How to install debian package manager into an embedded system?

Question: I'm working a vendor-supplied Linux on embedded target and certain functions like make , apt-get etc. are missing. is it possible to install a package manager onto my embedded target board itself? is it the right way to do it? tkx!
Answer: Tipically embebed systems have limited resources, small RAM and very small storage space by the current standards; hence the limited environment and the lack of development tools on the system.
Often alternative libraries like uClibc instead of glibc are also used to save resources.

The goal of uClibc is to provide as much functionality as possible in
  a small amount of space, and it is intended primarily for embedded
  use. It is also highly configurable in supported features, at the cost
  of ABI differences for different configurations. uClibc has been
  designed from the ground up to be a C library for embedded Linux. We
  don't need to worry about things like MS-DOS support, or BeOS, or
  AmigaOs any other system. This lets us cut out a lot of complexity and
  very carefully optimize for Linux.

Typically the development phase is done outside the system via cross compilers. So there is a requirement to install/setup a toolchain/development environment in another machine, possibly a full linux development server.
In some opensource projects, the toolchain is freely available, in commercial embebed solutions often you have to get it from the vendor.
From elinux

A toolchain is a set of distinct software development tools that are
  linked (or chained) together by specific stages such as GCC, binutils
  and glibc (a portion of the GNU Toolchain). Optionally, a toolchain
  may contain other tools such as a Debugger or a Compiler for a
  specific programming language, such as ,C++.

As for packages maintainers, check if is not there a native one - as it will have an official repository associated, with more utilities and security updates for your system ; for instance in OpenWRT it is called opkg.

Opkg (Open PacKaGe Management) is a lightweight package management
  system based upon ipkg. It is written in C and resembles APT/dpkg in
  operation. It is intended for use on embedded Linux devices and is
  used in this capacity in the OpenEmbedded and OpenWrt projects.
Answer: If you want to install Debian packages on a system running a Linux kernel, you can install a Debian hierarchy in a chroot with debootstrap. Installing Debian packages directly at the root is highly unlikely to work because the Debian package manager would compete with the base system to decide on the contents of key system files. Only one tool gets to decide what is /bin/sh.
Schroot is very useful to transparently execute programs installed in a chroot.
How do I run 32-bit programs on a 64-bit Debian/Ubuntu? has a tutorial on installing a Debian-like distribution as a chroot under another Debian-like distribution. It can be used with only minor adjustment if the outer system is not Debian-like; you'll just have to download debootstrap manually, or run debootstrap in two phases (see the manual): one with --foreign on your PC to prepare a directory tree, then transfer the directory tree to the target device as you see fit, and run debootstrap --second-stage on the target device.
But if this is an embedded device with limited resources (as opposed to, say, an Android phone), then Debian may be overweight. Rui F Ribeiro's answer has some recommendations for alternative, lighter-weight distributions.
Answer: The right way would be to install the software you want manually, without the package manager.
If a package manager is not available on your system, there are often good reasons for this. Either there are space constraints (not having make is a good indicator this is the case), or your system is not binary-compatible with existing repositories. So your attempt to install a package manager may be just wasting time.
Even if installing a package manager on your system is practically feasible, you'll probably have trouble using it on a system which is not supporting one. You'll have to somehow tell it which files you already have, and which dependencies those files satisfy. Basically, you'll have to reinstall the whole system from scratch using packages if you want to add new software via a package manager.
Answer: Yes, it is possible. The source code of apt is available here
Download and build the source and add it in your target.
A sepearate repository with packages must be maintained to use apt-get.


How to prove that $\frac 1{q_{n+2}}\leq \left|p_{n}-bq_n\right|$?

Question: We know that \begin{equation*}
a_0+\cfrac{1}{a_1+\cfrac{1}{a_2+\cfrac{1}{a_3+\cfrac{1}{\ddots+\cfrac{1}{a_n}}}}}=[a_0,a_1, \cdots, a_n]
\end{equation*}
If $\frac{p_n}{q_n}=[a_0,a_1, \cdots, a_n]$.

To prove that $$\frac 1{q_{n+2}}\leq \left|p_{n}-bq_n\right|\leq \frac 1{q_{n+1}}$$

Now I know that The consecutive convergents are alternately greater than and less than the value of $b$. Then we have that
$${1\over q_nq_{n+1}}=\left|{p_{n+1}q_n-p_nq_{n+1}\over q_nq_{n+1}}\right|=\left|{p_{n+1}\over q_{n+1}}-{p_n\over q_n}\right|=\left|{p_{n+1}\over q_{n+1}}-b\right|+\left|{p_{n}\over q_{n}}-b\right|$$
The last equality follows because the one is bigger and the other is smaller than $b$;  this is where it is essential that they are consecutive convergents.
This implies $$\left|p_{n}-bq_n\right|\leq \frac 1{q_{n+1}}$$
How to prove that $$\frac 1{q_{n+2}}\leq \left|p_{n}-bq_n\right|$$?
Answer: $$\left|{p_{n}\over q_{n}}-b\right|=\left|{p_{n+1}\over q_{n+1}}-{p_n\over q_n}\right|-\left|{p_{n+1}\over q_{n+1}}-b\right|\Rightarrow \left|{p_{n}\over q_{n}}-b\right|>{1\over q_nq_{n+1}}-{1\over q_{n+1}q_{n+2}}={a_{n+2}\over q_nq_{n+2}}>{1\over q_nq_{n+2}}$$
And the result follows.


Deleted comment

Question: My comment got deleted in the topic Aspiring scientist. It got deleted - fine. But I don't see who did it? Is it normal here, is it norm? I would like to be aware of moderators who do that without leaving a comment.
Answer: Comments are ephermal, in general they can be deleted without explanation.
In this case, the link was possibly non mainstrean and had been flagged (we disallow non mainstream physics here), and besides it had no potential of improving the post.
Please only use comments to point out mistakes, ask for clarification, or suggest improvements.
Comment: Either way, I cleared out the rest of the discussion and left a comment to that effect. Note that this does not indicate that moderators have to explain deleted comments every time.
Comment: @AsphirDom No. We [do define what is non mainstream](http://meta.physics.stackexchange.com/questions/4538/is-non-mainstream-physics-appropriate-for-this-site), however, that doesn't apply to comments. Comments can be deleted regardless of content -- if there are reasonable objections to a comment I may delete without checking the validity. I repeat, comments are ephermal. If this discussion was about a _post_, then yes, we would apply objective guidelines to delete.
Comment: @AsphirDom The comments section is not appropriate for that discussion. If you/anna wish I can recover the deleted text and present it in a chatroom for further discussion. Again, it wasn't deleted because I "knew" it was non mainstream. The deletion of that comment does not in any way represent the definition of non mainstream physics here.
Comment: So basically moderator determines if book is a maintstream? How do you detect mainstreamity? Basically you personally judge it?! Or?. Only undisputedly mainstream books are encyclopedias and university books and even they have mistakes. Im curious to find out your algorithm. If my line of arguments is correct you should put in FAQ that this site does not PRETEND to be objective and is only reflection of personal opinions of its moderators. Who in this case should be visible publicly with their names. That we can understand who is who.
Comment: And secondly comments are comments you can not judge which information they bare - useful or not. If they are not important get rid of them on whole website.
Comment: To be absolutely precise i would like to know who determined that motionmountain.net is not a mainstream book?
Comment: @AsphirDom Sorry, we don't reveal details of who flagged what
Comment: @AsphirDom I wouldn't mind deleting all comments. However, in general I leave comments alone unless there's a long discussion or someone is objecting to them. The comments feature is useful, but its purpose is not to be permanent.
Comment: So comment was deleted due to flag? Funny. Some people actually went to investigate that book like anna v. The question was far from obvious.
Comment: OK situation is clear. Basically according to your definition of mainstream every community created book or effort (wikipedia alike) which is NOT published (wikipedia is NOT published in journal or publishing house) is NOT a mainstream :) Wikipedia on physics is not mainstream we got it :)

Deleted comment


Was the cingulum militare any good as protection?

Question: Wikipedia information on the cingulum militare  is sparse. It is clear that it had a decorative function and displayed rank. The metal elements and widespread use of something similar by the Greeks create the impression it may have offered some protection. Yet that is difficult to imagine. For protection I would think something massive to be superior to stripes. At maximum I would expect 2 or three thick and rigid stripes for better mobility. So, was it purely decorative and symbolic, or is intuition misleading?
Comment: I'd strongly prefer supple to rigid. Supple will foul the blade and flex to protect the femoral; rigid is simply going to be displaced by the thrust, leaving the artery unprotected.  I don't pretend to be an armorer, just a guy who has spent some time thrusting sharp pointy objects at vulnerable opponents.
Comment: It would work as protection against cuts to the femoral artery - one of the sword forms I practice includes that as a target.  I don't practice Roman/HEMA, but I have to imagine that the groin was a great target for blades.  Loose stripes are  likely to protect against slashes & thrusts.  I can't _answer_ the question, but it seems plausible.
Comment: Still, if it were seriously effective at offering protection, you'd think it would be a good addition to the uniforms of the actual soldiers doing most of the fighting. It looks like it would have been cheaper than the chainmail shirt.
Comment: It occurs to me the modern placement of rank and decorations is roughly over the heart. Since that's one of the better places to aim to kill a modern soldier, a person could wonder if there's any connection.
Answer: SHORT ANSWER
Experimental archaeology has led to the belief that what is known as the 'apron' (hanging leather straps with studs) probably did not have any practical defensive purpose and was actually a handicap "during violent movement".
It has also been argued that straps would have been of limited use against both thrusts and slashes. Further, the 'apron' would have served no purpose against one of the most common enemies of the period, the Celts, due to their fighting style.
However, in the absence of primary source evidence to confirm this, it is impossible to be certain and some sources state that a defensive purpose is possible.
Finally, most sources point to the 'apron' as being both a fashion item and an indication of status.

DETAILED ANSWER
M.C. Bishop and J. C. Coulston, in Roman Military Equipment (2006), initially seem to sit on the fence a little:

It is thought that it offered protection to the area of the lower
  abdomen and groin, although practical experiments with reconstructions
  have shown that weighted straps swinging between the legs of running
  soldiers are more likely to pose an additional, unwanted, hazard in
  combat. A more attractive theory is that which see the 'apron' as a
  mark of status, reinforcing the soldier's ego with its jingling
  components

Later, the authors seem more definite:

First to 2nd century 'aprons' served no significant protective
  function, and indeed could have been a liabilty to the running
  soldier.

