Seeing The Light in a Black Hole

Question: I assume if light can't escape a black hole, then light is in a black hole. Does the light 'shine' inside a black hole
Comment: Could you please elaborate on your question? It's rather skimpy right now...
Comment: Could I simply say that your *assumption is wrong..!*
Comment: big ole meanies
Answer: This is really just an expansion on dmckee's answer, and if he wants to expand his answer I'll delete this one.
Anyhow, a light ray follows a path called a null geodesic. In flat spacetime this is just a straight line (or what we normally think of as a straight line) and the light can shine in any direction. So if you shine a torch at something the light can travel from the torch to the object then back to your eye, and you can see the object.
In curved spacetime light no longer travels in straight lines, which is why you get gravitational lensing. At the event horizon of a black hole the curvature is so intense that light can no longer move outwards. No matter which way you shine your torch the light always follows a path that moves inwards and eventually hits the singularity at the centre of the black hole.
So inside the event horizon a torch won't illuminate things. The light from the torch can only reach the object you're trying to see if the object is closer to the centre than the torch is. But then the light can't get back from the object to you. So you can't see things in the sense that you can use a torch to see things in a dark room.
However as twistor59 says in his comment to dmckee's answer, you can still see light from outside. If you have fallen past the event horizon you can still see the light shining from the outside world because you are nearer the centre of the black hole than the outside world is. So in this sense the answer is that yes, light shines into a black hole just as it does outside it.
If you want to pursue this further this blog posting gives a nice introduction and has useful links to more detailed descriptions.
Answer: We can't say for certain what happens to light in a black hole.  However, energy conservation doesn't dictate that light continues to shine, only that the energy doesn't disappear.  Consider light shining on a dark surface; the photons are absorbed, but their energy is converted to heat in the surface.
When light is absorbed into a black hole, the energy of the photon is added to the energy of the black hole, which increases the effective mass of the black hole.
Answer: Short-short answer: No.
From the horizon inward all geodesics point toward the center, so you can never see anything coming back toward you.
Comment: It depends what the OP meant by "shine inside the BH".  Light is "shining" in from the outside.  (There is also some HR from the past horizon, but I doubt that's what the OP was talking about).
Comment: @twistor59 Yes. I see what you mean.
Answer: Yes, light is shining there. If you would get into black hole and survive you would be able to see the light. However, there can be more space-time inside black hole than can be imagined. For example it can be the whole another Universe there. So, shining would not cycle there but would shine as usual.

Seeing The Light in a Black Hole


Why is random trading minus transaction costs not zero expected value?

Question: Somebody was telling me that if you buy randomly and assuming no transaction costs in todays market place, you wont make money 50% of the time and lose 50% of the time because of adverse selection. Im not quite sure I follow, does anyone know what this could be about?
Comment: Why don't you ask that person who told you this?
Comment: Would you consider the bid ask spread be considered a transaction cost? If not, a very simple counterexample could be provided. But I assume that is not what you are asking about?
Comment: @chrisaycock, good point, but I'm glad that Palace Chan asks the question here too because I'm also interested in the answer.
Answer: The first formal model to explain this was Kyle (1985).
Oversimplifying, imagine there is a group uninformed traders and an informed trader active in the market for a given security. Uninformed traders cannot make correct directional predictions. The informed trader knows --- with some uncertainty --- what the price will be at the end of a certain time horizon (e.g. he has inside information about earnings). The informed trader wants to profit maximally from his knowledge and achieves that by slowly trading in the direction he predicted. His profit will be equal to the aggregated returns of the uninformed traders.
Bottomline: As an uninformed trade, you trade randomly. If you are lucky, you counterparty is just as uninformed and if there are no transaction costs you stand a 50% of making a profitable trade. If you are not so lucky, you are ''adversely selected'' and your counterparty is an informed trader and your transaction will very likely a losing one. All in all, your returns from trading randomly will be less that the benchmark lucky case.
Several details need to be hammered out to make this intuition consistent, the most important ones are (1) that uniformed traders are noise traders and (2) how the interaction between these two groups and revisions to the price are mediated by a market maker. This intuition extends to toy models of the limit order book (for example, Rosu (2010)).
Answer: Assuming the following:

You consider bid/ask spread to be a transaction cost.
That you're interested in passive trading since you mentioned adverse selection.
As a random passive trader you simply place a bid to buy and an offer to sell at price $P$ and $P + Spread$, respectively.
You do no active order management and are therefore a naive trader with respect to order execution. You simply place your bid and offer and wait.

Given your question this would appear to be the only realistic scenario that makes sense. It would not make much sense to consider the case where you can, on demand buy at the bid and sell at the ask since it is impossible.
You can conceptually convince yourself that you will lose money given a random placement of passive, non-managed limit orders if you assume there are both informed and uninformed traders in the market.
First, define "adverse selection" as an uninformed participant trading with a more informed participant. An informed participant trades because he believes, rightly or not, that he has information relevant to the future price. As an uninformed trader you have no information that might impact your belief about the future price.
Second, consider that as a naive liquidity adder randomly placing bids and asks you will often only trade when it is worst to do so. Your bid at price $P$ will be hit with when the market is about to go down and your ask at price $P + Spread$ will be lifted when the market is about to go up.
Given this you'll typically start in a hole when comparing to the midpoint, having bought at the bid immediately prior to a tick down, or sold at the ask immediate prior to a tick up. This is why passive traders place a premium on queue position. The less orders in front of them the better, and the more orders behind them the better.
To illustrate, on average your starting unrealized $PnL$ for your bid order will be the future midpoint minus your current bid:
$PnL_{start} = P_{mid_{t+1}} - P_{bid}$
If you believe the above that the future midpoint, $P_{mid_{t+1}}$ will typically be below your current bid due to adverse selection, then you can see that you will always have a negative starting $PnL$ for the majority of your trades.
Answer: I would actually venture to say it will be very close to 50% over many transactions. Of course given you do not consider any transaction costs, meaning you buy and sell at the mid-point of cash equity traded prices, without slippage, or any other execution related expense. Also, my claim only holds if you consider cash equities, which are NOT a zero-sum "game". This assumption leads to the logical conclusion that even if there are "informed" (a.k.a. illegally acting on insider information) market participants in the market this does not necessarily stack the odds against a randomly picking trader. I am aware and have browsed through the papers which brought about "adverse selection bias" however, I find their cited empirical evidence very weak and do not believe that it necessarily means the rest of the uninformed traders trade at worse than 50% odds. The story can be quite different in options and futures markets. But regarding cash equities I would be very careful in supporting adverse selection. In that I would first like to make sure which asset class we are exactly talking about.
Comment: @down voter, care to comment on the down vote?


Parabolic induction for GL(2,Z/pn)

Question: Fix a finite extension $F$ of $\mathbb{Q}_p$. Consider its ring of integers $\mathfrak{o}$ with maximal ideal $\mathfrak{p}$. Set $R_n = \mathfrak{o}/\mathfrak{p}^n$. Let $\mathrm{B}$ be the upper triangular matrices. Consider a character $\mu : \mathrm{B}(R_n)\rightarrow \mathbb{C}^\times$. When is the induced representation $ \mathrm{Ind}_{\mathrm{B}(R_n)}^{\mathrm{GL}_2(R_n)} \mu$ irreducible?
Comment: I guess the exponent `$r$` here should be `$n$`?
Answer: A sufficient criterion for irreducibility is given, for example, in Theorem 4.6 in Hill: Semisimple and cuspidal characters of $\mathrm{GL}_n(\mathcal{O})$. Hill's result is more general, and holds for certain representations of $\mathrm{GL}_n(\mathcal{O})$, for $n\geq 2$. For $\mathrm{GL}_2(\mathcal{O})$ it says the following. Let $T$ be the diagonal torus, so that $T(\mathcal{O}_r)\cong\mathcal{O}_r^{\times}\times\mathcal{O}_r^{\times}$. Let $\theta=\theta_1\theta_2$ be a character of $T(\mathcal{O}_r)$, where $\theta_1$ and $\theta_2$ are characters of $\mathcal{O}_r^\times$. Suppose that the restriction of $\theta_1$ to $1+\mathfrak{p}^{r-1}$ is non-trivial, and that the restriction of $\theta_1$ to $1+\mathfrak{p}^{r-1}$ is not equal to that of $\theta_2$. Let $\tilde{\theta}$ denote the pull-back of $\theta$ to $B(\mathcal{O}_r)$. Then the representation $$\mathrm{Ind}^{\mathrm{GL}_2(\mathcal{O}_r)}_{B(\mathcal{O}_r)}\tilde{\theta}$$
is irreducible.
Answer: For PGL(2) I have the following reference :
Silberger, A.J. : PGL 2 over the p-adics : its representations, spherical functions, and Fourier analysis. Springer Lecture Notes in Mathematics 166. Berlin, Heidelberg, New York: Springer 1970
I don't have this book with me, but the basic idea is to apply Mackey's irreducibility criterion. For this you have to determine the double cosets of $G={\rm GL}_2 (R_u )$ mod $B=B(R_u )$. For $n=1$, just use the Bruhat decomposition. To get a set of representatives of the double quotient for $n>1$, you introduce the "Iwahori" subgroup $I$ of matrices that are upper triangular mod ${\mathfrak p}$. Then  $G=I\cup IwI$, where $w$ is the standard Weyl group element.  Next you have the following set of representatives of right (or left) $B$-cosets in $I$ : the lower triangular unipotent matrices with the coefficient varying over ${\mathfrak p}/{\mathfrak p}^{n}$.
Comment: In the end, I think the criterion would be that $\mu^{w}$ is not isomorphic to $\mu$.

