Diagonalizable Matrix real values

Question: Let $A=\begin{pmatrix}
        a & -b  \\
        b & a \\
        \end{pmatrix}$. For which real values of $a$ and $b$ is $A$ a diagonalizable matrix?
Answer: The characteristic equation of $A$ is
$$(a-\lambda)^2+b^2=0\ .$$
If $b\ne0$ then this equation has two different solutions and the matrix is diagonalisable.  On the other hand, if $b=0$ then $A=aI$ which is already diagonal.  So the matrix is always diagonalisable.
However there is a proviso: if $b\ne0$, you will need to use complex numbers in the diagonalisation.  If you are looking for a real diagonalisation, this is possible only when $b=0$.
Answer: Although David's answer already provides a sufficient algebraic explanation, I'd like to give a bit of a geometric one. Consider where this matrix sends the standard orthonormal basis
$$ \begin{pmatrix} a &- b\\ b & a \end{pmatrix}\begin{pmatrix} 1\\ 0\end{pmatrix} = \begin{pmatrix} a\\ b  \end{pmatrix} =v_1, \begin{pmatrix} a &- b\\ b & a \end{pmatrix}\begin{pmatrix} 0\\ 1\end{pmatrix} = \begin{pmatrix} -b\\ a  \end{pmatrix} =v_2 $$
Note that $v_1, v_2$ are orthogonal with lengths $\sqrt{a^2 + b^2}$. If you look at some cases youu'll probably notice that $v_2$ is always 90 degrees counterclockwise from $v_1$. This, is because if we write $a/b = \tan(\theta)$, and thus have $\sin(\theta) = b/\sqrt{a^2 + b^2}$, and $cos(\theta) = a/\sqrt{a^2 + b^2}$ then we can rewrite
$$ \begin{pmatrix} a &- b\\ b & a \end{pmatrix} = \sqrt{a^2 + b^2}\begin{pmatrix} \cos\theta & -\sin\theta\\ \sin\theta & \cos \theta  \end{pmatrix} $$
Which shows that our matrix is the composition of a scaling and a rotation. A rotation has real eigenvectors only if it is by $2\pi, \pi$ (half rotation or full/no rotation) in which case it already diagonal. The scaling of course, will not affect our analysis of diagonalizability.
As a final note, there is a beautiful reason why we should care about matrices of this form. They form a subring of all two by two matrices (that is, they are closed under addition, subtraction and multiplication). And in fact this subring is isomorphic to the complex numbers by the map $$a+bi \mapsto \begin{pmatrix} a &- b\\ b & a \end{pmatrix}$$
And even moreso, the map $\mathbb{R}^2 \to \mathbb{R}^2$ given by these matrices, is the same as the map of multiplication by $a+bi$ from $\mathbb{C} \to \mathbb{C}$.

Diagonalizable Matrix real values


Vaccination and Immunisation

Question: Why are oral polio vaccines advantageous over the killed ones?  I was told that the orally given polio vaccine prevents infection by causing intestinal immunity. How does it do that? Also, how does this make it superior over the intravenously injected polio vaccine?
Comment: What research have you done on your own to answer these questions yourself? For example, Google searches or even simply reading the Wikipedia pages for `polio vaccine` and `intestinal immunity` would give you a lot of information. The Biology.SE community has agreed that **questions that show little or no prior research effort** are off-topic on this site **unless you have shown your attempt at an answer**. Please [edit] your question and tell us where you've looked for answers, what you *do* know about the topic, and where exactly you still have questions.
Comment: There is a killed oral polio vaccine?
Comment: Just look up the 'cutter incident'. Use of OPV is more of a historical and silly reason than the IPV. For example, India after recent eradication of polio has started to switch from OPV to IPV. There are serious plausible risks of using OPV but was still used due to one cutter incident that tainted IPV
Comment: @polisetty thanks. For your reference. It did help. PS: irrelevant though I wanna say this :/ (don't blame me) I guess I know you! Vashishta polisetty?
Comment: @user129402 yup :) Hope I'd known you too.. only if you could give yourself a name :P
Comment: @user129402 because it's the virus's natural route to infection, hope you now understand.
Answer:
Oral polio vaccines are delivered in the site of the potential infection. You may think about them as about a realistic simulation of the infection. As it is not scientifically sound explanation, please see the answer about whether intramuscular vaccination leads to intestinal IgA secretion which protects against intestinal route of infection.
Oral polio vaccine (Sabina) contains attenuated (alive but weakened) polio virus, which can proliferate and compete in the environment with the really dangerous wild polio virus. That way also people which has not been  directly vaccinated may be protected - both by development of immunity after less severe infection, and by reduction of exposure to the wild virus.
The route of delivery is much more acceptable by children.

Vaccination and Immunisation


What are the rules on using the Stack Overflow logo?

Question: I want to use the Stack Overflow logo as an image on a blog post about this site.  What are the rules on using it?  Can I use it in any way?  Can I chop the words out and just use the image, or must I keep it intact?
Return to FAQ index
Comment: I really don't think you need *permission* to use the logo in a blog posting about the site. Do you need *permission* from Wal-Mart to write a blog entry about them and use their logo illustrating it? Even if you vandalize the logo, it's protected speech and fair use.
Comment: You can always make your question community owned and the downvotes won't hurt your rep at all. :)
Comment: @Jeff: I'm not sure but I believe you would need need permission from Wal-Mart to use their logo regardless of wether what you say is positive or negative...
Comment: Joel Spolsky has posted ... that should be pretty definitive.
Comment: For those who would use the logo linked to their profile: https://fontawesomeicons.com/stack-overflow
Answer: It is a trademark. The purpose of trademark law is to prevent consumers from being misled as to the origin of a product. So if you were making a product, and you used the name Stack Overflow or the Stack Overflow logo in your product or its advertising, in such a way that would mislead some consumers into thinking that your product was Stack Overflow, you would be violating the trademark and this would not be legal.
For example if you started a website called "Stack Overflow News" and used the logo, that would create confusion... people might think that the site was a part of Stack Overflow or was officially endorsed in some way. If enough people were reasonably confused as to the origin of your site, it's a violation.
The logo image itself is copyright. Copyright is different than trademark. Ordinarily you couldn't copy it. But if you were writing a news story or blog post about Stack Overflow, reproducing the image would almost certainly be considered "fair use" and thus permissible.
If you were writing a blog post, say, about Stack Overflow, for example, and the blog post was a description of the site, maybe a review, and there was no possibility that anyone reading that blog post would think that in some way YOU were Stack Overflow, then using the logo would be fair use under copyright law, and allowed under trademark law because you were not using it "in trade."
Trademark law is a lot more complicated than that, so you'd have to consult with a real lawyer if you thought you were doing something iffy.
See also our Stack Exchange Logos page and Trademark Guidance page.
Comment: he doesn't need to. If SO is a LLC (ie a proper company, and I'd expect J and J to have set it up like that), they get it automatically - you can't also call your company SO without passing off. But if you use the logo in an article ABOUT SO, thats usually fine.....
Comment: I can't find any trademark claim anywhere on the site; Jeff needs to fix that ASAP.
Comment: ... but use the logo (or part of it) for a development site - no way. Now, it gets murkey if you started a company called SO, but it was NOT in the software space at all. Then people MAY not be confused about which is which etc.
Comment: I'll add that even if you do something that could be technically legal, and a trademark or copyright owner might disagree and still try to take you to court over it with no repercussion aside from their own legal costs.  Defending yourself can be expensive, so you have to be very careful.
Comment: @JoelCoehoorn: But given that it's *Joel Spolsky* who said this, it seems unlikely that Stack Exchange would get very far in any attempt to sue a blogger for using one of their logos in a review.
Answer: There is a creative commons link on the bottom of every page, but it's unclear whether that covers all content or only question/answer content.  For lack of a clearer definition, you can probably get away with using the "all content" definition (pending remarks from Jeff Atwood or Joel Spolsky, of course).  Also, even if the site founders intend the logo to also have a CC license, the graphics designer they hired to create it may still have a say in that.
Finally, the CC license would only cover copyright.  The logo is being additionally used as a trademark, and while it's not registered (at least, they don't use the little ®  symbol),  you could still have issues just throwing it anywhere.
As long as you don't do anything that could cause 'consumer confusion' — where a someone might accidentally think some service provided by you is in fact provided by StackOverflow — you ought to be okay in that regard.
Answer: I'd just go ahead and use it.  If you are blogging about this site I think it is fair game given the CC thing and lack of TM or R logos.  If they have a problem with it they can contact you.
Given that you plan on using it to link/post about SO then it is probably appropriate.
I'd probably put something int he post about the logo being the property of SO or taken from SO.  (Can't say it is registered TM because I don't think it is)
Answer: Caveat: I am not a lawyer.
Common sense says: without explicit permission, don't do it - the logo is intellectual property that does not belong to you. Using it implicitly implies affiliation with and/or endorsement by Stack Overflow, which you do not have. Using it without permission invites a lawsuit. Whether the logo is trademarked or not is irrelevant. Would you use IBM's logo on your web page without their permission? Of course not. The same applies to any other business.
Best advice: follow Jeff and Joel on Twitter and just ask them for permission.
Answer: You might want to consider asking the people behind firstname.lastname@example.com (Click the 'contact us' link at the very bottom of the site
Answer: OK, so my comment on Joel's post got long, so here it is as an answer :)

I want to use the stackoverflow logo
  as an image on a blog post about this
  site. What are the rules on using it?
  Can I use it in any way? Can I chop
  the words out and just use the image,
  or must I keep it intact?

