smps transformer capacitance effects

Question: What are effects of interwinding capacitance in smps power transformer? What is the influence? For example, i have 83khz smps transformer with windings made of litz wire. The capacitance between windings is 250pF (i measured it by short-circuiting both windings and using u1732c agilent RLC meter). Is it good or bad?
Is electrostatic shield between primary and secondary helpful to reduce value of inter-winding capacitance?
Answer:
What are effects of interwinding capacitance in smps power
  transformer?

The easiest way to think about the main noticable effect is to lump that distributed capacitance into one component: -

Then consider what mid-point voltage you have on the primary and what the possible impedance to earth is: -

At the switching frequency, the peak-to-peak voltage on the primary winding might be 230V x 1.414 = 325 volts. This is the rectified DC bus voltage converted into a square wave at the switching frequency. The "effective" mid point voltage is about 160 Vp-p (an 83 kHz square wave approximately).
For an SMPS, the incoming lines are either coupled via capacitors to earth or live/neutral is regarded as "earth". We can now paint a scenario where we have 160 Vp-p at 83 kHz coupling via 250 pF to the output secondary winding. The scenario is likely to have very little impedance where I've shown a resistor and capacitor in parallel because of the switching frequency: -

This of course creates a lot of common-mode noise on the output of the SMPS and what manufacturer's do is add capacitors from the output to ground (if ground is available) to form a high frequency potential divider with the 250 pF interwinding capacitance. Thus, the high frequency 160 Vp-p seen on the secondary is reduced considerably with respect to earth and the device passes EMC testing.
When the SMPS uses a two-pronged earthless AC connection, a capacitor is usually added from secondary back to the "steady side" of the primary in order to try and flush the output noise down to earth via AC wiring. This produces a knock on effect of now seeing AC mains frequencies on both output wires of the SMPS - the subject of many questions on this site.
Typical example used by Power Integrations: -

Note the 2.2 nF 250V AC capacitor just above the transformer - this is that capacitor used to reduce output noise but also leaches 50/60 Hz to the output.

Is it good or bad?

It is what it is. Bigger transformers will have more capacitance and this cannot be avoided sometimes.

Is electrostatic shield between primary and secondary helpful to
  reduce value of inter-winding capacitance?

Only if you can connect it to earth - if you can't it probably makes the primary-secondary cross-coupling even greater.
Comment: @silkyre6xtenz if you are happy with an answer then please consider formally accepting it else raise a comment to get clarification.
Answer: Please note that in a high frequency transformer the effective inter winding capacitance has several effect, not all of them being linear!
Ideal model would need to distribute the winding capacitance across the whole contact surface, but actually working with two capacitors connected at each end of the winding works for most situations.

simulate this circuit – Schematic created using CircuitLab
In this case, the two windings are in parallel so the voltage A->B and C->D remains identical at all times (it is equal to the voltage x).
Now take the same transformer, but place the secondary winding in the other direction (I mean, mechanically wound in the opposite direction).

simulate this circuit
Now on this schematic, the voltage C->D remains equal to x, but the voltage A->B is now equal to x minus twice V1(t)
In this case, the inter-winding capacitance is no longer hidden from V1 and this is having quite some effects.
Let's see : if V1 was 1V with respect to the x source, then at the same moment B is -1V with respect to ... GND
How much voltage (ignoring DC voltage x) is there across capacitor C1? 2V, 1V due to A being above C, one other due to B being below D.
Because there is voltage, there is current; but because x is constant, this current cannot flow through capacitor C3 and fully flow through the source x!
So now if you were to measure capacitance across the source x (which would be the primary secondary capacitance) you would get a result depending on the frequency at which you measure the capacitance. Due to the internal way LCR meters measure (often RMS current/voltage measurement with low pass filtering of the measured impedance), you would get a capacitance increasing at the LCR meter get close to 1kHz, aliasing (getting very high and very low results) at 1kHz and then decreasing again.
So what is now the capacitance between primary and secondary? At the very least no longer a single value; and depending on the aliasing happening, not even a linear capacitor any longer.
To limit this effect, engineers place a capacitor across the two cold points of a transformer (in this case, CD) to limit the current flowing through x (you need in this case to consider x is not a true short circuit, at least for high frequencies).
Back to your question
The inter-winding capacitance of a transformer is by itself not an issue. Only  thing is, once the transformer is not 100% symmetric (like in my example, or also 10 turn pri, 2 turn sec) high frequency currents start to flow through the "source" x, generating common mode noise. Those noises are a big problem and cost a lot of money to filter out! Because they flow through the whole cables back earth (the source x), the very long travel distance mean they can radiate very effectively.
For example, a 1MHz V1 source would start making any AC cable above 3m into an antenna. THIS is a big problem.

smps transformer capacitance effects


Cumber red ki, is his regular ki or is it a transformation?

Question: In Dragon Ball, all saiyans have white/transparent ki with the exception of Vegita in a few chapters of Dragon Ball Z where he had light blue ki, and Goku Black who had black/violet/transparent ki before transforming into super saiyan Rose. What is Cumber red ki about then?  is Cumber red ki his regular ki or is it a transformation?
Answer:  The Dark Aura which surrounds Kanba here is just his ordinary ki which is supposedly considered to be a dark evil Ki. if you look at the Dragon Ball Heroes Universe Mission 3 trailer, you can see Kanba as a Regular Super Saiyan at the 0:09-0:10 second mark.Hence it is fair to assume that is Kanba's ki in his Base form. I have also attached an image of the same below.
Comment: If in base form he is as strong as super saiyan blue vegito, in super saiyan he might be the strongest character in all Dragon Ball Heroes


best practices for playing video instructions for illiterate/computer illiterate users

Question: My team will be deploying a piece of software to users who may be illiterate and computer illiterate, and ten to twenty users will likely share the same computer, account, and copy of the software. We want to auto play an instructional video each time they go to a different feature, as the user might not know to click the help button if they have not seen the video. How can we do this without being intrusive to users who have already seen the videos or are literate and or computer literate?
Comment: I believe using symbolism from the real world would be a great advantage. Colors too would be highly significant of actions. Such as Green to Start and Bright Red to Stop. Additionally to this, the Help can simply be a question mark. You could also observe the user's actions on the page and learn if it's a new user or an existing one and accordingly help them. Machine Learning is a good way to go about this.
Comment: How often is each user going to use the software? Is it a daily repetitive task, or something they might use every few months?
Comment: How illiterate are we talking? Very bad reading skills? Doesn't speak this particular language? Can only read numbers? Can they understand basic abstract symbols like X ! ?
Comment: I expect users to understand basic symbols, have limited reading ability, and use the software once or twice a week.
Comment: I would also recommend adding a few more examples for context in your question above, probably screenshots so that we have a clearer idea of what exactly you need and how we could help you with it.
Answer: I'm sorry to say that you're in a Clippy situation.

You can dodge some of the Windows '95 vibe by cutting to the chase, doing away with the avatar, showing a really simple X to close, and making sure that this help NEVER blocks the interface.
I would do the following:

Follow Clippy's lead for the first step. Try to detect what the user is trying to do. I'm not sure what that means for your user. Maybe you can prompt users as soon as there's any activity, detect frustration with lots of typos or a big wiggle of the mouse or not typing for a long time. That seems like the hardest part. Do some user testing to find where your pain points are, and then try to detect what you measured. But be careful. Clippy got things wrong often, and that's why people hated him.
Make the prompt small, with the video already playing, and with the sound muted. In the video itself, make a title card that's big enough to read when it's shrunken. This is becoming popular on news media sites lately, and I think it's an effective way to show your video content without being pushy. If you're worried about literacy, use animation to convey the message. Playing the video automatically gives the user a chance to preview what they're getting themselves into. You might think that transport controls aren't important at such a small size, but definitely include a tiny timeline and a countdown to show how long the video is.

If the user clicks the video, unmute it, rewind it to the start, make it bigger, and show the user full transport controls.

As I wrote above, user testing will tell you the most about what will work and what wont. Good luck!


Where can I put my rear light that is designed for the seatpost if the saddle bag is in the way?

Question: I have a Lezyne Strip Drive 150 but my saddle bag is in the way so I can't use it on my seatpost. If I increase the height of my seatpost then that would be uncomfortable, so what can I do?
Comment: A photo of your current setup might help.  How many other rear lights do you have ?
Comment: And how big is the bag? A small tool bag or a large bikepacking bag?
Comment: Can you use a top tube bag instead? I use this one because I hate saddle bags: https://www.bike24.com/p2409820.html
Comment: @Michael that's a valid answer - want to promote it into the Answer box?  I can't do that for you sorry.
Answer: You could attach the light to something else, like another part of the frame, or a tab on the saddle bag, or your backpack.
You could remove the saddle bag, attaching onto e.g. the handlebars or putting it into a rucksack.
You could buy a different light which does attach to the bag or another part of the bike.
Time to get logical
Comment: `Time to get logical`, yeah, frankly.  Buy some zip ties and velcro straps and work it out!
Comment: Most saddlebags have a loop for a light.  Does yours lack a loop, or is the loop not big enough for that light? You may need to mount it horizontally and/or use cable ties.
Comment: I want the saddle bag to be attached to the seatpost, that's the whole point of a saddle bag. I definitely want my rear light as it's expensive so I may need a different saddle bag.
Answer: You obviously have very little seatpost exposed. Most cyclists on compact (i.e. sloping top tube) bikes should not be in this situation, but some of us are on level top tube bikes and some of us have relatively short legs. NB: all products mentioned below are not necessarily endorsements; these are merely ones that I remember existing, and I have no commercial interest.
Many saddlebags have a loop on the back that's often got a reflective strip. Here's the Lezyne Caddy M:

However, the Lezyne Strip Drive doesn't have a corresponding clip that would mount to such a loop. You would have to get a light that clips to a strip like this. Moreover, not all saddle bags have these loops! I think that some panniers, if you use them, may have mounting loops or other places you could clip a light.
One possible alternative is if there are lights that clip to seat stays. However, these sit lower and may be less visible to drivers. I'm not sure which lights, if any, are designed to be mounted here. Another possible alternative is something mounted on your helmet, perhaps something like this Topeak light.
Less commonly, some saddles have dedicated but proprietary mounting points accessories. Specialized's mount for one particular taillight is here. Fizik makes two lights that can be mounted to its ICS saddle mount. If you use the Garmin Varia, which is admittedly more expensive, some companies on Shapeways offer dedicated mounts. Here is one for Specialized saddles. I think there may be more general saddle mounts, but these might need to clamp to the back of the saddle rails, and some saddles may be incompatible (e.g. Selle SMP saddles are incompatible with Bup Labs' 3d printed general mounts because their rails are tilted at too sharp an angle). These would apply to other lights using a Garmin mount, but I'm not sure any others exist yet.
Answer: I have that taillight. I put it on a seatstay, upside-down so that the angle is closer to correct.
Answer: I use the hard case luggage rack with the extra Hide My Bell adapter that is likely made not exactly for this purpose but somehow matches the desired shape and serves the goal very well. I bought it "from the view", was last in the shop under heavy discount. You only need to drill single hole to attach it:

It got a little bit angled for me but same way as the seat post is so the light sits even better.
Attaching such a thing to the bag from the flexible material like your seat post would be more challenging but it might work if to put some large enough plate with the hole on the inner side. You may also find some other place to screw it on.
The comparable part should not be very difficult to make even in a simple workshop, by attaching a L-shape elbow to something like thin plastic bottle of the suitable diameter.
Comment: That is a pretty novel approach.  Simple, yet effective.
Comment: Nice idea!   I made something vaguely similar for mounting an airhorn   https://www.tinkercad.com/things/iBoeeBqNPGq  ended up mounting just below the left-hand brifter and wrapping it in bartape.
Answer: Sounds like you want to keep the saddle bag in place. You can get lights which attach to the seat rails, see below, so you would be able to hang this behind the saddle bag no problem.
Not only will it bring you fleeting amusement, but on group rides you'll have the bonus advantage that nobody will ask you to take a turn on the front, you can sit on the back of the group the whole way.
HTH
Comment: Sadly, it also has some visibility from the front which may not be legal.  Many locales restrict red lights for rearward use only, and white for forward only.
Comment: @Criggie and with good sense I would think. Happily the saddle bag will be blocking a lot of the forward light, plus I don't think anyone will take this seriously... will they..?
Comment: It also has great visibility from the sides, which you don't get with every light
Answer: I'm not sure I'd use it as the only light on my setup, but I often attach a bright flashing additional light to my seatstay, on the side more visible to the traffic.  Check the viewing angles - it may be an option for you.  Or you could double up and fit a cheaper light on the other side.  I've done that too
Answer: One more option: Attach the light to the back of your helmet.
A riding buddy of mine has a lightweight rear light there.  I am not actually sure how he has it attached. I believe it is clipped to a strap or something/somehow, so this may not be applicable to every helmet. He also is pretty safety conscious so he was careful to not negate the safety features of his helmet by doing so.  He only uses it when his seatpost-mounted camera/taillight battery is drained, so it only gets occasional use.  The only real con is that it is more eye-level so riding behind someone with this setup is not as pleasant as with one mounted lower.
There are other helmet-mounted attachments for lights out there.  I have one for a forward light, so maybe there is another out there for attaching a taillight to the top of the helmet.
Answer: You can flip a Strip Drive upside down and mount it on a seat stay. It's not ideal to have such an expensive light mounted that way because it might find its way into the spokes and shatter; but it works.
Answer: Since you want 2 things to exist in the same place, you'll have to fashion some kind of thing for your light to attach to. I would find a flat piece of metal from the hardware store and bend it in shape to attach your light to.
A simpler solution is to get a rear rack and attach your light at the end, or other places as others have suggested.
Why the need for the saddle bag though?
Comment: People use saddle bags to carry a spare tube and basic tools; not everyone wants a rack mounted on their bike, or at least not all of their bikes.
Answer: I commute at night in dark areas, so rear lights are important to me.  I have:

one flasher on the rear of my helmet
one throbber hanging on the outside of my backpack
one solid inside my backpack (a red-LED flashlight, and this lights up the white material of the backpack nicely
one blinky on the seatpost
one solid between the seat stays.

I also have two more blinkies on the seat post as cold spares in case of batteries going flat or loss.   Higher mounting is helpful because it can be seen over obstacles like cars, where lower mounted lights can be obscured.
You could move the light to the frame's seat post strapped just above or below the top tube.  Don't go too low between the seat stays because then it can be hidden.  The wheel itself can hide the light if its on a stay.
Consider hooking the light to your riding clothes - a jersey pocket or a trouser belt.  And also contemplate adding additional lights as backups too.


Would a very strong force of gravity make things break apart?

Question: If I take an hammer and slam it on a table, I will not be surprised to see the table breaking and my anger slowly vanishing.
I remember a difference being made between impact and non-impact forces when I was in high school, but I can't really say how much was related.
Now, I'm older but I'm still meditating if a stronger gravitational pull will eventaully break things apart (like a table).
I might guess a link with why the fire is burning in the sun, and its constant fusion(fission?). An attempt :)
We, inhabitants of earth, know we can break things by applying a certain force to an object. I don't think impact time play an important role, as long as the force is of the same degree ( there is a misconception that a force should be applied for a very brief time, but I think what is usually meant is the impulse should rather be short ). Impact area seems relevant instead. Everyday experience seems to suggest that if you apply the same force it's easier to penetrate a table if you use a needle rather than a phone.
Again, It seems to me, but I might be wrong.
Anyway, force of gravity seems to act on everthing ( and everything's center of mass/gravity), but it apparently doesn't have any other effect except for pulling down things. It does not break them, at least(I've read that it does deform them on the atomic).
Moreover, is there really a difference between impact and non impact-forces?
Even if we suppose the existence of gravitons? :)
Comment: Not break 'apart' but it would crush the table down to a thin layer of atoms on the surface.
Comment: Make the table out of very thin balsa wood and then start piling books on it.  On Earth it will collapse due to the force of gravity, but would hold up quite a bit better on the Moon.  Net-net:  If gravity is stronger build stronger tables.
Answer: Take a wooden table and keep putting more and more weight on it little by little. At some point, the table will snap. Was that an impact force? I do not think so. But the result is like that of an an impact.
Gravity breaks apart stuff due to tidal forces and black holes spagetify things. But these are smooth and incremental effects. Anything abrubt would be due to the internal structural instabilities of a body and some snapping may take place just like the wooden table above.


why are new brakes squeaking?

Question: I had my brakes completely redone for my annual test and now they squeak whenever I use them.  It's really a bit annoying and I was wondering why they do that if there's anything I can do about it.
Answer: Were your brakes silent before this work was performed?
Some brake noise is considered normal. Different driving conditions can affect brake noise, including severe braking, dusty or sandy conditions,even humidity.
Certain high-pitched brake noise happens because the semi-metallic brake pads used on newer cars are harder. A high-pitched squeal often happens on smaller cars and is heard in the first few stops when brakes are cold and damp. Certain brands can be noisier than others, but there's an upside - these harder pads that have more metal generally last longer since they're stronger.
Sometimes your brakes will make noise. If you expect supreme silence, or expect your mechanic to make your brakes totally mute in every circumstance—that just may not be possible.A squeaking brake can stop a vehicle as quickly as a quiet one.
Take the car back and have them use either a paste or grease between the pads and caliper and lubricate the slides and pad contact points. If they know their stuff, they did it already. If not that may help. Also, new brakes take time to Bed In or Break In. You may have to wait for a few days for the silence to begin.
Comment: Please convert this large blob of text into paragraphs so that it can be more readable, and I will convert my downvote into an upvote.
Answer: I've had it happen before where my brakes would squeak after just being done. After driving on them for awhile the squeaking subsided. Depending on how loud the squeaking is, there is a good chance that it will fix itself. If you are really worried about it, check your pad levels all around for any uneven wear, and tighten everything down.
Applying anti-squeak compound to your brake pads can also reduce this. It acts like an adhesive I think, to keep them from vibrating when engaged.

why are new brakes squeaking?


foursquare request error with loading

Question: Hi guys i am getting a small error when i am trying to access the foursquare api to find information about a specific restaurant that i am putting in the search.
Cross origin requests are only supported for protocol schemes: http, data, chrome, chrome-extension, https, chrome-extension-resource.

Another thing that i am seeing is that when i put the search int he url to see what comes up i get some crazy code that appears on the page..
the http request results from the browser
here is the code that i have right now...
var fourSquareMain = 'https://api.foursquare.com/v2/venues/search';
var clientID = '?client_id=5LHFTY54EP5VLMYIIVZ0OQGMNZQEM2FUKDPFFA2OJHMO0AVI';
var clientSecret = '&client_secret=2TN3GQBAX4U2GPHGMCUZWS35Y2E5E2Y4NG0YWGVGNMXEPHAW';
var fourSquareVersion = '&v=20130815';
var fourSquareLL = '&ll=' + pointItem.lat() + ',' + pointItem.lng();
var fourSquareQuery = '&query=' + pointItem.name;

var fullFourSquareQuery = fourSquareMain + clientID + clientSecret + fourSquareVersion + fourSquareLL + fourSquareQuery;

var finalFSQuery = fullFourSquareQuery.replace(/ /g, '-');

console.log(finalFSQuery);

Answer:
The crazy code you are getting is 'what you had requested for' it is the raw json response from foursquare api.

