(Thought Question) What would a giant far away mirror look like to a telescope?

Question: If there was a theoretically perfect mirror the size of say, our solar system, somewhere out in space that had a focal point of literally earth. What would that look like to a space or earth telescope? Could it be distinguished from other parts of space? Could you identify earth in it? (A la By putting a mirror in space, would we be able to see into the past?)
Comment: This is a great question, but I'm voting to close this question because I think it more properly belongs on the World Building or Space Exploration Stack Exchange sites.
Comment: @ConnorGarcia we should only close questions when they are off-topic where they are asked, not for "I think it's better asked elsewhere" by itself. Some questions are on-topic in multiple sites and some are off-topic everywhere. There isn't always a 1:1 correspondence between questions and their sites. The OP decides where to ask. We can make suggestions, and we vote to close if we are pretty sure the question is off-topic locally.
Comment: If the mirror had a focal point of Earth, that would stand out as it would increase the light reflected to Earth.     If it didn't have the focal point of Earth and just reflected stars, I think it still might be visible as mirrors don't reflect all wavelengths of light.  With a good enough look, it should be recognizable as a mirror, I would think.
Answer:
If there was a theoretically perfect mirror the size of say, our solar system, somewhere out in space...

Great thought experiment so far!

...that had a focal point of literally earth...

Rats! I was hoping for a flat mirror so the answer would have been slightly simpler.
It is true that concave mirrors are "magnifying mirrors" and if we stay closer to the mirror than twice its focal point (see below) we can see a magnified image. I don't believe that it provides better optical resolution than a normal mirror, but since the construction of our eyes is fixed (we can't change the optical system nor "pixel density") we use the mirror to "blow up" the image in the same way that a photographic enlarger blows up the image on a negative without improving the resolution of the image.
 source
In optics image information is encoded in the wavefront at any point whether in focus at that point or not. If we know the mirror's diameter and distance from Earth, we can apply the principle of diffraction in a simple way no matter how complicated the rest of the optical system.
For a hard-edge circular mirror (top-hat shaped apodization) we know that the Airy disk is the right principle to apply, and a simple definition of resolution gives us
$$\theta \approx \text{1.22} \frac{\lambda}{d}$$
for the angular resolution. Let's use 500 nm green light for $\lambda$ and twice Neptune's orbital radius (60 AU) for $d$. That gives us $4 \times 10^{-18}$ radians.
If the mirror were at the distance of Proxima Centauri or only $4 \times 10^{+16}$ meters, then the impact on resolving a wavefront from the perfect mirror based only on diffraction of a circular aperture would be of the order of centimeters!
The focal length of a concave mirror is the parallel-to-point distance, so we would really need the mirror to be at roughly the point-to-point distance of twice the focal length.
If the concave mirror brought our image back to us, say on a sheet of paper, it would be incredibly dim i.e. pretty much no photons except from the Sun itself. But if we ignore that then we would see ourselves blurred by about 1 centimeter.
If the image was kilometers in front of us then we could focus a telescope on that image in space and re-image it at the entrance pupil of an eyepiece or on to a sensor.
If the telescope were 1 meter in diameter, we could see roughly a 1 meter wide swath of Earth.
Of course this doesn't work so simply because the mirror would have to be pointed such that the location of Earth 8.5 years ago would be imaged where we were today.
Conclusions
Yes this is kinda possible from a Gedankenexperiment point of view; a 60 AU mirror out at Proxima Centauri with a focal length of twice that distance could produce an image of Earth nearby Earth (light time considerations in force) and we could look at that location in space with a large diameter telescope and see a patch of Earth 8.5 years ago roughly vignetted by the size of the telescope's aperture.


JsonSerializer field order (don't want alphabetical) - Java

Question: I'm using JsonSerializer to convert an Object to a JSON String but the order is wrong. The attributes are automatically sorted alphabetically but I want them in the order they have been listed in the class (e.g. "endPoint" should not appear before "startPoint").
When I call JsonSerializer. I only see 4 methods (toJava or toJson). I tried doing includes with the order but it doesn't work/I'm not doing it right. The way I'm doing it is like this:
return new String[]{"errorDescription", "searchResultRecord.billOfLadingNumber",
"searchResultRecord.bookingNumber", "searchResultRecord.advancedManifest",
"searchResultRecord.inboundCustomsClearanceStatus", "searchResultRecord.cargoReleaseStatus", "searchResultRecord.freightChargeReleaseStatus",
"searchResultRecord.container.containerNumber", "searchResultRecord.container.latestEvent.event",
"searchResultRecord.container.latestEvent.location", "searchResultRecord.container.latestEvent.time"};

As you can see there is obj.obj.attr parts being included. But when I try to run this code I only see "errorDescription" in the output string. I then tried "searchResultRecord" without attributes but it only showed 2 of the attributes in the output :x
Any idea how to fix the order so its not alphabetical? All examples online seem to be from an older version of the class with more accessible methods~ Thanks for any info.
Answer: You can try using
@XmlType(propOrder={"startPoint", "endPoint"})

on the class you defined as @XmlRootElement. Those attributes and any other you want will sorted as you defined on propOrder.


How can I update my Samsung Galaxy S2 (GT-I9100) from Android 2.3.3 to a newer version?

Question: I have a Samsung Galaxy SII (GT-I9100). OS version-2.3.3. Whenever I connect it to Kies, it cannot find an available software upgrade. Is there any other way to upgrade my OS?
Answer: Sure, just be aware that doing so you'll lose the warranty! If you want to do it anyway, just go to sammobile.com and look for your phone (just type i9100 in the search box). In the result list, choose your firmware and download it.
To flash it, follow these steps:

Download ODIN v1.85 from here
Unzip the downloaded files, both Odin and the firmware
Power off your phone and boot into Download Mode. To do so, press and hold the Volume Down and Home buttons together, and then tap the Power button until you see the construction Android robot icon with a triangle. Hit the Power button again to confirm entry into Download Mode
Launch ODIN on your computer and connect your phone to it while your phone is still in Download Mode
In case your phone connects successfully, one of the ID:COM boxes will turn yellow with the corresponding COM port number. This process may be time-consuming
Choose the files to be flashed or installed on your phone, which can be found among the extracted files in Step 2
Click the PDA button and choose the file named 'CODE'. Tap the Phone button and choose the file named 'MODEM'. Ignore this step if such file is missing. Hit the CSC button and choose the file named 'CSC'. Ignore this step if such file is absent. Click the PIT button and choose the .pit file. Ignore this step if there is no such file
In ODIN, enable Auto Reboot and F. Reset Time options. In case of the Re-Partition option, check it ONLY if you chose a .pit file in the previous step
Click the Start button in ODIN and the ROM installation process will begin. It may take a few minutes to complete. DON'T DISCONNECT THE PHONE OR IT WILL IRREMEDIABLY BRICKED
Once the ROM is installed, your phone will reboot. When you see the home screen, disconnect the phone from the computer. This may take a LONG LONG time, so don't panic and give it a few minutes

Your Samsung Galaxy S2 I9100 is now successfully updated. Go to Settings > About Phone to verify the firmware version installed.
Enjoy :)
Comment: The EU prohibits outright denying the warranty when you load alternative software, it has to be proved that the alternative software is the cause for the defect (see [this article](http://fsfe.org/freesoftware/legal/flashingdevices.en.html) by the FSFE)
Answer: If there are any available custom recovery for your device this should work.
1st: Flash a custom recovery and download stock or custom rom that suits you (make sure they are compatible with your device)
2nd: After flashing custom recovery, go to recovery mode (custom) and factory reset and wipe system too
3rd: Go to install and find the rom and some patch files (like gapps or anything if needed)
4th: Flash the found rom and patch files (if needed)
5th: Normal boot and try the rom


Book set in a time of dragons featuring a boy and his dragon saving their homeland from weird monsters

Question: I have been trying to remember the title of a book I read like a year ago. It is based in a time of dragons and the two main characters in the book is a boy and a dragon. The boy and dragon are friends, and they have to try to save their homeland from weird monsters. There are also dwarves and other dragons. What is the title of this book? I think the book started with an E.
Comment: Were there fairies involved, then?
Comment: There were elves and elves are part of the fairy race.
Comment: This isn't much to go on. Please look at our [guide to asking a good story ID question](https://scifi.meta.stackexchange.com/q/9335/31936) and [edit] your question with any other details you can remember.
Comment: This is all I can remember about the story.
Comment: Even if you think that's all you remember, I recommend visiting that list of prompts Null linked. Even something as simple as whether you remember it as a paperback or hardback, or what reading level it was, can help us a lot to clarify the answer.
Answer: Might you be thinking on Eragon?

A Shade named Durza, along with a group of Urgals, ambushes a party of three elves. They kill two of them, and Durza attempts to steal an egg carried by the remaining female elf, but she uses magic to teleport it elsewhere. Infuriated, he abducts her.
Eragon is a fifteen-year-old boy who has lived with his uncle Garrow and cousin Roran on a farm near the village of Carvahall, left there by his mother Selena after his birth. While hunting, the dragon egg appears in front of him. The night after, a baby dragon hatches from the egg, and bonds with Eragon. Eragon names the dragon Saphira, after a name the old village storyteller Brom mentions.
He raises the dragon in secret until two of King Galbatorix's servants, the Ra'zac, come to Carvahall. Eragon and Saphira escape and hide in the Spine, but Garrow is fatally wounded and the farm is burned down by the Ra'zac. Once Garrow dies, Eragon and Saphira decide to hunt the Ra'zac, in vengeance. Brom insists on accompanying him and Saphira, and gives Eragon the sword Zar'roc.

It involves a boy, his dragon, elves, and weird monsters, and the title starts with an E.
Comment: That is the story thank you so much.
Comment: I'm glad I could help. I'm going to mark this question as a Duplicate, but please note that this does not mean it's a bad question, simply that it's been asked before, and we like to link them in the system. I hope you stick around. We're a fun site.
Comment: I plan on sticking around.


