What is the function of a Fourier Series?

Question: What is a Fourier Series?  What it is used for?
Answer: The Fourier series:
\$ V_t = \dfrac{a_0}{2} +    \displaystyle \sum_{i=1}^{\infty}[a_i sin(i \omega_0 t) + b_i cos(i \omega_0 t) ]  \$
The term \$\dfrac{a_0}{2}\$ is a constant, that's the DC level. It could also have been written without dividing by two, but this is the convention. The terms of the infinite sum are the sum of a weighted sine and a weighted cosine with the same frequency. If you would draw these as phasors in the complex Argand plane you'd see that the result is again a sine, but with a different amplitude, and phase shifted. Therefore the equation can also be written as
\$ V_t = \dfrac{a_0}{2} + \displaystyle \sum_{i=1}^{\infty}[a_i sin(i \omega_0 t + \phi_i) ]  \$
So we have the sum of sines, all multiple frequencies of a fundamental frequency \$\omega_0\$, each of them with its own amplitude and phase.
Fourier proved that you can describe every repetitive function this way. Sometimes the series is infinite, sometimes it has a finite number of terms. Sometimes terms are missing, which means their amplitude is zero.
One of the best known Fourier series is that of a square wave:
\$ V_t = \displaystyle \sum_{i=1}^{\infty}\left[\dfrac{sin((2i - 1) \omega_0 t)}{2i - 1} \right]  \$
or, expanded:
\$ V_t = sin(\omega_0 t) + \dfrac{1}{3} sin(3 \omega_0 t) + \dfrac{1}{5} sin(5 \omega_0 t) + \dfrac{1}{7} sin(7 \omega_0 t) + ...\$
So this is such a series with missing terms: a square wave has no even harmonics. The following image shows what it looks like in the time domain:

The top drawing shows the sum of the first two terms, then a third and at the bottom a fourth term is added. Each added term will bring the waveform closer to a square wave, and you'll need the limit of the series to infinity to get a perfect square wave.
Sometimes it's difficult to see the fundamental sine in it. Take for instance the sum of a 3Hz sine and a 4Hz sine. The resulting waveform will repeat once every second, that's 1Hz. The 1Hz is the fundamental, even if its amplitude is zero. The series can be written as
\$ V_t = 0 \cdot sin(\omega_0 t) + 0 \cdot sin(2 \omega_0 t) + sin(3 \omega_0 t) + sin(4 \omega_0 t)\$
All the following terms also have zero amplitude.
Comment: There are lots of \$t\$'s missing in the equations in this answer.
Comment: @Dilip - Oops, right. Fixed.
Answer: Every realizable analog signal, anything you can think of or draw legitimately on a voltage vs. time graph can be expressed in mathematical terms as the sum of an infinite number of sine waves of different frequencies - something of this form:
any_signal(t) = A*sin(f1*t) + B*sin(f2*t) + C*sin(f3*t) ....
Different signals are constructed by changing the values of A, B, C etc and f1, f2 and others.
When someone refers to a Fourier series they refer to expressing the waveform as a series of addition operations like above.
Realistically every analog signal has SOME content at every frequency - even if the amplitude is .1e-67 it's still there.  Ideally this isn't so - if I construct a pure square wave then I know for a fact it consists ONLY of frequencies that are an odd multiple of its period.  Thus 1Hz square wave is the sum of a 1Hz sine wave plus a 3Hz sine wave and so on down the line.  For other well-known waveforms such as triangle waves, and ramps people have done the calculations as to what frequencies are present and at what content.
Comment: You can take the Fourier transform of a non-periodic signal - but where the Fourier transform of a periodic signal consists only of discrete multiples of the base frequency the Fourier transform of a transient signal is continuous in the frequency domain - all frequencies have some content.
Comment: not quite any analog signal, the signal has to be periodic in nature (or you have to confine your analysis to a section of the signal which is periodic).  Your also not limited to analog signals and I would imagine that most fourier transforms today are performed on sampled (discrete) data, that is a DFT is performed rather than a 'normal' Fourier Transform.
Comment: I think he was just trying to make the point to specifically analyze a periodic signal you compute its fourier series, but a general fourier transform handles any signal. The OP was asking about fourier series. Just a note to clear it up.
Comment: True true, there is a distinction that can be made there.  I always thought of series referred to the fact that it was an infinite series of additions.
Comment: a Fourier transform is an amplitude density function in units of amplitude per Hz (or per rad/s). `F(w0) = A` doesn't mean the signal has a term `A*exp(j*w0*t)`. Instead you have to integrate over a spectral band to compute the corresponding time-domain function. As the bandwidth shrinks to 0, the time-domain value becomes infinitesimal -- unless the spectral band contains a delta function. In general you have an uncountably infinite (it can't be indexed) sum of infinitesimal amplitude sinusoids.
Comment: Two problems with your description.  First as others have already said, you really should point out that a Fourier series is for *repeating* signals.  Second, your equation is incorrect as it leaves out the phase offsets.
Comment: "When someone refers to a Fourier series they refer to expressing the waveform as a series of addition operations like above." is not quite correct. The *Fourier series* refers specifically to the situation where all of the frequencies are multiples of a given fundamental frequency.
Answer: The Fourier Series is a means of expressing a periodic waveform as the (possibly infinite) sum of 'harmonic' sinusoidal waveforms.
It is also used to express a signal on a bounded (compact) time interval as the infinite sum of sinusoidal waveforms.
Essentially, by establishing the relationship between a signal in the time domain (that is, a signal expressed as a function of time) and an equivalent signal in the frequency domain (that is, the signal expressed as a function of frequency), the Fourier Series enables the harmonic analysis of signals and systems, which is the basis of radio transmission theory, coding theory, control theory, quantum theory and many other very useful areas of engineering.
Whilst the Fourier series expression of signals seem more complicated at first, involving complex expressions and 'infinite sums', as a mathematical tool, they enable engineers to solve problems which can not be solved using closed-form expressions.
Put simply, it is sometimes useful to express variation in space and/or time as a variation in frequency and phase. Particularly for periodic variations. But even when the variation is not periodic, provided the variation is confined to some interval in space and/or time, it will also be confined to a corresponding interval (bandwidth) in frequency.
Application of Fourier Series has been instrumental in understanding channel bandwidth for communications systems, developing image compression algorithms and improving electrical power distribution system reliability.
Comment: I thank you very much if you suggest some readable references to realize your last paragraph "Application of Fourier Series has been instrumental in understanding channel bandwidth for communications systems ..." for me whose major is pure mathematics.
Answer: To add some practicality to the above comments, the Fourier time-domain series can be decomposed into it's frequency-domain components via algorithms such as FFT (Fast Fourier Transform) and DFT (Discrete Fourier Transform). One important practical result of being able to apply the algorithms is that in R&D and lab-testing, we often want to measure the spectral purity of signals against a noise floor (e.g. SNR or Spurious Free Dynamic Range) to see how pure or often, undistorted, our signal content is.  If we have a time domain output (such as a DA converter would process), we can't ascertain these values by just looking at the time domain response, so often on the simulation side, we will use a DFT module in order to transform the time domain signal into the spectral (frequency) domain. In lab, on an Oscilloscope, we need to have some tool that can look at the spectral properties (typically we use spectrum analyzers). The heart of these tools depends upon Fourier analysis and spectral decomposition methods. So there you have a practical reason about why Fourier analysis is important in EE.


What is the difference between Canon TS-E 24mm f/3.5L II and I?

Question: What are the major differences between version I and II of Canon 24mm tilt shift lens? Right now, used version I is half the price of II.
Answer: The biggest operational difference is that version II has a super-rotator style design that allows the tilt and shift axis to be varied at any point relative to each other. Version I allowed the tilt and shift axes to be either aligned or set at 90 degrees to each other, and changing between the two settings required partially dismantling the lens! With version II there's just a knob to control the relative angles of tilt and shift.
The other main difference is the optics, version one of the 24mm tilt shift is 22 years old now and the new version was designed for digital and features a more sophisticated design (16 elements vs 11), with  modern coatings which bring a host of optical improvements. Extreme corners feature much improved contrast and sharpness, with less lateral chromatic aberration.
Alongside corner improvements the image circle is significantly larger (67.2mm compared to 58.6mm) allowing greater shifts and reduced vignetting. Maximum tilt is increased marginally to 8.5 degrees from 8. There is also a switch on the lens to lock tilt in the neutral position if you only want to shift.
You'll notice the differences if you do a lot of shifts. If you're mostly using the tilt function then version I is a good buy, though you might want to consider the Samyang 24mm tilt-shift which is a similar price but offers a super-rotator design. Performance is pretty bad wide open, but if you intend on using the lens to extend depth of field then it may perform better than the old Canon in the corners at f/8.
Comment: Have you seen a few of the early reviews for the Samyang/Rokinon/Bower/Pro-Optic/Walimax/whatever other name it is being sold as? It is dreadfully soft in the center, not to mention the corners, until stopped down past f/5.6.
Comment: @MichaelClark I saw the very first samples (which I attributed to operator error as they were so bad) and the largely inconclusive first review on lensrentals. Now I've read thedigitalpicture review which agrees with the trend that it is terrible wide open. It may still beat the old Canon in the corners when stopped down as it does have a larger image circle...
Comment: AT f/5.6 the Canon is still a bit sharper in the corners. By f/8 the Samyang is *barely* sharper than the original Canon. But below f/5.6 the Samyang doesn't look usable to me. Especially with the *TS rotate*, there a myriads of ways to use the lens that require wider apertures to tailor the shape of the plane of focus. http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=841&Camera=453&Sample=0&FLI=0&API=2&LensComp=347&CameraComp=453&SampleComp=0&FLIComp=0&APIComp=2
Comment: I think that's unshifted though, want I want to see is the version I Canon fully shifted vs. the Samyang shifted the same amount to compare how quickly sharpness drops off when shifted. Still would have expected a bit more from Samyang given the reputation of their other lenses, this one seems over stretched.
Comment: I've seen charts with the Samyang shifted, but not the old Canon.
Comment: Are you sure the Samyang has super-rotator capability? It can rotate up to 90º between the mount and the shift mechanism, but based on all I've read it does not appear to have the capability to rotate between the shift movement and the tilt movement the way the TS-E 17mm f/4 L and TS-E 24mm f/3.5 L II can.
Comment: @MichaelClark I've not used the lens but all reports are that it can rotate between tilt and shift, from BHPhoto: *"To make the tilt-shift function even more seamless, both the lens mount as well as Tilt-Shift section may be rotated along the optical axis. The tilt-shift section can be rotated left by 90° (with 30° click-stop adjustment), while the lens mount may be rotated both in left and right direction by 90°, also with 30° adjustment."*
Answer: The most significant difference is the ability of the TS-E 24mm f/3.5 L II to do TS rotation. This means that the relationship between the tilt axis and the shift axis can be altered from between 90º and 0º and any point in between. This can be accomplished on the fly during normal use of the lens. The original TS-E 24mm f/3.5 L can only be set at either 90º (standard orientation when the lens comes out of the factory) or 0º between the tilt and shift axes, and requires that the lens be partially disassembled to change the angle. This feature vastly expands the possibilities of how tilt and shift may both be used in combination to affect the perspective of an image. If you are interested in taking photos that only require either tilt or shift, but not both, then this feature is not much of a factor. If, on the other hand, you are interesting in discovering the full creative possibilities of a perspective control lens, then it is revolutionary.
The review of the TS-E 24mm f/3.5 L II at The-Digital-Picture includes many comparisons to the original TS-E 24mm f/3.5 L it replaced in Canon's line up.
As the linked review above relates, the "II" version is also superior optically, especially in terms of sharpness and lack of chromatic aberration. If you look at the sample images the review provides, you can see that the differences are more than trivial - they are rather significant.


