Relational databases - to delete or not to delete?
Never delete entries? Good idea? Usual?
What are the strategies for getting feedback on articles? As an academic, one has to publish. Often, an article is drafted, and you need feedback of a colleague.  I see that quite often some perspective articles are often written by long-term collaborating pairs of authors.  What are some strategies people use to get feedback on their articles  (outside of immediate boss; and in the case that none of the friends in the field of work in the specific domain of the article, and one needs specific (not general) feedback)?   How do you approach a colleague to simply read your article. Or do you just mention it at a conference to the most suitable colleague - would you like to read an article and give me feedback? How do handle the co-authorship or acknowledgement? Do you establish the limits at the "approach time"?  What are some strategies to establish a "publishing" duos (buddies). Why do "df" and "du" commands show different disk usage? I cannot access ubuntu system on my pc, the error message: "the system is running in low graphics mode" and I tried some commands I searched from internet.   I found out a problems seems there is no available disk space. I used "df" and "du" commands to check, the results are as follow:  du -j --max-depth=1 23G  ./home 3.3G ./usr  ......  28G   and  df -Th  filesystem   Type   size    used   available   use%    mounted on  /dev/sda5    ext4   68G     68G    0           100%    /   how would I clean up the system for more disk space? For every $c\in [0;2]$ determine whether the sequence $\{a_n\}_{n\geq 1}$ which is defined as follows:  $a_1=c$, $a_{n+1}=1+\frac{(a_n-1)^2}{17}$ for $n\geq 1$  is monotonic for sufficiently large $n$, and determine whether its limit exits and if it exists, give its value.  I have no idea what to do with this problem. I was able to see that $a_{n+1}-a_n$ is a quadratic function and I also found ot that limit, if exists, is equal to either $1$ or $18$ (that's beacause if $a_n$ id convergent to $g$ then every subsequence is also convergent to $g$). So how to determine the limit for every $c\in [0;2]$? Is the function $f(x)=|x|^{1/2}$ Lipschitz continuous near $0$? If yes, find a constant for some interval containing $0$.   I think the answer is yes since I can find $L=1$ that satisfies Lipschitz continuity criteria in a interval close to $0$, am I right? Prove inequality $n<3^n$ using mathematical induction Prove that $n&lt;3^n$ where $n \in \mathbb N$,  when $ n=1 $, I have proved it's true. And assumed when $n = p$ , $p&lt;3^p$ is true. Can any body help me in showing that it is true for $n =p+1$ Open maps which are not continuous Let's say that I have a folder, within my Documents folder, that has files I want no one to access without a password.  Is there a way to lock down that folder so that it's password protected / encrypted?  In fact, is it possible to password-protect any individual folder? Prevent execution of parent event handler How to compare the differences between two PDF files on Windows? Can Hydrogen Fusion via CNO Cycle Occur in First Generation Stars CNO cycle requires the presence of carbon, nitrogen and oxygen to undergo hydrogen fusion. Does this mean that for first generation stars, no matter how big they are, can't undergo hydrogen fusion by CNO cycle because there is no carbon, nitrogen and oxygen present?   I can't seem to find any website which mentions this. All they say is if a star is large enough, it will undergo hydrogen fusion via CNO cycle, they don't specifically mention it having to be a second generation star. I have a .txt file with numbers ordered like this (on the same row):  106849_01373    106849_01967    106850_00082    23025.7_01059      I would like to convert them like that:  106849_01373 106849_01967 106850_00082 23025.7_01059   I have no idea which command to use. Can somebody help me with this? Can anyone please help and tell me if this sentence is correct?  &quot;A significant amount of zombies were detected in your city.&quot;  In my opinion it should be &quot;A significant amount of zombies was detected in your city.&quot; because &quot;amount&quot; should be in agreement with &quot;was&quot; even though amount usually refers to something plural. Are both (was and were) acceptable in this case? Edit1: Yes, &quot;number&quot; would be the correct one in this case. So allow me to ask one more thing.  &quot;A significant amount of purchases were detected...&quot;  Does the use of &quot;number&quot; apply in this case also? As purchase is not exactly a thing/person. And if no, is it correct to say &quot;A significant amount of purchases were detected...&quot;? Edit2: So, please tell me what is the correct phrasing?  &quot;A significant amount of purchases were detected...&quot; &quot;A significant amount of purchases was detected...&quot;  Or, since purchases are countable, is the use of &quot;number&quot; instead of &quot;amount&quot; correct here, as in:  &quot;A significant number of purchases were detected...&quot; &quot;A significant number of purchases was detected...&quot;  Or would amount be correct since a purchase involves money and it refers to the amount of money? Would greatly appreciate an answer, and if possible a detailed explanation. Can I kill an indestructible creature with -X/-X and sufficient damage marked on it? Can I hit a 4/4 indestructible creature with a  (3 damage) and give it -1/-1 with  to kill it? (Does it matter which way around I cast those?)  