Wikipedia:Reference desk/Archives/Science/2012 August 26

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August 26

landers and boulders

Neil Armstrong steered the Eagle to avoid a boulder field at the last minute. What can unmanned landers do about boulders? In this movie of Curiosity's descent someone says "We've found a nice flat place"; does that mean the lander had a way to look for one, or merely that "we" got lucky? —Tamfang (talk) 00:47, 26 August 2012 (UTC)

Mars today is much better mapped than the moon was during the 1960s. I wouldn't doubt that we have high resolution maps of the surface of Mars to a similar level that we have on earth; that was part of the idea of previous Mars missions like the Mars Reconnaissance Orbiter, which among its multifaceted mission is to scout and plan for landing sites for landers. --Jayron32 00:53, 26 August 2012 (UTC)

(ec)Recent landers on Mars and the Moon have benefited from surveys from long-term orbiting spacecraft like Mars Global Surveyor. That gives the mission planners a map from which they can select especially boulder-free areas. They pick an area quite a bit bigger than the error-bars for their lander's anticipated landing. -- Finlay McWalterჷTalk 00:58, 26 August 2012 (UTC)

It's worth mentioning the Lunar Orbiter program, the satellites which scouted the moon for Apollo landing sites. These remarkable gadgets exposed film, developed it themselves when orbiting the moon, and then tv-scanned the results back to Earth. They got a 2m resolution of the selected sites. The current Lunar Reconnaissance Orbiter gets about 0.5m resolution (so 16 times more data). Because its digital cameras aren't going to run out of film it can re-survey the same location over and over, when the Sun is at a different angle: comparing the shadows on different pictures gives further clues as to the terrain. -- Finlay McWalterჷTalk 01:44, 26 August 2012 (UTC)

This NASA blog entry implies that mission planners relied on whatever surveys were available (for the Curiosity mission, those would be 0.3 meter resolution surveys from the Mars Reconnaissance Orbiter) to select a region that was as boulder-free as possible, and then prayed like crazy that they didn't make an unlucky landing. TenOfAllTrades(talk) 03:59, 26 August 2012 (UTC)

In 2006 we had better images from Mars (Mars Reconnaissance Orbiter) than we were allowed to get from earth (military satellites made better immages but they were not available to everybody). Viking did a landing with very little knowledge on the places they landed. It seems that Nasa was lucky many times not to hit a rock or fall into a gully. --Stone (talk) 08:40, 27 August 2012 (UTC)

The only instrument Curiosity had for measuring the surface was an altimeter that returned a single value. The altimeter couldn't even be pointed, and measured the distance to wherever it happened to be pointed due to the spacecraft's oscillations. The descent imager, MARDI, imaged the surface during descent, but its images were not used to guide the descent in any way.

I think when mission control said "we've found a nice flat place", what they mean is that Curiosity avoided the black line and impact craters inside the landing ellipse: http://www.redorbit.com/media/gallery/mars-science-laboratory/573690main_pia14295-anno-full_full.jpg. The black material is sand dunes, the same ones in Curiosity's images from the surface, which aren't as flat as the rest of the landing area and are composed of soft sand that the rover easily sinks into. I don't know how mission control knew the rover had avoided those areas--presumably the tracking was accurate enough to determine that. --99.227.95.108 (talk) 05:26, 26 August 2012 (UTC)

The Opportunity rover famously landed by chance in 2004 in the middle of a crater (later named Eagle crater) in the generally flat and featureless Meridiani Plain. I assume the plain was chosen because it didn't have rock fields that might bog down or damage the rover, so the crater was a surprise. The scientists were not aiming for it nor did they even know it existed. The landing site itself was 25 km off-target.-- OBSIDIAN†SOUL 05:35, 26 August 2012 (UTC)

The landing site selection is done from two sides. The scientists choose places which are interesting and the engineers choose flat low areas. The landing ellipse has to be very save. When you built a rover with 5km drive distance and a landing ellipse of 100km you end up in the not that interesting area chosen by the engineers. With a rover with 50km drive distance and a landing ellipse of 20kmyou might be lucky. For a fixed lander like phoenix you have to take more risk.--Stone (talk) 08:40, 27 August 2012 (UTC)

re: "...and are composed of soft sand that the rover easily sinks into". They may be indurated, but I'm really looking forward to Curiosity having a look at them. Quite a lot of work has been done on dunefields in Gale crater and Curiosity has to get through that one. It certainly looks like it's active, or at least the ripples on the dunes are, according to a COSI-Corr analysis using HiRISE imagery. Sean.hoyland - talk 10:07, 27 August 2012 (UTC)

Is It Possible to Change One's "Handedness"?

