How can I invite people to my chat room?

Question: I have created the chat room for magento. I would like to invite top users of magento tag. How can I do this?
Comment: Manually, one by one, on the room "info" page.
Comment: possible duplicate: [How to send Request to join room to particular user on stack overflow?](http://meta.stackexchange.com/q/98617/165097)
Comment: @Thursagen that possible duplicate appears to be irrelevant; it also states that it is a possible duplicate of another question which was closed nine years ago, but the link to what it duplicates is broken.
Answer: If those users are not already involved in "chat", then there is (by design) no direct way to do this unless you are a moderator, as we do not want users bugged unless they want to be there. If they are on chat, you can request them individually, but please don't get carried away there. Where there is context you could also add a comment in the Q&A site "we could discuss this more in chat [link]"; however, again: do not go and spam everyone with a link - that would be... unappreciated.
We are also considering beefing up our relationship of rooms to tags, which would allow us to do a very targeted display of on-topic rooms, so the users could see the room naturally in the Q&A site.
Answer: To invite a user to a room, the particular user must be in chat. Once the person is in chat, you can click on their avatar & select: "Invite this person to a room.."

Alternatively, you can drop a comment to the user with a link to the room requesting the user to join the room


How is the numbering in phenylpropenes?

Question: Just wondering why the name of this compound is 3-phenylpropene? I understand the concept of phenyl groups but I'm confused where the 3 came from, because if it is referring to the double bond in propene, then shouldn't it be numbered 2?
Comment: 3 is referring to phenyl. The double bond is at 1. In propene it can't be otherwise.
Answer: Obviously, there are three carbons in propene to which a phenyl group might be attached. Let's have a look and name the compounds:

1 with the phenyl group at C-2 of propene is 2-phenylpropene, also known as $\alpha$-methylstyrene.
2 with the phenyl group at C-1 of propene is 1-phenylpropene. To be exact, the compound drawn is (E)-1-phenylpropene. E is for entgegen, that is on opposite sides of the double bond.
3 is 3-phenylpropene, also known as allylbenzene.
Answer: According to the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book), the ring or the chain can be the senior parent structure. For the preferred IUPAC name, the ring is selected as the senior parent structure. In general nomenclature, however, the context may favour the ring or the chain.
For the name that is given in the question, the propene chain is taken as the senior parent structure. Accordingly, the benzene ring is considered to be a substituent (i.e. a phenyl group).
The propene chain is numbered from one end to the other, the direction being chosen so as to give the lower locants to the double bond. (Only if a choice remains, low locants are given to prefixes that indicate substituent groups.) Thus, the numbering of the propene chain leads to prop-1-ene:

Accordingly, in this case, the substituent is assigned the locant '3':

Since this substituent is a phenyl group, the complete systematic name is 3-phenylprop-1-ene.

However, note that this is not the preferred IUPAC name. As mentioned above, the ring is selected as the senior parent structure for the preferred name. Therefore, the preferred name in this case is (prop-2-en-1-yl)benzene.
Comment: Note that the standalone name "prop-1-ene" for propene (PIN) does not follow P-184.108.40.206 (d).
Answer: When a simple substituent like, $\ce{-OH}$, $\ce{-NO2}$ is attached to the benzene ring then benzene is considered as the parent chain. But when a complex substituent like a long ($>6$) carbon chain, or a group with double bond/triple bond or another substituent is attached to the benzene ring, then benzene is considered the substituent, and named as phenyl group.
Here, the propene part is the main chain. Double bond gets more priority than phenyl substituent, so numbering is started from that end. Phenyl group gets number 3. So the more correct name should be 3-phenyl-1-propene. However, writing 3-phenylpropene does not cause any ambiguity (as the numbering is started from the double bond end)

How is the numbering in phenylpropenes?


One-way function and factoring

Question: I am confused about the hardness of the one-way function behind cryptography -- if someone could factor the large number produced back into two primes quickly then the one-way function would be broken?
     TIA
Comment: Welcome to Crypto Stack Exchange. There is no *the one way function*. There is a definition of the term *one way function*, and there are several candidates for such a function, some of them being related to factoring and others not. What do you actually want to know?
Answer: There is an interesting distinction to be made here:
On one hand, we have the ideal one-way function, which one can easily calculate in one direction, but not invert at all (other than by brute force).
Hash functions like MD5, SHA-1, SHA-2 etc. are trying to approximate this (with more or less success).
On the other hand, we have trap-door one-way functions - these are functions which are easy to calculate, but which can be inverted easily only with help of some hidden information. You normally want a whole family of such functions for use in cryptography (otherwise you call it a backdoor, if you are the only one knowing it).
In the case of RSA, a product $n = p · q$ of two large primes, together with a public exponent $e$, forms a public key, which gives you an one-way function by modular exponentiation. The inverse operation needs (as far as we know) another (private) exponent $d$, which is not easily derivable from the public one and the modulus $n$, but can be easily calculated from the two prime factors $p$ and $q$ (and $e$). The private exponent (or the two primes) can thus be seen as the trap door for the one-way function.
Thus, here the hardness of the factoring problem is necessary for the one-way property of RSA.
Other asymmetric encryption schemes use other trap-door one-way functions, which are not related to the factoring problem (or sometimes one-way functions without a trapdoor).
Answer: Well, there are lots of one-way functions in cryptography.  For most of them, it is not known how being able to factor is of any use  in inverting them.  For example, even if you have black box that can instantly factor any number, we still don't know how to practically find a preimage for SHA-512 (where, by preimage, I mean that, given the value of a hash, can you find a string that hashes to that value).
On the other hand, there are a few one-way functions for which being able to factor allows you to find preimages.  The most common one (and the one you're probably thinking of) is RSA.  In raw RSA, you're given the values $N$ and $e$ (and these two values are jointly known as the 'RSA public key'); the one way function is $RSA_{N,e}(M) = (M^e \bmod N)$.
Now, in RSA, $N$ is a large composite number; if you don't know the factorization of $N$, it's hard to invert; that is, given a random value $X$, it is usually hard to find an $M$ such that $RSA_{N,e}(M) = X$.  However, it turns out that if you do know the factorization of $N$, it's easy.
Comment: To clarify, my goal is to know what part of the RSA formula  to factor (and any other cryptosystem formula that requires factoring a large number).  Essentially I need to know the various formula components and how to get them into variables so I can try out some ideas about factoring in general.
Comment: P.S. Is there a way for newbies like me to pay for questions to be answered via donations or something (since I only have one badge)?
Comment: IcebergHotspot: For RSA, what you need to factor is the modulus $N$, which is part of the public key.  If you're asking how, given a public key, you find $N$, that rather depends on how the public key is encoded; the most common is http://www.rsa.com/rsalabs/node.asp?id=2125

One-way function and factoring


How to manage a system release containing multiple packages?

Question: What we need to do is be able to find a consistent solution to create a single package (lets call it Master package) that contains multiple packages, check that these packages are compatible with each other and version them.
The packages that we need to ship together are many (15+) and based on different technologies where many of them depend on each other, so consolidate them in a single repo is not a possible solution.
We need to take in account the eventual limitations of the tool we are using for CI/CD/Artifacts that is Azure Devops and Yaml pipelines.
At the moment we are producing a Universal Package for each component to be released, and we are versioning them using gitflow and semver (x.y.z version).
The main problem now is trying to find a way to put all these pieces together in a simple way and manage the compatibility of these pieces.
The distribution of these packages is out of the scope of this question, we only need to create the package containing everything, the installation/distribution process is already in place.
What we are doing now
At the moment the process is this.
For each component we are creating a Universal Package with an x.y.z version.
When we want to create a Master package (also a Universal Package) we have this pipeline on Azure Devops, which parameters are all the versions of each component, that by default download the latest version of a package (using '*' wildcard, so it doesn't support versions containing dashes, only x.y.z). Using latest as default parameter make the pipeline easy to run for everyone.
The problem with this approach is that:

Azure Devops pipelines parameters don't offer a way to display a dropdown list of available version for each package, so having to open Azure Artifacts feed every time we need to run a build, to choose a certain version is not a viable solution

We have no way to check if components are compatible with each other, having to hope that all the latest versions can work together

A way to handle the first problem that we implemented, is to create a release branch on the repo that contains the pipeline definition and use fixed version as default parameters of the pipeline, but if we need to bump a version we still need to make a new commit and requires still a lot of manual handling.
Some solution that I thought
A way to version the Master package could be using CalVer YYYY.MM.Build, given that is a standalone system.
To solve the problem of compatibility we could write a manifest file for each component and define inside of it a constraint on the version that requires from other components.
Example:
If component C depends on B and B depends on A
In the manifest file of C we say that B must be 1.*, and in the manifest of B we say that A must be 2.0.0
But in this solution, we may need to make commit and a new release of C or B only to bump the accepted versions.
To solve the problem of user experience we could create an external portal, in this way we could create some kind of dropdown list to make the version selection easier (is there already a solution on the market to solve this problem?). In this solution we could also integrate a check on the manifest file, so we can see beforehand if a Master package is consistent within itself.
Another solution that I thought, to solve the user experience problem, could be create a separate repo, where we write a manifest file in which we define all the packages and their version to pack together, and in some way pass it to the pipeline. In this way we resolve the problem of having to check foreach run the azure artifacts feed, but we still need to do a lot of manual handling, and it doesn't offer a solution to check the compatibility of packages (beside implementing it in the pipeline itself).
Answer: I am afraid that there is not a simple way to meet your demands.
The packages based on different languages/technologies may support different package managers (such as NuGet, npm, Maven, Python, etc..).
And these package managers normally cannot contain/combine each other by default.

For your case, as a workaround, you can try the following steps to see if it can meet your demands:

Build and pack each type of the packages using the related CLI corresponding to each package manager. When packing each package, you can specify the package version.
Put all the generated package files into a folder.
Publish all the packages as a Universal Package from above folder. You can set a version to the Universal Package.
Comment: All the packages are already packaged in a Universal package. And then all these Universal Packages are gathered in a Master package (also Universal). The problem is not really about compatibility of technology, but compatibility of features.
Comment: @Stepness, Ther is not such feature for Azure DevOps Artifacts. If your projects really need this feature, I recommend you try to report a feature request on [Developer Community](https://developercommunity.visualstudio.com/AzureDevOps/suggest).
That will make it more convenient for the product teams to receive and understand your ideas. And your feedback also could be helpful for improving the Azure DevOps products.
Comment: @Stepness, Is there any update from you?


