How close to pure math is cryptographic theory?

Question: I'm an undergraduate math student, and I'm thinking about topics for an undergraduate thesis. I have an interest in topological spaces and number theory, but I'm having trouble identifying a relationship between those and cryptographic theory. In On Post-Modern Cryptography, Goldreich talks a lot about rigorous analysis. But it's still not giving me a clear understanding of what type of math a person doing research in theory does in general. Is cryptographic research in the same line as formal mathematical proof? Is there a need for abstract mathematics in modern cryptography? I can program, but application is not really my interest and it would take too long in my degree to add a formal computer science aspect.
Comment: Take a look at the answers of https://crypto.stackexchange.com/questions/31/current-mathematics-theory-used-in-cryptography-coding-theory?rq=1 They answer your question fairly well.
Answer:
Is cryptographic research in the same line as formal mathematical
  proof?

Not always, but the large area of provable security is. Provable security is (essentially) the task of formally proving theorems about crypto, which will in general be of the form "if this mathematical hypothesis is true, then this cryptographic primitive is secure against a given type of attack". Each time a new primitive is suggested to address some security requirement, it comes with proofs of theorems providing hindsights regarding the security of the scheme (though that's not always the case, especially with papers from the early days of crypto). An important part of cryptography is also about analyzing and implementing cryptographic protocols and primitives, but that does not mean all cryptographers do also implement crypto. In many labs, 95% of the work will involve essentially pen-and-paper analysis - although even the most theoretical works sometimes lead to result that one might want to implement, if only to see how efficient it is.

Is there a need for abstract mathematics in modern cryptography?

Yes and no. A knowledge of the formalism in some area of abstract mathematics can help a lot into understanding and studying crypto, but in most cases, you will not need a deep knowledge of the most advanced results in abstract mathematics. For example, most results you would learn from an advanced math course about elliptic curves would be outside the scope of the background needed to understand elliptic-curve-based cryptography. Similarly, you would not need extremely advanced courses on algebra to understand the notions used in crypto (essentially, standard algebra results on finite fields and additive groups suffice for many things, plus some more crypto-related algebra result).
However, as is common in theoretical computer science, mathematics often show up unexpectedly when studying some problems, and relatively deep mathematical results can prove useful in the analysis of some cryptographic primitives. The first example that comes out of my head is this recent paper from ePrint (the crypto archive) which establishes lower bounds for a primitive known as order-revealing encryption (an encryption scheme that does not hide the result of the comparison between encrypted messages), and relies on (an extension of) a theorem of Erdös on tournament graphs.
The high level bit is: studying math is a very pertinent choice if you're planning to do theoretical crypto later, because being at ease with mathematical formalisms will make you way more comfortable than many with crypto. It is widely acknowledged in crypto that the field would benefit from having more mathematicians studying this area. However, do not expect your knowledge of advanced math results to be crucial to your work in crypto on a daily basis, and theoretical crypto in itself remains a science with its own formalisms and practices that you would have to study if you want to work in the field.
Comment: [+1 for the last statement](http://www.cryptofails.com/post/70546720222/telegrams-cryptanalysis-contest)


How do i get automatic coloured nicknames in Macirssi?

Question: How do I get automatic coloured nicknames in Macirssi? I've found a script for irssi that kind-of works, but only has a few colours. But for Macirssi I can't find anything.
Answer: If you are using OS X Lion you will need to use the development version (0.8.6.6.459), you can get this from the MacIrssi Github downloads page. The current stable version, 0.8.6.6, does not have Perl support on Lion.
Once you have the right version:

Install the script as per usual (place it in ~/.irssi/scripts/).
Run /load perl (the perl interpreter has to be manually invoked or you will get an error that the 'script' command can not be found)
Run /load nickcolor.pl (replacing nickcolor with the name of your script.

After that, any messages received should display the name in colour.


What is so special about "Twitter Bootstrap"?

Question: I have seen Twitter bootstrap and Yahoo purecss but I don't understand why they are becoming industry standards. People tend to directly use them for their project without thinking of something unique for their project. I would like to understand why using these framework can enhance your designs.
Answer: They're not used for the sake of design, but rather for fast implementation. Bootstrap allows developers to quickly prototype in HTML+CSS. Most projects will require at least some kind of grid system and CSS resets, so bootstrap and purecss fill that gap.
Comment: So, does that mean that these frameworks are not for designers but rather for developers?
Comment: @AnkitSharma - ish. It's more for designers and developers to quickly prototype with functionality that can't easily be mocked with Axure and the like.
Answer: We use frameworks because modularity is great. Frameworks lets us focus on solving unique tasks, not on reinventing the wheel.
There is no reason why a developer should have to retype the same lines of code over and over. This costs time/money, it is boring, and it is hard to maintain.


WP plugin updates

Question: I wrote a plugin for WordPress which requires regular updates.
Is it possible to notify user of new version being available (some of the other plugins have some kind of this option - when new version is available user can see it in his admin panel and update - everything using some built-in WP functions...)
Answer: There is a library for you. :)
Answer: I just released this plugin yesterday that does what you want: WP Updates Notifier
You can get your users to use this to be notified or take the plugin and bundle it into your plugin and modify to only notify about your plugin.

WP plugin updates


Program that can terminate other programs after a certain period of time

Question: Is there an application for windows that can terminate other programs after a certain period of time.
I would use this program for shutting down movie player when I want to watch only 30 minutes of lecture that lasts an hour for example.
Answer: For automating what you are asking and many other things in Windows there is a great and free scripting tool and app called AutoIt v3 which can do what you want with a little bit of basic programming (or a few clicks that can generate that script). You will find a lot of information on their site.
For example to do what you are asking could be as easy as writing (or generating) something close to
<code>$Timer1= TimerInit()

While True
     If TimerDiff($Timer1) > 30*60*1000 Then
        ProcessClose(<YOUR APP>)
     EndIf
     Sleep(1000)
WEnd
</code>
Autoit is very powerful and you can of course add more logic and function depending on your needs.
Comment: You should be able to put the app name such as "notepad.exe" for example. See: https://www.autoitscript.com/autoit3/docs/functions/ProcessClose.htm If your app name does not work maybe you are using it a bit differently check with Task Manager to use the correct name (Ctlr+Alt+Del Start Task Manager)
Comment: Tnx. Can you tell me what can I put in  other than PID? Because PID changes, I've tried, app name, and full path of app. @user3134164
Answer: Another well known program that can take care of many different kinds of automation is AutoHotkey.
With AutoHotkey you can write a script that is manually executed or is started with Windows and is running while Windows is running. It should meet your requirements because it can...

check if a program is running or a window is open
wait for a given duration before doing something specific
close a window/program

You can also build user interfaces (for example dialog boxes) to interact with so that you can have better control over your scripts.
Comment: Welcome to Software Recommendations – and thanks for sharing! Unfortunately, this post does not contain enough information to be considered an answer. Please [read our discussion on what makes an answer high quality](//softwarerecs.meta.stackexchange.com/q/356/185) to see if you can incorporate some of these improvements into your answer. Especially missing: How does it meet the requirements? How can it accomplish what the OP asked for? See e.g. how the other answer explains this.


Gettting ERC-20 token transfer count over an API

Question: I am building a service to monitor token activity. Does any service have an API to get the transfer count of a ERC-20 token? I am not interested in individual Transfer events, only their count.
Comment: yes, etherscan api
Answer: Yes I think you can use this Api to fetch all the transfer token data
curl --request GET \
     --url 'https://api.chainbase.online/v1/token/transfers?chain_id=1&contract_address=0x7d1afa7b718fb893db30a3abc0cfc608aacfebb0&page=1&limit=20' \
     --header 'accept: application/json' \
     --header 'x-api-key: demo'

And here is the doc and details about how to use it.
https://docs.chainbase.com/docs/how-to-get-all-erc20-transfers-by-contract


Should a data warehouse ever be a primary data repository?

Question: Typically a data warehouse is a means to consolidate multiple source systems, usually for reporting purposes. But are there any situations where it is a good idea to use the data warehouse as a primary database in its own right (i.e. capturing and managing data, not loading it from another system)?
Answer: The short answer - no, I don't think so.  You should first be designing a good, normalized database structure for the production database - and later worry about the data warehouse part.
Keeping the warehouse and the production database separate is considered "best business practice", perhaps most importantly it's a design consideration.  The data warehouse and the production database serves two different purposes.  The perhaps most important function of the production database is to capture transactions reliably, consistently and unambiguously.  This matters both when designing the database and when choosing the software, i.e. database engine.
The design part of it shouldn't be underestimated - I'd say that in most projects, a good database design is one the very first thing one should be doing.  Getting the table structure right is more important than choosing technology.
If you're planning to grow, it may also make good sense to try and isolate the data a bit into different databases - both because it makes it easier to split up the database later and run different parts on different hardware (when you hit the "bleeding edge", it's a lot cheaper to buy more servers than to buy more powerful servers) and because you may later want to split out software modules or reuse them independently of each other.  You wouldn't want to split up the data warehouse the same way.
So to recap, start with the production database, and build a data warehouse later - that can typically be postponed until you feel the urge to combine data from different sources or to add redundancy into the production database to achieve faster reports.

