Create Temporary Access to production support

Question: We're thinking of creating a web site where a manager can provide temporary access to a person for a limited set of data in our production SQL azure database for production support.   Auditing is mandatory.  The support user  would need to be their domain account so we can audit the activity.  Write it to a table, add the user to an AAD group that has needed permissions, a logic app would remove that user from the group after x minutes.
Is there an easier way or better solution for this?
Answer: We looked, and didn't find a packaged product that met our similar needs. We wanted to be able to get away from having so many developers with dbowner (and even sysadmin) access to databases and instances.
We ended up writing our own desktop application. It doesn't quite match your requirements, but it is close.

The user runs the application, which authenticates them via Windows authentication. There is a lookup that then determines which instances/databases they can request elevated permissions to. And how far they can elevate. All of which has to be approved ahead of time by their supervisor. There are four options for elevation level: (lowest to highest )

R+W – Read and write only on a specific database.
DDL and R+W – You can create objects, change schema on a specific database as well as read and write.
[DB]OWNER – Full access to a specific database.
SYSADMIN – Grants you full access to the instance and all the databases.

They also have to fill out a field to explain why they need the elevated permissions. The program then creates a temporary SQL login for them that they can use to do their elevated work. (We tried to do it by adding them to an Active Directory group, but something didn't work right. I don't remember what it was. We'll try that again some day.)
It logs the fact that they asked for elevated rights to a table that we can then run reports from. We also set up our third-party compliance auditing tool to specifically audit all activities from these temporary elevated logins. The process also sends an e-mail message to the person's supervisor whenever they request elevated access.
We then have a scheduled job that removes these temporary logins at 6:00 a.m. the next day.


How to resolve Checkout page continues loading issue?

Question: I am facing the issue in the checkout page, After clicking the "proceed checkout" from cart page then page continuously loading.
I have observed in console some require js issues are there, exactly I didn't find a solution for those console errors. Please check the attached screenshot for your reference.

console issues are
TypeError: window.checkoutConfig.payment is undefined[Learn More] vault.js:20:9
TypeError: quote.totals(...) is undefined[Learn More] totals.js:15:40
TypeError: can't convert undefined to object

Help me to resolve this issue.
Answer: Follow these steps:-
Remove the pub/static/frontend  : rm -rf pub/static/frontend

chmod -R 777 pub/*

php bin/magento setup:static-content:deploy

Make sure the JS existing on the path as mentioned in the screenshot.
Comment: Thanks for reply @Rakesh, I have tried what you mentioned still same issue


Delta function singularity in curvature

Question: Are there 3+1D spacetimes that lead to a $\delta$-function in curvature? Are there any examples that one can provide?
Comment: Might post a proper answer later, but the Israel junction conditions allow for "thin shells" in spacetime, which are hypersurfaces along which the curvature tensor exhibits a Dirac delta singularity concentrated on the hypersurface. More importantly, this is perfectly rigorous (or at least can be made so). There was a paper by Geroch and Traschen where it was proven that only these singular solutions of the EFE exist in general, hence any other form of singular sources like point masses or strings where the energy -momentum tensor has a delta term should be treated with suspicion.
Comment: The curvature of a non-rotating black hole has a measure of curvature called the Kretschmann scalar, which has the form $K=R_{abcd}R^{abcd}=\frac{48 M^{2}}{r^{6}}$. No delta-distribution present there. Generally, I think to see a delta-like curvature you'd need to solve the EFEs in a setting that is not at least $\mathcal{C}^{3}$, where the three-times differentiability requirement of the metric follows from the Riemann tensor involving second derivatives of the metric and the differential Bianchi identity adds another derivative.
Comment: I am not sure about that, but I think the curvature of a Black Hole is divergent at the centre of the black hole. I think one can show that
Comment: I don't remember however if they had concluded that definitely no other singular solution exists or only that they don't exist "generally".
Comment: This paper might be of interest for this question: https://aip.scitation.org/doi/abs/10.1063/1.524568?journalCode=jmp
Answer: A good analysis of this subject is contained in the paper R. Geroch, J. Traschen, Strings and other distributional sources in general relativity.
They conclude that thin shells (delta singularity on a codimension 1 hypersurface) are well-defined but higher codimension surfaces supporting delta singularities in the curvature are not.
I will not be completely rigorous with my use of distributions here, since it takes quite a lot of effort to state how the theory works on manifolds correctly. I will also not be completely general in the formulation in the sense that I will consider timelike hypersurfaces only (the spacelike case is identical with some sign changes here and there), even though with small modifications, the considerations here are also valid for general hypersurfaces with no assumptions on its causal type.
Let $M$ be a smooth four dimensional manifold (four dimensionality is not strictly required though) with a Lorentzian metric tensor $g$ on it and a hypersurface $\Sigma\subseteq M$ such that $g$ is smooth away from $M$ but is merely assumed to be continuous on $\Sigma$. It is further assumed that $\Sigma$ partitions $M$ into two disconnected subdomains $M_+$ and $M_-$ with $\Sigma$ being the common boundary surface separating the two.
Note that the induced metric $h=i^\ast g$ ($i:\Sigma\rightarrow M$ is the inclusion) on $\Sigma$ is not only unambigous under these assumptions, but is smooth.
One may then derive (this is the so-called Israel formalism for thin shells) that the curvature tensor exists as a tensor distribution on $M$ in the following form: $$ \mathrm{Riem}=\mathrm{Riem}_+\Theta_\Sigma+\mathrm{Riem}_-\left(1-\Theta_\Sigma\right)+Q\delta_\Sigma, $$ where 1) $$ \Theta_\Sigma(p)=\left\{\begin{matrix} 1 & p\in M_+ \\ 0 & p\in M_- \end{matrix}\right. $$ is the step function associated with the hypersurface and the Dirac delta $\delta_\Sigma$ associated with the hypersurface is defined by $$\langle \delta_\Sigma,\varphi\rangle=\int_\Sigma\varphi\mu_h $$ for any test function $\varphi$ (smooth with compact support) on $M$ with $\mu_h$ being the induced volume form of the metric $h$ on $\Sigma$,  2) $\mathrm{Riem_\pm}$ are the curvature tensors calculated from the smooth metrics $g_{\pm}$ in $M_\pm$ and 3) $Q$ is a smooth tensor field defined only along $\Sigma$.
Letting $(U,x^\mu),\ \mu=0,1,2,3$ be an "admissible" chart (i.e. one which passes through $\Sigma$ smoothly) on $M$ intersecting $\Sigma$, the coefficients $Q_{\kappa\lambda\mu\nu}$ of the tensor field $Q$ are $$ Q_{\kappa\lambda\mu\nu}=n_{\kappa}\left[K_{\lambda\mu}\right]n_{\nu}-n_{\kappa}\left[K_{\lambda\nu}\right]n_{\mu}+n_{\lambda}\left[K_{\kappa\nu}\right]n_{\mu}-n_{\lambda}\left[K_{\kappa\mu}\right]n_{\nu}, $$ where $$ [K_{\mu\nu}](p)=\lim_{q\in M_+\rightarrow p}K^+_{\mu\nu}(q)-\lim_{q\in M_-\rightarrow p}K^{-}_{\mu\nu}(q) $$ is the difference of the extrinsic curvature tensors of $\Sigma$ as calculated from the two sides.
This formalism gives a large class of metrics whose curvature tensors are singular.

I might update this answer with a concrete example in the future, but the book E. Poisson, A relativist's toolkit contains a number of worked out examples (for example Section 3.9).
The example in Section 3.9 considers a timelike hypersurface $\Sigma$ which is spatially spherical with the "interior" region $M_-$ being Minkowski spacetime and the "exterior" region $M_+$ being Schwarzschild spacetime. A singular dust energy-momentum tensor is placed on $\Sigma$. The resulting spacetime is a valid, albeit weak, solution of the Einstein field equations in which the curvature tensor has a Dirac delta singularity.
Answer: The simplest example I can think of is to have a "bumpy" metric (also here):
\begin{equation}
g_{\mu \nu} =
\begin{pmatrix}
-1 & 0 & 0 & 0 \\
0 & 1 + \theta (x - x_{0}) & 0 & 0 \\
0 & 0 & 1 + \theta (x - x_{0}) & 0 \\
0 & 0 & 0 & 1+ \theta (x - x_{0}) \\
\end{pmatrix}
\end{equation}
where $x_{0}$ the proper distance after which the spatial directions of the metric experience a sudden "jump". Any Christoffel symbol involving the derivative $\partial _{\mu} g_{ii} \, , \, i = 1,2,3$ yields a delta function $\delta (x - x_{0})$ times other stuff depending on the derivative at hand. Since some Christoffel symbols now have a delta function, so will the Riemannn curvature tensor:
\begin{equation}
R^{\mu} {}_{ \rho \nu \sigma} = \nabla _{\nu} \Gamma ^{\mu}{}_{\rho \sigma} - \nabla_{\sigma} \Gamma ^{\mu}{}_{\nu \rho}
\end{equation}
where $\nabla _{\rho}$ the covariant derivative (which itself will include a Christoffel symbol). Subsequently the Ricci tensor:
\begin{equation}
R_{\rho \sigma} = R^{\mu}{}_{\rho \mu \sigma}
\end{equation}
will also have components that contain a delta function.
The scalar curvature $R = g^{\rho \sigma} R_{\rho \sigma}$ will carry those delta functions trivially, since the inverse metric $g^{\rho \sigma}$ will have the Heaviside theta function in the denominator. The resulting curvature will be 0 everywhere except the pole $x = x_{0}$ where it diverges.
There is no physical example that I know of which exhibits any similar behaviour, but you can always find an infinite amount of metrics such as the one above, which lead to curvature tensors including delta functions in some of their components.
An important stipulation of course is that this kind of abrupt "jumps" and "bumps" on the metric are technically not well-defined mathematically when we perform differential geometry, since then the manifold you examine (your spacetime) is not smooth, thus a lot of the assumptions we take for granted in GR (General relativity) don't hold.
The above then remain relevant as a crude approximation of a metric that is smooth, but with abrupt changes at specific points.
Comment: The OP asked for spacetimes that lead to curvature which includes the delta function, they did not specify whether they want a physically realistic model or a spacetime that may describe a real system. For the second point, it is correct, but I assume we have the case of a metric whose topology is meant to describe the topology of the manifold itself.
Comment: -1: As you yourself said, it's not physically realistic and the OP is not merely asking for a manifold with a metric with a delta curvature.  So you too aren't answering the question - just one you've decided to answer as an appropriate reformulation. He asked for a 3+1d spacetime. Secondly, the manifold can still be smooth, it's merely the metric that isn't.
Comment: This also seems to be the best I can think of as well. I was thinking more along the lines of global monopoles hoping they might give me a delta singularity but they don't.
Comment: It seems either you can have a conical singularity which is effectively 2+1 D or a discontinuous metric.
Comment: The post pertains to GR, so it qualifies as physics. It is perhaps a more mathematical question or more abstract/less realistically applicable, but that doesn't mean it's not physics.
Answer: Delta functions are discontinuous at the origin. A curvature that is exactly describable by a delta function isn't possible in spacetime as spacetime is seen to be continuous and smooth and hence curvature must be too.
As delta functions have a point that is infinite, the appropriate forms of spacetime, given the criticism above, are spacetimes with an infinite point of curvature.
Such spacetime are given by the Schwarzschild spacetimes that describe black holes and which have essential singularities where geodesics end. These are points of infinite curvature. This could well be one good reason for including torsionful gravity as they do not have singularities such as the Einstein-Cartan theory. It's worth noting that supergravities, which superstring theories reduce to in the weak energy limit, have torsion and so they too do not have singularities.
Comment: This doesn't have a $\delta$-function
Comment: Also less related: do you have a good source for the lack of singularities in Einstein-Cartan? From what I've read, most people only claim it *can be* singularity free, not that this a generic property (and in fact people struggle to construct these with realistic parameters). Would be interested in any sources that have some physically realistic scenarios! Thanks

Delta function singularity in curvature


Good word/phrase for crazy?

