I have this mysterious problem with my rear hardtail wheel. Here's how it goes: I put in a brand new tube after getting a flat, works fine for a ride, next ride get a flat, change tube, get a flat next ride... and the constant theme here is that the tube rips right around the valve.  Now what happens is rather odd: I notice the like squishy part between the rim and the tube is shifted around the valve - so I have to force the valve in the rim hole. The tube works fine when out of the wheel, but when installed leaks.   Running stock wheels so I may just need to upgrade wheels, but the bike is pretty entry so.  Thanks in advance.
I'm fairly new to bicycling; apologies if this is a standard question but I couldn't figure out how to phrase it to search for it elsewhere.  I ride a KHS Urban-X with Kenda Kwest tires (just what it came with). I've gotten barely any use out of it since owning it, and it's been resting comfortably in the living room through the winter, so I decided today was a great day to get back on.   So I unscrewed the back tire cap, and began to hand-pump air into the tire. All seemed to go well, and the tire held pressure fine, but when I removed the tire pump, the pin appeared to remain pushed down slightly, and air flowed back out of the tire. I looked, and this is what I saw:    Several narrow gashes that appear as if the rubbed was ripped, cut, or separated somehow.  Questions   Is this a common occurrence? Again, I've ridden on this bike very little and thus filled up the tires even less. We have no animals and no bugs around that I know of that would gnaw or chew on such material. Is this fixable, or is my tube completely shot? It would seem to me that the latter is the case. Is there anything I can do to prevent this in the future? I use a hand pump but am gentle; would a stand-up pump be a better choice?  Do bike tires come with a standard warranty for cases like this, or do you know of any brands that do? If I have to purchase new tires, I'm going to purchase Is there any kind of "off-season" maintenance that I should be performing on my bike that could prevent things like this?   Thanks in advance for any help you can give!
Is it possible to nest a 'find -exec' within another 'find -exec'? Something like the following is what I what I'm after,  but my code doesn't work, no matter how I escape {} and + ;     find ./ -maxdepth 1 -type d -name '.*' -exec \     find {} -maxdepth 1 -type f -name '*.ini' -exec \         md5sum \{\} \\; \;   After seeing this ,  I found that the following code works, but it isn't nesting find as such, and I suspect there is a better way to do this particular job.       find ./ -maxdepth 1 -type d -name '.*' \ -exec bash -c 'for x; do     find "$x" -maxdepth 1 -type f -name "*.ini" \     -exec md5sum \{\} \;; \ done' _ {} \+   Is there some way to nest find -exec without the need to invoke  a shell (as above), with all its whacky quoteing and escape constraints?    Or can this be done directly in a single find command,  using a blend of its many parameters? Why AccessViolationException cannot be caught by .NET4.0 In the time-dependent Schrodinger equation, $ H\Psi = i\hbar\frac{\partial}{\partial t}\Psi,$  the Hamiltonian operator is given by  $$\displaystyle H = -\frac{\hbar^2}{2m}\nabla^2+V.$$  Why can't we consider $\displaystyle i\hbar\frac{\partial}{\partial t}$ as an operator for the Hamiltonian as well? My answer (which I am not sure about) is the following:   $\displaystyle H\Psi = i\hbar\frac{\partial}{\partial t}\Psi$ is not an equation for defining $H$. This situation is similar to $\displaystyle F=ma$. Newton's second law is not an equation for defining $F$; $F$ must be provided independently.   