Why is Samurai Jack season 5 episode 1 (53) numbered 92 (XCII)?

Question: I read through the wikipedia pages, but couldn't find any reference. Why do they start at 92? It's 50 years later, not 40.
Comment: The missing episode numbers needn't each represent a year, of course.  (But it was still worth mentioning.)  The comic book series did pick up where season 4 left off, but there's no clear correlation to the number of comic issues and the jump by 40 either.
Comment: @faintsignal: Ok, thank you. I didn't know there was a comic book series.
Comment: Is Jack 92 years old at this point?
Comment: My theory, which is kind of wishful thinking, is that considering that there is a gap of 39 episodes between 52 and 92, and that each original season consisted of 13 episodes, and that many SJ episodes a largely standalone, maybe Tartakovsky has three full seasons in mind, now that interest in the series has been rekindled. A hardcore videogame, designed for the latest gen consoles would be amazing too. And something for mobile too!
Answer: The way that I understand it now is that the creator wanted to set Season 5 with the 50 year timeskip represented as the conclusion of Season 5 as an unstated CII.
It's already established that 50 years have already passed but here's my theory. The season 4 episode began as LII (52), and season 5 began as XCII (92). When you as an audience finish watching XCII, you are technically finished with XCII and are at the start of XCIII (93) and so on.
With this in mind, and the fact that Season 5 is only 10 episodes, the last episode of the season will be represented as CI (101). This represents the beginning to the end. Once you reach the end of CI, you have reached the beginning of CII, hence, the 50 years are represented.
The actual time skip in the story is somewhat irrelevant to each episode's roman numerals, but not completely.
Answer: I guess, if you assume that the first 52 episodes took place in 10 years' time; plus the 40 years, as Jack says it has been 50 years, then that gives us 92. I think, Genndy has said somewhere that the episode title is just to show the passage of time. So, it's not important what the number is, unless it is a mystery that will be revealed later.
Answer: If this season did have 13 episodes, like all of the others, the final episode would have been CIV.  104 is 13*8, implying that there are three lost seasons that would have gone after season 4 and before season 5.  This just means that they wanted the starting number for the final season to match what would otherwise have been a starting number for a regular season.  They could have chosen to skip over 3 seasons in particular for any reason.
Personally, I'm still hoping that this means that episode CI will be massive, effectively the length of 4 regular episodes in order to keep with the 13 episodes per season pattern.  A guy can dream.


Why does the tongue of the door lock stay in the door, and the hole in the door frame?

Question: To me it seems entirely reasonable for the hole of a lock to be in the door and the "tongue" of the lock to be in the frame. Is there a reason we usually do it only one way?
Comment: You would also keep running into the tongue as you went past the frame.  The door is movable. so you walk around it. and normally avoid the tongue.
Comment: Wooden door frames usually thicker than a door.  Might have almost an inch of wood to hold the hole in place on a frame, but maybe a 1/4 or if lucky 1/2 inch of wood in a door.  Need two kicks with a frame, only half a kick with a door.
Comment: ah wait i see why its a security precaution ill draw a photo
Comment: strange question, how would the tongue move if it is in door frame
Comment: @Ruskes You know those electronic door locks that use an electric strike? In those, the strike swivels to release a fixed tongue. I'm imagining a similar mechanism, flipped over with the strike on the door side.
Comment: @Ruskes: keyhole in the door frame? Turn the key, tongue moves. I don't like it, but I don't immediately see that's it's impossible. Just less convenient than the typical arrangement :-)
Answer: The doorknob is attached to the door.  This allows someone to twist the knob to retract the "bolt" and then, as a part of a continuing motion, pull on the knob to open the door.
It's hard to envision a scheme where the "bolt" could be tied to the frame while still allowing the door to be opened with one hand.
Comment: I think every other possible reason could easily be engineered away (standard placement of door in a frame for example would solve depth of door frame), but this is the most logical. Having the handle on the frame requires two hands to operate or multiple separate operations.
Comment: +1 but this doesn't directly cover many key locks, especially mortice locks.  However indirectly it still does (rim locks where you can turn the key then push the door in one movement, mortice locks - to match everything else)
Comment: I can imagine a conventional knob or handle still being on the door (it just pushes the latch into the jamb), but I'm not sure there's any benefit to increasing the complexity. (And massively increasing complexity if the door is supposed to lock or deadbolt.)
Comment: @AloysiusDefenestrate and complexity in matters of security is often where vulnerabilities creep in
Answer: Setting the (several) other problems aside, a bolt sticking out of the door frame is a hazard. Not only can people get injured running into it, but loose clothing can get caught on it. Doors are chokepoints for emergency egress and are designed to keep out of the way when open so that the entire passage can be used for egress by panicking, distracted people. The door frame hoisting people by their own beltloops doesn't comply with this design.
Comment: I can attest to this.  My home has some old-timey-style latches where the catch sticks out from the door frame.  I've torn clothes on it and even hurt myself a couple of times on them.  I would love to replace them but my SO likes the look of them.
Comment: even as it is, I routinely get my belt-loops caught on strike plates because they happen to be at the exact same height. I am very thankful that there isn't an even bigger obstacle at that height
Comment: It's possible to have a projection from a door or gate interact with a recessed object attached to a stationary frame.  This is common with gates.
Comment: I have doors with locks where the tongues are in the door, and they don't stick out from the door when unlocked. Mortice locks being the main example: stick out when locked, not when unlocked. So why does the tongue of a lock have to stick out from the door frame? Just don't use a Yale lock, that sticks out whether locked or unlocked, and only briefly retracts while you're actually opening the door :-)
Comment: Which leads me to suspect that the issue isn't that the *lock* needs to be in the door, it's that the spring-loaded *latch* (not sure if that's the right technical term, but I'll use it) needs to be in the door. Then, combining the lock and the latch into a single unit is an obvious move, but strictly speaking not an essential one.
Answer: Doors are pretty standard so the locks and keys can be universal with minimum adjustments. Door frames, however, are not standard. Look at the variety of exterior door frames. The thickness of the frames vary greatly, some are brick, fancy stonework, siding, decorator trim and molding, etc. meaning the locks would almost have to be custom made. Plus, the installation of the locks and keys would be much more involved drilling through bricks, etc.
Also, the strength of the frame for holding the bolt would be greater than the strength of the door holding the bolt.
Answer: There are sound reasons, some of which have been mentioned already, but don't neglect the role of convention - if we all do things the same way round, fewer different designs are needed, and there's no real benefit to putting the lock in the frame.  There often isn't much frame before you get to the next bit of wall or similar, while the door is always going to be big enough to walk through and therefore have enough space to fit the lock.  That said I have come across largely-glazed front doors with very limited space for locks.  Upgrading the lock for greater security was challenging.
One modern reason that hasn't been mentioned is multi-point locking systems, where the lock mechanism in the door doesn't just lock a single tongue, but (on turning the key) engages bolts or hooks at several points on the door (usually at the top and bottom of the non-hinge side, plus 1-3 points on that side).  This provides far greater mechanical strength than a single point lock.
An interesting comparison comes from electronic door locks, where there's a need to get wires to the part controlled by the security system.  These are often combined with key overrides in the form of conventional locks, and then it's the striker plate on the frame that's wired.

Reinraum, CC0, via Wikimedia Commons
This deals with issues like the tongue of the lock snagging on people walking through the door (mentioned in the comments), and means it's compatible with existing locks.  At the same time it means no need for wires to be hinged.
Answer: Robustness by outside impact. Forcibly kicking open (in case of hurricane by wind) a locked door is much more difficult when the tongue is inside a rigid bulky wall embedded frame than when the tongue is in the flimsy movable plank of the door edge.
Answer: Wood door. Might be a piece wood inside the door knob mechanism.
Could also be wet. Wood swells when it gets soaked and wet.
Metal door the mechanism may just need a little cleaning and silicon spray lube. Safe to use on electric controlled doors. Just make sure power is off.
The propellant is flammable..
Comment: I think you're answering a different question than the one that was asked. They wanted to know why the lock is installed in the door and the strike in the frame; you've answered about why the lock mechanism may be getting stuck.


How do you scale uniformly, using the Scale Tool in Illustrator?

Question: When using Illustrator's interactive Scale Tool, how do you scale an object uniformly?
Comment: Yes, but the manual's information about the exact operation is actually plain wrong *when you have Smart Guides turned on*: Specifically the part saying "While using the Scale tool with the Shift key, start dragging at an angle of 45° horizontally or vertically but in an angle". This only counts for Smart Guides off, otherwise if using Shift, it will squash the object and only scale in horizontal or vertical direction.
Comment: ^ I should say, *sometimes*, not consistently. Which is why Shift should rather not be pressed when uniformly scaling with Smart Guides On (see gif in my answer below).
Answer: Depress and hold the Shift key and drag from a general corner area while using the tool.
If you drag closer to a side, you'll see the scale take on a more vertical or horizontal aspect, merely move the cursor (while still dragging) closer to a corner region.
Answer: Found the answer: If you have Smart Guides turned off, hold Shift while dragging. If you have Smart Guides turned on, holding Shift might render iffy results, sometimes squashing the object horizontally or vertically even if you're doing it right.

