Why does a capacitor act like a short-circuit during a current impulse?

Question: While trying to solve questions involving impulses and step functions, we are supposed to assume that an uncharged capacitor or an uncharged inductor acts as a short circuit and open-circuit respectively. But, I don't see the theoretical reasoning behind it. Furthermore, can an impulse show up against a capacitor or inductor with only a step source?
Answer: The basic equation for a capacitor is charge, Q = voltage, V x capacitance, C. If this is differentiated we get: -
\$\dfrac{dQ}{dt} = C\cdot\dfrac{dV}{dt}\$
And rate of change of charge is current, therefore: -
\$I = C\cdot\dfrac{dV}{dt}\$
A voltage impulse has very high dV/dt therefore I is also very high.
This to me, represents a short when dV/dt is infinite.
I'll leave you to use the formulas for an inductor to satisfy your curiosity and my laziness.
Comment: @HL-SDK why don't you do that dude, there's plenty of room to make your own answer.
Comment: Start with the basic inductor formula of V = L\$\frac{di}{dt}\$ and integrate both sides to find i
Comment: Judging by the question, the asker might be served well with a physical interpretation of what is going on (displacement current/dipoles and that magnetic thing that makes inductors work)
Comment: A current impulse (infinite di/dt) can only pass through a perfect inductor if the terminal voltage across the inductor is infinite. In a practical world, an inductor has self-capacitance and this means the impulse current bypasses the "magnetic" side of things and appears to pass through the inductor, but it doesn't theoretically. You haven't really stated what you would like to achieve (as I asked) - I've given you the best answers I can give but without a better idea of what you need (not how you want to implement it) I can't really help.
Comment: Thank you :) One more question if there is a step source in a circuit can there be an impulse of voltage or current in it. Or are impulses only spawned from impulses. The caveat I'm thinking of is a votlage step across a capacitor that would give rise to a current impulse, but is their a way to transfer that sudden current impulse to a inductor. Is it by putting it in series with the capacitor?
Comment: The impulse of current when the inductor is in series with the capacitor will be reduced dramatically. Maybe if you state what you are trying to achieve I can help better?
Comment: @Andyaka I am asking out of curiosity: I wanted to know if there exists a certain circuit design that  uses a step voltage source to create a current impulse through an inductor using capacitors. In light of HL-SDK comment, I would  appreciate a physical interpretation as well--as near as that might be.
Comment: @user29568 there is no such thing as a current impulse through an inductor - it would take infinite voltage to create one. Remember, because V = L\$\dfrac{di}{dt}\$, if di/dt were infinite then so would V.
Comment: @Andyaka Speaking hypothetically(because impulses aren't physically realizable), the only way for a current impulse to pass through an inductor is using a current impulse source or voltage impulse source?
Answer:
Why does a capacitor act like a short-circuit during a current
  impulse?

It doesn't act like a short circuit for a current impulse.  Here's the equation that defines the ideal capacitor:
$$i_C(t) = C\cdot \frac{d}{dt}v_C(t) $$
Applying the Laplace transform to this equation (assuming zero initial conditions) yields
$$I_C(s) = sC\cdot V_C(s)$$
The Laplace transform for the unit impulse is
$$\delta(t) \Leftrightarrow 1$$
Thus, if the capacitor current is the unit impulse, the Laplace voltage is
$$V_C(s) = \frac{1A}{sC}$$
Going back to the time domain, we have
$$v_C(t) = \frac{1}{C}u(t)\, V$$
Thus, the voltage across the capacitor is a scaled step.
If we instead approximate the unit current impulse with a current pulse
$$i_C(t) = \frac{1}{T}[u(t) - u(t - T)] $$
then the capacitor voltage is
$$v_C(t) =
\begin{cases}
0 & \text{if } t \le 0\\
\frac{t}{CT} &  0 \lt t \le T\\
\frac{1}{C} & t \gt T
\end{cases} $$
In any case, this is different behavior than that of an ideal short circuit where the voltage across is zero for any current through.
Comment: Looking at this example, http://i.stack.imgur.com/Dsvbi.png, doesn't the capacitor act as a short circuit during the current impulse of the source.
Comment: I think the problem that Alfred is bringing up that in the real world any short circuit will have finite current so the voltage must be 0 from \$V=IR\$.  In this purely theoretical realm with infinite current we have \$V=0*\infty\$ which is indeterminate and can be any value.
Comment: Naturally, the current impulse can be transformed into a voltage source but what does it mean in the bigger context.
Comment: @user29568 Did you really mean current impulse? Current impulse is not nearly as interesting as voltage impulse.
Comment: @user29568, a capacitor acts as short circuit in two different limits:  (1) as an AC short circuit as the frequency goes to infinity and (2) as an actual short circuit (assuming the capacitor is uncharged) as C goes to infinity.  Rather than thinking in terms of a short circuit, try thinking in terms of *the voltage across a capacitor must be continuous for finite current through*.
Comment: @AlfredCentauri I reckon you should write a book; it would make for one of the best EE books out there. With a current impulse, there would be a step voltage, and with a voltage impulse there will be a current impulse for a capacitor. Your summary easily reflects that thanks.
Answer: Andy gives a great answer addressing the motivation for such statements.  This answer will be the theoretical answer requested in the post.
Given an input voltage function \$V(t)\$ then the current through the capacitor is \$I(t) = C \frac{dV(t)}{dt}\$.
Strictly speaking if \$V(t)\$ is the unit step function then \$I(t)\$ is not defined at \$0\$.  The impulse "function" is even more problematic in that it is not even a function.
We basically have two options:
1) Realize that while \$C \frac{d}{dt} \$ is not strictly defined on this space it is defined on the space of differentiable functions.  However, this operator is linear on this dense set and extends uniquely to a linear operator on the entire space of functions.  In layman's terms, we can estimate the step/impulse functions by differentiable functions \$f_i(t)\$ and then \$C\frac{df_i(t)}{dt}\$ will estimate \$C\frac{dV(t)}{dt}\$.
2) Use  that the space of voltage functions, with appropriate mathematical adjectives, is self-dual to figure out how one can write this in the language of distributions.
Option 1) is pretty clear.  Any reasonable estimates of the step or impulse functions will clearly have a derivatives approaching infinity at 0.
Option 2) obviously takes more study but the answer is interesting to think about. As a distribution the impulse functional \$\delta\$ is defined as \$\delta(f)=f(0)\$ for all voltage input functions \$f\$ and the resulting current functional is (uniquely defined by) \$(C\frac{d \delta}{dt})(f) = C\frac{df}{dt}|_{t=0} \$ for all (smooth) voltage input functions \$f\$.  This is why you will see an "instantaneous" infinite short current when you feed in the impulse function.  You can do a similar computation for the unit step function.
Answer: First, you must understand what you are dealing with in terms of voltage and current. A capacitor is an electrical component across which the voltage can only change in a continuous manner; i.e. there can be no 'instant' jumps from one voltage to another. This is always true whether the capacitor is charged or not. This happens because the capacitor is designed to store voltages on its plates: as a external voltage is applied across a capacitor, it starts charging or discharging until it matches the voltage.
Similarly, an inductor forces the current going through it to always be continuous, regardless of whether it is charged or not because it is storing the charge in its magnetic fields.
The question specified uncharged capacitors and inductors as a means of setting both to voltage on the capacitors and the current on the inductors to zero before the impulse or steps occur.
So what happens when a step function first hits a capacitor? The voltage across the capacitor, which had been zero, cannot change instantly, so it stays at zero, while the current through it changes instantly to match the step function. For that instant, this is exactly the same behavior any wire or short-circuit would have.
A step function hitting a induction results in an instant change in voltage while the current flowing through remains at zero. This is exactly the same behavior as an open circuit.
Now, both of these components start changing over time. Given enough time, the capacitor starts acting as an open circuit and the inductor as a short-circuit. But you aren't dealing with that right now. You are just dealing with the instantaneous responses.
As to whether an impulse can show up against a capacitor or inductor with only a step source, the answer is it depends entirely on what part of the impulse you are looking for. If you are looking for the voltage across an inductor, for example, it will most definately show up. If you were looking for a current through the inductor however, no, an impulse will be invisible.
Answer: I don't know if this helps, but its the way I think about it: in short, the reason is that an impulse is imagined to be an infinite current in an infinitely short time. (the total charge is finite)
So when dealing with infinities, anything not infinite is effectively zero.  I.e. the capacitor can only pick up a finite charge (Q = CV) therefore it can only develop a finite voltage, which is treated as approximately zero in the heuristic impulse analysis.
Resistors will get infinite voltage across them, so they conduct according to V=IR (V is infinite).
However, inductors are open circuits for rapidly changing current, so do not conduct.
As for the step analysis, I think Brian Drozd above had a good answer.
Answer: At t=0, Vc(0)(=0) can not jump to step input voltage. So, Vc(0)=0, which means that the capacitor is short circuited at that moment. Thus, the step input voltage is transferred to the resistor.


are C# int? and bool?s always boxed when hasvalue = true?

Question: This MSDN reference seems to indicate that when an int? (or any Nullable<T>) has a value, it's always boxed (and hence a much less efficient store of data, memory-wise than an int).  Is that the case?
Answer: That page refers to when you are boxing the Nullable<T> struct, not the values inside the struct itself.
There is no boxing involved in storing a nullable type until you try boxing the nullable itself:
int? a = 42; // no boxing
int? n = null; // no boxing

object nObj = n; // no boxing
object aObj = a; // only now will boxing occur

This behavior is no different than when boxing a regular value type (with the exception of handling the null case) so it is really to be expected.
Answer: No. The Nullable object is a generic struct, and internally handles the value of T without boxing.
Answer: That's not the case. Nullable<T> is generic, so it holds the real int or bool.
The MSDN page is talking about what happens when you box a Nullable<int> or Nullable<bool>. If you never assign your nullable struct to an object variable, you won't incur boxing overhead.