Do you need multiple wallets to manage your cryptocurrencies?

Question: I was wondering those who have many different coins, do they need multiple wallets? or one wallet with that supports different coins is enough.
Answer: Almost every coin has its own infrastructure, so yes, you will need another wallet for almost every altcoin.
Luckily, there have been some people who invented hardware wallets which simplify the process.
Meaning you can hold multiple altcoins in this one program. They still have their own wallet, but is just much more user friendly.
See,
These wallets are both open source, and you are the only one who has acces to your private key, which means that these are pretty secure.
https://coinomi.com/

Supported Coins (64!!): BTC, ABN, AC, AUR, BTA, BELA, XBC, BLK, BRIT, CDN, CCN, CLAM, CLUB, COMP, DASH, DGB, DOGE, DGC, EDR, EFL, EMC2, ETH, ETC, EXP, FTC, GAME, GCR, GRC, NLG, INSN, IOP, JUM, LDCN, LBRY, LTC, MONA, XMY, NMC, NAV, NEOS, NVC, USNBT, NSR, OK, PKB, PPC, PSB, PIVX, POSW, POT, RDD, RICHX, RBY, SDC, SMLY, SLR, STRAT, SYS, UNO, XVG, VRT, VASH, ZEC, XZC

https://jaxx.io/

Supported coins (12): BTC, LTC, ETH, DASH (not on iOS), ETC, REP, ZEC (not on iOS), DOGE, ICN, GNT, GNO, DGD


flashing my a3900 lenovo mobile

Question: please house help me I can't flash my lenovo a3900 phone because it can't connect to my Laptop using the usb cable and it keeps hanging and showing "no command" MY usb cable works perfectly.
Comment: You're in recovery mode - stock recovery to be exact - it's not supposed to be responding to anything in the first place.
Answer: Since you didn't provide infos about the platform, I assume its the Mediatek version.
To flash this phone you'll need SP Flashtool and ROM file with scatter. You'll also need USB drivers which make it possible for your device to communicate with the computer. The phone needs to be connected in Preloader mode.

Downloaded SP Flashtool
Download MTK USB drivers
Download the Firmware

flashing my a3900 lenovo mobile


Is it a good idea to have your main actions as swipe gestures?

Question: Would it be a good idea to have swipe gestures (such as swipe left to delete and swipe right to archive - mailbox app is a good example) responsible for your app's main tasks? A lot of not so techy people also use handheld tablets these days. Although I plan on adding an introduction to make sure users are introduced to swipes quite early, I am not sure if users will be able to remember them coming back to app after say 10 days.
Comment: It's not possible to answer this question in a general sense.  Sometimes it's a good choice, and other times it's a poor choice.
Comment: Case study about gestures in UI http://www.fastcodesign.com/1673082/googles-new-phone-a-lesson-in-the-dangers-of-gesture-heavy-uis
Comment: @JohnGB In my Case, there are chances of users returning to this app after 5 - 10 days, given the functionality this app provides. If you look it in this context all the answers provided below make sense and I decided to not have swipe gestures responsible for performing main tasks in my app.
Answer: There's a lot apps with swipe gestures, like Clear, Twitter, Tweetbot, Mailbox and other, but from practice, I could say, that these actions are not very obvious and user have some problems with them.
Examples
Clear

Mailbox

Recommendations
So the best 2 recommendations are:
Provide walkthroughs (tour) about gestures on first time app launch (see Readtime or Limelight) and provide help button on every screen.

Dublicate actions with buttons (see Facebook app)
Answer: I'd say for mailbox app left and right swipe gestures are more natural for previous-next mail navigation. Delete and archive rather secondary actions.
Swipe navigation also could be familiar to the users, because it is used in others apps in a such way.
The easiest way to be more confident of your choice it to explore some competitors' apps.
Answer: With the exception of swipe as a scrolling action, swiping is one of the most non-discoverable user interfaces ever created.  As a user, you have no way to know what swipe gestures are going to do unless you just start trying random swipes (or someone else tells you what they do).  To make things worse, sometimes swiping with different numbers of fingers does different things.  It's a usability nightmare.
Having any form of swipe perform a destructive action (such as delete) is a terrible idea.  The first time a user encounters it, they will have no idea what they've done and most likely no idea how to undo the action.
An alternative could be to use a context menu when the user touches & holds (like Open in New Tab for links in Safari).  But a lot of users don't know about that either.
Overall, I think it's better if essential functionality is available through visible screen elements.
Answer: Swiping for actions is now built in to iOS 7.   For example, the iOS7 Mail app allows user to swipe and pres "More" for actions.
Comment: Those swipe gestures are for bringing up action menus, not necessarily doing the actions, which is what the question is about.


Voltage induced in high-tension magneto ignition system

Question: Why is there no voltage induced into the secondary winding (in high-voltage step-up transformer) when the ignition switch is closed (OFF).
When the current flows in the primary winding of the coil a magnetic field is generated. This interacts with the flux from the magnet. Assuming that the ignition switch is closed, the flow of alternating current created by the interaction of the two magnetic fields will flow to the ground. Will the flow of alternating current in the primary (while the ignition switch is closed, OFF position) induce a current in the secondary? If it does not, why not?
Comment: Can you edit to make it relate to aviation a little more please?  As it currently stands it might get a better response on EE.SE
Answer: I assume you're talking about an aircraft mag.  Mags are never really OFF off.  Instead of ON/OFF, it's more like ON, and "on but not on enough to work".
With the ignition switch OFF, grounding out the primary, the alternating current generated in the primary as the mag spins flows to ground, and it does induce a voltage in the secondary as the current alternates, but this voltage is much too low to be able to jump a plug gap.  So the mag is effectively off if not totally off.
To get a spark, the flow of alternating current in the primary needs to be fully cut off by the opening of the points within the primary to create a field collapse strong enough to generate sufficient high voltage to be induced in the secondary.
Comment: It makes perfect sense.
The amount of the voltage induced in the primary coil is determined by the rate at which the flux changes (as well as the number of turn of wires in the coil), therefore a collapse of the magnetic field provided by opening points will result in a high induced current.
If a reciprocating engine were to run at extremely high RPM, would it provide a rate of flux change high enough to induce a high voltage in the secondary if the ignition switch were to be closed - OFF position?
Comment: Perhaps but I'm guessing the RPM would have to be extreme and the mag would blow up anyway lol.
Comment: @Simone I doubt you could turn a piston engine fast enough for the magneto to still make a spark when the switch is off.  For the alternation to emulate the collapse time from points opening the engine would need to turn twenty or more times normal operating speed -- call it 50,000 RPM.  There'd be nothing left of the engine by the time you got the propeller hub turning that fast.


Why do some AFBs have planes parked at 45 degrees to others?

Question:
I'm assuming this is just a matter of available space but it seems you could get 4 across all aligned but maybe there is another reason. The image is from McGuire AFB but I've seen this on other AFBs.
Comment: Because that's how the lines are drawn on the ground.
Comment: It's for good luck! (Just kidding.) Aren't the 45° spots closer to the taxiway and would be for confining the wings, as you've noted, for available space? Perhaps there's more to it, can you show us other examples? Thanks.
Comment: To protect them from Japanese saboteurs.
Comment: I see it at Beale AFB, Tinker AFB, March AFB and Albuquerque Airport. There seems to be a lot of various layouts for fighters and tankers/cargo. Some are all aligned while some are all at 45s, but there are a few mixed and I'm just not sure why.
Comment: Look at the spacing of the planes.  The angled ones are closer to their neighbors.  But if you did them all that way you wouldn't be able to get them as close.
Answer: McGuire AFB being an Air Mobility Command (AMC) base, accounts for the very large C-5 Galaxy when it visits. It may not seem like it, but the 68 m (220 ft) wide C-5 when parked at a 45-degree angle saves ~20 m (65 ft) -- approx. one-third of its wingspan.
The reference used by the USAF is AFMAN 32-1084 (PDF), from which:

126.96.36.199.1. Parking Dimensions. Table 2.9 presents the minimum geometric criteria for fixed-wing apron design. When designing new aprons for AMC bases hosting C- 5, C-17, KC-10, and KC-135 aircraft, provide 15.3 m (50 ft) of wingtip separation.
EXCEPTION: When you are rehabilitating an existing apron, provide the maximum wingtip separation the existing apron size allows (up to 15.3 m [50 ft] but not less than 7.7 m [25 ft]). This additional separation is both desirable and permitted.

By applying that to the C-5 and adding the clearance to the taxiway, those angled spots are a perfect fit:

The measurement above (~83 m) shows two half-span C-5s (68 m) plus the clearance (15.3 m), with superimposed C-5s via pinterest.com

For the other examples you've stated in a comment: Beale AFB and Albuquerque Airport, Tinker AFB, and March AFB -- in that order:

The parking spots are between two taxiways, so it's the same reason as the main example. It also makes parking and taxiing out easier.

