Why is "Affirm / Negative" used instead of "Yes / No"?

Question: Does anyone know why we use Affirm and Negative in RT, rather than Yes and No? I assume it's to prevent confusion with accents and other languages - but Yes and No sound very different to me!
Comment: Welcome to Aviation.SE and with a good, original on topic first question!
Comment: Welcome! One question, one gold badge. Just go on!
Answer: Why do we say "TANGO" on the radio for the letter "T"? Because "T" could get garbled or misunderstood to be "B", "E", "or "V". "NO" could become "oh?", "YES" could become "us", and so on...the possible interpretations and permutations of short, monosyllabic words are many. Use a big word and it will be hard to confuse with others...
Comment: The term isn't so much "Parity" as ["hamming distance"](https://en.wikipedia.org/wiki/Hamming_distance) - the point is to ensure that there's always enough 'distance' between each transmitted symbol, that you can always detect a transmission error. That's why you get 'papa', 'charlie' instead of 'pee' 'cee'.
Comment: From an information-theory standpoint, the extra syllables (such as "niner" vs. "nine" that can sound a lot like "five" over a noisy connection) are "parity".  They do not add any information, but provide confirmation that the information has been received correctly.  The TCP packet used to upload this comment to SE includes a checksum that fulfills a similar purpose.  The web server's networking stack re-calculates the checksum and confirms it matches.
Comment: @MontyHarder There is also the zero-hamming distance of "nine" to German "Nein" (*no*) that should be avoided in an international context.
Comment: The 9 vs nein is an important one. Similarly 9 and "no" in English are still quite similar, as is "mine".
Answer: Because it makes you sound cool and very Top Gun!

Negative Ghostrider. The pattern is full

Seriously though, short words, especially at the end and beginning of transmissions are often clipped. When everything is busy, a question might only need a "yes/no" reply. Yes/no is easily lost in radio communication. Affirm/negative are not.
Also, with English native speakers, yes and no are absolute.  In some languages, yes and no are relative to the question.
Interpret this:

Don't you have enough fuel to make the field?
Yes, we don't.

or

No, we don't.

Of course, the question is not good as it contains a negative but, if a question can only have an "affirmative or negative" response, it also helps the questioner to form a good question:

Can you make the field?

This can only be "affirmative (always shortened to "affirm" to avoid confusion) or "negative".  There is no interpretation.
Comment: I don't understand the point of your "Don't you have enough fuel to make the field?" example. As you say, it's a bad question to ask since it can't sensibly be answered with either yes or no, regardless of what words you use to communicate the ideas of "yes" and "no".
Comment: French still has three words: *si* is for a positive response to a negative question. Middle English had four words. The Celtic languages have no words at all for yes & no: instead, you respond with a form of the verb. So yes, it's complex.
Comment: Perhaps as an example: You can't make it to the field? (Or ANY negative question, really.) With, for example, a German background this IS tricky, because German would allow both no for "no, you are wrong, we CAN make it" and "No, we indeed can't make it". Not sure how conventions for this work for a native English speaker.
Comment: @DavidRicherby Yes, it's not a good example is it? I'll try to conjure up a better one, although I'm not creative at that sort of thing. I was trying to get across the point, missed by many Western native English speakers that yes and no are not always absolute. In many cultures, they are relative and yes/no answers are often misinterpreted.
Comment: @DavidRicherby It's a good example of a bad sentence.  As an answer to the question "You cannot make it?", "yes" can mean "on the contrary, we can make it", whereas "affirmative" means "what you said is correct; we cannot make it".
Comment: I very much like that edit Simon. Note that ICAO specifies 'Affirm' vs 'Negative'. However, the FAA deviates from the international standard by specifying 'Affirmative' vs 'Negative'.  The latter can be confused easier in garbled radio communications. I appreciate your answer is now aligned with the international convention. +1
Comment: Could also add that in some African countries, it's common to first acknowledge that you *understood the question* with a "yes", and then answer it (with another "yes" or "no") - a habit they may also use when speaking English.
Comment: +1 for clipping - I remember back in the days of my Nextel phone with PTT, there were always people who'd push the button and begin speaking without waiting for the "chirp". Usually you knew what you missed from hearing the last 98% of their transmission but on a very short one like "yes" or "no" they'd actually be completely done vocalizing before the handset even began to transmit audio.
Comment: @Layna that is _exactly_ the point. It's just as confusing in English. Try this one, "Please turn down the air conditioning". Does that mean you want me to turn down the temperature (making it colder in the room), or that you want me to turn down the effectiveness (making it warmer)? It's a commonly made request in the US that always leads to confusion and the request for clarification.
Answer: "Affirmative" and "Negative" come from the radio procedure words that went into the aviation world. As a comment above it also adds on more complexity and length to the statement so that the receiver can understand even if the transmission got garbled up or cut off in some parts. It would be really bad if the "yes" or "no" got cut off somehow from the transmission which would be really easy because they take a really short time to say, making it easy to loose the entire word over radio.
Comment: Man years ago, I worked with computers and co-workers that had heavy accents. Our test machines were named 'svlnat01' and 'svlndt02' from the sysadmins which could be hard to differentiate from 'svlnap01' and 'svlndp02' style names.  The names we assigned to the test machines were "Trinidad" and "Tobago" ('T' for 'Test') and production machines were "Nevis" and "Nassau" ('N' for first letter of site name on prod). Each syllable reinforced what you where hearing on the previous one rather than listening for particular ones amidst noise of formality and chance of misunderstanding over the phone.
Comment: The use of the word "Affirmative" instead of "Affirm" seems to defeat the purpose you describe. Go guess what "crk...crk.. ative!" means.
Comment: @DmitryGrigoryev As opposed to just "crk...crk.." if they said "Affirm"?
Comment: I have this argument over server names at almost every job I go to. After someone accidentally shuts down the wrong server because of this, they start to pay attention.
Answer: It has to do with how radios in general work or worked. This is also true with telephones and some VOIP situations.
So take a plain old radio. You set it to a frequency, then you push a button to talk. When you push the button a circuit completes that lets electricity flow through some components (used to be the mic, but now it's gone through changes at times, but it doesn't matter). Next the sound of your voice is encoded and applied over a carrier signal. Because that carrier signal can't be sent 100% of the time there was/is a bit of distortion at the start and end. In some radios they use a beep or click to help "establish" the carrier signal. Remember that the simplest radios just applied your voices wave form over that of the carrier signals.
Now, on the the receiving end, the same thing happens in reverse. The receiver can actually listen to the carrier signal the entire time, but there is a tiny delay as it starts to notice modulation of that signal, and starts "decoding it". Again remember the simple radio has your voice as a modulation of the carrier wave. These days there is a lot of logic on this end to filter out noise, but even if there wasn't it would still take a tiny amount of time to "see" that the carrier wave changed.
So you have several points of distortion and delay at the start and end of a message;

User pressing the button
The mic circuits "turning on"
The start of signal modulation
The start of signal demodulation
The Receiving end starting to "play back" the signal.

Add to that all kinds of distortion and interference, and the fact that as people we have a tendency to think along the lines of "push button -> talk" so fast that we often start "talking" before we are actually transmitting, and you can get some pretty messed up messages.
To combat that there are a few common things that are done.

Using longer words
Limiting vocabulary to common words
A set of hand shake phrases that ensure that both sides are getting the same thing.

For example (not from anything in particular):

You want pizza
  ooo want pizza
  ooo ..aunt... pee..ah

While a bit odd, all three could be understood if you're having a conversation about dinner.

Yes
  ess
  sss
  ye..

Is harder to understand than

Affirm
  ..Firm.
  Affir..
  Ah.ff.

Specially when you are asking a yes or no question.

No
  oh
  n...
  ...  (this is actually pretty common as yes and no are fast words to say)

So if you say into you radio "Do you want Pizza" and you get back: "...", your SOL. If you get back "oh", is that "oh I don't know" or the end of no? If you get back "Neg.." or "N....itive" or "Negiti.." You're still in good shape ( you have your answer).
There are many things radio operators are taught to do to make sure they can understand one another in less than perfect conditions. Using "longer" words is one, using distinct words is another, and using scripted responses and questions is a third.  It's also important to remember that rarely is the radio a "primary job" it's almost always a  "secondary job". The pilot needs to communicate, but communication can't be so cumbersome that it gets in the way of actually flying. So whatever system is in place to cover the distortion and what-not has to be easy, and widely understood.
Last example:
If you had two people with training, and they were taught that the question: "Do you want pizza?" could only EVER be answered with "... Yes ..." or "... No ..." then you could use yes or no, they sound different. But that means that the operator answering would have to press the button, count in their head to three, say YES, then count in their head to three, finally releasing the button. However if that operator was distracted, and didn't wait, or if the operator was out sick and the new guy didn't know the protocol, or there was a large network of people asking the question all with slightly different protocols, now "...Yes..." doesn't work as well.
Comment: This good answer would be better if it used the actual "Affirm" from the question rather than "Affirmative", which is not recommended.
Comment: That's why a lot of systems use something other then Affirmative. Like just Affirm or 10-4 or Roger or such. Different systems different rules, but that's the basic problem that is trying to be addressed.
Comment: Affirm and Negative are different, Affirmative and Negative sound the same at the end so getting back a ".....itive" would be less than ideal.
Comment: What if you get "...itive"?
Comment: @GreenAsJade -"Affirmative" not recommended?  What guidelines say this, and do you happen to know of any US-based guidelines that say this?  (May be could be a new question-- )
Answer: Because it increases the number of syllables being spoken thus increasing the likelihood of correct communication.


