How will you fix the direction of the lines of force due to circular current?

Question: I have tried to learn it myself but I was unable to understand. Can you please explain it in detaails with simple example.
Thanks
Answer: By lines of force, do you mean the magnetic field? If so, you could determine the direction of the B-field by right-hand  rule.

The reason is that a current element flowing up will create a B-field circulating out of the screen on the wire's left, and into the screen on the right's right. This direction is chosen by convention.

Wrap the wire into a loop (making it flows counterclockwise), we find that the B-field will point into the screen outside of the loop,

and out of the screen inside the loop

Summing up all elements (Biot-Savart law) we will find that the B-field should look like

(Picture source: http://frank.mtsu.edu/~phys2020/Lectures/L12-L18/L17/Current_Loops/current_loops.html; Wikipedia)
Answer: A circular current, running counter-clockwise when viewed from above, induces a magnetic field whose field lines point mostly up through the center of the loop and then curl around to point down outside the loop.  A clockwise current's magnetic field lines point the opposite direction.
Here is a picture from this source


Sound Utility Technician

Question: I am about to do a gig  as a sound utility technician.  I was told by the production manager that I didn't need any equipment for the shoot.  Is the sound mixer going to expect me to bring any equipment? e.g. soldering kit, maglite. You know, small essentials if need be.
Answer: I would bring your basic kit. Film sets are crazy places. Someone somewhere always forgets something. Something unexpected always breaks at exactly the wrong time. There's no shame in being over-prepared.
Answer: Hi. No matter what I'm working on I'll always have a kit with me. I have a hard flight case on wheels that has the following inside:

Shotgun and rycote
Sound Devices MM1 Preamp
Multiple cables (various lengths and connectors)
Inline cable adapters (mainly audio but a few video bnc's etc) - these have come in very useful and gets you in the good books with the camera dept!!,
Spare batteries (someone will always need some)
Pair of two-way radios
Spare headphones
Spare torch
Spare leatherman
Cable ties, tape, strong string, velcro ties and strips.

That's what I'll always have with me. There are times when i've not had to open it and that made me think wether it's worth having with me all the time. But every time i've not had it with me someone asks for something that I would have had.
It's always better to be over prepared than under.
Good luck with the production.
Answer: I'd bring the basics - gloves, spare velcro, zip ties, flashlight, multitool, headphones.  I also always have a little pack with lav mounting supplies - mole skin, athletic tape, little rubber bands, twist ties, etc.  Bring set basics as well - pen and notepad, cash, granola bars (or similar pick me ups), hand sanitizer, EAR PLUGS, sun screen, bug spray, and a hat.
If your sound mixer is anything like any of us, they are also coming stupidly over-prepared and will have plenty of anything. If you really don't feel like bringing anything, at least bring "personal" items like gloves, headphones, ear plugs - things you have to wear and maybe don't want piles of other people's sweat on them.
Finish it off with a stylish fanny pack or this bad boy, a titanium spork (I never leave home without one.. my wife and I have a bunch), and you are so ready!
Answer: Always ask the mixer if it's the first time you are working with him or her, don't depend on reliable answers from the office in this type of situation. Be prepared to bring your basic kit as the others described, and above all: a notebook, a moleskin, voice recorder, whatever it takes to make notes. Mixers are particular people. You will be given notes on Comtek battery voltages, how to pack the cart, what Pelican that PZM mic is in that we will never use, but now need, what the heck did it even look like?, etc etc
Answer: Thanks guys!
I appreciate the feedback. I ended up not needing anything. I did bring my headphones and a soldering kit. The mixer has a whole truck worth of gear so it all worked out.

Sound Utility Technician


Rough ride on  LL Bean Subaru, are the struts the cause?

Question: I have a 2004 LLBean with 88,000 miles on it. It rides worse than my old 2001 limited.
The ride is hard. I was told that as long as the struts are not leaking oil, they are fine.
Is this true? I thought it was the cheap Capitol tires on it. I put a set of Michelin mxv4s
on, and it made hardly any difference. Can it be the struts, or does the Bean have a hard ride?
Comment: How long have you had the car? Since new? For how many miles has the ride been poor? When you say "hard" ride, I understand you mean that bumps feel harsher than they should. Is that right, or do you mean the car bounces up and down more than you think it should? Worn struts would make the car bouncier, not harder.
Answer: One way to check the struts is to jounce the vehicle. Push down hard and release quickly on the bumpers and see how many times the vehicle bounces. It should be no more than 1.5 times, more than that and the struts are bad.
Answer:
I was told that as long as the struts
  are not leaking oil, they are fine. Is
  this true?

No, this is not true.  Dampers can go bad without noticeable leaking.  However, dampers that wear out would not make the ride hard.  You may want to check the strut shafts to see if they are somehow restricted - maybe they are bent or maybe they are seized up by rust.  Any obstruction to the movement of the shaft would act as though you had a stiffer spring, i.e. making the ride harder (though if the obstruction was significant it would likely make the "hard" ride very severe).
It is quite possible that you are interpreting the the ride of your 2001 Limited as better because those struts are worn out.
If the struts in the 2001 are not damping at the same rate, the overall spring rate will be changed and the car will react less to bumps in the road - mimicking a softer suspension that a more luxurious car would have.  The change in damping may be enough to make the ride seem smoother but not so much as to make the ride obviously under dampened (bouncy).
In general, Subaru's are setup with a little stiffer suspension than many cars.
Comment: I bought the car recently.My 2001 subaru had the struts replaced.The car does not bounce it just has a hard ride. Some one said Beans ride hard, over bumps. The struts are not leaking oil.
Comment: The L.L. Bean edition uses the **exact** same suspension as the non-L.L. Bean models.
Comment: also, check my edit.
Answer: The ride on my Soob is getting harsher, and is likely due to the struts wearing out.  The mechanism for controlling the response of the strut is not simple, so IMHO there is not a simple, single failure mode of the ride getting bouncy.  That may have been the case for shock absorbers of yore, though, just not with the sophisticated modern suspensions.
There are a number of places online that sell OEM Subaru parts at a discount, I have no experience with any of them; they do offer around $110 a strut or so last I checked.
Allow me to expand.  Modern shock absorbers use a number of valves and orifices to achieve the ride characteristics desired by the OEM.  The shocks are also pressurized to prevent cavitation and increase performance.  They are more sophisticated hydraulic systems certainly than fifty years ago.  As the complexity goes up, the more there is to fail.
Comment: I don't think your assertion is true.  Dampers fail in two main ways: oil leakage or physical damage.  Oil leakage causes a reduction in damping forces, physical damage usually causes a restriction in movement.  Either of these failures effects a single variable in the suspension equation.  It's not magic or rocket science - nor is there such a thing as "shock absorbers of yore".  There are active systems, but those are not under consideration in this question, nor are they fundamentally different in any way.


Adobe Fireworks: How to make the master appear on all page states

Question: When I create new states for the page - the master is gone. It appears only on the first state and not on the others.
Is that how it works or am I missing something?
(CS5, ver 11.1, Windows 7)
Answer: You can share a layer to states by using the Options menu (top right corner of the Layers Panel) or right-click the layer in the Layers Panel and select "Share to States."
When a layer has been shared to states, an icon that looks like a film strip will appear to the right of the layer name, and if you edit the objects on that layer the change(s) will appear on all shared states.
Comment: That doesn't work. See this example. The master page has one layer that is shared to states. But on the first page, it is only shown on the first state. Is this a bug? See this simple example:
http://i.stack.imgur.com/5Gc7V.png
Answer: Fireworks assumes that the states you have created for separate pages correspond. So, the reason you are seeing the Master Page for State 1 of a given Page is that the Layers and Objects you created for the Master Page are on its State 1. If you create a State 2 for another page that is linked to the Master Page, unless your Master Page also has a State 2.
From Adobe Help:

In summary, state 1 of the master page shares to state of 1 all pages, state 2 of the master page shares to state 2 of all pages, and so on. If a regular page has more states than the master page, nothing is shared to those states from the master page until that state is created on the master page.
Answer: That option is also available through right click menu.


Starcraft 2 maintaining unit formations

Question: In Starcraft 2, I want to maintain unit formations. Other than having one unit type follow another, and then only directing the lead unit type to move, I maintain a pseudo formation, that is my longer ranged units in the back, etc...
Is this the only way?
Answer: Your options:

One control group per unit type, then move them independently.
One control group for everything, but tab between the unit types and move them independently.
One control group for the front group (which you move manually) and setting everything else on follow.
A combination:One control group per unit type and set some groups to follow others.

I prefer and recommend setting a group per unit type, but setting some of those groups to follow other groups as appropriate.
In your question, you describe a group for the melee units and simply having the ranged ones follow. This might be an easy way to keep formation, but when it's time to fight you will spend critical moments trying to get that ranged group to attack.
If you give each unit type its own group, you can gain instant control over any group when it comes time to fight. In the meantime, you can easily set ranged and flyers to follow the melee group so you keep a rough formation.
You could also use the tab method instead of multiple groups. In my experience, however, this fails when you have more than 2 unit types. In the heat of battle, having to tab or shift+tab to whatever group you want is wasted keystrokes and can cost you a few units in the time it takes to swap.
Comment: How can you have 1 control group but move units independently?
Comment: @Budda He answered it in his second bullet. If you're asking about a single unit, you have to click that unit or have that one unit on it's own hotkey (which would be silly).
Answer: I'd extend Shaun's answer a bit, and recommend grouping together units that go well together, and also having all units into control groups. Putting units into a follow command is unreliable and you'll end up leaving units behind.
For example, for Terran, all marines and marauders can very well be put into one command group, since they have the same movement speed and you can stim all of them at once. Tanks and even thors could be another control group. Both of them are support units and pretty slow, so they can be left behind a bit.
Zerg can put zerglings and banelings in one command group, roaches in another and mutalisks into a third.
Protoss should probably put melee units (zealots) in one control group, and ranged units (sentries and stalkers) into another.
If you need to micromanage a unit type individually (for example put marauders in front of banelings), it's easy to control-click (or double click) on one unit type, and all such units on the screen get selected.
But, to be honest, until you're out of silver/gold (or even platinum), you should do good with just putting all units in one control group if you're not playing zerg. But it doesn't hurt to get into the habit, if you have the hand speed, and control them individually. Zerg needs to tend to their units very much, so there it's good to get used to 2-3 control groups immediately.

