What would you estimate needs to be repaired in a bent fender/bumper?

Question: Hit a garage gate pole. Seems that the metal fender is bent quite well, and the bumper clamp area is also broken, hence its dislodged. What would you estimate would need to be repaired/replaced in this 2012 VW Passat?
Comment: Depends what you want - back to pre-impact condition, or just safe enough that the bumper isn't going to flap off as you drive?  Right now  the headlight looks to be shunted back and dropped down- I bet its misaligned and if all the mounts are broken could be held in by nothing more than the wiring harness.   That would be bad.
Answer: The metal fender needs re-shaping; a good body shop can repair the existing fender piece. The fender will then need to be painted to match the other panels on the car.
The bumper cover (the plastic piece that reaches around the front of the vehicle) has been pulled out of alignment. Often when this happens, the small plastic fittings (you can see four of them on the top edge in the first photo) are broken, and the bumper cover then needs to be replaced. The first photo, however, shows the four fittings in good shape.
What we cannot see is what kind of shape the other side of the connection is, which is on whatever the visible fittings connect to. That other side piece may be damaged and require replacement. In addition, while I don't see any big scrapes in the plastic, there may be cosmetic damage to the bumper cover that would require surface work (filling and sanding) as well as painting.
EDIT 6-14-22
I think @Criggie's comment is spot on: the headlight looks askew, and its mounts (or even itself) are likely damaged too. It is, unfortunately, a common experience that when digging into a body repair, as one digs one exposes more damage.
Comment: I doubt the time involved with trying to reshape the original fender is going to be less than a replacement part, especially if the part can be found 2nd hand and of the same (original) color. It would take *a lot* of work to get that crease out and then it'd never be perfect or factory fresh. Replacement is the by far better option here, IMHO. Also, if the loops in the bumper cover are not broken, more than likely the brackets which held it in place are ... it's the little things in these type situations which add up.
Answer: You could try the DIY method which is to heat up the dent using a hairdryer or a heat gun and then freeze it with compressed air. The heated panel will shrink and pull the dent out. This works on shallow plastic body part dents, but not on metal body parts.
Traditionally, auto-body shops would remove the bodywork and panel beat the dent out. Then they would sand and paint the panel. In those days car bodies were stronger and weren't designed to crumple to absorb impact. These days it is quicker and cheaper for the auto-body shop to simply replace the part of the car that has a dent and pass on the cost. That said, fixing dents is best left to the professionals and not DIY dent repair quick fixes.
Answer: The estimate came up to $3,192.24 and estimated to require 8 days. It took 8 days. The breakdown is as follows:

Parts: $1,491.52

A/M CAPA Bumper cover: 561807217BGRU  @ $245.77

A/M CAPA Absorber: 561807248 @ $66.67

LKQ Impact bar +25%: 561807109 @ $187.50

A/M LT Guide bracket 561807183A @ $13.72

A/M CAPA LT Headlamp assy: 561941005D @ $228.33

LKQ Radiator support +25%: 561805588B9B9 @ $250.00

A/M CAPA LT Fender: 561821021 @ $166.67

A/M LT Front bracket: 561821135A @ $28.33

A/M LT Fender liner: 561805911B9B9 @ $69.58

LT/Front Wheel, alloy +25%: @ $125.00

which is weird enough, because the rim was scratched, but they supposedly replaced it.

Body Labor: 15.8 hours @ $50.00 per hour, subtotal $790.00
Paint Labor: 8.1 hours @ $50.00 per hour, subtotal $405.00
Paint Supplies: 8.1 hours @ $30.00 per hour, subtotal $243.00
Other Charges: $2.50
Tax: $260.22

The bodyshop did all of the work. As a note, I wanted to do a State Inspection when I picked up the car from the shop, and it failed because the emissions were "Not Ready". Was told to drive ~100 miles or so and come back. Most probably because the bodyshop disconnected the battery during the repairs.
ON a different note, I have the repair manual for the VW Passat and will share here for reference:

 Grill Overview:

Removing and Installing the Front Wheel Housing Liner:

Fender:

Plenum Chamber Cover:


Does the FAA provide a CFI knowledge test guide?

Question: The FAA provides the Airman Certification Standards (ACS) for commercial pilots. It discusses the topics asked on the knowledge test. I have only been able to find the Practical Test Standards (PTS) for the Certified Flight Instructor (CFI) practical test. Does the FAA publish a similar document discussing what topics are covered on the knowledge test?
Answer: Here is a link to an FAA published document for the "Flight Instructor Airplane" sample knowledge test questions (100 questions). It's current as of August 2021.
Below is an example of the first question from the CFI-Airplane sample knowledge test with the associated "Learning Statement Code" (LSCCode: PLT195).

From the: Learning Statement Reference Guide for Airman Knowledge Testing: Clicking on this link will take you to a list of all Learning Statements and their associated area of necessary knowledge.

General: The expression 'learning statement,' as used in airman testing, refers to measurable
statements of knowledge that a student should be able to demonstrate following a defined
element of training. In order that the individual learning statements may be read as complete
sentences, they should be assumed to be preceded by the words: "Upon the successful
completion of training the student should be able to . . . . "

The LSCCode PLT195 refers to: "PLT195 Recall collision avoidance - TCAS"

Here is a link to other FAA published sample knowledge test questions for various airman certificates/ratings.
As of now, this is no ACS for the Flight Instructor practical test.


Minimizing or avoiding penalty for early withdrawl of IRA and 401k

Question: A friend of mine came to US to work for few years and he is forever going back to his original country because of personal reasons. He contributed to IRA, 401k and would like to take the money with him. However, since he has lot of years to go for 58, he is wondering whether he will incur heavy penalty and taxes from early withdrawal. Is there any way or qualified exception he can use ?
Comment: @ewr3243 yes, there are some conditions like "hardship", tuition, first home purchase, etc that allow qualified distribution.
Comment: Does it matter for taxes?
Comment: Is he leaving the US for any "bad" reason (like family issues, hardship, etc.)?
Answer:
Is there any way or qualified exception he can use ?

Not from what you've described.
One way I can think of would be using Sec. 72(t), i.e.: start drawing pension from these funds. That would make the withdrawals qualified, but would mean they're going to take a lifetime.
They might want to look into tax treaties their home country has with the US and whether a rollover across the border is a possibility (on the off-chance, I doubt it's possible).


How to attach node to user profile?

Question: How can I attach a node to a user profile with profile 2 (or some other way)? It says here that it is possible but it does not say how.
Comment: ask the same user @Nikit as comment to his answer..Probably he can guide through entire roadmap.. Have you checked this https://drupal.org/project/reply ?
Comment: I installed reply but I don't know how to work with it.no reply button anywhere.Anyway I want nodes for profile.it must be a good thing.I'm new to drupal so many things I dont't understand.Iil try askin Nikit but I don't think h will answer-the question is 1 year old. .thanks
Comment: no add comment button on that question.can someone answer here?
Answer: You could add an entity_reference field to the profile and reference the node in that field.
Answer: Please read documentation of this module. Another doc googled. Screencast.
About Profile2 module: As described in the documentation Drupal 7 allows adding fields to user account pages - what serves as simple way for building user profiles. The main differences between that and profile2 are:

With profile2 user account settings and user profiles are conceptually different things, e.g. with the "Profile pages" module enabled users get two separate menu links "My account" and "My profile".
Profile2 allows for creating multiple profile types, which may be assigned to roles via permissions (e.g. a general profile + a customer profile)
Profile2 supports private profile fields, which are only shown to the user owning the profile and to administrators.

How to attach node to user profile?


Are there any Xanathar Strategies for Skullport

Question: I played a game of Lords of Waterdeep and received The Xanathar as my lord, who in my opinion is the worst of them all.  My question is are there any viable strategies to win with the Xanathar, knowing that my opponents will avoid having minimal if any corruption tokens at the end of the game?  When playing this lord I always seem to end up in dead last, due to not having access to any bonus points.
Comment: See discussion on this here: http://boardgamegeek.com/thread/999951/the-xanathars-scoring. It appears many on the internet agree that Xanathar is too weak to be competitive.
Answer: As a general rule, you should be looking to take more actions that give you corruption than the other players. For all players, these actions give more resources than other actions in exchange for an end-game penalty. For The Xanathar, this end-game penalty is less than it is for other players. If you end the game with no corruption tokens with The Xanathar, then you haven't taken any advantage of his strategy, and you have just played the way you would have with any other Lord.
If you end the game with 10 corruption tokens, and no one else has any, then you will get -40 from the penalty, and 40 from The Xanathar's bonus. It is NOT accurate in this case to say that you got no bonus from The Xanathar. Rather, you got a 40 point bonus. The -40 that you got is theoretically offset by the extra-powerful actions and quests that you had throughout the game.
While other players will be taking those extra powerful actions and quests sometimes, they will also be spending other actions to get rid of corruption. Either way, this means that the player who ends with the most corruption should have gotten more out of their actions throughout the game than other players.
This doesn't mean that you should go crazy with taking corruption. If you have 19 corruption tiles, for -7 each, then the bonus isn't going to be enough to save you from that.
Finally, keep in mind that The Xanathar is more difficult to play than the other Lords, and it very well may be weaker in general.
Here are a few threads where this is discussed in depth:
How to win with the Xanathar
Xanathar, Halaster, Sangalor: New lord cards broken?
The Xanathar
Answer: I play on the iPad and I've been having to exclude the whole expansion, because there doesn't seem to be a way to just remove The Xanathar.
The problem is that there is really only one, very specific scenario where the bonus is of any real value: If you end the game with little or no corruption and all of your opponents also have at least that much. If everyone else has no corruption (or at least less than you), your bonus is effectively negated.
Since the strategy for this ecpansion seems to be ridding yourself of as much corruption as possible by round 8 (given that there are quite a few ways to do that), most games seem to end up where The Xanathar's bonus is basically worthless.
If there weren't ways to get rid of corruption and/or there were more ways to force your opponents to take corruption, it might be worthwhile, but as it is, it relies way too much on your opponents playing badly.
Cheers,
cScott
Comment: This doesn't make sense to me... If corruption hurts you less than it hurts any other player, then you should be ok with ending up with more corruption than the other players. If you have less corruption than the other players, then you aren't taking advantage of the fact that your corruption doesn't hurt as much.
Answer: I just played the Xanathar on the PC version and I was able to win, which is why I came to this thread because I was also looking for strategies to win as the Xanathar.  I was nervous the game because I didn't think I was playing the lord correctly.  But my plan worked out.  Basically, I tried to gather as much points as possible.  I completed quests that were in the mid level reward range (12-18 points).  I bought buildings that were popular and gave me good rewards.  I ended up with no corruption at the end, because the level was up to -9 and I would have lost points.  I feel breaking even is better than losing points.
Comment: "I tried to gather as many points as possible" - good plan!


