Blockchain.info testnet websocket doesn't work

Question: When I try to connect testnet websocket provided by blockchain.info api. Connection doesn't establish, when i looked into the code. It says for testnet it uses "wss://ws.testnet.blockchain.info/inv" url. I guess that blockchain.info stops the service for testnet. Is there any other websocket api provider for bitcoin testnet?
Answer: ~> curl --head https://testnet.blockchain.info
HTTP/1.1 503 Service Unavailable
It's likely the service just isn't something that exists.
Comment: I found out another way to do this. smartbit.com.au provide api for both testnet and mainnet for bitcoin with some awesome api playground. I built my app over this website. But thanks for your comment though. :)
Answer: I'd recommend using the Esplora API that powers blockstream.info for testnet blockchain data.
For example you can use curl to get the latest testnet block hash:
curl https://blockstream.info/testnet/api/blocks/tip/hash


Apache Webserver: check if decompression is supported

Question: With SetInputFilter DEFLATE I can force the apache to decompress incoming messages. Is there a way to ask the webserver whether it supports decompression of incoming requests. I would expect a specific HEADER information for that. The only HEADER information I know of is: accept-encoding (which is for requests, afaik) and content-encoding (which only tells the client that the response is encoded right?).
Answer: Apache documentation for mod_deflate explains this very clearly:

Input Decompression
The mod_deflate module also provides a filter for
  decompressing a gzip compressed request body . In order to activate
  this feature you have to insert the DEFLATE filter into the input
  filter chain using SetInputFilter or AddInputFilter, for example:
<Location "/dav-area">
   SetInputFilter DEFLATE </Location>

Now if a request contains a Content-Encoding: gzip header, the body will be automatically decompressed.
  Few browsers have the ability to gzip request bodies.
  However, some special applications actually do support request
  compression, for instance some WebDAV clients.

This means that by setting the input filter to DEFLATE, apache will search the request headers for Content-Encoding: gzip and will decompress the input only when this header is present.
Comment: Thanks for the hint. But let's say I'am writing a client to send compressed data to the apache but I don't know whether the apache is able to decompress it, is there any way to do that before and decide whether I want to send it compressed or plain ? I am thinking of a header information in the response, so that the client fires a dummy request in the first step to determine whether the apache supports compressed data.
Answer: Unless specifically configured otherwise, modern browsers and web servers handle the negotiation of the compression scheme automatically. Typically handled in 2 steps whereby the client will advertise supported compression schemes and the server will reply using a compression scheme that both support.
See this article for a fair treatment.
If you do wanted to "check" for it first, you could fetch any asset from the server and parse the value of "Content-Encoding" from the response headers
Comment: As far as I understand you are referring to the simple case where the server sends compressed data to the client. In this case the client sends a message with accept-encoding and the server answers with content-encoding header - so far so good. But what I am looking for is the other way around. I don't want the client to advertise the supported compression schemes but the server, so that the client decides whether it sends compressed data or not.


How to do delegated authentication in salesforce

Question: I am implementing SSO, the documents which are avaliable via Salesforce.com are hard to understand. Does anybody know an easy to understand document or blog where I can study and implement it. Thanks in adavance
Answer: http://wiki.developerforce.com/page/How_to_Implement_Single_Sign-On_with_Force.com
Refer the above article and thats the one of the best articles i have read on this .
You will first need to raise a case with salesforce to enable delegated authentication for your org.
https://help.salesforce.com/apex/HTViewHelpDoc?id=sso_delauthentication_configuring.htm&language=en
Not sure if you referred the above link to configure this .
Its a very simple process where once salesforce enables the delegated authentication for your org you will follow the below steps

1)In Salesforce, download the Web Services Description Language (WSDL) file AuthenticationService.wsdl from Setup by clicking Develop | API | Download Delegated Authentication WSDL
2)Add a link to your corporate intranet or other internally-accessible site that takes the authenticated user's credentials and passes them through an HTTP POST to the Salesforce login page.
  Because Salesforce does not use the password field other than to pass it back to you, you do not need to send a password in this field.
3)In Salesforce, specify your organization's single sign-on gateway URL from Setup by clicking Security Controls | Single Sign-On Settings | Edit. Enter the URL in the Delegated Gateway URL text box.
4)For security reasons, Salesforce restricts the outbound ports you may specify to one of the following:
  80: This port only accepts HTTP connections.
  443: This port only accepts HTTPS connections.
  1024–66535 (inclusive): These ports accept HTTP or HTTPS connections.
5)https://help.salesforce.com/apex/HTViewHelpDoc?id=sso_delauthentication.htm&language=en

Read the above document to understand the flow
Comment: The url you use must call login() method of salesforce.Say you have a .NET site and your aspx page should intitiate salesforce login() method .
Comment: Can you explain step 2 and 3 how to get the link to corporate intranet? can I put any address? is that url has to have some functionality?


What motor controller to use for this setup?

Question: I'd like to run two unipolar stepper motors at 6V 1.2A each and two geared dc motors at 9W 1.2A each simultaneously on the same motor controller. What options are there for this particular setup, and also, are there any benefits to splitting the setup into two controllers instead?
Answer: The common hobby motor driver boards only have one supply voltage.  Unless you find differently you will need one or more driver board for the 6V steppers and a separate driver board for the 9V DC motors.
I suggest you look at L298N motor driver boards.
If your steppers need 4 inputs you will need a motor driver board per stepper.
Answer: I would actually go with a L293 H-Bridge. Since its an H-Bridge Driver, it can control 2 motors per chip (one on each side of the chip) independently. You can also change the direction of the output current depending on input (also independent on both sides of the chip)
Just get 2 L293's, and use one of them to control the 6V stepper's and one of them to control the 7.5V (9W) DC's. It goes without saying that you need different circuits powering these. So if you want to use one power source to power both these circuits, you will want to look into using a mofset to turn a 7.5V current to a 6V current.
Also, you want to watch out that you only use the "bidirectional" functionality on your steppers since sending the opposite current to ur DC's could fry em.
Since you will use 4 inputs on the L293 controlling the stepper's, and 2 inputs controlling the DC's, you will use a total of 6 GPIO pins to send booleans to your chips. Furthermore, you will need a separate power supply (not from the Pi) since your motors will require far more than 5V @ 1.2 A to power. If using a circuit to the Pi and a separate one for the Motors, you only need 1 moffset. However, if you want to use one current to power both motors and Pi, you have to convert 7.5V @ 1.2A -> 6V @ 1.2A -> 5V @1.2A. Hence, you need 2 mofsets.
Benefits: It depends on what you want to accomplish. If you need one pair of motors to have the ability to rotate bidirectionally while leaving 2 only unidirectional, then there is a point. However, if you are just making a 4 wheeled vehicle, then this setup is a complete waste. Just get a chip that can send 4 outputs at once.
Comment: The L293 series and L929N are both dual full bridge drivers capable of driving motors forward and backwards and both may use PWM for speed control.  The L293 is less likely to handle the currents needed by the questioner.
Comment: Thanks! so two of [these](https://www.amazon.com/DROK-Controller-H-Bridge-Mega2560-Duemilanove/dp/B00CAG6GX2) would suffice?


How to cite in LaTeX using Mendeley?

Question: I know that it is required to first create a database of references stored in a .bib file. Mendeley exports my reference list in .bib format. But how can I know what to write in curly brackets in \cite{} to refer to a particular author? Do I need to keep the .bib file open and find the relevant name to cite? Or am I missing something? What is your recommendation for referencing in LaTeX?
Comment: I have answered a very similar question here: http://tex.stackexchange.com/a/173034/32374 If you turn on the "Citation Key" field, it will show in the main Mendeley interface. I look at this field when I try to find papers to cite.
Answer: You have several options here. One is, as you suggest, to simply keep the .bib file open in the text editor and search for the cite key as you need it. Another is to use some software such as JabRef or BibDesk to manage the .bib file, which will be somewhat complicated since Mendeley overwrites the auto-generated .bib file every time a reference is updated.
Thus, I prefer to use the better searching capabilities of Mendeley, so I usually look up the citation key there. Unfortunately, Mendeley have decided that citation keys should not be visible by default, so you have to turn them on. Here I'll copy from my answer to a different question: Go to the menu->Tools->Options->Document Details, then choose the document type (for instance, Journal Article), then check the Citation Key box. Then, a field for Citation Key should be visible in the details pane on the right hand side of the window.
Answer: Another simple way is to select the file in Mendeley list, then right-click and select "copy as", then "LaTex citation command" (which corresponds to ctrl+K), and last paste the thing inside the brackets of \cite{}
Comment: This solved a different problem for me! Some of the citation keys were blank, but by selecting all files and doing the "copy as" that @user92514 described, it also fills in all the blank citation keys.
Answer: The other answers work but I've found it much easier to use the LaTeXing plugin for Sublime text editor. From within Sublime you can search the titles and authors of all the papers in your online Mendeley account whenever you use \cite{}.
http://docs.latexing.com/stable/tutorials/setup-mendeley-with-latexing.html
It automatically creates a .bib file containing just the papers you have added using Sublime. Unlimited (so far) free trials are available for both Sublime and LaTeXing.
Comment: Is there a spellcheck you can combine with this? The reason I use TeXMaker is that it has a spellcheck which is very useful.

How to cite in LaTeX using Mendeley?


