How many amps per leg on a 220V circuit?

Question: If the nameplate on a piece of 240VAC equipment says 10.0 Amps, does that mean that the load is 10 amps per leg, or 10 amps total, therefore 5 per leg?
Comment: there is no `leg` ... whatever current flows out one wire, it has to return through the other wire ... that is how an electric circuit works
Comment: 220V draws from both legs, so 10 per leg.  There'll be no current flow on neutral.  It won't even be connected.
Answer: If you put a current meter one leg, it reads 10A; if you put it on the other leg, it also reads 10A. But that does NOT mean there is "20A" in the circuit. The current in the two wires is not additive. Current flows from one point to another through the CIRCUIT, and the circuit consists of those two wires.
Answer: The confusion is not the amperage. The confusion is how much power do you have. For the record a 10A 220V circuit will have a minimum 10A/2 pole Breaker.
In the USA a 110v, 10A circuit will pull 1100VA. A 220v 10A circuit will pull 2200VA, twice as much power as the 110v circuit. Technically on a 220v that is connected to 2 phases there is no return. That's as simple as I can make it for a DIY'er. Otherwise we need to get into a course on phase relationships.
Comment: 220-240v in the U.S. is 2 legs of a single phase. The 2 legs come off the transformer and have a center tap (the neutral) each leg to neutral is 120v or 240 leg to leg. If it were part of a multi phase phase system the leg to leg value would not be the same as adding each leg to neutral voltage.
Comment: Your answer states 2 phases and I was clarifying as many call 220/240 as 2 phase and it is not. This is the reason I made the comment.
Comment: @EdBeal - You are correct but what does that have to do with the question or the answer? Or should I edit it to say I don't want to get involved in electrical AC theory?
Comment: Answer seems way out in left field
Answer: 10A in one hot, 10A out the other hot
A 240V-only piece of gear connects to two hot legs and a ground (no neutral), so if it pulls 10A, that 10A has to be going in one hot leg and out the other hot leg -- there's nowhere else for it to go!  (In other words, it draws 10A, period -- the legs do not "add together".)
Answer: 10A, you're confusing current (measured in Amperes) with Energy (measured in Watts):
10A@ 12V  =>  120W
10A@ 120V => 1200W
10A@ 240V => 2400W
So the same current (directly related with wire thickness) can carry more energy rising the voltage.
Breakers are there to protect against overcurrent, so a 10A will break at 10A being at 24V, 120V or 240V.
All the current coming from one "leg" is going out trough the other (if the neutral is involved the vector sum on legs and neutral should be 0) It means than one leg may carry 9A, the other 10A and the neutral 1A (I'd say -1A because it's "going back" to the transformer).
Comment: Just to clarify, energy is not measured in watts.  Power (energy per unit of time) is measured in watts.  Energy is measured in Joules, Calories, BTUs, kilowatt-hours, foot-pounds, etc.
Answer: On a 240 volt circuit 10 amps is 10amps on each leg bot not calculated as 20 amps if you can slow it down the amps high pathetically when one leg reads 10 amps the other leg reads 0 alienating back and forth 10amps then 0
Answer: There are a lot of answers out there about this that don't get the idea across I think people are asking for. So adding to an old post that comes up a lot in search results for people getting frustrated with the same odd responses about 220v current measurement for non technical people. This is a long one but it's to cover a lot of the follow up questions and to get them to ask more detailed questions if they have them.
I am not an electrician, don't be dumb, it's your safety, correct me if I'm wrong, etc.
Three things to start out with:
All electrical current has to have a complete path, a full circle. Nothing happens if this path is broken, it's just waiting voltage but no current and no work getting done. You flip the light switch off and break the path, no current moving, but voltage waiting at the switch to start moving amps again when you reconnect. You flip the light on, current flows in and back out of the load (light in this case). Always needs two wires minimum.
AC means alternating current. That means that the positive and negative are reversing (about 60 times per second in the US). In this example, this is not ground potential moving around. This is each wire voltage potential moving above and below ground in opposite timing of the other. They swap places, alternating.
Measuring voltage is always in reference to something. For example: +12v in reference to ground. Usually when people talk about it, they automatically think it's in reference to ground or zero volts so they leave the "in reference to ground" part off. But it doesn't have to be in reference to ground, and in this case it isn't.
Here we go...
So a two wire 220v split phase (not real "two phase" or "three phase" which isn't common for people asking these question) system would have the positive and negative flipping back and forth. There are cases where you can imagine the amperage in this like a DC circuit and others where you can't. When there are any other active wires involved it needs to be measured and discussed like a split phase system. If there are only two wires and you aren't looking to understand any more about AC circuitry, you can imagine it like a DC circuit and shortcut the answer to just "X amps" for this half only.
Finding the amps from a 2 wire 220v AC system you measure the amps with a clamp meter on one wire of a pair. Done. That's your answer. Say you get 10 amps at 220v, which means that it draws 2200 watts. You can measure the other wire and it should be the same value of 10 amps. Great.

Skip the next bits to ---Skip to here--- if you want to get right to the next half of this answer.

Imagine it like measuring a point on a circle of wire. One leg starts then it goes through your dryer or AC or whatever and then back in the other leg. Big circle. Single effective wire to measure. Or you can imagine it like a single hose carrying water, measure any part of it and you'll get the same value, the hose circle is just squished into a long oval and you are seeing two sections as they pass you with water flowing in through one and back through the other, (and also having them flip directions but it's ok to ignore that part for only two wire 220v systems and a simple amp question). If you measured the flow of both wires at the same time it would be zero since you would see 10 amps flowing through one part of the hose on direction and the same 10 amps flowing back down the hose in the opposite direction and your total flow at that point with both hoses would be zero. Even when they flip it still nets zero. That's why you have to measure a single wire on the circle. Usually you can access them split apart at the breaker panel, inside the outlet box, or inside the appliance. Or create an extension cord with only the outer insulation removed, and the inner wires spread apart but still insulated so you can clamp onto them individually for measurement.
If you were to look at the actual amps over time with some better equipment than you're likely to have, you would see one wire increasing up to your measurement while the other one drops to a negative value of the same amps as it swings in voltage at the same time. Then both would meet back at zero and then flip. The wire you started with would show negative amps and the other would show positive. That's why you can measure only one wire. The other wire is 180 degrees out of phase with the first so the load is being carried through both wires at any time and the circle of amps is only the single wire value you are reading. Now this is happening very quickly but it acts like a DC measuring result for those not familiar with AC phases or neutrals, or extra correct math. Just use the correct equipment like a good clamp meter to test one wire of a 2 wire 220v AC system and you're done. The difference in voltage between the two wires will go from zero to 220v and back to zero as they cross paths and back to 220v, but in the opposite polarity. Each phase going positive to negative opposite the other. Not in respect to ground, but to each other, we get our 220v. Each wire in respect to ground is only 110v away.
Now we come to the issue of neutral or ground current. So far we're only measuring the voltage with respect to each other. One wire against the other equals 220v. But each wire is only going positive or negative 110v and the difference between them is the 220v we use in large loads. Your dryer may not only use 220v as measured across two wires. It probably has a ground for protection but not meant to carry any real operating current. It also has a neutral. 220v AC in most places is what's commonly called split phase. Because it can be split off and just use one side and have the return line be the neutral instead of the opposing phase wire. This is avoiding a lot of better explanations on two phase which is only actually used in residential in Pennsylvania and parts of Connecticut in the US and most of Europe I believe uses a single wire that carries 220v rather than having two at 110 to deliver the 220v. But again we ignore this for those asking how to measure amps for 220v as the neutral check will be the same or the wire won't be there.
Take the example above of measuring a a two line system at each line with a good ammeter that shows direction of current. You check one wire and it shows 10 amps going through it while the other wire shows -10 amps coming back down the path. Nice circle of current doing the work in your load and needing to return back around. Electricity always needs a full path. But with this setup, we need more info if they're not balanced exactly by only using two wires in a single circle.
If there's a neutral wire involved you can now expect that some component in your dryer or whatever uses a 120v AC leg to do something since it doesn't need the full voltage difference between two opposite legs. It only needs the 120v difference between one leg and zero. That zero is ground reference, neutral, which are roughly the same in a three wire system for simple explanation sake. So now you have your two wires heading in opposite directions to each go 110v away from ground and creating a total difference of 220v between them. But you attach something to only one side and neutral. A wire kept at ground potential (0v)in this case. You can use that power and for most of the USA we use that setup for lights, outlets, etc. Only using the full difference of each leg of the 220v for large appliances like dryers, heaters, air conditioners, etc. But here's the part where you likely came to read:

----Skip to here----

So like we said above. To measure something that uses the difference between two different phases of 110v that are 180 degrees apart, you can measure one wire since the other wire is just the return or source and will be carrying the current from or to the wire you're measuring. To measure a load that may be using a neutral to return current from one side or the other you need to measure three places to make sure you are taking into account all the amps. You could measure just two wires but we need to verify ourselves here.
Measure the amps in one wire of the 220v system.
Measure the amps in the other wire of the 220v system.
Measure the Neutral of that system.
Here's a likely set of results from those tests at a circuit breaker feeding a dryer, readings taken at a theoretical dryer that wouldn't use this ratio but is easy to visualize:
L1 = 10a
L2 = 13a
N = 3a
So what we have here is a load that is tapping into the large difference between the two wires at their maximum voltage difference of 220v and using 10 amps of current. But that is also using another 3 amps from the L2 wire to power some smaller motor or circuitry and feeding that current back through the neutral wire. So you would think of this as: This circuit draws 10 amps at 220v and 3 amps at 110v for a total of: (2200 watts plus 330 watts =) 2500 watts.
This is not the same as saying "13 amps" or even "13 amps at 220v" which would have been 2860 watts. Since we have a neutral we need to be specific about what amps we're talking about or describe the system as the total watts used.
You have to note the voltage and amps, or the total in a unit that takes this into account. You can't say that it "uses 13 amps" since that's not true at 220v or 110v. It's like having two hoses with different pressure and diameter, you can't total them without taking into account the subtotal of each to get your actual total. But since watts is the work done while taking into account the voltage and the amps, we can use that to get our actual total for the circuit. So we have amps at 220v and amps at 110v and total wattage for both.
For 220v circuit breakers that touch the L1 and L2 wires you need them to be able to pass that 13 amps since inbound or outbound could trip the breaker connecting that wire. If L1 sees 10 amps but L2 sees 13 and the breaker can only handle 10, it would trip because that wire is carrying 13 amps. Doesn't matter that only 10 are returning through the L1 wire. Most of the time in residential, they are just two 110v breakers with a bridging plastic piece to make sure they trip or get reset in tandem. They are measuring the amps through the L1 and L2 wires but don't care which way the current is going, just that it doesn't exceed the speed limit. We care since it's all just a big circle and not two hoses heading in the same direction feeding amps out at the same time.
From our example above with a large circle of hose this one adds a smaller hose to the mix in the form of he neutral wire. One is a big circle that carries 10 gallons per second or water, measure it along any point and it's carrying 10 amps. Until the load taps on to only one side and connects it to neutral. Now there's a part of the large hose that's carrying that additional water but it gets diverted to the neutral wire and doesn't show as flow in the rest of the large hose.
So you have one wire (L1) carrying up to 10 amps at any given moment and can measure that amperage.
Then you have another wire (L2) that's carrying up to 13 amps at any given moment, 10 of which came through the other wire already.
With the missing 3 amps heading from L2 and through the neutral wire to make our math all add up.
So remember you have to have all the elements to reference when talking about amps and volts in a split phase system if there's a neutral. If it's just two wires and they are the same 10 amps of current you're ok to say it's 220v at 10 amps since it's flowing in a big circle.
If you have a neutral you have to measure three points to make sure you've got all your paths accounted for. If they show L1 and L2 are equal at 10 amps and no current through neutral then you're done there. 220v at 10 amps.
But if you have different readings (10 amps and 13 amps) on L1 and L2 and the difference (3 amps) is on the neutral. You have to say it then as: 220v at 10 amps and 110v at 3 amps. The highest of which is seen on the 220v breaker. L2 in this case at 13 amps.
If you don't match this all up you could have ground leakage current which is outside this answer and you should talk to an electrician.
Answer: It means 10 Amps in parallel.
That is both legs pull 10 Amps, but because they're in parallel they never exceed 10 Amps.  The meter would read both legs when measuring kW
Edit: I made a drawing to help visualize. (using 20A load instead of 10A)
Comment: This is very confusing.  Are you suggesting 4 wires - an "out' path and a "return" path on each leg?  On a US 220 v circuit, the breakers are in series and there are only 2 wires involved.
Comment: The runners alternate from the source to the load. That maybe where you're getting 4 wires, but only two. Yes, a 240v load is basically a simple series circuit with each winding 180 degrees opposite in polarity to give a parallel source of power.
Comment: Also the current in is equal to the current out. This is why I drew two runners per ungrounded conductor


Do the Orthodox still Use Matchmakers?

Question: I recently read an article about Jewish matchmaking. I was not aware that such a thing still existed. Is this a universal Orthodox method? Is it enforced? Does a person have to accept the match made for them?
Comment: It exists. Some people use it. It isn't law and it isn't about forced marriages. http://www.theyeshivaworld.com/coffeeroom/topic/how-much-money-to-shadchan-for-being-set-up-1x-2x
Comment: Yes, it is extremely common among chassidim, very common among Yeshivish, and relatively uncommon among Modern Orthodox. Each side always has the choice to say no, and many people go through several matches (meeting each several times) before finally saying yes and getting engaged.
Comment: @msh210 yes, to show that such a thing exists but isn't compulsory ("Most shadchanim don't charge unless there is a good outcome")
Comment: @Danno, while your comment is afaik 100% correct… is that the page you meant to link to?
Answer: I live in a largely Orthodox community. My answer is a mix of my philosophy combined with the thinking of my kids' high school rabbis, whom, even after having graduated a few years ago, they still follow, to an extent.
The kids' rabbis as well as most shul rabbis in my neighborhood highly encourage the use of matchmakers as the sole means of setting up marriage prospects. A large part of this thinking stems from the idea of setting up a controlled environment where boys and gorls do not socialize in any format other than if they are st up for a shiduch / possible marriage prospect.
My wife and I met at a singles weekend. My kids attend a number of singles weekends, and, otherwise, date girls they meet in the neighborhood or at college. I know many people in my neighborhood who met their spouse on weekends or while studying in yeshiva or college.
So, in summary, nobody is enforcing the shidduch method, at least not in my community. And, as I know personally, one person, who tried a shidduch, and at the end, found her spouse on JDate. So, obviously, there is nothing that forces anyone to accept the matchmakers' recommendations.
I have no statistics on the marriage "longevity" rate of those that have used matchmakers vs. other methods (i.e., what percentage of such marriages stay that way without a divorce.) FWIW, a close friend of mine married via shidduch. Two years later, after having a baby, they split. But, instead of a clean divorce, the guy refused to give her a get, and she remained an aguna for about 15 years! So, there's no guarantee that matchmaking is a successful method.
Answer: It should already be clear that matchmaking is common among the orthodox. I just want to add (from personal experience) that at least one community, Lev Tahor, uses the closest possible to forced marriages.
There too, matchmaking is in principle practised, but instead of the involved parties' mutual research, matches are more or less* dictated by the leadership. The potential bride and groom generally** do not meet each other at all before the wedding.
Obviously, marriage cannot be completely forced within Jewish law***, as the bride has to acknowledge the betrothal somehow (usually accepting a ring), but practically, peer pressure and various punishments make it difficult to impossible for children of the community to reject a proposed marriage.
Leaving the community is usually not an alternative to a proposed marriage, as the community's children generally get married at a very young age, and are not educated enough to survive in the world outside of Lev Tahor.
Important: The conduct of Lev Tahor is the exception, rather than the norm, within the orthodox world.

*more or less: there have been cases of members pushing for specific matches.
**generally: there have been meetings when a match involved a party coming from outside the community.
***Except for yibum.

Do the Orthodox still Use Matchmakers?


How do I replace spruce leaves with oak leaves in Minecraft?

Question: I'm unhappy with the way I built something in Minecraft, and want to replace the spruce leaves with oak leave to match the rest of the build, but I do not know how to. Can someone tell me what the block data is?
Comment: Possible duplicate of [What is the command to replace blocks in Minecraft PE?](https://gaming.stackexchange.com/questions/341445/what-is-the-command-to-replace-blocks-in-minecraft-pe)
Answer: /fill command fills a region with some blocks or replaces specific blocks with other ones. Especially for your case, execute this:
/fill ~ ~ ~ ~10 ~10 ~10 leaves 0 replace leaves 1
Where ~ ~ ~ is the first position of the region, and ~10 ~10 ~10 is the opposite position of the previous one. leaves 0 and leaves 1 are for oak and spruce leaves respectively. Syntax of the fill command.

Block data is needed for differing various block variations from each other. For example, whether waterlogged the block or not. You should check block data for each block separately. The block data of leaves.


Have Subversion (in Eclipse) Ignore Specific File

Question: Is there any way to have Subversion (in Eclipse) ignore a specific file.  I've tried going to Team --> Synchronize with Repository, and the Mark as Merged option isn't available.  I don't think it's possible, but does anyone have any ideas?
Answer: Not sure about eclipse and what ignoring file has to do with marking as merged, but what I'd do is svn pe svn:ignore <path> and add the file there.
Comment: I just want the arrow to go away.  I have a file that has to point at local builds instead of release builds for development, so all of my projects are marked as out of sync, which makes life a little harder :)
Comment: So I was right (for what I can tell by your accepting the answer:)).
Answer: After having refreshed your project with the repo, you just have to right click your file and "add to svn ignore" in the Team menu.
The option is available only if your file is not already in the repo.
If your file already exists in the repo, you will have to delete it first and recreate it as if it is a new one.
You can ignore only a single file or setup a mask.
Answer: It sounds to me as if the file is already added, which is a state it can't be ignored from. You need to remove it first, and you need to synchronise it fully first such that the server and client views of the file are equal.
You can do this by reverting the file, but keep a local copy so you can fix the file after it has been deleted from both sides (you'll delete the client copy, and will have to put it back again). After that, delete the file from the client side, commit, synchronise, put the file back, and then mark it as ignored from the SVN team menu (do not 'add' the file).


Jitsi Meet server on Ubuntu 18.04

Question: I would like to create a video conferencing system with Jitsi Meet through Ubuntu core 18.04 installed on a Raspberry Pi 4. How should I do it?
P.S. when I control the raspberry remotely and write the sudo apt-get code it tells me that apt is not a valid command. How can I solve it? Thanks
Comment: Why not install Ubuntu server?
Answer: Ubuntu Core is snap-only.

Deb packages (which use apt) are not supported on Core, so the failure of an apt command seems like expected behavior.
As of June 2020, neither Jitsi nor the Jitsi community have created a Snap for Jitsi Server yet. Sorry.

It's possible on Ubuntu Core to create an LXD container that CAN run deb packages. However, it consumes resources and pi machines are not known for their copious resources....

Install the LXD snap.
Configure LXD
Install an Ubuntu-minimal or -server cloud-image into the container.

15GB recommended for a container storage group

Login to the container and install the deb using normal apt tools.

Alternately, you can replace Ubuntu Core with Ubuntu Server as the base OS on your pi. Pi install instructions
One nice thing about a pi, with it's replaceable SD cards, it that it's fairly easy to try both. If you do try both, be sure to let us know which worked best and why!

Jitsi Meet server on Ubuntu 18.04


Allometry of vision, can mice see their own fingers?

Question: Looking around, I've found a lot of research on the allometry of visual acuity and vision at a distance, but not so much on vision close-up. As I understand it, the "near point" of vision is largely determined by the optical/focusing power (diopters) of the lens, which is itself determined by the refractive index and lens curvature (lensmaker's equation). Assuming the refractive index is constant, this implies smaller animals should have the more powerful vision (assuming smaller eyes) necessary to resolve something as close to their eyes as their own claws. Does measurement agree with this hypothesis? What is the scaling relationship? Is there a single one, or is it sensitive to eye type like acuity is?
Answer: Exciting question, and anticipations are largely met for mice (featured in title). Mice have a closer focal point than humans. As less than 2 cm they can likely see their fingers. Assumption on constant refractive index would require to further assume that viewing angles are different as numerical aperture changes. Mice having a more powerful vision system could be considered true.
Recent publication with measurements underlying above: https://doi.org/10.1364/BOE.3.000715
Generalization beyond mice would be interesting, but likely require control for other things such as habitats and whether predatory animals, ....


