I've noticed that, any time I try to pick up Peskin and Schroeder, the main stumbling block it the leap in mathematical constructs from QM. Is there a good textbook that could teach me some of the math I need to know (advanced properties of Fourier transforms, vector integration tricks, etc.) to get a foothold on this?  I noticed this question might be misleading; I am not looking for a mathematical-physics take on QFT, anything regarding rigorous abstract algebra, topology, etc. Mainly I'm looking for what might be the textbook between the level of undergraduate and graduate math curriculum that contains principles used in introductory QFT.  Again, I am not trying to answer this question . I am an engineer with a decent background in QM but I can't understand the math in QFT. I am not looking for a mathematical approach to QFT as I would be hopefully lost, I am looking for a source to give me the mathematical pre-requisites for QFT.
I'm a student of mathematics with not much background in physics. I'm interested in learning Quantum field theory from a mathematical point of view.  Are there any good books or other reference material which can help in learning about quantum field theory? What areas of mathematics should I be familiar with before reading about Quantum field theory?
How can one prove the Bohr-Sommerfeld quantization condition $$ \oint p~dq ~=~2\pi n \hbar $$ from the WKB ansatz solution $$\Psi(x)~=~e^{iS(x)/ \hbar}$$ for the Schroedinger equation? With $S$ the action of the particle defined by Hamilton-Jacobi equation $$ \frac{\partial S}{\partial t}+ \frac{(\nabla S)^{2} }{2m}+V(x)~=~0 .$$ Slow SoapHttpClientProtocol constructor How many possible Enigma machine settings? I'm trying to calculate the amount of settings the enigma machine has. I have found several sites regarding this topic, but it seems like there are two answers to my question. The first answer is 158,962,555,217,826,360,000 and the second is 107,458,687,327,250,619,360,000. Where the difference is that in the second answer, it has been taken into account that the notched rings on the enigma could be set as well, giving 26 * 26 = 676 more settings than the first answer.   But which answer is the right one, and why? How many possible different Enigma machine settings are there and how can one determine this number? Compiler Errors in atlwin.h Is two-thirds plural? Is 2/3 always, sometimes or never plural?  E.g.     1a) 2/3 of the pizza were eaten.     1b) 2/3 of the pizza was eaten.      2a) 2/3 of the visitors were men.     2b) 2/3 of the visitors was men.   I feel that example 1 could go either way but example 2b sounds very wrong.  Is there a rule for this? Boot drops to a (initramfs) prompts/busybox I am running an HP pavilion dv6000 dual boot win7 and Ubuntu 12.04. (well, up until today).  After a reboot, the boot process drops to the BusyBox shell and I end up at the prompt:  BusyBox v1.18.5 (Ubuntu 1:1.18.5-1ubuntu4) built-in shell (ash) Enter 'help' for a list of built-in commands.  (initramfs)   I've been researching others who have had this same problem, but haven't been able to find any of those solutions to work for me.  I tried the method described , and after the final command   mount -t ntfs-3g /dev/sda1 /root -o force   it does nothing and gives me another (initramfs) prompt.  I can boot to a live CD (USB) and get to a terminal, but it doesn't seem to do much good, as I can see the /dev/sda1 in the ls command, but it doesn't recognize it when I try to cd to it.  One more question: using the command fdisk -l how can I tell which mount point (sda1/sda2) is my windows partition and which one is Ubuntu? Trouble trying to use Windows Search to search for file with a question mark in the content It seems that Windows Search is having trouble when I specify a question mark character as the content that I'm searching for within my files.  I've tried:   content:? content:"?" content:"\?" content:\? content:%3f content:"%3f" content:\3f content:"\3f" content:\00\00\00\3F   but each of these yield no results when I do indeed have files that contain ? within the scope of the search. If I instead search for something like content:happy it will indeed find all files with the phrase "happy" within those same files.  