Is there any book , Tutorial on very very advanced shell scripting

Question: I am looking for some tutorial where a simple script is written using very advanced methods so that i can learn more from
Comment: "A **simple** script written using **very advanced** methods" does not sound very probable to me...
Comment: ha ha Don't get me wrong , i mean to say i want to know advanced method writing
Comment: of course, I got what you meant, it just sounded a bit strange! ;)
Comment: The book "object oriented shell programming" is a good entry to higher level advanced shell programming
Answer: Once you've graduated from the Advanced Bash-Scripting Guide, I'd suggest the much more useful Greg's Wiki (especially the Pitfalls article). It's the single most useful Bash resource out there (please someone prove me wrong), and significantly, is an active (and actively moderated) wiki with even anonymous editing.
As for simple scripts using advanced methods, it's difficult to judge what would be advanced for you. One of my own most advanced scripts was one find and loop over all files matching a user-provided path, in such a way that it would be impossible to craft a search string or filename to break the code or perform some sort of code injection (Unfortunately Bash gets really complicated if you want to use it securely). The script was documented to explain the reasoning behind all the non-trivial syntax, so it might have some learning potential. YMMV.
Comment: +1 I can only second this. I've read tons of resources and books about Bash scripting but Greg's Wiki is by far the best resource I've found. Not only does it teach you Bash - the scripting language (in contrast to Bash - the glue language) it also goes into detail concerning pitfalls and portability considerations.
Comment: @JosephGarvin: I'd say so, but I wouldn't *recommend* it if you want security. It's [fiendishly difficult](http://www.dwheeler.com/essays/fixing-unix-linux-filenames.html) to do even stuff like file name handling properly.
Comment: thanks for that , but do i have to read all 8oo pages for advanced bash scripting guide , its too much
Comment: It's *possible* to use bash securely? :P
Answer: Rather than a book or tutorial, you might want to look at some of the init scripts that start up your machine. Understanding these will give you a good grounding in bash scripting and provide you with a lot more insight into how your machine runs -- and what you can do when it doesn't...
You can read a general overview of the whole process in this article, From Power Up to Bash Prompt.
Comment: Yes. Init is a wonderful place to learn. Thank you.
Answer: Not sure what very advanced methods would be, but I have the 'Expert Shell Scripting' by Ron Peters (available about anywhere). I'm happy with it :-).
Answer: I've had good experience with bash Cookbook: Solutions and Examples for bash Users from O'Reilly. It has got the solutions to actual problems/situations that I have needed to resolve. All the recipes come with a discussion on why it was done this way; and many also has ways it could have been done differently. Case-by-case learning.
Pretty cheap as an ebook.


My Screen Saver is awry & need help

Question: I have an iMac 21.5" 2.5 GHz Intel Core i5 Macintosh HD - Yosemite. My Screen Saver comes up with foreign words and gobbledygook that I don't understand.  Went into  Finder/library/Screen Savers (this is what is in my Applications) to see what I could do but there is nothing in this folder.  This looks bogus to me. Do you agree and what should I do?
Answer: Screensavers were developed do deal with issues that affected CRT displays. As nobody makes them anymore, and LCD displays don't have the same issues, we no longer need screensavers. A screensaver running on a flat screen monitor just looks pretty - there is no difference to the operation.
Open System Preferences.
Go to Desktop -> Screen Saver and set the "Start after:" value to Never.
Go to Energy Saver and set "Turn display off..." to whatever value you want.
This actually powers down the screen illumination and most of the GPU.
Comment: Up vote for the CRT reference!  Yep, just eye candy.  Legacy stuff.
Comment: CRTs are still made, and burn-in is still an issue with some non-CRT monitors.
Comment: @tubedogg CRTs are still made, but not for computer monitors. Apple (and pretty much every other domestic computer manufacturer) hasn't sold a CRT in 10 years. The burn-in issue apples to things like plasma displays, also not commonly found on Apple products.
Answer: To change your Screen Saver go to
<code>  > System Preferences... > Desktop & Screen Saver...
</code>

From there you can set the screen saver settings.  I suspect from your question (although it is not clear) that you have the Word of the Day screen saver selected.  You can check it's settings or change the screen saver all together.

My Screen Saver is awry & need help


At what size do objects burn up in the atmosphere when falling from orbit?

Question: As the title suggests, I am wondering the maximum size an object can be so that it will completely burn up when entering and falling through Earth's atmosphere. I'm focusing on man made objects, not asteroids or meteors. Also, how much does the make-up of the object affect its burn rate? I.e. metal vs plastic vs glass, and so on.
Thanks!
Comment: By burn, do you mean react with oxygen and turn into oxides, or get hot enough to melt/vaporize by friction with the atmosphere? The distinction will get you different answers.
Comment: I would gladly answer but it does not only depend on size, it also depends on the speed at which the object enters the atmosphere. A bigger object will have to enter faster to be disintegrated. So it's all about that ratio.
Comment: @Wayfaring Stranger: I'm pretty confident (though not 100% sure) that objects don't melt/vaporize due to friction. Densities are just too low for that. It's rather the heating up of the gas due to the rapid compression from the shockwave, when the object falls through the atmosphere
Answer: The Earth atmosphere protects us from small impacts from both asteroids and man made objects. This is well known from meteoroids, where meteoroids as large as a few tens of meters in diameter usually fail to penetrate into the lower atmosphere because they get fragmented and dispersed at high altitude. Fragmentation height depends mainly on the meteoroid strength, only strongest irons reach the surface in one piece.
We could extrapolate from meteoroids to man made objects that even large do not have the same physical strength than a massive meteoroid body. This means than nearly all man machine objects will disintegrate before reaching earth. Heavy metallic ones (iron) will disintegrate at lower altitudes than lighter ones such glass and plastic.
Two comments:

This is not true for objects not having reached orbit, e.g. rocket 1st or 2nd stage engines will fall without disintegrating.
Even if they disintegrate, nuclear powered satellites will cause some level of radioactive pollution, however widely scattered in the atmosphere.

Although the risk to human beings walking on earth is next to nil, there is a real risk of impact from man made objects littering Earth orbits to other spatial vehicles.
Reference: "The Impact Hazard", David Morrison, Clark R. Chapman and Paul Slovic, in "Hazards due to Comets and Asteroids", T. Gehrels, Ed., 1994, The University of Arizona Press


What is the best way to ship cards?

Question: I have about 25 cards I want to sell on Star City Games buy list. What would be the best way to ship them? I need them to arrive in the same order I sent them.
Comment: I feel "best" is going to depend a lot on what you're actually shipping; you should probably take a lot more care with a Black Lotus than you would with a few $10 cards.
Comment: Does this answer your question? [How should I ship cards?](https://boardgames.stackexchange.com/questions/45165/how-should-i-ship-cards)
Answer: Star City Games provides shipping guidelines/recommendations.

Packaging Guidelines

Following these guidelines will help ensure your collection arrives safely and your Sell List Request or Ship + Sell will be processed efficiently.

Remove all cards from binders, top-loaders, and sleeves (standard-style or inner sleeves, including side-loading or sealable).

Keep all cards facing the same way, in the same orientation (for example: all facing forward and right-side-up).

For Sell List Requests, put the cards in the same order as they are listed on the approved Sell List Request. This will be in the order in which you have entered your cards.

Failure to adhere to the above guidelines may result in processing time delays, a penalty of up to 5% off the final total, or our declining of the sale outright.

Ensure that all items are packaged safely and securely by packing cards using supplies such as bubble wrap, packing paper, or another flexible material to fill space.

Do not use regular envelopes, as these are sorted by machines at the Post Office and can result in damage.
Some packaging container suggestions that work well for Magic cards include:
Plastic card cases
Deck boxes
Fat Pack/Bundle boxes
Snap cases
Rowed card storage boxes
Cardboard trading card boxes
Plastic bags, rubber bands, or packaging materials with rough surfaces will damage cards. Top-loaders are not recommended due to damaging cards if bent in any way.

Send your cards or collection to us. Please use the correct mailing address based on your sale request method.

There will likely be other good answer based on personal experience, but this is a good minimum starting place.

What is the best way to ship cards?


Simulation of Feynman path integral in literature

Question: Can someone provide me a numerical simulation of Feynman path integral? Where the contribution of each path is added individually so that I can understand how much do the paths outside the light cone actually contribute and how they actually interfere destructively with each other?
Comment: You might be interested in Quantum Monte Carlo techniques, specifically Markov Chain Monte Carlo.  You don't sum over each path but you do a bunch of sampling techniques that make your life a lot easier and the computation far less intense.
Answer: There are an uncountably infinite number of paths, because spacetime is continuous, so direct computation of the path integral is impossible without some discretization, outside of some very special cases. You might want to look into lattice field theory, which is precisely the restriction of quantum field theory to a discrete spacetime lattice.
Answer: Instead of numerical simulations, consider to explore Feynman's checkerboard model for (massive) fermions in a discretized 1+1D spacetime. Much of the "sum over histories" of the FPI and the causal structure of the lightcone can be recovered from purely analytical considerations.