Difference between fancytooltips and fancy-preview

Question: I read the documentation for both fancytooltips and fancy-preview here, and I don't really understand what their differences are, or when I should prefer one over the other. I see that fancytooltips is a TeX package (a .sty file), while fancy-preview is a Perl script. But they seem to have the same capability (which is the capability in the pictures on this page.)
Comment: From the documentation it seems as if `fancytooltips` is what to use if you are generating the document in LaTeX, and `fancy-preview` is an external script you run to extract text from equations, theorems, etc into a separate PDF for use with `fancytooltips` (so you don't have to manually put the tool tip content into a separate PDF).
Answer: Fancytooltips allow to insert pictures (pages of external PDF file) on the page. The user have to prepare the external file and use commands to insert tooltips in the main document.
Fancy-preview creates the external file with tooltips automatically from equations, figures etc and adds the tooltips to \ref-like commands also automatically.
Both require pdflatex (pdflualatex should be also O.K.), but in principle it is possible to add support also for xelatex.
Similar solutions (add material to PDF page and allow buttons to hide/reveal this material) are ocg-x, ocg-p,ocgtools and the macro \tooltip written by AlexG as an answer to pdftooltip from pdfcomment package: Using LaTeX code in tooltip . In these solutions, the TeX code for the tooptip is in the main TeX file. ocgtools needs pdflatex (is is possible to add support also for xelatex), the other packages and macros allow xelatex or dvips route.
Similar packages are also cooltooltips and pdfcomment. These packages do not allow any LaTeX code in the tooltips, but the support in various browser may be better.


Login loop in Fedora 28

Question: After updating from Fedora 27 to to 28 when I tried to login, I am facing a login loop. After giving correct password, again login screen is coming. I checked journalctl and saw that gnome-shell is crashing. I have attached a log also. I have tried both wayland ang xorg, the result is same.
log-
https://hastebin.com/raw/tuvuxemilu
Comment: May be this can help https://ask.fedoraproject.org/en/question/108067/login-loop/
Answer: I had a similar problem and logged in a virtual terminal (ctrl + alt + f2) and disabled all gnome shell extensions with the following command:
gsettings set org.gnome.shell enabled-extensions "[]"

and then i was able to login again. Apparently an extension called system-monitor crashed my login every time
Answer: Did you have updates-testing enabled? I think you're probably hitting this bug caused by a misconfiguration in an update to Cinnamon. This should be resolved by a new update in the pipeline. (The problematic one was there for a few hours before we caught this, unfortunately.)

Hit ctrl-alt-f6 to get a text console. (May need the Fn key too on some laptops.
Log in
Run sudo dnf upgrade
Notice if you have an update to caribou, which in this case is the problematic update.
If so, that should fix it. Hit alt-f1 (no ctrl necessary from the text-mode console) to get back to the GUI.

If this doesn't fix it (like if the update is not yet available on the mirrors you are hittting), go back to the console and try

dnf remove caribou
or dnf install cinnamon-settings-daemon

Because the root of the problem is that caribou (an on-screen keyboard) is no longer used by default in GNOME, but is in Cinnamon, so it's on your system when you upgrade from the previous defaults, and then something in the update isn't defined correctly. If this is the problem, you'll see Settings schema 'org.cinnamon.desktop.a11y.applications' is not installed in your system log.
If you don't have the testing updates repository enabled, the problem is something else. If you do have testing updates enabled, thanks for helping Fedora test — but do realize that occasionally problems like this will get through.
(And, shameless plug: if you'd like to help us so that more things like this are caught automatically before even getting that far, we could use help with our Continuous Integration initiative.)

Login loop in Fedora 28


Age limit rules for postdoc position in China

Question: I got a postdoc position at age 34 years in China. My documents are verified and I got the invitation letter. My employer applied for a work permit which is in process. I am waiting for that to apply for Z visa. But it is delayed due to the Covid-19 pandemic and travel ban. If it is delayed further I will be more than 35 years which is supposed to be maximum age limit for postdoc. Can I still get the position?
Comment: Ask the institution offering it. They should know if anyone does.
Comment: Universities follow a rule of the age limit
Comment: Age limit set by whom?
Answer: In general Chinese universities are rather ageist, and treat age restrictions very seriously. It is likely that you would not get the position due to your age. However, there are many workarounds you can discuss with your potential advisor, such as getting a position as a 研究员 or 副研究员 (like a staff researcher or staff scientist) that don't have age limits, but also might not have the federal government salary support that foreign postdocs are eligible for in China. You would have to discuss with your potential advisor to see if such an option is available to you.
Having said that, the pandemic changes the rules for everything, so there is a possibility that in this special circumstance an exception might be made, you'd have to discuss with your advisor and see how willing they would be to spend political capital to secure the exception for you.
Comment: @SayanBiswas If you know anything about the government,  you will know they can change the rules whenever they feel like it.
Comment: But I already have the offer letter. I just wait for my visa application foe which I need the work permit that is still under process. I am 34 when I was offered the position
Comment: if you already have a contract, then you should be fine, assuming the government allows foreigners to enter China again within the contract period.
Answer: It is the University that has the age limit, not the Chinese government who issues the visa. For example, the postdoctoral research fellowships offered through the PIFI scheme at the Chinese Academy of Sciences have an age limit of 40 years (current announcement).
If your employer is still offering you the position, and you don't have other reasons you would be rejected for the visa, I expect it should go through.


How safe are Truecrypt-file containers?

Question: I have a question regarding the security of Truecrypt-encrypted-file containers. I know that there are security leaks in the software that allow to access an encrypted drive but can this technique be used to open an encrypted file container? I am using regular (nonhidden) containers because I like how easily they can be transported.
Thank you in advance.
Comment: Possible duplicate of [Is TrueCrypt safe enough to store clear-text-passwords?](https://security.stackexchange.com/questions/19666/is-truecrypt-safe-enough-to-store-clear-text-passwords). See also: https://security.stackexchange.com/questions/58940/is-truecrypt-not-secure-now-and-should-i-stop-using-it and https://security.stackexchange.com/questions/29375/is-7-zips-aes-encryption-just-as-secure-as-truecrypts-version and https://security.stackexchange.com/questions/85149/truecrypt-vs-bitlocker and many other questions with the truecrypt tag.
Comment: No, it cannot. TC was never directly compromised.
Answer: I spent some time seriously digging into the Truecrypt/Veracrypt source code and studying the issued audit, and I would bet one of my testicles that the container format is secure.
A simple TC reimplementation exists at https://github.com/bwalex/tc-play. It uses standard Linux kernel device mapper for mounting the TC volume. It reads the volume header, derives the encryption key from your password/keyfiles and seed stored in the volume header and uses the key and linux dev-mapper to mount the volume container. It uses standard symmetric key encryption implemented in the Linux kernel. It's the pretty same code as is used by LUKS - Linux crypto. So, if LUKS is safe than TrueCrypt is safe as well.
The only difference (as mentioned) is key derivation. However, it uses just standard crypto-primitives.
The only question is, whether the particular True/Vera-crypt implementation is safe. I would bet my second testicle that the tc-play  is safe. It's short, and I was able to read it and understand it completely.
You can find even another reimplementation in linux cryptosetup. Many people have been thinking about TC security which could be nother proof.
However...
If you look at the VeraCrypt sources, you realize it contains thousands of lines of code and 99% of the code is GUI. The possible backdoor could be hidden anywhere, and it would be complicated to find it.
If you compare VeraCrypt code and TrueCrypt code, you realize that VeraCrypt maintainer hasn't added anything interesting. He hasn't even fixed the known bugs discovered by the tc-play developer and noted in README. For instance:
"The keyfile pool is not XOR'ed with the passphrase but modulo-256 summed."
This is a documentation bug, which hasn't beend fixed in the VeraCrypt docs yet.
https://www.veracrypt.fr/en/Keyfiles.html (8.)
To implement new crypto-algoritm (which Vera does) is a simple task. Knowing how, you can put any new algo. within 1 hour of coding.
Answer: No such things as "leaks in the software". The related vulnerabilities are not that of TrueCrypt. TrueCrypt itself is as safe as anything can get.
You can transport them and mount them anywhere, as you would an .iso file.
From a security perspective, at this time, the TrueCrypt containers are 100% safe.
Comment: Do you have any sources for the claim that "TrueCrypt containers are 100% safe"?
Comment: "100% safe" is disingenuous at best. The deniability aspect isn't safe against differencing attacks. There's no explicit malleability detection; it just returns garbled adjacent blocks when you modify the ciphertext. It's safe enough in most cases but nothing is 100% secure.
Comment: Do you have any proof of the contrary ? You can always check any CVE database or other vulnerability reports at any time.
Comment: By that logic nothing is ever safe. With current processing power you cannot brute force a properly setup TC container. Which is infinitely better than the improper implementation of things like bitlocker which has been proven to fail.
Comment: @Overmind can you point to source on any such fail of bitlocker?
Comment: Like this, passing the problem instead of solving it: https://www.howtogeek.com/fyi/you-cant-trust-bitlocker-to-encrypt-your-ssd-on-windows-10/
Answer: Given that TrueCrypt has been mysteriously discontinued by it's developers for security concerns and has not been maintained, it is likely to have some issues. While I'm not sure if file containers themselves are affected, it would be a much better option to use VeraCrypt. VeraCrypt is the successor of TrueCrypt once it was condemned and has passed security audits. Here is an excerpt from the TrueCrypt download page:
<code>WARNING: Using TrueCrypt is not secure as it may contain unfixed security issues

This page exists only to help migrate existing data encrypted by TrueCrypt.

The development of TrueCrypt was ended in 5/2014 after Microsoft terminated support of Windows XP. Windows 8/7/Vista and later offer integrated support for encrypted disks and virtual disk images. Such integrated support is also available on other platforms (click here for more information). You should migrate any data encrypted by TrueCrypt to encrypted disks or virtual disk images supported on your platform.

