What if we can feel magnetic field?

Question: Suppose human being evolved a special type of sensory organ that can detect Earth's magnetic field, beside discarding compass when hiking what else can we benefit from this extrasensory gift in the present day?
Comment: If you add a suitable sense organ, it is *not* "extrasensory", as that means without using senses, e.g. physic powers.
Comment: @MichaelKjörling My guess is that, like sound, we'd be sensible to only some fields intensities/frequencies and we'd filter out the others. That's another thing I'm curious about, are we sensible to raw magnetic intensity or are we sensible to the oscillations.
Comment: Can we detect any magnetic field or are we just attuned to the Earth's? the former has some pretty interresting advantages.
Comment: What 3C273 said, though I'm not so sure it would be only advantageous. If this sense would detect *any* magnetic field (of sufficient strength), modern civilization would probably leave these being(s) rather confused from the vast number of different magnetic fields of varying strength and orientations. Have you ever tried using a compass near a high-voltage power line?
Comment: @3C273 my inspiration is how certain species of migratory birds or animals are able to find their nesting grounds despite being thousands of miles away. I have no idea how these animals feel this magnetic field but the brain can recognize familiar pattern and let you said it choose to ignore unimportant noise any idea what kind of pros we can gain from it?
Comment: @Michael Kjorling it could be a gift or perhaps like you said it's a curse either way I believe this is definitely worth exploring.
Comment: @JDlugosz you are right I used to think that the term extra sensory means beyond existing senses so it really means without physical components?
Answer: One group has connected a compass to the brains of blind rats and found it improved their maze navigation skills to be comparable to sighted rats: link. The point there is to develop a prosthesis for blind humans, so we might get to see this question play out in our lifetimes.
People with such a prosthesis (or whatever method your story uses to provide this sense) might be able to tell if nearby electronics were on, perhaps to the extent of detecting spy devices. That would take a lot of interpretation skill, though, so I suspect only a small percentage of people with this sense could detect things that small. As PipperChip pointed out, MRI machines wold trigger this sense so fake medical centers could be caught.
Other than navigation in the absence of technology, I don't think the average person would find this useful day to day.
Answer: Navigation would come a lot more easily to us which would probably have lead to human exploration and migration a lot earlier in history. People would travel further which I think would mean they would have more exposure to other cultures and as such would mean that in modern times, there is far more tolerance and understanding between civilisations and races, and the sharing of ideas leading to improved science / technology / society.
Whether this would have lead to an increase in war or an increase in peace (or perhaps just different wars and peace, war being more about competition for resources than cultural difference) is probably up to the writer.
Going back to more recent history, I'd think that empires would possibly have been larger.
I don't agree with the people saying that it would be odd or disorientating around machinery and magnetic fields. If it were something we evolved (rather than an implant or something), then our brains would be well able to tell the difference and make sense of it I think. e.g. it would be comparable to us being able to see, but not being disoriented by lightbulbs in the vicinity, or being able to smell without being overcome by every particle-emitting object we walk past. Also, devices would have been invented with this in mind.
Answer: A while ago a friend of mine attached small neodymium magnets to the backs of his fingernails with nail polish for a few months giving him a sense similar to the one you describe, though much more localized.
One day my friend and I were going through a shed full of tools and electrical equipment. My friend went to pull something out from under a desk when he yelled and suddenly jumped up away from whatever was under the desk. It turns out that whatever it was had been shorting 120v AC (what comes out of a wall socket in the US) through its metal chassis and thanks to the magnets on my friends fingers he could detect the electricity without receiving a shock.
So aside from the obvious navigational benefits, a magnetic sense would allow you to detect possibly dangerous AC in your environment.
Comment: I have had a small parylene coated neodymium magnet implanted in my left hand for over five years. It's worth noting then, that this only works for detecting very strong DC fields or slightly less strong AC fields. It does not work at all for Earth's magnetic field. Still, it's pretty awesome, even if not useful for navigation.
Comment: @Samuel Obviously you can't detect the earth's field, but I'm curious, what produced DC fields strong enough that you could detect them?
Comment: Permanent magnets.
Comment: Oh, I was thinking you were talking about enough constant current to produce a magnetic field which you could feel in your hand.
Answer: Some things to consider, if we have a bit of metal in our heads (perhaps like pigeons) which tell us which way is north:

Magnetic Fields from machines could be felt. MRI machines, labs with magnets in them, even strong speakers could feel very odd. This is because these things produce magnetic fields, which could interfere with this sense.
Local Variations in the Earth's Magnetic field could be felt. While it is true that a compass will generally point to magnetic north, this isn't the case in every location on earth. These variations could be another aspect of a place which makes it unique.
Getting lost, as the OP mentioned, would be harder, and not just during hiking. We would usually know which way is north, which can be helpful in every environment.
You may be able to detect buried power lines, as a current creates a magnetic field. (See Ampere's Circuital Law) This could be both good and bad; construction site diggers could tell where not to dig, but terrorists could find them more easily.
Comment: Nice answer, but don't overstimate the power of "knowing where the north is": it surely helps orientation-savvy people, but it would be completely useless for many others. I would still get lost everywhere.
Answer: Radio Waves are a type of electromagnetic radiation. Strong radio waves are known to cause confusion to species of migratory birds who rely on magnetic sensing ability to tell the direction.
Overall, my hypothesis is this:
If an evolved brain has the ability to sense magnetic field (and thus radio waves), they would be able to process it at least to some basic level (feeling signal strength of wifi, being able to tell population in an area by overlapping radio signals etc.
Furthermore, at some point, a mutation can cause a person to be able to decode signals and thus have the ability to directly receive digital communication which gives him/her the evolutionary advantage. From there on, the possibilities are endless.
Answer: JOURNAL OF NEURAL ENGINEERING : Beyond sensory substitution—learning
the sixth sense
A belt is worn that has 13 evenly spaced vibrating devices.  The device closest to magnetic north lightly vibrates.
Over a period of weeks the users would develop a feel for the orientation of different locations and how they related spatially to one another.
One experiment blindfolded the users and then led them along the edges of large geometric shapes.  The users were made to walk the last leg of the shape on their own.  Using the device, and being trained in using the device, increased the ability of the users to arrive closer to the origin point.

What if we can feel magnetic field?


Theoretical proof forbidding Loschmidt reversal?

Question: In a famous debate, Loschmidt criticized Boltzmann's new theory of statistical mechanics by asking what would happen if the velocities of all the atoms were reversed. Typical objections are that such a reversal would not be possible without a fine detailed control over all the atoms of the system. However, spin echo experiments are a clear counterexample, albeit one restricted to very special cases. Is there any theoretical proof that without a fine detailed control over most of the atoms of a totally isolated system, a Loschmidt reversal would be extremely improbable? Remember such a proof would have to cover all sorts of elaborate complicated contraptions. Are reversals impractical for theoretical reasons, or because of a lack of ingenuity?
Comment: Collisions are very often irreversible due to soft radiation. It is impossible to reverse the soft radiation in a general case. It is an inelastic process like breaking a glass into large and small pieces.
Comment: Quantum mechanics really forbids the kind of detailed microscopic control that would be needed for the Loschmidt reversal. While in classical physics one could say that for most initial states, the entropy will increase, while for a carefully selected special initial state, it may decrease, quantum mechanics says something else. It always predicts the probabilities only and the probabilities of a big decrease in entropy is small for *every* initial state, much like if one averages over initial states in classical physics.
Comment: @LubošMotl: Although QM deals with amplitudes of probabilities, it is not the reason for irreversibility. Irreversibility is first of all in creating and absorbing too many soft quanta, which are inelastic processes difficult to launch backwards. If one manages to create a gap in the energy spectrum, soft modes disappear and reversibility becomes manifest experimentally.
Comment: Related: http://physics.stackexchange.com/q/10690/2451 and http://physics.stackexchange.com/q/1822/2451
Comment: Note that what @LubošMotl says is only true if you measure the system before you try to reverse it. For an unmeasured, isolated system it's always in-principle possible to do the reversal. Also note that by "state" he means "density matrix" and not "wavefunction."
Answer: It's impossible to forbid Loschmidt reversal by any theorem. Poincare recurrence is the dreaded counterexample. Finite closed systems will return arbitrarily close to their original state. The only thing Loschmidt failed to anticipate is it would take far longer than expected: an exponential time.
Using the second law to "forbid" reversals is circular because this very same result is used to "prove" the second law in the first place.
Comment: Poincare recurrence needs strong assumptions that are violated for the universe as a whole. Thus there is no counterexample.
Answer: Lorschmidt reversal was an attack on naive Boltzmann ideas, based on a truncation of the full evolution to the Boltzmann equation. The Boltzmann equation is irreversible, it doesn't work backwards, and Lorschmidt is simply pointing out that it can't be right, because if you do a reversal, the Boltzmann equation must reverse in time, and it doesn't work backwards.
The reversal itself is not a problem for modern ideas--- you could probably actually do it. In modern ideas, the Boltzmann truncation is unnecessary, the entropy is directly defined on the unknown position of the state in phase space. So the entropy gain is only a measure of the loss of information. If you have a machine which can reverse the atoms' motion to approximately restore the original state, this means, by definition, that the information in the original state has not been lost yet, so the entropy has not gone up until the reversal no longer works.
There is no reason you can't build an (approximate) reverser, but it won't work perfectly. To make a perfect reverser would require infinite precision classically, it would require perfect knowledge of the particles (hence the reason you have a small entropy--- you know where everything is). Quantum mechanically, you would need to reverse outgoing photons, and do hopeless things.
The proof that you can't do Loschmidt reversal for a generic system is simply that it would reduces the entropy. Approximate reversals are fine, and the spin echo is an example.
Comment: Indeed, and there are some cases in which an approximate reversal is quite feasible - the most obvious being reversing light emanating from a point source through the use of a curved mirror.
Comment: Nice answer! For the irreversibility of Boltzman equation, see https://physics.stackexchange.com/q/636545/226902
Answer: Rather more hand waving than a "proof", but...
Note that in quantum mechanics the meaning of time reversal symmetry is subtly different then it is classically{*} and they system can not be expected to retrace it's history in reverse.
Add to this any degree of sensitive dependence on initial conditions (which is certainly possible in classical systems), and you can magnify quantum effects to macroscopic differences even in systems that appear to be fully amenable to classical description.

