sending specific date's data from data logger shield to serial port

Question: I was wondering if it is possible to save lots of data( exp: one year data) in data logger shield and then read them from serial port without ejecting the SD card... this part of my question is fine... the main subject is that i want to read specific date's data from the logger... To explain this better, lets say you have a humidity sensor and saved it's data for a year. Now you want to send the last 6 month's data to your phone via bluetooth. Is it possible?
Also, i wanted to use the circular buffer but that doesn't seem like a good idea because it's costly... any ideas will be such a great help.
Comment: how many lines are logged in one day?
Comment: Is it important? i wanted to lower the daily sampling, so maybe 2 times...
Comment: ok, it is not too much for one year. to copy part of the file to Serial you would read the file line by line from the beginning and start printing after you find the line with the requested start date.
Answer: I see a few questions (reading specific data from an SD) and the circular buffer; I think these are two different 'problems'.
Reading specific data from an SD
It depends how you save your data. Do you make one big file, or you create daily a new file for example?
Assuming the last, it's relatively easy, just sent the file contents of the files within a certain date.
In case you have a big file, you need to parse the file, in specific the time stamps you have to include in the file, and send everything within certain dates.
If this takes too long parsing, you could create a second file that contains the starting points (e.g. byte offset) for every day. So e.g. Jan 1 -> 0 means Jan 1 starts at byte 0, Jan 2 -> 3633 starts at byte 3633; you can use some kind of seek function to start reading the data file starting from date; and continuing also checking the end date's byte offset.
You can get the time stamp of a file:
void dateTime(uint16_t* date, uint16_t* time)
{
    DateTime now = rtc.now();
    // return date using FAT_DATE macro to format fields
    *date = FAT_DATE(now.year(), now.month(), now.day());
}

You can start reading from a certain position in a file by using the fseek function, see https://www.arduino.cc/en/Reference/FileSeek.
Circular buffer
This relates to sending bytes (via a peripheral/bluetooth). It is not costly at all. What you do is create a circular buffer (e.g. 50 bytes or whatever). Than you start writing bytes into it (which you copy from the SD file increasing the buffer space. Than you start sending bytes from it, decreasing the buffer space.
I never used Bluetooth, so I don't know how the packet (and size) is sent; if you can just sent packages of a certain or fixed length,  you don't need a circular buffer, just keep reading e.g. 50 bytes, put it in a fixed array, send it, and load it again etc until all bytes are sent.
Comment: The idea was to ask for any data history i want through mu cellphone... I wanted to make different files with specific time stamps but then if the period i want wasn't in the files it would be a problem...
Comment: And another thing i don't know is how can i specify a certain starting point for my files?
Comment: You can get the time by using:
void dateTime(uint16_t* date, uint16_t* time) { DateTime now = rtc.now();  // return date using FAT_DATE macro to format fields
  *date = FAT_DATE(now.year(), now.month(), now.day());
Comment: Can i also get the period of different times?
Comment: So after you write a file (each day), or for the last time once per day, you can get the date back, although it might be even easier to write the date in the file name (data_yymmdd.log)
Comment: Not sure what you mean … if you need 5 to 10 December, just read out the 5 files and send them (?)
Comment: About reading not from the start, see https://www.arduino.cc/en/Reference/FileSeek
Comment: yes for example from 5 to 10 December. how can i do that?
Comment: If you have a separate file for each day, read the 5dec file (in parts of e.g. 50 bytes or so), and send each packet, than do the same with the 6dec file etc.
Comment: How can i save each data in their own file? for example for 1 week, 1 month, etc. I mean the data from 1 week should also be in the data for one month... can you help me with the code?
Comment: That depends, better make some commands that send the information you need (like start/end period).


Syncing local state and remote state (Parse) with poor connectivity

Question: GOAL: 1) Enable users to play my game regardless of poor connectivity, and 2) have ~reliable user state stored on Parse for customer support and stats.
My Approach: I am using local client storage as the master (so that net connectivity is not required), and I am using Parse as a secondary synced storage so that I can address customer issues and maintain stats.

The game has a sequence of fixed levels.
User state for each level is stored locally in UserDefaults as the SOT (yes, a bit ugly).
I use Parse as a secondary replicated store for customer support issues and stats.
Thus, I also store the level state on Parse (i.e. PFObject="UserLevel": userId, level #, status, high score, #wins, #losses, etc.).
There should be only one (or zero) PFObject per level per user.

==> When the network connectivity is poor, I often create multiple PFObjects for the same level.
<code>e.g. A typical 5 minute game session:
</code>

User unlocks a level:
==> Create PFObject "UserLevel": uid=currentUser, level=#, status=UNLOCKED, wins=0, etc.
User plays this level and loses:
==> Query (async) Parse for PFObject (match userId & level #):
If one matching object found ==> ++losses... (saveEventually)
If >1 matching objects found ==>  object[0]:++losses... (saveEventually) (ignore all but one!)
Else (no matching objects found) ==> Create new PFObject. (saveEventually)
User plays again and wins:
==> Query (async) Parse for PFObject (match userId & level #)
If one matching object found: status=COMPLETED, ++wins... (saveEventually)
If >1 matching objects found, status=COMPLETED, ++wins... (saveEventually) (ignore all but one!)
Else (no matching objects found): create the PFObject. (saveEventually)
... etc...

As you can guess, if the network connectivity is slow, and the various queries and saveEventually's have not completed yet, this can easily result in duplicate PFObjects for the same level.
My guts tell me not to create the PFObject during an update if it does not exist. Instead, the Parse state these be sloppy/behind, and clean it up during app start (i.e. a clean sync).
I'm assuming this is a very common design pattern and that I'm missing some basic CS fundamentals. (I'm a newb to backend coding.)
Answer: The simple solution, since there are a fixed number of levels, is to pre-create each "UserLevel" and save them, and then everywhere else you just do updated instead of create/update.
Comment: I like simple. :-)  Thanks.


Can receive email, but can't have the server send email

Question: I have a script that is supposed to have the server send an email.  My problem is, that I can email my server, and receive that email, but the server will not send email.  Will only send email through the squirrelmail interface.  I have the MX record as: mail.mydomain.com and mydomain.com and an A record of mail.mydomain.com
Below is the script that should have the server send an email.
<?php
$fileatt = "Reports/$previousreport/$previousreport.pdf"; // Path to the file
$fileatt_type = "application/pdf"; // File Type
$fileatt_name = "$previousreport"; // Filename that will be used for the file as the attachment

$email_from = "example.com"; // Who the email is from
$email_cc = "firstname.lastname@example.com";
$email_subject = "$theData3"; // The Subject of the email
$email_message = "
";
$email_message .= "
"; // Message that the email has in it

$email_to = "$theData2"; // Who the email is to

$headers = "From: ".$email_from.
$headers = "\r\nCc: ".$email_cc;

$file = fopen($fileatt,'rb');
$data = fread($file,filesize($fileatt));
fclose($file);

$semi_rand = md5(time());
$mime_boundary = "==Multipart_Boundary_x{$semi_rand}x";

$headers .= "\nMIME-Version: 1.0\n" .
"Content-Type: multipart/mixed;\n" .
" boundary=\"{$mime_boundary}\"";

$email_message .= "This is a multi-part message in MIME format.\n\n" .
"--{$mime_boundary}\n" .
"Content-Type:text/html; charset=\"iso-8859-1\"\n" .
"Content-Transfer-Encoding: 7bit\n\n" .
$email_message .= "\n\n";

$data = chunk_split(base64_encode($data));

$email_message .= "--{$mime_boundary}\n" .
"Content-Type: {$fileatt_type};\n" .
" name=\"{$fileatt_name}\"\n" .
//"Content-Disposition: attachment;\n" .
//" filename=\"{$fileatt_name}\"\n" .
"Content-Transfer-Encoding: base64\n\n" .
$data .= "\n\n" .
"--{$mime_boundary}--\n";

$ok = @mail($email_to, $email_subject, $email_message, $headers);

if($ok) {
echo "You file has been sent
 to the email address you specified.

Make sure to check your junk mail!";

} else {
die("Sorry but the email could not be sent. Please go back and try again!");
}
?>

I keep checking the MX records but I can't figure out what is wrong.
Answer: Check the log files for any hints (/var/log/messages or /var/log/maillog).
Could you also better format your code to help me understand what exactly you are trying to achieve.
I doubt the issue is with the MX, more likely it's a coding problem (the $email_from variable has an incorrectly formatted address)


How to decode internal transaction in mempool

Question: i'm researching on how mev works. I know that they are watching all pending transactions, then define function that is swap on dex and calculate amount to do sandwitch. However, when user do a swap, they can use several contracts to do them which lead to different data field on transaction. how to decode them ? Thank you for your time!
Answer: One can utilize tools like Etherscan or other blockchain explorers to interpret the different data fields in transactions used by various contracts for swaps.
These tools enable the examination of the input data of a transaction, leading to a better understanding of the specific function calls and parameters used in the swap.
Analyzing the input data allows for the decoding and interpretation of the various contract interactions, providing clarity on the specific actions taken during the swap.
Additionally, referring to the documentation or source code of the involved contracts can provide further insights into their functionality.


How can I apply exact texture measure (cm) in uv mapping?

Question: So, i'm working at a bathroom and my main problem is with tiles. My tile is 25cm x 75 cm how cand I apply exact measurement of my tiles to fit the walls. Let's sey I can hardly apply exact uv mapping on one wall, but is more hard to fit the other walls at the same measurement.
Answer: The room to tile with 75cm x 25cm tiles:

1: Create or resize a tile texture.
It should have the same proportions as the 75cm x 25cm tile, thats to say 75/25 = 3:1. To keep things simple I like the idea of having 1pixel to 1mm. In the example below the tile texture size is 750px x 250px.

2: Open this texture in Blenders UV Editor:

3: Next is to UV unwrap the four walls A, B, C and D.
Before doing this it may make things easier if all all the surfaces that are not going to be tiled (UV unwrapped) are hidden (H key). Doing this will make it easier to select each of the remaining walls.
Select Wall A and in orthographic front view (numpad 1) UV unwrap using the Project from View option.

