Can there be a two-neutron bound state?
Why are the dineutron and diproton unbound?
Probability that 2 appears at an earlier position than any other even number in a permutation of 1-20 Suppose we uniformly and randomly select a permutation from the 20! Permutations of 1,2,3,...,20. What is the probability that 2 appears at an earlier position than any other even number in the selected permutation?  My approach :   2 in first position ==> 1*19! (1 is the position of 2)  2 in second position ==> 10 *1 *18!  2 in third position ==> 10*9 *1 *17!  . . .  2 in 11th position ==> 10*9*8*7*6*5*4*3*2*1*1*9!  But this was asked as a multiple choice question in GATE 2007 and the options were  (A) 1/2   (B) 1/10  (C) 9!/20!  (D) None of these  I am not able to reduce this analysis to a given option. I recently upgraded from blender 2.81 to 2.82a, and I've immediately noticed a problem. Blender is not rendering HDRI images like it used to. You used to be able to plug an HDRI image into the background node, and into the world output. However when I do this now, in Eevee or Cycles, it renders what can be described as "as solid color" version of the HDRI instead of the actual HDRI image.   Here are some images to show as examples, each has a difernt HDRI, one is in Eevee, one is in Cycles. Is this a new "feature" of 2.82 or is this a bug? Thanks. Print lines between (and excluding) two patterns How do I delete Windows.old in Windows? I used to run Windows 7 32 bit, but installed the 64 bit version because of a RAM upgrade. During the installation I got this message:      The partition you selected might contain files from a previous Windows installation. If it does, these files and folders will be moved to a folder named Windows.old. You will be able to access the information in Windows.old, but you will not be able to use your previous version of Windows.   The C:\ drive now has two (2) Windows folders:   Windows (15.3 GB) Windows.old (15.7 GB)     Don't see why I need the Windows.old taking over 15GB of space on my hard drive so I tried to delete it. It didn't work.  How can I safely delete this folder? How full is too full for mechanical hard drives? I have heard many claim that it doesn't matter how full a drive is until it starts cutting into temp and virtual memory space.  This doesn't make sense to me, given the nature of how the data is transacted on a hard drive. The inside of the platter presents less data per revolution than the outside of the drive does, by significant factors. The inside 40% of the radius of full size hard drive is used for the spindle, so only the outside 60% is used for data storage, but that still means that the inside track of a hard drive presents data 60% slower than the outside track.  By my calculation, a Hard drive that is only 10% full should perform about 2.25 times faster than a hard drive that is 90% full, assuming that the flow is constrained by other factors.  Am I wildly off base here? For all the drives I know, even the top speeds of the first 1% of the drive would be well within the bandwidth provided by a SATA 2 connection. MacBook Pro never goes to sleep I got a brand new mid-2015 MacBook Pro 15", OSX 10.11.3.  Display never turns off even it is configured to turn off after 10 mins in power adapter AND in battery mode. Screen saver (aerial) stays active forever. I tried disconnecting all USB peripherals connected - it did not help.  Any ideas? Does the Darkness spell block vision? In discussing , I came to realize that the real question was whether Darkness blocks vision or merely creates "darkness".    Per the wording of the spell:     Magical darkness spreads from a point you choose within range to fill a 15-foot-radius sphere for the duration. The darkness spreads around corners. A creature with darkvision can’t see through this darkness, and nonmagical light can’t illuminate it. (emphasis mine)   Normal darkness is defined in the game as creating a heavily obscured area and the only description added to the darkness is that it is magical, which (to me) just means that it is created by magic and is subject to the magical rules.    Darkvision is defined in the game as basically being able to see in darkness as if they were seeing in dim light. So, the text "darkvision can’t see through this darkness" merely means that it affects darkvision in the same way it affects normal vision. (See earlier versions of the spell below, which had similar wordings.)    I see nothing there that implies it is a barrier to vision, just an active  and utter absence of illumination.    Previous editions have varying descriptions.  and  give accurate accountings of the various versions.   The 1e Wizard version seems to actually imply a sphere of opaque blackness that even blocks infra/ultravision, while the 1e Cleric version is a reversal of the Light spell and creates totally normal darkness, with no block to special visions.   The 2e version is similar to the 1e Cleric spell. It creates an area of darkness "equal to an unlit interior room".   The 3.0e version comes closest to the 5e version. It "causes an object   to radiate darkness out to a 20-foot radius. Not even creatures who can normally see in the dark (such as with darkvision) can see in an area shrouded in magical darkness." Still no reference to any sort of opacity and the wording makes it clear that darkvision is being treated specifically here.   3.5e Darkness is similar, although instead of darkness, it creates "shadowy illumination". This affects darkvision as well as normal vision.   4e doesn't have a Darkness spell, but rather a Cleric Utility called Veil of Darkness, which creates "a zone that is heavily obscured and blocks line of sight." So, finally, a reference to opacity, in "blocks line of sight", although I question if opacity was the intent. How to properly install Microsoft Office in Ubuntu 14.04 with wine? I have been trying to install it many times using the Wine version avaliable from the Sofware Center. Is there a proper way to configure it for allowing the installtion? What is the difference between necessary and sufficient conditions? If $p\implies q$ ("$p$ implies $q$"), then $p$ is a sufficient condition for $q$. If $\lnot p\implies \lnot q$ ("not $p$ implies not $q$"), then $p$ is a necessary condition for $q$.   I don't understand what sufficient and necessary mean in this case. How do you know which one is necessary and which one is sufficient? error with inner class object How do I enable or disable the global application menu? I'm interested if any of the following explanations have enough predictive capability to explain the observations we see today. The claim is that the Universe is not expanding, and that red-shift of light is caused by:    Though a couple of these are simply ridiculous, I'm still interested. Keep in mind that I am not a creationist, but am looking for reasons to see if any of these are valid or invalid. How do I pack textures for sending off to a render farm Whenever i try to send a project off to a render farm such as sheepit, it says it needs the textures packing with the file in order to render correctly.  How would I do this? Using wired and wireless headphones simultaneously? I have 1 android device, 1 wired headphones, 1 wireless headphones, 2 ppl willing to watch film.  When I connect both of headphones only wired work.  Is it possible to use both of headphones simultaneously? What's the difference between 18 A & 18 Ah on a Battery What's the difference between 18 A &amp; 18 Ah on a 12 V Battery Does "Delete Local Content" retain save files? If you remove a single player game installation with the Delete Local Content option from the Steam Libary, in general will save files be deleted or retained? How to switch language keyboard combination? Proving that $\sum_{k=0}^{n}\frac{(-1)^k}{{n\choose k}}=[1+(-1)^n] \frac{n+1}{n+2}.$ I generated a key and copied it to my target:  ssh-keygen ssh-copy-id username@hostname   I left the the location of the key as default and did not set any passphrase.  For a small while after that, I was able to ssh username@hostname without being prompted for a password, and then it stopped working for some reason. UV Unwrapping a Modified Model I modified an existing model by removing unwanted vertices, then selecting surrounding vertices and creating faces one triangle at a time (By pressing 'F').  On UV unwrapping the mesh, the faces which were added by me seem to stretch from the very bottom left of the map, shown below.    How do I create a face so it appears on the UV map as expected?