By "sponge" I mean anything used to suck up liquids from surfaces, such as kitchen towels etc. I assume capillary action is a factor, and also maybe surface area and surface energy. What are the factors involved and what makes a good sponge?  In other words, how can one predict the best materials for creating a sponge?
If I take a sponge and place it in a shallow dish of water (i.e. water level is lower than height of sponge), it absorbs water until the sponge is wet, including a portion of the sponge above the water level. In other words, it seems the sponge pulls some water from the bath up into itself, doing work, and the water gains some gravitational potential energy.  Where does the energy required to do this work come from? My suspicion is that the answer involves physical and/or chemical bonds between the water and the sponge, or possibly the change in the surface area to volume ratio of the water.
How to best respond to a request to send a passport scan by unsecured email? It is not uncommon for travel or holiday accommodation companies to ask for a scan of your passport by email. Sometimes local laws require them to keep a record of the passport numbers of all visitors. I'm happy to provide that information but you usually have to send it in an unsecured email, which may have consequences .  Could these companies be more responsible, and provide a public cryptographic key at least?  Are there other steps you should take to protect yourself, if you do send by unsecured email? Incompatibility between TikZ and babel How to truncate all logfiles? can anybody give me a solution to truncate all logfile in /var/log/ directory?  and a question just for knowledge, is it a good idea or not?  #!/bin/bash LOGDIR="/var/log" for logfile in $(ls $LOGDIR/*log) do   truncate -s 0 $logfile done Terminal prompt overwrites current line What are the different endings in Dishonored? I'm trying to have a surface with soft body hold obects that are falling on it with rigid body physics, but for some reason, no what matter what mass I give it, the objects just fall trough the softbody enabled surface.  Is there a toggle or a value I need to change to make them stay there? Moving all files to a new computer, my concern is links I'm moving all files to a new computer, via an external hard drive. I am certain that broken links will be a concern. What can I do to fix this? Is there a 'Best Practices' kind of way to prevent this problem beforehand? I have many hundreds of .blend files, and of course, I fear losing them. Letter O with vertical line: operator null Validationengine jquery not working properly for localization How can I execute a file without giving myself execute permissions (with chmod u+x) for it?   If I try and tick the 'Allow executing file as program' checkmark, the checkmark is immediately removed. What are all the font styles I can use in math mode? As can be seen in above picture, there are lots of fonts or font styles that can be used in math mode.  What are all the fonts or font styles I can use in math mode, and which packages are required in order to use them?  Let's assume I'm using standard Computer Modern or Latin Modern (lmodern) fonts.  Edit: It'd be great to see examples of what the different styles look like, probably via images.    I'm not interested in a reproduction of the picture, which can be found at ; the picture is for illustration purposes only. Furthermore, this is supposed to become a one-catches-all question for questions like the beforementioned. If I actually were looking for these fonts, I wouldn't just lazily ask here but look e.g. at  , tables 3.14 and 6.4 first.) Let's assume that one has some modern HP printer and/or scanner which is not supported by HPLIP package from official repository. Currently Ubuntu versions have :  trusty (14.04LTS): 3.14.3-0ubuntu3.4 xenial (16.04LTS): 3.16.3+repack0-1 bionic (18.04LTS): 3.17.10+repack0-5 focal (20.04LTS): 3.20.3+dfsg0-2 groovy (20.10): 3.20.5+dfsg0-3build1 hirsute (21.04): 3.21.2+dfsg1-2   What can one do if printer is supported in newer version of HPLIP (checked this in )? What is the relation between computational security and provable security? I read the book "Introduction modern cryptography". It gives the notion of computational security of private-key encryption at first which comes from perfect security and statistical security.     Let $(E,D)$ be an encryption scheme that uses $n$-bits keys to encrypt $l(n)$-length messages. $(E,D)$ is computationally secure if    $$E_{U_{n}}(x_{0}) \approx E_{U_{n}}(x_1)$$   And then it introduces the secure game (e.g. CPA, CCA)? I think it is a part of provable security.  "Unconditional security" (or "information-theoretic security" or "perfectly secrecy") and "computational security" are two opposite classes of security. But I do not think "computational security" and "provable security" are two independent classes of security. I know that computational security emphasizes the power of attacker is bounded (polynomial-time algorithm). And the provable emphasizes the mathematical assumptions or cryptography primitives. But it also related to the computational power. For US federal tax, whether a taxpayer is subject to AMT is determined by a complicated way in Instructions for Form 1040, Line 45, which involves an incomprehensible "worksheet to see if you should fill in form 6251".  By simplification and approximation, is there a rule of thumb for an estimate of a salary value of a taxpayer, so that a salary above the value might cause the taxpayer to pay AMT with a big possibility, and a salary below the value might not with a big possibility?  Why do the following two sources seem to differ greatly in estimates of the boundary salary value:    says that  the possible boundary salary value for a single taxpayer  to pay AMT is $53,900.  says that      Taxpayers with small incomes fall within the AMT exemption limits.   That leaves the upper middle class to face the tax, especially those   with incomes between $200,000 and $500,000    Thanks. The full question: suppose N is normal in G and $[G:N]=p$ is a prime. Prove that for any $K \leq G$, either (1) $K \leq N$ or (2)$KN=G$ and $[K:K \cap N]=p$.  Since $N,K \leq G$, it is of course possible that $K \leq N$ could happen.  but for (2), we can show $KN \subseteq G$  but how can we show $KN=G$?  And what information does "$[G:N]=p$" give us? Should an apostrophe be used with a z at the end of a word? I know that if a word ends with an s then it should be made plural or possessive by use of an apostrophe with no extra s (e.g. "Thomas Harris' book was a riveting read." as opposed to "Gary Barlow's voice is so distracting.")  What about if the word ends with a z. For example, would it be Gomez' album or Gomez's album? I have a manuscript that is under review in a major journal which is a main result out of a few recent years of my research. When applying for faculty positions, I would like to send the draft as a part of my writing sample. But since the material is not yet published, I am not sure if it is a good idea.  What are the foreseeable disadvantages of sending an article in review to the faculty search committee?  My area is neuroscience / biomedical engineering.  Update: The paper got into a high-profile journal, and I got a job at a different place which did not require a writing sample. Prove that the difference between two rational numbers is rational This is a terribly simple question I'm sure, but I can't find a work-around in my proof. I must prove that the difference between two rational numbers is thus rational. Here is my attempt:     Let $a$ and $b$ be rational numbers. Therefore, \begin{align}  a=\frac{\lambda}{\beta},\:b=\frac{\xi}{\zeta},\:\ni\:\lambda,\beta,\xi,\zeta\in\mathbb{Z},\tag{1} \end{align} which gives us \begin{align}  a-b=\frac{\lambda}{\beta}-\frac{\xi}{\zeta}=\frac{\lambda\zeta-\xi\beta}{\beta\xi}.\tag{2} \end{align}   So I have shown that $a$ and $b$ are rational numbers which, by definition, can be represented by the quotient of two integers. But now how do I tackle the problem of the difference? By definition the difference between two integers is an integer. Does that require that this difference is thus rational?  Thank you for your time, Labels disappear while zooming I have a fairly modern desktop computer, an AMD Athlon II X2 based silent PC, that does not work.  When turned on, it will start physically (all fans are rotating, disks start up...) but not give a signal on any of the graphics ports (DVI, VGA, and HDMI, I tried all three). Also, the reset button does not seem to have any effect.  I have stripped the mainboard bare of all SATA connections, extension cards, and the one 2GB RAM chip to eliminate them as the problem source, but to no avail, so I think it's fair to assume it's either the mainboard or the processor that are at fault.  However, I have neither a replacement mainboard, nor a replacement processor handy to identify which one is broken. The cause of the defect is unknown, so for all I know, it could be both. Therefore, I'm reluctant to buy replacement hardware blindly before knowing more.   Is there any way to further diagnose (or at least get some indication) which component is broken without buying replacement hardware?