Question: The context is like "He'll probably think I'm crazy." The expressions I see mostly are 頭がおかしい and 気が狂う. I've also seen イカれる be used, but I've heard that's really slangy. Are there better expressions to use than these and is there a difference in nuance between these expressions?
Comment: What meaning of crazy are you asking about in particular? Actually mentally ill? Or perhaps, not literally mentally ill, but out of control or extremely agitated? Something else?
Comment: Why don't you edit that into your question?
Comment: Sorry for not clarifying. Not mentally ill but like someone is overly worried or paranoid about something and someone makes a comment like "quit being so crazy."
Answer: "どうかしてる", or "どうかしている"

Good word/phrase for crazy?


Nexus 5: /storage/emulated/0 not mounted

Question: Everything was working fine, and then one day I noticed some errors coming from Google Play store and I couldn't access any of my media. It seems that my external storage in /storage/emulated/0 is not mounted and that applications are looking for data there and not finding it.
I'm using MultiRom, so I flashed a new CyanogenMod 11 ROM and the same thing happened.
I tried CyanogenMod 12 ROMs but they don't seem to boot at all.
I also noticed that my date and time were not right and Whatsapp kept on telling me my date and time are not accurate even though I set them correctly.
I also installed Ubuntu on my phone using MultiROM and for some reason it appears to still be working fine so far so for now I'm using that.
Can anyone help me with this?
Answer: OK, so I finally fixed this problem.
I wiped my phone completely after backing up my data and I used fastboot to flash an all new recovery image and installed a new ROM but still the problem persisted.
Then I noticed that in the recovery I keep getting: "error mounting /persist".
I found and followed this link: http://forum.xda-developers.com/google-nexus-5/general/guide-to-fix-persist-partition-t2821576
And the problem was fixed!
Answer: try rebooting to recovery mode(assuming you have custom recovery installed) and mount data from there. hope it helps.
Comment: How will that help it be mounted when the phone is booted into the OS?
Comment: I booted into recovery mode and used adb shell to ssh into the phone. I saw that all my files were stored under /sdcard (although there is no sdcard in my phone) and I used adb pull to back them up to my computer. I'm pretty sure this is a software problem, so at this point I think I should just wipe the device and reflash a ROM.


bracket, but as a verb in the social sciences

Question: For the second time in a year, I've run across the use of the word "bracket" as a verb in the social sciences, to refer (I infer) to a rhetorical maneuver.  I have no idea what is meant by it, and the dictionaries I've checked haven't helped; this may be too recent or too field-specific a usage.
Examples:
This from a PowerPoint I found on the internet:

Preparing for button-pushing (bracket your values)

It's one of several bullet items on the list, and no useful context.
This is from an academic paper (Warren and Cottone, 2015, Detrimental association: An epistemological connection of dysfunction within and across paradigms, Journal of Mental Health Counseling) in the field of counseling, which can be considered a sub-branch of clinical psychology or of psychiatry:

DAs occur when individuals or systems create associations between psychological (internal) and sociological (bracketed external) variables that lead to poor mental health and well-being. These connections stem from the unintended, yet natural, matching or pairing of internal (self) and bracketed external ([environment]) variables found to encompass an individual or system. Thoughts, behaviors, self, and communication are types of internal variables. They emerge from innate disposition and are deeply ingrained in the individual or system. On the other hand, bracketed external variables, such as environment, power, or absolute truths, are contextually perceived; in other words, they constitute a construction of thoughts and experiences based on the external world.
[...]
At the philosophical level, all DAs are reduced to a single pair of distinct variables. True DAs comprise an internal variable and a bracketed external variable. Regardless of associations found at the practical or theoretical levels, all DAs appear to converge within the self (internal) and the [environment] (bracketed external).
[...]
While the psychological and systemic relational paradigms offer tradi- tional theories regularly considered in practice, there is continued momentum toward implementation of theories embedded in social constructivism. The social constructivism paradigm asserts that individuals, families, and society construct understanding of experience through a consensualizing process (Cottone, 2012). This process or understanding of shared experience occurs through the language used to create narratives of situations and life (Gergen, 2009). Society and subsets of society, such as the individual and religion, create knowledge and construct "bracketed absolute truths" (Cottone, 2012). Shared consensual knowledge or bracketed absolute truths remain relatively constant until they are challenged by a competing framework and a new understand- ing of experience emerges (Gergen, 2009). "Absolute truths" are specific to situations that occur in life and often evolve over time. These consensualities compel individuals to behave in ways that members of their community find acceptable. When consensualities from one facet of life are generalized to other facets, conflict typically arises (Gergen, 2009). And when consensualities conflict, DAs are common. The link between a bracketed absolute truth from one aspect of life and an individual's behavior will require severing or modification through other relational connections, such as counseling, when competing consensualities arise.
[...]
In social constructivism, there is an intimate association between language, relationships, and experiences. Several notable counseling theories, such as solution-focused therapy (Berg, 1993, de Shazer, 1985) and narrative therapy (White, 2007; White & Epston, 1990), fall within this paradigm and are useful in negotiating DAs between opposing sets of absolute bracketed truths.

I don't even know if these are the same usage.
What does this sense of "to bracket" mean?
And from what field or source does it originate?  Is this just an emergent usage, or is there an authoritative coinage as a term-of-art asserted somewhere?
Answer: Both uses of the word bracket are very non-standard.
In the first, the expression "bracket your values" seems to mean to not allow personal values to affect professional behaviour (see here
).
The Warren and Cottone example seems to be the authors' own definition of the word bracketed to refer to a subset of society. I.e. "bracketed external variables" derive from a limited group of like-minded people rather than society as a whole.


Why can't I use another google account on my phone for Pokémon Go?

Question: I let my boyfriend use my Google account because I have two, and now it only signs me on as him even though he signed in on his own phone. Since you can't make a trainer account I was wondering if any of you would know what I could do?! Thanks!
Answer: You can logout of the account by going to settings and you will be able to choose which account you want to login as when you select google login.
Answer: You need to sign out of the account that is logged into Pokémon Go. The associated account is simply used to associate used ID's to the account.
You need to log out of the Google Account he used on your phone, PokeBall -> Settings -> Sign Out, and then create a new trainer with your other account.


how to set NOCOMPRESS flag on a file in btrfs?

Question: according to https://btrfs.wiki.kernel.org/index.php/Compression#How_do_I_enable_compression.3F  there exist a "NOCOMPRESS" flag, how do i set the NOCOMPRESS flag on a file?
Answer: you could certainly have stolen my answer for yourself :)
the easiest is btrfs property set $THING compression none and a defrag to uncompress it. using btrfs property to set the +c force-compression flag is the most flexible, as you can specify a compression type to force, where using chattr it defaults to using zlib.
Comment: he's asking about setting `NOCOMPRESS` and you reply `+c` which is about setting compression, not unsetting ut
Answer: You're probably looking for chattr +m 'FILE'

m      A file with the 'm' attribute is excluded from compression on file systems that support per-file compression.

The +c option mentioned by @Andrew Keech is the opposite.
Note, however, that there are mount options in btrfs that will disregard the NOCOMPRESS flag, as mentioned in the docs you provided.


Galois group of $x^4 + 2$ over $\mathbb{Q}$

Question: I have a problem finding Galois group of $x^4 + 2$ over $\mathbb{Q}$. Not sure whether to start. It's irreducible over $\mathbb{Q}$ and also have 4 different roots.
Answer: Note that $\varepsilon_8^i\sqrt[4]2$, for $i=1,3,5,7$, are roots of this polynomial, where $\varepsilon_8=\frac{\sqrt 2}{2}+i\frac{\sqrt 2}{2}$ is the eighth primitive root of unity. Hence splitting field is $K=\mathbb Q(\varepsilon_8,\sqrt[4]2)=\mathbb Q(\sqrt[4]2,i)$. You can easily see that $|K:\mathbb Q|=8$, hence $Gal(K/\mathbb Q)$ has $8$ automorphisms. Automorphism $f$ is determined by $f(i)$ and $f(\sqrt[4]2)$, and $f(i)\in\{i,-i\}$ (roots of minimal polynomial of $i$ over $\mathbb Q$) and $f(\sqrt[4]2)\in \{\sqrt[4]2,-\sqrt[4]2,i\sqrt[4]2,-i\sqrt[4]2\}$ (roots of minimal polynomial of $\sqrt[4]2$ over $\mathbb Q$; it is $X^4-2$). So, every combination gives an automorphism.
Now you can calculate that $Gal(K/\mathbb Q)\cong\mathbb D_4$.
Comment: Could you briefly note what calculations one should do to determine this Galois group?
Comment: @GuusPalmer You can just write the Cayley table for $Gal(K/\mathbb Q)$ and compare it with Cayley table for $\mathbb D_4$.
Comment: The only problem is that we can't use such a table at an exam. In the lectures we discussed something about the group behaving transitively. Also, when you look at compositions of automorphisms of the extension and they can be interchanged (composition switch of the two automorphisms) then you have a certain Galois group like $C_n$ or $S_n$ and otherwise $D_n$. Is this somewhat the idea or am I thinking stupid now?
Comment: @GuusPalmer Galois group of a polynomial always acts on its roots, and every automorphism is determined by the values on the roots, so Galois group is a subgroup of $\mathbb S_n$, where $n$ is the (separable) degree of the polynomial. If the polynomial is irreducible, the above action is transitive. Now, above you know that $Gal(K/\mathbb Q)$ is a transitive subgroup of order 8 of $\mathbb S_4$, so you can deduce that it is $\mathbb D_4$. You can also note that it is a Sylow 2-subgroup of $\mathbb S_4$, so it must be $\mathbb D_4$. But it is really not a universal recipe.
Answer: Let $0<a\in \mathbb Q$ be an element which it not a square in $\mathbb Q$. The roots are $\pm\sqrt[4]{a}$ and $\pm i\sqrt[4]{a}$.
Now we determine $[L:\mathbb Q]$ where $L=\mathbb Q(i,\sqrt[4]{a})$ is the splitting field of $f$
We have $[L:\mathbb Q]=[L:\mathbb Q(\sqrt[4]{a})]\cdot [\mathbb Q(\sqrt[4]{a}):\mathbb Q]$
The first factor is two because the degree of the minimal polynomial of $i$ is bounded by 2. ($i$ is a root of $X^2+1$). However it can't be one because $\mathbb Q(\sqrt[4]{a})\subset \mathbb R$ and $L$ contains complex numbers, hence $[L:\mathbb Q]=8$.
The second one is $4$ because $a$ is not a square in $\mathbb Q$
There are 5 possibilities for $Gal(L/K)$. $3$ are abelian and $2$ not. But $1$ of the $2$ non-abelian groups has only normal subgroups (Q_8) in contrast to the other one (D_4).
So write down some elements of the Galois group and see if they generate a normal subgroup or not.
Note that the elements of the Galois group are determined by the images on the generators, for example:
Let $\phi_1:i\mapsto -i$, $\sqrt[4]{a}\mapsto \sqrt[4]{a}$. Then $<\phi_1>=\{\phi_1,id\}$
and $\phi_2:i\mapsto -i$, $\sqrt[4]{a}\mapsto i\sqrt[4]{a}$.
Now $<\phi_1>$ is not normal because $\phi_2\circ\phi_1\circ\phi_2^{-1}\notin<\phi_1>$, hence
$Gal(L/K)\cong D_4$
This list may also help.
Question: What is the Galois group if $a<0?$
Comment: I think you've done $X^4-2$ by accident here. The answer of @SMM is correct.
Comment: Like Nick said, this answeres a different question