PHP remember file field contents

Question: I have a form with text inputs and file inputs; the text fields are being validated. Is there a way to have the form remember which files the user has already selected if they hit submit but need to go back because one of the text fields didn't validate?
Comment: The files upload is already completed before the PHP script is called.
Answer: You can't "pre-fill" the contents of a file upload field for security reasons. Also, that would mean the file would get re-uploaded every time the form is submitted, which would not be good.
Instead, do this:

Create a file upload field with name file_upload.
On the server-side, process the upload in any case, even if the rest of the form validation fails.
If the form validation failed, but the file was uploaded, insert a hidden input into the form with name file containing the name of the just uploaded file.
Display a user-visible indication that the file is okay. If it's an image, display a thumbnail version of it. If it's any other file, display its filename and/or icon.
If the user chooses to upload a different file in the file_upload field, process the upload and store the new value in file.

Pseudocode:
<?php
    $file = null;
    if (!empty($_POST['file'])) {
        $file = $_POST['file'];
    }
    if (!empty($_FILES['file_upload'])) {

        // process upload, save file somewhere

        $file = $nameOfSavedFile;
    }

    // validate form
?>

<input type="file" name="file_upload" />
<input type="hidden" name="file" value="<?php echo $file; ?>" />
<?php
    if (!empty($file)) {
        echo "File: $file";
    }
 ?>

Important note
This mechanism can allow any user to claim other user's files as their own, by including a file name that they guessed exists on your server. You will want to ensure that uploaded files are clearly associated with a specific user to avoid this issue.
Comment: Thanks, I'm using the Codeignitor framework and I'm new to it but I'll try to implement this somehow.
Comment: Works now, it was easier to do in CI than I thought.
Comment: So good. but What should I do to save the photo in the database ?
Answer: files input fields are read-only you can't set an initial value for them
Answer: You can upload the Files anyway and display the filenames instead of the file select box. To remember the fields, you can use a $_SESSION variable.

PHP remember file field contents


Dual extruder clogging problem

Question: I have attached a dual extruder (2 in 2 out) to my 3D printer. There is a repeating problem of clogging while printing.
I have fixed Chimera hotend.

A big fan, which covers area more than the double extruder, cools both cold ends. An additional fan directly on the front (as seen in the picture) cold end cools the ribs directly. The back does not have an additional fan.
I tried to print after attaching an extra fan; the first print went well but from there on, the hotend gets clogged every time I print.
The clogging happens in melt zone. I have tried cleaning the hot-end, but to no avail...
My settings are as below:

Print speed = 60mm/sec
Temperature = 210C
Filament material = PLA
Filament diameter = 1.75,
Nozzle Diameter = 0.4
Dual extrusion switch amount = 16.5mm
Retraction speed = 40mm/sec,
Retraction Distance = 4.5mm,
Disabled Wipe and Prime tower and ooze shield

Please advise what to do.
Comment: Possible duplicate of [Extruder prints fine up until further down the print](https://3dprinting.stackexchange.com/questions/5968/extruder-prints-fine-up-until-further-down-the-print)
Comment: I advise you to clean your PTFE tube. As I see you are using custom plywood frame. There might be some dust in your tube. Also try to increase extruder temperature by 5 degree. You can also put glass on your base because wood is not smooth as glass.your extruder nozzle may catch some wood dust while printing. Apply some normal clear mineral oil (called Sewing Machine oil in INDIA) on PLA filament with cotton. I never face clogging issue in my Tronxy X8. I just put few drops of oil on cotton and rub it on filament for approx 1 meter.
Comment: @Himanshu Dust in tube can happen (usually filament grinding dust), but the nozzle catching up wood dust seems very unlikely. Also when suggesting using oil, please do mention it to be vegetable oil, as this oil forms a nice coating on the inside of the hotend preventing filament to stick to the metal hotend, synthetic oils will not do that.
Comment: Ok, you are using a Chimera hotend, *does it have all-metal heat breaks*?  This is kind of crucial for solving your problem. Please add that to the question by pressing [edit].
Answer: It appears (now confirmed in your question) that you are using a Chimera 2-in-2-out hotend like depicted below:

Chimera hotends generally use all-metal heat breaks (not confirmed yet) which are harder to operate than "normal" PTFE lined hotends. A common problem that happens is that heat creeps up causing problems as a result of too slow printing or too high retraction length settings. Basically your problem is clogging related to all-metal heat break printing. This is recently asked in this question: "Apparently systematic nozzle clogging". Please read the answers to that question as they describe very well what happens and what to do.
Quoting from this article explains that it is a heating/cooling issue:

Jams and clogs are often from a combination of excessive heat and
  non-optimal material flow.  This effect is worsened by poorly cooled
  all-metal hot ends, high torque extruder gears, small nozzles/layers,
  slow printing speeds, too thin first layer, and excessive retraction.

Please do read this article and the solutions they mention to get yourself acquainted with the problem and its solutions.
In your case this could well be a cooling issue in combination with a too high print temperature and a possibly too high retraction length setting (depends on the length of the Bowden tube). The fan you mounted in the front (onto the cooling ribs, so the rightt fan in your image) is too large for this hotend. You attached the fan to the left top mounting hole so that it exceeds the right and bottom area of your cooling ribs. Furthermore, this larger fan has a larger center (hub) to house the bigger engine so that you end up with a lower cooling flow for at least the right extruder as most of the cooling ribs area is blocked by the fan hub. Please fit a fan that fits this hotend. Printing a fan adaptors may not work as well, these fans have a very low static pressure difference, so a convergent duct may not work as well as you might think. Considering your temperature you are printing PLA; PLA could usually be printed well in the 185 - 195 °C temperature range (depending on the PLA), 210 °C seems a bit on the high side.
Another solution could be replacing the heat breaks for lined heat breaks:

As an aside, to explain a suggestion, in Himanshu's comment to coat your filament with some oils:

Apply some oil on PLA filament with cotton.

Oil does lower friction in an all-metal hotend, but please beware that this needs to be vegetable oil. The reasoning behind this is that the oil hardens inside the throat to create a smooth coating on the inside, not lube the inside of the throat. This thread has some interesting material on that.
However, general consensus is not to do that:

Micro-Swiss use slippery platings and such, they don't need it. I've
  also used B3 Picos and E3D v5, v6, Volcano and Chimera and even that
  one garbage QUBD mk7 knockoff. Never needed oil.

or

Seasoning hotends is a myth that refuses to die. Just don't do it, it
  does more harm than good.

Dual extruder clogging problem


How fast is electrostatic force?

Question: Suppose we have a charge $Q$ in deep space (isolated), now suppose another charge $q$ appears instantly (no matter how). Obviously it will feel electrostatic force but the question is how quickly (will the be felt instantly even at large distance).
As I mentioned electrostatic, both the charge are stationary
Comment: I'm closing this post (v2) as non-mainstream as a _charge $q$ cannot appear instantly._
Comment: But it is a reasonable thought experiment? And I'd say reasonable for the concept of the propogation of EM radiation.
Answer: Every charge that we have,makes a field that is called electrical field;shown by "E" and this field fills all the space around.if we imagine that there is nothing else in the universe to interact with the charge and the field,field of our charge fills all of the space.now we put a new charge in a random point;what happens is that new charge feels the field of first charge at the first moment that we put it in the space but,in this case a new field will appear that is for our new charge and 2 fields will interact with each other.at last we understand that,new charge will feel the field and force at the first moment, because there was a field before it and we have the equation: F=Eq but the new field and force of the new charge will travel to old particle with the speed of light and after that the old charge will feel the new field and force!
Answer: Any change in an otherwise static arrangement of charges and currents will lead to a change in the fields that propagates at light speed away from its origin.
Answer: The 2nd charge $q$ will be felt (by $Q$) after a time $t$ such that
$$
t=\frac{d}{c} \tag{1}
$$
Where $d$ is the distance between the charges and $c$ is the speed of light in a vacuum.
The effects of $Q$ on $q$ should be felt instantly (given $Q$ was already present for a sufficient time still given by (1)).
Comment: This is plain wrong, the field generated by the first charge will be already present at the position of the second charge (assuming the first charge was present long enough). So the force can be felt instantly (t = 0).
Comment: @Rob But the first charge $Q$ won't feel the effects of the second charge $q$ till a time $\frac{d}{c}$? Perhaps I should edit the answer to make it clearer which charge I'm referring to feeling an effect.
Comment: @Rob Could you remove the down-vote as I have clarified my answer please?

How fast is electrostatic force?


Playing Hi-Res audio files on mac with M-audio Revolution 5.1

Question: I have audio file with 192Khz/24bit sound, and Revo 5.1 and driver for Snow Leopard. This driver is not official, and it is only the kext, without any GUI, and I can't see sound quality playing right now. I just set up in Audio Midi Setup App sound format of 192Khz. How can I see be sure the sound playing in 192/24 quality, not just 192/16? Is 24bit/16bit sound switching begins automatically?
Answer: I used to own one of these cards and used it on a Windows PC. If I'm not mistaken, M-Audio (now owned by Avid) no longer supports this card. It's been declared obsolete and orphaned. Good luck.
Comment: This is unrelated to this question, but I wanted you to see this: http://meta.apple.stackexchange.com/questions/618/tag-wikis-should-not-contain-questions-about
Comment: Thank you, Kyle. You have brought something to my attention that I was not aware of. Please see my response at the link above.


