How can I fix a stripped hole in an aluminum piece?

Question: I have a tripod head that is made of aluminum. In the head there is a small hole that houses a small screw that secures a quick-release plate. After some time the hole stripped and the screw no longer holds. I suspect that there is no simple way to fix it, but in case there is, I wanted to see what you guys think!
Comment: Use a wider screw?
Comment: Yes, that's an obvious solution, but that's giving up
Comment: I sure hope that screw is an easily available size and thread.
Comment: Force it at an angle. With metal, this is sometimes an option, when using a bigger screw is not ([example](http://diy.stackexchange.com/a/38469/19565)). I have also fixed tripods by threading zip ties through the hole because the bolts were cruddy and kept coming undone.
Comment: Kludgery: Find a screw of the same diameter/thread count. Lightly oil the screw. Slather the hole and the screw with epoxy, and screw it into place. Do NOT screw the head up tight to the screw hole. Once the epoxy has set, apply  a vice grip to the screw head, and rotate it out. That should give you a new set of threads that will last a while. You'll probably have to remove excess epoxy from both sides of the screw hole. A razor blade commonly works well for that.
Comment: I would go with heli-coil as some answers below describe but I have also seen JB weld used to fill a hole then retapped to the original size.
Answer: Depends on the size of the screw and how much material you have to work with. If this is a clamp bolt, cheap tripods use screws going directly into the casting. Quality units either use a captured nut, Nyloc nut and eccentric toggle or a tee-head bolt with threaded knob.
If this is a plate with a fair amount of metal surrounding the hole and it's deep enough, I would get a Heli-Coil kit. With this kit, you drill the hole oversize with the supplied drill, use the supplied tap and then the tool to install the helical insert.

Another thread repair is Keensert which, if you have yet more metal because it's a larger device, a locking insert that doesn't require delicate use of Red Loctite to keep it in place.

All the above probably are not recommended in the case that the threaded hole is in a casting that doesn't have spare metal, so the previous recommendations of drilling oversize and tapping for a larger bolt might be the best. Which might not be a solution if the threads are common photography standard attachments between devices.
Comment: That's a great answer. I knew there were other options than just using a larger screw. Plus, I really want to keep the screw that came with the head - it matches and is more ergonomic than an alternative. I think I will try Heli-Coil.
Comment: I would use heli-coil also the new threads are stronger than the original because the insert is larger and now steel. When I put helicoils in metal I will usually use some thread locker on the outside of the threads prior to inserting this really helps with thin plates or no bottom to the hole so the insert stays put after cured.
Answer: The two options are:
Re-Thread the hole with a bigger screw (dont force a bigger screw into a damaged site).
Use a Reaming/Tap tool to increase the thread size to your desired size... (also, in order to use the heli-coil) you will need to ream/tap the hole.

Helicoil - places an insert into the site to reduce the thread size once again. you will need to match the size and thread pattern with your current screw.  so i suggest taking the screw with as a sample.

Comment: Note: with a helicoil the size of the hole is increased but the thread pitch stays the same. This means when fitting heli-coils you need to use the heli-coil tap.
Answer: Aluminum is a soft metal and screws stripping is very common.  Since I don't know of any way to make a striped hole smaller, short of welding in new metal then drilling and tapping, the only solution is to make the screw larger.  If you have a #6 screw now, use a #8 now. Simply replace the original with the next larger gauge.  BTW, that is not giving up, it's fixing the problem in an economical way.
Answer: If the screw has stripped out the treads in the hole it will go into, there is little choice. The hole is now too large, for a screw that is now effectively too small. You cannot simply "fix" this without some work.
You can use a larger screw, thus one with a larger diameter. This will require you to re-thread the hole for the new screw diameter. You might have to first pre-drill the hold to enlarge it more, depending on the tap you will use.
You could fill the hole completely, using an aluminum "welding" material. In theory, that material can now be re-drilled and then tapped for the screw thread you have. Be careful though to not overheat the aluminum body.
In either case, it will take some effort to repair.
Answer: Nutsert is a thread repair system that restores or installs threads in just about any material and any thickness. The threads are steel so they last through repeated use. They are available at "Fastenal" dealers/stores. There are two types flanged for thin materials and flangeless for thicker materials. The flanged units are similar to a large rivet with threads where the usual pin would be. While a rivet expands by pulling the pin into the rivethead, nutserts use a threaded insert that expands the insert and is then removed leaving the threads intact. I wouldn't be surprised if your local dealer would demonstrate how they work on your tripod.
Comment: There is also the idea of riveting the hole with a threaded insert (http://www.hansonrivet.com/w65.htm)
Comment: It appears to be the shared technology but with different names
Answer: I had the same issue...as a girl I took clear nail polish and slathered it around the screw. I waited a few min then attempted to screw it back in. It still wasn't 'solid' but I turned the fan on low and that seems to have dried and tightened the Polish and it now works just fine
Answer: You might try this:
http://www.amazon.com/Loctite-Form-A-Thread-repair-kit-grey/dp/B000WSEUII
There are also other brands of epoxy thread repair kits.
For a range of solutions see: http://www.repairengineering.com/thread-repair.html
Comment: Link only answers are discouraged. Please edit your answer to include a description of the fix.
Answer: use a tiny bit of solder and soldering iron, if the stripped threads is just a small amount of play just use super glue or super glue gel. this will tighened up your threads for the screw to grab, easy fix


Are trekking poles which fold small any more likely to be accepted in hand luggage in British airports (and elsewhere)?

Question: Trekking poles are normally not allowed in hand luggage at British airports. Is this the case specifically for trekking poles which are folded into multiple sections (three or more)? I am also interested in people's experiences at other strict airports (for example Dublin).
Comment: I just had a look and saw one answer on there about taking tents with metal tent pegs through security in UK airports and it seemed convincing enough. However on the whole I am not really familiar with Travel Stack, so I am happy with whatever users with higher rep than me want to do with my question.
Answer: The primary question the airport security should be thinking about is "can someone effectively hurt or incapacitate other people with it, if it ends up in malicious hands?"
If it does its job reasonably well as a trekking pole, then it probably also works as a melee weapon, which makes it a problem for airport security. If it is foldable, it will be more easily concealable, which I'd guess would make it less acceptable, not more.
Comment: Regardless of the pole structure the tips are functionally crude weapons.  I've drawn blood by getting a pole tangled in my legs.
Answer: According to the UK government, hiking poles are not allowed in hand luggage in the UK. There is no stated exception for poles which fold up. In practice, you may get lucky and encounter a screener who does not know about this restriction, but it would be a big risk to rely on that.
For what it's worth, the US has the same restriction.
Comment: I find this quite interesting, as I know senior citizens who use hiking staffs in lieu of a traditional cane.


Conversion of the nonlinear schrodinger equation from $\partial_zE$ to $\partial_tE$

Question: While reading some papers about the nonlinear schrodinger equation (NLS) I noticed that the authors sometimes use (for the linear case)
$$\partial_zE=\frac{i}{2k_0}\nabla^2E$$
and sometimes
$$\partial_tE=\frac{i}{2k_0}\nabla^2E$$
I assume it is possible to rewrite the first equation as
$$\partial_zE=\frac{\partial t}{\partial z}\frac{\partial E}{\partial t}$$
and by calculating $\partial_zt$ I just get a prefactor for the conversion.
Is that correct?
Assumed it is, I would calculate $\partial_zt$ as $\frac{n}{c}$, with $n$ the refractive index, and $c$ the speed of light in vacuum, resulting in a constant prefactor (assuming $n$ is constant, too).
Comment: A choice of an evolutional variable ($t$ or $z$) depends, mainly, on a way to form initial (and boundary) conditions  (IC). If at time $t = 0$, we create some field distribution in the system, and then observe the dynamics at late times, then, clearly, the evolutional variable is $t$. Another way to generate a wave is to excite a medium at point $z=0$. For example, we input light to a medium at $z = 0$ ($z$ is the longitudinal direction). A device at $z=0$ measures the field for all times $t$. This is our IC, and we observe the field evolution on $z$, while $t$ is the "spatial" variable.
Answer: When we use the NLS for  quantum systems such as  the Gross-Pitaevskii equation then $t$ is time. When we use the NLS equation for paraxial non-linear optics then $z$ is   the distance down the optical axis or the distance down the fibre. It's  mathematically the same equation but different applications, so different notation. There is no changing $z$ to $t$ by the chain rule.
Suppose, for example, that the dispersive properties of an optical
fibre are such that the associated  wavenumber for
frequencies near $\omega_0$ can be expanded as
$$
k= \Delta k+ k_0 + \beta_1 (\omega-\omega_0)+ \frac 12
\beta_2(\omega-\omega_0)^2+\cdots.
$$
Here, $\beta_1$ is the reciprocal of the group velocity, and
$\beta_2$ is a parameter called the  group velocity
dispersion (GVD). The term $\Delta k$ parameterizes the
change in refractive index due to non-linear effects. It is
proportional to the mean-square of the electric field. Let us write the electric field as
$$
E(x,t) = A(x,t) e^{ik_0z -\omega_0t},
$$
where $A(x,t)$ is a slowly varying envelope
function. When  we transform from Fourier variables
to space and  time we have
$$
(\omega-\omega_0) \to i\frac{\partial}{\partial t},\quad
(k-k_0) \to -i
\frac{\partial}{\partial z},
$$
and so the equation determining  $A$ becomes
$$
 -i\frac{\partial A }{\partial z}= i\beta_1 \frac{\partial A
 }{\partial t}
 -\frac {\beta_2}{2}\frac{\partial^2 A
 }{\partial t^2}+ \Delta k A.
$$
If we set $\Delta k= \gamma |A^2|$, where $\gamma$ is
usually positive, we have
$$
i\left(\frac{\partial A }{\partial z}+\beta_1 \frac{\partial A
 }{\partial t}\right)=  \frac {\beta_2}{2}\frac{\partial^2 A
 }{\partial t^2}- \gamma|A|^2 A.
$$
We may get rid of the first-order time derivative by
transforming  to a frame moving at the group velocity. We do
this  by
setting
$$
\tau= t-\beta_1z,\\
\zeta = z
$$
and using  the chain rule.
The equation for $A$  ends up being
$$
i\frac{\partial A }{\partial \zeta}= \frac {\beta_2}{2}\frac{\partial^2 A
 }{\partial \tau^2}- \gamma|A|^2 A.
$$
This looks like the usual  non-linear Schroedinger equation,
but with the role of space  and
time
interchanged! Also, the  coefficient of the second derivative has
the wrong sign!  To make it coincide with
the  Schoedinger equation with solitons we must
have $\beta_2<0$. When this
condition holds, we are said to be in the
anomalous dispersion regime ---  although this is rather a
misnomer since it is the group refractive index, $N_g=
c/v_{\rm group}$,  that is
decreasing with frequency, not the ordinary refractive index.
For pure SiO$_2$ glass,
$\beta_2$ is negative for
wavelengths greater than $1.27\, \mu{\rm m}$. We therefore have anomalous
dispersion  in the technologically important region near
$1.55\, \mu{\rm m}$, where the glass is most transparent.
In the anomalous dispersion regime we have solitons with
$$
A(\zeta,\tau)=e^{i\alpha|\beta_2|\zeta/2}
\sqrt{\frac{\beta_2\alpha}{\gamma}}{\rm
sech\,}\sqrt{\alpha}(\tau),
$$
leading to
$$
E(z,t) =
\sqrt{\frac{\beta_2\alpha}{\gamma}}{\rm
sech\,}\sqrt{\alpha}(t-\beta_1
z)e^{i\alpha|\beta_2|z/2}e^{ik_0z-i\omega_0t}.
$$
This equation describes   a pulse propagating at $\beta_1^{-1}$,
which is the group velocity.
Comment: Assumed I want to couple the equation written using $\partial_z$, i.e. a pulse propagating along a fibre, with another equation using $\partial_t$ (describing the internal processes in the whole fibre), how would I do that in this case (which was the motivation for my question), i.e. bring both equations into the same form?
Comment: Ill add a note on this to my answer.