IN SSRS, is there a way to disable the rdl.data file creation

Question: In SSRS, I noticed that the rdl.data cache files are being stored on my dev machine.  Are these files also stored on the Reports Server when reports are run?  If so, is there a way to avoid creating those files on the server?
Comment: microsoft connect request: https://connect.microsoft.com/SQLServer/feedback/details/468482
Comment: I've had a problem I thought was due to this but actually was because datasets are copied into `bin/` and then not removed when they're no longer in the project causing the report relying on it to fail to fail during local testing. Horrible.
Comment: Microsoft Connect is retired, so the link that @TimAbell provided is dead.
Comment: Microsoft, you're doing the internet wrong.
Archived copy: https://web.archive.org/web/20161026070847/https://connect.microsoft.com/SQLServer/feedback/details/468482
Answer: rdl.data files aren't created on the server - they're purely to speed up report execution time during development when you repeatedly run the report with the same parameters whilst tweaking the layout.
As a side point, I believe it's true to say that it's possible to configure the SSRS service to cache results for reuse.
I don't know the details of the caching mechanism that the service uses; it might use a file-based mechanism like rdl.data, or it might store the results in one of the ReportingServices databases.
Perhaps someone more knowledgable about SSRS can confirm the details of the mechanism.
Comment: I know this is a late comment, but SSRS caching happens inside the ReportServer and ReportServerTempDB database.

This might provide a starting point for understanding the SSRS caching model:  http://sqlcat.com/technicalnotes/archive/2008/06/26/report-server-catalog-best-practices.aspx
Comment: @Ed....great info.  Thanks!  And if anyone would care to comment on the server side service caching configuration....I'd be very interested
Comment: @warriorpostman thanks - used the wayback machine to track down the info to this current archive url https://blogs.msdn.microsoft.com/robertbruckner/2008/11/04/technical-note-series-on-reporting-services-performance-and-scalability/ the title is "" as part of "Building and Deploying Large Scale SQL Server Reporting Services Environments Technical Note Series" and here is a concrete sticky link http://web.archive.org/web/20080802051432/http://sqlcat.com:80/technicalnotes/archive/2008/06/05/reporting-services-scale-out-architecture.aspx
Answer: In development, you can turn the caching off (and eliminate the *.rdl.data files) by editing the designer config file.
For SQL Server 2008 SSRS, the default location would be:
C:\Program Files (x86)\Microsoft Visual Studio 9.0\Common7\IDE\PrivateAssemblies\RSReportDesigner.config
Change CacheDataForPreview to "false"
Source Link
http://blog.summitcloud.com/2010/05/disable-reporting-services-data-cache-in-development/
Comment: This doesn't work this connect issue has been open at MS for 4 years http://social.msdn.microsoft.com/Forums/sqlserver/en-US/0aa81692-352f-4c1f-a0e3-95fe6c0797ca/cachedataforpreview-in-rsreportdesignerconfig-not-honored
Comment: setting still exists in VS2013, but still doesn't stop the generation of `.data` files
Answer: I'm not convinced that zomf's answer works (and neither are Microsoft).  It sounds good in theory, but doesn't seem to work in practice.
I think the easiest thing to do is to live with these files.  If you're bothered, you could always set the AutoRefresh property of every report that you created to 1 second (although the irritating flashing effect and load on your server might make this option unfeasible).
Otherwise, just click on the REFRESH button when previewing your report.
One other option might be to create dummy parameters for a report, with a randomly generated value each time you run it.  Since SSRS only shows cached data when the combination of parameters entered is identical to the previous time you ran the report, this might solve the problem.  I haven't tested it in practice, however.
Answer: PowerShell to the rescue, just hide it - add a PowerShell project to your Reports solution and set it as the start-up project in your build configuration:
<code>$path = "../*.rdl.data"

$rdlDataFiles = Get-ChildItem -Recurse -Force -Path "$path";

Write-Output "$path"

$rdlDataFiles | ForEach-Object {
  Write-Output "Hiding *.rdl.data file $_"

  $_.Attributes = $_.Attributes -bor (([System.IO.FileAttributes]::Hidden))

  # Next line isn't required per say, but just a guard.
  $_.Attributes = $_.Attributes -bor (-bnot([System.IO.FileAttributes]::ReadOnly))
}
</code>


Was my question removed? If so, why?

Question: I recently posted here on meta asking for us to consider why we down vote questions. I can't find it.  Was it removed?  Can I ask why?  If, in fact, it was removed with no explanation, it sort of reinforces the point I was making about discouraging questions.
Comment: Huh. I don't see it either.
Answer: Apparently, my mod powers allow me to see it. I found it, and it is indeed deleted.

Since the deleter is given as "Community bot", your question must have triggered some rule and have been deleted automatically. I don't know the details of these rules, they are probably available somewhere on Meta.Stackexchange. But I suppose that the combination of a negative score and no answers might have been the trigger.
It is questionable whether that is a good trigger for our Meta, where downvotes do not denote bad quality, but simple disagreement, and people are not very active in answering. But I haven't heard of a way to opt out of such a feature - although to be fair, I haven't actively looked out for it either.
I will undelete now and we can see if it disappears again - hopefully, the system will be smart enough to know that a manually undeleted question should not be targeted by automated cleanup.

Was my question removed? If so, why?


Which modern songs/melodies use the "Devil's interval" augmented 4th, discounting the use of tritone substitution in jazz?

Question: Recently I was informed that the augmented 4th has historically been viewed as satanic or "the devil in music" and wanted to start a collection of relatively modern (say 20th century onwards) songs that include this rather strange three tone interval. I understand that this is used in jazz fairly frequently so I would like to discount most songs from this genre, on the other hand if a certain jazz song is particularly interesting in using augmented 4th chord patterns I'd love to hear about it!
So far I have found a small collection of songs/melodies that use the interval:
Britten's War Requiem touches on the F#-C tritone during the Requiem Aeternam in the knell of the chimes
The Beatles in Blue Jay Way, amongst a few others from Harrison
"The Song of Healing" from the video game "Majora's Mask"
Jimi Hendrix's Purple Haze
(Interestingly, though slightly off topic, while watching an episode of "The Clangers" one hears a tritonic scale used throughout)
Are there any other modern uses of this? Sorry if I have broken any unspoken rules over question asking here; this is my first post.
Answer: The Simpsons theme (The Siiimp -- sons :-)
Maria, from Leonard Bernstein's West Side Story
are the ones that come to my mind.
A note of caution, though, the association of the expression "diabolus in musica" with Satanism seems to be an historical equivoque, as it was originally used only metaphorically to express the abhorrence to the dissonance of that interval felt by music scholars since the middle ages. So it was because of that epithet that the tritone may have been associated with Satanism, not the other way around.
Answer: A number of metal bands, such as Black Sabbath (in the eponymous song, for example) have used it. Thrashers Slayer even have an album called Diabolus in Musica, a gave numerous interviews expounding the virtue of the augmented fourth.
Answer: The tritone note is part of the blues scale (for example in C: C Eb F Gb G Bb). Plenty of modern music, especially rock/metal genres, base songs off this scale as it is merely the minor pentatonic scale (in C: C Eb F G Bb) with one extra note, the tritone.
In terms of using the tritone melodically, an immediate example that comes to mind is 'The Beautiful People' by Marilyn Manson, which traverses the tritone as the main riff.


Is the singleton pattern prone to thread safety problems?

Question: Is the singleton pattern prone to thread safety problems?  If so, what are the best methods to work around them?
Comment: Well be very dependent on language.
Answer: If well implemented, with threading in mind, a singleton will be thread safe.
There are many implementations in many languages that are not thread safe - see this article by Jon Skeet regarding Singleton in C#. Most of the implementations suffer.
The best ways to "work around them" is to know your language, how it works with threads and ensure the code is thread safe.
Just to note - even if singletons were somehow thread safe by nature, you should not use them for this reason. They tend to be overused and make for un-testable code as a source of global state.
Comment: +1 for mentioning global state, global state is prone to thread safety problems, in any form, singleton or otherwise.
Comment: Singleton classes needn't hold state. Unless they're designed to. Global state has its place.
Comment: @MebAlone a singleton refers to a single global instance, that is the definition of global state. Yes it has it's place, but you can't write a singleton pattern that doesn't share state unless it's a singleton instance of null.
Comment: Not all classes have class variables. Classes that don't have class variables don't hold state. But the class may be a singleton whose instance is shared by all clients. Granted it's a non-issue because if the class weren't a singleton, calls to new wouldn't allocate any memory, just pointers to the same methods.
Answer: Yes, as other answers have noted, it can be implemented in a thread safe manner. That said, it tends to be prone to issues since it already requires careful implementation to avoid subtle issues due to initialization order. The possibility of multiple thread access exacerbates these concerns.
And it's still global state. Even if the singleton itself is threadsafe, the reliance on global state tends to add errors to the actual multithreaded code.
Answer: It is heavily depend on the programming language specification & how thread safety is you implemented.
For example: code provided below uses double-checked locking, which should not be used prior to J2SE 5.0, as it is vulnerable to subtle bugs.
public class Singleton {
        private static volatile Singleton instance = null;

        private Singleton() {   }

        public static Singleton getInstance() {
                if (instance == null) {
                        synchronized (Singleton.class){
                                if (instance == null) {
                                        instance = new Singleton();
                                }
                      }
                }
                return instance;
        }
}

Here is a referencing article on how to correctly implement thread safe Singleton Pattern in C#.
Comment: A correct implementation in Java is actually completely trivial: `private static Singleton instance = new Singleton(); public static Singleton getInstance() { return this.instance; }` - that's it. The double-checked locking crap is a red herring that keeps getting re-aired by people who love splitting hairs.
Comment: I have to agree with Michael. Everyone's complaint about singleton's and thread safety makes the assumption that this single instance is being created and deleted throughout the lifetime of the program. If that is the case then they have a point. However, in EVERY system I have ever seen, singletons are created at startup time and exist throughout the life of the program. In this case, all that locking stuff and thread safety issues are meaningless. Now complaining about singleton's because of global data and hard to test reasons are absolutely valid complaints.
Comment: Maybe the 'double-checked locking crap' gets brought up because someone, somewhere at some time actually had this problem.
Comment: Here is a reference that discusses the double-checked locking pattern WRT singleton in C++.  http://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf#search=%22meyers%20double%20checked%20locking%22  The authors are Scott Meyers and Andrei Alexandrescu who I think generally do a pretty good job explaining C++ issues.
Comment: I am pointing to condition "when used prior to J2SE 5.0" - at that time it is helpful to consider "double-checked locking pattern"
Answer: Best way to avoid thread safety issues with a singleton is not use them. :-D That said, if you're going to use them, whether or not they're thread safe in a naive form is highly dependent on the language. If there's a safety issue, it lies with the lazy initialization nature of singletons which could end up being executed in parallel.
With that aside, let's say you're working in a language where it's not thread-safe. Such was my case in the 90s with a C codebase that was migrated to C++ where the developers started getting all happy with design patterns, including singletons. The one thing I'd request you don't do here to achieve thread safety is start trying to do fancy things like double-checked locking. Instead of doing backflips and juggling chainsaws, there's a very simple solution to the problem if you insist on using singletons:

Just make sure the singleton is initialized in the main thread prior to it being accessed in others.