Jehovah's Witnesses Memorial of Christ's Death

Question: Why did Jehovah's Witnesses not use the Passover this year to celebrate the memorial, as has been their tradition since Jesus instituted this to celebrate his death ?
Comment: http://christianity.stackexchange.com/questions/14713/why-were-jehovahs-witnesses-holding-a-memorial-service-for-jesus-on-tuesday-ma       Check this question and answers for some good content. Especially Daniels answer that is linked from Judaism site basically this year is a leap year on Jewish calendar so the add another month which pushes the Passover back. Jehovah's witnesses like every year go with the first full moon after the spring equinox.
Answer: The Jehovah's Witnesses have the practice of celebrating the Memorial of Christ's Death on the 14th of Nisan which corresponds with the Jewish Passover.
"Jehovah's Witnesses commemorate Christ's death as a ransom or "propitiatory sacrifice" by observing the Lord's Evening Meal, or Memorial. They celebrate it once per year, noting that it was instituted on the Passover, an annual festival. They observe it on Nisan 14 according to the ancient Jewish luni-solar calendar. Jehovah's Witnesses are taught that this is the only celebration the Bible commands Christians to observe."
The year 2016 poses a unique set of circumstances as to why the Jewish community has decided to defer the celebration of their Pesach to such a late date this year. The Jewish Passover is to be commemorated on April 23 2016 starting  at sundown!
The Jewish calendar follows a lunar cycle calendar, which comprises of some 354/355 days. Since the lunar calendar is about 11 days shorter than a 365-day solar calendar, it is necessary to added an extra month every so many years to realign the two calendars! This is what is happening this year.
The Jehovah's Witnesses have apparently decided to keep the first possibility of celebrating the Commemoration of Christ's Death on the first possibility after the first full moon after the spring equinox (March 20/21), which falls on March 23 this year.
Nevertheless there are some communities that feel that the Jewish community should have chosen another year than 2016 to add the extra month than 2016 to realign their calendar and moving their Pesach to such a late date.


SELinux on Ubuntu 18

Question: I've been hitting my head agains the wall trying to configure SELinux on Ubuntu 18, is there any official documentation
to do that or is not supported anymore ?
I only can make it work on 16 LTS with enforcing. On 16 LTS by installing selinux package or
apt-get install selinux-basics selinux-policy-default auditd

and then run
selinux-activate

it works, but on 18 it seems something changed and cannot make it work, I been configuring the service at boot with this
Add security=selinux selinux=1 to GRUB_CMDLINE_LINUX_DEFAULT variable in /etc/default/grub. Run the following command: grub-mkconfig -o /boot/grub/grub.cfg.
Then I reboot, I get Permissive by default, then if I set to enforcing from command line everything stops working, I mean, if I reboot the server it does not boot anymore.
I cannot restart services, everything is denied which is wrong, so I would like to know if I should keep trying, as I said, on 16 LTS it works.
Thanks
Regards
Answer: Selinux works for me on Ubuntu 18. All I had to do was to install selinux and selinux-basics, and then activate it. Note that in my grub config I only have security=selinux and not selinux=1

SELinux on Ubuntu 18


Ubuntu desktop as terminal server

Question: its possible to run Ubuntu as Terminal (?) server? I want to use my PC as Ubuntu desktop and sometimes use my laptop to connect to pc login to same account and run everything as on my pc. PC will be a server where most of computing will work laptop will be only a terminal. I see something like this on my school but I'm not sure how it's on server side. Sorry for my English it's not my native language ;-)
Comment: If I understand you well, yes it possible. Just install ssh-server on PC and ssh-client on laptop and you can connect to PC using your laptop using ssh service.
Answer: Yes, your PC can be used as a server.
For "terminal" access you'll need a OpenSSH Server installed on your PC.
sudo apt install openssh-server
Once it's installed you should be able to reach your PC from your laptop, as long as you're in the same network (LAN).
Let's say your PC has local IP: 192.168.123.456
Then you can connect to its terminal with ssh:
ssh email@example.com
Where "login" is your PC account name.
You can check your local IP with:
hostname -I
or
ip a s
SSH Security
Keep in mind that running OpenSSH without additional configuration is not safe.
You should take additional security measures to make sure that your PC is safe with OpenSSH server running.
To secure your SSH server you should at least edit your /etc/ssh/sshd_config
sudo editor /etc/ssh/sshd_config
Prevent login into root account with:
PermitRootLogin no
Disable password authentication
PasswordAuthentication no
and use ssh-keys instead:

How To Set Up SSH Keys
How To Setup SSH Keys on a Linux / Unix System

Also append new line at the bottom of the file with:
AllowUsers yourlogin
to make sure that only this account can be used with SSH.
Also read more on SSH security here:

OpenSSH security and hardening
Top 20 OpenSSH Server Best Security Practices

Preventing brute force attacks with fail2ban
With fail2ban you can prevent brute force attacks, targeted on your SSH Server.
You can install fail2ban with:
apt install fail2ban
In case you change your SSH port please remember to change it also in fail2ban configuration.
Let's say you've changed your SSH port from 22 to 2222.
You can set it in /etc/fail2ban/jail.d/defaults-debian.conf
sudo editor /etc/fail2ban/jail.d/defaults-debian.conf
so it looks like this:
[sshd]
enabled = true
port = 2222
Then restart fail2ban with:
<code>systemct restart fail2ban
</code>
Network settings and firewall

If you want to reach your SSH Server from outside your LAN you will need to forward SSH port in your router's settings to be able to connect your SSH Server via public IP.
In case your public IP is dynamic you will also need to set DDNS (dynamic DNS) service with a domain name, to be able to connect your SSH Server with this domain name, even if your public IP will change.
Consider setting up a firewall with iptables to control connections made to your SSH Server.
Answer: With ssh you have the terminal and might even start something graphical but if you just want access to the desktop like in virtual desktop the easiest way to do that is with vnc server and vnc client. Also Remmina works good. VNC clients and server are in the standard Ubuntu repository so they can be found and installed with the standard Ubuntu Software.
The advantage of VNC is that there are clients on most Operating systems so a laptop or machine with windows, (any)linux, mac, android will work. If you tweak the server settings you can even connect with an old dos machine.
I remember fiddling with this and I stumbled on having to poke a port 23 or 5900 hole in the serverside ubuntu firewall to get it working.

Ubuntu desktop as terminal server


Some questions about counterbleeding

Question: Here are two words, "writing" and "riding". I know that there are two rules for them, as in the pictures. But in the first picture, can I say the /ai/ raising rule counterbleeds the tapping rule? I can also say the /ai/ raising rule feeds tapping rule, right?
Answer: Bleeding is where applying rule A first prevents B from applying, but B could apply if A had not applied – people often say that A "takes away" forms that B can apply to. Counterbleeding is where B would bleed A if B applied first, but A in fact applies first. By applying flapping first (which turns voiceless segments into voiced ones), you take away forms that could have undergone Raising (which applies before voiceless segments). Flapping applying before Raising is a bleeding order, because changing /t/ into [ɾ] removes an input to Raising. Applying the rules in the opposite order is counterbleeding. So, half right.
Feeding is where applying rule A creates a new environment for B to apply, and counterfeeding is where the opposite ordering would be feeding. No order of the rules affects applicability of flapping. The conditions for applying raising must be present in the underlying form: no rule creates a new environment for raising, so no order is feeding.
Comment: Thank you for your kind reply very much!
Answer: I agree with user6726's answer.  I find that it relieves confusion to always state the counter-relations in the passive voice -- that way, the rules are stated in the order they would need to be in a linear ordering theory.  If Tapping is before Raising, Tapping bleeds Raising. If Raising is before Tapping, Raising is counterbled by Tapping.  (Likewise for "feeds" versus "is counterfed by".)
There is also an interpretation (also due to Kiparsky) according to which the difference in ordering is due to whether rules' environmental restrictions are relative to rules' input forms, or their output forms.  For your example, in the counterbleeding dialect, the Raising rule is sensitive to its input, but in the bleeding dialect, it is instead sensitive to its output. In Kiparsky's terms, the bleeding relationship is "opaque", while counterbleeding is "transparent".

Some questions about counterbleeding


How do you express time independence in steady flow?

Question: If A is a property of the fluid, then in a steady flow is $\frac{dA}{dt} = 0$ or $\frac{\partial A}{\partial t} = 0$ ? My professor says it's $\frac{dA}{dt} = 0$ but I don't see how that makes sense. Isn't a flow steady if all of it's properties are independent of time? And if A is independent of time, doesn't that only mean that it isn't a function of time, i.e., that it doesn't explicitly depend on time?
Comment: It's the partial derivative at constant spatial position that is zero, not the material (Lagrangian) derivative.  So you are correct and your professor is wrong.
Answer: I think you are correct if temperature is constant.
Time Independent Fluids

This class of fluids is characterized by the fact that, provided the temperature of the fluid remains constant, the shear rate depends only on the shear stress and is a single valued function of it. Newtonian fluids which have a viscosity that is independent of the shear rate are described. This behaviour is exhibited by all gases and, in general, liquids, and solutions of materials of low molecular weight. Fluids whose viscosity is a single valued function of shear rate are termed non-Newtonian fluids.
Answer: I would argue that $\frac{\partial A}{\partial t}=0$ should be giving you time-independence in all fluid properties.
My idea here is that you can find a system in which the $v \partial_x v$-part of the co-moving time-derivative $\frac{dv}{dt}$, with  $$\frac{dv}{dt} = \frac{\partial A}{\partial t} + v\partial_xv$$ plays an important role and makes the system steady-state. Then you can argue for the remainder, a.k.a. $\partial A/\partial t$ being responsible for any time-dependent behaviour.
The system I suggest to look at is the three-way force balance in the 1D-Euler cartesian equations
$$ v\partial_xv = -\frac{1}{\rho}\partial_x P + g .$$
This system gives rise to a number of sonic-transition solutions which are all time-independent, i.e. if one would simulate them on a computer with the $\partial v/\partial t$-term, a found solution would not change. This system gives rise to solutions that can be called "solar wind" or "rocket nozzle flow" and others, if you're interested in the literature.
So, because the above system exhibits steady-state solutions, and the first term on the l.h.s is part of the co-moving time-derivative, I would say your notion is the correct one. But I would be curious as to what your prof's rebuttal of that would be.


