Can I really not close a checking account if I have a year old outstanding check?

Question: Over a year ago, I wrote a small check ($35) to an organization at my university. They never cashed it and finally just told us that they were "lost" in the changing of the offices of the national organization, and they want us to write new checks. I no longer use the account I wrote the original check from and have been planning to close it after this situation was resolved. I talked to my bank today and they told me that I shouldn't close the account until all outstanding checks are resolved. The organization says the checks are lost and they won't be cashed, plus the date is over a year ago (so no bank should cash it...right?). Is it safe to just go ahead and close the account? Stop payment costs $15 and only lasts for 6 months, so I don't really think that is an option.
Answer: Bank normally advise customers not to close accounts if there are outstanding checks. Its just advice so that the customer doesn't land in trouble if there are outstanding checks and the account is closed.
Tell the bank that there are no outstanding checks and close it.
There is no way the organization would try to cash a one year old check. If even they did it would bounce, by reason of the account being closed. The organization's bank may charge them a penalty. There is no penalty to you from your bank as you have already closed the relationship. If you were legally supposed to make the payment to the organization, then they can chase you saying you give them an invalid check ...
So that covers all the grounds as to what can happen ...
In your case it more looks like a simple small check misplaced, even if found the accountants normally see the date before cashing, so it would never make it to the bank.
Comment: Organizations may try to cash old checks: see [this question](http://money.stackexchange.com/questions/1551/do-personal-checks-expire-us); stale checks are cashed all the time. But I agree that in this case, no need to consider the $35 check as "outstanding" as it was lost and replaced.
Answer: By my definition, the outstanding check is resolved.  I would not hesitate to close the account.
Comment: @MrChrister  He _gave_ the source of that definition: himself!
Comment: Yes, my source is MY GIANT BRAIN.  Seriously, I don't have a source--just answering based on my experience and common sense.
Comment: I agree, but do you have a source of that definition?
Answer: Working for a bank, I can tell you that people close accounts with outstanding checks all the time.
IF the check is ever negotiated (deposited, cashed, or whatever), it will be returned unpaid by your bank.
Answer: Working as a teller for the last few years I can tell you that personal checks are stale after six months (unless otherwise noted) and therefore would not be accepted.  We run into this a lot with grandparents writing checks for birthdays and the like.   You should be fine to close that account.
Answer: If the amount was large and you were keeping the account open you could reduce the payment by the cost of putting a hold on the check number. The hold fee will vary by bank and might not make sense for a small check.
Then send them a replacement check for the new amount, with a letter telling them what you did.
Because you will be closing the bank account I wouldn't worry about it. Just send them a replacement check from the new account. If they find the original check and try to cash it the account will no longer exist. They can't complain because they would have been trying to collect twice.
Answer: Make sure they give you in writing that the check was lost and that they will not try to cash it if found, and go ahead and close the account. Although technically stale checks can be honored (although can be dishonored just as well) by a cashing bank, its none of your bank's business, its your problem if the check is cashed from a closed account, not theirs.
Comment: I would send such notice return receipt requested and keep the papers so that if they do try and cash it you can show that you notified them not too
Answer: I'm assuming they told you this because you asked, as they wouldn't know about the $35 check otherwise.
If you're really worried about it, leave the minimum balance in there and don't use the account. No big deal.


Why aren't "life support belts" used elsewhere in the Trek universe?

Question: "Life support belts" have only ever been seen in the animated series (and apparently a non-canon video game as well).  Is there any explanation for why?
Comment: @Izkata: "Do they exist" and "why don't they exist" are two separate questions, as pointed out by others when I tried to ask them both as the same question previously.
Comment: @MrLister I disagree, since the answer to the first question is probably "No," which would make this question redundant.
Comment: Isn't this pretty much the same as your other question, [Do "life support belts" exist outside of ST:TAS?](http://scifi.stackexchange.com/questions/28458/do-life-support-belts-exist-outside-of-sttas) ?
Comment: Just to note, Star Trek Online has it's own timeline/canon, if you'd like to call it that way. Also the personal force fields used there aren't suited for space walk; they still use full body suits for that.
Comment: @Izkata I agree with Flimzy; someone on the other question commented that this should be a new question, as editing the other one would have changed its meaning too much.
Comment: Um...'cos? I'm not sure I've ever seen a single statement on the subject. They're just...not.
Answer: The life support belts you mention were included as an item in the FASA Star Trek Role Playing Game in the early 80s. They provide a limited supply of air, pressure, and retain heat somewhat, but are otherwise not as good as an environmental suit. They won't work for extended periods or for combat (they put up a noticeable glow around you without providing significant shielding) or stealth.
In other words, they're mostly useful when you don't need them for a long time. They do, however, serve better for highly detailed work and they are better for keeping a team in easy visual contact. They can also be worn in a 'sleep' state where they activate in an emergency (such as when the air vents).
Thus, they are primarily used as a safety and backup item. Most likely the belts were new and Enterprise was testing them to determine their limits and utility during the timeline of TAS.
Out of universe, they were created for TAS because it was far easier to draw a yellow line around the characters than to give them all EVA suits and still be recognizable.
Answer: I recall reading about this in one of the novels at some point, but I couldn't say which one.
As I remember, their use was discontinued due to safety reasons. If they failed, the wearer could be killed very quickly. EV suits were considered safer.
I don't believe there ever was a canon explanation though.


Problems bounding Fourier transform to $O\left(\frac{1}{1+x^2}\right)$

Question: I'm going through an example in my textbook, and they mention that the Fourier transform $F(z)=\int_{-\infty}^\infty f(t)e^{-2\pi i z t}dt$ can be bounded by some $c/(1+x^2)$ for $f$ being bounded and $C^\infty$. More concisely, $|F(x+iy)|\leq c/(1+x^2)$ for $y$ being bounded, and it's supposed to follow by integration by parts. But I'm doing this out and running into a few problems; namely, by using integration by parts twice and letting $u=f$ and then $u=f'$, I have something like this:
$$|\hat{f}(z)|=\left|-\frac{f(t)}{2\pi i z}e^{-2\pi izt}|_{t=-\infty}^\infty-\frac{f'(t)}{(2\pi i z)^2}e^{-2\pi izt}|_{t=-\infty}^\infty+\int_{-\infty}^\infty \frac{f''(t)}{(2\pi i z)^2}e^{-2\pi izt}dt
\right|.$$
Letting $z=x+iy$, I don't see how this is $O(c/(1+x^2))$. I also know that I can change the contour of integration (that is, change $t$ to $t+is$), but even with these added terms I'm not seeing it. Would anybody have any thoughts? Thanks in advance.
Answer: You need to assume some decay/integrability of $f$ and its derivatives in addition to $C^\infty$. Then your first terms after integration by parts are bounded. In the last term you can put the $1/z^2$ out of the integral and you are basically done.


Is there a language where in declension number is affixed peripherally to case?

Question: Is there a language where, given that number and case are affixed seperately not fusionally, a noun can have the structure of , e.g. ithawen = itha-w-en [woman]+GEN+PL ("of the women, the women's")? I can only think of (1) languages that have indiscernible affixes combining case and number (fusional affixes in respect of number and case, e.g. Ancient Greek -ōn or Latin -orum, -ibus, that ‒ to my knowledge ‒ cannot (or no longer) be further reduced to a "sub-affix" component representing either number or case) or (2) languages where case is more proximal to the stem than number (e.g. women's).
Examples where case might precede number (as a suffix), the combination  may be treated as a new lexeme (is rather a derived than inflected form of the old lexeme), e.g. the Smithses meaning "the Smith's person + plural affix" ([[Smith]s]-es).
I beg to be corrected.
Comment: What about the languages where pluralisation can happen with a modifier + singular form instead of an affix?  If we count adpositions as equivalent to case then it seems fair.
Answer: That's Greenberg's Universal #39:

Where morphemes of both number and case are present and both follow or both precede the noun base, the expression of number almost always comes between the noun base and the expression of case.

Though Greenberg's sample was small, I can't seem to find later counterexamples.  The closest thing I could find is the standard reconstruction for Proto-Indo-European; accusative -m and accusative plural -ns could lead one to see the latter as n-s = ACC-PL (see #7 here), though when I look at the whole PIE paradigm, I think that's kind of a stretch.
Comment: In the Universals Archive homepage #2011 (https://typo.uni-konstanz.de/archive/ref/source_ref.php#Aikhenvald_1998) elaborates on Greenberg's Universal #39.
Comment: It seems that Kaytete's "pair" suffix comes after the case marker; but the pair suffix is distinct from normal number, even from dual (it marks two items that fit together as a semantic pair; Singer, [*The Inclusory Construction in Australian Languages*](https://minerva-access.unimelb.edu.au/bitstream/handle/11343/39215/67183_00003035_01_Inclusory_Const_thesis.pdf?sequence=1)).
Comment: Thank you! I have been looking for that website since ages!
Answer: If you allow another order of suffixes like Stem+PluralSfx+CaseSfx instead of your example of Stem+CaseSfx+PluralSfx, then Armenian language has such declension, except for few very old words like շուն[shun] (dog), տուն[tun] (home), etc., which are declined with fusion.
Here  PluralSfx is suffix for plurals, and CaseSfx is suffix for one of cases, including "zero" suffix for nominal case.
Example:

սեղան [seg^ ՛an] (table) -i type declension
սեղաններ [seg^ann՛er] (tables=pl.nominative-case)
սեղանների [seg^anner՛i] (of tables, plural, genitive)
...
սեղաններով [seg^anner՛ov] (with tables. plural, instrumental case)

Totally 6 lexical cases in Armenian.
Comment: I think the order of the suffixes was the whole point of the original question.
Comment: I read example of "women's" in p.2 like thing not passing the "separate suffix" criteria. But there is chance that OP meant just that order, CaseSfx+PluralSfx; in that case question could be formulated more specifically.
Comment: Sorry, *women's* was meant to be the negative example. I am looking for an example of Noun+CaseSfx+NumberSfx. Another fictional example *èpecen* = ep("man")+ec(GEN)+en(PL) where genitive suffix is proximal to the stem than plural suffix.


