Why is Poisson regression used for count data?

Question: I understand that for certain datasets such as voting it performs better. Why is Poisson regression used over ordinary linear regression or logistic regression? What is the mathematical motivation for it?
Comment: See my answer to this post for another viewpoint:  http://stats.stackexchange.com/questions/142338/goodness-of-fit-and-which-model-to-choose-linear-regression-or-poisson/142353#142353
Answer: Poisson distributed data is intrinsically integer-valued, which makes sense for count data. Ordinary Least Squares (OLS, which you call "linear regression") assumes that true values are normally distributed around the expected value and can take any real value, positive or negative, integer or fractional, whatever. Finally, logistic regression only works for data that is 0-1-valued (TRUE-FALSE-valued), like "has a disease" versus "doesn't have the disease". Thus, the Poisson distribution makes the most sense for count data.
That said, a normal distribution is often a rather good approximation to a Poisson one for data with a mean above 30 or so. And in a regression framework, where you have predictors influencing the count, an OLS with its normal distribution may be easier to fit and would actually be more general, since the Poisson distribution and regression assume that the mean and the variance are equal, while OLS can deal with unequal means and variances - for a count data model with different means and variances, one could use a negative binomial distribution, for instance.
Comment: Note that just fitting using OlS doesn't require normality - it's when you do inference on the parameters that you need the normal distribution asssumption
Comment: If you use the Huber/White/Sandwich estimator of variance, you can relax the mean-variance assumption
Comment: @Dason: I stand corrected.
Comment: @Dason While it's not strictly required, using the right form of model for what you're fitting almost always gives a better estimate, and you can see it in plots of residuals.
Answer: Essentially, it's because linear and logistic regression make the wrong kinds of assumptions about what count outcomes look like.  Imagine your model as a very stupid robot that will relentlessly follow your orders, no matter how nonsensical those orders are; it completely lacks the ability to evaluate what you tell it.  If you tell your robot that something like votes is distributed continuously from negative infinity to infinity, that's what it believes votes are like, and it might give you nonsensical predictions (Ross Perot will receive -10.469 votes in the upcoming election).
Conversely, the Poisson distribution is discrete and positive (or zero... zero counts as positive, yes?).  At a very minimum, this will force your robot to give you answers that could actually happen in real life.  They may or may not be good answers, but they will at least be drawn from the possible set of "number of votes cast".
Of course, the Poisson has its own problems: it assumes that the mean of the vote count variable will also be the same as its variance.  I don't know if I've ever actually seen a non-contrived example where this was true.  Fortunately, bright people have come up with other distributions that are also positive and discrete, but that add parameters to allow the variance to, er, vary (e.g., negative binomial regression).
Answer: Mathematically if you start with the simple assumption that the probability of an event occurring in a defined interval $T = 1$ is $\lambda$ you can show the expected number of events in the interval $T = t$ is is $\lambda.t$, the variance is also $\lambda.t$ and the probability distribution  is
$$p(N=n) =  \frac{(\lambda.t)^{n}e^{-\lambda.t}}{n!}$$
Via this and the maximum likelihood method & generalised linear models (or some other method) you arrive at Poisson regression.
In simple terms Poisson Regression is the model that fits the assumptions of the underlying random process generating a small number of events at a rate (i.e. number per unit time) determined by other variables in the model.
Answer: Others have basically said the same thing I'm going to but I thought I'd add my take on it.  It depends on what you're doing exactly but a lot of times we like to conceptualize the problem/data at hand.  This is a slightly different approach compared to just building a model that predicts pretty well.  If we are trying to conceptualize what's going on it makes sense to model count data using a non-negative distribution that only puts mass at integer values.  We also have many results that essentially boil down to saying that under certain conditions count data really is distributed as a poisson.  So if our goal is to conceptualize the problem it really makes sense to use a poisson as the response variable.  Others have pointed out other reasons why it's a good idea but if you're really trying to conceptualize the problem and really understand how data that you see could be generated then using a poisson regression makes a lot of sense in some situations.
Answer: My understanding is primarily because counts are always positive and discrete, the Poisson can summarize such data with one parameter. The main catch being that the variance equals the mean.


Does Linux put my laptop's HD in danger?

Question: I am supposed to be transitioning to using Linux for work, starting with Ubuntu. I was told that when I have a laptop with Linux I should not move it while it is operating before I make sure disc protection is enabled in Linux. Is this true? This is scary. Can I damage my disc so easily?
Comment: Who told you that? A MS sales person? ;)
Comment: A developer who moved to Linux 3 years ago and seems to be quite happy with it.
Comment: Have fun with Linux!
Comment: @Kim - this is pretty far fetched, even for a MS sales person :)
Answer: Most harddrives are designed, from the factory, to handle a fall from a certain height and still survive without data loss (shock resistance).  This is usually specified on the hard drive's sticky label.  Not sure how many Gs this is, but I would guess they should be able to survive a 2-3 foot fall onto carpet, say from a coffee table.  (If anyone knows better about this, like say from a purchasing group, please comment on this and I'll add the info to my answer).  Falls from say a boardroom table, I suspect, would really start to push it.  Of course, there are no guarantees here.  But most hard-drives are designed to take a bit of a beating.
When on, however, a drive's ability to survive a fall drops significantly.  Some laptops (notably ThinkPads) include accelerometers that can detect if your laptop is tipping or being jostled, and will turn off the drive if the software that governs that behavior is loaded, with the goal of improving data integrity.  I'm certain you can get an app for Ubuntu to do this too. Mainly the turn-off feature is useful when using your laptop in a bumpy environment, say on a bus or train, or in the back of an automobile, to limit the possibility of a head crash occuring.  No amount of software can prevent physical damage to your disk from a major fall, though. If your'e going to be moving your laptop around a lot, it's definitely something you'll want to have active.
As always - just be careful, don't let your kids attack your laptop, and try to limit the drops it makes to the floor as much as possible.  If you ride the bus/train/carpool and use your laptop during those rides, I'd try to get a jostle-detection tool on your laptop, assuming it has the appropriate hardware.  It's not the end of the world if it doesn't, though, as many other posters have noted.
Answer:
I should not move it while it is operating

This is a gross overstatement.  My laptop does not have a free-fall sensor, and I move it all the time while it is operating.  It would be bad for it to fall from any significant height, but "moving" is not a problem.
Answer: I believe "disk protection" (as in, if it detects a sudden drop, it disengages the read/write head to save the drive) is entirely hardware based. In any case, we got along fine for years without "disk protection", so just don't drop the thing and everything will be fine anyway.
Answer: replace the platter HDD with a Solid State Disk and bid farewell to fears of endangering the 'Laptop's HD' :)
other than that, treat it with care and it will last just as long as with any other operating system.
Answer: Short answer: no, hard drives may fail, and it has little to do with the operating system.
Answer: I have dropped my laptops (cheapo Acers and a Lenovo) many times over the years sometimes while booted in to Linux sometimes Windows. I also accidentally spilled whole glassfuls of water, soda and hot tea on them.
I only caused irrecovorable errors on a hard drive once through all of this. It was a fall from about 4'6" while I was walking and I was encoding a large AVI file. I tried to catch it in the air and ended up causing the laptop to do a few loops in the air before crashing on to the parquet floor hard.
Even then, I was able to recover most of my files by booting using ArchLinux on a USB key.
In any case, Linux does not cause hard drive damage. However, if you have a lot of processes writing to the disk at the time a physical shock occurs, the number of sectors damaged can be greater, regardless of the OS.
One thing you have to watch out for is your power saving preferences. The laptop mode tools FAQ list addresses such issues:

Spinning down too many times may kill hard drives
Desktop hard drives are usually rated for only 40,000-50,000 spinups, and one spinup every 10 minutes will kill your 40,000-spinup HD in 277 days. So this is NOT recommended for server use, unless you increase the spinup interval dramatically, to say once every hour or two. Laptop hard drives are usually rated for around 300,000 spinups, so those will last about 2083 days or 6 years if you have them powered on 24-7.


What creatures can apparate?

Question: It's known that House elves can apparate without a wand. Wizards can do it but usually with a wand. Are there any other creatures able to apparate?
Comment: Well, I imagine a gorilla could be trained to operate a boat and rob ships on the high seas.... oh, wait, I thought you said ape-pirate.
Comment: assuming you are meaning creatures that can initiate apparition on their own, rather than being a 'passenger' in side-along-apparition?
Comment: The question you linked to seems to conclude that a wizard **doesn't** need a wand to apparate.
Comment: @Nit Thanks, I fixed it.
Answer: Phoenixes and Diricawls can vanish and reappear at will, which may or may not count as Apparition.  Both of these are mentioned in the Fantastic Beasts and Where to Find Them book.  Professor Dumbledore's Phoenix Fawkes is even shown to vanish together with the Professor in Harry Potter and the Order of the Phoenix.  I don't have the book at hand, but I don't think any other creature is mentioned with similar abilities.
Comment: Yes I also think Peeves can float through walls like a normal ghost. But in this scene he appeared in the air with a loud bang same as the houselves before him. When there is a loud bang and someone appears out of nowhere it is mostly becauae of apparation. I can't quote the book because I only own the german version.
Comment: Poltergeists seems also to be able to apparate. In book 6 Peeves appears out of nothing while Dobby fights against Kreacher in the hospital wing.
Comment: @Lucharx I don't think so.  I suspect Peeves just floats through the walls of the castle, which is how he can arrive unexpectedly.