If Éowyn did not ride into battle with The Rohirrim would the outcome have been much different? Could The Witch-King of Angmar do that much?

Question: I was re-watching the movies and kept hearing that "no man can kill the witch king". I am wondering if this is true or was it basically the Witch-King bragging. Did Éowyn sneaking into battle actually win the battle?
Comment: See [Could Gandalf have killed the Witch King?](http://scifi.stackexchange.com/q/18874/30638)
Comment: Are you asking specifically about the book, or the movie?
Comment: @Mithrandir Either or, I am curious to what he could have done or even if a man could actually kill him
Comment: In your question title, you seem to be asking two questions: Would the battle outcome be different if the Witch-King hadn't died? And: Could anyone other than Eowyn kill the Witch-King?
Comment: I'm voting to close this question as off-topic because asking "what if" questions are off-topic: http://scifi.stackexchange.com/help/dont-ask
Comment: @Mooz You can use "primarily opinion-based" for that ...
Answer: At that point in the movie, the Witch King is probably bragging, as all bad guys should do in a movie when the good guy is almost but not yet dead. It is however based on some truth. Long ago, Glorfindel had prophesied the defeat of the Witch King, who had probably heard of the prophesy in the long years since:

"He will not return to this land. Far off yet is his doom, and not by the hand of man will he fall." - The Return of the King, Appendix A (iv)

The rest of the answer is partly of my own argument: The prophesied "hand" that will bring about the Witch King's downfall is not of Eowyn, but of Merry.
After all, is it not by the hand of Merry that the dark wards protecting the Witch King were dispelled, after which pretty much anybody can kill the Witch King? Merry's blow was the crucial one - Eomer could have replaced Eowyn and the Witch King would still be dead.
That said, we can also say that it was Tom Bombadil (not a man) who gave Merry (not a man) that enchanted blade, and it was Eowyn (not a man) who brought Merry into battle and then unwittingly distracted the Witch King (a man) from noticing Merry.
Edit: I read from an answer on another question here that an analysis suggests only Eowyn - a woman - is light enough to carry Merry into battle on a horse (remember in the movie Merry couldn't get his own horse moving) because a man and Merry combined would be too heavy for a horse. In that sense, you can argue that Eowyn's sneaking into battle is necessary to bring Merry there - otherwise who else in the Rohirrim wields an enchanted blade? It's not by Eowyn's hand, but by her weight, that Merry's hand can be present in that battle at all.
Comment: Not so simple. Because without the sword of the Westernesse that Merry stabs the Witch-king with Éowyn couldn't have delivered that fatal blow. Fatal of course means he became an impotent shadow but all things considered the same result. And he almost certainly heard the prophecy because he fled and was to be chased but for Glorfindel stopping that. So actually he wasn't just bragging. He knew very well his power but he didn't expect to be stabbed by the Westernesse blade either.


What benefits does The BRICS Development Bank to its members?

Question: What benefits does The BRICS Development Bank to its members? As you may know, a new bank called "The BRICS Development Bank" was established by the BRICS as an alternative to the World Bank. Is there a reason why they did this? What benefits could the BRICS countries get from such an arrangement?
Answer: The New Development Bank (formerly known as the BRICS Development Bank) has as its mission statement to support infrastructure and sustainable development.
One way of doing this is that they are building a knowledge sharing platform. They also directly solve was they see as a 'major infrastructure-financing gap', through the selling of bonds. The increased funding to solve that infrastructure gap said by them to have lifted people out of poverty.
For why the need for the new bank, its that the world bank was seen as too western. The new development bank helps to insulate and insure against the risk of another western slump such as the Eurozone crisis. It also lets the focus be on the particular needs of the developing countries, rather than in the developed. For example, in 2016 there was the effort for 60% of funding to be in renewables, which helps with the environmental issues caused in developing countries through overuse of coal.
Answer: The BRICS bank is mainly owned and controlled by China and Russia (wikipedia). And is essentially just a way for them to put up a little capital and hopefully take advantage of and reap big future rewards from small, poor, resource-rich African nations. They also get a cute name and some "international consensus" to hide behind.
China has already issued a lot of "loans" to small African countries, all of them backed by the countries' natural resources. Expect to see a lot of big, fat Chinese mines all over Africa in a few years.
And the Africans thought the Europeans were bad...
So to directly answer your question, what the BRICS member nations are getting is a smokescreen to hide behind while they use, abuse and take huge amounts of resources from poor nations.


"You have been logged in with a temporary profile" - Windows 7 PC on Windows Server 2012

Question: I know it is one of the most frequently asked question. But I've tried all the fixes which didn't help. We have Windows 2012 Server R2 as DC and a series of Windows 7 systems connected to it. Suddenly, we have been receiving the notification "You have been logged in with a temporary profile" whenever we login to our server for only some of the users. I've tried fixing both the systems and the domain. Nothing helped. Kindly help me out.
Answer: We get this every so often and what I always do is go into the registry and rename the profile in the 'ProfileList'. I then rename the profile folder in c:\users. Let the user log back in and see if it creates a new profile. If that doesn't work, I replace the DefaultProfile folder on that system and that usually does it. Have you tried this yet? I believe the direct path to the profilelist in the registry is:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
Comment: Sorry pal! This doesn't help. I've tried it already


adjoint of a matrix with real entries?

Question: An adjoint matrix $A^*$ is equivalent to the matrix conjugate transpose $A$, but I thought conjugate can only be calculated when there's complex entries.
How do I go about calculating the conjugate of a matrix with only real entries, $$A=\begin{bmatrix} 1 & 1 \\ 1 & -1 \\ 0 & 1\end{bmatrix},$$
for example.
Comment: The conjugate of a real number is the number itself.
Comment: But even simpler, the expression for the matrix of the adjoint operator doesn't have conjugation in a real vector space.
Answer: The conjugate of a real number is just the number itself. So the adjoint of a real matrix is its transpose. For the example you give, if $$A = \begin{bmatrix}1 & 1 \\ 1 & -1 \\ 0 & 1\end{bmatrix}$$ then $$A^* = \begin{bmatrix}1 & 1 & 0\\ 1 & -1 & 1\end{bmatrix}.$$
Answer: As you know the conjugate of $ a+bi$ is $a-bi$
Thus if $b=0$ the conjugate of $a$ is $a$ itself.
Same goes for  real matrices where the conjugate is identical to the matrix itself.

adjoint of a matrix with real entries?


Price of an equity

Question: An equity has a value of 100 Euros, and pay a dividend of 5 Euros in 6 months. The interest rate  of 6 months is 5% and the interest rate for 1 year is 6%.
I would like to compute the value of the price of this equity after 1 year ?
Comment: You can compute the forward value, but not the equity value, which is a random variable.
Comment: You can also simulate.
Comment: How to compute it ?
Answer: The relationship between interest rates and equity prices being at best unstable and weak, I'll assume that the level of interest rate is irrelevant here. So the answer to your question (price of the equity in a year) is 95, everything else being equal. Of course it's unlikely that the equity will actually price at 95 in a year due to market movements, but that's a different story.
If you ask for the forward value of the equity, you need to discount that future value with the relevant interest rates.
Comment: Ah I see, How about the forward value ?
Comment: https://en.wikipedia.org/wiki/Forward_price
Answer: We consider the forward value, which can be employed to estimate the equity value.
Let $T_1=0.5$ be the dividend payment time, and $T=1$. Moreover, let $r_1=5\,\%$ be the annualized interest rate to $T_1$, $r=6\,\%$ be the interest rate to $T$, and $d=5$ be the dividend payment. Then, the forward value, under the risk-neutral measure with the deterministic interest rate assumption, is given by
\begin{align*}
F &= E(S_T)\\
&=E\big( E(S_T\mid\mathcal{F}_{T_1})\big)\\
&=E\left( e^{rT} E\left(\frac{S_T}{e^{rT}}\mid\mathcal{F}_{T_1}\right)\right)\\
&=E\left(\frac{e^{rT}}{e^{r_1T_1}} S_{T_1} \right)\\
&=E\left(\frac{e^{rT}}{e^{r_1T_1}} (S_{T_1-} -d)\right)\\
&=\frac{e^{rT}}{e^{r_1T_1}} E(S_{T_1-}) - \frac{e^{rT}}{e^{r_1T_1}}\,d\\
&=S_0\,e^{rT} - \frac{e^{rT}}{e^{r_1T_1}}\,d\\
&=101.01.
\end{align*}

Price of an equity


what are the differences between reversible cells and rechargeable cells?

Question: My chemistry textbook says daniel cells are reversible, but not rechargeable.
Why is it that all reversible cells are not rechargeable?
Are all rechargeable cells reversible? why/why not?
Comment: Good question. I think the reason is essentially degree rather than kind: rechargeable batteries are designed to be discharged and recharged many times, with minimal deterioration in performance. But non-rechargeable cells, such as the Daniell cell, can be reversed but not brought back to nearly original state.
Comment: @AbenPhilip Water contains hydrogen.
Comment: Just as Poutnik said. Also, the cell is Daniell, not daniel.
Comment: Moreover reversible has subtle meaning. Often, although not in chemistry, reversible and rechargeable are used as synonyms.
Comment: when I researched a bit more on the internet, I found it is because when Daniel cell is allowed to recharge, reduction of zinc ions to zinc does not take place in the anodic compartment, but evolution of hydrogen takes place. But where did the hydrogen come from?
Answer: Per Wikipedia on Electrolytic Cells, to quote:

Galvanic cells compared with electrolytic cells
In an electrolytic cell a current is passed through the cell by an external voltage, causing an otherwise nonspontaneous chemical reaction to proceed. In a galvanic cell the progress of a spontaneous chemical reaction causes an electric current to flow. An equilibrium electrochemical cell is at the state between an electrolytic cell and a galvanic cell. The tendency of a spontaneous reaction to push a current through the external circuit is exactly balanced by an external voltage that is called a counter electromotive force or counter e.m.f. so that no current flows. If this counter voltage is increased the cell becomes an electrolytic cell and if it is decreased the cell becomes a galvanic cell.[1]

I do also, operationally, agree with Aben Philip comments, where apparently, attempting to recharge (aka, chemically reverse) a galvanic cell, may undesirably further introduce hydrogen gas. The problematic $\ce{H2}$ gas evolution can result in bursting and the usual safety concerns working with hydrogen (as in an explosion hazard).
More technically from a electrochemistry perspective, per another source, rechargeable batteries are again distinctly claimed again to an "Electrolytic Cell", characterized as having non-spontaneous oxidation-reduction reaction versus spontaneous for a galvanic cell. But further, in addition, they may also have a semipermeable membrane governing the flow of ions, which are not found in a galvanic cell.
I hope this helps.


