26 research outputs found
The Angular Trispectra of CMB Temperature and Polarization
We develop the formalism necessary to study four-point functions of the
cosmic microwave background (CMB) temperature and polarization fields. We
determine the general form of CMB trispectra, with the constraints imposed by
the assumption of statistical isotropy of the CMB fields, and derive
expressions for their estimators, as well as their Gaussian noise properties.
We apply these techniques to initial non-Gaussianity of a form motivated by
inflationary models. Due to the large number of four-point configurations, the
sensitivity of the trispectra to initial non-Gaussianity approaches that of the
temperature bispectrum at high multipole moment. These trispectra techniques
will also be useful in the study of secondary anisotropies induced for example
by the gravitational lensing of the CMB by the large scale structure of the
universe.Comment: 16 pages, 4 figures; typographical errors correcte
Gradient Optics of subwavelength nanofilms
Propagation and tunneling of light through subwavelength photonic barriers,
formed by dielectric layers with continuous spatial variations of dielectric
susceptibility across the film are considered. Effects of giant
heterogeneity-induced non-local dispersion, both normal and anomalous, are
examined by means of a series of exact analytical solutions of Maxwell
equations for gradient media. Generalized Fresnel formulae, visualizing a
profound influence of gradient and curvature of dielectric susceptibility
profiles on reflectance/transmittance of periodical photonic heterostructures
are presented. Depending on the cutoff frequency of the barrier, governed by
technologically managed spatial profile of its refractive index, propagation or
tunneling of light through these barriers are examined. Nonattenuative transfer
of EM energy by evanescent waves, tunneling through dielectric gradient
barriers, characterized by real values of refractive index, decreasing in the
depth of medium, is shown. Scaling of the obtained results for different
spectral ranges of visible, IR and THz waves is illustrated. Potential of
gradient optical structures for design of miniaturized filters, polarizers and
frequency-selective interfaces of subwavelength thickness is considered
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Improved dust representation in the Community Atmosphere Model
Aerosol-climate interactions constitute one of the major sources of uncertainty in assessing changes in aerosol forcing in the anthropocene as well as understanding glacial-interglacial cycles. Here we focus on improving the representation of mineral dust in the Community Atmosphere Model and assessing the impacts of the improvements in terms of direct effects on the radiative balance of the atmosphere. We simulated the dust cycle using different parameterization sets for dust emission, size distribution, and optical properties. Comparing the results of these simulations with observations of concentration, deposition, and aerosol optical depth allows us to refine the representation of the dust cycle and its climate impacts. We propose a tuning method for dust parameterizations to allow the dust module to work across the wide variety of parameter settings which can be used within the Community Atmosphere Model. Our results include a better representation of the dust cycle, most notably for the improved size distribution. The estimated net top of atmosphere direct dust radiative forcing is -0.23 ± 0.14 W/m2 for present day and -0.32 ± 0.20 W/m2 at the Last Glacial Maximum. From our study and sensitivity tests, we also derive some general relevant findings, supporting the concept that the magnitude of the modeled dust cycle is sensitive to the observational data sets and size distribution chosen to constrain the model as well as the meteorological forcing data, even within the same modeling framework, and that the direct radiative forcing of dust is strongly sensitive to the optical properties and size distribution used