Removing all unapproved comments from database dump file

Question: I got thousends of spam comments on my drupal 7 site. The mysql database file is grown to 1.9GB and the site is broken. How can i delete all comments (or even better: all unapproved comments) from the database dump file?
Comment: Drupal is a framework for building websites, it doesn't have tools for manipulating raw sql dumps. You'll probably want to write a script to identify what you consider to be spam, and remove it. This would be easier before the database is dumped, or after its restored, rather than trying to manipulate a text file - you might be able to find modules to help in those cases
Comment: I think you missunderstood me: due to an "accident", in order to restore the site, i've got only the file structure and a database dump. Since i could not import the dump back again because of its size, i would like to truncate the comments BEFORE importing; but i dont know what to delete (so it's sql question but with an drupal background).
Comment: I understand what you asked :) The only Drupal-related part would be the layout of the table (comments are in the `comment` table, you can use the `status` column to determine whether they're approved or not). Drupal can't help you with actually making the change, since it has no tools for manipulating mysql dumps. Neither does MySQL, to manipulate the data with SQL it needs to be in a database. There may be tools out there to help (I don't know of any), or the other option is a complex regular expression. To the best of my knowledge there's nothing Drupal can do to help you with this
Answer: From your dump file,  I would cut the part that insert the data to the comment table. Note: Leave the part that create the table.
In another file paste the part that you cut from the original dump file, using a text editor that can handle to search using regular expressions (as Sublime Text 2).
Create the regular expression that would give you as a result the complete row insert if that row has the status column value set to one.
Once that the regular expression is working, now use the search an replace.
Search all the matches and replace them with ''
When the search and replace is done, you can copy and paste to the sql tab if you are using phpMyAdmin, or even save the resulting file as .sql and import it.
Pretty much the laborious part would be to find the regular expression to use.
Hope this help!


Substituting ground red pepper for dried red peppers

Question: I have a recipe that calls for 4 dry red peppers to be bagged during cooking & taken out when finished. Instead of using those, how much ground red pepper should I use?
Comment: Anyway "red pepper" is hardly well-specified – those come in quite a spectrum of different spiciness grades, regardless of whole vs ground.
Comment: What are you cooking? What are the peppers supposed to be bagged in?
Comment: This will be different in flavour too....
Answer: I'm not sure if this works for cooking, but I use this method for oil or vinegar infusions: Get empty tea bags at the local tea or kitchen supply outlet. If the peppers are cayennes, put 1/2 teaspoon of ground cayenne per pepper into the bag(s), tie off securely, and use in your dish. Fish the bag(s) out at the appropriate time. Yes, grinding a pepper produces more than 1/2 teaspoon of ground pepper, but ground pepper has much more surface area than whole peppers, so you need to scale your ground pepper back to account for that. If the peppers are hotter than cayennes (habaneros, ghosts or reapers), cut back the powdered amount more. If they are mild, such as bell peppers or sweet pimentos, use 3/4 to 1 tsp of powder per pepper.
Comment: An interesting idea.  Does any of the powder escape the bag?  I could see using a tea infuser ball for crushed pepper (which wouldn't work for powders), but I've never tried the bags.  I know I see bits of tea in my cup when using tea bags.
Comment: You need to use finely textured, high-quality tea bags. (To be honest, I didn't realize they made a type that allows tea to escape into the liquid.) Also, to prevent the top from coming open during cooking, use a thin but durable, slightly rough twine, such as the type used to bind poultry for roasting, so the knot cannot slip.
Comment: I was talking about pre-bagged teas, which can contain rather fine bits of tea.  (the few times I've used loose tea, it was in a tea ball ... which has even larger holes).


What was the death toll of non-Americans in the Vietnam War?

Question: How many Vietnamese and Cambodians were killed in the Vietnam war? How many civilians, and how many soldiers? What are the best sources on this question?
Comment: I'm guessing you also don't want to count French, who were fighting there long before the Americans were. Do you want to count SE asian deaths from the French period in the conflict?
Comment: I'm mostly interested in the American stage of the conflict...but would be interested in all good data on this...
Comment: documents like these: http://www.soc.washington.edu/users/brines/vietcasualties.pdf
Comment: @T.E.D. and fraxture ... and the hundreds of Autralians killed?
Answer: 882,000 Vietnamese casualties, of whom about 444,000 were soldiers, and 200,000–300,000 Cambodian casualties, according to Wikipedia.
And, in addition, it is estimated that as many as 210,000 soldiers and civilians, from an assortment of other nations, primarily Laos, were also killed.
Comment: And, in addition ...
Comment: any more authoritative source than Wikipedia?


Can my choice of co-authors affect how often my article is cited?

Question: I am a post-graduate student in dentistry; planning to publish an article either in an Indian journal or an international one. How does having co-authors like our seniors or our professors affect number of citations for my published article?
Comment: Welcome to Academia SE. I edited your question to be more focussed on one question that has not been asked here yet. Please see whether everything is still according to your intentions. As for other implicit questions, I suggest that you browse the [tag:authorship] tag and in particular take a look at [this](http://academia.stackexchange.com/q/12030/7734) and [this](http://academia.stackexchange.com/q/19362/7734) question.
Comment: Everything else equal; more authors usually means more (self)citations, and more authors coming from different backgrounds and separate networks will mean more citations, since they will continue publishing independently afterwards. Citations (even if they are selfcitations) usually also leads to further citations, since each citation gives the paper exposure. This is naturally not a recipe for how authorship should be granted, but merely a couple of observations.
Answer: First of all, let me make it clear that I'm addressing your question with the hope that you tacitly mean co-authors who made significant enough contributions to deserve authorship, and not talking about gifting co-authorship to people who haven't. Ethically, the latter is wrong, even when the person in question is the PhD supervisor, and hasn't contributed enough to deserve authorship. Thus, what I'm referring to below is the issue of publishing with or without co-authors who deserve to be co-authors.
In an ideal world, what should matter is only whether the content of article is scientifically sound, and not the brand value of the authors. What is wrong does not become right when stated by a bigshot. But in parallel, there is a question of credibility, and that is generally higher for people who are known to have done some good work in the past, as opposed to a newbie. But even with that, it is not that people do not read the works of newbies, just that in the real world, people are less likely to be as critical of a bigshot, as they would be of a newbie. That's just to say that we do not live in an ideal world. However, if the science in the newbie's work is accurate, it will fetch respect too. That's how eventually everyone grows in stature.
However, we should distinguish between exposure and citations. Even with my arguments above, being on the same wagon as a bigshot may ensure more exposure (i.e. more people look at it, even though it may not go any further than that), citations are not really entailed by a greater exposure, but are more reflective of the utility of the article. Thus, a useful work is going to get cited irrespective of who is on the author list, and exposure only increases the odds of the same.
Comment: _the issue of publishing with or without co-authors who deserve to be co-authors_ — And this in turn means _the issue of doing research with or without others who might make a significant enough contribution to deserve co-authorship_.


Are there any cryptocurrencies with no mining beyond participation?

Question: I mean something where just participation in the decentralized network gives you coins somehow and you cannot do anything beyond (excluding more participation, of course, by having multiple PCs and IPs, for example) to increase the rate of achieving those coins. At the moment I have completely no motivation to leave my bitcoin or litecoin client on, because it doesn't gives me anything back for using me as a node in this network of hardcore miners. I'd rather find some ways to use it occasionally only when I need to do some transactions (few times a month, for example). I'm newbie in this topic, but doesn't this harm the network, when lot of people become using it this way?
Comment: Are you referring to Proof-of-Stake schemes such as used with [Peercoin](http://www.peercoin.net/)?
Comment: @GregHewgill, thanks, I didn't know about PoS schemes. That's interesting, but it would be even better to not have benefit of holding large amount of coins. Something like Proof-of-Work where "work" is being connected to network and doing some transactions, calculations and verifications, but not having possibility to invest more computing power to get more profit.
Comment: @Gracchus Mining signatures? Pardon my ignorance, what is that? Can you provide links to white-papers or the like?
Answer: On Bitcoin and Red Balloons suggests a method to incentivize network nodes, however no cryptocurrency implements it.
Answer: Cuckoo Cycle is close. It is a memory-hard proof of work system - substituting random memory access for CPU power.
Answer: The up and coming Safecoin will reward users for donating their bandwith and harddrive space, so they'd be "mining" by just leaving their computers on and connected, being compensated in safecoins.
To a lesser extent, the way forging in NXT works you also need to leave your computer turned on and connected the whole time so as to be taken into account for the raffle of who generates the next coin, though that doesn't ensure you'll receive any NXTcoins: since it's a 100% Proof-of-Stake coin the more coins you have the higher your probabilities of forging the next block.


Are there any iPad accessories that vibrate, for silent alarms?

Question: Are there any iPad accessories that vibrate, to permit the same kind of silent notification iPhones can?
Answer: Unfortunately not.
The OS would have to have support for said accessories, and anyway, there are no accessories for vibration.
You can submit feedback to Apple on the iPad here, but they won't respond and it might take them some time to implement the feature (if they ever do).


Carbon 14 disintegration

Question: When $\beta^-$ disintegration happens to a Carbon 14 atom, a neutron "turns into" a proton, and an electron is emitted. Therefore the result of the disintegration is a Nitrogen atom plus an electron (also an electron antineutrino, but that's not relevant here).
My question is : is the nitrogen atom ionized ? Since it has $7$ protons, it needs $7$ electrons to be electrically neutral, but it only has the $6$ ones that the Carbon atom had, so it should have a supplement positive charge, shouldn't it ? Or does the emitted electron stay with the nitrogen atom so that it's neutral ?
Answer: The ionisation energy of a nitrogen atom is about 14.5eV but in $^{14}$C beta decay the electron is emitted with an energy of 156keV, which is far higher than the ionisation energy. So beta decay will normally produce an N$^+$ ion and a free electron.
Comment: Even if the original carbon atom was rather positive (e.g. CCl4, chloroform) the excess energy is still enough to escape not just the atom but the whole molecule.
Comment: Thanks ! The book I have is a high school book and isn't very precise ; feel free to suggest me some further reading.

Carbon 14 disintegration


Is there a halacha for writing a biography of a gadol? If so, what is it?

