Hsiung on the Complex Structure of $S^6$

Question: In 1986 C. C. Hsiung published a paper "Nonexistence of a Complex Structure on the Six-Sphere" and in 1995 he even wrote a monograph "Almost Complex and Complex Structures" to further elaborate on his proof.
Yet answers to the 2009 question on this site all agree that the existence of complex structures on $S^6$ is still an open problem. Some recent preprints answering the question with opposite answers are also cited there.
I would like to know if there are any known mistakes in Hsiung's approach and if so I would appreciate some reference to a paper that points them out.
Comment: You might ask the same question about the paper of A.Adler "The second fundamental forms of $S^{6}$ and $P^{n}({\bf C})$", Amer. J. Math. 91 (1969) 657–670, which claims to prove the same result. In this case Steve Krantz says here http://books.google.com/books?id=mMZBtxVZiQoC&pg=PA215&lpg=PA215#v=onepage&q&f=false that he saw a paper of Y.T.Siu which explains precisely where Adler's error is. However, I couldn't find any paper of Siu where this is discussed.
Comment: @YangMills:  As for the error(s) in Adler's 1969 paper, the main breakdown occurs because his whole argument relies on Proposition 2 from his earlier paper *The Second Fundamental Form of a Kähler Metric*, Amer. J. Math. 89 (1967), 260–274, and this Proposition is simply wrong.  His error is that he assumes that the first Chern form of the LC-connection of an Hermitian metric on a complex manifold is necessarily of type $(1,1)$. (He just writes that it's "a known property", with no argument.)  This false claim is crucial for his construction of a Kähler metric when his inequality is satisfied.
Comment: I vaguely recall knowing about 3 separate published proofs that were not taken seriously by other experts but I don't remember the third one anymore. I've never found anyone who could explain to me what the error in either Adler's or Hsiung's proof is. But I never thought of asking Siu.
Comment: @Deane: maybe you were thinking about S.S.Chern's last preprint (2004)? It was never published, but you might have seen it.
Comment: Having said this, I don't know exactly where Hsiung's mistake is, I will search a bit and see what I can find.
Comment: YangMills, that might be right. Thanks!
Comment: @RobertBryant Thank you very much, I was not aware of this!
Answer: While it's good to have a source, such as Datta's paper that points out the error, I find that his explanation of why the key equation is wrong is not as clear as it could be.  In fact, with a little thought (requiring essentially no computation), it's clear why this equation must be wrong and what is wrong with the approach.  Since it's relatively short, I thought I'd put it in:
On page 263 of Hsuing's monograph "Almost Complex and Complex Structures", he claims the following result, from which, if it were correct, the non-existence of a complex structure on the $6$-sphere would follow immediately (and, in fact, Hsiung 'applies' this result to get exactly this 'conclusion'):
Theorem 6.1. Let $J$ be an almost complex structure on a Riemannian $2n$-manifold $M^{2n}$ ($n\ge2$) with a Riemannian metric $g_{ij}$ but without a flat metric or a nonzero constant sectional curvature or both, and let $J_i^j$ and $R_{hijk}$ be respectively the components of the tensor of $J$ and the Riemann curvature tensor of $M^{2n}$ with respect to $g_{ij}$, where all indices take the values $1,2,\ldots,2n$.  If $J$ is complex structure on $M^{2n}$, then
$$
J_{i_1}^iJ_{i_2}^jR_{iji_3k}+J_{i_2}^iJ_{i_3}^jR_{iji_1k}+J_{i_3}^iJ_{i_1}^jR_{iji_2k}=0
$$
for all $i_1,i_2,i_3,k$.
Now, this result cannot possibly be correct, as you can see from the following observations.
First, note that no relation between $g$ and $J$ is supposed.  If it weren't for the peculiar assumptions about $M$ not admitting a flat or constant curvature metric (which might have nothing to do with $g$), this would be a purely local statement, but, no matter, let's let $M$ be $\mathbb{CP}^n$ and note that, since $n\ge2$, $M$ cannot carry either kind of metric.  Let $J$ be the standard complex structure on $M$.  Then the above 'Theorem' would imply that, for any metric $g$ on $M$, its Riemann curvature tensor $R$ would satisfy the above equation.  Since any metric in dimension $2n$ can be locally transplanted onto $\mathbb{CP}^n$ and since all complex structures are locally equivalent, it follows easily that the above 'Theorem' implies that the above relation (which is a purely pointwise statement) must hold identically as an algebraic relation for any local pair $J$ and $g$.
(Moreover, since this doesn't involve any derivatives of $J$, the hypothesis that $J$ be integrable is irrelevant.)
Second, it's easy to check that this 'identity' does not hold:  Just choose a metric $g$ of nonzero constant sectional curvature and any local $J$ that is $g$-orthogonal, and you'll see that this says that the $2$-form $\Omega$ associated to $J$ by $g$ must satisfy $\Omega^2 = 0$, contradicting the fact that $\Omega^n$ cannot vanish because $\Omega$ must be nondegenerate.  (This is, in fact, Hsuing's argument as to why $S^6$ can't carry an integrable complex structure, because it has a metric of constant sectional curvature.)
Comment: Sorry, I misread your answer. I was referring to the book of Hsiung's collected papers here http://books.google.com/books?id=s85vcMYZDJgC&pg=PA673
Comment: Great answer! In the "erratum" paper (p.673 of the same book) Hsiung still states the same identical "theorem"...
Comment: @YangMills: Thanks.  You must have a different edition of the book than I do, since the copy in our library of Hsuing's "Almost Complex and Complex Structures" does not have more than 300 pages.
Answer: I just found this paper by B. Datta (later published in J. Indian Math. Soc. 60 (1994), no. 1-4, 171–190) that explains in details why one key equation in Hsiung's paper is wrong. See the whole discussion in section 4.
Also, in a 2001 book containing Hsiung's selected papers he added a short paper titled "Nonexistence of a Complex Structure on the Six-Sphere II" which looks like an erratum to his other one. He still claims the same result about $S^6$. This paper was never published.
Answer: There was a paper published in China (1987?) by Dong (and Guan).
It gave a reason why Hsiung was wrong. That was basically
the note of Guan when he sat in a talk of Hsiung. Dong came late and missed
the talk. Guan gave him his note ant told him that the proof was wrong. After
Guan left to America, Dong published the note and added his own
proof that there is no complex structure on S^6. After
Guan received Dong's note, he warned him about his mistake.
But it was too late and the note was published under the joint
authors Dong and Guan. Later on Guan met Hsiung in Lehigh University.
Hsiung showed Guan his book and said that Yau said that his proof
is correct. Guan again told Hsiung about his mistake without
any conclusion. It is more like politics to Guan.
Comment: Are you Guan the coauthor?
Comment: Here is the author:https://webvpn.ucr.edu/+CSCO+0h756767633A2F2F6A6A6A2E6E7A662E626574++/mathscinet/search/publdoc.html?pg1=IID&s1=194474&vfpref=html&r=1&mx-pid=1307945
Comment: The link is broken (it requires ucr.edu vpn), but I assume the answer to Scott's question is "Yes".
Comment: It is MR1307945 (96b:43008). He is from Henan University, China. Ask Kefeng Liu if you really want get to that person to get a copy of that paper.


Custom CSS for  tag?

Question: I'm building a music player web application which implements the HTML5 audio tag, however would like it to look consistent across browsers - is it possible to define my own custom CSS? And how?
Comment: Does this answer your question? [Is it possible to style html5 audio tag?](https://stackoverflow.com/questions/4126708/is-it-possible-to-style-html5-audio-tag)
Comment: The options are currently very limited, but you can use `outline` to help it stand out a bit.
Answer: There is not currently any way to style HTML5 <audio> players using CSS. Instead, you can leave off the control attribute, and implement your own controls using Javascript. If you don't want to implement them all on your own, I'd recommend using an existing themeable HTML5 audio player, such as jPlayer.
Comment: This answer is outdated, you can style the audio element using some obscure CSS selecors.
Answer: I discovered quite by accident (I was working with images at the time) that the box-shadow, border-radius and transitions work quite well with the bog-standard audio tag player. I have this working in Chrome, FF and Opera.
audio:hover, audio:focus, audio:active
{
-webkit-box-shadow: 15px 15px 20px rgba(0,0, 0, 0.4);
-moz-box-shadow: 15px 15px 20px rgba(0,0, 0, 0.4);
box-shadow: 15px 15px 20px rgba(0,0, 0, 0.4);
-webkit-transform: scale(1.05);
-moz-transform: scale(1.05);
transform: scale(1.05);
}

with:-
audio
{
-webkit-transition:all 0.5s linear;
-moz-transition:all 0.5s linear;
-o-transition:all 0.5s linear;
transition:all 0.5s linear;
-moz-box-shadow: 2px 2px 4px 0px #006773;
-webkit-box-shadow:  2px 2px 4px 0px #006773;
box-shadow: 2px 2px 4px 0px #006773;
-moz-border-radius:7px 7px 7px 7px ;
-webkit-border-radius:7px 7px 7px 7px ;
border-radius:7px 7px 7px 7px ;
}

I grant you it only "tarts it up a bit", but it makes them a sight more exciting than what's already there, and without doing MAJOR fannying about in JS.
NOT available in IE, unfortunately (not yet supporting the transition bit), but it seems to degrade nicely.
Answer: You can style audio element using some obscure css selectors. Here's a few of them.
audio::-webkit-media-controls-enclosure {
    background-color: #c6c6ec;
}
audio::-webkit-media-controls-timeline {}
audio::-webkit-media-controls-volume-control-container {}
audio::-webkit-media-controls-volume-control-container.closed {}
audio::-webkit-media-controls-volume-slider-container {}
audio::-webkit-media-controls-volume-slider {}
audio::-webkit-media-controls-seek-back-button {}
audio::-webkit-media-controls-seek-forward-button {}
audio::-webkit-media-controls-fullscreen-button {}
audio::-webkit-media-controls-rewind-button {}
audio::-webkit-media-controls-return-to-realtime-button {}
audio::-webkit-media-controls-toggle-closed-captions-button {}

Haven't found an exhaustive list of these, but here's the closest thing.
Answer: Besides the box-shadow, transform and border options mentioned in other answers, WebKit browsers currently also obey -webkit-text-fill-color to set the colour of the "time elapsed" numbers, but since there is no way to set their background (which might vary with platform, e.g. inverted high-contrast modes on some operating systems), you would be advised to set -webkit-text-fill-color to the value "initial" if you've used it elsewhere and the audio element is inheriting this, otherwise some users might find those numbers unreadable.
Answer: There are CSS options for the audio tag.
Like: html 5 audio tag width
But if you play around with it you'll see results can be unexpected - as of August 2012.
Comment: I think the OP was looking for CSS rules that are unique to Audio such that he can give it a customizable look.  Generic rules like width, though applicable, are not sufficient.