What creatures can apparate?


Why is the pH level of carbonation loss decreasing then increases afterwards?

Question: We have done an experiment of the titration of unsealed sprite soda to find the amount of carbonic acid being loss on various duration (0 to 1 hour), due to decrease pressure.
The calculation was to determine the pH of carbonic acid overtime, thus the number of concentration of flat and unsealed soda are subtracted and is converted to pH level using -log[concentration of flat soda - unsealed soda].This was done multiple times on multiple duration until 1 hour. Now the results has demonstrated that carbonic acid pH level was decreasing in the first 30 minutes but then afterwards it was increasing. This contradicts on what my hypothesis is as it states that due to pressure being decreased (by unsealing the soda) the pH will increase turning more basic. Is this due to the factors of pressure and temperature? Can you please describe this thoroughly? Thank you for your time on reading this.
Comment: Was that pH observation before the titration or after it ?
Comment: The pH observation was after the titration sir.
Comment: Is not the pH computation ignoring citric acid content ?
Comment: Plus, is not it ignoring the strength of the carbonic acid ?
Comment: Is it a question of kinetics ?
Answer: At the beginning, there was titrated mostly just the citric acid and the equilibrium amount of carbonic acid.
After that, carbon dioxide slowly converted to carbonic acid and $\mathrm{pH}$ has been decreasing.
Finally, the long term process took dominance as dissolved carbon dioxide together with carbonic acid were  leaving solution as gaseous carbon dioxide and $\mathrm{pH}$ have been raising.
Comment: Converted to pH level ? I thought it was measured... Do you mean estimation of pH of sprite soda drink before and after titration ? The best would be, if you rewrite the question as a detailed description of experiment, with  raising the clear questions about experiment details in a particular experiment stage.
Comment: I will do that. Thank you for your time
Comment: You know, the prerequisite for good answers is a good question. If others have to guess, imagine or interpret what is the real question, answers are rarely what was wanted and clarification wastes resources on all sides. :-)
Comment: Sorry I haven't specified the description clearly, we have titrated both the flat soda (where all carbonation is loss) and the soda that is titrated in various duration. The amount of moles has been determined for both of the flat soda and the 'duration soda' and was subtracted, resulting the moles of only carbonic acid. This was then converted to pH level and was done multiple times for various duration. I am very sorry that I wasn't clear on this.


How to get people to attend online meetings as a new Project Launch Manager?

Question: I'm a new Project Launch Manager at a corporation similar to Oracle that develops and sells Enterprise apps. I'm inexperienced in my role but I am a self starter and work hard. My problem is that this first Product Launch I am assigned to--I'm having a difficult time to get people to show up to online meetings. These initial meetings are important to assign deliverables, set due dates, and condense checklists and bill of materials documents. The people that I am working with are from all over the world--UK, Netherlands, U.S ect..When i set these WebEx conference calls either they will accept and not show up or decline. I feel that I am going to have this problem all throughout the release process. Can anyone recommend any solutions or methods that I can use? Thanks!
Comment: At the risk of stating the obvious, you *are* accounting for time zone differences when you send these meeting requests, aren't you? There's a five hour difference between Atlanta and the UK. I know I'd instantly decline and have a good laugh at the silly American PM if I got a request for a meeting at 1800.
Comment: Are these people you are meeting with clients or coworkers?
Comment: Hi Chad. They are co-workers representing different functional areas within the release i.e Product Management, Marketing, Pre-Sales/Sales, Support ect...
Comment: How many people are you trying to schedule for these meetings?
Comment: At the moment, 3 people in UK, 1 in NE,  and 3 in Atlanta.
Comment: Hi Joe. We've had 1 initial kick-off meeting for introductions and general next steps...after this meeting I started sending out invites for the working sessions I'm talking about. They are both formally assigned and also doing other tasks. So, yes, they are busy but these are still important meetings that are significant.
Comment: More than accounting for them--I am working outside of my working hours at 5 or 6 AM to accommodate for UK and Netherlands.
Answer: First do some glad handing.  Talk personally with the people you are inviting and get their buy-in to attend the meetings.  Its best if you can do this in person but if not even over the phone helps.  Explain what you are trying to accomplish, why their attendance is important, and find a time they are available.
Limit the people you are inviting to the people actually needed for the call.  If they do not need their input or feed back for the call better to offer them an optional invite and send them the summary.  The last thing anyone needs is another meeting where they have no real reason to be there.
Always get the managers buy in on the project before you invite members of their team.  Get the manager to assign people and get them to be involved with following the progress of the project.  Pressure from above goes a long way toward getting people to attend meetings they might otherwise want to skip.
A spoonful of sugar can go a long way with people.  Make people feel special and like their involvement with the project means a lot to you.  Compliment the work they do and give positive feedback to their bosses where appropriate.  Often times Corporate Drones feel stuck in their cubes and unappreciated.  A little recognition can go a long way towards getting them fully engaged in your project, which can often make a huge difference in the success or failure of the project.
Comment: Thanks, Chad. Great advice. I'm going to use some of the tips you've provided here. I think getting initial buy-in independently and getting manager approval will go a long way. Definitely shifting to this strategy.
Answer: Based on my experience with working with developers, product owners, etc. in different time zones, the key things are having the right people, having the meetings are the right times, and having the right frequency of meetings.
Working across times zones usually means one or more people need to be in the meeting outside of regular hours. Typically, I was the one that worked the odd hours to ensure everyone else would be in the meetings during working hours. In another team we were just one or two people in three time zones so we just agreed from meeting to meeting who would get the crappy time.
Making sure you have the right people in the meetings is important. Some would be required and others may be optional. In some cases those people may change from meeting to meeting depending on the agenda. When scheduling the meeting make sure the required people are all in agreement on the time.
For the people that are required, ensure you stress that these meetings aren't optional. I've had to go over peoples heads in the past. In some cases talking to their manager was cleared things up. In other cases we decided the person wasn't the right person for the project and they were replaced. This can be a tricky situation with coworkers as it can't affect working relationships.
Limiting the frequency of the meetings will also help, especially if there's a need for some people to be in the meeting during non standard working hours.
Consider splitting up the meeting into smaller meetings where possible. More people usually means longer meetings. With too many items to cover you may end up with people sitting in on a long meeting where they were only needed for a short time. These people are less likely to show up to the next meeting.
Answer: Is this meeting necessary?    Sounds like some of your people are telling you its not, and that their time is better spent doing anything else.
Make the meeting productive by: setting (and follow) an agenda, a list of things to cover.   Set action points and assign them to people with an expectation the action points are done by a certain date.  Note all this in some minutes while the meeting runs, and publish the minutes via email within 5 min of meeting close.
Too many people in the call can also distract from the purpose.  There's no point in having dozens of people on when the information is only relevant to a smaller group.  Set-up several different shorter meetings optimally for the immediately relevant people.
Also, video calls suck.  Seriously, have an audio call rather than a video call.  There's little benefit in seeing everyone's face, and video can be a turn-off for the average geek.
Finally - leading a meeting is way harder than simply attending a meeting.  Consider asking someone in management for advice on how to improve the handling of the meeting, and then the users will come.
Extra: DO cancel meetings if there's nothing worth covering by the group.
Comment: Meeting is necessary. It is a meeting to connect different functional areas within the project i.e Product Management, Marketing, Development and to set agenda items, deliverables, and due dates.
Comment: These are audio calls not video calls and they done via WebEx and screen sharing to work on action items described above. Absolutely essential to the initiation of the project. One point I did get from you is to create a clear bulleted agenda with clear expectations in the email.
Comment: And these are working sessions designed for 4-6 people max.
Answer: Identify the key people you need who haven't been making it. Call them up one by one before you schedule the next one, with the time in mind.

Hi, John. This is Steve, I'm the new Project Launch Manager over at X office/department. As you're aware we're setting up meetings to define schedule and deliverables for Y Project. I know you are an essential part of this because you are the lead developer/budget analyst/technical manager on this project/at the UK office/on the ABC project. It's really important to me that I get your input. I'm looking at setting up the next meeting next Tuesday at 4pm your local time. Does that work for you? ... In the future are there days/times that are easier/more common in your office? If you have any other feedback on how we've been organizing the meetings I'd love to hear it. ... Thanks looking forward to you representing at the meeting, I know you have a lot of valuable skills and perspective to contribute and I look forward to hearing from you in the meetings.

