Redshifting of Light and the expansion of the universe

Question: So I have learned in class that light can get red-shifted as it travels through space. As I understand it, space itself expands and stretches out the wavelength of the light. This results in the light having a lower frequency which equates to lowering its energy.
My question is, where does the energy of the light go? Energy must go somewhere!
Does the energy the light had before go into the mechanism that's expanding the space? I'm imagining that light is being stretched out when its being red-shifted. So would this mean that the energy is still there and that it is just spread out over more space?
Comment: That other question focuses mostly on some other things (energy conversion into mass, quantum fluctuations). Some but not all of the answers address the specific issue here. In my experience, this specific question about light in the expanding Universe comes up *a lot*, so I'd be inclined to let it go rather than closing it as a duplicate.
Comment: You're right that there's overlap, but I still think it's worth having a question that explicitly focuses on this specific issue. In my many years as a cosmologist, this is one of the most common questions that comes up.
Comment: Similar in spirit is not a duplicate. And questions with the same answer are not "duplicates" any more than "1+1" and "3-1" are the same question.
Comment: Enter [Noether's Theorem](http://en.wikipedia.org/wiki/Noether%27s_theorem). See also: [Is energy really conserved?](http://physics.stackexchange.com/questions/296/), the answers to which are the answers to this question, so I'm calling it a duplicate.
Comment: This question seems to be similar in spirit and content to this one [Effect of expansion of space on CMB](http://physics.stackexchange.com/questions/6698/effect-of-expansion-of-space-on-cmb). The two sound different but are essentially asking the same thing.
Comment: See also http://physics.stackexchange.com/q/1327
Comment: @Carl I was being diplomatic. Ok, so let's just say it. They both ask the same question - what happens to the energy of (CMB) photons due to space expansion? Now if folks want to answer it regardless that is their choice!
Answer: Dear QEntanglement, the photons - e.g. cosmic microwave background photons - are increasing their wavelength proportionally to the linear expansion of the Universe, $a(t)$, and their energy correspondingly drops as $1/a(t)$. Where does the energy go? It just disappears.
Energy is not conserved in cosmology.
Much more generally, the total energy conservation law becomes either invalid or vacuous in general relativity unless one guarantees that physics occurs in an asymptotically flat - or another asymptotically static - Universe. That's because the energy conservation law arises from the time-translational symmetry, via Noether's theorem, and this symmetry is broken in generic situations in general relativity. See

http://motls.blogspot.com/2010/08/why-and-how-energy-is-not-conserved-in.html
Why energy is not conserved in cosmology

Cosmic inflation is the most extreme example - the energy density stays constant (a version of the cosmological constant with a very high value) but the total volume of the Universe exponentially grows, so the total energy exponentially grows, too. That's why Alan Guth, the main father of inflation, said that "the Universe is the ultimate free lunch". This mechanism (inflation) able to produce exponentially huge masses in a reasonable time frame is the explanation why the mass of the visible Universe is so much greater than the Planck mass, a natural microscopic unit of mass.
Comment: That is hard to swallow :=(
Comment: Dear @Anixx, it is a law of physics but it only holds, via Noether's theorem, for systems whose laws of physics explicitly obey the time-translational symmetry. Cosmology doesn't belong to this list. Lawrence's confused presentation of cosmology as "photons in the Pound-Rebka experiment" i.e. in Earth's gravity field makes no sense because of the cosmological principle which guarantees that the photon energy can't depend on the location. At any rate, its energy is just getting lost in cosmology and there's no "non-vacuous" way to account for it. The law breaks down, much like the symmetry.
Comment: @Georg: Could you be please more specific and explain what is hard about it? These are just trivial consequences of well-known facts. Energy conservation is linked to time-translational symmetry. No time-translational symmetry, no energy conservation. Also, the specific examples how the total energy is changing in cosmological evolution - photon's energy drops; cosmological constant energy increases as the volume - are easy to understand (and prove), aren't they?
Comment: Maybe, Lubos, but we two have different qualification, age, wievpoints etc. So, its hard to swallow for me, that's all. A rather famous physics genius refused to "swallow" quantum as a basic truth :=)
Comment: Lubos, energy conservation is the fundamental law of nature. It cannot be violated at least in all currently accepted theories. As correctly stated in the answer by Lawrence, the decrease in photon's energy is compensated by the increase in potential energy.
Comment: @MikeDoonsebury I wish there was a downvote button for comments.
Comment: This is pure nonsense.  First, the universe is flat.  Second, if you come up with some theory that breaks the First Law of Thermodynamics, then that theory is wrong.  We already know that General Relativity doesn't work so well outside the solar system so it's nuts to think that it's more correct than the law that holds the Standard Model together.  There is no 'free' lunch and Guth and his adherents are symptoms of a collection of scientists that can't explain 95% of the universe.  That's a worse track record than economists or weathermen.
Comment: So space = energy?
Comment: @YashasSamaga - I wish there was a critical thinking criteria for cosmologists.  You are solidly in the realm of religion with your blind belief in something that can't be measured or detected.
Answer: Other answers have covered the key points correctly, but I'll jump in too, maybe emphasizing a slightly different angle.
It's not just that energy is not conserved -- even defining the total energy of the Universe (or even the total energy in any reasonably large volume) is problematic and, in some sense, unnatural.
What people usually have in mind when they talk about the total energy of the Universe (or a large volume -- from now on I'll stop writing that) is something like the following: Figure out the energy of each particle in that volume, and add 'em up. That's a sensible procedure for figuring out total energy in other contexts: it works great if you want to talk about the energy in all of the air molecules in this room. But it only works if all of the individual energies are determined in the same inertial reference frame. And in the expanding Universe (or any curved spacetime), there are no inertial reference frames that cover the whole region.
When people worry about energy non-conservation as applied to CMB photons, what they're implicitly doing is calculating each photon's energy in the local comoving reference frame (the one that's "at rest" with respect to the expansion). But all of the different comoving frames are in motion with respect to each other, so it's "illegal" to add up those energies and call the result a total energy.
Think of a Newtonian analogy: if one person measures the kinetic energy of something on board a moving airplane, and another person measures the kinetic energy of a different object on the ground, you can't add them up to get a total energy. And certainly the sum of those two things won't be a conserved quantity.
Just to be clear: I know that there are a bunch of contexts (e.g., asymptotically flat spacetimes) in which it does make sense to talk about energy conservation in various forms. But in this specific context, I think that the above is the essence of the issue.
Answer: The Friedman-Lemaitre-Robertson-Walker (FLRW) equations can be derived in an elementary way from Newton's laws, where the energy in the motion of a density of mass-energy in a region is determined by the gravitational potential.  The FLRW energy (so called energy) equation for the evolution of a scale parameter of spatial distance $a$ derived from the metric is,
$$
\Big(\frac{\dot a}{a}\Big)^2~=~\frac{8\pi}{3}\rho~-~\frac{k}{a^2}
$$
where $\rho$ is the energy density.  The Hubble parameter or constant with space at each time is $H~=~{\dot a}/a$. We set $k~=~0$ for a flat space $R^3$ to match observations, and which recovers what is derived from Newton's laws.  Energy density for photons scales inversely with the length of the box.  The box is thought of as a resonance cavity that is equivalent to a situation where the number of photons that leave is approximately equal to the number of photons that enter.  During the radiation dominated period things were in a near equilibrium, so this is not out of line with some physical reasoning.  In a stat-mech course an elementary problem of N-photons in a box uses the same logic, the energy of the photons scales inversely with the size of the box.  So the energy of photons $E~=~hc/\lambda$, and the wave length scales with the scale factor a.  So the density scales as $\rho~\sim~hc/a^4$.
So with this et up let us propose a time dependency on the scale factor a with time $a~\sim~t^n$.  Put this into the "energy equation" and turn the crank and you find that $n~=~1/2$.  The scale factor grows as the square root of time.  This is an energy equation, and the balance tells us that the loss of energy in photons is equal to the gain in gravitational potential energy. This connects well with Newtonian analysis and the Pound-Rebka experiment.
We may continue further, for the photons in a box exert a pressure on the sides of the box $p~=~F/a^2$, and the force induces an increment of change in the size of the box $dE~=~Fdx$.  The force is distributed on 3 different directions and so $p~=~ρ/3$.  This may then be used in the equation $pV~=~NkT$ to find that for $p~\sim~a^{-4}$ and $V~\sim~a^3$ with the above $E~\sim~1/\lambda$ that $\lambda~\sim~1/T$, which is Wein's law for the wavelength as the peak of the blackbody curve.  The proportionality of the energy density with scale factor and temperature also gives $E~\sim~T^4$.  So this physics is remarkably in line with laboratory understanding of the basic thermodynamics of radiation.
The matter contribution scales as $a^{-3}$, which was smaller than the radiation contribution for a time.  Around 380,000 years into the evolution of the universe the matter density surpassed the radiation density.  The CMB demarks this transition in the mass-energy which dominated the universe. The above dynamics still apply for photons, but radiation is now a minor player in the spacetime structure of the universe.
Comment: it might be better if you could clarify whether you intend this as a real derivation or a sort of hand-wavy motivation for folks who don't know GR. If the former, then it's incorrect. Newton's laws don't apply in cosmology.
Comment: Dear @Lawrence, the cosmological principle guarantees that the Universe is uniform. So if an object, i.e. a photon, had a potential energy, it would be independent of its position. The size of the Universe is the only genuine observable in the FRW equations and it's clear that the photon's "potential energy", whatever you may mean by that, could only be a function of this size. But the total content of photon-carried energy obviously isn't a function of the size only. It follows that your confusion/analogy between Earth's gravity field and cosmology is totally invalid.
Answer: There are 2 ways to look at the apparently redshifted energy we receive from distant galaxies

The energy we receive is less than the energy emitted.
The energy we receive is the same as the energy emitted, but our expectation is wrong.