Custom CSS for  tag?


.htaccess to not execute any files in that directory?

Question: How do i setup .htaccess for a specific directory to not allow specific types of file extension and NOT ALLOW any execution of a the files within that directory?
Answer: You cant.
A .htaccess file could only control the behavior of the webserver.
If you are speaking about CGI script, that get executed, than you should configure your CGI directories correct.
Apache does not execute any other file then CGI's.
To forbid the execution of files on system level, you have to remove the x flag. But be careful. If you remove the x flag from a directory, you wont be able to enter it.


Delete multiple sections of an audio file at once

Question: Here is what I want to do; I want to trim out all unwanted sections of an audio file at once. Is there an application that allows you to input time intervals (start and end) for all unwanted sections. Then at the click of a button or press of a key, all the sections would be trimmed out (deleted) leaving the remaining portions merged as a single file. Any suggestions? Thanks in advance.
Comment: Controlling it programmatically? Or just a software able to do that "moving around things with the mouse" by a human?
Answer: You can do this with Python and MoviePy, (which behind the scenes will use FFMPEG), just the other way round! To be specific you specify your audio file as an input and the time stamps of all of the segments that you wish to keep then generate a new file as the output.
All of the above are:

Free, Gratis & Open Source
Cross Platform

Of course you can do the same thing with FFMPEG manually but I personally find that harder to use.
An example:
<code>from moviepy.editor import *
orig = AudioFileClip('02 Nightmares.mp3')
orig.duration # Lets me see how long the original is 278.44 seconds in this case
clips = []
for start, end in [(0.0, 10.0), (15, 25), (40, 50)]: # My list of start/end times
    clips.append(orig.subclip(start, end))
final = concatenate_audioclips(clips)
final.write_audiofile("../test.mp3")  # or where you would like to save it.
</code>


Is there a way to find out how many activated, registered users there are?

Question: I am seeking to track some KPIs for my site, one of which is the number of activated, registered users there are on the site. Is there a way to get this number?
Answer: You can query the users table, counting the number of rows where status = 1, which will give you the number of active user accounts.
Answer: The Drupal way would be to use Views to create a report for yourself (I would avoid querying any tables in the db directly.)
If you don't have the Views module installed, download and install it from http://drupal.org/project/views.
Once installed, create a new View on the User object. You will be able specify which fields you want to display, sort order, and filters.
Depending on which version of Views you are using (might be Views 2 in Drupal 6) you may also need to use an additional module called Views Calc in order to get the count of records returned: https://drupal.org/project/views_calc
Comment: this looks promising - thank you! :) I much prefer doing it in a drupal way than querying tables in the db directly.
Comment: Thanks @tobiaseigen. If you think it's the best answer to your question, I'd appreciate it if you would identify that.


How to install gcc-4.1?

Question: 1) I need gcc-4.1 for Matlab mex usage, but I can't get it installed fully with apt-get install:
The following packages have unmet dependencies:
libstdc++6-4.1-dev : Depends: gcc-4.1-base (= 4.1.2-27ubuntu1) but 4.1.2-29ubuntu1 is     to be installed
Depends: g++-4.1 (= 4.1.2-27ubuntu1) but it is not going to be installed
E: Broken packages

2) I now only have gcc-4.1-base and -multilib installed. When compiling mex file:
/usr/bin/ld: cannot find -lstdc++
collect2: ld returned 1 exit status

Something is wrong with libstdc++6-4.1-dev.
So I went to http://packages.ubuntu.com/maverick/gcc-4.1 and download libstdc++6-4.1-dev_4.1.2-27ubuntu1_i386.deb.
But cannot install it:
Dependency is not satisfiable: g++-4.1 (= 4.1.2-21ubuntu1)
Thanks
Answer: After a bunch of searching to get gcc-4.1 & g++-4.1 in Ubuntu 10.10 (maverick), I found easy work around.
Add to the end of /etc/apt/sources.list source from 10.04 (lucid)
deb http://mirrors.us.kernel.org/ubuntu/ lucid main universe

Then run
sudo apt-get update

You have to specify version 4.1.2-27, as libstdc++6-4.1-dev has not been back ported to 4.1.2-29.
sudo apt-get install gcc-4.1=4.1.2-27ubuntu1 gcc-4.1-base=4.1.2-27ubuntu1 cpp-4.1=4.1.2-27ubuntu1 g++-4.1

Comment: broken ! :-(  That one works http://askubuntu.com/a/39629/317957
Answer: Not sure if it will function properly if you override the dependencies and roll your own deb, but it's worth a shot.
apt-get build-dep deb-name-here
apt-get source deb-name-here
cd package-dir/deb
nano control

and change the dependency to a > instead of an =
cd ..
debuild

It might work...
Another option is to use update alternatives to roll-back your versions(safer)
yet another option is to modify version number in the dependency required by the build
two of the three can break your package management though.
The last and best option is to compile from source in ~/src and install to /opt for the versions you need and tell the installer to look there for dependencies
Answer: Ubuntu strives to avoid the old "dependency hell" by assuring that distributions are self-consistent in their libraries. By using commercial software (Matlab) that is a few years behind, you've got a MEX system that is not ready for Maverick.
As aking1012 suggested, you have to do some significant rolling back of versions. It could probably be said that you can't have the cake of Ubuntu convenience and eat the old-style MEX stuff too (or not without mucking about quite a bit).
Answer: libstdc++6-4.1-dev is not available in Maverick - it was last available in Lucid
You can install a later version of GCC. You will get a warning message but the MEX will still compile.
If you get MATLAB R2010b you can roll with GCC 4.3
There are instructions regarding this at: https://help.ubuntu.com/community/MATLAB#MEX%20functions

How to install gcc-4.1?


How are two objects heated by friction?

Question: Let's say that we have two objects made of different materials, both at room temperature. Surfaces of the objects are rubbed together, producing frictional heat. Is the heat distributed evenly, i.e. will the surfaces of the two objects be at the same temperature after being rubbed? How does this depend on the materials?
Comment: Are you asking *why* objects heat up when rubbed together or are you asking how the heat distributes ?
Comment: The second: how the heat distributes
Answer: Friction generates vibrations which create sound waves.  Sound transmission occurs through molecular oscillations. The temperature of a substance is directly related to the energy of molecular oscillation; molecular oscillation ceases at absolute zero.  Sound wave absorption occurs through conversion to heat, which is absorbed by the interface materials.
The loud shrill sound of car tires braking obeys the inverse square law related to the distance from the sound source. Imagine the sound intensity 1mm from the sound of braking tires when it registers 90 decibels at 50 meters!   The high intensity of sound and its immediate conversion to heat energy as it is being absorbed fill our nostrils with the smell of burning rubber (Hamilton, Order in Chaos (2011): 71-77).
In fluid dynamics, in the phase of transition to turbulence, simple harmonic (SH) boundary layer oscillations appear. An oscillation is a vibration which produces a sound wave. SH oscillations in boundary layer air creates SH sound.  Turbulent spots, characterized by isolated spikes of in-phase oscillations (also intense spikes in sound waves) occur in late transition, followed by the emergence of many turbulent spots, high boundary friction and loud aerodynamic noise (Schubauer and Skramstad 1941).  It is probable that the intense heating of space re-entry capsules is related to intense sound generation, much of which may be inaudible ultrasound.
A thin layer of oil between two solid surfaces greatly reduces the heat of friction. The thinness of the oil drastically reduces the maximum amplitude of the oil boundary layer oscillations, reduces the sound generation and the heat energy creation by frictional sound (Hamilton 2011).
Comment: This answer contains a lot of information but it does not seem to answer my questions.

How are two objects heated by friction?


IIS Server Farm

Question: I've got 2 Server 2003 boxes that need to be put into a server farm.  While I can handle setting up the cluster, I need help keeping the content files synced.  The client has a habit of fiddling with html files, so I know they'll end up out of sync at some point.  What are my options for keeping them synced?
Answer: Windows DFS works pretty well for this scenario - but you probably will want to be on Windows 2003 R2.
Comment: Would there be a performance hit involved in this?  Does it require that I'm on domain?
Comment: It does require an AD domain to operate. I have never personally seen a performance hit while using it, but one anecdote is probably not a good thing to base your decision on.
Answer: Set up an FTP (or better yet, SFTP or SCP) server that is separate from the web servers. Set up an automatic job to sync the files in the FTP server to their rightful place in the web server cluster every few minutes. Then the FTP server is the canonical source, and the web servers are its slaves.
It's probably also a good idea to remove any FTP servers on the web cluster.

IIS Server Farm


Are there any solvents that dissolve talcum powder?

Question: I understand that talcum powder is insoluble to water, would alcohol or something be able to dissolve it?
Answer: Talcum powder is made from talc, a silicate mineral with formula unit: $\ce{Mg3Si4O10(OH)2}$. Silicates tend to be pretty much insoluble in water, but it is possible to dissolve them in strong acids. I don't know about talc specifically, but many silicates can be dissolved in concentrated nitric acid. Hydrofluoric acid is also commonly used for dissolving minerals for chemical analysis. Both are very very dangerous substances that really shouldn't be used without proper training and safety equipment. I don't think there's really anything accessible for a home experimenter, unfortunately.
Comment: Well it won't be talc anymore. Dissolving anything changes its properties to some extent. Talc is only talc because it has the composition it does in the atomic arrangement it does. In order to dissolve, the talc must lose its solid structure. In the case of using an acid, you're right that an oxidation reaction does sometimes cause dissolution, especially with things like elemental metals. When used for digestion, HF tends to pull out Si as $\ce{SiF4}$. In acidic conditions, I found a reference to this dissolution reaction for talc: $\ce{Mg3Si4O10(OH)2 +6H+ + 4H2O -> 3Mg^{2+} + 4H4SiO4}$
Comment: would dissolving talc in strong acids then make the properties of talc change? I understand that acids can be solvents but i would think acids are very strong and are mostly oxidizing agents (especially nitric acid)
Answer: I consider that there is no solvent that can dissolve talcum powder, indeed if you consider "solving" as having your material into solution but maintaining the crystalline structure, only some inorganic compounds (most of them transition metal complexes) are soluble even in water or in other organic solvents (like alcohol).
Quoting wikipedia, we find:

Talc is not soluble in water, but it is slightly soluble in dilute mineral acids.

In any case, solving it will keep intact its structure. This is naturally true for the case of silicates, which are characteristics by their insolubility.


LoadRunner basic question: records traffic or browser actions?

