How can I discourage mycelium and other fungi growth in containers?

Question: How can I discourage mycelium and other fungi growth in my plant containers?  And yes, is it even a good idea?
Answer: It's not something you should worry about - there's no way of getting rid of mycelium without using completely sterile soil. Even if you did that, the air is full of fungal spores and they may arrive anyway. All you can do is not overwater and ensure good drainage by not using pots without holes, etc,to discourage invasion by less friendly forms of fungi. In some cases, there is a beneficial or even symbiotic relationship between certain fungal mycelium and plant roots.
Under 'other fungi growth', you might be including fungal growths and infections which have aerial forms, like the mildews, black spot, rust, some varieties of phytopthera infection, but these do not produce mycelium in the soil, so I'm not sure whether you're including those in your question or not. Most are encouraged by warm, humid or damp, still air and insufficient air flow round plants; powdery mildew is often encouraged by dryness at the roots.
Answer: This is WHY potting soil is sterilized!  Did you try to sterilize any of the soil you made?  Shoot, there are some fungal and bacteria colonies you should embrace.  Such as Mycorrhize!  Especially if you are dealing with unknown garden soils/amendments in pots!!
You should have FANS going 24/7 for indoor plants especially those in crappy garden soil that hasn't been sterilized.  This is one of the best preventative measures for fungus.  Knowledgeable pruning and bio fungicides applied early on susceptible plants are two other measures to understand.  Fungicides are primarily a preventative sort of a 'raincoat' for plants.  There are fungicides for ornamental plants and a few for vegetables.  Milk and water seems to be very effective for powdery mildew.  Any other fungus needs preventative measures such as aeration pruning, fans, 'raincoats', not allowing water to splash up on plants (containing fungal spores galore), shielding from rain (get ready for powdery mildew, it is the lack of 'free water' or physical rain, water on the leaves, humidity/dryness such as under eaves of homes where rain is unable to reach that promotes powdery mildew as well as a plant's natural susceptibility).
Comment: I didn't. I was told that the soil is already sterilized. But maybe the garden soil I mixed wasn't sterilized, and that's where the problem arise. Well, I have used same proportion and same soil in 5 pots. The Mycelium is only growing in one pot. I will put more sterilized soil on top of the soil to cover it.
Answer: I also wondered about this at some point, because a potted plant I had died of damping off.
I've since incorporated cinnamon into a potting mix I used into an homemade self-watering pot. I thought some antifungal was a good idea in a constantly moist soil.
Maybe my reasoning was wrong, and there is no increased chance of fungus developing in my self-watering pots, but the facts are that I've had no problem whatsoever in the last 6 months, and cinnamon might have been the key. I also read chamomile tea could be used similarly to avoid damping off.
Comment: Sounds like your 'self watering pots' aren't doing their job!  Would it be a hassle to just water when you see and feel the soil is dry and they need more water?  There is usually plenty of water below the surface and no plant should ever be watered on some human schedule.  Learn the HEFT of a plant in its pot when watered and when it is dry.  The difference is dramatic.  Unless you are gone for weeks/months, water by hand.  Any plant in a pot is completely dependent on its STEWARD.  Completely.  To allow a 'self watering' anything is asking for problems. Don't do cinnamon, or chamomile...
Comment: Maybe "moist" was too strong to describe the humidity of the pot. My point was that while the top of the potting mix is dry to the touch, I expect the bottom to be in a constantly humid state, and I feared damping off as a result. I use those because I am frequently gone for 1 or 2 weeks, and as a result I only have plants that can survive not being watered during that time, and plants in self-watering pots with a reserve that can usually last 2 weeks.


Why is there still screen tearing even when fps are limited to be equal to monitor refresh rate?

Question: Why is there still screen tearing even when fps are limited to be equal to monitor refresh rate? Also if tearing occurs because of fps higher than screen refresh rate why don't games limit fps to be equal to the screen refresh rate by default?
Answer: Tearing occurs when the graphics card's buffer is sent to the monitor while that same buffer is being changed.  You still get tearing even if the FPS is limited to the refresh rate of the monitor because those things aren't locked together without vertical sync enabled.
Think of it like you're in a classroom, where the teacher is writing notes on the board.  You're taking pictures of the board as the teacher is writing them.  You want to take the picture when the board is full of notes.  If you take a picture while the teacher is working, or while they're erasing part of the board to write new notes, your photo will be missing some of the notes.
It doesn't matter if during the class period you take 6 pictures and the teacher fills the board 6 times, right?  You could take 6 pictures right at the beginning and miss everything.  You could take the pictures evenly spaced (every 10 minutes, say) and miss stuff because the teacher takes longer or shorter to fill the board each time.
Instead, it matters that you take the picture at the right time.  Your pictures must be "in sync" with the teacher.
"Taking the same number of pictures as there are blackboards full of notes" is locking the FPS to the refresh rate of the monitor.  There's no guarantee that every time the monitor refreshes, the graphics card is between frames.
"Waiting until the blackboard is full of notes before taking a picture" is vertical sync.  The graphics system is synchronized and thus only complete frames are shown.
Answer: Because even if your fps is the same as refresh rate of the monitor, it doesn't mean the frames are synchronized with the refresh rate. Screen tearing can happen at any fps, if vsync is off.
Comment: Nice and simple.
Comment: @Elise screen tearing can happen even when fps is lower than refresh rate of monitor? E.g if I am playing at 45 fps on 75Hz monitor, will it also cause screen tearing? Or will it cause only when I play at 75+ fps?
Comment: yes, it can happen even at lower fps, but it may not be as prominent


Can every continuous function between topological manifolds be turned into a differentiable map?

Question: Let $M$ and $N$ be topological manifolds that admit differential structures and let $f:M\to N$ be continuous. Can $M$ and $N$ always be given differential structures to become differentiable manifolds $\widetilde M$ and $\widetilde N$ such that $f:\widetilde M\to\widetilde N$ is differentiable? What if we impose further restrictions, such as $\widetilde M$ and $\widetilde N$ being smooth manifolds, or $f$ becoming smooth? Are there certain differential structures which we can't do this with (i.e. if we want to make $f$ differentiable, we can never make $N$ diffeomorphic to $\overline N$ where $\overline N$ is some differential structure on $N$)? What if $M$ already has a fixed differential structure?
Comment: There are multiple differential structures on $\mathbb{R}$. They're all diffeomorphic, but they are distinct. For a maximal atlas on $\mathbb{R}$ and a homeomorphism $h:\mathbb{R}\to\mathbb{R}$ we can take a chart $\varphi$ in the atlas and obtain a new chart $\varphi\circ h$. We can define a new atlas consisting of all the charts in the previous one composed with $h$. Clearly the transition maps are differentiable. So if $h$ wasn't itself differentiable, we have a new differential structure, since $h\circ\varphi$ and $\varphi$ clearly aren't compatible.
Comment: Shouldn't the 1-dimensional case yield examples? I mean there are continuous $f : \mathbb{R} \to \mathbb{R}$ which are not differentiable and I somehow think that there shouldn't be more differentiable structures on $\mathbb{R}$ then the natural one?
Comment: Sorry, the last part doesn't work. I confused $\varphi\circ h$ and $h\circ\varphi$. However, if $\varphi$ commutes with $h$, then it's fine, so if, e.g. the identity is a chart (which of course it is in some maximal atlas), then we have a new differential structure.
Answer: There is not necessarily a way to make a map smooth.  For example, suppose $M=\mathbb{R}$, and suppose $N$ is any topological manifold of dimension $2$ or more.  Let $f:M\rightarrow N$ be any continuous function whose image contains a non-empty open subset of $N$ (e.g., take a space filling curve onto $\mathbb{R}^n$ and then think of this $\mathbb{R}^n$ as a chart).
Then there are no smooth structures on $M$ and $N$ which makes $f$ smooth.  In fact, you cannot even make $f$ continuously differentiable.  One way to see this is to use Sard's Theorem: if you could make $f$ continuously differentiable, then the set of regular values would be open and dense.  Because $M$ has a lower dimension than $N$, regular values are points of $N$ which are not in the image of $f$.  But then the rest that the image of $f$ contains an open subset of $N$ means the set of regular values of $f$ is not dense.
Comment: This is a great answer.
Comment: I just updated the answer to change "smooth" to "continuously differentiable".


Failed to initialise the LWJGL display

Question: I added the fix of adding this line "Dorg.lwjgl.opengl.Display.allowSoftwareOpenGL=true" to vm arguments, updated my drivers but nothing is working......my error message still remain same has shown in the image
Answer: This error message is commonly caused by outdated video card drivers. To fix this, make sure you're using the latest version of LWJGL and have the latest version of your graphics card's video drivers installed.
Answer: First see Thomas's answer about upgrading your drivers, but there are also known issues with Java 64bit and OpenGL on Windows as well as known compatibility with EOL Intel Graphics chips. You haven't shown your configuration so we don't know what the issue is.
The solution for the first problem is to run the 32-bit version of Java, the solution for the second is an unsupported patch of the Intel HD Graphics driver. Usual caveats about installing drivers by some guy on the internet apply.

Failed to initialise the LWJGL display


Failed Redundancy for RAID 5 Disks

Question: I'm facing difficulties in regards to some disk issues if you guys can help me. I am using Windows Server 2003 for my File Server. For the past few days in Disk Management the status of two of my (Software RAID 5) disks are marked as "Fails Redundancy" but the disks are still working properly. I'm afraid of losing my data. What do you think I should do?
Comment: Repeat after us: RAID is not a backup. RAID is not a backup. RAID is not a backup. The primary purpose of small-scale RAID is to improve *uptime*, not to protect data.
Answer:
I'm afraid of losing my DATA

Anothernon-backup guy bytes the dust? Sorry, you deserver that. MAKE BACKUPS.

the status of two disks which are RAID 5 is (Fails Redundancy) but still the disks are
  working properly

Funny. Could be part of the disc being bad? Not really heard of that. You already did order the replacement discs? Start regenerating the array. Expect data loss without backup. Start doing backups.
Comment: Nope, i just lost some data to bacd backups, too. Having a failed raid and assume that a RAID was protecting is "work at McDonalds" qualification level. Tape drives aer not THAT expensive (though the are a little expensive for private people).
Comment: Graeme - bit of an odd one but while I find TomTom's comments funny I think that ultimately, however rude he comes over - and he does - he's almost always right. For instance this guy's got a 'dicky' raid array, and while we can help him fix it or deal with it one way or another it would be negligent not to very strongly suggest that now's the time to be ensure that he had a working backup system/strategy. Now he can learn this the hard way, probably will in fact, or we can tell him very clearly - TT is often TOO clear but I think it's better than letting it pass by. That's my opinion anyway.
Comment: You seem to get more snide with every new answer.
Answer: I'm guessing you have a 3 drive array and one drive has gone which hopefully should leave all your data intact, but your server is reporting you no longer have any redundnacy - i.e. if another drive has a problem, all your data is toast.
Backup all your data as advised by TomTom at the earliest possible opportunity - raid 5 can give problems when rebuilding - I have a test server at home and thought I would borrow a drive for use elsewhere - when I rebuilt the array, pretty much everything was there except I could no longer use that installation of windows. I considered myself lucky to just lose windows rather than my data - raid is no replacement for backups.