I was working for an online gambling company for 8 years.  I participated in the design of the production database, and I was later responsible for building the data warehouse - so the comments above are based on some of the mistakes done and experiences learnt.
Comment: Agreed. One thing I have found is there may be a case to make the DW the primary store of "reporting attributes" - things that are classified by the business manually and are only meaningful in reporting.
Answer: Good recap by @tobixen. One more thing about Datawarehouse best practice is you don't modify the data, you generally append the data ( so history is kept).
Most datawarehouse technologies are geared toward this pattern. So using a typical OLTP system or Master Data System over datawarehouse wont work properly.
The general flow is
OLTP Database -> Datawarehouse > Archiving.
OLTP Database may retain data for say 1 month to 13 months. Datawarehouse will retain data say upto 5 /10  years (not all details, probably summarized) and then goes to archiving.
Being said that BigData technologies like Hadoop / Hive is making it easier to store large amount of data ( say 10 years) and process them in cost effective fashion.
Comment: Good answer in general - however - a good star schema *does* contain the details of a transaction, so it can be sliced and diced every which way. Kimball recommends you keep things granular, and build summary tables if needed.
Comment: Re "in warehouse you add data, in OLTP you modify data" - it's also important with proper change tracking in the production db (and more general, to think about future reporting needs when designing the production DB).  Example: user accounts could be open or closed, marked with a boolean in the production db - not sufficient for reports on the number of open accounts at the beginning of the year.  I added "closing date=now()" in the ETL if the account was closed in prod but open in the warehouse - but that just wasn't good enough.  We needed an account closing log table in the production db.
Answer: I would have to say generally not, but ... we are being asked to build a DWH that has as one of it's source systems an "OLTP" system that collects Twitter data. In this case I think the Twitter collecting "OLTP" system only keeps 1 week worth of data and each day passes it across to the DWH for storage, then each day we feed summary information back to the Twitter OLTP system. In this case we will become the primary data repository for the Twitter data ... to be honest though this is the first time this is the case for us.
I would disagree with @Sathish Senathi I think on the statement that "Datawarehouse will retain data say upto 5 /10 years (not all details, probably summarized)". I would never summarise data going into a DWH, always keep the lowest grain transaction data, but obviously not all attributes that are in the OLTP system.
I admit to not having worked on online gambling which has very large data, but Ive worked in telecoms and insurance which have multi Terabyte DWHes. We always store down to the details of the phone call or premium/claim transactions themselves.


QuickCheck for Javascript

Question: Is there a version of quickcheck that works for Javascript and that is well maintained? I have found several such as check.js and claire, but none of them seem to support shrinking of failing test cases, which has always struck me as the most useful part of the whole problem.
Answer: I'm creator of jsverify. I'll try constantly to make it better, bug reports and feature requests are welcomed.
There are also a list of other javascript generative testing libraries in a readme. So far I haven't found any other good alternative to the jsverify.
Comment: Hey, in jsverify it says "Write properties about your function that should hold true for all inputs".  How then do you test functions with if/else decisions?  What if for example I want to test that when a string contains "foo", that the function does something?
Comment: @JK. John Hughes has  advice on specifying properties at https://www.youtube.com/watch?v=G0NUOst-53U. ScottW has suggestions at https://fsharpforfunandprofit.com/posts/property-based-testing-2/. I can recommend them, if you can grok the Haskell and F# syntax (the verbal explanations really help).
Answer: I recently released https://github.com/dubzzz/fast-check
I built it in order to answer several limitations I encountered in the existing quickcheck implementations in JavaScript.
It comes natively with a shrink feature which can shrink even combination of arbitraries (the frameworks I tried were failing on oneof like arbitraries).
It also can generate large objects and arrays.
By default it tends to try smaller values first in order to detect trivial edge cases while it covers all the possible inputs in next runs.
Lots of other features are on-going or already available :)
Cheers,
Nicolas
Comment: it's rare that I read through all the documentation at once for a library, but with yours I have! Can't wait to give this a bash. I've used and really enjoy JsVerify, so I'm very much looking forward to fast-check
Answer: I wrote quick_check.js, which has a nice library of generators. Shrinking is not there yet, but is planned.
Answer: There seems to be a dearth of good quickcheck-like testing tools in javascript.  However they are to be better supported in typed languages, and in fact you can write your tests in one of those languages if you wish.
To avoid dealing with runtime interop, I'd recommend going with a language which compiles to JS and runs on node.js (eg: Purescript with purescript-quickcheck), or a java-based language using the Nashorn engine provided in Java 8, for example ScalaCheck.  You could even use ghcjs and the original flavor of the quickcheck library!
Comment: These days I am using elm, as my interest in JavaScript is 100% about in browser operations. For backend code I use erlang
Comment: I was going to include Elm and https://github.com/TheSeamau5/QuickCheck in my answer, but PureScript integrates better with javascript (at least until Elm 0.16..)
Comment: @jazmit there's a more recent property based testing library from the same author for Elm: https://github.com/TheSeamau5/elm-check

QuickCheck for Javascript


Clarifying question on meaning of derivative of a linear transformation

Question: In my analysis class, my professor (and the textbook) reference the fact that $\mathbf{D}T(\bar{x}) = T$ for any $\bar{x} \in \mathbb{R}^n$ where $T \in \mathcal{L}(\mathbb{R}^n,\mathbb{R}^n) $. I'm wondering about the precise meaning of this statement. Is it that the differential of any linear transformation is also linear? Or is that the differential of any linear transformation is itself (and therefore also linear)? The second seems confusing to me because the derivative of a function is often not itself. For example, $f(x) = 2x$ is a linear transformation but $f'(x) = 2 \ne 2x$ for all $x \in \mathbb{R}$.
Answer: In this context the notation is slightly different than what you are used to.
Consider $f(x)=x^2$. In this notation the derivative of $f$ at the point $x$ acting on a vector $h$ is $(f')_x h = 2x h$. The derivative is the linear function $``$ Multiply by $2x$".
For $f(x) = 2x$ the derivative at the point $x$ acting on the vector $h$ is $(f')_x h = 2h$. Now the linear transformation is just $``$ Multiply by $2$".
Answer: If you consider $T = 2$ as a $1\times 1$ matrix, then $f' = T$ as claimed. (the map is "take $x$ and multiply by $T$")
In general, if you consider
$$
f(x) = Tx
$$
then $Df = T$, literally. You could check this by writing out the formula for $Tx$ in coordinates, then taking various partial derivatives of the various components to compute $Df$. In particular, the $i$th component of $Tx$ is
$$
\sum_j t_{ij} x_j
$$
and so
$$(Df)_{ij} = \partial_j (Tx)_i = t_{ij}$$
as claimed.


High humidity in bathroom!

Question: I cannot for the life of me figure out where this excess moisture is coming from. My bathroom has humidity about 10% higher then the rest of the apartment. The living area is fine. I check the humidity on a Humidity monitor and it is always very high in the bathroom, around 68%
The thing is its only 30% humidity outside so its not coming from outside. I have a fan that I use every shower and leave the door open. If I open the window it drops to about 58% (that is with the outside being 30%) It won't get lower then 58. As soon as I shut the window it goes back to 68 or so. I see no leaks under sink, no condensation on toilet. I don't know where this is coming from. I live on the 2nd floor of a 3 floor apartment complex that is only 2 years old. I have lived on the 2nd floor of a 3 floor complex before and never had this problem. And that bathroom didn't even have a window. This one does. I don't get it. Can someone tell my why it is so humid? What gives?
Comment: Do you have an exhaust fan? I know some places that have a window do not require a fan. My shower creates a bit higher level but my wife loves very hot showers and the fan can not keep up so the walls and ceiling get damp causing the levels to be quite high all day
Comment: Are you sure your humidity meter is accurate? They aren't that easy to get right.
Comment: Are you sure that the fan is clean and functioning? One test that I've seen listed before on other questions is to rip off a piece of toilet paper and hold it up by the fan. If the fan grabs and holds it up, then it's working. If not, this could be the problem.
Comment: Yes I do have and use the exhaust fan, plus open window after, and leave door cracked. Thing is it will be 24 hrs after any shower and still that high humidity.
Comment: What type of heating system do you have?
Answer: Definitely get the Landlord involved. Unless there's a standing pool of water, much bigger than the toilet, there's no apparent nor logical reason for any room to stay so noticeably different.
I'd say maybe a backdraft through the exhaust fan from a faulty damper, but you've disproven that. In the meantime, check with the neighbors & see if either are doing anything strange or noticed the same thing.
I'd suspect the 1st floor got a Hot Tub or started Indoor Gardening. A Room Humidifier or Air Conditioning System's Humidifier wouldn't even do anything like your saying.
Comment: I do wonder if opening the door and the window AND turning on the fan is somehow drawing in moisture. I find that my bathroom gets the most out of the exhaust fan when it's JUST the fan on, and enough of a gap at the bottom of the door.
Comment: Yeah, that's what I was thinking initially but she disproved that pretty handily. You're definitely right though, using the fan with only the door gap or the open interior door as the only air feed is the optimal operation. I'm assuming she's actually feeling the difference & not just playing around with some new Phone App.
Answer: Firstly, when your fan is running DO NOT open your bathroom window. Open one elsewhere and have your door ajar of if there is a good gap at the botton close it. Why? What you are looking to do is draw air ACROSS the bathroom space so the warm moist air is picked up and drawn out. By having the window open you have what's effectively a short circuit so air flows in through the window and immediately out of the fan picking up almost no moisture laden air on its journey.
It's important to keep the fan blades and duct clean as that encourages best flow rates.
Try this test. Put a candle night light on the floor by the door withh the door closed and the fan on. Watch the flame dance. Then open the window and watch the flame sit bolt upright. That tells you there is no through draught.
Make sure your fan runs for a good while post showering.

High humidity in bathroom!


looks not easy, seems not easy

Question: Are these sentences correct?

It looks not easy.
It seems not easy.

Or do I need to say like these?

It doesn't look easy.
It doesn't seem easy.
Answer:
It looks not easy.
  It seems not easy.

... are grammatically correct but would sound rather odd. It is not recommended.

It doesn't look easy.
  It doesn't seem easy.

... are grammatically correct and sound fine. This is how normal speech is and you should go with this.

looks not easy, seems not easy


How to remove gunpowder virus?

Question: I have recently been having problems on my device which includes random apps appearing on my phone and some chinese app that somehow was "pre-installed". As i scoured the internet for answers, i  learnt that my phone had contacted a virus called gunpowder virus that attacks from Nintendo emulators. Can factory reset resolve my problem?
Answer: As long as the infected app wasn't able to gain root and/or infect the <code>/system</code> partition, a factory reset will fix it.
However, if it was ... it would require re-flashing the ROM.
Comment: Or gaining root, so OP could manually delete the app on **/system** without having to mess up things too much.
Answer: If your device doesn't have the virus and you still want to remove the pre-built chinese apps, You can use a program called MTK Droid Tools..
It was designed for mtk handsets but the Chinese software removal tool only uses adb and root access to remove chinese ime etc...

How to remove gunpowder virus?


Detecting and removing Absolute persistence technology

Question: Absolute persistence technology amounts to a persistent rootkit pre-installed by many device manufacturers (Acer, Asus, Dell, HP, Lenovo, Samsung, Toshiba, etc) to facilitate LoJack for laptops, and other backdoor services:

The Absolute persistence module is built to detect when the Computrace
  and/or Absolute Manage software agents have been removed, ensuring
  they are automatically reinstalled, even if the firmware is flashed,
  the device is re-imaged, the hard drive is replaced, or if a tablet or
  smartphone is wiped clean to factory settings.
Absolute persistence
  technology is built into the BIOS or firmware of a device during the
  manufacturing process.