Parabolic induction for GL(2,Z/pn)


Can't save anymore in Fallout:New Vegas for the PS3

Question: I'm on level 22 and I can't save manually any more - my save just goes over the last one. What do I do so I can save again? Do I have to delete saves? If so, how do I do it?
Answer: You should check your hard drive space, which you can do in the system settings on the XMB.  Then you should try to free up some space.  This you can do by deleting downloaded content, and installed game data.
In any case, you can also try deleting save games.  Go to the games menu, go up, find your saves, find the fallout folder, see the saves.  Press triangle, do to delete.  Do this as often as you like.
Answer: Well, you should always check your hard-drive space, but I doubt that is the problem simply because you would have experienced similar affects in other games.
You can only have a limited number of save files I believe (I think it's 1000, so I somehow doubt that's the problem either). It could possibly be the ps3, have you reset it recently? But to delete save files, go to save files at the top of game scroll, open it and press triangle, and a right sidebar pops up with a delete option. Please be careful if you decide to do that, I accidentally deleted one of my brother's saves once trying to remove a file to a game I no longer had XD.
Fallout is also just a really glitchy game (no offense to creators, I love the game, it just has some problems), so I suspect it's a glitch. I have gone through the game 3 times, and 2 of those times there was a serious glitch, such as once it took all my items and sent me back to the beginning, with everyone in that town dead (which I took their side against the powder gangers, so I don't know why). Sorry, I wish I could help more :/
Answer: To help the game run smoother, and got under the game category, go to Saved Data Utility, press triangle and select Delete Multiple. You can go through and find the Fallout game data, and delete old Profiles and saves you don't need anymore. If you want to make it easier on yourself, you can click "Sort By" and choose how you want to organize it, which makes it easier to find the fallout data.


What is the difference between vagrant and juju?

Question: Are they both solving the same problem? Or are they for two different sets of problems? If so for what i it better to use vagrant, and for what better to use juju?
Answer: quick version:
vagrant is a tool for working with virtualbox instances.  This is typically used during development (on a mac) to test-deploy your app into virtual machines that look more like your eventual production (i.e., linux) environment.  It's got a customizable (ruby) stack of handlers to create such a virtual environment any way you'd like.  Vagrant is a powerful tool to programmatically manage virtual environments and provides for all sorts of "local" variations of continuous-integration-style development techniques.  It's most often used to run Ubuntu VMs on a Mac, but will run on various platforms and deploy various target operating systems.  Afaik, it only works with virtualbox as an underlying "provider".
juju is a tool to orchestrate services using various different underlying providers: ec2 clouds, openstack clouds, lxc VMs, and MaaS servers.  It shares a "local development" story (using lxc containers instead of virtualbox VMs) with vagrant, but that's really the only overlap.  In fact, I'd like to see a vagrant provider written for juju so juju can drive virtualbox containers on a local environment with the same ease that it drives cloud and lxc images.  That'd be a great fit!  Also, juju really derives a lot of its value from the set of charms/services that can be spun up straight out-of-the-box, whereas vagrant's essentially a lower-level local container provider.
In fact we provide a Vagrant box with Juju so that users can test the local provider from within a VM:

https://jujucharms.com/docs/1.25/config-vagrant
https://www.youtube.com/watch?v=qLNPn2rQynM

Note that there have been efforts to "unify" deployment scripts around vagrant so that the same scripts can be used to deploy to cloud instances as well as vagrant boxes.  These appear to be mostly one-off asides from vagrant proper, and frankly just highlight the need for a tool like juju.
Answer: Re "unifying deployment scripts around vagrant", Vagrant has excellent integration with Puppet and Chef, which can be used to automation system configuration across environments, from Vagrant boxes to local hardware to clouds. In fact many people use Vagrant to test their Puppet/Chef scripts before using them in production.
It would certainly be nice to add Juju to the list of automation tools that work with Vagrant.


How do I get Ocean Sapphire without mining as a profession

Question: I'm in need of Ocean Sapphires to get from jewel crafting 520-525. I've bought what's left of them in the Auction House. I do not have mining as a profession and am not sure if it's possible to get them any other way.
Answer: If you have an alchemist, you can get them through transmutation of 3 zephyrite and 3 Azshara's Veil. Other than that, you are pretty much stuck with buying ore and prospecting it, which you can do yourself as a jewelcrafter.
Answer: If you are a tank or healer, you can also get gems through the short-supply reward when there aren't enough of these two roles queuing for dungeons.  You can also get them from lockboxes that can be pickpocketed if you are a rogue.  However, these are random rewards, so it might take a while to get them.
Answer: You'll also get some Ocean Sapphires from Fire Prism's, which is how I grinded out my last 5 points to max Jewelcrafting (bearing in mind this isnt really the cheapest way to get your last 5 points anymore, so check AH first). Note this is a once a day crafted item that resets at midnight accordingly.


Effective design analysis

Question: Our team redesigns the legacy software and there are a lot of design meetings going on. Many of them are not very effective and lack good analysis of the proposed design. Is there any formal way to approach this kind of discussions to make them more effective? I heard about SWOT for example, but afaik it is used more for business projects.
Answer: Might I suggest Martin Fowler's agile, if heretic, StranglerApplication, a method that reminds one of BranchByAbstraction.
What you probably want is to define a set of interfaces that speak your business story, all the while ignoring the existing code, plug them in with a minimum rewrite, and then slowly reimplementing more and more of these interfaces. The formality in the process ends there, but I hope its practicality is obvious.
Comment: Or should I have said, the formality of the process can vary according to many factors.
Answer: I assume you want the redesigned system to behave exactly as the legacy system, at least in the beginning. This means to need to capture the concepts and behavior of the legacy system first as precisely as possible. I recommend to create architecture models and use them for discussion. Everybody should have a good understanding of the modeling language you use.
Check out the methology we use at SAP, which is described in this 2 part blog post:
http://scn.sap.com/people/bernhard.groene/blog/2008/01/09/how-to-communicate-architecture-technical-architecture-modeling-at-sap-part-1
Don't just create the block diagrams. I recommend to start with entity relationship diagrams and also add definitions of the entities. Then do the block diagrams - don't forget to describe protocol boundaries, and add a short description what each block does. Last thing should be one of the dynamic diagrams. Use the other diagram types if you need them.
What you will experience are lively discussions e.g. if there is a 1:* or a 1:0..* relationship between two entities. Or you will learn a lot about dependencies between components if you try to figure out where you could establish a system boundary, and so on.
If you use vague powerpoint drawings of your legacy system architecture, everybody will have his own interpretation and understanding, so you won't make much progress, and your new system will probably not reflect the legacy system.
Answer: Mihai Danila's suggestion of applying Fowler's StranglerApplication in replacing your Legacy app is in my opinion the best way of replacing any legacy system.
I blogged a couple of years ago about never rewrite a system. Basically like Strangler Application it is about inserting transparent facades in front of  interfaces to the existing systems and incrementally grow this redirection to the new system until the old system is no longer in use.
And never re-writing the whole system in one go as that will take way too long with no business benefit at least for a long while. You need to deliver business value along with replacing the existing legacy system.
As for the actual estimations, you can apply many time consuming in-detail estimations using various techniques. However they will all just be as wrong as a finger in the air estimate, just now wrong in detail as Dan North would say.
Create a few prioritised epics of what features are needed initially, break them up further if needed but not much more. Then just throw some order of magnitude estimates of various parts of the job (t-shirt sizes, 1-10-100 story points or days or whatever). Applying StranglerApplication and then deliver some tracer bullet stories to get a much better idea of the actual complexity and viability of the project.
Answer: Try going back to the basics:

Where are you now?
Where do you want to be?
How do you get there?
What's stopping you?

Ineffective meetings are a sign of lack of purpose and commitment. Meetings should have a clear objective and commitment by those to reach it. For some of the best examples of how to run a meeting, look to professional sports. They are some of the best run meetings in the world (on time, 100% attendance from participants, commitment, engagement, clear rules and outcomes). Where possible try to emulate that.
A lack of good analysis is normally struggling to understand the problem. If you're not addressing the root cause of the issue, you are not really creating a solution. And if you are not creating a solution, you are just creating another problem.
There is a lot of process, methodologies and diagram to help with this process. OpenUP is not a bad place to look at methodology documentation if you haven't before. That should at least provide some structure and templates to implement some of the above. Another resource I find myself coming back to is Alistair's Awesome guide to pretty much everything.With those and the rest of the internet at your finger tips, you'll be off to a great start

Effective design analysis


What does "to take someone at face value" mean?

Question: What does this mean? I hear it often, but not sure what its meaning is. I think it means to believe what they are saying without proof.
Comment: Isn't "something" used more frequently here than "someone"?
Comment: It's more like believing what they say without *needing* proof.
Comment: Is it maybe related to playing cards which have backs and faces? I'm not a native speaker, so it is just a wild guess
Answer: The opposite of "taking at face value" is to look for a hidden meaning or ulterior motives. Are they lying? Is this a trick? "Face value" means that there is nothing more than meets the eye and digging deeper isn't likely to reveal anything interesting.
Answer: The derivation of "face value" in this sense most likely has to do with the phrase as used in talking about currency: the value of a coin or bill is directly apparent from the numbers printed on it.
So it means taking the meaning of someone's speech or actions directly. (w/o looking for hidden meanings as the other answerers have said)
Comment: I wouldn't be surprised if this phrase had its origins in Ancient Greece.
Comment: I believe that the complete answer is a combination of the one from @mrhen and this one.
Answer: To take something at face value means to believe what is being said without looking for deeper meanings or hidden agendas.
Answer: Well, I couldn't take this question at face value and had to dig deeper (inspired by @sibbaldiopsis' answer).
There were two U.S. Supreme Court cases, Mandeville vs. Welch, 1820, and Lines vs. Sminth, 1851 that spoke of promissory notes needing to have the words "value received" written upon their faces. Could be some connection here.
The first instance of the exact phrase I could find in print was from Mason's Coin and Stamp Collectors' Magazine, 1870, referring specifically to the face value printed on postage stamps (in contrast to the value of the stamp to a collector).

The first instance of the term used for money I found was from Folsom's Logical Bookkeeping, 1873:

Currency too—the bank-note and
  greenback—has its face-value, which is
  its printed amount .

The first figurative use of the phrase I found, the most common way it is used today, was from O. F. Cook's 1891, Papers on Myriopoda:
Answer: I agree with Sibbaldiopsis above. My guess is that it goes back to Greek or Roman times. The rulers wanted to establish "fiat" currency rather than currency based on the commodity value of gold or silver. The ruler, whose face, a symbol of his authority, was on the coin, simply declared the value of the currency and expected merchants and consumers to trade with it at that value. In this way, debased currency could enable the ruler to increase the money supply without being tied to the intrinsic value of metals.
The currency we use today is "fiat" currency.
Answer: To take something at face value is the believe that what the person is saying is truth and rather than looking for the hidden meaning it's not understanding the bigger picture or motive behind what the person is actually saying.


