Composite Grains: Effects of Porosity and Inclusions on the 10$\mu$m
  Silicate Feature
  We calculate the absorption efficiency of the composite grains, made up of
host silicate spheroids and inclusions of ices/graphites/or voids, in the
spectral region $7.0-14.0\mu$m The absorption efficiencies of the composite
spheroidal grains for three axial ratios are computed using the discrete dipole
approximation (DDA) as well as using the effective medium approximation &
T-Matrix (EMT-Tmatrix) ap proach. We study the absorption as a function of the
volume fraction of the inclusions and porosity. In particular, we study the
variation in the $10.0\mu$m feature with the volume fraction of the inclusions
and porosity. We then calculate the infrared fluxes for these composite grains
and compare the model curves with the average observed IRAS-LRS curve, obtained
for several circumstellar dust shells around stars. These results on the
composite grains show that the wavelength of the peak absorption shifts and the
width of the $10.0\mu$m feature varies with the variation in the volume
fraction of the inclusions. The model curves for composite grains with axial
ratios not very large (AR$\sim$1.3) and volume fractions of inclusions with
f=0.20, and dust temperature of about 250-300$^{\circ}$K, fit the observed
emission curves reasonably well.