Those by the hangar are for ease of taxiing out instead of a hard left and potential for collision.

Plenty of space. I couldn't find a 45-degree parking.

(All imagery is via Google Earth)
Comment: Thanks for the info. I was also looking at Barksdale AFB, and in the google maps view there are 5 "rows" of B-52s, but only one of the rows has a plane at 45 degrees by the taxi line while 3 of the others do not. For Tinker AFB, the apron on the west side has the weird layout. For March, there is a C17 at a non-45 on the south side, but still at a weird angle compared to the others.
Comment: @WilliamTaft: For Barksdale, I checked the historic imagery, and [from Oct 2016 for example](https://i.stack.imgur.com/BiG7Q.jpg), the same B-52 location is used normally in line with the painted markings. Perhaps the current imagery the plane was being moved, or not yet moved into the final position. As for the March C-17, the apron is narrower there, and all the adjacent spots are also tilted, so it's for the same reason (making space).
Comment: Likewise for Tinker, because of the weird layout of *the apron itself.* Planes kept getting bigger, so they had to adapt the apron to make the best use of the available space.
Comment: If you look at the OPs image from McGuire, there appears to be plenty of wing-tip room to rotate the planes from 315° to 270°. However, for those planes that are parked at 315°, they would have a much sharper turn to make it to the 90° direction on taxi-out if they were parked facing 270° and that may not be a turn they'd be able to make. I do agree with your assessment of the images you posted, though.
Comment: @FreeMan: see now ;)
Comment: @ymb1 Smart alek! My Mk. I eyeball is never wrong!!!  :D


Should we close one of these questions about whether $\frac{1}{\infty}=0$ as a duplicate of the other?

Question: This question and this question are both asking about $\frac{1}{\infty}=0$, though the first one is specifically asking about interpreting it in the context of probability. Should one of these questions be closed as a duplicate? Or, should someone post an all-encompassing question (and answer) about this topic, so that others can be closed as a duplicate of it? If so, who's up for it?
Answer: These $\frac{1}{\infty}$ questions are annoying. Luckily, they are not terribly frequent, and the OP has found a variant.  My inclination is to interpret "duplicate" quite narrowly, and not close.
Comment: I agree—I think the particular focus on probability in the first of the two links makes it a distinct enough question.


How does "Do It Yourself" deck creation work during character creation?

Question: I noticed in Chummer it allows you to set "Do It Yourself" when putting together a deck during character creation, but I can't find the rules regarding this aside from talking about hardware tests after creation. Are there any requirements or penalties for putting a deck together yourself during creation?
Comment: My answer is very tentative to the sort of information you want to find.  Could you elaborate just a little?
Comment: Also, I absolutely can't find a "do it yourself" thing in Chummer
Comment: I made a mistake--it looks like the only place this option is available is when upgrading your deck, the options under "Commlink Upgrade." The question stands, but it's more specific than I initially thought.
Comment: @Josh Well, that kind of undermine the question actually, as there is no "deck creation" existing option. Are you asking if it's possible to *upgrade* your commlink yourself at character creation?
Comment: @Scrollmaster That sounds about right, yes. I'm curious also to whether you _can_ build a custom commlink at creation or if you're required to purchase one of the basic commlinks.
Answer: There is no official rule about Build/Repair tests during chargen, but you don't need it to build a custom commlink
While building a commlink from scratch would require at least a shop to manufacture the plastic casing etc, you can buy a cheap commlink and improve it at will with hard and soft ware from the (black) market.
SR4A p.222 - Upgrading Devices:

If you are looking for more power in your device, you can upgrade its
  Matrix attributes. Upgrading a device is simply a matter of having the
  proper hardware module (for Response and Signal) or software package
  (for Firewall and System). Once you have the module or package, simply
  install it into the device, a matter of a few minutes' work. A device's ratings
  may only be upgraded by +2 with regards to their original ratings.
  Further improvements have no additional effect on performance.
  You do not have to upgrade all of a device's attributes at once, even
  if the device has a Device Rating. In this case, the device can no longer
  be considered a "common" device, and should have its attributes recorded
  separately.
  A device may have only one hardware module or software package
  for each attribute.
  Rules for building your own modules or coding your own packages
  can be found on p. 228.

Remember that you can't buy anything at chargen with availability greater than 12 (SR4A p.86 - Gear), so if you look at the device upgrading table, you can't start the game with a response or a signal above rating 5. So you might want to start with buying a commlink with a rating 3 for those attributes, like a Novatech Airware (SR4A p.328).
Note: Runners's Companion offers a new quality, Restricted Gear, that allows to buy a piece of gear with an availability up to 20, for the minor cost of 5BP. You might want to look it up, but I'll assume for simplicity's sake that you won't take it.
You can then buy (SR4A p.330) and install your software on your custom Airware. Remember that your base Response limits your System, so you won't need to buy a System with a rating 6 right now (though you could, and gather enough money during runs to buy a Response-4 commlink and upgrade it to 6, so you wouldn't have to buy two Systems with different ratings.) System is also a limit to every program you commlink runs, so don't bother buying a Firewall with a rating greater than your response too.
So your commlink is a :

Novatech Airware (1.500¥)
Upgraded Response-5 (5.000¥)
Upgraded Signal-5 (1.000¥)
Custom System-5 (2.500¥)
Custom Firewall-5 (2.500¥)

And no skill test is even necessary.
Now, if you have some hardware skill and a very cooperative GM, you can propose a house-rule :
Using Building Hardware and Coding Software tables (SR4A p.228), you can get duration of an average extended test (with the buying hits rule, SR4A p.62), multiply it by the cost of a day (lifestyle divided by 30) and spend that much money. By no means it is an official rule, I'm just writing it here while I'm discussing DIY gear during chargen.
Answer: I'm not terribly familiar with Chummer, and I'm pretty sure Deckers aren't in 4th ed of Shadowrun but there are tables for setting up your Commlink in the core book.  Presently I'm using the 20th Anniv. Corebook, which on pages 327-328 has the information you need to set up a Commlink which is essentially the Cyberdeck in 4e (nobody cough whilst saying "Smartphone").
The model of the commlink determines the Response and Signal where the OS determines the System (touched on page 222) and Firewall (A catch-all defensive stat).  The extras in the Accessory table on 328 could fill in more of your DIY needs for extras.


Possible to get physical keyboard layout for a on-screen keyboard?

Question: I'm currently working on a on-screen keyboard for a touchscreen app.
I wonder if anyone have experience on how the keyplacement shall look? (Unicode, on other languages like Japanese, Korean, Norwegian, Swedish etc) Finished layouts etc...
I found this info regarding layout/scancodes: http://www.quadibloc.com/comp/scan.htm
If I build a 101/102/106-keyboards after this layout, with scancode 3 range, will it look "correct" physically for most people? Even when someone earlier stated that it is 150 keyboard layouts out there gasp, so I guess it wouldn't please all.
Microsoft have their own layout lists here: http://msdn.microsoft.com/nb-no/bb964651
The U+xxxx is virtualcodes, are there any tables like U+0031 (number 1) is the [x,y] -> [1, 0] position in a keyboard?
Thanks for any suggestion/help!
Answer: I'm from Israel, and I can help you with Hebrew lay-out if you need it. But that Microsoft site you posted looks pretty much enough
Answer: Do consult with locals on how the keyboard actually works. I've seen some where the thing printed on the right-hand side works with the right alt or with some other odd key. If you get that wrong the user is going to be very confused still.


Yerkes-Dodson Law and Drugs

Question: According to the Yerkes-Dodson Law, there is optimal point of arousal and performance. Suppose a person takes a stimulant such as Adderall. This would increase his arousal. However, it may increase his anxiety (e.g. side effects). Would combining a "downer" (such as alcohol) with an "upper" (such as Adderall) maximize productivity? This is assuming that at a baseline level, a person cannot maximize his productivity.
Answer: I think in this case, you should look at 2 graphs of optimal performance. So one inverted bell curve (Yerkes-Dodson Law)for the stimulant, and another for the 'downer'. So in this case, each has their own optimal productivity, and an interaction of the 2 isn't just a simple combination, because this would be a third graph altogether. So unless there is something you know of the exact interation effect of the particular stimulant, and particular depressant,I wouldn't risk mixing them for optimal productivity.

Yerkes-Dodson Law and Drugs


Active Directory - User cannot change password

Question: We are setting up a Windows Server 2008 R2 domain.  When we create a user within AD, the checkbox labeled "User cannot change password" in the Account tab is unchecked for every user we create.  Can this be changed so for each user we create this is checked by default?
Comment: Why do you not want users to be able to change their password? That goes against pretty much every security best practice.
Answer: To my knowledge this can't be set for a default for that tool.
However, you can set Group Policy so that users are disallowed from password changes at that level.
User Config -> Policies -> Administrative Templates -> System -> Ctrl+Alt+Del Options
There is a "Remove Change Password". There are some others scattered about, so look for them.
We're doing something similar. The reason for this is that we have a non-Microsoft password change procedure we've built, thanks to the need to synchronize password changes to multiple systems. If users change their AD password through native tools, their password won't get synced to other systems and they'll call the helpdesk when they can't get in. This also allowed us to put robust password quality rules in place before our underlying systems all supported it.
Answer: Perhaps another approach would be creating a user template account with "User cannot Change Password" enabled, and copying it for new users.
Answer: You can do this via code.  Take a look at the following MSDN article about half way down the page
"The following C# example shows a function that sets an ACE to deny a user the right to change their password. This example uses the managed ACL functionality available in .NET Framework 2.0."
http://msdn.microsoft.com/en-gb/library/ms180915.aspx


Difference between Data structure objects and cell array objects in matlab

Question: I want to know what are the differences between two data structures in MATLAB: Structure Arrays and Cell Array.
In what circumstances we can use each of them?
Comment: I think that this question might get a better answer at [Matlab forums](http://www.mathworks.com/matlabcentral/answers/index/).
Answer: Both structures and cell arrays are the most flexible data types built into matlab (as opposed to creating your own class), and that flexibility comes with a price - physical memory.
I'm not near a matlab-enabled machine, otherwise I would show you some examples; however, to get an idea of what I mean, create some data in matlab and then enter 'whos'. This will show you the memory usage of each data type. Cell arrays and structures are way more memory hungry than arrays, simply because you can combine different days types into a single variable (strings, booleans, numerics, etc.)
Now, to your question between cell arrays and structures, this is more of a question of preference in terms of writing, editing, and later understanding your code. I like structures because naming variable fields is easier to understand when multiple people are working on a project. Cell arrays take slightly more afterthought, because everything is based on a numeric index: what was cellData{:,2} again? It's easier with a structure: structData.address(:), oh ya those were addresses.
I'm a firm believer that matlab should be used so that it's as easy as possible to read and write. With bigger and more complicated projects, matlab itself becomes a bottleneck, and it would be better to write your code in another faster language.
Answer: As noted here, cell arrays and structs are both general enough to do the same things. However, one you access numerically (cell arrays) whereas the other you access fields by name (structs). In general, you choose the one that makes sense for readability. For example, if you want to loop through a bunch of things, probably put it in a cell array since the numeric indexing is convenient (though you can use structfun). If you want to store heterogeneous data in a convenient package to recall by name (such as different size matrices), then store it as a struct.