Register as versioned with move edits to base - when not to?

Question: What limitations do I get, when I chose to register as versioned with the option to move edits to base?
Answer: There are tradeoffs. I don't use this option because it limits the ability to create "check-out replicas" (show stopper for me). Another limitation when you chose this option is that you can't edit feature classes that participate in a topology.
Many people use this option because they need to support third party (non-ESRI) applications. When edits are made to the DEFAULT version that is registered with the option of 'move edits to base', those edits are immediately moved to the base tables rather than being stored in delta tables and requiring a sync operation... This is usually the only way that a third party application can interact with a versioned geodatabase.
ESRI Help Topic is here.
Answer: My SDE guru friend told me that if you allow move edits to base directly, there is no control or useful operations like undo or redo.What if sth bad happens ... Hopefully your database is backed up.


If Wolverine's skeleton is completely bonded with Adamantium, why are his teeth still white?

Question: In "X-Men Origins Wolverine", Logan undergoes an operation to have Adamantium bonded to his skeleton.
Why doesn't the Adamantium bond to his teeth?
Comment: Because Len Wein and Co. wanted Wolverine to **cut** through stuff and not **chew** through stuff! ;)
Comment: Teeth aren't made of bone.
Comment: Bones are mainly Collagen. Teeth are mainly Dentin. And that's just the internal difference.
Answer: Interesting point - since Wolverine is a fictional character, it could simply be because adamantium teeth are not good looking.
However according to this article It seems to be related that teeth do not have any cells to repair themselves, plus they are exposed to what we breath in and eat.
Maybe the bones that where bonded where only the ones that could repair themselves. Wolverine could heal himself quickly if not instantly, so it would stand to reason that the bones inside the body would be able to cope with the transformation, and the teeth couldn't.
Then again, it is only a theoretical answer for a fictional character.
Comment: But if his teeth are not indestructible, and not self repairing. How doe she have any left?
Comment: Theoretical is perfectly alright :)
Answer: In humans, teeth make up part of the skeletel system but they are not classified as bones. Teeth are made up of Dentin and Enamel whereas bones are made up of Osseous tissue.
So I imagine the adamantium only bonded to the Osseous and not the Dentin or Enamel which results in adamantium bones and shiny white teeth.
Answer: I think the most simpliest answer is that the adamantium was injected into his body, where it covered his bones.  In order for his teeth to be covered the injected metal would have had to ooze out of his gums into his mouth.
Answer: the goal of the experiment was to bond the admantium to the bones inside the body forming the skeletal framework only
When wolverine was 'bonded' with admantium, the experiments carried out were to inject and turn the bones into admanitum so that a skeleton of this 'super-metal' will make the body highly resistant to damage. The admantium was only injected into his bodily bones, and not over his teeth and other appendages. It is the same as asking why admantium was not put over his 'nails'. The experiment was limited only to the bones making part of body skeleton. As such, wolverines claws are automatically coated with the super-metal.
Unlike other experiments, where external claws and skin were tried to be bonded with admantium, Logan's experiment was limited to his bones.


Should I use a domain name registrar's free DNS hosting, or host DNS servers with another company?

Question: Should I use my domain name registrar's free DNS hosting service, or host DNS servers with another company? (or both?)
What are some advantages to using a DNS hosting company separate from the domain registrar?
Answer: Depending on the feature set of the Registrar you're using, it may be advantageous to host your DNS elsewhere.
If for example you require Dynamic DNS services (DNS records that are updated automatically when a destination's IP changes), or wildcard DNS (allowing <anything>.yourdomain.com to point to a certain IP), many Registrars do not offer these services.
If you do not require any special capabilities, in my experience, the difference (outside of the SLA of your Registrar vs that of a dedicated DNS host) is mostly moot.
Comment: Good point about the feature set / special capabilities.  The assist goes to @intlect's answer for mentioning control over TTLs as an example of that.
Answer: You should host your DNS elsewhere. It will save your behind when you switch registrars, it will allow you to control TTLs like crazy so you actually have close to 0 perceived downtime for users when you change hosting, etc.
I personally recommend DNS Made Easy. Have been with them for about 3 years now and they rule (at their price point).
Comment: Agree re DNS Made Easy. Been with them for years and never had a problem.
Comment: This was my second-favorite answer; I like the idea of having more control over TTLs etc.
Answer: If your site gets big enough where it's a problem (or your registrar sucks enough where it's a problem) then you should host DNS servers with another company. One that is known for such things.
Otherwise, stay with the hosting provider.
Hosting providers (especially the inexpensive ones) don't put the same effort into DNS as the companies that Do It For a Living.  It's sort of like running water, no one thinks about it until it stops working.
Answer: One advantage of using the name servers from the registrar is that they are very highly distributed, and that can effect the speed of lookups and global propagation.
For instance, Godaddy and Enom host so many domain names that the time to live of for newly purchased domains and for DNS modifications is SUPER fast.
Comment: That is, assuming it is a large registrar to begin with.
Answer: As others have said, I'm broadly in favour of self-managing DNS on external services. I use the rather excellent Afraid.org's service and have done so for a few years - now pay for a premium package so I can set invisibility flags on some domains, and just because I like the service. I even think I'm going to upgrade to the next tier.
It's mildly cumbersome setting up a new domain (as opposed to my registrar's system autocreating records... which I would still have to modify); for one of my personal accounts on Dreamhost they've made it much easier by providing all the DNS records on one page for me to copy and paste after the domain's live on their system.
Any disadvantages are vastly outweighed in speed, redundancy and separation from the actual registrar. One registrar I used in the past was notorious for dog slow refreshes of records after modification; afraid.org (like most other third party services) updates lightning quick and I can also force a custom TTL. Afraid also offers some nerdy and useful things like fallback DNS, dynamic records, AAAA records and other v6-related goodness, support for just about any record type you can conceive - with a clean, intuitive interface... Plus if you feel benevolent you can also share domains in the pool for other users to use (you can accept/deny requests to Private domains). It's free to try, I recommend it. I find it a far better service than DynDNS.com, which one of my customers insisted on using for years.
Answer: I recommend people shop for and select their domain registrar based on the quality of the DNS hosting service, which I feel is more important than the cost of the registration. It's critical to select a vendor like GoDaddy that offers anycast DNS service.
Answer: I keep my eggs separate, because the last small hosting place I used that did a registration for me, provided no tools other than a phone number to make changes.
You can see how moving away from the small host was a big problem for me.


What are the advantages and disadvantages of Buckets vs Carboys?

Question: Currently I use glass carboys because the glass seems easier to keep sanitary and you can fill them with your spare change if you ever stop brewing. I'm wondering if having a bucket would be an upgrade or a downgrade. What do you think?
Answer: Buckets are cheaper, lighter, and easier to deal with in general.  They're not advisable for long term storage though, as they allow some light and oxidation to occur.  Carboy's allow no oxidation, but they're more difficult to deal with.
If you get a carboy cleaner wand, this is an attachment to a garden hose or water tap that creates a powerful stream of water, cleaning a carboy should be pretty easy.  Personally I use a product caller PBR (Professional Brewery Cleaner) - soak the carboy with 2 tablespoons and some hot water, and everything comes off pretty easily.
I use a plastic bucket for the primary fermentation (about 10 days), then a carboy for the secondary, which can last anywhere from 2 weeks to 2 months or more.
Comment: Best six bucks I ever spent was on a [carboy handle](http://www.amazon.com/Carboy-Handle-6-5-Gallon/dp/B000Q636HC).  Saved my ass going up and down those basement steps.
Comment: for moving, consider a "brew hauler".  http://www.northernbrewer.com/brewing/brewing-equipment/fermenting-equipment/carboy-accessories/the-brew-hauler.html
Comment: most handles I've seen come with the warning that they're not intended for moving a full carboy
Comment: @STW, +1 for the BrewHauler.  I don't move full carboys any other way.
Answer: Choosing between buckets, glass carboys, etc is always a matter of personal choice.
The ease of use on buckets is high, but the durability is poor and they are much harder to keep sanitary over multiple uses. Any tiny scratch will make the bucket hold microbes you can't see or kill with a simple acid rinse, and now your fermentation vessel is a ticking time bomb, waiting to go off and ruin a batch. There is also no way to get into a bucket without opening a giant hole to the outside world for any old thing to fall into. Fermentations are also not something you get to watch.
Glass carboys are the "classic" choice, and they don't have many of the drawbacks mentioned above. However, they are harder to clean than buckets, and there is risk of serious injury if you break one. However in terms of long term durability and sanitation, they can't be beat by anything but a conical.
My personal choice is plastic carboys. I use 6gal "better bottles", which have the advantage of weighing pretty much nothing, they are nearly unbreakable, you can watch the ferment, and you're not going to get hurt by one. They are easier to clean than glass carboys if you use a bottle washer attachment for your sink. They are lightweight, easy to hold upside down, and easy to see when they are clean. One lesson I learned the hard way however: If you are used to using a bottle brush on your glass carboys, do not put that brush in the better bottle! You will scratch the inside, and ruin it just like you would a bucket. Use hot water and a good cleaner like Five Star PBW, and you've got an easy to maintain system that will last a very long time.
Answer: The biggest downside to the carboy I've found is in checking the specific gravity to tell if the initial fermentation is done.
The hydrometer simply falls too far to read well. We had to attach some dental floss to it so we could retrieve the thing! This was especially true during our last brew which had a VERY active fermentation with lots of stuff bubbling out through the airlock. This left a residue all over the inside of the carboy which made it especially difficult to check the specific gravity.
If I had my way, I'd do my initial fermentation in a bucket and then an optional secondary fermentation in the glass carboy (mostly because we already have it and it looks pretty in there :)).
Comment: I sanitize a turkey baster and use it to pull out enough beer to fill a test tube and then use the hydrometer in that.
Comment: We dropped the hydrometer in our first time and used floss to pull it back out. We later read that you should use a thief to pull out some beer to test instead. We ended up buying a rocket launcher (test jar) to put the beer in for testing. Much easier this way!
Comment: Right after I wrote this, I figured that there must be some type of ladle/test tube thing that would work for this. Do you have a link?
Comment: Here is a 3-piece theif so it should be easy to clean: http://www.northernbrewer.com/brewing/3-piece-thief-plastic.html
Comment: You may also be interested in a refractometer, which is an alternate method for measuring the sugar content in a liquid.  You only need a drop or two!
Answer: The down side to glass carboys is that they break and cut you.  I've heard of some pretty heinous injuries caused by dropped carboys.  Plastic buckets have never hurt anyone.
OK.  Maybe I am a bit paranoid about it.  But I'm always drinking beer while making beer.  I suspect I'm not the only one.  The idea of drunks carrying around large, heavy, glass bottles worries me.
Comment: NEVER use a carboy handle with a full carboy.  The neck of the carboy can snap off, possibly causing severe injury.  The manufacturer even states that they should be used only on empty carboys.
Comment: There are [carboy handles](http://morebeer.com/view_product/16660//Carboy_Handle_Blue_-_6.5_Gallon) that make it much easier to move a carboy. If you're imbibing so much you can't lift the carboy, you may consider placing it on a cart with wheels.
Comment: I was being a bit ridiculous about it when I wrote that.  But yes, the handles and the carboy carriers (the cargo net type) make them much easier to carry.  I still ended up with a stress fracture in one.  I suspect I bumped it against something when setting it down one time.  I don't trust that carboy now.  Glass is a strange beast.
Comment: consider getting a "brew hauler"; they support the carboy from underneath and are rater to 100lbs - http://www.northernbrewer.com/brewing/brewing-equipment/fermenting-equipment/carboy-accessories/the-brew-hauler.html
Answer: Buckets are much easier to deal with: they're lighter, easier to get material in and out of, easier to clean, and generally unbreakable.  I have a couple of carboys and a bunch of buckets.  I almost never use the carboys because they're just so much more work.
Be careful when cleaning a glass carboy with a hose pushed into the neck of the bottle.  If there is dirt or sediment in the bottle, it can get caught between the hose and the neck of the carboy and allow pressure to build up to dangerous levels.  True story: I was washing out a glass carboy that had dirt in it (had been a terrarium) in the back yard with a garden hose. Left it on its side with the hose running to flush out the dirt for a few minutes.  Stepped inside the garden shed for a few seconds and pow! The carboy exploded and embedded glass shrapnel in the shed door.  Glad I was inside!
Answer: Buckets are definitely easier to clean, since you can actually get in there and rinse and scrub, but if the plastic gets scratched, you might never be able to fully sanitize it again, as bacteria can get down into the scratches and avoid the sanitizer.
My personal preference is to use a carboy for the main fermentation work, as I can actually see into it and monitor the fermentation and settling.  I use a bucket, but only as an intermediary between the carboy and the bottles.
Answer: Buckets are great for primary fermentation. You can dangle your sterilized oak chips in sterilized nylon sock very easily and remove at will. You can add a couple of pints of crushed blackberries into your Merlot, to shake things up. the bucket is easy to lift in comparison and provides a good carry all when not in use. I have two buckets & three carbouys and use them all.
Salutee


