Explain me concept of vapour pressure like I am five

Question: I have browsed internet to understand the concept of vapour pressure but something isn't linking for me. How do we relate vapour pressure to temperature for liquid only and any simplified definition of vapour pressure would be more than welcome! Can we relate vapour pressure to critical temperature in any way? Thanks in advance.....
Answer: Molecules of liquid, similarly as molecules of gas, have a particular statistical distribution of energy.
Molecules of liquid bond each other by intermolecular bonds, that deny them to escape from liquid to gas and become free.
Well, it is denied for most of them. At any temperature, there always exists a fraction of molecules with high enough energy to break bonds and escape.
This fraction increases with temperature of liquid, approximately exponentially.
If you put liquid to a closed container with vacuum, the escaping molecules start forming a gas with growing pressure. That is the vapour pressure.
When a molecule of such a gas hits the liquid, it is trapped by the bonds and stays in the liquid. The rate of this process is proportional to the vapour pressure.
At the particular vapour pressure, dependent on temperature, the rate of escaping liquid molecules ( evaporation rate ) equals to rate of trapping of molecules ( condensation rate ) and the liquid  evaporation ( and condensation ) rate is zero.
This vapour pressure is called the saturated vapour pressure ( for given liquid at given temperature ).
This saturated vapour pressure does not depend on presence of other gases, like air, where it is called the saturated vapour partial pressure.(with partial often omitted)
The partial pressure is the contribution of a particular gas compound to the total gas pressure, proportional to its molecular fraction within the gas.


Book: smart science kid goes to Amazon, shoots bad guys with curare darts

Question: There's a book I read a while ago, and I forgot what its title was. In the book, there's this really smart science kid who goes on a trip to the Amazon to help in some sort of study tour. I don't remember the ending but he uses curare darts to take people out. I think it was evil industrialists and they were cutting down the forest and he was going to stop them 'cause it was displacing a group native to the land and so he starts using guerrila warfare type stuff to attack them. He's a kid from middle school who is crazy smart but gets bullied and would purposely fail tests
Comment: I also remember reading this book (but don't remember the title or author) between 1998 and 2003 (I believe it was new at the time). It's YA fiction, modern setting, limited if any Sci-fi elements. I read it in English. I don't remember anything about the cover.
Comment: The protagonist was an amateur biologist, and the trip was a grant or academic award of some kind. He was short and pudgy, but the adversity of the trip toned him up. Before he left for the trip he provoked the school bullies with spitwads made from hair remover, and when he got back from the trip he was tough enough to beat the bullies that were after revenge.
Comment: Hi, and welcome to Literature Stack Exchange. Could you please add the language in which the book was written (or the language in which you read it) and when you read it (approximately)? Also, do you remember anything about the book's cover?
Comment: @aherocalledFrog: I assume you are someone different from Ndolo?
Comment: @SeanDuggan Yes. I've remembered this book occasionally over the years, but couldn't be bothered to ask for myself, but since someone else asked I thought I would try to help.
Answer: Assuming aherocalledFrog is correct in the added detail of hair remover spitballs, you're thinking of Rob Thomas's Green Thumb.

Winner of two National Science Fairs for his work on plant life, thirteen-year-old Grady Jacobs isn't exactly Mr. Popularity. But he doesn't care. He's spending the summer with the famous botanist Dr. Phillip Carter in the Amazon jungle trying to save the rain forest with a new species of super trees. Although his duties are mostly relegated to kitchen patrol, Grady stumbles on a startling discovery: a binary system of sounds that enables him to control the movement of trees.
Even as Grady discovers the tree language, he realizes that Carter's super trees aren't replenishing the Amazon's ecosystem -- they're killing it. When his unauthorized experiments are discovered, Grady flees from Carter's camp and finds refuge with the Urah-wau Indian tribe. but even with the tribe's help and the secret tree language, can Grady stop Carter's super trees?
With his keen eye for popular culture now trained on the environment, award-winning author Rob Thomas tells a coming-of-age story bursting with action and adventure. Hanh on to that vine: It's going to be a wild ride.

This review mentions the spitballs:

I'm a big fan of Rob Thomas and this book did not disappoint. I'm also really glad it's directed at the younger reader since junior high kids have probably missed his other titles. (Rats Saw God, Slave Day, Satellite Down) The main character, Grady, is instantly likable while we witness him outwitting his football-star bullies by covertly pelting them with spitballs covered in hair remover. These bullies have beat him up for the last time, however, when he travels to the Amazon rain forest as part of a tree-growing research team. He loses his extra weight & puts on muscle. Not to mention saving the jungle from a mad scientist. It's a fun story that teens will love, with a main character that some may identify with. Keep 'em coming, Rob!!

Looking at Google Books, curare is mentioned a handful of times, primarily in that the protagonist is semi-immune due to previous exposure.
Found with a search for novel amazon spitballs "hair remover", also the accepted answer to Book about a boy that controls plants by whistling? on the SF&F SE.
Comment: Honestly, while this does, on the surface, match Ndolo's question, the details are more from aherocalledFrog's comments. Maybe it's best if he posts it as a new question and I post this answer there just in case it's two different books?


Non in front of hyphenated adjective

Question: If one wishes to add "non" in front of a hyphenated adjective, should one add a hyphen after "non?"
Comment: possible duplicate of [How to connect a word and a phrase with a hyphen?](http://english.stackexchange.com/questions/2977/how-to-connect-a-word-and-a-phrase-with-a-hyphen)
Comment: Could you please provide an example? For example "Non wind powered renewable energy" Where would you place the hyphen(s)? (I'm not even sure that makes sense, I just made it up on the spot)
Comment: Most writers include ***two*** hyphens in, say, [***non-coal-fired**](https://www.google.com/search?q=%22non+coal+fired%22&btnG=Search+Books&tbm=bks&tbo=1&gws_rd=ssl) [power stations, etc.].*
Answer: "non" isn't a word, so you can't write this:

non red-haired [noun]

This is less wrong, but I still don't like it:

non-red haired [noun]

We've lost the link between "red" and "haired," so someone might interpret it as "hairy [noun] which is not red."
I like this form:

non-red-haired [noun]

In this case, it's clear we're negating the entire adjective rather than just the color.
Answer: The Chicago Manual of Style, 14th Edition, addresses this question indirectly in section 5.117:

The en dash is also used in place of a hyphen in a compound adjective when one of the elements of the adjective is an open compound (such as New York) or when two or more of the elements are hyphenated compounds:
New York–London flight
  post–Civil War period
  quasi-public–quasi-judicial body
       but
  non-English-speaking countries
  not-to-be-forgotten moments

Since your usage is of the latter form (a normally hyphenated element in front of a hyphenated compound adjective), the use of multiple hyphens is therefore recommended:

He was the only non-red-haired person in his entire family.

Non in front of hyphenated adjective


Can we have an accessory while a principal is acquitted?

Question: Can someone be convicted of being an accessory to a crime while a principal is acquitted? By definition an accessory helps conceal evidence or persons involved in a felony. If a principal is not charged as a felon, but the crime is still a felony, then doesn't that require there being another principal who is the felon, or can we have a felony without a felon?
Comment: Or you may have situations where it is proven that A or B did the crime but not which one (and the other is known to be innocent, so nobody can be convicted), but it is also proven that whoever did it, you helped them.
Comment: I suppose you can hide or destroy evidence against someone, or provide a false alibi for someone who is _accused_ of a crime, whether that person did the crime or not.
Answer: Of course
The prosecution just needs to prove that the crime happened (or the defendant believed it to have happened) and you helped (in brief, there will be specific elements of the crime that each need to be proved). This would be easier if the primary crime had a convicted perpetrator but it's not impossible without.
Allow me to illustrate with an example. I will set out facts which are somewhat contrived and would not be so clear cut in a real case but for the purposes of the example please take them as undisputed and fully supported by evidence.

John and Jill are in a relationship.
This relationship is well known to be argumentative with frequent shouting matches and one or the other storming out.
This does not amount to domestic violence by either party.
John's friend Alan believes (wrongly) that there is domestic violence.
During an argument Jill drops dead of a heart attack.
John rings Alan distraught and says "I've killed her."
Alan assumes (wrongly) that John has murdered Jill.
Alan says "i'll take care of it. You go to your dad's".
Alan (alone) disposes of the body.
John is not guilty of murder (or indeed, anything).
Alan is guilty of accessory to murder even though the actual crime never happened. The fact that Alan believed it happened is enough.
Comment: Would an example be a case like the following? Peter makes written statements that are said to have included information linking him to a crime. John, a supervisor liable for Peter's actions and unsure as to whether the documents incriminate Peter, destroys these documents in hope of their existence never even being brought up. Because there is not enough evidence at the time of trial to convict Peter, he is acquitted. But because it is known that John destroyed documents related to the crime, he can be prosecuted as an accessory, regardless of who else is involved.
Comment: @TQuile1948 No, John is not an accessory to Peter's crime - he committed the independent crime of attempting to pervert the course of justice, or evidence tampering, or failing to report, or ...
Comment: Thanks. Ok. Would an example be a case in which Peter is shown to be not guilty of a felony crime by reason of insanity or other mental incapacity while John is still guilty of being an accessory for trying to cover his tracks?
Comment: @TQuile1948 I'll add an example.
Comment: Thank you. That makes more sense. An accessory is someone who had a specific intent to conceal _**a**_ crime. The definitions I've read do not seem to cover this kind of case, but I understand the codes are up for interpretation. (https://www.cmcdefense.com/california_penal_code_section_32.php)