Relationship between Electrostatic Force and Circuit Layout / Dimensions

Question: Super basic question, but I'm struggling to figure out how to word this: In the usual scenario, current in an electrical circuit is induced by some voltage differential (maybe this last term is redundant).  The voltage is based on the various electrostatic forces, which are represented as a field.  The field doesn't have to stay within the boundaries of the circuit's wire (since it's a field), whereas typically, the current does (I know there are exceptions in cases of high voltage).  Does that mean that the layout of the circuit (ie how close the components/wire are placed from each other) could affect it's ability to operate as expected?  For example, could you reduce a working circuit to a really small size and find that two different wires are really close together, causing some sort of interaction based on the comingling electrostatic fields?  Could this effect inhibit the circuit's proper operation?  (Maybe you could inadvertently create something like a primitive capacitor?)  Is there a limit to how big/spread out you could make a given circuit?
Comment: Your suspicions are correct. Crosstalk and electrostatic (capacitive) coupling can cause big problems if the circuit layout isn't done correctly.
Comment: These effects are often contributing to EMI-noise, so yeah the layout greatly contributes to the total electrical characteristic of the system. Every trace carrying a time-varying signal can be thought of as an antenna emitting that frequency.
Answer: If you scale all dimensions down capacitance drops linearly with scaling: -

If d halves and the dimensions of the plates also halve, then A reduces by 4. Hence capacitance halves for a 2:1 rescaling.
It's a the same for stray inductive coupling too.
Comment: For a single layer PC boards the area is in essence the copper thickness times the trace length and d the distance between traces.  Scaling down will not change C.
Comment: @user1831847 the traces will get shorter end-to-end and this will reduce capacitance of course. What scenario do you envisage that I'm clearly not able to see (bearing in mind that the question, as currently posed, does not restrict answers to only considering PCBs)?
Comment: you are right, the PCB traces will get shorter but the distances d as well.  No change to C then.
Answer: I think the answers posted here are missing the main point of the question:
in short, the answer is no, that is, not as you think: the potential in the wires is not due to an electrostatic field in the surrounding space; this is because unlike electrostatic class exercises, the wires creates boundary conditions that restrict the electric field to be very weak in the vicinity of the wires: only the component parallel to the wire plays a role in the displacement of the electrons along the wire, so, by itself, the electric field causing the electron motion does not affect the other wires.
BUT
as pointed out in the previous answers, other effects are playing here: firstly, there is the capacitive effect between the wires and between the other components of the circuit: anything has a self capacitance, and two close wires have also a mutual capacitance. This often create capacitively coupled circuit, much like as if you had put a capacitor between the two wires.
Second, there are also magnetic effects: if your circuit contains a wire that forms a loop, then the current moving in the loop will create a strong magnetic field, that will induce currents in other wires. That is why it is important to avoid loop in circuits (and also because this forms a loop antenna that grasp electromagnetic waves). In fact, even a simple straight wire cause a magnetic field in the surrounding space.
Finally, there are electromagnetic emission effects, that become extremely annoying as frequencies increase. Every wire subject to an AC current of high frequency behaves like an antenna. And any other wire can receive this signal. Here, this is different from the electric field you spoke about in your question, and is related to EM wave theory. An EM wave is a combination of an electric field with a magnetic field propagating in a medium, due to the superposition of the oscillations of infinitesimal electric dipoles.
These subjects are a complicated matter, known as "electromagnetic noise" in the circuits (EMI noise). There are many things to do to reduce the noise (good circuit design, reducing the length of the wires, shielding etc).
The final point: more or less, as far as the frequencies inside your circuit are low, and as far as the circuit is not high precision, you have not to worry with EMI noise: even if your circuit is wired in an awful manner, it will probably work. For precision or high frequency circuits, this is no more true and you have to take EMI noise into account in your design.
Answer: Consider wire-over-plate capacitance: Schaums Outline provides formula:
$$Capacitance/meter = 2*pi*E0/ln(2*distance/wireradius)$$
Compare to the parallel-plate formula:
$$Capacitance/meter = E0*Er*PlateWidth/PlateSeparation$$
The wire-over-plate has capacitance decreasing as 1/ln(2*distance) whereas parallel-plate is 1/distance. [The Schaums Outline author warns his formula is not accurate when wire is very close to the plate.]

If you want to tinker with integrated-circuit distances (100micron distance between OpAmps, the IC metallization placed 1micron above "gnd" (nominally substrate), then download the free tool Signal Chain Explorer from the website robustcircuitdesign.com and build yourself a signalchain. Click on the Gargoyles (the magnetic and electric field aggressors), click "update" and watch the SNR change as you edit either (1) the Global Interconnections (click the topright "I/C" button, or (2) the individual TRACES between stages. To see the traces, ensure the topmiddle "Show Interconnects" is clicked. Down in the WIRING WIZARD, you can alter the nominal distances to be silicon-distances, or even sub-atomic.
Here is an example


One certain person can't hear me when I call.

Question: I have an iPhone SE and when I tried calling my
Boyfriend, he couldn't hear me. I called my
Mom to see if it would happen but she COULD hear me. I could hear him clearly. This has never happened before and we've called multiple times. Why can he specifically not hear me? He used his phone earlier and was able to hear other people. What should I do to fix this?
Comment: iPhone let you conference call three people. What happens then? The short answer is your cellular carrier is the first place for help - but perhaps we can help you with some confidence to call them for help.
Answer: First, just try again, make sure it wasn't just a glitch.
Then, to fully test...
Reboot all 3 phones, yours, boyfriend's, mom's.
Ring each person to test - that's 6 phone calls - you to mom, mom to you, you to boyfriend, boyfriend to you, mom to boyfriend, boyfriend to mom.
That last couple might feel odd, depending on how well they know each other, but it's the only solid test to see if it is specifically just an issue between you & your boyfriend.
If only one/two of those tests fails [the expected ones], the next test would involve each person travelling far enough that they are certain to be using a different phone mast & repeat the process.
Answer: I've had something similar with an Iphone 6s. Some people could barely hear me, had to turn on the speaker, while others could hear me just fine.
When something else broke, I've send it back for warranty and at Apply they acknowledged the problem(s) and I received a new one (because It could not be fixed). With the new one I do not have this problem anymore.
Attention -> I received a new one because the broken button could not be fixed. I do not know what they would have done with only the sound issue. But you can always contact support?


sharepoint search boolean managed property

Question: I have a managed property isActive which happens to be a Boolean. I am creating a search query and I only want the ones that are active so isActive:true however I am having trouble with the correct syntax.
Can anyone tell me this I am using sharepoint 2013
Comment: which sharepoint version are you using 2010/2013?
Comment: edit has been made
Answer: Try isActive=1 this means it equals true. isActive:1 is a contains query.
Comment: When an answer actually answers the questions who is to say it's too short? I'll wait for the asker.
Comment: This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post.
Comment: Waquas, isn't that for the asker to decide? I believe it does answer the question.
Comment: it is too short and may be it provide the answer...in many cases you leave this as comment if asker says its work then you can put into the answer.
Comment: i appreciate your level of confidence...


How can I force Brasero to keep my mp3 playlist order of songs when I burn it?

Question: I have an mp3 playlist in Rhythmbox. When I drag and drop it in a Brasero data project the order of songs is lost. In fact their sorted in alhpabetical order. As you can imagine this is awful for a list of songs you want to listen to a particular order. This does not happen when I burn a list as audio and not data project.
Answer: An audio CD consists of tracks. They are numbered and do not contain any Data about Artist etc.
A data CD however contains just that: data. Your files can be ordered by the file browser that opens it. The playlist from Rhythmbox is not part of the mp3 files. You however try to export it as an m3u file. Most audio player software can read that format.
Comment: Confirmed. You can save your playlist as a M3u file (but also you can use the pls format Rythmbox uses for default when saving playlists) and then open it when creating an audio project in Brasero. It will keep the order of songs as you wish. Just tried that successfully. It works even just dragging the playlist. xD
Comment: Thanks Carsten. I saved it on m3u format and insert it in brasero. Problem solved.
Answer: Jdpipe over on ubuntuforums.org posted a great little python script to solve this issue.
It works by creating a sequence of symlinks from a playlist (m3u) and then feeding that to Brasero.
Worked great for me!
http://ubuntuforums.org/showpost.php?p=7503949&postcount=7
Make the python script executable and then run it from a terminal thus:
./m3utocd.py 'PathTo/MyPlaylist.m3u'


Should there be a refresh button if a page automatically refreshes once network is available?

Question: I have a view in my iOS app that displays an error if there is no internet connection. Upon detecting a working internet connection, the page will automatically refresh. Is there any point to having a refresh button on this error page?
Answer: Yes. Think of it as a way to evoke some sort of response for the user. It should only take a few seconds to realize that somethings not happening. Real life scenario: If I call you and you don't pick up I still hear a ringtone. If I call and you don't pick up I can hang up and call again. Calling again is like your refresh button. It's just another way to allow me to feel like I'm reaching my goal sooner.
If you do not wish to give the user this redundant option you will find that they will lose interest and think that something is wrong. When they think something is wrong and you have not communicated the problem to them you have now caused them to no longer trust you or your product. So providing a refresh button will be a great way to let the user know that something is in the works until they get their desired result.
Answer: Yes there is.
Urgent usage and the sense of control
From a user point of view, the fact that the page automatically refreshes may not clear.
Even if you do make it clear (by providing a message such as "This page will automatically refresh once a connection is detected"), within the context of urgent usage (and even outside it), providing such a button will give users an increased sense of control over the automatic behaviour of the system.
Racing

To give one example, the London underground network now have WiFi on each station platform, but not in between (the tunnels). Many users, like myself, are in a form of a race once reaching a station - first re-connect to the WiFi (which would normally mean going to the Settings app - which in itself is the same case as in with your app and may not be justified but psychologically driven), then switch an to the relevant app and perform whatever action they wish. Often, this means refreshing this feed or another, like in IM applications like WhatsApp. Normally, you only get connected by the times the doors shut, and then you have a mere few seconds to switch to the application and press refresh.
Even if the app gets notified when a connection is re-established, providing a refresh button to the users will provide a sense of control (although in such case it is illusive), which is a good usability practice.
The sense of vs. real empowerment
Consider the following statement:
The British government considers to conduct a nation-wide survey amongst its citizens, asking for their preferences of tax distribution amongst various government departments (education, military, transport, etc.). Each citizen will be asked to put a percentage next to each department, all sum to 100%. The government asserts that it may not account for the survey results. Are you in favour of such survey?
Despite the fact that the government states they may not account for the survey results, it is likely that most people will be in favour of the idea - which gives a sense of empowerment, although not necessary a real one.
It is a similar case with the refresh button - although it may gain nothing otherwise, it shall give users a sense of control.
Answer: What is the rate at which the page checks for a network connection? It is common to do the Gmail approach where you check for a network connection by a Fibonacci sequence in order to decrease server requests. If you are checking every 3 seconds (based on half of the average attention span of 8 seconds), then maybe I would not include a refresh button, but show the app is trying to reach a server. In all other cases, I would include it. This way, you are empowering users and giving them freedom to control the application, not the other way around.