Is there anything like Netflix in Estonia?

Question: I recently moved from the US to Estonia. The thing I miss most is Netflix streaming; is anyone aware of a company that runs a similar service in Estonia or the baltics? I don't so much care about DVD delivery.
Answer: You can use their streaming service from out of the country but if you are asking about DVD's by mail, I believe you are out of luck.
Comment: Hmm, I like this idea... I can't find anything saying either way, whether it's legal or illegal.
Answer: I've received comments about people using Netflix from outside US, using a VPN into some US-based host. Anyone have a good link about it? I dont know if a proxy is enough or you need a full tunnel.
Also, dont know the legal status of this, even if you are a US citizen.
iTunes on the other hand dont limit you to acces their content from abroad (they do not check source IP), but they do requiere you to pay with a US based credit card (US billing address).


What exactly is Bootleg in electronic music?

Question: It's not quite clear what a Bootleg is in the electronic music?
What's the difference between a Bootleg and a Mashup?
Comment: Possibly better asked on English SE?
Comment: What is the difference between vinyl and punk? Bootleg is about the legal status. Mashup is a music style.
Comment: Dr Mayhem - you're probably right but I wasn't quite sure I was going to get an appropriate answer there :)
Answer: For a long time, in popular music, a bootleg has been an unauthorised copy of some music. That would include unauthorised concert recordings, copies of masters stolen from record company archives, or just cassettes dubbed from commercial LPs. At various points in history, you'd find bootleg recordings as vinyl pressings, acetate pressings for DJs, as professional looking counterfeit cassettes, as obviously home-dubbed cassettes swapped by fans, or sold at markets. Later, of course, cassettes made way for recordable CDs.
As Wheat says, the term comes from smuggling and dealing in prohibited goods (for example, liquor was traded by bootleggers during America's prohibition years).
In around 2001, a scene emerged that became known as the "bootleg scene", or the "boot scene" -- in which people combined two well known records to produce a pleasing combination. For example Freelance Hellraiser combined an instrumental of The Strokes' Hard To Explain and the vocal from Christina Aguillera's Genie In A Bottle, to produce A Stroke of Genius.
These "boots" were distributed as MP3s on the Internet, and also pressed as limited release singles. Since they didn't have permission from any of the original copyright holders, these were bootlegs in the truest sense.
However, it's important to understand that an unauthorised recording of a Rolling Stones concert is also a bootleg in the truest sense.
When the record companies realised the popularity and commercial potential of the early 2000s mix-and-matching-records scene, some of them went on to produce authorised music in the same vein. For example, Richard X's combination of Adina Howerd's Freak Like Me and Gary Numan's Are "Friends" Electric was released as a single, with the vocals re-recorded by the Sugarbabes, and became a big hit. 2 Many DJs's "As Heard on Radio Soulwax Pt. II" -- a continuous mix -- was audited for copyright use, and released officially with great success.
Once everything was authorised and copyright-cleared, it was no longer appropriate to refer to these as bootlegs, so somebody coined the word mashup. Two (or more) recordings are mashed up together.
It's also important to note that this doesn't have to be an electronic process. While most creators of mashups do use computer software to align samples to each other, some do it all with vinyl source material, and turntable skills.
Comment: Ah, this explains why mashup night at one of the local clubs is called "Bootie."
Comment: Wow! is there any chance you are a music historian?
Comment: Nonetheless, I still hear both bootleg and mashup being used in electronic music.
Comment: I'm afraid I've just been alive a long time...
Answer: The term "bootleg" has nothing to do with electronic music, per se.
The term "bootleg", in general, means objects that are duplicated, transported and sold illegally.
In the music industry, the term "bootleg" denotes something that is used in violation of copyright laws, especially something that is duplicated and sold for profit when the person selling it has no legal right to duplicate it or sell it.
The origin of the term "bootleg" refers to smuggling; that is, transporting contraband by hiding it on a person so that the police or other authorities do not see it. It comes from the practice of a smuggler who hides small objects by stuffing them into the top of their boot or strapping them to their leg, underneath their trousers, and then walking through customs inspections or police inspections hoping that the objects will not be detected.
Comment: This doesn't answer the question, a link to the wikipedia page would be enough.
Answer: To sum up the answers: A "bootleg" mix, in the context you're likely referring, is a remix or mashup that is made without permission from  the copyright-holders of the original music.
Answer: Bootleg is a remix made using exclusively the final, full, integrated version of a song.
Mashup is a remix made using the individual components of a song (ie.vocals, bass, synth) and mixing, matching or integrating them separately.
Answer: A recording owned by the original artist of the song that is not been released. Copying or duplicating and distributing the unrelease version of the song without permission can be called bootleg and it is illegal.
Answer: My experience from hearing the term tossed around on the BBC Essential mix and even around my dj friends, is that a mash up (or a boot-leg) is the ability to take a song (normally with no connection to the genre being mixed) on the fly during a set and mix it in without interrupting the flow or beat of the mix.  Laidback Luke is a renowned mash up artist, and his live sets are incredibly dynamic due to how well he does mash ups.  One recent mash up I heard was a Boards of Canada track mixed into a house set.  The BoC track was incredibly ambient, but was supplemented by the dj with beats and a layered vocal track and was very enjoyable to hear.
All in all. Bootlegs and Mashups have many different terms, mostly historic, but, in reference to your exact question: "what a Bootleg is in the electronic music", it is what I described above.
Answer: Bootleg remix -
is a term used when a producer remixes a finished song without access to vocals, bass, melody etc.
Remix -
In a normal remix the producer normaly has access to vocals, bass, melody etc. And can remix them too, not just put a new layer of sound on it.
Answer: When referring to electronic music, especially on websites like soundcloud, a bootleg is a remix of a song which only has a beat, bass and some basic effects added.
A mashup is the mixture of two or more songs.
Example of Bootleg:

Example of Mashup:
https://soundcloud.com/mashupgermany/mashup-germany-top-of-the-1


How to copy links to Google Drive document

Question: When I copy HTML to Google Drive, I lose the URLs in the text. Is that normal behavior? If so, how do I get around it to keep the URLs?
Answer: You cannot (and shouldn't) copy raw HTML into a Google Drive document and expect it to render like how you see it in a browser. Instead, you should copy the rendered text (with the clickable links) and paste it directly into the Google Drive document.
The only problem with this, however, is that the formatting of the text will be different from the formatting of the rest of the text in the document.


Wordpress - Public side and Private side

Question: I'm wanting to setup a Wordpress site which has posts for public view and some which are only seen by people that are logged in (authors etc). I dont want the public people to see "Restricted Content" message or anything, just they cant see the posts and if the go to a post direct it'll push them back to the home page.
How can I achvied this so that its easy to select which posts can/can't be viewed by public users?
help please
Answer: What you want is Wordpress with members area. You can install third party plugins to do this the easy way. You can check this up : http://www.mytechopinion.com/2009/07/5-ways-add-membership-wordpress.html


How can I display incoming e-mail addresses (in my searches)?

