bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of electrostatic boundary conditions and system size on the interfacial properties of water and aqueous solutions
Authors: Spohr E.
Published: July 2002

The consequences of the choice of electrostatic boundary conditions on the interfacial properties of water and on the free energy of ion adsorption from aqueous solution have been investigated. The Ewald summation method for lattices, which are periodic in two dimensions, is considered to be the most adequate method in slabs of finite thickness in one dimension. In agreement with the physics of the problem a field-free region in the bulk phases is observed. The use of spherical truncation methods like the shifted-force method leads to unphysical results. The electrostatic potential depends on the size of the system. Ewald summation methods for three-dimensional lattices lead to results in qualitative agreement with the corresponding two-dimensional lattice sum. The computed value of the electrostatic potential depends on an additional parameter, namely the lattice constant c in the direction perpendicular to the interface. The results for Ewald summation in three dimensions converge to the results for Ewald summation in two dimensions for large c, the shifted-force results converge to the same limit, when the surface area of the simulation cell becomes very large and the cut-off distance increases accordingly.
An analytical derivation of MC-SCF vibrational wave functions for the quantum dynamical simulation of multiple proton transfer reactions: Initial application to protonated water chains
Authors: Drukker Karen , Hammes-Schiffer Sharon
Published: July 2002

This paper presents an analytical derivation of a multiconfigurational self-consistent-field (MC-SCF) solution of the time-independent Schrödinger equation for nuclear motion (i.e. vibrational modes). This variational MC-SCF method is designed for the mixed quantum/classical molecular dynamics simulation of multiple proton transfer reactions, where the transferring protons are treated quantum mechanically while the remaining degrees of freedom are treated classically. This paper presents a proof that the Hellmann–Feynman forces on the classical degrees of freedom are identical to the exact forces (i.e. the Pulay corrections vanish) when this MC-SCF method is used with an appropriate choice of basis functions. This new MC-SCF method is applied to multiple proton transfer in a protonated chain of three hydrogen-bonded water molecules. The ground state and the first three excited state energies and the ground state forces agree well with full configuration interaction calculations. Sample trajectories are obtained using adiabatic molecular dynamics methods, and nonadiabatic effects are found to be insignificant for these sample trajectories. The accuracy of the excited states will enable this MC-SCF method to be used in conjunction with nonadiabatic molecular dynamics methods. This application differs from previous work in that it is a real-time quantum dynamical nonequilibrium simulation of multiple proton transfer in a chain of water molecules.
Microwave spectroscopy of the NBr radical in the X 3Σ− state
Authors: Sakamaki Toru , Okabayashi Toshiaki , Tanimoto Mitsutoshi
Published: July 2002

The microwave spectrum of the NBr radical in the X 3Σ− ground electronic state has been observed by a source modulated spectrometer. The NBr radical was generated in a free space cell by a dc glow discharge in a mixture of N2, Br2, and He. The spectrum with three spin components of both two isotopomers, N79Br and N81Br, was observed. The spectrum showed complicated splitting by the hyperfine interactions due to both bromine and nitrogen nuclei. The molecular constants including the magnetic hyperfine and nuclear quadrupolar hyperfine interaction constants were determined by analyzing the observed spectrum. The spin density of the unpaired electrons was estimated from the observed hyperfine coupling constants to be 73.4% and 22.4% on the nitrogen and the bromine atoms, respectively.
Infrared spectroscopy analysis of the local atomic structure in silica prepared by sol-gel
Authors: Martı́nez J. R. , Ruiz F. , Vorobiev Y. V. , Pérez-Robles F. , González-Hernández J.
Published: July 2002

Infrared spectroscopy has been used to analyze the structural changes in samples prepared by the sol-gel method. Silica gels were prepared from alcoholic solutions of tetraethylorthosilicate (TEOS) with different H2O/TEOS molar ratios. The IR spectra of these gels, in the Si–O bond stretching region, shows that their structure strongly depends on the H2O/TEOS ratio. The relative change in intensity of the Si–O stretching modes, in samples prepared using different H2O/TEOS ratios, are interpreted in terms of different degrees of structural disorder. According to our infrared absorption data, a decrease in the H2O/TEOS ratio from about 7, the SiO2 structure evolves from a three-dimensional network toward a chainlike structure.
The permanent electric dipole moments of chromium and vanadium mononitride: CrN and VN
Authors: Steimle Timothy C. , Robinson J. Scott , Goodridge Damian
Published: July 2002