Use induction to prove that $n! \leq n^{n-1}$

Question: Use induction to prove that $n! \leq n^{n-1}$ for all integers $n\geq 1$. I'm having a hard time with induction and my professor said this is a good future test like question if someone can post a solution and explain it would help me out a lot. Thank you.
Answer: Call $n!\le n^{n-1}$ the statement $T(n)$.
$T(1)$ holds, because $1!\le 1^{1-1}=1^0=1$.
Now assume $T(n)$, i.e. $n!\le n^{n-1}$.
Then $$(n+1)!=n!(n+1)\le n^{n-1}(n+1)\le (n+1)^{n-1}(n+1)=(n+1)^n$$
So $T(n+1)$ holds too.
We've proved $T(1)$ and that $\forall n\in\mathbb N(T(n)\implies T(n+1))$. $\ \ \ \square$
Comment: @user212261 **please** ask this as a separate question. Do not use comments to ask questions!
Comment: @user212261: It is better if you can post this as a question with your work by highlighting where you stuck. Just posting the question is like asking others to do your work.
Comment: Another textbook question I'm stuck on says use induction to prove that for any complex number z (is not equal to) 1, and integer n(greather than or equal to) 1 ,                             (1+z+z^2+z^3+..z^n)={1-z^(n+1)]/(z-1)
Comment: @user212261 You mean $(1+z+z^2+\cdots+z^n)=\frac{z^{n+1}-1}{z-1}$. Observe that $\frac{z^n-1}{z-1}+z^{n}=\frac{z^{n+1}-1}{z-1}$ and clearly for $n=1$ we have that $1+z=\frac{z^2-1}{z-1}$ holds.
Comment: yeah that seems correct the only thing is in the textbook the right hand side is 1-z^(n+1) in the numerator not the other way around but that should be equivalent
Comment: @user212261 Let $S_n := 1+z+z^2+\cdots z^n$. Note that $zS_n = S_n + z^{n+1}-1$ and solve for $S_n$.
Comment: okay ill do that soon im new to the website idk how it works around here like what people do.@Mathi
Answer: Induction or not,
$$n! = 1\cdot 2\cdot 3\cdot\ldots\cdot n \leq 1\cdot n\cdot n\cdot\ldots\cdot n = n^{n-1}.$$
Comment: Not, in fact. ${}$
Answer: Hint $\,\ $ $\dfrac{n^{n-1}}{n!}=\, \dfrac{n}{n}\,\dfrac{n}{n\!-\!1}\cdots \dfrac{n}{3}\,\dfrac{n}{2}\, \ge\, 1,\,$ being a product of rationals $\ge 1$.
Remark $ $ This proof can be discovered purely mechanically by writing $\, {\rm f}(n)\, =\, \dfrac{n^{n-1}}{n!}\,$ as a telescoping product of its successive quotients $\rm\,f(k)/f(k\!-\!1)\,$ as below.
Multiplicative Telescopy
$\ \ \rm\displaystyle  f(a\!-\!1) \prod_{\large k\,=\,a}^{\large n} \dfrac{f(k)}{f(k-1)}\, =\ f(n) $
Proof $ $ Induct on $\rm\,n.\,$ Base is $\rm\, f(a\!-\!1)\frac{f(a)}{f(a-1)}=\,f(a)\,$ at $\rm\,n=a.\,$ Inductive step $\rm\,n\to n\!+\!1\,$ is
$\quad\ \displaystyle\rm  f(a\!-\!1)\prod_{\large k\,=\,a}^{\large n+1}\dfrac{f(k)}{f(k\!-\!1)}\, =\, \left[f(a\!-\!1)\prod_{\large k\,=\,a}^{\large n}\dfrac{f(k)}{f(k\!-\!1)}\right]\dfrac{f(n\!+\!1)}{f(n)}\, =\, \color{brown}{f(n)}\dfrac{f(n\!+\!1)}{\color{brown}{f(n)}} \, =\, f(n\!+\!1) $
Remark $\ $ Unwinding the induction yields a vivid depiction of the telescopic cancellation
$\quad \rm\displaystyle f(a\!-\!1)\prod_{\large k\,=\,a}^{n} \frac{f(k)}{f(k\!-\!1)}\,  =   \ \frac{\color{#c00}{\rlap{---}f(a\!-\!1)}}{1}\frac{\color{green}{\rlap{--}f(a)}}{\color{#C00}{\rlap{---}f(a\!-\!1)}}\frac{\color{royalblue}{\rlap{---}f(a\!+\!1)}}{\color{green}{\rlap{--}f(a)}}\frac{\phantom{\rlap{--}f(3)}}{\color{royalblue}{\rlap{---}f(a\!+\!1)}}\, \cdots\,  \frac{\color{brown}{\rlap{---}f(n\!-\!1)}}{\phantom{\rlap{--}f(n\!-\!1)}}\frac{f(n)}{\color{brown}{\rlap{---}f(n\!-\!1)}}\, =\  \frac{f(n)}{1} $
You can find many further examples of multiplicative telescopy in other posts here.


Where should Blender Download to?

Question: I am pretty new. About a month into this. Still learning so please excuse the noob question. I uninstalled it after my first animation. I thought it may be the reason for my Java problems. Not sure about that but that is fixed and I am back. I noticed this time when I installed it that it went into C://Program Files/Canon/Easy-WebPrint EX. That's my printer files. Is that normal? Do I move it out of there? Maybe that was the problem the first time. idk
Comment: no that is *not* the normal directory. If blender is working, then no you dont need to move it. I would recommend the zip just unzip, put it anywhere and run blender, no install required.
Answer: This is not a question about blender really, you can determine, and should know, where your files download to, it's a setting on your browser. Having said that, blender can be used two ways,
One is installing it using the msi file, in which case it makes  no difference where you downloaded the file to, because once you run the install file it will install to your programs folder. At that point you can safely erase the msi file.
If you choose not to install blender, use the .zip file. You just have to unzip (uncompress) the file and run the blender.exe program from the resulting folder. Just make sure that you don't download and use a temp file that might get erased next time you open the computer.
Answer: I would think it installs to where you choose to install it. But you can also download the zip-file and run that directly, without installing anything. So Blender would not cause Java-problems.
Answer: You may be confusing download location with installation location, both are completely different and unrelated.
If your file downloaded to that printer folder is because you chose to save it there, or through inaction (you didn't select a proper folder and just pressed Ok) let the browser save it there. Depending on your browser, that folder may have been the last used to save the last download so the next time you used it defaulted to the last used directory.
After download you must unpack (for ZIP files) or install for (MSI files). Where you install this from is irrelevant, what matters is the folder you now install it to. The MSI file should by default install to the correct location wherever you run it from, whereas the ZIP file will be extracted to where you tell it to, if you just right click it and coose Extract it will stay right in that weird printer folder you mentioned so it may seem like non standard location.
Either way non of that should cause any trouble for Blender or Java, Blender doesn't use or interfere with Java and the folder you run it should be mostly irrelevant.

Where should Blender Download to?


Installing 32 bit Python on 64 bit Fedora

Question: I have done a lot of digging and I can't seem to get any solutions to work. The one that looks the most promising is this one starting from "32 bit Python". However when I run the yum install command listed there I get
Error:  Multilib version problems found. This often means that the root
       cause is something else and multilib version checking is just
       pointing out that there is a problem. Eg.:

         1. You have an upgrade for glibc which is missing some
            dependency that another package requires. Yum is trying to
            solve this by installing an older version of glibc of the
            different architecture. If you exclude the bad architecture
            yum will tell you what the root cause is (which package
            requires what). You can try redoing the upgrade with
            --exclude glibc.otherarch ... this should give you an error
            message showing the root cause of the problem.

         2. You have multiple architectures of glibc installed, but
            yum can only see an upgrade for one of those architectures.
            If you don't want/need both architectures anymore then you
            can remove the one with the missing update and everything
            will work.

         3. You have duplicate versions of glibc installed already.
            You can use "yum check" to get yum show these errors.

       ...you can also use --setopt=protected_multilib=false to remove
       this checking, however this is almost never the correct thing to
       do as something else is very likely to go wrong (often causing
       much more problems).

       Protected multilib versions: glibc-2.18-11.fc20.i686 != glibc-2.18-12.fc20.x86_64
Error: Protected multilib versions: glibc-headers-2.18-11.fc20.i686 != glibc-headers-2.18-12.fc20.x86_64
Error: Protected multilib versions: glibc-common-2.18-11.fc20.i686 != glibc-common-2.18-12.fc20.x86_64

Does anyone know how to get 32 bit Python installed on a 64 bit machine? This is mainly to just get some Vim plugins to work properly (require 32 bit python).
Thanks
Answer: The problem is that you have the 64 bit libraries and development headers installed for libc common - you need to install the 32 bit (i686) versions yum, or another package manager, should let you specify that you need that version - alternatively you can download that specific package here as an rpm.
Comment: Fortran? Odd that Fortran would affect this, at least to my knowledge.
Comment: @thaweatherman: Thanks for pointing that out - corrected - I miss-read the file name - it is a libc common package.
Comment: So if I install the 32 bit glibc-common I will be good to go? Also, will that prevent me from using the normal 64 bit glibc-common?


Where did this new WiFi network with SSID 'SETUP' come from?

Question: After setting up my router (Linksys WRT120N) and my wireless network, upon clicking on the wireless icon and selecting "Join Other Network..." a new network called SETUP shows up when clicking the Show Networks button.  Where did this network come from?  It is password protected, but none of the user accounts and passwords can access it.  There is no way of deleting it.
The network that I have initially set up is, however, working fine.
(MB Pro; OS X 10.6.8)
Comment: Obvious thing to rule out first: could it belong to somebody else? It's quite normal for your Mac to be able to see WiFi networks from nearby apartments or houses.
Answer: This could be the network for a wireless printer. Its possible that someone nearby has bought a new printer with wireless functions.
Answer: Why don't you unplug your router and check to see if SETUP still appears on your MBP. If it does then it belongs to someone else near you.
Answer: It turned out that our Brother laser printer was responsible. Turning off wifi or properly configuring wifi helped to eliminate the "SETUP" wifi.


Determine the node voltages va and vb for the circuit

Question:
I set up the equations $$ -\frac{V_a}{4\Omega} - 3A - \frac{V_a - V_b}{2\Omega} = 0 \\\frac{V_a - V_b}{2\Omega}  + \frac{V_b}{3\Omega} + 4\Omega = 0$$
However when I row reduce them I get $$V_a = -12 \\V_b = -12 $$
but the solution is:
Comment: Your problem is with the second equation. You're assuming all the currents are going into the node b. But you are not consistent with the sign of \$\frac{V_b}{3}\$, it should be negative. Why? Because if you assume that current is going into the node, then you should have done \$\frac{0-V_b}{3}\$ (you are assuming current flowing from ground to node b.)
Answer: Just set it up and knock them down. The left side of the initial equation, for each node I set up, will be the currents leaving the node. The right side will be the currents entering the node.
Node 'a' first:
$$\begin{align*}
\frac{V_a}{4\Omega}+\frac{V_a}{2\Omega}+3A&=\frac{0V}{4\Omega}+\frac{V_b}{2\Omega} \\
V_a\cdot\left(\frac{1}{4\Omega}+\frac{1}{2\Omega}\right)+V_b\cdot\left(\frac{-1}{2\Omega}\right)&=-3A
\end{align*}$$
Node 'b' now:
$$\begin{align*}
\frac{V_b}{2\Omega}+\frac{V_b}{3\Omega}&=4A+\frac{V_a}{2\Omega}+\frac{0V}{3\Omega} \\
V_a\cdot\left(\frac{-1}{2\Omega}\right)+V_b\cdot\left(\frac{1}{2\Omega}+\frac{1}{3\Omega}\right)&=4A
\end{align*}$$
Those are your two equations in two unknowns. In this case, \$V_a=-1\tfrac{1}{3}V\$ and \$V_b=4V\$, if I did things right.
I can reconstitute my equation form into yours, more or less, as:
$$\begin{align*}
\frac{V_a}{4\Omega}+\frac{V_a-V_b}{2\Omega}+3A&=0 \\
\frac{V_b-V_a}{2\Omega}+\frac{V_b}{3\Omega}-4A&=0
\end{align*}$$
Or, in negated form:
$$\begin{align*}
-\frac{V_a}{4\Omega}-\frac{V_a-V_b}{2\Omega}-3A&=0 \\
\frac{V_a-V_b}{2\Omega}-\frac{V_b}{3\Omega}+4A&=0
\end{align*}$$
Perhaps you can see the differences here? This last equation pair looks like yours except for the sign of \$\tfrac{V_b}{3\Omega}\$. Probably, because you failed to realize it was \$\tfrac{0V-V_b}{3\Omega}\$, as a guess.
Let me know if you need me to walk slowly through how I set up the initial equations.
Comment: Thank you very much. I realized I didn't remain consistent with the KCL in the second equation and had a sign error. Your answer clearly spells it out.
Answer: When you apply nodal analysis to a circuit, it's useful to assume that all currents are going out or in the node, unless a current source tells you otherwise. That's the approach you took. To analyze node a, you assumed all currents were going out the node and it's correct, but in node b, when you assume that all currents were going out, you included the current give by the 4 A source, when it clearly shows it's not going out the node, it's going in. In your second equation you should've written the 4 amp current on the other side of the equal sign, because it's going in.


is it possible to place an element over flash that has wmode=window in chrome?