What happened to the Na+ ion?

Question:
I was in the middle of my acid and base schools questions when I came to a stop at this question. I have posted the answer to tell you what I am confused about. My teacher did not explain this very well, and my friends are not sure either. In the picture I posted, the teacher cancels out the Na from the chemical compound NaC2H2O2. I'm not sure why he did this, and then he proceeded to solve the problem via a separate equation using a hydrolysis reaction with H2O and C2H3O2-. Could someone explain to me why this happens, and would this happen with other acid and bases?
Comment: This is what happens to Na+: **nothing**. That's why it is not there in the equations.
Comment: Na+ does not participate in the reaction, i.e. it is a spectator ion. So, you can ignore it for the acid base part of calculation.
Comment: Now that I think about it, does this have something to do with weak acid and bases?
Answer: The $\ce{Na+}$ ion is a spectator ion in this case. It doesn't participate in the chemical reaction. It is found unchanged on both the reagent and product sides (red top-right and green bottom-right reaction formulas), so it can be canceled out to get the net reaction (red left). From there, he did the usual acid-base calculation to get a formula for $\ce{Kb}$. If you actually know $\ce{Kb}$, you can then find $x$, the $\ce{OH-}$ concentration, and from there, the $\ce{pH}$. Or, if you know the $\ce{pH}$ for this reactant concentration, then you can calculate $\ce{Kb}$.
The reason $\ce{Na+}$ doesn't participate, is as Aditya wrote: it is the conjugate acid of a strong base ($\ce{NaOH}$), so it is a weak acid (weak enough to be ignored). It can't abstract a proton from water, and has no protons of its own to donate. At most, it can combine with $\ce{OH-}$ to form $\ce{NaOH}$, but $\ce{NaOH}$ is very soluble, so it will break back apart right away. In solution, $\ce{NaOH}$ is just separate $\ce{Na+}$ and $\ce{OH-}$ ions.
Answer: Sodium ion is the weak conjugate acid of strong base i.e. NaOH. So the show which one ot of the two ions furnished undergoes hydrolysis to a greater extent the Na+(which does not react) is crossed and hydrolysis of stronger base C2H3O2- to produce OH- ions is shown.

What happened to the Na+ ion?


Word meaning a certain phrase?

Question: In Estonian, there is a word that roughly translates to "I want to sleep more, but I can't, so I am laying in bed". Is there a similar word or shortened phrase that means the same thing in English?
Comment: Do you mean a single word or a phrase? NB It should  be _I am lying in bed_.
Comment: The title needs editing. I rejected an edit because I thought the only appropriate tag was  'single word request'. 'Word/short phrase describing when you lie awake in bed trying unsuccessfully to get to sleep'.
Comment: What is this word out of curiosity?
Answer: A few thoughts: words like sleepless and  wakefulness, both describe an inability to sleep by one who desires sleep, though neither describes or requires being in bed at the time.
However, one who desires to sleep but is unable whilst laying in bed is often said to be, tossing and turning.

toss and turn: to move about and turn over in bed because one is unable to sleep (Websters)
Answer: Well, "restless" can be used to describe someone who can't sleep so "I lay restless in bed but longing for sleep" could work or something similar to that such as "I lay in bed but the sleep I seek is out of reach". I hope this was helpful!
Answer: Insomnia describes the first part: "I want to sleep more, but I can't" but not the second: "so I'm laying in bed."  It can also name it as a geberal patrern, say over several weeks or as a medical condition.

Word meaning a certain phrase?


What does a squiggly line above a note mean?

Question:
What does the horizontal lightning bolt over the C sharp mean?
Also, what do the double grace notes (the two semiquavers joined by a beam) mean?
Comment: For pieces such as this one, Chopin's Waltz in A minor, you can often find recordings and follow along with the sheet music in order to hear how the performer plays such ornamentation. There is such a recording included here: https://en.wikipedia.org/wiki/Waltz_in_A_minor_(Chopin)
Comment: See also https://music.stackexchange.com/questions/33573/squiggly-line-above-note?rq=1
Comment: Including the piece and edition that the picture is from within the question is usually helpful (event though Neal was able to pull it out).
Comment: If I'm reading things correctly, in this piece the upper mordent should be realized starting on C# as per Tim's answer (https://music.stackexchange.com/a/66166/2639); the question linked to as a potential duplicate indicates the older (Baroque) realization which would start on the auxiliary note.  If this is the case I do not believe that these are duplicates (in that the correct/accepted answer on the linked question is not the correct answer for this one).
Answer: It's an upper or inverted mordent. Play C#, the next note up in the key/scale, then C# again, all squashed into when the C# would be played normally.
The 'double grace note' is pretty well the same thing, just written out as played. I guess the tune's in A major, so why the F is sharpened, - don't know. Maybe it's in A minor, and modulated, rather than change the key sig., the composer used accidentals.
Comment: Yeah, it almost looks like there is no key signature, but it moved to A major via A minor.
Comment: That Chopin sure did like accidentals. I always wondered why he even bothered with key signatures.


Why is the restoring force directly proportional to extension?

Question: When deforming any spring the deforming force is always greater than the restoring force until equilibrium is reached. So, if a constant deforming force caused an extension in any spring the restoring force will increase until it becomes equal to the restoring force and equilibrium is reached. However, I do not understand how the restoring force even increases with extension. I imagine it is related to the fact that the more we deform a spring the more potential energy it has, but I do not know how exactly this affects the restoring force. An explanation which includes the behaviour of the bonds and molecules in any spring during the deformation is appreciated.
Comment: I don't see how this is a duplicate of the linked question.
Comment: Possible duplicate of [Why pendulum does not follow SHM for larger angular displacement?](http://physics.stackexchange.com/questions/206755/why-pendulum-does-not-follow-shm-for-larger-angular-displacement)
Answer: You can think of two atoms in a solid joined together via a bond.
The graph of potential (pe)  energy against separation of the atoms is shown below as is a graph of the force between atoms and their separation.
The equilibrium separation $r_o$ is when the potential energy is a minimum and the force between the atoms is zero.  In reality since quantum harmonic oscillators have non-zero amplitude even in ground state due to a finite zero point energy the equilibrium is a bit beyond $r_0$ due to the asymmetry of the potential, but we can ignore that effect here.

Now it so happens that for a lot of bonds the graph of force against separation is a straight line about the equilibrium position as shown in mauve in the lower graph.  This is equivalent to saying that a parabola fits quite well to the shape of the upper plot near equilibrium.
So in this region you can think of the atoms being connected by springs which obey Hooke's law with the spring unextended when the separation of the atoms is $r_o$.
Trying to increase the separation (stretching the solid) stretches the bond and results in an attractive force between the atoms which is proportional to the increase in the separation from their equilibrium position.
This attractive force summed over all the bonds will then become equal and opposite to the external force which caused the bonds to stretch.
A similar thing happens when the solid is compressed but now there is a force of repulsion which might be thought of as the negative electron shells between adjacent atoms repelling one another.
In terms of energy the external force stretching a solid does work extending the bond and that energy is stored as potential energy within the bond.
When the external force is removed the atoms move towards the minimum of potential energy, their equilibrium separation.
Answer: I will give you a more mathematical answer here. You can obtain Hooke's law for linear springs from the potential energy of a spring. The change in potential energy of the spring is;
$$
\Delta V=V_f-V_i
$$
Therefore;
$$
dV=\frac12k(x+dx)^2-\frac12kx^2=kxdx+\frac12 kdx^2
$$
where $x$ is the initial position of the end of the spring. Since differential value of $x$ is infinitesimal;
$$
dV=kxdx
$$
Due to conservation of mechanical energy;
$$
dE=dKE+dV=0
$$
Therefore;
$$
dKE=-kxdx=\vec Fd\vec x
$$
This leaves out;
$$
F=-kx
$$
Thus, the restoring force is directly proportional to the displacement of the spring since its potential energy does indeed increase.


What is 0 dB in digital audio?

Question: Everyone here should know that the reason decibels (dB) are unitless is because it is a ratio:

So, I somewhat understand why decibels are "negative" in Audacity an other digital audio workstations. However, what I don't get is, what are the decibels being based on? Like what would 0 dB be?
Answer: In The Old Days...
Prior to the invention of electronic calculators, multiplying and dividing long numbers was painful. Yet that was something engineers (including audio ones) had to do often.
Logarithms were invented in the 17th century to simplify calculations.
We have these fundamental rules of logarithms:

log(X * Y) = log(X) + log(Y)

And

log(X / Y) = log(X) - log(Y)

While rather innocent looking, they conceal great power: The ability to replace complex multiplication and division calculations with simple addition and subtraction ones.
There is a catch though - you needed to know the log value of numbers. But as the benefit outweighed the pain, soon books with log charts appeared showing the log value of numbers (my dad had one!).
So to multiply two long numbers, you find in the chart the log of both first, add them, and then search for the inverse log of your addition result.
Logarithmic rulers soon appeared, allowing quicker calculations:

Then Came Audio
With advances in electronics and audio recording technology it soon became clear that our perception of loudness is exponential, rather than linear.
That is, when reproduced via a speaker, the loudness change from 1V to 2V is not perceived as equal as the loudness change from 2V to 3V. The doubling of voltage is much closer to our loudness perception - 1V to 2V is roughly like 2V to 4V.
Log functions are exponential.
Bell Labs
Now guess what? The engineers at Bell Laboratories decided to make the log an integral part of audio. They gathered what you may have gathered by now:

Logs make calculations easier.
Logs lend themselves better to the exponential nature of our hearing.