2.It works on the URL but not on the script because when you run the script on your client site you are trying Cross Origin Resource Sharing (CORS) which is not allowed by some APIs for security reasons.
To work around this you will need to use JSON-P, a unique trick to allow cross-domain requests.
An easy way to do this is to create AJAX requests using jQuery.
In your case try to get name of the first venue from the search result
var fourSqrUrl = "https://api.foursquare.com/v2/venues/search?ll=40.7,-74&client_id=XXX&client_secret=YYY&v=20160128"
       $.ajax({
              url: fourSqrUrl,
              success: function(data) {
                $(div1).html('FourSquare Response : ' + data.response.venues[0].name);
                }
              });

`
You might have to read a bit about AJAX to get a better idea of how this works and how to read json data.

foursquare request error with loading


What are the advantages of TOTP over HOTP?

Question: HMAC-based One Time Password (HOTP) was published as an informational IETF RFC 4226 in December 2005. In May, 2011, Time-based One-time Password Algorithm (TOTP) officially became RFC 6238. What advantages does it introduce?
Answer: One of the advantages is purely on the human side of security. From RFC 6238's abstract:

The
     HOTP algorithm specifies an event-based OTP algorithm, where the
     moving factor is an event counter.  The present work bases the moving
     factor on a time value.  A time-based variant of the OTP algorithm
     provides short-lived OTP values, which are desirable for enhanced
     security.

(Emphasis mine.)
The TOTP passwords are short-lived, they only apply for a given amount of human time. HOTP passwords are potentially longer lived, they apply for an unknown amount of human time.
The reference to "enhanced security" is referencing (at least) two areas: The value of a compromised key, and ability to attack one.
First, should a current HOTP password be compromised it will potentially be valid for a "long time". Ensuring frequent use of the HOTP in human time is not a part of the HOTP design, so it is unknown how long the current HOTP password will be valid for and we have to assume the worst case, namely, that it will be a "long" time. This allows the attacker to use a compromised password at their leisure. But should the current TOTP be compromised, it will not be useful for very long because in one TOTP time increment it will be invalidated. Of course, in theory the attacker could grab and use the password in negligible time, but it does prevent a practical human aspect. For example, someone who gets a look at your current Paypal key (which rotates every 30 seconds, IIRC) can't go home and try to use it later, they would have to lunge for a computer in the moment. Someone who compromises they key may not realize it until after the key has expired. Etc.
Second, if you are attacking a key, your work is potentially invalidated or set back every time increment of the TOTP because the target has moved. Perhaps an attacker has discovered an attack against an OTP scheme that allows them to predict the next password only if they have some number of the last 10 passwords, but it takes about 2 hours of computing time to do so. If the OTP changes every minute, their attack is pretty much useless. Brute-force attacks are inhibited as well, because the next password is chosen the same distribution each time; it is possible to brute-force exhaust the password space and not find the password. TOTP doesn't eliminate those sorts of attacks, but hopefully it limits which ones have the ability to be effective.
Comment: I think the real challenge is getting the time to be SYNCHRONIZED on the client end along with the server , in case of TOTP.
Comment: @JaderDias - Neither of the algorithms need an internet connection
Comment: Is there any case where HOTP requires an internet connection while TOTP doesn't? Or vice-versa?
Comment: Each random brute-force attempt has the same probability to succeed, independently of the rotation of the target password. Thus TOTP doesn't really inhibit brute-force attacks: the average number of attempts to break one password remains the same, but the upper bound is removed.
Answer: Neither is worthwile.  Changing number codes were invented by RSA in 1984 to block keyloggers. More than 90% of todays internet breakins take place as a result of phishing, and we're seeing incidence of entire countries having more malware infected machines than clean ones (the boleto bandits, have pocketed $1bn cash so far, & are still going strong).
TOTP and HOTP are almost completely ineffective against todays' risks.
You need solutions that include mutual authentication, and transaction verification, not 30-years-old gizmos.
Comment: @Chris I must be missing something… how does that answer the question asking about the potential advantages (comparing RFC 4226 and RFC 6238)? Also, you state `TOTP and HOTP are almost completely ineffective against todays' risks.` – do you have any reliable source to backup that statement? (Note that I'm not asking for a link to some weird blog, but for a pointer to one or more scientific papers that provide analysis and proofs to the "complete ineffectiveness" you claim to exist.)
Comment: This answer makes no sense in relation with the question. TOTP and HOTP are intended as a form of authentication (usually as a what-you-have factor as the values are read off a token). They have nothing to do with other aspects of establishing a secure channel.
Comment: @Chris: You forgot the closing tag: ``
Comment: @PriiduNeemre Actually he forgot `[8]`


Receiving dollars directly into bitcoin wallet?

Question: Is there a way that I can set up my account to have my customers pay for services rendered in dollars directly into my bitcoin account via an online electronic funds transfer from their bank account?
Answer: BitPay appears to have an all-in-one solution that allows you to set up a store checkout in a lot of different currencies that will be handled through the use of Bitcoins. As I don't have a hands-on experience with that, I can't vouch for how the system works.
Another convenient way of setting up a payment system would be to use BitInstant which allows a user to quickly convert cash into Bitcoins through a variety of ways. It does not appear to be as automated as BitPay though, and you would have to handle your own payments.
Lastly, you can encourage your users to get their Bitcoins through more traditional means, such as the use of Bitcoin Exchanges. This option also requires you to handle the payments by yourself.
Comment: I checked out BitPay and I believe the setup that they provide is payments in bitcoin. I would prefer to accept payment in dollars into my bitcoin account and have my account convert to bitcoin. I want to encourage direct online payment for my customers seemingly as they would make any payment online. Customers unfamiliar with bitcoin would probably be scared away otherwise. My customers are usually one time customers and will likely be unfamiliar with bitcoin.
Answer: You can accept payments through OKPay.  The funds received can be used to purchase bitcoins at several exchanges which accept OKPay transfers (including Mt. Gox, and  others).

https://www.okpay.com/en/services/accept-payments

In the U.S., most consumers don't have "bill payment" where they can push an ACH transaction to any arbitrary bank account number.  There are several intermediaries which offer a bill payment option for businesses such as utilities and other businesses in which the funds are "pulled" from the customer's bank account.
Smaller businesses can accept the "customer push" payments capability by accepting PayPal, but the problem is those PayPal funds aren't easily moved to Bitcoin exchanges.  As a result, Dwolla becomes a good alternative -- as Dwolla funds received can be easily moved to Bitcoin exchanges.


Should I cook frozen salmon differently from fresh salmon?

Question: I bought some frozen wild-caught salmon fillets for the first time so see how we like it.  Can I broil it the way I usually cook salmon, or does the freezing process lend itself better to other methods, like sauteeing or poaching, or does it even matter?
Comment: Dear tangible3, our site has some strict rules. One of them is that we don't ask questions which have thousands of equally-good answers, such as "what dish can I prepare with ingredient X". Reading the body of your question, I see that you did not mean to ask that, but your old title was very easy to be interpreted this way, and I guess this is why somebody cast a close vote on your question.I edited the title in order to prevent such an interpretation and keep the question from getting closed; I hope it expresses your original intent well enough.
Answer: Once you thaw the salmon, you can treat it like you would fresh salmon.  Freezing may degrade the texture of the fish a small amount (it may not even be noticeable if they were commercially frozen in a blast chiller), or allow a little moisture loss, but otherwise the fish is essentially unchanged.
If there is any weeping or moisture coming out, pat the filets dry with a lint free towel or paper towel before high heat cooking methods like broiling or pan frying.
If the filets are thin, you can even cook them from frozen without pre-thawing them; they will thaw as part of the cooking process.
The best way to thaw them is to put them in refrigerator until they are thawed.   You can then proceed with your recipe like you normally would.


What are QR codes and How do you use them as request payment from Wallet?

Question: What are QR codes ?
How do you use the QR code for payment function on the wallet ?
When would you use it ?
Comment: See http://en.wikipedia.org/wiki/QR_code for your first question. With Bitcoin you generally scan the code with your smartphone app to know to which address to send the bitcoins.
Answer: When using bitcoin to pay at the point-of-sale or for a face-to-face transaction, there is the problem of how to communicate the Bitcoin address to be paid in a way that the person paying can use.
A bitcoin address is just data, but it is between 27 and 34 characters so that is way to much info to expect the person paying to have to manually type in.
A QR code can easily represent this amount of data in a machine-readable manner and do so reliably.  The QR code can contain other information as well -- such as an amount and a message and other fields as well -- thanks to a URI scheme for Bitcoin.
So with a mobile, a convenient way to pass that data is for the payment recipient (e.g., a merchant) to display a QR code with the Bitcoin address for the transaction, and then for the person paying to scan that QR code to obtain the bitcoin address.
A mobile app called Barcode scanner from ZXing is the most widely used app on Android for this.
If you are paying using the Blockchain for Android mobile app, then that app will let you touch the QR code button to launch the Barcode scanner app.  When the scan is complete, the Bitcoin address field (and amount field if the QR code contained the amount) will then be populated with the data from the QR code.  The person paying then hits send and the bitcoin transaction gets created and broadcasted by the mobile app.  Web-based wallets (e.g., Instawallet.org) can use a QR code as well, except the user may need manually do a paste of the clipboard contents after scanning.
The merchant or trader might use the same mobile app (e.g., Blockchain for Android) which has a built-in method to create and display the QR code for the customer to send payment to which occurs in just one step.  Many clients (including Bitcoin-Qt), EWallets and payment processors such as BitPay and WalletBit will show a QR code (or a method to get the QR code displayed) for receiving payment.
For those wishing to create a QR code manually can do so using a web-based service such as Wolfram Alpha or several other methods.  This does introduce a vulnerability however in that the provider of the QR code could detect that this is a Bitcoin address and maliciously interject another address that the provider controls -- thus directing the consumer to pay the wrong address.  So using only a trustworthy source to generate the QR codes is recommended.
Answer: As of November 2013, Bitcoin-qt generates a QR code.
Click the Addresses button at the top of the window, highlight the wallet address you want, and then click the "Show QR Code" button at the bottom of the window. Add a message, if you want, or not, and then click the "Save As" button. It will be saved as a PNG image file.
Answer: Nowadays pretty much every device has a camera built in so it is much easier to scan the QR code rather than typing very long Bitcoin account address. If you have wallet in your mobile phone and you want to send money to someone he can email you the QR code and you will be able to scan it quickly with your phone and send the money. Without that you would have to type in on your phone the whole Bitcoin address.
The same goes to receiving Bitcoins, you can easily send QR code to someone. If you make face to face transactions with Bitcoin you can exchange Bitcoin addresses just in few seconds, without typing.
To generate a QR code you can use one of the free online tools like http://qrcode.kaywa.com/ or http://goqr.me/, after generating the code you can save it as a JPG file, print it and keep it in your wallet or even order a custom t-shirt so people can donate you some Bitcoins in the shopping centre just by pointing their cameras at you :D
Comment: Good question, I have just extended my answer :)
Comment: Good answer, but how would you produce the QR code in the first place?
Answer: The easiest way to create a bitcoin qr code is to use www.btcfrog.com/qr and just fill in the address and maybe amount boxes and press "generate QR code".
It also has an option to generate html code to embed on your site. The code is an image tag that references a php script so you can have javascript, asp, php etc change the amount and regenerate the "image".