visible light spectrum

Question: Why do we see black objects? Colors of objects are formed when the spectrum of that color is reflected. Example Green objects are green because they reflect the green spectrum of light, red objects are red because they reflect red spectrum of the visible light and white objects because they reflect all the visible spectrum of light. When an object absorbs all the visible spectrum of light, it becomes black. But if nothing is reflected from the object, shouldn't it be invisible instead of black?
Comment: Black is the color we perceive in the absence of light, so it should indeed be black. To make something invisible you have to make it completely transparent - so that light behind the object can pass through it and into your eyes. However a perfect absorber would absorb any light hitting it from behind, and so not be invisible. Real objects aren't perfect absorbers, hence you can still see their texture.
Comment: simply, it's not a perfect black object ...
Comment: I think the answers given so far misinterpret the intention of the OP's question. I don't think he want's to know how black an object can be, but rather why can't we see through it. The comment by @Judge answers this.
Answer: I wrote an earlier answer to the question: "Is true black possible?" which addresses some of the points you mention. It includes this image of "the blackest substance known":

In particular, most "black" objects have a small amount of reflectivity, from which you can deduce clues about their shape. But the sample of really black material which I show is SO black that it looks like there is a hole in space - you can't see any shape in the surface, and it does indeed look "invisible" in the sense that you don't really see the object, you see a "hole". But you don't see what is behind the hole: black is not the same as "transparent", and the black object absorbs all photons. It's not actually possible to make a material that is black in one direction and transparent in the other - there's a simple argument to be made that such a material would violate the laws of thermodynamics. Instead, in this world we're stuck with the "reciprocity theorem" that tells us that blackness is a two-way street.
Answer: Even if a perfectly black object reflects no visible light, we can still distinguish its shape from a non-black background. Most real-life black objects are just much darker than the surroundings, not perfectly black.
Answer: Black is entirely a construct of your brain, created internally to fill in a spatial region in which you eyes detect no appreciable level of photon emissions. That may sound a bit surprising, but try this: Imagine red, then green, then blue. You could do it, right? Well, no photons were involved there either. Black is the same idea, since it too is something created in your brain without any photons from your eyes. Black is just a bit more vivid because it is directly linked into your external perception systems as a way to fill in those gaps.
Answer: I will address the "see" part.

Why do we see black objects? Colors of objects are formed when the spectrum of that color is reflected. Example Green objects are green because they reflect the green spectrum of light, red objects are red because they reflect red spectrum of the visible light and white objects because they reflect all the visible spectrum of light.

This is only partially true. We "see" the spectrum colors because the retina of the eye responds to the frequency. But at the same time the retina and the brain have a system that builds up colors from combinations of frequencies, even two frequencies are enough to produce color perception in the brain.
Thus one can have the black of the other answers, no reflected frequencies, but one can create a black paint that gives the same perception from the three primary colors. The eye perceives "black" from the confluence of the reflected frequencies.
Answer:
A related question is, why do we see white?

From a physics perspective you are correct, we should not see the object.  We should see a hole, a complete absence, like looking into the face of a shadow rider or a dementor.
However, from a biological and neuroscientific perspective, we autocorrect.  The limited light is detected by the super sensitive rods on the edge of our retina, limited information gets sent via ganglion and bipolar cells, down the optic nerve, through the thalamus and lands in the visual cortex near the back of your neck. This is where we create the virtual object which "pops out", at which point, your interpretation/version of what exists deviates from what actually exists. An interesting experiment would be to take a photo (as the one above) and look to the photo and then to the real object side by side, although your brain may also compensate for the photo and pop out an object!
The retinal rods and visual cortex (occipital lobe) also explain why we only see in black and white in low light.

Neuroscience aside, I wanted to provide a second answer.

I was actually interested in your questions on brane theory and faster than light travel but it seems that these don't conform to flat earth theory so were closed and unanswerable :)  On brane theory, I would guess yes, different fundamental laws, simply from analogy with air versus ocean.  If you walk on the beach you create constructs of sand, you walk to the ocean bio-dome and "cross over", then you are underwater and everything changes.  Dimensions must exist and perhaps facilitate the electron jumping lobes in the p-orbital, the "cross over" must be a common surface but the other side would be largely independently governed.
On the faster than light, there was a good "faster than light" wikipedia entry.  I would guess that yes, time would reverse but not in the "back to the future" sense. As with the 'why do we see black?' question, I would anticipate biology to act independently to physics and so time reversal is not the secret to eternal youth and once a cause has had an effect, it would not reverse. Further, I'm not sure relativity or newtonian physics would apply anyway, so if you want to travel across the universe, perhaps instead, you would be better off seeking out schrodinger's errant pets and missing electrons in your higher dimension.
Stay curious. xx
Comment: You should give links to the closed questions you are addressing. Otherwise the second part of your answer is a nonsequitur
Comment: Good call, thanks, links to [question 1](http://physics.stackexchange.com/questions/229862/when-we-say-parallel-universes-with-different-laws-of-physics-exist-what-do-we) and [question 2](http://physics.stackexchange.com/questions/229017/faster-than-light-travel)
Answer: As long as there is a discontinuity in the index of refraction ( real or imaginary parts) then there will be a reflection from the "black" object.  How your eye-brain perceives it is a different matter..
Answer: We don't actually see light itself. We see objects which emit, reflect, absorb or refract light. Where the light strikes our retina and which cone is triggered allows the brain to create images because of contrast. This visual representation of reality is what we see. Because we have binocular vision this image appears 3 dimensional. Of all the species on the planet, ours is the closest to objective reality but we only actually see about 1% of the universe.
Comment: Light is the only thing we see. That's why television and computer screens can work. The stuff we see on a screen is not there. It's just light.
Comment: You are not seeing light. The source of that light is a diode. This is what you see. Each diode emits a different wavelength of light.

visible light spectrum


How to pursue good career in Manual Testing

Question: I have 1.5 years of manual testing experience from a leading organization. Can you please suggest how I can achieve more and gain onsite opportunities from the organisation. Please do a little unicast.
Comment: By "leading organization" do you mean a test contracting organization? Also, what do you mean by "a little unicast"?
Answer: This is a great question. I am in nearly the same point in my career, about 15 months total in QA and honestly my career is taking off like a rocket in my mind.
The steps I follow are rather simple.

Learn something new constantly
This can be difficult depending on the situation you are in with your company and your experiences. I was an API tester with some personal development experience. I decided to create a GUI and a framework for the API and Data preparation that just made my job and the job of the people around me a lot easier and more efficient.
I did that in my personal and spare time at work so that I could still achieve all of my desired results from my daily tasks.

Be adaptable and flexible
By this I mean do what it takes to stand above the rest. Chances are you are one in at least 100 - 200 people in your department. When the person in charge of your department thinks of you, what will he think of? Will it be he is one of my testers or will it be he's the guy that gets stuff done. You want to be the second one. Always look for things to do, ways to productively spend your spare time and drive the department. For example, a couple weeks ago I went ahead and cleaned out my department's lab.

Learn the SDLC
Having experience with the Software Development Life Cycle as a whole will be extremely beneficial. A lot of people have expertise in their portions of the SDLC but have no clue what role others play in it. This gives you a huge advantage over others in your field since you can understand what the developers, PMs, BAs, SAs and such are looking for in the project. It also gives you the ability to have compassion and respect for their crucial roles in the project.

Find your niche
This is probably the most crucial. Find the area in your company where you stand out above the rest. This doesn't even have to be something directly related to your position. But it is important to be the best at something. Whatever it might be, make sure you are the best in your company.

When you combine all of the above together you get a couple of basic traits that will lead to a successful fruitful career.
TL;DR:

Adapt and Overcome
Be the go-to guy
Understand your co-workers jobs
Comment: Good Suggestions, If you love your work you will excel in it. Keep Learning, Be updated on areas of interest, never stop learning.
Answer: I'm struggling to understand your question, although I'd start by advising you to ask your line manager about the possibility of taking the ISTQB ISEB Foundation Software Testing course and exam. Depending on the type of testing you have been exposed to, ask if you can work on some other projects that would involve different testing techniques from what you have experienced thus far.
http://www.istqb.org/
Purchase the book and start reading the syllabus. You can get it from Amazon for around £20.


What happens when mixing elemental mercury with sodium hypochlorite solution

Question: Say you spilled elemental mercury from a thermometer and used household bleach on it, what would be the reaction if any?
Comment: More importantly, this is a very poor way to decontaminate anything where mercury has spilled.
Answer: There are several redox reactions can be taken place when you add household beach on elemental mercury metal. However, this question is more like a homework question. Thus, I give you insight to the answer and you may read a bit and find out what's happening. This reaction is studies and results have been published (Reference 1), the abstract of which states that:

The absorption of elemental $\ce{Hg}$ vapor into aqueous hypochlorite was measured in a stirred tank reactor at $25$ and $\pu{55 ^{\circ}C}$. $\ce{NaOCl}$ strongly absorbs $\ce{Hg}$ even at high pH. Low $\mathrm{pH}$, high $\ce{Cl-}$ and high-temperature favor mercury absorption.  Aqueous free $\ce{Cl2}$ was the active species that reacted with mercury. However, chlorine desorption was evident at high $\ce{Cl-}$ and $\mathrm{pH}<9$. Overall second-order reaction was observed between mercury and chlorine with an apparent second-order rate constant of $\pu{1.7\times 10^{15} M^{-1} s^{-1}}$ at $\pu{25 ^{\circ}C}$ and $\pu{1.4\times 10^{17} M^{-1} s^{-1}}$ at $\pu{55 ^{\circ}C}$. Gas-phase reaction was observed between $\ce{Hg}$  and $\ce{Cl2}$ on apparatus surfaces. Strong mercury absorption in water was also detected with $\ce{Cl2}$ present. Results indicate that the chlorine concentration, moisture, and surface area contribute positively to mercury removal.

