18 research outputs found
Theory and simulation of spectral line broadening by exoplanetary atmospheric haze
Atmospheric haze is the leading candidate for the flattening of expolanetary
spectra, as it's also an important source of opacity in the atmospheres of
solar system planets, satellites, and comets. Exoplanetary transmission
spectra, which carry information about how the planetary atmospheres become
opaque to stellar light in transit, show broad featureless absorption in the
region of wavelengths corresponding to spectral lines of sodium, potassium and
water. We develop a detailed atomistic model, describing interactions of atomic
or molecular radiators with dust and atmospheric haze particulates. This model
incorporates a realistic structure of haze particulates from small nano-size
seed particles up to sub-micron irregularly shaped aggregates, accounting for
both pairwise collisions between the radiator and haze perturbers, and
quasi-static mean field shift of levels in haze environments. This formalism
can explain large flattening of absorption and emission spectra in haze
atmospheres and shows how the radiator - haze particle interaction affects the
absorption spectral shape in the wings of spectral lines and near their
centers. The theory can account for nearly all realistic structure, size and
chemical composition of haze particulates and predict their influence on
absorption and emission spectra in hazy environments. We illustrate the utility
of the method by computing shift and broadening of the emission spectra of the
sodium D line in an argon haze. The simplicity, elegance and generality of the
proposed model should make it amenable to a broad community of users in
astrophysics and chemistry.Comment: 16 pages, 4 figures, submitted to MNRA
Radiation Damping in the Photoionization of Fe^{14+}
A theoretical investigation of photoabsorption and photoionization of
Fe^{14+} extending beyond an earlier frame transformation R-matrix
implementation is performed using a fully-correlated, Breit-Pauli R-matrix
formulation including both fine-structure splitting of strongly-bound
resonances and radiation damping. The radiation damping of
resonances gives rise to a resonant photoionization cross section that is
significantly lower than the total photoabsorption cross section. Furthermore,
the radiation-damped photoionization cross section is found to be in good
agreement with recent experimental results once a global shift in energy of
eV is applied. These findings have important implications.
Firstly, the presently available synchrotron experimental data are applicable
only to photoionization processes and not to photoabsorption; the latter is
required in opacity calculations. Secondly, our computed cross section, for
which the L-shell ionization threshold is aligned with the NIST value, shows a
series of Rydberg resonances that are uniformly 3-4 eV
higher in energy than the corresponding experimental profiles, indicating that
the L-shell threshold energy values currently recommended by NIST are likely in
error.Comment: 4 pages, 1 figures, and 2 table
Pre-treatment of Malaysian agricultural wastes toward biofuel production
Various renewable energy technologies are under considerable interest due to the projected depletion of our primary sources of energy and global warming associated with their utilizations. One of the alternatives under focus is renewable fuels produced from agricultural wastes. Malaysia, being one of the largest producers of palm oil, generates abundant agricultural wastes such as fibers, shells, fronds, and trunks with the potential to be converted to biofuels. However, prior to conversion of these materials to useful products, pre-treatment of biomass is essential as it influences the energy utilization in the conversion process and feedstock quality. This chapter focuses on pre-treatment technology of palm-based agriculture waste prior to conversion to solid, liquid, and gas fuel. Pre-treatment methods can be classified into physical, thermal, biological, and chemicals or any combination of these methods. Selecting the most suitable pre-treatment method could be very challenging due to complexities of biomass properties. Physical treatment involves grinding and sieving of biomass into various particle sizes whereas thermal treatment consists of pyrolysis and torrefaction processes. Additionally biological and chemical treatment using enzymes and chemicals to derive lignin from biomass are also discussed