Failed Redundancy for RAID 5 Disks


Theres something wrong with my viewport shading

Question: I'm a beginner and I was making a house while I found a problem. When I turn on the Scene World in viewport shading, weird shadow casts and my house turns black
Answer: The default in viewport shading uses an HDRI, which is an image that emits light from all angles, but your scene world has very low light, other than your area light that is pointing straight down.  The house "turns black" because nothing is lighting it.  You can go to the world properties and increase the strength of the world light or add an HDRI to your world.


Viewshed calculation using SQL

Question: Can i calculate viewshed in MS-SQL server? Viewshed analysis is Raster operation. I have elevation value vector observation as point vectors. Are there any methods to calculate Viewshed (using algorithm or something like that) ?
Answer: This question is fairly broad, and so I am going to give a largely theoretical answer.
In short, there is not a MS SQL Server tool that would do this. However, it's still possible, if not easy. You can run a visibility analysis (viewshed) on any array of elevation values (aka raster) using an external script/algorithm.
Python libraries (e.g. NumPy) are able to work with numerical arrays. You could convert the points to an array (directly, if you have enough, or else interpolate to have a full elevation surface) and then do the math to look for visibility obstructions for each point in the array. This is not a particularly efficient way to do it, and it's easier to put the points into a GIS environment (or script with GIS tools) and work with them there.
An additional side note: viewshed accuracy improves as the elevation surface resolution improves. If you do not have many elevation observations, your results may not be accurate enough to be useful.

Viewshed calculation using SQL


What happens if you get negative defense?

Question: According to the RealmEye wiki, the Seal of Blasphemous Prayer (commonly referred to as the "Oreo") gives -4 defense. I tested to see if this was possible using Pfiffel's dps calculator. It turns out you can have negative defense. So if you had -4 defense, would a 30 damage projectile deal 34 damage? What would happen?
Comment: The reason I didn't try this already myself is because I don't have the Seal of Blasphemous Prayer
Answer: The results are in!  I equipped an Oreo on a 0-defense character for a total of -4 defense.  The damage I took while I had it on was increased by 4 and was displayed in the regular red color.  Purple text means armor-piercing damage, not just 0 defense; otherwise it would be purple when your shots damaged pirates or other easy enemies.
So basically, it does what you'd think.
Answer: The damage done by all enemies would be pure damage. And if I am not wrong, the damage colour would be purple. Pure damage is the damage ignoring the defence of your character. Negative defence would mean there would be more damage dealt to you than the damage done to a person with 0 defence.
Comment: That was what I was thinking too, but I was hoping that there would be something like a picture or video to prove it. This is just theoretical.
Comment: I've got an Oreo and some spare time - I might do some experimentation and report back.


Why aren't superconductors shiny?

Question: Superconductors are really good at conducting electricity. Should they not reflect light very well too?
Comment: Super inductors are really good at conducting **DC** electricity.
Comment: Welcome to SE.physics. Before asking a question, better to check if it has not been answered. This question is the exact analogue of this one: http://physics.stackexchange.com/q/2409/16689 where it is discussed that superconductors are really good mirror for wave-energy below the superconducting gap.
Answer: A photon can only excite a pair in the superconductor if the photon's frequency is higher than the energy gap, so above this frequency the superconductor won't be perfectly reflective, and behaves somewhat like a dielectric with regard to optical properties. The analogy is not perfect since the dispersion of the pairs is not linear, and there may be excitations involved other than photons and pairs.
But, if the photon's energy is lower than this, then the photon can't excite pairs inside the superconductor, and has to produce a reflected photon.
For tin far below the critical temperature, this frequency is roughly 2.7 $\times 10^{11}$ Hz according to BCS theory, which corresponds to a wavelength of about a millimeter, much longer than the wavelength of visible light.
So for radio waves, a large enough slab of superconducting tin will be an excellent mirror, but looks basically like any other material at visible wavelengths and above.
For more dramatic examples of superconductors that look like mundane dielectric materials, magnesium diboride and certain perovskites spring to mind.

Why aren't superconductors shiny?


statistical regression vs machine learning regression

Question: I was trying to understand the difference between statistical regression VS machine learning regression. My background is from Economics and learned regression from statistical point of view for the first time. I learned machine learning later on and it also had regression. There might not be clear distinction between two but wanted to ask major differences.
What I can say (I might be wrong) now is there're from different areas and the model is different where statistical regression represents outcome consists of a set of independent variables with an error term whereas machine learning regression consists of outputs and inputs. Also, ML regression requires the process of training, testing to predict the unseen data sets but statistical regression doesn't require this process but analyze the past data and derives out the parameters (similarly weights in ML).
An intuitive explanations (no math or complex equations) using example might be helpful!
Comment: Much of why we care about assumptions in statistics has to do with inference, not prediction.
Comment: same thing except ML folks dont bother about assumptions. i doubt they even know about them
Answer: There really isn't much of a difference.  A strained distinction between the two might be consideration of the data generating process (what statisticians call the likelihood).  Statisticians care about this because different likelihoods lead to different types of inference. A hotly debated example of this would be the linear probability model (essentially linear regression on binary data) versus logistic regression.  I won't spark the debate here, only offer it to you for future research.  In general, machine learning doesn't seem to make many statistical assumptions about the data.
Leo Brieman's Two Cultures paper does a better job of elaborating on this difference.  To the extent there is a difference between the two (I'm not certain there really is), this would be it.


How can I get Ender Bees in Agrarian Skies?

Question: One of the final bee-related quests requires you to breed bees to produce certus combs. In order to get this bee, you need to have access to ender bees. How can I get ender bees in Agrarian Skies?
Answer: As of version 2.1.1 of the Agrarian Skies pack, Ender Bees are a reward for the "Work Harder" quest in the Bees and Trees quest tree.

Aside from that, you can only get Ender Bees with an Ex Nihilo artificial hive in The End, surrounded by End Stone.
Answer: Just FYI, I placed 5 scented hives in the End in various positions.  2 were in the center of a 5x5x10 block (in the center of each 5x5x5 cube) with views of the sky, 3 were placed on top of the 5x5x10 rectangular prism.  I got 2 End hives, both from on top of the cubes.


Migrate SSE2 to Arm NEON intrinsincs

Question: I have the following code in SSE2 intrinsincs. It processes input from a Kinect.
<code>__m128i md = _mm_setr_epi16((r0<<3)  | (r1>>5), ((r1<<6)  | (r2>>2) ), ((r2<<9)  | (r3<<1) | (r4>>7) ), ((r4<<4)  | (r5>>4) ), ((r5<<7)  | (r6>>1) ),((r6<<10) | (r7<<2) | (r8>>6) ), ((r8<<5)  | (r9>>3) ), ((r9<<8)  | (r10)   ));
md = _mm_and_si128(md, mmask);
__m128i mz = _mm_load_si128((__m128i *) &depth_ref_z[i]);
__m128i mZ = _mm_load_si128((__m128i *) &depth_ref_Z[i]);
mz = _mm_cmpgt_epi16(md, mz);
mZ = _mm_cmpgt_epi16(mZ, md);
mz = _mm_and_si128(mz, mZ);
md = _mm_and_si128(mz, md);
_mm_store_si128((__m128i *) frame,md)
if(_mm_movemask_epi8(mz)){ ... }
</code>
This basically unpacks 11 uint8_t (r0-r10) to 8 uint16_t in an SSE register(mmask is constant and created previously). It then loads two more registers with the corresponding elements from two arrays that serve as bounds. It checks them and creates a register which has the elements that don't fit in the criteria zeroed out. It then stores them and goes to further process each element. The movemask serves as a nice optimization when none of the elements pass in which case the processing can be skipped.
This works nice and now I want to port it to NEON as well. Most of it is straightforward except two parts. Looking at the assembler output(gcc) from the SSE2 code I see that instead of doing 8 uint16_t moves in _mm_setr_epi16 it shifts and ors them into uint32_t and finally does 4 moves. That seems efficient and since the compiler takes care of it I didn't change the code. Should I apply that manually in the NEON case? Instead of 8 vsetq_lane_u16 do the shifting and perform 4 vsetq_lane_u32? Will I have any issues with endianess and will it be worthwhile?
The final part is the movemask as I haven't been able to find an equivalent. Can anyone suggest something?
Answer: I'd prefer starting with plain C code instead of SSE2; there might be optimization opportunities not easily seen at this low level

Migrate SSE2 to Arm NEON intrinsincs


Unable to read text when using a dark theme

Question: Anytime I install a dark theme I am unable to read the text in the software center as well as many other applications because the text is white and the software center background is also white.
Does anyone know how I can fix this?
Comment: I know this problem and it is hard to describe. Can you give us a screenshot?
Comment: And the name (and download link) of a dark theme that illustrates the issue so that others who don't know the problem can take a look.
Answer: To install Delorean Dark theme in Ubuntu open Terminal (Press Ctrl+Alt+T) and copy the following commands in the Terminal-
sudo add-apt-repository ppa:noobslab/themes
sudo apt-get update
sudo apt-get install delorean-dark

Delorean dark offers theme for software center enter these commands in terminal to get it:-
cd /usr/share/software-center/ui/gtk3/css/ && sudo mv softwarecenter.css softwarecenter.css.backup
cd /usr/share/software-center/ui/gtk3/art/ && sudo mv stipple.png stipple.png.backup
cd && wget -O softwarecenter.css http://drive.noobslab.com/data/themes/delorean-dark-3.10/softwarecenter.css
sudo mv softwarecenter.css /usr/share/software-center/ui/gtk3/css/`
cd && wget -O stipple.png http://drive.noobslab.com/data/themes/delorean-dark-3.10/stipple.png
sudo mv stipple.png /usr/share/software-center/ui/gtk3/art/

To revert back software center theme simply enter these commands:
cd /usr/share/software-center/ui/gtk3/css/ && sudo mv softwarecenter.css.backup softwarecenter.css
cd /usr/share/software-center/ui/gtk3/art/ && sudo mv stipple.png.backup stipple.png

That's it.