So they simply devised a unit called Bell (in honour of Graham Bell), which is nothing but a ratio between two measurements, logged:

Bell = log(m1 / m2)

Soon though, the realisation came that for audio applications the Bells always had an extra significant digit to the right of the decimal point. So they introduced another unit called decibel, which, after working out the maths of the original definition of the bell, resulted in:

dB = 10 * log(m1 / m2)

Power vs Voltage
The decibel definition was devised for power measurements (watts), so we can look at it as a ratio between two power measurements:

dB = 10 * log(p1 / p2)

Once we throw into the equation voltages (where P = V^2 / R) and simplify it, the equation becomes:

dB = 20 * log(v1 / v2)

Which is most often written:

dB = 20log(v1 / v2)

Practically speaking, all dB equations are 20log, barring those dealing with power.
From Two Measurements to a Measurements and a Reference
So far, dBs allow us to express the ratio between two measurements. But what if we measured the level of our signal and ask:
"How loud is this in dBs?"
The answer will be:
"Well, how loud compared to what?"
So the idea was to choose a reference, so we can express the level of something in dBs by measuring it and comparing it to a standard reference. In equation form:

dB = 20log(m / r)

dB systems
So now we can develop various systems of dBs, each uses a different reference.

The dBm system uses 1mW as a reference.
The dBu system uses 0.775V as a reference (a number that was common in early electronic circuits).
The dBV system uses 1V as a reference (a much easier number to deal with).

dBFS
When digital audio emerged, it needed its own dB system, which brought the need to choose a reference. But there was a problem:
Digital audio can be 8 bits (sample values from 0 to 255) or 16 bit (0..65535) or 24 bit (0..16777216).
It seems like the common thing in all these bit depths is the zero, but we can't use it as a reference as we'll get:

dBFS = 20log(m / 0)

While this is sufficient to rule out 0 as a reference, there is another fact to consider: We know that during ADC a higher bit depth extends the dynamic range downwards not upwards. In other words, the loudest analog voltage an ADC supports always translates to the highest value the bits can represent. If the analog limit is 1V, in an 8 bit system it will get a sample value of 255, but in a 16 bit system it will get 65535.
This make the choice rather obvious - the reference for dBFS should be the highest sample value of the system bit depth. So:

dBFS = 20log(sample value / highest possible sample value)

Now in logs, if the numerator is smaller that the denominator, you always get a negative result; if the two are equal, you get 0. So in the case of 16 bits:

0dB = 20log(65535 / 65535)

and

-6dB = 20log(32768 / 65535).

Since the sample value can never exceed the highest sample value, dBFS values are always equal to, or smaller than 0.
dBVU and dBr
All of this is sound, but there's a bit more.
As users, we don't really care about the dB level of the signal within the system, we care for the dB level compared to the standard operating level of the system (above which you may clip).
So audio meters don't show the dBu, dBV or dBFS level of the signal (some do, but as an extra). Instead they show 0dB as the standard operating level of the system. In analog this is known as 0dBVU (dB Volumatric Unit), and for digital as 0dBr (dB reference). For pro analog equipment 0dBVU is calibrated to +4dBu; for semi-pro  equipment it is -10dBV. So regardless of the device itself, and the dB system used, dBVU always tells me how much below or above the standard operating level of the system the signal is.
DAWs are using 32 bit float internally, so the integer range of 0..65535 is aligned to the decimal range 0..1.0; While 65535 is 0dBFS, 1.0 is 0dBr. But floating point systems can go above 1.0, in fact, much higher than 1.0. Yet as at some point you'll have to go back to integers, the 0dB you see is aligned with 0dBFS.
Comment: It should be noted that the _FS_ in _dBFS_ stands for "full scale", i.e. dBFS = "decibels relative to full scale". Also, you need some way to represent negative values, so 16-bit audio actually ranges from -32768 to +32767, and dBFS is calculated by first dividing by 32768 (or 32767), not 65535.
Comment: "0dB = 20log(65535 / 65535)"  Actually, 16-bit audio is signed, so it goes from -32768 to +32767, so max amplitude is 32768.
Comment: Really good answer Izhaki and I'm looking into the dB and listener tests to see where I may have got my schooling (many years ago) mistaken. +1
Comment: >"Since the sample value can never exceed the highest sample value, dBFS values are always equal to, or smaller than 0."
Not true. They can exceed 0 when audio is represented in floating-point format. And it is even quite common when decoding some lossy audio files to floating-point (which is required to avoid introducing quantization noise again).
Comment: @CharlesWood That's a good question. In theory you shouldn't see something like dBVU on a DAW - being a more analog thing. If you do, then most likely 0dBVU is calibrated to 0dBr (ie 0dBFS if you bounce to integer). But, and it's a big BUT, dBVU meters on a DAW mimic the scale and ballistics of those in the analog domain, and too many engineers are terribly accustomed to these because they are everywhere on analog consoles. Being average, rather than peak meters, these reveal the approximate loudness of the sounds as they near your 0VU. Hope it makes sense.
Comment: To be honest, the comment I've left you made me doubt the accuracy of my own statement - that the choice of logs for dBs had something to do with our loudness perception. Although I'm pretty sure the exponential nature of our loudness perception was known at the time of the gramophone, I'm not sure it is something Bell engineers accounted for directly when they devised the Bell and decibel. But I haven't made it up - pretty sure I've read it somewhere, so I'm also checking the accuracy of my answer.
Comment: Well I doubted mine so I've amended it to give a little more historical credibility. Interesting subject though.
Comment: @chirlu, all your points are valid; as for the second one - sticking to positive numbers makes the explanation easier, it also saves the need to discuss amplitude vs magnitude.
Comment: Since 0dBFS integer is mapped to 1.0 in floating point, and in floating point you can represent numbers bigger than 1.0, you can say that "In floating point, you can exceed the number representing 0dBFS in integers". But by definition, 0dBFS corresponds to the highest possible sample value, which in floating point is 3.40282*e^38 (in Binary 0 11111110 11111111111111111111111); This value is 771dB above 1.0 (0dBFS in integer, or 0dBr in your DAW). But you still can't go above that max value.
Comment: It might help to point out that dB = 10 * log(p1 / p2) → 10 * log(v1^2/v2^2) → 2 * 10 * log(v1/v2)
Comment: @endolith  I noticed that, but then I also noticed that it was already mentioned in chirlu's comment.
Comment: This is a fantastic explanation, thank you so much! But can we get one more bit of info? If 0 dBVU is +4dBu or -10dBV in analogue equipment, what's 0dBVU in my DAW? Or is there no such thing, and the meters in the DAW are actually showing 0dBFS?
Comment: Regarding multiplying by 10 to change Bells to decibels, this is normal, nothing special about dB. For example, a deciliter is 1/10 of a liter. So 1.5 liters is 15 deciliters. You get the number of deciliters (15 in this example) by multiplying by ten. Same for dB.
Comment: @Matt You are right. 0.5 metres is 5 decimetres; thus 0.5 Bells is 5 decibels. I'll have to dig deep to find that equation from the original Bell Labs paper - I'm pretty sure in it you'll find that if you divide the power by 10 you get the x10 in decibel equation; but I'll have to dig MUCH deeper to find out if it was that or just a simple application of a deci- prefix. Anyhow, I've deleted the related paragraph and thank you so much for pointing it out.
Answer:
What is 0 dB in digital audio?

0dB does actually represent the largest signal that a digital system can produce. Once a signal is in the digital domain it takes on a life of its own and 0dB remains full-scale. If you took a digital audio file (maybe from a CD or wav file) and loaded it onto another machine, the new machine would see the same binary numbers as the original machine so 0dB represents the biggest value numerically in the "digital world".
But what if you have different quantization levels i.e. 24bit instead of 16bit (CD audio)? Well, the biggest unsigned peak number on 16 bits is 65,536 and on 24 bits it is 16,777,216 BUT, for each 0dB is taken as their maximum value. The 24 bit "system" will have greater depth of clarity because it is representing an analogue signal with over 16 million digital levels whereas the 16 bit system is only representing an analogue signal with a bit over 65,000 digital levels.

what are the decibels being based on?

The decibel is one-tenth of 1 bel and years ago in Bell laboratories (clue in the name) they conducted listener tests to see how the average listener perceived sound levels of different amplitudes with loudness variations being introduced by longer cable lengths. The following quote is taken from Wikipedia

The decibel originates from methods used to quantify reductions in
  audio levels in telephone circuits. These losses were originally
  measured in units of Miles of Standard Cable (MSC), where 1 MSC
  corresponded to the loss of power over a 1 mile (approximately 1.6 km)
  length of standard telephone cable at a frequency of 5000 radians per
  second (795.8 Hz), and roughly matched the smallest attenuation
  detectable to the average listener. Standard telephone cable was
  defined as "a cable having uniformly distributed resistance of 88 ohms
  per loop mile and uniformly distributed shunt capacitance of .054
  microfarad per mile" (approximately 19 gauge).[4] The transmission
  unit (TU) was devised by engineers of the Bell Telephone Laboratories
  in the 1920s to replace the MSC. 1 TU was defined as ten times the
  base-10 logarithm of the ratio of measured power to a reference power
  level.[5] The definitions were conveniently chosen such that 1 TU
  approximately equaled 1 MSC (specifically, 1.056 TU = 1 MSC).[6] In
  1928, the Bell system renamed the TU the decibel.[7] Along with the
  decibel, the Bell System defined the bel, the base-10 logarithm of the
  power ratio, in honor of their founder and telecommunications pioneer
  Alexander Graham Bell.[8] The bel is seldom used, as the decibel was
  the proposed working unit.[9]