I read  here and it says, damage is removed in cleanup step, so it should be on the creature still after both spells.     702.12. Indestructible   702.12a Indestructible is a static ability.   702.12b A permanent with indestructible can’t be destroyed. Such permanents aren’t destroyed by lethal damage, and they ignore the state-based action that checks for lethal damage (see rule 704.5g).   702.12c Multiple instances of indestructible on the same permanent are redundant. I'm reading Nano: The Essentials by T. Pradeep and I came upon this statement in the section explaining the basics of scanning electron microscopy.     However, the equation breaks down when the electron velocity approaches the speed of light as mass increases. At such velocities, one needs to do relativistic correction to the mass so that it becomes[...]   We all know about the famous theory of relativity, but I couldn't quite grasp the "why" of its concepts yet. This might shed new light on what I already know about time slowing down for me if I move faster.  Why does the (relativistic) mass of an object increase when its speed approaches that of light? Sass Interpolation of Mixin, Function, and Variable names Compile error with \href ToC and \apacite I would like to edit my document but I have a compile error somewhere between the \href and the apacite but can't locate it. I've tried blocking out code and taking out references, with varying results.  \documentclass[a4paper,12pt]{article} \usepackage[english]{babel} \usepackage[utf8]{inputenc}  % TOC, Citations, Refereneces, and Appendicies \usepackage{apacite} % \cite{ref1,ref2} %Warning - unsupported tocstyle code \usepackage[tocindentauto]{tocstyle}     \renewcommand{\thesection}{\Roman{section}}      \renewcommand{\thesubsection}{\arabic{subsection}.}     \renewcommand{\thesubsubsection}{\roman{subsubsection}.} %\usepackage{hyperref} %\urlstyle{same} %\hypersetup{ %   colorlinks=true, %   urlcolor=cyan, %   linkcolor=blue, %   citecolor=green, %   filecolor=magenta, %   pdftitle={Sharelatex Example}, %   pdfpagemode=FullScreen, %} \usepackage[toc,page]{appendix}  \begin{document}    ...to be installed \cite{church13,hershkowits97}. \bibliographystyle{apacite} \bibliography{bibliography} \end{document}   Here are the bibliography.bib entries then  @ARTICLE{church13,    author       = {K.H. Church and H. Tsang and R. Rodrigiguez and P. Defembaugh and R. Rumpf},    year         = 2013,    title        = {Printed circuit structures, the evolution of printed circuit boards},    journal      = {Circuit Insight},    volume       = {},    number       = {},    pages        = {},    howpublished = {},     url          = {http://www.808multimedia.com/winnt/kernel.htm}, }  @ARTICLE{hershkowits97,    author       = {N. Hershkowits and R.A. Breun},    year         = {1997},    title        = {Diagnostics for plasma processing (etch plasmas) (invited)},    journal      = {Review of Scientific Instrumentation},    volume       = {68},    number       = {1},    pages        = {880--885},    howpublished = {}, } Find $n$ such that $n/2$ is a square, $n/3$ is a cube, and $n/5$ a fifth power Counting number of subsets which contain a specific element There is a set $x = \{A,B,C,D,E,F,G\}$ and the question ask for counting the number of subsets which contain $D$. And the answer is $2^6$. why would it be $2^6$? I know the total number of subsets is $2^{|x|}$ is it realated? What package should I use to typeset units? I know there are a few packages related to typesetting units:   unitsdef units, which can be seen as a "base package" used by unitsdef SIunits siunitx, which is the successor to SIunits maybe others? like cjwunits and hepunits   What is the difference between them? Do they also work inside Math mode? And, more importantly, which one should I use?  Suggestion for people trying to answer this question: show some examples of how to typeset both simple and complex units. For instance, try typesetting these items:   100 Celsius 3 x 10^5 km/s gravitational constant is measured in N m^2/kg^2 10 kHz = 1 s^{-4} sin(x) meters   I think these examples cover most needs when writing scientific texts: simple measurements (value + simple unit), values written in scientific notation, simple fractional units, complex fractional and squared units, units without any value accompanying them, units with arbitrary exponents, and arbitrary math code instead of a simple value. I have to prove by induction that $$\sum_{r=0}^{n}\begin{pmatrix}n \\ r \end{pmatrix}=2^k$$, using the identity $\begin{pmatrix}n \\ r-1 \end{pmatrix}+\begin{pmatrix}n \\ r \end{pmatrix}=\begin{pmatrix}n+1 \\ r \end{pmatrix}$. I'm fine with everything except the inductive step, where I only managed to get as far as $$\sum_{r=0}^{k+1}\begin{pmatrix}n \\ r \end{pmatrix}= \sum_{r=0}^{k}\begin{pmatrix}n \\ r \end{pmatrix}+\begin{pmatrix}n \\ k+1 \end{pmatrix}$$ I tried to then use the identity and substitute $\begin{pmatrix}n \\ r \end{pmatrix}=\begin{pmatrix}n+1 \\ r \end{pmatrix}-\begin{pmatrix}n \\ r-1 \end{pmatrix}$ but all this did was just take me around in a circle. I also couldn't substitute $2^k$ for $\sum_{r=0}^{k}\begin{pmatrix}n \\ r \end{pmatrix}$ since this didn't properly simplify to give $2^{k+1}$. However, I think that I have to obtain the expression $\sum_{r=0}^{k}\begin{pmatrix}n \\ r \end{pmatrix}$ since it simplifies to $2^{k+1}$. But I've not been able to obtain this in anyway so I'm wondering if anyone can guide in what I need to or what direction I need to take to complete the inductive step.