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On Carrier Facilitated Transport Through Membranes

Description: Facilitated transport is a process, whereby the diffusion of a solute across a membrane is chemically enhanced. In this report an analysis is given of a facilitated transport system involving a volatile species A which reacts with a nonvolatile carrier species B to form the nonvolatile product AB.
Date: June 1980
Creator: Kaper, H. G.; Leaf, G. K. & Matkowsky, Bernard J.
Partner: UNT Libraries Government Documents Department

Multigroup Methods for Neutron Diffusion Problems

Description: Abstract: "The age-diffusion is adequate to describe the neutron behavior of a very large class of nonthermal reactors (all except those whose dimensions are comparable to the neutron mean free path). Thus, a convenient means of obtaining an accurate solution to this equation is very useful for general reactor calculations. Methods for reducing the age-diffusion equation to a finite set of coupled ordinary differential equations, called multigroup equations, are described. The relative merits of several alternate schemes are discussed. The multigroup equations may be solved by iterative procedures based on an assumed spatial distribution of the fission source neutrons. In practice the initially assumed source shape is accurate enough so that additional iterations are unnecessary. Analytical and numerical methods for solving the multigroup equations with the assumed source are discussed. The adjoint equations are also reduced to multigroup form, and examples of the adjoint function in obtaining improved reactivity values are given."
Date: August 20, 1953
Creator: Hurwitz, H., Jr. & Ehrlich, R.
Partner: UNT Libraries Government Documents Department

9-Zoom : A One-Dimensional, Multigroup, Neutron Diffusion Theory Reactor Code for the IBM 709

Description: The following document describes the usage and purpose of the neutron diffusion theory reactor program 9-Zoom, a memory-contained program that takes advantage of 709 features such as, for example, preferential order of multiply by zero, and for small problems approaches input-output limitations with excellent convergence properties.
Date: August 25, 1959
Creator: Stone, S. P.; Collins, E. T. & Lenihan, S. R.
Partner: UNT Libraries Government Documents Department

Multigroup discrete ordinates solution of Boltzmann-Fokker-Planck equations and cross section library development of ion transport

Description: We have developed and successfully implemented a two-dimensional bilinear discontinuous in space and time, used in conjunction with the S{sub N} angular approximation, to numerically solve the time dependent, one-dimensional, one-speed, slab geometry, (ion) transport equation. Numerical results and comparison with analytical solutions have shown that the bilinear-discontinuous (BLD) scheme is third-order accurate in the space ad time dimensions independently. Comparison of the BLD results with diamond-difference methods indicate that the BLD method is both quantitavely and qualitatively superior to the DD scheme. We note that the form of the transport operator is such that these conclusions carry over to energy dependent problems that include the constant-slowing-down-approximation term, and to multiple space dimensions or combinations thereof. An optimized marching or inversion scheme or a parallel algorithm should be investigated to determine if the increased accuracy can compensate for the extra overhead required for a BLD solution, and then could be compared to other discretization methods such as nodal or characteristic schemes.
Date: August 1, 1995
Creator: Prinja, A.K.
Partner: UNT Libraries Government Documents Department

NUMERICAL SOLUTION OF TRANSIENT AND STEADY-STATE NEUTRON TRANSPORT PROBLEMS

Description: A general numerical procedure, called the discrete S/sub n/ method, for solving the neutron transport equation is described. The main topics relate to the derivation of suitable difference equations, and to the problem of solving these, while maintaining generality, accuracy, and reasonable computing speed. A few comparisons with other methods are made. (auth)
Date: May 16, 1959
Creator: Carlson, B.
Partner: UNT Libraries Government Documents Department

Delta f Monte Carlo Calculation Of Neoclassical Transport In Perturbed Tokamaks

Description: Non-axisymmetric magnetic perturbations can fundamentally change neoclassical transport in tokamaks by distorting particle orbits on deformed or broken flux surfaces. This so-called non-ambipolar transport is highly complex, and eventually a numerical simulation is required to achieve its precise description and understanding. A new delta#14;f particle code (POCA) has been developed for this purpose using a modi ed pitch angle collision operator preserving momentum conservation. POCA was successfully benchmarked for neoclassical transport and momentum conservation in axisymmetric con guration. Non-ambipolar particle flux is calculated in the non-axisymmetric case, and results show a clear resonant nature of non-ambipolar transport and magnetic braking. Neoclassical toroidal viscosity (NTV) torque is calculated using anisotropic pressures and magnetic fi eld spectrum, and compared with the generalized NTV theory. Calculations indicate a clear #14;B2 dependence of NTV, and good agreements with theory on NTV torque pro les and amplitudes depending on collisionality.
Date: April 11, 2012
Creator: Kimin Kim, Jong-Kyu Park, Gerrit Kramer and Allen H. Boozer
Partner: UNT Libraries Government Documents Department

