Can we re-enter the US after leaving on the Visa Waiver Programme Next year we plan on flying to Florida, spend a few days there and then fly to South America and spend five nights there, then fly back to Florida and spend a week there and fly back home (We are British citizens). We were planning on using an ESTA to enter but we have a question:  Will we need to apply for two ESTA, for both entries to the US or can we use the same one and leave and comeback?
Can you re-enter USA on an ESTA? I am visiting the US in August 2014 for a week, returning home to the UK &amp; will then be visiting for another 2 weeks in October 2014.  My question is, can I use the same ESTA or would I need to reapply for the second visit? I think the ESTA lasts 90 days but I am unsure if you can leave &amp; re-enter?
Can I use old Minolta AF lenses on my new Canon? I just recently bought my first DSLR, a Canon Rebel t2i/550d. I use it mostly for video and it works wonderfully. I bought the kit lens with it, but I am looking to expand my lens collection. I found a set of old Minolta lenses from my dad, and I was wondering if I could use them on my new camera. The lenses are: a Sigma UC zoom 28-105 f4-5.6, a Minolta Maxxum zoom 70-210mm, a Minolta Maxxum zoom 28-58mm and a Kalimar 500mm lens. I know about the crop factor and that the auto focus won't work, but that does not bother me. Is there an adapter for Minolta AF/Sony to Canon EF mount? Any help is appreciated. Thanks! Erf as term for plot of land in a town or city. Is this word only used in southern Africa? The Free Dictionary website states and so does Wikipedia:     erf [ɜːf]   n pl erven [ˈɜːvən]   (Engineering / Civil Engineering) South African a plot of land, usually urban, marked off for building purposes   [Afrikaans]   The term erf is used in legal documentation and technical English throughout South Africa and Namibia, maybe even further afield in the region.  Is it used anywhere else, except maybe the Dutch/Flemish regions in Europe, where I assume the term originated?  An example:      The client purchased Erf 132, Windhoek for a large sum of money. He intends to build a house on this erf.   The capitalisation of "Erf 132" is commonplace, since it is a definition of a location. This is similar to capitalisation of towns or cities. I find it slightly awkward, but that is how it is done. Hi I would like to know whether the trace of the inverse of a symmetric positive definite matrix $\mathrm{trace}(S^{-1})$ is convex.  Actually I know that the trace of a symmetric positive definite matrix $S\in M_{m,m}$ is convex since we can find $B\in M_{n,m}$ such that $S=B^T\times B$ then we can write the trace as the sum of scalar quadratic forms, i.e. $\mathrm{trace}(S)=\mathrm{trace}(B^T\times B)=\sum_{j=1}^mb_j^T\times b_j$ where $b_j$ is the $j^{th}$ column of $B$.  for instance if we have  $trace([\begin{array}{cc} 1 &amp; 2  \\ 3 &amp; 4  \\ \end{array}] \times [\begin{array}{cc} 1 &amp; 3  \\ 2 &amp; 4  \\ \end{array}])= [\begin{array}{cc} 1 &amp; 2  \\ \end{array}]\times [\begin{array}{c} 1   \\ 2   \\ \end{array}]+ [\begin{array}{cc} 3 &amp; 4  \\ \end{array}]\times [\begin{array}{c} 3   \\ 4   \\ \end{array}]=30$  And so I wonder if $\mathrm{trace}(S^{-1})$ is convex too.. Two Circles and Tangents from Their Centers Problem Let $\Gamma_1$ and $\Gamma_2$ be two non overlapping circles with centers $O_1$ and $O_2$ respectively. From $O_1$, draw the two tangents to $\Gamma_2$ and let them intersect $\Gamma_1$ at points $A$ and $B$. Similarly, from $O_2$, draw the two tangents to $\Gamma_1$ and let them intersect $\Gamma_2$ at points $C$ and $D$.  Prove that $AB=CD$.  I've done some extensive angle chasing on this but have been unable to make any real progress. Can't decide whether $ABCD$ is supposed to be rectangle (as in my diagrams), a parallelogram or even a trapezium. There is a homothety taking one circle to the other but as far as I can see this doesn't help as we don't have a clearly defined center to this.  Any help/hints would be greatly appreciated. Finding Distribution function from probability density function It seems that a number of the statistical packages that I use wrap these two concepts together. However, I'm wondering if there are different assumptions or data 'formalities' that must be true to use one over the other. A real example would be incredibly useful. While I understand the intuition behind expectation, I don't really understand the meaning of variance and moment.   What is a good way to think of those two terms? Has the wall been repaired? As per the title, what is this new feature? Can a single player build a clan dojo? Is it possible for an one-or-two-person clan to build a dojo? If so, what are the resources involved?   