This also makes it ideal for adding in BB-code or other kinds of posts.


Animate transparency of entire layer

Question: Blender noob here. I'm learning my way around but could use some assistance. I'm working on a project having to do with human anatomy. I have a 3D model complete with skin, skeleton, muscles, organs and so on. Each of those are on a separate layer. I am trying to animate the transparency of the muscles however that layer is made up of several meshes/textures and I can't figure out how to simply fade them on screen. I have already done something similar with the skin layer but that is all one mesh. What's the easiest way to do this? Just so it's clear, I have my transparency set to about 20% on the skin to show the organs. See below
I then want to fade the muscle group on so it looks like this.

Is there a way to add keyframes to entire layer? I'd appreciate any help. Thanks!
Answer: I am not animation expert but I think what you want to do is... make your separate completed renders for organs, muscles, and then skin. then, in the compositor, create your fade-in animation from one completed render image to the next by using the alpha-over node. This example probably explains it better than I can - https://docs.blender.org/manual/en/dev/compositing/types/color/alpha_over.html

Animate transparency of entire layer


Shakespearean way of speaking

Question: Was the language used in Shakespeare's plays commonly used among people at that time in normal speech? I know that iambic pentameter was commonly used in formal, pre-prepared speeches at the time, but was the vocabulary and structure of normal speech similar to that shown in Shakespeare's plays? I ask this because I do not understand sentences in his plays from time to time, even when they were meant to be comedic. However, someone told me that the jokes he told were very popular and well-understood at the time. Does this mean that they were more educated than us in the English language?
Comment: The early modern English language was less than 100 years old in 1590 when Shakespeare was writing. No dictionaries had yet been written and most documents were still written in Latin. He contributed over 3,000 words to the English language because he was the first author to write them down. Of this number more than one tenth or 1,700 were used for the first time. https://www.rsc.org.uk/shakespeare/language - The language of Shakespeare - http://www.davidcrystal.com/?fileid=-4864
Comment: @Josh: English has been constantly changing since the 13th century, and the division between Middle English and Modern English in 1500 is entirely arbitrary. It's not like everybody suddenly started speaking a new language.
Comment: @PeterShor - Did I say that the change was an overnight thing? Anyway, however arbitrary it may be, the divisions into Old, Middle and Modern is an established fact conventionally accepted by the majority of sources.
Comment: You didn't, but this idea that "early modern English was less than 100 years old" seems to imply that the language was changing faster then.
Comment: The fact that people in Shakespeare's time found it easier to understand his vocabulary doesn't necessarily mean that they were more educated in the English language. It's like the joke about how impressive it is(n't) that "even the little children in France speak French!" Some words that Shakespeare used are obsolete now, but were in common use in his time. (And on the other hand, there are many modern words that would pose difficulties for time travelers from Shakespeare's era.)
Answer: Yes it was they way people all spoke - vocabulary not withstanding. English has changed a lot since the the of Chaucer.  Who also wrote in the style of English language at his time. The Bible translation times people also talked like that with all the Thees and Thous etc.
Answer: The reason you can't understand some of his jokes is that words are pronounced differently today, so the puns are a lot harder to hear.
Another reason you can't understand some of his jokes is that slang is different today, so some words that had slang meanings don't anymore.
And still another reason is that some of his jokes were very subtle – some actually only make sense if you know French – so that most people in the audience didn't understand them, and Shakespeare probably didn't intend them to.
Comment: I speak French but I still don't understand them :-(. Anyway, thanks for the answer!

Shakespearean way of speaking


At what point does the amount of data presented on a table become too much?

Question: The engineers I have worked with at various companies seem to be of one mind, in that they believe it's most useful to their clients if every field available in a given dataset is displayed in a datagrid. This can result in datagrids with gigantic widths, and lead to column-width issues, which I as a designer am assigned to fix. Looking at the glut of data presented in these tables, which somethimes even need to scroll offscreen, I cannot see how presenting this much information at once in such a manner can possibly be useful. Furthermore, it ties many of our tables to a fullscreen width, as the amounts of data cannot possibly be displayed in a useful manner in anything less. My question is this: how much data is too much to display, before the user feels overwhelmed, overloaded, and disinterested?
Comment: As an engineer interested in UX I find your starting sentence prejudicial. If you want for engineers that you have to work with to get a grasp on UX, I'd say that an inclusive/compassionate approach works better than a confrontative one. ;-)
Comment: The reason why dashboards are becoming more popular is partially due to the fact that data tables for complex information is not a very good way to help people make decisions. I would say that if you can't look at a data table and work out what you want to do and how it should be done, then the amount of data presented is too much.
Comment: This question is entirely based on your audience. There are multiple techniques to help with your situation, but testing it with a couple of users may be a good start. Simple questions such as, "Can you find [this] information on the table" will indicate how difficult it is in locating content. This may in turn convince some of your co-workers that displaying everything at once is not the best choice.
Comment: At the point that I have read so long that my bag of chips is empty, my chair has sunk in, my mind is wandering, my hands are tapping and I think I needed to go pee an hour ago!
Answer: The amount of data (both in terms of the types of data that are presented, and the amount of information presented for each type of data) presented in a table becomes too much when your users are unable to complete their goals, or are able to complete their goals with a lot of difficulty and overhead.  Which is to say, the amount of data that is presented is too much when your users tell you (directly or indirectly) whether it's too much.
You can quickly gather some information about whether you're presenting too much data by either interviewing current users about what they do with your product and how they go about doing it (if you have any; it's unclear whether this is a new product (or new feature in an existing product), or by conducting a usability study against your most important use cases with your current or potential users to see if they are able to accomplish their goals.
Comment: Much appreciated. Our clients have requested that all the data be present in many of these cases; of course I'm all for giving the clients what they ask for, but don't see how creating a garganuantuan table that doesn't fit onscreen is actually usable, and have suspicions they're asking for these things because they're used to working in Excel workbooks and want an interface that reminds them of this. Also, in many cases, these tables include a description-type paragraph in one or more fields that presents difficulties- do I let them stretch out the table cell, truncate the data, or other?
Comment: I don't think that you should give either users or clients everything that they explicitly ask for. A request from a user, or a client, is based on their assumptions and biases.  To create the best UX, you need to understand the underlying assumptions and biases. Most importantly, you have to understand the need that the request is based upon. The best way to meet the need might not be the way that is articulated by the user (or by the client). This isn't to say that you should ignore the user or the client, but to use their request to inform your design.
Comment: I've been leaning towards cardview listings for tables with these long data-types (this way, the longer fields can be placed on the bottom of smaller fields arranged side-by-side), if we can truncate a field that long without issue, what's the point of including it at all?
Comment: @EddiePrislac, and don't forget to invite a member of engineering team to the usability test.
Comment: I find the hardest part of UX design is actually figuring out what the users need vs what they ask for. The tendency is to get asked to do things that are terrible UX wise because they think in terms they already understand i.e. "I want Excel" even if the data isn't a good fit.
Answer: There are two aspects to this question:

Amount of data - this really depends on your audiance. For example if you are working with financial planners they would be comfortable dealing with more data in the same spreadsheet. Other way to think about it is that if the user needs access to data, then what's easier - scrolling or some other mechanism
Second aspect is how do they comprehend this large amount of data. This is where there are many techniques that can be applied - color coding values/cells based on a certain scale - e.g. all numbers greater than 100 are in green, between 50-100 are orange etc. You can add charts, allow filters, expand/collapse some data elements etc.
Comment: Thanks for the tips, Alok, the bits about color-coding may be especially helpful, however, since these are mostly text datagrids, I don't know how open my engineers would be to displaying the results in graphs and charts rather than numbers (path of least resistance and all that). Filtering seems to be the way they are most receptive to reduce the amount of data displayed on screen.
Answer: The point at which a user sees information that they don't want/need is the point where there is too much data in the table. Some users will need to see a lot others might not need to see all of this data. If you have many different audiences that have different needs then you should have a way for each user to adjust the presentation to suit their needs.
I am currently working on a project that has a datagrid with upwards of one hundred possible columns. This would be unmanageable so we allow users to hide/display columns and save the "layout". Users can create many layouts that have different column combinations that suit specific tasks.


