Why is information in a volume proportional to it's surface area?

Question: I read the wiki article on the holographic principle, but it never answered this question. Can anyone explain the math that leads to this conclusion?
Answer: Explaining the math behind the holographic principle would be lengthy exercise. Is that really what you want?
A short hand-waving argument would be that you can pack a limited number of qbits (in the form of photons) together in a given space. If you take long wavelength photons, you can pack a lot of them together before a black hole forms. Two fundamental principles limit the number of photons you can put in a sphere of radius $R$:
1) you can't make their wavelength too long as this would prevent you from localizing the photons within the sphere, and
2) if you make their wavelengths too short, the energy content within the sphere becomes too high and a black hole forms that would have a radius larger than $R$.
The bottom line is that you can pack no more than a number of photons proportional to $R^2$ into the sphere of radius $R$, provided these have wavelengths comparable to $R$.
If you would select massive qbits (rather than massless photons) things get worse.
Comment: You presumed correct, I wanted the handwavy math. The answer satisfies my curiosity sufficiently.
Comment: Also, for a black hole, the average density of the volume enclosed by the event horizon goes down as the size increases. This is why R^2 for information density vs R^3 for volume. Can even be applied to universal scales. If you can get an estimate of the mass of the real universe, including outside of our observable universe, convert this to energy, then you know how big the real universe was at the time of the Big Bang. Before that, I guess whatever was there exceeded this limit, but then it didn't exist, or it was under a different set of physical laws, or some other loophole...
Answer: Start from the De Donder balance law for the entropy
$$\mathrm{d} S = \mathrm{d}_\mathrm{i} S + \mathrm{d}_\mathrm{e} S$$
where the first term in the sum is due to production within the volume and the second due to flows crossing the surface that encloses that volume. The holographic principle (as string theory and BH thermodynamics) only deals with the special case when the production term is zero [*]
$$\mathrm{d} S = \mathrm{d}_\mathrm{e} S$$
By definition the flow term is
$$\mathrm{d}_\mathrm{e} S \equiv -\int J_S \mathrm{d} A \mathrm{d} t$$
where $J_S$ is the amount of entropy transferred per unit time and unit area [**].
If we further approximate $J_S$ by its average, using the decomposition $J_S = \langle J_S \rangle + \delta J_S$, and integrating, we obtain the traditional proportionality between entropy $S$ and area $A$ reported in the link that you give
$$S = \kappa A$$
with superficial constant $\kappa \equiv - \int \langle J_S \rangle \mathrm{d} t$
Although the "holographic principle" can be considered a true principle in a string theory sense, it can shown to be a theorem derived under the special conditions stated here (and other more technical that I have omitted).
[*] In rigor they can deal with situations where is nonzero, but then only can compute the difference $\mathrm{d}S - \mathrm{d}_\mathrm{i} S$.
[**] This is considered an "areic flow" in the last terminology, but less modern terminology names it "flux density" and older terminology names it "flux".
Comment: The entropy that you calculate is the amount of entropy that can enter the sphere in a given amount of time. You find that this is proportional to the area. However, if you finish the integration and actually integrate from T=0 to T=infinity, the quantity of entropy that will be in the sphere will be infinity. Hence you have not succeeded in proving that the maximum amount of entropy in the sphere is proportional to the Area of the sphere. Thoughts?
Comment: @AlexandreH.Tremblay. No, because for an infinite time span,  goes to zero to warrant a finite ĸappa and a finite transfer of entropy.


Maintainance of shock absorber

Question: I have a 125cc bike. My cousin uses my bike more than me. He is more than 110 kg in weight. So I feel that my bike's shock absorbers will be break down soon because of my cousin. So is there any simple and cheap way to maintain the shock absorber?
Answer: As long as your cousin isn't using the bike for jumps and stunts, and is just riding it on roads this shouldn't pose a problem. As @Bob pointed out in the comment below - the spring is what takes the weight. The damper is what slows down the movement of the spring, preventing bouncing.
If the shock bottoms out under his weight, then it may damage the mounting points or the shock itself, but under normal usage the piston is capable of moving it's full range without damage.
Comment: The important point that the OP might not understand is that the weight is carried more by the spring than by the shock.
Answer: Dirt is a killer of shocks.  Dirt on the cylinder ends up scoring the cylinders and getting into the seals, causing the effectiveness of the seal to drop.  Then you get leaking and eventual failure.  Keep the moving portions as clean as possible.  On our airplanes (which don't have any dust boots), we clean the struts with hydraulic fluid and a cotton cloth periodically.

Maintainance of shock absorber


How did the activities of protocells become inheritable?

Question: I have learned that first a protocell came to exist and its characteristics came to be passed on by genetic material. So how come genes for all the activities come to incorporate into genetic material? Did genetic material come first and random sequences made random proteins that were used to make cells ?
Comment: another side of the argument, which Richard Dawkins made is that replicators are necessary for selection.  Sure other metabolizing and energy utilizing systems might have shown up, but those which replicate are the only ones you will see over time.
Comment: I dont want to debate what came first. I want to know how RNA or DNA or whatever genetic material came first began to be " genetic material " . How did it "know" that this particular polypeptide ( for example ) will be coded by this particular sequence ?
Comment: The reason I mentioned the 'replicator' is that it posits that while the primordial chemical soup probably contained many millions of kinds of molecules, the nucleotide bases which were capable of reproducing themselves would win out very quickly.  it sounds a little circular, but that is how it 'knew' if you make 100s of billions of millions of RNA molecules, only those who replicate will quickly be the only ones you see.  we don't know much more detail than that.  the people looking at RNAworld research are trying to get a handle on that.
Answer: The sequence is believed to be opposite of that implied by the phrasing of the question: the inheritance of structures supporting inheritance came before protocells.  The important point is that you need a system of reproduction before building more complicated structures (such as a cell).  Without replication (reproduction), a cell would be little more than a soap bubble, and would disappear without a trace before long.
The initial (or very early) form of replication is thought to be based on a simple form of RNA. The reason for this is that (1) RNA does encode genetic information in a way that is replicatable, and (2) RNA can take on shapes and chemical structures that act as an enzyme (called a ribozyme) that catalyze chemical reactions.  The hypothesis is that an RNA molecule formed that catalyzed assembly of copies of RNA chains, including itself.
After such replication was established, probably some kind of enclosure like the cell membrane evolved to contain the chemicals, making the reactions more efficient.  After (or maybe before) this, RNA catalyzing assembly of simple protein-like molecules whose sequence was encoded by RNA sequences evolved, leading to protein-based cellular machinery.  This mechanism is still evident in life today in that protein assembly uses a ribozyme-based molecule assembly (the ribosome) to translate messenger-RNA into proteins.
Answer: Well.. This is a tough question (Something that has bugged me for years and still doing so). I don't fully agree that replicative potential came first. This is just my opinion based on some reasoning and I dont really have any reference.
If you compare a nucleotide and a protein, the likelihood of formation of protein is much higher because:-

Amino acids are simpler molecules and simplest of them did appear in the famous Urey-Miller experiment. Nucleotides on the other hand are much more complex
Peptide/amide bond formation is a well known phenomenon even in non-biological chemistries whereas Phosporic esters cant be called common compounds.

In my opinion function evolved first and then its codification. Initially the cell division must have been just like a huge drop dividing into two. I would like to differ from mgkrebbs on this. Lipids are simple molecules and they can spontaneously form compartments such as miscelles based on simple principles of thermodynamics. If miscelles get huge they can divide.
I still cannot understand whether it is chemical reproduction that came fist or sustained multispecies chemical reactions. I tend to believe the second with relatively more confidence.
The popular RNA world hypothesis is justified by certain observations and fits nicely in the Darwinian scheme of biology that we are so used to believe in all the time. But it doesn't answer the previously mentioned thermodynamic perspective. Also I fail to understand why an ancient RNA would code a protein. What advantage would it have to code a protein in the first place. So to conclude I don't have a doubt that proteins came first. The initial soup and the basic functionalities were provided by them. Then nucleotides evolved parallely and they became catalysts of protein synthesis. So the reactants came before the catalysts and the better catalyst got selected.
I again iterate that this is just my opinion which you may consider pondering over along with the answers that others have provided.
Answer: The general theory is RNA came first, then DNA. Both are able to replicate with simple changes in temperature (see polymerase chain reaction). So if we imagine a world with nucleotides making RNA, the idea is the survival of the fittest RNA. RNA for example that also had enzymatic activity was "fitter" than RNA that did not. Then go further down the line where RNA that made a certain protein was more "fitter" as thus it's concentration increased. Keep going down the line as this continues, whatever was favourable in the surrounding environment increased until we have what we have today.
Of course this is widely disputed.
Answer: AndroidPenguin and mgkrebbs both gave excellent answers to this. There are currently several ideas about the first life on Earth. Data for these methods are pretty useless because we can argue for what is the most probable and what can be modeled in the lab, but we can't (as yet) look for any fossil remains of molecules to see what really happened.
One of the most satisfying hypotheses is that protocells and self-replicating molecules (like RNA) probably came about independently, but in the same location. If the self-replicating molecule found a way to hide out in the protocell, this might be the beginning of something like what we call life.
A good talk on this topic is Martin Hanczyc's TED talk.
Comment: Can you give some references to support what you are saying?


How can I build a functional gearbox?

Question: I'm looking for a fully functional (manual) transmission / gearbox for my Technics motorized vehicle. How can I build this?
Answer: there are some lego-models that have a working gearbox built-in like the super street sensation (8448). just take a loot at the building instruction* to see how it works.
*page 18, 26, 72-81
Answer: Funny that you are asking because I just rebuilt my old 4x4 OffRoader (8466) with my son. it's a 4 wheels drive, V8 with a functional 5 speed gearbox (including reverse).

and in the truck (with the gearbox cover):

Looking at it in action is really good to understand the basics of a car's transmission.
Answer: I made a compact 6-speed, which you can find CAD and .pdf instructions in this brickshelf folder. (Maybe one was reverse, I don't quite remember...)
Please bear in mind that it wasn't intended to be motorized and might not perform well under load. However it should give you an understanding on how it can be done.
If you do not have those special gearbox transmission parts, you can do it by sliding a cross-axle with gears on, in one position it will be connected to one gear, in another position it will be connected to another gear. See this design by Sariel for clarification.

How can I build a functional gearbox?


