How do moons get captured?

Question: A moon-sized object is running loose in the Solar System, perhaps after a planetary collision.  As it approaches a planet, it's presumably following an approximately hyperbolic path.  If it goes on past, it's still on the same hyperbola, on a curve mirroring its approach (presumably).  How can the planet ever capture it, whatever the body's velocity?  Why doesn't it either collide or go on past?
Comment: Short answer: the Sun. The hyperbolic path is derived by solving the gravitational two-body problem. If Earth and Moon were the only two objects in the universe, then yes the Moon would have continued along that hyerbola. Once you add a third body into the mix, the resulting trajectories become radically more complicated.
Comment: @David H Thank you.  My own maths doesn't go beyond GMm/r^2 = mv^2/r, but putting it crudely, is it that the moon is 'swinging past' the planet but moving away from the Sun, so that the Sun's retarding effect converts the quasi-hyperbolic path into an ellipse?
Answer: How can a planet capture a moon?
There are 178 moons in the Solar System, according to the NASA Planetary Fact Sheet, so it seems to be a common event. The following sections will show that moon capture is actually unlikely, but when a planet has one or more moons capture becomes easier.
Initial Conditions
Starting from the initial conditions, the planet is in orbit about the sun, and an asteroid is in a different orbit about the sun.
In order for capture to become possible, the asteroid and the planet must come into proximity. When the asteroid comes inside the Sphere of influence of the planet, the gravity of the planet is the main factor in determining the path of the asteroid.
Possible Outcomes
Relative to the planet, the asteroid will be following a hyperbolic trajectory, and hence has sufficient kinetic energy to avoid capture. A large variety of outcomes may occur, but the ones that lead to capture are those where the asteroid somehow loses enough kinetic energy for its velocity to fall below the escape velocity of the planet while retaining enough energy to achieve a closed (elliptical) orbit. The main (not the only) possible outcomes are

the orbit of the asteroid is perturbed, by a greater or lesser extent, and it continues on its way out of the sphere of influence of the planet.
the orbit of the asteroid is perturbed, and the asteroid impacts the planet surface. That would usually be the end of the process, but current theories on how Earth captured the Moon are that a body named Thea impacted the Earth, and the Moon formed from some of the collision debris.
the orbit of the asteroid is perturbed, and the path of the asteroid intersects the atmosphere of the planet, losing kinetic energy as heat in the atmosphere (similar to aerobraking).
the orbit of the asteroid nears an existing moon of the planet and is accelerated (in the sense that deceleration is just acceleration with the opposite sign) by the existing moon, as used by the MESSENGER spacecraft to slow its speed before orbiting Mercury.

The last two cases admit the possibility of capture.
Possible Capture
After losing energy in the planetary atmosphere, if the asteroid has lost enough energy it may enter a closed orbit around the planet. The problem is that the orbit will intersect the atmosphere again, losing energy each time it does so, until it impacts on the planetary surface. Capture can occur when an existing moon is present and is in just the right place for its gravity to reduce the eccentricity of the orbit of the asteroid.
So, the most likely case where a planet can capture a free asteroid is when there is already one or more moons present. The incoming asteroid must avoid entering the Hill sphere of the existing moon - the region where the moon would dominate the path of the asteroid.
Gravity assist can accelerate an asteroid when the asteroid is passing outside the orbit of the moon, but can decelerate the asteroid is passing inside the orbit of the moon. In this case some of the kinetic energy of the asteroid is transferred to the moon. As is the case with aerobraking capture, gravity assisted capture requires the existing moon to be in just the right place.
Another mechanism
A rather elegant paper published in Nature (mentioned below) shows how two bodies orbiting each other as they approach the planet could have led to one being captured by Neptune. This mechanism could apply in other cases also. This Dissertation (pdf) discusses a similar process for Jupiter.
Irregular bodies
It turns out that irregular shaped bodies can be captured more easily than spherical bodies. Orbiting within the Hill sphere of the planet is not enough for capture to be permanent. Only orbits in the lower half of the Hill sphere are stable. Bodies in higher orbits can be perturbed by nearby planets, and the body can eventually be ejected. But irregular shaped bodies exert minute fluctuations in gravitational attraction on the planet, and actually orbit in a chaotic manor. When other moons or rings are present these chaotic orbits gradually transfer energy to the bodies in the lower orbits, causing the new body to orbit lower, and hence become immune to external perturbation. [citation needed]
Prograde vs retrograde orbits
The same analysis of chaotic orbits, and earlier work also concluded that retrograde orbits are more stable than prograde orbits. Whereas prograde orbits are only stable in the inner half of the Hill sphere, retrograde orbits can be stable out to 100% of the Hill radius. Hence retrograde capture is more commonly observed (this is not the whole story, it is still a matter if research).
Multiple existing moons, rings, and the early Solar System
While the probability of a single moon being in the right place at the right time is low, when there are multiple moons the probability of an initial helpful interaction rises linearly. But the probability of additional interactions rises geometrically, so the more moons a planet has the more likely it is to capture more. The existence of rings also aids capture by exerting a drag on the new moon, taking it's energy and lowering it's orbit, in much the same way that uncaptured gas would do in the early Solar System.
The biggest planets have the most moons
It may be obvious, but the biggest planets have the most moons. This is because they have deeper gravity wells, and sweep in more objects. Even though the probability of capture is low (most objects are just pulled into the planet), a steady trickle have have captured over millions of orbits.
Conclusion
Each capture mechanism requires a fortuitous set of conditions, and so is actually a quite rare event. One mechanism is a that a pair of co-orbiting asteroids become separated when one enters the planetary Hill sphere. The odds for an individual asteroid are improved when the asteroid arrives with low kinetic energy that must be given up to other bodies orbiting the planet, and when there are already many moons or a ring system.
See also

Could Earth's gravity capture an asteroid? - earthsky.org
Dynamics of Distant Moons of Asteroids - Icarus (pdf)
Hypothesis: New evidence on origin of the Moon support cataclysmic collision theory
Neptune's capture of its moon Triton in a binary-planet gravitational encounter - Nature
Planetary Fact Sheet - NASA
The use of the two-body energy to study problems of escape/capture (pdf)
Wikipedia
Aerobraking
Elliptic orbit
Escape velocity
Hill sphere
Hyperbolic trajectory
Gravity assist
Retrograde and prograde motion
Sphere of influence
Thea
Comment: Many thanks for such a thorough explanation. Evidently, the mechanisms that you describe do work, because when I first wondered about this in the 1960s, the Solar System had only 31 moons(!). Now flagged 'Answered'.
Answer: There are two effects that alter the simple hyperbolic (or elliptic) relative orbit of any minor body ("moon") and a planet.
First, the gravity of the Sun (and to a much lesser degree of Jupiter). To good approximation the planet-Sun system is a circular binary and the moon a test particle (its mass negligible). The orbits of test particles in such a system (known as the restricted three-body problem) are complicated, but the Jacobi energy, preventing capture (similar to the angular-momentum conservation for the hyperbolic orbit). Hence, capture requires deviation from this
approximation, in particular the moon's mass must not be too small and/or another  interacting body participates (the Wikipedia page on asteroid capture is quite disappointing).
Second, tidal forces can transfer orbital energy into internal energy (of the planet and/or moon), which is then dissipated (converted into heat). Under lucky circumstances this process can be sufficient to convert an unbound to a bound orbit. Once bound, tides will continue to bind the moon more and more.
Comment: Good answer, but the middle of the second paragraph (around the Jacobi energy mention) should be a little bit expanded for clarity.
Comment: And I personally would appreciate a source for the third paragraph (not because I doubt it, but because I was I was ignorant of it). I was aware of the dissipating effect of tidal forces on the Moon's spin-angular momentum, but I hadn't considered influences on orbital-angular momentum.
Comment: Thank-you, Walter.  That's a little beyond me, but I get the general idea, so I've marked it 'Answered'.
Comment: But usually you simply need another fourth body, or a mass of bodies, that number 3 can throw out to loose angular momentum. This at least is alot more probable/efficient in a your solar system, than the mentioned mechanisms.

How do moons get captured?


Is there an Indian equivalent to State of the Union speech?

Question: The US President usually gives an annual State of the Union speech during a Joint Session of the Congress. Is there an Indian equivalent to the US State of the Union speech?
Answer: In the Consistution of India, Article 87 states that,

(1) At the commencement of the first session after each general election to the House of the People and at the commencement of the first session of each year the President shall address both Houses of Parliament assembled together and inform Parliament of the causes of its summons.

This is likely the closest equivalent to the U.S. State of the Union, and according to PRS Legislative Research, the speech "essentially highlights the government's policy priorities and plans for the upcoming year" and "provides a broad framework of the government's agenda and direction."
The most recent address, as of the time of this post, appears to have been on January 29, 2018, given by President Ram Nath Kovind.
Comment: Note that a speech like this is common in parliaments modelled after the Westminster system. In the UK, it's called the Queen's Speech; in some Commonwealth realms, it's the Speech from the Throne. As in India, the purpose is the same: to set out the government's legislative agenda for the coming session.


How to prevent headphones from getting entangled?

Question: As a lot of people, I am using headphones daily in order to listen music, as I don't plan to buy bluetooth one, I was wondering if you had any lifehacks to prevent them from getting tangled everytime I put them on my pocket or in a bag.
Answer: After use:
Step 1. Grab both earbuds.

Step 2. Use your opposite hand to wrap the chord around the fingers you gripped the earbuds with leaving around two inched unwrapped.

Step 3. Remove the headphones from the hand
Step 4. Hold the headphones with your thumb and index finger.