OK, so you are writing an article about Stack Overflow. You are not in any way claiming to BE Stack Overflow, just writing about it. Then I would say you are good - there is nothing that can OR should be done against you by Stack Overflow Ltd. It's the same as if you write about Microsoft, you can use their logo, for example, as an illustration to go with the article.
I'm not sure on the legalities about having to file for TM protection, but general use says you are good - the same as general use (or whatever the legal term is) says that Stack Overflow Ltd have the rights to their own logo, even if they haven't officially (tm)'ed it.
Now, if you were using it as the logo for your blog or company, then: hell no. Even if your Stack Overflow Ltd was involved in something like paper stacking machines, it's still a confusion for a customer - just think about Apple Computer vs Apple Corps (the Beatles recording company) or iPhone (Apple) vs iPhone (Cisco). Both of these were settled in and then out of court. I think Apple lost (that is, had to pay) both, and it cost them a few million. Also, why is the Apple TV called Apple TV, and not iTV? Google "eye TV" from Elgato, which is an Mac-only TV tuner....*
So yeah - if you have a blog post about Stack Overflow, and want to put the Stack Overflow image inside the post: I can't see how Stack Overflow Ltd (ie, J and J and G and .... damn it, what's the other guy(s) names?) would have a reason to do anything "to" you. Even if your blog post said "Stack Overflow sucks munkeys, d00d". Are you legally allowed to do it? I'd say so, tho IANAL, and the worst that would happen is you'd get an email from J and J asking you to remove it.
I would try to use the image as-is if you can, BUT if you can find just the logo anywhere (it's in the favicon for example) then they have used that on it's own, so it's logical that you can too...

I think in this case, Apple decided not to turn on one of their more popular 3rd party vendors, so they just chose a better (IMO) name for the product. And they would have lost in court (Elgato Systems has been around for ages).
Comment: There's a UK independent TV channel called ITV (actually they have about a brazillion channels now)
Comment: yes, but they are not in the US, they got to the name before apple, and there is no confusing a consumer device and a TV channel, tho there is more overlap.... :)

that said, I work for their competition (BBC)


What are the differences between tactical and positional chess?

Question: Does one style of play have an advantage/disadvantage over the other?
Are today's GMs mostly tactical players or positional players?
What GMs should I follow if I want to be more of a tactical player or positional player?
Comment: Whoever down-voted, care to explain why?
Answer: I don't think one style has an advantage, or at the GM level, there would only be one style; the other would be extinct.
The very definition of a tactical player is Mikhail Tal AKA 'The Wizard of Riga.'  Others include Bobby Fischer and Garry Kasparov.  Anatoly Karpov and Tigran Petrosian are great examples of positional players.
Fischer himself said that tactics flow from a superior position.

Edit: I'd like to add that any of the top players can find the best move in a given situation. Where positional versus tactical considerations come into play is where there isn't a best move, as such.  That is, when there are several reasonable candidate moves.  Then some players show a positional tendency while others show a tactical tendency.  Petrosian, who is probably the most defensive GM, was more than able to uncork technical savagery if his opponent let him.  However, he preferred to tighten the noose instead of looking for a brilliancy.
Comment: I have always been interested in Mikhail Tal.
Answer: Tactical playing style has no advantage on positional playing style, and vice-versa.
Although, a single player may have a psychological edge on another player with opposite playing style, in specific situations. In a tournament, for example, if a positional player knows that he's facing a tactical opponent that for some reason needs the full point, may choose a solid system with very few victory chance but no weak points. The tactical player will probably try to force combinations even if the position on the board wouldn't allow such tactics. Then the solid player will only have to defend (supposing he's good at this), and take the full point himself after the opponent's suicide. The same is true also when who needs a full victory is the positional player. He'll try to go for an aggressive play, but he will face a tactical opponent who feels more comfortable in complicated situations, and eventually the positional player will make a blunder and get punished by the opponent.
The key is not the advantage that tactical play has over positional play (or positional over tactical). The key is that if you know that you're facing an opponent with a playing style that's the opposite of yours, you should try to involve him/her in positions he/she doesn't feel comfortable with, while you are. Mikhail Tal was a master at this: his style was so complicated and filled with tactics that when he managed to catch an opponent in his net he had no escape. Petrosian was a master on the other side, playing sober games, choosing super-positional and kinda-drawish systems so that he'd never lose, and win when opponents tried with no hope to break the wall he built.
Answer: As World Champ Magnus Carlsen often says "Having preferences means having weaknesses"
In reality there is no such thing as "positional" or "tactical" style. Objectively, it's simply the degree to which the position calls for calculation. This gradation is only necessary because, unlike computers, humans can tire and cannot look 20 moves ahead in an instant. Thus in quiet positions, we use positional understanding (try to improve our position). In sharp positions we focus on calculation because a single misslip usually costs the game.
Answer: I have seen an informal distinction between tactical and positional, or put another way between tactical and strategic play.
Tactical play was described as being what you do when you can force the issue. The play can be calculated and the outcome determined. Many lines in game analysis are of this type usually ending with something like "winning a pawn" or any other concrete goal.
Strategic or positional play was described as being what you do when you don't have anything to do. There are no tactical variations that you can use at the moment and so your play must be of the type to create abstract strengths. You increase king safety, or strengthen your hold on the center, or something similar.
Good positional play puts you in a position to find strategic play. Both are important. If you make a positional move while ignoring the strategic considerations it is a worthless move. I once played and game that my opponent analyzed for me afterward, one of his comments for a particular move was "Amazing this move is as good strategically as it is bad tactically" and I had hung the piece simply giving it away.
The other direction is harder to find but ignoring positional play when making a tactical move is the kind where you gain material but make positional compromises that hurt you. One really good example of this is the famous game know as the "Immortal game".  Here the winning player had sacrificed a bishop, both rooks, and his queen. Capturing all that material was tactical advantage but the positional considerations were such that the winner was still able to force a win in the end.
There is even some blurring between the two. You might carry out a tactical combination in order to gain a positional advantage.
Answer: There is a lot of confusion concerning the terms "tactical", "positional" and "strategic".
First of all, "strategic" and "positional" are not the same!
Positional thinking consists of static short-term considerations concerning the health of your position. I.e. mostly pawn structure and piece placement.
Strategy on the other hand means long-term planning. For example you might play an anti-positional move because it is part of a long-term strategy. Positional play requires a feeling for the position, whereas strategic play requires knowledge, logic and systematic considerations.
Now this "feeling for a position"-thingy makes a lot of people open up a dichotomy between the tactical and the positional player, where the tactical player does concrete calculation and the positional player just feels where to put his pieces.
There is enough truth in this dichotomy to make it a very persistent myth. Unfortunately it breaks down if you look at the reality. Being a strong calculator doesn't mean you are a tactical player and a very intuitive approach doesn't turn you into a positional player.
On the contrary, strong positional play is often based on very accurate calculation and strong dynamic play is often based on an intuitive grasp of the position.
Two examples: Positional genius Tigran Petrosian was well known for his exceptional calculation ability. Attacking wizard Mikhail Tal was able to play crazy positions better than anybody because of an incredible feeling for the dynamics of a position (he was regularly outcalculated by players like Kortchnoi).
From my point of view you need intuition for positional and dynamic play and you need systematic thinking for calculation and strategic planning. The most interesting battles often occur if an intuitive player is matched up with a "logician". Sometimes the intuitive player will be an attacking player and the logician will be the strategist (for example Tal-Botvinnik), sometimes it will be the other way round (Karpov-Kasparov). Two players of the same type are more likely to have a very lopsided score (Shirov-Kasparov comes to mind).
This also answers the question (finally…), no style has an advantage over the other. If you really want to dominate somebody, you best have the same style and do everything just a little bit better.
Answer: Positional chess DOES have an advantage over tactical chess in the sense that
Having a better position will bring about checkmate where the material advantage of tactical chess
May not necessarily bring about check mate
Comment: Having a better position does not necessarily mean anything beyond an advantage, just like a material advantage is just ... an advantage. You have to play this advantage out and convert it into a won game. This does not in any way imply a road to checkmate. I'd even argue that a material advantage is more likely to (and more easily!)  result in a win for an average chess player (who may either not even appreciate or have nuanced knowledge + experience about how to delicately exploit positional advantages or worse, not even know he has one!)
Comment: If I had to pick one, I'd rather say that the opposite is true! Players who are great at tactics often get more wins from otherwise "balanced" positions


How do you use a ROC curve to optimize a random forest classifier?

Question: I am using a random forest for a binary classification problem using sklearn. The sklearn implementation outputs both a predicted class, and a probability for each class. The sklearn implementation assigns to class B each event whenever the prob of belonging to class A and B are both 0.5. I believe it is not legitimate to override this decision by changing the threshold of 0.5, but I am not sure of this. I am using the ROC curve to make a better decision. I know that the curve represents the True Positive Rate as a function of the True Negative Rate, but how does one obtain the threshold that belongs to each point of the curve? I mean, each point is given by the x,y coordinates, but not a threshold itself. And, more importantly, is this threshold the threshold applied to the random forest predicted class probabilities for classes A and B, or what does it refer to?
Answer: So the threshold is a parametric parameter of the curve.  Where you can find the interval in which it is in by using the scores two points immediately adjacent to them.  You can also look into an $F_1$ score to help you pick an optimal threshold.


Acol Bridge card game

Question: I am playing game in 4 hearts and get four.  The opponents revoke on the 12th trick. If they had not revoked they would of taken us down one trick.
Do we get our four hearts?
I know a revoke does not get a penalty with the last two tricks of a hand being played.
Comment: No *penalty*, but the revoke is still *corrected.*. See the answer by Fabian velow.
Answer: From the ACBL Rules:

Law 62.D is first applied:

On the 12th trick, a revoke, even if established, must be corrected if discovered before all four hands have been returned to the board.

In Switzerland we have the same ruling for a trick 12 Revoke.
So the revoke will be fully corrected without penalty and the hand is one down.
Comment: I think that's actually from the World Bridge Federation Laws, approved by the ACBL, the European Bridge Federation and - most important since OP specifed 'Acol Bridge' - the EBU.

Acol Bridge card game


Using custom scaffold templates for Rails models and controllers? (`inherited_resources_controller` vs `scaffold controller`)

Question: After getting tired of rebuilding all my default scaffold models, views and controllers I decided to create custom templates as outlines on various blogs / SA questions etc.
I created:
/lib/templates/active_record/model.rb
/lib/templates/rails/scaffold_controller/controller.rb
/lib/templates/erb/scaffold/_form.html.erb.tt (and so on for the actions etc.)