Block Instagram for Android to access the Internet, using a software like SQUID on my Laptop/Desktop

Question: Is there any way I could block Android Apps for example Instagram from accessing the Internet, using the SQUID software or something similar on my Personal Computer?
Answer: If you have access to the WiFi Router you can block traffic and/or mac address. there are custom firmware for some router models like DD-WRT or Open-WRT. But the phone still can by-pass via mobile data.
Filter rules are complicated and may have unwanted effects. This is just a example
"Instagram" uses TCP protocol for communication.
TCP traffic analysis
Ports Range
Remote tcp port(s): 443, 80.
HTTP traffic analysis
HTTP traffic is found in Instagram's traffic.
Host(s) being connected(regular expression): ^..ak.instagram.com, ^..cdninstagram.com.
TLS traffic analysis
TLS connections are found in Instagram's traffic.
TLS Host(s) being connected(regular expression): instagram.com.
How to block Instagram?
Block the listed ports to block Instagram.
Block the listed http and tls domains to block Instagram.
Setup a content filter(ie: WFilter), which can block Instagram via signature
http://imfirewall.us/protocols/view.php?proto=Instagram


Remove Feed chatter in community

Question: Does anyone knows how I can remove the chatter in community for user profile. I don't want that shows up.
Please see the attachment, thanks.
Answer: Basically, you are trying to modify the User Profile component. Unfortuantely, you will have to create your own lightning component if you wish to remove certain fucntions. Standard lightning components are like little blackboxes, what you see is what you get.
Comment: Thanks for your answer. I was thinking that maybe I can set it up from profile setting but actually I couldn't find any.
Answer: You can`t, but you can change this deafult component.
Delete default componente, and search for this, User Profile Detail.

Remove Feed chatter in community


Can't install mysql-client-core* on ubuntu 14.04?

Question: I tried to mysql-client-core* install via apt-get on ubuntu 14 ; but, it was fail .
The following  that is my os:
xxx@ubuntu:~/pvz2/pvz2server/dockerfiles$ uname -a
Linux ubuntu 4.4.0-31-generic #50~14.04.1-Ubuntu SMP Wed Jul 13 01:07:32 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

installing infomation:
xxx@ubuntu:~/pvz2/pvz2server/dockerfiles$  sudo apt-get install -y mysql-client-core*
Reading package lists... Done
Building dependency tree
Reading state information... Done
Note, selecting 'mysql-client-core-5.1' for regex 'mysql-client-core*'
Note, selecting 'mysql-client-core-5.5' for regex 'mysql-client-core*'
Note, selecting 'mysql-client-core-5.6' for regex 'mysql-client-core*'
Note, selecting 'virtual-mysql-client-core' for regex 'mysql-client-core*'
mysql-client-core-5.5 is already the newest version.
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 mysql-client-core-5.6 : Breaks: mysql-client-core-5.5 but 5.5.54-0ubuntu0.14.04.1 is to be installed
E: Unable to correct problems, you have held broken packages.

If I use: apt-get install mysql-client-core-5.6 or  mysql-client-core-5.5 , can successfully to install , but don't to connect mysql server .
mysql -h127.0.0.1 -uxxx -pxxx

ERROR 2003 (HY000): Can't connect to MySQL server on '127.0.0.1' (111)
ERROR 2003 (HY000): Can't connect to MySQL server on '127.0.0.1' (111)

I hope to install mysql-client-core-5.6 than  mysql-client-core-5.5.
Who can help me ?
Comment: Is there MySQL server installed? `sudo apt install mysql-server`
Answer: I suggest running sudo apt-get clean && sudo apt-get autoclean && sudo apt-get autoremove && sudo apt-get update to clear old packages lingering on your system, and then updating the sources. Then install the program.


How to stop startup chime on boot up

Question: I am still on Catalina 10.15.7 and just did the latest security and Safari updates today. I would post the versions, but not sure where to look for them. Anyhow, now on boot up I get the Apple startup chime which I do not like. I've read that apple put in back with Big Sur - but I don't have that.  Can someone tell me how to disable the startup chime? Some people online are saying that there should be an option in Sound Preferences but I don't see that either. I'm guessing I can mute, but I only want to disable the startup sound not all sounds.
Comment: 99% of the time the only person who hears the startup chime on my Mac is me. And I already know that I'm using a Mac. If I'm around someone else using my Mac, I think the Apple logo is probably sufficient to tell them which computer I am using!
Answer: This is pretty easy. In fact there are articles out there that describe how to do this.
Briefly, open terminal app in /Applications/Utilities and paste in this command
sudo nvram StartupMute=%01
It will ask for your password and then just return to the terminal prompt. When you reboot the chime will be gone.
Note that if you reset NVRAM (some old farts like me still call it PRAM) the chime will return, you just have to do that command again.
to turn the chime on
sudo nvram StartupMute=%00
In case you change your mind...
Comment: Tk steve.  just asking - TJ suggested sudo nvram SystemAudioVolume=%80 and you sudo nvram StartupMute=%01  , are they the same?  im familiar with terminal but not a coding expert.  didnt know there would be so many variations for the same outcome as he lists even more.  just curious  tks.
Comment: The one I found turns it ON or OFF, that looks like it adjusts the volume. You could experiment with various two digit numbers till you find one you like.
Answer: Source: How to permanently turn off your Mac's startup sound - ChrisWrites.com
All commands to be entered in Terminal followed by Enter/Return. I recommend copy/paste.
Note: Any sudo command may prompt for your login password. Enter it as you would the login screen. It will not appear in Terminal as you type.
Try this first
sudo nvram SystemAudioVolume=%80
If that doesn't work, you can try these variations:
sudo nvram SystemAudioVolume=%01
sudo nvram SystemAudioVolume=%00
sudo nvram SystemAudioVolume=' '
To get the sound back or if something goes wrong…
If you change your mind, enter this:
sudo nvram -d SystemAudioVolume

How to stop startup chime on boot up


How to make a "light" build of GCC with language supports etc. pruned?

Question: Basically I would like to make a light build of GCC with only C/C++ support. Can this be done easily or does it require manual tinkering with source?
Comment: What exactly are you trying to achieve? 99% of the C compiler code is needed for C++, so I'm confused as to what you are trying to remove. Or do you mean `./configure languages=c,c++`.
Comment: Do you want only a subset of the full C++? Or to only install the C++ parts of GCC?
Answer: This is covered in Installing GCC and Configuration

--enable-languages=lang1,lang2,...
      Specify that only a particular subset of compilers and their runtime libraries should be built. For a list of valid values for langN you can issue the following command in the gcc directory of your GCC source tree:
<code>         grep language= */config-lang.in
</code>
Currently, you can use any of the following: all, ada, c, c++, fortran, go, java, objc, obj-c++. Building the Ada compiler has special requirements, see below. If you do not pass this flag, or specify the option all, then all default languages available in the gcc sub-tree will be configured. Ada, Go and Objective-C++ are not default languages; the rest are.

So, for your case using:
<code>../gcc/configure --enable-languages=c,c++
</code>
should be sufficient, besides other needed options, of course.
See also Building

Please note, that re-defining LANGUAGES when calling `make' does not work anymore!
Comment: Thanks, I somehow had missed that, even though I've been reading that manual for the past week or so!
Answer: You can also use:
<code>make install-strip
</code>
to reduce your installed size remarkably


Hubble's law distance and time dependence

Question: Hubble's law states that the recessional velocity is proportional to the distance. The further the observed distance, the further back in time one is observing. I want to know (generally) how this time dependence of observed light sources at different distances is accounted for in the law? Thx
Answer: From the non relativistic Doppler effect $$\lambda_o=\lambda_e(1+\frac{v}{c})$$$$\frac{\Delta \lambda}{\lambda_e}=\frac{v}{c}$$$$z=\frac{v}{c}$$ A plot of  redshift($cz$) vs. the physical distance $r(t)(a(t)\chi)$ is giving a linear relationship(best fit curve) implying $$cz  \sim r(t)$$$$cz=v(t)=H(t)r(t)$$
Comment: Thanks for the explanation but it's not really getting to the heart of my question or I just don't fully understand the solution. Here is some clarification. With respect to the law in would state that a galaxy twice as far away would be receding twice as fast, but what isn't mentioned is that this more distant galaxy was moving twice as fast but also twice the time in the past. The observed red shifted photons from the two galaxies have traveled two different distances and originated from two different times in the past.
Comment: Yes it is, two photons from two galaxies are emmitted say at $\chi _1$ and $\chi_2$ where $\chi_1\gt \chi_2$ (comoving distance) and if are received today $t_0$ then the physical distance travelled by then would be $a(t)\chi_1$ and $a(t)\chi_2$ where the emmision time would be $t_{e1}$ and $t_{e2}$ where $t_{e1} \lt t_{e2}$

Hubble’s law distance and time dependence


oral sex after breaking fast for the day during Ramadan?

Question: Is it permissible to give or receive oral sex after breaking fast for the day during Ramadan?
Answer: Given that it's between spouses...
EDIT: Yes, it's permissible to have sexual relations from after sunset to just before sunrise. Just like eating, you can enjoy each other too.
I don't want to get into the debate over whether oral is halaal or haraam. Other brothers and sisters can shed light on this.
Comment: The question says "after breaking fast" ... this implies that it happens at nighttime and not during the fast.
Comment: @UmH Whoops, my mistake :(


Structure of a metal in gas phase

Question: I'm going to use aluminium in my example, but this is applicable to all metals.
Aluminium has delocalised electrons. It has aluminium cation -electron attraction. It's easier to visualize the atomic structure of aluminium in solid form.
But if it's in the gas phase, will delocalised electrons return to the atom itself, or is there going to be an electron and cation mixture (electrons floating around)?
So can aluminium (or any other metal) conduct electricity as a vapour, and what would its conductance be compared to its solid form?
Comment: You need to be more specific: do you mean an isolated, electrically neutral Al atom? An Al ion of some kind?  A cluster of Al atoms? A cluster of variously ionized Al atoms?  A dispersed gas of Al atoms? A dispersed gas of Al ions? Etc. The answer depends somewhat on which specific system you're asking about.
Comment: no,i am talking about cluster of atoms.
Answer: Metal vapors do conduct electricity, as in the mercury vapor lamp (also used in fluorescent lamps), but, since the atoms are isolated or in small (molecular) clusters, conduction is ionic, not metallic. Since electrons are far less massive (and therefore more mobile) than the heavy ions, they are responsible for the majority of the conducted current.
Electrons are forcibly ripped away from the mercury atom (well, raised to higher levels) -- the first ionization potential is 10.39V, and its second is 18.65V, so in a mercury vapor lamp or mercury vapor rectifier, the potential drop of at least 20 volts implies more than one of the outer electrons are lost from many of the atoms.
Note that ionized gases are much less conductive than solid or liquid metals. Consider a 70 watt sodium vapor lamp, with an arc length of perhaps 10 cm and a potential drop of ~18 volts. The finest commercially available wire, 40 gauge, would have a potential drop of just ~1.3 volts for metallic copper wire, or ~4 volts for sodium, which has 1/3 the conductivity of metallic copper (if they made fine sodium wire), at the same length and current (~3 A).
See the useful chart explaining sodium-vapor ionization .