Question: I checked the first four search result pages on Web Applications and Google, but I didn't find an answer to my question and issue, which is also discussed on the Google Help forums by other people.
My issue is, I know from people that they might have more than one e-mail address, but I don't remember it, as most people use cryptic e-mail addresses, even older folks. Now when I search for a person, e.g. in this screenshot:

It doesn't help me to display and find the e-mail address of this guy. Important: I might not have saved this e-mail address of him to my contacts yet, thus it doesn't help me to search my Google Contacts! Also, if you don't want me to use Greplin, switching over to Google Contacts is another (time-consuming) step that I want to avoid.
And then of course there is the issue described in the Google help thread: Sometimes I simply want or need to see the e-mail address, even if obtaining it is not the problem.
I checked my IMAP client (Postbox 3), but their search is actually worse in regards to my goal.
Conclusion: As I am using several browser extensions that alter and expand the display and features of Gmail, I wonder if there isn't a browser (Chrome) extension also for this issue?
Answer: If you hover your mouse pointer over one of the names, you'll get a "contact card" which will show you the email address. (Plus other information if the person is actually in your contacts.)


Gas or charcoal grille which one to buy

Question: I need a grille for doing mainly chicken, there is an inkling to buy a gas grille but I heard charcoal grilles are better for flavour, I like the convenience of gas, but flavour is compelling, is this true?
Answer: This is very subjective but I think charcoal grilled food is better. Although I have found that larger quantities is easier to make on a gas grille because it is easier to keep the temperature on the same level for a longer time.
Answer: There are many advantages to gas: better heat control, easier to clean, less potentially carcinogenic soot.
In my experience, the flavor that can be imparted by charcoal is superior, especially with good charcoal like that sold at Trader Joes.
However, I have not tried any of the wood slabs that are meant for use with grilling. Perhaps these have some effect on the difference.
Comment: Thanks, I think I will just go for a gas grille with a smoke chamber just in case I need anything from wood.
Answer: Because of the differences others have mentioned, I actually own both. I prefer the taste of charcoal but just don't have the time or energy for charcoal sometimes.
My main grill is a gas grill, which is very large, convenient and easy to use.  I can have grilled chicken go from fridge to plate in about 15 minutes, including prep, without having to do almost any work at all.  I also have a smoker box for when I want to use wood chips in the gas grill.  I also sometimes cook on wood planks in my gas grill, such as salmon on cedar.  As johnny mentioned, when I have a large amount of guests, I find it much easier to work with my gas grill.
Then, for when I have the time or energy, such as when I have a couple guests over for a nice steak on a Saturday, I pull out my small, cheap charcoal grill and chimney starter (which heats the coals faster and more evenly).
Comment: Thanks, I have seen the smoke box thing mentioned on Primal Grill with Steven Raichlen.
Answer: I'm a big charcoal advocate.  You can get higher temperatures from charcoal, and a good grill (read: Weber kettle) offers a great deal of flexibility.  It's easier to deal with flare-ups, and once you attain a good skill level you can have more consistent temperatures across your cooking surface.  Plus, it tastes better.
Once I started using lump charcoal and a chimney starter, I have been able to get up and running a lot quicker.  Usually I'll start a chimney full of coals, then do my prep work on the food.  Within 10-15 minutes, the coals are ready for cooking (using Kingsford briquettes, it's more like 20-25).
However, I find the biggest benefit to be the use of indirect heat.  You can use a gasser to cook food indirectly, but it's just not designed to do cooks that way, making for a very inefficient cooking method.  I've used my big gas grill in the past, but it uses a lot of propane, and a lot of heat escapes from under the hood.  The kettle, on the other hand, is designed to convect heat.  Particularly for roasting/barbecuing at somewhat higher temps (350F+), charcoal is the way to go.
Overall, I recommend having both.  Spend 100 less dollars on whatever gas grill you want to buy, and complement it with a Weber One Touch Silver (80 bucks for the 22") or something comparable.

Gas or charcoal grille which one to buy


hydraulic clutch fails to fully disengage

Question: I have a 2005 Toyota Corolla Verso 2.0 D4D (UK model). The clutch does not disengage fully with clutch pedal fully pressed. This is a hydraulic clutch. When in gear and brake is released with clutch pedal fully pressed it will creep forward very slowly. The main issue is difficulty changing gears when stationary or downshifting.
There is no loss of fluid (this car uses the brake fluid reservoir) or visible leakage. The clutch pedal feels firm all the way to the floor.
Is there or any further diagnosis I can do? Or do I have to disassemble the master and slave cylinder next?
Answer: Check for a master cylinder leak by checking the firewall behind/underneath the clutch pedal for fluid.  You can start having disengagement issues with leaks small enough that the fluid loss won't be noticeable.  Repairing them is typically not done anymore, take it in and swap for a fresh factory unit.  Not sure where the slave cylinder is on that model, but you should check that too if you can.  While I've seen a number of master cylinder failures, I've yet to ever see a slave cylinder failure on the cars I've looked at.  A very rare possibility is that just bleeding the fluid will help (I have seen a car where someone overheated the clutch to the point that the fluid in the nearby hydraulics boiled!).


To differently gluing of two Riemann surfaces with boundary we get different surfaces

Question: If $M,N$ are two Riemann surfaces with boundary, then we can glue them along one of each of their boundary component, which is $S$, to form a new Riemann surface with boundary, but for different gluing we may form different Riemann surfaces with boundary, for example, there may be a $S$ twist, intuitively, it is just we rotate one $S$ an angle then glue it with another surfaces, but my question is how can we show the resulting two surfaces (twisted gluing and untwisted gluing) are different Riemann surface with boundary (their differential structures are the same because we can regard it as a kind of connected sum)? Thanks!
Comment: Changed Reimann to Riemann in the title.
Answer: Here is a particularly simple example. We will take a cylinder and glue its ends together in two different ways. The cylinder will be
$$C:=\{ z: 0 \leq \mathrm{Im}(z) \leq 1 \} / \mathbb{Z},$$
where $\mathbb{Z}$ acts on the horizontal strip by translation.
Let $\theta$ be a real number between $0$ and $1$. We will glue the ends of $C$ together by identifying $x+\mathbb{Z}$ with $(x+i+\theta) + \mathbb{Z}$, for $x$ real. Call the resulting torus $T_{\theta}$.
We claim that all the $T_{\theta}$ are nonisomorphic as Riemann surfaces. Here is a sketch of a proof: Let $\Lambda_{\theta}$ be the lattice in $\mathbb{C}$ generated by $1$ and $i+\theta$. Clearly, $T_{\theta} \cong \mathbb{C} / \Lambda_{\theta}$. Suppose we had holomorphic isomorphism $f:T_{\theta} \to T_{\theta'}$. Then $f$ would lift to a map on the universal covers, $g: \mathbb{C} \to \mathbb{C}$, and there would be some additive map $h: \Lambda_{\theta} \to \Lambda_{\theta'}$ such that
$$g(z+\lambda) = g(z) + h(\lambda)\ \mbox{for} \ \lambda \in \Lambda_{\theta}. \quad (*)$$
Let $D$ be a fundamental domain for $\Lambda_{\theta}$. The function $g$ is $O(1)$ on $D$ (compactness), so, applying $(*)$, we can deduce that $|g(z)| = O(\max(|z|, 1)$. Since $g$ is analytic, this implies that $g$ is of the form $z \mapsto az+b$. In particular, multiplication by $a$ must carry $\Lambda_{\theta}$ to $\Lambda_{\theta'}$.
But there is no complex number $a$ such that $a \Lambda_{\theta} = \Lambda_{\theta'}$, a contradiction.
Comment: Another method for showing that they are nonisomorphic Riemann surfaces is to show that their function fields are nonisomorphic (e.g., by noting that $\wp$ and $\wp'$ have inequivalent branch loci).
Answer: If your compact Riemann surfaces $M$ and $N$ have a hyperbolic metric in which the boundary curves are totally geodesic of the same length, then this follows from the Fenchel-Nielsen coordinate parametrization of Teichmuller space. Any compact Riemann surface with boundary has a uniformization to a hyperbolic surface with totally geodesic boundary (one may see this by doubling, and applying the uniformization theorem). If you perform this uniformization, and then compare the two sides, your identification between boundary components may differ from the parametrization given by Fenchel-Nielsen coordinates (for example, the lengths of the boundary components may differ), and so it's more complicated to see how the conformal structure changes. In fact, if $M$ or $N$ is a disk or annulus, then the conformal structure may not be changing at all. If $M$ and $N$ both have Euler characteristic less than zero, then large twists should change the conformal structure. For example, a twist by $2\pi$ will change the Riemann surface by Dehn twist, and therefore gives a different conformal structure (up to isotopy).
There's also a slight issue of moduli, in that a rotation by $2\pi$ changes the point in Teichmuller space, but not in moduli space. I'm implicitly assuming you're asking for the Teichmuller parameter. If you're asking for the parameter in moduli space, then the twist
will take you along a non-trivial closed loop in moduli space, so at least there will be uncountably many different conformal moduli as you twist.
Answer: It shall amount to understand precisely the parametrization of Teichmüller space. The key word is "pant decomposition".
If you are willing to admit the (length, twist) parameters of Teichmüller space, then simply decompose the two initial surfaces in pants. The union of the two decomposition is a pant decomposition of both glued surfaces, with different parameters, so that they must be  different surfaces.
Answer: When you glue $M$ and $N$, for example, along some boundary component $C$. Choose a closed geodesic $\gamma$ on $S$ intersect with $C$. It can be shown that the hyperbolic length of $\gamma$ is changed when you twist along $C$. This means that different twist makes different hyperbolic surface.


How Safe Are Heat Ray Guns?