Facebook "Like Button" Typeface Options

Question: When you ask Facebook for code to put a "Like" button on your website, you are given a choice of these typefaces: arial, lucida grande, segoe ui, tahoma, trebuchet ms, and verdana. Given that they are all pretty similar, what are some considerations in choosing among them? Recommendations?
Comment: Can you only specify one, or can you specify a sequence, as per CSS font-family rules?
Answer: I assume you're using this script to generate the "Like" button.  It appears that the default, if you don't select any font, is to try Lucida Grande, Tahoma, Verdana and Arial in that order, and to fall back to the browser's default sans-serif font if none of those are available.  If you do select a specific font in the form, it uses either that particular font or the browser default sans-serif font.
Given that, if you're not using any of the listed fonts on your page already, and don't have any strong preferences between them, I'd just go with the default (i.e. don't select any font in the form).  It's likely to look OK to most users, and match what they're used to seeing on other sites.
Answer: Just so you guys know, it seems that Windows only likes Trebuchet MS as the specified font when you select the XFBML version of the Facebook Like button box_count layout that displays the Send button underneath the main Like button. Use any other font selection than Trebuchet MS and the word "Send" gets cut off on the right side on Windows. Mac is fine either way. You can see this in action by going to the main Facebook Developers Like button page and specifying XFBML, checking the Send box, and selecting box_count layout.

Facebook "Like Button" Typeface Options


Amounts of various oils in hops.

Question: I have a beautiful chart that shows the level of various hop oils in different hops, as well as their typical alpha acid percentages.  Where can I find the raw data that would go into a chart like this?  I am interested in making an interactive version of that chart.  Also, there is at least one hop oil not measured in that chart. (cohumulone)
Answer: I've been trying to compile a sourced- and rolled-up list of hops for a project (brew-journal.com).  Data is very commercially driven, and hard to come by.   Feel free to use (look for the green-annotated "COMBINED" rows) and please let me know if you find another/appropriate source to be included.
Answer: Pick up a copy of Designing Great Beers. For an advanced homebrewer book, it gets real deep into 4 or so different types of oils, how isomerization in the boil works, etc.
The book is 2 halves... background science and research, plus a study of AHA competition winning beers. The AHA competition part is a little dated, but the other half of the book... great beer geek science.
You could also write to FreshHops... they have access to a lot of information.

Amounts of various oils in hops.


Minimal right ideals in finite semigroup

Question: Let $E$ be a finite semigroup. According to N. Bourbaki (Algèbre I p. 121 exerc. 14 c), if $M$ and $M'$ are minimal right ideals in $E$, then they are isomorphic. I spent some time browsing through Clifford and Preston's monography "the algebraic theory of semigroups", also reading a few articles by Rees, Clifford and Dubreil, and found absolutely no mention of this fact anywhere. Maybe I haven't looked hard enough. If there is any semigroup specialist, could you tell me what you think?
Answer: This is in Clifford-Preston. First every minimal left (right) ideal is inside the minimal two-sided ideal $I$ (which is unique), see Exercise 13 on page 84. Second, the ideal $I$ is a simple semigroup (obvious, but is also in C-P). Third, by Sushkevich's theorem (Appendix A), all maximal subgroups of $I$ are isomorphic. By Theorem 1.27, every minimal left ideal $L$ in $I$ is a left group, i.e. the direct product of the maximal subgroup and a left zero semigroup (whose order does not depend of $L$). Hence all minimal left ideals are isomorphic.
Answer: I will use Green's relations, definitions are here if you don't know them : http://en.wikipedia.org/wiki/Green's_relations.
If you represent the smallest D-class $C_\min$ by a box as in the wikipedia article, then the right (resp. left) minimal ideals are exactly the rows (resp. columns) of $C_\min$, i.e. its R- and L-classes.
This can be seen by the fact that every right ideal must contain a R-class of $C_\min$ (otherwise it would not be an ideal), and that it must also be included in a single R-class of $C_\min$ to be minimal.
Then it suffices to see that for all $e\in E$, if $R$ is a R-class of $C_\min$ , then so is $eR$, and $x\mapsto ex$ is an isomorphism between $R$ and $eR$.
Comment: Thanks for your answer. Why should $x \mapsto ex$ be an isomorphism? This map is obviously one-one and onto but why do we have $exy=exey$ if $x,y \in R$?
Comment: @Pnine You asked this almost a decade ago, but for anyone wondering: the fact that it is an isomorphism is Green's Lemma.


How to extract audio files from Diablo 3 installation?

Question: I love Diablo 3 music (who doesn't) and I would like to extract the audio tracks from my installed files and listening to with an external music player, for my pleasure. Is it possible in some way?
Answer: You can use MPQ Explorer.
This lets you open Blizzard's MPQ file format, which is where they store all their game assets including music.  The application has the ability to extract sound files from the MPQ files.
http://www.ehow.com/how_4705307_extract-music-world-warcraft.html provides an example on how to do it on World of Warcraft.  The only issue is that I don't think anyone has bothered finding which MPQ contains Diablo III's music yet, but there is only a limited number of options.
Comment: Thank you I found them. They are located in file Sound.mpq inside some subfolders name with pattern Music__ in SounbBank folder.
Answer: Unfortunately, most files are in some unknown format, so you won't be able to read them. A few are in vorbis, format, including the musics.


How to put a class on body tag in page.aspx created from master page

Question: I have 10 pages and each body tag has its own class because of different background images on them.  I was wondering how to do it in the master master page so that the class on the body tag when a new page is created is correct.
Answer: If I'm understanding your question correctly, you have 10 different types of pages in which the content area or body have specific classes depending on that content.  A master page isn't going to get you the desired results.  You'll want to have varying page layouts for that.  Each page layout can have it's content area defined with your appropriate class so that you get the desired effect.
Comment: exactly sir the classes will be different layouts in every page
Answer: It sounds as though what you are trying to do is generate unique content on each page but do it through the master page.
This is the wrong approach. Use your master page for elements of your branding that are consistent across all your pages. Of course because of the position of the body tag in your page element hierarchy you can't have that defined in the page.aspx, so you will need to define your background image some other way. This is a question for a CSS expert, but I would suggest, in your master page, using a single class for your body element (if you need one at all), and associating the particular image with that class in the page.aspx file. This could be something like a STYLE element or a link to a particular small CSS stylesheet.
Answer: I suggest using the same class, but override it in the specific pages, i.e. give the body tag a classname, then in the pages themselves override say the background-image property of this class. Since CSS is cascading the last read value will be used.
Answer: use jquery:
<code>var url = location.search;
if (url.indexOf('/page-1.aspx')>= 0) {
$('body').addClass('class1');
}
</code>
http://api.jquery.com/addClass/


Conditional Probability

Question: Suppose $P(A) = 0.6$ and $P(B) = 0.7$. Find the smallest possible value of $P(A \cap B)$. Instead of deducing this from $P(A \cup B) = P(A)+P(B)-P(A \cap B)$, could we just use the fact that $P(A|B)P(B) = P(A \cap B)$ and $P(B|A)P(A) = P(A \cap B)$? I notice that $(0.6)(0.7)^2 = 0.294$ which is close to $0.3$, the smallest value of $P(A \cap B)$.
Answer: From the equation in the second line
$$P(A \cup B) = P(A) + P(B) - P(A \cap B)$$
we have
$$P(A \cap B) = P(A) + P(B) - P(A \cup B)$$
In order to minimize $P(A \cap B)$, we should maximize $P(A \cup B)$ since both $P(A)$ and $P(B)$ are fixed. The maximum value for $P(A \cup B)$ is $1$, so we have the minimum value of $P(A \cap B)$ as
$$P(A \cap B) = 0.6 + 0.7 - 1 = 0.3$$

Conditional Probability


What book review sites allow authors to send a copy of their books for reviews?

Question: Since I'm published with smaller publications, getting reviews is often one of the best ways to make sales. But what professional book review sites out there will write a review in exchange for a copy of the book? I don't want ones that'll give you a good review just because you gave them the book, but ones that give honest reviews.
Comment: Related: [How can I get book my **non-fiction** book reviewed by professional reviewers?](http://writers.stackexchange.com/q/5926/26).
Comment: Please note that this question has been retained for historical reasons, and shouldn't be considered a typical example of a constructive question for this site.
Answer: You might not get the publicity you're looking for from these kinds of sites. Many don't have focus or the eyeballs that make giving away your product a good financial decision. Genre sites for genre books, are a good exception to that though.
This article spells it out better and has some advice on getting some real reviews in real publications.
Answer: LibraryThing is a good source for this. They have regular book giveaways where authors can specifically request a review in exchange of the book itself. This will work with a print copy or an e-book. With Goodreads, they only do giveaways with print copies. I have used LibraryThing with both of my fantasy novels and gotten some reviews as a result.
The consensus seems to be that you can usually expect 1 review for every ten copies you give away (at least with e-books). The ratio may be better with print books, but you are taking a bit more of a risk because you have to pay for shipping (plus the cost of the actual book).
With either type of giveaway they (LibraryThing) will give you the e-mail addresses and mailing addresses of the people that ultimately get selected to receive your book. Just make sure you follow up with the recipients with a polite thank-you/reminder for taking the time to read and review your book. If they haven't gotten around to it yet, it may help to encourage them to do so.
BTW - With my first book, I gave away 100 e-books and received 15 reviews at LibraryThing, 11 at Smashwords, 8 at Goodreads, and 6 at Amazon. With my second book I gave away 75 e-books and got 12 reviews at LibraryThing, 9 at Smashwords, 8 at Goodreads, and 6 at Amazon.
Comment: How much do you think the reviews you got helped sales?
Comment: Great question, but my goal wasn't to generate sales. I'm not doing much to promote either of these books right now, mainly because I've been concentrating on promoting a series of books published under a pen name. My main goal was to get the reviews out there in advance so that when I do start promoting I will have some reader feedback available for potential buyers. On my first book, however, I saw a very consistent complaint about the opening, so I am in the process of rewriting it based on that feedback.
Answer: Goodreads.com does that -- even better, you can get attention from as many individuals as you give out copies.
Comment: Goodreads is mostly user reviews, I'm thinking more "professional" reviews like http://www.reviewsbyjessewave.com/ or http://blbooks.blogspot.com/
Comment: Ahh, that I'm not sure about.
Comment: @RalphGallagher - I edited your question to clarify this, I hope it helps.
Answer: I'm not an official journalist or professional reviewer, but I give great feedback and honest reviews. I've recently found out that I can receive a free book in exchange for a review. While I am an average person (new mom, non-celebrity), my professional background and large social network make me a great candidate for something like this.
I am a business owner/ marketing professional with previous published articles. I enjoy promoting products through event marketing as well. One of the many services my company provides is web design and SEO, so when I post something on my website (like say a review in my blog), people in that audience will see it. I'm all over Google.
If anyone is interested in me reviewing your book, please send me additional information. (Certain genres don't interest me so that wouldn't be fair to you if you fell under that category.)
Answer: I used a company called Piece of Cake PR. They wrote a press release for me and distributed it to quite a few thousand journalists.
I then had lots of media outlets coming ot me asking for either a book in the mail or an eBook via email. Got me some great reviews that I put on my site, etc.
Think the service cost me around $180. Well spent IMHO.
Comment: This is a press release/PR company, and *not* a company that writes impartial book reviews, which is what was requested here. The question also asks for organizations that will review in return for a copy of the book.


