Why the interval equation have a minus sign?

Question: its a famous equation $$\Delta s^2=-(c\Delta t)^2+(\Delta x)^2$$
but why do we put the minus sign i heard its there because of that space is ruled by non-Euclidean geometry rules and if that was true what is the difference between a Euclidean and non-Euclidean geometry?
Comment: Related: https://physics.stackexchange.com/q/229864/2451 and links therein.
Answer: [I will work in natural units where $c=1$. I will, for the most part, consider $4$ coordinates in a coordinate frame. The coordinates of an event would be $x^\mu$ where $\mu$ runs from $0$ to $3$. $x^0$ is the time coordinate and the rest are the space coordinates. I will use Einstein summation convention throughout the treatment.]
The reasoning that the interval is $-\Delta t^2 + \Delta x^2$ because the spacetime is ruled by a non-Euclidean geometry is wrong. It is actually the other way around. Since the physical arguments dictate that the interval must have the signs that they have, we conclude that the spacetime actually has a non-Euclidean geometry.
The physical reasoning behind the signs can be presented something like this: What we want to construct by a quantity called the interval is a frame-invariant measure of the separation between events in the spacetime. How would we know whether a given quantity, expressed in terms of the coordinate measures $\Delta x^\mu$ is a frame invariant quantity or not? By expressing the quantity in terms of the coordinate measures of a different frame $\Delta x'^\nu$ and then expressing the primed quantities in the terms of the unprimed quantities (using the appropriate transformation law) and checking whether the expression for our quantity reduces to the expression for the same in terms of the unprimed coordinates.
In other words, if the quantity that we want to check for its frame-invariance is $I$ and $I=f(\Delta x^\mu)$ then for $I$ to be frame-invariant $f(\Delta x'^\nu)=f(P(\Delta x^\mu ))$ must hold; where the function $P$ is determined by the transformation law between the primed and unprimed coordinates.
Now, Special Relativity tells us that the coordinate transformation law between two inertial coordinate frame is the Lorentz transformation law.
$$\Delta x'^{\mu}=\Lambda^{\mu}_\alpha \Delta x^\alpha$$
where $\Lambda$ is a constant matrix for the given two inertial frames with the constraint: $$\Lambda^T\eta\Lambda=\eta$$
where $\eta$ is the following $4\times 4$ matrix:
\begin{bmatrix}
   -1 & 0 & 0 & 0\\
   0 & 1 & 0 & 0 \\
  0 & 0 & 1 & 0 \\
   0 & 0 & 0 & 1
\end{bmatrix}
Now, if I consider a quantity $\eta_{\mu\nu}\Delta x^\mu\Delta x^\nu$ then it can be shown that it is frame invariant in the following manner:
$$\eta_{\alpha\beta}\Delta x'^\alpha \Delta x'^\beta=\eta_{\alpha\beta}\Lambda^\alpha_\mu\Delta x^\mu \Lambda^\beta_\nu\Delta x^\nu=(\Lambda^\alpha_\mu\eta_{\alpha\beta}\Lambda^\beta_\nu)\Delta x^\mu \Delta x^\nu = \eta_{\mu\nu} \Delta x^\mu\Delta x^\nu$$
As you can easily see, $\eta_{\mu\nu}\Delta x^\mu\Delta x^\nu$ is simply $-\Delta t^2 + \Delta x_1^2 + \Delta x_2^2 + \Delta x_3^2$. Thus, $-\Delta t^2 + \Delta x_1^2 + \Delta x_2^2 + \Delta x_3^2$ is the invariant interval in Special Relativity.
Answer: Go and browse the related questions for the math. I'll still provide a handwaving illustration, hopefully it helps in understanding.
The difference between Euclidean and Minkowskian metric is precisely that minus. In general relativity, the metric gets more complicated, because the way how $\Delta t$ and $\Delta x$ are composed into the spacetime interval is where gravity comes in.
You will hear a lot of times, that the minus distinguishes the time coordinate from the spatial coordinates. How it does that, is the fact that in Minkowski metric, the space-time splits into two parts relative to a chosen origin: the time-like part (which can be related causally to your current point) and space-like (what cannot possibly influence the origin). This gives time its direction by restricting it from "rotating by 90 degrees" if rotations still worked the way they do in Euclidean space.
What would have been rotation, becomes boost - changing velocity of the reference frame, and gives you the hard limit of the speed of light.
This can be very well compared to the distinction between Elliptic differential equations: for instance, for solving the shape of soap on a wire frame, you need to solve it all at once: the boundary conditions influence everything and every point influences every other point, the solution needs to be self-consistent. Just because the equation has a plus: $\frac{d^2 f}{dx^2}+\frac{d^2 f}{dy^2}=0$.
If you take a wave equation, (which is a hyperbolic differential equation)
$\frac{d^2 f}{dx^2}-\frac{d^2 f}{dt^2}=0$
you can propagate the solution from the previous time: you need an initial condition and don't need to know anything about the future. All it takes is a little minus.
Compare to a circle ($x^2+y^2=1$) and hyperbola ($x^2-y^2=1$), one of which you can rotate properly, but the other has two asymptotes (which correspond to the speed of light in the light-cone defined by the zero space-time interval). In other words: a hyperbola in space-time is what defines the set of equal time-space distance (compare to the circle which defines points of equal distance in euclidean space).
Answer: The question raised was "Why" the interval equation has a negative sign. The answer that this is so because of Minkowski space lets the "why" in the air: "Why" Minkowski space?
A more in-deep answer could be that this minus sign is intrinsically related to the possibility of movement:
That our Universe is 4-dimensional is obvious from Albert Einstein's mass-energy equivalence $ E = mc^2 $ and the relativistic energy invariant $ E^2/c^2 - p⃗^2 = m_0^2 c^2 $. Measuring distance in light-seconds instead of meters, the speed-of-light c becomes =1, and we obtain the simple formula:
$ E^2 = m^2 = m_0^2 + p⃗^2 = m_0^2 + p_1^2 + p_2^2 + p_3^2 $
From this formula it is obvious that the rest mass $m_0$ is the fourth component of the momentum (or movement) vector, and that the energy or mass is the total length (absolute value) of the momentum vector.
A fundamental (empirical) law of physics stats that in a closed physical system energy, i.e. the above sum of four squares, is maintained during movement and during physical processes.
There is a mathematical identity, stating that a sum of four squares can always be written as the product of two sums of each four squares. (This holds as well for sums of two squares, and for sums of eight squares, but for nothing else).
Applying this to our formula for $E^2$, we can write:
$ (m_0^2 + p_1^2 + p_2^2 + p_3^2) =  (r_0^2 + r_1^2 + r_2^2 + r_3^2)(M_0^2 + P_1^2 + P_2^2 + P_3^2) $
wherein the components (proof by algebraic evaluation) are:
$ m_0 = (r_0M_0 - r_1P_1 - r_2P_2 - r_3P_3) $
$ p_1 = (r_0P_1 + r_1M_0 + r_2P_3 - r_3P_2) $
$ p_2 = (r_0P_2 - r_1P_3 + r_2M_0 + r_3P_1) $
$ p_3 = (r_0P_3 + r_1P_2 - r_2P_1 + r_3M_0) $
Now, let's assume that these sums of each four squares are metric products (scalar products) of vectors with themselves, noteworthy the vectors
$ P⃗ = (M_0, P_1, P_2, P_3) $
$ R⃗ = (r_0, r_1, r_2, r_3) $ and
$ p⃗ = (m_0, p_1, p_2, p_3) $
Then we can rewrite the formula for $E^2$ as
$ (p⃗)^2 = (R⃗ * P⃗)^2 $
wherein the multiplication $R⃗ * P⃗$ is defined as given above.
Let's now assume that $ R⃗ $ is a physical process operator which changes $ P⃗ $ into $ p⃗ $, and that $ R⃗ $ does not change the total energy $E$ of the system, i.e. $ (r_0^2 + r_1^2 + r_2^2 + r_3^2 ) = 1 $.
Given the bilinearity of the product $R⃗ * P⃗$, the vector
$ P⃗ = P⃗1 + P⃗2 + ...$ can be a sum of vectors, representing a complex physical system.
Also the vector $ p⃗ = p⃗1 + p⃗2 + ...$ can be a sum of vectors,
representing another complex physical system.
The formula:
$ p⃗ = (p⃗1 + p⃗2 + ...)  =  R⃗ * (P⃗1 + P⃗2 + ...) = R⃗  * P ⃗ $
describes now a general movement of a physical system $ P⃗ = (P⃗1 + P⃗2 + ...) $ into a physical system $ p⃗ = (p⃗1 + p⃗2 + ...) $ under the influence of a physical process operator $ R⃗ $, wherein the total energy $E$ is conserved.
Note that the energy contained in physical system $ P⃗ $ can be transferred, shared, or cumulated in the systems  $ p⃗1 , p⃗2 , ... $ under the effect of operator $ R⃗ $.
Note as well that the formula for
$ m_0 = (r_0M_0 - r_1P_1 - r_2P_2 - r_3P_3) $
shows the metric signature (+,-,-,-) of Minkowsky space.
Conservation of energy and movement is possible in 4 dimensional space because of the existence of the 4-squares identity, and movement necessarily follows a negative (hyperbolic) metrics, by the mathematical reasons outlined.
The corresponding metric differential equation in 4-space is
$ ( (1/c)^2  (∂^2/(∂t^2) - (∂^2/∂x_1^2) - (∂^2/∂x_2^2) - (∂^2/∂x_3^2) )A = μ_0 J  $
with
$ A = (φ/c,(A_1,A_2,A_3 )) $  the 4-potential composed of electrostatic and vector potential,
and
$ J = (ρc,(J_1,J_2,J_3 )) $ the 4-current density composed of charge and currents.
This equation is the 4-dimensional form of Maxwells Equations.
Due to its negative metrics, the solutions of this differential equation are wave functions. In other words, movement always and necessarily takes the form of a wave.
There are also stationary solutions to this differential equation:
$ ((1/c^2)  (∂^2/∂t^2) - (∂^2/∂x_1^2) - (∂^2/∂x_2^2) - (∂^2/∂x_3^2))Ψ = λΨ  $
and they represent the massive particles and their possible compounds.
Comment: Why is the product of 2 four vectors makes another four vector introduced?
Comment: The conservation of energy claims that I can only change the system $ (m_0,(p_1,p_2,p_3)) $ into another system $ (M_0,(P_1,P_2,P_3)) $ if the latter has the same total energy $ E $. Given that $ E^2 = m_0^2 + p_1^2 + p_2^2 + p_3^2 $ is a four-square, which can always be written as a product of two four-squares according to Euler's formula, there exist indeed unitary double-rotation operators which transform $ (m_0,(p_1,p_2,p_3)) $ into $ (M_0,(P_1,P_2,P_3)) $. This is the reason for the existence of physical processes.