How to edit a text box under another text box in Adobe Acrobat PDF?

Question: For the life of me I cannot edit the smaller text box area that is totally contained by a larger one. I just need to edit the text on this smaller box but unsure how I can access to it. I can select the text with the arrow but the edit cursor will not select the smaller box contained in the larger box, just opening up editing on the larger one every time.
Answer: A straight-forward solution is you could search for a specific text which that box contains, then you will be able to select that textbox, i.e, start from "Find" (usually Ctrl+F) and type in a part of the textbox's content until desired part is highlighted.
Voila!
Easy peasy, lemon squeezy.
Answer: Using Adobe Acrobat Pro DC:

click outside the bigger textbox to unselect it
Zoom in extremely deeply.
try clicking so, that your cursor will be entirely inside a (black) letterform of your smaller text box

I tried this a few times - and you need some luck and patience, but it can be done. The selection-markers for the text-frame will tell you when you got it right.
In Corel it used to be: Hold the ALT key and click the area several times until the lower object which you want is marked as selected. If there is something similar in Adobe, I have not found it.
Here is another working method, if you are couragious:
Select the bigger box and hit CTRL-X to cut it out. It will stay in your clip-board. Now easily edit the lower smaller text (but do not use any tool which would involve your clip-board of course (unless you have a clipboard manager like AceText)).
Once you are done editing, click outside the smaller text to unselect it. Then just hit CTRL-V to paste; and the bigger text will be put back to its original location.
Both not great solutions, but I guess that you will not do real heavy editing in an existing PDF document; probably just tweaking some typos or such, eh?
Answer: Click outside the large box so nothing is selected. Hold Shift and the mouse button and drag a box around the smaller box. It should be selected.
Comment: Welcome to Graphic Design SE. Please [edit] your answer not tonot use all caps as it is perceived like shouting basically everywhere and also more difficult to read.


What would happen if there were a cheap, instant, complete test for sexually transmitted diseases?

Question: If there was a small, cheap, simple device or test that anyone could obtain, which at any time could be used to immediately indicate if anyone was positive or negative for chlamydia, gonorrhea, herpes, HIV, HPV, syphilis, hepatitis, trich, chancroid, LGV, NGU, scabies, CMV, mono, etc., what would happen?
Comment: Everyone who wants to find out would know whether they have any of those? Unbounded "what would happen" can easily be considered to be too broad; can you edit your question to narrow the focus of any answers you seek? Also, look up the concept of "false positive" and "false negative" rates.
Comment: Please add detail to your question -- is it safe to assume that you're looking for a response detailing the possible **social & cultural impacts** of such a test?
Comment: You're likely to find out in a few years, as Apple's medical instrumentation improves.
Comment: I recall a SF short story with that premise,  where coin-op testing machines are installed in pick-up bars.  Unfortunately I can't recall enough to search for it and don't recall the ramifications and twists of the plot. Just that it has been done.
Answer: Firstly: healthcare professionals worldwide would get hold of this device and reverse engineer it for any other number of disease identification purposes. I feel this isn't really the answer you're after though, so:
Not a grand lot more than already happens.
The main issue with the efficacy of STD tests isn't how simple or cheap they are. It's that often people don't want to consider (or it just doesn't cross their mind due to ignorance or overconfidence) that they might need one. These tests would make it one hell of a lot easier for the safety conscious to check for STD's, but when it comes to transmission those aren't the people you need to worry about.
This device would be incredibly useful if mandatory testing were enforced (and in fact you'd pretty much need it to be able to even consider mandatory testing) but the kind of future where HIV is eradicated by enforced testing and social vilification of those infected is not a future I think most people want to live in.
One possibility would be if this device were a near field communication implant that instantly tells you when it detects an STD. That way people would slowly all start getting the implant just for peace of mind, as it would require no more thought after implantation. That then leads to the revolution in infection control that I think you're after.
Also: give serious thought to using such a device for all other infectious diseases. WHO would love it.
Answer: This would only make a large change if this test was available for self administration (somewhat like a pregnancy test kit), and allowed the user to test their potential partners before a sexual encounter.
If this was the case, then sexual mores and behaviours would change. If a person refuse to submit to a test, they would be dropped as a potential partner. Soon, the signal for an encounter might be "will you take my test?" (perhaps followed by a coy smile). As time passes, it will become considered strange for sexually active people not to have a testing kit on their person at all times, or saying you don't have a kit might be a polite (or not so polite) way to turn a person down. The institution of marriage might come under more stress, if it becomes common practice to demand a spouse submit to the test (this might be considered a not so subtle accusation of infidelity).
Unfortunately, there is a large enough reservoir of irresponsible or uncaring people out there who would neither carry the kit or demand testing (or submit to testing) but would still be sexually active. This means that while large scale social pressure to use the test would bring the rates of STD's down considerably, there will still be reservoirs of infection out there. The other thing this test might mask it the evolution and spread of new diseases that use sexual encounters to spread to new hosts, since the STD kit would be optimized to detect currently known diseases.
Comment: +1  I feel like you're the only one *(so far)* to grok both the concept and the far-reaching social implications of such a test.
Comment: Your first three sentences are exactly what I recall from the beginning of the short story I aluded to.  This was done quickly indicating general background "here is the situation" in the plot, before going into the details it was exploring.  In the story I recall, they were wall mounted at the bar, not carried by the people.
Comment: At the same time, the phenomenon of "barebacking" during the height of the AIDS epidemic among US gay men suggests that some will reject the social-engineering implications of the test, arguing that they should not be defined solely by their medical status.
Answer: I heard a story on a news magazine a while ago -- can't find a transcript so I can't give the exact quotes -- but they said that a study had found that almost 30% of people who were infected with an STD got it from a partner who had no visible signs of the disease. The panelists talked about how scary this was, how hard it was to protect yourself, etc. Then one panelist said that he thought that the really scary part was that over 70% of people who were infected with an STD got it from a partner who DID show visible signs of the disease. And then they apparently went ahead and had sex anyway.
So even if there was a 100% reliable test, apparently lots of people wouldn't bother to use it, or would ignore the results. The more difficult it is to use, the more expensive, the more trouble it is to get, etc, the fewer would use it.
And let's face it, how many people in a moment of passion are going to say, "Wait, before you finish taking off your clothes, let me run down to the drug store and get an STD test kit. I'll be right back. Wait right there."
Comment: If it really was a cheap and instant test, it's hoped it would be bundle-packaged with condoms.
Answer: They're actually fairly quick and accurate at the moment. Cost depends on whether you're in a country that scalps you for medical care or one that provides it for free.
In the "West", you'd end up with a massively reduced rate of transmission of STIs among intelligent educated responsible people, who would require a test before any sexual encounter, and a moderately reduced rate among the reckless and uneducated. I expect the US would charge people $150 a time for the test kit, it would be flagged on your medical record and future employers would be informed that you once had sex. The rest of the civilised world would get it for free from the local doctor or pay a token fee at a pharmacy. Similar to access to contraceptive pills today.
You'd get major campaigns for testing and treatment in African countries who would end up with reduced transmission rates across the population, though not total reduction due to the difficulties of teaching people that having sex with a virgin doesn't cure HIV (this makes me cry).
The more religiously oppressive regimes would ban it immediately for encouraging infidelity and probably stone anyone caught in possession of a kit.
Comment: ...Also, that's a real cheap dig at the US medical system.  We have instant HIV tests over-the-counter at drugstores just like other countries do.
Comment: You're not going to detect anything you've only just caught, but you're going to pick up the ones that you've had for a while. Also I'm assuming that the people who use instant rather than professional testing are going to be using these kits fairly regularly and hence will pick them up in the long term. I'd have to know more than I do about the point at which STIs become transmissible after initial infection.
Comment: Quick, but deceptively so -- people tend to ignore or misunderstand the concept of multi-week incubation periods for viral STIs, which are the Achilles heel of our current antibody-based testing.
Comment: You make a good point re: likelihood of transmission at X days after infection.  I commented because I think that without taking the question's "immediately indicate" phrasing very literally, then the answer would be uninteresting -- because then it'd be "well, whatever is happening now, because that's basically the technology we already have", sans some comprehensiveness.
Comment: Yep, [but it's too easy a target](https://www.washingtonpost.com/news/to-your-health/wp/2014/06/16/once-again-u-s-has-most-expensive-least-effective-health-care-system-in-survey/)
Answer: The second sexual revolution.
For purposes of a more compelling answer than "What would happen?  Well, basically whatever is happening now, because you've described something only slightly better than today's level of technology", I'm going to assume the following important things:

"immediately indicate" means that the test will successfully pick up an infection with effectively zero incubation period (say, within a matter of hours after intercourse)
100% sensitivity and specificity (all infections are identified, with no false positives)
as with existing cheap & instant HIV and pregnancy tests, the comprehensive test is available for home use (can be self-administered, as Thucydides pointed out)

