What is shown outside of the elevator at the end of Portal 2?

Question: At the end of Portal 2 you take an elevator ride and a bunch of small rooms flash past with turrets and other things in them. I've been through it a few times but I still couldn't make out what was in some of them. Any pictures I've seen have been too blurry or low-quality.  What's in these rooms?
Comment: I rewrote this to be a real question instead of a screenshot request.  The accepted answer is still perfect IMO.  [Relevant Meta discussion](http://meta.gaming.stackexchange.com/questions/2784/seriously-a-screenshot-service).
Comment: @MatthewRead Excellent. This should clear up any confusion over the intent of this question.
Answer: Here are the screenshots of the rooms you see on the elevator ride up to the surface at the end of Portal 2. Apologies beforehand as some of the screenshots are a little fuzzy, but the descriptions should help clarify any details that may be unclear.

A row of four turrets initially targeting the player who then go on to sing

Two turrets singing

Four partially assembled/defective turrets

Three turrets at 90 degree angles (apparently mis-assembled)

Four turrets staring at the Aperture Science Weighted Storage Cube

Four turrets surrounding another cube staring at the player

Eight turrets facing the player in two rows of four

Two turrets who appear to be behind a ruptured transportation tunnel (would explain the angle of the turret to the left) or possibly tangled in roots (see comments)

A large room filled with an assembly of turrets, in the spotlight is the 'tenor' turret and in the background is the oversized 'animal king' turret
Comment: On the second to last picture it looks more to me like the turrets have become entangled in some potato roots. What do you think?
Comment: The turrets at 90-degree angles are defective too, by the way.
Comment: Thank you so much! I understand that getting clear pictures can be a problem since they flash by so fast but these are the clearest pictures I've seen so far. :)
Comment: bnb, I'm happy to here that thank you very much it was a pleasure to answer your question since I am a big Portal fan myself and it has turned out to be one of my best answers so thank you.
Comment: Interesting hypothesis, the primary reason for me suggesting that it was a transportation tube was the splintered steel beams as well as the intense motion observed when watching the video however the potato roots is a highly likely possibility as it would be accustomed to Valve's sense of humour in easter eggs and hidden details.
Answer: Viewing this in 720p should help you see what's going on:


How do you keep a Turkey Meatloaf from getting too "dry"?

Question: I just made a Turkey meatloaf, using a standard recipe that usually turns out good with ground beef, but it was too dry - any help would be appreciated.
Comment: You can't just substitute one ground meat product for another and expect good results.  Yes, they're ground meat, but even in the various ground beef products, you've got a variety of fat content, etc.
Answer: My mom's meatloaf recipe included a couple slices of bread that had been soaked in milk and then blenderized with the egg before mixing in to the meat. The milk obviously provides moisture, and the bread a nice carbohydrate matrix to hold onto that moisture. Give that a shot, I bet it will hydrate your turkey. (Do you dare take meatloaf advice from a 25 year vegetarian?)
Comment: this is known as a panade. google the term for more info.
Comment: I think I'm going to try this next time I make meatloaf - one of my recipes calls for bread crumbs, so I'll just substitute this in for the carb/binder instead.  Sounds like a pretty solid idea.  Even if the OP doesn't take your advice, I'm game!
Comment: +1 for creating the word "blenderized." WAY more exciting than "blended."
Answer: Avery's "fattest turkey" advice is solid.  I try to find ground turkey breast as opposed to ground turkey, no matter what I plan to do with it, because it's easier to keep it from drying out in various recipes.  As he said, ground turkey is so easy to overcook.
You could always add some moisture by throwing some bacon grease into the mix, which I have done in the past with regular (ground beef) meatloaf to help make it as unhealthy and delicious as possible.  This should effectively counter the health benefits of using ground turkey over ground beef, but boy is it good!
When my mom makes turkey burgers for the grill, she adds some italian dressing into the mix and swears that it helps keep the burgers from drying out fast.  Haven't tried it myself, but I can see how the oil (and water and vinegar, but moreso the oil) would help.  It will likely affect the taste of the dish...but that isn't always a bad thing, as I find ground turkey to be significantly more "boring" tasting by itself than ground beef is by itself, probably because of the lack of fat.
Comment: A few pats of butter in the middle of the loaf might be yummy too.
Comment: Ground turkey breast is easier to keep from drying out?  I'd think that ground dark turkey would be easier (higher fat content, etc.)
Comment: I actually meant compared to "ground turkey" which seems to be a hodge podge of stuff, not just the breast.  Ground dark turkey is definitely preferred but I have a hard time finding that, and I don't have a grinder right now :(
Answer: It's best to use the fattest ground turkey you can find if you are worried about moisture.  Don't use the extra lean grinds as fat helps keep the meatloaf moist.  If you can find a mixture of ground turkey that is labeled turkey breast or has dark meat in it this will help.
Also, make sure not to overcook the meatloaf as turkey is by far one of the easiest meats to overcook.  Internal temperature should read 160-165 degrees max.  But I would pull the loaf at 150 and let it rest until it comes up to temperature, covered with tin foil.  Almost all cooked proteins will "carryover", that is they will continue cooking after it has been removed from the oven.
Adding stock or extra diced onions for moisture in the mixture will help with moisture but can affect the texture and taste of your loaf.
Answer: In general, fat in ground meat will keep dishes made with it moist. You can substitute a non-fat liquid (such as stock or tomato juice) for the fat to gain back some of the moisture, but it will change the texture. We've had good results using salsa in our meatloaf, since it provides acidity, vegetables, spice, and liquid. This reduces the amount of egg and other liquid we need. (We're down to one egg for two loaves.)
Another way to deal with the issue is to add more fat, but cook the meatloaf using a double-layered pan with holes in the top layer. (Such as a broiler pan or special meatloaf pan.) This allows some of the fat to drain off, reducing the fat and calories for the meatloaf.
Edited to correct the name from "grilling pan" to "broiler pan."
Comment: the "grilling pan" is also known as a "broiler pan"  (a least, that's what I've always heard it called )... and it's what I use when making meatloaf ... it exposes more surface area, giving lots of browned crusty bits.
Comment: Thanks! I couldn't remember the exact term -- broiler pan makes sense! I've changed the original entry to reflect.


A master-level game in which one player did not move beyond the third or fourth rank?

Question: Has there been a game of master level or above in which one player did not move any piece or pawn beyond the third or fourth rank?
Comment: Because of this I think you need to qualify your question, by either limiting it to the 3rd/6th rank (probably very few if any high level games or by specifying a minimum number of moves for the game or perhaps by excluding draws.
Comment: Plenty of shortish draws would qualify. For instance there is a well known three-fold repition in the Najdorf where white does not move beyond the fourth rank: https://chess.stackexchange.com/questions/15860/najdorf-threefold-repition Also it is a relatively popular line with grandmasters who are satisfied with a draw as white.
Comment: Many quick "grandmaster draws" have proceeded along these lines.
Answer: Thanks for your question and welcome to chess.stackexchange :-) This is the kind of question which Tim Krabbe would have answered fascinatingly!
I choose to focus on the question where both players didn't move beyond the fourth rank. There must be thousands of games where one player kept back.
Early games from the "romantic" period which featured open openings and aggressive sacrifices were the norm until the end of the 19th century. So don't expect anything from that time.
Later, the revolution led by Reti and Nimzowitch led to much more positional play with indirect control of the centre from a distance. However, it seems unlikely to be able to win such a game, without moving forwards.
If neither player moved beyond the 4th rank, then no captures have taken place. So it's hard to see what kind of winning advantage one side could have accrued. There must be many agreed draws, but they don't really count. I would be very interested to see what a won game would look like with this constraint, as I can't imagine it.


What is the test that determines doctrine from discipline?

Question: Some of the hubbub around the Synod on the Family in 2015 has been (at least superficially) around whether disallowing civilly remarried couples, without annulled marriages, whose original spouses are still alive from communion is a doctrine (and therefore unchangeable) or a discipline (and potentially malleable) so what makes this part of marriage  doctrine.  Are there other rules concerning marriage that are discipline and not doctrine? Is it possible to have invincible ignorance when it comes to receiving communion in an invalid marriage?
Comment: First time I remember seeing an emoji in a post :-)
Comment: Just for total clarity you might want to specify that this is a remarried person without an annulment.
Answer: Dogmas are truths proclaimed either directly by God or by God through His Church. That one cannot and should not receive Communion in the state of mortal sin is not a changeable discipline but a dogma of the highest degree, de fide.
The 24th Session of the Council of Trent says:

Canon VII.—If any one saith, that the Church has erred, in that she hath taught, and doth teach, in accordance with the evangelical and apostolical doctrine, that the bond of matrimony can not be dissolved on account of the adultery of one of the married parties; and that both, or even the innocent one who gave not occasion to the adultery, can not contract another marriage during the lifetime of the other; and, that he is guilty of adultery, who, having put away the adulteress, shall take another wife, as also she, who, having put away the adulterer, shall take another husband: let him be anathema.

Now,

adultery is a mortal sin (cf. Matt. 19:9).
Divorcing and remarrying is adultery.
Therefore, divorcing and remarrying is a mortal sin.