There are two gotchas when Smart Guides are On:
First, although arguably cryptically described in the manual, you have to drag along the exact tangent relative to the reference point, and then a guide appears indicating that you're scaling proportionally/uniformly. (Some people might've expected to be able to simply drag like when Smart Guides are off, but that won't workj until you've found that 'uniform line'.)
Secondly, and this is where the manual seems misleading: You should not hold Shift at all when dragging if Smart Guides are On. Reason being that, if you're dragging from a certain angle (this is getting complicated to describe, better see my included gif) your object will actually get squashed horizontally or vertically. This behavior is inconsistent, but annoying nevertheless. And simply not using Shift here, removes the issue. I.e. the opposite of what the manual is mentioning (Shift pressed).
Comment: Kind of confusing...`hold Shift while dragging an anchor point`.... erm.. you **don't** "drag anchor points" with the Scale tool.
Comment: @Scott you can drag anchor points, you dont have to offcourse but you can. Which is nbify if you want to match scale (and rotation)
Comment: @joojaa Hmm.. With the **Scale tool** I can't *drag* any anchor point.. I can *scale* an anchor point (and its handles) but I can't **drag** any anchor point. "Drag", to me, is associated with altering an anchors *position*.
Comment: @Scott so scaling does not alter position now? Ill shut up now ;)
Comment: @joojaa for an **anchor point** no. Scaling doesn't alter position. If you scale an **object** then, yes, its anchors will change position. To my point.. one does **not** "drag an anchor" with the scale tool - but if you scale an *object* yes the anchor positions will change, which *may* make it *appear* that the user is "dragging an anchor point" but the reality is they are not. It's no different than scaling with the Bounding Box.. you aren't "dragging anchors" even though their positions will change.
Comment: Admittedly, this distinction may be a bit overly specific. But there is a difference.
Comment: Its not actually smart guides that stop this but the alignment guides suboption overrides the drag.
Comment: @joojaa Interesting, where are those toggled?
Comment: In the preferences. This is important to know since alignment guides must be turned off at some point as your designs complexity exceeds a certain point.


How to integrate observational errors in goodness of fit tests?

Question: I have an astrophysical non-linear curve, specifically a power spectrum. I need to fit this curve with a model and obtain the goodness-of-fit (GOF). This gives me expected and observed values. The data also have observational errors related to instrumental uncertainties. Is there any way I can integrate observational errors with a chi-square test (or any other GOF test)?
Comment: Welcome to our site!  I have taken the liberty of making your question slightly more flexible--so it is not tied entirely to the chi-squared test--in case any respondents would care to suggest other tests that might better meet your needs.
Answer: Are you using some package to fit the data or is this a school problem where you are writing a non-linear least squares code? Just about every package allows you to input the errors on the data points and it will output the errors on the fitted parameters or full covariance matrix. In fact, you should be able to input the covariance matrix of errors (if you know it) but power spectra usually have fairly diagonal covariance matrices.
The basic idea is to look at weighted least squares. You don't want to just ignore the errors when doing the fit and then use them to calculate the error. The fitter needs the errors in order to optimize the fit.
If the errors are small enough, the distribution of errors may be reasonably well described as multivariate normal. The terms in the output covariance matrix actually comes from linearizing the model around the best fit solution.
If you really want to characterize the error distribution fully, you'll have to go to something like markov chain monte carlo.
Comment: I am using QDP to fit the data for my Msc. Thesis. Fitting is not the problem. After I obtain two fits, I have to derive a p-value to show that the second fit is better. F-test accepts as input chi sqr values in IDL package that I am using. However the problem is this: I could not find any reasonable way to add observation errors into calculation of chi sqr.
Comment: A researcher at NASA advised us to modify chi sqr test as follows: instead of dividing by variance, change the summation by dividing (o-e)^2/i^2 where o are observations, e expected values and i observation errors. This doesn't seem to follow from either Pearson's test or dividing by variance. How must I calculate chi-square in this case?


How secure is ChaCha20?

Question: I want to implement a stream cipher to encrypt very sensitive data in my Python code. I heard about the ChaCha20 algorithm and the
PyCryptodome library
, but how secure is it ?
Comment: Possible duplicate of [How secure is Salsa20?](https://crypto.stackexchange.com/questions/40542/how-secure-is-salsa20)
Comment: @EllaRose Although I can see where you're coming from when comparing ChaCha20 with Salsa20, I can imagine that users of this site may not. A bit more info about [Salsa20](https://en.wikipedia.org/wiki/Salsa20) would be welcome. Besides that, it *does* use a new round function; it may not be directly obvious how much this would influence security.
Comment: @MaartenBodewes It does say *possible* duplicate ;)
Comment: We cannot and should not comment here on the security of a library. You'd need to perform comprehensive research for that, possibly including a review of the given implementation (if those haven't been performed and well documented before). Answers here should focus on the algorithm alone and if the algorithm *can* be implemented securely.
Answer:
Aumasson et al. Showed that ChaCha6  can be attacked with time complexity $2^{139}$ and ChaCha7 with $2^{248}$.
Shi et al. gave an attack based on second-order differential with $2^{136}$ for ChaCha6 and $2^{246.5}$ for ChaCha7.
Maitra, chosen IV cryptoanalysis and the time complexity of the attack showed that it can be reduced to $2^{239}$ for ChaCha7.
Choudhuri and Maitra concluded ChaCha12 are
sufficient for 256-bit keys against differential cryptanalysis using a hybrid model of non-linear round functions and linear approximation...

\begin{array} {|l|l|}
\hline
Attack & Evaluation \\
\hline
\text{Differential Analysis }      &                    \text{No attack found}\\
\text{Rotational Cryptanalysis}     &                   \text{No attack found}\\
\text{Boomerang Attack}        &                        \text{No attack found}  \\
\text{Linear Cryptanalysis}      &                      \text{No attack found}\\
\text{Distinguishing Attack}     &                      \text{No attack found}\\
\text{Guess and Determine Analysis}       &             \text{No attack found}\\
\text{Time-Memory-Data Tradeoff Attack }   &            \text{Protected}\\
\text{Practically ChaCha Algebraic Attack}   &          \text{No attack found} \\
\text{Attacks on Initialization Process}    &           \text{No attack found}\\
\text{Single Power Analysis }           &               \text{Protected}\\
\text{Practically Difference Power Analysis }    &      \text{Protected Practically}\\
\text{Cache Timing Attack}         &                    \text{No attack found}\\
\text{Fault Injection Analysis }   &                    \text{Protected Practically}\\
\hline
\end{array}
The above table and results come from KDDI Research, Inc

simple power attack; though the rotation is vulnerable to power attack, they propose masking as a countermeasure.
differential power analysis; they demonstrated that adversary can get all keys except $k_1$ which can be found in $2^{32}$, proposed masking as a countermeasure.
Fault Injection Attack; they claim that the initial matrix $X$ or
matrix $X^{(20)}$ will be output if injection is performed on the addition.

A countermeasure against this sort of attacks is to separate variables; that is, distinct variables store the inputs and output of the addition. Consider an addition $z \leftarrow x+y$. The addition returns the initial value of variable z even if the addition is skipped. Thus, the adversary can get neither the value of variables $x$ and $y$. Algorithm 9 shows the implementation using countermeasure based on variable separation.
We should note that variable separation in source-code level does not work

They include all attacks upto 2017 in their document. I couldn't find one in 2018.
Comment: How is the conclusion that ChaCha is practically resistant to fault injection reached? That one seems highly dependent on hypothesis made. At least in a setup where the same Chacha calculation is performed multiple times, it seems fault injection could work.
Comment: If you want, Ill we go deeper.
Answer: ChaCha20 is a "primitive", in other words it's just one component of a secure cryptographic system (and PyCryptodome is a collection of primitives). So in a way, and from the perspective of a programmer, it's not secure at all. It's dangerous to use something so low-level.
In order to implement a secure crypto system, you need more than just encryption. Go with something like Cryptography or PyNaCl - they have already done all the work for you.
Comment: I've voted this down. On StackOverflow this could possibly count as an answer, as the question could suffer from the X-Y problem. But on crypto, when asked about the security of an algorithm, we want to focus on just that - not the protocol or system that the algorithm is used in.
Comment: Sure, I definitely answered the "real" question here. Maybe flag so that it can be converted into a comment. Or we change the question.

How secure is ChaCha20?


How important is it to use a Mobil 1 oil filter if you are using Mobil 1 engine oil?

Question: It seems like some oil changing stores do not use a Mobil 1 oil filter even if they use Mobil 1 engine oil. When using Mobil 1 engine oil, is it much better to use a Mobil 1 oil filter?
Answer: No, but using a quality part for your engine is. Some "cheap" filters may not have the performance or longevity of a quality filter.
Really, a "cheap" filter is poor economy considering the function of the filter and the cost of an engine.
This applies to fuel filters as well.
Use a quality brand - there are several...
Comment: Can't vote this up enough. Cheap filters meet the bare minimum of standards. More expensive ones from trust brands (such as Blue Print, especially with Japanese cars) tend to be built more to the specification of the original OEM parts. Where as Crossland or Wix filters tend to just meet the generic industry standard.
Comment: Perfect answer. OEM filters from the dealer are often surprisingly cost-effective (e.g genuine Subaru filters are cheaper from the dealer than from car parts stores)


What is the difference between 終に、遂に、and 竟に?

Question: What is the difference between 終に、遂に、and 竟に? All of them are ついに and have the same meaning in english too "finally". Thank you ^^
Answer: The reason ついに has three kanji is because the word was originally (i.e. a millennium ago) used to translate these three different Chinese adverbs:

終: in the end; finally
遂: consequently
竟: it turns out that; in fact

But, we no more intentionally distinguish these meanings, and most of them are already fallen into disuse in Japanese. Today we only recognize "finally" meaning while prefer 遂 kanji. You have no need to care about any difference between those kanji, only need to know that people could use any of them (plus all hiragana form) according to their tastes.

Ｗhat is the difference between 終に、遂に、and 竟に？


Do all LCD monitors look bad when rotated 90 degrees?