Windows time command equivalent

Question: There is a command in Linux that outputs system utilization called time. Is there a Windows equivalent? Or how else can I manually use the task manager commands in a batch file?
Comment: No time is what I need. I want to benchmark how long it takes to run the command but I want to do it on Windows so I can do it in a batch file.
Comment: Do you mean `uptime`?  The `time` command simply benchmarks how long it takes to run a command.
Answer: If your Operating System has powershell (older operating systems might need a download), you can simply use Measure-Command cmdlet.
Comment: Ok is there one to measure cpu utilization? Not just time but utilization as well
Answer: The Windows Server 2003 Resource kit includes a timeit utility. The resource kit works fine on XP as well, and I've used the individual tools on newer Windows operating systems as well.
Comment: again in powershell, you can do: (get-process processname).cpu, where processname is the name of the process. this is only a snapshot at the tiem so you need to do some sort of summing/averaging etc. yourself.
Comment: Ok is there one to measure cpu utilization? Not just time but utilization as well.
Comment: not directly i know of, but process explorer may fit your requirements. http://technet.microsoft.com/en-us/sysinternals/bb896653
Comment: I need a way to do it from the command prompt because eventually i need to do it in a batch script.
Answer: I found a tool which -- while not a direct port -- appears to give you the information you desire.
<code>C:\> timemem "find \"e\" myfile.txt"

---------- MYFILE.TXT
>ONE Homo sapiens alu
>TWO IUB ambiguity codes
>THREE Homo sapiens frequency

Process ID: 476
    elapsed time (seconds): 5.81
    user time (seconds): 0.55
    kernel time (seconds): 0.30
    Page Fault Count: 3150
    Peak Working Set Size (kbytes): 12420
    Quota Peak Paged Pool Usage: 78324
    Quota Peak Non Paged Pool Usage: 2240
    Peak Pagefile Usage: 917504
</code>
timemem.exe is available from Andy Fingerhut's page of code and the timemem source is hosted on github as part of the clojure-benchmark repo.
Much detail is available in readme-timemem.txt, form where I copied the above example.
(found from this neglected answer over on superuser)

Windows time command equivalent


Why not show (or make it optional) only hot questions in chosen communities?

Question: It would be more convenient than having the costumers manually filtering them, and it's useful too. Similar question websites supports such features after all.
Answer: Half of the point of Hot Questions is to serve up content from sites that you don't know exist. It's a way of discovering new sites as well as new questions.
By having a set of chosen communities you'd lose the ability to find new sites.
Not to mention how infrequently people would maintain their own list of chosen communities (i.e. maybe once to set them up, and then never again) so when new sites come along you'd never see questions from them, even if they were topics you were interested in.
Comment: Good point, and sorry for the duplication. I checked beforehand but found nothing.


What are the things that I should mention and avoid in the introduction e-mail to my team in my new job?

Question: I am joining my first job after my graduate studies. My manager asked me to send an e-mail to him with my short bio so that he will use it to introduce me to the entire team. I would like to mention my educational qualifications and interests outside work. I know the high-level idea of the product my team is working. Is it also fine to mention "how my skills will be helpful in improving the product"? I am a bit confused about this. I would like to know what are the things I should mention and as well as avoid in the introductory e-mail? Please let me know. Thank you.
Answer: A short bio is usually only a few sentences:

I have just graduated from the University of Southern North Dakota with a masters degree in Musicology, with an emphasis on bassoon duets.  I also enjoy hiking and fishing.

So, give an emphasis on your studies and technical training, with (perhaps) a short sentence on your personal likes.  If your manager wants more details, he will ask for them.
You can mention your skills, but they are probably not looking for your opinion of how they can be helpful in improving the product.  You're just starting: listen and find out more before assuming you know what they need.
Answer:
Be modest. "I am new to the company and to the team, andf I thank you for the confidence you are extending to me by letting me join the [fill in the name] team and [fill in the name of the company or subdivision]
Say something nice about the team - "I've heard great things about the team and the company during the interview process and, needless to say, I accepted the offer and I am looking forward with working with you"
Express confidence - "I graduated with a major in [state the major] from [state the university] in [give the date]. I look forward to being a full fledged, fully participating, engaged member of the team".
Express positivity and good will. "I am looking forward to meeting and getting to know you all of you as a team and as individual members of the team over the next few days"
Try to get something from them - "Feel free to take me out to lunch any time :)"


Calculation of sound pressure level created by arrayed sound sources

Question: I am trying to get a large sound pressure level by arranging individual horns, but I am curious how to design the arrangement structure to obtain a synthetic sound field with sharp directivity in the axial direction given the synthetic sound pressure level and the sound pressure level of the individual horns.
Answer: In the simplest case, where there is no gain shading (which effectively constitutes amplitude weighting, possibly frequency dependent) the response of an array consisting of omnidirectional sources (or receivers, due to reciprocity principle) is given by
$$Y(\psi) = \frac{1}{N} \frac{\sin \left( N \frac{\psi}{2}\right)}{\sin \left( \frac{\psi}{2}\right)}$$
with $N$ the number of elements in the array. Replacing $\psi$ with $\psi = \frac{2 \pi}{\lambda} d \cos (\theta)$ where $k$ is the wavenumber given by $k = \frac{\omega}{c} = \frac{2 \pi}{\lambda}$, with $\lambda$ being the wavelength, $c$ the speed of sound and $d$ the distance between the elements, you can get the response of the array for various angles of interest $\theta$ for any frequency of interest corresponding to a wavelength $\lambda$.
More information on this topic and a thorough explanation on arrays can be found in Optimum Array Processing: Part IV of Detection, Estimation, and Modulation Theory by Harry L. Van Trees (this is where I also got the information provided here). Of course there other resources that could provide some information. This is just a suggestion which had proved to be quite useful to me in the past.
Comment: thank for your excellent reply..
Comment: @ZaellixA, this is great, +1, glad to have you on board here. -NN
Comment: Thanks a lot NN, really appreciated getting that from someone like you. I am extremely glad to be on the same board with people like you.


What is the difference between the stable and nightly builds of Mozilla Firefox?

Question: I am aware that Firefox has nightly builds available at https://nightly.mozilla.org/ and was wondering what the difference was between the stable and nightly builds. Are they safe to use or are they primarily for beta testing?
Comment: Nightly builds are pretty much state builds and are not stable releases. They are more or less testing releases that are just made available to the public. For the most part, they'll work, but they should not be used as a regular production version.
Answer: Nightly builds feature the absolute latest changes, and are considered unstable. They are the most buggy, and will result in a higher crash count than stable Firefox Releases. They are to be used for seeking bugs, and then submitting them to Mozilla developers, so that the Beta and Release channels do not suffer from such bugs.
Nightly is usually many versions ahead - Currently on 9. So you will be seeing features added long before others, but at the risk of crashing more, and potentially broken parts of Firefox. I can confirm this by using x64 Nightly and not being able to use Flash properly anymore (Crashes x64 Flash)
They are to be used at your own risk and discretion. As they say, "These builds are for testing purposes only.", so don't count on Nightly when working.
Comment: @EBGreen It does not need to be another question though.
Comment: Thanks. Is it possible to run both the nightly builds and stable releases at the same time?
Comment: You can. They are stored in separate locations. I use both personally.
Comment: And before you ask (if you were planning to) you should make a new question along the lines of "How do I install production Firefox and Nightly Release Firefox on the same machine"
Comment: @EBGreen You download both installers, install both. It doesn't require anything fancy.
Comment: you are missing the point of my comment. What you posted should be the answer to a completely separate question, not a comment here.
Answer: The very top of the nightly build page:
Comment: ...and the developers' page: Nightly Builds: the Bleeding Edge

Created most weekdays from the previous day's work, these builds may or may not work. Use them to verify that a bug you're tracking has been fixed.

We make nightly builds for testing only. We write code and post the results right away so people like you can join our testing process and report bugs. You will find bugs, and lots of them. Mozilla might crash on startup. It might delete all your files and cause your computer to burst into flames. Don't bother downloading nightly builds if you're unwilling to put up with problems.
Comment: @Linker3000/EBGreen - Thanks. Please see my follow-up question to Simon
Answer: They're for those who want to live on the bleeding edge and don't mind instability as part if their daily browsing life. Maybe they're developers or testers.
People who want mostly stable builds should use Firefox's Beta Channel. If you want to be in on the newest features with the occasional crash, there's the Aurora Channel.
You can choose from the channels at http://www.mozilla.org/en-US/firefox/channel/


Only getting one element returned, OO PHP

Question: class Score
{
    var $score;
    var $name;
    var $dept;
    var $date;

    function Score($score, $name, $dept, $date)
    {
        $this->scores = ($score);
        $this->name = ($name);
        $this->dept = ($dept);
        $this->date = ($date);
    }

    function return_score(){
        return $this->scores;
        return $this->name;
        return $this->dept;
        return $this->date;
    }
}

$newscore = new Score("131313","James", "Marketing", "19/05/2008");
echo $newscore->return_score();

The above code is only echoing 131313. I am just beginning to learn OO PHP so please go easy! Totally lost, so any help would be much appreciated.
Comment: What output do you want? It appears you want all of the variables at once, but not sure.
Comment: I would like all the elements returned at once. Should i be returning each element separately?
Comment: Just a note, you have "var $score" but use "$this->scores" instead of "$this->score"
Answer: You can only return one value in each function or method.
In your situation, you should have a method for each of the class members:
public function getScore() {
   return $this->score;
}

public function getName() {
   return $this->name;
}

public function getDept() {
   return $this->dept;
}

public function getDate() {
   return $this->date;
}

Edit after the comments:
You could also need a method that returns all the members as a single string:
public function getAll() {
   return $this->getScore(). " " .$this->getName() . " " .$this->getDept(). " " .$this->getDate();
}

Answer: You can't return more than once in a function. You could return a concatenated string:
return $this->scores.' '.this->name.' '.$this->dept.' '.$this->date;
//added spaces for readability, but this is a silly thing to do anyway...