Question: I'm working on a page that has some ads on it. One of them loads in an ad with wmode=window. I don't have the ability to change that flash code. I need to put a modal box on top of that flash element, but every combination of using z-indexes and iframe shims has failed (both manually and using bgiframe). Is there a way to place html content on top of a flash element with wmode=window? I'm testing this in chrome so far... figuring if I can't at least get it to work there, it won't work anywhere.
Comment: heya im in australia, 5am, so im goin to sleep i will check tommorow
Answer: I'm afraid there is no way around it.
WMODE-window forces the browser to render the element on the very top layer, and it will overlap everything.
Rob
Answer: Yes it is possible, i had done this before using php and Css, your right though i did use the index "z" properties in my CSS Sheets than i had used php divs to what your trying to do, i maned to get 3 transparent flash Movies on top of each other , it was a pain for me and not much documents on this at the time,
trial and error is your best go, i had deleted my old web server i had used this method for, if you get desperate i will have a look through backup drives, but it is possible so dont give up


Lookup Column in Content Type hub

Question: I had to create a Content Type in the Content Type Hub which has a Lookup column... I created the list of the lookup in the CTHub and published the CT.
In my site collections I can see the new CT but i cannot see the lookup column... Why?
Answer: Lookup columns will only lookup data in lists in the same site/web. When the content type hub functionality deploys your content type to other sites, the lookup list does not exist there, so the column is removed.
The best way to do this is to use a managed metadata term set instead. The term set is globally available to all site collections. So you can add a managed metadata column to your content type, giving lookup type functionality, and the column can work in any site collection.
Comment: The problem with this approach is that you have a limit of 30000 items maximum per term set and that's a huge limitation for us
Answer: Alternatively, you can provision your lookup column with a feature receiver everytime you create a new website. You just need to make sure you have the lookup list available somewhere (which, by the way, CAN BE in a different web site). There is a quick and easy to implement guide which you can find here: http://sharepointbitsandbytes.com/2015/05/configure-lookup-fields-programmatically/ . This requires a bit of SharePoint knowledge, including features, receivers etc.
Comment: Yep, I cannot use this approach since we are using SharePoint online but thank you

Lookup Column in Content Type hub


How can I remove a broken plastic packing nut from a faucet?

Question: I have a leaky exterior faucet where the plastic packing nut has broken and the threaded end is still inside the faucet.  How can I remove the broken packing nut from the faucet?
Comment: Some plumbers doing work on the outside of my house broke the handle of the sill cock washing out some buckets and said it would be just as easy to replace it as it would be to fix it. I ended up getting a nice frost proof one for free that way.  Now sure how accessible the supply pipe is, but it might be easier for you to turn off the water, unscrew the faucet and just replace it, I think they are fairly cheap.
Answer: I'm assuming this is in reference to an outdoor garden faucet. If you can't get the old packing out, replace the entire faucet. But first, make sure you don't have a dope of a builder that would solder the threads. Try to unscrew the fixture from the wall (shutoff the outside water first). If it unscrews, then all you need to do is pickup some pipe dope and a new faucet from the store. Clean the old threads, put some pipe dope on the threads, and screw on the new fixture.
Answer: If you can do it without damaging a washer (or if the washer can be replaced easily), you can sometimes take a large bladed flat screwdriver and heat it with a plumbing torch, then while it is still hot, firmly push it into the remaining plastic until it is embedded. You can then twist it out fairly easily.
Answer: The heated screwdriver sounds a good idea. If that doesn't work I would try using an ordinary twist drill bit and power drill to make enough holes in the nut to be able to break it up and remove it. I would have to take care to avoid threads and other features of the faucet.
Answer: So this happened to me.  The nut was very brittle.  I tried hitting it at an angle but the plastic was too brittle.
Ended up heating the pipe with MAPI gas and held it there for a minute or so.  The nut liquified and I was able to push it away from the wall.  I was then able to pull it out with a pair of needle noise pliers after 10 seconds.
Comment: "The nut liquified and I was able to push it away from the wall." This is confusing. Care to clarify what you pushed away from the wall of what?
Comment: I heated up the pipe and the nut with the MAPI gas and used a flat head screw driver to separate the nut from the metal housing.  The plastic shrinks a bit as it melts and burns off-- then you just pull it out with pliers...


How can I find duplicate songs?

Question: The title says it all. How can I detect duplicates in my media library?
Answer: dupeGuru Music Edition is what you want. Set the scan type to "Audio Contents" in Preferences. Please note that the program is fairware so please contribute if you can.

I suggest you couple this with MusicBrainz Picard which can tag your music files automatically.
Comment: Too bad dupeGuru can only do 10 removals at a time with out putting down money.
Comment: PERFECT! Finally an answer that worked like charm :). A Banshee plugin or whatever would have been even better but this works great! I actually removed around 8GB of dupes, cheers!
Comment: The PPA is dead for recent Ubuntu releases. I had success installing the .deb directly from https://launchpad.net/~hsoft/+archive/ubuntu/ppa/+build/9735351 and then running `dupeguru_me`.
Comment: The most recent version has no limit on removals. However it doesn't seem to fingerprint the music, it just compares filenames/ID3 information. If you use a tool like Picard to tag your music first, it should do a good job :)
Answer: There is a plugin that was made some time ago for this. I've used it recently but it still leaves a little to be desired. There is a "PPA" for it - but no built packages yet, just the Bazaar branch. The install instructions go something like this:
wget http://scrawl.bplaced.net/duplicate-source.tar.gz -O tmp.tar.gz && mkdir -vp ~/.gnome2/rhythmbox/plugins/duplicate-source/ && tar -xf tmp.tar.gz -C ~/.gnome2/rhythmbox/plugins && rm -v tmp.tar.gz

If you're interested in using the Bazaar'd source code do the following instead:
mkdir -vp ~/.gnome2/rhythmbox/plugins && cd ~/.gnome2/rhythmbox/plugins && bzr branch lp:rb-duplicate-source duplicate-source

Once it's installed restart Rhythmbox and you should have a Duplicates Finder now in the plugin list.

After activating it - there are additional configuration options available.

After the plugin is enabled - and when it finds duplicates - it'll add an additional option to your library list:

A few settings that I've found as "odd" - I've tried this on a media library with over 120,000 songs (over 1,000 duplicates) and a library with about 1,000 songs and maybe 30 duplicates. On the former it took a VERY long time and crashed Rhythmbox several times during the search. I eventually went with Automatically "Remove from Library" to avoid having to rebuild the list. On smaller libraries everything works great though.
When a duplicate is found - if you have the default options selected - the lower quality version of the song will be added to the list. So it's safe to select all songs on the Duplicates list and "Remove" (Either delete from disk or remove from library).
Comment: Thanks a lot for giving this tip! However, nothing seems to happen once I've activated it. I can not find a new tab or whatever where the duplicates would be indicated.
Comment: You may need to move the threshold to 0.5 to help sort out duplicates. It'll show as an additional item in your Library list. I've updated the answer to show this.
Comment: Tried that out as well. No success.
Answer: You can use fdupes for that:
$ fdupes -r ~/Music

which gives you a list of all duplicate files.
You can easily install it with
sudo apt-get install fdupes

Comment: This worked better than the other options. However, it does not really seem to be suitable for audio files. The software does not compare tags etc. which leads to a very short list of files whereas in reality there are many many duplicates, however maybe not with exactly the same file size (as they might be from different sources).
Answer: I ran into a similar issue when I had a bunch of duplicate image files.  In my case, I just used md5sum on the files and sorted the results:
for file in $(find $rootdir -name "*.jpg"); do echo $(md5sum $file); done | sort

Files with the same contents generated the same hash, so duplicates could be found easily.  I manually deleted the dupes from there, although I could have extended the script to delete all but the first occurrence, but I'm always paranoid about doing that in an ad-hoc script.
Note that this only works for duplicate files with identical contents.
Comment: Faster: `find $rootdir -name '*.jpg' -exec md5sum {} + | sort`
Answer: It might be a dozen years late, but I just wrote a command-line program that tries to detect similar audio files by comparing acoustic fingerprints: https://codeberg.org/derat/soundalike
It uses the fpcalc utility from Chromaprint to generate the fingerprints, and then builds a lookup table to find possible matches before comparing fingerprints more rigorously.
Answer: Try FSlint or dupe gredtter
To install FSlint type in terminal (Ctrl-Alt-T)
sudo apt-get install fslint

hope this is useful..
Answer: I've used FSlint to find duplicate files in general. FSlint is "a utility to find and clean various forms of lint on a filesystem."
Comment: That is strange. FSlint does not find any of my duplicate songs!
Comment: FSlint is with default settings likely to find duplicate files measured by file name and file size, but not duplicate songs if it's different recordings with different size and file name.
Comment: Different recordings (remixes?) are not safe for deletion. They may have own value.
Comment: I have also used fslint for audio (with reasonable success) -- though given some of the alternatives in this thread, I'll probably try one of them next time.

How can I find duplicate songs?