Question: I've got a Samsung SyncMaster 204B monitor. One of the features it has is that it lets the user physically rotate the display 90 degrees so that the monitor is in portrait mode, which would be useful for looking at long documents. However, when I do this, there is a significant drop in display quality. Is there some setting I need to change? Or is this just how LCDs work?
Comment: Whaddya mean "significant drop in quality"
Answer: There are two issues.
First, the arrangement of subpixels - Microsoft's ClearType is optimized for horizontal arrangement of subpixels.  I'm not aware of any LCD panels that are made with vertical subpixels.  You might be able to configure ClearType to lessen this problem.
Second is the viewing angle of the display.  There are different LCD technologies, and the cheapest don't have very good vertical viewing angles.  When you rotate the display, those vertical viewing angles become horizontal viewing angles.
Comment: Oh sweet jesus, never turn off ClearType unless you want your eyes to bleed! Vista and 7 _automatically_ take monitor orientation into account when doing cleartype rasterizing; it's even handled on a _per-monitor basis+ so you can have one rotated, one not. Sub-pixel rendering definitely works best with a standard RGB or BGR, but readability is still improved when it's RGB vertical or BGR vertical.
Comment: Yeah so.. turn off cleartype.  That's great advice if I ever heard it.  Even if your monitor is in its normal orientation (I hate cleartype!)
Comment: ClearType does not support vertically stacked subpixels. Calibration does not help.
Comment: Actually if u not happy with fonts in Portrait mode Disable  - To "Smooth Edges of screen fonts".
http://www.sevenforums.com/tutorials/127337-smooth-edges-screen-fonts-enable-disable.html
Answer: Yes and no. Most consumer LCDs are based on the TN lcd panel technology (cause it's cheap) which doesn't have very good viewing angles. You can generally determine if you have a TN display by looking off center (up or down) at your lcd and if it appears that changing the viewing angle the brightness/contrast/color changes as well, then chances are, you have a TN. Now, when you rotate a TN, those vertical angles become horizontal angles and since your eyes look at the screen at slightly different horizontal angles, the monitor would look pretty bad. (I had a TN monitor mounted on a pivot arm and i basically had to look at the monitor at an angle to be able to read something in a portrait mode .. looking at the monitor straight on would give me a headache after a while since my right eye would see the monitor darker than my left eye. Looking at the monitor off center with the top of the monitor closer to you gives better viewing experience)
However, if you have an MVA panel lcd (or even better, an IPS based one), portrait mode would look so much better so in this case, the question to your answer would be no. Basically ... it's the old saying - you get what you paid for. If you are going to buy monitors that you want to use in portrait mode, make sure you buy one with excellent vertical viewing angles (i.e. get an IPS or MVA based lcd panel).
This site has brief description of the common lcd panel types if you are interested in reading more about it.
Answer: There are three types of LCD panel: TN, VA, IPS
These are in order of increasing cost and (generally) increased quality of image, so TN is the worst quality but cheapest, and IPS is the best quality and most expensive.
TN monitors have pretty terrible viewing angles, and so rotating one 90 degrees will give the change in quality you mention -- viewing them from anything but fairly straight-on will mean that colours start to go very strange and possibly inverted, and brightness can vary a lot across them.
So, to answer the original question:
No, not all LCD monitors do this.  Just the cheap ones!
edit: TN panels generally have poorer viewing angles in the specs, so they are likely to say something like "170 degrees vertical/160 degrees horizontal" rather than the 178/178 which VA and IPS panels will state.
Answer: It might be due to the TN panel in the monitor which leads to bad angles, so when you tilt it you get it horizontally instead of vertically which might be more unusual for your eyes then the bleeding and color-distortion you get when looking at it the normal way. It's the same for me when doing it at my university's monitors and probably something you can't get away with when dealing with TN panels.
Comment: It's not enough to just say "TN" - this technology has many variations, and some will be worse than others.
Comment: You are correct Mark, maybe the answer should have been more geared at the "community information gathering process" then at the specific question. Most TN panels I have ever been in contact with has the same set of problems, hence the answer. Your answer was above and it was mostly a continuation of that.
Comment: I probably wasn't clear with my first comment. Different versions of TN can have different characteristics. It's possible for a manufacturer to substitute one panel for another in the same model LCD, so you can't even be sure of what you're getting. Non-TN panels are also available but are usually not seen due to their expense.
Answer: What I just found to make the big difference (and solution!) was swapping the input (DVI / VGA):

normal (landscape) at VGA/analog
rotated (90degrees) at DVI/digital

It took me some time, some investigation (like reading this web site) and even changing a few monitors, to finally discover this big difference. I thought it might be helpful to share this for many others to save time, as almost all PCs and monitors today are by default setup with both ports.
So: normal situation with multiple monitors, there was no (apparently) difference/problem. Rotated a screen: poor quality (like resolution was too low). ClearType did not have to do with it. Solution: connecting the rotated screen on DVI (white connector).
Monitors used: HP L2245wg (1680x1050) and LG 2350V (1920x1080). Videocard NVidia GeForce 8400 GS. Running Windows 8.1
Comment: I can say almost opposite I have 3 monitors rotated 90 degree and Best quality was on VGA connected to PC through DisplayPort while DVI-D ones had dark area at certain AngleView.
Answer: This might be due to the arrangement of the subpixels. Using subpixel smoothing does not work in portrait orientation, and will look wrong, or depending on how smart your operating system is, will be disabled.


What is the dimension of the space of traceless $n × n$ matrices?

Question: I am trying to figure out what would be the dimenstion of the space of the traceless $n \times n$ matrices. Please help me  with this question.
Comment: *This question does not show any research effort*
Answer: I will not answer your question directly for you have not put any effort into it. However here are some questions that you can ponder about that may or may not help.
The space of $n\times n$ matrices has dimension $n^2$. Now we know that the trace of a matrix is the sum of the elements on its diagonal. So elements off diagonal have no effect on a matrix's trace. Hence are we free to choose such elements?
There are $n$ elements on the diagonal and say we choose $n-1$ of them and stop at the entry $a_{nn}$. Is there a constraint on how I choose $a_{nn}$?
Comment: Alternatively, note that $\operatorname{tr} : M_n(k) \to k$ is a linear operator on the space of $n \times n$ matrices over the field $k$...
Comment: What if a_nn=0 though?  That means the rest of the n-1 entries must also add up to 0 if tr(A)=0
Answer: Let $M_{n\times n}$ be the vector space of n by n square matrices. And so
$\forall A\in M_{n\times n}, \ A = \left \{ a_{ij}  | (i,j)\in [1,n] \right \}$.
Now every vector space has a basis(not going to prove this here but you can find proofs of it elsewhere on this site) so let's construct one:
Let $E_{ij}$ be the collection of n by n matrices with only 1 nonzero entry.
That is, for some $i,j\in [1,n]$,
$E_{ij}= \left \{  e_{kl}\  | e_{kl}=1 \leftrightarrow kl=ij,\ e_{kl}=0\leftrightarrow kl\neq ij
\ (1\leq k,l\leq n)  \right \}$
This is the standard basis for $M_{n\times n}$. We now can write
$A =  \sum_{i,j=1}^{n} a_{ij}E_{ij} \ | \ \forall A\in M_{n\times n}$  and this vector space has dimension $n^{2}$. Now let $K\subset M_{n\times n}$ be subspace of n by n matrices whose trace is equal to zero. Bear in mind that $ (\forall A \in M_{n\times n} ) \  tr(A)=0 \ \leftrightarrow  \  \sum_{i=1}^{n}a_{ii}=0$.
So for some $1\leq i\leq n$,
$trace(A)-a_{ii}$ = $0-a_{ii} =-a_{ii} = \sum_{j=1}^{i-1}a_{jj} +\sum_{j=i+1}^{n}a_{jj}$. And so you have a linear dependence relation.  We can see this by expanding our result for the i^th entry and writing it out as $a_{ii} = -(\sum_{j=1}^{i-1}a_{jj} +\sum_{j=i+1}^{n}a_{jj})$.
So if the trace of a square matrix A = 0, then one of the diagonal entries is constrained by the values of the other (n-1) diagonal entries as it is the negative sum of the other values. Now there are $n^{2}-n$ non-diagonal entries that do not affect the trace so they are independent of tr(A). So the Dim(K)= $(n^{2}-n)+(n-1)=n^{2}-n+n-1= n^{2}-1$.


Stain / residue on hardwood after years of rug covering

Question: I just bought a house from the mid 1800's. Hardwood throughout but two rooms have had rugs on the floor for obviously many, many, years. When we pulled up the rugs we found that the hardwood was extremely dirty and/or stained. I'm sure there are a hundred different answers as to what to what caused this and the best course of action, hoping to get some ideas for cleaning or if refinishing will be necessary.
Comment: You have a long process ahead of you in sanding and refinishing. (*The whole room, you will not get the rug area to  match well with  rest of the floor*.)   The end result will be stunning, so worth it IMO.
Comment: Cinderella floor.  Thanks for the photo!
Comment: Amusingly in my 1910 house I have the opposite. I believe they decided to save money and not stain under were the rug would go
Answer: You can try cleaning the grime off (thats some of the carpet pad impregnated with dirt), but ultimately you should refinish the wood floor.
This involves a commercial sanding machine and other equipment not readily available.
To clean try and scrape as much of the crud off as possible using a putty knife or a paint scraper. try not to gouge the wood or remove the stain (this is the difficult part). Next you should use some type of floor cleaner. I think a good cleaning product is TSP. It's made for heavy cleaning. Fill a bucket with hot water and mix in the appropriate amount of TSP. Wring the mop out so the floor isn't saturated with water and apply. Scrubbing with a bristle brush will help. Repeat as needed.
Comment: I agree, although after thoroughly scrubbing/cleaning it may look better than you expect. Wood floor refinishing has indeed become a DIY job and you should be able to rent any/all equipment necessary.
Comment: Looks like trowel marks from **carpet glue**. By the time you get all that off, you're going to *have* to refinish the floor. This can be DiY with a random orbit sander but it's going to take a lot of paper, elbow grease, and time. With professional equipment it's like three days; yourself, it's going to take a month, and likely look like it. You need an edger, a drum sander, *and* a RO sander, but most importantly, you need to know how to use them. Drums have a steep and unforgiving learning curve, and if you have a bad back; forget about it.


How to use sensors which are not at close distance with the Raspberry Pi using line wires?

Question: If my sensor is outside my house and I want to keep my Raspberry Pi inside the house, how do I connect them? If it is near the sensor I can connect them using jumper wires, but how to connect them using normal line wires?
Comment: What is the problem that you're facing? Did you connect the sensor and it doesn't work? Or you can't figure out how to mechanically attach longer wires? Or you don't have any wires and want to buy some?
Comment: I am asking whether longer line wires will work or will there be loss of data? @DmitryGrigoryev
Answer: There are small wireless boards, that provide TTL-level serial interface and can be connected to your RPi and whatever you use at home, your programs just send the data as over wired serial connection, but you don't need actual wires for that to work. Connection speed 9600bps can work as far as 100m, I have managed to lower the data rate down to 1200bps and improve range to a few kilometers.
The record was 60km with Yagi antenna =)
Comment: Can you post a link where I can buy them?
Comment: @ShreyasMishra ebay.com and search for "ttl serial wireless module"?
Comment: That will need electronics, at both ends.
Answer: There will be a voltage drop over long cables. Therefore you need to make your sensors work in a current mode, and ensure that you have enough voltage to drive them.
I would build an op-amp circuit or long tail pair transistor circuit. You will keep all components in side, except the sensor, and some of the cable.