Structure of a metal in gas phase


Getting notified about a new block on the Monero blockchain

Question: Is there any method, other than polling, to subscribe to new blocks being published on the Monero network? I want to get notified whenever a new block is published on the network on my app.
Answer: The current Monero release allows you to call a program in those cases:
When a block in added to the blockchain, you can trigger a command using monerod's --block-notify option.
When a transaction is received by the wallet (both when seen in the txpool and after its first confirmation), you can trigger a command using monero-wallet-{cli,rpc}' --tx-notify option.
Both of those options take as parameter a program and optional parameters. Every instance of %s will be replaced by the block hash or transaction hash which triggered the notification. Note that this is a program and optional parameters, and not a shell command, if you want redirection or pipes, you'll have to call a shell (eg, --tx-notify bash -e 'echo %s >> /tmp/hashes'). Parsing is limited, so you can't use quotes and backslashes to escape spaces. If you need complex parsing, write a script to do it and call the script.
Answer: No. Polling is the only way. You only need to poll once every couple of minutes at most though.
Comment: Can't websocket be used for the same?
Comment: No. The daemon doesn't implement a websocket server. Only RPC.


Triggering a 555 timer IC

Question: I need to trigger a 555 timer IC in astable mode as soon as it has power. It CAN NOT be done manually through a negative pulse like it usually is. The solution must be compact as space in my project is certainly at a premium. I either need a method of converting a constant high to a negative pulse, however this would require other components, or another method of triggering it. If neither are possible, is there an alternate astable IC I can use which would enable me to provide a 60s mark time followed by 1s space?
Thanks in advance for your time,
Regards,
Eerf
Comment: 1) How much space \$ L \times W \times H\$  do you have available? 2) How accurate do you need the output timing to be? 3)How much current do you need to drive your load?
Comment: Re: "The timing really has to have no accuracy." then 60s \$\approx\$ 0s. Problem solved.
Comment: My load is 150ma +-5% and I can spare no more than 2.5x2.5 for LxW but height isn't an issue. The timing really has to have no accuracy. The shorter the interval between pulses and the shorter the length of the pulses, the better, but 10s between pulses is plenty.
Comment: 2.5 x 2.5 centimeters? millimeters?
Comment: You don't usually have an external trigger in astable mode.
Answer: While what you need can be easily accomplished using a 555, in this instance - because of your space constraints - it seems a cheap 8 pin microcontroller might be a better fit.
In order to get the astable duty cycle you want, the 555 circuit will need two resistors and two  capacitors and, if you need to use the bipolar for the highish source and sink currents its output can provide,  the timing capacitor will be in the tens of microfarads for for an output high 60 seconds long.
A microcontroller will require, at the most, a power supply bypass capacitor and a ceramic resonator or crystal, or at the least, just the bypass cap if you choose one with an internal oscillator.
Comment: Thanks for the quick response,however surely another circuit in an 8 pin package with 2 resistors and caps will take up the same space as a 555?
Comment: Edit: Dupe. Ignore this.
Comment: @Eerf: You missed the point, I think.  A 555 will require three supporting discretes, while an MCU will require only one. And, possibly, even that one can be gotten rid of.
Comment: Ah I didn't realize a microcontroller would not require external components. Thanks!
Answer: 60 s is too long a time for a old analog timer like the 555.  Use a microcontroller.
This can be done by the cheap and tiny PIC 10F200.  It has only 6 pins and comes in the same package individual transistors do.  All it needs is power and a bypass cap.  The oscillator is built in, which is good to a few percent.  This solution will be smaller and take less power than a 555 timer, even if a 555 could reasonably do 60 s.

Triggering a 555 timer IC


Should I implement IDisposable for a User Control?

Question: I am creating a .NET User Control. Do I need to implement the IDisposable interface for my User Control?
Answer: Control already implements IDisposable
You only need to override the implementation if you need to dispose some unmanaged resources.
So the simple answer: no, probably not.
Answer: Actually, Control already implements IDisposable. The base implementation is usually generated in the .Designer.cs file if you did any sort of auto-generation of the Control using Visual Studio. You just need to add to the base implementation if you need to.
It has a virtual Dispose method which takes a boolean flag. If True, then Dispose was called via the interface. If False, then Dispose was called via the finalizer.
Answer: Only if you have external resources that need to be released quickly.  Otherwise, those resources may be held on to for as long as the object remains uncollected, and possibly longer than that.


SFMC/Exact Target Fuel SOAP API - is there any way to create scheduled email send definition in to custom folder instead of My Tracking folder

Question: I'm scheduling created email send definition from user-initiated folder with the node js Fuel-SOAP API library, this gone to My Tracking directory Is it possible to assign the tracking destination custom folder through the API?
Thanks in advance!
Answer: If you mouse over your custom folder you should see a numeric folder id in the link.  In  your soap request, use that ID in EmailSendDefinition.CategoryID property
Updated with example
<code>var folderID = 12345;
            var sendESD = new ET_EmailSendDefinition
            {
                AuthStub = myclient,
                CustomerKey = newSendDefinitionName,
                CategoryID = folderID
            };
            var sendESDResponse = sendESD.Send();
            Console.WriteLine("Send Status: " + sendESDResponse.Status.ToString());
            Console.WriteLine("Message: " + sendESDResponse.Message);
            Console.WriteLine("Code: " + sendESDResponse.Code.ToString());
            Console.WriteLine("Results Length: " + sendESDResponse.Results.Length);
</code>
Comment: I have tried your way but i have no luck. Can you please explain it with brief, or suggest me another solution, because I am stuck on this.
Comment: @KrishanKantSharma see updated example. you need to get the folderID from SFMC UI
Comment: No luck . I should have made my request more clear. If you are in the Marketing Cloud UI, I'm looking for how to assign the folder under Tracking -> Sends.
Same thread is here :
[link](https://salesforce.stackexchange.com/questions/142585/sfmc-exact-target-c-soap-api-is-there-a-way-to-assign-tracking-folders-to-ema?rq=1)


Finding the corresponding chords from sheet music

Question: I am a beginner in reading sheet music. I can understand what each notes are and one stave has a G clef and the other an F clef. I am trying to solo this on guitar and was wondering if there is a chord structure that I can play to this. How can I figure out the chord shape for this pattern? Is there a theoretical way to identify the corresponding chords?
Answer: Since you can read the notes, you can quickly work out that the first bar is Bbm.  Half way through the next bar might just be Ab or potentially Absus4.  Then the next bar Gb7.  You have to analyse each bar or half bar.  There will be passing notes and extra notes that don't need to be included in the guitar chords.  You have to decide what sounds right to you.  If you don't find these to be the most user-friendly chords on the guitar, you might like to use a capo on the 1st fret and play it in Am.
When you say you are "trying to solo this on guitar", are you wanting to include the melody with the chords?  If so, then that is a much more demanding procedure.
Comment: You need to do some musical analysis of what's going on harmonically.  In the 1st bar you have a Bb (as the bass note), Db and an F.  That is the triad of Bbm.  The Eb is just a passing note in the melody.  Half way through in the next bar it is not so clear cut.  It looks like an Ab chord, but some of the notes in the melody don't belong to that chord.  That's why I suggested it might be Absus4.  You might find a better fit.
Comment: Just analyse what the notes suggest to you harmonically.  Ab and Eb in the bass sound like it wants to be an Ab chord, but the extra notes in the melody suggest a more juicy chord than that.
Comment: Plus 1 for the capo suggestion.  Please consider editing your answer to incorporate your very well worded comment about musical analysis of what's going on harmonically.  That one comment is almost better than your answer ;-)
Comment: Could you expand a little on how you came up with that chords atleast for a bar or two?
Comment: Yeah, more like i want to do what a keyboardist can do looking at this. He will play both the base and the melody.  In my guitar classes i used to do it with songs when i have a chord structure , or just plain open notes. When its a chord its easy to play the base and the melody, that's why trying to generalise the procedure of identifying the chords from the sheet that i have.
Comment: Capo 1 with Am would definitely be much easier for a guitarist
Answer: Work out the chord shape? That's not always possible from piano music to guitar.
Work out the chords themselves is easier. First is to establish what key the piece is likely to be in. Here, with 5 flats, it's either D♭ major or its relative B♭ minor. You can read the dots, so in the first bar, there's predominantly B♭ F and D♭ notes. They, together, make up B♭ minor chord.
Half way through the second bar, there's A♭ E♭ and D♭. The chord springing to mind here is A♭sus4. So, all you do is look at the main notes - those on beats 1 and 3 initially, and translate them into a chord - often one that belongs to the key stated in the key sig. That's what you do!
Comment: Plus 1 for "First ... establish what key ..."  That would be an excellent way to narrow the potential choices of chords to try first.
Answer: The left hand part is just power chords (= root + fifth) so you can probably get away with just playing the root note (since the fifth is implied by being present in the overtones).
If you want to play full triads, then look to the key signature and the melody to find whether it's a major or minor chord.
Comment: The procedure called *harmonizing the scale* in the key of Db gives the chords Db Ebm Fm Gb Ab Bbm Cdim. So if you read just the lowest note, then you can use it to pick the chord from this list. This will work if there are no accidentals that change a note from flat to natural or sharp.
Comment: Could you explain this concept you shared with an example from the question?As i said , i'm new to this whole thing and i'm not sure i understand what you suggested.
Answer: In this particular case the job is easy.   The LH has a simple series of open 5ths.  We can assume these are the root and 5th of the chord.    So bar 1 and the first half of bar 2 are a B♭ chord, moving to an A♭ chord in the second half of bar 2.
Now look at the melody.  If the first chord was B♭ MAJOR we'd expect to see some D♮ notes.   If it was B♭ MINOR there would be D♭ ones.   Get the idea?   This method gives us a definite answer for the first and third chords.  The second one is undefined - it's SOME sort of A♭ chord but there's neither a C or a C♭ in the melody.  But it's a pretty safe bet to assume the key signature would prevail if there WAS a C.  Or maybe it's a sus4 chord.
Don't forget to learn to play the tune!   It's probably a better thing to play than any amount of guitar 'widdley'.
Answer: The notes in the staff would likely restrict the "chord shape".  If you simply had the letter names of the chords above the treble clef you would be free to choose how they are played for the most part (even chord names indicate an inversion when properly notated).  What you need to do is transcribe the bass clef so that all the notes are in the treble clef and see how they combine.  The chord structure should become pretty clear soon enough but you may run into some difficulty since (1) the bass clef does go lower than the lowest note on guitar, (2) Some of the bass may overlap the melody once it's brought into the treble clef, and (3) guitar is actually played an octave lower than written.  Despite being able to read both clefs you are trying to read this on an instrument that it was not written for and you may need to do some arranging.  My comments are more general and may not all apply to your example.  Also, if this were arranged for guitar one might transpose key so that it is in an open string key.  This would allow you to use open strings for the bass making multi voice upper registers easier to play.  Once all this is dealt with you can then focus on "shape", and there may be more than one possible fingering for the set of chords you have.
Answer: I do this type of stuff alot but I know music theory.  There's a lot moving parts (no pun intended) here.  There is a lot of good advice above.  Here's mine:

1st of all if you do not know the song and how it sounds AND have a good ear, there is no foolproof way to know if you assigned the correct chords short of someone like me reviewing it.
Many times in looking at the bottom line (bass line) on arrangements like this you not looking at the root of the chord (b note b chord) and so you have to know the song and know construction of chords and their inversions to determine the actual chord.
Then you have to learn to ignore passing tones in the Melody line (typically top line) and not allow them to dissuade you away from the simple chord progression of the song.
There's a little more to it than this, but these 3 things are important basics that will help guide you.
Comment: Thing 1 you must know the song and how it sounds, Thing 2 you have to know the song AND know constructions of chords and their inversions Thing 3 Ignore passing tones in the melody line.  Did I get that right?  Is there a theoretical way to identify what chords might be most appropriate (assuming you do know the song)?
Answer: If this sheet is from you and you want to find out what chords would fit to this music (apart of this rudimentary fifth) you should learn the basics of chords and triads, as you won't make any progress by asking for chords to each melodic pattern.
But if this bars are parts of a composer who knew what he wrote and why he just wrote this block chords of open fifths there's no need to find out the chords for guitar, as the accompaniment would be meant as it is: root tone and fifth and no third. Then the guitar should play nothing else than this tones.
(You could try to play on a keyboard 1-3-5 instead of 1-5 with the left hand and you will find out that this triad won't fit to every motif. So if you feel 1-3-5 doesn't fit just play 1-2-5 or 1-4-5, write the names of this tones and play them on the Guitar as a chord.)


Is a parallel 4 link safe compared to a triangulated 4 link?

Question: After researching the topic the closest article I've ever been able to find was written by Ridetech: "What's the difference between a triangulated 4 link and a parallel 4 link?".  However, a concern with running the Parallel 4 link wouldn't it be bad on the truck frame during vehicle articulation?  Most Parallel 4-link kits I've researched use Urethane bushings but wouldn't it ride like a covered wagon, too?
Comment: Your bags are going to take up most of the harshness in the ride. I don't think I'd worry too much about Urethane bushings. The bushings will help in other areas like for traction and stopping due to not allowing the suspension to load up during those events.
Comment: link dead. some "form error" code on their page.
Answer: How much 'articulation' do you need?  Is this a rock crawler?  Then do a double triangulated suspension and be done with it.  If this is a street truck with high spring rates, slammed etc.  You are not going to be leaning the truck far enough.
If you are building a race car, either triangulated (see NASCAR) or torque arm (see 1987-2002 Camaro/Firebird - or Griggs racing mustang).
The point being, you don't want any binding at all (stiction or otherwise) in your suspension.  Make the springs, shocks and swaybars do their jobs.  Suspension pieces just guide the axle.  You'll typically need solid bushings (rod ends or johnny joints).


Practical Book on Hamiltonian and Lagrangians?

Question: Are there any terse, accessible books that are geared specifically at learning these two formalisms and how to effectively use them? So far I've only see either topic introduced as a part of another book, like QM or classical mechanics. I was hoping for something focused more or less exclusively on these formulations that would then go on to explain important nuances and limitations, and then systematically show how to apply them effectively.
Comment: Marion and Thorton is pretty good.
Answer: I have finished reading a great book called "The Theoretical Minimum" by Leonard Susskind (a famous string theorist) and  George Hrabovsky. It's about classical mechanics but mainly talks about both the Lagrangian formulation and the Hamiltonian formulation of classical mechanics. It is great for beginners in physics or just about anyone. It also reviews the differential, integral, and multivariable calculus needed for understanding these topics. It also gives some examples on how to use both formulations. Oh, and also, at the beginning of each chapter, there is a fun short story!
To buy:
http://www.amazon.com/The-Theoretical-Minimum-Start-Physics/dp/0465075681
Comment: On that note, http://theoreticalminimum.com contains video lectures, available for free, on a variety of subjects in physics (including classical mechanics). Having looked through some of them myself, I must say that they are truly excellent.
Comment: Yeah, I've watched some of Susskind's videos for statistical mechanics and they've been great. Thanks for the recommendation


What is the best dictionary for learning a contemporary American accent?

Question: I'm using the Cambridge English Pronouncing Dictionary (18th edition, 2011). I know how IPA phonemes work and can also fathom American notations. So, which dictionary would best help a rookie to learn a contemporary American accent? Don't suggest age-old dictionaries.
Comment: I'm voting to close this question as off-topic because it's a request for resources
Comment: The Google lady on Google translate's "listen" feature (if the Google settings are US English) does a pretty good job of speaking individual words, and often entire phrases with a natural accent and intonation. Always best to check on ell.stackexchange.com if you encounter anything that sounds odd.  For example, this is pretty close to natural accent and phonology: `a paper bag` https://www.google.com/search?q=google+translate&oq=google+translate&aqs=chrome..69i57j69i64j69i60.1895j0j8&sourceid=chrome&es_sm=93&ie=UTF-8
Comment: @FumbleFingers where can i request resources? looking for the best etymological dictionary, or starters...
Comment: @user3293056: The gold standard is the full OED (Oxford English Dictionary). There's nothing remotely comparable, for English or any other language. Sadly, unless you can get free access through your university (or UK public library), [it costs $295/year](http://public.oed.com/how-to-subscribe/). The best etymological dictionary with free online access is [Etymonline](http://www.etymonline.com/), but see [this ELU Meta page](https://english.meta.stackexchange.com/questions/484/) for a more complete list of what we at ELU consider "reliable, online resources".
Answer: None: you cannot pick up an accent from a dictionary. You can only pick up an accent from listening to it.
There's far, far, far more to an accent than its phonology alone, let alone that part of its phonology readily expressible in IPA.  Note also that most dictionaries at best use phonemic transcriptions, not phonetic ones.  A phonemic transcription will not be enough to tell someone just learning the language how it is to be pronounced phonetically.
The Wikipedia article on accent points this out in the following citation:

Many adult and near-adult learners of second languages have unintelligible speech patterns that may interfere with their education, profession, and social interactions. Pronunciation in a second or foreign language involves more than the correct articulation of individual sounds. It involves producing a wide range of complex and subtle distinctions which relate sound to meaning at several levels.
Comment: True. However, if you want the correct American pronunciation for English words, the best (and by far the most convenient) source is [Kenyon and Knott](https://archive.org/stream/pronouncingdicti00unse?ui=embed#page/6/mode/1up). It also has a lot of practical information about regional dialects and English in America,
Comment: "Curse Twitter and Facebook for prose." As apposite as the word you used may sometimes seem, I suspect you intended *cruise*. @user116032.
Comment: It depends on which American accent you want: broadcast, New York, mid west, southern, Appalachian, Texan, Boston, etc...
Comment: Curse Twitter and Facebook for prose and enjoy Youtube for pronunciation.  English is so alive.  I doubt any published source (I assume you mean a published dictionary) can keep up.


Access a localhost server from wine on ubuntu

Question: I am running Ubuntu 12.10 and have a program call Construct 2 install through Playonlinux.  Construct 2 creates a localhost:50000.  Is there a way to get wine to allow me to access the localhost created by Construct 2 in my Linux Chrome install?
Answer: start browser, then put 127.0.0.1 instead of localhost
127.0.0.1:5000


Can the person who buys my old number access my old Viber contacts?

Question: I was using Viber on my old phone. I stopped using that SIM card/number and stopped using that phone. I forgot to deactivate my Viber account. When my old SIM card carrier sells my old number to a new person, does that person access my Viber contacts and people I was talking to?
Comment: Welcome to the site! That sounds like it may be a question for the particular application. But generally, applications that use your phone number as the only format of authentication could be abused in this way.
Comment: Thanks. Please look at the answer and let me know what you think.
Answer: Assuming the platform works similar to WhatsApp or Signal Private Messenger. Viber should only use your phone number as a unique identifier, and no content (contacts or messages) should be stored on the server side.
This seems to be confirmed by Viber such that message backups are done through a cloud service; Google Drive or iCloud. Also, Viber uses end-to-end encryption, so their servers cannot see the content of messages, only metadata.
Consequently, if someone does receive your old phone number, no messages can be seen (as no content is stored by Viber), and the same is applicable to contacts.
Comment: @Jack Put your SIM card in a new / formatted phone, and install Viber.
Comment: Also, on viber you have an option to see associated devices with your account, and you can deactivate them.
Comment: I emailed viber support. They said this:

"Thank you for contacting Viber support.

Please be advised that every account activation deactivates Viber from previous devices and a new activation sets up a new account. No previous data will be available for a new owner of your previous number.

Let me know if you have any further questions.

Best Regards,"
Comment: Thanks. How can I verify your answer for sure?
Comment: Thanks. But I've lost my old SIM card now.


Have there been any computer proofs that were found to contain bugs post-publication?