That's it. It's such a simple solution, and it's no big deal to apply. You don't have to come up with some headache-inducing way to access the singleton without incurring the locking overhead in the common case. Just make sure it's initialized in the main thread before other threads get access to it. Done. Now you can make the access function lock-free and move on with your life.


Automatic MOLAP Error Notification

Question: We are just setting up a number of SSAS Cubes using pro-active caching and one thing that concerns me is how we will know if cube processing fails.
Is there a way to get SQL Server to notify via email if something has fallen over?
Answer: One way is to process your cube from a SQL Agent job, there you can set up a notification so that if the job fails someone gets notified.
I have jobs that process cubes every hour and I use the method above

Automatic MOLAP Error Notification


lubuntu 14.10 gedit plugin folder

Question: Which directory should I copy gedit plugins for gedit to recognize them in? I was browsing around the web, none of proposed folders worked. I want to use ftp code editng gedit plugin.
Comment: have you tried the system-wide plug-in directory? `/usr/share/gedit/plugins`
Comment: Yes, I have, it does not work
Comment: Have you tried another plugin?  maybe this particular plugin isn't compatible with your version of gedit?
Comment: @Fabby, I am trying to install gedit-ftp-browser at https://code.google.com/p/gedit-ftp-browser/.
Answer: That is a plugin for gedit 2 and not compatible with gedit 3.
I tried downloading it, putting it in the right (3.0) directory, changing the interpreter from python to python3 and upgrading the version to 3 but it still didn't work...
Therefore, the solution is: contact the developer for a new version.
(Probably not what you wanted to hear, but alas)
Comment: As you're a reputation 1 user, don't forget to accept the answer by clicking on the grey check-mark to turn it green.  Better then posting "thank you" for the work I did!  ;-)

lubuntu 14.10 gedit plugin folder


If gravitational waves are ripples in space-time, then electromagnetic waves are ripples in what?

Question: If the answer is the electromagnetic field, then is it also ubiquitously present as space-time?
Comment: *"then is it also ubiquitously present as space-time?"* - Consider the [cosmic microwave *background*](https://en.wikipedia.org/wiki/Cosmic_microwave_background) (CMB):  "The CMB is a faint cosmic background radiation filling all space."
Answer: While it's commonly said (even by physicists!) that gravitational waves are ripples in spacetime this is a bit misleading because it makes them sound like ripples in water, and the obvious question is what is the gravitational equivalent of the water that's doing the rippling?
Mathematically we describe spacetime as a four dimensional manifold (I say describe because I'm not claiming spacetime actually is a four dimensional manifold, only that we can describe it that way - what spacetime actually is we leave to the philosophers). Any point in spacetime can then be labelled by a set of four coordinates $(t, x, y, z)$. Suppose we have some property $P$ that is defined for every point in spacetime, so we can write it as a function $P(t,x,y,z)$. Then we call $P$ a field.
So for example we can have an electric field that varies from place to place and also varies with time, and we'd write it as a function $E(t,x,y,z)$. This is just a function giving the strength and direction of the electric field at that place and time. The electric field is a vector field.
Likewise in general relativity we have a field called the metric tensor that we write as $g(t,x,y,z)$. This is rather more abstract than the electric field because the metric tensor isn't something physical but an abstract object that tells us about the distance between nearby points. But it is just a field - in this case a tensor field.
Both the electric field and the metric obey equations that specify how it changes with time and position, and in both cases there are solutions that vary sinusoidally with time and space and we call those solutions waves. With the electric field this is just the familiar electromagetic wave e.g. light and radio waves. With the metric the oscillating solutions are the gravitational waves.
The key point to understand is that in neither case are these waves like ripples in water or sound waves in air. They are not waves in anything. They are just oscillating values of a field.
So assuming you haven't got bored and given up by now, we can get back to your question:

If the answer is the electromagnetic field, then is it also ubiquitously present as space-time?

And the answer is that yes the electromagnetic field is defined for all points $(t,x,y,z)$ in spacetime. In that sense it is ubiquitously present, but be careful because that just means its value is defined everywhere and that value can be zero.
Comment: John, thank you for your answer. It was in relatively simple and easy to understand terms which gave me a clear idea of what is actually happening. From what you say, it seems that in this case, Mathematics gave way to the wave and field idea and not the other way around. Just curious to know if the wave and field idea was in fact born out of the equations, or if the equations were discovered because of an already existing wave-field idea.
Comment: The other question that rises for me is, what physical situation can make the value of an EM field be zero? If we analogically interpret the electromagnetic field as space-time, the only time it occurs to me that space-time can be zero is when there is an absence of it, which maybe is when the question is artificially constrained i.e. in a model or something or before the big bang. In the case of the EM field would it be the same?
Comment: @JoseMiguelCruzyCelis: The electromagnetic field isn't spacetime. The EM field has a value at every point in spacetime and that value can be zero. Spacetime is a manifold and doesn't have a value.
Answer: Ripples is a term describing  small waves; "small" is not a very good description of the waves generated in the place where the gravitational collapse happened, but fair enough by the time they were detected in the recent experiments.
All waves classically , whether in water or air or solids , even electromagnetic, are functions of spacetime, because that is the framework we live in. These functions describe the  transfer of energy  in space time , from one (x,y,z,t) to the next. Gravitation is described by General Relativity and also has this sinusoidal behavior in energy transfers. The only difference being that it is (x,y,z,t) itself that is changing as the energy passes.
Research the last hundred years has discovered that the underlying basis of the classical fields,  that also give rise to wave equations transferring energy, is quantum mechanical . Gravitation is not yet described rigorously by quantum mechanics, only effective theories are used. The other three forces, weak,strong, electromagnetic are beautifully fitted with the standard model of particle physics.. This model uses quantum field theory for its calculations, which fit the data beautifully, and can predict new phenomena.
Quantum field theory means that the basic building blocks of the world, are the particles shown here

For each particle there exists a quantum field in space on which the particles travel as distortions of this field, represented by creation and annihilation operators.
So one can say that a traveling electron is a "ripple" in the electron field, and a traveling electromagnetic wave is a "ripple" on the photon field.
Once gravity is definitively quantized , a unified view of how these "ripples" form on the respective fields will become clear in the future.
The only theory that gives glimpses of rigorous quantization of gravity is string theory, and it would be interesting to see what sort of ripples happen when there is one  elementary particle, the string,  and all the rest, including gravitons, are excitations of it.
Answer: The gravitational field is a reflection of the spacetime curvature. Also, according to the equivalence principle, locally the effects of gravitation are equivalent to the effects in an accelerating frame of reference. So gravitation and acceleration are a reflection of very specific properties of spacetime. Please note that this conclusion is a bit different from "ripples in spacetime", because these effects are not just due to spacetime in general, but to very specific properties (symmetries) of spacetime.
It so happens that there are more symmetries than just those responsible for gravitation. For example, there is a symmetry that in the group theory is called $U(1)$. This symmetry also is a very specific property of our universe that on one hand is very simple, but on the other has fundamental consequences. Mathematically $U(1)$ is the unit rotation by the angle $\theta$ in the complex plane expressed as the $e^{i\Theta}$ multiplier. At the quantum level it corresponds to the phase shift of the wavefunction.
When we require this symmetry to be obeyed locally, we look at how it works with the Lorentz transformations of Special Relativity. This reveals a force field of two components (that we call electric and magnetic) interacting with charges in the way described by the Maxwell equations of the electromagnetic field. The Maxwell equations follow directly from applying the local gauge invariance (under the Lorentz transformations) to the $U(1)$ symmetry.
So the answer to your question is that the electromagnetic field (including the waves) is a result of the $U(1)$ summetry (simple $e^{i\Theta}$ unit rotation) that exists in this universe plus the fact that our spacetime generally obeys the Lorents transformations (Special Relativity that defines the speed of light). Ultimately all interactions are a result of different symmetries that exist in our universe.
Comment: 1. *"more symmetries than just those responsible for gravitation"* What *are* the "symmetries responsible for gravitation"? 2. A physical theory can conceivably have more than one $\mathrm{U}(1)$-symmetry and, in fact, the Standard Model contains multiples of them (as subgroups of the symmetries of the weak and strong force). There is no "the $\mathrm{U}(1)$ symmetry". 3. Demanding a theory be a gauge theory with a $\mathrm{U}(1)$-symmetry does *not* lead to the Maxwell equations unless you very specifically demand it to be a Yang-Mills theory coupled to an external conserved current.
Comment: @ACuriousMind 1. (A) Invariance under diffeomorphims (B) Invariance under infinitesimal diff. (C) Invariance under local Lorentz transformations (acting on the tangent space). Note that while the Yang-Mills theory is a gauge theory, not all gauge theories are of the Yang-Mills type. 2. "There is no U(1) symmetry". Then, according to you... the phase of the wavefunction is observable? And birds can't sit on high viotage lines? 3. So what? The fact that the theory under U(1) is interacting comes right from the covariant derivative and the current is conserved per Noether based on U(1).
Comment: 1. (A) and (B) are wrong answers, since many theories without gravity are diffeomorphism invariant. (C) is only correct in certain formulations and is not true in the standard second-order formalism of GR in which only the metric is dynamical, cf. [this answer of mine](https://physics.stackexchange.com/a/346812/50583). 2. No, please read what I wrote. There is no *unique* U(1) symmetry, and, once again, the U(1) phase symmetry of quantum state is *not* the U(1) symmetry of electromagnetism. I won't reply further on this issue because you're simply wrong.
Comment: 3. Your answer claims *"the electromagnetic field is a result of the U(1) symmetry"*. This is wrong, the electromagnetic field or, more precisely, classical electromagnetism is only a "result" of U(1) symmetry if you demand a Y-M theory and an external conserved current that's conserved *off-shell*, i.e. without Noether. Your claim that U(1) symmetry alone is somehow responsible for electromagnetism or the electromagnetic field is wrong. U(1) symmetry is no more the reason for the electromagnetic field than rotational symmetry is the reason a sphere is round.
Comment: @ACuriousMind Yes, I won't reply on this anymore either, since your comments lack physical intuition and are but mathematical splitting hairs. Too often mathematicians with no physical sense pretend to be physicists while forgetting that math is a model, not reality. Your positions that gravitation is not a gauge theory and that U(1) doesn't cause electromagnetism are well known. Fortunately there is no shortage of better opinions on this forum. Agree to disagree. https://physics.stackexchange.com/questions/71476/gravity-as-a-gauge-theory
Answer: I am going to give a very simple answer. The expresion using GW as "ripples" in space-time is a little bit confusing since it depends on what you define as space-time. The electromagnetic wave is equivalent. So, let me first introduce some ideas:

Any interaction is A FIELD.
Gravity and electromagnetism are FIELDS.
Electromagnetic waves and gravitational waves are ripples or more correctly little local perturbations (deformations) in these FIELDS, satisfying wave-like equations (that is the origin of waves).