This has echoes of both Rakshasa and vPro.
Also, like other corporate rootkits, it increases the attack surface available on the host PC and thereby opens the door to additional malware:

The protocol used by the Small Agent provides the basic feature of
  remote code execution [and] creates numerous opportunities for remote
  attacks in a hostile network environment. ... A typical attack on a
  local area network would be to redirect all traffic from a computer
  running Small Agent to the attacker's host via ARP-poisoning. Another
  possibility is to use a DNS service attack to trick the agent into
  connecting to a fake C&C server. We believe there are more ways to
  accomplish such attacks, though this is beyond the scope of the
  current research.

If a user legally purchases, secondhand or new, a device that originally had Absolute persistence technology built-in and may even have had it activated, and wishes:

to detect whether the technology is still present in the device; and, if so,
to remove that technology from the device (i.e. disinfect the device),

how best should the user go about this?
I'm guessing that Coreboot is part of the answer.
Comment: Unless there is a dedicated chip onboard for storing such preinstalled modules, flashing with a clean or moded version of BIOS is enough. Coreboot also can be used. To detect the presence, the best way is to observe the system deeply and carefully, check settings in bios, reverse engineer the BIOS etc.
Comment: @Nikhil_CV, I've no idea whether there is a dedicated chip, or indeed if the rootkit persists by homing itself in multiple chips/firmwares/etc (e.g. is it related to "Intel Anti-Theft Technology" in many modern Intel CPUs?). If you know more than I do, then please expand on your comment in an answer, and provide sources for your information. Thanks!
Answer: "Absolute persistence technology is built into the BIOS or firmware of a device during the manufacturing process."
So, in addition to removing the agent, you will need to flash the BIOS or firmware of the device, with a version without the technology.
Since "core boot is a Free Software project aimed at replacing the proprietary BIOS (firmware) found in most computers", it is potentially part of an answer.
Of course, you haven't specified a device, so it's impossible to provide you with a detailed answer.  The only correct answer is 'it depends'.
The functionality of the technology requires that removing it remain infeasible, so its quality/repuation hinges on us being unable to provide you with a detailed answer.
It's really not one technology, but many; review the NSA's ANT technology codenamed DEITYBOUNCE, IRONCHEF, FEEDTROUGH, GOURMETTROUGH, etc; see https://commons.wikimedia.org/wiki/Category:NSA_ANT...
Comment: I'm not sure what you mean by "protected". Presumably, you mean one with the Absolute rootkit removed. Anyhow, this still begs the question of *how* to get both a protected and unprotected X60 (for instance) in order to make such a comparison.
Comment: I didn't specify a device because I'm interested in in the general case and I don't know whether there's a common implementation or if implementation varies from model to model. Still, if you want a specific suggestion, how about the ThinkPad X60?
Comment: That's cool.  The only correct answer is 'it depends', because the implementation varies from model to model.  I don't have specifics for the ThinkPad X60.  For the Juniper brand, for example, there are three implementations in the NSA toolbox.  Can these be detected?  Not readily.  There is no answer to your question 'till someone knows what the technology is in a specific case.

How to go about knowing that?  Buy the tech, and compare a protected system to an unprotected one.
Answer: The only way I know of is to contact Absolute Software and request removal of the agent. They are friendly enough, they will ask for some identifying information on the laptop, and then they will send a message to the original owner and ask if they sold it or got rid of it (I guess).
I waited on the order of six months for the final resolution, just got my message. Here is what it looks like:

The agent has been removed from device XXXXXXXX, make sure that the device is connected to a wired network, must have Windows O.S. installed, perform some reboots and please allow 24.5 hours in order to complete the whole process.
  Please let us know if you need further assistance.
Comment: Interesting to know that this option is available. However, it requires the user to trust MS and to place even more trust in *Absolute Software* than might otherwise be so. I.e. it requires the user to: trust *AS* with (pseudonymous?) contact info associated w/the PC in question; trust *AS* (& anyone they share info with) not to misuse their ability to correlate that identity w/the PC's connections to the Internet; trust the agent to do no harm while still present; trust *AS* to get back to you; and trust *AS* to be have been truthful if/when they finally tell you they have removed the agent.
Comment: Upvoted, because this is *plausibly the approach that AS intends for users who wish to remove the agent*. So, thank you for pointing it out. However, I have not marked this answer as "accepted", because the approach outlined in it seems to me to be slow, dangerous, and unverifiable; and because it does not address the "[how] to detect whether the technology is still present in the device" part of my question.
Answer: You could, as I did, write a windows service that loads early in the windows boot order ,in my case before network service, and waits for the service injected by the apm module to load. Once detected it will stop the apm service and delete the services file. I kept my service running in the background just in case the apm module could somehow re-inject and run the apm service.
This method worked with my acer travelmate from 2012, maybe things have come along since then.
Comment: Would you please provide the source code for your service and steps to go through for installation?
Answer: Basically
In addition to
WHO's NoToOldRx4CovidIsMurder, I would add:

Have a look at Coreboot's board status page, for information about your device.

Considering this sample: Board:lenovo/t420.

If a user legally purchases, secondhand or new, a device that originally...

Once firmware is flashed while computer is off, Absolute don't have chance to boot. From there, if you install new system from scratch, I think you can consider that this computer is your computer.**

As coreboot is open source, you could inspect code before compiling it, but coreboot is not the only solution! There a lot of opensource BIOS replacement projects...

Paranoid disclaimer: **
As absolute is a kind of backdoor installed from design by hardware constructor, but keeping in mind that constructor is mostly delegated in other contries ( regarding human work cost ), I'm not able to certify that no other backdoor was ever built... by vendor OR by real hardware constructor, for sample...
And they could even by located in any chipset, network interface rom, or even elsewhere... see Cyber-attack concerns raised over Boeing 787 chip's 'back door'
For this, I think the better way should be something like:

slow down your network Internet access,

watch for signal, using old oscilloscope,

then try to follow every communication, during boot time...
Comment: Maybe this: https://www.coreboot.org/Board:lenovo/x60 and https://www.coreboot.org/Board:lenovo/x60/Installation could help.
Answer: According to the FAQ:

What if the Absolute software agent needs to be removed from a device?
IT administrators that have been authorized to do so, may carry out
  this function themselves within the Absolute Customer Center for
  Computrace, or from within the Absolute Manage console for Absolute
  Manage software agent removal.

I.e. you have to allow CompuTrace to be installed, persuade Absolute that you are the authorised user now, get control transferred to you, and de-activate it using their managed service.
Which will certainly involve sending them money.
I am guessing that CompuTrace will be detected by any competent antivirus as "remote management software" which you can probably flag not to run.
Comment: As for using mainstream antivirus software to block the execution of any part of the Active system, that's unlikely to work: **"the [Absolute] rootkit is [white-listed by anti-virus software](http://www.zdnet.com/blog/security/researchers-find-insecure-bios-rootkit-pre-loaded-in-laptops/3828)"**.
Comment: I'm afraid this FAQ answer ("*What if the Absolute software agent needs to be removed from a device?*") doesn't address my question, as it would only remove the software agent, not the Active persistence technology.
Answer: I reached Absolute Software tech support at the provided number and gave him the PC serial number. He told me that their records said that Computrace had been disabled by the original PC owner 5 years ago, however there is nothing that Absolute Software can do to help, that my only recourse is to see about purchasing a replacement motherboard from the manufacturer.
Answer: My Thinkpad T490 has a bios option in the security tab to "permanently disable the Absolute Persistence Module". It's in no way clear what this option actually does, but I've just disabled it on my system. This option, or similar options, are available for many Thinkpads. For discussion, see https://forums.lenovo.com/t5/ThinkPad-T400-T500-and-newer-T/BIOS-option-to-quot-permanently-disable-quot-Computrace/td-p/104500
Answer: I have CTES From Absolute on my Dell laptop board and consider it Corporate spyware. This is how I defeated it. I went to C:\Windows\system32\ and grouped everything by manufacturer, made a list of everything from Absolute so I could create a .cmd file to delete it all, hey It's gonna come back right? Did the same in SysWOW64. There is 5 services to stop, CscService, Ctes Manager, CtesHostSvc, rpchdp and rpcnet. These were stopped using NET STOP in my .cmd file, before I deleted everything like this:
@Echo Off
NET STOP CscService /Y
Reg.exe add "HKLM\SYSTEM\CurrentControlSet\services\CscService" /v "Start" /t REG_DWORD /d "4" /f
NET STOP Ctes Manager /Y
Reg.exe add "HKLM\SYSTEM\CurrentControlSet\services\Ctes Manager" /v "Start" /t REG_DWORD /d "4" /f
NET STOP CtesHostSvc /Y
Reg.exe add "HKLM\SYSTEM\CurrentControlSet\services\CtesHostSvc" /v "Start" /t REG_DWORD /d "4" /f
NET STOP rpchdp /Y
Reg.exe add "HKLM\SYSTEM\CurrentControlSet\services\rpchdp" /v "Start" /t REG_DWORD /d "4" /f
NET STOP rpcnet /Y
Reg.exe add "HKLM\SYSTEM\CurrentControlSet\services\rpcnet" /v "Start" /t REG_DWORD /d "4" /f
DEL /F /Q /A C:\Windows\SysWOW64\cshost.dll
DEL /F /Q /A C:\Windows\SysWOW64\CTLojack.dll
DEL /F /Q /A C:\Windows\SysWOW64\DIAGDLL64.DLL
DEL /F /Q /A C:\Windows\SysWOW64\identprv.dll
DEL /F /Q /A C:\Windows\SysWOW64\pkgmgr.dll
DEL /F /Q /A C:\Windows\SysWOW64\pcnet.dll
DEL /F /Q /A C:\Windows\SysWOW64\wceprv.dll
DEL /F /Q /A C:\Windows\SysWOW64\instw64.exe
DEL /F /Q /A C:\Windows\SysWOW64\pkgslv.exe
DEL /F /Q /A C:\Windows\SysWOW64\rpcnet.exe
DEL /F /Q /A C:\Windows\System32\cshost.dll
DEL /F /Q /A C:\Windows\System32\CTLojack.dll
DEL /F /Q /A C:\Windows\System32\DIAGDLL64.DLL
DEL /F /Q /A C:\Windows\System32\identprv.dll
DEL /F /Q /A C:\Windows\System32\pkgmgr.dll
DEL /F /Q /A C:\Windows\System32\pcnet.dll
DEL /F /Q /A C:\Windows\System32\wceprv.dll
DEL /F /Q /A C:\Windows\System32\instw64.exe
DEL /F /Q /A C:\Windows\System32\pkgslv.exe
DEL /F /Q /A C:\Windows\System32\rpcnet.exe
RD /S /Q C:\ProgramData\CTES
RD /S /Q C:\ProgramData\Rpcnet
PAUSE