4: Hide wall A. Switch to the Back view (CTRL + 1), select Wall B and again UV unwrap using  Project From View.
Repeat for walls C and D. It is very important that you do not change the zoom in or out when selecting before each unwrap.

5: Unhide the Walls (Alt H)
With the four walls selected, in the UV editor the four islands may appear squashed in the Y axis so to correct this select all four islands and scale up by 3.

6: Next we need to get the lower left corner of each wall island snapped to the lower left-hand corner of the UV space. This is done for two reasons,  a) to have all  the walls lower edges aligned and b) so that they can be all scaled up together from the same single point. (X=0 Y=0).
In the UV menu enable the Constrain to Bounds option then select each island in turn and drag it down so that its lower left corner is snapped at X=0 Y=0.

7: Uncheck the Constrain to Bounds.
Assign pivot point to 2D cursor and check that the 2D cursor is at X=0 Y=0. Select all four islands and scale them up until the right-hand edge of the Wall A is aligned with the right-hand edge of the UV space (X=1).

8: Now we are ready to do the final scaling. The length of Wall A divided by the length of the tile 6000mm/750mm = 8.
With the pivot point (origin of the scaling) still using the 2D cursor and all four islands still selected scale them up together by a factor of 8.

Now when the tile texture is applied to all four walls it should be correctly aligned and correctly scaled.

Another way to do this could be to use the Mapping node in the Node editor, adjusting the X and Y values to suit. In this case the UV Unwrapping (mapping) method would be Project from View (Bounds).
Because the length of Walls A and B are not the same as Walls C and D the scale of Y value would be different. This would mean having to use two different materials.


Merging fat32 partition on external hard drive connected to ubuntu 12.04 LTS

Question: I have WD 160 GB hard drive and i have formatted it to fat32 file system i want to merge all multiple FAT32 file system partition to make it one. how do i do it on ubuntu 12.04LTS. Would also like to know if FAT 32 is good for sharing data between windows and linux systems and how to shrink "extended" partition on external hard drive.
Any help will be appreciated..
Answer: Due to the craziness with that partition table, I would recommend backing up any data you might have and then just deleting all partitions and making a new one. GPartEd can format the drive to be one 160GB FAT32 partition. If you want to keep that Linux Swap partition, create two partitions.
I don't think FAT32 is a good format for sharing data, because it has a hard file-size limit of 4GB. With larger file sizes (particularly video data files) becoming commonplace. You will run into this limit frequently. NTFS is now read/write supported on Linux, so you can use it, or even mount Ext3 partitions on Windows.


Android Junit Test Cases

Question: How can I stop the android Junit test application in the mid.I want to stop the execution of my application in particular place.Is it possible?Please give your suggestion..
Answer: Set the breakpoint in desired place in IDE and run test project in debug mode.
Note that debug execution is a bit slower than  run mode.
hope this answer satisfies your question
Answer: click on the stop button in the junit column. But again if you return, the testcases will be running from the beginning.

Android Junit Test Cases


Why does ipv6 specify 128 bit address, when there are only 48 bits in MAC addresses?

Question: So, I'm reading for a networking exam, and I'm just wondering if I have missed something basic. Is there a need for more ip addresses than MAC addresses, and how would a node with one network adapter be assigned many ip addresses in that case?
Comment: +1 despite it is obvious that MAC must be unique only for devices within one local network (connected to the same bus) whereas Internet layer consolidates all local networks into one global net whereby the fundamental design principle, divide an conquer, precisely prescribes that local networks be unaware of the local addresses within the other local networks to successfully communicate via global IP scheme, and furthermore, you can attach non-Ethernet based local networks to the Internet. So, I am interested to know what would be the answer if IP demanded Ethernet-only at the bottom level.
Comment: The transition from IPv4 to IPv6 was — and is — so slow and expensive that we don't want to face another transition ever again.  128 bits have reasonable chance to be enough "forever".  http://tools.ietf.org/html/rfc1606 is a great humorous take on that ("As the IP **version 9** protocol comes to the end of its useful life, once again due to address space exhaustion, ...")
Comment: @BeniCherniavsky-Paskin, the transition is slow because NATs mitigate the need. Again, this shows us that we do not need the local address space to cover the global address space.
Answer: MAC addresses only need to be unique in a local broadcast domain, not globally, so re-use of MAC addresses in different networks usually isn't a problem.
The internet isn't one global broadcast domain and thus needs to be divided into many blocks of addresses assigned to different ISP's and each ISP divides his blocks into smaller blocks for different customers/services. To allow each of these smaller blocks to contain many MAC addresses you need to have the IP-space much bigger than the MAC address space.
Comment: Also because of aggregation. 48bits would be more than enough IP addresses (40k per person), but that would mean each router needs to look at flat table of over 2PB, that technology does not exist.
Comment: This would warrant another question. But MAC address is done from 24b or 36b OUI number you purchase from IEEE, which should be unique, but in practice to save 1300USD some people use other peoples OUI, or some people manufact NIC with non-unique MAC. While MAC address is 48b, it's actually just 46b, since 1 bit determines if it unicast/multicast and 1 bit if it is global/local, if local scope bit is on, then all bets are off for uniqueness.
Comment: @ytti: At least until we all have ip-enabled nanorobots in our bloodstreams
Comment: They probably can use linklocal as only few of them would interface outside the local net.
Comment: On _paper_, they're supposed to be globally unique.  However reality has been known to differ.
Comment: Thanks for the explanation. I was under the assumption that MAC-addresses were globally unique, maybe I misunderstood the textbook, but then what happens when you get a MAC address collision in a local broadcast? Is it avoidable or is it just inconceivable?
Comment: It does seem odd that something that "usually isn't a problem" would be baked into a standard of such ubiquity.
Answer: Not all types of network interfaces use MAC addresses. MAC addresses are mostly associated with Ethernet, though quite a few other networking standards do use it. However, an IPv6 address can still be assigned to a network interface that doesn't use MAC addresses for Layer 2.
Also of note, a MAC address can be converted to an IPv6 host portion through EUI-64 conversion (mostly used for stateless autoconfiguration), by inserting the hexadecimal values FFFE between the leftmost and rightmost 24-bits of the 48-bit MAC address, and the seventh bit gets inverted.
So, for example, 0c:3a:bb:2a:cd:23 can be converted to the host portion of a stateless autoconfiguration IPv6 address. 0c in the above MAC addresses, represented as 0000 1100 in binary, would become 0000 1110 in binary or 0e in hexadecimal. Therefore the final EUI-64 host portion of the IPv6 address, converted from the MAC address, would be 0e:3a:bb:ff:fe:2a:cd:23.
Comment: You also need to flip the MAC address 'local bit'
Comment: I forgot about that part -- I edited my answer to reflect the information. Thanks for catching that :-)
Comment: Silly script to do it automatically: ruby -e'EUI=(ARGV[1]);k=ARGV[0].delete(":.").scan(/.{6}/).join("fffe").scan(/../);k[0]="%02x"%(k[0].hex^0b10);p EUI+":"+k.join.scan(/..../).join(":")' 74:66:30:42:42:42 2001:67c:17a0:0
Comment: The translation of MAC address to EUI-64 for use in IP allocation seems to be a later thing, the original IPv6 over Ethernet standard (RFC 2464) specified zero-prefixed MAC addresses.
Answer: Also, there's some layer 2 protocols with more than 48 bits in their MAC, for example Fibre Channel has 64-bit (or 128-bit apparently according to Wikipedia) as does FireWire (well, kinda), so they can fit in a /64 without the potential of overlap.
Answer: IPv6 SLAAC can only generate one address per prefix as it's using the MAC to generate a reasonably unique address.  Privacy extensions can generate one or more pseudo-random addresses which are then checked for any overlaps on the local segment.  Of course, local administrators can assign as many static addresses as they wish -- it's their job to ensure no overlaps.
[By reasonably unique I mean the likelihood of a collision is nil.  And if it does, you'll have a layer-2 problem first! (two machines on the same segment with the same MAC)]
Comment: Afaict privacy extensions were an afterthought when people realised that MAC based autoconfig was a privacy nightmare. Not one of the driving forces in the design of IPv6
Comment: Most of IPv6 is an afterthought... *Those who don't learn from history are doomed to repeat it.*
Answer: I think fundamentally it comes down to two key points.

Internet addresses don't just need to be globally unique, they need to be globally routeable. Routing every machine's address individually would result in prohibitively large routing tables. The IPv6 designers had a dream of a hierarchical routing system* to keep routing tables small.
The designers of IPv6 wanted stateless auto-configuration. Stateless auto-configuration requires the "host" part of the address to be large, to either accommodate an existing link address or to accommodate a random number large enough that collisions are very unlikely.

Put these points together and you need both the "host" and the "network" parts of an address to be large. Certainly more than 32 bits each. 64-bits each was probably overkill but better overkill than running out.
* The dream didn't really work out because the Internet is not a fixed hierarchy but this isn't about what actually happened in the 20 years or so since IPv6 was introduced, it's about what drove the design.


How to Identify/Change Blue-Bluish Colors in this Map in Photoshop

Question: I want to extract/mark/show all blue colors of the image because there are color blinds who see them as black/wrongly.
I need to estimate all blue-bluish colors there and be able to change the color group to some other colors if necessary.
I cannot change all bluish colors to something else but need to find some compromise.
I heard that you can do it by Photoshop (any edition) but I cannot find a way to do it.
Map of Paris
Answer: I have a solution you should try ..
1 - make a layer mask over your photo
2 - double click on the mask
3 - choose color range
4 - pick the first eye dropper ( you also should choose the " image " checkbox )
5 - start to click on the blue spaces which you want to hide or change
6 - you also can choose the second eyedropper ( with + sign ) to add a new color category to the selection
7 - if you accidentally choose a wrong color remove it with the third eyedropper
8 - once you selected all the parts you need just finish the mask and all this parts will be masked
9 - to change the color of this parts you may make a trick to make a new layer below this layer and fill color it whit any color you want ..
i tested it but the image is so blurry :D
i changed the blue parts with white
Comment: @Masi actually had you reversed this mask you would have gotten the answer of your other questions.
Comment: Great! I think this can work. I am going to experiment the quality of your mask in Matlab by the method described here http://stackoverflow.com/q/29800089/54964 Yes, I agree it is rather blurry.  I think the pick is too much. Is there any way about how you can tell me which exact colors you removed. This would help me to see why your work did that and that. - - Another way would be to be able to form a color group based on your image and original image. I think it is possible. http://graphicdesign.stackexchange.com/q/74252/18754
Comment: @joojaa You are right. I think output is blue colors then. I think you can do it with ImageMagick. Any proposal?