The Pe(1), F″=2.5 branch feature of the (0,0) D 3Π0e–X 3Δ1 band system of VN51 was recorded as a function of an applied static electric field. The resultant Stark splitting and shifts were analyzed giving values of 3.07(7) D and 6.1(4) D for the X 3Δ1 and D 3Π0e states, respectively, for the magnitude of the permanent electric dipole moment, |μ|. Similarly, the Ree(0.5) branch feature of the (0,0) A 4Π3/2–X 4Σ− band system of CrN52 was recorded as a function of an applied static electric field and analyzed to produce |μ| values of 2.31(4) D and 5.42(2) D for the X 4Σ− and A 4Π3/2 states, respectively. In order to facilitate the dipole moment determinations for CrN52 it was necessary to record and analyze the field free spectrum of the (0,0) A 4Π3/2–X 4Σ− subband system. A comparison of the dipole moments for the first row monoxides and mononitrides is made and trends are discussed with reference to a molecular orbital correlation scheme.
The vibrational distribution of the OH product from H2O photodissociation at 157 nm: Discrepancies between theory and experiment
Authors: Hwang Dennis W. , Yang Xuefeng , Yang Xueming
Published: July 2002

Photodissociation of H2O at 157 nm has been studied using the H atom Rydberg tagging time-of-flight technique. Vibrational state distribution has been measured for the OH product from H2O photodissociation. Comparisons with previous theoretical calculations and experimental results by laser-induced fluorescence (LIF) measurements have been made. The results in this work indicate that the relative populations for the high vibrationally excited OH(v≧2) products measured by the LIF technique are significantly underestimated, suggesting that LIF as a technique to quantitatively measure vibrational distributions of reaction product OH is seriously flawed. The experimental results presented here are in fairly good agreement with previous theoretical calculations, even though the calculated vibrational populations for the higher vibrational states of OH are still somewhat overestimated.
Nonradiative relaxation processes in condensed phases: Quantum versus classical baths
Authors: Egorov S. A. , Rabani Eran , Berne B. J.
Published: July 2002

We consider the problem of calculating the nonradiative multiphonon transition rate between two electronic states of an impurity embedded in a condensed-phase environment, where all the nuclear degrees of freedom of the bath are taken in the harmonic approximation, and the two electronic states are coupled to the bath diagonally and off-diagonally. The diagonal coupling term includes displacements of the equilibrium positions of the bath modes, the frequency shifts, and Duschinsky rotations of the bath modes between the two electronic states. We consider two forms of the off-diagonal coupling term—the first assumes that this term is independent of the nuclear degrees of freedom, and thus the coupling between the two diabatic electronic states is taken to be a constant; the second is based on the Born–Oppenheimer method in which the off-diagonal coupling term between the two adiabatic electronic states is taken to be a function of the bath momenta operators. This general model is used to examine the accuracy of several commonly used mixed quantum-classical approximations where the two electronic states are treated quantum mechanically while the bath modes are treated classically. We use the lowest-order perturbation theory to calculate the transition rate between the two electronic states, which is given in terms of the Fourier transform of the off-diagonal coupling-element time correlation function. Following the methodology of Kubo and Toyozawa, we obtain an analytic solution for the fully quantum mechanical time correlation function, and extend our method [S. A. Egorov, E. Rabani and B. J. Berne, J. Chem. Phys. 108, 1407 (1998)] to obtain its mixed quantum–classical counterpart. It is shown that the nonradiative transition rate between the two electronic states calculated using the mixed quantum-classical treatment can deviate by several orders of magnitude from the exact quantum mechanical result. However, the agreement is improved when the classical time propagation of the bath modes is performed with the arithmetic average of the ground- and excited-state nuclear Hamiltonians, and thermal averaging over the initial classical distribution is replaced with the averaging over the corresponding Wigner distribution.
Li
+
dynamics in a polymer nanocomposite: An analysis of dynamic line shapes in nuclear magnetic resonance
Authors: Yang D.-K. , Zax D. B.
Published: July 2002

