Is it possible for two or more photons to collide simultaneously with one electron, resulting in the emission of that electron from the metal surface? I searched for two photon absorption and found that an atom or molecule can absorb two photons if the sum of their energies is greater than the work function, but I want to know whether it is possible for two or more photons to interact with a single electron and cause its emission?
I understand that assuming light is quantized implies that if a lower energy interacts with  metal, it is possible that that quanta will not have enough energy to eject the electron. What prevents two quanta from interacting with the electron at the same time, though, and summing to have enough energy to release the particle. Indeed, what if two separate light rays of the same frequency impact the electron, why can't that free it?
Why isn't smoke flowing with the shape of the domain? I created this Smoke domain.    Then When I added smoke, it didn't stay within the domain, it went through the hole. When can a sum and integral be interchanged? Let's say I have $\int_{0}^{\infty}\sum_{n = 0}^{\infty} f_{n}(x)\, dx$ with $f_{n}(x)$ being continuous functions. When can we interchange the integral and summation? Is $f_{n}(x) \geq 0$ for all $x$ and for all $n$ sufficient? How about when $\sum f_{n}(x)$ converges absolutely? If so why? How can I view the contents of tar.gz file without extracting from the command-line? I want to see the contents (list of files and folders) of an archive, for example a  tar.gz file without extracting it.  Are there any methods for doing that? Do questions about specific StackOverflow implementation details belong on SO or Meta? has several discussion comments going back and forth about whether the question belongs on SO or Meta.  The question is asking about how a specific feature of the site is implemented from a coding perspective (so that the OP might duplicate it in their own implementation), which can make it a legitimate programming question.  According to the Meta FAQ: "If your "question is about ... Stack Overflow / The core Stack Exchange engine", it should be asked here.  Here are some similar example questions on Meta:         Where do these questions belong? Is there a way to show Spotlight indexing status/progress in Yosemite? In previous versions of OS X, you could click the Spotlight icon in the menu bar to show the status of the Spotlight indexing, and it would show an estimate ("6 hours left"), along with a progress bar.  I've updated to Yosemite yesterday, and I noticed that Spotlight is not showing some expected results, i.e. files I know to be there, but it just doesn't find them if I type in their name and file type ("kind:excel vacation").  When I start typing in the Yosemite Spotlight window, it shows a small progress bar under the search box, but there's no estimate.    Is there another way to show the progress or an estimation on how long the indexing is going to take? Polygon intersection using turf js Prove that a set of connectives is inadequate 70s TV miniseries: antagonist gets followers to his pacifist ideology through mind control devices I am trying to recall the name of TV-series that was aired in the 70s (possibly only in selected European countries?). IIRC it was a French production. The bad guy was using some kind of mind control devices. He was gradually getting more and more people as followers to his pacifist ideology (it was the cold war era, and pacifism might have struck a chord even without mind control).  His modus operandi was to send a dozen or so (mind-controlled) cronies to surround a new victim. They would form a square around the helpless target, forcing him to walk into a building, where mind control devices were surgically installed.  The protagonists were trying to organize a resistance movement. IIRC they failed, as the bad guy had good intelligence about their plans. White regions in DensityPlot — is this a bug with ColorFunctionScaling? Can we create a subsection of the References Cited section with different reference numbering? I need to add some more publications. I do not want to change the previous reference numbers, so I need to create new citations with difference reference numbering like [p1], [p2], etc. Can LaTeX do that? Can I achieve a torchlight effect (lighter area around a light source) in a 2D game? I am thinking of writing myself a simple 2D game. It will not shine with perfect graphics or gameplay at first, but I'd consider it my first step in PC game development. So, imagine such simple sprite-based 2D game (like Heroes IV or Startcraft BroodWar).  I want the gameplay to support day/night with the according lighting changes and at the same time it will be madness to have to create sprites for every lighting nuance. So, I decided adding a semi-transparent layer on top of other objects will be enough.   The issue with this solution is if I have a light source object in the game (like the hero wearing a torch, or a burning building), there must be a lighter area around it, right? Since I am putting my semi-transparent layer over everything, how would you suggest to achive the torchligt visual effect I want? Maybe redraw that layer adding 'gaps' or differently colored areas based on the lighting effect? What is the "Bootable flag" option when installing a distro? Is the "bootable flag" needed in today's distributions? If not, then why is it still in the installers? What is it exactly? I am going to change my machine: from a laptop with Ubuntu to another laptop where I am going to install Ubuntu...  I am quite happy with the current system, what I am afraid of is having to rebuild everything from 0.  So what do people often do to clone an Ubuntu system? That may include the data, packages, shortcut settings, etc... 2015 Macbook Air screen gradually dimming and dying This is not a problem at booting up. For a couple months now I'll be using my laptop when suddenly the screen dims to about 50% of normal. According to the brightness indicator the brightness is all the way up; I can make it dimmer, but not as bright as normal. The dimming isn't super even either, there are small areas of the screen that seem darker/brighter. In the past the problem easily goes away if I close the lid and reopen it... but now it's happening a lot and sometimes going completely black. Is this an easy/cheap fix? I'm traveling and can't do it myself. Is it worth bringing to the Mac store?  Thanks! I want to filter a java.util.Collection based on a predicate. What is the difference between 'git pull' and 'git fetch'? What are the differences between git pull and git fetch? What is the difference when you say "get off of something" and "get off something"? Meaning of "stackexchange" What does stackexchange mean? I have checked out this  to read about the Stack Exchange Network. Get real client IP in a Servlet Evaluating $\sum_{n=1}^\infty \frac{2^{2n-1}}{5^{n+1}}$