subadditive implies concave

Question: Let $f:R_+\to R_+$ be smooth on $(0,\infty)$, increasing, $f(0)=0$ and
$\lim_{x\to\infty}=\infty$. Assume also that $f$ is subadditive:
$f(x+y)\le f(x)+f(y)$ for all $x,y\ge 0$. Must $f$ be concave? The converse is obvious.
Answer: For not smooth surely not, take $f(x)=2x+|\sin x|$. I am nearly sure that for smooth answer is the same. For example, it looks like function $|\sin x|$ may be changed near points $\pi k$ so that it becomes smooth but still semiadditive.
well, more concrete construction is like follows (some details are however omited)
construct a function $f$ such that $f(x)=|\sin x|$ unless $|x-k\pi|<1/100$ for some positive integer $k$, $\sin 1/100\geq f(x) > \sin 1/100-1/1000000$ for $|x-k\pi| < 1/100$, $f$ is convex on $[k\pi-1.100,k\pi+1/100]$. When may $f(x+y) \le f(x)+f(y)$ fail? If $f(x+y)=|\sin(x+y)|$ then $f(x+y)\le |\sin x|+|\sin y|\le f(x)+f(y)$. If $f(x+y)\ne |\sin (x+y)|$, then $f(x+y)\le \sin(1/100)$, so if $f(x)+f(y) < f(x+y)$, then also $f(x) < \sin(1/100)$ and $f(y) < \sin(1/100)$. If both $x$ and $y$ are greater then $1/100$, then $f(x)+f(y) > 2(\sin(1/100)-1/1000000) > 1/100 > f(x+y)$.
Now without loss of generality $k\pi < y< x+y< k\pi+1/100$. Then $f(x+y)-f(y)=xf'(\theta)$ for some $\theta\in [y,x+y]$, by convexity $f'(\theta)\le \cos 1/100$. So, it suffices to prove that $x\cos(1/100)\le \sin x$, i.e. $\sin x/x\geq \cos 1/100$. Since $\sin t/t$ decreases on $[0,1/100]$, we have $\sin x/x\geq 100\sin 1/100\geq \cos 1/100$ as $\tan t > t$ for $t=1/100$
Comment: I'm not so sure about that intuition because x = k pi are where the subadditivity inequality is barely satisfied.
Answer: That the answer is "no" is also apparent (at least for the $C^0$ case) if you refer to the graphical interpretation of concavity and subadditivity of the function $f$ in terms of the sub-graph of $f$, here denoted S(f). "Concavity" is, of course: S(f) is convex; "subadditivity" is: a translation of S(f) that brings the origin to any point of graph(f), covers entirely graph(f) from that point on. Any increasing function with a suitable zig-zag shaped graph enjoys this property, while is not concave.
Answer: Let me try again (I deleted an earlier wrong post). First of all, a sufficient condition for subadditivity on $x>0$ is: $f(x)/x$ nonincreasing. This is easier to work with since it is a local condition. The proof is elementary (take $x\ge y>0$, then $f(x+y)\le f(x)(x+y)/x=f(x)+yf(x)/x\le f(x)+f(y)$). For smooth $f$ this is equivalent to $f'\le f/x$.
Thus it is sufficient to look for a non concave function $f(x)$ which is smooth on $(0,\infty)$, has right limit zero at zero, and satisfies on $x>0$ the inequalities
$$ 0\le f'(x) \le \frac f x.$$
Now, take $f=x^a$ with $ 0 < a < 1 $; we may start with any example, but just to fix the ideas. This is a concave function satisfying all the requirements of the problem.
Notice that actually there exists $d>0$ such that
$$ d\le f'(x) \le f'(x)+d \le \frac f x \text{   on   } (0,1].$$
Any function satisfying this condition is a good starting point.
We shall modify $f$ on a compact subset of $(0,1)$ so to make it non concave near a point.
Let us take a smooth non negative cutoff $g \in C^2_c(0,1)$ such that $|g'|\le 1$ and define $f_t=f+tg$, for $t$ a small positive constant. We have $f'_t=f'+tg'$, so if we restrict $t$ to $ 0 < t < d $ we have
$$ 0 \le f_t'\le \frac {f_t} x $$
everywhere. It is clear that $f_t$ for all $ 0 < t < d $ satisfies all the requirements of the problem. Can we choose $g$ so to make $f_t''(1/2)>0$? We have
$$ f''_t(x_0)=f''(x_0)+t g''(x_0) $$
so in conclusion we are looking for a smooth function supported in a compact subset of $(0,1)$, non negative, such that
$$ |g'|\le1 \text{ and } g''(1/2)\ge N $$
for a fixed $N$ arbitrarily large. This obviously exists, e.g. take a piecewise linear function and approximate it with test functions.
Answer: Subadditivity + $f(0)=0$ do not imply concavity, neither for regular functions.
Counterexamples are in Bruckner "Some relationships between locally superadditive functions and convex functions", Proc. Amer. Math. Soc., 15, 1964, 61-65, and in Bruckner-Ostrow "Some function classes related to the class of convex functions", Pacific J. Math. 12, 1962, 1203--1215.
Answer: Here is a sketch of how you could do this.
Start with a concave function f (ADDED: also, f satisfies all the conditions stated in the question). Consider now the interval $(1,1.1)$. We will try to modify f by increasing its value on this interval while preserving the values at the endpoints. Let's set aside smoothness for now.
What properties should the modified f have? Subadditivity is threateneded only in cases where the $x + y$ happens to land inside $(1,1.1)$. Because of the concavity up to 1, we can see that it suffices to ensure that the new variant $f_1$ of f satisfy:
$$f_1(1 + \epsilon) \le f(1) + f(\epsilon)$$
Basically, we can move the subadditivity condition to the boundary because of the known concavity property of f.
Thus, $f_1$ can be chosen arbitrarily subject to taking the correct boundary values and to being bounded from above by the expression indicated. Assuming strict concavity, there is some free space between the actual current function $f$ and the upper bound for $f_1$ given by the equation. We can therefore choose a $f_1$ that works. Maintaining the condition of being increasing is not problematic -- even if it were, we could just add a huge coefficient linear function to $f_1$ and make it increasing. Smoothness is the relatively harder part, but it could be fixed using bump functions.
EDIT: There's another constraint, that again is achievable: subadditivity when both $x$ and $x + y$ are in the interval $(1,1.1)$.
I also think that functions such as $2x + \sqrt{x}e^{-(x-1)^2}$ or variants thereof may work directly, but I don't know of any easy analytical proof of it.
Answer: How about this one... $f'(x) = ((x-5)/(x+1))^2$.  So (according to Maple)
$$
f(x) =
-\frac{-37x - x^{2} + 12 \ln (x + 1) + 12 \ln (x + 1) x}{x + 1}
$$
Now $f$ is not concave, since $f'$ is increasing above $5$.
EDIT Next attempt ...
$$
g(x) =
\frac{x \bigl(53140 x^{3} + 212550 x^{2} + 314500 x + 240625 + x^{4}\bigr)}{(x + 1)^{4}}
$$
so that
$$
g'(x) =
\frac{(x + 25) \bigl(x^{2} - 10 x + 385\bigr) (x - 5)^{2}}{(x + 1)^{5}}
$$
and
$$
g''(x) =
\frac{-25920(x - 5) (x - 10)}{(x + 1)^{6}}
$$
Comment: why is this f subadditive?
Comment: Nice.  Another way to write f(x) is

x - 12 (log(1 + x) + 3/(1 + x) - 3)

which makes it more apparent to me that f is subadditive.
Comment: Except actually it's not: 922.658 = 2 * f(500) < f(1000) = 953.059

subadditive implies concave


Why are colors brighter and more red on Sony HX100v?

Question: I have purchased a Sony HX100v. Can any one give me a review about its photography results? Till I am not more explore it. One thing I noticed about it was the color. Colors are brighter than actual object and the camera added more red tone. Why does this happen? Any ideas?
Comment: Each brand has his "style". Even if everithing is the same pictures taken with two different cameras look different. I think that Sony focus more on pretty looking colors than on "realistic" colors.
Answer: This is a question where a sample image would help us determine the causes of your results. For results others are getting with the same model, a Flickr search should give plenty of samples.
Without seeing any of your images, the usual suspects are

wrong white balance
saturation setting too high
the monitor used to assess the results needs calibration
Comment: Also, isn't red one of those colours that confuses metering sensors? I can't recall specific details but remember a bit of a fuss being made when the Canon 7D came out about its new iFCL metering, which handled reds better...
Answer: Camera sensors are linear capture devices, which does not match well to the human perception of light and color. So, after the raw image is taken, it is usually converted to something with more "pop" to the color. Since more pop equals more exciting first impression, most consumer camera models default to cranking these parameters right up to 11.
More advanced models will give a lot of control over this — either as direct control over curves, or as "film emulation", or sometimes as both. On your camera, this is known as Color mode, and there's a section on it in the manual. It looks like you have options of Standard, Vivid, Real, or Sepia or B&W.
If your camera is in Vivid mode, that's almost certainly what's going on. But even Standard may be too extreme for your taste, just as the default color options on most TVs are ghastly and toy-like: these settings sell product to consumers who care more about AWESOME than looking right — let alone good.
As I alluded to above, all of these conversions are happening after the raw capture from the sensor. Unfortunately, with your camera, you can't access this RAW data directly, as only JPEG output is supported, so you're stuck with the in-camera conversion options. If you had a camera which can save in a RAW format, you could use the different curve options of your RAW conversion software to get different results which may be more to your liking.
Answer: Please check which color profile your camera is set to.
I suspect it be set to 'AdobeRGB' - which may well have the effect you're seeing. To get expected results using anything else than sRGB you need to set up a properly color-managed workflow.