I wouldn't recommend it though as you'd be mixing you presentation of the object with its functionality - don't.
I'd suggest making a template of some sort (I'm imagining you might want to tabulate this data?). Each row would look something like:

  <?php echo $score->name; ?>
  <?php echo $score->scores; ?>

and giving it your object or objects in array (you know about foreach{} ?). I know it looks more long-winded, but separating these concerns is going to be better for you in the long run.
Assigning with = : you don't need the parentheses around the thing being assigned (usually).
Also:
Are you running PHP4? Your constructor function indicates you are. I'd recommend moving to 5.21 or higher if at all possible as classes and objects are much better. You can also use the rather useful __construct method (as opposed to using the class named method - in your case: Score()). This makes inheritance and extending easier because your classes are no longer having to remember in two places what class they are extending from.
Answer: First of all you should use public, protected or private instead of var
var $score;
var $name;
var $dept;
var $date;

such as
protected $score;

or with a coding standard prefix protected/private variables and methods with underscore like such
protected $_score;

This method can also be called __construct
function Score($score, $name, $dept, $date)
{

The var is declared as score but you assign a variable to scores. I also don't understand why you have parentheses around the variable.
        $this->scores = ($score);
        $this->name = ($name);
        $this->dept = ($dept);
        $this->date = ($date);

Replace with
    $this->score = $score;
    $this->name = $name;
    $this->dept = $dept;
    $this->date = $date;

}

The first return encountered will return that value from the function/method. I suggest you recode to add get/set for each variable, ie getScore() or to use PHP5 method overloading __set, __get and __call.
public function getScore() {
        return $this->score;
}

}
You can also look at the automatic methods to set and get variables Overloading


How can I frame and hanging large prints?

Question: Hope this is relevant to this site.  I have a 41"x48" print of a satellite photo that I'm trying to hang on a wall without a frame.  It's about 40 years old, so I want something that will be gentle.  I was thinking of sandwiching it between two sheets of acrylic and using clip frames.  Can you get clip frames for something that big?  Is there a better way to go about doing this?
Comment: Poster shops routinely mount 100+ year old paper images on linen, and these are then framed, usually under glass that does not touch the surface. Anything in contact with the face of the image, glass or plastic, risks damaging it. It is very common to see the surface of a print transfer to its glass or plastic cover, destroying the original.
Answer: I'm assuming you aren't the type of person that would just stick it to the wall using thumbtacks.
The best solution would be to get this print professionally conserved, and then have a reputable frame shop make a custom frame for it.
This process will probably cost in the $500 - $1,000 range including the frame, but depending on the print, it might be worth it.
The conservation process would stabilize the paper, and prevent it from further damage. It would entail flattening out the print, cleaning the dirt with special solvents, and then most likely putting a backing on it and then sticking it into a vacuum press to get all of the bubbles and folds out of it.
Once it has been conserved, a frame shop can walk you through the details of making the frame such as the style of frame, the type and color of matting, the glass, etc. The frame shop will then wire up the frame so it can be hung securely on your wall. At the end, it should look like something that could be easily found in an art gallery.
There are other options such as building the frame, and cutting the mat yourself, but the results won't be anywhere near what it would be if it was professionally made. The tools and supplies would also be expensive. The mat cutter kit alone is $200 or more. It definitely would not be worth investing in those tools yourself unless you plan to frame many other pictures.


What effect does a quaternary ammonium compound have on uric acid (urine)

Question: What effect does an Amine based quaternary ammonium compound have on urea/uric acid?
Will an amine based quaternary ammonium product react with uric acid and get rid of the smell?
Comment: The premise of this question is a little off. Urea and uric acid are both odorless; any smell is due to other compounds.
Answer: Uric acid, according to this site, is odorless:

Uric Acid is a white tasteless odorless crystalline product of protein metabolism, found in the blood and urine, as well as trace amounts found in the various organs of the body. It can build up and form stones or crystals in various disease states.

Urea, according to this site, is also odorless:

Other nitrogen-containing compounds are found in urine. A large number of different compounds can affect the smell of urine, and it can be influenced by diet (as people who've experienced the effects of eating asparagus can attest). Whilst the urea in urine is odourless, it can quickly break down into other nitrogen-containing compounds, such as ammonia and trimethylamine. Ammonia has a pungent smell, but a higher odour threshold than trimethylamine, which has a fishy odour – and is in fact the compound responsible for the smell of fish. These compounds are continuously created as urea breaks down, which explains why stale urine smells much worse than fresh urine.

You asked:

Will an amine based quaternary ammonium product react with uric acid and get rid of the smell?

Quaternary ammonium salts, on the other hand, might have a smell of their own. So if I understand your question, the answer is no.


Is it OK to store encryption key on Windows fileserver?

Question: Is it considered secure to store a symmetric encryption key in a file on a networked Windows file server, accessed through a "share"?  I would use the "Security" tab on the folder containing the key file to make sure only the needed service accounts have read access and the relevant support group has read/write access.
Answer: This totally depends on whether it meets your risk assessment for the task in which you are using it. It maybe totally fine or it maybe a very bad idea.
You need to know. What are the results of your risk assessment and what are your security policies?
No one on here can answer this without a more detailed question relating to the what you are are wanting to secure.
Just make sure if you do this that it meets all of your policy and legislation/compliance requirements you maybe following.
Answer: For most situations I wouldn't consider this a good idea, but as ISMSDEV said, it depends on your threat model and what you are protecting against.
But some of the risks you'd have to consider are:
SMB only supports encryption starting with v3, so you'd have to ensure that there was no way they key was accessed by older clients or if someone authorized accesses the key, an attacker could sniff it off the network.
There are also the risks associated with someone gaining direct access to the file server and getting access to the key.
But whether those risks are acceptable / manageable comes down to your threat model and what your defending against.
Edit: Corrected that SMB3 does do encryption
Answer: As other answers have said, it depends on your risk model. Let's explore what some risk models might look like, from weakest to strongest:
1. SMB is secure. Admins are trustworthy. Attackers have no physical access to the server.
If there is only a small amount of destruction or monetary loss that an attacker with the key could cause, then this is a perfectly acceptable risk model, and your solution is fine.
2. SMB has too many CVEs for my comfort
And it does, 94 listed with 20 so far in 2017, including the recent and devastating WannaCry ransomware the shut down large parts of the internet.
3. Admins are not trustworthy
Do Windows domain admins really need access to the key anyway?
4. Physical attacks on the server are possible
Attackers could yank the hard drive of the server, or do a cold boot attack by yanking the RAM sticks out of the running server. In this case, you're vulnerable as long as the key's plaintext exists on the file server's disk or memory. Full Disk Encryption like BitLocker helps with HDD-yanking, but not with RAM-yanking.

If 1. lines up with your threat model, then what you are doing is fine. But if your threat model includes any of 2. 3. or 4., then you probably want to do something like use public key encryption to protect the key file on the share, using tools like openssl or gpg, where each server / service account has its own private key.

Principle of least privilege
Rather than asking "is this good enough?", which is the mindset of starting with no security and adding it until you're comfortable, I would encourage you to change your thinking to:

Nobody has access except the people / accounts that actually need it.

This is a proactive defence-in-depth mindset.
If the admins placing the key on the file server are the only ones needing write access, then make sure they are the only ones with write access. If the service accounts are the only things needing read access, then make sure they are the only ones with read access. If there's no reason to have the key in plaintext on the file server, then don't. If the domain admins don't need to read/write the plaintext, then make sure they can't. And so on.
Answer: Obviously it very much depends on, what you are using the encryption key for. Be aware that this is not safe. Besides possible flaws in access configuration and windows share, you need to be aware that this key is stored plain text on the hard disk.
If this is a virtual machine, attackers could also get a copy of the VM image... and simply the key.
So obviously the group of humans, who have access to this key is much bigger than you might think.
I first wanted to provide the short answer no, but stackexchange asked me to type at least 30 characters ;-)


how to work with dynamics and animated objecs

Question: I want to drop several objects into a jar one by one, not all at the same time. How can I achieve this? I tried to hold objects with another passive rigid body and then animate that object away allowing objects to fall, but the active rigid body objects dont animate at all.
Answer: I'm new to blender myself, but I think your solution would lie in the timeline key frames. For each object you can start movement at one key frame, move, and stop at another key frame. Hope this helps.


in java what does the @ symbol mean?

Question: I know what it means in a comment for documentation purposes, but outside of that what does it mean? (I would normally just google this but every non letter symbol shows up in results)
Comment: [What does the @ sign means in java?](https://stackoverflow.com/q/2971521/6521116)
Comment: http://stackoverflow.com/questions/24221/java-annotations
Comment: http://stackoverflow.com/questions/19551022/the-symbol-in-java
Comment: possible duplicate of [How to get a nice URL like "http://stackoverflow.com/questions/1074/asp-mvc"](http://stackoverflow.com/questions/1227348/how-to-get-a-nice-url-like-http-stackoverflow-com-questions-1074-asp-mvc)
Comment: You can search in google with `java At` not `java @`
Comment: It means BAD language design.
Answer: The @ symbol denotes a Java Annotation. What a Java annotation does, is that it adds a special attribute to the variable, method, class, interface, or other language elements. (This can be configured when you declare the annotation) When you add an annotation to something, other parts of the program can check whether something has an annotation or not. It then can use this information to do whatever stuff they need.
Let me give you some examples:
The @Override annotation
public class SuperClass {
    public void someInterestingMethod() {
        System.out.println("Superclass!");
    }
}

public class DerivedClass extends SuperClass {
    public void someInterestngMethod() {
        System.out.println("Derived class!");
    }
}

And when you do this:
SuperClass sc = new DerivedClass();
sc.someInterestingMethod();

The someInterestingMethod() call should be dynamically dispatched, and print "Derived class!", right? Well the derived class' method was actually misspelled, so DerivedClass got its own separate method called someInterestngMethod(), totally unrelated to the superclass' someInterestingMethod(). As such, someInterestingMethod() is no longer overridden, and the superclass' implementation is invoked.
The @Override keyword is intended to help with this. It signals your intent to the compiler, that you would like the annotated method to be an overload of one of the ancestor class' methods. If it's not (such as in this typo case, or if the SuperClass API changed and renamed the method), the will fail your compilation, to alert your attention to the broken override.
The @SuppressWarnings Annotation
Here is a method:
public void someMethod() {
    int i;
}