+1dB means it got louder by about 10%. -1dB means it got quieter by about 10%.
From other experiments it was determined that the human ear works logarithmically because each time a doubling of perceived sound level occured, the associated instrumentation showed that the power of the signal increased by ten times. The upshot of this is that a 10W amplifier/speaker is twice as loud as a 1W amp/spkr and that a 100W amp/spkr is four times louder than a 1W amp/spkr and twice as loud as the 10W rig.
So in engineering, 10dB now represents a ten-fold increase in the power of a signal.
In electronics, engineers use the term 0dBm and this refers to the power of 1mW. Other commonly used terms are dbuV where the u means micro and the V is voltage.
Comment: "0dB does actually represent the largest signal that a digital system can produce."  No, "0 dBFS" does.  "0 dB" is a relative gain.  "0 dBFS" is an absolute level.
Comment: The 1929 paper from Bell Labs devising the decibel mentions nothing of the mentioned listener test. Nor am I aware that the 10dB as perceived doubling was researched until much later. The Fletcher-Munson curves, for instance, were only published in 1937. It'll be great to see a reference to the listening test mentioned.
Comment: @Izhaki - in case my schooling was wrong or I've become wrong over the years I've replaced the section you focussed on with a wiki quote. Bell labs did do average listener tests though.
Comment: The question asked was what does 0 dB reference to. I just copied and pasted the words the guy used asking the question. I think it's clear enough.
Answer: Since the dB is a ratio as you say, "0 dB" just means "no change". In the context of digital sampling, I'd consider 'full scale' to be the reference point -- i.e. 255 in an 8-bit system -- making anything less a negative dB value. But unless it's specified, (as in dBa, dBm etc) it's just speculation and open to interpretation.
There may be a DWS standard or consensus, but that's not my world so I can't say.
Answer: It is the amount of change.  0dB is full signal, negative dBs are a reduction in signal (down to -infinity which is fully off) and +dB are when a signal has a gain applied.  0dB is also sometimes called Unity.  This is consistent across digital mixing and analog mixing where anything below 0dB is reductive (the source signal is reduced) and anything above 0dB (when the board or software supports it) applies a gain to the signal via a pre-amp (in analog processing) or increasing the amplitude by the selected amount(in digital).
When metering, 0dB is often the either the maximum or ideal capability of the hardware or digital signal space you are working with.  In the case of setting it to the optimum strength, there will be some headroom above the ideal signal level before hitting clipping.  You should check documentation for the particular board or system you are using for the specific implementation.
Answer: Going to next level…
Sound pressure level (SPL), in dB, uses the threshold of human hearing as the reference level (denominator): A fluctuating pressure of 2x10^-5 Pascals.  I'd have to dig for the citation, but that reference was determined by averaging the response of healthy individuals (ears) back in the 1930's(???). So, 0 dB is the threshold of human hearing.
Sound power level is referenced to 10^-12 watts – the power that would produce 0 dB SPL when distributed over a sphere with a surface area of 1 m (r = 0.283 m)
Comment: Yes, so basically, 0dB is the 'relative' reference point. If the dB unit has a suffix, like SPL or A, it is known as 'absolute' because the suffix indicates the reference point. **Note**: With SPL, you have to also indicate at what **distance from the source**, the level is measured.
Comment: @MarcW Yes, you need to specify distance if the source is a point source that gets quieter as you move away from it.  If it's an ambient level in a room where it's the same everywhere, then you don't need to specify distance.  The important thing to understand is that the sound pressure is measured at a point in space, so you need to specify "what point?"  The SPL in the horn of a trumpet is different from the SPL 1 mile away.
Answer: Lots of lengthy answers here when all that is needed is a simple answer.
The 0dB that you refer to is actually 0dBFS which stands for dB with reference to "Full Scale".
0dBFS is the highest peak digital sample level. Anything below this is normal signal, therefore shown as a negative number.
-20dBFS is 20dB Below Full Scale.
Answer: It depends.
With a logarithmic scale like the decibel (or bel; 1B = 10dB), you usually need a reference point, and this reference point cannot be zero (otherwise the math involves division or multiplication by zero which doesn't get you anywhere). This reference point depends on what you're measuring. In audio, that's usually one of the following:
Voltage (potential): 0dBV = 1V, regardless of impedance. 0dBu = .7746V (the voltage inherent in a 600-ohm conductor dissipating one milliwatt of power). Home-quality audio equipment typically has a peak signal power handling of -10dBV (.316V), which itself is often marked as "0dB", while professional audio is typically calibrated to a much more powerful +4dBu (1.228V)
Wattage (power): 0dBm = 1mW. This is typically of value in wireless transmitters/receivers, to judge signal amplitude.
Sound Pressure: 0dBSPL = 20uPA (= .00002N/m2). This reference point was based on one series of tests to determine the threshold of silence in human hearing. Other studies say humans with healthy auditory systems may be able to differentiate sounds as faint as -10dB. These curves are calibrated for different kinds of sound environments; OSHA has two common "weightings", A and C. A is based on the average spectrum of industrial noise, while C is based on the spectrum common in amplified audio. Exposure limits are officially defined for and measured using A-weighting.
Answer: It's really simple. It's the inverse ratio. So, 0 is no less. -3dB is the ratio for 3 dB less than 0.
Decibels are used to describe a ratio, rather than a definite amplitude. To figure out negative decibels, you do the same thing you'd do with positive decibels, except with a negative number.
To create a 3dB increase, you'd multiply the sound's power by 10^(3/10), or 1.9952623149688796013524553967395 (approximately twice the original amplitude).
To create -3dB change, you'd multiply the sound's power by 10^(-3/10), or 0.50118723362727228500155418688495 (which is approximately 1/2 of the original sound).
So, in short, it's just the inverse. 3dB is about twice the amplitude, and -3dB is about half of the amplitude.
Comment: I'm confused as to why this was downvoted. It answers the question, and it's correct. Granted, it may not answer my question completely, but it does address something that would be too long to fit in a comment.
Comment: @Cole Johnson: I didn't vote, but your question was: "what are the decibels being based on?" This is not addressed at all. Additionally, the post's structure is unclear and repetitive.
Comment: for one thing, you've mixed up amplitude and power.  power is proportional to amplitude squared, so +6 dB increases amplitude by 2× and power by 4×.

What is 0 dB in digital audio?


How does your company measure end to end experiences for their products?

Question: At IBM we have a system that measures an offering's UX based on specific criteria. Does your company produce similar reports before a major release?
Comment: It would be helpful if you can expand on your question so that it is a little bit more than a YES or NO answer. And because I don't know if people are willing to share their own internal reports (even the structure if not the data), it would be good if you can highlight the exact problem you are trying to solve or answer you want to gather. IBM seems to have a pretty comprehensive design language and design system, so you would expect there to be a pretty solid way of measuring UX (although this is of course an assumption).
Comment: Yes, here at IBM we have a "design council" that measures ux based on certain quality dimensions. a few of them are discoverability, UX, IA, and visual design. This council then gives an offering a grade and how it can be improved. Im wondering if other companies do something similar? and how do they measure their products ux?
Comment: Are these dimension more qualitative or are they quantitative and benchmarked to internal/external standards? IA and visual design seem to be more difficult to assess compared to discoverability, and UX is pretty much the sum of everything I guess?
Answer: Yes, but I suspect this is something that varies from organisation to organisation, and from product to product (hopefully not).
Generally if any UX processes are involved, hopefully there will be an assessment of the usability (if not the entire experience) of the product in the form of either task completion analysis (for a new product) or benchmark against existing baselines.
Alternatively, if the product is externally reviewed, then there will be some metrics or reports from the external source that can be gathered and analysed (e.g. traffic or review ratings).
UPDATE (based on additional comments):
Rather than measuring and benchmarking against an absolute value, one approach that you might be interested in is a method I developed for one of the companies that I worked at.
The process involves defining different types of experience that the product or service is aiming for (e.g. Usable, Useful, Engaging, Delightful) and then comparing that to the processes used to achieve the outcome (e.g. Research, Design, Prototype, Test).
So for a product that is designed to just be usable, the minimum process required might be to do some usability testing. For a product that needs to be delightful, more processes would be required.
Therefore, each product gets a check against the experience that it is aiming for and the processes used to achieve the outcome. The benchmark would be to provide the minimum amount of process required to achieve a particular outcome, and obviously the more you can do the better.


Is there a software that rezises similar images to overlap

Question: I was working on a graph theory presentation and I have a series of operations on the graphs that I am demonstrating, thus I have very small changes in the graphs, such as 1 node being deleted or various colors changing but the overall structure is exactly the same. The only problem is the images are all different sizes and I don't have the time to go through every image and resize it. Is there a software that can do this?
Example:
Comment: There are two problems. 1. The background canvas is not the same size, and 2. The graphics themselves are not the same size either.  It's going to be very hard to automate this, and to be honest ,by the time you have worked out a solution it might be easier to do it manually in software such as Photoshop or GIMP. Obviously I don't know your skill level in image editing so this may be impractical for you. Perhaps consider paying someone to do it for you?
Comment: I believe one route would be to trim out all the whitespace and then batch resize them to all be the same width. I'm on mobile, but it seems to me like they may have varying amounts of whitespace on all sides right now. You could do it in like Photoshop or even ImageMagick
Comment: I noticed that the last example image just randomly has bigger balls and text in comparison to the other two. You can't really perfectly align them unless it's in a vector format. Then you could resize all of the ballsies and text around their center point.... but even then it would make more sense to export them out all at the same size from the source.
Answer: Adobe Photoshop has a feature called "auto-align layers" that can , as you might guess, automatically align layers.
Below I used this method:

I added your three example images to deliberately mismatched size canvases.
I imported these three images as layers in a new document.
I locked the "reference" layer.
Hit "Edit" > "Auto-Align Layers..."
I accepted the default settings, yo umight have even better results by adjusting them.

Below I varied the opacity of the top two layers, and you can see the alignment is really quite good. This could all of course be saved as an action, and run on a batch of files.
Comment: @theyve - I hardly remembered it myself haha, must be ten years since I used it. Solving problems here is a good way to brush up on seldom used functionality :)
Comment: great tip! I didn't know that.


What is the concept of soul in islam

Question: Does soul exist inside our body, does soul has any gender, how can I find that I have a soul , what is the concept of soul in Islam.
Comment: humans have very limited knowledge about the soul, many things are still secret
Answer: I'm sorry for my bad english.
Rooh is a large concept, like a container including several subtil organs.
We learn in the Quran that before coming in this mortal world, Allah grouped all human beings in the world of Roohs. (Quran, 7/172) He asked a question. We answered.
From this we understand :
Rooh is a name of an organization containing faculties like speaking without even without words, or hearing even without ears. From these subtil organs :

the Rooh itself, an special organ within this organisation. It's role is to receive the light from God. Each human being is receiving divine light. The Quran says : Know that God stands between man and his heart, and you shall all be gathered in His presence. (8/24) This verse is not about mu'min only. It concerns each human being.
Nafs :The faculty to desire ; we call it pejoratively Nafs or Ego. Some scholars explain thath Rooh is called Rooh when it is outside the body and Nafs when it's inside. But this explanation seems to be incorrect because lot of Hadiths say that death is the time where Rooh is extracting from the Body. It seems more appropriate to distinguish between the two.
'Aql : the faculty to analyse
Qalb : the heart ; it's role is to reflect the light coming from the Rooh, and enlightning all other faculties, that's why his importance is crucial. The Messenger of Allah was asking again and again "O Allah, keep my heart firm to your obedience, dont deviate it"
Memory : the faculty to remind and to forget
...