Is it allowed to bring condoms in airplane?

Question: I'm about to travel via Wizz Air and only have hand baggage. Can I bring condoms on board?
Comment: What exactly are you worried about? Is there a specific reason why you think you can't take condoms on board?
Comment: sometimes I don't bring any other luggage
Comment: If you are going to blow balloons with them in the cabin, then no. Else why would they refuse ?
Comment: @drat Presumably the concern that you might try to use them during the flight ;)
Comment: @DumbCoder balloons are a problem in [train stations](http://travel.stackexchange.com/questions/34695/why-are-balloons-prohibited-at-amsterdam-schiphol) but I don't see why they'd be a problem on planes.
Comment: Not sharp, flammable nor liquid. You will be able to stay protected while joining Mile-High Club
Comment: My fiancé had his condoms confiscated today by TSA at ACK airport.
Comment: @MeaghanHogan interesting, did they give the reason?
Comment: Maybe concerned about being accused of being drug mule?
Comment: @drat There is an old but untrue urban legend that condoms somehow loose their effectiveness as a result of the in flight pressurization / de-pressurization.
Comment: Don't see why any airline would have a problem with them as long as they're A) unused, B) legal in both the departure and destination country.
Answer: Yes, and there are great articles online detailing travelling with condoms.  They're not liquids, flammable or on any of the TSA unapproved lists, so you're totally fine to take them.  However, remember they're meant to be stored at room temperature as they are still medical devices you don't want to take risks with damaging them. Don't store them with sharp items in your carry-on (even pens etc).  If your laptop or phone gets really warm, it's best not to have them side-by-side either.
However, there are also stories of travellers being detained because of the condoms in their luggage, where they were accused of being working girls(!), so ... all things considered, it might be better to just get some at the destination.
Comment: Note that Wizz Air doesn't fly anywhere near the TSA.
Comment: As the old joke goes "Sir, why did you bring condoms? Now we're gonna have to do a full cavity search" -> "my plan is working~"


When an article for a long time is under review ,how can we send a letter to editor for status manuscript

Question: we have submitted our article to a journal  but for a long time status is under review .
what can we mention in our eamil to editor for condition the article?
Answer: Just write saying that your article has been under review for a long time and ask for a status update. Don't overthink it. Editors see this kind of email all the time, enough so that they probably don't pay attention to the exact wording.
Only thing is be sure to include the information necessary to identify the paper - e.g. the article ID number.


javascript library for css3 in old browsers

Question: Can you link me some javascript libraries, that can give me full support html5 and css3 on all browsers?
That library must get that support without any css file changing.(e.g. i made some gradients and shadows on page, and i dont want to rewrite them to be fully supported by that library)
Answer: You probably don't need everything. This list will help you pick the features you realy do need: http://github.com/Modernizr/Modernizr/wiki/HTML5-Cross-Browser-Polyfills
Update: Gradients and shadows in older Internet Explorers are easily handled by CSS3 PIE library.
Answer: What you want is CSS3PIE. You do need to make some minimal changes, but it's definitely the best way to go.
For border-radius and box-shadow you just need to add a line adding a behaviour, for gradients it's a little more.
You might find that you need to add position:relative; to elements to get the grad or shadow to show up.


Why aren't the user accounts linked in migrated questions?

Question: The MSO-MSE split has finally happened and the very first question migration done was this. But I do not understand why the user accounts in that question are not linked? I can see that only Shog's account is linked and all the other user accounts(the answerers) are not linked yet. As far as I know, if a migration happens and the user does not have an account in the migrated site, only then the account is not linked but in this most of users do have their accounts on the new MSO. Why aren't the accounts linked to the posts then? Can someone throw some light on this?
Comment: Probably a symptom of a Behaviour of Unexpected Genius.
Answer: You don't get a profile on a child meta by default. You still have to visit the site to have the profile created for you even if you participate on the main site.
If you look at /users right now and try to search for, say, ThiefMaster, you'll see that there's no MSO profile for him yet. He'll create one later, I'm sure, and then his contribution to that question would be properly linked up to his profile on this site... if the migration history wasn't cleared on that question.
I'll reassociate your answer with your profile, and we'll probably have to (eventually) do the same with the other ones on that question. Although honestly, it doesn't matter as much here since posts don't affect your MSO reputation, etc.
Comment: Yeah I know that it doesn't affect the reputation. I'm more concerned about looking for them in future. If it were linked to my account, it would be easier to find it than having to search it on MSO. This is just the start of the migration I guess. So this might become a bit troublesome in the future with more questions being migrated. Because having to link the accounts manually so many posts, is really going to be a problem, for the mods and the devs I suppose.
Comment: @Ɍ.Ɉ Clearing migration history is a manual step. If it becomes problematic, we can just not do that for a while until most profiles have been recreated and post ownerships remapped.
Comment: @OneKitten Comments are never reassociated if the author doesn't already have an account at the time of the migration.
Comment: @AnnaLear: oh wait, my bad, that was something else. Sorry.
Comment: I tend to associate the default gray user icon with "user has deleted his account, question probably isn't worth answering". I guess the user wouldn't receive any notifications even if his question got answered now, right? So I'd very much welcome any automatic process to create MSO accounts for everyone whose posts got migrated.


How to find ignition wire on mercedes truck

Question: Hi all I need to find ignition wire as I need to connect t to my ower supply. This should be behind the key lock right? How do I approach to it and how to know which one is right wire?
Truck s Mercedes Atego 2005 year
Answer: What are you trying to power? The ignition wires are generally only intended to power the ignition - if you want to run anything else you are better off taking an appropriate feed from the fuse box, or a relayed feed from the battery, depending on the power draw of the intended application.
Either way, the best place to look is a wiring diagram for the truck in question - usually found in the back of any decent workshop manual. This will give you the colour codes of the wires you are looking for - ignition-fed live feeds are usually red, but this does vary by manufacturer.
Comment: I need to send the signal to my unit when key is turned on or off. That's why I need this. Problem is there is now manual for it. Not that I can find of any
Comment: Ah, in that case you want to look for the signal wire going to the stereo - Yellow according to the proper ISO colour code, but again this may very according to manufacturer. The best place to look for that would be behind the stereo.
Comment: Thank you so much. So I just pull out the stereo and see where ign is going right? Yellow one you say? Yea that's usually the right color. I think it should be according to ISO as this is Mercedes :) They have standards
Comment: As the other reply says - check with a multimeter first to work out which is which! Looking at the link you posted below, I would expect the PSU to have two inputs, one expecting a permanent live feed and one taking a switched feed, so that it can send the 'power off' signal to the motherboard when you switch off the ignition. It'll draw more current from the permanent feed, so make sure you use a good feed, separately fused, for this.
Answer: I wouldn't necessarily jump to the stereo wire; this would depend on where your unit will be mounted and what it is. As stated; you shouldn't draw excessive amounts of power (>2-3 Amps or so) and it should be fused. If you will be needing lots of power then use the ignition wire to switch a relay with battery power, not to provide power itself.
If you're mounting it behind the stereo; then by all means use the stereo. Yellow is usually constant 12V from the battery (unless Mercedes is different in this regard) and Red is usually switched (only provides 12V when the ignition is in Accessory or On).
There may be other reasons you would not want to use either of these; first if the unit will not be anywhere near the stereo and second if you need ignition-on only (off for accessory).
My first stop would be the fusebox. That will contain most sources of power to tap into; accessory and ignition-on, ignition-on, and start. You'll need to find an appropriate fuse (avoid important ones like 'fuel inj.', etc.) and tap into the fused side if you want to do this; they even make terminals for such a job that straddle the fuse pin and present a terminal above the fuse. If you get lucky, there are many times empty slots with a live pin on one side that is the type you are looking for, so you can add your own fuse and not piggyback on another circuit's.
Comment: Hi thank you for your information. So basically why I need ignition off and on is to power a PC in the car. I have this power supply which gives me stable power. So what do you suggest me for this item? LINK: http://www.mini-box.com/DCDC-USB
Comment: I would want that on for both accessory AND ignition-on, if you want it switched at all. If you're mounting it near the stereo, pick up the wire that carries this to the stereo (most likely the red wire). Note that you should not add more than 2-3 amps to this wire; so depending of what you mean by 'PC', you should probably use a relay. However, if it were me, I would want the computer to stay on until shut off, even with the car off; maybe with some hidden on/off switch.
Comment: I will put it near the fuse box. I will take free one from the board for the input power. But there is not ignition on signal there right? I need to draw that wire from stereo for example. This unit that I have showed you is really great it starts after 20sec and delays shoutdown for 20sec and then cut the power source.
Comment: That will be in the fuse box as well. Probably 'Radio' or 'Accessory'. Take a test light and probe the tops of the fuses while you change the key position (start in accessory or ignition, whichever one you want) - you'll find one that's the right one.
Comment: Can I ask you what is the best way to connect to the fuse box? Are there any special wires? and when I will use ignition, it is a wire that is coming from fuse box? do you have some link of what elements I can use to connect to the fuse box? As I don't want to be screwing something and I'll do it by myself.. Please help. You can send me an email if you don't want to be talking in here
Comment: can you look at this fuse box and tell me where would you connect it? http://www4.mercedes-benz.com/e/trucks/atego/betriebsanleitung/vertiefen/d13e27648.html#d13e28711
Comment: the radio almost certainly has a 10 amp fuse, which if you convert to watts for 12 volts, is only 120 watt.  You need to find an unused fuse spot in your fuse block and tap in there, or tap into the wire for cigarette lighter if it has one.  Those are 20 amp.