Is it possible in certain cases to become able to write well with one's right hand when one was born left-handed (not ambidextrous), or vice versa? The reason I'm asking is that my dad was born left-handed but was forced to learn to write with his right hand in school, and is now able to write well with both hands (despite not being able to do this before). In contrast, I've heard and read that most left-handed people are unable to become able to write will with their right hand. My question is how frequent are cases like my dad's and why was my dad much more capable in this than most other people? Futurist110 (talk) 06:00, 26 August 2012 (UTC)

It simply takes practice. What do you think happens when people lose a limb? My father was beaten out of using his left hand, my sister wrote backwards for years with her left hand, and her son writes with both hands now, boustrophedonically. μηδείς (talk) 06:49, 26 August 2012 (UTC)

I assume King George VI wrote legibly. Clarityfiend (talk) 07:11, 26 August 2012 (UTC)

It was common in Australia up until the 1950's for primary school teachers, particularly with older teachers, to enforce writing with the right hand. However, it was later considered undesirable to force handedness. Theres was, supposedly, evidence that that if you were born left-handed, and if you were forced to be right-handed, then you would stutter or have some other speech impediment. I myself was born left handed, and made to write right-handed by a particularly nasty Grade 1 thru Grade 3 teacher. It happens that I did stutter for a while, but I managed to cure that in my 20's. Coincidence? A matter of how the brain is wired up, and some part forced to do what it was not intended to do? Could be. Incidentally, for years I could use tools equally well in either hand. Looking back, I reckon that schoolteacher did me a favour. Some things, such as guns & chainsaws, are dangerous for a left-hander to use, and being able to swap hands to do things is a great party trick. Wickwack124.182.52.89 (talk) 08:26, 26 August 2012 (UTC)

That attitude lingered for some time. My younger son is now 27 and has always been left-handed. When he first started exhibiting this, my mother was most concerned, and suggested we do something to nip what she saw as a negative trait in the bud. We respectfully declined to follow her advice. -- ♬ Jack of Oz ♬ ^{[your turn]} 09:14, 26 August 2012 (UTC)

My husband also was forced to use his right hand at school but is now totally ambidextrous. I can't tell which hand he's used to write something with. As has been said, it's practice. --TammyMoet (talk) 08:45, 26 August 2012 (UTC)

I'm right-handed, but when a colleague invited me to go trap shooting I decided to try it left-handed, because my left eye is the one that's better for distance. I hit two targets out of 25. But who knows — maybe I wouldn't have hit any, right-handed. Never did try it again to find out. --Trovatore (talk) 09:21, 26 August 2012 (UTC)

My right eye is the best, for both distance and close up. But my left ear is the clearest hearing. I think all these things are unrelated. Wickwack124.182.52.89 (talk) 10:40, 26 August 2012 (UTC)

Unrelated? Have you never heard of "The Fundamental Interconnectedness of All Things"? -- ♬ Jack of Oz ♬ ^{[your turn]} 12:59, 26 August 2012 (UTC)

In target shooting and archery, eye dominance is more important than handedness in determining whether you should shoot left or right handed. For about 30% of people, eye dominance and handedness are different, which is known as being "cross dominant". Alansplodge (talk) 02:12, 27 August 2012 (UTC)

I've done the little tests for eye dominance but I've never been quite sure what the results mean. My eyes have different focal lengths and I think that swamps any neurological difference. --Trovatore (talk) 03:06, 27 August 2012 (UTC)

A few people have "central vision" (ie neither eye is dominant) - this article tells all. Alansplodge (talk) 10:58, 27 August 2012 (UTC)

The U.S. president James A. Garfield could write equally well with both hands. As a parlor trick, he trained himself to write simultaneously, but different passages, with each hand. It isn't mentioned in his main article, but List of multilingual Presidents of the United States notes that he would write in Latin with one hand and Greek with the other. --Jayron32 02:16, 27 August 2012 (UTC)

See http://www.jneurosci.org/content/27/29/7847.full.

—Wavelength (talk) 02:37, 27 August 2012 (UTC)

Naked images from interstices in fabric?