If you define the spacetime with the aid of a metric field, a matrix, then you can say that a small perturbation in this field, with some simplications since gravity is a non-linear field, drives you to derive a wave-like equation for these perturbations. Essentially, something like this:
$$g_{\mu\nu}=\eta_{\mu\nu}+\varepsilon h_{\mu\nu}\rightarrow \square^2 h_{\mu\nu}=0$$
where $\square^2$ is the wave operator in spacetime. Indeed, I am keeping out certain subtle details since in the linear approximation, it is not $h_{\mu\nu}$ but $\overline{h}_{\mu\nu}$ (a modification that includes an extra piece in the so-called traceless transverse gauge, but it can be skipped to show the concept). In the electromagnetic field, you have a gauge field $A_\mu$, and when you "excite" it a little bit, you obtain something like
$$A_\mu'=A_\mu+\lambda a_\mu$$
It can be showed, with the aid of Maxwell equations and certain gauge selection that the electromagnetic waves arise from this in the same way, so
$$\square^2 a_\mu=0$$
From the fundamental viewpoint of the 20th century, fundamental forces are based on (quantum) fields. Perturbations of fields propagate using wave-like equations. Therefore, waves are local and small distortions in "fields". Beyond, the issue from the fundamental viewpoint is if...There is something that transcends the notion of field. I mean, according to general relativity, for instance, space-time IS and can-not be separated from the metric itself and the curvature tensor that defines the Einstein tensor $G_{\mu\nu}$. Space-time is the metric, and the derivatives of the metric defines the curvature and the strength of gravity via the Einstein Field Equations (EFE). Gravitational waves are certain solutions to the EFE. Classically, electromagnetism is based on a gauge field from which, similarly, through derivatives, we get the field strength $F_{\mu\nu}$. Maxwell equations in free-space time imply the existence of electromagnetic waves as special solutions in certain gauge.
In summary, you can observe the following answer to your question:

Gravitational waves are ripples or tiny deformations in the metric field $g_{\mu\nu}$.
Electromagnetic waves are ripples or tiny deformations in the gauge field $A_\mu$.
Chromoelectric and weak fields (W,Z) particles are ripples or tiny deformations in the massive gauge fields $A_\mu^{a}$.
The Higgs waves/particles are deformations of the Higgs field $H$ around certain vacuum, $h$.

You can even generalize this to matter/substance fields, and you get spinorial equations (Dirac-like equations):

Matter and substances are described by fields.
Matter follows spinor-like (Dirac-like, Weyl-like,Majorana-like) equations.
Matter waves are perturbations in matter fields described by spinors.

Then, the question is what is "a field"? That is much deeper question, since everything that we do know is a field...Literally, and how we define a field (classical or quantum) is to some extent something in our current description of the universe we don't understand completely, but Nature is apparently well described (5% at least) by quantum and/or classical fields. Any theory going beyond space-time or fields will have to generalize our understanding of field theory and space-time!
The fundamental concept of matter (substances) and energy (interactions) is, thus, the field. Perturbations into the fields create forces/substances, following equations that are wave-like for interactions and spinor-like for matter fields. The link between matter and energy is subtle due to mass-energy in special relativity, but it is OK. Difference of the fields are in the nature of the equations...And if you want, as matter is substance made of atoms, what are gauge fields and/or gravitational fields made of? Is there any other more fundamental description of Nature than that based on classical and quantum fields? Are light and space-time substances after-all too?


Spontaneous inequilibrium in a gas in an isolated system?

Question: Can an isolated system(of several phases) in equilibrium by itself move out of equilibrium?
if a system contains for example an inflammable gas dispersed with another combustible gas such that the molecular speed are insufficient to cause the reaction. but as the molecular speeds keep fluctuating, at some point, it may cross the energy barrier and may start the reaction which will eventually spread evenly but till then the temperature there would be high and thus the system in inequilibrium.
isn't this also an example that although the free energy is minimum and entropy maximum, some useful work would've been done if the temperature gradient had been utilised?
Comment: I'm slightly confused as to why you've specified multiple gases here -- an inflammable gas is, by definition, also combustible, and I'm not sure how that changes your question. Could you clarify?
Comment: it is just to make sure that at the point in space where the reaction begins there is quite a large difference of temperature created and hence the condition of inequilibrium is unanimously accepted. you can ignore that considering only the thought experiment
Answer: The short answer to the question "Can an isolated system(of several phases) in equilibrium by itself move out of equilibrium?" is NO.  Once the system is in equilibrium it will remain there.
If it is possible, as is asked in the second part of the question, to have some reaction be triggered at a higher temperature reached by fluctuation, then as has been commented, the answer is that the system was never in equilibrium.
We should never forget that there is no "absolute" starting temperature for a reaction.  If the reaction is physically possible, it will take place, but the rate of that reaction can be horribly slow.
Comment: Technically it can move out of an equilibrium situation spontaneously, since a spontaneous increase in free energy is only statistically disfavoured. If the potential energy landscape has a shallow minimum, reasonable fluctuations might happen. Though now I have two questions. Firstly, do we know of some equilibrium that fluctuates appreciably, and more interestingly, do we know one that does so around room temperature? Or does the mere free energy contribution of mixing overwhelm perceptible fluctuations? Secondly, are there any reaction equilibria with *more* than one free energy minimum?
Comment: @NicolauSakerNeto The presence of two minima in free energy is present in regular solutions wherein the presence of two minima necessitates the splitting of the mixture into two phases of the compositions corresponding to the minima. But I couldn't find examples of such conditions in proper chemical 'reactions'


Is the wobbly rope depiction of a radio wave inherently wrong? And how do vectors of parallel waves align with each other?

Question: I don't have a scientific education, yet I'm scientifically curious. Among other things, I'm struggling to understand the nature of electromagnetic waves.
What I have recently realized is that the depiction of a EM wave as wobbly rope is inherently wrong.
Until recently I was imagining radio waves to be invisible wobbly lines piercing the space in all directions. I bet that the absolute majority of common people visualizes radio waves like that.

But the wobbly rope image is not a depiction of a radio wave itself. It's a graph where X axis is distance (in the direction of the wave propagation) and Y axis is the "strength" (or "tension") of the field in each point of that distance. And a graph is not a depiction of an object. It's a documentation of a phenomenon. And the form of the actual wave (and even the concept of the wave itself!) has nothing to do with the wobbly rope.
After investigating this matter further, reading answers on this site (specifically from dmckee and CuriousOne, thanks!) and a couple of sleepless nights, I've figured out that:

In almost every graph, one of the axes is time. But the wobbly rope graph is an exception, it doesn't demonstrate time. To demonstrate time, those graphs are animated. This is the main reason of the wobbly rope discrepancy: a picture associated with a moving wave actually looks like a moving wave, but that's merely an unfortunate coincidence! :-O
Sometimes, Z axis is added. Y and Z both mean the same thing: "strength", but one is for the magnetic field and the other one is for the electric field.
The fields don't wobble. It's just every point of the field changes its state. Each point of the field is a vector. This means that each point's state consists of two values: a "strength" and a direction. Each point of a field is always stationary, but each is associated with a direction and "strength". When an electric or a magnetic wave propagates through a field, the points of the field change their directions and "strengths" but they themselves never move.
The direction of each point of the field is always perpendicular to the direction of the wave that propagates through that region of the field.
Electric and magnetic waves always travel together, and their directions in every point are perpendicular to each other. On the wobbly graph, the Y and Z axes are also perpendicular, but that's just a coincidence. Y and Z demonstrate amplitude, the "strength" of the field in every point, but the X axis demonstrates distance. Distance and "strength" are different things and don't correspond with each other! That's why those images are graphs, not illustrations of waves themselves.
Electromagnetic waves are not rays and neither they are composed of rays! (Mind: blown.) EM waves travel in fronts, i.e., they spread spatially like sound waves or water ripples. The graph represents not a spatial wave but a single longitudinal line copy-pasted from a spatial wave. That's merely a thought experiment.
Though it's technically possible to emit exactly one photon (a photon is a single unit of a wave), a photon is a quantum particle. It conforms to quantum laws. Human-world laws do not apply to photons. This means that it is not correct to speak about such thing as a "trajectory" of a single photon. Photons are kinda probabilities, not moving objects. (I can't get my head around this statement, please help me find a mental model for it! SOS!) This means that the wobbly rope illustration does not demonstrate a "single" wave. It merely demonstrates an 1D fragment of a 3D wave.
When an electromagnetic wave travels as a front, the photons interact with each other, they kinda form a single "object" -- a spatial wave. This wave would, roughly speaking, bounce off a metal mesh (a Faraday cage), even though a single photon could easily come between wires of the mesh.