Is there any module to create different menus per user?

Question: I would like to have different menus per user.
How can I achieve this?
I searched on drupal.org, but I found a module that creates a menu per role, not per user.
Answer: Yes. You can try OM Maximenu. It is really flexible and this means you will need some time getting the configurations right but it's really good especially when it comes to controlling menus per role.
Answer: You can try preprocess_page function in template.php and create menus as per user retrieving menus from database.
Answer: If it's whole menus, you may trigger them with the context module. Define a condition which relates to the user, and specify an action to display the menu's block on the proper region.


How do you delete a book on iBooks

Question: My brother downloaded some books on my iBooks account and I want it permanently off my purchased and all books thing. I have iOS 8.1.2 so none of the answers in the previous question.
Answer: Touch on "select" button

Select the book and touch on "trash" button

Or you have a similar question to completely delete an iBook :
Is it possible to COMPLETELY delete a Book from my purchased books?

How do you delete a book on iBooks


How an experienced user decides a download is safe?

Question: I am new to computer security. I was wondering what an experienced information security user would do when inspecting a file for potential download. Obviously, it would be very difficult to look through all of the files that download and all of the source code (the package is open-source). How does one know what to download and what not to download?
Comment: I just think "who wants to live forever" and run it.
Comment: You may want to try asking a more theoretical question like what to look for and hot to evaluate untrusted software. Asking for a specific website is like asking for a product recommendation and it may not be valid at some date in the future.
Answer: Deep down you don't; from a security perspective I have more software running on my phone than I could effectively ever review in my lifetime. My desktop machine would be 100,000 worse than that.
So you have to trust where you get the software from, you can check to see if it has been tampered with. But that's still no guarantee (for example a few years ago a tiny tiny change to debian caused a massive reduction in entropy of encrypted communications, to the point where data could be guessed, or proftpd (maybe vsftpd I don't remember which) had a malicious commit from a contributor that got missed allowing root level access when a user logged in with a hard coded username and password).
Answer: When you are downloading software from some site on the Internet, you have to see on what criteria, if any, you can establish trust and then determine if the basis for establishing trust is valid.
First, consider if you trust the developer. Is the developer some anonymous person, or is it a company or person with a real name, real contact information, etc. It's less likely that someone is going to purposely create malicious software if they are leaving a trail back to him/herself; of course the website could be stealing someone's identity. Does the author have a reputation, provide sources, publish release notes, ever provide updates, admit when security issues were found in the past?
Next, you can look at the source of the download. Is it from the author/publisher's website, or is it a third party website (like download.com) a torrent, etc. A third party may modify the program or package it with spyware or other junk. Is the website secure, are there reasonable assurances of that the file has integrity relative to what the author compiled and/or uploaded?
On the individual file itself, author's often publish a md5/sha1 hash, which you can use to compare against the file you have downloaded to ensure its valid. This is less robust then usually advertised, because a site could be hacked. More reliable would be if the author cryptographically signed the executable or zip file, this provides reasonable assurance of integrity and authenticity. Unlike publishing the hash on some website, the data for authenticity is part of the file you are downloading.
If you want to be careful, you can always run the file in a sanbox or a virtual machine to isolate it from the rest of your system and data. This gives you the opportunity to use it for a while, see what types of network requests are being made, run anti-virus on it. After evaluating in isolation, you can load it into your main system if this provides some tangible advantage.
You can solicit reviews or advice from other uses or people on the Internet, but this often provides false assurance: unless they are security and software experts, they can only provide anecdotal feedback from their experience, limited by their abilities to perform such an assessment, I'm sure you know someone who operates a computer loaded with malware, but doesn't seem to get there is a problem or anything wrong.
Ultimately, you can never be sure, and new vulnerabilities may be found in the future. "Security" can often better be though of as a process of risk management. In general, you have to establish some level or trust and then determine what additional steps you can do to reduce the likelihood of attack/compromise in case your trust was improperly established or there were criteria you did not or were not technically skilled enough to consider.
Answer: Assume that the download is malicious every time. Make sure you have antivirus software to scan it for threats every time, and realize that there may be nothing you can do to stop a threat from compromising your browser. Understand that even reputable sources of software can be compromised, and that you do not necessarily have to click "download" to download. Be very careful what you download, and do try to use trusted suppliers of software, and media, but watch out for problems with them too. Keep your computer secure, so that even if it is compromised, you can recover quickly. Never put yourself in place where you might hesitate to wipe your machine and start over.
What's worse than getting a virus, is to know you have a virus and not be able to anything about it.
Comment: Rather than rely on just one antivirus program, after downloading a file I upload it to sites like [VirusTotal](https://www.virustotal.com), [Jotti's malware scan](http://virusscan.jotti.org/en), or [VirSCAN](http://virscan.org/), which offer free scans of files with multiple antivirus programs. Even then one can't be sure that a downloaded file doesn't contain relatively new malware that none of their antivirus programs can yet detect. And, if only one or two of their antivirus programs report a file as malware, you have to make your own determination as to whether those are false positives.
Comment: Exactly. I think virus total might be a little advanced for a non technical user, however.


Is it possible to connect a reed switch to two separate arduino boards?

Question: I'd like to add a bit of redundancy to a security system. I use reed switches for doors. How can i safely connect the same reed switch to two separate arduino boards? (the boards are not connected between them in any way, they use separate adapters).
Comment: That's not redundancy.
Comment: I'm using the arduino just to read various sensors. The data processing is done on a linux machine (i have two of these). I'd like to connect all the sensors to two boards, to have two identical sensor-reading systems. I dont mind not having duplicate sensors since i have plenty of various types of sensors in each location (motion, ir sensor, video, etc)
Answer:
... How can i safely connect the same reed switch to two separate Arduino boards?
  (the boards are not connected between them in any way, they use separate adapters).

If they are not electrically connected and if you wish to maintain the isolation you could use an optoisolator or similar. The reed switch could provide current via the LED in the opto isolator or voltage switched by the reed switch could apply voltage to a resistor connected to the LED. A reed could drive 2 x LEDs in two optoisolators this way this way if it had its own power supply or using the power supply from one Arduino.
Placing the LED from an optoisolator in series with the reed switch adds a reliability hazrad - if the LED fails then the input fails on both Arduinos. Placing a few diodes or a zener across the LED such that Vdiode_string is slightly higher than V_LED_on will protect against LED failure as long as there is enough drive voltage.
There are other isolating means available but an opt-oisolator is about as easy and cheap as any.
If you do not wish to maintain isolation then by connecting the two systems' grounds together you could share a sensor. But, isolated systems seem with having in the context. One mode of attacking a security system is to use a TASER or electric cattle prod or similar. This tends to be poorly tolerated [tm] in most cases. If you wish half your system to live long enough to report the other half's death when under TASER attack you will need to rate the cross coupling isolators accordingly. One method I've heard of is to use a dummy video camera which is presented as first line target. It's health is monitored by the system proper. It's role is to act as a honey-pot TASER-attack sensor. [I won't tell you what country I heard about this from :-) ].
Comment: Didn't think of the taser issue. The two systems will be checked by a third system that can also send out gsm / email notifications in case of failure. I have a couple of linux-based systems that check each other and can do a "vote" to restart an unresponsive system.
Comment: I'm now thinking of doing most of the sensors as a separate circuit (+5v - wire - reed - wire - led - -5v) and connect 2 light sensors, one for each arduino, and tie the led and the sensors in electrical tape or put them in a small box with no light. That way i can "read" the led easily, and in case of a taser-related event i will only have to replace the 5v power source and the reed switches + leds. the arduino's and the linux systems would be on a different electrical sources.


Reading Web.config Many times and performance

Question: If i am reading one of my application settings from the web.config everytime when each of my ASP.NET page loads,Would it be a performance issue ?I m concerned about memory too.
Answer: It's not great, but in the context of serving up a page, it's just a drop in the bucket. It's not nearly as bad as reading it over and over in a loop, hundreds of times per page view.  Lots of pages do things like look up previous visit info (user preferences, cookie tracking, etc..) which usually requires opening a database connection and running a query. So hitting the config file is small potatoes.
You also have to consider how often this really happens. A thousand times per hour? Don't waste your time.  A thousand per minute? Stil probably not a problem (a datbase query would probably be a different story though).  A thousand times per second, and then you've got reason to try to optomize this.
Answer: I don't think I'd worry about it. It is a very small file, and reading from it is very fast.
If it concerns you that much, read it into an Application variable, and reference that throughout the app instead.


How does electromagnetic radiation affect the velocity of a charged particle?

Question: I've heard that the acceleration of a charged particle releases electromagnetic waves. So let's say there is a charged electron moving forwards in a region with a downwards magnetic field. If the magnetic field is a certain strength, it should cause the particle to travel in a circular arc. This kind of motion is centripetal acceleration, and since the particle is accelerating and is charged, it should release radiation. Is this correct? And if so, how is the kinetic energy of the charged particle affected by this release of radiation?
Comment: @CuriousOne Ah I see, so circular accelerators must constantly apply an electric field to counteract this loss of kinetic energy?
Comment: This is correct. The particle will radiate and has to lose kinetic energy. As a result the radius of its circular motion will decrease. This is one of the limiting factors for circular accelerators and storage rings.
Comment: Absolutely. Machines like the LHC are basically very large storage rings. Even after the particles have been accumulated and accelerated, one still needs to run the RF cavities, the active parts of the accelerator, to compensate for the beam losses due to these synchrotron radiation losses. The losses in the LHC are not that bad, on the order of 0.2W/m, I believe, but electron storage rings like the LHCs predecessor LEP can have losses in the kW/m range, which is a lot of x-ray radiation. Search for "lep synchrotron spectrum" and you can find lots of good stuff about it.
Comment: @CuriousOne Wow, fascinating, thanks for the info!
Answer:
since the particle is accelerating and is charged, it should release radiation. Is this correct?

This is the way experiments with radiation are often explained - radiation comes from places where acceleration of charge occurs.
Also, orbital motion of charged particles in a cyclotron was found to be always accompanied with EM radiation coming off apparently from the ring where the electrons are in circular motion.
Theoretically, this is based on a particular version of EM theory where the fields are purely retarded. This version is most common and intuitive and I suppose it is not a great mistake to say it is correct, but it does not follow that is what actually happens.
There are several possibly correct explanations - other views of the experiments, like those of Tetrode, Fokker, Frenkel, Feynman-Wheeler etc. where the radiation present/detected is not just the retarded (in particle originating) field of the charged particles. For example, the half-retarded, half-advanced field has two important parts - the retarded half compatible with the above view originates in the particle and spreads away to infinity, but the other one, advanced, comes from the infinity and collapses on the particle. This view is not usual, but it was considered seriously by the above people and it was never falsified.