This does the following things:

Puts a friendly voice to your name/email
Makes them feel important/valued
Restates what the purpose is for busy people who don't read every single meeting invitation
Gives them some input on when/how you are holding your meetings
Makes them feel like stakeholders not victims

The important part to add to this is, if you are running your meetings where you are delivering due dates and deadlines and goals without the group's input, you do not need a meeting. If someone is speaking up saying "Hey Steve, we can't make that date" you need to listen to them. If you say "Sure you can, the last project we did you got it done in 200 hours and I'm confident you can do in 100 this time" or say "sorry, that's the date management has assigned" you do not need a meeting. Just send emails out with the dates and call people individually. If you are not inviting feedback/willing to be flexible, that might be why people aren't attending. Or if every question/piece of information just gets agreement, you probably don't need regular meetings either. This is your job to manage this thing so it's important to you. It's probably their job to code/generate work and that's what's important to them. They don't get brownie points for spending an hour listening to schedule updates. If you work on ways to remove barriers to them getting their jobs done they will also value you more.
Comment: Thanks, great points and great email example. Your last paragraph is very helpful advice for the long term or once a project is underway. This question is more for the initial meetings where we set initial probable due dates and have working sessions to understand deliverables.
Comment: The quoted part was meant for a script for what you would say on the phone to them. I'm suggesting you pick up the phone and call people who haven't been showing and use that as your script to talking with them. If you just keep emailing / sending calendar invites, people won't really make the personal connection and might keep blowing you off.
Answer: Do you just set the dates? maybe the people don't have time when you have?
Try setting up a meeting using doodle. Also point out they should suggest other dates that would work for them.
http://doodle.com
Also, is it neccessary for all of them to show up at the same time? Can't you give them the task independently?
And Europe-US has a time difference of up to 9 hours if you live on the west coast, that means one team has to do the meeting when they start working, the other team before they leave.
Comment: There is a Scheduling Assistant on Outlook where you can check which time slots are free for everyone and I make them based on that. The first 2 were at a lat time slot for UK and Netherlands, so I've resorted to setting them earlier which ends up being 6 AM my time. There have still been people that don't show after accepting citing that they have a new conflict or decline from the outset.
Comment: Yes, this is a good suggestion to give them tasks independently. But it's much more efficient and agile to have the whole team on and speak have cross-organizational communication
Comment: for example: we are 6 people and we usually reschedule every second meeting due to new arising conflicts, urgent bugfixes, new client meetings, just stuff that is more important. would be probably impossible to ever get a meeting done with more people or if we were across an ocean.
Comment: also it is okay to do the meeting when most people are there, just give the others a memo what happened or if possible even a video of the chat? you won't get perfect input then, but those ideas can be discussed later too.
Comment: Yes this is something that I can definitely look towards for the future. Record the meeting and send to stakeholders and discuss later.
Comment: or make a short extracted version from the recording or write a protocol, whatever ~~works~~ makes people happy :)
Comment: @BenStien - Just because I do not have a meeting scheduled in my calendar at a time does not mean i am available for a random meeting.


Could the SCOTUS void a Presidential Pardon?

Question: Would it be possible for the Supreme Court of the United States to void a Presidential Pardon? If so how would they do it? If not why?
Answer: No, the Judicial Branch has no power over Presidential Pardons, which are vested solely within that office.
The President is granted this power in Article 2. Section 2.

The President shall be Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States; he may require the Opinion, in writing, of the principal Officer in each of the executive Departments, upon any Subject relating to the Duties of their respective Offices, and he shall have Power to grant Reprieves and Pardons for Offences against the United States, except in Cases of Impeachment.

Bradford v. Cardoza lays out the reasons.

Article II, section 2, clause 1 of the United States Constitution reads: "[The President] shall have power to grant reprieves and pardons for offenses against the United States, except in cases of impeachment." The draftsmen of this article intended it to be free of legislative control. (Schick v. Reed (1974) 419 U.S. 256, 263 [42 L.Ed.2d 430, 437, 95 S.Ct. 379], reh. den. 420 U.S. 939 [43 L.Ed.2d 416, 95 S.Ct. 1150].) [T]he pardoning power is an enumerated power of the Constitution and ... its limitations, if any, must be found in the Constitution itself." (Id., at p. 267 [42 L.Ed.2d at p. 439].) Congress therefore cannot modify, abridge or limit the President's pardon power.
Comment: @DVK - Sure you can.  [`High crimes and Misdemeanors`](http://en.wikipedia.org/wiki/Article_II_of_the_United_States_Constitution#Section_4:_Impeachment) isn't defined, so the House and Senate can theoretically impeach for any reason.  However, what they *can't* do is overturn the impeached President's pardon.
Comment: @Joshua - I'm not sure I follow what you're trying to say.
Comment: What bakes my noodle is, technically speaking you can't even impeach the president, no matter how awful the pardon was.
Comment: @Bobson: Do you want to find out what the results are of trying to hold up a pardon for which the sitting president was just impeached for the "crime" of writing the impeachment? A judge looking to uphold it might be next in the hot seat.
Comment: @Joshua, he's saying that if a President is convicted of a crime of issuing a pardon, a judge would not upload the pardon itself.
Answer:
"An unconstitutional act is not a law; it confers no rights; it
  imposes no duties; it affords no protection; it creates no office; it
  is in legal contemplation as inoperative as though it had never been
  passed."
  Norton v. Shelby County, 118 U.S. 425 (1886)
"At the time of the adoption of the Federal Constitution, American
  statesmen were most familiar with the prerogatives exercised by the
  king, so that obviously when the words "to grant pardons" were used in
  the Constitution of the United States, they conveyed to mind the
  authority as exercised by the English crown.Hence, it may be truly
  stated that we adopted their principles respecting the operation and
  effect of a pardon, and relied on the early writings of the common law
  for rules prescribing the manner in which it is to be employed."

The Pardoning Power of the Chief Executive, 6 Fordham L. Rev. 255 (1937).

"In the Constitution of the United States, and in most of the state
  constitutions, the pardoning power is there, in express, general
  terms, and by construction, since the greater includes the lesser
  power, it may be either absolute or conditional. This is true also in
  England. The pardoning executive may annex to his offer of pardon,
  then, any conditions that he may see fit to impose, either precedent,
  or subsequent. The only restriction upon this exercise of authority
  is that the condition must not be impossible of fulfillment, criminal
  or illegal in nature."

Emphasis added See United States v. Six Lots of Ground, 27 Fed. Cas. No. 16,299, at 1098 (C. C. La. 1872), aff'd, 91 U. S. 21 (1875); Kavalin v. White, 44 F. (2d) 49, 51 (C. C. A. 10th, 1930); Ex parte Prout, 12 Idaho 494, 498, 86 Pac. 275, 276 (1906); 1 Bishop, NEW CRIMINAL LAW (8th ed. 1892) § 915.
With reference to illegal, immoral or impossible conditions, it has been stated that

"If the condition is of a sort not permissible, it is void, and the
  pardon is absolute." I Bishop, NEW CRIMINAL LAW (9th ed. 1923) 659.***
  [Emphasis added] But, it seems clear that by declaring a condition
  precedent void, no such result should follow. See Canadian Prisoner's
  Case, 5 M. & W. 32, 49, 151 Eng. Reprints 15, 22 (1839) (if the
  condition upon which alone the pardon was granted be void, the pardon
  must also be void). That it should become absolute in the case of a
  void condition subsequent is supported by some authority. Taylor v.
  State, 41 Tex. Cr. R. 148, 51 S. W. 1106 (1899) (a pardon in which the
  governor reserved the right of revocation if the grantee violated any
  of the criminal laws of the state, held, condition void, pardon
  absolute); People v. Pease, 3 Johns. 333 (N. Y. 1803) (a proviso that
  a pardon was not to relieve the grantee of legal disabilities arising
  from his conviction, held, condition void, pardon absolute). Such
  decisions apparently rest upon a conception of pardons as of the
  nature of contracts or deeds. But the modern tendency is to regard
  them as acts in the interest of public welfare, wholly independent of
  the will of the prisoner. See Biddle v. Perovich, 274 U. S. 480, 486
  (1927). To construe any expressly conditioned pardon as absolute is a
  perversion of the intent of the executive and creates an
  uncontemplated danger to the public. The alternative of holding it
  invalid leaves it open to the executive to grant a new absolute, or
  properly conditioned pardon as he sees fit."

The Pardoning Power of the Chief Executive, 6 Fordham L. Rev. 255 (1937).
Hence, pardons granted as part of an illegal scheme to commit a crime like, Obstruction of Justice (to procure the silence or favorable false testimony of a witness), or Defrauding the United States (to conspire with as hostile foreign government to affect an federal election), or etc. would be void and unenforceable in court.
Hence, such pardons could not be relied upon to secure release from otherwise lawfully imposed punishment.
For example, if President Trump grants his family members or Mr. Manafort a pardon for purposes of a conspiracy to coverup a crime, such pardons are void and worthless.
Comment: Hey Bruce, thanks for your answer. As a new contributor (Welcome to the community!), I highly recommend checking out the formatting overview here: https://stackoverflow.com/help/formatting

Also, be sure to link to citations when possible to allow users to easily get the the full content you're relying on.

Your answer is also very heavy on quotes, but could use some explanation of why you believe the source quotes are applicable to the question. Perhaps breaking apart your quotes and walking the user through your thought process will provide clearer understanding?


Who might create the game pieces?