What DBMS' have tight integration with a dedicated OS'?

Question: It has always been my strong conviction that a large-scale multi-user DBMS should reside, stand-alone, on a dedicated server or clusters, with no other unecessary apps, processes or services which could steal resources from the DBMS. I also believe that the DBMS should be tightly integrated to an OS which has been tailored to provide the DBMS with the maximum performance possible! Proprietary systems such as Pick, Terradata and others were designed with this goal. Would the latest Sun/Oracle system fall into this category?.. Would it make sense to accomplish this kind of architecture with other DBMS' like INFORMIX?
Comment: Tight integration with the OS does not necessarily imply better performance.
Answer: If you have the odd quarter of a million USD to spend you can consider buying a slice of an Oracle Exadata machine.  This is a highly configured database appliance with highly-specified hardware chosen and Solaris tweaked until it squeaks to optimize Oracle's  performance.
Comment: You could scale to hundreds of database servers for the same million. That's a massive scaling out move. If that big box gets destroyed in an explosion, well, quite frankly, you're totally forked (@ThePlanet datacenter explosion).
Comment: @APC- That's not alot of money for an enterprise to invest in a large-scale multi-user DBMS!
Comment: Last time I checked the Oracle Spatial component was a $1 million license...
Comment: @APC- Exadata, Massive Parallel Grid.. impressive!
Comment: @FrankComputer - the list price for a quarter rack Exadata is USD300K plus some extra for storage, but that doesn't include the database licenses.  As @OMGPonies notes, buying those is a big chunk o' change.
Comment: @APC- Still justifiable for large-scale OLAP/OLTP where performance and scalabilty is a requirement. Decades ago, enterprises would spend millions for mainframes!
Answer: The integration between Oracle and Solaris is tighter than most.  I can't confirm that it meets your list of requirements, though.
Answer: In general, there are certain attributes of the ACID RDBMS that combine to yield polynomial-time performance characteristics when you put two or more computers together to serve one database.
There are a number of attempts to solve this problem:

Optimize the database as much as possible by reducing transactionality, reducing joins, etc.
Optimize one computer as much as possible to serve the database - such as optimizing the supporting operating system, optimizing the disks, etc.
Scaling vertically by serving the database with a single extraordinarily powerful computer.
Distributing the RDBMS by sharding or by putting different tables in different databases.
Using a truly distributed database, that drops some of the attributes of an ACID RDBMS, but offers true distribution and its attendant performance. E.g., Cassandra and others. And truly distributed databases can be run on commodity hardware because the performance of a distributed database is based principally on how many nodes there are, rather than on the performance of any given node.

There are hard limits to the first four methods. There are no limits to the fifth.
As database needs expand many times more rapidly than tweaks and hardware can keep up with, the inevitable solution will be a distributed database. Sure, many people will try to tweak their database servers, and then will be forced to upgrade to massive hardware, but that's just a stop-gap, and when that stops being sufficient, they will be forced to shift to a distributed database.
Answer: Very subjective.
Firstly, while SQL Server may be dedicated to the Windows OS on x86 hardware, neither the hardware nor software is specially designed to run a database platform. Furthermore, while SQL Server would be designed to make the best of Windows, it doesn't follow it is primarily designed for performance. In the case of SQL Server, I'd argue that, rather than optimize for performance, it has been optimized for administration and integration.
Secondly, hardware performance increases quickly over time, so what you buy as the optimum hardware this year will be past its peak in a year, and considerably dated in three years. Few buyers would be upgrading their hardware that frequently, so buying a database platform to gain an edge in hardware performance seems short-sighted.
Thirdly, if a database company is building an OS dedicated to its database, can it get the best OS people ? If not, it is a judgement call whether database software will run faster on a generic OS built by the best OS people or a dedicated OS built by the 'lower division'.
Finally, to some degree you can often improve performance by throwing more (or more expensive) hardware at the bottlenecks. For a given budget, you may get a better deal from putting the dollars to grade 'A' components in a generic build than a grade 'B' from a specialist. Generic is going to be cheaper because, the larger the customer base, the more the base costs can be spread (and the more price competition comes into play between suppliers).
PS. Obviously performance isn't the only criteria for purchase. Uptime, skills availability etc all come into play. As does the financial security of the supplier / line of business. I worked at a place that had decided, in the early 90s, Mac's were the best desktop machine. They were stuck with a bunch of machines with no upgrade path.
Answer: I'm assuming you want discussion rather than answers... but my answer is "No" anyway
In a big corporate shop, every Oracle, Sybase and SQL Server installation may use the lowest common denominator: the SAN. This may itself be transactionally replicated off site. Ask any corporate DBA.
In any shop, code quality will be a bigger factor then the server/OS. No amount of optimization and integration will save you from poor indexing, for example.
Other points:

A terabyte DB is more of a backup/restore/SLA issue IMHO
The active set of data or daily increase is what you have to worry about, performance wise
Answer: You should check out the IBM System i platform.  It supports DB2 for i, which isn't exactly compatible with DB2 UDB but it's close enough.
The database is very tightly integrated with the OS.  I'm told that this platform grants a level of efficiency and performance beyond the wildest dreams of users of any of the "mainstream" architectures of Windows/Linux/Solaris/etc.
I don't have any experience with it personally, but a lot of users of the System i platform swear by it, and it seems to meet your desire for tight integration.
Comment: "beyond the wildest dreams of users of the mainstream architectures" - you're speaking like Linux had an overhead of 50% and i has 1% overheard.


Is there a display screen with a Thunderbolt interface that is not made by Apple?

Question: Any suggestion for a non-Apple monitor to connect to MBA (mid-2011)? The display has to reach the same resolution without flickering. Does a non-Apple Thunderbolt display exist?
Answer: It's not advertised all that well, but Apple still sells the non-Thunderbolt 27" LED Display (Apple Store US Link).
As CajunLuke points out, there are other good 27" displays out there, notably by Dell and HP, just be careful that you're getting one that isn't low resolution (1920x1080 on a 27" won't look great - the good ones are 2560x1440), and has a native Displayport input - as you may be aware, the miniDisplayport to dual-link DVI adapters have some issues.
Comment: Many thanks guys! I think I'll buy apple display because the price is so similar. So buying apple monitor I'll have thunderbolt port and usb replicator...
Answer: Most any 27" display has the same resolution as the Apple Thunderbolt Display. However, the Apple Thunderbolt display is the only Thunderbolt display currently on sale.
If you simply want at 27" display that's not made by Apple, check out Dell and HP.
Answer: Asus allegedly demoed a 27" thunderbolt display at computex, but the disappointing thing is that the review says it's only 1920 x 1080.  There is no mention of the display on Asus' website.
Answer: According to the Thunderbolt Technology Community, Apple is, as of May 14, 2012, the only manufacturer to offer a display with Thunderbolt connectivity.


What limits a mobile phone to be upgraded to new Android version?

Question: What is the main reason that you can't upgrade your phone to new Android version?
Is it the lack of drivers, or simply hardware limitation? Are there other aspects?
Comment: Related: [Why aren't the manufacturers updating the phone to the latest Android version when it's available?](http://android.stackexchange.com/questions/290/why-arent-the-manufacturers-updating-the-phone-to-the-latest-android-version-whe)
Answer: Somebody needs to write and test the drivers and core apps. That's all.
Most applications that are written for Dalvik (i.e. most apk programs) are pretty portable across different Android versions, but not so much for core programs that were written in C, the Linux kernels and drivers, and the Dalvik VM itself. At the very least, these programs need to be recompiled; occasionally, the new Android version may require new capabilities from the drivers, and someone will need to write the code for them.
Additionally, for official releases, manufacturers and carriers often adds value-added customizations; these customizations need to be ported, tested, and often debugged against the new framework. In deciding whether to write upgrades, manufacturers (and to certain extent, carriers) faces a dilemma, they make better profit by selling to you a new device instead of writing upgrades for free, but poor upgrade history will put off customers as well; so they will often drop support for older phones and only write one or two version upgrades at most.
Hardware limitation has never been a problem for upgrades. While it's certainly true that certain new features might have a much higher hardware demand than older phones can conveniently handle (e.g. Live Wallpapers), these features are usually either disabled or left to give sub-optimal experience.
Other limitation is space limitation. Some phones have very small internal memory, and Android tends to get larger for every upgrade. To port newer versions for these phones, some sacrifices has to be made; whole libraries may be left out (e.g. who needs the NFC on a G1?). These modifications needs to be written and tested.
Answer: Your device will run any version of Android, even if your carrier or manufacturer won't have a official update available you can check out XDA-Developers and get an unofficial ROM, that are a lot better in my opinion.
For an example, the HTC G1 that everyone knows that is a bit slow and out-dated, but was the first device to get an unofficial port of Android Honeycomb for it, even if it was made only for tablets the developers manage to get the screen resolution working and the other stuff that wasn't compatible.
Another example I that I have: I had a HTC Touch Pro2 that by stock runs Windows Mobile 6.1, I've installed a unofficial ROM first(called Simplicity ROM), so I was running the latest build of Windows Mobile 6.5 and within Sense 2.5, so I bought my first Android phone. And some time after the XDAndroid developer team released a Android port for my device, and now I use it too, but on Android.
My first Motorola Milestone is running a custom Android 2.3 Gingerbread ROM, even that my carrier haven't released any official ROM for it. It runs very stable and it's a lot better than the 2.1(stock default) and the 2.2(custom too). So there are no problems if you can flash custom ROMs.
Comment: "If your phone is a bit old so it will be slow running a newer version of Android" - not exactly true.  I have an HTC Hero which originally came with 1.5 (and now comes with 2.1) but since I put CM6 (which is Android 2.2) my Hero is much faster and has better battery-life.
Comment: That's because Android made some system performance improvements **:)**
Comment: Exactly - which is why what you said is not exactly true.
Comment: Ok, corrected :)
Answer: Right now Gingerbread and Honeycomb use hardware acceleration for graphics. While it could be done without, phones that lack GPUs that can do this will not see these version.
To be Google Certified devices must be able to launch core apps within a certain amount of mili-seconds.
Comment: @liori: your phone can't display time in "miniseconds"? you should ask for a refund.