Why did these stalagmite-like structures form on the side of my candle?

Question: Two slender, "stalagmite-like" structures -- separated from the main mass of melted
now solidified wax -- have formed on the side of my candle, rising considerably above, and below, the level at which the candle is burning.  Explanations, theories, speculations, regarding what process or processes could have caused them to form would be much appreciated. [One speculation: rather than having been propelled upward, they were once drips that, relatively distant from the flame, did not subsequently melt as the candle burned down (?)]
Comment: I believe your hypothesis is correct with them being further from the center and early drips as what I have observed candles. Usually there is a curved surface of these drips in the inner side that is clearly observable. Perhaps the manner it re-solidified on the existing candle made it more resilient on melting...
Answer: Yes, you have it. As the candle melts the drips fall down the side and cool. As the candle melts further they are not only further from center, they are separate from the original and they bend further away from the flame allowing them to not melt with the original candle. Types of wax will determine how much this happens as different mixes of waxes will evaporate at their own rate. This may also account for why your candle did this. If one type of wax melts at a lower temp, it will leave behind a harder wax to drip down the side of the candle. Further increasing its ability to stay up.
I wonder more about the different effects on air quality, as we know parafin waxes are not good for us, I would like to know how beeswax effects this... but that's another topic ...


Need help wrapping my object

Question: So I've been working on a project and I'm trying to wrap my object with a camo color but for some reason the camo wrap is looks glitchy. Here's a photo, can someone tell me what I've done wrong.
Comment: Change tris to quads and then unwrap.
Answer: I'm guessing it's because of wrong or no UV mapping.
try to select the parts where you want your texture to be in edit mode, then press "U" and "Smart UV Project".
Otherwise you need to place some seams around the edges like this:

In edit mode select the edges you want and press "U" and "mark seam" after you done with placeing your seams select everything and "U" - "unwrap".
In the UV-editor it should look like this and your texture will be fine.

Need help wrapping my object


Transfer School on Resume

Question: I attended college for my bachelor's degree from 2010 to 2013. After my freshman year I transferred to a different school, which I graduated from at the end of 2013. The problem is, my resume listed the years that I attended school (2010-2013), but only listed the school I graduated from, even though I only attended that one from 2011 to 2013. Is this in error, or is only mentioning the school I actually graduated from okay? Thanks.
Answer: 10 years later, a prospective employer doesn't care too much about other schools, only that you graduated from one of them. All you need on your resume is something similar to the following;
Education: BSc Underwater Basketweaving from Oxford University, 2013
Comment: Nah. What they care about, if anything, is what school you graduated from, what you studied there, and what your GPA was -- but realistically, after a decade in the workforce, they are ***MUCH* more interested in where you worked and what you did at work; that's a far better indication of your current skill level. Academics at this point are mostly interesting for "Oh, they've had some exposure to X; that might be useful."
Comment: I was just asking because I have applied to jobs with that resume, and am waiting to hear back from them. (I have interviewed for one, but the resume question didn't come up). I was wondering if having to explain about the transfer would count as having had wrong information on my application and affect my chances of getting said job.
Comment: I would agree that outside of a specific situation, where the hiring official (or someone with hiring power) went to your first school, nobody would care about you attending a college you didn't actually graduate and receive a degree from.
Answer: Unless you're in a regulated profession (illegal to practice without a degree), employers don't normally look into the degree. Even if they do, you were correct in naming the diploma-granting school and skipping wherever your first year was.
This is for industry jobs. On an academic CV, you would list every school and specific years spent there.
Answer: You can put whatever you like on your resume
Putting the degree-granting school would be normal.  Don't put years attended, just the year the degree was granted.  In your case, it's fine, certainly not a problem if the company looks into it. I would expect your transcript from the finishing school to include the initial school transferred credits as well.
If the application process asks for all education institutions, you would be expected to put all schools attended.

Transfer School on Resume


Laplace transform on thermodynamics equation

Question: I'm trying to create a simple model of a single-flash geothermal plant which consist of 3 main parts (flash-separator, turbine, and condenser). Is there any way to create a transfer function using Laplace Transform (s-domain) of each parts based on the thermodynamics equation?
Comment: It depends on what you mean by "thermodynamics."  Thermodynamics usually refers to equilibrium conditions.  However, if the material- and energy balances are changing slowly enough and you are willing to include transport processes like heat transfer in the condenser into what you call thermodynamics, then the answer is yes.
Comment: given that I want to plot the turbine response and find the efficiency, from most of literature I read, they mainly use enthalpy and mass flow equation. The problem is I dont get how to transform the enthalpy and mass flow equation into a differential equation then use Laplace transform to find their transfer function in s-domain
Comment: Normally, you are concerned with the steady-state operation of such systems, especially when doing process design.  Is there a reason that you need to worry about the dynamic response (e.g., process control design)?
Answer: The first thing you need to do is write down the time-dependent mass- and energy balance equations for the turbine (using the open system control volume version of the 1st law of thermodynamics).  Then you express each the variables as the sum of a steady state part and a transient part.  Then you solve for the steady state part.  Then you linearize the time-dependent equations with respect to the perturbations about the steady state.  Then you can use the Laplace transform for the linearized perturbations.


What is the need for /boot and /tmp partitions in ubuntu

Question: What is the reason of /boot and /tmp partitions in Ubuntu ?
Comment: @siraj - I have merge all your identical questions into this one.  Please do not post similar questions.  The way we work is constantly editing your question with any further information until you have an answer that you can accept (clicking this tick button next to the answer).  Thanks!
Comment: You keep posting the same question. You need to follow the default partitioning setup, or read the [official documentation on partitioning](https://help.ubuntu.com/community/HowtoPartition). Posting the same question over and over isn't a good idea.
Comment: Nothing goes wrong if you do not have a /boot partition :)
Comment: /boot does not bother much. Even only giving swap areas(even not required today for better systems) and assigning only the root( / ) partition would get me my linux running. They why is it required to mention such long list of partitons?
Comment: Please clarify your question...
Comment: Curosity killed the cats but /boot is only meant to hold you boot up files. You want this if you do not want to mess up with dual boot issues and Grub and MBR corrupt problems. Otherwise, it is only need the "/" partition to be mentioned. :)
Comment: Have you solved your question?
Answer: There isn't any technical problem with not assigning a separate /boot partition. The following link may help you to understand why making an external boot partition is preferable. But as they say, it is only preferred, not NECESSARY to allocate a separate boot partition. I myself have used only the / (root) and swap area to partition my drive and I've installed Ubuntu without any issues.
https://help.ubuntu.com/community/CreateBootPartitionAfterInstall
Comment: make it an answer if it does :)
Comment: Its upto Siraj to make it an answer as he is the one who asked the question.
Comment: yeah, a hint for him ;)
Answer: Please take a terminal and type in "man hier". :)
Comment: +1, nice hint. Granted, not what the OP asked, but still, `man hier` is useful knowledge, and the question was poorly written anyway
Answer: I think perhaps there is a misunderstanding as to what partitioning does.
If you let the Ubuntu installer do the partitioning there will only be two partitions
~19 GB for '/'
~ 1 GB for swap

So what happened to /boot, /home, and /tmp?? Doesn't Ubuntu need those to function correctly?
Yes, it does. But it does not need them as partitions. It needs folders (aka "directories") with those names. And in the standard Ubuntu install, the filesystem in the partition for '/' will have directories with those names. So everything will function correctly.
If there is nothing on the hard disk when you install Ubuntu, then a few windows into the install you will get a window like the image below asking what type of an install you want to do.
My advice is that unless you have a some specific reason to split your installation into separate partitions, do not do it. Just use the entry which is selected in the example. Having one root ('/') partition which contains all of your data is usually the most efficient way to use the space on a hard drive.
Answer: Mounting /boot on another partition is useful if your root partition uses a file system that grub2 (the bootloader) cannot understand ; you can place enough components in /boot to mount the root file system. This is not the case in a typical Ubuntu installation, as grub2 understands the default recommended file system (ext4), and all the other choices available. Another situation where a separate /boot is useful is where you have particularly stringent security needs - you can avoid mounting the /boot partition unless you need to update the components within, which means that rootkits will find it harder to compromise the bootloader. Again, this is not a typical need and is a rare choice.
/tmp on a separate partition is useful if you have applications that need to heavily use temporary files and you would like to use a block device that is very fast. Alternately, if you are booting from an SSD, and would like to reduce the amount of wear on your SSD, you can mount /tmp on another drive, or in RAM. Again, this is an uncommon configuration.
Comment: mounting `/tmp` is not that uncommon... it is actually a *very* nice thing to do even if you don't have an SSD. I set up mine once in `/etc/fstab`, capped at 4GB (but it only uses what it needs, so very little actual RAM is allocated), and lived happy everafter
Comment: I've upvoted this for adding in the technical reasoning, even though I don't necessarily agree (as @MestreLion indicates) that mounting /tmp really is uncommon.  Perhaps uncommon for default desktop Ubuntu installations, but I'd agree that it's been quite common historically for Linux/Unix.
Answer: Yeah, use the entire disk if you don't understand the whole partitioning thing.  Besides, it is silly to separate the disk by limited sizes; when it get fulls then you have to increase size....
Just go with the full disk unless you have a special technical need for making separate partitions....
Answer: The only problem I see is
/tmp  5 Gb
/boot 5 Gb

