July 2007 ISSUE 22
Open Position
Scientist, T-Matrix Method (24.4.2007) http://diogenes.iwt.uni-bremen.de/vt/laser/wriedt/stellen/stelle-dsm.htm
Meetings
Workshop on Null-Field Method with Discrete Sources,
http://diogenes.iwt.uni-bremen.de/vt/laser/wriedt/Conferences/NFM-DS-
Workshop.html
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New
Publications
DDA
Jozef Klacka, and Miroslav Kocifaj "Effect of
Electromagnetic Radiation on Dynamics of Cosmic Dust Particles" In: Space
Science: New Research, Nova Science Publishers, Inc.,
Effect of electromagnetic radiation on dynamics of arbitrarily shaped
cosmic dust particles is investigated. Process of extinction, scattering,
absorption and thermal emission is taken into account. Equation of motion is
derived and physical meaning of the important terms is emphasized and
discussed. The equation of motion is written in a relativistically
covariant form. The equation of motion yields, as special cases, both the results
presented by Einstein in his relativistic paper written 100 years ago, and,
also the Poynting-Robertson effect, well-known in
astrophysics. Applications of the derived equation of motion are shown for
various systems in the Universe. The significance of the general equation of
motion is always stressed by presenting results both for spherical and nonspherical dust particles.
e-mail contact: klacka@fmph.uniba.sk , kocifaj@astro.savba.sk
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M. A. Yurkin, V. P. Maltsev, and A. G. Hoekstra, "The discrete dipole approximation
for simulation of light scattering by particles much larger than the
wavelength," J. Quant. Spectrosc. Radiat. Transf. 106, 546-557 (2007). http://dx.doi.org/10.1016/j.jqsrt.2007.01.033
In this paper we investigate the capabilities of the discrete dipole
approximation (DDA) to simulate scattering from particles that are much larger than
the wavelength of the incident light, and describe an optimized publicly
available DDA computer program that processes the large number of dipoles
required for such simulations. Numerical simulations of light scattering by spheres
with size parameters x up to 160 and 40 for refractive index m=1.05 and 2, respectively, are presented and compared with exact results
of the Mie
theory. Errors of both integral and angle-resolved scattering quantities
generally increase with m and show no systematic dependence on x. Computational
times increase steeply with both x and m, reaching values of more than 2 weeks
on a cluster of 64 processors. The main distinctive feature of the computer
program is the ability to parallelize a single DDA simulation over a cluster of
computers, which allows it to simulate light scattering by very large
particles, like the ones that are considered in this paper. Current limitations
and possible ways for improvement are discussed.
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M. A. Yurkin and A. G. Hoekstra, "The
discrete dipole approximation: an overview and recent developments," J.
Quant. Spectrosc. Radiat. Transf.
106,
558-589 (2007). http://dx.doi.org/10.1016/j.jqsrt.2007.01.034
We present a review of the discrete dipole approximation (DDA), which is
a general method to simulate light scattering by arbitrarily shaped particles.
We put the method in historical context and discuss recent developments, taking
the viewpoint of a general framework based on the integral equations for the
electric field. We review both the theory of the DDA and its numerical aspects,
the latter being of critical importance for any practical application of the
method. Finally, the position of the DDA among other methods of light
scattering simulation is shown and possible future developments are discussed.
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Penttila, A., E. Zubko
, K. Lumme, K. Muinonen, M.
A. Yurkin, B. T. Draine, J.
Rahola, A. G. Hoekstra, and Y. Shkuratov,
"Comparison between discrete dipole implementations and exact
techniques," J. Quant. Spectrosc. Radiat. Transf. 106,
417-436 (2007). http://dx.doi.org/10.1016/j.jqsrt.2007.01.026
The use of the discrete dipole approximation (DDA) method in wave optical
scattering simulations is growing quite fast. This is due to the fact that the current
computing resources allow to apply DDA to sufficiently
large scattering systems. The advantage of DDA is that it is applicable to
arbitrary particle shape and configuration of particles. There are several
computer implementations of the DDA method, and in this article we will compare
four of such implementations in terms of their accuracy, speed and usability.
The accuracy is studied by comparing the DDA results against results from either Mie, T-matrix or cluster
T-Matrix codes with suitable geometries. It is found that the relative accuracy
for intensity is between 2% and 6% for ice and silicate type refractive indices and the absolute accuracy for linear
polarization ratio is roughly from 1% to 3%.
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Y. Okada, T. Mukai, I. Mann, H. Nomura, T.
Takeuchi,
We present a method to derive the light scattering properties of very porous fractal aggregates composed of a large number of monomers where the size parameter of monomer is larger than unity. Our new method is based on the grouping of the aggregate: The aggregate is divided into groups, where each group is located along a line of the incident light, and the scattering properties of the group are calculated taking into account multiple scattering with monomers located inside the group, as well as those in a buffer region around the group. The scattering and absorption efficiencies are obtained by adding the resultant scattering properties for all the groups. We have shown that the method effectively works when the monomer scatters the incident lights predominantly in the forward direction, which is the case if the monomer size is large, compared to the wavelength of the incident light. The errors in resulting scattering and absorption efficiencies for porous aggregates are investigated for various refractive indices and sizes of monomers. We found that the errors are larger for low absorbing materials and they can be reduced by expanding the buffer region. In the case of the buffer region for each group consisting of 1/8 of the total number of monomers, the results show errors less than 15% and 10% for absorption and scattering, respectively. It is also shown that the errors have a small standard deviation (i.e., 2%) for different directions of the incident light.
Sample code is avaialble from: http://harbor.scitec.kobe-u.ac.jp/~okada/GAM/
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ADDA update
Dear
users of Amsterdam DDA,
I
am glad to announce that new version of ADDA (0.77) has been released. The most
important changes are:
*
The bug was fixed that crashed the calculation of radiation forces.
*
Handling of large integers was improved throughout the program. Now it
should work for any problem that fits
into memory. Checks of integer overflow were
added where necessary to avoid crashes.
*
Robustness of handling the command line and input files was improved.
* Makefiles were improved, in
particular, an option was added to use Intel compilers without static linking.
*
Command line option -store_dip_pol was added to save
dipole polarizations to
file.
*
The breakdown detection of the iterative solvers was improved. Now it should be
much more sensitive. Thanks to Sorin Pulbere for reporting a test problem.
* A
minor bug in Romberg integration, reported by Antti Penttila, was fixed.
*
Locking of files was made more flexible. A compile option was added to
independently turn off the advanced file locking.
*
Manual was significantly improved. "DDA formulation" section was
rewritten to be
self-contained, sections "Near-field" and "Comparison with other
DDA codes" were added. Sections on
compiling and running the code were extended to discuss in detail multi-core
PCs. Sections "Applicability of DDA" and "System requirements" were extended to include
recent benchmark results and discussion. Thanks to Vitezslav Karasek and Liviu Clime for their
feedback.
You
are advised to upgrade to a new version, which can be downloaded (both main
package and, if needed, executable for Windows) from the ADDA web site: http://www.science.uva.nl/research/scs/Software/adda/
There you can also find the full release
information.
Light-Scattering
Instrumentation news
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The
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Astropribor, 31 Akad.