Why are primordial black holes considered non-baryonic?
Are black hole regarded as baryonic matter in cosmology?
Find a recurrence relation for the number of ways to arrange $n$ dominoes to fill a $2$ by $n$ checkerboard. I am having trouble with this question, please take a look at it:     Find a recurrence relation for the number of ways to arrange $n$ dominoes to fill a $2$ by $n$ checkerboard.   I have just started reading the topic and it is one of the starting problem. Please help. You can give me some hints, a complete answer is also appreciated.  Thanks Why does it says "welcome back -user- click here to 'refresh page'" After logging into one Stack Exchange site, when I visit another SE site, it says to me, welcome back - user - click here to refresh - web page.   Isn't it possible to refresh the page using code &amp; without the user's interaction? There was a film from the 80s in which young people can teleport anywhere they can think of.   These guys are recruited to do studies with, maybe by the government or a secret company which wants the take advantage of their abilities.   I saw it on cable TV around 1990-1997.   Any clues? Does something like  exist for topological (eg. braided) circuits?   Alternatively, any ideas on how @ is getting  (or something similar)? What is the correct way to pluralize an initialism in which the final word is not pluralized by adding the letter "s"? I need to do this for displacement mapping, subdivision gives a bad result and makes triangles distinguishable.    Related to:   But I get the error "No other selected object found to use for projection". Accessing site-specific Help Center from iOS app Can the Stack Exchange developers add an option to access the site-specific Help Center via the iOS app?  My use case is when I read a question that I think is off-topic, and want to double-check that the wording from the site's Help supports that position, having the Help Center available would be nice. I know that atan2 gives me the absolute angle of any vector. But it doesn't give a value from 0 to 360 degrees. Instead, it gives a value (if I'm not mistaken), between 0 and 180, or between 0 and -180. For example, instead of giving angle 270, it will say -90.  This is a little confusing for me. Let me try to describe how I think this works, and please tell me if I'm correct. Actually, I'll draw it.    Is this correct? I'm having a little trouble understanding this. Thanks What is the difference between a symbolic link and a hard link? Recently I was asked this during a job interview. I was honest and said I knew how a symbolic link behaves and how to create one, but do not understand the use of a hard link and how it differs from a symbolic one. Sometimes we assume that regressors are fixed, i.e. they are non-stochastic. I think that means all our predictors, parameter estimates etc. are unconditional then, right? Might I even go so far that they are no longer random variables?  If on the other hand we accept that most regressors in economics say are stochastic because no outside force determined them with some experiment in mind. Econometricians then condition on these stochastic regressors.  How is this different from treating them as fixed?  I understand what conditioning is. Mathematically, it means we make all observations and inference conditional on that particular set of regressors and have no ambitions to say that inferences, parameter estimates, variance estimates etc. would have been the same had we seen a different realization of our regressors (such is the crux in time series, where each time series is only ever seen once).  However, to really grasp the difference between fixed regressors vs. conditioning on stochastic regressors, I am wondering if anyone here knows of an example of an estimation or inference procedure that is valid for say fixed regressors but breaks down when they are stochastic (and will be conditioned on).  I am looking forward to seeing those examples! I tried a small experiment. I posted a post on Facebook at exactly: 21:01 and waited to see how many hours ago it will say. When it was 22:50 it still said that my post was posted 1 hour ago.  Though some days back on this forum some people told me that when something started at 21:01 and it is 22:50 that I should say it started 2 hours ago.  So whom should I trust now?  All social networks like Facebook, Instagram and YouTube etc. use the system where it would say 1 hour ago even if it was 119 minutes already, so meaning they will never say it was 2 hours ago unless at least 120 minutes passed.  This was the way I used to express 1 hour ago as well. However, since I heard the answers from many other people I feel unsure about it right now...  I am talking about casual speech with friends etc. In such scenario. What would you say? 1 or 2 hours ago? Is Facebook/YouTube/Instagram wrong or?   if we decide to agree on the theory that if it is more than 1 hour and 40 minutes it is a good idea to round to 2 hours ago.   So what time span would you imagine if something happened let say 10:10, now it is 11:50.  If somebody said to me that something happened 2 hours ago and I looked on time saying 11:50 I would image that it happened some time between. (9:30-9:50)  That is why it feels so weird for me to say 2 hours ago thought it has not been more two hours yet.   I dont know why but more logical for me it feels to say 1 hour ago though it can already be more than 100 minutes  and still just say that it happened an hour ago when talking with friends, teachers, whoever in casual speech unless it is something super important i would say exactly hours and minutes.  How do you say it in your life? How do you express time in such situations? Do you express time the same way as Facebook or?   I know that some of you may think this is some kind of joke, unfortunately it is not and I am going crazy and depressed without knowing system for this... It has been already 2 months and I still feel overwhelmed with this ideas and questions... I cannot help myself, please help me, please.  