays taken during your life, use of nuclear isotopes in medical diagnosis and treatment etc? I will assume that you meant the natural background.

The higher the X-ray energy, the more penetrating it is. And if X-ray photons have fully penetrated a substance, then no energy was transfered to the substance and it cannot have been affected. This is why X-ray images taken to show bone structure are a lot less harmfull than X-rays taken to show soft tissue structure, where similar exposure times are used. It means that the natural X-ray exposure we experience includes X-rays from very high energy sources remote in the universe. In terms of exposure effects, very low energy man-made Xray sources very much over ride natural exposure.

Also note that in terms of effects on life, X-rays are just another sort of ionising radiation. The exposure to just natural X-rays is not important, but the total exposure to all sorts of ionising radiation can be.

Ratbone 124.178.43.47 (talk) 09:47, 4 May 2013 (UTC)

Maybe, he's talking about the cosmic microwave background? Plasmic Physics (talk) 10:43, 4 May 2013 (UTC)

I meant if you have a x-ray tube. How high acceleration voltage is needed to measure a higher dose than from ground rock (1 mSv/year?). I heard that CRT-TV-sets with acceleration voltage below circa 10 kV didn't make it out of the TV-set. So that only sets with higher voltage had any measurable radiation. Electron9 (talk) 13:30, 4 May 2013 (UTC)

Only the smallest CRT TV sets had an acceleration voltage as low as 10 kV. 17 to 20 kV is more typical for black and white sets, early colour sets were up to 25 kV. However, at typical voltages the X-rays are so soft normal materials used in sets (glass, wood, etc) stopped them.

You are still asking the wrong question - you are confusing photon energy with beam power. You can get a high effective dose from the lowest acceleration voltage that will produce X-rays of sufficient energy to penetrate the tube window - about 18 to 20 kV or so. You need to understand that Xray tubes are designed to produce Xrays - so the tube windows are constructed appropriately. TV sets are designed NOT to emit Xrays. For instance, the glass at the front of the picture tube is a three-layer sandwitch up to 18 mm thick and often lead loaded. Internally, older colour sets with internal parts such as the regulator triodes were designed so that Xrays from the triode had to pass through (typically) 2 layers of 12 mm plywood and a steel sheet barrier.

What affects dossage is the electron beam current and the exposure time. It is similar to exposing black and white photographic film with light. You can use a low power white light (say a 0.5 W krypton torch glode running at 4000 K filament temperature) or a high power light red light (say a 60 W globe run on low voltage so that the filament is running at only 1600 K and light output is reddish-orange). The first is analogous to making Xrays with a high voltage but a low beam current; the second is analogous to making Xrays with a low voltage but a high beam current. In both cases the higher power will have the greatest effect.

Not to be neglected is the fact that Xrays are emitted from Xray tubes in a fan-shaped beam, somwhat like light fans out from a light globe. This means that the further you are away from the Xray tube, the lower the dose, as you intercept a smaller fraction of the fan-shaped beam.

As I recall, you previously asked a question about making a homemade Xray apparatus. DON'T DO IT. You have so little undersanding of Xrays, you would be certain to cause harm to yourself and your friends.

As I said before, it is the low energy (ie from low acceleration voltage) that cause tissue damage. Very high energy Xrays pass through without lossing energy. If energy is not lost to the material passed through, there cannot be any effect on the material.

Ratbone 120.145.203.168 (talk) 15:21, 4 May 2013 (UTC)

There is information missing from your question. No matter how high the Voltage is, if no electron's are beamed down, no X-rays are produced. To answer your question you need to tell us the total number of electrons used by the machine per year. In other words, you have to tell us the current used by the machine. Other things to consider: How far from the X-ray source are you? Is there any radiation shielding? Dauto (talk) 15:28, 4 May 2013 (UTC)

Let's assume an x-ray tube and measurement 1 cm from the designed tube exit. If one study just one electron, how energetic (keV) does it have to be when striking the anode for the byproducts to just to make it out of the glass? before any shielding. If one electron makes it out, further electrons can make it. But if none makes it out, it won't matter how many there are. Ignoring the probabilistic nature of particles. Electron9 (talk) 16:09, 4 May 2013 (UTC)

Quite apart from the fact that what comes out depends on the thickness and type of glass, both of which will depend on the size and type of tube, which you haven't specified, it doesn't work that way, you can't calculate on the basis of a single electron, which may only result in one or 2 photons. Photons get absorbed on a statistical basis - some get thru, some don't. The fraction getting thru rises as the energy increases. Wickwack 120.145.8.232 (talk) 02:32, 5 May 2013 (UTC)