How to delete my name and initials from the title bar of Microsoft Word

Question: I'm using Microsoft Word with Office 365. In order to maintain anonymity, how do I delete my name from the blue title bar at the top right of the Word window, as well as the pink circle next to it that has my initials in the middle of it. Is this possible?
Comment: Who do you believe will see your name in the title bar, and how do you think they will see it? Specifically, are you wanting to remove that because you believe that, when you email the document to someone else, they will be able to see your name when they open it? (If so, do you have an experience in which you opened a document that another O365 user sent to you and saw _their_ user information in the same place, complete with a pink circle with their initials in it?)
Comment: @user128216 It does matter, because the question of removing it from their _own_ computer is much different from the question of removing it from _someone else's_ computer. At least one answer to this question interprets it as the latter.
Comment: @theh Perhaps he's recording a screencast that he wants to post to YouTube under a pseudonym? Who cares why he wants to do it?—it's not relevant.
Comment: You need to remove your name from the Office Account and substitute with an alias if you are allowed to
Comment: @TheHansinator I have the same question. I do Word tutorials via screencast and don't want my name attached.
Comment: @user128216 if Office doesn't easily provide this functionality, there could be workarounds if we know the use-case. There are e.g. tools which can automatically blur part of your screen in a video cast (for youtube or screen sharing). But if you are afraid of somone sitting besides you in the train and them knowing your name, you could for example use a special foil, which disables people from seeing your screen when sitting besides you...
Answer: The name in the title bar indicates you are signed in to Office.
According to the article provided below, if this is Office 365, then you'll have to stay signed in to Office to use the product. That is how the licensing works. Others are reporting that you just need to login once to activate and then can log out. You're mileage may vary.
If you want to sign out:
In any Office app, go to File > Account (or Office Account in Outlook) >  Sign out.
Or, from any internet enabled computer:

From any device, go to your Microsoft account, Installs page and sign in using your Microsoft account, if prompted.
Under Devices, locate the device where you want to sign out of Office.
Select Sign out of Office.

More information can be found here:
https://support.office.com/en-us/article/sign-out-of-office-5a20dc11-47e9-4b6f-945d-478cb6d92071
Comment: "If this is Office 365, then you'll have to stay signed in to Office to use the product". I've tested this with Office 365 Business Premium and signing out doesn't affect activation on Windows or Mac. Perhaps it works differently on the Home version?
Comment: @MrEthernet I'm referring to the article I linked to. I'm pretty sure Office will deactivate after a period of time.
Comment: @MrEthernet I suspect it's because "Office 365 for Home" and "Office 365 for Business" are actually different products which share branding but not implementation. For login, I think Home products use Microsoft Account (formerly Passport and Live ID), whereas Business products use something more like a hosted Active Directory. Meanwhile for licensing, there have always been different processes for businesses to allow bulk buying, unattended installs etc, which were separate from the consumer activation process.
Comment: The article you linked to appears to only apply to Office 365 for Home, as per its sub heading "Office 365 for Home". I signed out 6+ months ago from the Office suite on both a Mac and PC and they still allow full editing, show as activated in the admin portal and from within the Account tab of the Office suite itself. They also show my admin email associated with my license, so this appears to be by design rather than a glitch. I wonder why Microsoft decided to make "Sign out" do different things in the different versions. I'll call Office 365 support and ask them why this is so.
Answer: Only you will see that; another user opening the document will see his name in that place.
It is not a part of the document, but a part of your installation.
Unless you are talking about sharing or capturing your screen, you don't need to worry about that area.
Answer: If the question is about removing personal information from a Word file,
this is how:

Open the file in Word
In the File menu, click Info
Click "Check for Issues" and then "Inspect Document"
Select the items you want the tool to check for and especially
"Document Properties and Personal Information"
Click the Inspect button
In the window that opens, click Remove All next to the items you want to remove
Save the document with this information removed.
Answer: For Office365 to be activated, it usually requires to be attached to a user who has the right licence, and by entering that user/password once, actually two independent things happen at once - 1) activating the installation with that user (and periodically checking whether the subscription is still active), 2) logging-in that same user to Office and showing the name/initials, as well as allowing to save to remote locations on Onedrive/Sharepoint etc.
The trick is to log in to activate the Office but then log out. The activation still will be bound to that account, but the login displayed on the office apps won't. The disadvantage is then that it will perhaps not allow saving files to Onedrive/Sharepoint locations with the ability of Auto-save and simultaneous editation of the same document by multiple people/devices. You can however have the Office activated to another account thant he one who is logged in, so you can log in later with some dummy account without the right O365 licence, and still have the software activated with the former account.
Comment: "The trick is to log in to activate Office but then log out". I don't have an Office 365 Home subscription to test this on but this is certainly what happens with Office 365 Business Premium.
Answer: There is a workaround...
1) simply change entry in Registry Editor
CMD >> regedit
2) then navigate to
Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\Identities\
3) change key "FriendlyName" to whatever you like
Comment: This is the correct answer. That is, if you just want your Office window title bar to stop showing the name. The "pink circle" is still there but will show the initials of the new FriendlyName you just set
Comment: the FriendlyName value gets overwritten with the default one after Office updates
Answer: 1 Run regedit

Navigate to:
Computer\HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Common\Identity\Identities
Change string value FriendlyName to: space
Export \identities and save as FriendlyNameSpace.reg

2 Make batch file containing this text:

REG IMPORT C:\Users\NN\Documents\FriendlyNameSpace.bat
Save batch file as FriendlyNameSpace.bat

3 In Task Scheduler make a task that launches FriendlyNameSpace.bat at log on:

This task should contain two identical actions:
start program: C:\Users\NN\Documents\FriendlyNameSpace.bat
start program: C:\Users\NN\Documents\FriendlyNameSpace.bat


Why was the minimum turbulence intensity that commercial airliners have to withstand increased?

Question: From 50 fps turbulence intensity at VC to 90-100 fps turbulence intensity at VC. The amended FAR design criteria was introduced in 1980 or 1981 for commercial airliners. What prompted this change?
Comment: Assuming you're referring to [FAR 25.341](https://www.law.cornell.edu/cfr/text/14/25.341)?
Comment: I believe so. I've seen the 90 fps design criteria be referenced in documents from 1980 or 1981 at the earliest. I'll try see if I can dig those up later.
Answer: The FAA made that change in 2015.
Link to historical revisions of FAA regulations, specifically 25.341 gust and turbulance loads. You can see the 90fps was not in the 1996 revision, 1984 revision, or original 1965 rule.
Link to Amendment Number: 25-141, Effective Date: 02/09/2015 https://drs.faa.gov/browse/excelExternalWindow/C86DBFEBB41D816F86257DE80072BA20.0001
If the above link breaks try https://drs.faa.gov/browse/FAR/doctypeDetails browse to 25.341 Amendments - 25-141 (02/09/2015) , 25-86 (03/11/1996) , 25-72 (08/20/1990) , Initial (02/01/1965)
Rule making explanation. Generally just aligning FAA and EASA requirments with little to no practical effect on current production aircraft.
https://www.federalregister.gov/documents/2014/12/11/2014-28938/harmonization-of-airworthiness-standards-gust-and-maneuver-load-requirements
Answer: According to the FAA, "The final PSD continuous turbulence criteria were based on those studies and were codified in Appendix G to part 25 in 1980."
This matches the timeline you suggest, but the Appendix released in 1980 does not specifically mention 90fps.  (See Amdt. 25–54, 45 FR 60173, Sept. 11, 1980.)
Bottom line: research through time over the actual nature of turbulence and analytical procedures for modeling it resulted in the rule change, as explained in sufficient detail the first reference.


Feed elements of a tuple to a function as arguments in Haskell?

Question: In my Haskell program, I want to use printf to format a list of tuples.  I can map printf over a list to print out the values one at a time like this:
mapM_ (printf "Value: %d\n") [1,2,3,4]

Value: 1
Value: 2
Value: 3
Value: 4

I want to be able to do something like this:
mapM_ (printf "Values: %d %d\n") [(1,100),(2,350),(3,600),(4,200)]

Values: 1 100
Values: 2 350
Values: 3 600
Values: 4 200

But this passes a tuple to printf, not two separate values.  How can I turn the tuple into two arguments for printf?
Comment: related http://stackoverflow.com/q/6237259/168034
Answer: Function uncurry converts a two-argument (curried) function into a function on pairs. Here's its type signature:
uncurry :: (a -> b -> c) -> (a, b) -> c

You need to use it on printf, like this:
mapM_ (uncurry $ printf "Values: %d %d\n") [(1,100),(2,350),(3,600),(4,200)]

Another solution is to use pattern matching to deconstruct the tuple, like this:
mapM_ (\(a,b) -> printf "Values: %d %d\n" a b) [(1,100),(2,350),(3,600),(4,200)]

Answer: mapM_ (\(x,y) -> printf "Value: %d %d\n" x y) [(1,100),(2,350),(3,600),(4,200)]

Answer: A type-safe alternative to Text.Printf is the formatting package. Text.Printf.printf does not ensure at compile-time that the number of formatting parameters aligns with the number of arguments and their types. Read Chris Done's article, What's wrong with printf? for examples.
An example usage:
{-# LANGUAGE OverloadedStrings #-}
import Formatting

map (uncurry $ formatToString ("Value: " % int % " " % int)) [(1,100), (2,350), ...]
map (\(x,y) -> formatToString ("Value: " % int % " " % int) x y) [(1,100), (2,350), ...]

It requires the GHC extension OverloadedStrings to function properly.
While formatToString ("Value: " % int % " " % int) has the type Int -> Int -> String, uncurrying it gives the type (Int, Int) -> String of which the input type matches the elements in the list.
The rewriting process can be broken down; assuming f = formatString ("Value: " ...),
map (\(x,y) -> f x y)  ≡  map (\(x,y) -> uncurry f (x,y))  ≡  map (uncurry f)

That is, first you uncurry f to achieve the function that accepts tuples, and then you perform a regular Eta-conversion since \(x,y) -> uncurry f (x,y) is equivalent to simply uncurry f. To print each line in the result, use mapM_:
mapM_ (putStrLn . uncurry $ formatToString ...) [(1,100), (2,350), ...]

If you run hlint YourFile.hs, these rewrites will be recommended to you.


Norms are equivalent iff dual spaces for them are the same?

Question: It is trivial that if we have a vector space $X$ and two equivalent norms on it than $X'_1$ -dual space (of continuous functionals) for the first norm and $X'_2$ are the same spaces. Is the converse true? I asked myself and doubted at first glance, yet I failed to produce any counterexample. I will appriciate any kind of help.
Comment: Hmm I think taht gives an answear to a weaker question because I required that dual spaces are the same not isomorphic, so a given functional is continuous in one norm iff in the second one.
Comment: You unnecesarry deleted your comment it was helpful in a way.
Answer: Yes.
The Hahn-Banach theorem shows that if $Y$ is a normed vector space and $y\in Y$ then $||y||_Y$ is equal to the norm of $y$ regarded as a linear functional on $Y'$.
Say $X_1$ and $X_2$ are normed spaces consisting of the same space with two different norms, and $X_1'=X_2'$. We need to show that if $||x_n||_1=1$ for $n=1,2\dots$ then $||x_n||_2$ is bounded. So we need to show that $(x_n)$ is a norm-bounded subset of $X_2''$. By the Uniform Boundedness Principle we need only show that $f(x_n)$ is bounded for every $f\in X_2'$. But this is clear because $f\in X_1'$ and $||x_n||_1$ is bounded.
Comment: For what it's worth, professor, you might use '\| \|' to render $\|\cdot\|$ which looks better than the $||\cdot||$ rendered from '|| ||'.