I hope you will figured it out when you consider the standard reduction potentials of $\ce{Hg}$ and $\ce{OCl-}$ in any electrochemical series. For example, see Reference 2.
References:

L. L. Zhao, G. T. Rochelle, "Mercury absorption in aqueous hypochlorite," Chemical Engineering Science 1999, 54(5), 655-662 (https://doi.org/10.1016/S0009-2509(98)00263-2).
S. G. Bratsch, "Standard Electrode Potentials and Temperature Coefficients in Water at $\pu{298.15 K}$," Journal of Physical and Chemical Reference Data 1989, 18(1), 1-21 (https://doi.org/10.1063/1.555839).
Answer: As noted by @Mathew, sodium hypochlorite can be used to remove elemental mercury. It is a redox reaction involving oxidation of mercury to $\ce{Hg^2+}$. There are various papers which discussed about the reaction of sodium hypochlorite and mercury and its role in removing of mercury. This paper1 discusses about the dissolution of mercury in aqueous solution of sodium hypochlorite at pH of 5.9–8.5 and the mechanism of oxidation of mercury to $\ce{Hg^2+}$. There is also another paper[2] which discuss about the role of sodium hypochlorite in the removal of mercury by wet-scrubbing method.

The important step for increasing gaseous elemental mercury
  removal in wet scrubber systems is altering the chemical form of the
  Hg to a water‐soluble oxidized species. This work focuses on the
  removal of elemental mercury from simulated flue gas by aqueous sodium
  chlorite in a bubble reactor. The effects of initial oxidizing
  solution concentration, reaction temperature, pH and mercury
  concentration in the inlet of the reactor on mercury oxidative
  absorption in sodium chlorite were investigated. The results indicate
  that higher concentrations of sodium chlorite favor Hg removal, with
  a greater efficiency observed in acidic than in alkaline solution.
  High temperature inhibits Hg absorption in aqueous sorbent when the
  reaction temperature is lower than ca. 40 °C, and the removal
  efficiency increases when the temperature is higher than that value.
  In conclusion, the major influencing factors on the levels of Hg
  removal are pH and chlorite concentration in solution.

References

I. P. SizenevaV. A. Val'tsiferV. N. Strel'nikov "A Study of Mercury Dissolution in Aqueous Solutions of Sodium Hypochlorite" Russian Journal of Applied Chemistry April 2005, Volume 78, Issue 4, pp 546–548 (link)
Y. Zhao  S.T. Liu  C.M. Chen  X.Y. Ma "Removal of Elemental Mercury by Sodium Chlorite Solution" 28 February 2008 (https://doi.org/10.1002/ceat.200700381)
https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98JD02304


Can UHT milk be used to make yogurt?

Question: So I know you can't use UHT milk to make cheese, because of the way the proteins get denatured at that temperature.  But can you use it to make yogurt?
Answer: UHT (Ultra High Temperature) processing kills all the pathogens in the milk, so it can be conserved for a long time. However to make yogurt you add bacteria (lactobacillus), so if there aren't other microorganism it should be even better.
Comment: Right, except that UHT also denatures the proteins in the milk and prevents them from clumping in the same way as natural milk.  This is what prevents UHT milk from making cheese.
Comment: Are you sure it is the UHT that does that? I thought it was the homogenization. But anyway, yes you can use UHT milk to make yogurt.
Comment: In yogurt the proteins don't need to form long chains and precipitate out of solution in the way they do for cheese. If it's true that UHT can't be used for cheese (I don't know either way) I imagine it's because the denaturing prevent the proteins from binding together, which does not matter for yogurt.
Comment: Wikipedia: ["To produce yogurt, milk is first heated ... to denature the milk proteins so that they do not form curds."](https://en.wikipedia.org/wiki/Yogurt).
If @DanielBingham is right (UHT milk has denaturated proteins) it would be ideal to make yogurt.
Answer: UHT milk makes excellent yogurt. I have had it on several occasions and the texture was fantastic.
Even if you don't use UHT milk it is necessary to heat the milk to denature the albumin- otherwise it stays water soluble and washes out in the whey.
Comment: @verbose Good texture is smooth, homogeneous, and creamy verses bad texture which is grainy, stratified, or a fragile gel. It's really not a matter of thickness which is more affected by fermentation time rather than technique.
Comment: Can you explain in what way it was "fantastic"? Some folks like thick yogurt, others like it a bit thinner. So what X finds fantastic, Y might find lacking. It would help to have a more specific description.
Answer: yes you can.  a co-worker from a few years back did just that.  the fermentation comes from the culture, not from within the milk.  i didn't try myself though.
Answer: I just tried making yogurt with UHT Lactose-free milk (my kids and I are lactose-intolerant and there are few yogurt options where I live). It worked for me, but as mentioned in a couple of the answers here, I added powdered milk. (1 cup milk + 2 tbsp milk powder + 1 tbsp plain yogurt with live culture)
To test whether I need to heat the milk or not, I experimented and did one jar with heated UHT milk, and one jar with room temperature UHT milk. The heated batch was definitely thicker and creamier, but I suspect it has to do with some moisture loss during the heating process itself. I measured 1 cup of the milk into the saucepan, and one cup straight into the jar. After heating, the volume of the milk was (expectedly) smaller, so that's one hint right there as to why it's thicker and creamier.
The other things I did which, I believe, helped with the successful outcome were: (1) to keep the jar immersed in water that was at 100F, instead of 115F (the usual recommended temp) and did so for 8 hours; (2) I took the extra step of straining the yogurt for 2 hours.
So yeah, I was able to make thick, creamy Greek-style yogurt with UHT milk.
Answer: I have used UHT milk to make my yogurt for over five years now! Without adding milk power I have had a rich thick yogurt, Start it before bed in a yogurt maker and it's ready next morning
Answer: I use UHT milk for yogurt all the time. If you want a thicker texture try adding some powdered milk.
Answer: I agree with Jackie - just add a little powdered milk.  I've been using unheated UHT milk to make yoghurt for years, with fab results.  I've also made cheese quite a few times with it.  I've made yoghurt with pasteurized milk as well and the results were the same, just less convenient than UHT if you live in the boonies like me.
If you want to know how yoghurt and cheese are made, I suggest you get a book (yes, libraries still exist) and ignore the massive amount of 'evidence' on the internet.
And just 2 more points:
1) Greek yogurt is made by straining the whey from regular yoghurt.  Even in Greece (I lived there).
2) making yoghurt is a bit of trial and error.  never assume you don't like something after trying it only once.  you'll need to tweak lots of things until you get it right (kind of like making the perfect loaf of bread).
Answer: I always use UHT milk. I've tried all brands in Australia and all work well. I use a thermophillus + bulgaricus culture at 44c. 12 hours works for me.
Answer: yes you can, I do it all the time now. I have tried many different UHT types, the following are my experiences. I only used the full cream UHT type, I don't boil the milk, I just add some farmers union greek yoghurt to it and give it a shake, then start incubating.
Woolworthes UHT milk makes the thickest yoghurt.
Devondale UHT milk makes ok yoghurt.
foodland/coles UHT milk makes less thick yoghurt
Pauls UHT milk makes very runny yoghurt
Answer: I have been making yoghurt from full fat Devondale UHT for 4 years. The results are usually excellent, though I recommend allowing the cycle to run a bit longer for thicker results. I use an instant pot to boil and then ferment the milk for a bit more than 8 hours. I often start the process a little bit hot, as I can't be bothered to wait for the boiled milk to reach room temperature.
I believe that the starter culture makes a big difference. I have used a cheap Chinese culture (probably targeted at making yoghurt drinks) and two Danisco professional cultures (Yo-Mix 495 LYO 250 DCU and 883 LYO 50 DCU).
The 495 seems to be targeted at making Greek and does indeed produce a thicker, creamier, slightly less sour yoghurt.
I normally reuse some of the existing yoghurt to make the next batch, so buying good culture is worth it.
The ultimate thickness of the Greek yoghurt I make depends more on the straining process (I often leave it until all the weigh is separated as I like yoghurt cheese and the weigh is good in smoothies).
I haven't tried making the yoghurt without boiling; this is something that I intend to try since it would reduce the process time by about 4 hours (I make 5L batches).
Answer: I believe the same issue would apply since yogurt is essentially a step on the path toward cheese.  One recipe I looked at did say not to use UHT.
Comment: No, it didn't.  I've now seen recipes and comments where people say that their yogurt makers recommend UHT milk and that they typically do.  Best thing to do, as with so many cooking ideas/questions....give it a shot and see how it works!  Sounds like it must.
Answer: I have been making home-made yogurt for a month on an every-day basis.
I tried UHT once and it was extremely watery and flaky that I threw it away.
I have since sticked with fresh (skimmed/semi skimmed/whole) milk, which works perfectly.
I do notice that different brand of milk give a different texture too.
Puzzled, I searched on Google trying to find an answer why UHT milk can't be used, and found this. I do not have an answer myself but I thought it is helpful to share my own experience with making yogurt.
Comment: This shouldn't be downvoted. It is a differing experience, but an experience nonetheless.
Answer: My mother used to make yogurt with UHT milk. But as Lorenzo said before, it doesn't have any bacteria. That's the reason why my mother used to add a little quantity of an existing yogurt in the mix of milk and sugar. Afterwards she put it in the yogurt-maker for a few hours and tada! you've got your homemade natural yogurt!
As Gapton says, the resultant yogurt is more watery (texture doesn't anything to do with greek yogurt for example), that is right, but I love it!! it is very natural, it's my childhood yogurt and I am still alive ;)
Hope this helps!
Btw, happy pancake day!!
Answer: I have made excellent thick yoghurt with uht semi skimmed milk, for every 3 cups milk add 1 cup of skimmed milk powder and a couple of tablespoons of live yoghurt from fridge. I use my easiyo to make (I started with one of the packet mixes and used the yoghurt made to supply the 2 tablespoons - then I use the next batch to start a new one) works brilliantly. I use cup cake flavouring and stevia sugar to sweeten. Not fat free but low, thick and delicious and full of good bacteria. Tip - freeze some berries (I chop up grapes, strawberries, raspberries, blueberries and banana and put in single portion bags). When fully frozen tip into bowl and add 3-4 large spoons yoghurt above, stir in. Leave for 2 mins and yoghurt hardens. Just like having chunky icecream - I have daily yum!
Answer: I have used UHT skim along with powdered skim in my yogurt for years. Heres why 1. it works 2. it saves sterilizing the milk, I'm a rational male 3. its actually a little cheaper 4. I've read concerns that heat treating whole milk causes oxidation to cholesterol which has health implications, so skim all but eliminated the cholesterol. This may be wrong
Answer: Use UHT many years now.  To a 2 ltr container I add 1 cup of cream milk powder.  I always use fresh culture. The result is Greek strained type thick, rich yogurt that brings me MANY compliments
Comment: Hello, and welcome to Stack Exchange. Do you mean "I have been using UHT for many years now"?
Answer: UHT milk is great for making yoghurt. To thicken add a tablespoon of gelatine when the milk is approximately 45ºC then place the container in the yoghurt maker. You will only be able to thicken yoghurt by using an ingredient like gelative or guargum to thicken.
Comment: -1. You can make perfectly good, thick yoghurt without gelling agents. Thick enough for a spoon to stand in it without falling. #
Answer: I produce yogurt for sale. I use UHT milk but along with milk powder.
Based on all the responses claiming to have done it, you will notice powdered milk is involved.
Comment: No, all the responses claiming to have done it do not use powdered milk. It's not required.