Step 5. Using the excess cord wrap it in the middle
Step 6. Stick the last inch of the cord through the loop you just made. Now they're secure enough to put in your bag without getting tangled.
Comment: Well... this does not work. At least in my case. I usually try to tie my headphones this way before putting into pocket, and after some time the knot looks like the one on OP's image.
Answer: I use a plastic Ziploc bag, and leave the earbuds and the plug sticking out of the end. Then I close the "zipper" as far as it will go, leaving half an inch for the buds & plug. This prevents my cord from tangling, because none of the ends (bud #1, bud #2, or the plug) can pass through any loops in the rest of the cord.
I made a video about this years ago: https://www.youtube.com/watch?v=iV8LMekEy20


How to find the right Dhamma teacher

Question: The practice of Buddhism, as with any other spiritual development, largely relies on the guidance of a good master. With the large variety of traditions and practices out there, how should one go about looking for the right teacher to guide one along the (right) spiritual path? I have been to retreats conducted by teachers from the Theravada and Chinese Mahayana tradition, and I am interested to find out more about Tibetan Buddhism.
Comment: As I understand, this question is less about _picking_ a school and more about the "how" of "looking for the right teacher to guide one", i.e. about the mechanics of the search process, the places to look, - with the goal of finding personal guidance and not just generic lectures. @Sati, did I get this right?
Comment: Welcome again. This seems like a "broad comparison" question (if it's asking "Which is the best school and teacher for me?") -- see [Which type of Buddhism is for me?](https://buddhism.meta.stackexchange.com/q/393/254) where I asked if it's possible to ask that question.
Comment: Yes, you are right!
Answer: At this point I venture to say that the school one picks is largely irrelevant. It's much more about the teacher's ability to connect the map of the teaching with the jungle of your immediate living experience. Once you see how the two relate, you can start making progress. As was said in Kalama Sutta:

Come Kalamas. Do not go upon what has been acquired by repeated hearing; nor upon tradition; nor upon rumor; nor upon what is in a scripture; nor upon ... nor upon ... nor upon ... nor upon ... nor upon ... nor upon ... Kalamas, when you yourselves know: "These things are good; these things are not blamable; these things are praised by the wise; undertaken and observed, these things lead to benefit and happiness," -- enter on and abide in them.

The right teacher will capture your attention and inspire motivation by appealing to things that you yourself value high. Using samsaric inertia as the fuel and stepping stone, he or she will help you cut through habit and get a fresh look at obvious issues that you have been ignoring far too long. The right teacher makes you feel extremely uneasy AND inspired at the same time. Uneasy, because the teacher holds a mirror for you to see that you have been a fool all along. Inspired, because in front of your very eyes you see a perfect role model, a living example of what Dharma actually stands for, far beyond theoretical constructs.
In my experience, traveling/lecturing "rockstar" teachers rarely provide the level of up-and-close personal guidance required to break through. Retreats and books help to a degree but nothing replaces the immediate influence of watching a master go about everyday things.
I'm inclined to say, the best bet is to find a resident teacher/master/lama and join the sangha of students on a permanent basis. Many Zen masters run meditation circles, with some degree of study and personal guidance mixed in. Tibetan lamas regularly take students for the preliminary Ngondro course, from which one can graduate to Vajrayana proper to receive in-depth guidance. In any case, I would suggest, search locally for little sanghas organized around a resident master - whether at a temple, or a secular meditation circle.
Answer: I would recommend you to pick the tradition closest to the original teachings of the Buddha and try to find a good teacher within that tradition. Trying many traditions would probably lead you to spiritual confusion than progress.
You can discover a good Dhamma teacher by evaluating the following criteria

Are his teachings sensible, skillful and praised by the wise?
Is he living according to what he preaches?
Are the teachings inline with the Tipitaka and the commentaries?
Does your understanding of the Four Noble Truths increase by following his teachings?
Comment: I think the four items that you listed are maybe a quote. Could you add maybe a sentence or a little paragraph to each one, to clarify or give an example of what each one means? `"Are his teachings sensible, skillful and praised by the wise? For example, ..."`.
Comment: It's not a quote. It's basically excerpts of Kalama sutta coupled with personal experience. What do you mean by examples? Aren't they pretty straight forward?
Comment: `What do you mean by examples?` I meant "examples from your personal experience". But you don't have to write that, it was just a suggestion or invitation. `Aren't they pretty straight forward?` OK then. In or from the Kalama sutta, the "example" is the Buddha.
Comment: I'd rather not mention names of contemporary teachers to keep the answer general. Yes, the Buddha is the best teacher of them all. Next comes enlightened beings. Above four criteria can help to identify probable enlightened beings or at least those who are well on the way.
Answer: The Dhamma of the Buddha is the right dhamma teacher; as stated in the Pali suttas.

I have set forth the Dhamma without making any distinction of esoteric and exoteric doctrine; there is nothing, Ananda, with regard to the teachings that the Tathagata holds to the last with the closed fist of a teacher who keeps some things back... Therefore, Ananda, be islands unto yourselves, refuges unto yourselves, seeking no external refuge; with the Dhamma as your island, the Dhamma as your refuge, seeking no other refuge. DN 16
Answer: The Udayi Sutta (AN 5.159) describes the five qualities in one qualified to teach the Dhamma:

"It's not easy to teach the Dhamma to others, Ananda. The Dhamma
  should be taught to others only when five qualities are established
  within the person teaching. Which five?
"(1) The Dhamma should be taught with the thought, 'I will speak
  step-by-step.'
"(2) The Dhamma should be taught with the thought, 'I will speak
  explaining the sequence [of cause & effect].'
"(3) The Dhamma should be taught with the thought, 'I will speak out
  of compassion.'
"(4) The Dhamma should be taught with the thought, 'I will speak not
  for the purpose of material reward.'
"(5) The Dhamma should be taught with the thought, 'I will speak
  without hurting myself or others.'
Note: According to the Commentary, "hurting oneself" means exalting
  oneself. "Hurting others" means putting other people down.

And how do you know if the teacher teaches the right Dhamma? Use the criteria of the Kalama Sutta as mentioned in Andrei Volkov's answer.
Answer: I tried to follow everything from the nissayamuccaka-course which I described in this answer, when I was still in a monk-hood by myself; and I had a low-quality teacher for about five years; before I found a perfect teacher from pa-auk forest monastery
(this monastery also published other English-language Dharma articles here) who have all of the qualities listed below, that were specified in the tipitaka and commentary.
I met the pa-auk teacher too late, so I am being a layman now. However, it was my previous effort and experience which gave me the confidence to choose pa-auk to be my kammaṭṭhāna teacher.
The qualities of a teacher, and the operating procedure to choose and to apply with the teacher, have been briefly described in Chapter 4 of the Path of Purification.
Furthermore, in my opinion, the significant quality of a teacher is paṭisambhidā: because all ariya must have paṭisambhidā, at least in his kammaṭṭhāna. So he should have these qualities:

His teacher descent, he must derived from a tipitaka memorizer (buddha-sāvaka, suta-buddha; V.N. Mahāvagga Nissayamuccnakathā).
His enlightenment, he must achieved at least upacāra-samādhi and balava-vipassanā (4 paṭisambhidā; V.N. Mahāvagga Nissayamuccnakathā).
His tipitaka memory, he must graduated through at least
nissayamuccaka-course (V.N. Pācittiyakaṇḍa Ovādakasikkhāpada's commentary).
His tipitaka understanding, he must not cut tipitaka off or make
tipitaka conflict each other. Because tipitaka was memorized by
single commentary teacher group at 1st saṅgāyanā, so it  must be a
single package that compatibility with each other (pro in tipitaka relation, dhamma-paṭisambhida&attha-paṭisambhidā).
His pali skill, he must understand pali in advance (nirutti-paṭisambhidā).
He must be a genius one (paṭibhāna-paṭisambhidā).

Furthermore, in tipitaka and commentary tradition, since mahākhandhaka of vinaya mahāvagga is completed authored by upāli in 1st saṇgāyanā, all layman's teachers must have all of these qualities, that concluded by upāli in bhikkhunovādakasikkhāpada's commentary (which I translate below as follows):

Qualities of nissayamuccaka-bhikkhu (teaching lay people)

Proficient to recite pāṭimokkha-pāli and to understand it's commentary.
Proficient to recite and to understand 4 bhāṇavāra (~1,000 syllable) of sutta and their commentary, to teach laymen on uposatha
day.
Proficient to recite and to understand sutta for bhikkhu's life such as andhakavindasutta, mahālahulovādasutta, ambaṭṭhasutta, etc.
Proficient to recite and to understand sutta for teaching in 3 chances: banquet for saṅgha by layman (nidhikaṇdasutta), funeral
ceremony (tirokuṭṭasutta), and auspicious ceremony (maṅgalasutta).
Enough understand to judge/to decide about saṇgha's ceremony such as uposatha, pavāraṇā, etc.
Proficient to recite and to understand his kammaṭṭhānā throughout the nibbāna-course.
5 years experience in monk hood as a monk.

Qualities of bhikkuparisūpaṭṭhāpaka-bhikkhu (teaching bikkhus)
If above layman's teachers want to teach bhikkhus (ūpajjhā-ācāriya, nissaya-ācāriya), they must increase their skill level to all of the following qualities.
These are for abhivinaya teaching:

Proficient to recite mahāvibhagha and bhikkhunivibhaṅga (first 3 books of thai 45 books pali-tipitaka) of vinaya-pitaka-pali. At least, he
can relay with the other 3 bhikkhu. Proficient to understand it's
commentary, too.
Proficient to recite all saṇgha's ceremony in vinaya-pitaka mahāvagga and julavagga.
Proficient to recite 14 vatta in vattakhandhaka.

These are for abhidhamma (kammaṭṭhāna) teaching:

Proficient to recite one of this suttanta-pali: mūlapaṇṇassa (1st/3 parts of M.N.) for student in M.N. faculty, mahāvagga (2nd/3 parts of
D.N.) for student in D.N. faculty,
sagāthavagga+nidānavagga+khandhavāravagga of S.N. or  mahāvagga of
S.N. for student in S.N. faculty, before half of A.N.  or after half
of A.N.  or ekakanipāta+dukanipāta of A.N. for student in A.N.
faculty, jātaka+commentary  (because kammaṭṭhāna was described in
commentary) for student in jātaka faculty.

Qualities of bhikkunovdaka-bhikkhu (teaching bhikkunīs)
If above layman's teachers want to teach bhikkhunī, they must increase their skill level to all of these qualities:

Proficient to recite whole tipitaka-pali and commentary-pali. Or at least, he still must recite whole tipitaka, but he can recite just one
commentary of suttanta, first 4 parts of commentary of 7 parts of
abhidhamma. However, vinaya-commentary is what he must recite it all.