There will be a compiler warning saying that i is never used. So you can add the @SuppressWarnings to the method to suppress the warning:
@SuppressWarnings("unused")
public void someMethod() {
    int i;
}

Note that there is a parameter to the @SuppressWarnings annotation. Some annotations have parameters and you can look for the them in the javadoc. But for those that don't have parameters you don't need to add () like a method.
You can also declare your own annotations and use reflection to check for them. The above 2 annotations will be checked by the compiler.
Comment: @Alexander-ReinstateMonica I don't know why I forgot to fixe this for such a long time, but someone downvoting this again has made be remember that I had posted this particular answer half a decade ago... Now it's fixed :)
Comment: hey, thanks for addressing this. Would you mind if I suggested the edit? I have an example in mind that would better reflect the utility of `@Override`
Comment: Oh, my edits show up immediately without approval :| Curse of high reputation haha. Could you let me know what you think? Feel free to tweak/revert if you feel that's appropriate https://stackoverflow.com/posts/31822268/revisions
Comment: Glad I could help :) Deleted my now-irrelevant comment
Answer: The @ sign is used to specify Java Annotation.
https://en.wikipedia.org/wiki/Java_annotation
There are built-in Java Annotation and user defined Custom Annotation.
Annotations are used in various ways, such as suppress warning, associate method to URI (Servlet), associate variables to resource (JNDI) etc
Answer: The @ symbol is used for annotations.  In my experience, the most common annotation is @Override, which indicates that a method is declared in a superclass.  Other common annotations are @Deprecated, indicating that a method should no longer be used but still exists for backwards compatibility, and @SupressWarnings, to prevent warnings from showing up in the compiler.
Note that it's actually possible to get annotations which are not included in the core Java libraries and to declare your own annotations.
Answer: The @ symbol denotes Annotations. They provide information about a class, its field or method (above which they appear). They cannot perform operations. The compilers or special annotation processors use this information to make writing code less verbose.
In Java Persistence API you use them to map a Java class with database tables.
For example
@Table()
Used to map the particular Java class to the date base table.
@Entity
Represents that the class is an entity class.
Similarly you can use many annotations to map individual columns, generate ids, generate version, relationships etc.
Answer: As some other suggests, it is Java's annotation. It helps the compiler to validate your code and to notify the programmer as well.
Very simple code example:
public class SomeClass {

    @Override
    public String toString() {
        return "SomeClass";
    }

    @Deprecated
    public void doSomeOperation() {
        // some operation...
    }
}

The annotation from SomeClass#toString which is @Override helps the compiler to determine that it is an overridden function from the implicit inheritance to the class Object.
While the annotation from SomeClass#doSomeOperation will warn the programmer that the function itself is deprecated already and should be avoided to use.
Answer: The annotations are for the reader or compiler, not executable code.
Comment: This is not correct; annotations can be preserved in the compiled byte code, and can be read and used at runtime. Some frameworks such as the Spring Framework and Java EE use this a lot.

in java what does the @ symbol mean?


Replace 7 speed 14-34 cassette

Question: I want to replace my cassette which is 7 speed 14-34 shimano. The problem is I can't find exactly the same one. All I saw its 13-34 or 14-32 cassettes. So the question is: It is possible to replace my cassette with 14-32 or even lower e.g. 13-26 without replacing a chain or any other replacements? Thank you in advance.
Comment: You mean like this: [Shimano 14-34 Thread-on 7-speed Freewheel "Megarange"
](http://harriscyclery.net/product/shimano-14-34-thread-on-7-speed-freewheel-quotmegarangequot-778.htm) (I Googled "7-speed 14-34" and got at least a dozen good hits.)
Comment: Yep possible, I just check it on eBay.
Answer: As long as you're not adding larger cogs than you've got on right now, your existing chain should be a functional length.
One more thing to consider is that if your current chain has significant wear, running it with a new cassette can damage the cassette (effectively very rapidly turning your "new" cassette into your "old" cassette), so even though your old chain should work fine with your new cassette, it may be worth it to replace it anyway.
Comment: So if I will change the chain do I need to replace **chainrings** for the same reason?
Comment: That depends on how worn they are.  If a worn chain stays on for too long, it can damage the cassette and the chainrings, and all three should be replaced together.  But, because of the larger diameter, chainrings don't wear as quickly as cassettes, so it is quite possible that your chainrings are fine.  You should visually inspect the chainrings.  If it has been worn, you should see asymmetric wear on the teeth, often described as resembling a "sharktooth".
Answer: If you're replacing it with a similar range (1-2 teeth at either end) you should be fine. I wouldn't recommend changing the gear range significantly.
I replaced my cassette with a much smaller biggest (in terms of number of teeth) gear and it wouldn't shift into the top couple of gears. I believe the length of the pivot arm on your derailleur is tuned (to a certain degree) to the range of your cassette.
I agree with prototoast that you should probably replace your chain at the same time.
Answer: Also verify that it is a Shimano compatable cassette.It doesn't have to be a Shimano brand just Shimano compatable.
Comment: Does anyone even sell 7-speed cassettes that aren't Shimano-compatible?

Replace 7 speed 14-34 cassette


What External Evidence Do We Have For Samaritans Living In Babylon in the 6th or 5th Century BC?

Question: The vision of Zechariah 5.5-11 was given to the prophet to encourage the Jews that the wicked Samaritans who had been opposing their efforts to rebuild the Temple would be removed from Jerusalem and resettled back in their homeland, the land of Babylon. Unfortunately, while this interpretation seems to take into account the bulk of information better than any other interpretation, the primary problem with this understanding of the vision is that historians know of no movement of Samaritans back to Babylon. But this is an argument from silence. All we know is that historians know of no major migration of Samaritans back to Babylon in the 5th century BC, but historians cannot tell us whether or not a few key individuals were relocated to Babylon during the days of Zechariah.
Comment: How do you know that it refers to the Samaritans? And how do you know that it literally refers to Babylon? The Bible uses "Babylon" to symbolically refer to the city of evil.
Answer: My detailed answer to a more recent question posted has inadvertently directly answered this question and would be more appropriate to place here. Instead of duplicating the content here, please see the related question.
To add on to the referenced answer, since there is no evidence that the Samaritans physically migrated back to the city of Babylon, and much evidence to suggest they stayed in the land of Samaria, a refining of the interpretation and/or fulfillment of Zechariah 5:5-11 may be needed.
For Instance, assuming that the only people that Zechariah's vision can refer to is the people of Samaria and that they are to return home, a more figurative return makes greater sense to me. While they may not have physically returned to the city of Babylon, they did return their allegiance to the ruling empires of the time period. Specifically when compared to the Jewish people, according to the account of Ezra.
Also, the land of Judah at the time was controlled by Babylon consistently through the 6th and 5th centuries. Literally, under Babylon rule until the end of the 6th century and then figuratively under Persian rule. Since King Darius of Persia ended up making the city of Babylon the capital of the southern Empire, an argument can be made that this 2nd empire can also be the meaning of the Babylon reference in Zechariah. Regardless, the Samaritan people returned their allegiance to the Babylonian empire. Therefore Zechariah's vision can be considered fulfilled in this sense.
A natural follow-up question one might have with this explanation is, "Why would God give this vision to Zechariah if it would not be fulfilled literally?" My answer is that I see this vision as being very important to motivating the Jewish people to complete the Temple's construction. They were experiencing continuous interference from the Samaritans who were doing an excellent job playing politics to prevent its completion. Therefore, it may have been a demoralizing project that required a prophetic vision to overcome.
Comment: Hi Super, welcome to BH-Stack Exchange, we are glad you are here. Please be sure to take the [site tour](https://www.hermeneutics.stackexchange.com/tour) and read our [code of conduct](https://www.hermeneutics.stackexchange.com/conduct). Thanks!


Easy virtualization method

Question: We are developing an online judge system to test students' computational geometry problems solutions. At this moment wee need a testing environment: we have to limit time and memory usage (to accept only optimal solutions), and since we run untrusted code, we have to forbid some system calls (like fork), disable networking, etc. What would be the easiest (open source) virtualization solution for this task? As far as I understand, I will have to use a patched kernel (like OpenVZ), or it is possible to find a simple tool, which will accept restrictions and untrusted program as its arguments and run it?
P.S. If it is important — we run c++ code, however, we would like to use a universal solution.
Answer: If the problems involve only stdin/stdout, e.g. read some input then calculate output, you may have a look at seccomp It's really simple.
Also in near future a second mode of seccomp may be come into the kernel which will give you more flexible.

Easy virtualization method


Are there any good online training sites/videos for learning subversion?

Question: I am trying to learn subversion as best as possible but honestly anything I have read makes very little sense. I feel like I need a crash course in:

What subversion is?
How to install it.
How to use it.
Recommendations for best interfaces

I have a Media Temple DV 3.5 server running Subversion version 1.6.12 and while I know how to upgrade to 1.6.17, I have no idea what the implications are or if it is even necessry. Similarly, even though installed, I have zero idea how to use it or really what the benefits of using it would be. YUM's latest repo verion is 1.6.12 so it makes me think updating is not necessary at this time. My base understanding is version control for code but once I have my locally built files updated onto my server's subversion directory, how do I then put that into production code?
I know this seems basic and dumb perhaps but I am wiling to even pay for an online course/video learning piece which fully explains what subversion is and how to use it.
Even this page does a 'good' job of explaining the steps somebody went through to get subversion running on their system but it does not explain how things work, is likely outdated, and uses manual installs outside of the typical YUM CentOS process so makes me think it could be unstable.
Answer: Have you checked http://svnbook.red-bean.com/ ?  That's the "book" I've read 7 years ago to learn subversion, and still the reference I go to today if I get stuck on something.  It should be more than enough to cover your 1 and 3.


Can you spawn proof the soul sand valley in minecraft?

