bluuebunny/crossref_metadata_2025 huggingface dataset:
An adiabatic model for the photodissociation of CH3SH in the first ultraviolet absorption band
Authors: Stevens Jonathan E. , Jang Hyo Weon , Butler Laurie J. , Light John C.
Published: July 2002

The photodissociation of CH3SH in the first absorption band is studied via ab initio computation of the relevant potential energy surfaces and exact quantum scattering calculations. The effective valence shell Hamiltonian (Hν) ab initio many-body perturbation technique is used to calculate the global ground X 1A′ and 1 1A″ surfaces as functions of the C–S and S–H internuclear distances. The finite range scattering wave function (FRSW) time-independent quantum scattering method is used to compute the adiabatic dynamics of S–H and C–S bond fission on the 1 1A″ surface following excitation. Two calculations are performed, one in which the ground state is represented by a cubic spline function fitted to the ab initio data and another in which it is represented as the sum of two uncoupled Morse oscillators. Absorption spectra as well as the branching ratios and photofragment translational energy distributions corresponding to various excitation energies are presented and compared to recent experimental results. A final calculation examines how the branching ratio and product vibrational state distribution changes for the photodissociation of a CH3SH molecule with one quantum of vibrational excitation in the C–S stretch.
A new generalization of the Casimir–Polder potential to higher electric multipole polarizabilities
Authors: Salam A. , Thirunamachandran T.
Published: July 2002

An elementary method for calculating retarded interaction energies for a pair of molecules with electric multipole polarizabilities of arbitrary order is presented. In the multipolar framework of quantum electrodynamics, the interaction energy is viewed as arising from two-photon exchange and calculated using fourth order perturbation theory. It is shown how the energy may be expressed in terms of derivatives of the Casimir–Polder formula written in a special form as an integral over imaginary frequency. Explicit formulas are presented for (a) an electric dipole polarizable molecule interacting with an electric quadrupole polarizable molecule, (b) an electric dipole polarizable molecule interacting with an electric octupole polarizable molecule, and (c) an electric quadrupole polarizable molecule interacting with another electric quadrupole polarizable molecule. The results are expressed in terms of reducible and irreducible components of multipole moments. For case (b) it is shown that in addition to the weight-3 components of the octupole moments, weight-1 components contribute to the interaction energy. For cases (a) and (c) traceless components (weight-2) of the quadrupole moments contribute. The results are compared with other calculations and discrepancies pointed out.
An investigation of the quantum chemical description of the ethylenic double bond in reactions. I. The electrophilic addition of hydrochloric acid to ethylene
Authors: Bo/rve Knut J. , Jensen Vidar R.
Published: July 2002

The bimolecular reaction mechanism for adding hydrochloric acid to ethylene is studied within a number of contemporary quantum chemical models. The transition state structure and energy is examined in detail, and high-level calculations support a picture of an intimate association of a chloride anion and a bridged ethyl cation, with some covalent bonding retained between chlorine and hydrogen. A tunneling correction of 1 kcal/mol in the reaction barrier is obtained by the Bell equation. The methods employed include configuration interaction (CI) and gradient-corrected density functional theory (DFTG), with a range of basis sets. High-end CI and DFT methods perform equally well with respect to enthalpies of reaction and activation, when used in connection with large bases. However, when bases of double-ζ plus polarization quality are used, an unfortunate accumulation of errors makes DFTG inferior. This is in contrast to the excellent values for a number of ground state properties of relevance to the reaction barrier which are obtained at this level of theory. A recently proposed extrapolation procedure for CI energies (PCI-80) is shown to fail for the electron affinity of chlorine, leading to an exaggerated estimate of the barrier for the title reaction. The single-particle description of the π bond in ethylene converges very slowly with the number of basis functions, and this affects the reaction enthalpy as computed by DFT and CI methods to a similar degree.
Thermodynamic properties and homogeneous nucleation rates for surface-melted physical clusters
Authors: McClurg Richard B. , Flagan Richard C. , Goddard William A.
Published: July 2002

We predict the free energy of van der Waals clusters (Fn) in the surface-melted temperature regime. These free energies are used to predict the bulk chemical potential, surface tension, Tolman length, and vapor pressure of noble gas crystals. Together, these estimates allow us to make definitive tests of the capillarity approximation in classical homogeneous nucleation theory. We find that the capillarity approximation underestimates the nucleation rate by thirty orders of magnitude for argon. The best available experiments are consistent with our calculation of nucleation rate as a function of temperature and pressure. We suggest experimental conditions appropriate for determining quantitative nucleation rates which would be invaluable in guiding further development of the theory. To make the predictions of Fn, we develop the Shellwise Lattice Search (SLS) algorithm to identify isomer fragments and the Linear Group Contribution (LGC) method to estimate the energy of isomers composed of those fragments. Together, SLS/LGC approximates the distribution of isomers which contribute to the configurational partition function (for up to 147-atom clusters). Estimates of the remaining free energy contributions come from a previous paper in this series.
Dynamic simulation of flexible fibers composed of linked rigid bodies
Authors: Ross Russell F. , Klingenberg Daniel J.
Published: July 2002