Starcraft 2 maintaining unit formations


Scruggs Banjo Tuners - are they necessary?

Question: How necessary are Scruggs tuners when playing Scruggs-style banjo?  They seem like something of a novelty to me, and I'd rather just not install them or learn how to do it, but don't want to leave it out if it's an integral part of a Scruggs-style banjo player's toolkit?
Comment: Seems this questions should be more "Is Earl Scruggs' style defined by his tuners?"
Answer: It depends on the song. Many out there can play Earl's Breakdown without them, even though it was originally recorded and played with Scrugg's tuners. The part that uses them is minimal (less than 2 measures long) and is easily yet accurately spoofed.
Now a song like Flint Hill Special, as mentioned above, has a much more demanding Scrugg's tuner dependency. They are used constantly for almost 8 measures straight, so faking that would require a bit more mustard and creativity.
If you want to specifically add those types of songs to your professional repertoire, I would suggest getting a set of the Scrugg's tuners. If you want to just 'get by' when those songs happen to arise, you can certainly find ways to do that without them.
Answer: You can't do Flint Hill Special without them, but you don't have to play Flint Hill Special. I don't think I've heard Bela Fleck use them.
Answer: Scruggs-style definitely does not require Scruggs tuners.  Bill Keith also invented a similar device, but those are not required for "Keith style" (melodic) banjo playing.  Even Scruggs rarely used them in his playing, and most listeners would not miss them except for on certain songs.


How do you keep chicken breast juicy when grilling?

Question: Most of the time it ends up dry. Are there any special marination tricks?
Comment: whole chicken or pieces?
Comment: chicken breast..
Answer: Don't over cook it.  Aim for it to be a little under done.  It will still be hot and will finish cooking after you've taken it off.
Comment: Meat thermometer helps here. Pull it at about 155, and you should be set.
Answer: The longer the pieces of chicken are in dry heat, the more liquid escapes.
To keep the chicken juicier without undercooking it.
Brine it (increasing the salt content inside the chicken helps it retain it's moisture more).
Decrease the temperature difference between when you put it on the grill and the final cooked temperature. At the very minimum, make sure the chicken is thawed all the way through, but consider starting the chicken in a crockpot or wrapped in foil in the oven.
Increase the humidity of the air around the chicken. "Beer butt" chicken works by steaming a whole chicken from the inside while it roasts from the outside.
Answer: Brining is great to begin with.  Use a bone-in, skin on chicken breast.  Once it's done you can remove the skin and carve off the bone if you like.
Also, set up 2 heat zones in your grill (either by banking your coals or by turning off a gas burner).  Brown it for a few minutes over the hot zone, then transfer to the cooler zone to finish cooking, until temp comes to 165-170 degrees.
Then remove from heat and wait at least 5 minutes to slice.
Answer: I have had excellent results with beer can chicken.  Start with a 4 to 5 pound fryer chicken, A large roaster (over 5 pounds) will burn before it gets done.  Wash and dry with paper towels.  I usually just coat all over with any rub I happen to have around. Season salt works good too.  I have the grill preheating for 5 min and then on goes the chicken, the can and the two legs form a kind of tripod for it to sit nicely on the grill.  The heat goes to low on all three burners and 60 to 70 minutes later it is ready to eat.  No fuss, no hot kitchen, year round.  I have played around with putting various things in the can, beer, water with "additives" but at least to my taste buds, an empty can works good.  I just fish one out of the recycling bin: )
Answer: Trust me, if you haven't tried brining, you owe it to yourself. It is so quick and simple, and makes such a huge difference.
Brine your chicken about 45 minutes to 1 hour in a cold solution of 1/4 cup table salt, 1/3 cup table sugar and water enough to fill a larger mixing bowl. Do this as your first step in preparing your meal, before you light the grill, cut the veggies, etc.
As far as preparing the brine: boil enough water to just dissolve the salt and sugar in a large mixing bowl and stir together with a wisk until dissolved. A cup or so of boiling water is usually enough. Next add a generous number of ice cubes to make the brine cold. Add the chicken and enough cold water to fill the bowl, and place it in the fridge, or add another generous helping of ice to let this brine on the countertop while you get the grill ready. The important thing as that the brine is kept cold.
==TIPS==
Don't brine chicken longer than 90 minutes, otherwise you are wet curing it, and it will start to taste like chicken ham - blech. Longer brining times also make it so the chicken will stay pinker, even when fully cooked, which might gross out you or your dinner guests.
You can add ingredients to change the flavor a bit, and for chicken, I like to add a few sprigs of fresh thyme, and sometimes substitute brown sugar for the table sugar. I avoid dried and ground spices because of how they stick to the meat - dried thyme leaves are heinous to pick off a raw chicken breast!
Use Kosher salt only if you have to - the flavor difference is imperceptible, and table salt is not only cheaper, but generally has iodide, which you need in your diet.
Be creative and try adding other things to the brine: slightly crushed garlic cloves, a tablespoon of peppercorns, lime skins, chunks of hot peppers, etc.
Answer: You can marinate, or brine it, but you don't need to.
I tend to grill pieces (breast, legs, etc) over direct heat to start and get grill marks, then move it to a cooler part of the grill to finish and cook through.  I've also heard of people doing it the other way ... I assume to render out more of the fat.
If you're cooking chicken breast -- bone in, skin on will help -- taking the skin off robs you of a protective layer of fat.
For whole chickens, you could use a "beer can" chicken technique (and you can use other liquids besides chicken)
Comment: +1 for Bone in Skin on!  Brown the skin, and cook bone down until done.  Yummy.
Answer: Re-coat in marinade a few times during cooking. And don't pierce the skin and let all the juices run out.
Oh, and make sure you start out with good chicken in the first place too.
Comment: Re-coating in marinade has the potential to introduce bacteria to your cooking chicken... I'm not a fan.
Comment: +1, that's what I would advise too :) Cook in lower temperatures and pour marinade on top once in a while.
Comment: If you do this, reserve some of the marinde *before* putting the chicken in, so you're not putting chicken-tainted marinade (that might've been sitting out while grilling) on a couple of minutes before you serve it.
Answer: BBQ Expert Steven Raichlen recommends cooking it under a brick. http://www.primalgrill.org/season2/recipes/202_recipes.html
Answer: A simple brine of kosher salt and water has never let me down.
Answer: Joe has the best answer. Keep a cool side and a hot side to your grill.
Brine your chicken for a few hours/up to 12 beforehand. Bring it to room temperature before putting it on the grill.
Mark the chicken on the hot side of the grill, transfer to the cool side, let it cook in the ambient heat.
I personally don't like beer can chicken, as I have no idea what the burning paint fumes/offgasses from the paint on the can would be doing to me.
Comment: I find that brining for longer than 2 hours makes the breasts too chewy.


About the ring used in the definition of drinfeld modules. Why is that ring a dedekind domain?

Question: Let $K/F$ be a function field with exact field of constants $F$ ($F$ is a finite field of characteristic $p$ prime). A prime in $K$ is a discrete valuation in $K$ containing $F$. It has a unique maximal ideal $P$ which we can refer as our prime of $K$. Now, if I choose any prime $Q$ of $K$, then I construct the ring of $A$ as the ring of all elements of $K$ which are regular at every prime of $K$ different from $Q$. That is a generalisation of polynomial ring in one variable. In all the books I read up to now, they say that "IT is well known that $A$, is a Dedekind domain". I'm trying to find the proof of that but I cannot find it. Can, you tell me please why $A$ is a Dedekind domain?
Answer: There are two standard approaches to this, which I'll sketch.  I don't know your background, so I don't know which one will be easier for you to fill in.
(a) Using the following criterion for Dedekind rings, which is part of theorem 5.1 in May's notes:

An integral domain $R$ is Dedekind iff it is Noetherian and all its localizations at prime ideals are DVRs.

If you know enough algebraic geometry (or the underlying commutative algebra), checking this criterion is automatic.  If not, you may have to do some work.
(A long time ago, I wrote an expository paper for a class using this approach for the case of affine nonsingular plane curves.  It's available online on William Stein's website, with the caveats that it's the first expository paper I ever wrote, I didn't really know algebraic geometry at the time, and if I were to rewrite it, I would do it completely differently.  From my experiences writing it, I know how hard it is to find references for this sort of thing in the literature, although I expect they are easier to find now than they were in 2005.)
(b) Using the following theorem, which I'm citing from the Wikipedia article on Dedekind rings, although it should be easily found in commutative algebra books also.

Theorem: Let $R$ be a Dedekind domain with fraction field $K$. Let $L$ be a finite degree field extension of $K$ and denote by $S$ the integral closure of $R$ in $L$. Then $S$ is itself a Dedekind domain.

Now choose some non-constant element $a$ of $A$, and let $R = F[a]$ be the ring generated by $a$.  The ring $R$ is a polynomial ring, so Dedekind.  Furthermore, our function field $K$ is a finite extension of $\mathop{\mathrm{Frac}}(R)$, and $A$ is the integral closure of $R$ in $K$, so the theorem applies.
Answer: Thank you for the answer. I've got another problem. It seems to be obvious but I can't write the proof. Here is the statement:
If $A$ is a Dedekind domain contained in $k$ field, and $a\in A$, then for
a prime ideal $I$ of $A$, if the localization of $A$ at $I$ gives a place(or prime) of $k$ with maximal ideal $P$ , we have $v_P (a) = m$, where $m$ is the power of $I$ in the decomposition of $(a)$ as factor of prime ideals of the Dedekind domain $A$.
Comment: If you have another problem, you should make a new question.


How can I Install the Old TweetDeck version on Ubuntu 12.10 64bits?