I added this to my config/application.rb file:
config.generators do |g|
      g.orm             :active_record
      g.template_engine :erb
      g.test_framework  :test_unit, fixture: true
      g.skip_routes  true
end

I then run the scaffold:
rails g scaffold MyModel name description notes:text flag_active:boolean slug company_id:integer
Running via Spring preloader in process 52960
      invoke  active_record
      create    db/migrate/20200130165523_create_my_models.rb
      create    app/models/my_model.rb
      invoke    test_unit
      create      test/models/my_model_test.rb
      create      test/fixtures/my_models.yml
      invoke  resource_route
       route    resources :my_models
      invoke  inherited_resources_controller
      create    app/controllers/my_models_controller.rb
      invoke    erb
      create      app/views/my_models
      create      app/views/my_models/index.html.erb
      create      app/views/my_models/edit.html.erb
      create      app/views/my_models/show.html.erb
      create      app/views/my_models/new.html.erb
      create      app/views/my_models/_form.html.erb
      invoke    test_unit
      create      test/controllers/my_models_controller_test.rb
      create      test/system/my_models_test.rb
      invoke    helper
      create      app/helpers/my_models_helper.rb
      invoke      test_unit
      invoke    jbuilder
      create      app/views/my_models/index.json.jbuilder
      create      app/views/my_models/show.json.jbuilder
      create      app/views/my_models/_my_model.json.jbuilder
      invoke  assets
      invoke    coffee
      create      app/assets/javascripts/my_models.coffee
      invoke    scss
      create      app/assets/stylesheets/my_models.scss

The issues are that the model and controller templates are not used and the views work fine.
I found this post Scaffolding Rails4 Empty Controller detailing that active admin (which I use) uses inherited_resources_controller.  I am guessing that is part of the issue but I am at a loss how to fix this.  I can't seem to find an obvious solution posted anywhere else.
UPDATE
https://stackoverflow.com/a/20906765/1135515
The model template needs to be in:
/lib/templates/active_record/model/model.rb

And the controller template needs to be:
/lib/templates/rails/inherited_resources_controller/controller.rb

My updated question would be then why is rails using inherited_resources_controller vs scaffold controller and can I fix that?
Comment: I stumbled on half of the solution - if I put my controller template in `inherited_resources_controller` that seems to fix the controller template issue.
Answer: Covered by:
https://github.com/activeadmin/activeadmin/blob/master/docs/14-gotchas.md#rails-5-scaffold-generators
and
https://github.com/activeadmin/inherited_resources/issues/195
In short something like this:
Rails.application.config.generators do |g|
  g.scaffold_controller :scaffold_controller
end


Why is the Collector current of a BJT transistor independent of the Collector Base voltage?

Question: Ignoring the modulation of the effective base width, why is the collector current independent of the reverse bias voltage across the Base-Collector P-N junction? On one hand, it is easy to see that KCL must be obeyed, so the Emitter current flowing into the base must exist through the collector; but how is that "obeyed" given the large electric field the carriers roll down when they reach the Base-Collector junction. Surely the electric field in the depletion region accelerates the carriers which by the Drift current equation: , increases the current as E can be very large?
Comment: In the saturation region this is not the case. However, as Vce reaches a certain point you have two opposing mechanisms (caused by the increase in Vce) as I see it; (1) an increase in Vce voltage ought to push more current and (2) a widening of the base-collector depletion layer ought to produce less current. Just my simple way of thinking telling me that when you move from saturation there are then two opposing things that tend to cancel each other and current remains largely the same.
Comment: the base collector junction does leak a little, so changing V_BC will change I_C a little, so there's no exactly 0 effect from collector voltage, just mostly zero effect
Comment: Could you specify: which parameters *are held constant* while the collector–base voltage changes?
Answer: You seem to think that because the depletion area is large for the base collector junction that there must be a large field there. That is the opposite of how it works. The voltage difference between the emitter, base, and collector is dropped exclusively in the depletion region. Thus the larger the depletion region, the more spread out the field is and so the less strong the field is. In fact, back injection is one of the reasons for hetero junction transistors. In the non depletion regions, diffusion is the dominant mechanism. Thus by creating a large electric field that essentially acts like a reverse flow barrier, the BJT forces diffusion to occur. The reason the current flows from C->E (NPN) or E->C (PNP) is because the BJT uses different doping levels to create depletion widths for different purposes. The reverse biased C-B depletion region, being large, is dropped almost exclusively on the collector's side. That means there's very little length for diffusion. That small length means that the Collector becomes an excellent source of minority carriers for the base compared to the emitter, whose large electric field is almost insurmountable. When those minority carriers cross, they drive diffusion in the base. Once the base provides that minority carrier to the emitter, it can't get it back, so it must get another one from the collector.
In essence the collector current is dependent only on the amount that flows out of the emitter, not on the field, which is designed to drop almost entirely over the collector.
Please leave a comment on this if you don't understand, because I needed about 10 pictures to get this down in college.
Edit: The BJT picture to rule them all!
Comment: I completely overlooked the fact that a larger depletion region = a weaker field!. I am not sure if I understand the rest:

VCE, is designed to drop the largest at the base collector junction, this leads to a larger depletion region there, that ineffect decreases the electric field strength? So as VCE increases, its affect is compensated by a widening of the depletion region? However, current still increases in the active region because the effective base width also decreases thereby increasing the diffusion gradient?

PS the pictures would be nice :)
Comment: Okay so BJT's are a three terminal device and Vce is most of the time just a side effect of the more important Vbe, and Vcb. Because Vcb is a reverse biased pn junction, and because the collector is often doped at ~1/100th the concentration of the base, the majority of the field for **Vcb only** gets dropped on the collector side. The field from Vbe is used for a different reason. Since this is forward biased, the depletion region is small and the field is high. This high field makes it so that once a carrier has cross from b->e that it won't be able to go back, so it diffuses to metal contact


Can one learn meditation on their own?

Question: Can I learn Vipassana meditation or other Buddhist meditation techniques like Shamatha on my own using books and online videos?
This is because it is sometimes hard to find good genuine teachers.
Or do I definitely need to seek a teacher?
Answer: According to my understanding you can learn and start meditation (Samatha or Vipassana) using books and online videos. Of course there are some meditation practices which will be better to learn with a real teacher. Apart form that specially when you have any practical questions or troubles with the meditation or the practice, it is really helpful to get some advice from an experienced teacher.
Further, when you learn by yourself make sure to refer some credible resource (books or online videos) as there are a lot of verities available nowadays. Hope this helps.
Comment: Thanks. I started with books. I will go further in this path and will try to find meditation centers nearby. I just wanted to make sure if I wasn't going in a wrong path :)
Answer: You can learn meditation with books and videos but it will be very difficult to find the truth and answers to your problems. So a better way is to find a teacher. Try to find a Sangha who teaches meditation. If you can't find one then try with books and others. Anyway my dear friends, never stop the meditation even if you can't find a teacher.
There is an order to meditate.

Sila
Samatha
Vipassana

Sila is following precepts with at least five for considerable time(it depends on person).
Without Sila, samatha cannot be mastered. If someone try to use Samatha without Sila, they will understand that they are just wasting their time with increasing the tension. But with Sila you can feel the real cool nature of Buddhism.
Samatha meditation has 40 categories.
Kasina - 10
Asuba - 10
Anussathi - 10
Brahma Wihara - 4
Arupa - 4
Ahara prathikula Sagna - 1
Chathu Dhathu Wawaththana - 1
Kasinas concentrate on physical characteristics like color, heat and light.
Asubhas  concentrate on dead human bodies
Anussathis concentrate on reminding. Anapanasathi is reminding breath, Budhhanussathi is reminding characteristics of Lord Buddha, Kayagathasathi is concentrating about our body etc..
Brahma Viharas concentrates on Metta (friendliness with everyone), Karuna, Mudhitha and Upekka.
others are not recommended without better knowledge.
You have to select one category according to your characteristics. After having a progress in samatha you can step in to Vipassana.
Vipassana meditation method is only included in Buddhism and first introduced by Lord Buddha. In this meditation method, we concentrates on three facts,

Anicca/Anitya
Dhukka
Anatta

1. Anitya
My dear friends, Anitya is the theory that says everything which is generated from a reason(s) will be destroyed due to the destruction of the reason.
2. Dhukka
If we make desire to objects(not only physical) that generated with a reason then we have to expect sadness after the destruction of the object due to the destruction of the reason (helped to exist of the object)
Think of how I love the shine of my car. Shine exist due to the paint and smoothness. If paint or smoothness are both gone, then shine will also disappear. Then because I loved the shine I will feel sad.
Even when someone's car corroded completely I will not feel sad because I didn't like it.
With this logic Lord Buddha said that sad generates due to the craving towards something(Thanha) and not because of a God(s) or fate.
3. Anatta
with this Lord Buddha has said there is no thing called a soul in us. instead we have a mind. The mind is not a thing that exist the same all the time. It is born, exist and dies very, very quickly. So there is a time that the mind doesn't exist. At the time there was not a measurement to describe about the speed of the mind.
Once a Arhat Bhikkhu make a example to a king; think about 12 carts filled with rice seeds. You arrange all the seeds in a single line one after another. Then you can count all the seeds. Sir, there are more minds in a time of blink born, exist and dies.
There are one and only one mind exist at once. Due to the massive speed you feel it as a one single mind. When this mind takes signals from the body and send signals to the body you feel the whole process as a soul.
That's the process we are going to understand in Vipassana meditation. Then can you imagine the power of samadhi you need to maintain to understand that rapid changes? You can do it. The path is not simple. but it is not impossible.
Namo Budhhaya..
Comment: I like the first section of your answer, all the rest doesn't seem to be answering the question. Why did you add that?
Comment: Good question dear friend, All the things I have included here are relevant to the question. First part directly answers the question and second part helps to find a good teacher and books. If your teacher doesn't know about those things or your book doesn't say about them then you have to think of other solution. I think my answer will help to lot of people to find good teachers and books for very successful vipassana meditation.
Answer: Introduction to Meditation: How To Meditate
For me, I find these videos very helpful.  There are many other videos that Bhante have on his site that talks about meditations.  You can also down load book from this site as well. http://www.sirimangalo.org/teachings/how-to-meditate/
Answer: No matter what else, it will come from within. If you can learn it at all, a path already exists that may be found even by accident.
Each and every possible teacher you might find would have to have an unbroken link back to the Original Teacher if it wasn't possible. And the Original Teacher had to learn from within.
Whether innumerable missteps might be avoided easier with a teacher is a different question, but even missteps can teach valuable lessons if you choose to learn.
Comment: Just for clarification, when you say "have an unbroken link back to the original teacher", do you mean Gautama Buddha? Because I believe Siddhartha Gautama worked with 2 teachers before going off on his own. _/\\_
Comment: Consider the case of having two teachers. Either both worked with a single previous or each worked with a different one. If different, then go back another level. At some point, the lines either converge, in which case we only need to follow a single line, or they don't in which case we follow two single lines. Regardless, at some point, every line has a starting point where there was no previous teacher. Whenever (any) _Original Teacher_ is reached, it's a demonstration that it's possible to learn without a teacher. There is more, but that's enough to accept possibility.
Answer: I've attended courses run by my local Rigpa group - perhaps there is one near you that you can try out? http://www.rigpa.org/
I have also benefited greatly from the Headspace app https://www.headspace.com/ -- I think Andy is a great teacher for the on-line medium!
Hope this helps - good luck!
Comment: Welcome to Buddhism SE! I think the first part of your answer doesn't really answer the OP's question. He/she want to learn to meditate without taking classes. As for the second part, what exactly makes the Headspace app so great?
Comment: Welcome to Buddhism SE! In the current form, this is more of a comment like a quick reference than an answer to the question.  I would suggest formatting you answer to explain why these links answer the question.
Comment: Thanks for the rigpa link. They seem to be there in many locations. About headspace, I am not a fan of secular meditation. I would like my meditation to retain Buddhist elements. I read a quote of Bikkhu Bodhi about secular meditation which was something like, you get stress relief and would make you a more compassionate person but it would not take you a step closer to nirvana.
Answer: When you meditate there are sometimes "storms" or big mental disturbances that happen. So it is generally advise to have a guidance of a teacher through this is not necessary. What generally happens is you react and worsen the situation.
No matter what you should not loose the balance of your mind. You should be always equanimous. If you can do this there then you are fit to do meditation through books and other sources without a guidance of a teacher.
Answer: any place to start is the right place, just start.
Don't be too concerned about finding the right teacher or spiritual path. There is a true saying:
When the student is ready, the master will appear.
He, or she, will come running to inspire you, when the time is right, never before.
Please remember that everything is actually pre ordained. Just start.
Very best wishes and have a great week, Rajpal.

