4,732 research outputs found
Slow-roll inflation with a Gauss-Bonnet correction
We consider slow-roll inflation for a single scalar field with an arbitrary
potential and an arbitrary nonminimal coupling to the Gauss-Bonnet term. By
introducing a combined hierarchy of Hubble and Gauss-Bonnet flow functions, we
analytically derive the power spectra of scalar and tensor perturbations. The
standard consistency relation between the tensor-to-scalar ratio and the
spectral index of tensor perturbations is broken. We apply this formalism to a
specific model with a monomial potential and an inverse monomial Gauss-Bonnet
coupling and constrain it by the 7-year Wilkinson Microwave Anisotropy Probe
data. The Gauss-Bonnet term with a positive (or negative) coupling may lead to
a reduction (or enhancement) of the tensor-to-scalar ratio and hence may revive
the quartic potential ruled out by recent cosmological data.Comment: 7 pages, 2 figures, RevTeX, references added, published versio
Effect of lubricant environment on saw damage in silicon wafers
The chemomechanical effect of lubricant environments on the inner diameter (ID) sawing induced surface damage in Si wafers was tested for four different lubricants: water, dielectric oil, and two commercial cutting solutions. The effects of applying different potential on Si crystals during the sawing were also tested. It is indicated that the number and depth of surface damage are sensitive to the chemical nature of the saw lubricant. It is determined that the lubricants that are good catalysts for breaking Si bonds can dampen the out of plane blade vibration more effectively and produce less surface damage. Correlations between the applied potential and the depth of damage in the dielectric oil and one of the commercial cutting solutions and possible mechanisms involved are discussed
Time Quantified Monte Carlo Algorithm for Interacting Spin Array Micromagnetic Dynamics
In this paper, we reexamine the validity of using time quantified Monte Carlo
(TQMC) method [Phys. Rev. Lett. 84, 163 (2000); Phys. Rev. Lett. 96, 067208
(2006)] in simulating the stochastic dynamics of interacting magnetic
nanoparticles. The Fokker-Planck coefficients corresponding to both TQMC and
Langevin dynamical equation (Landau-Lifshitz-Gilbert, LLG) are derived and
compared in the presence of interparticle interactions. The time quantification
factor is obtained and justified. Numerical verification is shown by using TQMC
and Langevin methods in analyzing spin-wave dispersion in a linear array of
magnetic nanoparticles.Comment: Accepted for publication in Phys. Rev.
Parametrizations of the Dark Energy Density and Scalar Potentials
We develop a theoretical method of constructing the scalar (quintessence or
phantom) potential directly from the dimensionless dark energy function X(z),
the dark energy density in units of its present value. We apply our method to
two parametrizations of the dark energy density, the quiessence-Lambda ansatz
and the generalized Chaplygin gas model, and discuss some features of the
constructed potentials.Comment: 8 pages, 2 figures, ws-mpla.cls, Accepted for publication in Mod.
Phys. Lett.
Solving the Master Equation for Extremely Long Time Scale Calculations
The dynamics of magnetic reversal process plays an important role in the
design of the magnetic recording devices in the long time scale limit. In
addition to long time scale, microscopic effects such as the entropic effect
become important in magnetic nano-scale systems. Many advanced simulation
methods have been developed, but few have the ability to simulate the long time
scale limit and to accurately model the microscopic effects of nano-scale
systems at the same time. We develop a new Monte Carlo method for calculating
the dynamics of magnetic reversal at arbitrary long time. For example, actual
calculations were performed up to 1e50 Monte Carlo steps. This method is based
on microscopic interactions of many constituents and the master equation for
magnetic probability distribution function is solved symbolically.Comment: accepted for publication in Computer Physics and Communication
Parametrization of Quintessence and Its Potential
We develop a theoretical method of constructing the quintessence potential
directly from the effective equation of state function , which describes
the properties of the dark energy. We apply our method to four parametrizations
of equation of state parameter and discuss the general features of the
resulting potentials. In particular, it is shown that the constructed
quintessence potentials are all in the form of a runaway type.Comment: 6 pages, 2 figures, LaTeX2
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