A particle-level simulation method is employed to study the dynamics of flowing suspensions of rigid and flexible fibers. Fibers are modeled as chains of prolate spheroids connected through ball and socket joints. By varying the resistance in the joints, both flexible and rigid fibers can be modeled. Repulsive interactions between fibers are included, but hydrodynamic interactions and particle inertia are neglected in this implementation. The motion of a fiber is determined by solving the translational and rotational equations of motion for each spheroid. Simulations of isolated fibers in shear flow demonstrate that the method can reproduce known dynamical behavior of both rigid and flexible fibers. The transient behavior in the suspension relative viscosity under simple shear flow was also investigated. An oscillatory response similar to the experimental observations of Ivanov et al. was obtained for rigid fibers. Fiber flexibility reduced the period of oscillation, but had little effect on steady-state viscosities. These results verify that rigid and flexible fibers can be modeled with linked rigid prolate spheroids. Modeling fibers with fewer elongated bodies, as opposed to many spheres, significantly reduces computation time and facilitates the study of suspensions of many interacting, long fibers.
A theoretical simulation of the 1s→2π excitation and deexcitation spectra of the NO molecule
Authors: Fink Reinhold
Published: July 2002

We present ab initio calculations for the N and O 1s→2π photoexcitation spectra and the deexcitation electron spectra which result in the decay of these core excited states. The photoexcitation spectra are simulated with potential energy curves and transition dipole moments calculated with the multiconfiguration coupled electron pair approximation method. The energy lifetime width of the core excited states, which influences the form of these excitation spectra via the broadening of the vibrational progressions, was calculated by the one center approximation. The theoretical spectra are compared to recent experimental data. The deexcitation electron spectra, which monitor the autoionization of the core excited states, are reproduced by a combination of valence configuration interaction calculations to obtain the relative energies and the one center approximation which yields decay rates to the singly charged final states. Furthermore, we included lifetime vibrational interference effects using the recently proposed moment method of Cederbaum and Tarantelli [J. Chem. Phys. 98, 9691 (1993)]. The calculated deexcitation spectra compare extremely favorably with experimental data.
A laser photofragmentation time-of-flight mass spectrometric study of acetophenone at 193 and 248 nm
Authors: Zhao H.-Q. , Cheung Y.-S. , Liao C.-L. , Liao C.-X. , Ng C. Y. , Li Wai-Kee
Published: July 2002

The photodissociation of acetophenone (C6H5COCH3) at 193 and 248 nm has been studied using the time-of-flight mass spectrometric technique. For hν=193 nm, two major primary channels, C6H5COCH3+hν→C6H5CO+CH3 [channel (1)] and C6H5+CH3CO [channel (2)], are observed with comparable cross sections. Data analysis shows that ≈30%–50% of primary C6H5CO and CH3CO radicals further decomposes, yielding secondary products C6H5+CO and CH3+CO, respectively. The translational energy release measurements indicate that for both channels (1) and (2) at 193 nm, ≈25%–30% of the available energy is channeled into kinetic energies of the primary photofragments. Measurements at hν=248 nm reveal that the branching ratio of channel (2) to channel (1) is ≈0.01. For channel (1) at hν=248 nm, ≈42% of the available energy is directed as the kinetic energy of the photofragments. The observed maximum kinetic energy release for channel (1) at 248 nm yields a value of 85.0±2.2 kcal/mol for the C6H5CO–CH3 bond dissociation energy at 0 K (D0). The photofragment angular distributions are found to be isotropic for both channels (1) and (2) at hν=193 nm and for channel (1) at hν=248 nm. A minor photodissociation channel C6H5COCH3+hν→C6H5CH3+CO is identified at both hν=193 and 248 nm. The energetics for the dissociation reactions of acetophenone have also been investigated using ab initio Gaussian-2-type procedures. The heats of formation at 0 K (ΔfH°0) for C6H5CO and C6H5 calculated using the isodesmic reaction scheme are 33.9±1.3 and 87.6±1.0 kcal/mol, respectively. These results suggest that the literature ΔfH°0 values for C6H5CO and C6H5 are likely to be low by 3–4 kcal/mol. These theoretical ΔfH° values for C6H5CO and C6H5 yield a theoretical D0(C6H5CO–CH3) value of 85.1±1.4 kcal/mol, which is in excellent accord with the experimental results obtained in the present study.
An advanced dielectric continuum approach for treating solvation effects: Time correlation functions. I. Local treatment
Authors: Basilevsky M. V. , Parsons D. F. , Vener M. V.
Published: July 2002

A local continuum solvation theory, exactly treating electrostatic matching conditions on the boundary of a cavity occupied by a solute particle, is extended to cover time-dependent solvation phenomena. The corresponding integral equation is solved with a complex-valued frequency-dependent dielectric function ε(ω), resulting in a complex-valued ω-dependent reaction field. The inverse Fourier transform then produces the real-valued solvation energy, presented in the form of a time correlation function (TCF). We applied this technique to describe the solvation TCF for a benzophenone anion in Debye (acetonitrile) and two-mode Debye (dimethylformamide) solvents. For the Debye solvent the TCF is described by two exponential components, for the two-mode Debye solvent, by three. The overall dynamics in each case is longer than that given by the simple continuum model. We also consider a steady-state kinetic regime and the corresponding rate constant for adiabatic electron-transfer reactions. Here the boundary effect introduced within a frequency-dependent theory generates only a small effect in comparison with calculations made within the static continuum model.
Modeling Lewis acidity of transition aluminas by numerical simulations
Authors: Alvarez Luis Javier , Blumenfeld Alexander L. , Fripiat José J.
Published: July 2002