Deleting Aliases unchecks 'generate automatic alias'

Question: I'm sure this is a bug.
I have a bunch of alias paths set where page URLs are generated based on menu location. I'm testing to see if I restructure the site and move a lot of content around, can I use path-auto, bulk update to change all the URLs.
Obviously I can't update without deleting the existing ones first (tested).
So I went in and delete all the aliases via Admin > Config > Search > URL aliases > Delete aliases. All aliases deleted, great.
But Bulk update won't give me new aliases. After a bit of poking around it turns out that running Delete Aliases has caused the 'Generate Automatic Alias" checkbox to be turned OFF on all my content.
so...

Why did running Delete Aliases cause all my content to change to using custom aliases?
Can I (somehow) revert all pages to automatic aliases?

Note - I'm using the govCMS distribution, so adding modules like VBO is not an option. I have almost zero understanding of drush, but I'm willing to dive in with instructions.
Note again - I had pathauto persistant state enabled when this happened.
Answer: Okay, never mind. I spent over an hour with this repeatedly happening, dug through pages full of people having the same issue and the opposite issue, flicked persistant state on and off, and it suddenly started working in the time it took me to write this. Caching I guess


How to autostart a .sh after login?

Question: I have made a .sh (which works) to run a mono program. How do I make it run every time I login? (and display in a terminal, not just run in background)
Ubuntu server 12.04 with Unity desktop.
Answer:
First make your script executable.

chmod +x /path/to/script

Open Startup Applications, from the cog menu present at the upper right corner.

Click on Add.

Fill in all the details and click Add.

Logout and login back to check.
Answer: Yes you can start any script by navigating toSystem \ Preferences\ Sessions menu item and then just adding the command or the script you want to rin
Comment: is this 12.04 ? it's unity in 12.04, not gnome 2
Comment: sorry, I meant unity.
Comment: ok sorry for i took it for gnome. Well unity has its own preferences. The startup application in unity can be found at topbar as a drop-down menu option of power button, located before the shotdown options and all.
Answer: You could use $HOME/.bashrc
It is parsed and run like a script, every time bash starts. Bash is the default shell for Ubuntu.
I have a script that saves every command line I've used, like this:
$ tail -2 $HOME/.bashrc
/usr/local/bin/backup-historial.sh &

Comment: So I have to put my scirpt in .bashrc which is in /home? I tried this and it didn't work.
Comment: bad idea for those who may ssh into a box
Answer: Go into the Startup Applications dialog, click Add, give it a name and in Command put
gnome-terminal -e yourscript.sh

You can check it works first by running gnome-terminal -e yourscript.sh from a terminal (it should then open another terminal).
Answer: Put your script in a file (we call it yourscript.sh) and make in executable:
#!/bin/bash
#put your script here
echo "Press enter to close"
read line

Then open /etc/rc.local file using a text editor:
sudo gedit /etc/rc.local

Finally add the following code in the rc.local just before "exit 0" command:
gnome-terminal -e "./dirtoyourscript/yourscript.sh"

exit 0

Have a nice time.
Comment: I would believe, `/etc/rc.local` runs before X does (and thus, even before the login greeter); which  means `/etc/rc.local` is not appropriate for doing things "after login".
Answer: if you kown how to handle crontab , add this line :
@reboot gnome-terminal -e "./dirtoyourscript/yourscript.sh"

if you don't know ,
execute the following commands to edit your crontab
EDITOR=gedit
export EDITOR
alias editor=$EDITOR
crontab -e

How to autostart a .sh after login?


How to defend from animals while camping (golden jackals, boars, foxes)?

Question: I want to go camping somewhere (I am from Eastern Europe) but the zone is full of golden jackals/foxes. They are a bit larger than a fox, but they stay in packs. I have a husky dog that wouldn't be able to protect us, I think he might actually attract them to my camp. We are not allowed with any type of firearms where I live, unless you have a license which is almost impossible to obtain. An option I think would be something that produces a very loud sound (firecrackers or vuvuzela).
Comment: Jackals form packs, and are closely related to dogs.  (Red) foxes tend to be in no more than a family group, sometimes with more than one adult female; they're also easily scared by humans. The biggest examples of both are similar sizes and weights, but the average jackal is bigger than the average fox. So I suspect you're thinking of jackals, which are bolder.
Answer: Real life is not a video game. In most places in the world you don't have to "defend" from animals attacking you or your camp. Unless maybe if you count mosquitoes or other similar pests.
There are a few notable exceptions, mainly bears: black/brown bears in North America, brown bears in parts of Romaina, polar bears way up north. But even here it is mostly about not leaving food lying around your camp - with the exception of polar bears bears don't generally see you as prey.
The animals you listed (golden jackals, boars, foxes) all don't pose a serious threat to you that you need to "defend" against. They are generally shy and will avoid you whenever possible.

Don't leave food lying around your camp, or a fox or jackal might try to scavenge a bit.
Don't startle boars, especially a mother with young.
Don't approach or corner wild animals, or they might be frightened into attacking as a means of defence.

TLDR: Don't worry, you'll be fine.
Comment: :D ... On a related note, we've actually had issues with a particularly bold batch of urban foxes stealing stuff (shoes, belts, wallets, ...) out of our closed ten vestibules by wriggling below the tent edge... But that is very unlikely to happen out in the wild. :)
Comment: Concur about foxes -- in my experience, they will run away as soon as you approach. The worst they make is a mess of food left outside, or trash bags. Just hang them high or take them into your tent.
Comment: @phipsgabler, I can see hanging them up, but I wouldn't take a fox into my tent ;)
Comment: I thought about that, but I just can't imagine a fox getting into a double-wall tent. It likely won't dare, and it can't penetrate the mesh. Leaving stuff in the vestibules is differenent thing (I have had horses stealing my bread from there, and cats ripping the fabric while trying to cuddle with the people sleeping inside...)
Comment: Oh. Now I realize your wordplay :D (And my sloppy syntax.)
Comment: Great answer. Even in places with plenty of wildlife, in most trips you don't get to see a single (non domestic nor human) large mammal.
Answer: First, see Fsygin's answer.  Leave the animals alone, manage your food, and they will leave you alone.
But, if you need to, for your own peace of mind, I'd carry a solid walking stick.  Something about twice as thick as a broomstick, bit shorter.  If you were attacked by an animal like a jackal or fox, that would easily dissuade it.  And it's cheap and doesn't make you look like a lunatic.  Not so sure about a boar.  I don't think it's necessary, but as long as you don't use it as a license to annoy animals, there is value in having something that makes you feel comfortable and safe.
In camp you can also grab some rocks.  From my experience with stray dogs, throwing them in the general direction - you don't have to try to hit them, tends to be quite dissuasive.
Your dog I am not sure about at all.  Even if animals will not attack you unwarranted, they may not be so nice to a dog that chases after them.  If you have to bring it, I suggest you keep it leashed or well under control.
Comment: I don't know about jackals, but wolves and coyotes see domestic dogs as competitors for territory and will attack them without provocation.
Comment: Didn't know that.  I do know North American incidents with black bears often involve dogs.  I am sure a good *trained* hunting dog is a plus when camping and hiking in the wilderness, quite doubtful about urban pets.
Comment: Not wild animals, but I think here in Austria most incidents with cows also involve dogs.
Answer: How to defend from animals while camping (golden jackals, boars, foxes)?
The first defence is a positive offence. Always be prepared for the unexpected.

At night keep a small fire  going if you are permitted to do so. Always follows safe fire rules!

Do not set up camp near known or noticeable game trails. Wild boars habitually travel the same game trails.

Do not hike on known game trails of wild boars. They can do major damage to your legs in no time and can come out of nowhere, so always be observant of your surroundings.

Do not camp near animal dens, especially if young are present in the area.

If social animals like jackals are coming near you, make a lot of noise, especially the type that they are not used to hearing, like banging pots together. See this YouTube episode of Jaws of DEATH | I Shouldn't Be Alive Noise is a great defence against attacks!

Carry a good walking staff with you. If you are inventive you could have a removable spear tip put on it, in case of an emergency! Even a knife tied to the end of a stick may give you added protection.

Generally wild animals are shy of coming close to humans and will keep their distance. This does not always hold true especially if they are very hungry and you have lots of food with you. Make sure you know how to hang a bear bag

Separate food you food stuffs away from your camp and in a food cache (bear bag), especially at night.

While jackals usually leave people alone, even non-rabid ones can attack humans, including to grab for food from a child. They can also attack and transfer rabies to domestic cats and dogs. - Snacks for stray cats may be feeding a rash of jackal attacks
Answer: I have camped on Svalbard, where polar bears are a real threat and hence firearms are mandatory outside of town. However, that's only the last resort. More importantly than scaring them away or in the utmost case shooting them, is detecting them in time. We were traveling with sled-dogs, and they make up a very great watch for intruders. They start to bark very loudly if they see something approaching, even in the middle of the night.
Of course, if you are really scared, you should put up a watch, and if your company consists of several persons, that's always the safest thing to do if staying in an unknown area (but also the most uncomfortable). It protects you not only from animals, but also from other dangers, such as a fire, a flooding (when near water) or - beware - a thief. But you said you have a husky dog, so let him do the watching. He'll most likely bark when he scents foxes, and those will be afraid of him, since they're smaller than your dog. So just leash your dog to a pole outside the tent. A husky dog will be fine sleeping outside.
One important thing I forgot: Could there be rabies in the area where you hike? If so, that would be a real danger, both to you and your dog, as infested animals are aggressive. So make sure your dog is vaccinated against it (mandatory in most countries, ASFAIK) and talk to your doctor whether you need one yourself.
Comment: IMHO suggesting to keeping a watch is a overkill and unfeasible in most cases. After all you are out there to enjoy nature and maybe some exercise, not to undergo rigorous watch duty and lack of sleep.
Comment: And yet when I was on a similar island with my uncle's family, we found plastic bottles, cigarettes. When you get on the island you feel like all your problems are gone, surrounded by nature's paradise. And then you see a plastic bottle and a beer can left by an idiot and the paradise mood is ruined.
Comment: @fgysin I agree that keeping a watch is not something people want to do during their vacation, but it still is the safest thing to do. Even if it's vacation time, I'm always considering this option to keep me and my group safe.
Comment: The good thing is that I will be camping on an island in Danube river. It is very likely that I will be alone because to reach the island you need to drive from the nearest village trough fields of corn and wheat, then leave your car in a forest zone near Danube, then cut through the very very dense vegetation zone with a machete of about 300 meters carrying your tent/tools/food/water/ then when you reach the river you inflate your boat you place your stock in the boat, and you paddle to the island about 300 meters(it is possible to swim that distance, but you can't swim with stuff in hands)


Photonics, twist in laser beam, optical vortex

Question: If I have a Gaussian beam and I use a spiral phase plate (SPP) to convert it into a vortex beam, I get a donut-shaped beam with zero intensity at the center. Imagine that I design an obstacle which fits exactly the intensity profile so that all the light on the bright ring gets totally absorbed, but the dark area is completely unblocked. On the output I must get "nothing", darkness. Now, my question is: what if I let this "nothing" go through SPP back-converter? Will I get light back out of "nothing"?
Answer: The SPP is passive optics: it (ideally) moves light but neither absorbs it nor creates it. The light from the centre is moved towards the external ring (which is wider than the original Gaussian beam). If you further add an absorbing obstacle down the beam, there is no way a SPP recreates the light.
However, your description of such an obstacle is wrong: to have "norhing" at the output, you need to have 100% absorption everywhere (except on a single point, at the centre, but that is not physical). Obviously, if you have such a totally absorbing obstacle upstream, you can't have anything downstream which recreates the original beam.
However, you may want to approximate the above absorbing profile with something which absorbs everything in the ring, except in a small window around the centre, to only keep the "doughnut hole". The intensity in this hole is weak, but non-zero and is typically $∝r²$, where $r$ is the centre of the beam. This leads to a total intensity $∝R⁴$ in a window of radius $R$. This (weak) beam is still essentially a vortex beam, with the same phase profile, so, the SPP back-converter will convert it back to an approximately Gaussian beam, with no hole. But this beam will be very weak, having no more light than the one that passes through the obstacle, since the SPP does not creates "light out of 'nothing'."