And if so, how is the kinetic energy of the charged particle affected by this release of radiation?

That depends on whether the charge distribution is extended with finite density or point-like.
If the charge has finite spatial density everywhere, then the Poynting theorem can be derived. Further, if the fields are retarded, the Larmor formula can be derived which says the energy that comes off the particle per unit time is proportional to acceleration squared. If the particle has stable inner structure, per energy conservation this approximately equals to the loss of kinetic energy per unit time as well (there is always discrepancy due to EM energy in the vicinity of the particle) and so the particle loses kinetic energy until its motion changes into rectilinear motion or the particle stops moving.
On the other hand, if the particle is truly a point, the Poynting theorem cannot be derived and the Larmor formula cannot be derived. Furthermore, they cannot be consistently applied, even if we took them verbatim from the above case.
If the fields are retarded, such particle produces outgoing changes in the EM field, but these do not necessarily need to have any effect on the motion of the particle.
The cyclotron/synchrotron radiation definitely carries and is capable to release a lot of energy. This means that for these explanations to be applicable, either the particles themselves are extended charges or they are pointlike but then radiation comes off many of them synchronously, so they effectively form extended distribution in the physical sense.
Since the charges in cyclotrons are accelerated in so-called bunches (billions of electrons) and since no inner structure of electron was ever found, I think the second explanation is more likely - the beams of energy stream come off many particles close to each other rather than from one particle.
Answer: It will decelerate causing its speed to decrease, and because of $r=mv/qB$ the radius will decrease as well and you will get a spiral motion.
This deceleration due to radiation is known as the Abraham-Lorentz force of radiation backreation. Using these equations you can more precisely derive the spiral motion. This effect is also responsible for the failure of the classical picture of the atom, because of the collapse, which is saved by the uncertainty principle.


Question regarding when it's a homoplasy in a phylogenetic tree

Question: If you have 2 organisms that both come directly from the same common ancestor on a phylogenetic tree, and that common ancestor does not have trait "x", is it possible for both of its direct descendants to develop that trait "x" independently, and would that be an example of a homoplasy?
Comment: Can you draw what you are describing?
Answer: Phylogenetic tree vs first generation offspring
Please note that on a phylogenetic tree, the time scale is big enough so that the generation time is completely undistinguishable. Hence, questions of first generation offspring won't rise. Also, in practice when reconstructing a phylogenetic tree, our level of accuracy does not allow us to distinguish exactly at what generation did specific mutation occur.
Rephrasing your question
The term homoplasy is typically used in the context of phylogenetics. Also, most of the time the term homoplasy refer to phenotypic trait and not to genetic sequence but I will not go into these specific complications here. The term is also mainly used in intro textbook and not so much in the peer-reviewed literature. In all cases, one can define the concept of homoplasy as a shared trait that is caused by a mutation that is not identical by descent. In other words, if in two lineages/individuals that share the same trait, the trait is caused by the same mutation(s) (same, not only by its state but by descent), then the shared trait does not represent a homoplasy.
With this, I can rephrase your question as

If two siblings share a (heritable) trait that the direct parent does not have, are the traits identical by descent?

If two siblings share a (heritable) trait that the direct parent does not have, are the traits identical by descent?
Well.. it depends as to whether the mutations happened happened twice independently in the two different gametes or if the mutation happened once in the (germ line) lineage that gave rise to these gametes in the parent body.
The second is much more likely. Because, it is very unlikely for the same mutation to happen twice independently in two different gametes for the same individual and much more likely that the mutation happened once in a cell that gave rise to the two gametes, it is very much more likely that the shared trait among the two offsprings is caused by a mutation that is identical by descent. Hence, not a homoplasy.
Comment: *editted* I think I did a poor job of explaining my question and for that I apologize, let me rephrase it. I am trying to take a tree that is in a state of synapomorphy and turn it into a tree that is not. So can I create the condition of a homoplasy simply by moving the introduction of a trait to the branches that come off after the common ancestor instead of before the common ancestor?
Comment: did you see my most recent comment?
Comment: I did but did not quite understand it so I ignored it. If you could maybe make a drawing in the post, that might help.


When should you force automatic updates?

Question: Here's an interesting question - when should you force automatic updates? I was thinking about application updates recently, how software like Google Chrome forces automatic updates, how Microsoft uses automatic updates but doesn't force them if you don't really want them, and how some leave it up to the user entirely.
One one hand, forcing automatic updates can be good, for reasons of:

Security
Stability
Breaking changes happen for everyone at once
No need to service older releases
Everyone's got the latest and greatest all the time
"I don't want to upgrade because I don't think I need to" whereas the user's judgement may be flawed in this case

Imagine if IE had forced automatic updates - the number of users who had hacked away in order to use IE6 would be so tiny we wouldn't have had any of the problems we did because of it (and still do and will for a small while longer).
On the other hand, forcing automatic updates can be bad:

Might break things
Some users feel it invades their privacy
Using system resources the user might not have/want to use at the time
"User knows best" (or do they?)

Do you think forced automatic updates are good or bad always? Or does it depend on the situation (I think we can all agree they are never ALWAYS good, but are they ALWAYS bad)? In what situations do you think they should be used?
CW'ed since I think this is fairly subjective.
Answer: Minor revisions and security update are fine to force.  So long as the gui and general proformance of the program doesnt change.  By force I mean tell the user "Updates are ready" or something like that. Or "application will update next startup"
Major version changes that include gui changes and proformance changes should always be the end users choice.  Although strongly suggesting updates may be ok depending on the application.
the are exceptions to this ofcourse.  Games usually get updated to the latest version for online play.  Web browsers should always be the the latest version and only really let the user choose fora major update.  If that was more enforced the internet would be a better place.
Adobe I admit is a bit obnoxious but its just a bit better to get it over with.  Or you can just block the applications from accessing the internet then they stop complaining.
Its also nice when updating doesnt get in the way of using it.  Like it update while your using it but those updates only take effect when you restart the application.  Something like that.  Firefox is a good bad example.  I hate starting it up only to learn this add on needs to be updated, I can understand it from a security view but I just find it irritating.
A setting somewhere is probably the best way to go.  Let the user choose to let the application automaticly update or ask them before updating.
Comment: I wish they just auto-updated if they're going to force update.
Comment: I think your last sentence sums that up pretty well. +1
Answer: Never unless all the users of the application work for your own company and you have some authority over which version of the software they need to be using.
On the other hand, asking me 3 times a week to update the app is also obnoxious, DO YOU HEAR ME ADOBE????
Comment: I wouldn't mind if adobe Flash updated itself automatically so long as I don't have to see it everytime I start my PC
Comment: @Graphain - Not to mention forcing a reboot!
Answer: I think Google's philosophy is that they see Chrome as no different to, say, GMail. In GMail, everybody gets the "updates" as soon as they're uploaded to the server. There's no possibility for you to use older versions. So they automatically update Chrome so that the experience is similar to that.
It requires a lot of care on Google's part. I'm also pretty sure that forced automatic updates would not fly with many larger corporations who need to administer 10s of thousands of desktops (just imagine the additional bandwidth it would require for 10,000 people to all updated their copy of Chrome at the same time: 17MB* x 10,000 = 170GB of data!)
In some ways, I wish Windows had a standard central repository of software like the various Linux distros have. I can imagine the legal headaches that would cause for Microsoft, though, and can understand why one doesn't exist...

* According to this.
Answer: Another perspective to take is that many many apps are moving to the cloud as web based apps. In this case everyone gets updates at the same time. Obviously, there is a difference between web apps and native apps, but in some ways the differentiation is arbitrary. So I think the notion that auto updates are bad always is stuck in the "installed app" paradigm that is fading away.
Comment: That's a good point - I wonder if everything will be online in the future? (not any time soon of course!)


randomly generating selectively keys in a hashmap

Question:
Possible Duplicate:
Is there a way to get the value of a HashMap randomly in Java?

I want to generate random keys and show their associated values in a Hashmap but not all the keys. For example if there are 40 key value pairs I just want 10 to be randomly displayed.
Answer: <code>List keys = new ArrayList(theHashMap.keySet());
Collections.shuffle(keys);
for (int i = 0; i < Math.min(keys.size(), 10); ++i) {
  map.get(keys[i]);
}
</code>


unable to upload doc files in android latest version

Question: I am not able to upload  .doc files on my android mobile.I have Kingston software installed so whenever I use the upload button from the webpage it just displays my gallery, camera, voice and video recorder. It does not display the file browser so that I can select the file from my file system.
Comment: Please consider that we don't all have exactly the same software as you, so we don't necessarily know what this "Kingston software" is you mention, nor what webpage you're talking about. To get better answers, [edit] your question to describe the problem more fully, and include your phone and Android version.
Comment: This is a genuine question. I just did a factory reset on my Android 4.2.2 and there is no Kingston software. But when I try to attach a file in Gmail, I am not given an option to choose a file from the filesystem. Even trying to attach a file from Google Drive doesnt work
Answer: I don't know the software you're using but I'd recommend looking into Airdroid, it installs a small application on your phone and lets you manage it from a web interface. After starting the service you can copy all data in both directions.
Comment: And how does that help uploading files to a website? Airdroid is to remotely manage your Android device, which is a completely different task.
Comment: "Kingston" is similar to MS Office where you can edit/modify doc, xl, pdf and view presentations. I have read similar issues I am hearing about EStrong File Explorer and androZip. Are they helpful software ? can resolve my issue ??.
Comment: that might be right Izzy and is now clear when I know that Kingston seems to be some kind of office suite.
@RizwanSA So what "webpage" are you trying to upload your files to?
Answer: By installing androZip my problem is getting resolved :)


How to create a user after ldap authenticaion?

Question: I am using ldap for Drupal 7.  After successfully authenticating, how do I create a Drupal user.
Comment: People -> add? Or what exactly are you trying to ask?
Answer: The LDAP module will also allow you to automatically create a user after authentication.