Question: Could a little meddling with the frequencies of the Heat Ray Gun beam result in frying crowds rather than dispersing them?
Comment: fry won't be a correct term!! boil might be! :P
Comment: @Vineet Well, if you have an oil gun near the heat ray gun, you sure could do some delicious frying!
Answer: Basically, no. I am no fan of the technology, but to answer your specific question, a little meddling with the frequencies should not yield physical damage. Wikipedia has a decent first introduction to dielectric heating by high-frequency electromagnetic radiation. Both deposited power and penetration length depend only weakly on the exact frequency. However, the energy transfer (and potential amount of skin or tissue damage) is directly proportional to the power of the RF wave, so I'd say that's the most direct threat.
Answer: To pick up from F'x's answer: the frequency has been chosen so it's absorbed very quickly by the skin. This means it is heating only a very thin layer of your skin so it doesn't need very much power to raise the skin temperature.
Suppose you changed the frequency so the radiation penetrated ten times as far into flesh. That means ten times as much flesh is being heated so the temperature increase would be a factor of ten smaller. You'd need to use ten times as much power to get the same temperature increase. That's why F'x says the most direct threat is the power of the beam rather than the exact frequency used.

How Safe Are Heat Ray Guns?


How can I frame a ceiling tray in my dining room?

Question: We have a 12x14 dining room and are looking to add a shallow 6"h x 15"w tray border around the outside. One of the longer sides will not hit any ceiling joists, so I will be using toggle bolts to keep my framing attached to the ceiling on that side. In order to keep the weight down for the framing and rock, I was thinking about using 2x2s instead of 2x4s. Being that the 1/2" sheetrock pieces will be fairly small in dimension does anyone see any safey issues with that idea? All other pieces will hit studs & joists. No issues expected with moisture, etc and not planning to run any electrical through the tray.
Answer: Since you are going to be mudding and taping sheetrock anyway, you could cut into the ceiling and add some supporting 2x4's between the ceiling josts to attach your new trey framing too.
Answer: I think you're OK, though it's not ideal. The devil is in the details. I'm assuming the ceiling is also 1/2" sheetrock, and that it's properly attached. If the first ceiling joist is close to the tray edge, rather than 9" away, that would be better but not a deal breaker.
Focus on a good wall connection, such that the tray practically cantilevers from the wall, the toggles becoming more of a backup. Then don't skimp on the toggles. A single one may not hold much, but the strength of several actually amounts to something.
That said, this probably does not meet code, as you are supporting an architectural element with a non-structural material. But I don't see it as a life/safety hazard.
Comment: thanks for the help, this is exactly the advice I needed.


When did the Holy Roman Empire collapse?

Question: In the 1500's, the Holy Roman Empire was a relatively powerful country. By the mid 1800's, it seemed to be superseded by in importance by its states.
When did the unified "Holy Roman Empire" really collapse and why?
Comment: One can argue that Germany unified by the Prussians is a modern reincarnation of that Empire...
Comment: @Greg Except that the Prussians were in the main not Catholics, but Protestants.  (Mostly Lutheran or Reformed)
Comment: @KorvinStarmast 1) Guess what, many if not most German kingdoms were already protestant - just because the Hamburgs were Catholic, it doesn't define the empire. 2) There are several historical examples when an empire or kingdom changed religion: China, Japan, Roman Empire. 3) Protestantism is just as much a continuation of the early Christianity as Catholic Church. Based on your argument, the Empire would have stopped existing every single time when they had a political argument with Rome.
Comment: I am not making the strawman point that you choose, but alluding to the  seat of HRE continued in Austria, not Prussia (where it never had been), up until Napoleon put paid to Austria and that long dying vestige of the HRE. It wasn't until Bismarck, and Germany, that the torch was successfully passed, if ever, in terms of a Reich in the heartland of Central Europe.  Bismarck fused Germans (of both major sects) in a heck of a political coup over a three decade period.
Answer: The Holy Roman Empire actually persisted into the early 19th century. At this time it was centralized in the loosely defined and allied Germanic states/kingdoms. Following the rise of Napoleon and the defeat of many different, unaligned German kingdoms' forces by Napoleon's forces, Napoleon was able to sweep across the nation we now know as Germany. One of the first things Napoleon did was to dismantle the once-proud Holy Roman Empire as well as install a number of administrative and economic reforms. Doing so actually laid the foundations of a (loose) sense of German nationalism that had not existed prior to this and led the way to many of the revolutionary happenings of the 19th century in central Europe (more specifically in Germany, Prussia, Hungary, Austria, Denmark, France, and many other tiny German principalities and duchies).
Sources used: David Blackbourn's History of Germany, 1780-1918: The Long Nineteenth Century
Comment: Indeed, this was basically the case. It is interesting to analogise the collapse to that of the actual Roman Empire, which had been decaying and diminishing in power and control for a couple of centuries before its invasion and official destruction.
Answer: Officially it collapsed after falling to Napoleon with the 4th treaty of Pressburg, but had been fading for some time before that. The empire was pretty decentrized in nature, but various events such as the Peace of Westphalia after the thirty years war, which granted dominions effectively independence in all but name. Nations, especially the Hapsburgs in Austria, looking to consolidate their own domains over that of the empires, and the thwarting of policies that would have brought more centralization to the empire's rule.
Comment: +1 for mentioning the thirty year war. [Europe's tragedy](http://www.amazon.com/gp/product/0141006145/ref=pd_lpo_k2_dp_sr_1?pf_rd_p=1278548962&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=0674036344&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=1DMT42VEYNHNQC4JAXAG) is a very good scholarly reading on that war and the peace treaty that concluded that war.
Answer: To build on GPierce's answer, the HRE functionally collapsed much before that time. The Thirty Years War (1618-1648) had really taken a toll on the HRE's central government. It left the country politically and religiously divided, which was a major issue to unification at that point in time. The country was ruled by princes who controlled city states that were loosely connected. This remained until Napoleon, as Gpirece stated, swept across modern day Germany.
Answer: The Holy Roman Empire (of the German Nation) officially ceased to exist one fine day in August of 1806 when Francis II went to the Imperial Diet and resigned. He of course continued to be the Emperor of Austria-Hungary, but that is another story.
What only a small number of people thought about was the fact that for the first time since 31 BC,there was not a single political institution called "Roman Empire". In that year, when Octavian had fought the Battle of Actium and established himself as Princeps (First Person) in a situation that was widely regarded as an imperial arrangement, there had been a Roman Empire of some sort. Whether as a Principate, a Dominate, an Eastern and a Western Empire, an Empire in the East that called itself "Romaioi" (Greek for "Romans"), or as a Germanic Empire that called itself "Holy Roman", there had ALWAYS been a Roman Empire! And yet, as TS Eliot would later say of the  world, it died, "not with a bang, but a whimper".
Why did it die? Well, it failed to make a Nation-State out of Germany. It failed to ever have a stable method of succession to the throne. And the Emperors had a hard time justifying their right to rule, given the first two limitations.
Of course, the immediate cause of death listed by the Coroner was the Battle of Austerlitz and the creation of the Confederation of the Rhine. But the  above three reasons had rendered the Empire impotent for years.
As I stated in my answer on Frederick II, the book will be out in a few years and then you will know WHY those three things above happened as they did. But for now, those reasons are sufficient, as explaining why the reasons obtained will be a book-length answer.
Comment: Worth noting that (a) Francis II created the title *Emperor of Austria* in summer of 1806 specifically so as to not lose his imperial dignity upon dissolution of the HRE; and (b) that the title *King of Hungary* was always separate as Hungary lay **outside** the HRE.
Comment: @Pieter Geerkens  Francis II, Elected Emperor of the Romans, proclaimed that he was also Hereditary Emperor Francis I of Austria in the summer of 1804, not 1806.
Comment: @MAGolding: Yes - unfortunately I noticed after the 5 minute edit window had expired.
Answer: The Holy Roman Empire was a bit more unified during even its latest phase than many answers have said.
After the thirty ears war many German sates rallied to support he Emperor in the period calling the Imperial reaction which lasted until the 1720s when Emperor Charles VI had to curry favor with the various states to get their support for his daughter's succession.
By 1720 Charles VI had become about as powerful in Germany as Ferdinand II had been at is peak in the Thirty Years War, but without fighting any battles.  But then he had to negotiate support for the Pragmatic sanction with the princes treating them as his equals.
If either Joseph I or Charles VI had had a son who grew to adulthood the imperial Reaction may have continued much longer and the war of The Austrian Succession might not have happened and the rivalry between Prussia and Austria might not have happened.
Also during the War of the Spanish succession Emperor Joseph I was able to confiscate several small states in the Kingdom of Italy or Lombardy, and in one particular year he actually manged to collect more Imperial War Tax from the Kingdom of Lombardy than from the Kingdom of Germany, so Italy was not yet totally outside of the Empire.
Comment: This is a very good answer, especially for bringing up the Kaiserliche Reaktion. Perhaps you would consider registering an account.
Answer: When Frederick II came to the throne in 1215, he tried to extend the HRE even more towards Italy (his father married the heiress of the throne of Sicily). His main ambition to create such an empire was because of the constant clashes with the papacy. His vain efforts to gain strength in Italy only weakened him in Germany, leaving the German dukes and princes free to govern Germany.
After the death of Frederick II, the HRE rapidly declined. The German monarchs continued to be called HRE emperors, but they held little power.
Comment: This is not true. Carolus V was the strongest monarch in the world for his own time and for centuries before and after.
Comment: Well, although Charles was the most powerful in the world, this is primarily due to the position he had as King of Spain and her possessions in the New World. It is true that as HR Emperor, his powers WERE limited.
Answer: The Holy Roman Empire was never a real "country," but rather a motley confederation of mostly independent (mostly German-speaking) states. During the Middle Ages, it did, however, prove itself capable of rallying behind an elected Emperor for crusading or other religious purposes.
In contrast to other answerers above, I date the (de facto, not de jure) collapse of the Holy Roman Empire to the Thirty Years War, 1618-1648, between the Swedish-led (Protestant) north German states, and the Austrian-led (Catholic) south German states. By splitting the "empire" into Protestant and Catholic camps, the long war destroyed the common ethos that had hitherto bound the different states, and made the "confederation" a shell of disunited, often warring entities.
Answer: There is a presumption here that "Germany", "France", and "Italy" existed long before unification -- which result was, again a presumption, some good thing. The 20th century demonstrated quite the contrary. France arrogantly tried to remake the map of Europe, Germany twice tried to impose its will on the rest of Europe, and Italy invaded Africa. The success story was Britain which won by losing. Even from a modern trans-European  ideal (which is moot), it is not language which unified  but religion. With the disintegration of that metaphysical division, one can only hope that European unification will indeed bring peace and prosperitiy -- but religion can play absolutely no role in that process or success will turn into an ignius fatuus and waft away. Europe needs an objective even to survive. I might try unifying peace and prosperity by which means it may bury a VERY sordid past yesterday, and bury it in the past. A little isolationism is good for meditation, and contemplation of the future is a better bet than monumentalizing the past. That is particularly true of Europe, where the reminders keep creeping in between now and the future.


