Showing papers on "Momentum published in 1989"
TL;DR: In this paper, the basic equations of turbulence in gas-liquid two-phase flow were derived based on the local instant formulation of two phase flow and its averaging, the conservation equations of mass and momentum were obtained for the fluctuating part of the velocity.
203 citations
TL;DR: In this paper, a microscopic theory based on orthogonal correlated basis functions is developed for the single-particle spectral function of an infinite Fermi system, where spin-isospin and tensor correlations are fully taken into account.
192 citations
TL;DR: In this paper, the euclidean action of gauge theories is derived, taking due account of the restriction of the physical configuration space to the interior of the Gribov horizon.
157 citations
TL;DR: In this paper, the Schrodinger wave equation (SWE) was introduced as a plausible assumption as to how nature works, based on the principle of minimum Fisher information (or maximum Cramer-Rao bound).
Abstract: It is shown that the assumption that nature acts to make optimum estimates of position maximally in error leads to the Schrodinger (energy) wave equation (SWE). In this way, the SWE follows from a simple statement of uncertainty. The approach grows out of probability estimation theory, in particular the principle of minimum Fisher information (or maximum Cramer–Rao bound). The minimized Fisher information turns out to be proportional to the mean kinetic energy of the particle. This approach is an attractive supplement to conventional ways of introducing quantum mechanics to students, since it avoids the use of imperfect physical models (such as vibrating strings) or the immediate need for complex momentum operators, and follows from a plausible assumption as to how nature works.
146 citations
TL;DR: In this paper, the effects of optical thickness and scattering on the flow and temperature fields and heat transfer rates of a radiating fluid in a square enclosure were studied numerically and the coupled momentum, energy, and radiative transfer equations were solved by an iterative procedure.
Abstract: Natural convection of a radiating fluid in a square enclosure is studied numerically. The coupled momentum, energy, and radiative transfer equations are solved by an iterative procedure. The solutions to the equation of radiative transfer are obtained by the discrete ordinates method using S4 and S8 quadratures. The method is based on control volume formulation and is fully compatible with the SIMPLER algorithm used to solve the momentum and energy equations. The effects of optical thickness and scattering on the flow and temperature fields and heat transfer rates are analyzed. The changes in the buoyant flow patterns and temperature distributions due to the presence of radiation in inclined or heat generating enclosures are also studied. Comparative results obtained by the P-I differential approximation are presented.
139 citations
TL;DR: The momentum distributions of projectile and target residues from spallation reactions induced by relativistic projectiles already in the literature are transformed into consistent quantities and compared and the longitudinal momenta depend on the velocity but not the mass of the reaction partner.
Abstract: The momentum distributions of projectile and target residues from spallation reactions induced by relativistic projectiles already in the literature are transformed into consistent quantities and compared. The momentum imparted to the residual nucleus is presented in terms of a longitudinal velocity, 〈${\ensuremath{\beta}}_{?}$〉, and a root-mean-squared momentum, ${P}_{\mathrm{rms}}$. These parameters from all spallation products from many disparate systems display the same systematic dependence on observed mass loss. The rms momentum is shown to depend on the square root of the observed mass loss due to momentum conservation in either of three competing processes with no dependence on the initial reaction. The longitudinal momentum is shown to depend on the observed mass loss and therefore on the excitation energy with only a kinematical factor from the entrance channel. Thus, the longitudinal momenta depend on the velocity but not the mass of the reaction partner.
114 citations
01 Jan 1989
TL;DR: In this paper, the authors proposed a Momentum Space Coordinate Transform (MCT) algorithm for numerical calculations of Diatomic, Neutral and Anionic Systems with Numerical Orbitals.
