Impacts of air pressure on the evolution of nanosecond pulse discharge products

Based on the nonequilibrium plasma dynamics of air discharge, a dynamic model of zero-dimensional plasma is established by combining the component density equation, the Boltzmann equation, and the energy transfer equation. The evolution properties of nanosecond pulse discharge (NPD) plasma under different air pressures are calculated. The results show that the air pressure has significant impacts on the NPD products and the peak values of particle number density for particles such as O atoms, O3 molecules, N2(A3) molecules in excited states, and NO molecules. It increases at first and then decreases with the increase of air pressure. On the other hand, the peak values of particle number density for N2(B3) and N2(C3) molecules in excited states are only slightly affected by the air pressure.     

Simultaneous measurement of particle size, velocity, andtemperature in thermal plasmas

The in-flight measurement of particle parameters (size, velocity, temperature, and local number density) can prove insight into the plasma processing of solid materials. A measurement technique for simultaneously obtaining the size, velocity, and temperature of particles entrained in high-temperature flow fields is described. Particle size and velocity are obtained from a combination laser-particle-sizing system and laser Doppler velocimeter. The particle temperature is determined by a two-color pyrometry technique and the data rate is a measure of relative particle number density. Typical measured temperatures and velocities for the 5-100 μm particles used in plasma spraying are 1600-3500 K and 100-300 m/s, respectively. Since particle size, velocity, and temperature are measured simultaneously, cold particles (<1600 K) are identified and their relative number density can be quantified. Data from two plasma spray systems, a metal one (Ni-Al) and a metal oxide one (Al₂O₃), are presented and their application to understanding the plasma spray-coating process is illustrated     

Aggregation of finite-size particles with variable mobility

New model equations are derived for dynamics of aggregation of finite-size particles. The differences from standard Debye-Hückel and Keller-Segel models are that the mobility of particles depends on the configuration of their neighbors and linear diffusion acts on locally averaged particle density. The evolution of collapsed states in these models reduces exactly to finite-dimensional dynamics of interacting particle clumps. Simulations show these collapsed (clumped) states emerge from smooth initial conditions, even in one spatial dimension. Extensions to two and three dimensions are also discussed.     

Two-dimensional simulations of plasma flow and charge spreadingacross barrier pixels in AC plasma displays

Two-dimensional multispecies simulations of adjacent pixels separated by a barrier height 80% the gap height in a plasma display pixel cell are performed. The fill gas pressure is 400 torr with 2% xenon in helium. The simulations using a minimum number of excited states of helium and xenon are performed for different cell widths representing different display resolutions. The simulations show plasma transport through the gap to the adjacent pixel which is in the sustained off state. In a sustained off state, there is no discharge in the pixel at the sustained voltage. The simulations show that for low-resolution displays, the plasma overflow does not cause a discharge in the adjacent pixel that is in the sustained off mode, while for a high-resolution display a 20% gap in the barrier height could result in a breakdown in the adjacent off pixel. A higher pixel resolution, or equivalently smaller pixel pitch. requires higher firing and sustained voltages due primarily to increased particle losses as a result of the reduced particle transit times. Finally, using a larger number of excited xenon atomic states including the xenon [6s, j=1] and [6s', j=1] radiative states and the molecular xenon dimer, an isolated single pixel is simulated to model the transport of excited states including the radiative states. The model shows that the density profiles peak in the cathode fall region spreading out to the side walls with decreasing intensity     

Field-driven dynamical demixing of binary mixtures

ABSTRACT

We consider mixtures of two species of spherical colloidal particles that differ in their Stokes coefficients, but are otherwise identical, in the presence of an external field. Since the particle–particle and particle–field interactions are the same for both species, they are completely mixed in the thermodynamic limit in the presence of any static field. Here, we combine Brownian dynamics and dynamic density functional theory of fluids to show that for sufficiently large differences in the Stokes coefficients of the particles (and corresponding differences in their mobilities) dynamical demixing is observed. These demixed states are transient but, under certain conditions, packing effects compromise the relaxation towards the thermodynamic states and the lifetime of the demixed phases increases significantly.     