The bulk and surface features of an alumina particle obtained by molecular-dynamics simulation are used to support the experimental distribution of aluminums with respect to their coordination number obtained by NMR (nuclear magnetic resonance). This information was obtained by using results of various editing procedures of the Al27 nuclear magnetic resonance, such as the classical one-pulse (1P) magic angle spinning, the cross polarization (CP) from the protons of chemisorbed ammonia and the 1P or CP rotational echo double resonance (REDOR). Because the REDOR technique revealed that the acid Lewis sites are constituted by pairs of four or fivefold coordinated aluminum atoms about 3 Å apart, these pairs were counted in the simulated particle. The agreement with experimental surface density of Lewis sites is satisfactory.
Hyperfine sublevel correlation spectroscopy in lithium silicate glasses
Authors: Astrakas L. , Deligiannakis Y. , Mitrikas G. , Kordas George
Published: July 2002

The structure of γ-irradiated (Li2O)0.1(SiO2)0.9 glass has been studied with two-dimensional hyperfine sublevel correlation spectroscopy (HYSCORE). The theoretical evaluation of the HYSCORE experimental data revealed the existence of weak couplings between the electron spin and nearby Li. The anisotropic hyperfine coupling T is equal to 4.0 MHz suggesting a nonbridging oxygen—Li distance of 2.0 Å and an angle of ±60° away from the gz axis. The Aiso value is equal to 0.5 MHz, corresponding to 0.135% contribution of the Li 2s orbital to the ground state. Thus, an estimation can be made of the covalent character of the bond between the nonbridging oxygen and the alkali.
Spectroscopic constants of gold and eka-gold (element 111) diatomic compounds: The importance of spin–orbit coupling
Authors: Liu Wenjian , van Wüllen Christoph
Published: July 2002

Scalar-relativistic density functional calculations in the zeroth-order regular approximation as well as fully relativistic Dirac–Kohn–Sham calculations have been performed to investigate spectroscopic constants of the eka-gold (element 111) compounds (111) X (X=H, F, Cl, Br, O, Au) and the dimer of element 111. For calibration, we also report results for homologous gold compounds. The bond lengths for the compounds of element 111 are similar but slightly larger than those of the gold compounds. Spin–orbit coupling increases the bond length by a few pm. For the hydride and the halides, the force constants of the eka-gold compounds are generally larger than those of the gold compounds although the dissociation energy is smaller. The oxide of eka-gold is more strongly bound than the gold oxide. The dimer of element 111 has an open shell instead of a closed-shell electronic structure and is less stable than the gold dimer. The effect of spin–orbit coupling on the dissociation energy depends on the extent to which spin–orbit coupling is quenched in the molecule. This effect has been estimated based on a spinor occupation population analysis.
Pressure dependence of the local and global dynamics of polyisoprene
Authors: Floudas G. , Reisinger T.
Published: July 2002

We report on the pressure dependence of the local segmental and normal modes of a type-A polymer (polyisoprene) using dielectric spectroscopy. We find that external pressure exerts a stronger influence on the dynamics of the segmental mode as compared to the longest normal mode which results in the crossing of the two modes at higher pressures. The predictions of the Rouse model are not adequate to explain the different shift factors even at elevated temperatures.
Theoretical study of polymeric mixtures with different sequence statistics. II. Brazovskii class: Linear random copolymers with diblock copolymers
Authors: Qi Shuyan , Chakraborty Arup K.
Published: July 2002

We use a Landau theory to study the instability of the homogeneous state of a mixture of linear random copolymers and diblock copolymers. Interesting features of the calculated structure factors for different components of the mixture are found, which can be directly compared with scattering experiments with selectively deuterated samples. We also investigate the least stable concentration fluctuations and find four different types of segregation modes at the spinodal depending upon the characteristics of the mixture (e.g., average compositions, statistical correlation lengths and volume fractions). The different segregation modes are also indicative of the kinetic pathways leading to the formation of ordered microstructures. Experiments probing these pathways are suggested.
The use of locally dense basis sets in the calculation of indirect nuclear spin–spin coupling constants: The vicinal coupling constants in H3C–CH2X (X=H, F, Cl, Br, I)
Authors: Provasi Patricio F. , Aucar Gustavo A. , Sauer Stephan P. A.
Published: July 2002