Questions

Are the above conclusions correct?
Say a spatial EM wave propagates through the EM fields. We "take a snapshot" of the field and from that snapshot we crop an 1D line perpendicular to the direction of the wave. How will vectors of each point on that field line relate to each other? Will they all be pointed at the same direction? Or will they form a sine-like wobbly pattern? If yes, is that pattern's period equal to (or derived from) the wavelength? See two variants below.
The second variant would explain for me the Faraday cage: how the size of the mesh step (a transverse parameter) can depend on the wavelength (a longitudinal parameter). The second variant might also explain circularly polarized waves.

UPD
Here's a fresh one:

And it's a poster of an educational video about the nature of light!
Answer: Many of the things you write sound OK. But I wouldn't say that the other directions in the graph are mere strengths, they indicate the actual value (strength/magnitude and direction as well) of the electric and magnetic fields.
First note that technically the electric field is a vector and it is a field so it should have a vector (possibly zero at every point). Each vector has a head and a tail. You can think of the location of the tail as telling you the place where the field has a particular value. Then you can think if the difference between the head and the tail as telling you both the magnitude and the direction of the electric field at that point, in some specified unit system.  So imagine a bunch of arrows all the same color the location of each is telling you where it is telling you the field and how the arrow points from there tells you the value.
Then draw the magnetic fields in a different color. And in both cases you can't draw a vector at every single point because it would just be too much to see them all.
For a plane wave traveling through vacuum there is a great deal of regularity.
 If the wave travels in the x direction then the electric and magnetic fields all point in the y-z plane. And their values only depend on time and on x, so you can draw just one longitudinal line and it will tell you about all of the values at all the locations. And since the electric fields and magnetic fields all point in the y-z plane you can reimagine the y-z plane as like the independent axis of a graph.
And for a classical plane wave travelling through a vacuum your picture should have the electric and magnetic fields both be strong together at one plane of a fixed value in the longitudinal direction and then at a different plane corresponding to a different fixed value of the longitudinal direction. Strong together and weak together and then strong again but pointing in the opposite direction.
If so, you get a picture much like the first one you drew (though that is just for one the electric and magnetic fields, a wave has both). That is all fine for a classical wave travelling through a vacuum.
For your other questions I think you should look at existing questions about the different topics.
From a quantum perspective it is much more complicated. From a quantum view there isn't an electric or a magnetic field, there is a photon field. When you have a large number of photons all in phase with each other it can look or act like an electromagnetic wave, but it is still different, and if you have a small number or they aren't in phase then it just truly different.
The electric and magnetic fields classically are stand-ins for saying how charges interact (though they do have their own energy and momentum, pressure and stress, etc.) And in quantum mechanics different interactions are possible and so the photon field is a stand in for saying how those different interactions go.
Since in quantum mechanics the charges don't have a location and momentum saying that their momentum changes based on the field where the charge is located just isn't going to be possible because you have none of those things. And if you can't verify the field's values at any location it becomes difficult to say it is there in that way.
We make the objects we need to predict results, for quantum mechanics we need different objects because we are predicting different interactions. Only in some limits (that only hold sometimes) do we expect quantum mechanical effects to start to approximately look like classical effects.
As for a transverse spacing in a Faraday cage stopping a wave that varies only in the longitudinal direction remember that you were drawing only the simplest case, the case of a plane wave.
In a plane wave the entire plane parallel to the y-z plane has the exact same electromagnetic field. This very simple (to describe) solution allows the wave to travel entirely in the x direction, over time each part of the wave simply slides over, the new value at distance $x=x_0+\Delta x$ over is the old value at $x_0$ a time $\Delta x/c$ earlier.
But no real wave is ever that perfect. They might expand in a spherical front instead of a plane front. They might have a central region where it is strong and it gets weaker farther out (like a Gaussian beam) some people even make beams where the energy and momentum travels along a cone so there is a central strong region but if you place a small object there the region beyond it still gets light because the light from farther out came from a base of the cone that started out farther from the central region.
Sort of like if you had some racers all lined up for a race but instead if running in their own tracks they ran towards the same point that is in front on the center runner. The center runner gets there first, but if parts of the center of the track are damaged the runners that left later will eventually close in and it won't matter that that the runners originally closer to the center got affected.
So a real wave has a more complicated wave front. And in fact if you are trying to avoid the wires of the Faraday cage you need your beam to be focused to not extend out too far in the direction transverse to the direction of propagation. And this isn't restricting the amplitude, this is saying that the actual wave shouldn't have field values spread out in the yz plane, it should be focused to a small portion of the yz plane.
Imagine you shot narrow beams all towards the same hole in the Faraday cage, you need very precision aiming each point has to has "its x" aimed very precisely to get in that same hole.
In general if you aim your initial propagation directions with accuracy on the order of the wavelength then you gave changed the wave.
Thus is because the direction of propagation isn't a magic thing you can freely associate with a point. It depends on how the electromagnetic field varied in space.  When you field didn't vary in the y and z directions then the field travelled in the x direction. Now you are trying to get each region to aim slightly differently so you try to adjust the electric and magnetic field here and there to have each part aim just right.
Waves tend to spread, so if you aim some at that one whole, lots will be lost in other directions and what aimed well for one whole is nor going to aim for the other holes, so the Faraday cage succeeds at blocking almost all fields coming at it assuming the cage is big enough to have many many holes.
I think many of these question can be (and have been) asked as separate questions.
Answer: What Maxwell derived was from radio waves. Radio waves are modulated photon radiation. Electrons in an antenna rod get accelerated at once and emit photons. The density of this photons distributes in space. Detecting this radiation with a receiver one get a sinus wave form. The frequency of this wave has to do with the frequency of the antenna generator and has nothing to do with the frequency of the single photons in this wave.
But all this photons form the electric and the magnetic component of the radio wave. Hence each photon has an electric and a magnetic component. Photons once emitted are indivisible units. Imagine photons as bubbles, inflated at one moment to the left and right as a magnetic dipole and in the next moment inflated to the top and bottom as an electric dipole. Both inflations ar e perpendicular to the propagation of the photon. More details see in my paper.


Real part of Raman response function in linear response theory?

Question: When we calculate the Raman scattering, we usually derive the imaginary part of the Raman response function. The general formula of the imaginary part is given by
\begin{align}
\text{Im}[I(\omega)] \propto \sum_{f}\left|\langle f|R|i \rangle\right|^2 \delta(\hbar \omega - (E_f-E_i)),
\end{align}
where $|i\rangle$ and $|f\rangle$ denote the initial and final states of the system. The delta function relates to Fermi's golden rule and therefore this imaginary part means the energy dispersion (the other words, the energy absorption (emission)). In this case, what is the physical meaning of the real part? Naively, the real part is given by
\begin{align}
\text{Re}[I(\omega)] \propto \mathcal{P}\sum_{f}\left[\frac{\left|\langle f|R|i \rangle\right|^2}{\hbar \omega - (E_f-E_i)}-\frac{\left|\langle f|R|i \rangle\right|^2}{\hbar \omega - (E_i-E_f)}\right].
\end{align}
Answer: This can be understood on general grounds through the theory of linear response. In Raman scattering and many other cases, we're typically interested in the response of a Hermitian operator to a real-valued perturbation, for which the time-domain response function (or generalized susceptibility) $\chi(t)$ is itself real, which upon Fourier transforming leads to a complex response function in frequency space,
$$
\chi(\omega) = \mathrm{Re} \chi(\omega) + i\,\mathrm{Im}\chi (\omega).
$$
The real and imaginary parts are related by the Kramers-Kronig relations, in a way that enforces causality in the sense that the response for $t<0$ (i.e. before the scattering event) vanishes. The imaginary part (odd in $\omega$) is often called the dissipative (or absorptive) part of the response since, as your equation shows, the delta function involves an energy transfer of $\hbar\omega$ due to the scattering process.
The real part (even in $\omega$) is in-phase with the perturbation and is known as the reactive part of the response. It is the Fourier transform of the time-reversal symmetric part of $\chi(t)$, which corresponds to reversible processes and does not know about the arrow of time. There is a heuristic argument relating $\mathrm{Re}\chi(\omega)$ in a scattering system to virtual transitions in J. S. Toll., Phys. Rev. 104, 1760 (1956).
Comment: Thank you for your response. I had not considered the behavior of the response function with respect to time reversal. I would like to know if there is an experimentally observable physical quantity that corresponds to the real part.
Comment: @rtrtw I'm not aware of one in scattering experiments, since the cross section is entirely related to the imaginary part. Reconstructing the entire $\chi$ from scattering is sometimes known as the "phase problem", and I've only seen it done using the Kramers-Kronig relations.
Comment: Thank you so much!


Can you respond to קדושה if you are not already done with your own ש''ע?

Question: Can you respond to קדושה if you are not already done with your own ש''ע? I heard that you can if you are past a certain point after שים שלום/שלום רב. I just want to know if that's true and, if so, exactly what point in the ש''ע must you have passed?
Comment: Hello anonymous, and thank you for bringing your very relevant question to Judaism.SE! Consider registering your account to keep track of your contributions. Hope to see you around!
Answer: Yes, this is true. This refers to after you have said the first "yih'yu l'ratzon" and are now in middle of "elokai n'tzor". Different authorities disagree on how you may interrupt, so here's some sources.
This website says:

"one may answer Amen for Kadish, Kedusha, Barchu (and all the other things permitted Bein HaPerakim of Shema), and according to some Poskim any Amen for any Bracha, as Shemona Esrei is over already."