Most would agree with statement 1, so I will explain statement 2
If we are observing from some distance (say a million km from Earth) a photon emitted from Earth and a similar photon emitted from the Moon, we expect that the one emitted from earth will have a very slightly lower frequency due to gravitational redshift.
So we are expecting a lower frequency from the earth generated photon because the fabric of the universe has been compressed around earth more than it has around our Moon.
Looking back in time, the fabric of the universe was more compressed than it is now. So maybe we should expect that a photon generated a very long time ago would have had a lower frequency than its modern day counterpart.
Answer: The answer is the energy goes into the gravitational field.
If you take the simplest case of a spatially flat homogeneous cosmology with no cosmological constant then the equation for energy in an expanding volume $V(t) = a(t)^3$ is
$E = Mc^2 + \frac{P}{a} - \frac{3a}{\kappa} (\frac{da}{dt})^2 = 0$
$M$ is the fixed mass of cold matter in the volume, $\frac{P}{a}$ is the decreasing radiation energy in the volume with $P$ constant, and the third term is the gravitational energy in the volume which is negative. The rate of expansion $\frac{da}{dt}$ will evolve in such a way that the (negative) gravitational energy increases to keep the total constant and zero.
For a more general discussion of energy conservation in general relativity see my paper  http://vixra.org/abs/1305.0034


StatusBarStyle for Full Screen UIViewController

Question: I currently have a application that sets the status bar style to light content.
[UIApplication sharedApplication].statusBarStyle = UIStatusBarStyleLightContent;

This works as expected except for a full screen modal window. Here is the code to create the modal UIViewController:
@implementation PostCard
- (id)initWithToRecipients:(NSArray *)toRecipients subject:(NSString *)subject message:(NSString *)message isHTML:(BOOL)isHTML
{
    if ([MFMailComposeViewController canSendMail] && (self = [super init]))
    {
        self.viewController = [MFMailComposeViewController new];
        self.viewController.mailComposeDelegate = self;

        [_viewController setToRecipients:toRecipients];
        [_viewController setSubject:subject];
        [_viewController setMessageBody:message isHTML:isHTML];

        self.viewController.modalPresentationStyle = UIModalPresentationFullScreen;
        self.viewController.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
    } else {
        NSLog(@"Cannont send mail from current device.");
    }

    return self;
}
...
@end

The postcard's view controller is then presented as
[myOtherViewController presentViewController:myPostCard.viewController animated:YES completion:nil];

In full screen mode, the statusBarStyle reverts to dark content. If I change the modalPresentationStyle to UIModalPresentationFormSheet, the light content is preserved.
Is there a way to programatically set the 'statusBarStyle` of a modal window? Or tell it to inherit from the presenting UIViewController? Or is this a bug? (Note, I've also tried setting my project properties as well without success.)
Thanks in advance!
Answer: - (UIStatusBarStyle)preferredStatusBarStyle
{
    return UIStatusBarStyleLightContent;
}


I want to repair an LED Christmas light string with 3 wires per bulb. How is this string wired?

Question: My prelit tree has strings of LED lights and each bulb has three wires going to it.  Looking on the web there are a number of sites that describe how to repair strings wired in series that have two wires per bulb.  However I cannot find any reference to strings with three wires per bulb.
Comment: Dimmable lights? We need images or a bit more info to answer this...
Comment: There should be a site for how do I search with intelligent keywords https://www.google.ca/search?q=xmas+string+light+repairs&ie=utf-8&oe=utf-8&gws_rd=cr&ei=8PxVWJPWFMvejwTd9KNY
Answer: I took a string apart and traced the circuit.  It's interesting- pairs of LED's are in parallel and these pairs are wired in series.  The string uses a full-wave rectifier (improves flicker) and splits the diodes between the plug end and receptacle end (so both plug and receptacle are not too large).  So for an extra wire per bulb this design gains redundancy- one bulb of any or multiple pairs can be missing or open and the string still lights.  However if both bulbs of a pair are missing or open the string is dark.
Of course a parallel string is better for reliability but I think that would require four wires per bulb and a brick power supply of some type.
So as far as repairing it seems best to replace burned out bulbs immediately.  This is because if the other bulb paired with a burned out bulb goes then the entire string goes.  Then tracing which bulb is bad requires special effort.  Of course I've read that sometimes LED bulbs fail shorted instead of open.  So this helps.
Here is a schematic:
Answer: Typically one of the wires would be parts of the series string and the other two would be connected to each side of the power. That allows sets of series strings to be daisy-chained. Below diagram from here:


Start shell script on Raspberry Pi startup

Question: I have a python program which posts to my local web server. The script runs on a raspberry pi running the latest version of raspbian 3.18. How can I make the Python script run at startup? Raspbian has a login password which is the first thing I have to remove. If the power ever goes out I want the pi to reboot and start running my script again. Should I be using Raspbian for this? The script is the only thing the pi is used for. I tried adding the script to /etc/init.d but I do not think it will run either way if the pi requires login info upon booting.
Comment: http://stackoverflow.com/a/12973826/3745735
Comment: Zudo's link will work without the need of login in
Comment: Thanks but im not sure if that will run the program without having to login. Can someone confirm this?
Comment: I tried all the steps in the link above and it still did not work
Answer: You can use the Linux crontab to run the Python script. Let's go to root and create a shell script.
sudo -i
nano startup.sh
Then type your python script on this bash script. navigate to home directory, then to this directory, then execute python script, then back home.
cd /
cd home/pi/your directory
sudo python yourpythonscript.py
cd /
Save the script and then exit. Make this sh script executable by giving it permission.
chmod 755 startup.sh
Now open and edit rc.local file.
nano /etc/rc.local
Add /root/startup.sh & before exit 0
now save and exit from the file and reboot your pi.
sudo reboot
Answer: Make sure the program is executable
chmod +x filename.py

open /etc/rc.local in your editor of choice
sudo nano /etc/rc.local

and add
python /FULL PATH TO SCRITP/filename.py

before the exit


Digital electronics - how does a circuit determine when some element (like adder) is done? (delay handling)

Question: Take for example a ripple carry adder, how does a circuit handle delays of some elements?If ripple carry adder starts working from some clock cycle, we can't expect that it will have correct results on the next clock cycle.
Answer: The circuit doesn't, the designer has to do. Maximum delays are typically fixed, you have to plan the circuit appropriately, which potentially means that you design it to wait one clock cycle.
If needed, the designer can route out a "ready/conversion done etc" signal.
Comment: @user3711671 You seem to have a fundamental misunderstanding of how combinational logic works. Delays are not **introduced**, they are **inherent** in the operation of the circuit. We don't **design** the delay values, we design **in spite** of the delay values. The designer must make sure that all combinational logic has settled before using (or latching) the output of that logic.
Comment: How is the delay implemented?Do designers use counters or is there some another approach?
Comment: @user3711671: if needed, you just intoduce a chain of inverters or schmitt triggers
Comment: @ElliotAlderson I know that delays are an inherent problem but these delays have to be taken in mind, that's what I was interested in.How are circuits designed with delays taken into account?If we have to idle for certain amount of clock cycles, then how do we achieve this idle state?Maybe using counters?
Comment: @user3711671: for most switching elements a counter is not efficient, since the clock cycle of your counter is going to be on the order of your switching times, whus you can delay the trigger (e.g. using the RC time constant of the input)
Answer: You imply in your question that delays are being "introduced" or "implemented". They are neither implemented nor introduced
Delays happen because gates take time to pass signals. They are intrinsic. If you have a long adder with a lot of gates, it will have a long delay, and you have two options:
1)  Lower the clockspeed so that each cycle lasts longer than the delay.
2) Implement a multi-cycle adder where part of the addition happens on the first cycle, then part on the second, etc. Then set your clockspeed so that the slowest stage of your adder has less delay than the duration of your clock cycle. This can be done using common logic elements such as D flip flops that take a value on clock cycle transitions.
Answer: No.
The ripple effect takes as long as it takes. It is up to the designer to make sure that the result is stable when it is used.
On purpose I don't write "the next clock edge" as the designer can invoke a so called multi-cycle path. In that case the result is not used until two or three clock cycles later.
If this is supposed to be the next clock edge, the designer must make sure the clock frequency is low enough.

How are delays introduced?Are counters used for that purpose?

Sometimes but in general you try to avoid adding delays. From what I gather from your questions is that you are looking for the answer how to do what we call in the profession timing closure.
Timing closure is a very complex process which involves various solutions depending on if you have set-up, hold time or maximum frequency problems.
It would take many pages and is thus beyond the scope of stack exchange to tell you even the beginning principles and techniques, but I hope with that as search term you learn a lot from the internet.
Just for completeness: delays are only added when a register has hold-time problems but has slack in its set-up time.
Comment: How are delays introduced?Are counters used for that purpose?
Answer: Ensuring various types of delay are properly evaluated so a circuit operates properly is the responsibility of the designer of the circuit. The designer must ensure that the operational speed of the function can meet the overall requirements.
Take your ripple counter example - an asynchronous design. If I were to implement such a circuit using separate flip flops such as this one, I would need to know the worst case propagation delay which is 14 nsec.
In addition, if using D flip flops (where the D input is fed from the #Q output), the setup time would also need to be evaluated which in this case is 7 nsec.
So the maximum rate at which such a counter could be operated at for a single device is 47MHz for guaranteed operation (provided the maximum toggle rate of the device is rated for it, which in this case is true).
For more bits, all the delays need to be analysed if there must be a particular duration where the output result is correct.
Answer: Delays, rise times and setup times are defined by design due to CMOS voltages, RdsOn, Ciss, Ciss etc and given in no times for each discrete part.
You can choose a multiphase clock to decide when the output is guaranteed to be settled to improve clock rates by a state diagram pipeline so you get what you compute for worst case delays to guarantee the logic is valid within these delays for the next clock edge and state values.
All FET including those used in  CMOS have a 50% production tolerance for Vt  = Vgs(th) and a temperature with Vdd (=Vgs) dependency for all these delay times.


