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  1. J

    I Plummer distribution of stars

    Hi all, I refer to the following pdf document, in particular the appendix: http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1974A%26A....37..183A&link_type=ARTICLE&db_key=AST&high= End goal is to distribute N stars each having mass m (looks like equal mass stars is the easiest...
  2. J

    B Orbital parameters of stars orbiting Sagittarius A*

    I was going to try and do an animation of stars orbiting Sagittarius A* but can't seem to find any useful data for it. The Wikipedia page has some data https://en.m.wikipedia.org/wiki/Sagittarius_A* and was trying to reconcile this with https://en.m.wikipedia.org/wiki/Orbital_elements since I...
  3. J

    Python Making a pretty n-body simulation

    Hi all, I have recently created an nbody simulation in Vpython for a few thousand particles where each particle is about 4000 times the mass of our Sun. Vpython is doing exactly what I want it to do the only problem being the output is extremely low quality (black spheres on a white...
  4. J

    Newtonian mechanics and inclined planes

    hi, i am interested in finding a website which has lots of questions (and solutions) on newtonian mechanics to test my knowledge. things i had in mind include applications of F=ma,inclined planes, tension on ropes,springs etc. thanks
  5. J

    Fractional Brownian motion

    hey there, i'm curious as to why they call it fractional Brownian motion. please don't say its Brownian motion that is fractional :tongue2: many thanks
  6. J

    Change of variables for PDE

    hi, i am having difficulty trying to find a change of variables to solve this partial differential equation \frac{\partial f}{\partial t} = t^\gamma \frac{\partial ^2 f}{\partial x^2} not sure how to pluck out a change of variables by looking at the equation as its definately not obvious to the...
  7. J

    Related rates of increase

    hey guys, just wondering if i did this correctly a spherical balloon is to be filled with water so that there is a constant increase in the rate of its surface area of 3cm2/sec . a) Find the rate of increase in the radius when the radius is 3cm. b) Find the volume when the volume is...
  8. J

    SATA hard disk

    hi, a friend is heading over to malaysia in the next few days and asked me if i wanted a 10000rpm ( 8mb cache, SATA ) 74 GB WESTERN DIGITAL 10000RPM hard disk. i would say yes but i am not sure if it will work on my pc my motherboard is an ASUS P4P800SE with Intel 865PE Chipset can someone...
  9. J

    Parallel transport

    hi, i am trying to show that the amount by which a vector is rotated by parallel transport around a triangle whose sides are arcs of great circles equals the excess of the sum of the angles over 180 degrees. this is what i have found out so far call the angles of the triangle (assuming...
  10. J

    Error in schwarzchild metric

    hi recently i attended a lecture where a current researcher from my university was talking about black holes and the schwarzchild metric. basically he was saying no current theory predicts black holes and the schwarzchild solution is not actually correct, his solution was accepted because...
  11. J

    Density calculation

    does anyone know how to calculate the density of a solution of 0.7M (say) NaOH solution. if so, could you please show me how its done i have looked everywhere on the net but to my extreme surprise i couldnt find it thanks jim
  12. J

    Probability problem

    hi i am trying to show that for 2 probabilities p_{0} and p_{1} that X=\frac{p_{1}}{p_{0}} cannot be further from 1 than Y=\frac{p_{1}(1-p_{0})}{p_{0}(1-p_{1})} how i went about the problem was as follows: i split it into 3 cases, case 1 is where p_{0}=p_{1}, case 2 is where p_{0}>p_{1}...
  13. J

    Gauss Law

    if u have an uncharged,perfectly conducting hollow sphere of thickness t and radius R, and a point charge Q is placed a distance D from the centre of the sphere so that R-t>D, what would the electric field, E, be? i just treated it the same as if Q was in the centre of the sphere and the...
  14. J

    Solving a partial DE

    hi all i have been trying to solve to following problem, \frac{\partial^2 u}{\partial x^2} - \frac{\partial^2 u}{\partial y^2} + 2\frac{\partial u}{\partial x} + u = 0 u=u(x,y) after a bit of work using the change of variables \zeta=\zeta(x,y)=y-x and...
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