Can UHT milk be used to make yogurt?


Boolean Modifier Dissapearing

Question: When I apply a Boolean modifier to say a cube during an animation and link a cylinder as the Boolean object and animate the cylinder going through it, when the cylinder goes all the way through the Boolean modifier disappears on the cube and it becomes solid again, is it possible to make the cube contain the hole through it after the cylinder has passed through it. I have tried the carve feature instead and it still doesn't work. Any help is appreciated, thanks.
Answer: For animaton you need to create keyframes, that are inserting by pressing I. Creating or removing smf are not a operation that can be keyframed.
Instead of this try to animate displaying of modifier. So do the following:

Go to the 1 frame
Hover cursor on eye icon  and/or camera icon and press I
Go to a frame that you want to hide modifier
Disable modifier (eye icon disables in viewport, camera - in render)
Hover cursor on eye icon  and/or camera icon and press I

It will create an animation, that will hide modifier after chosen frame
For creating a hole, I recommend to create a copy of cylinder, that will not leave a cube, and make them invisible for render:

You can do it in outliner.

Comment: That's know really what i  wanted to know but good information for the future, I want to know how to make it so that the modifier doesn't automatically disappear after the cylinder has passed all the way through. I have a cylinder animated so its traveling through the cube and it disappears after it gets through and the cubes "fills itself" right after I want to know how to make it so it doesn't disappear and the cube maintains the hole.
Comment: Create a copy of cylinder, remove animation for this and hide it from render. So, one cylinder will be for hole, one for animation.

Boolean Modifier Dissapearing


Is there a taboo about a younger groom marrying an elder bride? Any references where a younger groom marries an elder woman?

Question: As the question says, are there any taboos/guidelines or any references to authoritative texts or incidents where a younger groom marries an elder woman?
Comment: "Radha-Krishna" can be a reference, if we consider that "Gandharva Marriage" happened between them.
Comment: Silly. Do you think that this is right. Has Lord Krishna, Rama followed this. Seetha was 6 years elder than Rama. Krishna married thousands of women. were they really younger than him. Radha was elder to Krishna. Is there any proof that every wife of Krishna belongs to low caste than their sisters whom Krishna married before them.
Comment: Age and caste never matters. Only true love matters.Rukmini was a kshatriya whereas Krishna was a yadava. Don't you think that everything that is said in great books is true. There are many mistakes in them. And no book is perfect to attain complete goodness but one
Comment: @Dinesh Sri Krishna is Chandravanshi Kshtriya from Yaduvansh of King Yayati. This Yaduvansh has nothing to do with modern day yadavs of India as that Kshtriya Yaduvansh was completely destroyed during Dwapar Yuga by Lord. Few yadus were Lord's eternal companions who returned to Vaikuntha with Sri Krishna. Like Ayodhya residents and Vanars,who were companions of Lord and Devas took jala samadhi with Sri Rama. Other yadavs who were egostic earned curse from a Sage after insulting Him and a curse from Sri Krishna Himself for sins. Leading to their complete annihilation. Refer Bhagavatam book 11.
Comment: @Dinesh also what is your source of Mother Seetha being older to Sri Rama? I have heard about Radha Krishna but never about Seetha Rama.
Answer: Yes, there is a scriptural basis for the restriction.
Here is what Krishna says to Uddhava in the eleventh  chapter of the Uddhava Gita of the Srimad Bhagavatam:

One who desires to establish family life should marry a wife of his own caste, who is beyond reproach and younger in age. If one desires to accept many wives he must marry them after the first marriage, and each wife should be of a successively lower caste.
Comment: Great, what more authoritative can one ask especially one that's from the horse's mouth?
Comment: @Keshav - I remember, reading  mahabharata, shanti parva, where bheeshma answers such questions
Comment: @Krishna Are you referring to the Anushasana Parva, where Bhishma gives talks about wives' ages which are a third of the husband's age? http://www.sacred-texts.com/hin/m13/m13b009.htm That is based on verse 94 of this chapter of the Manu Smriti: http://www.sacred-texts.com/hin/manu/manu09.htm  In any case, Medhatithi's commentary on the Manu Smriti says that verse 94 is just giving examples of suitable ages, it's not saying that everyone has to follow those ages.
Comment: @Keshav - May be Anushashana parva. I dont remember the exact parva. I thought it is in Shanti parva. I could be wrong. Even the uddhava gita can be dusmisssed as just being prescriptive in nature. your answer doesnt mandate it.
Comment: @Krishna Well, I think the two cases are different.  In the case of the Uddhava Gita, no commentators (as far as I know) state that that verse is merely a suggestion or example.  In the case of that Manu Smriti verse, all the commentaries I've looked at say it's merely an example.
Comment: @KeshavSrinivasan I think it's just only suggestion... we have examples of marriage of Balarama and Kakudamis daughter... she was born earlier than Balarama...  also I think we have stories of Apsaras married with Sages... in such condition also Apsaras already existed before birth of Sages...
Comment: @Tezz Well, Apsaras are an unusual case, but at least for marriage between one human and another the man has to be older than the woman.  And Revati is also an unusual case, because her biological age didn't match her chronological age.  But in any case, it's not just a suggestion, it's a firm rule described in numerous Dharma Shastras.
Answer: Any references to authoritative texts or incidents where a younger groom marries an elder woman?
Yes, there are few incidents of boy marrying girl older than him:

As per Śrīmad-Bhāgavatam (Bhāgavata Purāṇa): Skandha 9: Chapter 3, Revatī was much (twenty-seven catur-yugas!) elder than Baladeva (Balarama). Brahma advised Revatī's father to offer his daughter to Balarama.
As discussed in Was Radha aunt of Krishna? post, Radha was fourteen years elder than Krishna and Brahma had performed the marriage of Radha with Krsna (Brahmavaivarta Purana: Prakrti-Khandam: Chapter 49).
As per SB 10.55, Kamadeva took rebirth as Pradyumna. Māyāvatī's (Rati) used to live as a cook in the household of Śambara when Pradyumna arrived there as a just born baby. So Mayavati was much older than Pradyumna.
Comment: why so..keep on reading and u ll find that Pradyumna addresses her as mother as he was unaware of their incarnation...this indicates the age gap...also here 'short time' doesn't mean few hours...also, many younger man looks elder to female of more age and vice versa but age should be age only and not like how old one looks...
Comment: The third one you are referring may not be exact...... See this statement **After a very short time, Pradyumna grew to youthful maturity, entrancing all the women with His beauty**  https://www.vedabase.com/en/sb/10/55
Comment: Please consider this statement also: **Taken from the fish's belly, and carefully protected by his wife, Pradyumna suddenly grew to become a young man. Then he understood what his enemy had done**. [25] http://wikikrishna.com/index.php?title=GS_6.8:_The_Marriages_of_All_the_Queens
Answer: As it is already said in above answer that marriage between elder bride and younger groom is restricted but for answering the second part of this question that asks for the reference of such marriage, there is a very famous example of marriage between Lord Balarama and Revati is described in Bhagavatam here where Lord Brahma says following words to Kakudmi (Revati's father):

tat putra-pautra-naptṝṇāṁ
gotrāṇi ca na śṛṇmahe
kālo 'bhiyātas tri-ṇava-
catur-yuga-vikalpitaḥ
Twenty-seven catur-yugas have already passed. Those upon whom you may have decided are now gone, and so are their sons, grandsons and other descendants. You cannot even hear about their names.
Answer: It is said that a man shall marry a maiden who is much younger than him.
See about that in the Vishnu Purana: Book III: Chapter X:
http://www.sacred-texts.com/hin/vp/vp084.htm

"If he marry, he must select a maiden who is of a third of his age"
Comment: That Vishnu Purana is based on a line from the Manu Smriti, and I think both the commentators on the Vishnu Purana and the commentators on the Manu Smriti are unanimous in their claims that this is meant as a rough guideline concerning appropriate ages, especially at the lower bound, and not a rule that has to be followed exactly.
Answer: Yes.
Sanathan Dharma avoided marriage between younger groom and elder woman and allowed marriage only between elder groom and younger woman.
While listing the duties of a householder, Yajnavalkya told that wife should be younger than husband.

The wife should be a, girl young in years and not previously
married to any other husband, in the possession of sound health and
having had uterine brothers of her own, and not related to him by any
tie of Sapinda relationship, nor belonging to the same spiritual
clanship (Arsa Gotram) as his own. She should be taken from any of the
sixteen reputed families of the rotriyas, not related to the
bridegroom within five and seven degrees in the lines of his mother
and father respectively.
[2-3, Chapter 95: Duties of house-holders, Achara Kanda, Garuda Puranam]

It has been mentioned that one should avoid intercourse with elder woman. We can understand that marriage should be avoided.

The six things, such as the use of a new wine or Trimulakam (lit.,
horse radish in its three different forms) the partaking of curd in
the night, or of dried meat, sleep during the, day, and the bed of an
elderly woman, should be abjured.
[25, Chapter 114: injunctions as to the distinction of friends and enemies (in the Nitisara), Achara Kanda, Garuda Puranam]

Intercourse with elder women is an depletive agent that reduce strength and vitality  of the person.

Dried meat, exposure to the rays of the autuman, sun (in Virgo), curd
of more than two days manufacture (Tarunam Dadhi), intercourse with a
woman older than one's own self, and sleep and coitus in the morning
are the six depletive agents that tend to reduce strength and
vitality. coitus in the morning
are the six depletive agents that tend to reduce strength and
vitality.
[31, Chapter:  114: injunctions as to the distinction of friends and enemies (in the Nitisara), Garuda Puranam]

It has been mentioned multiple times across the scriptures to avoid marriage with women who is older than the groom.