Motivation For Weight Choice In Pooled Variance

Question: In the formula for pooled variance, the estimated variance of each population of size $n_i$ is weighted by $n_i-1$.  Is there a good motivation for this?  I would assume the formula is always unbiased, even when different weights are chosen.  But my guess is that the variance of the variance estimation is minimized by this choice, assuming a nice distribution of the 'real' error.  If that's true, where can I read a proof of it?  If not, what other motivation is there for this choice?
Comment: If you're not aware of what's in my answer below, you're missing a basic point.
Comment: Thanks for your answer, but I think I didn't fully get it.  Can you just reformulate the gist of your argument, if not minimizing variance, what is the reason for those weights?
Answer: This question was already asked at How to derive "Pooled Sample Variance"?, but the accepted answer is wrong and the author of the question hasn't been on the site since $2014$, so instead of trying to get them to unaccept the answer, I'll post my answer here and vote to close the other question as a duplicate of this one.
As shown there, the weights should be in inverse proportion to the variances of the individual variance estimators. This is easiest to show for the combination of two estimators, where we have $\hat v=\lambda\hat v_1+(1-\lambda)\hat v_2$ with $\lambda\in[0,1]$ and thus $\mathsf{Var}[\hat v]=\lambda^2\mathsf{Var}[\hat v_1]+(1-\lambda)^2\mathsf{Var}[\hat v_2]$, which is minimal for $\lambda\mathsf{Var}[\hat v_1]-(1-\lambda)\mathsf{Var}[\hat v_2]=0$ and thus for
$$
\frac\lambda{1-\lambda}=\frac{\mathsf{Var}[\hat v_2]}{\mathsf{Var}[\hat v_1]}\;.
$$
The variance of the unbiased variance estimator $\hat v=\frac1{n-1}\sum_i(x_i-\bar x_i)^2$ is
\begin{eqnarray}
\operatorname{Var}[\hat v]
&=&
\mathsf E\left[\hat v^2\right]-\mathsf E\left[\hat v\right]^2
\\
&=&
\mathsf E\left[\left(\frac1{n-1}\sum_i(x_i-\bar x_i)^2\right)^2\right]-\sigma^4
\\
&=&
\frac1{n^2}\mathsf E\left[\left(\sum_ix_i^2-\frac2{n-1}\sum_{i\ne j}x_ix_j\right)^2\right]-\sigma^4
\\
&=&\frac{\mu_4}n-\frac{n-3}{n(n-1)}\sigma^4\;,
\end{eqnarray}
where $\mu_4$ is the fourth central moment. So in general, even if the populations all have the same central moments, the optimal weight factor depends on the sizes of the populations in a more complicated way. However, for a normal distribution we have $\mu_4=3\sigma^4$ and thus
$$
\frac{\mu_4}n-\frac{n-3}{n(n-1)}\sigma^4=\frac{3\sigma^4}n-\frac{n-3}{n(n-1)}\sigma^4=\frac2{n-1}\sigma^4\;.
$$
Thus, for a normal distribution, as you suspected, weighting the individual estimators by $n-1$ minimizes the variance of the pooled estimator.
It's not a coincidence that this works out nicely for the normal distribution, as many things do; it's related to how the normal distribution factorizes and the sums of the data and the squared data are jointly sufficient statistics for the parameters of the distribution; intuitively speaking, the data are additive, and each unknown mean acts like a missing data point.
Specifically, with $n=\sum_in_i$, the likelihood of the data is proportional to
$$
\frac1{\sigma^n}\exp\left(-\frac1{2\sigma^2}\sum_{ij}\left(x_{ij}-\mu_i\right)^2\right)\\=\frac1{\sigma^n}\exp\left(-\frac1{2\sigma^2}\sum_i\left(n_i\left(\mu_i-\overline x_i\right)^2+\sum_j\left(x_{ij}-\overline x_i\right)^2\right)\right)\;,
$$
so the sample means $\overline x_i$ and the sum of the squared deviations from them over all populations are jointly sufficient statistics; we wouldn't retain any extra information by retaining the separate sums of the squared deviations for the individual populations. If we assume a uniform prior for the unknown means $\mu_i$ and integrate them out, the result is proportional to
$$
\frac1{\sigma^{n-m}}\exp\left(-\frac1{2\sigma^2}\sum_{ij}\left(x_{ij}-\overline x_i\right)^2\right)\;,
$$
where $m$ is the number of populations. Setting the derivative with respect to $\sigma$ to $0$ shows that the pooled variance estimator
$$
\frac1{n-m}\sum_{ij}\left(x_{ij}-\overline x_i\right)^2
$$
is the maximum likelihood estimator for the common variance $\sigma^2$.
Comment: Thanks so much for the reply!  After posting the question I thought my guess was totally off and you minimize the variance by just sampling from the variable with the largest population, the fact that you can reduce the variance of a compound variable by adding little bits of the variable with the larger variance was not on my mind at all!
Answer:
my guess is that the variance of the variance estimation is minimized by this choice

This sort of thing is sometimes the reason for a choice of weights in this kind of problem, but in this case there is a reason that hits you in the face before that question comes up, so I hadn't actually thought of the above-mentioned reason before.
Say you have $X_1,\ldots, X_n\sim\text{i.i.d}\operatorname N(\mu,\sigma^2)$ and $Y_1,\ldots, Y_n\sim\text{i.i.d}\operatorname N(\nu,\sigma^2),$ and
\begin{align}
\overline X & = (X_1+\cdots+X_n)/n \\[4pt]
\overline Y & = (Y_1+\cdots+Y_m)/m \\[6pt]
S_X^2 & = \frac {(X_1-\overline X)^2 + \cdots +(X_n - \overline X)^2} {n-1} \\[6pt]
S_Y^2 & = \frac{(Y_1-\overline Y)^2 + \cdots + (Y_m - \overline Y)^2}{m-1}
\end{align}
The pooled estimator of $\sigma^2$ is
$$
\frac{(X_1-\overline X)^2 + \cdots + (X_n-\overline X)^2 + (Y_1-\overline Y\,)^2 + \cdots + (Y_m-\overline Y\,)^2}{(n-1) + (m-1)}. \tag 1
$$
Recall that
$$
\frac{(X_1-\overline X)^2 + \cdots +(X_n-\overline X)^2}{\sigma^2} \sim \chi^2_{n-1}
$$
and
$$
\frac{(Y_1-\overline Y)^2 + \cdots +(Y_m-\overline Y)^2}{\sigma^2} \sim \chi^2_{m-1}.
$$
Thus the numerator in $(1),$ divided by $\sigma^2,$ is distributed as $\chi^2_{(n-1)+(m-1)}.$
The reason for the weights is that the numerator in $(1)$ is $(n-1)S_X^2 + (m-1)S_Y^2.$


What is the downside of having many inodes?

Question: Too few inodes can result in you not being able to store anymore files. What is the the downside of having many inodes ? (more than default)
Comment: The only downside I see is more space will be reserved for inodes and as a result the actual space on the disk will be reduced.
Comment: By how much ? How does it work ? What does it look like ?
Answer: Inodes reserve space on the disk that cannot be used for storing your data.  That is about the only issue.
Answer: Any operation that scans the inode table will be slower.  This can affect fsck or other recovery functions.  Also, when the inode table is cached this can take up memory. This answer may also provide insight
Comment: I believe that the only inodes that are cached in memory are those that are active (open, in the process of being exec'ed, somebody's working directory, a mount point, etc.). A larger number of inodes allocated in the filesystem on disk should not affect the usage of the in-memory inode table.


Wiring to a shed

Question: I have a 20 amp breaker and 12 gauge wire running out to a shed that is wired with 14 gauge wire. The shed has 3 receptacle, 1 light switch and 1 light receptacle. Is this safe?
Comment: How. Far from panel to shed? What will you be plugging into shed receptacles?
Comment: What are you using as a disconnecting means at the shed?
Answer: No. You must not have any 14 Ga wire on a 20A breaker. Change the wire to 12 Ga or the breaker to a 15A.
Comment: To expand on this. There will be no warning, no sirens, and it will seem things are ok. When you exceed 15A on that circuit, the wire will burn down whatever it is run through, and the fire department will find out the wrong wire is used and you will not have insurance coverage, if you lived to worry about insurance.
Comment: I would think it might be advantageous to the 12ga wire feed a subpanel within the shed that contains one or two 15A breakers.  If one can split the shed wiring into two 15A circuits, this would allow the shed to safely use more than 15A provided that no more than 15A was on either circuit.  Even if one only uses a single 15A circuit, I would think having a 20A breaker in the main panel and 15A in the shed could be advantageous both because moderate overload conditions would be likely to trip the shed breaker while leaving the main breaker untripped (note that short circuits...
Comment: ...would likely trip both).  If one would be using tools that might sometimes cause an overload (e.g. if a saw or drill gets bogged down in material) being able to reset a breaker in the shed may be more convenient than having to visit the main panel.
Answer: You could install a pony panel in the garage. Where I live, the panel needs to be more than 3 feet above the ground, but within 6 feet of where the power enters the structure. Please check you local electrical code. You would install a small breaker panel with a 20A disconnect and then 15A breakers for your circuits on 14 Ga wire. This would allow you to have your light on one local circuit and the outlets on other circuits, so, if you trip one of the outlet circuits, the light will stay on.
You can use a single phase, 120V panel with 4 or 6 slots. One of the slots would be your 20A disconnect; a regular breaker with the "load" connected to the supply. It looks a little funny, but it will work and it should meet code.

Wiring to a shed


What is the XML spec for importing into Microsoft Project?

Question: From our existing, internal tracking system I would like to create an XML export that I can then bring into Microsoft Project 2007 to further display and manipulation.  I've been unable to find a straightforward explanation of how the XML should look for this kind of import.  I want to be able to create dependencies, assign resources, etc.  The Excel/CSV imports don't appear to offer all these capabilities so I think XML is the better way...if I could just get a spec for it.
Answer: If you are working in Java or a .Net language, you may find it convenient to use MPXJ to achieve this, rather than writing the XML directly as it provides a more "user friendly" API, insulating you from the detail of the XML schema. It will also allow you to read/write other project data formats if required.
Jon
p.s. Disclaimer: I maintain MPXJ, hence my interest!
Answer: Someone on Google Groups answered my question.  The spec is available here: http://msdn.microsoft.com/en-us/library/bb428843.aspx


How to force glusterfs peer to attempt to reconnect to rebooted node?