What's the meaning of 'bootstrapped' in this context?

Question: From the description of the game called Natural Selection 2: 'Choose to play as a bootstrapped Marine or a beastly alien in the action-packed battle for ultimate survival. Natural Selection 2 flawlessly combines a multiplayer first-person shooter with real-time strategy elements for a game that is addictive, immersive and exciting! The tightly designed shooting mechanics combined with intricate maps create a competitive challenge for all players.' The text comes from: http://www.humblebundle.com/
Comment: I wonder whether the copywriter got confused and really meant "[strapping](http://www.thefreedictionary.com/strapping)".
Comment: I have put here the whole game description, and the source, maybe then it would be easier to guess the meaning.
Answer: I'm familiar with this game so have some context. Since the game is about marines deployed on alien planets or infested human colonies, and the fight to survive, I think the use of 'bootstrapped' is meant to confer a sense of self reliance, or self initiative. The marines are in it alone and can only rely on themselves to survive.
Answer: Bootstrapped

Verb: To promote and develop by use of one's own initiative and work
without reliance on outside help
Adjective: Undertaken or accomplished with minimal outside help.

By these definitions, it sounds as if they're trying to say the soldier is an individual who 'does things on his own, without any outside help'.
It's an awkward construction to be sure, but given the context of it being a Marine in a video game, and it being a player character, them being 'all on their own' seems very likely.


Fusion drive suddenly not bootable: "Too few free segments", made read-only

Question: I've dealt with a lot of disk issues over the years admining lots of different OSs, but this one is new to me... help/ideas appreciated before I give up and restore!
Woke up this morning to my iMac (5K, 27", Late 2014, SSD + 3TB Fusion, OS X 10.11.3) having shut down overnight (no power issues elsewhere in the house, or on that outlet...). Rebooting a normal boot causes a shutdown before the graphical UI fires up.  Safe boot does the same thing. During a verbose boot, I saw that the boot drive wasn't able to be mounted and the system gives up, going into a clean shutdown.
So, I booted into Recovery and ran Disk Utility. The Fusion drive was grayed out but running First Aid on it found no problems with the CoreStorage or actual HFS volume. It refused to mount by hand in a Terminal window (even with the readOnly option).
Next I booted into single-user mode where I was able to capture these unusual messages:

The key here seems to be the 3rd line Too few free segments, mark MLV as readonly. I assume this is from the CoreStorage structure but Googling find very few references to phrases like this. It crossed my mind that it could be referring to the SSD as well, but I'm honestly not too familiar with their storage details. After that, you can see the journal replay fails due to "privilege violation" (presumably the read-only status). On normal or safe boots, this pushes the system into a clean shutdown since it can't mount the root volume read-write with the permissions issue and a dirty journal (see more below).
Interestingly, in single-user boot the drive is mounted read-only at / just fine. I've skimmed through the directories and nothing looks odd. Running fsck_cs and fsck_hfs by hand report no errors at all. But the drive fails to mount read-write at any point. From single-user, I was also able to look at the system.log, but no real clues there either. The last bits in the log look like typical sleep cycle messages.
In any case, the HFS volume is only ~60-70% full, as confirmed in single-user mode. Curiously, DU shows the volume as full when booted into Recovery, but I'm not sure I trust that since it clearly isn't booting the volume there (e.g., there's no breakdown on the drive space into file types... it's all "Other").
Booting from an external drive didn't give results much different from Recovery—the drive can't be mounted, even read-only. Here's the output from fsck_cs:
   Executing fsck_cs (version 517.20.1)
** Checking volume
** disk0s2: Scan for Volume Headers
** disk1s2: Scan for Volume Headers
** disk1s5: Scan for Volume Headers
** disk0s2: Scan for Disk Labels
** disk1s2: Scan for Disk Labels
** disk1s5: Scan for Disk Labels
** Logical Volume Group 56BA393B-9EF3-4BE6-8CA0-240920F97724 spans 3 devices
** disk0s2+disk1s2+disk1s5: Scan for Metadata Volume
** Logical Volume Group has a 210 MB Metadata Volume with double redundancy
** Start scanning metadata for a valid checkpoint
** Load and verify Segment Headers
** Load and verify Checkpoint Payload
** Load and verify Transaction Segment
** Incorporate 0 newer non-checkpoint transactions
** Load and verify Virtual Address Table
** Load and verify Segment Usage Table
** Load and verify Metadata Superblock
** Load and verify Logical Volumes B-Trees
** Logical Volume Group contains 1 Logical Volume
** Load and verify DF9F3BA2-1863-4EEF-AA29-EEA46DE5151E
** Load and verify 13503CA3-FAC4-4CB1-ACF4-6930800B12E8
** Load and verify Freespace Summary
** Load and verify Block Accounting
** Load and verify Live Virtual Addresses
** Newest transaction commit checkpoint is valid
** Load and verify Segment Cleaning
** The volume 56BA393B-9EF3-4BE6-8CA0-240920F97724 appears to be OK

And here's what the Console reports as the system tries to mount the drive when fsck_cs finishes—these are nearly identical to the boot error messages:
com.apple.kextd[24]: LVG changed
kernel[0]: CoreStorage: fsck_cs has finished for group "56BA393B-9EF3-4BE6-8CA0-240920F97724" with status 0x00
com.apple.kextd[24]: LVG changed
kernel[0]: thr <ptr> Upgrading read-only MLV to at least read-only LV because LVG is sparse
kernel[0]: thr <ptr> Too few free segments, mark MLV as readonly
com.apple.kextd[24]: LVG changed
kernel[0]: hfs: early journal init: volume on disk2 is read-only and journal is dirty.  Can not mount volume.
kernel[0]: hfs_mountfs: hfs_early_journal_init failed, erroring out
kernel[0]: hfs_mount: hfs_mountfs returned error=22 for device disk2
diskarbitrationd[46]: unable to mount /dev/disk2 (status code 0x00000001).

This is pretty frustrating since the single-user boot (and DU) seems to indicate that the HFS volume is just fine. It's been running well for the last year or so. Nothing special was tweaked the day before this happened, either. If it matters, a BootCamp partition on the HDD still boots just fine. And I see no i/o errors in logs that are often preludes to disk failure.
At this point I am out of ideas other than destroying and re-creating the CS/Fusion volume with a TM backup, but I'm looking for other threads to follow before I waste a day doing that process.
Answer: I had this same problem, (out of free segments in mlv) and I used DiskWarrior 5 to repair my drive's permissions and rebuild the directory, and it fixed it for me.
Comment: Welcome to Ask Different!  We're trying to find the best answers and those answers will provide info as to why they're the best. Explain why you think the software you recommended is better than others out there.  Providing links can also help the OP, and others, find the software and evaluate it themselves.  See [answer] on how to provide a quality answer. - From Review -


How do I prevent Live Agent from automatically opening subtabs in service console

Question: We're going through Live Agent and Service Console deployment and when a chat request is received it automatically opens subtabs to the transcript in service console for lead, contact, account, and case. Our reps want to manually open or associate the transcript with one of those on close without having to close tabs for all the opened ones. Anyone know how to prevent them from auto opening?
Answer: You can control which tabs open when a chat arrives within your Console settings. In the Setup tree go to Create->Apps and edit the console you're using. There's a section called 'Choose Chat Workspace Options' where you can add or remove these tabs.

https://resources.docs.salesforce.com/sfdc/pdf/live_agent_administrator.pdf
Comment: Thanks so much Paul. It looks like when I do that though I don't then have the option to manually lookup and attach to records from those objects after closing the chat. And unlike current experience where it opens them but closing the parent tab and not saving changes at the end closing everything without creating a case, if I remove the related tabs here it actually automatically creates the case and saves it even when I exit. A happy medium would be great but at least I know the option. Thanks again!


Is there a term for words that consist of the same syllable repeated?

Question: Words such as "mama", "papa", and "cancan" have only one unique syllable, and the whole word is just that syllable repeated once. Is there a name for such words? I am aware of reduplication, but I believe it refers only to other forms of a word that consist of repetitions of the base word. I'm looking for a term that refers to the base word consisting of repetitions of a syllable.
Comment: A reduplicative root. In Malay, for instance, where reduplication is often used for something like the plural, there are roots which are nevertheless already reduplicated. So, while _kurakura_ means plural 'turtles', the rhyming verb _purapura_ 'pretend' always appears reduplicated. Oh, and by the way, this probly ought to be moved to linguistics.
Comment: It would appear this question is language-agnostic. It's not specific to English.
Comment: Here's a connected question: http://linguistics.stackexchange.com/questions/6392/root-reduplication-to-mean-singular
Answer: The term is indeed reduplication. That term does not refer just to forms which repeat an existing base word. Reduplication may copy repeat just a syllable, or two syllables, or an entire word, and it frequently happens that only the reduplicated word exists without there being a simpler form.


According to Marx, is Communism a workable system or an unreachable ideal?