Angular distributions in pre-equilibrium reactions

A new model is proposed for calculating angular distributions in preequilibrium reactions. In this model, as in the model of Feshbach et al. the system consisting of target plus projectile initially branches into two sets of states with either no particle in the continuum (multistep compound states) or with at least one particle in the continuum (multistep direct states). The multistep compound emission is assumed to be isotropic while the angular distribution of the multistep direct emission is described using the fast particle model of Mantzouranis et al. A similar master equation is used for both chains of states differing only in the angular dependence of the emission rates. The two chains of states are treated independantly neglecting inter-branch transitions. The angular distributions for 14.6 MeV neutrons calculated using this model are found to be in better agreement with the data than the fast particle model.     

Spectral-time characteristics of combined-target laser plasma

From the analysis of the contours of the spectral lines of target-material atoms, the electron and atomic concentrations and their variation with time are determined in the laser plasma of a combined Cu–Al–Cu target. The time dependences for the concentrations of electrons and atoms in the ground and excited states are explained within the framework of a model that allows for plasma decay being determined by processes of three-particle recombination and ionization as well as by the variation in the particle concentration in plasma expansion. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 426–432, May–June, 1998.     

The Influence of Bound States on the Electrical Conductivity of a Partially Ionized Plasma (Born Approximation)

The partially ionized plasma is described by a model Hamiltonian containing bound (localized) as well as orthogonalized free (itinerant) electron states. The equations of balance for the single particle states are given, and the correlation functions arising in the equations of balance are treatet in the Born approximation. The conductivity is obtained with the aid of the Kohler variational principle. The electron density dependence of the conductivity is presented for different values of the bound state energy level and of the temperature.     

Tailoring steep density profile with unstable points

The mesoscopic properties of a plasma in a cylindrical magnetic field are investigated from the view point of test-particle dynamics. When the system has enough time and spatial symmetries, a Hamiltonian of a test particle is completely integrable and can be reduced to a single degree of freedom Hamiltonian for each initial state. The reduced Hamiltonian sometimes has unstable fixed points (saddle points) and associated separatrices. To choose among available dynamically compatible equilibrium states of the one particle density function of these systems we use a maximum entropy principle and discuss how the unstable fixed points affect the density profile or a local pressure gradient, and are able to create a steep profile that improves plasma confinement.     

Maxwell's Demon and detailed balancing

A particle of molecular dimensions which can exist in two states is associated with a membrane pore through which molecules of a gas can pass. The gas molecules from two identical phases on either side of the membrane may pass only when the particle is in one particular state. If certain restrictions are imposed on the system, then the particle appears to act like a Maxwell's Demon⁽¹⁾ which “handles” the gas molecules during their passage through the pore.     

耗散量子隧道系统的变分法研究

本文用变分法研究了耗散量子系统中的声子基态及其对局域-退局域相变条件的影响。发现:1.声子基态不仅存在通常的位移效应,而且还有形变效应。本文提出的位移-压缩态可同时描述这两种效应;2.声子基态的选择对相变条件有很大影响。随着声子基态能量下降,相变曲线将向强耦合方向移动。 关键词：     

Vacuum tunneling in the four-dimensional Ising model

In the broken phase of the four-dimensional Ising model tunneling between the two degenerate minima of the effective potential takes place in a finite volume. We study this phenomenon numerically. The energies of the lowest zero momentum states are determined on both sides of the phase transition and their different correspondence to particle states in the infinite-volume limit is discussed. A Z₂-invariant definition of the field expectation value and susceptibility is exploited for calculation of the quantities in finite volumes.     

The two-state random walk

We develop asymptotic results for the two-state random walk, which can be regarded as a generalization of the continuous-time random walk. The two-state random walk is one in which a particle can be in one of two states for random periods of time, each of the states having different spatial transition probabilities. When the sojourn times in each of the states and the second moments of transition probabilities are finite, the state probabilities have an asymptotic Gaussian form. Several known asymptotic results are reproduced, such as the Gaussian form for the probability density of position in continuous-time random walks, the time spent in one of these states, and the diffusion constant of a two-state diffusing particle.     