Is frozen crabmeat OK to use for crab cakes?

Question: I have some frozen precooked crab meat that I was going to use in a sauce for pasta but thought maybe crab cakes would be a nice change of pace.
Does the fact that it has been frozen make it unsuitable because of texture change?
Answer: Most crabmeat is pasteurized, so the texture has already suffered a bit.  Crab cakes are basically a binder, crab meat, and seasoning.  The binder can add all sorts of interesting textures.  There are recipes with Panko, bread flour, flour, eggs, ...  If you are worried about it being dry, add mayo as @Darin suggested or increase the oil a bit.
Look at the packaging, the crab meat may be already cooked, so you may get away with cooking it less.
Answer: Agreed on the moisture issues. The thawing process will leave a lot of lost crab juice that would need to be replaced with some fat. Recomend thawing and then draining before mixing with binder and seasonings.
Answer: Previously frozen crabmeat is fine for crab cakes.  Should the crabmeat have dried a bit from being frozen, the mayonnaise that is typically added will replace some of the lost moisture.
Answer: Freezing crab meat breaks the cell walls and causes the meat to be mushy, not firm. That is why you have so much water in the bottom of the container when you thaw it. It works fine for crab dip, where the texture is not critical, but I would not use it for crabcakes.
BTW: ALL crab meat you buy is precooked, I've never seen "raw" crabmeat. It is already steamed, then picked and put in a container. "Fresh" is just not pasteurized, so the shelf life is much shorter, but it is definitely cooked.


How can I initiate a modem connection from the command line?

Question: I am looking for a way to initiate a PPP connection with my EVDO modem from the command line instead of having to go to System Preferences -> Network and hit "Connect".
Comment: You might be able to use two terminal windows to determine where your pppd script is stored. One window running `opensnoop`, the other `fs_usage` (without your modem, it's hard to guess where your scripts are stored)
Answer: To connect a network device, use the System Events dictionary:
tell application "System Events"
    tell current location of network preferences
        connect service "Sprint 3G"
    end tell
end tell

assuming the name of the service is Sprint 3G:

To disconnect, change connect to disconnect:
tell application "System Events"
    tell current location of network preferences
        disconnect service "Sprint 3G"
    end tell
end tell

Once you've saved your scripts with names, you can use the terminal open command to kick off either script.
Comment: Well done! I hope you don't mind me adding an open command to finish this off in the terminal way.
Comment: Looks great. I ended up using this with [Alfred](http://www.alfredapp.com/) so I could just type `connect 3g` or `disconnect 3g`.
Comment: Here's what a screenshot of the Alfred integration looks like: https://img.skitch.com/20110831-pg1nht8jbnb46nwgx27saw2uxc.png
Comment: How do you call Alfred from the command line? Perhaps you just meant to script it in response to a shortcut key.
Comment: Yes, I just mean that I was able to use the script in response to a keyword in Alfred.
Comment: alfred looks to be great - glad you have it - it might be a nice replacement for us old timers using FastScripts and storing scripts on the filesystem...
Answer: I'm sure there is a more elegant way, but this could be done with UI scripting.
I don't have an EVDO modem, so I can't give the specifics of the script that would work, but first you would go to  -> System Preferences -> Universal Access and make sure "Enable access for assistive devices" is checked.
Then, you could write a script using a text editor. As I said, the specifics of the script would depend on your system and the layout of the screen you're trying to control, but it would look something like this:

#!/usr/bin/osascript
tell application "System Preferences"
activate
set the current pane to pane id "com.apple.preference.network"
click button 1
tell application "System Preferences" to quit

You'd save the script, make it executable, and then you could enable your modem from the command line. I'm sure there's a more elegant way that doesn't involve popping up a window and that doesn't involve so much trial and error at the "click button 1" stage, but this is a start.
Comment: I would really like to find a way to do it without needing to actually open the System Preferences.
Comment: Of course. As I said, my approach is distinctly inelegant, but still scriptable. I'd love to see a better answer, and I suspect something involving pppd is more likely to be viable, but I have less advice to offer on that front.
Answer: I think this can be done using pppd. You'll need to find the device name (/dev/tty...) and read through the long list of available options but it looks like that could work.
Comment: I don't have a modem anymore to test this unfortunately, but I have used it in the past. (This is exactly what's used for [modem connections in linux](http://www.linuxjournal.com/article/5467), for example.) If this answer is "negatively helpful" I would appreciate learning why it was downvoted with a comment.


Can I obtain the hashing algorithm if I know both the input and the output?

Question: Suppose I have a string "Hello World".
And I pass it through an unknown function which gives output as "6Xbhkfo520/78".
So, using several input and output pairs, can I determine the algorithm of the hashing function?
Comment: I take it you don't have a list of candidate algorithms to just check that input/output pair against? If you want to reverse engineer the function given only a single input/output, that might be hard: Even assuming you found *some* function that worked for that input/output pair, that doesn't guarantee it's the one that was actually used.
Comment: Not really but theoretically given a large enough amount of input/output pairs a deep nn or other form of ML could be trained to imitate the hashing algorithm
Comment: Similar to: https://crypto.stackexchange.com/questions/60055/figure-out-algorithm-to-numeric-key-generator-with-one-known-input-and-output?
Answer: It is weird to assume a hash function is private. This contradicts Kerckhoffs's principle. If you are talking about keyed hash functions, then I think the answer is no in theory. They are typically used to construct message authentication codes like HMAC, of which the keys cannot be derived from several hash inputs/outputs.
Answer: You cannot directly determine what function is used. You can't even tell IF a hash function was used. Secure hash functions can be modeled as a random oracle. Input/output pairs of the form $(m, hash(m))$ are indistinguishable from pairs of the form $(m, \text{random-value})$.

Slight tangent: This is probably related to one reason why "challenge" questions, "what algorithm is this", and "crack this ciphertext" questions are banned from this website. If you want to prank someone then say to them "I challenge you to crack this cipher from ciphertext only." Then give them a fake ciphertext string chosen randomly. You can easily waste their time by asking them to solve a puzzle with no answer.
Additionally there exists an infinite number of potential (mathematical) functions consistent with one input/output pair. Even if you find one function that is consistent with any number of functions, you cannot be sure that it's the same function because there are infinitely many alternatives.

What you can do is come up with a hypothesis like "This hash function is MD5." (Or SHA-1. Or any other known algorithm.) Then test your hypothesis. If $hash(m) \neq \textit{MD5}(m)$ then you reject your hypothesis. Repeat for every candidate function you can think of.
When the given output does not match the computed output, you can conclusively say "The hash algorithm is not vanilla MD5." On the other hand if the two values are equal, then you cannot say for certain that your hypothesis is correct. For a secure hash with a long output you, as a person, may be confident that your hypothesis is correct. These functions wouldn't result with many (or any) false positives because there outputs are too large to allow matches to happen by chance. But as I noted before it cannot allow you to mathematically prove your hypothesis is correct (unless you rule out every other function in the universe of all possible functions) because of the infinite number of alternatives.

Second aside: Sebastián Mestre's suggestion to use machine learning is (very) wrong for the same reason. You could train a neural net that produces identical results for any given set of input/ouput pairs, but the operation the neural net does will be a function not necessarily or likely the original function. This is the "over-training" phenomenon. Or "over-fitting" a function. Furthermore neural net training does not work well for this type of thing. There is no gradient for pseudo-random discrete things. And if a hash algorithm could be succinctly represented by a neural net that would imply a very flawed cryptographic algorithm.

Back on the main topic: In practice you would need to further complicate the method of "For each  hash algorithm test if it fits." There are lots of variations on algorithms that are possible.
As a heuristic for choosing potential hypotheses you can look at the output of the function. If it's 512 bits long then you should look at things like SHA-512, SHA3-512, Skein-512, Blake-512, Blake2b, ... You get the idea. It's probably not going to be MD5 or SHA-1 because they have less than 512 bits of output.
This can be complicated though. If you have 256 bits of output, then maybe you have a SHA-256, SHA3-256, SHA-512 truncated to 256 bits, SHA-512/256 (which is different from both SHA-256 and truncated SHA-512), truncated SHA3-512, two MD5 outputs concatenated together, etc.
So far I have ignored text encoding of hash function output. That is, for the sake of simplicity, I treated the output string as the raw output of some hash function (a binary string) not an ASCII string like "6Xbhkfo520/78".
If you have a 64 byte output and every single byte is an ASCII character 0-9 or A-F, then maybe you should assume you are looking at a hexadecimal encoding of a 32 byte value, not a 64 byte binary string that happened to fit this description by chance.
You should try different encoding methods. Counting the number of unique characters in the output is another good heuristic, this time for guessing encoding methods. Look for other distinguishing characteristics of encoding methods, like separator characters or padding characters. (A string ending in two equal signs is likely a variation of base64. Which one though would be less certain. There are many base64 and base32 "alphabets" to choose from so you'll want to try the most common ones.)
You should notice that this is essentially a brute force method. (Except unlike password cracking or brute forcing a key for a known algorithm you're testing known input/output pairs against many possible hash functions and encoding algorithms.
This is backwards compared to Kerckhoffs's principle. (A cryptosystem should be secure even if everything about the system, except secret keys, is public knowledge.) Attempts to defend yourself using some obfuscation method you have come up with is usually referred to as "security through obscurity". "Security" through obscurity is not good security but it might make someone's work a bit more difficult. This problem, for example.
There are lots of ways one could obfuscate hash outputs or the hash algorithm used. Uncommon text encodings, character substitution, character transposition, double hashing, encrypting input before hashing, encrypting output of the hash function. If you want bad ideas then look at "clever" password hashing solutions people come up with. (Like in the PHP documentation comments section, assuming they haven't cleaned that up.)
If you're trying to make it difficult for outsiders to compute your hash function, then there are better alternatives to using secret algorithms. You can use a public (secure) algorithm with a secret key. HMAC, for example. This has the benefit of being easier to implement securely. And it doesn't require every person who could possibly want to hack you being much much less "clever" than you.
Although HMAC is only one algorithm (which utilizes a hash function of your choice), you can think of every instance of HMAC with a distinct key as a separate hash function, even when every instance uses the same hash algorithm. (HMAC has a quirk in that there are equivalent keys, but it's not a security issue with randomly generated keys.)
Other methods of turning one hash function into a family of hash functions include salting, personalization strings, and non-standard IVs.
Salting usually refers to a value that is not required to be kept secret. Non-standard IVs may make a secure algorithm insecure. Personalization strings are pretty much the same as salts.
Since brute forcing many different hash functions, encodings, and additional input is probably the best method of determining a hash function, then using a secret key with enough entropy will make it impossible to "obtain" the function without hacking the system protecting the key. For this post I assume obtain means you have full knowledge of how to compute identical input/output pairs for any input.
Important: Passwords should be hashed with an algorithm like Argon2 or bcrypt using an unpredictable and globally unique salt. It's possible to hide the salt and output of these functions by encrypting both with a secret key protected by a HSM. This actually provides a greater degree of security than you could get with only a salted password-stretching hash algorithm. It is not security-through-obscurity because it only requires correctly implemented algorithms and protection of key material.
Comment: I have observed that questions like this are really common. Sometimes they're "What algorithm is this?" Sometimes they are misconceptions about standard-security vs obscurity-security . Sometimes they're people confused why everyone doesn't just keep what algorithm they use for password hashing secret. I'm not aware of a good single resource so I went overboard explaining the how and why of obtaining-the-hash-function as well as the how and why of mitigating that "problem". Let me know, anyone, if you find a better resource or find errors in this answer.
Comment: Not a "better" resource, but a supplementary one might be [this answer](https://crypto.stackexchange.com/q/59825/29554) to a recent question about the same subject.