Question: I was thinking of writing a magazine article on a rabbi I knew well before his death some years back.  I wrote to his son to see if he could help me with stories, history, photographs, etc.  He declined, worried that he might speak loshon hara about the members of the community, and he wanted me to make sure that I was familiar with the "halachos" regarding writing a biography of a gadol.  To be frank, I had no idea that there were specific halachos on this subject.  Could someone explain to me what he is talking about?  Is it something beyond shimiras haloshon?
Comment: An [article of interest](http://en.wikipedia.org/wiki/Making_of_a_Godol).
Comment: The halacha is called shmiras hanefesh. People don't want to hear that gedolim are or ever were people. And they will torture you if you imply such a thing. My Zeida would tell us funny stories about future roshei yeshiva while they were still young in Shanghai. These stories aren't going to make anyone more religious if they hear them, and the people who tell the stories will get ostracized so what's the point?
Comment: @user6591 I agree. I also use to hear stuff about the freedige' yoren that were fun and amusing. But they don't help anyone grow.  Just practically it's not useful. But unfortunately because we don't have true right mindset to properly place these stories in their proper context and take them too far, ala some known "Jewish historians" who are just glorified batlanim who ramble on for 2 hours. Instead for our own good they are censured. Stuff repeated in the yeshiva coffee room aren't ראוי to be printed. Wish the Kotzkers advice was followed more.
Answer: There is no official set of laws called "hilchos biography", perhaps he was using the word "Hilchos" colloquially to say "do you know the way to go about writing a biography" ie. How to phrase certain things, what to leave out, what names to change etc.
However, there are Laws of Slander and Gossip, as well as embarrassment. And those halachos should guide the author in his attempt to draw a sketch of the person being written about.
In the desire to show the greatness of the personality being written about, too often the prohibition of Lashon Harah is glossed over.
Furthermore, a biographer must know the audience he is writing to, some things which in different cultural milieus would have been understood and taken for granted, might be grossly misunderstood in our day and age, and therefore embarrassing to the family of the deceased.
Thus, I would assume the son meant the concerns mentioned above when he said you must know the "halachos" of writing a biography.
Comment: what makes you assume that there aren't Halachos of Lashon Hara, and possibly Chilul Hashem, that this person may have been referring to? There is a way we need to speak about our Gedolim. No, I'm not advocating writing Artscroll typ biographies, though surely not everything should be published.
Comment: "What to leave out" like boring things?
Comment: I don't know, depends on the author and family of the one being written about
Comment: Congregations can be fickel, especially back in the 1950s and 1960s where many rabbis had congregations with few, if any members who were observant.  Rabbis were treated as mere employees.  It is hard to write about the bravery of those rabbis without denigrating the congregation to some extent.  Rabbi Emanuel Feldman, in his Tales Out of Shul, was quite blunt about his congregants when he first came to Atlanta.  Could a biographer be so blunt?
Comment: @Nafkamina I will only say that he died a sudden and violent death and that he is buried in Bet Shemesh.  Also, there is a very long eulogy written on his matzevah by his son, referring to the Rav as a martyr, among other things.
Comment: Can anyone help me understand why I received a down vote? I would like to make my answer better
Comment: @Nafkamina I suspect that the sons might themselves write a biography of Rabbi Anemer, z'tl.
Comment: @Zvi see my most recent edit


Can't uninstall emacs on Debian

Question: I want to purge emacs from debian in order to install the newer version from git but when I do apt-get purge emacs and then emacsit still runs. Any idea on how to get rid of emacs ?
Answer: The Debian package emacs is a metapackage. These are empty packages that only describe dependencies. As such, they don't actually contain any programs, just links to other packages to install. Further, removing a metapackage does not result in its dependencies being removed.
This feature allows package managers to use transitional metapackages to more-or-less gracefully move users from using one package to another with a different name.
So, removing the emacs package didn't actually remove any programs. That's why you needed to remove the rest of the emacs packages (apt-get purge emacs*) to get rid of emacs on your system.
Regarding the --purge flag to apt-get:

When a Debian package is removed, the configuration files are retained in order to facilitate possible re-installation. Likewise, the data generated by a daemon (such as the content of an LDAP server directory, or the content of a database for an SQL server) are usually retained.
To remove all data associated with a package, it is necessary to "purge" the package with the command, dpkg -P package, apt-get remove --purge package or aptitude purge package.

Thus, purge only removes system-installed config files (such as you might find in /etc/ or /var/), not user-generated config (usually somewhere in /home/<user>/. It would be a very bad thing if the package manager erased user-generated files!
Answer: apt-get purge emacs* did the trick even tho it didn't really purge the config files (̀.emacs.d still present...)
Comment: Purge deletes all the system-installed config. It shouldn't ever touch .emacs.d, that's where user config goes

Can't uninstall emacs on Debian


Find $I:=\lim\limits_{R\to \infty}\int\limits_{-R}^R \frac{x \sin(3x)}{x ^2+4}dx$ using residues

Question: Find $I:=\lim\limits_{R\to \infty}\int\limits_{-R}^R \frac{x \sin(3x)}{x ^2+4}dx$ using residues. Let $f(z)= \frac{z \sin(3z)}{z ^2+4}$. First define two contours:
$$\Gamma_1: z=t \text{ where } -R\leq t \leq R$$
$$\Gamma_2: z=Re^{i\theta} \text{ where } 0\leq \theta \leq \pi$$
And $\Gamma_3=\Gamma_1+\Gamma_2$. Basically $\Gamma_3$ is the closed half circle in the upper half of the complex plane and $\Gamma_1$ runs along the real axis from $-R$ to $R$. Now we have:
$$I=\lim\limits_{R\to \infty}\int\limits_{\Gamma_1}f(z)dz=\lim\limits_{R\to \infty}\oint_{\Gamma_3}f(z)dz-\lim\limits_{R\to \infty}\int_{\Gamma_2}f(z)dz$$
We can compute $\lim\limits_{R\to \infty}\oint_{\Gamma_3}f(z)dz=\lim\limits_{R\to \infty}\oint_{\Gamma_3}\frac{z\sin(3z)}{(z+2i)(z-2i)}dz$ fairly easily after recognizing that it has simple poles at $z_0=\pm 2i$ and only $z_0=2i$ is enclosed in $\Gamma_3$. By the residue theorem:
$$\lim\limits_{R\to \infty}\oint_{\Gamma_3}f(z)dz=2\pi i \left(\mathop{Res} _{z=2i}(f)\right)=2\pi i \lim\limits_{z\to 2i}(z-2i)f(z)=2\pi i \frac{2  i\sin(6 i)}{2 i +2i}=\pi i \sin(6i)$$
Now the only obstacle to finding the value of our original integral is finding $\lim\limits_{R\to \infty}\int_{\Gamma_2}f(z)dz$. If $f(z)$ were such that the degree of the polynomial in the denominator was at least 2 higher then the polynomial in the numerator (ignoring the $\sin$) we could easily show that the integral vanishes. I still think this last integral should vanish but find it hard to show why. Any help would be appreciated. Also any suggestions on different methods of solving for $I$ are welcome. Thanks!
Comment: You can simplify $\pi \sin(6i)$ further and get the real expression $\frac{\pi}{2}(e^{-6}-e^{6}) = -\pi \sinh(-6)$.
Answer: You can't ignore sin, but you can deal with it virtuously. It blows up exponentially both in the upper and in the lower half-plane, but you can split it into its $\mathrm e^{\mathrm ix}$ and $\mathrm e^{-\mathrm ix}$ components and complete the contour in the upper half-plane for the former and the lower half-plane for the latter. This gives you exponential damping, so you no longer need another power of $x$ in the denominator. If you did, you could get it by integrating by parts.
Comment: Thanks for your answer! When i said ignoring the sin I meant I was just looking at the degree of the polynomials.Since i am integrating over a contour in the complex plane, does this mean that in the formula $\int u'v dz= uv]_{a}^{b} -\int u v'dz$ my $a$ and $b$ would just be the staring and end points of the contour? in this case $\pm \infty$ informally speaking. I think I can figure it out this way!
Comment: Sometimes it is necessary to use this method rather than the simplification I used. For example, I think
$$
\int_{-\infty}^\infty\frac{\sin(x)}{x(x^2+1)}\,\mathrm{d}x
$$
encounters difficulty unless we use two contours.
Comment: @TeunVerstraaten: if the problem involved integration by parts, that would be valid.
Answer: Hint:
$\sin(z)$ does not vanish along $\Gamma_2$. In fact, it blows up exponentially in $\mathrm{Im}(z)$. The way to get around this is to note that your integral is the imaginary part of
$$
\int_{-\infty}^\infty\frac{x\,e^{i3x}}{x^2+4}\,\mathrm{d}x
$$
Now $e^{i3x}$ does decay exponentially in $\mathrm{Im}(z)$.
Answer: A not unrelated method of attack is to write the integral as
$$\frac{1}{2 i} \int_{-R}^R dx \frac{x}{x^2+4} \left (e^{i 3 x} - e^{-i 3 x} \right ) $$
Now work each piece separately.   For the $e^{i 3 x}$ piece, you use a contour in the upper half plane; for the $e^{-I 3 x}$ piece, use a contour in the lower half plane.
Comment: Thanks, this should work out perfectly. I think this is also what was meant in the previous answer by joriki.
Comment: Oh my, @joriki said pretty much what I said.  My apologies for repeating him.  I should also mention that this is a perfect application of Jordan's Lemma.  The choice of which contour to use is hardly an arbitrary choice.


Can I mine with XMRig and the Monero GUI at the same time?