Rendered image is not as detailed as in rendered view

Question:
Does anyone know why the top is so low quality compared to the actually rendered image. The plane has True displacement enabled. Does anyone know the problem, if you need further more details I can give them.
Comment: Look at the subsurf modifier, make sure that you have the same number of subdivisions for rendering than you do for preview.
Comment: may be you should decrese the dicing rate
Answer: It is from your subserf modifier. If your using the experimental or adaptive, make sure both values from the view and render are the same, i.e. the Dicing Rate must be 1 and the levels must be proportional to it.
And also the view angel will affect your render in adaptive subserf. Objects at the far will have less subdivision than those from the front, i.e, if your camera is pointing at the front and you are looking at the back, there will be a noticeable difference.


Circuit to detect only one zero crossing when a sine wave changes from negative to positive half cycle

Question: In a Grid Tie Inverter design, I need a circuit which can detect only one zero crossing of the Grid signal, (when the signal will change from negative to positive half cycle). I have made a circuit, which detects both the zero crossings. So please guide me, that which circuit will perform this function? I have made the circuit attached herewith, but it detects both the zero crossings.
Comment: What about a divide by 2 [like this](http://verilog-code.blogspot.com/2014/03/frequency-dividing-circuit-with-minimum.html?m=1)?  Also, harmonics causing extra crossings may goof you up.  How about half-wave bridge instead of full?
Comment: https://circuitdigest.com/electronic-circuits/zero-crossing-detector-circuit-diagram
Answer: You could use any safe method of illuminating an LED directly from mains which only conducts on one of the half cycles.
Two common arrangements are:

simulate this circuit – Schematic created using CircuitLab
The LEDs represents the LED in the optocoupler.
The diodes are included to protect the LED from reverse voltage on the other half-cycle. You have to be careful in selecting the resistor value and the protection diode.
Target just a few milliamps -- perhaps even just 1 mA -- for the LED current. Also remember to do a power dissipation calculation for the resistor. You may need to go to a 1/2-watt resistor or use two resistors in series.
Comment: Thanks Mr. ErikR for your reply, but this circuit will not do that job, because the led will be on during the whole positive half cycle, so there would be a pulse equal to the duration of half cycle.  I need a circuit which will generate an impulse, when the zero crossing before starting the positive half cycle appears.
Comment: Usually events are described by transitions from HI to LO or LO to HI. A microcontroller, for instance, can generate an interrupt when a certain transition occurs on an IO pin. To translate an edge transition to a pulse look up "monostable multivibrator", for instance [here](http://www.n5dux.com/ham/files/pdf/Working%20With%20Monostable%20Multivibrators.pdf). There are a lot of other implementations -- they are also called "edge detectors".
Comment: In fact, the circuit does generate a pulse -- the pulse is about 1/100-th of second long (assuming 50 Hz). If you want a different pulse length look up monostable multivibrator / edge detector circuits.


Get the number of concurrent users in Apache?

Question: We want to know how many concurrent users the apache is serving at one time? Can I do it by installing some statistics tools? I tried webalizer but it only shows hourly hits, not the number of users. Or I have to analyze the log using some tools?
Comment: Apache Module mod_status would be the standard tool I think
Answer: You may want to check out Apache Top.
Or you can write your own script from the command line that just check the number of current connections on the port Apache is running on (usually 80), for example:
netstat -plan | grep :80

Or, if you just want the number:
netstat -plan | grep :80 | wc -l

This could ideally be done through a cron (e.g., run every minute and check number of connections, average over time, etc.).
Comment: I think the "grep :80" is not working as expected, more if you have services like tomcat or couchbase which run on ports "80XX"...
Answer: Here is a small script that I use. I have an SSL based site, so I'm checking the active connections on port 443.  You might want to update 443 to 80, depending on what you would like to monitor.
#!/bin/bash

[ $# -eq 0 ] && { echo "Usage: $0 <refresh time>" ; exit 1; }

while true
do
        clear;
        echo "Number of Active Connections:";
        netstat -an | grep 443 | grep tcp | grep -v 0.0.0.0 | grep -v ::: | cut -d':' -f2 | cut -d' ' -f12 | sort | uniq | wc -l;
        echo;
        echo "Current Active IP's:";
        netstat -an | grep 443 | grep tcp | grep -v 0.0.0.0 | grep -v ::: | cut -d':' -f2 | cut -d' ' -f12 | sort | uniq;
        sleep $1;
done

One thing to keep in mind is that, if you're behind a VIP, then your web server will only see 1 IP (the one from the VIP).  Since this script is checking for unique IP's, it will always show 1 connection.  One way to resolve this is to remove the text "| uniq".


About my faith and how to strengthen my nats on the right path

Question: Am a 19yr girl in an boarding school in abroad and I had a sexual relationship with a girl in school and I regret doing it and I have the feeling that I am bisexual but I don't like it
What should I do to get rid of this feeling.
Answer: If you are really bisexual, meaning you feel attracted by both men an women, you have the option to lead a life with a husband, it will be the easier way of life to live this option.
If you are in fact clearly lesbian, meaning that you do not feel attired by men at all, Islam lacks an answer for the question what to do with your life; see this question. Although the question is not actually specifying gay or lesbian, the answers in there actually refer to gay people.
As to lesbian women, the particular interdiction of homosexual acts is rather extrapolated because it originally refers explicitly to men. It can however be concluded from the interdiction to have sex before marriage that there is an interdiction, too, as lesbian marriage has never even been thought about in the times of the Prophet or long time after.
Comment: Thank you . May Allah grant you the best reward
Answer: Assalm o Alaikum
The Holy prophet P.B.U.H has told us to read a Dua in such a condition when you are stuck in a habit you want to get rid of that...
So this is very useful دعا.. Please try to read this dua more and more.
رَبِّ إنّيٍ مَغْلُوبٌ فَانْتَصِرْ
Rabbi Innee maghloobun fantasir...
Insha, ALLAH you will get rid of that habit
Comment: Thank you so much. May Allah Allah grant you the best of rewards


Marking DAT section as shellcode in ghidra

Question: I have a binary that loads a DAT section as code (calls ((code **) DAT_something)(0, 2)), and I'd like to be able to disassemble the DAT_something data region. Currently, when looking at the DAT_something region, the data type is undefined (everything is filled with ??s), and I do not know how to mark the section as shellcode. Right click > Disassemble also fails, because the memory is "uninitialized". How would I go about disassembling this shellcode?
Comment: Does the column next to the address display a question mark followed by the actual bytes at the address or is it only a question mark? Question mark followed by a known byte indicates that the data is known but a datatype is not. In my experience, you can hit `d` to disassemble in this case. Sounds like you can't.
Comment: If you have a question mark followed by a known byte, maybe you can't disassemble because the area of code bytes isn't big enough for your opcode or you aren't disassembling a valid opcode.
Comment: @MatthewTingum Both columns are filled with question marks. Hitting `d` does nothing, right clicking and pressing "Disassemble" shows the "uninitialized memory" message.
Answer: This sounds like an artificial section for externs. Let's say you have extern char buffer[256]. You compile to an object which doesn't care about externs because you're not linking or you somehow do link but ignore unresolved extern errors. Your elf knows the symbol name and the datatype of the symbol but not much else about the external dependency. Ghidra will recognize this, create an artifical block, and move on about it's day.
Why does the artificial block exist? Why doesn't it end up in a relocation table with got and got.plt entries? This is because the external data is not relocatable. The linker has no notion of how to access this data. It wasn't present when linked.
We can test this with a small example.
#include <stdio.h>

extern char extern_string[256];

int main(int argc, char **argv) {
    printf("%s\n", extern_string);
    return 0;
}

Then compile with:
gcc -c main.c

You're left with main.o. When I throw main.o in Ghidra, I find the following:
                             //
                             // EXTERNAL
                             // NOTE: This block is artificial and allows ELF Relocations
                             // ram:00101000-ram:0010100f
                             //
                             extern_string                                   XREF[1]:     main:0010000f(*)
        00101000                 ??         ??
        00101001                 ??         ??
        00101002                 ??         ??
        00101003                 ??         ??
        00101004                 ??         ??
        00101005                 ??         ??
        00101006                 ??         ??
        00101007                 ??         ??

8 bytes from the extern so it must be looking for a pointer on my x86_64 machine. Perhaps a better example could demonstrate a larger area.
The point is, I never linked this with anything that would explain where extern_string is. Ghidra knows that it exists but simply can't locate it. Ghidra gives us a placeholder to say as much.
I wish I could give an example that demonstrates a larger artificial block. I feel like that would provide a more complete answer. Unfortunately I don't know how to generate that.
Comment: This does look similar to what I encountered, although I don't know if that comment was there. Thanks!


Charging a battery with a lower voltage battery

Question: Is it possible to charge a 44.4 V LiPo battery with a lower voltage LiFePO using a boost converter and some form of overcharge protection? I have a battery powered plane using a 12s lithium polymer battery, and I am wondering if it is possible to extend the flight time (even if marginally) using solar cells. The solar cells would be connected via an MPPT controller to a lithium iron phosphate battery and this would be connected via a boost converter to the lithium polymer battery. A problem I can see occurring is balancing.
Comment: I'm just _guessing,_ that if you use the same kind of rigid, crystalline cells that are used for most stationary solar panels, the added weight will rob your plane of more power than the cells produce. I'm guessing that you'll need some kind of fancy, light-weight [thin-film cells](https://en.wikipedia.org/wiki/Thin-film_solar_cell) to get any benefit at all. Maybe find thin-film cells printed onto some flexible substrate that also can be used as the skin of the airplane.
Comment: mass is indeed an issue but there's plenty to trade if all you want is time in air.  have you considered a blimp instead?  Usual solution with solar cells is to connect enough small ones in series to get the voltage you need.  its less massive than the same cells plus another battery.
Comment: Eliminate the second battery. Just boost the solar panel voltage to the LiPo pack voltage (or ensure the panel already exceeds it).
Answer:
I am wondering if it is possible to extend the flight time (even if
marginally) using solar cells. The solar cells would be connected via
an MPPT controller to a lithium iron phosphate battery and this would
be connected via a boost converter to the lithium polymer battery.