MacBook 5,1 Upgrade, Leapfrog to Yosemite and MBA Backup

Question: My 2014 MacBook Air was recently stolen, but I have a full backup available via Time Machine saved to an Airport Extreme base station. For now I'm using an old MacBook 5,1 with an Intel Core 2 Duo processor and 2 GB RAM.  After using the Air for so long I kind of like the feel of this machine better and don't mind of the bit of extra weight. I am inspired by all the info available about upgrading this model, and I think it's a better solution for me than buying a new MacBook.  There seems to be plenty of info available about the process, but before I dive in I'd like some input from the folks that know a helluva a lot more than I do about this kind of thing:
My plan is to upgrade the 2012 MB with an internal SSD drive and enhance the memory, but once that is done, can I then use the Time Machine backup from my 2014 MBA to populate this computer, or will the format switch from MBA to this MB wreak havoc?  If it is a problem, can I just upgrade and do a clean Yosemite install and then just move over key files and applications from time machine to the 2012 MB?  As mentioned, the backup is saved on a Airport Extreme base station, and I have a memory stick startup disk from a clean re-install that I did on my MBA about a month ago.  Obviously I can't recreate that without my 2014 MBA, so can I use that or will it also cause issues? In the AppStore I still have the option to download Yosemite, so if I can't use that start up disk what are my options?  I'm only as good as the last YouTube video I watched about this stuff, which is dangerous.
Comment: possible plan of action. New Yosemite install, then treat the backup as a Migration. https://support.apple.com/en-us/HT204350 [from time machine is well down the page]
Comment: So would I make a startup disk from the 2012 MB and then just load yosemite?
Answer: No, your Time Machine backup should restore to a supported Mac just fine.  I do it all the time to save time installing multiple machines from scratch.


Aperture won't lower

Question: I have Tamron 90mm f/2.8 Macro Lens on my Nikon D5500. I'm trying to get my aperture to go to its lowest which is 2.8, however, I can't get it to go lower than 3.0 or 3.5 (its lowest changes often and I'm not sure why). I've tried it both Aperture priority mode and Manual.
Any advice would be greatly appreciated.
Comment: Related: ["Do modern IF Macro lenses have true constant apertures?"](https://photo.stackexchange.com/questions/95493/do-modern-if-macro-lenses-have-true-constant-apertures)
Comment: Also: [Does maximum aperture change with focus distance with the Canon 60mm f/2.8 macro lens?](https://photo.stackexchange.com/q/20300/15871) and [tokina at-x pro 100mm f/2.8 macro for Nikon - aperture automatically changes while in manual mode](https://photo.stackexchange.com/q/76803/15871)
Comment: Related: ["Why does the max aperture change when use Nikon 60mm AF-D Micro on D90 camera?"](https://photo.stackexchange.com/questions/20332/why-does-the-max-aperture-change-when-use-nikon-60mm-af-d-micro-on-d90-camera)
Answer: The lens is reporting the effective aperture at your current focus distance. Note that as you focus closer, the reported maximum aperture reduces; the closer you focus, the higher the f-number you'll get.
This is actually a good thing, particularly if you are relying on external metering. It saves you having to calculate the true exposure based on the "bellows draw" (that is, how far the lens is being moved away from the sensor or film plane as you focus). If you are shooting things at low magnification, the difference between the exposure at infinity and the exposure at your focusing distance is negligible no matter how the lens works, but at higher magnifications - as you move into macro territory - the difference between an internal-focus (rear-focus) lens and a unit-focus (traditional-type) lens becomes important. If the lens is moved far enough away from the sensor or film to focus at 1:1, you lose two stops of effective aperture. So a "90mm f/2.8" lens focused at 1:1 is either not 90mm anymore, or not f/2.8 anymore.
If a lens intended for macro shooting keeps a constant reported maximum aperture, it could be telling you one of two things:

the focal length of the lens is being reduced as you focus closer, in which case the effective aperture for exposure purposes remains the same, but you lose working distance; or
the focal length of the lens is remaining constant, but you will be underexposing unless you figure out the bellows factor and compensate if you are not using TTL metering at the time of shooting.

Some lenses are a little bit of both, too, so you can't just look at the focus distance and make a quick calculation. If the focal length is being reduced, but not as much as in a "pure" IF lens, while the lens as a whole is effectively being moved further from the sensor, you'll have had to do some testing ahead of time to know what compensations to make with external metering, or take test shots as you go.
It's best, then, if the lens tells you what's really going on. Even if that seems somewhat counter to your expectations.
Comment: Regular lenses normally are not able to focus close enough to see that effect, but close is the purpose of macro lenses.  And of course, at such close distances, the depth of field will be so small that a wide aperture is counterproductive to results. That would be the time to stop well down, like say f/16, to have any depth of field at all.
Answer: The question is: Does the Tamron 90mm f/2.8 Macro lens maintain a constant aperture as you close focus and if not, why not?
My believe is; a true macro lens should maintain a constant aperture regardless if working at infinity or unity (life-size otherwise called 1:1 or magnification 1).
A general purpose lens is optimized to work at infinity and close-in to about 1 meter (3 feet). A true macro is optimized to work at unity and slightly compromised when tasked to work at infinity. Let me add that it's unlikely you will notice any degration.
That being said, when we work in close with a non-macro lens, f/numbers becomes invalided for close distances starting at 1 meter or shorter. This is because, as we work closer and closer, we must rack the lens further and further away from film/digital sensor, to achieve focus. You should know that the distance lens-to-film/sensor is called the back-focus distance.
Now the f/number is computed by dividing the focal length by the working aperture diameter. When we close focus, the back-focus distance replaces the focal length distance for this f/number calculation. The net result is, the further the back focus, the dimmer will be the image. The change in image brightness, as you approach unity is severe. Unity is magnification 1 and formula to compensate for the dimming of the image is called the bellows factor. This formula is (M+1) X (M+1). Thus at unity, M=1 and the math is (1+1) X (1+1) = 2 X 2 = 4.. This tells us that at unity we need to multiply the shutter speed by 4 or open up two f/stop to allow 4X more light to play on film or sensor.
As to a true macro: A macro is optimized to work at unity and thus should maintain a constant exposure as you close focus. A true macro accomplishes this by design. The upfront lens group magnifies the apparent size of the aperture hole, as seen from the front. This magnified view allows more light to enter the lens. As you close focus, the apparent size of the aperture changes and compensates for any light loss.
If the lens is not a true macro, compensation will be only partial or nonexistent. You might check the specifications of your lens to check. Don't worry if it is not a true macro, modern cameras with thru-the-lens metering provide compensation for light loss. Usually this will be in form of lengthened exposure time and/or elevated ISO or both.
I know nothing about your specific lens. I have been wrong more than 1000 times. Because of this I usually label my responses as gobbledygook.
Comment: @AlanMarcus The aperture is not stopping down, the camera is just reporting the difference in brightness as a smaller aperture sometimes (Nikon) and sometimes not (Canon). The same thing happens in both cases: The aperture diaphragm stays the same size but as magnification is increased the field density of the light at the film/sensor becomes dimmer.
Comment: So the [MP-E 65mm 1-5X Macro](http://gdlp01.c-wss.com/gds/7/0300003517/02/mpe65f28-1-5x-im2-eng.pdf) is, by your definition, not a true macro lens?
Comment: @ Michael Clark - I have never laid hands on the MP-E 65mm so I can't pass judgment. In my mind, a macro maintains a constant f-# down to 1:1. The poster observed this lens stopping down when close focusing. Seems to me, if true, it's close but no cigar. Likely just some more gobbledygook from me!
Comment: Can you add a link to some authoritative source for what defines a "true macro"?
Comment: In the case of the MP-E 65mm 1-5X Macro, unity is the *smallest* magnification of which it is capable. 5:1 (*not* 1:5) is the MM. There is only a single focus distance for each magnification: the minimum focus distance and the maximum focus distance are the same at each magnification level, which can be adjusted continuously from 1:1 to 5:1. The information for *effective aperture* at each reproduction ratio is covered on pages 7-8 of the user manual linked above.