Question: I've designed a game which requires 3D geometric pieces. For a prototype, I'd like to see these make from metal, and to look elegant. Who might craft such items? I'm not even sure which profession I might investigate.
Comment: Can you use components from other games?  If its just a prototype and your just checking mechanics of a game work does the 'look' matter at this stage?
Comment: Alas their shape is important. They should also have the weight of metal (rather than, say plastic.)
Answer: A gold smith/jeweler could do your thing from metal and look elegant, but it might be quite expensive.
Answer: A 3D printing service would be an ideal solution.
I have no experience with any of the online services available, but as an example Shapeways seems to offer the option to print in a variety of plastic and metal materials, including the most common metals such as Steel, Silver, Aluminum, Gold, Platinum, Brass, Bronze, etc.
Shapeways 3D Printing
Answer: If the pieces have an axis of rotational symmetry then I would turn them on the lathe, (or you could search for a local machinist). If not then you could cast them. If you make originals out of wax then you can set them in oil-sand and cast them using the lost-wax method.

Who might create the game pieces?


Why peel tomatoes?

Question: Everyone seems to think it is necessary to peel tomatoes before canning or freezing them. Since I do not peel tomatoes when I'm cooking with them (soups, salsa, etc.), I'm wondering if I can freeze them without peeling them. Does freezing/canning do something to the texture of the tomato that makes the peel a problem?
Answer: When tomatoes are cooked (which I assume you plan on doing for canning or after freezing) the skins become tough and usually detach from the tomato.  Since you usually don't mind this, you shouldn't mind it with canned tomatoes either, but many people do - even when pureed the texture is different.
When freezing you can freeze whole and the skin should come off easily when thawed.
One way to get around the texture issue would be to puree the tomatoes and then force them through a food mill, which will help to remove tough bits - do this either before canning or after freezing.
Comment: The whole point is that the skin peel gets between the teeth and you should want to avoid that. As @Rebekah doesn't mind this, it's optional.
Comment: Some say the skin is also somewhat bitter, though not as much as the [seeds](http://www.culinate.com/columns/front_burner/tomatoes). This becomes most prominent if you're making a sauce.
Answer: I have put tomatoes in the freezer, whole, peeled , not peeled, pureed.  Later, when I cook with them, everything tastes so much better, I don't think it matters how you store the tomatoes in your freezer.  I follow the same prep that most of these sites list. The tomato sauce with spaghetti in the middle of winter is divine.

Why peel tomatoes?


What electric bikes are for sale in the US, and how good are they?

Question: I am interested in purchasing an electric bike but am puzzled as to what brand is best. It seems as though most companies are importing their products from China, which is great because they are low cost but they look bulky and maybe even cheap quality. There aren't many electric bike manufacturers let a lone traditional bike manufacturers in America.
Comment: Last year I was on a week-long tour where one lady had a Schwinn electric-assisted bike.  (Battery in the rear rack, front hub motor, rear 5-speed hub, IIRC.)  She indicated that the bike performed well (though note that this was not an exceedingly challenging tour, and the lady was reasonably strong without the motor).  (I'm sure most/all of the components were Chinese.)
Comment: I'll add that the Schwinn seemed to be reasonably well-built, with decent components, though certainly not lightly built.
Answer: One of our bikes is an electric bike.  It's an older iZip HG 1000, and although we got it through the American "manufacturer" (Currie Technologies), like most of the low-end ebikes it's made in China of heavy steel and uses cheap, cheap, cheap components.  For example, it has these awful band brakes because they're slightly cheaper than cantilevers.  (Those pics are not of my bike.)
When we bought it a couple years ago, most of the department stores (WalMart, Zeller's, Canadian Tire) had bikes of similar (low) quality available under a variety of brand names - iZip and Schwinn (both also from Currie) were the most common.
However, even though I've always referred to our ebike as a cheap, made-in-China piece of junk, in the first 6 months we had it I commuted 40km a day and put 2500km on it.  It hasn't been used as much since then, but it's still going.  OTOH, it has required some work...  For various reasons, it has a two-part drive-train: a short chain from the cranks to an intermediate sprocket, then another chain from there to the freewheel.  As shown in the following picture, I managed to shear off all 4 bolts that held the two cogs on the intermediate sprocket together.  (And to get access, I first had to take apart 4 or 5 pieces of plastic bodywork.)

So it comes down to: you get what you pay for.  If you don't abuse it, a cheap ebike might do ok, but fundamentally it's made with heavy, low-quality steel, and cheap components.  Bikes like that can be serviceable, but are simply not very good.
One brand that seems to be associated with somewhat higher-quality bikes is BionX.  I think they are still mostly a supplier of LiIon battery packs, motors and controllers, and many different companies sell ebikes built with BionX drive systems.  You could look for local dealers who sell bikes made with their components.  I'm sure there are other companies that supply drive systems to bike shops.
Answer: Trek makes some electric assist bikes. Although I've never ridden one of their electric bicycles, Trek is known for making high quality bicycles.  Definitely one of the brands you should look into depending on your budget. The base price as listed on their website is just a little over $2000.  So much more than the Walmart electric bikes, but you get what you pay for. I've seen them in the bike stores up in Canada, and that link is for their US site, so they shouldn't be too hard to find a store that carries Trek bikes.  Their electric bikes basically look a lot like their commuter or hybrid bikes, with an electric assist motor attached. The FX Plus Electric, to me looks like the 7.5 FX with slightly different components, and an added electric motor.


How were the scenes with Gazelle shot?

Question: In Kingsman: The Secret Service Gazelle is disabled. I was surprised to discover that the actress playing the role (Sofia Boutella) is not. How were the scenes with her shot? Did she actually wear limbs, or had a stunt double, or it's just special effects?
Answer: They likely had Sofia Boutella wear special socks/coverings and added the assasin prosthetics later.
Effects like this have been achievable for quite some time now, as shown by the special effects shots of Gary Sinise as Lt. Dan in the film Forest Gump. Sinise wore blue socks during filming, and his legs bellow the knee were digitally removed in post production. For some scenes they may have used a double that was also a double amputee, but given how far special effects have come since then, and the level of action required, I doubt this is the case.
Comment: Note too that most shots of her did not show her blade-feet-prosthetics. Most shots framed her from the knee up, waist up, or shoulders up. In those shots no visual special effects were required, but the sound editor would need to include the unusual sound of her prosthetics touching the floor as she walked, in order to keep up the illusion for the audience.
Comment: You're exactly right - they used green stockings with reflective dots to allow for post dimensioning to help with the animation plus also used computer controller cameras so that they could get a matching 'background-only' plate as the metal lets were inherently thinner than the actresses.
Comment: You can see the chroma socks in one of the [videos here](http://www.fxguide.com/featured/kingsman-not-so-secret-effects/).
Comment: Very true, and likely done to cut down on the amount of special effects shots that would be needed, likely to allow more time and money to be devoted to the action sequences which would require tons of work to look and feel right.
Comment: I love this actor, but I can never remember his name. Sorry Gary, I'll always refer to you as "Lieutenant Dan".
Comment: How do I accomplish this effect by myself in Final Cut Pro or Premiere?
Answer: The actress (Sofia Boutella) did do all the scenes shot, but in blue leggings. Later the special effects team put the prosthetic rapier (like) legs to finish off the shots.
Comment: What value does it adds to existing answer?

How were the scenes with Gazelle shot?


Tor hidden services

Question: If i host a server as a tor hidden service what happens if that server needs to download an update or something else? Does it all go trough Tor just like it was a client? And the exit relay can see what the server is downloading?
Answer: There are three separate questions here :

Will my server download updates over Tor?

You could configure it either way, but the hidden service setup has nothing to do with the server downloading updates.  I believe almost all instructions for setting up hidden services will only discuss the hidden service, not downloading updates over Tor.

If my server downloads updates over Tor, and runs a hidden service, then can these activities be linked by an exit node?

No, there is no exit node in hidden service circuits, so no attack vector here.

If my server downloads updates over Tor, then how secure are the downloads?

All depends upon what the update procedure is.  I donno if Debian, or other distributions, restrict themselves to https or might ocasionally fall back to ordinary http.  All Debian packages should include hashes that prevent tampering.
A question you did not explicitly ask : How do I make my server download updates over Tor?
I'm dubious that servers should ever do OS level transparent proxying.  I'd rather run an https proxy like privoxy and selectively configure tools like apt-get to use it, thus controlling exactly what connects to the outside world via tor.
If you've basic stuff working over tor, then you should consider enabling iptables rules build by ferm or whatever that prevent outbound connections, except from the debian-tor user, or whoever that runs the tor process.
At that point, you could observe clearly what OS services now fail due to the iptables rules.  You can go through these individually and choose if they should run over tor or not, depending upon your threat model.
In particular there might be subtleties in configuring NTP securely either over Tor or not over Tor when hosting a hidden service.
Answer: All traffic is routed throug tor only if you are using transparent proxying on OS level.
For a the most common setup the webserver will pull updates and such through the regular internet connection.
So unless you have set up the machine for transparent proxying a exit relay cannot see what updates are getting requested.
There is more information about the transparent proxy setup here:
https://trac.torproject.org/projects/tor/wiki/doc/TransparentProxy
Answer: Normally, no.
There is nothing special about a hidden service. It is just a normal (web?)server. It may even be accessible via the clear net.
The actual 'hidden service' is the Tor instance that points to it. It provides access to the service through the Tor network.