He who receives Communion in the state of mortal sin, i.e. "unworthily…shall be guilty of the body and of the blood of our Lord. … [He] eateth and drinketh judgment to himself, not discerning the body of our Lord." (1 Cor. 11:27,29).
Living in sin also causes more sins: scandal, temptation to other spouse to commit adultery, and a grave injustice to the children.
Answer: The short answer is that doctrines are truths, whereas disciplines are practices. Doctrine can be known, whereas disciplines are actions that we need to do.
Moreover, doctrines merely reflect the reality that God has entrusted the Church to teach the faithful (the so-called deposit of faith). In other words, the Church does not invent doctrines; she merely reports them (much as a scientist does not, or should not, invent his findings, but merely states what he has observed). On the other hand, disciplines entail a specific decision by the Church to act in one way and not another.
Here is how the Church defines "dogma" (which includes those doctrines that have been solemnly defined by the Church, or else are so fundamental that one cannot deny them and remain Christian):

The Church's Magisterium exercises the authority it holds from Christ to the fullest extent when it defines dogmas, that is, when it proposes, in a form obliging the Christian people to an irrevocable adherence of faith, truths contained in divine Revelation or also when it proposes, in a definitive way, truths having a necessary connection with these. (Catechism of the Catholic Church [CCC] 88)

Although there is no "official" definition of the term doctrine, in Church documents it is generally used to mean truths that the faithful are obliged to hold, which includes, evidently, the dogmas, but also less central truths which the Church has definitively proposed. (Have a look at a 1998 motu proprio called Ad tuendam fidem and the commentary by then-Cardinal Ratzinger, especially no. 9.)
Likewise, there is no "official" definition of discipline, but it always entails certain practices, such as the Western Church's practice of choosing only celibate men for the priesthood.
For example, the hot-button issue discussed in the synod that has just closed—regarding the possibility of admitting couples in irregular marital situations to Communion—has to do with several important doctrines:

A consummated, sacramental marriage (a marriage between two baptized persons in which the marital act has already taken place) is indissoluble by any human authority whatsoever. Only the death of one of the spouses dissolves it (CCC 1612-1617).
Attempting a new marriage when one is already married is gravely sinful. (By definition, it entails an act of adultery; see CCC 1650 and 2380-2381.)
Receiving Communion when one is in the state of grave (or "mortal") sin—i.e., when one is not in friendship with God—is a sacrilege (CCC 1388, 1415; see also 1 Cor. 11:27).

Note how, although these doctrines include moral precepts, nevertheless they are simply statements of what the Church knows about the natural law and the nature of marriage and the other Sacraments. They are not things that Church has had to decide; she is merely transmitting what our Lord has given her to teach.
On the other hand, the current practice of the Church is to withold Communion from those persons who engage in publicly and persistently in gravely immoral actions:

Those who have been excommunicated or interdicted after the imposition or declaration of the penalty and others obstinately persevering in manifest grave sin are not to be admitted to holy communion (Code of Canon Law [CIC] 915; see also the 1994 document by the Congregation for the Doctrine of the Faith regarding this issue and Familiaris consortio 84).

Note how this is a conscious decision by the legislator, directing the Church's pastors to act in a certain way. Of course, this discipline follows quite naturally from the doctrine. Although the Church could change her practice somewhat, she could not do so in such a way as would blatantly contradict the doctrine.
For example, the Church could find new ways to facilitate the process to investigate the nullity of previous (attempted) marriages (as the Church, in fact, has recently done with Mitis iudex Dominus and Mitis et misericors Iesu), or else find ways to move couples in irregular marriages to repentence (for which the first step, doubtless, is making sure that such couples know they are not excluded from the Church and should feel a part of it, even while recognizing the irregularity of their situation).
Simply admitting couples in irregular situations to Communion, however, does not seem to be compatible with the doctrine.
Answer: Let's start of by saying what the Church teaches [= Doctrine] regarding communion for divorced and civilly remarried Catholics:

However, the Church reaffirms her practice, which is based upon Sacred
  Scripture, of not admitting to Eucharistic Communion divorced persons
  who have remarried. They are unable to be admitted thereto from the
  fact that their state and condition of life objectively contradict
  that union of love between Christ and the Church which is signified
  and effected by the Eucharist. Besides this, there is another special
  pastoral reason: if these people were admitted to the Eucharist, the
  faithful would be led into error and confusion regarding the Church's
  teaching about the indissolubility of marriage. – Pope St. John Paul
  II > Apostolic Exhortation > Familiaris Consortio, 84, November
  22, 1981.

And

Today there are numerous Catholics in many countries who have recourse
  to civil divorce and contract new civil unions. In fidelity to the
  words of Jesus Christ - "Whoever divorces his wife and marries
  another, commits adultery against her; and if she divorces her husband
  and marries another, she commits adultery"[Mk 10:11-12] the Church
  maintains that a new union cannot be recognized as valid, if the first
  marriage was. If the divorced are remarried civilly, they find
  themselves in a situation that objectively contravenes God's law.
  Consequently, they cannot receive Eucharistic communion as long as
  this situation persists. For the same reason, they cannot exercise
  certain ecclesial responsibilities. Reconciliation through the
  sacrament of Penance can be granted only to those who have repented
  for having violated the sign of the covenant and of fidelity to
  Christ, and who are committed to living in complete continence. –
  Catechism of the Catholic Church, CCC 1650.

Understanding Doctrine to be Any truth taught by the Church as necessary for acceptance by the faithful [Cf. Dictionary: Doctrine | Catholic Culture] and Discipline to be … any of the laws and directions set down by Church authority for the guidance of the faithful [Cf. Dictionary: Discipline | Catholic Culture], the words of the great and saintly pope in his Apostolic Exhortation can be read as However, the Church reaffirms her practice, which is based upon Sacred Scripture, of [the discipline of] not admitting to Eucharistic Communion divorced persons who have remarried.
Another scriptural passage on which this teaching is based is:

28 Let a man examine himself, and so eat of the bread and drink of the
  cup.29 For any one who eats and drinks without discerning the body
  eats and drinks judgment upon himself. - 1 Cor 11:28-29 (RSVCE)

Returning to the question, is the not admitting to Eucharistic Communion divorced persons who have remarried  to Eucharistic Communion doctrine or discipline? It is both doctrine and discipline. Doctrine because this has been the Church's practice based upon Sacred Scripture and it is discipline in the sense it is one of her laws and directions set down by Church for the guidance of the faithful.
It is good to recall here that the Supreme law in the Church is the salvation of souls [cf. Can 1752]. If the Church were to admit to Eucharistic Communion divorced persons who have remarried but who are not living as brother and sister, she herself would then become the vehicle of leading to damnation not only these persons, but also all the faithful who would be led into error and confusion.

To the question is it possible to have invincible ignorance when it comes to receiving communion in an invalid marriage?
Perhaps a father confessor can better answer this but in this day and age and its means communication and their ubiquity, chances for that are very slim.
I can see those civilly dicorced and remarried receiving communion, not so much from invincible ignaorance, but because it is what everyone does, as a result of poor catechesis and because of lax and bad clergy, etc.


How to check the integrity of my BIOS?

Question: Could it be possible that a virus rewrites my BIOS with some malicious code? If so, how could I protect against it, or at least how can I check that the BIOS hasn't been modified?
Comment: Assuming this is a PC do you know the motherboard make and version?  They often have utilities to check on the BIOS.
Comment: and for the initial question, Konboot is very good at checking the integrity of your bios...you can either get it at their site or download it with a host of other utility software from Hirens boot disk on the web
Answer: It is certainly possible. See this presentation for example: http://www.coresecurity.com/files/attachments/Persistent_BIOS_Infection_CanSecWest09.pdf
One way to achieve protection is by requiring a flash bios password that some implementations support.
Another way is by using a TPM which does almost exactly what you are suggesting: It creates a SHA-1 hash of the BIOS image before loading it - and if Secure Boot is enabled it compares it to a stored value.
Now, how to check if the BIOS is compromised:
The general idea is that you can take a BIOS backup image at any time and compare the hash of that image to the hash of a previous one - maybe one you took after flashing.
But, in theory, if the BIOS modification is malicious enough, it will serve you something that won't be suspicious - so you won't actually be able to check but only just re-flash (and this may not be enough if the flash procedure itself uses bios functions that are hooked).
Generally to check the integrity of anything, you have to perform the checking operation at a level lower that the level of the object you check. With BIOS this is pretty hard - and this is one of the reasons TPMs were invented.

How to check the integrity of my BIOS?


What is the mechanism to protect photos uploaded on social media?

Question: I know water mark the photograph is one method to protect ones copyright over the picture. is there any other technique through which one can prevent or detect the plagiarism of photos.
Comment: As is, your question is pretty vague. What do you expect of a 'protection mechanism'? Do you wan to assess proof of ownership for exact copies, modifications and derivative works, what kind of modifications? What kind of watermarking are you expecting, visible or invisible?  Watermarking is a complicated matter and depends a lot on the use case.
Comment: i edited your tags to be more specific - if you search those tags here, you will see a lot of options
Comment: Watermarking is not one method but many of them. You can add hidden marks which are detected by crawling the whole internet for pictures, or you can put visible mark to say that it's copyrighted material.
Answer: There's not any fool proof way. If you upload or host a photograph on a server and it's accessible by users or it's accessible by anyone with an internet connection the content becomes fair game for anyone to take/reuse/re-upload/edit/copy.
Here are some mechanisms that certainly slowdown people form misusing your content:

Watermarking (as you mentioned)
Stenography can be used to hide information in the photo that lets you do an image search via google's image search and always find instances of your photo, then you can ask the user to remove the misused content.
Preventing users from taking screenshots (poor form and i.e only)
Preventing users from right-clicking image
Comment: Forget steganography. Steganography is not a security feature, its goal is to make information statistically hidden in a collection of images, so that there is no efficient way to distinguish which image contains information and which does not other than running the decoding process (which is time consuming).
Comment: There is a critical difference about watermarks and steganography. Steganography aims at reducing the amount of (statistical) alteration made to the image so that one cannot infer the presence of the mark. Whereas in watermarking, the goal is to have a resistant mark to be able to maintain proof of ownership over modifications of the media. This goal is not compatible with the goal of steganography. Obviously the two techniques share some concept, but they are not the same.
Comment: That's the point. One must hide the information so that others do not know it's in the image. Once you encode the content you should be able search for it based on your encoding method, much like i mentioned in the answer. I will say that it's REALLY out of the way and very similar to a hidden watermark. This is what movie agencies use on movies they give to critics for advanced screening and if they movie is leaked they will know exactly who leaked the content as it is singed with a digital signature iirc.
Comment: You've said the same thing twice. With Stenography you sign the image with information. Someone misuses the information and climes the the work as their own. To prove ownership you decode the hidden message, or show that their content does not decode properly ect. This is a simple example. The fact is that one can use all of the listed methods to help slowdown the misuse of their content and track it, which was the point of my original answer. IMHO if you have more to discus I think it's time we take this to a chat so i can make edits to my answer if need be.
Comment: @car I believe M'vy's point is that it is desirable for a watermark to survive changing format (eg if someone changes your watermarked png to a jpg it would ideally still be there), whereas stenography just wants to keep data hidden, and modifying something enough to survive format changes would likely make it much easier to discover.