Music during game or not?

Question: We tried to use background music during gaming sessions, but it turned out to be an annoyance. Do you have success stories, and which music did you use ?
Answer: Can you imagine watching your favorite movies without a soundtrack? Film directors use music to control audience expectation and trigger emotional responses. As a GM, you too can make use of these techniques at your gaming table.
The simplest plan is to put an album on to play. Slip in a CD, get your iPod out, and press play. I once ran a Sci-Fi campaign with just two soundtrack albums: The Matrix and Ghost in the Shell.
Keep the volume low and the music acts as a backdrop. During battles and other exciting moments pump up the volume and select a more upbeat track. At little more volume can wake up your players, make them fight a little to be heard, and raise their heart rates!
Take it further by using playlists, on your iPod or laptop. Playlists can be much longer than a album and less repetitive. Set up playlists for various situations, and leave them to run through on repeat. As the mood of the game changes, simply switch to another playlist.
To add sound effects such as explosions, spells, or battle sounds you could explore soundboards. Soundboards are simple online flash applications that trigger different sounds at the click of a button. A search online will turn up soundboards with effects that interest you.
For the deepest experience, there are applications available for GMs that combine music and sound effects. The best are RPG Soundmixer and Softrope, they both allow you to build complex soundscapes from small loops of sound. These combine into larger, less repetitive combinations. If you want complete control over sound effects and music at your table then both applications are worth exploring further.
What music can I play?
Find a movie or game that matches the genre of your current RPG and buy the soundtrack. You can often lift soundtracks from a computer game's install. Baldur's Gate and all of its sequels, for example, are a great source of background music.
When selecting music, try to avoid anything too distracting. Usually it is best to stick to instrumental tracks, as vocals can be very off-putting. There are exceptions, the last time I used a vocal track was to add atmosphere to a seedy retro jazz bar on a backwater space station.
It is well worth choosing a theme tune for your campaign, it helps focus the player's attention. Play your theme tune after the players have had their weekly catch up and it unconsciously signals that it is time to start. Signature themes also work well for your reoccurring villains.
One final tip: Keep your finger near the volume control. Volume is a key tool for reacting to your table. Read the table carefully and lower the volume when you can see it is detracting from the experience, then raise it again as the players are reacting positively and having fun!
Comment: +1 for quiet ambiance, minimize lyrics. The GM of a dark sci-fi campaign that I played in used Philip Glass CDs, if I remember correctly, to good effect. Not sure about the soundboard/sound effects, be careful with those. They can easily become too intrusive, but could work if mixed well into the background or used for some important (infrequent) special event. Final Fantasy victory music after a battle is popular with my group, to celebrate and lighten the mood a litte. =)
Comment: great answer (I would've written something like this myself :D), it touches upon everything I think important. I just have one point to add: besides game and movie OSTs (original soundtracks), "lyricless" instrumental pieces in the categories of ambient, dark ambient, noise and the like can also be great mood enhancers - and there's tons of these freely and legally available online by lesser known bands and composers. for examples, try browsing and exploring http://bandcamp.com/tag/ambient (or, if you're into cthulhu gaming, go straight for http://cthulhumusic.bandcamp.com/album/the-fourth :))
Answer: I will take the dissenting view.  I never use music as part of a game, except for very specific narrow situations where it's a plot point or one time gimmick.  It is distracting, both for players and for the GM - either you let whatever's on play and it isn't really appropriate to whatever's going on, or you waste GM time fiddling with it and losing momentum - you already have plenty to fiddle with in most games.
Of course we always game in peoples' quiet homes so we don't need to drown anything out, either.  Except each other when it gets loud - and sometimes we have enough trouble with people getting loud and talking over each other; adding music adds another couple decibels to everyone's voice.
Answer: The only success I had was with appropriate movie sound tracks or classic music played very, very quietly. I don't worry about the music fitting the scene as queueing up a new song takes time and disturbs the flow.
Answer: I've never enjoyed soundtracks for the sake of soundtracks. But when the PCs ended up in 1969 San Francisco, I did create a soundtrack for them, of action-appropriate music (to the best of my ability) that was also music from the period.
The difference between this and "mood music" is that this was music the player characters were hearing, if not at exactly the "same time" they heard it out-of-game. They were able to talk to the NPCs in character about the lyrics of the songs and gain important clues about the adventure.
I only timed one pair of songs: two tracks from the Charles Manson collection; when those tracks came on, I segued into an encounter with a street guitar player and his adoring fans.
Having the music be music in the game worked very well.
Answer: I have used it before, but I don't commonly. IMHO, the three most common mistakes I've seen when people use music are that they turn the volume up too loud, that they choose songs that will distract themselves or other players, and they feel compelled to fiddle with the song selection during the session.
I personally define "too loud" as anything that I can't talk quietly over. I define "songs that distract" as any songs with intelligible lyrics, as well as songs that are genuinely aggravating in some way (Major Lazer's Pon de Floor, for example). Finally, "fiddling" is manipulating any element of the sound system or music player while the game is being played (during break is fine). Making these mistakes results in attention going away from playing to focus on the music.
Answer: Computer game sound tracks are great since they are designed to loop in most cases.  There are plenty on-line that you can get cheap: Dragon Age, Mass Effect, Assassin's Creed, Silent Hill, Resident Evil (aka Biohazard) and the Witcher just spring to mind as good to set moods.
Finally, Two Steps From Hell are a treasure trove of awesome music. thier producers, Extreme Music are worth a visit as well but you will not be able to buy any tracks, just listen to them.
Comment: Riven's soundtrack is surprisingly good for dungeoncrawls.
Comment: @GMJoe: Myst, Riven, and Longest Journey are all well worth having. Many games have brilliant soundtracks.
Answer: Well, a lot depends on what you're trying to do.  @Buccaneers Guild has pretty much nailed a lot of how to handle setup...the primary thing it to have it all queued up and ready beforehand, so you don't really have to take a break to do anything: if it can just flow completely natually, it can be great.
Volume is important to consider as well: rpging is based on talking, so people should never have to raise their voices; it should be pretty quiet most of the time. They'll still get the effect.
As far as what to play, that's tougher, since styles are so different among DMs/themes/etc. One good source I can recommend are anime soundtracks...you obviously have to preview them beforehand and cull out the inappropriate, but you can get some good stuff on some of them.  I've taken some tracks from Wolf's Rain, Last Exile, Spirited Away, etc.
Another popular source is E.S. Posthumus.  Very atmospheric and often builds up to a big climax; good for some fight scenes.
Finally, there is Midnight Syndicate.  A lot of people like them for their background music for RPGing.  A lot of their music tends toward creepy/horror, rather than the classical D&D style, but they also the creators the official D&D soundtrack.
Answer: Music, despite being a soundtrack to the story if You fit it well, reduces distractions as GM and players hear less sonds from the surrounding world.
Music is for players ears what a candle is for the eyes. It keeps focus/attention and helps building the atmosphere.
[I'm not a WoD kind of guy - the candles helped me while playing good old fantasy]
Sidenote:
I've once put a tape (yup, it was long ago) in a player and I made the whole session fit the music by improvising situations that the music well ilustrated at the moment. It was quite successful.
Answer: I need to keep things simple, so I will usually just use one or two albums. Play heavy metal when they fight. Play Ghost in the Shell soundtrack in a Sci-Fi setting, Ultima V soundtrack in old school fantasy settings, Vagrant Story soundtrack in a dungeon, an album by Lustmord when it gets very creepy, or some folk music when they don't fight.
A success story involved a fair being overrun by evil faery creatures. At first I played generic happy folk music, then I switched to Tom Waits's Black Rider album.
Another success story involved players reaching a door to some overpowered opposition. They did not know and debated the issue. I switched the music to Lustmord and suddenly they were afraid of opening the door. Good for them!
Answer: Music can be a great addition to any RP session.  However, keeping an appropriate choice and volume of the music is essential.  One DM I've played with in some D&D sessions likes to keep his iPhone handy with various movie soundtracks.  Of course, the music of John Williams (Star Wars, Indiana Jones, etc.) is a common and very effective feature.
Answer: We normally have music on in the background, something that fits the game we're playing and sometimes to fit what we're doing.  It's mostly there to set the underlying tempo and feel without being intrusive or dominating.
Sometimes a game becomes strongly linked to the music - I now can't listen to Nick Cave without thinking of Vampire campaigns.
Answer: I've tuned a Pandora station. A bit of classical, a bit of matrixy stuff, string quartet covers of metal/rock tunes and some instrumental/electronic. It works pretty well, and I've been tuning it long enough that I almost never have to thumbs down a song anymore. When I get back to some serious GMing I think I'm going to split it into three stations "upbeat for battle", moderate/bland for travel/background and a eerie/spooky channel for adding tension when they're exploring tombs or the like.
Answer: I've done it in the past, and it works best, IMO, when using a computer to control the music.  Just a soundtrack running music, not so much.  And I'd save it for key scenes - the big fight, the romantic interlude, the secret meeting with the king's minister at the hole in the wall inn outside of town...
But, yes, I've used it, sparingly, and it does add to the experience.
Answer: We never used music to set the tone or anything like that, but we always had some album on in the background.  Some of my favourite memories of Roleplaying are evoked when I listen to an old album (Guns and Roses - Appetite for Destructions, Mary Coughlan - Tired and Emotional, Cure - Love Cats - I'm aging myself here) and I remember a particular RPG scenario that we were involved in while listening.
Just stick something on, but down low so it doesnt interfere.
Comment: I completely agree with Toby. My "old school" music selections include Led Zeppelin, the Doors, Black Sabbath, the Rolling Stones, etc. Keep it low, and keep it rockin. Don't get fancy with soundtracks or thematic music.
Answer: One of our GM's collected a bunch of songs he thought would fit certain situations.  He had them on his phone to play at key moments (death of a boss, etc.)  I thought it was a failure because, even if I knew the song, I couldn't enjoy or even identify it because of the clipping (high volume setting on a very small speaker) and the three excited conversations going on at the same time.
Sometimes the girls will start a CD or a playlist on YouTube, but that, too, can be overwhelming in the heat of things or when half the party is distracted with a side conversation.

Music during game or not?


Is it worth taking the time and making a game scripting engine instead of directly coding?