The main problem with charging an auxiliary battery and using it to charge the main one is the extra weight. The solar panels won't be powerful enough to charge the battery quickly, so unlike eg. an electric vehicle with dynamic braking there is little advantage in storing energy in another device for later use when you can just make the main battery larger. This will also be more efficient than charging a battery and then discharging it to charge another one.
If you must have solar panels then use the MPPT controller to charge the Lipo battery directly while the sun is shining. As soon the battery has run down a little (ie. shortly after takeoff) it will have the 'room' to store more energy. If the plane can handle more weight then better to have that weight in the main battery where it can achieve higher capacity.

A problem I can see occurring is balancing.

Balancing shouldn't be a problem if your lipo battery is in good health. The cells should maintain 'top' balance without any help, so in the unlikely event that the solar panels manage to fully recharge it balancing shouldn't be necessary.


Is $n^{\log \log n}$ polynomial in $n$?

Question: Is $n^{\log \log n}$ polynomial, exponential or subexponential in $n$?
Answer: Not polynomial in $n$. For let $K$ be a (say large) constant. We show that ultimately $n^{\log\log n}\gt n^K$. We can do this by taking the $\log$ of both sides. On the left, we get $(\log n)(\log\log n)$. On the right, we get $K\log n$.
If $n$ is large enough, $\log\log n\gt K$. But $\log\log n$ grows glacially slowly, so we don't miss polynomialness by much. The behaviour is often called sub-exponential. For any $\epsilon \gt 0$, in the long run $n^{\log\log n}$ grows more slowly than $e^{n^\epsilon}$.
Answer: Well, taking the logarithm gives $\log \log n \cdot \log n$.  This is sub-polynomial, so $n^{\log \log n}$ is sub-exponential.

Is $n^{\log \log n}$ polynomial in $n$?


can I use UF B cable to wire a dryer?

Question: Can UFB cable be used for wiring my dryer?  Normally I'd just run some NM able, but I found a good deal on 8 AWG UF B and wonder if this is code compliant (NEC 17) or not....or maybe there is another unforeseen problem.
Comment: Finding a "good deal" on 8 ga uf is unusual, but if so great for you.   Is it 8/3 with ground? For many years now, dryer circuits require a 4 wire feed:  2 hots, a neutral and a ground.  In the past 3 wire feeds were normal, but not now.   Also, you may have some trouble getting 8 ga wire into a 30 amp breaker.
Comment: As long as it's 10 ga, you should be fine. I'm not posting this as an answer bc I'm not sure. You mentioned THHN which would go in conduit. Are you running conduit?  Normally NM cable in most areas would suffice.   UF would be hard to pull thru conduit and is a PITA to work with, but as long as you pay attention to fill capacity of conduit, I think it's code legal. Wire pricing is very weird right now. Another recent post mentioned UF being cheaper than NM, which makes little sense, other than it's strictly market based pricing.
Comment: @George Anderson Good point.  I'm upgrading from 8/2 to 8/3 and we have a 40A breaker.  Even if I don't use it for the dryer 8 gage at $0.62/ft is too good to pass up.
Comment: @George Anderson It's actually 8 gage, so bonus for me!  Sorry, my brain hasn't kicked on yet today.  I'd normally rum NM or THHN if I have conduit.  No conduit here...I'll update the question.
Comment: Thanks George.  I'm at the store and don't have access to my NEC.
Comment: It would be overkill and no fun, but if you enjoy a challenge go for it! NEC says it has to be installed  according to the rules for NM, and isn't limited to the 60°C amperage limits when installed as NM.
Answer: Presumably the dryer receptacle will be a NEMA 14-30.  Since it is a 30A receptacle, you will be required to use a 30A breaker.  NEC 210.21(B).
Remember for wires any larger than this, aluminum wire is your friend.  Even in today's market, 4-wire #2 aluminum feeder (90A) is only $1.40/foot.  You either select sockets rated for aluminum wire... or go to a main-lug subpanel (which is definitely rated for aluminum; the lugs are aluminum).
Answer: Yes, this is fine as long as it's 8/3
UF is permitted anywhere where NM can be used, in addition to its more traditional uses outside/underground, and an 8AWG wire certainly has enough "grunt" to carry a 30A dryer circuit, so as long as this is an 8/3 W/G UF cable you're talking about, then you're good to go.
Answer: UF is used the same as NM because it is NM but the nonmetallic cover is heavier and there is not paper that could wick water so yes you can use UF to wire the dryer. As others have suggested you need 4 wire and depending on the code version in use for your jurisdiction possibly a GFCI breaker.

can I use UF B cable to wire a dryer?


What do I enter as the server and delegate URLs for using delegation with my Stack Exchange OpenID?

Question: I've been using OpenID delegation with MyOpenID.  I want to do the same with a Stack Exchange OpenID, but I'm not sure what to enter as the server and delegate URLs.  Can someone tell me?
Answer: We've added an easier way to get at the data needed for OpenID delegation.
First, go to the Open ID site for Stack Exchange:
https://openid.stackexchange.com/
And login.  From there, you'll be taken to your profile page.  It's also available via the "Profile" button at the top:

The "Use your own URL to log in" link is present below profile information.  Click it and you'll be presented with the markup to place in the  section of the HTML page served up by your URL:
Comment: Is there a way to use delegation via a DNS entry rather than the HTML method? I don't have hosting for the domain I want to use..
Comment: Apparently, this account is independent from regular profiles you may have at sites from the network such as Stack Overflow. You can just click on "Register" and create a new account. You'll still be able to use your delegated URL to log into your existing Stack Overflow account.
Answer: If I remember correctly, delegation is a way to let your SE id be used in place for other openId. You have some délégation example on sourceforge.net to be able to use sf.net as openid for your Google openid or other.
At the moment I did not see anywhere in the SE openid interface any implementation of delegation. But maybe I'm wrong. By the way the service was beta some days ago, so it must satisfy only few functionalities.
Comment: [Well, actually,](http://tirania.org/blog/archive/2011/Feb-17.html) delegation is a way to let you use a custom URL in place of the OpenID provider's URL.  You can then enter that custom URL wherever an OpenID is required.  Should you later wish to change OpenID providers, you only have to edit your delegate rather than having to enter the new provider's URL into all of those sites.
Comment: No the fact is you can't use a custom URL. You can use a provider's URL to mask other providers URL. This is understandable since a site should be able to request someone with the URL. Then you can allow this someone to act as another openid you have. But indeed the function has to be implemented. And I think it's not.
Comment: See [Using Your Own URL as Your OpenID](http://blog.stackoverflow.com/2009/01/using-your-own-url-as-your-openid/).


Lippmann-Schwinger Equation the need for $i\varepsilon$

Question: The Lippmann-Schwinger equation is often solved by the addition of the factor $i\newcommand{\p}[2]{\frac{\partial #1}{\partial #2}} \newcommand{\f}[2]{\frac{ #1}{ #2}} \newcommand{\l}[0]{\left(} \newcommand{\r}[0]{\right)} \newcommand{\mean}[1]{\langle #1 \rangle}\newcommand{\e}[0]{\varepsilon} \newcommand{\ket}[1]{\left|#1\right>} \newcommand{\bra}[1]{\left< #1\right|}\e$ such that we have:
$$\ket{\psi}=\ket{p}+\f{V}{E-H_0\pm i\e}\ket{\psi}$$
which produces a Green's function of the form (in the 1d case):
$$G_\pm=\bra{x}\f{1}{E-H_o\pm i\e}\ket{x'}$$
This is a pain to solve, requiring contour integration. It is much simpler to just solve the equation:
$$(H_0-E)G=\delta(x-x')$$
which defines $G$ with the appropriate boundary conditions on $G$. This latter method does not involve the introduction of any factors of $\e$, but I have never seen it done like this. Why not? is this method in someway wrong?
Comment: the $\epsilon$ is what fixes our in and out scattering states.  See Chapter 6.1 in Sakurai for a full derivation.
Answer: Actually, one has to introduce $\epsilon$ in the latter method as well, while solving the equation on the Green's function. There are may be many methods to solve it, but in the simplest one, which includes Fourier transformation, one has to integrate over the real axis on which there are poles of the integrand, so one is forced to deform a contour. There is a few ways to do it, and the choice influences the boundary condition for the equation. The simplest cases are ingoing and outgoing wave conditions which require introducing $\epsilon$ in precisely the way you cited.
Comment: I can see how it may come in when using the Fourier method, but I cannot see how it comes in if we first solve $(H_0-E)G=0$ then apply boundary conditions (i.e. continuity of $G$ and discontinuity of $G'$ defined by $\delta$) at $x=x'$. Any ideas?
Comment: @Quantumspaghettification You must be talking about 1D case. Are you sure that in this case the LS equation has the same form? What I was talking about is D>1 case, where $\delta$-function leads to a singular behavior near the origin $r=0$, not to the jump of the first derivative on the $x$ axis.
Comment: I was talking about the 1D case, also the LS equation is of (nearly) the same form. But even for $D>1$, you would just get a jump in the derivative $G'(r-r')$ at $r=r'$?
Comment: @Quantumspaghettification There is no jump in $D>1$, because $r \geq 0$. There is just a singularity analogous to the point charge solution of Poisson equation.


What is the advantage of probability algorithm?