Question: I have heard opposing arguments about whether or not Communism was intended to be an unreachable ideal, or a workable system. Has Marx ever commented, either in the communist manifesto or otherwise, on which one is true?
Comment: re: "failure every time" rests (IMO) on some pretty shaky *No-True-Scotsman* logic needed to discount China. Doesn't affect the OP question in any case.
Comment: Most of the times I've heard this argument it was in relation to the argument that [communism fails every time it is tried](https://politics.stackexchange.com/questions/586/do-did-non-dictatorial-communist-societies-exist) but it could be talked about in other situations too.
Comment: @PeteW given China's [gini coefficient](https://www.sciencedirect.com/science/article/pii/S2213020915000518) I'd love to hear the Marxist-economic rationale behind calling them Scottish in this case ;-)
Answer: The main thrust of Das Capital is that Communism is not only a workable system, but an inevitable consequence of the flow of history, and of the instabilities inherent in the capitalist system, which would result in a series of crises ending with the radical overthrow of the system and establishment of communism.  In later works he seems to think it possible that countries will reach the same state by gradual processes rather than violent revolution.
Its less clear whether he considered communism to be an ideal, or merely "better than what we have now".  He doesn't consider a post communist world, which suggests  that he considered communism to be a natural and stable system, and the one to which countries would evolve if history is allowed to take its course.
Comment: Incidentally, the failure of every communist system is rather irrelevant here, since Marx died before any revolution claiming to be communist.
Comment: @JamesK, wait, even the [1871 Paris commune](https://en.wikipedia.org/wiki/Paris_Commune#Marx,_Engels,_and_Lenin)? I think Marx had [a lot to say](https://en.wikipedia.org/wiki/The_Civil_War_in_France) about that.
Comment: Directly related is Lenin's thinking in his famous pamphlet *[What is to be done ?](https://en.wikipedia.org/wiki/What_Is_to_Be_Done%3F)* The main plank here concerned the need to educate the proletariat in the doctrine of Marxism, and he talks about a "Vanguard" party, selected from dedicated Marxists who will form an initial revolutionary government that will carry the message to all. It is not a direct answer (and I doubt anyone knows of one, since Marx focuses little on the practicalities) Hence I have not posted it as such, but it is closely related to the topic.
Comment: @JamesK Concerning the last paragraph: Not really, it's just that this system would operate under different material and social conditions which he couldn't foresee so it's simply impossible to predict what would happen after that. I mean up to that point the day was dictated by work however since productivity rose greater than the Malthusian trap there was a possibility for a greater freedom outside of the necessity of the material conditions.
Answer: As best I can interpret Marx, it's a mistake to think of Marxism — referring to that ultimate form of political community — as a particular system, structure, or process. Marxism is any of a set of systems that might occur when all class distinctions are erased and the ideal of liberty is achieved. For Marx, the failure of capitalism is the same as the failure of socialism, or of feudalism, or of most any form of political economy: one group in a society takes control of the tools and resources necessary for material production and social sustenance, and uses that control to exploit other groups. For Marx, if we eliminate the notion of class — remove the possibility that one group might take hegemonic control over resources that the entire community needs, so that no one suffers any existential threats — then whatever form of government or economics the community chooses to implement will be intrinsically non-oppressive and non-exploitive.
In simplistic terms, Marx is pointing out that we cannot cow happy, secure, well-fed people into doing something they don't want to do. We can't coerce them into low-paying jobs out of fear they might not get any job at all; we can't convince them to work exhausting hours or in dangerous conditions; we have no economic stick to drive people forward, so the society as a whole has to lean towards the carrot. We end up having to treat everyone as people-just-like-us, with all the same kinds of needs and desires, and that creates the conditions for fairness and justice.
As to whether this is a practical ideal... This approach has been used fruitfully within monastic orders and faith communities across any number of religions, through most of human history: Christian communes, Buddhist monasteries, Orthodox Judaism, Quaker and Mennonite communities, certain Islamic sects, etc. It's clearly feasible within small, dedicated communities, and it's part of the Liberal ideology that informs most of the modern world, but it seems to be a far off state in the current large-scale political-economic environment. It smacks of an idealism that jaded cynics like myself tend to scoff at. This is why, I think, Marx focused so heavily on the labor-revolution model. For Marx, getting people to see that they are part of an exploited class — at least people within liberal societies, steeped in lIberal values — was the first necessary step in getting them to reject exploitation and demand their own place in society.
Comment: I had a professor of European history, I think Soviet era was his specialty, that suggested that many western capitalist countries didn't see as much Communist influence because of unions and guilds. That workers fought their employers for concessions through unions and therefore were not motivated as much by Communist ideals, that unions are just part of the capitalist system. Possible that a capitalist's headache prevented his nightmare?
Comment: Modern Hutterite communities might be the best example of what Marx was referring to when he talked of socialism and communism, for they are about as classless as any society today.
Answer: Marxism is considered a workable system, but people forget that in works like Critique of the Gotha Program and Das Kapital, Karl Marx considered reaching the final stage of communism to be a process. From capitalism, some form of lower stage communism/socialism would form (the dictatorship of the proletariat, Permanent Revolution, syndicalist worker's cooperative, etc.) to guide the common workers towards the final stage of communism & a stateless, moneyless society. As socialist thinker Philip Gasper puts it: "Marx and Engels never speculated on the detailed organization of a future socialist or communist society. The key task for them was building a movement to overthrow capitalism. If and when that movement was successful, it would be up to the members of the new society to decide democratically how it was to be organized, in the concrete historical circumstances in which they found themselves". So while communism was considered a workable system by Marx, true communism was supposed to be the end goal after capitalism was overthrown, some type of anti-capitalist state/cooperative/worker's union was formed as an alternative, and that successful revolution defeats capitalism to create a true communist community. As I stated in a previous answer, that was kind of the goal of many of the socialist revolutions we saw in the real world throughout the twentieth century: form a socialist state to compete with capitalism, defeat capitalism, then have the state erode away through a final revolution or natural human advancement in order to reach a clean, stateless communist society at the end of everything.
Answer: The best know quotation on this by Marx himself would be the — rather surprising for many — excerpt from The German Ideology:

Der Kommunismus ist für uns nicht ein Zustand, der hergestellt werden soll, ein Ideal, wonach die Wirklichkeit sich zu richten haben wird. Wir nennen Kommunismus die wirkliche Bewegung, welche den jetzigen Zustand aufhebt.
[Communism is for us not a state of affairs which is to be established, an ideal to which reality [will] have to adjust itself. We call communism the real movement which abolishes the present state of things. (— English translation)]
— Die deutsche Ideologie, MEW 3, p. 35

Big caveat: This book alone can be quote-mined for the term "communism" for – hm, quite a lot of instances? That's of course no wonder at all, given the centrality of the concept within his thought. But that also gives a firm warning not to use this one quote to explain 'Marx on communism as ideal or process' once and for all. Marx elaborates quite a lot over the concept over the years and neither Marxists nor other historians must fall for the 'myth of coherence' over one quote from 1846 to describe Marx' view on the subject matter in total.
Answer: I'll repeat the quote posted by @Tyler Mc

Marx and Engels never speculated on the detailed organization of a future socialist or communist society.

It's an important point because since Marx never proposed a complete system he had nothing to comment upon as the question asked. What is called Marxism most of the times refers to several different system proposed later by other philosophers or leaders often with conflicting opinion, so there is not a single framework anyone agrees upon.
Just to give an idea how much Marxism as it is understood deviated from the original ideas I can point out that in The Eighteenth Brumaire of Louis Bonaparte Marx spoke against the systems based on a strongly centralised bureaucratic machine. He knew them well because he had to do with the French and the German ones for a big part of his life.
Answer: Marx basically had a philosophy of history and saw various polities such as hunter gatherers, villages, city states, feudalism and industrial capitalism in a progressive line in light of this philosophy.
He took economics as his bedrock motor of change and its the various crises of economics that propelled the change from one kind of polity into another. He called the stage after capitalism, communism and it will be the crises of capitalism into the next stage.
In line with Hegel, he understood the progressive changes in these polities as furthering the emancipation of man. Steven Pinker, who is no communist but a psychologist has argued that on many indicators, human life has increasingly flourished. This is evidence for Marx's thesis.
Marx saw this progression as inevitable. So, yes, he did think communism was achievable. He did not lay out a programme how this might be achieved. When, gor the sake of argument, we consider feudalism lasted in Europe for a thousand years and suppose the next stage, because of increasingly rapid change, would last half that. Then we get a figure of around five hundred years for industrial capitalism. Given that the industrial revolution began in England roughly two hundred and fifty years ago, then we're merely half-way through this period and there's another two hundred and fifty years to go. These are obviously very rough and ready figures. But its really to give a sense of historical perspective to Marx's thesis.
This philosophy of history, which Marx took from Hegel in broad outline, is so identified with Marxism that Fukuyama, an American political scientist, wrote a book on the dissolution of the Soviet Union titled The End of History meaning the end of Marxism.
Personally, I think Marx is correct. I don't see it being 'utopian'. After all, had you told a medieval peasant that people will be able to fly, have fresh water, light at the flick of a switch, instant world-wide communication, he would only snort and say, "what do you take me for? A fool!?"
Comment: As if one can't be a psychologist _and_ communist! But Steven Pinker is neither; "cognitive psychology" is very, very different to what is usually understood as "psychology". (And anyway, he's more of a linguist). But this is tangential; the main point is: flourishing mankind does not, in any way, confirms Marx' theory of inevitably changing social formations. We've seen degradation, we've seen societies 'skipping' formations he believed were inevitable, etc... And even if it did line up perfectly, it could have been mere correlation.
Comment: @Zeus: A general trend upwards does not imply that at every moment the the graph is upwards, but only that the trend is upwards. It's quite possible to have major or minor swings downwards but these are counter-acted by major and minor swings upwards; with, on balance, the swings upwards more than counterbalancing the swings downwards. I very much doubt it's just 'correlation' because human beings are intentional beings. Science didn't spread at random but because people saw the advantages. A cognitive psychologist is still a psychologist - my post isn't about how to pigeon-hole Steven Pinker
Answer: Communism was not invented by Marx. He just improved it. Marx was a materialist and all of his ideas were realistic. That's why Marx thought communism was reachable.
But there are a lot of complicated technologies needed for that. Look to the Star Trek series. It's reachable, but will take a long time.
Comment: If technology had anything to do with socialism, capitalism would have ended a long time ago.   We live in a highly technological world already.  Economic systems are based on class, not technological development.
Comment: @beginner-biker Capitalism that Marks can see ended a long time ago. Now we speak about universal basic income - not about barracks or reduction of the working day to 8 hours