Question: I'm curious if there are any known examples of proofs using a computer which after being published, (in a journal or otherwise) turned out to have bugs in the software which invalidated the proof. I'm particularly interested in examples where the "proved" conjecture turned out to be false.
Answer: Not exactly the answer you are looking for but still interesting, from "New Scientist":
In 1998 Thomas Hales submitted a computer-assisted proof of the Kepler conjecture, a theorem dating back to 1611. This describes the most efficient way to pack spheres in a box, wasting as little space as possible. It appears the best arrangement resembles the stacks of oranges seen in grocery stores.
Hales' proof is over 300 pages long and involves 40,000 lines of custom computer code. When he and his colleagues sent it to a journal for publication, 12 reviewers were assigned to check the proof. "After a year they came back to me and said that they were 99% sure that the proof was correct," Hales says. But the reviewers asked to continue their evaluation.
However, this tiny uncertainty did not disappear with time. "After four years they came back to me and said they were still 99% sure that the proof was correct, but this time they said were they exhausted from checking the proof."
As a result, the journal then took the unusual step of publishing the paper without complete certification from the referees (Annals of Mathematics Vol. 162, p. 1063-1183, 2005).
Also a fun to read: https://phys.org/news/2016-05-math-proof-largest-terabytes.html


Girlfriend's / future wife's modesty issue

Question: Thank you for your answers. It was very interesting and helpful.
I wish you all the best in your lives.
Comment: Masha Allah, it's very nice that you are even thinking about it bro. I will pray for you.
Comment: Is there possible that you marry in your family? I believe that if you look around you in your family you will find a very nice, islamic partner.

Even though I was involved in such issue, but due to arrange marriage, now I am very happy, now my partner obeys Allah and therefore every day, every moment I feel more love for her. So, trust your parents and ask them to find a religious girl having latest education as well
Answer: I pray Allah SWT guides you. Remember that there is no pleasing the creation of Allah when the Creator is displeased.
Please note that is it prohibited for a man to act so freely with a woman who is not lawful for him (not married to him nor a mahram).
Additionally, one should strive to seek the forgiveness of Allah SWT and do everything in his life according to what pleases his Lord.
Jarir b. 'Abdullah reported:
I asked Allah's Messenger (ﷺ) about the sudden glance (that is cast) on the face (of a non-Mahram). He commanded me that I should turn away my eyes.
(Sahih Muslim)
I think the following fatwa has the answer to your question:
Should he marry a girl who insists on going out wearing adornment (tabarruj) even though her character is good?
Additionally, know that Allah SWT is the Most Forgiving but this is not a free ticket to sin as a part of Tawbah (repentance) is deep remorse and regret.
Comment: Alhamdulillah very nice answer. please look into my comment in the question and tell me if I am right? @Naziha
Answer: From Sister Naziha Answer, I am posting the link material here for more understanding.

Praise be to Allaah.
Firstly:
The Prophet (peace and blessings of Allaah be upon him) encouraged us to marry women who are religiously committed. He said: "Women may be married for four things: their wealth, their lineage, their beauty and their religious commitment. Choose the one who is religiously-committed, may your hands be rubbed with dust (i.e., may your prosper)." Narrated by al-Bukhaari, 5090; Muslim, 1466.
And he (peace and blessings of Allaah be upon him) said: "This world is transient comforts, and the best of the comforts of this world is a righteous woman." Narrated by Muslim, 1467. Whoever fails to find a righteous wife misses out on the best of the comforts of this world, one that is better than wealth, children and status, etc.
This should motivate the Muslim to seek a wife who is religiously committed and of good character, and to give such a woman precedence over all others, and not to be heedless about the best of the comforts of this world.
A righteous woman is the one who pays attention to the rights of Allaah and the rights of other people, and the person who has the greatest rights over her is her husband.
Persisting in sin is worse than the sin itself, because it is indicative of weakness of faith and failure to respect Allaah, and it means that the person is careless about things that may be detrimental to his religious commitment.
Secondly:
As well as being an act of disobedience and sin, going out wearing one's adornment is also indicative of a woman's bad attitude and lack of modesty. How can a chaste and modest woman be content to have people look at her and enjoy her beauty?
But because of her weakness of faith and the strength of her whims and desires, the woman who goes out wearing her adornment does not realize how bad her action is, as Allaah says (interpretation of the meaning):
"and Shaytaan (Satan) made fair‑seeming to them that which they used to do"
[al-An'aam 6:43]
Many of those who used to go out wearing their adornment, when Allaah blesses them with guidance, become appalled at their former immodest ways.
There are well known reports which warn against tabarruj (wanton display of one's beauty and adornments), such as the words of the Prophet (peace and blessings of Allaah be upon him): "There are two types of the people of Hell whom I have not seen: people with whips like the tails of cattle, with which they strike the people, and women who are clothed yet naked, walking with an enticing gait, with something on their heads that looks like the humps of camels, leaning to one side. They will never enter Paradise or even smell its fragrance, although its fragrance can be detected from such and such a distance." Narrated by Muslim, 2128.
And he (peace and blessings of Allaah be upon him) said: "Any woman who perfumes herself then passes by the people so that they can smell her fragrance is an adulteress." Narrated by Abu Dawood, 4173; al-Tirmidhi, 2786; al-Nasaa'i, 5126; classed as hasan by al-Albaani in Saheeh al-Nasaa'i.
If this sin is repeated, it creates a black spot on the heart, until the whole heart is blackened, as the Prophet (peace and blessings of Allaah be upon him) said: "If the believer commits a sin, a black spot appears on his heart. If he repents, gives it up and seeks forgiveness, his heart is cleansed, but if he does more then (that spot) increases until it covers his heart. That is the raan (covering of sin) which Allaah mentioned in the Qur'aan:
"Nay! But on their hearts is the Raan (covering of sins and evil deeds) which they used to earn"
[al-Mutaffifeen 83:14]
Narrated by al-Tirmidhi, 3334; Ibn Maajah, 4244; classed as hasan by al-Albaani in Saheeh al-Tirmidhi.
You should note that marriage to a woman who persists in going out wearing her adornment can only mean one of two things:
1 – That the husband has given in to her, and is keeping quiet about her evil action, so he will carry a burden of major sin in the Hereafter and shame in this world, for he is a shepherd who is responsible for his flock.
How can a wise man accept to walk with his wife in the street when she is showing her adornment, and the men around him are looking at her and enjoying the view?!
2 – That he will stay with her in a state of conflict and fighting and disagreement. This may be a cause of distress and anguish which no wise man would accept. So err on the side of caution, for there is nothing like being on the safe side. Look for a wife who is religiously committed, for a righteous woman will be good for you, praise be to Allaah. A righteous woman is the best of the comforts of this world; she will help you to obey Allaah, remind you of what is right and proper, guard herself and her husband's wealth, and raise righteous children for him who will worship Allaah.
We ask Allaah to guide you and give you strength.
And Allaah knows best.
Answer: Wa alaikumselam,
To begin with, why do you want to marry firstly?

To do sex in halal way?
To do progress your life more flexible?
To have money? if she or her family is rich?

Or

To be an intermediary of children, given birth for the sake of
ALLAH(s.w.t.) and for the properness of Ummah of Muhammad(pbuh) ?
She will be a mother, you will be a father.

If your first criteria is the last one go on reading, otherwise don't waste your time to read.
Brother, there are some vital points to be concerned and pondered literally carefully toward marriage though most Muslims(at least they called theirselves as Muslim) don't heed the points.
You shouldn't keep advices of those saying that C'mon, the girl will have danced to your tune by the mid of the marriage.
You must satisfy yourself,at least, concerning the following rules. No exemption can be tolerated.

The first of which is Namaz(salah), 5 times in a day. If you don't perform it, 5 times in a day, YOU CANNOT EXPECT A GIRL WHO HAS THE FOLLOWING FEATURES, including this one.

Fasting

Talking to any other boys(namahram) without you or your
surveillance. (why does the girl need to talk to another? what can he
do anything else than you can?)

Hijab (no exemption too) ( if you don't look at other girls , don't lie yourself, your most important wish from is that from your future wife )

Whenever you wish you should access her mobile phone, laptop etc. She can do same things to you of course

If she accepts the followed criteria, fall on the girl. You don't need to think too much. She will be tune in with you inshaALLAH.  No worry.


Search for .bashrc or other dotfiles in Finder

Question: When I search for files in my home folder that have a filename equal to ".bash_history", I don't get any results, even though that file is there. How can I search for dotfiles in Finder? (I know how to find them in the terminal, however, some programs such as Integrated Development Environments have an open dialog that forces you to go through the Finder to locate the file you want to open).
Comment: The dot files aren't hidden at the file system level. This is an historical Unix naming convention. Hence the Finder should give a way to access them easily rather than to let people think there is any protection associated with these files. This is a Finder conceptual bug and should be repeatedly explained to Apple.
Comment: @danielAzuelos Apple's perspective probably is that for people who don't know enough to find these, then they don't want them touching them because messing up even one can cause a world of grief, and for those that do know how to find them and what they are, they will use the shell. **Bash** `ls`, at least in the Mac version of it still has `.` as hidden. You need to add `-a` to be able to see them in the terminal.
Answer: In pretty much any Open or Save dialog in OSX Yosemite (and several previous versions) you can type shift + ⌘ commmd + . to make invisible files visible within the dialog.
So you can easily open TextEdit (or any given app).
Type ⌘ command + O.
Type shift + ⌘ command + . to reveal invisibles.
Type shift + ⌘ command + G in the Open Dialog and enter ~ (tilde) in the Go-To field to navigate to your home directory.
Type . + P to get to .profile or very close thereto.
Or as AMR says if you know it you can paste the whole path to the desired file in the Go-To field and get directly to it.
If necessary you can always display invisible files in the Finder itself.  I've got this function in ~/.profile to toggle them on/off.
#--------------------------------------------------------------------
# Task: Finder — Toggle All-Files-Visible On/Off
# dMod: 2015/07/29 02:48
# Test: Yosemite
#--------------------------------------------------------------------

function toglffvis()
{

if [ $(defaults read com.apple.finder AppleShowAllFiles) = 1 ]; then
    defaults write com.apple.finder AppleShowAllFiles -boolean false
else
    defaults write com.apple.finder AppleShowAllFiles -boolean true
fi

sleep 0.2;
killall Finder;

}

#--------------------------------------------------------------------

Comment: In Mavericks 10.9.5, shift + ⌘ command + . doesn't do anything in open windows (for me, at least). I do have AppleShowAllFiles enabled, but it still does not show up in the open file window.
Answer: .<filename> is designated as a hidden file for OS X and Finder's search and Spotlight will not find them, even if you have made your hidden files visible.
You can however use the Terminal to find the location of the file. Use:
find ~ -name ".bashrc"

Highlight and copy the path that is returned.
Then in the IDE dialog press shift + ⌘ command + G to display the Go input box.
Paste your path and filename there and you should be good to go.
Note: If you don't want to see all of the warnings of directories that your user account does not have access to, especially if you are running find on your root find /, then you can run it with sudo and that will avoid all of the Permission Denied warnings about searching locked directories.