The newer editions of Siddur Tehilas Hashem have a chart of permitted/prohibited interruptions. It appears that most of the laws are the same as bein haperakim of shema, except for putting on talis and tefillin. It says that:

you may answer "amen" to birchas hatorah.
for kaddish, you may answer only "amen yehei sh'mei...." and the last "amen".
for kedusha, you may answer only the responses of "kadosh", "baruch", and "yimloch".
for answering modim, you say only the first three words: "modim anachnu lach".
you may answer barchu.
you may answer "amen" to "hakel hakadosh", and "shomeya tefillah".
you may go up for an aliyah, but you should not read along.
you may say the blessings on lighting and thunder.
you may not say shema with the minyan, rather you should continue davening but with the tune of shema.
everything else is not allowed.
Comment: @ydk keep in mind that these are printed in Tehillat Hashem, and so are most likely from Shulchan Aruch Harav, who may pasken differently.
Comment: "continue davening but with the tune of shema"?! I am shocked.
Comment: Also, these laws are assuming you do not have enough time to step back.  If you do, it is better to skip tachanunim (elokai-netzor...) than to respond to the above while still standing in tefilla (end of OC 122:1 http://hebrewbooks.org/pdfpager.aspx?req=49623&st=&pgnum=286)  Which makes the aliyah one kind of strange.
Comment: Shulchan Aruch haRav says the same language: http://hebrewbooks.org/pdfpager.aspx?req=25072&st=&pgnum=370
Comment: @YDK You are correct. I too, then, wonder what it means when it says you should go up for an aliyah. Perhaps it is disrespectful to make the Sefer Torah wait the time it takes to step back, or perhaps the chart maker just copy-pasted the halachos for bein haperakim of shema. Unlikely that, I think, because they _did_ differentiate between halachos of tallis and tefillin. Perhaps I'll ask someone I know in Kehos....
Comment: Unless you arrived to "Elokai Nesor" you may not. However, once you arrived Elokai Nesor you may answer "Kadosh" and "Baruch." See Siddur Avodat Hashem in Shemone Esre on the bottom.
Comment: @h'gabriel. I'm not sure what you are adding here. That you can't say "yimloch"?
Comment: Sephardic source and that fact as well
Comment: @h'gabriel. Then I suggest you undelete your answer, and add some more information on how its different from mine, to it.
Answer: Yalkut Yosef vol.1 Hilchot Tefila pg. 176 he says that one should answer "Kadosh" and "Baruch" in the middle of Elokai Nesor as well as the first 5 Amenim of Kadish (the Ben Ish Hai holds that one may even answer Amen DeBerachot. However, Hacham Ovadia I believe writes in Yabia Omer 6:48:4 that one may not do so). However, if one didn't say the first "Yehi Rason" he may not stop for kedusha or kaddish (first 5 Amenim) because it is part of the Tefila.
However, if one already said the second he may answer any davar shebikdusha, including Baruch Hu UBaruch Shemo. (see Yechawe Daat 5:10)


How can I find the UIView for a specific UITabBarItem?

Question: I am using an external library called SwiftyWalkthrough, which allows me to expose only certain views on the screen to guide a new user through my app's UI.  The first item I want exposed to the user is a UITabBarItem.  I need to find the UIView associated with that specific UITabBarItem.  I know the index for the item, and I have given it a tag.  But I haven't found a way for them to help me find the view.  Of course, I only want to use public interfaces to accomplish this.
Comment: There are many views in the tab bar item. which one are u looking for?
Comment: The one that encloses the title and icon on the tab bar at the bottom of the screen.  I expect it to be rectangular, having a height identical to the entire tab bar, and a width equal to the tab bar width divided by the number of tab bar items.
Comment: i think there is no access to the UITabbaritem backgroundView, we can only put the custom image for the tab bar item, but cannot get the backgroundView for the tabbar item.
Answer: I solved my problem by accessing the subviews of the tabBar.  The views with userInteractionEnabled are UITabBarItems.  Sorting them by their minX values guarantees that they are in the same order as the tabBar.items array.
extension UITabBarController {
    func orderedTabBarItemViews() -> [UIView] {
        let interactionViews = tabBar.subviews.filter({$0.isUserInteractionEnabled})
    return interactionViews.sorted(by: {$0.frame.minX < $1.frame.minX})
    }
}

Comment: Thanks! Really nice and elegant. I know this can potentially break in the future, but there doesn't look to be a better way...
Answer: Swift 3 version of for Carl Smith's answer
func orderedTabBarItemViews() -> [UIView] {
    let interactionViews = tabBar.subviews.filter({$0.isUserInteractionEnabled})
    return interactionViews.sorted(by: {$0.frame.minX < $1.frame.minX})
}

Answer: Tested in iOS10 with Objective-C:
[alert setModalPresentationStyle:UIModalPresentationPopover];

    UIView *view = [self.tabBar.selectedItem valueForKey:@"view"];

    alert.popoverPresentationController.delegate = self;
    alert.popoverPresentationController.sourceView = self.tabBar;
    alert.popoverPresentationController.sourceRect = view.frame;
    alert.popoverPresentationController.permittedArrowDirections = UIPopoverArrowDirectionDown;

    [self presentViewController:alert animated:YES completion:nil];

Comment: swift `if let view = tabBar.selectedItem?.value(forKey: "view") as? UIView { }`


where did the word 'skunt,' meaning to cut your grass very low, come from?

Question: growing up in the 60's in Dallas, Texas, we would cut our lawns very short at the beginning of the growing season, believing that this would cause the lawn to grow fuller in the summer.  We referred to this practice as "skunting" the lawn.  People would say, "Are you going to skunt your lawn."
Comment: You should check UrbanDictionary.com for other usages of the word 'skunt.'
Comment: Or, alternatively, don't check it and keep the classical meaning in mind.
Comment: I don't recall ever hearing it.
Answer: It's possible that this is a slang outgrowth of skinned.  To skin something is to make it bare or remove the surface of something, which could be figuratively extended to cutting a short crop or lawn.

skinned > skint > skunt

Some sources I found in newspaper corpora use "skunt" to mean, clearly, "skinned."

he's dead an' gone to the Bad Place 'cause he skunt a cat--I don't mean skin the cat on an actin' pole like me an' Wilkes Booth Lincoln does--he skunt a sho' 'nough cat that was a black cat

1912 - Frances Boyd Calhoun, Dixon Evening Telegraph (Dixon, IL) 13 Jun, 6/1 (paywall)

Green's Dictionary of Slang lists skint as a slang variant of "skinned" with a cross reference to "skunt out," although it does not directly address this particular sense of "skunt."

without money, out of funds; thus as v., to make penniless.

The etymology here is listed as Standard English "skinned."
It looks likely that this sense of "skint" meaning "penniless" as a variation of "skinned" is similar to "skunt" meaning "cut bare" or "cut very short."
Comment: This is the first time that I have realised that 'skint' (meaning having run out of money) was an allusion to being skinned.
Answer: In a 1947 short story anthologized in Twenty-one Texas Stories, a man and his nephew discover that the caretaker in whose hands they left an inherited Hill Country farm has likely been helping himself to the profits as well as a few head of cattle:

"Because me and you's done been skunt out of no tellin how much money," Uncle Mark said.

The expression is not limited to Texas, but also known in AAVE, or at least Joel Chandler Harris's version of it in 1880:

"So I kin git some water ter clean you wid atter I done skunt you, Brer Rabbit.' "Please, sir, lemme go, Brer Wolf.'"

So we've got Brer Rabbit about to get skinned, a couple of guys who got skinned by an untrusty caretaker, and most likely, ya'll's skinned lawns in Dallas.
Those who used skunting had apparently lost any sense of the word being a past participle and just begun using skunt as a regular verb.
Skint, however, is originally a British take on skinned from ca. 1925 and remains a primarily British term. It should thus be seen as a parallel rather than related form.


Restoring broken Kali Live USB or Rescuing files?

Question: I was trying to update my Kali live usb with the feature that restarts kali and when it boots up again it updates not through the terminal with apt-get. The update stopped by itself before it was done causing my Kali live usb to break. Now I can boot into Kali but I can't open anything or see any icons. If I try to open terminal it goes into the screen you usually get before the desktop appears when you boot up normally except it does nothing. The way I set up my live usb does not allow me to choose to boot into safe mode. I have some files that I really need to rescue if possible. What can I do to try to restore Kali or at least be able to access the filesystem and save those files?
Answer: If it were me in this scenario, to save myself the headache, I would plug the USB into another computer or a virtual machine, and use a file browser to copy the files from the root (/root) or user directory (/home if you used it). You should be able to do this with any Linux distributions including Debian and Ubuntu. Then format the drive and create a new live USB. A fresh install can never hurt anyway.


Will the entropy change be equal if a state change is brought about reversibly and irreversibly?

Question: Since entropy is a state function so it doesn't depends on the path followed. So will the entropy change be equal if a state change be first brought about reversibly and then irreversibly.
Comment: The Q/A model of StackExchange network does mean the question title is the question and the question body is the answer. The title is to be a summary question or word expression and the body is expected to contain the full question elaboration. But it is not really a question if you already knew an answer, so why it was posted ?
Comment: In my text book it was mentioned that in irreversible process the entropy change of system+the entropy change of surroundings taken together is greater than zero and in reversible process it is equal to zero, so i was getting a bit confused. That's why I asked if the entropy change would be same Or not. Can you explain the above point to me that why in irreversible process it happens so?
Answer: If the initial and final states of systems are the same for both reversible and irreversible process, the entropy change for the systems will be the same.
But the entropy change for the surrounding will not be the same, as the final states will be different. The surrounding for the irreversible process will end with higher entropy.
Therefore the total entropy change  is zero for reversible processes, but positive for irreversible ones.
The irreversibility condition applies not only to system-surrounding interactions, but for system internal processes as well.
Answer: Yes, that is how we determine the entropy change of a system for an irreversible process .  We determine the entropy change for a reversible path between the same two end states.
Answer: Yes, they will be the same. As you know, entropy is a state function and it only depends on the initial and final states. Whether the process is reversible or not does not affect the entropy change (i.e. the entropy change does not care about the path).


Is one hour enough for changing planes in Newark?

Question: I am coming from Miami and will change planes at Newark, my final destination is Beijing. I only have 1 hour from arriving to departure, is that enough time or must I have change to an earlier departure from Miami?
Comment: As usual with such questions: are the two flights on the same ticket/booking, or where they booked separately? Do you have checked luggage? What airlines/flights and/or what terminals?
Comment: 1 hour sounds too close for comfort just about anywhere to me
Comment: I would not try this short a connection even if booked on a single ticket with no checked luggage.
Comment: Is there an additional flight from Newark to Beijing after your flight?  In that case you can risk, and hope for a seat on second flight. Closing door on long haul flights are often 45 minutes before departure (+ 15 minutes to choose if remove baggage or not, you will not have baggage on board, so they will not wait for you.)
Answer: If this has been booked as a single ticket than

It's a legal connection that meets the minimum connection time
Statistically you have an ok chance of making it, if all goes well.
If things do not go well and you miss it, the airline will book you on the next available flight for free. However, that my be a day later.

