Search results for "Mathematica"
showing 10 items of 7971 documents
Wronskian representation of solutions of NLS equation, and seventh order rogue wave.
2012
This work is a continuation of a recent paper in which we have constructed a multi-parametric family of the nonlinear Schrodinger equation in terms of wronskians. When we perform a special passage to the limit, we get a family of quasi-rational solutions expressed as a ratio of two determinants. We have already construct Peregrine breathers of orders N=4, 5, 6 in preceding works; we give here the Peregrine breather of order seven.
Density-Functional Calculations of Auger and X-Ray Photoemission Shifts for Metallic Elements
1982
ΔSCF density-functional calculations are reported for Auger, and core level binding energy shifts in sp-bonded metals. The basic model, atom-in-jellium-vacancy, gives good agreement with experiment, especially in the Auger case. The chemical and relaxation contributions to the shifts are discussed. The shifts are calculated also by using the thermochemical model and the results obtained are in agreement with experimental data. The applicability of the "excited-atom" approach to the Auger energy shifts is found restricted.
XANES and EXAFS modelling of configurational disorder in silver borate glasses
2005
The sensitivity of X-ray absorption spectroscopy (XAS) to the local structure around a selected atomic species (symmetry, distances and angles) is commonly exploited to quantitatively describe systems where all the configurations around the absorbing atoms may be approximated by the mean one. However, in many cases of disordered systems a simple description of the local structure with singleconfiguration models cannot be reconciled with experimental spectra. In this paper the necessity to analyse the XAS spectra by considering a multiplicity of atomic structural configurations is demonstrated in the case of silver borate glasses. The local coordination around Ag cations in (Ag2O.nB2O3) glas…
High-pressure x-ray absorption spectroscopy study of tin tungstates
2015
Room-temperature pressure-dependent (0-25 GPa) x-ray absorption spectroscopy at the W -edges of α-SnWO4 and β-SnWO4 was performed using a dispersive setup and a high-pressure nanodiamond anvil cell. The detailed analysis of experimental x-ray absorption near-edge structure and extended x-ray absorption fine structure data suggests that upon increasing pressure, a displacement of tungsten atoms by about 0.2 A toward the center of the WO6 octahedra occurs in α-SnWO4, whereas the coordination of tungsten atoms changes from tetrahedral to distorted octahedral in β-SnWO4.
Local structure studies of SrTi16O3and SrTi18O3
2014
In this work we report on the local structure of Ti in SrTi 16 O3 (STO16) and SrTi 18 O3 (STO18) investigated in the low temperature range (6‐300K) by extended x-ray absorption fine structure and x-ray absorption near edge structure (XANES) spectroscopy at Ti K-edge and by optical second harmonic generation (SHG). By comparing XANES of STO16 and STO18 we have identified the isotopic effect which produces at T < 100K a noticeable difference in the measured mean square relative displacements (MSRD) of Ti‐O1 bonds: while STO16 follow the expected Einstein-like behavior, for STO18 we have measured an increase of MSRD values with decreasing temperature. This is an indication of an increasing off…
Modeling the Spatial Distribution of Xylella fastidiosa: A Nonstationary Approach with Dispersal Barriers
2022
Spatial species distribution models often assume isotropy and stationarity, implying that spatial dependence is direction-invariant and uniform throughout the study area. However, these assumptions are violated when dispersal barriers are present. Despite this, the issue of nonstationarity has been little explored in the context of plant health. The objective of this study was to evaluate the influence of barriers in the distribution of Xylella fastidiosa in the demarcated area in Alicante, Spain. Occurrence data from 2018 were analyzed through spatial Bayesian hierarchical models. The stationary model, illustrating a scenario without control interventions or geographical features, was com…
On finite involutive Yang–Baxter groups
2021
[EN] A group G is said to be an involutive Yang¿Baxter group, or simply an IYB-group, if it is isomorphic to the permutation group of an involutive, nondegenerate set-theoretic solution of the Yang-Baxter equation. We give new sufficient conditions for a group that can be factorised as a product of two IYB-groups to be an IYB-group. Some earlier results are direct consequences of our main theorem.
Methods to Compute Pressure and Wall Tension in Fluids containing Hard Particles
2011
Colloidal systems are often modelled as fluids of hard particles (possibly with an additional soft attraction, e.g. caused by polymers also contained in the suspension). in simulations of such systems, the virial theorem cannot be straightforwardly applied to obtain the components of the pressure tensor. In systems confined by walls, it is hence also not straightforward to extract the excess energy due to the wall (the "wall tension") from the pressure tensor anisotropy. A comparative evaluation of several methods to circumvent this problem is presented, using as examples fluids of hard spheres and the Asakura-Oosawa model of colloid-polymer mixtures with a size ratio $q=0.15$ (for which th…
Bounds to internal forces for elastic-plastic solids subjected to variable loads
1979
Considering an elastic-plastic workhardening solid with piecewise linear yield surfaces and a piecewise linear workhardening law, we give a method for constructing bounds to the internal forces and to the (hardened) yield stresses produced by the action of variable loads at any point of the body and at any time. The loading history is supposed to be unknown, but the loads range within a given domain.
Shakedown theorems for elastic–plastic solids in the framework of gradient plasticity
2008
Abstract Static and kinematic shakedown theorems are given for a class of generalized standard materials endowed with a hardening saturation surface in the framework of strain gradient plasticity. The so-called residual-based gradient plasticity theory is employed. The hardening law admits a hardening potential, which is a C 1 -continuous function of a set of kinematic internal variables and of their spatial gradients, and is required to satisfy a global sign restriction (but not to be necessarily convex). The totally produced, the accumulated and the freely moving dislocations per unit volume, distinguished as statistically stored and geometrically necessary ones, are in this way accounted…