Why? Both are not needed. /tmp is a temporary directory so it is not likely to hold alot of files. And those files tend to get deleted fairly quickly aswell. So I would discard that one. Same goes for boot. When you have more than 1 OS and want to save space you can share /boot with all those OSes but there is not really a need for it. It can be handy but in this case I would go without and focus on the low disc space.
My root at this moment is 5.9 Gb large so I would increase / a bit so you do not run into a disc full notice.
/ = 10 GB
swap = 2 GB
/home = 8 GB (my files music, videos etc are saved in my pen drive or cd)

sounds better to me.
If you use your pen drive for storage I would even suggest you should focus on the low disc space and even forget about a /home partition:
swap 2 Gb
remainder as /

Comment: nothing! Most people do not bother with a /boot partition. I added in some more details.
Comment: Nothing goes wrong if you do not mention /boot. Just mention the root partions. It is for programming purpose, that temp partiition is sometime required to be mentioned externally, but **ONLY ROOT PARTITION MATTERS**
Comment: What happend doing partition whitout /boot
Answer: Well, there are many guides out there for the partitioning in ubuntu, I would prefer to partiton it in this way:
First, Just follow this link and let me know if you are getting stuck to any point out there. Now I also want to know wether or not you are doing the partition in a preinstalled windows hard disk or a fresj installation over entire disk?
EDIT: Well, I would first recommend you to use gparted to create and manage partition. Just create four 5 gb primary partitions and format it with ext4 file system in it. Then just create a extended file system on one of the four primary partition because they won't allow you to create more than 4 primary partitions on the disk. Now on the extended one, create a 3 gb and a 2 gb logical paritions. Now you just got the partitions in the following way:
partition 1    size: 5 Gb   type: Primary
Partition 2    size: 5 Gb   type: Primary
Partition 3    size: 5 Gb   type: Primary
Partition 4    size: 5 Gb   type: Extended
**Partition 4** -->
     Partition 5     SIZE: 3 GB    Logical
     Partition 6     SIZE: 2 Gb    Logical

Now just format and assign each of the partition as their respective choice and use it in either way you want. Linux gives you the better way to do it threw Gparted.
Comment: No reason really to have this as a second answer -- why not combine?


OAuth and OauthLite diffrence

Question: I am a beginner to OAuth - so i want to know what is the difference between Oauth and Oauth   Lite
Answer: OAuth is an authorization protocol.
OAuth::Lite is a perl library implementing the OAuth 1.0 protocol. If you develop a web service that should provide OAuth authorization or if you develop a perl application that should connect to some OAuth provider, you can use this library.
For OAuth 2.0 there's respectively the OAuth::Lite2 library.

OAuth and OauthLite diffrence


nginx or apache for comet based PHP application?

Question: I am building a PHP comet based application. Which web server should I use in the backend? Apache / nginx (this is what most forums say) or something else would be better?
Answer: I would recommend not using PHP at all for this purpose. PHP is synchronous, therefore every open comet connection will block a PHP process (or Apache process if mod_php). Here an asynchronous language shall be used, JavaScript for example. (See Node.JS. If you are using comet for a chat, have a look at node_chat)
Answer: I'm building a comet app too, i guess apache + php (a classic) and APE with comet server beside may be a great solution
ape-project.org/


How do you as product owner decide that a product is feasible?

Question: You as a product owner just got an idea from a stakeholder and need to decide if it's feasible? What steps should you follow in order to make sure the product is not going to be a total fail?
Note: Stakeholder really believes in the idea but you are responsible for selling the idea to the development team with right arguments for success
Comment: Assumming the Stakeholder convinced you, what makes you think the developers won't be convinced? Why can't you use the same arguments & data?
Comment: me as a PO I need to believe in it that is feasible in order to go to the team. What stepts should I follow?
Comment: What steps you should follow so *you* are convinced? I don't know, wouldn't that be up to *you* to determine?
Comment: Are you asking how you determine the MVP, market fit, or the practical requirements and consequences of the technical implementation? These are very different questions.
Answer: This is a really good question and one that doesn't get asked enough!
Some things you can do to gain confidence in the feasibility of an idea:

Build a business case for the idea (testing likely value versus likely cost)
Build a prototype or a mock up that allows you to gauge customer response
Build a minimum viable product (MVP) - something that is just functional enough for you to gain valuable feedback

It is also important to run the idea by the development team to check the technical feasibility of the idea.
Answer:
How do you as product owner decide that a product is feasible?

Ideally, you should "determine", not "decide". If you have an idea or you have identified a need that a product can meet, then you can do a Product Feasibility Study/Analysis and try to gather some data for various KPIs you might be interested in (these will vary depending on what you are interested in).
The data you collect will help you validate some of the assumptions you may have, and stop the project if something seems amiss. But even if the data is good, nothing is a guarantee for success; you will find out when you build it and release it (one recent example comes to mind: CNN+).

Stakeholder really believes in the idea but you are responsible for selling the idea to the development team with right arguments for success

You use the results from the previous feasibility analysis.


Writing a Python wrapper for difficult C header file using Cython

Question: A while back I wrote an thin wrapper around a commercial DAQ library
using ctypes.  Since then I've come across Cython and wanted to give
it a go, thinking it might make it better/cleaner all around than what
I had before.  Most of the Cython documentation makes sense, and I've
found most of what I know but the library I'm wrapping is highly
windows specific and does things a little different than standard C/C+
+ code, at least as far as I can tell.
Here's a couple of snippets from the header file, that I'm not exactly
sure how to wrap.

<code>#ifndef DAQ_H
#define DAQ_H

#ifdef   __cplusplus
extern "C" {
#endif

#if !defined(_DAQAPI32_)
  #define  DAQAPI   __declspec(dllimport)
#else
  #define  DAQAPI
#endif
</code>

From what I gather, I probably can ignore most of this in my cython
definition?  I've tried compiling C code with gcc, but it throws errors at every function definition.  With ctypes I accessed the library directly, and did not use the header file at all.

<code>/* Handle Type Definition */
typedef  INT   DaqHandleT;

/* Initialization and Locking Prototypes */
DAQAPI DaqHandleT WINAPI   daqOpen(LPSTR daqName);
DAQAPI DaqError WINAPI     daqClose(DaqHandleT handle);
DAQAPI DaqError WINAPI     daqOnline(DaqHandleT handle, PBOOL online);

/* Error Handler Type Definitions */
typedef VOID CALLBACK      DaqErrorHandlerFT(DaqHandleT handle,
DaqError errCode);
typedef DaqErrorHandlerFT  *DaqErrorHandlerFPT;

/* Error Handler Function Prototypes */
DAQAPI DaqError WINAPI  daqSetDefaultErrorHandler(DaqErrorHandlerFPT
handler);
DAQAPI DaqError WINAPI  daqSetErrorHandler(DaqHandleT handle,
DaqErrorHandlerFPT handler);
DAQAPI DaqError WINAPI  daqProcessError(DaqHandleT handle, DaqError
errCode);
DAQAPI DaqError WINAPI  daqGetLastError(DaqHandleT handle, DaqError
*errCode);
DAQAPI VOID CALLBACK    daqDefaultErrorHandler(DaqHandleT handle,
DaqError errCode);
DAQAPI DaqError WINAPI  daqFormatError(DaqError errorNum, PCHAR msg);
</code>

This is basically how most functions are declared and operate.  They
only return error codes, all important information to get out of it is
done through pointers.  I couldn't find anything in the documentation
on how to work with pointers for return types, I probably didn't look
hard enough.
Can anyone point me in the right direction for wrapping these sorts of
functions?
Things like DaqError are actually enums declared in the header file,
they go abit enum crazy in this library, some 1500 lines of it.
Thanks for any help,
Answer: Create a cython typedef with the return type. In this way cython will use the same Macros of original library.
<code>cdef extern from "header.h":

    ctypedef void * win_api_t "DAQAPI DaqHandleT WINAPI"
    win_api_t daqOpen( char* )

cpdef pyDaqOpen( pystr ):
    daqOpen(pystr)
</code>


Is there a specific word for fertile hybrids?