Can one learn meditation on their own?


How much would be a fair raise or salary increase to ask for at work?

Question: I have not got a raise at work for some time - almost two years - and I think I am due. I did not ask during the crisis because other companies were laying off, etc. Mine didn't lay off, we actually came through OK. Anyway, how can I figure out what is a fair amount to ask for? I have been working for five years since I graduated and my responsibilities have grown in these past two years. My last raise was modest but nothing spectacular. Do you have any tips on how I can figure out what is fair? I don't want to be seen as greedy but I also think I deserve more than I am making now. Thank you in advance.
Answer: Here are some more thoughts:
Consider inflation as a foundation...
People often overlook inflation when requesting a salary increase.  The cost of living is almost always rising.  If you're going to ask for a raise, make sure you take that into account.  (See also:  How much is inflation?)
Try to find out how much inflation has been over the time period since your last raise.  In order for your purchasing power be restored to what it was originally, you need to win a raise that at least matches inflation.  e.g. An offer for a 2% increase shouldn't suffice if inflation was 3.5% over the same period.
...Plus, you're experience has increased.  What's the "new you" worth?
Let's say you get a raise matching inflation: You're keeping up, but not actually any better off.  How could you have justified more?  Consider: your boss now has an employee with more experience, but is paying the same, in inflation-adjusted terms, as before.  The new you is a bargain at the old you price!
If you believe increased skill & experience are worth something and are confident you're providing more value for money, don't just aim for a raise matching inflation.  Demonstrate how much more productive you are.  The list of achievements and salary survey JCarterRN mentions are helpful to make your case.
...Finally, learn how to negotiate.
I really like the book Getting to Yes: Negotiating Agreement Without Giving In, by Roger Fisher & William Ury.  There's a good summary of the ideas in the book at Getting to YES – Wikipedia.  The book describes principle-based negotiation, objective criteria, and understanding your BATNA, or Best Alternative To a Negotiated Agreement.  I find myself re-reading Getting to Yes the night before an important negotiation.
Comment: The problem with this answer is that inflation has nothing to do with the current market rate for a salary.  What someone can make depends on what employers in the area are willing to pay for a person with the skill set in question.  If the supply is greater than demand, salaries can actually trend *downward*.
Comment: @17of26 Admittedly. But who would **ask** to have their salary reduced/stay the same? But you raise a good point: By "inflation", one could instead examine a more focused inflation figure, e.g. wage inflation for the region and/or industry, provided more detailed data is available.
Comment: My point is simply that inflation isn't a factor in determining a "fair" raise.  The only way to determine "fair" is by researching current market salaries for a given location, skillset, and experience level.
Answer: Others may disagree, but I'd recommend simply asking for a raise and see what they suggest.  I've done this a few times and had them give me more than I would have asked for.
Comment: An excellent rule of negotiation: let the other guy name a number first. Applies during the hiring process, and the review process.
Answer: Salary.com can give you a salary range for your position in your area.  If you feel you're above average, aim for the high end.
If you have a close enough relationship with any of your coworkers, they may be willing to tell you what they're making, but of course that can be an awkward conversation, so don't be pushy if they're not offering.
Before you go asking for anything, make sure you can defend your case.  It's not greedy if you really do deserve it.  Come up with a list of your achievements, focusing on how it has benefited the company (especially financially).  Print out the numbers from salary.com, if you want.  And I think it's better to give your boss a heads up before busting into his or her office to talk about compensation.  Depending on your management structure, the person you're asking for a raise may not know what you currently make off the top of his or her head.  Email ahead of time and request to set up a meeting to discuss "your future with the company" or something like that that makes it clear what you're talking about while avoiding saying, "Can we meet so I can ask you for a raise?"  You may want to send your achievements list ahead of time, too, so your boss has time to review it.
Good luck!  Let us know how it goes.  :)


Why are desires in The Five Hindrances only about "sensual" desires?

Question: The five hindrances consist of sensual desires. ill-will, sloth and torpor, restlessness and doubt. I have often wondered why the first hindrance are limited to sensual desires as this is leaving out the desires/attachment that one can have to other things, like desires for power/control, to be loved or approved of, to achieve, to feel secure. I have always wondered why these are not included as obstacles to spiritual freedom in the dhamma, as they are often much more in the foreground than sensual desires when trying to obtain concentration. Thoughts like "I should have done otherwise", "why did she say so to me", "I need to find a solution", "I must improve" are coming from such needs or attachments. I cannot understand why the first hindrance only talks about sensual desires when there are all these other desires?
Comment: There are 6 senses, technically, in buddhism. craving & ill-will can perfectly have mental states for objects, such as emotions or mind-states (love, peace, calm, etc etc). I would challenge your question in what it presupposes. 5H are definitely are about senses, but not in the western sense, but including the mind itself - all 6 senses.
Answer: It seems that the five hindrances are obstacles to the five factors to be developed in the first jhana. There are other hindrances but these five are important in the context of progress in meditation.
According to Access To Insight:

Buddhaghosa states that the abandonment of the five hindrances alone
  is mentioned in connection with jhana because the hindrances are the
  direct enemies of the five jhana factors, which the latter must
  eliminate and abolish. To support his point the commentator cites a
  passage demonstrating a one-to-one correspondence between the jhana
  factors and the hindrances: one-pointedness is opposed to sensual
  desire, rapture to ill will, applied thought to sloth and torpor,
  happiness to restlessness and worry, and sustained thought to doubt
  (Vism. 141; PP.147). Thus each jhana factor is seen as having the
  specific task of eliminating a particular obstruction to the jhana and
  to correlate these obstructions with the five jhana factors they are
  collected into a scheme of five hindrances.

The Jhanas in Theravada Buddhist Meditation
https://www.accesstoinsight.org/lib/authors/gunaratana/wheel351.html#ch1
Comment: The aim was to show that the point of the five hindrances is that they are hindrances to factors required in the jhanas (and therefore do not need to cover all forms of desire). Sensual desire is considered an obstacle to meditation. In the quote, it lists the five hindrances and factors as pairs. One-pointedness is not singled out.
Comment: Why are "the desires/attachment that one can have to other things" (i.e. the topic of the OP) not also "opposed to one-pointedness" (the topic of your answer)?
Answer: Meditation teacher Gil Fronsdal comments here on why this hindrance is focused on sensual desires rather than other desires:

Perhaps sensual desire is singled out as particularly hazardous to
  meditators because reaching for pleasure and avoiding pain are more
  basic than other desires. Even when the mind is still enough not to be
  caught up in other desires, the enticement of pleasure can still be
  operating. When the grip of sensual desire is strong, it often pulls
  us into the world of fantasy and imagination. Sometimes it is the
  pleasure of fantasizing itself that holds us more than the object of
  our wants.
While there is nothing inherently wrong with sensual pleasure, the
  desire for it is called a hindrance when it interferes with our
  ability to stay present. During meditation, even the most innocent
  desire can distract awareness from the razor's edge of the present
  moment. If we want to stay on that edge, we need to let go of anything
  that causes us to slip off it.

