86,099 research outputs found
Neutrino oscillations in de Sitter space-time
We try to understand flavor oscillations and to develop the formulae for
describing neutrino oscillations in de Sitter space-time. First, the covariant
Dirac equation is investigated under the conformally flat coordinates of de
Sitter geometry. Then, we obtain the exact solutions of the Dirac equation and
indicate the explicit form of the phase of wave function. Next, the concise
formulae for calculating the neutrino oscillation probabilities in de Sitter
space-time are given. Finally, The difference between our formulae and the
standard result in Minkowski space-time is pointed out.Comment: 13 pages, no figure
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
Pressure dependence of elastic and dynamical properties of zinc-blende ZnS and ZnSe from first principle calculation
The density-functional theory (DFT) and density-functional perturbation
theory (DFPT) are employed to study the pressure dependence of elastic and
dynamical properties of zinc-blende ZnS and ZnSe. The calculated elastic
constants and phonon spectra from 0 GPa to 15 GPa are compared with the
available experimental data. Generally, our calculated values are overestimated
with experimental data, but agree well with recent other theoretical values.
The discrepancies with experimental data are due to the use of local density
approximation (LDA) and the effect of temperature. In this work, in order to
compare with experimental data, we calculated and discussed the pressure
derivatives of elastic constants, the pressure dependence of dynamical effect
charge, and mode Gr\"uneisen parameter at \Gamma.Comment: 10 pages, 6 figure
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