This one literally came to me in a dream. :) With the ever-increasing resolution of gigapixel images and increasing camera speed and precision of digital photos to make it meaningful, is it possible to look at a seemingly routine photo of someone wearing a light fabric which is commonly regarded as opaque, and have software pick out specifically the holes in the fabric and interpolate them into a naked image? Or for fabric without any holes, however small, with some further processing, to automatically infer effective hole values by comparing the values from the spots where the fabric is thickest and thinnest? Wnt (talk) 10:40, 26 August 2012 (UTC)

The ultimate resolution of a camera is set by fundamental principles of optics. Diffraction sets a limit on the detail that can be resolved, so utilising the holes to look through a fabric would not be possible unless the fabric is so open you can do it with your own eyes (assuming your eyes are good). Some facility is possible by using an extended color response and filtering. Some fabrics have partial infrared transparency. I remember some early (1950's) colour transparency films had an extended infrared response and, depending on the dress material, would sometimes reveal a lady's underclothing and legs outline that was not visible to the naked eye, generally blury because of lens chromatic aberation. See http://en.wikipedia.org/wiki/Diffraction-limited Wickwack124.182.52.89 (talk) 11:23, 26 August 2012 (UTC)

I don't think the size of the gaps between individual threads in a piece of clothing is anywhere near the diffraction limit. :) While it is possible that the eye comes near this limit in observing detail, a camera with a larger CCD chip or a higher zoom level should not, I think. The point of the idea was that in a high-resolution image the individual swatches of non-fabric color can be joined together in an image, removing the distracting impression of the fabric. Wnt (talk) 12:01, 27 August 2012 (UTC)~

If the eye can't do the job, and is operating near the diffraction limit, then obviously a camera can't do it either. Wickwack60.228.241.5 (talk) 15:14, 27 August 2012 (UTC)

Optics, image size, and other possible things apart… I think you can have any given image with some area you want to leave (in your case, the skin, ->‘As’) and other area that you want to replace (the cloth, ->‘Ac’) and all depends of the relationship of this two areas, ‘As/Ac’ if there is too much ‘Ac’ or not enough ‘As’ is very probable that the interpolation algorithm will not work properly.

Some fabrics are a little bit trasnparent to the eye. That's because the eys is doing the interpolation between the threads and the gaps, as the thread pitch is too fine for the eye to behold. Its the same thing as you not seeing the dots in your computer monitor image unless you peer very closely. Do you realy think an camera is going to be different, unless it senses wavelengths the eye cannot. Sheesh. Wickwack60.228.241.5 (talk) 15:14, 27 August 2012 (UTC)

But even in the case you have enough ‘As’ there is not 100% certainty that you will have an accurate result, this will depends on the interpolation algorithm

Perhaps you will end faster by telling the lady: honey… clothes off!! And then taking the picture!

Iskánder Vigoa Pérez 14:34, 27 August 2012 (UTC)

If by "end" you mean "be mocked mercilessly". -- NellieBlyMobile (talk) 16:47, 29 August 2012 (UTC)

Does Unriped fruits contain less sugars?

Or, in other words, does they potentially makes u less fat?, thanks from all heart !!! 109.64.151.131 (talk) 13:21, 26 August 2012 (UTC)

Yes, unripe fruit contains less sugar. But since it also contains less flavor, I don't think that's a reasonable way to avoid gaining weight. You might as well eat paper, which contains no sugar at all. Looie496 (talk) 17:31, 26 August 2012 (UTC)

Just because the starches have yet to be broken down into simpler sugars via enzymes does not mean there will be less carbohydrate-based calories, though. As an amateur brewer I say this because of my understanding of malting, not from scientific background per se, so take it with a grain of salt. I recommend reading Starch#Starch sugars and Fruit ripening#Ripening indicators for a start, since those bits of reading are less technical in nature. This LiveStrong.com article seems to be implying that starches and sugars in bananas both have the same calorie/gram concentration. Diastase is a particular type of enzyme, and that article may shed more light into exactly what goes on, should you be interested in technical reading to determine the caloric difference in these processes. BigNate37_(T) 17:48, 26 August 2012 (UTC)

With a grain of salt? Would this equate to homoeopathic Burtonising? {The poster formerly known as 87.81.230.195} 84.21.143.150 (talk) 14:34, 28 August 2012 (UTC)

It isn't just calories/gram however that effects how carbohydrates affect things like weight gain, however. The glycemic index also is relevent: foods with a high glycemic index cause rapid spikes in blood sugar, and lower GI foods cause a more steady, slower increase in blood sugar. Higher GI foods have an association with greater weight gain and also with things like type-II diabetes, so it isn't just how many calories you are getting, the source of the calories has an effect on how your body processes the food and the effect it has on weight gain. --Jayron32 02:09, 27 August 2012 (UTC)