Emitter follower voltage regulator misbehaving

Question: To make a crude voltage regulator, I've made a simple emitter follower using a BD139 transistor. When the 0.5A load is connected, the circuit behaves as expected: the voltage across the load sits at about 0.8V below the voltage at the base. However, if I increase the load impedance, or disconnect the load, the output voltage rises to equal the voltage at the base. That's a problem, because I want the output voltage to be constant despite variations in output current. Any ideas, please?
Comment: Need minimum load current, a resistor works well
Comment: Look at the IV curve of a diode with zero current- zero voltage, add a resistor for at least a few mA of constant load
Comment: Also the shorthand relation for the base-emitter voltage is for every 10x increase in current deltaVbe is +60mV
Comment: @sstobbe Great stuff added here. Are you going to write a nice answer about it, showing how setting a minimum load can help in the direction of achieving the goals? It seems you are the right one to do it -- you've covered all the right bases in your comments -- and the OP still seems to need the hand-holding.
Comment: your Ie/Ib ratio is too HIGH, try a current sensing MOSFET with BJT feedback instead or a darlington or really.. an LDO, don't reinvent the wheel.l reverse engineer what is commercially avail. in LDO's then understand before you fail
Comment: Thanks, both! I don't quite understand why a HIGH Ie/Ib ratio would cause my symptoms; and as a Darlington pair seems to be a way to Increase Ie/Ib, how does it help? Sorry, I'm being dim.
Comment: I tried a 1kR minimum load (my real load varies from about 8R to many kR). That improved the voltage fluctuation when I varied the real load, but there was still about half a volt of fluctuation.
Comment: @jonk Sure, will do. user3910824 what output voltage? (8*0.5 = 4 VDC), so are you going for 4V Typ?
Answer: An emitter-follower operates on the principal that the base-emitter voltage of a forward biased transistor is approximately equal to 0.6 or 0.7 V. So for some input voltage on the base, the emitter tracks the input minus one diode drop.
$$ V_O = V_I - V_{BE} $$
Of course this is just the shorthand approximation, the actual base-emitter voltage is given by:
$$ I_C = I_S \exp \left( {\dfrac{V_{BE}}{V_T}}\right)$$
A sample IV plot is the following,
Note the scale on the x-axis is in 60 mV graduations to illustrate a common rule of thumb for transistors. Every 10x increase in collector current is a 60 mV increase in base-emitter voltage near room temperature.
To answer your first question of,

However, if I increase the load impedance, or disconnect the load, the output voltage rises to equal the voltage at the base.

Looking at the sample IV plot, you can see that when you have zero load current, the base-emitter forward voltage is also ~ 0 VDC. So Vbe = 0, i.e. the base voltage equals the emitter voltage.
As a simple shorthand approximation, if you load the output with 1/10 your max rated current, you will achieve 60 mV of load regulation. A restive load at 1/10 rated current is a simple solution.
Impedance Transformation
When the transistor is operating in active mode (Vcb>0), the transistor also provides an impedance transformation of the source resistance by \$1/\beta\$. A sample schematic of a common-emitter buffer amplifier:

simulate this circuit – Schematic created using CircuitLab
From standard transistor theory, you are aware that \$ I_C = \beta I_B \$. So, as you begin to load the output of Q1, \$ 1/\beta \$ of the load current is sourced through the base. As a result of having a finite source resistance from your reference, the voltage right at the base terminal of Q1 droops by \$ I_B * R_S \$.
As a practical example assume RS = 10 ohms and \$ \beta \$ = 100, the output appears as having an output resistance of
$$ R_o = \dfrac{R_S}{\beta} = 0.1 \textrm{ Ohms} $$
Your goal here is to keep the source resistance small enough so the the output voltage only depends on the IV curve of your transistor.
Summary
The three most important design choices to make are

RE, for minimum load current
Rs, lower for lower Ro
beta of Q1, must have good beta over the full load range

Asides

For DC don't worry about the 1/gm you see in typical amplifier notes, its just a linearization of the Ic-Vbe curve (unless you care about its ac output impedance) just look at the IV curve
There is also thermal design to consider, Vbe, as rule of thumb has tempCo of -2mv/deg. This does work in your favor as you pull more load current the transistor heats up and thermally pulls Vbe back up
Comment: Wonderful. I'd add that there is also a Shockley equation \$\frac{\textrm{d}V}{\textrm{d}I}\$ at the emitter tip, based upon the operational value of \$I_C\$, and that this adds to the effective resistance. In your example, and taking the OP's \$500\:\textrm{mA}\$ peak load example, that would add to make about \$150\:\textrm{m}\Omega\$ instead of \$100\:\textrm{m}\Omega\$ and that it will be worse with lower loading. Every BJT also has some Ohmic RB (20 ohms for 2N3906?) and RE. So the \$R_o\$ result could be "improved," depending on the level of the OP to process such added info.
Comment: @jonk Thanks for the great feedback, I agree more could be added regarding the effective Ro. My hope was to illustrate the two main points independently Ic(Vbe) and Source Resistance. I will try to incorporate your suggestions into a better post
Comment: I'm not even expecting an addition. It would be interesting only if you can explain it simply enough to reach the OP well. But say looking at small variations around \$I_C=100\:\textrm{mA}\$, with \$R_b=20\:\Omega\$, \$R_S=10\:\Omega\$, \$R_e=100\:\textrm{m}\Omega\$, \$\beta=250\$, then \$R_o= R_e+\frac{R_b+R_S}{\beta}+\frac{26\:\textrm{mV}}{I_C}\approx 500\:\textrm{m}\Omega\$. And here, \$\frac{\textrm{d}V}{\textrm{d}I}\$ is more than half of it. Spice confirms the result, too.
Answer: The problem is that the 500 to 700 mV or so voltage drop across a silicon junction is just a approximation at reasonable currents.  Base to emitter of a NPN transistor is such a junction.  You got about 800 mV because the current was relatively high for that transistor.  That's all reasonable.
However, when the current is 0, the voltage drop is also 0.  The voltage is roughly the log of the current once you get to reasonable levels, so it is relatively constant over a reasonable current range.  0 is well below reasonable for the approximation.
The simplest solution is to always guarantee some minimum load by putting a resistor permanently on the output.  Even 1 mA will probably cause over 500 mV of drop.  If so, you now only have 300 mV variation between no load and full load.
A even better solution is active regulation.  If the B-E voltage drop is inside a feedback loop, the feedback can compensate for it.  Here is a example:

Due to the feedback around the opamp, it adjusts the base voltage of the transistor to whatever it needs to be so that its emitter is at the reference voltage.
In the simplistic version of this circuit, C1 and R1 wouldn't exist, and the negative input of the opamp would be directly driven from Vout.  However, the overall gain the opamp provides is low, and there is some non-linearity going on in the B-E junction, so the opamp might get unstable.  C1 feeds back the high frequencies where the opamp is more likely to be unstable at, directly from its output to its negative input.  That slows the opamp response and increases stability.  R1 provides some impedance so that the signal thru C1 doesn't get swamped.  This example is quite conservative.  Many opamps will be stable with well less than 100 pF for C1.  Even with these values, the opamp can still respond to load changes up to about 160 kHz.
R2 is just to put some load on the output so that there isn't a large jump needed from the opamp between no load and the first little bit of load.
This circuit should regulate the output to within a few mV from the full range of 0 to maximum load.  Eventually either the transistor can't pass more current or the opamp can't supply enough base current.
Comment: Thank you very much! My thoughts were beginning to drift in the op-amp direction also, but your answer moves them forward a lot. :-)


What are good, low cost, actuators for a braille tablet to be controlled by arduino?

Question: I want to basically make a pin matrix controlled either by spring, electromagnets or small motors(spring being the most viable option), something like what's shown in the image. I'm pretty new to arduino and hardware in general so any input would be appreciated.
I mostly know the arduino end but don't have clue about the hardware part. Plus I don't have the technical expertise, as in I know electromagnets won't be a good option as I have to control individual pins and not clusters. Plus springs have the disadvantage of pushing them back in but other than that a very option. And its not viable to have individual motors for so many pins.
Comment: Can you elaborate on what you mean by 'spring'? Shape memory alloy actuators perhaps? (For others following this question there is a parallel question here: http://engineering.stackexchange.com/questions/11165)
Comment: @Aditya_Krishn Focused questions will get a better response. I have adjusted the question to reflect what you seem to be asking. Please verify that it is indeed what you are asking. If you can edit your question with some more detail, it will help.
Comment: You don't want to control individual pins... So you are basically looking for a mechanical matrix interface to... build a mechanical matrix interface? Apart from MEMS mirrors and some ultra-expensive ultrasound emitters, none come to mind. --- is there a specific reason you do not want to use multiplexing to interface with your matrix?
Answer: Check out this hackaday project. They use micro stepper motors from aliexpress. They include a link as well. The steppers are a little annoying to interface with but they are cheap and they work for this application.
https://hackaday.io/project/10849-refreshable-braille-display


Is there any point to posting app bug reports?

Question: I've discovered some bugs regarding the SE iOS app but recently learned that there are no active personnel on the development team for the apps. If this is the case, is there any reason to post bug reports for these apps as a sort of backlog if development does start again in the future? Or are there really no plans to do so making bug reports a waste of time?
Comment: The situation has changed from the time this was answered, and the apps are no longer supported: [How can I report bugs with or request features for the Stack Exchange mobile apps?](https://meta.stackexchange.com/questions/348075/how-can-i-report-bugs-with-or-request-features-for-the-stack-exchange-mobile-app)
Comment: Same answer: [Are more mobile app review or moderation features coming?](https://meta.stackexchange.com/q/299862) "No, and no."
Comment: Related: *[Mobile app infrastructure has been decommissioned](https://meta.stackexchange.com/questions/383026/)* (2022-10-19).
Answer: Yes. Based on what I've seen here, on MSE, they are continuing to maintain the app but are not actively developing it. This is what hairboat said on a related question:

As far as I understand it, updating the app for iOS 11 / the new iPhone is part of ongoing maintenance for the app. They aren't working on new features, but are carving out time to keep it up to date.