WARNING: Using TrueCrypt is not secure
</code>
Comment: Since the same TrueCrypt containers are still valid containers in VeraCrypt, I don't believe this is true. Any issues with TrueCrypt were likely related to run-time vulnerabilities or key exposures.
Comment: @JohnDeters "While I'm not sure if file containers themselves are affected" I did not say that the container is insecure, I merely advised that TrueCrypt is not used which you seem to agree with.
Comment: The original question was specifically about the security of the containers, not the app itself. Yes, I agree, use VeraCrypt instead of TrueCrypt. But you can still use VeraCrypt with TrueCrypt containers, which is why I answered that the advice to change them wasn't valid.
Comment: @JohnDeters But doesn't using the container with TrueCrpyt inherently make it insecure? That is why I recommended VeraCrypt.

How safe are Truecrypt-file containers?


What is a callback URL in relation to an API?

Question: I've been scouring the net, and can't seem to wrap my head around the idea of a callback URL. In my case I have a few callback URLs that I have to define myself. A popular one is a "default callback URL". What is this exactly? Can you give an example in plain english?
Answer: A callback URL will be invoked by the API method you're calling after it's done. So if you call
POST /api.example.com/foo?callbackURL=http://my.server.com/bar

Then when /foo is finished, it sends a request to http://my.server.com/bar. The contents and method of that request are going to vary - check the documentation for the API you're accessing.
Comment: Would it cause an error if the callback URL is not set correctly?
Comment: @user3768495 I would expect it would not, but that's going to depend on the implementation of the API. It could, in theory, make the callback part of a transaction internally, and roll back any changes made by the original request if the callback doesn't return a 2xx response.
Comment: Do I need to send a response to the POST request at /api.example.com/foo ?
Comment: @Abhijeet You never *need* to. If it's appropriate to include a response, yes, do so.
Comment: similar question: https://stackoverflow.com/questions/28391359/what-is-callback-url-in-instagram-api-and-how-to-can-i-implement-it
Comment: How does an application make a callback url available to the API without opening up security holes, where anyone can access that callback url? wouldn't the API not be authenticated?
Comment: @Khatri - it's data that is given from the client to the server.  So _both_ sides need to keep it (until they no longer need it).
Answer: Think of it as a letter. Sometimes you get a letter, say asking you to fill in a form then return the form in a pre-addressed envelope which is in the original envelope that was housing the form.
Once you have finished filling the form in, you put it in the provided return envelope and send it back.
The callback URL is like that return envelope. You are basically saying, "I am sending you this data; once you are done with it, I am listening on this callback URL waiting your response." So the API will process the data you have sent then look at the callback to send you the response.
This is useful because sometimes you may take ages to process some data and it makes no sense to have the caller wait for a response. For example, say your API allows users to send documents to it and virus scan them. Then you send a report after. The scan could take maybe 3 minutes. The user cannot be waiting for 3 minutes. So you acknowledge that you got the document and let the caller get on with other business while you do the scan, then use the callback URL when done to tell them the result of the scan.
Answer: If you use the callback URL, then the API can connect to the callback URL and send or receive some data. That means API can connect to you later (after API call).
Example

YOU send data using request to API
API sends data using second request to YOU

Exact definition should be in API documentation.
Answer: It's a mechanism to invoke an API in an asynchrounous way. The sequence is the following

your app invokes the url, passing as parameter the callback url
the api respond with a 20x http code (201 I guess, but refer to the api docs)
the api works on your request for a certain amount of time
the api invokes your app to give you the results, at the callback url address.

So you can invoke the api and tell your user the request is "processing" or "acquired" for example, and then update the status when you receive the response from the api.
Hope it makes sense.
-G
Answer: I'll make this pretty simple for you. When a transaction is initiated, it goes under processing stage until it reaches the terminal stage. Once it reaches the terminal stage, the transaction status is posted by the payment gateway to the callback url which generally the merchants use as a reference to show the success/failure page to the user. Hope this helps?
Answer: Another use case could be something like OAuth, it's may not be called by the API directly, instead the callback URL will be called by the browser after completing the authencation with the identity provider.
Normally after end user key in the username password, the identity service provider will trigger a browser redirect to your "callback" url with the temporary authroization code, e.g.
https://example.com/callback?code=AUTHORIZATION_CODE

Then your application could use this authorization code to request a access token with the identity provider which has a much longer lifetime.
Answer: Here's a common example of how a callback works - something that most people who've bought online probably have experienced. You've made a purchase on your favorite website and clicked the "Submit" button. Chances are you'll be sent to an external service that handles the payment processing (like PayPal) where you confirm your order, or just wait while you watch the word "processing..." blink on the screen. After the transaction completes you are directed back to the original shopping site. The page that you see is the callback URL. Though you didn't know it, you left your favorite online store's website during the processing, and the external site you visited returned you back to it. Barring any glitches you should see the page the store wanted you to see after an order. It might be a thank you page, or other page with order confirmation information, next steps, or their home page. It may vary depending on what you ordered, when you ordered, and how you ordered.
Basically a callback URL gives directions to an external system on where to go next. What is at that URL could be anything. It doesn't have to be a static URL. More
Answer: In the OAuth workflow, Callback URL would be the url to which the user will be redirected after authorisation from the OAuth provider. Like how 'Sign in with Google' takes you to a Google page and then sends you back to the app where you clicked the 'Sign in with Google' Button.


Unmanaged x64 assemblies in mixed .NET development environment

Question: What do we do if we have some devs working on 64 bit machines and some on 32 bit machines, but we need to reference unmanaged assemblies that need to be in x86 for half the team and x64 for the other half? Is there a solution besides manually updating the references every time someone on a 64 bit rig gets latest?
Answer: You want to do this as part of your build, right?
Write a pre-build step to copy the referenced DLL from a permanent position in your source tree to the local project. Use the $(ConfigurationName) or $(PlatformName) macro to select which version of the unmanaged DLL actually gets copied. You just keep your DLLs in separate folders with names that match the configuration name or platform name.
Comment: Actually, this is at design time. We have the solution for the build process in place, but a few of the devs anctually compile in Debug | x64.
Answer: It is rather odd that the devs with the x64 machine willingly run the 64-bit version.  Visual Studio doesn't support Edit+Continue in x64 mode, that's quite a loss.  The workaround for that is simple, set the Platform Target to x86.  Automagically also solving your unmanaged DLL problem.
Comment: It is odd, and I will discuss it with the three black sheep, but it would be even better if there were a solution to this. I guess it's a pretty fringe case, but I'll keep looking.
Answer: There is another solution that involves editing your code a little. It is described in the answer from Milan Gardian to this question.
Basically it involves writing your own assembly reference handler to determine which assembly to load at runtime, provided that you have access to both (32- and 64-bit) versions of the assembly. I have just implemented this solution my self, and it works like a charm.
My situation is this:
I'm developing a .NET program targeted for "Any CPU" on Windows 7 64-bit. I have added the 32-bit assembly reference, and set Copy Local to false. I use post-build events to copy the 32- and the 64-bit assembly to the output folder, and I make sure to give the 32-bit assembly a different name than in the reference. This is because I want to force my custom assembly resolver to kick in and do its thing, due to the fact that .NETs default assembly resolver can't resolve the reference. At runtime the correct assembly is loaded, and at compile time i get no errors. It should be noted that I haven't had the time to actually confirm that this is now working on 32-bit OS, but I don't see any reason why it shouldn't work.


Which photons pass through a circular annulus?

Question: Passing light through a circular sieve:
Well, actually, let's think about radar or microwaves with a wavelength of order a centimeter or two, so you can tailor your aperture, say by etching a silver screen on glass.
If you have a reflective metal screen, and you cut a long narrow rectangle in it, it will pass (some) photons of the properly oriented linear polarization of wavelength shorter than the length of the rectangle.
What if you cut a narrow circular annulus into your screen?   Would it pass circularly polarized radiation of the proper wavelength?
Bonus Points: What about an elliptical annulus?
Please ignore photons of wavelength shorter than or comparable to the narrow dimension of the slit.
Answer: You can make beams of light that have orbital as well spin angular momentum and they can go through an annular aperture.
So circular versus linear isn't enough. Linear has the phase advance orthogonal to the advancement with the polarization at a fixed angle. Circular has the polarization rotate but with an annular filter you can give the wavefront a twist where it can have an integer number of twists as it goes around the angle so you allow orbital angular momentum.
Electrons can do the same thing.
One way to produce such beams is via holography. A defraction grating with a point that has multiple lines coming from the top to be one line going down can produce a beam with orbital angular momentum with the amount related to how many lines came into the point. So the lines look like a lower case l or the number 1 but then there is a capital Y in the middle or maybe a Y and an I and so forth.
As for the polarization being linear in a vertical or a horizontal slit. If you had a rope going through a vertical slit it might be obvious that it is easier to shake it up and down. But an electric field is located at all the points along the lone it propagates and the vector points in a direction. The size of the field is measured in V/m and so isn't directly related to how tall the vertical slit it. So unlike the rope, the amplitude of the vertical electric waves isn't directly limited by the height of the vertical slit. Its limited by things like dielectric breakdown of the air and vacuum polarization and whether it would destroy the material you hope will block it.
But there is a general difficulty of passing a wavelength through a slit that is smaller in width than the wavelength. This is more a diffraction effect and isn't obvious at all.
But you asked about polarization. Of s material can pass both vertical and horizontal polarization through, and pass them both through with the same phase then it passes both kinds of circular polarization as well.
Comment: Points for considering orbital angular momentum
Answer: I am not totally sure of this answer, which is why I asked the question.
However,   I think the answer is that only relatively short wavelengths can pass through an annular aperture.
Specifically, I think that if the outer radius of the annulus is R and the width is W, where  W <<  R,  the maximum wavelength that passes through is  approximately 2R times the square root of 2W/R, or more exactly 2R Sin(ArcCos(1-W/R)).  No Wavelengths comparable to R pass through this annular filter unless W is itself comparable to R.