Conditions two & three are definitely important, but I feel that number one is key.  This, combined with the comprehensiveness of the test, would provide ironclad assurance that a potential sexual partner was not a health risk.
The Achilles' heel of the current generation of STI tests is that they are based on antibody response -- which is variable, and takes too long.  This is a nuisance for the responsible, and the root of the sexual health threat posed by those who are not.  With an instant test, waiting for incubation periods to pass, and indeed, waiting for test results at all, would become a thing of the past.
The stigmatization of premarital sex took a heavy hit when contraception and abortion became widely available.  The stigma of multiple sexual partners being a health safety concern will likewise come under fire, as the threshold of effort and self-control required to be cautious with one's personal sexual health would be drastically lowered.
It would become socially expected to test oneself in the presence of a new sexual partner prior to intercourse, as a gesture of openness and respect.  Refusing would be like not buckling your seat belt in a car -- what possible excuse could you have?  It is to be hoped that it could even be packaged directly with traditional forms of contraception.
Additionally, we have two things now widely available that the first sexual revolution did not:  social networking and location-aware communication devices.  It would be short work to adapt already-existing dating apps for more overt purposes.  This creates the potential for unintended and possibly unsettling consequences, like the network-wide "blackballing" of STI-positive individuals.
Comment: Think the **percentage** of **bold** words are **in ballance** for your **point**?
Comment: @JDługosz: Nah, needs more cowbell.
Answer: Via the Internet this is already available however of course there are disclaimers. And what would happen if this was available as you suggest I'm sure the instructions at the bottom in small print would read in case of any positive test result please refer immediately to a licensed health care provider for further assistance. Blah blah blah in a nut shell we not responsible you are so i think that puts you back to square one. However on a positive note there may be a smal decline in the spread of stds since id like to believe there are caring responsible people still in this world who may have been embarrassed to see a doctor or could not afford
Comment: Today's current antibody-based quick tests are woefully insufficient in sensitivity, and nothing is available today which matches the comprehensive quality described in the question.


Fix the UI for initiating a Docs edit so improvement requests are not erroneously handled

Question: Most of my improvement requests are "handled" erroneously thanks to what I hope is a UI oversight.
Here's the usual pattern:

Helpful user arrives at a Topic
They have a look at improvement requests
They think "Hey, I have some ideas for edits too"
They think "And here's this bright blue 'edit' button!"
They edit as they see fit, typically not handling the requests
Improvement requests all disappear

As a result, improvement requests are rarely addressed in my tag, instead being "handled" almost at random. Here's the UI I'm referring to. Assuming you have had a look at the improvement requests, the most obvious way to edit the Topic or Example is this the blue button below:

(Please ignore the substance of these requests. I just mean to illustrate the UI.)
And after you click it, SO quietly assumes that you are attempting to handle all of the improvement requests with this edit, and checks the box next to every request for you:

In my experience, it is much more common that the editor is attempting to handle none of the improvement requests. And why should we assume otherwise? They clicked an "Edit Example" button, not a "Resolve everyone's issues with this Example" button.
Request/proposal: Change the text on that button. Leave those boxes unchecked by default. Maybe put another "Edit" button in the right pane, below the "Topic Outline."
Some concrete examples:

Here, I was berating the editors for subsetting mixed tabular data as if it was a matrix ... which the editor did not have any intention of addressing. As a result, I had to re-post my request, and will have to do so again and again after every edit anyone makes. I've had this experience on a few other examples as well.
Going beyond examples, I have had the same experience with Topic Requests. I requested a "Randomization" topic with several features. Someone "handled" it by addressing the first one, making all record of the others disappear, so I had to re-post it. This issue was brought up in July, too.

Maybe the discussion section can somehow do a better job of not destroying improvement and topic requests, but I'm posting this to clarify some of the most infuriating features of the current system.
Answer:
And why should we assume otherwise? They clicked an "Edit Example" button, not a "Resolve everyone's issues with this Example" button.

Because the button is in the improvement request section... or such is the theory. I agree that right now the buttons are drawing far too much attention. I'll get with the team to see how we could clarify this behaviour. Maybe something along the lines of a "handle these requests" link/button that brings up the list of available actions. We'll see.
Thanks for the detailed write-up!


How will we recognize a conscious machine?

Question: How will we recognize a conscious machine (or AI)? Is there any consciousness test? For example, if a machine is aware of its previous experiences, can it be considered conscious?
Comment: No one knows: there is no empirical test known to physics that can distinguish a conscious entity from one that this not. Heuristically, I know that _I_ am conscious but I only _suspect_ that other people are: they could be 'Dennett Zombies'...
Answer: There are two main subjects you need to look at to understand the problem:
The Turing Test

The Turing test, developed by Alan Turing in 1950, is a test of a machine's ability to exhibit intelligent behavior equivalent to, or indistinguishable from, that of a human. wiki

See also: Turing Test (Stanford Philosophical Dictionary)
There is a linguistic element, which is that intelligence can be interpreted in many legitimate ways.  Some maintain that Artificial Intelligence has not yet been achieved; other feel a simple automated switch constitutes the most basic form of AI.
Bear in mind that "intelligence" is distinct from consciousness in the sense of "self awareness", but the generalized Turing Test can also be understood as a gauge of the appearance of consciousness.
This leads to Searle's Chinese Room Argument.  I highly recommend reading the Stanford Philosophy link, but the wiki gives a simpler synopsis:

The Chinese room argument holds that a program cannot give a computer a "mind", "understanding" or "consciousness", regardless of how intelligently or human-like the program may make the computer behave.

The real problem may be, how does one know an algorithm is truly conscious and not merely simulating consciousness?

Philip K. Dick approaches from the opposite direction in Electric Sheep, where one of the conclusions is that "life is life" whether organic or artificial.  This might be said to lead to the "Duck Test" for consciousness: "If it looks like a duck, and quacks like a duck, then it's probably a duck."  (Dick's philosophy was heavily influenced by Christianity, and his view on artificial life may be though of as radically humanist.)
(A parallel philosophical argument might be "how is the appearance of free will distinct from the actuality of free will?"  Free will has been fruitlessly argued about for millennia, but whether the universe is actually deterministic or not, we perceive ourselves to have free will.  If the universe turns out not to be strictly deterministic, it wouldn't functionally change anything.  To make matters more fuzzy, true randomness is nature is only found at the quantum level and then only within certain models. Quantum uncertainty has been proposed as a basis for free will, but we don't know.  Possibly uncertainty is a condition of individuality, which must be subjective in relation to a system or other subjectivities.  Nevertheless, how do we know we are not "robots" acting out a pre-determined sequence of actions, which we perceive as decisions?)
I personally very much like the idea of recursion as function of self awareness.

At the phenomenal level, consciousness can be described as a singular, unified field of recursive self-awareness, consistently coherent in a particular way; that of a subject located both spatially and temporally in an egocentrically-extended domain, such that conscious self-awareness is explicitly characterized by I-ness, now-ness and here-ness. SOURCE: Peters, Frederic Consciousness as Recursive, Spatiotemporal Self-Location

I'd also posit that being able to read and interpret your own code is a form of self-awareness.
This brings me to the idea that understanding (Chinese Room) is a red herring, and what we're really talking about is interpretation.
We are trapped in subjectivity, humans and automata, and perfect certainty is only achievable in a very limited set of circumstances, such as solved games. (There is also the idea of completeness of a system vs. consistency.)
When we talk about understanding in the sense of anything abstract, by which I means semantics as opposed to syntactics, meaning vs. form, one can say that understanding is a function of interpretation, regardless of the accuracy of the interpretation.
--------------------------------------
Fun Speculation:
I've learned never to underestimate the insight of artists, and the best speculative fiction authors are narrative philosophers in the tradition of Plato.  Dick related memory to identity, regardless of whether the memories are real or artificial.  This might be thought of as the narrative conception of the self--I am a product of my experience.  The real "me" is not merely my body, but "the story of me"--the subjective history that led to this moment of me-ness.
I think it is a not unreasonable assumption that artificial consciousness may arise out of understanding of narrative.  Words are just symbols, and there are all kinds of semantic issues, but actions have a concrete aspect.  Game theory studies actions in the form of choices, not only in the sense of equilibria, but also as a form of communication.   (See: iterated dilemma)  The choices agents make in iterated dilemmas constitute a narrative history than can be analyzed and understood mathematically, and these analyses are used for decision making.
It seems to me that the idea of consciousness can be related to decision making.  If you're just a transistor, that consciousness is quite limited, more akin to a cell than a complex organism. It may come down to whether one considers intelligence and consciousness to be spectrums as opposed to thresholds.
If you believe consciousness to be a spectrum, then limited artificial consciousness has already been achieved. Consciousness analogous to human-level self-awareness is still in the future.
See Also:
Definitions of the Self (wiki); Self Knowledge (wiki)
Answer: I think general artificial intelligence will only be possible with some form of self awareness included. Many aspects of human communication do not work if one of the communicating partners does not have self awareness. A good example are many of today's chat bots. They seem to not even hear what they say and only rarely seem to have episodic memory.
Advances in machine to human communication and collaboration will eventually create systems with an ever increasing complex inner model that allows the system to interact in a natural way with humans and to fulfill tasks which require human level intelligence and flexibility. However, unless we have developed a very advanced understanding of consciousness it will be hard to judge how similar or different such a machine consciousness is compared to human consciousness.
Comment: [γνῶθι σεαυτόν!](https://en.wikipedia.org/wiki/Know_thyself)
Answer: "Consciousness" does not have a universal definition. However, if you are really into "consciousness", you should probably read about Searle's Chinese Room experiment or Marvin Minsky's society of mind.
In my opinion, there are many more fundamental obstacles in current AI research that we have to tackle first.
Furthermore, a more formal question would be about how an artificial general intelligence (AGI) would emerge. Even for that, there is no clear roadmap, since we are still very new to understanding the true power of neural networks or other successful AI methods.
Franchois Chollet said in a tweet

For all the progress made, it seems like almost all important questions in AI remain unanswered. Many have not even been properly asked yet
Answer: As far as I think, the key to this answer lies in the area of unsupervised learning.
Why?
How do we define consciousness? Probably being aware of our existence. The key to understanding our existence starts by asking questions or finding answers which may not have any questions. This all may sound quite philosophical, but in terms of AI, it may just be finding patterns and logic from what we observe around us.
Just a theory but worth giving it a thought.