That said, Brian later stated that updating the app for the iPhone X seems to require more work than they're able to manage in "maintenance" mode.

Unfortunately, even for an app like ours which supports a wide variety of screen sizes and configurations, updating to the iPhone X will be a major undertaking. Not only do every screen edge hugging elements (e.g., the draft indicator) need to be revisited but every screen needs to be tested in portrait and landscape. I've estimated bare-bones support for X as a 2 month project, but given current product priorities that's no target start-date for the project.
The good news is there's really no path forward with iOS development that doesn't involve supporting the X, so when development resumes it'll need to be the top priority.

So, they do hope to be able to go back to active development on the app but it may not be for a while.
As such, that seems to imply that bug reports should continue to be posted, even if they're iPhone X specific, so they know what to work on when they do go back to active development.
Comment: Disagree. I won't recommend anyone to waste time by posting bug reports that will never be fixed. I know Brian **wants** to fix them, but just can't. "may not be for a while" means "never", as far as I can tell, and personally I'm sure enough of this to totally stop caring for the apps. Still using it as before, but won't bother reporting any bugs, asking for new features, and won't encourage others to do any of those.
Comment: Sounds good. So in 'maintenance' mode they only keep it up to date with no bug fixes?
Comment: Not sure. Hopefully Brian will give us a more canonical response. I was looking at the iOS app questions here recently and none of the recent ones are status-completed. The most recent one I can see was in July. https://meta.stackexchange.com/questions/tagged/ios-app+status-completed?sort=active&pageSize=50


Why do we see smoke before ignition of Falcon Heavy?

Question: We can see smoke at some regions before the main ignition takes place. Why is that?
Comment: Can you be more specific i.e. at what video time index do you see smoke before ignition? As I see it, there are fog clouds which I assume are being formed by vented hydrogen and oxygen, and then there is the water deluge, and finally the exhaust plume as the engines are started a few seconds before lift-off. The only odd thing I see is a rather large bank of fog in the foreground, which I assume is from vented cryogenic propellant (hydrogen or oxygen) somewhere off screen.
Answer: The white smoke coming from the second stage, and three boosters is LOX venting to relieve the pressure of the LOX turning to gas.
The Liquid Oxygen is sub cooled, so it is even cooler than usual LOX (increases density, more can be stored in tank, and engines produces more thrust) and in the warm Florida sun the tanks start to warm up as soon as the LOX is pumped in.
Normally a booster would just refill the LOX that vents out (And I guess SpaceX does that as well) but because this is sub cooled, just refilling it does not entirely help. This is why SpaceX cannot recycle a launch very fast. Once it warms up too much, they have to pump out all the LOX and refill it.
So you are seeing literally air. Liquid Oxygen, warmed up in the tank to return to gaseous form, and released to relieve pressure in the tanks.
Comment: "So you are seeing literally air." No, you are literally seeing water.
Comment: You may have missed the comment; is the thing which is visible "air", or "liquid oxygen", or is it more likely to be water vapor present in the Florida air which has condensed into an aerosol of water droplets, not unlike what's seen opening the door to a freezer to retrieve ice cubes for beverages suitable for watching such launches?


Announcer no longer announces every kill

Question: I believe this started with Patch 5.22 for the preseason.  The announcer no longer gives audio for every single kill like it used to. It still calls multi-kills, and an unknown pattern for other individual kills.  Is there a setting or something to re-enable this? I like the audio cue to know how many champions are still alive, particularly in large teamfights where it can be hard to keep track of which particles mean something is dead or not.
Comment: 5.22 patch notes do not designate any changes to the announcer, and I cannot find anyone else mentioning similar problems. i have had a delay in announcement when multiple kills were made or when turret kills and champion kills happened at the same time. it may be a bug. you can try contacting customer support.
Comment: Same here. I've experiences delays but I've not been paying attention enough to notice that the announcer missed to broadcast a kill.
Comment: The visual cue is still there, just not audio
Comment: I have experienced this (in ARAM). It doesn't even always call out the multi-kills and shutdowns, and also when there no kills for > 30 seconds before or after a kill. I think I have experienced this in most if not all ARAM games I've played since 5.22
Comment: As mentioned before, this wasn't documented anywhere. Try using the repair function in the game patcher and see if that helps. If not, it's probably an unintended bug and you should mention it on the boards.
Comment: The announcer sometimes mixes things up for me. If an enemy got a triple kill she tends to say triple kill first and then double kill for some reason.
Comment: For me there can be a major delay but all or most of the kills will eventually be announced. I mostly noticed this on ARAM and I think it is a result of the sound bites queueing up for all of the kills in rapid succession.
Answer: According to my researches (which came up empty) i would assume that somewhere in the game code they must've made so the sounds don't overlap (so you won't hear double and triple kill at the same time) and i guess (again sorry for not being sure of anything, these are assumptions and speculations, but i couldn't find anything online) that if a certain time passes they no longer play the audio since it's pointless by then.
Again, do not take anything i said has a certainty this is all speculation on my part , for which i am posting to try and give some possible reasons has to why this happens (again, not sure on anything!!)
This question is something either a Riot Staff or a person who know's or has access to the actual game code (Or someone who knows someone there, you get where i'm headed don't you?) to be able to specify the reason, it might even be an actual bug in the game that Riot themselves haven't noticed, or have but haven't made any impactfull changes to fix it since it doesn't affect the actual gameplasy (What's wrong with missing the announcemment on a kill or two? You can still see the kill feed and score).
What i'm trying to say is, all we can do is wait until Riot either fix this, or just cry about the announcer not saying Pentakill when you are playing Full Ap Amumu (It works some games!)
Comment: League's announcer sounds haven't been able to overlap since I started playing over 2 years ago, so this doesn't seem correct.
Comment: I'm not saying it is correct, just giving some thoughts of what i think might be the reason has to why the announcer doesn't announce everything
Comment: I think it might be a change to make it so that announcements don't go on forever when a bunch of announcements get queued up at once. I'm not sure what the priority is, but if someone gets a triple and there's a double ace and the minions take a tower, you'll get two ace messages, a triple message, and a tower down message, but none of the single kill announcements. Like I said, I don't know the priority (or if this is even how it works) but anecdotally, I feel like this is the case.
Comment: Well for all we know, that is how it works, only Riot Staff and people that have access to the actual code and such will know
Comment: Actually, not even a Riot Staff may know **exactly** how it works.  The current version is most likely the end result of a series of bug fixes, and unless someone decided to document exactly how the announcer fixes were done (unlikely), nobody will know exactly how this works unless they go spend hours and reverse engineer all the code.  From observation, we just know that it doesn't overlap, and does not play all the queued sounds, so somewhere there is logic that drops announcements to make it less annoying.


Why do images not appear inverted when looking directly through a pinhole camera?