EXPORT_SYMBOL() for Windows drivers

Question: Is there any WDM mechanism, similar to EXPORT_SYMBOL under Linux, such that one can use symbols from a driver (A.sys) in another driver (B.sys)?
Answer: This is same mechanism as user mode, basically drivers are same PE images as user mode. Simplest approach to mark functions that you wish to export as _declspec(dllexport). And add to header definition _declspec(dllimport):
_declspec(dllexport) void ExportSymbol1(void);
void ExportSymbol1(void)
{
    KdPrint(("exported call\n"));
}
and
_declspec(dllimport) void ExportSymbol1(void);
Also you can use export driver approach (http://msdn.microsoft.com/en-us/library/windows/hardware/ff542891(v=vs.85).aspx)

EXPORT_SYMBOL() for Windows drivers


How are solar sails maneuvered by sunlight? Are they pushed or pulled?

Question: On 20 May, 2010, Japan launched IKAROS probe with primary propulsion by a solar sail. If the radiation pressure, that helps the sail to move, comes from the sun, then shouldn't it be pushed away from the sun? But the IKAROS probe actually passed by venus, which is nearer to sun as compared to earth by any means. Can someone please expalain that?
Comment: Keep in mind that light sails are generally *reflective*. So they experience a momentum transfer that depend on both the incident and out-going light directions. Now, you can't tack "upwind" but you *can* get a significant non-radial impulse. Then you combine that with the usual *"East takes you Out, Out takes you West, West takes you In, In takes you East. Port and Starboard bring you back.* business of orbits and you can do some surprising things.
Comment: @dmckee  why dont you write an answer , the question migh get many hits in searches.
Comment: A bit of clarification to @dmckee's point:  when the sail is tilted relative to the outward light radiation from the sun, the net push can have a component that goes in the same direction or opposite to the orbital velocity.  If it's in the same direction, the sail will rise to a higher orbit; if it's against the orbital velocity, the sail will drop to a lower orbit.
Comment: So, the sail is not used to *push the probe closer to the Sun* - it is used to *slow it down in its orbit* which causes it to *fall* toward the sun! Cool!
Comment: Frankly I was hoping someone a little more expert would chime in, but I've written something.
Answer: Light sails are generally reflective, so the impulse provided by the light depends on the difference of the momentum of the incoming light (directed radially outward), and that of the outgoing light (which can point in any direction, depending on how you tilt the sail, though your effective area drops significantly if you tilt too much).
The result is that the sail can be used, not only to push you outward but also to increase or decrease your orbital angular momentum, which will change the shape of your obit. (For that matter you can change the plane of your orbit as well.)
Reflect the light "forward" (i.e. in the direction of your orbital motion) and your orbital motion will slow and your path will bend more toward the primary. Reflect it "backward" and your orbit speed will increase and your path will bend away from the primary.
Getting into a lower orbit (as in going to the neighborhood of Venus from the neighborhood or Earth) means first slowing yourself so that you can fall in toward the primary, then speeding up again to match velocity with the target. Always keeping in mind that light sails provide little thrust so these evolutions are not at all fast.

That said, you can't get the sail to push you radially inward: you must rely on gravity to move you in.


Relationship between Young's modulus and Bulk modulus

Question: I recently came across a statement in a publication "The Young's modulus and Bulk modulus are independent of each other for a uniform isotropic material".
Is this valid considering the two are related in terms of Poisson's ratio?
Answer: The bulk moduli of steel and water are 163 GPa and 215 GPa, respectively, which are similar. Their Young's moduli are 200 GPa and zero, which are very different. So yes, I'd say these parameters are suitably independent. The Young's modulus (i.e., the stiffness of a long section of material loaded in the direction of its length) is strongly dependent on the shear modulus, and a fluid cannot sustain a shear stress.
Answer: The Poisson's ratio can have a range of values i.e. different materials will have different Poisson's ratio.
So if you consider a range of material with the same bulk modulus they can have different values of the Young's modulus. Or likewise materials with the same Young's modulus can have a range of different bulk moduli. I suspect this is what the statement means when it says the bulk and Young's modulus are independent.


Why the electric field $\vec{E}$ is constant (=position independent) for an infinite 2D sheet of constant charge?

Question: So I'm reading a text on electricity and it talks about using the integral to compute the total charge of a collection of points, which I mostly understand.  But then we get to finding the electric field due to a charged collection of points and I find things that don't make sense to me.  For instance, for an infinite sheet of constant charge, the text says that the electric field is constant on any one side of the sheet.  But that seems intuitively wrong to me, since I would think the field should be stronger the closer a point is to the sheet.  I mean, if I'm standing 10 meters from a sheet, holding a charged particle, and walk closer to the sheet, I'd think the particle would react more strongly.  I follow the mathematical derivation fairly well, which leads me to think I must not be thinking about the physics correctly.  Can anyone help make this make sense?
Comment: You can get this result without Gauss's law, just on dimensional grounds. There's no way to put together any equation in terms of the charge density and the distance $r$ from the sheet that will have the right units and vary with $r$.
Answer:
for an infinite sheet of constant charge, the text says that the electric field is constant on any one side of the sheet. But that seems intuitively wrong to me, since I would think the field should be stronger the closer a point is to the sheet.

There's a geometric scaling argument at hand, and you probably need to appreciate Gauss' Law to get a real sense of it. It follows the same thinking that the $1/r^2$ law does.

In this argument for $1/r^2$ field strength from a point particle, it is seen that the solid angle that "A" occupies decreases at larger radii. If you consider a charged ball, then think about squishing it from a 3D object into a 2D piece of paper. That represents the area-based charge density.
An unsaid assumption for this line of thinking is that the field strength is determined by:

The solid angle occupied by charged material

times

The 2D charge density presented by that material

So extend this to an infinite sheet. No matter how close or far away it is, if you're looking parallel to the sheet, the sheet occupies exactly half of your field of vision. Furthermore, the surface charge density and angles of the sheet are also irrelevant of your normal distance.
Illustratively, you could apply this via the image above. Just remove the "A", and consider that this is an infinite sheet. As you expand the distance, you expand the area you sweep, but the angle times the charge density is invariant. Thus, the field is constant with distance.
Comment: I see, I'll go re-read Gauss's Law.  But as I see it right now, the explanation seems to be:  As you get close, sure, the field strength from any one point is stronger, but the component of that strength which is directing you toward/away from the sheet is diminishing because of the angle at which it "hits" you.  The rest of the components just cancel with the forces coming from a symmetrically located other point on the sheet.  Hrrrrrrn, very cool!
Answer: It's definitely strains one's intuition.  But think about this:  if you are in the vicinity of an infinite sheet of charge, how can you determine whether you are close to it or you are far away?   I can tell if I'm close to or far from a sphere by comparing my distance to the sphere with the radius.  If I'm close the sphere looks big.  If I'm far away it will look small, even like a point.  The size of the sphere "sets the scale".  Not so for an infinite sheet.  No matter where you are, the sheet looks exactly the same.   There is no scale.  From this point of view one might say "what else could it be but constant" (and pointing perpendicular to the sheet).
Comment: But what about a point charge? The scaling argument doesn't work here, does it?
Answer: Interestingly, as AlanSE mentioned above, this can be derived from Gauss's Law very intuitively if you consider that an infinitely large sheet (a plane) is identically the same as a sphere of infinite radius.  Therefore, the flux of your test particle through this sphere (and vice versa) is the same regardless of its position within this sphere, which can be said to extend to all points in the space.
Comment: With a point in space and a plane running through the origin, there is a (shortest) distance to the plane.  I don't see how we can similarly regard this as a sphere of infinite radius unless you mean some kind of analogue to higher dimensions.


Virtual image on screen

Question: As plane mirrors always form virtual images and virtual images can not be obtained on a screen then how can we obtain the image of sun on wall or anything (screen) by plane mirror as on  sunny day. Usually children here in India do mischief while focussing that light on other people's eyes.
Comment: That might be explained in terms of _virtual objects_. When a convergent beam of light is blocked by placing a mirror in between, it creates something called a _virtual object_ which can create real images.
Answer: Reflecting sunlight with a mirror doesn't create an image. It creates a area which appears brighter than the surrounding area. This is because more photons are striking that area than the surrounding area. The same happens if you reflect the light into someone's eyes.
Comment: Isn't that what a real image is?
Answer: A small mirror that reflects the sunlight creates a patch on the wall that is the same size as the mirror, but convolved with the (angular) size of the sun.
This is, in some sense, like a "pinhole camera" - except that the light is being reflected rather than transmitted by the "pinhole" (the small mirror).
If the mirror is small, and the distance to the screen/wall is large, you will in fact create an image of the sun - you can confirm this by seeing that if a cloud moves in front of the sun, you will see the image of the cloud.
I tried to illustrate that below. On the left is the situation of a "small mirror" generating an image of the sun; on the right, a "small sun, large mirror" situation where the image is essentially the image of the mirror. Of course any real situation is somewhere between these two.

Virtual image on screen


what is the word or expression?