Question: I've tried to install Adobe Air 2.6 and then the old version of TweetDeck (0.38.2) but it's not working to me. Can anybody help me please?
Answer: Adobe Air for Linux is no longer supported by Adobe. Their 64 bit support was pretty bad to begin with. The chances of you getting this to work well are pretty slim. I would recommend just using wine.
You can use the older version of tweetdeck by installing air in wine then installing tweetdeck. This should work quite well (though it's obviously not ideal).
You also install the newer version of tweetdeck via wine.
Here are some links to get you started.
New Version Post, A new version announcement stating wine works, Some poor instructions for air and wine, and finally the winehq page for air.
Answer: You can get it working not too hard: make sure to read through all the steps first
http://ubuntuforums.org/showpost.php?p=12102341&postcount=2


Dualizable classifying spaces

Question: If $G$ is a finitely generated free group, then its classifying space $B G$ can be presented as a finite CW complex (a finite bouquet of circles), and therefore is Spanier-Whitehead dualizable.  Are there any other discrete groups $G$ with the property that $B G$ is Spanier-Whitehead dualizable?
Answer: Dualizable is equivalent to $BG$ being finitely dominated (a retract up to homotopy of a finite cell complex).  In Wall's "Finiteness conditions on CW complexes, I" Wall shows that finite domination is equivalent to $\pi_1$ being finitely presented and also, the chain complex $C_*(EG)$ being chain finitely dominated over $\Bbb Z[G]$. This means there is a finite resolution of $\Bbb Z$ by finitely generated projective $\Bbb Z[G]$-modules. In the group cohomology literature, this last condition is called "FP"
Answer: Any finitely presented group of type FL admits a finite classifying space. (A group $G$ is of type FL if $\mathbb{Z}$ admits a finite length resolution by finitely generated, free $\mathbb{Z}G$-modules.) This is Theorem VIII.7.1 in Brown's book "Cohomology of groups".
More examples are given in section VIII.9 of Brown. These include knot groups, finitely generated nilpotent groups, and certain arithmetic groups.
Also the non-orientable surfaces (other than $\mathbb{R}P^2$) are examples.
Comment: Thanks; the reference to Brown's book is exactly what I needed.
Answer: I'll answer a related question: in the $K(n)$-local stable category, $BG$ is dualizable for all finite groups $G$, moreover, each is self-dual. You can find this in Hovey and Strickland's 'Morava $K$-theories and localisation' Corollary 8.7.
More precisely, the result states that if $G$ is finite, then the $K(n)$ localized norm map:
\begin{equation}
 L_{K(n)}\Sigma^\infty_+ BG\rightarrow F(L_{K(n)}\Sigma^\infty_+ BG, L_{K(n)} S)
\end{equation}
 is a weak equivalence. This is because Tate cohomology lowers chromatic complexity (Hovey-Strickland 96, Kuhn 2004), so the cofiber of the localized norm map $L_{K(n)}t_G(L_{K(n)} S)^{G}$ is weakly contractible.
Comment: I thought that BG wasn't exactly self-dual in the K(n)-local sense. Isn't there a twist?
Comment: I expanded the answer to clarify what I meant. If the new answer does not allay your concerns, perhaps you can tell me what you mean by a twist?
Answer: This property is closed under taking products of groups, which gives you other examples.
Also, any genus $g$ surface (for $g>0$) is a $K(G,1)$, and hence a $BG$, and is clearly a finite CW complex.
Answer: This example is undoubtedly covered by John Klein's general response, but is somewhat illustrative in its own right.
By the Cartan-Hadamard theorem, the universal cover of every connected, non-positively curved manifold $M$ is homeomorphic to $\mathbb{R}^n$.  So if $\Gamma = \pi_1(M)$ is the fundamental group of $M$, then $M = \mathbb{R}^n / \Gamma = B \Gamma$ is the classifying space of $\Gamma$.  If $M$ is itself compact, it is dualisable.
One tends to consider the case when $\Gamma$ is a discrete subgroup of $Isom(\mathbb{H}^n)$, the group of isometries of hyperbolic space.  If $\Gamma$ acts freely and cocompactly on $\mathbb{H}^n$, then $B\Gamma$ is stably dualisable.

Dualizable classifying spaces


Spinors in more dimensions and new degeneracies?

Question: As you more than probably know spinors dimensions go as $2^{\frac{D}2}$ in D spacetime dimensions. If we look at the peculiar case of D=2*4, spinors have 4 components and we usually say that's related to the 4 "degrees of freedom": particle/antiparticule & spin up/down?*. So basically linked to the degeneracy in energy and spin. But if we know go to D=6, they have 8 components, I am asking myself if it's not the appearance of a new physical degeneracy, but I don't really see what could it be. Maybe the group of rotation in 6 dimension has one more Casimir operator. Am I seeing it in a totally wrong way?
Answer: This is a property of the compatibility of Weyl and Majorana conditions, and this happens periodically in dimension with period 4. Weyl fermions have half the dimension of Dirac fermions, Majorana fermions half again, so that when Weyl and Majorana conditions are compatible, you get 1/4 the number of components.
The Weyl-Majorana dimensions are 2,6,10, and you are noticing the issue with 6. The two and ten dimensional cases are equally interesting, being the worldsheet and spacetime dimensions of string theory with a free worldsheet action.
This is reviewed well in many string theory sources.


Cleaning bottles - What's a good cleaning agent?

Question: At this point I am using regular dishwashing liquid for cleaning my bottles. This is not perfect, I know and I think, I am seeing a detrimental effect on the foam, but I do not know a good alternative. Can you guys name any?
Comment: can you reuse and store diversol? and for how long is it still good? i have been storing it in a carboy. is this okay?
Comment: related - http://homebrew.stackexchange.com/questions/1205/wiki-bottle-sanitizing-techniques-pros-cons
Answer: I soak in OxiClean Free, warm to hot water for 20 minutes or so.  Then, rinse thoroughly with hot water.  It helps to shake around the rinse water in the bottle, as OxiClean leaves a slick film that won't come right off unless you agitate the rinse water or use a scrub brush.  OxiClean is great at stripping off beer residue and also helps to remove the labels.
Other similar products that are brewing-specific include B-Brite and PBW (Powdered Brewery Wash).  PBW can be rinsed with cold water, which can be helpful if you find yourself using a lot of hot water in cleaning (or if say, your wife is doing laundry and dishes while you're trying to clean your bottles and you run out of hot water).
After using any of the above to clean the bottles, it is still necessary to sanitize.  I finish by soaking in Iodophor for at least 20 minutes and letting them dry completely by hanging them upside-down on a bottle tree.
Comment: Thanks for the answers, all of you. Problem is I am in Sweden and don't think we have OxiClean around here (definitely can't get it in my local homebrew-store). What is it wrt ingredients? Maybe there is something comparable.
Comment: How high do you concentrate the PBW for bottle cleaning?
Comment: I'm not sure what shipping costs and/or import issues there would be, but you can definitely get OxiClean online: http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=OxiClean&x=17&y=20
Comment: Tobi, I just follow the instructions as to how much to use (not sure off-hand).  Doesn't take much though!
Comment: Pretty much any percarbonate based cleaner will be about the same as Oxiclean or PBW.  You should be able to find something in Sweden.
Comment: Instead of OxiClean I use Napisan where I live.  The active ingredient of both is Sodium Percarbonate.  It also makes a great cleaner for keg lines & the rest of the kit.
Answer: I use either Oxiclean (the Oxiclean Versatile works as well as  the free and leaves no odors or residue) or PBW.  I did some tests and found that PBW works better than Oxiclean, but it close, and for the lower price Oxiclean is a great choice.  If you always rinse your bottles as soon as they're empty it makes cleaning them much easier.
Answer: I do a 15 minute soak in hot water and OxiClean Free.  Night before bottling, I run through the dishwasher on high-heat, heated dry with no soap.  So far, it has worked well, although I will likely be adding a sanitizer step in there somewhere.
Answer: To clean up the bottles use dishwashing powder (the stuff you put in the auto dishwasher) as it will dissolve all the dried on beer residue quickly and it rinses off quickly in hot water. I usually add a good teaspoon or two to each bottle and fill with hot water and let soak. When I rinse I shake the bottles out hard and rinse 4 times.
To sterilise - in order to preserve the beer quality & head retention I only use boiling water.
I heat a 10l pot to the boil and fill the bottles half way before shaking the hot water out. Use gloves. This also ensures a final rinse of any chemical residue.
Answer: I've used TSP(Trisodium Phosphate) in my carboids when they get a little crusty and it works well in the bottles too.  Should be available in most stores that carry paint.  Needs a good rinse after, and like others I give the bottles a run through the dishwasher without soap and sanitize with iodophor before use.
Answer: Diversol is a great cleaning / sanitizing agent, but it requires a 20-minute soak (unless you mix it at contact-sanitizing strength) and a rinse.
Answer: I using oxiclean to remove the labels & soak after use. on bottling day I run the bottles through the dishwasher (no soap).
Answer: For simplicity and effectiveness, I have only soaked bottles in a bleach solution. 2 oz./5 gallons. I usually let them soak for at least an hour and rinse them thoroughly with hot water. Soak longer to get stubborn labels/glues off. I have had no problems with contamination afterwards.
This is such a critical step, of course! Thankfully, the chances of contamination in all of your bottles is very low if you are careful and kill the beer-hungry bugs.
Comment: Bleach will not work with removing soil or beer stone. Bleach is a sanitizer not a cleanser.


Creating typefaces and what widths to use?

Question: I was wondering when you create a typeface do you stick to specific widths and proportions for certain letters. If so how do you got about this other than all b/d/p/q etc widths being the same how would you go about this.
Answer: There is no rule for this. While type design is a craft, it's also very much an art, and decisions like this will ultimately come down to aesthetic calls--and often subjective aesthetic calls.
In addition, typefaces come in all sorts of widths and shapes and flavors. The bigger issues is overall visual consistency, rather than technical exact-width measurements.
Answer: No doubt you are aware of monospace fonts, where each glyph is equal in width. Contrast that to a font like Futura, where there are extreme variances in width between an 'm' and an 'i'. So, like @DA01 says, it's up to you.
If you're not REALLY good with typography, then definitely reference other fonts while making your own. Unless you're doing something really weird, your font will have similar characteristics to others, and you can see how they do it. I created glyphs for a really old-fashioned-looking font once, and while it looked different than fonts like Times or Chaparral, I spent a lot of time looking at those. When you zoom in and look at glyphs, you'll find some interesting quirks that are often worth imitating. For example, even though you'd think that 'p', 'q', 'b', and 'd' are just flipped and mirrored glyphs, they rarely are. An 'o' is rarely a perfect circle. And so on.
If this feels like copying, it's okay. Typography has evolved through the years and many fonts are inspired by others. We humans have somewhat of an unconscious expectation of what our languages' letters are supposed to look like, so you don't want to deviate too far from that.