Abstract: Main Lectures.- Basic Mathematical Properties of Electronic Wave Functions in Configuration Space.- Basic Mathematical Properties of Electronic Wave Functions in Momentum Space.- The Analytical Structure of Atomic and Molecular Wavefunctions and its Impact on the Rate of Convergence of Variational Calculations.- Stochastic Methods in Quantum Mechanic.- Computational Strategies and New Applications in Green's Function Monte Carlo.- Numerical Determination of non-Relativistic and Relativistic Pair Correlation.- Fully Numerical Calculations for Diatomic Systems.- Very Accurate Calculations for Diatomic, Neutral and Anionic Systems with Numerical Orbitals.- The Development of an Efficient Numerical Orbital Algorithm for Polyatomic Systems: A Review of the Various Options.- Electronic Structure Theory in Momentum Space.- Short Contributions.- Should Numerical Orbital Calculations be done with Basis Sets?.- Quantum Chemistry by Random Walk: High Accuracy for Large Molecules.- Prolate Spheroidal Wavefunctions.- Error Estimate in Variational Calculations of Eigenvalues and Eigenvectors.- A Momentum Space Approach to Improve ab initio Hartree-Fock Results Based on the LCAO-GTF Approximation.- Isotope Shift MCHF Calculations in Strontium.- Finite Element Method for the Accurate Solution of Diatomic Molecules.- Momentum Space Coordinate Transformations and their use in Numerical Orbital Calculations.- Moller-Plesset Calculations with Explicitly Correlated Wave Functions.- On the Coulomb Sturmian Basis.- An Analytical L2 Method for Continuum and Autoionizing States.- Application of the Two-dimensional Fully-Numerical RHF Method to Open-Shell Hydrides.- Interpolation of Numerical Orbitals in Momentum Space.- On the Accuracy of the Algebraic Approximation in Relativistic Electronic Structure Calculations.- Numerical MCSCF in One and Two Dimensions.- Numerical Methods for Calculating Multicenter Integrals for Arbitrary Orbitals.- Nonlinear Sequence Transformations for the Efficient Evaluation of Auxiliary Functions for GTO Molecular Integrals.- Concluding Remarks.- List of Participants.
104 citations
TL;DR: Checks of both linear and nonlinear parts of the hydrodynamic description of lattice-gas automata have been achieved, and the well-known logarithmic divergence in the viscosity is observed in the automaton and is shown to disagree with the earliest theoretical predictions in this system.
Abstract: Lattice-gas automata have been proposed as a new way of doing numerical calculations for hydrodynamic systems. Here, a lattice-gas simulation is run to see whether its behavior really does correspond, as proposed, to that of the Navier-Stokes equation. The geometry used is the two-dimensional version of laminar pipe flow. Three checks on the existing theory are performed. The parabolic profile of momentum density arising from the dynamics is quantitatively verified. So is the equation of state, which arises from the statistical mechanics of the system. Finally, the well-known logarithmic divergence in the viscosity is observed in the automaton and is shown to disagree with the earliest theoretical predictions in this system. Proper agreement is achieved, however, when the theory is extended to include three extra (recently discovered) conserved quantities. In this way, checks of both linear and nonlinear parts of the hydrodynamic description of lattice-gas automata have been achieved.
100 citations
TL;DR: The momentum potential theory of time-stationary fluctuating flows is briefly reviewed and then extended to include energy flux carried by momentum fluctuations in this paper, where the mean energy flux can be expressed as a linear superposition of mean, turbulent, acoustic and thermal components.
95 citations
TL;DR: In this article, the influence of momentum dependent interactions and of in medium corrections to the nucleon-nucleon cross sections in the framework of the microscopic QMD model is investigated.
93 citations
TL;DR: In this article, a version of ECMWF's first spectral model with a comprehensive physical parameterization package has been used for long-term integrations in perpetual January mode, and the model has 9 sigma-levels in the vertical and the expansion of the horizontal fields are truncated at total wavenumber n = 31.
