Hanging curtain rods - metal stud above window?

Question: I live in a new construction and want to install curtain rods above my full height balcony door and windows.  I'd like to hang them half an inch above the window but my stud finder has a metal mode and seems to be identifying metal.  Is this a metal stud frame around the window?  Is it okay to drill or screw in?
Answer: If you are only 1/2" above the opening and there is a drywall return, you are probably detecting a drywall corner bead:

It is ok to drill a pilot hole through it and send a screw right through into the wood framework.
Answer: What you have there is drywall. Without drilling a hole or tearing the drywall off, it's impossible to tell what's behind it.
Maybe turn off the "metal mode" of the stud finder, then wave it around and have it look to see if it detects any wood. If all it detects is metal then you've probably got metal studs and will have to take appropriate measures. If it detects wood, then you're 100% good to go with regular wood screws.

Important consideration:
If you're trying to put a screw 1/2" above the corner of the drywall, you are either going to put that screw edge-on into the horizontal drywall that forms the bottom of the soffit, or you're going to put it so close to the bottom of the stud (assuming wood) that it will have effectively ZERO grip. It might even just go through the edge of the stud, tearing out the wood and effectively making a gap between the drywall and stud and not being firmly attached to anything.
Your screws may support the weight of the mount, but may collapse when you add the bar. It may support the bar, but collapse when you add the curtains. It may support the curtains, but collapse when you first open/close them. i.e. a screw with that little purchase won't hold much weight if any.
I understand that there's likely another screw above this one, but the bracket is designed with 2 screws for a reason, and that reason is to have both screws helping to hold it to something firm.


can Rpi 4 model b work as keyboard emulator to two pc?

Question: I am using Raspberry pi model B. I Connected one keyboard to it in usb2 port and I want to write in two pc whatever i am typing on keyboard. right now i tried for one pc. connected keyboard and OTG c pin port to pc. but my question, can i config one of usb ports so it can display on another pc what i type on keyboard simultaneously on both pc?
Comment: Sorry, but this is not clear. A USB port certainly cannot display anything, and I doubt you can type simultaneously on two keyboards.
Comment: no no. sorry if not understood. its my bad. i want to type in single keyboard and want to display on two pc. in keyboard emulation example, otg port i am connecting to pc that i want to see on another pc also. single keyboard(single input) and two output like 2 otg. but in rpi4 only one otg is there. so i have to use one usb if possible. so usb can be used in such a way?
Answer: You can emulate low speed USB (1.x) over GPIO.  You might need some circuitry for 5V 3.3V interfacing but it is doable.  Here is an example of someone patching such a system into an esp https://github.com/cnlohr/espusb


Migrating from an IP addressing scheme to another one?

Question: I have been tasked to migrate one of my customer's IP telephony network from 192.168.11.0/24 IP addressing scheme to 172.27.72.0/23.  My customer has deployed Cisco Call Manager and Cisco Unity Express. I just want to know what all things I should take care of, so this transition happens smoothly? I do not have much experience in handling such migrations, any help is highly appreciated.
Comment: We need a lot more to help you. A network diagram and detailed description of how everything is connected. Also what type of network equipment is used and the configurations.
Comment: The main things I'd also ask are how many phones are involved, whether they are remotely managed, and what amount of downtime is considered acceptable.
Comment: The customer wants me to do the reconfiguration only for one site.They have 87 IP phones and all are managed by the CUCM at their branch. I have one full day to reconfigure things.They also have a couple of SIP trunks, if I change the IP address of the CUCM how the tunks will be affected?
Comment: Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
Answer: One thing that I have learnt the hard way is migrating CUCM and UNITY. Make sure you change the ip address on the web interface by going to SYSYTEM > SERVER
and changing the ip address to the new one (eg.172.27.72.1)
Then you need console access to them. If they are running virtually then this is a benefit. Login to each server an issue these commands:
set network gateway *<gateway>*
set network ip eth0 *<ip>* *<subnet mask>*
The server will then reboot and have the new IP you set. But make sure you change in on the WEB gui first to avoid being locked out!
I do not know about the SIP trunks that you have setup and how they have been configured.
Comment: No problem, let me know if you need more help
Comment: Does changing the IP address of the CUCM and Unity invalidates the existing License? Do I need to get a new license from Cisco after the change?
Comment: No, this shouldn't change anything with Cisco UCM


What is a gift called that is given to you to possess and keep but can be taken back at any time?

Question: I have this gift that was given to me as a present for my birthday, but was informed that is not mine permanently but to keep until my friend wants it back. What is that kind of gift called?
Comment: I'm no lawyer, but if you haven't signed any agreement or contract then the "gift" is yours to keep. Unless we are talking about a substantial piece of property; e.g. an apartment can be loaned, but you will never be its owner. But if it's an electric toaster, well... I'd keep that and chuck away the "friend". :)
Comment: It's a loaner (or possibly stolen property which needs to chill for a bit). Often the terms of the loan are just the right of first refusal if the person decides they want to get rid of it. @Mari-LouA There's nothing wrong with the idea, it's quite a common practice. It may make perfectly good sense if, say, one person can carry it on insurance, but the other can't, or if there is still a lien on it. I might give someone a good guitar if they are taking lessons, conditional on them continuing the lessons, but they can't go hock the thing. Think of it as paying it forward, with stipulations.
Answer: This is often referred to as a permanent loan

A form of loan agreement in which an individual, trust, or company
  loans artwork or other objects to a museum for an extended period of
  time. The loan agreement may stipulate that the museum must display
  the loaned artwork in a specific area of the museum, that the artwork
  is to be displayed as part of an exhibition, or that the artwork is
  not to be shown in a touring exhibition.

Despite the word permanent in this phrase, such loans are not necessarily that:

Accepting artwork under a permanent loan does put a museum at a risk,
  however. While the word "permanent" is used to describe the time
  period of the loan, objects loaned under this sort of agreement can
  still be withdrawn at any time. For example, the heirs of a wealthy
  collector may request a painting be returned.


Finding a Cartesian coordinate transformation matrix

Question: I have a vector, $u := [u_1, \ldots, u_n]^\mathrm{T}$. I am trying to find a coordinate transformation matrix, $Q \in \mathbb{R}^{n \times n}$, which is nonsingular, satisfying:
\begin{align*}
\begin{bmatrix} 0 \\ \vdots \\ 0 \\ ||u|| \end{bmatrix} = Q u.
\end{align*}
I would appreciate any idea to find this matrix, $Q$.
Answer: Recall that if $W$ is a subespace of $\mathbb{R}^{n}$, then
$$\dim(W)+\dim(W^{\perp})=n$$
Take $W$ as the span of $u$, so
$$\dim(<u>)=n-1.$$
You can construct a matrix $Q$ that will satisfy the same condition taking any set of $n-1$ vectors $v_i$ from any basis of the ortogonal complement of the span of $u$.
$$Q=\left(\begin{array}{cccc}
v_{11}&v_{12}&\cdots&v_{1n}\\
v_{21}&v_{22}&\cdots &v_{2n}\\
v_{31}&v_{32}&\cdots&v_{3n}\\
\vdots&\vdots&\vdots&\vdots\\
v_{n-1,1}&v_{n-1,2}&\cdots&v_{n-1,n}\\
\displaystyle{\frac{u_1}{\vert\vert{u}\vert\vert}}&\displaystyle{\frac{u_2}{\vert\vert{u}\vert\vert}}&\cdots&\displaystyle{\frac{u_n}{\vert\vert{u}\vert\vert}}\\
\end{array}\right)$$
where $v_{i}=(v_{i1},\ldots,v_{in})^{T}$ are vectors in a basis $\{v_{1},\ldots,v_{n-1}\}$ of the ortogonal complement of the linear span of $u$, for all $i$ with $1\leq i\leq n-1$.

Remark: This matrix $Q$ is non singular because it's rows are linearly independent because the following set is a basis of $\mathbb{R}^{n}$:
  $$\mathcal{B}=\{u,v_1,\ldots,v_{n-1}\}$$
Also: You can use Gram Schmidt process to get an ortogonal basis of $<u>^{\perp}$ starting from $u$. In this way you will find the rights vectors $v_i$ such that $Q$ is inversible.
Comment: Thank you for your comment. I omitted an info that Q should be nonsingular.
Comment: Oh ! Yes sure, you want a matrix to do change of basis :)
Comment: You said it when you refer to coordinate transformation matrix, this matrix should be inversible. So, is my mistake :)
Comment: @H.C.: You can use my matrix $Q_1$ and Gram Schmidt algorithm see here: https://en.wikipedia.org/wiki/Gram%E2%80%93Schmidt_process
Comment: @H.C.: Look to this answer also: https://math.stackexchange.com/questions/1766613/proof-sum-of-dimension-of-orthogonal-complement-and-vector-subspace
Comment: Thank you for your answer. It perfectly makes sense and I could solve my problem.
Comment: No problem. Nice question :)


Is there an API for adding/editing posts and viewing inbox in the works?

Question: I'd really like a full blown android-client for Stack Exchange, and I don't mind making one myself, however there are a lack of APIs available for adding, editing, voting and such, and checking if the currently logged in user has permission to add/edit/vote. All in all there is a lack of API where a user can log in at all, which I find kind of frustrating, so I was just wondering (and I'm not even sure I'm asking at the right place) if there is any work in progress to create a more full-blown API for the Stack Exchange sites.
Answer: The API is currently read-only.  But rest assured you are not the only person pushing for a full API.
Comment: Yeah, I've seen, I was just wondering if there was any non-readonly api in the works or not.
Comment: @Alxandr: You and the rest of SO...
Comment: lol, that so, so don't devs like hang out around here and chill, answering these kinds of questions? :-P
Comment: @Alxandr yep. The SO team are: http://stackoverflow.com/about/team from which you should be able to find SO/Meta profiles. Jeff Atwood is the top user by rep of MSO and he's the CTO, so yes, they do.
Comment: @Alxandr: They typically do but don't count on it.  If you're lucky, you might get an official response in a day or two.  The Dev team is really small compared to the user base so it takes a lot longer to get a response when only the SO team can answer.