Obsession with more complex desires would fall under the hindrance of restlessness and worry:

Frustrated desire and pent-up aversion are common causes of agitation.
  Fear and resentment are others. Dissatisfaction is a cause that can
  keep the mind restless with searching. Trying too hard in meditation
  can also stir up the mind. When any of these are primary, it can be
  more useful to be mindful of them than the restlessness. Ignoring the
  causes can keep us skimming the surface; being mindful of the
  underlying causes can help with the settling.
Answer: The five hindrances is a teaching for meditators &, originally, obviously primarily for monks. Therefore, the worldly desires mentioned are generally not relevant to the life of a monk. The point of sensual desire is, obviously, it is a biologically based desire (in relation to sex & food) that is difficult to extinguish.
As for some of the other examples in the question, such as  "I should have done otherwise", "why did she say so to me", "I need to find a solution", "I must improve", these appear to be examples of the hindrance of restlessness & remorse. "Why did she say so to me" could also be ill-will.
Answer: Perhaps desires for "things" are ultimately sensual ... including power, social status, physical security ... because how could you desire these things if you were unable to sense them?
But some desires might not be considered unwholesome, a hindrance: wanting to improve, wanting to find liberation, etc.,  may be considered skillful.
Thoughts like these may be quieted eventually but I'm not sure they're a hindrance (or not necessarily and unambiguously a hindrance) as such.
Some desires (i.e. chanda as opposed to tanha) are seen as wholesome and even necessary.
Answer: Chanda = will; aspiration, being interest.
Kāmacchanda = akusala-chanda = will+sensual desires, aspiration of sensual desires. interest and attaching, needing.
Kusala-chanda = will+wholesome mind and mind factors,  aspiration of wholesome mind and mind factors. Being interest but not attaching, ready for giving.
You can found them in  AN 10.51, PTS: A v 92, Sacitta Sutta:

{51.1}  Sace bhikkhave bhikkhu paccavekkhamāno evaṃ jānāti
  abhijjhālu bahulaṃ (=kāmacchandho)    viharāmi   byāpannacitto  bahulaṃ  viharāmi  thīnamiddhapariyuṭṭhito  bahulaṃ viharāmi  uddhato
  bahulaṃ  viharāmi  vicikiccho  bahulaṃ  viharāmi  kodhano bahulaṃ
  viharāmi   saṅkiliṭṭhacitto   bahulaṃ   viharāmi  sāraddhakāyo
  bahulaṃ  viharāmi kusīto  bahulaṃ  viharāmi  asamāhito  bahulaṃ
  viharāmīti  tena bhikkhave bhikkhunā tesaṃyeva pāpakānaṃ akusalānaṃ
  dhammānaṃ pahānāya adhimatto chando (=kusala-chanda) ca vāyāmo ca
  ussāho  ca  ussoḷhi   ca  appaṭivānī  ca sati ca sampajaññañca
  karaṇīyaṃ
When reflecting if the bhikkhu knows, for most of the time I abide coveting (=abhijjhālu=kāmacchanda), abide with an angry mind, abide with sloth and torpor, abide restlessly worrying, abide with doubts, abide with hatred, abide with a defiled mind, abide with a violent angry body, abide lazy and distracted, he should arouse a lot of desireinterest (=kusala-chanda), effort, zeal, unhindered action and mindful awareness to dispel those demeritorious things.

Note: In this sutta, buddha used 'abhijjhālu' word instead of 'kāmacchanda' word to avoid the confusion between kusala-chanda (kāmacchanda) and akusala-chanda (chando in above sutta). It likes an avoiding confusion between made-known-viññāṇa (object) and knowing-viññāṇa (subject), when buddha used 'viññāṇa' word as object (focused point) of the practitioner, 'citta' word as the practitioner (focusing doer/undoer;subject) in anattalakkhaṇasutta.
In path of purification:
chanda:

(xxviii) Zeal (desire) is a term for desire interest to act. So that zeal has the characteristic of desire interest to act. Its function is searching for
  an object. It is manifested as want for an object. That same [object]
  is its proximate cause. It should be regarded as the extending of the
  mental hand in the apprehending of an object.

kāmacchanda:

Of these, greed has the characteristic of grasping an object, like birdlime (lit. "monkey lime"). Its function is sticking, like
  meat put in a hot pan. It is manifested as not giving up, like the dye
  of lamp-black. Its proximate cause is seeing enjoyment in things that
  lead to bondage. Swelling with the current of craving, it should be
  regarded as taking [beings] with it to states of loss, as a
  swift-flowing river does to the great ocean.

kusala-chanda:

(xiii)–(xv) By its means they are not greedy (na lubbhanti), or it itself is not greedy, or it is just the mere not being greedy
  (alubbhana), thus it is non-greed (alobha). The same method applies to
  non-hate (adosa) and non-delusion (amoha) [na dussanti, adussana =
  adosa, and na muyhanti, amuyhana = amoha (see §§171,161)]. Of these,
  non-greed has the characteristic of the mind's lack of desire for an
  object, or it has the characteristic of non-adherence, like a water
  drop on a lotus leaf. Its function is not to lay hold, like a
  liberated bhikkhu. It is manifested as a state of not treating as a
  shelter, like that of a man who has fallen into filth.

You can also see the abhidhammatthasaṅgaha for more information and relativity of chanda compare with lobha (kāmacchanda).


How to generate a Linux Apache password file on a PC running Windows 7?

Question: My development machine is Windows. I use the htpasswd program that is part of the Windows XAMPP package, version 1.7.7, to generate a Windows Apache password file.

C:\xampp\apache\bin\htpasswd.exe -bc .htpasswd usename password

I need to generate a password file for a Redhat Linux machine but have no access to the htpasswd program on that machine. If I can generate a valid Linux Apache passwd on Windows then I can FTP it over to the Linux system.
The htpasswd documentation says that I can use the -d flag to force crypt() encryption which should work on Linux instead of the default MD5 encryption that works on Windows.
My problem is that

C:\xampp\apache\bin\htpasswd.exe -bcd .htpasswd usename password

generates a file but gives a message which says "Automatically using MD5 format".
How do I generate a valid Apache password file for a Linux machine from a Windows PC?
Comment: Apache on Linux will work happily with MD5 password hashes.
Answer: You can use an online tool such as this to get the job done.


Does the material of the slits affect the pattern of the electrons in the double-slit experiment?

Question: The question comes from thinking about the way how electrons act on the slits. Do material of the slits affect electrons motion? Assume the radius or length of the slits are set in this case.
Answer: Does the material affect the double slit experiment?  No, but with some important conditions.
The double slit experiment is designed to measure the diffraction interference pattern of the wave-nature of matter like photons and electrons.  The material used to make the slits is meant to either completely block the incident particles where there isn't a slit or let them pass completely through where there is a slit.  The boundary between the material and the slit is supposed to be sharp.  That's why the barriers S1 and S2 don't need labels:

If you chose a material that didn't have these properties (or if you made the barrier so thin it could be tunneled through) you wouldn't really have the double slit experiment anymore.
So, given an appropriate choice of material, the experimental results don't change from material to material.  The experiment is based on the geometry of the slits and the wavelength of the incident particles and not the particle-material interaction.
Comment: I had checked your answer, but having thought further on this, I think that the real experiment is a solution of the quantum mechanical equation with boundaries for the  electron  the two slits, and in this case the conductivity for example should play a role at some level. It should not just be geometry if one could solve exactly.
Answer: "The material of the slits" (it would be more correct to say "the material of the screen with slits", as there is no material in the slits) definitely "affects electron's motion". For example, "In the course of our previous qualitative study an unexpected broadening of the diffraction peaks was observed.27 We show that the broadening of the diffraction
peaks is affected by the type and thickness of metallic coating" (http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1060&context=mrsecfacpubs ). The reason is the "image charges" in the screen with which electrons interact depend on the electric properties of the screen.


Bentley DGN format to Oracle Spatial

Question: Did anyone ingested the DGN (all versions) to Oracle Spatial?
Comment: We do every day using FME http://www.safe.com/fme/fme-technology/fme-desktop/overview/
Answer: @Rao, ogr2ogr can do this (at least, the OGR formats page shows both Microstation DGN as well as Oracle Spatial); however, you'll need a GDAL/OGR installation that includes support for Oracle. If you're using Windows, you should find everything you need on Tamas Szekeres site, otherwise check here and look for an OS-specific approach to installing GDAL.
Presumably, your ogr2ogr instruction should look something like this (based on a quick look at the documentation):
ogr2ogr -nlt "geometry" -f OCI OCI:username/password@database samp4.dgn
Although, both the DGN and the Oracle formats have a number of particulars, so you may want to consider translating your DGN files to shapefiles first, then translating the shapefiles into Oracle. I only suggest this because using shapefiles in the middle would allow you to isolate any DGN or Oracle-specific driver-complexities to one side of the equation at a time.
Take a look at this conversation between Loskot and Warmerdam for some additional insight.

Bentley DGN format to Oracle Spatial


What should I look for in a cycling jersey?

Question: Time has come to refresh the wardrobe a little, and the old woollen cycling jerseys need some young blood to compete against.  What should I be looking for in a modern cycling top?  Is lycra used anymore?  Does the cut of the jersey (other than being tight) have any effect?
Comment: An attractive cyclist of your chosen gender?
Answer: Fit is the most important thing I look for.  A cycling top should fit snugly, without being skin-tight.  Having less extra fabric will mean less air resistance, which makes a surprising difference at higher speeds.  Also, too much excess fabric will flap in the wind, which can be annoying too.
Make sure that the length in back is long enough to cover your lower back when you're riding in an aggressive position.  If a long-sleeve, the sleeves need to be long enough to cover your wrists with your arms extended out front.  (some normal clothing fails these two checks)
One last caveat about jersey style:  make sure the zipper opens far enough for you to be able to take it off after a long sweaty ride.  I have one with a short zipper and it's a real struggle.
For materials, there's lots of nice synthetics to choose from that are lightweight, wick away moisture and are very comfortable in hot weather.  But for cool or wet conditions, nothing beats wool.
Comment: I generally only buy jerseys with full zippers now. If you've ever tried to use a porta-john while wearing bib shorts and a charity ride jersey with a short zipper you know why...
Answer: One essential feature I have learned to appreciate in cycling jerseys is a tight fit around my neck, preferably with a zipper. I've had a wasp enter my shirt while I was doing 70+ km/h down hill on two occasions and it was all I could do to keep my bike under control while breaking as hard as possible.
Apart from that, like darkcanuck, I look for a tight fit, a long back, and long enough sleeves (for long-sleeve jerseys anyway). I prefer light synthetic materials for summer riding and wool for when the weather gets colder (I actually wear woolen jerseys all year round here in the Netherlands). An extra advantage of wool I like is that it doesn't pick up the sweaty smell as quickly as synthetics do.
Answer: If you do longer trips then check if the bags on the back are large and solid enough. I also like summer jerseys that have zippers to the bottom or at least low enough. This is especially practical when riding uphill on hot days.
Answer: Agree with previous posts, you want a perfect fit first and foremost.
Personally I also look for the particulars, like a good quality zip and proper stitching - its a dead giveaway between a knock-off and something that is going to last you the years to come.