Characterization of dynamics of the charge-carrying species in polymer electrolytes has proven difficult. In this work we focus on a nanocomposite polymer electrolyte created when poly(ethylene oxide) (PEO) is intercalated into a layered silicate, Li–montmorillonite. We characterize both the Li+–silicate distance and the cation dynamics by analysis of the changes in Li7 nuclear magnetic resonance (NMR) line shape observed as the temperature is changed and cation diffusion is enabled. The observed spectra are compared to spectral simulations which emphasize the role of dipolar fields, associated with the static paramagnetic Fe3+ ions randomly distributed at the Al3+ lattice sites, interacting with the mobile cations. Low temperature line shapes are asymmetric, and not simply related to line shapes of more typical NMR interactions. Simulation of Li7 NMR spectra and comparison to experimental spectra shows that the Li+ interacts most strongly with the silicate surface layer, and all our evidence indicates that the cation diffusion is restricted to the surface. Line shape narrowing is observed over the temperature range 270⩽T⩽420 K reflecting diffusion along the silicate surface. At higher temperatures motional narrowing leads to a limiting linewidth which depends on the spacing between silicate planes and not on the spacing between Li+ and those planes. The high temperature line shape has the same orientation dependence as chemical shift anisotropies. Li+ diffusion rates appear consistent with values reported previously for this system and with a simplified line shape analysis.
Fivefold symmetric homonuclear dipolar recoupling in rotating solids: Application to double quantum spectroscopy
Authors: Hohwy M. , Rienstra C. M. , Jaroniec C. P. , Griffin R. G.
Published: July 2002

We describe a new fivefold symmetric approach to homonuclear recoupling in rotating solids that is based on rotor-synchronized, spin-lock rf irradiation of the type employed previously in MELODRAMA and C7 (and their derivative sequences) for C13–13C recoupling. The fivefold sequence, like its sevenfold relatives, is γ-encoded, and therefore exhibits a theoretical efficiency of ∼73% for double quantum filtering (2QF). However, since the ratio of rf field strength, ωrf/2π, to spinning frequency, ωr/2π, is lower, it is possible to operate the sequence at higher spinning rates, and we have investigated the 2QF efficiency as a function of H1 decoupling field strength at high spinning frequencies. We observe dramatic oscillations of the recoupled signal with a period ∼ωr/2π indicating that the H1 reservoir is behaving partially inhomogeneously. This kind of double quantum recoupling is explored in multiple spin systems and we derive analytical forms for polarization transfer and double quantum excitation relevant for uniformly labeled systems. Finally, the wide applicability of the fivefold sequence is demonstrated with INADEQUATE type spectra of uniformly C13 labeled sucrose and L-alanine.
Tailored grids for numerical simulation of quantum molecular dynamics
Authors: Dumont Randall S. , Assalone Rosa
Published: July 2002

A semiclassical estimate of exponentially decaying tails of energy eigenstates is used to tailor grids in configuration space for specific quantum molecular dynamics computations. The estimate is demonstrated to accurately describe the eigenstate tails of constrained (T-shaped) rare gas triatoms, permitting construction of highly efficient basis sets for accurate numerical simulation. The algorithm is designed to demand minimal exploration of configuration space, and to provide considerable savings in computation time in the case of many degrees of freedom.
Observation of boson peaks by inelastic neutron scattering in polyolefins
Authors: Annis B. K. , Lohse D. J. , Trouw Frans
Published: July 2002

Inelastic neutron scattering was used to probe the nature of the boson peak in atactic polypropylene (aPP), head-to-head polypropylene (hhPP), polyisobutylene (PIB) and a 1/1 mass ratio hhPP/PIB blend. Atactic polypropylene is among the most “fragile” of glass formers and was found to have a shoulder rather than the distinctive peak exhibited by the other three polymers. This difference is already apparent at 15 K where relaxations are not expected to occur. The results suggest that the fragility of hhPP is intermediate between aPP and PIB. Within this group of polymers which have similar chemical structures the position of the boson peak appears to correlate with the glass transition temperature and the cohesive energy density. The possibility of a correlation with chain stiffness as expressed by the characteristic ratio is also discussed.
Frequency-dependent polarizabilities, hyperpolarizabilities, and excitation energies from time-dependent density-functional theory based on the quasienergy derivative method
Authors: Aiga Fumihiko , Tada Tsukasa , Yoshimura Reiko
Published: July 2002

A time-dependent density-functional theory for systems in periodic external potentials in time is formulated on the assumption of the existence of the Floquet states from the quasienergy viewpoint. Coupling strength integration, which connects a noninteracting system with an interacting system, is introduced by using the time-dependent Hellmann–Feynman theorem. Coupled perturbed time-dependent Kohn–Sham equations are derived from the variational condition to the quasienergy functional with respect to parameters. Explicit expressions for frequency-dependent polarizability and first hyperpolarizability are given by the quasienergy derivative method. Excitation energies and transition moments are defined from poles and residues of frequency-dependent polarizabilities, respectively. In contrast to the previous theory, our formulation has the following three advantages: (1) The time-dependent exchange-correlation potential is defined by the functional derivative of the exchange-correlation quasienergy. (2) The formal expression for frequency-dependent polarizability, which corresponds to the exact sumover-states expression, can be obtained. (3) Explicit expressions for response properties which satisfy the 2n+1 rule can be automatically obtained.
On the ground-state spectroscopic constants of Tl2
Authors: Han Young-Kyu , Hirao Kimihiko
Published: July 2002