Are countries with lower life expectancy expected to have lower death rates due to Coronavirus?

Question: Coronavirus death rates are higher for people in the range of 80+ (14,8%) and 70-79 years old (3,6%). However, there are countries, specially in Africa, where life expectancies are in the 50-60 and 60-70 years old range. Some people (like Bill Gates) warned about possible catastrophes if the virus massively reachs Africa. Could it happen than the lower life expectancy of those countries prevents more people from dying? Is people who lives 60 years old in countries with lower life expectancy, expected to have the mortality rates for Coronavirus of the people of the same age in countries with higher life expectancy, or a person of 60 years old in countries like those is in a physical state of an older person in a more developed country and as such have a higher mortality rate?
Answer: Age is a red herring, only a secondary characteristic correlating to death rates.
It's people that are already seriously ill or already have weak immune systems that are most likely to die soon after contracting Covid-19.  And it's when people are clustered in a close community that they are most likely to contract the disease.
In our society, the people in those circumstances tend to be old and in health-care facilities.
As a result, most of our deaths so far have involved people over 80 years old.
In other societies, a lack of old people doesn't necessarily mean a lack people living in close quarters, that are weak or sick.
There's certainly no shortage of such conditions in many parts of Africa.
From Coronavirus Disease (COVID-19) - Our World in Data:
Answer: Death risk from COVID-19 increases greatly with underlying diseases:

Patients who reported no pre-existing ("comorbid") medical conditions
  had a case fatality rate of 0.9% (Worldometer, Feb 29, 2020).

The most common underlying diseases in those who died from COVID-19 were: cardiovascular disease, diabetes, chronic respiratory disease, hypertension and cancer. So, it's not really age, but an underlying disease that increases the risk of death in COVID-19.
The median age of those who died so far from COVID-19 in Italy with life expectancy 83.4 years was 81 years:

Borrelli said the median age of the people who have died from the
  virus in Italy is 81 years of age (CNN, March 6, 2020).

and in China with life expectancy 74.6 years, it was 75 years:

On 23 February 2020, the number of people diagnosed with COVID‐19 in
  China was 1879 times of that on 10 January 2020. They estimated the
  case fatality rate of COVID‐19 to be 2.84% based on their patient
  pool. The authors also found that the ratio of male to female deaths
  was 3.25:1, the median age of death was 75 years (Journal of
  Medical Virology, Feb 25, 2020).

In the US with life expectancy 78.9 years, it was 80 years.
The risk of death from COVID-19 increases with chronic diseases and therefore with age. Moth deaths so far have been on Northern hemisphere in countries with life expectancy above 74 years. Moth countries with life expectancy lower than 65 years are on Southern hemisphere or around equator, where it is warm now, which is a likely reason for much fewer cases of infection there.
In countries with low life expectancy, mainly in Africa, there are other potential risk factors for COVID-19: widespread parasitic diseases (malaria, intestinal parasites, etc.), malnutrition and less available health care, which are not associated with age.
In conclusion, even if in the countries with low life expectancy, lower average age (and hence less chronic diseases) can be a protective factor against COVID-19 deaths (Worldometer), we do not yet know the effects of other risk factors in these countries.
Comment: @Jan, Given that the fatality rate of 20-29 year-old is 0.2%, and that the proportion of those in this range with comorbidities are probably higher than 0.2%, is it safe to assume that a healthy 20-29 year-old has statistically negligible risk of death just as common cold and flu?
Comment: @Math.StackExchange, if you ask this as a new question, I'll answer.
Comment: I think that article says the median age of infected people in China is 51 years old, not the median age of people who died, though not sure
Comment: @Pablo, that's correct; I found a reliable source that says that median age of death from COVID-19 in China is 75 years.
Comment: It's no surprise that a country with a higher life expectancy has a higher median age of death (there are simply more old people), so that observation does not support your final point about death rates. On the contrary, Italy's death rate is notably *higher* than China's, which exactly in line with the hypothesis that a higher life expectancy is associated with a higher death rate.
Comment: @NuclearWang, I'm editing my conclusion. Anyway, I was not talking about "median age of death" but about median age of death due to COVID-19."
Answer: The Accepted Answer by Ray Butterworth, while reasonable when it was written (March 2020), now appears to be wrong. Hardest hit countries have mainly been those with longest life expectancies (Europe, N. America) while Africa has had very low death rates from Covid (Europe 964 per million,  Africa 70 per million, Our World In Data, 2021 Feb 5). Multiple studies have found a high correlation between life expectancy and covid deaths, e.g. Frontiers | Covid-19 Mortality: A Matter of Vulnerability Among Nations Facing Limited Margins of Adaptation,
Factors associated with COVID-19 infections and mortality in Africa: a cross-sectional study using publicly available data | BMJ Open


How to append parent MID sendlog with tracking dataviews from sub-business unit

Question: We have a newly created 2.0 account where one of our business units stopped writing to the parent sendlog. In order to get the process to work properly, we were advised to delete various sendlog file(s) that were inadvertently created in that business unit(filters were being run against these rogue "sendlogs" for reporting.) Is there a way to recover that sendlog(s) data so we can append the parent sendlog file?
Answer: If you deleted records from these individual Data Extensions, you may not have many options open to you, other than see if you can assemble what would have been in the data extensions based on the _Sent data view and other Data Extensions from which you were logging values to these Send Logs.
If you simply dropped the Data Extensions in the child Business Units, you would need to get back in touch with Salesforce Support to have the Data Extensions you deleted reinstated. Data Extensions are only soft-deleted and Support have access to a utility to "undelete" them.
Once reinstated, ensure your Enterprise Send Log Data Extension is in a Shared Folder and create and execute Query Activities in each of the Business Units that append to the Enterprise Send Log.
Finally, re-delete all the child Business Unit send log Data Extensions.


How can I count operations in C++?

Question: How can I count operations in C++? I'd like to analyze code in a better way than just timing it since the time is often rounded to 0 millisec.
Comment: Specify what do you mean by "count operations". There are instruments to analyze the function calls in your code like a profiler, but you may also see, adding the appropriate switch, the generated assembly code.
Answer: If you are timing code, it's worth running it a lot of times in a loop to avoid the effect of the timer resolution. So you might run the thing you're timing 10,000 times and measure the amount of time it takes to run all the iterations. It will probably only take a few seconds to run and you'll get better timing data.
Comment: The only difficulty with this can be that the benchmark thoroughly warms the 'caches', whereas the code normally runs on cold caches.  But measuring cold cache performance is hard.
Comment: Yes, unless you're measuring the performance of the cache itself, you'll need to disable caches for proper performance testing.
Comment: Doesn't disabling your CPU caches give misleading results in the other direction? Instead of not knowing when you'd lose performance to cache misses, now you don't know when you'd gain performance by cache hits.
Comment: Oh, I wasn't suggesting disabling the CPU cache. I was thinking of things like application-level caches.
Answer: Using "the number of operations" is a bad idea when thinking about performance. It doesn't  take into account the differences between the best case/worst case cycle counts for each operation, the costs of cache misses, pipeline misses, potential (automatic) parallelisation etc.
As Greg says, usually it's a better idea for a microbenchmark to just run the same code enough times to get a decent span of time.
Even better is to run your whole application with a realistic workload and measure the metrics you're really interested in, but that's a different matter...
What is certainly useful is to work out the complexity of your code - know when a method is going to be O(1), O(log n), O(n) etc. That typically doesn't involve knowing the details of what the individual instructions in C++ do - although you do need to know the complexity of anything you call. (Joel's story of Shlemiel the Painter and strlen being the most obvious example.)
Answer: A sample profiler is a good choice here.  On Windows, you can use the profiler built into Visual Studio, or the xperf tools from the Windows organization.   The xperf tools are free.   Here is series of posts on the xperf tools from myself. This one is about profiling.
Answer: Generate the assembly and count operations. Then review the cycles/op that your processor uses. Then remember you're working on a pre-emptive OS and none of that is valid.
More seriously, jack up your n and scale your program to obscene sizes. That will give you an idea of what your program speed is.
Answer: Use valgrind on Linux. It has instruction level timing, including cache analysis.
Answer: You can do precise measurements by reading the time-stamp-counter (tsc) of the CPU, which is incremented by one at each cpu-clock.
Unfortunately the read is done inlining some assembler instructions in the code. Depending on the underlying architecture the cost of the read varies between ~11(AMD) and ~33(Intel) tsc. With 1 Ghz CPU you can virtually have the nano-second precision.
In order to perform a reliable and non-invasive measure of a section of code you can:

prevent the cpu scaling frequency by disabling the cpu features such as AMD cool'n quite or Intel SpeedStep.
repeat the test several times, collecting the measures in an array and then saving data to file for an off-line analysis.
choose a real-time scheduling policy for the process under test such as SHED_RR or SHED_FIFO. Realtime policies reduce the number of context-switch between the process under test and other normal processes/kernel threads, that are blocked.
lock all the process's virtual address space in RAM by means of mlockall() system call.

Here you can find a quasi-portable C++ class I wrote for Linux, derived from the Linux kernel and designed to read tsc for the architectures i386, x86_64 and ia64.
Comment: The TSC can sometimes be unreliable, especially in multicore systems.  See http://en.wikipedia.org/wiki/Time_Stamp_Counter for more details.
Answer: If you want an actual operation counts coming from your hardware, then you may want to consider installing a package like PAPI - Performance API - which works across many different OS and processor combinations.  It uses actual hardware counters and reports either direct or derived values for a lot of different performance metrics such as Total Ops, FLOPS, cache hits/misses, etc.  It can also give access to higher resolution timers.
It's not the easiest package ever, but the level of reporting can really help you analyze the behavior of your application on your hardware.
Answer: Use a higher-resolution timer.
Answer: If you're concerned about making your program go as fast as possible, and it is single-thread, and you're using an IDE, check this out:
How to Optimize Your Program's Performance
Answer: Why do you not just run your code under a profiler? That typically gives you data about how much time is spent in functions as well as how many times they are called.
Knowing how many times a function is called is useful because it can allow you to spot potential performance problems if a function is being called far more often than you feel it should be.
Of course using a profiler makes your code slower but that is unavoidable when adding any kind of instrumentation.
Answer: If you want precise timing (on windows) without using a profiler you can have a look at this thread which presents different ways of profiling C++ code.