What are the technical details of how airline seats are installed on an airliner?

Question: What are the technical details of how airline seats are installed on an airliner? The step by step.  Not made how they are installed.
Comment: Are you asking about crew or passenger seats? And there are several types of each.
Comment: @fooot, I am referring to passenger seats.
Answer: Economy seats are removed (and installed) row by row. The row of seats (typically 2 - 5 individual seats) are bolted to a track on the airframe floor. You can see them being removed in this video (~18:30) during a D-Check. The rows are usually held in place with bolts, often in the corners and where seats meet. You can see an example bolt pattern here.
Modern First class seats (the more sophisticated individual ones) will be removed one at a time often with the whole entertainment center around them. The above linked video also shows this.
And, of course, installation is the reverse of removal.
Answer: On most western jets, there are seat-tracks where the seats are fitted. The tracks are fixed to the floor beams and while the seats are fixed to this track, they are not rigidly fixed. This is to allow slight movement when the aircraft flexes. If they were rigidly fixed they would cause localized stress which is undesirable. In fact most of the stuff in the aircraft is not fixed rigidly to the airframe .. Overhead racks and bulkheads included.
The part on of the seat which interfaces with the rack has a circular part which corresponds to a cut-out in the seat-track. You fit this part in and then slide it so that its in between two cutouts. A bolt is then used to prevent further movement.
Similar tracks are used on aircraft ULDs (containers and pallets).


Acceptors with very high energy level in semiconductor

Question: I have gallium arsenide (energy gap of 1.4 eV) doped with silicon in concentration of $10^{14} cm^{-3}$ and energy level very close to the conduction band so it's act like a donor. Now we put in also chromium with concentration of $10^{17}cm^{-3}$ that act like accepotr. The problem is that the energy level of the chromium is in the middle of the bang gap, so the thermal energy is not enough to create holes in the valence band. Now i need to calculate the conductivity and mobility but i don't understand how the chromium effect them, from my understanding he has no effect on the conductivity because they are very far from valence band.
Any idea?
Comment: How would you go about it if the chromium was close to valence band edge? You would probably calculate the occupation of the states depending on the energy level of the acceptor states. Why can't you do it in the same way now?
Comment: Because you will need very high temperature to overcome 0.7 eV
Answer: The deep chromium acceptors take away electrons from the silicon donors. As they outnumber the donors there will be no charge carriers left except for a very small number, due to thermal ionisation of the deep acceptors and E en fewer intrinsic electrons and holes. The material will have very low conductivity.


LED Shoplight Dim

Question: Have 48 led (2 Banks of 24) Shoplight with a standard AC plug into ceiling outlet, controlled by awall switch. Shoplight operated normally for the past year. And then, one day it didn't. It Powers up, but all the LEDs are very dim. Every once in a while, it works normally, but have not been blessed with that for a week now... It is on the garage ceiling, not exposed to moisture... What to check?
Comment: Hello, and welcome to Stack Exchange. It's quite likely that some component has died inside the shop lamp, but it's hard to tell from here.
Comment: Durability of LED fixtures is largely decided by the quality of the electronic driver circuit, and there are a lot of places to cut corners there. Was it a cheapie?
Comment: You did not state the brand/model of LED light ?  Possible a loose connection  ... but typically the drivers can go bad - even be affected by power spikes and brown outs. Depending on manufacturer some really back their products others don't respond at all. CREE is a very good brand of LED bulbs but I don't think they make shop lights. I know they warrant their bulbs with no hassles. Perhaps this shop light has built in obsolescence ?? Just like incandescent bulb manufacturers got together years ago and decided to sell bulbs they needed to make them to fail after about 1000 hours.
Comment: As a disclosure for my planned obsolescence comment ...Just for reference: http://economicstudents.com/2012/09/planned-obsolescence-the-light-bulb-conspiracy/ , there is a bulb in a Fire station in California it has been on 24 / 7 since around 1907 and never changed but still lit.
Comment: that 100-year old lightbulb is very inefficient and cost a lot to make, not practical...
Answer: Thanks for the suggestions... Solved --- sort of...
Took fixture apart to search for loose connections. Initial inspection showed nothing out of the ordinary.  All the bulb connections are of the permanent type, hardwired rather than plugged.
I touched and checked everything I could see at both ends, and pushed to ensure they were all tight.   plugged fixture in, and voila, lights.... 10 seconds later, no lights... (actually back to very dim).
Thought perhaps the chain pull switch on fixture may be the culprit, so cut wires and hardwired around the switch.  Lights, then no lights.
Tried to pull the circuit board out, thinking there was a wire that had a bad solder joint or something similar, but couldn't remove it. Banged my screwdriver on the metal top of the light, and lights came on...  left them on a while, and then eventually turned off the power strip. Turned strip back on, and no lights. Tapped top again with screwdriver, and lights came back on.
So, again tried to remove the circuit board, again unsuccessfully. Stuck my finger in the area circuit board is located, and pressed on all the components and solder joints I could reach, and plugged fixture in again, lights instantly on and stayed on. Powered down and on again the strip down and on again and lights off and on normally. Cussed a bit, and put fixture back together again.
Tested one more time successfully, so reinstalled fixture in garage. Has been working normally since, but recognize this is not necessarily a permanent fix.   Have narrowed solution to circuit board, and will wait till next failure before I assault the circuit board again.  Believe there is a questionable solder joint or component somewhere on the board.
Again, thanks for all the suggestions.
Comment: Jerry, please accept your answer so the question is resolved.
Comment: percussive maintenance!
Answer: These lights consist of an LED strip (in your case two strips) and a AC/DC voltage converter referred to as a "driver". Typically when LED drivers fail, they fail completely. The failure you describe is typical of a bad connection - most likely at the LED strip. If you can disassemble it gain access to the strips you should see two "poke in" connectors where the wires go in. I suspect that's where the problem lies.
Answer: I just had this happen where 1/2 the LEDs did this in a cheap LED shop light. It turned out that there were two series circuits in the fixture so a failure of one LED would kill half the lights (or severely dim them). I found the defective LED and bypassed it to get the other LEDs working again.

LED Shoplight Dim


My villagers are leaving my village

Question: I was building a village (Minecraft pocket edition, creative, peaceful). I spawned 2 villagers, after a while, there were 50 houses and a lot of villagers, but they went further and further away from the village. Is there a way to prevent it (except building a wall)?
Answer: The only way to prevent this besides building a wall is by building more houses in the designated village area. Villages paths go out to the age of the area so that gives you a clue. But since you have 50 houses, villagers can no longer stay. this is because the village is, "Over crowded" so there is no other way you can do this.

My villagers are leaving my village


How to set chapter markers in YouTube

Question: Does anybody know how they got the little yellow lines indicating "chapters" in this YouTube video?
Comment: Those are ad breaks and they're automatic (for YouTube partners).
Comment: Uh I guess they are and only because of how the show is structured with it's commercials, they coincide with the different chapters... I suppose there are no ads playing for me b/c of AdBlock?
Comment: Then maybe Youtube Partners can choose when they want their ads, but it's automatic (every X intervals) if you just upload the video. And yeah, it's ads, you don't see them because of AdBlock.
Answer: As mentioned in the comments, those chapter markers aren't chapter markers but ad break markers. Ad breaks are only available on videos longer than 10 minutes, and can be placed either automatically or manually.
Putting ads in places where a new chapter or sequence begins makes sense of course (as opposed to putting one mid-sentence), so those ad-markers do double as chapter markers as well.
See also: Manage ad breaks in long videos - YouTube Help
Answer: While those are indeed ad break markers in the screenshot of the question, the answer is:
You can create chapter markers for a YouTube video by adding timestamps and some verbiage to the video description.
Take this video for example: https://www.youtube.com/watch?v=ckYN_TwbGiQ&t=194s
You can see that the play bar is broken up into segments, each segment being functionally equivalent to a chapter.

Below, in the description, are the aforementioned timestamps.  The format is
<code>[h:m:s] Freeform text[CRLF]
</code>
wherein h:m:s is hours, minutes, and seconds.  Hours may be omitted if the timestamp is less than one hour into the video, and the hours and minutes may or may not be zero-padded, at your preference.
For example, this video description should create chapter markers in a hypothetical 10 minute video:

This is my awesome video, please comment and share!
0:00 Intro
1:45 Meet my Cat
5:22 I Eat Spaghetti
9:32 Time for Swimming or Whatever

Note that in the example pictured, the text Video Markers; appears atop the list of chapters.  That's not necessary, and nothing need precede the list.
(This is poorly documented, and not used very often.  It worked on the video pictured and I verified all of this using a video on my YouTube account.  I can't guarantee that it will work on all accounts, and YouTube has a tendency to dole out features depending upon account status.)
Answer: YouTube has a guideline for adding chapters to videos.
BUT. This feature doesn't work for many people as you can see in the comment section under the video from the guideline. Some say it stopped working, some say it works only when it wants to.

How to set chapter markers in YouTube


What is the technical term or name for pop-up menu for seeing profile?