Question: I cannot find the basic information about LoadRunner: does it record browser actions (like QTP) or network traffic (I mean packet sniffering?).
It is not clear to me since there is Script view that resembles QTP object actions. But on the other hand there is no browser opened when running the tests.
I would need to understand how it works, thank you in advance!
Answer: VuGen records the traffic on a protocol level. This means that all traffic "as seen" from TCP perspective is inspected. I will assume you want to understand the HTTP(S) recording here since you talk about browsers.
HTTP(S) can be recorded in a number of different ways, but all result in a recording log that is then inspected and the script is "generated" based on that. In the "Recording Log" and "Generation Log" tabs you can see the actual traffic recorded and how the script was generated.
When running a script the commands generated send the raw HTTP(S) requests to the target server, without any UI. Depending on the request mode the resulting data may also be inspected for references to other resources, such as images, css or js files etc.
Answer: It records both (and then some) depending upon the protocol selected.  Keep in mind that LoadRunner can execute QTP scripts as GUI Virtual Users.   It can also execute Citrix and Remote Desktop Protocol Scripts at a layer even outside of the client interface.
It can also record at a variety of levels of application and presentation layer protocols, all the way down to the Winsock level,


Why do polaroid lenses reveal rainbow patterns on some surfaces?

Question: I was wearing polaroid sunglasses and happened to look at the lenses on a pair of reading glasses and noticed a rainbow pattern. I have also noticed vertical bars when looking out car windows while wearing the sunglasses. What is happening here?
Also as a related question, when my LCD tv is off, it reflects the light from a nearby lamp and I can see a similar rainbow light diffraction... Is this because the liquid crystals are acting as small prisms?
Answer: the polaroid lenses reveal colored patterns in things like automotive safety glass and other eyeglasses when those things contain either residual stresses which were frozen into them during their manufacture or when the manufacturing processes produced some net alignment or anisotropy of the molecules in them (in the absence of residual stresses). either of these things can slightly alter the polarization of light passing through them, which the polarizing filter then makes visible for you.
In the days before cheap computer modeling, stress concentrations in engineering parts could be visualized for purposes of analysis by machining a replica of the part out of a chunk of clear plastic that tweaked the polarization of light when under stress. You then applied the stress and took pictures through a polarizing filter of the resulting colored fringe patterns in the part.
Answer: Try moving your head sideways to see if the rainbow pattern moves. If the rainbow pattern then maintains a fixed position on the surface, it is due to stresses in that surface. However, if it moves along the surface it is due to a birefringent film on the surface. Car windows may have been tinted with a polyester fiim that is birefringent. I guess a tv screen is more likely to contain a birefringent layer than to contain residual stresses.


Side by Side upgrade and migrate SQL

Question: Here is the story: We want to do side by side SQL upgrade from 2016 to 2019 with a new windows of 2016. My SA wants to robocopy all drives except drive C from the old server to the new server. Do I get any issues with live or offline databases (data and log files) after transfer? will they get corrupted?  Please provide me your ideas.
Answer: If the SA is building a new server then you best option is to do a migration not an upgrade (upgrades also do not have a good rollback plan and therefore is not recommended to do in production).
Here is a decent article with migration steps to start with but there may be adjustments for your environment. https://www.mssqltips.com/sqlservertip/1936/sql-server-database-migration-checklist/
Migrations should not be scary but they need everyone's involvement to make sure that if you do run into snags that they get fixed asap and hopefully documented for future reference.
Answer: You can only do this "robocopy everything" approach if you stop all services on the source server, and then attach the databases on the destination. But even that won't work 100%, because unless you copy the msdb and master databases as well, which I do not recommend, you won't bring over logins, Agent jobs, and other things like that.
I'm soapboxing a little here but as a DBA, I would not allow a systems administrator who does not have good SQL Server experience to perform the installation and migration of SQL Server, in part because of what I mention above.
Instead, I suggest doing a full migration using the dbatools PowerShell module, specificially the Start-DbaMigration function.  The "easy" way of using it is to install your new 2019 instance, make sure that the accounts that both the source and destination services run under (preferably gMSA domain accounts) have access to a common file share, and then run that function with a backup & restore (via that share) to copy the databases.
Start-DbaMigration will pull over the entire instance - databases, security, XE sessions, Resource Governor, Agent jobs, dbmail settings, linked servers - literally everything on the instance will be brought over. You can exclude individual components if you like as well.
Manual migrations leave too much room for error, they're slow, and so 2012. Automation rules in 2020.
Here's a 50-second demo of it.
Comment: What if all databases are encrypted ?
Comment: AFAIK, TDE-encrypted databases are supported as well. The certificates will be migrated as well.
Answer: You can Attach/Detach or Backup/Restore user databases but and general data (e.g. jobs) & configuration (e.g. Logins) stored in System Databases, And you can't use the same approach as user databases.
SQL Server migration will completely be done if you do it right with SQL Server Upgrade Wizard but mix it with RoboCopy or any external tools could damage your System Databases.
Comment: The SQL Server Upgrade wizard only applies for in-place upgrades, which the OP Is not going to be doing (and I recommend against).

Side by Side upgrade and migrate SQL


What are Jewish conventions regarding honeymoons?

Question: What are Jewish conventions regarding honeymoons? Is a honeymoon taken, and, if so, is it done immediately after the wedding--or later, once the woman is again tehora?
Comment: The Jewish tradition is called Sheva Berachot.
Comment: The words do literally mean "seven blessings" and these blessings are also recited at the wedding, **but** they also refer to the festive meals thrown for the couple in celebration of the wedding for up to a week after the wedding at which the same seven blessing are also recited.
Comment: Really? I thought the sheva berachot were the blessings said at the wedding...
Comment: How hilarious is it that R' Abadi refers to a honeymoon as ירח דבש?
Answer: The modern custom of honeymoons raises a significant halachic question, famously addressed by R. Yitzchak Abadi in his sefer Ohr Yitzchak which is the problem of "dam besulim". After the first time a couple is intimate on the wedding night, they are normally required to avoid relations until the wife becomes pure again, as you allude to in your question. But on honeymoons, which most couples take immediately after the wedding, couples are generally assumed to have relations again, within the prohibited timeframe. R. Abadi attempts to find a way around this problem in order to make sure that the majority of couples that go on honeymoons are not transgressing. His approach is rejected by R. Shlomo Zalman Auerbach, whose response is published in R. Abadi's sefer along with R. Abadi's rebuttal.
Comment: Look at the second page of the tshuva (שכז), the very top line and you'll see honeymoons, specifically.
Comment: The _Or Yitzchak_ discusses issues of _n'gia_ (touching one another) and _zera l'vatala_, but I don't see that he mentions honeymoons specifically, and AFAICT his concerns seem to be independent of whether the couple honeymoons. By your answer ("couples are generally assumed to have relations again" on honeymoons) do you mean to imply the issue is one of _mar'is ayin_? I don't see that in the _Or Yitzchak_ at all. I'll admit, though, that I haven't read every word of it.
Comment: Thank you! I take back my objection re "I don't see that he mentions honeymoons specifically", but still don't see why he does so: why is he concerned more about such a case than any other? because (as he puts it) "who is the watchman over them in such days and in such places"? Who watches them in the bedroom anyway (viz, if they're at home)? Why is this more of a concern if a honeymoon is taken than otherwise?
Comment: Because he assumes that in regular married life the people are careful to use the mikveh normally (although you can see he has his doubts about that too), but he sees the honeymoon as a common problem where people are not careful, and thus is motivated to try to find a solution. Since the idea of taking a vacation together (a honeymoon) became common, the temptation is much greater and thus he hopes to find a solution.
Answer: There is no sanctioned "vacation" in Judaism or Jewish weddings.  The whole concept appears to be a "new invention" even in Christian Society.
However, "honeymoon" periods do exist.
Firstly, there is the week of sheva brachot, where all meals are supposed to be joyous and glad with many members from the community. There is also a custom to invite people who could not make it to the wedding.
After the week of Sheva Brachot, there is also a concept known as "Shana Rishona" Or "The first year".  During the first year of marriage, the couple, if possible should never spend a night apart. They should not invite guests for Shabbat, and A soldier should not go to war.  Over the generations, other customs have grown out of "Shanna Rishona"
As for the aspect of being Tahor I have seen various customs on the issue, some of which arguably go against halacha.
One custom I have heard of is that after the first night of marriage, the couple does not consummate the marriage, so that they may touch each other during the week of Sheva brachot, and only once the stress has been reduced, and family is gone, and "life is normal" do they sleep together.  As far as I am aware, this is a common custom, yet not approved by anybody.
Another custom is to have a 'honeymoon' on the evening of the wedding, where the bride and grooom will spend the evening in a fancy hotel, and they will spend the first day together before getting involved with the family and friends for the sheva brachot.
Another custom I have seen, is to take a "honeymoon" months after the wedding, waiting for a good time in the calendar where they can have a long weekend together and go away.
Comment: Sounds to me like a misunderstanding. It is extremely common for things to "not work out" the wedding night, and thus the bride is still available on subsequent nights. Not everyone realizes this, and when the yentas talk about how they witnessed the chassan passing the salt to the kallah, all kinds of misinterpretations arise.
Comment: Never heard about a custom of refraining from relations on the wedding night. Frankly, it is preposterous. Has anyone else heard of such a thing?
Comment: Do you have a source for "a custom to invite people who could not make it to the wedding" or "should not invite guests for Shabbat"? And can you make more explicit what you mean by "some of which arguably go against halacha", please?
Comment: @Barry  You can read about it all over the internet.  Here is one such example:  http://www.hashkafah.com/index.php?/topic/64329-getting-around-dam-besulim/
Comment: https://tiffanieatillman.wordpress.com/2013/04/16/the-newlyweds-honey-year/ -1 for plagiarism.
Comment: @DoubleAA I'm not sure who you are giving the -1 to, but that link was written about a year and 2 months after this post was written... I certainly did not plagiarise anybody.
Comment: https://nypost.com/2017/04/24/the-surprising-history-behind-honeymoons/
Answer: Saw three opinions re: taking a honeymoon immediately after a wedding cited in this OU article about Sheva Berachot:
1) Rabbi Ovadiah Yosef
Even though making daily sheva berachot is not obligatory, halachah does not endorse the secular custom of a honeymoon either. Rabbi Ovadiah Yosef (Yabia Omer 3:EH:11:11) strenuously objects to such a practice and views it as indicative that the couple "is not interested in the berachot."[15]
2) Rabbi Aryeh Kaplan
On the topic of the honeymoon, Rabbi Aryeh Kaplan (Made in Heaven: A Jewish Wedding Guide [New York, 1983]) writes:

It is not the Jewish practice for the bride and groom to "escape" on a honeymoon right after the wedding. Rather, they remain in their home community. They are beginning their married life, not separated from the community but as an integral part of it (p. 230).