Question: I understand that the way light takes through a pinhole creates an inverted image on a surface behind the pinhole. I remember this effect from school experiments, it's also described in this wikipedia article. I punctured a piece of paper and looked through it (instead of watching the reflection), the image appeared as normal to me. Why is that? Why doesn't the scene appear upside down when looking through the hole?
Comment: How far is your eye from the paper with the hole in it?  How big is the hole? (a ~ 100 um or a few mm?)
Answer: Ignoring diffraction, the pinhole can't change the orientation of what you see because it doesn't change the position or direction of any light rays. It just blocks some of them.
When you put a screen in front of an illuminated object, every point on the object emits light in every direction, which hits the screen at every point. You can imagine that the screen contains superimposed images of the object with every possible position and orientation, but you can't see them because they average out to a uniform blur. Putting a punctured sheet between the object and the screen blocks out most of those images, making the remaining one visible. It doesn't create the image, as such. Blocking the light differently would leave different images visible. For example, if you replace the punctured sheet with a laptop privacy filter, you ought to get a blurry upright image (I haven't actually tried this). A filter that creates a sideways image is also possible in principle.
But no matter what filter you put between the object and your eye, you can't change which image orientation your eye sees, because it has its own mechanism for extracting an image from the mess of light rays in the environment, and you are only giving it less to work with.
Comment: Interestingly, there are lots of non-inverted images among the superimposed ones; an aperture (pupil, pin hole) simply blocks all of them and only allows crossing light pathways, thus permitting only inverted images. A large bundle of parallel glass fibers (or small tubes) going from the object to a screen would do the opposite and allow only parallel rays, providing a upside-up image.
Comment: Would it be correct to say that the pinhole camera and the pinhole that is your eye's pupil form a straight tunnel, which specifically negates the pinholey nature of the effect?
Comment: @Flater I'd rather say "pinhole and pupil become effectively a single aperture". That's why you have to be as close as possible to see something; with increasing distance between eye and pinhole the visible area becomes just smaller and smaller because the maximum angle of  the rays crossing at the pinhole but still making it into your eye becomes smaller. The resulting image on your retina is still inverted.
Answer: The directly-through-the-pinhole image is upside down on the retina of your eye. But all images on the retina are upside down. When the lens in your eye forms a real image on the retina it is inverted. It only looks the right way up to you because you brain post-processes the retina image  in the visual cortex.
By looking with your eye at   the image formed on  the screen  at the back of the camera you see  a triply inverted image – inverted once by the pinhole, once by the lens in your eye, and once by you brain – so you see an upside down image.
Comment: Let's ignore those "once by the lens in your eye, and once by your brain" occasions because this is invariant regardless of pinholes. You'll be left with an extra inversion by the hole either way.
Comment: the OP said it looks like it is the right way up, how is this answer correct at all?
Comment: "It only looks the right way up to you because you brain post-processes the retina image in the visual cortex." - or alternatively, because we are actually upside-down. The earth is above us and the sky is below, but we think it's the other way around because our eyes flip it upside-down. Of course, that's not actually true because the definition of "above" is "away from the earth" so even if you flip it, the earth is still below. Welcome to the concept of *qualia*. Try to forget it immediately without thinking about it.
Comment: @nanoman why is the pinhole projection inverted on the retina? Why didn't the eye's lens flip it?
Comment: @heinrich : maybe Mike is right? I'm thinking that looking through the pinhole is like a pinhole camera consisting of two pinholes in series. However I don't know the answer to this.
Comment: @theonlygusti The first paragraph of this answer is about OP's observation "when looking through the hole". The second paragraph is about the scenario of "an inverted image on a surface".
Comment: Because a ray passing theough the center of a lens is not deflected. So a ray coming from from above the  centre of the lens strikes the retina below the centre, and *vice versa*.
Comment: @theonlygusti The barrier with the pinhole in it just blocks some rays but doesn't bend anything. So the image on the retina is in the same position as if the barrier weren't there.
Comment: @heinrich: While we should ignore the double inversion itself, what we shouldn't ignore is that if you look through a pinhole camera, you're doing a **double** pinhole (the camera and your eye), notably with a non-zero distance between them. The light that travels between the pinholes must invariably travel in a straight line, and thus the first pinhole's effect itself is destroyed. This is the same thing as putting two pinhole cameras behind one another.
Answer: The answer is one about simple geometry and has nothing to do with what happens on the retina or in the brain: you are not looking through a pinhole camera when you are looking through a small hole in the paper.
Either you are relatively far away from the hole. Then it acts simply as a block. All rays from whatever is on the other side that do not go straight from the source through the hole into the lens of your eye will be blocked. Since the hole is relatively far away, basically everything is blocked, and you will see the hole simply as a little twinkling dot of light.
If you are relatively close to the hole, then the fact that there is paper around the hole simply doesn't matter, and you are seeing the unobstructed view of what you would have seen anyways.
In both cases, the pinhole changes nothing about the route the rays travel to your eye, it simply blocks a more or less significant amount.
The actual pinhole experience happens if you put a white wall behind the hole. Now the rays go from the source through the hole, and hit that wall (inverted, as you expected). Then those rays are bounced off the wall into your eyes - and remarkably from the wrong vertical part, leading to the illusion of being upside down. It is this two-stage operation which leads to your eyes being able to actually see an inverted image. By looking through the pinhole directly, you are removing this aspect.
Answer: The totality of light that fills space, even in a geometrical optics approximation, is a complicated light field that is difficult to visualize in full. Each point in space generally receives rays of various colors and from various directions simultaneously. We do not perceive or measure the light field unless something is placed in it to absorb or scatter the light -- ultimately our retinas.
Many surfaces that interact with light are not strongly sensitive to the direction from which it comes. These include matte (diffuse) screens, photographic film/CCDs, and our retinas (but not mirrors). At each point, the response effectively integrates rays over all incoming directions.
At a random point in space, this is likely to work out to a general ambient illumination that does not select for where the light originally came from -- i.e., does not form an image. Forming an image requires a specially manipulated light field (often, as in the eye, using a lens) that counteracts the tendency of bundles of rays to diverge and mix.

Now, we can clarify the pinhole situation (diagram inspired by seeking to clarify and correct pwf's answer). A pinhole is designed to form an image on a surface (screen or film) without the need for a lens. This is accomplished by restricting the light field without bending any rays. The image is, of course, inverted (relative to the actual objects).
When your eye is looking directly through the pinhole, an image will form on the retina. The lens of the eye has makes relatively little difference in this case, assuming your focus is relaxed enough to look "through" the hole rather than "at" the hole. The image on the retina is inverted (relative to the actual objects) just as if you were looking at the same scene without any barrier. Therefore, your perceived view of the objects is non-inverted.
If you place a screen (not shown in diagram) facing the pinhole, it will show the inverted image. However, this is visually observed via diffusely reflected/transmitted light from the screen that forms its own light field. This light field is inverted relative to the original light field because its source (the pattern on the screen) is inverted relative to the original objects.
You perceive what is on the screen when your eye forms an image from this new light field. Therefore, the image of the screen that is formed on your retina is non-inverted (relative to the actual objects), and perceived as inverted.
Comment: IOW, when your eye looks through the pinhole close enough to the hole, it is still perceiving the non-inverted light field. To perceive the inverted light field, one would need to place another lens (or screen) situated out in the inverted field, where it would collect (or diffract) the image field in a way that your eye could then perceive the inverted image.
Answer: You don't see an inverted image by looking through a pin hole because the pin hole is acting as a beam limiting collimator, not a lens - which is to say pinholes do not bend light direction.

light rays from points in the scene only reach points on a screen (placed behind the pinhole) if they are very nearly parallel (accounting for pinholes having a non zero diameter) and traveling along a line drawn from the scenic point to the pinhole.
Such parallel rays from scenic points pass directly through the pin hole and continue to travel in a straight line before reaching the screen without being bent as they would in a lens.
Geometrically, because rays from high low, left and right areas of the scene will pass through the pinhole and arrive at low, high, right and left areas of the screen respectively, the resulting screen image is inverted.

If you use an eye to look through the pinhole however, you just see a nearly parallel set of rays arriving from points across a small area of the scene that are reaching the pupil - everything else has just been blocked out by the paper surrounding the pinhole.
The beam collimation effect of the pinhole is to limit light to a notional tunnel formed between the circumference of the pinhole at one end, and the circumference of the pupil (of an eye) at the other. Light which enters the pinhole but leaves the tunnel goes unseen.
The closer the pupil is to the pinhole, the less collimation takes place - rays don't have to be so parallel to reach parts of the pupil's surface and you see more of the scene. The brain interprets rays arriving from the unblocked area of a scene in normal fashion: upright and non inverted - just as it would the same photons arriving without a pinhole in place.
I'll leave details of perception and operation of the visual cortex to another time :)
Answer: Has the OP just reduced the size of his pupil by adding another aperture (the pinhole) in front of his eye?
A smaller aperture of the will make the scene seem dimmer and if the OP requires corrective lenses their vision will improve as the "stopped down" aperture improves depth of field.
Comment: Exactly this. It's basically become an additional pupil (which is why we need to get real close for it to work). No need to fiddle with specifics.
Answer: The answer is rather simple, when you look through the hole, the hole disappears!
A hole in an opaque object is called a $hole$ precisely because to look through the object, the only place you are gonna get any light is when you are looking through the hole. But when you look through the hole, light from objects behind can reach you just fine - in effect there is no opaque object left that light rays need circumvent or be affected by.$^1$
This scenario is exactly the same as if there was no pierced sheet of paper to begin with.
$\ldots$
The effect occurs only when you look through the hole and not when you look at a screen placed some distance away in front catching an image. This is because the size of the hole is relative to the size of the screen.

if you (your eyes are the screen) or a screen are brought increasingly closer to the hole, relatively speaking the hole is getting larger and larger. Near the hole, the hole is relatively infinite$^{1.5}$. All of light can reach you here without undergoing inversion.

if instead one uses a telescope from afar to peer through the hole, one once again sees an erect$^2$ image. This is because nice parallel rays are able to reach the telescope exactly like when there was no screen.

Imagine a tiny little screen, comparable in size to the hole, placed very close to it $\ldots$imagine yourself to be a microscopic point observer gliding on wind currents through the hole. Do you expect to see the object behind inverted?

$\ldots$
When a screen is placed at some distance from a hole, the only way light can reach the  now relatively large regions of the screen is if it angles in. The only part where it reaches straight is, well to reiterate, comparable to the hole's size.

$^1$ignoring diffractive effects
$^{1.5}$ This idea that the closer you get, the larger (or effectively $\infty$) the thing becomes, is a common modelling theme in physics$\ldots$ $multipole$ and what not
$^2$telescope's optics notwithstanding

A1. The model of the observer (be it the eye or its lens or some DSLR or a piece of cardboard) has nothing to do with the physics here. As long as the observer is large enough when far away and small enough when close by, your observations hold.
Answer: I assume that what you are describing is peering through a pinhole such that the field-of-view you get is smaller than normal. That is, I assume you describe a looking through the pinhole that comes with "tunnel-vision".
So, I assume that what you are describing is peering through a pinhole such that for the light to traverse the distance from the pinhole to the point where the light transits into the eye is like traversing the length of a short tube.
The distance from your eye to the pinhole is very short. The closer your eye is to the pinhole, the larger the field-of-view you obtain (but some reduction of field-of-view is inevitable).
So: think of peering through the pinhole directly as peering through a tube. When you are peering through a tube you are not surprised that your field-of-view is smaller, and you are not surprised that what you see is still the right side up.
Comment: @heinrich In order for the pinhole camera effect to occur at all the image must form on a *screen*. The human eye performs the same function as a pinhole camera (image is formed on the retina), except in the case of the eye a *lens* is used (which allows more light to be gathered, allowing you to have vision in twilight). If you use your eye to look through a pinhole the pinhole camera effect cannot occur.  The pinhole camera must form the image on a *screen*, and then you look at that screen. Think of the pupil of your eye not as a screen, but as itself effectively a pinhole.
Comment: I am talking about a very small hole in a sheet of paper. Do you suggest that the hole is too large so the "pinhole camera effect" does not manifest?
Comment: Really nice answer.
Answer: Looking through a pinhole is like looking through a lens which is close to the eye.  You are seeing an erect virtual image.
Answer: Consider the following situation:

a flamingo is standing behind a screen with a pinhole
you look at the flamingo through the pinhole from a position above the pinhole
you will now see the bottom, i.e. the feet, of the flamingo
if you move your eyes down to below the pinhole, you will see the head of the flamingo

If you were to put photosensitive paper in the plane where you moved your eyes, you could capture an inverted picture of the flamingo, but basically your eyes are doing the same.
The paper is capturing at once what your eyes would see if they scanned over the entire surface of the paper. The paper sees the whole flamingo at once, whilst your eyes only see a tiny bit of the flamingo at once (if not, your pinhole is not really a pinhole).
What your eyes see:

What a pinhole camera would capture:
Answer: Let's say you're looking at a tree for simplicity, and the hole is at ground level. The light scatters off the tip of the tree in many directions, but only some of it goes towards the hole.
When you look in the hole, the light is coming from above, so you see it pointing up. When the light has to go to the screen, the rays from the tip go below the hole, so you see it pointing down.
Answer: Put simply, there are two factors:
Pinholes don't flip the image, but filter light rays.
A point on the subject/source will cast rays of light in many directions, but only one will make it through the pinhole. The image is mirrored about the pinhole because the remaining rays are those that cross the point (e.g., from top to bottom), but that ray would have still been there if the "pinhole" was just a "hole".
Your pupil acts as a second pinhole.
Imagine two pinholes in sequence. The first one filters out some light, and the second one does as well. But the image is not "flipped" twice! When you stick your eye up to a pinhole, you are simply re-filtering the light (and bending it, but that's not the cause of the "flip" effect).