Question: I have a six-node glusterfs cluster running. This morning, I noticed that one of the machines was behaving strangely, so I rebooted it, just to be safe - a manual STONITH, if you will.
After rebooting, three of the other nodes recognize the rebooted machine as "Connected" in gluster pool list and gluster peer status, but the other two show a status of "Disconnected". Strangely, even the nodes which show "Disconnected" in gluster pool list still show it as "Connected" in gluster volume heal [volname] info.
I've tried gluster peer probe from both sides with no effect.  I have verified that I can connect to both port 24007 and port 49154 (the brick port shown in gluster volume status on the peers which recognize it as Connected) on the rebooted node from the machines which consider it to be "Disconnected".
/var/log/glusterfs/glustershd.log on the nodes which see the rebooted server as Disconnected contains:
[2018-01-09 11:36:39.258109] I [MSGID: 114018] [client.c:2280:client_rpc_notify] 0-palantir-client-4: disconnected from palantir-client-4. Client process will keep trying to connect to glusterd until brick's port is available
[2018-01-09 11:36:50.074074] E [socket.c:2309:socket_connect_finish] 0-palantir-client-4: connection to xxx.xxx.xxx.205:24007 failed (No route to host)

However, an hour and a half later, it has not reconnected, despite the first log entry's claim that it would keep trying.
Given all this, what do I need to do to get the two errant peers to reconnect to the rebooted node?
Answer: After much web (and soul) searching, I took the chance of stopping and restarting the glusterfs server service (systemctl restart glusterfs-server) on the two nodes which saw their rebooted peer as Disconnected and this got things back in sync.
Most importantly, performing these restarts resulted in no lost data, even though one of the restarted nodes was the replica of the peer it saw as Disconnected.  Presumably, replication was still taking place by way of the nodes which still saw the rebooted peer as connected.


How do you access the "Piercing the Shroud" mission if you've already completed the campaign?

Question: I beat the campaign and then saw that I was 25/26 on missions. I did some research and found out about the secret level, Piercing the Shroud. I went back and got the secret (avoiding a spoiler here) and then beat the level. However, on my "Mission Archives" screen I can't find that level. Also, I can't get back to the Star Map to select it. What do I have to do to select that level, or do I have to start the campaign over?
Comment: @raven completely different question, and different answer. i'm asking about after you've finished the campaign are you able to access the mission. he's asking if he has to complete the mission in order to access the secret mission.
Comment: possible duplicate of [SC2 WOL Secret mission: Once it is unlocked, do I have to finish the unlocking mission?] Slightly different question, same answer. (http://gaming.stackexchange.com/questions/6015/sc2-wol-secret-mission-once-it-is-unlocked-do-i-have-to-finish-the-unlocking-mi)
Comment: did you actually look at the answers to that question? They answer the exact question you ask. Quote: "If you then later replay the level after finishing the campaign, and collect the secret documents, piercing the shroud will not unlock."
Answer: You'll have to start the campaign over. Or, if you have a saved game before you started the Char mission, you can reload that and you'll have to unlock the secret mission again, but you can play it through the mission archives as long as you're still aboard the Hyperion.
Answer: Uh...all these other guys are way off.  Maybe this was fixed somewhere along the way?  At least in whatever the current version of Starcraft II is, after you finish the campaign, you can go on back to Media Blitz from the mission screen,  and pick up the secret papers.  Then after you finish the Media Blitz mission again, the Piercing the Shroud mission should appear at the very bottom of the list-after the All In Char mission.  There's not a lot of plot development in this situation, though...it just sends you back to the mission screen after you beat it.
And yes, if you beat Piercing the Shroud like this it does count towards the completionist achievement...


How do I record partial payments?

Question: My client frequently needs to record  partial payments for events and memberships. When I open the transaction history, I  don't see a way to record the partial payment. In fact, all registrations seem to get recorded as completed by default. Any suggestions for a workflow which better records the transactions and the status of payments?
Comment: Sounds like a workflow problem as well. Are people signing themselves up, or are these being manually added by someone with the organization? Because until they are fully paid, registrations should be something like pending, pending (pay later), partially paid, etc.
Answer:
First, record the payment with a status of Pending.
Click the triangle next to the contribution to open up the payment listing (see screenshot below).
Click Record Payment (or Submit Credit Card Payment).  You can log a partial payment from here.

In my screenshot below, you can see the $55 donation has a status of "Partially Paid".

How do I record partial payments?


Could A Building Hold A Kaiju?

Question: Assume the Kaiju is 200 feet tall and weighs 4,000 tonnes. The building is 180 feet tall and pretty much your average flat building. Could most buildings carry that weight on top or crawling up the side of them? Or would it simply collapse?
Comment: @DavidHambling I am taller and heavier than the chair I'm sitting on, and it puts mostly air between me and the ground, yet it works, so I think there's at least some precedent that the building might be able to handle the weight.
Comment: Aside the kaiju this is a pure engineering question: can the roof of most building carry 4000 tonnes?
Comment: The building is 180 feet tall, the kaiju is 200 feet tall. It doesn't crawl up the side...given that the kaiju is solid and the building is mainly air, I think we can guess what's going to happen.
Comment: Are you able to harness whatever physics-defying effect lets you have 200-foot-tall kaiju for building buildings, or not?
Comment: @WorkerJoe point taken but there's a scaling effect: the building is (say) 100 time bigger, so has 10,000 times as much supporting cross-section but has to support 1,000,000 times the weight -- it gets harder as you get bigger.
Answer: The answer is no, for one simple reason: contact points. Could I build a building that could support the weight of 3000-4000 medium sized cars? Yes, probably. Parking garages exist. But if I put all the cars in a huge pile in the corner of one level, they would instantly break through the floor. As soon as the kaiyu would grab the side of the building anywhere and try to pull itself up, they would take a huge chunk out of the building instead.
Most buildings are constructed to spread out the weight as much as possible, to get the most value out of as little (cheap) material as possible. Upset that balance, and you'll have a bad time.

Could A Building Hold A Kaiju?


Quick way to check my broadband speed

Question: What is the simplest way to check my actual broadband connection speed?
Comment: Every such test I've ever tried is hopelessly optimistic. They report the peak speeds, even though that peak may have been achieved for a very brief fraction of the test.  Average throughput (total data / test time) would be far more appropriate.  But the providers want to make their numbers look good.  Truth? Not so much.
Answer: www.speedtest.net
Or google broadband speed test.
rough idea may be ascertained to what your modem thinks your speed is if you poke around the interface. Some tell you the connected speed. Speed tests are inaccurate as it depends on what you're hopping through, but give a rough idea.
EDIT - To have a more complete answer, as others pointed out, there are other sites that will test your speed. I've used DSLReports for information before and they seem reliable as well. I can't speak to other sites, though.
I would point out that all these sites have other variables involved in measuring your speed and can only give an idea. Don't place complete faith in the results of any place...get averages from multiple sources and treat them as rough estimates, and go from there.
Comment: @BrianFenton I seriously think that some of the ISPs have some kind of anti-throttling going on with speedtest. I upgraded my connection and decided to run a test.  I pay for 18 Mbps, but SpeedTest was reporting around 30 Mbps. Yet in day-to-day use I rarely see anything over 10 Mbit (perhaps various sites don't allocate much more than that to a single user).
Comment: Speedtest is not reliable. One time, I had superceded a cap on my data on my connection, so the ISP had cut the speed down to 128k. Speedtest.net consistently told me I had 18m! And when the ISP reinstated my normal speed, Speedtest.net's result didn't change. Either the ISP is gaming the results, or simply Speedtest.net is not accurate.
Answer: Speedtest is crap. Seriously. They consistently overrate my connection speed by 15Mbps.
As near as I can tell, many ISPs (I have Cox Cable internet) use modems that do compression. Speedtest.net appears to use test-data that is highly repetitive.
The end result is they often overestimate your connection's speed by as much as 100%!
DSLreports and TestMy.net both use largely incompressible data, and seem far more accurate. I still get a fair bit of variance between their results (and variance between the different types of test), but they're in a far more believable regime than speedtest.net.
(Copied from my answer here.)
Answer: Try Bandwidthplace.

Quick way to check my broadband speed


Converting PCAP to WAV

Question: How would I go about converting a RTP stream from a pcap file to wav format with a command-line tool such as sox?
Answer: Here you go!
 1. Enter RTP in the display filter in Wireshark when the capture is open.
 2. Now select an RTP packet in any stream and click on the menu option Telephony.
 3. Go to RTP>Stream Analysis and click on Save Payload button.
 4. Change the format to .au and choose a name (lets say test.au) and location for your file.
 5. Play it using your favorite audio player.
OR
 5. Run the following command to convert the .au file to .wav if you like .wav files better: sox test.au  -V -t wav -b 16 -c 2 test.wav
Hope that helps!
Comment: Is it possible to do this completly via command line?
Answer: This Docker container has a command line tool called mediaMin that handles pcaps with multiple concurrent RTP streams, different codecs, and streams that create child streams per RFC8108. Cmd line examples use pcaps included in the container.  Output wav files are generated for each stream and optionally for "merged audio" of all streams.
.sdp files can be used to override codec auto-detection and/or select only specific streams
Disclaimer: I work for the company that created this tool

Converting PCAP to WAV


Jquery autocomplete UI , Populating key instead of value

Question: enter code hereI am using jquery autocomplete ui.
I have a text box in which user types name of a US state and autocomplete suggestions are made. Here an ajax call is made and json results are returned as expected.
eg. when user types "new" , the json response returned is:
{"NH":"New Hampshire","NJ":"New Jersey","NM":"New Mexico","NY":"New York"}

What i want is when user clicks a state from the suggest list , eg "New York" , instead of populating the text box with the state name , its state code ("NY" here) be populated.
my current code is :
$("#selectAllStateList").autocomplete( { source: "getStateList.html"
         });

*******Update ***
Ok .. now so I have changed the response format . So when I type "de" , I get the response.
[{"label":"DE","value":"Delaware"},{"label":"RI","value":"Rhode Island"}]

The autocomplete suggestion box shows me DE and RI , but when I click on RI , Rhode Island gets populated in the text box instead of RI which I want.
Can someone help me how to do that.
Thanks in anticipation
Rachit
Answer: Got it .. simply changed labels with values.