OK services stopped, everything deleted. CTES is now off the system temporally, temporally because it's on the motherboard and it will reinstall to your system, but now you have your .cmd file you can run but that's not enough, CTES must contact a server to update itself and then upload data, and it's considerable. Go to the CTES folder and have a look at CtesPersistence.txt to get an idea of what's happening. I stopped that Internet traffic cold by blocking these servers in the hosts file:
127.0.0.1 search.namequery.com
127.0.0.1 search2.namequery.com
127.0.0.1 search64.namequery.com
127.0.0.1 eol.absolute.com
127.0.0.1 si.namequery.com
127.0.0.1 d.namequery.com
127.0.0.1 a.fc.namequery.com
127.0.0.1 fo.fc.namequery.com
127.0.0.1 resources.namequery.com
127.0.0.1 cdta.namequery.com
127.0.0.1 eum.absolute.com
127.0.0.1 api.absolute.com
127.0.0.1 ps.namequery.com
127.0.0.1 amp.namequery.com
127.0.0.1 ps.absolute.com
127.0.0.1 ctm.server.absolute.com
127.0.0.1 gcm-http.googleapis.com
127.0.0.1 bh.namequery.com
127.0.0.1 sv.symcb.com
127.0.0.1 s.symcb.com
127.0.0.1 s1.symcb.com
127.0.0.1 s2.symcb.com
127.0.0.1 crl.thawte.com
127.0.0.1 cdp.thawte.com
127.0.0.1 cacerts.thawte.com

I have effectively disabled a rather well thought out piece of Corporate Spyware. CTES service still installs because it's on my laptop board. I have Process Hacker from Source Forge, it notifies me when the CTES service installs, so I give it an hour then go to %ProgramData%\CTES and confirm that nothing was updated or uploaded.
To understand just how persistent this is, have a look at Administrator's Guide for Absolute Agents Once the software is activated, you can only block it. And most laptops are shipped with it activated. Please note this is my system, yours may be different, but it's a jumping-off point.
So to answer the question, I will say quite definitively that this technology is not coming off that board... ever. It can only be managed.
Here's some reference:
search.namequery.com    22.214.171.124  80 and 443  Absolute agent communication for Windows and Mac
search2.namequery.com   126.96.36.199   80  Data Delete & Device Freeze
search64.namequery.com  220.127.116.11  80  Absolute Consumer agent
eol.absolute.com    184.108.40.206   443 End of Life (EOL) Data Delete
si.namequery.com    220.127.116.11  80  Absolute Persistence 2.x
d.namequery.com 22.214.171.124  80  Absolute Persistence 2.x
a.fc.namequery.com
fo.fc.namequery.com 18.104.22.168    80  Real-Time-Technology over IP (RTT-IP)
resources.namequery.com 188.8.131.52   443 Absolute 7 components
resources.namequery.com 184.108.40.206   443 Absolute 7 components delivered from Microsoft Azure Content Delivery Network
cdta.namequery.com  126.96.36.199  80  Data Transfer
eum.absolute.com
.and embedded URL   18.104.22.168    443 End User Messaging
api.absolute.com    184.108.40.206  443 Web Services API
ps.namequery.com    184.108.40.206   443 Professional Services
amp.namequery.com   184.108.40.206   443 Professional Services
ps.absolute.com 18.104.22.168  443 Professional Services
ctm.server.absolute.com 18.104.22.168  443 Absolute agent communication for Android and Chromebook
chrome.google.com   220.127.116.11   443 Absolute for Chromebooks Extension Web Store
gcm-http.googleapis.com 188.8.131.52   443 Google Cloud Messaging for Android and Chromebook
bh.namequery.com    220.127.116.11  80  Absolute holding account
sv.symcb.com    184.108.40.206 80  CRL Distribution Point
s.symcb.com 220.127.116.11 80  CRL Distribution Point
s1.symcb.com    22.214.171.124 80  CRL Distribution Point
s2.symcb.com    220.127.116.11    80  Authority Info Access - On-line Certificate Status Protocol
ts-ocsp.ws.symantec.com 126.96.36.199    80  Authority Info Access - On-line Certificate Status Protocol
ts-aia.ws.symantec.com  220.127.116.11 80  Authority Info Access Certification Authority Issuer
ts-crl.ws.symantec.com  22.214.171.124 80  CRL Distribution Point
ocsp.thawte.com 188.8.131.52    80  Authority Info Access - On-line Certificate Status Protocol
crl.thawte.com  126.96.36.199 80  CRL Distribution Point
cdp.thawte.com  220.127.116.11 80  CRL Distribution Point
cacerts.thawte.com  188.8.131.52    80  Authority Info Access Certification Authority Issuer
ocsp.digicert.com   220.127.116.11 80  Authority Info Access - On-line Certificate Status Protocol
crl3.digicert.com   188.8.131.52 80  CRL Distribution Point


Guitar picking technique: anchoring the picking hand

Question: Is it a good idea to pick strings without anchoring your right hand?
The right hand just stays hanging in the air while picking.Does it decrease accuracy ?
Comment: Glad that I stopped anchoring .My picking hand movement is so smooth now and switching between lead and rhythm has become so easy.
Answer: I have taught guitar for over 30 years and I am finding some of the answers above quite annoying and misleading. Anchoring is absolutely fine IF it allows you to do what you want to do. Technique should never be about what works for someone else. It should always be about what works for you. A good teacher will never insist that you do things the way they do. They should always help you find your way of doing things.
Anchoring is not a bad technique at all. Many top guitarists anchor. Some of the fastest and most technical guitarists I have seen use anchoring. Just look at Michael Angelo Batio. Steve Vai uses anchoring at times. I think that people who do not use anchoring have found what works for them. That doesn't work for everyone. I am quite a technical guitarist and I have developed high speeds. Sometimes I anchor my wrist, and sometimes I don't, it really depends on what works for the peice or section that I am doing.
I find that anchoring when finger picking doesn't work at all for me, and yet my friend, who is an exceptional guitarist, uses it all the time. He found what works for him.
So is it wrong to anchor? No. It is only wrong for you if you cannot acheive what you are trying to do because it restricts you.
Answer: In most of my students, yes! Floating around can hardly do anything except decrease accuracy. In initial stages at least, resting the hand just behind the bridge will anchor it sufficiently to move the picking onto the next string. And for the next few years too.  And for palm-muting, move it across a little. Some find it beneficial to rest pinky on the guitar body, just under the top string.
Comment: I have always rested my pinky on the guitar,but now I am being told change it ,and play without anchoring not even on the bridge ,in order to be more agile while switching between rhythm and lead.
Comment: Seems an odd reason to change, as we don't need to be that quick going from one to another, and that apart, can't see how much quicker it could be anyhow. If it's your teacher telling you, ask for valid reasons, and proof. Seems a pointless thing - to me! I'd want justification.
Comment: I'd want justification as well. I would never play an electric with the pick 'floating around'.
Comment: Why would that be a problem on electric?
Answer: Interesting question. I play with a pick and most of the time I anchor my picking hand when I'm improvising lead parts. However it might be interesting to learn to play un anchored which would allow me to play away from the bridge where I might find other tonal characteristics on the guitar. If I were to learn to do this, I don't think I'd give up anchored picking completely, but it might be nice to have those alternative skills on occasion.
Answer: What I do is to keep my pinky on the guitar's scratching board (or simply on the body if your guitar doesn't have one) while playing lead.
Its a good practice as it increases accuracy while playing lead. However, if your're playing power and barres chords, wherein you've barred 4-6 strings, you can remove your pinky. The same goes for open chords.
But, for short chords (short forms of full barred chords), you can keep you right hand anchored.
Answer: Anchoring is a pretty bad habit to develop.  If you are serious about developing exceptional technique then invest the time in a floating right hand. It is more difficult and will take a lot of practice but in the end you will develop greater accuracy.
Anchoring does two things that will come back to bite you.  The first is that guitarists that anchor will more likely than not play in one area of the instrument or one a small group of strings.  The second is that in many cases when playing fast an anchored right hand can actually cause you to push away from the guitar making the pick miss notes (this is very sloppy and inaccurate).
There are exceptions to every rule.  For example Mike Batio, Yngwie, and Wes Montgomery all anchor, but they have specific ways to do it that work for them.  Yngwie does not always anchor, and Wes is using his thumb, pushing in as he plays.  So the general comments do not apply.  People have written text books analyzing Yngwie's technique, if you like that sort of thing you can look it up.  But there are many great shredder who do not anchor in this manner and still fly.  You do need to develop a haptic connection to the instrument and for beginners it is tempting to anchor to help them "feel" where they are on the guitar.  But the truth is you don't need this for accuracy.  What you need is lots of practice.  In finger style classical guitar your connection is the forearm touching the edge of the body, no anchoring of the fingers on the top.  And some players lift the arm when playing across all six strings (essentially floating the arm).
If you look at Frank Gambale's technique he rarely (never as far as I can see) anchors the fingers on the top but he keeps the palm of his picking hand very close to the strings, to the point where he probably touches them.  When Eddie van Hallen tremolo picks he floats his picking hand in the air and he is extremely accurate.
For me personally, anchoring limits mobility and speed.  With practice a floating hand is just as accurate as an anchored hand (in my experience more so) and I teach my students a floating right hand style.
Answer: Dude, you need to find a finger, usually the pinky and plant it for an anchor on your strumming hand, don't leave your strumming hand flap around, unless the song calls for it, slap picking.  Find a spot on the bridge to put your pinky, just try and use it as a guide for the rest of your hand.  I use my strumming hand to mute strings, so I have to have an anchor so I mute the right strings, the pinky is what I use for a reference so I don't have to look.  When your speed picking you will definitely need an anchor point, that will help with muting and proper string picking.
Well I've said enough, take it or leave it, we're all different, and styles are all different.  Willie Nelson used to wear holes in his guitar's body while he was doing some crazy strumming!  Good luck.
Comment: Anchoring is one of the worst habits you can develop


Sharepoint framework (spfx) failes to create new project

Question: I use yo @microsoft/sharepoint and it hangs at `Found npm version 6.5.0,no error the console is not closing it just stops. (files are not produced and multiple enters don't do anything)
Guys do you have some suggestions?
Comment: I used yo @microsoft/sharepoint and yo @microsoft/sharepoint --component-type "webpart" --framework "react" and it was the same result
Comment: Run npm update (Update to the latest npm and retry the step once again)
Comment: @AIM4DREAM npm update shouldn't update the package.json? the problem is that yeoman doesn't generate anything
I've recorded a gif of it here
https://drive.google.com/file/d/1nYmKw_Xh4ZTiybOLBXNc52dlnlRc5tIA/view?usp=sharing
Answer: Try to reinstall node js version 8.* https://nodejs.org/dist/latest-v8.x/ It is officaly supported version by Microsoft.
Then try to run yo generator without the parameters.  Only yo @microsoft/sharepoint.
Perhaps try to update Microsoft generator.