Setting a clipboard kind without setting "styled Clipboard text"

Question: I am developing a tool to add a HTML-ized version of a text to the clipboard. Currently, I'm using applescript to manipulate the clipboard.
Unfortunately, I realized that in addition to the entries I ask it to add, it also adds the entry styled Clipboard text. This, I believe, causes applications like Pages to fail to paste the HTML-ized version.
To see the current state of the clipboard I use (with the word "while" in the clipboard).
$ osascript -e "the clipboard as record"
«class utf8»:while, «class ut16»:while, string:while, Unicode text:while

I add the HTML variant as follows (the HTML is encoded as a hex string):
$ osascript -e "set the clipboard to ((the clipboard as record) & {«class HTML»:«data HTML3c6d65746120636861727365743d277574662d38273e3c7072653e3c7370616e207374796c653d22636f6c6f723a20236364303063643b223e7768696c653c2f7370616e3e3c2f7072653e0a»})"

After adding the HTML variant, the clipboard contains:
Unicode text:while,
string:while,
styled Clipboard text:«data styl01000000000010000E00030000000C00000000000000»,
«class utf8»:while,
«class HTML»:«data HTML3C6D65746120636861727365743D277574662D38273E3C7072653E3C7370616E207374796C653D22636F6C6F723A20236364303063643B223E7768696C653C2F7370616E3E3C2F7072653E0A»,
«class ut16»:while

Pasting this into Pages (-09) cause the plain text version of the text to be inserted.
However, when copying the same from the gmail editor in Chrome it can be pasted with highlight information into Pages. In this case the clipboard contains:
«class utf8»:while,
«class HTML»:«data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»,
«class ut16»:while,
string:while,
Unicode text:while

My conclusion is that the difference is the styled Clipboard text entry.
So, over to the real question. How can I set the HTML entry without setting the styled Clipboard text entry.
I have tried several approaches. For example, I have tried to set the clipboard to only contain a string and a HTML entry, but still the extra entry is included. I have also tried to set the styled Clipboard text entry to the empty string but that also set all the plain-text entries to the empty string as well.
I don't think the pbcopy command line tool is powerful enough to do this, as it set the clipboard to a new value.
While I'm currently using applescript to do this, I'm open to using any tool available, preferably a scriptable one (so that I don't have to ask the users to perform a compilation).
Answer: After some investigation I found that you can manipulate the Pasteboard from Python, without having it introduce the styled Clipboard text entry. I reimplemented the ruby/applescript module in Python, so now I can copy syntax highlighted text from Emacs and paste it either into dumb applications like the terminal window or applications that can handle formatted text, like Pages.
Comment: Would you be willing to share a snippet of the Python? GitHub or here or on SO? Lots of people get very stuck on multiple clipboards on macOS.
Comment: Yes, just click on the word "reimplemented" in the answer above.


What is the difference between deleting a private key and deleting an address?

Question: On Blockchain.info, when deleting private keys from your wallet, it asks if you want to delete only the private key or if you want to delete both the private key and the address. If you choose to delete the address in addition to the private key, does this mean that unless the address is generated again, it doesn't exist anymore? If not, what does it do?
Answer: An address can be generated from a private key. But you need to have the private key from the address to be able to spend it's funds.
So, when deleting the address, it will just be completely removed from your wallet. (Note that there is no such notion of "whether or not an address exists". All addresses exist, but if nobody owns a private key for the address, the balance will be unspeakable.)
When deleting the private key only, the address will still be in your wallet, but it will be watch-only. This means that you will see the address's balance in your account, but you won't be able to spend the funds unless you enter the private key again. The main reason to do this is for security. If you write the private key down on a piece of paper, f.e., you could delete the private key from your wallet so that a person that hacks into your wallet will not be able to spend the funds.
Answer: It just removes the address from your wallet, so that you are no longer watching it. Any valid address can always have Bitcoins sent to it, and anyone who knows the corresponding private key can always spend them. Wallets are only needed to make spending or watching convenient. They aren't needed for funds to actually be received -- that takes place entirely on the blockchain.


Transformers and DC voltage

Question: Ok, if I have a transformer with 100 coils of the primary and 200 coils on the secondary and I connect a 9 volt battery to the primary, how many volts should I expect from the secondary coil? I know the answer is 0V DC but I need to know why that is the answer.
Comment: How could a direct current from a battery ever transmit power to the secondary coil?
Comment: @ACuriousMind, an ideal battery produces a constant voltage, not a constant current.  To produce a changing flux, we need a changing current.  This question has merit and the correct answer probably isn't what you think it is.
Answer:
I need to know why that is the answer.

(Jump to the summary if you want to skip the details).
As you may know, a transformer is essentially two inductors that share most if not all of the magnetic flux linkage.
Recall the formula for the voltage across an isolated inductor
$$v_L(t) = L \frac{di_L}{dt}$$
Now consider two inductors, $L_1$ and $L_2$ with perfect magnetic coupling.  The voltage across each is given by:
$$v_1(t) = L_1 \frac{di_1}{dt} + M \frac{di_2}{dt}$$
$$v_2(t) = M \frac{di_1}{dt} + L_2 \frac{di_2}{dt}$$
where
$$M = \sqrt{L_1 L_2}$$
This configuration is essentially a (nearly ideal) transformer.  Let $L_1$ by the primary and $L_2$ be the secondary.
Assume the primary has a constant voltage $V_1$ applied at $t=0$ and the secondary is open (which means that the secondary current is zero).
According to the above, the current in the primary changes at the rate of $\frac{V_1}{L_1}$ amps per second thus the voltage across the secondary is
$$v_2 =  M \frac{di_1}{dt} = \sqrt{L_1 L_2}\frac{V_1}{L_1} = V_1 \sqrt{\frac{L_2}{L_1}}$$
The voltage across the secondary is non-zero and constant!  At least according to this model it is.
What's missing in this analysis?  We haven't taken into account the non-zero resistance of the windings.
Initially, the analysis above holds but, as the primary current increases, the resistance of the primary winding becomes a significant factor.  Instead of a steadily changing current, the primary current is of the form
$$i_1(t) = \frac{V_1}{R_1}\left(1 - e^{-\frac{tR_1}{L_1}} \right)\cdot u(t)$$
where $R_1$ is the resistance of the primary winding and $u(t)$ is the unit step function.
When the voltage is connected to the primary, the primary current initially changes at the maximum rate but rather quickly approaches a constant value.  But the secondary voltage is proportional to the how quickly the primary current changes.
Thus, the voltage across the secondary is
$$v_2(t) = V_1\sqrt{\frac{L_2}{L_1}}e^{-\frac{tR_1}{L_1}}\cdot u(t)$$
In other words, at the instant the voltage is connected to the primary, the secondary voltage jumps to its peak value and decays exponentially to almost zero by time $t = 5\frac{L_1}{R_1}$ seconds.
To summarize, the reason that the secondary voltage is not constant and decays quickly to zero is that the primary current rapidly approaches a constant determined by the applied voltage and the primary winding resistance.
Comment: Good if slightly lengthy explanation. In short - for a real transformer when you apply a step (DC) voltage at the primary you will see a brief step at the secondary which will decay with the time constant given. In the steady state there is constant current in the primary - no change of flux and no induced emf.
Comment: @Floris, in short, that's correct.
Answer: The transformer operation is based on Faraday's Law
$$
\nabla\times\mathbf{E} = -\dfrac{\partial\mathbf{B}}{\partial t}
$$
This law relates the generated electric field (resulting in electromotive force in a circuit) with the variation of the magnetic flux density.
Also indicates that a changing electric field generates a density also varying magnetic flux.
Therefore, if a battery to the primary of a transformer is connected, not a variable flux density occurs, and therefore no energy transfer to the secondary winding. This concludes that no voltage is observed in the secondary.
To be more exact, in moments of connection and disconnection of the battery, you can register a voltage in the secondary, but this is only temporary.
Comment: Assuming that the primary voltage is constant does not imply that the magnetic flux density is constant.  I've addressed what's missing in my answer.
Answer: I'm going to write a really simple answer...
A short summary of what goes on in a step-up transformer:

In an AC source, both the magnitude and direction of current changes
As the primary windings of the transformer is connected to an AC source, there will be a change in magnetic flux (remember: the magnetic field strength around the coil is dependant on the current though the coil- change in current causes change in magnetic field strength and thus a change in magnetic flux)
Thus there is a varying magnetic flux in the iron core which in turn causes a varying magnetic flux in the secondary coil
According to Farady's law, as there is a change in magnetic flux through the secondary winding, there will be an emf induced. (You may think of the coil "cutting" magnetic field lines if that makes it easier to understand)

Now if you think about, its really because of the AC source in the first place that caused the varying magnetic flux which eventually caused the emf to be induced in the secondary coil.
Look at this diagram: (focus on the red graphs)

The first graph shows a DC source. As you can see, the current is unchanged. As magnetic flux density and thus magnetic flux of the coil is dependent on current, no change in current means no varying magnetic field. No change in magnetic flux through the secondary coil means no emf is induced.
In the second graph, a changing current causes a change in magnetic flux and the process continues as stated above.
(I took the image from here)
Answer: In order for an emf to be induced in the secondary coil, the flux through it must be changing; therefore, the current in the primary coil must also be changing. If a constant voltage is supplied to the primary coil, no emf would be induced in the secondary, and therefore, the secondary voltage would be zero.

Transformers and DC voltage


How do I change the RAILS_ENV for rspec integration or remote specs?