How can I count operations in C++?


C++ standard API

Question: I am a student, and new to C++. I am  searching for a standard C++ API that is as comprehensive as the Java API. So far I have been using cplusplus.com, and cppreference.com.
Please any help would be greatly appreciated.
Comment: Are you looking for a comprehensive reference for the C++ standard library?  Or are you looking for a C++ library that is as comprehensive as the Java library?
Comment: @Dustin I think the closest thing would be Qt library. http://qt.nokia.com/products/
Comment: What do you mean by an API? What features do you want? What's bad with the standard library?
Comment: The sites you mentioned cover everything that can be considered C++ API.
Comment: @ james, I am looking for a c++ library that is as comprehensive as the java library.
Comment: There really isn't _one_; you'll probably need to use pieces of several libraries.  What libraries you need to use depends entirely on what functionality you need.
Answer: C++ and Java have very different standard libraries because they make very different assumptions about what they are going to be used for.
Java assumes that applications or applets will be running on a host with a full featured OS, with a defined way of doing most normal things.
There's a lot of content in that, for instance, in java, the output will be an application or applet.  C++ does not make that assumption, because C++ can be used for building OS Kernels and drivers for kernels, it can be used for programming full stack real time applications on microcontrollers, or processing blocks in supercomputers.
C++ can be used for implementing the very operating system on which it will run.
For these reasons, the standard library assumes almost nothing about what it will have available, and so the standard library doesn't make any dependencies on those features.
The only exception is with files and streaming, because almost any operating system like stack has something that looks like a file stream if it has anything like files at all.
If you want a richer set of OS Specific api's you need to look at something non-standard.  A great choice is the Qt framework, which provides many tools similar to what is found in the Java libraries, is cross platform, and works well with native C++ idioms.
Comment: I agree, I think the standard library, boost, and Qt make for a very comprehensive set of libraries with minimal dependencies and are easy to get up and running (one of my pet peeves... dependency hell).
Answer: C++ has a standard library.
You can try reading the "The C++ Standard Library: A Tutorial and Reference". While I don't own it myself, it's on our book list (which I recommend you check out), so it shouldn't be bad.
Note C++ isn't Java, so the libraries don't necessarily have the same functionality. Another resource you'll want to look at is Boost, which serves as a source for well-written C++ libraries for things the standard library lacks.
Answer: GNU C++ Standard library documentation is the one I refer to most often.
Answer: Java is a virtual machine language and as such attempts to have a comprehensive api to provide a platform independent method of drawing/wrtinging to files / anything.  IN the guts of JRE they are taking these generic inputs and using them to do platform specific things.  In C++ you are the one that does that work.  Many c++ libraries are platform specific see MFC, ATL or code that is written for XWindows it your job to decide how you want to implement a feature and see if that is a platform specific feature or can be done in a platform independent manner.
If you are writing on windows or unix I can assure that the OS API is very complete and will allow you to do what ever your trying to accomplish.  Also take a look at cross platfom libraries like lib qt.
Answer: Java's standard library is aimed at providing ready-to-use functionality, while the C++ standard library is aimed at providing building blocks that aren't defined by the core language. The Boost library has mainly the same orientation as the standard library (with a few exceptions such as image processing). I think the closest you can get to something like Java's standard library is the Poco library.
However, when I tried on the Poco library I found that it was a bit too C-oriented for my taste.
That is, it's not "modern". You get that impression straight away without even looking at the APIs, because the online docs uses 1990's frames. :-) However, it may fill your needs.
Answer: If you mean the c++ standard library I'd look at www.cplusplus.com. It covers the current standards. After familiarizing yourself with that, you could try looking at boost.
There are a number of changes in the upcoming c++0x standard. Wikipedia has info on a number of these as does SO.
The number one book, IMO, for c++ is Effective C++ by Scott Meyers.

C++ standard API


Image conversion to PNG vs JPG using ImageMagick

Question: I'm trying to convert some images into either PNG or JPG and trying to find out which format will result in the smaller file size. With most of the cases PNG will give me the best compression but some odd images I get better compression out of JPG. I have two questions:

What characteristics of image will cause it to give better results?
Is there a way to pre-determine which format will give me better
results without converting them first?

This photo gives better compression result using PNG

This photo provides substantially better compression using JPG
Comment: You may also like this one: http://superuser.com/questions/499749/automating-the-choice-between-jpeg-and-png-with-a-script
Comment: In general, PNG is better for computer-generated images and JPEG is better for realistic, camera-taken photographs. In general, computer-generated images have smaller palettes of colours (less variation) and photos have higher frequency components (things that change very rapidly as you move around the picture). Hard to tell in advance... maybe looking at the image statistics would give you a start.
Comment: Possible duplicate of http://stackoverflow.com/questions/2336522/png-vs-gif-vs-jpeg-when-best-to-use and http://stackoverflow.com/questions/610530/what-image-type-should-i-use-when-gif-jpg-or-png and many other questions linked to those...
Comment: It's not the question of JPG vs PNG so the stackoverflow questions are irrelevant, superuser one is rather interesting. Thanks
Comment: Can you provide a link for the original PNG version of the first image please? It's hard to comment on the difference between a `JPG` and a `PNG` when the `PNG` has been converted to JPEG!
Comment: That's Stackoverflow doing it, sorry
Answer: I have absolutely no time to develop this line of thought further but the image entropy is probably a good discriminant for selecting JPEG or PNG - see my earlier comment on your question.
If you use ImageMagick, you can calculate the Entropy easily like this:
identify -verbose -features 1 image.jpg | grep -i -A1 entropy

Your top image gives output like this:
identify -verbose -features 1 t.jpg | grep -i -A1 entropy
Sum Entropy:
    0.703064, 0.723437, 0.733147, 0.733015, 0.723166
  Entropy:
    1.01034, 1.12974, 1.14983, 1.15122, 1.11028
  Difference Entropy:
    0.433414, 0.647495, 0.665738, 0.671079, 0.604431

and your bottom image gives output like this:
identify -verbose -features 1 b.jpg | grep -i -A1 entropy
  Sum Entropy:
    1.60934, 1.62512, 1.65567, 1.65315, 1.63582
  Entropy:
    2.19687, 2.33206, 2.44111, 2.43816, 2.35205
  Difference Entropy:
    0.737134, 0.879926, 0.980157, 0.979763, 0.894245

I suspect images with a higher entropy will compress better as JPEGs and those with a lower entropy will fare better as PNGs - but I have to dash now :-)
There are 5 values for each type of entropy - horizontal, vertical, left diag, right diag and overall. I think the last value is the only one you need consider.
Updated
Ok, I have had a little more time to spend on this now. I do not have a pile of sample images to test my theory on, so I did it a different way. I made a little script to calculate the following for a given input file:

ratio of JPEG size to PNG size
entropy

Here it is:
#!/bin/bash
f="$1"
jsize=$(convert "$f" -strip JPG:- | wc -c)
psize=$(convert "$f" PNG:- | wc -c)
jpratio=$(echo $jsize*100/$psize | bc)
# Make greyscale version for entropy calculation
rm temp*.jpg 2> /dev/null
convert "$f" -colorspace gray temp.jpg
entropy=$(identify -verbose -features 1 temp.jpg | grep -A1 "  Entropy:" | tail -n 1 | awk -F, '{print $5}')
echo $jpratio:$entropy

So, for a given image, you would do this:
./go image.jpg
8:3.3       # JPEG is 8x bigger than PNG and entropy is 3.3

Then I took your image and added different amounts of noise to it to increase its entropy, like this
for i in {1..99}; do convert bottom.jpg +noise Gaussian -evaluate add ${i}% xx${i}.jpg;done

that gives me files called xx1.jpg with 1% noise, xx2.jpg with 2% noise and so on, up to xx99.jpg with 99% noise.
Then I ran each of the files through the first script, like this:
for f in xx*.jpg; do ./go $f;done > data.txt

to give me data.txt.
Then I created the following gnuplot command file plot.cmd:
set title 'Plotted with Gnuplot'
set ylabel 'Entropy'
set xlabel 'JPEG size/PNG Size'
set grid
set terminal postscript color landscape dashed enhanced 'Times-Roman'
set output 'file.eps'
plot 'data.txt'

and ran it with
gnuplot plot.cmd

And I got the following plot which shows that as ImageMagick's entropy number increases, the ratio of JPEG size to PNG size improves in favour of JPEG... not very scientific, but something at least. Maybe you could run the script against the type of images you normally use and see what you get.
Comment: To the OP: As the answer comments out, the lesser the entropy on the image is (that is, the less "information" you have on the image) the better it will do with PNG, because PNG tries to save ALL the information. JPEG, on the other hand, is a lossy format, and it will do better for images with lots of information, because JPEG doesn't actually care about the information, it will try to represent it as accurate as possible but never losslessly. Therefore it is a matter of entropy, as @Mark Setchell says. I'd personally accept this one, pal.
Comment: Wow! What a great answer Mark! That's exactly what I was looking for :)
Answer: That depends very much on your use case.
1) JPG is usually not as good for text because the artifacts tend to "smear" or blur the image. For photos, this is usually not a problem; also for high-resolution textual images the problem will be much less pronounced (because the blur radius is smaller relative to image size).
Note that PNG is usually used to losslessly compress images, while JPG is inherently lossy. With a higher compression ratio, JPG files will be much smaller, but the artifacts will be more pronounced. Note also that there are programs that are able to do lossy compression in PNG (which could well beat JPG compression in some cases).
In short: PNGs will work well with computer-generated images, because those tend to be quite regular and thus easy to deflate. JPGs will fare better with photos which tend to have more jitter, which is hard to compress. When you move away from ImageMagick and libpng, there are other possibilities.
2) While it would be possible to train a neural network to decide whether JPG or PNG would compress better, it would probably take longer and be less exact than just trying both and looking at the output. Note also that there are some approximative measurements that can tell you if an image is too blurry (which may help you setting the correct compression level if you want to tune further).
Answer: One big difference is that PNG allows for alpha transparencies so that you can see parts of what is behind the image.  Jpg will block out a rectangle.
Comment: That's not what I'm asking