{*} The cross-section for the time-reversed reaction is the same as for the forward reaction in all cases{+}, but you can't pass "backward" through the "collapse" of the wave function (however you understand the selection of eigenstates to proceed).
{+} Well, for the CPT-reversed reaction, anyway.
Answer: The Loschmidt paradox is valid only in bounded systems with finitely many degrees of freedom, as the proof of Poincare recurrence fails in an unbounded domain, or if the number of degrees of freedom is infinite.
As the true degrees of freedom are those of fields (though actually quantum fields), hence infinitely many, there is no Loschmidt paradox.
Actual reversal can be done experimentally ony for systems with a tiny number of degrees of freedom, typically just one.
Comment: While you're right about the "unreality" of the paradox for everyday large enough systems (and only for those, entropy is macroscopic), you're not right about the recurrences in principle (the first paragraph). First, it is not known whether the Universe is spatially closed and even if it is not, the Poincare recurrences do occur because the entropy of our Universe is at most $10^{120}$, as determined by the de Sitter cosmic horizon, and by the black hole complementarity applied to the cosmic horizons, it applies everywhere. After $\exp(10^{120})$ units of time, there have to be recurrences.
Comment: @LubošMotl: Why does a bound on the total entropy imply Poincare recurrences?


How many queens can be on a chessboard without attacking each other?

Question: What is the maximum number of queens that can be placed on a standard 8x8 chessboard such that no one of them is capable of attacking any of the others in a single move?
Comment: See related discussion at meta http://meta.puzzling.stackexchange.com/questions/63/are-two-person-strategy-games-on-or-off-topic
Answer:
 8.

Because:

 Obviously, you can't have more than 8, since you would have a row (and column) with more than one queen on it.

According to Wolfram-Alpha, there are

 12 unique solutions, plus an additional 80 solutions from rotation/reflection.

One possible solution is:

A list (and images!) of all

 12 base solutions can be found both at the above Wolfram-Alpha link and Wikipedia.  (Thank you Kevin for the link).
Comment: http://en.wikipedia.org/wiki/Eight_queens_puzzle
Answer: Sorry for reviving a 5 years old question, but I can fit:

 16 queens

I hope to avoid downvotes by pointing out that this troll solution satisfies all the conditions of the original question.

 (
Comment: A troll solution is still a solution. Take it as an oportunity to see the importance of a good design in puzzle creation and an example of thinking out of the box.
Comment: Is there *really* a point to necroing a 5 year old question with a response you openly acknowledge is a troll answer that clearly doesn't address the intent of the question? Please don't.
Comment: Why is this a troll solution? Seems perfectly reasonable to me
Comment: Yes, pawns are not prohibited in the question, nice creative thinking!
Comment: Just missing to approve that it is the maximal solution.(+1)
Comment: @Rubio - given that the point of this site is entertainment, I would say this is a great answer. There are many questions (especially with the riddle tag) where the funny yet obviously wrong answers are sometimes the most fun of all, especially when they fit within the parameters of the puzzle. I'm pretty sure I have my fair share of them. [Here's one.](https://puzzling.stackexchange.com/q/33734/17024)


During the Berlin Blockade, why didn't the people in West Berlin just go over to buy food in East Berlin?

Question: It wasn't until 1961 that the Berlin Wall that was set up, what was to prevent the West Berliners from going over to the east?
Comment: Something is seriously wrong when it comes to the tagging of this question.
Answer: Note that food was rationed at that time, not generally bought.
Wikipedia says, emphasis mine:

In response, starting on 1 August, the Soviets offered free food to anyone who crossed into East Berlin and registered their ration cards there, but West Berliners overwhelmingly rejected Soviet offers of food.

So, yes you could get your food in East Berlin, but it basically meant "giving in", becoming a citizen of the Soviet zone.
Note that most people in West Berlin were quite happy to not be part of the Soviet sector, and wanted things to stay that way.
Answer: West Berlin wasn't just shut off to the Allies, it was under total blockade. Quoting from the relevant Wikipedia article:

On 24 June, the Soviets severed land and water connections between the
  non-Soviet zones and Berlin.[34] That same day, they halted all rail
  and barge traffic in and out of Berlin.[34] On 25 June, the Soviets
  stopped supplying food to the civilian population in the non-Soviet
  sectors of Berlin.[34] Motor traffic from Berlin to the western zones
  was permitted, but this required a 23-kilometer (14.3-mile) detour to
  a ferry crossing because of alleged "repairs" to a bridge.[34] They
  also cut off the electricity relied on by Berlin, using their control
  over the generating plants in the Soviet zone.[31] Surface traffic
  from non-Soviet zones to Berlin was blockaded, leaving open only the
  air corridors.

The sources indicated by the footnotes are Miller's To Save a City and Turner's The Two Germanies Since 1945.
Answer: After WW2, the German currency (The Reichsmark) took a large hit in value, both due to losing the war, and the Soviets continuing to print RMs (precisely to prevent the economic recovery of Germany). The Western Governments, to facilitate the recovery of (Western) Germany introduced the Deutsche Mark (DM), which the Soviets disapproved of, banning the use of the DM in the eastern sector, while introducing their own new currency for their sector.
Due to Berlin's status as an enclave within the Soviet zone, the Western Allies did not initially introduce the DM to Berlin, seeking a agreement with the Soviets. As the Soviets were against the new currency in general, they refused, and decided to introduce their new currency to their sector, including Berlin. This led to the West introducing the DM to their sectors of Berlin
The introduction of the DM to Berlin was what precipitated the Blockade, and one of the goals of the Soviets was to force West Berlin to adopt the Eastern Currency. By forcing the West Berliners to purchase food from the east, the Soviets would have insured that the only currency they could use was theirs. Due to the success of the Airlift, this was never required of West Berlin, which kept the DM over the East Mark.
The precipitating reason for the blockade is on page 18 of Miller's To Save a City.


What are general tips to test a static website?

Question: One of the NGO which work for the children welfare ask me to test their website. That's a completely static website on the single page simple navigation toward the section so I need general tips to test the website, honestly speaking I am feeling bad because I could not find any bug or mistake in it.
Comment: What do you mean by "general tips" ? Are you asking about what should be addressed by your tests or more generally about how you should test the website and communicate the results? Keep in mind that testing a website is more about validating a scope/usage than hunting bugs.
Comment: How testing an 'NGO site for children' relevant for the question?
Answer: Look & Feel

Test for appearance like how does it look in IE, Chrome, etc.
Test for accessibility so that your site is adopted for people with impaired vision (fonts, colors, contrast, etc)
Test for mobile devices layout
Test if it is comfortable to interact with the site using touch pad
Check for the proper favicon
Check for "error pages". Make sure they are no default and have the site common style.
If there are the forms check if the order of switching the field focus when user presses TAB is correct

Integration with 3rd-party

If there is the social media intergation check for "Share" button or analogue
If there is some donation services integration, check it
Check integration with site analytics systems if any (e.g. Google Analytics)

Security Testing

If there are the forms, check for input limitations
Also, if there are some forms, check for vulnerabilities: https://www.owasp.org/index.php/Category:OWASP_Top_Ten_Project
Check the server for negative cases. You can pretend to be a website or an attacker and try to send different requests of different composition to check how the server is reacting

Performance Testing

Check for some non-regular load to be sure the site will not go down with the growth of popularity

SEO

Check for robots.txt to make sure it masks out the pages which are not to be indexed by search engines.
Check for site.xml to make sure there is a proper structure described

Other

Check for console to make sure all the page resources are loaded properly
Check console to make sure there are no javascript errors (for all the browsers).
Check for cookies: either they are used to define a user session for a site or for site analytics.
Comment: If site use SSL, [...], else use SSL.
Comment: @kubanczyk: Modern trends are moving towards it effectively being not optional. Why would you not provide it? Why do you want your users to not have privacy?
Comment: @AlexeyR. what financial resources? I can run an nginx server with a free certificate from LetsEncrypt on a $5/month DigitalOcean instance. If the site is popular enough that it's getting more than ~20 hits per second then they should be able to spend a little more on a larger instance.
Comment: Not enough for a new answer, but I'd also say you'd want to review colors for both modernness and visibility to a color-blind person.  For example, you could use something like Google's Material UI to determine good color combinations. https://www.material-ui.com/#/customization/colors
Comment: If site use SSL, make sure make sure there is no mixed content. Also how it looks on mobile.
Comment: @aloisdg It's optional for a reason, and nowadays it's called TLS.
Comment: @kubanczyk you are right
Comment: I think sometimes this is a question of budgeting since having ssl worths  something. If you do not transfer a sensitive data between server and client you might not need to waste financial resources for keeping SSL and computational resources to encrypt the data.
Answer: no one has mentioned these yet.