Where did Jon Snow get his sword?

Question: Whose sword did Jon Snow use to kill the White Walker in Game of Thrones S05E08?
Comment: Come on, try to do some basic research first!
Comment: @StannisBaratheon Exactly. GoT has actually been pretty good at making valuable previews/flashbacks. That being said, I think the OP was confused that the sword he eventually used was actually **his** sword. It was clear to me but the fight scene was a bit frantic.
Comment: It's **his** sword. Please **DO NOT** put **spoilers** in titles.
Comment: Now I think there is some value in previews before episode, they even showed it how Jon got it .
Answer: In episode 9 of season 1 ("Baelor"), Jeor Mormont gave Jon Snow the Valyrian steel sword, Longclaw, in thanks for saving his life from a wight.
In the books, it originally had a bear's head as the pommel, but Mormont had the pommel refashioned into a wolf's head of pale stone with ruby eyes for Jon. It's a "bastard" or hand-and-a-half sword (half a foot longer than a longsword), rather than a longsword or greatsword.  It is the Mormont sword in the way that Ice was the Stark sword.  Jorah Mormont inherited it when his father took the black, but had enough honor to leave it behind when he was exiled in disgrace for trying to sell poachers into slavery, and Maege Mormont (Jeor's sister) who now rules Bear Island, sent it to Jeor at the Wall.
Comment: I have to admit that it was hard to tell that it was his sword, especially considering how he had a sword before that was shattered.
Comment: +1 I kind of assumed sword was made to look like ghost since he is Jon's direwolf.
Comment: Nice!  Thanks for this.  I think the OP may be confused to whether the sword Jon used on the White Walker was his own or not.  You might point that out but nice answer, in general.
Comment: @StannisBaratheon Yup. Didn't feel like mentioning the Ghost-appearance, though, since in the show, Ghost isn't an albino with red eyes. I also deleted an entire peroration on the Mormont women in the books (Maege being sent off to find Greywater and Howland Reed; Dacey buying it at the Red Wedding, etc.)

Where did Jon Snow get his sword?


Are there any open-source trading bots out there?

Question: Has anyone published an open-source trading bot that runs on a Bitcoin exchange?
Comment: Instead of commenting each answer I'll write it here. All answers on this page can be improved by adding a little bit of explanation about the software that you're linking to. Answers with just links are not very good answers.
Comment: Google results contain several such bots.
Answer:
ga bitbot
from the project page:

ga-bitbot is a distributed genetic algorithm tuned automated mtgox trading system for Bitcoin which includes market data collection, gene client/server, reporting tools, and automated trading.
The intention of this project is to create a high frequency capable trade platform for the bitcoin p2p currency.

bitcoin arbitrage
From the project page:

bitcoin-arbitrage - opportunity detector and automated trading
  It gets order books from supported exchanges and calculate arbitrage opportunities between each markets. It takes market depth into account.
Currently supported exchanges to get data:
MtGox (USD, EUR)
  Bitstamp (USD, ~EUR)
  Bitcoin24 (EUR)
  Bitfloor (USD)
  Bitcoin-Central (EUR)
  BTC-e (USD, EUR)
  Intersango (EUR)
  Bitfinex (USD)
Currently supported exchanges to automate trade:
MtGox (EUR, USD)
  Bitstamp (USD)
  Bitcoin-Central (EUR) - closed
(under MIT licence)
*TODO:
Tests
  Write documentation
  Add other exchanges:
  icbit
  BitFinex
  Update order books with a WebSocket client for supported exchanges (MtGox, Bitcoin-Central)
  Better history handling for observer "HistoryDumper" (Redis ?)
  Move EUR / USD from a market to an other:
  Coupons
  Ripple ?
  Negative Operations
  use Litecoin or other cryptocurrencies trades
Comment: Please add a description, do not post just an URL.
Answer: I wrote a simple market maker bot in Python: https://github.com/chrisacheson/liquidbot
This software allows you to place orders on MtGox market.

Liquidbot uses ezl's wrapper code to interface with MtGox: https://github.com/ezl/mtgox

Aricie runs a hosted market maker bot platform: https://dnnbitcoin.aricie.com/default.aspx
Answer: You can try this one also https://github.com/rokj/bitcoin_dealer.
From the README file on the repo:
Bitcoin dealer is simple Django program (trading bot) for trading bitcoins currently only on MtGox exchange.
Bitcoin dealer supports MtGox API version 1 with following currencies: USD, EUR, GBP, PLN, CAD, AUD, CHF, CNY, NZD, RUB, DKK, HKD, SGD, THB, JPY and SEK.
Although program is really simple, it supports stop orders and maybe something more, but I am not really familiar with trading techniques and jargon.
Program is most useful for those who do not have time to watch price of bitcoin all the time, have a PC running all the time and know how to write few "Hello worlds" with two if cases.
Also, the link is not dead at time of editing (21/07/2013).
Comment: Welcome here. Please add a description of the software, do not post just an URL.
Comment: Link is currently dead, so unless edited this answer is worthless now.
Comment: Link is now live again.
Answer: When considering a bitcoin trading bot, you must decide where you will trade, generally which exchange you'd like to trade at, such as Binance or Poloniex. From there, you can either use a 'pre-packaged' strategy for buying and selling or developing your own based on various indicators.
I have developed a youtube course where I describe the open source development of a crypto trading bot in python, with all crypto trading bot python code publicly available through github. With this bot you can create and set your own strategies.
Other than my previous description, another well developed crypto trading bot is 'Gekko', open source on NodeJS and can has great, easy functionality to create and implement strategies with large community support.


Are CFLs available with mini candelabra bases?

Question: Trying to replace a light bulb that has a mini candelabra base and want to replace this bulb with a CFL bulb but can't find any. Are CFLs available with mini candelabra bases?
Answer: Sounds like you know what you want, an E-11 base CFL, not the more common E-12 sized base candelabra that Mr. Sherman linked to. Unfortunately, the mini term gets thrown around alot, referring to the over all size, not the base size. As you have found, E-11 CFLs are pretty rare, if they exist at all. However, you can get adapters that fit in E-11 sockets and accept E-12 based CFLs. Obviously they extend the height of the final installation, and some E-12 CFLs are fairly huge in the first place. However, if you look around, you can find E-12 CFLs that are reasonably sized, and even have something similar to the traditional candelabra shape. Happy searching :)
Answer: I found the Sylvania Micro-Mini candelabra base to fit fine. The fluorescent corkscrew was also small enough to fit under my paddle fan's diffuser, unlike a couple other brands I tried. I found them at my local Lowes, picked them up with a few other options, tried them all out, and returned the ones that didn't fit.
If these don't fit, it's possible you're out of luck.


What are the advantages of point to point (PTP) wiring?

Question: What are the advantages of having a pedal or amp that is point to point wired as opposed to one that is built on top of a printed circuit board? Are there any disadvantages of PTP?
Answer: Advantages to the user of PTP: you can maintain it much more easily. You can simply see the signal path and often component spacing is less fiddle.
Potential advantages in PCB design is often easier to make robust circuits. Broad generalisation, but a well made circuit board can be very resistant to drop damage, whereas a larger layout PTP may suffer from more of a bending moment if dropped. Analysis tools for PCB design are also readily available.
I always prefer to PTP in prototype and finalize on PCB.
Answer: Theoretically, there's not necessarily any difference.
Practically speaking, however, there's a fairly fundamental difference: air has a much lower dielectric constant than epoxy (which is what most PC boards are made out of). This means even a fairly small gap of air between PTP wires reduces the capacitative coupling to a very low level. Achieving exactly the same (or even less) capacitance between traces on a PC board is always possible, but often quite impractical.
As already noted, however, that all goes out the window if you bundle wires together -- the minute you have direct insulation-to-insulation contact between the wires, you're dealing with the dielectric constant of the insulation rather than of air (and it's typically in the same general range as epoxy -- much higher than air in any case). The higher dielectric constant of insulation is why some people actually use uninsulated PTP wiring -- as long as you assure against the wires touching, it (nearly) minimizes capacitative coupling (though, of course, there is that oh-so-minor detail that catastrophic problems change from "if" to "when").
Comment: I'd say it's exactly the opposite. Theoretically, there's a small difference concerning the signal quality, coupling and so on. The amount and sign of the difference depends on the PCB and PTP designer, it's possible to deliver bad designs in both approaches. Practically however, there is no hearable difference in sound.
Answer: You're going to pay more for PTP than PCB and that is the only difference.  I challenge anyone to post an audio clip where you can discern the difference between PTP and PCB of the same design, because there will be no audible difference if the boards are laid out and made properly.
Additionally, even observing w/oscilloscope or running noise analysis on the board vs point-to-point should give you nearly exactly the same results.
PCBs were really expensive back when Fender was making the Deluxe, that's why it was all PTP.  Now they're cheap, so there's no reason to go through the extensive labor.
Also there's talk about parasitic or inter-channel capacitances and other phenomenon like that.  Analog stuff found in electronic warfare at extremely high frequencies like 6GHZ+ work great on PCB and they are astronomically more sensitive to noise than a guitar signal is - you'll never find that stuff wired PTP because I suspect you'll actually start to hit more unknowns in workmanship such as inconsistent contact being made.  In fact, the one trick they use for RF analog designs is to use large ground plane "pours" on boards.  If there's any improvement over a standard PCB it isn't to go PTP, it's to design a very well grounded board.
That said I've owned a 5E3, but that's just because they are awesome :) Get what you like, but don't be fooled by the pseudo-science
Comment: "You're going to pay more for PTP than PCB and that is the only difference." -- have you seen the price of a Mesa Boogie Mark V? :)
Answer: I'll give you the answer from an electrical engineering perspective:

PTP can be easier to service when the problem is with the interconnects between components. If you've got a bad lead from one component to another it's an straight forward matter to unsolder a wire and replace it with a new one. Bad leads on a PCB design aren't impossible to repair, but they aren't as easy either.