Question: I don't know exactly everything there is to game programming and I forget things so I like to write libraries that are easy to use so I can use the thing that's hard to do such as file serialization. Anyway this brought me to a question, should I write a small game engine that writes code such as rendering objects for me and all I have to do it use a GUI? I know it takes a long time to do but the question is whether it's worth it and will it save time to do it.
Answer: Any graphical programming language is really geared towards people who are not programmers.    It all deals with abstractions at some level.  You'll eventually find some edge case you didn't prepare for, then have to implement that case in your system before you use it.
If you're good enough at programming to write a system that actually works well, then you're a good enough programmer to actually write the code itself or (more likely) more comfortable with just writing the code directly.
If not, then you're likely not going to be able to author a system like you want.
Short answer: no.
That being said, there are engines and tools that abstract out a lot of that stuff for you.  Specifically, look at using the Unity engine with the Playmaker addon:  http://www.hutonggames.com/showcase.html
Answer: No.  What scripting are you even going to support?   Write Games, Not Engines.  It sounds like you're just trying to make tech for tech's sake, not solve an actual problem.  Make a real game and see what comes of that.  If you end up with s useful generic game tool, fine.  Set out to make an actual, specific game, though.
Answer: One reason you would want to write a game scripting engine is if you wanted your engine to run on multiple platforms.  You could then separate programming concerns into the low-level platform details and the high-level game.
Imagine you've written a game that supports PC, iOS and Android.  Now you want to put out a major update to the game.  Having all 3 platforms share a common scripting language could be the difference between copy/paste and serious programming effort.
Comment: Any kind of significant programming effort to make something cross platform is going to be the same whether you're writing your game code directly or writing an abstraction layer for said game code.
Comment: I think that the usefulness of an abstraction layer increases with the lifespan of the project.
Comment: Unity's already cross platform supported and to a degree that an indie developer will never achieve.
Answer: It can't possibly save time on a single project because whatever you need for the game will need to be in the engine, plus anything the game doesn't need but the engine does.
Generally speaking you should write games, not engines. Writing engines takes longer, and the engine won't be good enough unless you have enough experience to make it correctly, and you won't know what needs to go into it until you have made a full game with it. For that reason, new engines should usually be created based on finished games, not the other way around.


What is the smallest plaintext/ciphertext size for an algorithm like?

Question: When I read about a choosen plaintext attack, for example on AES the block size is always 128 bits, does it mean the attacker will only supply 128 bits data words as "plain text" ?
Comment: I edited known to choosen
Answer: "Known plaintext" means that the attacker has knowledge of some data and its encrypted counterpart, but he did not choose either (it is "chosen plaintext" when the attacker chooses the plaintext and obtains the corresponding ciphertext, and "chosen ciphertext" when he chooses the ciphertext and obtains the corresponding plaintext). What is "plaintext" depends on what the attacker is trying to attack.
AES is a block cipher: it operates on fixed-size values (the "blocks", 128 bits for AES). When encrypting arbitrary messages, a mode of operation is used; the mode decides how the input data is to be split and mangled and reassembled; the block cipher being only the central part of the process. However, whatever the mode is, at some point some block-sized values will go through the block cipher, because the block cipher cannot use anything else.
So, when discussing attacks on a block cipher (as opposed to: attacks on a symmetric encryption scheme which uses a block cipher and a mode of operation and possibly many other things), we concentrate on the number of (distinct) block values for which the attacker needs to know the plaintext and the corresponding ciphertext. For instance, linear cryptanalysis, when applied on DES, requires $2^{43}$ known plaintexts, i.e. 64-bit plaintext blocks and corresponding ciphertext (DES uses 64-bit blocks). With common modes of operation such as CBC, a block cipher with $n$-bit blocks will be invoked once every $n$ bits of input data, so this requirement translates to $2^{46}$ bytes worth of data (somewhat over 70 terabytes).
Huge amounts of known plaintext are of course impractical. Cryptographers still consider an attack to be "genuine" as long as it requires less than $2^n$ known plaintext and $2^{k}$  effort: if, for $n$-bit blocks, you have $2^{n}$ plaintext/ciphertext pairs, then you have the complete codebook and you do not need the key anymore; and with a $k$-bit key, trying out all possible keys has cost $2^{k}$ invocations of the block cipher. An attack is "real" (in an academic sense) if it does better than that, even by a small margin.
Comment: sorry, edited my question
Answer: No. A known plaintext attack uses some real-life plaintext-ciphertext pair which the attacker somehow got to know (or guess, in the case of plaintext), or multiple such pairs known (or assumed) to be enciphered by the same key.
As you normally don't use a block cipher as-is, but in a mode of operation, this means usually some sequence of blocks, together with an initialization vector. In some modes it can even be a non-integer number of blocks, or even less than one block (for CTR mode).
When the key size is larger than the block size, there are multiple keys which map one plaintext block to the same ciphertext block - here you would need multiple different blocks to find the right one. (Of course, for AES even finding one key by brute-force is quite hard.)


Does a rear derailleur guard provide effective protection?

Question: I recently caught my rear derailleur on a log and snapped it in two. I have done some recent work on some department store bikes and noticed that some come equipped with an axle mounted guard around that surrounds the derailleur. Does anyone have any experience with these. Do they work or is it just something else to get snagged by brush and vines?
Comment: I've seen them and thought it a good idea, though I've never tried one.
Answer: I had a mate fall off with one attached it got bend and jammed the derailleur so bad we had to walk home, as the tools we carried were not good to get it off. I have seen many prangs where the derailleur took bigger hits with no problems. Most that I have seen (Department store ones) are too light and cheaply build to be anything other than cosmetic.
It also depends on the bike - better bikes have a derailleur hanger that is sacrificial and bends, protecting the derailleur in many common prangs. Department store bikes often don't have a hanger, hence the derailleur takes the full impact.
I have though about it, but with years of Mountain biking, many falls (some big), only ever bend a hanger. They may work, but I asked - why do no mid/high end bikes them. Is it purely weight, do the want to sell more parts, or is it just not worth weight and money required to make a bike so strong it cannot be broken in a fall.
I decided (for me) they a not worth while.....
Answer: I had one on my bike in Japan. I never had problems with them, my derailleur stayed intact. I didn't take it through many bushes, but I did drop it a lot on the right side (naturally get off that side, and I never use a kick stand) and have bumped against posts and stuff. The riding I do now is in the mountains, lots of rocks but not much brush so I don't ever think about it anymore.
The one I had was bolted to the dropout, but covered the same area as the ones I have seen on the axle. If you are going through some pretty tough brush, it might not protect against everything, but for the protection it does give, it is definitely worth the effort.
Answer: I have seen some bikes with the derailleur being bent because the bike fell on the derailleur side. So I usually recommend to have one so that your derailleur is protected, and it proved useful for me a few times, but some guards are just too light and they bend and then bend the derailleur, so it must be heavy to really protect your derailleur.
Yes it makes your bike heavier, but what the heck, to gain weight on your bike just wear short pants instead of jeans, you'll gain more weight than using costly parts on your bike.


How can I convert D&D 3.5 to 2nd Edition or older AD&D?

Question: I have accumulated a lot of D&D 3.5 modules and adventure settings, but I play older editions of the game. What is the best way to convert these to an older edition, say AD&D 2nd edition?  Is there a "quick fix" that makes conversion easier, or must it all be done one "piece" at a time?
Answer: I don't think there's a quick fix, but I do think it's something you can do on the fly once you've got some practice. The idea is to used the 3.5 material as a guide for what to put into the game rather than as a (more, or less) strict recipe for the adventure.
For fights, it depends on how you run your AD&D. If you don't worry about encounter balance and prefer to leave it up to the players whether to fight, run, or invent a third option, then you can run modules as-is just by dropping in 2nd edition creature stats for the appropriate enemies. (If you do care to balance things as much as 3.5 assumes, then I've got nothing. Sorry!) Essentially, read a set of detailed stat blocks for six 2nd level Orc Warriors and one 5th level Orc Warrior chieftain as "six orcs with good gear and maybe +2hp and one orc with great gear and full hp."
The balance won't always be the same—some fights will be easier and some harder—but since 2nd edition isn't so tactically-oriented, a well-matched fight isn't usually the play objective. For creatures that don't have 2nd edition equivalents, either reskin an existing creature or just create a new creature inspired by the 3.5 version. The idea is to take the 3.5 material as the guide to what 2nd edition material to populate the adventure with.
You can do pretty much the same with magic items. Some will translate 1-for-1 between the systems. Others will be weaker or more powerful, which I personally think is fine. Some things, like tindertwigs or whatever "mundane" magic items 3.5 had, and items that are specific to how 3.5 does things, you might not want to keep—in that case you can go straight to the good ol' random magic item charts and have fun replacing them with 2nd ed stuff.
The harder part is going to be where the 3.5 module assumes a robust skill system. For physical skill checks you can fall back on ability checks with or without modifiers, or just let them do it if they've got a well-described plan for how to get the job done.
For social skill checks you can use the skill suggestions as a guide for how to roleplay the NPCs. If the 3.5 material is using a (say) diplomacy check as a fork in the road for how the module will go, replace that by asking yourself a question: "What could the PCs do for/give to the NPC to get what they want?" Once you know that, let it come out when the PCs interact with the NPC. Don't make it hard to find out or necessarily even hard to do—concentrate on making it something that will make the PCs really think about whether they want to grant that concession to the NPC, or whether they'd really rather not change the NPC's mind. And, of course, allow for creative alternatives that the players might concoct to influence the NPC…
Not all situations are going to have that obvious kind of plot structure, though. In 2nd edition, when I really don't know how the NPCs are going to feel about the PCs and I just want a roll to tell me, I often use the NPC reaction chart to find out what their disposition is, and then mentally keep track of how that might change up or down as the PCs try to influence the NPC. There's no solid, systematic way of doing it, but I find it works with practice and a generous GM spirit.
All of this presumes that you're playing closer to a 2nd edition feel. If you really want to be faithful to the 3.5 material, then more work is going to be required. However, most of the time you can probably get away with converting just the core bits of the 3.5 material one piece at a time before play, and using these techniques to smooth out the less-critical sections in between.
Comment: This is really close to what I'm looking for....especially since I am not a stickler for such things as absolute balance or skill level. The skill checks seem to be the major roadblock.
Comment: When I play AD&D I ditch the clumsy non-weapon proficiency system and go with "secondary skills", just letting PCs make ability checks with a good chance of success when it falls into their background.