Check for Spelling Mistakes
Check for Grammar Mistakes
Check for use with Page Readers for the Blind
Keyboard only Navigation

Keyboard Navigation and Page Readers go hand-in-hand
Comment: On a similar note as page readers, the readability for those who are colorblind.
Comment: Spelling mistaks are one of my pet peeves
Answer: Try with different screen resolutions and different web browsers including mobile.
Answer: Test with Google Pagespeed and make sure you're minifying css/js, using gzip, and optimizing images with something like ImageOptim. If you're self-hosting, try accessing it on your phone on cellular data, to make sure it's accessible outside your network.
Answer: In that case, some of my tests would be:

Test whether the appearance (GUI) is fine.
Check the common contents like menu, logo etc are consistent in every web page in case of multiple web page site.
Test the basic functionalities in the site are working properly.
Check the website appearing and working properly after any update is done.
Media and other files are showing and downloading properly.
Check in multiple browsers (Firefox, Chrome, IE, Edge, Safari etc). Check in both old and latest versions.
Check in multiple OS platforms (Windows, Mac, Linux etc), specially in the latests.
Check the site from mobile (Android, IOS, Windows phone etc).
For cross browser and cross platform testing, I use this site:
Browserstack: https://www.browserstack.com/
Test whether all internal links are working properly.
For example: Personally I use Xenu tool that checks websites for broken links.
Xenu : http://home.snafu.de/tilman/xenulink.html#Description
Check title and status bar message.
Check for grammatical and spelling errors in the contents.
Perform load and performance testing on the site. JMeter is an open source load testing tool that you can use.
JMeter: https://jmeter.apache.org/
Perform security testing. @Alexey R. and @drewbenn described this nicely.
Answer: I'd certainly run the site through accessibility checkers if it's public facing to ensure it's appropriate for as wide an audience as possible.
Ideally you'd want to ensure it's accessible for screen readers, keyboard accessible etc
https://wave.webaim.org/
https://webaim.org/resources/contrastchecker/
https://achecker.ca/checker/index.php
Answer: To test the performance of the web site- google provides free tool:
https://developers.google.com/speed/pagespeed/insights/
You just need to provide portal address of your website and, click on analyse.
It will quickly perform page searching and heath test.
It will also provide result and points to address to enhance the performance.
Comment: that page is only for load speed, I am not sure that this answer fully answers the question because this is not a Manual Test,  this is automated by Google and only looks at the speed in which the page is loaded.  please correct me if you see it otherwise.
Answer: As usual, when you are confused or unsure about something, it might be useful to get back to fundamentals of testing and see whether they provide any guidance.
Testing is gathering information with intent of using it when making a decision. Bug is something that threatens value of the product. (These are simplified versions of definitions promoted by context-driven school of testing.)
These are some questions that immediately come into my mind:

If I support case of this NGO case and want to support them in particular, how do I do it? How can I send them money? How do I get in touch with them to work together? Are these topics covered anywhere on the website?
If I consider supporting them, but I am unsure, how can I learn more about their past performance? What have they done? Is this verifiable by independent 3rd-parties?
If I know about something that might be potentially interesting for them (like I suspect that child in my neighbourhood might be abused), how do I get in touch with them? Can I do it anonymously?
If I am child that suffers from abuse, how can I reach out to them to help me?
What is area that they operate on? One district, one city, region of country, entire country, internationally?
If I am government official, can I easily verify that all relevant laws are being followed?

To summarize. First, you should understand why they have website and whether the thing that they have fulfils that purpose. Then, you should think if there are any other reasons why they should have website that they haven't thought of.
Example: maybe they have website to raise awareness of all the things that they are doing. Then, you should verify if their current website does good job at that. But website is also great way to secure some additional funding. If they aren't making it easy for people to donate, you should point this missing opportunity out to them.
Don't be afraid to speak about problems even if you suspect they might not be able to fix them. But never insist that they introduce certain changes - you are here to provide valuable feedback, but it's up to them to decide how will they use it.


Is it possible to have a negative output using only ReLU activation functions, but not in the final layer?

Question: I know that if you use an ReLU activation function at a node in the neural network, the output of that node will be non-negative. I am wondering if it is possible to have a negative output in the final layer, provided that you do not use any activation functions in the final layer, and all the activation functions in the previous hidden layers are ReLU?
Answer: Yes, if there's no activation function in the last layer, the weights could simply be negative there, so the network would multiply a positive value with a negative weight, therefore outputting a negative value.
There is still an activation function, but it is the identity.
Answer: I guess you are using NN for Regresions.
In the most common aplication a scale of the outputs is implemented.
This is recommended. Specialy if you have more than one output with diferent scales.
Otherwise, you will remunerate the neural network for correcting the error of one variable over the other.
If you still want to avoid a scale of the outputs. Yes. You can use the identity function in the output layer or a linear function (tha same with different slope).
The weights and bias of some conections will become negative and the hidden neurons are going to work as always.


Rotation in 3D space using Quaternion

Question: System Configuration
I have two simulation systems (which I am going to call Sim-A and Sim-B) where I am going to spawn an entity created in Sim-A inside Sim-B.
Expected outcome
The entity created in Sim-A appears in Sim-B in the right position with the correct orientation.
System Input
The position of the entity created in Sim-A received in Lat/Long/Alt format (it assumes WGS-84 spheroid) and the orientation in Euler angles.
The Euler angles would help me to transform an entity from its world coordinate system to entity coordinate system by applying the Euler angles in the order of heading, pitch and yaw. Below is how it is documented.
" The order of rotation is first, rotate about z by the angle psi (), then about the new y (y') by angle theta (T), then about the newest x (x'') by the angle phi (I). The positive direction of rotation about an axis is defined as clockwise when viewed toward the positive direction along the axis of rotation."

However, in Sim-B this rotation is defined in Quaternion and it assumes a perfect sphere for the world (not WGS-84). As a result, I have to convert Euler to Quaternion before sending the information to Sim-B.
I have achieved this by applying ZYX conversion (page A-11) given in [here][2].
Challenge
When I pass the position and orientation of an entity created in Sim-A to Sim-B ( Sim-B uses ECEF system, so I do another conversion to go from LLA to ECEF), it appears in the correct LLA position but its orientation is incorrect (shown in the figure.).

This can be fixed by adding some value to the pitch and roll but it is not mathematically sound. Also, these values might change (haven't tried) if you spawn the entity in a different location of the earth due to its shape.
So, I would like to know the right way of correcting this issue (i.e. how to make the entity to stand upright). Assume that I can get the Up, Front and Right vector of the entity when it is spawned in Sim-B.
Answer: If you can obtain the Up, Front and Right vector, you have a full orthonormal basis to reconstruct the quaternion, you don't need to worry about Euler angles, just forget the Euler angles and build the quaternion directly from the Orthonormal Basis (x axis = -Right, y axis = Up, z axis = Front).
The simplest way to do this is to build a rotation matrix from the basis and then construct the quaternion from the rotation matrix, should be straight forward and should always give you the expected result.
Here's how to do the first step:
http://renderdan.blogspot.cz/2006/05/rotation-matrix-from-axis-vectors.html
Here's how to do the second:
http://www.euclideanspace.com/maths/geometry/rotations/conversions/matrixToQuaternion/
Hope it helps.

Rotation in 3D space using Quaternion


Question is how to deal with customer that is not paying through proper website channel and goes on increasing his offer?

Question: Yesterday i got an offer from a client to give 1500 reviews and 50 post on his social account,The client offered me $250 but he was saying that i will pay you by paypal not through website pay channel.i said to him that i will start my job until you send payment through proper site channel now he goes on increases his offer.I'm now confused whether i accept it or not? There is also a risk involve in this as after job completion possibility that he will not pay so what should i do?
Answer: Do not budge on this. If you have an acceptable payment channel established already and this client reached out to you through this platform, then there is no reason he should be demanding you to use another service. Furthermore, no sensible client would substantially increase the amount they are willing to pay strictly on the basis of be allowed to use Paypal over your trusted payment method.
This client may be legitimate, but they are acting in a suspicious manner that suggests unknown ulterior motives.


Can the new iPad record dictation while recording audio?

Question: Apple has featured Voice Dictation as one of the marquee features of the new iPad. Either through a app that ships with the iPad or an App Store one, can the iPad record audio (as for a podcast) and at the same time transcribe the text therein?
Answer: No, this does not work.
I started a background recording with DropVox, then switched over to PlainText and tapped the dictation button and dictated a sentence. I then switched back to DropVox and it looked like it was still recording (the counter was still going up). I stopped it, it uploaded the file, but when I listened to it the start and end were there, but the part from when I started dictating to when I opened DropVox back up wasn't. Very strange, but ultimately the answer is it doesn't work.
If you're curious, the resultant audio file can be found here. "And it looks like the timer's still going" was said after DropVox opened back up.
Comment: alas! Transcripts of podcasts would have been a great thing.
Comment: @DanielL We might be able to feed the podcast file through the dictation feature
Answer: OK, so a possible workflow is thus:

Record audio file
Transfer audio file to iPhone or iPod touch
Sit iPhone/iPod touch next to iPad
Get text editor app set up to transcribe on iPad
Play audio via speakers on iPhone/iPod touch
Generate transcript of audio file
Answer: I've had a look in developer docs and I don't think it's possible for any app to do this. I was thinking of a line input recording audio while Voice Dictation processes input from the built-in mic - but the developer docs don't show me any way to select which audio input is active at any one time.
There is only a simple boolean available to AVAudioSession, the class providing the recording context for an iOS app, to determine whether an audio input source is available with no means of enumerating or selecting any specific input.


What would happen if Jupiter and Earth were at the same distance as the Moon is from Earth?