How to get 2-state PDA for CFG?

Question: I'm studying for my Computing languages test and there's one idea I'm having problems wrapping my head around, as far as I know for any Context Free Grammar (CFG), we can design a 2-state Pushdown Automaton (PDA). I am however a little bit confused that why this is possible.
Comment: Have you read the proof for the fact that PDA and context-free grammars are equally powerful?
Comment: Please don't edit away your question after answers were provided, that's just impolite. Note that, in case you want to cover your tracks after getting help on, say, an exercise problem, that a) [all revisions are kept](http://cs.stackexchange.com/posts/19946/revisions) and b) we don't support such behaviour.
Answer: Depending on your acceptance definition, you might be able to get away with only a single state. The basic idea is to keep the state information on the stack. The first thing you'd try is for each symbol on the stack to contain the "current state", i.e. each symbol is a tuple $(s,X)$, where $s$ is a state of the original PDA and $X$ is a stack symbol in the original stack alphabet. That way, the state information is stored on the stack. There is a problem here, however: if we pop $(s,X)$, we don't know what state the PDA should be in. For the solution, see these lecture notes. The construction heavily relies on non-determinism.
Answer: Transforming a PDA into a CFG is hard, as we need to get rid of the states.
The converse, transforming CFG into single state PDA is straightforward, using an expand-match technique, see wikipedia. Single state when using empty stack acceptance. Two sates are necessary when transforming into final state acceptance (you need two to distinguish yes/no accepting, of course).

How to get 2-state PDA for CFG?


In AirPort Utility, what is the menu item "Restore Default Settings"?

Question: In AirPort Utility v.6.3.2, what is the menu item "Restore Default Settings..." I see under "Base Station" and does it relate to a soft, hard, or factory default reset? Thank you.
Answer: According to AirPort Utility 6.x: Reset your base station, it will reset your base station to Apple factory settings, meaning that you will lose your current setup and it'll be just as if you were setting it up for the first time out of the box.
Use this option if you're having issues with your base station and nothing else seems to be helping ... or when you're getting ready to sell it.


sendmail default mail path

Question: I have just configured the postfix+dovecot and its working fine as I tested with configured in Outlook. Same way I am trying to setup a sendmail+dovecot,
The mail problem I am facing here is the mail-directory path of sendmail.
In postfix and dovecot I have configured /home/user/Maildir ,but in sendmail I am unable to find the exact parameter where I set the directory path ?
Particularly in /etc/mail/sendmail.mc file ?
Answer: Usually, neither Postfix nor Sendmail are in charge of the location of users' mailboxes. Both of them hand off local mail delivery to a local delivery agent and it is the local delivery agent that is responsible for knowing the location and format of users' mailboxes.
In your case, since you are using Dovecot with Maildir folders located in each user's home directory, the best choice of local delivery agent to use is probably Dovecot's own LDA. Being a part of Dovecot, the Dovecot LDA uses Dovecot's own configuration to set the location and format of user's mailboxes, so you can't go wrong.
In Sendmail, the path to the local delivery agent is set with the m4 macro LOCAL_MAILER_PATH. In Postfix, it is set with the configuration directive mailbox_command.
Comment: In postfix main.cf I have found  " # The home_mailbox parameter specifies the optional pathname of a
# mailbox file relative to a user's home directory. The default
# mailbox file is /var/spool/mail/user or /var/mail/user.  Specify
# "Maildir/" for qmail-style delivery (the / is required).
#
#home_mailbox = Mailbox
home_mailbox = Maildir/   "    I just want to know what the exact similar parameter in sendmail configuration file ???
Comment: Finally got your point !!!   just edited the configuration in /etc/dovecot/conf.d/10-mail.conf   #   mail_location = maildir:~/Maildir
   mail_location = mbox:~/mail:INBOX=/var/mail/%u
#   mail_location = mbox:/var/mail/%d/%1n/%n:INDEX=/var/indexes/%d/%1n/%n
thats it

sendmail default mail path


Using a Magic Item as an Edge Pre-requisite

Question: Can a character take an Edge with an Advance that uses an Edge they got from a Magic Item as a pre requisite. For Example say I had  a "Gum  Shield of Frenzy" could I get Improved Frenzy.
Answer: I see a few options here. I'm a generous and fun-loving GM so I've sorted them in my preference.
Yes, but only when using the item.
Let the character take Improved Frenzy, but they must maintain the prerequisites to use Improved Frenzy. If they stop using the shield, they lose all benefits of Improved Frenzy until they regain Frenzy (by any means.)
No, but make the edges cumulative.
Let the character learn the Frenzy edge. The shield provides the benefit of Frenzy or Improved Frenzy depending on who wields it.
No, suck it up.
It's a tough world. Just because you have a crutch that lets you walk doesn't mean you can use it to run.
Comment: Of the options above, I would probably go for 2, Make the edges cumulative.
Comment: I think 2 is the simplest option besides "suck it up".  I would personally roll with that.
Comment: I like 1 & 3. I think it probably depends on the background feel of the Campaign.


Unable to checkout log4j repository

Question: I'm using tortoiseSVN to checkout the log4j v1.2 source from - http://svn.apache.org/repos/asf/logging/log4j/trunk
But I keep getting this error:

Error: OPTIONS of '': Could not
  Error: resolve hostname `svn.apache.org': No such host is known.

The funny thing is that I can access 'svn.apache.org' from my browser but if I try to ping it from the command prompt, it says host not found.
Does any body else face this problem? Is there any other way to get the source for log4j v1.2?
Answer: The regular downloads include the source.
Comment: Thanks Thilo.

Boy...do i feel stupid now.

I would still need a way to be able to commit extensions though.

Unable to checkout log4j repository


Facebook won't log in to new activity - android

Question: I have a log in activity that connects to Facebook at the moment, after the user logs in I want it to connect to facebook and then I want it to connect to my Activity2  class but currently it redirects back to my original activity instead.
Is their anything wrong I'm doing in this part of my code:
  private CallbackManager mCallbackManager;
private FacebookCallback<LoginResult> mCallback=new FacebookCallback<LoginResult>() {
    @Override
    public void onSuccess(LoginResult loginResult) {
        AccessToken accessToken = loginResult.getAccessToken();
        Profile profile = Profile.getCurrentProfile();
        if (profile != null) {
            Intent intent = new Intent(getActivity(), MainActivity2Activity.class);
            startActivity(intent);
            }
        }

Answer: Checking if profile is null wouldn't work as ProfileManager fetches the profile asynchronously and getCurrentProfile() would likely return null immediately after logging in.
You could instead check if loginResult.getAccessToken() returns a non-null value.


What methods can be used to remove remjet from the back of motion picture film?

Question: Cinema film has a carbon remjet backing. If it is to be shot as stills the remjet usually has to removed in a home darkroom before processing. What are the best ways to do this?
Answer: The Rem-Jet coat is a dispersion of lamp black (soot) in a binder of cellulous acetate phthalate. This binder is an "acid plastic". It can be softened and washed away using an alkaline solution. Machine processing uses a pre-bath to temporarilly harden the film so it better withstands transport in a fast moving film processor. The pre-bath softens the Rem-Jet and spinning rollers, much like paint rollers scrub off the Rem-Jet.
You can make an alkaline solution and hand buff with a well washed "T" shirt. This can be performed the film has been processed but before drying.
Water 27 to 38°C (80 to 100°F) 800 mL 800 mL
Borax solution 15 g/L use 20g
Sodium Sulfate (Anhydrous) 100 g
Sodium Hydroxide 1.0 g
Water to make 1 L
The Rem-Jet serves to protect the film from exposure from the rear. Many motion picture cameras with thru-the-lens viewfinders leaked light if the photographer looked away. It serves as an anti-halation backing. It protects the film when large rolls are loaded and unloaded in subdued light.
Comment: Are you saying that if you process your ECN-2 film yourself, you can first develop it with rem-jet still intact and then take the film out into the light and wash the rem-jet off while the film is still wet?
Comment: The alkaline pre-bath is used to soften the acid plastic that holds the removable jet black (lamp black) to the film. It is also a pre-hardener as the normal process is an automated roller transport machine. You can develop without removing the Rem-Jet -- you remove it after processing as an alterative method.
Comment: Interesting. Thanks for the info! I'm still far from developing color film myself, but I'll keep that in mind.
Answer: In the ECN-2 process there is an alkaline bath applied at the beginning of the proces that releases the remjet coating which is afterwards removed before development. This is hard to replicate manually  in complete darkness, because you don't have visual feedback if the layer was properly removed everywhere. But the developer is alkaline as well and releases the layer, too.
You can develop, bleach and fix the films with remjet and after final rinse remove what is left with a soft sponge under running water. Then rinse again and use stabilizer or wetting agent as usual. This will make your developer and other baths dirty, but it does not seem to have any impact on the prints.
Answer: You can get bulk ECN2 chemicals that are up to spec. Probably cheaper per quantity than using weak kitchen chemicals.
The problem with "manually" removing remjet is that it ruins the emulsion...with contains your latent image! All of the DIY advice and Youtube videos will result in ruined film. If whatever method your using recycles the wash, and doesn't filter out the washed away remjet particles--or if it doesn't protect the emulsion side of the film during the process--remjet particles will be embedded in your film.
Kodak states in their ECN2 processing guides (still available), that it takes approximately 30 psi of water to remove the anti-halation backing satisfactorily. But you can't use 30 psi on the emulsion side without risking damage. Even commercial ECN2 processor machines ruin frames here and there. Whatever method you think up, either low-pressure water or cool air needs to protect the emulsion side of the film.