Once you configure your server, look at the third tab LDAP
authorization Choose edit to configure that server
Under basic, enable and Only apply the following LDAP to drupal role
configuration to users authenticated via LDAP.
You can set the role of the new user by checking  drupal roles are
specified by LDAP attributes under IIB. Also name the field that will
be use to determine role
Configure part III. LDAP to drupal role mapping and filtering For
example, if the title field is Staff you may want to give a staff
role Staff|staff
Part 4    IV.B. When should drupal roles be granted/revoked from
user? Check "When a user logs on"
IV.C. What actions would you like performed when drupal roles are
granted/revoked from user? Check Revoke drupal roles previously
granted by LDAP Authorization but no longer valid.

There are other settings that you can configure but this should get you started.
Answer: the Ldap and Simple LDAP modules both can create Drupal user accounts for you after authentication. Read the project documentation and readme files.
For example from the Simple Ldap project page:

Simple LDAP User
This module allows authentication to the LDAP directory configured in
  the Simple LDAP module. It also provides synchronization services both
  to and from LDAP and Drupal. It supports mapping LDAP attributes to
  Drupal user object fields (both native, and using Field API).


proving :$\frac{ab}{a^2+3b^2}+\frac{cb}{b^2+3c^2}+\frac{ac}{c^2+3a^2}\le\frac{3}{4}$.

Question: Let $a,b,c>0$ how to prove that :
$$\frac{ab}{a^2+3b^2}+\frac{cb}{b^2+3c^2}+\frac{ac}{c^2+3a^2}\le\frac{3}{4}$$
I find that
$$\ \frac{ab}{a^{2}+3b^{2}}=\frac{1}{\frac{a^{2}+3b^{2}}{ab}}=\frac{1}{\frac{a}{b}+\frac{3b}{a}} $$
By AM-GM
$$\ \frac{ab}{a^{2}+3b^{2}} \leq \frac{1}{2 \sqrt{3}}=\frac{\sqrt{3}}{6} $$
$$\ \sum_{cyc} \frac{ab}{a^{2}+3b^{2}} \leq \frac{\sqrt{3}}{2} $$
But this is obviously is not working .
Comment: No suggestions?
Answer:
(2018-01-01) Ahhh, so sweet, silent revenge donwvotes... Happy New Year!

Using the change of variables $x_1=a/b$, $x_2=b/c$, $x_3=c/a$, one asks for the maximum of $T$ under the constraint $S=0$, on the domain $D$ defined by $x_1\gt0$, $x_2\gt0$, $x_3\gt0$, where
$$
T=\sum\limits_{k=1}^3R(x_k),\qquad R(x)=x/(3+x^2),\qquad S=x_1x_2x_3-1.
$$
The extrema in $D$ are located at points such that the gradients of $T$ and $S$ are colinear. For every $k$, $\partial_kT=R'(x_k)$ with $R'(x)=(3-x^2)/(3+x^2)^2$ and $\partial_kS=(x_1x_2x_3)/x_k=1/x_k$, hence the condition is that $U(x_k)=x_kR'(x_k)$ does not depend on $k$.
The function $x\mapsto U(x)$ is smooth on $x\geqslant0$, increasing-then-decreasing and nonnegative on $0\leqslant x\leqslant\sqrt3$, and decreasing and negative on $x\gt\sqrt3$. Assume that $U(x_1)=U(x_2)=U(x_3)$ and call $v$ their common value. If $v\lt0$, the equation $U(x)=v$ has only one solution $x_v\gt1$ hence $x_1=x_2=x_3=x_v$ and $S\ne0$, which is absurd. If $v\gt0$, the equation $U(x)=v$ has at most two solutions in $(0,\sqrt3)$ hence either $x_1=x_2=x_3$, then their common value is $1$, or the $x_k$ are not all equal, then two of them are equal to some $x$ and the third one to $1/x^2$ and $U(x)=U(1/x^2)$. This last condition reads $W(x)=0$ with
$$
W(x)=(3-x^2)(1+3x^4)^2-x(3x^4-1)(x^2+3)^2,
$$
which has no solution $x\geqslant0$ except $x=1$. Finally, the gradients of $T$ and $S$ are colinear at the point $(1,1,1)$ and only there hence the only extremum on $D$ is $T(1,1,1)=3/4$, which is a local maximum since, for example, $T(x,1/x,1)\to1/4\lt3/4$ when $x\to0^+$.
To see what happens on the boundary of $D$, introduce the interval $K=[1/2,6]$. Then $R(x)\leqslant2/13$ for every $x$ not in $K$ and $R(x)\leqslant1/(2\sqrt3)$ for every $x\gt0$. Hence, as soon as one coordinate $x_k$ is not in $K$, $T\leqslant2/13+2\cdot1/(2\sqrt3)=0.731$. Since $0.731\lt3/4$, this proves that the supremum of $T$ is reached in $K\times K\times K$, and finally that this supremum is the maximum $T(1,1,1)=3/4$.
Caveat: The assertions above about the variations of the function $U$ and the roots of the polynomial $W$ were checked by inspecting W|A-drawn (parts of the) graphs of these two functions. To complete the proof, one should show them rigorously.
Answer: I have a Cauchy-Schwarz proof of it,hope you enjoy.:D
first,mutiply $2$ to each side,your inequality can be rewrite into
$$ \sum_{cyc}{\frac{2ab}{a^2+3b^2}}\leq \frac{3}{2}$$
Or
$$ \sum_{cyc}{\frac{(a-b)^2+2b^2}{a^2+3b^2}}\geq \frac{3}{2}$$
Now,Using Cauchy-Schwarz inequality,we have
$$ \sum_{cyc}{\frac{(a-b)^2+2b^2}{a^2+3b^2}}\geq \frac{\left(\sum_{cyc}{\sqrt{(a-b)^2+2b^2}}\right)^2}{4(a^2+b^2+c^2)}$$
Therefore,it's suffice to prove
$$\left(\sum_{cyc}{\sqrt{(a-b)^2+2b^2}}\right)^2\geq 6(a^2+b^2+c^2) $$
after simply expand,it's equal to
$$ \sum_{cyc}{\sqrt{[(a-b)^2+2b^2][(b-c)^2+2c^2]}}\geq a^2+b^2+c^2+ab+bc+ca $$
Now,Using Cauchy-Schwarz again,we notice that
$$ \sqrt{[(a-b)^2+2b^2][(b-c)^2+2c^2]}\geq (b-a)(b-c)+2bc=b^2+ac+bc-ab$$
sum them up,the result follows.
Hence we are done!
Equality occurs when $a=b=c$
Comment: How do you get the second inequality?
Answer: I have answered this question in a slightly different way.
Let us assume the following : $ \frac{a}{b}=x$ and $ \frac{b}{c}=y.$ This converts the above equation to a equation
with two variables. $$ f(x,y)=\frac{x}{3+x^2} + \frac{y}{3+y^2}+\frac{xy}{1+3(xy)^2}$$ Now to get a maxima or minima point of $f(x,y)$ we partially differentiate it with $x$ and $y$ and equate them to $0$. Hence we have $$ \frac{\partial f(x,y)}{\partial x}= \frac{3-x^2}{(x^2+3)^2}+\frac{y(1-3x^2y^2)}{(3x^2y^2+1)^2}=0 $$ $$\Rightarrow \frac{3-x^2}{y(x^2+3)^2}=\frac{(3x^2y^2-1)}{(3x^2y^2+1)^2}...........Eqn(1)$$ Since $f(x,y)$ is symmetric with $x$ and $y$ ,we also have for $\frac{\partial f(x,y)}{\partial y}=0$ $$\frac{3-y^2}{x(y^2+3)^2}=\frac{(3x^2y^2-1)}{(3x^2y^2+1)^2}...........Eqn(2)$$ Combining equation 1 and 2 we get $$x \cdot\frac{3-x^2}{(x^2+3)^2}=y \cdot\frac {3-y^2}{(y^2+3)^2}$$ This immediately shows that $x=y $ is a critical point (maxima or minima). Now this clearly shows that at the critical point $$x=y$$ $$\Rightarrow ac=b^2.........Eqn (3)$$ In a similar fashion assuming $\frac{b}{c}=x$ and $\frac{c}{a}=y$ we again the same set of equation $$ f(x,y)=\frac{x}{3+x^2} + \frac{y}{3+y^2}+ \frac{xy}{1+3(xy)^2}$$ Following the same steps we get $$x=y$$ $$\Rightarrow ab=c^2...........Eqn(4)$$ Equation 3 and 4 show that $$a=b=c$$ at the critical point. Hence $a=b=c$ gives us that $$\frac{ab}{a^2+3b^2}+\frac{cb}{b^2+3c^2}+\frac{ac}{c^2+3a^2}=\frac{3}{4}$$ is a maxima or a minima. To check maxima we double differentiate and check $\frac{\partial^2f}{\partial x^2}$ and $\frac{\partial^2f}{\partial y^2}$ We get the following : $$\frac{\partial^2f}{\partial x^2}=\frac{\partial^2f}{\partial y^2}=\frac{2x^3-18x}{(3+x^2)2}+\frac{18x^4-18x^8}{(1+3x^4)^2}=-\frac{16}{64} $$ at $ x=y=1$. Both being negative we see that the function $f$ has a maxima at $a=b=c$ which is $\frac{3}{4}$ Hence $$\frac{ab}{a^2+3b^2}+\frac{cb}{b^2+3c^2}+\frac{ac}{c^2+3a^2} \le \frac{3}{4}$$
Answer: By AM-Gm $$\sum_{cyc}\frac{ab}{a^2+3b^2}=\sum_{cyc}\frac{ab}{a^2+b^2+2b^2}\leq\sum_{cyc}\frac{ab}{2\sqrt{2b^2(a^2+b^2)}}=\frac{1}{2\sqrt2}\sum_{cyc}\sqrt{\frac{a^2}{a^2+b^2}}.$$
Thus, it remains to prove that $\sum\limits_{cyc}\sqrt{\frac{x}{x+y}}\leq\frac{3}{\sqrt2}$, which followos from C-S.
Indeed, $$\left(\sum\limits_{cyc}\sqrt{\frac{x}{x+y}}\right)^2\leq\sum_{cyc}\frac{x}{(x+y)(x+z)}\sum_{cyc}(x+z)=\frac{4(xy+xz+yz)(x+y+z)}{\prod\limits_{cyc}(x+y)}\leq\frac{9}{2},$$
where the last inequality it's just $\sum\limits_{cyc}z(x-y)^2\geq0$.
Done!
Comment: +1. Again, great proof! Is there a nicer way to see the very last inequality than expanding out all the terms by brute force?
Comment: @Hans Thank you! For the proof of last inequality we can use also uvw.
Answer: From the question it is obvious that equality is achieved when $a=b=c$, this hints at the use of AM-GM. Firstly, use the fact that $ab \le \frac{1}{2} (a^2+b^2)$, we just need to show
$$ \frac{a^2+b^2}{a^2+3b^2} + \frac{b^2+c^2}{b^2+3c^2} + \frac{c^2+a^2}{c^2+3a^2} \le \frac{3}{2},$$ which is equivalent to (after removing a constant 1 from each term in LHS)
$$ \frac{b^2}{a^2+3b^2} + \frac{c^2}{b^2+3c^2} + \frac{a^2}{c^2+3a^2} \ge \frac{3}{4},$$
by AM-GM, $a^2 + 3b^2 \ge 4 \sqrt[4]{a^2b^6} = 4\sqrt{ab^3}$, hence we just need
$$ \frac{\sqrt{b}}{\sqrt{a}} + \frac{\sqrt{c}}{\sqrt{b}} + \frac{\sqrt{a}}{\sqrt{c}} \ge 3, $$ but this is obviously true by one more application of AM-GM.