Spin

If the moon did not exist our earth would spin faster. How short would our days be on the equator? Pass a Method talk 06:26, 4 May 2013 (UTC)

Not necessarily. The most popular theory Giant impact hypothesis is that the moon was formed in an impact that span the earth up to have something like a five hour day. Otherwise it would probably have something in between the very long days of Mercury and Venus and the roughly equal day of Mars is my guess, maybe somebody has worked out a typical value to be expected. Dmcq (talk) 10:46, 4 May 2013 (UTC)

What makes you think the Earth would spin faster? Dauto (talk) 12:14, 4 May 2013 (UTC)

Using debatable assumptions: momentum must be conserved, ergo, lunar recesion decreases Earth's angular velocity. Plasmic Physics (talk) 12:31, 4 May 2013 (UTC)

Also tidal locking between the Earth and the Moon is transferring rotational energy from the Earth into orbital energy in the Moon, and friction in the tides converts some Earth rotational energy into heating the Earth. Both of these cause the length of Earthdays to gradually increase. BTW, the day/night cycle are the same length no matter where you are, (as long as you are not within the polar circles. Did you mean the length of daylight? CS Miller (talk) 14:11, 4 May 2013 (UTC)

I'm not the OP, I'm just infering their logic. I'm certain, they are refering to the period of the angular motion of the Earth, not the length of daylight. Plasmic Physics (talk) 04:43, 5 May 2013 (UTC)

Hassium

Emsley's Nature's Building Blocks (both editions) say that IUPAC did not feel Hesse merited having an element named after it as a reason for their changing the name to hahnium in 1994. Does anyone know why they felt this way? It's quite odd in light of all those elements named after places! The only reason I've found that they mentioned themselves is that they wanted elements named after Hahn and Meitner to stand side by side on the periodic table to honour their joint discovery of nuclear fission. (Yes, this is for an article.) Double sharp (talk) 08:51, 4 May 2013 (UTC)

I guess no one seems to know the answer, which was not entirely unexpected as I've been searching for it for months. :-) Double sharp (talk) 12:44, 8 May 2013 (UTC)

How to get shine/glow in face like celebrities?

They have glow in face [1][2][3] How can I get this glow? Note it is not medical advice, just a health and beauty question. --Yoglti (talk) 09:03, 4 May 2013 (UTC)

That's just the choice of lighting on the part of the photographer, nothing more. Someguy1221 (talk) 09:08, 4 May 2013 (UTC)

These examples are paparazzi happy-snaps! What lighting choice have they got but their mono flash and ambient illumination?--Aspro (talk) 19:20, 4 May 2013 (UTC)

It's makeup too. Yes, even for Tom. Looie496 (talk) 14:50, 4 May 2013 (UTC)

See section: 'Add some glow:[4]--Aspro (talk) 19:15, 4 May 2013 (UTC)

And there's Photoshop and Airbrushing. HiLo48 (talk) 23:43, 4 May 2013 (UTC)

Oh yes Photoshop. That will only cost you about £400. Whereas GIMP is about £ 000,000,000 per free download Aspro (talk) 00:42, 5 May 2013 (UTC)

Yes, I'm well aware of that, but where I come from the word Photoshop has become a generic verb meaning to use any computer software to enhance/modify a digital image. Maybe I shouldn't have Wikilinked it. HiLo48 (talk) 00:47, 5 May 2013 (UTC)

A lower-case p would be indicated in that case (cf. thermos, hoover, xerox, google ...). -- Jack of Oz ^[Talk] 01:37, 5 May 2013 (UTC)

I haven't stopped putting a capital G on Google, even when using it as a verb. Has the lower case G become the recognised norm? Am I old and behind the times again? HiLo48 (talk) 01:42, 5 May 2013 (UTC)

Don't worry. I spend most of my life pretending to know what people are talking about. I even get it right sometimes. You have your good days and your bad days ...

But about Google: It has become far and away the most popular search engine; a lot of people would not even know there are others out there, or how to find their names. This means that those who do choose some other engine are consciously dissociating themselves from Google, and would not be using that word. So, maybe the verb has two existences and two meanings:

(a) google = to use any search engine in general (including Google); and

(b) Google = to use Google specifically (this would be used by people who use other search engines often enough that using Google, when and if they ever do, is a conscious choice).