And that's it.
As for disadvantages:

It's a harder thing to lay out a PTP amp because you don't get to lean on software to ensure that your signal routes are sane. With a PCB-based amp you can use software to ensure that parasitic capacitances in parallel traces aren't a problem, that traces are sized properly for the power they're expected to handle, that components are spaced adequately and so on. And it's an easy thing to change the layout, in software, and simulate new designs for problems without having to resort to a time-consuming prototype build.

And that's it.
It's pretty minor stuff really.
Comment: Cheap components are not unique to PCB or PTP amps. And poor layouts are not unique to PCB or PTP amps. Both components to use and the manufacturing method are entirely a *design* decisions. Signal quality can be better or worse in either a PCB or PTP build method. They are a product of the designer and design decisions, not the build method. "I think the signal quality is a little better on a PTP amp" is **not** empirically true at all.
Comment: Great info. About a year ago my Orange amp melted down. Why? Crappy components: the heaters had plastic interconnects and the melted down causing circuit failure. I had everything point to point wired by Will at Orange USA and in addition to a more resilient amplifier, it sounds stronger, cleaner, and with much more kick-in-the-pants. Not to start a holy war, but I think signal quality also is a little better on a PTP amp.
Answer: There's a nice article called "PCB vs. HANDWIRED" at The Pro Guitar Workshop's site.
Basically it says a good PCB can be as good as good PTP.
The way I look at it, super-high-end audio circuits like we'd find in expensive stereo amps and radios, recording equipment and synthesizers, among many other devices, which have a lot higher frequency and sound accuracy demands than guitar, use PCB. So, a printed circuit board has the capability to move audio around at least as well as point-to-point wiring. It comes down to the components and care taken when designing it all.
Answer: Without going into too much technical detail (since it is a bit over my head...) One very good thing about a PTP amp is that they are easy to maintain and repair compared to a PCB...
The biggest disadvantage of building a PTP amp is cost, since it takes a lot of planning and wiring by hand compared to a PCB!
As for the differences I think a well planned and well built PCB will be as good as a well planned PTP (and a lot cheaper to make).
Comment: I'm actually looking for technical details :), but these are good thoughts nonetheless! Not sure I agree with this yet though: "As for the differences I think a well planned and well built PCB will be as good as a well planned PTP (and a lot cheaper to make)"
Answer: I find it much easier to modify a PTP circuit than a PCB, even for simple mods that only involve adjusting the value of a preamp cathode resistor or capacitor.
You might like to draw a distinction between a PTP "rats nest" circuit with a dozen resistors hanging off valve sockets and PTP circuits built around an eyelet board or turret board.  Personally I prefer eyelet or turret boards for their tidiness, which to me is an advantage when servicing or repairing.
Answer: If you don't plan to modify your amplifier much, get the PCB. I have played both types and can't tell the difference. If you are building one, it will be a lot easier to change and modify the circuit to get "that sound" YOU want to hear with PTP wiring. I would reccomend using a turrret board or tag board to build the next one, if you are planning to duplicate the amp for sales or a stereo guitar setup.
Answer: Certain components, especially paper capacitors, have characteristics that are dynamically affected by variations in the mechanical forces on their leads and/or the ambient air pressure.  If a paper (and foil) capacitor sits with a certain loosely-maintained level of bias voltage, forces that would squish the foil layers together will tend to reduce the voltage, while those which would pull them apart would increase the voltage.  It would be difficult to engineer an amplifier so that this would have a particularly predictable and controllable effect, but if one builds an amplified speaker assembly where the board is subjected to vibrations produced by the speaker, the interaction between the speaker and the capacitors could color (distort) the sound in ways which would be difficult to characterize or produce by other means, but which might be reasonably consistent among amplifiers constructed in the same fashion from the same kinds of components.
A point-to-point-wired circuit would likely subject its components to mechanical vibrations in a fashion different from a printed circuit board.  Questions of which was "better" or "worse" would likely be influenced more by subjective aesthetic factors than technical ones.  What's most important is not the way in which a particular amp is constructed, but rather whether the person using it likes the sound it produces.
Answer: I converted an AC30 with a PCB to point-to-point. It definitely sounds better now. I fiddled with everything, and experimented with different kinds of caps (and though the values may be the same, they definitely can sound different). Now the amp is more warm and open and musical. It just feels right, it was 'harder' sounding before. It's night and day really, I don't care what anybody says. Though I guess I can't say for certain if it's simply because it's not on a PCB - all the components changed.
It took a lot of time and money though, I wouldn't really recommend this process! But I would always go PTP after my experience with it.
Answer: A point to point wired amp will generally have a rectifier, a nice big transformer, simple but high quality components, and be connected to a decent speaker; anyone with a PTP amp probably has a decent sounding axe. This will sound better. Rectifiers have nice natural compression. Seems a lot of people haven't heard old amps much. There's a reason they're expensive. They sound better. I know transistors can be good, but I also know old hard wired amps can be great.
Comment: "Vintage" gear was PTP.  Therefore PTP is better.

Untrue.  But a powerful marketing point to some people.


Panniers and handlebar pack

Question: I am planning to tour and would prefer highly visible panniers and handlebar packs.  Also waterproof.  Do racks come with panniers? Suggested brands please?
Comment: Welcome - please read the [tour] to learn how the site works.  Specifically, product recommendations are off topic because they're not long-term useful, and tend to be quite regionalised.
Answer: Racks generally do not come paired with panniers, although there are some exceptions. Waterproof panniers are widely available. There are some high-vis panniers out there, and some that have reflective patches.
We generally avoid specific product recommendations here on bicycles.se, but Ortlieb is a standby pannier maker.
Comment: The main exception to the racks and panniers being sold separately is a few varieties where the interconnection system between them is custom.
Answer: Racks and panniers are separate items. Buy the best waterproof panniers you can. A small pocket on the outside for tools, oil, a pump and a tube is always nice. If you are travelling you want fully waterproof. They will likely cost $200 each, give or take. Don't scrimp on this item.
Remember though, watch the sizing. They can get heavy when filled.Only you will know how much you can carry up the hills.
Answer: Did a 500mile tour in college with panniers. I just shopped at the local outfitters store. It's not a specific product but the racks I used had Black- in the name. Honestly can't remember the full name. You want a solid rack fit so no wobblies, I appreciated the mount system to my fork/frame braze-ons. Don't skimp on rack quality, you want a light frame to mount, but a firm metal. Oh, n be friends with the local mechanic, you might need to swap out longer allen bolts for same braze-on hole fender/rack mounting. I'm not ashamed to have been bribed with pizza as a wrench turner ;D... The panniers I had hooked on the top and had an attached bungee looped system on bottom to attach, EZ off/on to pack into a tent n secure. My panniers were purple, but I put reflectors, red blinky lights and high viz reflective tape on them too. LOLz, I get your waterproof idea, we had rain in August at the end of summer on South Pacific coast, go figure. Weather similar to the Hawaiian Islands, blue skies, then mild rainfall and unprepared for it. Two words, plastic bags... Made ponchos n wrapped everything we didn't want wet. Don't forget fenders, actually liked this the best, no butt skid marks! Oh, n test run everything weighted with books n junk a bit, then look for hardware coming loose before the ride. Happy n safe trails to you!

Panniers and handlebar pack


How do I store HCl safely?

Question: I'm in a textile unit, where we use different chemicals. My question is what type of material should I make my tank out of to store my hydrochloric acid?
Comment: You should always have secondary containment (e.g., a deep tray) so that any spill will be contained. Redundancy is important in safe chemical storage.
Comment: How strong is your HCl?
Comment: Well, it's typically stored in glass bottles :) You want bigger container?
Answer: This question is related: Handling and storing sodium hydroxide, hydrochloric acid, hydrogen peroxide and isopropyl alcohol
In the industries the handling of chemicals maybe periodic and, with routine, one tends to forget the hazardous and risks related to this. There's a lot of information on the web (http://water.usgs.gov/admin/memo/policy/wrdpolicy94.006.html):
STORAGE: Hydrochloric acid should be kept in a tightly closed container and
stored in chemical area that is compatible with other chemicals.
Store in a secure, well-ventilated area, that is well marked, and
away from the general work population.  Do not store near oxidizing
materials.
This manual should be helpfull too: http://www.jsia.gr.jp/data/handling_02e.pdf
1. Types of Containers:
The shipping containers used for hydrochloric acid are those rail tanks be tightly sealed, such as acid-resistant bottles (including polyethylene containers, etc.), and steel drums tank trucks, tank cars, and tankers with corrosion resistant linings
If you keep reading the manual there is valuable information about handling, transportation, and rules to keep the human safety.

How do I store HCl safely?


remove a recessed light can

Question: i have old (late 1980's) recessed lighting. i cannot figure out how to remove the can. there are no springs,ears or anything i can see inside the can. the bulb holder is secured by 2 spring clips that fit into slots at the top of the can. the cover is white plastic that fits into notches in the can and screws to lock in place. i have removed the plastic cover and removed the bulb holder and felt around the top of the can for any type of release pin. it appears that the can is pushed into the ceiling and then spring clip secure it to the drywall.
Comment: What makes you think that your light can is an "old work" type and isn't mounted to the framing with standard brackets?
Comment: it could very well be mounted in that manner. i have no access to check. (attic) the can can be pulled down about 1/8" and it will not twist or turn.
Comment: i did try to verify that a bracket was present by bending a coat hanger and probing around the outside of the can thru the hole at the top of the can where the bulb holder was removed. i did not (or could not) "feel" anything that may have been a bracket.
Answer: Chances are that this fixture was installed at the time of the home's construction. It'll likely have two crossbars that were installed across the gap between the two adjacent roof trusses or floor joists:

Removing it would require access above the ceiling, or you can attempt to cut and disassemble the unit through the hole in the ceiling. If you can release any tabs that secure the can itself to the base plate you may be able to push the can up out of the way, allowing access to the crossbars.
Be aware that there's likely blown or batt insulation above and around the can. Take precautions to not get it in your eyes or any other sensitive or delicate places.
Comment: the trim ring or flange is part of the can and therefore cannot be pushed up thru the ceiling. that is why i am thinking it must be secured by some kind of clips that extend once the can was pushed up into the hole. to me, it looks like the can must be pulled down to remove. however, i cannot rule out your bracket mounting theory.
Comment: I suggest you Google some images (or find your model number) and examine the various ways that they're mounted. I can't offer much more.
Answer: Can you see what brand it is?
What you describe sounds very similar to what I had in my ceiling. It was an older Lightolier model.
My Lightolier can was shaped more like a rounded cone, rather than a cylinder. At the top of the "cone" was the electrical connection and bulb threads, which you could pop out by pressing on two spring clips. I couldn't figure out how to remove the can either, but my electrician managed. My guess is he twisted it about or released some of the clips somehow. But he managed to remove it pretty easily.
At any rate, if you can get the brand and model, maybe instructions are available online.
Possible similar can. (Photo borrowed from another website)
Comment: this is very close to what i have. mine does not have the slots seen in your pic. i will try to twist it. if that does not work, i guess i will have to cut it out.

remove a recessed light can


The final death of a black hole

Question: What are the different death scenarios for a black hole?  I know they can evaporate through Hawking radiation - but is there any other way?  What if you just kept shoveling more and more mass and energy into the black hole?
Answer: Hawking radiation is a very slow process of the black hole losing energy and shrinking. If you counter this by supplying a little bit of matter or energy falling into the black hole you can easily overcome it and sustain the black hole.
Other than Hawking radiation I don't think there is any known process for black holes to shrink. The area theorem in classical general relativity states that the area of black hole horizon always increases in any physical process. So at least classically there is no way for black holes to die, or even shrink a little. Hawking radiation evades that because it is a quantum  process (which is also why it is a slow process).
As for the final stage of the evaporation, I think the honest answer is nobody knows. The logical possibilities are either the black hole shrinks to nothing and disappears, or it leaves behind some long-lived "remnant". Either one of this possibilities has its strong and weak points, but ultimately you'd need to know more about a quantum theory of gravity to know for sure.
Answer: If you shovel lots of mass and energy into a black hole, you will most likely get a bigger black hole.  It will not get indigestion, and it will not explode due to being full.  You may get accretion and jets if your shoveling is suitably generic.
Any list of possible "final death" scenarios will depend on your threshold for improbable events, and possibly which theory of quantum gravity you choose to accept.  Hawking radiation appears to be a fairly random process, and there is a very small but nontrivial probability for a black hole to destroy itself with a spontaneous eruption of big chunks of matter and energy.  The far more likely scenario seems to be that the temperature (and hence the flux from the radiation) increases steadily as the mass of the black hole decreases, until there is a very small hot black hole whose behavior can't be described well with semi-classical methods.
(This paragraph is very speculative, and may not reflect expert opinion.)  It seems possible to me that a collapsing body can form an apparent horizon (with respect to distant observers), and not collapse to form a singularity.  The final death may just be that it emits Hawking radiation until the radius crosses some threshold and the horizon disappears to reveal a dense macroscopic object made of matter.
Comment: Scott, once horizon has been formed (or to be precise, there is a "trapped surface") singularity is unavoidable, which is the content of Penrose's original singularity theorem. This is statement in classical GR, and maybe quantum effects such as Hawking radiation can change that, but not for large black hole for which the collapse process is fast, and the Hawking radiation is faint.
Answer: A black hole with an event horizon that is thermally equal to its environment will not be in equilibrium.  A black hole with the mass of about the moon and in free space would have the same temperature as the CMB. If it absorbs a unit of energy its horizon increases in size and it become cooler.  This means it will preferentially grow.  If it emits a quantum of Hawking radiation it will becomes smaller and preferentially radiates more radiation.  So there is no equilibrium.  This is because the effective heat capacity of an event horizon is negative.
There is no physically possible way to hold a black hole in an eternal state, except for one case.  This is a black hole in an anti de Sitter spacetime.  In this case the geodesic of the AdS are "repelling," or equivalently any clock observed close to the boundary is seen to demark time at a faster rate.  So the BH will not crash into the boundary.  Also the Hawking radiation emitted by the BH will reach equilibrium with the AdS.  This is one reason researchers are so interested in AdS spacetimes.
Around $10^{50}$ years from now there will be within regions bounded by cosmological horizons large galactic BHs.  The temperature of the horizon by Hawking-Gibbon radiation will be lower than the horizon temperature.  As a result these BHs will quantum radiate away so that around $10^{100}$ years into the future they evaporate away in a final flash of radiation.
Answer: Well, you could merge it with another black hole, so that is a way of reducing the total number of black holes in the universe, but I'm not sure you would call that "death."
It may also be possible to accelerate its evaporation by distorting its surface via tidal interactions with a nearby object, such as a fly-by of an unbound black hole, but all the radiated gravitational wave energy might just come from the tidal energy and not the initial BH mass.
Choptuik and Christodoulou both showed that you could create a naked singularity by the collapse of a very special scalar field, but I don't know what its fate would be.
Answer: As you mentioned, it could evaporate away by Hawking radiation. We don't know how this ends for sure but it is most likely that it ends in a shower of elementary particles.
The second possibility is that it keeps growing because matter or radiation keeps falling in. It could even reach a thermal equilibrium with its own radiation if held inside a heat proof box. Over very long time scales this scenario might not be viable because matter may decay and be dispersed by the universes expansion so that the black hole has to evaporate away.
A third possibility is that it ends its life by falling into another black hole. The fate of that black hole then has the same possibilities.
There might be other ways a black hole could end that we don't really know about because we don't have all the theories. E.g. it might be possible for a black hole to be wiped out by a decay of the vacuum. It might also be possible for it to fall into a wormhole and pass into another universe. Perhaps in the other universe times arrow points the other way and it mutates into a white hole. I'm not saying these things can happen, we just don't know enough physics to say whether they can or not.
And don't forget that it can become a quantum supposition of different states that suffer different fates.

The final death of a black hole


Translation of "Too many people have opinions on things they know nothing about. And the more ignorant they are, the more opinions they have."

Question: Can anyone provide an accurate translation for this quote? I would try to do it myself, but my Latin knowledge is limited as I am still learning.
Comment: @Quidam If Deven knows no Latin, it's of hardly any use to try to provide a translation. But if they are learning, I agree that it's useful to provide a rough translation. Feedback on it will help learning.
Comment: Please, try first, even if it's not good or perfect.
Comment: "Limited", yes, it can be a real novice or someone who tries to learn, but he will tell us if it means he is an absolute beginner. It's just to avoid the "translate it for me" questions, without giving a background.
Comment: Welcome to the site, Deven! Is the sentiment behind that quote general or does it refer to something specific? Are you planning to use it in a specific context or medium?
Answer: Here's my initial, somewhat florid, stab at this:

quotus quisque de rebus sibi notis opinatur? quin fit plerumque ut quo magis quis ignorat, eo plures opiniones teneat.
There are few people who express opinions on matters that are known to them. In fact, it generally happens that the more ignorant someone is, the more opinions he has.

This second version is a bit more literal and straightforward:

nimis multi de rebus sibi ignotis opinantur; qui quo magis ignorant, eo plures opiniones tenent.
Too many people express opinions about matters that lie outside their knowledge/experience. And the more ignorant these people are, the more opinions they have.
Answer: Here's a more compact translation, with some inspiration from cnread's great suggestion:

Plurimi nescientes opinantur. Immo quo magis nesciunt eo magis opinantur.

Literally translated, this means:

Very many opine without knowing. Indeed, the more they do not know, the more they opine.
Answer: Nimis multiores viri opiniones de quibus rebus nesciunt habent. Cum etiam minimos sciant, tamen opiniones habent plurimos!
"Rather too many men have opinions about which things they are ignorant. When even they know the least, still they have the most opinions."
(You can remove plurimos and replace it with nimis. This would give the sense of "still they have opinions exceedingly much." I don't know if nimis works, but starting with 'nimis' and ending with 'nimis' would have a lovely symmetry.)

Note that I am unsure of these words in my sentence, and that this should be considered a rough draft:
The second 'nimis.' I'm not sure if works in the sense I'm thinking. Could I use an adverbial nimis here, or would it have to be inferred as an adjective modifying "opiniones?"
'opiniones' There might be a better word, but I intuited that sententias didn't feel right here. It seemed too certain and directed a thought. Perhaps "putatos" could work as an alternative? "To reckon" gives more the feeling I think we're looking for.
'quibus rebus' Could I fit in a "quare" here, for a more idiomatic Latin sentence?
The first 'sciunt.' Should this be subjunctive for a relative clause of characteristic? I think it works both ways, but the indicative seems to emphasize the things themselves that are wrongly believed, and the subjunctive would emphasize the character of the people having opinions -- that they always think they know everything.
Comment: Thank you so much! I know I should've tried it on my own first, but I only just started learning latin, so it was hard to know where to start. Thank you for explaining your translation too, and how it works, This will really help my learning!


Do 50% of prostitutes have HIV?

Question: The Prostitution Statistics You Have to Know claims that:

50% of prostitutes throughout the world have contracted the HIV virus

(For this statistic it references this BBC news article: The men who sleep with prostitutes)
Is this true?
Comment: The referenced BBC article doesn't seem to me to say anything about that claim.
Comment: @AndrewGrimm, complete with the Word grammar squigglies :)
Comment: The claim is probably too general. It is very likely that the prevalence of HIV in prostitutes varies enormously across the world (as it does for whole populations). It might be better to ask whether the prevalence *in any country* is known to exceed 50%.
Comment: @matt_black While that *might* be a better question, that's not what this particular claim is about. The quoted claim *is* a very broad claim.
Comment: I bloody hate it when people put lots of text into image files, like the sex-crimes.laws.com page has done!
Comment: It's as if they are aware they are biased but they put it anyway as if it's objective.
Answer: It may be true or true-ish among some sub-populations.
THE PROSTITUTE PARADOX from 1993 says,

In New York City, for example, 40 to 50 percent of streetwalkers (a very low caste of prostitute) who have used IV drugs over the past
  decade are HIV seropositive.
Among call girls in New York City (a higher caste of prostitute), no seropositivity was found among those who were drug free. These figures
  were constant between 1984 and 1989.
The same sorts of figures have been found in all Western nations.