Question: The way "species" has always been described to me is that a species is different if the two animals cannot have fertile offspring, with the caveat that language is imprecise and sometimes different species can produce fertile hybrids. For example, "pizzly/grolar" bears, which are grizzly/polar bear hybrids produce fertile offspring. Another example is coywolves, which are wolf coyote hybrids. So, I was wondering if there is a specific name for fertile hybrids. The Wikipedia page on Hybrids doesn't specifically talk about fertile hybrids as a group. To be clear, to me, "fertile hybrids" is a sufficient descriptor. I just wanted to know if there was a more scientific term that is used in place of "fertile hybrids." My guess is that there is not, because I think I would have come across it by now, but I just wanted to be sure. Thanks.
Comment: The definition you're using for species there is called the "Biological Species Concept". It has a lot of problems.
Comment: In animals it is simpler, but in plants fertile hybrids are extremely common in certain families (e.g., Rosaceae) and even hybridogenous apomyctic lineages are often sexually fertile to a certain degree and give birth to new hybridogenous types that cause extremely complicated taxonomy in brambles, dandelions and similar.
Comment: "Admixed individual"? there are a variety of archaic and rather nasty words that mean more or less this, but as a society we have thankfully moved away from terms like "bastard"; "mongrel" is equally nasty when referring to people, but seems to still be standard for e.g. dogs.
Comment: Not that an exhaustive list is possible, but the hybridisation of neanderthals & homo sapiens is of particular interest, & undergone recent dynamic change in understanding. & the ape chromosome fusion that seems to have initiated the speciation of hominids, is an interesting example of a highly unlikely set of chance circumstances, leading to a significant biological change - a punctuation in equilibrium, rather than steady mutation.
Answer: I'm not aware of a single word term in use, "fertile hybrid" seems like a reasonable descriptor. Something like 4000 hits on Google Scholar so it appears it's definitely used, hybrid fertility matches about 3000. In cases where the hybridization is quite well known to be fertile, I'd expect people to drop "fertile" and just speak of hybrids, especially among plants (which may or may not be designated the same species; species are just labels and can be messy).
Another relevant term is introgression, which occurs when hybrids breed with one of the parent species and therefore has the ultimate effect of transferring genes from one species to another. Describing introgression as occurring also may clarify a bit what sort of hybrid fertility you're talking about, because it may be that hybrids are only fertile with one of the parent species, or either parent species but not another hybrid.
Comment: Another term related to introgression are [hybrid swarms](https://en.wikipedia.org/wiki/Hybrid_swarm). Without introgression we can get [hybrid speciation](https://en.wikipedia.org/wiki/Hybrid_speciation).
Answer: Genetically viable?

Genetic viability is the ability of the genes present to allow a cell, organism or population to survive and reproduce. The term is generally used to mean the chance or ability of a population to avoid the problems of inbreeding. Less commonly genetic viability can also be used in respect to a single cell or on an individual level.


"Do you want [article] chocolate?"

Question: If I have a white chocolate like this on a table. I am sitting at the table and I want to ask my son, who is near me. Whether he wants [article] chocolate or not?
Which article is correct?
Answer: Do you want...
some chocolate? (unspecified less than all quantity)
a chocolate? (one piece)
a piece of chocolate?
this piece of chocolate?
this chocolate? (could be all/some/one)
Comment: And, of course, if there is one chocolate sitting on the table, staring my son in the face, I say, "Would you like the chocolate?"
Comment: A good coffee or good cofffee?
Answer: Chocolate (and white chocolate) is usually a mass noun, therefore it does not usually work with a. This is the same for other mass nouns such as coffee, beer.
However, if you are talking about a serving of chocolate/coffee/beer, you can use a:

Would you like a white chocolate?

as you can say

Would you like a coffee/beer?

When referring to the single piece on the table, you can also use the:

Would you like the white chocolate?

This can refer to the specific piece on the table. However, in other contexts, it can also refer to the substance white chocolate in general:

Do you want the white chocolate or the dark chocolate?

Note that the usage of the indirect article does not work for all mass nouns. We (at least, I) would not say

??Would you like a cake?

It would have to be:

Would you like a piece of cake?
Comment: 'Cake', like just about any noun, can be used as either a mass noun or a count noun. You can count cakes. But you can also count pieces or slices of cakes. We  say don't usually say *how many cakes did you eat?* but *how much cake did you eat?* But we say *How many cakes did you bake?* So it's both mass and count.
Comment: But we do say "let's bake a cake"..

"Do you want [article] chocolate?"


Can we book the train ticket separately (via perurail.com) and then expect tour guides to walk us through Machhu Pichhu, upon our arrival?

Question: We are looking to travel to Macchu Picchu around late November, by train. Can we book tickets separately via www.perurail.com and then avail of tour operators to walk us through the ruins?
Answer: The train takes you to Aguas Calientes town, which is at the bottom of the hill on which Machu Picchu sits.  From Aguas Calientes, you will need to get hold of:

A bus ticket from Aguas Calientes to Machu Picchu (you can walk, but it's a fair distance and uphill all the way).
An entrance ticket to Machu Picchu.
A guide - apparently now mandatory.

Per this guide, it's possible to get the guide reasonably easily when you get to the site entrance.  Per the same site and this one, you can get bus tickets and entrance tickets in advance - the entrance you can do online but the bus tickets may have to wait until you arrive in Cusco or Aguas Calientes.
Taking the train to Aguas Calientes and then trying to book a tour there will probably be probably not much simpler than just sorting it out yourself.  Most people will have either booked a tour in Cusco or will do the whole thing independently.  My (2007) Lonely Planet does not list any tour operators based in Aguas Calientes.
One of the advantages of getting a tour is Cusco is the fact that they mostly
put you on the train at Ollantaytambo, not Cusco.  This is significantly quicker (the switchbacks on the railway line outside Cusco are slow) and the rail service from Ollantaytambo is much more frequent.
Comment: Besides, Ollantaytambo is worth a visit. [Especially in June](https://www.youtube.com/watch?v=s8cKFpvZ1-E&t=204s) ;-)


How to visualize Nerve of stars of all vertices of a simplicial complex?

Question: I came across a theorem which states that a simplicial complex is a geometric realization of the nerve of the stars of its vertices. Here, we consider open stars (set of open simplices of which the vertex is a face).
I feel that the collection of stars of all the vertices of the complex will give the complex itself, and the complex is then trivially the geometric realization of the nerve of itself.
Could someone help me with visualizing the collection of stars of all the vertices of a simplicial complex?
Thanks
Answer: A face of the nerve of the covering of open stars is (by definition) precisely a non-empty finite set of vertices, whose open stars intersect non-trivially.
That is $(v_1v_2\cdots v_r)$ is a face of the nerve of the stars if and only if there is some point in the interior of a simplex, whose vertices include $v_1,v_2,\cdots,v_r$.  This happens if and only if $(v_1v_2\cdots v_r)$ is a simplex in the original simplicial complex.
That is you end up with the same simplicial complex that you started with, so of course they have the same geometric realisation.
Comment: Okay, so that reassures my visualization that the nerve of the vertex stars gives the same (abstract) simplicial complex.. right?
Comment: Yes absolutely.
Comment: Okay, thanks a lot


Does Amazon RDS support other storage types than EBS?

Question: In the RDS FAQ it says, "Amazon RDS uses EBS volumes for database and log storage". Is there any way to get RDS to store its data on another kind of storage? I'm asking because EBS has a reputation for being kind of slow.
Answer: It doesn't make much sense to use DB with ephemeral storage as losing your instance will mean losing your data. Therefore, using EBS with its better durability is preferred.
You can use Provisioned IOPS for your EBS and with a combination of RAID0 on multiple EBS with P-IOPS on "EBS Optimized" instances you can get up to 10,000 IOPS which is rather enough for most DB applications. See more about Provisioned IOPS in RDS here: http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Overview.ProvisionedIOPS.html
See how to improved the performance of EBS here: http://docs.amazonwebservices.com/AWSEC2/latest/UserGuide/EBSPerformance.html


HTTP request header missing "cookie" from prod server, but includes from local environment

Question: I have a web app that uses PHP session cookies. I have this app running on a cloud LAMP server and on my desktop with MAMP. I'm providing access to this app via an iframe on another website with a different domain. The app works fine on FF and Safari, but I'm getting an issue on chrome. If I set the iframe to point to my local MAMP environment, the iframe receives "cookie" in http request header, and works fine, but if I set it to my prod server, the request header is missing "cookie." Please help me fix this.
Answer: When you are running it from your production server you have a 3rd party cookie and I'm guessing you would have the same issue on IE.
You need a P3P policy in place:
http://www.w3.org/P3P/usep3p.html
Google found a way to cheat so check this out, it may help:
http://blogs.msdn.com/b/ie/archive/2012/02/20/google-bypassing-user-privacy-settings.aspx
Comment: Also suggest reading about same origin policy as relates to iFrames.  https://developer.mozilla.org/en-US/docs/HTML/Element/iframe


Limit size of WAL files for PostgreSQL database

Question: I'm using AWS RDS PostgreSQL 13 database in a master-slave configuration using logical replication with pglogical extension.
Recently, one of the application migrations has updated the schema of the master database, which in turn severed the replication process. No problems here, this is pretty much expected. However, after the replication stopped, the database has started to consume enormous amount of disk space:

In just one day it consumed around 17 GB of the free disk space and caused the entire server to fail (all disk space was used). What makes it weird is that entire database is only ~150 MB in size and has a very low number of write requests.
What strategy should I use to prevent such misbehavior from happening in the future? What would be the recommended approach to limit the amount of disk space used for replication? I don't want the master server to fail in any circumstances (however, I'm willing to "sacrifice" the replica if the need arises).
Answer: This is what max_slot_wal_keep_size was implemented for in PostgreSQL v13.  It sacrifices the replica when it demands too much WAL be retained on the master.  I have never used it on RDS, but I do see it is available for users to set via the RDS control panel, so presumably it works.


How to update only a single vector layer in QGIS map canvas?

Question: I want to update a single vector layer as I am working on 8 vector layers and they are getting fast data from serial port so for updating I use mapCanvas().refresh() which refresh all the layer and I have almost 20 static S57 layer so the refresh takes a long time.
Answer: Not sure if there is a direct way at this date, but my guess there isn't. But this might help you:
http://osgeo-org.1803224.n2.nabble.com/refresh-one-layer-td4427445.html

It's kind of possible. From 1.4 release there's support for caching of
  rendered layers (turned off by default). You can turn it on in options
  dialog. Then always make sure to erase cache for the layer that has
  been changed (layer.setCacheImage(None)). It will get rendered again,
  while the rest of the layers should stay untouched (their cache image
  will be displayed).
Comment: no thats not working
Comment: That's strange, for me it is working. But I don't change extents or do any other modifications to other layers
for example this fucntion:

mainLayer = iface.activeLayer()
mainLayer.invertSelection()
iface.mapCanvas().refresh()

was very long with no cache and very quick with it.
Comment: >kindly tell me the procedure I m using QGIS 1.6.

I will comment it here. Firstly use 1.7. Go to Settings > Options>select Rendering>Use render caching where possible to speed up redraws. Restart Qgis (probably not needed, but whatever, will not hurt anybody). Now if you make changes to one layer only, qgis should leave the rest as they are. However if you zoom in/out/do other modifications for all layers, it will redraw all of them (tested by me).
Comment: kindly tell me the procedure I m using QGIS 1.6


Are there complexity requirements on potential hosts to be susceptible to parasites?