Question: If Spock came with a super machine capable of moving planets, and placed Earth so close to Jupiter as the Earth's moon, the gravity of Jupiter would make us fall into it?
Comment: To sum up Gerald's answer, we would be doomed.
Comment: @ott-- On the contrary, this question is about the astrophysical effects of a counterfactual. It's perfectly fine here.
Comment: This belongs to Science Fiction, not to a serious SE site.
Answer: That's no good idea. Earth wouldn't necessarily fall into Jupiter in the short run, provided it orbits Jupiter fast enough (within about 1.7 days), and on a circular orbit, but we would risk to collide with Io, destroy it by tidal forces, or change its orbit heavily.
The other Galilean moons would get out of sync and change their orbits over time.
Tides would be severe on Earth, not just limited to oceans, but also for "solid" ground, as long as Earth isn't tidally locked. This would result in severe earth quakes and volcanism.
Our days would be dim due to the distance to the sun. After tidal locking of Earth and ejection/destruction of Io the tides as heat source would be lost, oceans would freeze, temperature would fall to about -160°C mean temperature. During the polar night oxygen would probably condense from the atmosphere and form lakes, may be even nitrogen. By this atmospheric pressure would drop.
Since Spock is smart enough to know these consequences in advance, he wouldn't do it.
Comment: Some, but not all, of the bad effects could be alleviated by changing the conditions a bit: Move Jupiter into Earth's current orbit around the Sun, and put Earth into a circular orbit around Jupiter in tidally locked rotation. Once Earth's shape settles down from the new tidal forces, conditions shouldn't be *too* bad. Interactions with Jupiter's other moons might be a problem -- so move them. Interactions with Jupiter's magnetic field and radiation belts would still be, ahem, interesting. We should get some truly spectacular auroras, and we could see how Jupiter reacts to the extra heat.
Comment: @KeithThompson Even with your improvements, I think (can't do the math to be sure), but 384,000 KM (are we doing distance from Surface or from Center - with Jupiter, that matters a lot), but that would be close to the liquid roche limit.  Add the magnetic field and I think Earth would fairly quickly lose it's atmosphere and oceans, giving Jupiter a temporary, very pretty ring system, which solar heating and Jupiter's hot van Allen belt would make mince-meat out of fairly quickly, leaving the Earth a barren, dead, rock.     Still not a great outcome for us, even with your adjustments.
Comment: I think it would be outside the Roche Limit at 384000 Km, as all four inner moons of Jupiter are closer than that (Metis, Adrastea, Amalthea and Thebe), and Amalthea (at least) is either ice or a rubble pile, since it has a density of around $0.9 g/cm^3$.  EDIT:  Just looked it up.  Thebe is (officially) outside the fluid Roche limit, Amalthea inside (though somehow is holding together despite its composition).
Answer: The what if is superficial it could never exist, but if one were to imagine then; the out come would be very bleak for Earth and Mankind alike. Jupiter has the strongest gravitational pull of any planet in our solar system. It is one of our solar system's gas giants,or Jovian planets; most of it is made of metally hydrogen, the gas succumbs to the ultimate power of Jupiter's gravity, mass and temperature. It then turns from a gas to a liquid metal. These immense elements make it impossible for such an event to ever occur, but still cool to wonder about.
Comment: It's symptomatic that an utterly clueless answer with a large unattributed picture maintains a positive score on this site.
Comment: What do you mean by "H3"?
Comment: "Jupiter has the strongest gravitational pull ... most likely in our galaxy."     Huh???
Comment: i will be changing my answer
Comment: Jupiter's innermost core is probably made of similar elements as Earth, Iron, Nickle and other heavy elements.  It might well have a metallic hydrogen core around that, but no H3 (if by that you mean Tritium). Tritium has a very short half-life and so there's essentially zero of it on or in any planets.


Add feature in carto builder

Question: With carto editor I could add feature but now in carto builder I don't know how to do it. Where is the button "Add feature"?
Answer: Now you can add and edit your layer features in BUILDER using the Geometry edition feature in CARTO BUILDER as explained in this guide. On the one hand, you can create a new map with an empty dataset and start adding new geometries/features. Do notice that as soon as you add one, the rest will be have the same geometry type (point, line or polygon).

On the other, you can edit points and/or edit/remove vertices of polygon/line features and its thematic data after clicking on them.

Finally, something to point out is that only BUILDER layers without any analysis attached could be edited in this way. Source layers could be accessible if the user can drag the layer node out.
Answer: Add feature to Carto builder.
The CARTO Editor had the option to share the viz.json URL
The CARTO Builder does not have this option.
According to CARTO, it seems that the current version of CARTO.js (v3.15) is not fully compatible with the Builder.
https://carto.com/learn/guides/intro/migrating-from-carto-editor-to-carto-builder

Add feature in carto builder


Did Hitler, or any non USSR residents in the 30s-40s know about Stalin's purges?

Question: In Downfall, Hitler laments about how he should have purged the military officers like Stalin did, so my question is: would people have actually known about Stalin's purges during that time ?
Comment: Dunno did anyone read the NY Times? http://query.nytimes.com/gst/abstract.html?res=9B05E6DB1638EE3ABC4953DFB5668383629EDE
Comment: Please provide citation for "Downfall"  The NYT article makes me wonder if this is trivial.
Answer: Of course. It wasn't much of a secret. Some 85% of the Soviet military's top positions were removed; the scale alone makes it rather impossible to hide. In fact, knowledge that Stalin had decapitated his own army's backbone was one of the factors motivating Nazi Germany to invade.

But not only did [the Great Purges] do incalculable damage to the future construction of Soviet military strength; they also instilled in Hitler and his advisers an indelible notion of the weakness of the Red Army. To Hitler, this very weakness was an invitation to strike before a powerful military machine could be constructed. In Hitler's eyes, then, Stalin's purges gave him the chance. He thought Stalin must be mad.
 - Kershaw, Ian. Fateful Choices: Ten Decisions that Changed the World, 1940-1941. Penguin, 2007.
Comment: much the same is opined in Edvard RadzInsky's "Stalin" (Doubleday, 1996).
Answer: Yes there were many trials. The extent was not nesscarily known but the removal of many senior officers was well known.
http://en.wikipedia.org/wiki/Moscow_Trials
Answer: This is a very good question. The answer is: yes. Everyone who wanted to know, knew.
(This includes Hitler).
There were plenty of people who managed to escape to the West, they published their accounts. There were plenty of other sources: Soviet union was never closed completely.
On the other hand, enormous pro-Soviet propaganda, supported by many left-wing Western intellectuals (some of them simply bribed by the Soviet regime) strongly influenced the public opinion. As a result the "general public" did not know much. The Soviets used assassination and intimidation to silence those who wrote on the subject in the West.
By the way the same happens now: Russia continues to manipulate the media of the West to a large extent. I mean the Russian aggression in Ukraine, of course, but not only that.
Everyone who cares knows about assassination of Litvinenko, who exposed Putin's regime, for example.
(Downvoting of this answer is another proof of what I wrote, by the way).
Comment: I suspect the down-vote(s) are due to a lack of sources rather than Putin targeting you.
Comment: References? You want a list of published in then West accounts of Soviet atrocities? It will be too long.
Comment: Well Alex start with the oldest sources (and keep the sources on topic)? E.g. the Times article I posted as a comment to the question - just as evidence that it the existence was known. And if you feel the need to address Russian Propaganda (maybe even slant a few left-wing intellectuals) this is a great example - quote Satre & Busch. But be subtle
Comment: I suspect (and hope) that the downvoting comment by Alex was, at least, partially a joke. However, I should note that if anyone would genuinely and honestly care to compare the amount of anti-Russian propaganda to the amount of pro-Russian propaganda (we are talking about last 20 years, and publications outside of Russia, mainstream media only please) then the result cannot be in doubt. And if I am being too subtle -- what I meant is that the ratio of the former to the latter is most likely wa-a-y above 10.
Answer:
Yes, he knew, and almost anyone who cared knew - see all the answers before this one
From many sources we know that Germany actually actively used Stalin's paranoia to "provide" some damaging information alleging that some generals in USSR's High Command (Tukhachevsky et al.) conspired against Stalin - therefore "helping" Stalin to weaken the Soviet army
Hitler's lament is mostly infantile and self-serving. First of all, one of the reasons that Hitler even dared to invade USSR was that he himself and his military command judged the Soviet Armed forces significantly reduced in their preparedness and overall might by these purges. Second, level of resistance to Hitler in his army was still extremely low even after 1944 overthrow attempt and deterioration of Germany's standing in the WWII at the time. It is well known that quite a few of his generals complained about his many incompetent decisions in the military matters -- but still went along with them as it was nearly impossible for them to defy his orders. So his "lament" basically only served his need to move the fault to someone else.

However, there is some evidence to the following
a) some German generals were not great military commanders who failed because they followed Hitler's "stupid orders"
b) some in the Germany High Command pursued their own agenda, which sometimes undermined Hitler's plans - but general consensus says that does not seem to have played a major role in Germany's defeat
Sources:

Williamson Murray and Allan R. Millet, A War to Be Won: Fighting the Second World War, The Belknap Press of Harvard University, Cambridge, Massachusetts, 2000
Geoffrey P. Megargee, Inside Hitler's High Command. University Press of Kansas, 2002
Leopold Trepper, The great game: memoirs of the spy Hitler couldn't silence. Нью-Йорк: McGraw-Hill, 1977


Solspace FreeForm notifications

Question: I'm a bit confused by the notifications set-up in Freeform. The instructions state 'The notification template used to send an email to the email value entered into this field (optional).' I selected the template and entered an email address in the field below, but an email notification is sent to the user of the form as well as the administrator following a submission. So how do I set up a notification to send to admin only? And if I wanted to create a separate notification for the user, how do I do that?
Answer: It's not obvious, but you need to select the email field in the form settings, then select a notification from the pane on the right to send to the value in the field.
Answer: Freeform allows you to send email notifications 5 different ways (all of them each being able to have their own notification templates, etc).
For Submitter Notifications specifically, you would follow these instructions:

Email notifications can be sent to the user submitting the form using the Email field type. This is often used to send an email confirmation for the user. To setup:

In Field Editor (Freeform -> Fields) or Composer Quick Field (Add New Field button at left), create a new field of the Email field type.
  In Composer interface for the form, drag that field into field layout.
Click on field inside field layout and look over to the Property Editor (right column).
Select and/or add an email template.

When the form submitter enters their email address in this field, Freeform will use that email address to send the email notification to.

Solspace FreeForm notifications


Tower defense game for Android that supports two players

Question: I am looking for a tower defense game for Android that supports two human players (either collaboration or 1 vs. 1). I use Samsung Galaxy S3 with Android 4.1.2 and Nexus 7 with Android 4.4.2. Each player would use its own Android device.
Answer: I found Bloons TD Battles:

Test your tower defense skills against players from all over the world in two awesome game modes. In Assault Mode, you balance your income between building defenses and sending groups of bloons at your opponent. In Defensive Mode, you don't send bloons directly and instead outlast your challenger against endless waves of bloons. Either way, the last player standing wins, earning Medallions that will unlock new monkey towers, powerful upgrades, and cool bloon decals with which you can customize your attacks.
  If you are new to Bloons tower defense games, don't worry - a helpful tutorial walks you through the game, and matchmaking will help balance the opponents you face. And if you want to battle against your friends, you can easily create and join private matches with anyone on your Facebook friends list.

