Processing Power In Python
How to get current CPU and RAM usage in Python?
Basic voltage divider issue in my amateur circuit XBee Once again I need your help in my project. I have a 4,5v powered circuit. I put a voltage divider with 2 resistors in series to reduce my initial voltage of 4.5 V to 3.4 V (to feed an XBee module).  The issue is that if I do not connect the xbee, the voltage divider reduces the input voltage to the desired voltage(3.4 V), but when I connect the XBee module, the resulting voltage divider voltage drops to a value very low (0.85 V), making the XBee malfunction. Surely it is a basic mistake, I am asking something that is very clear, but I'm newbies.   Basic Circuit:  Vin(4.5 V)-----R2(10 kΩ)---------R1(33 kΩ)--------GROUND                        |                        |                  Vout desired (3.4 V)                        |                        |                       XBee Someone who gives unsolicited explanations in a condescending way I'm reading Galois Theory by Steven H. Weintraub (second edition), and finding that I'm at least somewhat short on the prerequisites. However the following proof looks wrong to me - am I misunderstanding something, or is it actually an incorrect proof?  Lemma 2.2.3. Let $F$ be a field and $R$ an integral domain that is a finite-dimensional $F$-vector space. Then $R$ is a field. Proof. We need to show that any nonzero $r \in R$ has an inverse. Consider $\{1, r, r^2, \cdots\}$. This is an infinite set of elements of $R$, and by hypothesis $R$ is finite dimensional as an $F$-vector space, so this set is linearly dependent. Hence $\sum_{i=0}^n{c_i r^i} = 0$ for some $n$ and some $c_i \in F$ not all zero.  It then goes on to show, given the above, that we can derive an inverse for $r$. However, if I consider examples like $r = 2 \in Q[\sqrt{2}]$, $r = \sqrt{2} \in Q[\sqrt{2}]$ or $r = 2 \in Q[X]/{&lt;X^2&gt;}$, the set $\{1, r, r^2, ...\}$ doesn't look linearly dependent to me. I do believe the lemma is true (and might even be able to prove it), but this does not look like a correct proof to me. Am I missing something? [Edit] Well yes, I am. Somehow I had managed to discount the possibility of any $c_i$ being negative, despite repeatedly looking at each fragment of the quoted text in an attempt to find what I might be misunderstanding. How to backup an Android device? Can anyone recommend a good way to backup Android devices? Ideally I would like to do this wirelessly and, not only backup my data, but also my user settings. Is it possible to backup an image of an Android device - so that one doesn't even need to reinstall apps? It would be particularly useful to hear from users that have restored backups, as to how easy, and complete, their processes were. Thanks If $E$ has Lebesgue measure $0$, must there exist a translate such that $E\cap E+x=\varnothing$? If $y\in E\cap E+x$ then $y=h=h'+x \implies x=h-h'$ for $h,h'\in E$. Likewise, if $x=h-h'$, then $h\in E\cap E+x$. So that $E\cap E+x$ is non empty iff $x=h-h'$ where $h,h'\in E$. Thus, if there exists a real $x$ which cannot be expressed as above, the result is proven. The problem is I cannot prove that such an $x$ must exist. I have tried assuming that all real $x$ are of that form, but that gives me nothing except that $E$ must be uncountable and unbounded. Any hints? Is there a systematic way of solving cubic equations? In my text book, to solve cubic equations, I need to    find by trial &amp; error what $f(a)$ will make the equation 0. The factor will be $(x-a)$ then the other factor will be $Ax^2+Bx+C$ then I can solve using compare coefficient   But for te first part, is there any other way apart from trail &amp; error? Or is there some technique to guess the factor of an equation?   The question I am currently doing happens to be $2x^3+3x+4=9$   UPDATE:  $2x^3+3x+4=9$ should be $2x^3+3x+4=9x^2$   UPDATE 2  So I am going to try substituting   $x=\pm{1}, \pm\frac{1}{2}, \pm{2}, \pm{4}$  When $x=-\frac{1}{2}$, one of the provided answers,   $2(−0.5)^3−9(−0.5)^2+3(−0.5)+4=-18.75\neq 0$   did I make a mistake? Why is fundamental group insufficient to classify manifolds? I have heard that some issues in group theory prevent classifying all manifolds upto homotopy using the fundamental group invariant. Does anyone know what are those issues?  Thanks, K. Why do some devices have 200V on the case? I recently got a desktop LED lamp, and I feel a "strange" slight vibration when touching the metal case. I found that other devices also have high voltage on their case.  What is the reason/trade-off to design the PSU that way? Are "real" transformers inefficient? Even if it's harmless, why is the high voltage connected to the metal case, and not just through insulated wires?    