Question: My nether portal spawn is in a soul sand valley, is it possible to spawn proof to keep all of the skeletons from spawning and attacking me as soon as I step through?
Answer: You have a number of options available to you, all of which are available on the Minecraft Wiki. I've excluded some options as they don't apply here, such as lighting an area up as that does not spawn proof the nether, but the list includes:

Bottom slabs or other partial blocks like dirt paths
Transparent blocks like glass or leaves
Carpets
Redstone components, including buttons, levers, pressure plates, and all types of rails

Thoroughly coating the area around your portal with one of these options should do the trick. I personally recommend either buttons or dirt paths as they would be the cheapest ways to cover a large area.
Comment: Fluids like lava also work (as stated on the Minecraft Wiki) but are suboptimal given the circumstances.
Answer: You can spawn-proof an area by covering it in non-full blocks. This can be cheap blocks like cobblestone slabs or carpets, or if you really want to show off you can use blocks like enchanting tables if you really wanted to.
There are many ways to spawn proof an area and it should be very easy to find one.


Debian 8.2 computer freezing+crashing randomly

Question: I have a Debian media server which seems to be crashing several times daily for no apparent reason at all. It simply freezes up, without restarting, until you manually restart it. I have uploaded the syslog here and the kern.log here
Any restart indications in the log file were done manually by me and not as a direct result of the crash.
Comment: Post your logs to pastebin, I would rather not download a file
Comment: Just updated the links.
Comment: Have you looked at all of the things that say "temperature alarms"? That might not be the answer, but it's a good thing to look in to at least
Comment: I thought that as well. But it seems as though that sensor in particular is a virtual sensor created by lm-sensors since it always stays at 127.0°C.
So it doesn't seem to be an overheating problem.
Answer: I don't see any explicit question here, but here's what I would do to start debugging this issue.
The first thing I do in cases like this is to run memtest86 or memtest86+ a few hours on the machine. This will rule out a lot of the common hardware errors.
If that passes, I run mprime for good measure. It will check that the CPU continues to calculate most things correctly under stress. I've had subtle errors after several hours running this, although I have not had to use it in a couple of years.
Now, if these tests passes, your hardware and cooling should be fine. After this I'd try running the system from a live CD if possible, perhaps trying an i386 version instead of amd64, to see if there's something wrong there.
If this does not give any insight, feel free to update the question with any new information!
Comment: There have been regular complaints about instability in Debian 8, specially from the ARM community mainly due to buggy wifi cards and temperature issues. I would uninstall all the fluff, like avahi, and upgrade to the latest kernel 4. At least, that is what I did at home.
Comment: The computer in question is not running on ARM hardware.
Comment: After checking the logs to verify the CPU model I see that he is using **nouveau**. I have had massive problems with that on a more recent kernel. I would comment on the original post, but alas, I don't have enough virtual points here.
Comment: pipe, write the answer and I will give you points.
Comment: @pipe I ran a memtest overnight, 0 errors.
So do you think I should upgrade to the latest kernel, or do you have any other suggestions?


Active Directory in VB.Net

Question: How can I get a list of computers and their properties from Active Directory using VB.Net and Visual Studio 2008?
Answer: You're going to want to use the System.DirectoryServices or the System.DirectoryServices.AccountManagement to access your domain.
These namespaces have classes you can use to search your directory and examine the objects it finds.
Is there something you're looking for in particular?
(it's worth noting that is most cases you need to add a reference to these namespaces in your project)
Answer: Working with Active Directory, even with the help of the DirectorySearcher class, is no mean feat. It is not a task to be taken lightly. If you haven't done it before, I'd read up on it before attempting to do so.
I highly recommend The .NET Developer's Guide to Directory Services Programming.
That being said, the classes in the DirectoryServices namespace do some of the work for you, but certainly nowhere near enough of it.
Answer: Check out the DirectorySearcher class.

Active Directory in VB.Net


How to use ADC for battery operated application?

Question: In my application VDDA = ADC Reference voltage and VDD = Microcontroller supply voltage changes due to battery drain form 3 V to 2 V so because of that my adc count not stable so what can I do to make stable?
Comment: Use the internal reference voltage to calculate the actual vdda. Then use that for the normal adc conversion.
Comment: more "?" don't make a question better. Clear structure does! Add punctuation (your sentences end somewhere; a new sentence starts there. Put a "." between.).
Comment: I will try to add some detail later.
Comment: You do not need it actually . Measure the Vdda first using the internal voltage. Then knowing the Vdda do your measurements.
Answer: The STM32 microcontrollers have an internal voltage reference source, and that can be used to determine an unknown VDDA, VDD value. The necessary informations are found in the datasheet, for example for the STM32F030 series:

it is 1.23 V typically. Now, given that this reference voltage is known to be 1.23 V you can calculate the ADC reference voltage VDDA by reading the internal reference's valute with the ADC.
The formula is the following:
$$ \frac{V_{REFINT} \:[V]}{VDDA\: [V]} \times 4096  =  digital_{VREFINT}$$
In this equation the following values are known:
$$ V_{REFINT} = 1.23\:V $$
$$ digital_{VREFINT} = \text{from reading the internal ADC channel}$$
So the VDDA, aka battery voltage can be calculated:
$$ \frac{V_{REFINT} \:[V]}{digital_{VREFINT}} \times 4096  =  VDDA\: [V]$$
Performing this calculation before your normal ADC readings will give you the reference voltage value you need.

A more accurate value can be calculated using the internal voltage reference's calibration value which is individually measured for each part by ST during production test and stored in the system memory area. It is
accessible in read-only mode. Here are the specs:

It is actually the digital value of the internal reference voltage that was measured with VDDA = 3.3 V. The actual VDDA can be calculated as follows:
$$ VDDA = 3.3 \: V \times  \frac{digital_{VREFINTCAL}}{digital_{VREFINT}} $$
3.3 V is known from the table above, the calibration value from the memory and the actual value by reading the appropriate internal ADC channel.
Generally this is the most cost effective and the easiest way to use the ADC with not constant VDDA.
Answer: The solution is to supply VDDA with a stable voltage.
There are linear regulators made specifically for providing the reference voltage to ADCs.  Pick one which can operate on your battery range and still provide a stable reference.
These usually have low quiescent current (they don't draw much current for their own operation) and low current output (the ADC doesn't need much current from the reference) so they won't suck your battery down fast.
This of course means that your reference voltage is lower than the lowest battery voltage.  You will have to scale your analog signal to match the lowered voltage range of the ADC.

There are some voltage references with enable pins so you can shut them off to save power when the processor is sleeping.  Something to keep in mind if you are going for a long run time from a small battery.

Another thing to keep in mind is that some processors have a built in voltage reference.  You can either wire it to VDDA, or some a configuration bit or similar that connects the reference voltage internally.
Comment: @JRE: the question is tagged as `stm32`, so I think it's about an STM32
Comment: [This is an example of what I mean.](https://www.maximintegrated.com/en/products/analog/voltage-references/MAX6018A.html). That is from Maxim, and is the first I found that would appear to meet your needs.  That's just an example.  Using that, you can search for related devices.  For all I know, the one I linked to is a finicky piece of crap.  Check its datasheet, see if it meets your needs.  Compare to similar parts from other manufacturers.  Check the prices.
Comment: Most, if not all STM32 have an internal regulator providing a stable reference. There is no need for a second one for most applications. These controllers are _designed_ for battery operation.
Comment: @berendi:  Didn't see that.  I've added a hint to check for a built in reference.
Comment: We require 1.5volt to 1.8 Volt ADC reference so which linear voltage regulator should we use  ???
Comment: Battery Specification
Comment: 1) CR2032 Coin Cell 3V(discharge up-to 2Volt) so which linear regulator should we use ?
Comment: @berendi:  Well, that assumes the application is using an STM32.  The question doesn't mention the processor type.  I read the question as applying to a processor for which you must supply the reference - though of course it may well have one and the OP just doesn't know about it.


Bent front-derailleur

Question: I biked to school today with my bike in perfect condition. Locked it up and went to class. When I went to my bike a couple hours later, the derailleur was bent out of position. My bike's front gear was at 3, but the derailleur was forced to the first/smallest sprocket. Now I can't shift gears on my front wheel as the derailleur won't move. Is this fixable? Or do I need to buy a new derailleur. If it's fixable, would it be difficult for me to do it myself out should I simply take it to a shop?
Comment: Can't really tell from the picture what's bent.  But if it's just the cage then that can usually be straightened up with a pair of pliers.  The tricky part is not straightening it, but removing it to work on it, then getting it back on and properly aligned/adjusted.
Comment: (And note that it's possible that it's not actually bent, but simply got twisted on the seat tube or has slipped.  It kind of looks suspiciously like it's slipped down the seat tube.)  (A picture from the side would help us see it better.)
Answer: You say it's bent, but we can't confirm that by the picture. (Your picture is very sharp, but a side view would be helpful) It looks (as someone else commented) like the derailleur may have slipped down the seat tube. If you can't determine exactly what the problem is, you probably should take it to a shop.
Answer: Several possibilities... its happened by normal wear and tear, or someone's put a boot into your bike and bend things.
If the latter, then the cage could be bent or rotated.  Hang the bike up and spin the pedals by hand, while using your other hand to change gears.  Try and eyeball what's not working.  Do be mindful of hair and fingers getting caught in moving parts - this hurts.
Try moving the cage directly by hand, and also by pulling on the right wire.  Could be that the wire clamp has slipped and the cage has been moved by the spring.
If you think it was damaged by someone, just don't park your bike on the end of the rack.  Same defence helps with knife-induced punctures etc - there are some vandalistic people out there, and some of them even ride bikes.
Finally - bikes are just simple machines.  Don't be scared to give it a try.  The worst that can happen is it doesn't work right, so try again.  Do let us know how you get on.

Bent front-derailleur


Question about open drain

Question: In which region does a NMOS work when its drain is open circuit? Let's say the input is high voltage lavel, how can I determine whether it is saturation of triode region when drain is open?
Answer: When the drain is completely open, there's no current :-) You need to think about a load on the OD = e.g. a pull-up resistor or a constant current source. Maybe your reasoning can take off from there.
Comment: If I do not have a load, will the open circuit voltage be equal to ground when I have a high voltage input?
Comment: Yes, definitely. If your "source" electrode is grounded, that is the only reference point of such a circuit (with "drain" floating free). So whatever finite resistance you end up having between D and S, the free-floating D will gravitate to S.