How often should I dust the inside of my computer?

Question: I would like to avoid frying my computer.  I understand dust collects inside on the boards and the CPU cooling unit.  How often should I open up the chassis and what process should I use to safely remove the dust?
Comment: My father once hoovered inside his computer. It stopped working after that. Just a heads up.
Comment: Yeah, most vacuums are sources of computer-killing static electricity.
Answer: This depends greatly on how dusty your house is. I open mine up every few months, and use some pressurized air to blow out all the vents, etc.
You'll want to pay special attention to the areas that usually get hot - for instance, the CPU. Make sure there's proper air flow through the system, and if you turn your computer off a lot, you'll notice a build-up on the fans as well.
If you live in a dusty area, or are a smoker, you'll want to do this on a very regular basis.
Answer: Its a good idea to run temp monitoring software in your systray (like motherboard monitor)  to watch the ambient/Cpu temps - this should allay your concerns with frying your machine.  Typically if your CPU cooling / case ventilation fans are installed properly, you SHOULDN'T have cooling problems.
Most modern cases have filters on the fans that draw air into the case as well.
That said, compressed air is your best bet.  Unless your house is super dusty or you're a smoker, chances are you can get by blowing it out with an air duster a few times a year.
Your main cleaning areas should be

CPU heatsink/fan assembly
motherboard chipset fan assembly
powersupply if accessible
case fans
hard drives.
Answer: Don't dust.
Air in a can instead.
If your fans seem to be speeding up sooner than before, its time for a clean. Thats the rule I go by.
Best practice is to keep the area clean though!
Answer: I think most users should never dust the inside of their computer.
I won't say that I haven't done that with my pc ever, but I do know that I can count the times I have done that on one hand. But then I'm not like 'most users'.
Answer: If you keep your computer area clean and dust free as much as possible around the outside of your computer, most computers should last a few years without inside dusting.  But I personally open mine every 6-12 months just to give it a good compressed air blast.
Answer: Personally, I clean my PC at least once a month just to reduce the build-up inside. Disconnect the cables, take the motherboard out, clean the casing and the fans, and put them back in.
It's rather dusty where I live, and since we don't have airconditioning, that's what we usually do.
Answer: Don't bother. By the time there is enough dust to cause a problem, the computer is probably obsolete. =)
Comment: How do you finish them off?


Cooked whole chicken has congealed blood around joints and bones, should I worry?

Question: So I just roasted a whole chicken and finished carving/cleaning the carcass today.  I discovered a great deal of congealed red matter surrounding many of the joints and bones.  Looks like congealed blood.  Normally, I wouldn't worry about it, except that there's a lot more of it than there usually is.  And it's a brighter red, as opposed to the dark reddish brown I'm used to.  Should I be worried?  Did I undercook the chicken?  Was this chicken just not as well drained as ones I've gotten previously?
Answer: This exact thing happened to me about a month ago - roast whole chicken, bright red leaky blood around the bones and joints.
I looked it up back then.  I didn't find a truly authoritative source like the USDA, but I did find several instances of people saying that this happened even with highly overcooked chicken.  I also found several links similar to this one:
Bloody Chicken
The author (a Ph.D according to that page) did a number of experiments where he cooked a chicken and checked the internal temperature everywhere, ensuring that it was in fact pasteurized and thus free of any bacteria, and parts of it were still bloody on the inside.
According to him (and a few other sources I found), it's because the chickens are very young and their bones have not hardened properly; when you cook them, the marrow seeps out and ends up looking as you describe.
If you're using a meat thermometer to test the chicken for doneness, and you are certain that it got hot enough, then don't worry about the blood.  It's not appetizing, but it's not harmful either.
FWIW, I ate the chicken when it happened to me, and did not get the slightest bit sick.
Comment: not unhappy, or malicious. ;)
Comment: if you can get over the look, marrow is quite delicious.
Comment: ... [and nutritious!](http://brothersgrimmandgorey.blogspot.com/2009/10/chicken-bone-marrow.html)
Answer: In an of itself, brighter blood doesn't mean anything, so I wouldn't worry about it, unless you also noticed any of the following:

Was the meat pink? Undercooked chicken has a distinct color, very different from cooked.
Was the texture off? Undercooked chicken has a distinctive texture, completely different from cooked chicken
Were the juices bloody when you pierced the meat? Clear juices indicate the meat is properly cooked
Was the temperature too low?
Answer: I cooked two chicken at once and indeed had some redness around the joints in the thighs drumsticks and the breast bone i am sure i cooked it thoughly since the juices where clear and the oven temp was at 350 for 3.5 hours they where about 8 pound birds this should be long enough. the meat was not pink its was just at the bones. tasted fine and i ate it not sick yet its been over 6 hours.After letting it cool i de-boned it at frist it seemed really red but after a bit it became redish brown so i am sure it safe to eat but at frist it dose seem a little unappatizing.


Migrating Theme from MOSS 2007 to 2010

Question: Can any of the post readers help me out how to make my moss 2007 custom theme work in sharepoint 2010.
Thanks in Advance
Manoj
Answer: Your theme cannot work in 2010 unless you use the visual upgrade view. If you are deploying to a new environment, you will need to create the theme in the same location as in the MOSS environment. If you are upgrading using a content database attach, then it will automatically show in the MOSS view with the theme applied. If you are creating new sites in 2010 and want to do this, you will have to use a PowerShell command and set it to show in the MOSS view instead of 2010. The PowerShell command can be found here: http://www.toddklindt.com/blog/Lists/Posts/Post.aspx?List=56f96349%2D3bb6%2D4087%2D94f4%2D7f95ff4ca81f&ID=173&Web=48e6fdd1%2D17db%2D4543%2Db2f9%2D6fc7185484fc.
You can only show a MOSS theme in this manner as the masterpages and page layouts use completely different CSS classes than 2010. Themes in 2010 are completely different, all they do is change a few colors and fonts for you.
You should be aware that if you use the MOSS view instead of the upgrade to 2010 you will lose some functionality. I would suggest taking the CSS you have for your theme and work on upgrading it to work with 2010 and creating a custom masterpage to call this alternate CSS. You can then install this as a solution and activate it on multiple sites using a PowerShell command.
Answer: Create new theme in PowerPoint

Migrating Theme from MOSS 2007 to 2010


What makes the focus ring on a lens go smoothly?

Question: I'm curious about the smooth movement of the zoom or focus rings on a lens. How is the smooth movement done? Is there some kind of liquid with high viscosity? That doesn't sound very probable. On the other hand, I have no idea how to get the smooth movement by purely mechanical means. Please enlighten me before I go disassembling my lenses. :)
Answer: The twisting motions you apply to focus and zoom rings are converted to forward and backward movement by helical threads and tracks cut into the barrels inside the lens. This photo shows an example of the threads that do the focusing duties in a partially-disassembled Nikkor prime:

Note the tracks cut into the inner barrel and the metal rails in the outer one which force the inner one to slide forward and back.  Zooms that don't use a push-pull mechanism do something similar with less-dense threads so you don't have to rotate the ring many times to get through their entire range.  (This technical illustrator's site has some excellent examples as well.)
High-quality lenses have precisely-cut metal threads that fit together with very tight tolerances.  A very light coating of viscous grease provides smooth travel and the drag that we tend to associate with "quality."  Less-expensive lenses forgo the metal and instead rely on molded plastics.  This isn't always a bad thing; many auto-focus lenses had to sacrifice the feel and keep weight down as a way of reducing the load on focus motors to make them work faster.
If you're interested in seeing how all of this works without taking your lenses apart, order a service manual or ask a repair shop if they'll let you browse through one.  Most show a complete tear-down of the lens and the illustrations will give you some idea how all of the parts work.
Answer: Part of it is due to the grease on the moving parts, yes. On my Canon 70-200mm f/2.8L, I can feel the notches in the gearing. I think plastic parts have more "give" and also wear down slightly to give a smoother feel.


Does environmental (or food/drink) temperature have an effect on the voice?

Question: Does ambient temperature (i.e. winter vs summer) or food/drink temperature (i.e. cold vs hot) have an effect on voice:

Texture
Pitch/range
Strength
Comment: I'm a bit confused by your use of the word 'diet' - are you asking  whether diet drinks have an effect or whether a person's diet has an effect?
Comment: diet = solids , drinks = fluids
Answer: I haven't found any trustworthy resources about the effect of hot and cold weather on the voice, so I can't comment on that. Humidity of the environment CAN affect the voice, for example the air conditioning in hotels or on airplanes can dry you out significantly, making singing uncomfortable and especially affecting tone (which may be what you mean by 'texture'?) of the voice. Various resources therefore recommend taking a humidifier to environments which would otherwise be uncomfortably dry.
The only problem I've noticed with hot/cold environments is that
(a) cold - shivering gets in the way of performance!
(b) hot - sweating can make you dehydrated, so you need to drink more water to compensate.
On temperature of food/drink:
Ice-cold drinks and food (like ice-cream) are considered not helpful for singing, as they make the throat tighten, making it harder to sing. I've personally found this to affect tone and my higher range.
Hot drinks (that don't contain caffeine) may be helpful. Although vocal cords are kept hydrated mostly through drinking plenty of water in order that your whole body is hydrated, organisations such as the British Voice Association also recommend inhaling steam, which can reach the vocal cords. So drinking hot water may provide the dual benefits of hydration and relaxing the vocal cords. I don't know whether this has a directly beneficial effect on tone or range, but I have certainly found it to help stamina when I've had a lot of singing to do over a short amount of time.
I can't find any information about the effect of hot food or very hot drink, so I hope someone else can comment further.
Answer: It's worth mentioning that caffeine and alcohol have a diuretic effect. That not only makes you go to the bathroom, it dehydrates you, and can reduce the amount of saliva and mucous available to your mouth and throat and larynx. When you sing and your mouth, throat and larynx feel dry and don't have lubrication, you fatigue your voice, your tone suffers, you may have trouble singing high notes or long sustained phrases, and you may cough while trying to sing. In the long run, you can damage your voice if you continue to sing while drinking or eating caffeine regularly. It's a common cause of frequent laryngitis.
Some people are much more sensitive to this than others. I recommend that you don't drink or eat (as in chocolate) any caffeine during the time that you'll be practicing singing or performing, and see if your voice feels better and your tone seems stronger and more free, with less fatigue.