Question: May I ask if somebody knows what is the name of the pop-up menu when the user clicks on the profile? There are many interface techniques and I would like to improve the interface for the existing project I am working on.
Comment: Didn't you just call it by it's name, though? I don't think there's much more to it than being a slightly more specific version of a generic "Pop Up Menu".
Comment: I am wondering if there is some technical term for it. What do you mean by call it by its name though please?
Comment: I just meant that "pop up menu" is already the name that you used, I wouldn't make it any more complicated :)
Comment: "pop up menu" is a behavior and not a menu name.  I would call it "user menu"
Comment: @xaa, thank you. "behavior" and "names" are different terms. I agree with you. May I ask if any reading resource is available to learn about behaviour, names and other terms?
Comment: I don't have specific suggestions but you may like the abookapart.com and mashingmagazine.com books. I found them very well written and instructive.
Comment: @xaa, thanks again. :)
Answer: there is really no agreed general semantic term for this interface component.
Shopify regards it as a Popover menu in their Polaris Design system.
IBM regards to it as an Overflow menu in their Carbon Design system
The Ant Design system refers to it as a Popover menu.
Bootstrap refers to it as a Dropdown menu.
I personally think it's an Enhanced Popover.
Answer: At its essence, It's a card that contains user profile info. Its called a User Card or User Profile Card presented in a popover and triggered by mouse hover/touch/click.
Many designers and Design Systems consider it a variation of the card component.
There is a lack of naming standards. Since there is no consensus, there are many fancy names out there. Some of them are:

UXSE calls it a Flair and User Card Popup on Mouse Hover
Hero Image Card by Hubspot Canvas
Raised Card by Semantic UI
Cards by BBC Gel


Giving focus to a desktop icon using the keyboard

Question: When I start Windows 7 none of the icons on my desktop have focus. I have to click on one of the icons with the mouse to give it focus. Is there a keyboard shortcut to give focus to an icon? (It doesn't need to be a particular icon.)
Answer: Use Alt+TAB or Windows+D to get on the desktop and then start to move with the arrow key
 on the desktop to switch on your desired shortcut. By default first shortcut(which is left side in upper corner) will highlight. I would suggest personally use Windows+D shortcut because this is the most fast way to see desktop rather than switch among many applications.
Answer: Go to the desktop by pressing WIN LOGO + D to go the desktop immediately and pressing the arrow keys once or more than once should help.
Always works for me.
To shift your focus to the taskbar press WIN LOGO + the numberly order of your app, this should work.
To shift the focus to the notifications area press WIN LOGO + B, you'll find the ^ button highlighted.
Answer: Try Alt + tab as well as switching between active applications it should allow you to select the desktop as well
Comment: Well, I can't make it work if there are no active applications. (But I usually have at least one active application, so I appreciate your answer).
Comment: @user12816 I'll have a try when I'm next on my windows box, I'm sure that's worked before.
Answer: Press in sequence:
- WinKey (Start Menu popups, or Desktop appears on Windows 8).
- Shift+Tab
You are now focused on the Desktop.
You can even start typing the name of some icon on the Desktop (for example, "Documents"), if you want to focalize it (start it by pressing Enter, of course).
This method works on any Windows version (98, 2000, XP, Vista, 7... could someone, please, confirm for Windows 8? I am not completely sure) or edition (Server, Home, Pro, Ultimate... etc).
This method does not affect the position of any window nor notification ballon on the notification area (sometimes it is mostly nagging to close all your windows to give focus to the desktop).


What are the ways to force all network traffic to pass through a device?

Question: I would like to know if it's possible to redirect all network traffic to a device (it can be Firewall or Transparent Proxy). My lab has the image layout (Physical Connection), how can I force all traffic through the firewall (Logical Connection)?
Answer: Traffic within a network is sent directly from host-to-host, so you would need to put each host in its own network and VLAN to force the traffic through the configured gateway on each host. In this case, the firewall.
The firewall would need to be configured as a router-on-a-stick with a subinterface in each network, and a different interface or subinterface to the router.
The router would need to know about all the networks behind the firewall, either statically configured (does not scale) or through a routing protocol run between the router and firewall.
Comment: I could use vlans for each final host, have a trunk interface where the firewall will receive all the packets and redirect the data through a specific vlan where it can only talk to the router? it works?

The best situation would be to have a router/firewall, right? I would like to understand how this is done in big companies.
Comment: "_I would like to understand how this is done in big companies._" This is not something normally done. Either you prevent traffic between hosts using private VLANs, or you allow (must allow unless it is a private VLAN) traffic directly between the hosts on the same VLAN. Firewalls are placed at the network edge for traffic into and out of the network, and, no, a large company will have a dedicated firewall (actually multiple firewalls).
Comment: right, I understand that in the case of the firewall it is on the edge and we can do the manipulation using the vlans, the same can be done for a transparent proxy? would it be just replacing the position of the firewall with the proxy?
Comment: Proxies are configured per application, normally for HTTP and HTTPS, but there are proxies for other application-layer protocols, too. Unfortunately, host configurations and protocols above OSI layer-4 are off-topic here. You can ask about those on [sf] for a business network.
Answer: Unless you're using VLANs to separate the subnet between firewall and router/gateway from the rest of the network, your physical setup is flawed. You cannot permit end nodes to talk to the router directly when you want them to use a firewall. A firewall needs to be the only connection between different network zones.
So, either

set up a separate VLAN between firewall and router and trunk the end-node VLAN and the router VLAN to the firewall
use separate, physical connections that resemble your desired logical connections

If the firewall is transparent (bridging) it might not support variant 1. If it's routing this setup is sometimes called router-on-a-stick.
Comment: Traffic between hosts on the same VLAN would still not travel to the firewall, and the OP, twice, says "_all traffic._"
Comment: Thanks guys, I already know which way to go.


(Animation Nodes) How can I make objects rotate to face the direction of the normals of a mesh?

Question: I'm trying to recreate Mystique's transformations from the new X-men movies, and I cant figure out how to get the directions of individual polygons or vertices. I can get the location and "normal," but the normal vector doesn't seem to correspond to any sort of rotation. Help?
Comment: Please illustrate "*Mystique's transformations from the new X-men movies*" not everyone is familiar with what you want to achieve. Please edit your question and provide some reference images and what you have done so far and why it failed.
Answer: Use an Object Mesh Data node to get the face data of the target object. Connect the Polygons output to an Object Instancer and create a loop subprogram that has a polygon and an object iterator. With the Mesh data node selected you can press W and choose polygons to create the loop and add another object list iterator to it.
For the subprogram, connect the object to an Object Transform Output and use a Polygon Info node to get the location and normal of each face. Connecting the polygon normal to the object rotation input will create a Direction to Rotation node that gives the direction you want. The center output will give you the location to place each instance.
Comment: I realize my problem is that I forgot to check all the boxes in the transform output node. I feel stupid now.
Comment: @sambler Can you help me with this question please? https://blender.stackexchange.com/questions/163003/animation-nodes-how-to-make-an-object-face-camera-yet-let-the-object-rotate-ar


How to solve $x$ in $(x+1)^4+(x-1)^4=16$?

Question: I'm trying my hand on these types of expressions. How to solve $x$ in $(x+1)^4+(x-1)^4=16$? Please write any idea you have, and try to keep it simple. Thanks.
Answer: HINT:
Just expand in Binomial Expansion to find a Quadratic Equation in $x^2$
Comment: There will four roots of the given bi-quadratic equation as http://mathworld.wolfram.com/PolynomialRoots.html
Answer: Using the expansion $$\left(a+b\right)^n = \sum_{r=0}^n\binom{n}{r}a^rb^{n-r}$$
$$\require{cancel}{x^4+\cancel{4x^3}+6x^2+\cancel{4x}+1+x^4+-\cancel{4x^3}+6x^2-\cancel{4x}+1 = 16}$$
$$x^4+6x^2+1=8$$
$$t^2+6t-7=0\quad\text{with}\quad x^2=t$$
$$t=1,-7$$
Since $x^2=-7$ doesn't have solutions in reals, $x^2=1\implies x=\pm1$
Answer: We have our equation to solve for:
$$(x+1)^4+(x-1)^4=16$$
First, expand the terms in the left hand side.
$$x^4+4x^3+6x^2+4x+1+x^4-4x^3+6x^2-4x+1=16$$
Simplify the left hand side.
$$2x^4+12x^2+2=16$$
Factor $2$ out from both sides.
$$x^4+6x^2+1=8$$
Move $8$ to the left hand side.
$$x^4+6x^2-7=0$$
Let $x^2=a$. Now our equation becomes:
$$a^2+6a-7=0$$
Factor it.
$$(a-1)(a+7)=0$$
Reverse the substitution.
$$(x^2-1)(x^2+7)=0$$
Factor some more (yes even the sum of squares)
$$(x+1)(x-1)(x+\sqrt7i)(x-\sqrt7i)=0$$
The four roots are $x=\pm 1$ and $x=\pm \sqrt{7}i$. But if you do not want complex roots, then the two real roots are $x=1$, $x=-1$.
Hope I helped!
Comment: The left hand side should simplify to $2x^4+12x^2+2$ in your first step.
Comment: Oh woops thanks for the correction
Comment: No problem. Looks good now. (+1)
Answer: Let denote by $P(X)$ the following polynomial:
$$P(X)=(X+1)^4+(X-1)^4-16.\quad\quad(1)$$
We immediately see that $X=1$ and $X=-1$ are roots of $P(X)$. Therefore, $P(X)$ can be written as:
$$P(X)=(X-1)(X+1)Q(X), \quad\quad\;\;\;\;\;\;(2)$$
where $Q(X)$ is a polynomial with degree $2$. Hence, $Q(X)=aX^2+bX+c$ for some $a$, $b$, and $c$.
Now, if we develop $P(X)$ for both $(1)$ and $(2)$ we get:
First, with $(1)$:
$$P(X)=2X^4+12X^2-14.\quad\quad(3)$$
Second, with $(2)$:
$$P(X)=(X-1)(X+1)(aX^2+bX+c)=aX^4+bX^3+(c-a)X^2-bX-c.\quad(4)$$
Hence, $(3)=(4)$
$$2X^4+12X^2-14=aX^4+bX^3+(c-a)X^2-bX-c.$$
Then,
$$ \begin{array}{lr}
    a=2\\
    b=0\\
    c=14
  \end{array}$$
And finally,
$$P(X)=(X+1)(X-1)(2X^2+14)=2(X+1)(X-1)(X^2+7).$$
Now it is clear how to solve $P(X)=0$ (how to find the two other roots):
$$S_{\mathbb{R}}=\{-1, +1\}.$$
and
$$S_{\mathbb{C}}=\{-1, +1, +i\sqrt{7}, -i\sqrt{7}\}.$$
Answer: Looking at $(x+1)^4 + (x-1)^4=16$, I recall that $16=2^4$. So I look at the equation trying to see if I could get a $2^4$ in there. This sugguests that we guess $x=1$ to make the left term a power of $2$.
Plugging in $x=1$,
$$ (1+1)^4 + (1-1)^4 = 2^4 + 0^4 = 16 $$
So $x=1$ is a solution.
This problem has a symmetry property. Notice that sending $x\rightarrow -x$ doesn't change the expression on the left.
$$ (x+1)^4 + (x-1)^4 \rightarrow (-x+1)^4 + (-x-1)^4 = (x-1)^4+(x+1)^4$$
So we know that $x=-1$ will also be a solution.
Some thought should convince you the only possible solutions are between $-1$ and $1$ since any large values of $x$ will immediately make the expression on the left bigger than $16$.
Looking at the derivative of the expression on the left,
$$ y' = 4(x+1)^3 + 4(x-1)^3, $$
we see that the derivative is $0$ at $x=0$ and monotonically increasing for $x > 0$ which means that there are no other solutions since our graph can only intersect the horizontal line $y=16$ once.
Answer: $(x+1)^4+(x-1)^4=16\\
\implies (x^4+4x^3+6x^2+4x+1)+(x^4-4x^3+6x^2-4x+1)-16=0\\
\implies (2x^4+12x^2+2)-16\\
\implies 2x^4+12x^2-14=0\\
\implies 2(x^4+6x^2-7)=0\\
\implies 2((x^2)^2+6(x^2)^1-7(x^2)^0)=0$
Now let $x^2=a$:
$2((a)^2+6(a)^1-7(a)^0)=0\\
\implies 2(a^2+6a-7)=0\\
\implies a^2+6a-7=0\\
\implies (a+7)(a-1)=0\\
\implies a=-7 \text{ or } a=1$.
Letting $a=x^2$ again, we get
$x^2=-7\text{ or } x^2=1$.
Hence the real solutions of $x$ are $\pm1$.
Answer: Here's the way you can deal with your exercise. I hope it will help you!
Answer: polynomial equation step by step. I hope it will help you!
Comment: Rather than typing this up using some other software and posting it as an image, it's much better to just post the text here (which is searchable, accessible, and takes less space). This site supports most TeX syntax through MathJax. More info on formatting can be found under "help" at the top of the page.