Why is my resolution so low on my textures in the viewport and in renders? (Blender 2.8)

Question: I have been having a beginner issue that I cannot seem to find the answer for. I am following a tutorial on YouTube and my image has a way lower resolution and is so much more jagged both in viewport and renders.
Answer: Looks fine to me, but you can raise the Viewport sampling value (see Render context menu, right side of each of your images) to improve the quality of the viewport render. Of course, this will cost you performance, so don't go crazy. If you just care about Renders, raise the sampling value for Render. 64 is very low for a lot of renders. Use 64 or fewer samples to make sure the composition is good then crank it up to around 500 for detailed scenes. For less detailed scenes, you can change the sampling to 100 and turn on Denoising in the View Layer context menu. Those are just my preferences--they work for me. But as a rule, render quality is proportional to the number of samples (up to a certain point, which is why I advise you shoot for 500 and not 1000)
Comment: Thanks for your response, I think it might be a texture issue because I messed around with the resolution and the samples that you referred to to no avail. I created this using JSPlacement and then imported it into Blender to be used as a texture.
Comment: What are the resolutions of those grayscale displacement textures? Are those in a library someplace or are they generated like in Substance Designer? You want to make sure that those are pretty hi-res, maybe even 4K to 8K. If you are generating them with the addon, make sure you are choosing a hi resolution output. That will solve your problem
Comment: They are 8192x8192, pretty high res. I just moved on to another project maybe I will learn what the problem is for that one in the future, Thanks.


What did Westinghouse use for power to drive Tesla's generators during the 1892 World's Fair

Question: I did manage to find technical drawings of the World's fair after considerable searching but probably I am not savvy enough to find the right items. In one of the drawings it does show what appears to be almost a geothermal structure of some type.  Other drawings clearly show the alternating current generation room , and in fact that was one of the main attractions at the fair, but I cannot make out where the drive shaft is going to make it spin. Does anyone happen to be a late 1800 historian of the "alternating current wars" will probably know off the top of his head.  Thank you
Comment: I once tried to find the answer to this question but gave up.  My guess though it that the generators were steam powered.  However, since the direct result of Westinghouse/Tesla success at the Chicago World's Fair was winning the power plant project at Niagara Falls, it could have been maybe Hydro but I have no idea where the Hydro source would have been. I am confident that the energy source was not Nuclear and Not Gas-Turbine (aka Jet engine).
Comment: The sketch I saw looked like there was a large pipe going under the ground...possibly hydraulic as you suggest but it appears to be a unique situation and that is way I was trying to find out how it was actually done. very puzzling to me....but thank you for trying./...by the way you can google on the 1982 World's fair and look at the schematics yourself...they are interesting but hard to figure out.
Answer: The  Tesla Society has a photo of a "Allis-Corliss Engine."
Wikipedia identifies this as a large steam-powered engine.
And over at vintagemachinery.org,  it is stated explicitly that

The duty of the World's Fair [Corliss] engine will, however, be of a different
  nature from that of the Corliss engine at the Centennial, which
  transmitted its power to the main jack shaft. The Allis engine is
  belted by two belts made by the Page Belting Company, of Concord, N.
  H., to two Westinghouse dynamos, each of a capacity of 10,000
  incandescent light. The speed necessary for these machines to produce
  20,000 light of sixteen candle-power is 200 revolutions. The
  illustration shows only one belt, but when completed the second belt
  will be directly over the f1rst connected to the second dynamo
  immediately beyond. The fly-wheel is thirty feet in diameter, and at
  sixty revolutions, will have a periphery speed of over 5500 feet per
  minute. The face of the wheel is seventy-six inches, not as large as
  many others the Allis Company have built, but in construction it is
  probably stronger than any of its size ever made. It has twelve arms
  and the rim is made up of the same number of segments. It weighs
  complete 135,900 pounds, the rim itself weighing 88,000 pounds.

I'd add in passing that, having lived on Chicago's South Side only a few blocks from the Midway,  I can attest there's no chance of a Hydro-powered source anywhere near there :-)
Comment: I have never lived in Chicago but been there lots of times and I never saw evidence of a nice Hydro source.  I live in Washington state and the Columbia river has a zillion (or a little less) Hydro generating stations on it and I can usually recognize those kind of plants.


hard wiring a wall unit a/c

Question: The wires coming from my wall A/C unit are not color coded. The unit was hard wired  and is being replaced. the wires that are coming from the a/c unit into the power connection box are not colored . both are stranded copper straight out of the plastic sheathing. the connection wire IN the power box ARE BOTH BLACK ....just seems weird to me. Any suggestions?
Comment: Is the unit operating on 120 V or 240 V? What is the size of the unit in BTU/h?
Comment: Can you post photos of the wires in question and of the A/C's nameplate?
Comment: I'm not sure we care about the old unit (although we could). Is the new AC unit going to be hardwired, or are you putting in an outlet? Do you have a meter or power tester? What gauge is the wire IN the box and what size is the breaker supplying power to it?
Answer: Nothing weird about that.  Being hardwired, most likely it's a 204V air conditioner.
Wire colors are to distinguish wires.
Sometimes two wires are just instances of the same thing.  If you swap the wires, everything works.

the two "Messengers" in 3-way switch circuits
2/3 phases in NYC or Euro style mains power, e.g. 208V or 388V to an A/C unit
The two "hot" poles in 240V wiring of split-phase North American power

The wires are interchangeable and it's useless to distinguish them from each other.  But very useful to distinguish them from other wires with other duties.  Therefore, no reason to waste a color.
However, 120V line cords are sometimes ribbed
That said, cheaper line cords, e.g. used on 120V lamps, often have no inner colored insulation, just an outer sheath that can be split.   They distinguish sides with one side of the cord being ribbed. The ribbed side is neutral.   However in the above cases, it makes no difference.
Why do you expect them to be red-black?
Because of the stock colors found in multi-conductor cable.  They make each one a different color because they have no idea what your use will be.

/2: Bare Black White
/3: Bare Black White Red
/4: Bare Black White Red Blue

That makes sense. Why stock several color combos of /3, when we can just tape the wires to mark them different colors?
For instance, white/gray=neutral (as well as green/bare=ground) are the only mandatory colors. Other than that, anything goes. In house wiring, the convention of Black=always-hot and red=switched-hot works reasonably well for simple boxes.  But on a complex box it can get out of hand really quick, and that's when you want to do things like tape the messengers yellow, tape the second hot and neutral brown/gray, etc.

hard wiring a wall unit a/c


Are there any playable Twilight Imperium 2 player variants?

Question: I love TI 3rd edition, but can't always get together 3 players willing to commit the amount of time it takes to play a game.
Are there any 2 player variants of this game?
Answer: There is no official 2-player variant; the game just wasn't designed for it.
But as always, the internet provides.  Various fans have proposed two-player rule sets.
The Roland Wood variant is probably the most commonly used, building on earlier suggestions by other players.
(There was another popular version in the "Shattered Expansion", but I can no longer find a live link.)
Comment: Personally I don't actually *recommend* 2-player TI; like Cosmic Encounter, it's one of those games where the correct objective of a two-player game is "find a third player".  However, some people find it to be a blast; your personal taste may vary as always.
Comment: IT's worth trying, I don't think I'll get a chance to try it for a wee while though as I'm about to go travelling, and TI is not a travel friendly game.
Answer: After trying out normal games, princess, and automata, we came to what plays fastest/simplest and balances the races altogether with flow, so no one gets too pwned. Introducing:
IDLE, NOT SO IDLE, BOT
SETUP: Bot has all his units set up on the board (no war suns or flagships), home system only having max PDS and 1 space dock -

reinforcing all BOT's systems (1/3 of map if one BOT), with heavier fleet towards home system, placement ignores all rules and is symetric.

MISCELANIOUS: After both players pick 2 strategy cards each, they each pick 1 for BOT.
MISCELANIOUS: BOT plays the top strategy card for players to have opportunity to use it's secondary effect on his "turn". Bot does not benefit from its primary ability.
MISCELANIOUS: BOT always has maximum amount of commodities and no victory points.
ACTION PHASE: Player trade - Active player can trade any amount of commodities with BOT, if spending 1 "BOT influence token" per commodity altogether;
ACTION "command bot": Choose one system with BOT's units, pay "BOT influence token"s for each of his SPACE units in that system -

activate adjacent system containing any non-BOT units, move in, attack, capture with all BOT's space and ground forces. Player can then PRODUCE any amount of BOT's casualties in his previous location.

TRADE CARD: When a player plays trade card, and chooses BOT to replenish commodities, BOT looses all his commodities to the void, and replenishes.
DIPLOMACY CARD: Alternatively a player can use it to "command bot" without "BOT influence token" price (production costs would still apply).
STATUS PHASE: Before anything, Each player gets 2 "BOT influence token"s. Loosing player gets additional token, commodity and trade good per VP difference.
AGENDA PHASE: BOT votes yes for himself, and his adjecent planet to home towards direction of speaker; His influence is a sum of both players VP
AGENDA PHASE: Player can bid any amount of tokens any amount of times for all BOT's influence towards to be of his desire, even when denied from voting; No affect on tie.
AGENDA PHASE: Players can ADD votes any amount of times, until both agree that the decision is final.
Use anything you like for "BOT influence token", would it be m&m's or bottlecaps or tokens from another game.