What are the female parts called?

Question: What is the proper term for the "female" section of the piece that the "studs" insert into? I have heard "pipes", "tubes", "underbits". Is there an actual term for the female section?
Comment: Interesting question. To help finding a good term, it would be useful with a good example to use this in a phrase. Do you have an example of use in a natural context?
Comment: It was an analogy to demonstrate how you can plug an API into your website. So, the statement went something like "You have a LEGO piece (representing the API) with it's studs and you need to attach it to your website, so you need do build the [underbits/tubes/stud receptacle] to plug the API into."
Comment: See also this question for naming other features of a brick: http://bricks.stackexchange.com/questions/1636/is-there-an-official-lego-terminology-for-the-features-of-basic-pieces
Answer: Chapter 1, Page 4, The Unofficial LEGO Builder's Guide:

The tube is the other half of the mechanism that helps bricks stick
  together. Tubes capture the studs so that you can join LEGO elements
  and know they won't fall apart.
Comment: I have to disagree on that somewhat, or at least try to add some undertone. The tubes do indeed capture the studs, but not by themselves: the studs are (usually) captured between tubes, or between tubes and brick walls; they don't "insert into" them in conventional builds. Also, not all parts feature tubes, so what would you call the underside of a 1x1 brick?
Comment: The underside of a 1x1 brick? How about "The square version of the tube that is the bottom of a 1x1 round brick"?
Answer: Bricklink (at the time of writing) has 5 catalog items using the term 'stud receptacle'.
Answer: Members of the French club FreeLUG refers to these as antistuds, and there is at least one LDraw part that uses that same naming. Considering a lot of other parts don't, however, it's probably not widely accepted. And it's not valid at Scrabble either.
You could also use mortise by analogy with the woodworking assembly (a stud is also usually called tenon in French), but again, I've never heard it in LEGO circles. Slot might be appropriate too.
Comment: I think "slot" would be more descriptive of an open spot in a construction where a particular part fits.

What are the female parts called?


What is the Schrödinger equation used for exactly?

Question: The Schrödinger equation is just another way of writing the conservation of energy, right? So how can you use it to find the quantum wavefunction? I mean in every example I've seen the wavefunction is calculated using sines and cosines so I don't see how you can use the Schrödinger equation to find a wavefunction. All I can see it being useful in is finding energy levels which doesn't help calculate the wavefunction. I'm pretty sure I'm wrong about everything I said because the Schrödinger equation is a big deal in QM, so can you please explain me what this is actually used for? I've had this question for ages now. Any help would be helpful.
Comment: Are you talking about the time-dependent or the time-independent Schrödinger equation?
Comment: *The Schrödinger equation is just another way of writing the conservation of energy, right?* No, this is a mischaracterization of it.
Comment: well...both if you could...  first time independent then time dependent . thanx
Comment: Related question by OP: https://physics.stackexchange.com/q/581926/2451
Comment: One use of the wavefunction of a particle is to compute its expectation value of position, momentum, etc.  That is a big subject but you can find numerous examples of them on the web.
Comment: BTW, you mentioned "sines and cosines"; these are encoded in the $|{\psi}\rangle$ that appears in various answers below, so they are still there.
Answer:
The Schrödinger equation is just another way of writing the conservation of energy, right?

Wrong. The original motivation for Erwin Schrödinger can be read in his 1926 paper An Undulatory Theory of the Mechanics of Atoms and Molecules (behind paywall, but freely readable copies can easily be found on the web).
Namely, the ansatz is the Hamilton-Jacobi equation, whose solution $W(x,y,z,t)$ is seen as a set of constant-value surfaces in $(x,y,z)$ propagating in space as time $t$ changes, one (possibly disjoint) surface for a chosen constant value. Reinterpreting these surfaces as the constant-phase surfaces, or wavefronts, of some waves, gives us the idea of the quantum wavefunction (whose actual interpretation was not known until Max Born formulated the rule named after him).
Now, when we try to solve the time-dependent Schrödinger's equation, we find that it can be in general variable-separated for the time dimension $t$ to yield an expansion of the wavefunction in eigenfunctions of the Hamiltonian operator. This then gives us the time-independent Schrödinger's equation for the individual eigenfunctions.
This is not much different from what we do when we solve e.g. the wave equation for oscillation of a drum-like membrane. The nodes of the eigenmodes of vibration of such a membrane form the famous Chladni figures.

I mean in every example I've seen the wavefunction is calculated using sines and cosines so I don't see how you can use the Schrödinger equation to find a wavefunction.

The cases when you can form a wavefunction with merely sines and cosines are very rare. They are the most trivial types of problems that you can solve with Schrödinger's equation. Even the harmonic oscillator in quantum mechanical description requires the use of a set of functions that are definitely not sines nor cosines.
To understand how to use the Schrödinger's equation to find a wavefunction (I'm assuming you mean the eigenfunction of Hamiltonian, rather than time evolution of an arbitrary wavefunction), try reading the derivations of the solutions of various problems like quantum harmonic oscillator and hydrogen atom.
Answer: There are two equations commonly called the Schrödinger equation. Most physicists I know would prefer to call*:
$$i\hbar \frac{d}{dt}|\psi\rangle = \hat{H}|\psi\rangle$$
'the' Schrödinger equation. This is also called the 'time dependent' Schrödinger equation. It is the quantum mechanical replacement for Newton's second law:
$$ m \frac{d^2}{dt^2}\vec{r} = F(\vec{r}).$$
The TDSE tells you what $|\psi\rangle$ will be at time $t+dt$ if you know $|\psi\rangle$ at time $t$ and the operator $\hat{H}$. By incrementing by small time steps in this manner you can predict the state of a quantum system arbitrarily far into the future if you can solve the TDSE.

The other equation people call the Schrödinger equation is the 'time independent Schrodinger equation'. This is a mathematical tool used in the process of solving the full TDSE. This equation reads something like:
$$\hat{H}|E\rangle = E|E\rangle$$
where now we interpret the state $|E\rangle$ not an arbitrary state, but a state with a definite value of energy equal to $E$. The TISE then is read as an equation that, given the form of $\hat{H}$ tells lets you solve for the shape of states with each definite energy $E$. For many models it will turn out that this is only solvable for certain discrete values of $E$. That means that there are not states with intermediate definite energies, which in turn gives rise to the discreteness of atomic spectra etc (and the name 'quantum', ultimately).

*P.S. the notation $|\text{stuff}\rangle$ just means 'quantum state of system'. It's convenient because it means you can label a state $|E\rangle$ because it has energy $E$ and not get the symbol for $|E\rangle$ the state and $E$ the number confused.
Answer: Essential knowledge about the Schrödinger-equation SE (I limit my post to the time-independent equation) is that it is an eigen-value equation.
I assume that you know the basics of linear algebra so if you take a, for instance a 2x2 matrix $A$, an eigen-value problem can be set up:
Let's assume
$$A= \left( \begin{array}{cc} 0 & 1 \\ 1 & 0 \end{array}\right)$$
there is the following eigenvalue problem:
$$ A v = \lambda v$$
that has a simple solution:   $\lambda_{1,2} = \pm 1$ and $v_1 =\left( \begin{array}{c} 1\\ 1 \end{array} \right)$ and $v_2 =\left( \begin{array}{c} -1\\ 1 \end{array} \right)$. In particular the space of solutions
$$ v= \langle v,v_1\rangle v_1 + \langle v,v_2\rangle v_2$$
spanned by $v_1$ and $v_2$ is 2-dimensional.
The Schroedinger-equation  is basically the same with a couple of differences: the matrix $A$ is substituted by the Hamilton-operator $H$ and $\lambda$ are the energy (eigen)-values and $v$ corresponds to the wave-function $\psi$.
$$ H\psi = E\psi$$
However, the subtle difference of the SE to the linear algebra problem is that the space the eigen-vectors of this equation belong to is infinite (and called Hilbert-space). One strategy of finding the wave-function is searching for a basis in this infinite space. Evidently this is not so trivial. But the tools of mathematical physics provide us with a whole pool of special functions.
For instance let's look at the 1-dim. quantum harmonic oscillator. In this case we are lucky since eigen-vectors can be constructed from the Hermite-polynomials $H_n$ that have the following form (and are of infinite number):
$$\psi_n(x) = \left(\frac{m\omega}{\pi \hbar}\right)^{1/4}\frac{1}{\sqrt{2^n n!}} \exp(-\frac{m\omega}{2 \hbar} x^2) H_n(x\sqrt{\frac{m\omega}{\hbar}})\quad \text{for} \quad n=0,1,2,3,\ldots $$
and the solution of the SE can be constructed as an infinite linear combination of these eigen-vectors:
$$\psi = \sum_{n=0}^{\infty} \langle \psi, \psi_n\rangle \psi_n $$
with $\langle \cdot, \cdot\rangle$ is the scalar product on the Hilbert space.
We are even more lucky: Here (that's not always the case!) each element of the infinite basis even fulfills the eigen-value equation:
$$H\psi_n =E_n \psi_n \quad \text{with} \quad E_n =\hbar\omega (n+\frac{1}{2})$$
Of course, there might be problems which do not require to compute the eigen-vectors,
where the computation of the eigenvalues is sufficient. This also happens in linear algebra. But the eigenvectors, i.e. for the SE the wave-function, fulfills an essential role in the SE-eigenvalue problem.
A final word: the domain where the problem is posed also plays an essential role. In case of the harmonic oscillator it is $(-\infty,\infty)$, but for infinitely deep potential well it is $[-a, a]$. In the latter case the basis of the Hilbert space (here you might indeed get $\sin$'s and $\cos$'s) is a completely different one to the basis of the Hilbert space in case of the 1-dim. harmonic oscillator.
Moreover, symmetry and dimension plays a crucial role:
Again, an appropiate basis of the Hilbert space for the 3-dim. hydrogen atom is completely different to the one's already mentioned.