Ability checks feel weird and arbitrary at first, but they do the job. Any time you don't want to just say, "you succeed/fail", have them check Dex or something.
Answer: Just replace the monsters with their 2e stats and see what happens. Give it a go. If it's looking too easy or too hard then adjust it on the fly.
Even if you are rolling your monster roles out in the open you can still fiddle monster hit points and tactics whilst the battle is going on.
Comment: This.  Remember that balance between the strength of the party and the strength of the encounter didn't matter so much back in the day.
Comment: That's pretty much what I do: I don't spend more than a small amount of concern over finicky conversion. Typically, I just try to drop in the "equivalent creature" from the other edition -- in a few cases, the relative difficulty of some monsters have changed rather significantly over time it seems: in those cases, I tend to swap out for another creature with hit dice more in line with what's needed (if possible) or scale down with a thumb.
Comment: Yeah, this. This is what I said in my answer in maybe too many words. :)
Answer: Swapping out "normal" monster stats is the easy part, just replace the 3.5e manticore or whatnot with the 2e one.  The NPCs and levelled monsters are harder.  Something like a goblin or orc, you can just treat as a levelled human, but weirdo stuff may present more of a challenge.  Just swap it out for something else.
Keep in mind difficulty levels go up from 2->3->3.5->Pathfinder - assumption of party average hit points and DPS goes up sharply, so even with swapping in monsters do NOT try to run a 3.5e for "levels 5-7" for a 2e party of levels 5-7.  It'll be like twice as deadly.
Really you can do without skill checks, because the 2e and earlier mode of playing didn't rely on them - we used to just let the PCs do it, or make a stat check, or let them figure it out with clues and player knowledge.  Besides, most 3.5e adventures don't formalize skill stuff like they're 4e skill challenges, they just require Search DCs to find stuff or Balance DCs to not fall down.  Replace stuff with thief skills where appropriate and stat checks where appropriate.
[Although - one of my biggest 2e house rules was a Perception stat.  Then when 3e came along and rampant Perception/Search was there, it wasn't much of a change for me.]
Answer: I upvoted SevenSidedDie's answer, but here's my take, for what it's worth...
No matter what game system the adventure was written for or that you're using, this is how you convert on-the-fly: Simply ignore any stats or mechanics in the module. Pick an appropriate monster, treasure, or mechanic from the game you're running based only on the text descriptions in the adventure.
When there isn't an exact match, pick something similar. Then you can either simply make it the thing you picked instead or use the stats/mechanics for what you picked and describe it to the players as what the adventure described.
For the d20 System to older D&D's specifically, though: For most skill checks, first ask yourself if it works for the PCs to simply succeed automatically. The d20 System adventures have a tendency to call for a skill check where before none was needed.
Comment: "d20 System adventures have a tendency to call for a skill check where before none was needed." Very true! +1 for that insight.


What is an appropriate software for furniture design?

Question: I want to master a software for furniture design but I don't know what's an appropriate and powerful solution.
Answer: there are plenty of software available depend on your need and pocket
check these links

Sketchlist (easy to learn and you might finish your design within the 14 day trial period. It also contains all the drawings and reports you will need to make the wardrobe.)
ecruso
gama 3d
Topic discussed on Software recommendation

wish  to see  you soon as successful furniture designer :) all the best
Answer: Many furniture makers use Sketchup which is a free software that used to be owned by Google. There is a strong community with interest in the woodworking world. Sketchup has an easy to learn interface and will get you producing working designs pretty quickly. Most 3d software is time consuming to learn and expensive to acquire. Check out the forums at sketchucation.com to learn more.
Comment: Good of you to point out that more complex 3d software does indeed take long to master!
Answer: AutoCAD for drafting, modeling and detailing.
3ds max for render with realistic materials.
Adobe photoshop for post production.
Comment: I recommend Maya over 3D Studio Max
Answer: Usability is the key - possibly more than completness of functions.  Some design packages offer so much it's hard to grasp it all.  A 2D layout or design actually accomplished as Microsoft Word drawing or Paint image can be better than no design at all (sometimes :) )  One reviewer of CAD packages wrote in a woodworking magazine: "Basic test of a product is if I can draw a line.  Most of the times that test fails".  So answer the question"  "Can I actually use the software to accomplsih what I need?"
Comment: indeed, nice words.
Answer: As others said, there is plenty of 3D software. I have on the other hand only seen it done with Rhino 3D. Probably because it can import many file types (screw templates, hinges), is very quick in contructing with somewhat simple shapes, can combine surfaces and volume models and adding dimensions is rather easy. All this is probably doable with other software too (especially AutoCAD) but it seems designers favor it for it's simplicity and because it is easy to learn the software.
Comment: a good item for the list


What is the use of password encryption?

Question: Why do we encrypt passwords?  Is it to protect the password from eavesdropping? to protect the password after saving it in database?  both?  or for some other reason?
Answer: I wrote a blog article specifically on that subject. Summary: password should be hashed ("encrypted" is not the correct term for that) to protect against attackers who gain read-only access to the database where a server stores whatever it needs to verify passwords.
Answer: Encrypting a password is typically used to protect it from eavesdropping. For example, when you log in to a website which has been setup properly, your password is encrypted thanks to SSL. No eavesdropper can snatch the password in transit.
As for saving an encrypted password in a database, unless there is a very good reason to do this and you know what you are doing, this is a bad idea. Storing a digest (e.g., sha-256(salt+password)) is a much better idea. The reason for this is that where is the encryption key stored? On the server. So if a hacker can break into the machine and steal the database, surely she can steal the encryption key and easily decrypt every password.
One valid example I can think of, however, for storing a password encrypted in a database is a password manager.
Answer: The right way is not to store passwords (even encrypted), but rather store a salted hash of the password.
Sometimes you do need to store a password, usually to login/access into other systems.
Then you should store it encrypted so if somebody gets it (via SQL injection or whatever) he will not be able to use it to access those systems.
Comment: @rox0r, that part of AaronS answer refers to credentials for other systems.
Comment: I think you meant to say "store it hashed" not encrypted.
Answer: Use hashing, instead of encrypting passwords.
Why? Well, to encrypt something, you need another key (another password). So how would you store that key securely? You would be trapped in a loop.
So, use a hashing function. Looking around the internet, you find millions of articles and suggestions stating to use functions like MD5, SHA1, SHA256, HMAC, Salted Hashes, ... and so on. The list is long, but do not use them.
Use PBKDF2 with a 64-bit salt per user (possibly derived from a cryptographic pseudorandom number generator). One of the reasons for using PBKDF2 over any other hashing function is that it is slow, which means it is not very vulnerable to brute-force attacks. A salt per user helps protect against rainbow table attacks.
So, you would store
<code>USERNAME, PBKDF2DIGEST, SALT
</code>
as a record in your SQL table and you are good to go!
(i prefer PBKDF2 over bcrypt since it feels more used and hence more tested)
Answer: Hashing is used to protect passwords within the database (Whether in an OS like Linux, or an App). To protect the hash from attacks like rainbow tables, a salt value is add to the hash. The salt will make rainbow tables attacks impractical because the salt value is unique for every user.
Protecting the password from eavesdropping usually uses encryption. For example send the password over SSL.
Answer: Please follow Thomas Pornin's answer above.  Knowing that you should hash+salt your passwords before storing is not enough.  It's just enough information to get you in trouble.
For example, one round of md5 hashing is tremendously weak, with an 8 GPU setup and 33.1 Billion hashes a second, you can break all 8-digit passwords made up with alphanumeric characters in 15 hours.
Thomas talks about bcrypt and PBKDF2 and the background behind using them.

What is the use of password encryption?


What features differentiate Nikkor and Tamron/Sigma lenses?