Unfortunately you can only play against each other, as far as I know.
It supports Android 2.3 or higher, so that shouldn't be a problem.
EDIT: I found it! Toy Defense 2 ($0.99, also has free version)

Your Facebook friends can help you in battle and become heroes under your command

Toy Defense 3 ($1.99, also has free version) also supports playing with friends. And not only that...

Invite your friends to join you in a magical world!
Cooperate or compete with your friends' courageous knights
Answer: Here is what you are looking for. Tower defense Games
This is the best tower defense game.


Struggling to understand Jacobian Inverse Kinematics

Question: I'm trying to find a method to control a moveo 5dof arm. My goal is to calculate the right angle to turn for each stepper motor to reach a desired point in real environment. I've spent time looking at the jacobian inverse kinematics, but it really got me confused. According to some articles I've read, Jacobian is useful to calculate joints' velocity, but as far as I know, stepper motors operate at a fixed speed. So my question is can I use this method to just calculate the necessary angles for the steppers, or should I use another method? In both cases, can you please introduce to me some helpful articles to refer to?
Many thanks
Answer: You will find it helpful to keep the physical robot and the math separate.
The kinematics equations map joint parameters (which are often grouped as a vector $q$) to Cartesian coordinates ($x$,$y$,$z$).
If you take the first-order partial derivative of the kinematics equations, you get a set of equations that map a change in the joint parameters to a change in the Cartesian coordinates. The Jacobian is another name for this first-order partial derivative.
It's true that if you consider a change over a fixed amount of time, you can call it a velocity, and you can use the Jacobian to map joint velocities to Cartesian velocities. But you have to be careful because these are instantaneous velocities and as soon as the position changes, the mapping between velocities changes as well.
To calculate inverse kinematics using the jacobian you will need solve or approximate inverse equations that map Cartesian changes to joint parameter changes, and then use an iterative algorithm to find the solution.
If you are not interested in learning the mathematics and numerical methods required to implement inverse kinematics, there are software libraries available that already solve the problem.
If you use an existing library, you should keep in mind that solving the inverse kinematics is a hard problem that often has no solutions or more than one solution.
Comment: I may have got it worng here, but should I take the derivative of the product matrix of transformation matrices?
Comment: let's assume your output function $\vec{y}$ is the cartesian position of your robots end effector,
then the derivative of $y$ w.r.t. time $t$ can be formulated as a product of the partial derivative $dy/dq dq/dt$ where the matrix $dy/dq$ is called the (manipulator) jacobian.
Answer: Without using the Jacobian, inverse kinematics provide joint angles to put the robot at a desired pose.  But using inverse kinematics to move from one pose to another does not say anything about the path the robot will take between poses.  Therefore, you can choose target poses that are pretty close together to have a robot follow a desired path.   When those poses are infinitesimally close to one another, you enter the subject of Jacobians.   These matrices map differential joint velocities to differential Cartesian velocities for a given pose.   So if you are at pose A, the inverse Jacobian will provide a joint velocity vector in the direction of pose B.   These have to be updated rapidly, though, because the Jacobian is only accurate in a small neighborhood of where it is computed.
Incidentally, stepper motors are not necessarily constant-velocity motors.   They move one step for every pulse they receive.   You can change the rate of the pulses to change the motor's velocity.
Comment: So if i I got it right, then with the joint velocitie provided by the Jacobian, we can plan the specific path that the joints should go. Is it correct?
Comment: And I'd like to ask if I really needed to calculate path as I'm using stepper motors, or would joint angles only do just fine? What's the difference between having the path and not having it?
Comment: To go from point to point, you only need to use inverse kinematics.  With those equations you can compute the joint angles needed to reach a desired pose, then convert those angles to the number of steps each motor needs to move.  You only need the Jacobian if you care about the speed of the robot along the path.  Even then, there are control methods you can use with just the position equations (such as via points) so you may not need the Jacobian at all.  It depends on what you are trying to achieve.


What are the pros and cons of giving SQL's service account administrator privileges?

Question: What are the pros and cons of giving SQL's service account administrator privileges?
Comment: SQL Server 2000 or SQL Server 2005/2008. There are big differences...
Comment: Hello gbn - assume 2005 +
Answer: Run the SQL service account under non-admin for SQL 2000 is tricky. I tried it once and it took a good deal of trial and error, setting rights for the custom account on registry, files, etc, etc.  At the end of it , it seemed to work, but I hand no idea if it would always work in all scenarios.
For SQL 2005+, really there is no excuse. The MS SQL team provides configured roles on installation with the appropriate rights-- just drop in a non-admin account and voila, a MS approved way to run SQL without windows administrator rights.
If you have stored procedures or what have you that requires administrator rights, you should rewrite them, remove them, replace them.  This is highly unlikely unless you are loading custom extended stored procedures or COM objects that do something that requires admin rights, or trying to run arbitrary code with xp_cmdshell.
As an Evil Hacker(TM), I'd say the biggest PRO: is being able to run fdisk via a SQL Injection attack :-)
Don't forget that the Slammer virus, which causes global internet failures was a SQL Server  vulnerability.
Comment: To be fair, slammer was caused by unpatched SQL Server installations and port 1434. Local admin would have made no difference.
Answer: Pro: full access to the local system
Con: full access to the local system
In addition, if the service account is also a domain account then SQL also has access to whatever network resources the account has access to which can be good or not.  In SQL 2005+ you still have to specifically enable some of the features that present dangers down at the system level via the surface area configuration (xp_cmdshell, CLR, etc) but once they're enabled then....
Making it local admin is a lazy man's way of doing things, albeit much easier.  In my opinion you have to weigh the risks.  Much safer and best practice, though, to make it a non-privileged account and grant privileges as necessary.  Use the principle of least privilege on the servers.
Answer: The major one is security, especially if you need something like xp_cmdshell for backward compatibility. It could make it easy to run any command on the machine.
Service accounts don't get there passwords changed to often and lead to another possible atack vector.
So the safest approach is to keep service accounts to the least privilege.
Answer: Security. I suggest contacting the vendor of the app that the DB is supporting and find out exactly what the service account needs to do. Sometimes vendors get lazy and just throw a blanket "requires root" in their documentation, but when pressed you discover that they only need certain insert rights.
Remember, root is very unforgiving.
Answer: I haven't built a SQL Server 2000 instance in years!..
For SQL Server 2005/2008, I don't even add it as a local user! Of course, the installer grants the user account log on as batch job privs. Then you have to give it privs to lock pages in memory and perform volume maintenance tasks. Also, the installer doesn't grant privs to any mount points that may be involved, so you should take care of that manually before you run the installer.
Only trouble I've run into is that the service account can't access ODBC DSNs. I'm sure there's a way around that, though...


Does a node that is more geographically centered in the Monero network have a higher chance of mining a block?

Question: As nodes are in competition with each other over who mines the next block first, does geography play a role in that competition? Would a 100 KH/sec mining pool located in, for example, Plettenberg Bay, South Africa have a more difficult time winning a block reward than a 100 KH/sec mining pool located in New York City?
Answer: What matters is where the last block was found, and this is due to latency. So if the last block was found on a pool server in new york, another pool server located in new york will be notified of the new block a lot faster than a pool located in france.
Granted, we're talking on the scale of milliseconds here, but if you do the napkin calculations of a 1 megahash per second pool, a 100 msec delay between a new york server and a server in france means that the new york server can perform 100,000 hashes before the pool in france is even aware of the new block.
Ultimately, these minuscule advantages are for edge cases when a pool gets lucky and finds a new block very quickly. More often than not, multiple seconds have passed before a new block has been discovered and these latencies do not matter, so ultimately it does not matter where a node is geographically.
Answer: I fully agree with Ginger Ale's answer, though I think - in a way - it only partially answered the question.  Ginger Ale correctly pointed out a miner is at a disadvantage if the most recent block was mined at a geographically distant location.  Let's ignore that initial geographical bias for a moment, even though it still would make a different in real life.  Actually, in my answer, the geographical bias is irrelevant.
Using the example in the question, let's say that a block is mined simultaneously in both NY and SA.  Let's also assume for this discussion that average internet speeds within and into/out of North America, East Asia, and Europe are twice as fast as speeds for Africa.
In this scenario, news of the new NY block will reach North America, Europe, and East Asia before news of the SA block.  News of the new SA block may only reach Africa and Southwest Asia in the same period of time.  Once the blocks have propagated, each blockchain will be the same length, each with an equal amount of work performed on it (at least for this argument, we'll assume PoW is exactly the same).
Ever since the moment when the NY and SA blocks were mined, on average (even assuming an evenly-distributed miner population, which is likely not true), more hashing power has been working on finding the next block on the NY blockchain, due to the previous block reaching those miners first.  Therefore, there is a greater chance that a block will be found first on the NY blockchain.
Since the NY blockchain is more likely to have the next block, and therefore next block after that, it will eventually clearly demonstrate to the network to have a larger proof-of-work.  When that happens, the SA network will reorganize around the longer NY blockchain, which will leave the orphaned block on the SA blockchain, and which will accept the NY block as the "true" block that was mined.  In this way, miners that have a higher proximity to other network hashrate are at a slight advantage.  This is one example of a reason that block-size is said to be relevant to the success of a cryptocurrency.


How do I Restore a ClockworkMod backup with a busted power button or through ADB?