How to make ubuntu not ask for password after login

Question: I'm not trying to delete my password or anything. I just want ubuntu to remember my password after I login as an admin user and use that when installing/removing software or running sudo commands. The non-admin users should be prompt for the admin password though. Is there a way to do that and if so why doesn't ubuntu do that as default?
Answer: There's no such thing as "an admin password" in Ubuntu. Any user can elevate his privileges by using sudo as long as that is available to him. And by default sudo requires you to re-authenticate for security reasons. This is a sane default for this reasons as it fits with the "secure by default" policy.
However, it does remember it for a short period of time. Here's a question on how: How does sudo remember you already entered root's password?
Several options to go from here:

Passwordless sudo
From the manpage of sudoers(5):

By default, sudo requires that a user authenticate him or herself before running a command. This behavior can be modified via the NOPASSWD tag.

Just change the lines in /etc/sudoers to include this. E.g.:
%admin  ALL=(ALL) ALL
%sudo   ALL=(ALL:ALL) ALL

becomes
%admin  ALL=(ALL) NOPASSWD: ALL
%sudo   ALL=(ALL:ALL) NOPASSWD: ALL

Extend timeout
By default sudo will "remember" your password to elevate your privileges again for fifteen minutes. You can extend this to a much longer time, let's say a day. Do note that this is not unlocked on login, but only triggered the first time you are elevating your privileges.
To extend this, edit the /etc/sudoers file and locate the line
Defaults        env_reset

and append ,timestamp_timeout=1440 to it so it becomes
Defaults        env_reset,timestamp_timeout=1440

Alternatively, use -1 (a negative value) to have a really indefinite timeout. Read more about this on the Ubuntu Community wiki: RootSudoTimeout.

Important note! Editing the /etc/sudoers file should be done with great care. Incorrect syntax will result in a system on which you are probably not be able to elevate your privileges again and you'll have to perform a rather complicated password recovery. To edit it safely, use the sudo visudo command in the terminal. It will not directly write to the file, but only when you exit and save it and the syntax is correct. This will prevent a lot of trouble.
Comment: I'd like to just point out that there is a reason for why the password prompt is there, and that by disabling it, you're effectively removing critical parts of the security layer - and that this shouldn't be done on any kind of production machine.
Comment: What I wanted was to be asked for password at only login screen and never after that point. You are saying it is not possible?
Comment: maybe possible, but certainly not adviseable
Answer: In your system settings - little gear icon in right top corner - you can open Users.
Click on the user you want to modify for the passwordless login.
In the settings dialogue you can change the setting automatic login.
Comment: I don't think this is a login setting to change as I think OP is asking for a way to have an indefinite sudo password remember time.
Comment: But it's this answer that other people may have looked for, when searching Google for `ubuntu automatic login` ;) It's this answer that I was looking for, at any rate.


How OIS swap rates behave when we receive or pay OIS swap rates?

Question: I am reading a news article regarding how OIS swap rates behave when we receive or pay OIS swap rates.
The article states that when we receive OIS swap rates it makes swap rates fall. When we pay swap rates, the swap rates rise.
What would be a logical explanation for this?
Answer: This is just simple supply and demand.  Same as saying that if people buy a lot of stock X , the price goes up.
Comment: It is funny how financial markets work: if you see a big swap rate of course you want to *receive* and as you (and others) increase your position more and more you find that the swap rate moves against you, making it less attractive. It is unfortunate, but that is how *all systems* subject to *equilibrium* tend to work, action leads to reaction that lowers the reward to the initial action. The attractiveness of a particular trade tends to disappear
 when acted upon by enough ppl.
Comment: @dm63 Can you please elaborate on your answer keeping in reference my question
Comment: I thought the comment of @nbbo2 was a good elaboration


Is GTA Online protected by an anti-cheat engine?

Question: I play regularly on GTA Online with my mates, in the last couple of weeks we almost already encounter cheaters while in a public session. They can do whatever they want which is very annoying (and being always in passive mode to protect ourselves is not funny), so we are asking ourselves if GTA Online is cheat-protected ?
Answer: The servers are, yes.
Hackers/Cheaters get banned every ban wave - which seem to be every couple months (unless a serious hack/cheat is found and a hotfix is pushed).
Definitions of hacks/cheats are cloudy, but this article suggests it's 2 things

We're trying to find out exactly what the ban criteria is, but it seems to be anyone who's used either a cheat engine or a DLL injector – things like Script Hook and the Field of View mod.

If a hacker/cheater drops you money, I'd be cautious to pick it up, because as the same article says

There's also some uncomfirmed reports that if you happened to have received $GTA from a modder then you have been banned too, but then some people who did this have been banned, others haven't

This is an e-mail from Rockstar detailing what will get you banned;

(source: gta5cheats.com)
You can never really stop hacks/cheats from being used. This steamcommunity posts explains some things about the ban, but doesn't cite sources, so I'm unsure if they're reliable.
Comment: No anwser from Rockstar, but there's a similar question here: http://gaming.stackexchange.com/questions/221566/what-should-i-do-when-a-hacker-gives-me-hacked-money
Comment: I asked the Rockstar Support about the money drop hack https://twitter.com/EpocDotFr/status/605675292410146817
Comment: Rockstar just announced they implemented "new systems" to target cheaters "more efficiently" http://www.rockstargames.com/newswire/article/52451/update-targeting-cheaters-in-gta-online
Answer: I've been cheating actively for 2+ years. I have fun doing missions with infinite ammo, zero gravity, and stuff like that, and I have the power to control my environment. They only ban people cheating IN FRONT of other people recording.
Comment: This seems more like an opinion-based answer. Unfortunately, our format isn't a good fit for opinion-based answers, and it doesn't really answer the question.


Ubuntu VirtualBox Graphical Glitches/Black Screens

Question: The windowing system in Ubuntu has off and on problems for me. I've had to restart X a few times (from another terminal) losing all my work which has been a real pain. What can I do to fix these problems or more gracefully recover when I need to restart X? Forgive any improper terminology, I'm new to Ubuntu.
I'm running Ubuntu 16.04 LTS in VirtualBox. I have 3D Acceleration enabled. I have an Intel i7 running with the Integrated HD Graphics. My host OS is Windows 7.
The problems are all graphical but vary in intensity. Some I can work with and some I can't. The keyboard and mouse still seem to function no matter how bad it glitches out.
Here's one example where the window control icons are black.

I've had it sometimes that it will replace title bar drop down menu titles with stretched icon pictures. I've had it get stuck at a black screen. I've also had it get stuck like this.

I have only successfully recovered once and that was by manually telling VirtualBox to reset the display size and everything came back. This hasn't worked in other instances. Running sudo service lightdm restart always fixes the problem but I also lose my work. There seems to be some small correlation between Chromium (and possibly WebGL) and these issues but they have occurred in other instances.
Comment: Have you installed the guest additions?
Comment: @CelticWarrior Yes.
Comment: Turning off 3D Acceleration so far seems to be more stable but I want to give it a couple days.
Answer: It seems the issue was the enabled 3D acceleration and my VM is now much more stable to the point where I haven't had any glitches since.
The only issue now is that my 3D applications run much slower.


Avocado plant wilting

Question:
I recently transplanted my avocado plant from a cup of water to a pot of soil (ph6.5-7) as the tips of the leaves started going brown.
Since being transplanted the leaves have now drooped and are drying/curling at the ends (picture is of the worst one, which also has small light coloured spots the rest do not).
I've checked the water level with a meter and it says it is sitting at moist which is the middle of the meter.
It has not been sitting in direct sunlight and todays weather has been around 12 degrees Celsius.
Comment: Looks like the roots are rotting.
Answer: Avocado does not like to have its roots disturbed at all. When moving from water to soil if you broke or twisted or bent any of the larger roots this will cause it to have a major headache. The best you can do right now is leave it be, moist but not wet in well drained soil and if it recovers introduce it to more and more light. Avocado does best in full sun but clearly needs to be introduced slowly after the shock of transplanting. For future experimenting now that you have seen roots in water and benefited from the educational experience, next time better to germinate from the start in soil. Then you can transplant to a larger pot with the root ball intact with minimal damage to roots.
12 deg C is pretty cool for an avocado. They are happier at 20-30 but will protestingly survive cooler, so do not expect a lot in cold temperatures.

