Recent content by kop442000

  1. K

    Why perpetual motion machine wouldn't work.

    Thanks everyone. I agree that they are not really worth discussing, but explaining why they don't work to my friend is useful I think. Sophie could you say a little more about the extra energy needed to set up, as this seems to be the crux?
  2. K

    Why perpetual motion machine wouldn't work.

    I'm trying to explain to my friend why the following would not work, but embarrassingly, I'm having trouble. You have a ramp that allows a ball bearing to roll up, and a strong magnet at the top which is able to pull the ball up the ramp. But there is a hole halfway up the ramp, and so the...
  3. K

    Geometric series with modified terms

    I am looking for a way to sum some numbers. I understand that if I want to sum pi, I can use the geometric series: \sum\limits_{i=0}^N p^{i} = \frac{1-p^{N+1}}{1-p} But can anyone help me with what to do when I need: \sum\limits_{i=0}^N p^{i} q^{ti} where t is just a constant...
  4. K

    Uncertainty on best fit gradient

    Thanks Simon. Yes it seems that the software (within Python) just does a least squares fit, compares the data points to the best fit gradient and let's you know how well they fit. I wanted something that took into account the error bars on the data too - for the reason that you mentioned above...
  5. K

    Uncertainty on best fit gradient

    Hi everyone, I have a plot of some data points that have error bars on the y axis. A bit of software I am using gives me the best fit gradient and a "Standard Error", but it doesn't take the size of error bars into consideration. I'm assuming that it just looks at how well the gradient...
  6. K

    Calculating Poisson Uncertainties with Changing Observation Durations

    I am trying to plot the flux from an Astrophysical source as a function of time. Due to the nature of the source, I am only receiving a handful of photons in each time bin. So imagine I had 10 observing periods of 10 days each, in which my telescope received the following number of photons...
  7. K

    Difference between thermal and non-thermal Bremsstrahlung

    Thank you I've just seen this reply sorry. I'm still not sure that I understand. Are you saying that synchrotron radiation for example is non-thermal bremsstrahlung? I thought that bremsstrahlung was when a charged particle was accelerated in the region of a nucleus. Also, if thermal...
  8. K

    Difference between thermal and non-thermal Bremsstrahlung

    Can anyone give me a nice explanation of the difference between thermal and non-thermal Bremsstrahlung? Thank you!
  9. K

    How to tell if my trend is real?

    Hi guys, I'm working on a research project that looks at the amount of cosmic rays coming out of a particular region of the sky in certain time intervals. There are 13 readings taken: 9,9,6,6,7,1,6,6,1,6,4,1,0 When this is plotted, it looks like a downward trend - meaning the source...
  10. K

    Programs Oxford vs Cambridge: Which Astrophysics PhD Position is Best?

    All other things being equal (project, supervisor etc.) then would it be better for your future to take an Astrophysics PhD position in Oxford or Cavendish at Cambridge? Thank you!
  11. K

    PhD in Cosmology: Best UK Universities

    I'm a UK student. I have a first class MPhys in Physics with Astrophysics, and am now studying for a MSc by research - so just in the middle of applying for a PhD position. Thank you.
  12. K

    PhD in Cosmology: Best UK Universities

    Could anyone suggest good universities in the UK for studying cosmology at a PhD level? Thank you!
  13. K

    What do the units of diffusion coefficient mean?

    I see that the diffusion coefficient (of diffusivity) D has units of something like cm^2 / s. I'm having trouble understanding what those units mean. For example, speed has such units because something travels a certain LENGTH in a certain TIME. Could someone explain this for me? Thank you.
  14. K

    Statistical anisotropy calculation

    Hi guys, this is not homework, but just something my supervisor asked me to think about, but I'm not sure how to start. Homework Statement How many events are needed to get an anisotropy of 9% at 9 sigma. (We were talking specifically in the context of Cosmic Rays). I just want a...
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