Question: I am a beginner and doing CPU mining on my laptop. My question is, can I mine with XMRig and the Monero GUI at the same time?
Answer: Yes, you can mine with both at the same time, but you won't get any benefit.
XMRig is a dedicated, optimized miner, so as long as it's been configured correctly, it will give you the best hashrate for your system.
If you mine using both XMRig and the GUI on the same system at the same time, at best you'll get the same hashrate as just using XMRig, but more likely, your overall hashrate will be worse.
Comment: MANY THANKS FOR YOUR SUPPORTIVE AND INCLUSIVE REPLY. 1. CURRENTLY XMRIG IS MINING AT +/- 500 H/S. 2. CAN YOU PLEASE HELP ME CONFIGURE IT FOR MORE SPEED? 3. IS THERE ANY OPTION TO FURTHER EDIT THE CONFIG. FILE?
THANKS A LOT
Comment: https://xmrig.com/wizard


What is the correct order of chemical reactivity in terms of oxidising property for the following elements: F, Cl, O, and N

Question: This is a textbook question. I am confused as to which factors i should consider while sorting out these elements. If I take electron gain enthalpy, then Cl should be greater than F, but if i consider electronegativity F is greater than Cl . I'd be grateful to anyone who provides  some idea..
Comment: Fluoride ion has very high hydrtation enthalpy and low F-F bond enthalpy.These are the two main reasons for fluorine being a better oxidising agent than chlorine (actually the best).
Answer: See, F is the strongest oxidising agent in the entire periodic table. Also, according to periodic table trends, oxidising character decreases down the group and increases across a period. You should check the reactivity of any element according to the question given, here, according to the oxidising character. If nothing is given, usually IE and Electronegativity is considered.
Therefore, I think the order should be F>O>Cl>N. Cl>N because Cl is more oxidising than N.
I must add that a simple Google search would have yielded the same result.


google services has stopped wont stop long enough for me to fix the problem cant even get into my settings

Question: google services keeps looping gives me no time to fix due to it just keeps forcing me back to same looping message cant even get into my settings for long enough to repair because it just throws me back to the same looping error screen
Answer: This happened to me also and here is how I got past it. I also used this to recover my friends phone.
The high frequency of the app failures makes it very hard to access the settings menu and make your selections. Even so, tap the failure messages to get them to close. In between tap or try pulling the settings menu down from the top of the screen. After several tries it seemed there was very slight pause in the failure cascade. I used that slight pause to make my settings menu selections. Either way, after pulling down the settings menu I selected Back up / Reset. You have to keep closing the failure messages and try flicking the menu down to the option you want but it is possible if you are quick and persistent. I just factory reset mine, but I've read suggestions to clear the caches of several apps central to the phone's operation. Tomorrow I have another to do and I'll try clearing caches then return to update on how that worked.  Best of luck.


How to include periods of non-academic work on an academic CV?

Question: I have, since completing my PhD (in pure mathematics), worked in both non-academic and post-doc positions. I am brushing up my CV, and I would like some advice as to how one should detail non-academic work. My non-academic work has been quantitative, but otherwise entirely unrelated to my field of academic expertise, so my gained skills (in eg statistical packages) are of no use to the purely research position I am aiming to apply for.
Answer: Simply list in the section about employment who you worked for. The places you apply for may ignore this if they so choose, but at least you can document that you were working during this time and were not, as one could be tempted to speculate, in jail, unemployed, or homeless.
But then, it may also be that the people who look at your application think that it is quite beneficial to the program to hire someone who has seen other parts of the world, whether or not you learned specific tasks and skills there that are useful for your postdoc work.
Answer: I have two categories for work expiereince in my CV. The first, I call 'academic' and I list my academic employments there. The second, I call non-academic. It contains any work I currently am doing or have done without any academic background.
This makes it easier for anyone to skip the parts that is of no interest for them. However be sure to list your tasks and experiences for both categories and the respective jobs. Mixing both kinds of employment makes your CV intransparent (in my opinion).


Why is it that the Pauli matrices and error correction operator act only on $|\psi\rangle\langle \psi|$ and not on state vector $|\psi\rangle$ itself?

Question: I saw that the Pauli matrices really work, that's rotating a state by 180 degrees, only if you take the density matrix for example with X it only works if first we take X $|\psi\rangle$  and multiply it by itself dagger. Then you can see it rotating around the X-axis. Same with Y and Z.
Also, in error correction, you use the R mapping only after you created a density matrix, but you don't use it on the vector state itself. Why is it?
Answer: Describing the Pauli-$X$ matrix as a rotation by $\pi$ about a particular axis is specifically referring to how you would visualise the action of the gate with regards to the Bloch Sphere picture. This most naturally maps to the density matrix, which is why it's most apparent there. But you can apply it to the pure state picture as well. Note that you can parametrise any single-qubit pure state as
$$
|\psi\rangle=\cos\frac{\theta}{2}|0\rangle+\sin\frac{\theta}{2}e^{i\phi}|1\rangle.
$$
This has a Bloch vector of the form
$$
\vec{n}=(\sin\theta\cos\phi,\sin\theta\sin\phi,\cos\theta).
$$
Now, let's consider $X|\psi\rangle=e^{i\phi}\left(\cos\frac{\theta}{2}e^{-i\phi}|1\rangle+\sin\frac{\theta}{2}|0\rangle\right)=e^{i\phi}\left(\sin\left(\frac{\pi}{2}-\frac{\theta}{2}\right)e^{-i\phi}|1\rangle+\cos\left(\frac{\pi}{2}-\frac{\theta}{2}\right)|0\rangle\right)$. By the same mapping, this has a Bloch vector
$$
\vec{n}'=(\sin(\pi-\theta)\cos\phi,-\sin(\pi-\theta)\sin\phi,\cos(\pi-\theta))=(\sin\theta\cos\phi,-\sin\theta\sin\phi,-\cos(\theta)).
$$
This is exactly a $\pi$ rotation (or reflection) about the x axis.
In error correction, it's a completely different reason for using the density matrix - you're trying to deal with possible errors, and that means you need an ensemble of states (one for each possible error), not just a pure state.
Answer: Most error correction schemes suppose that the transmitted vector state becomes mixed on the receiver end. For example, the transmitted state $|00\rangle$ can turn to $|11\rangle$ with probability $p^2$, to $|10\rangle$ with prob $p(1-p)$, to $|01\rangle$ with prob $(1-p)p$ and to $|00\rangle$ with prob $(1-p)^2$. So, the state in the end is a mixed state which can't be associated to a single vector state.
You still can work with probability distributions of vector states instead of density matrices (and apply whatever rotations you like just on vectors), but generally this is not that fruitful. Density matrices capture the essence of the physical state.
Comment: Of course. If $|\phi\rangle$ is a vector state and $U$ is some rotation then the result is $U|\phi\rangle$. But in terms of density matrices the result is $(U|\phi\rangle) \cdot (U|\phi\rangle)^\dagger = U |\phi\rangle \langle\phi| U^\dagger$.
Comment: Thanks.  Strange thing is that I tried to work out the Pauli rotations. I found that they really rotate by 180 only when applied to the density matrix of a Bloch sphere vector from both sides
Comment: Yeah I know. It's just that I couldn't see that x|ϕ⟩ is doing the rotation. Only on density matrix


What are the things one should consider when invited to contribute a book chapter?

Question: What are the things one should consider, as a postdoc, before accepting or rejecting an invitation to contribute a book chapter? The proposed book is a handbook in a developing field of engineering.
Comment: I think the (all important) value of a book chapter in your CV can vary widely across different areas and different universities.
Comment: I can give you my experience here http://forthescience.org/blog/2008/04/26/so-you-want-to-write-a-book
Answer: It almost certainly won't earn you any money.
It probably won't be read by many people. It will be cited by even fewer.
The collaboration may lead to future projects together.
It may involve a lot of work.
You might enjoy the process. Or hate it.
It may or may not help your career progression, depending on your field, your career to date, and the posts you apply to. If it's a book that will become a standard for one or more taught courses, your contribution may be crucial for your future teaching career.
In this particular case, when the putative author is a rising young authority in an engineering field, it's a rapidly-developing field that's attracting significant international interest, and many universities are introducing new courses in the area, then, (depending on the publisher, the other authors, and the other chapters) there's potential for the book to have quite a significant audience, so contributing to the book chapter would be attractive.
Comment: Why "It probably won't be read by many people."? If any, I thought books had a higher visibility than articles.
Answer: When I get an invitation to contribute a book chapter (or conference paper in an invited session), I usually ask myself the following questions:

Can I have a reasonable contribution ready for the proposed submission deadline?
Is the venue I am invited to a good fit and does it provide the best possible visibility for my contribution?
Do I want to invite the person inviting me to similar occasions in the future?

Ideally, you should be able to answer at least questions 1 and 2 with "yes" before accepting the invitation. If your answer to question 2 would be "no", it may still be wise to accept the invitation in view of question 3. For this type of invitations, I would try to find a smaller contribution which fits the visibility of the proposed publication venue. In a book chapter, for example a summarizing synthesis of some of your previous results might be appropriate.
Answer: I would like to add the following:

If there are other, more experienced, persons in the specific field, who would likely do a better job than himself, perhaps it is best for him, for the sake of all the potential readers of the book, to decline the invitation and recommend these other people instead.
An invitation is something that is unexpected, and meeting it would likely require an extra effort in addition to his normal responsibilities. Unless he is able to manage his resources well without encroaching what belongs to his family, for example, then perhaps it would be prudent, despite all the prospects it might offer, to decline the invitation.


About the phrase '' pay off ''

Question:
My belief paid off well.

About the phrase, should I add the word "was" before "paid off"?
Answer: Short answer: "paid off" if you meant your belief lead to a positive result. "was paid off" if you meant that your belief/faith/trust in something was justified/repaid, but you might want "was paid back" in that case, to be more idiomatic.
Long answer: "pay off" is an idiom. There are two similar usages:
bets "pay off" when the winner gets paid for winning the bet.
loans "are paid off" when the lender finishes paying the principal and interest due on the loan.
The former has passed into an idiom beyond betting to mean any action taken that had a good result (in a context where you could have had a negative or zero result) or had a zero result (when no positive result was possible, only negatives and zero).
Thus, you get "The long hours of study paid off when she passed the test". "My guess paid off." "My belief paid off."
So if your belief lead to a positive result then your "belief paid off".
If, on the other hand, you meant you were "repaid" for your belief, as in you gave them your belief, and they paid you back by fulfilling your trust in them, you would use "was paid off" but almost always follow with "by x" or preceded with an example of how it was paid back/paid off.
Example: "I trusted Jane, and she never let me down. My belief (in her) was paid off." "I trusted Jane, and my trust was paid back with many years of loyalty."
Answer: Pay off with no object means "to bring profit" - it can be followed by for X to say who benefited, otherwise the assumption is the subject.