Question: I would like to create a set of remote specs "specs/remote" that run with the RAILS_ENV = 'remote'.  These specs need to use a different database than the model specs.  I would make them integration specs if that was easiest.
Ultimately, what is the easiest way change the RAILS_ENV from test and run a group of specs?
Answer:
Create remote.rb in
config/environments
Tell rspec to use your custom
environment by setting export
RAILS_ENV=remote at the shell
prompt.
Add the remote environment to your
config/database.yml with the
appropriate settings for your
alternate database.

Don't forget you can use YAML to include one environments configuration within another:
base: &base
  adapter: mysql

development:
  database: dev_database
  <<: *base

test:
  database: test_databae
  <<: *base

remote:
  database: remote_databae
  <<: *test

etc.


How do processes know the addresses of shared library?

Question: As far as my understanding goes, when I compile my C source code, GCC/LD does the address binding at compile time. Typically, this address starts at zero. When I call a function from shared library, how does the compiler know the address of the shared library in advance? I know shared libraries get their address at load time. Please correct me if I am wrong.
Comment: It doesn't, that's why it's called dynamic linking.
Comment: Searching for "dynamic linking" (which you already appear to know since you selected that tag) yields loads of information already. What specific questions do you have? (Covering the whole process is quite a task.)
Comment: suppose I called the printf() function. How the compiler will know the memory location of printf() function at compile time?
Answer: You can do a few things to help yourself understand this.
ldd /usr/bin/cat
On my laptop, that gives this output:
1771 % ldd /usr/bin/cat
        linux-vdso.so.1 (0x00007ffc37fba000)
        libc.so.6 => /usr/lib/libc.so.6 (0x00007f1ea7018000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f1ea73bc000)

You'll notice that linux-vdso.so.1 and libc.so.6 don't have a fully qualified path, and that ldd shows you what the actual path that would be used to dynamically link in libc.so.6 is.
You can check that (and learn a bit) by doing the ldd again, with a little variation:
1790 % export LD_LIBRARY_PATH=/lib
1791 % ldd /usr/bin/cat
        linux-vdso.so.1 (0x00007fff0a5a0000)
        libc.so.6 => /lib/libc.so.6 (0x00007fa257535000)
        /lib64/ld-linux-x86-64.so.2 (0x00007fa2578d9000)

Looking closely, you can see that the dynamic linker (/lib64/ld-linux-x86-64.so.2 in this case) will now choose /lib/libc.so.6 as the C library. So the enironment variable LD_LIBRARY_PATH is important to deciding which files actually get used in dynamic linking.
The other thing you can do is strace:
strace -o cat.trace /usr/bin/cat /etc/motd

The file cat.trace will have a record of what system calls your subject process performs. Some of them will be mmap() of the files shown by ldd as getting dynamically linked in. Follow up by googlling for mmap.
Further reading: man ld.so.
See if you have the readelf command installed, or if you can install it, or compile it. Run readelf -a /usr/bin/cat. The actual ELF specification is impenetrable in my opinion, but there is some good ELF format information out there. Try to find it.
If you have the musl libc installed, or can install it, doing the same experiments as above on a simple executable compiled with musl libc can be very informative. Even something as complex as dynamic linking can have two different, working implementations on the same operating system.
Comment: Additionally, today's `Linux`systems support [ASLR](https://en.wikipedia.org/wiki/Address_space_layout_randomization)


Time zones and country ISO codes

Question: I am looking for a simple CSV with the list of country names, country ISO codes, city, time zone UTC and DST... It seems simple, but I am struggling to find it. Any advice/help would be very much appreciated.
Comment: Many countries have more than one time zone (Russia has 11) – how would you want the data to handle this? You could use a single time zone for the national capital, or have multiple rows for each country, but this complexity might be one reason you're struggling to find all the information in a single dataset.
Comment: Thanks @MattAshby for your comment... You are right indeed. Actually my request concerns any type of structured data related to time zones. I will update my question to reflect that: country code and city.
Answer: There is IANA tzdb with a list of all timezones. It's quite complex and changing since timezones change too, for example in Russia timezones changed several times during the last 20 years.
Answer: geonames offers this both through their API and bulk dumps.

Time zones and country ISO codes


What's the name of this plug?

Question: This is the plug on the MH-Z19B Carbon Dioxide Monitor Sensor. What is this plug called? We need to find a breakout board for it (header?), a connector we can plug that into that have pins that are further apart that can fit in a breadboard. Is this just a standard JST 7 pin connector? There seem to be different versions of this, where the distance (pitch?) of the pins are further apart and also the size of the pins? How do we make sure we get the right thing? How do we figure out the pitch?
Comment: The pitch is 1.25mm according to the [manual](https://www.winsen-sensor.com/d/files/mh-z19c-pins%26terminal-type-co2-manual(ver1_2).pdf).
Comment: Have you tried measuring the pitch?
Comment: I have asked the manufacturer for you. If they respond with adequate detail, I will provide the information in the form of an answer. Given the time zones, it will be at least 10 or 12 hours.
Comment: Looks like a JST XH or EH or one of those. They're hard to tell apart without dimensions.
Comment: it's a 7 pin jst connector of some sort. You can probably also use dupont connectors if there's no mechanical stress or movement on the connection.
Comment: also, if you have the cable, you can just chop it and terminate it however you need to. It looks like 5/7 pins are broken out on the unit's PCB's plated through-hole annular rings behind the connectors, trace them with a DMM in beeper mode.
Comment: You can buy a few sizes and return the ones that don't fit if you're in a hurry and have to order online. you didn't get that idea from me...
Answer: My Identiconn identifies the header as an Amphenol MINITEK®1.25 P/N 101148.

This picture (from Digikey) is for the 5-pin version. I couldn't find a picture for the 7-pin version. Note the square openings at the bottom: they match yours.
The plug, Amphenol 10114826-00007LF, also matches your picture.

{Digikey}
Note the square holes in the plug: that plug is for square pins, not for blades. Hence, your connector is not a Molex Picoblade.
Answer: Page 4 of the manual shows 0.1" pin headers soldered directly onto tabs on both ends of the module.  Unfortunately, the two rows are not on exact 0.1" centers; they are 1.16" apart.  If you angle both rows, the module should plug into a standard protoboard without cables.
If the pins on standard 0.1" headers are too stiff, then use a standard header on one end and five pieces of #20 or #22 wire on the other.  These should bend easily in a short zig-zag to align with protoboard holes.

What's the name of this plug?


Multisim 14.2 issue

Question: Using Multisim 14.2 to simulate a capacitor's charge cycle , I've noted that when the simulation starts for the first time, even if the SPST switch is OFF, the capacitor starts fully charged. Any idea?
Comment: In simulators this may be called "ic" or initial condition.  Some allow you to set this as a part parameter, such as 220uF and ic=0.  I am not familiar with MC but perhaps it is similar.
Comment: In LTspice, S1 might toggle between two resistor values: one very large value, simulating the "open" condition, the other a very small value simulating the "closed" condition. In both cases, the initial steady-state voltage of C1 would by +12V due to that resistive path through the switch. Perhaps Multisim simulates switches similarly?
Answer: Most (if not all) simulators "try and help out" by calculating all the steady-state DC conditions first then, the simulation is run so, your capacitor has already been forced into the steady-state situation.
In micro-cap there is a tick-box called "operating-point" and if I uncheck it, the simulation begins right from the very start without calculating steady-state DC conditions.
The same will be true of multisim but, I can't help you find that "checkbox" because, I don't use multisim.
Comment: If you have no more questions @M4Biz .....[What should I do when someone answers my question?](https://electronics.stackexchange.com/help/someone-answers)
Answer: we assign our parameters to the switch model (these are the limits for Multisim)

The program supports values 1e308 1e324 1e-308 1e-324 In each specific case, you need to slip them in, and the program itself will sort out what it cannot do

Multisim 14.2 issue


Game development equivalent of Movie Director

Question: Is there a job in game development that is equivalent to being a movie director?
Comment: I'm voting to close this question as off-topic because it depends on the studio; there's no right or wrong answer to this.
Answer: As Almo says, roles within game development vary quite widely from studio to studio, or sometimes even between projects for a single team. But there are common patterns.
I think the closest equivalent here would be termed a Creative Director:

The creative director is responsible for the overall vision of the
  product: game play, visual style, story, audio assets, cinematics, and
  marketing materials. This person is often the creator of the game
  concept, and may serve as the primary designer. He or she works under
  the supervision of the producer and is tasked with managing the teams
  of artists, designers, and programmers, interacting directly with
  senior supervisors of each department.


limit of $x \cot x$ as $x\to 0$.

Question: I was asked to calculate $$\lim_{x \to 0}x\cot x  $$
 I did it as following (using L'Hôpital's rule):
$$\lim_{x\to 0} x\cot x = \lim_{x\to 0} \frac{x \cos x}{\sin x} $$ We can now use L'Hospital's rule since the limit has indeterminate form $\frac{0}{0}$. Hence $$\begin{align}\lim_{x\to 0}\frac{(x \cos x)'}{(\sin x)'}   &= \lim_{x\to 0}\frac{-x\sin x + \cos x}{\cos x} \\ &= \lim_{x\to 0}\frac{-x\sin x}{\cos x} + 1 \\[4pt ]&= \lim_{x\to 0} - x \tan x + 1 \\[4pt] &= 1 \end{align}$$
I think that the result is correct but are the arguments correct?
Answer: HINT: rewrite your term in the form
$$\frac{\cos(x)}{\frac{\sin(x)}{x}}$$
Answer: Welcome to MSE! As best as I can tell your reasoning is sound, although as other users pointed out you could have done this in a few less steps. Regardless, your work is clear and your answer is correct. On an aside I am happy to see that you formatted your question with $\LaTeX$. I added some additional formatting to clean things up a bit, but overall nicely done.
Answer: Notice,$$\lim_{x\to 0}xcotx  $$  $$=\lim_{x\to 0}\left(\frac{x}{\tan x}\right)=1 $$  Or using L-Hospital's rule for $\frac{0}{0}$ form as follows $$\lim_{x\to 0}\left(\frac{x}{\tan x}\right)=\lim_{x\to 0}\frac{\frac{d(x)}{dx}}{\frac{d}{dx}(\tan x)}$$ $$=\lim_{x\to 0}\frac{1}{\sec^2x}=\frac{1}{\sec^2(0)}=\frac{1}{1}=1$$
Answer: You could have stopped at
$$
\lim_{x\to0}\frac{\cos(x)-x\sin(x)}{\cos(x)}=\frac11
$$
but otherwise, your answer is fine.