Avocado plant wilting


All the natural numbers are of form $x^2+y^2+z^2+w^2+xy+zw$

Question: Is there any natural number that cannot be written as $x^2+y^2+z^2+w^2+xy+zw$, where $x,y,z,w$ are integers? If there is none, how do I prove that all the natural numbers are of form $x^2+y^2+z^2+w^2+xy+zw$?
Comment: For searching purposes, this would be called a [universal quadratic form](http://en.wikipedia.org/wiki/Universal_quadratic_form).
Answer: $x^2 + xy+ y^2$ represents exactly the same numbers as $u^2 + 3 v^2.$ You are asking whether $$ s^2 + 3 t^2 + u^2 + 3 v^2   $$ is positive universal. It is.
More: a variation of quaternion multiplication shows that, when this form represents two numbers, call them $m,n,$ then it also represents $mn.$ Meanwhile,
$$ s^2 + 3 t^2 + u^2  $$ is a regular ternary form, in particular it represents $1,2,3,$ and all numbers not divisible by $3,$ which includes all other primes. From the multiplication property, it follows that all (positive) numbers are represented.
For information about what numbers are represented by $s^2 + 3 t^2 + u^2,$ see the entry for $1,1,3$ in Dickson_Diagonal_1939.pdf at TERNARY. Acomplete proof is given as Theorem 89, pages 97-99, of Dickson's book.
Comment: Every prime $\equiv 1\pmod 3$ is $u^2+3v^2$, so naturally I can represent multiplications of these primes via composition. How can I represent a $p\equiv -1\pmod 3$?
Comment: @IanMateus, $x^2 + y^2 + 3 z^2$
Answer: By the $15$ theorem, it suffices to check all naturals up to $15$. The margin is too small to fit my proof so the task is left to the reader.
Comment: I think you would actually need to apply the 290 theorem here as the associated symmetric matrix contains halves. So your "too small proof" will need to be twice the size! (please correct me if I'm wrong here)
Comment: I should emphasize that this type of form, with odd crossed terms $xy$ and $zw,$ is not covered by the 15 Theorem; it is covered by the 290 Theorem, which is complete but may never be published.
Comment: Haha, sorry, fixed the statement ;)
Comment: @WillJagy: has anyone ever attempted a proof of the 15 and 290 theorem through the Jacobi triple product and Lambert series identities, as far as you know?
Comment: @JackD'Aurizio, not quite those words. series estimates are a key part of the 290 work; it is possible to say that a positive form in at least four variables does represent all numbers larger than a specific bound (different bound for each form), and then numbers up to that bound checked by computer. No need for the 15 Theorem, Bhargava's insight was that every example had to contain a regular ternary form as a sub-form. There is no shortcut for the 290 problem.
Comment: @JackD'Aurizio, note that the existence of **some** bound was known early, but a good deal of work to confirm that the number really is 290.


How much electronics can I bring duty-free on a plane to Ireland from outside the EU?

Question: I'm travelling to Dublin, Republic of Ireland from Malaysia very soon for postgraduate studies. I have this Asus MG279Q gaming monitor that I would like to bring along. Are there any charges if I were to bring this monitor as a check-in baggage? Import taxes, duties and whatnot, or anything like that?
Comment: Just so you know, the charges don't change if its a checked-in or carry-on item.
Comment: So you are more or less moving to Ireland for a period of time and not just there on a short visit as a tourist?
Comment: Are you sure you want to trust the airport baggage handlers with a monitor that large?  I suspect they won't be liable for damages.
Comment: Well, bringing it over is a last resort. I am currently trying to sell it off before my trip. But if I can't sell it by the time i go to Dublin, then i feel it's better to bring it along since it would just sit here and collect dust if i leave it over here.
Answer: As I understand it the rules depend a lot on the circumstances surrounding your travel to the EU (I think the rules for this are similar across the EU but i'm not 100% sure on that) and the purpose of the goods.
As JonathanReez says there is an allowance of E430 (E215 for under 15s). This is only for noncommercial imports though, if you intend to sell the goods after importing them then it doesn't apply. http://www.revenue.ie/en/customs/leaflets/pn1878a.html
If you are resident (or have recently been resident) in the EU and are returning home from a trip abroad then anything you purchased while outside the EU is subject to this relatively small allowance. Stuff you took out with you should be able to be brought back without paying any further duty/taxes http://www.revenue.ie/en/customs/businesses/importing/#section4 . For high-value goods it's wise to take evidence that it was bought in the EU (or previously imported legally).
If you are visiting the EU on a short visit then personal belongings intended for your personal use can normally be brought in on the assumption that you will take them with you again when you leave http://www.revenue.ie/en/customs/leaflets/cdpn46.html . Temporary imports are also possible for other types of goods but will often need to be explicitly declared. Items intended to remain in the EU will be subject to duty/vat if they are imported for commercial purposes or the total value is above your allowance.
If you were previously resident outside the EU for a significant period of time and are taking up residence in the EU then there are special rules that apply allowing you to import your personal belongings without paying duty/vat on them subject to some conditions. http://www.revenue.ie/en/customs/leaflets/pn1875.html
I'm not sure if your studies will count as "visiting" or "taking up residence" for these purposes. I suspect it will depend on the length of the course.
Answer: According to the Irish Tax and Customs website:

You are allowed to bring in goods (including gifts, souvenirs, perfume and clothing) free of duty, the combined value of which does not exceed:
€430 in the case of an individual aged 15 years or over
€215 in the case of an individual aged under 15 years

However note that in general, items intended for personal consumption (e.g. an expensive Mac laptop) are not a concern for customs, as it's presumed you will take the item with you when you leave the country. Therefore as long as your monitor is unboxed and you can reasonably explain you will need it for the duration of your course, no duty will normally be charged.
Comment: There's aren't necessarily the right rules if the OP is moving to Ireland for the duration of their studies (which they probably are).
Comment: @CMaster I would estimate at least 50% of all international travelers are carrying goods costing over the limit, for any types of stay. No one ever bothers them unless it's clearly not for personal use.

I cannot find any official regulations regarding this though.
Comment: Most travellers carrying laptops, expensive clothing etc are either legitimate visitors who intend to take the goods back with them when they leave. Returning residents who took their laptop out with them, or migrants who can benefit from the special rules for migration.
Comment: @PeterGreen Yes, most of them are 'legitimate travelers', but where's the actual regulation regarding this? It'd be nice to have an official answer :)
Comment: I've found sources for people bringing stuff they took out with them back home and for people migrating but i'm not 100% sure on the case of visitors bringing their personal belongings.
Comment: OK, found a source for the visitors case (see my anwer).
Answer: I would suggest you to bring the invoice with you, to show that this is not a brand new item. Then there is a good probability that it won't get even checked.


Php function to determine if a string consist of only alphanumerical characters?

Question: Is there a Php function to determine if a string consist of only ASCII alphanumerical characters?
Note: I'm sorry if the question sounds dumb to some, but I couldn't easily find such a function in the Php manual.
Answer: Try ctype_alnum
Answer: preg_match('/^[a-z0-9]+$/i', $str);

Edit: John T's answer is better. Just providing another method.
Answer: This is my solution
<?php
public function alphanum($string){
    if(function_exists('ctype_alnum')){
        $return = ctype_alnum($string);
    }else{
        $return = preg_match('/^[a-z0-9]+$/i', $string) > 0;
    }
    return $return;
}
?>

Answer: My long, but simple solution
strspn($string, '0123456789qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM_') == strlen($string)

Function strspn() finds the length of the initial segment of $string that contains only letters, numbers and underscore character (second argument). If entire string consists only of letters, numbers and underscore, the returned value will be equeal to the length of the string.
Comment: Add some description to the answer.


How to find all item ids of items that can be found on the market board?

Question: In Final Fantasy XIV, each item has an in-game item ID. In the market board, you can filter items by item ID. They all seem to be numbered in between a rough range from 1 to 37000. However, not all ints are linked to in-game items and not all of them will be available on the market board. Is there a list somewhere of all the item IDs I might find on the market board?
Comment: Hi. These questions seem more appropriate on [GameDev](https://gamedev.stackexchange.com/) since you're asking about API. Here on Arqade we discuss only about gameplay, and not game development.
Comment: I rephrased the question to be more player-based.  All items in this game have a game item id.  I want to find a list of all the items sellable on the market board and find the id of each one.
Comment: I/I'll consider this a gaming/game specific utility, which is on-topic as listed in our [help page](https://gaming.stackexchange.com/help/on-topic).
Answer: https://universalis.app/docs/index.html has this info under the following API with all marketable items.
<code>curl -X 'GET' \
  'https://universalis.app/api/marketable' \
  -H 'accept: text/plain'
</code>
However note that not all marketable items will actively have sales on the ah.  There seems to be around 13,500 items that can be sold on the ah, but not all of them will be up on a single market board.  In my studies, I found only around 1,500 different items were on my market board at once.
Answer: There is a tool on GitHub for this called FFXIV Lodestone Item ID. As of writing, it is still maintained by the developer. Here's the jist of it:

This repo provides a list of Eorzea Database items' id. ... lodestone-item-id.txt contains one id per line, and the line number (starts at 1) is corresponding to its in-game id.

Alternatively, you can look it up yourself.
You'll have to find a way to extract a .csv file containing the directory of items in the game. Once you have it, I imagine you can do a quick CTRL/CMD + F and look up your item from there, where all its metadata is stored near its name, including the item ID, which can be anywhere from 1-5 digits long.
Things start to get a little blurrier when it comes to breaking the Terms of Service, though, and you're at risk of getting your account banned, as datamining can potentially be used to cheat or otherwise play unfairly, so do this at your own risk!


How can i hide product slider extension from Contact us, Terms and conditions, and 404 not found page?

Question: I have installed a third party product slider extension in my Magento 1.9. I have enabled it only in the homepage. As in the backend (CMS->pages) the pages contact us, terms and conditions and 404 not found page comes as the sub of the homepage. Since the product slider is showing in all those pages. How can i remove slider from all other pages and retain it in the homepage only?
Thanks in advance
Comment: can you share screenshot or url? Which extension are you using?
Answer: In layout update tab of CMS page you can remove it for those particular CMS pages.
Add following one:
<code><reference name="content">
   <remove name="YOUR_SLIDER_BLOCK_NAME"/>
</reference>
</code>


Should I heat water first and let it cool before watering in winter?