Going to school paid off. (Going to school brought me profit)
Going to school paid off for Marvin.  (Going to school brought profit for Marvin)

Pay off X means "to pay enough to settle debt or debtor X"

I just paid off my school loans (I don't owe the bank anymore money).

It can also mean "to bribe" and in this case the adverb well will work:

I paid off the guard pretty well.  We can just walk in.

X is/was paid off is an idiom that means "Debt/debtor X received all his/her/its money"

My school loans are paid off. (The bank received all its money)

Paid off can also mean "bribed" as well.
So ...

My belief paid off well.

If your belief profited you, then you want to keep this sentence as is.
If your belief is something you would need to bribe, then my belief was paid off well might make sense.  It is unlikely you mean this unless you are being literary.
Answer: What you are doing is trying to is use the passive voice.
In this case, "pay off" figuratively means "To become worthwhile; to produce a net benefit." (Wiktionary). In this sense, "pay off" is intransitive. Intransitive verbs cannot take objects in English.
In addition, intransitive verbs cannot utilize the passive voice in English, except for some prepositional constructions.

The rats were eaten by the cats.

In this case "eat" is used transitively, so it can take a passive.
Here is a plain awful sentence:

That speech was listened by John.

but

She wasn't listened to.

is okay.
Comment: I don't think this is correct.  The question has nothing to do with passive voice, and everything to do with separate and distinct meanings for "pay off" vs "was paid off/will pay off" as the other responses indicate.  It's an issue of idioms.

About the phrase '' pay off ''


Fashion photography mini studio

Question: If I wanted to start a mini studio for fashion photography, what equipment will I be needing as basics?
Comment: Voting to close. Equipment recommendations are off topic, this is an overly broad and opinion based question (I could say beauty dish, someone else could say big softbox (technical term). Neither answers are wrong. But provide entirely different results) and not enough information, e.g. size, is it a home studio or commercial. If commercial will it be rented?
Comment: *Specific* equipment recommendations (i.e. Brand C vs. Brand N) are off topic. General recommendations as to what *type* of equipment might be needed for a particular type of photo are not off topic. E.g. "What qualities should one look for in a lens for astrophotography" is on topic. "What is the best lens for astrophotography" or "What lens should I buy" is not.
Comment: Equipment is a personal choice and varies from person to person. We can't suggest cameras or lenses here. But if you have any doubts about specific equipment compatibility, we can answer that.
Comment: As asked, though, the question is awfully broad.
Answer: You would need at the very basic level:
A working camera including a lens.
A source of light.
Enough space to allow your camera to focus on your subjects.
A subject to shoot.
All else is optional.

Fashion photography mini studio


Personal checks containing entire account number

Question: I noticed that when I login to my bank account online I have to type my password twice in order to see my full checking account number. Then I was writing a check and noticed the entire account number is at the bottom for anyone to see. That seemed like a security issue to me. Am I being too paranoid or would it be wise to avoid using personal checks because of the account number being visible to anyone? Also, is it possible to request personal checks with the account number partially hidden?
Comment: See this answer on another question: https://money.stackexchange.com/a/15223/149
Answer:
That seemed like a security issue to me.

Technically, you are correct: having your bank routing number and account number on checks is a security risk.

Am I being too paranoid

Not paranoid, but (young and) inexperienced.  People and companies write billions and billions and billions of checks every year.
And how much check fraud is there?   A lot less than there is of debit and credit card fraud, that's for sure.

would it be wise to avoid using personal checks because of the account number being visible to anyone?

That's my absolute least concern when writing checks.

Also, is it possible to request personal checks with the account number partially hidden?

No.  Check readers at banks need to see the whole thing.
Comment: And what check fraud there is seems to be mostly people writing checks on their own account without having money to cover them.
Answer:
is it possible to request personal checks with the account number partially hidden?

No. The whole point of the account number is so that the banks that process the check can identify the account, so they know what account to take the money from. If there is not a complete account number on your check, how could they do that? If there isn't enough information for a fraudster to identify your account, then there isn't enough information for a legitimate user to identify your account either.
Is this a security issue? Sure. But it's a relatively minor one. Normally no one will see your check except the person you gave it to and the banks that process it. The person you gave it to could copy the number and then print counterfeit checks or enter it into a computer and make fraudulent ACH charges. That's pretty much the same problem you have with credit cards: Someone you give it to to could copy the account number and then make fraudulent charges. This happens, of course, but it's relatively rare.
Okay, technically, they don't HAVE to print your account number on your checks. One could imagine a system where each check is assigned a unique number that can only be used once, and those numbers are not sequential or otherwise easily predictable so you can't figure out what the next number is from seeing any one number. Or I'm sure some clever person could come up with some better scheme to make knowing someone's account number useless. But it would be a pain, and the fact that no one has done it is probably evidence that the amount of fraud isn't worth the trouble. It's cheaper for the bank to just eat the loss now and then than to come up with some complex scheme to prevent it.
Comment: The clever solutions could probably be implemented now, but could they have been implemented in 1969, with the computers they had then?  (Remember the oft-cited factoid about a smart phone having more computing power than all of NASA had that year?)  How about 1945?  The system we have has been around a long time, it works pretty well, and most people understand it.  So why fix it?
Comment: @jamesqf Yes. Unless and until this sort of counterfeiting -- getting someone's account number of a check and printing fake checks or using that account number on line -- becomes a serious problem, there's no incentive to change the system.


API or websocket

Question: I am trying to develop an crypto traking site like coinmarketcap, for market data I am using exchanges API.I would like to know whether i should use api or websocket? any suggestion would be appreciated.
Answer: REST API, you would have to poll for data periodically and make changes for every poll you do.
Websockets allow you to essentially listen for changes and make changes on your end accordingly based on whatever changed, almost instantly.
They both have their advantages and disadvantages.
REST polling allows you to cache data in a much easier fashion, which will be a big deal once your dataset get's large the more you collect. The downside is that it's more intensive to process the data each time you poll.
Websockets allows you to process data much faster since you only receive data that changes. The downside is dealing with a constant open connection opens up potential security issues and caching data is a bit annoying.

API or websocket


How to find perpendicular line given a line?

Question: I have two points that form 1 line. I want to find a point that creates a perpendicular line.
Here is an image showing what I am looking for:

How do I find the red point to form a perpendicular line?
Comment: is this 2d or 3d?
Answer: when a given line with certain equation is give. it has slope of m. so the line that is perpendicular to it has slope of -1/m
check this link:
https://www.mathsisfun.com/algebra/line-parallel-perpendicular.html
you have one point and find out the wanted slope so you can build equation of new line
Answer: There is not a specific answer to this question as stated. (Assuming that this is in 3d space, as the coordinates list three values.) Technically, there are infinite perpendicular lines rotated around the black line.
If you have a third point, you can use the Cross Product to get a perpendicular vector, like:
i = B - A;
j = C - A;
p = (i.y * j.z - i.z * j.y, i.z * j.x - i.x * j.y, i.x * j.y - i.y * j.x);
N = A + p;

Where A, B, and C are the points, and i and j are vectors representing their relationship. The vector p will point in the direction perpendicular to the three points and N will be the point relative to the original, as in the picture.
Given that in your question the y coordinate is 0 for both points, it seems you may be interested in an answer in 2d space. In 2d space, there are two possible answers. Given two points A and B:
v = B - A;
p0 = (v.y, -v.x);
p1 = (-v.y, v.x);

You can find more info in this answer
For the coordinates you specified, this would work if you ignore the y coordinate and use z in its place.
Answer: There is one LINE that solves this problem if this is a 2D question (supported because the known points in the image have '0's for y-coordinates, so your line will be entirely in XZ-plane). However, as a line is a set of infinitely many points, any point that is on the solution line will be a solution point.
You need a line through (-1.75, 0, -2.32), perpendicular to a line through (-1.75, 0, -2.32) and (0,0,0).
Considering only X and Z coordinates, slope of known line is the difference in Z-coordinates divided by difference in X-coordinates:
m = (0-(-2.32))/(0-(-1.75)) = 232/175.
The perpendocular slope is
m_perp = -1/m = -175/232.
To get the slope of the line ne in the XZ-plane perpendicular to this one, through (-1.75, 0, -2.32), use the perpendicular slope and the XZ coordinates of that point in the point-slope equation:
Z-Z0 = m_perp(X-X0)
Z - (-2.32) = (-175/232)*(X - (-1.75)).
Solve for Z:
Z = -175X/232 - (175^2)/232 + 2.32
(I'm on a phone and don't want to break that down rn)
Now, ANY X coordinate you plug into this will return a valid Z coordinate, giving you a point (X,Z) on the line.
Comment: I followed your answer until you said this `Z-Z0 = m_perp(X-X0) Z - (-2.32) = (-175/232)*(X - (-1.75)).` Everything after that I can't seem to follow, can you explain it in more detail? What is Z0 and X0?


What is the best tool for Amazon Kindle book publishing?

Question: What is the best tool for Amazon Kindle book publishing?
Comment: You need to explain the type of book you want to publish -- do you want it to be either print or digital or both?
Answer: I'm going to give the easiest answer -- though learning it can be hard.
Adobe Indesign lets you produce both pdfs and epub files (to convert into kindles).
If you want to do everything in one tool, then Indesign is your solution. (They charge a monthly fee for renting the software which is quite reasonable). Then you can convert the epub file to kindle .mobi file by using the Kindle Previewer.
Another solution is to pay a formatter or a publishing company to produce the book. Surprisingly, it is not particularly expensive (you can probably pay about $250-$500 for the job -- possibly less; I should know because that's the work I do). If you're not comfortable with technical stuff, paying for that might be easier.
Some more ebook options are discussed in the "Amazon Kindle Publishing Guidelines" (Version 2015.4) (For some reason, the URL is always changing; you may have to hunt a while on amazon.com to find it).
Finally there are several tools that I have not mentioned. For example, you can use MS Word to print a pretty awesome printed book. I have done this before using the MS templates specifically for books. (After googling  "book MS Word template" I found a great template from one book designer for less than $50-- it looked great).
For producing epubs, you can use calibre or sigil or something similar.
The key thing is downloading the Kindle Previewer program from the Amazon site to convert from epub to .mobi
I'm making the production process sound a lot easier than it really is. For example, testing and quality control is quite complicated and time-consuming. But this is the basic information you need.
Answer: There are some very good, free EPUB editors like Calibre and Sigil (see bottom of page for files). Then you can upload that to Amazon. It has enough information to get converted to whatever format Amazon is using now. Better to have enough information in an EPUB than to fool with a Word DOC or DOCX which is frustrating for many people.
EPUB files support all kinds of meta information too, like multiple authors, multiple subjects (for library catalog classification).


