Neutral particle transport

Currently only Monte Carlo approaches can handle the wide range of surface geometries, reflection models and support complex atomic and molecular processes that occur in real fusion edge plasmas. Therefore the neutral particle transport (ionization, dissociation, etc.) as well as impurity ion transport in the edge region of fusion plasmas is often treated by Monte Carlo simulation on a kinetic level. 

D.B. Heifetz Neutral Particle Transport. In Physics of Plasma-Wall Interactions in Controlled, Fusion, ed. by D.E. Post, R. Behrisch (Plenum Press, New York London 1986) pp. 695-772... 

In the kinetic neutral particle transport codes (such as DEGAS, EIRENE, etc.), besides the cross-section (or rate coefficient) information on atomic collision processes, information on energy and angular distribution of reaction products is also required. We have omitted this aspect in our discussions of... 

A. F. Bilajev, Fundamentals of the Monte Carlo Method for Neutral and Charged Particle Transport. University of Michigan, Ann Arbor, Michigan, 2001. 

The remaining problem is to evaluate the terms (2.12) for all collision processes to be considered. Due to the special notation chosen here, however, these terms are already exactly in the format to which Monte Carlo kinetic particle transport codes can be applied directly. The probabilistic formulation is particularly suitable for these procedures. We refer to standard literature on Monte Carlo methods for linear transport, such as [19]. Here it is only important to note that one may write equation (2.12) as linear functional of the neutral particle distribution function / ... 

In particular, for sources and sinks due to inelastic processes in the Bra-ginskii equations, and with fa = we see that integrals /o,o,-fo,i and /o,2 are involved, whereas the integrals /io,/i,i and /g2 (i.e., with the diffusion-or transport cross-sections) appear in the expressions from elastic neutral particle plasma interactions. 

To determine the relative abundance of ionization stages, there are no alternatives to spectroscopic measurements. In fusion devices, the distribution of the ionization stages deviates from coronal equilibrium, due to transport and finite confinement of the ions as well as charge exchange recombination with neutral hydrogen. Both the particle transport and the diffusion reduce the... 

The M cells found in Peyer s patches have also been suggested to transport particles. These are specialized absorptive cells known to absorb and transport indigenous bacteria (i.e.. Vibrio cholerae)-, macromolecules, such as ferritin and horseradish peroxidase viruses and carbon particles, from the lumen of the intestine to submucosal lymphoid tissue (33,37,38). It has been reported that hydrophobic, negatively charged or neutral particles of size smaller than 5 pm are better taken up by M cells particles smaller than 1 pm in size accumulate in the basal medium, while larger particles remain entrapped in the Peyer s patches (39). Transport of absorbed materials to the systemic circulation... 

A membrane is a layer of material that serves as a selective barrier between two phases and remains impermeable to specific particles, molecules, or substances when exposed to the action of a driving force. Some components are allowed passage by the membrane into a permeate stream, whereas others are retained by it and accumulate in the retentate stream. Membranes can be of various thicknesses, with homogeneous or heterogeneous structure. Membranes can also be classified according to their pore diameter. According to the International Union of Pure and Applied Chemistry (lUPAC), there are three different pore diameter (dp) size classifications microporous (dp < 2 nm), mesoporous (2 nm < dp < 50 nm), andmacroporous (dp > 50 mn). Membranes can be neutral or charged, and particle transport can be active or passive. The latter can be facilitated... 

The transport of neutrons through material is governed by the neutral particle Boltzmann transport equation, one form of which is given by... 

Cathode and anode catalyst layers (CLs) are key elements of any fuel cell. Participants in electrochemical reactions are charged particles (positive and negative) and neutral molecules in the gaseous or liquid form. Any catalyst layer is thus a composition of three ingredients electronic and ionic conductors and voids for gas/liquid supply. The reaction itself occurs on a surface of precious metal particles (typically Pt), which must be connected to the avenues for charged and neutral species transport. 

With suppressed migration, the only way to transport ions to and away from the electrode is dijfusion. For a reversible electrode reaction, the overall reaction rate is then said to be dijfusion controlled. The laws of diffusion are valid for ions as well as for neutral particles. Particles diffuse in the direction where a lack of substance exists, i.e. towards a negative concentration gradient. As soon as a substance is consumed at an electrode surface (e.g. by electrochemical reduction of ions), particles start to move in order to compensate the deficiency. 

A typical catalyst layer is a composite of four ingredients (i) voids for neutral molecule transport, (ii) ionic (proton) conductor, and (iii) electron conductor with (iv) catalyst particles hosting the electrochemical conversion. In most cases, such a composite consists of three interpenetrating random clusters of transport avenues for molecules, ions, and electrons, so that each representative volume of the CL contains the same fractions of all the three components. 

When transport by diffusion of reacting neutral particles (like that of O2 in the internal oxygen cycle (Fig. 1.25)) precedes the transfer reaction, the actual concentration is reduced with increasing current. If Cj reaches zero, a further increase of the current is not possible. Such a situation is called a (diffusion) limiting current, which according to Eq. (28) is given by... 

Lipoprotein particles transport lipids in the blood to the appropriate tissues. The core is neutral lipid (TAG and cholesterol esters) and is surrounded by a shell of apoproteins, cholesterol and phospholipid. Chylomicrons have the lowest density and carry the most lipid. HDLs have the greatest density and carry the most protein. 

The transport of particles in the plasma is diffusive or convective for the neutrals, whereas the charge carriers move under the influence of the external and internal electric and magnetic fields. The drift velocityv of the charged particles is proportional to the electric field E ... 

Since NFI3 is highly water-soluble and neutralization within the droplet occurs rapidly, " the rate-limiting step in acid neutralization is normally NH 3 transport to the air/droplet interface, which is dependent on [NH3]4 and particle surface area. At high [NH3J4, the rate of NH, uptake across the air/droplet interface is given by... 

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