In his article The Early Imperial Apron Bishop also says that

It has been traditional to explain the apron as an item of body armour
  designed to protect the soldier's lower abdomen and private parts.
  However, this is to misunderstand not only the dynamic behaviour of a
  series of straps, but also to ignore the main traits in Roman armour
  development in the first century AD.
If a thrust from a sword, dagger, or spear were aimed at an apron, it
  would pass straight through, as the straps, with nothing to hold them
  together, would simply part. A cutting or chopping blow would most
  likely out clean through the straps, deflected from the studs (which
  never overlap and are not attached to each other) onto the leather.

On the trends in Roman armour design, Bishop notes

Many Roman foes were Celtic and fought with a downward slashing blow
  from a sword: this explains why Roman armour in the first century AD.
  is always reinforced on the shoulder area and why the helmets are
  designed to deflect downward blows. The whole philosophy of armour
  design is against the downward blow, not against the thrust to the
  midriff

On the left, "Grave stone of the legionary Caius Valerius Crispus, about 75 CE, here's [sic] he served in the Legio VIII Augusta. At his death he was 40 years old." On the right, "Detail of the full-figure tombstone of Annaius Daverzus of cohors IIII Delmatarum from Bingerbrück."
A more recent source is Stefanie Hoss' The Roman Military Belt in Koefoed, H., M.-L. Nosch (eds), Wearing the Cloak. Dressing the Soldier in Roman Times (2011). She is more definite in her assessment:

This 'apron' has often been argued to have been used as a real or
  psychological protection of the wearer's lower abdomen and groin area.
  Experimental archaeology has proven the contrary, namely that during
  violent movement (e.g. running), the weighted straps swinging between
  the wearer's legs are apt to form a risk to the groin area. It seems
  more likely that the apron had no practical use, but has to be
  interpreted as a mark of status for the soldiers, maximising the
  characteristic jingling.

Adrian Goldsworthy, in The Complete Roman Army (2003) says much the same as Hoss on "the experince of modern re-enactors" and adds some details about the 'apron' which are consistent with the idea that it was primarily decorative. The 'apron'

might consist of one to nine straps, usually studded and with
  decorative metal terminals. Four to six such straps are most common.
  These may have served as a defensive function, even if the protection
  offered to a soldier's groin was more psychological than real.

Graham Sumner, in Roman Military Dress (2nd edition, 2009), also accepts the findings of re-enactors and notes the changing styles of the 'apron' during the 1st and 2nd centuries. He refers to the 'apron' as a "popular fashion". Further, Hoss notes that, in the 2nd century,

the introduction of enamel decorations... made the belt quite
  colourful.

Bishop, in The Early Imperial Apron, concurs:

It is easier to say what it was not for, but the unex— citing answer
  to the question must be that it was fashionable. Indeed, this is one
  of the most appealing explanations for the appearance of studs bearing
  portraits of the Flavian emperors.

Bishop concludes with:

Perhaps the best explanation of the apron lies in a sociological,
  rather than military, interpretation.

The 'apron', whatever its true purpose, was not around for long. It is first noted in the Flavian period (69 AD to 96 AD) but fell out of use well before the end of the 2nd century.

Whatever its purpose the apron gradually declined in size and does not
  appear to have lasted beyond the Hadrianic period (117 AD - 138
  AD).

Hoss more or less concurs, stating it died out during the Antonine period (Antoninus Pius succeeded Hadrian in 138 AD).

Note: The term 'cingulum' does not appear to have been used until the 3rd century. Before then, the belt was referred to as a 'balteus'.
Answer: Used as mark of status (rank) than as armour (defensive use).
Stefanie Hoss a Provincial Roman archaeologist with a PhD on the culture of Roman bathing and the baths in Palestine and another one in Roman military belts.
From her second Doctoral Thesis at Leiden University (2014) (emphasis mine):

Abstract
The Roman military belt was a "marker" piece of equipment of the Roman soldier, distinguishing him from civilians when he was not wearing arms and armour. This is corroborated both by ancient literature and the frequency and accuracy of the depictions of the military belt on the gravestones of the soldiers. The immense ideological value invested in the belt originated in its function as sword belt, but then developed independently from it.
This comprehensive study of the Roman military belt combines the written sources with the pictorial representations of belts and the archaeological finds of the metal mounts, buckles and hangers of the belt. In addition to discussing typological features and analysing the distribution and dating of the different types, questions on the social significance of this distinct piece of equipment are discussed. The book aims to give as broad a picture as possible of the Roman military belt; from its origins and development to its visual, acoustic and physical characteristics and from its ideological value to its influence on the everyday posture of the Roman soldier.

Source: Cingulum Militare : Studien zum römischen Soldatengürdel des 1. bis 3. Jh. n. Chr.
Comment: That proves that the symbolic value was important. But had it any defensive value or not?
Comment: I follow your argument and agree for the symbolism completely. It's just that I interpret the question as different. Primary function: symbolism (have you read about the castration fears? Freud is always fun!). To fully address the Q with your reasoning so far you might want to *really* disprove (not stressing that other functions are just more important) that there is any real defensive function or that it "would have been" almost meaningless.
Comment: Whether it has real defensive value depends on whether it is used as armour. Since it is not treated as armour, the logical conclusion would be no defensive value. To paraphrase Hoss (her first sentence), when Roman soldiers are **not wearing arms and armour**, the military belt is used to denote status/rank, etc. In any case, we have to wait till Aug to read the details.
Comment: Although it *is* funny, I am not kidding on that one. Compare that belt business  to cod-pieces, wooden phalli carried into battle etc. I do not say that anythin from Hoss (or you) is incorrect. I just feel that how the Q is framed, it's incomplete.  (btw her work is "under embargo": have you fulltext access?)
Comment: I see where your line of thought is going but the crunch comes down to this: **Why would a piece of item that signifies rank (a social role) be evaluated on its  defensive ability (a military purpose)?** That wouldn't make sense (in my mind anyway).


How to connect Magento different instances to a central database in an development environment

Question: We have Magento community edition in our office. The DB server is separate ; we would like to connect a single Magento DB  to multiple instances on separate machines (within LAN network)
Currently each developer has to get a separate DB on his own machine
Any suggestions?
Answer: The actual Magento configuration of this is not too difficult, the configuration of your network and Database server is also key.

To begin with you need to take care of your networking and security. Ensure your Magento DB server has a consistent IP address and it can accepting connections on the DB port from all other developer machines on your LAN. (Security aside: make sure it doesn't accept connections from anywhere on the internet, that would be dangerous) If you're using MySQL, take this time to set up an individual database for each developer.
Take a look at the Magento CE 1.9.1 system requirements to make sure you have all the requirements on your developers machines. You will need php modules such as curl,gd and mcrypt installed for Magento to run. Once you have your local web host and php environment configured, unzip Magento into the docroot.
Now the easy part: fire up your browser on each developer machine, and point it to the location you installed Magento and the installation procedure should start. When you get to the configuration section shown in the image below. Fill in the IP address and port of your DB server at the location of the purple arrow and the unique database for the developer at the location of the red arrow. Once all your networking and database credentials are all sorted out, you should be on your way.


signed up in 2010-now trying to access

Question: Back when I signed up with bitcoin and received 2 bitcoins, I haven't done anything with my account/wallet since 2010 is there a way for me to access my bitcoins or have they been lost, I still have the same email address, thanks
Comment: What does "I signed up with Bitcoin" mean? Did you run some program? Did you go to some web site?
Answer: IF you still have your wallet:

This means you still have your private key
This also means you have your public key (you call it the same email address i assume)
syncronize the blockchain on your bitcoin client in case of using bitcoin-qt. This will take some time (+-2 days)
Copy your public key and go to blockchain website and past you key in the search bar. This will show you if the bitcoins still exist.
In case they still exist on the blockchain then once the blockchain has been syncronized and completed it will also appear in your wallet.

If you lost your wallet and you never wrote your private and public key down then they are lost for ever!
Comment: okay went to the login location and filled out info on lost both wallet/key and all I had was my email address and it wouldnt accept--saying "invalid GUID"  I don't know what that means? I can't remember my passphrase but if I knew what kind of response -I do have my old tower from back then--but hate to dig that out and search if the coins are lost thanks so much
Comment: What wallet did you originally use?
Comment: I cant remember any of it -I think it was about day-2 of them being available, before this whole sub-language developed, whatever I did would have been the first version of everything, I looked for what GUI means -couldnt find that so i cant even enter my request to look for my old data.
Comment: If you downloaded the Bitcoin client, you would have a "wallet.dat" file somewhere with the keys in it. It would help a lot if you described the process in as much detail as you can remember. What did you need your email address for?

signed up in 2010-now trying to access


Quantifying chromatic adaptations made by the brain

Question: What are the ways one can use to measure the kind of adaptations done by the brain to provide colour constancy? Has this been done before?
Comment: Colour constancy is largely the outcome of complex processes. Could you elaborate what you mean by "measuring adaptions"? For example, the brain analyses the coherency of shadows and light sources on the visual scene so to alters the perceived colours. What exactly would you like to measure in such a process?
Comment: Hey, thanks for your answer. In your example, I'd be interested to measure the amount of alternation done by the cones in relation to the amount of the variables (e.g. coherency of shadows, light sources). I am aware that this is unlikely to have a solved formula, but I'm interested in what has been done towards finding the formula, and what it was replaced with for the time being?
Answer: You have specifically asked about the "adaptations done by the brain" in your initial question and an interest in "what has been done towards finding the formula and what it was replaced with for the time being?" By formula, I'm assuming that you meant a perceptual algorithm that can be useful in machine learning and the attempt to reverse-engineer human's perceptual systems.
Yes, there has been extensive work done on this. I cannot give you an extensive answer on this platform, but hopefully point you towards the right direction. I have mentioned two papers and their abstracts, the former is more accessible, and the later in case you want a sneak-peak of the mathematical methods involved in making a computational model of color constancy and chromatic adaptations.
On the other hand, if you're new to this or you want to simply refresh your memory - I have attached my ex-Professor's notes from a Perception class I took a few years ago to give a clearer idea. It might just be best to first read through those first, in which case you should skip the first two papers I have mentioned.