What does "Minimizing the variance" mean in Statistics?

Question: I am wondering what "Minimizing the variance" in Statistics mean. As far as I understand that the variance is one of the parameters of a probability distribution, for example, a normal distribution and it is a measure of how spread the data points are from the mean. However, what is there between "Minimizing the variance" and the spread of data points?
Comment: A statistical estimator is a random variable, hence is endowed with a variance of its own.
Answer: A common task in statistics is to perform parameter estimation.
The parameter estimator is a function of the sample.
For example, consider the following two parameter estimator for the mean of  normal distribution:

$\hat{\mu}_1=\frac{X_1+X_2}{2}$

$\hat{\mu}_2=X_1$

We have $Var(\hat{\mu}_1)=\frac{\sigma^2}{2}$ but $Var(\hat{\mu}_2)=\sigma^2$. Even though both are unbiased estimator of the mean, we would prefer the first estimators.
Given a few unbiased estimators, we would prefer the one with the smallest variance.


Help get rid of light spots!

Question: I need help removing the spots in this picture. How do I do that. I only have an older version of Photoshop elements.
Comment: @user287001 - LOL. Yeah I remember that. There's also another example when an elderly lady tried to restore [a painting of Jesus](https://imgur.com/6s6PmDK)
Comment: Hi. Welcome to GDSE. There's nothing you can really do to remove the one over the guys face. Half of his face is obliterated. There's nothing recoverable. Sorry. Maybe if you have another good photo of his face, you could perhaps copy and paste it on the image.
Comment: Other possibilities might include painting it back, or cloning using the other half of the face. A highly skilled edit though if you want to make it look even half decent.
Comment: But manualy redrawn face can be even better than the original; remember Whistler's Mother by Mr. Bean.
Answer: I'm not completely sure of the capabilities you have with Elements. But if there is no other image of the gentleman that you can paste in a face image, some cloning labor can work. But don't demand perfection. Here I've copied the opposite side of his face, carefully cloned in some parts of his shirt, beard, and background. His smile is just a clone trick by copying over what part of his mouth is available. Again, not perfect and possibly not accurate. But give it some careful cloning and patience.
Comment: You did a pretty decent job on a particularly difficult task.
Comment: Thanks. It was an adventure...but an honorable one. :)
Answer: It depends really on the background behind the lens flare spots.
The three dots in your picture likely will need 3 different methods.
For simple backgrounds like the shirt the "Spot healing tool" will work great.
The spot on the shoes is probably best done with the "Stamp tool". Though a colour correction layer with a mask could work too.
The head will be the most difficult one. The easiest option should be to replace it with a different face.
Comment: not to belabor the obvious, but perhaps there's another photo of the male that can be transplanted.
Comment: Yes that was the idea. Just that I would not have one of those photos of corse. And if I would have had one, I would not have bothered to do this. As where would be the fun in that?

Help get rid of light spots!


Added a new field to user profile, how do I set a value for existing users?

Question: I have added a new field to the user profile on my site (i.e. in /admin/config/people/accounts/fields), a boolean value that can be either 0 or 1. Existing users have no value. How can I easily set a value for all existing users?
Comment: The duplicate only mentions nodes but the answer is exactly the same (just replace 'node' with 'user' if you use a code solution)
Answer: Use Views Bulk Operations Module to update field values

This module augments Views by allowing bulk operations to be executed
  on the displayed rows. It does so by showing a checkbox in front of
  each node, and adding a select box containing operations that can be
  applied.

Create a view of type users
Add Bulk operations: User field and choose Modify entity values checkbox to select your boolean field


Imported bitcoin address to block-chain un-spendable

Question: I imported a bitcoin address to my block-chain wallet. The bitcoin shows as un-spendable in the wallet. The address was used previously by me and worked fine. How do i fix the problem to make the spendable.
Answer: Assuming this is a standard P2PKH/P2WPKH address, your wallet will need knowledge of the private key that was used to derive this address, in order to spend the funds locked to it.
Addresses are public info, so when you 'import an address' to a wallet, that just means you have instructed the wallet to watch that address, and report back the apparent balance of it. Anyone can do this with any address, since they are public knowledge.
In order to spend those funds, you would need to 'import a private key' to your wallet (and then ensure that your wallet derives the correct address from that key, eg, segwit vs legacy addresses). Your wallet will then be able to use this private key to create a signature on a transaction that spends those funds.


Retrieve the associated annotation from Uniprot

Question: I have a dataset that I extracted using Cytoscape and STRINGAPI
Hoz can I retreive the annotation of that network from uniprot  as it has more than 1k proteins . and doing it manually is not possible
Comment: Do you want anything specific from the annotation?
Comment: not really but it should contain the name the associated id , function maybe ...
Answer: You can upload your list of accession numbers to the batch retrieval service for the UniProt Konwledgebase, http://www.uniprot.org/uploadlists
A video tutorial for this service is available at https://www.youtube.com/watch?v=kLdgjqWoMZc
Once you have retrieved your proteins, you can click on "Columns" to customize your output and add columns, e.g. for function annotation. See also http://www.uniprot.org/help/customize or http://insideuniprot.blogspot.ch/2015_03_01_archive.html
Results can then be downloaded in tab-separated format.
If you have any additional questions, please don't hesitate to contact the UniProt helpdesk.


HTTPS posts to HTTP URL's insecure?

Question: Have to deal with some incorrectly assigned/redirected posts from an HTTPS server to HTTP URL's.  How much of a security risk are these?  Are they vulnerable to something like a man-in-the-middle attack?
Comment: What do you mean? If you're sending a POST over HTTPS, how could it suddenly transform into HTTP? Where is this HTTP transfer taking place? Do you have a form with a HTTP target URL?
Comment: BTW, a redirected `POST` ceases to be one - it'll come through as a `GET` without the form data.
Answer: <form action="http://example.com/"> would post data insecurely, even if the page the <form> is on is itself HTTPS. Data sent in this manner can be intercepted / MITMed.
For the same reasons, <form action="https://example.com/"> on a HTTP page is sent securely. However, the page the <form> is hosted on in this situation can itself be MITMed to inject malicious JavaScript or a changed action that could send the data elsewhere.
If you're working with sensitive data, both the page with the form and the form action need to be HTTPS.

HTTPS posts to HTTP URL's insecure?


Why does the Arctic warm so fast despite being so white?

Question: It may be a silly question but why does the Arctic warm so fast despite being so white ("albedo" is the word, I believe)? Isn't all that whiteness supposed to deflect all those pesky sun rays back into space (or wherever)? I heard on BBC that they use white paint in India to paint rooftops so that it's not so scorching hot inside
Comment: Do you mean "so fast" relative to the rest of the globe?
Answer: The answers so far focus on feedback effects. But to my mind, those do not explain the phenomenon on their own, because there needs to be some warming signal to feed back, if you see what I mean.
I think there are a few first-order contributors, including:

Ice is not a perfect reflector, so the sun warms the ice up a bit. Almost all reflectors absorb net radiation like this.
The atmosphere is not perfectly transparent, so some of the reflected light is scattered and trapped in the atmosphere.
The Arctic's climate is not a closed system, so for example it is subject to atmospheric conditions across the northern hemisphere and eventually the globe.
The Arctic ice-cap floats entirely on the Arctic ocean, which is not a closed system either, so it is affected by the temperature of the world ocean. (And water has a large specific heat capacity, so it's a very effective carrier of heat. This is also why rain in Greenland is such a big issue.)

And for the reasons given by other respondents, all this is made much worse by the various positive feedback effects (which include more than just surface albedo; methane trapped in permafrost is a substantial problem).
Comment: I don't know the relative sizes of these contributing factors. But you're right, they're not in order of importance -- I was thinking more 'near field' to 'far field'. FWIW there's quite a nice 'warming / feedback' graphic half-way down [this article](https://eos.org/science-updates/understanding-causes-and-effects-of-rapid-warming-in-the-arctic).
Comment: This is an interesting attempt to dive deeper that I haven't seen much of in the past, and really helps make the strength of the question come out.  I'd have thought it were mainly 3 and 4, as 1 and 2 would be fairly small to get things going more... but https://www.youtube.com/watch?v=x1SgmFa0r04 seems to hit that CO2 collects more near the Poles around the cold season.  Though April-June maybe the time that gets things going most?
Comment: A quick skim of the monthly arctic plots on http://www.karstenhaustein.com/climate (well down the page), seems to hint that at least July and August tend to maybe be quiet periods in terms of anomalies at the poles most years, whereas winter is often more extreme??  I'd be quite interested to see a monthly graph of Arctic temperature anomalies.  Of course that could be because there's limited ice that time of year always, whereas missing ice in typically colder months, particularly the equinox months with more sunlight, means bigger anomalies, and so is more result than true starter.
Comment: But maybe that's part of the answer too... there's always a large decrease in ice each year... more energy returned during the swing months may mean the ice takes longer to refreeze around the edges of the Arctic... and those altered ocean\air temperatures in areas slower to refreeze are very near the Arctic and so the feedback a bit more local in 3/4?  Seems to fit the evidence as the pathway roughly at least.
Answer:
So how is climate change and associated global heating driving Arctic amplification? This amplification is primarily caused by melting ice — a process that is increasing in the Arctic at a rate of 13% per decade.
Ice is more reflective and less absorbent of sunlight than land or the surface of an ocean. When ice melts, it typically reveals darker areas of land or sea, and this results in increased sunlight absorption and associated warming.
Polar amplification is much stronger in the Arctic than in Antarctica. This difference is because the Arctic is an ocean covered by sea ice, while Antarctica is an elevated continent covered in more permanent ice and snow.