Excel Interop Exception (2007 installed, Office.Interop.Excel used - ver 1.6 (12)) - 0x800A03EC HResult

Question: Trying to make an excel file using this code:
app = new Excel.Application();
    app.Visible = false;
    object misValue = System.Reflection.Missing.Value;

    workbook = app.Workbooks.Add(misValue);
    worksheet = (Excel.Worksheet)workbook.Worksheets.get_Item(1);

and all get if I'm trying to do anything (worksheet.Cells[0,0] = "text")
results in {"Exception from HRESULT: 0x800A03EC"}
I've tried changing the locale:
System.Threading.Thread.CurrentThread.CurrentCulture = new System.Globalization.CultureInfo("en-US");

and I've tried also setting "Trust access to the VBA project object model" to true.
Nothing helps.
any ideas ?
Answer: Does this happen when you write to any other cell?
This is based off 2003, but I don't think you can write into cell 0,0. The start of the cell is 1,1 which is (A,1)
Comment: It doesn't matter which cell I try, (1,1) sends the same exception.


Has Apple released updates for its Airport base stations to protect against the KRACK vulnerability?

Question: Regarding the vulnerability in WPA2 known as KRACK, has Apple released firmware updates yet for the Apple-branded AirPort Base Station devices?
Comment: While the question is not exactly a dupe (iOS versus AirPort), the premise is and the answer is the same.  Possible duplicate of [Has the WiFi KRACK vulnerability been patched for iOS?](https://apple.stackexchange.com/questions/302360/has-the-wifi-krack-vulnerability-been-patched-for-ios)
Comment: @Allan Actually the technical issues for KRACK may differ by access point versus client-side, according to early reports. Even issues regarding iOS versus macOS may differ according to some reports. One of the keys to success for a Stack Exchange is narrow specificity. Makes sense to me to keep theses platforms distinct regarding KRACK, to avoid confusing intertwining threads of coverage in the Answers.
Comment: The question, as written, is "if" Apple has released a fix, not what the differences are in the security fix.  The answer provided addresses the availability of security fixes for **all**  Apple products which answers the question.  That said - there really is no distinction between AP and client - the vulnerability is the same.
Comment: @Allan No, access points at at a different risk than clients. As described on the [KrackAttacks](https://www.krackattacks.com) website that discloses the vulnerability, some access points may not need any update. Just because Apple may have clients that need patching does not mean their access points will need patching. As much as you may want a simple one-size-fits-all answer to the KRACK problem, there is not one. As for your mention of an Answer addressing "**all** Apple products", please link. I do not see AirPort Base Stations covered.
Comment: @Allan It's not really a duplicate. Routers seem only affected if they use/provide special protocols (802.11r/802.1s). The real duplicate would be: [Patching the KRACK WPA2 Vulnerability in Airport wireless routers](https://apple.stackexchange.com/questions/302354/patching-the-krack-wpa2-vulnerability-in-airport-wireless-routers). This linked question has another flaw though.
Comment: @klanomath Your proposed duplicate is not a duplicate, as that one calls for speculation about Apple's future behavior (and so was correctly closed as off-topic) while my Question here asks for factual history.
Answer: At present there are no updates for the AirPort product line.  Apple is notoriously tight lipped about security issues.

For our customers' protection, Apple doesn't disclose, discuss, or
  confirm security issues until an investigation has occurred and
  patches or releases are available. Recent releases are listed on the
  Apple security updates page.

If/when Apple releases an update that's security related, it will be listed on the Apple Security Updates page.  You can get more info about this from the question/answer "Has the WiFi KRACK vulnerability been patched for iOS?"
Additionally, you can check the AirPort Firmware Update page which will provide directions, links, and details on the updates and how to apply them.
At the time of this post, the most recent update were (dated Dec. 20, 2016)

7.7.8 for the AirPort Extreme and Time Capsule 802.11ac products
7.6.8 for the Airport Extreme, Express and Time Capsule 802.11n products

Therefore, at the time of this answer/post there have been no updates to address the KRACK vulnerability.


Cannot be blank as rule in sharepoint designer and infopath

Question: Is there a way inside workflow rules to make this rule: "if field A is not empty, then field B cannot be blank"?
Answer: You can use a rule on the Submit button that sets a trigger field. This trigger field (which can be in a secondary data source, an XML file, for example) controls the formatting of a section to hide or show. The section contains a message for the user ("Please enter Field B").
Use two rules on the submit button. The first rule will fire when Filed A has a value AND Field B is blank and set the trigger field, hence displaying the message to the user. Tick "Don't run remaining rules ...."
The second rule will fire when all fields are present and will submit the form.
This way, a form can only be submitted if both Field A and Field B are filled in.
Answer: You can just use column validation under List Settings >> Validation Settings and add a formula. Alternatively, if you need it in a workflow as specified in the question, you can create a local workflow string variable and not set it, then use it to compare to field A and field B... but at the time a workflow is running, the values would already be saved.
Answer: U could do this with infopath validations rules.
As I understand you have 2 Fields. Field A and Field B

Rightclick Field B
Choose Rules...
Click new validation
Give it a name
Click on none under condition
Fill in Field A is not blank AND Field B is blank as condition
Don't forget to fill in a screentip, otherwise it won't work properly.

This way Field B has to be filled in when field A is not blank.
Please test and let me know if it doesn't work.


Allow users to access only terms that he created

Question: Terms from user that created nodes are stored in vocabulary tags. When user creates new content i would like to allow him to only choose from list of terms he created instead of whole vocabulary.
Is that possible ?
Comment: That tags widget is autocomplete ?
Comment: It can be any widget, as there will be no more then 10-15 tags per user.
Comment: Different widgets need different code approaching, what's the point in changing widgets ?
Answer: There is a module that stores authoring information (author, published date and updated date) for the taxonomy term.
This module is views integrated. Exposes authoring information fields (author, published date and updated date) to views configuration (fields/filters/arguments/sorts/relation).
Taxonomy Term Authoring Information
After installing this module, create a view that filters terms and displays only terms created by the current user then change the field widget to use that view.
Comment: Which module you recommend for using views results in node field ?
Comment: autocomplete deluxe
Comment: https://www.drupal.org/project/autocomplete_deluxe


Could a quantum computer simulator be faster than a normal computer when running on a normal computer?

Question: I'm very new to quantum computing. I was just wondering if a quantum computer simulator could be faster than a normal computer when running on a normal computer. Could it?
Answer: I could argue your answer in either way, based on semantics.
The basic answer is as Michele said: no. The classical simulation of a quantum algorithm is itself a classical algorithm. So that cannot outperform the best possible classical algorithm.
However, you can turn that around a little bit. It is possible that the classical simulation of a quantum algorithm can outperform the best classical algorithm currently known. You get a new "quantum inspired" algorithm that performs better than anything we had before. In that sense, it can be a valuable research direction, for example.
Comment: I think that the nuance in this answer is very important to the OP!
Answer: No, it could not.
First of all, when you simulate a quantum computer, you simulate it at executing a quantum algorithm on a specific problem instance. If you manage to simulate such an execution on a classical computer, this means that the result of your quantum computation could be achieved by means of a classical algorithm, so it is not interesting.


Lysosome function

Question: Does any cell have lysosomes in it? Or maybe there are other organelles that do the same function. I read about it a lot and I can't find a good answer.
Comment: Yes, lysosomes (note spelling) exist. see https://en.wikipedia.org/wiki/Lysosome
Comment: The very first sentence of the Wikipedia article on lysosomes: *"A lysosome (derived from the Greek words lysis, meaning "to loosen", and soma, "body") is a membrane-bound cell organelle found in most animal cells (they are absent in red blood cells)."* So yes, any cell except RBCs would have lysosomes, as they are essential to the function of a metabolizing cell (which RBCs are not).
Answer: The function of a lysosome is to essentially digest and break down molecules (often compared to the stomach of the cell).
For example, a cell with high proportions of lysosomes would be a macrophage, as its function is to neutralize pathogens. After the pathogen is engulfed by the macrophage, the vesicle formed, called a phagosome, fuses with a lysosome, and the lysosome's digestive enzymes work on breaking down the pathogen into harmless bits and pieces.
In most cells, however, lysosomes also function to recycle the cell's own components, called autophagy. Damaged organelles are broken down by the lysosome and recycled.
So, yes, there are many cells that do have lysosomes.
The importance of the lysosome is shown when there is a malfunction in the lysosome. These diseases, called lysosomal storage diseases, occur when the lysosome does not function properly and the cell eventually is impaired by the buildup of a molecule that should have been broken down by the lysosome (e.g. Tay-Sachs disease).
References
The AP Biology textbook

Campbell Biology 7th Edition, Chapter 6 - "Lysosomes: Digestive Compartments", although this is pretty much the same in any edition of this textbook
Campbell Biology in Focus, Chapter 4 - "Lysosomes: Digestive Compartments"
Comment: Welcome, and thank you for your answer. You may want to consider an edit to provide some references to the information in your answer. It can help to provide the person who asked the question or others reading your answer who would like to research further a starting point.

Lysosome function


Is there any application of control engineering to the study of algorithms stability or computer science theory?