Sensory, computational and cognitive components of human colour constancy.
Smithson H.
Philosophical Transactions of the Royal Society, Biological Sciences. 2005; 360(1458): 1329-1346.

Abstract
When the illumination on a scene changes, so do the visual signals
elicited by that scene. In spite of these changes, the objects within
a scene tend to remain constant in their apparent colour. We start
this review by discussing the psychophysical procedures that have been
used to quantify colour constancy. The transformation imposed on the
visual signals by a change in illumination dictates what the visual
system must 'undo' to achieve constancy. The problem is mathematically
underdetermined, and can be solved only by exploiting regularities of
the visual world. The last decade has seen a substantial increase in
our knowledge of such regularities as technical advances have made it
possible to make empirical measurements of large numbers of
environmental scenes and illuminants. This review provides a taxonomy
of models of human colour constancy based first on the assumptions
they make about how the inverse transformation might be simplified,
and second, on how the parameters of the inverse transformation might
be set by elements of a complex scene. Candidate algorithms for human
colour constancy are represented graphically and pictorially, and the
availability and utility of an accurate estimate of the illuminant is
discussed. Throughout this review, we consider both the information
that is, in principle, available and empirical assessments of what
information the visual system actually uses. In the final section we
discuss where in our visual systems these computations might be
implemented.

Color constancy using natural image statistics and scene semantics.
A. Gijsenij and T.Gevers.
IEEE PAMI, 33(4):687–698, 2011.

Abstract
To achieve selection and combining of color constancy algorithms, in
this paper natural image statistics are used to identify the most
important characteristics of color images. Then, based on these image
characteristics, the proper color constancy algorithm (or best
combination of algorithms) is selected for a specific image. To
capture the image characteristics, the Weibull parameterization (e.g.,
grain size and contrast) is used. It is shown that the Weibull
parameterization is related to the image attributes to which the used
color constancy methods are sensitive. An MoG-classifier is used to
learn the correlation and weighting between the Weibull-parameters and
the image attributes (number of edges, amount of texture, and SNR).
The output of the classifier is the selection of the best performing
color constancy method for a certain image. Experimental results show
a large improvement over state-of-the-art single algorithms. On a data
set consisting of more than 11,000 images, an increase in color
constancy performance up to 20 percent (median angular error) can be
obtained compared to the best-performing single algorithm. Further, it
is shown that for certain scene categories, one specific color
constancy algorithm can be used instead of the classifier considering
several algorithms.

Below are examples of a few experiments that can be played out from behind your computer screen:
From Jonathon Winawer's notes on Perception:

Color Constancy and Chromatic Adaption
Take a photograph under fluorescent light, and compare it to the same picture under daylight. The colors come out totally differently - greenish under the fluorescent light and reddish under daylight - unless you do some "color correction" while developing the film.

But  you wouldn't  see  it  that  way if  you were  in the  room.  To  you the  colors  would  look  pretty much the  same  under both  illuminants.  This  phenomenon  is  called  color  constancy,  analogous  to  brightness  constancy that  we  discussed earlier.  The  eye  does  not  act  like  a  camera,  simply recording  the  image.  Rather,  the  eye  adapts  to  compensate  for the  color  (SPD)  of  the  light  source.

Above  is  another  example  of  a  pair  of  photographs  taken under  different  lighting  conditions  without  color  correction. The  physical  characteristics  of  the  light  reaching  the  camera  is  very different  depending  on  the  color  of  the  illuminant. This  results  in  dramatically  different  photographs.  But  if  you  were  there  when  the  pictures  were  taken,  this  object would  look  pretty  much the  same  to  you under  both illuminants.

Glance  at  the  penguin and  dragon pictures  above  by fixated  on the  dot  between them.  The  penguin picture  looks very  blueish  and  the  dragon looks  very yellowish.  Next,  you will  hold  your  gaze  on the  dot  between the  blue  and  yellow fields.  Continue  staring  at  that  dot  for  30  secs  or  so.  Then look  back  at  the  penguin and  dragon by fixating  the  dot between them.  What  do  you see?  Why? The  change  in percept  following  adaptation is  due  to  chromatic  adaptation.  Chromatic  adaptation is  like  light  and dark  adaptation  but  instead  of  adapting  just  to  light  and  dark,  it  adapts  to  whatever  the  color  is  of  the  ambient illumination.

Each cone  type  adapts  independently.  For  example,  a  given L  cone  adapts  according  to  local  average  L  cone excitation.  Likewise  for  the  M  cones.  Thus,  the  retinal  image  adjusts  to  compensate  not  only for  the  overall  intensity of  the  light  source,  but  also  to  compensate  for  the  color  of  the  light  source.

Chromatic  adaptation,  like  light  adaptation,  can  give  rise  to  dramatic  aftereffects.  For  example,  adapt  to  this  green, black,  and  yellow  flag  for  60  secs,  then look  at  a  white  field  and  you will  see  an afterimage  of  a  red,  white,  and  blue flag.  Red/green,  blue/yellow,  black/white  are  complementary colors.  Normally,  when  you look  at  a  white  field,  L  and  M cones  give  about  the  same  response  so  the  red/green opponnent  colors  mechanism  does  not  respond  at  all.  If  you adapt  to  green,  the  M  cone  sensitivity is  reduced.  Then,  when you look  at  a  white  field,  the  L:M  cones  are  out  of balance;  the  L  cones  are  now  more  sensitive  than the  M  cones  so  the  red/green mechanism  gives  a  positive response  and  you see  red  instead  of  white.  This  only lasts  for  a  couple  of  seconds  because  the  M  cone  sensitivity starts  to  readjust  right  away. The  visual  system  is  designed  to  try to  achieve  a  perceptual  constancy.  But,  as  with the  various  brightness  illusions  I showed  earlier,  color  adaptation  also  results  in  some  misperceptions.  The  colored  afterimage  is  an undesirable consequence  of  chromatic  adaptation coupled  with color  opponency.  Usually chromatic  adaptation does  the  right thing,  it  compensates  for  the  color  of  the  illuminant.


Galaxy Note 2 JellyBean update

Question: I have a Galaxy Note 2 GT-N7100 running on Android 4.1.1 JellyBean. The 4.1.2 update has been released a while back, but I still am reluctant to upgrade. I have read over the Internet that it causes the battery to drain faster than normal. Is there any truth to this?
Answer: Yes there was Issue with Battery drain but they had solved the issue and you can go for 4.1.2 and performance is good.
Comment: Yes its true and write know the issue is fixed so no need to worry u can update you version to 4.1.2.

Galaxy Note 2 JellyBean update


Making android ROM "e:signature verification failed"

Question: I have a ROM (zip file) which I put it inside SDCard and then flash phone in boot.
I extracted the zip file, removed an app (or even tested without any change to stock ROM) then zipped the package (by winrarzip archive). Put it inside phone and getting error:

e:signature verification failed

I noticed stock ROM zip archive had a comment called "signed by APKsign". So, I installed cygwin and prepared kitchen. Put stock zip ROM in "Original update", set up working folder from ROM, then built ROM from working folder, signed the package during making ROM, BUT again:

e:signature verification failed

Then I tried Rooting the package (2.Add root permission) before making ROM.

The same problem

Then I tried unzipping stock ROM, Then zip it again with winrarzip archive. Put this zip file in Original update folder, Then using (0. Advance option) and (22. sign apk or zip files), then sign this zip file.

The same problem

What is the problem? Why can't phone detect the signature in spite of being signed by kitchen?
My ROM is "huaqin75_cu_ics-ota" it is the ROM for MT6575 phone.
Answer: There are a few solutions here, one is to disable signature checking in your recovery (CWM/TWRP) this would be a temporary quick solution however the permanent solution
we ca try resigning using java, i created a simple script with a gui years ago to do this for me when i was hacking into early android http://www.modaco.com/topic/313829-pc-tool-zip-signer-v11/ for windows only
when i had my huawei pulse mini i used a dodgy recovery which gave me a similar sort of error for a portion of signed zips


Javascript question: Cannot add eventlistener for event loadstart on body of html page

Question: I am trying to add eventlistener for event loadstart on body of html page but it is not working.
Html code:

<!doctype html>

        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Rotate Text</title>

Javascript code (rotate_text.js):

var body = document.getElementsByTagName("body")[0];

function populate_body() {
    alert("Called");
} // end of populate_body

// body.onloadstart = populate_body(); // ====> THIS WORKS
body.addEventListener("loadstart", populate_body); // ====> THIS DOESN'T WORK

Why is addEventListener for event loadstart on body not working? Am I doing something wrong?
Answer: The problem is that you call populate_body() immediately when you assign it, that's why it worked :)
body.onloadstart = populate_body();

Answer: The loadStart event occurs when the browser starts looking for the specified media and it can not applied on body element.
// body.onloadstart = populate_body(); // ====> THIS WORKS

This line of code doesn't add event listener, it shows the alert because you have called populate_body() function.
I'm not sure but maybe onload event is what is you are looking for.
function myFunction() {
 alert('body element loaded')
}
document.body.onload = myFunction;

Comment: Better to prefer using `document.body.addEventListener('load', callback)` for event listening.


How many concurrent requests can dockerd handle?

Question: We have 1 swarm cluster with 3 managers and 10 workers for performance test. When 100 concurrent requests(create service) sent to one swarm manager, dockerd may accept all the requests to dispatch to workers. But if we increase the num of concurrent requests, the dockerd error log says:
<code>Error creating service serviceXXX: rpc error: code = 4 desc = context
deadline exceeded"
</code>
Is there a default value of max concurrent requests that dockerd can handle in code? How could we increase the concurrent requests that dockerd can process successfully?
The daemon is version 17.03.
Answer: As commented in issue 29987, this error message is not very explicit:

I think whenever we encounter a context deadline exceeded error, we should rewrite it to a coherent explanation of what timed out, and perhaps list possible reasons that could cause the timeout (loss of quorum, etc).
When working on docker/docker-e2e, I had problems where things were timing out causing context deadline exceed errors, but the root cause of the timeout was some other error that was getting ignored, superseded, or otherwise buried.

As detailed in issue 33631:

This error can have various causes (See this search for existing issues mentioning this error).
The error itself is quite generic, and could mean that the manager was not able to communicate with other managers in the cluster.
From just the error, it's not easy to discover why it fails to communicate (it can be either a bad network connection, other managers did not properly re-join the cluster, therefore you lost quorum, or it could be if (e.g.) managers did not have a static IP-address, and the IP-address changed - which is currently not supported).