Rather than eat unripe fruit, I suggest you mix ripe fruit with something that needs sweetening to be palatable, like shredded wheat cereal and milk. This is a better approach than either adding table sugar or buying sweetened cereal (fructose may be healthier than sucrose, and especially sweeteners like corn syrup) . StuRat (talk) 10:02, 27 August 2012 (UTC)

No medical advice, StuRat ... after all, he could have gluten intolerance or something. ;) Besides, in terms of calories, there's little difference between sugar and starch - only the fiber portion of the wheat would be advantageous. Wnt (talk) 12:03, 27 August 2012 (UTC)

As previously mentioned, there's the glycemic index. Also, unsweetened wheat cereals have other nutrients besides fiber (some of which are due to fortifying the cereals): [1]. Another good option is adding ripe fruit to unsweetened oatmeal (the real stuff in the cylinders, not the crap in the packets). StuRat (talk) 12:15, 27 August 2012 (UTC)

-- Good point! I was reading the headline, missed the question. The calories in sugar are the same, but the effect on weight can be different because it triggers insulin production (thus fat accumulation) rather than slowly sustaining metabolism. Wnt (talk) 03:11, 29 August 2012 (UTC)

Men always taller than their mothers?

An acquaintance recently told me that except for congenital disorders and diseases mature male humans are always taller than their mothers. Is it true? Roger (talk) 14:05, 26 August 2012 (UTC)

Factors affecting height are discussed in Human height#Determinants of growth and height. A number of factors make the probability that a son will not be taller than his mother quite low. However, if a tall woman has a son by a short father, the probaility is increased - congenital disorders and diseases are not required. A mother who was quite young at the time of birth, perhaps food shortages during the early life of the son, and moving to a cold climate may increase the probability. In western countries, there was an improvement in food quality in the years 1850 to 1950. This has apparently resulted in a gradual increase in height. Since then, food quality has not usefully improved, so the probality of a son not taller than his mother has increased slightly. Wickwack124.182.52.89 (talk) 14:58, 26 August 2012 (UTC)

(ec) The short answer is 'no', but men are often taller than their mothers, for a number of reasons.

• Men are, on average, taller than women, so if you were to randomly select one man and one completely unrelated woman from the population there's still a better-than-even chance he'll be taller than her.
• The average adult height has been increasing for decades. The typical individual born twenty years ago is taller than one born forty years ago, who is in turn taller than one born sixty years ago. (This can be attributed to a range of lifestyle and medical changes.) [2]
• Even on an otherwise identical genetic background, a male will tend to reach a taller adult height than a female. (This follows plausibly from the first point.) In other words, your mother would likely have been taller if she had swapped an X for a Y chromosome at conception, and her (his?) body had been exposed to the usual male complement and doses of hormones. This assumption may break down if she had a 'tall' variant of one of the genes affecting human height on the chromosome you swapped out.
• Most women, for cultural reasons (and/or evolutionarily-driven cues), procreate with men who are taller than they are.

Put all of those together, and you get the observed result—most male children are taller than their mothers. That said, neither congenital disorders nor disease would be required to explain a short son. The easiest case is where Mom is tall and Dad is rather short; you'd expect their offspring's height to – on average – fall somewhere in the middle, and if their height disparity is sufficiently large then even the top-ups Son gets from being male, born in a later decade, and with access to better health care and food won't make him taller than Mom.

That said, you can certainly get ahealthy Son shorter than both Mom and Dad. So far there are something like two hundred genes that have been associated with human adult height. Aside from the ones on Dad's X and Y chromosomes, both parents carry two copies (sometimes the same, often different) of each of those genes. In the random lottery of conception, Son gets one copy from each parent; if he's particularly (un)lucky, he gets the 'short' copy of most of those, and ends up shorter than Mom. TenOfAllTrades(talk) 15:05, 26 August 2012 (UTC)

The paper [3] cited by TenOfAllTrades may be skewed - it focused on European countries. I think that if it included data from North America and British Commonwealth contries, it would be shown that in recent decades height has not increased. In Australia, there was a drop in height after each World War - it is thought that taller men are more likely to be killed in trench and jungle warfare - a sor of evolutionary selection for low height. Wickwack124.182.52.89 (talk) 15:16, 26 August 2012 (UTC)