Thanks for your help. How to check if sed has changed a file Why is the space between words in my source code listing so big? I used the following code to list my java code, but the it looks like there's too much space between words. What can I do?  % source code listing \usepackage{listings} \usepackage{color} \usepackage{xcolor}  \usepackage{caption}  % citation style \usepackage{apacite} \DeclareCaptionFont{white}{\color{white}} \DeclareCaptionFormat{listing}{\colorbox{gray}{\parbox{\textwidth}{#1#2#3}}}  \begin{document} \begin{lstlisting}[label=some-code,caption=bind to service call] bindService(new Intent(this, Recognizer.class), recConnection, Context.BIND_AUTO_CREATE); \end{lstlisting} \end{document}   The snapshot of what I got. The code not completely shown, and space too wide, in function bindService. How to cook a pork sirloin roast? I picked up a pork sirloin roast yesterday, it's a little over three pounds.  I've never cooked one of these before and I am not sure what to do.  My seasoning plan is salt, pepper, thyme, and rosemary, and I might poke a couple holes for cloves of garlic as well.  My cooking plan is 8+ hours in the crock pot on low, with about an inch of water in there.  Will this turn out OK?  I'd like a tender and moist result, obviously.  Any tips would be greatly appreciated. Is a semigroup with unique right identity and left inverse a group? We know that a semigroup with a right identity and right inverse for all elements is a group (e.g. see ). Symmetrically, also a left identity together with a left inverse implies a group. We also know that a semigroup with a right identity and a left inverse is NOT necessarily a group (see ). My questions are:   in a semigroup, is the existence of a UNIQUE right identity together with the existence of a left inverse enough to have a group? in a semigroup, is the existence of a right identity together with the existence of a UNIQUE left inverse enough to have a group?   I think both these claims are false,  ut haven't found a counter-example so far. Should operator<< be implemented as a friend or as a member function? That's basically the question, is there a "right" way to implement operator&lt;&lt; ? Reading  I can see that something like:  friend bool operator&lt;&lt;(obj const&amp; lhs, obj const&amp; rhs);   is preferred to something like   ostream&amp; operator&lt;&lt;(obj const&amp; rhs);   But I can't quite see why should I use one or the other.  My personal case is:  friend ostream &amp; operator&lt;&lt;(ostream &amp;os, const Paragraph&amp; p) {     return os &lt;&lt; p.to_str(); }   But I could probably do:  ostream &amp; operator&lt;&lt;(ostream &amp;os) {     return os &lt;&lt; paragraph; }   What rationale should I base this decision on?  Note:   Paragraph::to_str = (return paragraph)    where paragraph's a string. Going through the spells, I see the phrase "Willing creature" used to determine who you can cast some spells on. I don't ever see a proper definition of what a willing creature is, but I would assume that it would go something like if you asked them "Can I perform this spell on you" they would answer yes. Is there a more formal definition of what makes a target willing in 5e?  What are the ways I could make an otherwise unwilling creature willing? Suggestion spells, for instance, should probably work but what other options do I have? What's the recommended max width for the main container and for the main column, for large screens? Based on this question,  and its comments and answers, I did some research, but I didn't find a complete answer.   For me it is obvious that it is a good decision to limit the width of the main container, but what is the recommended max-width for the main container for large screens, in 2017, when the screens become larger and larger? What variables should be considered in this decision?  Also, let's say a website has multiple columns in the main container, what is the max-width for the main column?  Update: I have now a related question. I recommended to one client to reduce the width of the main container on the homepage, but I can't convince him. It is a website with photos, like pexels.com. It is in this case important to limit the width if the elements are not one more important than other? Does Java Connection.close rollback? Send data from Lightning Web Component (LWC) to a Visualforce page I am adding an LWC component in visualforce and need to add a handler for an event fired in the LWC component on the visualforce page. When googling all I can find is examples of how to do this with aura component using application events. LWC controller: handleSearchClick() {              const searchinfo = {          shipper: this.shipper,         system: this.system,         product: this.product,         status: this.template.querySelector('c-lwc-multi-select').value(),         period: this.period       };     this.dispatchEvent(new CustomEvent(         'dosearch',          {             detail: { data:  searchinfo},             bubbles: true,             composed: true,         }     ));     console.log({ 'lwcNominationSearch searchinfo': searchinfo }); }  AURA app: &lt;aura:application extends=&quot;ltng:outApp&quot; access=&quot;GLOBAL&quot;&gt; &lt;aura:dependency resource=&quot;c:lwcNominationSearch&quot; /&gt; &lt;aura:dependency resource=&quot;markup://force:*&quot; type=&quot;EVENT&quot;/&gt; &lt;/aura:application&gt;  Visualforce: &lt;div id=&quot;rcontainer&quot;&gt; &lt;/div&gt;  &lt;script&gt;     $Lightning.use(&quot;c:NotificationSearch_ltngoutApp&quot;, function()     {         $Lightning.createComponent(         &quot;c:lwcNominationSearch&quot;,         {},         &quot;rcontainer&quot;,         function(cmp)         {             console.log('component created');              //$A.eventService.addHandler({ &quot;event&quot;: &quot;c:myEvent&quot;, &quot;handler&quot; : visualForceFunction})               $A.eventService.addHandler({                 event: 'dosearch',                 handler: function (event) {                          console.log(&quot;vf event success&quot;);                 }             });          });     }); &lt;/script&gt;