How to clear beer

Question: I am brewing my first homebrew an American cream ale.  Was just reading into secondary fermentation.  In the directions and books I've read it seems to suggest doing this.  But as I search online and read more into it, it seems many say to avoid this and allow the beer to sit in the primary until complete and ready to move to a bottling bucket.  I was just curious if leaving it in the primary then going right to bottling, is there a way to give it a little clarity, I'm not looking for bud light clear here but just want to make it look a bit more appealing without sediment flowing around.  And the main way, without adding chemicals, seems to be secondary racking.  Any help would be greatly appreciated!
Comment: Good question. Upvoted.
Comment: I actually forgot to add Irish Moss last time, and racked to secondary after a week of fermentation and was very surprised how much it cleared up after that!
Answer: Racking to secondary and letting it sit for a few more days or a week can improve clarity slightly but is by no means necessary. It will however make things easier to bottle without stirring up sediment in the process. If you're careful you can bottle straight from primary with about the same results.
I'm guessing since this is your first brew that you will be carbonating naturally in the bottles? In this case, even if your beer is extremely clear when you bottle, the yeast still have to eat and multiply quite a few times before carbonation is complete, so you're going to have sediment either way. The only way around that is to force-carb which requires a bit more equipment (keg, CO2 tank, beer gun) but affords you the ability to filter your beer and have it ready to drink immediately, and avoids bottle bombs or undercarbonation.
Answer: There are a variety of techniques to clarify beer. Filtering is the quickest method but will strip out the yeast you need for natural carbonation, and potentially also some flavor compounds. Finings (gelatin, isinglass, others) will help large particles drop out; I'd recommend reading posts here about finings and/or talking to your LHBS about techniques with finings.
Settling over time is the easiest, as it requires no additional equipment. Chilling the finished beer can help, but make sure to do so slowly and not to freeze the beer, in order to protect the remaining yeast in suspension from death and stress.
You may transfer to secondary to help with settling, I have done this in the past for longer clarifying (two weeks) of low-flocculating strains. Mind that the act of transferring is going to stir up sediment, and is not truly necessary.
The best method is to leave your beer in the primary fermenter for a couple of weeks until it is clear, and then gently siphon from the top to a bottling bucket or keg, doing your best not to disturb the sediment as you go.
Answer: In my experience, the biggest cause of non-clear beer in your glass is chill haze.  You can rush from fermentation being complete to bottling, without any significant "conditioning" time, and the beer in the bottles will become crystal clear quite soon.  But put those bottles in the fridge and you'll have chill haze by the time the beer is at drinking temperature.  Leave that same beer in the fridge for a few weeks and it will likely be very clear.
This will all be true too if you let a beer settle at about room temperature for several weeks, with or without racking to a secondary.
So I'd say that getting a clear beer isn't so much about racking out of the primary or not, but rather what are the conditions (particularly temperature) of the beer after fermentation.
I don't do much cold-conditioning myself, but I'd say if you really want clear beer, and you have the means to do so, rack to a secondary and keep it at near-freezing temperature for about 2 weeks.
Answer: Avoiding sediment floating around in the glass is often a function of carefully pouring from the bottle.  If bottled beer is allowed to sit and condition properly, given time the yeast and other solids in suspension will settle to the bottom and create a fairly tight sediment in the base of the bottle.  Upon opening a careful pour should leave much of it behind.  I just pour slowly and watch the beer coming out of the bottle  As soon as I see a little trail of sediment coming down the neck I stop pouring.  This does mean that to pour the clearest beer you are serving maybe only 10oz of a 12oz bottle...
Allowing the beer to sit in primary a little longer than most texts recommend achieved the same thing as secondary.  Which is allows more stuff to settle to the bottom.
Lastly, the less stuff you transfer from the fermentor (primary or secondary) into the bottling bucket obviously limits the stuff that will need to settle out in the bottle too.
Gelatin fining is a good idea to but it really works at its best if you can chill the whole fermentor down to near serving temps prior to adding the gelatin (or any fining agent for that matter).
Answer: The basic problem you will have is that you need some yeast in suspension for bottle carbonation (if you don't have them, you need to add them).
Racking to secondary will increase the clearness of you beer, while adding another chance for getting the beer infected. Generally all literature today recommends you not to rack to secondary unless you have to since the old problem of getting bad taste from the old yeast is not a problem with today's yeast strains.
So unless you are kegging, the clarity is a non-issue at bottling time. And regardless if you are bottling or force carbonating, if you let the beer sit a while, everything will settle. In a Keg, you might get a few glasses of yeast in the beginning, in a bottle, pour carefully and don't take any sediment if you don't like it.
Answer: Racking to secondary most definitely helps with clarity, if you are unwilling (or unable) to rack to a secondary another great option is using gelatin to clear up the brew.

2/3 cup water
1 tsp gelatin

Heat the two ingredients together in a microwave (most recommend 15 sec increments) shoot for about 150F and then stir to dissolve the gelatin into the water.
Once its fully dissolved you can dump it into your fermenter, gently stir  and wait for nice clear beer.
Gelatin works best in a cold environment and you could clear it up nice within two days or so. If you cant store cold, you may need to wait a week for the gelatin to do its thing.
Cheers!
Answer: The addition of irish moss in the boiling process helps act as a clarifying agent.  1/2 tsp in the last 10 minutes of the boil.
Answer: A fairly recent development (I think it is recent) is the use of Brewer's Clarex. Add the recommended dosage to the wort at the same time you pitch the yeast. Is working for me, and appears to eliminate chill haze.
Answer: There are multiple methods for producing clear beer. The least expensive in terms of money is to place the beer in secondary for 1 to two weeks. I would not let my beer set in primary much longer than it take to ferment. It can give you off taste if you do so. But flavor is subjective right?The longer a brew sets in secondary the clarity will occur. But who wants to wait weeks to enjoy their brew? I have tried both gelatin warm and cold. Cold crashing produces much better results. bit now your talking refrigeration. If you are bottle conditioning your beer as other posters have suggested, you will not have clear beer all the way to the end and sediment will occur in the bottom of the bottle. Kegging your beer gives you the best opportunity to provide crystal clear beer. But more equipment more money. If you are kepping try the gelatine, then filter 5 microns or less. If you still have chill haze after all that Irish moss and a longer boil time 90 mins

How to clear beer


A Gronwall-type inequality.

Question: I want to derive a Gronwall-type inequality from the inequality below. Here all the functions are nonnegative, continuous and if you need some assumptions you may use that.
$$ f^2(t) \leqslant g^2(t) + \int_0^t (f(s) +c) f(s) ds  \;\;\;\; (t \in [0,T]) $$
So please help!
Answer: Consider the function
$$h(t):=\int_0^t f(s)e^{t-s}ds\,,$$
which solves the ODE $h'=h+f$ with $h(0)=0$, so $$h(t):=\int_0^t \Big(h(s)+f(s)\Big)ds\, .$$
Adding the term $-c\, h(t)$ to both sides, your inequality takes a more familiar form of a Gronwall inequality:
$$f(t)^2-c\;h(t)\le g(t)^2 + \int_0^t \Big(f(s)^2 -c\;h(s)       \Big)ds  $$
relative to the function $f(t)^2-c\; h(t)$.
Answer: Consider g=0, c=2, f(t)=t.
By the way, what did you mean by "if you need some assumptions?" Are there folks out there who prove things without them?

A Gronwall-type inequality.