Pros and cons of a Single Page site versus a Multi page site

Question: I am working on trying to re-design the site for the agency I work for and a recommendation was made that we should move to a single page site with a vertical scroll which which walks through all the work that has been done. I am not a big fan of that since I am not sure how intutive that would. Is there research into what are pros and cons of a single page and when they should/should not be used as opposed to using a multipage site.
Comment: Not sure if there is research into it, but my 2 pennoth (I'm English ;)

It's not to much about a single page vs multi page as it is the structure of the information. You could have a single page with expanding pods or tabs; you could use a video or audio content - can you say more about what you are trying to communicate?
Answer: I don't know of much in the way of research, instead I will draw from my own experiences here.
The main difference between the two lies within the structure of information. With any site marketing its goods or services, you'll want to take the user on a journey, creating a story for them to follow. This is where the single page reaps huge rewards.
You control the flow of information here, rather than the user choosing their own path and flicking between pages (this is where important information can be missed). Although I have nothing to back this claim up, I also believe that a single page design has the psychological affect of seeming simple and free of any hassle. Which, of course, is what the consumer is ultimately looking for.
That said, and perhaps slightly off the topic of UX, a multi-page site can prove more beneficial in terms of SEO, as it will allow you to target keywords around specific topics/sections. One thing you'll struggle to do with a single page design.
Janis Lanka carried out some research using AB split testing on a shopping cart process, one design featuring multiple pages and the other containing each step on a single page. The results showed that conversions increased considerably when using the single page design, along with a few other surprising findings (such as an average increase in order value).
He Hypothesizes:

Fewer steps result in fewer distractions and reduces opportunities for customer to change their mind.
Comment: Nice one! I like the "fewer steps" analogy!
Comment: As far as I understood, question wasn't about check-out process, but a portfolio "all the work that has been done." The link is good anyway ;)
Comment: Link is broken.
Answer: 37signals did a AB-Test on their Homepage-site, where they experimented with an extreme long sales letter. It actually performed better, despite the "above the fold" mantra one hears often. As other answers said, the structure of the content was crucial - I recommend to read even the comments on their Case Study - Behind the scenes, because there is an analysis going on.
And you might be interested in the Life below 600px, which gives you some hints, how to visually guide visitors eye downwards.
Scratching Off-topic - the Fold Tester displays percentages of screen resolutions above your online page.
Comment: @oligofren So if you read the article you might have seen, that the old version was a multi-site page and they moved to a single page, AB-tested it and the conversion was better. One of the findings was that the structure of flow of onformation/stprytelling is essential for a good performance. But this did I already wrote. May be not in well structured text with highlights and bulletpoints, but I did not only post a link without writing what is it about.
I read the question as a question for landing page for an agency to showreel their work not a RIA singlepage app.
Comment: how does this answer the question?
Comment: check the case study link and you will know - pro and cons, analysis etc
Comment: UX@stackexchange might not be as strict as StackOverflow, but at least on SO, merely linking to an article is not considered good form. I actually read the articles, and it was an interesting read, but a good, useable answer is none the less one that will summarize the most important points. Good links though :-) BTW. Just realized that my initial reaction was due to me thinking the poster asked for pros/cons of Single Page Applications vs more traditional multi-page server-rendered versions ...
Answer: Likewise, an answer lacking in empirical research!
I've built lots of sites, both multi-page and single "long-scrolling" page. However, the latter have for the vast majority, been promotional microsites, with a single purpose/call-to-action or sign up and in that context they work well.
However, I'd never recommend a single-page scrolling site for a "full" company website. The division of data is important, a clear nav structure is important and can easily become obfuscated/confusing on a single page site, plus a "proper" site requires full, unique URLs for SEO/linking and relying on hashbangs is a filthy practice that deserves punishment.
Answer: I'm not sure how relevant this would be in the developed world with fast internet connections, but in the developing world a single page may take considerably longer to load (if you include a lot of high quality media) over a slow connection. If you are considering delivery to mobile platforms, it may also have an impact on delivery over slow cellphone carrier networks, or people with limited bandwidth plans.
I know it seems silly, but my gut reaction would be to at least have a choice of seeing a content-heavy page, or have that broken up over multiple pages. I'll hopefully get to see what I want, when I want, in smaller chunks (depending on my connectivity).
Answer: There have been written a lot of landing page optimizing and what I've read is that there seem to be a higher conversion rate when you keep everything on one (long) page instead of splitting up the content into several pages. There seem to be a couple of reasons for this:

you have to rely on that the visitor really clicks through all the pages and that is not always the case. There could be for example other content that is distracting.
It takes less effort to scroll than to click and wait for other pages to load.
If the visitor doesn't really know what he or she is looking for it is more convenient for them to let you serve them the content on one page.


Mail 7.3 with iMac running 10.9

Question: I just upgraded from an iMac with 10.6 to a newer iMac with 10.9. When I use the Mail 7.3 program and go to print and email, it prints all previous emails from the same sender as well. I don't want all the other emails printed, just the current one. Is there a way to disable the other emails from printing, or to disable the grouping of emails?  Thank you...
Comment: Are all emails a part of same email?
Answer: I assume you are talking about same email with multiple messages (emails) in it.
In order to print specific email embedded in that email chain:
Select the single message window: It will have a highlighted border.
The other emails will be separated with page separator.
It looks like this (sorry I had to black out my personal info), but you can see 3 emails in this chain and only the top one is selected for printing.

In top Right (circled) of that window you will find the Print Icon, that will print the selected message only.

Mail 7.3 with iMac running 10.9


What does it mean when actual member reaction is 100% of allowed?

Question: I received construction documents for an extensive residential remodel and looking at the engineering there's a glulam drop beam with a calculated member reaction that is 100% of allowed (3965 lbs @ 5 1/2"). No other member comes close to 100%.
Does this have any practical implications? Is this common?
Comment: The problem is probably lack of bearing surface. Try add more end bearing width
Answer: This means that the member is considered to be fully loaded for a failure mode which is being analyzed by that stress calculation.
Some things to (probably) keep in mind include:

Some conservatism likely exists in the analysis/design calculation. A member reported to be at 100% capacity is (probably) not actually at 100% capacity. This conservatism could include anything from assuming larger loads than actually exist, assuming smaller section sizes, assuming longer member spans, etc.
The load case used to arrive at the conclusion that this member is at 100% capacity (probably) considers a transient load of some sort (like wind, seismic, dynamic water pressure, etc.) that isn't acting on the structure at all times.
Structural members are usually checked for several different failure modes. An indication that a member is at 100% capacity for one failure mode (probably) doesn't mean that it is at 100% capacity for all failure modes.
Sometimes a member shown to be at 100% capacity based on the stress/design calculation may not be at 100% of it's strength capacity. Many times structural members will be controlled by their serviceability requirements instead of their strength requirements.
Answer: For a light weight design (e.g. an aircraft) you would try to achieve 100% of the allowable loads for every part of the structure, under some operating condition (not necessarily the same condition for every part, or course). But in building design, other considerations may be more important - for example using consistent sized components could minimize cost (by ordering in bulk) and/or simplify the construction. If a set of beams are all specified as the same size, you can't install the "wrong size" in some particular location.
Common components like beams are manufactured in a standard range of sizes. If the full range of different sizes in the relevant building codes and standards are not available locally "off the shelf", it may be cheaper and/or quicker to use over-sized beams rather than find a supplier for the minimum size that is actually required. Of course that will reduce the load factors in the oversized parts.
Also, the stiffness of some parts of the may be more important than their strength. For example it would be a bad idea to design a floor that was perfectly safe to carry the expected loads, but which flexed up and down when you walked across the room.


Add Class to a div using a filter?

Question: is it possible to add a dynamic class to a div using a filter in the functions.php? I know it's possible for the body-tag - also for a custom defined div with an id?
if ( !is_search() ) {
   $customclass = 'myclass';
}

Answer: You could try using one of the following methods, I don't think there is a specific way to do this other than these two options below.
Option 1
In your template file, add the post_class(); to your div like this:
<div id="your-div" <?php post_class(); ?> >

Then you can use post_class filter in your themes or plugins functions file, something like this:
// Add dynamic post class
    function royal_custom_class($classes) {
        global $post;
            $classes[] = 'your-class-name'; // Add your class however its generated here
            return $classes;
    }
    add_filter('post_class', 'royal_custom_class');

Option 2
Your other option, if the div was defined in your actual content then you could use the_content filter and replace and update it.
Something like this:
function updated_page_content( $content )
{
     return '
Whatever goes inside
'. $content;
}
add_filter( 'the_content', 'updated_page_content' );

References from Codex for these two methods
Post Class Filter - WordPress Codex
The Content Filter - WordPress Codex
Answer: You could also do something like (this goes into functions.php):
function add_new_class(){

    if (is_page()) {
    return "page";
} elseif (is_single()) {
    return "post";
} else {
    //add other elseifs
}
}

And then, this is how you could call this within different templates:
<header class="entry-header <?php echo $new_class = add_new_class(); ?>">

WordPress will load different value based on which template (post/page/search/archive, etc.) you are currently on.

Add Class to a div using a filter?


What was Shakespeare's inspiration for the several cross-dressing episodes in his plays?