Abstract: A version of ECMWF's first spectral model with a comprehensive physical parameterization package has been used for long-term integrations in perpetual January mode. The model has 9 sigma-levels in the vertical and the expansion of the horizontal fields are truncated at total wavenumber n = 31. In order to simulate the observed January climate both in terms of mean-fields as well as the spectral distribution of the kinetic energy as accurately as possible, a series of experiments has been performed with varying parameterizations of some physical processes, especially the damping mechanisms. The inclusion of a simple gravity wave drag is found to have a substantial impact on the simulations. The position and depth of the mean sea level quasi-stationary low pressures in the northern hemisphere is more in accordance with their observed counterparts with the gravity wave drag included, and the excessive stratospheric polar night jet, which is developed in the model without the drag, is effectively controlled by this parameterization. The sensitivity due to changes in the vertical diffusion of momentum, heat and moisture has been considered by crude variations in the mixing length. It turns out that even large changes in the value of the mixing length have a quite modest influence on the mean fields simulated by the model. The horizontal diffusion is necessary in order to represent the effect of the unresolved scales on the explicitly predicted scales. The parameterization of this effect is incorporated in the model as a linear term utilizing that in a spectral formulation, a linear diffusion can easily be formulated with any scale dependency. It is found that an increase of the diffusion in the smallest scales may result in an increase of eddy kinetic energy of the larger scales and even an increase in the total eddy kinetic energy. Moreover it appears that it is quite possible to formulate the linear diffusion of the model to simulate the observed spectral variations of kinetic energy for the medium and smaller scales. DOI: 10.1111/j.1600-0870.1989.tb00390.x
TL;DR: In this article, it was shown that the superintegrable chiral Potts model which has zero momentum and is the ground state for small λ is not the ground states for λ = 1 by exhibiting a state of nonzero momentum whose eigen value crosses the zero momentum eigenvalue at a value of λ less than 1.
TL;DR: In this paper, the effect of hot-phonon production on the steady-state high-field transport properties of electrons in bulk and quasi-2D semiconductors is discussed within the framework of a simple theoretical model in which Cerenkov effects and phonon drift are assumed to be negligible.
Abstract: The effect of hot-phonon production on the steady-state high-field transport properties of electrons in bulk and quasi-2D semiconductors is discussed within the framework of a simple theoretical model in which Cerenkov effects and phonon drift are assumed to be negligible. The model also assumes a single spherical parabolic band for the electrons whose distribution is a displaced Maxwellian, with scattering confined to polar optical phonons, restricted to interface modes in a deep square quantum well in the quasi-2D case. A finite phonon lifetime of 7 ps is shown to reduce the energy relaxation rate and to increase the momentum relaxation rate. The result is to lower the mobility and to delay runaway to higher fields, these effects increasing with the electron density. It is pointed out that nondrifting hot phonons tend to quench intervalley and real-space-transfer NDRS and to reduce the drift velocity for a given field. It is shown that, in general, the effective energy relaxation time is field dependent.
01 Jan 1989
TL;DR: In this paper, the carbon monoxide-hydrogen-oxygen system is simulated by solving the corresponding conservation equations (i.e., conservation of mass, energy, momentum and species mass) for one-dimensional geometries using a detailed reaction mechanism and a multi-species transport model.
Abstract: Ignition processes in the carbon monoxide-hydrogen-oxygen system are simulated by solving the corresponding conservation equations (i.e. conservation of mass, energy, momentum and species mass) for one-dimensional geometries using a detailed reaction mechanism and a multi-species transport model. An additional source term in the energy conservation equation allows the treatment of induced ignition, and a realistic model for the destruction of reactive species at the vessel surface is used to treat auto-ignitions in static reactors. Spatial discretization using finite differences and an adaptive grid point system leads to a differential/algebraic equation system which is solved numerically by extrapolation or backward differencing codes. Minimum ignition energies are calculated for various mixture compositions and radii of the external energy source. Ignition limits are computed, and a sensitivity analysis shows the rate-limiting reactions.
TL;DR: In this article, a numerical model for predicting wave reflection and transmission over a submerged impermeable breakwater is proposed by modifying the numerical model developed previously to predict wave reflections and run-up on rough or smooth impermeability slopes.
Abstract: Monochromatic wave reflection and transmission over a submerged impermeable breakwater is predicted numerically by slightly modifying the numerical model developed previously for predicting wave reflection and run‐up on rough or smooth impermeable slopes. The slight modification is related to the landward boundary condition required for the transmitted wave propagating landward. In addition to the conservation equations of mass and momentum used to compute the flow field, an equation of energy is derived to estimate the rate of energy dissipation due to wave breaking. The computed reflection and transmission coefficients are shown to be in agreement with available small‐scale test data. The numerical model also predicts the spatial variation of the energy dissipation, the mean water level difference, and the time‐averaged volume flux per unit width, although available measurements are not sufficient for evaluating the capabilities and limitations of the numerical model for predicting these quantities.
TL;DR: Determination des lois de conservation de la quantite de mouvement dans 2 systemes independants de gaz d'electrons bidimensionnels dans les heterojonctions GaAs−GaAlAs.