Abstract nonsense versions of "combinatorial" group theory questions

Question: In particular, I'm just curious whether there's a version of the Sylow theorems (which are very combinatorially-flavored) which allows horizontal and/or vertical categorification? Or at least can be stated in more category-theoretic terms?
Comment: I was wondering this just last week.  I have prelims to start worrying about, and categorical statements always stick best.
Comment: alexzander, that's my justification too. I never did like abstract algebra 'til I learned to start thinking of it in categorical terms.
Comment: Although in my case it's not prelims so much as undergraduate-level abstract algebra test, so I'm probably overthinking it. Still curious about the question on its own merits, though.
Answer: Sylow subgroups are an example of a type of object satisfying a sort of universal property.  Exploring other objects with similar properties gave birth to the modern theory of finite soluble groups in the 1960s.
If $X$ is a class of finite groups and $G$ is a finite group, then $P$ is an $X$-covering subgroup of $G$ if $P$ is in $X$, and whenever $P \le H \le G, N \unlhd H$, and $H/N$ in $X$, then $PN=H$.  In other words, $P$ covers every $X$-factor of $G$.  If $X$ is the class of finite $p$-groups, then $X$-covering subgroups of $G$ and Sylow $p$-subgroups of $G$ are the same thing.  Indeed, if $P$ is an $X$-covering group, and if $H$ is a Sylow $p$-subgroup containing $P$ and $N=1$, then we must have $H=P$.  If $P$ is a Sylow $p$-subgroup and $H$ contains $P$ with $N \unlhd H$ and $[H:N]$ a power of $p$, then $[H:NP]$ is a divisor of $[H:N]$ and $[H:P]$, so must be $1$.  Notice how the "containment" part of the Sylow theorems is replaced with a "covering" condition that behaves better with the normal structure of the group.
If $G$ is a finite solvable group and $X$ is the class of nilpotent groups, then there is a sort of "Sylow nilpotent subgroup", the $X$-covering groups or Carter subgroups.  They were studied by R.W. Carter who described them as self-normalizing nilpotent subgroups.  Like Sylow $p$-subgroups, there is exactly one conjugacy class of Carter subgroups, and they have some reasonable arithmetic properties.  People tried to determine which classes $X$ of groups are such that $X$-covering groups exist and are unique up to conjugacy.  Roughly speaking, this was the dawn of the modern theory of finite soluble groups, with Gaschütz's (et al.) classification of such $X$ as "saturated formations".
This shifts focus away from the subgroup $P$ to the class $X$.  If $X$ is sufficiently nice, then there will be a nicely embedded X-subgroup for any finite group.
Sylow $p$-subgroups also satisfy a dual condition, they are also $X$-injectors for the class $X$ of finite $p$-groups.  If $X$ is a class of finite groups, and $G$ is a finite group, then $P$ is an $X$-injector of $G$ if for every subnormal subgroup $N$ of $G, P\cap N$ is a maximal $X$-subgroup of $N$.  The dual definition of covering group (for $X$ a saturated formation) is that $P$ is an $X$-covering group iff $PN/N$ is a maximal $X$-subgroup of $G/N$ for every $N \unlhd G$.  If $X$ is the class of finite nilpotent groups, then $X$-injectors are called Fischer subgroups and again form a single, well-behaved conjugacy class of subgroups.  A Fischer subgroup of a finite soluble group is a nilpotent subgroup that contains every nilpotent subgroup that it normalizes.  This is similar to the idea that a Sylow $p$-subgroup contains every $p$-group that it normalizes.  $X$ such that $X$-injectors form a unique conjugacy class are called Fitting classes, due to their similarity to Fitting's lemma on subnormal nilpotent subgroups.
A very approachable introduction to these ideas is B.F. Wehrfritz's tiny textbook for a Second Course on Group Theory.  Some of these ideas are described in Robinson's textbook for a Course in the Theory of Groups, but I believe it spends very little time on general formations.  The standard textbook source for formations, especially in the soluble universe, is K. Doerk and T. Hawkes's book Finite Soluble Groups.  Doerk&Hawkes explains several of Gaschütz's arithmetically defined Xs, which you might find a good contrast.
Answer: This may be splitting hairs, but I think the Sylow theorems are more arithmetic than combinatorial.  Depending on your standards of good categorification, I think this makes it difficult to encode precise congruence behavior such as the index of the normalizer being congruent to 1 mod p, and so on.
There is a homotopy-theoretic way to look at the Sylow theorems involving fusion systems.  These are categories that encode the conjugation data between the p-Sylow subgroups of a finite group, and let you study the homotopy type of the p-completed classifying space of a finite or compact group.  Bob Oliver has some papers on this subject.  I don't know if this level of sophistication will help you learn the basic theorems, though.  When I was studying Sylow, I personally preferred exercises, like showing that there are no simple groups of order 56.
Comment: J.L. Alperin's "Sylow Intersections and Fusion" (MR0215913; DOI: 10.1016/0021-8693(67)90005-1) is a nice group theoretic introduction to some of the key ideas behind fusion.  It is a more precise version of Sylow's conjugacy theorem.  Linckelmann's introduction (MR2336638) is one of the easiest ways to read the category theoretic version of fusion.  Alperin's Local Representation Theory textbook introduces the Brauer subpairs theory nicely; that is the other main source of fusion systems.
Comment: I learned the Sylow theorems precisely like that.  Homework problem in my abstract algebra class "Show that there are no nonabelian simple groups of order less than 60."
Comment: Yeah, okay, good point; it's probably too much to hope for there to be something easy enough to apply in day-to-day situations. But there's no obvious reason (to me, anyway) that there shouldn't be an extension even to finite groupoids.
Answer: You might find the theory of fusion categories interesting (this is, unfortunately for the terminology, disjoint from Scott's mention of "fusion systems").  A fusion category is a type of tensor category which generalizes both Rep(G) and Vec_G, the latter being the category of vector spaces graded by a group G (so it's Groethendieck ring is the group algebra kG).  These are tensor categories which are semi-simple and have finitely many isomorphism classes of simple objects.  Each simple object has a notion of dimension, called Frobenius Perron dimension, and the categories themselves have a dimension associated to them, such that in the two cases Rep(G) and Vec_G, the dimension of the category is |G|.
While I don't know of Sylow theorems for fusion categories per se, there are many familiar theorems, saying e.g. that every fusion category of order p^k is nilpotent, and classifying groups of small orders p, pq, pqr, p^k, etc.  There is also a version of Burnside's theorem stating that every category of dimension p^aq^b is solvable.  It's quite possible that there are some analogs of Sylow's theorems in this direction.
I'd recommend "On Fusion Categories" http://arxiv.org/abs/math/0203060, by Etingof Nikshych and Ostrik, which introduces many of these ideas.  More extensively, there are course notes from a class Etingof taught on this, which can be found on his webpage, http://math.mit.edu/~etingof.  Papers by various subsets of (these three, union Gelaki) introduce the concepts and claims I mentioned above.
As Scott mentioned, this kind of abstract nonsense won't help much with prelims questions, most likely, but might make for a fun distraction =].
Answer: One of the simplest consequences of Sylow's first theorem is the Cauchy theorem, saying that
a group of order divisible by a prime $p$ contains an element of order $p$.
I'd like to point out that there is an analog of Cauchy's theorem for semisimple Hopf algebras, arXiv:math/0311199, which has been generalized to quasi-Hopf algebras (i.e., fusion categories with integer dimensions) in  arXiv:math/0601012.
Answer: Philosophically I think of the Sylow theorems as a statement about "localization of groups" at a prime.  For abelian groups one can make this precise, since abelian groups, as Z-modules, can be realized as sheaves over Spec Z and the stalk over p is precisely the Sylow p-subgroup (although for finitely generated abelian groups these are trivial to describe).  The hard part would be trying to carry this picture over to general groups.


Why is fractional statistics and non-Abelian common for fractional charges?

Question:
Why non integer spins obey Fermi statistics?
Why is fractional statistics and non-Abelian common for fractional charges?
Answer: Both  fractional/non-Abelian statistics and fractional charges
come from the same origin: long-range entanglements.
This is why fractional/non-Abelian statistics common for fractional charges.
One way to realize long-range entanglements
is through the string-net liquid phase of a pure bosonic model.
The ends of strings in string-net liquid are non-local and are topological defects. They can have fractional statistics. The ends of strings can also carry fractional charges/spins due to the same reason: the ends of strings are non-local and are topological defects.
My recent paper explains such a phenomenon in simple terms. See also  Topological Charge. What is it Physically?
Answer: Half-integer spin particles obey Fermi-Dirac statistics and integer spin fields obey the Bose-Einstein statistics – it's true because of Pauli's spin-statistics theorem.
Concerning the second question, I suppose you meant fractional spin, not fractional charges. In the case of 2 spatial dimensions, the trajectory of one particle around another is non-contractible (if we allow to cross the other particle) so even 2 rotations fail to return us to the original state. That's why the wave function may change by more than by the sign: it may pick a general phase (fractional statistics) or it may even be multiplied by some general unitary matrix (non-Abelian statistics). See Fractional statistics on Wikipedia.


Classifying spaces of topological categories

Question: I try to understand and compare the following facts about maps into classifying spaces of topological categories. Consider first the following definition cited from Moerdijk's Classifying Spaces and Classifying Topoi.
A linear order over a topological space $X$ is a (set-valued) sheaf $L$ on $X$ (also known as etale topological space) together with a subsheaf $\mathcal{O} \subseteq L\ \times_X\ L$, such that for each point $x \in X$ the stalk $L_x$ is non-empty and linearly ordered by the relation
$$
y \leq z \quad iff \quad (y,z) \in \mathcal{O}_x
$$
This defines a simplicial topological space $N_{\bullet}$ with
$$
N_m(L) = \{(y_0, \dots, y_n) |\ y_0 \leq \dots \leq y_n\ in\ L \}
$$
Now let $\mathcal{C}$ be a category internal to topological spaces. A morphism of linear orders is a map of sheaves which restricts to an order-preserving map on the stalks.
An augmentation of $L$ is a map of simplicial spaces $N_{\bullet}(L) \to Nerve_{\bullet}(\mathcal{C})$. A morphism of augmented linear orders is a morphism of linear orders that respects the augmentations. The category of augmented linear orders will be denoted by $Lin(X,\mathcal{C})$. Two elements of this category will be called concordant if there is an augmented linear order over $X \times [0,1]$, such that it restricts to the given ones over the endpoints. Denote by $Lin_c(X,\mathcal{C})$ the concordance classes.
The last theorem in Moerdijk's book says:

If $\mathcal{C}$ is a locally contractible topological category and $X$ is a CW-complex, then there is a bijection
    $$ [X, B\mathcal{C}] \cong Lin_c(X,\mathcal{C}) .$$

There is another result about maps of this kind, which is quite similar and can be found in a paper by Baas, Bökstedt and Kro and says

Assume that $X$ is a CW-complex and $Z_{\bullet}$ is a good simplicial space, then geometric realization induces a bijection $$Con_{Z_{\bullet}}(X) \cong [X, |Z_{\bullet}|] $$

where the elements of $Con_{Z_{\bullet}}(X)$ are given by maps of simplicial spaces of the form $\mathcal{U}_{\bullet} \to Z_{\bullet}$, where $\mathcal{U}_{\bullet}$ denotes the ordered Cech-complex as a simplicial space build from an ordered open cover of $X$. Taking $Z_{\bullet}$ to be the nerve of $\mathcal{C}$ we get a bijection
$$
Lin_c(X, \mathcal{C}) \cong Con_{Nerve(\mathcal{C})_{\bullet}}(X)
$$
for nice enough topological categories $\mathcal{C}$.
After this lengthy explanation here is my question:

Since you can cook up a linear order from an ordered covering of $X$ there is a map $$Con_{Nerve(\mathcal{C})_{\bullet}}(X) \to Lin_c(X, \mathcal{C})$$ which should fit into the setup described above.
    So somehow it seems to be the case that every linear order is concordant to one coming from an ordered covering. Is this true? Can this be proven directly?
EDIT: Can I prove directly that the above map is a bijection, i.e. does every augmented  linear order come from one induced by an open covering?
Answer: Let $L_0$ and $L_1$ be two linear orders over $X$ (I think of these as being the etale space). Let $L'_0 = L_0 \times [0,1)$, which is an etale space over $X \times [0,1]$; let $L'_1 = L_1 \times (0,1]$ which is another etale spacer over $X \times [0,1]$.
Define $L = L'_0 \coprod L'_1$, with the order relation that everything in $L'_1$ is larger than everything in $L'_0$ (in each fibre). This is a linear order over $X \times [0,1]$, so a concordance from $L_0$ to $L_1$. This shows that any two linear orders are concordant. In particular, the result you wanted follows immediately.
Comment: Thank you! This seems to solve the case, where $\mathcal{C}$ is the category with one object and one morphism (i.e. where there is no augmentation). Or is this also the answer to the general case? I clarified the question a little.
Comment: No, it doesn't. I had misunderstood your question.