Question: Are there lower bounds to complexity for hosts and how are these described or modeled? In other words, one would expect an organism to have a certain amount of "surplus tissue" in order for parasites to be able to feed on it, at least without killing the host too soon for the parasites to thrive.  For example, humans have surplus blood (we can draw a lot of blood and survive), making it possible to live with a few leeches, ticks, etc. Is this supposition really true? That is, do we know that "very simple" organisms cannot have parasites? If so, how do we characterize what is "too simple to be a host" and does it have anything to do with having "surplus tissue"? (I assume "surplus" is not the term used in parasitology because I haven't seen it in the books...)
Comment: yes it most at least have cells otherwise it does not qualify as a host.
Answer: "Complexity" is a difficult term to operate with in biology; most people that use it don't have an idea of how they'd like to operationally define it, and without an operational definition it isn't meaningful.
Phages are effectively parasites of bacteria - one could bicker that a virus can't be a parasite because it's not "alive", but I think this is just a semantic argument about what it means to be alive, and many of the definitions that exclude viruses are problematic because they those same terms exclude animal parasites.
Not all parasites are of the "feed on the host just a little bit" variety, either. Parasitoid wasps, for example, typically consume the entire target host, sometimes paralyzing it at the same time an egg is laid. Cordyceps is another fun group of (mostly) parasites, whose targets include other fungi and insects.
The only limit seems to be that the host must somehow be of use to the parasite. It must also be complex enough to be considered a living organism in its own right: you can't have a parasite of something that's already dead, for example, since that has a different meaning. I think these meanings are rather tautological, rather than interesting, though, so I'd answer your title question to say "no, not in any meaningful, non-tautological way".
Comment: @Antoshka I don't think you'll be able to do anything mathematical here in order to develop any "rule", just to look at examples, and biology is pretty good at coming up with exceptions to any rule you think you found. It's certainly not true that parasites of the type you describe only feed on "surplus" tissue: tick infestations can be fatal to deer, weakening them to the point they cannot recover.
Comment: Thank you this is very interesting! I guess I asked the  question a bit wrong: I meant specifically hosts that are multicell organisms and specifically parasites that feed on a host for an extended period (as opposed to consuming it or killing it entirely). In these restricted senses, one would expect (although I am asking because I'm not sure) that the host must have "surplus tissue" to be able to yield to the parasite without dying. I guess I am interested in this from an evolutionary perspective: do we see the entry of parasites as correlated to the development of "surplus tissue"?


Used wrong two letter country code for xkblayout

Question: I did something very stupid. I typed the wrong two letter code when I tried to change my keyboard layout. Seems this code is not used, since I'm just typing squares afterwards... Any advices to get my settings back (default - whatever just let me type again).
Comment: Search for the appropriate config file, SSH into the Pi and make the necessary changes to the file. Failing that  backup any important data and re-flash the SD card.
Answer: Ah found a solution. Get access via ssh! Thank you all nevertheless :)


Find subgraphs that can only be reached by two nodes

Question: I want to find subgraphs in a graph that are only connected to the rest of the graph by two nodes; for example, node A is connected to the rest of the graph, as well as node F, but nodes B-E are only connected to each other and A and F (don't have to be fully connected). Is there a name for this? And is there an algorithm for finding such subgraphs? The distance of A and F is defined by their shortest path: for example, if d=4, I would want to find all subgraphs where the shortest path between A-like and F-like nodes is at most 4.
Comment: Welcome to COMPUTER **SCIENCE** @SE. If "the naming" is important to you, consider tagging [tag:terminology]. (*induced components*?)
Answer: I don't know if there's a name for such subgraphs, but here's something to get you started.
If you require the subgraphs to be connected
A polytime algorithm for $G=(V,E)$ would be: for every possible unordered pair $(A,F)\in \binom{V}{2}$ consider the connected components of the graph induced by $V\smallsetminus\{A,F\}$. Then consider the classes which contain at least a neighbour of $A$ and one of $F$ (this step is required if the original graph was not connected). Then for each subgraph you found you can "add $A$ and $F$ back in" and look for their distance in the graph.
Let's sketch correctness (only the step about the subgraphs we are looking for being the connected components needs to be verified).

All components are solutions: by construction they only share links with themselves and A and F, and are connected.
All solutions are components: they are connected and only connect to the rest of the graph through A and F.

I am guessing you can do much better in runtime, but your problem seems to be in $P$ at least.
If you don't
You need to also consider combinations of the subgraphs found above, but in terms of the minimum distance it doesn't change much.


Why am I getting a "failed to create pid file...Permission Denied" error?

Question: If a program requires write permission how should I set it with chown? Specifically, what would program foo's permissions be to solve this error?
failed to create pid file '/var/run/bar.pid': Permission denied

Answer: If you have a program foo trying to create/write to a file, the permissions of the foo binary don't matter, but the user it's running as makes all the difference.
In this case, foo is trying to write to /var/run, which is owned by root and only writable by root.
So you would have to run the program as sudo foo for it to create that PID file. Please consider the security implications of allowing a program to run as root before you do it...
Comment: if the permission on the binaries are something: rw-r-r then would the program be executable given that i am running the program as root i.e allowing to create a process id under /var/run ?
Comment: @Ankit: if a binary has no executable permissions at all it won't "run"; but anything you do run as root will be able to create a pid under `/var/run`
Comment: Alternatively, write the pid file elsewhere (many applications let you specify the path to the pid file).
Answer: What I did is simply add the creation of a folder just before the start-stop-deamon is executed. This works because the script is generally executed as root during start up. It just creates the folder in /var/run and changes the owner immediately, so a PID can be written.
In the example below, I check for the existence of the subfolder of /var/run where i put the PIDs as the current run user, in this case user 'pi' (since I am on a raspberry).
Also check this link since it was very educational to me: Python script to run as service, however, it did not cover the problem discussed here.
Example portion of my shell script:
# The process ID of the script when it runs is stored here:
PIDFILE=/var/run/power/$DAEMON_NAME.pid

do_start () {
    log_daemon_msg "Starting system $DAEMON_NAME daemon"
    if [ ! -d /var/run/power ]; then
        mkdir /var/run/power/
        chown pi:pi /var/run/power/
    fi
    start-stop-daemon --start --background --pidfile $PIDFILE --make-pidfile --user $DAEMON_USER --chdir $DIR --startas $DAEMON -- $DAEMON_OPTS
    log_end_msg $?
}

Comment: Got a version of this for systemd?
Answer: General approach: determine the user and group of the process trying to access the file. This is often found in the configuration of the software (such as webservers/mailservers/...), but if the software is already running use this:
ps aux

Look for the process you want to configure access rights for. The first column tells you under which username it's running.
groups <username>

This will tell you to which groups the user belongs.
Change the owner or group of the file to match the service.
Note 1: As the question points out that the file is in /var/run/ I'm assuming only one process needs access, if this is not true, you shouldn't change owner or group, but you might consider adding the process' user to the group or creating a new group for this file/folder.
Note 2: Funny things can happen with apparmor, which is a security system: it can prevent processes from writing to files and folders to which they have (on filesystem level) all necessary rights. With aa-status you can see whether a specific rule for your service is active.


Raster to Vector: Displaying classes in Vector Layer - GRASS GIS

Question: I use Maximum Likelihood classification to classify Landsat image into two landuse classes - one of my interest and rest including all others. Inorder to assess the accuracy I export it in vector format using r.to.vect with feature type as area. But I find no option to export it in such a way that I can differentiate between two classes. Is there any way to do that?
Answer: Would it be an option to use r.reclass to assign for example 1 to areas of interest and 0 to others. Then use r.to.vect with the -v flag.
Answer: Doing that, you should have a new vector layer with an attribute containing the values. You then use v.colors to specify the desired color for a given value attribute.
See the exemple at the bottom of the given page to understand how the rules mechanism works.


Why is there a current in R1 in this MOSFET circuit? Isn't it supposed to be zero?

Question: When I run a circuit simulation, I get a current in R1 which is around 16 mA. Isn't the current supposed to be zero, since this is an N-Channel EMOSFET, which I also think is symmetrical?
Comment: I remember dealing with a 4-terminal FET long ago when they were not really popular. The 4th terminal was the "body" of the transistor and this made the whole thing symmetrical. Most FETs have the body connected to the source and symmetrical they are not.
Answer: 16 mA is about right.  Since you have a positive supply at the source, you are forward biasing the body diode of the FET, and you have 6 V - 0.7 V across 330 ohms, or 16.1 mA.
You can see this more clearly if you look at the device symbol with the body diode shown explicitly (from here):

Just about all commercially available power MOSFETs have a body diode as part of the structure, so you have to keep that in mind when applying them.  If you need to block conduction in both directions one option is to use back-to-back FETs.
Comment: I mean, it's not like you can manufacture a MOSFET without the body diode :) you can leave the body floating and hook it to a pin though.
Comment: @VladimirCravero True- Years ago we made 4-terminal FETs like that with the body connected to a separate pin at the request of a particular customer.  There wasn't much of a market for them though, so they were never offered as a catalog part.  Don't know if anyone is making power MOSFETs like that these days.
Answer: Take a look at the datasheet for a 2N7000.  Look at the symbol for the device on page 1, see the diode from source to drain?  This is the body diode, and it is present in most discrete MOSFETs.  On page 4, you'll see the "Drain-Source Diode Characteristics" and a typical Vf of 0.88V.  (6V-0.88V)/330 Ohms is 16mA.
Answer: You are forward biasing the bulk/body diode inside the MOSFET and, that will cause about 5 volts to appear across R1: -

Image from here.

