Search results for "classical"

About Compactness of Faddeev Integral Equations for Three Charged Particles

1999

Momentum space three-body integral equations of the Faddeev type can not be used for Coulomb-like potentials, for energies above the breakup threshold. The reason is the occurrence of singularities in their kernels which destroy the compactness properties known to exist for purely short-range interactions. Using the rigorously equivalent formulation in terms of an effective-two- body theory, we prove that the nondiagonal kernels occurring therein possess on and off the energy shell only integrable singularities, provided all three particles have charges of the same sign (ie., only repulsive Coulomb interactions). In contrast, if some of the charges have opposite signs the nondiagonal kernel…

Combined complete C5 and partial C4 deficiency in humans: clinical consequences and complement-mediated functions in vitro.

1990

A family is described with two siblings who suffered at different times from a single episode of meningococcal meningitis by Neisseria meningitidis groups B and C, respectively. In the two subjects, hemolytically active fifth component of complement (C5) was not detectable and antigenic C5 was less than 0.05% and less than 0.7% of normal, respectively. Repletion of sera by purified human C5 (70 micrograms/ml) restored total complement hemolytic activities. The asymptomatic first degree family members had C5 levels compatible with a heterozygous state of C5 deficiency. C4 allotyping revealed an inherited partial deficiency (Q0) of C4A and C4B in the family with a combined C4AQ0 and C4BQ0 het…

Complement receptors on lymphocytes

1981

The classical concept of mass: theoretical difficulties and students’ definitions

1993

An analysis of the concepts of mass in classical physics on the basis of their historical, philosophical and semantic connotations is given. A classification of the most current definitions of mass is proposed from its physical representation and topic area. The definitions of mass, and some related issues, given by several groups of secondary school students are analysed. The results seem to confirm a generalized qualitative‐teleological view of scientific concepts in contrast to the more orthodox formal‐quantitative formulation of physics.

Fermion sign problem in imaginary-time projection continuum quantum Monte Carlo with local interaction

2016

We use the Shadow Wave Function formalism as a convenient model to study the fermion sign problem affecting all projector Quantum Monte Carlo methods in continuum space. We demonstrate that the efficiency of imaginary time projection algorithms decays exponentially with increasing number of particles and/or imaginary-time propagation. Moreover, we derive an analytical expression that connects the localization of the system with the magnitude of the sign problem, illustrating this prediction through some numerical results. Finally, we discuss the fermion sign problem computational complexity and methods for alleviating its severity.

Stochastic analysis of dynamical systems with delayed control forces

2006

Abstract Reduction of structural vibration in actively controlled dynamical system is usually performed by means of convenient control forces dependent of the dynamic response. In this paper the existent studies will be extended to dynamical systems subjected to non-normal delta-correlated random process with delayed control forces. Taylor series expansion of the control forces has been introduced and the statistics of the dynamical response have been obtained by means of the extended Ito differential rule. Numerical application provided shows the capabilities of the proposed method to analyze stochastic dynamic systems with delayed actions under delta-correlated process contrasting statist…

Efficient parallel computations of flows of arbitrary fluids for all regimes of Reynolds, Mach and Grashof numbers

2002

This paper presents a unified numerical method able to address a wide class of fluid flow problems of engineering interest. Arbitrary fluids are treated specifying totally arbitrary equations of state, either in analytical form or through look‐up tables. The most general system of the unsteady Navier–Stokes equations is integrated with a coupled implicit preconditioned method. The method can stand infinite CFL number and shows the efficiency of a quasi‐Newton method independent of the multi‐block partitioning on parallel machines. Computed test cases ranging from inviscid hydrodynamics, to natural convection loops of liquid metals, and to supersonic gasdynamics, show a solution efficiency i…

Visualization_1.mp4

2018

Images obtained with a Walsh Zone Plate and with the equivalent periodic zone plate of the same resolution.

Visualization_1.mp4

2018

Images obtained with a Walsh Zone Plate and with the equivalent periodic zone plate of the same resolution.

A Meshfree Solver for the MEG Forward Problem

2015

Noninvasive estimation of brain activity via magnetoencephalography (MEG) involves an inverse problem whose solution requires an accurate and fast forward solver. To this end, we propose the Method of Fundamental Solutions (MFS) as a meshfree alternative to the Boundary Element Method (BEM). The solution of the MEG forward problem is obtained, via the Method of Particular Solutions (MPS), by numerically solving a boundary value problem for the electric scalar potential, derived from the quasi-stationary approximation of Maxwell’s equations. The magnetic field is then computed by the Biot-Savart law. Numerical experiments have been carried out in a realistic single-shell head geometry. The p…