Issue 13,  November 2004

NEW  LIGHT-SCATTERING CODES:

 

The scalar raditiave transfer code  SCIATRAN_2.0 is available at http://www.iup.physik.uni-bremen.de/sciatran

The vector radiative transfer code  SCIAPOL_1.0  is available at http://www.iup.physik.uni-bremen.de/~alexk

 Alexander Kokhanovsky

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A new release of the discrete-dipole approximation scattering code DDSCAT is now available -- DDSCAT 6.1.

This release supersedes the previous release, version 6.0. DDSCAT 6.1 continues to support MPI and FFTW

(as in DDSCAT 6.0) but includes several new features:

* An automatic procedure for calculating angular averages for the   scattered radiation.  The user now specifies

an tolerance parameter ETASCA.  The number of scattered directions is proportional to   [(3+x)/ETASCA]^2

where x=2*pi*a_eff/lambda is the scattering parameter.  The number of scattering angles used therefore is determined

by the ratio of target size to wavelength.  The accuracy of the angular averages in relation to the choice of ETASCA is

discussed in the UserGuide.

  * DDSCAT 6.1 introduces two versions of DDSCAT.

* The "plain" version for new users or users who do not require support for MPI, FFTW, or netCDF, and who therefore

do not want to be concerned about making sure the appropriate libraries are installed.

* The "full" version for users who want to use one or more of MPI, FFTW, or netCDF.

* DDSCAT 6.1 now calculates the second moment <cos^2(theta)> in addition to the first moment <cos(theta)> of the

scattered radiation, where theta=scattering angle.

* The output files written when the netCDF option is specified have been modified to include more relevant data and to be

more easily read.

   * DDSCAT 6.1 includes a new target option: ANIREC, for calculating scattering by anisotropic rectangular prisms.

  * The UserGuide has been expanded, and now includes notes on

     * application of DDSCAT to calculations of scattering in dielectric media

     * discussion of the dependence on ETASCA of the accuracy of the angular averages over the scattered radiation.

     * brief discussion of installation of DDSCAT on non-unix systems.

The complete distribution of DDSCAT 6.1 is available for download at  

http://www.astro.princeton.edu/~draine (click on DDSCAT 6.1) or  

ftp://ftp.astro.princeton.edu/draine/scat/ddscat/ver6.1/   right-click on ddscat6.1_plain.tgz for the "plain" distribution,

or  dddscat6.1_full.tgz for the full distribution. or by anonymous ftp from ftp.astro.princeton.edu in the directory

draine/scat/ddscat/ver6.1/

 

As always, please let us know if you encounter problems downloading or using DDSCAT.  We hope that DDSCAT 6.1

will prove useful in your research.

 

Bruce Draine

 

LIGHT-SCATTERING MEETINGS:

 

NATO advanced research workshop on Optics of Biological Particles

Novosibirsk Russia October 3 - October 6, 2005  http://cyto.kinetics.nsc.ru/OBP/

 

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A New Session of PIERS-2005 (August 22-26, 2005; Hanzhou, China)

 

Dear Colleagues,

We would like to inform on a new session of the Progress In Electromagentic Research Symposium (PIERS) in Hanzhou,

China (August  22-26, 2005). We are organizing a session for PIERS-2005:Session title: Light Scattering and Radiative

Transfer: Basic Research and Application  We cordially invite you to attend this session. If you plan to attend PIERS-2005,

please submit an abstract of no less than 250 words in English. A full-length paper is NOT required. The deadline of the

submission is December 10, 2004. We strongly recommend that you use online-submission (http://piers.org).  In general,

papers on the theoretical and experimental studies on light scattering and radiative  transfer are solicited.  Papers on

remote sensing, which involve light scattering and radiative modeling efforts, are also welcome. However, remote sensing

papers based on “pure data analysis” would more properly belong in other meetings.

 

China. Information about the registration, lodging, and sightseeing tours can be found in PIERS webpage at http://piers.org

Best regards,

 

Organizers: Ping Yang and Warren Wiscombe

Chairs: David Winker, Yongxiang Hu, and Hong-Bin Chen

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NEW PAPERS:

Modelling the optical properties of composite and porous interstellar grains

N. V. Voshchinnikov1,2, V. B. Il'in1,2, and Th. Henning3

1 Sobolev Astronomical Institute, St.~Petersburg University, Universitetskii prosp. 28,
           St.~Petersburg, 198504 Russia
2 Isaac Newton Institute of Chile, St.~Petersburg Branch
3 Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany

E-mail contact: nvv@astro.spbu.ru

There are indications that interstellar and interplanetary dust grains have an inhomogeneous

and fluffy structure. We investigate different methods to describe light scattering by such

composite particles. Both a model of layered particles and discrete dipole calculations for

particles with Rayleigh and non-Rayleigh inclusions are used.

The calculations demonstrate that porosity is a key parameter for determining light scattering.

We find that the optical properties of the layered particles depend on the number and position

of layers if the number of layers is small (≤ 15). For a larger number of layers the scattering

characteristics become independent of the layer sequence. The optical properties of particles

with inclusions depend on the size of inclusions provided the porosity is large. The scattering

characteristics of very porous particles with inclusions of different sizes are found to be

close to those of multi-layered spheres.

We compare the results of these calculations with the predictions of the effective medium

theories (EMT), which are often used in astronomy as a tool to calculate the optical properties

of composite particles. The results of our analysis show that the internal structure of grains

(layers versus inclusions) only slightly affects the optics of particles provided the porosity

does not exceed 50\%. It is also demonstrated that in this case the optical properties of

composite grains calculated with EMT agree with the results of the exact method for layered

particles. For larger porosity, the standard EMT rules (i.e., Garnett and Bruggeman rules) give

reliable results for particles with Rayleigh inclusions only.

{Accepted by Astronomy & Astrophysics, http://xxx.lanl.gov/astro-ph/0409457)

 

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