I purchased bitcoin in 2014. After I paid, it shows on the transaction ledger that it was sold 40 minutes later, but not by me. Is it lost forever?

Question: As per the title - I paid for BTC in early 2014 and appear to be the victim of fraud. Are the coins lost forever? Any help is gratefully appreciated.
I purchased them through quickbitcoin.co.uk, which no longer exists. I made a bank transfer to the purchaser at the time, and have their bank transfer details and wallet address.
The BTC was apparently sent to me, and I was given transaction details, however these show that the BTC was 'sold' shortly after my bank transfer was made - I was not aware of this at the time of course.
Having spoken to some 'scam recovery' solicitors in the UK, it seems that any transactions over 6 years old cannot be pursued.
Can anyone help please - to either help gain clarity on what has happened, or to direct me to a bona fide international BTC fraud firm?
Thanks very much in advance!
Comment: Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
Answer:
The BTC was apparently sent to me, and I was given transaction details, however these show that the BTC was 'sold' shortly after my bank transfer was made

When Bitcoin is sent to you it is sent to an address, the address likely started with a 1. In order to own that address you would also have needed a private key. If you have neither of those things there is probably no way anyone can assist.
The word sold NEVER appears on a blockchain explorer and only appears on exchange trading order books or transaction history. It would be helpful to see the supposed transaction details you were given. If the coins were sent to an address belonging to a private key that you own, no one would be able to move them. If on the other hand you never custodied your own coins, there is no way to know where they are. You can attempt to investigate fraud if you want at the control of your local law enforcement + chain analysis firms (I'm not sure which ones are good), but to the extent that you did not take the basic steps to self-custody it is unlikely anyone can help you here.
Tldr: If you do not have an address, private-key, mnemonic phrase, old working wallet software, it is unlikely anyone can help you recover this from the Bitcoin side of things. Please Read: https://www.swanbitcoin.com/assessing-risk-in-bitcoin-custody/


How to compile a shell script in FreeBSD?

Question: How can I compile binary shell script for FreeBSD? I tried the Linux binary emulator but it doesn't work.
Comment: What script? What language is it written in?
Comment: bash is used. I tried shc -f /test.sh inside freebsd 8. but the script is killed immediately. Command "file /test.sh.x" return : ELF 32-bit LSB executable, Intel 80386, version 1 (FreeBSD), dynamically linked (uses shared libs), for FreeBSD 8.0 (800107), stripped
Answer: The solution is to use only ksh insteed of [ba]sh as script interpreter.
Answer: There is really no such thing as a binary shell script (script means not binary) - although it is possible to tack an executable binary or a compressed file on the end of a shell script, which usually just contains a tail command to strip the shell script and decompress/preprocess and execute the binary.
If correctly set up the script should include the shell to use (#!/bin/sh would be the traditional unix default), or should use only commands common to all shells.  Simple thing is to make it readonly for safety and open it with vi and have a look, and then just execute the payload command(s) on the file yourself (with adjustments as needed - often the point is to set up some environment variables or do some preprocessing, most often including decompression).
Answer: The shc program is not a real shell compiler. From the manual page:

shc itself is not a compiler such as cc, it  rather  encodes
       and encrypts a shell script and generates C source code with
       the added expiration capability. It  then  uses  the  system
       compiler  to compile a stripped binary which behaves exactly
       like the  original  script.  Upon  execution,  the  compiled
       binary  will  decrypt and execute the code with the shell -c
       option.  Unfortunatelly, it will  not  give  you  any  speed
       improvement as a real C program would

Some scripting languages like e.g. Python convert scripts into bytecode before executing them. Shells that can be used interactively usually don't, they are just interpreters.
One could even argue that save for some embelishments like variables, loops and other control structures, shells are mostly a front-end for the fork and exec functions.


Does isochoric expansion make sense?

Question: My introductory text book on thermodynamics has just one  ambiguous mention of something like "Isochoric expansion of an ideal gas " . But does it really make sense ? Or is it just a blunder ?
Comment: It doesn't make sense. Isochoric process doesn't have volume change. Expansion has the volume increased.
Comment: @sammygerbil: Seriously? This type of question is one of the reasons *for* this site: clearing up confusions about physics.
Comment: @KyleKanos : The highest voted answer in that post opens : "It depends. Generally speaking, yes, you can ask about what you think is an error in a book (or paper), but make sure you're asking an actual answerable question, rather than **just looking for people to agree with you.**" I claim that the OP here is doing the latter.
Comment: I'm voting to close this question as off-topic because this is a question about a possible editing error in a textbook, not a question about a physical concept or principle.
Comment: @KyleKanos : Yes, seriously. The OP is clearly not confused about physics and is merely pointing out an isolated "blunder" in an unidentified textbook. I don't think the purpose of this site is to point out editing errors in textbooks.
Comment: @sammygerbil: So the question "Does [isochoric expansion] really make sense?" is not a physics question worthy of asking? Further, if textbook errors are off-topic, then why do we have a tag specifically for that: [tag:textbook-erratum]?
Comment: @KyleKanos : No I don't think such a question about a definition is worthy of asking. The only possible answer is to refer to an authoritative definition, which the OP could easily do for himself as well as the most expert physicist on the site. No application of physical principles or concepts can answer such a question. ... The existence of a tag does not define site purpose or policy. The question still needs to be *on topic*, and to be asked out of  genuine confusion rather than simply pointing out textbook errors.
Comment: @sammygerbil: Okay, I'm stepping back from this because you're obviously confused about this site & how/when to close questions and I don't have the time to explain it to you. FWIW, though, the relevant meta post on the subject of textbook errata [can be found here](http://meta.physics.stackexchange.com/q/756/) (hint: you're wrong on this point too)
Answer: In his lectures on thermodynamics, Fermi defines an isochoric transformation as one in which the system doesn't do any external work. In this sense, the free expansion of a perfect gas (AKA Joule expansion) is an isochoric process.
However, I must say that that's the only place where I've seen an "isochoric process" defined in this way, the common definition is the one given by annav, so it might as well be just a blunder.
Answer:
An isochoric process, also called a constant-volume process, an isovolumetric process, or an isometric process, is a thermodynamic process during which the volume of the closed system undergoing such a process remains constant. An isochoric process is exemplified by the heating or the cooling of the contents of a sealed, inelastic container: The thermodynamic process is the addition or removal of heat; the isolation of the contents of the container establishes the closed system; and the inability of the container to deform imposes the constant-volume condition

You should give more of the context where you found the quote. It might mean a "uniform expansion of volume".  I found it here "expansion and compression of gas" so it might be describing an instant in an expansion.
Comment: Please could you be more specific about your reference to the Homework Solutions document - it has 11 pages.
Comment: @sammygerbil  search for "isochoric" in the document. I give it as a possibility of how "expansion" and "isochoric"  can be found in the same page, as the OP does not give really a context.
Comment: Well I did as you suggest. I found 6 instances of "isochoric" but I don't think any of them can be interpreted as anything other than $\Delta V = 0$. I found no instances of "expansion and compression of gas" nor "uniform expansion of volume". Sorry to be pedantic but I don't understand the point you are trying to make with this reference. The co-existence of the words "isochoric" and "expansion/compression" in the same document does not prove anything.
Comment: @sammygerbil  the question is about the association , "isochoric expansion of an ideal gas" and I am trying to make the OP give the context, maybe it is similar to this. Maybe he /she found it in a similar document" . The "univorm expansion"  I am talking about is similar to the one the chosen answer says: a large volume, a guess, and a gas expanding within it.

Does isochoric expansion make sense?


Acceptable values for discrimination parameter - 2PL IRT Model

Question: What is the acceptable range for discrimination parameters with the two-parameter IRT model? I have information from Baker (2001) but would love additional information. I have heard discrimination parameters must be above 0.5 to be acceptable but am having trouble finding a citation for that value.
Comment: Seems rather arbitrary, though it probably had to do with the author's justification for the information criteria. Slopes that are too small don't discriminate individuals well, and might as well be dropped from the test.  It really depends on the context anyway, and what matters more is the contribution of all the items for test response functions rather than individual item contributions.
Answer: I think that the cut-off of 0.5 is related to the historical factor analysis tradition of requiring a standardized loading of |0.3| (where loadings can range from -1 to 1). To see this, first transform the discrimination value into the standardized loading form with the formula
$$f = \frac{a}{\sqrt{(1 + a^2)}} $$
where $a = \alpha / 1.702$ because of the scaling of the logistic metric compare to the normal ogive. In this case, $\alpha = .5$, therefore the standardized loading is $f = 0.2818$, or approximately 0.3. This matches very closely to the standardized loading cut-off, and is probably the reason why Baker adopted it.
Note that in the same spirit of traditional factor analysis cut-off, this criteria is rather arbitrary and should generally be discouraged. You should be more interested in the meaning of the item to understand if this value is reasonable and contributes some amount of information to your test (indeed, some low discriminating items even have some use at the beginning stages of a computerized adaptive test), and also be mindful of the sampling variability via estimates such as the standard error.
Comment: Useful answer. Question: if I use your mirt package and get IRT parameters using coef() with IRTpars = TRUE, does this use the same 1.702 scaling factor? In other words, if that gives me an a = .50, does that correspond to an f = .28 as in your example?
Comment: @psychometriko the IRTpars = TRUE just performs a transformation into a classical parameterization which is still in the logistic metric. So you'd need to still divide by 1.702 when converting to standardized slopes (see the output from `summary(model)` to check)
Comment: @philchalmers,what's `F`,`h2` in the `summary(model)`?what's the  relationship with `a`?
Answer: In the 2PLM, the discrimination parameter is on the logit scale and thus theoretically could take on any value from - to + infinity. I would not necessarily agree that discrimination parameters have to be above .5 to be acceptable; recall also that they can certainly be negative as well. Size of discrimination parameters will also depend on sample size, response patterns in the indicators, and the corresponding bivariate contingency tables.