We have calculated the vicinal indirect nuclear spin-spin coupling constants 3J1H1H  in the series of molecules H3C–CH2X with X=H, F, Cl, Br, and I at the self-consistent field level and using the second order polarization propagator approximation (SOPPA). We have studied the effect of electron correlation and of the substituents (X=F, Cl, Br, and I) on all four contributions to the coupling constants. But in particular we have investigated the possibility of using locally dense basis sets, i.e., we have carried out calculations with basis sets, where the basis functions on the hydrogen atoms were optimized for the calculation of spin–spin coupling constants whereas on the other atoms smaller, contracted sets of basis functions were used. This changes the results for the couplings by ∼0.3 Hz or 3%. However, the change is almost entirely due to the orbital paramagnetic term and is independent of electron correlation, which enables one to estimate the SOPPA results in the full basis sets. Furthermore we find that the Fermi contact term is the dominant contribution to the vicinal coupling constants, because it is about an order of magnitude larger than the other contributions and because the two orbital angular moment terms almost cancel each other completely. Also the changes in the calculated couplings due to electron correlation are solely due to the Fermi contact term. However, the shifts in the coupling constants caused by the different substituents arise in equal amounts from the Fermi contact and the orbital diamagnetic term, whereas the changes in the orbital paramagnetic term are smaller and are in the opposite direction. In comparison with the experimental data we find very good agreement for C2H6 and C2H5F. However, the agreement becomes less good with increasing nuclear charge of the substituent X.
Derivation of rate expressions for nonadiabatic proton-coupled electron transfer reactions in solution
Authors: Soudackov Alexander , Hammes-Schiffer Sharon
Published: July 2002

This paper presents a derivation of rate expressions for nonadiabatic proton-coupled electron transfer (PCET) reactions in solution. The derivation is based on a multistate continuum theory in which the solvent is described by a dielectric continuum, the solute is represented by a multistate valence bond model, and the transferring proton(s) are treated quantum mechanically. In this formulation, a PCET reaction is described as a transition between two sets of diabatic free energy surfaces associated with the two electron transfer states. For PCET reactions involving the transfer of one electron and one proton, these mixed electronic/proton vibrational free energy surfaces are functions of two scalar solvent coordinates corresponding to electron and proton transfer. The Golden Rule is applied to these two-dimensional free energy surfaces in conjunction with a series of well-defined approximations. The contributions from intramolecular solute modes are also included. The final rate expression is similar in form to the standard rate expression for nonadiabatic single electron transfer, but the reorganization energies, equilibrium free energy differences, and couplings are defined in terms of the two-dimensional free energy surfaces. The practical implementation of this rate expression and the calculation of the input quantities are also discussed.
Regular subalgebras of Lie superalgebras and extended Dynkin diagrams
Authors: Van der Jeugt Joris
Published: July 2002

Using the method of extended Cartan matrices and extended Dynkin diagrams, a classification of maximal regular semisimple subalgebras of the basic classical Lie superalgebras is obtained. Especially in the case of exceptional Lie superalgebras, some curious inclusion relations are discovered.
N-body quantum scattering theory in two Hilbert spaces. V. Computation strategy
Authors: Chandler Colston , Gibson A. G.
Published: July 2002

In this paper the development of our previously published theory of approximations for the Chandler–Gibson (CG) equations is continued. In particular, our approximation theory is rigorously brought to the point where N-particle scattering calculations can begin. This is accomplished by mapping the CG operator equations into a function equation form, where the unknowns belong to a new (third!) computational Hilbert space ℒ. This mapping is facilitated by rescaling the Jacobi momentum variables for the relative free motion of the asymptotic clusters so that surfaces of constant kinetic energy are hyperspheres. The input terms to the resulting equations are expanded in a basis on the surface of the kinetic energy hypersphere. This leads to a system of infinitely many coupled one-dimensional integral equations with the kinetic energy as the continuous variable. The half-on-shell variant of these equations is then transformed to a K-matrix form. Our approximations result from truncating this system to a finite number of equations, which is equivalent to using a finite basis approximation of the original input terms. The basis sets could be hyperspherical harmonics, but the use of hyperspherical spline functions is also proposed. Our method generalizes the well-known method of partial waves for channels with two clusters, and it accommodates breakup channels in a straightforward way.
Higher-order Lagrangian systems: Geometric structures, dynamics, and constraints
Authors: Gràcia X. , Pons J. M. , Román-Roy N.
Published: July 2002

In order to study the connections between Lagrangian and Hamiltonian formalisms constructed from a—perhaps singular—higher-order Lagrangian, some geometric structures are constructed. Intermediate spaces between those of Lagrangian and Hamiltonian formalisms, partial Ostrogradskiĭ’s transformations and unambiguous evolution operators connecting these spaces are intrinsically defined, and some of their properties studied. Equations of motion, constraints, and arbitrary functions of Lagrangian and Hamiltonian formalisms are thoroughly studied. In particular, all the Lagrangian constraints are obtained from the Hamiltonian ones. Once the gauge transformations are taken into account, the true number of degrees of freedom is obtained, both in the Lagrangian and Hamiltonian formalisms, and also in all the ‘‘intermediate formalisms’’ herein defined.
A class of affine Wigner functions with extended covariance properties
Authors: Bertrand J. , Bertrand P.
Published: July 2002

Affine Wigner functions are phase space representations based on the affine group in place of the usual Weyl–Heisenberg group of quantum mechanics. Such representations are relevant to the time–frequency analysis of real signals. An interesting family is singled out by the requirement of covariance with respect to each solvable three-parameter group containing the affine group. Explicit forms are given in each case and properties such as unitarity and localization are discussed. Some particular distributions are recovered.
The initial value problem for a class of general relativistic fluid bodies
Authors: Rendall A. D.
Published: July 2002