Question: I am an undergraduate student in Electrical and Computer engineering. In our 5th semester we have a obligatory "Introduction to control systems course". I was wondering if these bunch of math theories is applicable to other directions of my school rather than the obvious (in the next semester we choose majors and there is one called signals and automation which basically involves every "advanced" control theory module, but I want to know if it is useful other than that).
I like the ideas of the course, but I am not really into the hardcore applications of it. I think I want to follow a more theoretical path which involves math applicable to computer science. So if I do not go for the "automation and signals major" but into computer science, hardware and math major, is there any chance I find it useful? For example because it involves the stability, I have seen some advanced graduate seminars where people talk about the convergence of algorithms ...maybe some control theory theorems are useful there?
Comment: Most of these have been studied and worked on because they are useful. If you want things that are not useful (yet) then consider Pure Mathematics.
Answer: Basic control theory is very useful in a wide range of situations.
Really advanced control theory is specialized and useful to theory and complex design of certain actual control systems.
I had math in grad school,  and EE undergrad, worked as a Systems Engineer.
I had control theory in both undergrad and grad school.
I do not see any use for control theory in convergence of algorithms or in a setting of math theorems.
That said you may find an application and become a star in a new math field.
Answer: Possibly this is a slightly old question...
An "introduction to control theory" course sounds unlikely to cover this stuff, but one of the control courses in the Masters' year I'm in right now includes topics that might be of interest to you:

Convex optimisation
Semi-definite programming to guarantee stability
Distributed algorithms (most importantly proximal algorithms)
Scenario approach to make probabilistic guarantees

We don't ever study the implementation of any solvers, but this whole course is basically on convergence and stability and draws on quite a lot of areas. Helly's theorem was a bit of highlight!
This book talks about the interpretation of the ADMM algorithm as integral control of a dynamical system in chapter 4: https://web.stanford.edu/~boyd/papers/pdf/prox_algs.pdf
The nyquist criterion will likely be included in the introductory course which does draw on results like Cauchy's argument principle, which is some fairly abstract maths too, but you'll probably need to do your own reading for the details. Sutdy of dynamical systems relies a lot on results from topology: the "hairy ball theorem" makes me laugh every time. Most things are applicable to other things in engineering though it seems! Control theory seems like a great place to start for computer science to me, but fred probably does know better, I am a lowly undergraduate too!


ssh session (from ubuntu to centos) prompt delayed after a while

Question: I do a lot of work on a centos (7.2) machine into which i ssh from an ubuntu (14.04) machine.
Everything works fine, almost. But after a while on the remote, usually a couple of minutes, I have to wait for the next prompt (e.g., after just pressing enter) for a couple of seconds. This is really annoying.
Logging out and back in fixes this temporarily, but it happens again after a couple of minutes. I'm not talking about the password prompt upon login or so, that part's fine. It's the regular prompt after being logged in for a while that becomes slow.
Any idea where to look for a solution?
edit:
it also happens logging in from other boxes, but seems to be specific to my user account.
ssh -v shows no additional output when the shell hangs (so after login there's nothing new until logout). here's the last couple of lines from ssh -v:
debug1: Authentication succeeded (password).
Authenticated to X.X.X.X ([X.X.X.X]:22).
debug1: channel 0: new [client-session]
debug1: Requesting firstname.lastname@example.com
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: client_input_channel_req: channel 0 rtype email@example.com reply 0
debug1: channel 0: free: client-session, nchannels 1
debug1: fd 2 clearing O_NONBLOCK
Connection to X.X.X.X closed.
Transferred: sent 11888, received 26136 bytes, in 329.2 seconds
Bytes per second: sent 36.1, received 79.4
debug1: Exit status 0

htop shows "-bash" to use 100%cpu while i'm waiting for the new prompt.
Comment: it might be useful to out put ssh -v the next time you connect
Answer: It's hard to tell what may cause this but in my opinion it looks like a normal connection delay, this can be tweaked by modifying the way you connect to centos.

Edit your /etc/ssh/sshd_config : Compression yes to use compression, and service ssh restart on server side to disable dns lookup.
Force IPV4 or IPV6 ssh -4 user@host or ssh -6 user@host

(Also changing the authentication method can help)
Comment: thanks for the pointers. i don't think it's a server-side issue, though. it only happens when i login from this particular machine, not from somewhere else. (i'll edit the question accordingly)
Comment: by now it also happens form other machines, but apparently only for my user account. compression does not change anything, neither does ipv4. also, i'm pretty sure this is not normal.


Quadcopter Props? Wood vs Plastic vs Carbon Fiber

Question: All the pro FPV builds and the more expensive quads don't seem to be using plastic props. Any reason for this?
Comment: I have since switched all my multirotor aircraft back over to good quality plastic props and I definitely get better flight times with them.
Answer: Plastic and wood props wear and tear over the time while carbon fiber props have very less tendency to wear and tear hence are more durable ad last long. I have seen plastic props breaking in flight as it was used for long duration. So if you are making expensive setup the it is always better to use carbon fiber props as their strength is far better than plastic or wooden props.
Also carbon fiber props are more rigid than plastic props. Hence you can have better efficiency out of carbon fiber props which will result in less power consumption resulting in more flight time which is a very crucial factor while designing and build qauds or any multirotor for FPV.
Comment: Sorry but can you please point me to the test data proving this remark? I have been monitoring the flight times and efficient with both good quality plastic props and CF props and I find I get less flight time from CF props.

This prompted me to look further into where this theory came from the CF props are better. Was it simply to have stronger more damage resistant props? Was it just from an assumption CF is so good in many other areas it should automatically be a given it would be the best material for multirotor aircraft props as well and just becasue its rigid?
Comment: So far I have drawn a blank to find any significant test data to support this claim other than people make a comment without foundation on forums like this one.

I have never seen any significant test data to prove they are more efficient or not either way. But just going on my own observations and experience with using the exact same aircraft, I actually get less flight times using CF props. I have also now seen others starting to find the same.
Answer: Maybe this would help. The flex is just a twist. The twist causes a lower angle of attack, progressively worsening the further out the blade you travel and as the revolutions are increased (where and when you're getting your most lift). It's the point hitting the air hardest.
Less angle of attack means less bite, resulting in less lift and less response (this is also the reason variable pitch works). The denser the air, the less angle of attack needed and vice versa. Also the twisted blade takes less power to rotate. Flatter blades give less lift and less response but will increase the flight times due to less drag on the twisted prop. A prop is just a wing that rotates - drag and lift.
The tests were done long before quads through. Sikorsky might have been the first to do wind tunnel and lift capabilities tests I think if you would like another place to search. I hope this helps.


Security and backup if documents in library are not synced

Question: Is there any reason why I would not want to store all of my business documents and not sync them? Should I have any concerns about security or losing data? I don't need to have my documents synced because I don't need them if I'm not online, but I don't know if there's a risk of losing the information.
Comment: where you want to store the documents, do you want locally or store them in document library?
Comment: I just want to store them in the document library.
Answer: The documents are stored locally, so anyone with access to your computer would have access to those documents like they were any other locally stored document.
There is a minute amount of network traffic as the sync has to check if it's up to date regularly.
The only way to really risk losing the information (and this involves willful, perhaps laboriously foolish effort) is if you delete the local copies or vandalize them in such a way that the data inside of them is replaced, but if you have versioning turned on for the library or access to the SP recycle bin, that's a correctable issue.
Answer: If you just store the document in the library and dont want to sync them to local directories, their is no issue at all with your backup or security.

backup depend upon the your Farm backup procedure.
their is no risk of losing the information as far you have your backup process in place.
I don't see the any security concern as long you have proper permission policy.


How do I remove a bottom bracket?

Question: I have managed to remove the threaded locking mechanism of this bottom bracket. However, I can't get the bracket out. I have tried to just bang it out, but it doesn't move. I don't know what else to do. ideas? help.
Comment: See the threads? Untwist it.
Answer: Look at the thread on the exposed cup. That tells you which way you need to turn the cup to get it out (there are multiple standards here, and one of the key differences is that some use left hand threads instead of the usual right hand). It looks to me as though the top of that cop should rotate to the right to remove it, in which case it is a left hand thread.
You should be able to fit a spanner onto the raised part on the cup nearest the camera in that photo. Preferably a large spanner with nice sharp edges on the jaws, since the flats are not very deep.
The other side possibly has a couple of holes rather than more flats like this side. In which case you can use a pin spanner or a hammer and chisel to tap it out. Or, as Sheldon suggests, just put a big bolt through and use that to turn the cup.
Comment: Yeah, place you're fingernail in the groove of the cup and "unscrew" your hand.  Whichever way "unscrews" vs going tighter is the direction you need to turn the cup.  That *appears* to me to be a "normal" right-hand thread that will unscrew in a counter-clockwise direction, but it's hard to tell for sure in a picture.  Definitely use a wrench with good square jaws, since if you muck up the shoulders of the "nut" it's a lot harder to get it loose.  A well-equipped bike shop *might* have a flat wrench to fit.

How do I remove a bottom bracket?


Question about the Lorenz gauge in classical electrodynamics

Question: The Lorenz gauge is the gauge such that $$\nabla \cdot \mathbf{A} = -\mu_0\epsilon_0\frac{\partial\Phi}{\partial t}.$$ This condition dictates what $\lambda$ is in $$\mathbf{A}' = \mathbf{A} + \nabla \lambda.$$ However, $\Phi$ can be adjusted via the equation $$\Phi' = \Phi - \frac{\partial \lambda}{\partial t}.$$ This seems circular to me because $\lambda$ is found using $\Phi$ which itself depends on $\lambda$. I don't know if $\lambda$ can be solved for in this case. I'd appreciate it if someone would dispel my confusion.
Comment: Related question by OP: https://physics.stackexchange.com/q/463075/2451
Answer: The Maxwell equations are independent of the gauge function $\lambda$. Our gauge condition is given by
$$\nabla \cdot \mathbf{A} = -\frac{1}{c^2}\frac{\partial\Phi}{\partial t}$$
However, note that there is still a subspace of nontrivial gauge transformations that can be made when we take  $\mathbf{A} \to \mathbf{A}'$ and $\varphi \to \varphi'$. Note that this still doesn't completely fix the gauge. Since we can can still make the transformations
$$ \mathbf{A}' = \mathbf{A} + \nabla \lambda$$
$$\Phi' = \Phi - \frac{\partial \lambda}{\partial t}.$$
for some special kinds (but not uniquely defined) of $\lambda$s  and still have a valid solution to Maxwell's equations. That is, if we can fix $\lambda$ then we fix the gauge.
But what do I mean by special? To figure that out we apply the gauge transformation to the Lorentz condition
\begin{align*}
 \nabla \cdot \mathbf{A} = -\frac{1}{c^2}\frac{\partial\Phi}{\partial t} \to &\nabla \cdot \mathbf{A'} = -\frac{1}{c^2}\frac{\partial\Phi'}{\partial t}\\
&= \nabla\cdot \mathbf{A} + \nabla^2\lambda= - \frac{1}{c^2}\frac{\partial\Phi}{\partial t} + \frac{1}{c^2} \frac{\partial^2 \lambda}{\partial t^2}
\end{align*}
So we see that we still have the freedom to choose any function $\lambda$ that satisfies
$$
\nabla^2\lambda = \frac{1}{c^2} \frac{\partial^2 \lambda}{\partial t^2} \tag{c}.
$$
Note that any such $\lambda$ satisfying (c) is still a valid solution to Maxwell's equations (it should be clear that there is not just one $\lambda$ that does this). That is, there is still a redundancy in the theory. To completely fix the gauge you need to add boundary conditions to equation (c).