Body diode characteristic
Comment: Given the substrate-to-channel junction symbol (triangle), isn't the body diode symbol somewhat redundant? I know of course that everyone draws these body diodes explicitly, so it's not a comment on your use of a common symbol, but rather on whether I understand the symbology correctly.
Comment: @Kubahasn'tforgottenMonica a bit like how many loops you show on an inductor symbol or how many squiggles on some resistor symbols.
Answer: The diagrams with piggy-back diodes always amused me; does no one teach kids anymore that symbology means anything?  Well, apparently not.  Matter of fact, I don't think anyone told me when I was in school, I had to figure it out myself.  Well, go figure, then.
So, on that note, it's as simple as this:
Arrows denote P-N junctions, pointing in the direction of conventional current flow.
BJTs show the emitter; the collector can be drawn the same way (as a "double emitter" symbol), but one is usually left off to denote the asymmetrical junction, suggesting the direction of intended flow.  (Transistors haven't been symmetrical since the germanium days!*)
*With some exceptions, or near exceptions.  But by and large, diffused and epitaxial BJTs have low Vebo and much higher Vceo, among other effects.
JFETs, show the gate-channel junction.  UJTs (back when they were relevant, heh) likewise; just drawn differently to imply the different function/behavior from JFETs (which they are otherwise fairly similar to, structurally speaking).  The right-angle line segments to the FET channel suggest ohmic connections rather than rectifying (Schottky or PN) junctions.
And MOSFETs use an arrow, just as well.  The substrate-channel junction, or "back gate", is the middle connection.  The channel is the three line segments in a row (sometimes they are drawn as a solid line, particularly for depletion-mode FETs, which are "default on", hence a continuous line, eh?).  Normally, substrate is tied with source, but this doesn't have to be (rarely, discrete parts are available this way, and it's the standard method in ICs).
You'll note sometimes a "MOSFET with emitter" sort of symbol is used.  This newer style is all the more grating when you realize what the arrow is supposed to mean...  Alas, that meaning has, it seems, been widely lost to time.
So, needless to say -- your diagram shows a diode from V6 to R1; but at least now it should be apparent.  Cheers!
Answer: The symbol of the device includes everything needed to figure this out. The various parts of the symbol represent functional features of the device:

There is a junction diode from the source+body terminal to the channel. This diode is forward-biased and conducts when the source+body terminal is above the drain.


automated unit test case for iphone

Question: for last three days i am trying to create unit test case using OcUnit. but not succeed yet . every time i google i get new tutorial with different configuration. and apple tutorial is the only which worked in xcode 3.2.5 . plz if any one know step to create logic test as well as application test please let me know .
Answer: Apple's approach forces you to make an artificial and unnecessary distinction between "logic tests" and "application tests". It also makes debugging a real pain.
For iOS unit testing, try GTM or GHUnit instead.
Update: Xcode 4 changes everything. I now use the built-in OCUnit for iOS unit tests. See Xcode Unit Testing: The Good, the Bad, the Ugly
Answer: i use GHUnit, is a test framework for Objective-C, you can follow the instruction on the GHUnit page or see the video TDD for iPhone Development , GHUnit it's easy to use and very helpful.
hope this help.

automated unit test case for iphone


What is runaway excitation?

Question: Can someone give me a brief explanation of this term? Found it in a paper but there doesn't seem to be an explanation that is consistent out there to my knowledge.
Comment: Can you provide a link to that paper? It might be more easy to help you this way.
Answer: When I have used (or seen) this term, it usually means that recurrent excitatory connections in a network have become stronger than the inhibitory feedback. This means that excitatory activity will grow stronger and stronger, without inhibitory influences to keep it in check. Eventually, the activity within the network will be limited only by spike-rate saturation. This type of network configuration is sometimes used as a model for an epileptic seizure.

What is runaway excitation?


How can I adjust the temperature of my hot water?

Question: I live in California and the winter has been a lot warmer than expected. I would like to decrease the water temperature in my home to try to save money and conserve energy. How do I do this?
Comment: Note that you may not want to reduce it too much as [the answer to this question explains](http://diy.stackexchange.com/q/29929/2196).
Comment: Including the make and model of the heater will help us offer a more specific answer.
Answer: There should (might actually) be a thermostat control on the water heater unit. Typically, in the US at least and on the units of which I've experienced, it's a big, round, red knob which will give you suggestions like "HOT", etc. Today's more efficient units may even have an "Energy Efficient" specific setting.
Adjust it to your liking.
Note that this may not be a feature on all models, particularly an electric heater; I know mine doesn't.
Answer: Most (virtually all) electric models have a non-obvious and inconvenient (but you don't usually need to adjust it that often) thermostat associated with each element. Since you need to expose the element electrical connections to see and adjust it, turn the power off first.
Repeat - turn off the power to the water heater before looking for or adjusting the element thermostats.

This is under the access covers that hide the connection to each element. As noted in the answer @Bmitch linked to, you should likely keep it set at 125F or above (not as shown here.)
You will probably get far more savings (what you really want) from adding insulation to the hot water pipes and posibly to the hot water heater itself (older ones are more poorly insulated than most newer ones,so they benefit more from additional insulation.) Uninsulated hot water pipes (and the cold water pipe feeding the hot water heater) waste considerably more energy than a few degrees on the hot water heater (since you will normally adjust the water temperature to suit, using less hot if the hot is hotter.) Lower temperatures will slightly reduce standby losses, but standby losses on a tolerably well insulated water heater are quite small, normally.


Interpreting Geographically Weighted Regression (GWR)

Question: I have a question. As you know, we use Geographically Weighted Regression (GWR) to discover the association between exploratory and dependent variables.
Now the question:
Do the standardized residual values (shown in red and blue graduated map) indicate a positive or negative association and the direction of this association ? *Can it be concluded that where the standardized residual values are high and red, in these areas the correlation between the variables is positive and significant?? (I want only interpret the standardized residual values).
Answer: The high negative and positive StdResiduals are areas that the model poorly fits the data.  They do not indicate positive or negative association. See the ArcGIS documentation here, where you will see the exact same map you included in your question.
The documentation states:

(C) Examine the output feature class residuals.
Over- and underpredictions for a well-specified regression model will
be randomly distributed. Clustering of over- and/or underpredictions
is evidence that you are missing at least one key explanatory
variable. Examine the patterns in your OLS and GWR model residuals to
see if they provide clues about what those missing variables might be.
Run the Spatial Autocorrelation (Moran's I) tool on the regression
residuals to ensure that they are spatially random. Statistically
significant clustering of high and/or low residuals (model under- and
overpredictions) indicates that the GWR model is misspecified.


Years as continuous variable

Question: Can I use "years" as a continuous variable ("years" as calendar years from 1984 to 2014) to see if NDVI (normalized difference vegetation index), of the same area at the same time (summer), has changed positively or negatively over the years, for example with a GLMM or GLM?
Comment: The possibilities are endless. I've seen applications in which distinct years are in essence best treated as discrete or categorical and applications in which fractional years made sense (e.g. 2020.25) for data indexed by say daily dates or monthly dates within a year. With environmental data I've often found fraction of year useful for looking at seasonality.
Comment: If you had stock index prices hour-by-hour, you probably wouldn't be asking. In real data, 'continuous' variables must be rounded in _some_ way. Yearly data are more severely rounded than hourly data, and it is a matter of judgment whether yearly data are too 'coarse' to be useful. // However, notice the the point made in the link that it may be convenient to have a 'zero' year and give other years relative to that year.
Answer: Yes, there is no GLM assumption that would preclude that

Years as continuous variable


How do I delete the next line in vim?

Question: In emacs, whenever I want to delete a few lines of text, I just use C-k until all the text is gone.  However, in vim it seems a bit more complex.  I know I can do d$ to delete until the end of the line and dd to delete the entire line I'm on, but how do I delete all of the next line?
Answer: Assumption: You want to end up at the line you started on.
My answer: jddk

j (moves down)
dd (deletes current line)
k (moves up)

Try it – it's quick!  In fact, it's two keystrokes less than the currently accepted answer because:

you don't need to hold [Shift] to enter the colon ':' and plus '+' characters, and
you don't need the implied [Enter] at the end of the sequence, since jddk is entered all in visual mode as opposed to command mode.

Plus, jddk is all on home row of the keyboard.
I spent a long time using h, j, k, l to navigate in vi, long before the terminal emulation software I used started supporting arrow keys.  (I'm talking about ~20 years ago ;-)
Comment: hjkl is faster anyway.  I've never used a keyboard that didn't have arrow keys on it, and I began to greatly value the efficacy of these keymappings about 10 minutes after I stopped being annoyed at the unintuitiveness of them.
Answer: Like this:
:+1d

Answer: I strongly recommend reading this answer in stack overflow, which got over 500 upvotes:  https://stackoverflow.com/questions/1218390/what-is-your-most-productive-shortcut-with-vim/1220118#1220118  -- the answer is long, but helps to understand why vim is powerful...
Comment: Thanks for pointing that out!  Very thorough and informative answer about grokking vim and vi.
Answer: You may also be interested in visual mode. Just use v to enter and y to yank or d to delete. Checking :help is a great place when you're stuck as well. For instance :help delete will give you the manual for most of the usual delete commands.
Answer: If you want to delete a bunch of lines in a row, you can use dd to delete the line you're on, then keep hitting (or hold down) . (period) to repeat the command.
Comment: or type *Ndd* where *N* is the number of lines to delete.  say, to delete the current line and the next two lines (3 total), type **3dd**

How do I delete the next line in vim?


How do I make 14.04 stable on my E machine

Question: How do make 14.04 stable on my old machine (E machine 1624) have 13.10 currently. I have downloaded from the Ubuntu site via an image on disk, external HD all is fine until I log in then desktop freezes have to hard re-boot ... process starts again.
Answer: Download 14.04 .iso image from ubuntu.com. Burn .iso onto flash drive by using ubuntu cd burner application.  Boot your computer with your flash drive and see if it is stable. If so install it by clicking install icon on your desktop.


What is the idea behind occupying domains?

Question: I see that most domain names that contain some nice words like: www.pixelmania.com , www.musicbox.com and so on... are registered but look just auto-populated with some random data. Why they do this ? Is it for me to pay extra to get that domain? Is it for advertising purposes (all of them have insane amounts of ads on them)? Or what ... ?
Comment: They hope to resell them, they are simple a pain in the neck to whoever wants to run a real business using one of those domain. If I was the TLD authority I would force people to use a domain by setting up a real website or someothing otherwise the domain is impounded!!!
Answer: They're probably expired domains that were snapped up by companies that build huge networks of domains with the sole purpose of showing advertising. They make countless millions of dollars a year doing it.
Comment: "Countless millions of dollars" out of it, are u sure?
Comment: Yes. The biggest player in the biz sold the company for an insane amount of money. I tried to find it so I could link to it but wasn't able to locate it quickly. But it was big bucks. And there are lots of companies doing this.
Answer: Its nothing. Just few bunch of selfish freaks, who are planning to make more money selling them in future.
But sometimes... they are also used to reserve the domain for future development to avoid the risk of losing them in future. And they try to utilize this unused to domain by advertising and earn a little money on the mean time. :D
Answer: In addition to the other answers, they are sometimes registered to catch typos. For example if someone typed gogle.com instead of google.com (although Google owns that misspelling!).
pixelmania.com could be set up to catch visitors for pixmania.com
Answer: There are several reasons

for money - sell the name for more;
prevent phishing;
prevent other people (companies) steal some fame from your product (JavaScript for example);
future expand of the original site (local site for every country);
expired domains as John Conde sayd. I think the ads and the random data is available only in the "possible renew" period;
there is a small number of domains that are registered for system use only (.arpa). Not Exactly sure about "net.net" ...