Caveat: Most of the preceding is made up. -- Jack of Oz ^[Talk] 02:18, 5 May 2013 (UTC)

A high school student (obviously an excellent, reliable source) told me the other day that the most popular search term on Bing is "Google". (Actually, it's probably "google", but he didn't write it down, so I'll never know.) (Have we got far enough away from this topic yet? Sorry everyone.) HiLo48 (talk) 02:30, 5 May 2013 (UTC)

"Bing"? μηδείς (talk) 02:37, 5 May 2013 (UTC)

Yep, Bing. -- Jack of Oz ^[Talk] 02:53, 5 May 2013 (UTC)

Bing is used when you croon the internet. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:28, 5 May 2013 (UTC)

Bing Crosby did certainly star and croon in a film were Danny Kay sang “There once was an ugly duckling” but I don't think Danny was referring to Bing growing up be to " A Very-Fine-Swan Indeed!" If you get my point. Dammit what was that film?Aspro (talk) 16:08, 7 May 2013 (UTC)

That would be Hans Christian Andersen (film). -- Jack of Oz ^[Talk] 21:04, 8 May 2013 (UTC)

efficiency

what is more efficient, a dolphin or shark moving its tale, OR, a machine as strong as the dolphin's or shark's muscles with a rotor? — Preceding unsigned comment added by 123lmon (talk • contribs) 13:16, 4 May 2013 (UTC)

Dolphins and sharks are much more efficient, they move their bodies in response to the actual flow of water so that it gets altered in the most optimal way. Count Iblis (talk) 13:34, 4 May 2013 (UTC)

Cooling of smartphones

Smartphones have nowadays as much as processing power as laptop did a while ago. However, when laptops had that much processing power, they had a cooling fan. Why don't smartphones don't need a cooling fan? Why do laptops need them? 123lmon (talk) 13:21, 4 May 2013 (UTC)

When a computer chip processes, that means electrons are whizzing around through it. That heats it up; if it heats up too much, it can actually melt the processor core. Newer chips can run much cooler than the ones of a few decades back — much cooler. The most common smartphone processor is known as ARM, and it was specifically engineered to have very low heat output and relatively low power requirements. So something on par with a smart phone, or even an iPad, doesn't really require a specialized cooling source, because they've been engineered to dissipate what little waste heat they have pretty effectively. (They don't alway succeed — the iPad will basically shut down if its internal temperature exceeds 95ºF.) Older processors, or modern processors of the speed that would be found in a laptop or desktop computer, still usually require fans to keep from overheating. --Mr.98 (talk) 13:43, 4 May 2013 (UTC)

Also the operating voltage of CPUs is gradually dropping - it used to be 5 Volts, and is now 0.8V (I think). The capacitance of each transistor is gradually decreasing, these both reduce the amount of power needed for each gate to change state, and thus for each operation the CPU performs. CS Miller (talk) 14:05, 4 May 2013 (UTC)

The low-power technology that permits all of that computation with such long battery life is the same thing that minimizes heat production. In the end, the energy from the battery turns (almost 100%) into heat inside the case...so things with long battery life and small batteries run cooler than things with short battery lives and large batteries. SteveBaker (talk) 14:06, 4 May 2013 (UTC)

I think smaller die geometries also plays into this. Electron9 (talk) 14:16, 4 May 2013 (UTC)

Also, the procesors used in cellphones where designed quite recently from scratch with an optimised instruction set. Intel compatible processors used in PC's and laptops have always been designed with backward compatibility stretching back to the original 8086 CPU designed in the early 1980's. Maintaining compatibility means they are a lot more complex internally. Also, the actual processor core is only part of what consumes power. A PC processor has to interface with external devices, external memory, and other bus devices. Cellphone procssors are one-chip devices that aviod the need for much power dissipating interface circuitry. Ratbone 120.145.203.168 (talk) 15:32, 4 May 2013 (UTC)

ARM goes back to 1983. I'd hardly call that "recently from scratch" ;-). It is a RISC architecture, although modern processors put a lot of additional functionality into silicon. --Stephan Schulz (talk) 22:26, 4 May 2013 (UTC)

To sum it up:

• Efficient heat paths (little has really changed over the years however)
• Less voltage
• Less capacitance (due to less wire surface?)
• Efficient use of existing gates (MIPS, ARM, etc)
• Integrated peripherals

Electron9 (talk) 16:14, 4 May 2013 (UTC)