You can see a similar case here but this happens also with less queries.


JControllerForm and JControllerAdmin

Question: What is the difference between JControllerForm and JControllerAdmin in joomla component?
Answer: In simplest terms both are subcontrollers for JControllerLegacy.
JControllerAdmin is essentially the controller for tasks such as displaying a list of records from the database.
JControllerForm is the controller for tasks that act upon data being edited for database entry.
Here is a link to the Joomla Docs that sums it up pretty well JController Overview

JControllerForm and JControllerAdmin


How come when we pick up a baby or first reaction is to rock them, even if you have never ever held a baby before?

Question: My mother just had a baby girl yesterday and I have always been the youngest so I have never held a baby before until yesterday. When I held her for the first time yesterday my immediate instinct was to start bouncing her softly/ bobbing her up and down. I started talking with my mom and wanted to know why it is the human beings instinct when holding a baby?
Answer: It isn't instinctive. Many new parents have difficulty learning how to rock and hold babies.
Generally, though, most people learn it through behaviours through their childhood.
An odd quirk, though, is that babies often like to be rocked faster than the person holding them would expect - we first encountered this when we became parents: our kids liked being rocked nearly twice as fast as I would have thought comfortable, but after asking people and searching online this seems the norm.
Comment: It is indeed true. Some kids like to be rocked in a manner I would call 'violent rocking' (I don't advocate it, though.) This is especially true of babies of mothers who were very active during the entire pregnancy, for example, runners. When you think that a baby probably slept while its mother was running, you can well imagine a gentle rocking will not suffice. :)


re using 'better' "You had better do that" (meaning you should do that) or "You better do that"?

Question: re using 'better'  "You had better do that" (meaning you should do that) or "You better do that": are they both correct?  If so, what part of speech is the word 'better' in each case?
Comment: They're both correct, though informal.
Answer: The structure normally is "You had better go home now, you are drunk". I take it that "had" is a subjunctive form, as an indicative makes absolutely no sense. But even when interpreted as subjunctive the expression is somehow twisted and not very logical. It seems speakers try to improve this twisted expression by dropping "had". You don't read "you better go home now" so often, but it is possible.
As the formula is twisted and possibly elliptic it is futile to rack one's brain about better. It is the normal word, either adjective or adverb. I racked my brain about "had". Perhaps it was "did* (subjunctive), shortened to "'d" and confused with "had/'d". A mere idea, I have no evidence for this assumption.
Oh yes, there is a kind of evidence. The German parallel would be:
Du tästest besser daran heimzugehen. That is an expression that makes sense and "tätest" would correspond to an English subjunctive did*.
Answer: Yes, they are both correct. "Better" is an adverb in each case and "had" is an auxiliary verb. Together they form the modal idiom "had better", which is typically used to advise the best course of action.


convert pdf to jpeg on linux?

Question: Sometimes clients email me a poster which they received from a graphic designer in pdf format that they want added to the site.  I have generally told them to ask the designer to export it in jpeg format.  This has been working out OK, but is there any easier option?  The only other way I have figured out is to do a screen shot of the pdf and then crop it using gimp, but that's kind of time consuming.
Comment: This is more appropriate on Superuser or perhaps the Ubuntu StackExchange site.
Comment: Oh, and BTW, Gimp should be able to import PDF files as read-only. So you just need to drag the PDF into Gimp and save-as JPEG.
Answer: ImageMagick (and the iMagick extension if you're using PHP) should work reasonably well for this task.

convert pdf to jpeg on linux?


Do specification sheets for older Shimano components exist?

Question: You can find official Shimano spec sheets on their website. They reach back to the year 2004. Do older spec sheets from the 80s and 90s exist?
Answer: Yes they do.
They way Shimano did it for a very long time (I don't have the date range) was that each model of component released had two different documents released for it, which were Shimano's primary means of communicating technical specs to the world. These were the "SI" (Service Instructions) and "EV" (Exploded View) documents. The SIs contained throwaway legalese, setup instructions, and compatibility type information, for example total capacities and max large cog numbers on a rear derailleur, or recommended spindle length for a crank. Sometimes the compatibility type information you need is actually hiding on the EV, especially when what you're trying to figure out is a small part number, i.e. for cross-compatibility parts ordering type purposes.
The EVs still exist in the same form as ever, but at some point (again I don't recall the year), they stopped doing SI documents and instead now do the UMs (User Manuals) and DMs (Dealer Manuals) found on si.shimano.com for the procedural and cautionary/legalese type content, and their spec tables for compatibility information.
As far as I know, the 2004 date you mention was the beginning of Shimano releasing spec data in table form. SIs were still around then, so in this period both types of document were released and had some of the same information. For parts not covered in those archives, the main source for that kind of data is the SI documents. There are some entities out there who have taken it upon themselves to archive them for the public, and a lot of those dating pretty far back in time can be found by searching the model number plus "si". Shimano has also added some older SI documents to their own site.
Prior to the Dealer Manual PDFs, their current form of communicating core procedural information, there used to be yearly paper "STI Guides" that dealers got. It was a maddening and backwards system because there was some technical material in them that wasn't available anywhere else, but getting old ones was difficult, and so was finding what you needed even if you did have a huge stack of them. They were also the source of compatibility charts akin to what's in the Compatibility section of si.shimano.com now. STI Guides persisted well into the internet age, but I'm not sure when the last one came out.
Answer: In some cases, but not in the same format and note that those links are not complete in that they omit information provided elsewhere
here are some links:

various Shimano catalogs back to 1973 which vary between collections of exploded views or spec lists, line-up charts, etc: http://www.disraeligears.co.uk/Site/Documents_-_Shimano.html

1974 Shimano Bicycle Parts with collections of exploded views https://www.flickr.com/photos/stronglight/sets/72157625399206479/

various catalogues https://vintagecannondale.com/info/shimano/

various early-2000s compatibility charts

https://www.celebrazio.net/bicycling/shimano_compatibility.html#charts
e.g.

various catalogues here http://www.retrobike.co.uk/gallery2/v/Manufacturer+Archive/Shimano+Archive/Catalogues/

various other places e.g. this 1993 catalogue scan http://www.tearsforgears.com/2009/11/1993-shimano-ultegra-600.html http://www.tearsforgears.com/2009/10/1993-shimano-catalog.html

1994 catalogue here http://cyclespeugeot.web.fc2.com/reminiscence/shimano94.htm

web.archive.org e.g. this 2002 Dura-Ace 7700 which is different from information now available online  http://web.archive.org/web/20020225203704/http://bike.shimano.com/road/dura-ace/index.asp or this 41-page 2003 disc brake catalog which provides technical information and installation details or this from the EU Shimano web catalog on the differences between the 7700 RD http://web.archive.org/web/20040119025927fw_/http://www.shimano-eu.com/cycling/catalogue/content_prodx.phtml?pid=10102&psid=36 and the 5500 RD http://web.archive.org/web/20040131113619fw_/http://www.shimano-eu.com/cycling/catalogue/content_prodx.phtml?pid=10124&psid=38 (which provides far more detail than in the archived spec lists available online - e.g., on pivot seals or their absence) http://web.archive.org/web/20030509114347/http://bike.shimano.com/services/images/english/Shimano_Disc_Brake_Systems.pdf (try Bike.shimano.com, shimano.com/cycling cycle.shimano.co.jp)

the list of Shimano part numbers from 1980 to 2006 from Allgemeiner Deutscher Fahrrad Club http://www.fa-technik.adfc.de/Hersteller/Shimano/Gruppen2000.html http://www.fa-technik.adfc.de/Hersteller/Shimano/Gruppen.html http://www.fa-technik.adfc.de/Hersteller/Shimano/Gruppen80.html This is probably better than any other source for finding groupset data.

using the preceding enter the part number into https://si.shimano.com/ where most Shimano parts back to about 1980 are now detailed, although not all printed documents have been scanned and the absence of a part is not proof it never existed.

sites such as 'weight weenies', where for example you can find the weight of obsolete Shimano parts that pre-date their 2004 catalogs online https://weightweenies.starbike.com/listings.php

Usenet archives; around 2000 the best source of information would have been Usenet discussions. In particular https://groups.google.com/g/rec.bicycles.tech/
Answer: Try https://si.shimano.com/
Search for the model or series number you want. The manuals go back a way, but not forever. Some series/parts more than others. If you go to 105, for instance, there are tabs for R7000, 5800, 5700, 5600, 5500 and ARCHIVE. It's easy enough to navigate.
Having had a browse around, there are a significant number of older documents added from last time I had a look, early 90s or even late 80s,
Comment: Some favourites include: https://si.shimano.com/api/publish/storage/pdf/en/si/P-24/SI-P-24-000-00-ENG.pdf   https://si.shimano.com/api/publish/storage/pdf/en/si/M-97/SI-M-97-000-00-ENG.pdf


Ride By Attack and Pounce on a mount

Question: Pounce would allow me to make a full attack on the end of a charge. This bonus also applies on a mounted charge. However, what happens if I combine a mounted charge with a ride-by attack? Can I still make a full attack against my target, or not, since the square he occupies is not (strictly speaking) the end of my charge.
Comment: What mount are you using that has pounce?
Comment: None. I (Or rather, the player for whom this is relevant) has pounce.
Answer: Despite the awkwardness of the situation, yes, you can.
Ride-By Attack itself details how it should be handled. It's mechanic is separated into two steps: normal charge and additional movement.
"Normal charge" part works, well, like normal charge. So, if you are allowed to execute full attack at the end of normal Charge action, you can execute it at the end of the first part and then go to the second one.