Abstract: We directly determine the momentum conservation rules for tunneling processes between two independently contacted two-dimensional-electron-gas systems on GaAs-GaAlAs heterostructures. In transverse magnetic fields, the conservation of the canonical momentum results in a new and giant broadening of the subband resonances. As a consequence, the mean values of the wave functions, even for nonoccupied subbands, can be determined directly.
TL;DR: In this article, a model is presented to describe the dynamical processes of trapping/desorption as well as direct and indirect inelastic scattering on singlecrystal surfaces.
Abstract: A model is presented to describe the dynamical processes of trapping/desorption as well as direct and indirect inelastic scattering on single‐crystal surfaces. Newton’s equations of motion are integrated for a system consisting of a rigid rotor interacting with a slab of 19 surface atoms. The surface atom which is closest to the center of mass of the molecule is permitted to translate only along the surface normal. In turn, this mobile surface atom is harmonically coupled to a microcanonical heat bath consisting of three subsurface atoms. This method is much less computationally intensive than the typical generalized Langevin equation (GLE) approach. Direct comparison is made between the predictions of this model and experiment for the NO/Pt(111) system. In the case of trapping/desorption, the model accurately describes the observed dependence of rotational alignment on rotational quantum number. For the inelastic scattering regime, the model successfully reproduces the degree of rotational excitation and qualitatively accounts for the observed rotational alignment. In addition, the model predicts correlations between final state velocity and final state rotational angular momentum (both direction and magnitude), as well as the effect of molecular orientation and surface impact parameter on the overall trapping probability.
TL;DR: The concept of thermal momentum as the derivative of the kinetic potential with respect to the entropy flux is introduced; this quality plays a fundamental role in the extension of Gibbs's equation to describe a nonequilibrium fluid with heat flux.
Abstract: Extended thermodynamics of heat-conducting fluids is used to give explicit formulas for non- equilibrium energy density of ideal gas expressed as functions of classical variables and the diffusive entropy flux (a nonequilibrium variable). A Lagrangian density associated with the energy density is used to obtain the components of energy-momentum tensor and corresponding conservation laws on the basis of Hamilton's principle of stationary action and Noether's theorem. The heat flux appears naturally as a consequence of a free entropy transfer (independent of mass transfer) and a momentum transport is associated with tangential stresses resulting from this entropy transfer. The compatibility of the present description with the kinetic theory is shown. Hamilton's principle is extended so that the flux of entropy as well as the fluxes and densities of mass are varied independently. The concept of thermal momentum as the derivative of the kinetic potential with respect to the entropy flux is introduced; this quality plays a fundamental role in the extension of Gibbs's equation to describe a nonequilibrium fluid with heat flux.
TL;DR: In this article, an implicit solution of the Navier-stokes equations including detailed chemistry in two space dimensions is performed by a method of lines, where spatial discretization on a two-dimensional grid that is adapted statically in two spatial directions leads to a differential/ algebraic equation system which is solved numerically by an implicit extrapolation method to overcome stiffness problems caused by the multiscale character of the system considered.
Abstract: Globally implicit solutions of the compressible Navier-Stokes equations including detailed chemistry in two space dimensions are performed by a method of lines. This has become possible by the recent development of numerical methods for the solution of stiff differential /algebraic equation systems together with the availability of fast computers with high storage capacity. Computations of ignition processes are performed by solving the corresponding conservation equations (i.e., conservation of total mass, momentum, energy, and species mass) using a detailed reaction mechanism for the ozone-oxygen system (consisting of six elementary reactions) and a multispecies transport model. Thermal ignition is simulated by an additional source term in the energy conservation equation. Spatial discretization on a two-dimensional grid that is adapted statically in two spatial directions leads to a differential/ algebraic equation system which is solved numerically by an implicit extrapolation method to overcome stiffness problems caused by the multiscale character of the system considered. Results are presented for the simulation of a laser-induced thermal ignition in an ozone-oxygen mixture in a cylindrical reaction vessel. However, the method can be generally applied to two-dimensional reactive flows in relatively simple geometries.
IBM1
TL;DR: It is shown that the viscosity of a very dilute gas decreases monotonically with the decreasing density, and it is predicted that at higher Kn, the slip coefficient is predicted to depend on the Knudsen number.