Question: Winter is approaching. It gets cold here. Cold water. Would the cold water shock the roots of the plants or not?
Comment: 4K I am assuming you are talking about your indoor plants.  Why would cold water all of a sudden be a problem?  It was cold in the summer and I'll bet 'dollars to donuts' (whatever that means) you thought they could 'cool' off.  But winter, that same water might be too much?  Sweetie, you are anthropomorphizing, attributing HUMAN feelings to plants.  Plants in soil are far tougher than us hairless humans, grins.  What a plant guy!
Comment: @stormy I agree to that. But in summer, water here is warm. In Winter, water is ice-cold. It is cold right now, and winter has just started. So I thought it better to ask the question here first. :)
Comment: Some gardeners also advocate the slow release of liquid water from ice cubes.  Kind of a good idea if you don't want lots of water draining down the sides of the soil and pot and not being able to be absorbed.  Never have seen any negative reactions with cold water.  Hot water, boiling water now that would be different.  Otherwise, ice water is just fine.  For us humans, drinking pure, unadulterated ice water is the BEST way to re hydrate.  No electrolytes, no sugar, no carbohydrates to slow down getting the water into our bodies.  I haven't yet heard the WHY but this is the truth.
Answer: Very cold water can shock some plants, especially if the surrounding temperature is warm.
You didn't mention where you are, but in most large cities, water has at least some chlorine in it, which is a growth inhibitor.
It's a good idea to let water sit in the pot for a couple hours or more to let it get to room temperature and to allow chlorine to evaporate before watering your plants.
Comment: In 'some' cities?  Find me one city that has tap water services without chlorine or fluorine and a multitude of chemicals.  I have a well so I am lucky.  In the past living in ANY city I would never water with tap water, ever.  Causes any plant to start a slow decline to death.  Allowing chlorine to vaporize is good but there are many more chemicals, salts in tap water. Far better to buy distilled water.  We humans should NOT be drinking tap water yet we believe that our government bends over backwards for our health and well being.  Grins.  My opinion.
Comment: @stormy: you should just forget cities near oceans or in plain. Mountains and hills help. Welcome in countryside cities in Europe.
Comment: This is an important topic for me and certainly others...duh.  Please explain in more detail.  Are you saying Tap water is ok on the coasts?  Plains?  One thing I have found in my bits of research is that our poop gets trucked to the closest PLAIN from the coast and pumped INTO the water table.  Hello.


Civilization cards with toolmakers

Question: If, for any reason, the card remains unused till the end of the game, when scoring the toolmakers, do we take into account the value of "one-time" tools or just the permanent value of tools on our board?
Comment: You do not get to add the value of unused one-time bonuses. I'd post this as an answer if I had a more reliable source than just my experience playing this (both cardboard and digital).
Comment: Chaz, when I want to answer a questions I find most rules are available online somewhere.  Stone Age rules can be found at https://www.yucata.de/langnet/1/StoneAgeRules.pdf  if you want to cite the relevant bit.
Comment: The rules appear to not have a definitive statement about it; but Chaz is correct. Just can't find a source at the moment either.
Comment: Im not very familiar with the game so dont want to answer the question myself.  But it seems that from the picture example scoring tools it just shows scoring for players tools and not the bonus ones on cards.  Also the cards.  in the explanation civ card it says ". He can add this tool once to a die roll"  this would infer thats the only thing it can be used for and can not be used for scoring.  But as I say its a game I've only played a few times years ago so dont feel confident enough to answer myself.  I think that lack of source in the rules is perhaps proof its not possible?
Answer: No, the "one-use tool" cards do not count for scoring tool makers.
The rules specifically call out "Tool tiles" in the scoring section:

The "one-use tool" cards are exactly that: cards (i.e. not tiles). Nowhere in their description are "tiles" called out:
Comment: I see. The english version calrifies it much better.

Civilization cards with toolmakers


The difference between 何/なに (nani) and なん (nan)?

Question: In そうなんですか (sounandesuka) the なん (nan) is used to explain something, give reasoning, or to emphasize something but in これはなんですか (korewanandesuka) the なん is treat as "what", how to know when to use, is it all depends on context?
Comment: I'm confused.  There is no mention of なに in the question or any of the answers.  Is the title supposed to be `何/なん (nan)`?
Comment: That's what I mean.  You mention it in the title, but nowhere else, and none of the answers do either.
Comment: It was in the title :).
Answer: Simply, see what comes before なん. If the word before な is something that can take だ/です (a noun, a na-/no-adjective, そう, よう, いつ/だれ/どこ/etc), it means this な is a form of だ and ん is an explanatory-no. See the usage pattern of explanatory-no here.

学生なんですか。  So you're a student?
簡単なんですか。 So it's easy?
だれなんですか? Who is it?

If なん is preceded by は or nothing, なん is "what".

これはなんですか。 What is this?
なんですか。 What (is it)?

EDIT: As broccoli said, は is commonly omitted in casual speech, which makes a sentence like それなんですか technically ambiguous.

それなんですか。

So it's that one (that we are talking about)!
What is that?

But a comma is usually inserted after それ if the latter meaning is intended. Even if there is no comma, you can easily tell the intended meaning from the context.
Comment: What about それなんですか? :)
Comment: @JohnAdams A comma is always unnecessary in Japanese. It's just an arbitrary reading aid.
Comment: So the commas would only be used if は is omitted? If は is not omitted then a commas is not necessary?


How are current and voltage related to torque and speed of a brushless motor?

Question: I know that electric vehicles have different performances depending on battery and motor, but it's not clear how electrical and mechanical units are related.
Will a 100V motor raise against slopes better than a 50V motor?
Comment: Possibly, but it's impossible to say without knowing the current which can be supplied or the efficiency, allowable loading (thermal, magnet damage if a PM design, etc) for the duration of the time it takes to climb the hill, or even the gearing.  Consider that a 120v electric eraser is most likely inferior at drilling holes when compared to a 12v cordless drill.
Answer: The relationship between a motor's electrical characteristics and mechanical performance can be calculated as such (note: this is the analysis for an ideal brushed DC motor, but some of it should still apply to a non-ideal brushless DC motor).
A DC motor can be approximated as a circuit with a resistor, and voltage back-emf source. The resistor models the intrinsic resistance of the motor windings. The back-emf models the voltage generated by the moving electric current in the magnetic field (basically a DC electric motor can function as a generator). It's also possible to model the inherent inductance of the motor by adding an inductor in series, however for the most part I've ignored this and assumed the motor is at quasi steady state electrically, or the motor's time response is dominated by the time response of the mechanical systems instead of the time response of the electrical systems. This is usually true, but not necessarily always true.
The generator produces a back EMF proportional to speed of the motor:
$$
V_{emf} = k_i * \omega
$$
Where:
$$k_i = \text{a constant.}$$
$$\omega = \text{the motor speed in}\ \text{rad}/\text{s}$$
Ideally at stall speed there is no back emf, and at no the no-load speed the back emf is equal to the driving source voltage.
The current flowing through the motor can then be calculated:
$$
I = (V_S - V_{emf}) / R = (V_S - k_i * \omega) / R
$$
$$V_S = \text{source voltage}$$
$$R = \text{motor electrical resistance}$$
Now let's consider the mechanical side of the motor. The torque generated by the motor is proportional to the amount of current flowing through the motor:
$$
\tau = k_t * I
$$
$$k_t = \text{a constant}$$
$$\tau = \text{torque}$$
Using the above electrical model you can verify that at the stall speed the motor has the maximum current flowing through it, and thus the maximum torque. Also, at the no load speed the motor has no torque and no current flowing through it.
When does the motor produce the most power? Well, power can be calculated one of two ways:
Electrical Power:
$$
P_e = V_S * I
$$
Mechanical Power:
$$
P_m = \tau * \omega
$$
If you plot these, you'll find that for an ideal DC motor the maximum power comes at half the no-load speed.
So all things considered, how does the motor voltage stack up?
For the same motor, ideally if you apply double the voltage you'll double the no-load speed, double the torque, and quadruple the power. This is assuming of course the DC motor doesn't burn up, reach a state which violates this simplistic ideal motor model, etc.
However, between different motors it's impossible to tell how two motors will perform compared to each other based only on the voltage rating. So what do you need to compare two different motors?
Ideally you'd want to know the voltage rating and stall current so you can design your electronics appropriately and you'd want to know the no-load speed and stall torque so you can calculate the mechanical performance of your motor. You may also want to see the current rating of the motor (some motors can be damaged if you stall them for too long!). This analysis also somewhat neglects the efficiency aspect of the motor. For a perfectly efficient motor, \$k_i = k_t\$, or rather \$P_e = P_m\$. This would cause the power calculations using the two equations to be equal (i.e. electrical power equals mechanical power). However, real motors aren't perfectly efficient. Some are close, some aren't.
p.s. In my calculations I used motor speed as \$\text{rad}/\text{s}\$. This can be converted to Hz or \$\text{rev}/\text{s}\$ by dividing by \$2\pi\$..
Comment: For many of us non-experts, if we automatically understood what each of the symbols in the formula stood for, we'd have no need for your otherwise fascinating explanation. Perhaps you could improve your answer with a bit of "where τ = fill_in_the_blank" and "where ω = fill_in_the_blank" ?
Comment: I also think that a higher voltage motor is "better" as it involves lower currents, hence lower energy loss due to Joule effect.
Comment: So in brief, V is proportional to ... V  :-)  and I is proportional to torque.
Comment: Defining the constants in the answer would be useful.  Showing an ACTUAL example of the calculations would be VERY useful.
Comment: @zeffur the Kt and Ki constants, and also R, are intrinsic of the motor, as they depend on how it is built, so they are written in the datasheet.
Answer: After 4 years using and studying electrical vehicles I figured out that  "gradeability" (ability to raise a slope of specific grade) depends on motor torque, and torque depends on current.
Voltage instead "regulates" how fast a motor can run: the maximum speed a motor can reach is the speed at which the motor generates a voltage (named "Counter-electromotive force") which is equal to the voltage it receives from battery (disregarding power losses and frictions for simplicity).
How much current a motor can tolerate when a voltage is applied depends on how much thick the coils wires are (thicker = higher current = higher torque), due to coils internal resistance (the higher the resistance, the higher the heat produced, till wires melt).
Considering a 1000W motor:

providing 100V/10A you'll be able to reach high speed but you won't be able to raise much slope.
providing 10V/100A you'll move very slowly but you'll be able to climb high-grade slopes (assuming the motor can tolerate 100A).