The ground-state Re, ωe, and De of Tl2 are evaluated using the multireference Kramers’ restricted configuration interaction method with relativistic effective core potential and spin–orbit operators. The best computed (estimated) values are 3.11 (3.05) Å, 75 (79) cm−1, and 0.34 (0.38) eV. These results are in accordance with the Raman experimental data of 3.0 Å, 78 cm−1, and 0.43±0.04 eV(D0) for Re, ωe, and De, respectively. The relevant treatment for nondynamic correlations is necessary to obtain reliable spectroscopic constants, although the spin–orbit operators are introduced from the Hartree–Fock stage.
Generalized Burgers equations and Euler–Painlevé transcendents. II
Authors: Sachdev P. L. , Nair K. R. C.
Published: July 2002

It was proposed earlier [P. L. Sachdev, K. R. C. Nair, and V. G. Tikekar, J. Math. Phys. 27, 1506 (1986)] that the Euler–Painlevé equation yy″+ay′2+ f(x)yy′+g(x) y2+by′+c=0 represents the generalized Burgers equations (GBE’s) in the same manner as Painlevé equations do the KdV type. The GBE was treated with a damping term in some detail. In this paper another GBE ut+uaux+Ju/2t =(gd/2)uxx (the nonplanar Burgers equation) is considered. It is found that its self-similar form is again governed by the Euler–Painlevé equation. The ranges of the parameter α for which solutions of the connection problem to the self-similar equation exist are obtained numerically and confirmed via some integral relations derived from the ODE’s. Special exact analytic solutions for the nonplanar Burgers equation are also obtained. These generalize the well-known single hump solutions for the Burgers equation to other geometries J=1,2; the nonlinear convection term, however, is not quadratic in these cases. This study fortifies the conjecture regarding the importance of the Euler–Painlevé equation with respect to GBE’s.
Algebras of distributions suitable for phase-space quantum mechanics. I
Authors: Gracia-Bondía José M. , Várilly Joseph C.
Published: July 2002

The twisted product of functions on R2N is extended to a *-algebra of tempered distributions that contains the rapidly decreasing smooth functions, the distributions of compact support, and all polynomials, and moreover is invariant under the Fourier transformation. The regularity properties of the twisted product are investigated. A matrix presentation of the twisted product is given, with respect to an appropriate orthonormal basis, which is used to construct a family of Banach algebras under this product.
Relative number state representation and phase operator for physical systems
Authors: Ban Masashi
Published: July 2002

A relative number state (RNS) representation of a system composed of two distinguishable subsystems is proposed. A phase variable as a quantum mechanical operator conjugate to a relative number operator is defined based on the RNS representation space. The phase operator is expressed as a unitary exponential operator. The properties of the relative number operator, the phase operator, and their eigenstates are investigated in detail. The phase variable has a maximum uncertainty in any stationary state. Also, a time operator as a dynamical variable can be defined in the RNS representation space. The RNS representation is closely related to the Liouville space formulation and to thermofield dynamics. The RNS representation is shown to be a suitable method for investigating the Josephson junction with ultrasmall capacitance. A basic formulation of number-phase quantization in the Josephson junction is given in terms of the RNS representation.
Z
3 -graded algebras and the cubic root of the supersymmetry translations
Authors: Kerner Richard
Published: July 2002

A generalization of supersymmetry is proposed based on Z3 -graded algebras. Introducing the objects whose ternary commutation relations contain the cubic roots of unity, e2πi/3, e4πi/3 and 1, the operators whose trilinear combinations yield the supersymmetric translation generators can be constructed. Cubic matrices forming a ternary algebra are the generalization of Pauli’s matrices. The general properties of Z3 -grading, some other representations of such algebras, and their possible pertinence with regard to the quark model are briefly discussed.
Some remarks on representations of jet groups and gauge groups
Authors: Albeverio S. , Torresani B.
Published: July 2002

