Quantization of energy A mirror reflects all electromagnetic waves that fall on it in the visible spectrum. How does the mechanism of reflection work? Is it because when a photon hits an electron, the electron jumps to a higher energy level and then to come back to its initial energy level, it emits a photon.  If the energy levels of an atom are quantized, how can a mirror absorb all e.m waves in the visible spectrum? Shouldn`t it absorb only specific wavelengths?
Explain reflection laws at the atomic level The "equal angles" law of refection on a flat mirror is a macroscopic phenomenon. To put it in anthropomorphic terms, how do individual photons know the orientation of the mirror so as to bounce off in the correct direction?
Partitions for Ubuntu and Windows 7 dual boot on SSD + HDD setup When something gets wet, it usually appears darker. This can be observed with soil, sand, cloth, paper, concrete, bricks...  What is the reason for this? How does water soaking into the material change its optical properties? Logistic Regression - Adding interactions makes Independent variable statistically insignificant My name is Abhi &amp; I am trying to better understand logistic regression by solving a few practice problem. I am using R and RStudio as the development environment  Problem Statement  Given the age, sex and class(first,second,third) for each passenger can you predict if he survived or died when the titanic sank   Attempt1  Simple Logistic Regression. Use age,sex and passenger class directly. The formula (in R)  Survived~Pclass+Sex+Age  This gives fairly decent results - accuracy of 79% and all of independent variables are statistically significant   Attempt2  Add interactions between age,sex and passenger class. Accuracy has improved to 80% but age is no longer significant. Also none of the new terms(age-sex,age-class,sex-class,age-sex-class) are statistically significant. The formula (in R) Survived~Pclass*Sex*Age   Can some one explain why this is happening? I can accept that the new terms may not be significant but why is age no longer significant?   Any help would be much appreciated How to show a group is cyclic? One question asking if $\mathbb{Z}^*_{21}$ is cyclic.  I know that the cyclic group must have a generator which can generate all of the elements within the group.  But does this kind of question requires me to exhaustively find out a generator? Or is there any more efficient method to quickly determine if a group is a cyclic group? $X$ is Hausdorff if and only if the diagonal of $X\times X$ is closed Let $X$ be a topological space. The diagonal of $X \times X$ is the subset $$D = \{(x,x)\in X\times X\mid x \in X\}.$$   Show that $X$ is Hausdorff if and only if $D$ is closed in $X \times X$.   First, I tried to show that $X \times X \setminus D$ is open using the fact that $X \times X$ is Hausdorff (because $X$ is Hausdorff), but I couldn't find an open set that contains a point outside $D$ and is disjoint to it... Usually when a word starts with a vowel, we will use "an" before it. But for union, it is "a union" not "an union." It is not explained in the previously mentioned  why union is an exception. It explains how to know exceptions for h like hotels.   Also are there any exceptions for the opposite side, where there should be an "a" but is an "an" instead? (Unfortunately I have no example of a case like this.) Why do metals only glow red, yellow and white and not through the full range of the spectrum? Overlapping text in Database Schema SEDE Over at , there is overlapping text in the Database Schema under Close-As-Off-Topic-Reason-Types:  that makes it really hard to read.  This is also happening underneath &quot;Pending Flags&quot;, and seemingly with every long line in the schema.  This would be fine if you could increase the width of the list as you can with the height, which would in theory separate the lines, but you can't.  Can we fix this, please?  UPDATE: I have found that  post is almost exactly the same as mine, but steady on with duplicate votes.   comment says that it will be fixed, but that question was asked more than five years ago, and in that time the problem has not been resolved.  UPDATE 2: It seems that  would help.  I changed a little CSS/HTML, and came up with this:  Although mine is a little cruder than it could be.  