Checkerboard coloring problem

Question: Consider a $n\times n$ checkerboard. Each cell can be colored white or black. $n$ is even. How many configurations are there so that each row and each column have an odd number of white cells?
Answer: Fill the $(n-1)\times(n-1)$ board arbitrary with the black and white.now you should just set the parity with the last row and column.
the last cell($a_{n,n}$) will be same color for both last row and last column because of the parity of the $n-1$ first row is equal to parity of the $n-1$ first column and that is because your board is $n\times n$ and $n\equiv n \bmod{2}$ and if rows parity differ from column parity it is contradiction.
Finally the total answer is $2^{(n-1)\times (n-1)} $.
Update I asked generalized version of this question before.
Answer: Coloring the entire board with the parity constraint is equivalent to arbitrary coloring a sub-board with one row and one column removed.  The first restricts to the second and can be uniquely reconstructed from it given the parity condition.
You can predict without going through the complete analysis that the number of solutions is a power of 2.  This is because the problem can be phrased as a system of linear equations mod 2 and the number of colorings will be $2^t$ where $t$ is the dimension of the solution space.  For example, the way I found the answer in the first paragraph is to think in terms of the linear equations and afterward recognize that they can be removed.
The $(m-1)(n-1)$ as dimension of solution space occurs constantly in statistics as the number of degrees of freedom in contingency tables.  In that generality there is a $m$ by $n$ matrix with specified row and column sums and, exactly as in the case of the checkerboard, one can uniquely fill the whole table from any filling of the subtable with one row and one column removed.
Comment: The element at the intersection of the removed row and column might be impossible to color in this case, I think.
Comment: @user16367, it is always possible, because the parity at the intersection is equal to the sum of the the whole (n-1)x(n-1) sub-board. The "row" and "column" constraints on that square turn out to be identical so there is no additional condition to satisfy.  But as you point out, one has to check this as part of the statement that a coloring of the sub-board extends uniquely to a coloring of the whole board of size n.

Checkerboard coloring problem


Ampere's Law Confusion

Question: I had this question recently in a test. Different methods are yielding different answers. Can someone point out the mistake?

We are given 4 infinite wires carrying current out of the plane as shown. Find  $$\int_{-\infty}^{+\infty} \vec{B}\cdot\,\mathrm d\vec{x} ,$$  (along x axis)

My logic for line integral along the infinity part being zero is that by using Biot-Savart law, the field produced by the current carrying wires would definitely tend to 0 at infinity.
 The answer given is $$ \bar u (-3) $$ , which seems like average of both the values. Can someone point out my mistake?
Comment: Sorry for the trouble, its not a vector, i meant u• (meu not) at the end
Answer: When you do the loop integral about one set of wires you are ignoring the other set of wires. Going from $-\infty$ to $+\infty$ around your first loop, you "collect" half of the B field due to one set of currents (the other half comes when you go back in the other direction - your assumption that it's zero "because you are far away" is wrong. You know it is, because a complete loop integral "at infinity" must give you the same value as if you were close).
The actual field is of course the sum of the fields due to the four wires. So you add the two loop integrals, and divide by two (because you only go halfway around the loops).
Comment: I think I got the first part on why I am wrong. Can you explain the method to get correct answer more elaborately? If the line integral at infinite distance isn't zero, then how would you proceed? We have to add the complete integral. RHS is (-6)U° ... LHS is two integrals along different paths. I don't see how adding them would give 2×(required integral) as other terms would also be there when we break the integral
Comment: Take a straight line from - to + infinity, then a semicircle to get back. The integral of the semicircle is exactly half the integral if you went all the way around the circle. So you get a value of $+\frac32 \mu_0 $ for the first integral (around the 1 and 2 A wires), and $-\frac92 \mu_0 $ for the second. Their sum is $-3\mu_0 $.

Ampere's Law Confusion


remove values from search result in catalog search top search box

Question: i have tried core/Mage/catalogSearch/Helper/Data.php
and ResultController.php in Controller and Query.php in model but couldn't find code so i can fix it   here is snapshot attached which i have to remove ..
Comment: Are you looking to remove the auto-suggest option ?
Comment: NO I JUST WANT TO REMOVE EXTRA NUMERIC VALUE COME WITH SUGGESTION  AS SHOWN IN SNAPSHOT
Answer: you can enable show template and show block name
in adminhtml.
admin->system->configuration->for develop
change you webstore to Default store view;
end emable options template hints and hints block and save your configuration.
after you can update search result page, and see your path to template.
if template location in core directory themes, you need copy this file to your theme. And search this link and comment...
Comment: i used display none in style 'THE LAST OPTION'
Answer: Go to system -> Configuration -> Catalog -> Catalog Search and (Show Autocomplete Results Count) select No in dropdown. This is work for me.


Living quarters don't have power

Question: The living quarters don't have power and I don't know why? I tried upgrading them, but it didn't work. I have a power generating room, but my living quarters still don't have power. How do I generate power in the living quarters?
Answer:
Electricity doesn't travel forever. After some distance it gets weak, the same applies in the game. Any room that is too far away from the Power Generators/Plants will start losing power first. Easy fix if you put Power rooms in the center of your Vault or just make more near the rooms that keep losing power.

Source

Living quarters don't have power


Flux in transformers

Question: I have found it very difficult to find what actually happens with primary and secondary generated flux in transformers, I understand the normal transformer theory but it doesn't add up in reality! I am hoping someone can shed some light. Simply put, if magnetic lines of flux cannot cross or actually cancel does this mean that the secondary coil is an air core?
Comment: Could you explain why you believe the secondary coil is air-cored. Both primary and secondary are wound on the same core and the same magnetic flux flows through both windings.
Answer: You could begin an argument about transformers like this: -

A transformer has magnetizing flux due to current flowing into the whole of the primary winding when the secondary is open circuit i.e. the transformer is an inductor.
When extra current flows in the primary due to loading of the secondary this flux increases
The current flowing in the secondary winding also increases flux (incorrect, it totally cancels the ampere turns in the primary due to loads on the secondary)

However, the massive flux generated by the primary due to loading the secondary is totally cancelled by the reverse magnetic flux due to current flowing in the secondary. Consider these scenarios: -

Scenario 1 is just the primary winding with Imag flowing
Scenario 2 is two windings wound close together - Imag (the same as above) is shared by the two windings
Scenario 3 is the 2nd winding open circuit - it has the same voltage as the primary winding
Scenario 4 is the secondary load - Iload currents are in opposite directions and their fluxes cancel.
Comment: @StevenCarr No, you are incorrect, the load associated fluxes cancel completely leaving just the flux due to magnetization. This is why transformers can sometimes trip breakers when unloaded - they are close to saturation due to the mag current. With a load current present there is a slight volt drop due to leakage inductors and this slightly reduces mag current and hence slightly reduces saturation. Most people don't find this intuitive but nevertheless it is true.
Comment: Scenario 4: the flux cannot cancel in reality, it still requires a path.
Comment: Looking closer at this issue, I think no additional flux is generated by the secondary (maybe a small amount on initial loading) as only secondary field intensity increases and this is cancelled by an equal and opposing primary field intensity, then looking at the BH curve this would then leave the primary flux almost the same under load .
Comment: @StevenCarr Yup, that's what I said. Ampere turns on primary and secondary cancel except for mag current.
Answer: The flux lines (mostly) link the two coils- lines pass through the primary and through the secondary. The closed loops are a consequence of the lack of magnetic monopoles- unlike electric charges there are no sources and sinks of magnetic fields. Real transformers have a certain amount of flux that does not link the coils- that is called leakage inductance.
Magnetic field lines are a visualization aid to help understand intuitively a vector field. The flux line density is related to the magnitude of the field and the tangent to the field direction is the line direction.
Another way to visualize this in situations where most of the field is within a core is to think of it like current in a circuit- like a loop with a certain voltage applied (magnetomotive force) through an impedance (reluctance) or conductivity (permeability) and results in a current (flux) and current density in the conductor (flux density).
Comment: Ok, so for the flux lines to link, the coils must have similar poles if on the same core space i.e if both primary and secondary are wrapped around the same core space and at one instant one end of the primary coil is North at the same instant the same end of the secondary coil will be North. This scenario would seem to be suggesting both coils been additive to the field not opposing/cancelling as transformer theory implies? If the scenario is opposite then the core must be of suitable area to accept flux in both directions, so half domains aligned one way and vice versa?
Comment: Any induced secondary current must be set up in a direction to oppose the changing flux that created it - Lenz's law
Comment: Yes I understand Lenz's law, I was looking to understand practically which path the secondary flux takes. Looking at the BH curve more closely I think no extra flux is created by the secondary coil, as the field intensity is increased in the secondary this doesn't imply that flux has to flow, if an opposing (primary) field of equal intensity is cancelling it. That seems to make sense to me now. @Spehro
Answer: I'd like to try to summarize:
When the primary windings are energized (voltage applied), current begins to flow and will produces magnetizing flux in the core.  The flux induces a BEMF on the primary winding that opposes the applied voltage, which limits the current flow in the primary.  On the secondary side, the flux in the core will induce a voltage, about the same if N_turns is 1:1.  If the secondary circuit is completed (shorted or loaded) secondary current will flow.  This current will then produce flux that counters what... the initial magnetizing flux? Has to if there was no load current/flux in the primary to start with. So what else?
It seems that this is an ongoing iterative process. As the magnetizing flux is opposed by the secondary, the BEMF in the primary is reduced and the applied voltage can drive more current (load current) in the primary. This current then contributes about the same amount of flux that was previously countered by the secondary (i.e. flux in the core ends up about about the same, no net change).  On the secondary the load current continues to increase based on the load characteristics, assuming the secondary voltage is constant or increasing, and the iterative process continues: increased secondary current, counter secondary flux, reduced primary BEMF, increased primary current, increased primary "counter-counter" flux until the secondary side settles out to satisfy good ole Ohms law.  But only at an instant in time since the input is AC and it never really settles.  This is sort of what happens with levitating super conductors; things move, fields and currents are induced, and equal counter fields are produce instantaneously so it all balances out.
The primary and secondary fluxes except the for the initial magnetizing flux, which requires the core to link the flux with the windings, i.e., an air core will not work very well.