Updating a trial webform with a new trialforce template

Question: Our TSO was approved with a previous version of our template. Now we have updated our template and want our webform to be associated with the new template instead of the first template. I have already created new templates and created a new trial but the trial created is off of old template. I quickly skimmed through the webform html and did not see anywhere where the template id was specified. How can I make sure the new trials are created using the new template?
Comment: Same instructions as creating a new one: https://developer.salesforce.com/docs/atlas.en-us.packagingGuide.meta/packagingGuide/trialforce_creating_template.htm
Comment: Please post your current html so we can point where the templateId is - it should be there
Answer: You'll need to log a case. The following paragraph was part of instructions from SF when I first received the web form:

"4. If you want to make changes to your trial experience, please make
  the edits in your source org, create a new template, and log another
  case so support can update your formname with the latest template.
  Please provide your formname, template ID, and source org ID in the
  case description."

Another option is to create a new trial from Environment Hub. It allows you to specify what template you want to use to spin off trials


overnight index swaps OIS

Question: I'm writing a paper where I am using expected federal funds rates at different horizons and wanted to use the OIS as a proxy for what the market expects the FFR to be post FOMC-meetings. However, I can't seem to find the data anywhere. Does anyone know where I can get these and if not, what else I can use as proxies about market expectations about the FFR?
Answer: Just use meeting date OIS - cleanest way to do it.
Sources: inter-dealer brokers such as ICAP, banks, data vendors such as Bloomberg or Reuters.

overnight index swaps OIS


making predictions from detrended data

Question: I am building a machine learning based model (random forest in scikit-learn) to predict maize yields in the U.S. based on data on historical maize yields and temperature and precipitation information. Since there is a trend in maize yields, I detrend the yield data first, then fit the model and then predict for current year. However, I assume that the predictions from the model are detrended as well. How do I go about making predictions that are not detrended? Any pointers and literature reference would be helpful
Answer: If you have detrended your target (maize yields) then you should reinsert the trend to your ML predictions. E.g. For new_yield(t) = yield(t) - trend(t). If p(t) is your 'detrended' prediction then your retrended prediction is p(t) + trend(t).
Check this free ebook:
https://otexts.com/fpp2/decomposition.html
Answer: I'm just guessing but I can think of two options:

Train the model from the original data, including features which represent the current trend so that the model can integrate it. It makes the job of the model more complex so it might not work very well.
Since you can untrend the data I assume that you can calculate the trend function. So you could train an independent model for this trend function and apply it on the predictions obtained with the untrended model. In this case performance depend how accurately the trend is predicted.

making predictions from detrended data


phase transition by sublimation

Question: Why do sublime solids sublimate in the first place? Is it that their melting point and their liquid's boiling point are the same so that they manage to magically skip the liquid phase? (if so, why does it have to be so?)And is the reverse possible?
Answer: $CO_2$ sublimates at atmospheric pressure, lets have a look at the phase diagram.

Now if you notice the triple point exists above atmospheric pressure. Below this the system  can only transform directly from the solid to the gas phase and vice versa by changing the temperature. At the triple point the substance can coexist in all three phases at one distinct temperature and pressure. Beyond the triple point the three phases are distinct with respect to temperature, so via heating or cooling you can witness all three different states.
The opposite of sublimation exists and is called deposition, an example of which would be frost.
A link to a deeper explanation:
http://www.av8n.com/physics/melt-sublimate.htm
Comment: While helpful, the phase diagram isn't so much an explanation for phase changes as a concise collection of phase change data. I don't mean to put you down, I'm just hoping someone touches on the thermodynamic explanation based on free energy.
Comment: yeah, It would be better if yo hit upon the thermodynamics directly
Comment: The answers given above are not the explanations, but more the statements of this same fact in more accurate terms. The explanation should appeal to a theory of the phenomenon. I, however, have never seen such a theory before. I may guess that this is due to the fact that the crystallization transition is very poorly understood. As much as I know, only a so-called, weak crystallization theory is developed (see e.g. Kats et al, Physics Reports, 228, pp. 1–91 (1993)). The weak crystallization, however, does not describe such cases as the CO2 mentioned above.
Comment: Without such a theory, one cannot explain the triple point gas-liquid-solid. This was, at least, a status about 10 years ago, when I stopped to follow these works. I would be delighted, if something have changed since that time.
Answer: Solids may sublimate because they are below the critical pressure, at which the solid has to liquefy upon heating. The boiling point changes depending on pressure. If the solid is at a pressure below which it liquefies, it can go directly to gas. And yes, the reverse is possible. Deposition is the name for this process. Dry ice is  deposited carbon gas, which solidifies because the pressure is not high enough for carbon to liquefy at low or ordinary temperatures.

phase transition by sublimation


jQuery in sharepoint returning Object Expected

Question: When I add jquery to sharepoint 2007 (MOSS) and try and use it on a page no matter what I write on the client i get an "object expected" at the line/column where the "$" appears.
I have used fiddler to check that the client is downloading the query JS (which it is)
But its like its being ignore and therefor eth "$" is not understood.  Searching google everybody is saying its the selector not finding the elements but see code below I do not see how it can not find my very simple example.
In master page in header

version 1.4.2
On a page
  Testing

Answer: Put your JS right at the bottom of your page and rewrite it as:
        $(function() {
        function abc() {
            $("#simon").css("border", "3px solid red");
        }
    });

Answer: It might be using jQuery in noConflict mode, so try using:
jQuery("#simon").css("border","3px solid red");

Answer: I'd change to this overall:
Testing

Content Here

Best to attach your events as handlers instead of in-line, and you need to this on document.ready, which $(function() { }); wrapping does.  This also lets you do all this in an included javascript file instead of including it in the page every time.
Answer: Problem seemed to be that I was using the jquery from Googles CDN, downloaded from jquerry.com and now works.
Thanks everybody for your answers, very helpful.
Simon


How do I recover my questions from a closed account?

Question: How do I recover the questions I asked before I closed my previous account. I closed my first account which is under the same name on the account I am using now, I noticed that after I closed my first account my questions and answer appear under  user35499. The closed account was under the same username that I now currently used.
Comment: I'm not sure you can get them back. I suggest you ask at [meta.se].
Answer: Being incredibly old-fashioned, I keep a log of all links to my questions (and all my answers). This is on my computer, and I also print-out hard-copy stored in a clip-file. Dates are essential, of course. This will be of no use to you for 'lost' questions on your closed file, but I mention it so that you might start afresh, doing that, from now on. This is a "closing-the-stable-door-after-the-horse-has-bolted" answer, yet it might be helpful from now on. I hope so.


AD: Roll out an MSI application at midnight

Question: Using Windows Server's Active Directory and Group Policy, is there a way to roll out an MSI file at a scheduled time, like midnight?
Answer: Strickly speaking no.  GPOs are not scheduled tasks.  They run when the system updates (reboots, etc).
We use Quest's GPOAdmin.  It allows for time-based deployment of GPOs.  This could help somewhat.
Sounds like you really need a software deployment systems (SCCM, LANDesk, etc)
Comment: Sounds like he needs a scheduled task, set to run at midnight, to reboot the machines that are running and wake machines that are asleep. I do this kind of thing fairy frequently. It's very handy.
Comment: Thanks for your answer. It took me a while to create a mirror account here. As a product developer the problem is using a baseline that all clients will have, and it is a disappointment to see that GPO and Active Directory only provide "immediate" deployments, but no forced "run x script daily at 4pm regardless of whether someone's logged off"


Oracle Script -Materialized View & synonym

Question: I've got a question about script in Oracle!
I have a materialized view on a prebuilt table, in my BBDD, (this MV is of the user DAT_OWN, other 2 user (APP & BO) have synonym on this MV)
I have to change the MV and add a column. I know that I need to drop this MV and create a another one, but what's append with the synonym?
I have a previous script like:
DROP SYNONYM APP.STAT_VOZ;
CREATE SYNONYM APP.STAT_VOZ FOR DAT_OWN.STAT_VOZ;

DROP SYNONYM BO.STAT_VOZ;
CREATE SYNONYM BO.STAT_VOZ FOR DAT_OWN.STAT_VOZ;

DROP MATERIALIZED VIEW DAT_OWN.STAT_VOZ;
CREATE MATERIALIZED VIEW DAT_OWN.STAT_VOZ
ON PREBUILT TABLE WITH REDUCED PRECISION
REFRESH COMPLETE
START WITH TO_DATE('21-ene-2013 19:20:00','dd-mon-yyyy hh24:mi:ss')
NEXT (trunc(SYSDATE,'HH')+19/72)
WITH PRIMARY KEY
AS
  SELECT           TO_CHAR (SUM (COUNT)) AS sum_count,
         start_date AS date_hour,
         input_type AS input_type
    FROM DAT_OWN.another_table
   WHERE start_date > TO_CHAR (SYSDATE - 60, 'yyyymmdd')
GROUP BY start_date

Why would somebody do a drop synonym APP and create synonym APP drop synonym BO and create synonym BO BEFORE dropping of the materialized View?  In my opinion, I have to do
drop synonym1
drop synonym2
drop Mview
create Mview
create Synonym1
Create Synonym2

I'm sure that the programmer before me did a good job, but I can't understand why they did it  that way! Can somebody explain me this, please?
Regards
Answer: Your original script was probably just written by an "old school" developer. Most people are accustomed to dropping objects immediately before recreating them.  As you've noticed, the sequence is not important.
Most people these days use CREATE OR REPLACE syntax instead of first dropping the object.  Here is a good explanation of that concept.
Answer: There is probably no need to touch either synonym in the script.
A synonym is just a pointer.  There is no requirement that the object pointed to by the synonym exists at all.  If you simply drop and re-create the materialized view, the synonyms will automatically point at the newly created materialized view.  Of course, after the materialized view is dropped and before it is recreated, if a session tries to use the synonym to query the materialized view, that session will get an error that the object doesn't exist.  But, presumably, you're waiting to drop and recreate the materialized view until no one will be using it so that generally isn't a major concern.