All these faculties constitute the Rooh as a container, and Rooh as the soul is also in this subtil organization.
For example : a person starts speaking but stops abruptly. His faculty of speaking even without words is so fast that it spoke in himself without activating his voice.
Sorry for my bad english.
Answer: According to my best knowledge
1. The soul exists inside your brain or in whole body but you can't find it it is intangible like it belongs to other dimension which humans can't reach.
2. It is ambiguous that soul have gender but there is two categories good soul and bad souls in Islam which are immortals but they must have to leave your body to become immortal.
3. The concept is of soul is that you your body just physical representation in this temporary world your soul will get rewarded or punished according to your virtues
NOTE:remember i am not scholar this is just community contribution so might still need to refer to scholar.
Answer: And they ask you [O Muhammad] concerning the rooh [the spirit]. Say: 'The rooh: it is one of the things, the knowledge of which is only with my Lord. And of knowledge, you (mankind) have been given only a little.' [Quran, Surah al-Israa 17:85]"
Comment: This can hardly be regarded as an answer for the question: Evidences don't speak for themselves. See [answer].

What is the concept of soul in islam


How to programatically sign into a hotspot-type network?

Question: I often connect to a network, that is open, but requires a key-pass authentication before used in a webpage. Is it possible to automate the authentication with a script?
Answer: What a fun problem.
While I'm sure ændrük's answer would probably work, I'm slightly adverse to letting something dependant on desktop software manage the network availability.
I would suggest you play around with Python's Mechanize library. You can install it from the repositories via:
sudo apt-get install python-mechanize

Then get scripting. You need to start by finding out the stucture of the page you're submitting to. You need to find where you form comes and what fields need to be entered to submit. Once you know that, it's really as simple as just writing a quick little form parser and submitter. Mechanize does all the heavy lifting. Here's a quick example adapted from their docs on forms:
import sys
from mechanize import ParseResponse, urlopen, urljoin

# replace this with the actual login page
# you'll need to do some research
uri = "http://theloginpage.com/"

response = urlopen(uri)
forms = ParseResponse(response, backwards_compat=False)
form = forms[0]
print form
form["username"] = "your username"
form["username"] = "password"

# form.click() returns a mechanize.Request object
# (see HTMLForm.click.__doc__ if you want to use only the forms support, and
# not the rest of mechanize)
print urlopen(form.click()).read()

Depending on how their system works, this might be enough. You might have to tie in some cookie jarring to keep a session alive while they turn the connection on, but technically speaking, there's no argument why they should require that.
Then you just need to tie this into the networking system so it gets called. Loading it from /etc/network/if-up.d should work but I suggest you prefix your code with a check to make sure you're really on the hotspot that your login works for.
Comment: Wonderful, I didn't know about mechanize. I'm excited to try it out.
Answer: Depending on the type of captive portal in place, you might be able to authenticate via a POST request sent using Wget (use Tamper Data to learn what data needs to be sent) or by using an iMacros script in Firefox.
You can add a script to /etc/network/if-up.d to make it run every time a network connection is established. Have the script verify what network you're on with iwconfig before doing anything, and be sure to start commands using sudo -u yourusername so you don't run your web browser as root.


Who decides Venezuela annual budget nowadays when the presidency is being disputed since January 2019?

Question: Since January 2019 the presidency of Venezuela is disputed with 57 countries recognizing Guaidó as president and the rest of the countries either supporting Maduro, the national assembly or being neutral. In this context, who decides in Venezuela the annual budget, import taxes, and the usual tasks of the executive power? Or are even these tasks splitted somehow in the country now between the 2 factions?
Answer: International recognition is of secondary importance here. What really matters in a power struggle like this is the military.  While there are some in the military that would support Guaidó, the main part remain loyal to Maduro.
This allows Maduro to be the de facto president.  He has been able to introduce price and currency controls, for example.
Normally it would be the assembly to propose a budget, but much of the basic function of government is not operating at the moment. It seems that Maduro's government is able to raise money (for example by selling oil) and isn't depending on the national assembly pass a budget, since the national assembly has been ruled unconstitutional.  This is what I mean by a non-functioning government.
There is not much point looking at the written constitution or the opinions of world leaders.  This is now a government that exists as a result of support from the army, not as a result of a mandate from the masses.
Comment: The point is diplomatic pressure.  Since there is not great desire to tighten sanctions further (which would hurt the people more than the leader) and there is certainly no suggestion of a military action, diplomatic pressure is all that countries like the USA have left.
Comment: What's the point of other countries to receive ambassadors of Guaido if in practice they can do nothing? Are those countries having zero relations with Venezuela?


invoke the action

Question: Can its possible to invoke a action automatically in Struts2. means when run the application, action can be execute without submit or clicking any event.
Answer: If you want to use your action directly without submitting or clicking any event you can use it directly by typing it in your adress bar.
eg;) http://ip:port/proj-name/package-namespace/ActionName
It also works if you use it with  tag. the action will be invoked if user clicks the tag.

Hope this is what you were looking for

invoke the action


How can I do Facebook video calls?

Question: My question is how I can do video calls on Facebook, I'm new to Linux, recently installed Ubuntu 11.10. I really like the OS but I can not make video calls on Facebook and this is terrible. Please anyone who can help in this.
Comment: Aren't Facebook video calls available only on Windows?.
Comment: "This is terrible" Let's be positive.
Comment: you will have to try to use skybe coz video call is not supported yet in facebook and i had the same issue
Answer: Unfortunately, Facebook does not support video calling on Ubuntu yet, as explained on the Facebook Help Center. They haven't developed their plugin yet.
However, video calling (popularly known as Hangouts) works on Google+, for example (after installing a plugin). If you are curious in upcoming technologies, you also can take a look at WebRTC.
Comment: what if we install windows mozilla firefox on ubuntu through wine?? am not sure what I am saying but it does makes sense. I think..
Answer: 14.04+
Full support now (January 2015). You no longer need to install a special plugin or anything. You only need a supported browser which is firefox or chrome/chromium etc.
Opera is mentioned but I would be surprised if anything other than the Opera developer version for linux was supported because linux opera is severely outdated but who knows, all I know is that it works fine and tested less than 10 minutes ago on firefox-34.0 with nothing to install.
To start a video call:

Open a chat window with a friend
Click  in the top right corner

If your friend isn't currently able to receive a video call the will be grayed out, and you'll see a message that says "[Name] is currently unavailable for video calling."
Answer: Facebook does not currently support Linux. If you were to go to someone's profile, you would only see 'message' and settings. We can only wait for Facebook to accept Linux.
As Agmenor mentioned, video calls are available for Google+ and also for Skype
Answer: You cannot make Facebook video call on Ubuntu for now.

Video calling is not currently available on Linux.

Source: Facebook Help

How can I do Facebook video calls?


Game token in Solidity ETH

Question: I'm designing a game that will run NFT.
In the last few days I've been studying a lot about Solidity and I managed to understand a lot (I even followed the CryptoZombie classes).
But I have a big doubt about the prize, the token that will be used as a reward.
My questions are beginners, I'm sorry, but I couldn't find anything on the internet that would help me, if you have any content you can share I'll be happy.
My questions:
1st For me to create a rewards token, for example, the SLP that axie has, will I create this contract in ERC720 or 721?
2nd How do I create the token like the SLP? And how do I give my players this prize token? Looking at Axie's systematics for example, at some point I use the "claim" option on their website, I believe that the SLP is saved in the database and after the action it starts to exist in the ETH portfolio, right?
3rd I want to put items to be sold that will use the token as currency, I believe this action is "burn" because we want to burn the currency in exchange for items, how is this done? Do you have an example to point me to?
4th Another question I would need to have different contracts for my SLP example currency, for the characters that will be NFT, for the Items and etc...? Is this analyzing the long term and giving the possibility of growth?
5º Contracts are immutable, my question would be, for example, I want in the future to have the marketplace option in the game, however, do I need to create these types of contracts now? Or can I create a contract in the future called marketplace and thus create the rules and etc of it?
I know these are starter questions but I couldn't find answers, thank you community for your help.
Answer: I don't have answer to all of your questions but can provide for the 5th one. You don't need to have such a contract now but when you do you would have redeployed the solution on-chain again.

Game token in Solidity ETH


How to determine whether difference in RMSE is meaningful

Question: I often run into the situation where I have several regression models, each of which gives a RMSECV, and I need to choose which one is "best". Of course, I can choose the one with the minimum RMSECV, but sometimes several models have very similar values. What is the correct way to determine whether a difference in RMSECV is meaningful? Or conversely, how do I tell when two regression models have RMSECVs that are close enough that they should be considered statistically equivalent?
Comment: I would argue that's a subject matter decision and not a statistical decision.  Also, with the same data and associated results, one model might have a slightly higher RMSE but is either much cheaper to implement than a model with more expensively obtained predictors.  And there are many times political considerations which might likely change over time.  So, in short, there are no correct answers but probably reasonable answers for which you might find a consensus.
Comment: https://www.rdocumentation.org/packages/forecast/versions/8.1/topics/dm.test
Answer: If you are using a regression method that is not complex and not stochastic, you should have always a fixed performance value for each attempt. Therefore, the higher -> the winner. However, if you are using for example ANNs, then you always have a random component in your results. If this is your case, you might want to know if the difference in the results come from this random component or if indeed you have actually found a better (or worse) predictor.
To make sure about this, you can use repeated cross validation a good amount of times for each predictor. After that, you just need to compare using hypothesis tests if the differences are significant enough or not.