Why doesn't an inductor have polarity?

Question: Let's say we have a DC source connected to an inductor. The orientation of the magnetic field through the inductor depends on which direction the coil was wrapped (right hand rule). But why do we not care about it's polarity when we use inductor in the circuit? I guess we do care about polarity in terms of mutual inductance, but what about when only one inductor is used in the circuit?
Comment: @DKNguyen You're introducing complexity where none need exist. OP asked about an inductor not a transformer, and made no mention of centre taps etc. For a simple inductor, the only time a polarity might be detectable is when it is when it is in a magnetic field, including (to a very small extent) the Earth's.
Comment: Simple inductors are just a wire coiled up. They are symetrical.
Comment: @DKNguyen Yes but if the polarity depends on the curent but the part itself is materially symetrical, then we are talking about the polarity of a circuit, not of a part. I don't really understand the question.
Comment: @Fredled This isn't true. Sure, you can always re-orient two unpowered coils wound in the opposite direction to be in the same orientation since there is nothing to differentiate the ends, but things are different when you send current through it since the act of sending current through it a front and back by virtue of polarity which produces a defined CW or CCW direction.
Comment: @Fredled Materially maybe. We use them magnetically and when magnetized they are definitely not symmetrical. OP is basically asking why we don't care which end is north and which end is south when sticking an inductor into the circuit. I am not even sure what the plane of symmetry is for a helix. Can't seem to pin it down. It must fall under a more complete math definition of symmetry.
Answer: We only care about the polarity of an inductor when the polarity of the magnetic field is important.
Such as with electromagnets or common mode chokes and measurement transformers.
Comment: @user207787 When we do care, that's when the inductor has the dot on one end of it to indicate polarity relative to another coil.
Comment: Okay, that's what I thought. Thanks!!
Answer: You might care. For example, if you have a filter choke that has a permanent magnet biasing it.

Or if there is another inductor magnetically coupled to it, then the relative polarity matters.
Comment: I love how a pirate is related to a Joule thief. :D
Answer: Suppose you have two identical inductors, except one has a right-handed winding, and the other has a left-handed winding. Ramp up the current through the right-handed inductor. This produces a changing magnet field which induces a voltage in the inductor. That's self-inductance. Now do the same with the left-handed inductor. The handedness reversal reverses the relationship between the current and the magnetic field, but it also reverses the relationship between the magnetic field and the induced voltage. With the double reversal, you get an identical induced voltage, so the self-inductance is the same.
Answer:
Actually we do care about Inductors, especially with DC circuits. The polarity depends on the direction of the current flowing through it. If a current is moving from point A to point B (say), the Inductor stores the current in the coil inturn producing magentic field. Now if the device is turned off, the inductor that had the current stored in it must dissipate. But because of the reverse EMF (according to your right hand thumb rule) the current travels form point B to A. This current can spike up and destroy your circuitry. That's why you have bypass diodes connected across node A and B such that it creates a loop. Eventually the current dissipates with all its might saving the circuitry behind it. Hope this helped.
Comment: But inserting the inductor with the connections reversed doesn't change anything in this situation. You may have missed the point of the question.
Comment: *The polarity depends on the direction of the current flowing through it.* This is not polarity of the component. And it doesn't answer the question.
Comment: Not my interpretation of the question but the comments are very useful and on topic. So I voted it up.
Comment: I wanted to convey that inductance polarity matters and there a certain significance taken into consideration. At least that was my interpretation of the Question. But Apologies for the inconvenience.

Why doesn't an inductor have polarity?


Should we require prior research?

Question: Lots of questions on Music SE could have been answered almost instantly with a quick Google search (e.g. this one). Should we require questions to demonstrate at least a minimal amount of prior research effort? Lack of research is given as a downvote reason, maybe it should be a close reason as well.
Comment: @Lyd I've just seen that this has all been discussed [before](https://music.meta.stackexchange.com/questions/2089/regarding-closing-questions-because-of-lack-of-previous-research?rq=1). It might be a good idea to accept an answer there and mark this question as a dupe. (Sorry, I failed to do what I'm preaching: research)
Comment: [elu.se] has this rule. It leads to lots of closed questions.
Comment: @marcellothearcane But do *good* questions get closed? On German Language they're also strict about this, it stops people using the site as a dictionary.
Comment: Out of interest, you have a 'new contributor' badge with 2.7k rep - is that because you haven't done much on meta?
Comment: @PiedPiper LOL! I completely forgot that happened! It was like 4 years ago though, so it's a good idea to revisit how the community feeling about it now.
Comment: It cuts out most of the cruft to be honest. A lot of people ask 'give me the codes'-type questions which we can do without. Some users complain that we are a little too frivolous with the close votes on ELU though.
Comment: @marcellothearcane I can only assume it's because I haven't done anything on Music meta.
Comment: @PiedPiper I'm watching to the German Language SE most viewed and voted questions, and big portion of them show zero research effort. Perhaps the rule is a little sketchy in the first place.
Comment: @PiedPiper: The formulation of my question should have made clear that I have googled before I asked it. I agree with you that most questions here could be answered looking up at wikipedia. This SE is quite different from other SE like English or German language. But to quiet you ... As for me: I know how to google ;) But at least I try to ask questions that are not elementary.
Comment: @AlbrechtHügli I just took that question as an example because googling "vox humana organ" turns up a whole page of links to useful information. "Vox humana orgel" does the same and even just "vox humana" still produces good results.
Comment: Stirring this 2-year-old pot to wonder: Okay, *how much* research? There's a point I'm curious about that is clearly covered in a certain book. I can't access it electronically. I could do an Interlibrary Loan and wait for it to come in. (Maybe, if I lived elsewhere in the world, that's not even an option for me.) I know [SO's position](https://meta.stackoverflow.com/a/261593/6850209) is "This should your place of last resort." I wonder how we should feel about "I know where the answer can be found, I just can't access it at the moment." Probably not a reason for closure, but...
Comment: @AndyBonner Anybody who can say "I've discovered the answer is in a book which I can't access at the moment" has demonstrated they've done prior research. We don't need to close that kind of question.
Answer: The very first suggestion on the How do I ask a good question? page is "search, and research":

Have you thoroughly searched for an answer before asking your question? Sharing your research helps everyone. Tell us what you found and why it didn't meet your needs. This demonstrates that you've taken the time to try to help yourself, it saves us from reiterating obvious answers, and above all, it helps you get a more specific and relevant answer!