Abstract: Molecular-dynamics simulations were used to study the heat and momentum transport phenomena in very dilute gases flowing through a two-dimensional channel. Aside from pronounced slips in velocity and temperature at the wall, Navier-Stokes equations seem to be valid up to the maximum Knudsen number (Kn), 0.27, studied. It is further shown that the viscosity of a very dilute gas decreases monotonically with the decreasing density. For Kn less than \ensuremath{\sim}0.05, the slip coefficient, 1.16, calculated from the simulation is in good agreement with theoretical results, ranging from 1.134 to 1.230. However, at higher Kn, the slip coefficient is predicted to depend on the Knudsen number.
TL;DR: Les fluctuations de paires independantes ne provoquent pas d'instabilite dans un liquide de Fermi bidimensionnel degenere, avec une faible interaction attractive.
Abstract: Independent pair fluctuations with large total momentum do not cause an instability in a degenerate two-dimensional Fermi liquid with a weak attractive interaction.
TL;DR: Longitudinal and transverse cross sections for the reaction 4 He(e, e′ p) 3 H were determined for missing momenta p m up to 190 MeV/ c and momentum transfers q up to 829 MeV / c as discussed by the authors.
01 Jan 1989
TL;DR: In this article, the hamiltonian dynamics of coupled structures is discussed and a theorem due to Smale has a useful role in the study of relative equilibria, a group of symmetries can be determined using the energy-Casimir (or energy momentum) method.
Abstract: : The hamiltonian dynamics of coupled structures is discussed. There are geometric parallels in earlier work on the Newtonian (gravitational) many- body problem. In the study of relative equilibria, a theorem due to Smale has a useful role. Relative stability module a group of symmetries can be determined using the energy-Casimir (or energy - momentum) method. For nongeneric values of momenta, the Poisson structure can affect stability.
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TL;DR: In this paper, the authors constructed exact localized oscillating finite energy solutions of the massless wave equation which move like massive relativistic particles with energy E = λω and momentum p= λ k, λ = const, where ω is the frequency of the oscillating lump and k its wave vector.
TL;DR: In this article, the authors introduce the effective finite-range interaction of Gogny in the semi-classical description of heavy-ion reactions based on the Landau-Vlasov equation and show that this energy dependence increases the flow and reproduces the values obtained with stiff local Skyrme forces.
Journal Article•
TL;DR: In this article, the mass, momentum, and energy conservation equations for a distribution of fluid particles (bubbles or droplets) transported by a continuous fluid medium were derived for a nuclear fuel channel and used to model nonequilibrium, two-phase, dispersed, fluid flow behavior.
Abstract: The behavior of water droplets in a heated nuclear fuel channel is of significant interest to nuclear reactor safety studies pertaining to loss-of-coolant accidents. This paper presents the derivation of the mass, momentum, and energy conservation equations for a distribution of fluid particles (bubbles or droplets) transported by a continuous fluid medium. When coupled with the appropriate closure equations, the conservation equations can be used to model nonequilibrium, two-phase, dispersed, fluid flow behavior.
TL;DR: In this paper, the three dimensional electron-positron momentum densities have been obtained on Ti and Zr from measurements of two dimensional angular correlation of positron annihilation radiation followed by an image reconstruction technique based on direct Fourier transformation.
Abstract: The three dimensional electron-positron momentum densities have been obtained on Ti and Zr from measurements of two dimensional angular correlation of positron annihilation radiation followed by an image reconstruction technique based on direct Fourier transformation. Augmented-plane wave band structure calculations have been carried out and the results are compared with the experiments. Agreement between the experiment and the theory leads to a conclusion that both Ti and Zr have electron surface sheets which are centered at H and hole surface sheets which are running along the \(\varGamma\)-A axis.
TL;DR: It is found that a separation of space and momentum correlations is favored if the coupling between the components takes place at low frequencies or if the frequent collisions at high densities suppress the dynamical polarization.
Abstract: We study pair correlations in a plasma of two repulsive components at different temperatures and a neutralizing background. The validity of the polarization approximation and the hypernetted-chain approximation is examined by comparing with computer simulations for weak and strong coupling, respectively. We find that a separation of space and momentum correlations is favored if the coupling between the components takes place at low frequencies or if the frequent collisions at high densities suppress the dynamical polarization.