What are the best online photo classes?

Question: I bought an entry-level DSLR at Christmas time (Nikon D3000 with 18-55mm and 55-200mm lenses) and have been figuring my way around the camera.  I know the very basics, but want to take a class and can't logistically take one offered in my area.  Are there good online classes for learning about lighting, exposure, composition, etc.?  Or maybe sites with good exercises for beginners?
Answer: There are many great sites on the net that can help you get started. I am not sure about official "classes", however the following sites should be useful:

Digital Photography School

Great info on camera usage, composition, lighting, post-processing, etc.
For Beginners Section

Cambridge in Color

Another great educational site for new DSLR users
Lots of great tutorials covering all the technical details
Great techniques section describing specific scenarios
Comment: The Digital Photography School is great!  I haven't had a chance to browse the other too much but it looks useful as well.  Thanks!
Answer: Creative Live! Hands down! http://creativelive.com/
They are not specifically all photography related, more like art/creativity stuff. But their photography classes are superb - so superb to the point I was willing to pay for them. Some are free, but to get the archive, download, etc, you will need to pay for some. But they are worth it!
Comment: For beginners, nothing beats John Greengo's course at CL!
Answer: Oh dear, this is going to be a hard one to answer. Since there's so much courseware. But I'll share the ones I have appreciated. Unfortunately not a lot of this stuff mentioned below will get you college credits (if any), but you'd probably be pretty pleased with yourself at the end of it all being in the situation of knowing rather than not knowing. I wouldn't be surprised if you end up coming back to these to supplement for-credit courseware.
General:
It goes without saying that hopefully Q and A sites such as photo.stackexchange.com (or whatever its final name will be) will someday be the source of course reading material.
Photo.net is another huge source of articles. Some mercifully abridged, glossing over everything, for the most innocent of new photography learners--others surprisingly deep. If you haven't read them all, you should. They make a great course just as they are. I still go back there and discover that something well understood and worth heeding goes completely unheeded by me for far too long. Alumnis of photo.net education should return often. Photo.net exist partly thanks to people like Philip Greenspun and his photography buddies. Photo.net and slightly gated online discussion groups and bulletin boards tend to be generalist, but there are some focusing on one system at a time (the Nikon system for instance). Or specialization (children photography for instance). They are wonderful. In fact, never read a Photo.net article without also reading in the comments of the readers chiming in. It's never a waste of time in my book. What people discuss can be surprisingly deep, so the few dollars required annually to register for a discussion forum related to your photography craft is money well spent. Definitely be a team player here: learn and share likewise.
Total Training and Lynda.com:
Incredible resources at a subscription price you can't ignore. All laid out clearly for the new comer or the photographers who knows that they'll need to be power users from day one. Post processing with Adobe Photoshop, presentation and media with Adobe InDesign,  Adobe  Illustrator, Adobe Flash and so on. They are really great for a first pass through the material, so that you know what's possible or probable with these software at your disposal. From there, it's good to couple these videos with a well bookmarked notes so that you can dig up the details without having to find the exact minute and second tick mark required to relearn something from these videos.
Post processing:
Luminous Landscape by Michael Reichmann and his photography education friends all did a great job distilling everything you might want to know down to short videos between the time the RAW files leaves your camera and ends up hanging on the wall. I would still read 2000 pages on color management because I am insane like that, but if you want the short version--I can't think of anyone better.
For photography lighting:
David Hobby and his Strobist.com has tried to provide some fantastic free or nearly free material. He confesses to stand on the shoulders of giants, such as the late photography lighting educator Dean Collins and recommends Dean's material highly. I think both are fantastic for lighting. David and Dean's videos have a courseware component to them. They illustrate how it's done, why it's done, and challenge you to replicate the successes in your own DIY (or sourced from commercial light modifier makers) efforts. It seems to me that David might go into talk about lighting for cinema in the next little while on Strobist.com, stretching himself and forcing himself to learn just a tad more than the rest of us just a few hours ahead of us. That's big. That takes a great deal of confidence, hard-work and research so I wish him the best.
Transition to video:
Vincent Laforet, Chase Jarvis, B&H, and creativeLIVE all came together to address the thousands of issues that we haven't thought about in our transition from stills to video in a three day web-casted workshop. It's a really good basecamp to figure out how to navigate the terrains of your eventual transition to video. They blog too, and what Vincent and Chase has blogged over the year probably can't ever be fit into a three day workshop no matter how they squeeze.
Marketing:
Dan Heller has been writing about photography, the business and marketing of photography for a long while now. And has some great ideas to share. There's no set 'class'. Lots of great material that you'll want to at least read once-through and decide for yourself the merit of each point.
I think it's really really really wonderful that these people share so much of their time with us through blogs, videos, writing and workshops. They have been keen on helping to raise the art/biz/sci average for all photographers. They do it for a variety of reasons, for the fame that will keep their calendars booked with the clients they want to work with; or just so they never have to explain something for the Nth time with their friends; or even so that their children would someday know what mom and dad did.
Off the buzzword charts:
Video courseware is not a new invention, it's been around since before Betacam and VHS. So do know that folks have been making actually timeless classics for a long long while. Check your reference libraries. You'd be quite surprised by the relevance and creativity behind some of the tips being shared from some of the old old videos. On marketing, on business, on the very act of taking photos. I mean, we are still capturing light--that hasn't changed at all for many many years.
Answer: In The UK the Open University have a course, T189 , that is all about digital photography.
Comment: What makes this particularly good?
Answer: You might find a course you like at Kelby Training
Comment: Why might I find a course I like there?
Comment: Is it really worth the price? Are the videos useful and carfully designed for beginners?
Answer: For free step-by-step lessons consider Photocritic Photography school. It's free, and involves photographic homework after each lesson and critique by participants.
Answer: Use a FREE Camera Simulator
See the results of changing Aperture, ISO, and shutter speed, and your light meter in real time with this online (or download the offline one) Camera Simulator.
Camera Simulator
Answer: The B&H Event Space has good videos on a variety of topics. They're not very well organized, but as good as some of the paid videos I've seen from other websites (sometimes offered by the same instructor). When looking at the playlist look for videos that are 1-2 hours long as anything shorter than that is probably a product showcase video (still informative, but not the best videos in the playlist).
Answer: http://www.brighthub.com/multimedia/photography.aspx offers a lot of quick tipps. Many are not really in detail, but to get an overview over a topic it is nice and quick. Other topics like composition are treated in several articles and therefore provide more in depth information.

What are the best online photo classes?


Mirror a browser session

Question: I am doing some regression testing (changes to underlying database structures) where I'm lucky enough to two separate environments which should contain the same data.  What I'd like to do is open a browser session in each environment and then have one browser mirror the other (ie I click on a control for example) so I can check the results between browsers without having to repeat actions in each browser.  Does such a tool exist?  Ideally the targetted browser is IE.
Answer: Building off of @Bruce McLeod's answer with Selenium.  Using Selenium WebDriver to do what you want to do isn't terribly hard. Briefly, this is how it could be done.
Typically, web tests built around Selenium WebDriver only open one browser session and perform all operations on that session.  However, there's nothing stopping you from opening up two browser sessions and performing the same operation in both sessions then comparing the results like so...
<code>//Begin test
ie = openBrowserSessionIE()
chrome = openBrowserSessionChrome()

ie.open(url)
chrome.open(url)
compareResults(ie, chrome)//non-exhaustive comparison of page elements

ie.click(xpathToElement)
chrome.click(xpathToElement)
compareResults(ie, chrome)

close(ie)
close(chrome)
//etc. etc.
</code>
You'll want to compare only the essential features of each page since an exhaustive search is really going to slow down your test.
Answer: There are plenty of tools that allow you to record scenarios and then play them back at any time, even changing the url that you navigate to.  There are also tools that will show you the same URL in a number of different browsers.  I don't know of any tool that does what you are asking though.
Would recording a scenario and playing it back be enough?  Would you want it to click the exact x/y coordinates (compared to the top left of the browser window) or the same element even if located at different x/y coordinates?
If clicking the exact same coordinates would be enough you could probably write this tool fairly simply importing the mouse_event library.  An example is here: http://pinvoke.net/default.aspx/user32/mouse_event.html
If you want to click the same element regardless of coordinates and you wouldn't mind playing it back (rather than seeing it happen simultaneously) you can use the Selenium IDE: http://seleniumhq.org/projects/ide/.
Clicking the same element simultaneously would be a little more work I'd imagine.  You'd need to basically combine the code to record and playback from some record/playback tool such as Selenium to happen at the same time.
Answer: I don't know if this exactly covers your desire, but if you are testing servers, and if you are willing to automate your testing (probably a good idea anyway) you can just use scripts to send requests, or with javascript even to run from within a browser and simulate user interaction.
Answer: Whilst there is no commercial tool that could do this you could definitely "roll your own". For demo purposes I have built tools that fire up four browsers simultaneously.
The challenge though, especially with IE it that if you are doing this on the same machine then you will get "session corruption", and the browsers will be effecting each other. Some examples are:

Logging in to one browser will most likely log in both.
If a pop up occurs, which session created it ?

If you can live with this, I would look into using selenium, via http://selenumhq.org.

Mirror a browser session


Do you still bracket your photos?

