Wikipedia:Reference desk/Archives/Science/2017 January 10

= January 10 =

Feynman Lectures. Lecture 43. Lecture Summary
Can you show how did he get $$\frac{n_a}{n_0}$$ ? In Lecture 43 he wrote $$D = \tfrac{1}{3}lv$$, $$D = \mu kT$$ , but never $$D = \mu kT \cdot n_0$$. Username160611000000 (talk) 09:43, 10 January 2017 (UTC)

How is gluten-free flour made?
How is gluten-free flour made? Since gluten is supposed to give bread its shape and structure, do gluten-free products taste as good as the traditional wheat/barley/rye products? Also, since some people eat gluten-free because of health risks of eating gluten-laden foods, can they just switch to rice? The gluten-free diet article just points out that wheat/barley/rye contains gluten, not rice or cauliflower (which can be made into a rice-like powder) or quinoa. 66.213.29.17 (talk) 17:54, 10 January 2017 (UTC)


 * It's as you say: gluten-free flour is made from gluten-free plant species Dr Dima (talk) 19:04, 10 January 2017 (UTC)


 * Gluten-free bread is a huge area of research! You can find information on the rheology of GF bread, crumb characteristics, moisture, and many other aspects of many formulations. You can even see images from scanning electron microscopy, and analysis of loss modulus (e.g. ). Anyway, as for the taste: nothing beats some personal experimentation, as taste is somewhat subjective. However, we do have scientific research on that as well:
 * "Breads with legume flours showed good physico-chemical characteristics and adequate sensory profile".
 * "Panellists commented that this bread "looked more like real bread" and that the loaves had "loaf volume and crust color similar to wheat bread" SemanticMantis (talk) 20:07, 10 January 2017 (UTC)


 * Without gluten you need a substitute to hold the bread together. Eggs are one option.  See . StuRat (talk) 23:12, 10 January 2017 (UTC)

Is it scientifically proved that menstruation causes women to be irritated or nervous or it's a myth?
If it's true, then what is the physiological / psychological (psychophysiological) explanation for that? 93.126.88.30 (talk) 20:03, 10 January 2017 (UTC)


 * See premenstrual syndrome, and the second reference cited there . Here are a few relevant scholarly references as well . There is much variation in the mood and affect of individual women during different phases of the menstrual cycle, but real changes in mood (and hormones, and physiology) do occur. SemanticMantis (talk) 20:17, 10 January 2017 (UTC)


 * On a related topic, at one time it was commonly asserted that PMS had a strong 'nurture' component and that women who experienced difficulty did so largely due to seeing other females having difficulty (i.e. that is was largely psychosomatic). If there's any doubt about that not being the case, this 2014 study states outright that there is "a clear genetic influence in premenstrual syndrome." Matt Deres (talk) 01:24, 13 January 2017 (UTC)

Earth Axis Axial Precession
I have a question about the Wikipedia article on Earth axis axial precession. This article depicts this precession as going in a counter-clockwise direction as projected on the celestial sky. But an Astronomy Online article depicts this precession as going in a clockwise direction on the celestial sky. Which is correct? Jfandrus57 (talk) 21:59, 10 January 2017 (UTC)
 * Some diagrams can be ambiguous, but I think our article is correct. Which article shows it clockwise?    D b f i r s   22:31, 10 January 2017 (UTC)
 * By way of an independent confirmatory source, I have here A Field Guide to the Stars and Planets, 1964 edition by Donald H. Menzel. On page 330 is a diagram showing the north celestial pole precessing anticlockwise against the fixed stars, the same as is shown in this section of the Wikipedia axial precession article (and the dates in the diagrams also agree).
 * Side comment: on first viewing the top diagram in that article, my initial reaction was that it showed precession going the other way. Once I thought about it I realized that this is because when it draws a reference circle to illustrate the precession, it's shown from the other side, looking toward the Earth rather than toward the stars.  Nothing's ambiguous there, but I did find it misleading and I wonder if it might be better to substitute a different diagram or else add some words of explanation. --69.159.60.210 (talk) 05:39, 11 January 2017 (UTC)