Will LD33V voltage regulator overheat with 12V 2.4A dc input?

Question: The circuit works and it provides a stable 3.3V output, but it heats up and I'm afraid it can overheat and cause problems.
Comment: The problem is not the source.  It is the load.  How much current are you using in the 3.3V section?
Comment: @JRE I'm using about 700mA
Comment: @MaxPower Then you can calculate how much power your regulator will have to evacuate, and then find a radiator with low enough thermal resistance. Or better replace that linear regulator with a buck switching regulator, like a LM2576.
Comment: @user2233709 That is so cool, I will definitely use switching regulator in future, but for now I already have a circuit ready. I will try calculating, but I'm not exactly sure how :)
Thanks for answers
Comment: @MaxPower Enric Blanco did the math for you.
Answer: Check the datasheet and do the math. Short answer: YES, it will overheat A LOT!
With that huge 8.7 V voltage drop, if the load required the full 0.8 A that the LD1117V33 can output then the power dissipation would be approx 7 W, which is well below the 15 W maximum rating.
However, the temperature rise at 7 W dissipation without using a heatsink (50 C/W) would be a mind-boggling 350 C, and the junction temperature would go far above the maximum 150 C rating.
At Tamb = 25 C, the maximum allowable temperature raise would be 125 C. At 50 C/W the maximum allowable power dissipation for that temperature rise would be 2.5 W. This would mean a maximum 0.36 A current draw from the load. And you should derate this to 50% (or 70% at most) for reliability reasons, so let's say your maximum current draw should be 180-250 mA.
If your load draws more current than that, then you'll need a heatsink in order to reduce the temperature rise. The maximum thermal resistance (junction to ambient) for a temperature rise of 125 C at 7 W dissipation is 17.8 C/W. The case itself has 3 C/W (junction to case), so the heatsink should have a maximum of 14.8 C/W (case to ambient). You should derate this too, so you actually want a maximum of 7.4-10.4 C/W for your heatsink.
However, the best solution by far is to use a switching regulator / DC-DC  step down converter. A linear regulator is very inefficient power-wise, when used with such huge voltage drops. The switching regulator will not need a heatsink because it doesn't dissipate that much power to begin with.
Comment: Thanks! That's a delicious answer and it clears a lot of questions :)
Comment: Please note that operating at higher ambient temperatures will **reduce** you maximum allowable temperature rise. This in turn will mean either 1) lower maximum current draw without heatsink, or 2) lower maximum thermal resistance required for the heatsink. You might want to redo the math according to your actual operating temperature range (I just did the math for 25 C as a reference for you to follow).


Token for full path in Texmaker

Question: I am configuring custom commands in Texmaker, I can use <code>%</code> as a token for the name of the file (minus the extension) but I cannot find an equivalent for the full path.
Answer: I'm afraid such a token might not exist. The Texmaker manual, section 1.2 Configuring the latex related commands only mentions these tokens:

The % character represents the name of the file without the extension (the master document in the "master" mode) and the @ character will be replaced by the current line number.
  Additional parameter : # will be replaced by the current file name without extension (even in the "master" mode)

But you can see if there's a similar feature request on the Texmaker issue tracker already, and if not, file one.
Comment: I've added a feature request: https://code.google.com/p/texmaker/issues/detail?id=496
Comment: @Ben Your feature request seems to have been deleted -- did you get any feedback why?
Comment: I don't remember - I haven't kept any of the emails so I couldn't say. I seem to recall that people misunderstood the subtle problem and said I was mistaken for adding it.
Comment: ...I seem to recall that people misunderstood the subtle problem (Opening the PDF in Foxit Reader if FR was already open), or thought that I was mistaken and that such a token would never be necessary under any circumstance. Presumably the working directory of the reader is set to the directory containing the PDF, so that a full path is not necessary - except if the reader is already open in which case it fails.

Token for full path in Texmaker


Hefsek (interruption) between the blessing on food and eating the food

Question: Is it considered a hefsek to play with one's fingers or silverware or such while waiting for the challah to be passed around on shabbat, after the blessing made on it? Even though it isn't talking, it is an activity unrelated to eating bread.
Answer: I don't have any sources off the top of my head to corroborate this, but I would say it's not a problem. The whole problem with talking in between making the bracha and the concluding act of eating is that you are taking the attention away from the main activity of the moment - waiting for the bracha to be said. Although playing with your fingers is not related to this, as long as it's not disruptive, it should have the same status as adjusting your seat when you sit down at the table.
Comment: Perhaps it'd depend on whether one is paying attention to the fingers he's playing with or just playing mindlessly? (Just thinking aloud here.)
Comment: also adjusting your seat is letzorech achila.
Answer: I did not find any sources which explicitly address this (which is itself somewhat telling), but we could try to construct a picture based on the cases that are discussed.
There are two parts to the question, as with all discussions of hefsek.  1 - Is this something you are allowed to do? 2 - Is this something that, if I have done it, will cause me to need to make a new blessing?
I think part 2 is easier to draw support that in your case you would not need to make a new blessing:
Rashi (Berachos 40a) s.v. טול ברוך, writes:

ואף על גב דשיחה הויא הפסקה כדאמרינן במנחות (פרק ג' דף לו.) סח בין תפילין לתפילין צריך לברך
(Summary) Conversation is a hefsek, as we say regarding Tefillin.

Rashi understands that the laws of hefsek from birkas hamitzvah can be extrapolated to Hamotzi (and presumably all birkas hanehenin).
By Tefillin, the Mishna Berura 25:29 cites the Artzos Hachaim (Malbim) that לכתחילה you should not interrupt by making gestures with your fingers or hinting with your eyes.  But if you did, it would not constitute grounds to need a new blessing.  Tapping your fingers, even very consciously and intently, is no worse than that, and tapping mindlessly is surely much better.  Therefore, I think it is safe to conclude that you would not need to make a new blessing.
Part 1 is not as easy to support so directly.  The discussion in the Shulchan Aruch only mentions hefsek of delaying (O.C. 206:3):

כל אלו הברכות צריך שלא יפסיק בין ברכה לאכילה. הגה: יותר מכדי דבור

and hefsek of actual speech (O.C. 167:6):

יאכל מיד ולא ישיח בין ברכה לאכילה ואם שח צריך לחזור ולברך

Minchas Yitzchok (7:9) adds humming a tune, and Sefer Birkas HaBayis (38:2) adds grunting or making noises to intimate alacrity or anger (basically, saying "nu?!)"  As mentioned above, pointing or making eye motions would also be ideally prohibited.  These all seem to have the common denominator of being related to communication in some way.
The Mishna Berura (Shaar Hatziyun 167:28) extends this issue to walking around.
No one seems to extend the issue to something done mindlessly, so that would seem to be okay.  If you were doing it with serious intent, it is still not included in the list of things mentioned explicitly.  Perhaps it could be on a level comparable to walking around, but in my mind it is less of a real "action" to just play with your fingers.
Comment: +1 I'm not sure humming a tune has to do with communication. Will have to see the responsum inside.
Comment: @DoubleAA You're not Chassidish enough then. :)
Answer: see משנה ברורה ס'רו ס''ק יב who says clearly so long as one did not talk after the bracha it is only a hefsek if he is מסיח דעת which means so long as he didn't start thinking about something else, and take off his mind what he is waiting for (or talk) it is not a hefsek and he does not (and can not) make another bracha.
Comment: Isn't that only talking about Bedieved?
Comment: yes לכתחילה one should not be מפסיק longer than כדי שאילת תלמיד לרב ,see mishna brurah quoted above, i was only saying it is not a problem if one did so....
Comment: But here he's waiting anyway for the challah to be passed. So does it matter if he's doing something else non-verbal in the meantime?


How can I keep my Kumquat tree from growing too tall?

Question: I'm planting some Kumquats along the side of the drive. However, I notice they grow to 3-4 metres (10-13 feet) high and wide. How can I keep them smaller? I considered putting the pot into the ground to stunt their growth but am concerned the plants will become weak.
Answer: You can't, really, not and still have them fruit anyway. Putting them in pots and planting them in those into the ground won't work either - restricted in a pot (unless the pots are extremely large) they will eventually die; but it's highly likely the roots will break through the holes in the bottom and root into the surrounding soil anyway, which rather defeats the object. The only pruning these trees require is removal of any sucker growth and a fairly light prune to reshape immediately after harvesting the fruit and well before they flower in spring. If you're not worried about flowers and fruiting, then you might be able to prune them back more often. More info on growing these trees here: Kumquat Tree Care: Tips For Growing Kumquat Trees.
Answer: Orchardists regularly tip the leaders of their trees to keep them smaller so they are able to restrict their growth.  The backlash is this sends all that energy back to the branches to encourage lateral buds, suckers to grow.  That is why they create dwarf varieties.  Those apical or terminal buds have the most energy within the entire tree/shrub.  When those are cut, that energy is then distributed among the lateral buds.  Do not put them in pots to bury in the ground.  I'd rather have vigorous too high trees than do that...root pruning does not necessarily dwarf a plant.  It does reduce the vigor and ability to pull chemicals out of the soil that it needs with which to do photosynthesis.  I would nip the leaders, prune the suckers and make sure I did not give my trees too much nitrogen...which promotes vegetative growth not reproductive growth.  And buy a ladder or two, grins.!e
Comment: Thank you both very much. Your answers were very helpful indeed. I'm new to all of this so bear with me :). Excuse my ignorance, what are the 'leaders' of the tree? The upwards growing i can manage but I assume this means I will need to plan a little further apart than I'd anticipated, I guess 3 metres apart?


Is $\sf{P^{NP \cap coNP}} = \sf{NP \cap coNP}$?