Question: I'm wondering if anyone has an opinion about Nikkor vs. Tamron and/or Sigma lenses.  Is it worth the extra money to purchase Nikkor lenses?  I haven't had the chance to compare these.  Are the Nikkor lenses sharper?  If you think Tamron and/or Sigma are comparable, is there a certain brand that is superior?
Comment: Related question: [What constitues the quality difference in the lens with exactly same specifications but different brand names?](http://photo.stackexchange.com/questions/18276/what-constitues-the-quality-difference-in-the-lens-with-exactly-same-specificati)
Answer: There are enough variations in lenses that it's hard to make a generalization about an entire brand vs. another.  A lot of folks stick to the lenses from their camera manufacturer and I think that in the past the quality tended to be better.  That said, some of the third party lens manufacturers have some great lenses, and some of the lenses by Nikon and Canon aren't necessarily the best.
I generally recommend that if you're looking for a particular focal length, aperture, or other feature, compare the various lenses that meet your needs.  Based on review sites such as DPReview and Fred Miranda, you can make an educated decision about your particular need.
Answer: If your interest is primarily the optics, you need to look at individual lenses, not brands as a whole. You can't depend on a Nikkor (or Canon, Pentax, Sony, etc.) necessarily being sharper than something like a Sigma, Tokina or Tamron.
OTOH, unless you're pretty sure you're buying a lens to keep it forever, the third party lenses don't seem to be nearly as good of an investment. Just for example, years ago I bought (at just about the same time) a Minolta 35/1.4 and a Tamron 70-210/2.8. If I recall correctly, paid about $350 for the Minolta and about $750 for the Tamron. If I were to sell them now, I'm pretty sure those prices would be roughly reversed; getting $750 for the Minolta would be easy (in fact, $900 would be fairly reasonable), but I'd probably have a hard time selling the Tamron for more than $300 (and $250 wouldn't be particularly surprising).
Answer: I think the question is a bit subjective, however, I will say that Nikon makes some very, very, good lenses and at the high end they are hard to beat. Sigma and Tamron also make some very good lenses, including some that nobody else has (for example, Sigma has the widest rectilinear lens on the market for SLRs at 8mm). And all three make lenses that are, well, base consumer grade that aren't really very good at all.
Net effect, there is no general answer to the question, because it depends on which lenses you are comparing, and when you do that it is best to find a lens review site and check the performance vs cost benefits to determine which best works for you. At that point, I think you will find that it's sometimes a Nikkor lens and sometimes it is Sigma or Tamron.
So, if you are contemplating a lens option, it might be better to restate the question with some specifics. As it stands, the question is so broad and general that we can only give you a broad and general answer.
Answer: As always, the answer is to choose carefully!
From experience I can say that although both Nikkor lenses and Sigma lenses cover a range of quality and price, Sigma covers a wider range. By that I mean that the worst Sigmas are quite bad and the top ones are absolutely superb. My absolute favorite Sigma for example is the 100-300mm F/4. It is extremely sharp, fast and nearly distortion-free.
Tamron could be similar but I've only seen terrible ones and mediocre ones so far. Most people seem to go for that brand based on price alone.
So, what you must do now is compare a specific lens from Nikkor vs specific ones from a third party brand. Note there are other differences than image quality, such as the focus motor performance, stabilization effectiveness, body compatibility (Sigma and Tamrons tend to require more upgrades when Nikon updates camera bodies) and - as silly as it may seem - the direction you have to turn the zoom and focus rings (it can drive you crazy if one lens turns 'backwards' compared to your other ones).
Finally, you forgot Tokina. Unlike Sigma and Tamron which makes most of their money selling low-quality lens and very low cost, they actually have only (9) lenses with some unique specifications and are generally of high quality. The Tokina 11-16 F/2.8 for example is extremely well-regarded.
Comment: +1 for mentioning the Tokina 11-16 which is a very good complement to the branded nikkor's.
Answer: It depends on the lens.  Look at reviews: Where can I find reviews of lenses?
Answer: I used Sigma and Nikkor lenses. I can say the quality built of Nikkor is better than Sigma. But Sigma offers cheaper lenses with subtle quality difference. If you are rich enough just go for Nikkor, you won't go wrong and lessen your worries. If you compare the price between the 2 same specs and find the differences not worth it, just get the cheaper one.
Answer: I have a few Nikon lenses, and a Sigma 10-20mm for super-wide shots. When I was looking to get a wide lens, I researched the options, which included the Nikon equivalent (at the time) the 12-24mm. (they've since released the 10-24mm).
My research indicated that while first-party gear may be slightly better quality, the reality is that the difference is pretty small. I decided the extra cost of the Nikon wide wasn't worthwhile, plus it wasn't as wide, so I got the Sigma.
My point: in general, first party lenses tend to have somewhat better build/photo quality, but at an extra cost. Third-party lenses seem to be pretty competitive on both cost and quality,Sigma at the least. You need to decide if the extra cost is worthwhile to have all your lenses coming from the same company.
Answer: Reading reviews about the specific lenses you're interested in getting. The Digital Picture does very thorough reviews of Canon lenses.
I have had a number of Canon lenses and a single Sigma lens, their 20mm f/1.8, which also comes in a Nikon mount.  The review from the aforementioned site summarizes my own findings well — for the (relatively cheap) price, the Sigma lens is decidedly ok at what it does.  The biggest complaint I had was that it opens to f/1.8 but things aren't very sharp until you get to f/2.8.  This is in contrast to something like the Canon 50mm f/1.4 (their mid-range 50mm), which is usably sharp at f/1.8.
Other sites with good lens reviews include DPReview and Ken Rockwell's reviews.
One more thing you can do is rent lenses from a place like Borrow Lenses.
Answer: The only way to do is to compare 2 specific lenses and read the data and MTF charts for each of those lenses.. I use photozone.de to get all my info for a price estimate, feature comparison etc before deciding on a lens.
Comment: MTF data is a very incomplete representation of a lens quality. It only describes sharpness, not vignetting, not distortion, not aberrations, not color-shifts, etc. It is very hard to characterize a lens, although both slrgear.com and depeview.com both do a decent job.
Comment: The site I mentioned does all that.. I didn't say to "just" read MTF charts. I asked to read data _and_ mtf charts.


How sitemap.xml influences indexation?

Question: If a page is missing in sitemap.xml (but crawable through HTML hyperlinks), may this cause it not to be indexed? (I mean it would be indexed without sitemap, but not indexed with sitemap because it is missing in the sitemap.)
Answer: If the page is crawlable, then it will be indexed unless you have explicitly marked it as noindex. The sitemap.xml is another way for Google to discover pages on your website as Ilmari Karonen mentioned in the answer. The only thing that will happen is that the page will not be found via the sitemap but by other means.
Answer: No, leaving a URL out of your sitemap will not prevent Google from indexing it.
To quote Google's sitemaps FAQ:

"Sitemaps provide an extra way for us to understand what pages you have on your site, and can help speed up the discovery of new and updated pages on your site. But neither HTML nor XML Sitemaps replace the normal crawling process."

In fact, having an up-to-date partial sitemap may, in some cases, even speed up the discovery of pages that are not included in the sitemap.  For example, if you create a new page X and link to it from a page Y in your sitemap, and update the "lastmod" date of page Y in your sitemap to reflect the fact that the new link was added, then Google will notice the update and schedule page Y for crawling, which will cause them to notice the link to page X and add it to their crawl queue as well.
That said, one can also think of scenarios where a partial sitemap could slow down the indexing of pages not listed in the sitemap.  For example, let's say your site was divided into two distinct sections A and B, with few if any links between them, and your sitemap only covered section A.  Since Google uses the last modification dates in the sitemap to prioritize recrawling, it's at least plausible that, if you kept updating the content in section A (and your sitemap of it) frequently enough that Googlebot stayed busy recrawling it, pages in section B might not get recrawled as often as they would be in the absence of the sitemap.
Of course, this is kind of an artificial scenario, and easily avoided.  Still, it at least does show that, theoretically, it's possible for a partial sitemap to slow down the indexing of pages not included in it.
Answer: As you don't need to provide an XML sitemap to be indexed by Google, then I think it's fair to assume that leaving a page off the XML sitemap won't cause it to be exlcuded either.
On the flipside there is not any evidence that XML sitemaps do anything for your Google ranking. It is merely implied that giving Google a helping hand by providing an XML sitemap, should help.
Answer: The lastmod label with an expired date (p.ex 06-10-2013) is a possible cause of not indexing sitemaps.
I have a very big website and my sitemaps in google where not indexed at all. Google only was indexing small parts of my sitemaps. Today, I have changed all my lastmod labels, actualizing them at today.
There is any possibility that the lastmod was the cause of wrong indexing pages.

How sitemap.xml influences indexation?


Why does a Bar mitzva boy publicly read from the Torah?

Question: Why do bar mitzva boys publicly read from the Torah for their bar mitzva? Where does the minhag come from?
Answer: Taken from Matazav.com
The source is found in the Orchos Chaim - a French Rishon. He mention s that Rav Yehudai Gaon made a Baruch Shepotrani after his son leined by his Bar Mitzvah. He also mentions that this is done to show that the Bar mitzvah boy is a Gadol & can be a Shliach Zibbur
Answer: This tradition is actually becoming less common in the more "yeshivish" communities. The idea is that the enormous amount of time and effort spent memorizing the leining could be better spent learning gemara. This is probably true, but on the other hand, if you learn how to lein instead of just memorizing, that is also a very valuable skill and benefits the community greatly. Perhaps a compromise is to have the B"M boy lein just an aliya or two and also make a siyum on a masechta.
But in the end, it is really the peer pressure of the other 13-yr-old boys in the community that will determine what any individual boy chooses to do, much as it will be for the rest of their lives.
Answer: First of all you don't have to Lein for your bar mitzvah but I think the choice so it show your becoming of a man And it is very amazing that you get to read out of the torahh correctly at only 13
Answer: I once heard from Rabbi Nissan Kaplan that he did all mitzvos before then except for teaching torah to the masses. this is why he gives a drasha on the bar mitzva.
maybe the torah reading is similar idea. and also, maybe, to put him in the spot light and give him some honor, like a chatan to make the occasion a great simcha for him


What's the best time to see the monster of Loch Ness?

Question: Next year I'm planning to go to Scotland. I'm really interested in nature and so I think the Scottish Highlands are worth a visit. Besides all the marvellous old castles I would really like to visit some famous lakes. First of all I'm interested in Loch Ness. I also heard from various people that there is a monster living in this lake. So when is the best time (season and time of day) to see it?
Comment: I suggest the 35th of May, if it falls on a Thursday.
Comment: Go on a foggy day, when you can more easily fool yourself into thinking you saw it. ;)
Comment: Be sure to take biscuits. She loves biscuits. And belly rubs.
Comment: the best day is February 31 (http://en.wikipedia.org/wiki/February_31).
Comment: I think after visiting 5 distelleries and 10 pubs in one afternoon the chances of monsters sights will grow rapid.
Comment: Seems like something that belongs on [skeptics.se] to me.
Answer: Right, despite missing out on the first day of my tour there while my train broke down, the rest of the gang went and unfortunately for me, I missed out on an opportunity to see Nessie.  One day though, one day...
Firstly, you need to be aware of the geography.  Loch Ness is in a natural cleft between Fort William and Inverness in the Scottish Highlands, and is 23 miles long. It's also nearly a mile wide in places, and is VERY deep (up to 226m).  Statistically, this poses a problem for someone hoping to see Nessie, even if she does surface.
Next, consider the weather.  Edinburgh, further south, has 186 days of rain a year.  That's HALF the year.  And it's considered the SUNNY side of Scotland.  Wind, rain, mist and snow are a feature of the Scottish highlands (it rained every day but one of my tour, but it was still amazing), but don't help with visibility.
Next, the location north.  Scotland is pretty far north.  In winter, like now, by the end of November the sun  has already set by 4pm.  This doesn't give you much daylight time to go Nessie hunting.  Statistically this means from June to August you're probably going to have the best shot, with weather and sunlight matching this.  Of course this is when more tourists are there, and naturally this aligns with July and August being the most common months for sightings.
Most sightings have been early morning or early evening.  This could be argued that it's because low light plays tricks on the eyes, especially with mist hanging around, but if she's reptilian or amphibian, they often try to avoid moving lots in the heat of the day anyway, so avoid searching around lunchtime.
There are boat tours on the water as well, so I'd consider that your best chance in summer, get out on the Loch and be close to Nessie.  The castle in the north east also offers dramatic views and has had some sightings.
Good luck! We expect pictures ;)
Comment: I think I didn't miss out on not understanding what you didn't miss out on \-:
Comment: "You didn't miss out on seeing Nessie" ?? So you saw Nessie?? (=
Comment: Impressive, the double negative has two meanings.  They didn't see Nessie, so I didn't miss out on that.  Yes, that totally makes sens ;)
Comment: I always confused on double negative statement
Answer: Judging from this list of sightings, your best bet is in the month of August, but no later than October. May also seems pretty common as well. Most of the time the sun was not out when the reports were filed (a fairly easy thing to imagine, honestly).