Multiple Particle Species Research Articles

Lagrangian formulation for neutrino–plasma interactions

A Lagrangian formalism is used to derive coupled nonlinear equations for collective interactions between an intense neutrino flux and a relativistic cold plasma fluid with multiple particle species. In order to focus on the self-consistent (collective) treatment of neutrino–plasma interactions, quantum effects are ignored throughout and the (spinless) neutrinos are represented by a complex-valued Klein–Gordon scalar field. Through the application of Noether’s method, the conservation laws for energy, momentum and wave action are derived explicitly. The transfer of energy, momentum and wave action between the neutrinos and the electromagnetic-plasma is discussed in the context of astrophysical applications (e.g., type II supernova explosions).

MOMENTS: The Modular Monte Carlo Environment for Charge Transport Simulation, Overview and Applications

We present MOMENTS, a newly developed software library lbr Monte Carlo simulation of semiconductor devices. This library uses object-oriented design principles to provide a flexible, extensible toolset that allows rapid development of a wide variety of Monte Carlo simulation applications. It allows concurrent simulation of multiple particle species (e.g. electrons and holes) with arbitrary user-defined interactions between species (e.g. generation – recombination and carrier – carrier scattering) in arbitrary geometries using either analytic or numerical bandstructure representations. The modular design allows virtually all simulation parameters to be freely varied across the simulation domain. MOMENTS also takes advantage of the parallelism inherent in the ensemble Monte Carlo approach, employing a scheme that can support a wide variety of parallel architectures with active load balancing. To demonstrate some of the library's capabilities, we also present preliminary results from a GaAs avalanche photodiode (APD) simulator based on MOMENTS.

Wear Mechanisms in Centrifugal Slurry Pumps

Abstract Starting from the typical wear mechanisms encountered in centrifugal slurry pumps, the paper outlines a computational approach for wear distribution in the pump channels. The two-phase flow parameters (solid concentration, velocity, paniculate stresses) at the wetted walls are related to the wear distribution as a function of particle dynamics, material characteristics and the presence of other surface processes such as corrosion and scaling. The probabilistic flow analysis enhances the ability to model the wear process based on the microstructural aspects of the flow and materials. The approach is applicable to two- and three-dimensional problems, for slurries with single and multiple particle species. It can be used to estimate the wear rate distribution, cumulative wear and equipment wear life.

Further resolution and comparison of the heterogeneity of plasma low-density lipoproteins in human hyperlipoproteinemias: type III hyperlipoproteinemia, hypertriglyceridemia and familial hypercholesterolemia

The heterogeneity of the plasma low-density lipoproteins (LDL) in subjects with type III hyperlipoproteinemia (3 cases), with hypertriglyceridemia (4 cases) and with the heterozygous form of familial hypercholesterolemia (FH, 4 cases) has been evaluated using a new, high resolution equilibrium density gradient ultracentrifugation procedure. The mass distribution profile, physicochemical properties, particle heterogeneity and apoprotein B content of a series of 13 LDL subfractions was examined in the 3 hyperlipidemic groups and the data were compared with those reported earlier in normolipidemic subjects. In FH, LDL mass was distributed as a narrow peak of ( d ∼ 1.031−1.034 g/ml, whereas the distribution in hypertriglyceridemia was markedly asymmetric with a single peak of elevated density ( d ∼ 1.037−1.043 g/ml); the distribution in type III subjects was distinguished by its bi- or trimodal nature and broad profile. The chemical composition of LDL gradient subfractions in FH and in hypertriglyceridemia markedly resembled that of the respective parent LDL of ( d ∼ = 1.019−1.063 g/ml, displaying elevated proportions of cholesteryl ester in FH and of protein in hypertriglyceridemia. LDL subfractions in type III disease were enriched in free cholesterol. The Stokes diameters of LDL particles in corresponding subfractions from the 3 hyperlipidemic states were similar; however, whereas a single particle species was characteristic of each LDL subfraction in both FH and in our normolipidemic group, 2 species were frequently present in each subfraction in both type III and type IV diseases; in addition, subfractions from type III subjects occasionally exhibited 3 size species. Apolipoprotein B-100 was the predominant protein component in LDL subfractions from all 3 hyperlipidemic groups. Plasma LDL consist then of multiple particle species which constitute a particularly complex spectrum in type III hyperlipoproteinemia and in hypertriglyceridemia. The origin(s) of such particle subspecies is indeterminate at present; moreover, they may differ in their intravascular metabolism, in their degradation in tissues and in their relative atherogenicities.