61,376 research outputs found
Rotordynamic response analysis program
Computer routine is similar to Holzer's method in torsional vibration treatment, and Prohl's and Myklestad's approach in computing rotor deflection. Matrix iteration technique is used to compute rotordynamic response by a simulated discrete mass system
Suppression of local haze variations in MERIS images over turbid coastal waters for retrieval of suspended sediment concentration
Atmospheric correction over turbid waters can be problematic if atmospheric haze is spatially variable. In this case the retrieval of water quality is hampered by the fact that haze variations could be partly mistaken for variations in suspended sediment concentration (SSC). In this study we propose the suppression of local haze variations while leaving sediment variations intact. This is accomplished by a multispectral data projection (MDP) method based on a linear spectral mixing model, and applied prior to the actual standard atmospheric correction. In this linear model, the hazesediment spectral mixing was simulated by a coupled water-atmosphere radiative transfer (RT) model. As a result, local haze variations were largely suppressed and transformed into an approximately homogenous atmosphere over the MERIS top-of-atmosphere (TOA) radiance scene. The suppression of local haze variations increases the number of satellite images that are still suitable for standard atmospheric correction processing and subsequent water quality analysi
Remittances and inequality: a dynamic migration model
We develop a model to study the effects of migration and remittances on inequality
in the origin communities. While wealth inequality is shown to be monotonically
reduced along the time-span, the short- and the long-run impacts on income
inequality may be of opposite signs, suggesting that the dynamic relationship
between migration/remittances and inequality may well be characterized by an
inverse U-shaped pattern. This is consistent with the findings of the empirical
literature, yet offers a different interpretation from the usually assumed migration
network effects. With no need to endogenize migration costs through the role of
migration networks, we generate the same result via intergenerational wealth
accumulation
Medium modification of the charged current neutrino opacity and its implications
Previous work on neutrino emission from proto-neutron stars which employed
full solutions of the Boltzmann equation showed that the average energies of
emitted electron neutrinos and antineutrinos are closer to one another than
predicted by older, more approximate work. This in turn implied that the
neutrino driven wind is proton rich during its entire life, precluding
-process nucleosynthesis and the synthesis of Sr, Y, and Zr. This work
relied on charged current neutrino interaction rates that are appropriate for a
free nucleon gas. Here, it is shown in detail that the inclusion of the nucleon
potential energies and collisional broadening of the response significantly
alters this conclusion. Iso-vector interactions, which give rise to the nuclear
symmetry energy, produce a difference between the neutron and proton
single-particle energies and alter the kinematics of the
charged current reactions. In neutron-rich matter, and for a given
neutrino/antineutrino energy, the rate for is
enhanced while is suppressed because the
value for these reactions is altered by , respectively. In the
neutrino decoupling region, collisional broadening acts to enhance both
and cross-sections and RPA corrections decrease the
cross-section and increase the cross-section, but mean field
shifts have a larger effect. Therefore, electron neutrinos decouple at lower
temperature than when the nucleons are assumed to be free and have lower
average energies. The change is large enough to allow for a reasonable period
of time when the neutrino driven wind is predicted to be neutron rich. It is
also shown that the electron fraction in the wind is influenced by the nuclear
symmetry energy.Comment: Version submitted to PRC, 10 pages, 6 figures (Additional discussion
of RPA effects added
First Principles Derivation of Effective Ginzburg-Landau Free Energy models for Crystalline Systems
The expression of the free energy density of a classical crystalline system
as a gradient expansion in terms of a set of order parameters is developed
using classical density functional theory. The goal here is to extend and
complete an earlier derivation by L{\"o}wen et al (Europhys. Lett.9, 791,
1989). The limitations of the resulting expressions are also discussed
including the boundary conditions needed for finite systems and the fact that
the results cannot, at present, be used to take into account elastic
relaxation.Comment: 12 pages, no figures, sumitted to Physica
CRLBs for Pilot-Aided Channel Estimation in OFDM System under Gaussian and Non-Gaussian Mixed Noise
The determination of Cramer-Rao lower bound (CRLB) as an optimality criterion for the problem of channel estimation in wireless communication is a very important issue. Several CRLBs on channel estimation have been derived for Gaussian noise. However, a practical channel is affected by not only Gaussian background noise but also non-Gaussian noise such as impulsive interference. This paper derives the deterministic and stochastic CRLBs for Gaussian and non-Gaussian mixed noise. Due to the use of the non-parametric kernel method to build the PDF of non-Gaussian noise, the proposed CRLBs are suitable for practical channel environments with various noise distributions
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