What is the meaning of power radiated by a black body per unit frequency? If you have a black body with a frequency filter around it set to 530nm and you calculate the energy radiated in 1 second  you will get a definite (not a differential) value. So where does "per unit frequency" come from? What is its physical meaning? Edit: There is a physical anamoly in my argument as, suppose, at 530 nm we get 5 watt energy, so at 530.01 nm the power will approximately be the same 5 watt, and similarly for 530.001nm. But I still don't get the flaw in my argument (even though I get that the result is wrong). What is it that I am missing?
We were discussing Kirchoff's theorem on blackbody radiation in class today and the equation was: $$e_{f}= J(f,T)$$  $e_f$ was defined as power per unit area per unit frequency. What does per unit frequency refer to here? I know what per unit time means but don't understand 'per unit frequency'.
Pointer to class data member "::*" I came across this strange code snippet which compiles fine:  class Car {     public:     int speed; };  int main() {     int Car::*pSpeed = &amp;Car::speed;     return 0; }   Why does C++ have this pointer to a non-static data member of a class? What is the use of this strange pointer in real code? How can I check if an application is running from a batch (well cmd) file?  I need to not launch another instance if a program is already running. (I can't change the app to make it single instance only.)  Also the application could be running as any user. In JavaScript, the "this" operator can refer to different things under different scenarios.   Typically in a method within a JavaScript "object", it refers to the current object.  But when used as a callback, it becomes a reference to the calling object.  I have found that this causes problems in code, because if you use a method within a JavaScript "object" as a callback function you can't tell whether "this" refers to the current "object" or whether "this" refers to the calling object.  Can someone clarify usage and best practices regarding how to get around this problem?     function TestObject() {             TestObject.prototype.firstMethod = function(){                       this.callback();                       YAHOO.util.Connect.asyncRequest(method, uri, callBack);              }              TestObject.prototype.callBack = function(o){               // do something with "this"               //when method is called directly, "this" resolves to the current object               //when invoked by the asyncRequest callback, "this" is not the current object               //what design patterns can make this consistent?               this.secondMethod();             }             TestObject.prototype.secondMethod = function() {              alert('test');             }         } Why would a journal accept my previous paper for publication, but reject latest manuscript due to being "outside of the journal's scope?" I submitted a manuscript last year to an IEEE journal, and the paper was accepted for publication. I recently submitted a new manuscript to the same journal, but, this time, the paper was rejected, and I was told that I should submit to another journal since my paper was not within the journal's scope. The two papers both target similar applications. Furthermore, the second paper uses some work in the first paper, making substantial improvements at solving a much more difficult problem. Based on the reviewer's comments (and my own personal assessment), I do not believe that the work presented in the second paper was "incremental" in nature. Far from it. Two of the three reviewers gave positive reviews. The third reviewer, however, mentioned the "outside of journal's scope" issue and the associate editor and editor-in-chief both sided with the 3rd reviewer, and the paper was stopped dead in its tracks.  I'm scratching my head trying to come to terms with how in the world my first paper could be accepted by this journal, but the second paper focused on the same application space and achieving substantial improvements on a much more difficult problem (backed up with measured results) could be rejected. Any ideas? How to disable pagebreak on \hline in longtable? How to disable pagebreak on \hline in longtable?  This is an example illustrating my problem:  \documentclass[12pt,a4paper,oneside]{letter}  \usepackage{longtable}  \begin{document}  \begin{longtable}{ | p{5cm} | } \hline Table header\\* \hline Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris pharetra porttitor turpis, id egestas neque congue in. Nam sed lorem lorem, ac tristique tellus. Nunc ornare feugiat orci, a blandit turpis facilisis ut. Aenean pharetra ornare ante. Sed tempus leo in dolor eleifend placerat. Integer at enim augue. Ut nisl tortor, interdum ac porttitor ac, sagittis quis libero. Vivamus nibh metus, ornare vel pulvinar nec, fringilla nec orci. Maecenas mollis nulla a nibh fringilla nec convallis augue varius. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere   cubilia Curae. \\ Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris pharetra porttitor turpis, id egestas neque congue in. Nam sed lorem lorem, ac tristique tellus. Nunc ornare feugiat orci, a blandit turpis facilisis ut. Aenean pharetra ornare ante. Sed tempus leo in dolor eleifend placerat.  Integer at enim augue. Ut nisl tortor, interdum ac porttitor ac, sagittis quis libero. Vivamus nibh metus, ornare vel pulvinar nec, fringilla nec    orci. Maecenas mollis nulla a nibh fringilla nec convallis augue varius.   Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere   cubilia Curae. \\ \hline Table header\\* \hline Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris pharetra porttitor turpis, id egestas neque congue in. Nam sed lorem lorem, ac    tristique tellus. Nunc ornare feugiat orci, a blandit turpis facilisis ut. Aenean pharetra ornare ante. Sed tempus leo in dolor eleifend placerat.    Integer at enim augue. Ut nisl tortor, interdum ac porttitor ac, sagittis  quis libero. Vivamus nibh metus, ornare vel pulvinar nec, fringilla nec    orci. Maecenas mollis nulla a nibh fringilla nec convallis augue varius.   Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere  cubilia Curae. \\ \hline \end{longtable}  \end{document}   I'd like to have second header on page 3. I do not control table contents, so I can not do page breaks manually. When I choose the Connection Type in VPN Connections, I have only PPTP and I can't find OpenVPN, but I already installed it via terminal with the command sudo apt-get install openvpn easy-rsa  Why I can't find it? Programming pattern to generate VGA signal with micro-controller? I want to generate VGA signal with micro-controller (like TI Tiva ARM which runs at 90/120Mhz speed).  I'm not sure how to make accurate timings with micro-controller. Which programming pattern I need to use?  Do I need any inline assembler code? How to wisely use interrupts?  Would be great if anybody show some pseudo code how to generate VGA signal.  I successfully generated VGA signal with FPGA. But I just can't figure out how to do it with MCU. I have always wondered why diamonds shine. Can anyone tell me why? Let $G$ be a finite semi-group with identity such that it has only one idempotent.Is $G$ a group?  It only remains to show that for any $a\in G$ $\exists b\in G$ such that $ab=ba=e$ where $e$ is the identity of $G$  Also $e$ is the only idempotent of $G$ .How to proceed next? What's a common interjection for the reaction to something creepy and disgusting (like some insects or spooky places, etc.)? In how many ways can a number be expressed as a sum of consecutive numbers? Modify TikZ coil decoration Can I modify the existing tikz coil decoration, so that the downstrokes are not drawn in a certain interval, to produce a picture like this?    Edit: Previous attempts, code and MWE has been moved to or superseded by my own answer. In superluminal phase velocities, what is it that is traveling faster than light? I understand that information cannot be transmitted at a velocity greater than speed of light. I think of this in terms of the radio broadcast: the station sends out carrier frequencies $\omega_c$ but the actual content is carried in the modulated wave, the sidebands $\omega_c\pm\omega_m$. The modulation envelop has its group velocity and this is the speed at which information is being transmitted. We also know, for example, that x-rays in glass have a phase velocity which is greater than the speed of light in vacuum.   My question is, what exactly is it that is travelling faster than the speed of light?    EDIT: I know it couldn't be anything physical as its superluminal. My problem is, what is it that has absolutely no information content yet we associate a velocity with it. Best font for programming? Evalute $ \lim_{n\rightarrow \infty}\sum^{n}_{k=0}\frac{\binom{n}{k}}{n^k(k+3)} $ How to I deal with unwrapped UVs orientation?   Delete the default Cube. Add a Cylinder Edit mode and edge select the Top and the Bottom and a single connecting edge. Make them into seams UV Unwrap (standard Unwrap mode)   The unwrapped UV now shows two circles above a row of quads. I can save this and open it in an image editor and paint over those areas and get the texture to align on the cylinder back in blender.  But, the pattern(just happens to be text) that was inserted in place of the row of quads is now upside down on the model. Any attempt to flip or align just makes things worse, from upside down to mirrored or the Top/Bottom not aligning.  So my real question is how could I have known that the quads represented an upside down view of the world?  Do other blender users export UVs and mark them with arrows and colours just to see how they align on a model before actually painting for real?  I tried selecting the edges in step 3 in different orders before making them into seams and it made no difference.  I also looked at the Normals but they appear to be only Inside/Outside not Up/Down.  Blender 2.70 Query a region within a larger region with GeoDjango REST API I have a working Django REST API which can query all the counties in a country. //My model class kenya_counties(models.Model):   objectid = models.BigIntegerField()   id_field = models.BigIntegerField()   county_nam = models.CharField(max_length=80)   const_code = models.BigIntegerField()   constituen = models.CharField(max_length=80)   county_cod = models.BigIntegerField()   shape_leng = models.FloatField()   shape_area = models.FloatField()   geom = models.MultiPolygonField(srid=4326)    def __str__(self):       return self.county_nam  //My Serializer class CountiesSerializer(serializers.ModelSerializer):   class Meta:      model = kenya_counties      fields = ('objectid', 'id_field', 'county_nam', 'const_code', 'constituen', 'county_nam', 'county_cod', 'shape_leng', 'shape_area')  //My view @api_view(['GET', 'POST']) def counties(request):    if request.method == 'GET':        data = kenya_counties.objects.all()         serializer = CountiesSerializer(data, context={'request': request}, many=True)         return Response(serializer.data)     elif request.method == 'POST':        serializer = CountiesSerializer(data=request.data)        if serializer.is_valid():            serializer.save()            return Response(status=status.HTTP_201_CREATED)                 return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)  //My url     re_path(r'^api/gis/counties/$', views.counties),  I get . How can I query just one county and display it on a react-leaflet map as shown below? &lt;MapContainer center={position} zoom={13} scrollWheelZoom={false}&gt;     &lt;TileLayer       attribution='&amp;copy; &lt;a href=&quot;http://osm.org/copyright&quot;&gt;OpenStreetMap&lt;/a&gt; contributors'       url=&quot;https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png&quot;     /&gt; &lt;/MapContainer&gt; Does anyone know what song plays at about ? I am creating a model of a glass and I would like to put a drawing on it (a png picture).  I know how to do it using Blender Render, but not with Cycles Render. Help :) Does the equivalence $$\neg\neg (P \rightarrow Q) \leftrightarrow (\neg\neg P \rightarrow \neg\neg Q)$$ hold in propositional intuitionistic logic? In propositional classical logic the equivalence holds obviously since $P \leftrightarrow \neg\neg P$. However, the similar-looking implication $\neg\neg (P \vee Q) \rightarrow (\neg\neg P \vee \neg\neg Q)$ is . The validity of the backward implication comes up in  as well.