Ethernet-Connection ubuntu with VMware Player

Question: I installed VMware Player 7.1.2 on my Windows 7. On my VM I installed ubuntu 14.04. Now I have problems connecting to internet. With my computer I am connected with ethernet. Ubuntu can connect with it but I am not able to connect to internet. Which settings do I have to change. There are a lot of settings (VMware Player Network Adapter, IPv4 Settings and and and...) and I am not a pro ;-)
Answer: Without further data, the easiest fix is to go into the VM's settings directly, select the virtual network adapter, and edit it so that it is using NAT.
This will let it communicate outbound via the host computer's connections which are already active.  (This is also the least headachey to set up)
Comment: I tried it with NAT, Bridged, Host-only and Custom. I am not sure, if ubuntus connections settings are all right. Maybe the IPv4 Settings should not be Automatic (DHCP). But I have no clou, which addresses I could type in. I tried several ones.
Comment: Then the issue is a VMware one, and not an Ubuntu one, you should go to Super User and ask for help diagnosing VMware Virtual networking on a Windows 7 Host.  VMware Player works Out Of The Box typically, if it's not, it's not an Ubuntu problem, and a bigger one outside the scope of this site.


Does the corruption ability of Corrupters stack?

Question: Does the corruption ability of Corrupters stack?  In other words, if I corrupt a battlecruiser once, it takes an extra 20% damage.  If i corrupt it again,does it then take 20% more damage?  I can't seem to find a reference anywhere for this.  In brood war, it was obvious that devourer's spores did stack, because the unit portrait for the victim unit would tell you how many spores were on it.
Answer: I've tried, and sadly, it does not stack.
Comment: I can't think of any ability effect in Starcraft II that stacks.
Comment: agreed.  I did some testing myself and when a unit is corrupted, it does get a little icon on it's portrait.
Comment: @carl the only thing that comes to mind is the VR charge level.


How to repeat a command immediately after calling it?

Question: I've just called an interactive function (i.e., a command).  I want to call it again, with the same arguments.  I know that I can call a keyboard macro again by using e right after running it the first time.  Is there something similar regarding interactive functions?
Comment: This must be a duplicate. This has been asked and answered before, I'm pretty sure...
Answer: You are looking for repeat, bound by default to C-x z.  The
first part of the docstring:

(repeat REPEAT-ARG)
Repeat most recently executed command.
  If REPEAT-ARG is non-nil (interactively, with a prefix argument),
  supply a prefix argument to that command.  Otherwise, give the
  command the same prefix argument it was given before, if any.

If you use evil, you also have access to the beloved dot command
from Vim.
Comment: Nice! Too bad that it repeats **any** command - just repeated `next-line`...
Comment: Will the site keep both answers?  Someone doing a search and finding this question might actually be looking for either.  They are both useful in their own way.
Comment: @MAP: yes, all answers will remain on the site, so it won't be a problem to move the acceptance to the other answer.
Answer: There is also repeat-complex-command (normally bound to C-x ESC ESC as well as several others (that's the one I use, so I remember that)).  This will go back further in the history to the last command that required interaction (i.e. prompted for input).
Comment: @MatthewRock : if this one is closer to the solution you had in mind, feel free to unaccept the answer I posted and accept this one instead.
Comment: That's a great addition! This command is exactly what I was lacking in the previous answer. Wish I could accept both.


IPFS for media files

Question: I'm trying to build an nftmarketplace that takes in an audio file, can I use IPFS for storing my URi, was wondering if the file would be too large as all the tutorials I've worked with mainly used Images
Answer: you definitely can use ipfs. there is no limitations on type of file.
you should decide on that case that you want to involve backend into your system or not. is that centralized or decentralized?
if everything must be handled on frontend side, the uploading process on ipfs takes much more time for large media and do it sync on browser tab of user. you can use some platform such as pinata , nft.storage, moralis sdk, ... and other similar platforms instead of fully boot up an IPFS server or maintaining this particular server. (search for pin feature in ipfs)
if you decide to handle some parts on backend, it will be handled all above operation on backend and also async. it means the user will upload the file on backend and then backend take care of uploading the file to ipfs.
another usages of backend is that we have a problem to getting the file from ipfs is that it take more time rather than retrieving data from CDN like Aws S3.
you actually store the file on multiple places.
plz vote it up if it is useful :)
Comment: This was very helpful, thank you unfortunately I cant upvote yet
Answer: IPFS is not good for large files. I did some research and found that supducks was a few MB and that was the biggest I saw among many projects. Even 10mb could be considered a large file. I have not checked Arweave but want to.
Comment: Hey, thaank you that was incredibly helpful, was wondering if I could dm you as I shave some questions
Comment: Please upvote and feel free to DM.

IPFS for media files


Is window based sequencing a good idea to obtain more training data for LSTMs?

Question: I am trying to do an unsupervised autoencoder based outlier detection for time series using LSTMs. Here, there are multiple time series, and an entire series is to be considered as an outlier.
However, I only have around 25-30 time series instances to work on (though each series comprises ~10k points).
I wanted to know whether creating sliding windows for each time series to generate more data is an okay idea for training the autoencoder more accurately. Also, in that case, how does one merge the results to selectively identify which of the original 25-30 time series is an outlier?
I am relatively new at working with LSTMs and would really appreciate suggestions on whether this idea is feasible.
Comment: In my opinion, this question can only be answered with domain knowledge or by experimental testing and does not depend on the fact that you are using LSTM's, but on the nature of the data itself.
Comment: Agreed with ncasas. I think your idea highly depends on how much time points you actually need to see that an outlier is actually an outlier, your windows should be greater than that. In principle your approach seems good enough to at least give it a try
Comment: You pretty much have to split the time series for an LSTM, certainly, a 10k long sequence probably isn't going to perform well. I suspect the problem you have is if as I understand it you only have 1 label per sequence (i.e. the sequence either contains an anomaly or it doesn't). If this is the case - is the anomaly present for the entire time, or only for a period of time. If the entire series is anomalous splitting it and assigning the same label to each split may work. If the anomaly comes and goes then you may struggle
Comment: My current problem is that I have a lot of parameters to tune -  window size, stride for the sequencing, and then the actual LSTM architecture itself - like the activations, epochs etc. And then I have to figure out how to combine the results of each individual splits into the combined time series. Because if I just consider that one of the time splits is anomalous, the entire series is anomalous, and so I am getting a lot of series as anomalous (when the data actually has just 1-3). And it's a bit overwhelming because I don't know how to check where I can improve the model.
Answer: Splitting a time-series into analysis windows, usually with overlap, is quite common practice. In anomaly detection, but also in classification or forecasting. It works great as long as your anomalies can be detected by analyzing such windows independently.
In such a setup, the length of the analysis window becomes a critical hyper-parameter - and will be data/task-dependent.
To get an overall anomaly score you can use any standard statistics to merge scores for individual windows. A simple mean would be the first thing to try, but there are more approaches.


LNK1124 error debugger cannot find .exe file

Question: image of error
I'm having an error with visual studio every time I'm trying to use cin to get the guess of the user without that it works fine.
code
console message with error
Comment: If you think this can help other users then please post the question in a proper manner and then post answer on your own.
Comment: thank you for telling me i'm new here
Comment: I strongly recommend reading [ask] and reworking the question to meet the site rules. Do not use images where text will do. For one thing, I can't compile and test a png file and doubt few others can.
Answer: this happening to me since I install visual studio 2017 just a couple of days ago.
I'm trying to learn c++ for unreal engine just started learning and i came across
that error anyone who have this error maybe this can be helpful for them.
first, let me tell you wah t the problem was i was trying to run a 32bit debugger on my 64bit pc cause visual studio install it that way so if you are getting this error on any of your projects all you have to do is change the project to an x64 bit project.
go to the Top bar  "Build"
then go to "Configuration manager"
in there change it to x64 bit instead of 32bit
hopefully this can help someone
the link to the page that i read to fix is here.
after all the changes code runs well and no error anymore.
Comment: Glad to know that this issue has been resolved, if so, please mark your solution as the answer, so it could help other community members who get the same issue as yours. Have a nice day:)


How do Junction Objects - Many To Many Relationships - work?