Tor hidden services


Alternative to Python's Naive Bayes Classifier for Twitter Sentiment Mining

Question: I am doing sentiment analysis on tweets. I have code that I developed from following an online tutorial (found here) and adding in some parts myself, which looks like this:
#!/usr/bin/env python

import csv, string, HTMLParser, nltk, pickle
from sklearn.feature_extraction.text import TfidfVectorizer
from sklearn.naive_bayes import MultinomialNB

test_file = 'Dataset/SmallSample.csv'
#test_file = 'Dataset/Dataset.csv'
csv_file = csv.DictReader(open(test_file, 'rb'), delimiter=',', quotechar='"')

pos_tweets = {}
neg_tweets = {}

for line in csv_file:
    if line['Sentiment']=='1':
        pos_tweets.update({(line['SentimentText'],"positive")})
    else:
        neg_tweets.update({(line['SentimentText'],"negative")})

tweets = []
labeltweets = []
for (text, sentiment) in pos_tweets.items() + neg_tweets.items():
    text = HTMLParser.HTMLParser().unescape(text.decode('utf-8'))
    remove_punctuation_map = dict((ord(char), None) for char in string.punctuation)
    cleanedText = [e.translate(remove_punctuation_map).lower() for e in text.split() if not e.startswith(('http', '@')) ]
    shortenedText = [e for e in cleanedText if len(e) >= 3]
    tweets.append((shortenedText, sentiment))

# Produces list of all words in text of tweets (including duplicates).
def get_words_in_tweets(tweets):
    all_words = []
    for (text, sentiment) in tweets:
        all_words.extend(text)
    return all_words

def get_word_features(wordlist):
    # This line calculates the frequency distrubtion of all words in tweets
    # e.g. word "love" appears 5 times, word "dog" appears 3 times etc.
    wordlist = nltk.FreqDist(wordlist)
    word_features = wordlist.keys()
    # This prints out the list of all distinct words in the text in order
    # of their number of occurrences.
    return word_features

word_features = get_word_features(get_words_in_tweets(tweets))

def extract_features(document):
    setOfDocument = set(document)
    features = {}
    for word in word_features:
        features['contains(%s)' % word] = (word in setOfDocument)
    return features

training_set = nltk.classify.apply_features(extract_features, tweets)
classifer = nltk.NaiveBayesClassifier.train(training_set)

The code imports a large csv file and creates two dictionaries out of it, depending on whether the tweet is positive or negative. It maps these dictionaries like so:
("United won a !game today", "positive")

The for loop that follows this performs basic HTML stripping for unescaped syntax and removes all punctuation and words less than length of three, combining these into one large list, with this format:
(["United", "won", "game", "today"], "positive")

It then creates a list of just the text words (ignoring the positive/negative sentiment) and uses the nltk FreqDist method to create a frequency distribution of all words used like this:
<FreqDist:
    'this': 6,
    'car': 2,
    'concert': 2,
    'feel': 2,
    'morning': 2,
    'not': 2,
    'the': 2,
    'view': 2,
    'about': 1,
    'amazing': 1,
    ...
>

and then removing the accompanying numbers, just leaving the "word features".
The method extract_features then compares the tweet input to a list of words, like this:
Input: ['love', 'this', 'car']
Output:
{'contains(not)': False,
 'contains(view)': False,
 'contains(best)': False,
 'contains(excited)': False,
 'contains(morning)': False,
 'contains(about)': False,
 'contains(horrible)': False,
 'contains(like)': False,
 'contains(this)': True,
 'contains(friend)': False,
 'contains(concert)': False,
 'contains(feel)': False,
 'contains(love)': True,
 'contains(looking)': False,
 'contains(tired)': False,
 'contains(forward)': False,
 'contains(car)': True,
 'contains(the)': False,
 'contains(amazing)': False,
 'contains(enemy)': False,
 'contains(great)': False}

Finally, the line:
training_set = nltk.classify.apply_features(extract_features, tweets)

is used to build this training set of data from all provided tweets, breaking them down like this:
[({'contains(not)': False,
   ...
   'contains(this)': True,
   ...
   'contains(love)': True,
   ...
   'contains(car)': True,
   ...
   'contains(great)': False},
  'positive'),
 ({'contains(not)': False,
   'contains(view)': True,
   ...
   'contains(this)': True,
   ...
   'contains(amazing)': True,
   ...
   'contains(enemy)': False,
   'contains(great)': False},
  'positive'),
  ...]

This information is finally fed in to the trainer, like so:
classifier = nltk.NaiveBayesClassifier.train(training_set)

When I ran this on my sample dataset, it all worked perfectly, although a little inaccurately (training set only had 50 tweets). My REAL training set however has 1.5 million tweets. I'm finding that using the default trainer provided by Python is just far too slow.
Is this too large a dataset to be used with the default Python classifier? Does anybody have any suggestions or alternatives that could be used to do this operation? In all responses please bear in mind I could only accomplish this with a tutorial and am totally new to Python (am usually a Java coder).
Original SO post
Comment: What did you end up doing here?
Answer: take a look at the answers in
Is there a rule-of-thumb for how to divide a dataset into training and validation sets?

"If you have 100,000 instances, ... indeed you may choose to use less training data if your method is particularly computationally intensive)."

Good luck!


Why doesn't New Horizons have a tracking function

Question: Dr. John Spencer mentioned in the live feed for the Ultima Thule flyby they're taking a series of LORRI shots along a precomputed path hoping to capture the KBO. What were the obstacles to equip the spacecraft with object tracking capability?
Comment: flying 10km/s and passing 3600km above some object looks exactly like flying 10km/h and 1km above another (and smaller) object, so, no, i do not expect this to be a part of the problem
Comment: Object tracking at a few km/h and object tracking at a few km/s are quite different technological challenges. I expect this to be part of the problem.
Comment: Possible duplicate of https://space.stackexchange.com/questions/33139/using-ai-on-deep-space-probes-to-select-targets-of-opportunity
Comment: @AlexHajnal not at all a duplicate. Tracking capability doesn't need AI, we've had IR-guided tracking of high relative motion objects for [sixty years](https://en.wikipedia.org/wiki/1960_U-2_incident#Event) that used no (digital) computer at all. So it's quite reasonable to ask why a 21st century craft doesn't do something a bit similar.
Comment: How so?  The machine is making the decision itself; whether the means are analog or digital doesn't matter much.  I specifically discuss the New Horizons case in my question.  TLDR: It could have been done so but in the as-launched configuration it would be awkward to do.  If the science computer (C&DH) had a tad more RAM or the flight computer (G&C) had direct access to the science data flash memory then the task would be a lot easier to do (and quite feasible in my opinion).
Comment: Yea, I changed the title because "AI" seems to have the wrong connotation.  I use the term "AI" to refer to any case of a machine making a decision on its own. This question is also more specific than mine so on second thought it's not a duplicate IMO.
Comment: @uhoh I've tweaked it a bit. Better?
Answer: New Horizons has an object tracker, a star tracker needed for navigation and attitude control.
There are two redundant A-STR star trackers. 10 times per second a wide area image of the background is taken and compared to a stored star chart containing 3000 stars.
Only bright stars may be used to get an image with a short exposure time. Faint stars and Kuiper belt objects are too dark to be imaged by this star camera in a short time.
The LORRI camera used for the many excellent pictures of Kuiper belt objects has a very small field of view: 0.29 degrees and needs long exposure times of 1 up to 30 seconds.
The detection of unknown Kuiper belt objects using LORRI is very difficult due to the very small field of view and the necessary long exposure time. To assemble a very moderate wide angle view of 30 ° width and height, about 10700 single images are needed for the mosaic. For detection of unkown objects, a series of such images should be compared to find tiny differences caused by the moving objects between the many fixed stars.
Comment: I'm not sure this is quite the point. As I understand it, the question is asking about tracking 2014MU69 during the encounter to optimise pointing and minimize "wasted" exposures where  the KBO is not in view.
Answer: TLDR: It probably would be possible but would only be feasible during the approach phase.

In theory the New Horizons probe probably could do so.  In practice is would be awkward to implement and would likely negatively impact data collection.
New Horizons has two computers (plus one spare for each). The first is "Command and Data Handling" (C&DH) which handles the science instruments, science data storage, radios, and system health monitoring.  The second is "Guidance and Control" (G&C) which handles power, navigation (star and sun trackers, IMUs), attitude control, propulsion, and thermal control.  Each computer is similar in specs to a ca. 1989 workstation (SGI Personal Iris 4D/20 or /25) with a 12 MIPS1 CPU and 16MB of RAM2.  While there is some very detailed information available on these systems there are also a lot of big gaps.  This makes it hard to definitively answer but I'll do my best.
1 I've seen this given as 15 MIPS but the R3000 CPU isn't superscalar.  They may be underclocked 15 MHz parts.
2 At least for the G&C; I suspect that the C&DH has about the same.
Raw CPU
The most obvious bottleneck is the CPU.  The CPU used is essentially a pipelined MIPS R3000 CPU that (ideally) can retire one instruction per clock cycle.  Let's look at a toy example to see whether it's up to the task.  Let's scan an image buffer and do something for non-zero pixels; in (non-ideal) MIPS assembly:
<code>      LA   $1, buffer      # Load buffer start address (to register 1)
      LI   $2, size        # Load buffer size in pixels (to register 2)

