Recent content by kderakhshani

@Drakkith Thank you for your comment. In a wider prospect "legal" means "concordance with the rules of the game". In scientific workss it stands for "not violating the discipline, some scientific law, etc.". For example, if something violates the LAW of conservation of linear momentum, it will...

The code I used for some globular cluster (NGC 2419) was NMODY, which had been written for COLLISIONLESS stellar systems. For NGC 2419 it is legal, cause its relaxation time is very long (longer than the Hubble time). (K.Derakhshani, ApJ, 783, 48, 2014) Now, I want to use it (or some other...

Hi all. I'd like to use a software package, that has been designed for collisionless dynamics, to investigate general globular clusters. As they are highly collisional, at least in their inner parts, this perhaps makes no sense. However, it may be meaningful for some time- or length-scales or...

Dear Repliers, I made the correction you suggested. Apparently that error is fixed, but I've received the attached response from the arXiv processor. My tex file is also attached Would you please help me again? Thanks a lot.

Dear DrClaude, Sure. The following are the lines 178-206: (line 191 is the ‎\begin{tabular}{cccccccc}‎ ) ‎\begin{figure}‎ ‎\includegraphics[scale=0.7]{images/LOSVD_ov_del_ratio.eps}‎ ‎\caption{Ratio of difference overall line-of sight velocity dispersions of the simulated model globular...

Dear Friends, Thank you all for your replies. However, as I (maybe somewhat implicitly) said, I did upload all files, including the .cls. When I asked help from the arXiv admins by email, they answered as the following: "The relevant error is: Extra alignment tab has been changed to \cr...

Dear Friends, Thank you for your useful replies. OK, let me ask the question that is boggling my mind: When T_{μ\nu}=0 then R_{μ\nu}=0 but R_{μ\nuλρ} is not necessarily equal to zero. In fact R_{μ\nuλρ} = C_{μ\nuλρ} , the Weyl tensor. What is the "source" or cause of this...

Dear Bill_K, Thank you for reminding the Bianchi identities to me. Regarding your last paragraph, the gravitational or pp waves have energy densities and momentum fluxes. Aren't they considered as "sources" ?

Dear Bill_K, Thank you for reminding the Bianchi identities to me. Regarding your last paragraph, the gravitational or pp waves have energy densities and momentum fluxes. Aren't they considered as "sources" ?

@ofrig Thank you for your reply. I feel I should clarify my point. Imagine a point very far away from any source of gravitation (mass, energy, radiation, etc.). According to the Einstein's field eq. the space-time around this point is Ricci flat. But not totally flat. Because the Riemann...

Dear Friends, As you know, one of the best preprint servers for physics papers is arXiv.org, and almost everybody desires to post her/his paper on this server so that it can be commented/corrected/improved by peer reviewers before publishing. However, the price is that arXiv.org is...

Hi everybody, As you know, the Einstein field equation R_{μ\nu} - 1/2Rg_{μ\nu} =κT_{μ\nu} implies that at any point with vanishing energy-momentum tensor the Ricci curvature also vanishes: T_{μ\nu} = 0 \Rightarrow R_{μ\nu} = 0 hence a Ricci-flat space-time (the vacuum...

Hi everybody, In most classical or quantum optics texts an angular momentum is considered for the EM radiation as the following: J = ε_0 ∫_V r × [E(r, t) × B(r, t)] d^3 r Then it is claimed that: "Using the usual formula for a double vector product and integrating by parts...

PeterDonis, Thank you for your detailed reply. Right. A metric can do that, but it is not just a trivial task of index gymnastics! A metric does not convert the vector to itself, but to its dual which is a one-form. There IS a 1-1 correspondence here, but vectors and their corresponding...

OK! Now remember that the angular momentum is an axial vector (it gains no minus sign under inversions). On the other hand, it is the cross product of x and p, both of which are contravariant vectors. In the component notations, it is the product of the Levi-Civita symbol and two contravariant...