Is it legal for an elected official to sign a contract binding him to vote in a particular way, if no value is exchanged?

Question: For instance, a candidate for a legislature promises to vote yes or no, on a specific piece of legislation, or perhaps agrees to introduce a bill that is written at the time the contract is signed. The contract does not give the candidate anything in exchange for that vote or agreement to introduce legislation (as this would obvioulsy be bribery), but if he does not carry through with the agreement could be sued in court, and be financially liable? I am specifically wondering about the USA, but if someone knows if this is viable elsewhere I'd be interested as well.
Comment: Since there is no counterpart to the person signing the document, I would talk more about a pledge than a contract (a contract needs at least two parties to it). And AFAIK, while legal, unenforceable.
Comment: @aceinthehole Sorry, I meant who is the damaged party, and how is money meant to compensate them?
Comment: Financially liable for what?
Comment: Liable for breaking the contract.
Comment: @origimbo The counter party could be some lobbying organization? Or would that not work? and couldn't the financial consequences be written into the contract as a deterrence mechanism? Say AAA goes to a candidate with a contract that he will write this bill to help drivers, and in return we give you nothing, and if you get elected and do not introduce said bill you owe us 10k. Would that be illegal?
Comment: @origimbo see above the amount of money would be written into the contract used as deterrence from breaking contract.
Comment: A contract has to have some equitable exchange to be valid.  You cannot legally have 1-sided contracts.
Answer:
The contract does not give the candidate anything in exchange for that vote or agreement to introduce legislation (as this would obviously be bribery)

In that case there is no contract.  In order for an agreement to be a valid contract there must be an exchange of consideration.  That is, each party to the contract must promise to give the other something of value.  Since nobody is giving our hypothetical legislator anything of value, there is no consideration, and thus no contract.  The purported "contract" is merely a pledge, and the legislator may suffer political consequences for breaking it, but it wouldn't be legally actionable.
In point of fact, politicians in the US (and I imagine elsewhere too) make such pledges all the time.  Notable examples include the 1994 "Contract with America" (not a contract, despite the title) and the "Taxpayer Protection Pledge" this decade.  These pledges are usually written vaguely enough that politicians can wriggle out of them, but sometimes they break them pretty obviously.  George H. W. Bush's "Read My Lips" pledge is a famous example of the latter.  What followed is pretty illustrative of the value of such pledges:  his political opponents made some hay out of it for a while, late-night comedians had a field day with it, and then some other news happened and everybody pretty much forgot the whole thing.
Comment: DIdn't GHWB lose an election due to that pledge?
Comment: That's equivalent to asking, "Would Bush have won in '92 if he hadn't made that pledge?"  Like all counterfactuals it's debatable, but I'm skeptical.  Bush was facing an uphill fight in that election for a lot of reasons, and people who were mad about tax hikes probably would have been no less angry had he not made the pledge (and supported the same tax hikes.)
Answer: Since you're asking if he could be sued in court and be held liable, you need to look at this from a legal perspective.
Standing
Who would have standing to sue Congressman Smith for breaking his oath?
Since no one paid him for making the promise, no one is out any money.   Its not at all clear who the aggrieved party would be.
Lots of people may be unhappy about the broken promise, but unhappy and actually injured are not the same thing.
Duty
Why exactly does the hypothetical Congressman have a duty to uphold his end of the contract?  If there is no "other-side" to the contract, since the other party didn't give him any money, or promise to provide re-election help, or anything else, there isn't really a contract, and he doesn't have a legal duty to keep up his promise.
Recourse
Would the injured party seek an writ of mandamus, ordering the politician to vote according to the contract? It seems highly inappropriate for the court to interfere with the business of a Legislative body. (separation of powers and all that).
Would the injured party seek financial compensation?  They aren't out any money for a contract that went unfulfilled, since you specified they didn't actually exchange money (or other goods).   If the legislation were something like a tax-bill or a trade tariff, maybe the injured party did suffer financially, but lots of legislation has financial impacts.
Defense
Even if the suit does make it before the court, the Congressman would have some pretty easy defenses.  He could give virtually any reason for changing his mind between signing the contract and actually casting his vote:  The economic conditions changed.  The political situation was changed. Different legislation was introduced.  A committee report came out with new information..... anything.
He has a duty to vote his conscience with the best information available, and as information is constantly changing, it'd be pretty easy to give a good reason for changing his mind and getting the suit dismissed.


How to remove the "Powered by Cognito Forms" link at bottom

Question: Anyway to remove the "Powered by Cognito Forms" link at the bottom? Sometimes people will accidentally hit that instead of submit and they lose the form and have to fill it out all over again.
Answer: I am a developer for Cognito Forms.
To provide context to this question, you are asking is it possible to remove the link to Cognito Forms that appears below the form when you send out a link to the form.  This is what this looks like:

So the answer is yes and no, so I will explain both.
Yes, if you embed your form on your own website the Powered by Cognito Forms link, along with the Report Abuse and Terms of Services links, will not appear.  This is the immediate and best answer to your question.
No, you cannot remove these links at the bottom when the form is actually displayed on https://www.cognitoforms.com.  The reason for this is we must alert the user filling out the form that Cognito Forms is hosting the form but is not responsible for the content.  This is our obligation, along with the opportunity for users to report abuse.  We tried to clearly separate these links from the rest of the form, but still need them to appear and be close enough to be effective.  Having said this, I will make the Powered by Cognito Forms link open in a new window (like the other two already do), which should alleviate the issue you reported.
Thanks for alerting us of this issue!
Comment: In this case they are using an iframe to embed the direct form link.  Our embed option definitely does not include any Cognito branding or links.
Comment: Here is a site with an embedded Cognito form, at the bottom of which is the Powered by Cognito Forms link, along with the Report Abuse and Terms of Services links: http://www.jazmyadesign.us/#!website-design-questionnaire/cih0
Answer: With our May 2016 release of Cognito Forms, we have completely removed branding for all paid plans.  This change includes both public and embedded forms, and all email notifications and confirmations.
Comment: I suggest editing your previous answer would be better.
Comment: Since this represents a completely different answer, would it better to edit the original answer and completely replace the answer with a new answer or add this as an EDIT: at the top and leave the original answer?

How to remove the “Powered by Cognito Forms” link at bottom


DES-encrypted cipher

Question: Suppose that you knew that a plaintext was encrypted with DES and consisted only of 16-bit Unicode letters, numerals, and punctuation marks available on a standard English-language QWERTY keyboard.  How could you use this knowledge to attack the DES-encrypted cipher?
Answer: Pure, raw DES has a key length of 56 bits, which makes it trivially vulnerable to a brute-force attack. Just try all $2^{56}$ possible keys to decrypt the message and stop when you find an English message. On average, this will happen after $2^{55}$ trial decryptions. See the Brute Force Attack section on the DES Wikipedia page for more information on how this has been done historically.
Detection of English text can be automated in several different ways, mostly using metrics that have been computed for large English corpora. Examples are the index of coincidence, letter frequency, and (more generally) n-gram frequency. Counting the number of spaces in the putative plaintext also works surprisingly well; textual documents tend to have quite a few of them.
Attacks under this model are called known-plaintext attacks. Secure ciphers are not vulnerable to known-plaintext attacks: if you replace DES with 3DES, AES, Salsa20, ... in your question, then the answer is "there is no known attack." But DES's key length is short enough to enable brute-force attacks. Note that the only attacks on DES faster than brute-force are not practical: they require an obscene amount of known (or even worse, chosen) plaintexts.
Comment: and you can't make use of the knowledge that every other byte is 0?

DES-encrypted cipher


Can we freeze amount of token, amount of time with smart contract code?

Question: Is there a smart contract code to freeze amount of token amount of time. For example i have 20 ether, with a smart contract code can i freeze it 1 year, even i can not touch it? With that code our ether will freeze in our account or blocked somewhere else?
Answer: You could create an escrow contract that hold your Eth for you and only allows the original sender of the Ether withdraw after a certain amount of time.


Is it right that questions of religion can have only one right answer?