Question about open drain


Are separable solutions to the Schrödinger equation always complete?

Question: I'm just starting to learn quantum mechanics, and the book I'm reading (Griffiths) states that every solution to the Schrödinger equation can be written as a linear combination of the separable solutions:
$$
\Psi(x,t) = \sum_{n=1}^{\infty}c_n\psi_n(x)e^{-iE_nt/\hbar}.
$$
However, it does not provide a proof that the set of $\psi_n(x)$ is a complete basis, even for arbitrary $V(x)$. I understand that completeness can be proven in specific cases such as the infinite square well, simple harmonic oscillator, et cetera, by solving for the separable solutions first. I also know that if $V$ is not time-independent the whole separation of variables scheme falls apart. My question is, do the separable solutions always form a complete basis, even for arbitrary $V(x)$? If so, what does the proof look like?
Comment: This follows from the fact that any Hermitian operator is diagonalizable with orthonormal eigenvectors. Griffiths discusses this fact in chapter 3 of his textbook. The Hamiltonian is a Hermitian operator, so it admits a complete orthonormal basis which spans the Hilbert space.
Answer: This result is called the spectral theorem. For a finite-dimensional Hilbert space $\mathscr H$, the statement is that given any self-adjoint$^\ddagger$ operator $H$, there exists an orthonormal basis $\{\hat e_i\}$ consisting of eigenvectors of $H$, and that all of the corresponding eigenvalues are real.
The proof of this statement goes as follows.

By the fundamental theorem of algebra, $\mathrm{det}(H-\lambda \mathbb I)=0$ has at least one solution - say, $\lambda_1$.  This implies that there exists at least one non-zero vector $\hat e_1$ (which we normalize for convenience) such that $(H-\lambda_1 \mathbb I) \hat e_1 = 0 \iff H\hat e_1 = \lambda_1 \hat e_1.$
Because $H$ is self-adjoint, we have
$$\lambda_1 = \langle \hat e_1,H\hat e_1\rangle = \langle H \hat e_1 ,\hat e_1 \rangle = \overline{\lambda_1} \implies \lambda_1\in \mathbb R$$
Let $\{\hat e_1\}^\perp$ denote the orthogonal complement of $\hat e_1$ - that is, the set of all vectors $v\in\mathscr H$ such that $\langle \hat e_1,v\rangle = 0$. Because $H$ is self-adjoint, we have that
$$\langle \hat e_1,Hv\rangle = \langle H\hat e_1,v\rangle = \lambda_1 \langle \hat e_1,v\rangle = 0 \implies Hv \in \{\hat e_1\}^\perp$$
We say that $\{\hat e_1\}^\perp$ is invariant under the action of $H$.  As a result, if we let $\hat e_1$ be the first element of our orthonormal basis, then $H$ takes the form
$$H = \pmatrix{\lambda_1 & \matrix{0 &\cdots&0}\\\matrix{0\\\vdots\\ 0} & H'}$$
where $H'$ is an $(n-1)\times (n-1)$-dimensional self-adjoint matrix. This process can be repeated for $H'$ and so on, eventually yielding a diagonal matrix with real entries and the claimed basis of eigenvectors.

For an infinite-dimensional Hilbert space $\mathcal H$, this situation becomes more complicated because the spectrum $\sigma$ of an arbitrary operator can consist of discrete points (called the point spectrum, $\sigma_p$) as well as a continuum (called the continuous spectrum, $\sigma_c$).
If the spectrum of $H$ is pure point (so $\sigma_c = \emptyset$), then the proof is similar in spirit to the finite-dimensional case, but there are technicalities which come into play if $H$ is not bounded; nevertheless, the conclusion is the same except for the fact that the basis in question does not have a finite number of elements.  If the spectrum of $H$ contains a continuous part, then even more technicalities arise, and the full machinery of functional analysis is required; in physics, this operationally corresponds to the appearance of non-normalizable (or generalized) eigenstates, such as the ones which appear for the free particle Hamiltonian $H:= \frac{\hat P^2}{2m}$.

$^\ddagger$It's easy to show that if $H\neq H^\dagger$ but $[H,H^\dagger]=0$, then $H=A + i B$ where $A,B$ are commuting self-adjoint operators. This allows us to generalize this proof to so-called normal operators, and the only thing that changes is that the spectrum of $H$ may be complex.
Comment: Why is it obvious that the TIS is *always* self-adjoint? I mean if you take a circular waveguide and fill it with dielectric only partially you get complex eigenvalues. When I first learned of this I could not believe it but then I saw with my own eyes ...
Comment: @hyportnex Indeed, the self-adjointness of an unbounded operator is rarely *obvious* (as opposed to its Hermiticity, which is easy to check).  Checking for self-adjointness requires a careful analysis of operator domains and boundary conditions, and is typically beyond the scope of an undergraduate course in QM. However, [one can show](https://link.springer.com/article/10.1007/BF01427943) that if $V$ is locally square-integrable and bounded from below then $H := -\frac{1}{2}\nabla^2 + V$ is [...]
Comment: @hyportnex [...] [essentially self-adjoint](https://math.stackexchange.com/questions/2227359/definition-of-essentially-self-adjoint-operators) on the space of smooth, compactly supported functions, and therefore has a unique self-adjoint extension.  If the Hilbert space in question is not $L^2(\mathbb R^d)$ - e.g. the waveguide you reference - then boundary conditions may play an important role in deciding whether the operator is self-adjoint (or even Hermitian).


How far can a HC-SR04 can stand from the microcontroller?

Question: I was wondering if I connect a HC-SR04 to an Arduino or any other microcontroller by normal cables, what would be the maximum length of this cable so that the measurements will still be true, and not affected by the length of this cable?
Answer: I have a couple measuring the liquid level of two tanks.
The units are distanced from the microcontroller by 12' of 18ga solid-core copper cable.
Testing was done with another microcontroller with the sensor attached by 6" cable to ensure accurate readings.
That's the longest I needed, so I haven't tested beyond that.
Answer: The signal of an HC-SR04 is the pulse on the "Echo" wire. The length of that pulse is directly proportionate to the distance from the object.
Since cable length does not affect the duration of that pulse, measurement accuracy isn't affected either.
Comment: Though that doesn't mean, that you can use any cable length. At some point the resistance of the cable might get too high, thus pushing the voltage too low for the Arduino to detect correctly. Also the increasing capacitance can smooth out the edges of the signal. But that can only be tested with the used cable, since there is no standard for a "normal cable".
Comment: Oh, absolutely. I don't think it'll have much influence in practise though - the input impedance on Unos is quite large, and so is the pull-up resistor. If all else fails, you could probably even analogRead the port.
Answer: this problem consists of 2 things :

supply level drop (this one has severe effect)
signal level drop (a little more forgiving)

as the signals on the cables don't have high frequencies, the problem narrows down to just voltage level drop due to cable resistance.
supply level drop: the datasheet for SR04 says a maximum active current of 20mA is required for device to work properly. the supply voltage is 4.5~5.5v. so if you provide a 5v power for it, the cable must not drop it under 4.5v. the maximum resistance for the cable is calculated

R=V/I => R = (0.5/20)*10^3 = 25 Ohms

. you can use this value to find out maximum cable length using resistance tables provided by cable makers. e.g. if you have bought a 5ohms/meter cable, the maximum length should be under 5 meters to ensure a good power delivery.
the signals on the other hand, have very little current going between them. as the MCU/Module pins have a very high input impedance. so they are not as severe as the supply drop.
using a 100uF cap near SR04's supply pins would be great.


Is Simplified Technical English based on American English or British English?

Question: Simplified Technical English was originally developed for use in aviation maintenance manuals, but has expanded beyond this use into a variety of technical fields. It is a "separate" controlled language consisting of a highly restricted subset of simple English words. Are these words are derived from American English, British English, both, or neither?
Comment: Is this the same as [Simplified Technical English](https://en.wikipedia.org/wiki/Simplified_Technical_English)? A quick look at their dictionary should tell you whether they use, for example, *color* or *colour*. Since it's standardized by a European organization, I'll guess it's *colour*.
Comment: Whoops, that's what I meant. Edited to fix.
Comment: Looking around, it seems an American industry association was also involved.  The late 1970s and 1980s.  With English the language of aviation, both commercial and military aircraft needed maintenance manuals that could be unambiguously understood throughout Western Europe.  I bet Eastern Europe used them too.  Could be an interesting bit of history.
Answer: This is explained in ASD-STE 100 (issue 7, January 2017):

STE approved meanings are based on American English (Merriam-Webster's
  dictionary).

Rule 1.14:

Use American English spelling.


What visibility and cloud clearances are required for airplanes conducting visual approaches?

Question: What visibility and cloud clearances are required for airplanes conducting visual approaches during IFR while flying under FAA regulations? Is the visual approach a purely VFR maneuver requiring the usual VFR weather minimums for the airspace being flown? Or does the visual approach maneuver flown under IFR supersede normal VFR weather minimums?
Answer: This depends:
Under part 91, you just have to remain clear of clouds and have a minimum of a 1,000 ft. ceiling and 3 SM visibility.
Commercial operations (121 and 135) are further restricted by their Operations Specifications and have to maintain VFR weather minimums appropriate for the airspace that they are in (among other things, see below).
Here is an excerpt from the AIM (there is more details there for different operations, with the differences between controlled and uncontrolled fields, etc.)

5−4−23(a). Visual Approach
a. A visual approach is conducted on an IFR flight plan and authorizes a pilot to proceed visually and clear of clouds to the
  airport. The pilot must have either the airport or the preceding
  identified aircraft in sight. This approach must be authorized and
  controlled by the appropriate air traffic control facility. Reported
  weather at the airport must have a ceiling at or above 1,000 feet and
  visibility 3 miles or greater. ATC may authorize this type approach
  when it will be operationally beneficial. Visual approaches are an IFR
  procedure conducted under IFR in visual meteorological conditions.
  Cloud clearance requirements of 14 CFR Section 91.155 are not
  applicable, unless required by operation specification.