How to configure D7 so files get uploaded to a different server

Question: In Drupal 7, the default path for uploading is set in the File system options in the Public file system path.  Is it possible to specify a different server in this path?  I have a Drupal 7 web site we are developing that is going to have about 20k files and I'd like to put them on a different server than the web server.  If not possible to specify a different server than are there any user contributed modules that can handle this?
Comment: Have you completed this Task.
Comment: Any module regarding this?
Answer: I do something very similar.  If you're running infrastructure that is capable of this configuration, I recommend serving up a share on your file server (Linux or Windows Server) and just mount it in Drupal's public file path, wherever the public directory is for that particular field.
For example, take the following Samba configuration (found in /etc/samba/smb.conf if you run a Linux-based file server).  This comes at the very end of the file after all other configuration options:
[data]
    comment = Data directory
    browseable = yes
    writable = yes
    valid users = "@DOMAIN\Domain Admins"
    path = /data
    create mask = 0664
    force create mode = 0664

The valid users syntax there says "allows this group of users" to access this share.  In this case we're using PAM to hook up our file server to Active Directory, and this particular group is made available once you hook the two up.
On your web server, whatever is hosting your Drupal site, navigate to the public files directory.  Say the particular field you need to make the files available for is public://field_with_20k_files/.  You'd run a similar mount command like so:
sudo mount -t cifs -o user=domainadministrator,uid=domainadministrator,gid=apache //fileserver/data /path/to/field_with_20k_files

I have the gid set to whatever process is running the web server so it has access to that directory.  Most likely you'll want to ensure that the web service has read and write access to the web server is actually capable of uploading files.
Comment: All the answers are good but since we have control of the infrastructure, this answer is the easiest and most straightforward from a Drupal standpoint to implement since we don't have to install any new modules. We're in a Windows environment but thanks for the incredibly detailed steps provided!
Comment: In that case then you can basically just skip the Samba configuration and just run the mount command directly using a username and password that has the appropriate Windows permissions setup.  Let me know if you have any questions.
Comment: I'm trying to do this, but I'm having issues.  My service center was able to mount the Windows server, but we didn't know where to go from there.
I tried to use /mount_file_path as the public file directory, but I get an error that it doesn't exist and could not be created.
Answer: Also an excellent option would be the Storage API. Here is a quote about it (from the module's project page):

... is a low-level framework for managed file storage and serving. Module and all the core functions will remain agnostic of other modules in order to provide this low-level functionality. Submodules are welcome to allow Storage API to interact with other contributed modules, but there shall never be a dependencies[] statement in the storage.info file unless it is necessary for the low-level function of this module.
It has the following features:

Pluggable architecture - it can be extended to work with any storage service.
Redundancy - it can be configured to store your files in multiple services and instantaneously change which one is serving. This means your site will not be brought down by a service having problems.
Access control API - can be used for e-commerce.
Deduplication - when files that are identical are stored in the same container, only one instance will be created. This saves bandwidth and storage.
File and image field integration - enable the "core bridge" sub-module.
Audit module - compares a manifest of files with what is recorded in the database to ensure that the record is accurate.
Answer: Two modules that may also help in this area are CDN (used by many big sites, including Economist.com) and Amazon S3 (specifically for using Amazon S3 instead of the local file system).


How many wireless devices can connect at once to a TP-Link TL-WA901ND?

Question: I'm trying to find out what the max number of wireless devices is, but don't see it on their website or in the User Guide. Or probably I don't know what term I'm looking for there.
Answer: My TP-Link TL-WR843ND is seemingly limited to 15 concurrent usert (MAC addresses). After that it simply refuses anothe connection
Comment: Yes, mine TL-WR841N is also around 15-20.
Answer: My TD-W8961ND seems to be limited to 8 wireless connections. Note that my DHCP settings have an IP pool count of 100, that is not the bottleneck on my router.
Answer: The WiFi chip in an access point has to hold the MAC address of each connected device. In budget chips there is only space for 8 MAC addresses. If you can find out what chip is in a device, you can find out the maximum number of MAC addresses. For example, an RTL8051 can handle only 8 MAC addresses.
Comment: Source for a chip only being able to handle 8 devices?
Answer: None of the router manufactures mention exact number of device that can connect the wireless router. But there may be limited number of device can connect and its almost depends on the network bandwidth. Think this might be the reason manufacturers not specify number of device which can connect and its also depends on many factors.

@Rory WiFi connection and speed is mainly depends on bandwidth availability. On a typical decent router the number of DHCP address will be limited by the allowance made by the subnet mask, which is usually a /24 allowance, so 255.255.255.0. This automatically limits the number of DHCP clients to 255, but one IP address is always taken by the router so 254 is the max you will get on most routers.
In case if the DHCP ip's are allotted to printers or systems in LAN then you will face reduction in 254 count.
I checked that website you gave and noticed that it has 4 Guest WiFi SSIDs it means each can set up to 16 at an average it means your modem can handle 64 client request with out any issues theoretically.
Note : Just call the customer care of that product and get the benchmark values what they got for their product in testing lab.
Comment: Any idea what a normal number supported is? 15, 20, 50, 100?


when do smart contract wallets need to sign transaction by themselves?

Question: Do smart contract wallets ever store priv/pub keys or something ? Of course, It would be then seen on the blockchain if it did, but I am asking this because somewhere, I've read that sometimes smart contract wallets SIGN the transaction. Not sure what that means but explanation and a little bit example would be great.
Comment: Well, obviously, when a smart-contract account executes a non-constant (neither `pure` nor `view`) function on some other contract, it implicitly signs the transaction. But there is no need to store a private key anywhere for this purpose.
Answer:
sometimes smart contract wallets SIGN the transaction.

I'm not sure what you read, but what you said is incorrect or just worded in a confusing way. I'll try to unpack a summary to help sort things out.
There are two kinds of addresses in Ethereum: Contracts, and Externally Owned Accounts (EOA).
Contracts:

Have code
No one knows the signing (private) key. It exists, but since no one knows it this is moot.
Cannot initiate a transaction
Must execute code when a transaction is received

EOA

Does not have code
Someone knows the singing key
Can initiate a transaction by signing and sending

The term "Smart Contract Wallets" is a misnomer. A wallet is a signing device that knows the signing key for one or more EOAs. Those senders can possibly send a transaction to a contract but it's an indirect link. No one is signing for the contract.
msg.sender
A contract can interact with another contract. In that context, the "sender" will be the contract that sent the message. The only way that can happen is if someone sends an instruction to the contract, from their EOA, and the contract does what the code tells it to do.
Hope it helps.


iMessages between two devices are received by the device sending the message

Question: When my husband sends me an iMessage from his iPhone 5c it sends it to him. If I send him a message from my iPhone 5c it send it to me. This has just happened since we updated yesterday.
Comment: Are you sure the iCloud/iMessage email account are set correctly on the contacts ?
Answer: You are using the same Apple ID or the same cellphone number to receive iMessages on both iPhones' iMessage clients. Doing so will lead to you receiving your own sent message, like I am:

Here's a quick fix:

Open Settings>Messages.

Tap "Send & Receive".

Tap "Add another Email".
Type a diiferent email ID. It will now show a "Verifying..." status. Open that e-mail inbox and confirm verification.
Answer: This is most probably happening because you are either using the same account on both devices or you have the same phone numbers or email addresses registered on each account.


Launch timeout has expired, giving up wake lock! Activity idle timeout for HistoryRecord. Is this something to worry about?

Question: In my application I use AsyncTask in oncreate. Sometimes I get "Launch timeout has expired, giving up wake lock! Activity idle timeout for HistoryRecord" in the logs. Can this cause any issue, or we can just ignore this ?
Comment: How can we be expected to help you without seeing any error logs or code? We can't simply divine what is wrong with your code
Comment: My question is: is this ok to get this in the logs... I mean is it something that can be ignored?
The logs say -
03-16 15:17:24.233 W/ActivityManager( 1628): Launch timeout has expired, giving up wake lock!
03-16 15:17:24.273 W/ActivityManager( 1628): Activity idle timeout for HistoryRecord{40632cf8
Answer: Finally Found the answer.
This can be ignored.
This means that your main thread is continually running, pumping message through its message queue without ever going idle.  If that is what you want, there is nothing to fix.  This is why the log message is a warning, not an error.
Source : Google Groups
Comment: Nopes, it's not just warning but in case you are running this application in lower device it may cause to struggle with your device and unfortunately restart device subsequently.


Understanding the initialization of the Needleman-Wunsch algorithm

Question: I would like to ask why when we initialize 0 as the starting point, there are 3 gray boxes that are not used as shown (highlighted in the red box) in the pic?

 Are these boxes to show that they are gaps or just to align them properly?
Comment: Welcome to the site Heeh. You can [edit] your question to add things to the question like more information. Could you clarify what do you mean by "how dynamic programming plays a part"? Do you want to know what is dynamic programming? Or perhaps why it is needed for this algorithm?
Comment: I would also like to ask how dynamic programming plays a part in filling up the rows and columns in the matrix. (I'm new to bioinformatics)
Comment: Hi I would like to know both about dynamic programming and why it is needed for this algorithm. I searched the meaning of dynamic programming but I do not understand the meaning behind recursive.
Answer: The first column is added in order to be able to align the sequences. They might be gaps if the alignment ends up beginning in different positions than the first. Without the first empty row and column it wouldn't be possible to have gaps at the beginning of the alignment
The dynamic programming is useful because you need first to calculate the score for each position, and then once you have the score, you can calculate the optimum path. So you solve your problem by first calculating what would happen if (there was a gap, there was a mismatch...) and then you find the optimum alignment.
Comment: Dynamic programming isn't strictly needed, it's just convenient to use recursion to handle the rows (depending on the implementation, you can also save memory by not storing the full matrix then).


Voice over Ethernet without WiFi in airplane mode

Question: Is it possible to make calls with an active Ethernet connection only (with an Ethernet adapter) without a mobile & WiFi connection? Effectively Ethernet-Calling, like WiFi-calling.
Comment: Theoretically yes, as long as the Wifi calling is not limited to a certain Wifi (e.g. special Wifi from mobile network provider). For Wifi calling you just need a network connection. However Ethernet via USB adapters is not very common on Android therefore I don't think that somebody will test this when developing the system firmware. Therefore it might work or not depending if you are lucky or not.
Answer: It does work using services like Google Voice (free phone number), Hushed, or iPlum on my 2 phones (Moto G4, G7) Android 7-10.
Plugable makes a Micro-USB ethernet adapter ($14) that works with Android devices or a plain USB ethernet adapter that can be used with USB-C devices with an OTG converter ($5) to make many Android tablets and phones work. They maintain a list of tested devices on their site. Device Compatability Chart: AX88772 Compatibility List USB2-OTGE100 : USB2-OTGE100
The issue is you must use a third-party app like those mentioned, not the phone app that comes with the phone. That means you must have a second number associated with the app to call. If you don't care about letting Google listen to your calls, Google Voice is free. True ethernet calling may be coming in Android 11. WiFi calling is available on some phones now and this may allow true ethernet calling from the native phone app—it depends on your carrier. I am testing this option using RedPocket soon.
Comment: Do you have any source for the claim that Ethernet calling may be coming with Android 11?