Steve Turton, Adjunct Professor of Environmental Geography at CQUniversity Australia.
Comment: @SergeyZolotarev Arctic ice forms and melts in a regular cycle every year, of course, so the system is not in a steady state. The increased insulating effect of increasing atmospheric CO2 would apply to that regime, as well, but also you have water flowing from warmer climes carrying heat into the Arctic. See https://scripps.ucsd.edu/news/heat-bombs-destroying-arctic-sea-ice.
Comment: Perhaps you can give us a quick summary so as to make it a quicker read\encourage people to want to click the link, and also to fight link rot?
Comment: But why does it start to melt in the first place if it's white?
Answer: The process is a positive feedback: Global warming, as a result of the anthropogenic enhancement of the atmospheric greenhouse effect, leads to loss of ice on planetary surfaces which decreases the planetary albedo (Earth becomes "less white"). This results in less solar radiation reflected back to space, and this further enhances global warming, thus accelerating ice melting, and so on.
Answer: While the Arctic may be 'whiter', it is also immensely sensitive.
Some context: during winter, there is an extended snow and ice cover; further, there is less incoming solar radiation during winter due to the axial tilt of the Earth.
During summer, snow melt, as well as young ice due to solar radiation increase (it is summer, right). Surfaces become brown, dark, in the tundra and rocky deserts.
Ice caps and glaciers are very thick, may loose mass and surface if their mass balance is negative which is usually the case presently. Also older ice (as in perennial or multi-year ice) is more compact and resistant to thawing than young ice, and thus count a lot for the albedo balance in the Arctic.
Then what happen is that climate changes are making perennial ice surface-area shrink: so once it is gone, it is gone. For example, the breakout of the Ward Hunt Ice Shelf (this is 83 degrees N):

An ice island about 1.5 kilometers long, 250 meters wide, and 30 meters thick moves into the Arctic ocean after the fracturing of the Ward Hunt Ice Shelf in August 2002.

And it is gone.
Of course the year after during winter a 1-2 m thick ice cover will form, and in July, will be thawed. So during August, September, the dark, black water of the sea will accumulate heat, warming since the albedo changed from whitish to dark, preventing an eventual restoration of the shelf in the short-to-medium term.
See this video (NASA) where the 1979-2020 shrink-expand cycle of the sea ice in the Arctic. Old ice is going away, and new ice is not living to the year after. More waves, stronger, during a longer interval since there is less cover means more energy and thus worse conditions for ice to reform.
Mid-latitudes to low-latitudes are also warming, but there is no loss of albedo equivalent to polar regions, explaining why the polar regions are sensible in comparison.
Comment: First sentence: I think 'sensitive' might be the better word in English than 'sensible'? (Maybe coming from French?)
Comment: Agreed - (and yes coming from FR) will update !


What is this grass?

Question: I need help settling a debate between me and my wife. She says it is a weed and I'm saying its not. Who is correct? This grass looks very soft and grows in clusters too.
Comment: One plant per id question. See https://gardening.meta.stackexchange.com/questions/826/for-identification-please-only-post-one-plant-per-question-and-be-specific-whe for more information.
Comment: @NiallC.: Where are the other pictures? Did you just remove them from the question?
Comment: You can find them in the first revision: https://gardening.stackexchange.com/revisions/38709/1
Answer: If you didn't plant ornamental grasses, then both the grasses are just grass. A 'weed' is just a plant growing where you don't want it, but I'd consider this grass as a 'weed'.
Unless you've grown plants that seed themselves, generally, anything that pops up unbidden in unoccupied soil (unless it's something like a perennial or bulb you've forgotten you planted) is most likely a 'weed'.
Answer: I am guessing Fescue
The trick is to get to those baby weeds while they are babies.  Hula hoe works beautifully. Rips up baby plants and that is all it takes. I clean out the trenches between my lawns and beds and dump that soil on top of those baby plants.  Or use Gro-Co, mulch for ornamental plant beds...no weed seeds, no pesticide residues, completely decomposed and ready for the soil organisms to consume...Seattle area only that I am aware.
Weeds are my absolute last worry in my gardens, even gardens of properties under maintenance contracts.  Weeds are too easy to control and although I was licensed as a Commercial Pesticide Applicator, they taught us how not to need to use pesticides.  Pesticides are a bandaid on a problem we should have known about.  We made the problem.  All soils are full of seeds. Not talking about potting soil. If one blocks out the light to weed seeds, doesn't water shallowly and frequently and makes sure to cut them down during infancy as a seedling way before they go to seed, there will not be weed problems. Weeds are not super natural plants.  Just survivors.  People think that a little seedling will regenerate from a root.  Not happening.  Perhaps established perennials like crab grass or Equisetum, but there are few plants that grow from a segment of root.
For argument or debate purposes, grins, that top pic that might be a fescue grass is sold for 10 bucks a gallon potted plant.
Comment: @stormy: "Weeds are not super natural plants. Just survivors." - My thinking is, its a shame that we punish those plants for being good at surviving even in an unforgiving environment.
Comment: One plant per question; see https://gardening.meta.stackexchange.com/questions/826/for-identification-please-only-post-one-plant-per-question-and-be-specific-whe for the site policy
Comment: @stormy: Thanks for recommending Gro-Co.
Comment: @yasouser do you have access to Gro-Co?  Oh my!  You've heard of this stuff?  Do you live in the PNW?  Gro-Co...I won't use any other mulch in landscapes.  Just won't.  Where is it that you live?

What is this grass?


statistical careers where you get to move around?

Question: I'm about to get my PhD. My background is in engineering and applied mathematics. My research in statistical & machine learning methods for biological applications (without being too specific).
I love mathematics and doing research, but I'm astoundingly terrible at politics and I think I have 0 chance of success in academia. I've looked into (and done internships in) corporate engineering & data-science positions, and it's not for me. I've also taught and, oh boy, I am not a teacher.
I'd really love work where I got to move around a lot (not staring at a computer all day), and where I got to work closely with a small team. I don't mean a career where I had to travel a lot to different cities necessarily, but rather one where I just physically have to go places and talk to people and maybe work with physical objects on occasion.
Do you have any suggestions for career paths where I might combine these desires with my love of mathematics?
Comment: I voted to close this as I fear answers will be primarily opinion based.
Answer: What about consultancy in data science etc?
Comment: even management consultants who need some statistical support


What are the advantages of materialized view compared to a denormalised table?

Question: For new requirements of client,we need to setup non-key column search. I want to avoid Index creation so assessing a new table creation with the non key column of Original table as partition key would be better OR Materialized view would be better option here. As both new table and materialized view would occupy storage (And Client thinks it is wastegae of storage as we are saving same data twice per node) so what extra we may achieve by creating Materialized view?(Also its prompting not suitable for production).
By any chance there is other way than creation of Index/materialized view/new table with Non key column (Of original table) as partition key to manage this kind of situation where Non key column search query would be introduced
Comment: '"*I want to avoid Index creation*" - Why?
Comment: Because indexes in a distributed database generally need to do exhaustive polling of every node in the cluster.
Comment: Also Maintenance of index would be tough. Even if data would be removed,Index keys won't get cleaned. We have to drop and recreate periodically
Answer: Materialized views (MV) are classified as an "experimental feature" in Cassandra because there are scenarios where the view gets so out-of-sync that the only known workaround is to drop and recreate the view.
MVs are disabled by default which is why you get a warning if you try to create a view (CASSANDRA-13959). I've written about it in Should we reconsider using materialized views in Cassandra?.
The advantage with MVs is that Cassandra automatically creates and maintains the new table for you. However, there are some disadvantages with the first being that updates to the view are asynchronous so you cannot immediately see the data.
One misconception is that the data is not duplicated which isn't correct. The data in the base (source) table is duplicated to the view so it doesn't save on storage as you are expecting.
From your post, it is clear to me that you are already aware that secondary indexes are not the solution, particularly if performance matters, so the only option you are left with is to design a table for each application query. Cheers!
Comment: Thanks Erick and Aaron


Problem with attribute field in rasterizing tool QGIS

Question: I am trying to rasterize a vector layer using the "rasterize tool" in QGIS...
The problem is that there is no "attribute fields" available to choose from (even though they exist!)...
Comment: Two possible problems come immediately to mind. If you're dealing with a shapefile that is an invalid field name - can't have any spaces. The other is what datatype is that field? I believe it would have to be numeric to work (preferably int based on visible values), and it could currently be a string depending on how it was created.
Comment: I agree with Chris, that's most likely to be the problem (either or both). It is possible that there are some issues with spatial reference. GDAL_Rasterize can use (and up to recently needed) an existing raster - if it exists ensure that the cell size suits the spatial reference of your data (or specify a different output that doesn't exist).
Comment: Thanks guys!!!!! ;) :D
I edited my table in excell and the field I wanted to rasterize wasn't defined as numeric
Answer: As you figured out, the column is not defined as 'Integer' or 'Real' type. You can use Field Calculator to add a new column of type integer and write an expression such as below to have a field you can use in conversion.
<code>toint("TEXTURA LA")
</code>
Comment: also, as Chris pointed out, you can't have a field "TEXTURA LA" because of the space, you would need to change it to "TEXTURA_LA". Field calculator wouldn't like the space in the from field name so it's doubtful if that would run, if it did that would fix it.
Answer: I had a similar problem although the shapefile was ok. Going to "geoprocessing tools" and using the "gdal" "rasterize" directly instead of using the "rasterize" linked in the Qgis main menu (Raster>Conversions>Rasterize) solved the problem.


Is there a way to create a sphere shaped paragraph in powerpoint 2013

Question: Is there a way to create a sphere shaped paragraph in powerpoint 2013.
Something like this
Comment: No, there is no such thing.
Answer: You can create an oval and add text to it. This will break the text at the edges of the oval. Next you can apply the warp operation Inflate to it.
It's not as nice as your rendered output and would not fit my understanding of aesthetics, but it's "something like this".
Answer: Unfortunately, what you see in the text Warp dialog is what's available:

So you'll only be able to warp some lines of text, in some ways. You can always create the sphere in some other program and export it as an image.
Image source


Daily reputation counter. Possible bug.

Question: My daily reputation counter on the main site in the "drop down infobox" at the top of the page did not reset from yesterday. So it shows I have 290 rep for "today" which includes the 100 rep I earned yesterday. The reputation information on my user page is correct, though. Has anyone else encountered this anomaly?  Is there anything to be concerned about?
Comment: There is already a meta report filed at Meta StackOverflow [here](http://meta.stackexchange.com/questions/125694/activity-overview-not-displaying-todays-reputation-correctly)
Comment: @KannappanSampath That'll explain it. Thanks :)
Answer: So, the way the columns in the profile popup that shows when you hover over your name at the top of the page is implemented is that we just have a column that stores and increases the number throughout the day. Then, at exactly 0:00 UTC, we have a job that sets everyone's daily value to 0, and the increasing begins again.
Unfortunately, last night, there were some, um, issues, and the servers were very unhappy with us. This prevented the column from being reset to 0.
This has been naturally corrected at the UTC rollover just now. We left it as is for today as this isn't very high priority for the work to fix it.