loop: LHU  $3, ($1)        # Read one pixel of image data (to register 3)
      BEQ  $3, $0, cont    # Skip processing for zero pixels (register 0 is always 0)
      JAL  do_something    # Call subroutine for non-zero pixels
cont: ADDU $1, $1, 2       # Increment buffer pointer (16-bit pixels)
      SUBU $2, $2, 1       # Decrement length
      BGTZ $2, loop        # Loop if we still have data to process
</code>
Let's assume that all code is cached, that we never encounter pipeline stalls, and that all loads are free.3  The above loop would then average 6 clock cycles to examine one pixel so at 12 MHz we can look at 2 million pixels or about two sparse 1024×1024 LORRI frames every second.  Actually doing something useful would probably be at least an order of magnitude slower.  So a bit slow but certainly feasible.
3 This is unrealistic but good enough for a very rough estimate.
Memory
Any new program added takes up memory and New Horizons only has 768kB of RAM devoted to program storage on each processor.  Any image analysis program added would need to small so as to not impinge on other programs.  Since there's always a trade-off between size and speed any added program would likely favor small and slow.
Image processing can require a lot of memory.  One frame from LORRI takes about 2×1024×1024 bytes (2MB).4  The NH computers only have about 16MB5 of RAM6 each so even a single image buffer takes up a lot of space.  I would think that in its as-launched configuration RAM is likely at a premium especially since the system already likely needs large buffers for IO and compression.  The CPUs do support up to 256MB of DRAM or 192MB of SRAM so NH could have been designed with enough RAM for in-depth image analysis but probably doesn't actually have it.  More RAM would have resulted in higher power requirements, higher total system cost, and greater chance of system failure, all good reasons to keep RAM to a minimum.  Though RAM would probably be too scarce to do non-trivial image processing during a flyby it might be possible during approach when large IO buffers aren't needed.
4 LORRI actual uses 12-bit words, not 16, but 16 is easier to process so I'll use that.
5 I've actually only found a value for the G&C but let's assume they're similar.
6 It's not clear whether this is DRAM or SRAM.
Real-time multitasking
The New Horizons computers run multitasking operating systems yet are also real-time systems.  Care must be taken not to overload the system and to avoid deadlocks or resource starvation.7  There are mitigation techniques and NH implements some of them8 but heavy processing (even as a low-priority task) is still something to avoid during critical mission phases.
7 This isn't just theoretical; on July 4, 2010 NH experienced an overload while concurrently recording new commands to flash and compressing science data.  The system went into failsafe mode and about 30 observations were lost.
8 For example, New Horizons won't go into safe mode during a flyby.
Limited bandwidth
Though New Horizons has two computers, sharing bulk data between them is slow.  The cameras are connected to the C&DH and its only connection to the G&C computer is a 1Mb/s bus9 that is shared by all subsystems on the G&C side.  Assuming exclusive use of the bus, a single LORRI frame would take about 15 seconds to transfer.  Offloading image processing tasks to the second processor (G&C) could thus be possible but would be slow and might be impractical in practice.
9 As with many of the numbers quoted here, this value is a best guess based on multiple sources.
Software
The image analysis software would need to be written and thoroughly tested.  There is limited program memory available so making it both small and fast could be a challenge.  Interaction with existing software and the impact of program-commanding maneuvers on thruster fuel consumption would need to be carefully considered.
Other solutions
Had the system design been changed before flight a number of other approaches could have been taken:

Allow G&C access to flash memory — As mentioned above, one option would be offloading image analysis to the second processor; this approach is hampered by the slow bus speed. One way to speed up data transfer between the sensor data (e.g. from LORRI) and the G&C computer would be to allow direct access by G&C to the 8GB flash memory holding the imaging data.  I see two issues with this: 1) Added complexity and new point of failure in a critical area (the flash memory holds all the science data) 2) Any flaws in software, hardware, or the interaction of the two systems could destroy the data gathered.  I think therefore that this approach would be unlikely.

Dedicated processor card — The C&DH has a standard PCI bus and an dedicated card could be added to handle object search and tracking.  Such a card could have a full computer on-board including dedicated processor and RAM10 and would run little risk of impacting the rest of the C&DH's operations.  Being on C&DH's high-speed bus would make image transfer fast and easy.  Some of the downsides to this approach are higher power budget, thermal considerations, and of course development and hardware cost.
10 The various instruments already have similar systems embedded.

Dedicated subsystem (sensors and processor) — A dedicated subsystem could have been added to the G&C side.  Placed on the G&C's bus, it would have its own dedicated processor and RAM as well as one or more cameras11.  Such a system could find and track targets on its own then, say, feed attitude control commands directly to the G&C computer.  Costs/benefit considerations are similar to those for a dedicated processor card with the caveat that costs would be much higher due to the dedicated imaging system.
11 New Horizons' star trackers are quite similar to this. Note that since the star trackers are absolutely critical it's highly unlikely that they would be modified to search for anything but stars.  Using similar hardware (perhaps with the addition of a narrow-field camera) with modified firmware could be an option though.

Conclusions
The computers and systems on New Horizons are limited in capability but in theory could be used to do simple object tracking.  Running a heavy algorithm such as target search during a flyby is probably not feasible.  Up until maybe 12 hours before flyby target selection and programming could be done from the ground.  This leaves the approach phase as the only time when on-board image analysis and targeting would be both feasible and useful.
New Horizons specifications
New Horizons block diagram

Source: New Horizons Launch Press Kit, p. 26, NASA/JHUAPL/SwRI
(cropped, enhanced, and highlighted)
All computers (and most subsystems) configured as redundant pairs.  Note that many of these subsystems are full computers themselves with the own CPU, RAM, etc.

Guidance and Control computer (red)
Responsible for attitude control, orientation sensing, power control, and thermal control
12 MHz Mongoose-V CPU, 16MB RAM (768kB for programs)
1MHz MIL-STD-1553 bus connecting to rest of system

Command and Data Handling computer (blue)
12 MHz Mongoose-V CPU, 16MB RAM (768kB for programs)
PCI bus for subsystem connections, connection (slave) to the G&C's 1Mb/s MIL-STD-1553 bus
Each C&DH has:

SSR — 64Gb (8GB) solid state recorder (dark blue) with up to 13Mb/s bandwidth
Instrument Interface card that connects to all science instruments.
ALICE, RALPH (MVIC and LEISA), and LORRI (the imagers) have high-speed LVDS links (purple) to each C&DH for image data.
All other connections are 480Kb/s RS-422 serial lines
Downlink Tx card for transmitting science data back to Earth and for conducting radio experiments

Science, radio, and health-monitoring systems (cyan)
Connect directly to the C&DH

Guidance, power and propulsion systems (yellow)
These (along with the C&DH) connect to the G&C over a 1Mb/s bus (green)

Mongoose-V functional blocks

Source: Synova via the Internet Archive
References and further reading

New Horizons Launch Press Kit
Covers all aspects of the mission
Spacecraft Overview
Nice overview of New Horizons' systems
Inside New Horizons
Another overview of the systems
The New Horizons Spacecraft  (doi:10.1007/s11214-008-9374-8)
Fairly detailed technical overview of New Horizons' computer systems
Mongoose-V 32-bit MIPS Microprocessor Architecture Description
The Mongoose-V is the radiation-hardened version of the MIPS R3000 CPU used on New Horizons
Star tracker scan mode capability for the New Horizons mission
Very interesting (but unfortunately paywalled) paper on the New Horizons star trackers
See here for how you might get a free copy
Answer: Excellent answer Alex, thank you.
For the technical implementation aspect I'd like to add 2 points:

it might be possible to forgo taxing the cpu and not processing full resolution LORRI images in
defining the target as a region at least a few pixels across and sampling a raster.
as there's already 2 star trackers in there, I imagine adapting one for the task should have been
possible at an acceptable time/cost overhead.

Speculating, I guess this wasn't implemented also because New Horizons was primarily conceptualized
as a Pluto exploration mission, for which a programmed exposure pattern was good enough -
the Kuiper Belt extension Alan Stern had to propose to NASA afterwards (he's a media savvy guy ;).
Nevertheless, it's quite a waste of valuable exploration (and downlink) time, even diregarding the risk
of a miss.
I also assume with precise position information, it would have been possible to compensate for motion blur,
thus enhancing resolution.
Comment: "sampling a raster": Devil's advocate asks how you decide where to sample.  Regarding the star trackers: AIUI, they're sealed units (like the rest of the instruments) and while they do have computers I don't believe there's any provision for changing the firmware after-the-fact ([more info](http://pluto.jhuapl.edu/Mission/Spacecraft/Systems-and-Components.php)), see also below.  "New Horizons was primarily conceptualized as a Pluto exploration mission" sums it up nicely IMO; anything beyond that was a bonus.  I do think this is an area worth researching though.
Comment: Very interesting (but unfortunately paywalled) paper on the New Horizons star trackers: **[Star tracker scan mode capability for the New Horizons mission](https://doi.org/10.1016/j.actaastro.2005.07.059)**  You might try emailing the author, etc. to get a free copy; [see here](http://holly.witteman.ca/index.php/2017/12/11/getting-access-to-paywalled-papers/) for other tips.