If these are two separate tickets, you will NOT make this connection.
There are a few things that can help speed things up

Make sure you check in for both flights and getting boarding passes for both segments.
Familiarize yourself with the airport layout and map. Figure out which gates these flights arrived the day before and check how you would get from the arrival to departure gate. If you are flying United, most likely you'll arrive and depart from Terminal C
Newark is a huge airport and the distances between gates are quite long. If you have any mobility issues, call the airline right now.
Not checking luggage helps


real functions or complex functions

Question: There are many questions from students about (presumably) real functions of (presumably) real variables. I say presumably, because information is often scarce. Now with real functions there are often issues with domain. Examples are $\sqrt{1-x}$, $\space$ $\log(1+x)$ and $\tanh^{-1}(x)$. You may manipulate these functions for arguments outside of their domain, but the result is usually meaningless. It is for this reason that students are taught to first examine the domain of a real function, before the actual calculation (differentiation, integration) is performed.
Now functions such as those above can be analytically extended to the complex plane. Whether this is intended by the teacher or whether it leads to a meaninful answer is unclear. But the answer is then quite different from the real case. The outcome is a complex number; often branch cuts have to defined. The student may well be unfamiliar with these concepts.
So how should functions such those above be treated? As real functions with a domain, or as complex functions? I am not aware of a policy on this matter. I have seen questions where an expert gives an answer, based on the concept of complex numbers. Such answers are then upvoted by the community. The fact that the question may actually belong to the real function category is dismissed. I have also seen opposite cases, where the expert treats the function as real. The answer gets upvoted. If someone else treats it as a complex function, the answer is ignored. Or it leads to comments that it is inappropriate to use complex numbers in this particular case.
A recent example is How to integrate $\int_{0}^{1} \int_{0}^{1} \tanh^{-1}\left(\frac{x}{y} + \frac{y}{x}\right) \,dx\,dy$. Quanto gives good advice on how to simplify the calculation, but in doing so he ignores the important fact that the integrand does not exist because of a domain problem. I pointed this out, but the community is silent.
Answer: The student should provide context as to whether the function is real or complex. If context is not provided, I feel like a quick comment to ask for clarification should do the job. If they don't know what you're talking about, then it is probably safe to assume they are dealing with a real function.

real functions or complex functions


why is my p-value large?

Question: I have a hypothesis "People are better at detecting a lie when they are able to see a persons expression, compared to people that are not". The results were that 3 out of 20 people detected a lie correctly from seeing a facial expression and 5 out of other 20 people correctly detected a lie from only hearing it.
I've done a chi-square test in R and it gave a p-value of 0.4292, which is higher than 0.05. This basically means, that i should accept the hypothesis. But how can I accept it if I clearly see that there were more people that detected a lie from hearing it rather than seeing a facial expression? In a logical way, my p-value should be less than 0.05, but its not. How do I explain it?
Comment: Intuitively, is 5 out of 20 really "much more" then 3 out of 20? I'd say no. Moreover, your sample is really small so the test is reluctant to reject the null.
Comment: What year did you use?
Comment: why is that important?
Answer: The null hypothesis would be "Seeing facial expressions makes no difference to people's ability to detect a lie".
Your p-value of 0.4292 would be the probability of getting 3/20 assuming the null hypothesis is true.
As this is more than 0.05, you fail to reject the null hypothesis, using a significance of 0.05.
In other words there is a fairly high probability of getting 3/20 if there is no difference. Your 3/20 is just down to chance, it's not significant.
So you have no evidence to support the alternative hypothesis "People are better at detecting a lie when they are able to see a persons expression, compared to people that are not"
Comment: Your discussion seems to treat the 5/20 as the null case, but the test should be a two-sample test; it's really about whether 3/20 and 5/20 could be consistent with each other than whether 3/20 unusual in itself
Comment: what is the formula for computation of  p-value ?  and what is the database ?
Answer:
"Pearson's chi-squared test (χ2) is a statistical test applied to sets
  of categorical data to evaluate how likely it is that any observed
  difference between the sets arose by chance."

The null-hypothesis of the test is that both sets do not differ in the frequency. The alpha of p<0.05 is the threshold at which you would reject this null hypothesis (i.e. conclude that sets differ). However, p is far from 0.05, therefore the conclusion is that frequencies of lie detection do not differ significantly between groups. The p value of 0.429 indicates that there is a 42.9% chance of observing a difference this large, or larger, between the two sets assuming the null hypothesis. In other words: The difference between groups is so small that it may likely arise by chance, even if there was 0 difference.
Answer: If you Start with a one sided hypothesis (as you stated in your problem), you should not use the Chi-Square test which is intended for testing a two-sided hypothesis. Also - you should get a p-value greater than 0.5 because the results are opposite to your initial hypothesis - more people detected the lie when hearing. You cannot change your initial hypothesis after you see the results!!

why is my p-value large?


What beat is We Can Still Stop Her in?

Question: This piece (We Can Still Stop Her by Michael Giacchino, Inside Out OST) has a strange beat. It seems 4/8 at first, but something isn't right: it takes 9 bars for the melody to repeat, but it's two repetitions of the melody. Does that mean that the piece is in a 18/8 beat instead? Or is it a simple 4/8 with occasional 2/8 bars inserted?
Answer: I would interpret the beginning section as 9 beats of 2 quavers each arranged as alternating bars of 4/4 and 5/4. Writing it as 9/8 or 9/4 would imply three groups of three (triple time) which doesn't match the rhythm.
Answer: Listening to it I'd have put it into 9 (or maybe 4+5 if 9 always means compound, and it definitely doesn't have a triplet feel).  This puts it in 3/4: http://www.musicnotes.com/sheetmusic/mtd.asp?ppn=MN0153795
Comment: Listening to it, I would have put in in 9/8 time, but three-bar phrases of 3/4 might be better than longer bars and lots of 16th-notes for an "easy to play and read" version. It's a bit deceptive, because the rhythm doesn't emerge very clearly on the youtube recording till about a minute into the track, and it's not obvious from the recording that it starts with a pickup beat rather than at the beginning of a bar.
Answer: Short answer
I would conduct this piece in 3/4, as that provides the simplest, consistent way of keeping the parts aligned.
Short of being able to examine the score, however, any analysis is speculative in the sense that we can't know the composer's intent.
Why 3/4?
3/4 vs. 9/8

Pulse strength: In strict theory terms, in 3/4 every third beat (i.e., every downbeat) receives equal, primary emphasis; whereas, in 9/8, only every third, third beat (i.e., beat 1) receives primary emphasis, and the other two, third beats are only semi-strong.

S = strong
s = semi-strong
w = weak

3/4: 1 2 3 1 2 3 1 2 3
     S w w S w w S w w
     S w w s w w s w w
9/8: 1 2 3 4 5 6 7 8 9

Once the piece takes on a clear, regular triple feel (around 0:43), the downbeats feel equal, as in 3/4 time, rather than a strong downbeat followed by two weaker ones.

Phrase lengths: Some parts of the piece comprise 6-beat segments, rather than 9. For example, the sustained string notes beginning at 1:31 are six beats each. So, too, are the sustained notes that close the piece. A 3-based meter is the better fit for these passages.

Okay, sure, the full orchestra sounds 3/4-ish, but what about the irregular metric pattern in the entire rest of the piece?!?!?!?!
Well, first of all, please don't abuse the punctuation marks.
The key here is that the opening features regular pulses, but the pulses themselves are undifferentiated. That is, they are not rhythmically accented. Rather, the melodic contour suggests accents, and the nature of the melody makes these accents irregular. The opening does make a good case for interpreting the piece as polymetric.
My case for 3/4 rests in part on there being multiple metric interpretations based on how the melody is perceived. To illustrate, I've chosen 9/2 to mitigate the conventional associations with 9/4 and 9/8, and I've placed the two perceived pulse patterns above and below the notes, respectively.
<code>X:0
T:We Can Still Stop Her
T:Opening
C:Michael Giacchino
K:A minor
M:9/2
L:1/4
V:V1 clef=treble middle=b
"^>"A B [|: "^>"c A B c "^>"d A B d "^>"e d c B "^>"c A "^(>)"B ^G "^>"A B :|]
s: > ** > *** > *** > * > * > * >
</code>
In the first (upper) case, we would conclude either 4+4+4+4+2 or 4+4+4+2+2+2. In the other case, we would conclude 3+4+5+2+2+2.
The situation is clarified somewhat with the entrance at 0:07, which is clearly 8+10 (i.e., 4+5 with two pulses per beat).
However, these interpretations fall apart once the brass enters at 0:43. At this point, the piece becomes clearly 3/4.

What beat is We Can Still Stop Her in?


Difference between diameter of a graph vs longest path of the graph

Question: I am curious what is the difference between diameter of a graph vs longest path of a graph. I just read diameter of a graph can be solved using Floyd warshall in O(V^3) while longest path can be calculated in O(V + E) using topological sort.
Answer: The longest path of the graph is the longest path between any two vertices. There may be several with the same longest length.
Since you are comparing with the diameter, which is an integer, you probably mean the length of the longest path
The diameter is the length of the longest of the shortest path between any two
vertices. That means that you compute the shortest path for any pair
of vertices, and take the longest one of them.
The distance between two vertices being the shortest path, the diameter is the longest distance between two vertices,
Comment: Well, this was a word confusion started by the fact that the question mixed a distance with a path to begin with. But you are right.
Comment: I know you know this, but it is not necessary to compute the shortest path distance for every pair of vertices to find out what the diameter is. It is, of course, the obvious way of doing it.
Comment: It might be useful to include a small example where the two notions don't coincide.
Comment: @Raphael: A triangle works.  In general, $K_n$ has diameter 1 and paths of length $n-1$.
Comment: @Juho Yes. But I believe definitions should always be as simple as possible, the rest being a matter for theorems. But when two properties are equivalent, it is a matter of taste which should be the defining one.
Answer: In general, they are not the same thing. Also, for the general graph, it is easy to compute the diameter, but hard to compute the longest path. In the graph below, the diameter is 4. A path from $6$ to $2$ is highlighted, which is of length 4.