Matrix with linearly dependent columns

Question: Is there an example of a $3\times 3$ matrix $M = [v_{1}\, v_{2}\, v_{3}]$ (where $v_{i}$ are $3 \times 1$ vectors) such that $v_{1}, v_{2}, v_{3}$ are linearly dependent however if we have $av_{i} + bv_{j} = 0$ then $a, b = 0$ for each $(i, j)$ pair?
Answer: Yes:
$$v_1 = (1,0,0)$$
$$v_2 = (1,1,0)$$
$$v_2 = (0,1,0)$$
Answer: Yes, $v_1=[1,2,3]$, $v_2=[3,2,1]$ and $v_3=[4,4,4]$. Clearly the three vectors are dependent. However it is trivial to check that pairwise they are independent.
Answer: In general, any three vectors that span a two dimensional space, but such that there is no vector a multiple of another.
For a subset of two such vectors will still span a two dimensional space, hence be linearly independent.
Both other answers fall in this category.

Matrix with linearly dependent columns


SharePoint Foundation search scope

Question: Is there any way to create a scope for searches in SharePoint Foundation or am I stuck with the out-of-the-box features?
Answer: If you have SharePoint Foundation, you will need Search Server Express 2010 to be able to take advantage of the more advanced search features like scopes.  Search Server Express will essentially deploy a simplified version of the service application available with the full blown SharePoint Server.
Here is the url to Search Server Express with requirements and download info.
Answer: Foundation search is restricted to the site collection or list / library that the user is in.
These boundaries are removed when moving up to SharePoint Server.

SharePoint Foundation search scope


Why re-pitch light to dark?

Question: It is often said that, when re-pitching yeast, you should generally go from low- to high-gravity, and dark to light beers.  When I repitch, I use trub directly.  I understand why using a yeast from a high-gravity fermentation is ill-advised, since the yeast has been stressed, but why go light to dark?  Is this just a matter of color?  If so, how much darkening would you expect to get when brewing, say, an APA after a stout?
Answer: There is no reason...that's an old, disproven myth.  I've gone from dark to light many times without any problems.  The theory is that as you mention you'd carry over color.  There's so little color carried over that it's unnoticeable.  For example, I've pitched yeast from a dunkel into a pils and not had it darken the pils.
Answer: it's about transferrence of color and to some extent flavor. Even though the slurry is heavily diluted, by 20 times or more, you wouldn't want coffee or caramel notes transferring from your dunkelweizen into your hefeweizen. I depends on the beers, and how much of the previous cake you're reusing.
With brewing on top of the yeast cake, there definitely is some carry over. To avoid it, collect some slurry, let it settle and pour off the beer on top before pitching. The amount of transferrence is then much less, and can be considered a non issue.
If you want to figure out why it's a non issue, consider that you're pitching a dense slurry, say 250ml / 10oz. Of that, let's say half is still beer and the rest is trub/yeast. That's 5oz of beer from the previous batch being repitched into 5 gallons, which is a dilution ratio of about 120 fold. With a very dark stout of 50L that would give you about 0.4L color difference. For more moderate beers, the color change and flavor transferrence is tiny.

Why re-pitch light to dark?


Self-closing vs.self-deleting

Question: What are the circumstances which determine whether a question Asker can close or delete his question? If the Asker hasn't got a good answer even after setting a bounty, should he delete his question or just close it? What happens to the reps in this case?
Comment: See: http://meta.stackexchange.com/questions/5221/what-can-cause-a-post-to-be-deleted-and-what-does-that-actually-mean and http://meta.stackexchange.com/questions/5215/etiquette-for-closing-your-own-questions
Answer: That's all pretty hypothetical isn't it?
Normally you'd assume you only ask a question because you want an answer and have a vested interest in doing your best to get an answer. So that means no, you should not be deleting it because you'd would want to wait to get an answer even if it takes a long time.
Besides, even if you learn to live with it or find an alternative solution, the eventual answer might still benefit someone else.
If your question is very localized, for example because you corrupted your OS and that was causing the issues and reinstalling the OS fixed it. In that case getting the question closed would be appropriate.
So really what you should ask yourself: "Does this question provide a lasting value to somebody on the internet?" If the answer is yes, then you should not delete it.
So posts with varying degrees of poor quality would not pass that test and therefore could or even should be deleted to keep things clean
Answer: Neither. A question's asker cannot delete a question after answers have been posted or a bounty has been offered. In the case that a question was asked and is fundamentally flawed (but isn't obvious from the perspective of the community) but has received answers, you can flag the question for moderator attention and explain why it should be deleted.
In any case, though, unless the question is just plain nonsense, consider leaving it and allowing the community to maintain it; if it's not suitable, it will be closed and likely ultimately deleted. Otherwise, it could still help someone else solve a problem.
If the issue is simply that the question hasn't gotten any answers, then leave it. Like above, if it's too narrowly scoped, it'll probably end up closed. If not, it will fall into the dungeon of unanswered questions and get occasionally popped to the top, or someone may search and find it.
Comment: do u mean questions without bounty cannot be deleted
Comment: @refhat: Sorry, no; bounty questions cannot be deleted. I've corrected that oversight.

Self-closing vs.self-deleting


Best practices for keeping UNIX packages up to date?

Question:
How do you keep your servers up to date?
When using a package manager like Aptitude, do you keep an upgrade / install history, and if so, how do you do it?
When installing or upgrading packages on multiple servers, are there any ways to speed the process up as much as possible?
Answer: On Linux/Debian based systems, cron-apt is a very handy tool that can manage automating apt via cron.
I'm using it to apt-get update every day and send me an email if new updates has to be installed.
Here's a short and well-done introduction on that tool.
Comment: I like to have the minimum of auto-updated packages and the important ones are the security updates. For this reason, I add the following to the cron-apt config file:

`OPTIONS="-o Dir::Etc::SourceList=/etc/apt/security.sources.list"`

and then make /etc/apt/security.sources.list have just the Debian security repositories enabled. That way, I get all the security updates automatically installed in a timely manner (each night) and I can do other, riskier upgrades that might break things by hand.
Answer: Regarding your third question: I always run a local repository. Even if it's only for one machine, it saves time in case I need to reinstall (I generally use something like aptitude autoclean), and for two machines, it almost always pays off.
For the clusters I admin, I don't generally keep explicit logs: I let the package manager do it for me. However, for those machines (as opposed to desktops), I don't use automatic installations, so I do have my notes about what I intended to install to all machines.
Comment: wow; is everyone upvoting because I'm so brilliant, or are people racing to get a badge? ;)
Answer: Similar to cron-apt, I use apticron.
Answer: I use apt-history for history. I've no idea why this useful tool isn't included by default, it's the first package I deploy with puppet.
Comment: How does apt-history differ from what's recorded by default in /var/log?
Comment: I wasn't aware of what you're referring to (from your answer); I guess I got to know apt-history and accustomed to it.
Answer: I run /usr/bin/apt-get update -qq;/usr/bin/apt-get dist-upgrade -duyq as a cron job every night.  In the morning I have notification of what packages need to be upgraded, and the files have already been downloaded on the machine.
Then I typically take a snapshot of the machine (most of our servers are virtual), do an apt-get dist-upgrade, check nagios and ensure everything is still working, and remove the snapshot.
Finally, I keep a running list of all changes made to every server on a wiki, in order to track any problems that arise later.
As far as limiting redundant downloads, I understand that you can set up a cacheing web-proxy (squid?) between your servers and the internet that will cache the .deb files the first time they are accessed.  Perhaps this is simpler than setting up a local package repository - and has the added benefit of speeding up general web browsing.
Answer: apt-cacher is handy for caching packages, it'll cache the first time they're needed rather than completing a full mirror of the entire repository thus saving disk and bandwidth.  It's also handy as it streams the first request of a package direct to the requester while caching it at the same time so there's no additional delay.
Answer: Running a local repository is the best way to manage exactly what's on your local servers.  It also lets you easily deploy custom backports or custom local packages.  I've been known to make local 'meta packages' that are just a huge ilst of dependencies to make a local install easy. (eg. 'apt-get install local-mailserver').  This has the side effect of also letting you 'version' your config changes.  (For more complicated config managment you'll need something like Puppet)
Answer: For our Windows boxes we have a local WSUS server, and a standard window to apply the monthly patches.  For the Linux systems (RHEL) we have a RHN satelite server on campus that they are all joined to.  That provides a nice dashboard of every joined system that you administer, as well as the unapplied updates for each system.  For those that are in puppet, we push out a script that auto applies patches during a regular window and sends an email notification with the results.
Answer: You can have a local repository and configure all servers to point to it for updates. Not only you get speed of local downloads, you also get to control which official updates you want installed on your infrastructure in order to prevent any compatibility issues.
On the Windows side of things, I've used Windows Server Update Services with very satisfying results.
Answer:
When using a package manager like
  Aptitude, do you keep an upgrade /
  install history, and if so, how do you
  do it?

apt keeps a log in /var/log/apt/, and dpkg uses /var/log/dpkg.log. dpkg in particular is fairly parsable.
Answer: On OpenSuSE Linux, SLES, and Novell OES (all SuSE-based products), we've got a script that runs zypper and looks for packages that need to be updated. When it finds one, it submits a ticket to JIRA and assigns it to the sysadmins. When we install the updates, we close the ticket, which leaves an audit trail that tells us when it was installed and by whom. This can be reconciled/confirmed with the zypper and sudo logs, which are centralized on a syslogging server.


Why can some Facebook users currently be messaged, but not others?

Question: According to Facebook's current messaging policies, all users should be capable of receiving messages. However, when viewing some profiles, belonging to Friends of Friends or non-Friends, while logged in with my account, the "Message" button is missing. Also, mail sent to such users' Facebook email addresses bounces back. My account has not been blocked by these users.
Answer: In the case when you are NOT fb friends already, it will depend on the privacy setting of the profile owner. E.g. they can make their profile searchable/non-searchable, and in case of searchable, they can also set if they will allow strangers to message them. My profile is set up in this way, so if people want to be friends and they know me, they can just message me to indicate the interest.
Answer: They can Block that option ( to receive messages from other people but your friends, or certain friends) from Privacy settings.
Answer: Previously, users had an option in privacy settings to control who could send them a message.  Facebook is rolling out a change that will allow messages to be sent to everyone, although if the message is not from a friend the message may go into the "Other" section of messages and no notification may be received (unless the sender pays a fee of $1 to $100).  If you are attempting to send a message to someone that does not yet have this change and they have previously restricted this privacy setting then the Message option may not be available.