A body or collection of bodies made of perfect fluid can be described in general relativity by a solution of the Einstein–Euler system where the mass density has spatially compact support. It is shown that for certain equations of state there exists a wide class of solutions of this type corresponding to appropriate initial data given on a spacelike hypersurface. This class is not constrained by any symmetry requirements. The key element of the proof is to write the equations as a symmetric hyperbolic system which is regular both for nonvanishing density and in vacuum.
Analysis of an inhomogeneous generalized Epstein–Hurwitz zeta function with physical applications
Authors: Elizalde E.
Published: July 2002

The inhomogeneous generalized (Epstein–Hurwitz-like) multidimensional series Em(s; a1,...,am;c1,...,cm;c2) ≡∑n1,...,nm=0∞ [a1(n1+c1)2 + ... + am(nm+cm)2+c2]−s is investigated. By means of a nontrivial, asymptotic recurrence, it is reduced to the one-dimensional case F(s; a,b2) ≡ ∑n=0∞[(n + a)2+ b2]−s, which is then studied in full detail. In particular, asymptotic expansions for F and its derivatives ∂F/∂s and ∂F/∂a—together with analytical continuations of the same in the variable s—are explicitly obtained using zeta-function techniques. Several plots and tables of the numerical results are given. Some explicit applications to the regularization, by means of Hurwitz zeta-functions, of different problems that have appeared recently in the physical literature, are considered.
Toward quantum mathematics. I. From quantum set theory to universal quantum mechanics
Authors: Schlesinger Karl-Georg
Published: July 2002

We develop the old idea of von Neumann of a set theory with an internal quantum logic in a modern categorical guise [i.e., taking the objects of the category H of (pre-)Hilbert spaces and linear maps as the sets of the basic level]. We will see that in this way it is possible to clarify the relationship between categorification and quantization and besides this to understand that in some sense a categorificational approach to quantization is a discretized version of the one taken by noncommutative geometry. The tower of higher categorifications will appear as the analog of the von Neumann hierarchy of classical set theory (where by classical set theory, we will understand the usual Zermelo–Fraenkel system). Finally, we make a suggestion of how to understand all the different categorifications as different realizations of one and the same abstract structure by viewing quantum mechanics as universal in the sense of category theory. This gives the possibility to view extended topological quantum field theories purely as involving an abstract notion of quantum mechanics plus representation theory without the need to enlarge the class of kinematic structures of quantum systems on each step of categorification. In a future part of the work we will apply the language developed here to deal especially with the question of a categorification of the manifold notion.
Transport equations for a general class of evolution equations with random perturbations
Authors: Guo Maozheng , Wang Xiao-Ping
Published: July 2002

We derive transport equations from a general class of equations of form iut=H(X,D)u+V(X,D)u where H(X,D) and V(X,D) are pseudodifferential operators (Weyl operator) with symbols H(x,k) and V(x,k), where H(x,k) being polynomial in k and smooth in x,V(x,k) is a mean zero random function and is stationary in space variable. We also consider system of equations in the above form. Such equations cover many of the equations that arise in wave propagations, such as those considered in a paper by Ryzhik, Papanicolaou, and Keller [Wave Motion 24, 327–370 (1996)]. Our results generalize those by Ryzhik, Papanicolau, and Keller.
Numerical analysis of the Poiseuille and thermal transpiration flows between two parallel plates on the basis of the Boltzmann equation for hard-sphere molecules
Authors: Ohwada Taku , Sone Yoshio , Aoki Kazuo
Published: July 2002

The Poiseuille and thermal transpiration flows of a rarefied gas between two parallel plates are investigated on the basis of the linearized Boltzmann equation for hard-sphere molecules and diffuse reflection boundary condition. The velocity distribution functions of the gas molecules as well as the gas velocity and heat flow profiles and mass fluxes are obtained for the whole range of the Knudsen number with good accuracy by the numerical method recently developed by the authors.
Spectral transfers in two-dimensional anisotropic flow
Authors: Smyth W. D.
Published: July 2002

Nonlinear transfers of kinetic energy and enstrophy in the unidimensional Fourier spectrum that is obtained in a two-dimensional shear flow are investigated. Detailed conservation laws reveal the existence of closed pairs of transfers that involve a source mode, a recipient mode, and an advecting mode, which mediates the interaction but is not directly affected by it. The methodology of spectral transfer diagnosis is applied in the study of two simple, linearly unstable, initially parallel shear flows, namely the Bickley jet and the hyperbolic-tangent shear layer. In each case, the transfer spectra are found to be dominated by wave–mean flow interactions and by downscale cascades that are associated with vortex mergers. Cascades are driven by the advective deformation of small eddies by the large-scale vortices (i.e., filamentation), and appear in the transfer function maps as local transfers driven by nonlocal interactions.
Phase conjugation by four-wave mixing in inhomogeneous plasmas
Authors: Williams Edward A. , Lininger Diana M. , Goldman Martin V.
Published: July 2002