Question: I have read about many-to-many relationship in Salesforce and it is possible through Junction Object. That I got, but what I haven't got is that "How it works internally ?" Please help me to visualize the concept of Junction Object.
Comment: Accept the answer which provided the required information you needed so that other people with same question get benefit from it.
Answer: To create Many-to-Many relationship you need Junction object(as you mentioned in your question).
Lets take Opportunity and Product for example to explain this.
If you want Opportunity A should have Product A and Product B, and Product A should be available in Opportunity A and Opportunity B you should have a Junction object to hold the relationship.
So OpportunityLineItem is the Junction object which will hold multiple records in combination of Opportunity and Product like below
OppotunityLineItem1 - Opportunity A, Product A
OppotunityLineItem2 - Opportunity A, Product B
OppotunityLineItem2 - Opportunity B, Product A
Opportunity A have Product A and Product B and Product A is available in Opportunity A and Opportunity B.
Hope it helps.
Comment: Still i'm not clear :(
Comment: This is A good Example...you should let it sink in your mind..inside the Junction Object you have 2 Lookups (Can be as MasterDetail). One is pointing at Product and the Other is Pointing to Opportunity. This Relation between the 2 Objects has Attributes Fields Such as Quantity Sold and Date for example are relevant only to the Opportunity Line Items... Then you can aggregate the results of total Quantity to Opportunity Level..
Comment: So you are telling like if `Junction Object` will contain only those fields which are in relationship with both objects. Like result of `Cross Product` of two tables.
Comment: It will have master detail relation to both objects. It can additionally have fields specific to it.
Comment: @YuvalV / Vigneshwaran : Can you tell me what is `OppotunityLineItem1` here? Is it field/column or record/data? Actually i'm trying to understand how the relations of two objects are stored in `Junction Object`.
Comment: OppotunityLineItem1 itself a junction object which establish many to many relation ship with opporuntity and product.
Comment: Thank you everyone. I got something from every comments and answers and it helped me a lot to get it.  Thank you again
Answer: Salesforce supports 2 kinds of relationships like Master Detail and Lookup. They are both one-to-many relationship, and they are both  defined from the many-to-one side, that is from a child to a parent. They can be made one-to-one relationship by adding validation rules, or maybe triggers to enforce the one-to-one nature, i.e. only one child is allowed.
Junction objects are used to create many to many relationships between objects. If you take the Recruiting application example, you can see that a Position can be linked to many Candidates, and a Candidate can apply for different Positions. To create this data model you need a third object "Job Application" that links the 2.
So you'd create a lookup field for both Position and Candidate object on the "Job Application" object. This will establish many to many relationship between Position and Candidate via the "Job Application" object known as the junction object.
Fore more information, read this article https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/langCon_apex_SOQL.htm
Answer: It may be worth creating a Developer Org if you haven't already and checking out the Force.com Platform Fundamentals guide which will take you through creating a recruitment application for a pseudo-company and covers this type of question. It's also a great introduction into earning the DEV-401 qualification!
Let's go with this example. Picture having your Candidates object for potential employees and your Positions object for jobs. You can't relate these directly because one candidate could apply to many positions and positions should have many candidates. This is where a junction object comes in. In this example, you'd have another object called Applications. A candidate can create many applications and many applications can be linked to a position.
There are two fields to achieve this: the Lookup and Master-Detail fields. Check out this YouTube video for a more in-depth explanation, but effectively:
Master Detail:

You cannot have a detail record without a master.
The detail record inherits sharing rules from the master.
You cannot update the relationship to the master in a master-detail relationship.
The number of master-detail relationships you can use are limited.
You cannot set profile object permissions for a detail record.
Master-detail relationships are automatically included in report
record types.

Lookup

Lookups are generally for use where you may or may not need to have a relationship between two objects.
Lookups are generally used to reference commonly shared data, such as reference data.
Lookups are used to link two objects together when you don't want the behaviour of the master-detail - particularly around sharing rules, profile permissions and cascade delete.
Lookups are used when you need to relate multiple 'parents' to the detail record.

Hope this explains things for you!
Thanks.
Answer: Ultimately, the best way to understand how these relationships work, is to try to create one in your Sandbox. This Salesforce Documentation is the only guide you need to follow.
But this may be easier to understand if you consider how these relationships appear from a user's point of view.
The user doesn't need to know that the Junction records exist. The only difference is that rather than a lookup field appearing in the detail section of a page layout, the other object's record is looked up in the related records section, after clicking the New Junction Object Name button on the related record list.
The below show's a Junction object, linking Projects to Opportunities.

Once the relationship's been created, you can choose to display the fields of the record that's been looked up, in either object's related records list, rather than the fields from the Junction object itself.

So for all intents & purposes, the looked up record appears to be the record that's related to the record which is being viewed (a Project, in this example).
The end result is that the related record's name is displayed as one of the related record's fields, which can be clicked to access that record directly.


Is the value of a frequency bin of a DFT-output the average of the 'real' frequency values within that bin's range?

Question: I am wondering whether the value of a frequency bin with a certain resolution is the average of the fourier transform values of the 'real' frequencies within that bin's range.
Answer: I'll start with a counter-example:
Assume your continuous-time signal is a sinusoid at freqeuncy $f_0$. You then sample that signal, and use a rectangular window to select $N$ samples. Feed those $N$ samples to your DFT, and you will see non-zero values in the whole spectrum (unless in the special cases where $f_0$ is a multiple of $f_s/N$).
So you start with a signal whose energy is concentrated in a single frequency, and you end up with non-zero values in all DFT bins.
To understand what is happening:

Start with a continuous-time signal $x_c(t)$.
(Optionally) filter the signal to make it band-limited to $f_s/2$.
Sample the signal to get $x[n] = x_c(n/f_s)$.
At this point, the spectrum is given by the sampling theorem. You will have spectrum aliasing if the sampled signal was not band-limited in step 2.
Now apply a window of size M. The window type depends on your application (Rectangular (ugly), Hann, Hamming, Blackman, Flat top, etc.).
At this point, your spectrum is that of the sampled signal, but convolved with the window (depending on window size and type, you will get some energy spread to other frequencies). This spectrum is $X_w(e^{j\theta})$.
The DFT of the windowed signal will return samples of its spectrum, at frequencies $Y[k] = X_w( e^{j 2\pi k/N})$.
Comment: Thanks for your answer.
 To clarify:
Assume I have a 'perfect' sinusoid with frequency f0 and I sample the signal with a frequency that is high enough fullfilling Nyquist. However I only put N samples into the DFT resulting in a resolution of $f_S/N$. Then assuming a frequency bin happens to be centered around f0. Is this bins's value the average over the 'real' frequency values within this bin's range?
Answer: The frequency response of a single FFT bin (when using the default rectangular window) is that of a periodic Sinc or Dirichlet function. If using a non-rectangular window (Hann or Hamming, etc.) the frequency response of each FFT bin is that of the transform of the window applied before the FFT.
It's not the average of the signal energy within the bin width, because energy within the bin width, but not at the exact bin center frequency gets spread to (all) other FFT result bins, thus lessening its contribution to the closest FFT bin center.
Comment: For a real frequency the bins don't follow a Sinc expression. You must be thinking of a complex exponential.
Comment: So, a frequency bin is centered around an interesting frequency $f_0$. Assume the spectrum is such that there is no spectral leakage from other frequencies to that specific frequency $f_0$.
Now. I center a frequency bin around $f_0$. The value of this bin is then the value of EXACTLY this frequency '$f_0$ and is not affected by frequencies that also lie in that bin's range.
A frequency bin covers the value of its center frequency (+ eventual spectral leaks to that center frequency) ?
Comment: Not only can there be "spectral leakage" into an FFT result bin.  But energy leaks **out** of a bin for any signals that are not pure sinusoids which are exactly integer periodic in the entire FFT length (the energy "leaks" mostly into other adjacent FFT result bins).


Best way to add navigation for a site with lots of pages

Question: I am designing a knowledge center site for a large consumer company. Currently there are more than 800 pages on the site that are all different. In order to navigate the site, we decided to go with drop down menus that had up to three layers. However, the associates of this company are limited to a screen resolution of 900x1024 and wouldn't be able to view all the pages in the menu because they would go off the screen to the right. Any suggestions on a better navigation plan?
Comment: People likely don't want to navigate 800 pages. My guess is they want to search for something specific. I'd maybe focus on the search angle more than navigation angle.
Comment: Jakob Nielsen says "mega-menus" work well for large sites http://www.nngroup.com/articles/mega-menus-work-well/
Answer: Without knowing any specific details I may suggest the following:

Add search with autocompletion

Group pages somehow and let user go deeper into the hierarchy while narrowing down the context.
You may use tagging or labeling for reducing number of items.  Tags or labels may be represented as a list or as a tag cloud.
Answer: You might also want to have a look at elastic lists:
New York Times Archive search
http://moritz.stefaner.eu/projects/elastic-lists/NYT/
Nobel prize search
http://well-formed-data.net/experiments/elastic_lists/


How do I make edges tube-shaped?

Question: I have a large block. I want the edges of this block to have a cylindrical mesh centered around them, spanning the entire length of the edge. I want to be able to choose the circumference of the cylinder. I want it to follow the edges like with the curves in the first 5 minutes of this video. If this is possible, how do I do it? If possible, link a video because i am not very good with technical terms.
Comment: Hello and welcome. While files, images, and external videos or links may be helpful additions they should not be the only way to obtain information about your issue. Don't make understanding your question rely on downloading a file, watching a video or visiting an external site. Use the builtin tools to upload [images](https://meta.stackexchange.com/questions/75491) or [gifs](https://blender.meta.stackexchange.com/questions/963), along with thoroughly explaining the problem in written form so it can be indexed and searched for thus helping future visitors with similar issues.
Comment: i doubt if the video is really necessary to understand my issue but the problem is i don't have any image of what i want.
Comment: the step by step seems to be what i want but right now it is way too thicc, it looks more like a pancake then what you showed, how to i thinn it out?
Comment: never mind ctrl a worked
Answer: I think this method may work:
Step 1: Press delete and select "Only faces"

Step 2: Add a skin modifier

Make sure to select "Smooth shading"

Step 3: add a subdivision modifier

Step 4: enter edit mode with "X-Ray" enabled

Step 5: Press CTRL + A to adjust the radius

Step 6, and all the ones after are optional, but they can give your object a more defined shape.
Step 6: Subdivide your edges in edit mode

Step 7: Select only the newly created vertices

Finally, press CTRL + SHIFT + B to bevel the vertices. Adjust untill you get a result you like

How do I make edges tube-shaped?


Text size on my monitor

Question: The text on my monitor is extremely small, almost unreadable.I downloaded the NOOBS software, I am using an HDMI lead and a television monitor with HDMI input. Also trying to run the Scratch program which says to move a block of code from the left panel and locking the bars should move the image according to to code, eg "move 10 steps" nothing happens, just a small movement.
Regards Steve
Comment: Just ask about the text size problem on this question and move the bit about Scratch programming to another question.
Answer: about the text size...

run
ls -l /usr/share/consolefonts | less
pick a font you like
then run
setfont [font name sans extension]

I'm using (I'm pulling this from memory)
<code>setfont Uni2-Terminus48x24
</code>
**the less command will allow you to scroll the screen using the up and down arrows keys. run with and without the | less and you'll see the difference

Text size on my monitor


Using to SOAP API in SpringBoot application to get the DE data

Question: I'm new to SF Marketing Cloud and need to use Soap API in SpringBoot application to get DataExtensions data to do some manipulations. I'm not sure where to get MC DataExtensions API/end Point as well as what jar files required to add within SpringBoot Project. If any one having same example, can you please share
Answer: Here are some links to get you going.
Get started with SOAP API
https://developer.salesforce.com/docs/atlas.en-us.noversion.mc-apis.meta/mc-apis/getting_started_developers_and_the_exacttarget_api.htm
You'll be able to read data extensions rows using

Method - Retrieve. https://developer.salesforce.com/docs/atlas.en-us.noversion.mc-apis.meta/mc-apis/retrieve.htm
Object - DataExtensionObject. https://developer.salesforce.com/docs/atlas.en-us.noversion.mc-apis.meta/mc-apis/dataextensionobject.htm

You'll need to update the data using

Method - Update. https://developer.salesforce.com/docs/atlas.en-us.noversion.mc-apis.meta/mc-apis/update.htm
Object - DataExtensionObject.