Can two different objects or system of molecules have different temperatures, but having same internal kinetic energy?

Question: If I take an extreme case, where a body has only an internal potential energy with zero internal kinetic energy, does this body have a temperature? Another question related to it: if two objects A and B having different temperature: A: having only internal potential energy and B having only internal kinetic energy, can heat flow from A to B ?(temperature of A > B)
Comment: If A has only internal potential energy, its temperature is 0°K. It can't be hotter than B.
Answer: Yes.   According to the accepted theory of gases, a diatomic molecule
(like N2) has both translational kinetic and rotational kinetic
energy, five partitions (two rotation axes, and three directions of travel
in space), which each can hold kT/2 energy, on average, for
a total thermal average energy of 5kT/2.     A neon atom, on the other
hand, cannot hold rotational energy (it is too cold, at any ordinary
temperature, to hold one quantum unit of angular momentum along
any of the three directions), so holds a total thermal energy of 3kT/2.
So, air (containing both neon and nitrogen) fits the description.
Different amounts of energy at the same temperature means different
heat capacities, there are  many examples (and this is only one).
Comment: It's not possible for a spinning diatomic molecule (N2) to transfer
Comment: Sorry, but this answer does not seem to answer either of the questions asked.
Comment: Great. Then if both have different kinetic energies why there's no transfer of heat between them? (I know both are at same temperature)
Comment: A transfer of heat DOES happen from time to time, but the complex (diatomic) molecule has multiple heat-containing modes (including rotation of the molecule) and the monatomic gas can only gain/lose momentum in three directions.   Statistically, the extra modes of the N2 molecule mean it has more heat energy per molecule, on average, than the Ne atom.   Actually, Ar (argon) is a more likely air constituent.
Answer: If a body (substance) has zero kinetic energy then we should suppose that it is a perfect crystal at absolute zero and all motion is in the vibrational ground state if it is a molecule. If an atomic solid then only zero point motion in the lattice. So yes it has a temperature. The potential energy is that within and between the molecules or atoms.   In your second question if the temperature is different in two isolated bodies but in contact with one another then energy will flow from one to the other until equilibrium is reached. Energy is always convertible from one form to the another.
Comment: Energy is always convertible from one form to another???? Consider a chemical explosive at close to 0°K. It has an enormous amount of internal potential energy. It has very little internal kinetic energy. Is its chemical potential going to spontaneously turn into heat? How long do you have to wait for this to happen? I think this is essentially the OP's question, but I'm not sure.
Comment: Yes, energy is always interconvertible, we see it happen all the time. Molecules convert potential energy into kinetic energy and vice versa every time they vibrate in their normal modes. Your explosive molecule does have zero point energy, kinetic and potential at 0 k and bond energy. It always has the potential to explode but only if you give it enough energy to reach the activation energy will it do so rapidly. We exist at room temperature and are exothermic wrt burning in oxygen, luckily activation barriers are large. Thermodynamics says nothing about the rate of reaction.


Cannot connect after Availability Group automatic failover

Question: We have a SQL Server setup with Availability Groups. In the cluster we have four nodes, two in one datacenter and two in another datacenter.
There are four AGs on these cluster nodes, each primarily on one of the four nodes. One other node is in the same datacenter for synchronous HA and the other two for asynchronous in the other datacenter for DR.
We have one listener for each AG.
One AG seems to automatically failover at certain times due to various Network issues; however, the AG seems to failover fine. The HA secondary becomes primary, and all databases come online. However, applications seem unable to connect and we see various connection error type messages such as:

Cannot connect to SQL Server instance 'HH-SQL-D11' :
A transport-level error has occurred when receiving results from the
server. (provider: TCP Provider, error: 0 -
The semaphore timeout period has expired.) : The semaphore timeout
period has expired [121] (requires acknowledgement)

and

named pipes provider error 40 the network path was not found

Yet when we failover manually the connection is fine and works as expected. Other AGs on the cluster have automatically failed over and have worked fine. I have checked various things like the SQL Instance is up, TCP/IP and Named pipes enabled, remote connections enabled. I have asked the networks team to check things like firewalls and they say they are all ok.
I have tried to read the cluster logs but I am not sure what to look for in here and I am unsure of how to fix this issue. It's a problem as it means that HA is not operating. And if it does failover automatically, applications connecting to it will not work.
Comment: What about you ? After that automatic failover, can you connect in SSMS using the listener ?
Comment: I cannot connect to the listener using SSMS or even ping it or its IP address through a cmd prompt.
Weirdly though it seems as if my monitoring tool (Spotlight) can connect.
Answer: If you cannot reach the listener from SSMS, then it seems to be an issue with networking or name resolution (DNS).
You can try do to a NSLOOKUP of your listener and make sure it point at the primary node. If not, it means you have an issue with DNS update. Your windows admin should be able to help you.
If it points to the right server, but you cannot ping it or connect to it, then I would provide that information to the network team, asking them to assist with this specific situation.


What creature could this be?

Question: I've had a friend, in a 3.5 / Pathfinder game, pull up a creature with abilities I haven't seen. It (in his description) was a shade, but it had the ability to mimic my movements and upon contact, take my physical form and turn me into a shade.  Any explanation?
Comment: Do you have any more information on it? Because from this description it could be any number of creatures. 3.5 has a LOT of books.
Comment: Did the DM control this (*ahem*) shady creature or was the "shade" a fellow PC? When this "shade" touched your character, what happened? (Did you keep or lose control of your character? Did your character gain or lose special abilities?)
Comment: Remember it could possibly be a homebrewed creature!
Comment: +1 for homebrewed creatures. Nothing is more boring than having players ID some creature and them have a script for dealing with them because they've read the Monster Manual or whatever too.  The unknown is where the excitement lies. "There are more things in heaven and Earth, Horatio, than are dreamt of in your philosophy"
Answer: That's the Shadow Simulacrum Template
It was introduced in Shadowdale: The Scouring of the Land (pg. 156).
The template can be applied on a living creature, it must have 10 HD or more, and a minimum Charisma score of 6.
It grants a Supernatural Ability called Possession, which works similarly Magic Jar, but with some changes. This posession has no set duration, and no way to free the target is given, other than killing the possessed target, or abilities that specifically deal with posessions.
The creature is incorporeal when not possessing another creature, and lives on the plane of shadows.
The Shadovar
In the Forgotten Realms campaign setting, there are a group of shades called the Shadovar, which were created by a specific ritual that infuses a creature with part of the plane of shadows.

By removing a part of your soul and replacing it with the essence of shadow, a Shade could be produced. This is an extremely complex and painful process but the result is a being with a prolonged life, and a greatly strengthened set of abilities when in the presence of shadows.
Comment: Interestingly, while the template *can* be applied to any creature that meets the listed criteria, a creature can only create a shadow simulacrum of *itself.* (So, for example, if this is the correct answer and the PCs got a good look at the shadow simulacrum (no easy task!), the PCs may be able to discern its creator.)
Comment: Various other supplements have provided general rules for exorcism, though, that would presumably apply to this creature's possession as well.
Comment: Indeed. I was refering only to the ability as given though. Specific rules should be able to remove the posession.
Comment: Im unsure how to explain how his friend became a shadow, but that most likely was due to it being victim of a shadow shard, not the shadow simulacrum herself.

What creature could this be?


Change commerce kickstart admin toolbar logo

Question: Hello I want to change the logo of the admin toolbar of commerce kickstart how to do it I cannot find any .tpl with that piece of code for chage that logo
Answer: Ho it was easy, just add a css class in your subtheme css with the class
<code>body.toolbar #toolbar-home a span
</code>
from there you can change the background image
Answer: Your self-answer will only work if you are using the Overlay module.  If you aren't, you can go to profiles/commerce_kickstart/modules/commerce_kickstart/commerce_kickstart_menus/images and overwrite the logo-menu.png image with another 130x40px sized one.
If you want to change anything else in the toolbar (logo size, colors, etc...), that's also the module to look at.
Comment: Do not forget: Your logo get's overwritten on every Commerce Update. You have to re-apply those changes.


More console information on error in xcode

Question: Hi I've got this error in my console :
2012-05-25 15:42:32.157 Mehdi Bensafi[426:f803] *** Assertion failure in -[UITableView _endCellAnimationsWithContext:], /SourceCache/UIKit_Sim/UIKit-1914.84/UITableView.m:1021

But I want more information, is it possible ?
For example I've seen some complete error message like this :
An exception was caught from the delegate of NSFetchedResultsController during a call to -controllerDidChangeContent:.  Invalid update: invalid number of rows in section 0.  The number of rows contained in an existing section after the update (5) must be equal to the number of rows contained in that section before the update (5), plus or minus the number of rows inserted or deleted from that section (0 inserted, 3 deleted). with userInfo (null)

Answer: Use the backtrace (or bt) command on the console.