Question: What is the advantage of probability algorithm? e.g. Las Vegas. I would also like to know some applications of the randomized algorithms. Are there any recommendable courses or books?
Comment: [Book](https://dl.acm.org/doi/book/10.5555/2523343) by Motwani and Raghavan.
Comment: Randomization is like a middle point between being totally non-deterministic and being deterministic. So essentially, adding probability to algorithms is believed to allow us to solve things faster (it definitely wont make anything slower)
Answer: What is advantage of probability algorithm (we usually use randomized algorithm instead of probability algorithm)? Well this is a big question, e.g. we don't know if $P = BPP$, if so then we would say that deterministic algorithm is the same as randomized algorithm. If not, i.e. $P \ne BPP$ then randomized algorithm gives us more power than deterministic algorithm. I think randomized algorithm can give us some polynomial speed up but I'm not sure if it can give us an exponential speed up over deterministic.
Note that P is the class of all problems that can be done by efficient algorithm (i.e. polynomial algorithm in the size of the input) while BPP stands for Bounded-error Probabilistic Polynomial time, i.e. it contains all problems that have a non-deterministic TM with at least 1/2 of the branches accepts and less than 1/3 of the branches rejects.
A quick example of a randomized algorithm is verifying polynomial identities, e.g. given (x+2)(x-4)(x+22)(x-43)(x+11) = x^5-2x+4. The question is: Can you verify that the right-hand side is equal to the left hand side? One way to do is to multiply all terms together which takes O(n^2) where n is the number of terms. But we can do it in O(n) time by selecting some random number and text whether they are equal or not. Yes, there is a probability of wrong answer, but with many run of the algorithm (say 100) if there is at least one counterexample, then this is enough.
There are two major textbooks in randomized algorithm which are:

Probability and Computing - Randomized Algorithms and Probabilistic Analysis by Michael Mitzenmacher and Eli Upfal

Randomized Algorithm By Rajeev Motwani and Prabhakar Raghavan

I recommend the first since it is easier and have one or more examples in each chapters while the second is good if you are interested in randomized complexity.


Timing of ability when Control Minion used

Question: When the Geeks use "Control Minion" on a played minion (a Shoggoth in the case in question), who gets the benefit of making other players draw Madness or destroy a minion?
Answer: The controller steals the effect.
As long as you play Control Minion according to its special, the controller uses the minion's entry effect. Otherwise, the card would say "Special: Play after another player plays a minion."
The game uses "after" a minion is played to clarify that its entry effects occur first (such as with the Leprechaun). That wording isn't used here.


My vagrant instant is not working

Question: Got this error while running vagrant up:

There was an error while executing VBoxManage, a CLI used by Vagrant
  for controlling VirtualBox. The command and stderr is shown below.
  Command: ["startvm", "df5a654c-fa01-499a-ac48-e4161821edc7", "--type", "headless"]
  Stderr: VBoxManage: error: VT-x is disabled in the BIOS for all CPU modes (VERR_VMX_MSR_ALL_VMX_DISABLED)
  VBoxManage: error: Details: code NS_ERROR_FAILURE (0x80004005), component ConsoleWrap, interface IConsole

Can someone help me with this ? Vagrantfile is already ready.
Answer: Seems the question has already been answered here:
Error: VT-x is disabled in the BIOS for all CPU modes (VERR_VMX_MSR_ALL_VMX_DISABLED)
Here is also a youtube link for the fix: https://youtu.be/ERnKeUMEFXU
Answer: go to cmd--->Type the command-->Systeminfo.exe-->Hyper-V Requirements:      VM Monitor Mode Extensions: Yes
Virtualization Enabled In Firmware: No
Second Level Address Translation: Yes
Data Execution Prevention Available: Yes
if this is no
Goto Settings-->Update&Security-->Recovery-->Advanced Restart-->Troubleshoot-->Advanced
-->UEFI firmware--->System Configuartion---Enable virtualization---Save and Exit.

My vagrant instant is not working


python: key combinations such óíúéáöïò with pyhook

Question: I'm learning about pyhook as keylogger and coding some examples.
I dont know how to log key sequences like óíúö because the result thats something like this -> ´´i´´o
anyone knows how to solve this issue ?
thx you.
Answer: I have an example on my site that allows you to see a lot of the information that pyHook provides.  http://fadedbluesky.com/2011/using-pyhook-to-block-windows-key/
Perhaps it can help you find the ScanCode for the key you want.


How to get xml request and xml response from netbeans client to ws

Question: I have created web-service client to the existing service in netbeans, and ide makes all in oop style correctly, but I need to log xml request and response to and from service, how to log these information?
Comment: Which stack of web services you are using? Is it JAX-WS, CXF....? How are exposing your web service endpoint?
Comment: I use jax-ws, web-service is deployed on glassfish
Comment: Netbeans generate all code, and I do not know how to get xml data
Answer: For the purpose of logging the request and response of your web service, you need to create your custom soap handler for JAX-WS which implements SOAPHandler<SOAPMessageContext> interface.
The method to do anything you like with a message is handleMessage(SAOPMessageContext messageContext). From the message context you will be able to get the SOAP message and log it.
See my post here how to implement SOAP handler interface and override handleMessage method for the specific requirements.
This post leads to what you are trying to achieve.
Take a look at this article. It might be helpful as well. If you are not able to set up your handler, come back with more specific problem.


Energy Density is expressed in Liters, Liters of What?

Question: When looking at energy density of batteries it is often expressed as Wh/L. For instance, Wikipedia says Lithium Ion batteries have a density of 250–693 W·h/L. Liters is supposed to express the volume but the volume depends on the density of the substance. So liters of what? Water?
Comment: "The volume depends on the density of the substance." This might be where the misunderstanding is coming from
Answer: Volume is volume. A (large) battery that is a cube 10 cm on a side has a volume of 1 liter regardless of what it is made of, or what density it has.
Answer: I think you are getting confused by the word "density".
The actual use of "density" refers to any quantity measured relative to a unit volume.  What we often call "density" actually means mass density, or mass per unit volume.  That is likely why you are associating mass with density.
When they say "energy density" though, they are referring to energy per unit volume; and it isn't really related to mass density; besides that they are both quantities expressed per unit volume.
Answer: A liter is simply a unit of volume equal to 1000 cm$^3$. It could be a volume of anything (air, water, a solid). Technology is trying to pack more energy into a smaller volume of a battery to save space.
Hope this helps.
Answer: To answer your question directly, the energy density is expressed in liters of battery.
Lithium Ion batteries have a density of 250–693 W·h/L of battery.


How do I access the ith column of a NumPy multidimensional array?

Question: Given:
test = np.array([[1, 2], [3, 4], [5, 6]])

test[i] gives the ith row (e.g. [1, 2]). How do I access the ith column? (e.g. [1, 3, 5]). Also, would this be an expensive operation?
Answer: With:
test = np.array([[1, 2], [3, 4], [5, 6]])

To access column 0:
>>> test[:, 0]
array([1, 3, 5])

To access row 0:
>>> test[0, :]
array([1, 2])

This is covered in Section 1.4 (Indexing) of the NumPy reference.  This is quick, at least in my experience.  It's certainly much quicker than accessing each element in a loop.
Comment: This create a copy, is it possible to get reference, like I get a reference to a column, any change in this reference is reflected in the original array.
Comment: More helpful section of the docs: [Dimensional indexing tools](https://numpy.org/doc/stable/user/basics.indexing.html#dimensional-indexing-tools)
Answer: >>> test[:,0]
array([1, 3, 5])

this command gives you a row vector, if you just want to loop over it, it's fine, but if you want to hstack with some other array with dimension 3xN, you will have

ValueError: all the input arrays must have same number of dimensions

while
>>> test[:,[0]]
array([[1],
       [3],
       [5]])

gives you a column vector, so that you can do concatenate or hstack operation.
e.g.
>>> np.hstack((test, test[:,[0]]))
array([[1, 2, 1],
       [3, 4, 3],
       [5, 6, 5]])

Answer: And if you want to access more than one column at a time you could do:
>>> test = np.arange(9).reshape((3,3))
>>> test
array([[0, 1, 2],
       [3, 4, 5],
       [6, 7, 8]])
>>> test[:,[0,2]]
array([[0, 2],
       [3, 5],
       [6, 8]])

Comment: `test[:,[0,2]]` just accesses the data, e.g, `test[:, [0,2]] = something` would modify test, and not create another array. But `copy_test = test[:, [0,2]]` does in fact create a copy as you say.
Answer: You could also transpose and return a row:
In [4]: test.T[0]
Out[4]: array([1, 3, 5])

Answer: Although the question has been answered, let me mention some nuances.
Let's say you are interested in the first column of the array
arr = numpy.array([[1, 2],
                   [3, 4],
                   [5, 6]])

As you already know from other answers, to get it in the form of "row vector" (array of shape (3,)), you use slicing:
arr_col1_view = arr[:, 1]         # creates a view of the 1st column of the arr
arr_col1_copy = arr[:, 1].copy()  # creates a copy of the 1st column of the arr

To check if an array is a view or a copy of another array you can do the following:
arr_col1_view.base is arr  # True
arr_col1_copy.base is arr  # False

see ndarray.base.
Besides the obvious difference between the two (modifying arr_col1_view will affect the arr), the number of byte-steps for traversing each of them is different:
arr_col1_view.strides[0]  # 8 bytes
arr_col1_copy.strides[0]  # 4 bytes

see strides and this answer.
Why is this important? Imagine that you have a very big array A instead of the arr:
A = np.random.randint(2, size=(10000, 10000), dtype='int32')
A_col1_view = A[:, 1]
A_col1_copy = A[:, 1].copy()

and you want to compute the sum of all the elements of the first column, i.e. A_col1_view.sum() or A_col1_copy.sum(). Using the copied version is much faster:
%timeit A_col1_view.sum()  # ~248 µs
%timeit A_col1_copy.sum()  # ~12.8 µs

This is due to the different number of strides mentioned before:
A_col1_view.strides[0]  # 40000 bytes
A_col1_copy.strides[0]  # 4 bytes

Although it might seem that using column copies is better, it is not always true for the reason that making a copy takes time too and uses more memory (in this case it took me approx. 200 µs to create the A_col1_copy). However if we needed the copy in the first place, or we need to do many different operations on a specific column of the array and we are ok with sacrificing memory for speed, then making a copy is the way to go.
In the case we are interested in working mostly with columns, it could be a good idea to create our array in column-major ('F') order instead of the row-major ('C') order (which is the default), and then do the slicing as before to get a column without copying it:
A = np.asfortranarray(A)   # or np.array(A, order='F')
A_col1_view = A[:, 1]
A_col1_view.strides[0]     # 4 bytes

%timeit A_col1_view.sum()  # ~12.6 µs vs ~248 µs

Now, performing the sum operation (or any other) on a column-view is as fast as performing it on a column copy.
Finally let me note that transposing an array and using row-slicing is the same as using the column-slicing on the original array, because transposing is done by just swapping the shape and the strides of the original array.
A[:, 1].strides[0]    # 40000 bytes
A.T[1, :].strides[0]  # 40000 bytes

Answer: To get several and indepent columns, just:
> test[:,[0,2]]

you will get colums 0 and 2
Comment: How is this any different from Akavall's [answer](https://stackoverflow.com/a/16121210/369450)?
Answer: >>> test
array([[0, 1, 2, 3, 4],
       [5, 6, 7, 8, 9]])

>>> ncol = test.shape[1]
>>> ncol
5L

Then you can select the 2nd - 4th column this way:
>>> test[0:, 1:(ncol - 1)]
array([[1, 2, 3],
       [6, 7, 8]])