Question: I've heard that Shakespeare borrowed ideas from the events and other literary works from the time. He uses cross-dressing as a major plot device in several plays. Where did this come from?
Comment: Note that in Shakespeare's own productions of his plays, all the actors were male. So you had men (or boys) pretending to be women pretending to be men.
Comment: I think Mikado's comment serves as the answer to this question. Here Shakespeare was exploiting a fact of the contemporary theatre, not borrowing from another literary work.
Comment: Related: [When did men dressed as women stop being the norm in English theatre?](https://literature.stackexchange.com/q/2607/17) As mikado says, cross-dressing was much more common in real life in Shakespeare's day - at least in theatre - than it is today.
Comment: Thanks for these comments. That can explain why there men played the roles of women. But tales like As You Like It and The Twelfth Night have cross-dressing in the core of the story itself.
Answer: Among Shakespeare's contemporaries, the motif of a woman disguising as a man had been used before, for example by George Peele in his play Sir Clyomon and Sir Clamydes, which was written around 1570 and by John Lyly in his play Gallathea (around 1588). (See my related question.)
In his diary, John Manningham had noted similarities between Shakespeare's Twelfth Night and the Italian play Gl'ingannati / The Deceived Ones, which dates from 1531, predating Peele's and Lily's plays. (There is no hard evidence that Shakespeare knew this play, though.) The play introduces Lelia, dressed as a boy. According to Yasuo TAMAIZUMI, Gl' Ingannati contains the earliest example of a female page.
However, the motif of cross-dressing is much older than the Renaissance. For example, Achilles on Skyros is a story available in Publius Papinius Statius's unfinished Achilleid in which Achilles disguises himself as a girl.
In summary, Shakespeare may have found inspiration in sources from Antiquity, from the Italian Renaissance or from contemporary works.

References:

Accademia degli Intronati: Gl'Ingannati / The Deceived
Gl'Ingannati, an Italian play about twins and mistaken identity, British Library.
The festival of Twelfth Night in John Manningham's diary, British Library.
Yasuo TAMAIZUMI: On Shakespeare's Twelfth Night, Transactions of the Japan Academy, Volume 74 (2020) Issue 3.


What is the practical purpose of a lens hood if any?

Question: If a hood is to block unwanted light coming from the sides of the lens in use, because such light is detrimental to the picture taking, then hoods would be used at all times,because there almost always be light hitting the lens from all angles,  however hoods are not used that much.
Comment: "...however hoods are not used that much." I guess it depends who you hang out with. Mine are never off their lenses!
Answer: The reduce or prevent lens flare from bright light sources at the edges of the lens.
It's not a bad idea to you use lens hood whenever possible as it will help prevent the lens from knocks.
I don't really agree with the statement that they aren't used that much because in fact they are used very broadly.


Is Git/GitHub a good WordPress deployment solution?

Question: I'm currently developing my WordPress locally, committing my code to GitHub with Git and then SSHing into my server and doing a "git pull" to update my code. Is this a good option for code deployment onto a WordPress site (I obviously have root level access to my server in this case.) I know of things like Capistrano, but would that be overkill for deployment to a WordPress site? How can I make the most of Git/GitHub in this case?
Comment: I use http://www.deployhq.com/ and really like the features they offer. It's a paid service but I find the price to be reasonable. If you happen to host with WP Engine (I do) they recently rolled out a git push feature: http://git.wpengine.com/.
Comment: How do you handle this use case? You have done some customisations on WordPress, WordPress themes folder, and did some settings change in a plugin (that plugin stores the settings in db). Like this, we did many such plugins installs, and settings changes in localhost, now without repeating the settings changes of plugin how can I setup in hosting server.  The biggest challenge is your hosting server has 1000 blog posts that are live. without loosing the challenge how will you deploy your localhost wordpress on the live server.
Answer: I use git for this and find it works really well. A few suggestions:

Add your uploads directory (wp-content/uploads) directory to your .gitignore file.
Run a web server and database server on your development system so you can test changes locally before pushing them to production.
Keep your database connection settings consistent beween dev and prod, or add wp-config.php to your .gitignore file to prevent your development wordpress settings overwriting your production ones.
Avoid updating plugins on your production system using the admin interface of Wordpress - as at best, your git copy will overwrite any plugins you update as soon as you push/checkout, at worst you'll get conflicts. Do your updates using the the admin interface on your development system, commit, push and checkout in production.
Consider adding a git post-receive hook to checkout your updates automatically into the directory you use to publish wordpress via your web server (e.g. /var/www). This allows you to only check out the files themselves, avoiding any git metadata finding it's way into your web server's document root, and also means you can add any permission changes into the post-receive hook so your permissions stay consistent every time. An example is included below:
#!/bin/sh
unset GIT_INDEX_FILE
# the directory your web server serves wordpress from
export GIT_WORK_TREE=/var/www/example.com/
# the local directory where your remote git repository sites
export GIT_DIR=/home/git/repos/example.com.git/
# below user is for debain - you want the user and group your webserver uses
sudo git checkout -f
sudo chown -R www-data:www-data $GIT_WORK_TREE
sudo chmod -R 755 $GIT_WORK_TREE
sudo chmod 600 $GIT_WORK_TREE/wp-config.php
sudo chmod -R 775 $GIT_WORK_TREE/wp-content

Comment: I'm not familiar with the plugin updating process in wordpress but what happens if the plugin update makes changes to the database?  How will those local changes get pushed to the production server?
Comment: Is the backtick appearing after `unset GIT_INDEX_FILE` a typo?
Comment: James has pretty much summed up my worfklow, except I only add the theme files to the git repo once I have the staging/test/production site established.

Also I totally recommend using a post-receive hook on the remote server, saves logging in and doing a git pull etc.
Comment: That, along with SSH aliases means I can push to the live theme repo using 'git push live' etc
Comment: @User that would vary from plugin to plugin. Core wordpress does schema version checks, so if you update Wordpress without using the built in updater, it will do the DB updates seperately. My advice would be if you are using any plugins that write to the DB, that you check the admin area of Wordpress, as schema updates are usually handled there regardless of how you update the plugin code.
Comment: As I am learning this, too, I have included only my active theme and my custom plugins to the repo. The question about what happens when a plugin on the site updates, but then you overwrite it with a pull is why I .gitignore all plugins except for custom plugins. I also .gitignore uploads, because the media files on my dev machine are not necessarily the same as on the production server. A bigger issue I want to bring up is that GIT should not be the same as a backup-restore. Two very different operations. Git shouldn't be your backup-restore solution.
Answer: I would highly recommend setting up Capistrano - it's a little bit of upfront work the first time, but after that you can easily use it for new setups.
The main advantages are

being able to deploy from your desktop. It may not sound like much, but ssh-ing into the your remote server, and doing a git pull is still a pain in the ass.
easy rollback to a previous version if you need to
able to do cool things like setup deployment to staging/production environments.

I'm adding a set of capistrano scripts to show you how I set things up.
Capfile
require 'railsless-deploy'
load 'config/deploy'`

deploy.rb
set :stages, %w(production staging local)
set :default_stage, "staging"
require 'capistrano/ext/multistage'

set :application, "" # your application name - used to set directory name

set :scm, :git
set :repository, "" # use the ssh repo access line you get from the provider eg email@example.com:name/repo.git
set :deploy_to, "/var/www/#{application}" #this is the root site folder on the remote server
set :deploy_via, :remote_cache # get directly from repo
set :copy_exclude, [".git", ".DS_Store", ".gitignore", ".gitmodules", "wp-config.php"]

# makes capistrano ask for sudo password or other remote inputs
default_run_options[:pty] = true

namespace :tasks do
    task :fix_links  do
        run "ln -nfs #{shared_path}/uploads #{release_path}/wp-content/uploads"
        run "ln -nfs #{shared_path}/wp-config.php #{release_path}/wp-config.php"
      run "ln -nfs #{shared_path}/blogs.dir #{release_path}/wp-content/blogs.dir"
      run "ln -nfs #{shared_path}/.htaccess #{release_path}/.htaccess"
      run "sudo chown -R www-data.www-data #{release_path}/"
    end
end

after "deploy", "tasks:fix_links"

and finally, a sample environment file (if you use the multistage gem, then you can have one of these for each stage of your environment, eg local, staging, production)
config/local.rb
server "", :app  #hostname
set :branch, 'develop' #choose branch to deploy
set :use_sudo, false #don't use sudo

set :deploy_to, "/var/www/#{application}" #overwrite default path to deploy to

These files might not work without tweaking, and you'll need some basic Capistrano knowledge, but hopefully will help some people.
This was the first tutorial I used that got me going with Capistrano and WordPress: http://theme.fm/2011/08/tutorial-deploying-wordpress-with-capistrano-2082/
Comment: @dirt the problem with the post-receive hook is that unless you've got a decent CI infrastructure in place, one incorrect merge can bring down your whole site. The likelihood of this increases if you're working on a project with multiple devs who have commit access to your repo. That's why I, personally, like to deploy via capistrano instead, but I can see why others might not worry about it so much.
Comment: If you use git post-receive hooks, they negate the need to ssh in to the remote server and do a git pull
Comment: You use a bare git repo so the merge issue is not relevant
Comment: `git post-receive` hook is the way to go!
Answer: I actually did a WordCamp presentation on this topic. Rather than repeat myself, here's a screencast of it and here's a very simple deployment script to accompany what I discussed.
In short, I use GitHub to host the repo, and use a webhook to deploy changes based on the git ref. This allows you to use Vincent Driessen's git branching model and opens you up to having unlimited webheads, staging servers, testing servers, etc., all with automated deployment. I also cover keeping wp-config.php under version control while maintaining separate dev/production versions (by renaming the files and symlinking).
Answer: I know this question is a little older however as I've not seen this as answer here, I'd like to share what I normally do for single-site git based setups and deployments and it's working really well, also with working from multiple devices, locations and with multiple developers (all having their own local repos they operate in as it is common for git).
I can warm-heartedly suggest the following setup:

A web-focused Git workflow (by Joe Maller; Nov 2008)

It is also outlined in (if you need a second resource to wrap your head around it):

Using Git for Deployment (by Dan Barber; Apr 2011)

It basically works (with at least three repos) by:

putting the website on the live-host under git,
create a new bare git repository on the live host.
And then fork from the bare repository to your local development git repo(s).