Network Access - SonicWALL VPN options

Question: Does the built-in VPN client connect to SonicWALL?
Comment: What VPN protocol does your device use?
Answer: "The client side is set up in the usual fashion" - I've had different results due to Firewall Unique Identifier. At least on a Mac OS X 10.8 client.
The SonicWall configuration guide (Equinox document SonicOS_Standard-6-EN.pdf) clearly states a need for Firewall Unique Identifier. It's "Item 1" in things to write down and have users enter into the client software.
Firewall Unique Identifier appears to be a non-standard extension (its not discussed in RFC 2409). Fortunately, Equinox sells VPN Tracker Personal for $130. I believe that's known as Vendor Lock In.
Answer: Yes you can set up the sonnicwall to work with the built in L2TP vpn client.
You are a little short on config options but it works for most setups.
You have to leave the WANGroup profile on the sonnicwall as standard for its ipsec setup.
You need to make note of your shared secret for the WANGroup profile.
Then turn on the L2TP vpn section on the sonnicwall.
Set up a local ip address range for the l2tp users and make them of a group that has access. (trusteed users is a good default)
Next in the PPP tab of l2tp setup please make sure MSCHAPV2 is at the top of the lists.
The client side is set up in the usual fashion.
Should work fine.
In the client console if you see that Phase1 is not connecting check your shared secret.
If you need to change the WANGroup profile to work with other ipsec clients then you will not be able to make it work.
In that case you may be better working with the ipsecuritas software on the mac.
Hope that helps.
Comment: It did not work for me when I had MSCHAPV2 first on the SonicWALL (error: MS-CHAPv2 mutual authentication failed). Once I moved CHAP before MSCHAPV2 it worked. My client is Mac OS X 10.8
Answer: While I cannot definitively say for every model of Sonicwall, it's unlikely. L2TP over IPSec is(and has been) available, I've never heard of Sonicwall being able to take advantage of that built-in configuration.
You may know all of the following, but I'm throwing it out there anyway:
There have been three ways to connect to Sonicwall as VPN gateways in the past: the free IPSecuritas, the (paid) 3rd Party VPNTracker, or the (free) Java-based NetExtender SSL-VPN client that Sonicwall provides for some models that never was particularly optimized for a mac experience, but had basic functionality.

Network Access - SonicWALL VPN options


Change menu item order

Question: My primary navigation menu consists of pages, categories, and custom taxonomy. It appears to be in a random order. How do I adjust the order of the links? (the drag/drop in wp menus panel doesn't seem to have any effect)
Answer: This may depend on the theme you are using. Recent themes support the selection of primary of main menus and potentially other menus, go to yoursite.com/wp-admin/nav-menus.php and create a menu, then set it as the main menu, in the top left "theme locations" section. If you do not see this section then you need to enable it for your theme.
this gives you full control over hierarchy of your menu, what items are included and the order of the items.
Comment: I have it set as Main Menu under theme locations. So it would appear my theme supports it. (I'm using "Bones" theme if you are familiar. Moving them up and down is not reflected in the order on the front end up the site; though hierarchy is...
Answer: Turns out under my theme (Bones) bottom position is actually the first one to display on front end. I had it backwards.

Change menu item order


Chocolate-Flavored Cheese

Question: Would it be feasible to make a chocolate-flavored cheese?  The idea that originally occurred to me was the use of chocolate milk for this purpose, but I'm not sure that's the best solution.  Does this food already exist?  What kinds of cheese are doable in this situation?
Comment: Are you talking about making your own cheese, or flavoring existing cheese?
Comment: I've had many chocolate cheese cakes...
Comment: I've seen white Stilton with chocolate chips. There are better combinations with white Stilton.
Comment: @Jefromi- neither, as I know relatively little about the practice of cheesemaking and have yet to attempt it.  But I was referring to concocting a cheese from scratch.
Comment: It does already exist, yes.
Comment: I have had chocolate cream cheese (Philadelphia brand) from the supermarket. Don't know if it is generally available or just a seasnoal product, as I don't recall seeing it lately. Still, I wouldn't recommend imitating it, as I found the taste rather bad. (Maybe there are ways to make tasty chocolate cream cheese, but the manufacturer just used a bad one).
Comment: Trader Joe's used to carry a chocolate marbled cheese, FWIW. So it can be done. http://www.whatsgoodattraderjoes.com/2012/02/trader-joes-chocolate-cheddar-cheese.html
Answer: The other answers refer to products that are cheese-flavored fudges or cream cheeses blending with cocoa.
Your question seems like it is asking about making a cocoa flavored cheese from scratch.
I have not tried chocolate in particular but I have been experimenting with flavoring cheese (and tofu) and have some data points that might be helpful.
I have not had much success with flavoring the milk before it is curdled. The curdling and pressing process is designed to force out water and water soluble compounds. I would expect much of the cocoa dissolved in the milk to be wasted. Additionally, I wouldn't expect store-bought chocolate milk to work very well because of all the additional sweeteners, emulsifiers, and thickeners that are included. I don't know how it would behave when making cheese but I wouldn't be surprised if they got in the way of forming a good curd.
I have had more success with adding dry flavorings to the curd after it is drained and before it is pressed into the final shape. This is the same time that the salt is added. Some water is still pressed out and so some flavor is lost but much less than in earlier stages.
I am still experimenting with how much dry flavoring can be added before the curd doesn't set properly. The cheese becomes more fragile the more ingredients interfere with the milk proteins.
An easy way to start would be with a simple paneer or queso fresco. Simply heat up milk, stir in some acid (lemon juice, vinegar, citric acid, etc), let the milk protein precipitate out, strain it, mix in salt and some cocoa powder, and let the mass drain in a cloth until it is the consistency that you want.
Answer: When thinking of food combinations, I try to think similar combinations that exist already.
I'm sure I've had cheesecake with chocolate decorations.  Without a doubt, the flavor combination works in that type of food.  Likewise, I've also had chocolate cupcakes with cream cheese frosting, as well as chocolate cake-pops with cream cheese frosting.
If I had to generalize, I would say keeping the two flavors discrete (i.e. frosting has one, cake batter has another) seems to have better results.  I haven't heard of chocolate going with heavily salted (or otherwise flavored) cheeses, but this isn't to say that such a combination can't be done well.
Answer: I have tried chocolate cheese. It is Awesome! We bought it in Frankenmuth MI
Answer: http://www.shullsburgcheesestore.com/chocolatecheesefudge.aspx
It's OK, if you don't think of it as cheese.
Answer: I never actually tried it, but at Michigan State's Dairy store, they sell chocolate cheese.
From: http://dairystore.msu.edu/dnav/109/page.htm
This fudge-like delicacy blends the finest cheese with sugar, vegetable oil, peanuts, and chocolate powder.
Comment: Your link does not work. Is this the link you want: http://dairystore.msu.edu/products/cheese/chocolate_cheese_confection ?

Chocolate-Flavored Cheese


Checking whether my private members access my Google Site or not?

Question: I am creating a private Google site page for a university project, and only my project's teammates can access the site. (of course) But I want to make sure that everyone participates by coming to the site. Is it possible to check whether your private members access the site or not?
Answer: There's no automatic logging of the specific users that visit your site. You can, however, get general metrics from Google Analytics. If you need to know whether people visit a page, you could try requesting an action by all users which is logged. For example, they could comment on the page or submit a form.


Ubuntu won't appear on laptop startup

Question: I've recently installed Ubuntu along with Windows Vista.
So normally when the laptop is starting up it shows two options whether I want to log on Windows or Ubuntu. One day I shut down the laptop and I open it the next and it just logs onto Windows automatically without giving me the option to choose.
I go to check if Ubuntu was un-installed or something, but it was still there and everything, but I can't open it.
I don't know if there's any additional info I should add because I'm not very good with computers, and I don't want to re-install it because I have my stuff on it so I'd lose it, and I'm having trouble backing it up.
Any suggestions?
Answer: Check the bios for startup alternatives. Press F12 (or whatever key that takes your computer to the BIOS settings) and check your startup/boot alternatives.
Comment: I tried that as well, didn't work.
Answer: For some reason i don't know, looks like your MBR(Master Boot Record) has changed and replaced GRUB with Windows.
There are a few steps you can follow to recover the ability to boot Ubuntu again.
1) You need a DVD or a USB stick with Ubuntu into it. Boot the laptop from it. Choose to run, not to install Ubuntu.
2) Once there, check if all your data is there. Open Nautilus, the file explorer and look for you partitions.
3) Next open Terminal and run this command: sudo fdisk -l. It will show all available Hard Disks and partitions in you laptop. Choose the one you have installed Ubuntu. If you don't know which one, just post the results here and we will help you.
4) Only do this step if you know which partition contains Ubuntu! Run this on Terminal: sudo mount -t ext4 /dev/sdaX /mnt. Where sdaX is the partition number Ubuntu is in, and ext4 is the default file system.
5) Then run this last command: sudo grub-install --root-directory=/mnt /dev/sda
Any questions just post the results here.

Ubuntu won't appear on laptop startup


Can I freeze stock and can later?

Question: I have a lot of frozen stock and need to free up freezer space. Can I thaw and then can this stock in a pressure cooker?
Comment: Absolutely no issue doing this.... No issues there whatsoever...
Comment: Out of curiosity, why do you say a pressure cooker specifically?
Answer: If it was frozen immediately or quickly after coming off the heat, then it's not much different from "fresh" stock. Food keeps indefinitely in the freezer, safety-wise, and the quality isn't going to be impacted very much because it's mostly water to begin with.
Just don't can any meat products that have been exposed to room temperatures for more than 2 hours, and follow the same safe canning practices (i.e. pressure-canning) that you would for any low-acid product.
Answer: The Food and Safety Inspection Service division of the USDA has this to say about refreezing foods:

Do not refreeze any foods left outside the refrigerator longer than 2 hours; 1 hour in temperatures above 90 °F.

I would apply the same rule of thumb to canning previously-frozen stocks, as the purpose of canning is largely the same as freezing--to preserve food for long periods of time.  The only difference is that freezing attempts to halt biological growth by suspending water molecules in a solid state, which prevents most biological life from reproducing.  Canning attempts to halt biological growth by removing/limiting the amount of oxygen available.

Can I freeze stock and can later?


