Search results for "value"
showing 10 items of 5321 documents
Self‐similar problems for modeling the surface chemical reactions with the gravitation
1998
The mathematical model of a chemical reaction which takes place on the surface of the uniformly moving vertically imbedded glass fibre material is considered. The effect of gravitation is taken into account. Boussinesq's and boundary layer fittings allow to derive boundary value problems for self‐similar systems of ordinary differential equations. First Published Online: 14 Oct 2010
Three-dimensional scattering of dielectric gratings under plane-wave excitation
2003
The problem of scattering of electromagnetic plane waves by one-dimensional (1D) periodic dielectric gratings, under the most general condition of oblique incidence (3D incidence), is rigorously solved. A recently developed vectorial modal method for obtaining the modal spectrum of 1D dielectric periodic guiding media has been extended to consider 3D incidence. Polarization coupling effects are included in the analysis, just demonstrating the impossibility of the separation between the transverse electric and transverse magnetic polarizations traditionally employed in the two-dimensional (2D) case. A study of the scattering parameters of a multilayered dielectric periodic structure is accom…
Pattern selection in the 2D FitzHugh–Nagumo model
2018
We construct square and target patterns solutions of the FitzHugh–Nagumo reaction–diffusion system on planar bounded domains. We study the existence and stability of stationary square and super-square patterns by performing a close to equilibrium asymptotic weakly nonlinear expansion: the emergence of these patterns is shown to occur when the bifurcation takes place through a multiplicity-two eigenvalue without resonance. The system is also shown to support the formation of axisymmetric target patterns whose amplitude equation is derived close to the bifurcation threshold. We present several numerical simulations validating the theoretical results.
Hyperfine structure constants of the CaII states 4s 2 S 1/2 and 4p 2 P 1/2, 3/2 and the nuclear quadrupole moment of43Ca
1991
The hyperfine structure splittings of the 4s 2 S 1/2 → 4p 2 P 1/2, 3/2 transitions in43CaII have been measured by fast ion beam collinear laser spectroscopy. The resonant laser interaction was observed using non-optical detection based on optical ground state depopulation pumping, state selective neutralization and charge state separated particle counting. The extracted magnetic dipole hyperfine structure constants for43CaA(2 S 1/2)=−805(2) MHz,A(2 P 1/2)=−145.5(1.0) MHz andA(2 P 3/2)=−31.9(0.2) MHz are in excellent agreement with relativistic many body perturbation theory predictions available for this alkali-like ion. The combined results are used to evaluate the semi-empirical analysis m…
The Ramsey method in high-precision mass spectrometry with Penning traps: Theoretical foundations
2007
Abstract This paper presents in a quantum mechanical framework a theoretical description of the interconversion of the magnetron and modified cyclotron motional modes of ions in a Penning trap due to excitation by external rf-quadrupole fields with a frequency near the true cyclotron frequency. The work aims at a correct description of the resonance line shapes that are observed in connection with more complicated excitation schemes using several excitation pulses, such as Ramsey’s method of separated oscillating fields. Quantum mechanical arguments together with the “rotating wave approximation” suggest a model Hamiltonian that permits a rigorous solution of the corresponding Heisenberg eq…
Multicanonical Monte Carlo study and analysis of tails for the order-parameter distribution of the two-dimensional Ising model.
2003
The tails of the critical order-parameter distribution of the two-dimensional Ising model are investigated through extensive multicanonical Monte Carlo simulations. Results for fixed boundary conditions are reported here, and compared with known results for periodic boundary conditions. Clear numerical evidence for ‘‘fat’’ stretched exponential tails exists below the critical temperature, indicating the possible presence of fat tails at the critical temperature. Our work suggests that the true order-parameter distribution at the critical temperature must be considered to be unknown at present.
Dynamics of a Quantum Particle in Asymmetric Bistable Potential with Environmental Noise
2011
In this work we analyze the dynamics of a quantum particle subject to an asymmetric bistable potential and interacting with a thermal reservoir. We obtain the time evolution of the population distributions in both energy and position eigenstates of the particle, for different values of the coupling strength with the thermal bath. The calculation is carried out using the Feynman-Vernon functional under the discrete variable representation.
X-ray spectroscopy and dosimetry with a portable CdTe device.
2007
Abstract X-ray spectra and dosimetry information are very important for quality assurance (QA) and quality control (QC) in medical diagnostic X-ray systems. An accurate knowledge of the diagnostic X-ray spectra would improve the patient dose optimization, without compromising image information. In this work, we performed direct diagnostic X-ray spectra measurements with a portable device, based on a CdTe solid-state detector. The portable device is able to directly measure X-ray spectra at high photon fluence rates, as typical of clinical radiography. We investigated on the spectral performances of the system in the mammographic energy range (up to ∼40 keV). Good system response to monoener…
Driven harmonic oscillators in the adiabatic Magnus approximation
1993
The time evolution of driven harmonic oscillators is determined by applying the Magnus expansion in the basis set of instantaneous eigenstates of the total Hamiltonian. It is shown that the first-order approximation already provides transition probabilities close to the exact values even in the intermediate regime.
Manifestation of Hamiltonian Monodromy in Nonlinear Wave Systems
2011
International audience; We show that the concept of dynamical monodromy plays a natural fundamental role in the spatiotemporal dynamics of counterpropagating nonlinear wave systems. By means of an adiabatic change of the boundary conditions imposed to the wave system, we show that Hamiltonian monodromy manifests itself through the spontaneous formation of a topological phase singularity (2 - or -phase defect) in the nonlinear waves. This manifestation of dynamical Hamiltonian monodromy is illustrated by generic nonlinear wave models. In particular, we predict that its measurement can be realized in a direct way in the framework of a nonlinear optics experiment.