The effects of density, temperature, and velocity gradients on four-wave mixing (FWM) in a plasma are investigated. A fluid model is used in which the stimulated Brillouin terms are included, but pump depletion is neglected. The steady state phase conjugate reflectivity and signal transmission coefficients are calculated and discussed for both degenerate and resonant FWM. The substantial effects of inhomogeneity on the use of FWM as a plasma diagnostic are discussed.
Electromagnetic wave scattering in dusty plasmas
Authors: Bingham R. , de Angelis U. , Tsytovich V. N. , Havnes O.
Published: July 2002

The cross section for transition scattering of electromagnetic waves on charged dust particles in a plasma is calculated, extending the results of a previous paper [J. Plasma Phys. 42, 429 (1989)] where the case of longitudinal waves has been considered. For the case of nonlinear screening of the charged dust by the plasma particles (i.e., ‖eφ0/Te‖ ≫ 1, where φ0 is the dust grain surface potential and Te is the electron plasma temperature), numerical and analytical results are presented, showing a significant enhancement, proportional to the square of the grain surface charge, in the cross section with respect to scattering by free electrons. The effect is independent of the sign of the charge for wavelengths larger than the Debye length.
Gyro-Landau fluid models for toroidal geometry
Authors: Waltz R. E. , Dominguez R. R. , Hammett G. W.
Published: July 2002

Gyro-Landau fluid model equations provide first-order time advancement for a limited number of moments of the gyrokinetic equation, while approximately preserving the effects of the gyroradius averaging and Landau damping. This paper extends the work of Hammett and Perkins [Phys. Rev. Lett. 64, 3019 (1990)] for electrostatic motion parallel to the magnetic field and E×B motion to include the gyroaveraging linearly and the curvature drift motion. The equations are tested by comparing the ion-temperature-gradient mode linear growth rates for the model equations with those of the exact gyrokinetic theory over a full range of parameters.
The radial structure of the ion-temperature-gradient-driven mode
Authors: Romanelli F. , Zonca F.
Published: July 2002

An analysis of the radial structure of the ion-temperature-gradient-driven mode is presented and the dependence of the radial correlation length Lr on parameters such as magnetic shear is discussed. It is found that Lr decreases algebraically with increasing shear for moderate to large shear values, and it decreases exponentially with decreasing shear for low shear values. These results seem in qualitative agreement with several experiments which observe strong reduction of the transport coefficients close to the magnetic axis.
Evolution of the plasma rotation and the radial electric field for a toroidal plasma in the Pfirsch–Schlüter and plateau regimes subject to a biased electrode
Authors: Coronado M. , Talmadge J. N.
Published: July 2002

In this paper, the fluid equation approach is used to analyze the time evolution of the plasma rotation and the ambipolar electric field in a nonsymmetric toroidal plasma subject to an external biasing voltage induced by a probe. Under consideration is a plasma with low rotation speed in the Pfirsch–Schlüter or the plateau regime that includes the effects of a background neutral gas. A time-dependent charge conservation equation is used to determine the ambipolar electric field as a function of time. It is found that, after the application of the biasing voltage, the electric field and the plasma rotation change quickly and reach steady-state after a time inversely proportional to the sum of the momentum damping rates due to parallel viscosity and ion–neutral collisions. The steady state is characterized by a radial electric field and a plasma rotation that are proportional to the electric current flowing through the biasing probe. The direction of the plasma flow is determined by the relative magnitude of the momentum damping rates on the flux surface. From the steady-state solution, an expression for the radial electric conductivity is obtained, which includes the effect of collisions with neutrals as well as viscosity. Axisymmetric systems without neutrals are also discussed, which is a special case since there is no momentum damping in the toroidal direction. Here, the toroidal velocity increases continuously in time with the bias and never reaches steady state. Finally, a model for nonsymmetric magnetic fields is presented and the viscous damping rate, the radial conductivity and the spin-up rate for a plasma in the Pfirsch–Schlüter regime are calculated. As examples, the cases of the rippled tokamak and the classical and helically symmetric stellarators are evaluated.
Sonoluminescence and diffusive transport
Authors: Vuong Vi Q. , Szeri Andrew J.
Published: July 2002

A new model is presented for the gas dynamics within a bubble at conditions that lead to the phenomenon of sonoluminescence. The spherically symmetric Navier–Stokes equations with variable properties are solved together with momentum and energy equations in the liquid. Calculations are presented for bubbles of argon, helium, and xenon in liquid water. The first main result is that in contrast to recent models of air bubbles in water, there are no sharp shocks focusing at the origin of the bubble. An alternative mechanism for energy focusing in noble gas bubbles is proposed that is consistent with a smooth onset of sonoluminescence with increasing acoustic forcing, as observed in experiments. The second main result concerns an observed correlation between sonoluminescence intensity and the thermal conductivity of the gas, which suggests that heat transfer plays a dominant role in the focusing of acoustic energy. It is shown instead that mechanical effects associated with the molecular mass of the gas figure prominently in determining the peak temperatures and pressures in the bubble, when the bubble is forced strongly enough to engender wavy disturbances that focus on the bubble center.
Mean field theory and coherent structures for vortex dynamics on the plane
Authors: Lim Chjan C.
Published: July 2002