Irreducible unitary representations of the three first jet (or Leibniz) extensions Gkm of a compact group G are studied, focusing on the neighborhood of the trivial representation. Some associated irreducible unitary (continuous tensor product) representations of the gauge (or current) groups of mappings from a Riemannian manifold into Gkm are described.
Spherical wave expansion for any spin
Authors: Hughes James
Published: July 2002

The spherical wave expansion is derived for fields of particles of arbitrary spin and mass, and for arbitrary helicity, massless particles (such as the electromagnetic vector potential corresponding to photons). The starting point is Weinberg’s characterization of relativistic, higher spin fields that transform according to general irreducible representations of the homogeneous Lorentz group. The expansion is a relativistic generalization of the familiar tensor and spinor spherical harmonics. It is useful for central force problems that arise, for example, in scattering processes off spherically symmetric solitonic backgrounds such as monopoles or skyrmions.
An approach to the relativistic brachistochrone problem by sub-Riemannian geometry
Authors: Giannoni Fabio , Piccione Paolo , Verderesi José A.
Published: July 2002

We formulate a brachistochrone problem in Lorentzian geometry and we prove a variational principle valid for brachistochrones in stationary manifolds. This variational principle is stated in terms of geodesics in a suitable sub-Riemannian structure on ℳ. Moreover, we prove the regularity of the solutions of our variational problem and we determine a differential equation satisfied by the brachistochrones. Some explicit examples are computed.
Equivalence between chain categories of representations of affine sl(2) and N=2 superconformal algebras
Authors: Feigin B. L. , Semikhatov A. M. , Tipunin I. Yu.
Published: July 2002

Highest-weight-type representation theories of the affine sl(2) and N=2 superconformal algebras are shown to be equivalent modulo the respective spectral flows.
The theory of kinetic effects in two-dimensional degenerate gas of colliding electrons
Authors: Gurzhi R. N. , Kalinenko A. N. , Kopeliovich A. I.
Published: July 2002

A mathematical method based on a reduced representation of the electron–electron collision operator acting in the space of quasi-equilibrium functions is constructed. A number of kinetic phenomena such as the evolution of highly anisotropic and high-energy electron distributions, the quasi-hydrodynamic effect in electrical conduction, and a new nonlinear transport mode are described from a unified point of view. Kinetic effects which can be observed in experiments on electron beam propagation and electrical conduction of (GaAs)Al wires with a high mobility of charge carriers are predicted.
On dynamic properties of a two-dimensional degenerate electron gas
Authors: Buhmann H. , Molenkamp L. W. , Gurzhi R. N. , Kalinenko A. N. , Kopeliovich A. I. , Yanovsky A. V.
Published: July 2002

A detailed theory of electron–electron scattering in two-dimensional degenerate systems in heterostructures is constructed as a result of analysis and numerical computations. The conditions are formulated and the values of characteristic parameters are obtained for which specific two-dimensional effects predicted earlier from theoretical considerations can be observed. New properties of scattering indicatrix, viz., a beam of electrons flying almost antiparallel to the primary beam and a very narrow beam of holes flying in the forward direction, are found.
Symmetries within chaos: A route to effective mixing
Authors: Franjione John G. , Leong Chik-Weng , Ottino Julio M.
Published: July 2002

Experimental studies show that simple two-dimensional time-periodic flows can produce chaotic mixing. However, the mixing is not always complete; depending on the choice of the period, there can exist large dynamic structures, called islands, that stretch and compress in a time-periodic manner but remain segregated even after long times. Obviously, a flow that contains very few islands is desired. Unfortunately, in most real systems, an analytic expression for the velocity field (or the motion) does not usually exist, making theoretical prediction of the location and size of islands virtually impossible. However, using only minimal knowledge of the gross properties of the velocity field, the flow can be analyzed in terms of its symmetries. Symmetries can be detected without reference to precise mathematical equations. Large islands are located on lines of symmetry, or in pairs on opposite sides of the line. With this knowledge, it is possible to manipulate symmetries in a systematic way so as to move an island into a region of good mixing. Applying this idea repeatedly results in a recursively generated flow history that is neither periodic nor random, but is self-similar. Mixing in these flows is efficient over the entire flow domain. In addition, the idea of recursively generated flow histories might have implications for understanding the mechanisms of turbulent flow.
The effect of surfactant on the transient motion of Newtonian drops
Authors: Milliken W. J. , Stone H. A. , Leal L. G.
Published: July 2002