Please help identify

Question: I purchased this mini plant in GA over the weekend in a Pikes Nursery. It is only labeled as a Peperomia species pixie plant. I have looked ALL over the internet and cannot seem to identify this cutie.
It has very, very soft, velvety foliage with red coloring on the bottoms. It's so pretty and seems to move/bend towards light source fairly quickly.
Please help if you're able.
Answer: One of the favourite things for people in garden centres to do is keep the place tidy by picking up random plant labels from the floor and sticking them in random pots that need a label.
I think this one is an Episcia, but which species is a puzzle. Note that the plant is hairy; all Episcias are hairy and have the silver veining. E. lilacina leaves frequently have "often rose purple beneath" (Hortus III), but so does E. cupreata the regular Flame Violet. What leaves me in a little doubt is the pattern of veining which on this one appear to have veins coming from the base of the leaf, and minor veins branching from the mid rib. Most flame violet have one main vein but many branches.
The elongated stems indicate low light conditions so flowering might be difficult to achieve, but that would certainly be a great help in identification.
Comment: Omg, thank you so much for your detailed comments. I truly appreciate it and it is a major help to the identification! Thank you once again. Also, funny about plant shops labeling with random labels they've found, seems to be very accurate LOL.

Please help identify


Can we connect a specific Marketing Cloud's BU to a sandbox of service cloud?

Question: I want to use a BU as a test environment by connecting it to a sandbox of service cloud. And perform development and testing activities. Is it possible?
Answer: Yes, definitely possible, you will need to enable multi-org for that.
You will also need two Marketing Cloud API Users, one Service Cloud API user and on Sandbox API user.
Here is the outline of the connection:
<code>PROD BU ---- MC PROD API User ---- Service Cloud API User
Sandbox BU ---- MC Sandbox API User ---- Sandbox API User
</code>

Read more about Multi-Org Account and User Configuration here.
Considerations for connecting to a Sandbox:

Sandbox promotions are not possible in Marketing Cloud. Org sandboxes can be promoted into production orgs. You can't promote changes in a 'test' business unit into another 'prod' business unit.
Sandboxes are often used for testing items that are high risk for adversely affecting accounts, such as load tests, performance tests, or volume tests. Connecting your production account to your sandbox org elevates the risk of harming your production account.
Marketing Cloud business units are not data-isolated. Test data and production data are co-mingled when using a sandbox, which impacts data cleanliness and adds complexity to reporting, audience creation, and so on.
All business units receive code at the same time. You can test Sales or Service Cloud changes before the release. However, Marketing Cloud changes go live at the same time, regardless of whether the business unit is tied to a Sandbox.
Answer: It is possible, but it requires configuring the entire Marketing Cloud instance to a Multi-Org instance, which is not reversible.
To enable this, you'll need to contact SFMC Support. Check the FAQ to understand all the implications and limitations before you request it.
Comment: Since it is not reversible, does it have any disadvantages?.
Comment: What would be a best setup for development and testing purposes involving Service cloud and marketing clous


Which port(s) does XMPP use?

Question: I´ve searched and didnt find which ports does XMPP uses.
I need to implement XMPP server and client and use XML transfer, file transfer and streaming.
Do they use different ports?? Is there a way I can make them use all the same, so I dont need to bother the network admin?
Thanks
Answer: According to Wikipedia:

5222 TCP     XMPP client connection (RFC 6120)        Official
5223 TCP     XMPP client connection over SSL          Unofficial
5269 TCP     XMPP server connection (RFC 6120)        Official
5298 TCP UDP XMPP JEP-0174: Link-Local Messaging /    Official
             XEP-0174: Serverless Messaging
8010 TCP     XMPP File transfers                      Unofficial

The port numbers are defined in RFC 6120 § 14.7.
Comment: There's a bunch of other comments about recommended port #'s in the RFC in sections 2.3, 2.4 & 2.5 as well (http://www.ietf.org/rfc/rfc3920.txt)
Answer: According to Extensible Messaging and Presence Protocol (Wikipedia), the standard TCP port for the server is 5222.
The client would presumably use the same ports as the messaging protocol, but can also use  http (port 80) and https (port 443) for message delivery. These have the advantage of working for users behind firewalls, so your network admin should not need to get involved.
Comment: But for file transfer I will need another port, dont I ?
Answer: The ports required will be different for your XMPP Server and any XMPP Clients.  Most "modern" XMPP Servers follow the defined IANA Ports for Server-to-Server 5269 and for Client-to-Server 5222.  Any additional ports depends on what features you enable on the Server, i.e. if you offer BOSH then you may need to open port 80.
File Transfer is highly dependent on both the Clients you use and the Server as to what port it will use, but most of them also negotiate the connect via your existing XMPP Client-to-Server link so the required port opening will be client side (or proxied via port 80.)
Answer: The official ports (TCP:5222 and TCP:5269) are listed in RFC 6120.  Contrary to the claims of a previous answer, XEP-0174 does not specify a port.  Thus TCP:5298 might be customary for Link-Local XMPP, but is not official.
You can use other ports than the reserved ones, though:  You can make your DNS SRV record point to any machine and port you like.
File transfers (XEP-0234) are these days handled using Jingle (XEP-0166).  The same goes for RTP sessions (XEP-0167).  They do not specify ports, though, since Jingle negotiates the creation of the data stream between the XMPP clients, but the actual data is then transferred by other means (e.g. RTP) through that stream (i.e. not usually through the XMPP server, even though in-band transfers are possible).  Beware that Jingle is comprised of several XEPs, so make sure to have a look at the whole list of XMPP extensions.

Which port(s) does XMPP use?


Are index fund expense ratios "priced in"?

Question: I'm coming from a Robinhood "day trading" mentality, so I'm used to public advantages being "priced in", more or less. It seems like many people pick index funds based on their expense ratio. I would think that this kind of thing is already priced into the index fund's value. Is this true?
Answer: To paraphrase the late great John Bogle, there are only two "free lunches" or "pure wins" in investing: One is diversification and the other is minimizing investment costs (fees). You really do come out ahead by choosing a lower-cost mutual fund or ETF.
So why is this advantage not arbitraged away by the market, as your trading intuition suggests? Free market arbitrage eliminates differential returns only to the level of the costs of arbitrage.
Mutual funds issue and redeem shares at NAV, while ETFs do so in exchange for a basket of securities. Thus, a mutual fund cannot "price in" anything but its holdings, and if its costs are uncompetitively high its assets under management will head toward zero. An ETF holding liquid securities will likewise track market value (for currently held quantities and prices) regardless of its expense ratio. In both cases, the costs will erode the holdings per share over time, of course, but a change in costs has no immediate price impact.
The fund costs (if not excessive) are accepted by retail investors because they have no better way of owning the index -- commissions to buy all the holdings individually would be prohibitive, but professional investors with negligible trading costs can perform the arbitrage. An exception would be an ETF holding illiquid securities, where low costs could result in a market premium because the ETF could become the most efficient way to invest in its holdings even for professionals. This is the one scenario where a fund would "price in" its expense ratio.
The other type of arbitrage would be shorting high-cost funds against a long position in their index to capture the erosion in holdings per share, but this is thwarted because a high fee is demanded to borrow such high-cost funds.
Answer: No, they are not. The expense ratio is not an indispensable part of the assets held by the ETF, like an expense, faced by company and impacting its share price.
An ETF provider is always ready to redeem or subscribe shares at the NAV price (subject to a fee and minimum volume), so that it is highly unusual that an ETF would deviate a lot from its NAV. Even if an ETF provider were to increase tremendously their fees, most shareholders would redeem the shares at NAV thus making the ETF way smaller, but not necessarily impacting the price (barring any effect the ETF selling its holdings in the market has on the prices of the holdings).


How to handle even and odd convolutional filter sizes and images

Question: Is there a rule of thumb for determining the size of a convolutional filter given the shape of the input? Specifically, if you want to do a 1D convolution over an even-length vector, does the kernel need to be a divisor of the vector length? Does the kernel need to be even? I understand that when using an odd-length kernel, you align the center element with the stride position on the input vector, but with even-length kernels there is no center position. For example, if I have a vector [a,b,c,d] and a kernel [0,1], should the kernel start by aligning 1 with a or should 0 align with a?
Also is there any theory on why and how much padding and stride you should use when convolving and trade-offs between these two parameters?
Answer: It's usual to use stride 1 and pad the input layers such that the output layers so that they are the same size as the input layers. Using stride lengths of 1 separates the processes of feature extraction (the job of the convolutional layers) and making the model invariant to spatial translation (the job of the pooling layers). Padding the input layers ensures that the model doesn't slowly lose information about edge elements.
Answer: The size of your convolutional filter depends on your application. For convolutional networks, the size ,  padding and stride should be treated like regular hyperparameters. In some applications, the size of your convolutional filter is important. For example, you may want a Linear Phase filter so you will need an odd length filter but this is more important for signal and image processing.


At the start of the New 52, how many people know the identity of Batman?

Question: In the old continuity, quite a number of people ultimately knew Batman was Bruce Wayne. How has that changed with the re-launch of the New 52?
Answer: The extent of the changes made in the wake of the New 52 are still being revealed. We have to wait and see for the most part, although Batman is said to have suffered the least amount of changes.
It is certain that Catwoman no longer knows his identity. We have to wait for an appearance by other characters who knew his identity such as Riddler and Ra's to see if they still know or not.
Answer: Spolier Alert
I've just started reading the series, but as far as I know despite his Bat Family (Alfred, Nightwing, Robin aka Damian, Redhood, BatGirl) no one else knew it in start. Joker seems to know it, but in the end of "Death in the Family" Bruce argued that Joker doesn't know and doesn't even want to know who's behind the mask, because it'll ruin the fun ;-)
Talons knew it in the Court of the Owl series, since they attacked his BatCave, but they learnt it by accident and it was not in the start of the series.
Later, the whole Justice League starting member knew it (obviously).
PS: I'll update the answer, as soon as I keep reading the comics.