How to solve this question by the two-phase simplex algorithm?

Question:
A clever, but ethically corrupted, mathematics student used to sell assignment solutions to her lazy fellow students. The student, however, learned that she can make much more money by charging the students fees for doing the assignments with them.
This semester the students need to complete three assignments:

One in Statistical Models
One in Introduction to Partial Differential Equations
One very difficult one in Optimization and Financial Mathematics

It takes 2 hours to explain the assignment to one student for Statistical Models, 1/2 hours for Introduction to Partial Differential Equations and 5 hours for Optimization and Financial Mathematics. The student can charge \$5, \$0.50, and \$10 per hour for Statistical Models, Introduction to Partial Differential Equations and Optimization and Financial Mathematics, respectively.
In Statistical Models there are not more than 10 students wanting her service. In Introduction to Partial Differential Equations there are more than 50 students wanting her service and she has obligations to take at least 50. In Optimization and Financial Mathematics,the course with the most diligent students, there are not more than 2 students wanting her service.
How many students from each course will the clever student offer her service to maximize her profit, if she does not want to spend more than 50 hours on the assignments?
(a) Formulate this as a linear programming problem
(b) Solve the problem using the two-phase simplex algorithm.

I do not know how much should I charge, because it is my first time to ask a question here. I am so sorry about this, but I am really need to know the solution.
Comment: How much is she charging for the solution to this problem?
Comment: I do not know how much should I charge, because it is my first time to ask a question here. I am so sorry about this, but I am really need to know the solution.
Comment: I am studying Optimization and Financial Mathematics by myself, I found this question is challenge for me.
Answer: A good way to start a problem such as this is to identify the variables, then the objective and constraints.  What quantities does the question ask for?  What objective is being maximized or minimized?  Then see how you can express the objective and constraints in terms of these variables, and perhaps others.
Comment: In fact, I know how to solve part a, but part b is a little hard for me


Why does propeller slip (efficiency) change during the flight (fixed-pitch)?

Question: I was wondering how the efficiency of a fixed-pitch propeller changes during different stages of flight and why it does so. I suppose when we are talking about propeller efficiency we are actually talking about propeller slip. So my follow up question is what causes propeller slip to
change, what conditions make a propeller lose efficiency. I am aware that it has to do with Pitch, but I can't figure out why efficiency changes throughout the flight. THANKS
Comment: Are you looking for a detailed engineering explanation, or just a big - picture understanding?
Comment: Big Pitcure understanding
Answer: The reason that efficiency is reduced during phases of flight that are flown at high airspeeds is because the angle of attack between the propeller and relative wind is reduced. If an aircraft is stationary on the ground, its propeller is taking a larger "bite" of air because there is no relative wind. When there is more air moving past the prop, it takes a smaller "bite" of air, therefore producing less thrust and being less efficient. The advantage of a constant speed prop is that you can change the pitch of the prop depending on your airspeed, so it maintains a constant angle of attack, and is more efficient in every phase of flight. I'm not totally sure that's what you are asking, but that's what I got :)
Answer: Pitch is essentially how much the propeller would move forward in a complete rotation if it was by itself. You can now rotate the propeller at any rate (read RPM) you can achieve. So if you pitch is 10 cm, and your RPM is 1000, then in 1 minute it would 10000 cm in 1 minute ,ie 100 metres, giving a velocity of 1.66 m/s. If the propeller could move at that speed there would be zero slip, but it in reality it is attached to a shaft and has certain "loading". While moving through air, it experiences drag as well as generates thrust, and since it has a body attached to it, that also experiences drag and cumulatively a significant drag. So the actual distance travelled is may be 60 m, giving a speed of 1 m/s. (40m is the slip here). The drag is a closely related to velocity (for entire aircraft) and rpm of propeller (for the prop). Now the propeller pitch being fixed, and the velocity changing through out the flight, the velocity would be changing in the entire flight regime and consequently drag and therefore slip.
Hence you can imagine, there would be velocity for which the slip is the least. This would be the design speed, where efficiency is maximum (the peak). To either side of this speed efficiency would be lower.


Failed to attach the USB device Broadcom Corp. Bluetooth USB Host Controller

Question: I am unable to pass through the host Bluetooth USB through my Kali. I am using VirtualBox on Mac Mojave. When I select it through 'Device', I get the above error

[Failed to attach the USB device Broadcom Corp. Bluetooth USB Host Controller [0168] to the virtual machine].
Could not find USB with uuid {xxxxx-xxxx-xxxx-xxxx-xxxxx}
Callee RC: NE_ERROR_FAILURE (0x80004005)

I have tried almost everything posted in StackOverflow under similar questions/issues, but could not resolve the issue.
Also, I am noticing a strange behavior, when I am passing through my Logitech USB Optical Mouse, it stops responding, and when I uncheck it again under 'Device', it starts to respond, meaning I am able to use the mouse.
Little bit more context- I noticed this issue, after I upgraded to Mac Mojave from Sierra, if this helps. Earlier it was working without any issue.
Thanks
Answer: Try the following:
1 - Open the Finder;
2 - Go to options menu: 'Go ->  Go to Folder...';
3 - Write the '/Library/Preferences';
4 - Remove the file called 'com.apple.Bluetooth.plist';
5 - Restart the macOS.
That way it is working for me.


Implementing a large scale (planet-like) level in XNA 4.0

Question: What is the best way to implement continuous level throughout the game, using XNA? Imagine that I have a level with the size of a whole city (like in MMORPGs) however, the game will currently be mainly single-player. I'd like to be able to split this huge planet into parts which load asynchronously as I enter them. However, I also have other questions, such as, what happens with the part that I've come from. Its state should be stored on the disk, right? Then, what if I need to make some changes to that part, when the player comes back. Obviously, other characters should have done something rather than standing still. What's the best way to grab the state as I stored it, and modify it a bit, based on certain parameters, before I load it and let my player return.
Comment: I've heard there's something called 'chunking', which is basically this.  I don't know how to implement it, though... Otherwise, the question is potentially a little broad, and subject to design constraints.
Comment: This is a hard open ended question. Try finding some info on how other large games/MMOs did it. This problem is not specific to XNA and the ideas learnt this way should be easily transferable to XNA :). You already seem to have the basic idea right!
Answer: In world of warcraft, the adjacent "tiles", which are pretty large, are loaded as a low poly model
This is done so you (as a player) do not see the "end of the world".
Then, once you know where the player is going, you have a Loading engine start to load the assets of the "tile" the player is going, asynchronously
Unload the once from the "tile" the player is moving from,
This "in short" is how Blizzard does it
Hope you can make something of it.


Is it possible reduce swap memory size?

Question: The matter is that my computer has 3Gb of memory ram. Therefore i think that i don't need too much swap memory size, and i really need free space in the hard disk.
sorry by my English
Comment: possible duplicate of [How to resize partitions?](http://askubuntu.com/questions/126153/how-to-resize-partitions)
Answer: Yes.  You can change the size of the swap partition, by using GParted.  You can install it from the Ubuntu Software Center.
Remember that gparted won't work on a mounted partition. When you are working on the swap partition, you have to unmount it first with swapoff.  When you are done, to active the new swap space you do it with swapon.
NOTE: You might want to consider doing this from a live/bootable CD or USB, to be safe.  Also keep in mind that anytime you deal with partitions, there is risk involved in doing so.
NOTE: When dealing with partitions, always make sure that a backup is available in case something goes wrong.  You may consider Clonezilla
Comment: **It's inadvisable to change the partition table on the system drive from which the OS is running.** When the size of a partition changes, that is done by editing the partition table. There are many good applications of GParted on installed Ubuntu systems, but this mistake is why it's not installed by default. To resize partitions, you should boot from an OS not installed on the physical drive where you're doing it. (So you can use an Ubuntu live CD/DVD/USB for this.) I'd recommend editing your answer to account for this. (If you prefer, though, I could post a separate answer.)
Comment: I changed the partition using this method, but this changed the UUID of the swap partition, and thus the file /etc/fstab was not correct any more and had to be modified.
Answer: I think that your best option is to lower the "swappiness" value, dealing with the partition table of your HDD can be tricky and dangerous.
run this command
gksudo gedit /etc/sysctl.conf

add this line
vm.swappiness=0

restart the computer, the kernel will not use the swap, the swap will be mounted but unused.
you can set this between 0 and 100, the meaning of this option is about the percentage of use of the swap space, 0 = never use the swap.
Comment: This doesn't "*free space in the hard disk*" (which the question asks for). To do that the swap partition must be shrunk, removed, or reformatted with its own filesystem where data may be stored. Shrinking it is probably the best of those three options.

Is it possible reduce swap memory size?