The Part 135 Ops Spec for this contains the following requirements for a visual approach:

b. Terminal arrival IFR - Visual approach or a Charted Visual Flight
  Procedure (CVFP).
  The flightcrew may accept a visual approach or a
  CVFP provided all the following conditions exist. The flightcrew may
  not accept a visual approach or a CVFP unless the limitations and
  provisions of subparagraph f. of this operations specification are
  met.
(1) The flight is operated and remains in Class B, C, or D
  airspace, within 35 miles of the destination airport in Class E
  airspace, or the airspace beneath the designated transition area.
(2)
  The flight is under the control of an Air Traffic Control (ATC)
  facility.
(3) The flightcrew must maintain the basic cloud clearance
  as specified in Section 91.155.
(4) For a visual approach without a
  CVFP - The flightcrew must be able to establish and maintain visual
  contact with the airport or maintain visual contact with the traffic
  to be followed as directed by ATC. In addition, the following
  provisions and weather conditions at the airport during the approach
  must be met:
(a) Reported visibility must be as specified in Section
  91.155, but not lower than a visibility of three miles and reported ceiling must be 1,000 feet or greater, or
(b) When in the terminal
  area with the reported visibility not lower than three miles and
  ceiling not reported, the flightcrew may continue to a landing if the
  runway of intended landing is in sight and the flightcrew can maintain
  visual contact with the runway throughout the approach and landing,
  and
(c) Ceiling and cloud clearance must be as such to allow the
  flightcrew to maintain the minimum altitudes prescribed in Section
  91.129, 91.130, or 91.131, as applicable for the airspace class in which the flight is operated.
(5) For a CVFP - The flightcrew must be
  able to establish and maintain visual contact with the airport or the
  charted visual landmark(s) for the CVFP throughout the approach and
  landing. In addition, the weather conditions at the airport at the
  time of the approach must be reported to be at or above the weather
  minima established for the CVFP, but never lower than the VFR landing
  weather minima stated in Section 135.205 in uncontrolled airspace.
...
f. Special Limitations and Provisions for Visual Flight Rules. All VFR operations authorized by this operations specification shall be
  conducted in accordance with the following limitations and provisions.
(1) The certificate holder must identify obstacles and use airport
  obstacle data which ensures that the performance requirements of Part
  135 are met.
(2) The weather conditions must allow the flightcrew sufficient
  visibility to identify and avoid obstacles and safely maneuver using
  external visual references and to maintain minimum altitudes.
Answer: What visibility and cloud clearances are required?
VFR, as per 91.129, 91.130, or 91.131 for the various classes of airspace
Comment: Can you expand your answer a bit? The mention of VFR sounds like the required weather for the conditions, but the required cloud clearance can vary.
Comment: I see that you updated your answer. This seems to contradict the other answer. You're saying that VFR weather minimums for the particular airspace must be respected?


ODBC Driver "Oracle in OraClient11g_home1" required but can't seem to get it on Windows 10

Question: Not sure if this was the right StackExchange for this. My job recently upgraded their machines to Windows 10 and I thought setting them up would be a breeze, but I can't for the love of me figure out how to get the correct ODBC drivers on it. I've tried every download I could find and it isn't giving me the right driver.

Not sure where to get the drivers I need. I thought it'd be simple but I just can't find it anywhere after hours of searching. I don't know enough about database connections to know if I can just utilize one of these drivers and somehow translate the configuration from before onto them (old driver just had main entries for Data Source Name, Description, TNS Service Name, and User ID - that's all I enter to make the connection work.)
Answer: Never mind. I was looking in the 32bit drivers without realizing. But the problem I have now is that it's a 64bit driver and the Excel sheet that utilizes the connection is looking for the 32bit one.


What to do with NFS server (UTF-8) and Windows 7?

Question: NFS share is mounted using mount server:/share x: command.
File(cyrillic) "Новый текстовый документ.txt" created with samba share (and using UTF-8) is shown as "Новый текстовый документ.txt" under windows via NFS share.
How to make windows use UTF-8?
Comment: I already saw that it has only 'ansi', some chineese encodings (How usefull). fu..ing windows!
Comment: As much as I hate Windows-bashing, lack of Unicode support is a good enough reason.
Comment: it is a windows component.
Comment: We have no clue what NFS client you're using.
Answer: There is no solution with Microsoft's NFS client in Windows 7
There are no way to solve your problem under this setting, not even the method given in the "Correct Answer" of this question. This is not a mistake, it is by design to create the barrier you are facing. It is not possible that the designer of NFS Client offer the option to use BIG5, EUC-KR, EUC-JP, ksc5601, GB18030, SHIFT-JIS and simply forget UTF-8 and keep forgetting patching it up in a decade. All these codings are used by various versions of Windows except UTF-8, not a coincidence. In fact, Microsoft's intents to bridge old UNIX and Windows, to foster migration from Unix to Windows, and it must be carefully measured that this does not give its competitor Linux an easy environment to exist. Any feature makes Linux different from Unix or modern Unix different from old-unix-to-be-replaced are excluded. It's precision in marketing, job well done.
Let me show you how every way is blocked:
To workaround the client side is no go:
Idea is to find some software that can dynamically transcode file names, for example by inserting itself a layer between FS and the OS. Or, find some software that can setup an environment for another software to use that file system. No known Windows software can do this. This does not work, because unlike Linux that allows each application to use a different encoding, Windows configure an encoding for a FILESYSTEM.
To workaround the server is no go:
Most NFS servers are Linux. In theory one could use fuse-convmvfs to make a mirror of the filesystem and export that. Oleg Lobach demonstrated the code to do this, and it is marked correct without test. It doesn't work because Linux's NFS server can only export FUSE file system in NFSv4, not in NFSv2/v3, in the meantime, Windows 7 (as well as Services for Unix v3.5) only support NFSv2/v3, not NFSv4. I demonstrated this limitation in detail in another answer.
The problem is elaborated in TechNet:

A POSIX filename is not ASCII but a stream of bytes.  The same goes for
filenames on NFS filesystems.  The interpretation of the byte stream as a
filename in a certain codeset is left as an exercise to the client
application.  If the filename byte stream represents a valid UTF-8 string,
but the client application has set the codeset to, say, ISO-8859-5, any
problem is the fault of the application.
But we're talking about Windows.  On Windows, the interpretation of a
filename is not left to the application.  Rather, the filename byte stream
sent from the NFS server to the Windows client machine has to be converted
to a UTF-16 string to be digestible by the OS.  Therefore the interpretation
of the filename byte stream has to be performed by the NFS client service,
on a per mount point basis.  The application has no say in it.
And here's the problem.  If the remote codeset used to create filenames is
UTF-8, as is the default for many years in the POSIX world, there's no
chance to get a correct filename from the Windows application point of view,
because the interpretation of the filename is already done by the Windows
NFS client which doesn't allow the conversion from UTF-8 to UTF-16.  In
fact, the NFS client only supports a restricted number of codeset
conversions to UTF-16, all of them rather old-fashioned.
This is not just a specific scenario.  You have this problem in all
scenarios in which you're accessing NFS shares on machines set to use MBCS
like UTF-8 or GB-18030 from Windows NFS clients.

There are solutions if you opt for a switch:
The best solution is of course abandon Windows. It is not important nowadays, and the global trend is no longer to release Windows-only software. If you are stuck with old Windows applications, you can change your requirement:

Switch NFSv2/v3 Client: you can install dokan user-land mount driver for Windows, then Neko NFS drive, which maps NFS to a device driver with an option "Unicode". Click that option to get UTF8 working. It supports NFSv2 and v3, but not v4. It doesn't support symbolic link yet (as Microsoft's client do).

Switch NFSv4 Client: you can leave the in-built NFS Client for the free reference implementation of NFS 4.1 for Windows by UMICH CITI, although difficult to install, should either eliminate the problem (because NFS4 explicitly requires UTF-8) or made it possible to use workaround fuse-convmv mentioned above.

Switch OS: Windows Server 2012 added support for NFS 4.1 server, so there is a chance that they included an NFS 4.1 client too.

Both switches would not work if your server only support NFSv3, for example, if you use OpenWRT (even the latest version of OpenWRT server still cannot do NFSv4).
Answer: You can use fuse-convmvfs: mount your server folder by fuse-convmvfs (input charset - utf8, output - cp1251) and configure nfsd to use converted FS
example:
> convmvfs /mnt/converted-folder -o srcdir=/path/to/source/foleder, icharset=utf8,ocharset=cp1251

> vi /etc/exports
/mnt/converted-folder 192.168.1.*(rw,sync)

Comment: I'll mark it correct without testing and delete my useless answer
Answer: I just wanted to note that I tried the UMICH CITI NFS client, but I ran into secure boot troubles.
Upon trying to run:
bcdedit /set testsigning on

as instructed by the instructions, I received the following error:
An error has occurred setting the element data.
The value is protected by Secure Boot policy and cannot be modified or deleted.

So unless you want to mess with your secure boot settings, I do not recommend trying to use the CITI client.
The optimal solution to this would be for CITI to sign the driver so it can be used without test mode. But considering it's quite old, I don't think this is going to happen.
Answer: [machine translation from Russian]
If someone came here, like me, looking for a solution for shared folders over NFS under Windows 10, then the solution is in the region and system language settings. There is a section "Administrative language settings" where you can select UTF-8 as the system encoding 1. This works for filenames in mounted network drives. In the picture 2 a whole partition with the Ext-4 file system is shared over NFS from Ubuntu (running in a virtual machine) and is natively mounted in Windows.
Если кто-то пришёл сюда также, как я, в поисках решения для общих папок через NFS под Windows 10, то решение есть в настройках региона и языка системы. Там есть раздел "Административные языковые параметры" где можно выбрать UTF-8 в качестве системной кодировки 1. Это работает для имён файлов в примонтированных сетевых дисках. На снимке 2 целый раздел с файловой системой Ext-4 раздаётся по NFS из Ubuntu (запущенной в виртуальной машине) и примонтирован в Windows нативно.
Comment: This is a working solution, helped me a lot. Thanks!
Answer: Ответ от Alex Kart вполне рабочий, но, к сожалению, в Windows 10 и в Windows 11 поддержка UTF8 находится на уровне бета тестирования (забавно, но факт). Поэтому при монтировании каталогов в проводнике все будет видно в нужной кодировке, однако многие приложения этого по прежнему не поддерживают и будут сбоить при выводе. Так что пока вариант с бутербродом из fuse хоть и костылен, но оптимален.
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