When I turn the lamp on, the setup in the picture measures the power line (220V) 214Vpp (59Vrms). When I also touch the metal case, the voltage drops down to around 30V.  AC adaptor: New users who have less than 125 reputation are subject to a , network-wide.  Today, however,  was able to post two questions within 8 minutes of each other, bypassing this rate limit: , and  today. (Both links are 10k-only.)  How was this user able to bypass the network-wide question asking rate limit? (I'd imagine one easy hack would be to exploit a race condition, but if that were the case, the two questions would be posted at exactly the same time, not 8 minutes later.)  Is it because the rate limit only considers the IP address, and not the account, so if the same account makes the post from a different IP address, it's allowed?  This is not a duplicate of , as back when that was asked, the rate limit worked quite differently, and wasn't even enabled on some sites; today, according to the very first link, it is now enabled network-wide. Let me start by explaining my particle physics background is very patchy, so this question may not be as coherent as  I would like it to be.   In general terms, what is the difference between a resonance found during a particle experiment and a particle?   From reading Wikipedia it seems to be mostly based on timescales. If a heavy particle decays quickly, how can we distinguish it from a resonance?  I would not be posting this question except for the fact that the Wikipedia page says "This page has some issues".        and I would be interested in knowing more about the subject. Are the eigenvalues of $AB$ equal to the eigenvalues of $BA$? (Citation needed!) First of all, am I being crazy in thinking that if $\lambda$ is an eigenvalue of $AB$, where $A$ and $B$ are both $N \times N$ matrices (not necessarily invertible), then $\lambda$ is also an eigenvalue of $BA$?  If it's not true, then under what conditions is it true or not true?  If it is true, can anyone point me to a citation?  I couldn't find it in a quick perusal of Horn &amp; Johnson.  I have seen a couple proofs that the characteristic polynomial of $AB$ is equal to the characteristic polynomial of $BA$, but none with any citations.  A trivial proof would be OK, but a citation is better. Best Fake Proofs? (A M.SE April Fools Day collection) How to update to the latest numpy and scipy on Ubuntu 14.04LTS On my Ubuntu 14.04LTS, for python3, I have   &gt;&gt;&gt; import numpy  &gt;&gt;&gt; import scipy  &gt;&gt;&gt; numpy.__version__  '1.8.2'  &gt;&gt;&gt; scipy.__version__  '0.13.3'   I want to update numpy and scipy to the most , I tried with the following commands  sudo pip3 install --upgrade numpy sudo pip3 install --upgrade scipy   both commands ran successfully, but the version numbers didn't change to 1.9.2 and 0.16.0 at all for both python packages (after restarting the computer). Anyone knows how to update to the most version? Thank you very much!! Trying to remember a book that had people (I think they turned white?) segregated into a compound Can Clerics have divine power without it being provided by a god? How to add "Refresh" option to right click menu in Lubuntu? I have many users at the place I work, expressing the notion of switching to Ubuntu.  Most of them, for whatever weird reason wanting to know if its possible to have refresh added when you right click on the desktop.   Is that possible? How can I find out if someone really holds a doctoral degree? We're currently interviewing candidates at my company and I'd like to verify if some of them really have the academic degrees they claim. One in particular claims a doctoral degree from a German university.  I've contacted the university, and the dean wrote back saying that they could not provide this information without the written consent of the individual.  I found this policy rather odd; I would have thought that the granting of a doctoral degree was public information. Is this normal? Is there anything else I can do to find out?  I obtained from the library a copy of the thesis in question but it was in German. I also found through Google  which appears to be a list of dissertations published by that university, but it is unclear whether these are doctoral dissertations or not. The person in question and his dissertation are in that list. Will wolves attack Ocelots? PHP variable variables I want to store courseworks marks of n courseworks into n variables, such as cw1 and cw2 etc. Using variable variables how can I come with cw1, cw2 etc.   How can I dynamically create variables? Is there a way to convert an image to grayscale?