Wikipedia:Reference desk/Archives/Science/2011 June 22

= June 22 =

Microstrip step discontinuity
Does anyone have a set of equations for the S parameters (or similar parameter set) of a microstrip step discontinuity? Readro (talk) 09:26, 22 June 2011 (UTC)
 * I may have some old paper notes with s-parameters derivations for most basic geometries, I can dig them out when I get home tonight. What parameters do you know already?  You'll probably need the characteristic impedance of each strip, the geometry of the gap, and the strip width (and possibly the height).  I probably also have some experimental measurements for 50-ohm copper-tape-on-FR-4, if you want those.  Nimur (talk) 00:07, 23 June 2011 (UTC)
 * There's no gap, just a discontinuous step in the line impedance. I know all the dimensions and impedances. Readro (talk) 08:05, 23 June 2011 (UTC)
 * Not sure if it is of any use, but there is an approximate expression for the characteristic impedance in our microstrip article. Gandalf61 (talk) 08:19, 23 June 2011 (UTC)
 * Since you know the impedances of each line, you should be able to determine the VSWR. Knowing that, you can apply the fllowing formala to obtain the S parameters.

From our page on S parameters At the input port, the VSWR ($$s_\mathrm{in}\,$$) is given by


 * $$s_\mathrm{in} = \frac{1+\left|S_{11}\right|}{1-\left|S_{11}\right|}\,$$

At the output port, the VSWR ($$s_\mathrm{out}\,$$) is given by


 * $$s_\mathrm{out} = \frac{1+\left|S_{22}\right|}{1-\left|S_{22}\right|}\,$$

--92.25.108.158 (talk) 14:47, 23 June 2011 (UTC)

State of the Art in Abiogenesis Research
What's the most complex amino acid polymers they've been able to create so far in experiments starting with completely lifeless beginning conditions and trying different changes to the test environment? 20.137.18.50 (talk) 18:12, 22 June 2011 (UTC)


 * RNA Plasmic Physics (talk) 11:19, 25 June 2011 (UTC)

Quick births
Why don't/cannot women give one big push and pop the baby out in a minute during childbirth? Why does it apparantly take hours? 92.24.183.164 (talk) 19:42, 22 June 2011 (UTC)


 * A baby's head a very large compared to the woman's pelvis. That means the cervix has to dilate (get bigger) a lot, which takes time. --Tango (talk) 19:47, 22 June 2011 (UTC)


 * We have an article on childbirth that describes the phases of labor. Note that the time required to complete the phases of childbirth can vary quite a lot.  The part of labor that is usually dramatized (i.e. the "pushing" part) can be variable and does not usually take "hours".  --- Medical geneticist (talk) 20:56, 22 June 2011 (UTC)
 * If it was that easy to pop a baby out, what would stop sneezing from causing premature births? lol. Vespine (talk) 22:57, 22 June 2011 (UTC)


 * Many animals do give birth with rather less effort, but the head of a human baby is very large in comparison to the size of its mother, due to us having evolved nice big brains. This page discusses the evolutionary balancing act between big brained babies and small pelvissed(?) mothers. Apologies if I just made-up a word! Alansplodge (talk) 23:29, 22 June 2011 (UTC)


 * The other issue is that we walk on two legs, which means our pelvises are rotated 90 degrees compared to other mammals. That means the baby has to come out between the legs, where there isn't much room, rather than behind the mother, where there is plenty of room. --Tango (talk) 23:36, 22 June 2011 (UTC)


 * One more instance of poor design.--Shantavira|feed me 07:04, 23 June 2011 (UTC)
 * Except in this case, the idea behind the whole process being sub-optimal is specifically enumerated in Genesis 3:16. &mdash;Akrabbimtalk 15:13, 23 June 2011 (UTC)
 * Some of that only comes about if you force women to give birth in weird positions, like flat on their backs, or (*shudder*) on their backs with their feet in stirrups! (Is it true that American hospitals do that?) Childbirth is still hard and dangerous when you let the mother move into comfortable positions that feel 'right', there are still risks and difficulties, you still have to wait for the cervix to slowly dilate enough for the babies head so that you're less likely to rip important parts of yourself, there are still contractions and the various bleeding-to-death dangers, but the baby does tend to emerge somewhat 'behind' the mother rather than simply 'between the legs'. The mother often chooses positions in which gravity plays a large role in helping the baby out. 86.164.66.52 (talk) 09:29, 23 June 2011 (UTC)