Technically this links to the Music.SE search (suggesting it's an on-site search, not a full Internet search), but I've always understood this suggestion to indicate a search anywhere for your answer, not just on the Stack itself.
My understanding is that we have closed questions on the basis of "lack of research" before, but I might be thinking of another SE site.
Comment: I don't think we have ever closed questions on the basis of lack of research. I've seen plenty been downvoted, but not closed. Research is thrown as a blanket statement as common patterns in questions with good form, not as a requirement. If you mouse over the downvote image, you can see "does not show any research effort", so this part is left to the user discretion. Does the question need research? Do i want it to have it? Many (if not most!) of the most useful and viewed questions, both here and in SE, have ZERO research effort, for what it's worth.
Answer: I think there's a few different scenarios here.
On one hand, asking a question that could be as easily typed into Google may be a pointless exercise if all it yields is a "Let-Me-Google-That-For-You" kind of answer.
On the other hand, I've seen cases where a user with a knowledge gap in some area may lack the ability to google something themselves due to not quite knowing the right search terms, and those questions being criticised for lack of research.
There are also cases where a question is easy to google and get answers for, but less easy to get answers that can be trusted. A user might be asking here to get some peer verification on an answer.
It's always good for questions to contain the necessary context, and prior research is part of that. But I wouldn't agree with a blanket requirement to explicitly demonstrate prior research effort - sometimes it might be the case that a user has made that effort but doesn't feel that describing that effort adds clarity to the question.
Comment: I have no problem with scenario 2 "I've searched, but  I don't know the right search terms" and scenario 3 "I've found an answer but don't know if I can trust it". I have have no problem with another scenario "I've found an answer, but I still don't understand". The problem is scenario 1: "Google this for me". How do we distinguish between these cases?
Comment: In TeX.SX, a common problem is that people ask how to code this or that in LaTeX (specifically with TikZ, a package to draw graphics) and only provide a picture of what they like to have coded. This is considered bad practice, and typically the community tells them to at least come up with some lines of their own code. Maybe, one could establish a similar system here so that people need to state at least one source that they searched when asking a question? I don't know whether this really helps, though.
Comment: @PiedPiper In music Q&A specifically, I don't think there's need to distinguish in the first place. You either want to help and share your knowledge, or not. If it's not a duplicate, I don't see why we should over worry and over think about the googlableness of each question. Music isn't as pragmatic as programming. Also, we have downvotes to deal with that kind of thing already, don't we? So, if you feel personally aggravated, you can always downvote.
Comment: @PiedPiper You don't have a problem with some scenarios, but how do you distinguish between them? Even if a user just wants you to google for him (something that I think happens a lot less than you are giving it credit for), that user can just write "i don't understand what i found" and be on the "i'm ok with it" category. Because of that kind of stuff, requiring previous research in this SE doesn't make much sense.
Comment: RE: "..lack the skills to google something..."   It's not the job of SE to help out the functionally incompetent.  Compare, e.g., people asking how to spell a word here because they don't know how to use a dictionary.  Waste of time and electrons.
Comment: @CarlWitthoft 'skills' was the wrong word. Edited.
Answer: Not all googleable questions have good quality answers, or answers that are worded and thought for a specific expertise level, or same depth, context, form, style, genre, etc.
In sites like Stack Overflow, with more pragmatic subjects, it makes a lot of sense that previous research is asked for, but music is much less pragmatic, along with the questions and answers derived from it.
So, should we require previous research? I don't think so. Some users don't even know what words and terminology are used formally, and some of them are in languages all over the world (Greek, Latin, Italian, Spanish, English, etc).
Should we close questions that Google has answers for? I don't think so. Is the answer found in google correct? Can it be understood by the level of expertise of the asker? Is it obsolete, or are there new things to say about it? Is it in the context of the correct genre, style, and time frame? Who is policing and deciding all these variants?
And most importantly, why should it matter? Is it a problem right now, in this SE? I don't think it is. So we would be denying knowledge with the basis of "we just felt like not doing it". Also, don't we already have downvotes to deal with that kind  of stuff, based on each user's discretion?
If you browse through the most viewed, voted, and useful questions both here and in Stack Overflow, you'll notice that most of them show zero research effort. So, the assumption that a useful question must contain previous research doesn't hold that well. Some questions definitely do benefit greatly from previous research, but at least in music, I don't think it works as an absolute generalization.
Comment: The point is probably that with doing some research (and showing this) before asking your question you show that you appreciate the unpaid effort of the community you ask, because you only asked them after having tried to solve the problem on your own. This has nothing to do with quality of the question (or the answers to it) per se.
Comment: @Lyd To make it clear: I do not personally ask for any kind of appreciation here on SX, but I personally do feel that I should do some prior research before asking not only in order to avoid duplicate questions but also to express my appreciation of the help of the community here. Maybe it's just my personal feeling though …
Comment: @JasperHabicht It is your personal feeling, and that's perfectly fine! But one thing is to prefer previous research (up and down votes), and another one is to require it (closing questions). I just don't see how this SE would benefit from it, or how is it needed. No one here has given an argument that doesn't appeal to emotion. I'm just not buying it.
Comment: Again, it's really not that hard to figure out how to translate a word, or to find a  dictionary of musical terms.
Comment: @CarlWitthoft And we are one of the places that will show results for musical terms! If you check the most viewed questions, many of them are of that type. We are supposed to be that site that shows when you search. We are a Q&A designed specifically for that kind of stuff! You are just arbitrarily choosing what we are and what we are not. So much ego!
Comment: @JasperHabicht I feel like we are above "appreciation", as a Q&A site I don't think it's even relevant. I don't feel personally offended for lack of research, and I don't look for personal research when I find an answer in SE, you go straight to the solution(s). You said it yourself, "this has nothing to do with quality", so it's just you asking for some "appreciation". Some questions benefit from it, some not. It's that simple.
Answer: Some questions seem to be from people who know the subject pretty well, but are soliciting a definitive answer for the SE archive  And thats fine.
What might be a good idea would be to be a lot more lenient about initialy rejecting questions and responses, but create a seperate Archive section for topics considered worth keeping.

Should we require prior research?


How to measure server power consumption?

Question: We have data center running more than 2000 servers. We are planning to shutdown the servers on a weekend for cost cutting purpose. How can we calculate which servers are consuming more power in the data center so that we can shutdown those many servers only . What is the best way to determine power saving on hourly/daily/weekly basis.
Answer: You can get amp meters to measure the power. or you could take meter readings from your electric meter.
The best way to get good readings is to do this for 24 hours. Not just a few hours. (You mentioned the weekend) and that obviously is a good time. But if you are able to get 2000 servers available for downtime at a weekend, do you need all of those servers?
Comment: +1 Also, many LOM modules report power usage. And, [Kill-A-Watt](http://www.amazon.com/P3-International-P4400-Electricity-Monitor/dp/B00009MDBU/ref=sr_1_1?ie=UTF8&qid=1326223551&sr=8-1)
Comment: Many CDU/PDU systems report per-tower or per-infeed -- a few even exist that support per-outlet information (e.g. http://www.servertech.com/products/smart-pdus/smart-pdu-cs-12hd )
Comment: Yea I know the datacenter we use, measure the amp use of every server.
Comment: Thanks for your comments. I wanted to shutdown only highly power consuming servers depends upon the availability on servers
Answer: Use PDUs [See footnote 1] that provide metering capabilities, such as these Metered Rack PDUs from APC. Monitor the PDU using software-- APC provides software which allows continuous power monitoring, and there are other options. Your best bet is to monitor power consumption trends over time.
Some PDUs only monitor down to the circuit which will still allow you to localize servers with high power consumption. Some of the newer PDUs allow monitoring all the way down to the outlet.
From what I know, a typical Datacenter spends more then 50% of it's energy budget on cooling. Computers generate heat, which then needs to be cooled by energy-intensive methods. Heat is one of the primary drivers of energy cost. Nearly every major air-handling vendor offers equipment which allows the company to monitor the power consumption.
Really, there is an entire industry out there which can help you monitor power consumption in your datacenter.
Footnote 1: PDUs are fancy power strips. Some people, especially electrical contractors, use the term "PDU" to refer to the big box which distributes power from the mains or the UPS.
Answer: Its mostly the CPUs that are consuming power. You can look up their wattage in their specs. But they will be most propably be in low-power mode when there is nothing to do. So look up these specs as well (it depends on your OS which power-saving mode will be activated).
Additionally there is the wattage used by the disks.
So all in all the fastest multi-cpu-monsters with lots of internal disks are probably the power-eaters.
Comment: that was my point -- You could have a 64 CPU box with no disks sitting idle and it would use less power than a 1 CPU box with 24 disks :)  Generally speaking you never want to spin down rotating drives if you don't have to :)
Comment: Idle CPU wattage is usually lower than idle (spinny) disk wattage -- unless you spin down the drives :)
Comment: @voretaq7 problem is I never wanted to spin down server disks. So my assumption is that you leave the disks running anyway. But nice idea - I have to check this on a server that monitors its own wattage and is not in use any more.
Comment: Ok - so your point is with current CPUs the disks are the culprits. I had my old Pentium HT in mind that can`t clock down much. The question also does not include the OS - so perhaps the OS is not able to power down CPUs at all...
Answer: The question is old but as it is very interesting to me and I may have a solution, here it is.
There is a pretty recent project that allows to measure the power consumption of your servers and the processes running on it: scaphandre
It's working for most amd/intel x86 cpus built after 2012.
There is also an "example" dashboard that shows what kind of metrics you can get.


changing winform properties for different clients

Question: I have a winforms app and want to customize for differents clients, I need a simple mechanism to create a version for client1 with one commandline app for example. I only want to change the color of the window and of buttons and a smart logo. I dont want to change it manually every time I need a client1 version.
Answer: Maybe you can put in your app.config some configuration tags, some properties you need. And then let's say, through your setup process, you modify the configuration based on client desires( that's if I understood correctly.
Answer: I don't know what kind of app you have but I had an app that is accessible for 3 different types of users which are admin, receptionist and patient. I used password authentication and inside the forms, I used simple if/else clauses according to authentication types to arrange which user could use which parts of the app. But as far as I understand you need something like an interface in case any other client takes part in the app later.


How do I create a portable solar panel lipo charger?

Question: We're working on a quadcopter that will carry a solar panel on top that will continually charging the lipo battery of the quad. What's the smallest and easiest way to recreate a charger that will allow safe charging for the lipo battery?
Comment: You're the second person to come asking about putting solar panels on a quad copter on the last week or so. Have you actually performed any power-to-weight analysis that shows this is even feasible? To provide net power to charge batteries, the solar panel must provide more than enough power to keep itself aloft. If such panels existed, then solar powered drones would be everywhere. They are not. I think you are better off just investing in a larger battery.
Comment: Unless the quad lands and charges while idle. I see no problem with that. True, the silly notion is *slightly* implied that during flight the panel will somehow recharge (or even how a noticeable effect on) the batteries, but it's not necessarily a requirement.
Comment: There have been a lot of people researching on solar powered quadcopters. And yes I think the other one who asked the question is one of my group mates. The idea we're creating in this "solar powered quadcopter" is to charge the lipo batteries while in the air. We'll have two batteries carried by the quadcopter along with the solar panels. One battery will be used while the other one is on idle. When the first battery dies, the quadcopter will then use the second one and the first battery will charge. So on and so forth.
Comment: Back to the question, how do I recreate a lipo battery charger using solar panels? Due to the possible "unstable voltage" output by the solar panels, it will be very bad for the lipo battery itself. How do I exactly "stabilize" or at least minimize these pulses to charge the battery safely?

Let's disregard the fact that it will be used on a quadcopter first.
Answer: Make sure you understand Lithium Ion battery safety before proceeding.
Lithium Ion batteries have limits on charging current and charging voltage. The typical charging technique is to provide the maxiumum charging current until max charging voltage is reached, then provide the max charging voltage until current drops to zero.
If you can find a solar cell array with Isc less than the battery max charging current and Voc at the max charging current you might be able to hook the solar array directly to the battery.
Otherwise, a DC-DC converter between the array and the battery which will convert the array voltage to max charging voltage, with a max current that matches the max charging current of the battery. You'll loose 15% of your energy though.
If you don't have an electrical engineer (or student of EE) on your team, go find one.
Comment: I'm making some big guesses about your system but I'm going to estimate something on the order of 100W to keep your quad in the air. Your solar cells are going to be on the order of 1W power production. That would extend a 20 min flight by 12 second.... That assumes all your extra electronics and solar panels weight nothing and don't affect the aerodynamics.
Comment: You're the guy who answered my group mate's question here in stack exchange. I thank you for answering that and this one too.