3) Rabbi Shlomo Aviner
Rabbi Shlomo Aviner ("Rayim Ahuvim" pp. 167-169) is in the minority when he says he sees no problem with a honeymoon and that couples should do as they please.
AGAIN, IMPORTANT TO NOTE:
Even those cited above who are opposed to honeymoons (R' Ovadia, R' Aryeh Kaplan), they seem to be only referring to a honeymoon IMMEDIATELY after the wedding.
A honeymoon taken a few weeks/ months after the wedding would seem to be fine to everyone as it's nothing more than a nice trip for the husband and wife!


esc_attr not working in shortcode

Question: I have a shortcode that outputs a block of html. One element in the block is an anchor tag with an image caption in the title attribute. Some of the captions I am using have double quotes in them, so I am wrapping them in esc_attr(), but none of the quotes are being encoded. If I put an echo statement in the shortcode with esc_attr() around the caption, it outputs an encoded string, but it doesn't seem to work when I return the html as you are supposed to do in a shortcode. Is this the nature of esc_attr()? If so, how can I encode a string to be returned from a shortcode?
Answer: I think I have figured out the problem, though I have yet to solve it. I am running the shortcode in a WP Types custom WYSIWYG field. The shortcode works perfectly everywhere else, including directly in my theme files and in the native WordPress content WYSIWYG, so it seems it is a bug in WP Types. I'm submitting a bug report, but hopefully my findings will help someone in the meantime.

esc_attr not working in shortcode


How can I search for a place amongst my visited places in the Google Maps Android app?

Question: How can I search for a place amongst my visited places in the Google Maps Android app?
Answer: I'm not aware of any method to manually search your visited places in the native Google Maps application; the best I've been able to find is by opening Timeline and navigating by date, which isn't very helpful if you don't already know the date of your visit in advanced.  Instead, I would use a browser and navigate to your Google account's activity controls page, and filter by Maps; this will allow you to directly search your maps visited places.


How to extrude random individual faces

Question: Is there a method to extrude faces randomly to get uneven height of the extruded mesh?
Comment: I am not sure, but maybe you could extrude it in the same height, put all those vertices in the vertex group and use displace texture on only those vertices in the group... But to randomly extrude? I don't think that there is a default way to do it, maybe with help of proportional editing, ..... hmm I just tried it, and no, my thought is not possible to achieve, so maybe there is some other way
Answer: It's a few steps but I found a way do do this.
I Select all the faces you want to extrude and extrude them with no movement. You can also instead use an inset with size 0 if you want your edges to separate the heights.
(if your faces are not aligned with a global or local axis, now would be the time to create a custom axis by clicking the little + in the transform orientations dropdown)
II Use the Mesh>Transform>Randomize Operator with an Amount of your choosing, Uniform set to 0 and Normal set to 1.
III Set your Pivot Point to Individual Origins and scale along the relevant Axis by 0 (the one normal to your faces)
It's done
Answer: A work around could be:
-Extrude the individual faces that you want CTRL + F > Extrude individual faces
-Then solo those faces Shift + H and deselect all after that.
-Go to Select > Select Random
-Move the faces G + (any axis) a bit and finally unhide everything Alt + H
Answer: What got me what I wanted was enabling the Add-on Mesh: Edit Mesh Tools from the preferences and using "Multi Extrude".
Comment: Good tip, thanks for the information, always glad someone can share more techniques!

How to extrude random individual faces


In Minecraft, how do you get sheep named "jeb" to return back to their normal colour?

Question: Accidentally did this. How do I revert it without using another name tag?
Answer: First of all, you could just get a new sheep. Looking at your question, that probably isn't it, but might as well get it out there. Unfortunately, you cannot change the sheep back to normal without using another name tag. Since the reason of the color changing is the name, it cannot be reverted without another one.
Answer: Dyes will not work on the Rainbow _jeb sheep, so giving the sheep another name tag, (naming the sheep "Dinnerbone" will work, but it will flip the sheep upside-down, like the name does for any other mob) will revert it to its original color.
Comment: Real quick side note, the name "Dinnerbone" can't affect Squids or the Ender Dragon (Name Tags don't work on the Dragon period, its official name is "Jean?")


job control doesn't work when I try to set up getty over serial

Question: I am trying to set up getty to log in over serial (mainly as an experiment).
With almost any configuration, the same thing happens.  If my default shell is bash, I get this message after I log in:
-bash: cannot set terminal process group (15297): Inappropriate ioctl for device
-bash: no job control in this shell

and then to prove that it doesn't work, I can't use ctrl+C to stop programs:
$ sleep 30
^C

and it doesn't seem to send the signal.
These are the configurations I have tried:
I have tried both of these commands
# copied from raspberry pi:
sudo /sbin/agetty --keep-baud 115200,38400,9600 ttyUSB0 vt220
# something else I read somewhere
sudo getty -L ttyUSB0 9600 vt100
# (I know I'm mixing and matching a lot of differences but the result is the same)

I have tried both screen and picocom as a client.
I have tried using a rasberry pi as a server, and two different ubuntu laptops.
I have tried two FTDIs, two RS-485 usb adapters, and a built in RS232 on the getty side with a USB RS232 on the client side.
I have also tried changing my default shell to sh and dash. I don't get the message, but ctrl+C still doesn't work as expected
The funny thing is - when raspberry pi's automatically configure /dev/ttyAMA0, and it uses exactly the getty command that I have put, job control works!
And the terminal settings are almost identical.  (except for -iutf8 actually)
here are the terminal settings with the FTDI connection, and picocom running:
$ stty -a -F /dev/ttyUSB0
speed 9600 baud; rows 24; columns 80; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D;
eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q;
stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W;
lnext = <undef>; discard = <undef>; min = 1; time = 0;
-parenb -parodd -cmspar cs8 hupcl -cstopb cread clocal
-crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr
-icrnl ixon ixoff -iuclc -ixany -imaxbel -iutf8
opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0
tab0 bs0 vt0 ff0
isig -icanon -iexten -echo echoe echok -echonl -noflsh -xcase
-tostop -echoprt echoctl echoke -flusho -extproc
$ stty -a -F /dev/ttyUSB1
speed 9600 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D;
eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q;
stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V;
discard = ^O; min = 1; time = 0;
-parenb -parodd -cmspar cs8 hupcl -cstopb cread clocal
-crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr
-icrnl -ixon -ixoff -iuclc -ixany -imaxbel -iutf8
-opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0
cr0 tab0 bs0 vt0 ff0
-isig -icanon -iexten -echo echoe echok -echonl -noflsh -xcase
-tostop -echoprt echoctl echoke -flusho -extproc

What am I doing wrong?  And why does it work with the built in configuration for the built in serial port on the raspberry pi?
Answer: It's not the commands but the environment in which they run that is the difference.
Normally getty is spawned directly from the system service manager (init) – both with systemd where it is a .service, and in the SysV world where it has an inittab entry (and not an init.d script!). This has several differences from being spawned from within another terminal:
Primarily, a process started from a terminal inherits it as its "controlling terminal", which is the most important parameter for shell job control. You can see this in ps aux or ps -ef – service processes have no ctty at first, so when getty opens the indicated terminal, that becomes its controlling terminal for job control once the shell is run.
But a getty that was started from your xterm will continue to have that xterm pty as its controlling tty despite its input/output now being routed to the serial port – and while getty itself doesn't mind, the shell will also inherit the wrong controlling tty, and that'll make job control impossible.
$ ps -C agetty
  PID TTY          TIME CMD
 1136 tty1     00:00:00 agetty
14022 pts/22   00:00:00 agetty
      ^-- should be ttyS0!

The controlling terminal defines /dev/tty; it defines which processes job-control signals are sent to; it defines which processes are killed (SIGHUP'd) once the terminal closes. If your shell has inherited a controlling tty that's different from its stdin/out tty, all kinds of weird things may happen.
There are ways that a process can detach from its previous terminal, such as calling setsid() – and traditionally /etc/init.d scripts did this to 'daemonize' – but getty does not use them automatically because it doesn't expect to be run this way, so it wasn't programmed in. (There is a setsid tool that could be used to force this to happen, but you shouldn't use it here either; you should do things the right way from start.)
You should ideally just systemctl start serial-getty@ttyUSB0 and let getty run in a clean environment. If custom options are needed, it's better to customize that service using systemctl edit [--full] instead of running getty directly. (If systemd is not used, then edit /etc/inittab; it usually has an example included. Run telinit q to reload the inittab.)
There are many other, relatively minor differences between processes started from a shell vs through a service manager – stdin/stdout/stderr will start off as being your terminal at first (getty will close and reopen them, but not all services do); environment variables will be inherited from your 'sudo'; the cgroup will be inherited, which might affect your resource limits; from cgroups, the systemd-logind session will be inherited, and the serial login will not be permitted to start its own); your SELinux security context (or AppArmor profile, or SMACK label) will be inherited if that's in use; etc.


Trying to remember TV show sci fi episode from 60's or early 70's. Astronaut returns and morphs into alien with hard "crust"

Question: I know I saw this episode. I have checked every episode of The Twilight Zone and Outer Limits. Can't find it. The episode is black and white. The astronaut returns to his home and there is a lot of interaction with his wife. He slowly realizes that there are changes occurring in his body as he is beginning to develop a crust or hard shell until eventually he morphs into a creature more like a large insect than anything human. Presumably he has contacted something in space which is triggering this metamorphosis into perhaps an alien species.  There are scenes with NASA or space administration doctors who of course don't know what's happening to him either.
Comment: But it sounds vaguely like The Quatermass Experiment, which was previously asked about [here](https://scifi.stackexchange.com/questions/202559/sci-fi-movie-abandoned-spaceship-returns-to-earth/).
Comment: Sounds like the basic plot to the Fantastic Four, with Ben Grimm returning from space and turning into the Thing. They had some cartoons in the 60s and 70s, but I don't think any live action shows.
Comment: Are you completely sure it was an episode of a TV show and not a movie?
Comment: Dark Universe ? Plot matches, but it is from 1993: On its way back to Earth, the space shuttle Nautilus passes through a cloud of alien spores causing its sole occupant, astronaut Steve Thomas to transform into a blood-thirsty monster. The shuttle crashes into a swampy region of central Florida, creating a situation which threatens contagion and/or death to all who encounter the shuttle or its mutated pilot. https://horrornews.net/85038/film-review-dark-universe-1993/
Answer: This may be The Quatermass Experiment, a 1953 black and white TV serial later made into a sci fi movie by Hammer Productions. A man retirns from space and morphs into a hard skinned plant, like creeping leprosy.
From Wikipedia:

Along with his laboratory assistants, Professor Bernard Quatermass anxiously awaits the return to Earth of his new rocketship and its crew, who have become the first humans to travel into space. The rocket is at first thought to be lost, having dramatically overshot its planned orbit, but eventually it is detected by radar and returns to Earth, crash-landing in Wimbledon, London.
[...]
Carroon is abducted by a group of foreign agents whose government wants the information they believe obtained while travelling in space. It is clear that there is something critically wrong: he appears to have absorbed the consciousness of the other two crew members, and is slowly mutating into a plant-like alien organism.
Answer: It sounds a lot like the Doctor Who story The Ark In Space. That was colour, and broadcast in 1975.
The man doesn't have a wife, he has a female second in command.
The story is set on a space station. There's an alien who lays its eggs inside people. The infected people gradually change into aliens, who look like giant insects.
THe infection starts on a man's hand.
https://ichef.bbci.co.uk/images/ic/624x351/p00vd75c.jpg
It spreads:
https://upload.wikimedia.org/wikipedia/en/f/f4/Ark_in_Space.jpg
And finally turns him into an insect.
https://doctorwhogroup.weebly.com/uploads/4/9/4/0/49406159/9215208.jpg
Comment: the story takes place in the far future in which the institution of marriage apparently doesn't exist. but dialogue indicates that they have "pair-bonded", making them the equivalent of husband and wife.
Answer: It doesn't match up perfectly to your description, but the first thing I thought of from your description was "Cold Hands, Warm Heart", an Outer Limits episode, starring William Shatner.