Dolphin file manager hangs when opening a directory from the terminal

Question: Whenever I attempt to open a directory with dolphin (both with dolphin /home/user and dolphin --select /home/user) from a terminal it hangs, which seems very odd since opening dolphin without specifying a directory works fine (just dolphin). I suspect this is the reason why xdg-open and other applications file dialogs do not work. Any idea why specifically passing in a directory would break things? Distro I'm using at the moment is nixos
Answer: This is only a partial answer, and quite frankly more of a hack than a solution imo, but it does seem to fix the issue with xdg-open and other applications file dialogs, which was the motivation for me posting this to begin with.
If you make a copy of the org.kde.dolphin.desktop file, place it within $XDG_DATA_HOME/applications, and edit Exec=dolphin %u to be Exec=dolphin --new-window %u, xdg-open appears to function properly (along with application file dialogs).
This still doesn't fix the underlying issue however, without that flag dolphin still hangs. Furthermore, upon more inspection from me attempting to solve the problem this wasn't the only argument that causes dolphin to hang. --daemon also appears to cause dolphin to hang as well.


What is the evidence for laryngeal in *méh₂tēr?

Question: Wikitionary shows a PIE word *méh₂tēr but I never seen this word spelled with a laryngeal. There was a long vowel there but how is it correct to analyze it to be *-eh₂- rather than just *ā?
Comment: I don't remember that much about PIE, but isn't it (sometimes?) assumed that PIE had no /a/-like vowels, and that hence all later a's are due to vocalization of nasals, laryngeals, and whatnot?
Comment: It seems that Cerberus is trying to describe the Laryngeal Theory.
Comment: @Cerberus I never heard this theory. There are roots with -a- along with roots with -e-, although there are relatively few of them.
Comment: Quite a few IEists hold the theory Cerberus mentioned.
Answer: Depending upon the specific view that one accepts concerning the development of the accent systems of Baltic and Slavic, the Baltic cognate would compel a reconstruction with *h2.
Lithuanian (nom.) móteris [the acute diacritic here indicates the surface word accent] 'woman' belongs to the third accent class, which indicates that the stem moteri- contained a so-called "acute" intonation (the use of the terms "acute" and "circumflex" in Baltic and Slavic accentology is fraught and convoluted -- beware). If one follows the position of Kortlandt (though also more or less sustained in Petit's recent Untersuchungen zu den baltischen Sprachen) that only IE laryngeals or voiced stops in syllable codas could eventually produce "acute" intonation, then the reconstruction *meh2-ter- would be necessary.
Furthermore, insofar as one does analyze the word into a root and suffix -ter, no IE root whatsoever that participates in derivation lacks a consonant following the root's full-grade (confer the roots in the Lexicon der Indogermanischen Verben). IE grammatical elements that lack final consonants consist exclusively of particles (e.g., *su 'good, well'), prepositions (e.g., *pro 'before'), and pronouns.  Thus, IE constraints on licit root structures would exclude *mā- as a root. So even setting the Baltic considerations aside, *meh2-ter remains a preferable reconstruction.


Measure the the impedance of a 'black box' under two symmetric frequencies

Question: I often see some equipment measure the impedance of a 'black box' with symmetric frequencies (the black box may be a complex high order network, but not only a simple one order). Such as if we want  to know the target circuits impedance under utility frequency, but in order to minimize the utility frequency interference, they may measure it at fu+5 and fu-5, then use their average as a result. I think there may exist some 'approximation'. Any one can give the math in detail?
Comment: give links to specs of "some equip"
Comment: Such as overhead power transmission line parameter measurement equipments.
Answer: I think you are referring SFRA line impedance analyzer which can measure from mHz to MHz.
It works on the basic principle like a Network Impedance Analyzer except with HV power lines using capacitive voltage couplers. I think it uses a constant current swept frequency sourcing with sophisticated signal processing.
It may also include Partial Discharge impulse sensing detectors.
Search Doble and Omicron equipment.
Value $50k ~ $150k
Purpose
Effective maintenance test techniques and diagnostic measurements to improve the
performance and reliability of Power System Transformers. (Assets worth $0.5m ~ $5m)
Uses
• Turns ratio, vector group and excitation current measurement
• Static winding resistance measurement
• Dynamic winding resistance measurement to test the On-Load Tap Changer (OLTC)
• Sweep Frequency Response Analysis (SFRA) measurement
• Frequency dependent capacitance and dissipation factor measurement
• Di-electric Response Analysis
• Partial Discharge (PD) measurement


How closely does the Initial D anime follow the manga?

Question: I have been watching the Initial D anime, but still haven't read the manga. How far does the anime cover, in respect to the manga? Are there any manga or anime exclusive content?
Answer: Altough the series stays pretty loyal to the story as told in the manga, there are a few exceptions. But these don't influence the story that much. One of the biggest factors affecting this is that a lot of the story in the manga got cut out.

We Initial D fans love those little details. It's a shame they had to cut out so much in order to fit one race in each episode. Watching Fifth Stage almost feels like watching an extended version of Battle Stage... And for that reason, it's strongly recommended to read the manga after watching the anime. That way, you don't miss all the details from the original storyline. - ID fan forum

As to where to how much it covers, Fifth Stage episode 4 ends at Chapter 499. (I stopped reading at chapter 501, so I ain't too sure how far the rest of this season covers.) I do know that the new season Initial D final stage will cover the left-over chapters, making this series fully covered by the anime.
With this said, there is a ton of manga-exclusive content: like I said, a lot has been cut-out in the anime. There is also some unique anime content (fillers) in the series. A few I remember would be Initial D Episode's 13, 22, and 23.
There might be some more but I couldn't find a source to confirm this.
Comment: I made some edits for grammar -- on the off-chance I'm changed the meaning of something (I'm slightly unsure about one change I made), my apologies, and do make any appropriate changes.
Answer: In the manga that was translated by Tokyo Pop, Itsuki did not crash by Shingo but after Takumi drove Iketani's S13 Shingo challenge Takumi to a Gum tape death match all at the same night in the manga.


What is the difference between developing personas and scenarios?

Question: Personas is more about who the user is, while scenarios are more about the situation the person is in. It sounds pretty simple to grasp, but when developing personas and scenarios the difference becomes hazy.

How do personas affect design decisions in a way that differs from scenarios?
Scenarios are built upon personas, but can personas be built upon scenarios?
How can I differentiate between the two? Especially while I am brainstorming?
Answer: Persona contains a lot of information, including demographic, personal and social data, possible working environment description, his needs and goals.
For example, persona's age could lead designer to some decisions in visual design of a system. Usage frequency could affect information architecture of a system.
Scenario includes persona and scenario not only aligned with persona's goals, but implements concrete user's task. So user goals from Persona divided on set of tasks, which are the core of every scenario.
Analysis of existing scenarios could give some insights and ideas on Person, so the Person could be improved, a kind of reverse engineering. But using scenarios as the only source for Person creation is bad idea. Scenarios are too narrow for this task.
To distinguish Person and Scenario you could use the sentence structure analogy: Person is a Subject, Scenario is a Verb. But distinguishing while brainstorming possibly not good idea. This could be done in analysis phase.
Answer:
How do personas affect design decisions in a way that differs from scenarios?

You build persona's to help understand (and spread understanding) of who your users are. They're about breaking away from simply designing from use cases, scenarios and task analysis. They're written in a way that creates a richer image of what a user may do or feel when using your product. They help remind you that your product exists in a wider context that is different from one user to another.

Scenarios are built upon personas, but can personas be built upon scenarios?

Scenarios and personas should be part of a living and breathing design document, where each step and every discovery feeds back into (and improves) steps already taken. Thinking about scenarios with the personas in mind will inevitable provide new insight into your personas.

How can I differentiate between the two? Especially while I am brainstorming?

From Sleeswijk Visser, F (2009) Bringing the everyday life of people into design  :

A persona makes the data more lively and addresses socio-political and 'quality of life' is- sues, including the values, fears and aspirations of the users. 'They have names, likenesses, clothes, occupations, families, friends, pets, possessions and so forth. They have age, gender, ethnicity, educational achievement, and socioeconomic status. They have life stories, goals and taks. They are not 'agents' or 'actors' in a script, they are people.' (Grudin and Pruitt, 2002). A persona must be liked.

If you're putting too much scenario into your persona in a way that doesn't add to the above, you're probably making them too specific to the problem you're trying to solve. Your persona's should be like people, not simply actors in a play about your product.
Answer: A persona is a rich picture of an imaginary person who represents your core user group.
A scenario will have several
of these personae covering different types of intended users and different roles. The personae will
themselves be based on studies of actual users, observation, etc.


Can I post answers or some code that I have created to stack overflow?

Question: Lets say I just want to share with people and provide code, should I post code using the question method or is there some other way?
Answer: Assuming this is related to the actual site and not just a desire for a blog or something, the info you want to share should be put in a Q&A format.
But you can answer your own questions easily and actually immediately. There's a checkbox when you ask a question to immediately provide an answer to your own question at the same time the question shows up.

I always felt this is a weird thing to do (it looks like someone talking to himself), but I've seen some users utilize this to great effect. Here is one example: What's the standard/official name for universal references?
This is a very useful question, likely on the mind of many C++ users, with an equally useful answer.
You should make sure you have something truly worthy to share. The question should be something a lot of people are wondering about, and the answer should really hit the spot. But if you have info to share which fits this format well then I'd suggest go ahead, answer your own question immediately.
Answer: I'd recommend you create your own blog for that. You can easily create a Jekyll-based blog on GitHub nowadays which will also allow other developers to contribute back to you (e.g. via pull-requests). https://pages.github.com
Alternatively, you can use one of the many other great static site generators out there: http://www.staticgen.com