[4] suggests average height has been increasing in Australia, but not by much. Similarly [5] for the US. Both sources concur the increase in recent times hasn't been as much as in many European countries. Nil Einne (talk) 17:01, 26 August 2012 (UTC)

I found Nil Einne's first reference interesting until I got to the part where it says human evolutionary change is speeding up - that's a startling claim. Then when I got to the part where it implies this is happened within the last 80 years - that destroyed the article's credibility for me. Evolution can only happen if the evolutionary presure affects the death rate of folk before they have children, or affects the birth rate, or affects the survivability of children, either directly, or in some cases, affecting survivability thru the availability of older parents and grandparents. In Western countries in the last 80 years, improved medical care & cultural change has removed all these factors. We have just about stopped human evolution.

The second reference only talks about height increase in children, which has increased due to high calory diets causing earlier growth spurts. Its a different thingsto what the OP was asking. Wickwack22:59, 26 August 2012 (UTC) — Preceding unsigned comment added by 124.178.50.4 (talk)

Careful, selective pressure can also be based on sexual selection, as well as group selection, kin selection, cultural selection, and so on. Biocultural evolution contains a few more links. In short, I believe your criteria for selection are a bit too strict. All these factors can potentially influence the "speed of evolution", independent of generation time. SemanticMantis (talk) 23:17, 26 August 2012 (UTC)

Good point. However, in western countries at any rate, virtually all men find a partner, and virtually all women find a partner, and they have their statistical 2.1 children or whatever, and modern medicine ensures that nearly all children get old enough to reproduce. An example: I have a friend who is parallyzed from the waist down due to childhood disease. He never the less is employed (in IT) on a good salary, found a wife who has her own challenges due to a severe road accident, and they have had 2 children. Not so many decades ago that could not have happened. Both of them would have been institutionalised at best. The road accident rate, higher for teenagers and young adults who have not yet married, drug addiction, and military service seem to be the only reproduction rate interferences and thus evolutionary drivers left. Of these, only military service can affect height, negatively. Wickwack60.228.241.5 (talk) 01:55, 27 August 2012 (UTC)

I read several years ago that among Americans the increasing height trend suddenly stopped with those born about 1960 – my cohort – and no one knew why. (I'm distinctively tall myself.) In the last couple of years I've noticed a lot of startlingly tall young people, so maybe the trend started up again. —Tamfang (talk) 07:12, 27 August 2012 (UTC)

Maybe it was all the dope their parents smoked/snorted/swallowed/shot up. Seriously, I've seen indications that the "hippie generation" was generally less healthy than the previous and subsequent cohorts. Roger (talk) 07:48, 27 August 2012 (UTC)

Or maybe hippie women had more appreciation for short men with a great personality? Who knows - you can't re-run the experiment with a control group - but I've never heard of dope affecting the growth of successive generations, even if it is nominally conceivable as one of any number of potential epigenetics related phenomena. Wnt (talk) 12:13, 27 August 2012 (UTC)

My "dope" comment was a joke - the serious part is the generally worse health of that cohort of parents. Roger (talk) 16:53, 28 August 2012 (UTC)

Worse health? I'm not aware of life expectancy going down. And there was a lot of wising up about toxic chemicals and pollution in that general era - no more scrubbing the floors with carbon tetrachloride! I'd think the general increase in middle class income during the 1950s would have improved health, though I didn't look it up so take that with a grain of salt. Wnt (talk) 03:07, 29 August 2012 (UTC)

Every recent study I have read indicates that evolution in humans is running quite fast now. Historically, groups like the Ashkenazim have expanded quite quickly. Nowadays sexual selection is the thing, with women with fathers with average-sized penes choosing men with large endowments to father their offspring. See baby mamas. μηδείς (talk) 04:23, 28 August 2012 (UTC)

Huh!!?? How does an article on an American slang arising from Creole prove that??? Wickwack124.178.52.176 (talk) 14:56, 28 August 2012 (UTC)

When women don't marry the father of their child for his brains or money, on what criteria do you suspect they choose him? μηδείς (talk) 16:43, 28 August 2012 (UTC)

Love. --NellieBlyMobile (talk) 16:52, 29 August 2012 (UTC)

They can't explain, it's surely not his brain. Fish gotta swim, birds gotta fly. Kern explains it all for you. --Trovatore (talk) 05:44, 30 August 2012 (UTC)