How to trigger specific font when changing language?

Question: I use Pages as my main word-processing application and regularly have to type in both English and Greek. I use either Times New Roman or Hoefler Text in English and GFS Porson for Greek. Is there a way to automatically trigger a specific font (in this case, GFS Porson) anytime I switch over to the Greek keyboard?
Comment: This is not an answer for your actual question, but might solve your need.  Have you considered finding a typeface with both good latin characters and good greek?  For example, many of the Adobe "Pro" fonts support Latin and Greek (e.g. Text Pro, Minion Pro, Garamond Pro...)
Answer: Pages doesn't itself have a way to do that exactly, but the app Nisus Writer does, via preference settings.
In Pages I'd recommend creating "styles" for Greek and English in your preferred fonts.  Styles can be attached to keyboard shortcuts.


gzgrep help in multiple large archives - solaris

Question: In solaris- i need to perform a gzgrep of archives.  But i need to filter so not searching ALL the archives- maybe just files with '09.30-12' in the name.. then i want to search IN that particular file or files for a particular expression.  I have this close.. but it takes WAY too long as its searching unnecessary files first and matching on those.. then moving onto the October archives and finding what i need in them. I need to basically search any files in which filename contains 'x' then look in those files for text 'y' and output to > fileoutput.  Perhaps just change the *.gz to just match on a set of files?? i cannot figure out how though.  Any help is MUCH appreciated.
Something like this works- but i get way too much output and it takes way too long.
gzgrep 'firstexpression' *.gz > /fileoutput.file
Answer:
maybe just files with '09.30-12' in the name..

You could say:
gzgrep 'firstexpression' *09.30-12*.gz > fileoutput.file

or
gzgrep pattern_to_search *filename_pattern*.gz > outfile


Having a mystical or "religious experience"

Question: This isn't really a question, more of an observation, but I don't think I've ever had a genuine "religious experience" where I have some kind of direct experience or connection with Hashem or the divine. I've been religiously observant (Orthodox) my entire life, and I have a yearning for some kind of profound mystical experience or connection with G-d (not sure how else to describe it). I sometimes find myself envying the generation that had the privilege to experience Matan Torah or other open miracles firsthand. All of the conventional avenues (mitzvos, Torah, davening, etc.) are great but they've never given me the profound spiritual revelation I wish I could experience. I wish I could experience Olam HaBa or Hashem speaking with me (even though I know it would probably be so overwhelming that my brain couldn't handle it). Does anyone else here feel that way?
Comment: Rabbi Tzvi Freeman [says](https://www.chabad.org/library/article_cdo/aid/712708/jewish/Why-Doesnt-Gd-Show-Himself-Anymore.htm) "In our own lives, He remains silent only when we do not know how to listen". One of my favourite posukim is where we read that G-d is calling Shmuel, but he think Eli is calling him. Why? Because Shmuel does not know that it is G-d calling him, yet. So too with this. We need to train ourselves to hear G-d speaking to us. Unfortunately it is not that simply, but this popped up to me when reading your question.
Comment: It seems that during the time of the Beis Hamikdash, these experiences were more common, with greater presence of Shechinah. The loss of these experiences is part of what we should mourn during the Three Weeks.
Comment: One of the finest scenes of religious contemplation is walking into the woods. God created nature, so experiencing God's creation is the best "religious experience" you could possibly have.
Comment: "_All of the conventional avenues (mitzvos, Torah, davening, etc.) are great but they've never given me the profound spiritual revelation I wish I could experience._" How much time or effort have you invested in those conventional avenues? How far have you gotten?
Comment: I guess a fair amount but obviously I could still do much more
Comment: Press hard into prayer. Read the Psalms and don't just recite them, cry out with the things that are there in your own words. The Prophets have much to say about hindrances and helps to seeking Hashem. Blessings to you!
Comment: Learn *kabbalah*.
Answer: Here are a few thoughts:

Learning Torah deeply, teaches one to switch from seeing nature as natural, to seeing it as miraculous, e.g. the story of R' Chanina Ben Dosa and the vinegar. Once one sees it as miraculous, you've achieved your goal. For example, if you see the feeling of love as just a physical manifestation of hormones affecting a nervous system, it will never be a spiritual experience, but once you start to learn how love has no place in a physical world, and comes from much higher, then every time you feel love, you have a mystical spiritual experience, and not even the lofty things, like love, but even the basic physical world of nature will do this. Here is an interesting article on this idea.

We are all numb nowadays, for various reasons including yeridat hadorot and others*. Part of the reason we might feel that life is devoid of spirituality is because of how numb we are. If we can only recall from our childhoods the true experience of intellectual excitement, the true feeling of deep emotion - and all the other amazing qualities of being a human being with a neshama in their proper expression - I doubt many of us would be struggling with this common question. See this answer for discussing walls around the heart.

As you've brought in your question, engaging in Torah, mitzvot and davening isn't working for you, as it isn't for many people. I would venture that for a lot of people, this is because they don't see Hashem as real, and this is one of Tanya's approaches in answering this common question. He is somehow abstract, distant and disconnected and therefore doing mitzvot becomes an abstract disconnected venture. Once He becomes real, and one realises that they are His mitzvot, and He needs us to do them, and the Torah is Him telling us about Himself. I.e. once He becomes an actual real someone to us, and we come to appreciate how we are His and He is ours, then every letter of Torah, and every detail of halacha becomes a true service of Him, and a profound spiritual experience.

All of the above I think would be useful for a lot of people, and certainly within reach of everyone. Higher things like ruach hakodesh and prophecy, the more commonly understood notions of "spiritual experiences" are likely out of reach for us until Moshiach comes... However, I think by yearning to connect to Hashem, you are doing alright, and I am highly optimistic that with this amount of yearning, and heartfelt davening, Hashem will bless you with success in this!
Until then, we should also be aware of a fair point, which is that we are here for one reason only: to do a mission. Having a spiritual experience isn't necessarily part of that mission for each person, in the sense that we aren't doing it for the reward, and the principle reward is not in this world, as we say every shabbat:

וְדַע, מַתַּן שְׂכָרָם שֶׁל צַדִּיקִים לֶעָתִיד לָבֹא:

I hope that helps.

* See also Ma'amar Hageula 1:4, even fruit is lacking in taste; Sota 48a; and further explanation Da'at Tevunot 40 p. 30
Comment: No, it's a great answer (so was Shmuel's). I appreciate it
Comment: "and would definitely count as a low quality answer" - why would you think that? Let's have a look at the amount of upvotes you've got. Great answer :)
Comment: Even the natural is miraculous in the sense that God created nature and this creation of everything is a miracle. No need to switch off God's beautiful creation.
Comment: @Shmuel thanks both of you. I've added basic sources to make it a higher quality answer, and added Shmuel 2's point, as I wasn't hoping to imply that we should switch off nature
Answer: According to Pinchas Ben Yair, in the Talmud (Avodah Zarah 20B and other places), if one wants spiritual revelations they must work on themselves until, after a many step process, they are refined enough for G-dly revelation:

מכאן א"ר פנחס בן יאיר תורה מביאה לידי זהירות זהירות מביאה לידי זריזות זריזות מביאה לידי נקיות נקיות מביאה לידי פרישות פרישות מביאה לידי טהרה טהרה מביאה לידי חסידות חסידות מביאה לידי ענוה ענוה מביאה לידי יראת חטא יראת חטא מביאה לידי קדושה קדושה מביאה לידי רוח הקודש רוח הקודש מביאה לידי תחיית המתים וחסידות גדולה מכולן שנאמר (תהלים פט, כ) אז דברת בחזון לחסידיך
From here Rabbi Pineḥas ben Ya'ir would say: Torah study leads to care in the performance of mitzvot. Care in the performance of mitzvot leads to diligence in their observance. Diligence leads to cleanliness of the soul. Cleanliness of the soul leads to abstention from all evil. Abstention from evil leads to purity and the elimination of all base desires. Purity leads to piety. Piety leads to humility. Humility leads to fear of sin. Fear of sin leads to holiness. Holiness leads to the Divine Spirit. The Divine Spirit leads to the resurrection of the dead. And piety is greater than all of them, as it is stated: "Then You did speak in a vision to Your pious ones" (Psalms 89:20).
Comment: "_According to Pinchas Ben Yair, in the Talmud (Avodah Zarah 20B and other places), if one wants spiritual revelations they must work on themselves until, after a many step process, they are refined enough for G-dly revelation_ ..." That isn't apparent in the passage you quote. In fact, "מביאה לידי" ("leads to") implies a natural progression (compare with "[שהבטלה מביאה לידי זימה](https://www.sefaria.org.il/Ketubot.59b.7?lang=bi&lang2=en)"). There is no mention, in the quote you bring, of the work on oneself, that you say is required.
Comment: @Tamir. In order to get to the next level, you have to attain the previous level. This requires working on yourself to attain those levels. See Mesilat Yesharim for an entire work on this theme https://dafyomireview.com/mesilat.php/mesilat/mesilat/mesilat/mesilat.php?d=2
Comment: "_In order to get to the next level, you have to attain the previous level. This requires working on yourself to attain those levels. See Mesilat Yesharim for an entire work on this theme_". All Mesilat Yesharim says about R. Pinchas Ben Yair's statement is that it "_encompassed all of these divisions_ [of divine service] _in different words arranged according to **the order of steps** needed to properly acquire them_". Anything the book says about working on oneself to attain those levels, it does not attribute to RPBY's statement. Why not cite/quote Mesilat Yesharim, instead?
Comment: @TamirEvan because the way I understand it, it is self evident that RPBY is talking about a journey of self-refinement, not something that just happens accidentally because you started learning Torah.
Comment: I'm not suggesting that RPBY is talking about something that just happens _accidentally_ because one _started_ learning Torah. (I'd say he is talking about a _natural progression_ from learning [not _starting_ to learn] Torah, though [not everybody brings his statement starting at 'Torah'](https://hebrewbooks.org/pdfpager.aspx?req=38522&pgnum=57)) I am questioning your understanding that the need to work on oneself is [self-]evident in the quote you bring. I am doing so, based on the wording (the use of "מביאה לידי") there.
Comment: @TamirEvan because I understand it as "Mastering step A leads to step B". The act of mastering the level is what I'm calling working on oneself.
Answer: As stated in the comment above, Rabbi Tzvi Freeman writes:

In our own lives, He remains silent only when we do not know how to listen. If you are waiting for a booming voice from the sky to answer your prayers, you may be like the child who is riding her bike into a wall and waiting for her father to catch and stop her. But if you will look into your own mind and heart which G‑d has given you and the signposts He places all around you, there, if you seek with sincerity, you will surely hear His voice loud and clear—and find the brakes right on time.
In truth, in His absence He and His kindness towards us is found even
more than in His presence. That is His greatness and that is His
awesomeness.