Moved from a Comment
If you can use
$$
\lim_{x\to0}\frac{\sin(x)}x=1
$$
it would simplify the computation as well.

limit of $x \cot x$ as $x\to 0$.


Reference request: Gauge natural bundles, and calculus of variation via the equivariant bundle approach

Question: Let $P\rightarrow M$ be a principal fibre bundle with structure group $G$, $F$ a manifold and $\alpha: G\times F\rightarrow F$ a smooth left action.
There is an associated fibre bundle $E\rightarrow M$ with $E=P\times_\alpha F=(P\times F)/G$.
As it is well known, one may either treat sections of the associated fibre bundle "directly", or consider maps $\psi:P\rightarrow F$ which satisfy the equivariance property $\psi(pg)=g^{-1}\cdot\psi(p)$, where $\cdot$ denotes the left action. Let us refer to this latter method as the "equivariant bundle approach".
I am interested in describing the gauge field theories of physics using global language with appropriate rigour. However, most references I know treat this topic using the "direct approach", and not with the equivariant approach, the chief exception being Gauge Theory and Variational Principles by David Bleecker.
Bleecker's book however doesn't go far enough for my present needs.

Bleecker only uses linear matter fields, eg. the case where $F$ is a vector space and $\alpha$ is a linear representation. Some things are easy to generalize, others appear to be highly nontrivial to me.
Bleecker treats only first-order Lagrangians. The connection between a higher-order variational calculus based on the equivariant bundle approach and between the more "standard" one built on the jet manifolds $J^k(E)$ of the associated bundle is highly unclear to me. Example: If $\bar\psi:M\rightarrow E$ is a section of an associated bundle, its $k$-th order behaviour is represented by the jet prolongation $j^k\bar\psi:M\rightarrow J^k(E)$, but if instead I use the equivariant map $\psi:P\rightarrow F$, what represents its $k$-th order behaviour? I assume it is related to something like $J^k(P\times F)/G$, but the specifics are unclear to me.
In Bleecker's approach, connections are $\mathfrak g$-valued, $\text{Ad}$-equivariant 1-forms on $P$, however I am interested in treating them on the same footing as matter fields. Connections however are higher order associated objects in the sense that they are associated to $J^1P$. Bleecker absolutely doesn't treat higher order principal bundles.

In short, I am interested in references that consider gauge theories, gauge natural bundles, including nonlinear and higher-order associated bundles and calculus of variations/Lagrangian field theory from the point of view where fields are fixed space-valued objects defined on the principal bundle (equivariant bundle approach), rather than using associated bundles directly.
Answer: NATURAL AND GAUGE NATURAL FORMALISM FOR CLASSICAL FIELD THEORIES A Geometric Perspective including Spinors and Gauge Theories
https://b-ok.cc/s/?q=NATURAL+AND+GAUGE+NATURAL+FORMALISM+FOR+CLASSICAL+FIELD+THEORIES+A+Geometric+Perspective+including+Spinors+and+Gauge+Theories


How can I tell what my military camera was used for?

Question: I have an original U.S. WWII Army Air Force Graflex k-20 Aircraft camera. Is there any way to tell what missions my camera was used on?
I do have the serial number for it.
Comment: @benrudgers while that statement is in itself true, the military usually tracks all equipment for the purpose of proper maintenance cycles and mission readiness. This camera was also used in surveillance during world war 2 so it very well may have held great importance in terms of life and death during the smear.
Comment: My guess is that such fine grained information is not available because nobody really cared enough to write it down because it didn't really matter relative to life and death at the scale of the war.
Comment: One starting point would be locating a resource that identifies units to  which Graflex k-20 cameras were assigned since this is necessary to search for camera maintenance logs. The next step would be finding those units lists of missions. Lastly, a resource identifying the particular cameras used on those missions is needed. I'd describe the first step as likely to be substantially challenging.
Comment: Apart from the serial are there any other stamps etc made into the camera? (I can't really speak for the US stuff but WWII British gear is filled with after manufacturer stamps which can be useful to identify stuff such as which regiment it was assigned to, constructiondates etc, it can help narrow it down where it may have been!)
Comment: @CrazyDino there is a contract number on the camera stamped next to the serial number. Additionally there is a sticker from the Department of he Interior, Fish and Wildlife service. Serial number : USN 42-2427. Contract: NXs - 7310
Answer: The K-20 was near ubiquitous among U.S. Army Air Force units that did any kind of photographic reconnaissance. You'd literally be looking for a needle in a haystack.
It's highly unlikely you could use the serial number to trace the camera from the manufacturer to a unit that might have used it. It's more likely that you might find the serial number in maintenance logs or inventory records of any specific unit that used the camera. Your biggest problem is the sheer number of units who used the K-20 and the geographic distance between various locations of any records that may have survived.
If a unit used your particular K-20 in action during WWII and if the maintenance or inventory records from that particular unit are still in existence then probably the only way for you to find it would be to manually examine such records of such units line by line looking for your particular serial number. It's highly doubtful that any such records regarding recce cameras have been digitized, and certainly the case that all of them collectively have not survived, much less been digitized. You'd have to use some old fashioned pre-information age shoe leather to do your search.
Folmer Graflex Corporation only made the K-20 under license from Fairchild, who designed the K-20, between the years of 1941-45. If your K-20 is one of the 15,000 or so K-20 cameras branded as a Graflex it certainly was made during the war years. As was the case with much of the wartime industrial production of the U.S. near the end of the war, it is possible your example was produced too late and never left the U.S. before the war ended. Although a totally different category, most of the surviving WWII "warbirds" in the U.S. were examples that were manufactured near the end of the war and never left the U.S. before the treaties were signed. Some were used by training units here in the U.S. at the end of the war and in the following years before they were replaced by newer technology.
Fairchild, who was a major defense contractor that specialized in imaging devices that worked with visible light, radar, and x-ray, continued to sell the K-20 after the war, but they no longer licensed other companies to do so after the cessation of hostilities.
Comment: I did find some graflex mentions in the national archives (and even an assignment for Ansel Adams!) - it seems that the Forest Service utilized a lot of these. You're right though - most of the records are references and will need to be looked at physically as they haven't been scanned.
Comment: On a brighter side - there was a K-20 on board of Ebola Gay taking photos of mushroom clouds. Likely not your K-20, but the same model. That is some connection to history, isn't it?
Comment: @osullic But it is, *literally*, a common figure of speech. :-)
Comment: A lot of other federal agencies that did survey photography wound up with surplus K-20 (and other aerial type) cameras after the war.
Comment: @Corey Those newsreels of returning GI's pushing aircraft and ground vehicles overboard into the sea may have implications regarding attitudes toward boxes of routine paperwork at the end of the war.
Comment: On a semantic point of order, if you were _literally_ looking for a needle in a haystack, then you would be looking for an actual needle in an actual haystack ;) This might be the epitome of the proverbial needle in a haystack. But it's not a literal needle in a haystack.


Debian Squeeze and RAID firmware after kernel update

Question: I've installed Debian Squeeze on my server several days ago. During install process installer asked me to provide USB flash drive with firmware aic94xx-seq.fw (file disappeared likely due to licensing, you can find it on adaptec site: http://www.adaptec.com/en-us/speed/scsi/linux/aic94xx-seq-30-1_tar_gz.htm). All went fine. Today I installed all updates to my system with "U" in aptitude. Aptitude installed kernel update 2.6.32-5 and created initrd accordingly. But now I can't boot up my system because it can't find LVM volumes on harddrive connected to Adaptec RAID card.
How can I boot my system now? I have USB with firmware. I have netboot CD.
Unfortunately when I tried to edit boot records in grub I found that there is no my old kernel anymore. The only kernel grub sees is the new vmlinuz kernel and new initrd
How take make my server alive?
Answer: Getting to where you need to get to fix this is going to be tough.  If the livecd has the adaptec driver you need, if you can keep it from loading the driver until after you mount the USB stick and copy the file to /lib/firmware/ a reasonably good livecd should be able to load the firmware automatically.  If you can't get it to load the firmware automatically, you'll need to do it by hand according to the instructions at the bottom of this page, which would involve probably something like
echo 1 > /sys/class/firmware/something/loading
cat /some/usb/folder/aicwhatever.fw > /sys/class/firmware/something/data
echo 0 > /sys/class/firmware/something/loading

(You have 10 seconds from when the driver loads to do this, or else the driver fails to load.)
That should get the raid controller to work in the livecd.  From there, you'll have to mount your drives and recreate your kernel's initrd/initramfs.  This page has instructions on doing this for Squeeze's netinstall CD image, theoretically the process should be the same for an installed system.  Based on the comments at the end of the firmware section of the install guide, you need to install a package of the firmware in order to keep the version up-to-date, if you don't then you're responsible for keeping a version of the firmware that matches the kernel version.
Comment: Just for the record, the firmware file as linked in the question has disappeared and can be found here: http://www.adaptec.com/en-us/speed/scsi/linux/aic94xx-seq-30-1_tar_gz.htm and that link I found on http://rpmfind.net/linux/RPM/centos/6.2/x86_64/Packages/aic94xx-firmware-30-2.el6.noarch.html
Comment: OK. What I've done so far to overcome this issue is I've swapped my boot disk on RAID (it was JBODed) and connected it to motherboard dirrectly. Other two drives which have been using all of my two SATA ports were moved to RAID array (again JBOD). Then I tried to boot and realised that bootloader was on one of the drives migrated to RAID card. That was no a big issue and I booted to Debian NetInstall in resque option (which even asked me to provide firmware driver so it was an option) and chrooted to my real root on LVB. install-grub /dev/sda fixed all. So DerfK was rigth.
Answer: Did you try to re-create initrd with drivers provided with your controller? In theory it should be done automatically during kernel upgrade but sometimes it does not work with custom drivers.
Comment: You can boot from LiveCD, mount your file system, re-create initrd on it and then try to boot. I do not remember exact commands since I do not do it often, but you should be able just google it.
Comment: First I can't boot my server. Second if i'll got livecd then how can I point booted livecd to load firmware and discover my LVM to chroot into?
Answer: If you need to boot from the raid controller, you will need to re-generate the initramfs (using update-initramfs) with the firmware-file copied in /lib/firmware.
Then you can boot using this initramfs, and you should have the firmware available.
You should use the -b option on update-initramfs, or mount the root fs (and dev/proc/sys) and chroot in the root fs. Otherwise it will update the initramfs from the bootable cd..
Comment: OK. First of all I need to mount my LVM root somehow. How? Secondly what happened with debian when it updated my kernel, regenerated initramfs (for sure) and not included firmware to it when previous kernel was working just fine? And the most interesting: why can't I find my old kernel and initramfs in /boot? There is just one kernel and one initramfs: http://img854.imageshack.us/img854/1819/25734134.png
Answer: You'll need to boot into Rescue Mode, modify your /etc/fstab to comment out the offending filesystems, then boot normally and rebuild your initrd.
Comment: If I would have been able to boot to resque why don't I have been able to boot to normal mode? No, haven't been able to boot even to resque. /etc/fstab is on filesystem on RAID which my kernel doesn't know how to work with
Answer: Maybe you are missing the lvm2 modules? Try this:

Boot rescue
Add lvm2 packages to rescue (I can't remember if rescue does it automatically, probably yes but check it)
Use the lvm2 commands and modules to be able to see your partition

Use pvscan, vgscan and lvscan to find the lvm chain and mount it. From there you can use chroot to change to your production system and use the initramfs tools to regenerate it. Be sure to include all modules, just for sure. Quick tip: after chrooting to the correct partition, use su - to apply environment variables to the chrooted environment, makes the work easier.
Comment: No. LVM modules are presend. The only problem is firmware and I know it 101%


Do fast copy programs work?

