Is there a way to free memory?
How do you empty the buffers and cache on a Linux system?
First axiom of sheaves: in noetherian topological spaces the direct limit presheaf is a sheaf. To my understanding, "Control" can have two meanings in statistics.   Control group: In an experiment, no treatment is given to the member of the control group.  Ex: Placebo vs Drug: You give drugs to one group and not to the other (control),  which is also referred as "controlled experiment".  Control for a variable: Technique of separating out the effect of a particular independent variable. Some of the other names given to this techniques are, " accounting for", "holding constant", "controlling for", some variable.  For example: In a Football viewing study (like or not like),  you may want to take out the effect of gender as we think gender causes bias, that is, male may like it more than female.     So, my question is for point (2). Two questions:  How do you "control"/ "account for" variables, in general. What techniques are used? (In terms of regression, ANOVA framework).   In above example, does choosing male and female randomly constitutes control? That is, is "randomness" one of the techniques for controlling other effects? What diode modifiers are used in practice to model LEDs with SPICE (Berkeley v.3f5)?  are available to me:  #       Name    Parameter                    Units      Default Example  Area 1       IS      Saturation current             A         1e-14   1e-14    * 2       RS      Ohmic resistance               Ω         0       10       * 3       N       Emission coefficient           -         1       1.0 4       TT      Transit-time                   s         0       0.1ns 5       CJO     Zero-bias junction capacitance F         0       2pF      * 6       VJ      Junction potential             V         1       0.6 7       M       Grading coefficient            -         0.5     0.5 8       EG      Activation energy              eV        1.11    1.11 Si                                                                  0.69 Sbd                                                                  0.67 Ge 9       XTI     Saturation-current temperature exponent  3.0     3.0 jn                                                                  2.0 Sbd 10      KF      Flicker noise coefficient      -         0 11    AF      Flicker noise exponent         -         1 12    FC      Coeff. for for.-bias dep. cap. formula   0.5 13    BV      Reverse breakdown voltage      V         ∞       40.0 14    IBV     Current at breakdown voltage   A         1.0e-3 15    TNOM    Parameter measurement temp.    °C        27      50         The dc characteristics of the diode are determined by the parameters IS and N. An ohmic resistance, RS, is included. Charge storage effects are modeled by a transit time, TT, and a nonlinear depletion layer capacitance which is determined by the parameters CJO, VJ, and M. The temperature dependence of the saturation current is defined by the parameters EG, the energy and XTI, the saturation current temperature exponent. The nominal temperature at which these parameters were measured is TNOM, which defaults to the circuit-wide value specified on the .OPTIONS control line. Reverse breakdown is modeled by an exponential increase in the reverse diode current and is determined by the parameters BV and IBV (both of which are positive numbers).   For example, using this basic, cheap red:      I don't care much about high-frequency characteristics -- just would like to be able to match it's IV-curve within its operating specs (-10uA/-5V leakage to +100mA/+2.2'ishV forward): "The train will leave" vs. "is going to leave" vs. "leaves" vs. "is leaving" Pass Method as Parameter using C# how many conditional sentence types are possible? I wonder how many conditional sentence types are possible. Basically, there are four main and two mixed types. By mixing tenses, it could be up to nine of them. Are the rest viable?  I came across the following examples in Full Spate Pre-Profficiency Primer:   After you have just sold alcohol to a young guy. If he is if under eighteen, you should not have sold him the alcohol. If he promised to bring the drinks, he will. If you will take a seat, the doctor will see you shortly. (Likely, the former will demonstrates politeness only.) I would be grateful if you would tell me a little about your friends. (The same politeness, but would instead.) If he will keep eating all those biscuits, he can not expect to stay as slim as he used to be.   