Reference: tipitaka and commentary of vinaya pācittiyakaṇḍa bhikkhunovādakasikkhāpada and vinaya mahāvagga mahākhandhaka.

(I still find it difficult to reference the tipitaka and commentary using english resources: there's no translation, very long pages, confused categories, cutting some parts off the tipitaka, cutting commentary off from pali canon, etc.)

Related topic: Should Lay Buddhists Teach the Dhamma?
Comment: I tried to improve the formatting. I think it's readable, thank you.
Comment: This is an important question and answer. I will very appreciate to one who help me prove my answer. I use al most all my free time to research and to write each topic. I don't want to make it as just an unreadable answer one, but my english skill still not too good enough.
Answer: Be wary of the concept of guru and especially the person who claims to be one. Extraordinary teachers are rare and impossible to find. It is better to find a traditional and experienced teacher who makes no special claims. You may even consider a modern meditation center that offers MBSR, MBCT, and psychotherapy that has a large membership. Progress in meditation is largely psychological.
Answer: Sati,
assuming that a seek "for a right Dhamma-teacher" underlies here by the desire to gain Awakening and answering the question of what a seeker might possible do, for finding a proper teacher, is very good given in Bhante Thanissaro's Essay:

The Power of Judgment, by Thanissaro Bhikkhu (2011; 6pp./19KB)
  Developing good judgment is the key to becoming a true friend — first to yourself and then to those around you.

All of the possibility to gain such a teacher is by the seeker at least, or let my person say be being touched, good or bad, comes it's way.
How it happens, that a person gain Dhamma, enters the stream, is sure best explained by the Buddha himself as reported:

[Kapadika Bharadvaja:] "To what extent is there an awakening to the truth? To what extent does one awaken to the truth? We ask Master Gotama about awakening to the truth."
[The Buddha:] "There is the case, Bharadvaja, where a monk lives in dependence on a certain village or town. Then a householder or householder's son goes to him and observes him with regard to three mental qualities — qualities based on greed, qualities based on aversion, qualities based on delusion...

This Sutta and good sorted others, as well as practical advices, Orion may find in the given essey:
Into the Stream - A Study Guide on the First Stage of Awakening
[Note: This is a gift of Dhamma, not meant for commercial purpose or other gain in the world]

How to find the right Dhamma teacher


Are paper charts required for flights outside the USA?

Question: Can international flights by a US operator be performed paperless or do you need complete paper charts?
Comment: Any other detail? Plane size? Type of operation? Route?
Comment: [Closely related](https://aviation.stackexchange.com/q/254/62)
Answer: With virtually every major US air carrier today using EFB's, the use of paper charts in the flight deck has largely fallen to the wayside. Flight crews are still being provided with the exact same information, only now it is in digital form. Most, if not all US air carriers use navigational charts and plates published by Jeppesen. Unlike FAA NACO charts and plates, Jeppesen publishes charts for airports all across the world in a greatly standardized form. This allows information to generally remain similar across countries and helps to reduce some of the differences pilots operating international flights would otherwise face. Whether paper or digital, US based flight crews would likely receive charts from Jeppesen.
All of the EFB apps in use by airlines are designed to automatically provide pilots with current charts and plates needed for any given flight in the carrier's network, provided the area is covered in the chart subscription. Prior to operating an international flight, an airline (likely their dispatch department) will review their chart subscription package to ensure charts/plates are included to cover the routing, destination, and alternate(s) of any international flight. Any areas needed that are not currently included in their subscription would be added. Once added to the airline's subscription, the charts would then automatically populate to the EFBs issued to pilots. Pilots would then just need to make sure the new charts were downloaded and they would be good to go. Pilots would then be receiving the exact same information digitally that they would if they had been provided paper charts.
From a regulatory perspective, the FAA, EASA, and ICAO have all developed standards for EFBs and as a result pretty much all developed countries allow their use. As long as an airline has received the appropriate approvals and meets standards, the use of EFBs should be a non-issue. In the US, FAA EFB standards meet or exceed ICAO standards, and ICAO standards would likely be the minimum requirement while operating internationally. I am not currently aware of any country that disallows the use of EFBs for charts, but should such a scenario arise, then an airline could potentially be forced to use paper charts. However, the odds of that happening are slim to none.
Answer: I know of at least one Part 121 carrier that routinely flies internationally with no requirement for full paper charts, and beyond the approvals for the EFB's as a replacement for paper charts in general, I don't know of any special approval needed to go without them internationally.
We do have paper High enroute charts for international (but not domestic) airways; I can't find a reference if those are required or not (and if so, by whom: FAA, other countries, or our company).
It's always hard to prove a negative, but I suspect that if your operation is approved to go EFB-only, then that approval isn't limited to only domestic routes. There may be some country that requires everybody to have the paper charts, but I don't know who.
Overwater ops has its own rules; for that, a paper plotting chart may well be required even with EFB's for enroute & terminal reference.


Special offer: 2 questions in the price of 1!

Question: What should we do with "questions" such as this, that are really two questions disguised as one? Flag them? Edit them? Close as "not a real question"?
Answer: It depends on if it's two questions that go hand in hand or really have nothing to do with each other. In the first case, leave it alone. In the second case, try to split it up.
Often, when this happens, you have to be quick. Once there are answers, there's rarely a point in editing the question – in that case, vote to close or flag as not a real question.
But, if there aren't answers yet, I'd propose to make a bold move and edit the question for the OP, so that the post contains only one question. For example, remove all additional unrelated questions. Show the OP how it's done, and if they really want to ask their second (or third, or fourth, …) question, they'll just post another one. Of course this is a radical change, so make sure you know what you're doing – and it might be that edits like these are not accepted when suggested by users below 2k reputation.
In any case, leave a comment telling them that questions should be reasonably scoped. Point them to the FAQ where it says that. Ask them to post another question, but mention that they should link back to the original post just in case. Maybe something like this:

Please only ask one question at a time. According to the [FAQ#dontask], questions should be reasonably scoped. This will get you more precise answers and makes it easier for others to find the topics later on. I've edited your post to remove additional questions – feel free to ask them as separate posts, and link back to this question. Thanks!
Comment: When editing out and leaving a comment I would be careful to be polite in what you say as this is a radical change to the OP's question. Could you perhaps place a sample comment for users to use as a template?
Comment: Done – let me know if you think this can be improved!
Comment: Perfect! Thank you.
Answer: Ask the user to separate the questions out - as there are no answers this should be easy enough.
EDIT: I misunderstood - mods cannot move some answers ony al of them - so the following can't apply unfortunately - we can only ask people to duplicate them and makes it more important to catch these questions early.
If there were answers then after the questions were rewritten then you would have to flag for a moderator to migrate some answers to the new question
Comment: @Mark Mods can't migrate/move specific or *only* answers. It's all or none. When we do a merge, it moves all answers from question A to B, and locks question A
Comment: You cannot selectively migrate answers.
Comment: @slhck A moderator can - which is what I tried to say
Comment: Not even a moderator can migrate selected answers. Questions can be migrated. Answers can only be locked or deleted. Feel free to prove me otherwise, but I'm 99% sure that it's not possible without needing a developer.
Comment: @slhck - the non homebrew answers on http://stackoverflow.com/questions/9070074/how-to-install-pil-on-mac-os-x-10-7-2-lion/11368030#11368030  were merged from another question (Imy answer was the accepted one on the other)
Comment: Hm.. *Merging* is different. When merging, you can more or less select what gets "migrated" by deleting answers – but in the case kinokijuf mentioned, there is no merging process, because you would keep both questions open and *not* merge the first one into the later posted one.


XServer not working

Question: After I remove the perl.i386 using yum remove, Centos 5.4 upon boot cannot start the XServer. How can I configure XServer to get it working? How can I add the other remove packages?
Answer: You have to put perl back. Perl is critical to quite a few bits of CentOS. You may have broken your system to the point where only a reinstall will truly fix it, but your first step is to put perl back.
Comment: I have re-installed perl using rpm. But what about the issue with XServer. By doing yum reinstall perl.i386 will work?

XServer not working


Why isn't saving photos as TIFF files a popular choice by DSLR manufacturers?