Flux in transformers


New sitemap submitted still large number of 404s showing

Question: One of the sites I work on had 262 404 errors in early December, I recreated the sitemap submitted and the 404s then were 130. Now I have again recreated and submitted the sitemap and the 404 count is 130. I am unable to understand why submitting a completely new sitemap and removing old ones is still causing 404s. Why are 404s showing?
Comment: Sitemaps are largely ignored. Check the links on your site carefully to make sure there are not errors. If all is clean, it is possible that links on other sites to your site are the problem. You can drill-down in Search Console to see. Otherwise, it can take some time. Also know that these are notices and my not disappear. Do not mark them as being fixed. Cheers!!
Answer: Are the URLs actually 404ing? If you copy the URL into your browser, are you given a 404 page, or the correct 200 page?
If they are 404ing, you will need to 301 redirect the pages in order to 'fix' the 404s, not just change your sitemap.
Once the pages are indexed, they may stay indexed for any length of time, regardless of what your sitemap says. Even if you remove them from the sitemap, the will still technically be 404s as the content is still not found.
If the URLs are NOT 404ing, then the most likely explanation is that Google (or whatever search engine) has not recrawled the sitemap/URLs. You can resubmit your sitemap in Search Console, and also submit your homepage to the index to ask Google to re-crawl it (https://www.google.com/webmasters/tools/submit-url) and its links.


Significance blessing for Moses like Aaron

Question: I've found no significance reward for Moses dedicated service, neither for his descendants unlike Aaron that got almost, if not all the blessings in Numbers 18:8-20. My question is, are there any significance reward given to him and his descendants?
Comment: Interesting question. This would involve what Moses _represents_ in scripture : what his office was and whether - or not - that office would continue in perpetuity ( as opposed to the priesthood).
Answer: Remember that Moses and Aaron were both Levites from the Kohathites (Ex 6:16,18, 20). So any of Moses' children would have also been Kohathites and had similar privileges but just not the priesthood.
Moses also had the singular privilege of witnessing God's glory (Ex 33:18-23). He also was the mediator of the Law covenant (Ex 24:3-8). He oversaw the building of the tabernacle of which the pattern was given to Moses by God himself (Ex chaps 25-29; Le chaps 8,9). And most significantly, Moses spoke to God "face to face" (Nu 12:6-8).
Comment: I think it is clear from scripture what you state in your second paragraph. But the question was about the reward to Moses and to his descendants, which you have not addressed.
Comment: You did a good job in corroborating the widely available blessing for all Levites, which doesn't give a distinction for Moses special blessing for service. I'll like to know if there's any. To this I'll say he's just a lump in the crowd of Levites who collects tithes from the Israelites. The whole best of things went to Aaron and his descendants, and nothing was ever mentioned of Moses or his descendants getting special benefit.


Why does ammeter or voltmeter measures RMS value

Question: When there's an alternative voltage, why does the voltmeter measures rms value instead of the value at that specific time?
Comment: I don't think your question is clear. For one thing, not all volt meters display RMS. They sample repeatedly and update the display each time they sample. What do you think they should do? Are you wishing for something with a button so you could push the button to tell the meter to capture the voltage at the moment you press the button, and display it until you clear it somehow? There are certainly times when that would be useful. You can do something similar with an oscilloscope if you put it in manual trigger mode.
Comment: @mkeith my teacher said that rms value is the value that you see in ammeter or voltmeter, so I was curious why does it show only the rms value. But now I got the answer thank you all
Answer: I'm assuming that you are asking about an old-fashioned moving-coil meter.
These meters measure AVERAGE value, not RMS.  An AC meter is calibrated to read RMS voltage with a sinusoidal waveform.
These meters can indicate the exact voltage at some particular point in time IF the waveform is changing so slowly that the meter needle can follow the waveform.  This is possible at frequencies significantly less than 1 Hz.
At higher frequencies, the mechanical inertia of the meter movement acts like a low-pass filter and the needle indicates the average value of the input.
Answer: If you are measuring a 10Khz signal, what value would you read ? What value would be useful to you ? It would be constantly changing. What good is a constantly changing value on an LCD  display especially if its changing so fast. A 10Khz signal has a period of 100 microseconds, so depending on the number of sample points taken, you are looking values changing much less than 100uS. This all assumes that the meter is even capable of sampling so fast.
A light bulb connected turns on and off at 50Hz to 60Hz depending on your region. Do you see if turn on and off ? You don't because our eyes can't detect that change - our eyes are too slow. 60Hz has a period of 16.67ms. Now imagine its changing less than 100uS.
RMS is a fixed value. Regardless of the constant changing values, the RMS value will be fixed for that particular peak or peak to peak voltage.
If you require to see the signal, then a oscilloscope would be better suited.
See comments for corrections about flicker and detectable flicker frequencies for eyes
Comment: Regarding what our eyes are capable off, they can very well see 50Hz and 60Hz (remember good old CRTs, you aimed for 75Hz at least?). The fact that you cannot see a light bulb flicker is because of the thermal mass of the light bulb, it never really turns off because it doesn't cool as fast.
Comment: @efox29 - sorry to pick a nit, but at least for incandescents, they don't turn on and off at line frequency. The filaments just don't turn on or off that quickly. Standard flourescents, on the other hand, do respond that quickly, and their flicker is part of the reason a lot of people don't like them. And a second nit: any flicker will occur at twice the line frequency, so it's 100 or 120 Hz.
Comment: I can't remember my CRT. It was such a long time ago :( However, I did NOT know about the flicker. Interesting stuff though. If I flicker an LED at 60Hz, I'll see the flicker ? I should try this!!
Comment: Try watching this (maybe turn your volume down first): [Light Bulb Turning Off (Slow Motion - High Speed)](https://www.youtube.com/watch?v=9HUrYoqxQpw) you can see the filament still glowing with the AC voltage applied before it is turned off completely.
Comment: @Arsenal that was pretty cool. Never knew. Good to know! Also found this http://www.digikey.ca/en/articles/techzone/2012/jul/characterizing-and-minimizing-led-flicker-in-lighting-applications
Comment: @WhatRoughBeast no need to apologize. I can learn and correct myself for future discusion. And ya thinking about it, it does make sense that it would flicker at twice the the line frequency (positive and negative cycles).
Answer: There are a variety of properties which tend to be related to RMS voltage.  For example, the amount of heat generated by a resistor which is fed by an AC voltage source will be equal to ...

the average of (voltage times current), which will in turn be equal to...
the average of (voltage squared divided by resistance), which will in turn be equal to...
the square of (square root of the average of (voltage squared)) divided by resistance, i.e.
the square of the RMS voltage, divided by the resistance.

Note that while higher quality meters will actually compute the RMS voltage, lower quality meters will actually measure something else (e.g. the peak voltage or the time-averaged rectified voltage) and multiply it by scaling factor.  For example, since the RMS voltage of a sine wave will be proportional to its peak voltage divided by sqrt(2), a meter that measures peak voltage would scale its readings by a factor of about 0.707.  Since average rectified voltage is about (2/pi) times peak voltage, a meter that measured average rectified voltage would scale by 1.11.  Such measurement techniques will work fine when measuring sinusoidal waveforms, but will yield inaccurate results when measuring anything else.
Answer: When measuring AC voltages or currents, the value displayed is calculated ('integrated') over some time, this is not an instantaneous measure (contrary to, for example, an oscilloscope)
The indicated measurement is not always the true RMS value, only instruments made for "true RMS" can measure the RMS value of any waveform, simpler ones gives a correct measurement only for sine waves.
The interest of RMS over peak or average measurements is that it indicates the energy, or power, of the signal.
Answer: Normal AC power goes through one full cycle (from 0 volts to maximum positive voltages, back to 0, then to max negative, and finally back to zero) 50 or 60 times a second.  A normal meter can't read and display voltages fast enough to follow the instantaneous voltage - and if the meter could, our eyes wouldn't be able to make any sense of the result.
The RMS voltage is the effective voltage of that continuously varying voltage, so it the value that is most often of interest to us.


How does the Earth remain in its shape?

Question: I know only stars do nuclear fusion to keeps its shape from gravity. Then what about the Earth? Earth doesn't do nuclear fusion. How does the Earth keep its shape even though the gravity keeps pushing Earth inward?
Comment: Do you mean why isn't the Earth compressed by its own weight?
Comment: Related. [Why are planets not crushed by gravity?](https://physics.stackexchange.com/q/287622/104696)
Answer: If there was only gravity, earth would indeed compress into a black hole. But don't forget about electromagnetism! It is the same reason you can not stick your hand through a table. The electron clouds from the atoms in your hand are repelled by the electrons from the atoms in the table.
For Earth this means, while gravity pulls inward, there is a force equilibrium due to the outward push from the electrons. You need a higher mass to overcome this. Once you reach a critical mass, a process called deleptonization happens. The electrons are "ejected" and you're left with a neutron star. Now, there's the strong force between atomic nuclei which balances the gravitational pull. Once there is enough mass so that even the strong force is too weak, your body will collapse into a black hole.
Answer: Stars are (mostly) in hydrostatic equilibrium: at each depth in the star the pressure gradient balances the gravity, preventing it from compressing the star. This happens because a combination of the equation of state (relating temperature, pressure and volume; see also polytropes) and that the fusion processes heat up as the star gets compressed. The polytrope for stars is typically of the form $\rho=K P^{n/(n+1)}$, where $\rho$ is the density and $P$ the pressure, with $n\approx 3$ for main sequence stars.
Planets are in hydrostatic equilibrium because their equation of state typically behaves like $\rho = c + K P^n$ with $n\approx 0.5$. The reason is that they are solid or liquid rather than gaseous (gas giants are obviously slightly different). Inter-molecular forces increase a lot when one tries to compress such matter, and hence the density does not increase that much: the matter is stiff. For heavy planets degeneracy pressure starts to matter: when squeezing matter together electrons resist it fiercely since they would be forced into the same quantum states.