Fast equilibration of hadrons in an expanding fireball

Because of long chemical equilibration times for standard hadronic reactions in a hadron gas in relativistic heavy ion collisions, it was suggested that hadrons are born into equilibrium after the quark gluon plasma is formed. We develop a dynamical scheme, using master equations, in which Hagedorn states contribute to fast chemical equilibration times of baryons and kaons, just below the critical temperature, estimates of which are derived analytically. The hadrons quickly equilibrate for an initial over- or underpopulation of Hagedorn states. Our particle ratios compared to BNL Relativistic Heavy Ion Collider show a close match.     

sine-Gordon模型与高斯波泛函方法

应用高斯波泛函方法,研究了sine-Gordon模型的基态、单粒子态和两粒子态。在Cole-man临界点附近,sine-Gordon系统趋于零质量玻色子系统,从而具有共形对称性。本文同时证明,当重整化质量有限时,在两粒子态中存在束缚态。 关键词：     

Radiation of a charge moving over the diffraction grating

The states of a charged particle with a finite free path are determined in the field of a resonant electromagnetic wave. The exact resonance conditions, the modulation and beam instability mechanisms, the charge and current densities (Ohm's law) are obtained for the collisionless beam of resonance particles. Quantum theory of radiation is developed for the resonant adiabatic interaction between a particle and a wave taking into account the interaction with a constant magnetic field induced at the grating surface by the charge and nonresonant waves. The radiation power, the spectrum, and the range of generated frequencies are determined. The results obtained can be used in the plasma and solid-state theories and in electronics.     

Long-distance quantum teleportation assisted with free-space entanglement distribution

Faithful long-distance quantum teleportation necessitates prior entanglement distribution between two communicated locations. The particle carrying on the unknown quantum information is then combined with one particle of the entangled states for Bell-state measurements, which leads to a transfer of the original quantum information onto the other particle of the entangled states. However in most of the implemented teleportation experiments nowadays, the Bell-state measurements are performed even before successful distribution of entanglement. This leads to an instant collapse of the quantum state for the transmitted particle, which is actually a single-particle transmission thereafter. Thus the true distance for quantum teleportation is, in fact, only in a level of meters. In the present experiment we design a novel scheme which has overcome this limit by utilizing fiber as quantum memory. A complete quantum teleportation is achieved upon successful entanglement distribution over 967 meters in public free space. Active feed-forward control techniques are developed for real-time transfer of quantum information. The overall experimental fidelities for teleported states are better than 89.6%, which signify high-quality teleportation.     

Stochastic resonance and energy optimization in spatially extended dynamical systems

We investigate a class of nonlinear wave equations subject to periodic forcing and noise, and address the issue of energy optimization. Numerically, we use a pseudo-spectral method to solve the nonlinear stochastic partial differential equation and compute the energy of the system as a function of the driving amplitude in the presence of noise. In the fairly general setting where the system possesses two coexisting states, one with low and another with high energy, noise can induce intermittent switchings between the two states. A striking finding is that, for fixed noise, the system energy can be optimized by the driving in a form of resonance. The phenomenon can be explained by the Langevin dynamics of particle motion in a double-well potential system with symmetry breaking. The finding can have applications to small-size devices such as microelectromechanical resonators and to waves in fluid and plasma.     

On current-density algebras,gradient terms and saturation

The equal time limit of commutator matrix elements of conserved currents is rigorously calculated by means of structures which follow from general principles of relativistic quantum field theory and current conservation. We prove: (a) In general derivatives of δ-functions occur (gradient terms). — (b) The proper (non-gradient) part of the equal time limit is exactly given by the divergence-free causal one particle structures constructed from those intermediate one particle states which have the same main quantum numbers (mass, total spin and total isospin) as one of the external states (saturation by two one particles states!). — (c) All the other intermediate discrete one particle states drop out completely and the continuous many particle states contribute at most to gradient terms. — (d) The gradient terms emerging from the remaining two discrete intermediate one particle states can be removed without any restrictions on the form factors. — (e) From current algebras of conserved currents in the form proposed and used in the literature one cannot deduce any predictions for form factors beyond the algebraic conditions for coupling constants which already follow from the algebra of the charges.