Question: You didn't think highly of something and after you hear good things about it and can you say ("It looks different now")?
Is the expression correct? If it isn't, how would you say when you want to say something like the expression in the bracket.
Comment: Are you asking about how to say that you are revising your original negative opinion of something after having heard someone else praise that thing?
Answer: You could say "Now I see things in a different perspective".
Answer: Not really, "It looks different now." might imply something physically looking different.
A more suitable response might be "I've changed my mind.", meaning you have thought about it and now your opinion is different. Marriam-Webster's definition:

to change one's decision or opinion about something

If it is stronger of more emotional, you could use "I've had a change of heart." Marriam-Webster's definition:

a reversal in position or attitude

Such as in

I was going to destroy everything on earth, but then I had a change of heart, and started gardening.
Comment: "It looks different now" doesn't at all imply anything physically looking different.
Comment: @RobbieGoodwin - On the contrary, that is the only thing that sentence implies.

what is the word or expression?


What Hot Shoe Accessories are Available for a Canon T3 / EOS 1100D?

Question: Specifically, what hot shoe accessories are available for the T3 / 1100D that use the hot shoe electronics to communicate with the camera (besides flashes)?
Comment: Does it have to be two-way communication, or would reacting to flash signal suffice?
Answer: I'm not quite sure exactly what you are looking for. There are only a few main things that I commonly see hot shoes being used for these days:

Flash Units
Flash Cords
Bubble levels
Video Lights
Microphones
GPS Units

In the past I have seen them used for a few other things, but this is much less common:

Special viewfinder type units
Light meters

Since you don't specify any particular need, that is about all I can tell you:)
Comment: Considering the Canon hot-shoe is so standard, it would have  been easier to list those which it does not support ;)
Comment: Gotcha.  I should have worded by question differently.  What I meant was, what hot shoe accessories are available for the T3 / 1100D that use the hot shoe electronics to communicate with the camera.  The bubble level would not.  The flash would.  I do not believe there is a GPS or microphone available for the camera that can communicate via the hot shoe.  I updated the question.
Comment: Thanks.  Specifically I was wondering if any of those beyond the flash units were compatible with the T3 / 1100D.
Comment: @ChuckC. - Sure any of the items in the first list would work. They all can work independently of the camera actually, depending on which model and features you are looking for. It might be better to ask for compatibility with a specific accessory rather then asking this wide open question.


What is ECMA on Ethernet controller advanced settings?

Question:
By googling there was only answer i found it is related with European Computer Manufacturers Association = ECMA.
What does this option do? can be Enabled or Disabled.
Answer: It's almost certainly ECMA-393 "proxZzzy" sleep proxy service in the NIC. It allows the host to sleep while the NIC stays awake, and the NIC can do things like respond to ARPs and other simple jobs to keep the host "visible" on the network even while it sleeps. If some important traffic comes in for the host, the sleep proxy service in the NIC can wake the host so the real OS can do the right thing to handle the traffic.
Comment: So basically just enabling this option has nothing to do with data loss / checksum errors on uploading / downloading from internet?
Comment: @SeiyaSouji.  Correct.
Answer: Read https://www.ecma-international.org/publications/files/ECMA-ST/ECMA-393.pdf
ProxZZZy was developed by Intel. Source Look at the data sheets to find out what protocols your lan/wifi card used or you can find out if its available and enabled on your adapter in Windows and disable it  under your adapters advanced settings "ECMA." Make sure you do this in linux as well. Disabling ProxZZZy and 'Wake on Lan' will prevent "denial of sleep attacks" and possibly mitigate against other potential unforeseen vulnerabilities.
Intel's ProxZZZy also allows for remote access protocols, what has been described in the above document as "wake up" protocols; while the ECMA admit Intel's ProxZZZy can be hijacked, they do not provide all the data and security risks that are present. It remains to be determined if disabling Intel's ProxZZZy at the software level effectively mitigates hardware level exploitation. An on an already compromised host, software mitigation's would be futile, as attackers could simply re-enable the hardware level attack vector.
There are other standards, such as Microsoft Wake on Lan, Magic Packet, and others which provide similar functionality; On every Intel chipset designed since 2006 Intel Management ensures the onboard Network card remains irreversibly enabled and active while the computer is turned off and allows total remote control and exploitation of users PCs, critical infrastructure and all the rest  Source 1, Source2; As of the time of this post, users of Intel chipsets are forced to buy new products or wait for Intel to release updated firmware. The cat and mouse game goes on ad infinitum until it is totally disabled. Intel's ProxZZZy looks be as dangerous as Intel ME.

From the document:
4.2 proxy, network proxy:
An entity that maintains network presence for a sleeping higher-power host (The proxy is the man in the middle; you are the host)
If your Network card supports Intel's ECMA-393 proxZZZy™ for sleeping hosts; the following can occur!
A.2 Security Considerations; according to its designers:
This Standard does not specifically address Security concerns arising out of the proposed proxy protocol design. However, a number of potential threat scenarios have been identified and potential mitigation is suggested below.
• Denial of Sleep Attack – It is possible that an adversary may send periodic unauthenticated end-to-end packets to the proxy, denying the system from entering or staying in the Sleep state. This can be partially mitigated by using defense mechanisms (Firewalls, Intrusion Detection and Prevention systems), either externally and/or as part of the system.
• Compromised Proxy – It is possible that an adversary may assume control of the proxy and use the Proxy to launch attacks on the system, on the network, or on other Internet connected machines. This can be partially mitigated by using System measurement techniques for ensuring the integrity and robustness of
the software/firmware/hardware that executes within the proxy.
• Subversion Attacks – It is possible that an adversary may take control of the proxy and use it to generate IP packets with Option headers that circumvent external defense mechanisms. This can be partially prevented by disallowing the proxy to generate IP packets with Options in its header.
(editor: Packet generators can be used to launch a ProxZZZy attack on any supported host, hijacking the proxy, then the proxy (which includes an embedded packet sniffer) can be turned into a rogue packet generator)
• IPsec - IPsec can be deployed in one of two modes – tunnel and transport modes. Tunnel mode is used for IPsec-encapsulation of VPN traffic where a remote client accesses one or more nodes in a trusted network via a VPN gateway. Traffic to the nodes in the trusted network is typically in-the-clear.
IPsec Transport mode is used to protect individual connections between IP endpoints within a network. In this case, each peer-to-peer connection between nodes could be protected by an IPsec Security Association (SA). The decision to protect or not is by IPsec policy, and the recommended enterprise IPsec policy is to require inbound IPsec but not require outbound IPsec. The receiver challenges the initiator to establish IPsec if needed. The visible side-effect is initial TCP connections (TCP SYN) are sent in the clear. Furthermore, under these policies, the IPsec negotiation happens in parallel with the connection request. Traffic after the initial TCP SYN, including additional retires of the TCP SYN, will likely be within IPsec, as will further traffic.
Although not the common policy, the initiator policy may also require outbound IPsec. If this is the case, the connection setup will be preceded by a probe packet to the IKE or AuthIP UDP port.
In the IPsec use case with a proxy, the initial IPv6 TCP SYN packet from the initiator used to wake the host may be encrypted by IPsec (if an existing SA matching policy has been previously negotiated between the peers). However, the expected common-case is for the initial IPV6 TCP SYN packet to be sent in the clear (by the recommended enterprise IPsec policies mentioned above). To simplify these two cases, the host should explicitly delete or invalidate existing IPsec SAs prior to going to sleep and transition to proxy mode.
If IPsec is configured to either use "shared secret" or require outbound IPsec, then the initial IPv6 TCP SYN will first be IPsec authenticated and encrypted. In either of these sequences, the wake can be from the IKE negotiation initiation. The proxy should be enabled to wake on an IKEv1/AuthIP pattern to handle this configuration.

The potential remote access dangers of proxzzzy
Intel's ProxZZZy gives the host Ethernet / Wifi adapter the ability to accept remote "Session initiation protocals"

What is a Session Initiation Protocol?
Session Initiation Protocol
Also called a SIP server or SIP proxy server, in telecommunications it is one of the main components of an IP PBX that is used by SIP to perform many of the call set-up functions.  As described in RFC 3621 - SIP: Session Initiation Protocol SIP makes use of elements, called proxy servers (SIP proxy) "to route requests to the user's current location, authenticate and authorize users for services, implement provider call-routing policies, and provide features to users".
Within the SIP network the SIP proxy actually manages the setup of calls between SIP devices including the controlling of call routing and it also performs necessary functions such as registration, authorization, network access control and in some cases it also handles network security.
IP PBX Short for Internet Protocol Private Branch eXchange, a telephone switch that supports VoIP. An IP PBX provides services similar to PBX services, but over data networks like a LAN or WAN rather than circuit-switched networks. IP PBX typically can switch calls between VoIP on local lines or between VoIP and traditional telephone users in the same way PBX does. IP PBX may also be seen abbreviated as IPPBX or IP/PBX.