iPhone SDK 4 available only for Mac OS X Snow Leopard?

Question: I am about to download SDK 4 for iPhone development but on their website the download is for Mac OS X Snow Leopard. The current version on my Mac is Mac OS X Leopard 10.5.8... Won't I be able to install the SDK without upgrading to Mac OS X Snow Leopard?
Comment: An upgrade is $29 and worth it.
Answer: Specifically, Xcode 3.2.3 with iPhone SDK (iOS4) is a Snow Leopard install only, as far as I see.
Answer: I think that iOS4 is bringing a lot more feature parity between itself and snow leopard. So I don't think apple will be releasing this download for leopard any time soon. Though check the developer forums to make sure.
Sadly though you may need to upgrade if you want to continue to develop for iOS4.


Pre-populate a user reference field during drupal commerce checkout - buying a gift for a user without manual username entry

Question: I am creating a gift shop website where users can buy gifts for other users. So on every user profile i want to add a link "buy gift for this user" which takes you to the product page. After adding items to cart and checkout, a "gift recipient" (user-reference) field is already pre-filled with the name of the user from whose profile the shopping was initiated (not the name of the logged in user). Is this sort of thing possible in drupal 7? How can i achieve such? Thanks.
Answer: I don't know ready solution from the box for your use case but it's possible to implement it with Drupal Commerce and Line items functionality.
You can extend Line Item with the user reference field "gift recipient".
User value will be saved on line item but not a product.
Than everything is in your hands.
E.g. you can click on option "Include this field on "Add to Cart" form. Or you can prepopulate this field using special get parameter in the "buy gift for this user" link.
For more information about extending Line Items see the video: http://vimeo.com/31459435


What is on my sink faucet? Trying to install RO system

Question: I just moved into an apartment and I want to install a counter top RO system. These usually screw onto the faucet but the faucet in my apartment seems to have this plastic thing attached to it instead of any threading. What is this called? Can i install an RO system with it? If not, should/can I remove it(safely?), or try to get some kind of adapter? Is there an adapter for this even?
Answer: That is just a cheap plastic aerator and should unscrew. Turn clockwise looking down on the faucet. There will probably be female  threads in the faucet. Good luck.
Answer: Might be a "washing machine adapter" or "dishwasher adapter" - same thing, really - a quick-connect fitting to allow use of an appliance via hose at full-bore flow.  Not the same as the one I use for my bottlewasher, but I'm sure there are multiple incompatible designs out there. Anyway, you can unscrew it and have the normal threads available.


engine speeds on startup (wont idle) after sitting for years - 1986 honda civic

Question: Engine speeds on startup (wont idle) after sitting for years - 1986 honda civic.
As soon as I turn the key on it will keep speeding up higher & higher.
Answer: Check your throttle linkage, make sure the throttle plate is returning to idle. Look for vacuum leaks on all the hoses. The Car is idling high because it's getting too much air


Chromium on Raspberry Pi B w/ Raspbian Jessie

Question: I have a Raspberry Pi 1, and I would like to install Chromium for my cloud print server. The only trouble is that sudo apt-get install chromium-browser does not work. Additionally, I tried a method for installing Chromium on RPI, but it was for RPI2 only. I am a noob, and I was wondering whether it is possible to get Chromium on Raspbian Jessie on Raspberry Pi 1. Thank you.
Answer: Chromium can now be downloaded and installed (with sudo apt install chromium-browser) , and now comes preinstalled on the PIXEL desktop environment, but it does struggle to load pages on the small power of earlier Raspberry Pi models, however the model 4B (and to some extent the 3B+ and 3B) can load pages much faster.
Comment: I would like to note that Chromium in some instances will also be run as root, while your user is not a sudo user. But from my experience, I can tell you that you are going to have a bad time running chromium.


How do Qiskit simulators generally work?

Question: Qiskit offers a number of quantum simulators (e.g. AerSimulator, QasmSimulator, StatevectorSimulator). But I don't know how these simulators actually work. Quantum operators and quantum states can be represented by unitary matrices and vectors respectively. So I guess quantum simulators are actually performing matrix multiplications when applying quantum operators on some quantum state? But if this is the case, how could we use them to achieve any quantum advantage over classical computers which do the same thing?
Comment: Hi there, discussions of simulating quantum computations using classical computers is discussed in several places on QC.SE checkout the answer and comments to https://quantumcomputing.stackexchange.com/a/22022/11793
Comment: I vote for this question to be closed, as it was already answered in a clear manner in the duplicate.
Answer:
But if this is the case, how could we use them to achieve any quantum advantage over classical computers which do the same thing?

We can't. Simulators are used to test a code using a low number of qubits theoretically. Even though some simulators are optimized so that they don't perform $2^n\times2^n$ matrix multiplication for each gate applied on the system, the point is only to ensure that the code one has written yields the correct result.
Indeed, simulating allows one to get the exact statevector, which can be used to test for the correctness of the code. On the other hand, directly running your code on a real quantum computer is cumbersome, since:

You don't have access to the final statevector
Noise may perturb your measurements

Of course, it is not possible to test a useful circuit with a high number of qubits using a simulator (depending on the circuit, you may not have enough RAM or wait for ages).
As a final note, note that it is possible to define simulators which don't perform $2^n\times2^n$ matrix multiplication. For instance, if you restrict your self to Pauli gates, you are able to efficiently simulate your quantum circuit. Of course, no useful quantum circuit can be decomposed into Pauli gates only, the point is only that for a given assumption on the gates one is allowed to use, it may be possible to optimize the simulator, still without any quantum advanatage.
Comment: Thanks for your detailed explanation! So, even though we implement some quantum algorithm using quantum simulators, we can not get any quantum advantage? I mean quantum advantage might stem from quantum algorithms which solve the same problem in a more efficient way than classical algorithms.
Comment: @Liuji Indeed. You can run a quantum algorithm using a classical computer (that's what simulators do), but the time and memory complexities would be exponentially worse, so you would not get any quantum advantage like this. Fundamentally, they are valid, classical, algorithms for the problem they are trying to solve, they're not "quantum algorithms" if they're run on a classical computer.


Reference showing that only deep learning algorithms benefit from using huge datasets

Question: Andrew Ng in his deep learning course on Coursera.org states that there is a boundary on sample size where machine learning algorithms stop improving and such boundary is nonexistent for the deep learning algorithms, as they always improve when feeded with more data. Could you point any reference that goes into more details and describes actual research on the phenomenon?
Comment: I don't believe what he says is true if he is talking about a predetermined neuron count. If you build a very big network, obviously it will take a lot of data points to saturate it, but it will still saturate eventually. If we are talking about throwing in more neurons as we get more data, then it is more likely to be true.
Comment: @CagdasOzgenc: and of course, if we allow the model to increase in complexity as we feed in more data, then non-DL models may also hit no hard improvement limits.
Comment: @Tim I think this reference can be useful. https://pdfs.semanticscholar.org/1759/4df98c222217a11510dd454ba52a5a737378.pdf. Rational weighted recurrent neural network with sigmoid activation and Turing Machine equivalency. I would post it to Computer Theory group to get more information as it is related to limits of computation rather than statistics.
Comment: @CagdasOzgenc thanks, but Andrew Ng talked only about model performance, not computational poewer and this is the only aspect of interest for me.
Answer: Revisiting Unreasonable Effectiveness of Data in Deep Learning Era Shows performance of RNNs has roughly linear relationship with the log amount of data. See also
Deep Speech 2: End-to-End Speech Recognition in English and Mandarin, table 10. Regularization techniques for fine-tuning in neural machine translation and Scaling Recurrent Neural Network Language Models seem to say the same thing.
I couldn't find any sources, but simpler models with limited number of parameters, at least in my experience, have a much lower "hard-limit" of performance.
Comment: The "*Unreasonable Effectiveness of Data*" by Pereira et al. was such an opinionated and enjoyable paper when it came out, thank you for bringing attention to one of its intellectual descendants. (The new paper is a bit too lax in  my opinion; all the examples are based on Comp. Vision which clearly is not *everything* big data are used for but OK... Thanks again! +1)