What does Architecture of the project mean

Question: I'm working on website and java application for my project and I'm writing report and there is question that say "What is the architecture of the project" I don't know what should I write because I don't understand what does it mean
Comment: Ask the person who gave you the assignment. That word has never had an official or precise meaning.
Comment: Ask 10 developers and you get 11 descriptions of what "architecture" is.
Comment: I always liked Ralph Johnson's remark about architecture--it's the stuff that you wished you could have gotten right in the beginning and is too hard to change later.
Answer: If they were asking for the architecture of some code or files, they might be asking about what classes there are and how they interact.  However, in a project, we group classes into larger components, and these components interact.
Given that they're asking about the project, they're asking for the big picture of top level components and their interactions.  Modular construction means that we bundle various kinds of things together into larger more modular units.  Things within the same bundle enjoy a certain freedom of access to each others internals.  Things between bundles use some kind of abstracted messaging to communicate between them, and it is significant as to when/how those messages occur.  It is significant to architecture that which is persisted vs. what is computed and which component persists what (kind of) information; as are queries a component is capable of and commands it can perform.
If you are using a design methodology you might have some of these classifications already.  If not, you can describe them more ad-hoc.
On one level, you explain conceptual components, their individual capabilities, and how they interact with each other (what triggers interaction; what are the contents of interactions; how one component is responsible for management and persistence of certain objects whereas another component is responsible for some others) and as wired together, these components form a project or system.
For example, if there is networking (e.g. client-server, or server-server) these should be called out as interactions between identifiable components; this can form the basis of one of the larger views of components and their interactions.
Going deeper, we can also add detail to the pictures of persistence, component capabilities, and the inter-component wirings, and, we can explain the performance/scale out (e.g. load balancing, threading models, etc..), and maintenance/failover capabilities, all of which add a lot more complexity to the conceptual picture.
Going bigger/broader, the project exists in the context of a (business) domain.  The business domain is a view on the business entities and their interactions (customers, suppliers, regulators, and various other interested parties, such as advertisers, merchandisers, etc..).  The project architecture should satisfy the operational requirements of the intended subset of the business domain, meaning it should address those relevant roles and their responsibilities in the domain via the capabilities of the interacting (software) components.
Answer: It's, probably, asking you for to describe your strategy at the time of conceptualizing the project. An overview of your solution.
For example:
What kind of software are you proposing? Server-client? Desktop? Movile? And why?
What requirements are you meeting with your choice?
This will introduce your architecture at high level.
Once architecture is introduced it's time to go deep in details progressively. Do mention the design patterns involved (if any). And again... Why did you follow such patterns?
Which requirements do you expect to meet?
If your projects is formed by two or more applications, it's time to explain what does each of them. Their responsabilities inside the global solution. How they interact each other (protocols, e.g: Http, FTP, sftp, ssh, socket, websocket,...). If there's comunications it's time to mention what kind of comunication is going to happen (which do request and which do response). If there's any sort of messaging it's also time to mention data formats: XML, json, CSV,...
For any choice there's a why question to answer. The answer will explain which requirements are you trying to meet. It's advantages over discarded alternatives.
Finally you could go little bit further and to explain how do you expect to take forward the solution. For example mentioning technologies: programming languajes, frameworks, servers,... Each technology is going to be used for a good reason, so, explain it.
I don't think the question is asking you for low level details (classes, files, configurations). These are commonly demanded in technical designs.
Answer: If it's a high-level architecture summary, I would list the technology stack.

"ASP.NET MVC, SignalR, and SQL Server".

..

"Node.JS, RabbitMQ, MySQL"

..

"It's an enterprise bus based solution using Azure Service Bus and REST services that interact with a Cassandra database."

Generally, given an overview of the core technologies and patterns. Diagram it, perhaps.
If they want details, the other answers apply. I submit this answer because in my opinion the other answers are, in my opinion, suggesting too much detail for what the question seems to be asking. If I was a customer and I asked someone to build me a Widget, and I didn't know what they were going to build it with, I might ask, "Can you please tell me about the architecture?", to which I would expect a basic summary of the building blocks of what the Widget consists of and what high-level application patterns were used to correlate them.


What are the limits of a stage name?

Question: Can an actor use their stage name to open a checking account (and deposit checks made out to a stage name), or to get a driver's license, or to sign a notarized document, or to get a credit card?  Or do they always have to use their real name in cases like that?  If a stage name is acceptable in those cases, what prevents anyone from using one?
Comment: I've seen "dba" notations for assumed names in business contexts.  Google found me this, for the United States (what jurisdiction is your question?) https://www.sba.gov/starting-business/choose-register-your-business/register-your-business-name
Answer: In the U.S., you cannot get a driver's license in a stage name and cannot use it to notarize a document. (Germany permits certain kinds of "nicknames" such as a stage name or a name taken upon admission to the Roman Catholic clergy in addition to a birth name on certain forms of official identiciation and documentation, but makes it much harder to officially change your name entirely.)
In the case of a checking account or credit card, in the U.S., the bank needs your actual name as it needs to match your social security number which the bank also needs. But, the bank can put a different name on a check or on a credit card as a convenience user name, as a doing business as name if the dba is registered in accordance with state law, or as an entity account with the stage name treated as a unincorporated entity (much like a general partnership) with its own taxpayer ID number. As long as the name on the account can be tied to the name of a natural or legal person that has their own taxpayer ID, it can be done. But, otherwise, it would be a tax evasion tool and is prohibited.
Answer: The tenor of the question implies Witness Protection ID 44583292 is interested in the US. I am not aware of any law telling a US notary whether or not a document that gives the signer's stage name can be notarized. Obtaining an official ID in a stage name would be difficult, but notaries don't have to limit themselves to official IDs. Every state allows notaries to rely on identification by one or two credible witnesses. Every state except California allows notaries to notarize for a person who the notary knows personally.
Comment: This is not an answer to the question. Responses to a different answer should be made as comments to that answer.

What are the limits of a stage name?


Acidity of gut contents

Question: How does the pH of the contents of the gut vary from the stomach to the anus?  I know that chyme is very acidic, but after that?
Answer: Not sure if I answered this right:
leaflady.org

The system begins in the mouth, where the pH of saliva is 5.7 – 7.0.
  In the esophagus the pH is 7.0. The stomach pH is 1.5 – 3.0. In the
  Duodenum (upper part of the small intestine) pH is 4.0 – 5.0, and in
  the lower part of the small intestine (jejunum and ileum), pH 6.5 –
  7.5

The reason for it:
livestrong.com

In order to carry out their individual functions, each section of the
  digestive system maintains a pH that suits the needs of the
  environment. The first part of the system prepares the food for
  digestion. This section's weak acidic surroundings begin the process.
  The second area, the stomach, must supply enough acid to break the
  food into its nutrients. However, when the food continues into the
  intestines, it no longer needs acid. Both intestines bring the matter
  closer to the pH of the body

Basically these values stay consistent with some minor changes, unless a person is experiencing a acid-base imbalance. These are life threatening and can be extremes in acid or alkaline. The pH as you can see stays within the range it needs to be, in order to process food.
Comment: I made a minor edit (I hope that you don't mind, but you can always roll back to the original version if you do), because you wrote yourself that pH fluctuates in all parts of the GIT. A further reference that you might use: http://gut.bmj.com/content/30/5/573.abstract. The only part I slightly disagree with is the part about acid-base imbalance: the 'allowed' range of the pH in blood is far more narrow than that in the GIT, hence gut and stomach pH fluctuations will be higher than those in blood. For acidosis/alkalosis, the kidneys and lungs are the organs that compensate, not GIT. Overall +1
Comment: @Justin I'd have to research that. But I'm not sure about that. It might be..........
Comment: Good answer but I sure wish you could find a more definitive source for the PH numbers. Leaflady doesn't state where they got those numbers.
Comment: I would expect the product of an ileostomy (called what?) to be neutral-ish.  Why, then, is it so acidic that it attacks the skin?

Acidity of gut contents


Can you mine remotely

Question: Is it possible to set up a rig in a location where you will only be once a few months, antminer. In summer temp may reach high 80s during day otherwise cooler temps... I wasn't sure what would go down if there is a power outage or if it gets too hot...
Answer: It's certainly possible, there's nothing stopping you from doing so. You can easily manage mining hardware remotely with SSH. You can even leave the hardware unattended, but you might have some problems if there are issues that you have to actually start/stop the machines or deal with physical issues.
An option for remote management is colocation. With colocation, you let someone else manage your hardware and be physically on location with it. The hardware is anaged with other people's miners as well (hence the "co" part). Some colocation services will also allow you to remotely manage the hardware through SSH too and the people on location only deal with physical issues.
Comment: How can I find a collocation service? Thanks...
Comment: Use google. Many have websites or are announced on Bitcointalk or Reddit. Just search for "Bitcoin mining colocation".

Can you mine remotely


Beta distribution and beta binomial distribution

Question: What is the difference or relation between beta distribution, beta binomial distribution and binomial distribution?
Comment: There are a number of differences. What application are you looking at? In what context did this question arise? There are too many differences to feasibly list them all, and even then we would be guessing to answer you question. Can you provide us with more information?
Answer: To quote Wikipedia:

The beta-binomial distribution is the binomial distribution in which the probability of success at each trial is not fixed but random and follows the beta distribution.