Question: What to do when more than one point of view is valid, based on interpretation or subjectivity?
How should this site reconcile that, when the SE format encourages only one correct, accepted answer?
Comment: Yes! No! Maybe? I know there's one right answer to this, erm...
Answer: Subjective questions should be avoided. They are generally considered to be a bad fit for the Stack Exchange format. There are exceptions to this, however. For that, see: Good Subjective, Bad Subjective.
However, if you see questions that will likely lead to a voting contest between different religious views, consider voting to close as not constructive.
Comment: @wax eagle: Clarified my stance a little; I realize it came off as a bit strict. Subjectivity may be ok in some cases, but they should be the exception, not the rule.
Comment: Better and lines up with this site's general policy
Comment: Are subjective questions and subjective answers really the same thing? Many objective questions here will have faith/belief based answers which may or may not be seen as subjective.
Answer: There can be a single good answer to a question on which Christians have different views. The single good answer would be:
"This denomination teaches that, while that denomination teaches the other"
or
"Most Christians believe this, while a minority believe that".
Comment: Why would this be unreasonable? Any person knowledgable about Christianity should be able to articulate the leading viewpoints on a subject. They don't have to agree with all of them to articulate them.
Comment: This requires multiple POVs in an answer, which seems to be [an unreasonable expectation](http://meta.christianity.stackexchange.com/q/46/60). *(Maybe we should re-discuss that, as the referred bad question might have affected the discussion. I certainly would like to see expert questions where single POVs are off-topic.)*
Comment: my thoughts exactly.
Answer: As much as any of us would not like to admit it, all religious questions are subjective unless the Lord Himself stands before us to answer them.  We provide official church documentation where we can, we interpret scripture where we can't, we offer dogmatic explanations where nothing else is available (or when we're lazy, this I agree we should not promote).  Unfortunately, unless every question is written, "what do the XXXXX's believe about YYYYY?" there is no quesiton that cannot and will not be answered by multiple faiths --- each of whom inherently believe their answer to be "correct."
Hammar (above) thinks that SO's structure is more important than comparative religion.  No matter how a question is structured, there can be only one answer (because that's all SO allows) and if any question leads to multiple churches posting their individual points of view, that's somehow wrong and should be marked closed as not constructive.  We might as well decide which church claiming Christianity is the one and only church allowed to use c.so.com --- because that's all that POV is good for.
DJClayworth also believes we should crowbar comparative religion into SO's structure.  To ensure there's only one answer, that answer should include the opinions of all participating churches.  That, of course, means the minority views within each church are denied access or there are editing wars to get one's "subjective" discussion into the one-and-only answer permissible.  (Either that, or he thinks there are enough peple on c.so.com who can answer on behalf of many other churches in a way that those churches would agree with.  That's very unlikely and eliminates the ability of most people to participate on c.so.com.)
In both cases, we're trying to force the greater Christian movement to conform to SO's programmatically limited structure.  (Or the moderators are trying to promote their own religions... I prefer to believe the former.)  Remember, SO started as a way for programmers to get problems solved.  People with a PHP question will never have to entertain answers that would prefer the OP used Python or C++.
A good example of the problem is this question.  It had been asked before, but the original discussion was shut down because a moderator felt the question would lead to answers that were "primarily opinion based."  That tag makes a lot of sense for a programmer's-problem forum where "what's the best way to build a login form" can at best lead to a "best practice" answer but usually leads to an hundred slightly different answers and no difinitive solution.
But this is religion.  All our churches exist because we have sometimes major, often minor differences of opinion about our common source material --- the Bible.  By definition, every answer submitted is subjective and every church's POV is valuable.  Meaning there may never be a "correct" answer that everyone can agree with --- but that doesn't mean people aren't benefitting from the answering process (it only means the answers won't get a reputation boost by being "the only one").
The easiest solution would be to ease off on closing questions.  I wouldn't have minded so much that the above referenced question was closed had the "original" question either (a) had the opnions from the several churches not presently represented at the original question or (b) had the "original" question been left open so that the new answers could be added.
Ultimately, c.so.com's moderators have failed the community leading to Andrews perfectly valid question by imposing their own "subjective" opinions as to what should or should not be answered ... and by whom.  This is not a programming site.  There will rarely be one answer multiple churches agree is the best.  Expecting something different is simply another form of proselyting.  Therefore, I perceive only two possible solutions:
(1) Every question submitted to c.so.com must conform to the format, "what does XXXXX believe about YYYYY?"  This guarantees minimal subjectivity at the expense of of c.so.com's value to Christiantity at large.
(2) The moderators only shut down questions after the answering process has proven to lack value or insight into any denomination.  In short: moderators stop pre-judging questions.  Yes, it means Moderators must permit questions like, "What does everyone think about ZZZZZ?"  But it guarantees c.so.com's maximum value to the Christian community only at the expense of the Moderators doing a little extra work to be sure they're not getting in the way of what's important to someone else.


How many transactions per block on Ardor? Plans for scaling?

Question: How many total transactions are there in each Ardor block? Out of the total transactions per block, how many are child chain transactions? What are the limits and what types of scaling solutions are being developed to address these limitations?
Answer: If I'm right, the current hard-coded limitations are:

100 tx/block for main chain (block spacing is 1 minute)
100 tx/block for every child chain.

The current maximum capacity (if there were 100 child chains) would then be 10000 tx/minute (or about 160-170 tx per second), because child chains' transactions are bundled into a main chain ChildChainBlock transaction. A more realistic value would be 5000 (with 50 child chains), so there is space for 50 ARDR transactions per minute.
I guess that's largely a anti-spam measure and can be lifted once it becomes necessary. But even the "realistic" 5000 tx/min would mean about ten times Bitcoin's capacity. It would need relatively powerful nodes, but once child chain pruning is implemented, it would become much faster to sync and "catch up".
Waiting for an official developers' answer though ;)


motorcycles and vehicle ground loop detectors

Question: I have been asked if it is feasible to make a motorcycle accessory that will trigger the traffic ground loop antenna sensors that typically fail to register the motorcycles presence. Reading up on these sensors, I find that they detect a vehicle by driving a signal into a loop and measuring a change in frequency due to the inductive skin effect from the metal in the vehicle over the sensor.
This makes me wonder if it might be possible to build a low power transmitter to drive an antenna mounted directly under a saddlebag to force a change in the ground loop operating frequency actively, as opposed to the change registered from the passive inductive skin effect.
The only antennas I have made so far have been from following ARRL guides to the letter.
So I am hoping that someone might be able to detail what the antenna and loading coil construction would be and its drive requirements to accomplish this.
Some of my references are:
http://www.editraffic.com/wp-content/uploads/loop_install_guide.pdf
http://www.marshproducts.com/pdf/Inductive%20Loop%20Write%20up.pdf
http://www.editraffic.com/wp-content/themes/eberle/flash/loopCalculator.swf
http://www.fhwa.dot.gov/publications/research/operations/its/06108/02.cfm
Comment: Great idea. You won't need an actual antenna, just a coil, maybe 20 turns, 20 cm. The ground loop detectors are essentially just metal detectors. Problem is there are many ways of making a metal detector, simple ones use steady state oscillator and detect a shift in resonance, but better ones use pulses of AC and observe the decay of the fields. You might need a microcontroller that tries several different modes, to fool it.
Comment: From my experience, if you simply call the city and complain about faulty sensor (and they are required to be sensitive enough to feel motorcycles, at least where I live), it gets fixed rather quickly. Doesn't cost much money too.
Answer: That may work, but a strong magnet low on the bike is more cost-effective.
When I ride my (aluminum and carbon) bicycle, I put a flat neodymium magnet in my shoe and stand on the terminals (where the loop starts and ends).  This seems to work well.
Comment: I'm not an expert in this, but putting such a magnet in your shoe would be considered dangerous?
Comment: Not normally.  Just remember to take it out before you get an MRI!
Answer: I think the idea to add a coil proposed by Oleg might be the best idea, but a 20 cm circular coil would cause a pretty minor change in the inductance, compared to the skin effect of your average car. Go back to phasors, think of this in terms of z = jwL, and then see if you can find a way to produce a reasonable frequency shift. I don't know how much inductance is required to trigger the sensor, but I bet you could figure something out by running a coil around the engine itself. It would be a huge pain to work around though if maintenance is ever an issue, so you'll have to find a balance.


Which Tumblr themes displays all tags on landing page?

Question: Among dozens of gratis Tumblr themes, I've hardly seen any that offers to display tags on the front-page. Have you? Can you provide some links? It doesn't have to be all fancy, like tag clouds.
Comment: Tumblr doesn't have tag-cloud generator by default. It can be added only with a 3rd-party script.
Answer: Update (2017-04-08): the generator seems out of service at the moment.
Here is a tag cloud generator, that you can insert on your tumblr home page:
https://heatherrivers.com/tumblr-tag-clouds
Answer: I've found some themes
1.there is Esten theme, it shows several (maybe 10) tags at the bottom,
2.a theme by Dominic Valenciana, idk the name, but I know that it shows up to five tags in top bar
3.leen themes has Sandy- theme that shows up to 12 tags in sidebar
4.and there was one theme I've found by searching 'tag list' or maybe 'tag cloud' on that 'search way more themes' in tumblr- it is a grid theme called photogrid or photoportfolio or something like that, you can recognize it because on the header image there is a title in which every word has a white background, and it is THE ONLY theme that automatically lists all your tags.


EIGRP : Feasibility Condition not satisfied

Question: What happen if the Feasibility Condition not satisfied and we can not pick a feasible successor?
Comment: Did any answer help you? if so, you should accept the answer so that the question does not keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer.
Answer: A feasible successor is just a backup route. Feasible successor routes are not used to forward traffic, only successor routes are. It is not necessary to have a backup route. If the successor route disappears with no feasible successor, then it triggers a recalculation and reconvergence for that route (queries sent to neighbors), and it may be possible that there is no other route to that destination, causing the route to be dropped.


Using a gradient mesh to color lines in illustrator

Question: So I have this line design in AI, and I made this super colorful gradient mesh with the color design I want to apply to the lines. (They are in separate layers if that is relevant) How do I use the color design of the gradient mesh to color the lines?
Answer: If the line design isn't too complex, one way of solving this problem is to create a clipping mask:

convert the strokes of the object to outlines,
merge the resulting objects together using pathfinder tools,
create a clipping mask with the line design on top of the gradient mesh.

This works in Illustrator CS5 and i can't say if newer versions allow to do it in a different way.


When was the date of the appointment of Mohammad as prophet?