Ubuntu-Touch can not load on nexus 5

Question: Good day!
I have some problem with booting my nexus 5 after installing ubuntu-touch.
It freezes on load with Google label.
Could you help please.
Comment: try re-flashing the device - also which version did you flash, where did you download, what instructions did you follow.
Answer: Ubuntu touch is not officially supported for Nexus 5 and I think we can't support unofficial ports here, like we can't support unofficial spins of Ubuntu desktop. There are other good channels though, in both chat and mailinglists. Look at the bottom of this page for details: https://wiki.ubuntu.com/Touch/Contribute#Discuss
Answer: Nexus 5 is supported by ubport and has a great installer. Try again now.

Ubuntu-Touch can not load on nexus 5


How is insulin transported in vivo in mammals?

Question: What is the mechanism for transport of insulin in mammalian cells?
Comment: Do you mean how does insulin get secreted and absorbed? The insulin *gene* stays in the DNA in the nucleus, just like all other [genes](http://en.wikipedia.org/wiki/Gene). Have you read the Wikipedia article on [insulin](http://en.wikipedia.org/wiki/Insulin)? It has a lot of information that should help you understand the pathway. If you have more specific questions, please [edit] your question and describe them in detail.
Answer: The process is described here. This is my summary, plus a few extra details:
The primary gene product of the INS gene is preproinsulin. As the N-terminal signal sequence (pre-) emerges from the ribosome during polypeptide elongation the signal sequence binds to a signal recognition particle which arrests elongation until the nascent chain has engaged with the translocation apparatus in the membrane of the endoplasmic reticulum (ER). The preproinsulin polypeptide is translocated across the ER membrane in a cotranslational process, and the signal sequence is cleaved off by signal peptidase.
The proinsulin molecule folds in the ER lumen, assisted by various chaperones and, in particular, by protein disulphide isomerase, which ensures that the correct disulphide bonds form. The correctly-folded proinsulin polypeptide is exported from the ER in COPII-coated vesicles which deliver it to the Golgi. At this stage the proinsulin is cleaved by furin-type proteases (pro-hormone convertases; cleave at pairs of basic residues), removing the internal C-peptide (pro-) and after a little C-terminal trimming, leaving the insulin A and B peptides covalently attached via disulphides. This is mature insulin.
The mature insulin leaves the Golgi in secretory vesicles. Since insulin secretion is regulated, these vesicles do not fuse with the cell membrane constitutively, they are stimulated to fuse by a Ca2+-dependent signalling pathway. Vesicle-membrane fusion is mediated by SNARE proteins. At this stage the insulin has been released from the pancreatic β cell. Notice, however, that the insulin has been extracytoplasmic since it was translocated into the ER: all other steps in the transport process are achieved by rounds of vesicle formation and fusion.


What was the biggest miracle in the time of the Megilla?

Question: There were many miracles in the time of the Megilla. What was the biggest one?
This question is Purim Torah and is not intended to be taken completely seriously. See the Purim Torah policy.
Answer: It mentions in the Megilla "מחשבת המן" - Haman had a computer.
Which type of computer could he have? The Gemara says that Haman is connected to "Hamin Heitz" - Haman is a tree. The only tree computer that exists is an Apple, Therefore, Haman was an Apple.
Now, Apples are known to be stable computers. Yet, Haman was still able to be hung.
Comment: Which, incidentally, is why the Baker (in the Egyptian Jail) was hung. You see, he was having too many dreams. Dreams are called " **Chalo** mos" which shares the same root as " **Chalo** nos" (which is particularly connected to Challa, which again is in the domain of the Baker). "Chalonos" are Windows, and everyone knows how easy it is to "hang" Windows.
Comment: +1. We can probably extend this to some other characters in the Megillah as well. Achashverosh had סריסים = eunuchs = Unix; Mordechai had DOS (פתשגן כתב הדת), and Esther - not sure, but it definitely wasn't DOS (אשר לא כדת).
Comment: You forgot about Apricot computers!  Also from a tree. (Apple II days clone).
Comment: @Alex Mordechai was Linux (penguin), after all, he **did** wear a black hat and white shirt.
Comment: Note his computer was female.
Answer:
"In the third year of his reign, he made a feast unto all his princes and his servants; the army of Persia and Media, the nobles and princes of the provinces, being before him.  When he showed the riches of his glorious kingdom and the honour of his excellent majesty, many days, a hundred and eighty days." -Esther 1:3-4

One hundred and eighty days of drunken debauchery, and yet there is no mention of anyone having a hangover.  That is truly a miracle.
Comment: On a more serious note, maybe that's why Achashverosh seems to do whatever anyone tells him to do.
Comment: @ Seth J. haha. sorry
Comment: @AriA Boo. Purim Torah only.


Script to delete null value rows in data extension

Question: I am trying to create a script that deletes any rows in my data extension that have a certain field value of null. SSJS and Ampscript seem to be able to do this, but this is my first Marketing Cloud script and I have no Ampscript/little JavaScript experience. Any advice is appreciated!
Comment: I understand and will do better in the future. It was a little intimidating to post my code. First time poster. Trying to get my feet by tackling some real-world problems after self-practicing with a few languages in the past.
Comment: For questions like this, it is usually best to include a good faith attempt or sample code of what you are trying to do, even if you have no experience.  The forum is here to help support, not provide development services.
Comment: Glad to have you join the community and never feel intimidated - we are a forum for solving issues and helping, not for judging or berating.
Answer: When dealing with NULL values I usually tackle this with a combination of SQL query and SSJS script. If you are trying to delete a row based on an actual value then you can easily skip the SQL step.

Create a SQL query to SELECT any record where the certain field IS NULL and set a field on that record to something like 'FlagRemove' on UPDATE.
Run a SSJS script like var rows = Platform.Function.DeleteData('Data_extension_name',['FlagRemove'],['true']);
Comment: Using a "flag" field to delete has worked well, but is there a way for me to delete the field when it is no longer needed? This is only to cleanup a few error records and get familiar with scripting. The script will not be running much, if any, in the future.
Answer: The simplest way I have found this is to not even use any AMPSCript or SSJS.
I use 2 SQL statements (and 2 DEs) that would run in an automation.
SQL 1:
SELECT yourColumns FROM yourOriginalDE WHERE notNullColumn IS NOT NULL
Have this target the secondDE and have the ACTION set to overwrite.
SQL 2:
SELECT * FROM secondDE
Have this target yourOriginalDE and have the ACTION set to overwrite.

With the action of overwrite, it will delete all records and then fill in only those that were pulled in the SQL query.  Thus, removing all the NULL values without a DELETE function.
By using SQL only I find it usually runs much quicker than using AMPScript or SSJS and it also is much simpler to write/edit.
Comment: In Marketing Cloud I am using Automation Studio - Activities to access SQL Query. It will not let me use INTO, only query. What should I do?
Comment: There is no need to use 'INTO' you write the query as shown above (replacing placeholders with your columns and DE names) and then the action radio buttons (not in the SQL) set to overwrite. This should be on the screen where you select the target DE.
Comment: Thanks for your help, Gortonington. It was extremely helpful!


Increase simultaneous connections with apache2

Question: How can I increase the number of simultaneous connections in apache2?  I'm using a javascript application that polls the server regularly and I'm trying to prevent clients from getting locked out.  I know I should switch to a non-locking webserver, but until that, is there any kind of hack I can do in apache to optimize this?  Thanks.
Answer: Perform a search on this site for 'MaxClients' which should turn up quite a bit of information to get you started.
There may be a few directives you want to look at depending on your server resources that could affect the number of simultaneous connections and thus performance of your web server.  Here are a few examples (some may or may not need to be configured depending on your environment):

StartServers
MaxSpareServers
MinSpareServers
MaxClients
ServerLimit
MaxRequestsPerChild
KeepAlive
KeepAliveTimeout
MaxKeepAliveRequests:
Answer: On the Apache level you'll want to maximize the MaxClients value without ever running out of RAM. You could, for example, set MaxClients to 1000 and it would run fine until you had so many concurrent connections that you run out of RAM and begin to use the swap, at which point your server's performance will plummet.
As a rough guide you can run top and look at all the httpd entries taking the difference between the RES and SHR columns. This value is the approximate memory used by the Apache client processes. Divide the total number of memory you wish Apache to use by this number to get an initial MaxClients. For example, for an average Apache process size of 20MB to use 3GB works out to 3000/20 = 150 MaxClients.
If you want to increase MaxClients further you can try to reduce the size of the Apache processes by not loading any module you don't need.
As you mentioned, you may wish to consider an alternative web server, or possibly dual Apache web servers, to increase the number of concurrent connections possible. When Apache is configured to server dynamic pages (PHP, etc...) it is relatively memory hungry which puts a relatively low limit on how many connections you can have before running out of RAM. The usual choice in this case is to use a lighter web server (Lighttpd, Nginx, etc...) to serve all the static content and leave Apache to just serve the dynamic pages.


Which codecs does ubuntu-touch support?

Question: Which codecs does ubuntu-touch support? Can I add restricted-codecs package?
I've copied an .avi file to ubuntu-touch, and I can hear it, but I can't see anything.
Answer: I'm not sure about any complete list of codecs but in order to play most "oncommon" codecs e.g. mp4 you have to install some libraries. You should be able to play avi if you install the ubuntu-restricted extras library.
sudo apt-get install ubuntu-restricted-extras

You can read more about it here
You should of course also be aware of the Consequences of using apt-get in ubuntu touch.
That being said I'n not sure if there is any equivalent of e.g. VLC app or anything you can use that wraps the necesarry codecs. Hovever, if you do find one I'm intrested in hearing about it.
Also see simmilar question.

Which codecs does ubuntu-touch support?


Why my long fuel trim readings are higher than short trim ones?