You can read more about the beta distribution here, the binomial distribution here, and the beta binomial distribution here


Use English alphabet along with IPA

Question: IPA is not known by everyone, especially when the site is aimed for learners. It is expected that people here are likely to be ignorant about it (e.g. myself). Therefore, I suggest contributors here use less IPA in their questions/answers so that everybody can understand the posts. For example, I found this answer amazing and a pleasure to read. The answerer added IPA, but as a side note. I enjoyed reading the answer as I could understand it well. So I request people here to use the English alphabet more to clarify the pronunciations. However, IPA can be added as a side note.
Comment: What do you mean by "alphabets" here? I do not think that that word means what you think it means.
Comment: @mcalex You should have said *letters*; you've listed letters, not "alphabets".  An alphabet is an entire (usually ordered) set of letters used for writing a particular script, such as the Greek alphabet, the Latin (=Roman) alphabet, the Cyrillic alphabet, etc. Computer programmers may sometimes call letters "alphabetics", although just plain *letter* is almost always better. You'll also hear "alphanumerics" in computer contexts, which means letters or numbers, and almost always numbers restricted to decimal digits. English uses the Latin alphabet, although it has added its own letters.
Comment: @tchrist, "a","b","c",...... etc. If not alphabet what should have I said then?
Comment: @tchrist elL, alphabets shouldn't be plural, but there's nothing wrong with the word choice.
Comment: @mcalex I disagree: see his comment, and mine.
Comment: @tchrist I'm guessing your first comment to me is to Mist?  :)  To the discussion: all the letters (a, b, c ... etc) == the alphabet.  He's saying he wants the IPA alphabet (or all the IPA letters if you prefer) used less predominantly.
Answer: You cannot explain how something is pronounced using the normal letters used in English, because the mapping between spelling and pronunciation in English is extremely complex and even idiosyncratic.
That's why the standard International Phonetic Alphabet was invented: so there can be a standard way of indicating pronunciation.  You cannot do that using simple A–Z.
Comment: @Matt That doesn't work for most words, because not everyone says them the same.  Even here you got it wrong, since there is no schwa in the stressed syllable of *only*, as you allege to occur in the first syllable of *only*, It really does not work.
Comment: You *can* explain it with A-Z, it's just you cannot do so succinctly. For instance, "phonetics" can be described as "'ph'. which sounds like 'f' in fox, 'on' as in 'only', 'et' as in 'net', 'ics' as in 'bricks'". This is somewhat less succinct than /fəˈnɛtɪks/ though.
Comment: Further, there are some permissible phoneme sequences that cannot be unambiguously notated using an ad-hoc spelling system. Either we use the IPA, or some formal transcription system (Wikipedia has one, based on one of the dictionaries').
Comment: Each word would have many, many IPA transliterations.  How many English accents are there!?
Answer: I agree with @tchrist: IPA is a response to phonetic ambiguity. A scientific response.
But I agree with you, too: a language learner is less likely aware about IPA (than a linguist).
Please take a look at this discussion. Your question seems to be a subset of that one.
The answers from there suggest a dual approach:

Do not throw away terminology just for sake of simplicity.
Always expand the meaning so that an average ELL grasped it quickly and started using in their future study.

Personally, I would place IPA first, but that's negotiable.
Answer: I don't entirely disagree with other answers.  However, I can't read IPA without a dictionary/google in front of me (I certainly wouldn't try writing it - dictionary or otherwise), and I am a native speaker who has a fairly good understanding of the language. (Mental note: pleeease try not to forget to check spelling. :-)
In addition, regardless of the how the IPA says to pronounce a word, there are so many different accents in so many different English speaking countries that natives using one will disagree with different natives using another.  English is not a scientific language.  OTOH, grass rhymes with glass whether it's pronounced with a long or short 'a' sound, so using one to assist with pronouncing the other works whichever way you come at it.
Don't get me wrong, I think answers with added IPA information - as per the OP example - are excellent and deserve upvoting.  I've also come to the realisation that I'd better start learning IPA if I'm going to remain hanging around. :-) My concern is that answers won't be deemed as showing much effort if the IPA info isn't there - much as somebody referencing Wikipedia would (correctly) be called out for not including a link to the page.  I don't think people unaware of IPA should be downvoted for not including it in an answer.
Answer: Even among people who know IPA there is great variation in how they use it, and worse, many of them are ignorant of the variation and believe there is only one correct way to us it.
Of course this problem also exists for ad-hoc transliterations "spelling in phonetic English".
For instance how to indicate the first vowel in "ago", the vowel in "slur" or the vowel in "roof" and is it the same as the vowel in "book" or the sound in "boot"? In the end you either leave some people confused or have to come up with an actual system that everybody has to learn to use correctly.
Pragmatically I would say:

Sometimes we can render the sound of a word clear for all who know English without needing a system.
Sometimes if we are not careful in rendering the sound of a word "in normal English letters" it will represent different sounds to different people. To avoid this we would need to choose one system and stick to it.
It should never be "wrong" to include IPA alongside a "normal English letters" rendering of the sound of an English term. IPA has fewer ambgiuities so those who know it will be able to edit the "plain English letters" in keeping with it when the plain letters turn out to have an interpretation other than what the writer intended.
Comment: So do you indicate _IPA is not free of errors_ even though it is "a scientific response" as per an answer here. I think your point 3 indicates that.
Comment: "Errors" is not the best word to describe any shortcomings or weaknesses in the IPA, as for how people use it sometimes errors are made and sometimes there are more subtle problems mostly due to misunderstandings.
Answer: Unfortunately, there is no standard representation of English phonemes.
IPA is widely used among linguists; but it is not really satisfactory, since it represents pronunciations rather than phonemes. It implies that some phonetic realizations are preferred to others, and it draws distinctions which are not necessarily perceived by hearers. It is, moreover, ethnocentric; it employs the Roman alphabet in a manner which is (relatively) easy for speakers of most European languages to grasp, but is bewildering to those whose principal knowledge of that alphabet derives from the study of English.
Over on ELU, John Lawler has endorsed this scheme; but that is still dependent on non-Roman-alphabet characters.
I think the best course is that which OP and mcalex recommend: to describe pronunciation using ordinary English spellings, and annotate with broad-transcription IPA. That has its own pitfalls—how, for instance, does one regularly distinguish /æ/ in 'ordinary English spelling'?—but I really don't see a better way.
Comment: This is not true. IPA can be and is used for both phonetic and phonemic transcriptions. The custom is to wrap the former in square brackets `[thus]` and the latter in a pair of forward slashes `/thus/`.
Comment: @hippietrail Yes, IPA can be used for phonemic representation, but it is not designed for it. How, for instance, do you represent 'oh' - as /əʊ/ or /oʊ/ or /o/? What glyph do you use to represent 'R'? ... It is the same problem which you very cogently raised against Wiktionary's favouring one spelling over another.
Comment: Please provide some corroborating evidence for your claim that IPA is not designed for phonemic representation. The vast majority of English dictionaries published outside the US, including Oxford, have used the IPA for phonemic representation this way for decades.
Comment: It's a very common misunderstanding that there ought to be one single correct way to use IPA to represent phonemes of a single language. If you look in any dictionary which uses IPA you will find a pronunciation guide telling you which symbol is used for each sound, just as you will find in dictionaries using a pronunciation system not based on IPA. This is indeed a weakness in *using the IPA alone on this site*. Personally I prefer `/əʊ/` for "oh" in British and Australian pronunciation and `/oʊ/` for it in American. I avoid `/o/` for English. For "r" I prefer `/r/` in most cases.
Comment: @hippietrail  And syllable-terminant 'R'?! I think in fact we're in agreement. Two critical questions you have raised (*how to avoid favouring one pronunciation*, here, and the [*status of the phoneme*](http://linguistics.stackexchange.com/questions/212) on linguistics.SE) are united in the practical question What can we usefully tell learners who come from and are seeking to enter very different speech communities? Phonemic representation is essential; but Whose phonemes? and How shall we represent them?
Comment: Yes @StoneyB this is a big question! Like I said we will surely have to adopt a system and have a pronunciation guide, even if we have a "plain English system". But we might only need to use it for ambiguous cases and give leeway when there's no ambiguity since most people here will be beginners. For syllable-final "r" in American IPA there a couple of special "hooked" vowels, including schwa. I'm not sure what's done in other rhotic English varieties like Irish English. British and Australian English have a "joining r" that's only pronounced when followed by a vowel. For this I use (r).

Use English alphabet along with IPA


Liquid nitrogen blood?