Question: Why do many DSLRs have the option to save in RAW or JPEG but not in TIFF? It would be useful to save it as a TIFF file using lossless compression. It would be a midway between RAW and JPEG. Is it because the size of TIFF files is huge?
Comment: Whats the use case?  Where would you want to deal with TIFF straight out of the camera vs one of the other two?
Comment: Many mid level and up Nikon DSLRs do have the option to save as TIFF...
Comment: @akram - why manufacturers standardised on jpeg would make an excellent question on it's own.  The short version is that it offered a good size reduction with an acceptable quality loss without needing too much processing when they were debating what formats to use - it was a bit of a no brainer at the time.
Comment: I'm wondering why did the camera manufactures chose JPEGS instead of other formats; specially TIFF since it can be lossless and you can use it to preview the photos (without having to apply transformation to the RAW). It'll also allow you to change WB without degrading the image quality. But in the same time it's not the sensor's information, so it's kind of midway between RAW & JPEGS. It certainly outperforms JPEGS so why not using it? And this is based on my understanding for the _TIFF_ format, perhaps I'm wrong so feel free to correct me
Comment: Same with Pentax and Olympus.
Comment: mmmm... looks like many cameras have this option but it's not popular as RAW + JPEG?
Answer: Noting other answers, and having had a bridge camera that did TIFFs, I'd suggest that for DSLRs TIFF is pointless except as an add on if it can be managed.
TIFF is a lossless way of saving an image, once an image is generated, BUT the image that it saves is an interpretation of what the sensor records.
RAW gives you the maximum possible flexibility in dealing with the available data.  Software to convert to TIFF or JPG is provided by the camera maker plus the various commercial RAW converters are a small fraction of a good DSLR price.
JPG gives you user usable images at a compression level that suits the user.
RAW + JPG gives you all the advantages of RAW plus some of the advantages of JPG (as it usually does not allow selection of JPG compression level and the JPG provided may be not be the highest quality JPG the camera provides in pure JPG mode.
 eg in a Sony A700, straight JPG comes in Extra Fine, Fine, Standard.
 But with RAW + JPG, the provided JPG is "fine" and not "Extra Fine".
TIFF loses data relative to RAW and is far larger than any sensible JPG and has no great quality improvement over the best JPG. Once it is "not RAW" then it is subject to manufacturers decisions.
Useful where available is Compressed-RAW and Compressed RAW + JPG.
 Available eg on Sony A700 but not on the newer A77 where it would be useful due to largr file sizes.
 Compressed-RAW provides a lossless compression of the RAW file at the expense of processing time and a somewhat non-stanard format.
Comment: @Akram If you processing your images to the extent that flaws in the JPEG are showing up then you really should be shooting RAW in the first place!
Comment: I agree that TIFF doesn't outperform high quality JPEG but it certainly more flexible than JPEG in post processing
Comment: @MattGrum yeah you're right
Answer: They do actually but not all of them. Even some bridge cameras can save as TIFF.
Unfortunately, TIFF was given a bad name because its files were huge. Early on, compression was not used for TIFF files by digital cameras and so that gave rise to the files being huge which also slowed down the camera considerably. One of my first cameras used to take 24s to save a single TIFF file.
You are right that it would be highly desirable to have a complete image out of the camera (rather than RAW data) but without compression loss and--equally important in my opinion--higher color-depth and dynamic-range than JPEG can store.
In reality any high-bit-depth file-format could do but camera makers do not see it as important yet. This will probably come as displays start showing more than 8-bits per channel and operating system support becomes more common (this exists already but in very limited numbers at this time).
Answer: I own an Olympus Camera that has the three options you mention. Tiff files generated by the camera where somehow more than twice as big as the raw files.
My speculation here is that the RAW file, as it holds almost exclusively the information from the sensor has by nature less information to compress. That is, if the sensor where, say 10 bits per photosite, the RAW file would contain only this, arranged in a way that the conversion software will later decode knowing to which color channel each photosite corresponds.
To compose the TIFF file, the camera needs to calculate a pixel from several photosites, taking to account that some algorithms use a photosite several times to compute adjacent pixels. A pixel must be completed with its three channel values, if a 16 bit color depth image need to be encoded, you need tree values held by 16 bits each, thus you need 48 bits per pixel in the final image. Compare that to the 10 bits per photosite in the hypothetical sensor mentioned before.
Answer:
Difference of file size between a lossless TIFF and RAW is not huge.
More time is needed to save a tiff than a raw, so to avoid delay in shots.

Jpg will also take more time due to the processing, but will have a significant file size reduction, hence jpg was used.
Comment: On modern hardware, JPEG is usually faster than RAW, because CPUs are faster than I/O to flash memory.
Answer: RAW files are better than TIFFs in almost every respect:

RAW files are smaller (as only one colour component per pixel is stored)
RAW files capture more data
RAW can be totally lossless (TIFFs don't lose data in compression but do in demosaicing)

The only disadvantage is the need to demosaic and process the images before they can be viewed. Which is where JPEG comes in. JPEGs are better than TIFFs in a number of respects:

JPEG files are smaller
There are lots of very cheap chips that do hardware JPEG compression. TIFF compression is marred with patent claims and doesn't to the best of my knowledge have the same hardware support.
JPEG files offer almost the same level of quality, unless you push the files around in post, in which case you really really should be shooting RAW.

So this is why camera manufacturers mostly offer RAW + JPEG. It used to be the case that older bridge and compact cameras offered TIFF files, but this was before RAW conversion software was popular and most people lacked the ability to do the conversion, hence TIFF was offered if you really needed to avoid image compression artefacts.
Answer: Boy, I can not believe the amount of disinformation there is about .tiffs! Basically, a .tiff file is an uncompressed jpeg. Similar to a jpeg, it lets the camera set the contrast, white balance, etc. for your picture (which you have pre-set in the camera for the situation you are photographing). If you're using camera-specific software when processing raw files, the quality is probably no different after processing than if you made the same settings
in-camera and saved as a .tiff.
There are camera models such as the Nikon D300s, that allow you to shoot native .tiff in the camera. If you can set the camera to make an excellent photo, much like a photographer in the past shooting a transparency, then by all means shoot it as .tiff! Camera RAW, does have all the information saved, and then you can go in and modify that, so you can set contrast, density, color, etc., then save as a .tiff for the highest quality file to send to ad agencies or printers.
BUT if you can set that in the camera, and would have been happy with a jpeg version, all the .tiff file is, is an uncompressed version of that.
In addition, .tiff is a lossless file format. If you shoot .tiff and need to get in and change the color a little, or density, or contrast, no problem, you can resave it with no loss. If you need to get in and change it a lot, RAW is better, but maybe you shouldn't be a photographer if you're that far off!
Comment: A .tiff *can* be losslessly compressed, but it can also use lossy JPEG compression. http://en.wikipedia.org/wiki/Tagged_Image_File_Format#Flexible_options
Comment: It can be 'group 3 fax' too IIRC which makes jpeg look highly desirable in image quality terms...
Comment: Your last assertion is not correct. Every time you make a change and save a TIFF file, you lose information.  Not through compression, if you are saving as lossless TIFF, but through changes to exposure, color, contrast etc. which irreversibly change pixels.  You can't undo those changes like you can in RAW.


Hebbian Learning Rule, Local or Global?

Question: I just learned about the Hebbian Learning Rule. It essentially says "Neurons that fire together, wire together". I'm wondering if the learning rule is affected by the spatial distance of the two neurons. When two neurons are far from each other, why is the connection formed?
Comment: Like anything else with a cutesy slogan or mnemonic, the underlying mechanics are a tad more complicated.  Hebbian update rules are still quite useful in models and simulations, though.  I may have an answer to this, but I need to dig up the papers.
Comment: The papers I had in mind was for synapses that were formed at farther distances down a given dendritic tree, so I don't think they address your question directly.  I'll keep looking.  I think some of the answer to your specific question is going to be entrenched in what is largely there through development already, though.
Answer: It's a local rule.  All that it means is that the connection between two neurons gets stronger if you use that specific connection more.  The specific connection (the synapse) must be used though; it doesn't apply to two random neurons that aren't connected that happen to fire at the same time.
Hebbian learning is generic term for outcome; there are actually two separate mechanisms I know about (probably many more, too).  First, there's "silent synapses" which have only NMDA receptors, but not AMPA receptors.  NMDA receptors have Mg+ molecules blocking their channels and require AMPA activation to expel the NMDA.  So if you have a synapse with no AMPA, it won't be an effective synapse.  However, if you have another synapse activing the tissue, expelling the magnesium, then the silent synapse has a short window to activate the synapse during the Mg expulsion.  As it does this, it activates a series of protein signaling and transcription signaling that tells the cell to bring more AMPA up (a response to all the Ca signaling that these signals rely on).  This is also a mechanism for conditioning (the two different synapses representing the pathway of the conditioned and the unconditioned response.  The conditioned response would be the pathway with the silent synapse).
Another example is astrocytic regulation of glutamate levels.  ATP is what your whole body uses for energy, but there are ATP detectors in astroctyes, which couple in the tripartite synapse as a synaptic regulator.  As the synapse is more active, ATP is released, which activates the astrocyte and causes it to release extra glutamate, bringing the postsynaptic neuron closer to firing.
All of these require only that the neurons make contact at a synapse, distance between somas is not a factor. Of course, the distance between the axon and the dendritic spine have to be close enough to form a synapse.
Comment: While it's true that neurons only connect to adjacent neurons, the networks that form between them are the result of hebb's rule.  We start out with an over-abundance of neuronal connections and the networks that don't get used (redundant ones) are systematically get killed off.  Hebb's theory is critical in understanding neural networks.
Comment: I don't particularly disagree with your comment, but I'm not sure of what your point is.
Comment: Your answer indicates that the "rule" only affects local neurons but the rule/theory applies more broadly than just local neurons.  Indeed, it wouldn't be of much use at all if it weren't for chaining these neurons together into larger networks.
Comment: I don't think I indicate that it only *affects* local neurons.  How the rule affects network outcome requires a higher level of inference and appears outside the scope of the question to me.  I didn't comment one way or another on networks.

Hebbian Learning Rule, Local or Global?


What were the U.S. Air Force's first 2-crew fighter planes?

Question: The Navy has had 2-crew planes since at least as early as 1944 with the Grumman F7F Tigercat but when did the U.S. Air Force adopt 2-seaters. Does the Navy prefer 2 crew and the Air Force prefers 1? Was the McDonnell F-101 Voodoo one of the first AF 2-crew?
Comment: @RonBeyer not sure but the question seems to be focusing on fighters.
Comment: *Does the Navy prefer 2 crew and the Air Force prefers 1?*  You need to break that out as a separate question rather than asking that within the body of a different question.  Even so, it's basis is doubtful.  In the 1960's the Navy was flying both F-4 (two seats) and F-8 (one seat) at the same time; fast forward twenty years (80's)  and the Navy is flying 2 seat (F-14) and one seat (F-18) at the same time.  Again, that sub question belong as its own question.  Feel free to ask it as another question.  SE sites are designed for "one question / one answer" as the normal mode.
Comment: Are you asking specifically about fighter aircraft? Because at the time the US Air Force was formed (18 SEPT 1947), they basically just took everything that the US Army Air Corps had and flew that. One of the first operations for the US Air Force was [Operation Vittles](https://en.wikipedia.org/wiki/Berlin_Blockade) and used [C-54 Skymasters](https://en.wikipedia.org/wiki/C-54_Skymaster) which had a crew of 4.
Answer: The first two-crew fighter aircraft to enter service with the US Air Force was the Lockheed F-94 Starfire.

