January 2009 ISSUE 28
Meetings
PIERS in
Dear Colleague,
There will be a session entitled
"Light Scattering and Radiative Transfer: Theories and Applications"
at the upcoming PIERS meeting in
Detailed information on this
session can be found via the following link:
http://piers.mit.edu/piers2k9Moscow/session.php?session_id=S016
The deadline for abstract
submission is February 20, 2009. More information can be found via the
following link:
http://piers.mit.edu/piers2k9Moscow/
We are very much looking forward to
your participation in this conference.
Ping Yang and Michael Mishchenko
==================================
DDSCAT
7.0 release
A new release of
the discrete-dipole approximation scattering code DDSCAT is now available --
DDSCAT 7.0 . This release
supersedes the previous release, version 6.1
DDSCAT 7.0 contains a number of new features. In particular:
* Draine & Flatau (2009) show how
the DDA can be used to calculate
scattering and absorption by targets that are periodic in one or two
dimensions. DDSCAT 7.0 can calculate scattering by isolated targets, by targets that are periodic in one
dimension and finite in the other two, or by targets that are periodic in
two dimensions and finite in the third. This has obvious
application to light scattering by arrays of nanostructures.
* The DDSCAT 7.0
package includes a separate program DDfield.f90 for postprocessing to calculate E
and B fields in or near the target.
* DDSCAT 7.0 can
now calculate absorption and scattering by targets containing
arbitrarily-oriented anisotropic materials.
* DDSCAT 7.0 is
written in portable fortran 90, and uses
dynamic memory allocation.
* DDSCAT 7.0 can
be compiled in either single or double precision.
* DDSCAT 7.0
supports use of MPI for running parallel calculation on separate cpus.
* DDSCAT 7.0
supports OpenMP, allowing certain
parts of the calculation to be done in
parallel if multiple cores are available on the compute node.
* DDSCAT 7.0
allows use of the Intel Math Kernel Library (MKL) DFTI routines for computing FFTs.
* The MPI, OpenMP, and MKL features
can be easily enabled or disabled by setting flags in
the Makefile.
* As with previous
versions, DDSCAT 7.0 comes with an extensive UserGuide:
http://arxiv.org/abs/0809.0337
The DDSCAT 7.0 package can be
downloaded from http://www.astro.princeton.edu/~draine/DDSCAT7.0.html
DDSCAT 7.0 is gratis, subject to the GNU General Public License. You may
copy, distribute, and/or modify the software identified as under this
agreement. If you distribute copies of this software, you must give the
recipients all the rights that you have.
As always, please let us know if you encounter problems downloading DDSCAT, or
if you have trouble using DDSCAT (but **please** read the manual carefully
before reporting problems!!). If you were a user of DDSCAT 6.1, note that
you will need to modify your ddscat.par files before
they will work with DDSCAT 7.0 . The UserGuide explains what is needed.
We hope that DDSCAT will prove
useful in your research.
B.T. Draine P.J. Flatau
===================================================================
New
Papers
Mishchenko, M. I., M. J. Berg, C. M.
Sorensen, and C. V. M. van der Mee,
2009: On definition and measurement of extinction cross section, J. Quant. Spectrosc. Radiat. Transfer 110, doi:10.1016/j.jqsrt.2008.11.010.
Tishkovets, V. P., and M. I. Mishchenko, 2009: Approximate calculation of coherent
backscattering for semi-infinite discrete random media, J. Quant. Spectrosc. Radiat. Transfer 110, 139-145.
Mishchenko, M. I., and J. M. Dlugach, 2008: Accuracy of the scalar approximation in
computations of diffuse and coherent backscattering by discrete random media,
Phys. Rev. A 78, 063822.
Mishchenko, M. I., 2008: Broadband
electromagnetic scattering by particles, J. Opt. Soc. Am. A 25, 2893-2895.
Liu, L., M. I. Mishchenko,
and W. P. Arnott, 2008: A study of radiative
properties of fractal soot aggregates using the superposition T-matrix method,
J. Quant. Spectrosc. Radiat. Transfer
109, 2656-2663.
The publications are available at http://www.giss.nasa.gov/~crmim/publications in the PDF format
Y. Okada, I.Mann,
T.Mukai, M.Koehler,
"Extended calculation of polarization and
intensity of fractal aggregates based on rigorous method for light
scattering simulations with numerical orientation averaging", JQSRT,
accepted.
http://dx.doi.org/10.1016/j.jqsrt.2008.05.014
Abstract
The
intensity and polarization of fractal aggregates have been
investigated using both rigorous and approximate methods for light
scattering simulations. However, previous studies using the analytical
orientation averaging version of the rigorous method were generally limited to a few hundred monomers when the
monomer size parameter was around 1.7. In this study, we propose using
numerical orientation averaging instead of
analytical orientation averaging. The numerical averaging is performed together
with a fixed orientation version of
the rigorous T-matrix method for clusters of spheres. This approach enables increasing the number of monomers by a
factor of 2-7 or the size of monomers by a factor of 8-10 compared to the
analytical orientation averaging version. We investigated the influence
of monomer size and the number of
monomers on the light scattering of silicate aggregates (refractive index
m=1.68+0.03i) for incident light with a wavelength of 0.6 um. We
considered ballistic particle-cluster aggregates (BPCA) and ballistic cluster-cluster aggregates (BCCA)
composed of 128, 256, 512, and 1024 monomers with radii between 0.11 and
0.17 μm. Our results show
that the size of monomers plays an important role in
reproducing the negative polarization branch for all the BPCA and BCCA.
Silicate aggregates with the monomer radius of less than 0.17 μm contribute to reproducing the negative polarization
branch, while aggregates with monomers larger than 0.17 μm do not have the
negative polarization branch. Polarization oscillation with scattering angle occurs for larger monomers (i.e., monomer radius
> 0.3 μm). The
maximum polarization decreases for increasing monomer radius
between 0.11 and 0.17 μm. However, the
negative polarization branch is
generally enhanced for monomer radii up to around 0.15 μm, and reduced for
further increase of monomer size. The number of monomers also has a large
influence on the negative
polarization branch in the case of BPCA. The increase in the number of monomers from 128 to 1024 shifts the scattering angle
of minimum polarization to larger angles for BPCA. In addition, the increase in
the number of monomers reduces the values of negative polarization for BPCA
while the variation with the number of monomers for BCCA is small and is not
monotonic.