Question: If it is unknown, are there reasons to believe that they might not be equal?
Answer: First, this result is listed in the complexity zoo: https://complexityzoo.uwaterloo.ca/Complexity_Zoo:N#npiconp. Alternatively, it's possible to prove without much trouble (which I do below).
We want to show that $P^{NP \cap coNP} = NP \cap coNP$. Clearly, one direction is obviously true: $NP \cap coNP \subseteq P^{NP \cap coNP}$. To prove the other direction, it is sufficient to show that $P^{NP \cap coNP} \subseteq NP$ since then $P^{NP \cap coNP} \subseteq coNP$ follows simply by complementing all the languages involved and as a result $P^{NP \cap coNP} \subseteq NP \cap coNP$.
So let's prove that $P^{NP \cap coNP} \subseteq NP$.
Suppose we have a deterministic polynomial time machine $M$ which makes oracle queries for languages in $NP \cap coNP$. We define a new, non-deterministic machine $M'$ based on $M$ as follows:
Simulate $M$ until $M$ needs to run an oracle query on some input $x$ for some language $L$. At that point, run a subroutine which branches $M'$ into some number of branches each of which attempts to learn the answer to the oracle query. The subroutine is designed so that no branch learns the wrong answer, at least one branch learns the correct answer, and some branches get "inconclusive" as a result when trying to learn the answer to the query. In $M'$, the branches with inconclusive results then reject. At this point, the only branches left are ones which know the correct answer to the query. Thus we can continue the simulation of $M$ in these branches. At the end of the simulation, the only branches which haven't rejected are the ones which successfully got through all of the steps of the simulation. These branches accept iff $M$ accepts, so the overall $NP$
Since $L \in NP \cap coNP$, there exists a NP machine $N_L$ with language $L$ and another machine $N_{\neg L}$ whose language is the complement of $L$. To simulate the oracle query (is $x$ in $L$), $M'$ first runs $N_L$ on $x$ and then runs $N_{\neg L}$ on $x$ in every branch. Every resulting branch will have one branch of $N_L$'s computation and one branch of $N_{\neg L}$'s computation. Within any single branch, both the $N_L$ computaion and the $N_{\neg L}$ computation cannot be accepting since that would require $x$ to both be in $L$ and in $\neg L$. Thus each branch will have either the $N_L$ computation accepting, the $N_{\neg L}$ computation accepting, or neither computation accepting. Furthermore, there must be at least one accepting branch of either $N_L$ or $N_{\neg L}$. Next, $M'$ rejects in the branches in which the computations of both $N_L$ and $N_{\neg L}$ reject. In all other branches, $M'$ has learned the answer to the oracle query (since either $N_L$ or $N_{\neg L}$ accept $x$ in the particular branch considered in this $M'$ branch). At that point, $M'$ can continue the simulation of $M$. Note that the simulation will actually continue in at least one branch since at least one accepting branch of either $N_L$ or $N_{\neg L}$ exits.
Comment: In my proof, I rely on the existence of both an NP machine and a coNP machine for the language of the oracle in order foor the simulation to branch such that each branch either gets a result of "inconclusive" or the correct answer. If all you have for the language of the oracle is an NP machine, then you are not guaranteed that some branch gets a conclusive answer: in the case that the NP machine rejects, every branch rejects, which is inconclusive. Thus the same proof fails to show $P^{NP} \subseteq NP$. More generally, an $NP$ oracle is more powerful than an $NP \cap coNP$ oracle.
Comment: Thanks! I actually checked the complexity zoo but somehow missed the "Equals $\sf{P^{NP \cap coNP}}$" statement. I have only one question. Why would your proof fail to show $\sf{P^{NP}} = NP$? I'm always hesitant when designing a non-deterministic algorithm/Turing machine to do anything else after the non-deterministic branching to not fall in the trap of giving a $\sf{P^{NP}}$ algorithm instead of an $\sf{NP}$ one. In your proof if the oracle were just an $\sf{NP}$ oracle, then couldn't M' simulate it the same way as you described here (only run $N_L$ in the simulation) ? Where's the catch?
Comment: (just to add a clarification, $\sf{P^{NP}}$ contains $\sf{coNP}$ since the $\sf{P}$ machine can just negate the answers of the $\sf{NP}$ oracle. So if $\sf{P^{NP}} = \sf{NP}$ then $\sf{NP} = \sf{coNP}$ and the polynomial hierarchy would collapse)


Hypergolic Propellant Combination

Question: Is Rocket Grade Hydrogen Peroxide and Liquid Hydrogen a hypergolic propellant combination?  I recall, seeing the combination somewhere on the www, however I couldn't retrace the source where I saw it.
Answer: I'm going to say yes, depending on how loose you want to be with definitions. Hydrogen peroxide as rocket fuel is decomposed by passing it through a metal catalyst screen, producing water, oxygen, and heat. At 90% concentration the temperature is around 800 °C (see figure 2). The autoignition temperature for kerosene is 210 °C. It worked for the Bristol Siddeley Gamma engines used in Britain's Black Arrow, and which used 85%. So it's not that hydrogen peroxide and hydrogen will spontaneously ignite, but that the decomposition temperature of hydrogen peroxide is high enough to ignite the hydrogen. On the other hand, you just put a catalyst on the injector, it's not like you have to shoot a pyrophoric slug into the combustion chamber.
Edit: I said kerosene. I don't know why I said kerosene. Actually, I know why -- because I didn't read the question carefully. But the answer doesn't really change.
Answer: As far as I know the answer is no.
The autoignition temperature of Hydrogen is 536 °C according to Wikipedia.
Although this temperature could vary with pressure, I am also unaware of LOX/LH2 being hypergolic, hence adding water to the mixture (you asked about hydrogen peroxide) should not make things that much easier.
Comment: I'm not sure what you mean by tranferred heat, If you run peroxide over a catalyst, it releases enough energy to heat *itself* to about 600C, so if you then added some hydrogen it would very possibly auto-ignite  with the oxygen in the decomposition products, so you wouldn't need an additional igniter.
Comment: It's possible that the hydrogen would catalyze the decomposition of the peroxide, which produces oxygen and steam at something not far from that autoignition temperature.
Comment: @SteveLinton You could add some other catalyst as well to start the combustion, but if a certain amount of transferred heat needs to be given for the reaction to start, I'd argue that by definition it would not qualify as an hypergolic mixture.
Comment: To clarify: A combustion essentially sustains itself by producing enough heat to activate more of the same chemical reaction, causing a chain effect, but it requires ignition to begin. Hypergolic implies spontaneuous combustion, so the activation energy should be around the available energy of the involved particles.  You make a fair point that by heating one element *and then* mixing you technically did not use an external ignition, but I believe this is somewhat a borderline case. I'm also unaware of this being technically feasible.
Answer: No.
For a propellant (i.e. oxidizer and fuel) combination to be hypergolic, either one of the following two conditions need to be met:

One of the propellants reacts rapidly and exothermically with the other OR
One of the propellants induces rapid, exothermic decomposition of the other

Hydrogen does not react directly with hydrogen peroxide (unless you can generate highly reactive hydrogen atoms which only exist at high temperatures). Also, liquid hydrogen is not a good catalyst for hydrogen peroxide decomposition. Besides, the very low temperatures of liquid hydrogen will hinder decomposition and reaction rates.
However, one way of making this propellant work is by first using a metal catalyst to decompose the peroxide. The heat and oxygen generated from this can then be used to reliably ignite the liquid hydrogen. But then again, going by the strict definition, that's not a hypergolic combination.

Hypergolic Propellant Combination


How to change shell without the command line

Question: Something broke my fish and I have no idea how to fix it so is there a way to change shell to zsh without using the command line
Comment: Use `gedit` or another GUI editor and change the shell in `/etc/passwd`. Alternatively, boot Live media and edit `/etc/passwd`.
Comment: thanks, that worked
Comment: @berndbausch Editing `/etc/passwd` manually is a bad idea. If you make a mistake, it can be very difficult to recover.
Comment: I know one should not edit the passwd file. Right now, however, OP is already in a difficult to recover situation.
Answer:
Something broke my fish

It's probably your fish configuration file. Use a GUI (e.g. a file browser) to rename ~/.config/fish to a different name. That means navigate to your home directory, then to the .config subdirectory, and then rename the fish entry to fish.save.
Alternatively, configure a terminal emulator to open a different shell. Most fancy-GUI terminal emulators let you set up profiles with different settings such as which command to run. Arrange to use another shell, for example zsh, while you fix fish.
Alternatively, use your desktop environment's "launch program" feature and tell a terminal emulator to run a different command, for example xterm -e zsh or gnome-terminal -e zsh or whatever terminal emulator you want.
If you want to change your login shell from fish to zsh, run the chsh command in the terminal. (Without sudo! It needs to run from your own account.) Alternatively, this can be done from most desktop environments' user administration panel.
Answer: There are more than one places the default shell of a user may be stored in a system. The default location, on a fresh installed linux system, probably will be the file /etc/passwd.
This file includes all the users of your operating system. Each line, contains information separated by a colon (:). The last part of each line represents the default shell of the user. This is the place you are looking for.
In order to edit this file without using command line, I suggest two different ways:

You may boot from a Live CD, like ubuntu and edit the file /etc/passwd located in your disk.
If you can't boot from a live cd, you may unplug your disk from your computer or laptop and plug it in another computer. After mounting it, you will be able to find and edit the file.
Comment: That "this file" being `/etc/password`. On your run-of-the-mill system, without LDAP or such..
Comment: You are correct, I update the answer. Preoccupied with a single leaf, you won't see the tree.


How to populate multiple coordinates on map

Question: I have two custom objects in Master-Detail relationship, there is a GeoLocation field on child object, now I have to display pin all the location of child record on the Master object page.
I am able to do this using API http://maps.googleapis.com/maps/api/js
but was wondering, would it be possible to download map and save it within Org,
and then using JavaScript, pin the locations.
I am not pro at JavaScript, and this could strange idea, but I have been asked avoid use of googleapis :(
Answer: Soon, you won't even need Javascript. Check out the apex:map and apex:mapMarker components. I believe they are in beta, but then again the same is the case for the Geolocation field type.


How do we get users to accept answers?

Question: I'm noticing a few active members of this site with very low accept rates. Is there a generally accepted method for enouraging those members to go back and accept answers? Or at least to get them to revisit the question if none of the current answers are acceptable?
Answer: I think you're doing exactly the right thing, by gently reminding them of the option to accept an answer (some may not be aware of this option) and by explaining why it benefits them and the community to select an accepted answer if one of the answers did solve their problem.  Keep it up!
Comment: This is probably the best approach for now. It isn't a lot of users, so pointing it out to them directly isn't too hard.
Comment: An automatic notification would maybe also do: your question was answered $x$ times but you selected no answer. Maybe at intervals of exponentially increasing durations. Maybe with a reset of the time interval whenever a new answer is provided.
Answer: It depends on the kind of user you're talking about.
Some simply do not know about the feature, and you(or better the software) should tell them about it.
If you're talking about the more active users with bad accept rate, like fgrieu or me, then I don't think there is much you can do about it. When I don't accept an answer, I either need to do some work myself like investigate the answers or improve the question, which I haven't done yet, or nobody posted an answer yet that answers the question.
I believe in accepting an answer only if it answers the question fully, and just up-voting but now accepting if it makes good points, but isn't complete.
Looking over my own questions with unaccepted answers:

No acceptable answers:

Why do new versions of TLS use an explicit IV for CBC suites?
Proof of work for standard computers
Which blind signature schemes exist, and how do they compare?
Using same keypair for Diffie-Hellman and signing

Need to improve question:

In which situations is a length-extension attack a problem?