We present a new derivation of the Onsager–Joyce–Montgomery (OJM) equilibrium statistical theory for point vortices on the plane, using the Bogoliubov–Feynman inequality for the free energy, Gibbs entropy function and Landau’s approximation. This formulation links the heuristic OJM theory to the modern variational mean field theories. Landau’s approximation is the physical counterpart of a large deviation result, which states that the maximum entropy state does not only have maximal probability measure but overwhelmingly large measure relative to other macrostates.
Experimental observations of the interaction of a laser generated cavitation bubble with a flexible membrane
Authors: Shaw S. J. , Jin Y. H. , Gentry T. P. , Emmony D. C.
Published: July 2002

In this paper we present new observations of a laser generated cavitation bubble interacting with an inertial boundary. Employing schlieren photography and Mach–Zehnder interferometry techniques, we present photographic sequences of a cavity interacting with a flexible membrane. During expansion the membrane is deformed away from the bubble centroid but during the collapse phase, instead of moving with the expected fluid motion caused by the contracting bubble, the flexible membrane introduces a certain asymmetry into the problem which in turn results in novel fluid motions around the bubble.
Laminar flow past a rotating circular cylinder
Authors: Kang Sangmo , Choi Haecheon , Lee Sangsan
Published: July 2002

The present study numerically investigates two-dimensional laminar flow past a circular cylinder rotating with a constant angular velocity, for the purpose of controlling vortex shedding and understanding the underlying flow mechanism. Numerical simulations are performed for flows with Re=60, 100, and 160 in the range of 0⩽α⩽2.5, where α is the circumferential speed at the cylinder surface normalized by the free-stream velocity. Results show that the rotation of a cylinder can suppress vortex shedding effectively. Vortex shedding exists at low rotational speeds and completely disappears at α>αL, where αL is the critical rotational speed which shows a logarithmic dependence on Re. The Strouhal number remains nearly constant regardless of α while vortex shedding exists. With increasing α, the mean lift increases linearly and the mean drag decreases, which differ significantly from those predicted by the potential flow theory. On the other hand, the amplitude of lift fluctuation stays nearly constant with increasing α (<αL), while that of drag fluctuation increases. Further studies from the instantaneous flow fields demonstrate again that the rotation of a cylinder makes a substantial effect on the flow pattern.
Natural convection in a rectangular cavity heated from below and cooled from top as well as the sides
Authors: Sezai I. , Mohamad A. A.
Published: July 2002

A three-dimensional, numerical simulation of Rayleigh–Benard convection in a cavity, having aspect ratios Ax=4 and Ay=4 has been performed using multigrid method, for Ra⩽1×104. The effect of the thermal boundary conditions of the vertical side walls on the flow bifurcations has been investigated by considering isothermal and conducting side wall cases. It has been found that the steady state flow patterns and the critical Rayleigh numbers for transition from one pattern to the other are completely different for each of the above mentioned boundary conditions. The local heat transfer distributions at the bottom and top plates are obtained and variations of the average Nusselt number for the isothermal and conducting side wall boundary conditions are compared for the range of Rayleigh numbers investigated.
Nonlinear gyrokinetic Vlasov equation for toroidally rotating axisymmetric tokamaks
Authors: Brizard Alain J.
Published: July 2002

The nonlinear gyrokinetic Vlasov equation is derived for an arbitrary magnetized plasma in a local reference frame moving with the nonuniform equilibrium fluid velocity u(r). The derivation of the guiding-center and gyrocenter Hamilton equations, which appear as the characteristics of the gyrokinetic Vlasov equation, is based on the use of Lie-transform perturbation techniques. Although a general form for u is initially used, attention is later focused on an incompressible toroidal equilibrium flow when considering axisymmetric tokamak geometry.
Current driven nonlinear Langmuir structures in plasmas
Authors: Psimopoulos Michalis , Tanriverdi Sevim
Published: July 2002

The nonlinear stationary states of an electron beam moving in a homogeneous positive background are calculated for the full range of amplitudes Em of a longitudinal self-induced electric field in the collisionless limit. The parameter that controls the system is κ=Em/(4πn0mev02)1/2, where n0,v0 are the number density and velocity of the beam when electrons are submitted to maximum force. If κ≪1 the beam variables vary harmonically in space. As κ increases within 0<κ⩽1, the beam variables become gradually anharmonic but their wavelength remains constant and independent of κ. If κ>1 it is shown that no wave breaking occurs. Instead, the electric field becomes discontinuous at certain points and the electrons delay there forming periodic electrostatic (Langmuir) structures centered around negatively charged planes. The size and charge of the above structures as well as their wavelength, which now depends on κ, are derived.
Self-focusing dynamics of nonlinear waves in media with parabolic-type inhomogeneities
Authors: Bergé Luc
Published: July 2002