Source: Wikipedia Public Domain
The aircraft's first flight was on April 16, 1949 and entered service in May of 1950.
Comment: It may help to answer the original question to explain why two crew were needed here and if that trend continued in later aircraft.
Comment: Thanks Ron Beyer. Do you know about the AF pattern with 2 seater fighters? Was the F-101 Voodoo revolutionary at all in it being a 2 seater for the U.S. Air Force?
Answer: The US Army Air Corps has flown bombers with 4+ crew members since the 1920s, for example the Huff-Daland LB-1 introduced in 1927.
In the WWI and interwar era, a few biplane fighters carried an observer/gunner; the Berliner-Joyce P-16 introduced to the USAAC in 1932 was one such. As aircraft speeds increased through the 1930s, the open-cockpit flexible gun mount became less practical and the weight penalty of a second crew member in an enclosed turret was rejected for fighters.
During WWII the introduction of radars small enough to put on a plane led to the development of "night fighters" or all-weather fighters with a second crew member dedicated to operating the radar equipment. (This Q&A discusses the tradeoffs between single-crew and multicrew designs in more modern combat aircraft.)
The long-range P-82/F-82 Twin Mustang entered USAF service in early 1946. Early models had two identical crew cockpits allowing pilots to alternate control on long flights; later night fighter versions introduced between 1946 and 1948 put the radar operator in the right cockpit.

Depending on what you consider a fighter, the Northrop P-61 Black Widow night fighter entered service with the USAAF in 1944 with a crew of 2 or 3 (pilot, radar operator, and optional gunner).

The Black Widow wasn't a traditional dogfighter, but carried radar and heavy guns to intercept bombers at night.
Similarly, the P-70 was a night fighter in USAAF service from 1942, but it was a conversion of a light bomber design.
Answer: I would have to agree that the P61 Black Widow, which carried the formal designation of Pursuit (fighter), was the first multi-crew FIGHTER in the US inventory. It was a dedicated night fighter, and like most multi-crew intercepters, carried additional crew to work the complex weapons systems (or radar, in the case of the P61).
Interesting note: due to special wing flaps, the P61, while not much smaller than a B-25, could roll at about the same rate as a Mustang, though obviously it would lose a lot of airspeed from sharp turns, and take longer to get that speed back.
During the war, a 2 seat night fighter variant of the P38 Lightning, the P38M was produced in small numbers (75 total).
The British did field the Bristol Fighter in WW1, and it was quite successful. They tried this again in WW2 with the Boulton Paul Defiant that was a dismal failure. Plus the German BF 110, which wasn't as bad, but not really competitive with single seaters.
Comment: I didn't think about WWI and interwar era fighters; USAAC had a 2-seat biplane fighter in '32.
Comment: Looks like the US built copies of the Bristol during WWI as well.


Kalman filter - question about matrices

Question: In order to familiarize myself with Kalman filter I decided to see how it work step by step. I would gladly use your help.
Let's say I have a falling object with air resistance proportional to its velocity. Since my measurements are not perfect let's say that position measurement is gaussian with standard deviation of $15m$, so is velocity with deviation $5 \frac{m}{s}$. Equation for this system is $\ddot{x} = g - \frac{b}{m}\dot{x}$, where $b,m$ are constant. Now how do I find matrices $A$ and $B$. Do I simply convert to space-state form? Also, how do I determine the processing noise $\mathbf{v}$? And finally, how do I find covariance matrices of of processing($\mathbf{Q}$) and measurement ($\mathbf{R}$)? If you are kind enough to help me I would gladly ask you some more questions tomorrow.
Comment: By the way, have you read http://www.bzarg.com/p/how-a-kalman-filter-works-in-pictures/
Comment: @MarcusMüller, That's a great reference!
Answer: According to the scenario you formulated, you only have measurement noise and no input noise. You are correct that you might need a state space model. For example,
$$
\begin{bmatrix}\dot{x} \\ \ddot{x}\end{bmatrix} = \begin{bmatrix} 0 & 1 \\ 0 & -\frac{b}{m}\end{bmatrix} \begin{bmatrix}x \\ \dot{x}\end{bmatrix} + \begin{bmatrix} 0 \\ 1 \end{bmatrix} u + \begin{bmatrix} 0 \\ 1 \end{bmatrix} v,
$$
$$
\begin{bmatrix}y_1 \\ y_2 \end{bmatrix} = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix} \begin{bmatrix}x \\ \dot{x}\end{bmatrix} + \begin{bmatrix}w_1 \\ w_2\end{bmatrix},
$$
with $u$ always equal to $g$, $v$ the input noise (which assumed to be zero), $y_1$ the measured position, $y_2$ the measured velocity and $w_1$ and $w_2$ zero mean Gaussian noise.
Since we did not take into account input noise, therefore you can also view it as a zero mean Gaussian noise with also zero (standard) deviation. When calculating the covariance matrices you can take the variance (standard deviation squared) on the diagonal, if all random variables are independent (which I assume $w_1$ and $w_2$ are). This would yield,
$$
Q = \mathbb{E}(v^2) = \begin{bmatrix}0 \end{bmatrix},
$$
$$
R = \mathbb{E}\left([w_1\ w_2]^T [w_1\ w_2]\right)= \begin{bmatrix}225 & 0 \\ 0 & 25 \end{bmatrix}.
$$
But depending on whether you want to implement a Kalman filter in continues or discrete time, you might first have to discretize the state space model.
Comment: Thank you very much for the answer. It is really helpful. Now - let's assume that we have some Gaussian noise as processing error. My questions: 1) What exactly is this processing/input error? I know that measurement error comes from uncertainty of measurements since we are not able to measure things perfectly, but how about this processing error? How do I calculate/estimate it? 2) How do I detemine whether or not error (let's say $w_1$ and $w_2$ are corelated?
Comment: @G.Fil If you are doing exercises like these, then they should be given. But if you want to determine this for a physical system then I would guess that you would determine those from a measurement. I have not done this myself, so I am not completely sure about this. Especially about how to get both $v$ and $w$ out of it. But once you have a time series of them you can easily calculate $Q$ and $R$ using [covariance](http://mathworld.wolfram.com/Covariance.html).
Comment: Thank you very much for you answers, really helped me :) I guess i'll go and ask one of my professors about some more details.

Kalman filter - question about matrices


What is the RPM of A Typical Reel To Reel Recorder?

Question: What is the RPM of a reel to reel recorder?
Comment: I just realized that reel speeds change but the capstan which is located between the two reels that does the traction and pulling the tape at certain IPS governs all the tape mechanism while the reels just adapt to it...the reason I was confused about this rpm speed was that I thought the capstan was the pivoting mechanism of the collecting reel...thank you all for all the input and guiding me to the right direction.
Answer: Audio tape speeds are measured in ips (inches per second) or in cm/s (centimeters per second), not RPM (i.e. there is no typical/common RPM).
The actual RPM of the reels changes with the amount of tape. The speed of the tape is not controlled by the reel motors them selves, but rather the capstan motor, which then ensures a constant speed (and typically the reels simply follow).
On the capstan a roller of varying diameter from model to model is mounted - typically around 1 - 2 inches, which means somewhere between 4-5 inches of tape is transported per round (1.5 * 3.14159 = 4.7). If the speed is e.g. 30 inches per second, then that gives 30 / 4.7 * 60 ~= 383 RPM for the capstan. The reels are harder because many different reel types exist, with varying starting inner diameter.
Some common speeds are

120 ips (304.8 cm/s): Loop bin duplication, analog instrumentation
60 ips (152.4 cm/s): Loop bin duplication, analog instrumentation
45 ips (114.3 cm/s): Digital audio recording
30 ips (76.2 cm/s): The highest standard professional speed.
15 ips (38.10 cm/s): Most common speed multi-track pro studio recording and otherwise professional speed for reel-to-reel including multitrack recorders.
7-1/2 ips (19.05 cm/s): Most common pre-recorded playback speed, highest domestic speed
3-3/4 ips (9.53 cm/s): Second most common pre-recorded playback speed
1-7/8 ips (4.76 cm/s): Lowest common reel-to-reel speed

A more comprehensive list of different tape speeds and their main application can be found here. Additional info on the reel-to-reel tape recorders, tape speed and fidelity can be found here.
Comment: So I guess we are looking at the average angular speed of the sum of two reels constant changing RPMs, even though they change their ratio one to another stays the same to keep a constant IPS on the reader head...since one gets faster because its circumference getting bigger, while the second feeding reel gets smaller and slower in RPMs to compensate, the two reels keep an average constant RPM so the IPS always stays the same at the magnetic player head...my question is what would be that average RPM?
Comment: Depends on how much tape is on the reel & how large the reel centres are. You're actually asking a question which is the equivalent of "how long is a piece of string?". It's something no-one has ever considered before; so long as the reels keep sufficient back-tension to prevent tape-slack, no-one has ever cared before either.
Comment: Alright - you should probably update your question to reflect this. I added some additional information about the capstan role and speed.
Answer: 7.5, 15, 30 are all common.  Perhaps there are 3 3/4 ones also.  There is  a wide range of reel to reel type recorders. If your asking about a specific one you would need to provide some more info.
Comment: are you sure you are not talking about IPS inches per second? if so how does it relate to RPM...one is inches per second,and other is revolutions per minute, I guess RPM is angular speed, just like hertz...I know we can divide the capstan circumference by the ips to find how many seconds it takes for the reel to complete one revolution or period then take the reciprocal of the period and multiply it by 60 seconds for RPM...
Comment: I am, sorry I read your question incorrectly.
Answer: As the tape speed in front of the heads has to be constant (in ips as mentioned), there's no constant RPM for the reels as it is continuously changing as the reel empties or fills.


How can I undo what I did when I accidentally booted linux host inside itself with VMware?

Question: I'm dual booting XP and Kubuntu. I wanted to boot to my existing raw scsi XP partition inside Kubuntu, not a virtual XP instance. I accidentally booted Kubuntu inside itself. I know this is a big mistake, so I interrupted the VM, which saved the state and closed. I rebooted the host and now I can't load the Kubuntu partition at boot time. I get a maintenance shell and the Kubuntu partition is read-only. I am able to boot XP as usual. I removed the HDD and tried to mount it on another computer as an external drive and neither partition (XP or Kubuntu) will be recognized, it just appears to be one device that still mounts and appears empty. From the maintenance shell I can see all the files are still on the Kubuntu partition.
How can I undo what I did when I accidentally booted Kubuntu inside itself? Is it a matter of unlocking some files somewhere? how can I do that on a RO filesystem?
Thanks!
Answer: GRUB -> recovery mode -> fsck -> WIN!