Question: My understanding of long trim vs short one is that the short trim readings will adjust the long trim after awhile right? For example my short trim readings are in the -5 to positive 7% max while the long trim will never ever drop below 10.9% and sometimes 17.2%. I was expecting the long trim to drop after seeing the short one hover around -3 to positive 5% range. I will attach images for this morning readings taken after engine is warmed up on idle.
Answer: You are right the STFT will replace the LTFT after a given amount of time. IIRC, the LTFT is the adjustment to the tune itself to compensate for fueling issues over a longer period of time. If the STFT is large for a long period of time (whether +/-), the LTFT will be adjusted accordingly. If the LTFT is at +17% and the STFT is steadily at -3%, then after a period of time the LTFT will drop to +14%, which should then move the STFT to zero. Then if the STFT needs to move to -3% again to adjust, after a period of time the LTFT would be moved to +11%. I don't know what the "time period" is for when it makes adjustments. I'm sure it's probably different per manufacturer's specifications.
It sounds like everything is doing its job, however, +10% is quite a bit of adjustment for LTFT. I believe 17% is pretty close to maxed out. I'd ensure the O2's are in good working order and the fuel system is clean (including injectors & fuel filter if equipped).
Comment: By "fueling issue", I mean the ECU is keeping up with what is needed to compensate, but yes, it could be caused by an exhaust &/or vacuum leak as well.
Comment: Interesting! So if the LTFT stuck at number that is higher than STFT than it is a fueling issue? Cause i was thinking to focus only on the exhaust & vacuum leak.


How did Doris Sparrell (1892-1985) spend her time as a young lady?

Question: What did young women like Doris Sparrell (1892-1985) who lived in Massachusetts, USA do for entertainment as "teenagers"?
Comment: The strict answer is nothing: she was never a teenager, as the word didn't come into use until circa 1941. (Teenage as an adjective was first used in a publication in 1921).
Comment: I've downvoted, not because of the mistaken use of 'teenager' because that's easily fixed, but because I think this is thinly-disguised cousin bait. Adding more information about Doris might make it less so, such as: where she lived; and what was her socio-economic situation. Alternatively, it could be generalised to ask about the activities of young women of a particular class in a certain time and place.
Comment: what is a 'thinly disguised cousin bait'? This was an honest attempt at http://meta.genealogy.stackexchange.com/questions/1661/how-to-increase-our-question-rate and the suggeston for more self-answered questions.
Comment: 1) What searches are likely to find this Q high on their answers? Only searches for Doris Sparrell 1892-1985. 2) Has any effort been made to generalise the Q or the self-A to be of use to anyone other than descendants or relatives of Doris Sparrell? No. So what we have is a Q that is almost entirely the name dates and location of an ancestor/relative, and a self-A that is basically 'I found this out about Doris' without explaining how, or how it might benefit somebody else.
Comment: It's a pity, because with a little work it could be a decent question - generalised to ask what sources are available to understand how young women of that class/place/time spent their leisure hours, and then answered with a detailed example about Doris Sparrell and how the information was found.
Answer: The ideal source for information on how a particular person spent her time at a particular time and place will be her diary -- an original record made by the participant immediately after the event.
Sadly, few of us have the luxury of access to such a source and are forced to rely upon accounts of what was "typical" of the community. A local newspaper will contain reports of the activities undertaken by young people in the area and may even include references to individual names. Do not overlook advertisements as excellent indicators of what was happening in the area.
Published histories of the town or county frequently include "colour" by using extracts from those same newspapers or other contemporary documents to illustrate the broader trends in employment, education and recreation across time.
Of course, whether a particular individual took part in those activities depends upon the extent to which she was "typical" of her place and time. The enormous variations with location and time are overlain with socio-economic factors. If the person you are researching was the sole support of a widowed mother and several younger siblings in the period 1905-1913 then there is a very high probability that what she did was WORK long and hard and then for entertainment she slept. On the other hand, a young lady in a comfortable middle-class family might have read widely, played music and sang, or produced beautifully embroidered pieces of fancywork.
You have highlighted the fact to get a fully rounded picture of the life of an ancestor we need to collect a wide range of information across several dimensions of his or her life. Any single, simple answer is almost certainly inadequate or even misleading.
Answer: The following was found in an article in the Cambridge Sentinel (Volume 6, Number 31, 19 June 1909) that is available online thru the Cambridge Public library:

Tuesday evening a large sized audience attended the entertainment in
  the vestry of the Universalist church, given by the young ladies of
  the Y. P. C. U.
  …
  The little comedy, "No Men Wanted," was liberally
  interspersed with jokes and caused much laughter. The characters were
  Isabel Granger, Doris Sparrell; Elizabeth Rawley, Elfreda Veazie;
  maid, Corrinne Thies. Masters Raymond and Frankie Thies made a decided
  hit with their songs, as did also Miss Mabel Butler, who played the
  overture and officiated at the piano.

The newspaper shows the play as 'No Meu Wanted' but I believe it was actually "No Men Wanted",  A Sketch in One Act,  published in Baker's Edition of Plays in 1903.
Comment: Hi Duncan, I've down voted this answer, because it's really not an answer at all. It's a quote, just sitting there. You haven't even said "They participated in theatre projects." I agree with everyone that this question AND ANSWER could be so much better if you filled it out more. Tell us, what is her family's income like, what is her neighbourhood like, what are the major political issues going on as she hits teen years? This will flesh out the characteristics that affect her decisions for leisure.


Ways to isolate DC power source

Question: I need to isolate my circuit from the power source of 5V dc. Since this is for medical use, and the device is powered by USB, the isolation needs to be at least 4kVrms, 5mm clearance, 8mm creapage distance. I searched for isolated DC-DC converters couldn't find any with those ratings and in small size. The remaining option I have, seems to be using 2 dc-dc converters in series. But that will be very inefficient and large in size. What could be the other ways to achieve this isolation?
Comment: Current requirements?
Comment: @MattYoung The device requires very low current requirements ~ 10 mA.
Answer: I don't agree that you need to be an expert in medical device design to accomplish this task, but you do need to do some research.

Get a copy of IEC60601 and study it. There is a lot more to this type of project than just isolating the patient from the computer.
You're going to need to treat your USB connection as if it were mains. Find a transformer that was designed to IEC60601, and matching driver. Design from there.
Find a testing house that does IEC60601 compliance testing. They will test your device to the standards, and give you a 180+ page report.
Go through the report, fix the problems, and test again.

Do not skimp on compliance testing. It will save your bacon.
Comment: Hi, I have already gone through 60601. The values of 4kVrms, 8mm distance, I got from there and this is for working voltage of 250V (because of USB). I tried seaching for the suitable DC-DC converters in Farnell, Digikey but couldn't find a suitable one. Limited board space and the small current requirements are the main trouble. Otherwise I could use two converters to achieve the requirements. I am just looking for other alternatives now. One could be to use a transformer with a driver such as MAX845. But I have same problem finding medically approved small size transformer.
Comment: Don't use the MAX845. It's getting long in the tooth and sometimes hard to source. Take a look at Wurth Elektronic transformers.
Comment: While in *theory* someone can learn all that is required to create a medical device starting from a basic level of electronics, this is really not a good idea.  Knowing the regulations and compliance testing is only part of it.  In the US, the paperwork that goes with filing a 510k is not trivial, and there are probably similar issues in other juridictions.  You need to have someone on board that has been thru these processes before, else this will be a *very* expensive development effort with lots of delays.  Don't skimp on expertise, it will save your bacon.
Answer: No, Olin Lathrop is absolutely correct. I work for a FDA compliant medical device manufacturer, (also a pharmaceutical manufacturer). Designing your device is the least of your worries.  Outside the scope of massproducing said device. If you still decide to build this "medical device" make sure you contact your business's insurance underwriter. if the failure of your device directly or indirectly affects any patient or provider, the legal actions sought against your company will never be worth what you got paid to make the device. And I agree, From an EE perspective, you either are trolling us.. or you are in over your head.
Comment: This is absurd. You can't just design a medical device and have it go into production. It will never see a patient without first passing rigorous 3rd party testing and qualifications. He's asking how to start designing this. If he can't do it properly it will fail quality and never see use. That shouldn't mean we have to discourage him trying with snarky remarks. Medical device design starts somewhere.
Answer: If you have to ask this kind of basic question about a medical device here, the answer is: You don't.  You get someone that knows what they are doing to do this.  Then you can learn from what they do and maybe next time you're ready to do it yourself, but not this time.
This is not a do-it-yourself or learn-on-the-job project.
Comment: The best way to avoid injury while skiing is not to ski...
Comment: -1 Share your knowledge and if necessary add dire warnings and disclaimers.
Comment: -1: Not an answer.
Comment: @Armandas: Read carefully.  Yes it is, just not one you and the OP want to hear.

Ways to isolate DC power source


training and validation accuracy increasing - XGBoost

Question: I am running 10-folds 10 repeats cross validation over my data. I am using XGBoost Classifier with hyper parameter tuning. The learning curve looks as follows:

However, both the training and validation accuracy are increasing, am I overfitting ?
Comment: Not necessarily, though at some point you want to see the plateau. But how exactly are you doing the cross validation?
Comment: @NULL Basically my data has the size of 620. I split the data into 80% training and 20% training. I do cross validation with hyper parameter tuning on the 80% training data using stratified kfold cross validation to ensure equal class distribution (Specifically, 10 folds with 10 repeats [link](https://scikit-learn.org/stable/modules/generated/sklearn.model_selection.RepeatedStratifiedKFold.html)). After that, I choose the hyper parameters that gave up the best accuracy in cv.
Comment: I'm not really following. You're training and testing accuracy is improving as you train the model on more samples, this is what you would expect.
Comment: @MatthewDrury I thought I was overfitting, so this should be the normal behavior of any "good fit" model ? I am neither underfitting nor overfitting, right ?
Answer: I'm assuming you are performing nested cross validation often called m-by-n fold validation where m is say 5 and n is 10.
There are two important points here that I want you to note before answering your question:

Your validation set is the one used for parameter tuning (inner loop in nested CV). Your test set (actual unseen data) is the one that is not used/seen in anyway during training/tuning your model (here the outer loop of CV). So you test your best model m times and get a m-component vector of performance (each value is from one round of test) and then say average it to get the final performance.
You need to make sure you have enough samples in your validation and test set. If you don't have enough samples in your validation, you will get optimistic performance results and that would affect your model selection (tuning). If you have small number of test samples, that's bad, because then you are conclusion is not that reliable.