Why did Maul bother fighting Kanan

Question: In the Star Wars Rebels Season 2 Finale, we find out that Darth Maul is alive, and he helps Ahsoka and Kanan kill the Inquistors, and helps Ezra get a Sith Holocron. He eventually betrays Kanan, blinds him, and attacks Ahsoka. Ahsoka eventually tells Maul that he'll have to fight Kanan before they can continue fighting. Kanan gets up, Maul attacks him, and he manages to beat Maul. My question is, why did Maul attack Kanan, since he was blind, Kanan wouldn't have been able to stop him if he continued after Ahsoka. Maul could have just left Kanan there and continued on to the top of the Sith Temple. There was really no reason for him to fight Kanan, so why did he do it?
Comment: Maul hates the Jedi. It's his defining characteristic and leads him into making terrible choices, like not just blowing Obi-Wan and Qui-Gon into smithereens with a bomb instead of ambushing them
Comment: Why did the evil, dangerously unpredictable villain do something villainous and unpredictable?
Comment: It seemed unnecessary for Maul to fight him. If he had been left there by Maul, he would have been killed by the Temple's activation.
Answer: The most straightforward answer is that he wanted Kanan out of the way so he'd be free to continue to corrupt Ezra to the dark side. If left alive there's a chance he could have interfered with that, even blinded.
On a more personal level, it's clear from his tone that he found the notion of a blind Kanan being any serious physical threat to be amusing. In his eyes, it would have been something of a mercy killing, hence: "I...(suppressing a chuckle)...will make this quick."
On an even deeper emotional level, this can all be boiled down to "because he could and wanted to", which is pretty much why any Sith does anything. They're all about self gratification.
Answer: While it's not Canon anymore, in Jedi Knight, Jerec (the end boss) was blind.
I does not seems to bother him more than Matt Murdock...
Still canon,  in episode IV, one of the first (easiest ?) training of Luke involve being blinded.

I don't think blindness is a big drawback for a Jedi.
Comment: Fill out the details of Luke's blindness training (I assume you mean with the blaster droid) and this could be a great answer.
Answer:   It's all about apprentice.
  In last years of his life Maul was broken man (Zabrak actually :) ). He was desperately searching for purpose in life (hope as he defined it). Ezra, as apprentice, was in his mind a way to create his legacy, to create something lasting from his experience and knowledge. Also, as he was alone and going mentally unstable, Ezra's companionship would ease his pain (loss of family , loss of legs, loss of whole clan (Nightsisters and Nightbrothers) and his criminal empire) .
  Of course, Kanan was obstacle in his endeavor, because Ezra was currently his Padawan. Also, even before Maul blinded Kanan we see that Kanan didn't trust him much and tried to shield Ezra from his influence. So, for Maul, it was obvious he has to eliminate Kanan to get Ezra for himself ("Ezra will be mine!") .
  Now, after blinding Kanan, Ahsoka intervened and prevented Maul from finishing him. Maul did duel Ahshoka but he did not expect that Kanan would recover so fast and use Force to see. Again, Ahshoka was not so important to Maul, because simply she was not Ezra's master. It is very likely he sensed connection between Kanan and Ezra, not between Ahshoka and Ezra. So, when Kanan recovered and Ahshoka run away (sort of), Maul switched back to his primary target but lost.

Why did Maul bother fighting Kanan


How do I configure a Trigger action on entity duplication

Question: A duplicate operation for entities exists within Content Hub. How can I configure a trigger to fire an action when an entity is duplicated`?
Answer: Yes, You can create a trigger which will fire an action whenever a duplicate entity will be created.
Lets take an example of an asset, create a new trigger and select objective "entity creation", you can select execution type "In background" which is recommended.

On the condition tab select add definition and choose Asset and start adding conditions. See the example screenshot: I have added 2 conditions

In the action tab you can select any action of your choice which will be fired when the condition will match.


How do I edit a page made from a master page?

Question: I am using SharePoint Designer 2010 to create a new master page. I duplicated my v4.master and then added a couple of lines of text and a picture to the Main Place Holder area. Then when I try to make a page from the master I get the message that I have to edit the page in advanced mode. When the editor opens up there is only two lines of CSS and I am unable to add anything to the page. I tried making a page from the v4.master which I have not touched and get the same problem. I do have publishing enabled and have full control permissions for the entire site.
Answer: Two things; firstly, you're not creating a page based on a masterpage. The masterpage is set at the web level, not at the page level. What you're likely seeing is that the page layout you're using for the page doesn't contain any editable regions within SharePoint Designer, thus it wants you to put it into edit mode. Most of the time you're going to create a custom page layout for things like your homepage. The page layout sits on top of the masterpage and contains the actual containers for webparts, rich text, etc. Those elements don't actually sit on the masterpage itself. Header/footer/navigation/etc. is contained within the masterpage. The page layout contains the structure of the actual body of the page.
Secondly, SharePoint Designer is arguably the worst thing you can use to brand a SharePoint site (especially if you've started editing things in advanced mode). Once you customize a page using SharePoint designer, you separate that page from the original file definition that Microsoft ships with SharePoint. That file now lives in the content database, and is associated with this specific site collection where you've set it up. This becomes an issue in two scenarios: the biggest of which is when you decide to upgrade SharePoint 2010 to 2013. Now that you have non-solution based customizations, there becomes a HEAVILY manual process that you have to go through to manually remove all of those customizations to make sure that your site can upgrade without errors (since the upgrade process hits every file in the content database). The second scenario is if you need to make changes to the solution (such as a copyright year in the footer, or a color change). When you brand with SharePoint Designer, you have to manually make that change on every site collection.
The best practices approach to branding is to deploy a SharePoint solution package (WSP file) to the environment that contains a site feature to enable your branding. This is repeatable across multiple sites/server farms, and is much cleaner to upgrade when the time comes.
Answer: It turns out all I had to do was move my cursor over to the right side of the MainPlaceHolder and click the arrow button that popped up and then select "Create Custom Content." I somehow skipped that line in the Microsoft tutorial.


Using IntellijIdea within an existing virtualenv

Question: I want to use Intellij Idea within my existing python django project which was built within a virtual environment in ubuntu. How do I configure Intellij Idea to use the libraries of the virtual environment?
Answer: For PyCharm 2018
As per documentation from Pycharm:

In the Project Interpreter page, click  and select Add.
In the left-hand pane of the Add Python Interpreter dialog box, select Virtualenv Environment. The following actions depend on whether
the virtual environment existed before.
If Existing environment is selected:

Specify the required interpreter: use the drop-down list, or click Select an interpreter and find one in your file system.
Select the check-box Make available to all projects, if needed.

Click OK to complete the task.

For Pycharm 2016 and later
To add an existing virtual environment to the list of available interpreters

In the Project Interpreter page, click .
In the drop-down list, choose Add local.

In the Select Python Interpreter dialog box that opens, choose the desired Python executable, located inside the virtual environment folder, and click OK.

Go to this link for more information.

For Older versions:
Well I solved the above problem. I have added virtualenv folder's python to project sdk. The virtualenv directory's python( for example venv/bin/python2.7) needs to be added to Intellij Idea project path. Example: need to go to file>project structure (intellij Idea)

press new in Project SDK, and add new path to virtualenv's python directory like this:
Go to Modules>Dependencies and set your module sdk to Python SDK which is marked on this picture:
Click on Django (option marked in next the image) and set Django project root, Settings,Manage Script like this:
Now press ok and final look of the Project settings:
Now need to run the project.
Comment: Please correct me if I misunderstood: actually they don't show the hidden directory in the file browser, but if you type the directory name, then type `/` it will take you inside the hidden folder. It worked for me in 2016 versions. Haven't tested in 2017 edition. Directly copy pasting the path of the python file ie `/home/user/proj/.env/bin/python` in the file browser also works. @DavidPortabella
Comment: it works, thx! when the file dialog appears, typing / will prompt for the path.
here it also explains that you can use Command-Shift-. to show hidden files, and Command-Shift-G as an alternative to typing /.
https://intellij-support.jetbrains.com/hc/en-us/community/posts/205435510
http://osxdaily.com/2011/03/01/show-hidden-files-in-mac-os-x-dialog-boxes-with-commandshiftperiod/
Comment: this page describes how to add an existing pythong virtualenv
https://www.jetbrains.com/help/pycharm/2017.1/adding-existing-virtual-environment.html

however, on OSX, it opens a file dialog, and it doesn't allow to navigate to "hidden" dirs, such as the typical ~/.virtualenvs

any idea?
Comment: For IntelliJ, when using `Existing Environment` option, make sure you have to select `[...]/venv/bin/python` (not simply `[...]/venv/`)
Answer: The above answer is based on older version of IntelliJ. For new, look here: https://www.jetbrains.com/help/pycharm/2016.1/adding-existing-virtual-environment.html


PCB height adjusting mounting

Question: The PCB has a pulse oximeter mounted on the surface, and it's tolerance is 0.6mm. The problem is the pulse oximeter needs to touch the bottom case at all times. How to best mount the PCB in the case without putting too much stress on the pulse oximeter? Will screws with flexible washers be all right? Sadly separating pulse oximeter from main PCB is not an option.
Comment: This question is almost entirely mechanical. One idea is closed cell foam. Another is spring clips. Spring clips would be more reliable over a long time period. Foam might break down over time. But you probably need to talk to a mechanical engineer and show them all the details.
Answer: I would put a machined guard around the pulse oximeter to keep the surface from it at about 0.2-0.3 (if it is and SMD part soldering height tolerance is about 0.2mm) and then simply screw down the resulting assembly.
Otherwise use weak springs to push the p.o. against the case, need to know the allowed stress on the body for that

PCB height adjusting mounting


Can you say 「普段に○○」 or does it have to be「 普段は○○」?

Question: Can you say 「普段に○○」 or does it have to be「 普段は○○」?
Answer: Both are possible but in (subtly) different contexts.
Roughly 普段に means for non-special occasions, daily uses and its implication is that something different is used for special occasions. 普段は means usually, with implication being that the speaker is doing otherwise for some reason.