Source: https://www.ecma-international.org/publications/files/ECMA-ST/ECMA-393.pdf
5.7 Remote Access using SIP and IPv4
In this Standard, SIP (RFC 3261) is used by a remote entity to wake a host. SIP proxies along the path can facilitate the traversal of NATs and firewalls. The reason for waking the host (i.e., the particular host application that needs to be used) is outside the scope of this Standard. SIP methods and responses used in the remote wake functionality are REGISTER, INVITE, ACK, and SIP Status Codes.
The following diagram (see above document) shows a sample SIP implementation that may be used by the proxy to wake the host. Only the messages into and out of the Device Network Proxy are included in this specification. All other messages and entities are a possible implementation and not covered by this specification.
5.8 Remote Access using Teredo for IPv6 (Teredo (RFC 4380) is an IPv6 transition technology that allows peer to peer connectivity between peers behind a NAT. The Teredo protocol encapsulates IPv6 packets inside UDP IPv4 packets. One of the tunnels a
Teredo client maintains is with the Teredo server in the cloud. The proxy maintains this tunnel by sending Router Solicitation (RS) messages at regular intervals. The proxy ignores any responses from the server to
the RS packet.
And what is the unobstructed out of bound communication they are referring to in their document? Surely there are many OOB applications and functions. Intel ME / AMT's remote access protocol's function in OOB. Using an aftermarket network card will bypass Intel ME OOB.
Out-of-band management
In computer networks, out-of-band management involves the use of a dedicated channel for managing network devices. This allows the network operator to establish trust boundaries in accessing the management function to apply it to network resources. It also can be used to ensure management connectivity independent of the status of other in-band network components.
About Blocking Clients and Out of Band Management,
Blocking AMT-Based Computers in Configuration Manager
https://technet.microsoft.com/en-us/library/ee344337.aspx

Intel's Prozzzy mandatory vs optional components:
IPv4 ARP Mandatory
IPv6 Neighbor Discovery Mandatory
DNS Option
DHCP Option
IGMP Option
MLD Option
Remote Access using SIP and IPv4 Option
Remote Access using Teredo for IPv6 Option
SNMP Option
Service Discovery using mDNS Option
Name Resolution with LLMNR Option
Wake Packets Mandatory


what is the meaning of scalar and vector field line integrals?

Question: I know the classic line integral and is lengh of the curve and I compltetly understand the logic. But when I am trying to think about the meaning of  line integral on vector field or scalar function
I am not sure what are those expressesion are represent and how should I think on it.
Answer: Let $\gamma:[a,b] \rightarrow \mathbb{R}^2$ be a soft path. Let's keep things in $\mathbb{R}^2$ for simplicity.
Vector fields
In physics there is a thing by the name of "Work". Imagine that we have a block and, due to the action of a force $F$, the block moves $k$ meters to the right. Then the work is
$$W=F\cdot k\cdot \cos(\alpha)$$
where $\alpha$ is the angle between the Force vector and the direction of motion.
See this image
The problem is the following: This formula works fine only if the path is a straight line and if the force vector is constant. But what if the line is curved? If the line is curved the value of $\alpha$ is allays changing with time, and If the vector $F$ is allays changing the this becomes even more complex.
The solution is the following:
If you notice, if we thing of $\textbf{k}$ as a vector pointing from the beginning to the end of the trajectory then, if our trajectory is a line and if the force is constant:
$$W=F\cdot k\cdot \cos(\alpha)=\textbf{k} \cdot \textbf{F}$$
The key to generalize this for any trajectory is the following:
Let's divide the path $\gamma$ into a bunch of smaller paths: $\gamma_i$. This smaller path are so small that they look almost like a straight line.
Let $\textbf{F}(x,y)$ be our vector field that tells us the fore applied to the block in any position $(x,y)$.
Then we can calculate a little work done in one of the smaller paths by:
$$\Delta W_i = \textbf{F} \cdot \Delta \gamma_i$$
Where $\Delta \gamma_i$ is a small vector pointing from the beginning of $\gamma_i$ to it's end.
$\Delta W_i$ is the work done in each segment $\gamma_i$ of our initial trajectory. Then, if we want to know the total work, we simply sum over all segments:
$$W = \sum_i \textbf{F} \cdot \Delta \gamma_i$$
This is just an approximation, but if we divide the initial line into smaller and smaller segments, then we get an even better approximation. So in the limit this becomes accurate and we get:
$$W = \int_\gamma \textbf{F} \cdot ds$$
This is how I think about the meaning of line integrals over vector fields and I think this is a good intuition for the motivation of their invention and their meaning.
Scalar Fields
Now let $F(x,y)$ be a scalar function. You should know that the image of this function is an surface above the $\mathbb{R}^2$ plane.
If you can recall (I think you do), the meaning of
$$\int_a^b f(x)dx$$
is just the area under the curve from $a$ to $b$. This is the same meaning of the line integral over a scalar function.
When we calculate:
$$\int_\gamma f(x,y)ds$$
We are simply calculating the area over the line $\gamma$ (that lives in the $\mathbb{R}^2$ plane) and the surface $f(x,y)$ above it: See this small animation
Comment: that was great explantion!
about the vector field part, if I understand you correctly the line integral over vector field is is the amount of work the vector field did along the path? or is that just specific case?
Comment: Thank you. It's not a specific case. Let $\gamma$ be any path and $\textbf{F}$ be a vector field. Then the line integral over that vector field is the total work done by the vector field as something travels through that path. And this is the same meaning for any dimension, not for only $\mathbb{R}^2$
Comment: This is why line integrals over vector fields are used a lot in physics
Comment: But although the meaning is work, mathematically it's a fundamental, It's involved in a lot of theorems and has a lot of applications within math.


How paste text from firefox to GVIM on ubuntu11?

Question: I found that I can not paste text to GVIM from firefox or other editor, anyone can tell me how to set my GVIM(GNOME) on Ubuntu11 ?
Answer: The way I usually do this is to ensure that vim is in insert mode, select the text in Firefox (or whatever) and then middle click in vim - this is called the X11 selection, and is very handy.
You can also use the * and + buffers. So to paste from the X11 buffer into vim you can do (inside vim):
"*p

And if you have done Ctrl+C (or right click and "Copy") then you could do:
"+p

(Note that as usual, lower case p will paste after the cursor, and upper case P will paste before the cursor).
Note that "* and "+ work both ways. So if you have selected text in visual mode in vim, you can copy it to the X11 selection using "*y or to the standard clipboard using "+y.
Answer: I used "Shift-Insert" earlier today with text copied from firefox and pasted into a terminal (vi) for a co-worker stuck with the same issue on 11.. Not sure what needs to be changed in gvim to sync up the clipboards.
Answer: @Hamish's answer is nice and works fine for VIM. Another way, perhaps more general, is to use xclip (apt-get install xclip).
Run this (or, more realistically, bind it to some key):
 xclip -selection clipboard -o | xclip -selection primary -i

It will take your clipboard (where things end up after pressing ctrl-C, generally) and move it to your primary X selection (what you paste when you press the middle mouse button). So you can then press the middle mouse button to paste into VIM, GVIM or any other application.


Can I pull 120v outlets from a 220v box with no neutral?

Question: I want to run a couple of 110 volt plugs from a box that has 220 volts.  Both the black and white wires are 110 volt and there is only a ground wire with them.  Can I tie into one of the hot wires and just connect the neutral wire to ground?
Comment: Is this a dedicated circuit? Any other 220V loads on the circuit?
Answer: NO!
That would be a National Electrical Code violation and a dangerous practice.
That would energize the the ground wire and someone could be electrocuted from a wire they can normally expect to be safe.
Comment: You would need to run a new cable with 3 wires and ground or just run a new 2 wire with ground for the receptacles. Or retask the 220 volt circuit to 120 volt by switching the white wire back to being a neutral.
Comment: How can I safely complete the circuit?
Answer: If you cannot pull new cable with a proper neutral AND ground conductor separately, then the only legal way to attain 120V would be to use a 240-120V transformer and power the transformer from the 240V circuit, then let it create a new 120V circuit from it with a legal Neutral that is now bonded to ground at the transformer. This is called a "separately derived source". That transformer would also need to have proper primary and secondary circuit protection based on the size / capacity of 120V that you need. Trust me, it would likely be cheaper to rip open the walls and run a new cable...
Answer: Neutral is not ground, and you must never misuse neutral for ground or vice versa. It can cause a serious safety hazard.
Most 240V circuits are dedicated to a single machine, device or receptacle.
If this circuit serves only this location, or if you are able to convert all its locations to 120V, you can convert this circuit to 120V.
Change how it's punched down in the service panel, so instead of white and black going to the two sides of a 240V breaker, the white goes to neutral.  (the black can still go to 1/2 of a 240V breaker, so you don't even need to move it).  Now change each receptacle to the appropriate type.

Remember that if your circuit breaker is 30A, all its receptacles must also be 30A.  If you need to plug 15-20A plugs into that, check out a PDU or power distribution unit intended for computer servers.  You could also downsize your breaker to 20A, as the breaker size decides circuit size.  Don't upsize breakers without fully understanding wire size and the rules there.