Okay, now that you know these, the figure looks fine because all it is showing is that the more samples the model see, the better its performance is on unseen data. I'm assuming validation here is the actual unseen data (test set).
But there is a catch, on x-axis you are showing the training set size, what is your validation set size? And again is this the test set you call validation or the parameter tuning set (the actual validation set)? That's very important. Is it getting smaller and smaller? I assume so, then yeah, that's not ideal, particularly if you have an unbalanced dataset.
So be very careful with your performance evaluation metric. Read about different methods available and choose one that makes most sense, I'm afraid accuracy is often not the best choice.


Modal logic and set theory question

Question: So if n is a member of the set of natural numbers, such that n is greater than 1 and lesser than 3, then n=2 necessarily?
Comment: What does this have to do with philosophy?
Comment: @Keelan If the question is (as the inclusion of "necessarily" suggests) about the modal status of mathematical claims, then it is very much on topic. The question of whether or not we must take all mathematical truths to be necessarily true (and what sort of modality is at issue) falls well within the purview of, and receives attention within, the philosophy of mathematics (and, philosophy of modality).
Comment: That being said, the question could definitely use a bit more fleshing out (*insert @JosephWeismann template request for clarification*).
Comment: @Kantian: that is no clarification, it's merely writing the same proposition in another written language. What in your philosophical investigations has motivated you to ask this question? What are you hoping to clarify --- merely this question, or some broader principle?
Comment: In which system? If you specify the set of axioms, you may get a proof.
Comment: To "clarify" here's the symbolic form (n∈ℕ|1□(n=2)
Answer: This is more on the lines of commentary on your question, rather than an answer.
If one uses the usual natural numbers then yes. But are there other systems of natural numbers?

There are non-standard integers: The integers are axiomatically defined by the Peano Axioms. We actually obtain them in a model. The question here is are all such models isomorphic - that is categorial. If we use second-order logic, they are; if first-order then not. But the initial segment of any non-standard integer model is isomorphic to the usual ones. So this doesn't work.
We could use topos rather than semantics for the PA axioms, this means the axioms are interpreted in a topos. This means that the topos must have a Natural Number Object. Whether there is a topos, within which the condition you specify fails, is for me, an open question.
Answer: Yes, if "natural numbers" is the commonly agreed on term from arithmetic.  When there is no other possibility, there can only be the distinct, unqualified answer.

Modal logic and set theory question


I don't understand how energy is determined as "potential energy"

Question: I've only formally learned as far as college level physics 1, but I don't understand potential energy. I get it in the equations, such as when the ball is just about to drop over the ramp its filled with potential energy, but what determines that it IS potential. The ball isn't moving yet, it's on a flat surface, and honestly probably won't fall unless its pushed. So how does a ball atop a ramp have potential energy, but one sitting flat on the ground doesn't? And since the entire earth is moving, how does it ever have 0 kinetic energy? Is this just one of those arbitrary things that's taught to get a grasp on concepts or is it used eternally through classical physics to the level of practiced physicists?
Comment: Physics determines how the potential energy of a system can be calculated so that the energy might be stored or put to use.
Answer: At a very high level, potential energy is the energy that's available to cause motion, but it isn't energy that is actually associated with motion (i.e. kinetic energy). Potential energy can only convert into kinetic energy (i.e. motion) when there is a gradient of potential energy, and the object will want to move from high potential energy to low potential energy -- in the process, it will convert the change in potential energy into kinetic energy.
So with that high level overview, let's consider your specific examples. When a ball is at the top of a ramp, it has some amount of potential energy. If the ball were sitting at the bottom of the ramp, it would have some other, lower amount of potential energy. And so there is a gradient of potential energy -- it is high at the top, low at the bottom, and so the ball moves from high to low (rolls down the ramp). And as it moves down the ramp, little by little, it's potential energy decreases and converts to kinetic energy.
The ball sitting on a flat ground has no gradients in potential energy. If it moves left or right, it still has the same amount of potential energy it did before. So there's no gradient, and no conversion of potential to kinetic energy.
Now, an important and subtle point here -- gradients of potential energy are what matter. Not the "total amount" of it. So, for convenience, we often take the bottom of the system in your examples to have zero potential energy. But we can add any arbitrary number to the whole field and the gradient is the same. Meaning, if the bottom of the ramp is $P = 0$ and the top is $P = 10$, then the ball behaves the exact same as if we said the bottom is $P = 1000$ and the top is $P = 1010$. Or -1000 and -990.
To your next question, kinetic energy and why it is zero if the Earth is still moving. First, it's important to recognize than when we work example problems, we usually work on an isolated system. Meaning, we ignore things that have a minimal impact on our problem. So, for a ball rolling down a ramp, the spin of the Earth and the movement of Earth through space don't matter really, for a small enough ball and ramp, so we don't have to worry about it.
But another, more subtle point, is that kinetic energy depends on your reference frame. So, a ball on a ramp sitting motionless on the floor has zero kinetic energy in the reference frame of the floor. Even if that floor is on a high speed train. But, somebody outside the train would see the ball and ramp go past them very quickly and so in their view, the ball has a lot of kinetic energy.
At the end of the day, the specific values of energy are rarely important. It's always the gradients of energy (in either time or space) that are really important, and those are preserved when we add constants to the fields (to use other words, for inertial motion).
Comment: Ok, so PE and KE are system relative, not a universal value. I'm very bad at abstracts and that was never explained to me, I'm assuming because they figured it was implied
Comment: @TheBasementNerd I recall it not being made terribly clear to me when I was learning classical mechanics either at the high school/AP/college intro level. It's usually just kind of implied when they tell you to calculate potential energy as $g \Delta h$ -- implicit in that is that potential energy is 0 at the bottom of whatever you're looking at.
Answer: These are actually more than one question.
First for the potential energy: Generally when speaking about potential energy (and therefore also total energy), only energy-differences are meaningful. So when you say that a ball lying on the floor has no potential energy, this means that you define where the zero is. In this example the "nicest" definition might be defining the zero to be at the center of the earth, but the you would have to calculate with very big numbers, which is not so nice. So independent of where you define the zero to be, the physics remain the same. With the zero being defined at your floor, a hole in your floor must have negative potential energy, which sounds weird, but isn't forbidden or anything.
Next kinetic energy: Kinetic energy depends on the frame of reference. If this doesn't mean anything to you, you should read up on this concept. In your frame of reference a ball lying on the floor doesn't have kinetic energy, but in the frame of reference of the sun it does have a lot of it. The amazing thing is, that as long as you are in an so-called inertial frame which isn't being accelerated with respect to other inertial frames (kinda bad definition, but stick with me for the moment), the physics remain the same. Technically your frame of reference is NOT an inertial frame, because you are being accelerated by the earth spinning and so on (see Coriolis "force" / virtual forces). But for most experiments you can approximate it as being inertial because the effect of the earth spinning is way smaller than most things you can measure.
Comment: So its just that PE and KE are based in the frame of reference and system, not as universal or measurable values that anyone can get the same reading of. They're used to measure stuff in a system, not determine a value about an object like mass or electrical conductivity
Comment: Only energy differences are physical (and to compare measurements you have to take them in the same frame or transform them to the same frame). This is similar to voltage which is always compared to the ground, while the total electrical potential is also not physical. This concept is called gauge freedom (there is a lot more to it, but this is the basics).


Getting .xap file of an installed app

Question: I wanted to get the install file (.xap file) for a certain purpose from an installed app on my phone. My phone is Nokia Lumis 625 running Windows 10.0.14393.693 and is interop-unlocked. Any way to get this done on my phone? Thanks.
Answer: For an interop-unlocked W10M device, the app you want is App Data Manager, available on the XDA-Developers forum.
Install (sideload) and launch it, go into Apps (may take a while to build the index), select the app you want to extract, and hit "Create archive from installation path". Select the location to save the created file.
Note that you may need to modify the contents of the archive a little bit (and change the extension to .xap or .appx, as appropriate) to get it back into a sideloadable state, if that's what you're going for. If you just want a look at the app's binaries or data files, though, that should be all you need to do.
Comment: It seems that I can't get the archive to a sideloadable state by changing the extension to any of .xap, .appx or .appxbundle. What modification would I need inside the .zip file to make it sideloadable? (While deploying using the wp8.1 sdk application deployment, I get the error of app manifest file missing; this info may help)
Comment: @SagnikPal: Been a long time since I tried that, though I'm sure the instructions are online somewhere. One of the manifest files gets renamed during installation, which is probably causing the error you see; you'll have to in-rename it. You may also need to remove a signature/DRM file, if it's a store app. I recommend comparing the archive contents and layout against a homebrew/dev package and seeing if there's anything obviously missing / extra / different.
Comment: @SagnikPal
Has anybody of you figured out how to re-create a .XAP from an deployed layout or not?
I would need this information as well urgently, since there is no way to install apps from MS Store on WP8

Getting .xap file of an installed app


Can I use docker compose to run application container and its dependencies on google cloud or digital ocean, the same as locally?

Question: I have a spring boot application, angular front end app, couchbase, and redis. They are all defined in a docker compose yaml file. I can make the application up and running locally. Is there a way to use docker compose tools/commands to do the same in google cloud or digital ocean?
Answer: If you don't want/need platform-specific integrations and transforming your services to a cloud I guess GCP Compute Engine is for you -- it's like a usual virtual machine that you can start, SSH to it and have all privileges to install and run software the same way you did it on your dev machine.
Answer: If you want to avoid Kubernetes, then the simplest of the GCP options for a docker container is probably their Container-optimized VM images?
That lets you put the parameters to your docker run ... command in the VM config as per https://cloud.google.com/compute/docs/containers/deploying-containers#gcloud
This assumes you are able to publish your image to a repo that is accessible to your GCP compute VMs.
Answer: I don't know about Google Cloud but yes on Digital Ocean, I do it all the time! Just make sure you have Docker Compose installed on the droplet and then run the commands the same as you do locally.
Comment: Why was this downvoted.  I'm asking as it fits my use case perfectly so keen to understand why it's not considered a good answer.
Comment: @Auspice I would like to know that myself! I think it's a perfectly valid answer, it could have just been someone being spiteful. I recently started a new job and my new company also uses docker-compose on their servers, although it's not Digital Ocean.
Comment: Thanks Jacob (sorry couldn't insert your @name.  Actually since I posted my comment I have made progress doing exactly this.  In fact on Digital Ocean there is a specific Droplet Template which comes with Docker ready installed which made it very easy, so not only is this a valid answer, but it's the one I used.
Comment: That's great @Auspice glad I was able to help! I've also updated my name so it should be taggable now, thanks for letting me know!


