Search results for "PERTURBATION"
showing 10 items of 811 documents
Modelling uncertainties in phase-space boundary integral models of ray propagation
2020
Abstract A recently proposed phase-space boundary integral model for the stochastic propagation of ray densities is presented and, for the first time, explicit connections between this model and parametric uncertainties arising in the underlying physical model are derived. In particular, an asymptotic analysis for a weak noise perturbation of the propagation speed is used to derive expressions for the probability distribution of the phase-space boundary coordinates after transport along uncertain, and in general curved, ray trajectories. Furthermore, models are presented for incorporating geometric uncertainties in terms of both the location of an edge within a polygonal domain, as well as …
Calculation of atomic properties of superheavy elements Z=110–112 and their ions
2020
We calculate the spectra, electric dipole transition rates, and isotope shifts of the superheavy elements Ds ($Z=110$), Rg ($Z=111$), and Cn ($Z=112$) and their ions. These calculations were performed using a recently developed, efficient version of the ab intio configuration-interaction combined with perturbation theory to treat distant effects. The successive ionization potentials of the three elements are also calculated and compared to lighter analogous elements.
Resonant Kelvin-Helmholtz modes in sheared relativistic flows
2007
Qualitatively new aspects of the (linear and non-linear) stability of sheared relativistic (slab) jets are analyzed. The linear problem has been solved for a wide range of jet models well inside the ultrarelativistic domain (flow Lorentz factors up to 20; specific internal energies $\approx 60c^2$). As a distinct feature of our work, we have combined the analytical linear approach with high-resolution relativistic hydrodynamical simulations, which has allowed us i) to identify, in the linear regime, resonant modes specific to the relativistic shear layer ii) to confirm the result of the linear analysis with numerical simulations and, iii) more interestingly, to follow the instability develo…
Two frequency oscillation of a photorefractive oscillator as a perturbation of the mirrorless oscillation
2010
We consider the properties of the non-degenerate two frequency regime of oscillation of the semi-linear photorefractive oscillator and analyze its relation with the mirrorless oscillation. We consider the oscillator with or without a frequency shifted feedback by a vibrating mirror. This study shows that these two apparently different phenomena are closely related. We conclude from the obtained results that the two frequency oscillation can be considered as a perturbation of the mirrorless oscillation.
Hydrodynamical and Emission Simulations of Relativistic Jets: Stability and Generation of Superluminal and Stationary Components
2001
We present 2D hydrodynamical and emission simulations of the jet stabilityafter the introduction of strong perturbations on a relativistic jet. These simulations show that the interaction of a single strong perturbation with the underlying jet results in the formation of multiple conical shocks with very specific observational properties.
Longitudinal and Transverse Correlation Functions in the 4 Model below and near the Critical Point
2010
We have extended our method of grouping Feynman diagrams (GFD theory) to study the transverse and longitudinal correlation functions G⊥(k) and G‖(k) in φ model below the critical point (T < Tc) in the presence of an infinitesimal external field. Our method allows a qualitative analysis without cutting the perturbation series. The long-wave limit k → 0 has been studied at T < Tc, showing that G⊥(k) a k−λ⊥ and G‖(k) b k−λ‖ with exponents d/2 < λ⊥ < 2 and λ‖ = 2λ⊥−d are the physical solutions of our equations at the spatial dimensionality 2 < d < 4, which coincides with the asymptotic solution at T → Tc as well as with a nonperturbative renormalization group (RG) analysis provided in our paper…
The CC3 model : An iterative coupled cluster approach including connected triples
1997
An alternative derivation of many-body perturbation theory (MBPT) has been given, where a coupled cluster parametrization is used for the wave function and the method of undetermined Lagrange multipliers is applied to set up a variational coupled cluster energy expression. In this variational formulation, the nth-order amplitudes determine the energy to order 2n+1 and the nth-order multipliers determine the energy to order 2n+2. We have developed an iterative approximate coupled cluster singles, doubles, and triples model CC3, where the triples amplitudes are correct through second order and the singles amplitudes are treated without approximations due to the unique role of singles as appro…
A one-loop study of matching conditions for static-light flavor currents
2012
Heavy Quark Effective Theory (HQET) computations of semi-leptonic decays, e.g. B -> pi l nu, require the knowledge of the parameters in the effective theory for all components of the heavy-light flavor currents. So far non-perturbative matching conditions have been employed only for the time component of the axial current. Here we perform a check of matching conditions for the time component of the vector current and the spatial component of the axial vector current up to one-loop order of perturbation theory and to lowest order of the 1/m-expansion. We find that the proposed observables have small higher order terms in the 1/m-series and are thus excellent candidates for a non-perturbat…
Numerical Stochastic Perturbation Theory and the Gradient Flow
2013
We study the Yang-Mills gradient flow using numerical stochastic perturbation theory. As an application of the method we consider the recently proposed gradient flow coupling in the Schr\"odinger functional for the pure SU(3) gauge theory.
Comment on "Dynamics and properties of waves in a modified Noguchi electrical transmission line"
2016
A recent paper [Phys. Rev. E 91, 022925 (2015)PRESCM1539-375510.1103/PhysRevE.91.022925] presents the derivation of the nonlinear equation modeling envelope waves in a specific case of band passed filter discrete nonlinear electrical transmission line (NLTL), called "A modified Noguchi electrical transmission line" according to the authors. Using the reductive perturbation approach in the semidiscrete approximation, they showed that the modulated waves propagating in this NLTL are described by the ordinary nonlinear Schrodinger (NLS) equation. On the basis of their results, the authors claimed that all previous works on the band passed filter NLTL, which considered the vanishing of the dc c…