このセーターを普段に着る
このセーターを普段は着る

普段に(1) means I wear this sweater for non-special occasions. The focus of the sentence is simply on this sweater, and it is saying that the sweater is nothing special and the speaker wears it for daily use. Practically, you see it in combinations like 普段に使う, 普段に着る etc. A relevant related phrase in this sense is 普段使い.
普段は(2) means I usually wear this sweater, and the implication is that the speaker will wear something different for some reason (by the function of は, you may already know this or can search on this site).
An additional set of examples to clarify the difference:

このドレスを普段に着る
このドレスを普段は着る

3 is rather unlikely unless the speaker is someone who has a party almost everyday. 4 is fine (assuming the speaker is a party goer) and it means I wear this dress normally (on a occasion like this or for most parties).

Note that all of the above sentences (esp. 1) may sound a little strange by themselves. They would appear more like このセーターを普段に着るのは躊躇する I hesitate to wear this sweater daily (because I cherish it so much or it is so expensive).

Can you say 「普段に○○」 or does it have to be「 普段は○○」？


I have a site that doesn't' have a ribbon, how do I fix this?

Question: I am fairly new to sharepoint, so if I don't use the right words please let me know.
I have inherited a sharepoint 2007 farm and one of the sites doesn't have the usual "site actions" and "browse | page" tabs at the top.
I need to add a new user to the page to allow them to view and edit docs (the page appears to be a document library)
So I can see the site in central admin, but I don't have the user permissions and such that I need. I guess my question is how are these pages managed when the tools are hidden?
Sharepoint designer lets me load the page but again, I couldn't find any user permission settings there.
Thanks
Answer: do you have full control on the Site collection, try to add yourself as Site collection admin and then check
Answer: Someone has access to the site collection. If you do not see the site actions, or are missing menu items, chances are that the account you are using does not have the proper permissions.
You can do this through central administration:

Open Central Admin
Click Application Management Tab
Click Site Collection Administrators (SharePoint Site Management
Section)
Click Site Collection Drop Down
Click Change Site Collection
Click Web Application Drop Down
Click Change Web Application
Click Web Application you want to change
Click OK
Type user name you want to add as site collection admin
Add secondary admin if you choose
Click OK

Then try to go back to that site and see if you have the access needed.
Comment: OK, the user was set to an old employee, so I changed that to the farm administrator service account. However it did take about 15 minutes and a few re-freshes for the page controls to appear but this fixed it. Thanks so much!
Comment: And you now have access?


Real-world cross-platform decentralized asynchronous peer-to-peer communication

Question: My knowledge about network programming is limited, so, all the comments are more than welcome. Essentially my question boils down to the following question:
Q1. Is there really such a thing as decentralized asynchronous cross-platform peer-to-peer communication?
Let me explain myself.

If we have two http servers running on computers with actual IP addresses, then clearly the answer is yes, assuming one writes a protocol for the interaction.
To go one step further, if one of them (or both) is (are) behind a router, then, with port forwarding the communication can still be established. However, here the problems start because if someone wants to run such a server on the background, say in a mobile phone, the app that is relying on this server really works when one is at home (we can not really expect to request port forwarding everywhere we go).
But even beyond that,
Q2. do mobile phones obtain an actual IP address from telecommunication companies when someone is not using a wi-fi?
If this is true, then clearly one can have cross-platform asynchronous peer-to-peer communication at the expense of not using wi-fi by running an http server on a smartphone. (I understand that this is not convenient, but it is certainly doable.)

Concluding, the two (perhaps there are more) relevant questions that I can think of are:

Q3. How does Skype really work?
Q4. How does Viber really work?

Based on the answer for Skype, it says: If one of the callee or both of them do not have a public IP, then they send voice traffic to another online Skype node over UDP or TCP.
So, it appears that there is no direct communication in Skype, because they have to use a man-in-the-middle for such a scenario.
Regarding Viber, I could not find a good-thorough answer to this particular question. Do people talk to each other through a Viber centralized server, or, do they establish a direct connection? Of course if they do establish a direct connection, then I really want to know how they manage such a thing since a mobile phone may or may not have a physical address. How is a Viber message routed to my cell phone from a friend of mine even when Viber is not running and I am behind a router?
I guess the answer to Viber is really push notifications, but as far as I can understand, all the variations of push notifications rely on open connections, and then the servers of the applications send the notifications to the clients through such connection(s). So, this approach gives us the feeling that it is asynchronous, but essentially it is not. We are cheating, in the sense that there is a constantly open connection to a server, and moreover, as far as I can understand, the application server has to push the notification through that server. Schematically:
A > Central App Server > Central Server w/ open connection to my cellphone > me
So, this seems to be once again a centralized approach.
Honestly, the only approach that I can think of that is both decentralized and asynchronous (on mobile phones as well) is to run an http server on every platform/device, but this comes at the expense of not using Wi-Fi and assuming that a telecommunication company really assigns a physical IP address to every mobile phone (which I do not know if it is true, do you?).
What about WASTE, darknets, F2Fs, etc? Do they offer advantages in the sense of a more direct asynchronous communication between some interested parties? Are there real-world applications (also including mobile phones) using such approaches for communication.
Really, this is not the actual problem that I would like to work on, but I would like to know what the state of the art is so that I can figure out how I can proceed from there. So, all comments are really more than welcome. If you have references for the state of the art I would like to know about them as well, but a brief description would also be nice.
I appreciate all your time and effort in advance.
Answer: You asked many questions, here is the beginning of the answers:
Q1: Yes. For example, take BitTorrent's very successful 10 million+ node network. Aside from the bootstrapping process, the protocol is entirely decentralized and asynchronous. See here for more info.
Q2: Yes! Go to www.whatismyip.com on your mobile telephone, and you will see your assigned IP. However, you are likely to be very filtered (e.g: incoming traffic on port 80 is likely to be blocked).
Q3: It has elements of P2P and clever tricks to get around NAT issues -  see here for more info.
Q4: I don't know.


I keep getting a weird email address trying to facetime me on my iphone5? is this spam?

Question: I've received two calls today, both which I ignored, to facetime with an email address that i don't know.  is this spam or an attempt to hack?  has this ever happened to anyone else?  also, the first call was then followed shortly by another weird email, but this time by text.
Comment: My wife and I had one of these calls each from firstname.lastname@example.com
Within 10 minutes of each other we both ignored and blocked the caller, think it's some kind of scam.
Answer: Just ignore it and do not reply. It will stop eventually.
You might want to make your Facetime profile private, and consider changing your password just in case.
You might be targeted by a spammer.
Check you settings in Facetime:
Comment: No harm, ever, in changing your Apple ID password. I'd do it in this case, or anything doubtful / suspicious - and have.


How can I tell if BitLocker is successfully enabled on remote hosts?

Question: All machines from my network should have BitLocker successfully applied to them.
Is there a way that I can remotely query the machines to see if:

Bitlocker has been enabled,
Bitlocker has fully encrypted the drive.

Ideally I am looking for a way to do it without admin rights.
Answer: With this PowerShell command, you can check the BitLocker status on a volume:
Manage-bde -status -cn <computername/ip> <drive letter>

Where the -cn argument is optional. Examples:
Manage-bde -status C:
Manage-bde -status -cn 192.168.1.2 C:

The command can also be run remotely.
Reference:
https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-R2-and-2012/ff829849(v=ws.11)
Comment: This seems to be not working without admin rights.
Comment: This doesn't work on a large majority of Dell machines I maintain...
Answer: For a remote host:
manage-bde -status -computername **computername**

Answer: That is the command that gives the information you need.
Manage-bde -status C:

Comment: Thanks for posting an answer on our site. It would be highly beneficial to summarise what exactly is in the image you posted, so that users with vision impairments can benefit from it too.
Answer: manage-bde -status -computername "COMPUTERNAME" c:

The computer must be on and on the network however, does not work for machines out of network or that are off.
Comment: also this will not query all drives, notice the c: that is just for the drive, for multiple drives I recommend querying the drives and then using the last part as a variable with a for each loop
Comment: the answer above that forgoes the C: will query multiple drives


Can composite material be used in leading edge of airfoil instead of aluminium through Additive manufacturing?

Question: I want to know about, is it possible to replace aluminium by additively manufactured leading edge of airfoil by changing different infill patterns to improve the impct strength from bird impact on it.
Comment: The title and the subject seem to be asking slightly different questions here.  What do you mean by "composite material"? Carbon fiber composite?  What do you mean by "additively manufactured"? Laser powder bed fusion?  Are you proposing to replace an traditional aluminum lead edge with an AM leading edge?  or replace an aluminum leading edge with a carbon fiber composite edge?
Answer: Lots of aircraft use composite material for their leading edges.
There is no need to use additive manufacturing to accomplish this.
That said, you might be interested in filament winding, automated tape laying, and automated fiber placement machines.


Gnome Extensions Disabled after upgrading to 20.10

Question: am looking into why the Gnome extensions would stop showing after upgrading from 20.04 to 20.10. After rebooting they are now turning themselves off automatically and if I try to enable then, they do not show in the Top header.
Answer: Extensions may not anymore work on a newer version of Gnome Shell, which is at 3.38 in Ubuntu 20.10. Make sure your installed extensions are up to date. "Clipboard Indicator" is updated for Gnome Shell 3.38, so that one should work if you have the correct version installed. The latest supported version of Netspeed is 3.34, so indeed there is a possibility that that extension won't work anymore on 3.38. The same goes for " Sound Input & Output Device Chooser", which at this time is available for Gnome Shell up to 3.36.
Comment: Thank you Vanadium but that was the first thing I tried. Clipboard for example is using 3.38 with extension 36 (As of right now). It does not work.
Comment: There is nothing else you can do than file issues to the developer.
Answer: in terminal you can browse through the extension settings.
gsettings list-schemas

to view available options and
gsettings list-recursive

to view all of the schemas sub settings and their current state.
for example to disable the redundant user home folder on the desktop in ubuntu 20.10
gsettings set org.gnome.shell.extensions.ding show-home false

hope this will help and making changes via terminal will "stick" for you. good luck.


How to create random extrusion distance for n x n square model?