Daily reputation counter. Possible bug.


elastic beanstalk php git eb command line configuaration

Question: I'm using Elastic Beanstalk to deploy my web application. I have successfully deployed my PHP/MYsql application by using git and the eb commmand line.
Every time I close and reopen the terminal to update my application the eb command is not recognised and I have to add it back it with the export command;
export PATH=$PATH:/eb/linux/python2.7/
I then have to go and add in all the Elastic Beanstalk configuration for my instance back in again.
Also I found that if I deploy another application and use the same path to the above eb folder, it overwrites the settings of the first application.
My question is firstly, how do I prevent having to add in eb and reconfigure my instance every time I reopen the terminal. And secondly, will each application have to point to a separate eb directory in order to separate the AWS configurations. i.e.
<path to unzipped EB CLI package>/app1/eb/linux/python2.7/
<path to unzipped EB CLI package>/app2/eb/linux/python2.7/
<path to unzipped EB CLI package>/app3/eb/linux/python2.7/

Comment: What OS are you developing on?
Answer: I'm not sure what OS you're developing on, so here are several common options:
Mac OSX

Open .bash_profile in your favorite text editor
Add export PATH=$PATH:/eb/linux/python2.7/ to the bottom of this file
Save and close

Ubuntu (possibly other *nix distros)

Open .bashrc in your favorite text editor
Add export PATH=$PATH:/eb/linux/python2.7/ to the bottom of this file
Save and close

Windows

Right click on My Computer
Click "Advanced System Settings" on the left hand side
Click "Environment Variables" at the bottom
In "System variables", find the row with "PATH"
Click the "Edit" button
Add ";/eb/linux/python2.7/" to the end of the "Variable Value" input
Click "Okay" repeatedly until all the dialog boxes are closed

Here's a youtube video walkthrough to set environment variables in Windows.


A very torsioned closed curve in space

Question: Is there a  simple  smooth closed curve $\gamma$ in $\mathbb{R}^{3}$  such that for  all $x,y\in \gamma$  with $x \neq  y $,  $l_{x}$  and  $l_{y}$ are  skew  lines, where $l_{x}  $ and  $l_{y}$ are straight lines tangent to $\gamma$ at $x,y$, respectively? What  about real  analytic  case?
Answer: If by "skew" we mean nonparallel and nonintersecting, then the answer is NO. Every smooth closed curve in $\mathbf{R^3}$ has uncountably many pairs of intersecting tangent lines. This follows from Poincare-Hopf index theorem; see
M. Ghomi, Tangent bundle embeddings of manifolds in Euclidean space,
Comment. Math. Helv., 81(2006), 259-270.
The lowest dimensional space where a closed curve with nonparallel and nonintersecting tangent lines may be constructed is $\mathbf{R^4}$. A very natural example is given by
$$
\mathbf{C}\supset\mathbf{S}^1\ni z\longmapsto (z,z^2)\in \mathbf{C}^2\simeq\mathbf{R}^4,
$$
as described in the above paper.
On the other hand, if we require the tangent lines only to be nonparallel, then the answer is YES, such curves do indeed exist in $\mathbf{R}^3$. They were first constructed by Beniamino Segre, to disprove a (short-lived) conjecture of Hugo Steinhaus,  in 1968:
B. Segre, Global differential properties of closed twisted curves, Rendiconti del Seminario Matematico e Fisico di Milano,
December 1968, Volume 38, Issue 1, pp 256-263.
They are not difficult to construct: one starts with a closed spherical curve $T\colon[a,b]\to\mathbf{S}^2$ parametrized by arc length which does not have any self intersections, is disjoint from its antipodal reflection, and contains the origin in the interior of its convex hull. The last property ensures the existence of a (positive) density function $\rho\colon [a,b]\to\mathbf{R^+}$ such that the center of gravity of the weighted curve $\rho T$ is the origin, i.e., $\int_a^b\rho(s)T(s)ds=o$. Then we integrate this curve to obtain:
$$
\gamma(t):=\int_0^t\rho(s)T(s)\,ds.
$$
Choosing $T$ and $\rho$ to be smooth periodic functions will ensure that $\gamma$ is smooth as well.
 The resulting curve $\gamma$ will be closed, due to the center of mass condition, and will have no pairs of parallel tangent lines, because its tangential spherical image is $T$ by construction.
The first explicit example of these curves probably appeared in
M. Ghomi, Shadows and convexity of surfaces, Ann. of Math., 155 (2002) 281-293,
where it was used to solve Henry Wente's shadow problem. The example in the above paper is both simple and analytic (it is given by polynomials). Also it lies on a convex surface. Later, Bruce Solomon and I studied these curves, which we called skew loops, some more in
M. Ghomi and B. Solomon, Skew loops and quadric surfaces,
Comment. Math. Helv., 77 (2002) 767-782.
where it is shown that the only closed surfaces in $\mathbf{R}^3$ which do not admit any skew loops are ellipsoids. The higher dimensional analogues of these objects are also studied in
M. Ghomi and S. Tabachnikov, Totally skew embeddings of manifolds,
Math. Z., 258 (2008), 499-512.
Here the term totally skew means nonparallel and nonintersecting.
Comment: Nice example. But how does one make sure that no two tangents intersect?
Comment: @Sebastian Goethe: Sorry, I interpreted "skew" as nonparallel. It is not possible for a closed curve in $R^3$ to have nonintersecting tangent lines, but one can construct these in $R^4$. This is described in the paper with Serge Tabachnikov mentioned above.
Comment: A very similar construction is also used in http://arxiv.org/abs/1211.3162 to solve a regularity problem for cosmic strings.
Comment: I just edited my answer above to clarify different interpretations of the term "skew", and corresponding answers in each case.
Comment: @ Willie Wong: Thank you for this reference. Constructing a curve with a prescribed tangential spherical image is the simplest example of convex integration theory which goes back to Whitney.  The center of mass trick to ensure that the curve closes up is also mentioned on p. 168 of the book "Partial differential relations" of Gromov.
Comment: @MohammadGhomi  Thank  you  very  much for your very interesting answer which contains very helpful technical  and  historical information.

A very torsioned closed curve in space


What is the speed of acceleration of the inflation of the universe?

Question: Is the inflation speed of the universe accelerating or is it a constant speed of expansion proportional to distance between objects.
Answer: See At what speed does our universe expand? and Speed of Universe Expansion for related questions, but I take your question to be specifically asking if the rate of expansion is increasing. The answer is that the expansion rate is increasing, and this was measured experimentally in 1998  by Perlmutter and Riese's groups.
The reason for the increase is another matter. We tend to ascribe it to dark energy, but no-one knows for sure if this is a good description or what the physical origin is.
Response to comment:
We tend to work with a deceleration parameter $q$ given by:
$$ q = -\frac{\ddot{a}}{aH^2} $$
where $H$ is Hubble's constant. It's called the deceleration parameter because it was first used long before the acceleration of the universe was discovered - for acceleration $q$ has a negative value. Anyhow, to calculate the acceleration change over the radius of the Earth we use:
$$ \ddot{a} = -qH^2r_E $$
Some quick Googling suggests the current value of $q$ is about -0.55, the radius of the earth is 6,371,000m and in SI units $H$ is about 2.3 $\times$ 10$^{-18}$/sec so the acceleration works out to be:
$$ \ddot{a}_E \approx 2 \times 10^{-29} ms^{-2}$$
I can see why you asked as it would be interesting if the acceleration due to dark energy was comparable with the acceleration due to gravity. However there is around 29 orders of magnitude difference! The acceleration is only detectable at cosmological distances.
Comment: Is there anyone out there that can calculate this apparent acceleration speed given by  the Perlmutter experiment, based on the diameter of our earth as a distance?  Will it be close to the acceleration of gravity per chance?
Comment: @GeorgeJones: I've updated my answer to respond to your comment.
Comment: Hi @JohnRennie, I think there is something wrong with your formula for acceleration.  If I plug in 13 billion light years instead of the radius of the earth I only get 4*10^-10 m/s^2 which seems too low!  Also the link where you got q=-0.63 is broken, so I could not debug the problem myself.
Comment: @FrankH: I've updated the link. You might want to post your comment as a new question.
Answer: As the universe stands today its not said to be "inflating" but it is "expanding". I think one way to make the distinction is to say that during inflation the radius of the causal horizon ($\frac{1}{aH}$ in FRW universe) falls (linearly) whereas during expansion it increases (being equal to half the conformal time for EdS universe).
I would love to know if some other answers can make it more precise.
Also about how much and for how long did inflation happen - I think Wikipedia gives a number in the first paragraph of the entry on cosmological inflation.
I would love to know if there is any theoretical derivation of these mind-boggling numbers.
Answer:
When we talk about universe inflation we should have in mind that the four cosmic forces did not appear yet, because at inflation no elements were formed yet.
scientists say that at 0.03 second the inflation reached four light-years, also said that if it had continued at the same rate, it would have been disappeared during the second have of the first second.
before the Big Bang the inflation speed was zero. And time is zero.
now we can say:
Light travels during four year = 300,000 km/s x 60 s x 60 min. x 24 hours x 365 days x 4 years = 37.843 x 10ᴧ12 km, this distance was within 0.03 of first second of Big Bang, means 37.843 x 10ᴧ12 km / 0.03 seconds = 12.6 x 10ᴧ14 km / Sec. Thus, inflation speed at the peak (before the effect of the four cosmic forces) in regard to speed of light is = 12.6 x 10ᴧ14 / (3 x 10ᴧ5) = 4.2 x 10ᴧ9 times the speed of light.
-s = v 1 * t + 1/2 a * tᴧ2:
s: distance at certain time = 37.843 x 10ᴧ12 km. v 1: speed at zero time = 0. a: acceleration. t: time = 0.03 second.
37.843 x 10ᴧ12 km = 0 + 1/2 a * 0.03ᴧ2
a = (2 * 37.843 x 10ᴧ12) km / 0.03ᴧ2 = (75.686 x 10ᴧ12) / (9 x 10ᴧ-4) = 8.41 x 10ᴧ16 km/sᴧ2.
the acceleration at universe inflation stage is: 8.41 x 10ᴧ16 km/sᴧ2
When the elements were formed starting with Hydrogen, the inflation speed came down due appearance of the four cosmic forces that started action, and the universe expanding started with much lower speed than the speed of light.


What is the best way to transfer an object between two iOS devices running the same app?

Question: I'm trying to give my iOS app the ability to transfer an object to another iOS device running the same app.  The object is on the order a few thousand KB of memory.  Does anyone have a suggestion as to how to do this?  I am considering using FTP, but that seems a little messy.  Does anyone have any suggestions on possibly using GameKit?  Or something else?
Answer: GameKit would probably be your best bet. This link seems to go over it pretty well
Answer: As an alternative, I've found the SimpleNetworkStream example that apple gives an exact match as to what I want to do.  Simple Peer to Peer file transfer might be the best solution....  It seems that people are having a lot of trouble transferring large data objects with GameKit.


Why did we lose the war?

Question:

I really don't understand why we lost the war. We thought we will won the war because we used less attacks.
Answer: It doesn't matter how many attacks you use in a war in this type of situation. It is the overall destruction of the enemies' bases that will be the tiebreaker.
In this case, your clan got 96 percent overall destruction while the other clan got 96.2 percent. That means the other clan wins as they got 0.2 percent more destruction that your clan did. Close, but all it needs is higher score to win.
Answer: When there's a draw (in terms of stars earned), the winner is not selected on the number of attacks taken to get those stars, but rather on the overall destruction percentage.
Answer: You lost the war because if the clans tie they judge it by the percent of damage made and which ever clan did a better percentage of damage wins.