Bluemix create container group linking to another container

Question: We have a Java application running with MongoDB, each one in a different Bluemix container. Both are SINGLE Bluemix containers.
We want to serve the Java app using one of our subdomains: https://subdomain.mydomain.com, which is already pointing to Bluemix. How can we do it?
OUR APPROACH
Because the Java container needs to link to the Mongo container, we created both containers programmatically (we didn't find in the UI a way to link a container to another container) like this:
sudo bluemix ic run --name mongo-container -p 27017 -m 128 registry.eu-gb.bluemix.net/mycompany/mongo

sudo bluemix ic run --name java-container --link mongo-container:mongo -p 8080 -m 128 registry.eu-gb.bluemix.net/mycompany/java

This works well, but the Java app is only accessible through an ugly Blumix IP, not through https://subdomain.mydomain.com as we want.
What about using a Bluemix container GROUP (SCALABLE container in the UI)?
Again, we don't know how to link containers from the UI, so it should be something like
sudo bluemix ic group-create --auto --name java-scalable -p 8080 -m 128 --hostname subdomain --domain mydomain.com registry.eu-gb.bluemix.net/mycompany/java

BUT according to the documentation we cannot link a container group to a container, since there is no --link parameter.
Back to the original question. How can we serve the Java app using https://subdomain.mydomain.com?
Answer: So following the second approach, you may be able to create a MongoDB service before creating the Bluemix Container Group. During Bluemix Container Group creation you have the ability to bind an existing service under the Advanced Options section in the UI:

You can also choose to use a custom Domain during Container creation, if you have previously created one:

In this case you would have a container with a custom Domain that also includes an existing service.
You can find more information about binding an existing service in the Container Integration Documentation. You can learn more about creating a custom domain in Bluemix in the Updating Apps Documentation.
Answer: The link option basically creates environment variables in one container to reach the other one.
You can do the same with your scalable container in Bluemix.
Here are the steps I did:
1) Create your MongoDB container:
bx ic run --name ads-mongo -p 27017 -m 128 registry.ng.bluemix.net/namespace/mongo

2) Inspect the MongoDB container to find the private IP address:
bx ic inspect ads-mongo

The private IP will be at end of the output, I am adding just part of the output below for brevity:
  "Ports": {
                "27017/tcp": [
                    {
                        "HostIp": "172.31.0.235",
                        "HostPort": "27017"
                    }
                ]
            },
            "PublicIpAddress": ""

3) Run your scalable container and include one or more environment variables with your MongoDB credentials. Make sure you change your Java code to get the credentials from the environment variables you are passing to the scalable container:
bx ic group-create --name ads-node -e "MONGO_URI=mongodb://172.31.0.235:27017" -p 3000 -m 128 --hostname ads-node --domain mybluemix.net registry.ng.bluemix.net/namespace/ads-nodebx

In my test I used a Node.js application and it reads the MONGO_URI environment variable for the MongoDB credentials.
You can assign a public IP for your MongoDB container as well if desired, the end result should be similar. The only difference I see is that you can then access your db using mongo command line or other tools to connect to the database.


Mean versus imputation for missing data in the case of an ordinal scale

Question: Is mean or mode better for replacing missing data for an ordinal scale? I'm thinking mode is better because the respondent has to choose between integer values (1, 2 and so on) bu I am wondering is mode imputation doesn't create bias by favoring the value that appears most often. Thank you!
Comment: How can _ordinal_ scale (which is categorical, not just discretized) can ever have a specific mean?
Answer: Answer: Neither.
The best choice is multiple imputation (MI), which is an iterative process of probabilistically estimating missing values based on observed information from across your data set. The great thing about MI is that not only does one get (A) decent estimates of the missing data values, one also gets (B) estimates of the increased uncertainty in one's analysis due to data missingness.
References
Donders, A. R. T., Heijden, G. J. M. G. van der, Stijnen, T., & Moons, K. G. M. (2006). Review: A gentle introduction to imputation of missing values. Journal of Clinical Epidemiology, 59(10), 1087–1091.
Rubin, D. B. (1976). Inference and missing data. Biometrika, 63(3):581–592.
Rubin, D. B. (1996). Multiple imputation after 18+ years. Journal of the American Statistical Association, 91(434):473–489.
Schafer, J. L. (1999). Multiple imputation: a primer. Statistical Methods in Medical Research, 8:3–15.
Comment: You cannot just blindly apply multiple imputation to your data. We must have a better understanding of the data before applying this method. There are assumptions that must be made (and preferably verified) before using multiple imputation. for example, the data must be missing at random (MAR).  Furthermore, the model used to generate the imputed values must be correct, among others. There are multivariate tests for MAR that can be applied for this. A careful look at the data & understanding of the data is required before applying any type of imputation, lets your risk biasing your estimates.
Comment: @StatsStudent All of which entail precise the same limitations you are raising in your original comment, and all of which run afoul per Rubin's argument that (absent actual knowledge of the determinants of missingness in NCAR data) *all* single imputation regimes (a) fail to estimate variability/uncertainty due to missingness, and (b) produce less statistical validity that multiple imputation regimes.
Comment: @StatsStudent My answer was in the context of the OP. Can your provide an example where simple mean or mode replacement in ordinal data performs better than multiple imputation?
Comment: Well, @Alexis, since you never defined, "best," I'd argue that mean or mode replacement is the best choice in terms of simplistic imputation strategies.  But more to my point, mean and mode replacement aren't the only remaining choices.  Other viable solutions include, hot deck imputation procedures, parametric fractional imputation, cold-deck imputation, stochastic regression imputation, etc.
Answer: The best choice is to use an R package like mi (mice, or amelia should also work). It will scan your data and propose the appropriate format for each variable (which you can also manually change if needed)
In the case of categorical (ordered or not) variables in the MI package - a series of chained, ordinal regressions are run with the variables targeted for imputation as the DVs. This is done until some convergence criteria are met (which can be adjusted in the package
You could think of it as a markov chain of regressions using all included data to predict missing data in all of the variables you included in the analysis
Comment: In light of @ttnphns's comment, it would be nice if you could briefly explain how MI works in the case of categorical variables.
Comment: @chl, you should quantify the manner in which it is "best." How are you defining "best" here?
Comment: @StatsStudent I am not sure to follow: Where did I talk about something "best"?
Comment: Sorry, chl, I meant to have directed that comment toward @nolanconaway who indicated "the best choice is to use an R package like mi."


how to create all dynamic ubercart product images for CDN module to sync

Question: I have enable CDN module to handle image/css and js requests from a static server.
As drupal creates product images for different styles dynamically there are many products whose images are not present at the time to CDN and my domains syncing of images.
How can i handle the request to new product images in this scenario >
Right now the missing images are coming blank
Answer: This worked with the following setting in default/settings.php file
$conf['image_allow_insecure_derivatives'] = TRUE;


Is it valid to do confirmatory factor analysis on correlation coefficients derived from a meta-analysis?

Question: I have just read a paper in which the authors performed a meta-analysis to extract correlation coefficients (specifically between five personality variables and emotional intelligence). They then used confirmatory factor analysis to test if all the variables involved formed a higher-order factor (specifically a general factor of personality correlated with EI). The total number of samples was 128; these were also broken down into subsamples, as there are various measures of EI (k ranged from 18 to 45). I was wondering if it is valid to use CFA in this way, particularly with such small subsamples? Specifically, one of the analyses they reported in detail was k = 22 and there were six variables with fifteen inter-correlations in the analysis. Would their results be meaningful, or are they over-interpreting the data?
Answer: In a meta-analysis, $k$ typically refers to the number of correlation coefficients that were meta-analyzed. An aggregated coefficient could therefore be based on thousands of individual observations. So, no, without knowing more about this particular paper, there is nothing here to indicate problems with this.
By the way, what the authors are doing falls under the general label of "meta-analytic structural equation modeling" (MASEM).
Comment: And just to add that if the OP wants more on this he could do worse than visit Mike Cheung's pages [ere](https://courses.nus.edu.sg/course/psycwlm/internet/) where he will find links to some reading.


I want to invest in Asian technological firms. In which ETFs or other product should I invest?

Question: I am looking for an Asian Nasdaq index or something like that. Maybe investing directly in the US market where some of the largest Chinese companies IPO have taken place makes sense. Any insights?
Comment: Your question as written will be closed because it asks for us to make your investment decisions ("In which ETFs should I invest?")  But you can salvage it by asking how to find ETFs that meet both criteria: region (Asia) and sector (technology)
Answer: There are a number of web sites that offer ETF information.  One of them that I have used is  ETFDB.  It has a free screener.  For example, it shows that there are 121 Asian ETFs for Developed Asia.
There are other screening choices as well. You can select an ETF and click on is holdings.  That will provide the major holdings.  It requires a subscription if  you want to  export the entire list of holdings,


Fastest way to get rich in Grand Theft Auto 4 - Episodes of Liberty city: The ballad of Gay Tony Singleplayer

Question: What is the fastest way to get rich in GTA IV: TBOG SingleplayerT? What I do now, is betting on Cage matches. Is there perhaps another way?
Answer: Betting on and spectating cage matches is indeed the fastest way to make money.  Similar to the OTB horse race trick in San Andreas, the best strategy is to save at the nearby safehouse before you place your bet, and then load the game if you lose.
Since you essentially can't lose, betting all of your money is the way to go.  If you've got a small nest egg of a few thousand, you can very quickly grow it into a few million with this method.
Comment: IIRC, you triple your bet when you win, so output_funds = (input_funds)*3^(number_of_rounds_of_betting) - that's pretty darn fast growth!
Answer: Drug wars are also good. I have 13,00 bucks and got RPG, auto sniper rifle, ak47, p90, tons of grenades, auto shotgun,   And desert eagle pistol
Answer: I do drug wars and a tactic for this is when are near drugs kill ALL people because then more ur shot when u have em the more money goes from mission shoots vital to pick up after the gun shots are over
Comment: You really have to rephrase that, it is very hard to understand.


Example of the quotient group of a multiplicative group?

Question: Could someone offer me an example of the quotient group of a specific (not arbitrary) group under operation multiplication? I am trying to better conceptualize quotient groups via examples, and I have done so with integers modulo n under addition, but I am struggling to find a specific example of a quotient group of a specific group under multiplication.
Comment: It is not clear to me what you mean by multiplication. A group has exactly one type of operation, which is sometimes written as $+$ (if the group is abelian) and sometimes written as $\cdot$. Do you mean multiplication in the sense of multiplicative subgroup of a field/ring or more specifically of the real numbers/complex numbers/matrices?
Comment: I apologize, I mean under operation · , My professor of my group theory course uses the term "multiplication" often for ·
Comment: No need to apologize :) Multiplication is indeed commonly used to refer to the group operation, the confusion arises when you start to refer to specific examples. For example one could say that the addition of integers is the group multiplication, which sounds odd and is confusing. So my question still is: Do you want **any** example of a factor group other than $\mathbb Z/n \mathbb Z$ or do you explicitly want groups, whose operation is given by multiplication in some ring?
Answer: Consider $S=\{z\in\mathbb{C}:|z|=1\}$ which is the unit circle in plane. Elements of $S$ are complex numbers of the form $z=e^{it}$ for some $t\in[0,2\pi)$ and for $z_1=e^{it_1},z_2=e^{it_2}\in S$,
$$z_1z_2=e^{it_1}e^{it_2}=\begin{cases} e^{i(t_1+t_2)}&\text{if }t_1+t_2\leq2\pi\\
e^{i(t_1+t_2-2\pi)}&\text{if }t_1+t_2>2\pi \end{cases}$$
ans $S$ is an abelian group with this multiplication. Now try the quotients like $S/H$ where $$H=(e^{2\pi i/n})$$ is the cyclic subgroup generated by $e^{2\pi i/n}$. Note that $|H|<\infty\iff n$ is an integer.
Answer: Here are some examples of factor groups:

obviously $\mathbb Z / n \mathbb Z$
$G=(\mathbb R,+), H=2\pi\mathbb Z$ then $G/H \cong (S, \cdot)$, where $S= \{z \in \mathbb C \mid \Vert z \Vert =1\}$ via the group homomorphism $t \mapsto e^{it}$.
$G = (GL_n(R),*), H = (SL_n(R),*)$, where $SL_n(R) = \{\text{matrices with det }1\}$, yields $G/H \cong R^{*}$ via the group homomorphism $M \mapsto \det M$
Factor spaces of vector spaces i.e. $V/W$ (just forget scalar multiplication, you have underlying abelian groups)


TLS 1.3 client communicating with TLS 1.2 server

Question: I am testing TLS 1.3 for my application. Can a TLS 1.3 enabled client communicate with a TLS 1.2 enabled server? If yes, what should be the record layer for the initial client hello? Currently, I am seeing TLSv1 record layer for some and Tlsv2 record layer for some interfaces. I see Tlsv1.3 record layer when client and server are both enabled for Tlsv1.3.
Answer:
...  if TLS 1.3 enabled client can communicate with TLS 1.2 enabled server.