Close button on mobile registration process

Question: I am working on a registration process for a mobile site which uses a progress tracker. On completion of the registration the user is instructed that they need to check their email to activate their account. Below the message I've added a 'close' button so the user can close the browser window as their journey has come to an end. I did think to put 'exit' on the button but wasn't sure if that was clear enough. Are there any other suggestions or best practice anyone has come across which relate to this?
Answer: I don't think the user needs an extra link to help close their browser window, as there's already a standard close button that they know how to use.
Instead, suggest that they've completed registration, and tell them that they can close the window. And, even better, have a button to go to what they were trying to do before they registered (like commenting on a SO post!)
Answer: Without knowing the context, I would be more inclined to link someone back to login page or homepage after this type of registration. This way, they could have some options if they haven't received an email/spam etc.
However, if you're set on your initial approach I would go with something like:
Thank you + check email to activate message.
Btn - 'Close Window'
Comment: Thanks for the feedback on this. I don't want to add any 'extra step' for the user but want them to know this is the end of the journey and they have the functionality to close the browser window after the reading the messaging.


How should I order an espresso to get a less sour shot?

Question: I often find that standard espresso shots at many high-end coffeeshops to be more sour than I prefer. I tend to order straight espresso, or Americanos with only a little water, or maybe a macchiatto, so there's not much fat to cut the tartness. What should I say to get a less acidic shot?
Answer: Here's a few thoughts based on what causes sourness/acidity in coffee and ways to temper it.
Order an espresso lungo. Sourness (acidity) is characteristic of the "stuff" that is extracted relatively early in the brewing process. In other brewing methods that take longer to perform (e.g., coffee press, drip, or pour-over) this can be balanced by the more bitter notes that take somewhat longer to fully extract. For this reason, you might get a result that is more appealing to you by ordering an espresso that takes longer to pull, i.e., espresso lungo. Not everyone behind every coffee counter will be immediately familiar with this, but at good cafes with good machines an espresso lungo should be no problem.
Try a darker roast. Darker roast coffees tend to be less acidic than lighter roasts, at the expense of losing more of the varietal/regional notes. Many cafes have really only one bean/roast that they use for every espresso (often because of the practical considerations of having several grinder hoppers full of beans), but if you have an option, try a darker-roasted bean.
Try beans from a different region. To my taste, Indonesian coffees tend to have less pronounced acidic notes than African or American coffees. Again, if multiple coffees are available for espresso, pick a coffee that you like (or find less sour) for any other preparation.
Pick beans further off of the roast. This is really only for completeness, but beans that were very freshly/recently roasted (i.e., less than a few days) can have accentuated acidity because some undesirable volatiles haven't yet had a chance to leach out. This is more toward what @daniel noted; this is the kind of thing you shouldn't need to be concerned about at a cafe -- they should!
A cafe affiliated with a local roaster (or any specialty cafe) should be able to tell you lots of things about the coffee when asked, such as region, varietal, roast level, and roast date. Here's a Serious Eats article about "problems" and related solutions that touch on some of the things I talked about above. Here's another link from Coffee Cuppers about regional and roast considerations in general.
Comment: I agree with the most of your answer just a didn't get why would you order a coffee with more water, i.e. _lungo_, in this case? From a chemical point of view to reduce a pH index (or acidity, sourness) you need to add a lot of water and lungo offers just an infinitesimally small portion of the needed water.
Comment: @simplicisveritatis - For the lungo recommendation, it's not about the volume, but rather about the *length of time* for the extraction. My argument is that you'll balance out some of the acidic notes with the bitter notes that will come out with a longer extraction. Just a thought!
Comment: ♦ Fair enough :)
Answer: Taste is subjective but a high-end espresso should not taste sour. Old coffee, poorly roasted coffee, and inferior grade coffee are the main culprits.
The following is a pet theory, not science: cafes that charge a lot for coffee to cover overhead--or just because they think they can--sometimes have a low regard for the customer. Sometimes the best cup of espresso comes from a smaller cafe that depends on loyal customers for survival or is in business because the owner takes pride in serving good stuff.
You shouldn't have to say anything to get a less acidic shot. If you are paying for good espresso you should get it--with the qualification that any cafe has a cycle of re-stocking and so some variation in quality is normal.
Comment: I agree with OP that some espresso *just tastes more sour* than others. I agree with you, though, that good espresso shops should certainly be expected to serve high quality product without specially requesting it!
Answer: As it was already mentioned some of the main parameters determining coffee taste are:

Coffee related:

beans origin and quality.
beans roasting and time passed.
beans grounding and time passed.

Machine related:

water quality.
water desalination frequency.
general cleanliness of the machine and the environment.
lower water temperature of extraction. If the machine temperature is lower due lack of periodical calibration, the coffee tastes sour and flat.

Preparation related:

extracted coffee exposure to the atmosphere. The longer is stays exposed, the more it reacts with the atmospheric oxygen and oxidizes, thus becoming more sour. This is true especially for all the coffees with added water (Americano, lungo) that breaks the thin layer covering and preserving the coffee's nice taste qualities.

Consumption of additional beverage or/and snack together with the coffee.

if the additional food or/and drink consumed together with the coffee contains more sugar, then your coffee will always taste sour. (The effect is similar to when you eat chocolate first and then eat an apple, the apple tastes much sour.)
smoking affects taste receptors as well and it should be taken into consideration, i.e. you receptors are less sensitive and there is no point in buying coffee from high-end shops, as you are unable to feel the taste.

Generally, if you want to experience the best quality of a given espresso, you should order it ristretto. The ordinary espresso extraction time is around 25 seconds (1ml / sec) and you get a full shot. Ristretto reduces the extraction time, usually by half, and cuts the last drops of water that contain lower concentration of coffee extract, thus keeping the strong aroma and different taste balance. In the ideal case it should be consumed as fast as possible, just like a gourmé meal.


Is it possible to find tool and die set for my forge?

Question: I am on day 57 and almost visited every place of interest. The forge in 7 days to die require 3 items i.e anvil, callipers and tool and die set. Anvil is easy to make and i found callipers in working stiff crates. Tool and die set is no where to be found. Googling for the solution just gives some random comments on random forum which are different for different versions. I am currently playing alpha 15.
Comment: I know that I was able to find them on the console version of the game. It took me a very long time. I'm past 60+ days but I want to say I found them before that. I believe searching a car is where I found them. Try getting your scavenger level up.  I'm not sure but I think you find better stuff with a higher level.
Answer: First of all, ask yourself if this is an issue for you. "Tool and Die" set so far (A15) required only for rocket launcher ammo production.
Second of all, you have to check Trader from time to time. Trader is most reliable source of such items.
And last, well obviously, loot more of specific containers. Consult this page for more information: http://www.7daysdb.com/item/tool-die-set, it says:

Working Stiffs Crate
Normal cars
Damaged cars
Miner's Chests and on the Zombie Miner (1)
Comment: @RishabhSharma, ah, ok. Then you'd better to ride bike to some distant (if it MP, in SP any non looted) city with Working Tool shop and loot it. I was able to get Tool and Die set even before Callipers on my run.
Comment: I wanna find tool and die set to craft some rocket launcher ammo.
Comment: I play in a populated server. I guess this makes it even harder to find them. Most of the building are already looted and the building that aren't looted have useless junk in them.
Comment: @RishabhSharma, on the other side Cars are numerous. Especially in Industrial biome. And they are more easy to locate and loot from
Comment: @RishabhSharma Looted containers respawn after a certain period of time set by the server (Loot Respawn Time) so don't despair! It's also possible you're on a server with a low Loot Abundance setting. Check [the server settings](http://7daystodie.gamepedia.com/Game_Settings) listed on the right hand side of the server list.
Answer: This ended up being too long for a comment, so here is some more information on the loot locations for the Tool Set and Die, obtained from the data files, in version 15.1.
The Tool Set and Die can be found in the Working Stiffs crates, with a 67% probability and the rareTools loot group with a 9% probability.
Rare Tools can also be found in Working Stiffs crates, or where normal Tools are found (though never more than one in a loot box.).  They can also be obtained from lumberjacks.
Normal Tools can be found on Zombie Bikers, Zombie Farmers, and Zombie Utility Workers.  They can also be found in the automotive-tools-junk loot group (21% chance) and the minerloot loot group.
Automotive junk is only found in cars, currently.
The miner loot can be found in Miner's Chests and on the Zombie Miner.
Please note that all of this is subject to change with every patch, at the whim of the devs, but hope it helps.
Also note that certain containers, like cars, will reveal different items depending on what tool is used to harvest from them.  The item you are looking for, however, is a drop from the cars, and not from the harvest.
Comment: Nice addition about Miners in A15.1. Since my answer was marked, I append this to it.
Answer: In addition to the other answers, you can increase the chance a trader might have it in their Secret Stash by leveling up the Secret Stash perk. Remember when talking to the trader their Secret Stash items do not show up in All. You must check them separately.
I suspect (though I cannot confirm) you could also find it in a Supply Crate from an air drop if you're playing with those turned on. They often contain schematics, ammo, medical supplies, and uncraftable items like beakers. Listen for the sound of an airplane, look for an orange flare, and (if the server has it on) a bright orange marker on your compass.
Finally, if you're on a server using the Economy Plugin
 you can often buy it with zCoins. I personally feel this detracts from the game, but I won't judge you -- much -- for using it. :)


Does the use of sunscreen inhibit Vitamin D production?

Question: Vitamin D is produced in the skin when exposed to sunlight.
Therefore, when using sunscreen on the skin, is Vitamin D production inhibited?
Comment: Excellent question!  Love seeing this kind of Q here :)  I edited it slightly to add the sun-skin-VitD mechanism you were indirectly referring to, which is more in line with question guidelines.  Thanks for asking!
Comment: Where are the twitter feed bots when you need them? +1 excellent question indeed.
Comment: May I add to the question: If  yes ( i.e. sunscreen block vitamin D production) , so what are healthy ways to substitue this blockage and get the production of vitamin D?
Answer: This has been a controversial question for many years. The current evidence suggests that sunscreen does block a part of Vitamin D production, but with negligible amounts.