This is just an example. Why does the collada exporter not export texture references? I've been having trouble exporting collada objects from blender, so I stripped everything back and textured a single cube, and exported it.  This is a completely trivial model, one cube, with one material assigned to it, the material has a single 'g.png' texture assigned to it.   The exported collada data looks like this:    &lt;library_materials&gt;     &lt;material id="Material-material" name="Material"&gt;       &lt;instance_effect url="#Material-effect"/&gt;     &lt;/material&gt;   &lt;/library_materials&gt;   Where:    &lt;library_effects&gt;     &lt;effect id="Material-effect"&gt;       &lt;profile_COMMON&gt;         &lt;technique sid="common"&gt;           &lt;phong&gt;             &lt;emission&gt;               &lt;color sid="emission"&gt;0.2879998 0.2879998 0.2879998 1&lt;/color&gt;             &lt;/emission&gt;             &lt;ambient&gt;               &lt;color sid="ambient"&gt;0 0 0 1&lt;/color&gt;             &lt;/ambient&gt;             &lt;diffuse&gt;               &lt;color sid="diffuse"&gt;0.2163267 0.1845119 0.2121569 1&lt;/color&gt;             &lt;/diffuse&gt;             &lt;specular&gt;               &lt;color sid="specular"&gt;0.5 0.5 0.5 1&lt;/color&gt;             &lt;/specular&gt;             &lt;shininess&gt;               &lt;float sid="shininess"&gt;50&lt;/float&gt;             &lt;/shininess&gt;             &lt;index_of_refraction&gt;               &lt;float sid="index_of_refraction"&gt;1&lt;/float&gt;             &lt;/index_of_refraction&gt;           &lt;/phong&gt;         &lt;/technique&gt;         &lt;extra&gt;           &lt;technique profile="GOOGLEEARTH"&gt;             &lt;double_sided&gt;1&lt;/double_sided&gt;           &lt;/technique&gt;         &lt;/extra&gt;       &lt;/profile_COMMON&gt;       &lt;extra&gt;&lt;technique profile="MAX3D"&gt;&lt;double_sided&gt;1&lt;/double_sided&gt;&lt;/technique&gt;&lt;/extra&gt;     &lt;/effect&gt;   &lt;/library_effects&gt;   This seems to be missing the texture data associated with the object.   By comparsion, exporting a wavefront object generates this .mtl file:  # Blender MTL File: 'basic.blend' # Material Count: 1  newmtl Material Ns 96.078431 Ka 0.000000 0.000000 0.000000 Kd 0.790000 0.790000 0.790000 Ks 0.500000 0.500000 0.500000 Ni 1.000000 d 1.000000 illum 0 map_Kd g.png   &lt;----- ie. Blender is aware of this texture   So... is the collada exporter for blender just broken, or does it require some kind of special config in order to function correctly?  If the latter, how/what is required to make this work?  (NB for what it's worth, the UV coordinates are exported in the .dae, abit they obviously are completely useless without a texture assigned to them; I've also tried adding two different textures to see if the exporter needs that because it naively assumes 'one texture = don't bother, it's one texture for the whole model'. That didn't work either) Several years ago I heard of something called dummy subjects in high school. It was then stated that, for example, it is a dummy subject when it starts many instances of sentences, e.g.        It is rainy today.   It is hard to imagine how hard is to live alone.   It is not my university degree that matters here.     My question is if we can use it with plural subjects? For example in       If some think that in Mahmoud Dowlatabadi’s works it is only social themes that matter and the writer is ignoring fictional arrays and artistic techniques, at least, endings of his stories show wrongness of this idea.     My question deals with the italicized part. If this usage is OK, can we also write they are social themes that matter? I mean can they also play the role of a dummy subject? Why there is a $\frac{1}{2}$ in the distance formula $d=\frac{1}{2}at^2$? I'm preparing for my exam, but I have difficulties in perceiving why there is a $\frac{1}{2}$ in the distance formula $d=\frac{1}{2}at^2$? Integral of Wiener Squared process I don't have a background of stochastic calculus.   It is known  that definite integral of standard  from $0$ to $t$ results in another Gaussian process with slice distribution that is normal distributed with mean equal to $0$ and variance $\frac{T^3}{3}$ i-e  $$ \int_0^{t} W_s ds \sim \mathcal{N}(0,\frac{t^3}{3})    $$  Question:  What if we square the standard Wiener process and then integrate i-e $$ \int_0^{t} W_s^2 ds \sim ?    $$  Would that be scaled Chi-square distributed ? Trying to find some simple SQL Server PIVOT examples.  