An Expression for the Temperature Gradient in Chaotic Fields

Description: A coordinate system adapted to the invariant structures of chaotic magnetic fields is constructed. The coordinates are based on a set of ghost-surfaces, defined via an action-gradient flow between the minimax and minimizing periodic orbits. The construction of the chaotic coordinates allows an expression describing the temperature gradient across a chaotic magnetic field to be derived. The results are in close agreement with a numerical calculation.
Date: December 22, 2008
Creator: Hudson, S.R.
Partner: UNT Libraries Government Documents Department

Stationary neutrino radiation transport by maximum entropy closure

Description: The authors obtain the angular distributions that maximize the entropy functional for Maxwell-Boltzmann (classical), Bose-Einstein, and Fermi-Dirac radiation. In the low and high occupancy limits, the maximum entropy closure is bounded by previously known variable Eddington factors that depend only on the flux. For intermediate occupancy, the maximum entropy closure depends on both the occupation density and the flux. The Fermi-Dirac maximum entropy variable Eddington factor shows a scale invariance, which leads to a simple, exact analytic closure for fermions. This two-dimensional variable Eddington factor gives results that agree well with exact (Monte Carlo) neutrino transport calculations out of a collapse residue during early phases of hydrostatic neutron star formation.
Date: November 1994
Creator: Bludman, S. A. & Cernohorsky, J.
Partner: UNT Libraries Government Documents Department

THE FIRST FERMI IN A HIGH ENERGY NUCLEAR COLLISION.

Description: At very high energies, weak coupling, non-perturbative methods can be used to study classical gluon production in nuclear collisions. One observes in numerical simulations that after an initial formation time, the produced partons are on shell, and their subsequent evolution can be studied using transport theory. At the initial formation time, a simple non-perturbative relation exists between the energy and number densities of the produced partons, and a scale determined by the saturated parton density in the nucleus.
Date: August 9, 1999
Creator: KRASNITZ,A.
Partner: UNT Libraries Government Documents Department

Stopping power, its meaning, and its general characteristics

Description: This essay presents remarks on the meaning of stopping, power and of its magnitude. More precisely, the first set of remarks concerns the connection of stopping power with elements of particle-transport theory, which describes particle transport and its consequences in full detail, including its stochastic aspects. The second set of remarks concerns the magnitude of the stopping power of a material and its relation with the material`s electronic structure and other properties.
Date: June 1, 1995
Creator: Inokuti, Mitio
Partner: UNT Libraries Government Documents Department

Corn Pone: A Multigroup, Multiregion Reactor Code

Description: Report covering the development of a set of difference equations for machine solution. In addition, this report serves as user's manual for Corn Pone, which is a code for the Oracle, the Oak Ridge National Laboratory computer.
Date: 1961?
Creator: Kinney, W. E. & Coveyou, R. R.
Partner: UNT Libraries Government Documents Department

CLIP 1--AN IBM-704 PROGRAM TO SOLVE THE P-3 EQUATIONS IN CYLINDRICAL GEOMETRY

Description: A second order form of the cylindrical P-3 equations is obtained for the case of an isotropic source. The boundary conditions and numerical method are discussed. Input preparation and operating instructions are included. (auth)
Date: May 1, 1962
Creator: Anderson, B.; Davis, J.; Gelbard, E.; Jarvis, P. & Pearson, J.
Partner: UNT Libraries Government Documents Department

Automated Approach to Quantitative Error Analysis in Neutron Transport Calculations

Description: A method is described how a quantitative measure for the robustness of a given transport theory code for coarse network calculations can be obtained. A code, that performs this task automatically and at only nominal cost, is described and has been implemented for slab geometry. This code generates also user oriented benchmark problems which exhibit the analytic behavior at interfaces.
Date: September 1976
Creator: Bareiss, Erwin H. & Derstine, Keith L.
Partner: UNT Libraries Government Documents Department

Slow Neutron Leakage Spectra from Spallation Neutron Sources

Description: An efficient technique is described for Monte Carlo simulation of neutron beam spectra from target-moderator-reflector assemblies typical of pulsed spallation neutron sources. The technique involves the scoring of the transport-theoretical probability that a neutron will emerge from the moderator surface in the direction of interest, at each collision. An angle-biasing probability is also introduced which further enhances efficiency in simple problems.
Date: February 1980
Creator: Das, Shashikala G.; Carpenter, J. M. & Prael, R. E.
Partner: UNT Libraries Government Documents Department

Time-Independent One-Speed Neutron Transport Equation with Anisotropic Scattering in Absorbing Media

Description: This report treats the time-independent, one-speed neutron transport equation with anisotropic scattering in absorbing media. For nuclear gain operators existence and uniqueness of solutions to the half-space and finite-slab problems are proved in L₂-space. The formulas needed for explicit calculations are derived by the use of perturbation theory techniques.
Date: June 1980
Creator: Hangelbroek, Rutger Jan
Partner: UNT Libraries Government Documents Department