Movie about a cave dwelling monster

Question: Does anyone remember a movie, I think from the 50's or 60's, revolving around a hairy creature that was capturing people and bringing them to a cave. He would then cocoon them to a cave wall and feast on their bodily fluids at his leisure, just barely keeping them alive.
Comment: What language?  Black and white, or color?  Where/when did you see it?
Comment: I think it was black and white but not certain. It would have been on cable , as a repeat , quite a few years ago.
Answer: Another possibility is Beast from Haunted Cave from 1959.  Some crooks plant explosives in a cave as a distraction for a gold robbery.  The explosion releases a spider monster.  It captures people, and spins a web cocooning them to the cave wall.  Just as you describe, the creature doesn't immediately kill them.  It keeps them alive, and feeds off of them slowly.  The full movie is on youtube.  This link will take you directly to footage of someone trying to rescue the cocooned victims.
The B&W film takes place in the winter, with scenes of snow and skiing and a remote cabin, if any of that jogs your memory.
The movie isn't well regarded, but I rather like it.  It was Hellman's first film and made cheaply for Roger Coreman's AIP.  Monte Hellman is a favorite director of mine who went on to make some critically acclaimed non-genre films in the 1960's, most notably Two Lane Blacktop, The Shooting, and Cockfighter.
Answer: This might be The Spider (original title, Earth vs. the Spider), from 1958.

When a man doesn't come home one night his daughter and her boyfriend go out searching and encounter a giant spider in a cave near the man's wrecked car. Coming back with the Sheriff, the spider is seemingly killed by DDT spraying, and the body then hauled for storage in the high school gymnasium. However, a loud dose of rock music by a teenage garage band revives the arachnid and sends it rampaging through the town.
Comment: That is an amazingly B movie sounding B movie.

Movie about a cave dwelling monster


Transfer of progress onto my PS4 from friend's PS4

Question: I played Call of Duty Advanced Warfare on my friend's PS4 and logged into my PSN account. I have now got a PS4 and the game myself and was trying to figure out how to get the progress I have achieved on my friend's PS4 onto mine?
Answer: If you're talking about progress in the single player campaign, game saves are stored locally on the console. To transfer them from your friend's PS4, plug in a USB-Stick or external hard drive and in the main console menu go to

Settings > Application Saved Data Management > Saved Data in System Storage > Copy to USB Storage Device

There, search for your Advanced Warfare save files and copy them to your storage device. Then plug it in to the other console and go to

Settings > Application Saved Data Management > Saved Data on USB Storage Device > Copy to System Storage

and copy the files onto your own console. It's important that you are signed in with your own PSN account when you copy the files from your friend's PS4, because according to the PS4 User's Guide you need to have signed in at least once with the same account you used when you copied the saved data.
If you have an active Playstation Plus subscription, you can also upload your save data to your cloud storage and download it on the other console. To do so, follow the same steps as above, but instead of copying onto a USB device, select "Upload to Online Storage" on your friend's console and "Saved Data in Online Storage" when copying the data to the other one.
If you're talking about online progress: Your multiplayer progress in Advanced Warfare is stored on game servers online and are automatically associated with your PSN account, so you don't need to transfer save data for it manually.
Comment: hi, i am wondering if I could tranfer to different accounts,is it possible?


Is it okay to cite a paper from arXiv?

Question: I have found a very good overview of a topic and I want to cite it in the introduction of my paper. The writers are very well known people in the field. Is it then okay to cite the paper that is not published and is only available in arXiv?
Answer: There is nothing wrong with citing paper, reviews, etc., which have appeared on the arxiv (and only on the arxiv). Go ahead and cite the paper.
(If your paper gets accepted at a journal, they might ask you to update in case the paper has been published in a journal in the meantime, but in the fields where the arxiv is commonly used, journals and referees will have no issues with references to the arxiv.)
Answer: I recommend using "peer-reviewed" rather than "published" for a paper on arXiv (or otherwise on the internet), because such papers are literally published, in the sense of being publicly available (even more than those behind pay-walls). The distinction that may matter is peer-reviewed (or not).
The question of whether peer-reviewed papers are more reliable than arXiv papers by well-known, reliable, experts is a separate question.
But my point, somewhat tangential to the literal question, is that "things on the internet" are published. They are cite-able. The question of their relative reliability is subtler. Peer review is no guarantee of correctness...
So if you use something from arXiv, cite it. These days, in math, for example, everything appears on arXiv or on peoples' homepages a long time before it is "peer-reviewed", and the latter may be "never"... simply because in some peoples' perceptions that "peer review" does not add value, but is fairly expensive in time and trouble.
Answer: If you use the work and you found it only on arXiv then you must cite it there (or elsewhere) to avoid plagiarism.
But, the publication process takes a long time. I suggest that you cite what you have found, especially if the paper isn't formally published yet and watch for it to appear. If it is ever going to appear it may well show up before your paper is finalized.
But failure to cite is a serious matter. But a more permanent citation is preferred over arXiv. You don't need to wait for it to be finalized to cite it.
Comment: @user151413, it was just a general statement about avoiding plagiarism intended to make it as clear as possible. _Not_ citing it is not an option here. I just made it clear why that is the case. Sorry you were offended.
Comment: Your answer seems to suggest that the OP wants to use the results but not cite them. I can no-where see that in the question.
Answer: You can cite everything that you want, including arXiv contributions. However, you might want to look for alternatives. In case of review/overview articles you often will be able to find some and use them instead without risking plagiarism. In academia, peer review is the standard way to make sure a paper meets the necessary quality criteria, so peer reviewed publications are more trusted sources.

Is it okay to cite a paper from arXiv?


Website Testing with multiple languages and multiple domains

Question: How do you go about testing a site before deployment across multiple languages(English, German and Spanish) and multiple domains(.in, .fr, .de etc). If an automatic framework already exists in QTP for testing the site on one domain and in one language can it be easily extended across all other domains and languages ?
Or is there any other more convenient option or tool available to do the same.
Answer: This is a built in capability in QTP, object repository parametrization.
You can parametrize the language specific part of the description of test objects in the object repository.


The degree of extension

Question: I have two extensions and must find their degrees: a) $\mathbb{C}:\mathbb{Q}$; b) $\mathbb{R\{5}\}:\mathbb{R}$. I know that a) degree is infinity and b) is 1. It for me seems trivial, but how it explain in mathematical way? Maybe somebody knew simple definition of degree of extension?
Comment: The degree of a field extension is its dimension as a vector space over the subfield; $\pi\in\mathbb C$ is transcendental over $\mathbb Q$, and $5\in\mathbb R$
Answer: The degree of an extension $E/F$ is by definition the dimension of $E$ as a vector space over $F$. For example, if we look at $\mathbb{C}/\mathbb{Q}$ then the degree is obviously infinite. Why? Well, suppose $\mathbb{C}$ is a finite dimensional vector space over $\mathbb{Q}$. Then there is a finite set $\{z_1,...,z_n\}\subseteq\mathbb{C}$ such that $\mathbb{C}=\{q_1z_1+q_2z_2+...+q_nz_n: q_1,q_2,...,q_n\in\mathbb{Q}\}$. But that means $\mathbb{C}$ is countable which is of course a contradiction.

The degree of extension


Ford Mondeo mk3 Radio 6006e ISO adaptor

Question: I need to replace a radio-cd 6006e and I need the ISO adaptor. I don't know what is it or where to find that information.

Thanks,
Answer: Finally I did it with the following adaptor.

There are different series with different connectors, the one that pointed @CharlieRB was for an other one.
This fits on 6006 and 6000 eon radios but... losing the steering wheel control.
If you want to continue using it, you need an adaptor interface wich cost more than a cheap radio (avoid poor quality interfaces, they can produce extrage behaviour in the car electrical system).
Take note that the orange and black sockets are connected into the green radio socket, one on top of the other. The radio antenna have their adaptor too.
Good luck,
Answer: Suppliers vary depending the part of the world you live in. What you are looking for is a wire harness adapter that will allow you to connect your aftermarket radio to the factory wire harness. It essentially plugs in where you unplugged from the radio.
Do an Internet search for "ford mondeo iso adapter". It will look something like this.

Some are complete, while some require you to splice the wires from your new radio harness to this adapter.

Ford Mondeo mk3 Radio 6006e ISO adaptor


How to save terminal output to file?

Question: There are, of course, many ways to save terminal output to a file. However, all the ones I know of require you execute them before the commands who's output you want to save. Is there a command for saving terminal output that's already in the terminal?
Comment: Not really, unless your terminal emulator allows you save the contents of its history buffer.  Anything that has already been sent to stdout or stderr and displayed on the terminal is in the past, and isn't something that's really able to be "seen" by the shell anymore.
Comment: I've seen Luke Smith's video on Youtube explaining his version of `simple terminal` that allows him to copy the output of previous commands without re-running the command. But I can't remember which one.
Answer: This can be dependent on the terminal you're using and if you're using a GUI at all. if you are then the easiest and most common way would be to

triple-click the last line
press shifthome or
press shiftclick first line
Then either right click copy or CtrlShiftc or right click the top bar of your terminal click Edit-copy (can also select all from there) and paste

Command line tools for this would be xsel and yank
But again this is depending on your distro.
If you could provide some more info I could be more specific with a solution
Answer: You may want to change your problem by using a terminal multiplexer like screen or tmux.
With tmux you can save a selected text from the buffer with the following key command.

Ctrl+B, [
move to the start of the selection you want to save
Space
move to the end of selection
Enter

You can then paste the content of the selection with Ctrl+B,], in a text editor for example.
screen has the Ctrl+A,H to copy the current content of the window in a file named hardcopy.<n>
Answer: On FreeBSD there's
script

To record terminal sessions. I'm sure it's also available on Linux.

How to save terminal output to file?