Question: I was trying to flash a new ROM, but can't get it to boot. Usually, I would have just booted into my recovery and restored my last backup. But I can't do that now as my power button is broken and it is impossible to select the "backup and recover" option after booting into the recovery.
Answer: Unfortunately send key events via ADB in recovery mode is impossible, otherwise navigating through the recovery options menu would have been easy.
But fortunately, my version of CWM supports the soft keys on my phone. The 'search' button substituted as the selection button (usually the job of the power button). Using that, I was able to navigate into the backup and restore menu and restore my phone.
Hope this helps someone in the future.
Answer: You can compile your own version of ClockWorkMod. While I haven't done it myself, I know that each phone port of CWM has different key layouts, so it should be a simple question to a developer who has ported CWM to their phone. Find out the keycodes for the rest of the keys on your phone, then remap the keys in the source of CWM.
Alternatively, you can write a script that runs when you boot into CWM. You can tell the script backup, restore, install a new Rom, etc. See this forum for a push in the right direction.
Another solution is to replace CWM with TWRP. You may need this to do automated scripts, as some newer versions of CWM encrypt the extendedcommand so that only ROM Manager can automate it.
Answer: @vr3690, it is very much possible. You just gotta study the events.
Here's something that's gonna help: http://forum.xda-developers.com/showthread.php?t=1875094


Address re-use and snapshot

Question: If an address was used more than once to spend, as was the case in the September claim, are addresses that were weakened for violating the Winternitz, One Time Signiture architecture of the tangle, still vulnerable to cracking after the snapshot. Does this mean the seed must be emptied and never used again?
Additional,  because addresses are reused after each snapshot, due to the deterministic order of their generation, is every address used before the last snapshot theoretical vulnerable to cracking?
Answer: You should never send iota to an address that was already spent. This will make it possible for an attacker to steal your iotas. This rule is uninfluenced by any snapshot.
The problem after a snapshot is, that every node deletes the transaction history, only the balances are saved. Usually your wallet doesn't show any spent addresses anymore (thus preventing you from double spending), in this case, however, your wallet can no longer verify that you haven't used this particular address.
Let's make an example:
Generally, the seed provides your wallet with an endless list of addresses. So when one is used, it will keep taking the next one until an unused one is found.
Let's assume you have 2 addresses. All your IOTA is at the second one, your first address is already spent.
Normally, the wallet would now show you the 3rd address to receive, because the first one is spent and the second one has balance. Because of the snapshot, however, the wallet will show you the first, as history is gone and the wallet can't see that this address was already spent and will show your first address instead. Additionally, the wallet won't even take a look at the second address, and your balance won't show up.
To fix this, you have to attach every address in the tangle, until you reach an address that you have never used in the past. In this case, simply attaching the first address will fix it. If you had more addresses, you will have to repeat the process a few time.
Your seed is still save, you just have to watch out that you don't accidentally use an address that you have already used before the snapshot
Answer: The seed itself is still safe to use, the one time signature weakening occurs only for that specific address (you leak part of the private key "paired" with the address itself, not part of your seed).
After a snapshot, you keep reattaching addresses (from index 0 upwards) until you arrive to an address that contains some iotas. If you always follow the rule of never reusing the same address, and only ever use 1 address from the same seed at a time, you now know that the first address you obtain that contains iotas is the address that contains ALL your iotas and has NO spends.
It gets trickier if you do use multiple addresses from the same seed (but still following the one time send rule). In that scenario, you have to keep reattaching until you obtain ALL the addresses that have iotas, and you have to know for yourself how many addresses/iotas that is.
In order for you to be able to forget how many addresses you've used/how many iotas combined your addresses have, and NOT end up reusing an address/"lose" your iotas, you would need to either:

keep a local copy (so for example your wallet would keep a history of every used address),
obtain the history from a permanent node that keeps the transactions after snapshots (you have to trust that the node does not "lie" to you, not sure if/how you'd verify the permanent node does not give you bogus info)

Address re-use and snapshot


Is it encouraged to delete your own questions if they have possible duplicates?

Question: If I post a question after searching and determining it hasn't been asked. And later find out, on my own or by a fellow user that the question is a possible duplicate. Is it encouraged to delete the questions, or should I wait for the consensus of users that vote to close it ?
Comment: NO!  Dupes are a good thing - they make the original question easier to find.
Answer: No
DO NOT DO THIS
I'm sorry for shouting, but I've wanted to say this to a few people recently; I got a bit excited.
There are a couple of reasons you shouldn't do this:

Your question may not end up getting closed. For a recent example, see In Star Wars: "The Force Awakens," how could this lightsaber have turned up where it did? and How did Maz Kanata acquire Luke's lightsaber? (but don't if you're avoiding The Force Awakens spoilers). There was a bit of a debacle around these, but there was a time when each had close votes pointing to the other. Obviously only one of them got closed (and then re-opened and the other closed, but that's a different story). Either JMFB or RedCaio could have deleted their questions upon getting close votes, but they shouldn't have, because nobody knew which would end up getting closed.
Admittedly, this is probably more true for questions where the dupe and the original were posted at similar times. Still, its worth noting that we don't necessarily close the newer question in all cases.
There are also a number of cases where duplicate close votes are disputed by the rest of community. To coin a phrase, a single close vote does not a duplicate make.
By far the biggest reason is that having the duplicate question up makes it easier to find the original. Obviously the original wasn't terribly easy to find, since you weren't successful in your search. With your closed question, there's now a whole new collection of searchable terms floating around the Internet, with a great big neon sign pointing to the original question (and answer).
In other words, you just made the question (and its answer) much easier to find. This is a good thing.
Closed questions aren't counted terribly harshly against you when determining a question ban. However, deleted questions definitely count against you, especially if they make up a large proportion of your total answers; quoting that FAQ I linked to (links in the quote are preserved from the source):

It's not a problem to have deleted posts. But if a large percentage of your posts are deleted by yourself or the community, then apparently they are not suitable for the site. Posting them consumes time from users who read them, edit them, or respond to them. Therefore deleted posts have an effect on the filter, among many other factors

The Problem
As far as I can tell, there are two reasons why a user would feel pressure to delete a question that has close votes (or has already been closed):

The view that closure is a censure. To users who aren't excessively familiar with the SE network (and even to some who are), a close vote feels like a rejection. It can feel like the question is undesireable, when in fact it is not. I suspect that many users see a "Possible duplicate of X" comment as implying:

What the hell is wrong with you? This has already been asked, why are you asking it again?

So the natural desire is to delete it; the question has already been asked, so what benefit can it possibly be adding to the site?
Of course that's a false assumption, which is the point I made earlier in this answer. There's probably some room for user training on the benefit of having duplicate questions, but that's a different issue.
The view that closed = bad. This is problem both for askers and for voters. For askers, the issue is similar to the above:

Oh, I asked a bad question. I should delete it.

Relatedly, there may be the expectation that a duplicate question is going to be downvoted. This is probably not such a critical issue in practice; while there may be many duplicate questions that have attracted some downvotes, according to this SEDE query (inspired by phantom42 doing something similar in comments), only 130 of our duplicate questions have a negative score.
Comment: People don't typically downvote questions *just* for being duplicates, so I'm not really sure how it's penalizing from a reputation point of view.
Comment: If a dupe is getting a lot of downvotes, usually that means it was trivially easy to find the original question; in those cases, IMO, the OP is justified in deleting the question (which removes the rep penalty) since the duplicate is unlikely to help anyone in the future.
Comment: since i was curious, we have [1,058 dupes with a positive score](http://scifi.stackexchange.com/search?q=score%3A1+duplicate%3Ayes), [356 with a zero score](http://scifi.stackexchange.com/search?q=score%3A0+duplicate%3Ayes), and [126 with a negative score](http://scifi.stackexchange.com/search?q=score%3A...-1+duplicate%3Ayes)
Comment: I've seen some decent questions, that were duplicates certainly, get downvoted harshly. But maybe I've just witnessed bad examples.
Comment: @yondaime008 Could be, I have seen the same thing. The downvotes might of course also have been because it was blatantly obvious the asker had not done a search (the question titles might have been phrased virtually identical, which woud mean the "older" title have would have shown up when they typed in their own).
Comment: Often it depends on the question. If say a question has been asked multiple times everyday since release of a new film *cough star wars cough* some people may have a grudge or at least a bias. Can't really take any of it personally though, random votes and stuff happens to everyone :).
Comment: @turinsbane Yes, each site can (and does) have its own rules and culture (though some things are part of the SE platform and transcend individual sites). My advice here, however, is fairly broadly applicable; I've never seen an SE site where what I've written here doesn't apply
Comment: I fully agree, but that's still very penalizing from a reputation point of view.
Comment: Additionally, you can flag it for a moderator to close as a duplicate, if you don't want to wait it out for fear of down votes.
Comment: Deleted questions definitely hurt you more. I had some bad dupes on stackoverflow and was still able to ask questions. I decided to delete them and bam! Question ban
Comment: Are the rules the same for all SE pages?On history SE my questions seem to often get voted to be closed,whereas on Sci fi SE i have no probs
Comment: Wow. This answer needs to be advertise in a FAQ or something
Comment: @Kalissar It already is: check the tags on the question :-)


Multi-photon states in photonic quantum computing?

Question: Within photonic quantum computing, one of the ways to represent information is the dual-rail representation of single-photon states ($c_0|01\rangle \ + \ c_1|10\rangle$). Is it possible to utilize multi-photon states (for example, two optical cavities with total energy $2\hbar\omega$, using a state like $c_0|02\rangle \ + \ c_1|20\rangle \ + \ c_2|11\rangle$, where $|02\rangle$ represents two photons in one cavity, $|20\rangle$ represents two photons in the other cavity, and $|11\rangle$ represents one photon in each cavity?
Answer: Yes. The kets themselves can have arbitrary labels, and it's just for you to establish the connection between them and the physical scenario. There's no reason why you can't have the physical scenario you've specified and, indeed, people frequently do.
Answer: This is very much possible. And is a very general technique of how product systems in composite states are coupled. Here of the form $|n_1\rangle |n_2\rangle$. This kind of general ket is a solution of the Hamiltonian interaction/coupling terms like $V\sim (a_1^\dagger a_2 +h.c)$ which describe the exchange of one quanta (between the two optical cavities here). $a_i (a_i^\dagger)$ are the annihilation and creator operators for $i^{th}$ cavity in second quantisation. It follows similarly for more systems coupled in the form of product states.
A very general and frequently used is a spin (with an excited and ground state as $|e\rangle,|g\rangle$) in an optical cavity with solutions like $|\psi\rangle=c_1|e,n\rangle+c_2|g,n+1\rangle$ where $n$ is the number of photons in the cavity, and so on for more complicated systems.


How do I determine if a point is within a rhombus?