I would be grateful if someone could shed more light on the topic. Does a controlled mount share its rider's turn? From "Controlling a Mount" on p.198 of the Player's Handbook:     The initiative of a controlled mount changes to match yours when you mount it. It moves as you direct it, and it has only three action options; Dash, Disengage, and Dodge. A controlled mount can move and act even on the turn that you mount it.   Does this mean that the rider and mount share a single turn? I tried logging in with a Google account, but I got the following error: Smooth structure of embedded submanifolds Here is a rather long quotation from "Introduction to smooth manifolds" by J. Lee.     Proposition 5.2 (Images of Embeddings as Submanifolds). Suppose $M$ is a   smooth manifold with or without boundary, $N$ is a smooth manifold, and   $F: N \to M$ is a smooth embedding. Let $S = F(N)$. With the subspace   topology, $S$ is a topological manifold, and it has a unique smooth   structure making it into an embedded submanifold of $M$ with the   property that $F$ is a diffeomorphism onto its image.      Proof. If we give $S$ the subspace topology that it inherits from $M$,   then the assumption that $F$ is an embedding means that $F$ can be   considered as a homeomorphism from $N$ onto $S$, and thus $S$ is a   topological manifold. We give S a smooth structure by taking the   smooth charts to be those of the form $(F(U), \phi \circ F^{-1})$, where $(U, \phi)$   is any smooth chart for $N$; smooth compatibility of these charts   follows immediately from the smooth compatibility of the   corresponding charts for $N$. With this smooth structure on $S$, the map   $F$ is a diffeomorphism onto its image (essentially by definition), and   this is obviously the only smooth structure with this property. ...   My question is about the bold sentence. He says that it is obvious, but it is not obvious to me. Why is the constructed smooth structure the only smooth structure that makes $F$ a diffeomorphism between $N$ and $S$? How do I start with in-camera JPEG settings in Lightroom? I'm a novice shooting in RAW and find that half the time my camera JPEG images come out better than my Lightroom tweaks to RAW files.  So to give myself a better start I'd like to apply the JPEG settings that are applied automatically by the camera to my RAW files in lightroom so that initially my RAW files look exactly like the JPEG files.   How can I do this? In Mootools, I'd just run if ($('target')) { ... }.  Does if ($('#target')) { ... } in jQuery work the same way? $A \in M_3(\mathbb Z)$ be such that $\det(A)=1$ ; then what is the maximum possible number of entries of $A$ that are even ? Let $A \in M_3(\mathbb Z)$ be such that $\det(A)=1$ ; then what is the maximum possible number of entries of $A$ that are even ? Short version: In what circumstances is dd safe to use for copying data, safe meaning that there is no risk of corruption due to a partial read or write?  Long version — preamble: dd is often used to copy data, especially from or to a device (). It's sometimes attributed mystical properties of being able to access devices at a lower level than other tools (when in fact it's the device file that's doing the magic) — yet dd if=/dev/sda is the same thing as cat /dev/sda. dd is sometimes thought to be faster, but . Nonetheless, .  Problem: dd if=foo of=bar is not, in fact, the same as cat &lt;foo &gt;bar. On most unices¹, dd makes a single call to . (I find  fuzzy on what constitutes “reading an input block” in dd.) If read() returns a partial result (which, according to POSIX and other reference documents, it's allowed to unless the implementation documentation says otherwise), a partial block is copied. Exactly the same issue exists for write().  Observations: In practice, I've found that dd can cope with block devices and regular files, but that may just be that I haven't exercised it much. When it comes to pipes, it's not difficult to put dd at fault; for example try :  yes | dd of=out bs=1024k count=10   and check the size of the out file (it's likely to be well under 10MB).  