The possibility of accelerating the self-focusing dynamics of light beams in nonlinear and dispersive media with either a constant or a weakly oscillating parabolic density profile is investigated. It is shown that the self-compression of wave packets, that freely self-focus in homogeneous media, can be enhanced by the action of appropriate parabolic inhomogeneities, whose lensing influence shortens the focal time of the wave. A similar property also occurs when the scalar envelope of a nonlinear waveform interacts with a uniform external magnetic field. The motion of light beamlets, originating from the filamentation instability of an incident beam, is analytically described for inhomogeneous media with focusing and defocusing density profiles.
Fundamental limitations on plasma fusion systems not in thermodynamic equilibrium
Authors: Rider Todd H.
Published: July 2002

Analytical Fokker–Planck calculations are used to accurately determine the minimum power that must be recycled in order to maintain a plasma out of thermodynamic equilibrium despite collisions. For virtually all possible types of fusion reactors in which the major particle species are significantly non-Maxwellian or are at radically different mean energies, this minimum recirculating power is substantially larger than the fusion power. Barring the discovery of methods for recycling the power at exceedingly high efficiencies, grossly nonequilibrium reactors will not be able to produce net power.
Stability of a charged plane surface of an electron–positron–ion plasma
Authors: Tsintsadze Levan N.
Published: July 2002

A general description is presented for the stability problem of a charged surface of a plasma in the presence of a negative pressure. Conditions under which the charged surface becomes unstable are obtained. The relevance of this investigation to astrophysical and laboratory plasmas is pointed out.
Gyrokinetic perpendicular dynamics
Authors: Qin H. , Tang W. M. , Lee W. W. , Rewoldt G.
Published: July 2002

Gyrokinetic perpendicular dynamics, an important component not systematically considered in previous gyrokinetic theories, is identified and developed. A “distribution function” S and its governing gyrokinetic equation are introduced to describe the gyrokinetic perpendicular dynamics. The complete treatment of the perpendicular current rendered by the gyrokinetic perpendicular dynamics enables one to recover the compressional Alfvén wave from the gyrokinetic model. From the viewpoint of gyrokinetic theory, the physics of the compressional Alfvén wave is the polarization current at second order. Therefore, in a low frequency gyrokinetic system, the compressional Alfvén wave is naturally decoupled from the shear Alfvén wave and drift wave. In the gyrocenter coordinates, the gyrophase dependent parts of the distribution function S and f̃ are decoupled from the gyrophase independent part f̄. Introducing the gyrokinetic perpendicular dynamics also extends the gyrokinetic model to arbitrary frequency modes. As an example, the Bernstein wave is recovered from the gyrokinetic model. The gyrokinetic perpendicular dynamics uncovered here emphasizes that the spirit of gyrokinetic reduction is to decouple the gyromotion from the particle’s gyrocenter orbit motion, instead of averaging out the gyromotion.
Eigenmode analysis of phase-locked semiconductor laser arrays
Authors: Twu Yihjye , Chen Kuo-Liang , Wang Shyh , Whinnery J. R. , Dienes A.
Published: July 2002

A self-consistent model of phased-array diode lasers, which takes into account the interaction of the carrier and the field, is presented with numerical simulations on both ideal dielectric coupled waveguides and active phased arrays. While essential agreement between the results of this model and those of coupled mode analysis is obtained for passive waveguides, important differences are found for active arrays. Our results show the development of patterns for the various array modes in the active regions.
Velocity distribution of molecular fragments from polymethylmethacrylate irradiated with UV laser pulses
Authors: Danielzik B. , Fabricius N. , Röwekamp M. , von der Linde D.
Published: July 2002

Polymethylmethacrylate samples are irradiated with pulses from an ArF excimer laser at λ=193 nm. The velocities of ablated particles are measured with the use of a quadrupole mass spectrometer. For laser fluences <120 mJ/cm2 we observe thermal, Maxwell–Boltzmann velocity distributions. The photofragments possess a common temperature which increases with fluence to values as high as 3000 K.
Auger recombination in silicon at l
o
w carrier densities
Authors: Yablonovitch E. , Gmitter T.
Published: July 2002

We have discovered a simple chemical preparation method for silicon which virtually eliminates surface recombination. This has enabled us to rapidly survey wafers from many different boules in order to identify those in which bulk (defect assisted) Shockley–Read–Hall recombination happens to be unusually low. Thus, having minimized the two major sources of electron-hole recombination, we find that Auger recombination becomes dominant, even at carrier densities as low as 3×1015/cm3. The Auger coefficient we observe is significantly larger than the value extrapolated down from high density.
Reinvestigation of the carbon films prepared by ArF excimer laser-induced chemical vapor deposition
Authors: Kitahama Katsuki
Published: July 2002

It has already been reported by the authors [K. Kitahama, K. Hirata, H. Nakamatsu, S. Kawai, N. Fujimori, T. Imai, H. Yoshino, and A. Doi, Appl. Phys. Lett. 49, 634 (1986)] that the formation of diamond was confirmed in an ArF excimer laser-induced chemical vapor deposition experiment using acetylene as a carbon source. However, a careful reexamination of the reflection electron diffraction photographs afterward reveals that the deposit is something other than diamond. Raman spectra of the deposit were compared with those of other homologous substances. It is concluded that the structure of the deposit consists of individual graphite layers which are randomly translated parallel to the layers and rotated about the normal of the layers, although separations between individual graphite layers are kept constant. The structure is identical with that of the material known as a ‘‘heat-treated carbon black.’’