It says that the risk factor is the using of intravenous drugs.
Two more data points:

List of countries by HIV/AIDS adult prevalence rate states than in a few countries (Lesotho, Botswana, and Swaziland) in Africa, the incidence is 25% in the general population of adults (it's 17% in South Africa), and I imagine it may be higher than that already-very-high average among any prostitutes there.
Perceived transmissibility of STIs: lack of differentiation between HIV and chlamydia claims (based on Mastro TD, de Vincenzi I. Probabilities of sexual HIV-1 transmission. AIDS1996;10(Suppl A):S75–82.) that,

The estimated probability of HIV transmission from an infected heterosexual man to a woman in one act of unprotected vaginal intercourse is 0.1%

Probability of Heterosexual HIV-1 Transmission per Coital Act in Sub-Saharan Africa cites another study which says that 0.2% is a baseline: when the man is known to be HIV positive, and the rate of condom use is high (in the 78% to 93% range).
My guess is that 50% is too high to be a world average, especially in populations where HIV isn't pandemic.
However the maths says that infection rate of 0.3% implies a 50% chance of infection after 230 sex acts, when a condom is used more-or-less regularly, if all clients are HIV-positive.
If 10% of clients are HIV positive then the number is 2300 instead of 230.
Comment: @trav1s Chance of not getting HIV after 1 act is 0.997 ... chance of not getting HIV after 230 acts is `(0.997 ^ 230) = 0.501` (where `^` means 'to the power of').
Comment: "However the maths says that infection rate of 0.3% implies a 50% chance of infection after 230 sex acts, when a condom is used more-or-less regularly, if all clients are HIV-positive." Are you certain that's the right math on that? Where are you getting this?
Answer: According to this article published in the International Journal of Public Health by the Institute of Tropical Medicine, Antwerp, it's, on average significantly lower than 50%:

Source: http://link.springer.com/article/10.1007%2FBF02084300
Funnily enough, this is actually the most recent chart I could find like this. I guess no one bothered to do another study in the last 25 years. However, there are a few more articles I found that give more recent percentages for certain areas.

Nigeria's growing commercial sex industry is a major source of human immunodeficiency virus (HIV) transmission, and studies undertaken in Lagos suggest that up to 20% of female prostitutes are HIV-infected.

Source: http://www.popline.org/node/288578
But there is one more problem with the chart above, in that it only takes into account prostitutes that don't use intravenous drugs, and just assuming 0% in that field is just ludicrous.
According to one PubMed article, Human immunodeficiency virus seroprevalence and condom use among female sex workers in Italy, about 37% use intravenous drugs:

Overall, 131 of 802 (16%) were HIV positive: 36 of 558 (6%) professional sex workers and 95 of 244 (39%) sex workers who used intravenous drugs.

Source: http://www.ncbi.nlm.nih.gov/pubmed/9800254
Sadly I can't personally find one specifically for the US. But, that said, based on the information above, I would hazard a guess that it would be significantly less than 50%

Do 50% of prostitutes have HIV?


Are barbells really more beneficial than dumbbells?

Question: A lot of experienced bodybuilder a will claim that dumbbells are less beneficial and for higher reps and that the barbells are what is really important... Is this true?
Comment: -EricKaufman I am referring to building overall mass throughout the entire body
Comment: Well, barbells can be loaded to a much higher degree than dumbbells and are easier to use due to racks. However, dumbbells have superior ranges of motion for a lot of different movements and are better at fixing / avoiding side-to-side muscle imbalances.
Comment: IMHO dumbbells offer benefits over barbells.  When I injured my shoulder, the only thing I could "bench" was dumbbells as they allowed my shoulder to move more naturally (opened up a little bit as I brought them down).  Barbells keep your hand position locked in place which gives stability, but again, IMHO it is less of a natural movement.  Finally, the act of balancing the dumbbells utilizes other muscles which may be under utilized with a barbell or over corrected by a stronger side.
Comment: More beneficial for what? What are your goals?
Comment: Even to this day, I bench inclined barbell and flatbench dumbbells - and I'm not a small dude.
Answer: Barbells lets you use significantly more weight than dumbbells because you don't have to use as much balance, very few people use dumbbells half as heavy as their barbells, personally, I can add about 25% of the weight I'd use with dumbbells in total.
This means you can put a heavier load on your triceps, pecs and shoulders (maybe), which in turn means more mass building.
Answer: Bodybuilders are more concerned with isolation work than strength athletes are. Body building, at it's core, is about body modification. With dumbbells you can get a lot more specific and target certain things in very specific ways.
Barbells shine in certain key areas however:

Squats/deadlifts/cleans. You can sort of do these with dumbbells, but not in any realistic way at big weights. With big compound movements that involve the largest muscle groups in your body at maximum force, the amount of weight you can move is simply too large to reasonably be found in dumbbells. IE, no one's deadlifting a pair of 250lb dumbells.
A big thing to hold onto. Again, for something like a snatch or clean, you can throw a lot of weight in the air and you need something big enough to handle it (like a barbell).
Incremental loading. Most gyms allow you to add 2.5lb (~1 kilo) weights to a barbell, allowing for 5lb (~2.2 kilo) adjustments. A lot of serious athletes bring fractional plates which allow you make adjustments at even smaller levels.
Really heavy dumbbells are a pain in the ass. The heaviest object you work with in barbell land is ~50lb. The plates never go over that, the bar never goes over that. So moving things around is relatively simple. With big dumbbells, it's not trivial to move a 150lb dumbbell around.
They're smaller, sort of. A stack of 300lb's of plates and an olympic bar fits in a smaller area than an equivalent rack of dumbbells.

Dumbbells are great too in different ways:

They're safer to bench. It's really not safe to max barbell bench press without a spotter. You can get really injured if you can't get the bar off you. With dumbbells, you just drop them.
You can do more isolation work. Personally I'm not a fan of body building techniques in general, but there's no argument that they allow for more direct targeting of particular muscles. My concern is that isolation work is the last thing a new gym goer should concern themselves with.
They're not as intimidating. Most new people stay away from barbells but dumbbells just seem more straight forward.
They develop more stabilization muscles and keep imbalances in check. With something like the overhead press, both arms need to get each weight up. You can't rely on your right arm to compensate for a bit of weakness on your left. Also, the (dumbbell) weight is simply less stable so you'll get more muscle activation across a broader range of muscle groups.
Comment: The only thing I disagree with you on is that it's not safe to max barbell bench. If you have a standard bench press rack, no. But if you have access to a power rack or a bench press rack with safeties, then there's nothing dangerous about it.
Comment: You can't get low enough with those; full range of motion on a bench (and powerlifting rules) require the bar to touch your chest. Partial repping with safety pins in a squat rack is exactly that: partial repping.
Comment: It might depend on the person, but if you use enough back arch to extend your thoracic spine, you can get your chest above the safeties (at least I can). On a failed rep, you simply release the extension and your chest goes below the safeties and you're good to go from there.
Answer: Flipping the explanation in the answer provided by Mârten, I believe the downside of barbells is that they could potentially prevent you from developing both sides of your upper body equally.
Put another way, a benefit of dumbbells is that they force both arms to work independently of the other. Working each arm individually may help you to develop the ability to lift heavier barbells.
So I thought the opposite was true, but to answer your question, this article from Men's Fitness says that each method has its advantages.
Dumbbells

Great for beginner safety
Developing form
Great for single-limb training/improving strength imbalance

Barbells

Have a higher maximum weight than dumbbells, therefore they are better for "serious strength training"
Provide an even load to the spine when squatting
Best for exercises which "require the entire body to move as a coordinated unit" (e.g. the clean or press)


Modelling Pay what you want

Question: I have been trying to model a Pay What you Want scheme. Now, for a monopoly it is clear that monopoly will have more profit by setting monopoly pricing assuming all players are selfish. But consider a scenario of 2 sellers one posting a fix price and other a PWYW strategy. In a market of selfish players the PWYW will make huge losses and market would move on to the fix price seller who can now act as a monopoly. So does this imply that there is an incentive for the selfish players to keep PWYW firm in market ? Also, how do I extend this idea to more than 2 firms ?
Answer:
So does this imply that there is an incentive for the selfish players
  to keep PWYW firm in market ?

No, unfortunately not. In general equilibrium models (as @FooBar already mentioned) buyer's do not think about the influence of their actions on the seller. Therefore, they would just buy at the lowest possible price.
However, if you have a game theoretic model including uncertainty about profits of the PWYW firm and risk-averse consumers who prefer the PWYW firm for some reason you might get Nash-equilibria in which PWYW firms have positive profits.
Another way to model PWYW firms is to include non-monetary benefits from paying. For example a disutility for being seen as a cheapskate or for exploiting the firm or a positive utility from "doing the right thing" (i.e., paying the price that they think is appropriate). The selfish, rational players will pay a positive price and will generate profits for the firm.
I think in reality the impact of non-monetary benefits is much higher than the impact of asymmetric information with risk-aversion.

Also, how do I extend this idea to more than 2 firms ?

I don't really think it is really interesting to extend this to more than two firms (especially without having solved this for 2 firms), but for both modeling options presented it should be "easy enough".
Comment: Thanks. But consider a fairy tale scenario where there are 2 firms and one uses a PWYW strategy and the other firm the posted price. Now wouldn't the selfish players now have an incentive to keep the PWYw player in market as if he is thrown out then the remaining player acts like a monopoly. Also, I have assumed this is an infinitely repeated game. P.S. This looks like a different account but stackexchange messed up and has set up a different account on same email address :/
Comment: @Arcapol Is it a game? Or a general equilibrium model as suggested by your question (and its tag)? If this is a GE model, then my answer applies. If it is a game, you should write it down formally. As of now, I suspect that you are not really sure what you want to model.
Answer: Not it is not. You're assuming that each selfish player actually has enough market power to keep PWYW firms in the market. Usually, we rather think about buyers as atomistic - each individual's purchase decision has no impact on the seller, which is why they usually do not take into account these externalities.
If you had a monopolistic consumer however, he would pay the PWYW firm exactly the marginal cost: Just enough to keep the firm alive, but no surpluses what-so-ever. The opposite of a monopolistic firm, if you will.
However, I don't think that selfish and rational preferences will get you a solution that gives rise to PWYW firms: As I just hinted at, even if the buyers had market powers, the firm wouldn't make profits, and should just go for the standard oligopoly pricing strategy. The latter weakly dominates the former in all market sizes, and strictly dominates in markets with positive market power.

Modelling Pay what you want