Want to do some damage control

Question: I applied for a job in a company. The initial conversation went well.They sent me an assignment and asked me to write a web application, and send it in a specified time. It seemed fairly simple. I completed and sent it to them. Now my mind is completely revolving on the code that I wrote, and now I feel that, there was one small requirement which I did not fulfill. Before they give the verdict shall I be proactive and admit it. Definitely they will find it and I am certain of it. I can send them email saying that I forgot to add that.
What shall I do? Is there anything I do for damage control?
Answer: Honestly just forget about it. I doubt they will care that you missed one small bit. The purpose of the exercise was to ensure in general terms that you knew what you were doing. Keep applying for other jobs and don't get too fixated on this particular job.
Comment: +1 I agree, don't short sell yourself. It is an honest mistake, that's why we have customer acceptance tests. Be open to feedback if they come back to you with it.
Answer: I'm all for being proactive and telling them about it. If I were the one looking at your code and I noticed an unfulfilled requirement, it would say something important to me that you not only realized the error on your own, but that you were willing to do something about it.
Answer: Might as well admit you forgot one of the requirements. If you are certain they will notice, then you have nothing to lose. They might appreciate you being forthcoming about it and if they don't, then it's better that you don't work there.
Answer: You are leaving out some pertinent details.  Was there a time crunch and that is why you forgot the item?  Did you just think it's a simple app and didn't take the time to write your design down before and reviewing it before sending it in?
What I'm sensing is too much emphasis on something that is already done with.  If you forgot something, let them know, but explain why with a plausable explanation.
Are you quitting the field if you don't get this job?  Do your best whenever you can, but don't let this slow you down or stop you.
I would express the truth, your desire for the position, hope for the best and move on to the next position if it doesn't pan out.

Want to do some damage control


File from Ubuntu to phone?

Question: I am looking for an app  that works similar to "Chrome to Phone", but for file transfer from a desktop. With a right click on a file you can choose "Send to phone" and an application on your Android phone will see it and receive the file. Does anyone know a solution? And does it work on Ubuntu Desktop? And if it doesn't exist; What is the best alternative to send a file to my phone through the internet and without Bluetooth or a USB cable?
Comment: possible duplicate of [Quickly send file from phone to PC via internet?](http://android.stackexchange.com/questions/3774/quickly-send-file-from-phone-to-pc-via-internet)
Answer: You could also use a browser based remote desktop tool like Airdroid or Remote Web Desktop
Answer: An alternative to the Dropbox way of sharing files is Ubuntu One
Answer: I use FTP file transfer using FileZilla. Its easy,secure, and offers decent data transfer rates. So you don't need Bluetooth or a USB cable to store and retrieve stuff from your device. There's a software called Software Data Cablethat allows you to transfer data wirelessly from and to your device using FileZilla. Using both of them together is simple. Hope this helps.
Answer: I don't know of any shell utilities that will let you just right click and send, but for transferring files to/from my device in general I am a huge fan of Files Anywhere plus it can send/receive faxes from your phone.  You can upload files from your machine via their web interface, then download using the app.  It's a free service, too.  For Ubuntu, you might be able to write a shell script incorporating this and then add it to your right click options.
I reviewed Files Anywhere on my blog some while ago if you want to read more about it.
If you just want to transfer files while on your LAN and you're using wifi, Samba Filesharing works super well.  You can just browse to your phone's SD card like it was a regular network samba share from your desktop.
Answer: I use Dropbox for that.
Answer: You could use Bluetooth to send it; use your Ubuntu system to do the sending and just make sure that Bluetooth is activated on your phone.
Alternatively, connect your phone to your desktop via USB and change your phone's Connection Type to be Disk Drive and then mount the disk drive on your computer(my Ubuntu system does this automatically). Copy it over using the desktop's interface of your choice. Then when you disconnect your phone, use a file browser like Astro File Manager to open the file.
Alternatively, if you have somewhere to put the file, Astro can get it via either SFTP or SMB. If you have wifi in your house, then you would be able to access it via SMB. There are boxes provided for Server, Share, Domain, Directory, User Name, & Password. Or you could use a data connection, but that would involve both your ISP not blocking the needed ports(mine does), and sending your password in the clear over the open Internet.
Comment: OP specifically asked for solutions that don't involve BT or the USB cable
Comment: @Logos: I saw that and had started an edit, but could not finish due to time constraints and my schedule. The edit is now posted.

File from Ubuntu to phone?


Is it possible to connect to a Test Resource in HP ALM as a database?

Question: I know how I can connect to an Excel sheet as a database using the ADO objects, but as it is, I need to download the spreadsheet from Test Resources and store it locally.  How can I connect to the spreadsheet in ALM without downloading it from Test Resources?
Answer: If the file is available on the network you might be able to set up an DSN to use with and ODBC connection that you can use with the ADO objects.  Here are a couple references that might help
Connect to Excel using ODBC in C# - a basic example in c#
Unable to create DSN for Microsoft Office System Driver on 64-bit versions of Windows - some details around working around the 32/64 bit differences ins ODBC drivers for office.


Why do some liquid metals have anomalously-high surface tension/heat of vaporization ratios?

Question: In a didactic article, Victor Weisskopf estimated the size of molecules in a liquid from measurements of their surface tension and heat of vaporization. If atoms are exceedingly small, then only a small portion of them will be on the surface, so the surface tension will be small compared to heat of vaporization. If they are larger, surface tension will become more significant.
Specifically, he considers a molecule in the body of the liquid to have six bonds with neighbors while one on the surface has five. Boiling consists of breaking all bonds present while moving to the surface consists of breaking just one bond for each surface atom. With this, Weisskopf gets good estimates (within 10%) for the size of molecules/atoms of CCL4, Ne, and Ar. For water, his estimate too small by about a factor of two because water molecules are polar and can rearrange themselves on the surface to minimize energy, leading to a smaller surface tension and smaller estimate of molecular size.
However, he states that for Hg, Mg, Fe, and Cd the estimate for the atomic size comes out too big by a factor of three or so, meaning either the surface tension is anomalously high or the heat of vaporization is anomalously low. He says he doesn't know why this is the case, but I didn't find a response explaining it published in the journal.
Why does the estimate fail for these metals, and why does it give an atomic size too large, not too small? (It doesn't fail for all metals.)
link to article (behind paywall) http://ajp.aapt.org/resource/1/ajpias/v53/i1/p19_s1
Answer: Looks like the following article might be relevant: Fluid Phase Equilibria 283 (2009) 89–92.
The author offers some model that seems to be a good fit for a lot of elements. There is no data for Fe and Cd, the agreement looks good for Hg and fair for Mg.


How many copies of Mountain Lion does one App Store download get me?

Question: I understand that this is a pretty basic question but I cannot find a direct answer anywhere. I have two computers running Snow Leopard: a Macbook Air (2011, pre-thunderbolt) and MacBook Pro 2009, which can both run Mountain Lion. According to my programmer / Apple friend, I can download Mountain Lion once from the App Store and use it to upgrade both machines. Is this true? I'm using one 'account' I guess but it's still two different machines, but my (trustworthy) friend was insistent I could. I can't find confirmation in any of the reading I've done here or on the Apple website.
Comment: What leads you to think there is a limit? Also - are you having a problem or more curious about discussing the topic?
Answer: You can install Mountain Lion on several Macs, provided that you use the same Apple ID for downloading it on them.
The Mountain Lion License Agreement explicitly says:

Mac App Store License. If you obtained a license for the Apple Software from the Mac App Store, then subject to the terms and conditions of this License and as permitted by the Mac App Store Usage Rules set forth in the App Store Terms and Conditions (http://www.apple.com/legal/itunes/ww/) ("Usage Rules"), you are granted a limited, non-transferable, non-exclusive license:
  (i) to download, install, use, and run for personal, non-commercial use, one (1) copy of the Apple Software directly on each Apple-branded computer running OS X Lion or OS X Snow Leopard ("Mac computer") that you own or control.

You can read the license by clicking the Terms and Conditions link at the bottom of the App Store window (left of the FAQ currently) and searching the license for the words "product usage" (presuming your store's terms are in english).
Answer: There are two different questions embedded in your question.
One is about license: If you purchase Mountain Lion, how many machines are you licensed to install it on.
The second is about the actual file you download: how many times can you use it without having to download again.
Perhaps surprisingly, the answer to the first is simpler than the answer to the second. You are allowed, as the license says, to install Mountain Lion "directly on each Apple-branded computer running OS X Lion or OS X Snow Leopard ("Mac computer") that you own or control."
Can you do this without re-downloading the (rather large) file?
Yes, but…
You need to download the Mountain Lion installer, then make a copy of the installer onto some external media before installing the operating system. The installation procedure will, by default, delete the install file once it is done, meaning that you can download it from the store again without buying another copy, but unless you copy the file before installing, you can only use the downloaded installer once (a rather frustrating experience, given how long it takes to download).
Answer: Yes you can. The way I did it was simpler than some suggestions imply. I purchased it and directly downloaded it to one computer. Then when it came time to download and install on a second, I just went into the Mac app store the same way , clicked download. It says it is $19.99, but once you click to purchase and enter your apple ID, as long as you have already bought it on another computer under that Apple ID, it then gives you a message saying such, and that the download is free.


Samba NAS not showing in workgroup automatically

Question: I'm currently trying to setup my raspberry pi as a NAS. I would like it to be visable to anyone on my workgroup connected to the network.
Currenly it can be accessed should you go to \Ip-address although it will not show up automatically in the network.
I've tried looking everywhere for help on this, although I still think I have made a mistake in my conf file. I'm pretty new to this, but I understand that it should keep it simple although the default conf file does have alot of jargon,
Please can you help me setup a conf file which will share the folder on the network and show up for everyone connected without authentication.
This is my current conf file. My share is at the bottom labeled "share".
Thank you.
<code>[global]

## Browsing/Identification ###

# Change this to the workgroup/NT-domain name your Samba server will part of
   workgroup = WORKGROUP

# server string is the equivalent of the NT Description field
   server string = %h server

# Windows Internet Name Serving Support Section:
# WINS Support - Tells the NMBD component of Samba to enable its WINS Server
   wins support = yes

# WINS Server - Tells the NMBD components of Samba to be a WINS Client
# Note: Samba can be either a WINS Server, or a WINS Client, but NOT both
;   wins server = w.x.y.z

# This will prevent nmbd to search for NetBIOS names through DNS.
   dns proxy = no

# What naming service and in what order should we use to resolve host names
# to IP addresses
;   name resolve order = lmhosts host wins bcast

#### Networking ####

# The specific set of interfaces / networks to bind to
# This can be either the interface name or an IP address/netmask;
# interface names are normally preferred
;   interfaces = 127.0.0.0/8 eth0

# Only bind to the named interfaces and/or networks; you must use the
# 'interfaces' option above to use this.
# It is recommended that you enable this feature if your Samba machine is
# not protected by a firewall or is a firewall itself.  However, this
# option cannot handle dynamic or non-broadcast interfaces correctly.
;   bind interfaces only = yes