How does the Earth remain in its shape?


Attaining a calm mind

Question: During the last 5 months I made observation regarding my inner mind process. The inner chatter which most people know during their day disappeared completely in my mind.
I practiced mindfullnes during my day and meditated as well. Is their a specific term in Buddhism which refers to achieving a quite or calm mind?
Answer: One could call it jhāna or dhyāna which is the meditation with a calm mind. You are on a great path. Perhaps you want to meditate on the heart sutra where it says:
"No suffering, no origination,
no stopping, no path, no cognition,
also no attainment with nothing to attain. "
The moment where you recognize a calm mind (the absence of something) as achievement, the ego crawls back up and claims having attained something. The true you is just about to get this ego to quite down. As you begin to research terms and more about having attained this great achievement you might create artificial distance again. Always remember that you are neither the mind nor the body.
Answer: A quitened or a calmed mind is an important and a dangerous milestone. It is important because it is a mark of your concentration that the mind's chatter has quitened down. It is dangerous because it is not the final stage- things change and the chatter may come up again and you may start despairing when that happens  and so generate more misery.
The term for it may be one of the four jhanas or the stage of rapture/bliss. They are all intermediary stages. But it would be better if you further read on these stages, since only you would know the precise details of your meditative progress.

Attaining a calm mind


Incremental file back up by date

Question: Is there any backup tool that supports partial back up by date? What I mean is that I have some small drives such as on a laptop that can't hold a full copy of all the files on an external 2TB drive. I want to keep the latest files, which are usually the ones I'm working with, on the laptop. But at the same time I want to be able to synchronize other drives with limited storage space. So each small drive should contain files that have been created or modified beyond a certain date, such as 3 months ago. Say I have 2 laptops and each has a different disk size. For the laptop with a smaller drive, I may only want files from the last month to be present. All files on both laptops should be backed up on the large external drive, along with all the other archived files that are greater than 3 months old. So the external drive should mirror both smaller drives and keep them in sync. I've tried using unison but it doesn't seem to support back up by date. Maybe rsync with a few shell scripts could work, but I want to check first if a solution exists before implementing a new one.
Comment: This seems very complicated/personalized. Everything you describe can be done with `bash` and `rsync`. If I were you I would combine http://webgnuru.com/linux/rsync_incremental.php ,  http://serverfault.com/questions/205251/rsync-only-files-created-or-modified-after-a-date-and-time and http://stackoverflow.com/questions/4259101/rsync-only-files-created-or-modified-after-a-date-and-time
Comment: I'm surprised it isn't a common use case. Perhaps I described it with too many concrete details. Basically what I want is a persisted storage that can be partially synchronised with other sources. `unison` has better algorithms for synchronizing, so maybe I can write a script to narrow down the target files by date.
Answer: I haven't used any dedicated programs for this, but it is quite easy to organize and fine tune with a combination of cron, bash, tar (incremental dumps) and/or rsync. In my mind, there are two optimal solutions, and I use both or one of them depending on the context. I think the first will be more appropriate for you, but I'll describe both here.
Incremental tar archives
The core of this solution is a script that might look something like this:
#!/bin/bash

# You will need to set the variables $EXCLUDE, $DATA and $BACKUPS
# as environment variables, in ~/.bashrc or somewhere.

OPTS="--create --no-check-device --bzip2 --verbose -X $EXCLUDE"
for d in `ls $DATA`; do
    SNAPSHOT=$BACKUPS/$d.snar
    if [ $1 == full ]; then
        echo "Archiving $d (full)..."
        rm -rvf $SNAPSHOT
        ARCHIVE=$DATA/$d.`date --iso-8601`.full.tar.bz2
        tar $OPTS --file=$ARCHIVE --listed-incremental=$SNAPSHOT $DATA/$d
    fi
    if [ $1 == increment ]; then
        echo "Archiving data/$d (increment)..."
        ARCHIVE=$DATA/$d.`date --iso-8601`.tar.bz2
        tar $OPTS --file=$ARCHIVE --listed-incremental=$SNAPSHOT $DATA/$d
    fi
done

This assumes there are subdirectories in $DATA and backups each one in a separate archive. If your setup is different, customize the script.
You can schedule the backup in your crontab like so:
# m  h  dom mon dow   command
  44 1  1   */2 *     ~/bin/backup_data full > ~/backups/data/logs/`date --iso-8601`.full.log 2>&1
  44 5  *   *   *     ~/bin/backup_data increment > ~/backups/data/logs/`date --iso-8601`.log 2>&1

As you can see, in this case a full backup is created once every two months, and incremental backups starting from that full dump are created every day. Problems with incremental archives in tar start when you lose one file or even change a timestamp. So, it is prudent to create a full dump once in a while.
As far as synchronizing between machines and removing old files, you should separate that task from the backing up itself, since it really is orthogonal. Of course, use rsync for synchronization, without the --delete option so that you don't lose any data on the large external drive. So your command for that might be:
rsync -av /backups/data /mnt/external

if the external drive is mounted on the laptop. Otherwise, you will need to do it over the network like so:
rsync -av /backups/data user@external:/backups/data

If you want to clean archives older than 90 days from your laptop, you can do so like this:
find /path/to/files -type f -mtime +90 -delete

Again, put these things in your crontab.
Incremental backups with rsync
You can use rsync alone to incrementally backup things. I especially like using timestamped snapshots and hardlinks for that, and it is just one command. Here is an example close to what I normally use:
rsync --verbose --progress --stats --human-readable --archive --link-dest=/backups/data/`date --iso-8601 -d "one day ago"` /data/ /backups/data/`date --iso-8601`/

which basically creates hard links to the snapshot from the previous day (the one given by --link-dest) for files that have not changed. If you will be running irregularly, you can use a symbolic link that points to the latest snapshot, and update that symlink after backup, like so:
rsync --verbose --progress --stats --human-readable --archive --link-dest=/backups/data/last /data/ /backups/data/`date --iso-8601`/ && rm -rvf /backups/data/last && ln -vs /backups/data/`date --iso-8601`/ /backups/data/last

On top of this, you will need to organize the synchronization with the external drive and delete old snapshots. This, generally, is done the same way as in the first solution I outlined above. However, when rsyncing snapshots between machines, make sure to use the -H options to preserve the hard links.
Summary
Compared to the solution using tar, the second one in my mind is somewhat simpler to manage and has all the files available at all times. Using archives, on the other hand, makes use of compression, uses fewer inodes, and has other pros on non-server machines.
Again, do all this in crontab whenever possible, so you don't have to remember about it. If you don't have the laptop turned on all the time, choose a time when it is often used, and perhaps do it several times a day so that at least some of the cron jobs start. Better yet, use something like anacron.
You can also run the backup script by hand , and fine-grain the dates in the filenames/directories if you want to do incrementals more than once each day. Obviously, you will need to play around with these solutions to make them fit your use case.
Update: a repository with an example script I use: https://github.com/langner/backup.sh/blob/master/backup.sh
Comment: I stopped there to keep the length reasonable. With this as a starting point, there are more detailed tutorials and writeups on the topic you can search for if such a scriptwise solution is what you want. Common utilities like `tar`, `rsync` and `cron` are very powerful yet widely under-appreciated. Reading their manual pages is often a fruitful experience.
Comment: Thanks for this thorough answer. I especially like all the practical examples from your own use cases.

Incremental file back up by date


k2: How to remove default term "Children Categories" and give it a different title

Question: Implemented k2 extension on client's website. Would like to know how to remove default term "Children Categories" and give it a different title (http://www.wilddusk.com/wild-india).
Answer: Dont change the orginal language files of an extensions. All your changes will be lost at the next update.
Instead use Language overrides
a tutorial how to use is there : http://www.inmotionhosting.com/support/edu/joomla-3/languages/overrides
Answer: It's in K2 language file (/language/en-GB/en-GB.com_k2.ini).
Search 'CHILDREN CATEGORIES' and change the text whatever you want.


How do I make a cut parallel to an edge?

Question: How do I make the cut in the picture parallel to the active edge? How do I also make sure the thickness of the cut of area is a certain value (in this case 3mm).
Answer: To get a precise value, you can use Bevel

Bevel the selected edge with 2 segments, Profile = 1
Adjust the thickness in milimeters
Delete > Dissolve the unnecessary edge
Comment: Thanks :D Realized this doesn't work in all situations though :( When other edges interferes with the Bevel this doesn't work. Still, it's a good trick to have :)

I really think they need to enable Axis snapping to edges rather than just X,Y,Z and rework the knife tool to be more inline with the other tools, but this works great for my case while I'm waiting for the Blender team to do their magic :)
Comment: Glad you found it useful :). You're right, it's a dirty workaround not suitable for many cases.


What kind of floor is this?

Question: I got different answers from different contractors and I am so confused now.
Some said this is hardwood, and some said this is bamboo.
If is it wood, is it possible to tell what kind of wood is this? Can you really tell by eye what kind of floor is this?
Comment: A person who works with wood a lot, or is in the flooring business, should be able to tell you what it is simply by looking (or at least have a good guess). The grain pattern is one of the most notable characteristics used to determine species. From my limited knowledge, based purely on the grain I'd say this is not Bamboo.
Comment: Looks like engineered maple.
Comment: @tester101, The grain pattern looks like a veneer, like what they put on plywood. Also, the pieces are really tight against each other, like some engineered products, and the edges look too sharp to be solid wood.  Could be wrong, so I didn't answer.
Comment: Definitely not bamboo. Could be some species of solid hardwood, some species of engineered hardwood, or laminate.
Comment: That is NOT bamboo. Doesn't really look like Oak, could possibly be Maple...
Comment: @Edwin What leads you to believe it's engineered?
Answer: Looking at different images may help you determine the species. Keep in mind I'm not a wood expert, and wood being a natural material will vary widely.
Oak
Oak tends to have a bold tight grain

Ash
Ash tends to have a bold semi-tight grain.

Hickory
Hickory tends to have a more subtle longer grain.

Maple
Maple tends to have a subtle semi-tight grain.