As I mentioned above pounce on iteratives sounds awkward for me. Still, awkward or not, rules do allow that, so untill your DM bans it, the combination you want may be executed.
Comment: @Arthaban As far as I know, it is considered that it is a creature who make attacks who must jump to achieve Leap Attack benefit on those attacks. May be if your mount somehow has Leap Attack as well, you may pull all that staff together. Still questionable, though.
Comment: Possibly overstepping the boundaries of this question, but would that mean one can also benefit from the bonuses given by the Leap Attack feat if their mount makes a jump during the charge?
Comment: @Arthaban This DM would allow it as an extension of *You [the rider] move at its [the mount's] speed, but the mount uses its action to move* (*PH* 157). That is, a mount jumping, essentially, *is* the rider jumping. (In fact, a mount's ability to jump is *dictated* by it rider: The Ride skill use leap (DC 15) says, "You can get your mount to leap obstacles as part of its movement. Use your Ride modifier or the mount's Jump modifier, *whichever is lower*, to see how far the creature can jump" (*PH* 80; emphasis mine).)
Answer: When your mount charges, your own pounce isn't applicable
For reference, this answer is based on the Pounce special ability's wording in the 3.5 SRD:

When a creature with this special attack makes a charge, it can follow with a full attack — including rake attacks if the creature also has the rake ability.

The basic rules for mounted combat use the following wording:

[...] Your mount acts on your initiative count as you direct it. You move at its speed, but the mount uses its action to move.
[...]
If your mount charges, you also take the AC penalty associated with a charge. If you make an attack at the end of the charge, you receive the bonus gained from the charge.

(Emphasis mine)
You direct your mount to make a charge, which is not the same as charging yourself. This means that a human riding, say, a tiger, can direct it to charge and pounce (using the somewhat misnamed 'fight with warhorse' Ride option). But a catfolk riding a horse can't use his own pounce ability with his horse's charge.
To me, this seems to also make more sense from a thematic/narrative perspective - a tiger or a catfolk can pounce thanks to their own agility, covering the distance to the target in one swift leap. This isn't the case when they are mounted.
Finally, the rules for mounted combat also have this to say:

If your mount moves more than 5 feet, you can only make a single melee attack. Essentially, you have to wait until the mount gets to your enemy before attacking, so you can't make a full attack.

Which also seem to indicate that pounce shouldn't apply.
Personally, I'd allow pounce-while-mounted for situations where both the mount and the rider can pounce, e.g. a catfolk riding a tiger (it's just too thematically cool to disallow), but we'd treat that as a houserule...
Comment: This answer would be improved by citing the rules for Pounce (and specifying which variant, I would be surprised if they were all worded exactly identically). For example, *Catfolk Pounce* says: *If you use the charge action, ...* which indeed conflicts with *If your mount charges, ...*.
Comment: @MatthieuM. Rider uses Charge action to execute a mounted charge. His mount may have no valid target at the end of the movement, but rider must. It is him who charges, and mount may charge too if it can meet all criteria, but if it can't (or does not want, or more likely rider does not want) it just executes movement part of charge action without attack at the end (still with penalty appropriate for a charge). That is why authors sometimes refer to that activity by saying "mount charges" even if mount usually doesn't follow it's movement with an attack when mounted character charges.
Comment: @MatthieuM. - done - thanks for the feedback.

Ride By Attack and Pounce on a mount


Out of the box functionality for Leads and Campaigns

Question: Good day all,
I am new to SFDC and wanted to know where I could find information that shows me what is available to my company native and "out of the box" for Leads and Campaigns.  COuld someone please point me in the right direction.  We will be integrating with Eloqua but I wanted to know what SFDC has in place.  Thanks for your help!
Answer: I would also recommend reading up on campaign influence. This is standard Salesforce functionality, and can be incredible useful for marketers. In my experience, however, it can be very confusing to wrap your head around at first glance.
Great blog post here: http://certifiedondemand.com/salesforce-com-certified-administrator/sales-cloud/understanding-salesforce-campaign-influence/
Salesforce documentation here: https://help.salesforce.com/HTViewHelpDoc?id=campaigns_influence_intro.htm&language=en_US
Answer: To quickly get an idea, I'd advice you to watch some of the youtube content. Everything you see there is standard Leads and Campaigns.
E.g.:
Leads:  http://www.salesforce.com/_app/video/Sales_Cloud_General/help/Manage_Leads_Opptys_video.jsp
Campaigns: http://www.youtube.com/watch?v=FXVbFKRoZOM
For a deeper dive, you could start with the SF help function:
Leads: https://help.salesforce.com/HTViewHelpDoc?id=leads_def.htm&language=en_US
Campaigns: https://help.salesforce.com/HTViewHelpDoc?id=campaigns_def.htm&language=en_US
Answer: If you purchase Professional Edition or above, you will get access to campaigns.
If you have Campaign functionality, you should use campaign members / responses as often as you have the ability to -- especially if you've spent cash on a specific campaign.  So for example if someone registers for one of your webinars, you should track that as a campaign member response.  If they download an asset, you should track that as a response to another one of your campaigns.
The campaign member history accumulates on leads and carries over to contacts and is indelible.  The campaign response is one of the most durable and useful objects in the entire salesforce.com ecosystem!
Assuming your sales reps create Opportunity Contact Roles, the aforementioned Campaign Influence reports will work.
Salesforce by default will apply the "Last Campaign Response" as the Primary Campaign in the opportunity an opportunity is created is directly by lead convert or directly from a campaign.
If you need more sophisticated way of looking at a more complex campaign consumption environment, you should check out a cheap add-on app like the Magic Robot Campaign Influence Analyzer & Contact Role Creator


Transfer funds from Scotiabank to US account at Bank of America

Question: What is the best way to transfer a large sum of money from my checking account at scotiabank to my new account at Bank of America?
Comment: This _has_ to be a duplicate; we've covered just about every possible aspect of interbank funds transfer...
Comment: Right, but need the link.....
Answer: You didn't specify where in the world you account is - ScotiaBank operates in many countries.
However, for large amounts where there is a currency conversion involved, you are almost guaranteed to be better off going to a specialist currency broker or payments firm, rather than using a direct method with your bank (such as a wire transfer).
Based on my assumption that your account is in Canada, one provider who I have personally used with success in transferwise, but the best place to compare where is the best venue for you is https://www.fxcompared.com
In the off chance that this is an account with Scotiabank in the United States, any domestic payment method such as a domestic wire transfer should do the job perfectly well. The fees don't matter for larger amounts as they are a single fee versus a percentage fee like you see with currency conversions.


Internal mic is not working on a Dell Studio 1558

Question: I made upgrade from Ubuntu 10.10 to Ubuntu 11.04 (amd64 version) at my DELL Studio 1558 notebook. After that internal mic is not working (at previous version all was ok). But external microphone, connected to to computer is well working. How to solve this problem?
Answer: There is a bug report related with this issue. See the link below. No easy solution so far.
https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/731706
Answer: I had the same problem, I followed the instructions on the blog posted by Gianni and didn't work,although it helped me a lot. Here's what I did to fix it:

Run alsamixer in a CLI prompt
Ensure that there's that a 00 appears at the bottom of the master meter.
Hit tab
Check that the Mic meter is up to 100 (First column)
Check that capture is enabled (Second Column)
Ensure that Input Source (Fourth column) says Internal M, originally it said Mic and when I changed it my mic started working.

Hope this helps
Answer: I have a similar problem on my DELL Studio 15. After a fresh installation of Ubuntu 10.10 the internal microphone worked but suddenly (I don't know what I did) it stopped working. Even now after updating to Ubuntu 11.04 it does not work.
Have you tried to boot from the Life CD and check if your microphone does work? In my case it worked.
Answer: Give this a try. When I upgraded from 10.10 everything was working for a day or so then I did an update and the microphone stopped working.
Comment: Whilst this may theoretically answer the question, [it would be preferable](http://meta.stackexchange.com/q/8259) to include the essential parts of the answer here, and provide the link for reference.


Identifying book about a boy forced to destroy a Holocaust survivor's wooden model

Question: Book was set in the 1950s about a boy working for a racist store owner. The main character's brother was killed in a hit-and-run which sent his father into a deep depression. The store owner he works for is extremely racist and prejudiced, mocking his customers behind their backs. It's also heavily implied he abuses his wife and daughter. Eventually, the boy meets a Holocaust survivor who lost his family in WW2. He doesn't speak much and tips his hat to everyone who passes by him. He learns that the man is creating a wooden model of his old village. When he tells his boss about the man, his boss threatens him with expulsion from school unless he destroys the man's model.
Comment: Welcome to the site! You say the book was *set* in the 1950s, but when was it *written* - also in the 1950s, or much more recently? Or at least, when did you read it? What language was it written in, and was it translated? Which country did you find it in, and where was it set? (I'm guessing Europe, but it could have been a Holocaust survivor who fled elsewhere in the world.) All these little bits of information will help to narrow the search. There's more such questions in the [ID tag wiki](https://literature.stackexchange.com/tags/identification-request/info) that might help jog your memory.
Answer: This is Tunes for Bears to Dance To by Robert Cormier.

12-year-old Henry Cassavant moves with his parents to a new town to escape from the memories of Henry's older brother Diltz, who was hit and killed by a car. Henry contributes to his family by working at a grocery store for Mr. Hairston, a deceptive old man who makes rude and racist comments about the townsfolk that would walk by his store.

Henry follows the old man to an art center, where he meets him in person. From George Graham, the supervisor of the center, Henry learns the old man, Mr. Levine, is a Holocaust survivor who lost his family to the SS. Mr Levine goes to the art center every day to carve out a model of his old hometown, complete with carvings of all the people he had lost, including his wife and children.

Mr. Hairston tells Henry that he will let him keep the job and he will get his brother's headstone on one condition: he must destroy Mr. Levine's model village.

It's an exact match to what you describe, I don't have much more to add to this answer. How I found it: the winning search query was 1950s novel boy shop owner "holocaust survivor" lost family "model of his village" destroy. The exact quotes were a risk, as I didn't know if those exact phrases would be used even if all the details matched, but luckily it led me to this page where the book is described by the following blurb:

Eleven-year-old Henry Cassavant works in a grocery store for a racist grocer
in a neighborhood of immigrants. His employer's racist comments disturb Henry, who has
recently befriended a Holocaust survivor, Mr. Levine, who works tirelessly each day at the
city's arts and crafts center, carving an intricate model of his village which was destroyed
during World War II. When the village is finished, Mr. Hairston coerces Henry to destroy
the village, threatening to fire him, to have his mother fired from her job, and to ensure
that neither of them will be employed by any other merchants in town.

(second half of the plot summary removed because of spoilers, for anyone else who may read this)


How well will the max transformation rounds in Keepassx deter an attacker for the next twenty years?