Question: Do any of the programs that purport to copy files faster than the built-in Windows Explorer file copying, really do what they claim to do?  I am thinking of using ExtremeCopy and am wondering if it will really make a difference to my copying times.
Comment: You might want to look into [TeraCopy](http://www.codesector.com/teracopy.php) - it's fast, supports queued copying (which should be your primary motivation for replacing the Explorer Shell's copying mechanism), and **does have a free version**.
Answer: Hands down the BEST large file copying utility in Windows is ESEUtil. Use the /Y switch. More info on the Technet blog here: http://blogs.technet.com/b/askperf/archive/2007/05/08/slow-large-file-copy-issues.aspx
Here are a few of the faster-than-Explorer copying methods to try (command-line based unless noted), somewhat in order of speed from slower to faster

Copy (Comes with Windows)
XCopy (Comes with Windows)
Robocopy ( http://www.microsoft.com/downloads/en/details.aspx?FamilyID=9d467a69-57ff-4ae7-96ee-b18c4790cffd&displaylang=en )
FastCopy (GUI, http://ipmsg.org/tools/fastcopy.html.en )
TeraCopy (GUI, http://www.codesector.com/teracopy.php )
EMCopy (Comes with EMC tools)
ESEUtil (Comes with Exchange).
Comment: Now if anyone has any tools that make copying ~3,000,000 10k files a bit faster, I'm all ears; All of the above are equally suck for millions of tiny files as far as I can tell.
Comment: There's also `XXCOPY`, which has tons of switches, and `RichCopy`, from Microsoft, which can copy using simultaneous threads.  It's GUI and command line based.  You can use the GUI to get the multitude of switches you may want to use and copy it from one of the windows.
Comment: If you've got a 64bit computer and windows 7 you can run robocopy 64bit which is multithreaded and apparently insanely fast.
Answer: I don't know about that one but one that does indeed work faster depending on what you are copying and has stop/resume support is TeraCopy:

TeraCopy is designed to copy and move files at the maximum possible
  speed. It skips bad files during the copying process, and then
  displays them at the end of the transfer so that you can see which
  ones need attention. TeraCopy can automatically check the copied files
  for errors by calculating their CRC checksum values. It also provides
  a lot more information about the files being copied than its Windows
  counterpart. TeraCopy integrates with Windows Explorer's right-click
  menu and can be set as the default copy handler.
Answer: There's a handful of tools that claim to copy faster than built in windows copy - i was about to name teracopy , but in this case, i'll take richcopy as an example.
Threading is one way to speed up file copies - in short rather than transferring files one by one, you can transfer multiple files at once.
The other is the option to not transfer files that are identical.
I also believe the method of buffering files, pre copy makes a difference in copy speed.
So, since microsoft themselves make a better copying tool than standard windows copy and xcopy, it is possible. I can't comment on the specific example tho
Comment: Threading does not help unless you are copying multiple source files spread out over multiple physical drives to multiple destinations that are also on different drives.  If all of the source files are on the same drive, then trying to read and write multiple things at the same time slows it down since the drive has to constantly seek back and forth.
Comment: RichCopy was discontinued in 2009, and it was waaaaay old before that. https://en.wikipedia.org/wiki/RichCopy
Comment: This answer reminds me of a recent spam title, *GS Richcopy 360*. Not sure if it's a coincidence, though.
Comment: co-incidence. The real richcopy is a MS application and kind of a good example of what I was trying to talk about... 6 years ago.
Answer: I'd suggest using robocopy with /MT:16 option (multithreading). It will help a lot with copying a large amount of small files, but won't help much with big files.
It's built into Windows by default, but it requires command line knowledge and has a lot of switches - that seems to deter most users.
If you want to use robocopy in a simple manner and you want it to behave like normal copy, you can check out my RCWM project - I've built robocopy into right-click menu to speed up my workflow. Hopefully this set of tools can help other people as well.

Do fast copy programs work?


Intentional RF emitter failing unintentional emission test?

Question: Suppose a commercial product uses a FCC pre-certified WiFi module. If the quality is not consistent throughout the batch, I'd guess some pre-certified modules may produce unacceptable emissions. In that case, could these emissions fail the unintentional emission test for the final product? Or is it that pre-certified modules are somehow isolated during the test such that the emissions produced by the pre-certified modules will not affect the unintentional emission test outcomes?
Comment: There are a lot of "Ifs", "guesses" and "coulds" in your question - individual modules may well be certified **but** by creating a new product you also create new opportunities for unwanted emissions (e.g. power lines/tracks acting as aerials). The only way to **know** is to test the final product.
Answer: Well possible that an unit that has approved building blocks fails as one new system. The cumulated total emission can be too much due a simple summing or due increased individual emissions caused by new interactions. Do not rely only on "all my parts already have the certificate".
Do not believe? What interactions????
Think about a radio device and a too high voltage power supply for it. The higher voltage can easily raise the spurious outputs too high or the output at the legitimate frequency can have too high power.


Does a planar triangulation always contain a Hamiltonian path?

Question: What about a Hamiltonian path in a triangulation of an n-gon? If not, how long is the longest path?
Answer: There are two planar triangulations on 14 vertices without hamiltonian paths. This is the smallest size. For sure these are well-known.

Those answer the question for $n=3$. For $n=4$ the first examples appear at 12 vertices. Same for $n=5$. For $n=6$ one with 10 vertices. For $n=7$ one with 11 vertices.  And so forth.
Answer: It is a famous theorem of
Whitney (1931*) that
a $4$-connected planar triangulation has a Hamiltonian cycle.

Example of non-Hamiltonian triangulation from Joseph Malkevitch,

obviously not $4$-connected: removing $3$ vertices (surrounding one) disconnects.

(A graph is $4$-connected if it requires removal of $4$ vertices to disconnect it.)

*
  H Whitney.
  A theorem on graphs.
  Ann. of Math., 32 (1931), pp. 378–390.

In response to the OP's query:

A connected triangulated graph with no Hamiltonian path.

Perhaps the OP may be interested in this paper:

Arkin, Esther M., Martin Held, Joseph SB Mitchell, and Steven S. Skiena. "Hamiltonian triangulations for fast rendering." The Visual Computer. 12, No. 9 (1996): 429-444.

  (Springer link.)
Comment: I should clarify that by a planar triangulation I mean this: http://mathworld.wolfram.com/TriangulatedGraph.html The second example is not a planar triangulation.
Comment: Thank you for the reference! But what about Hamiltonian path?
Comment: The answer is still *No*, but now you need a maximal planar triangulated graph with at least $8$ "separating triangles." This is easily constructed, and it has no Hamiltonian path.
Answer: See the answer to this question. The magic word is "Kleetope". For more information than you imagined possible, see Guido Helden's Thesis.


How to create new Date in Groovy at specific date and time

Question: I wonder if there is other way how to create new Date in Groovy at specific date and time than parse it from String with Date.parse method. Can I get complete list of Date creation in Groovy?
Answer: You can use the existing Java methods to create a date:
// takes the date encoded as milliseconds since midnight, January 1, 1970 UTC
def mydate = new Date(System.currentTimeMillis())

// create from an existing Calendar object
def mydate = new GregorianCalendar(2014, Calendar.APRIL, 3, 1, 23, 45).time

Groovy also provides some streamlined extensions for creating Dates.  Date.parse() and Date.parseToStringDate() parse it from a String. The Date.copyWith() method builds a date from a map.  You can use them like this:
// uses the format strings from Java's SimpleDateFormat
def mydate = Date.parse("yyyy-MM-dd hh:mm:ss", "2014-04-03 1:23:45")

// uses a format equivalent to EEE MMM dd HH:mm:ss zzz yyyy
def mydate = Date.parseToStringDate("Thu Apr 03 01:23:45 UTC 2014")

def mydate = new Date().copyWith(
    year: 2014,
    month: Calendar.APRIL,
    dayOfMonth: 3,
    hourOfDay: 1,
    minute: 23,
    second: 45)

Comment: Here is the other way. [`set()`](http://groovy.codehaus.org/groovy-jdk/java/util/Date.html#set(java.util.Map)). `def mydate = new Date();
mydate.set(year: 2014, month: Calendar.APRIL, dayOfMonth: 3, hourOfDay: 1, minute: 23, second: 45)` @michal.kreuzman
Comment: Good point @dmahapatro.  That one has the advantage of not creating an extra Date object.  Too bad it doesn't return the Date object so it can't be used as an initializer.
Comment: Wow nice one and the most readable one I've seen so far. If you could complete other possible ways of creating `Date` I will definitely accept your answer.
Comment: Agree. That is why did not add as an update to your answer. ;) `copyWith()` was a better fit compared to `set()`.
Comment: Deprecated, check Basil Bourque answer
Answer: The other answers are outdated as of Java 8 and later. The old legacy date-time classes such as java.util.Date/.Calendar/.GregorianCalendar have proven to be poorly designed, confusing, and troublesome.
java.time
The java.time framework supplants those old classes.
Groovy can use these classes of course. I do not know the Groovy syntax, but it should be easy to adapt this simple Java example.
LocalDate/LocalTime
The LocalDate and LocalTime classes have no concept of time zone. So they do not represent actual moments on the timeline.
LocalDate localDate = LocalDate( 2016 , Month.JANUARY , 2 ); // year, month, date.
LocalTime localTime = LocalTime( 12 , 30 , 0 , 0 ); // hour, minute, second, nanosecond.