However, there is a longer (simple) path from $6$ to $2$ of length 5.
Comment: And there's an even longer path of length 7, though not between those two vertices.
Comment: @DavidRicherby Yeah, you'll find one between say 7 and 3.
Comment: "hard" meaning NP-hard here.
Answer: Topological sort is only defined for directed acyclic graphs so you can't use it to find longest paths in general directed graphs or undirected graphs. Finding the longest path in an undirected graph (in the whole graph or between two specific vertices) is NP-hard.  I assume this holds for cyclic directed graphs, too.
Note that it's "unfair" to compare Floyd Warshall with an algorithm for finding the longest single path in a graph. Floyd Warshall computes $\Theta(n^2)$ different things (the length of the shortest path between every pair of vertices) so it's running time is, in a sense, $O(n)$ per answer.


In Views, how can I display an edit link if a node relationship exists, otherwise display an add link?

Question: I have a view of assignments, and want students to be able to post their work from that node. If they already have a work node, I want to display an edit link. Otherwise, I want to display an add link. In a previous version of this view, I used a Views PHP field that queried the DB for a work node matching the assignment, but I am rewriting the view because of a bug and I wanted to revisit this because it seemed a but ugly. Can anyone think of a better way?
Comment: I think you have to add both add and edit links, then you can take the help from this post http://stackoverflow.com/questions/4360432/how-to-conditionally-hide-a-field-in-a-drupal-view
Answer: I have had a similar situation and I did the following which is probably not the best thing to do - I will use your terms:

When an assignment node is created a work node for each student is created with the field field_submitted set to false
On the view, the field field_submitted is included but excluded from display
I have a php field with this code which displays edit or submit, both are actually sending to the same node but they will give the student some insight about what he should do next:
if(!empty($data->field_field_submitted[0]['raw']['value']))
   echo l(t('edit')/*, ... */);
else
   echo l(t('submit')/*, ... */);

Answer: I am assuming the following things for this answer

There is a content type called assignments.
There is a content type called workbook which has a reference to
the assignments content type
The view is of the assignment content type.

Now to achieve what you are looking for follow the below steps

Add a relationship of the type "Entity Reference: Referenced Entity"
Now add the field Content: Edit link. Choose the relationship we created in step one
Set the "NO RESULTS BEHAVIOR" and add the link to add a workbook
page like   Add workbook
Add a CONTEXTUAL FILTER of the type "Content: Author uid" and provide default value and select "User ID from Logged in user" from the list.

That should do it.


Android JNI Debug: Eclipse : Project specified in the launch configuration is not a C/C++ one

Question: I'm on Eclipse Indigo.  I'm trying to Debug the JNI/C++ portion of an Android Eclipse Project.  I don't want to convert my Android project over to a C++ project for obvious reasons.  I don't mind adding C++ nature but the options I have tried so far change my project to a C++ project that needs a make file.  So the debug proceedures is that I start a Java Android Debug session, startup the ndk-gdb debug server, and then I need to attach the C++ debugger somehow. So I created a C++ Debug Profile in addition to the Android Java Debug Config.  But when I start it up I get Project specified is not C/C++.  Should I create a dummy C++ project just to get the debug session working? Thanks
PS: I am following the steps in this guide to debug JNI in Android:
http://mhandroid.wordpress.com/2011/01/23/using-eclipse-for-android-cc-debugging/#more-23
And it does not indicate the need to create a separate C++ project.
Answer: The option "Convert to C/C++ project" is what you need.


Are PCs really vulnerable to Spectre type attacks due to virtual user space addressing?

Question: Are Windows OS user programs vulnerable to Spectre and the other recent Intel flaws? Wouldn't the virtual memory assignment in Windows prevent such attacks, or their usefulness? Sorry if I miss something, the attacks seem complex, and not even deterministic.
Comment: All major modern OS use virtual memory  and Windows is no different to this. Also, Meltdown is exactly about bypassing some protections offered by virtual memory. *"I haven't found time (or even interest to make time)"* - there are enough information out there so that you don't need to read the technical papers. And, this is not a site for providing information just because the OP was too lazy to do some own research. If it does not seem to really interest you then why even ask?
Answer: Virtual addressing does not make spectre or meltdown more difficult to exploit.  All of the proof of concept exploits have been performed on systems with virtual addressing.  Virtual addressing by itself is not a security feature, it's merely a convenience for multitasking OS.
Page permissions are intended to provide isolation between different processes and between user-space and kernel-space, but the whole problem with Meltdown is that it provides a mechanism for leaking information across that boundary.
Rendition Infosec has built a nice slide deck describing the vulnerabilities and their implications in a condensed format.


What objects are interactive on the playing board?

Question: When playing against slow opponents I spend most of my time clicking the interactive areas of to boards like the catapult, bonfire and farm.
I have multiple times though I had found them all but then found a new place to click.
So what are the places you can click on each board to have something happen?
Comment: Related question: http://gaming.stackexchange.com/questions/147473/when-you-click-on-the-scenery-in-hearthstone-does-your-opponent-see-it
Answer: Orgrimmar board

Zeppelin - tumbles when clicked
Rock by the zeppelin - tumbles more and more when clicked like it's going to fall
Gates - can be closed and opened
Vines by the gates - If you hack them enough they spread a bit
Forge - clicking black smoke will exhaust / "ignite" it
Banner by the forge - flops a bit when clicked
Catapult - you can put rock in it and fire it on the enemy,than cork it back and re do

Stranglethorn board

Diamond in the statue - if you click enough it will fall out
Eyes in the dark beneath the statue - makes some roar or hiss sound
Vines on the gates - if you click enough you can cut them
Skull on top of the gates - makes drumming sound
Coconut tree over the gates - coconuts can fall off
Waterfall - clicking water makes splashing sound and effect and can create rainbow
Bushes - will make them move a bit
Tent door - makes snoring sound
Tent roof - clicking the pelt will make it "jump",dust off and change(leopard,zebra,tiger)
Fire by the tent - Clicking can ignite it

Stormwind board

Glass around church doors - can be broken
Lamp near the church - turn on/off
Church roof - bell sounds
Armory sign - one chain can be broken by clicking
Armory door - open/close
Armory roof - one tile can fall out
Armory window - turn lights on/off
Bushes near church and armory - can be clicked
Clock tower roof - boards can be broken
Clock - makes ticking sound,adds a minute,and should be set to current time
Well - splashing effect until the bucket falls in,also one of the bricks can be broken off
Gryphon - Moves and follows you mouse when clicked
Banner under the Gryphon - swirls when clicked
Haystack - hay straws flying effect when clicked
Crates behind haystack - can be broken

Pandaria board

Kite - moves a bit when clicked
Wooden stake that holds the kite - you can pull it out and lose your kite :(
Round paper light - moves a bit when clicked and makes a sound
Window light - on left building can be turned on/off no sure for the right building window
Doors on watermill - makes opene/close sound
Water wheel - you can help turning it by clicking
Gong - makes weak gong sound,each few hits it makes louder effect
Bush with flowers near gong - you can pop flowers
Fruit on farm - can be squashed
Water(irrigation) on farm - makes squashed fruit grow back(as different fruit)

Naxxramas board

Floating crystal - moves when clicked,after enough clicks it starts to crack
Egg sacks - can be poked,after enough clicks spiders crawl out from it
Spider eyes in the dark - when they appear you can click on them,usually spider just makes hissing sound and hides,sometimes bats flew out and rarely the spider bites your cursor
Skull,left eye - diamond falls out
Skull,scalp - tapping sound
Skull,left tusk - if you click it it just moves a bit,but if you click and hold the sludge will start pouring out from skull
Mushrooms - you can poke them,after enough clicks they release green gas
Sludge pit - bubbles
Sludge still,2 hatches - they can open/close
Sludge still,valve - can be turned,if turned enough times and if both hatches are closed the still will boil and release the sludge,otherwise it just releases steam
Sludge still,screw - 2nd screw from the left can be turned until it pops out
Sludge puddle - splashes

Goblins vs. gnomes board

Switches and red button on teleporter - pressing red button will spawn vegetable,fish,boot,diamond,bomb,banana,kite or chicken-bot inside teleporter.Setting of switches doesn't appear to matter.
The teleporter corner - The tiny screw laying on the board can be clicked and will screw itself into the hole above it.
Laser gun - can be turned around and fired.Shooting at enemy hand will play a "Ouch!" sound. Shooting under the satellite dishes near the rocket will launch it.
Satellite dishes - play scanning sounds.
Furnace - holding furnace doors opened few times can ignite both of the nearby fireworks

Blackrock Mountain board

Left lava pool - clicking rune combinations can make maul/periscope/inflatable animal sink/surface.

valve on the periscope can be turned
inflatable animal can be popped

Right lava pool - Upper chain fills up the pool,lover one drains it.
Dragon eggs - can be squashed
Torch - can be lit or extinguished
Anvil - Clicking makes it glow more and changes nearby weapons(axe/sword/polearm)
Shield - Can be turned in to a round one

...And you can poke the dirt on the ground,which you will end up doing most when waiting.
Comment: He doesn't.It would be very distracting if you were playing your turn and someone would keep clicking around.
Comment: Does the other player see your interactions?
Comment: Clicking the forge smoke actually turns it off, and clicking again turns it back on.
Comment: :( cant upvote or accept again sadly
Answer: Every corner "location" of the board has at least one interactive point:
Stranglethorn:

the jewel can be removed from the eye socket, making it drop in the jungle;
the menacing eyes in the jungle disappear when clicked;
clicking on the vines on the gate cuts them;
the eyes on the skull above the gate lighten up;
the waterfall, when clicked, creates a rainbow;
the fire can be put out by clicking on it;
the pelt on the tent changes when clicked, from tiger to leopard to zebra and back to tiger.

Stormwind:

clicking on the stained glasses of the cathedral breaks them;
the streetlight can be put out;
the bucket falls in the well when clicked;
the inn sign moves;
the door of the inn gets closed when clicked and you can turn off the lights inside too.

Pandaria:

the kite moves in the wind;
the wheel in the mill moves when clicked;
the gong makes a sound when clicked.

Orgrimmar:

the zep moves in the wind;
you can play with the catapult by putting rocks on it.

This is what I remember, I'll update when I can test a little more.