Question: Keepassx lets you decide how many transformations rounds need to be run in order to unlock your Keepass database.  In my version of Keepassx (2.0.3) the max value seems to be 999,999,999.  With that setting it takes my laptop about 22 seconds to unlock the database.  I imagine that a beefy workstation would take less time than that.  With that in mind, how well can this setting deter someone else from accessing your database, assuming that they managed to get access to it?  Let's just say an individual (not an organization) with a computer made to do this kind of work.  How much work can you assume that they will have to do per try with the kind of computation power that they will have access to in twenty years?
Comment: I'm not sure that anyone can guess what computing power will look like in 20 years ...
Comment: Are you sure that you need to be able to keep the data inside secret for 20 years? By rolling over the password once every 2 years, you just need to be able to secure it for 2 years max, 1 year average.
Comment: @schroeder Sure, but it's pretty easy to create a sane upper based on trends and our understanding of computing hardware. While 100 years is very likely too distant in the future to guess where technology will be going, I'd be willing to bet big bucks that, 20 years in the future, we're still using the same basic technology (fast switching semiconductors, probably still silicon on various substrates).
Comment: @MechMK1 That would be more sensible.  :-)
Answer: The passwords kept in the password manager database can be arbitrary long, because user doesn't need to remember them, he will just copy them from the password manager. But the *master password is not stored in the database. It should be either remembered or stored somewhere else (e.g. in hardware like Yubikey or Titan key). Passwords of what length can you remember? 10 characters? 12?
A human readable password of 12 characters means entropy of about 72 bit. This is can be brute-forced easily. To slow brute-forcing down, Keepass uses transformations.
How much slowness is needed?
Suppose you have password of 12 characters, each one from the range of "human friendly" characters (a-z, A-Z, 0-9 --> 62 characters). There are 62^12 possible passwords, this is about 10^22.
Suppose password transformation takes 1s. Suppose an attacker has 1 000 000 CPUs. The he will be able to check 1 000 000 passwords/s.
There are about 3x10^7 seconds in a year. The attacker will check 3x10^7 x 1 000 000 = 3 x 10^13 passwords per year.
To check all 10^22 passwords he will need 10^22 / (3 x 10^13) ~= 3 x 10^8 years.
If you use less iterations so transformation instead o 1s takes 0.001s, then the attacker will need 3 x 10^8 x 0.001 = 3 x 10^5 = 300 000 years.
Not only takes it long. It costs also money: to purchase these CPUs, to supply electric power, etc. Who will rent a cluster of 1 000 000 CPUs for many years just to break your password?
It is much cheaper to install some hardware like video cameras or key loggers and obtain your password in a short time.
To your question: even transformation of 0.001s and password of 12 random characters will deter an attacker for many thousands of years.
Comment: 80+ or even 90+ entropy passphrases are pretty easy with diceware.
Comment: 72 bits _cannot_ be brute forced easily, though it's not impossible with enough money.
Comment: @Guildenstern: As I showed you *don't have* to wait 22 seconds to open database. Even if you adjust the number of iterations so that transformation takes 1s, it will take 3 x 10^8 years to brute-force it. Waiting 22 sec each time you are just loosing time without effectively getting more security.
Answer: A bit of math allows you to easily understand how many extra bits of security these iterations provide. The general rule is that the number of bits of security you gain is the base 2 logarithm of the number of iterations. Rounding your maximum value of iterations to 109 iterations, you gain log2(109) ≈ 30 bits.
Is an extra 30 bits enough to deter an attacker for the next 20 years? That depends on how many bits of entropy your initial password has. If your original password started with 70 bits it would be difficult, but not impossible, to break even today. If you add an extra 30 bits through 109 hash iterations, you will have effectively 100 bits of security, which is likely to deter most attackers for the next 20 years.
Comment: The answer is not quite correct. You ignore the performance. Suppose they changed internal implementation and put 1 000 000 todays transformations into a loop and call it a single transformation. So that 1 000 new transformations need the same computational resources as 1 000 000 000 todays transformations. You may say that the entropy increases in log2(1 000) = 10 bits, which is 20 bits worse than in todays scenario, and that it is essentially easier to brute-force it. But that is not true, because the hacker still needs *the same* computational resources.
Comment: Another example: Suppose you have a 4-digit PIN. A 256-bit key is derived from it and derivation takes 1 hour. Because of 256-bit random IV precalculation makes no sense and the attacker has to test every single PIN. Then it does not matter that the attacker can perform let say 10^12 tests of 256-bit passwords per second, tests in the sense "does this 256-bit key decrypt this AES-256 encrypted message. He will need at least **1 hour** to brute force this 4-digit PIN having 10 000 CPUs/computers.


TFS Could not connect to database

Question: On my home machine I have lost the databases that were mapped to tfs2010.
Now it says that I cannot connect to database.
Need to create Collection but does not allow me.
how can I proceed without reinstalling tfs2010 all over again?
thanks
Answer: I gather this is was a single-server installation, i.e. database and app server on the same machine? If so, if the database tables are truly gone (deleted) then there's nothing you can do I'm afraid, because "everything" was in them (work items, source code, you name it). Anything you had stored there is gone anyway, so you might as well re-install TFS.
Before doing anything this radical, I would open SQL Server Manager and look for the databases. Maybe you have backups of them?
Answer: There is a DB named TFS_Configuration that stores the TFS server lever configuration.  If you lost that than you will need to uninstall then re-install TFS and run the configuration wizard;  the TFS install used to be a pain,  but as of TFS 2010 it is easy now - if you just reinstalling it like this it will be straightforward.

TFS Could not connect to database


Importance of Kripke–Platek set theory

Question: What would be importance of Kripke-Platek set theory? I know that Saul Kripke is one of the most important philosophers in the world, but curious in what place he is in set theory.
Comment: I do not understand what you mean by importance. If what you are asking is whether it is a central part of the subject, or it is isolated, or a curiosity, the theory of admissible sets, which is what Kripke-Platek is, is used all over the place, in recursion theory and set theory. Both in classical results, and in fairly recent ones. (I do not know how to measure "people's place in set theory", nor do I think this is the right venue to address that.)
Comment: @Mathemagician1234, that is an pretty extreme example of name dropping...
Comment: Importance for what?
Comment: General development of set theory.
Answer: Kripke-Platek set theory is important foundationally as a natural intermediate between weaker theories such as second-order arithmetic and stronger theories such as ZF.
The transitive models of KP are known as "admissible sets". The ordinals $\alpha$ for which $L_\alpha$ is admissible are called "admissible ordinals". These are key subjects of study in a generalized computability theory known as $\alpha$ recursion theory. In turn, admissible sets are closely related to descriptive set theory. The simplest nontrivial admissible ordinal is $\omega^{CK}_1$ which is tightly connected to hyperarithmetical theory, which $\alpha$ recursion theory generalizes.
From a different point of view, a key feature of KP is that separation and collection have been restricted to "predicative" formulas. The $\Sigma_0$ formulas that are allowed in these schemes in KP have only bounded quantifiers, which means that they do not quantify over the entire universe of sets, only over a fixed subset of the universe.
There are also connections between admissible sets and the infinitary logic $L_{{\omega_1},\omega}$. One example of this is the Barwise compactness theorem.
Two detailed references on this are Generalized Recursion Theory by Sacks and Admissible Sets and Structures by Barwise. I believe both of these are now freely available in Project Euclid.  A shorter survey by Makkai is in the Handbook of Mathematical Logic.

Higher Recursion Theory by Sacks  at projecteuclid
Admissible Sets and Structures by Barwise at projecteulid
Makkai: Admissible Sets and Infinitary Logic (from Handbook of Mathematical Logic By Jon Barwise) at
Google Books
Comment: I've added links to the references you've mentioned - I hope you don't mind. Of course, if you don't like the format, you can edit the post. (I've added the links at the end, since I did not want to make changes in your post.) I think having links here might be useful for the people reading your post.
Comment: I am also not sure, whether the link which I gave to Sacks' book is the one you had in mind.
Comment: @Martin: Thank you for the links. That was exactly the book I had in mind. I typed the wrong title originally.

Importance of Kripke–Platek set theory


FormsAuthentication isn't preserving the UserData field after Postback in .NET 3.5

Question: I've created a FormsAuthenticationTicket from scratch, but found that when retrieving it at a later time, the UserData isn't coming back. Here is the code used:
FormsAuthenticationTicket ticket = new FormsAuthenticationTicket(
                        1,
                        user.UserId,
                        DateTime.Now,
                        DateTime.MaxValue,
                        false,
                        user.UserType);

HttpCookie cookie = new HttpCookie(
     FormsAuthentication.FormsCookieName,
     FormsAuthentication.Encrypt(ticket));

Response.Cookies.Add(cookie);

However, when reading this back on the next Request, I found that the UserData field is now empty:
string encryptedCookie = Request.Cookies[ FormsAuthentication.FormsCookieName ].Value;
FormsAuthenticationticket ticket = FormsAuthentication.Decrypt(encryptedCookie);
Assert.IsTrue( ticket.UserData.Length == 0 ); //TRUE!