Starting Tornado with Nginx on Ubuntu 10.04 automatically with domain name

Question: I've managed to set up my nginx.conf file and it looks like this:
root       www www;

worker_processes 1;

worker_rlimit_nofile 8192;

events {

  worker_connections  8000;

  accept_mutex off;

}

error_log  logs/error.log;
pid        logs/nginx.pid;

http {
  # Set the mime-types
  include       mime.types;

  # And the fallback mime-type
  default_type  application/octet-stream;

  # Format for our log files
  log_format   main '$remote_addr - $remote_user [$time_local]  $status '
    '"$request" $body_bytes_sent "$http_referer" '
    '"$http_user_agent" "$http_x_forwarded_for"';

  # Click tracking!
  access_log   logs/access.log  main;

  # ~2 seconds is often enough for HTML/CSS, but connections in
  # Nginx are cheap, so generally it's safe to increase it
  keepalive_timeout  5;

  # You usually want to serve static files with Nginx
  sendfile on;

  tcp_nopush on; # off may be better for Comet/long-poll stuff
  tcp_nodelay off; # on may be better for Comet/long-poll stuff

  # Enable Gzip
  gzip  on;
  gzip_http_version 1.0;
  gzip_comp_level 2;
  gzip_min_length 1100;
  gzip_buffers     4 8k;
  gzip_proxied any;
  gzip_types text/html text/plain text/xml application/xml application/xml+rss text/css text/javascript application/javascript application/json;

  gzip_static on;

  gzip_proxied        expired no-cache no-store private auth;
  gzip_disable        "MSIE [1-6]\.";
  gzip_vary           on;

  server {
    # listen 80 default deferred; # for Linux
    # listen 80 default accept_filter=httpready; # for FreeBSD
    listen 80 default;

    # e.g. "localhost" to accept all connections, or "www.example.com"
    # to handle the requests for "example.com" (and www.example.com)
    server_name _;

    # Path for static files
    root /srv/www/example.com/public_html/src/static;

    expires 1M;

    # Static assets
    location ~* ^.+\.(manifest)$ {
      expires -1D;
      root   /srv/www/example.com/public_html/src/;
      access_log /srv/www/example.com/logs/static.logs;
    }

    location ~* ^.+\.(ico|ogg|ogv|svg|svgz|eot|otf|woff|mp4|ttf|css|rss|atom|js|jpg|jpeg|gif|png|ico|zip|tgz|gz|rar|bz2|doc|xls|exe|ppt|tar|mid|midi|wav|bmp|rtf)$ {
      # Only set expires max IFF the file is a static file and exists
      if (-f $request_filename) {
        expires max;
        root   /srv/www/example.come/public_html/src/static;
        access_log /srv/www/example.com/logs/static.logs;
      }
    }
  }
}

My questions for nginx file is:
1) I would want to host my application with the domain name : www.example.com, which line of the nginx.conf file do i change?
My nginx.conf file is found in the same folder as app.py.
2) When I was trying to start nginx by typing /etc/init.d/nginx start, I received the following error message:
Error Message:
Starting nginx: [emerg]: bind() to 0.0.0.0:80 failed (98: Address already in use)
[emerg]: bind() to 0.0.0.0:80 failed (98: Address already in use)
[emerg]: bind() to 0.0.0.0:80 failed (98: Address already in use)
[emerg]: bind() to 0.0.0.0:80 failed (98: Address already in use)
[emerg]: bind() to 0.0.0.0:80 failed (98: Address already in use)
[emerg]: still could not bind()
nginx.

I have not done any configuration to the nginx.conf file found at /etc/nginx
My questions for this part are:
3)  How do i fix the error?
4) How do i start nginx automatically?
I've tried running my Tornado app by typing
python app.py
Than I navigate to http://xxx.xx.xxx.xxx:8888 , and my app works correctly.
However, should I close my terminal ( killing the process ) , my tornado app is no longer active.
My question here is:
5) how do i start tornado app automatically?
6) How do i run tornado on a domain name?
Thank you all for your kind patience.
Best Regards.
Comment: If you haven't done so already, try cross-posting this to ServerFault
Comment: You need to give more information about the environment your working in; eg. which version of linux you have installed, which version of nginx/python, etc.
Answer: 1) Change the server_name.
2) You probably have Apache running.
3) Stop the service (using something like service httpd stop) and then start nginx.
4) Try the following commands:
$ chkconfig httpd off
$ chkconfig --add nginx
$ chkconfig nginx on
$ service nginx start

5) Look at using supervisor for running python apps
6) Check out the nginx wiki for information on reverse proxying; nginx handles requests to the domain and passes those requests to your tornado backend.
Answer: about the error message: the same problem when using Ubuntu 11.10 , it seems that Opera occupy the port 80, so just modify the value.


Is my bathroom project prohibited due to a low ceiling height?

Question: We would like to install a half bath in our finished basement in Colorado. The issue that I seem to have is that the ceilings are short at only 73". My understanding is that code requires the ceilings to be 80" in front of the fixtures. We can't do anything about the ceiling height, so does this mean that a bathroom wouldn't be an option in our basement?
Comment: I thought the ceiling needed to be 7'6".
Answer: It may be possible to be granted an exception regardless of what code states depending on the flexibility of the Authority Having Jurisdiction.
Ask the Authority Having Jurisdiction. In other words, ask your local building department or whomever has authority to approve permits where you live to see what they require and whether they would permit such an exception.
For example: When I was finishing my basement, I have a point that goes below minimum required ceiling height for my state's building code. My local building department follows my state's building code. My state's building code is generally based on the International Residential Code, but has a few exceptions (one noted difference in my state is the required minimum height for finished ceiling heights and protrusions when finishing pre-existing unfinished basements). My building department granted me the exception I listed in the submitted plans. This example also shows exactly how locale-specific this question is.
Answer: I don't think that means a bathroom isn't an option, more that it's considered a "non-conforming" bathroom which may or may not count in potential listings for sale.
If we go off of my local code (2012 IRC), the minimum ceiling height is 6'8" (OP mentioned this with their 80" comment). Looks like you're just 7" short.
Now, if this is because of a beam or other obstruction that isn't normal ceiling heights, looks like you can lower that requirement to 6'4" (according to 2012 IRC), but that's still 3" too short.
I'd be willing to bet the space, although probably nice and definitely a bonus, is really just all non-conforming basement area, regardless of what else is down there, due entirely to ceiling height.
Comment: Are you saying it's okay to build the shower if it doesn't comply with the Code?
Comment: There wouldn't be a shower, just a sink and toilet. So if I am understanding you, since there isn't an option of raising the ceilings to the 6'4", the bathroom would probably just be listed as non-confirming one we sold the house? How would this work with permits and inspectors when we are working on the bathroom build?
Comment: Based on other discussions regarding this subject, you may be able to talk to your local permitting department about getting a variance, but this is entirely up to them. if they say it's not possible, then it sounds impossible.


Transformer with a single turn plate as secondary

Question: What kind of applications are transformers with a single turn secondary used for?
I believe a high current is generated, but couldn't really figure out a good practical example where this might be used.
Answer: A Weller gun-style soldering iron is one good example.
soldering gun http://static.emedco.com/media/catalog/product/Cooper-Hand-Tools-Wellerreg--Professional-Soldering-Guns-DD678-ba.jpg
Also, pretty much any spot-welder for sheet metal.

(source: harborfreight.com)
Answer: I've used a single turn secondary with the wires passing through a current transformer for testing it at hundreds of amps. The primary was fed from a variac so I could control current fed through the CT. Checking linearity was the objective.
Rf transformers are quite commonly made with one or a few turns to make them work effectively at VHF and UHF.
I've also made data coupling transformers where one winding was on a rotating spindle. Single turns had to be used because the data rate was so high ie tens of Mbps.
Same sort of idea for transmitting power across a small gap on rotating apparatus. Single turns were used and resonated with tuning capacitors.
Answer: I saw one in a 12V 800W server power supply (Ablecom PWS-801-1R).
In case you were wondering - the PSU provides 12V and 5VSB, the other voltages are generated by the backplane.


Antivirus that runs only by request

Question: I just want a lightweight antivirus for my Mac that doesn't keep running on background but only scanning a file by request. Is there any?
Answer: I personally use Sophos Antivirus. You can disable On-access Scanning from within the configuration settings.
Answer: ClamXav (free/donationware)

Scan only the files you tell it to or your entire hard drive,
  whichever you prefer.

Antivirus that runs only by request


Can I Wish for a card outside my Commander's colors?

Question: I have been told that Wishes work differently in Commander than in normal casual Free-For-All (FFA) mtg. Do the comprehensive rules cover how wishes work in Commander? Do the rules for wishes differ from normal FFA multiplayer?
Answer: Wishes are non-functional in Commander, unless your group specifically allows them and defines where they work.
The comp rules define the basics of the format but mostly point you to mtgcommander.net for the up-to-date official definition. Per mtgcommander.net,

Abilities which refer to other cards owned outside the game (Wishes, Spawnsire, Research, Ring of Ma'ruf) do not function in Commander without prior agreement on their scope from the playgroup.

Basically the Rules Committee's reasoning was that using wishes in their original, casual-play way (searching your entire collection) wastes too much time in play1. So they used to restrict you to searching your sideboard, which is how wishes work in competitive MTG. However, Commander's sideboards are "optional" and Sheldon has generally come out against them, so the default is that wish cards don't work at all.
Sideboards still have to follow all the normal deck-construction limitations, like in any other format; for Commander, this means you can't have break the one-of restriction or violate color identity just because a card is in the sideboard. Thus, if you group agrees to play with wishboards, you'll still be limited to your commander's color identity.
(Note also that the official sideboard size is 10 cards, not 15 like 60-card constructed.)

1 – Which is also why Shahrazad was finally banned after some time as the only Vintage-banned card legal in Commander.
Comment: I got 99 cards but a Wish ain't one... sorry, I had to.
Answer: I have done a search for all Commander references in the CompRules and have found nothing specific. There are several points to consider when determining this question in particular:

Commander is a semi-official format. It's covered in the official rules, but it has been invented and is maintained by regular players. So questions specific to the format that are not answered by the CompRules should be probably be asked and answered there.
Going by the rules, I would argue that Wishes work the same as in regular games: Since a Commander game is casual only, you are allowed to get any non-ante card from your collection. In sanctioned events, Wishes can only get cards from your sideboard.
Going by the philosophy of the format, Wished cards should probably be restricted to cards in the Commander's color identity. But that is more a house rule, as the CompRules don't regulate that particular point.