After completing the first manned mission to orbit Venus, astronaut Jeff Barton (Shatner) returns to Earth with recurring nightmares and an increasing inability to stay warm. Barton's condition continues to worsen and is accompanied by a peculiar webbing of his fingers. Only after his nightmares become more vivid does he recall an unrevealed alien encounter in the Venusian atmosphere. Barton's doctors suspect the astronaut had been genetically affected by his mission, and they then struggle to treat and cure him before his mutations completely take over.

It's been a long time since I've seen the episode, but my recollection is that Barton's transformation is reversed at the end, and he never stops looking mostly human.


"Not hindered with any knowledge"

Question: In Dutch we use the translated equivalent of not hindered with any knowledge to indicate somebody without any knowledge on the subject. It is not necessarily negative. It can mean that somebody is complete open and new to the subject, which may lead to new ideas, insights etc. But in a different context it may also carry a sarcastic tone indicating somebody with the biggest mouth and slightest knowledge. Is this equivalent comparable and usable or are there better constructs?
Comment: Recently I saw on slashdot.org: "I've run into more than a few people who have made it through college quite uncontaminated by knowledge"
Answer: The phrase blank slate is a good match to your first meaning.  It does not necessarily carry any negative conotations.
For the second meaning, I would probably use the word clueless.  It doesn't imply a big mouth, but it clearly states that the person you are referring to is so lacking in knowledge that they may not even realize how little they know.
I could also refer to myself as clueless on a given topic.  That does not carry the same negative conotations as when I use it referring to someone else.  It would in fact be a good match for your first meaning, but only when the speaker is referring to themself.
Comment: On a side note, to say "unhindered by knowledge" but without the negative connotation, you could say "unhindered by preconceptions", because "preconceptions" and "preconceived notions" are quite neutral.
Comment: I was working on the same answer when you posted!  Great minds think alike.
Answer: "Not hindered with any knowledge" is meaningful; I don't know how common it is.  I've heard "unencumbered by knowledge" and "unencumbered by facts"; the latter is more negative.
You might also say "uninformed about X".
Answer: In English, I would expect that phrase to be used mostly, or even entirely, in the sarcastic sense:  "My manager has a unique ability to make a decision unhindered by knowledge" -> he routinely tells me to do things that I know make no sense.
For the sense of someone simply entering into a completely new realm of learning or experience, adding a word or two to make it clear that you're talking about their knowledge up to now might be helpful:  "He started learning about the new software unhindered by any prior knowledge of its quirks and foibles" or "As a new user unhindered by prior knowledge, John has a unique ability to ask questions that make us rethink our assumptions."
Comment: Thanks for formulating the contexts, these are also the contexts I was referring to in my question. It covers exactly what I meant.
Answer: Normally a person not hindered with knowledge is called  a blank slate (which is the English translation of Tabula Rasa), but it usually doesn't have the sarcastic overtones.
I personally like the construct you used.

Not hindered with any knowledge

It could be either a biting, witty reply or a serious description without any overtones.
-edit-
Another way of stating the same thing is as follows:

Unfettered by knowledge.
Comment: @Mike, I agree.  I do, however, like the additional formality imposed by the "not".
Comment: "Unhindered by knowledge" is probably a better phrase -- it's easier to say and more direct.  Perhaps, "inexperienced with".
Comment: I tip my hat to you, sir.  I have been writing for English-ignorant readers, for far too long.  I recently overheard someone say, "Those [foreigners] gotta learn to speak American."  *Sigh*
Answer: If you are looking for a single construction that can convey both ideas, you could try the adjective ignorant. It is used in an impersonal sense to denote a lack of knowledge about a given subject. But it can also be used acerbically to imply a lack of knowledge about everything.
Answer: I think the closest equivalent we have in English is the concept of somebody "knowing just enough to be dangerous". This is used for people who perhaps aren't experts on a subject, but know enough to think they know what they are doing. People who think they know what they are doing tend to lose the caution a neophyte would posess.
More accurately your "not hindered with any knowldege" person we might say "doesn't* know enough to be dangerous".

"Not hindered with any knowledge"


Multi Collinearity in SEM

Question: in Structural equation modeling, can Collinearity occurred only between multiple independent (exogenous) variables or it can occurred between a latent mediation variable and a latent dependent variable too?
Answer: Collinearity is about the correlation between predictors.
If a mediator and outcome are highly correlated, that will change the parameter value of, and increase the standard error of, the indirect effect.
Is that what you mean?

Multi Collinearity in SEM


Light speed travel precautions

Question: How strong would need to be gravitational shield on the ship if would encountered meteorite dust in diameter 50mm² at that speed?
Comment: So . . . you have a ship with mass traveling near the speed of light and you want to shield it from dust? You won't be able to do that with gravity.
Comment: What is a gravitational shield? Also, [the answer to this question](http://physics.stackexchange.com/questions/71358) suggests that we probably don't have to worry about dust colliding with spaceships.
Comment: Please continue, solution's would be?
Comment: In process off speeding with car from 0-100km/h in this gravity we feel acceleration only short time. Amount off time to get that speed equivalents to the energy that we feel on our body as the puling force off acceleration. Gravitational shield would be technique that can eliminate or compensate that energy. And that I think could be possible.
Answer: This . . . is going to be tough to answer. One of the issues is that it's impossible for non-massless particles to travel at the speed of light; moreover, any object going near it will have an enormous amount of kinetic energy. Add to that the fact that we can't go anywhere near that speed and you have a tough, if not impossible, question to answer.
This can only be reasonably answered by talking about shielding used in spacecraft (admittedly going way slower than the speed of light). There are a few options used on the ISS:

The Whipple bumper: Helpful for impacts with high-velocity objects, this configuration uses a metal plate attached a short distance away from the main structure of the vehicle. The initial "bumper slows down the incoming particle enough so the "catcher" plate behind it can resist the further impact.
The multishock (aka stuffed Whipple) bumper: This is similar to the Whipple bumper, but it inserts more layers of material in between the bumper and the catcher. Like the normal Whipple bumper, the outer bumper is often made with aluminum.
The mesh double bumper: This uses "metallic mesh" to protect the spacecraft.
Comment: [Related answer on Space Exploration.](http://space.stackexchange.com/questions/4132/what-happens-if-an-astronaut-is-hit-by-a-tiny-micrometeorite/4134#4134)
Comment: In any case, the mechanically created protections are only technological achievement.
Comment: What do you mean?
Comment: I'm currently interested in technology that allow speed acceleration from 0 to the 15G in minimal time X. Where could be created gravitational field in the field, the minus 14G in speed acceleration of 15G would still be 1G.

Light speed travel precautions


How to revert (Roll Back) a checkin in TFS 2010

Question: Can anyone tell me how to revert (roll back) a checkin in TFS 2010?
Answer: You have two options for rolling back (reverting) a changeset in Team Foundation Server 2010 Version Control.  First option is using the User Interface (if you have the latest version of the TFS 2010 Power Tools installed).

The other option is using the TFS 2010 version control command-line application:
tf.exe rollback

I have information about both approaches on my blog post.
For Team Foundation Server 2012, 2013, or Visual Studio Online, rollback is now built-in directly to Source Control Explorer and when you are opening a changeset's details in the Team Explorer Window.  You do not need to install any release of the Power Tools for this functionality when using Visual Studio 2012 or later.  There is a great MSDN article discussing details about rolling back a changeset now available here:  http://msdn.microsoft.com/en-us/library/ms194956(v=vs.110).aspx
Comment: In Visual Studio 2012 TFS changesets can also be rolled back directly [from the Source Control Explorer UI](http://msdn.microsoft.com/en-us/library/ms194956(v=vs.110).aspx)
Comment: @EnricoCampidoglio Thanks a ton!  I went ahead and updated the answer with your additional information for Visual Studio 2012.
Answer: For 2010, use the rollback command from the command line.  There is not integrated support in the IDE for this, as of yet.
Rollback command
Basically, the way that it works is that it creates an "anti-delta" to negate the impacted changeset.  You can accomplish the same thing manually by doing a Get Specific Version, adding a space to the file so it looks like it changed, and checking it in.  I still go the latter route to back out a change if I need to for a single file, as I find it quicker to do.
Comment: On one machine, tf.exe is located at C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\TF.exe" rollback. You need to run rollback from one of the mapped folders connected to the collection you want to roll back.
Comment: see this video for a very fast demo of tf rollback:  http://www.youtube.com/watch?v=ar6E88Tpf9I
Answer: Without using power tools or command line:

ensure Tools->Options->Source Control->Visual Studio Team Foundation Server UNCHECK Get latest version of item on check out
View the history of project folder in Source Control Explorer and right click on the changeset to roll back to and choose Get This Version
Check out for edit on the project folder in the Source Control Explorer (this should keep your local version you just got from the history)
Check in pending changes on the project folder in the Source Control Explorer
if visual studio asks you to resolve conflicts, choose keep local and attempt check in of pending changes on the project folder in Source Control Explorer again
Answer: Rolling back changes for another user
If you are attempting to rollback changes for another user, make sure you get latest on the files you are attempting to rollback; otherwise you will see the error:

"No changes to roll back."
Comment: Thanks for the tip, but this is more of a comment than an answer
Answer: You can rollback a changeset (in TFS2010) through command line doing:

Open CMD or Visual Studio Command Prompt
Change directory to your workspace folder. Example: cd C:\myWorkspace
Run following tf command (where 123 is changeset number)
C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\tf.exe" rollback /changeset:123 /recursive
Go to Pending Changes window to check files marked with edit,rollback and do a Check In.