#### Debugging/Accounting ####

# This tells Samba to use a separate log file for each machine
# that connects
   log file = /var/log/samba/log.%m

# Cap the size of the individual log files (in KiB).
   max log size = 1000

# If you want Samba to only log through syslog then set the following
# parameter to 'yes'.
#   syslog only = no

# We want Samba to log a minimum amount of information to syslog. Everything
# should go to /var/log/samba/log.{smbd,nmbd} instead. If you want to log
# through syslog you should set the following parameter to something higher.
   syslog = 0

# Do something sensible when Samba crashes: mail the admin a backtrace
   panic action = /usr/share/samba/panic-action %d

####### Authentication #######

# "security = user" is always a good idea. This will require a Unix account
# in this server for every user accessing the server. See
# /usr/share/doc/samba-doc/htmldocs/Samba3-HOWTO/ServerType.html
# in the samba-doc package for details.
   security = share
   map to guest = Bad User

# You may wish to use password encryption.  See the section on
# 'encrypt passwords' in the smb.conf(5) manpage before enabling.
   encrypt passwords = true

# If you are using encrypted passwords, Samba will need to know what
# password database type you are using.
   passdb backend = tdbsam

   obey pam restrictions = yes

# This boolean parameter controls whether Samba attempts to sync the Unix
# password with the SMB password when the encrypted SMB password in the
# passdb is changed.
   unix password sync = yes

# For Unix password sync to work on a Debian GNU/Linux system, the following
# parameters must be set (thanks to Ian Kahan <<email@example.com> for
# sending the correct chat script for the passwd program in Debian Sarge).
   passwd program = /usr/bin/passwd %u
   passwd chat = *Enter\snew\s*\spassword:* %n\n *Retype\snew\s*\spassword:* %n\n *password\supdated\ssuccessfully* .

# This boolean controls whether PAM will be used for password changes
# when requested by an SMB client instead of the program listed in
# 'passwd program'. The default is 'no'.
   pam password change = yes

# This option controls how unsuccessful authentication attempts are mapped
# to anonymous connections
   map to guest = bad user

########## Domains ###########

# Is this machine able to authenticate users. Both PDC and BDC
# must have this setting enabled. If you are the BDC you must
# change the 'domain master' setting to no
#
;   domain logons = yes
#
# The following setting only takes effect if 'domain logons' is set
# It specifies the location of the user's profile directory
# from the client point of view)
# The following required a [profiles] share to be setup on the
# samba server (see below)
;   logon path = \\%N\profiles\%U
# Another common choice is storing the profile in the user's home directory
# (this is Samba's default)
#   logon path = \\%N\%U\profile

# The following setting only takes effect if 'domain logons' is set
# It specifies the location of a user's home directory (from the client
# point of view)
;   logon drive = H:
#   logon home = \\%N\%U

# The following setting only takes effect if 'domain logons' is set
# It specifies the script to run during logon. The script must be stored
# in the [netlogon] share
# NOTE: Must be store in 'DOS' file format convention
;   logon script = logon.cmd

# This allows Unix users to be created on the domain controller via the SAMR
# RPC pipe.  The example command creates a user account with a disabled Unix
# password; please adapt to your needs
; add user script = /usr/sbin/adduser --quiet --disabled-password --gecos "" %u

# This allows machine accounts to be created on the domain controller via the
# SAMR RPC pipe.
# The following assumes a "machines" group exists on the system
; add machine script  = /usr/sbin/useradd -g machines -c "%u machine account" -d /var/lib/samba -s /bin/false %u

# This allows Unix groups to be created on the domain controller via the SAMR
# RPC pipe.
; add group script = /usr/sbin/addgroup --force-badname %g

########## Printing ##########

# If you want to automatically load your printer list rather
# than setting them up individually then you'll need this
#   load printers = yes

# lpr(ng) printing. You may wish to override the location of the
# printcap file
;   printing = bsd
;   printcap name = /etc/printcap

# CUPS printing.  See also the cupsaddsmb(8) manpage in the
# cupsys-client package.
;   printing = cups
;   printcap name = cups

############ Misc ############

# Using the following line enables you to customise your configuration
# on a per machine basis. The %m gets replaced with the netbios name
# of the machine that is connecting
;   include = /home/samba/etc/smb.conf.%m

# Most people will find that this option gives better performance.
# See smb.conf(5) and /usr/share/doc/samba-doc/htmldocs/Samba3-HOWTO/speed.html
# for details
# You may want to add the following on a Linux system:
#         SO_RCVBUF=8192 SO_SNDBUF=8192
#   socket options = TCP_NODELAY

# The following parameter is useful only if you have the linpopup package
# installed. The samba maintainer and the linpopup maintainer are
# working to ease installation and configuration of linpopup and samba.
;   message command = /bin/sh -c '/usr/bin/linpopup "%f" "%m" %s; rm %s' &

# Domain Master specifies Samba to be the Domain Master Browser. If this
# machine will be configured as a BDC (a secondary logon server), you
# must set this to 'no'; otherwise, the default behavior is recommended.
#   domain master = auto

# Some defaults for winbind (make sure you're not using the ranges
# for something else.)
;   idmap uid = 10000-20000
;   idmap gid = 10000-20000
;   template shell = /bin/bash

# The following was the default behaviour in sarge,
# but samba upstream reverted the default because it might induce
# performance issues in large organizations.
# See Debian bug #368251 for some of the consequences of *not*
# having this setting and smb.conf(5) for details.
;   winbind enum groups = yes
;   winbind enum users = yes

# Setup usershare options to enable non-root users to share folders
# with the net usershare command.

# Maximum number of usershare. 0 (default) means that usershare is disabled.
;   usershare max shares = 100

# Allow users who've been granted usershare privileges to create
# public shares, not just authenticated ones
   usershare allow guests = yes

#======================= Share Definitions =======================

[homes]
   comment = Home Directories
   browseable = no

# By default, the home directories are exported read-only. Change the
# next parameter to 'no' if you want to be able to write to them.
   read only = yes

# File creation mask is set to 0700 for security reasons. If you want to
# create files with group=rw permissions, set next parameter to 0775.
   create mask = 0700

# Directory creation mask is set to 0700 for security reasons. If you want to
# create dirs. with group=rw permissions, set next parameter to 0775.
   directory mask = 0700

# By default, \\server\username shares can be connected to by anyone
# with access to the samba server.
# The following parameter makes sure that only "username" can connect
# to \\server\username
# This might need tweaking when using external authentication schemes
   valid users = %S

# Un-comment the following and create the netlogon directory for Domain Logons
# (you need to configure Samba to act as a domain controller too.)
;[netlogon]
;   comment = Network Logon Service
;   path = /home/samba/netlogon
;   guest ok = yes
;   read only = yes

# Un-comment the following and create the profiles directory to store
# users profiles (see the "logon path" option above)
# (you need to configure Samba to act as a domain controller too.)
# The path below should be writable by all users so that their
# profile directory may be created the first time they log on
;[profiles]
;   comment = Users profiles
;   path = /home/samba/profiles
;   guest ok = no
;   browseable = no
;   create mask = 0600
;   directory mask = 0700

[printers]
   comment = All Printers
   browseable = no
   path = /var/spool/samba
   printable = yes
   guest ok = no
   read only = yes
   create mask = 0700

# Windows clients look for this share name as a source of downloadable
# printer drivers
[print$]
   comment = Printer Drivers
   path = /var/lib/samba/printers
   browseable = yes
   read only = yes
   guest ok = no
# Uncomment to allow remote administration of Windows print drivers.
# You may need to replace 'lpadmin' with the name of the group your
# admin users are members of.
# Please note that you also need to set appropriate Unix permissions
# to the drivers directory for these users to have write rights in it
;   write list = root, @lpadmin

# A sample share for sharing your CD-ROM with others.
;[cdrom]
;   comment = Samba server's CD-ROM
;   read only = yes
;   locking = no
;   path = /cdrom
;   guest ok = yes

# The next two parameters show how to auto-mount a CD-ROM when the
#   cdrom share is accesed. For this to work /etc/fstab must contain
#   an entry like this:
#
#       /dev/scd0   /cdrom  iso9660 defaults,noauto,ro,user   0 0
#
# The CD-ROM gets unmounted automatically after the connection to the
#
# If you don't want to use auto-mounting/unmounting make sure the CD
#   is mounted on /cdrom
#
;   preexec = /bin/mount /cdrom
;   postexec = /bin/umount /cdrom

[share]
    path = /media/shares/data
    comment = Test Share
    writable = yes
    browsable = yes
    read only = no
    guest ok = yes

local master = yes
preferred master = yes
</code>
Comment: FWIW, I have a share defined with these same properties, and additionally `guest only = yes`, `available = yes` and `public = yes`. Put these in, restart Samba and see if it matters.
Answer: I see you've added "local master" and "preferred master" settings to the config file, presumably because you've seen that suggestion elsewhere. They need to be in the global section of the config file. The "local master" option is redundant, as "true" is the default value for it already. The "preferred master" value is likely what you need for it to trigger master browser elections on starting the service, however this can be dangerous for performance if you have more than one system on the network with this setting enabled.


Why geometrically four acceleration is a curvature vector of a world line? And what is proper acceleration?

Question:
Why geometrically four acceleration is a curvature vector of a world line?