Need to investigate answers(and possibly write my own):

Purpose of outer key in HMAC
Answer: Isn't it a vanity to want members to accept one of the answers? My practical experience is:

Have a question
'search for it' (google)
Find existing question on stackexchange
use fragments from three answers
go off and user them
(sometimes I find a better answer and then I come back and add what I've found)

Obviously I like votes and badges and the like, but for me it does not matter, (I'm probably missing something but I'm already back working by the time you read this.)
Comment: I wouldn't say it is a vanity in most cases, definitely in some though. Reputation points help establish the community, identify experts, and help other users with the same question at least know which answer was best in the OPs mind.

How do we get users to accept answers?


Estimating the uncertainty of regression models

Question: Given a regression model, with n features, how can I measure the uncertainty or confidence of the model for each prediction?
Suppose for a specific prediction the accuracy is amazing, but for another it's not. I would like to find a metric that will let me decide if, for each frame, I would like to "listen" to the model or not.
Comment: Mean squared error? Mean absolute error? What kind of loss function are you using? // Do you mean that you want to know by how much a single prediction misses the true value, even if you don't know the true value? That presents challenges.
Answer: This is evaluation and it's done experimentally: with a test set of fresh instances containing the true target value, apply the model and measure the error across all the instances (e.g. with MAE, MSE, RMSE...).
Assuming that the test is a sufficiently large representative sample of the data, it's possible this way to estimate the quality of the model statistically. For example, we can say that an instance is in average predicted within range $x$ of the true value.
But in general it's impossible to know how good a prediction is for a specific instance: by definition, a model gives its best prediction. If the model was able to know that its prediction is bad, logically it should give a different prediction. Note that if this was possible, it would also be possible to build a near-perfect model iteratively: as long as the prediction is bad, try again.
For the record, there are some task-specific cases where one attempts to estimate the confidence of a supervised model (for example MT quality estimation). This is done by building a new supervised model in order to predict a confidence score. This new model can also make errors, of course.
Answer: To answer my question, I will use three types of models -

KNN Regression
Regression Trees
Complex models like NN or SVM

KNN Regression
It is a non-parametric regression model, and the confidence might be explicitly modeled using mean absolute error or mean squared error. At the test time, for a given instance, K nearest instances will be found, and depending on their average distance with the given instance, we can compute mean absolute error or mean squared error. We can estimate the confidence using these metrics. A higher mean absolute error or mean squared error would result in a lower confidence value and vice versa.
Regression Trees
When building the tree during the training time, we make the leaf nodes by assigning the average target value of the associated instances to the node. While doing so, we can also assign and maintain the average mean absolute error or mean squared error between the average target value and the target values of the associated instances of the node. Similar to taking the standard deviation of the target values of the instances of that node. So, at the test time, for a given instance, when the tree reaches a specific leaf node, along with the regression target value, we will also get the mean absolute error or mean squared error we can expect for instances that end up at these nodes. And as explained in KNN regression, we can model confidence accordingly.
Complex models like NN or SVM
These simple techniques discussed above could be applied to these models as well. Just like KNN regression, at the test time, for a test instance, we might be able to find the nearest K instances from the training set and compute mean absolute error or mean squared error to get estimated confidence. But, there is a lot more we can do. You can read more on this thread (https://stats.stackexchange.com/questions/247551/how-to-determine-the-confidence-of-a-neural-network-prediction) where people discuss something very similar that you might find useful.


200+ phototransistors and reading them

Question: Im hoping to get some suggestions and ideas on how to read in 200+ phototransistors voltages (0-5) into an ADC?   I only need to look at 1 by 1 rather than all at once.
Comment: Can you not use a camera instead of phototransistors?
Answer: One approach would be to multiplex your ADC with lots of analog multiplexors (muxes).
Another approach is to connect all phototransistor collectors together to one ADC channel.  Connect the emitters to digital i/o pins.  If the i/o pin is floating, the phototransistor is not driving the ADC.  If the i/o pin is low, the phototransistor is driving the ADC.  This allows you to select one phototransistor at a time.  You would need as many digital i/o lines as there are phototransistors.  In this approach, you trade analog muxes for digital i/o.
Somewhere in between is a matrix approach.  Suppose, you have 256 phototransistors.  You could arrange them in a matrix.  8x32, for example.  8x ADC channels (or 1x ADC channel with 8-to-1 analog mux).  One for each row of the matrix.  All collectors in one row are connected together.  32x digital i/o.  One for each column.  All emitters in one column are connected together.  Digital i/o works in the same way as in the 2nd paragraph, except one i/o activates a column of 8x phototransistors.
Answer: The 74HC4067 is a 16-channel analog multiplexer/demultiplexer, so cascading two levels of them gives you up to 256 inputs.
You use 16 devices for 16 \$\times\$ 16 inputs, and connect the 16 outputs to a 17th device to make the final selection. The 16 input multiplexers share the same 4-bit select word, and with a 4-bit select word for the second level you have an 8-bit select word for 2\$^8\$ = 256 input channels.
edit
Rocketmagnet has his doubts. This is indeed not the minimum parts solution, but it's the easiest to control:  set 8-bit phototransistor address, read analog input. Also, depending on the location of the phototransistors, it may be easier for signal routing than a matrix.
Comment: @Rocketmagnet - Not to control it: set 8-bit phototransistor address, read analog input.
Comment: Surely a matrix is simpler?
Comment: vs. set column bit, read ADC channel. Both are simple.
Comment: @Rocket - clear previous column bit, convert phototransistor number to ADC channel, select ADC channel, convert phototransistor number to column, set column bit, read ADC channel.
Comment: I think there are multiple ways you could use that 7th 74HC4067...  Instead of using it as another level of analog mux in the tree, you could also use it as a digital demux to drive the enable pins of the other 4067's, and just connect all of the 16 analog outputs from each chip together and to the input of your ADC.  I'm not sure which has better SNR, but the latter design is probably easier to route.

200+ phototransistors and reading them


How to seal this crack in plywood subfloor?

Question: I'm suspecting that this crack is causing squeaky noises when the region holds weight. What's the best way to seal this?
Comment: It's for sound dampening, as Jack said, a cellulose based fiber board. Is it possible to work from underneath instead of from atop?
Comment: Looks more like a goof with a circular saw. Maybe add some screws along the seam?
Answer: Well it would help to have more information, This looks like cement backer that was cut. not a crack created by normal movement. If it is a crack RUN OUT OF THE COUNTRY! Because cracks don't show up 1/8" wide and and are gone in this short distance. The noise problem could be caused by the structure., not being glued and screwed or just cheap construction. I am not sure it really needs to be filled and I am sure it is not the root cause of the squeak. If you or any one out there can develop a "crack in plywood " anything like this you would make the record books. But if it is just old vinyl glue that makes it look like backer the problem may be more screws are needed, maybe some shims from the bottom. But filling the cut won't help.
Answer: That is a layer of a product called homosote, at least it is called that back east. Your subfloor is under that. Homosote is not structural, it is usually 1/2" thick and resembles gray cardboard.
To get to the squeak, you will need to set a circular saw a 1/2" deep and cut out a section to get to the subfloor below, say maybe a 3' square. The joints are every 4' apart in one direction. perhaps there is a factory edge that is near to the squeak that simplifies the section you need to remove.
After you get that up and out of the way address the squeak.
With that much homosote out of the way, you should be able to see 2 rows of joists. You may only have a squeak at one location and perhaps the cutout can be smaller than I suggest but I would screw down the neighboring joists as well while you are at it.
Since there is a subfloor under the homosote it would not take that much effort to pull all the nails out of the whole sheet instead of cutting out a section.
If you do choose to cut out a small section, PLEASE do confirm the thickness of the homosote.


How to get the whereused list for component template, schemas, page templates either using C# TBB or through sql query on content manager database?

Question: How to get the where used list for component template, schemas, page templates either using C# TBB or through sql query on content manager database in SDL Tridion 2011 SP1? Using Tridion core service is not an option as on our SDL Tridion CMS server core service is not functional.
Comment: You could, of course, take action to get the core service to be functional. What is wrong with it?
Answer: You can download the 2011 TOM.NET API reference from the Downloads=>Documentation menu on SDL Tridion World (login required)
You can definitely get a where used collection or Xml using a C# TBB.
Code examples on Coded Weapon
You can google "Tridion GetUsingItems" to find more examples.
Comment: You're welcome. Sample code and examples are definitely needed to get comfortable with the Where Used functionality. I often get confused (even though it is actually logical) by the fact that GetUsingItems gets you the "Used In" tab if you look at the UI and GetUsedItems gets you the  "Uses" tab. But that's also clarified in Alex's blog article.


How to set up a spreadsheet so that I can type a number and it will be added to the current value?

Question: I have a spreadsheet with dollar amounts that i occasionally need to add to. is there a way to set it up that i can type a number into a cell, and it will automatically add it to the current value already in the cell?  ex:+--------+---------+----------+-------+-------+
|----------- Jan ---| Feb ---| March | April |
+--------+---------+----------+-------+-------+
| Costs  | 230----| 756----| 1234--| 1543  |
+--------+---------+----------+-------+-------+
| Income | 450    - | 1867 -    | 2104  | 2354  |
+--------+---------+----------+-------+-------+
sorry that it came out a bit unclear. If I would want to add 250 to the Income in January, is there a formula i can use to add it by typing in that square?ps. if not, is there an efficient alternative, like a separate cell (call it D26) that i can put a value in that will add it to the income cell and won't be removed from the income cell if i delete the contents of D26?
Comment: You will have to be a bit clearer than that to get a coherent response. Can you post what you've tried so far, sample data and expected output? You may want to read [this](https://superuser.com/help/how-to-ask)
Comment: Some diagrams or screen shots of your data would help us understand your question. Please [edit] your question to include some example (mock) data (before and after). See [Format Text as a Table](https://www.tablesgenerator.com/text_tables) for a web utility that will help you to create a nice data table you can paste into your question. Upload any image(s) to [Imgur](http://www.imgur.com) and you will get link(s) you can share. [Edit] your question to include the link(s) and someone with sufficient reputation will inline the image(s) for you.
Answer: You can't do exactly what you're requesting but there are a couple of options.
Option 1 - use a formula
You already have value 450 stored in your January income. You can convert it to a formula =450+250. You don't need to retype the original value - press F2 to edit it.
Option 2 - paste special

Type your value 250 into an arbitrary cell (you suggested D26).
Copy the cell
Select the target cell (January income)
Paste special, Paste:Values, Operation:Add
Optionally clear the value from arbitrary cell