Can a webform list who has already signed up for an event?

Question: I would like to use a webform for people to signup for an event - but they need to see who else has signed up as these events need at least one of each gender. The event is a kind of 'first aid' event where you must have both men and women on duty - not just all men or all women.  I've used webforms for signing up individuals for events, but not run into this requirement before.
Answer: You can list the people using CiviCRM Views and add the View to the same page as the webform.  Easiest is to put the View into a block, but you can also do this with the Paragraphs module or Panels.
Comment: Thanks Jon - how do I restrict the view of the participants to the event that the user has selected?  i.e. the user may be scrolling through several events & of course I just want show who's signed up for each currently selected event - (maybe this is a separate question!)
Comment: If you have a small number of events, you can simply have multiple display views and assign them manually.  If you have a larger number, you're going to need to use the "contextual filter" feature.  The trick is telling the contextual filter the event ID.  Is there a change the event ID is in the URL or can be added to it?
Answer: Create a link and point potential registrants to the standard CiviCRM public participant listing -
https://dmaster.demo.civicrm.org/civicrm/event/participant?reset=1&id=3
Where id=3 is the event ID.
There's a participant listing option in the events info and settings section -
To allow users to see a listing of participants, set this field to 'Name' (list names only), 'Name and Email', or 'Name, Status and Register Date'. You will need to set Access Control permissions to include 'view event participants' for any Roles you want to access this listing.
Comment: Thanks, but what I need to see is name, role and gender so the View solution below is probably what I need.


Creating a master artboard

Question: I need to create a master artboard containing one or more other artboards to export work as sprites. However, the only way I can figure out how to do this is to create a blank artboard of the necessary size and then drag artboards into it. Is there a better way to do this - perhaps a keyboard or mouse shortcut?
Answer: Illustrator doesn't really have a "master artboard" option.
If you need one artboard which contains all other artboards, then you are going about things the proper way. Simply stack artboards as needed.
If you are looking for the ability to have identical items on several artboards, simply create the first item on one artboard. Drag it to the Symbols Panel. Then choose Edit > Cut followed by Edit > Paste on all Artboards.
The paste command will place the element in the same position on all artboards. If you need to then edit the object later, simply edit the symbol and all instances on all artboards will be updated as well.
Answer: You can always save the master template as a separate file and then just include it in your files as a linked file. This way whenever you change the master template, it will automatically update in the linked files.
Answer: You can create a "Symbol" in Illustrator that will help you do this. However, Adobe InDesign CC is a better tool for this because it has a "Master Layer" option

Creating a master artboard


As a company, how can we prevent penetration testers from compromising our system?

Question: What tools or techniques can companies use to prevent penetration testers from behaving maliciously and exfiltrating data or compromising the system? I cannot imagine that the only protections companies use are contractual ones.
Comment: As a homeowner, how can I prevent that plumbers make my water heater leak?
Comment: Think of them as advanced computer locksmiths. They are the good guys you are hiring to test your "locks." You're not hiring actual burglars(I hope).
Comment: @MichaelRichardson at first it sounded like that to me too, a stupid question. But if you think about it, what the OP might really be asking is: if I'm really concerned about the security of my data, should I blindly trust a pentester, just because that's their job? Then, at least, it makes sense to talk about checking CVs/resumes, requesting a security clearance, getting insurance, etc. (see Anonymous's answer for example).
Comment: @reed The original question is essentially, I need to hire someone to test my security.  How can I prevent them from penetrating my security?  Would the answer be to hire someone else to test my security?  And how would we prevent that new group from penetrating my security?  Is it turtles all the way down?  Or do you trust the people you are hiring for their expertise to properly make use of their expertise.
Comment: @reed quite the opposite, a standard external penetration test is exactly about testing (and demonstrating) what every "stranger" can achieve without any privileged access or information and the client's employees are not supposed to ignore any alarms - literally the *only* difference in response to a social engineering attempt should be that in the end, the perpetrator does not go to jail because they had permission. If you don't investigate further, that's a process flaw that a competent pentest will exploit and document so that you can fix it afterwards (e.g. fake "get out of jail" letters)
Comment: @reed Since you're trusting everyone else, you might as well trust the pentester too.
Comment: @reed What prevented these people from compromising your security *before* you hired them? All the same preventative factors still continue to apply after you hire them. If they wanted to do some damage, they could have done it just as easily before the contract, so the hiring event does not introduce additional risks that would need additional mitigations. In any case, you're going to be blindly trusting all the pentesting companies which you don't hire.
Comment: If you care you can always supervise them, but this will be very expensive. Also if you do not give them priveledged access you basically have to worry the bad guys will do it anyway. You can also have them check other environments, but that might not give you the weakness of the production systems you care about,
Comment: The point in hiring penetration testers is to avoid breaches. When they are successful in breaking your security, others that do not have a contract with you are the worse threat. When your security is good enough, there is not threat at all. For an actual advice: Look at the reputation of the penetration testers you're hiring. Who did they work for before? How did they came into the business, what is known about them?
Comment: @fraxinus, you hire two more plumbers, who will check if the first plumber is doing everything correctly. Or are you guys telling me that if the NSA needs to fix a faucet, *any* plumber will be trusted, just because hey, he's a plumber, he knows what he's doing, we should trust him? The question asked by the OP is not as stupid as it might sound at first.
Comment: @fraxinus I can't think of anything the plumber will gain by making your water heater leak.
Comment: @Peteris, I suppose someone you hire is able to gather much more information and have access to your systems more easily, compared to a "stranger". I also imagine some interesting social engineering tricks become possible when you act as a pentester. "Oh sorry, the alarm went off by accident, while I was just testing other stuff (yeah right)". And you forgive them, and don't investigate further.
Comment: @DavidSchwartz, but who said everyone else should be trusted? I agree that it's kind of stupid to worry about a pentester, and then not worry about anyone else. But the OP didn't say they are trusting everyone else.
Comment: @Peteris: There is also a minor difference that a paid pentester is usually going after specific pre-agreed targets, wheras a hacker is going after production data.
Comment: @Peteris A good pentest is best when the pentesters are given some information about the system. In some cases perhaps even code, as it makes it easier for them to find vulnerabilities.

The idea is that if a pentester can't get in with all this extra information given to them, then it's unlikely that a "stranger" can get in while only having access to what's public.
Comment: @fraxinus that's a pretty useless comment
Answer: You're looking for a technical solution to a legal problem. This won't work.
What you worry about is primarily a legal problem. Penetration testers operate under a Non-Disclosure Agreement, which is the legal equivalent of "keep your mouth shut about anything you see here". Non-Disclosure Agreements, or NDAs for short, are what prevents a penetration tester from talking about the cool vulnerabilities they found when they tested ACME Corp. last week.
But why would a penetration tester honour a NDA? Because not doing so would basically destroy their career. If the company learns that a penetration tester disclosed internal information, they will sue the pen-tester for damages, which can be upwards of millions.
Furthermore, it'll completely destroy the reputation of the pen-tester, ensuring that nobody would ever hire them ever again. To a penetration tester, this means that the knowledge they have spent years or decades to accumulate is essentially worthless. Even if the idea seems sweet to a morally corrupt pen-tester, the punishment is magnitudes worse.
Furthermore, most pen-testers just have no interest in compromising a client. Why would they? It's in their best interest to ensure that the client is satisfied, so that they hire them again and again.

As for why you would not put in technical restrictions, there are several reasons. First, as a pentester, you feel like you are treated like a criminal. A lot of pentesters are proud of the work they do, and treating them like criminals just leaves a sour taste in their mouth. A pentester understands that a company has certain policies, but if a company goes above and beyond and escorting them with an armed guard to the toilet, just to make sure they don't look for post-it notes with passwords on them on their way back, they will feel mistrusted. This can and most likely will lower morale, and may cause a pentester to not          give their absolute best.
Furthermore, absurd technical constraints can also just make things difficult for a pen-tester. For example, if their company-provided domain account gets blocked as soon as they start Wireshark or nmap, it takes time for that account to get reactivated. It prevents a pentester from launching all their tools to find vulnerabilities as effectively as possible, and wastes a lot of their time.
This is bad for both the pentester and the customer, and will likely result in a worse overall experience for both of them.
Comment: Plus, when you're hiring somebody whose job is already to act malicious and find ways around things, you'd only be giving them another challenge to solve if they were truly motivated to break the contract.
Comment: Might be worth adding that you want *the pentester* to breach. Because that person will tell you how they did it. A real hacker wont be as nice :)
Comment: This answer is technically wrong (but I won't downvote, I hardly ever do). You are basically saying that a pentester should be trusted because there's a contract, and it's a matter of professionalism and reputation. But who tells you that a penterster is not malicious? How do you know if you are dealing with a real pentester or an impostor? Imagine calling the plumber to fix a faucet, and then Kevin Mitnick shows up telling you he's the plumber. Nice! So Anonymous's answer is more correct IMO.
Comment: Plus, adding those technical restrictions not only makes the pentester's job harder, it makes their report less worthwhile. Because, if you escort them with an armed guard to make sure they don't look for post-it passwords (a vulnerability in your system!), the fact that they're around won't be on the report. And unless your team is having that armed guard with *every single guest*, there's an unknown security hole. You end up testing "these are the vulnerabilities available to a hacker who has to operate under [these technical restrictions]; probably extra vulnerability for others."
Comment: @AndrewSavinykh It's a simple formula: The gain of a malicious activity needs to be larger than the punishment of being caught, times the chance of getting caught. If the punishment is severe enough, then I need to be *reeeeaaallly* sure that I would not get caught.
Comment: @reed Sure, that is a valid point, and I agree that Anonymous made some very good points. That's why people shouldn't just stop reading after one answer
Comment: There's one aspect that I think should be added to this answer: in at least the United States, violating the terms of a contract involving something like pentesting may incur not just civil liability, but (severe) criminal liability as well. In addition to the most obvious of the CFAA, other fraud/criminal trade secrets/etc related charges (either state or federal) may be possible (especially if the related damages can be claimed as fairly high).