Aperture won’t lower


Design Document Contents

Question: What is the minimum content that a game design document should have?
Comment: For what purpose? To make the game or to pitch it to an investor?
Comment: To make the game.
Answer: I come from a different stream of life (TV Production), but it's basically the same.
You need a production bible. But, to put it more simply - you need what you need and nothing more.

Character list
Levels list with each level set list (areas that need/deserve special attention)
Prop list

Each list contains layout sheets (or character layouts for characters - front, side, 3/4), notes, mechanics notes for animation, etc. Whatever you need or might need.
Story/Game production sheet.

Screenplay and X-Sheets for animators if you have a story and dialog/VO
Run through screenplay which describes game as though linearly progressed (if game is intricate enough to need it and is, of course, linear in nature)
Game mechanics per game/level/mini game with set goals, obstacles, rewards - you can do this per level list and only a big idea in run through screenplay

In short, whatever works for you and size/scope of your team.
Answer: Having just begun studying design documents, I've come to the conclusion that no-one really knows what goes in them.
The design document itself should be what you need to progress from pre-production to production. How do you turn the game design from this nebulous idea to something that can be created and executed? Too little detail and there's too much ambiguity, creating uneven results, too much detail and you limit possible creativity from your team.
It's not easy, and the science of game design documents is woefully under-explored in comparison to other software domains.
A good paper on this is Requirements Engineering and the Creative Process in the Video Game Industry.
Answer: The size and scale of the project documentation completely depends on the size of team and the scope of the project.
Typically large games aren't built off monolithic design documents, but a distributed document system. Either a series of smaller targeted docs or a wiki. Personally I prefer the wiki approach as allows readers to quickly jump between related topics which maps well to system designs which are often integrated.
When using a Wiki there are a few guidelines that can help with:

One Wiki Page per system/character/level/...
Keep the Wiki highly organized and structured, each content type should have a defined template. You need at least one WikiNazi to keep the site clean.
Describe the design briefly and with bullet points, a design document is not the place for narrative text
Keep pages short and focused, the goal being no longer than 1-2x screen height.
Pictures are indeed worth 1000 words, use diagrams to help get your point across.
Comment: While the above answer is correct that design documents are not the place for narrative text, there is definitely a place for this when developing your design! User stories, often told from a first person perspective, can be helpful when forming the initial definition of gameplay. If you have a wiki or other set of documents that encompass pre-production design work it makes sense to include these narratives, likely in a different section from the design specifications.
Answer: There are no minimum / maximum. It should contain everything you need to start work on the game. Nothing more and nothing less.
You should not require yourself to add information that you think you need just because some template has it.
Comment: Then wouldn't the minimum essentially be:  everything you need to start work on the game. :p
Comment: @Noctrine by definition, sure :)
Answer: I'd say you should work out what the gameplay is, who your character is, and what the environment is like. But my advice would be to start making playable prototypes as early as possible.
Answer: I like to have headings related to what Art, Sound and Storyline I'll need going forward as well as a basic coding design I can follow when I am coding the engine.
However it is a personal thing and everyone varies on how much detail they put in. Mine are fairly short since I like to jump straight into the code rather than dwelling on design.

Design Document Contents


Adverb "now" in the present simple and the continuous

Question: On the use of present simple and continuous, the business textbook I have (Market Leader) says the time expression "now" is used in the present continuous, but in the exercise below where "now" is used, it gives the answer with main verb "spend" in the present simple form "spends".

eBay ..... now [spend] $20m a year analysing suspicious sales.

The cases I have managed to see where "now" is being used in the present simple are all with state verbs like (have, hold and own) not dynamic ones like "spend". However, I used to think that now in contrast with the past could be used in the present simple tense regardless of the verb being stative or dynamic as in the contrived example below. Now I am not sure any more.

They used to make small cars, but now they manufacture all kinds of
  vehicles

According to the book's rules, the ebay exercise above with the adverb "now" calls for the continuous use. However, the answer uses the present simple and it feels okay to me especially with the yearly expenses. If the book's answer is correct then I would to see why. What is the justification anyway?
N.B
"Now" seems like "by some time" in the quote below with a yearly rate. However, present continuous in the passive form is used.

By 1907, 1.7 million toy animals were being made a year.

The Businees Pre-intermediate, Macmillan p.52
Edit:
I do not trust the book because I have spotted some errors with tables containing grammar rules causing inconsistency in the meaning. For example, claiming the adverbial "at the moment" a common present simple and present continuous time expression. There are others but I have to go over the text again to list them.
Answer: In the first clause, "eBay ..... now [spend] $20m a year analysing suspicious sales" the verbs spend is wrongly conjugated. It should be spends because eBay is a singular noun in this sense.
As you once believed, the adverb now can be used regardless of the verb being stative or dynamic. You were right.

eBay now spends $20m a year analysing suspicious sales.

This is the correct present simple form.

eBay is now spending $20m a year analysing suspicious sales.

This is the correct present continuous form.


Is mast*rbating as a teenager haram to do?

Question: I'm sorry, i know this is an embarrassing question to ask, but since this is anonymous anyways and i need to know it. Is it haram when you mast*rbate as a teenager?! Because of the hormones we can't control it sometimes so it just happens. Is it a sin because most of the time I do regret it but it just happens.
Comment: i' m sorry i didn' t know
Comment: Another question about masturbation. We really don't need more. Please check the site before asking. I guess just by clicking on the first five posts that a click on your chosen tag will display you will find an answer of your question.
Comment: Since we have so many of these types of questions, I will give an answer in 10 words, "Sin. Fast and lower gaze. Break habit. Allah is forgiving."
Answer: Okay so, It is understanding about the hormones and all but, you know it really is the waswasa that is making you do it! anytime you have that feeling, go and read some Quran, or even Al Nas, Al Falaq, and Al Iklas!
those will chase all the bad Jinns, Shaytan, and the Waswasa!
Lailah.


Can we ask for recommendations for E-books on this website?

Question: Is asking for recommendations for E-books relevant to this website? for instance, asking for recommendation about a new complete series of E-book(s) for learning C++ programming language.
Comment: You could ask it on the chat site, but unfortunately it seems to be quite dead these days: http://chat.stackexchange.com/rooms/12058/the-appendix Perhaps one of the stack overflow chat sites would be a good place to ask (e.g. for C++ https://chat.stackoverflow.com/rooms/10/loungec)
Answer: No, sorry. This site is really focused on the writing, editing, production, and publication of ebooks. Content-based recommendations are off-topic and highly subjective, which doesn't tend to work well in our Q&A format.


Is the whole universe is rotating on an axis?

Question: Most of the celestial bodies we know are rotating or spinning on its axis.Is there any chance for the universe to rotate on its axis?
Answer: From what we observe it is extremely unlikely the universe is rotating, but it is a good question nonetheless.
Perhaps you thought that since we see galaxies moving away from us they could be being pulled outwards as a result of the rotation. All the galaxies we observe (outside the local group) are accelerating away from us, and this includes galaxies in all parts of the universe. If the universe were like a giant spinning cylinder (or whatever object you like) then the galaxies "above" and "below" us in the cylinder would appear stationary since they are rotating at the same radius.
This observation does not support the claim that the universe is spinning on some invisible axis.
As always we should remember that our local universe may not represent the entire cosmos, and we would in fact be spinning around some axis. As more observational evidence is gathered we understand more and more about the universe, and one would be foolish to rule out a theory based on current observational evidence.
Comment: Simultaneous rotation about two orthogonal axes could make the rotational component of expansion even out in all directions?
Comment: The universe could be expanding AND rotating at the same time. Even objects on the same radius would then be observed to move away from us.
Comment: Hubble's law does not appear to depend on direction. There is no obvious axis.
Comment: I have read that the measurements of the cosmic microwave background indicate that the Universe has a flat geometry on large scales. Flat geometry, by the way, allows to hypothesize that Universe could be thought as a disk (?).
Answer: I wondered the same thing until I focused my studies on the "cosmological axis of evil" regarding the CMB. It appears that some cosmologists believe that due to the fact the Cosmic Microwave Background appears to have an axis, this alludes to the expansion of the Universe having a rotation. Similar to how the earth rotates upon an axis. This, however, is not widely accepted.
Answer: As long as we are in the universe, we'll be unable to determine if the universe is rotating or not.
To decide whether an object is rotating, we need some other object for reference. Since universe is a term which includes everything we know in space, we don't have a reference to watch the universe relative to, to answer this question.
Comment: Unlike linear motion, rotation can be measured absolutely without an external reference.
Comment: Wouldn't there be hints of a rotational motion of the cosmos? Like unexplained gravitational phenomena? We could call it "dark matter".....


How do we know how many BTC have not been spent since being mined? Any tool to see this information?