Bamboo
Bamboo tends to have a long straight tight grain.

The next question is to determine if it's solid, engineered, or locking. The best way to figure this out, is to look at the ends of a plank.
Solid
If it's solid, it will look like a solid block of wood.

Engineered
If it's engineered, it will look like the edge of a plywood sheet (a bunch of thin layers of wood).

Locking
Locking will tend to be thinner, look more like Medium-density fibreboard (MDF) or plywood from the side, and will have a funny looking tongue that locks with the adjacent plank.
Comment: Correct me if I'm wrong, but I think the easiest way to identify bamboo is to look for a somewhat regular pattern where the grain seems to be "broken up" at intervals of 8" or so.  The picture doesn't really show it, but all the samples of bamboo I've seen have such a pattern.
Comment: Don't know that much about bamboo, but I think the distance between "knots"  depends on each seasons growth. If the "knots" are too uniform, I would suspect it's a printed pattern on locking flooring. Part of the beauty of real wood, is the lack of uniformity in the grain.
Comment: If you look at the Wikipedia page on bamboo, you'll notice that the bamboo stems (also called culms) have ring-like structures around the perimeter.  It is those ring-like structures that create the pattern I was talking about.
Comment: I agree. But I think the distance between the rings depends on the growth pattern. I could be wrong, since I don't know much about bamboo.
Comment: I wouldn't expect the pattern to be *precisely* regular in natural bamboo, though I have no idea how much variation is normal.  My point is that that each bamboo floorboard will have multiple places along its length where the grain is broken up by the rings in a way which is totally unlike any kind of wood I've seen.
Answer: That is maple. Plain old, flat sawn rock maple. There's no way to tell from the pictures if its engineered or solid but if you knock on it the sound will tell you. Solid sounds very dull, like knocking on a sidewalk. Engineered hardwood, even if its installed very well, sounds a bit hollow. You might not notice it when you walk across the room but if you tap on it with your wedding ring you'll know. I might suggest not contracting with the guy that thought that was bamboo because apparently he doesn't know what either bamboo or maple looks like, which is not a great sign.
Comment: How do you know this person is married?
Answer: Flat sawn (note the cathedral pattern), but more than that? Meh. Likely maple, but there are a bunch of central / south american woods that are cheap and similar in appearance.
Definitely not bamboo, which is a monocot, and has a distinctive appearance.
Comment: Breaking out some biology! Nice work busting out 'monocot' on us!

What kind of floor is this?


Why I had lost my reputation while I do nothing and no one was removed?

Question: My reputation now is $1.083$ but i remember that in a several day ago my reputation is about $1.1\text{k}$
I didn't downvote any answers and i didn't receive any notification about someone downvote my answer, question or user was removed.
Answer: Make sure you're being shown removed posts
Answer: Your reputation still displays as 1.1k if you go to your profile page and look under "Communities", which appears to be where you got your original screenshot.  So all that's going on is that the site rounds 1,083 to 1.1k when displaying your reputation in certain contexts.
(The only such context I can find at the moment is in fact the "Communities" list on the profile page; in most contexts reputation scores are not rounded or otherwise abbreviated unless they are at least 10,000.)


What should I use to fill the gaps in tile before placing luxury vinyl planks over them?

Question: I'm installing luxury vinyl planks with an underlayment in my basement.  They will go over top of an existing tile floor.  I've heard mixed opinions on whether filling in the gaps in the tile is necessary, especially if you use an underlayment.  However, the gaps in this case are quite large - 0.75" wide and 0.1" deep, so I'd like to fill them in.  I'm hearing from a few sources that a cementitious product would be best to use like a self-leveling cement, thin set mortar, or grout.  However, I'm a little skeptical of how well those will bond to the old grout below and I'm concerned about it cracking over time since it'll only be 0.1" thick, but perhaps those concerns are unfounded.  The other products I've considered are silicone or a construction adhesive, which would likely be a lot more expensive given the amount that I would need but I think they'd bond better and hold up better over time.  Can anyone provide any insight?
Comment: Is the bottom of the gaps clean cement/grout, or full of dirt?
Comment: "Embossing leveler" is usually the correct product. It's designed for exactly this.
Answer: "Embossing leveler" is usually the correct product. It's designed for exactly this. Read some labels and choose one that claims to work on ceramic.
Answer: This may be a little unconventional, but I believe it will work will. Since this is just to fill in gaps and then will be covered with underlayment and planks, I would use polymeric sand. Pour and brush it in all the gaps, then wet it down with water. Let it set up and finish up the rest of your project.
Comment: I would not use anything that's going to disintegrate into dust and grit with movement.


What is the purpose of this site if it is not to ask for legal advice?

Question: Law Stack Exchange does not allow questions that ask for, or answers that provide, specific legal advice. What is the purpose of a legal question-and-answer site that does not allow legal advice?
Comment: It sounds like you're pretty  disappointed that you didn't get to buy a thousand dollar scope for eight bucks. Can I suggest that perhaps that was not actually an injustice, and that getting all shirty with everyone who tells you so is not going to help you get over said disappointment?
Comment: I'm voting to close this question because it is not a question, but a complaint about the site
Comment: If you already know you are right, what do you need this site for anyway?
Comment: You may wish to try [r/legaladvice](https://www.reddit.com/r/legaladvice/s/mZKW9TwCZ1), which does not share this site's aversion to dispensing legal advice.
Comment: Hi, welcome to the site. Discussion about the site itself belongs on Meta.
Comment: Certainly anyone asking questions in either forum should not rely on the answers they get being any more valuable than what they paid for them.
Comment: @bdb484: I have heard several critiques of r/legaladvice (supposedly they have a habit of giving out bad advice). I must say that I find it hard to believe that any licensed attorney is going to hang out there and possibly accidentally create an attorney-client relationship, even with their rather flimsy "informational purposes only" disclaimer.
Comment: I think that risk is wildly overestimated. Licensed attorneys certainly hang out both here and there, just as legal hobbyists hang out both here and there, resulting in both good and bad advice both here and there.
Answer: The purpose of this site is to answer questions about what the law says, not how it applies to individual circumstances. Hypothetical scenarios, or, in some cases, real situations, can be used as examples, but if a question asks how the law applies to a particular scenario in which you are involved, it is generally off-topic. This serves two purposes: to protect askers from bad advice, and to protect answerers from liability.
First, we do not allow specific legal advice to protect the interests of those asking questions. Most of us are not lawyers, so we do not necessarily have enough legal knowledge to give reliable advice. Even those of us who are attorneys are not your lawyer; they do not know enough about your situation to give good advice. You would be putting yourself at risk of legal issues if someone here gave you specific advice and you followed it; our policy is intended to protect you from that.
Also, we prohibit legal advice to protect answerers from liability. While it is unlikely, it is not entirely impossible that giving legal advice on this site could be considered practice of law; this could expose answerers who are not lawyers to liability for for unlicensed practice of law (UPL).
You are welcome to ask questions about laws that are relevant to you, however, as long as you do not ask for specific advice. "I did XYZ. Did I violate law ABC?" is off-topic, whereas "What does this clause in law ABC prohibit?" is acceptable, even if you intend to use the answer to help determine whether your actions violated that law. You still should not rely on what users here write; however, we will often give references to sources that are authoritative, such as statutes and court rulings.


Best way to deploy a projector screen from the bottom?

Question: I want to design a system for an electronically deployable projector screen, where when not in use the screen is stored at the bottom and there are no structural elements sticking up significantly, but once the screen is deployed it is pulled up from the bottom. I am currently stuck on how to ensure the system is stable once deployed, as I have investigated both scissor lift mechanisms and telescoping poles, but I don't see how to ensure stability in the extended state.
Comment: How much stability do you need? When a screen is deployed from above, they are usually just weighted sails and will shift in the wind from someone walking by. Also how big/tall of a screen are we talking here? are we looking at something in the 72" range or are we talking something like IMAX? Now they also have inflatable screen for beach and park shows too that would deploy from the bottom upward
Answer: A pull cord.
Or fixed threaded rods and rotating nuts that then drive the rods up taking the screen with them. That way the rods will only be "visible" when extended, but covers can also be arranged.
Comment: Hey Downvoter, where is your better answer?


What is the behavior of __faststorefence?

Question: In regards to this question, I'm interested only in x86 and x86-64.

For MSVC 2005, the documentation for __faststorefence says: "Guarantees that every preceding store is globally visible before any subsequent store."

For MSVC 2008 and 2010, it changed to: "Guarantees that every previous memory reference, including both load and store memory references, is globally visible before any subsequent memory reference."

The way the latter is written, it implies in my opinion that this would also block the CPU's reordering of loads before older stores.  This is different from the first definition, which implies that the intrinsic is only to deal with blocking or the reordering of non-temporal stores with older stores (the only other reordering x86(-64) does).
However, then the documentation appears to contradict itself: "On the x64 platform, this routine generates an instruction that is a faster store fence than the sfence instruction. Use this intrinsic instead of _mm_sfence on the x64 platform."

This implies that it still has sfence-like functionality, and thus loads can still be reordered with older stores.  So which is it?  Can someone clear up my confusion?

PS: looking for a GCC version of this function, I came across long local; __asm__ __volatile__("lock; orl $0, %0;" : : "m"(local)); but I think it's from 32-bit code; what would be the 64-bit analog?
Comment: Can you possibly give a better question title than `__faststorefence`?
Comment: @JaredFarrish: Better late than never? :)
Answer: The GCC version you quote is equivalent to the code that MSVC generates. It relies on the fact that the x86/x86-64 processor architecture docs specify that loads and stores are not reordered with a LOCKed instruction.
I am not clear whether this applies to non-temporal stores, since in general the memory model restrictions do not apply to those instructions.
Comment: This intrinsic is only available in MSVC on x86-64; I don't know why. I would expect it to have the same cost on x86-64 as on x86 with respect to `MFENCE`, since the architecture is essentially the same. If you ignore non-temporal stores then this is a sufficient fence for sequential consistency.
Comment: Hi Anthony, thanks for the answer.  What remains unclear is why the documentation for this intrinsic specifies that it is faster on the x64 platform, rather than on both 32 and 64. Does it mean to imply that a locked instruction is cheaper than an mfence only on x86-64?  Additionally, if it prevents both loads and stores from being reordered, is this a sufficient fence for sequential consistency (excluding the case of non-temporal stores)?