Question: Do you find that bracketing your photos is still in general a good practice, or has photo editing software greatly reduced the need for this?
How To Bracket
(Why You Should) Bracket Your Important Photos
Answer: I'll put it this way: I've often regretted not bracketing, but rarely regretted bracketing.
Meters still make errors, and data which exceeds the dynamic range of the sensor is gone forever, regardless of post-processing software. I recommend bracketing any images which have complex lighting or any particularly important images, certainly until you understand very well how your meter behaves in the situation.
The alternative is chimping and checking the histogram, which provides immediate feedback but slows the shoot and is prone to error (as the histogram shows data processed as if for JPEG even if you're shooting raw).
Comment: I believe many cameras compute a JPEG even if it's not saved (e.g., raw formats often include a small JPEG preview), but that's a good point. I'll edit.
Comment: You may want to reword that slightly, as it can't show the JPEG data where is no JPEG (but it may show the data if as processed using the shot settings, such as white balance, which can have an effect on the histogram)
Comment: @Rowland: Is there any camera that shoots RAW and does *not* embed a JPEG preview inside the RAW file?
Comment: @Jukka, @Reid According to [dcraw](http://www.cybercom.net/~dcoffin/dcraw/dcraw.1.html) *some* cameras store the thumbnail as a PPM format image. I seem to remember that CRW format raw files do not have a thumbnail - on cameras using this format, they use a sidecar .THM file instead
Comment: Just for the record: How much offset do you usually use when bracketing? is it 0.3, 0.5, 0.7, 1.0 or even more?
Answer: Bracketing still has its uses, and is encouraged for HDR images (High dynamic range).
It remains the case that it is better to get things right in-camera, but using tools like the histogram that most cameras (at least those that support brakecting) can be useful to tell whilst you're there and see if you've got the exposure right, which does reduce the need for bracketing.
Answer: When to not Bracket

If the situation involves even illumination with good lighting with no excessive shadows or blow-outs.
High resolution quality is not paramount.
You need to do your photo shoot quickly.

When to bracket

If you have a complex lighting situation such as a bright foreground and dark background, you may get lots of image noise.  Bracketing and using an HDR will help alleviate the problem.
If quality is paramount and or you plan to blow up the image, use bracketing.
When noise elimination is paramount.

Summary
RAW processing indeed allows you to recover a tremendous amount of detail in your pictures but only to a point.  In post processing, my experience has shown me that excessive boosting of the exposure or brightness will get noise to rear its ugly head.
Certainly, there are many great applications that deal with noise, but I find they all weaken the quality of the image in some way.  The best you can do is get the best image you can when you're on site.  If the dynamic range of your principle photo is poor, you always have the back-up exposures to enhance the quality of the image.
Don't rely on your Camera's LCD or the histogram screen to determine if you got the entire dynamic range in your shot.
It is painful to think that I've had to waste excessive time to fix cruddy images only to wish that I had taken alternative exposures to enhance them.  To save time in post processing and to deliver a better product, I highly recommend bracketing.
Comment: Hi Jules! Welcome to Stack Exchange, and thanks for the helpful answer. You don't need to (and shouldn't) put a signature on your posts, since every post is automatically signed with your name and avatar. You can definitely link to your website in your profile, though (which is linked-through from your name on every post).
Answer: I've tried bracketing once, and was annoyed about all the extra pictures. It wasted a lot of my shooting space and cost me a lot of time in postprocessing, filtering the images.
Now I pay way more attention to get my exposure right on set, so I'll don't have extra work in postprocessing.
There had been some rare occassions where I would like an additional underexposed image, but for me these are not worth the extra space needs and work.
Answer: I don't bracket with digital unless I'm blending multiple exposures to get greater dynamic range.  A quick look at the histogram tells me all I need to know about whether the exposure is good or not, and I either adjust exposure and reshoot or move on to the next photo.  The histogram is like having a field densitometer.
Answer: I never use bracketing.  I don't want the shot where the composition subject's expression is just perfect to be the one that got underexposed or overexposed by the bracketing.  Minor adjustments in exposure can easily be made in post-processing.  Telling people at an event to strike the same pose again is much more difficult.
I do regularly check the exposure after taking a shot and use exposure compensation to adjust the following shots as needed.  I find that as long as I watch out for blown highlights, the metering and dynamic range of modern digital cameras is good enough that I don't have to throw away any shots because the exposure couldn't be fixed in post-processing.
Or maybe I'm just lazy.  Exposure compensation can be dialed in directly and set in small steps on any serious camera.  The amount of overexposure and underexposure used by bracketing is usually buried in some menu.
Comment: If you're shooting RAW, that's a very good point, since you can do so much more correction after the fact. But if you're shooting JPG, bracketing might help you out.
Comment: Yes, I shoot raw.
Answer: I think in addition to the other answers this can boil down to a philosophy for your own development in your skill.
Some people feel if you are more conservative in the shots you take you will learn more. I know I have taken a bunch of shots thinking that "I will study them and figure out why the one that is right was the best" and just don't do that.  If you only take a couple shots and miss what could have been a great shot because you didn't chose the best settings you really remember why that happened.  The emotional impact of a failed picture helps make the impact in memory.  This development can also help if you get involved in action photography such as sports or wildlife because you're chances to get the right moment are limited.
The flipside of this of course is that you will end up missing a shot that might have worked.
Answer: Only when I am shooting very high dynamic range subjects.
Otherwise, RAW gives me enough leeway for even tonemapping.
Answer: Regarding bracketing for HDR, I regret bracketing when I don't need to, esp. when it leaves three times as many photos clogging up my computer/iPhoto library. Now I just try to look for better lighting.
Answer: I rarely use bracketing, but not because I can fix it in post-production. It's because digital photography means I can take a test shot and check the exposure (including looking at a histogram) right there. With film, bracketing is a way to cover uncertain exposure situations; with digital, there's less uncertainty about what the result will be.
Answer: I highly recommend building into your gestalt a certain bat sense about when to use bracketing. I think you'll quickly figure out when, it's when your camera's meter is guessing every thing wrong and yet you still don't want to go full manual.
Another equally impressive type of bracketing is aperture bracketing [used together with a very steady hand, or tripod/monopod]. There's amazing things you can do when you have full control over how sharp your subjects are and how blurry/sharp your backdrops are. Aperture bracketing affords you that. It's a type of technique that finds themselves in more and more use in this age of almost mandatory photoshopping.

Do you still bracket your photos?


Why does a semiconductor hole have a mass?

Question: I have read that holes in semiconductor are nothing but vacancies created by electrons. But how can this vacancy i.e. hole has a mass?
Comment: See http://physics.stackexchange.com/a/10858/3811 for more details about "what is a hole" than you usually find :-)
Answer: A quick answer:
Imagine an array of billiard balls with one missing in the middle of the array; there is a "hole" where the billiard ball is missing.  For this hole to "move", a billiard ball must move into that position, leaving a hole at the ball's previous position.  Since, in fact, the hole movement is entirely equivalent to the billiard ball movement, we can speak of the mass of the hole even though it is the billiard ball's mass that is physical.
Now, in the case of electrons moving through the unfilled valence band, the effective mass is greater than the mass of a mobile electron so hole mass is typically greater than mobile electron mass.
Answer: While the answers above are correct in essence, the inertia of the hole is due to the electrons that must flow to fill up the hole, there is a simple way to understand what the mass of a hole is in a tight-binding model.
If you have an electron in a lattice, and it can hop from one site to another with amplitude a, then the time evolution of the wavefunction is by
$$ {\partial_t \psi(x)} = a\sum_{\langle y,x\rangle} \psi(y) $$
where the sum is over nearest neighbors of x (not including x). If you redefine the phase of the wavefunction in a time-dependent way $\psi(x)\rightarrow e^{iNat}\psi(x)$$ where N is the number of nearest neighbors, you subtract a term from the right hand side which leads to a standard form of the lattice Laplacian, so you have a discretized Schrodinger equation. The continuum limit of this is the normal Schrodinger equation:
$$ {\partial_t \psi} = a\epsilon^2 \nabla^2 \psi $$
Where $\epsilon$ is the lattice spacing. From this, you can read off the effective mass $m={1\over 2a}$.
The point is that mass of a quantum excitation is just the inverse of the hopping amplitude, so it is universal to describe any localized excitation that moves coherently with an effective mass. The harder it is to hop, the more massive the object is. The result is in principle independent of the actual mass of the fundamental particles--- if you make an optical lattice and place a metal BEC in each optical trap, the electrons have to tunnel from one trap location to the next in order to flow, and the effective mass can be as large as you like. In real materials, the effective mass is usually close to the electron mass, but sometimes can be hundreds of times bigger.
If you fill up all the electron states, and consider one hole, there is an amplitude for the hole to hop to a neighboring location. This gives an effective mass as above, proportional to the inverse hopping amplitude. Unlike in classical systems, you don't have to consider dissipation--- the effective mass description is exact. Further, if the hopping amplitude for a hole is fundamentally the same as the hopping amplitude for an electron to fill the hole from the neighbors.
Answer: I think that the answer should be searched in surface metal (dielectric)free electrons.
When an electron start to move it became heavier or easyer throgh absorbtion or radiation
of some Planck energy.The change in speed is : speed is increasing if electron go through band gap by absorbtion.(Fourier Generalised Tf. and antenna radiation)
In orbital valent position the electrons and the holes in which it is formed a filler.When the electron leave the filler , the filler hole mass is the mass of
electrons plus the mass of received energy and other posible interaction with other orbital or nucleous .
Comment: Could you please improve the grammar and/or sentence structure of your answer? It is very hard to understand what you're saying as of right now.
Answer: For a very common practically important classical mechanical equivalent, consider a bubble of air in the water. The apparent inertia of the bubble is on order of the mass of water displaced by the bubble, as the water around the bubble has to move for the bubble to move. This is an important consideration for ships, submarines, torpedoes, fish, etc, that end up having considerably more inertia than their own mass, and end up accelerating slower with the engine on.
One time I did mathematics for realistic barrel falling into water in computer game; the apparent 'increase' of the mass, in combination with the conservation of momentum, rather accurately describes a large part of the deceleration of object when it is entering water.


What the most efficient way of testing cross platform (i.e. iOS and Android) applications?