Shinaelestran Guardian - Guardian Defense exploit

Question: Martial Power 2 introduced the Shinaelestran Guardian paragon path for Rangers.
One of its features is the Guardian Defense.

Guardian Defense (11th level): Whenever you gain a bonus to attack rolls from one of your ranger class features, you gain a +2 bonus to AC until the end of your next turn.

I think the intent of this feature is to work in synergy with either Prime Shot (from Player's Handbook) or Running Attack (from Martial Power 2).

PRIME SHOT
  If none of your allies are nearer to your target than you are, you receive a +1 bonus to ranged attack rolls against that target. You do not gain this feature if you choose the Beast Mastery fighting style.
RUNNING ATTACK
  This class feature replaces the Prime Shot class feature.
If you use a standard action that lets you move (such as a charge or the skirmish shot power), and you end that movement at least 2 squares away from where you began that move, you gain a +1 bonus to attack rolls made as part of that standard action.

These feature are very situational and thus the Guardina Defense's AC bonus doesn't kick in
all the time. However, Heroes of the Forgotten Kingdoms later introduced the Hunter and Scout implementations of the Ranger class.
Hunter's Weapon Talent and Scout's Two-Weapon Style (Flashing Blade Mastery) both grant a +1 bonus to attack rolls with every attack.

WEAPON TALENT
  You gain a +1 bonus to the attack rolls of weapon attacks.

TWO-WEAPON STYLE
  Gain flashing blade mastery or spinning axe mastery.
Flashing Blade Mastery
  You gain a +1 bonus to weapon attack rolls while you wield a light blade in your off hand.
Spinning Axe Mastery
  You gain a +2 bonus to weapon damage rolls while you wield an axe in your off hand.

By RAW it seems that every weapon attack will trigger the +2 AC bonus. However, it seems questionable because of the specified paragon path came out before these classes have been published, and it seems like an unintended synergy.
Is there any official FAQ on the matter?
Comment: A lot of D&D is about unintended min-maxing ...
Comment: Of course :) But it usually ends up being an arms race between min-maxers and errata compilers :)
Answer: From what I can tell, those are not explicitly listed as Scout features and thus are eligible for the PP feature that you listed. Also a Scout is a type of Ranger, and thus any feature that is a Scout feature can also be classed as a Ranger feature.


"Closest pair of points" algorithm

Question: I'm having a problem understanding why I just have to consider the next 7 points in the
Closest pair of points - algorithm.
Can someone explain it in greater detail?
Answer: I've simply included the diagrams (here they're larger than on the webpage you linked us to!), along with the caption below the figure: "Key concepts".
Together, with thoroughly reading the "Correctness" (and proof of algorithm) section of the exercise, hopefully you'll be able to answer your question.  If not, feel free to edit your post and specify, in much greater detail than you first provided us, what it is exactly that you're confused about.  We'll be in a much better position that way to satisfactorily answer your question(s).

Figure #33.11: Key concepts in the proof that the closest-pair algorithm needs to check only $7$ points following each point in the array Y'.
(a) If $p_L \in P_L$ and $p_R \in P_R$ are less than $\delta$ units apart, they must reside within a $\delta \times 2\delta$ rectangle centered at line $1$.
(b) How $4$ points that are pairwise at least $\delta$ units apart can all reside within a $\delta \times \delta$. On the left are $4$ points in $P_L$, and on the right are $4$ points in $P_R$. There can be $8$ points in the $\delta \times 2\delta$ rectangle if the points shown on line $1$ are actually pairs of coincident points with one point in $P_L$ and one in $P_R$.
This last point may be the key, in terms of understanding why the there can be no more than $8$ points in a $\delta \times 2\delta$ rectangle. The maximal number of points in a $\delta \times \delta$ square, such that any pair of points is at least $\delta$ units of distance apart is at most $4$.
Why? Try dividing a $\delta \times \delta$ square into $4$ squares (each of dimension $\delta/2 \times \delta/2$. The maximum length between any possible two points in any given subdivided square is the length of its diameter: $\sqrt{2}\delta/2$, which is less than $\delta$. In this way, each such subdivided square can contain at most one point, and, thus, at most $4$ points can be contained in the $\delta \times \delta$ square.
Comment: Thank you. I now understand. ;) My problem was that I couldn't understand why the  δ × 2δ rectangle has at most 8 points. But now I see that there will be a contradiction if there is more than 8 points.
Comment: @user11775: Great! It isn't the easiest of webpages to read (tiny print), and the diagrams were pretty small (certainly hard to make out deltas and such!), but they seemed helpful to understanding the "key concepts" and "correctness" explanation.
Answer: It's explained below the headline "Correctness". At most 8 points may reside in the $\delta \times 2\delta$ rectangle because at most 4 may be found in the left square and at most 4 may be found in the right square. With 8 points in total, it is enough to check for 7 points in the array $Y'$. The background of the proof is complicated and is described on the page you mentioned.
Comment: I know. I'm confused about the part:

"it is easy to see that we need only check the 7 points following each point in the array Y′."
Answer: There are 2 things to understand:
(1) The first is described well in the text you linked to:
After finding the closest pair of points on the left side (denote the distance between them by $\delta_L$), and the closet pair of points on the right side (denote their distance by $\delta_R$), we are only interested in knowing whether there is an even closer pair of points, of which one lies in the left side and the other in the right side. So we're only interested in such pairs $(p_L, p_R)$ which are less than $\delta=min(\delta_L, \delta_R)$ units of distance apart.
So the distance between $p_L$ and the the line $l$ (see figure $(a)$) must not be more than $\delta$ and the distance between $p_R$ and the line $l$ must not be more than $\delta$. That is, it's enough to only consider the points lying in the infinite vertical strip shown in figure $(a)$. Further, the vertical distance between $p_L$ and $p_R$ must not be more than $\delta$ (this is shown in figure $(b)$).
So, we can first filter out all points lying outside the vertical strip (figure $(a)$). Then, remembering that we have the points sorted according to their $y$ coordinate, we see that it's enough to consider for each point, all the points above until we encounter a point more than $\delta$ units of distance apart vertically. How many points might we check until this happens? This is bounded from above by twice the maximal number of points in a $\delta \times \delta$ box, under the constraint that no two points are less than $\delta$ units of distance apart (remember that each of these two $\delta \times \delta$ boxes is entirely contained either in the left side or the right side, and recall how $\delta$ was defined).
So, how many points is this?
This is the second part to understand, which is actually not really proved in the text you linked to:
(2)
The maximal number of points in an $\delta \times \delta$ box, such that any pair of points is at least $\delta$ units of distance apart is at most 4. The proof is easy:
Divide the box to 4 boxes, each of size $\delta/2 \times \delta/2$.
The diameter of each such box is $\sqrt{2}\delta/2$ which is less than $\delta$. Therefore, in each such small box you can have at most one point and hence there are at most 4 points in the $\delta \times \delta$ box.

"Closest pair of points" algorithm


Which ports are potential security risks for nmap?

Question: I'm using nmap and I am having trouble finding which ports are dangerous and pose the greatest security risks.
Which ports are potential security risks for nmap?
I was thinking samba, telnet, vnc and ftp will pose security risks but I'm unsure.
Answer: It doesn't really work like that.
Ports don't pose a security risk in themselves; it's the application listening on a port that has the risk attached.
And, how vulnerable any given application might be depends on many factors - is the application well patched? Is it well configured? So you can't just say "VNC is a risk", what VNC server is it? What version? How is it configured?
And, of course, security is always more complex. For example, I bet you picked telnet because everyone always says "telnet's insecure, use SSH instead", right? Which is true, but that's because the protocol telnet uses isn't secure against eavesdroppers, it's nothing to do with there being exploits for telnetd (i.e. the application that typically listens for telnet connections).
What you're meant to use nmap for in this context is to check that only the applications that need to have a port open actually do have a port open.
If a host doesn't need sshd, but nmap finds one listening, then you know to go onto the host and fix that. Which is nothing to do with how secure sshd or ssh is.
Answer: All open ports providing services are a potential security risk. The nature of the security risk depends on nature of the service that a program provides. Services providing Samba, VNC, FTP, SSH, HTTP, ... protocols all pose a risk to your security, each in its own (but not unique) way.


Software suggestion to locate stars

Question: I want to photograph the night sky and maybe get a Milkyway in the shot but dont know what position or time. Can you please recommend a software or a website that can let me know the position of the stars and what would be a good time to shoot them?
Answer: If you have an android phone with geolocation and compass, Google nightsky is outstanding. Or if you're on your computer http://www.google.com/sky/ google sky. I'm sure you could find better software for the task, but if you're just trying to get the milky way or a constellation or two, it will do the trick.
Answer: There is a wonderful and hugely popular, open source, cross platform based software called Stellarium which is available at http://www.stellarium.org/. It is free and has tons of features. You can track almost every celestial object with it.
Answer: There is a bunch of real time apps for the iPhone and iPad. I played with an app a few months ago which used the camera with the location services and it was projecting constellations and stars directly onto the image captured by the video camera in real time. I think the app is SkyView.  (there is a free version of that too) Pretty cool but it was processor-intensive so newest gen device would probably work better (4s) you will also need a pretty fast 3G/4G with strong signal or wifi with location services on.
The nice thing about this app was that as I was moving the iphone around with the camera on the stars and constellations were being continually updated.
Answer: On iOS my favorite night sky app is Planets. I have personally used it with good results for the following tasks:

find out when there is no moon, to avoid light pollution
determine the best time of night to capture the milky way on a given location
locate planets and constellations

I have found it accurate for the area where I live (USA, Pacific Northwest) and also during a trip in Ethiopia.
Planets is a free app.

Software suggestion to locate stars