Question: I want to recreate the attached image as best I can. Is there a good/easy way to create randomness in how much each face is extruded? My goal is a square grid that is approximately 10 x 10, and then those random extrusions with a color gradient. I am relatively new to Blender so any help is very appreciated. Thank you!
Answer: You can use a very simple Geometry Nodes setup for this.
Start with a grid with 11 vertices so that you have a 10x10 face grid. Next use a Split Edges node to seperate these faces. Scale down these faces by a small amount if you want seperated columns. Next, use a Extrude Mesh node to extrude these faces. Plug a random value node into the Offset Scale. Finally use a Set Material to assign a material to this geometry.

The material setup is one of the simplest ones. Just seperate out the Z component and use it as an input for an Emmision Shader. (Use the object coordinates instead of the generated ones if you don't want the gradient to always stay from 0-1.)

This should give you something that looks like this:

If you want the outlines too, there are a few different ways to go for it. The simplest one would be the inverse hull method. But there are a few different other options. There are a lot of existing resources for outlines, and therefore, I won't include that in this answer.
Answer:
⬆ ShiftA, M, P Add a new Plane.
⭾ Tab Edit Mode
$\color{#888}{█0}\color{green}{█}$ right mouse button, S Subdivide
F9 Specify the number of cuts.
⎇ AltE, then I Extrude Individual Faces
✲ CtrlI Invert Selection
H Hide everything but the top faces
Enable proportional editing, random falloff.
GZ Move vertices up, don't confirm yet
$\color{#888}{█}\color{green}⬇\color{#888}{█}$ mouse wheel down until all verts have roughly the equal distribution.
Click to confirm movement, O disable proportional editing.
A Select all.
., I Set Pivot to Individual Origins
SZ0 Flatten on $z$ axis.
⎇ AltH Reveal hidden


Fields or Particles

Question: What is more fundamental, particles or fields? I keep reading what appears to be conflicting answers on this, but I am sure it is just a limitation of my understanding. I have heard some physicists say that everything is fields. That the particles are the excitation of these fields. The way to help you visualize this would be like a rope (the field) is moved up and down and the particle would be the wave in the rope. Ok. Then I read that, for example, the electromagnetic field is made up of photons. So does that mean the field is actually made of a huge number or photons making a field. Which is it? The field excited to make the photons or the huge number of photons making
 the field. It seems to make more sense that the field comes first but I don't know. Can someone clarify this?
Answer: Quantum field theory is the most powerful theory of reality we have at the moment. It states that the fundamental nature of reality are indeed fields. The photon is an excitation of the electromagnetic field. You might have seen written that an electromagnetic wave is "made up of photons". What this really means is that the energy of the wave is not continuous, but instead comes in packets of energy. This packets are photons, which are quantised excitations of the electromagnetic field.

Fields or Particles


Whose picture is it anyway?

Question: I've read that while the writer/screenwriter creates the story, it's the director's vision that makes the motion picture. So, whose picture is it, anyway?
Comment: Can you give a clearer definition what exactly you want to know? A movie is project created by a multitude of people. How do you define the "ownership" you are talking about?
Comment: @CGCampbell This reminds me of an anecdote a professor related in film school. A director was being interviewed about his "technique" in his latest film. The director talked at length about how he created his movies. Soon after the interview was published, the writer of the movie sent 120 blank pieces of paper to the director, along with the note:  "Try to apply your technique to these." (In my film major, I focused on screenwriting.)
Comment: At the moment this seems like very fuzzy and slightly subjective question. *"Whose picture is it?"* - Well, officially the producers'/studio's, I guess. But it's a very interesting point you adress in general (especially if someone could present a more in-depth historical survey of the ermergence of modern day's director-culture in an answer) and I would be glad if someone could back the question with a little more substantial wording.
Answer: Movies are always collaborative efforts, unless the writer, director and cinematographer are all the same person:

The writer creates the story, so that's theirs.
The screenwriter adapts the story from what's usually a novel, play or existing movie into a screenplay, a script with limited character interaction details. The amount they add to the project really depends on how much they've changed the story to fit a movie format.
The director and cinematographer (a.k.a director of photography) will then collaborate to create a storyboard which adapts the screenplay into actual shots, describing blocking (character positions and movement) and set design.

And even if they are the same people, actors on set can always adlib which can give scenes more depth than was originally described.
Comment: Not to forget executive producers who make the movie possible from an organisational and financial point of view, editors, cutters, CGI and other post production staff who have a large influence on atmosphere, tone, visual and audio experience. As you said, its a collaborative effect, even if the director usually gets most of the credit in the end.
Comment: Not to forget the production designer, who is ultimately responsible for the physical appearance of everything visual in shot (costume, set design, props, location..)
Comment: @JohnSmithOptional Don't you have some insightful answer about *Auteur Theory* and its influence, advantages and disadvantages up your sleeve?
Comment: I think just drawing attention to auteur theory (and its detractors), as you have done, is probably enough!
Answer: In addition to other answers, that already pointed out the collaborative nature of film-making (and thus the complexity of making a definite decision "whose picture it is"), I'd like to share some additional info, be it only to further emphasize how difficult a definite answer actually is. But beware that this information is entirely Wikipedia-based and I'm far from an expert on the topic.

First of all, there is the so-called Auteur Theory, which emerged in France in the 50s (first and foremost advocated by François Truffaut and fellow critics from Cahiers du Cinéma), which said

that a director's film reflects the director's personal creative vision, as if they were the primary "auteur" (the French word for "author"). In spite of—and sometimes even because of—the production of the film as part of an industrial process, the auteur's creative voice is distinct enough to shine through studio interference and the collective process.

So they basically tended to place the director as the primary creative force behind a movie and encouraged directors to actively imprint their own visions in the final product, favouring directors who acieved to mark their works with a distinct and consistent audiovisual style.
This might have been a direct reaction/aversion to the Hollywood Studio System, in which movies seemed to be an entirely industrialized process with the writer/director/cinematographer/actors simply being employees to produce the movies for the studios' profit. And this artistic and director centric approach later ushered in the movies and directors of the French New Wave (Nouvelle Vague) (and probably also the New Hollywood as a consequence of the collapsing Studio System).
Yet, this director-centric view was also frowned upon from different sides, mainly because film-making is a collaborative process and people saw that fact hurt by privileging the director that much. Special criticism came also from writers, who disagreed with the idea of directors being more authorial than screenwriters (and exactly for shifting the attention to the screenwriter, David Kipen developed the so-called Schreiber Theory as a reaction, yet in turn a rather intentionally exaggerated reaction it seems) and from people that claimed that Auteur Theory did not withstand the economic and industrial realities of film-making.
Personally speaking, I am a bit torn on the topic myself, too. While I agree that the director is usually the person with the most artistic influence on the final movie (which is so much more than just a story) and definitely deserves credit for that (in the end Auteur Theory didn't emerge out of nothing), the director-centric view of modern culture (maybe largely influenced by Auteur Theory and its decendents) sometimes tends to be exaggerated too much, in my opinion, especially when the screenwriter gets forgotten in discussions about a movie's plot. Film-making is a collaborative effort and the director is by far not the only major contributor, even if maybe the most important one.

But so much to the artisitic aspect of this whole question. With movies usually being industrial products there is however also a legal and economical aspect, which might not be any easier to answer, but nevertheless should have a more definite answer due to the more uncompromising nature of law.
Given that it is indeed usually the producers or the studio that give their money for the realization of the movie they in the end carry the financial responsibility of it and deserve to be called the "owners" of the movie in an economical sense, I guess (and are also the ones who sack the Academy Award for Best Picture for that matter).
Though, copyright law is another legal aspect that needs to be considered, and which can vary from country to country. For example Wikipedia says that under the influence of the afore mentioned Auteur Theory:

In law, the film is treated as a work of art, and the auteur, as the creator of the film, is the original copyright holder. Under European Union law, the film director is considered the author or one of the authors of a film.

But I have a strong feeling that this whole matter of copyright laws and legal ownership is far more intricate and needs to be investigated further. But suffice for now to say that there is both an aritistic/creative aspect of ownership as well as a legal/economic one and they both might not always walk hand in hand.

All in all the whole matter of "whose picture it is" can most probably not always be answered in a clear or definite way and might even vary from movie to movie. Yet, I think modern culture seems to largely agree that the director is generally more important than the screenwriter, however correct that might be to you or to reality.
Comment: Man, I am continually finding myself slightly at awe of your expertise. Wiki-based or not.
Comment: @CGCampbell Thank you, but to be honest it is really just a single Wikipedia article that I read some time ago and that sprang to my mind when this question appeared.
Comment: To all, I've changed this to my accepted answer. While the original one was an answer, I beleive that Napoleon's interpretation of what he read to be more so. He also brings in the "legal" and "copyright" views. Personally, I am strongly of the opinion that the current world wide consternation et. al. copyright and their violations is dooming creativity, instead of helping to protect it.
Answer: The general idea is that:
Theater is the writer's medium.
TV is a producer's medium.
Cinema is a director's medium.
Each of these general idea's come from who is being billed as the "storyteller" of a particular piece.

Whose picture is it anyway?