Answer: This is not multidimensional. It is 2 dimensional array. where you want to access the columns you wish.
test = numpy.array([[1, 2], [3, 4], [5, 6]])
test[:, a:b]  # you can provide index in place of a and b

Comment: `2` is a 'multi'.  `multidimensional` is not limited to 3 or 4 or more.  The base array class in `numpy` is `ndarray`, where the `n` stands for any number from 0 up.  2 dimensional is not a special case, except that it fits our intuitions about rows and columns the best.
Answer: This question has been answered but a note on view vs copy.
If the array is indexed using a scalar (regular indexing), the result is a view (x below) which means whatever change made to x will reflect on test because x is just a different view of test.
test = np.array([[1, 2], [3, 4], [5, 6]])
# select second column
x = test[:, 1]
x[:] = 100        # <---- this does affects test

test
array([[  1, 100],
       [  3, 100],
       [  5, 100]])

However, if the array is indexed using a list/array-like (advanced indexing), the result is a copy, which means any changes to x will not affect test.
test = np.array([[1, 2], [3, 4], [5, 6]])
# select second column
x = test[:, [1]]
x[:] = 100        # <---- this does not affect test

test
array([[1, 2],
       [3, 4],
       [5, 6]])

In general, using a slice to index will return a view:
test = np.array([[1, 2], [3, 4], [5, 6]])
x = test[:, :2]
x[:] = 100

test
array([[100, 100],
       [100, 100],
       [100, 100]])

but using an array to index will return a copy:
test = np.array([[1, 2], [3, 4], [5, 6]])
x = test[:, np.r_[:2]]
x[:] = 100

test
array([[1, 2],
       [3, 4],
       [5, 6]])

Regular indexing is extremely fast and advanced indexing is much slower (that said, it's still almost instantaneous and it certainly will not be a bottleneck in the program).
Answer: I just want to clarify harmand's comment under mtrw's highest score answer is confusing. He says:

This create a copy, is it possible to get reference, like I get a reference to a column, any change in this reference is reflected in the original array.

While actually this code
import numpy as np

arr = np.array([[1, 2], [3, 4], [5, 6]])

barr = arr[:, 1]

print(barr)

barr[1] = 8

print(arr)

prints out
[[1 2]
 [3 8]
 [5 6]]

I would appreciate if you note this in the comments under mtrw's answer as my reputation is too low yet.


Need help installing CiviCRM on backdrop CMS

Question: I'm starting a social work, family help and education center in Germany (empathus-erziehungshilfen.de). I would love to work with CiviCRM to document cases and spent time for me and my employees. I tried to install backdrop CMS (as well as WP and Drupal) but I couldn't really get it to work properly. Everything within CiviCRM I can do on my own, it's only a proper installation and initial setup for CiviCRM to work as it should. I am searching for a good-hearted CiviCRM pro who would help me install it. I'll provide the SFTP login and everything that's needed. We are a non-profit organization and I don't have much money to spend but I could afford $50 for your help.
Answer: Welcome to SE!
Have you looked at CiviCRM Spark?  Just sign up and start using it.
Alternatively you can find a list of partners in Germany or globally who undertake paid work on CiviCRM.
Also, just checking you have found the installation guide


How does the "Index Of Nearest" node work in blender 3.6?

Question: How does the "Index Of Nearest" node work in blender 3.6?
Comment: Usually we are focusing on officially released versions here, since the main goal of this site is to help with issues which is pointless if the problem exists in alpha or beta builds of Blender which might be subject to change before they are released. This might not be the case here, but even simple things like the inputs you listed here might be different when 3.6 is finally released. Apart from that, as Harry already pointed out, please put the answer in the answers section, don't enclose it in the question. Users looking for this question will only see it as unanswered in the list.
Comment: Hello and welcome. Thank you for sharing. Can you kindly separate the answer part from the question? Post the answer as a separate answer post.
Comment: @SpicyMelon.. when (and if) you split the answer portion out, can you include a link to documentation / the version you're talking about? I can't find this node.
Comment: Ah ok I see, thank you for your feedback everyone. I had no idea! So I fixed HarryMcKenzie request and also RobinBetts request.
As for GordonBrinkmann comment, that makes sense, yes thank you. I didn't realized this was only for main builds but that makes sense. Should I let this post stay? Or remove it until it comes out officially? Could be a long time though.
Answer: I have been searching for an answer to this for a while but fortunately I have figured out how it works and thought it would be nice to put it out there for others if they have the same question.

The Index of Nearest node is a vector math node in Blender's Geometry Nodes editor that allows you to find the index of the nearest point or vertex within a specified group or category. The node is available in Blender version 3.6 for the specialized PR104619 build.
You can find it here: https://builder.blender.org/download/patch/blender-3.6.0-alpha+main-PR104619.3edcc6a4a83a-windows.amd64-release.zip
The node takes three inputs:
'Position' defines the vector in space that the distance calculation will use,
'Self Group ID' defines the group or category that each point belongs to, while
'Group ID to Search' specifies the group or category to search for the nearest point.
The node outputs the index of the nearest point within the specified group or category. If 'Group ID to Search' and 'Self Group ID' are the same, the node will exclude the current point from the search results.
This node can be useful in various applications, such as creating particle effects, controlling the behavior of simulations, and generating procedural geometry."

Pointed out by Mod Nop:

First, the positions are split into groups based on their Self Group ID.
For each group, a separate KDTree is built.
If no Self Group ID is provided, all positions are put into the same KDTree.
When searching for the nearest node, a Search ID is used to specify which KDTree to search through.
If no Search ID is provided, the same KDTree that the position is in will be searched.
The KDTree is built by recursively partitioning the positions based on their coordinates.
The KDTree is then used to efficiently search for the nearest node to a given position.
The search can be either within the same group or any other group, depending on the specified Search ID.
Answer: Foreword:
Index of Nearest node isn't accepted yet. So you cannot find this node in 3.6 builds. But you can find this node in specialized build of PR.
Answer. Technically Index of Nearest node build KDTree for eaht positions. After that each position lookup nearest other one. Groups used for:

Splitting positions during KDTree building in multiple different KDTree.
Splitting positions for lookup nearest one. If second one socket (Group ID to Search) isn't connected, this group is the same as first one.

As a result, the search can be either within the same group or any other group.
More about what KDTree is: https://en.wikipedia.org/wiki/K-d_tree
Comment: So let me see if I understand you.
Each point is put into a KDTree based on the Self Group ID. If no ID is provided then they are all put into the same KDTree. Then for the Search ID, this is telling which KDTree to search through to find the nearest point in that KDTree. And if this search ID isn't provided then it searches the same KDTree that its in?

I will add to my answer with this information! Let me know if I get it wrong!
Comment: Actually, it's really not that clean and it can be changed. I found this description:
Imagine that the vertex is in school. The first input says which classroom she will be in. The second talks about which classroom to look for a friend in.


Can I reset my game in Genocide In Undertale?

Question: I have done a pacifist run and a couple of neutral runs, but now I'm doing genocide. But I'm only in Snowdin and I feel bad. Can I reset, and how?
Answer: But the game is all about Genocide runs. To make you feel bad about destroying the world, and to show you that some actions have pretty heavy consequences.
There are some methods on the internet that involve manipulating save files or deliberately corrupting save files to fool Steam Cloud sync broken saves. It will also depend on what version you own (GOG, Steam, DRM-Free...). Reinstalling the game and disabling cloud sync(by playing offline) could be an option.
It is also a complicated topic cause that is what this game is about: Showing that not everything in life can be "undone". That is the LESSON!
Comment: I'd just point out that the OP has NOT finished the Genocide run yet (according to the question), so shouldn't it be as simple as resetting from the title screen in this specific case?
Comment: I thought that true reset worked, but now that I have finished a pacifist run, WOW SO CREEPY
Answer: Since the question didn't mention actually finishing the genocide run you are able to reset and stop at any time. You may get a few strange bits of dialog when you reset but since you haven't completed the genocide run through to completion you are free to reset and still have the non-genocide pacific endings.
As long as you do not complete the final cutscene in the game you are able to reset at anytime without your game becoming corrupt from the genocide run.
Answer: If you want to restart fresh without a genocide then follow these steps.
Windows Users:

Exit Steam
Go to the folder "C:\Program Files (x86)\Steam\userdata*Whatever number your user ID is*\391540\remote"
Open "system_information_962" or "system_information_963" in "Notepad", delete everything in it, save and quit.
Delete "remotecache.vdf" from the "391540" folder
Start up Steam and Undertale. If a "Cloud Sync Conflict" window appears, you've done everything right so far.
While the "Cloud Sync Conflict" window is open, delete everything in the 391540 folder.
Click "Upload to the Steam Cloud" in the "Cloud Sync Conflict" Window. This will automatically start Undertale.
While Undertale is open, go into Steam right click on the Undertale application and go to "Properties".
Go to the "Updates" tab and uncheck "Enable Steam Cloud synchronization for Undertale".
Exit Undertale and Steam.
Delete the "391540" Folder. Now, the tainted files are removed from your steam cloud, but there's one more file to delete.
Open the start menu and type "Run" into the search bar and open "Run".
Type "%appdata%" into Run and hit enter. This open the "Roaming" folder in "Appdata"
Back out of "Roaming" into the Appdata folder, then open the "Local" folder.
Find and open the "Undertale" folder and delete "system_information_962" or "system_information_963" from that folder.
Open up Steam and Undertale and the game will have completely reset!

Mac users:

Go to go to folder and type ~/Library/Application Support/Steam in the box
Userdata and you see some numbers, click on it, its different for everybody
Then click on 391540
Then click on remote
Then open system information 962 with TextEdit and delete everything in it
Delete remotecache.vdf
Open Steam and Undertale And if you did right you will see Steam cloud open keep steam cloud open
Delete Remote and remotecache.vdf
Click on upload to the steam cloud
In steam, right click Undertale click on properties Click on updates and disable steam cloud
Close out of steam
Delete 391540
Go to go to folder And type ~/Library/Application Support/com.tobyfox.undertale/ in the box
Delete system information 962 and if you see it delete system information 963
Enable steam cloud
Answer: You don't have to do anything to reset genocide run than patiently waiting.
Comment: Could you clarify? You can simply wait in order to reset?
Comment: Unfortunately, this doesn't answers seem to add anything that the current answers didn't.
Comment: Could be fleshed out a bit. This answer seems to deal with the case where you have actually completed genocide (beaten Sans), rebooted the game, and it now gives you a black screen with a howling wind sound, and you want to play anew, not necessarily restore to pristine state. Waiting for ~10 minutes 'restores' the game if you make a deal (although there may be some permanent *nasty surprises*, see @user65252's answer.).