My assumption is that Windows Search is treating some characters such as the question mark as a special character likely for the purpose of wild card expressions. To test this theory I've also searched for files containing an asterisk * and indeed I have the same issue as when searching for content of question mark. What I'm wondering is whether there is any way to get a search to work where I can search for a literal expression without any type of wildcard matching or at least a way to escape the special characters within the expression.  By the way I'm using Windows 7 Enterprise. How do I read and parse an XML file in C#? I am looking for either an online tool or one that I can download to convert DD to DMS.  For example, I want to convert from:  41.590833, -93.620833 to 41° 35′ 27″ N, 93° 37′ 15″ W ...  Those are the coordinates, according to , for Des Moines. How to find out who called a method? How can i find the python triggered by the GUI? I want to fully automatize some of my blender processes, an i run into a lot of problems not finding the correct commands, not using the correct args...  Can i just "see" in a log somewhere what were the commands blender ran ?  To be very precise, i want to load a gltf file, and export it to stl.  No problem through the gui, but i'm stuck with that bit of code :   import bpy import sys import os  file = open(r"C:\Users\theo1\Documents\GitHub\Hackathon2020\map&amp;mapdata\mini.gltf")  bpy.ops.import_scene.gltf(file) bpy.ops.export_mesh.stl(filePath=r"C:\Users\theo1\Documents\GitHub\Hackathon2020\map&amp;mapdata\mini.stl")   Which gives me this :   Traceback (most recent call last):   File "&lt;string&gt;", line 1, in &lt;module&gt;   File "C:\Users\theo1\Desktop\impExp.py", line 7, in &lt;module&gt;     bpy.ops.import_scene.gltf(file)   File "C:\Program Files\Blender Foundation\Blender 2.81\2.81\scripts\modules\bpy\ops.py", line 198, in __call__     C_dict, C_exec, C_undo = BPyOpsSubModOp._parse_args(args)   File "C:\Program Files\Blender Foundation\Blender 2.81\2.81\scripts\modules\bpy\ops.py", line 151, in _parse_args     raise ValueError("1-3 args execution context is supported") ValueError: 1-3 args execution context is supported   thanks. An insurance company supposes that the number of accidents that each of its policyholders will have this year is Poisson distributed, with a mean depending on the policyholder: the Poisson mean Λ of a randomly chosen person has a Gamma distribution with the Γ(2, 1)-density function fΛ(λ) = λe−λ (λ > 0). Find the expected value of Λ for a policyholder having x accidents this year (x = 0, 1, 2, . . .).  I am not sure how to incorporate the gamma parameters. So far I have found P(X = n|Λ = λ) = Poisson(λ) and fΛ(λ)= Exp(λ) so by integrating P(X = n|Λ = λ)fΛ(λ) then letting the integral of Gamma (n + 2, 2) equate to 1, I have worked out P(X = n) = (n + 1)/2^(n+2). How do you find the expected value of Λ from that? I have seen that a Gamma-Poison mix has E(X) = αβ which would give 2 but I have tried integrating fΛ(λ) and can't seem to get 2. Page number position I am working on a long document in LaTeX with documentclass book. I need the page number to always be in the upper right corner of each page, even if that page is the first page of a chapter (right now on 1st pages of chapters, the page number is bottom-centered, on all other pages it's top-right).  I control the position of the page number with fancyhdr:  \usepackage{fancyhdr} \pagestyle{fancy} \lhead{} \chead{} \rhead{\thepage} \lfoot{} \cfoot{} \rfoot{} \renewcommand{\headrulewidth}{0pt}   Also, I don't know if the problem is related but my chapters do not start from the top of the page. There is a white area, then comes chapter X, then a newline with the chapter line. What I also want is the chapter to start from the top of the page.  