As Rabbi Kaii mentions, learning Torah is one way. The Lubavitcher Rebbe would often emphasise that learning Torah will connect you with G-d, since Torah is G-ds inner will. However, in your question, you write that this is not working enough for you.
Please be reminded that in the end, Holiness is a gift, as the Mesilas Yesharim writes:

For that which is in man's ability to do is the initial exertion, pursuing true knowledge and continual thought on the sanctification of deed.

If you try and don't succeed, please bear in mind that:

The Holy One, blessed be He, will guide him on this path he desires to follow and imbue His holiness upon him, and sanctify him. Then this matter will succeed and he will be able to achieve this clinging with the blessed G-d constantly.

A great tip of the hat, can be found in the same chapter of Mesilas Yesharim:

One whose mind and intellect is always fixed on G-d's greatness, blessed be He, and His exalted holiness, such that it is as if he is actually among the lofty angels while still in this world.

You write that you wish that Hashem talks to you. To be honest, He does. Refer to my comment regarding Shmuel HaNavi and Eli. Shmuel did think that Eli was calling him, but in truth, it was G-d who was calling Shmuel. He did not know that yet. So too with us. We need to train ourselves, make ourselves "pure" in order to hear G-ds call. But, "a man is unable to do this on his own". You'll need to pray to G-d that He gives you "a listening ear".
The Mesilas Yesharim assures that if a person purifies himself, and follow the steps that he writes in that chapter, he will be able to cling to G-d.
Answer: The other answers are great. Just a small contribution:
There is a perception amongst some that having a cataclysmic religious experience will make things religiously better. Or, at least, that having this kind of experience every once in a while will only serve to better ones connection to Hashem.
I think the beauty of our connection with Hashem, and one which is endowed with the framework of Torah and mitzvot, is in 'bringing it down' to the day-to-day. The Torah tells us (Devarim 30):

12: לֹ֥א בַשָּׁמַ֖יִם הִ֑וא לֵאמֹ֗ר מִ֣י יַֽעֲלֶה־לָּ֤נוּ הַשָּׁמַ֨יְמָה֙ וְיִקָּחֶ֣הָ לָּ֔נוּ וְיַשְׁמִעֵ֥נוּ אֹתָ֖הּ וְנַֽעֲשֶֽׂנָּה:
It is not in heaven, that you should say, "Who will go up to heaven for us and fetch it for us, to tell [it] to us, so that we can fulfill it?"
יג: וְלֹֽא־מֵעֵ֥בֶר לַיָּ֖ם הִ֑וא לֵאמֹ֗ר מִ֣י יַֽעֲבָר־לָ֜נוּ אֶל־עֵ֤בֶר הַיָּם֙ וְיִקָּחֶ֣הָ לָּ֔נוּ וְיַשְׁמִעֵ֥נוּ אֹתָ֖הּ וְנַֽעֲשֶֽׂנָּה:
13: Nor is it beyond the sea, that you should say, "Who will cross to the other side of the sea for us and fetch it for us, to tell [it] to us, so that we can fulfill it?"
ידכִּֽי־קָר֥וֹב אֵלֶ֛יךָ הַדָּבָ֖ר מְאֹ֑ד בְּפִ֥יךָ וּבִלְבָֽבְךָ֖ לַֽעֲשׂתֽוֹ:14
14: Rather, [this] thing is very close to you; it is in your mouth and in your heart, so that you can fulfill it.

I think that the Torah is imploring us to imbue our life with purpose in how you deal with everything in the world. Connecting to Hashem is not 'beyond the sea' in a miraculous event, it is in the here and now in every little action that we do.
The path to Hashem is not in the unbridled miraculous mystical experience. It is in the day-to-day, our interactions with friends and family. Elevating the mundane experience. Imbuing every moment with awe and wonder.
Furthermore, I have had some experience with people who went through kiruv who were often looking for these kinds of "miraculous" moments e.g., the type from chassidic tales or kiruv books. But life is not really like that. If a person really feels that a momentous event was the sum total of what gives their life purpose, the strength of this anchor is only as deep as that event; which, believe me, wanes with time. Granted, the experience of Sinai was categorically different. But, for the average person, its important to build depth and breadth in all walks of life in all ways that you can.
Cast your net wide and your roots deep. Find meaning in the small and the big. Build relationships: a family, friends, community. The sum total of all of this is synergistic. The Jewish life lesson, as we can see from challenges of our forefathers, is that the Torah is not inherited (Avot 2:12). You need to earn your keep, shoulder responsibility and love Hashem. He gave us the Torah and mitzvot as a gift. We must cherish it, implement it, love Him, always search for Him and He will search for you.
With all the noise and hustle and bustle of the world around you, you should know that there is always a "still small voice" (Melachim 1, 12:19) to listen out for.


Fatal error at Ubuntu VM run

Question: I have installed VM on my Windows 8, but FATAL error has occurred . How can I fix it, what's wrong?
Comment: Are you using Ubuntu version 12.04? Please add the version number in your question.
Comment: Looks like you neglected to insert the Ubuntu install .iso file into the Virtualbox virtual CD drive. It's a common first-time oversight for folks who didn't check out any of the many great Virtualbox tutorials or quite well-written documentation.
Comment: I have a flash disk with ubuntu instalation but i do not know the version. I believe it is 20.04
Comment: @user535733 Right, how can I fix it ? How can I insert it.. I have my iso on the flash disk.
Comment: @user535733 I a complete beginner to VM. Could you give me a hint where my virtual CD is at best via a picture. I definitely do not orient myself at help and videos.
Answer: As @user535733 has mentioned, you've likely not loaded the installation ISO file. Looking at the screenshots, it looks like you may have several issues that will need to be resolved before you can install Ubuntu:

the system memory is insufficient for Ubuntu Desktop (but okay for Ubuntu Server)
the video memory is insufficient for Ubuntu Desktop (but okay for Ubuntu Server)
the storage space (1.49 GB) is insufficient for any modern version of Linux
the network adapter may be better set as "Bridged"

So, with this in mind, let's go through the process of creating a VirtualBox installation of Ubuntu Server 20.04 from scratch. Many of these steps you've likely already done but, if this is your first Ubuntu VM, it may be good to double-check.

Open VirtualBox (if it's not already open)

Create a new Virtual Machine by pressing "New" (or the equivalent thereof)

Give the VM a descriptive name and ensure it is set to "Linux" and "Ubuntu (64-bit)":

Give the VM at least 2GB of RAM. Ubuntu Server can run with less, but 2GB is a good start:

You can always change this later if needs be.

For the storage, choose "Create a virtual hard disk now" and press "Create":

Choose "VDI (VirtualBox Disk Image)", then "Dynamically Allocated". This will ensure the disk image does not instantly use all the space you will assign.

Set the amount of storage to a number greater than 25GB:

Note: Because the disk image is dynamic, it will not use all this space immediately. It is simply a maximum.

Press "Create"

Now the basics are in place for the VM, but you will need to make a couple of changes:

Press the "Settings" icon (with the gear) and choose "System" from the left-side menu. Set the "Processor" to a good number of CPUs, with 2 being  good number for a simple VM:

Checking "Enable PAE/NX" may be worthwhile, but not a requirement.

Under Storage, mount the Ubuntu 20.04 ISO that you downloaded to the CD:

You will need to use the <code>.iso</code> file, not a flash disk with the ISO "burned" to it. If you don't have the ISO, you can download one from Ubuntu.
Ensure "Live CD/DVD" is checked:

For Audio, feel free to disable it if you are running Ubuntu Server

Under Network, select "Bridged Adapter" so that the VM connects to your network. Click "Advanced", then choose "Allow All" under the "Promiscuous Mode" setting. This will make it easier for you to use the VM like a normal server on your network:

Press "OK" to close the settings panel. The other settings can be left as they are for now. You can tweak them later if you wish.

Now that the basic settings are done, you're ready to press "Start" and install Ubuntu Server:

Welcome to Ubuntu Linux
Comment: Considering all the work you put into this fabulous answer, you might consider adding it as an answer to https://askubuntu.com/questions/6328 also. And perhaps to tutorials.ubuntu.com also.
Comment: According to Canonical, there are [over 60,000 packages](https://ubuntu.com/server/docs/package-management) that can be installed. Not sure if you want to install *most* of them. That said, if there is a specific package (or packages) that you would like, feel free to create a new question, as that would be a separate topic from this one
Comment: Evrything works fine, but how can I install **most of** existing packages, the editor Joe and perl among them, automatically ?
Comment: buntu@ubuntu:~/Desktop$ sudo apt-get install -y joe
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package joe
ubuntu@ubuntu:~/Desktop$
Comment: @matigo I can only post every 40 minutes so please wait.
Comment: @matigo [Here](https://askubuntu.com/questions/1389200/how-can-i-install-joe-on-vm-ubuntu) it is.

Fatal error at Ubuntu VM run