Personally I prefer option 1 because the formula can represent the history of the cell. It started with 450 then had 250 added.
Comment: if it can be done, can you please post an answer?
Comment: You're mistaken.  You can do EXACTLY what is being asked.
Answer: No, because when you enter a value into a cell in any spreadsheet, be it Excel, Libre Office, Apache Open Office, Google Sheets, or others, it replaces the previous value.
Comment: I am not very good with excel but can't something be made in such a way that column A has the grand total and has a formula in it where each cell in column A can be refreshed to something like C1=C1+e1(where e1 might be on a different sheet which we can call raw data) and then when you refresh the main sheet you can get the added values?
Comment: @CAO - yes, except that what you describe is not what I understood Antheloth to describe, hence my asking for sample data, etc.
Comment: @CAO  putting 'C1 = C1 + E1' inside a cell cause most Excel users to get a circular reference error with "0" in C1 no matter what value is in E1. Walking through the formula: let C1 = 1 and E1 = 2, so  C1 = 1 + 2, obviously 3; because C1 is adding itself to number and C1 is now 3 we have C1 = 3 + 2,  and then C1 = 5 + 2  ... and so on.  Iterative calculations can be enabled up to X iterations but it is off by default.
Comment: Ahh, didn't know that. Thanks. I was thinking we could make it some run time thing which runs only when we want it to and then resets the values of the cells in raw data sheet to zero
Answer: There are ways of doing what you want but they are NOT easy. They are quite difficult and require that you write a macro and have the macro running all the time to track the pre-existing contents of the cell and then add the new input to the existing values.
The method you ask about also has the disadvantage that you will lose the history of what numbers you have already added into the cell.
It also has the disadvantage that if you accidentally mistype a number and it replaces the pre-existing number with the pre-existing number plus the new number, the sheet will not show a record of what numbers you have already typed in, and it will be very difficult for you to fix things.
I suggest a simple spreadsheet such as in this.
This first image shows the sheet as it would appear when you are using it.
SuperUser.com won't allow me to insert the images I prepared because I don't have enough points yet. But do this.
Cell A10, enter Income
Cell B9. enter Jan
Cell C9, enter Feb
Cell D9, enter Mar
Cell B10 enter 450
Cell B11 enter 250
Cell B13 enter "=B10+B11+B12" (without the quotes.)
I'm not sure if this helps or not, but it is the way I would do what you are asking about. I would avoid, at all costs, anything that overwrites the contents of a cell.
Comment: I gave +1 for being the only answer to acknowledge a fact: it is possible to satisfy the OP's requirements.  But you're a bit off on a few things.  The program doesn't need to be running all the time with the worksheet change event.  History isn't lost and restoration/error recovery is retained if cell edits are logged to a file procedures are written to reference it.  And finally, I would agree that thisi adds complexity but the difficulty change is purely relative.


Flows and Lie brackets, $\beta$ not a priori smooth at $t = 0$

Question: Let $X$ and $Y$ be smooth vector fields on $M$ generating flows $\phi_t$ and $\psi_t$ respectively. For $p \in M$ define$$\beta(t) := \psi_{-\sqrt{t}} \phi_{-\sqrt{t}} \psi_{\sqrt{t}} \phi_{\sqrt{t}}(p)$$for $t \in (-\epsilon , \epsilon)$ where $\epsilon$ is sufficiently small. Does it follow that$$[X, Y](f)(p) = \lim_{t \to 0} {{f(\beta(t)) - f(\beta(0))}\over t}?$$Thoughts. I know that $\beta$ is not a priori smooth at $t = 0$ because of the $\sqrt{}$ terms. But I do not know what do from here. Could anybody help?
Comment: Non-smoothness is a red herring; replace $t$ with $t^2$.
Comment: @QiaochuYuan Sorry, why is it a red herring? I do not doubt that you are right, but I do not see why. If I have the function $f(t)=t,$ this is differentiable at the origin while $f(\sqrt{t})$ is not. What is the difference here?
Comment: To be a bit more precise, I am of course aware of the fact that if $g$ is not smooth at a point $p,$ and $f$ is smooth, we can still have that $f \circ g$ is smooth at $p$. My question is, why is it true that the composite is smooth in this situation?
Answer: Let me please put $\alpha(t):=\beta(t^2)$. We are asked to prove
$$\left.\frac{d}{dt}\right|_{t=0}\alpha(\sqrt{t})=[X.Y]_p.$$
Fact: $$\left.\frac{d}{dt}\right|_{t=0}\alpha(t)=
\left.\frac{d}{dt}\right|_{t=0}\psi_{-t}\phi_{-t}\psi_t\phi_t(p)
=-\psi'_0\phi_0\psi_0\phi_0(p)-\psi_0\phi'_0\psi_0\phi_0(p)
+\psi_0\phi_0\psi'_0\phi_0(p)+\psi_0\phi_0\psi_0\phi'_0(p)=0.$$
Fact: $\alpha(t)$ has a Taylor expansion near $0$ which I notate as
$$\alpha(t)=\alpha(0)+\alpha'(0)(t)+\frac{\alpha''(0)}2t^2+O(t^3).$$
Note that I can drop the $t$ term since the coefficient is $0$.
Then $$\left.\frac{d}{dt}\right|_{t=0}\alpha(\sqrt{t})=\lim_{t\rightarrow0}
\frac{\alpha(\sqrt t)-\alpha(0)}t=\lim_{t\rightarrow0}
\frac{\left(\alpha(0)+\alpha'(0)(\sqrt t)+\frac{\alpha''(0)}2(\sqrt t)^2+O(t^{3/2})\right)-\alpha(0)}t=\frac{\alpha''(0)}2.$$
So it is necessary and sufficient to show $$\left.\frac{d^2}{dt^2}\right|_{t=0}\alpha(t)=2[X.Y]_p.$$
Now, for two vector fields $X$ and $Y$ with local coords $X^i\partial_i$, $Y^j\partial_j$, where here and henceforth I omit the summation symbol over indices, there is a convenient formula for the bracket
$[X,Y]=\gamma^i\partial_i$, namely
$$\gamma^i=X(Y(x_i))-Y(X(x_i))=X(Y^i)-Y(X^i)=(X^j\partial_jY^i-Y^j\partial_jX^i).$$
In a similar way (following this answer), we may write a Taylor expansion of the flow at $p=p^i$ (implicit summation):
$$\phi_t(p)=p+tX(p)+\frac{t^2}2X(X(x_i))(p)+O(t^3),$$
finding (summing implicitly)
$$\phi_t(p)=p^i + t \; X^i(p) + \frac{t^2}{2} X^j(p) \; \partial_j X^i(p) + O(t^3).$$
This is true, since
$$
\frac{d}{dt} \phi_t(p) = X^i(p) + t X^j(p) \partial_j X^i(p) + O(t^2) \\
= X^i(p + t \; X^i(p)) + O(t^2) \\
= X^i(\phi_t(p)) + O(t^2).
$$
The second (middle) equality here follows from Taylor expanding $X^i$. The third (i.e. last) follows from substitution.
With this understanding, we can actually compute
$$
 \psi_t \phi_t(p) = p^i + t X^i + \frac{t^2}{2} X^j \partial_j X^i + t Y^i + \frac{t^2}{2} Y^j \partial_j Y^i + t^2 X^j \partial_j Y^i +O(t^3),
$$
$$
 \psi_{-t} \phi_{-t}(p) = p^i - t X^i + \frac{t^2}{2} X^j \partial_j X^i - t Y^i + \frac{t^2}{2} Y^j \partial_j Y^i + t^2 X^j \partial_j Y^i +O(t^3).
$$
Now, we don't write out exactly the composition of these two fields but we write only the $t^2$ term. From pairing $\frac{t^2}{2} X^j \partial_j X^i$ with $p$ and likewise for $Y$, we get a contribution of
$$\frac{t^2}{2} X^j \partial_j X^i +\frac{t^2}{2} X^j \partial_j X^i + \frac{t^2}{2} Y^j \partial_j Y^i + \frac{t^2}{2} Y^j \partial_j Y^i.$$
From pairing $t X^i$ with $-t X^i$ and $t Y^i$ with $-t Y^i$ we cancel this term. From pairing $-t X^j$ with $t Y^i$ we cancel one of the two $t^2 X^j \partial_j Y^i$, and are left with
$[X,Y]_pt^2$ from $-t Y^i$ with $t X^j$ and the remaining $t^2 X^j \partial_j Y^i$. It is now also easy to see explicitly that the linear term vanishes and $$\alpha(t)=p+[X,Y]_pt^2+O(t^3).$$
Hence $\alpha''(0)=([X,Y]_p t^2)''(0)=2[X,Y]_p$; that's it.


When is an RSA key used in TLS handshake?

Question: Can someone explain the difference between RSA key agreement and DH key agreement as far as the use of the RSA key is concerned.  For example, I have an RSA key and have agreed to use TLS_RSA_WITH_AES_256_CBC_SHA for this TLS session.  When does the server use the RSA key and when does the client use the key. Who encrypts/decrypts and who signs/verifies.  The other scenario would be TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA. I am having difficulty finding out who is using the key and when in these two scenarios.  Thank you for help.
Comment: Possible duplicate of [TLS-RSA vs TLS-ECDHE-RSA vs static DH](https://security.stackexchange.com/questions/166063/tls-rsa-vs-tls-ecdhe-rsa-vs-static-dh)
Comment: That question does answer the DH part of my question but not the RSA key exhange part.
Comment: 166063 says "RSA = Client will use server's public key to encrypt the PMS and send over to server, server will decrypt the PMS and generate the same PMS. The secret is sent in the wire" -- how does that not answer your question?
Answer: This question is kind of confusing. While the title asks where RSA is used in the handshake the first sentence asks about the difference between RSA and DH key exchange regarding the RSA key. Note that the key exchange is part of the (full) TLS handshake but there is more to the handshake, specifically the authentication. But in short:

No RSA key is used within the DH key exchange. See "Diffie-Hellman Key Exchange" in plain English for more.
In RSA key exchange the public key is used in the client to encrypt the pre-master secret and the private key is used in the server to decrypt it.
Outside the key exchange but inside the TLS handshake the RSA key is used in the given ciphers for authentication. This is done by the server signing some data with the private key, where the data at least partially depend on the client. The client then can validate this signature and thus verify that the other party has access to the private key matching the public key of the certificate.
Comment: Thank you for the response.  I apologize if the question isn't worded correctly.  I just want to make sure I understand.  If  TLS_RSA_WITH_AES_256_CBC_SHA is used then the server will encrypt using its RSA private key and the client will decrypt using the RSA key from the certificate passed over.  Does signing/verifying occur? If TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA is used then the server will sign the using its private RSA key and the client will verify using the certificate passed over.  The RSA key is not used for encrption/decryption. Is that correct?
Comment: @user3375401: In the first case you've mixed up the roles of client and server. The second case might be correct provided that the unknown "the" in your *"... the server will sign __the__ using its private ..."* is the right thing.


install Oracle jdbc driver in Apache Geronimo

Question: I tried to install Oracle JDBC driver to Apache Geronimo without success. I'm using ojdbc6.jar.
I copied it to the repository folder and tried to setup, first an Oracle XA pool using Geronimo's Admin console, without success. It complained that the driver was missing with a ClassNotFoundException for OracleDataSource.
Then I tried to setup a regular Jdbc Driver (oracle thin). I wrote user/pass/sid etc and managed to succeed a ping to the database. Then when I saved this connection pool, it complained again with a ClassNotFoundException, this time for oracle.jdbc.driver.OracleDriver.
What can I be missing?
Answer: http://oss.org.cn/ossdocs/geronimo/development-deployment/database.html - Section 6.1. JDBC Drivers - has an example for oracle driver.