Geometrically, four-acceleration is a curvature vector of a world line.
  Therefore, the magnitude of the four-acceleration (which is an invariant scalar) is equal to the proper acceleration that a moving particle "feels" moving along a world line. The world lines having constant magnitude of four-acceleration are Minkowski-circles. (Wikipedia)

And what is proper acceleration?
Answer: Curvature of a plane curve is defined as the (magnitude) rate of change of the unit tangent vector over the length of the curve:
$$\kappa =\left | \frac{d\mathbf{T}}{ds} \right |$$
This is a natural definition, because for example the curvature of a circle is just $1/r$, so when the circle is small it has large curvature and when it's big it has small curvature. The unit tangent vector, as you know, is just the velocity vector divided by its magnitude:
$$\mathbf{T}=\frac{\mathbf{u}}{|\mathbf{u}|}$$
Do a bit of calculus and you find that $d\mathbf{T}/ds =\kappa (s) \mathbf{N}(s)$, where $\mathbf{N}$ is the unit normal vector. So you can define $d\mathbf{T}/ds$ as the "curvature vector" of the curve which points normal to the curve and is scaled by the curvature.
In SR, the four-velocity $U^\mu$ is defined such that its magnitude is always $c$. Also, we tend to work in units where $c=1$, so the four-velocity is actually a unit tangent vector to the worldline. The four-acceleration, which is defined as $A^\mu = dU^\mu /ds$, is therefore the curvature vector of the worldline, the magnitude of which is the curvature.
Proper acceleration is just a fancy way of saying "the acceleration that you would be able to measure with an accelerometer." The magnitude of four-acceleration is always proper acceleration, so geometrically the proper acceleration of an observer is the curvature of his worldline.
Comment: Mostly a fair answer, IMHO; it could be more explicit on how to measure $U^\mu[ s ]$ and $s$ separately, in order to evaluate $d/ds[ U^\mu ]$.
But the last paragraph seems backwards. Instead, "what you read off a good accelerometer" is at best a covert, unspecific way of saying "magnitude of four acceleration $A^\mu := d/ds[ U^\mu ]$". At worst, "what you read off some accelerometer" is "not even wrong", w/o considering the definition of the quantity to be measured, and thus without a way of determining whether or to which accuracy the given accelerometer had been "good" in any given trial.
Answer: An object moving on an inertial path has a straight worldline in special relativity.  The four-acceleration then measures how non-straight the worldline is.
When gravity is involved, an inertial (free-fall) path may be curved due to gravity.  Four-acceleration still measures the acceleration relative to such a path, and proper acceleration is basically just that four-acceleration converted to a three-vector.  For example, a free-fall path in the vicinity of Earth would be, well, one in which you freely fall towards Earth's center.  Such a path has zero proper acceleration in the absence of other forces.  If instead you're standing on Earth's surface, your proper acceleration is radially directed away from the center of the Earth, with magnitude $g$.
Answer: this is why 4-acc is Geometrically curvature.
$$A^{\mu}=\frac {d^2x^{\mu}}{ds^2}+\Gamma_{\alpha\beta}^{\mu}\frac {dx^{\alpha}}{ds}\frac {dx^{\beta}}{ds}=0$$


Role of unit vectors in cylindrical coordinates

Question: I know how the unit vectors are defined in cylindrical coords. If I have a point P, how do I express it as a combination of the unit vectors uρ, uφ and uz. In the case of Cartesian coordinates this combination is linear. But what about cylindrical coords? Does such a combination exist for them?
And, BTW, could you suggest a simple Physics problem where the use of cylindrical coordinates is convenient or, in general, the reason to choose them?
Answer: skymandr has covered a useful application of cylindrical coordinates.  There are many problems with this kind of symmetry.
However, I must differ on one thing: the $\hat \phi$ unit vector doesn't enter into a position vector at all.  Any general position vector can be written as $\vec r = \rho \hat \rho + z \hat z$.  This is because the direction from the origin to any given point goes along only $\hat \rho, \hat z$.  However, the vector between two arbitrary points (that is, when one of the points is not the origin) may involve $\hat \phi$.
If you think about that statement even more closely, you might realize the expression for such a vector will be different depending on which point you choose to evaluate the basis vectors (because they change with $\rho, \phi$).  This is a feature absent in Cartesian coordinates but most coordinate systems do exhibit this behavior, and it's something you should account for.
Comment: This is a correct statement about the position vector. 'skymandr' is right about an arbitrary vector, which they appear to be concerned with. So there doesn't appear to be a disagreement.
Answer: Cylindrical coordinates is appropriate in many physical situations, such as that of the electric field around a (very) long conductor along the $z$-axis. Polar coordinates is a special case of this, where the $z$ coordinate is neglected.
As for the use of unit vectors, a point is not uniquely defined in the $\phi$ direction ($\phi +n2\pi$ maps to the same point for any integer $n$), but otherwise any point can be uniquely written as $\vec{v} = A\vec{\hat{z}} + B\vec{\hat{r}} + C\vec{\hat{\phi}}$, just as in Cartesian coordinates.
In terms of the Cartesian unit vectors, the cylindrical can be written:

$\vec{\hat{r}}=\cos\phi \vec{\hat{x}} + \sin\phi \vec{\hat{y}}$
$\vec{\hat{\phi}} = -\sin\phi \vec{\hat{x}} + \cos\phi \vec{\hat{y}}$
$\vec{\hat{z}} = \vec{\hat{z}}$


Is it Safe to enter Google Password in 3rd party apps?

Question: I would like to get a RSS reader application for my iPad.  It will need to be able to sync with Google Reader because I use Google Reader on my phone and at work.  However, I am concerned about providing my Google password to a 3rd party application.  If I enter my Google password in a 3rd party app, I am assuming that the app could easily send my password back to a home server, store it, and then do anything they want with it.  Is that not the case?  Do Apple or Google provide some kind of password hiding scheme so that 3rd party apps can use passwords without actually being able to see them?
Comment: This is my question too. Even using two step authentication, the iphone is already a trusted computer. The app could log into the google account and do a search for sensitive info and then send it back to the author.
Answer: If you're worried about it, my suggestion would be to use Google's 2-step verification on your account. Basically, when you're signing in to your Google account from an untrusted computer (one you haven't successfully signed in with before) then in addition to your password you will also need to provide a 6-digit code that can be generated by an iPhone app or texted to your phone. That way, even if your password is compromised, no one can log into your account without your phone.
For apps like RSS readers, Google also lets you set up randomly-generated one time use passwords to sign into those apps that you can revoke at any time.
Answer: How are the app ratings on the App Store? Anyone complaining of their password being stolen? Is the app popular? Using a third party app that ties into Google's API's is like any other app, and requires a degree of trust. If you have reason to not trust the app, don't use it...but realize, too, that your normal use of Google Reader isn't significantly more secure from attacks.
If you're concerned about encryption, those authentication tokens and passwords aren't sent in the open for any joe to read; It's as secure as you can hope for.


Thick, moist, fluffy, flavorful pitas

Question: Are there tricks for baking thick and fluffy pita bread?
The ones I make come out fine, with an even puff and nice pockets, but they are on the thin side.  I would really love to be able to make thicker ones, like those common in the Middle East.
Answer: I accidentally made a thick pita by simply rolling my pitas thicker.  In my experience, technique is king with pita.  The temperature of the oven (I bake at 450 degrees) and making sure to roll smoothly without any punctures in the dough, then place directly on the rack make perfectly puffy pitas every time.  The thickness of the dough surrounding the pocket is entirely dependent - in my case - on how thick I roll.  I use the lavash cracker recipe from Peter Reinhart's Bread Baker's Apprentice as my dough.
Answer: When using a pan on a stove top, cook bread for about 20 seconds to crust, then flip to start cooking. The crust helps to "hold onto the air" and get a pocket. Granted it won't puff like in an oven, but you will get more of a pocket.
As justkt says, roll the dough a bit thicker. It also helps to cook the breads on a pizza/baking stone (or unglazed tiles from the local hardware).
I use the recipe and method from bakers (Alford and Dugard, I believe) from an old episode of "Baking with Julia." You can probably find it online somewhere.
Answer: Mine have been coming out thicker and fluffier, but without a real pocket. The differences were using half bread flour, half all-purpose flour, and cooking on the grill on medium high heat with the lid down.
2 cups flour
1/2 cup warm water
1 tbsp honey
1 tbsp yeast
1/2 tsp flour

Thick, moist, fluffy, flavorful pitas


Is it efficient to install X/Lubuntu and use KDE/Gnome applications

Question: I often met people stating they want to install XFCE, Gnome or other desktop manager in order to get better performance. But as the conversation goes on, it appears they use plethora of apps from other desktop. Which means they have to install and run related librairies.
So is it interesting to install a « light » desktop manager if you use apps from different desktop ?
Answer: If you only "sometimes" use an application, which uses GTK or QT libraries, but usually don't use them, then it is worth it as the libraries are only loaded if one application uses it. Furthermore, most applications only use "some" of the libraries, not as many as the window manager itself might require to be loaded. And in addition to the libraries there are more things which a window manager loads, which are not loaded when using another window manager even with the libraries of this manager.
Finally you will for sure notice a faster bootup of your system when using a lightweight window manager.
Answer: You should try to avoid using, for example, KDE apps loading kde-modules (try, i mean; there's nothing wrong with them but the point of keeping the system light) There's nothing wrong with using Qt apps; for example, comparing Amarok and Clementine, they are similar apps but Amarok is based around KDE while Clementine is just plain Qt; and so on with Gnome apps, although as they are Gtk apps usually you will have less dependencies and libraies to load if you are in Xfce or Lxde.


What are my options to get an bird's eye view of the Niagara falls?

Question: What options do I have to see the Niagara Falls from a bird's eye view?
Answer: The views are pretty sweet from some of the hotels. Here's one from a room that cost me $25 extra for a "falls view room":

Really, it's from the room:

I'm pretty sure it was the Sheraton.
Update: since someone mentioned the Skylon tower, here's a shot (on a fairly old cellphone) from the restaurant.

Go up for dinner on a night they have fireworks, and you can see fireworks from above, which is very cool.
Comment: Based on the angle (and the window frames!) this looks like the old "Sheraton Fallsview" which is now the "Marriott Gateway on the Falls".
Comment: And at this time of year you can get some sweet, sweet deals on Niagara Falls hotel rooms.
Answer: You can do a helicopter tour, many tour agencies provide this kind of tour on both the USA and Canada sides. Prices are a little bit expensive ($110+) but it's worth every penny.
I picked up random tour agencies from Google search, one on the Canadian side and the other on the American side.

Furthermore, there is a skydiving center near Niagara falls, not sure if you will be able to see the falls from that high but you can give it a try for $299.
Answer: In addition to the hotels and helicopter tours that are already mentioned, it is also possible, to access one of the two towers that were built for that purpose:
The Konica Minolta Tower Center has a visitor platform at 99 meters and offers a view over the Horseshoes Falls.

A more popular option is the Skylon Tower that offers a really great view over all of the falls.
Answer: We stayed at the Crowne Plaza Hotel with a falls view room and we had great views of both the American and Canadian falls. We fell asleep watching the light show on both! Exceptional!


Conditional Probability

Question: Four fair 6-sided dice are rolled. The sum of the numbers shown on the dice is 8. What is the probability that 2's were rolled on all four dice?