Why did we lose the war?


Duplicate detection in two excel colums

Question: I have two columns of data in Excel 2010. One column has about 5,000 cells and the other has usually has 20-30. I need to be able to compare the two columns and output to a third if there is a duplicate. Any ideas?
Answer: The fastest way is to use conditional formatting and highlight the duplicates:
Click on the Home tab.
Click on the Conditional Formatting icon on the ribbon to open the drop down menu.
Choose Highlight Cell Rules > Duplicates Values... to open the conditional formatting dialog box.
Select Light Red Fill with Dark Red Text from the list.
Click OK to accept the selections and close the dialog box.

Duplicate detection in two excel colums


Bashrc file opens up continuously

Question: When i turn on my raspberry pi in command line mode it opens up with bashrc each time i startup my pi.If i open my terminal the same bashrc script opens first.Can anyone give me a solution. Thanks in advance
Answer: I'm guessing you've been misled by tutorials or blogs which imply or explicitly state that .bashrc can be used for things you want to happen at boot.1 This is essentially false, although it has side effects that might make it seem that otherwise.
.bashrc is a shell initialization file.  There are a few different flavours of these, which you can read about in man bash under INVOCATION.   For example:

When  an  interactive  shell that is not a login shell is started, bash reads and executes commands from ~/.bashrc, if that file exists.

You can think of an interactive shell as the command line. "An interactive shell that is not a login shell" applies to almost any shell that opens in a terminal, amongst other things. The "that is not a login shell" is often negated by the fact that ~/.profile and/or ~/.bash_profile, which are initialization files called when starting an interactive shell that is  a login shell, source ~/.bashrc.  When this is the case, .bashrc is run when starting any interactive shell.
Booting the system and starting an interactive shell are very different events, so if you put something in .bashrc and expect it to run at boot, or to only run at boot, expect to be surprised.

Authors of which should be banned from posting anything about how to use computers on the internet.
Answer: Undo the modification you have done.
Bashrc is a simple file name and has no special meaning but the bash shell (that what makes the command line) uses a configuration file $HOME/.bashrc. Notice the dot at the beginning of the filename. It makes the configuration file invisible. You can show it with ls -a. Check if you have the .bashrc file.
Comment: I have been using UNIX/linux (as a casual user) for ages, but I still don't understand why and how to use the weird dot thing.  I still remember once upon a Rpi2 time it took me 3 hours to search for a invisible dotted file (and no luck and gave up!) .  To me Windows and Linux are relatively like heaven and hell.  Actually I gave up Rpi after Rpi1 altogether, only came back at Rpi3 when GUI has become barely bearable.  I hope Rpi5, Win10, with SuperShell, only for super users and never newbies.  I always think UNIX/C are for geeks with IQ above 120 (poor me only 97!)

Bashrc file opens up continuously


front-end configurable products from simple products in magento?

Question: a client has imported 1000 items to magento as simple products. many of these SHOULD be configurable products (ie, 4 yellow dresses of different sizes).  the psuedo-configurable products all have the same "Style" number, so our 4 yellow dresses would have different SKU values but all 4 would share the Style.  is there a way to program magento on the front end to display these 4 simple products as one configurable products?  we need to keep them as simple because of the inventory system the store is using.
thanks very much,
Answer: I'm sure there is a way to do it - but I haven't heard of one yet, and I keep up on Magento stuff pretty well.
Unfortunately, Magento does not import configurable products through the backend.  Typically what you have to do is write your own script utilizing the Magento API, or import all the simple products, and then manually (or again, using the API) create the configurable products assigning the simple products to them.


Spectrum of OFDM with raised cosine window

Question: I'm having trouble implementing OFDM with a raised cosine (RC) window in Matlab. I know how to generate an OFDM signal and how to show its spectrum, I just don't know how to generate the window extensions. Each OFDM symbol is extended by $TW$ samples at both ends to smooth the transitions between successive symbols, this is done mainly to improve the out of band spectrum and reduce the interference to adjacent channels. I'm hoping someone here knows how to do this.
Comment: **@ Deve ..Last W samples of an OFDM symbol should be added to the first W samples of the successive symbol.** Does the term "added" mean addition or append.
Comment: @user2014 It means mathematical addition, see the expression for $u(t)$.
Answer: This spectral shaping technique is applied in time domain, after adding the guard interval (GI). But I find it easier to add GI and the cyclic extension for windowing in one step. Let $x(n)$ be an $N$ subcarriers OFDM symbol without guard interval. Then $W + G$ samples are copied to the beginning accounting for guard interval and windowing samples. Additionaly, $W$ samples are copied to the end, also for windowing:
$$
y(n) =
\begin{cases}
x(n+N) & \text{for} & -G-W \leq n \leq -1 \\
x(n) & \text{for} & 0 \leq n \leq N -1 \\
x(n-N) & \text{for} & N \leq n \leq N + W -1
\end{cases}
$$
In the next step, the raised cosine function is applied to the first and last $W$ samples of $y(n)$, respectively. The windowing function $w(n)$ is given by:
$$
w(n)=
\begin{cases}
\cos^2\left( \frac{n+G+1}{W-1} \frac{\pi}{2}\right) & \text{for} & -G-W \leq n \leq -G-1 \\
1 & \text{for} & -G \leq n \leq N - 1 \\
\cos^2\left( \frac{n-N}{W-1} \frac{\pi}{2}\right) & \text{for} & N \leq n \leq N+W-1 \\
0 & \text{otherwise}
\end{cases}
$$
$w(n)$ is similar but not equal to the transfer function of a raised cosine filter often used as impulse shaper in single carrier transmission systems. The two differences are: (1) the raised cosine function is applied in time domain for OFDM systems and in frequency domain for single carrier systems and (2) the "flat top" is usually much longer for OFDM systems, whereas its length is in a fixed relation with the flanks' length, given by the roll-off factor, for single carrier systems.
Finally, the OFDM symbol including GI and spectral shaping is calculated by
$$
z(n) = w(n)y(n)
$$
When transmitting several OFDM symbols $z_i(n)$, two consecutive symbols overlap at $W$ samples. The discrete transmit signal $u(n)$ is therefore given by
$$
u(n)=\sum_{i=-\infty}^\infty z_i(n-i(N+G+W))
$$
The implementation in Matlab should now be straightforward by substituting $n$ with $n' = n + G+ W+ 1$ in the above equations. Leave a comment if not.
Comment: Thank you for the answer. Lets say the windowing extension is $16$ samples, the CP length is $16$ samples, so I will copy the first $16$ samples and append them to the end of the OFDM symbol, and copy the last $32$ samples (last samples before the previous step) and add them to the start of the symbol. Then I'm going to apply the left and right window to the first and last 16 samples respectively.  I'm going to do this for every OFDM symbol. With this each symbol is extended by $32$ samples, however each symbol should be extended by only 16 samples. How are symbols going to overlap?.
Comment: The last $W$ samples of an OFDM symbol should be added to the first $W$ samples of the successive symbol. This means that each symbol effectively has an overhead of $W+G$ samples. If the overhead needs not to exceed $G$ you could use a cyclic pre- and postfix of $G/2$, respectively and apply the window function to this. However, this will introduce inter-symbol interference in a dispersive channel.
Comment: I understand that each symbol should effectively be extended by $W+G$ samples. However, we already added $W+G$ and $W$ symbols to the start and end of the each symbol. So, even after adding the last $W$ samples of the current symbol to the first $W$ samples of the next symbol, that leaves each symbol extended by $G+2W$ samples. I guess my question is implementation wise, or may be I missing something.
Comment: @user4259 If two consecutive symbols overlap by $W$ symbols at beginning and end, each OFDM symbol has an additional overhead of just $W$ samples. You have to take into account either the last or the first $W$ samples as overhead, but not both, because the overhead can only "belong" to one symbol not to to two at once.
Comment: OK, that explains what I was missing. Thank you.


Why are undirected graphical models called Markov networks?

Question: Undirected Graphical Models are usually known as "Markov Networks" and Directed Graphical Models are known as "Bayesian Networks". This is naming is not very clear to me. It might be because of some historical background, though I am just curious to know if there is any concrete reason for this naming.
Comment: My impression, from Koller/Friedman's book, is that the 'Bayesian network' name may come from the fact that such models are generalizations of what is called a 'Naive Bayes model'. (I.e. mostly historical, as you guess.) For 'Markov Random Fields', I think this is also a historical term derived somehow from the statistical physics literature, in particular from work about the so-called 'Ising Model' (note that 'field' can mean very different thing in physics than in, say, some areas of math). I'm not 100% about either of these though, hence why this is only a comment.
Answer: An undirected graph is not necessarily a Markov Network (Markov Random Field), and likewise, a acylic directed graph (ADG), more commonly known as, directed acyclic graph (DAG), is not necessarily a Bayesian Belief Network (BBN), if not at all.
Formally, a BBN is a pair(G,P) and satisfies the Markov condition.

P is a joint probability distribution over U, P(U)
U is a set of variables, U = { X1, X2, ..., XN }
G is a DAG defined by the pair (V,E)
V is a set of vertices with 1-to-1 correspondence with variables in U
E is a set of directed edges
Markov condition states that a node is conditionally independent of its nondescendants given its parents

A Directed Graph can be cyclic or acyclic, in a BBN, G is a DAG, so you have to be precise in usage of terms.
Also, G is only one of the three things that contributes to defining a BBN. So, you should not say, a DAG is a BBN or a BBN is a DAG.
Furthermore, a DAG is used to represent other things, not necessarily variables and dependencies (as in a BBN).
Whoever names an undirected graph a Markov Network, or a directed graph a BBN, probably doesn't have the full picture.
Research Andrey Markov on etymology of MRF, Markov Network, Markov blanket, Markov condition, etc... BBNs build on Markov's work, reusing as much as is applicable, just like quantum BN's build on and reuse the work of BBNs.
Answer: It's probably not the best name. In a Bayes Net, a directed edge from A->B represents the conditional probability $P(B|A)$. If A represents an unknown parameter, then the network is parameterized with a prior on the parameter, and running inference amounts to using Bayes' Rule. In a Markov Network, you don't (/ can't?) parameterize the model with the prior. The potentials on the nodes aren't generally singleton marginals.
Comment: Why do you say "In a Markov Network, you don't (/ can't?) parameterize the model with the prior."?
Comment: In a Bayes Net of A->B, there is a parameter $\psi(A)$ which happens to be equal to $p(A)$, which is the prior. In a Markov Network of A-B-C, there are parameters on the cliques $\psi(A, B), \psi(B,C)$. Neither of these are P(A). You can also add a parameters $\psi(A), \psi(B), \psi(C)$, but they are not generally $P(A)$, etc.