Question: I know the coordinates of the 4 rhombus' vertices. I also have the coordinates of another arbitrary point (the result of a click on the screen).
How do I determine if that point is within the rhombus?
Comment: Are you working in $\mathbb R^2$? (Also, since this is really an implementation problem, you might want to try this question on some of the programming-oriented stack-exchanges instead.)
Answer: Let's give the names $A$, $B$, $C$, $D$ to the four vertices of the rhombus. Let $Q$ be the center of the rhombus. You can calculate $Q$ as either $\tfrac{1}{2}(A+C)$ or $\tfrac{1}{2}(B+D)$. Also, let $a = \tfrac{1}{2}\Vert C - A \Vert$ and $b = \tfrac{1}{2}(\Vert D - B \Vert$. We're going to work in a coordinate system that has its origin at $Q$, its $x$-axis along the line $AC$, and its $y$-axis along the line $BD$. Let $U$ and $V$ denote unit vectors along these $x$ and $y$ axes respectively. In fact, $U = (C - A)/2a$ and $V = (D - B)/2b$. All of this is shown in the figure below:

In our chosen coordinate system, $C$ has coordinates $(a,0)$ and $D$ has coordinates $(0,b)$, so the line $DC$ has equation
$$  \frac{x}{a} + \frac{y}{b} = 1 $$
Using symmetry, the other three sides have similar eqautions. I think it's fairly clear that the point $(x,y)$ is inside the rhombus if (and only if):
$$  \frac{\vert x \vert}{a} + \frac{\vert y \vert}{b} \le 1 $$
In your code, you should first pre-compute (once):
Q = 0.5*(A + C);           // center point
a = 0.5*distance(A,C);     // half-width (in the x-direction)
b = 0.5*distance(B,D);     // half-height (y-direction)
U = (C - A)/(2*a);         // unit vector in x-direction
V = (D - B)/(2*b);         // unit vector in y-direction

Then, given a point $P$, the inclusion test is as follows:
W = P - Q;
xabs = abs(W*U);    // here W*U is the dot product of W and U
yabs = abs(W*V);    // here W*V is the dot product of W and V
if (xabs/a + yabs/b <= 1) then inside = true;

So, pretty efficient -- you can decide inclusion just by doing a vector subtraction and two dot products. All of the above assumes you have functions for doing basic vector arithmetic, of course (addition, subtraction, dot products).
Answer: The interior of a square, rhombus, rectangle, parallelogram, are given in $(x,y)$ coordinates by inequalities. One pair of parallel edges gives
$$ E \leq A x + B y \leq F,  $$
the other pair of parallel edges
$$ G \leq C x + D y \leq H,  $$
for constants $A,B,C,D,E,F,G,H.$ If all four inequalities are strict, the new point is strictly inside the figure, if one of the four indicated inequalities is actually an equation the point is on an edge.
Meanwhile, the four boundary equations such as $Ax+By=E$ are just the lines between consectutive vertices of the figure. You need to exercise care in choosing $\pm$ signs throughout, as writing it this way necessitates $E<F$ and $G <H.$
Answer: Here is one way of doing it, perhaps not the most elegant. First note that the rhombus is the intersection of 4 half planes determined by the lines that bound the rhombus. If you know the 4 points then you can figure out the 4 equations of the lines that bound the rhombus and therefore the 4 inequalities that define the desired half-planes. Therefore a point $p$ will be in the rhombus iff it is in all of the half-planes that determine the rhombus.
Answer:
Here is a single equation that gives you an idea of when a point lies inside , outside or on the boundary of a regular octagon of radius 15. You can easily write in your test a meaningful and useful expression .( I have written out the equation for the  boundary of an octagon, inside use the equation in the form of an inequality , and the same for points that are exterior of the octagon with the sense of the inequality turned around. )  Hope this helps.
Comment: Oops ! My bad, next time I'll read the question before replying !!!
Answer: I would do this with some vector math. Take two edges of your rhombus and consider them unit vectors of a custom coordinate system. Transform the point to this system. If the point has its x coordinate between 0 and 1 as well as its y coordinate between 0 and 1, it is inside.
This should work well for any true rhombus. (Including exactly vertical and horizontal edges, but excluding things with an area of zero)


Synchronizing/merging Empathy logs and Google chat logs

Question: If I use Empathy to log into my Google account and chat with people, I can enable logging and have it save chat logs to my computer.
The problem is, I don't only use one computer, so I end up with logs all over the place. I could use Dropbox or something to synchronize them, but that only works on computers I use Empathy on. I would still lose out on chat logs that I make from within Gmail or Google Plus or on my phone or anywhere else.
An ideal solution for me, as someone who only chats through my Google account, would be if Empathy would just use Google's chat log, the same one I access through Gmail. This would be used to display previous conversations when a chat window is opened, and to view chat logs in Empathy's UI.
Is this possible? I tried Googling but I couldn't even find anyone asking this question.
Comment: 12.10 beta 2 still not saving the chat log to gmail :(
Answer: I have the same problem. As far as I can tell, syncing the logs with the Google account was the default behaviour until the last update. Perhaps you can make it work simply by rolling back to a previous version.


Load testing selenium scripts in visual studio

Question: I am wondering if someone has some advice for running load testing in visual studio, preferably with a selenium webdriver script. I know that JUnit can be integrated with JMeter, so that you can test load on a certain automated test. But I cannot find any information on load testing in visual studio with a selenium type script. Basically, the test is login to the system as a user, get requirements for student, upload documents, and submit the file. This is easily achieved in selenium, but I am wondering how to simulate 1, 10, 25, 100, MAX users. Thanks for your insight ahead of time.
Answer: I would recommend looking into Visual Studio load test tool. You will need an Ultimate license. This tool will make it much easier to do all the things necessary to create a useful performance test while minimizing time to script and hardware needed to drive the test.
You can read more here...
https://msdn.microsoft.com/library/dd293540(v=vs.110).aspx
I understand you have the Selenium scripts already created but that will not save you much time compared to what it would take to scale out a Selenium test into a valid/useful performance test. Using Selenium to performance test would adding a layer between Visual Studio and the system under test that is not needed. It would be the wrong tool for the job. I hope this helps!
Comment: Do I have to have an ultimate license to do load testing? Currently I have professional 2013.
Answer: It is possible to do, but old versions of NUnit doesn't deal well with multi-threaded code.  Ie NUnit itself was design to be single threaded.
You can use PNunit which will give you that functionality.
Using NUnit 3 or above has PNunit included.  You can find more information on how to use it on this page


What should I be mindful of in everyday mindfulness?

Question: I am not sure what to focus on when practicing everyday mindfulness. For example, when washing dishes due we focus on what we notice in our current experience; like as I wipe the dishes I can focus on the feel of my hands on the plate or the view or sound of the wiping.
Or do I decide to pick one thing(sense) and focus on that purpose for a few seconds?
Or do I try to focus on everything in the now which seems like information overload?
Answer: This is a good question.
Always the mindfulness should be in the 4 foundations of mindfulness. One objective of mindfulness is to remove defilements or letting go. Pahāna Sutta gives an outline in brief. Another is to keep you on the path as outlined in Maha Cattarīsaka Sutta. Any sensation is unsatisfactory this is the link to understand the 4 Noble Truths and also with sensation, according to dependent origination, arises craving. If you miss this link you miss the path.
That is the when taking the 1st foundation of mindfulness, the body, feel the elements like the temperature of the water, the texture of the plate, etc. and you reaction. The water is too hot, my hand is burning or water is too cold, etc., i.e., evaluation you give as this is desirable, undesirable or neutral and satisfaction, dissatisfaction and neutral feeling that follows. The look at the posture and position. The pain and resulting dissatisfaction from standing a long time near the sink, pleasure from changing postures when the previous posture becomes uncomfortable, the pain for wariness from hard work (movement - scrubbing), and the pleasure of rest, etc. [Dhātu Vibhaṅga Sutta, Titth'ayatana Sutta, Indriya Bhāvanā Sutta, Sal-āyatana Vibhanga Sutta, Dīgha,nakha Sutta]
The examin feelings in general. Are you evaluating something as favorably, unfavorably, or neutrally and the resulting feelings of pleasure, displeasure and neutral feelings. [Mahā Sati'patthāna Sutta, Dhātu Vibhaṅga Sutta, Titth'ayatana Sutta, Indriya Bhāvanā Sutta, Sal-āyatana Vibhanga Sutta, Dīgha,nakha Sutta, Cūla Vedalla Sutta, Mahā Vedalla Sutta, Samma Ditthi Sutta]
Also mental analysis of the situation. Plates are dirty hence displeasure. I have better things to do then displeasure. Or whatever else that might arise either pleasure, displeasure or neutral by your evaluation of liking, disliking or do not care. For more detail refer the 18 investigation in Dhātu Vibhaṅga Sutta, Titth'ayatana Sutta & Indriya Bhāvanā Sutta and also see Cha Chakka Sutta. Also note the feeling arising from whether you like it, hate it, what kind of thoughts are aroused (my friends are at a party while I am washing dishes) etc. and thinking pondering and planning that follows and what you feel about it.
Also see if you are transgressing any moral principles. There is an ant in the sink, I should not kill it and perhaps save it. [Maha Cattarīsaka Sutta]
Ultimately whatever feeling that arises you should be aware of its arising and passing nature.
Also see The Satipaṭṭhāna Suttas: An introduction and Vedanā (Feeling) by Piya Tan

In general situation, regarding the body, when you see a body you perceive as beautiful hence pleasurable and so on. Again in these situation you should be mindful of the perceptional evaluation beauty / smart, ugly, plain and the feelings that arise with it. [Maha Dukkha-k,khandha Sutta] You can also go to the extent of cemetery contemplations if you are very lustful to overcome Vipallasa. [Mahā Sati'patthāna Sutta, Kaya,gatā,sati Sutta, Maha Dukkha-k,khandha Sutta, Vipallasa Sutta]. Maha Dukkha-k,khandha Sutta more detail on the mechanics than the Mahā Sati'patthāna Sutta.
Also when wanting to answer a call of nature the feeling of tightness and the displeasure before and the subtle pleasure of release. [Mahā Sati'patthāna Sutta]
Also you can be mindful of the breathing. Is it deep or shallow. If you are displeased what happens and what happens when you are pleased and what is it like when you are neutral. [Mahā Sati'patthāna Sutta, Kaya,gatā,sati Sutta, Ānâpāna,sati Sutta]
Also the aggregates, the faculties and their experiences, phenomena, etc. all having the universal characteristics. Expecting something positive as permanent gives disatisfaction when it happens to be impermanent and likewise for other combination. [(Anicca) Cakkhu Sutta, Cūla Vedalla Sutta]. Also see: Nibbida by Piya Tan which has more ferences of relevant Suttas towards the end of the essay.