Book request for an abstract treatment of QM without using any particle formalism

Question: I am an electronics and communication engineer, specializing in signal processing. I have some touch with the mathematics concerning communication systems and also with signal processing. I want to utilize this knowledge to study and understand Quantum Mechanics from the perspective of an engineer. I am not interested in reading about the historical development of QM and i am also not interested in the particle formalism. I know things have started from the wave-particle duality but my current interests are not study QM from that angle. What I am interested is to start studying a treatment of QM from very abstract notions such as, 'what is an observable ? (without referring to any particular physical system)' and 'what is meant by incompatibility observables ?' and then go on with what is a state vector and its mathematical properties. I am okay to deal with the mathematics and abstract notions but I some how do not like the notion of a particle, velocity and momentum and such physical things as they directly contradict my intuition which is based on classical mechanics ( basic stuff and not the mathematical treatment involving phase space as i am not much aware of it).
I request you to give some suggestions on advantages and pitfalls in venturing into such a thing. I also request you to provide me good reference books or text books which give such a treatment of QM without assuming any previous knowledge of QM.
Comment: Why not sakurai?
Comment: Possible duplicate: http://physics.stackexchange.com/q/5014/2451
Answer: An unconventional approach would be to study quantum computation or quantum information theory first.
What is 'unusual' about quantum mechanics is the mathematical underpinnings, which is essentially a generalization of probability theory. (I have heard more than one colleague say that quantum mechanics is simply physics which involves 'non-commutative probability', i.e. in testing whether some collection of events are realized for some sample space, there is a pertinent sense of the order in which one tests those events.) To the extent that this is true, it is not important to be learning the actual physics alongside that mathematical underpinning, so long as you can learn about something evolving e.g. under the Schrödinger equation or collapsing under measurement.
Studying quantum information evolving under a computational process is one way you could achieve that. Because the narrative of the field is less about the crisis in physics in the 20s–40s, and more about physicists and computer scientists struggling to find a common language, the development is clearer and there is a better record of justifying the elements of the formalism from a fundamental standpoint. By studying quantum information and/or quantum computation, you will be able to decouple the learning of the underpinnings from the learning of the physics, and thereby get to the heart of any conceptual troubles you may have; and it will give you a tidier sandbox in which to play with ideas.
To this end, I recommend "Nielsen & Chuang", which is the standard introductory text of the field. It's suitable as an introduction both for those coming from a computer science background, and from a quantum physics background; so apart from learning some of the formalism, you can get some exposure to some of the physics as well. There are other texts which I have not read, though; and about a bazillion pages of lecture notes floating around on the web.
Answer: Try "Mathematical Foundations of Quantum Mechanics" by George Mackey. It is about 130 pages with a chapter on classical mechanics. The author is a very well know mathematician, and I think the books is what you are looking for. Also on higher level is the book "Quantum mechanics for mathematicians" by Leon Takhtadzhian. The book by Folland on Quantum Field Theory has a chapter on Quantum Mechanics, which can be read independently of the rest of the book.
Edit: Since this came up on the first page, I'll add one more. F.Strocchi "An Introduction to the Mathematical Structures of Quantum Mechanics. A Short Course for Mathematicians."
Answer: I strongly advise you Quantum Theory: Concepts and Methods by Asher Peres.
I think this book is answering the questions you're asking. Like 'what is an observable ?'
Answer: That's quite an unusual request i.e. to start with an abstract formulation of quantum mechanics, especially for someone in a profession so closely connected with the "real world".  However, to answer your question, I think what you're looking for is an axiomatic approach to quantum mechanics.  Such treatments will keep the physical examples to the minimum and skip to the mathematics straight away.
You could start with this reference (just for a chatty treatment of what the postulates look like !), and maybe search for quantum mechanics textbooks with "axiomatic" in the title.
For many people, the fact that the quantum mechanical predictions of physical quantities  are sometimes counterintuitive is precisely what gives the subject its appeal.
Hope this helps.
Edit:  It appears not so easy to find "Axiomatic Quantum Mechanics" in textbook titles !  However Google returns a few articles featuring those words.
Of course there is also Von Neumann's "Mathematical Foundations of Quantum Mechanics".
Answer: You might find articles by Leon Cohen of interest. He has considered the relationship between classical and quantum theory from a signal processing since the 1960s. For example, PROCEEDINGS OF THE IEEE, VOL. 77, NO. 7, JULY 1989, "Time-Frequency Distributions-A Review". This concentrates on the relationship between the Wigner function in quantum theory and various concepts in signal processing.
This might not answer your question so much as point to something that you might find more broadly helpful because of its signal processing provenance. The mathematics of Hilbert spaces only enters into a small fraction of the signal processing literature, but the vast majority of it could be put into such mathematical terms (signal processing is, after all, preoccupied with Fourier and other integral transforms).
Answer: I always recommend Tony Sudbery's Quantum Mechanics and the Particles of Nature, don't be put off by the bad word in the title: he is fairly axiomatic and has both the abstract part and the concrete part.  I recommend them more highly than either Mackey, already cited, or Varadarajan, both of which are idiosyncratic.  Prof. Sudbery is an expert in Quantum Information Theory but does not take a biassed or idiosyncratic approach in his text.
Answer: Here is a little book by a physicist trained as an engineer in fluid dynamics applied to aircraft:
"Foundations of Quantum Physics" by Toyoki Koga (1912-2010), Wood and Jones, Pasadena, CA, 1980.
This book has forewords by Henry Margenau and Karl Popper.
Another book by him is "Inquiries into Foundations of Quantum Physics", 1983.


Quantum mechanics as classical field theory

Question: Can we view the normal, non-relativistic quantum mechanics as a classical fields?
I know, that one can derive the Schrödinger equation from the Lagrangian density
$${\cal L} ~=~ \frac{i\hbar}{2} (\psi^* \dot\psi - \dot\psi^* \psi) - \frac{\hbar^2}{2m}\nabla\psi^* \cdot \nabla \psi - V({\rm r},t) \psi^*\psi$$
and the principle of least action. But I also heard, that this is not the true quantum mechanical picture as one has no probabilistic interpretation.
I hope the answer is not to obvious, but the topic is very hard to Google (as I get always results for QFT :)). So any pointers to the literature are welcome.
Comment: These are quantum field theory notes, but they discuss your question http://www.damtp.cam.ac.uk/user/tong/qft.html page 9.
Comment: The Schroedinger lagrangian defines a non-relativistic quantum field theory, which is equivalent to many-body quantum mechanics. You may ask whether this field theory has a classical limit. It does, under the usual condition (the states have to be highly occupied). This means that you should look to Bosonic states, for example the case that $\psi$ describes an integer spin atom.
Comment: related: https://physics.stackexchange.com/q/357091/226902
Answer: You certainly couldn't recover quantum effects with a classical treatment of that Lagrangian.  If you wanted to recover quantum mechanics from the field Lagrangian you've written, you could either restrict your focus to the single particle sector of Fock space or consider a worldline treatment.  To read more about the latter, look up Siegel's online QFT book "Fields" [hep-th/9912205] or Strassler's "Field Theory without Feynman Diagrams" [hep-ph/9205205] for applications of the technique.
Answer:
Can we view the normal, nonrelativistic quantum mechanics as a classical fields?

Yes, you can view the wave function $\psi(x,t)$ as an ordinary complex-valued field in the spirit of, say, classical electrodynamics. This field describes the quantum mechanics of a single electron, but it is classical in the sense that it's an ordinary function $\psi(x,t) : \mathbb R^3\times\mathbb R \to \mathbb C$.
As usual, you can have a lot of fun with the Lagrangian. For instance, you can note that there it has a (global) $U(1)$ symmetry $\psi \mapsto e^{iθ}\psi$ and apply the Noether theorem. You will find a continuity equation for the quantity $\psi^*\psi$, which we commonly interpret as the probability density.
Of course, the Schrödinger equation is limited to non-relativistic physics, so people started to look for a relativistic equivalent. Dirac's eponymous equation was intended to be precisely that: an equation for a classical field that describes a quantum mechanical electron in a Lorentz-covariant way. Of course, there should be an equivalent of the probability density $\psi^*\psi$, which is always positive, but no matter how you spin it, this just didn't work out, even for the Dirac equation.
The solution to this problem is that electrons don't live in isolation, they are identical particles and linked together via the Pauli exclusion principle. Dirac could only make sense of his equation by considering a variable number of electrons. This is where the classical field $\psi$ has to be promoted to a quantum field $\Psi$, a process known as second quantization. ("First quantization" refers to the fact that the classical field $\psi$ already describes a quantum mechanical particle.)
It turns out that second quantization is also necessary to explain certain corrections to the ordinary Schrödinger equation. In this light, the classical field $\psi$ is really an approximation as it does neglect the influence of a variable number of particles.
The process of considering a variable number of particles is actually quite neat. If you go from one to two particles, you would have to consider a classical field $\psi(x_1,x_2)$ that depends on two variables, the particle positions. Going to $N$ particles, you would have a field $\psi(x_1,\dots,x_N)$ depending on that many variables. You can get all particles at once by considering an operator valued field $\Psi(x)$ instead, which creates a particle at position $x$. It turns out that you can just replace $\psi$ by $\Psi$ in the Lagrangian to get the right equations of motion for all particles at once.
Alas, I have to stop here, further details on second quantization and quantum field theory are beyond the scope of this answer.
Concerning literature, I found Sakurai's Advanced Quantum Mechanics to be a very clear if somewhat long-winded introduction to quantum field theory that starts where the Schrödinger equation left off.
Comment: As I know your statement that Dirac equation has negative probability density is totaly wrong, it is actually positive, but it is true that Klein-Gordon equation had negative one, and one of Dirac's goals was to solve that, but the problem Dirac had is negative energies, and that was solved by considering antimatter, not the exclusion principle.
Comment: You have to say specifically that this fails for two electrons. That's the whole thing that makes quantum mechanics different from classical field theory.
Answer: Indeed, the true Lagrangian for the Schrödinger equation takes this from
$${\cal L}=i \hbar\psi^*\dot\psi-\frac{\hbar^2}{2m}|\nabla\psi|^2-V({\bf x},t)\psi^*\psi$$
and the action becomes
$$S=\int dtd^3x{\cal L}.$$
A Lagrangian for the Schrödinger equation has a meaning only in a quantum field theory context when you do a second quantization on the Schrödinger wavefunction. This applies in a lot fields and mostly in condensed matter and, generally speaking, to many-body physics. In this case, you have to generalize this equation to the Pauli equation and work with spinor and anticommutation rules to describe ordinary matter.
Then, the probabilistic interpretation applies to the states in the Fock space for the many-body problem you are considering.
Answer: I am no expert in classical fields, but I guess you have no entanglement there, that is, there is no difference with a single particle, but there is a big difference with more than one.
Answer: Tong's lecture notes cover this in detail. In particular, your lagrangian is easy to obtain from a complex scalar field that obeys the Klein-Gordon equation in the non-relativistic limit. This lagrangian does lead to a conserved Nöther current of the same form as that of Schrödinger's, but this does not have the interpretation of conserved probability, because $\psi \psi^*$ is not the probability density for a particle to be in specific position at specified time. In order to obtain QM, you'll need to quantize the field, construct the wave-function as the superposition of single-particle position states, then obtain the hamiltonian and the Schrödinger equation.