Question: I work on several projects were the client wants basically the same application implemented in both iOS and Android. At the end of the day, you have to test both - they are distinct pieces of software, just wondered if anyone has found any tips / tricks here. We've started doing client acceptance testing with one platform, then using this as a baseline for the 2nd platform - this kinda though turns into a 'spot the difference' competition.
Comment: possible duplicate of [What are some tools for testing Mobile web apps?](http://sqa.stackexchange.com/questions/1/what-are-some-tools-for-testing-mobile-web-apps)
Answer: What I do when testing the same code under 4 different OS's is to identify the common parts, then I build a plan where each OS is tested for it's unique part plus some of the the common part, making sure everything is covered at least once.
From time to time we rotate the tests between OS's or repeat some test on a different OS.
All of the above must be planned carefully using some kind of risk management and after consulting with someone who knows the code and differences between OS'
Answer: You'll want to create configurable fixtures / tests, so you can you the configured parameters to say, e.g.,:
if(config.environment.Equals("iOS")){
    //do this thing (e.g., interact w/ UI button)
}elsif(config.environment.Equals("Android)){
    //do this slightly different thing (e.g., interact w/ slightly different UI button)
}

This allows you to reuse automated tests and fixtures.
There are screenshot tools that might be able to help you . . . I don't know what they are, but I know that they are out there.  You might want to create methods that hide the environment dependencies for UI testing, e.g.:
public void ClickLoginButton(){
   ... //use a statement like the if-else above in here
}

Then you can write UI automation code like:
public void Login(string username, string password){
    EnterUsername(username);
    EnterPassword(password);
    ClickLoginButton();
}

e.g., mostly environment independent.
Otherwise, do as much functionality testing at the API level as you can (where environment is less key to test structure) to reuse tests.  You will still need your E2E tests and probably some manual UI tests, but this should increase test reusability.  Then you just make sure you have the right configuration files set up for your different environments that you test on, and test on both environments.
BTW, I haven't dealt with hugely different OS's before, just different versions of Windows, so I could definitely be missing some subtleties that arise with this combination of OS's.  This worked for us, even with some annoying differences in OS's (XP doesn't have admin mode, Vista does, some UI changes, etc.).


Is it too late to start using the sneak playstyle?

Question: I'm level 10 now and all my perks so far have been spent in Destruction (3), Restoration (3), Alchemy (1), and Speechcraft (2). Whilst doing the Thieves' Guild/Dark Brotherhood quests, I realised that sneaking around and stabbing things is way more fun. Is it too late to start putting my perks into one handed/sneaking, am I always going to be underpowered because I wasted those perks in Destruction?
Comment: It's NEVER too late!
Answer: It is never too late to start playing the game the way you want to play it. Your sneaky assassin character has a background in magic. If the game seems too tough you can always respec your perk points but that will disable achievements as noted in the answer.
Comment: Yeah, that's only 10 perk points of a possible 50-70. You'll be able to fill the Stealth perk tree easily, if you so wish.
Comment: I'm playing on the Xbox, so I can't respec.
Comment: i think you'll be fine to start playing sneaky. if your only lvl 10, i wouldn't blame you if you started over, i know missing perks would bother me.
Answer: I'm not a power gamer, and my guy's a stealthy, magically gifted wood elf who can also handle a sword ;), but I must say I'm pretty happy with him and I also have a bunch of perks in non-sneaky branches. I'd say just go with it; the most important thing is sneaking skill points (as opposed to perks), and then (at least for my playing style) as soon as I got 3x bonus on stealth archery, I was mostly done in the Stealth skill perks (the backstabbing perk is pretty spectacular when put to use though :). So I'd say just go with the flow. And there's always situations where you need brute force so destruction will come in handy anyhow.
Answer: Adding some more to the answers already on here.
I suggest that you get the Shrouded Armor from the Dark Brotherhood sanctuary. These are very light and add very little weight to the inventory and some of them increase your sneaking abilities. You can switch back and forth between regular Armor and this clothing depending on what you are doing at the moment.
Also, enchanting some items with less weight(like a ring) with sneak helps. Get the Muffle spell(Illusion spell i think) helps when sneaking. I realized much later than you that I wanted some sneaking abilities and these helped a lot.
Learn how to brew Invisibility potions. This along with the Muffle spell above and I was able to sneak up on some enemies with higher level very easily even with heavy armor on.
Comment: The Nightingale armor set (reward from a [Thieves Guild quest](http://uesp.net/wiki/Skyrim:Trinity_Restored)) are good 'stealth' armor too.
Answer: Not only is it not too late, but the perks you have already aren't even negatives. A little Destruction's nice for at least setting runes, some points in Restoration are almost a must, and Alchemy and Speech work fine for all builds. If you'd thrown everything into Heavy Armor and Block you wouldn't have many synergies, but the most effective characters all dabble at least a bit in magic, combat and stealth.
A good example for Destruction is that, when I'm using stealth and have several enemies descend on me, I can hold them off a bit with the Impact perk (most dualcast spells will stagger an opponent). This is especially true against large targets, like dragons.


Is it possible to subtract/multiply numbers using homomorphic encryption?

Question: Most of the libraries I've seen allow you to add encrypted numbers. Is it possible to subtract and multiply them?
Comment: Have you read the Wikipedia article on homomorphic encryption?  That'd be a good starting point.  Also, search on this site.  I think you'll find some answers....
Answer: Have you read Wikipedia: homomorphic encryption and
Bruce Schneier: Homomorphic Encryption Breakthrough?
In summary:

Is it possible to subtract numbers using homomorphic encryption? Is it
  possible to multiply numbers using homomorphic encryption?

Yes, there are many known partially homomorphic cryptosystems, each one can either multiply or add numbers.
To add two encrypted numbers, one could use Benaloh, Damgård–Jurik, or several other known partially homomorphic cryptosystems.
(Many of these "addition-only" cryptosystems can also be tweaked to support subtraction.
Asking "how do I do that" would be a great separate question).
To multiply two encrypted numbers, one could use Unpadded RSA, ElGamal, or several other known partially homomorphic cryptosystems.

Is it possible to subtract and multiply numbers using homomorphic
  encryption?

To multiply one encrypted number by a plaintext number (which, alas, is not sufficient for fully general computation) and also add two encrypted numbers, one could use Paillier, Naccache–Stern, or several other known partially homomorphic cryptosystems.
Subtraction can be implemented by encrypted "multiply by a plaintext -1" followed by encrypted addition.
(Asking "how do I do that" would be a great separate question).

Is it practical to express any computation whatsoever as a series of multiplies and subtracts?

Yes. In fact, computations on decimal numbers, text strings, 2D images, etc. are almost always done by converting to binary representation, using a series of Boolean computations internally, and then converting back to a human-friendly representation.
(Boolean computations can, in turn, be implemented using multiplies and subtracts, although that is slightly less efficient).

Is it possible to encrypt a few numbers, send them to a distant server
  that uses homomorphic encryption to do a series of
  "encrypted subtraction" and "encrypted multiplication" operations
  on those
  numbers, and then sends the encrypted result back -- a message that can be
  decrypted to give the same result as a corresponding series of
  subtractions and multiplications on those numbers?

Cryptographers have been hunting for such a "fully homomorphic encryption scheme" for decades.
After a few decades of searching and coming up empty, cryptographers were starting to think perhaps fully homomorphic encryption is impossible.
The first known fully homomorphic encryption scheme was discovered by Craig Gentry and announced in 2009. It is an amazing theoretical breakthrough.
Alas, in that scheme, the "encrypted subtraction" and "encrypted multiplication" operations are so complicated that it's not really practical.
Now that one fully homomorphic encryption scheme has been demonstrated,
cryptographers have high hopes that other, more practical systems will be discovered.
The current situation is something like the current situation with manned moon missions.
People have been dreaming about traveling to the moon for centuries,
but it was long thought to be completely impossible.
In a great technological breakthrough, one method of traveling to the moon put 12 men on the moon, demonstrating that it is possible.
However, that particular method is so expensive that it is not really practical.
Still, futurists have high hopes that other, more practical systems will be discovered.
Answer: Yes it is.
Given $m_1$ and $m_2$ two numbers, if you take their naive encryption under a El Gamal public key $(p, h = g^r)$ where $p$ is a prime and $g$ a generator, $r$ a random number youl get that:
$c_1 = h^{m_1} \pmod p$; $\;$  $c_2 = h^{m_2} \pmod p$;
and
$c_1 \cdot c_2 =  h^{m_1} \cdot h^{m_2} = h^{m_1 + m_2} \pmod p$
so, decrypting you'll get the sum of two numbers $\pmod p$
It has be said that when you use asyimmetric cryptography your messages are numbers. A layer of "translation" (or encoding) has to be added to transform plain english to a sequence of numbers to be used as plain text in an encryption scheme
Comment: this is just one example of how you can add numbers. I think every "malleable" encryption scheme allows to you to make some controlled transformations on plaintext playing only with their ciphertexts.
Comment: seems like you've answered the question for addition "so, decrypting you'll get the sum of two numbers" I need a scheme which allows subtraction of numbers
Comment: Addition and subtraction, algebraically speaking, are the same thing.
Comment: @pg1989 - you mean I could simply use Modular Arithmetic?
Comment: try to write the same thing I wrote but with $-m_2$, or if you prefere, try to compute $c_1/c_2$ ...
Comment: Well, kinda. In these kinds of groups modulo a prime, every element $x$ has an additive inverse, which can be called $-x$ because $x + -x = 0 \mod(p)$.
Comment: Yes, I meant the same saying "$-m_2$".
Comment: The formulas in your answer are not consistent with how ElGamal works. Do you mean Paillier? http://en.wikipedia.org/wiki/Paillier_cryptosystem


Blow torching meat after sous vide - add fat or not?

Question: After I pull the meat out of the sous vide and then use a blow torch to sear it, should I use a fat on it or not?  Will that get a better crust on it?
Answer: I have not noticed any real difference from using a fat, so I skip it. What does make a difference is thorough drying the meat.
I haven't ever had great results from a torch though. I prefer a screaming hot pan or grill, although both are way more effort.
Comment: Yes. If it's hot enough to sear off quickly, then the oil splatters everywhere. The issue is the clean up, not the cooking.
Comment: Set pan on stove, turn stove on...its *that* much more work?
Comment: I use a blow torch and get great results but I have a commercial/industrial blow torch, not a little kitchen model.  This is the torch I use which hits 3,450F : http://www.homedepot.com/h_d1/N-5yc1v/R-202185047/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=torch&storeId=10051
Comment: Ah, that makes a bit of sense, gotcha.
Comment: One way to make this a lot easier is to throw it in the freezer for like 10 minutes before you sear (or even better deep fry) since the freezer will freeze the outermost later of the meat, dry it out, and protect the inner meat from overcooking from the searing process.
Answer: At least one commercial chain (Panera Bread) uses fat when searing meat that is prepared sous vide.
Here is a video example.  After cooking sous vide, they dry the meat and use a very hot cast iron pan with generous amounts of butter.
Sous vide followed by searing in butter
Answer: I haven't noticed any real difference with or without oil or fat to be honest. When searing in a pan, the oil would simply aid heat transfer from the pan to the meat by eliminating insulting air pockets.
However, I have experimented a little with brushing a weak glucose syrup onto steak before torching, and believe (without scientific measurements) that this results in a nicer crust with a lower propensity to blacken due to the flame. This is based on something I read in McGee's On Food and Cooking, which implied that the browning Maillard reaction would be accelerated by the addition of glucose. Apparently glucose is more reactive than sucrose found in normal sugar.
I've also discovered that drying the surface of meats with a paper towel just before blow-torching results in nicer and more rapid browning. I'd speculate this allows the surface temperature to rise more quickly as there is less liquid to boil off first.