When the work is done you push against the remote bare repo you've cloned from. The bare repo has hooks to sync with the live repo (in the codes above called prime).
As Wordpress specific settings in the repo I have this .gitignore:
# uploads are data, excluded from source tree
wp-content/uploads/

The rest incl. the plugin and theme configuration I keep under version/configuration control. This allows me to easily track changes and review code before using it live. I can also more easily merge against remote trees with my own changes. That is especially useful against the Wordpress core which is available on Github.
This works pretty well for most of my Wordpress needs. The bare repo prevents you from pushing conflicting changes. It also syncs to a remote copy first before updating the live-site. That means, updating the live-site is normally pretty fast. Because of the hooks you can even call Wordpress update hooks afterwards if you like.
If have not experimented how much this can be improved with Github hooks, but I normally do not need them as the code is under local version control, not Github.
To set such a system up for the first time, you should take some time to evaluate if you've got all the tools available on your remote host:

SSH access
GIT
A private directory you can put files and sub-directories in (e.g. for your bare git repo)

The setup-time for the first time should be possible within one two hours incl. the whole environment and you first publish push.
Depending on your host, you might also want to shield the .git directory from web-access. Here is some example .htaccess code that even does so having Wordpress placed inside a sub-directory, which leaves space in the repo not published online (useful):
Options -Indexes

# fix trailing slash for .git / make it disappear + .gitignore and similar files.
RedirectMatch 404 ^/\.git(.*)$

# mask 403 on .ht* as 404
<Files ~ "^\.ht">
  Order Deny,Allow
  Allow from all
  Satisfy All
  Redirect 404 /
</Files>

RewriteEngine On
RewriteBase /

# map everything into public and set environment var
# to tag the request being valid
RewriteCond %{ENV:REDIRECT_sitealias} !set
RewriteRule ^(.*)$ /public/$1 [E=sitealias:set,L]

In short, everything not inside the public directory is not online. Inside the public directory can be the wordpress codebase for example, for the .htaccess there you need then:
RewriteEngine On
# mask as 404 if directly accessed
RewriteCond %{ENV:REDIRECT_sitealias} !set
RewriteRule .* - [L,R=404]

This prevents direct access to public. Part of this .htaccess-foo you can find outlined here: Requests to .htaccess should return 404 instead of 403. For the environment variables you need to test if that works in your environment. Also you need to decide if you put that under version control or not.
If you have more control on the hosting, you can do more stuff here (and differently / more optimized), the examples above are targeted for typical shared-hosting environments (that offer GIT, some users say you can easily install it your own as well, I normally ask my hosters to provide such because I prefer if they take care that's what I pay them for).
On the negative side, this has some of the common problems also outlined in the other answers. One thing I'm not proud of but what works is to give the development host a change to it's host file to have the database server point to the development copy. So you can keep one database configuration. Not really cool esp. because of the credentials.
Automatic Backups
However I normally don't care much here but instead have daily backups run on the remote systems which are incrementally which themselves are stored in another remote location then. That's easy and cheap and allows you to restore both the Wordpress install as well as the file-uploads, the database and the git repo. Also for my backup commands I might not be perfectly alright, but those work for me:
mysql: mysqldump --host=%s -u %s --password=%s %s| gzip > %s
git  : git gc
       git bundle
files: tar --force-local -czf %s %s

What I do suggest here is that you keep the processes around your Wordpress installation out of Wordpress. They need to run on a specific system, so you normally do not have them inside the application (e.g. application can go down but you need to have these continue to work).
Enabled for Teamwork
Another nice benefit is that you site is enabled for team-work already. Thanks to the additional bare repo you can't do much wrong and you can even share remote branches apart from a master or live branch with your colleagues.


Are snort rules applied per packet or per flow

Question: I would like to understand if snort rules are applied for each packet in a flow between a source and destination separately?
For instance, when packet 1 of the flow arrives at the IDS, all the rules in snort get evaluated, followed by packet 2 and so on?
If this is not true, when do the rules actually get evaluated?
Answer: Stream. Here is a good document regarding how snort uses libpcap to apply heuristic and signature based anomoly detection to network traffic; http://www.pearsonhighered.com/samplechapter/157870281X.pdf and when in doubt consult the manual https://www.snort.org/faq/readme-stream5
Comment: To casual viewers who may not understand what you mean. What is the difference, if any, between packet, flow, and steam?
Comment: TCP, BGP, UDP, etc all generally include multiple data grams and to effectively determine if a payload includes a threat libpcap, (the packet creation and disassembly library under the hood of snort & surricata) it must utilize stream based analysis techniques. However I am not certain that all detection techniques use just a stream
Comment: Well here is the official documentation regarding the streams processing and configurable parameters https://www.snort.org/faq/readme-stream5
Comment: It may help to update your answer to reflect the requested information in my comment. :]


Did any sounding rocket ever fly through a noctilucent cloud?

Question: Noctilucent clouds are the highest clouds forming above the Earth, up in the mesosphere. They form in late spring / early summer and above latitudes closer to the poles. Was a sounding rocket ever sent through these exceptional clouds and did it film its flight through them? Afaik, there are cosmodromes in Norway, Sweden, Russia (Plesetsk and Vostochny) and Germany (Peenemünde) from where sounding rockets could reach noctilucent clouds at the time of the year they appear. Or did perhaps some reentering orbital spacecraft fly through noctilucent clouds and film their flight through them?
Comment: That's rather specific, and may be better asked over at Earth Science
Answer: Google is your friend.   I heartily recommend using it as a first go.
Project Possum  says:

Sounding rockets have provided in-situ observations and measurements
of atmospheric constituents since 1962, when particle collectors
revealed an abundance of particles of much greater size when the
rocket penetrated a noctilucent cloud layer [Hemenway et al., 1964].
Later in 1982, the Cold Arctic Mesopause Project (CAMP) successfully
mapped the temperature distribution of the summer mesopause [Philbrick
et al., 1984].  Then in 1993, The NLC-93 rocket campaign at Esrange,
Sweden, investigated the vertical structure of a noctilucent cloud
layer in-situ, showing little vertical variation [Gumbel and Witt,
1998]. The question of particle size was further addressed in 1999
with the MIDAS-DROPPS rocket campaign, which used the scattering phase
functions of NLCs through optical photometers [Gumbel et al., 2001].
Then in 2007, the PHOCUS rocket-borne experiment  found no general
difference between neutral and charged particles. [Hedin et al, 2007].

FWIW there are photos online which ISS crew took.
Comment: And how did you find that? I never heard of a "project possum". Thank you.


Save buffer at each modification

Question: I'd like to know if it is possible the buffer is saved at the exact moment of modification; at the instant of the key up event.
Comment: You will receive other answers, but you may be interested in the auto-save-buffers-enhanced:  https://github.com/kentaro/auto-save-buffers-enhanced/blob/master/auto-save-buffers-enhanced.el
Comment: Do you have a specific reason for wanting this? This would be pretty insane. I don't type fast, but I know even a fast SSD couldn't keep up with my typing. (At least not in emacs)
Answer: (defun my-instant-save-buffer (eins zwei drei)
  "To be hooked into list `after-change-functions'

`after-change-functions' expects functions receiving three arguments.
Arguments are ignored here, but slots needed by add-hook"
  (save-buffer))

(add-hook 'after-change-functions 'my-instant-save-buffer)

Comment: This should come with a warning: just because you *can* do it does not mean that you *should*. I haven't tested but I think that this is likely to impact performance substantially.
Comment: @NickD Agreed. However, just answered the question, not giving as hint of good practice.
Answer: I had the same requirement and auto-save feature of emacs hasn't worked well for me because it can't addadvice to c functions. So, I wrote a package real-auto-save for that. It is available on melpa.
You can install it by
M-x package-install RET real-auto-save

and in your config you can add
(require 'real-auto-save)
(add-hook 'prog-mode-hook 'real-auto-save-mode)
(setq real-auto-save-interval 1) ;; in seconds

After every second, if your buffer is modified, it will be saved automatically.
If you specifically want to save after key up event, you can write a lisp function for that.
Answer: You can enable auto-save-mode, so Emacs automatically saves your current buffer in a different file. Then, add this function to auto-save-hook to also write it directly on the actual file you are editing:
(defun save-buffer-if-visiting-file (&optional args)
   "Save the current buffer only if it is visiting a file"
   (interactive)
   (if (and (buffer-file-name) (buffer-modified-p))
       (save-buffer args)))

(add-hook 'auto-save-hook 'save-buffer-if-visiting-file)

According to the Emacs manual on auto-save control:

The variable auto-save-interval specifies how many characters there are between auto-saves. By default, it is 300. Emacs doesn't accept values that are too small: if you customize auto-save-interval to a value less than 20, Emacs will behave as if the value is 20.

So, if you want Emacs to save for every key press, change auto-save-interval to 1:
(setq auto-save-interval 1)

Comment: The manual you quoted says anything less than 20 will make Emacs behave as if the value is 20. How does it work with 1 then?
Answer: It's a little bit elaborated version of @andreas-röhler's answer somewhat adressing @NickD comment.
Saves after 50 milliseconds of inactivity and rapid buffer changes would not cause tons of savings.
(let ((timeout 0.05)
      (timers-alist nil))
  (cl-flet* ((get-timer (key)
                        (cdr (assoc key timers-alist)))
              (set-timer (key timer)
                        (push (cons key timer) timers-alist))
              (drop-timer (key)
                          (setq timers-alist (assoc-delete-all key timers-alist)))
              (save-buffer-and-drop-timer (buffer)
                                          (with-current-buffer buffer
                                            (progn
                                              (save-buffer)
                                              (drop-timer buffer))))
              (save-buffer-deffered (buffer)
                                    (unless (get-timer buffer)
                                      (set-timer buffer
                                                (run-with-idle-timer timeout
                                                                      nil
                                                                      #'save-buffer-and-drop-timer
                                                                      buffer)))))
    (defun save-file-buffer-deffered (&rest args)
      (if (buffer-file-name)
          (save-buffer-deffered (current-buffer))))))

(add-hook 'after-change-functions 'save-file-buffer-deffered)

Comment: It's doesn't addressing exact question, but where is nothing similar to this topic came up for me in search.

Save buffer at each modification


Does smart lock check all active verification methods or only one of them?

Question: I've recently started using smart lock. I've enabled two features: a trusted place and a trusted face. I cannot understand if in this case both of these mechanisms should pass to unlock the device or passing any one of them is enough. For example, is my face (theoretically) enough to unlock my device when I am not in a trusted place? I haven't been able to do so, but maybe I'm just doing something wrong.
Answer: Smart Lock will unlock your device if any of the trusted places/faces/devices/etc. are found. Configuring multiple verification methods does not mean that you have to match all of them. You should be able to unlock your device with just your face without being in your trusted place. You can also unlock it by being in your trusted place and not showing it your face.
Comment: This seems logical. What confuses me is that my device won't even attempt to recognize my face when I'm not at home (the lock icon doesn't turn into person icon)