Search results for "Monte Carlo method."
showing 10 items of 1217 documents
Magic numbers, excitation levels, and other properties of small neutral math clusters (N < 50)
2006
The ground-state energies and the radial and pair distribution functions of neutral math clusters are systematically calculated by the diffusion Monte Carlo method in steps of one math atom from 3 to 50 atoms. In addition the chemical potential and the low-lying excitation levels of each cluster are determined with high precision. These calculations reveal that the “magic numbers” observed in experimental math cluster size distributions, measured for free jet gas expansions by nondestructive matter-wave diffraction, are not caused by enhanced stabilities. Instead they are explained in terms of an enhanced growth due to sharp peaks in the equilibrium concentrations in the early part of the e…
Inspirations for EO polymer design gained from modeling of chromophore poling by Langevin dynamics
2013
One of the possibilities to create organic molecular material for NLO applications are polymers with dispersed NLO active chromophores. These molecules must be acentrically ordered by applying an external electric poling field. The NLO efficiency depends on dipole moment, molecular hyperpolarizabilities, concentration of the chromophores and external poling field strength. Calculating, from first principles, the extent of the alignment and via this NLO efficiency has proven to be challenging. One approach to solve this problem is pure analytic statistical mechanics treatment, what could be enhanced by Monte Carlo ( MC ) statistical mechanical modelling. The chromophore molecules usually hav…
Shear moduli of two dimensional binary glasses
2012
The shear moduli of two-component glasses in two dimensions are studied within mode coupling theory. Varying the concentration, strong mixing effects are observed along the glass transition lines for two interaction potentials. Nonoverlapping disks with size ratios between 0.3 and 0.9, and point particles interacting with (magnetic) dipoles of strength ratio between 0.1 and 0.6 are considered. Equilibrium structure factors (partially obtained from Monte Carlo simulations) and glass form factors, and perturbative calculations show that a softening of the elastic shear constant of glass upon adding another component arises from a dilution effect of the majority component. For very disparate m…
Monte Carlo Simulation of a Modified Chi Distribution with Unequal Variances in the Generating Gaussians. A Discrete Methodology to Study Collective …
2020
The Chi distribution is a continuous probability distribution of a random variable obtained from the positive square root of the sum of k squared variables, each coming from a standard Normal distribution (mean = 0 and variance = 1). The variable k indicates the degrees of freedom. The usual expression for the Chi distribution can be generalised to include a parameter which is the variance (which can take any value) of the generating Gaussians. For instance, for k = 3, we have the case of the Maxwell-Boltzmann (MB) distribution of the particle velocities in the Ideal Gas model of Physics. In this work, we analyse the case of unequal variances in the generating Gaussians whose distribution w…
Magic numbers, excitation levels, and other properties of small neutral 4He clusters (Nor = 50).
2006
The ground-state energies and the radial and pair distribution functions of neutral 4He clusters are systematically calculated by the diffusion Monte Carlo method in steps of one 4He atom from 3 to 50 atoms. In addition the chemical potential and the low-lying excitation levels of each cluster are determined with high precision. These calculations reveal that the "magic numbers" observed in experimental 4He cluster size distributions, measured for free jet gas expansions by nondestructive matter-wave diffraction, are not caused by enhanced stabilities. Instead they are explained in terms of an enhanced growth due to sharp peaks in the equilibrium concentrations in the early part of the expa…
Monte Carlo simulation of many-arm star polymers in two-dimensional good solvents in the bulk and at a surface
1991
A Monte Carlo technique is proposed for the simulation of statistical properties of many-arm star polymers on lattices. In this vectorizing algorithm, the length of each arml is increased by one, step by step, from a starting configuration withl=1 orl=2 which is generated directly. This procedure is carried out for a large sample (e.g., 100,000 configurations). As an application, we have studied self-avoiding stars on the square lattice with arm lengths up tol max=125 and up tof=20 arms, both in the bulk and in the geometry where the center of the star is adsorbed on a repulsive surface. The total number of configurations, which behaves asN∼l γ G–1μ fl , whereμ=2.6386 is the usual effective…
Erratum: “TG-43 U1 based dosimetric characterization of model 67-6520 Cs-137 brachytherapy source”
2012
Purpose: Brachytherapy treatment has been a cornerstone for management of various cancer sites, particularly for the treatment of gynecological malignancies. In low dose rate brachytherapy treatments,C137s sources have been used for several decades. A new C137s source design has been introduced (model 67-6520, source B3-561) by Isotope Products Laboratories (IPL) for clinical application. The goal of the present work is to implement the TG-43 U1 protocol in the characterization of the aforementioned C137s source. Methods: The dosimetriccharacteristics of the IPLC137s source are measured using LiF thermoluminescent dosimeters in a Solid Water™ phantom material and calculated using Monte Carl…
Monte Carlo simulation of high‐order harmonics generation in bulk semiconductors and submicron structures
2004
To qualify the feasibility of standard semiconductor materials and Schottky‐barrier diodes (SBDs) for THz high‐order harmonic generation and extraction, the harmonic intensity, intrinsic noise and signal‐to‐noise ratio are calculated by the Monte Carlo method when a periodic high‐frequency large‐amplitude external signal is applied to a semiconductor device. Due to very high signal‐to‐noise ratio heavily doped GaAs SBDs are found to exhibit conditions for frequency mixing and harmonic extraction that are definitively superior to those of bulk materials. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Split decomposition A technique to analyze viral evolution
1993
A clustering technique allowing a restricted amount of overlapping and based on an abstract theory of coherent decompositions of finite metrics is used to analyze the evolution of foot-and-mouth disease viruses. The emerging picture is compatible with the existence of viral populations with a quasispecies structure and illustrates various forms of evolution of this virus family. In addition, it allows the correlation of these forms with geographic occurrence.
Residual-based block bootstrap for cointegration testing
2010
We propose a new testing procedure to determine the rank of cointegration. This new method is based on the nonparametric resampling procedure, so-called Residual-Based Block Bootstrap (RBB), which is developed by Paparoditis and Politis (2003) in the context of unit root testing. Through Monte Carlo experiments we show that, in small samples, the RBB cointegration test has good power properties in relation to the other two well-known tests for cointegration, such as the Augmented Dickey–Fuller (ADF), applied to the residual of a cointegrating regression, and the Johansen's maximum eigenvalue tests. Likewise, this article looks at the influence played by the correlation of the ‘X’ variables …