How can I make my flash website more search engine friendly?

Question: I've got a website where just about all the content is in a flash movie. Is there anything I can do to improve my search engine ranking or make my content more indexable?
Comment: Rebuilt it in HTML + CSS + JS. :) Just kiding, but it would be definitely more search engine friendly.
Answer: Yes you can. This article explains it fairly well.
http://www.actionscript.org/resources/articles/1007/1/Flash-SEO-Best-Practice/Page1.html
My opinion on the matter (take it or leave it)
It is a real pain in the butt in my opinion. I would highly advise you to abandon an all-flash website. Take the time you would put into making it SEO-friendly and rebuild it using HTML.
Answer: A few links on Flash SWF file indexability:

SWF searchability FAQ (Adobe)
Flash and other rich media files (Google)

What Google has to say is:

Google can now discover and index text
  content in SWF files of all kinds,
  including self-contained Flash
  websites and Flash gadgets such as
  buttons or menus. This includes all
  textual content visible to the user.
  Google supports common JavaScript
  techniques. In addition, we can now
  find and follow URLs embedded in Flash
  files. We'll crawl and index this
  content in the same way that we crawl
  and index other content on your
  site—you don't need to take any
  special action. However, we don't
  guarantee that we'll crawl or index
  all the content, Flash or otherwise.

I've never seen significant search traffic to Flash files.
Comment: I can confirm that terms *only* inside a flash file will show up in Google searches though. I was amazed the first time I saw that. It is rare for this to be useful outside the "gee whiz it works!" factor though.
Answer: When a bot comes to your page you can display all the text contained in the flash instead of the flash. This way you will be able to select what text will be index and your page will have content associated to it.
Comment: Technically this is bad. You maybe flagged by Google if you display different content to them vs users.
Comment: I'm thinking about it again, and that's indeed a bad idea. I'll just leave it as an exemple of what not to do.
Comment: -1 for 'cloaking'. See http://www.youtube.com/watch?v=kFOgZjbX9NU&feature=player_embedded. Cloaking is bad mmmkay. Note: if you don't know who Matt Cutts is, google him.


Why do I need 125 reputation to downvote but only 15 to upvote?

Question: I've been looking at the reputation tab recently and I noticed that to upvote, you need 15 reputation, but to downvote, you need 125 reputation. Why do you need so much more reputation to downvote than to upvote?
Comment: On MSE: https://meta.stackexchange.com/questions/178529
Comment: And by the way, you may be interested in this help center page: https://stackoverflow.com/help/privileges
Comment: @qqqqq there is a daily vote limit of 30 (up and down) with an additional 10 for questions. See https://stackoverflow.com/help/privileges/vote-up
Comment: My view is surely colored by my own rep and rep history, but from where I'm standing, the difference between 15 and 125 rep is large only in a relative sense.  110 rep isn't that much.
Comment: Is/should there be an upper cap (daily/weekly/monthly/)on down votes ?
Comment: Why have voters deleted the answers? Is it appropriate to vote to delete any answer that we disagree with, even if accepted?
Comment: @user000001 Not a single one of the deleted answers make any kind of sense.
Answer: Downvoting indirectly moderates users to an extent, and this power should not be given lightly.
There are, today, 1.7 million accounts which can upvote posts, and only 580,000 accounts which can just downvote today (reference - SEDE query).
Because downvotes do directly impact a user's ability to post questions or answers - Stack Overflow moreso than any other site on the network - allowing 1.7 million people to suddenly participate in downvoting others would be a significant problem, since there's no guarantee that those downvotes wouldn't just be out of spite.
Worse yet, it doesn't take much in the way of effort to get to 15+ reputation, so mass downvotes could be orchestrated in a more efficient and coordinated way.
It's too much power to give someone who barely understands its long-term impact.
Comment: @dwirony yes. 100 is the [association bonus](https://meta.stackexchange.com/questions/141648/what-is-the-association-bonus). Requiring 125 reputations means users who are part of one community on the SE network must at least put in some effort to participate in another community before downvoting there.
Comment: @MarkD:  The vote was likely appropriate.  Up or downvotes represent usefulness or lack thereof, respectively.  Your answer was useful when it was posted to it was worth upvoting.  Your answer is not useful now, so it's a likely candidate to be downvoted.  You could always add a disclaimer that this is how it was in an older version of whichever software/technology you were using, but outside of that, I wouldn't deride others for using the system to indicate the true value/usefulness of content.
Comment: I have been downvoted because my answer is out of date  (1 years later).  This can occur if say the post is about a bug in a service and that bug was fixed.  My post now looks like it is wrong.  I don't see a way to mark a question or answer as out of date. That would help prevent some unnecessary downvotes and loss of reputation.
Comment: @Braiam:  Anonymous users and anonymous posts are anymore treated like red-headed stepchildren.  They exist but the amount of concern I as an average Metahound give them is a rounding error on even the most sympathetic of days.
Comment: Upvoting directly moderates a user, too.
Comment: "since there's no guarantee that those downvotes wouldn't just be out of spite." note that anonymous users, don't have this problem.
Comment: @Matoko Is there any significance of 125 rep? Why not 100 or 200, for example?
Comment: @makato, good advice and that is what I do now - I add a comment.  I guess there is some confusion in me between the value of my questions (that can be downvoted to -1) and my reputation. The other side is the ranking of usefulness and I agree with your point.  Take .net  4.6.0 and 4.6.1.  If my answer pointed out an issue in 4.6.0, then that remains valuable for anyone using 4.6.0.  It could be downvoted because 4.6.1 fixed the issue though.  As your suggestion, I can clarify that in an update.  I'm good with your answer (and I won't downvote it :-) )
Comment: One of the few times I've downvoted one of your posts. I cannot understand why would we trust someone who doesn't know the site to say "this is useful" but not to say "this is not useful". People upvote crap and downvote excellent answers. BTW, massive upvotes/downvotes are dealt with pretty quickly, so I don't understand that point either.
Answer: An upvote signifies that a post was useful.  A downvote is more complicated.  It can signal deviation from "community standards".  It can also indicate that a post has a flaw.
Anyone can find something useful, and we want to encourage new folks to become part of the community.  But, before you can start criticizing other folks' posts, you really need to prove that you know a little about those standards and that you've spent a little time on the site.
It doesn't take long to earn 125 rep if you know a little about what you are talking about.  During that time, you learn what's acceptable and what's not just by taking part in the community discussion.  Until you do, you really shouldn't be downvoting other SO members.
Consider the real world.  If you work on a team, and you have, say, one year experience.  If you show your code to a senior team member and to a team member who joined last month (right out of school).  You'll accept compliments from the new team member, but you would be very doubtful of any negative feedback from someone with a three-month old bachelor's degree.  On the other hand, when you get criticism from that senior team member, you're likely to respond with: "thanks, that was a great catch".
Comment: If you're doubtful about validity of someone's feedback, what does it matter whether said feedback is positive or negative?
Comment: @DanMašek: Going back to the junior and senior members of the team I work on.  A junior member may be assigned a task, find some of your code, use it (either directly, or after modification) and then, the next day say in a stand up "I was able to get this done faster than I thought because of Flydog's code" - that's an upvote.  But, if the same member finds some code that's well documented and used in several places in the project, comments that it's not good because, I don't know, it's too abstract - well, then I may not think his/her comments are a valid downvote.