Studies have found that by blocking ultraviolet rays, sunscreen limits
  the vitamin D we produce. But the question is to what extent.
A few studies have concluded that the effect is significant — a
  reduction as great as tenfold. But more recent, randomized studies
  that followed people for months and in some cases years suggest that
  the effect is negligible. While sunscreen does hamper vitamin D
  production, these studies say, it is not enough to cause a deficiency.
[...]
  Dr. Lim added that rather than cutting back on sunscreen, people
  concerned about vitamin D should consume more foods rich in vitamin D,
  like salmon, milk and orange juice.
Source: New York Times Article, Emphasis Mine

Studies cited in the article

Matusoka LY et al. Chronic sunscreen use decreases circulating concentrations of 25-hydroxyvitamin D. A preliminary study. PubMed link
Marks R et al. The effect of regular sunscreen use on vitamin D levels in an Australian population. Results of a randomized controlled trial. PubMed link
Farrerons J et al. Clinically prescribed sunscreen (sun protection factor 15) does not decrease serum vitamin D concentration sufficiently either to induce changes in parathyroid function or in metabolic markers. PubMed link
Answer: Vitamin D is produced in the skin. There are two subtypes of UV radiation: UVA and UVB. UVA is primarily responsible for photoaging, and UVB for the superficial burning that results from sun exposure (2).
UVB electromagnetic radiation converts 7-dehydrocholestrol to pre-vitamin D3, which is then converted into Vitamin D3 (1). Sunscreens with an SPF rating absorb or reflect (depending on the filters used) UVB light (2). Without UVB light, 7-dehydrocholestrol cannot be converted into pre-vitamin D. It may also be of interest to note that glass blocks UVB (but not UVA radiation) and thus has a similar effect on Vitamin D production (1).
In reality, however, people rarely apply sunscreen well enough so that Vitamin D production completely ceases (3).
In short, yes sunscreen does inhibit the production of Vitamin D, although in most cases not to such an extent that Vitamin D deficiency becomes a concern.
References

https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
http://www.skincancer.org/prevention/uva-and-uvb
https://www.health.harvard.edu/staying-healthy/6-things-you-should-know-about-vitamin-d
Answer: In addition to the other answers:

[C]linical studies have never found that everyday sunscreen use leads to
vitamin D insufficiency. In fact, the prevailing studies show that
people who use sunscreen daily can maintain their vitamin D levels.
One of the explanations for this may be that no matter how much
sunscreen you use or how high the SPF, some of the sun's UV rays reach
your skin. An SPF 15 sunscreen filters out 93 percent of UVB rays, SPF
30 keeps out 97 percent, and SPF 50 filters out 98 percent. This
leaves anywhere from 2 to 7 percent of solar UVB reaching your skin,
even with high-SPF sunscreens. And that's if you use them perfectly.

Sun Protection and Vitamin D By Skin Cancer Foundation

There are claims that one needs to get a certain amount of sun
exposure every day in order to produce enough vitamin D to be healthy.
It's just not true
David J. Leffell, MD, Yale Medicine dermatologist and chief of
Dermatologic Surgery

Vitamin D Myths 'D'-bunked - Yale Medicine
Comment: Related: https://medicalsciences.stackexchange.com/q/16586/7951


How important is union membership for sound designers and production sound mixers?

Question: Being relatively new to production sound mixing and post production sound, I've been wandering my way through the indie world not doing too much studio work.  How important will it be for me to be a union member to begin working on large-scale projects?  What are the unions or professional societies that I need to focus on?  Are they a source of work, or more of a source of credentials?
Answer: Production Sound Mixers - very important - if you want to be playing with the big boys (Devlin, Novik, Ulano, etc...) on union sets.  Union sets generally won't hire you unless you're union.  The only catch is, once you're union, you're only allowed to work on one or two non-union sets a year.  So you'd better make sure you're good and are plugged in before you go union, or you'll be out of work!
As for Sound Designers, I don't think its really that important.  I don't know of many that are union.  There are organizations, such as CAS, that a lot of Sound Designers (and Production Mixers) join, but those aren't usually unions.
Personally, I think unions have outstayed their welcome.  They were very useful pre-war, but I think they do more damage than good anymore, IMHO.
Answer: Hi VCD,
The union here in Los Angeles (MPEG Local 700) doesn't recognize the title "sound designer" as an official classification. The closest you would get would be either a sound editor or a re-recording mixer. (Guess the "sound designer" fits somewhere between those two.) So with that in mind, you'd need to figure which of those best fits your skill set.
AMENDED: Without a union membership you're not able to be on union payroll. That being said, I think independent sound designers can work on union shows but cannot accumulate hours towards pension, health benefits, etc .
As a "PS" to Colin's opinion, I'll say that although the union certainly isn't perfect, it is the way the industry works. On the plus side, the health benefits are great - and that can be worth more than money.
Comment: True, it is the way that the industry works.  If you want to work on the big stuff in the industry (production side) you're going to need to be in a union (MPEG Local 700, IATSE Local 695).  I just wish it wasn't that way.  It limits what you are allowed to work on, and I don't like the way unions are run.  But I don't see it changing any time soon.
Comment: I personally love that unions make sure you get paid a living wage for your work.  My experience in LA has shocked me as so many people are winning bids by undercutting.  I know a lot of talented dudes working on great work who can't afford to live in safe neighborhoods and have health insurance. I want in on a union gig for sure. I am hard working and work extremely well in a team.
Answer: if you wish to work on Union films or TV (which are pretty much all the big films and TV shows), you must be in the union- there are some workarounds, like having a very specific skill that is not available from the pool of union talent pool, but that will simply allow you a 30 day period of employment which will satisfy the union for membership.
The other clear way into the Union directly is to organize a film or TV show. That will allow all the crew to be admitted directly.


Has Ask Patents impacted frivolous patent claims?

Question: I just read about the site's mission against frivolous software patent claims. I'm really intrigued by the idea and I wanted to know how much of an impact it has had since its inception. I wasn't able to find any statistics, like % of software patents denied after being discussed on Ask Patents, or anything like that. I would certainly be willing to donate my time for this cause if that would actually change the world in a small way. I'm sure many other people feel the same way.
Answer: At least 2 or 3 patents have been rejected and/or claims modified due to prior art searches performed by Ask Patents.SE. You can view examples of this at the following link, and then sort by votes: https://patents.stackexchange.com/questions/tagged/prior-art-request
While this may not seem like a large number in the larger number of patents being approved, it shows that this community can affect change in patent status.
Answer: While the contributors to this site know a lot about patents, they aren't necessarily experts in the technical field of prior art requests. What might be useful would be to take acceptable prior art requests and then in some way link them to other specific StackExchange sites where technical experts reside. Ask Patents could vet the question, edit it and decide on which (if any) StackExchange site is appropriate.


What would be the name for foreshadowing if it is referencing the past?

Question: In literature, if foreshadowing is reference to future events, what would it be called if it is referencing a past event which the reader does not know?
Answer: Narratology uses the terms prolepsis and analepsis to refer to two types of discrepancies between the order in which events are told and the order presented in the plot.
Prolepsis refers to a so-called "flash-forward by which a future event is related as an interruption to the 'present' time of the narration" (Baldick, page 205).
Cuddon gives the following example from stanza 27 of Keats's Isabella (emphasis added):

So the two brothers and their murder'd man
Rode past fair Florence, to where Arno's stream
Gurgles through straiten'd banks

Analepsis refers to a chronological discrepancy "by which some of the events of a story are related at a point in the narrative after later story-events have already been recounted". This is often referred to as retrospection or flashback.
Gérard Genette distinguishes homodiegetic and heterodiegetic analepsis or prolepsis, depending on whether the chronological discrepancy concerns something in the narrative's primary foreground or not (quoted from Herman & Vervaeck):

If the analepsis or prolepsis concernt the element in the foreground of the primary narrative, Genette calls them homodiegetic. For instance, if a dying man remembers a moment from his own life, this would constitute a homodiegetic analepsis. If, however, he remembers something about a person who does not appear or has only a minor role in the primary narrative, then the analepsis is heterodiegetic.

References:

Baldick, Chris: The Concise Oxford Dictionary of Literary Terms. Second edition. Oxford University Press, 2001.
Cuddon, J. A.: The Penguin Dictionary of Literary Terms and Literary Theory. Third edition. Penguin 1992.
Herman, Luc; Vervaeck, Bart: Handbook of Narrative Analysis. University of Nebraska Press, 2005. (Translation from the Dutch Vertelduivels. Handboek verhaalanalyse. Vantilt, 2005.)
Answer: Foreshadowing is not necessarily reference to future events.
A foreshadowing is a reference to events which will be revealed later in the story. They're in the future from the point of view of the reader, but not necessarily events which are in the future "in-universe".

Foreshadowing is a literary device in which a writer gives an advance hint of what is to come later in the story.
-- Wikipedia, Literary Devices

(It should be noted that neither of the sources linked above are very good. I'm not sure what's a better dictionary of literary devices, but would be very happy to be directed to one.)
In this context, "later in the story" means later in the physical book or otherwise in the telling of the narrative - not necessarily events which actually occurred later within the world of the story. For some examples of foreshadowing of earlier events, in a somewhat famous work of modern literature, see this Q&A:

"I wouldn't mind knowing how Riddle got an award for special services to Hogwarts either."
"Could've been anything," said Ron. "Maybe he got thirty O.W.L.s or saved a teacher from the giant squid. Maybe he murdered Myrtle; that would've done everyone a favour..."
-- Harry Potter, book 2, chapter 13

It's revealed later in this book that Riddle did in fact murder Myrtle, several decades earlier. The event being foreshadowed is well in the past, and only the revelation of it is in the future.

"Dumbledore believed Snape was sorry James was dead? Snape hated James..."
"And he didn't think my mother was worth a damn either," said Harry, "because she was Muggle-born...'Mudblood,' he called her..."
-- Harry Potter, book 6, chapter 29

It's revealed in the next book that Snape's "Mudblood" outburst was out of character, and in fact he not only didn't hate Lily (Harry's mother) but had in fact been in love with her since childhood. Here Snape's love for Lily is a continuing state through the past, present, and future ("After all this time?" "Always."), but there's foreshadowing because the revelation of it is in the future.

So to answer your question:

what would it be called if it is referencing a past event which the reader does not know?