Test scenario for Android porting test

Question: I am new to testing of Android porting. Could you kindly share with me a testing scenario, any reference document or ref. template for such test case?
Comment: Hi urvish - Out of curiosity what sort of porting are you doing?  Is it porting the OS to another device?  Is it porting an app from a different platform to Android?  The more specific you can be the better answers that the community can provide.
Answer: You can get ideas from
Android unified testing initiative
It has a comprehensive list of tests for Android applications.  And here are some types of Android application tests from the AQuA website:
1.1 OTA Install
1.2 Long launch time
3.1 Send/Receive Data
3.4 Resource downloading
5.2  Message  – Receive
5.3 Incoming call
6.1  Memory card operation
7.1 Readability
7.3 Screen Repainting
7.5 Key Layout ease of use
7.8 Function progress
7.10 Multiple display format handling
7.11 Different screen sizes
7.12 Multiple format input handling
7.14 Spelling errors
7.15 Technical text errors
8.1 Language – correct operation
8.3 Language – supported formats
9.1 Suspend/resume from main menu
9.2 Suspend/resume while executing
10.1 Application Mute option
11.1 Help and About
12.1 Functionality Sanity Check
13.1 Scrolling in menus
13.3 Pause
15.1 Application Stability
15.2 Application behaviour after forced close
16.2  Data Deletion
Comment: Please just don't post links.
Answer: Might you can get your stuff from https://groups.google.com/forum/?fromgroups#!forum/android-porting
Comment: Please just don't post links.

Test scenario for Android porting test


How to read guitar pro chord strumming tabs

Question: How should I read something that looks like this? I hear the different pattern of strumming but I don't know how should I read this tabs and play accordingly.
How can I find up which of them is "up" and which "down"?
Answer: This notation is a simplified notation of regular scores. It does not show whether you need to strum up or down -- that's something you'll just have to decide for yourself, judging on what feels best and what sounds best -- instead it shows the rhythm of your strumming.
This website has an easy-to-understand list of what each symbol means, so take a look at that. In your example, most notes are sixteenths and eighths, with a couple of quarters as well. A few notes are also followed by a dot, which means that the note is played 50% longer.
I suggest you try to understand these notations first, and carefully look at the tab while using Guitar Pro's playback option. That usually makes it a lot easier to understand how exactly you need to interpret the tab.
Comment: Thanks, now I understand. And I see that every connected notes are always 4 sixteenths. So on the 3rd line there is dot, that means that I'll play on 1st and 4th sixteenth, right? And on first line, I'll play 1st, 3rd and 4th. It was quite complicated from first.
Answer: As general rule, when there are 4 beats in a bar, beats 1,2,3 and 4 are strummed down. Any strums on the 'and' are up-strums - in order that the next beat is a down strum.
Double up the timing, and make 8 downstrums in a bar instead of the original 4.Now each beat will have down, up, down, up in it. So on that first bar, the first strums will be D,D,U. As the next 'strum' is actually tied to that last U, a ghost strum D is made in its place.Then it's U, ghost D and U again.Then D, D U and D, D for the end of the first bar.
In other words, you've put a potential 16 strums into a bar, 8 D and the alternating 8 U. DUDU DUDU DUDU DUDU. This keeps the strumming arm moving regularly, and not stuttering.Each beat has 4 semi-quavers (16th notes) but not every one is strummed. If tapping your foot helps, tap 8 per bar - when your foot rises,, that's an up-strum. Obviously, you need to be able to read the pattern of notes, value-wise.
This probably sounds complicated, but the objective is to keep the rhythm arm pumping up and down regularly, as each bar will then only be a matter of when you catch the strings on a D or U, and when you ghost strum them. When the rhythm changes, or you want to change it anyway, don't change the down/up pattern - only the strum or ghost strum.


Is interpreted malware easier to detect than compiled malware?

Question: Is compiled code more of a security risk than interpreted code? I'm under the impression that it is due to the fact that compiled code can hide malicious code from malware scans.
Comment: Actually, using power shell to bypass anti-virus software is a pretty common trick these days. They both have advantages and disadvantages.
Answer: No.
Compiled code is just translated into machine code, an attacker can alter instructions for both, compiled and interpreted. Whatever you could do with one, you can also do with the other.
Your decision for either compiled or interpreted should be dependent on what you actually want to do with your code. Compiled languages usually have a higher performance, while you can easily modify interpreted code. It is easy to implement and you can run/test it on the fly.
There should be no difference between interpreted and compiled code regarding security issues, and languages should not be categorized that way in my opinion.
Answer: There is no difference between compiled code and interpreted code as far as the detection goes. The reason most malware authors use compiled code for their malware is due to the fact that native compiled code is not dependent on any external library or interpreted environment. A native exe is going to run on a Windows or Linux machine without requiring any other software on the victim's machine. By contrast, a malware that is written in perl or python needs perl or python interpreter on the target environment for its execution. Therefore, the stacks gets lower if a given malware will run on a machine or not if it is dependent on any special environment or configuration.


Canon EF 24/28 mm f/2.8 IS USM Autofocus Lenses

Question: Is there a good reason to choose one lens over the other?
Granted that the 24mm lens is a bit wider than the 28mm lens but are there any other reasons?
Answer: One chooses a prime lens primarily for its focal length/field of view (and secondarily for its aperture), so the fact that one is a 24mm lens with its characteristic field of view, while the other is a 28mm lens with a different field of view is the deciding factor. It really doesn't matter whether one is marginally sharper or has better distortion or aberration characteristics than the other; the fact is that each can take pictures the other cannot.
(I suppose you could crop a 28mm-sized picture out of a 24mm exposure if the 24 is an objectively "better" lens, but are you gaining quality that way? The 24 would have to be in a whole different performance class just to balance the scales if a 28 is what you need.)
Answer: As noted in the review for each lens at the-digital-picture.com:

...focal length is the biggest and really, only, significant difference...[between the lenses]

The obvious difference is the focal length. They are similar, but 24mm will be noticeably wider. The 24mm is also 20g heavier and slightly longer(.2").
Overall just choose the focal length you like most and either lens will perform the same otherwise.
Answer: 4mm at the wide angle makes a lot of difference, especially compared to 4mm at the tele angle.
My analogy is like this. Stand two chop sticks vertically next to each other on a table about 5cm apart. Now make a triangle with the top ends touching and hold it. Hold them so they cross each other and move down towards the table about 5cm.
Now cross them at the bottom and while holding the point where they cross and move up 5cm. The angle of difference is much more significant.
Looking at this:

This is because we see the focal length as a linear scale, but the angle changes at a (logarithmic) trigonometric scale.
So, in answer to your question, it depends what you want to shoot.
Comment: The angle doesn't chance on a log scale. Tertium non datur doesn't apply. Here it is a trigonometric relationship...


Algebraic P vs. NP

Question: I recently attended a lecture where the speaker mentioned that what he was talking about was connected to the algebraic version of the $P$ vs. $NP$ problem. Could someone explain what that means in a simple way or point me to a source suitable for a non-expert mathematician? Thanks.
Answer: I suspect that the question under consideration is whether or not $VP=VNP$; this is the problem directly studied by geometric complexity theorists, as I understand their work.  This project is described in some detail here (this paper is by Bürgisser, Landsberg, Manivel, and Weyman, describing work of Mulmuley and related people)--it is aimed at algebraic geometers; so you will likely be comfortable with it.  The description of the complexity problem under consideration is in section 9.
The algebraic $VP$ vs. $VNP$ conjeture is due to Valiant, in this paper and his paper "Reducibility by algebraic projections" which I can't find online at the moment, unfortunately; these are references [63] and [64] in the paper I link to above.  Valiant is, as I recall, a very clear writer, so hopefully you will find these papers readable as well.
Essentially, Valiant argues that some algebraic properties of the permanent and related varieties should have complexity-theoretic implications; a reasonable heuristic for this might be the many combinatorial interpretations of the permanent.  Unfortunately, as far as I know there are few implications between these algebraic versions of P vs. NP and the problem itself; there are some results assuming GRH.  See e.g. this paper by Bürgisser.
Hopefully, this is the algebraic analogue of P vs. NP you were looking for.
Comment: Hi Daniel, yes, this sounds like what I was looking for. Thanks!
Comment: No problem!  It seems like pretty cool stuff; I am, alas, not qualified to evaluate how promising these techniques are.
Answer: There's a paper by Michael Shub, On the intractability of Hilbert's Nullstellensatz and an algebraic version of $``{\rm NP}\ne{\rm P}?''$.
Answer: In Sapir, Mark V.; Birget, Jean-Camille; Rips, Eliyahu Isoperimetric and isodiametric functions of groups.  Ann. of Math. (2)  156  (2002),  no. 2, 345–466 we proved that P=NP if and only if the word problem in every group with polynomial Dehn function can be solved in polynomial time by a deterministic Turing machine. Thus to show that P=NP one "only" needs to find an algebraic description of finitely presented groups with polynomial Dehn functions (similar to Gromov's description of groups with polynomial growth functions).
Comment: Is there a statement with $RP=NP\iff\dots$?
Answer: There is also the famous algebraic characterization of NP by Fagin (Ronald Fagin,
Generalized first-order spectra and polynomial-time recognizable
sets. In Complexity of Computation. SIAM-AMS Proceedings. 7,
43--73, 1974):
The membership problem for an abstract (i.e. closed under isomorphisms)
class of finite algebraic systems is in NP if and only if
it is the class of all finite models of a second-order
formula of the following type:
$$\exists Q_1\exists Q_2\ldots \exists Q_n (\Theta)$$
where $Q_i$ is a predicate, and $\Theta$ is a first-order formula.
This also gives an algebraic characterization of P=NP.
Also the Constraint Satisfaction Problem gives another algebraic approach to P=NP. That problem is very popular in Universal Algebra now (see, for example, Barto, Libor, Kozik, Marcin,
Constraint satisfaction problems of bounded width. 2009 50th Annual IEEE Symposium on Foundations of Computer Science (FOCS 2009), 595–603, IEEE Computer Soc., Los Alamitos, CA, 2009.)

