198 research outputs found
Fine-sorting One-dimensional Particle-In-Cell Algorithm with Monte-Carlo Collisions on a Graphics Processing Unit
Particle-in-cell (PIC) simulations with Monte-Carlo collisions are used in
plasma science to explore a variety of kinetic effects. One major problem is
the long run-time of such simulations. Even on modern computer systems, PIC
codes take a considerable amount of time for convergence. Most of the
computations can be massively parallelized, since particles behave
independently of each other within one time step. Current graphics processing
units (GPUs) offer an attractive means for execution of the parallelized code.
In this contribution we show a one-dimensional PIC code running on Nvidia GPUs
using the CUDA environment. A distinctive feature of the code is that size of
the cells that the code uses to sort the particles with respect to their
coordinates is comparable to size of the grid cells used for discretization of
the electric field. Hence, we call the corresponding algorithm "fine-sorting".
Implementation details and optimization of the code are discussed and the
speed-up compared to classical CPU approaches is computed
The Impact of Elevation-SMB Feedbacks on the Evolution of Thwaites Glacier, West Antarctica
The Amundsen Region of the West Antarctic Ice Sheet is one of the major active contributors to global sea level rise. Thwaites Glacier is a large, fast-flowing glacier in this region which is experiencing mass loss, flow acceleration, and rapid grounding line retreat, indicative of the marine ice sheet instability. Although there are many factors that may influence the potential destabilization and collapse of Thwaites Glacier, surface mass balance is an important factor as the balance of precipitation and ablation change with changing glacier geometry. This study investigates a surface elevation-SMB relationship and its influence on projected future stability at Thwaites Glacier. Observational data and regional climate model outputs are used to identify a strong elevation-SMB relationship at Thwaites Glacier. The Ice-Sheet and Sea-Level System Model is then then used to simulate Thwaites Glacier’s evolution with an added elevation-SMB feedback. Incorporating an elevation-SMB feedback increases the model prediction for ice mass loss by 5%-10% over a 200 year transient simulation.Undergraduat
Scaling laws for dielectric window breakdown in vacuum and collisional regimes
The scaling laws for the initiation time of radio frequency (rf) window breakdown are constructed for three gases: Ar, Xe, and Ne. They apply to the vacuum, to the multipactor-triggered regime, and to the collisional rf plasma regime, and they are corroborated by computer simulations of these three gases over a wide range of pressures. This work elucidates the key factors that are needed for the prediction of rf window breakdown in complex gases, such as air, at various pressures.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87804/2/261501_1.pd
Rubric-based holistic review represents a change from traditional graduate admissions approaches in physics
Rubric-based admissions are claimed to help make the graduate admissions
process more equitable, possibly helping to address the historical and ongoing
inequities in the U.S. physics graduate school admissions process that have
often excluded applicants from minoritized races, ethnicities, genders, and
backgrounds. Yet, no studies have examined whether rubric-based admissions
methods represent a fundamental change of the admissions process or simply
represent a new tool that achieves the same outcome. To address that, we
developed supervised machine learning models of graduate admissions data
collected from our department over a seven-year period. During the first four
years, our department used a traditional admissions process and switched to a
rubric-based process for the following three years, allowing us to compare
which parts of the applications were used to drive admissions decisions. We
find that faculty focused on applicants' physics GRE scores and grade point
averages when making admissions decisions before the implementation of the
rubric. While we were able to develop a sufficiently good model whose results
we could trust for the data before the implementation of the rubric, we were
unable to do so for the data collected after the implementation of the rubric,
despite multiple modifications to the algorithms and data such as implementing
Tomek Links. Our inability to model the second data set despite being able to
model the first combined with model comparison analyses suggests that
rubric-based admissions does change the underlying process. These results
suggest that rubric-based holistic review is a method that could make the
graduate admissions process in physics more equitable.Comment: Follow up to arXiv:2110.04329; Parts of manuscript originally
published as a conference paper (arXiv:1907.01570
A method of incorporating general relativity in electromagnetic particle-in-cell code
An algorithm is presented that incorporates the tensor form of Maxwell's
equations in a general relativistic electromagnetic particle-in-cell code. The
code simplifies to Schwartzschild space-time for a non-spinning central mass.
The particle advance routine uses a fourth-order Runge-Kutta algorithm to
integrate the four-velocity form of Lorentz force. The current density is
calculated using the curved space-time of the metric.Comment: 17 pages, 8 figure
An Arbitrary Curvilinear Coordinate Method for Particle-In-Cell Modeling
A new approach to the kinetic simulation of plasmas in complex geometries,
based on the Particle-in- Cell (PIC) simulation method, is explored. In the two
dimensional (2d) electrostatic version of our method, called the Arbitrary
Curvilinear Coordinate PIC (ACC-PIC) method, all essential PIC operations are
carried out in 2d on a uniform grid on the unit square logical domain, and
mapped to a nonuniform boundary-fitted grid on the physical domain. As the
resulting logical grid equations of motion are not separable, we have developed
an extension of the semi-implicit Modified Leapfrog (ML) integration technique
to preserve the symplectic nature of the logical grid particle mover. A
generalized, curvilinear coordinate formulation of Poisson's equations to solve
for the electrostatic fields on the uniform logical grid is also developed. By
our formulation, we compute the plasma charge density on the logical grid based
on the particles' positions on the logical domain. That is, the plasma
particles are weighted to the uniform logical grid and the self-consistent mean
electrostatic fields obtained from the solution of the logical grid Poisson
equation are interpolated to the particle positions on the logical grid. This
process eliminates the complexity associated with the weighting and
interpolation processes on the nonuniform physical grid and allows us to run
the PIC method on arbitrary boundary-fitted meshes.Comment: Submitted to Computational Science & Discovery December 201
Relativistic Jets from Accretion Disks
The jets observed to emanate from many compact accreting objects may arise
from the twisting of a magnetic field threading a differentially rotating
accretion disk which acts to magnetically extract angular momentum and energy
from the disk. Two main regimes have been discussed, hydromagnetic jets, which
have a significant mass flux and have energy and angular momentum carried by
both matter and electromagnetic field and, Poynting jets, where the mass flux
is small and energy and angular momentum are carried predominantly by the
electromagnetic field. Here, we describe recent theoretical work on the
formation of relativistic Poynting jets from magnetized accretion disks.
Further, we describe new relativistic, fully-electromagnetic, particle-in-cell
simulations of the formation of jets from accretion disks. Analog Z-pinch
experiments may help to understand the origin of astrophysical jets.Comment: 7 pages, 3 figures, Proc. of High Energy Density Astrophysics Conf.,
200
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