Regarding satellites and their 'safety'

Question: Are satellites nowadays designed so that if one fails or its orbit degrades the scientists involved can send it various codes so that it will starts to 'beak-up' into smaller and smaller parts where when the parts are small enough they burn up in the atmosphere. So this automated 'forced breaking up' until its parts are small enough,could be a safety feature for satellites. Is this feasible?
Comment: Would [space.se] be a better home for this question?
Answer: No - satellites typically do not contain self-destruct devices. Malfunctions would be a) expensive and b) create lots of space junk.
What they do when a satellite is expected to enter is they will start it tumbling - the rotation helps the thing break up due to the re-entry forces hitting different parts.
If the satellite is defunct or has no maneuvering fuel remaining, it just burns up as-is hopefully not hitting anything important.
Comment: I don't mean a self- destruct device. I meant a set of special encrypted codes that could be sent to the satellite ordering it to disassemble into many smaller sections.
Comment: That would, for all intents and purposes, qualify as a 'self-destruct device' - it is now destroyed, and it required no outside assistance. It doesn't have to be explosives, that's just a common method because it's cheap, fast and effective.
Comment: But if the satellite was caused by remote control to break up into so many pieces so it would all disintegrate we would never hear about a satellite falling to Earth on the News (and that it might be a threat to someone). The fact we have heard about 2 or 3 satellites falling to the Earth recently means they do not use this method I describe.
Comment: Could a failing satellite be made to 'disassemble' ( by remote control ) into many little pieces that would definately burn up in the atmosphere?

Regarding satellites and their 'safety'


resource drbd not migrating to other node manually

Question: I have two nodes corosync and pacemaker
The funds are vip, apache, and drbd.
All work. But if I migrate the drbd resource to another node it goes to all other resources and nothing is migrated. If I restart or standby or put anything not migrate. However the resource is started on the source node or whether this fixed in the same nó.mas have not configurate force to rotate in the same node. And in the logs I see many blocked messages when trying to migrate, this may be because of the network. Or it could be a conf corosync or something on the network that blocks multicast.
Thanks to those who help.
Answer: If you use DRBD alone (without pacemaker), can you switch the Master ?
drbd rosource is master/slave type, is NOT active/standby type.
If you use pcs as the setting tool, setting example is follows:
# pcs resource create drbd ocf:linbit:drbd \
    drbd_resource="r0" \
    op monitor interval="10s" role="Master" timeout="20s" \
    op monitor interval="20s" role="Slave" timeout="20s" \
    op start interval="0" timeout="60s" \
    op stop interval="0" timeout="60s" \
    op promote interval="0" timeout="60s" \
    --master meta master-max=1 master-node-max=1 clone-max=2 clone-node-max=1 notify=true

Please disclosure your software version, configurations and logs.


What is "worried" part of speech in "I'm worried about something"

Question: First, I think the part of speech is"verb",but it is passive.then, I think it is"noun",but the sentence can't use "worried",should use "worry".
Answer: In this case, worried is an adjective (in other words anxious or troubled, see: https://en.oxforddictionaries.com/definition/worried).
It cannot be verb in passive, because it wouldn't make sense - it is the person (I) who is worried about something/someone else, so the pronoun I is an agent of the verb.
You can use worry as a verb in passive, for example, "a lamb was worried by a wolf.", as someone suggested here. However, the meaning of worry in this context is different, it means hunted, chased, attacked. There are more very different meanings of worry as a verb (see: https://en.oxforddictionaries.com/definition/worry)
I don't think you can use worry about in passive with the meaning to feel anxious or troubled. It is not possible to find these examples even in the dictionaries. I thought about an example: "He is constantly worried about by his parents." (active voice: His parents are constantly worried about him)  but it doesn't sound natural.


How to estimate an influence of electromagnetic devices on each other?

Question: I have a few electomagnetic devices: one is a gps antenna, next is a receiver (950 Mhz), third is a radio transmitter that radiates with 2.41 GHz and the last is a height sensor that uses 24 Ghz signals for measurements. All they are placed quite close - about tens of centimeters from each other. They are going to be set on a drone. How can I reduce the possible technical troubles?
Comment: Test. Screen between devices internal to the drone. Spread antennas out. However, this type of setup is not unusual for drones or balloons launched by high school science classes.
Comment: What type of screen do you mean? One with a special metal film patterns which reduce the EM radiation with help of diffraction? I think a simple metal sheet will have no effect as is polarised
Comment: Just solid copper foil will be enough.
Answer: If you were designing for collocation you'd design filters to isolate somewhat the harmonics or spectral sidelobes in band to others, and if it was serious you'd test on some aircraft model. This sounds like a home project.
It sounds like you just bought the equipment, you have to live with whatever comes out. You could try filtering some between the antennas and the RF equipment. In spreading the antennas you might find some scalloping of the patterns and if you move them some it can improve. The 24 GHz is probably the safest, far enough from the others, but it depends on some possible offending LO harmonics or others leaking out. Gps and the 2.4 GHz transmitter coexist in all cell phones, though 2.4 in cells and wifi's are sharing freq by sometimes using their own times lot. Don't know if your 2.4 radio is a continuous signal, or time slotted, and the biggest concern is if it's high power. If just wifi powers you might be ok.
Unless you want to spend some time calculating possible harmonics etc power levels test with the radio transmitter separated from the other antennas first, move around the most likely offenders and sensitive receivers.
Comment: Comprehensive answer. Many features noticed. Thanks


How can I use a dll compiled with .Net Framework 4.0in a Windows Metro App

Question: I am new to Windows 8 app development and professional C# dev. I have run into a problem where a client wants me to interface with a printer (DYMO 450 Turbo) and the SDK only comes with a dll that has been compiled using .net 4.0 . The samples show referencing the dll from the app which I can not do because the app is written in Javascript using WinJS. The metro apps use NETCore where the dll uses NETFramework. My best solution so far is to write the code to interface with the printer as a server in .NET 4.0 that listens for requests sent from Javascript over XMLHttpRequest. My gut tells me there HAS to be a better way, but either Ihavn't figured it out or maybe I just don't know enough to figure it out yet. Any help would be appreciated. Thanks in advance.
Comment: Possibly helpful: http://stackoverflow.com/questions/9650654/how-do-you-reference-a-c-sharp-class-library-from-a-win8-javascript-metro-applic
Answer: You cannot use a standard .NET 4.0 assembly in a Windows Store app. You can only use WinRT components. That said, your existing component may or may not be easy to convert to a WinRT componenet. If you simply include the project for your .NET 4.0 component and then change the Output Type (under the project properties) to Windows Runtime Component, you can have a look at all of the compiler errors that are thrown and get an idea of how big of a chore it's going to be to convert it. This article will let you know what the restrictions are on WinRT components.
Answer: Suggest add a project using project template c# - windows runtime component, to build a winrt component in c# that can use your sdk dll. winrt component can expose a wrapped impl. winrt component can be referenced in the winjs project.
I have used this for simple utils functions but not for integrating with third party sdk. suggest you give it a shot.


Is SSH security necessary on an internal network?

Question: I am running a VM on a spare laptop we have in the office, and have set it up for SSH access from my workstation. Currently I am using user/password authentication, but I would like to remove the password with the NOPASSWD flag to make it easier to run sudo commands and for my coworkers to use it. My office network doesn't allow SSH access from outside the local network. Is this a bad idea?
Comment: Not that this is what you were directly suggesting, but the notion that a local network can be inherently trusted is quickly becoming defunct. SSH keys make sense if you wish to remove password access otherwise my personal position is to consider all environments as hostile
Answer: In general any authentication with empty password is a bad idea.

My office network doesn't allow SSH access from outside the local network.

SSH is not the only way an attacker might gain access to the internal network. A password means enhanced security and security means that when a system fails it fails gracefully or at least as gracefully as possible. If the VM is not designed to be a honeypot then in any other case a password is necessary.

I would like to remove the password with the NOPASSWD flag to make it easier to run sudo commands and for my coworkers to use it.

Then consider using ssh-keys for authentication, it's considered more secure way to login and you don't have to type the password every time.
Answer: TLDR - It could be a bad idea if you think you have something that you don't want others to see / modify / delete.
Long Answer: -
Depends on the risk. Let's assess it through a QnA session.

What do you do with the VM?
a. Why do other people need access to it?
b. Does it contain any data that others need?
c. What type of data is that?
d. Is it ok if un-identified people change / see / delete it?
Is the VM / or the host machine connected to internet?
a. If the answer to the above question is 'Yes', is it possible to connect back to your workstation from the VM? How do you connect? Is the password blank in this case as well?
Do you have a habit of using blank passwords elsewhere on the network?

Answer to these questions will help you understand the risks to your data because of this weak control. If there is very little risk, go ahead and do it.
We as a security people cry every time we see a weak / blank password because we know that this might set a precedent and people will start using blank passwords everywhere without context (what do you mean "blank passwords are bad!"? Don't show me that face! the security guy told us that it is alright in that case1. Now you can't be a hypocrite and tell me it can't be done in this case2. Rules must be same for every person / case!). This puts us in a bad light.
In reality, context is everything and the security controls should match the criticality and sensitivity of the data being protected. You won't protect useless data / machines with 2FA!


Can I change jobs after 4 months as a Blue Card holder in germany?

Question: I have received a better job offer than the one I'm currently in and I was wondering if it's possible to change jobs?
Answer: It is possible for a Blue card holder to change jobs in Germany freely if you have been there for 2 years.
As you are under the 2 years then you must get permission from your local Ausländerbehörde (ABH) / Immigration office.  You need to make an appointment and take along the contract offer for the new role.
So long as the new role is in the same area and pays the same or more, and everything is OK with the new employer then it should not be an issue.  But you must go through this process to ensure that you will be accepted.
Here are for example details from the Berlin branch.  But you would have to find your local one where you live.
https://service.berlin.de/dienstleistung/326856/standort/121885/en/