We'll be using Lithium Polymer batteries but this might as well apply to it as well. We've found solar cells that has these specs:

Average Power: (Watts): 0.63 Wp
Average Current: (Amps): 1.26 lmax
Average Voltage: (Volts): 0.5 Vmax

The batteries used will be a 3-cell, 2700 mAH Lithium Polymer Battery. What do you mean by losing "15% of the energy"?
Comment: We've considered looking into the DC-DC converter. But does it allow the amplification and stabilization of both the voltage and the current?
Comment: DC-DC converters (like every other power converter, whether mechanical, electronic, fluid, or thermal) waste some of the energy during conversion. 15% is a rough estimate. DC-DC usually try to control voltage and leave current uncontrolled. I'm guessing you are using hobby batteries which I prefer not to call [Lithium Polymer](https://en.wikipedia.org/wiki/Lithium_polymer_battery#Design_origin_and_terminology). They are some flavor of Li Ion. I'm pedantic that way. And seriously, [SAFETY](https://www.horizonhobby.com/pdf/EFL-LiPoSafetyWarnings.pdf)  if you start messing with your own charging.
Comment: The problem with the DC-DC is the fact that it will lower the current output to the battery. That's our current problem now (pun intended). We'll not be  using solar cells as our main power source for our quadcopter. So the battery will be the power source of our quadcopter.
Answer: The easiest way to accomplish lithium charging is to use a brownout tolerant DC-DC converter. By brownout tolerant I mean the converter should automatically derate output voltage to maintain the max current limit with no need to reset or recover once the condition clears.
The output current limit of the converter should be less than or equal to the current limit for the constant current phase of the charge curve. The output voltage should be less than or equal to the constant voltage phase of the charge curve.
In this scheme, when the battery is low on charge, it will also be low on voltage. A larger voltage differential will draw more current, up to the current limit on the converter, which should be approximately equal to the constant current charge limit.
The battery charges and, as it does,  the terminal voltage rises. At some time the voltage differential decreases to the point that the brownout condition ends and the DC-DC converter resumes rated voltage output, which should now be at the constant charge voltage.
A couple of notes, though:

As @hauptmech points out in their terrific content, assume the copter runs 10min at 100W for flight. This means the battery stores about 16 Watt-hours, or 1000 Watt-minutes of energy. Assuming the solar cell outputs 1W, this means it will take about 1000 minutes, or about 16 hours, to recharge the battery. When you try to connect the solar cell output to the system to charge, there is a very high likelihood that you will brown out the solar cell because of the power draw. This means the DC-DC converter needs to have a wide input voltage range, conceivably down to near 0V input, AND that the solar cell needs to be short-circuit tolerant, as that's likely to be the normal operating condition. You could get a DC-DC converter with a current limit closer to the equivalent power output of the solar cell, which may help.
Charging lithium batteries is dangerous. They are banned on most flights, banned on most air mail services, for good reason. See also: hover boards.
You need to be sure to stay under the max ratings. Exceeding the current limit causes heat issues (not that I think you'd exceed a lithium battery's current limit with a solar cell), but exceeding the voltage limit causes dielectric breakdown in the battery, which also causes fires. That is very possible with a solar cell.
Again, as hauptmech mentioned, you need an EE. This isn't really something to guess at, and if you're here looking for advice you should honestly consider if you know what you're doing and seek guidance at least from a senior EE student.
Comment: Currently, we have a solar panel with 3.45A and 1.07V specifications.
Comment: @HenryLachica - Is that peak current at rated voltage, or peak current and peak voltage? What is the max power output of the panel?
Comment: Currently, we have a solar panel with 3.45A and 1.07V specifications.

So from what I understood, the DC-DC converter we design must be able to accommodate the power needed by the quadcopter. So in this case, the lithium polymer battery needs 12.4 V or more and 2.7A to be able to charge properly. I know that DC-DC converter can boost the voltage of the solar panel but will not maintain the current as it might go down. How do I handle this?

Sorry the comment did not finish
Comment: That's the setup for 4 total solar panels. 2 of them are in series, and the series are paralleled into another 2 cells in series. It was measured during a very sunny day. So it probably maybe both its peak current and voltage.
Answer: I don't know of any application where the LiPo is charged and discharged at the same time. It might not be a good idea, due to the delicate charging cycle procedure that LiPos require.
Have you run a power consumption analysis with the given solar panel figures, to see if it is worth the effort? I suspect that the net power profit will be negative, due to the increased system weight and complexity.
Comment: We'll not be charging and discharging the batteries simultaneously. The quadcopter will we be doing has two batteries in it. One will be charging an one will be discharging and be used by the quadcopter.
Comment: Back to the question at hand, what parameters should I consider to make a safe charger for my lipo batteries?


What does the notation $8.9875517923(14)$ mean?

Question: The number $8.9875517923(14)$ appears in Coulomb's constant.  I have read that it has something to do with the uncertainty of the accuracy of the number but answers have been unclear.
Can somebody define the meaning of such notation?
Comment: Does this answer your question? [Uncertainty in parenthesis](https://physics.stackexchange.com/questions/158589/uncertainty-in-parenthesis) Also see https://physics.stackexchange.com/q/320744/123208
Comment: Someone please close due to being a duplicate / not doing sufficient prior research.
Answer: It's the uncertainty in the last two digits:
$$8.9875517923(14) = \color{blue}{8.987\,551\,79}\color{red}{23} \pm \color{blue}{0.000\,000\,00}\color{red}{14}. $$
Comment: Note that $a\pm b$ here really means a random value whose distribution has mean $a$ and standard deviation $b$ (or some multiple thereof depending on the confidence interval used), and is likely to be approximated as Gaussian.
Comment: Interesting notation. What is it called?
Comment: @J.G. Unfortunately, I've been taught that means "all our observed values are within the plus and the minus"; I wouldn't be surprised if there were papers out there that used the notation (wrong) like that.
Comment: @l0b0 That notation doesn't have a specific name. You can find guidance on how to report uncertainty, and the definition of that notation, in [this document](https://www.bipm.org/utils/common/documents/jcgm/JCGM_100_2008_E.pdf), section 7, and in particular section 7.2.2.
Answer: The number $8.9875517923(14)$ can also be expressed as $8.987\,551\,7923\pm0.000\,000\,0014$. The parentheses give you the precision on the last digits of the number. As you can see, this is a much more compact way of writing that expression than the usual $a\pm b$ format.
Answer: Since a key part of the answer is only stated in a comment (see comment from J.G. above), I will restate this here again.
If we write something like $\hat m = 1.234\, 5(67)$ we usually mean that
\begin{align}
\textrm{the }\bf{average \;value}\textrm{ of our measurement is }
\bar m &= 1.23\color{red}{4\, 5}\textrm{, and that}\\
\textrm{the }\bf{standard \;deviation}\textrm{ of the measured values is }
\hat\sigma_m &= 0.00\color{red}{6\,7}.
\end{align}
If we assume that the error of our measurement is a normally distributed random variable, this implies that we are
approx. 68% confident that the "true value" (=mean value of the population) lies within the interval $\bar m \pm \hat\sigma_m$, and
approx. 95% confident that the "true value" lies within the interval $\bar m \pm 2\hat\sigma_m$ -- the confidence statements are only valid if the sample size is "large enough" so that Student's $t_\nu$-distribution is approx. equal to the normal distribution.
According to ISO/IEC GUIDE 98-3:2008 the parentheses format is recommended, while using $\hat m = 1.234\, 5 \pm 0.006\,7$ should be avoided for historical reasons. However, the ISO standard also states that one should state explicitly what the values in the parentheses are representing. It also helps if you state explicitly which "type/component of uncertainty" you are referring to, e.g.
accuracy, repeatability, reproducibility etc.
Comment: Yep:  _ISO standard also states that one should state explicitly what the values in the parentheses are representing._
Answer: Go to the BIPM website which describes the notation and the language used. The key document is Guide to the Expression of Uncertainty in Measurement. https://www.bipm.org/en/publications/guides/
https://www.iso.org/sites/JCGM/GUM/JCGM100/C045315e-html/C045315e.html?csnumber=50461

Could also have a look at the NIST site, which clearly explains the notation as well.
https://physics.nist.gov/cgi-bin/cuu/Info/Constants/definitions.html


My flash drive bent and the board is broken. Can I recover my data?

Question: My Sandisk iXpand Flash Drive 16 GB 3.0 was connected my laptop when it was placed down and bent. The back popped off and the connectors are still intact from what I can tell, but the board seems to be broken? Am I able to recover my data?
Answer: That depends.
If any of the memory ICs are physically broken, then no, you can't recover your data.
But if the memory ICs are intact, then it might be possible to either repair the board, or transplant the memory ICs to another USB flash memroy module of the same make and model. You'd need to find an electronics technician with micro-surface-mount de-soldering and soldering equipment and skills. How much such a person would charge you, is between you and him/her.
Answer: Most likely you can recover your data.  The question is how much effort and/or cost will it incur.  Your post lacks description, so I am assuming the drive is no longer functioning.
I am also assuming you lack electronics skills, such as soldering and testing.  Try taking the USB drive to a cell phone repair shop, or a computer shop that specializes in electronics repair, as well as data recovery specialists.  You should be able to google these in your local area.  Assuming the flash memory is not damaged, which I would doubt, the data can be recovered.  This is definitely something you would want to shop around to various places, as their prices can be wildly different.
Answer: for whom it may concern;

I helped someone retrieve his files.
After dissection, the motherboard turned out to be broken by two, without anything noticeable on the outside.
but what turned out:
In the ixpand flash drive 3.0, there is a micro SD card hidden in the black plastic of the USB plug. I am not sure if you can get the micro SD card out without removing the metal shell. (maybe through the small holes on the side)

I had to use recovery software because the micro SD card was not readable. It turned out to be a damaged fat32 partition, and I was able to recover everything.
So the conclusion is: Do not use, the ixpand flash drive 3.0. the motherboard is way too thin, and the device too expensive. IOS on Fat32?
Regards Spookytronix
enter image description here
enter image description here
Answer: My iXpand Flash Drive were plugged in my laptop and when I went to bathroom, my 120 lbs German Shepherd ran over the charging cable and knocked down my laptop landed unto the floor with the Flash Drive first. Sure enough it's broken in 2 pieces. I tried to solder it but seems to be too small and I don't have the equipment. So I use thumb tack push pin to wiggle around the holder, I was able to pull out the Micro SD XC chip out and was able to retrieve a very important files from there, here's the link to the short video of how to remove the micro SD XC chip from inside the USB plug: https://youtu.be/y1QgROfoeRQ. I hope this short video helps if you ever encounter the same issues. Have a good one.
Comment: All of the information for the answer MUST be in the answer post. It should not be necessary to follow a link for the answer. You've spent all your text telling a nice story, but in order to get an answer, you need to follow the link. Please correct this by using the EDIT button.