As to the gain vs risk: experts in fields like this rise or fall on their reputations, the risk is ALSO any chance of lucrative future work.
Comment: _Even if the idea seems sweet to a morally corrupt pen-tester, the punishment is magnitudes worse._ That's fine, just don't get caught ;)
Comment: @MechMK1 That being said, people are bad at calculating those probabilities. That's why there is no point in punishing pickpockets with chopping off their hands; it will deter few who were not already deterred by a fine and possibly a night in jail, because someone who thinks they won't get caught thinks that regardless of what punishment there is.
Comment: @Arthur While I agree that people are very bad at calculating chances - the existence of the gambling industry is proof enough for that - the idea of chopping off a hand stems from more than just "severe punishment". For once, it has a symbolic factor, which is removal of the part of the body that committed the crime. Secondly, it brands the thief as a thief among others in society. This should help upstanding citizens to identify criminals and prevent them from accidentally associating with them. If it sounds cruel, well, it was a different time back then.
Comment: @MechMK1 And yet there were pickpockets back then too. Knowing they would get their hands chopped off. Seing people around them with chopped-off hands. Many of them may have been desperate, but it was not as strong a deterrent as one would think if your formula was followed correctly. Having other reasons behind the punishment doesn't change how it factors into your risk-reward calculation.
Comment: @Arthur I'm not saying it prevents crime, nor do I say severe punishments prevent people from committing crimes today.
Comment: @MechMK1 You kind of did though. "It's a simple formula: The gain of a malicious activity needs to be larger than the punishment of being caught, times the chance of getting caught." this implies that crime outside of this formula wouldn't happen. The argument is that the formula is only relevant if we assume perfectly rational individuals
Comment: If you're capable enough to put in viable defenses against a penetration-tester, you probably don't need to hire a penetration-tester; rather you can do all the penetration-testing yourself.
Comment: @taswyn I'm not a legal expert - not even a novice at that - so all I can do is give cookie cutter advice to abide by the applicable laws and regulations.
Comment: @JeremyFriesner Most of the time, it's organizational "defenses". Something like "Yes, we want you to pentest this system. No, we won't allow your client to connect to it." Then you need to spend hours finding the MAC of a client who can, spoof it, etc... It's not impossible, just annoying as all hell, and in the end everyone is worse off.
Comment: @MechMK1 absolutely, and I'm not suggesting that you try to address specific laws, merely that the legal issues MAY (depending on jurisdiction) be such that breaching a civil contract can *additionally* create criminal liability (this has, for example, been tested with the CFAA in court and successfully prosecuted) depending on the specifics. Pentesting can often involve actions that would be illegal if they weren't contractually agreed to, and the *possibility* of an actual criminal angle being created if acting outside of contract (& breaching NDA often voids contract) is worth noting imo
Answer:
I'm asking if companies can use some tools, some techniques to avoid
  that penetration testers behaving maliciously can exfiltrate some data
  or compromise the system permanently.

You could record all the traffic behind your firewall or stay awake all night long watching Wireshark output but without technical skills it's going to be hard to make sense of the bits flying in front of you.
A data loss prevention system is probably what you have in mind, but it is going to interfere with the pentest, unless this is precisely the equipment that you want to test.

The answer is due diligence. Before hiring a company check out their credentials. Ask questions, ask for sample reports too.
Some outfits will do little more than run an automated scan and tick boxes on a template sheet. This is not what we want. What we want is talented pentesters who think outside the box and devise original, manual attacks based on their reconnaissance efforts (which for the most part are automated). A good pentest should be a tailor-made operation and not a cookie cutter exercise.
I wouldn't do business with a company that won't provide sample reports (curated reports of course).
My biggest worry is not dishonesty but rather lack of competence which means you pay for a useless deliverable.
So this is my first filter. A box-ticking company is in my opinion less ethical because it knowingly provides a service of questionable value. Probably better than nothing but you want value for money.
I cannot remember one single instance of a pentest company being used for criminal actions. However a few have been sued for what would amount to 'malpractice'. Example: Affinity Gaming vs Trustwave.
The contract should be clear as to what is allowed and what isn't. Make sure there are no misunderstandings and that the person hiring you has full authority. What could possibly go wrong: Iowa vs Coalfire
Surely, 'rogue penetration testers' (oxymoron) who want to break into your systems won't ask for your permission to test and then go beyond the scope of the assignment. They will just invite themselves.
Don't know if you are one of those, but some companies/government agencies require a security clearance. That raises the bar a little bit: felons are unlikely to have a clearance. There are exceptions like Mr Snowden, 0% risk doesn't exist.
If your company is involved in objectionable activity, damaging the environment, selling weapons to tyrants then you may legitimately be worried about whistle blowers. This is a conundrum - you have sensitive information and want to keep it secret, but to protect it you must allow an outsider to have access to it. You should select a provider that has experience working with companies in your field of activity and is comfortable with what you do. Perhaps your trade body or business partners can provide recommendations. Word of mouth.
If you think your company could sustain financial damage/fines in case of data exposure (accidental or otherwise), talk to your insurance company. By the way, the pentest company should have liability insurance too. This is one question to ask.
Breaches are a fact of life. Pretty much any company has been hacked at least once, or will be hacked in the future. This is something to consider. You should have a disaster recovery plan ready, regardless of whether you decide to proceed with the pentest. Which I think is a good idea: if things go wrong at least you can demonstrate that you undertook reasonable efforts to prevent a breach. A company that is found to be negligent can expect stronger sanctions in terms of: regulatory fines, lawsuits, consumer backlash, negative media exposure, shareholder revolt etc.
Comment: Perhaps change the  Affinity Gaming vs Trustwave site to a non pay-to-view article?
Comment: You can't actually require a security clearance if you aren't an organization that has access to the systems that contain evidence of said clearances.  You also probably want to consider that requesting consultants with security clearances might induce the vendor to charge you the rate for consultants who need to have clearances, which is going to be considerably higher than the rate for equally competent and ethical consultants who aren't required to have a clearance, including the exact same consultants who simply aren't on a clearance-required project.
Comment: Strange, I didn't have the paywall yesterday and read the article in full. I will put another link.
Answer: If you're developing products, you should have an SDLC pipeline with different environments like DTAP, where you should have penetration testers testing on the acceptance environment. It's a security best-practice to keep the environments completely seperated from production. So your acceptance environment should be a functional copy of your production environment, but it should not contain production credentials, data from your users, connections to production environments, etc.
Creating an acceptance environment for a company is often a challenge on the network and server level. If this is the case, you can make a claus saying they should stop the moment they hit a production system. If penetration testers do manage to find production credentials somewhere, or hack a production server by accident, you just act like a real breach happened - except for calling the police - and the change login credentials / monitor the server / etc.
Comment: When I say users, I don't mean user accounts, I mean human beings, who are often the weakest point in a security system.
Comment: This is a good approach when viable, but it is worth noting that differences between test and live environments can mean a pen test fails to find something in a test environment that would be possible in a live environment. Most obviously, test environments don't have users, so attacks that rely on user actions or errors may not work.
Comment: @James_pic I've seen pentest scenarios that start with compromised user accounts - because it's a reasonable assumption that no matter what the company does, any reasonable sized company *will* have someone who falls for a spearphishing campaign, so you don't need to bother your users with testing if spearphishing is a risk because you already know that, but you want to test all the *other* security and detection measures for an attack through a compromised low-privilege user machine. If lateral movement or escalation needs reasonable user interaction, then that can be simulated by the client.
Comment: The only answer that *answers the question* here, instead of handwaving to project self-importance. OP, your question is not stupid, as others have implied. I'm a bit surprised that you didn't choose this one as the correct answer.
Comment: It's true that acceptance is not always an exact copy of production, but performing security tests on the acceptance environment is a best-practice and is most common in the field. The idea that test environments don't have users is simply not true. In fact, sometimes it's easier to create test accounts than production accounts. A hip way of testing production environments is with red-team assignments.
Comment: To test user behaviour in production you normally perform social engineering and/or phishing tests, apart from normal pentests. The whole point of properly securing systems is that security holds, even if some users mess up. If your main line of defense is having smart users, your design fails to begin with. Modern pentests take this into account and don't bother with users, unless explicitly scoped.
Answer: The conceptual / contractual side has been covered in other answers, and it's very important.
However, there is also a technical side, especially in terms of "worst case impact" and limiting unnecessary access. Companies should come prepared to the pentest.
Here are some examples:

It should be possible to test system X without access to unrelated system Y.
This may sound obvious, but many companies have a single login system for employees that gives access to all systems -- in other words, the test credentials for X are also valid to access Y, Z, etc.
Instead, the company should be able to issue "limited access" tokens. When designing the credentials system, this requirement should be added even if useless at first (few employees, everyone normally trusted, ...).
Pentests should happen on a realistic environment
Again, may sound obvious but... is your testing environment holding realistic data / scripts / programs / etc.? Do you have an automatic generator for that? Are all interesting cases covered? If not, is it feasible to snapshot and anonymize the real data?
Testing on an empty shell is very unrealistic, and while you could ask the pentesters to populate a database for you they won't know all cases that you care about.
Perhaps surprisingly, your testing system should be more complete than the real one -- you should add all tricky cases that come to mind, even if you haven't really encountered them yet.
Communication lines and expectations should be established beforehand
Who should the pentesters contact in case of trouble? Are you ready to quickly restore the testing (or production!) system and bring it back up?
Do you expect to be notified of critical issues as soon as discovered? Are you going to patch the system while the test is ongoing? Do you expect persistence to be attempted? Cross-server attacks / "lateral movement"? Social engineering?
Even trickier: should pentesters read suspicious data, can they confirm the situation? ("that's testing data, continue" vs. "we didn't expect this data to be there / to be accessible, stop immediately")
What is in scope? Closely related: what is your threat model?
While you can ask pentesters to "figure it out", that's probably not what you want -- remember, the results need to be useful to you and represent your security boundaries.
It's usually best to figure this out together with the pentesters, and be ready to evolve things during the effort if necessary.