This is still foreshadowing. If the reader doesn't know but will find out later, then the revelation is in the future and it's foreshadowing, regardless of whether the event being referenced is in the future or the past.
Comment: What if you are referencing a point earlier within the physical book? What if the reader clearly does know that information but you want to clearly reiterate that past event through this "foreshadowing"? I'm searching for this because I used a contradictory narrative after this specific event I want to clearly re-enforce to the reader. It's not to add new information but to clear up the narrative


Recursive polynomial relation

Question: So we have the following: $1^4 + 2^4 + 3^4 + ... + n^4$
How do you find a polynomial formula for this recursive relation? My attempt is to set it up as following: $(n+1)(n^3+1)$ but it does not look right.
Answer: Note that we have
$$(k+1)^5 - k^5 = 5k^4 + 10k^3 + 10k^2 + 5k + 1$$
Now sum this from $k=1$ to $n$ to get that
$$\sum_{k=1}^n \left((k+1)^5 - k^5 \right) = 5\sum_{k=1}^n k^4 + 10\sum_{k=1}^n k^3 + 10\sum_{k=1}^n k^2 + 5\sum_{k=1}^n k + \sum_{k=1}^n 1$$
The terms on the left hand side can be simplified by telescopic cancellation to get
\begin{align}
(n+1)^5 - 1 & = 5\sum_{k=1}^n k^4 + 10\sum_{k=1}^n k^3 + 10\sum_{k=1}^n k^2 + 5\sum_{k=1}^n k + \sum_{k=1}^n 1 \tag{$\star$}
\end{align}
Now make use of the fact that
\begin{align}
\sum_{k=1}^n k^3 & = \dfrac{n^2(n+1)^2}4\\
\sum_{k=1}^n k^2 & = \dfrac{n(n+1)(2n+1)}6\\
\sum_{k=1}^n k & = \dfrac{n(n+1)}2\\
\sum_{k=1}^n 1 & = n
\end{align}
in $(\star)$ to get the value of $\displaystyle \sum_{k=1}^n k^4$. If you are not aware of the above relations you can micmic the procedure we used to compute $\displaystyle \sum_{k=1}^n k^4$, to compute these as well.
Comment: I'm not the one who asked this, but I really like this proof. Clever!
Answer: Note that the polynomial $p$ you desire will have the properties that $p(0)=0$ and $p(n+1)-p(n)=(n+1)^4$ for all (nonnegative) integers $n$. That turns out to be enough to completely characterize the polynomial. To narrow it down a bit further for you, though, it will be a degree $5$ polynomial, with $\frac15$ as leading coefficient.

Recursive polynomial relation


Combining multiple Videos

Question: Does any one know about any free software for windows with which I can combine multiple videos and create a video like this?
Comment: Its a shame you didn't get a better answer.  What did you end up using?  I imagine this stuff can be done with Final Cut quite well.  Syncing the audio will be the hardest part, and may be better done separately in something like Pro Tools... But I agree, should be a single app to do this.  More info here. http://avp.stackexchange.com/questions/895/how-to-make-videosongs
Comment: I didn't get anything yet... Thanks for the link though... :)
Answer: On Windows, for free, your best (albeit complicated) bet might be Blender.
You could create a series of several plane meshes in the layout you wanted, in front of the camera. You'd then create a separate material for each of the planes, setting them to shadeless, and giving each a different video texture. You'd have to mix the audio separately (Windows Movie Maker, or Blender also has a built in video editor).
I'll note that using a 3D approach for something like this isn't ideal at all - a 2D compositing program like Adobe After Effects would be much better (Blender itself does have a 2D compositing component, but since it uses nodes instead of layers, it might actually be more difficult).
Answer: There are several free or cheap video editing programs for Windows; Microsoft themselves provide Windows Movie Maker, and then as an opensource alternative there's VirtualDub.

Combining multiple Videos


Calculating the electric relative permittivity of fluid or medium?

Question: I'm unsure of how to calculate the permittivity of a fluid.  Permittivity differs from one fluid to another:
$$\varepsilon=\varepsilon_r\varepsilon_0$$
Since it is an electrical property combined with an electrical capacity, it is possible to measure it indirectly in a capacitive sensor. I have used a capacitive sensor to measure electric relative permittivity factor of a dielectric medium can be expressed as a ration of capacity, $C_x$ of capacitor, which space between and around the electrodes is completely filled with the medium, to capacity $C_0$ of the same electrodes in vacuum.
$$\varepsilon_r=\frac{C_x}{C_0} $$
I know and measured $C_0$ value. I am facing problems with calculating $C_x$ of capacitor, which space between and around the electrodes is completely filled with the medium.
I am using method as described below.
I am applying an AC signal ($125\: \mathrm{kHz}$) to the capacitive sensor which is filled with some fluid, in response I am getting AC signal with some phase difference. I am able to measure the amplitudes of sensor input, sensor output signals and their phase difference also. I am trying to make equation that will give $C_x$ value from above known values ($V_g$ (input), $V_r$ (output), $\phi$ (phase difference)).
Comment: Hello Verendra, you can use LaTex-like markup here to print nicer symbols and not having to rely on the - sometimes somewhat limited - unicode symbols.
Answer: I would use a capacitance bridge. This is by far the most accurate way to measure capacitance. If you're at a university there's probably someone around who has a commercial capacitance bridge. If not, you can easily make one.
Comment: The link is broken.


Gantt charts with ranged estimates?

Question: I'd like to create Gantt charts with ranged estimates (for reporting to non-technical execs) but don't want to use a web service (LiquidPlanner). How can I get Gantt charts with range estimates?
Answer: I personally will use Excel Gantt template provided by Vertex42 or any other templates available out there (use your best tool google it): enter link description here, and will adjust the range estimates as the work progress or stalls and share it  with executive team using a file sharing provider (one single source of the truth) in order for them to get always the up-to-date version.

Gantt charts with ranged estimates?


How do you know if a VOR is High, Low, or Terminal?

Question: Is there any way of telling on both a VFR and IFR chart what type of VOR we are looking at?
Comment: Related: http://aviation.stackexchange.com/questions/24040/when-is-a-vor-shown-on-maps
Answer: The range of the VOR is included in the Airport/Facility Directory data under the name class
From A/FD legend:

Example:

Service volume for each class:
Comment: One thing that can trip you up when looking for the info is that VORs which are located on an airport do not have a separate entry but are shown at the bottom of information for the airport in the 'Radio Aids to Navigation' section.
Answer: Typically terminal VOR's do not have compass roses around them if they are strictly terminal VOR's. I can't find an example of one so I don't have an image for it.
Edit I found an example:

Source: SkyVector
The DEN VOR has no compass rose, so its either a terminal VOR or they omitted the compass rose for clarity. There are two other VOR's in close proximity, MILE HIGH on the North East side of the field and Falcon to the east of Buckley AFB. According to AirNav NavAid Info its a high VOR.
As far as high/low VOR, one way to tell is to look at the High/Low enroute IFR charts.
For example, here is a portion of a low-enroute IFR chart:

Source: SkyVector
You can see two VOR stations on here labeled Minot Intl and Devils Lake Rgnl with a victor airway between them (V430).
Here is the same area from the high enroute IFR chart:

Source: SkyVector
You can see that the VOR symbol around Devils Lake Rgnl has disappeared and (although its difficult to see) the VOR symbol has also disappeared. NavAid Website lists DVL (Devils Lake) as a LOW VOR and also lists MOT (Minot International) as a HIGH VOR.
There is no differentiation between the VOR high/low symbols on a VFR chart because low altitude VOR's can serve aircraft up to 18,000 feet where you would need to file an IFR flight plan anyway, so all VOR's regardless of high/low are available to VFR flights.
Putting it another (technical) way is that high/low VOR's have the same service volume for VFR and low-enroute IFR flights, so they do not need to be distinguished on VFR or low-enroute IFR charts.
Comment: This guy got a bunch of downvotes for saying exactly what you said so I am just trying to find an official source. http://www.askacfi.com/9869/how-can-i-determine-if-a-vor-station-is-h-l-or-t.htm
Comment: I think that guy got downvotes because people may have misunderstood when he said that you know if its high or low by it having a compass rose, you know if its a terminal one by it not having a compass rose, but both high and low have compass roses on them (well, not always, but typically). There are cases where a high/low VOR does not have a compass rose usually to reduce clutter on the VFR chart near an airport, which makes it almost indistinguishable from a terminal VOR.
Comment: @jskypilot I edited my answer with an example of a VOR that does not have a compass rose (first image).
Answer: From the chart you can understand what type of VOR is that  But there are also other ways . By checking the frequency band you can also understand the type of that VOR.   There are basically two types of them and they are Terminal VOR(TVOR) and Airway VOR. The whole VOR frequency range is VHF-108 to 117.95MHz.  ILS frequency shares some portion of the TVOR. The terminal VOR are mainly of low and the airway VOR are mainly of high type.

TVOR frequency band are from 108.00 to 112.00MHz. In details, TVOR uses even first decimal and even first decimal +50KHz upto 112MHz. Like 108.00MHz, 108.15MHZ, 108.20MHz, 108.25MHz etc
and the ILS uses odd first decimal and odd first decimal +50KHz upto 112.00MHz. Like 108.10MHz, 108.15MHz,108.30MHz, 108.35MHz etc.
Airway VOR uses the remainder of the frequency band 112.00MHz to 117.95MHz.
other than this you can understand the VOR type from the chart the people has already shown.


How to set cookie crumbs

Question: When a receipe uses cookie crumbs mixed with melted butter for a base, it usually requires it to go into the oven for about 10 minutes. I am wondering why it needs to go into the oven as opposed to the fridge. I'm thinking that the fridge will help set the butter and make it more solid so it can be sliced, unlike the hot oven. Does anyone know the reason for heating the crust? I know the oven will toast the crust a bit, but the directions on the receipes usually say that it is to "set the crust".
Answer: When you bake a crumb crust, a few things happen. Related to "setting the crust" the baking step allows the butter to seep in to the crumbs, making the whole thing more of a unified unit. It also toasts the crust as a whole, giving the crust some imperviousness to the liquid in the filling, helping the crust to avoid becoming soggy before the whole cheesecake or pie is baked. Lastly, baking brings out the aromas of the ingredients in the crust. If you don't bake a crumb crust prior to filling, it'll just be butter moistened crumbs, not a "crust".

How to set cookie crumbs