Any ideas?
Comment: Old question, but two options seem likely here:  1) writing cookie to early, so it's overwritten (like `_Authenticate` vs `_LoggedIn`),  2) `FormsAuthentication.RedirectFromLoginPage()` rewrites the cookie.
Answer: I think I found the problem. If you make up your own cookie name it seems to be fine! So change from:
HttpCookie cookie = new HttpCookie(
     FormsAuthentication.FormsCookieName,
     FormsAuthentication.Encrypt(ticket));

to
HttpCookie cookie = new HttpCookie(
     "SiteCookie",
     FormsAuthentication.Encrypt(ticket));

And then retrieve it as per the question:
string encryptedCookie = Request.Cookies[ "SiteCookie" ].Value;
FormsAuthenticationticket ticket = FormsAuthentication.Decrypt(encryptedCookie);
Assert.IsFalse( ticket.UserData.Length == 0 ); //Hooray! It works

Its possible .NET does some tricky stuff with it, so by putting it in a new one works fine.
UPDATE:
Also, the ticket needs to be refreshed, as otherwise the ticket will expire while the user is using the website:
FormsAuthentication.RenewTicketIfOld(ticket); // Do before saving cookie

Answer: I have also encountered this problem.
But I think the real reason is that the server set the same cookie twice and the second override the first which contains your UserData field.
You can capture the cookie writing process by Fiddler, and here is a screenshot that show this problem:

So, how this happened? In my situation, I use the Login control to authenticate. In the Login control's Authenticate event, I set the cookie with my UserData after check the username and password manaully. Then, I set the AuthenticateEventArgs.Authenticated=true, at this time, in the debug window, I see a new cookie is queued to the response which name is also equal to  FormsAuthentication.FormsCookieName ! My solution is redirect to the Default page instead of setting the AuthenticateEventArgs.Authenticated=true.
So, you may debug your code to see if the authentication cookie is queued to the response twice.
Answer: This works for me:
//Create Form Authentication ticket
FormsAuthenticationTicket ticket = new FormsAuthenticationTicket(1, currentUser.userid.ToString(), DateTime.Now, DateTime.Now.AddMinutes(60), false, currentUser.ToString(), FormsAuthentication.FormsCookiePath);

string hashCookies = FormsAuthentication.Encrypt(ticket);
HttpCookie cookie = new HttpCookie(FormsAuthentication.FormsCookieName, hashCookies);
cookie.HttpOnly = true;
HttpContext.Current.Response.Cookies.Add(cookie);


JQuery UI Datepicker, reverse the order of the year in the dropdowns

Question: I have a datepicker with changeyear: true. The 'year' drop down displays the title as 2009, then instead of the next year below the title being 2008, 2007, 2006 and so on it starts at 1999 and counts upwards. I can't seem to find an easy solution to reverse this order?
Comment: This is inside a calendar popup, it actually gives the the user three options, either type it themselves (which is recommended in that article), select it from a popup calendar or use the drop down to select the year. Im pretty sure that is a usable solution!
Comment: I really hate the poor usability on dropdowns for selecting years and generally recommend avoiding them. Here's why: http://www.useit.com/alertbox/20001112.html.
Answer: I wouldn't recommend editing the original ui.datepicker.js as Cuong suggested because your changes will be lost as soon as you or another developer replaces the file when a new version is released. Remembering what customisations have been made in order to re-apply is not practical. Instead, you can override the existing _generateMonthYearHeader method in your own separate JS like so:
// store original so we can call it inside our overriding method
$.datepicker._generateMonthYearHeader_original = $.datepicker._generateMonthYearHeader;

$.datepicker._generateMonthYearHeader = function(inst, dm, dy, mnd, mxd, s, mn, mns) {
  var header = $($.datepicker._generateMonthYearHeader_original(inst, dm, dy, mnd, mxd, s, mn, mns)),
      years = header.find('.ui-datepicker-year');

  // reverse the years
  years.html(Array.prototype.reverse.apply(years.children()));

  // return our new html
  return $('
').append(header).html();
}

I just wrote this for something I'm working on and it does the trick nicely :)
Comment: // Add the below if condition. Other wise the year is not displayed when not a dropdown.
    if(years.is('select'))
      years.html(Array.prototype.reverse.apply(years.children()));
Answer: I think the best way to hack the plugin without ripping it is assigning a event handler to the year select item.
//Hack for reverting year order
$(document.body).delegate('select.ui-datepicker-year', 'mousedown', function() {
  (function(sel) {
    var el = $(sel);
    var ops = $(el).children().get();
    if ( ops.length > 0 && $(ops).first().val() < $(ops).last().val() ) {
      $(el).empty();
      $(el).html(ops.reverse());
    }
  })(this);
});

This code must work fine! :P
Answer: There is a "way" to get the year started from the last date:
dateFormat: 'mm/dd/yy',
changeMonth: true,
changeYear: true,
yearRange: "-70:",
maxDate: "-13Y"

Instead if using yearRange as fixed years yearRange: "1900:-13"  it's better to use this from bottom up: "-70:", and set the maxDate.  Now I get my year select box starting from 2004 and not 1900.
P.S: All the other solutions have been tested. They are very slow, and some don't work so well (especially the old ones - sets current year instead of 2004 for example).
Answer:
Open the file ui.datepicker.js
Find the method _generateMonthYearHeader: function(inst, drawMonth, drawYear, minDate, maxDate, selectedDate, secondary, monthNames, monthNamesShort)
Find the following loop in the method
for (; year <= endYear; year++) {
    html += '<option value="' + year + '"' +
        (year == drawYear ? ' selected="selected"' : '') +
        '>' + year + '</option>';
}

html += '</select>';

Insert the following code before that loop:
if (year-100 < 1900) // Check year is lower then 1900
    year = 1950;     // change start point of above loop, it helps you having the
                     // year's dropdownlist starting at 1950, and ending of current year plus 10.

Answer: I have an answer to you, but it's not exactly what you may want to hear.
After searching the internet for a solution that would reverse the order of the years in the dropdown, I have come to this:
{
    changeMonth: true
    , changeYear: true
    , yearRange: '-65:'
    , maxDate: '1999/12/31'
}

This will have the maxdate preselected, and therefore choosing a year you will automatically see the last entry, thereby being able to scroll up to choose an earlier date.
Edit: yearRange is added arbitrarily, to create a starting point 65 years ago. maxDate is also chosen arbitrarily, as a date 12 years prior to writing this comment. Basically this menu will allow someone to choose an age between 12 and 65 years.
It's not ideal, but it works well enough.
Answer: Replace the first line of the for loop with:
var minYear = year;
year = endYear;
for (; year >= minYear; year--) {


Why does the Authorized Version use the name "Jehovah" only in four verses?

Question: What's special about Exodus 6:3, Psalms 83:18, Isaiah 12:2, & Isaiah 26:4? Why does the Authorized Version translate the Tetragrammaton as Jehovah in those four verses, but replace it with LORD or GOD everywhere else?
Comment: Isaiah 12 and Psalm 83 are both specifically saying "my name is Jehovah". It would not make sense to render that "my name is the LORD" even if you rendered the name "the LORD" elsewhere. The other two are "Lord Jehovah" which I believe is a rendering of a specific phrase, something like "Lord Yahweh" which would also not make sense to render as "Lord LORD"
Comment: I believe that the Tetragrammaton is usually rendered as "LORD" except in the phrase Lord YHWH, which is rendered as "Lord GOD".
Answer: The general policy of the writers of the Authorized Version was that the divine name, also called the Tetragrammaton  (usually rendered "YHWH" or "Yahweh" today but often "Jehovah" in older times), would not be rendered directly, but would be replaced with "the LORD".
There are a number of exceptions to this. These exceptions are:

When the Tetragrammaton is specifically referred to as the name of God. This is the case in Exodus 6 and Psalm 83. Writing things like "my name is the LORD" would make little sense.
When the divine name is used as part of a place name, such as "Yahweh Yireh" (or  "Jehovah-jireh"). Again replacing the name with "the LORD" makes no sense in these circumstances. These cases are not listed in the question.
When the name is repeated by combining it with a derivative or alternate version of itself. Again "the LORD LORD" does not make sense (although other translations render it "the Lord, the Lord himself"). This is the case in Isaiah 12 and 26.
Comment: You are welcome to your opinion but it makes sense to many people and many other translations do it.
Comment: It makes no sense to ignore the Devine name and replace it with LORD in any circumstances
Comment: @DJClayworth, The linked Wikipedia article on the Tetragrammaton mentions that observant Jews don't read aloud the name, instead replacing it with words like "Adonai" (meaning "my Lord"). Could this have anything to do with it being replaced by LORD in the King James Version (i.e. could the translators have been honoring the Jewish tradition)?
Comment: Also potentially relevant (precedent from the Greek Old Testament): https://books.google.com/books?id=q5lKAwAAQBAJ&pg=PA60
Comment: @SamuelBradshaw I believe that [the linked question](https://christianity.stackexchange.com/q/67403/214) may be relevant to your question.
Answer: It is unarguable that the ancient Hebrew text of what we now call "The Old Testament" had the divine name written 6,961 times. Those four Hebrew letters spell YHWH, often rendered as Yahweh. This is the Tetragram and, in some translations is transliterated as Jehovah. Yes, the Authorised (King James) Version has it in the four places stated in the question.
However, it should be pointed out that it has it in three other places, as follows:

"And Abraham called the name of that place Jehovah Jireh" [Jehovah
will provide]. Genesis 22:14
"And Moses built an altar, and called the name of it Jehovah Nisi"
[Jehovah is my banner]. Exodus 17:15
"Then Gideon built an altar there unto the LORD, and called it Jehovah
Shalom" [Jehovah is peace]. Judges 6:24

The first instance referred to a place in Jerusalem, afterwards called Moriah. The second instance was circa. B.C. 1491 to commemorate the defeat of the Amalekites. The third instance was after a miraculous communication from God to Gideon, circa. B.C. 1256
So, there are seven instances. Of course, that is still woefully short of the total of 6,961 times where the Tetragram was originally written! This seems to be an  instance of inconsistency in the Authorised Version. There would be nothing wrong with transliterating it as either Yahweh or Jehovah all 6,961 times, to be consistent. Young's Literal Translation (1898) does that, as Jehovah.
I looked through what articles and literature I have of the Trinitarian Bible Society, but could not find one on their use of the Tetragram. I also looked at their web-site but could not find any way of tracking down that specific point. Really, the best way of getting an answer would be for you to contact them and ask them directly about this inconsistency. Their web-site is http://www.tbsbibles.org
Comment: @User 14 I use the YLT (Jehovah nearly 7K times in the OT) and the K.J.V (7 times) but the TSB who only print the K.J.V, have no problem, as you think. It is the N.W.T. that has a problem as the TSB shows in their article "Christ in the Desert: the testimony concerning Christ found in the N.W.T. of the Jehovah's Witnesses" (Quarterly Record mag. issue 531, 1995, pp.2-6. Also see article "The Name of the LORD: a strong tower", Quarterly Record issue 518, 1992, pp.4-11). To give one sample quote: "The purpose of this article is to demonstrate that unsaved men cannot entirely remove the
Comment: the testimony which the Scriptures give concerning the person of the Lord Jesus Christ. Here, by their use of the name 'Jehovah' in the New Testament, they prove that Jesus is God…" I would encourage you to e-mail the TSB and ask them to let you see that first article I quote from, and also the second one mentioned.
Comment: So Anne which translation do you prefer and how many times does it transliterate the Tetragrammaton as Yahweh or Jehovah?
Comment: The TBS won't admit it but the fact is that having "Jehovah"in the Bible nearly 7k times is a problem for the  acceptance of the trinity doctrine that they promote


Do Auslander-Reiten quivers coincide with the McKay quivers for arbitrary subgroups of GL(2,C)?