How to verify if SSH Client is not recording my login information?

Question: there are lots of SSH Clients one can use with Android, for example JuiceSSH client, so i have a security concern, that is, how can i know or verify, that this app is not recording my credentials to when i authenticate to my server?
Answer: It is hard to verify that your login information is not being transmitted to third parties. A malicious application could choose to share your credentials directly (or at a later moment) with an attacker (possibly in encrypted form).
Possible solutions or mitigations:

Use an opensource SSH client such as ConnectBot, the source code is available so you could audit it or build it yourself.
Use SSH keys instead of password-based authentication. While an attacker can also copy the private SSH key to a third party, revoking a SSH key should be easier than changing and remembering a new password.
Trust on the (number of) users and reviews of the product, check the background of the author.
Answer: I highly recommend reading
Reflections on Trusting trust a short speech By Ken Tompson  It shows just how difficult it is to verify nothing malicious is going on in a program you are running. You must trust the author of the program, and of the compiler and the compiler compiler and the OS and the BIOS etc. etc.
You can minimize the risk, use a well reviewed program, possibly review it yourself. Though some issues may be hard to find even if present in the source code: http://www.underhanded-c.org/)
You can try to monitor behavior of the application, for specific suspicious behavior, like connecting to some other server you didn't ask it to, but there are techniques for ex-filtrating data which are hard to detect, especially if they are novel.
Most of us focus on using well known open source software fetched from a trusted source and signed by a trusted source. Extra measures are possible though usually not worth it.


When should I inspect the Error Log?

Question: I've had a varied career, but I have never found relevant information in the SQL Server Error Log. Under what circumstances should I consider inspecting it?
Answer:
I've had a varied career, but I have never found relevant information in the SQL Server Error Log.

I'm happy you've had an easy time with SQL Server :)

Under what circumstances should I consider inspecting it?

An extremely abbreviated list would be:

Every day, because who knows what is happening.
When any sort of issue arises that is more than superficial query issues.
When you want to learn how things work.
When you're hunting for new features/functionality/changes.

I've, quite literally, troubleshot the worst SQL Server issues and without the errorlog you're flying blind. In a large majority of cases it is just impossible to troubleshoot without it.
This isn't to say the errorlog is all you need. The basic core items that should always be captured or checked if there are issues or for general health and welfare of the instance are the errorlog, Windows event log for system and application, and the cluster log if using clustering.
Comment: @J.Mini It'd be nice if there was a database or server level option for that, but instead we have TF3226 which may help you.
Comment: Well darn. It looks like I should be checking that thing more often. Usually, it's just flooded with info telling me that my log backups are working great. Hopefully `dbatools` can rescue me from that.
Answer:
Well darn. It looks like I should be checking that thing more often. Usually, it's just flooded with info telling me that my log backups are working great.

If you'd like a free tool that narrows the scope of error log results to ones that aren't useless, you may want to try my sp_LogHunter.
The idea behind it is to only return error log entries of critical importance without all the fluff and nonsense.
Answer: Here's three more cases, in addition to Sean's list:

When the instance won't start properly (as vonPryz noted).
In similar vein, when a database won't come back online.
When a user is encountering login failures. For security reasons, only a generic error message is shown to the end user. The troubleshooting details that describe the actual problem are stored in the SQL Error Log.
Answer: A few small additions to the good answers from Sean Gallardy and J.D.:

I've used the SQL Error Log when troubleshooting problems with encrypted connections.  In the first ten or twenty seconds after starting up, SQL will tell you about the certificate it is using. For example:

The certificate [Cert Hash(sha1) "B91B739DBF6780EA40F45C8ED9D8F0D2AEBC1EDD"] was successfully loaded for encryption.

Or if it is using a self-signed certificate:

A self-generated certificate was successfully loaded for encryption.

And if it fails to load the designated certificate, it'll look like this:

TDSSNIClient initialization failed with error 0xd, status code 0x38. Reason: An error occurred while obtaining or using the certificate for SSL.
Check settings in Configuration Manager. The data is invalid.

It can be a handy way to confirm what port SQL is listening on. You'll see something like this in the first ten or twenty seconds:

Server is listening on [ 'any'  50481].

It can tell you if SPN registration is successful or not:

The SQL Server Network Interface library successfully registered the Service Principal Name (SPN) [ MSSQLSvc/myserver.domain.local:50481 ] for the SQL Server service.

When should I inspect the Error Log?


Difference between javacore, thread dump and heap dump in Websphere

Question: Can someone tell me the exact difference between javacore, thread dump and heap dump? Under which situation each of these are used??
Answer: A thread dump is a dump of the stacks of all live threads. Thus useful for analysing what an app is up to at some point in time, and if done at intervals handy in diagnosing some kinds of  'execution' problems (e.g. thread deadlock).
A heap dump is a dump of the state of the Java heap memory. Thus useful for analysing what use of memory an app is making at some point in time so handy in diagnosing some memory issues, and if done at intervals handy in diagnosing memory leaks.
This is what they are in 'raw' terms, and could be provided in many ways. In general used to describe dumped files from JVMs and app servers, and in this form they are a low level tool. Useful if for some reason you can't get anything else, but you will find life easier using decent profiling tool to get similar but easier to dissect info.
With respect to WebSphere a javacore file is a thread dump, albeit with a lot of other info such as locks and loaded classes and some limited memory usage info, and a PHD file is a heap dump.
If you want to read a javacore file you can do so by hand, but there is an IBM tool (BM Thread and Monitor Dump Analyzer) which makes it simpler. If you want to read a heap dump file you need one of many IBM tools: MDD4J or Heap Analyzer.
Comment: MDD4J is deprecated. Memory Analyzer is the recommended tool.
Answer: JVM head dump is a snapshot of a JVM heap memory in a given time. So its simply a heap representation of JVM. That is the state of the objects.
JVM thread dump is a snapshot of a JVM threads at a given time. So thats what were threads doing at any given time. This is the state of threads. This helps understanding such as locked threads, hanged threads and running threads.
Head dump has more information of java class level information than a thread dump. For example Head dump is good to analyse JVM heap memory issues and OutOfMemoryError errors. JVM head dump is generated automatically when there is something like OutOfMemoryError has taken place.  Heap dump can be created manually by killing the process using kill -3 . Generating a heap dump is a intensive computing task, which will probably hang your jvm. so itsn't a methond to use offetenly. Heap can be analysed using tools such as eclipse memory analyser.
Core dump is a os level memory usage of objects. It has more informaiton than a head dump. core dump is not created when we kill a process purposely.
Answer: Heap dumps anytime you wish to see what is being held in memory Out-of-memory errors
Heap dumps - picture of in memory objects - used for memory analysis
Java cores - also known as thread dumps or java dumps, used for viewing the thread activity inside the JVM at a given time. IBM javacores should a lot
of additional information besides just the threads and stacks -- used to determine hangs, deadlocks, and reasons for performance degredation
System cores
Answer: A Thread dump is a dump of all threads's stack traces, i.e. as if each Thread suddenly threw an Exception and printStackTrace'ed that. This is so that you can see what each thread is doing at some specific point, and is for example very good to catch deadlocks.
A heap dump is a "binary dump" of the full memory the JVM is using, and is for example useful if you need to know why you are running out of memory - in the heap dump you could for example see that you have one billion User objects, even though you should only have a thousand, which points to a memory retention problem.
Answer: Thread dumps are javacore show snapshot of threads running in JVM, it is useful to debug hang issues, it will provide info about java level dead locks and also IBm version of javacores provides much more useful information, such as heap usage, CPU usage of each thread and overall heap usage along with number of classes laded by the JVM.
Heapdumps, provides information about Java heap usage by an JVM, which can be used to debug memory leaks. Heapdumps are generated by IBM JVMs when a JVM is runs into outofmemoryerror, Heapdumps are only for heap leaks in java, native out of memory error may result system dumps usually with an "GPF" General protection Fault.


Which version of AndEngine (gles1 or gles2) should I learn?

Question: I m new to Game Development. I've chosen AndEngine, but there are 2 versions: gles1 and gles2. I tried sample code from both and found that gles2 code is not run on an emulator, but required an actual device. And in gles2 there are also BaseGameActivity and SimpleBaseGameActivity. I'm a little confused. Which is best?
Comment: Beginners should normally use the newest stable version possible. What do you mean by "requiring an actual device"? All software requires hardware.
Comment: For testing code emulator is required but when i tried to run it on emulator it give me this error org.andengine.opengl.view.ConfigChooser.chooseConfig(ConfigChooser.java:183) and when i search on this error i came to know that it(AngEngine gles2) will work only on actual device(means mobile or tablet) is this true? Thanks in Advance.
Comment: Is [this](http://gamedev.stackexchange.com/questions/35260/should-we-always-prefer-opengl-es-version-2-over-version-1-x) what you're asking?
Comment: I don't know about the AndEngine, but I've gotten gles2 applications to run fast on a virtual device. You just have to create an x86 Ice Cream Sandwich image with HAXM support enabled and host GPU enabled. Unfortunately this only works with pure Java applications or those that have native elements built for x86.
Answer: USE GLES2
AndEngine is a little tricky to get configured properly the first time you try.  I recommend installing the version stored at RealMayo's github, which is a stable version.  That's a version of GLES2 and yes, it's definitely worthwhile to use GLES2 over GLES1.  Many new features were added that make life easier, improve performance, and add great features to your games and projects.   When you're ready to install, follow the instructions at this link and follow them precisely.
GLES2 WILL run on an emulator, I do it every day, so if you're having some problem running your app, you need to show us the log output.  It might be a memory issue if your computer doesn't have enough memory to run the emulator and install it to the emulator.  See this thread.
BaseGameActivity versus SimpleBaseGameActivity

The first thing that we have to realize is that BaseGameActivity for
  GLES2 (the version we are using) and BaseGameActivity for GLES1 are
  completely different. When AndEngine updated, so did BaseGameActivity,
  but a lot of people that were using GLES1 didn't like the changes and
  wanted to work with a class they were already familiar with.
  Therefore, SimpleBaseGameActivity was created for GLES2.
  SimpleBaseGameActivity is practically the same as BaseGameActivity for
  GLES1, which is what a lot of the AndEngine developers wanted at the
  time.

(source).  My advice (and practice) is to use GLES2 with the BaseGameActivity.


What is the difference between a union and an "isa" disjoint relationship?

Question: To me, it seems that a union and an "isa" disjoint relationship are the same. What is the difference between the two?
Answer: A isa usually indicates a subset. e.g. a male cat is a cat is a mammal. A union is the combination of two sets e.g. the union between cats and males is all cats and all males. Union is bidirectional whereas isa goes in one direction.