Difference between Speed and Velocity

Question: What is the difference between Speed, Velocity and Acceleration? Could any one describe it pictorially?. I am more over confused even after investigating many times. I am unable to relate myself practically.
Answer: Speed has no direction while velocity does. For example, if I say that I'm running at 10 mph, I have given you my speed. If I say that I'm running 10 mph north, then I have given you my velocity. Acceleration is the rate of change in velocity. Imagine this: I am in my car and you look at me before I even press the gas pedal. You close your eyes then open them (imagine the blinking only took a second). Now, I'm going 10 mph north. You blink again. Now I'm going 20 mph north. Every second my velocity increased 10 mph north. This means my acceleration is 10 mph every second or 10 mi/h/s.
Comment: for eg: Sometimes we describe the speed of a vehicle to be 60Km/hr to our friends when we mention about the trip details ..Does it really mean the speed?..Isn't it the acceleration or velocity?
Comment: @ddpd yes it means speed
Comment: for it to be velociy, there would need to be a direction, so 60 Km/hr north or even 60 Km/hr that way
Comment: For it to be acceleration the car needs to keep going faster, or it needs to change direction as shown in the picture
Answer: Speed is a scalar quantity which means that it is described by only magnitude.
Velocity is a vector quantity which means that it is described by magnitude and direction.
And acceleration is the rate of change of velocity with respect to time.
i. e. Acceleration= $(V_2-V_1)$ / Time required to travel this distance

Difference between Speed and Velocity


What is the relationship between potential energy and inertia?

Question: It seems to me that the two are very similar! Potential energy seems to either explain, or partially explain, directly or indirectly, the law of inertia.
I already know that bodies do not move because of inertia, they move due to forces acting on them that change state of rest or constant motion, and i also know that inertia is the resistance of object to move.
Answer: Potential energy depends upon the presence of a force, and the actual configuration of objects. So a rock at the top of a cliff has potential energy $U=mgh$, due to $m$, the mass of the rock, $g$, the acceleration due to gravity, and $h$, the height of the cliff.
Inertia, as described by Newton's First Law of Motion, is that property of matter which, in the absence of external forces, keeps a body in motion travelling in a straight line at unchanging speed, which gives it a kinetic energy of $T=mv^2/2$, where $m$ is the mass, and $v$ is the velocity of the mass, with respect to a stationary observer. Of course, if the body was not already moving it would not start moving; this is also a part of the Law of Inertia.
So the Law of Inertia is not directly connected to potential energy. You obtain potential energy by arranging things to resist a force; a roller coaster is a typical class room example, where the car is initially at rest at the top of the system, having used work to haul it up their: it has a certain amount of potential energy from its position and gravity -- just like the rock on the cliff -- and when it is kicked into motion, by application of a mechanical force, it rolls downhill, converting the potential energy of its position into kinetic energy of its motion.
Answer: Potential energy and inertia are related via Einstein's famous equation $E = mc^2$.
A compressed spring has more potential energy and therefore more inertial mass compared to an uncompressed one, making it more difficult to accelerate because of its increased inertia.
Comment: By the looks of it, Einstein's equation seems to be a modification of the equation of kinetic energy, or is it the other way around?
Comment: Not quite. That equation is the special case of $v=0\Rightarrow\gamma=1$ for the more general equation for the total energy, rest+kinetic, of a moving particle of mass m: $E = \gamma mc^2$.


Implement github.com file seamless file navigation

Question: I just noticed a recent change when browsing github repositorys. When you select a file or folder, the new file slides in and pushed the old file out. This is easy enough to do with jquery, but what's really different is that the URL itself actually changes so that bookmarks still work. I've been struggling to create this for a book navigating site I'm working on but haven't been able to update the url without a full page refresh. Any ideas on how github does this?
Comment: https://github.com/blog/760-the-tree-slider
Answer: It's using the new HTML5 API history.pushState/history.replaceState for doing this (so it only works in modern browsers).
See https://developer.mozilla.org/en/DOM/Manipulating_the_browser_history#Adding_and_modifying_history_entries for more details.
If you want a solution for all browsers, then you have to stick to modifying the fragment (the bit after the #)
Comment: Modifying the fragment is the way to go for now :)
Answer: I haven't looked at the underlying code, but I believe it is a combination of the new HTML5 spec of web history and location (well, location is old, but it's an updated spec).

Mozilla docs
W3C history spec
W3C location spec

The W3C specs are very verbose (after all, they are specs), so that can be hard to read. I think this other answer on Stack Overflow is in the right direction.
You have to keep in mind that this is part of the HTML5 specs, so not every browser will be able to handle this functionality. We are building this type of navigation out on a project at work, and if the browser doesn't support this feature, it's just a regular page refresh.


What do I need to know before Ruby?

Question: I'm looking to learn Ruby, I have some basic programming experience but would still class myself as a rookie to be honest. Which languages do I need to be aware and familiar with before  beginning to learn Ruby?
Comment: What makes you think there are any?
Comment: English? (Seriously, though, none. Just dive in.)
Comment: Pick an answer if you reckon you've got what you need :)
Answer: None. Ruby works well without prior knowledge/experience.
Ruby draws inspiration from Smalltalk, Lisp and Perl, but there's no reason you'd need to know them before learning ruby (as a matter of fact it's probably easier to learn than the former two and learning Perl will probably teach you some habits you'll need to unlearn to write idiomatic ruby).
Answer: None, my advice:  just pick a good pick about Ruby that is written for programming beginners and learn it.
There is no real need to learn another language before ruby if your goal is to program in ruby.
Of course you might learn some C (or Assembler) to get a better feeling about how stuff actually works behind the scenes. But thats not really essential.
You could also learn a Language that is more like Ruby. But you will learn how to program Ruby-style best if you just start with it.
Answer: You can get straight into programming with ruby.
In terms of generic things to know I suggest you read a book, so you get one consistent message explaining all the basics.
This is a great book to teach you programming in general and it teaches you using ruby.
http://pragprog.com/titles/ltp2/learn-to-program
Also have a go with
http://tryruby.org  - Quick ruby tutorial in your browser
Finally check out the hackety-hack project it's designed to help people learn to program, although version 1 is only just out.
http://hackety-hack.com/

What do I need to know before Ruby?


Content is not visible After publishing

Question: Changes published to Sitecore 10.0.1 are visible in cd server but they are not reflected on site. Only after an app pool is recycled, changes reflect. How to make changes visible without app pool recycling.
Comment: This can be caching issue, are you clearing cache on publish:end event?
Comment: There isn't really enough information here to form an answer without first asking a series of questions. Posts like this are generally not accepted on the Sitecore Stack Exchange but are best taken to either Sitecore Slack or the Sitecore Community Forums.
Comment: So, its making it to the web database but not showing on the site. It is most likely caching but based on how your application is coded, it could be multiple things
Comment: Assuming that you are talking about static content and given that recycling the app pool starts showing the content on site, it should be Sitecore caching the content. You should check if it is a specific rendering on the page which is being cached and then check its cache settings. Also, publish:end and publish:end:remote shall be patched to clear the cache.
Comment: Did you find the answer to this issue ? we are also facing the same issue in Sitecore 10.0.1.
Answer: So, its making it to the web database but not showing on the site. It is most likely caching but based on how your application is coded, it could be multiple things:
Output caching - If that is turned on for your layouts or renderings, they may not be getting cleared properly. It is supposed to when you publish but you may want to check your pipelines to see if that is still in place
CDN - Do you have a CDN? Is it being cached there?
Enterprise cloud security - Do you have something like cloudflare or any other enterprise security system? These can cache pages as well.
Given it clears after app pool recycle, it can also be in the code where server memory cache is being used. Check that too.
Also, are there no-cache headers on these pages? If not, add them. This will prevent browsers from caching the pages, at the least.
Answer: For this kind of Issue, would recommend to uncheck caching on related component(Rendering Item) where facing issue while testing. After the change no additional step would required. For reference attached screenshot.

Only change/update Sitecore item, save and publish.
Try to render page, if still facing caching issue just to hard refresh (CTRL_Shift+R or CTRL+F5).

Content is not visible After publishing


Web Services using J2ME and Java Version 1.4

Question: We are trying to program an MFP (Multi-function-printer) to communicate to our backend using Web Services. We are sending large images so using MTOM is important. Since we are dealing with a very constrained environment I would rather not use Axis. Does anyone know of another smaller WS library that will work with JDK1.4, or would it be better to 'Roll our own'?
Answer: AXIS comes with J2ME implementation of JSR 172,
http://svn.apache.org/repos/asf/webservices/axis/trunk/contrib/j2me/
But I doubt it supports MTOM.


Find my Bitcoin please

Question: I purchased $100 worth of bitcoin when it was first introduced. Maybe back in 07/08/09.   I never done anything with it  I have no idea even what computer system I was using at that time, or even what old email addresses I used. Is there any hope for recovery.  Is there a way to use an IP address and using any keywords.  It might have even been on an old AOL account.  Any one have any thoughts other then I'm a loser.  Thanks
Comment: It can't be 07 or 08. There is a possibility it was in 2009 , but do you remember where you purchased the Bitcoin? Most exchanges popped up after 2010. Honestly, I can't even name one place/exchange that sold bitcoin in 2009.
Answer: What wallet did you use at the time? Probably the standard wallet so you would have to look for a wallet.dat file.
So grab every old harddrive and computer you can find and use a custom search program like search everything (voidtools . com) to search for wallet.dat file.
If you found it: Make a backup copy first (or two or three..)
Then on a different computer, download bitcoin core and sync the blockchain. After sync has finished, replace the wallet.dat file bitcoin-core created automatically with the old one you've found.
After that core will rescan the blockchain and after that you are good to go.
Good Luck!
(Since you might be a multi millionaire in case you find that coins I would appreciate a tip ^^ 1HcgC2jpqXZhkia7sxriE6S435qqR8zKqq)

Find my Bitcoin please


Do I keep my free Games with Gold if I cancel my Xbox Live Gold membership?