Question: I would like to know how many BTC have not moved from the block they were mined in - never transferred or spent. (With this information I believe could have an idea of how many BTC have been lost). Is there a tool to see this kind of information?
Answer: I don't think your question quite makes sense. Bitcoins aren't "transmitted", they simply sit in the block chain until someone chooses to spend them. There's no way to tell if a particular Bitcoin is lost or not because that depends on whether anyone knows they key needed to claim it. That key could be written on a piece of paper for all we know.
When your client tells you that you have 50 Bitcoins, it is doing that in a purely passive way. Nobody can tell that your wallet contains the keys needed to claim those Bitcoins, and this is by intentional design.
You could fairly easily measure how many coins hadn't been spent since they were mined. But that wouldn't really tell you anything. Some of those coins may have lost keys and some may not. And some coins may have been spent once and then lost.
Comment: I don't think it's reasonable to infer that a coin is lost just because it hasn't been spent in a year. However, I suppose it is reasonable to infer that the longer the time since a Bitcoin was last spent, the more likely that it's lost. So a coin age histogram might give you some clue how many coins are lost. But so far as I know, there is no good information that would permit making reasonable assumptions about what percentage of coins are lost based on their age. Many people are intentionally holding coins without moving them.
Comment: I just would like to have an information to speculate how many coins are "obsolete" (lost). To know this kind of information I think could exist a tool where I could filter something like: Total of coins that was not spent last year, or since the beginning of Bitcoin and so on.
Answer: I don't believe anyone has compiled the information but you could obtain it all from block explorer.
You would need to go through block chain and record the signing destination of all 144,667 blocks.
Here is an example:
http://blockexplorer.com/block/00000000000000f993d2fd712906ff1a5f79125d12f2832aa0616de1d4949e6e
These are the "original" (as of today) 144,667 blocks.  With a list of them you could simply scan the block chain to look for at least one transaction (other than signing transaction) involving that address.
A couple of issues:
a) like David said above just because it hasn't been spent doesn't mean it is lost (unrecoverable).  Many of the early adopters racked up hundreds of thousands of bitcoin.  Highly probable that many of them are still accessible and simply haven't been transferred.
b) second issue is the existence of pools.  With mining pool there will always be one transfer.  From the pool to pool member.
Comment: a better statistic might be "length of time since last transfer", though this would require some custom programming and it is still arguable how much information one can actually infer from it.
Comment: Agreed.  "lost" is an invalid assumption but one could however write software to parse the chain and provide stats like "18% of addresses had a transaction in the last year".  Like you said it may be of dubious value but it can be done.  Saying "x% of bitcoins have been lost" is simply impossible.
Comment: Yes, what I mean is some easy tool to provide stats like (How many % of address had a transaction last year or month...) (What month had more or less transactions done) and so on...
Comment: @Leo.  As far as I know that doesn't exist yet.  Should be an interesting programming project though.


Control Picklist value for a profile with out record type

Question: How can I restrict a picklist value to be shown for a profile without record type controlling?
Comment: Out of the box, using record types and page layouts is the way to go.
Answer: Having the same problem myself, I came to this via Google. The VF solution doesn't appeal because it only deals with one part of the UI - the original picklist will still be visible elsewhere.
Our proposed solution is to have "proxy picklists":
Put all the options in the original picklist e.g. Industry: {Aviation, Marine, Schools, Universities}
Then create a couple of extra "proxy" picklists:
Industry-Transport: {Aviation, Marine}
Industry-Education: {Schools, Universities}
Add some simple Process Builder/Workflow/Trigger to copy changes in the proxies back to the original Industry picklist.
Then, use field-level permissions in the Profiles to make sure that Transport profile can see only Industry-Transport; and Education profile can only see Industry-Education.
Answer: Without using record types to control the values the only other option (without doing a lot of VF development etc.) would be to create validation rules to ensure that X profile cannot select values Y & Z.
Answer: With the new release Summer 17, you can set default values based on formulas. So if in your object you create a new picklist field to set as master for the rest of the picklist using field dependencies you will have to place the default value of that master picklist depening on the user profile.
In example, the new field is control with the values prof.1 , prof. 2, prof. 3
Then you make  your existing picklist Industry, depending on the new picklist control
So if user has profile 1 the values to be shown are Chemical, Pharmacy, Marketing
If user has profile 2 the values to be shown are Textile and Retail
If user has profile 3 the values to be shown are Hospitality, Restaurants
So that all was posible before summer.
Now the change is:
When creating the new field control you can built a formula to define a default value like:
"CASE ( $User.USerProfile.Name,'Profile 1','Prof.1','Profile 2','Prof.2', 'Profile 3','Prof.3','')
Anytime a user tries to create the value on control picklist will be automatically populated based their correspondant profile and as the rest of picklist depends on that value you'll have the picklist restricted as you wanted.
I hope this helps!
Answer: If you want the functionality without using record types, you can create a VF component and embed it on your object's page layout and populate the picklist values based on profile in controller extension.


Replacement for glDrawElementsBaseVertex in OpenGL ES?

Question: I am porting my game engine(c++) to Emscripten, which unfortunately only  supports OpenGL ES 3.(Not 3.2) Therefore I don't have access to glDrawElementsBaseVertex, which is needed by my renderer(Canvas2D Renderer). It is needed because this way I can combine all my triangles in one draw call, instead of multiple hundred draw calls. So I need something that does the same. I can't just use normal draw calls, because it would be horribly slow and would require redesigning my Canvas2D class.
The reason I need so many draw calls is because the user can use a Canvas2D to draw single/multiple 2D triangles on the screen, which are then combined into one array. Because the user can also send multiple triangle set's, the indexes need an offset to work correct, which is why I need glDrawElementsBaseVertex.
Does anyone know how to replace glDrawElementsBaseVertex with something that does the same?
Thanks!
Answer: If there was something that did the same thing, why would OpenGL have even had that as a separate function?
The only thing you can do is pre-offset the indices you're assembling in your index buffer.


Finding coordinates of centroids?

Question: I have a few thousands of polygons, which I found the centroid for each one of them. Now I want to find the coordinates of each centroid. But for some reason the x and y columns are empty and I don't know how to fix it.
Comment: Have you checked the answers here: https://gis.stackexchange.com/questions/45243/how-to-determine-the-centroid-of-polygons?rq=1?
Answer:
Open Field Calculator for your centroid layer
Tick 'Update existing field'
Select your 'x' field in the dropdown menu under this tickbox
Enter the expression $x in the expression box and click 'OK'
Repeat 2-4 for the y field
Answer: QGIS now has a centroids tool builtin.
Go to Vector > Geometry tools > Centroids

Select your input polygon layer, and output file, and Run

That gives you the centroids on the map, but the coordinates may be hidden in the geometry column and not shown to you in the attributes table, so finally you may wish to...
Export as CSV

Now viewing the attribute table gives the coordinates:
Answer: Use Point on Surface, not use Centroid (irregular polygon).

Create column "x" and "y" (data type decimal).
Use the field calculator expression:
x(point_on_surface($geometry)

Optional.
In Form Editing (Qgis 3.X) you can use this expression value default when update the vector layer.

Finding coordinates of centroids?


What do they do to fancy costumes used in movies after use?

Question: When they use fancy costumes like in star wars or even simple costumes in period films what do they do after use. Of course they cannot wear it again for another movie. Are they recycled or the actors keep it for themselves?
Comment: The production company owns most of the costumes unless it is something that the actors bring in. All costumes are retained by the production company. Some are later auctioned off and some generic costumes are sold or reused.
Comment: @BobbyAlexander That's a good answer; you should move it to the "answers" section below and get yourself some up-votes!
Answer: The production company owns most of the costumes unless it is something that the actors bring in. All costumes are retained by the production company. Some are later auctioned off and some generic costumes are sold, rented or reused.
In fact most studio have a division that rents out costumes and props. It is a secondary source of money. They have large warehouses of this stuff. For eg: here is a link to Warner Bros costume department.
Comment: One notable example of reusing costumes is that the Alliance soldiers from series *Firefly* wore the costumes from the movie *Starship Troopers*.
Comment: It's also of note that it doesn't take much to modify a costume to make it look entirely different. My Grandmother used to work as the primary seamstress for a theater production company in California (HARD). She would do this all the time rather than pay to create new costumes.
Answer: In addition to the answer given by @BobbyAlexander , I have seen them on display at theaters in Los Angeles, and on traveling displays regarding the movie. For example, I saw a traveling Star Wars collection that included a Darth Vadar costume, stormtrooper costumes, even Yoda. It also included other props from the movie such as light sabers, droids, and miniatures models (X-wings, Y-wings, tie fighters, etc.). They were set up as if they were a museum exhibit - miniatures on pedestals, and larger pieces behind red ropes or glass, with printed descriptions next to each piece.  (It was pretty cool!!)
Also, for movies & shows with more "ordinary" clothes, the actors sometimes get to keep the clothes they wore. For example, Sarah Jessica Parker claims that she "kept about 70 percent of her Sex and the City wardrobe after the show."  article on people.com
Comment: I would bet this was the same exhibit which was displayed in the Smithsonian here in DC. It was pretty fantastic.
Answer: In addition to Bobby Alexander's and BrettFromLA's answers, I would like to add that sometimes costumes are put to an auction for fund rising and charity purposes. Sometimes, actors may buy the costumes if they're interested. And as per your question, costumes in the movies like star wars, Iron man etc are put in the online stores for sale. Check these sites, propstore, propworx.


How to roll the 'R' when it is followed by an 'L'

Question: So far rolling the R (in words like hacer, abrir, perro, pero) works quite well for me. But I have a problem when the R is followed by the letter L, like in hacerlo. It works a bit better when I widen my mouth and say the word very slowly, but maybe you have any other hints for me. Where to put my tongue, how to open my mouth. Thanks!
Answer: The words that have an 'r' behind any consonant sound kind of strong, similar to the double 'r' like in the word "perro". You could try pronouncing first the verb "hacer" and then pronounce "lo". After that you slightly decrease the space between the pronunciation of them.
I hope this was helpful.
Comment: Agreed. The best way is first sepparating all syllabes, then increasing speed. Words to practice: Carlos, perla, chirla, Merlos, orla, estraperlo,...
Comment: It's all about having a strong tongue. Once you can roll the Rs without forcing it, you will be able to do it at any point in a word. It's just a matter of practice. Try saying "recorrerlo alrededor" over and over, or the good old tongue twister: "Erre con erre cigarro, erre con erre barril, rápido ruedan los carros por los rieles del ferrocarril".