Tag Info

Hot answers tagged

29

Assume also that I have access to an immense amount of parallel computing processing power (I do). Unless you are an important person in the Chinese computational science world (using Tianhe-2), or you have access to secret government computers us mere mortals don't know exist (so they don't appear in rankings of the best supercomputers in the world), I ...


3

By the sounds of it you have made a mistake with the units. In fact, you should not be using SI units at all in your simulation; astronomical values in SI units vary by such huge orders of magnitude that they are often a source of floating point errors that can destroy trajectories. You should instead use the astronomical system of units. Specifically, ...


3

The instantaneous temperature of a system of $N$ particles of masses $m_i$ and velocities $v_i$ is $$ T(t) = \sum_{i=1}^N \frac{m_iv_i^2(t)}{k_BN_f} $$ where $N_f$ equals the number of degrees of freedom, typically $N_f=3N-3$ for fixed total momentum. Note that the instantaneous temperature will fluctuate 5-10% about the true (thermodynamic) temperature ...


2

Yes, the refraction index will be changed, but the absorption will differ even more. Look at similar situation. (P.S. I'd like to add this as comment but I cant yet, cause of reputation)


2

Let's dive right into an example -- let's say you are simulating a fluid. First, you need to pick your reference frame. Are you going to simulate a fixed domain in space and have your fluid move through it, meaning you have a grid and at each point on the grid you store and solve for the fluid properties (Eulerian frame)? Or will you track each discrete ...


1

There is nothing to do. If you force your system strongly, energy will build up and your hydrodynamic flow will become more and more intricate. At the same time, the dissipation becomes more and more efficient since it is proportional to the spatial derivative of the velocity field. You reach a steady state when both effects compensate each other. The ...


1

As a chemist turned engineer, I think I am well placed to answer this question. Does there exist a graphics engine that is as true to our reality as possible given our current understanding of physics? Given appropriate constraints and simplifications, it is possible to build a useful model from simple elements. Whether you consider this "true to ...


1

While lemon's answer is of course correct, it is not the only way to calculate the temperature from a molecular dynamics simulation: it can also be obtained from the configurations, that is, the particle coordinates, of the system. This is called "configurational temperature" (see, e.g., this article; pay-walled). The key identity is (for a canonical ...


1

In my experience (PhD student working on laser plasma interaction experiments) these PIC codes are pretty closely guarded by their creators. There are a few out there, for example OSIRIS, VORPAL, and TurboWave in addition to VLPL. Of these I think only VORPAL is commercially available (through Tech-X) and the others you would need to contact the groups ...


1

The premise of your question is flawed. It is not possible to know everything with perfect accuracy, even in a non-quantum fully deterministic system. (In a quantum system, even if you do know its state with perfect accuracy, you can't predict it accurately.) Ever hear of chaos? the butterfly effect? the three-body problem? No matter how well you know the ...



Only top voted, non community-wiki answers of a minimum length are eligible