Incidentally, I believe most pentesters will happily provide advice on this matter. No one really wants to deal with the fallout of accidental damage or privacy repercussions.
Comment: Well, there are many hatchways :) It's valid to ask for a "recon style" pentest: from zero, find credentials or another way to access (sometimes, find the site itself :D). However, it's also important to see what an authenticated user can do, what are the risks there, etc. For example, employees can legitimately login to the HR system and see their own pages, but generally should not be able to see other people's or edit their own info beyond what the policy allows.
Comment: I'm not sure how testing system X without access to system Y matters with penetration testing. If someone is breaching your system, and can access unrelated system Y through system X, that should be something you'd want to know. If anything, accessing unrelated systems is how most breaches occur.
Comment: That would be a cross-server attack ("lateral movement"). I was referring mainly to access credentials. For instance, let's say we're pentensting the sales tracking system: pentesters will need some form of access credential. Can we limit that? Or we have to give a company-wide employee account that has access to all systems (email, HR, file shares, ...)? Sometimes companies do "wide" pentests where ~everything is in scope, but most commonly the scope is limited -- think of it this way: pentesters have limited time, where do you want them to spend it? Should you take unnecessary risks?
Comment: Why would you give them access credentials? Their job is to figure out how to gain access starting from no credentials. Whether that's a vulnerability in your server, phishing email, some other form of social engineering, etc. If you have access credentials, you're already inside the airtight hatchway.
Answer: The question is of course, turning in circles: if you could prevent the tester from certain access, then you would definitely want to prevent foreigners/attackers from accessing this.
So your measures to keep the pentester from access are exactly those that you have in place and want to test. There should be no difference.
The only possible alternative would be to have the pentesters go after a dedicated test environment duplicated from your prod environment but w/o live data, which is of course more costly and you risk that this clone might nevertheless be different in details and dilute the results.
A milder variation of this could be to cut off only most valuable IP and cilent data databases/NAS etc or attach dummy db's to your prod systems.
Your question is much more about risk treatment of your concerns, which should be covered by proper treatements as defined in Third Party Risk Management:

perform a risk analysis identifying the actual risk potential/value;
this should no only cover data leaks, but also the linked
reputational damage, possible service disruptions (might they shut
down your production or web presence/shop during the test?) etc.
identify possible providers (Pentesters) and do proper due diligence / research. Your concerns are mostly about trust to the
engaged party, so what you need is to build / gain trust and be sure
that this trust is built on facts
Please only use a pentester from our own jursidiction! If something happens, you need to be able to get them in court at your
agreed place of jurisdiction and that evaporates if the tester has no
legal entity there.
define the (legal) boundaries of the tests to be executed
and most importantly: define the legal consequences in your contract (this is often forgotten - people only agree what to or not
to do but do not nail down what happens, if this is violated) in
terms of proper liability clauses, cancellation rights, payment
variations and penalty fees.

As an additional measure for the actual issue of a data leak after the pentest to be able to prove a linkage, you could add some honeypot data to your real data just for the time of the pentest. So, if there is a leak and it contains the honeypot data, you have better proof that the data leak is actually from the pentest.
Answer: You are asking the wrong question. Penetration testers test security by simulating what attackers will do. If you are more worried about pentesters stealing your data than malicious actors I would advise rethinking your security architecture.
In a secure environment, there should be "defence in depth" that has multiple security controls to provide redundancy in case one fails. The controls can be technology (like firewalls, IPS, EDR), policy (don't use your company creds on outside system), or user training (don't click on that phishing link).  The multiple controls should be designed to catch anyone behaving maliciously. The point of pentesting is to find gaps where there aren't multiple or any controls. Finding these gaps then allow for remediation in the form of implementing additional controls in the form of more technology, or procedures, or user awareness training.
Pentesting isn't supposed to be adversarial. It should be a good collaboration by both the pentesters and the admin/security team.
Comment: Some false premises here. "If you are more worried about pentesters stealing your data than malicious actors" -- no evidence to suggest this. There is a difference between having a weak lock that someone could break and inviting people to try to break locks. "Pentesting isn't supposed to be adversarial." -- OP is not suggesting being adversarial, but performing normal due diligence. You do not acknowledge that there *could be* malicious pentesters (when in fact, it's a thing) and assume that there is no risk in hiring a pentester (when there is).


Range of values in slope and aspect changes when I try to unproject my projected rasters

Question: I use the SRTM DEM and I have used the "Project Rater" tool in ArcGIS10.2 in order to project it from GCS_WGS_84 to a certain UTM zone in WGS84. With my projected elevation raster, I have calculated slope (min: 0, max:73 in degrees) and aspect (0-360). When I try to convert again the projected slope and aspect into GCS_WGS_84 (my analysis must be carried out in latitude, longitude) their values change, and I get for slope min:-1,24 max:74 (in degrees), and for aspect I get 1-460! Why does this happen?
Answer: You are correct to use an appropriate projection for computing slope and aspect.  The problems occur when reprojecting those results to another coordinate system (such as lat-lon).  Two things happen:

Grid values must be resampled in order to interpolate them to the new cell centers.
Aspects, being circular data, must be specially handled.  Otherwise the resampling will blithely average, say, 359 and 1 degrees (which are almost the same aspect) and obtain 180 degrees (which is exactly the opposite of the correct average).

To deal with (1), it is usually best to use "cubic convolution" for the resampling, because this tends to preserve the whole statistical variation of the data.  Other methods, especially bilinear interpolation, are local averages and therefore will always reduce the ranges and variances of the data.  Regardless, expect some small changes in statistical summaries of the values.
To deal with (2) is harder.  One of the simpler approaches is to compute two grids from the aspect: its cosine and its sine.  Reproject those, then recompute the angle from the reprojected values (using an arctangent function).  Watch the process carefully, because much GIS software is schizophrenic concerning trig functions: it tends to use degrees to report angular values (like aspects) but to insist on radians as input to trig functions.  Spot-check the cosine and sine grids to make sure the calculations are correct.
You have to be careful with ESRI grids, because they tend to use a code of -1 to represent unknown aspects (horizontal cells).  Before doing anything, convert those codes to NoData values--otherwise the codes will be averaged with the aspects of their neighbors, completely screwing things up.  You can always convert any NoData values in the final aspect grid back to -1 (or whatever).
A slightly better approach is to combine the slope and aspect grids into grids to represent the gradient of the UTM values: one will be the partial derivative with respect to x and the other with respect to y.  Reproject those and then recompute the slope and aspect from them.  Since this is rarely worth the bother--greater errors are typically created by whatever coordinate system is used for the calculations--I will not provide details here.
Answer: Projecting a raster results in a resampling/alteration of the values in that raster because the size/shape/number of cells are changed. It's basically creating a whole new raster and interpolating the values of the new cells based on how that grid lines up with the source grid. The help file usage notes describe some of the issues involved in detail.
Comment: It is better to project the DEM then create the slope/aspect from that rather than projecting slope/aspect, the resampling of the slope/aspect rasters makes them almost unusable.
Comment: @Michael Away from the vicinity of the Equator, both aspect and slope will be badly calculated if lat-lon is used as the coordinate system.  They should be computed in a reasonably accurate projection and then reprojected, which seems to be the opposite of what you are recommending.


Where can I find a list of cooperative "beat the game" games?

Question: I know of Pandemic and I remember having played a game about mountain climbing where the goal was to as a team climb the mountain and get back down safely but there must be more of these games where one play as a team rather than against each other. Where can I find a good list of such games?
Comment: "Flash Point: Fire Rescue" & "Zombicide" are two good ones
Comment: [What cooperative board games are there that I could safely play with my wife?](http://boardgames.stackexchange.com/q/9/50)
Comment: By the way, I think this question is really just an instance of, "Where can I find a list of games that meet specific criteria?"
Comment: @AndrewVandever I totally agree. However without a link to what you mean with that comment I have a hard time understanding what you mean... Is it missing some tag for that or what point are you trying to make?
Comment: So for example you could check here: http://boardgamegeek.com/tag/cooperative. @sitnaltax's answer is really good. My point is that 95% of it is also applicable to the questions, "Where can I find a list of 2-player games?", "...worker placement games?", "...deck building games?", "...Lovecraft-themed games?", etcetera. So this is a very specific question with an answer that is very general. I would also say that the identify-this-game tag seems to generally consist of questions for which the answer is very specific (http://boardgames.stackexchange.com/questions/tagged/identify-this-game).
Answer: BoardGameGeek's advanced search can be used to find a large list of co-op games. You can then sort or filter this list in several helpful ways. This form is a little bit daunting, but powerful. From the "Board Game Mechanic" list, select "Co-operative play". You will probably also want to check the "Filter Expansions" box and, if you are interested in widely available games, a minimum rating and minimum number of user ratings such as 200. (Here is a direct link which will perform that query for you.) You might want to sort the results by Geek Rating, which penalizes games that have fewer ratings, or by Average Rating, which does not.
Comment: An excellent answer. I would like to point out, however, that this search does have some false positives, such as _Betrayal at House on the Hill_ -- the game is co-op at the start, but once the Haunt begins, the game is almost guaranteed to become one-vs-many or a free-for-all (depending on the specific Haunt that occurs, which is random with some weighting). I say "almost" guaranteed, because IIRC there are one or two Haunts which maintain the co-op aspect of the game... but _Betrayal_ 2nd edition has 50 different Haunts.
Comment: True. It is interesting (and perhaps a testament to the fuzziness of definitions) that Betrayal, Scotland Yard, and Shadows over Camelot have the "Co-operative" mechanism tagged, while Letters from Whitechapel and Battlestar Galactica do not.
Answer: Check out http://boardgamegeek.com/ and play with the advanced search feature. You'll find everything you need. It probably will be a better source of knowledge than your local game store, as BGG is not limited to what it has on the shelves and does not try to sell you something.
(btw,  the game you played was most probably K2)
The link to boardgamegeek for coop games.