Note: you must use tf.exe full path even in Visual Studio Command Prompt to avoid "Unable to determine the workspace" error. More info here

Rollback reference (TFS 2010)
https://msdn.microsoft.com/en-us/library/dd380776(v=vs.100).aspx
Answer: There is no undo option in TFS (up untill 2008, I haven't used 2010 yet).
There are some command line power tools you can use to rollback changes that may help:
http://msdn.microsoft.com/en-us/library/ms194956%28VS.80%29.aspx
HTH
Answer: right click file in Visual Studio and Source Control/View History
then select last changeset, right click and click Rollback
After rollback done, you should check in again.


Apex trigger to create record through data loader and assign to the related list of account

Question: I am importing data into Account object through data loader.I want that the contact that i imported to the contact object should automatically assign to the Account Name (that is given in the account Name of  contact) and contact should be shown in the assign account related list. Would i need to write a trigger for this and how i can write trigger for automatically assign contact in account related list
Comment: Do you have duplicate Account names in Account CSV file?
Answer: No need to write any automation for your requirement. Please follow guidelines for importing Accounts and contacts in Salesforce through data loader.

Import the Account records.
Export those newly created records or maintain the success file of imported records (It will include the recently created record Id (i.e AccountId)).
Use VLOOKUP to create a new contact CSV file which matches the contacts with the exact account ID.
Import the contact records.

It will associate the existing account with newly created contact records and you will see the related list of associated contacts on Account record.


CLT for bounded and dependent sequence

Question: Let $\displaystyle X_1,X_2,...X_n$ be identically distributed such that $\displaystyle Pr\{a \leq X_i\leq b\}=1$ for bounded constants $\displaystyle a,b$. Further Let $\displaystyle cov(X_i,X_j)=\alpha$, $\displaystyle E(X_i^2)=\mu_2<\infty$. What do we then know about the distribution of $$\frac{1}{\delta n}\sum_{i=1}^n(X_i-EX_i)$$
Is there a proper $\delta$ that we could choose to have some "known" (or "anything close to known") asymptotic distribution?
Answer:
Every square integrable centered distribution can be a limit.

To see this, assume that, for every $i$, $$X_i=B_iZ+(1-B_i)Y_i,$$ where $Z$ is centered, $(Y_i)$ is i.i.d. and centered, $(B_i)$ is i.i.d. Bernoulli with $P(B_i=1)=p$ and $P(B_i=0)=1-p$ for some $p$ in $(0,1)$, and $Z$, $(Y_i)$ and $(B_i)$ are independent.
Then, for every $i\ne j$, $$E(X_i)=0,\qquad\mathrm{var}(X_i^2)=pE(Z^2)+(1-p)E(Y^2),\qquad\mathrm{Cov}(X_i,X_j)=p^2E(Z^2).$$ Furthermore, $$S_n=\frac1n\sum_{i=1}^n(X_i-E(X_i))=R_nZ+T_n,\qquad R_n=\frac1n\sum_{i=1}^nB_i,\quad T_n=\frac1n\sum_{i=1}^n(1-B_i)Y_i.$$ The usual strong law of large numbers applies to $(R_n)$ and $(T_n)$ and shows that $R_n\to p$ and $T_n\to0$ almost surely, hence $$S_n\to pZ\quad\text{ almost surely}.$$
Another example is to pick some $Z$ and $(Y_i)$ with $(Y_i)$ i.i.d. and independent of $Z$ such that $E(Z)=0$ and $E(Y_i)=1$, and to consider $$X_i=Y_iZ.$$ Then $E(X_k)=0$, $E(X_k^2)=E(Y_1^2)E(Z^2)$, $\mathrm{Cov}(X_i,X_j)=E(Z^2)$, and $$S_n\to Z\quad\text{ almost surely}.$$
Edit: More generally (and this might answer a comment), assume that $X_i=u(Y_i,Z)$ for some $Z$ and $(Y_i)$ with $(Y_i)$ i.i.d. and independent of $Z$, then $$\frac1n\sum_{i=1}^nX_i\to v(Z)\quad\text{almost surely},$$ where the function $v$ is defined as $$v(z)=E(u(Y_1,z)).$$ Furthermore, for every $i\ne j$, $\mathrm{Cov}(X_i,X_j)=E(v(Z)^2)$.
Comment: Did: These are very nice examples. But I had some other sequence in mind. When establishing a CLT, in general, "X_i"'s admitting a suitable decomposition, as your examples clearly show, simplifies the math. But sometimes it is not so clear how to do this. For example let $X_i=\frac{aY_i+bZ}{cY_i+dZ}$, where $Y_i$'s are iid, and we know that moments of $X_i$ exist. Then what would think? I appreciated your hints.
Comment: See Edit. $ $ $ $
Comment: its been quite some time since you kindly helped me with this result, could you please explain how to establish the general result? A reference would be most helpful. Many thanks again.

CLT for bounded and dependent sequence


Unity3d - deploy game to android device off site

Question: I am using Unity3d to develop my game and my friend with android device wanted to test it. I am natively IOS developer and have no knowledge of deploying Android platform. What do I need other than Unity3d? The scenario here is that I have to send to my friend who is not developer to install and test on his device via internet. We used to have TestFlight App but that is history now.
Answer: Well, here is the minimum you need:

You have to install android sdk and set path to it in Unity preferences
You have to switch target platform to android and set settings you need in Player Settings (like supported android versions etc.)
Click "build" in Build Settings - if everything is fine you'll get an .apk file that you can send to your friend

But again, you might run into some problems. It depends of your project and your code. For example, if you have some plugin code that works only for iOS (using [DllImport] attribute) you might have to turn it off or rewrite for android (using AndroidJavaClass, for example). You might also be using some features that are not supported on android.
There might be some other problems, but there is no answer which ones - you should try it and find them out by yourself.
Also, you can test your .apk on android simulator before sending to anyone else (in this case install android studio or eclipse to make it a little more comfortable).
Answer: It sounds like you are talking about what is required to deploy to test devices. Luckily, it is significantly easier on Android than it is on iOS. Your tester will have to enable the installation of non-market on their Android device, after which they can just click on a link for an APK and download/install it through their phone's browser. To enable non-market executables, direct them to go to Settings, then Application Settings, and then to enable Unknown Sources. This will allow them to install non-market executables. If this is not suitable for your purposes, you can also go into the Android Marketplace portal and create your application, and from there you can add testers to your app. They should then be able to search and install it through the Android marketplace, but it will not be visible for users who are not in your app profile until after it has been officially released.


Can Thevenin voltage ever be negative?

Question: So in context of Thevenin's and Norton's theorem, can Thevenin voltage $V_{th}$, as in http://en.wikipedia.org/wiki/Thevenin_theorem, ever be negative? I know that $R_{th}$ can be negative, but never thought of $V_{th}$ one until now.
Answer: Yes.  It depends on how you define the direction of positive voltage in your equivalent voltage source.   In other words, if you switch the positions of the "+" and "-" on a typical diagram, the sign of the voltage will switch.

Can Thevenin voltage ever be negative?


Converting guid to string with entity framework

Question: I'm trying to pass a GUID as a string over web services, however I've hit a bump in the road. The GUID is stored in SQL Server as a UNIQUEIDENTIFIER and EF pulls it as a GUID. What I would want to do is in my query do this:
var query = myEntities.Foo.Where(q => q.Id== Id)
                .Select(bar =>
                        new Bar()
                            { BString = bar.GUID }
                        );

Now, C# throws a build error that you cannot convert System.Guid to string, so I'd think that you could do this:
{ BString = bar.GUID.ToString() }

or even
{ BString = Convert.ToString(bar.GUID) }

But both end with runtime exception:

There was an exception, it was System.NotSupportedException: LINQ to
  Entities does not recognize the method 'System.String
  ToString(System.Object)' method, and this method cannot be translated
  into a store expression.

So I gather that in both cases, it's not able to figure out a T-SQL equivalent of going from UniqueIdentifier to varchar.
Is there a way around this besides retrieving the object, then iterating over my return set copying each object to a new object and converting guid->string at that point?
Thanks.
Comment: here's a workaround .Let your bar type has a property that returns its Guid as string then use this property in your Linq queries
Comment: what is the value of query after the lambda statement gets executed..?
Answer: Convert it to a string outside the query part of the LINQ statement.
var query = myEntities.Foo.Where(q => q.Id== Id).Select(r => r.GUID)
  .AsEnumerable()
  .Select(guid =>
    new Bar()
    { BString = guid.ToString() }
  );

The .AsEnumerable() is the important part: it casts the result from IQueryable to IEnumerable, having the effect of running any further operations on the client after the database query has been made. (You could also use .ToArray() or .ToList() in its place.)
Comment: Thanks, I'll work with the second query that you have until I can get a chance to performance test.  Otherwise I might have to swap to something like an sproc like Zruty was mentioning.
Answer: If performance isn't a concern, you probably should re-map your GUIDs to strings manually, as you suggested yourself:
var query = from entity in myEntities.Foo
            where entity.Id == Id
            select new { GUID = entity.GUID };
var response = from item in query.ToList()
               select new Bar { BString = item.GUID }

This is similar to what @Tim Rogers suggests, but explicitly split into two queries.
Another option I come up with is writing a stored procedure that converts GUIDs to strings using the T-SQL's native convert() statement. This will work around EF's inability to map GUIDs to strings automatically.
Answer: It is now possible to use new Guid(<your string>); to convert the string into a Guid instead of converting the Guid into a string.
Comment: How does this answer the question?


can you put a shimano XTR M980 175mm stage power meter on a XT M785 175mm setup?

Question: I would like a stages power meter on my set up but cant figure out if the bottom bracket sizes are correct and if even the new crank will fit at all?
Comment: I just came across this and I am in the opposite boat. I have a M785 and am considering to upgrade to the XTR M9000 (1x11) groupset. I'm wondering if I can still use my XT M785 power meter?
Answer: Both the M785 and the M980 are hollowtech II systems and compatible. They use a compatible bottom bracket sm-bb70 and sm-bb93, which are English threaded 68/73mm.
The M980 uses the same clamping system as other Hollowtech II systems which is different to earlier xtr cranksets which required specialist tools.
The stages power meter comes as a replacement crank arm with the meter built in, so while this set up would work for aesthetic purposes wouldn't it be better to get the m785 meter?