ZonedDateTime
Apply a time zone (ZoneId) to get a ZonedDateTime. Use a proper time zone name, never the 3-4 zone abbreviations commonly seen.
ZoneId zoneId = ZoneId.of( "America/Montreal" );
ZonedDateTime zdt = ZonedDateTime.of( localDate , localTime , zoneId );

Instant
You should avoid the old date-time classes. But if required, you can convert. An Instant is the java.time class to represent a moment on the timeline in UTC with a resolution of nanoseconds. Look for new methods on the old java.util.Date class for converting to/from an Instant. We can extract the needed Instant object from our ZonedDateTime.
Nanosecond vs Millisecond
Note that converting from java.time involves data loss! The java.time classes support nanosecond resolution (up to 9 digits of decimal place on fractional second) while the old java.util.Date supports only milliseconds (up to 3 decimal places). Any 4th to 9th digit of fractional second is truncated. For example, 2016-04-28T02:05:05.123456789 is truncated to 2016-04-28T02:05:05.123.
Instant instant = zdt.toInstant();
java.util.Date utilDate = java.util.Date.from( instant );

Going the other direction, from java.util.Date to Instant. The 4th to 9th decimal place of fractional second will be zeros, the 1st-3rd for any milliseconds.
Instant instant = utilDate.toInstant();

Answer: Groovy is good.
new Date(2016-1900, 7, 16, 20, 32, 25)

Tue Aug 16 20:32:25 PDT 2016
Note that the year must be massaged, but you can create a new Java Date representing any second you want.
You can see more Groovy Goodness at http://mrhaki.blogspot.com/2009/08/groovy-goodness-working-with-dates.html
Answer: As far as I know there's no other way. You can also pass exact time in millis to constructor of Date class but first You need to get the time in millis.
Maybe this link will be helpful.
Or this code snippet:
def calendar = new GregorianCalendar(2011,1,7,15,7,23)
def date = calendar.getTime()
println date

Answer: You can get current date using Date() and format it the way you want using:
    /*
     y: year
     m: month
     d: day
     h: hour
     m: minute
    */

Date().format('yyyy-MM-dd hh-mm')
Date().format('yy/mm/dd hh')

The return type is a string.
Answer: LocalDateTime.now().format('yyyy-MM-dd hh-mm')
Comment: As it's currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer).


Tankless water heater needs 58 amps, what breaker is needed?

Question: I installed a tankless water heater that needs 58A, what is the correct double pole circuit breaker for this application?
Comment: What is the size of the electrical wire from the service panel to your heater?
Comment: @ThreePhaseEel Nope, inapplicable.  Read 424.1 Scope.  That's one thing I learned about government regs: First stop the applicability section.
Comment: @Harper -- good catch mate!  Turns out 422.10(F)(3) applies instead -- which means subdivided protection's not needed here.  (That is, if this is a potable application, which I presume it is because electric resistance boilers on hydronic systems are a rather silly idea if you ask me.)
Comment: Wouldn't it be a 60-A breaker and #6 AWG wire? That' what the Rheem RTE-13 tankless heater calls for.
Answer: The correct breaker depends on the size of wire which connects from the panel to the water heater.
Is the wire heavy enough for the full capacity of the heater?  For 58 amps residential (which implies the heater will not run full power for more than 2–3 hours), you can use wire rated for 60 amps.  If it is likely the heater will run full power for longer than 3 hours, then you need wire capacity for at least 72.5 amps (80% derating).
In solid core copper romex, it needs 4 AWG for the former and 3 AWG for the latter.  (For aluminum, it needs heavier wire than copper.)
4 AWG uses up to a 70 amp breaker and 3 AWG requires not more than an 80 amp breaker.  A smaller breaker can be used for additional wire safety, but to reduce nuisance tripping, a little headroom above 58 amps, like 65 amps, is a good idea.


Servos jitter when powered by power module

Question: I need 48 sg90 servos to move to a specific position each minute. Now I am using two arduino mega boards to power everything through 6 bread boards but it seems I need more power because some servos are ticking and are delayed. I cant get the external power supply to work independently of the computer. Once I unplug from my computer the servos jitter. Any help would be greatly appreciated.
Comment: ...Schematic...?
Comment: make sure you have connected all the grounds together, i mean from both the Arduino boards, i had similar issue when using ESP8266 module and Arduino UNO together! check this first and also make sure the power supply is regulated and sufficient for your needs.
Answer: Most servos use an analog signal (width of a pulse) for positioning.  Any perturbation in that signal will cause unexpected behavior.  Activating 48 servos simultaneously will likely indirectly or directly affect the analog signal.

The unexpected behavior might be mitigated through changes in software or hardware.  These mitigation efforts may include:

Staggering the servo changes so that only 1 servo moves at a time.
Perhaps less effective but worth trying, staggering the servo changes so only 1 servo starts moving at a time.  In this scenario more than 1 servos may be moving at a time.
Using a power supply which maintains the expected voltage even during events such as all servos starting simultaneously.

These are only 3 options to consider.  Many more exist but may not be pertinent to your situation.  More information is needed.
Comment: For 3: A short power surge could also be handled with a big capacitor between Vcc and ground. Those could provide the current needed for the spike and prevent the voltage from dropping


How to Unit test MapBasic Programs?

Question: Is there unit test frameworks available for MapBasic? I've been searching, but have not found anything.
Comment: Not that I am aware of, but just a comment based on your recent questions:

It's important to remember that to many, MapBasic is not a true programming language. Its principle goal is to customise and automate MI Pro. The fact that many clever people have created stand alone applications is amazing, considering the limitations you're hitting on.

In a nutshell, you're trying to take a 1987 Yamaha Jog 50cc Scooter and compete in the MotoGP. The scooter is great BTW, and very handy, but perhaps not always fit for purpose.
Comment: @MorganEllingham I agree that it would make very little sense to write any kind of standalone application in MapBasic. There is a team at the place I'm currently doing work for, which maintains a about 100k lines of code MapInfo/MapBasic application. Without unittests. That is amazing to me. And it's far beyond a little automation of MapInfo. :)
Comment: ouch! I'm a massive fan of MapBasic, in fact its something I really enjoy working with - when its fit for purpose.

Troubleshooting and testing it is an art and something which takes intimate experience to get good at, but, it is possible, you just have to create your own methodology. If you are committed to keeping it that is.
Answer: In my past MapBasic days I did write unit test in MapBasic - without any framework.
But creating my own test methods, comparing expected values with hard coded correct value did help me a lot, when I made updates and changes to my code.
Answer: I have now written a quite crude library for unit testing MapBasic code.
It's called MapBasicUnit
http://steenhulthin.github.io/MapBasicUnit/
Comment: Well done!!! Might try it out later.

Oh and it would be a really good idea to post this to the MapInfo-L google group. There are probably 20x the MapInfo users there than there are here. I know quite a few would appreciate this.

How to Unit test MapBasic Programs?


Notify the user by e-mail after the creation of a post

Question: I've a button, where the user create a post after click it. I want to notify him just after 10 min. I don't know the best way to do this with PHP. I know how to send the email, what I don't know is how to schedule this email for a specific time after the action. Has someone an idea?
Answer: There's wp_schedule_single_event:
<code>$in_ten_minutes = time() + 10 * 60;
$post_id = get_the_ID();
wp_schedule_single_event( $in_ten_minutes, 'notify_post_event', array( $post_id ) );
</code>
or similar - I've no idea if it's just the post ID you need, or whether get_the_ID() is the right way to find it when you're handling this action. Depending on where the button is and how you want to handle the button press (AJAX? POST back to the page?) this may need to go in an AJAX handler somewhere, and have the post ID and any other values passed in.
And you'll need a handler function too, e.g.
<code>function notify_post_event_handler( $post_id ) {
    $the_post = get_post( $post_id );
    $author_email = get_the_author_meta( 'user_email', $the_post-post_author );

    wp_mail( $author_email,
        'Here is your ten minute reminder',
        'Post: ' . get_post_permalink( $post_id ) );
}
add_action( 'notify_post_event', 'notify_post_event_handler', 10, 1 );
</code>
and this will be triggered after ten minutes by the wp_cron processing, so you'll need to make sure you have something set up to regularly trigger wp_cron jobs if you don't have enough constant volume of visitors to trigger it automatically after ten minutes.
Comment: Thanks, sorry if I didn't see in the documentation before, I didn't know about this function. It is really working outside the ajax function. I understand about pass the variable. But I made a very simple function to be executed as this event (create a post). It works outside the Ajax function, but when I call via ajax, it doesn't work. Maybe it is because of the hook? Because this same function to create the post works inside the ajax call, but without the wp_schedule_single_event()


Is decoherence even possible in anti de Sitter space?

