What zoom 70-300mm lens should I get for my Nikon D3300?
What type of lens will auto-focus on Nikon bodies without a focus motor?
I want to append several shapefiles in QGIS. The ftools 0.6.1 add-on is installed.   But under Vektor>Datenmanagement-Werkzeuge>Shapedateien zu einer zusammenführen (=append shapefiles) is only the possiblility to choose the Eingabedatei (input file) and the Ausgabedatei (output file) but not a further Datei (file) for the append itself? (Even though there are  several shapefiles in the same folder)  //Furthermore the icon "In neue Projektion exportieren" (export to new projection) is also not appearing under the: Vektor>Datenmanagement-Werkzeuge? Do I need a further add-on?//  Has anyone an idea why I can't choose a shapefile for the appending?  Thanks in advance! phil Is there any way to generalise this problem? Number of elements in a finite $\sigma$-algebra For some results returned in Google Search, on the right side it displays the company details, logo, contact numbers, etc...   For example, see the following screenshot:    I'd like to know what contributes to this so that I can try to achieve it for my site too. LaTeX Classes or Styles for Schedules and/or Calendars? Maybe TeX isn't the best for this particular problem, but any teachers out there use a particular class or package to plan lessons?  Right now I'm just using a spreadsheet, but I always find myself wishing there was a 'lessonplan.sty' or 'classschedule.sty' file out there somewhere so I could still use the LaTeX for equations, tables, lists etc.    A bit of searching yielded a few results, but there doesn't seem to be a consensus.  Anyone used any of these:        Any recommendations from anyone on best way to make calendar-based class schedules and/or lesson plans? Prove that the product of four consecutive positive integers plus one is a perfect square I need to prove the following, but I am not able to do it. This is not homework, nor something related to research, but rather something that came up in preparation for an exam.     If $n = 1 + m$, where $m$ is the product of four consecutive positive   integers, prove that $n$ is a perfect square.   Now since $m = p(p+1)(p+2)(p+3)$;     $p = 0, n = 1$ - Perfect Square      $p = 1, n = 25$ - Perfect Square      $p = 2, n = 121$ - Perfect Square   Is there any way to prove the above without induction? My approach was to expand $m = p(p+1)(p+2)(p+3)$ into a 4th degree equation, and then try proving that $n = m + 1$ is a perfect square, but I wasn't able to do it. Any idea if it is possible? Proof for two sequences producing the maximum value when sorted I am trying to improve my discrete Math skills by doing some proof exercises. But I am struggling to understand how to start proving the following hypothesis:  $$ S = {x}_1{y}_1 + {x}_2{y}_2 + \ldots + {x}_n{y}_n $$ Where ${x}_1,{x}_2\ldots{x}_n$ and ${y}_1,{y}_2\ldots{y}_n $ are ordering of two different sequences of positive real numbers, each containing n elements. S takes its maximum value when ${x}_1,{x}_2\ldots{x}_n$ and ${y}_1,{y}_2\ldots{y}_n $ are sorted in non decreasing order.  I was thinking that I should maybe use a proof by contradiction. Where the negation of the hypothesis is: S takes it minimum value over all ordering of the two sequences when both sequences are sorted into non increasing order.  However I am not sure my negation of the hypothesis is correct or how proceed from there. I do not want the complete proof because I am trying to learn how to do it myself but if some one can tell me how to make a start on this I would be grateful. Which cyan colored line is produced in the Thomson e/m apparatus? Related:   After reading Lisa Lee’s OP on an electron deflection tube, although she had some misunderstandings on its operation, I still believe that her question is still relevant. If one looks at the Thomson e/m tube filled with helium gas (made by ), the tracer light is created by de-excited electrons, not by an electron beam interacting with a phosphor as in Lisa Lee's OP. That is, the accelerated electrons scatters off of a low pressure helium gas and emit a tracer line to follow the electrons path, as shown below.     Now if you look at the bright line spectrum of helium,     One can clearly see that there are two “cyan” color lines around 500 nm. Following in Lisa Lee’s footsteps, there is a series of question one can ask: (1) which line is emitted by the Helium gas atoms? Or are both lines emitted? (2) How can a variable accelerating voltage for the electrons always produce the same tracer line color? In theory, I assume that if I decreased the energy of the electron beam, I could produce red (around 670 nm) or yellow (around 590 nm) tracer lines, but that doesn’t happen. Somehow, it appears to me that the e/m tube is “tuned” just right so that the emitted light is always this “cyan” color. Why? Different colors for different types of blocks in beamer In a beamer presentation, I’d like to set up different colors for normal blocks, definition blocks, theorem blocks, proof blocks, example blocks…  Ideally I’d set those up using \usebeamercolor commands. I can do it for example blocks, and for all other kinds of blocks at once, as illustrated in the sample below (compiled using XeLaTeX). But I can’t find how to do it for specific, non-example, types of blocks.  I suppose “” points towards some solution, but I’d prefer (somehow) inheriting from the existing special block environment definitions rather than define new environments from scratch.  \documentclass{beamer} \usepackage{fontspec}  \useinnertheme[shadow=true]{rounded}  \setbeamercolor{block title}{use=structure,fg=structure.fg,bg=structure.fg!20!bg} \setbeamercolor{block body}{parent=normal text,use=block title,bg=block title.bg!50!bg}  \setbeamercolor{block title example}{use=example text,fg=example text.fg,bg=example text.fg!20!bg} \setbeamercolor{block body example}{parent=normal text,use=block title example,bg=block title example.bg!50!bg}  \begin{document} \begin{frame}     \begin{block}{My block}         A block.     \end{block}     \begin{definition}[My definition]         A definition.     \end{definition}     \begin{theorem}[My theorem]         A theorem.     \end{theorem}     \begin{proof}[My proof]         A proof.     \end{proof}     \begin{example}[My example]         An example.     \end{example} \end{frame} \end{document} Is there anyway I can connect resistors to allow them to take more power such as using 4 1/4 watt resistors to get a 1 watt resistors. Or do i just have to use 1 1 Watt resistor. Superluminal neutrinos I was quite surprised to read this all over the news today:     Elusive, nearly massive subatomic particles called neutrinos appear to travel just faster than light, a team of physicists in Europe reports. If so, the observation would wreck Einstein's theory of special relativity, which demands that nothing can travel faster than light.   &mdash;  Apparently a CERN/Gran Sasso team measured a faster-than-light speed for neutrinos.   Is this even remotely possible? If so, would it be a real violation of Lorentz invariance or an "" effect?   The ; a webcast is/was planned .  News conference video How are Clash of Clans multiplayer battles determined Are battles determined by level or trophies? Just curious. What would happen if every person in the world gathered at a minimum possible area and jumped all at once? Would that have any effect on Earth? I'm self studying J. Lee's Introduction to Topological Manifolds, and after doing all other exercises on chapter 2, I can't seem to come with the proper counterexamples for this one.      For each of the following properties, give an example consisting of two subsets $X, Y \subset \mathbb{R}^2 $, both considered as topological spaces with their Euclidean topologies, together with a map $f: X \rightarrow Y$ that has the indicated property.         Open but not closed/continuous   Closed but not open/continuous    Continuous but not open/closed         etc... (all cases)   I think the reason for my difficulty is a lack of geometric intuition of what open, closed and continuous maps look like as deformations of shapes in $\mathbb{R}^2$ (I can construct counterexamples from artificial made up spaces).   I tried squashing balls and 'pumping space' into lines, as well as joining strips in annulus shapes, but all the examples I seem to come up with are either too well behaved (i.e. all 3) or too misbehaved.   Instead of a case by case answered I would prefer a couple worked out cases and some intuition on how to visualise open / closed maps in this context. Mobile SE sites not allowing edits to edits When you have less than 2K rep and your edit goes in a queue, you are usually allowed to revise your edit while it is being reviewed, by clicking the edit button again on the question page. However, when on mobile SE sites, the edit button disappears when you have submitted an edit for review.    Editing  by  into the question: It seems that the cause of this is when the mobile site hides the edit link (when there is a pending edit), it doesn't check who is making the edit, which means that it hides it for your own as well as other's edits. How to properly play .mkv files? I am having a problem while playing .mkv files. Every time I play a .mkv file, the audio can be heard but video cannot be seen. The only way to see the video if I actually right click on it or put a window in front of it and it displays one part of the video but not all.    The link of the picture above basically describes what I am saying. While I was trying to take the screenshot, the window for the screenshot disappeared and displayed part of the video. I hope someone could help me on this. Thank you!   EDIT: I was running Unity 2D when I have the problem but when I run Unity 3D, it works. So I need to make this work on 2D. Please help. Cannot modify files installed by `snap` I have installed a package using snap and I need to modify one of the files but when I try to change its ownership or permissions, I always get the following message:  sudo chmod +x ./my_file.js chmod: changing permissions of '/snap/my_app/my_file.js': Read-only file system   How can I modify files that are installed via snap? Force JavaScript exception/error when reading an undefined object property? Proof of orthogonal matrix In the following question we regard vectors in $\Bbb R^n$ as columns and define the dot product in the usual way which means that $x · y$ = $x^{t}y$  a) If A is an n × n matrix show that $A_{ij}$ = $e_i \cdot A e_j$ where $e_i$, $i =1, \dots , n$ are the standard basis vectors in $\Bbb R^n$  b) Show that a matrix $P$ is orthogonal if and only if ($Px$) · ($Py$) =$x · y$ for all $x, y$ ∈ $\Bbb R^n$  Working -   I got part (a) alright but have no idea of where to start with part (b) except to use the information that an n x n matrix $P$ is orthogonal if $P^{-1}$= $P^{t}$ and that $P^{t}$$P$=$I$, $P$$P^{t}$=$I$, where $I$ is the identity matrix. Any suggests are gracefully appreciated. Feel free to edit my question for clarity. Thank you Why is ATP the most prevalent form of chemical energy storage and utilization in most cells?