The main question here is how I can get the page number to always appear in the upper right corner, I mention the thing with the chapter title position only in case that might be related. In C, are arrays pointers or used as pointers? Distorted circles in axis environment with TikZ With a fresh installation of TeX Live (updated just before writing this post), circles in axis environments are distorted. Consider the following MWE:  \documentclass{article} \usepackage{pgfplots} \pgfplotsset{compat=1.16}  \begin{document}  \begin{tikzpicture} \begin{axis}[   ymin=-3, ymax=3,   xmin=-3, xmax=3 ]  \draw (1,0) circle [radius=1.5]; \fill (1,0) circle [radius=1];  \end{axis} \end{tikzpicture}  \end{document}   The output looks like this:   Obviously, the circles aren't even circles. I haven't encountered this problem before. Did I do anything wrong while setting up my new system?  EDIT: It's not an issue of using axis equal or not since the axes are scaled more or less equally already. Instead, the circles appear as rotated ellipses that are strongly stretched out in one dimension.  EDIT 2: Here's the output of \listfiles:  article.cls    2019/12/20 v1.4l Standard LaTeX document class   size10.clo    2019/12/20 v1.4l Standard LaTeX file (size option) pgfplots.sty    2018/03/28 v1.16 Data Visualization (1.16) graphicx.sty    2019/11/30 v1.2a Enhanced LaTeX Graphics (DPC,SPQR)   keyval.sty    2014/10/28 v1.15 key=value parser (DPC) graphics.sty    2019/11/30 v1.4a Standard LaTeX Graphics (DPC,SPQR)     trig.sty    2016/01/03 v1.10 sin cos tan (DPC) graphics.cfg    2016/06/04 v1.11 sample graphics configuration   pdftex.def    2018/01/08 v1.0l Graphics/color driver for pdftex     tikz.sty    2020/01/08 v3.1.5b (3.1.5b)      pgf.sty    2020/01/08 v3.1.5b (3.1.5b)   pgfrcs.sty    2020/01/08 v3.1.5b (3.1.5b) everyshi.sty    2001/05/15 v3.00 EveryShipout Package (MS) pgfrcs.code.tex  pgfcore.sty    2020/01/08 v3.1.5b (3.1.5b)   pgfsys.sty    2020/01/08 v3.1.5b (3.1.5b) pgfsys.code.tex pgfsyssoftpath.code.tex    2020/01/08 v3.1.5b (3.1.5b) pgfsysprotocol.code.tex    2020/01/08 v3.1.5b (3.1.5b)   xcolor.sty    2016/05/11 v2.12 LaTeX color extensions (UK)    color.cfg    2016/01/02 v1.6 sample color configuration pgfcore.code.tex pgfcomp-version-0-65.sty    2020/01/08 v3.1.5b (3.1.5b) pgfcomp-version-1-18.sty    2020/01/08 v3.1.5b (3.1.5b)   pgffor.sty    2020/01/08 v3.1.5b (3.1.5b)  pgfkeys.sty pgfkeys.code.tex  pgfmath.sty     pgfmath.code.tex pgffor.code.tex tikz.code.tex l3backend-pdfmode.def    2020-02-03 L3 backend support: PDF mode supp-pdf.mkii epstopdf-base.sty    2020-01-24 v2.11 Base part for package epstopdf epstopdf-sys.cfg    2010/07/13 v1.3 Configuration of (r)epstopdf for TeX Live Resolving ambiguous overload on function pointer and std::function for a lambda using + How can see call history in iPhone one month back, i also tried with tried party software but that is not perfect , is the any solution from apple? moderncv: How to control the length of cvitems and cvlines? Post apocalyptic journey in search of knowledge from fallen society (ours) I'm racking my memory for a post-apocalyptic novel that I borrowed from a library maybe 15 years ago, but I'm sure it was published a few years before that though (maybe early 90s?).  I remember a party of people travelling across the flooded USA after some kind of apocalypse (climate change/flooding?). Towards the end of the book the group makes their way to New York(?) and finds a partially flooded library, discovering a set of books that gives hope for the return/rebuilding of society. Game about placing pennies on table This problem is from The Art and Craft of problem solving book:  Consider the following two player game. Each player takes turns placing a penny on the surface of a rectangular table. No penny can touch a penny which is already on the table. The table starts out with no pennies. The last player who makes a legal move wins. Does the first player have a winning strategy?  Now its not hard to see that the first player will always win if you place the coin in the center. But I have been thinking about what would happen If I also allow Quarter, Loonie and Twoonies. Does the first player have a strategy to always win? Could someone provide an explanation?