I'd like to experience the whole Dojo building experience so I don't plan to join an existing Clan with a dojo already. I understand the difference between LET and LET* (parallel versus sequential binding), and as a theoretical matter it makes perfect sense.  But is there any case where you've ever actually needed LET?  In all of my Lisp code that I've looked at recently, you could replace every LET with LET* with no change.  Edit: OK, I understand why some guy invented LET*, presumably as a macro, way back when.  My question is, given that LET* exists, is there a reason for LET to stay around?  Have you written any actual Lisp code where a LET* would not work as well as a plain LET?  I don't buy the efficiency argument.  First, recognizing cases where LET* can be compiled into something as efficient as LET just doesn't seem that hard.  Second, there are lots of things in the CL spec that simply don't seem like they were designed around efficiency at all.  (When's the last time you saw a LOOP with type declarations?  Those are so hard to figure out I've never seen them used.)  Before Dick Gabriel's benchmarks of the late 1980's, CL was downright slow.  It looks like this is another case of backwards compatibility: wisely, nobody wanted to risk breaking something as fundamental as LET.  Which was my hunch, but it's comforting to hear that nobody has a stupidly-simple case I was missing where LET made a bunch of things ridiculously easier than LET*. Why are there two tensions on my free body diagram? A man sits on a platform attached to a pulley and pulls himself up as shown (ignore the angle of the rope - it should be vertical). Apparently, the man/platform object has a force of 2T pulling it up. Why is it not just T?  Much appreciated! Why {are you / you are} making noise? I always get confused between these two sentences:     Why are you making noise?      Why you are making noise?   Could anyone put light in the differences between the two? If you have a conducting hollow sphere with a uniform charge on its surface, then will the electric field at every point inside the shell be 0. The reason the electric field is 0 at the center is clear from the symmetry of the sphere, but for a point at a certain distance from the center, shouldn't a net electric field exist?  I saw a similar question on the site but it was vaguely explained. When should "farther" and "further" be used? Cannot access to (or find out) main Settings program How can I break an align environment for a paragraph? I would like to have two displayed equations, broken by a short paragraph, but with aligned equal signs (as if using the align environment).  Is there some way to "break" the align environment temporarily? For example block cipher AES-128, Key size is 128bit and it is used to make a 10 round key which is total 320bit.  Question 1. If i use another Key schedule algorithm in AES, then security decreased or remain same? In other words, if the key schedule algorithm of AES has some relationship with AES encryption itself, then it will be decreased, or it will be same if the new key schedule algorithm is safe enough.  Question 2. Why we expand key? brute force will take O(2^128) time regardless of the key schedule is strong or not. what is the advantage of making key expend? I was curious about this when I was learned about 3DES. Which developed because the former DES has weak key length 56bit so vulnerable to brute force attack, i was wondering why doesn't they just remove key schedule process and use the whole round key as a key. Evaluating $\int P(\sin x, \cos x) \text{d}x$ Suppose $\displaystyle P(x,y)$ a polynomial in the variables $x,y$.   For example, $\displaystyle x^4$ or $\displaystyle x^3y^2 + 3xy + 1$.  Is there a general method which allows us to evaluate the indefinite integral     $$ \int P(\sin x, \cos x) \text{d} x$$   What about the case when $\displaystyle P(x,y)$ is a rational function (i.e. a ratio of two polynomials)?   Example of a rational function: $\displaystyle \frac{x^2y + y^3}{x+y}$.    This is being asked in an effort to cut down on duplicates, see here:   and here: When should we use proximity rule in "either/or", and "neither/nor"? According to this , if at least one of the nouns involved is plural then it should take the plural form of the verb. Otherwise, it should take the singular form of the verb. But in the last part it says not all grammars agree to those rules thus proximity rule applies. However, it doesn't explain when to apply the proximity rule and when not to use the former rules.