Question: Would it be possible for an alien species to have liquid nitrogen for its blood? What would be required for that to work? What kind of environment would it need to exist in?
Comment: That would be quite a cool alien.
Comment: @CelestialDragonEmperor Titan isn't cold enough. You might be thinking of the similarly-named Triton, which has liquid nitrogen geysers.
Comment: @Logan R. Kearsly that's an oof, I got them mixed up for a bit.
Comment: All I know for a fact is that liquid nitrogen only happens in extreme cold. Titan is a good example.
Answer: Short answer is no. Longer version goes as follows...
Blood exists for a number of reasons in an organism, but the primary one is the distribution of oxygen to all the other cells in the body. Nitrogen isn't inert per se, but the fact that it exists in such large quantities in the Earth's atmosphere but doesn't react with the 22% or so O2 should tell you that it's not going to 'store' oxygen to carry it around the body.
The reason why our blood contains a lot of iron (hemoglobin) is because iron reacts very well with oxygen. You've no doubt seen how quickly iron left exposed rusts; well rust is actually just Iron Oxide, or iron that's reacted with oxygen. That reaction allows the blood in a normal body to capture oxygen and then release it where it's needed so that all the cells of our body can get oxygen for their normal chemical processes.
If on the other hand what you're really asking is can a being exist that captures an oxidiser in a form that allows it to be in a really cold environment, you might want to look at using fluorine as an oxidising agent; my understanding is that you can work at much lower temperatures using halogens to transport the fluorine in much the same way as hemoglobins transport the oxygen in life on earth.
But for the sake of argument
The temperature at which oxygen becomes liquid is only about 10 degrees higher than the temperature at which nitrogen becomes liquid. Which means there's another possibility...
If you have a VERY cold planet, AND instead of an 'atmosphere' you have a 'sea' of liquid N2 and O2 in similar proportions to that on Earth, AND you have some mechanism to replenish O2 once it is used by an organic creature, that creature may not need to have blood at all.
Imagine (if you will) a creature that looks somewhere between a fish and a piece of lace; it swims about in this sea, and instead of gills, it allows the sea itself to pass through all parts of its body, which then extracts the liquid O2 for the metabolic needs of all its cells. It might exist in the form of (say) a hollow tube with propulsion mechanisms inside. The idea is that the tube itself would have many hollow tunnels through it, maximising internal surface area and allowing the organism to breathe.
The precedent may be insect life on earth today, which doesn't have lungs but instead absorbs its O2 needs through its carapace via osmosis. This is sufficient for a very small creature and it's the primary limitation on insect growth; if they grow too large, their internal organs literally suffocate.
But, our lacy or tubular fish should have access to sufficient amounts of O2 that it can feed its own cells out of the sea.
This wouldn't be blood per se, but if the sea ran through many different arterial entry points and through the body before being expelled, it would function while inside those tunnels through the body in a manner similar to blood. It, like insects, would be limited in the size it could grow to but would at least experience liquid nitrogen running through it as an oxidising medium.
Comment: This seems like a non-sequitur. The liquid part of our blood is not what carries (most of) the oxygen content, so replacing water with liquid nitrogen in and of itself should be irrelevant. Even if a cryogenic alien lifeform still used oxygen in its metabolism, presumably it would have some sort of carrier molecule suspended in the blood, just like we do, so if you want to eliminate LN2 blood on the grounds that it couldn't carry oxygen, you would have to show that there are no molecules that can reversibly bind oxygen at that temperature.
Comment: @LoganR.Kearsley: While it's right that the water in our veins doesn't carry any oxygen (under normal pressure), the answer is still valid insofar as the temperatures at which nitrogen is liquid will inhibit (or slow down to the point of practically inhibiting) pretty much every chemical reaction, i.e. the creature's metabolism. Plus, nitrogen lacks the other important-for-life properties which water possesses, such as e.g. acid-base equilibrium or a high heat capacity. Organisms, no matter what they are based on, need kinda stable conditions. Water provides much of that "automatically".
Comment: Your answer relies entirely on the assumption that all life forms require oxygen to exist. But alternatives have [certainly been theorized](https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry), if rarely (never?) observed.
Comment: @Damon most of all, water is _polar_, which makes it more useful as a solvent for interesting compounds. Your argument about reaction speeds isn't valid: you could say much the same thing about many reactions that actually happen in organisms on Earth; coming from pure chemistry one would expect these reactions to run far to slowly to be any use. But life solves this problem with _enzymes_, which are amazing catalysts.
Comment: @TheArchitect you may want to re-read the 4th paragraph where I describe the possibility of other oxidising elements...
Answer: Liquid nitrogen could form the (majority of) blood of a creature
If the ambient temperature/pressure conditions are right for nitrogen to remain liquid, it would be a reasonable kind of blood substrate, the equivalent of water in human blood. The primary function of blood in a living organism is to transport dissolved molecules around the body, such as hormones and cells in humans.
Several papers have investigated the solubility of chemicals in liquid nitrogen, so it is fairly appropriate for this purpose.
However, the blood would not be pure liquid nitrogen, no more than human blood is pure water. The carried cells and hormones are what makes it blood, and the dissolved materials would be crucial for the liquid-nitrogen-based blood to be blood.
Answer: Blood serves to transfer heat.  Liquid nitrogen is good at this.
I have speculated about a super cold creature based on the phenomenon of superfluidity.  Superfluids are sort of animal like in that they crawl around, seeming to defy the laws that govern hotter things.  A boojum is a weird pattern that can form on superfluids, a superconducting current giving way to a geometric shape.

Pair of point defects, called "Boojums," in a thin, hybrid-aligned nematic film.
https://www.nsf.gov/news/mmg/mmg_disp.jsp?med_id=68656&from=mmg
It is spooky and otherworldly.  A creature based on these phenomena would be good stuff for concept-drives SF.
And the liquid nitrogen - it would be for heat transfer.  That is what we use liquid nitrogen for and it is also an important role of our blood - moving heat from hot places to places where it can be shed in sweat and breath.  So too your Boojum - its liquid nitrogen blood would move heat off to the radiant organs to be emitted, keeping its superconducting body chilly.
Comment: The image above actually depicts a nematic field of liquid crystal observed under polarized light microscopy: https://www.nsf.gov/news/mmg/mmg_disp.jsp?med_id=68656
Answer: First, define "blood". There are lots of terrestrial organisms which we might colloquial refer to as having "blood", but which technically speaking do not. E.g., arthropods have hemolymph, a fluid "equivalent to blood", but which is not actually blood. In insects, it doesn't even need to carry oxygen, because the animals tissues are directly oxygenated by tracheal tubes.
So, what functions do you want a solution based on LN2 solute to perform in order to be comfortable with calling it "blood"? That will determine whether or not having liquid nitrogen is possible!
One of the characteristics of blood is that is an extracellular fluid. I.e., LN2 need not necessarily perform as the primary biosolvent, analogous to water, in an organism in order to have other properties which would allow us to call it "blood". Perhaps, for example, you could have an organism that uses oxygen diflouride as its intracellular biosolvent (like the aliens from Robert Forward's Camelot 30K), despite existing in a larger LN2 environment. Such a creature might have cell membranes that are monolayered, to interface between the polar internal solvent and the non-polar external environment, or even non-existent, with cells being bounded solely by the interface between a bubble of OF2 and the surrounding N2 (although it would be difficult to develop multicellularity in that case, which would kind of preclude the development of "blood" entirely--so we'll assume that the creature does have proper cell membranes of some sort, at least!) Given the relative scarcity of fluorine, this might make a lot of sense for an organism that needs to manufacture its own internal biosolvent, and thus needs to use it as sparingly as possible, while taking advantage of some other more abundant fluid in its environment for other purposes.
Such a creature could "inhale" and "exhale" LN2 for heat regulation or propulsion, but it seems to me that one of the critical defining characteristics of "blood" should be that it is contained inside the organism, and separated from the environment. So, what could such a creature using internally-circulating LN2 for. so as not to waste its primary biosolvent? Well, there's heat regulation, and while LN2 isn't a fantastic solvent, it can dissolve some things, so it could transport simple hormones & metabolites (like dissolved methane or hydrogen)... and really, blood doesn't need to be a good solvent, even to do all the same stuff our blood does, because it can carry non-dissolved, suspended solid particles (e.g., blood cells). So, an LN2 circulatory system could serve as a critical means of transporting immune cells, metabolite transport vesicles, and all sorts of other suspended stuff around a cryogenic creature's body.
Lots of answers focus on the problems of transporting oxygen in LN2-based "blood", but I think that's a red herring. For one thing, the ability of our blood to transport O2 is not dependent on its solubility in water; we use specialized proteins in solid, suspended oxygen-transport cells for that purpose, and so could a cryogenic creature. Furthermore, I don't think oxygen, or even oxidizer, transport needs to be a criterion for calling something "blood", at least in a colloquial sense, anyway. Maybe the creature breathes hydrogen, instead, which may or may not be primarily transported by it's blood.
So, yeah, if we accept that it is plausible for life to exist at the relevant temperatures at all, I'd say liquid nitrogen blood is entirely possible.
And if we accept that much, it's not that much of a further stretch to accept LN2 actually acting as a primary biosolvent after all. LN2 isn't a fantastic solvent, largely because it's just so freakin' cold, but there's actually a surprising amount of stuff that does dissolve in it, including several classes of organic compounds and silanols. Silanols (the silicon-based equivalent of organic alcohols) are highly reactive at our temperatures, but would be far more stable and useful for building metabolic processes out of at LN2 temperatures. It may therefore not be exceptionally likely, but certainly plausible enough for the purposes of a hard science fiction story, for there to exist cryogenic life using a mixture of organic and silicon-based chemistry in an LN2 solvent--and thus naturally having LN2-based "blood" as well.
Answer: Nitrogen is liquid at very low temperatures for pressures around 100 kPa, and is not so reactive with other gases to be useful in the same way blood is.
You might object that also water alone is not a so good at carrying gases (no living creature uses pure water as blood), but blood is a water based solution, therefore there could be a liquid nitogen based solution suitable for carrying gases. True, but at those low temperatures solubility and reactivity of other substances into nitrogen is going to be very low, therefore you cannot simply rely on physical or chemical transport. And, again, at those temperatures also other oxyding gases (oxygen, fluorine, chlorine, etc.) are liquid, so it would be hard to have some breathing as we know it, without even mentioning the hardship of having life suited chemical reactions in those conditions.
Comment: @someone-or-other, I made clear that at those temperatures there are no other gases, but liquids.
Comment: It could just be very slow life. Makes sense, as everything is slow at that temperature.
Comment: Solubility of other gasses doesn't really seem relevant. Oxygen transport in human blood doesn't rely on solubility of other gasses, after all; it relies on oxygen being bound to solid particles suspended in the blood stream.
Comment: Also, if it did rely on solubility (which it doesn't for life on earth), it seems relevant to mention that the solubility of a gas inside a liquid actually improves at lower temperatures. That's why carbonated beverages go flat if you don't keep them cold.
Comment: @LoganR.Kearsley, fixed
Comment: @LoganR.Kearsley I was a scuba diver and solubility of gases on the blood is very important to calculate the [gas partition](https://en.wikipedia.org/wiki/Blood%E2%80%93gas_partition_coefficient)
Comment: @DanielDarabos, except we don't know any life based on solid state reaction... (as water is solid at those temperatures)
Comment: @jean Could you explain why that is relevant?
Comment: @jean I didn't make a comment about oxygen being a solid particle. That is indeed clearly ludicrous. But I made a comment about oxygen being *bound to* and *carried by* solid particles suspended in the blood (namely, red blood cells), which makes solubility largely irrelevant to transport. How quickly oxygen (or any gas) can be bound to and discharged from carrier cells would indeed depend on its solubility, but there are mechanical approaches to dealing with that.
Answer: This is pretty tricky and I miss few points in the answers provided by others.
First lets understand the purpose of blood itself. It exists mainly to transport oxygen and other substances needed for keeping the chemical processes in the organism. Oxygen is necessary for burning - to produce the energy. Other materials are used either as a fuel for burning (sugar), as a building particles of the body (proteins, to some level also fat) or to be used to control the chemical balance of the organism (pretty much everything else). Of course the role assignment is somewhat simplified.
As pointed out in other answers, blood also transports heat.
Now before we move on, one should argue what should we actually call life. In a traditional approach it is a form based on carbon, that uses oxygen to produce energy etc. But a more general approach is that it can be any form that is self sustainable, capable of reproduction, consuming whatever nutrition it needs and producing various kinds of metabolism products. Again it is a vast simplification and Wikipedia has a good article to start with this discussion.
The carbon based protein cannot serve their role in life in the temperature necessary to keep the nitrogen liquid. They need a water based solvent and water freezes below 0 Centigrade. Some organisms manage to keep their temperature higher than that but still it is nowhere close to the temperature where nitrogen is no longer a gas.
Now let's drop the carbon part of life as we know it on Earth and think of some very cold environment (already suggested by others in their answers and comments - like Triton). Your life form will have to be build of something totally different, like silicone, metals, maybe some naturally created alloys and other chemicals that are fluid in the range of temperatures where the nitrogen remains fluid. If those minerals can be solved in nitrogen then your creature could use it as main body solvent and consequently as a base for your blood.
I am no expert in this area but the basic Google search results show there are minerals for which liquid nitrogen can be a solvent.
So imagine a creature that in terms of its building particles resembles more our electronic devices, with silicone based "neural" cells for example and you might end up with a creature whose blood is mostly liquid nitrogen.
Note - I lack knowledge to imagine other necessary particles to make such life form, but you have a point to start.
Comment: yeah, sorry. I'm not a native English speaker. Fixed.
Comment: by coal do you mean carbon?
Answer: One thing to consider is that it would be quite difficult for life to evolve in temperatures around the temperature of liquid nitrogen.  Evolution and biology need chemical reactions, and those are rather few and far between at -196 C.
I am not saying it's impossible, but your aliens would be very special indeed ;)
Comment: Welcome to the site @jtwilson! Your answer is nice and concise, well done :) You might want to consider adding some links or citation(s) to go further into the details with extreme negative temperatures and chemical/biological reactions. Keep it up!
Answer: Unlikely; consider a nitrogen atmosphere with ammonia oceans/blood instead
First, large reservoirs of molecular nitrogen (N2) are rarely found in the universe.  Instead, nitrogen is more commonly found in ammonia (NH3).  We happen to have N2 in Earth's atmosphere because it was a byproduct of early life; it came from the NH3 in the primordial atmosphere.  We have yet to find another planet with naturally occurring N2.
Using N2 as a biological solvent thus creates a chicken-and-egg problem.  How does life which uses N2 arise from a planet which does not naturally have N2?
Second, the boiling point of N2 is -196°C = 77 K.  At those temperatures, chemical reactions will occur so slowly that life will arise and evolve at an incredibly slow rate.
Finally, at the temperature and pressure needed for liquid N2, there would be few materials left in a gaseous phase to comprise the atmosphere of your planet.  You need at least some atmosphere to create pressure to keep the N2 from boiling!  And don't expect N2 to stably co-exist as both a liquid and a gas -- the rotation of a planet is one of many causes that would shift the temperature and pressure off of a phase boundary!
Instead, consider ammonia (NH3) itself as the solvent for life.  Advantages include:

It is the most common form of nitrogen in the universe, and ubiquitous among known planets.
Liquid form between -78°C and -33°C.  This would be a planet much colder than Earth, but still common enough in the universe and warm enough to permit a decent rate of chemical reactions.
Like water, it is polar and dissolves nearly the same materials.  Alkali metals such as sodium and potassium easily ionize -- producing blue solutions and thus a blue planet --  as well as other electropositive metals such as calcium and magnesium.  Salts ionize easily in ammonia.  Many organic compounds undergo acidic or alkali reactions when dissolved in ammonia, forming polar compounds and thus becoming soluble.
Has its own acid-base chemistry.  Just as water dissociates into hydronium (H3O+) and hydroxyl (OH-) ions, ammonia dissociates into ammonium (NH4+) and amide (NH2-) ions, with a dissociation constant of about $K = 10^{-30}$.
Water dissolves easily in ammonia, as both are polar molecules, forming a solution that is more acidic than neutral ammonia.  Indeed, water could a poisonous waste product of life, just as ammonia is to our life!
Like water, dissolved substances diffuse readily.  This another important property that contributes to life, as living things often do not need to actively transport molecules to bring them together for chemical reactions.  Diffusion happens more rapidly in ammonia that water due to the lower viscosity.
Also like water, nonpolar molecules don't mix with ammonia.  Lipids (oils, fats, and waxes) form into membrane sheets, which can further wrap into 3-dimensional compartments (organelles and cells) with solutions of ammonia on the inside and outside.  The membrane keeps the inside substances inside, and the outside substances outside, preventing diffusion.  Because living things need structure, they need to keep things where they belong, and membranes provide this separation.
Ammonia is a good material to transport and dissipate heat.  It has a decent heat capacity and heat of vaporization.  Many organisms could circulate sap or blood made primarliy of ammonia, to help the organism avoid overheating.  Some organisms could also evaporate ammonia for "sweating".
As shown in the Miller-Urey experiment, it is part of an abiotic mixture of compounds that can form simple organic molecules like lipids, sugars, and amino acids.
Nitrogen gas N2 could evolve as the equivalent of our O2.  It would be a waste product of early photosynthetic bacteria, become abundant in the atmosphere, and then become the respiratory gas for most living things.  It is very soluble in ammonia (0.1124 vol/vol) -- no need for a hemoglobin-like carrier!
Answer: You can't use ONLY liquid nitrogen. Blood is supposed to transfer O2 to various parts of the body, keep your warm, etc. It could be the plasma (the liquid in which the cells go around in), and have many other cells in it. But,  those cells would have to be adapted to surviving in an EXTREMELY cold environment (eg: Uranus, Pluto).
Answer: Would it be possible for an alien species to have liquid nitrogen for its blood?
Since I am not familiar with all the biological processes of this alien I am unable to determine whether or not liquid nitrogen would be a viable blood analog. That said, it seems reasonable enough to me and verisimilitude is always context dependent.
What would be required for [liquid nitrogen as a blood analog] to work?
Most answers have referenced a low temperature as being a necessity for liquid nitrogen; however, it is theoretically possible for nitrogen to be in the liquid phase at normal ambient earth temperature given enough pressure. From what I can tell, this hasn't been done for practical reasons but it may be within the realm of possibility. The pressures required are likely a few orders of magnitude higher than earth atmosphere. Related discussion may be found here https://physics.stackexchange.com/questions/29523/pressure-of-sealed-in-liquid-nitrogen
What kind of environment would [the alien] need to exist in?
In order for internal pressures of this magnitude to exist in this alien, I can think of two possible scenarios.

The alien has an incredibly robust vascular system to resist the strain caused by the difference between the internal and external pressure
The alien lives in an extremely high-pressure environment to counteract the internal pressure.

This opens up the possibility of an alien with a highly developed internal hydraulic system. Perhaps it would be similar to what can be seen in jumping spiders. They are able to jump great distances without the necessity of highly developed muscles which other creatures such as a grasshopper rely on.
https://en.wikipedia.org/wiki/Jumping_spider#Behavior

Liquid nitrogen blood?


Is it consistent with veganism to own a pet?

Question: Is someone a vegan when he or she owns a pet for their own fulfilment?
Comment: I agree with Zanna. There are many interesting questions to be asked concerning veganism and pets, but this particular one would require answers to be hugely opinionated.
Comment: I think the underlying issues make for a valuable question: how do you balance the needs of your pet animal and the welfare of the animals kept and killed for pet food? How can animal welfare be safeguarded when keeping a pet, if at all? Is there vegan pet food? But the question should be reworked along those lines.
Comment: I agree to a certain extent but I feel like this can't be something opinion based right? Being vegan means to not use animals in any way shape or form for one's own pleasure or entertainment, be it food, clothes or anything else. If you think of it that way, saving an animal from death by adopting it would mean you're vegan, but buying a pet dog which was bred simply to make money would mean you aren't vegan, right?
Comment: @Zanna Well I'm sorry for not formulating my question properly. I'm not asking for just food for carnivores, I'm asking about the idea of owning a pet for one's own fulfilment. But I see now that this isn't a question that is going to be answered here so I might aswell close it.
Comment: If your formulate your question something like this, I think some folks would be able to answer it: "is keeping a pet for one's own fulfillment consistent with the vegan ideal to avoid the exploitation of animals for human use?" I guess the answer is "no, and the pet breeding industry is very un-vegan, but there might be some circumstances where vegans would feel it was ethical to keep an animal such as x, y, z, and many do so". Feel free to [edit] your question so that it reflects what you actually want to know. We can only read what's on the page really :)
Comment: @Zanna I've created a different, but similar question, which is less about opinions [environmentally focussed vegans]. It also depends *why* the person is vegan. https://vegetarianism.stackexchange.com/questions/999/which-pets-are-environmentally-friendly-to-own
Answer: I always say that you can't own an animal. Can you own a human person?
A reasonably broadly acceptable definition of veganism is an effort to avoid exploiting non-human animals for human use.
According to this definition, keeping an animal as a companion "for one's own fulfillment" would perhaps be considered not consistent with veganism.
Many vegans object to the industries that breed animals for human use as pets.
On the other hand, many vegans are animal-lovers and do keep animals. Most of the vegans I know who have "pets" or companion animals living with them do so because the animal was rescued. Often, they have an injury or disability that caused them to be rejected by pet-breeding industries or earlier "owners".
In this situation, keeping the animal might be considered an act of compassion, which is a key principle or driving emotion behind many people's vegan practice.
Of course, if you are keeping an animal, they might require non-vegan food, and then the vegan is put in the awkward position of obtaining such food, which is one of those difficult compromises that inevitably arise for people who commit themselves to an ethics of non-harming. I don't think you'd be able to find a self-professed vegan who's never compromised on something, chosen the lesser of two evils, or acted against strict vegan principles out of basic necessity.