Question: I was wondering about the date of the appointment of Prophet Mohammad (His prophetic mission).
Do you know when its date is?
Both Sunni and Shia view welcomed. I'd be grateful if you present some authentic sources for your responses.
Comment: Hello since you are asking about to different views please ask a separate question for each view. Also please clarify your question
Comment: I've heard that Prophet(pbuh) is considered born Prophet by Shias, is it true, forget about his mission, because Sunnis believe he got prophet-hood at the age of 40..
Answer: Sunni view:
At the age of forty years on the authority of ibn 'Abbas:

Narrated Ibn `Abbas:
Allah's Messenger (ﷺ) started receiving the Divine Inspiration at the age of forty. Then he stayed in Mecca for thirteen years, receiving the Divine Revelation. Then he was ordered to migrate and he lived as an Emigrant for ten years and then died at the age of sixty-three (years). (Sahih al-Bukhari a slightly different version on his authority is also available in Sahih al-Bukhari)

and Anas ibn Malik:

Narrated Anas bin Malik:
The Prophet (ﷺ) was neither conspicuously tall, nor short; neither, very white, nor tawny. His hair was neither much curled, nor very straight. Allah sent him (as an Apostle) at the age of forty (and after that) he stayed for ten years in Mecca, and for ten more years in Medina. Allah took him unto Him at the age of sixty, and he scarcely had ten white hairs on his head and in his beard. (Sahih al-Bukhari)
Anas b. Malik reported that Allah's Messenger (ﷺ) was neither very conspicuously tall nor short-statured, and his color was neither glaringly white nor brown; his hair was neither very curly nor very straight; Allah commissioned him (as a Prophet) when he had reached the age of forty years, and he stayed in Mecca for ten years and for ten years in Medina; Allah took him away when he had just reached the age of sixty, and there had not been twenty white hair in his head and beard. (Sahih Muslim)

Note that Quran also emphasizes on the age of forty years in 46:15 so it might have some meaning! (see also https://www.missionislam.com/family/ageforty.html)

Imam an-Nawawi in his commentary on sahih Muslim said there's consensus about the fact that the Messenger of Allah has been living in Mekka 40 years before his commission and in Medina 10 years the only thing where there is a dispute is the amount of years he stayed in Mekka after his commission and the most correct is 13 years (see for example here). This means his age when he died was 63 years. (See this answer https://islam.stackexchange.com/a/35220/13438)

Al-Mubarkapury المباركفوري even calculated an exact date in ar-Raheeq al-Makhtoom:

فيقول المباركفوري في الرحيق المختوم في تحديد تاريخ البعثة: وبعد النظر والتأمل في القرائن والدلائل يمكن لنا أن نحدد ذلك اليوم بأنه كان يوم الاثنين لإحدى وعشرين مضت من شهر رمضان ليلا، ويوافق 10 أغسطس سنة 610م، وكان عمره صلى الله عليه وسلم إذ ذاك بالضبط أربعين سنة قمرية وستة أشهر و12 يوماً، وذلك نحو 39 سنة شمسية وثلاثة أشهر، و22 يوماً. انتهى.
(Islamweb, Fatwa #42006)

saying it was on Monday the 21st Ramadan (at night) the equivalent to the August the 10th 610 C.E. and he was at the time 40 -moon- years 6 months and 12 days old and about 39 -sun- years three months and 22 days.
Answer: According to the view of Shiite, the date of the appointment of Prophet Muhammad(s) (Prophetic Mission) was the 27th of Rajab, 40th year of elephant (610 C.E.). For instance (as authentic sources of Shiite): Marhum Koleini, Sheikh Sadoogh, and Sheikh Tusi have mentioned its date.
But according to Sunni view: There are some probable dates, such as:
17th, 18th or  24th (of Ramadhan).
Or even according to some narrations : 10th or 12th of Rabi'ul Awwal.

Source(s):
www.sibtayn.com
http://rasoolnoor.com
Comment: Don't shia's believe he(pbuh) was a born prophet???
Comment: "But according to Sunni view:", is it also in the same year i.e. 610 CE????
Comment: What's the meaning of 40th year of elephant (610 C.E.) you wrote?
Comment: As a helpful related link: http://en.wikishia.net/view/%27Am_al-Fil   ________  Good luck


Equivalence principle and quantum gravity

Question: Do new concepts  of gravity negate the validity of the equivalence principal?  or do all theories (waves, string, etc) and mathematics apply equally to gravitation and accelerating frames?
Answer: I don't think the equivalence principle is important in String Theory for example, which is a theory of gravity; it's already taken for granted that the graviton - the quantised particle for gravity is a spin-2 particle and its shown that the string theory spectrum has a spin-2 particle in its spectrum.


How do I find the circumcenter of a triangle in 3D?

Question: I want to find the circumcenter of a triangle.  Wolfram only shows how to find the circumcircle of a triangle in R2. How can I find the circumcenter of a triangle in R3?
Comment: You can define a plane using the 3 points of a triangle and then the problem is back into R^2 for which you already know the method.
Comment: what I meant was a unique plane can be defined using the 3 vertex of the triangle and in that reference plane, the triangle is 2D. This will however require appropriate transforms (which I did not elaborate) and hence just put this as a guiding comment rather than answer
Comment: @Ani The [formulae for circumcircle](http://mathworld.wolfram.com/Circumcircle.html) involve only x and y, but a 3D triangle, in 3-space plane, uses x, y and z variables.
Comment: Yes, in fact I thought I was going to have to rotate the triangle to the xy/xz/yz plane, then apply the 2d formula.  Hence why I shared the Triangle in R^3 formula I found at Geometry Junkyard below
Answer: The circumcenter of a triangle can be found by the following formula, which I mined from an old posting by Jonathan Shewchuk from the Geometry Junkyard
$$\begin{align}
&\text{Triangle in } \Bbb R^3\text{:}\\
&m = a + \frac {\lVert c-a\rVert^2 \left[(b-a) \times (c - a) \right] \times (b-a) + \lVert b-a\rVert^2 \left[(c-a) \times (b - a) \right] \times (c-a)}
{2 \lVert (b - a) \times (c - a) \rVert^2}
\end{align}$$
Where \$m\$ is the circumcenter of the triangle.
Some C++ code, given Vector3f's with overloaded +, -,
Vector3f a,b,c // are the 3 pts of the tri

Vector3f ac = c - a ;
Vector3f ab = b - a ;
Vector3f abXac = ab.cross( ac ) ;

// this is the vector from a TO the circumsphere center
Vector3f toCircumsphereCenter = (abXac.cross( ab )*ac.len2() + ac.cross( abXac )*ab.len2()) / (2.f*abXac.len2()) ;
float circumsphereRadius = toCircumsphereCenter.len() ;

// The 3 space coords of the circumsphere center then:
Vector3f ccs = a  +  toCircumsphereCenter ; // now this is the actual 3space location

Here is a picture of a triangle and its circumsphere
Comment: len2() is squared length ?
Answer: JavaScript - MY WORK - 5 TRIANGLE CENTERS IN 3D
function incenter(A,B,C) {
    var a=vlen(subv(A,B)),b=vlen(subv(B,C)),c=vlen(subv(C,A));
    var x = multv(C,a), y = multv(A,b), z = multv(B,c);
    return divv(addallv(x,y,z),a+b+c);
}

function centroid(A,B,C) {
    return divv(addallv(A,B,C),3);
}

function midpoint(A,B) {
    return divv(addv(A,B),2);
}

function orthocenter(A,B,C) {
    var c = circumcenter(A,B,C);
    return addallv(subv(A,c),subv(B,c),subv(C,c),c);
}

function circumcenter(A,B,C) {
    var z = crossprod(subv(C,B),subv(A,B));
    var a=vlen(subv(A,B)),b=vlen(subv(B,C)),c=vlen(subv(C,A));
    var r = ((b*b + c*c - a*a)/(2*b*c)) * outeradius(a,b,c);
    return addv(midpoint(A,B),multv(normaliz(crossprod(subv(A,B),z)),r));
}

function nine_point(A,B,C) {
    return midpoint(orthocenter(A,B,C),circumcenter(A,B,C));
}

function outeradius(a,b,c) { /// 3 lens
    return (a*b*c) / (4*sss_area(a,b,c));
}

function sss_area(a,b,c) {
    var sp = (a+b+c)*0.5;
    return Math.sqrt(sp*(sp-a)*(sp-b)*(sp-c));
    //semi perimeter
}

If you need the remaining functions, you can fint them in this
working code example - hit the pyramid button twice.
Comment: This isn't a good answer. You use a lot of functions, that aren't self explanatory and aren't included in vanilla JS. `divv`, `addallv`, etc.
Comment: @Bálint since the question asks for an algorithm, not tagged with a specific language, I think this is no worse than the accepted answer that assumes a suitable definition of `Vector3f` in a C++ program. That answer doesn't define the `cross` or `len2` methods, but we can infer they're the cross product and squared length reasonably easily, just the way in this answer we can infer that `addallv` sums the provided vector arguments, and `divv` does scalar multiplication between a vector and the reciprocal of a scalar. I certainly wouldn't complain about more explanation, but it's legible as-is.
Comment: thanks for the help but its find not fint. and its more than "twice."  (more models)
Comment: hmf, looks like gravity was busted, found the error. Sorry, get the new file. and ctrl-f5 is supposed to reload but ... oh well. and given the response well ... I know better. no good deed goes ... outta here. make something cool and quit asking questions. all u need is one good program and your done asking questions.
Comment: "I think this is no worse than the accepted answer that assumes" uhm, you wont ever see a better more complete example for triangles centers, and if you ever do, call me lol
Comment: also you wont see all 7 sin/cos laws as working functions like this. which I wrote of course but dont know where to post it.
Answer: //Unity/C#
Vector3 ac = c - a;
Vector3 ab = b - a;
Vector3 abXac = Vector3.Cross(ab, ac);

// this is the vector from a TO the circumsphere center
Vector3 toCircumsphereCenter = (Vector3.Cross(abXac,ab) * ac.sqrMagnitude + Vector3.Cross(ac,abXac) * ab.sqrMagnitude) / (2f * abXac.sqrMagnitude);
float circumsphereRadius = toCircumsphereCenter.magnitude;

// The 3 space coords of the circumsphere center then:
Vector3 ccs = a + toCircumsphereCenter; // now this is the actual 3space location

Comment: This answer can be improved with additional content rather than having just a code snippet not everyone might understand.