Gutenberg change/remove "Write your story" placeholder in custom blocks

Question: When created a new page or post or columns blocks we get the "Write your story" placeholder. Can this be removed or replaced, in custom blocks? How?
Comment: Sure, but could you post the code you've worked thus far when you tried to get this to work? [How to create a Minimal, Complete, and Verifiable example](https://stackoverflow.com/help/mcve)
Comment: @admcfajn there is no code, as far as I know for this, recommended in the Gutenberg docs. I can think of a few hacky ways to remove it but I'm interested in an official way of doing it, and so are many people because it's not documented. That's the point of the question.
Comment: Here's try this out, there's a handful of custom blocks in this repo you can dig into: https://github.com/WordPress/gutenberg-examples/blob/master/03-editable/block.js
Answer: There does seem to be a filter to modify the default: https://github.com/WordPress/gutenberg/blob/master/lib/client-assets.php#L1574
<code>'bodyPlaceholder'        => apply_filters( 'write_your_story', __( 'Write your story', 'gutenberg' ), $post ),
</code>
So you should be able to use the WordPress add_filter() function.
Answer: Here's an example block taken from WordPress/gutenberg-examples with placeholder text added.
<code>const { __, setLocaleData } = wp.i18n;
const { registerBlockType } = wp.blocks;
const { RichText } = wp.editor;

setLocaleData( window.gutenberg_examples_03_esnext.localeData, 'gutenberg-examples' );

registerBlockType( 'gutenberg-examples/example-03-editable-esnext', {
    title: __( 'Example: Editable (esnext)', 'gutenberg-examples' ),
    icon: 'universal-access-alt',
    category: 'layout',
    attributes: {
        content: {
            type: 'array',
            source: 'children',
            selector: 'p',
        },
    },
    edit: ( props ) => {
        const { attributes: { content }, setAttributes, className } = props;
        const onChangeContent = ( newContent ) => {
            setAttributes( { content: newContent } );
        };
        return (
            <RichText
                tagName="p"
                className={ className }
                onChange={ onChangeContent }
                value={ content }
                placeholder={__('wpse316624 placeholder text', 'custom-block')}
            />
        );
    },
    save: ( props ) => {
        return <RichText.Content tagName="p" value={ props.attributes.content } />;
    },
} );
</code>
Comment: That's a placeholder for a paragraph richtext element not the initial block placeholder. Answer should be removed.
Comment: I agree with you CyberJ, but since Gutenberg is still pretty new I'll leave it up just in case it helps point someone in the right direction.


D - Latch or D Flip Flop?

Question: I have a diagram (https://i.stack.imgur.com/UK16E.jpg) where it is either a D Latch or D Flip Flop. I am trying to figure out which one it is and why. If it is a D Flip Flip, I also need to know which input is the clock. Can someone help me out ?
Answer: This feels like a homework question, but I'll at least try to point you in the right direction.
The difference between a latch and a flip-flop is that a flip-flop is clocked.  At first glance, I thought it was a latch since there was no clock labelled as such, but this might not actually be the case. The clock is an input that will determine when the state of the flip-flop can change, so take a look at both of your inputs and figure out what will happen to the main RS latch (the two gates on the right) in each case. In particular, your A input catches my eye since it's directly tied to the two gates directly tied to your main RS latch.
Keeping these in mind may help:
NAND RS latch truth table:

D flip-flop excitation table:
$$\begin{matrix}
Q & Q(t+1) & D \\
0 & 0 & 0\\
0 & 1 & 1\\
1 & 0 & 0\\
1 & 1 & 1
\end{matrix}$$
Comment: o ok, thank you! I received A as clock and that it is a flip flop. Can you verify this?
Answer: A D flip-flop has a clock input (else it would not be a flip=flop) and a data input D. There are also gated D flip-flops which have a a gate input--the clock and data inputs are ignored unless the gate is enabled.

D - Latch or D Flip Flop?


Can anyone decipher this (1)?

Question: The following is what I found on the door of a shop. I can recognize some of them but not all of them. I think the first four are 國舅手執陰陽板、湘子瑤池品玉簫, the fourth one is 品玉簫, and the sixth 長生酒.
Comment: This kind of compound word is not officially recognized, nor is it used by the people. You can think of it as a kind of artistic creation, and no one can understand it except the designer himself. There's no need to try to understand the words, it's not the right word, it's like you modify many letters to form one letter.
Answer: Something similar here

國舅手執陰陽板,拐李先生法道高

湘子雲中品玉簫,鍾離磐石把扇搖

仙姑敬奉長生酒,洞賓背劍清風客

釆和花籃獻蟠桃,果老騎驢樂逍遙

Everything is almost identical except in the third group "雲中" is changed to "瑤池", in the fifth group "仙" is written as "僊", and in the seventh group "釆和花籃" is changed to "藍採背山"
仙-->僊 and 釆 -->採 are both wrong words
Comment: Where do you see 藍採背山? I don't see it.

Can anyone decipher this (1)?


Does the Detect Magic spell detect itself?

Question: If I cast detect magic in a circle around myself, can I see the aura of my own spell and thus know where it ends?
Comment: Is the concern that something is slightly out of range, but since your character doesn't know the exact distance (and the DM is being stingy) so you cannot know if it's unmagical or out of range?
Comment: @captain man this question was inspired by one talking about an anti magic zone. I figured that if you could see your own aura you would be able to tell when you approached one. It was just curiosity.
Comment: Got it. The only reason I asked is because if this were about not knowing if something was slightly less or slightly more than X distance you may get different answers and I wanted to make sure you were getting the most useful info.
Answer: If anything, you would see a divination aura around your own body.
To the extent that Detect Magic has a target, the target is you, the caster. The 30-foot sphere is not the target, but simply the range of the special sense granted to the caster by the spell. (By analogy, consider what Detect Magic would see for a Darkvision spell.) So, if you held your hand up in front of you while using your action to see magic auras, you might see the spell's own divination aura around your own body, but the spell itself would not produce any other aura.
You might see nothing at all
Consider that the always-on magic-sensing feature of the spell would be completely useless if the spell detected itself, since it would always detect some magic within 30 feet 100% of the time. It would be logical to extend that self-exclusion to the aura-viewing feature as well, especially since doing so has no mechanical impact. In this case, you would not see the spell's own aura, although another wizard casting Detect Magic would see the aura on you (and you would see theirs).
Comment: I can see doing the self-exclusionary part as that makes sense... but the spell is still pretty useless as written unless your DM is really kind about it... if ANY of your companions or even you has even one magical item you detect magic... most DMs ignore that little issue but sometimes I throw it in so my players might know something is up.
Answer: "I cast detect magic in a circle around myself."
Except you don't. Detect magic doesn't have a range, you don't make a spell attack roll to cast it. It isn't an area of effect spell either. You cast it only on yourself, gaining a specialized sense. You'd be able to see the aura around yourself caused by detect magic, and an aura around any creature or object that is affected by magic. Your improved sense, once the spell is already cast, has limitations of distance (within 30 feet of you) and can be blocked by certain types of barrier.
Answer: No.
The relevant text of Detect Magic is

For the duration, you sense the presence of magic within 30 feet of you. If you sense magic in this way, you can use your action to see a faint aura around any visible creature or object in the area that bears magic, and you learn its school of magic, if any. (DnDBeyond entry for Detect Magic)

Perceiving specific information about the spell requires using an action to look at the creature or object that has been affected by a spell, which would be yourself in this case. So the bit about auras answers the question-as-written definitively. The aura of a spell only surrounds the creature that has been affected by the spell. So you could look at your own hand and see that you're under a magical effect. But you wouldn't learn anything new about the area the spell is affecting, nor perceive that sort of information about the spell.

If we're talking about perceiving that a magical effect is present, this comes down to how your DM is going to interpret the word sense. A visual perception would definitely qualify, but the text of the spell does not say that you can necessarily see the presence of magic, or that you would necessarily understand properties of the spell (like the area it covers).
If your DM says that you can sense the spell visually, you might be able to see the affected area and by comparison with regions where the spell isn't in effect, perceive the boundaries of the effect. But it's just as possible that you sense magical effects in some other way, perhaps by sound or odor or feeling, which would not give you the "free" understanding of the areas the spell is affecting. You should be able to perceive a magical effect around yourself, but you'd already know about it since you cast the spell.

You also don't need this effect to know the boundary of the spell. Its effective range is 30 feet in any direction from yourself, and any number of other options would allow you to know how far from you 30 feet is. That may or may not suit your need, but Detect Magic itself doesn't.


How can I insert a transparent rectangle but with the edges mark?

Question:
I want to do exactly what is shown in the image. Some know the way to do it?
Comment: "Exactly what is shown on image" - what exactly ? If you want to overlay one image on top of another then do you really need 3D modeling package ?
Answer: Instead of having a bitmap, it could be better to just use a mesh, like this:

here I also used a shadless white material, to get the idea.
Another way could also be curves with tapers, probably...
Using real geometry, instead of having a fixed bitmap, allows you to adapt the mesh to different needs, and ensures optimal resolution...
Answer: You can use Box Masks in the compositor.
Add two Box Mask nodes, make one of them slightly smaller and set it to subtract from the other box mask. Use the result as the factor input of a Mix node, where you mix the original image with the color you want the edge of the rectangle to be.
Answer: You can create the "Graphic" in an application like Photoshop or Gimp with an alpha channel. Save it in a format that supports alpha channels like .PNG. Then import that "Graphic" as a plane into Blender. In Blender you can go to "File" > "Import" select "Images as Planes" and check off "Use Alpha"in the import options.


Can I use a time machine volume to store additional data?

Question: I have a large external hard drive that I am using as a time machine backup volume. Since I don't need all the storage space for backups, I'm considering storing additional data on the drive. Is there any danger of this usage interfering with the backup system or is this an always-safe storage spot?
Comment: I'll add that I actually do this. I have a TM backup on a 2TB drive as well as other large video files that are not a part of the backup. So far, this hasn't caused any problems...
Answer: Seeing that external storage is relatively inexpensive, I would leave the existing TM drive alone and purchase another external drive. That way, you can backup the additional data on the new drive to the TM disk, too. You wouldn't be able to do this if the additional data resides on the TM drive itself.
If you do choose to use the TM disk for non-TM data, I recommend partitioning the drive to separate the TM data from the non-TM data. If you ever need to reformat the TM partition, you won't need to move that additional data to another disk first, or visa versa.
All that being said, it is technically possible to use the TM disk to store additional data. I used to do it until #4 (below) happened and I lost ~10k .mp3 files I then needed to re-rip from CDs. (I did re-rip about 80% of the lost files to Apple Lossless format, so it wasn't a complete disaster, but I did lose thousands of files.)
There are several drawbacks you should keep in mind:

Time Machine will delete older backups more frequently when available space is low.
Performance on the drive will suffer when TM is running and you are accessing the additional data at the same time.
If you need to transport the additional data off-site, you'll also be taking your TM backup with you.
When (not if) the entire disk crashes hard, you will lose the additional data unless it is backed up somewhere.
Comment: Good list of drawbacks. Here are things I do when I have a large USB drive with hundreds of GB of free space (my backup grows a GB a month typically). Store ripped DVD for viewing, cache large software downloads, move large databases there to run a test script on them when I don't want to operate on live data. All of these don't need to be backed up and as long as I'm aware of the less usable space / increased chance TM will start deleting old backups - it works very well.
Comment: I suppose it depends on the use case how much this impacts the decision. For example I use the same drive for my time machine backup and for other backups I do by hand (e.g. backing up steam games). Also, I keep "template" copies of clean virtual machines there. I've found that time machine backups of Parallels VMs are unreliable when restoring.
Answer: Yes - you are free to use that disk to mix storage and Time Machine backups. Stay out of the Time Machine folder/disk image and you will be fine.
Since Time Machine can back up to a network store and a locally connected drive - the details on where Time Machine squirrels away it's backup data is slightly different, but you are free to use the rest of either disk to store whatever files you wish.
The only down side to storing files on the same volume that is being used as a Time Machine destination is that you cannot use Time Machine to both back up those other files and store backups from elsehere. Even with the dual destination rotation scheme added in Mountain Lion - Time Machine is hands off for any drive listed as a destination.
Answer: None, as far as you know what you are doing and don't change the name of the volume. Also make sure that the partition table type is GUID.
The only possible side effect would be your transfer speeds getting slow because a backup is happening.