Question: It is a theorem of Auslander that if $G< GL(2,\mathbb C)$ is a finite subgroup without pseudo-reflections, then the Auslander-Reiten quiver of $K[x,y]^G$ coincides with the McKay quiver of $G$ with the canonical representation. I would like to know what is known for arbitrary finite subgroups of $GL(2,\mathbb C)$, even those which contain pseudo-reflections. Do we still get this correspondence? If no, why not? Is there some specific cases where this is still true? Thank you.
Answer: This is not true.
First up, you need to take the completion of $k[x,y]^G$ before the statement even makes sense; for an AR sequence to exist you need your endomorphism rings to be local.  Also, you might want a Krull-Schmidt category too, and this for these reasons Auslander studies $k[[x,y]]^G$.
Now in the case of pseudoreflections, being the quiver of the quotient stack, roughly speaking the McKay quiver remembers the action of G, as well as the lines of reflection.  On the other hand, the category of CM modules of $k[[x,y]]^G$ only sees the singularity, not how it is created, which in the case of pseudoreflections is much "smaller" a singularity than you might expect.  Thus, based on this intuition, we should expect the AR quiver to be smaller than the McKay quiver in general.
Indeed this is the case. Consider the example $\frac{1}{4}(1,2)$, then the invariants are $x^4$, $x^2y$ and $y^2$, which if we label as $A$, $B$ and $C$, satisfy the equation $AC=B^2$.  Thus the AR quiver of the category of CM modules is (by Auslander) the McKay quiver for the group $\frac{1}{2}(1,1)$ which has only two vertices.  On the other hand, the McKay quiver of $\frac{1}{4}(1,2)$ has four vertices.
The general statement is that the AR quiver of $k[[x,y]]^G$ is the same as the McKay quiver for the group $G/N$, where $N$ is the subgroup of $G$ generated by pseudoreflections.
Comment: Thank you very much for this complete answer. I think it makes sense when thinking about the result of Chevalley: If a group $G$ acting on $k[[x,y]]$ is generated by reflections, then there exist $G$-invariants $u,v$ such that $k[[x,y]]^G\cong k[[u,v]]$. Thus, in this case the Auslander-Reiten quiver as only one vertex, while the McKay quiver of $G$ is more complicated in general.


Angular Frequency interpretation?

Question: I just began a topic on waves and oscillations and came across a term angular frequency ($\omega$) which was stated as $2\pi f$. However, I have seen the same symbol $\omega$, used for angular velocity. I know how to interpret angular velocity as the rate of change of angular displacement and how it relates to rotational motion, however I'm really confused with angular frequency as it relates to Simple Harmonic Motion and how I'm meant to interpret it.
Answer: You can take it as simply a definition, but the best way to motivate the definition is to observe that simple harmonic motion is the motion of the projection onto a straight line of the motion of a particle undergoing uniform circular motion (i.e. with constant angular velocity about the circle's center).
So, imagine a particle undergoing uniform circular motion on a unit radius circular path centered at the origin of a Cartesian co-ordinate system and with the motion confined to the $x-y$ plane. If the particle's constant angular speed is $\omega$, then the $x$-component of the particle's motion is described by $x=\cos(\omega\,t+\delta)$, for some constant phase $\delta$.
Comment: So angular frequency is simply the projection of the angular velocity on a straight line? ?
Comment: Might be helpful for some users to note that the projection scheme is sometimes called the "reference circle" and that from a slightly more technical perspective it is formally a "phasor".
Answer: The function describing a simple harmonic oscilator is:
$$x(t) = A \cos(\omega t+\phi)$$
which satisfies
$$m\frac{d^2x(t)}{dt^2}=-k\,x(t).$$
You can also verify that
$$\omega=\sqrt{\frac{k}{m}}.$$
Now imagine having a vector with length A and imagine that this vector starts rotating with a constant angular velocity $\omega$ and phase $\phi$. It's clear that the projection of this vector on the x-axis is exactly equal to the first equation.
We conclude that these two motions can be described with equivalent equations and therefore we call the parameter $\omega$ the angular velocity of the HO.

Angular Frequency interpretation?


Take any three-digit positive integer, reverse its digits, and subtract. The difference is divisible by 11.

Question: Take any three-digit positive integer, reverse its digits, and subtract. For example, 742 − 247 =
495. The difference is divisible by 11. Prove that this must happen for all three-digit numbers abc
Answer: \begin{align}
x &= 100a + 10b + c \quad &\text{Any three digit number can be expressed in this form}\\
y &= 100c + 10b +a \quad &\text{This is the number once the digits are reversed}\\
x-y &= 100a - a + 10b -10b +c -100c = 99a-99c\\
x-y &=11 \cdot(9a-9c)
\end{align}
Answer: The first number, what you've called "$abc$", is equal to $100a+10b+c$. "$cba$" is $100c+10b+a$. Thus, their difference is:
$$100a+10b+c - (100c+10b+a)\\
=99a-99c\\
=11(9a-9c).$$
Since $9a-9c$ is necessarily an integer, $11$ divides $abc-cba$.
Answer: A three digit number can be expressed as
$100x+10y+z \cdots1$
Where $x,y,z$ are the digits in the number .
Lets reverse it
We get
$100z+10y+x \cdots2 $
Subtract equation 2 from 1
We get
$99x-99z$
Which can be expressed as
$11(9x-9z)$
Thus it will be multiple of 11.
Answer: A more fun trick is:
Let $abc > cba$ (in other words) $a > c$.
Let $abc - cba = def$  (If $d = 0$ write it as a distinct zero)
Then $def + fed = 1089$.
...
To subtract $abc - cba$ you must subtract $a$ from $c$.  But $a > c$ so you must borrow.  That leaves $(10 + c - a)$ in the one's place.  The ten's place is $b - b$ but you borrowed from the $b$ so you have $(b-1) - b$.  $b > (b-1)$ so we must borrow again.  So that leaves $10 + (b -1) + b = 9$ in the tens place.  Then to subtract the hundreds place we have $(a-1) -c = (a-c - 1)$.
So $abc -cba = [a-c -1]9[10 + c-a]$
Reverse and add $[a-c -1]9[10 + c-a]+ [10+c-a]9[a-c-1]$
The ones: $(10 + c -a) + (a-c-1) = 9$.
The tens: $9+9 = 18$ write the $8$ and carry the $1$.
The hundreds $[a-c -1] + [10 + c -a]=9$ plus the $1$ we carried gives us $10$.
So $[a-c -1]9[10 + c-a]+ [10+c-a]9[a-c-1]=1089$  (which can be though of as $9*100 + 2*9*10 + 9$ which is $9(121) = 9*11^2$.  (Food for thought.)
Also as $[a-c -1]9[10 + c-a]$ if you add the odd places $[a-c-1], [10+c-a]$ you get $9$.  And if you add the even places you get $9$.  As they are equal this is divisible by $11$. (And that explains why that rule works in the first place.)


What is this noise coming from my gas furnace?

Question: Whenever I change my air filters in my furnace, I hear a boom noise. The last time I called DEER and they came out and fixed the problem (I can't remember what the part was called that was needed). It happened again, the booming sound, after I changed the filters. What could be causing this problem and how can I get it fixed and never have it happen again, even after changing the filters?
Comment: Could you define DEER, tell us the furnace fuel, post a picture, and try to localize the sound?
Comment: As you're sliding the filter in, the boom happens? Are you using a sledgehammer to install the filter?
Comment: If you hear the boom when the furnace turns on, it could be the furnace sucking the filter against the intake hole. If the filter bracket has a bit of wiggle room, the filter may not sit right against the inlet. When the blower turns on, a low pressure area is created inside the furnace. The higher pressure air in the cold air return rushes to balance the pressure, which forces the filter to slam into the filter frame as it's forced against the inlet.  However, this is all speculation, since you haven't provided enough information to definitively answer the question.
Answer: Assuming no sledgehammers were used, you could be hearing a sheet metal change shape, triggered by temperature.  It will likely be a large flat area of metal somewhere...


How to evaluate contour integral

Question: I have a homework problem to evaluate the integral
$$
\oint_{\gamma}\frac{\cos z}{(z+i)^3}dz
$$
along the curve $\gamma(t)=-i+e^{it}, t\in[0,2\pi]$. I proceeded to plug the given information into the definition of a contour integral and got to the expression
$$
\oint_{\gamma}=i\int_{0}^{2\pi}\cos(-i+e^{it})e^{-2it}dt
$$
which seems hardly helpful. I don't know how to evaluate this or manipulate it any further and I suppose there is some trick earlier on to make the integration more manageable. I just can't figure it out so I'd be grateful for any help.
Comment: This is a typical exercise about Cauchy's integral formula.
Answer: With rediue theorem
$$\oint_{\gamma}\frac{\cos z}{(z+i)^3}dz=\dfrac{2\pi i}{2!}\lim_{z\to-i}\dfrac{d^2}{dz^2}\cos z=-\dfrac{2\pi i}{2!}\cos i=\color{blue}{-\dfrac{\pi i}{2}\left(e+\dfrac1e\right)}$$
Answer: Hint: As Jose hints in the comments, we want to use the fact that
$$f^{(k)}(z_0)=\frac{k!}{2\pi i}\oint_{\partial B_r(z_0)}\frac{f(z)}{(z-z_0)^{k+1}}dz$$
with the correct holomorphic function $f(z)$

How to evaluate contour integral


Emulate program behavior using neural network

Question: I have an exe file but no access to its source code. It takes as input a list of 8 parameters and prints text files containing the output. I was wondering if it is possible to write an AI-based program that (given that I am a newbie with IA) can "train" a neural network using the input and output of my exe file to kind of create a black box that emulate the given exe file.
Answer: If the program is a black box - that is, it actually computes its output from the values of the inputs within its own code (which means, it does not, for example, go out and read values off some device, or rely on some external service whose results are not predictable) - then, yes, you can write an AI that emulates the program.   Unless the program is fairly trivial, however, the emulation will be approximate - that is, for at least some inputs, the output will not be correct.   How close you can get to adequate emulation will depend on the details of how the inputs are processed, and how much training effort you are will and able to afford.
If you want to do this, you should probably start learning about reinforcement learning toolkits.   Rllib is one popular such tool set, if you're using (as I would assume you are) Python for your experiments.