Managing Virtual Macs on a closed network

Question: I have a lab of VMWare virtual Macs on a network with no Internet access.  What options do i have for managing these Macs, other than one at a time?  I am looking at ARD and JAMF at the moment...
Comment: So OS X is the virtual environment?  What are the host computers?
Comment: Hosts are Late 2013 Mac Pros running ESXi 5.5, virtual Macs are running 10.9.5 and 10.10.1.
Comment: Might be a silly question, but why have a Mac Pro run a virtual OS X environment?
Comment: Apple allows for virtual Macs when the software is run on Apple hardware.  This affords us the luxury of having test Macs that we may quickly reset, and greater flexibility is setting up those Macs.
Comment: I've since parsed out how to get ARD to work just fine within this virtual environment.  Provided the network does not span across too many vLANS, ARD will be just the right answer.
Answer: Apple Remote Desktop turns out to be the answer.  It is important that ARD have a separate administrative user account, and I recommend that the account be hidden from users' view.


How do I alter certain module form output

Question: Some of my node types use fields from extra modules (such as Open Hours or Get Locations). How do I change the way those modules render their fields inside the form? I mean Get Location for example renders fieldset with fields in it. I'd like to change it at all. Also I'd like to change the order of fields and so on.
Is there anyway to make it using something like field--field-name.tpl.php for output fields?
Sorry if this is a common question but I couldn't find any complete guidance on this.
Answer: The form elements for fields (or "Field Widgets" as Drupal calls them) are defined using hook_field_widget_form(), e.g.
function hook_field_widget_form(&$form, &$form_state, $field, $instance, $langcode, $items, $delta, $element) {
  $element += array(
    '#type' => $instance['widget']['type'],
    '#default_value' => isset($items[$delta]) ? $items[$delta] : '',
  );
  return array('value' => $element);
}

They use the form API, and don't have associated templates/themes unless one is explicitly set on a contained element.
You can use hook_field_widget_form_alter() to manipulate the elements; the simplest example (from the docs) would add a class to a particular element:
function hook_field_widget_form_alter(&$element, &$form_state, $context) {
  // Add a css class to widget form elements for all fields of type mytype.
  if ($context['field']['type'] == 'mytype') {
    // Be sure not to overwrite existing attributes.
    $element['#attributes']['class'][] = 'myclass';
  }
}

But obviously you're only limited by what the form API can do. So if you wanted to provide a specific theme for an element:
function MYMODULE_field_widget_form_alter(&$element, &$form_state, $context) {
  if ($context['field']['type'] == 'mytype') {
    $element['#theme'] = 'MYMODULE_some_theme';
  }
}

Then it would just be a matter of implementing hook_theme() and creating the template file to do what you need.
Just for posterity (and because I accidentally answered the question with this first time round); the following relates to formatting the output of a field when its parent entity is displayed:
As listed in Drupal 7 Template (Theme Hook) Suggestions, and originally defined in template_preprocess_field(), these are the built-in patterns you can use to override specific field templates:

field--field-name--content-type.tpl.php
field--content-type.tpl.php
field--field-name.tpl.php
field--field-type.tpl.php

You could also add your own using a template preprocess hook:
function MYTHEME_preprocess_field(&$vars) {
  // This will let you use field--foo.tpl.php as the template name for any fields that pass the condition.
  if (some_condition()) {
    $vars['theme_hook_suggestions'][] = 'field__foo';
  }
}

As far as changing the order of field output goes, that's usually done through the UI in the "Manage Display" forms available for the various view modes for each entity type.
Comment: mm. Seems like I couldn't explain clear enough what do I need. I know how to theme a results using field--name.tpl.php. I need to change the way those fields appear in new node form (on a node creation).
Comment: No you explained it perfectly, I mis-understood. Sorry about that, just writing another answer...
Comment: Added a bit more...
Comment: Thanks Clive. Let me bore you a bit more if you don't mind.)
I can't get the last (about MYMODULE_field_widget_form_alter). Can you show some example step by step, please? Let's say I need to alter Geo Location module form elements. So I put a geolocation_field_widget_form_alter() into my temlpate.php, right? then I put
$element['#theme'] = 'MYMODULE_some_theme' there. then what? how do I name my tpl file? How can I see a list of all variables available to use in the template?


Why is AES better than one-time pad?

Question: From my limited research into this topic, it seems that AES can be brute-forced. One-time pad, on the other hand, cannot. Why then is it better to use AES than it is to use one-time pad? The only answer I have come to is performance, but this doesn't seem quite right.
Comment: How much keying material must be securely exchanged to transmit a 1 Megabyte message with AES?  With one-time-pad?
Comment: @bdegnan That's not a problem, and neither is it brute force. Extraction of key bits will get you nowhere as they are only used to protect the part of the plaintext that you already know. This is in contrast with a cipher such as AES, where known plaintext can help by validating a guessed key which is also used for **other** parts of the message. Of course, a block cipher should protect against guessing the key in the first place, but if you can validate the key then the cipher is not information-technically secure.
Comment: @DarcySutton A one-time-pad can actually be brute forced if you have enough data.  For instance, if you know anything about the plaintext, you likely can extract the key.
Comment: So it is just performance and logistics then?
Answer: For One Time Pad (OTP), you need to distribute the key. Consider that you want to send 1GB of encrypted data. In this case, beforehand you need to generate 1GB uniform random key and distribute it to the other party in a secure way. Do you see the problem now? Now, start using it, even before you start to use it, pretty sure you will leave it aside!
The other main problem with the OTP is the depletion of the one-time key. What will you do? Wait or Reuse? Both have problems. The first one leaves you out of touch/order/sync and the other will have catastrophic results; loss of the perfect secrecy with the two-time pad attack as done in history (Venona project) or now automatized.

A Natural Language Approach to Automated Cryptanalysis of Two-time Pads by Mason et al. at ACM CCS 2006

See also these nice Q/As from our site;

Taking advantage of one-time pad key reuse?
How does one attack a two-time pad (i.e. one-time pad with key reuse)?
Little problem with Vernam Cipher

Now instead of some mentioned problems of OTP, consider this;

Both parties have public and private keys 1;
Exchange keys with ECDH ( or choose one of the candidate post-quantum schemes) to have forward secrecy ( ECDH, ECDH has only secure against classical adversaries, Shor's algorithm beat Dlog, too ).
Use KDF on the exchanged key
Encrypt with AES-GCM-SIV ( or XChaCha20-Poly1305) so that one has

Confidentiality,
Integrity, and
Authentication

Here, GCM uses CTR mode that uses computational security instead of perfect secrecy. Yes, There are still pitfalls to using AES-GCM incorrectly
OTP on the other hand has only confidentiality. Yes, one can use OPT-HMAC to provide Integrity and Authentication, however, you left the perfect secret domain. To stay on the on the path you need Information Theoretic MACs ( for example the ones from strong universal functions (SUF) - see chapter 6).

AES can be brute-forced.

Even AES-128 withstand all attacks for more than 20 years. Direct brute forcing will take around $2^{35}$ years even if you combine all the Bitcoin miner's powers on brute-forcing AES. It is safe against the classical attacker, however, to be safe against quantum adversaries use AES-256 so that one can withstand even against the optimal Grover's algorithm.

1Well, not that easy of course! To be sure that you are correctly communicating with the other part one either uses TOFU ( Trust On the First Use) like Signal or degraded WhatsApp or well-established certificates. This is the top of the rabbit hole!
Comment: @MarcIlunga you  are too fair, I need to modify that part.
Comment: To be fair, if we are even considering using OTPs, then one can certainly use Information Theoretic MACs.
Answer: As the others have said, the fundamental disadvantage of a one-time pad, is that you have to securely exchange a key of equal length to the plaintext. This might not be practical for very large plaintexts.
In contrast, a cipher like AES uses a fixed length key, e.g. 128 bits (16 bytes) long, to encrypt messages of almost any length. This is clearly more convenient and practical as far as securely exchanging keys is concerned.
And AES can not in any way, shape or form be "brute forced", if by "brute forced" you mean trying each of the possible (say) $2^{128}$ keys in turn. It's not even possible to increment a counter from 0 to $2^{128}$, let alone do a trial decryption for each of those values, using any current or foreseen techniques.
Of course, a particular system might take a password or passphrase, and turn that into an AES key, using a key derivation function (KDF). Such systems are vulnerable to dictionary attacks, where you try many common words and phrases to see if any work. For example, if your password was "password", this would undoubtedly fall instantly to a dictionary attack. But that's quite different to a brute-force attack in my opinion.
In summary, one time pads are really not practical in many cases because of the need to securely exchange a key of equal length to the message. Ciphers such as AES are much more practical, as long as you choose your keys uniformly at random from the available keyspace, or (when using a KDF) choose unpredictable passwords or passphrases to reduce the risk of dictionary attacks.
Comment: Passwords and - to a lesser extend - passphrases generally do not have 128 bits of entropy. You'd have to use a generated password to come close to 128 bits, and a good password hash / PBKDF will only take you so far.
Comment: When I say "brute forced", I mean if you had an infinite amount of time and computing power, is it even possible to compute. This terminology is probably incorrect, hence the confusion. Obviously, a one-time pad cipher cannot be "brute forced"  under this terminology, as brute-forcing a one-time pad cipher would yield every possible text of the given length with no distinguishing factors.
Answer: It's not.
Firstly, "better" is a qualitative assessment like a feeling. It's not a scientific metric as in is meat "better" than vegetable?
The answer is that AES is more "convenient" than the OTP in the majority of use cases. So three examples championing the OTP over AES:-

OTPs are informationally secure for all time. This or the other side of the quantum computer revolution.  AES isn't. It may already have been broken. And we certainly can't predict the future 20 years out. Both the US and China are slurping up vast amounts of internet traffic for decryption "later". Consider the F-35 stealth fighter.  Civilian academics can't design one of those, therefore some might say they can't exist. But they do as nation states can design and build them. And nation states might be able to break AES. It's an extension of the "rolling your own" paradigm. Just because you can't break it, doesn't mean no other country can't. Post hoc ergo propter hoc.
Key exchange is thought to be problematic. Consider wanting to message a chap in another place. If you've never met, how can you trust him? AES-GCM can't help you. And if you've met him, you can exchange key material. NATO, the US, China, Japan, Switzerland, the EU, the banks and half of the world's best technical universities are investing billions into quantum key distribution networks that securely exchange key material. It is possible though that all of those thousands of bankers, scientists and engineers are wrong.
Authentication is thought to be problematic. What if a HMAC were appended to the OTP? That would create the situation whereby you'd have unbreakable theoretic security, and integrity and authenticity equal to that of AES-GCM.  Or much better if a one time MAC were used. A win-win.

3 ½. Just how much messaging do you want? 1 GB of key is sufficient for 3 ½ million Tweet sized messages. You should not be using OTPs to transmit 8K UHD movies.
AES isn't better than a OTP. It's just more practical in more  cases. Unless it's already broken of course. Cryptographic monoculturism is extremely perilous, and the only field of human endeavour where all our eggs are de facto shoehorned into one basket. Ask any Irish potato or Dust Bowl farmer about monoculture.

Why is AES better than one-time pad?