Question: I know that I lose access to my free games if I cancel my PSN+ membership, but does it work the same way for Xbox Live Gold? Can I redownload and play the game for free on my Xbox 360 even if I cancel my XBL Gold, or do the games lock without a current subscription? MS doesn't have a direct answer on their Games with Gold website.
Answer: In a nutshell: Yes
In the website it says:

...grab them before they're gone and keep them no matter what.

And after further talk with the Xbox Customer Support so that everything is clear:
Free Games purchased in Games with Gold will still be yours if you cancel gold membership, you can play them offline and with a free membership.

Once you purchase the games in Xbox Live you can re-download them whenever you want (if they are still available on XBL and have not been removed).

Note that there are some games where the situation is different, like:

Doritos Crash Course 2
Happy Wars

Games like these, can be downloaded with free or gold membership but can only be played with gold privileges.
As always any game that have multiplayer functionality will need gold membership to play multiplayer.
Answer: just to be clear... this part "Free Games purchased in Games with Gold will still be yours if you cancel gold membership, you can play them offline and with a free membership."  is NOT true!! My account just expired and I was unable to play any of my "free" games. It said I had to renew my gold membership to play them. I renewed and they were available again. Not really the value it was cracked up to be...your basically renting the games instead of owning them.
Comment: Were these XBox 360 or XBox One games? you lose access to XBox One games with gold if your subscription expires.
Comment: From: https://support.xbox.com/en-AU/my-account/xbox-live-membership/games-with-gold-faq

What happens to my Games with Gold games if I cancel my Xbox Live Gold subscription?

On Xbox One, you'll no longer be able to access your Games with Gold titles if you cancel your subscription. However, if you decide to renew your subscription at any time, you'll be able to access and play your previously redeemed Games with Gold titles again.

On Xbox 360, any Games with Gold titles that you redeem as an Xbox Live Gold member are yours to keep, regardless of whether you continue your subscription.
Comment: Were these online games?  Did you read the last line of the answer: "As always any game that have multiplayer functionality will need gold membership to play multiplayer."
Answer: From the Games with Gold for Xbox FAQ:

What happens to my Games with Gold games if I cancel my Xbox Live Gold or Xbox Game Pass Ultimate subscription?
On Xbox One, you'll no longer be able to access your Games with Gold titles if you cancel your subscription. However, if you decide to renew your subscription at any time, you'll be able to access and play your previously redeemed Games with Gold titles again.
On Xbox 360, any Games with Gold titles that you redeem as an Xbox Live Gold or Xbox Game Pass Ultimate member are yours to keep, regardless of whether you continue your subscription.


How do I disable tooltips for field help text in Bootstrap?

Question: On the user registration page, my help text for fields is displayed as pop-up text when I use the Bootstrap theme, but this doesn't work well on mobile devices, and most of my users are visiting through their phones.  How do I get rid of the tooltips?
Answer: There is a setting for this.

admin/appearance/settings/bootstrap
Javascript -> Uncheck Enable Bootstrap Tooltips
Answer: In addition to the GUI way of disabling the tooltips, there are other ways of disabling these tooltips. Following are the options that I know of.
Option 1: Admin interface
First and generally best way through the theme settings in the admin interface (see Patrick Kenny's answer)
Option 2: theme .info file
Through the bootstrap.info file or your own Bootstrap subtheme's info file:
; Tooltips
; --------------
settings[bootstrap_tooltip_enabled] = 1
settings[bootstrap_tooltip_animation] = 1
settings[bootstrap_tooltip_html] = 0
settings[bootstrap_tooltip_placement] = 'auto left'
settings[bootstrap_tooltip_selector] = ''
settings[bootstrap_tooltip_trigger]['hover'] = 'hover'
settings[bootstrap_tooltip_trigger]['focus'] = 'focus'
settings[bootstrap_tooltip_trigger]['click'] = 0
settings[bootstrap_tooltip_delay] = 0
settings[bootstrap_tooltip_container] = 'body'

Option 3: Disable tooltips per element
If you do not want to disable tooltips theme-wide, you should be able to disable them by element. You could use hook_form_alter() with underneath setting for most existing forms or set it directly on your form when creating it.
// Set #smart_description to FALSE, to disable tooltips
$form['my_element']['#smart_description'] = FALSE;


embedded fonts in TeX

Question: How can I introduce, as embedded subsets, the fonts: Symbol, Times-Bold,Times-Roman, TimesNewRomanPSMT-Bold, TimesNewRomanPSMT-Bolditalic in Plain TeX, under Ubuntu?
Answer: It should be possible with ps2pdf.
After generating a PS file, I have used the following script for creating a PDF with embedded fonts:
ps2pdf \
-dCompatibilityLevel=1.4 -dCompressPages=true \
-dUseFlateCompression=true -dSubsetFonts=true -dEmbedAllFonts=true \
-dProcessColorModel=/DeviceGray -dDetectBlends=true -dOptimize=true \
-dColorImageFilter=/FlateEncode \
-dAutoFilterColorImages=false -dAntiAliasColorImages=false \
-dColorImageDownsampleThreshold=1.50000 \
-dGrayImageFilter=/FlateEncode -dAutoFilterGrayImages=false \
-dAntiAliasGrayImages=false -dGrayImageDownsampleThreshold=1.50000 \
-dDownsampleMonoImages=true -dMonoImageResolution=1200 \
-dMonoImageDownsampleType=/Average -dMonoImageFilter=/FlateEncode \
-dAutoFilterMonoImages=false -dAntiAliasMonoImages=false \
-dMonoImageDownsampleThreshold=1.50000 \
-dEPSCrop=true \
$1 $2

The magic words would be -dSubsetFonts=true -dEmbedAllFonts=true
Comment: OK, but the anove mentioned fonts are not shown as being embadded. It this a problem with Adobe Reader 9?
Comment: I would rather suspect that it's a problem with ps2pdf. If you can share a copy of the generated PDF, we could also check if the fonts are there. Otherwise, did you try Martin Schröder's answer below?
Comment: How else can I verify the embedded fonts, except for Adobe Reader 9? I tried several methods, but the result is always the same, i.e. NOTHING added. Thank you!
Comment: You could try it with Okular too. Under File/Properties/Fonts, it should say "Embedded (subset)" for your fonts. If not, I'm not sure how to help you.
Answer: Your TeX system can be configured so that all pdf producing apps (pdftex/xetex/luatex and dvipdfmx) always embed the standard 14 PDF fonts into PDFs by issuing updmap-sys --setoption pdftexDownloadBase14 true (for pdftex/xetex/luatex) and to always embed the standard 35 PostScript fonts by issuing updmap-sys --setoption dvipsDownloadBase35 true (for dvips).
Comment: @ManuelKuehner: Yes. See the updated question.
Comment: Is this also possible for pdflatex? Thx.
Answer: I don't have enough rep to comment, but:
For Windows, Supernormal's answer will not work. Apparently ps2pdf (at least the version of ps2pdf I have) requires # instead of =, so anyone telling you to write something along the lines of this:
‐dPDFSETTINGS=/printer  ‐dMaxSubsetPct=100  ‐dSubsetFonts=true ‐dEmbedAllFonts=true

For Windows it should be like this:
‐dPDFSETTINGS#/printer  ‐dMaxSubsetPct#100  ‐dSubsetFonts#true ‐dEmbedAllFonts#true

That worked for me.

embedded fonts in TeX


How to calculate shortest distance from start to end of river?

Question: How can I calculate the straight distance from the start to the end point of a river (red line in image)? I don't know how to do this automatically.
Comment: What software are you using?
Comment: I am using in 90 % ArcMap sometimes qgis.
Answer: You can use Feature Vertices to Points tool with the option to put the points at the Start and End of the line.  Then use the Near tool or the Point Distance tool, this will then give you the linear distance between the end and start point.  This can be added to a model to automate it.
http://help.arcgis.com/EN/ARCGISDESKTOP/10.0/HELP/index.html#//00170000003p000000
https://geonet.esri.com/thread/43024
Looking for a Tool to Calculate Distance Between Points (Between Layers)
Comment: Dissolving the line prior to ed.hankins suggestion will help if there are multiple line segments within a reach. The XY to Line tool will give you actual lines on a map if that is important to you - http://help.arcgis.com/EN/ARCGISDESKTOP/10.0/HELP/index.html#//0017000000tv000000 .
Answer: It depends on what coordinate system you're using. If you are using a projected coordinate system (with units in meters or feet), you can use the field calculator (use the Python parser) with this expression:
math.hypot(!SHAPE!.firstPoint.X-!SHAPE!.lastPoint.X,
           !SHAPE!.firstPoint.Y-!SHAPE!.lastPoint.Y)

Or if you want distance on the earth's surface (if you're using a geographic coordinate system with decimal degrees), check out the answer to this question for the haversine formula (https://stackoverflow.com/questions/4913349/haversine-formula-in-python-bearing-and-distance-between-two-gps-points). For this, you would put the haversine function in the code block of the field calculator and call on it in the expression below the code block.
Either way, the thing to use is the !SHAPE!.firstPoint and !SHAPE!.lastPoint (http://desktop.arcgis.com/en/arcmap/10.3/analyze/arcpy-classes/geometry.htm)
EDIT: I just double checked the code and realized it needed some edits before it would work in a field calculator. If you're doing this in ArcMap, add a field (like endDist) of type double, select Python parser, and paste the following into the "Pre-Logic Script Code" window:
def haversine(lon1, lat1, lon2, lat2):
    """
    Calculate the great circle distance between two points
    on the earth (specified in decimal degrees)
    """
    # convert decimal degrees to radians
    lon1, lat1, lon2, lat2 = map(math.radians, [lon1, lat1, lon2, lat2])

    # haversine formula
    dlon = lon2 - lon1
    dlat = lat2 - lat1
    a = math.sin(dlat/2)**2 + math.cos(lat1) * math.cos(lat2) * math.sin(dlon/2)**2
    c = 2 * math.asin(math.sqrt(a))
    r = 6371 # Radius of earth in kilometers. Use 3956 for miles
    return c * r

With the following expression:
haversine(!SHAPE!.firstPoint.X, !SHAPE!.firstPoint.Y, !SHAPE!.lastPoint.X, !SHAPE!.lastPoint.Y)

That will work. Hope that helps!