About the point of ARM and other RISC like architectures, note that Intel is desperately trying to compete in the tablet and smart phone market. (To a lesser extent, so is AMD in the tablet market.) The Atom (system on chip) isn't really used in any significant smart phones and even in tablets has only really found success in Windows 8 ones but most reviews have found that it isn't terrible, for example performance and battery life seem somewhat comparable to similar speced ARM devices. Edit: Although I believe one additional problem is the newer A15 and similar architectures e.g. Krait as well as their lower powered contemporaries e.g. A7 are now starting to become common and the current gen Atom SOCs are less able to compete. Although this is likely helped a great deal by Intel's process advantage, in addition even before the smart phone let alone tablet market really took off they were already heading quite heavily to power efficiency (including various ways of reducing power when idle). As for why they haven't had much success getting major manufacturers to use them in significant product lines, I suspect cost is a factor, even with Intel's efforts including discounting. Another reason is because there's little advantage even if it's not necessarily worse. In fact ARM has the advantange in the Android smart phone and tablet world. Although Dalvik is a VM, a fair few apps on the Android market place use the NDK and while there has been an x86 NDK for a while, you still have to convince developers to actually compile for it. Edit: Actually I removed the process advantage claim. Although Intel does generally have a process advantage and this may play a factor in the SOC, it's far from clear cut at the moment because their current SOCs are still using older processes. See also [5] which suggests an additional problem is Intel's baseband is still behind major competitors, obviously significant for smart phones and any tablets with mobile network support. Nil Einne (talk) 18:57, 4 May 2013 (UTC)

It looks like Intel is now trying to exploit its process advantage for the Atom processor rather than just thinking of it as the runt of the litter. They'll not be able to achieve a knock out and a monopoly so I don't see the strategy behind that as anything it does there will eat into the price differential it charges. I think they would have been better off just offering their process to others for the low end or even making ARM's themselves making sure it kept the differential and beggared the other manufacturers. Anyway I'm sure Intel's strategists are far more expert than me so the next few years should be quite interesting. Dmcq (talk) 07:46, 5 May 2013 (UTC)

Science of mating in humans

In humans, mating and relationships have evolved into being sophisticated but could it be argued that the process of "picking up" women in nightclubs actually takes this back to being more animalistic. — Preceding unsigned comment added by Clover345 (talk • contribs) 13:44, 4 May 2013 (UTC)

Well, it could certainly be argued - but I'm not sure that the argument would be a valid one. What exactly is your question here? If you're asking: "Is the process of picking up women in nightclubs 'animalistic' behavior?" then we first have to ask what is meant by "animalistic". We are, after all, animals. Animals have a huge range of mating behaviors - from female spiders that eat their mates immediately after copulation to love-birds that mate for life and die soon after their mate is killed. I'm sure you could find at least one other species that exhibits comparable behavior to the one you're referring.

However, I think you're somewhat missing the point here. You're probably seeing this behavior from only one side - the male. Sure, men go out to nightclubs with the specific goal of finding a woman to mate with...but women go to nightclubs in the knowledge that this is a common thing to happen. This in itself is a sophisticated, nuanced, layered behavioral pattern...it's not so different from composing sonnets and singing outside of a woman's bedroom window...or whatever else you'd consider "sophisticated". SteveBaker (talk) 14:03, 4 May 2013 (UTC)

A Martian would be better at answering this one. As homo-sapiens ourselves, we can't step back and objectively separate ourself from what we 'think we are' from our basic animal instincts. Humans (with the exception of a few of my neighbors) have also developed a complex form of 'culture' in conflict to our basic instinct. Picking up women in nightclubs is no different in modus operandi from searching for mates in 16th century church congregations. Anthropologists consider (or so they tell me) that both early and modern primitive groups consist of about 140 to 160 individuals. Once their juvenile children's hormones start running wild, they need to mix with other individuals of their same age but from different geographical locations (to avoid the instinctive aversion to incest and all that). In the modern world, one of these opportunities presents itself in nightclubs. 200 hundred years ago the equivalents could have been down at the bubbling brook were teenagers get together to go skinny-dipping and splash water at each other (– at least, that is what they probably told their parents when they got home that night – who in-turn had probably frequented the same spot on the bubbling brook when they were young). So the world goes round and round. Singing sonnets outside of a woman's bedroom window may have worked for Shakespeare in his time but in this modern age, it would likely end up with one being committed to a mental hospital for observation.Aspro (talk) 20:26, 4 May 2013 (UTC)

Or arrested for stalking. HiLo48 (talk) 22:53, 4 May 2013 (UTC)

Or as Jerry Seinfeld put it, "Yelling out the car window and honking the horn are about the best ideas we've come up with so far." ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:46, 4 May 2013 (UTC)

Are you saying Jerry_Seinfeld#Personal_life is a good role model?Aspro (talk) 21:29, 4 May 2013 (UTC)

You could do a lot worse. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:34, 4 May 2013 (UTC)