Question: Is decoherence even possible in anti de Sitter space? The spatial conformal boundary acts as a repulsive wall, thus turning anti de Sitter space into an eternally closed quantum system. Superpositions remain superpositions and can never decohere. A closed system eventually thermalizes and undergoes Poincare recurrences. Whatever the dual is to an interacting conformal field theory, is it really a theory of quantum gravity, or does it only look like one superficially?
Comment: @Lubos: I see now, you wanted a finite number of degrees of freedom. I imagine that a suitable box will do, or a toy model, you don't need a full cosmology. But it has to be fully unitary and AdS-like in this sense. I am aware that AdS has infinitely many degrees of freedom, but they are unitarily evolving, and there are suitable truncations of the transverse coordinates, just take N=4 SU(N) gauge theory in a periodic box.
Comment: In large enough de Sitter space, like our Universe, the local physics is surely de facto indistinguishable from that of a flat space or a large AdS space, isn't it? Why do you find the cosmic horizon relevant for decoherence? Macroscopic things decohere within $10^{-50}$ seconds, long before things reach the cosmic horizon. And yes, dS space eventually thermalizes which in its case means that it gets empty, except for thermal quanta of wavelength comparable to the dS radius. What's the problem? Recurrence is just a very low-probability effect of a dropping entropy. Is this problematic?
Comment: @Lubos: dS and AdS are separate issues entirely, the difference between an open and closed system.
Comment: theorist says "Superpositions remain superpositions and can never decohere." They certainly can, at least in a large enough AdS space, as Luboš points out. Decoherence means that wavepackets in the combined system+environment configuration space have spread out and aren't interfering. Once that has happened, decoherence has occurred, regardless of whether unusual dynamics or Poincare recurrence later cause "recoherence" by bringing them back together.
Comment: @Mitchell: Lubos is using dS space to illustrate, which is a bad illustration, because dS thermalizes and is weird, while AdS is well defined. deSitter won't have poincare recurrences, which is why Susskind says it must always be unstable to decay to something else. I don't know the answer, because QM in dS space is not worked out. This is not about the question, but about the comments. I agree that the idea of decoherence is that the observer will decohere the system with information gained, later Poincare recurrence will happen long after tha observer's information is lost again.
Comment: OK, I thought the question was about dS rather than AdS, because the OP mentioned Poincare recurrence and it only exists in dS, not AdS, because AdS has an infinite number of degrees of freedom. So the question was internally inconsistent but that changes absolutely nothing about my answer, namely about the fact that decoherence doesn't care whether the surrounding space is dS, AdS, or flat. Decoherence doesn't depend on cosmology in any way.
Answer: Your question is not about AdS at all, it is about a closed quantum system with a finite number of degrees of freedom.
If you examine the space-time near a finite area quantum black hole, you will see an approximate AdS space. For this reason, my original answer included AdS spaces in the list of finite systems, although this is completely false for what people would call a normal classical AdS space. Thse spaces are unbounded and make open systems. The near horizon extremal black hole is presumably sitting in an infinite spacetime, so it is also an open quantum system. So it is best to reformulate the question for the domain you intended:
How can you have irreversible decoherence in a closed quantum system with a finite number of degrees of freedom?
The same question can be formulated to a certain extent in a closed classical system, where Poincare recurrences still occur. How can you reconcile poincare recurrence with irreversible information gain by an observer?
I think the many-worlds point of view is most useful for understanding this. If you have a closed quantum system that contains an observer, it is the observer's gain in information that determines which relative branch of the wavefunction becomes the real one for this observer, a branch selection from the decohered branches which occurs outside the theory. The branches are still effectively dechered so long as the arrow of time is still forward, because the wavefunction is spreading out into new regions of the enormous phase space. It is reasonable to think that the system will need to thermalize and destroy all the observers long before the recurrence makes the entropy decrease to the initial value.
This observer can only exist while there is an arrow of time, so there is no real paradox. You can have effective decoherence and measurements for the thermodynamic arrow-of-time stage. The same is true in classical closed system, the observer will have to dissociate and reform in order for the system to have a poincare recurrence.
But perhaps you meant this as a counterexample to the claim that irreversible decoherence can occur in pure closed-system quantum mechanics. In this case, I agree that it is obvious that the closed system cannot really decohere irreversibly, since it will eventually recohere to close to its initial state.
Comment: There are no Poincare recurrences in the AdS space or any other non-integrable system with infinitely many degrees of freedom (dS space is the only exception with a "finite maximum entropy" where it may occur), so your whole answer is totally wrong. Moreover, the very idea that decoherence depends on some big-scale cosmological properties of the spacetime is entirely misguided. One may say that you copied both of these misconceptions from the OP but that doesn't change the fact that your answer lacks any positive value.
Comment: @Lubos: I agree with you. I was assuming that the OP was interested in the case where the system is not open, so I said "your question is not specific to AdS space" right at the beginning, but I did not make it clear that AdS is open, and I should have. I immediately thought of finite degree of freedom truncations. But this answer explains what the OP is confused about. I edited it to incorporate the valid points you made. I will point out that I always think of AdS as shorthand for "near horizon", and to get a finite system, just think of a finite area extremal black hole.
Comment: Thanks, @Ron. I still think that there are many confusions, however. AdS is a near-horizon geometry of a black hole geometry but AdS itself doesn't have any horizon. Also, the reversibility may require the system to be closed and finite, and AdS isn't one. More generally, I don't understand the logic of the original question because it mixes cosmology with local quantum prcesses, but that's not really your fault.
Comment: @Lubos: That there are confusions is true, but these confusions are not solely mine--- there isn't a good picture of the classical AdS/CFT world, or else one would be able to follow a massive object falling into a black hole and reemitted. Gubser analyzes this, but I am sure wrongly, by considering a stack of branes with one brane moving slowly to a direct collision with the others. I thought about this also. The solution should be oscillatory and reversible, corresponding to a harmonic oscillation in the AdS space (at least when the brane has a small velocity and starts out tightly bound)
Comment: But Gubser suggests that the noncommutative description makes this irreversible for arbitrarily small temperature on the brane-stack. his argument is that there are many more noncommutative degrees of freedom, so that when the single brane hits the stack, it will mix up into a noncommutative mess in an irreversible way, corresponding to irreversible absorption. This idea is not at all plausible to me, although I can't rule it out definitively. The picture should have a classical geodesic interpretation with classical in-out motion. That explains the mismatch between the horizon structures.
Answer: This depends on whether your space includes the observer. In presence of the observer there will be decoherence. Without the observer there will be unitary evolution.
I am ready to answer any additional questions that can arise from my answer.
Comment: The question was about decoherence of small observer-less systems. It was about whether there is a sensible decohered limit in a closed system (and whether AdS counts as a closed system). The OP is aware of the observer issues in QM, as were the previous answers, they are just not the topic of the question.
Answer: Decoherence is more than anything a matter of what you define to be the "environment". The environment is supposed to be external to the system of interest and entangling interaction with it produces decoherence. If the environment in question is a part of the adS space then the subsystem can certainly decohere. If what you are asking is whether the space as a whole can decohere when it's isolated from its environment then the answer must by definition be no.


Unable to shrink logical drive in Window 7

Question: I have a primary partition C: and a logical drive E: on my Win 7 machine. I want to shrink the logical drive (E:) and create one more partition. I tried using the in built Disk Management Tool but volume shrink does not happen as the available disk space is only 4 MB as per the shrink tool. But actually there is 107 GB free space on it. I have tried de-fragmenting but it gives the same result. How can I resolve this issue?
Comment: Try using Easus Partition Manager Free version and post an image of list of drives that you get.
Answer: You can do it very easily using GParted. It is a very advanced tool for partitioning hard drives and will of course suit your need specified.
How to boot from that USB/CD/DVD can be found here.
After you have booted, select GParted Default from the boot screen.
GParted will now run after a short while. When it does, it will scan all your hard drives on your computer and provide you with a list of your partitions. Note that all your partitions will not be specified like in Windows. In Windows you have drive letters(example: E: F: G:), here you will have the likes of sda1, sda2, sda3, etc. Here, the sda means your first hard drive, if you a second or even a third hard drive, they will be specified as sdb and sdc respectively. sda1 means first partition on your first hard drive, sda2 means second partition on your first hard drive, sda3 means your third partition on your first hard drive, and so on.
For resizing you will need to know which partition to shrink. You can easily find that out if you have a Label for your E: drive, and the size of the drive, i.e 107 GB can also be used to figure that out.
From here on it is very simple. Right click on the partition you want to shrink. Click on Resize, then put the size you want to make it in the New Size field, press Tab button, then click on Resize/Move. And it should be done in a bit.
To make a new partition, you will now see some 'unallocated' space. Right click on that, select New, fill in the details of the size, Label you want it to have, etc. But do notice the File System. Select ntfs as your filesystem. Then click Add.
You should now exit from that GParted live session, to do that just double click on Exit from the Desktop.
After you boot into Windows, you should see a new partition.


"J'étais là" or "J'y étais" ?

Question: To say "I was there" would you say <j'étais là> or <j'y étais>? Why would you choose one over the other? I understand that both versions literally translate to "I was there" but what are the specific contexts in which you would choose one over the other?
Comment: Both could be said, you should provide more context, and say what you think would be best. Please reand this part of the help centre: [How do I ask a good question?](https://french.stackexchange.com/help/how-to-ask).
Comment: Depends if you want to say "I was: there" (in this location. Then use "j'étais là"), or "I was there ..." (ie, I was present for and lived that (emotionnal or not) event, in which case you can use "j'y étais")
Comment: Related:  https://french.stackexchange.com/questions/16245 https://french.stackexchange.com/questions/12953 https://french.stackexchange.com/questions/7481
Answer: Both "y" and "là" can mean "there", but there are differences in nature and in usage:

"là" is an adverb which can only refer to a place. As an adverb, it can be at various locations in the sentence
"y" is a nonpersonal pronoun which stands for any "à + noun" combination - not just locations. It is always placed right before or right after the verb.

See here
https://www.quora.com/What-is-the-difference-between-y-and-la-in-French#:~:text=%22y%22%20is%20a%20relative%2C,%22J'y%20vais%22.
Comment: so can you expand on the context where one would be chosen over the other?
Answer: It depends upon whether you want to stress the "was" or the "there".
E.g.:

I hear Jean and Jacques had a big argument.
I know.  I was there!  (J'étais là)

Or:

I thought you'd be here at the mall.
I had to come home. I was there. (J'y étais)

French doesn't make much use of word stress, so the different wording makes it obvious whether "là" or "étais" is the more important word.
Comment: @Lambie Can you give your analysis? I'd love to figure this out.
Comment: To give the English without the French misses the point entirely. In any case, I disagree with your analysis of the French in terms of translation.
Comment: @TaylorMitnick I don't know why they closed the question. Personally, I think it was a good question. Bear in mind that J'étais lá, **can also mean** I was here. (for example) On the phone: Il est là Jean ou pas? Is Jean there or not? Answer: Oui, il est là, Tu veux lui parler? Yes, he is here. Do you want to talk to him? That's another reason they should have left it open.
Comment: I didn't vote either to close the question but the reason why it was closed is explained in the first comment. If you want it to be reopen, edit your question and provide more details about what meaning(s) you expect, give more context, more examples.
Comment: @jlliagre Même sans ces détails, la question n'aurait pas dû être close. J'ai l'impression qu'assez souvent, les gens se dépêchent trop, et que pas mal de questions auraient pu être laissées telles quelles.

"J'étais là" or "J'y étais" ?