How do I calculate what antenna I need for my cubesat?

Question: If I want to make a communication satellite, like MarCO, what formulas do I need to calculate the perfect antenna? Is there a difference between the X-Band and the classic UHF? If the cubesat is destined for some saturn moon, does it have to have a larger antenna due to the interference of its other moons? How do I receive the antenna information?
Comment: If you want to a large high gain low beam width antenna dish, you need a precise attitude control of your cubesat. If the directional antenna is not oriented precisely to the Earth, communication is lost.
Comment: This is not a duplicate but you may find some helpful information in answers to [How does the pattern on the MarCo cubesat's antenna boost data-transmission?](https://space.stackexchange.com/q/34789/12102)
Answer: There are too many general questions here that require book-chapter-length-like answers. I would like to specify first:

Do you want to calculate antenna performance, antenna pattern, or what exactly? Additionally, which antenna do you have in mind: ground station antenna for an uplink scenario, antenna on-board of the CubeSat for a downlink? In terms of performance, I would suggest to look for such calculation generalization as a link budget, as by calculating solely the antenna performance you won't be able to say if you can successfully close the link with your planned CubeSat. There are tons of examples in Internet and scientific publications, thus I advise you to review those first. For instance, this presentation will give you a good feeling what link budget is.
There is, of course, difference between bands. X-band is a frequency band between 7 to 11.2 GHz, while UHF is between 300 MHz and 1 GHz. In terms what frequency suits your mission in a best way, it is again quite broad question. It really breaks down to the mission requirements and subjected towards thorough trade-off analysis.
Larger antennas on CubeSats (and satellites in general) are nothing to do with interference. The main advantage of a larger antenna (let's assume parabolic reflector) is the larger gain. What is gain? See here.
You, of course, can do some engineering assumptions regarding your antenna when doing your link budget calculations. However, without prior knowledge of state-of-the-art or specific antenna device in mind, it is a hard task. Considering the desired deep-space scenario, I would recommend you to do a thorough literature research, check the flight heritage of successful missions, what kind of communication strategies they used. Having the previous experiences in mind, you can start an iteration process where you combine all the elements of your communication scenario into a link budget calc and see what kind of resources would you need to successfully close the link. This process would take a while, as it is considered to be a compromise between the desired performance, available power resources and current state of the technology.

But again, I advise you to make some effort and provide us with some rather more specific questions. So far there are so many ambiguities in your question that you cannot expect anyone would provide you with precise answer.
Comment: @ValentinoZaffrani Uwe pointed out some important assumptions (in addition to those in my answer) that you should define first. You are asking ambiguous questions and instead of clarification to you initial questions, are just starting to ask even more ambiguous questions. Please, write a comprehensive description of your problem and we will try to figure something out. In addition, you can yourself find tons of information regarding MarCO and its communication scenario. Google scholar and researchgate are your friends for that!
Comment: Its an antenna for a cubesat 1U, for a communication network betwen Titan and the earth
Comment: @ValentinoZaffrani What about the transmitter power of the cubesat, what are the expected datarates for downlink and uplink? What about the antenna and transmitter and receiver used on Earth?
Comment: A RTL-SDR on onmnidirectional and with eight all connected betwen,  if we send a prove to mars,  and do the same we have a full time communication
Comment: How is marco-earth communication? What band? And marco-mars?
Answer: There is no such thing as a "perfect" antenna.  Antennas are only better or worse than each other for a specific purpose.  Choose a different purpose, and generally a different antenna will become best.  Antennas embody design tradeoffs; having an outstanding strength in one application usually requires having outstanding weaknesses in other applications.  Antennas with no notable weaknesses also have no notable strengths, unless lack of weaknesses is itself your goal.
The constraints of your mission clarify things considerably.  Advice I would give for generic cubesats in low Earth orbit is not applicable when your target location is Saturn.  Given that, you are pretty much forced into the highest-gain antenna you can manage, because Saturn is vastly farther away than typical satellite orbits, so you need to make up the extra free space propagation loss somehow.
The main problems you will have are size and control.
First, for a given transmission frequency, increasing antenna gain is most easily done by making the antenna physically larger.  There are other things you can do, but they require complicated design details, like nonuniform aperture weighting.  Physical size is a very tight constraint in a 1U cubesat, and you will be seriously pushing the limit of what you can carry, deploy, and control.
Second, the higher the gain, the more it suffers from being pointed incorrectly.  Thus, the more important it becomes to both know where you need to point, and be able to stay pointed there, minimizing drift and jitter.  For a LEO cubesat, I would advise going with Uwe's comment, and making the gain as small as possible, to remove or at least reduce precision pointing requirements, in order to get away with much simpler, smaller, and cheaper attitude determination and control.  In your case, there's probably no way to avoid using a very high gain antenna, since the angular size of the Earth as viewed from Saturn is miniscule.  You only need to track the planet, not a particular ground station, but the planet looks so small that the pointing requirements aren't all that different.


RJ11 socket in Eagle libraries?

Question: I am trying to add RJ11 (telephone wire) sockets to my PCB on Eagle but am having trouble finding it in the libraries.  Is this a standard socket that is included or do I need to install some external library?  If the latter, where can I find such a library?
Answer: Sparkfun releases many of the parts used in their products in the form of the footprint and schematic symbol.  It seems like they have an RJ11 connector in their connections library.  You can download them from the linked github page.
As for more Eagle library resources:

Adafruit also releases their eagle parts as well, although I'm not sure if they have an RJ11 connector.
I have published and maintain my own as well, although I take great care to make sure they are correct, they are still unverified so take them w/ a grain of salt.

Generally if you can't find the part, you'd have to make it yourself.  There are many tutorials explaining how to make a part in Eagle.
Answer: The best way to deal with a missing component is to make your own.

Find a component that meets your spec.
Draw a schematic symbol for it.
Draw a PCB footprint.
Marry the two as a component.
Place the component you created in your design.

Relying on third party libraries is not good practice. Unless you check every part, you cannot be certain that the pin mapping is correct, or the part will match the footprint.
Answer: The SparkFun connectors library has a footprint + schematic for an rj11 socket that they sell. I doubt there's such a thing as a generic rj11 socket.
https://github.com/sparkfun/SparkFun-Eagle-Libraries

RJ11 socket in Eagle libraries?


Downshifting to a stop- wear and tear?

Question: I drive a Mustang GT, and I love the deceleration "pop" that you get when the engine revs climb without the accelerator being pressed, so as one might surmise, I tend to downshift to a stop at lights and stop signs to hear that "pop pop rumble". Generally it's from 5th at 40 mph to 2nd, which is well under redline, but it's a large enough increase in engine RPM to give a few good pops. I haven't noticed any signs of additional wear and tear, but I figuredd I should ask those more versed in this sort of knowledge than I about it. Is there any significant increase in wear and tear on any of the drivetrain components from doing this?  Things I can think of are maybe the clutch, the transmission output shaft seal, and possibly the gears themselves either in the transmission or in the rear end, but I think those last two are unlikely. I'm thinking over time I might end up clogging a cat as well, but I'm not exactly sure how quickly that would happen either.
Answer: The synchros will be forced to bear the brunt of downshifting like this
The synchromesh gears are gears inside the manual transmission designed to help the engine transition smoothly to its new RPM.
They will wear out eventually, but the wear and tear will be accelerated by downshifting without adding throttle to help the engine match its new speed.
The act of adding throttle helps by increasing engine speed, allowing it to accommodate the ratio of the lower gear without loading the synchros as much. If the throttle input is such that the engine-to-driveshaft speed ratio corresponds to the gear ratio (rev-matching), the synchro has nothing to do (zero load).
A worn synchro will result in a crunchier, more notchy gearshift. It makes shifts more difficult to perform. In such a case, refreshing transmission fluid will only have a temporary effect. The only true remedy is to replace the worn synchro, which involves pulling out the transmission from the vehicle and disassembling the gearbox.

Downshifting without throttle input will accelerate wear on the clutch as well, but not to the same extent as what the synchros will experience.
I don't think downshifts will result in clogged catalytic converters.
Comment: Hmm, I don't get it. The synchro is needed to bring the motor-side _shaft_ of the gearbox to its new RPM during shifting, not the entire motor. The motor changes its RPM when releasing the clutch. Of course, sudden change to the motor RPM causes high loads on the gears and the clutch, but I don't understand what you mean by "syncros help the engine transition..."
Comment: @sweber : The key word in that sentence is "smoothly". The speed of output shaft of the gearbox (which goes to the wheels) will be governed by the speed of the vehicle. Switching to a lower gear while pressing the clutch will make the engine-side gearbox shaft spin faster than the engine. Upon engaging the clutch, there is a mismatch between the speed of the engine and the gearbox shaft that has to be equalized in some way. The clutch allows for very little slip between the engine crankshaft and gear input shaft, so it is up to the synchros to pick up the slack while the shaft speeds match up.
Comment: @sweber : Here's another way to look at it. The gearbox in some older cars lack a synchro. Changing gears (both up or down) can be quite a jarring experience because of the abrupt change in RPM that the engine-side of the driveline is subject to
Comment: The worry about the cats is minor, but since the decel pop comes from raw fuel making it into the exhaust and then burning, I assume a small amount of fuel makes it to the cats themselves, which I understand is not good for them, although I suppose the amount that makes it there before burning is small. Thanks for pointing out the synchros. I wonder if this is just the excuse I need to get a Magnum XL T56 :)
Comment: @Zaid: To my knowledge, the synchros work like this: When the stick is pushed into a gear (while clutch pedal is pressed), the synchros speed up the engine-side shaft until its RPM matches the RPM of the gear wheel. Right after that, you can push the stick further into its final position, which locks the gear wheels to the shaft. Now, there is no force on the synchros any more. If you release the clutch, all torque is transferred by the gear wheels, but not by the synchros. So,the synchros wear a little when speeding up the shaft, but the high torque when speeding the motor goes to the clutch.

Downshifting to a stop- wear and tear?