Online manga about a boy accidentally summoning a demon at his school who fights people

Question: This online manga was about a boy who had to summon a monster for something at his school and finds a book and summons a demon. She easily defeated multiple people and their monsters and that's pretty all I can remember other than that the demon the boy summoned was hot and I read it on a website not any apps if that helps, I don't remember the website name.
Comment: If someone posts the correct answer, you can accept by clicking on the checkmark by the voting buttons, as per the [tour]. If an answer is wrong, it's an excellent chance to [edit] your question to provide new details you've realized by comparing your memories to the wrong answer.
Comment: Hi, welcome to SF&F.  Where and when did you read this?
Comment: "monster Afro something"? And was this a webtoon that was originally on the web? A scanlation you read online? Was fighting in general done by summoning mons?
Comment: Sorry about that mistyped word, it was ment to be "for" not "Afro"
Answer: Might this be Magika Swordsman and Summoner?

15 years ago, the world discovered magic as well as mythical beings from another dimension. Humankind learned to summon these dangerous mythical beings and used their power to great effect. Seven countries formed contracts with these "gods" and gained their allegiance as a result. Summoners on their 14th birthdays will be chosen by a God and given a stigma. Schools have been set up to train summoners and magical swordsmen as a result.
15 years later after the finding of magic, Kazuki Hayashizaki is chosen as a summoner and given a stigma to indicate that. It is surprising because males aren't chosen as summoners due to their low amount of mana compared to females. As the first male to become a summoner, Kazuki is under a lot of scrutiny by almost everyone.

His "diva" summon is Lemegeton.

Leme is a petite young girl who has long silver hair, dark tan colored skin, yellow eyes as well as white star-shaped tattoos on her forehead, arms and legs, Leme is always seen with a white tunic and black armbands. When Leme transforms to her original form, she becomes noticeably taller and her breasts become bigger, in this form she wears a revealing black dress with yellow bracelets. The marking on her forehead becomes bigger and a black "halo" appears behind her.

Found with a search for manga school fight "summon * demon"
Answer: Vermeil in gold is something I know of. It is the same story and holy the demon is OP.
Comment: Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer).


Web services to mine the social web?

Question: Are there any web services that can be used to analyse data in social networks with respect to a specific research question (e.g. mentioning of certain products in social media discussions)?
Answer: Tweepy is one of the best libraries for analyzing and hacking around with the Twitter API.  (Being a contributor for tweepy, I can vouch for it's stability and quality)
For a Python wrapper for the Facebook graph API, you can use the Facebook-Insights library, which is well-maintained and neat documentation.
There are services out there which can mine you information, but they are limited to the complexity of the query.
For example: "How many people tweeted about banana on Monday?" can be answered from existing tools
"How many people happy people tweeted about banana on Monday" can also be done, but would require more efforts and the software or tool should be able to detect emotion.
So, if you are into research, I would advise you to go with the API's and good ol' programming!
Comment: +1 for the information about Facebook-Insights library, any chance you've got a demo of how that works? I'd love to see code mining the Facebook graph API
Comment: @wacax We use it in our Django framework, in my team. But, I don't have any code in public repos, though!   However, the md doc there, is self-explanatory :)
Answer: Twitter's API is one of the best sources of social network data. You can extract off twitter pretty much everything you can imagine, you just need an account and a developer ID. The documentation is rather big so I will let you navigate it.
https://dev.twitter.com/overview/documentation
As usual there are wrappers that make your life easier.

python-twitter
twitteR

There are also companies who offer detailed twitter analytics and historic datasets for a fee.

Gnip
Datasift

Check them out!

Web services to mine the social web?


Salesforce database structure for sales cloud and service cloud

Question: Do any one here have any doc related to database model of salesforce. Model of sales cloud and service cloud. I go through doc which salesforce have https://www.salesforce.com/us/developer/docs/api/Content/data_model.htm but its to confusing. If there any youtube video or doc form where I can understand it much better how salesforce is using there objects of marketing, sales and service cloud apps.
Comment: How and what specifically is this confusing to you ? I'm not aware of many video's or recorded talks about the datamodel that are in any way better understandable than the documentation you refer to. To really answer you and help you, it's important to understand why you are unable to understand the data model in the way it's described in the documentation.

  Consider updating your question with more detail, so that we can answer also with more detail.
Answer: The easiest way to get this information is to sign up for a free Developer Edition of Salesforce here, and then go to Setup > Build > Schema Builder.
You can then pick and choose which objects you want to look at and see all of the relationships between them.
There are also some more traditional schema diagrams available in the documentation:

Salesforce Data Model
Sales Objects
Support Objects

There are also these two presentations from Dreamforce last year which concentrate on the administration of Sales Cloud and Service Cloud but should hopefully help your understanding of how the features and objects actually work and interact:

Hands-on Training: Get Started with Sales Cloud Administration
Hands-on Training: Get Started with Service Cloud Administration
Comment: Hi @Alex i went through this traditional schema diagrams but not able to understand. Its confusing a lot.
Comment: @Anu Have you tried setting up a Developer account and using the objects rather than just reading about them? It might help you to understand how it fits together.
Comment: perhaps a valid question could be that do you guys have a combined diagram between Sales and Service cloud objects. I am looking for one if anyone have one to share. Else I will put together one myself.
Answer: There are some third party solutions to getting a data model from Salesforce.   The Schema Builder is good for relatively small models, but if you want to use a more 'industrial strength' modelling environment, then you probably want to be able to get the metadata out of SFDC and do some scoping and analysis.    I suggest you google Safyr, which is a tool for just this.   Its from Silwood Technology.


facebook like button on my site only shows up after you refresh the page. does it have to do with all.js

Question: I used code from
http://developers.facebook.com/docs/reference/plugins/like/
to add a like button on the site.   I have the script tags right after the body as described and the div further down by my header, but when I load the page, the like button is not there.  but if I hit refresh its there.   my guess is that the all.js is taking too long to load and its missed somehow on the 1st load.  on the 2nd refresh, I assume the js is cached and things work as expected.
any idea how to wait on this?  I have tried putting the script in the head, at the bottom.
Answer: When you say "I have the script tags right after the body", do you mean outside of the body? If so, try putting it in side the body, but after all other element inside of the body.
<code><body> ...other code ...other code ...other code
  <script>Put your script here</script>
</body>
</code>
Comment: Could you possibly provide a link to your test page. It would help if I could inspect your code.


Does anyone have any frameworks to setup custom post types and related actions/filters?

Question: So I know that setting up custom post types ranges from just registering them to adding custom permalinks, custom sorting, customizing columns in the admin, etc.  I was wondering if anyone had a template or framework that they use regularly to set up custom post types in projects?  Do you start from scratch every time or do you have a base line you start from that you customize?
Comment: I was running this from scratch every time and it was quite time consuming. I built a framework for this last week and it's saved me a ton of time already. I'll push it to the plugin repo in a week or two and I'll comment here with a link.
Answer: The Custom Post Type Demos by toscho hold some nice basic classes, that you can use. I'd recommend taking a look at this source (as he's a trusted author and a pretty good coder).
Answer: There is the promising Piklist which does a lot more than CPT (settings, widgets)
All in a fashionable way and very easy to maintain. (I'm not the author)
Comment: I just started using Piklist and so far I'm very impressed
Answer: I recommend to check PODS, its very powerful and useful, with deep relations and very easy to use. It save a lot of time and.
Answer: I'm tending to just write code directly for adding Custom Post Types now, but I have used Easy Post Types (http://easyposttypes.com) before, I've found however that they've been slow to bring out updates and never responded to any bug reports I sent to them. I'd also suggest checking out the Magic Fields plugin (http://magicfields.org), since V2 it uses CPTs and offers a lot of useful features.


Using Synchronized data extension fields in journey builder decision splits

Question: I want to use synchronized data extension fields in the form of contact data in journey builder splits.
Let's say my journey is abandoned cart and when the customer enters the journey through API based entry event, the customer recieves the first email after an hour. However, the customer could potentially make an order in that hour which ends up as an order record in Salesforce. We have a decision split configured, if the customer makes a purchase for the cart that it abandoned, after it entered the journey(by saving timestamp and then comparing it with order createddate), so we exit the customer from the journey.
I am not able to use the synchronized data extension fields and compare it with the journey data. Since some of the fields on the synchronized data extensions are nullable, I cannot compare it with journey data, as it gives me a warning. The alternative, that I have tried to use journeydata through {{Event.event_definition_key."cartId"}}, which works for update contact activity, but does not work in decision splits.
Has anyone successfully tried to use synchronized data extension fields(not required on object level in Salesforce but marked as non-nullable in synchronized data extension) in decision split and compare it with journeydata?
Answer: You'll need to create a custom attribute in Contact Builder - Data Designer with the fields that will connect to the subscriber in the Journey.
(1) Create a query or multiple that pulls from the synchronized data extensions as the source (FROM) pulling in the fields subscriber/contact ID, cartID and order createddate.
(2) Create a data extension that will feature the contact/subscriber key that will relate to the ContactKey for the subscriber (Contact ID or Lead ID) and the cartId and order createdate fields.
(3) Create an automation that will run the querys in step #1 at the frequency needed.  If hourly is too long add 2-3 fifteen to twenty minute wait steps in the automation.
(4) In Contact Builder Data Designer build a custom attribute linking the Contact Key to the Contact/lead ID in your data extensions.
(5) In the decision splits in your journey set the 1 to 1 relationship with your subscriber by selecting the contact/lead ID in your custom attribute and check the Attribute compare checkbox and add in your contact/lead ID from your Journey DE equal to the attribute id.
(6) In the same decision split add another filter to compare the order createdate.