Usually this is the case. But the client might also have disabled TLS 1.2 support, in which client and server don't share a protocol version both support.

If yes, what should be the record layer for the initial client hello?

From the TLS 1.3 standard RFC 8446:

<code>  struct {
      ContentType type;
      ProtocolVersion legacy_record_version;
      uint16 length;
      opaque opaque fragment[TLSPlaintext.length];
  } TLSPlaintext;
</code>
legacy_record_version:
MUST be set to 0x0303 for all records
generated by a TLS 1.3 implementation other than an initial
ClientHello (i.e., one not generated after a HelloRetryRequest),
where it MAY also be 0x0301 for compatibility purposes. ...

Thus it will be TLS 1.2 (0x0303) but might be TLS 1.0 (0x0301) in ClientHello.

I see Tlsv1.3 record layer when client and server are both enabled for Tls1.3.

This is not the record layer information but what Wireshark shows as interpretation since it has determined that TLS 1.3 is spoken.
Comment: Thank you! Can I assume the client is trying to communicate using TLS 1.3 as I see the extension supported_versions with TLS 1.3 which is TLS 1.3 specific even though client hello shows as TLS 1.2 or TLS 1.1 for protocol in wireshark?
Comment: @user282171: `supported_extensions` is exactly where TLS 1.3 shows what protocol versions are supported, i.e. no longer in record layer.
Comment: @user282171: yes the 'protocol' column _in Wireshark message-list pane_ for ClientHello is probably the record layer version but is not related to the actual protocol version; for everything _after_ a seen ClientHello it _is_ the protocol version but is not the record layer version.


Conservation of angular momentum with no net torque

Question: Suppose there is a point mass with mass m1 orbiting around the z axis at a radial distance r1 with tangential velocity v1. So I would say the angular momentum of this point mass is m1•v1•r1. Then I exert forces on m1 in the radial directions such that m1 is now orbiting the z axis and 2r1. I would say now the angular momentum is m1•v1•2r1. Clearly the angular momentum has increased by a factor of 2. However there was no torque applied to this system about the z axis  as the forces that moved m1 to 2r1 were completely in the radial direction. Isn't this a violation of the conservation of angular momentum?
Answer: $v$ will not be constant in this example.  The new angular momentum would be $m_1\cdot v_2\cdot 2r_1$, where $v_2\neq v_1$.
If you insist on keeping $v$ constant, then you would actually have to apply a torque to stop the particle from changing its speed to conserve angular momentum, so there is no contradiction here.
If you don't believe that $v$ will change, the classic example to visualise is a figure skater spinning around.  When they have their arms tucked in, they spin at speed $v_1$.  As they stretch their arms out, they slow down to conserve angular momentum (try it yourself on a spinning chair, but be careful of your surroundings!)
Comment: There is no force in the tangential direction at anytime so how is it possible that the object decelerates in the tangential direction?
Comment: If you're working in the frame of reference of the particle, there actually *is* a pseudo Coriolis force which makes its tangential speed change.  This comes from coordinate transforming from a stationary frame to a non-inertial rotating frame.  Physics can be a little weird in accelerating frames!


Grounding a dryer

Question: I have 4 prong dryer outlet that the previous owner wired up with 10 ga 3 conductor wire.  He wired it "correctly" with a red, what, and black conductors.  The ground terminal isn't connected to anything.  I want to move it and add a ground.  Would it be okay to run a separate green 10 gauge alongside this wire to get my ground?
Comment: ...are the wires run in a conduit? is the conduit metallic? If so, there's your ground.
Comment: Can you post a photo of the inside of the box?
Answer: Absolutely.  You are allowed to retrofit a ground.  In fact, NEC 2014 greatly softened the rules for retrofitting grounds (I believe this was legal before, but now there's no question.)
You can use green or bare wire, but if you use bare, use solid.  It needs to be 10 AWG.  The basic rules of laying the wire are the same as any other kind of cable.  How often to fasten it, make splices inside junction boxes, etc.
Ground can follow any route back to the same panel the circuit is served out of.  It can take any feasible route and does not need to run alongside the supply cable.  (since current only flows momentarily during a fault condition).
It will suffice if you can reach a nearer junction box which has a 10 AWG or larger ground path back to that same panel, such as a water heater, range, air conditioning unit etc.  Intact steel conduit counts as a rather thick ground wire.   (Grounds can be shared because current only flows during a fault condition, and two circuits faulting at once isn't likely).

Grounding a dryer


creating token on solana blockchain

Question: Created token on solana blockchain using tutorial on internet but then seen this message that solana repo is closed and have to find another way to create token.
It says :
"Adding a New Token
You can use one of two tools at the time of writing:
Strata Protocol Token Launchpad - https://app.strataprotocol.com/launchpad/manual/new
Token Creator Demo - https://token-creator-lac.vercel.app/"
Is that actual? it says powered by Solana on second link. Is it a scam or is it actually working those both tools?
please help ^^
Answer: This is the actual token creator, not a scam
Token Creator Demo - https://token-creator-lac.vercel.app/"

creating token on solana blockchain


Is it possible to perfuse chemicals into brain after removal from body?

Question: I've read studies where fixatives (eg glutaraldehyde) have been perfused into the brain while it is still inside the skull. I would have thought that this could also be done after the brain is removed, provided all the veins/arteries are connected to a perfusion machine. Is this possible, and are there any major obstacles?
Answer: Of course it is possible to perfuse an organ once it has been removed from the body. It is probably unwise to do so with the brain as the delicacy of the structures and high levels of lipids make rapid fixation necessary and difficult. I think the major obstacle is the speed at which the brain could be removed with arteries intact and then perfused as ultrastructural changes occur rapidly once ischemia (oxygen deprivation) begins.
Answer: The main obstacle would be connecting all of the arteries to a perfusion machine.
 The neurovasculature is complex, and begins branching prior to entering the brain, therefore it is easier to do in situ. With a larger brain, the meninges and skull are also important for supporting the brain stucture. If unfixed brain is removed from the skull, it will begin to deform and collapse under its own weight. For fixation, especially, it is much safer to fix in situ and remove post-fixation.


running application on android emulator

Question: I am trying to run hello world program on andriod emulator using eclipse. emultor starts but my application never loads on emulator.
I thought it may be because of my windows version or slow RAM or processor.I am using windows 7 starter 32 bit, 1GB RAM , intel Atom 1.66 Ghz processor.can any one tell me what the problem could be?
Answer: Please open the task manager and check the process status and CPU usage.
I guess CPU usage should be 100% when eclipse and emulator are running at the same time.
Emulator and Eclipse consume a large amount of memory while running.
Even I faced the same issue.
Ran the same program in a system with higher RAM and it ran smoothly.
I guess you are facing the same issue.
It will be helpful if you can paste what you are getting in Eclipse console.
Answer: Try checking the logs in the logcat .It is located in DDMS. It will give you the reason why the emulator is not starting. And also this problem is either related to a buggy code or a wrongly setup android project configuration. Because of slow ram and hardware it may load slowly but it will load eventually.
Answer: First check whether the emulator has been recognized by eclipse or not. You can do it by opening DDMS and see list of devices, if your emulator is listed in devices then run the app. If the emulator is not listed in Devices then close the current emulator and try to start it again until you see the emulator on devices.

running application on android emulator


How to customize my Folder View in Windows

Question: How do I set my Folder view such that my images and videos are in Thumbnail view while my Folders and Files are in icon view. Is there any 3d party software for this
Answer: In Windows XP, you can only select one of the default view types (Details, Filmstrip, Icons, List, Thumbnails, or Tiles). It is not possible to mix those types into another type. However, you can play with your icons as you want. How-to Geek has a good article about customizing your icons in Windows XP.
Answer: Not sure if this is exactly what you are looking for but it will set all Explorer windows back to the thumbnail view you want.
In regedit navigate to the following key HKCU\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell\Bags\AllFolders\Shell
and then change, or create, the value for FolderType from whatever it is to NotSpecified.
Log off and back on and things should be as you wanted.
Comment: ah not this , i don't want to change all to thumbnail view
Comment: Didn't sound like this was what you wanted but was worth a shot.


Applied for Schengen visa with current visa still valid

Question: My current Schengen visa expires on 06/04/2018, and I intend to travel to Belgium on 17/04/2018. I submitted my application today. Does the fact that I still have a valid visa mean that the embassy cannot begin to look at my application until after the 6th? I'm worried the visa may not arrive in time as it can take up to 10 working days.
Answer: Since the visa you already have will not be valid for the trip you're planning, it does not prevent the issuance of a visa that will be valid on your proposed travel dates.
There's no rule saying that holders of a currently valid visa cannot apply for a necessary visa for a visit in the future.