Is my reasoning (and the analogy) correct, or is the answer deeper than that? Developer Accounts for ExactTarget How can I tell if an ETF is expensive? For stocks, I can easily look at the price/earnings ratio, and, according to The Intelligent Investor, stand clear of those with a ratio higher than 20.  How can I tell if the current price of an ETF is a good price to buy it? Are there such simple metrics? How do I know if food left at room temperature is still safe to eat? By Cauchy's theorem, if a prime number $p$ divides the order of a group $G$, then there is an element $g$ in $G$ whose order is $p$. In addition, if $|G|$ admits a prime decomposition with a factor $p^k$, then Sylow's theorem tells us that a subgroup of order $p^k$ must exist.   My question is the following. If $|G|$ admits a prime decomposition with a factor $p^k$, does this imply that an element of order $p^k$ must exist in $G$?   Update: As explained in Mindlack's answer (among others), the implication does not hold and simple counterexamples exist. In the comments, Mindlack discusses special cases where such an element exists. Why is the potential energy equal to the negative integral of a force? Why is the potential energy equals to the negative integral of a force? I am really confused with this negative sign. For example, why there is a negative sign in the gravitational potential energy and what does it mean?   I read that the negative sign means you do the same force but in the opposite direction.  Doesn't that mean the object shouldn't move? Centos recently updated to 7.3 and there's been problems with sshd sftp group permissions. I have one user that is chrooted to it's home directory, and that user is in group sftponly. Then i have the /var/www directory, which has 775 permissions and owner is apache and owner group is sftponly. I have a bind link pointing from /home/user/files/web --> /var/www, so the user can access /var/www even though being chrooted to it's home directory. I can view files in /var/www with that user, but impossible to edit or add anything. This worked fine before the big Centos 7.3 update, and now it's stopped working. Any ideas? Let $(a_k)$ be a sequence of real numbers and let $b_k=\frac{a_1+a_2+\dots a_k}{k}$ for each $k\in \mathbb{N}$.  Prove that if $(a_k)$ converges to $\alpha\in \mathbb{R}$, then the sequence $(b_k)$ also converges to $\alpha$.  My answer: Let $\epsilon &gt; 0$. Since ($a_k$) converges to $\alpha$, then there exists a $N_{\epsilon1}\in\mathbb{N}$ such that $|a_k - \alpha | &lt; \frac{\epsilon}{2}$ for all $k \geq N_{\epsilon1}$. Notice that $\frac{a_1+...+a_n - n\alpha}{k}$ converges to $0$ as $k$ approaches infinity. Thus, there exists $N_{\epsilon2}\in\mathbb{N}$ such that $|\frac{a_1+...+a_n - n\alpha}{k}|&lt;\frac{\epsilon}{2}$ for all $k&gt;N_{\epsilon2}$. Now, let $N= $max$ (N_{\epsilon1},N_{\epsilon2})$. Then for any $k&gt;N$ we get,  $$\begin{array}{rcll} |b_k-\alpha| &amp;=&amp; |b_k - \alpha*1|&amp;\\ &amp;=&amp; |\frac{a_1+...+a_k}{k} - \frac{k\alpha}{k}|&amp;\\ &amp;=&amp; |\frac{a_1+...+a_n}{k} + \frac{[a(n+1)+...+a_k]}{k} - \frac{(k-n)\alpha}{k} - \frac{n\alpha}{k}|&amp; \text{(notice that $N_{\epsilon1}\leq N&lt;k$)}\\ &amp;=&amp; |\frac{a_1+...+a_n - n\alpha}{k} + \frac{[a(n+1)+...+a_k - (k-n)\alpha]}{k}|&amp;\\ &amp;=&amp; |\frac{a_1+...+a_n - n\alpha}{k} + \frac{[(a(n+1) -\alpha) + ... + (a_k - \alpha)]}{k}|&amp;\\ &amp;=&amp; |\frac{a_1+...+a_n - n\alpha}{k} + \frac{(a(n+1) -\alpha)}{k} + ... + \frac{(a_k - \alpha)}{k}|&amp;\\ &amp;\leq&amp; |\frac{a_1+...+a_n - n\alpha}{k}| + |\frac{(a(n+1) - \alpha)}{k}| + ... + |\frac{(a_k - \alpha)}{k}|&amp; \text{(by the triangle inequality)}\\ &amp;=&amp;|\frac{a_1+...