How to embed metadata into a spatialite layer in QGIS?

Question: Example usage:
I have a spatialite layer which contain my fiber optic cable routes. In that layer there is a column named 'Cable types' with coded integer data: 1 for aerial cable, 2 for underground cable... Now I want to send the spatialite database to a colleague. Is there anyway to preserve the meaning (description) of cable types without having to send the QGIS style file for that layer?
Answer: I don't think you need to bother with style files. If all of the project data is in a Spatialite database all you should need to do is send your colleague the database together with your QGIS project file (*.qgs). When your colleague opens the *.qgs file in QGIS the project should load, showing exactly the view that you saved, with the styles, labelling and so on, intact. For this to work, before you save the project you need to ensure that the *.sqlite file and the *.qgs file are in the same directory and that you save the project using relative addressing (I think this is the default nowadays).
Proof of concept (140 MB):
http//:confound.me.uk/maps/su.zip
Nick.
Comment: Hi Nick, I think I will employ 2 of your techniques:
 1. 1st one in your previous answer - that to remind myself in case I forget after some time and the project file may be corrupted
 2. your second answer - for a quick and easy solution for my colleague.
Thank you for your answers - that helps alot.
Comment: 1st point is from the answer of Nathan W, 2nd point is from your (nhopton) answer. Sorry for my mistake!
Answer: A couple of options:

Create a non-spatial table called Cable Type in the spatailite database to store the interger and the value.
Do 1. but create a view that joins the two tables together so your colleague gets the cable type name rather then the integer.
Comment: Thanks for your answer but my colleague is not a specialist in GIS or database user, so I want it to be simplest possible for him and others to retrieve that data. In this case, I think it would be best if I can embed into the layer metadata (my colleague just have to select metadata tag in the layer properties). Do you know any way that is as simple as the one I thought of?
Answer: Why not just add an extra column, call UPDATE on the table for each integer value to set that column's value to some text matching the table, and then ship the result.


Choosing hexadecimal web colours

Question: How can I choose hexadecimal web colours (like #000000 and #fffff) to use in system and third party apps? (e.g. an image editor like GraphicConverter)
Comment: Things I've tried which haven't worked: I've checked the manual and Google of course, and I've tried looking through the default Apple color picker which I could swear used to let you choose this (I'm now on OS X 10.7).
Answer: Skala Color is another solution, that works very well in the latest versions of Mac OSX.

You can select HEX to appear in place of the RGB code, which appears in the above picture.
I used Hex Color Picker for a long time but finally got tired of it trying to be smarter than me. Frequently I would type a single character and it filled in all 6 values for that same number; other times I would get through 2 characters and Hex Color Picker would repeat that. For whatever reason, I had to constantly copy/paste values into the picker, because it kept thinking it knew what I wanted (it didn't).
Comment: I just installed this. It only works now with TextEdit and Mail. No longer works with Pages, Keynote or Numbers. You will need to use the answer from @user173032.
Answer: In newer versions of the stock OS X Colors utility: Select sliders from the toolbar and then "RGB Sliders" in the drop down - this will allow you to both read and enter RGB values hex:

Not sure in which version of OS X this was introduced, but it's relatively newish.
Answer: Use Hex Color Picker:

Comment: this tool is abandoned now
Comment: I'm finding it not as stable with newer versions of OS.
Comment: I did some more checking. It only works now with TextEdit and Mail. No longer works with Pages, Keynote or Numbers. You will need to use the answer from @user173032.

Choosing hexadecimal web colours


When are infinities okay?

Question: I'm a little confused about how to handle infinities in physics. On the one hand, I always here things like infinities are not physically tenable answers. GR can't answer anything about the origin of the universe because of singularities. Throw away the radial solution that gives an infinite potential when solving the Laplace equation in spherical coordinates. But then there are other times that the infinities are okay. For instance, it is usually okay to set the reference point for your potential at infinity. There are certain times in David Tong's quantum field theory lecture notes where he seems to almost to hand wave away infinities. So, philosophically, physically, and mathematically when are infinities okay, and when are they not okay?
Comment: In his work titled "The Infinite Book", the recently-deceased physicist John Barrow included a listing of where various thinkers, from Plato to Godel, stood on what he'd considered to be the three categories of infinities:  If I remember correctly, they were "mathematical", "physical", and "absolute", with "absolute" basically corresponding to theological (or, at least, philosophical) conceptions of infinity.  Some of the results were very surprising.
Answer: The difference in your examples is generally pretty clear cut -- when we get a number that is infinite, that's usually a bad sign. Things like $\frac{1}{0}$ indicate something probably went wrong somewhere in our theory and we're missing some important aspect of the physics.
But for things like potentials located at infinity, we are actually being much more subtle and saying "As the potential's position tends towards infinity."
In other words, it's usually only okay to use infinity why you are taking the limit of an expression as values approach infinity. But if you get singular values, it's a sign there is something missing in the approach you are using.
Answer: There is no problem, in principle, to mathematically deal with infinities. As a matter of fact there are formulations that allow arithmetical operations on infinitely large and infinitely small numbers (ordinal and cardinal arithmetics, surreal numbers). The condition is that you have to assume the existence of an infinite set.
In physics, the situation is a little bit different and is related, in my opinion, to the concept of measurability. A measure of infinite magnitude cannot be performed. Therefore any time you get, for a quantity that can be measured or has "length", an infinite value you are doing something unphysical.
On the other hand, supposing infinity without measuring it is perfectly ok. You can assume the universe is infinite in extension, as long as you are not able to measure its extension. Also to assume a punctual condition at infinity is not a problem, because is something related to a limit (as said in the other answer) and not to measure of an infinite quantity.
Comment: But if a calculation based on measurements yields an infinity to represent some physical circumstance, would that also be considered "unphysical" rather than just that the circumstance indeed may just be infinite, or at least functionally-so, relative to the measurements?
Answer: Let me answer the opposite of your question: When are infinities not okay?
Some (and perhaps even many) quantities cannot attain arbitrarily large values only because it contradicts our understanding of what they are. That would be a paradox that indicates that either the theory predicting such values or our understanding of what they mean is flawed. Examples include the infinite energy or density required in the singularity that (classical, i.e. QM-free) general relativity predicts for the big bang.
The difficulty that you are obviously grappling with is which instances of e.g. infinite energy is problematic in that sense. In a potential, having an infinite value in the limit of either infinite distance (think Hooke's law for a spring that is stretched to infinite extension) or at zero distance (think two masses occupying exactly the same location) is not a conceptual problem at all: These instances are usually unphysical limits anyways. This becomes obvious by considering just how one would produce such a situation. That is only possible by exceeding the proposition that lead to the mathematically idealized concept of this potential. For example, linearizing a spring (obtaining Hooke's law) is only an approximation that is valid for sufficiently small displacements. The idea that (fermionic and thermodynamically warm) masses can be placed anywhere breaks down at very small separations approaching zero.
Hence, if you have infinities that do not contradict any notion of having to describe a finite and actually existing (in reality, not just in some conceptual idealization) quantity, there is no problem at all. It is only because we have honed our human everyday intuition on things that tend to be very real (or, due to familiarity with the concept, feel that way to us) that we tend to think that just about "anything" worth talking about tends to be real and naturally finite.
Answer: I always found the following example intriguing.
Take the integral of $1/x$ between $x=1$ and $x=2$. Easy:
$$
\int_1^2 \frac{1}{x} dx = [ \ln x ]^2_1 = \ln 2
$$
Now let's do it another way, with $f(x) = 1/x$:
$$
\int_1^2 f(x) dx =
\int_0^2 f(x) dx
- \int_0^1 f(x) dx
\\
= [\ln x]^2_0 - [\ln x]_1^0
= \ln \frac{2}{0} - \ln \frac{1}{0}
$$
So now it goes wrong. This second way to do the integral might seem rather artificial, but this is just the sort of thing that goes on in the renormalisation problem in quantum field theory. When you build the theory up from the free fields one finds oneself formulating various infinite integrals, but the physics is all in the differences between the integrals. It is ok as long as we can argue that the infinity is just an artefact of the mathematical method and not really there if one looks at the calculation differently.
In field theory this is handled by various strategies which amount to tackling the illustration above by using something like
$$
\lim_{\nu \rightarrow 0^+} \left\{
\int_\nu^2 \frac{1}{x} dx
- \int_\nu^1 \frac{1}{x} dx \right\}
$$
The limit is well-defined and everything is ok.
I offered this example as a way to show why sometimes infinity is a problem but it can be worked around. In this example it amounted to a poor way of doing an integral, but sometimes this kind of way is the best we know.
Infinity is not ok when its presence in a calculation implies something we know to be untrue, such as that a body has infinite energy or that an electromagnetic field has infinite field strength. Infinity is ok when it is just a way of saying "so far away that to go any further would not make any difference", or it can be a way of saying when lines are parallel (as is done in optics). I know of no situation where spatial infinity is actually required. If the universe is spatially finite then no calculations go wrong in any way we can observe.

When are infinities okay?


How can I silence this noisy SMPS board?

Question: I have a receiver and it's  SMPS board is making a constant hissing sound which is noticable from a few steps away, so I'm sure it's not normal. The source is probably the ferrite transformer on it, but I'm not 100% sure because it's hard to tell. What components are the most likely to cause this problem (and why)? Because they all measure ok, but I only tested them with a multimeter and in circuit. Or what can I do with the transformer if that alone is responsible for the noise? The noise is there whether or not the SMPS is loaded, there is only a little difference.
The schematic is here (page 112):
https://www.manualslib.com/manual/950375/Denon-Avr-3311ci.html?page=112#manual
Should I just change all electrolytic caps and hope it will go away? If not, then what?
Comment: If there are ceramic capacitors, they can do this due to piezoelectric effect.
Answer: The noise comes either from the ceramic caps (due to piezoelectricity) or magnetics (due to magnetostriction). If it's the caps, you could change them for flexible termination ones which are designed to prevent vibrations from propagating to the board. If it's the transformer, you're screwed.
The document linked in the question does not mention how much current this power supply can output, but a 5V 50W power supply of good quality costs about €20, which means replacing the whole board may be a reasonable option.