Algebraic P vs. NP


Is there a map of the particles in outer space?

Question: Since outer space is not quite a vacuum, and the distribution of various heavenly bodies is locally inhomogeneous, it seems reasonable to expect that the density and variety of particles 'contaminating' the vacuum varies with time and space.  Are there any maps or data sets which detail this variation?
Answer: Depends on at what scale you are talking about.
Our galaxy is mostly vacuum, but we have a really good idea of where the mass lies within the galaxy.

This is a multi-wavelength image of the whole sky, and the blue band in the centre is the galactic plane, and the blue hazy structures are gas and dust from the galaxy.There are several other ways to map out the mass distribution in our galaxy, like the galaxy rotation curve.
If you're talking about mass distribution on the scale of the universe, that's a much more complicated question. It's a lot tougher to see small objects really far away. So we tend to see only the really big ones, and given how large the universe is, sometimes it's hard to notice the really big ones if they aren't bright enough to be seen. (Note - Because the universe is expanding, if something is far away, it is also older. And far away things suffer from cosmological dimming, hence the brightness constraint).
But there is a map of the Cosmic Microwave Background radition (CMB radiation) that's been made

As the wikipedia article I linked to explains in more detail - The small scale variations in this map give us an idea of how mass is/was distributed in the universe. A few really high redshifted (really old) galaxy clusters have been discovered through CMB anisotropies. This happens through a process called the SZ Effect, which is a pretty cool effect.
I've probably missed out on a few other ways of estimating mass, but these are the observational ones that I know about.
Answer: This is a short answer, but there are some direct observation maps as well as simulations.  As noted, the particles are largely called "gas" although the molecular/atom separation is obviously much larger than what we see in day to day life here on earth.


Swapping the integral sign for $ \int_0^1 (\int_0^s x(u) \, du )  ds$

Question: In trying to prove the iterated formula for the Volterra operator, I get stuck with a basic integration problem.
Let $x$ be any $L_2$ function. To what extent can we simplify, and in particular, swap the integral signs in the following expression:
$$
\int_0^1 \left(\int_0^s x(u) \ du\right) \ ds
$$
A change of variable would remove the $s$ from the second integral but that doesn't really help. I would appreciate any suggestion.
Answer: The geometric way to interpret the integral, as hinted at by DonAntonio, is the most elegant way to look at it. A mechanical method hinges on the use of the Iverson bracket $[p]$, which evaluates to $1$ if the condition $p$ is true and $0$ if the condition $p$ is false.
Now, one can easily transform the double integral being considered to the Iversonian format:
$$\iint [0\leq s\leq 1][0\leq u\leq s]x(u)\;\mathrm du\mathrm ds$$
and the double integral is taken to be doubly infinite; this works out since as already mentioned, the Iverson bracket is zero if the condition within it is false, thus suitably restricting the domain.
Now, the Iverson bracket has the neat property that $[p\text{ and }q]=[p][q]$; applying this property to the double integral gives
$$\begin{align*}
\iint [0\leq s\leq 1][0\leq u\leq s]x(u)\;\mathrm du\mathrm ds&=\iint [(0\leq s\leq 1)\text{ and }(0\leq u\leq s)]x(u)\;\mathrm du\mathrm ds\\
&=\iint [0\leq u\leq s\leq 1]x(u)\;\mathrm du\mathrm ds\\
&=\iint [0\leq u\leq s\leq 1]x(u)\;\mathrm ds\mathrm du\\
&=\iint [0\leq u\leq 1][u\leq s\leq 1]x(u)\;\mathrm ds\mathrm du\\
\end{align*}$$
and we can now convert back to the more conventional notation:
$$\int_0^1 x(u)\int_u^1 \mathrm ds\mathrm du=\int_0^1 (1-u)x(u)\mathrm du$$
Answer: If you're in the $s$-$u$ plane , the innermost integral is from zero to the straight line $\,u=s\,$, so changing the order of integration leaves us almost the same:
$$\int_0^1\left(\int_0^sx(u)du\right)ds=\int_0^1x(u)du\int_u^1ds=\int_0^1x(u)(1-u)du$$


Creating User Generated Subdomains

Question: The company I work for is close to being finished with our first web app and we recently made the decision to offer hosting for our smaller customers. (We provide software to lending companies and our larger customers are required to buy redundant servers to host their application). What we are trying to work out right now is how to create user generated subdomains that will hold a new instance of the software.
So a user will be able to sign up and say that the company name is XYZ Credit once they click on the create account button a url of xyzcredit.ourcompanyname.com is created and the user is redirected to it.
The servers that we want to use are running CentOS 5.5 and Virtualmin 3.83.
Thank you for your help,
Nick
Answer: Take a look at Matt Mullenweg's suggested way of doing this: http://ma.tt/2003/10/wildcard-dns-and-sub-domains/

Creating User Generated Subdomains


Can Firefox 4 and Firefox 3.6.15 coexist on the same OSX machine?

Question: Firefox 4 is out and I'm a little bit worried about the lack of compatibility of my loved Addons on this new version.
Can I install Firefox 4 to try it without the need to upgrade the 3.6.15 version?
Answer: Yes, you can have both versions. In fact you can install the new Firefox in your home directory's Application folder (and it will be only accessible with your account). If you don't have ~/Applications folder, you can create it (and Finder will mark it with the same icon as the /Applications one). Note that you cannot use both versions simultaneously. You can also rename the Firefox.app to Firefox 4.app, and install it in /Applications - it'll work flawlesly.
ps. I prefer the first method - Install applications that I'm testing in my home Applications folder, and when I'm sure they're ok, move them/replace application in /Applications.
Answer: OS X: Install and Run Firefox 3 and Firefox 4 on the Same Computer | Mozilla Firefox | Tech-Recipes
Or just make copies of ~/Library/Preferences/org.mozilla.firefox.plist and  ~/Library/Application Support/Firefox/.
Answer: Once you install it in separate directories, you can in fact run them both simultaneously.
It just takes a little Firefox flags magic as explained here in this article.


What are my accommodation options when traveling with toddlers through Morocco?

Question: We are going to Morocco with our kids. We intent to rent a car and independently travel a bit through the country. From reading through online resources, I have learned that a Riad is a must-do, but what are our other options if we plan to travel between Marrakech, Agadir and Essaouira? Are, given the colonial history with France, Gites and Chambre d'hotes (Bed & Breakfasts) as common as in France?
Answer: Skip Agadir, unless you are extremely exited about tourist traps.
Marrakech is very nice, as is Essaouira, although the two are not comparable; Marrakech is a proper city with an old historic city centre, cluster with souks (=markets); Essaouira is a laid back town at the coast, it also has an historic centre, but is much smaller.
Accommodation is generally easy to find. There usually are plenty of places to sleep and/or eat, although it can get pretty busy in the high-season.
As far as I know, a 'Riad' is what we would call 'inn' or 'guesthouse' i.e. a place for travellers to sleep. I know some nice and luxurious places call themselves a Riad, but I've also stayed at some very-low-budget (€ 3,- per peson/night) accomodations that where called a Riad; those accommodations where not aimed at tourists but at moroccans.
The other options you have greatly depend on the amount of time you plan to spend in the country as well as what you like to do; visit cities, explore caves, climb mountains, visit the (edge of the) Sahara, go see the 7th largest mosque on earth, go surfing in Dakhla or relax on the beach in Rabbat.
Answer: Riads are traditional Moroccan houses, not more than a couple of storeys tall and built of bricks / mud bricks. Due to the architecture, it's like staying in an olden-day house when people used to have multiple families living in one house. This experience is definitely suggested. Most riads except for the really cheap ones are quite comfortable, have 'Western-style' flush toilets et al. So in that sense, riads in Morocco are like B&Bs anywhere else. What many of them do lack is any kind of heating / air conditioning; the structure and the materials the house is built with itself is supposed to help regulate temperature.
Given the exchange rate, you may even find it quite cheap to stay in budget hotels and get a slightly more comfortable stay without breaking the bank. I would say, in Marrakech, stay in a hotel and in Essaouira, stay in a riad. Essaouira is a really small town and there's not much to see so I'm guessing you won't be stopping there for long, so  if you decide to stay in hotels elsewhere than you can at least have the experience of staying in a riad at one place.
Answer: We are currently travelling through Morocco with our kids. It is really a very good choice to go with young children. On the downside, we learned that one thing NOT to do while traveling with kids, is to stay in a Riad. How romantic and beautiful they might look, the internal square makes your stay an accoustic nightmare. Not only for you, but also for your fellow travelers.
After two nights of constantly trying anything to keep the kids quiet we came across a brilliant kasbah, close to the Ouzoud falls, who had berber tents. From there on we just asked the owner for recommendations on similar settings around our next destinations. Works like a charme. Both the kids and the parents are enjoying the vacation to the fullest
Answer: Riads will be quite expensive if you are traveling with kids.  Nice ones can easily be 80-100 euros and that normally only gets you one bed so you would probably need two rooms.  They also tend to have a very small number of rooms so your two rooms may not be next to each other or even on the same floor.  Given that, every riad is different so you may certainly find one that has a suite-style room that could accommodate your whole family.  Booking riads is quite an endeavor since there are dozens of them and each is very small, so I suggest you don't get your heart set on a particular one since they are often booked up when you try to reserve.
The other option besides a riad is a standard western hotel.  These will be outside of the old towns in the new city, so less character and you will need to take a (cheap) taxi to get anywhere.  Often there will be a Hotel Ibis right next to the train station.  These are reasonably priced but don't include breakfast and the rooms are small and charmless.
(Personally, even as a young couple, we got a bit sick of riads and ended up staying a few nights in a hotel to get a comfortable bed and a decent bathroom with a good shower.)