Most of the examples that I have found involve counting or summing up numbers.  I just want to pivot some string data.  For example, I have a query returning the following.  Action1 VIEW   Action1 EDIT   Action2 VIEW   Action3 VIEW   Action3 EDIT     I would like to use PIVOT (if even possible) to make the results like so:  Action1 VIEW EDIT   Action2 VIEW NULL   Action3 VIEW EDIT     Is this even possible with the PIVOT functionality? I've got a Windows 8 (not .1, not Pro; OEM with a Lenovo Z580 laptop), which I want to use for WP8 development.  I've read  and , and a few more articles.  I have enabled in BIOS what looks like it has to do with hardware virtualisation - "Intel Virtual Technology" (is this VMX?). No signs of EPT or XD.  I've got the four Hyper-V items in the enumeration that msinfo32 shows.  However, in the 'Control Panel/Programs and Features/Turn on|off windows features' list, I don't have Hyper-V.  Is this available at all on my machine, and if not what can I do to get it working?  Thanks in advance. I tried installing Office 2007 in Ubuntu with Wine but it was throwing an error after installing and also when I tried to open a PowerPoint document and save it. Has anybody gotten Office 2007 installed without any issues? Please help me. How to evaluate $\int_{0}^{+\infty}\exp(-ax^2-\frac b{x^2})\,dx$ for $a,b>0$ Why are rockets so big? I'm curious why rockets are so big in their size. Since both the gravitational potential one need to overcome in order to put thing into orbit, and the chemical energy burned from the fuel, are proportional to the mass, so if we shrink the rocket size, it would seem to be fine to launch satellites. So why not build small rocket say the size of human? I can imagine small rocket would be easier to manufacture in large quantities and easier to transport. And maybe someone can make a business out of small rocket, carrying one's own satellite. Blurring/Feathering a Procedural Pointiness Mask I'm trying to create a procedural mask to affect the sharp edges of my model using the Pointiness output from the Geometry node, leading to the eventual idea of using it to create customisable weathering effects, such as .  This is the base setup that I've got so far.   How is it possible to blur/feather the black edges of the mask so that they would essentially expand across the object until the whole object is rendered black?   I've had a look at both of the go-to texture blur methods suggested for cycles found  and  however these seem to rely on there being a vector input/output for the texture, which is not the case in my example.  The Procedural Cracks tutorial by CGMasters came closest to what I was trying to achieve with the 'Worn Edges' section of the , but I didn't have any success trying to convert it to my situation.  Any ideas would be massively appreciated! :)  EDIT: Not sure if it was clear enough from the description but I'm trying to steer clear of baking/UV-Unwrapping/the Works on this one... Purely procedural :)  UPDATE: I've made a couple of updates to the shader which has given me slightly better results, although it's still not quite there and the mask blur/expansion issue is still not successful.  This is what it now looks like:   The issue is now coming from the grey values of the mask 'leaking' out across the whole mesh and not stemming from the black values... if that makes sense? :P   In researching weathering effects in blender, I stumbled across , which is exactly what I want to achieve?  UPDATE 2: Still no luck achieving the desired effect in the gif, however I feel I'm slightly closer from adding another colour ramp node after the previous ones.    Does anyone have any more ideas?  UPDATE 3: Found a working solution, added an answer below if people are interested :) Is selenium webdriver capable of database testing? After reading so many answers and forums it makes me confused. Some people say: Selenium webdriver is a browser automation tool and it has nothing to do with the database. And some other showing JARs and code that how we can connect selenium to the database and we can test database using selenium webdriver. So I would really like to know if we can do database testing using selenium? If yes then which databases tool it supports like Mysql, SQL server, Oracle... And if selenium is not suitable for database testing then please recommend to me the best tool for database testing. Number Theory: Prove that $m | \phi(a^m - 1)$