 * This brings up an interesting Q, how could people be better designed for childbirth ? Perhaps the baby could be born out the front, above the hips, approximately where the navel is ?  To accomplish this, humans (or perhaps just the females) might need to be a bit taller, to carry the baby higher, without impinging on other organs. StuRat (talk) 07:23, 23 June 2011 (UTC)
 * Make humans a marsupial. Then the kid would be much smaller when born and cause minimal trouble.  Googlemeister (talk) 13:59, 23 June 2011 (UTC)
 * There's a price to pay for intelligence. ~ AH1 (discuss!) 16:24, 24 June 2011 (UTC)


 * I wonder... has there been any sign of psychological benefits from the agonies of childbirth? Does the stimulus somehow tie in to maternal instinct?  Is there any psychological downside to Caesarian birth? Wnt (talk) 19:42, 24 June 2011 (UTC)


 * Can't think how there would be any benefit. The only downside of a C-section would be from the scars it can leave. StuRat (talk) 18:34, 25 June 2011 (UTC)

Hand skin color
What is it that causes the skin on the palm of a dark-skinned person to be lighter than the rest of their body? Is it a lack of melanin? If so, why is there a difference? Dismas |(talk) 20:08, 22 June 2011 (UTC)


 * I'd expect less tanning there, as most people don't walk around with their palms raised to the sky. StuRat (talk) 20:12, 22 June 2011 (UTC)
 * Most blacks don't walk around with their genitalia raised to the sky either, but that is just as black as the rest of them Googlemeister (talk) 21:12, 22 June 2011 (UTC)


 * In general, there's no pigmentation on the palms of the hands and the soles of the feet. This is observable on anyone "of color", such as Africans, Indians, etc. White folks don't have pigmentation on their palms and soles either, but not so obviously since it's all pretty much the same color. But check it out the next time you get a suntan. ←Baseball Bugs What's up, Doc? carrots→ 22:21, 22 June 2011 (UTC)


 * Thanks for that. So the question remains as to why this is the case. Dismas |(talk) 22:31, 22 June 2011 (UTC)
 * The Melanin article doesn't answer the question, but one could infer that melanin occurs only in certain types of tissue, and not just the skin, by the way. But keep in mind that the nature of the skin on the palms and soles is somewhat different from the rest of the body's skin. No melanin, no hair, but plenty of lines and grooves that aid with gripping, which are of course absent on the back of your hands. ←Baseball Bugs What's up, Doc? carrots→ 22:43, 22 June 2011 (UTC)
 * On googling this question, I have seen several claims on the interwebs (very possibly erroneous), that the epidermis on the hands and feet is thicker, and because melanocytes occur only in the underlying dermis, this makes the hands and feet appear lighter. Hence, the claim is that the thick overlying epidermis gives a lighter appearance even though the underlying tissue is just as pigmented as elsewhere. I have no idea if that is true, though it seems at least somewhat plausible. Dragons flight (talk) 23:29, 22 June 2011 (UTC)
 * (EDIT, just bet me to it Bugs) Another observation is that even hairy primates have bare palms and soles, so that leads me to suspect that there's a bigger difference to the skin on those areas then just lack of pigment. Vespine (talk) 22:54, 22 June 2011 (UTC)
 * One other difference is that the skin on the palms and soles has a stratum lucidum layer, unlike the skin on most parts of the body. I'm not saying the stratum lucidum is responsible for the lack of pigmentation there, I'm just supporting the notion that skin on the palms and soles is a somewhat different kind of tissue than skin found elsewhere.  Red Act (talk) 23:35, 22 June 2011 (UTC)
 * And to add further to that, I'll mention the time I was pulling weeds during a school cleanup and yanked out some poison ivy (unknowingly). The palms of my hands were unaffected, but the tiny droplets of urushiol that landed on the back of my hand and forearm were enough to make a rather horrible rash. Tough skin there! Matt Deres (talk) 14:14, 23 June 2011 (UTC)