The maximum current a motor can tolerate is named "rated current", which is way lower than the motor "stall current", i.e. the current flowing in  the motor wires when voltage is applied and the motor is kept halted. The motor CANNOT tolerate its own stall current, which will soon melt wires. That's why electronics limits maximum current to rated current value.
Comment: +1 for actually answering OP's question, instead of effectivey answering "it depends".
Comment: added details about relation between voltage and maximum speed
Comment: This answers why so many industrial DC motors have small voltages generally around 9V-24V when most outlets are 120V-220V AC. At those higher voltages, you can only get so many amps necessary for torque. If you can step down the voltage by a factor of x, you step up the amps by x, resulting in x times the torque.
Answer: In any motor, the basic principle is very simple:

rotational speed is proportional to voltage applied
torque is proportional to current pulled

A 100 volt motor is a motor that can take a maximum of 100 volts, and a 50 volt motor a maximum of 50 volts. Since the 100 volt motor can take more volts, if all else is equal, it can give you a higher maximum speed.
But the difference in voltage does not affect the torque. To get more torque to go up a hill, you need to supply your motor with more current. A motor that can take more current (and a battery and motor controller that can supply more current) will give you more torque to help you up the hill.
Comment: To clarify, if you have two otherwise identical motors, but one of them has  twice as many turns in its windings as the other, the low turn count motor will draw the same amount of power at 50 V as the double turn count motor would at 100 V. Both would spin at the same speed, and the 50 V motor would draw twice the current as the 100 V one.
Comment: Certainly the design of the motor affects its torque constant and its velocity constant. But that doesn't change the fact that speed is proportional to voltage, and torque to current. Those are important facts that many people do not seem to understand.
Comment: You start out right, but reach a mistaken conclusion when you neglect to consider not only the magnetic design, but different wire sizes and turn counts wound on what is otherwise the same motor structure.
Answer: Electric motors can be designed over a fairly wide range of voltage and current for the same speed and torque out.  Just comparing the intended operating voltage of two motors doesn't tell you much about what those motors can ultimately do.  Motors designed for high power do tend to work at higher voltages, but that is mostly so that the current can be within a reasonable limit.
To compare two motors for a particular job, you have to look at the output parameters.  These will be the torque, speed range, and power.
Comment: Would you provide an example of how that is calculated? :)  For example:  Suppose I wanted to shake a flat grate 6" with a 30 lb load on top of the screen to sift through smaller bits.  How would one go about calculating what size motor would be needed to do that?
Answer: The mechanical performance of a motor will of course depend mainly on it's physical build, not necessarily its nominal voltage. High power motors will operate on higher voltages, but that does not tell you much.
I won't elaborate on the specifics, but there is a good rule of thumb to use when you want to estimate the parameters of a motor by look. A long motor will achieve higher rpms, and a wide motor will be able to deliver more torque. You can perhaps imagine how this works - a wide motor will have a wide rotor, so the forces of the magnetic fields inside will create a larger torque.
So, if you have two motors of identical length, but one of them is wider, you can expect the wider one to be able to generate higher torque.
Answer: In very basic terms (helloworld's answer has the science bit covered):
Power is voltage * current (P=IV). For a given power, say 1000 watts / 1 kW, you can design a 10 V motor that uses 100 A or a 100 V motor that uses 10 A for the same nominal power:
10 V * 100 A = 1000 watts
100 V * 10 A = 1000 watts

Your next consideration is how the various efficiencies stack up - for each part of the power train there will be some optimum way of building each part that gives best efficiency for the price. For example, if you went for the 10 V option you need a lot of big heavy wires (or bus bars) to handle 100 A, whereas 10 A will flow happily down quite skinny little wires.
However, maybe it's harder to build a control unit / charger that works at 100 V than at 10 V (it's certainly safer for the average user if there's no high voltages kicking around for them to stick their fingers in).
So, there's a juggling act to be done to work out how the system stacks up - for each watt of power you put in, how much useful energy can you get out the other end?
It's a bit like the difference between a big lazy V8 and a screaming turbo motor, both can make the same power, but each is a very different answer to the problem.
Answer: All you have to think about is the power rating and nominal voltage. If the voltage you apply is high (must be within the voltage range) then it can take less current and less torque which indeed can be found out from the speed-torque curve for a fixed voltage.
Voltage is proportional to speed, and torque is proportional to the current. The maximum current it could take is rated current and the corresponding torque can be found out from speed torque curve (as you know the speed from voltage (rpm=k*v)) where k is the speed constant of the motor).
Comment: Not everyone is a native English speaker.  Stack Exchange sites allow you to edit answers for reasons such as this.
Comment: For reasons such as this, nobody should be allowed to "down-vote." Not getting up-voted, is already "punishment enough!"
Comment: -1 for sloppy punctuation and capitalization.
Answer: Voltage and current are the essential components of power a.k.a. the ability to perform work. To do work by means of spinning machinery requires a rotary-acting force - a torque. The rate at which the work proceeds (introduce time) and the measurement becomes of power. More power - increase either current or voltage or both.


Should a Risk Management Plan include a Risk Register?

Question: Is it within the scope of a Risk Management Plan document to include a Risk Register?
Or should a Risk Register be created separately, and the plan merely state that a register will be created?
Answer: Your risk management plan lays out the method, process and tools you will be using throughout the project to manage risks. It's a document you do at the beginning of the project and that should get signed-off. It should cover how you will identify, assess and track risks and will also include things like responsibilities, governance and decision-making processes related to risks. It should mention the tool you will use to track risks (i.e. the risk register) as well as things like how risks will be reviewed and reported (e.g. as part of a dedicated regular meeting, or through the regular status report).
So the risk register stems from the the risk management plan, but it is a separate and live document where you record information about risks as and when they get identified. Usual information in a risk register includes risk ID, name, description, project area or workstream, severity, likelihood, ownership, action/mitigation plan, dates (registered, closed, etc.). See also this question on what to include in a risk register.
Answer: I differ a little bit in definition from Angeline but would result in pretty much the same.  In my view, the risk register or log is part of the risk management plan.  However, we end up using different tools, creating two different artifacts.  The plan is developed using a word application like MS Word while the register is created using another, more conducive application like a spreadsheet or database, allowing for easier data entry, analysis, and reporting.  In this case, the register would be incorporated into the plan by reference.
I think it is prudent to consider the risk plan and register to be a single subordinate Project Management Plan (PMP).
Answer: As each plan is in fact a prognosis, the PM should "weigh items with risk" while planning (i.e. write down risks immediately). And since you baseline your plan, describe assumptions etc., a similar thing is advised with any risks identified in the beginning. In that sense, keeping these risks in a charter or initiation document is advised. Whether this is a "risk management plan", a "project management plan"... - this seems secondary and differs from framework to framework.
Later on a separate register / log (e.g. Excel sheet) is used typically.


Book Recommendations on Quantum Mechanics and Quantum Information processing (with specific topics mentioned in the description)

Question: I an an undergraduate in 2nd year of study and doing an internship this summer on Quantum information Processing and related concepts. Since I had very less exposure to Quantum mechanics I was suggested to read R. Shankar's "Principles of Quantum Mechanics". I am currently following the book . I am also asked to study about Density matrices and Liouville-Von Neumann equation for my project work. I'd like some book recommendations on Quantum Mechanics containing the mentioned topics . I was unable to find them on a Google search.
Comment: Why don't you ask your supervisor?
Answer: I followed the book Quantum Computation and Quantum Information by Michael A. Nielsen and Isaac L. Chuang for a Quantum Information course and found it clear and providing good physical insight. I think it is quite self-contained and in the firsts chapters it provides an overview of Quantum Mechanics to understand Quantum Information. (In particular, it covers Density matrices too.)


Joomla field logic control plug-in

Question: Is there a plugin in joomla that controls the display or hiding of another field based on the specified field similar to the XML showon attribute, or similar to the conditional logic in the WordPress ACF plugin that can be set directly?
Answer: I don't think there is a built-in plugin that does something like that and I'm not aware of a custom one (presumably you have searched the JED (extensions directory) but if you are up against the limits of showon (eg wanting a condition that uses a value from a different xml fields spec - showon can conly use values in the same xml) then it is possible to add a custom attribute to a custom field which will implement more complex conditions for rendering the field.
Check the FormHelper::parseShowOnConditions() function which you can use to parse a custom renderon attribute in your custom field type.
$oparr= FormHelper::parseShowOnConditions((string) $this->element['renderon'], '', '');

If this might help then I can give a more complete example if you can clarify an example of exactly what you are trying to achieve.
Another approach I use for conditionally hiding fields in a view search form (for example if the menu entry or request for a view has specified a specific category you might want to hide a category filter field in the search form, but allow it if no category is specified) is to override the /layouts/joomla/searchtools/default/filters.php with an additional element hide=[fieldname] which you can set in order not to show specific field(s) in the search form.
Again I could post more detail if this is what you are trying to achieve.
(disclaimer - I only use J3, so if you are on J4 my answers might not work - it helps to use the j3 or j4 tag on questions)

Joomla field logic control plug-in