+a_n - n\alpha}{k}| + \frac{|(n+1) - \alpha|}{k} + ... + \frac{|a_k - \alpha|}{k}&amp;\\ &amp;&lt;&amp; \frac{\epsilon}{2} + [\frac{\epsilon}{2}/k + ... + \frac{\epsilon}{2}/k]&amp; \\ &amp;=&amp; \frac{\epsilon}{2} + \frac{\epsilon}{2}*\frac{(k-n)}{k}&amp;\\ &amp;&lt;&amp; \frac{\epsilon}{2} + \frac{\epsilon}{2}&amp; \text{(since $k-n&lt;k$)}\\ &amp;=&amp; \epsilon&amp; \end{array}$$ And since we found such an $N$ for arbitrary $\alpha$, then $(b_k)$ converges to $\alpha$ by definition.  I'm not sure i kept all my variables straightened out. How does this look and if you have a better idea let me know! What do I need for extreme macro photography? I am wanting to venture into some extreme macro photography, specifically insects, such as . After doing some research I have believe that my 1::25 macro lens will be sufficient if I am to use some extension tubes (which I have bought).  I would like to shoot the in the wild, is this possible/likely? Or is this always a catch, then release style of shooting?  Regarding the link I've posted, would this be possible with a 1:25 macro and extension tubes? I have a set of three (21mm, 31mm and 13mm). How would you go about shoot a blue bottle for example? Surely they are going to fly away? Should I use a tripod or will that cause more of a hindrance than a help? Are there any techniques/tricks I could use to get a sharp focus on my subject? What is the distinction between "among" and "amongst"? Is there a way to disable file:/// protocol in google chrome?  Is there some option, or some switches that can disable this feature?  Please help I'm supposed to calculate: $$\lim_{n\to\infty} e^{-n} \sum_{k=0}^{n} \frac{n^k}{k!}$$ By using WolframAlpha, I might guess that the limit is $\frac{1}{2}$, which is a pretty interesting and nice result. I wonder in which ways we may approach it. How to prevent search engines from indexing a single page of my website? What is the name of an anime from 80s-90s movie/series in which there is a scene, maybe the end, where a girl (who has an​ armor) exchanges age with a dying man in a beach, so the man transforms into a baby and the girl grows to a woman? Let $P(z)=a_0+a_1z+\cdots+a_nz^n$ be a polynomial whose coefficients satisfy $$0&lt;a_0&lt;a_1&lt;\cdots&lt;a_n.$$  I want to show that the roots of $P$ live in unit disc. The obvious idea is to use Rouche's theorem, but that doesn't quite work here, at least with the choice $f(z)=a_nz^n, g(z)=$ (the rest).  Any ideas? I recently got a Windows 10 laptop. Opposite to my Macbook, I must swipe right-to-left to go to the right virtual desktop. Is there a way to reverse this, so I swipe left-to-right to go to the right virtual desktop? Suppose the default shell for my account is zsh but I opened the terminal and fired up bash and executed a script named prac002.sh, which shell interpreter would be used to execute the script, zsh or bash? Consider the following example:  papagolf@Sierra ~/My Files/My Programs/Learning/Shell % sudo cat /etc/passwd | grep papagolf [sudo] password for papagolf:  papagolf:x:1000:1001:Rex,,,:/home/papagolf:/usr/bin/zsh # papagolf's default shell is zsh  papagolf@Sierra ~/My Files/My Programs/Learning/Shell % bash # I fired up bash. (See that '%' prompt in zsh changes to '$' prompt, indicating bash.)  papagolf@Sierra:~/My Files/My Programs/Learning/Shell$ ./prac002.sh  Enter username : Rex Rex # Which interpreter did it just use?   **EDIT : ** Here's the content of the script  papagolf@Sierra ~/My Files/My Programs/Learning/Shell % cat ./prac002.sh  read -p "Enter username : " uname echo $uname The sum of powers of two and two's complement – is there a deeper meaning behind this?