Spectral families of commuting operators

Question: Consider two self-adjoint bounded operators $A$ and $B$ on a separable Hilbert space. According to the spectral theorem we can write
$$
A=\int_{-\infty}^{\infty} x d E^{A}_x, \quad B=\int_{-\infty}^{\infty} y d E^{A}_y
$$
where $E^{A}_x$ and $E^{B}_y$ are the spectral families of projectors of $A$ and $B$ respectively. Is there a simple way to prove that if $[A,B]=AB-BA=0$, then $[E^{A}_x,E^{B}_y]=0$ for all $x,y$?
Answer: From $AB=BA$, you get $A^nB=BA^n$ for all $n$, and immediately $p(A)B=Bp(A)$ for any polynomial $p$. By Stone-Weierstrass, $f(A)B=Bf(A)$ for any $f\in C(\sigma(A))$.
Now let $$\Sigma=\{\Delta:\ \Delta\ \text{ is Borel and } E^A(\Delta)B=BE^A(\Delta)\}. $$ From the fact that $E^A$ is a spectral measure, it is quickly deduced that $\Sigma$ is a $\sigma$-algebra. If $V\subset\sigma(A)$ is any open set, it may be written as a disjoint union of intervals, which allows us to see that there exists a sequence $\{f_n\}\subset C(\sigma(A))$ such that $f_n\nearrow 1_V$ pointwise. Then, for any $x\in H$,
\begin{align}
\langle BE^A(V)x,x\rangle
&=\langle E^A(V)x,B^*x\rangle
=\int_{\sigma(A)}1_V\,d E^A_{x,B^*x}\\ \ \\
&=\lim_n\int_{\sigma(A)}f_n\,d E^A_{x,B^*x}
=\lim_n\langle f_n(A)x,B^*x\rangle\\ \ \\
&=\lim_n\langle Bf_n(A)x,x\rangle=\lim_n\langle  f_n(A)Bx,x\rangle\\ \ \\
&=\lim_n\int_{\sigma(A)}f_n\,d E^A_{Bx,x}
=\int_{\sigma(A)}1_V\,d E^A_{Bx,x}\\ \ \\
&=\langle E^A(V)Bx,x\rangle.
\end{align}
As $x$ was arbitrary, $E^A(V)B=BE^A(V)$. So $V\in\Sigma$, and thus $\Sigma$ contains all open subsets of $\sigma(A)$, and then the whole Borel $\sigma$-algebra of $\sigma(A)$. Thus $E^A(\Delta)B=BE^A(\Delta)$ for  any Borel $\Delta\subset\sigma(A)$.
So far we haven't even used that $B$ is selfadjoint; but now we can use the fact to repeat the above argument for a fixed $\Delta_1\subset\sigma(A)$, to obtain
$$
E^A(\Delta_1)E^B(\Delta_2)=E^B(\Delta_2)E^A(\Delta_1)
$$
for any pair of Borel sets $\Delta_1\subset\sigma(A)$, $\Delta_2\subset\sigma(B)$.
Answer: What you need is a way to construct $E_A$ and $E_B$ directly from $A,B$. This is accomplished through Stone's Formula:
$$
       \frac{1}{2}\left(E(a,b)x+E[a,b]x\right) \\
= \lim_{\epsilon\downarrow 0}\frac{1}{2\pi i} \int_{a}^{b}(A-(r+i\epsilon)I)^{-1}x-(A-(r-i\epsilon)I)^{-1}x dr
$$
This is a contour integral around $[a,b]$ with the vertical pieces missing. Using strong limits you can isolate $E(a,b)x$ and $E[a,b]x$ through limits in $a$, $b$. You can actually do this in a constructive way using the $\tan^{-1}$ function to explicitly integrate and take the limit in the strong topology.
If $AB=BA$, then
$$
         (A-\lambda I)B = B(A-\lambda I) \\
          (A-\lambda I)(B-\mu I)=(B-\mu I)(A-\lambda I) \\
          (B-\mu I)(A-\lambda I)^{-1} = (A-\lambda I)^{-1}(B-\mu I) \\
           (A-\lambda I)^{-1}(B-\mu I)^{-1}=(B-\mu I)^{-1}(A-\lambda I)^{-1}.
$$
From this and Stone's formula, you have a constructive proof that the spectral measures of $A$ and $B$ commute. I think it helps to see how the spectral measure is constructively determined on intervals of $\mathbb{R}$.


Is it okay to just ask for an algorithm to a problem?

Question: Is it ok if I pose/quote an algorithmic problem and just ask for a solution to it? Or at least can I ask users to point me in the right direction (give me the name of a known algorithm/tell me where to look for)?
Comment: Folks, asking _is this sort of thing acceptable on the site_ is precisely how people that aren't sure try to avoid irritating others before _actually going and doing it_. If you down-voted this post by someone that actually _checked_ before doing something, then you're just discouraging people from doing the very thing we want them to do. No one is proposing that this _should_ be okay, they're just asking if it _is_ okay, because they (presumably) don't know. What purpose does down-voting something like this serve, other than making someone feel bad about doing what we asked them to do?
Comment: @MatthewLundberg Programmers.SE is no more a "give me the algorithm" site than Stack Overflow is a "give me the code" site.  Major difference there, is that because P.SE has a low enough volume we actually have a chance of enforcing that with close votes in a timely manner.
Comment: @Deduplicator "Support" is described as "A request for assistance with one of the site's features." What I was asking wasn't IMO a feature so I didn't use this tag. Honestly, no tag (of the 4 to choose from) seemed fit for my question.
Comment: @TimPost Meta downvotes are typically used as "I disagree with the premise of this question" because it doesn't affect reputation.  If it's starting to happen on Meta Stackoverflow, that just means users are starting to see it like a site-specific meta site instead of the whole-stackexchange meta like it used to be.
Comment: Might it be better on programmers?
Comment: difficult to say, it relly depends on your question and the thoroughness of it. if it sounds like simply "give me" then it wouldn't be as likely
Comment: @izkata I hope you see the irony of trying to explain how meta votes work to a guy who gets paid to sit on meta all day.
Comment: If by an algebra/mathematic algorithm, perhaps it would be better on the math site.
Comment: @MichaelT Thanks, I'm not active there, but of course that is to be expected.
Comment: @TimPost: Might have had something to do with it being tagged discussion and not support. Good thing you finally corrected that. Besides that, I certainly concurr.
Comment: @TimPost: how many times more will you repeat it with the SE crew without addressing this issue in its core?
Comment: @corsiKa Depends on what meta he sits on all day.  If it was mostly/only Meta.SO before the split into MetaSE (which is possible given his role), he might not have picked up on it.
Answer: In all questions, you should clearly state what you're trying to accomplish. Something like this:

I want to implement a search that first goes to the most distant (or possibly least relevant) nodes first, indexes them, and then works its way back to the beginning. I've tried recursive directory searches, but those end up stopping at the most distant nodes instead of actually starting there. Here's some of the code I've been using. Note, this works (technically), but doesn't do what I want ..

And of course someone is likely to answer:

Oh, you want a breadth-first search. Those can be tricky, here's an example of how you could do it ..

Just explain the problem as well as you can, and if there's a known algorithmic solution that actually pertains to your described implementation, someone is sure to let you know what it is. Where I think we could be a little more lenient  is judging the perceived level of effort someone put into solving their problem, because occasionally you really do keep hitting a blank screen every time you try to actually write something.
So, if you're doing a really complicated sort, just describe the input, the desired output, the expected complexity and all thinking you've put into it if you don't yet have code to post. It's not that folks don't want to just give you an answer, they just want to make sure someone else trying to find a shortest-path implementation is likely to find their answer as well, so you really need to describe the problem in order to make it easier for folks to discover. Knowing precisely where you're stuck also helps folks cut right to the chase in their answer, you've optimized for their time, and that's important.
It's downright hard to search for something if you don't know what you're searching for, and folks do take that into consideration. But, simply stating:

I need an algorithm that accomplishes {work}

... is a bit presumptuous, and will likely be interpreted as this is hard, so I want someone else to do it for me, and it won't be well-received.
Comment: +1 Your answer hits the nice balance between the effort that the people want to see before answering a question, and the fact that algorithm questions don't always have "half a solution" that can be presented like normal programming questions.
Comment: More concisely: **Yes**, it is OK (because the [help on topics](http://stackoverflow.com/help/on-topic) mentions "a software algorithm" as one of the typical question topics), but (1) **do some searching** yourself before and (2) make sure you **describe your problem well**. Both is discussed in the [help on question form](http://stackoverflow.com/help/how-to-ask).
Answer: If you're talking about programming contest questions:  State which contest it's from and be sure that contest is over before asking.  Don't just copy the question wholesale; you don't own the copyright.  I, and probably quite a few others, really don't like seeing programming contest question dumps here, especially from active contests.
If you're talking about questions that actually arise in practice:  Ask away.  But don't just give us an idealised version of what you think is important about the problem; give as many details of your use case as you can.  This sort of question is explicitly permitted by the help centre, and they're quite often very interesting.
Answer: The important thing is - why do You need this answer?
For students who try to solve their homework copy-ready solutions will not give any benefit.
For people who are not familiar with programming and need to solve particular problem, then never get back to it - complete solution is best answer.
For people who ask questions because it's work-related ( or simply, they earn money by this ), time sometimes is more valuable than fully understanding the solution and logic beneath it. They can analyse it later.
So shortly - yes, you can ask such questions if you need. I think it's our personal response ability to value experience over solution sometimes.
Comment: Maybe I didn't specify my question - I meant asking for an algorithm/name of a known algorithm, not for a code.