For example, when washing dishes do we focus on what we notice in our current experience;

Your current experience is what you sense or feel. So concentrate on what is felt like in the Pahāna Sutta. This is one of the simplest forms.

like as I wipe the dishes I can focus on the feel of my hands on the plate or the view or sound of the wiping.

Focus on both. Sounds may trigger other things. You may be irritated by the sound. Also it may trigger memories. Whatever sense door body (hand) or ear just be mindful of the evaluation and sensation. (18 evaluations above.)

Or do I decide to pick one thing(sense) and focus on that purpose for a few seconds?

In normal work no need to pick. Just keep a check that your awareness is present on some sensation or the other.
In simple terms, your focus should be on the arising and passing of sensations like in the Pahāna Sutta.

Or do I try to focus on everything in the now which seems like information overload?

Your focus should be on what is felt (feelings / sensation) and their impermanence as in the Pahāna Sutta.
Comment: thank you. this was helpful without being too vague or too specific.
Comment: I expanded a bit more with additional references again. It covers the situation of washing dishes in your example and a few more which might not arise when washing dishes.
Comment: Also how can I make this more specific to what you are looking for?
Comment: @Dharmasena Thanks but I think I have enough information to get started with. Don't need overload 8^)
Comment: OK. I made a simplification towards the end. Hope fully this will make it simple.
Answer: In Buddhism, 'mindfulness' does not mean to meticulously 'observe' things.
Instead, 'mindfulness' means to 'bring to mind' or to 'remember to practise' the Buddhist path.
When washing dishes, mindfulness does not mean to observe & feel the water, dishes, etc, but, instead, mindfulness means to wash the dishes with a mind free from greed, hatred & delusion.
Therefore, the practise of Buddhist mindfulness in everyday life is to do things with a mind free from greed, hatred & delusion.
In other words, Right Mindfulness is do things with Right View, Right Intention, Right Speech, Right Action & Right Livelihood, as explained in the Maha-Cattarisaka Sutta.

One is mindful to abandon wrong view & to enter & remain in right view: This is one's right mindfulness.
One is mindful to abandon wrong resolve & to enter & remain in right resolve: This is one's right mindfulness.
One is mindful to abandon wrong speech & to enter & remain in right speech: This is one's right mindfulness.
One is mindful to abandon wrong action & to enter & remain in right action: This is one's right mindfulness.
One is mindful to abandon wrong livelihood & to enter & remain in right livelihood: This is one's right mindfulness.
Maha-Cattarisaka Sutta
Comment: Thanks. I think the ultimate goal of mindfulness is to have a mind that is fully aware without judging the world. I think you mean the life without judging. In West, many people have a 'monkey mind'. To stop this they must become more aware and so the first step is to become more aware of  the present. That is what I am trying to learn currently.
Comment: Yes. Non-judging is a most excellent starting point (since it makes the mind concentrated & calm). To be adept in non-judging is very beneficial. However, ultimately, mindfulness also includes judging experiences in the right/wise way & not in the wrong/ignorant way. But, as you said, non-judging is a way to stop monkey-mind & should be developed as a starting point to gain mastery over the mind. Regards
Answer: For everyday mindfulness, you need to focus on your movement (physical) and your thoughts, the ability to know (mental). For the example you mentioned, you need to focus on washing dishes in every details states (as much details as you can).
Below is some details you can watch and know yourself you are doing (not limited to this level of details, if you can do concentration on much more details).

Taking dish
opening tap on basin
putting dish under water (...)
rubbing dish under running water
close water tap
moving wet dish to dish washing liquid dispenser
get some dish washing liquid on dish
get sponge
rubbing sponge on dish (...)
open water tap
rinsing dish under running water
putting dish on the shelf

For normal lay people, it is very difficult to accomplish every day routines to be focused and known details of movements, thoughts. Because people do business and job; just focusing on mindfulness cannot help in professional activities. Sometimes it can even lead to problems/conflicts.
So if you really want to do mindfulness and meditation, you need to do proper retreat. Buddha said many times the life of normal people (with profession and/or family) is like narrow/confining, like road with dusty air. By staying as life of normal people, it is difficult to practice all the Buddha teachings (complete mindfulness here). So if you want complete/full mindfulness, you need to approach meditation center, do retreat and get guidance from there.
Answer: Some coaching I have received before is:

Do whatever you are doing as if it is your one and only chance for self-expression, freedom, and peace of mind.

Or as J Krishnamurti said:

[awareness] is like living with a snake in the room; you watch its every movement, you are very, very sensitive to the slightest sound it makes.
Answer: If you have enough concentration in sitting meditation, you will find easier in everyday chore how to be mindful. Actually, just start with gross act like the most distinct fact cold or hot or touching the plate or something like that. If your concentration deepen, every acts you come to know, that is your notice on what you are doing become more detailed without much effort. Then just "know it, know it" is enough. Please refer to Mahasi Sayadaw basic meditation practice. But it takes time to focus in every day acts at first. If you keep on doing so, you will surely get enlightened, it is so simple Buddha gave us, for lay disciples to practice meditation while cooking, washing etc.
Answer: Cause & Effect, breathing ...
Comment: Hello and welcome to Buddhism SE. Maybe you could elaborate on your post a bit and explain why cause and effect and breathing are important to focus on. We are looking for high quality answers on our format. See also [How do I write a good answer?](http://buddhism.stackexchange.com/help/how-to-answer).
Comment: your answer reminds me of how Buddha replied to some gods when they challenged or ask him questions.  Buddha would reply with very short answer.  like when this this no-name god told to Buddha, "first child bring most joy to parents" Buddha replied "most obedient child brings most joy".  tons of trivia facts like that which i find fascinating.  another one of my favorite when a god told Buddha ocean was the mightiest water, Buddha replied, "rain fall is the mightiest" without further explaination.
Comment: Thank you @Lanka. Like Dean A. said, Buddha would often give short responses. That's because ... well, the more you say, the greater the chance something wrong will be found (which I why I write all this in an after-comment rather than 'edit my original response').

I believe that 'Cause and Effect' is (in the Lotus Sutra or some other Buddhist writing) called 'a supreme law of the universe' ... the way everything CAUSES something else to happen; even among Buddhas, the 'sounds of the world' (_ren-ge_) change the way The Divine Sound (_Myo-_) *sounds*.

"Breathing" is one reason why.


VNC Performance

Question: Is it normal for VNC performance to be really slow? In our small network, windows remote desktop works seamlessly, but when using VNC to connect to some ubuntu machines I can barely work even on 640x480!
Answer: 2 things:

Use UltraVNC or tightVNC. They're both optimized for speed.
If using UltraVNC, install their Mirror driver.  It makes the
control session very smooth and flicker-free.
Comment: I've seen some pretty drastic performance differences using different apps, I definitely recommend trying new software.
Answer: In my experience Windows Remote Desktop is usually faster than VNC but on the same network VNC shouldn't be running super slowly.
If your video card drivers are not up to date you could see some lag caused by that. You might also try turning off Differential Compression. You can do this by clicking Start and typing optionalfeatures.exe into the searchbox and press enter. Then just find it and untick it.
As Bob mentioned, part of this is also going to depend on which VNC you are using. Other than the two mentioned by him I have also used Crossloop which was only little slower than RDP. You might also notice an issue between Vista and XP machines.
Answer: Too many clients using a single served desktop will cause wicked latency and lag because control of the screen is round-robin scheduled (like a token ring network).
How many is too many depends on CPU, network latencies, etc...

VNC Performance


Nyquist sampling rate

Question: Please i need help in understanding Nyquist sampling rate. What is the implication of sampling at a lower rate than the Nyquist rate, at exactly the Nyquist rate and at a rate higher than the Nyquist rate.
Comment: dupliucate question. the fastest sine wave needs at least two dots ,',',',',
Answer: Implications of the Shannon-Nyquist sampling :
a. Sampling rate below Nyquist rate: Aliasing happens: shifted spectra of the sampled signal will overlap; i.e., high frequency signal content will be aliased into lower frequency regions of the spectrum and low frequencies into higher, therefore, irrecoverable misinterpretations happen about the authentic (true) content of the sampled signal spectrum;
b. Sampling rate equals Nyquist rate : Depends on the signal type. If there is no impulse at the Nyquist frequency, or the spectrum is zero at the Nyquist frequency, then this will in principle satisfy Nyquist sampling rate, but requires an ideal anti-aliasing filter to be practically implemented and thus usually avoided and a slightly higher sampling rate is preferred instead.
c. Sampling rate larger than Nyquist rate : Satifies Shannon-Nyquist sampling theorem, allowing perfect and unique recovery of the original continuous-time signal from its samples. However, going too high, unless necessary will increase system cost. So practically it's best to limit the sampling rate to a satisfactory minimum or an achievable maximum.
Comment: @lilfancy I'm glad I could help..! If you think that it's a satisfactory one then you can select it so that the question will not float indefinetely ;-)
Answer: dupliucate question. the fastest sine wave needs at least two dots ,',',',',  so you need ,' to give amplitudes of the fastest possible sound's peak and trough, as each sound is a vibration around zero. so you need twice as many dots as your frequency. so a 44k cd can replay 22k sine wave which consist of 2 dots, and 11k that consist of 4 digital dots. the dots can be 16bit, 8 bit, any precision level at that sampling rate.

Nyquist sampling rate