Question: In what circumstances is dd safe to use for copying data? In other words, what conditions on the block sizes, on the implementation, on the file types, etc, can ensure that dd will copy all the data?  ( has a fullblock flag to tell it to call read() or write() in a loop so as to transfer a full block. So dd iflag=fullblock is always safe. My question is about the case when these flags (which don't exist on other implementations) are not used.)  ¹  I've checked on OpenBSD, GNU coreutils and BusyBox. I've been trying to find this darn series of books for ages, I read them back in early 2001-02 and can't really remember much of them. I think there were 10-ish books, it was an easy read but a long series. On early publications, the covers, were mainly yellow, with small pictures of whatever happens in that book.  The book began with two siblings, a brother and a sister, running in a forest. She conjures up what can only be remembered as a golem type creature. He then uses a high magic 'blast' and wipes out the golem, knackering himself. His sister laughs at him for being 'powerful' but expending himself too much on one big magic blast. The beginning I remember vividly, the rest, not so much.  The story continues as a conflict happens, I believe two worlds are involved? The brother and sister are split up, but this is where my memory becomes vague.  The mechanics of the world seems that there are gems, or stones, set in the backbone, which in turn give access to magic. When the person uses them, they can draw too much, which ends up exhausting them. The 'big bad evil king' kills their father, and destroys their farm early on in the story. The meaning of Bit-wise NOT in Python Computing Galois Group of $\mathbb{Q}(\sqrt{2},\sqrt{3}):\mathbb{Q}$ Galois Group of $\mathbb{Q}(\sqrt{2},\sqrt{3}):\mathbb{Q}$ is cumbersome to computing. Is easy to find the all four possible candidates but is cumberstone to show that they are automorphisms:  For multiplication is too long showing that  $f((a+b\sqrt{2}+c\sqrt{3}+d\sqrt{6})(a'+b'\sqrt{2}+c'\sqrt{3}+d'\sqrt{6}))=f(a+b\sqrt{2}+c\sqrt{3}+d\sqrt{6})f(a'+b'\sqrt{2}+c'\sqrt{3}+d'\sqrt{6})$  For some non trivial candidate since the left hand side expands in $16$ terms. What about $\mathbb{Q}(\sqrt{2},\sqrt{3},\sqrt{5}):\mathbb{Q}$? there are $7$ non trivial candidates and multiplication expands in $64$ terms!   How to do it in a tricker form?  Edit(Let me be more precise in my question):   I know that if $f\in\Gamma(\mathbb{Q}(\sqrt{2},\sqrt{3}):\mathbb{Q})$, then $f(\sqrt{2})=\pm\sqrt{2}$, $f(\sqrt{3})=\pm\sqrt{3}$ so there are $4$ candidates for $\mathbb{Q}$-Automorphisms. Candidates are given by:  $f_1(a+b\sqrt{2}+c\sqrt{3}+d\sqrt{6})=a+b\sqrt{2}+c\sqrt{3}+d\sqrt{6}$  $f_2(a+b\sqrt{2}+c\sqrt{3}+d\sqrt{6})=a-b\sqrt{2}+c\sqrt{3}-d\sqrt{6}$  $f_3(a+b\sqrt{2}+c\sqrt{3}+d\sqrt{6})=a+b\sqrt{2}-c\sqrt{3}-d\sqrt{6}$  $f_4(a+b\sqrt{2}+c\sqrt{3}+d\sqrt{6})=a-b\sqrt{2}-c\sqrt{3}+d\sqrt{6}$  But I need to check that they are $\mathbb{Q}$-Automorphisms in $\mathbb Q(\sqrt{2},\sqrt{3})$. All candidates $f_i$ fixes $\mathbb{Q}$ and is obvious that all preserves sums, $f_1$ obviously preserves product also since is the identity, but is cumberstone to show that $f_i(xy)=f_i(x)_if(y)$ to conclude $f_i\in\Gamma(\mathbb{Q}(\sqrt{2},\sqrt{3}):\mathbb{Q})$. Why is the sun brighter in Australia compared to parts of Asia? Rules and guidelines for drawing good schematics There are a lot of poorly drawn schematics here. A few times people have actually asked for critiques of their schematics. This question is intended as a single repository on schematic drawing rules and guidelines can point people to. The question is  What are the rules and guidelines for drawing good schematics?     Note: This is about schematics themselves, not about the circuits they represent. About free quarks and confinement I simply know that a single free quark does not exist. What is the reason that we can not get a free quark?  If we can't get a free quark then what is single-top-quark? $\operatorname{rank}(T^3) + \operatorname{rank}(T) \geq 2\operatorname{rank}(T^2)$ for finite-dimensional $V$