The answer should be 1/(# of ways 4 numbers sum to 8)
However, I can't find a way, other than listing all possibilities, to find the denominator.
Comment: So list, perhaps using shortcuts. For instance there are $4$ patterns of the type 5-1-1-1.
Answer: Possibly brute force is nearly the best available option here.
\begin{align}
2+2+2+2 & & & 1 \text{ way} \\[6pt]
1+2+2+3 & & & 12\text{ ways} \\[6pt]
1+1+2+4 & & & 12\text{ ways} \\
1+1+3+3 & & & 6\text{ ways} \\[6pt]
1+1+1+5 & & & 4\text{ ways}
\end{align}
So you get $1/35$.
Answer: I proved a relevant theorem here ( for some reason this was closed )
Theorem 1: The number of distinct $n$-tuples of whole numbers whose components sum to a whole number $m$ is given by
$$ N^{(m)}_n \equiv \binom{m+n-1}{n-1}.$$
to apply this to your problem , you need to take into account that the theorem allows a minimum value of zero, but the dice show a minimum value of one. So you can just add one to each die so we are looking for the number of 4-tuples whose components sum to 4. I guess we are lucky that no element could possibly be greater than 6, so it will work for 6 sided dice.
The denominator is thus given by $$\binom 73 = 35 $$ which I have verified by enumeration.

Conditional Probability


Where can I find paying markets for flash fiction?

Question: I've written a great deal of flash fiction, < 1000 word stories. I know I can send them out to literary journals and online literary journals, but are there paying markets for this sort of thing?
Answer: There are very few, if any, paying markets for Flash Fiction. There's not really a large market for readers of flash fiction, so it's not worth the investment for most places to pay for them. A lot of authors usually only write flash fiction with the intent to give it away for free. It's a marketing tool. It gets the author's name out there and can get them readers for their paying fiction.
Answer: Not necessarily disagreeing with @Ralph's answer, but if you're interested in genre fiction you might want to search at Ralan's or Duotrope. (For example, Daily SF pays 8c a word for flash.)
Many markets have upper limits but not necessarily lower limits for word counts.
Answer: There are quite a few paying markets for speculative flash fiction.  Fewer for mainstream.  And when I say "paying," that can mean as little as $10.  However, look around and you'll find plenty of markets.  Here's Absolute Write's list, but it's not all inclusive.
Answer: I'm not familiar with markets that specialize in flash fiction, though these may exist. However, if you feel you've got a worthwhile, marketable story, I think most venues are happy to consider flash fiction submissions. So if there's a market that would be appropriate for a story "if it were longer," it might be appropriate as-is, as well.
I've seen stories that could be described as flash fiction in, say, The Magazine of Fantasy & Science Fiction. Flash fiction has a certain advantage in that it's short, and can be used as a sort of "filler," making it easier to juggle page count and not incurring much cost to bring aboard. On the other hand, as Ralph touched upon, many readers find flash fiction unsatisfying and uninteresting, and there may be a certain glut because (presumably) it's easy to churn out a lot of mediocre flash. My guess would be that in total, if it's very good you can probably sell it (eventually), and if it isn't then you probably can't. Just like pretty much any story :)
Answer: In my experience with self-publishing e-books, I have found that a lot of authors will use flash fiction or short stories as freebies to encourage people to buy their longer works. I also know several people who will sell their self-published flash fiction and short stories at a very low price, and then sell larger collections as the real breadwinners.


Conditional Probability

Question: I'm not liking this at all. Can't even figure a single thing out.
Question
In a $50$ group of people there are $15$ who are lefties and blonde, $15$ neither of them, and $20$ blondes.
A. Draw venn diagram.
B. One is chosen, calculate the probabilities of the person being lefty?
C. One of the lefty is chosen, calculate the probabilites of the person not being blonde?
My answers so far which are completely wrong.
A.
U = 15
$P(A\cup B) = 35$
$P(A\cap B) = 15$ (lefty and blonde)
$P(A)= 20$ (blondes)
$P(B)= 5$ (lefty)
B. No idea, I've tried $15/35 = 3/7$ can't figure out , I've been doing this for $4$ hours literally.
C. Same as $B$.
Comment: In a 50 group of people there are 15 who are lefties and blonde, 15 neither of them, and 20* blondes. 20 BLONDES INSTEAD OF 15
Comment: Correct it **immediately** in the question itself !
Comment: You can edit your question to show any changes: just click 'edit' in the bottom left corner of your question. Also, do the 20 blondes include the 15 who are blondes and lefties?
Comment: Doesn't include who they are, I guess it's only a one gender sided.
Answer: Lefties alone:$x$
Lefties & blondes:$15$
Blondes alone: $5$
Neither:$15$
$x = 50 - (15+5+15) = 15$
P(lefty) = $\dfrac5{50}$
P(blonde | lefty) = $\dfrac{15}{15+15}$

Conditional Probability


Dwarf Fortress Shell Shortage

Question: I have a dwarf that is demanding shells, but I have no fishable above-ground water. I've dug down to the first caverns and set some zones down there as 'fishable', and my fishermen fish for a while then report that there are no fish to catch. The zones on the surface have a 0 next to the 'fishing' option when zoning; the zones in the first cavern have a 1 or higher. Am I doomed to lose every dwarf that demands shells, or is there a way to get shells somehow that I haven't figured out yet?
Answer: Currently if you can't get shells from your map, they are doomed. An alternative is to mod another creature to drop shells and butcher it (dogs work well).
In the latest versions, only dorfs with a "shell fetish" will demand shells for their artifacts.
See the df wiki for more info.
Comment: Offer the maximum possible for turtles when your dorf liason comes calling.
Answer: You will see lots of experienced players bring 1-2 shells during embark to solve this exact issue. It may not help your current fort, but you can keep it in mind for the next one. Its definitely worth the tiny cost to keep that dwarf alive and get a legendary crafter.

Dwarf Fortress Shell Shortage


Role of skewness in portfolio optimization?

Question: What is the role of skewness in portfolio optimization?
Comment: This is a vague question. Do you have an actual issue you need solved? We try to limit the scope of this site to questions that affect professional quants.
Comment: Type of portfolio optimization? Skewness of what? Can you detail a bit your question? It would help clarify it.
Comment: @fred i want to discuss about my project with you can u plz give me some time?
Comment: what skewness actually say about the returns of some stock market?
Comment: I don't understand the question.
Comment: See this question it has good answers that may help  http://quant.stackexchange.com/questions/1557/how-do-i-calculate-the-skewness-of-a-portfolio-of-assets
Answer: There are many portfolio optimization paradigms that include a preference for skewness.  These are generally alternatives meant to replace the modern portfolio management mean-variance framework developed by Markowitz.  Skewness (or, more generally, higher moments) are only relevant in portfolio optimization if (a) assets are not normally distributed, and (b) agents have a preference for positive skewness above and beyond their preference for a higher mean and lower volatility.
One of the leading alternative paradigms which implicitly takes skewness into account is Conditional-Value-at-Risk Optimization.  Attilio Meucci has a (rather long) introduction to both classical and state-of-the-art portfolio optimization.  A google search for "skewness preference" also yields plenty of additional background on this topic.
A similar question on this topic is:
What is the relationship between risk aversion and preference for skewness and kurtosis in portfolio optimization?
Answer: the question is very broad, Here is the brief summary of the role of all moments in portfolio optimization:
expected value- the 1st moment represents the reward. All the even higher moments
represent the likelihood of extreme values. Larger values for these moments indicate
greater uncertainty. The odd moments represent measures of asymmetry. Skewness belongs to the second category so it represents the assymmetry. Positive skewness is desirable for investors.
Skewness affects the Utility of the investor through the skewness preference. however till recently the role of higher moments in portfolio optimization was ignored in the literature. One reason for this can be the difficulties in calcualting higher moments. Becasue, to calculate the skewness or kurtosis of the portfolio the number of co-moments should be calculated.The more assets included in the portolfio, the more number of co-momnets should be calculated. On this issue I would recommend the following papers: "Improved Estimates of Higher-Order Comoments and Implications for Portfolio Selection" by Lionel Martellini and Volker Ziemann and "Optimal Hedge Fund Allocation with Improved Estimates for Coskewness and Cokurtosis Parameters" by Lionel Martellini, Asmerilda Hitaj,and Giovanni Zambruno.
Answer: Assuming you're talking about optimizing a portfolio that has options included in its investment universe.
Skewness isn't directly modeled in the optimization, although many formulations involve using implied vol as the currency numeraire. (i.e. modeling the components of skewness, instead of skewness itself)
The main impact on the optimization though is that the type of solver used changes if you want to guarantee solution uniqueness/global optimality.  (Second order cone - solver).
However, this solver change is a result of simply having options in the investment universe, not from skewness per se.


Conditional Probability

Question: The inhabitants of Liarland tell the truth $40\%$ of the time. One-third of the inhabitants have six toes on their right foot.
You ask four inhabitants of Liarland whether the King of Liarland has six toes on his right foot. They've all seen the King's feet, since the King always goes barefoot, and they all say yes.
What is the probability that the King's right foot has six toes?

My train of thought, I believe, is oversimplified.
Since $4$ people are asked and there is a $40\%$ probability they are telling the truth, the probability is $(.4)^4$.
Answer: Let $A$ be the event the king has six toes on his right foot, and let $B$ be the event they all say yes. We want $\Pr(A|B)$, which by definition is equal to $\frac{\Pr(A\cap B)}{\Pr(B)}$.
What is $\Pr(B)$? The event $B$ can happen in two ways (i) the king has $6$ toes on his right foot, and they all tell the truth or (ii) the king does not have $6$ toes on his right foot, and they all lie.
The probability of (i) is $\frac{1}{3}\cdot (0.4)^4$, and the probability of (ii) is $\frac{2}{3}\cdot (0.6)^4$. Add.
Now you should find it easy to find $\Pr(A\cap B)$ and complete the conditional probability calculation.
Remark: In our calculation, we have assumed that the people lie or tell the truth independently, and that their choice of whether to lie or tell the truth is independent of toe facts about the king. So in answering the question, they each toss an appropriately weighted coin in order to decide whether to tell the truth or to lie.  We have also assumed, possibly unreasonably, that the probability the king has $6$ toes on his right foot is $\frac{1}{3}$.
Comment: $\dfrac{\frac{1}{3}\cdot (0.4)^4}{\frac{1}{3}\cdot (0.4)^4+\frac{2}{3}\cdot (0.6)^4}$. This can be simplified in various ways.
Comment: So what's the final answer?

Conditional Probability