3,620 research outputs found
Load management strategy for Particle-In-Cell simulations in high energy particle acceleration
In the wake of the intense effort made for the experimental CILEX project,
numerical simulation cam- paigns have been carried out in order to finalize the
design of the facility and to identify optimal laser and plasma parameters.
These simulations bring, of course, important insight into the fundamental
physics at play. As a by-product, they also characterize the quality of our
theoretical and numerical models. In this paper, we compare the results given
by different codes and point out algorithmic lim- itations both in terms of
physical accuracy and computational performances. These limitations are illu-
strated in the context of electron laser wakefield acceleration (LWFA). The
main limitation we identify in state-of-the-art Particle-In-Cell (PIC) codes is
computational load imbalance. We propose an innovative algorithm to deal with
this specific issue as well as milestones towards a modern, accurate high-per-
formance PIC code for high energy particle acceleration
Overeducation in the early career of secondary education graduates : an analysis using sequence techniques
Based on monthly observations of their labour market status in the first seven years after leaving education, this paper uses optimal matching sequence analysis to construct a typology of entry-patterns of Flemish secondary education graduates. Our main finding is that for a significant number of young people overeducation constitutes a persistent problem, affecting about half of the sample for nearly the full observation period. Investigating the risk factors involved, we find that some factors, such as having lower human capital endowments or facing job search constraints, enhance the risk of following disadvantageous trajectories. Having a lower reservation wage seems to make being persistently overeducated more likely. Yet, starting as ‘overeducated’ does not necessarily lead to being stuck in that state for the rest of the career. About 7% of our sample succeeds in entering an adequate position even after being overeducated for a relatively long period
Computationally Efficient Implementation of Convolution-based Locally Adaptive Binarization Techniques
One of the most important steps of document image processing is binarization.
The computational requirements of locally adaptive binarization techniques make
them unsuitable for devices with limited computing facilities. In this paper,
we have presented a computationally efficient implementation of convolution
based locally adaptive binarization techniques keeping the performance
comparable to the original implementation. The computational complexity has
been reduced from O(W2N2) to O(WN2) where WxW is the window size and NxN is the
image size. Experiments over benchmark datasets show that the computation time
has been reduced by 5 to 15 times depending on the window size while memory
consumption remains the same with respect to the state-of-the-art algorithmic
implementation
Trans-Debye Scale Plasma Modeling & Stochastic GRB Wakefield Plasma Processes
Modeling plasma physical processes in astrophysical context demands for both
detailed kinetics and large scale development of the electromagnetic field
densities.
We present a new framework for modeling plasma physics of hot tenuous plasmas
by a two-split scheme, in which the large scale fields are modeled by means of
a particle-in-cell (PIC) code, and in which binary collision processes and
single-particle processes are modeled through a Monte-Carlo approach. Our novel
simulation tool -- the PhotonPlasma code -- is a unique hybrid model; it
combines a highly parallelized (Vlasov) particle-in-cell approach with
continuous weighting of particles and a sub-Debye Monte-Carlo binary particle
interaction framework.
As an illustration of the capabilities we present results from a numerical
study of Gamma-Ray Burst - Circumburst Medium interaction and plasma
preconditioning via Compton scattering. We argue that important microphysical
processes can only viably be investigated by means of hybrid codes such as the
PhotonPlasma code.
Our first results from 3D simulations with this new simulation tool suggest
that magnetic fields and plasma filaments are created in the wakefield of
prompt gamma-ray bursts. Furthermore, the photon flux density gradient impacts
on particle acceleration in the burst head and wakefield. We discuss some
possible implications of the circumburst medium being preconditioned for a
trailing afterglow shock front. We also discuss important improvements for
future studies of GRB wakefields processes, using the PhotonPlasma code.Comment: 11 pages, 6 figures, to appear in proceedings of "Cool discs, hot
flows: The varying faces of accreting compact objects", Sweden, March 2008,
AIP Conference Proc. Rev1: Minor changes, in compliance with referee
comments. Rev2: corrected some citation formattin
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