Nginx and php-fpm trouble again

Question: Dears
I try to deploy wordpress on amazon ec2, I am facing the trouble on nginx and php-fpm, thanks for your help in advance.
I got the error as the following when nginx and php-fpm are running.
[error] 16282#0: *1 FastCGI sent in stderr: "Primary script unknown" while reading response header from upstream,

But if I stop php-fpm, and use "php-cgi -b 9000" instead, it works fine.
I have another question is how to debug the issue on nginx and php-fpm, it throws little error message in the log files even I set log level to debug or info.
Looking forward to get your response. Thanks a lot.
The following is my configue files.
/etc/nginx/conf.d/default.conf
server {
    listen       80;
    server_name  127.0.0.1;
    root /usr/www/ROOT/wordpress;

    #charset koi8-r;
    #access_log  /var/log/nginx/log/host.access.log  main;

    #location ~ \.(htm|html|gif|jpg|jpeg|png|bmp|ico|css|js|txt)$ {
    #    root /usr/www/ROOT/wordpress;
    #    expires 24h;
    #}

    location / {
    #    root   /usr/www/ROOT/wordpress;
        index  index.php index.html index.htm;
    }

    #error_page  404              /404.html;

    # redirect server error pages to the static page /50x.html
    #
    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
    #    root   /usr/share/nginx/html;
    }

    # proxy the PHP scripts to Apache listening on 127.0.0.1:80
    #
    #location ~ \.php$ {
    #    proxy_pass   http://127.0.0.1;
    #}

    #location / {
    #   proxy_pass http://127.0.0.1:8080;
    #}

    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
    #
    location ~ \.php$ {
        #root   /usr/www/ROOT/wordpress;
    fastcgi_pass   127.0.0.1:9000;
        fastcgi_intercept_errors on;
    fastcgi_index  index.php;
        fastcgi_param  SCRIPT_FILENAME $document_root$fastcgi_script_name;
        #fastcgi_param  SCRIPT_FILENAME /usr/www/ROOT/wordpress$fastcgi_script_name;
    #fastcgi_param SCRIPT_FILENAME $request_filename;
    include        fastcgi_params;
    }

    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one
    #
    #location ~ /\.ht {
    #    deny  all;
    #}
}

part of the config in /etc/php-fpm.d/www.conf
; Start a new pool named 'www'.
[www]

; The address on which to accept FastCGI requests.
; Valid syntaxes are:
;   'ip.add.re.ss:port'    - to listen on a TCP socket to a specific address on
;                            a specific port;
;   'port'                 - to listen on a TCP socket to all addresses on a
;                            specific port;
;   '/path/to/unix/socket' - to listen on a unix socket.
; Note: This value is mandatory.
listen = 127.0.0.1:9000

; Set listen(2) backlog. A value of '-1' means unlimited.
; Default Value: -1
;listen.backlog = -1

; List of ipv4 addresses of FastCGI clients which are allowed to connect.
; Equivalent to the FCGI_WEB_SERVER_ADDRS environment variable in the original
; PHP FCGI (5.2.2+). Makes sense only with a tcp listening socket. Each address
; must be separated by a comma. If this value is left blank, connections will be
; accepted from any ip address.
; Default Value: any
listen.allowed_clients = 127.0.0.1

; Set permissions for unix socket, if one is used. In Linux, read/write
; permissions must be set in order to allow connections from a web server. Many
; BSD-derived systems allow connections regardless of permissions.
; Default Values: user and group are set as the running user
;                 mode is set to 0660
;listen.owner = nobody
;listen.group = nobody
;listen.mode = 0660

; Unix user/group of processes
; Note: The user is mandatory. If the group is not set, the default user's group
;       will be used.
; RPM: apache Choosed to be able to access some dir as httpd
user = apache
; RPM: Keep a group allowed to write in log dir.
group = apache

Comment: I have a feeling that you have SCRIPT_FILENAME declared in fastcgi_params file as well and it doesn't point to the right location. Or `apache` user does not have permissions to access those files. Try using runusuer and run `php-cgi -b 9000` as `apache`.
Comment: Are the parent directories of your directory readable and traversable?
Comment: Thank a lot for your response, very kind of you. I tried to run php-cgi as apache, it works again. And it did not declare SCRIPT_FILENAME in fastcgi_params file, the file is the default one.
Comment: To Michael: Thanks. I have rudely run "chmod 777 -R" to the root of wordpress directory.
Answer: You are defining the extra fastcgi_param lines before including fastcgi_params file. This means that fastcgi_params defines will override the ones you define here.
So, move include fastcgi_params before fastcgi_param lines.
Comment: Thanks. I tried your way, but it did not work. It works if I use "php-cgi -b 9000".... So I guess the issue is on php-fpm side.

Nginx and php-fpm trouble again


Why does boiler need minimal demand before heating water?

Question: If I turn my kitchen tap on hot to a gentle stream, the boiler doesn't turn on to heat the water at all. It will stay cold forever. It's only when I unleash a jet wash torrent of gushing water out of the tap that the boiler finally turns on and begins making the water hot. If I turn the tap pressure down below a certain threshold after it's heated up, it will turn cold again even though it's still running. Why is this?
Comment: What type of boiler?  Sounds like a boiler that only serves that tap(instant hot water type).  State the make/model in your question.  Imagine there is some adjustment for it.
Answer: Some instant or on-demand water heaters have the ability to vary their firing rate according to the amount of water flowing through. In other words, they can modulate the amount of gas they burn or the amount of electricity they pass to a heating element. This allows the heater to approximately maintain a set discharge temperature across a range of flow rates (gallons or liters per minute). Others do not have this ability; they're either full-off or full-on. This latter kind gives hotter water when the flow is low and cooler water when the flow is high.
The variable-firing heaters aren't perfect, though. They switch on with some minimum amount of gas burning (or electricity flowing). While in theory we could engineer a heater to be continuously variable all the way down to zero, in practice that would definitely increase cost and would likely reduce reliability.
Both the variable and the fixed-firing rate heaters have a "minimum flow" threshold: they require a certain volume of water to be flowing before they'll turn on any heat at all. This is a protection for both the heater itself and for the people who will use the hot water. The minimum flow guarantees that the heater will not activate when there is zero flow, potentially resulting in a steam explosion. It also guarantees that the heater will not activate when the flow is too low for the minimum firing rate, which would release excessively hot water with the potential to scald or burn the user.
Comment: It sounds like I must have exactly a variable-firing heater. The water is hottest on maximum flow, and gets colder as the flow rate decreases, but there's a clear point at which it drops from significant heat to no heating at all.
Comment: I think they set the heat to kick on at a minimum level for two reasons. One is that inefficiency would be quite high at low volumes. The other is the 'single handle problem' where single handle faucets get turned on for cold but not fully cold, so they still request a tiny bit of hot. There's no reason to fire up a boiler in that scenario.
Comment: Might also be wise that the low flow of a dripping tap does not cause the boiler to fire 24/7


Trouble with the sudo dd command

Question: I've been having trouble writing an image to my usb, heres the thing i tried:
<code>/home/josho/Downloads# sudo dd if=antergos-minimal-2016.11.20-x86_64.iso of=dev/sdb bs=1M
dd: failed to open 'dev/sdb': No such file or directory
</code>can anyone tell me what's wrong? would be appreciated <3
Answer: You are missing a / before dev in your command
<code>sudo dd if=antergos-minimal-2016.11.20-x86_64.iso of=/dev/sdb bs=1M
</code>
The command you posted tries to write to /home/josho/Downloads/dev/sdb which does not exist.
Answer: dd is a very powerful but also very dangerous tool. It does what you tell it to do without any questions. So if you tell it to wipe the family pictures ... and it is a minor typing error away. I have tried to help more than one user at the Ubuntu Forums after dd had acted 'data destroyer'.
So I made mkusb in order to wrap a 'safety belt' around dd, to help you install iso files and compressed image files into USB pendrives and memory cards in a safe way. The connected drives will be displayed so that it will be easy to identify the target drive, and there is a final checkpoint, where you can double-check, that you will write to the correct target drive.
See the following link, help.ubuntu.com/community/mkusb and the mkusb quick start manual.

Trouble with the sudo dd command


Was the woman who visited Angela Eragon's mother?

Question: In Eragon, a woman was able to talk to Solembum, the werecat. I remember there being a suspicion that it might have been Eragon's mother, but I don't remember if the fact was confirmed either in later books or other words.
Comment: Don't really remember it now. But I think the woman's name was same as Eragon's mother.
Comment: Yes, that is the case, confirmed by my reading another 3 pages beyond asking this question...
Answer: There is some considerable evidence that it is indeed his mother. First of all:

The woman's name is Selena, which is the same as Eragon's mother.
The timing seems to be coincident with Selena's visit to give birth to Eragon, from the vague time references made.
The woman was extremely sorry. No doubt Eragon's mother would be in the same situation.
Answer: While there is some evidence that she is, Christopher Paolini will stay not say so outright.
When asked this very question in his recent Reddit AMA, Christopher Paolini skirted the question, possibly implying that there might be more to the story.

Was the woman Angela talks about in Eragon as having been able to talk to Solembum Eragon's mother?
  Could have been.
(Source)


Can I set non-full stop ISO values on my D3400?

Question: I recently got into photography and use a Nikon D3400. I have started shooting in Aperture Priority and Manual modes about 2 weeks ago and I noticed something strange regarding the ISO. When I am manually setting it, it starts from 100 and then the values keep doubling. If I switch over to Auto mode however, I get photos with odd ISO values, like 360. Is it at all possible for me to set an ISO value, for example between 400 and 800? If not, why does Auto mode seem to have more control over the ISO than the other modes?
Answer:
Is it at all possible for me to set an ISO value, for example between 400 and 800?

Not on the D3400. It is on higher end cameras.

If not, why does Auto mode seem to have more control over the ISO than the other modes?

Because Nikon decided to implement it this way. The are two arguments for this, both of which are probably somewhat true:

The D3400 is an entry-level camera and as such it makes sense to keep the available options as small as possible. More options give more settings for beginners to mess up.
Restricting the D3400 to only full stop ISO settings gives another way for Nikon to differentiate between their low end and high end models without fundamentally changing the hardware. Therefore they make more profit.

(For avoidance of doubt, this isn't an anti-Nikon rant; Canon definitely do the same thing, Fujifilm do something similar with shutter speeds and I suspect other brands do the same as well).
Comment: For what it's worth, my Fuji X100s also sets automatic exposure times which aren't available manually with 1/3 stops increments. (e.g. 1/70s or 1/105s).
Comment: it's also not really useful or needed. you can easily correct an image's exposure by a factor of 2-4, so a factor of 1.5 in ISO is without consequence (and nearly rounding error for the camera)
Comment: I have a Nikon D500 (very high end apsc from nikon) but I doesn't found that option to set ISO values to something like 282 or 734 (and yes I have photos in autoISO with such kind of strange values)
Comment: @Horitsu But you can set third stop ISOs on your D500. As Aganju points out,  any more than that is definitely beyond the realms of "necessary". I'd put money on those odd ISO values being from mobile phones.
Comment: @PhilipKendall Nope that are real ISO values from my D500. So where is my money? ;)