The effect of dilute, insoluble surfactant on the deformation and breakup of a viscous drop is examined. Two cases are considered: the deformation and stretching of a drop in a uniaxial extensional flow and the surface-tension-driven motion of an elongated drop in a quiescent fluid. Aside from rescaling the mean capillary force through an average decrease in the interfacial tension, surfactants alter the motion of a viscous drop through gradients in interfacial tension. The effects of surfactants are found to be most pronounced for small viscosity ratios, where Marangoni stresses substantially retard the interfacial velocity and cause the drop to behave as though it were more viscous. Surfactants are found to facilitate the formation of pointed ends during drop stretching, and this may explain the observation of tip streaming in experiments with viscoelastic drops. Surfactant gradients also allow drops to be elongated to a larger degree without producing end pinching.
Variational bounds for transport coefficients in three-dimensional toroidal plasmas
Authors: van Rij W. I. , Hirshman S. P.
Published: July 2002

A variational principle is developed for the linearized drift-kinetic, Fokker–Planck equation, from which both upper and lower bounds for neoclassical transport coefficients can be calculated for plasmas in three-dimensional toroidal confinement geometries. These bounds converge monotonically with the increasing phase-space dimensionality of the assumed trial function. This property may be used to identify those portions of phase space that make dominant contributions to the transport process. A computer code based on this principle has been developed that uses Fourier–Legendre expansions for the poloidal, toroidal, and pitch-angle dependences of the distribution function. Numerical calculations of transport coefficients for a plasma in the TJ-II flexible heliac [Nucl. Fusion 28, 157 (1988)] are used to demonstrate the application of this procedure.
Surface plasma structures in the kinetic regime
Authors: McCullen J. D. , Montierth L. M. , Morse R. L. , Neuman W. A.
Published: July 2002

A numerical study is done of a plasma in contact with a solid surface that reemits some fraction of the incident plasma as neutral gas. The calculation uses a steady-state, kinetic treatment of the transport equations in one space dimension and one or two velocity dimensions to determine self-consistently the distribution functions of the interacting species and the electrostatic potential. The dominant phenomena are the ionization of the neutral gas and the acceleration of the resulting ions away from a potential maximum that is predicted to form in the ionization region. Other effects involved are a Debye sheath structure between the solid surface and the potential maximum, and collisional trapping and untrapping of electrons in the well represented by the potential maximum. Results are presented from a nondimensional model with a monatomic returning neutral species, and for diatomic molecular deuterium returning from the surface. For each set of physical parameters chosen, a one parameter family of solutions is obtained. A hypothesis is presented for the choice from this family of solutions that would be found experimentally.
Effect of ion temperature and plasma density on an ion-acoustic soliton in a collisionless relativistic plasma: An application to radiation belts
Authors: Singh Sanjay , Dahiya R. P.
Published: July 2002

The effect of ion temperature and plasma density on the behavior of an ion-acoustic soliton in a collisionless relativistic plasma is studied. Based on an appropriate set of coordinate transformations, a reductive perturbation analysis is carried out to obtain the Korteweg–de Vries (KdV) equation for the one-dimensional soliton motion. By solving this equation for a single soliton, simple expressions for the soliton phase velocity, soliton amplitude, soliton width, peak soliton ion density, and peak soliton potential are derived. These results are applied to the plasma parameters of the radiation belts. The soliton phase velocity λ0 increases with an increase in the relativistic effect. The effect of the ion temperature on λ0 is, however, negligible. It is shown that for the constant ion temperature and plasma density, the soliton amplitude, soliton phase velocity, peak soliton ion density, and peak soliton potential increase, and the soliton width decreases as the relativistic effect increases. With the increasing ion temperature, however, the soliton behaves in an entirely different way. It is further shown that for a constant value of the ion temperature, the amplitude and peak ion density increase and the width decreases, whereas the peak potential remains unchanged as the plasma density increases.
A ‘‘new’’ approach to the quantitative statistical dynamics of plasma turbulence: The optimum theory of rigorous bounds on steady-state transport
Authors: Krommes John A. , Kim Chang-Bae
Published: July 2002

The fundamental problem in the theory of turbulent transport is to find the flux Γ of a quantity such as heat. Methods based on statistical closures are mired in conceptual controversies and practical difficulties. However, it is possible to bound Γ by employing constraints derived rigorously from the equations of motion. Brief reviews of the general theory and its application to passive advection are given. Then, a detailed application is made to anomalous resistivity generated by self-consistent turbulence in a reversed-field pinch. A nonlinear variational principle for an upper bound on the turbulent electromotive force for fixed current is formulated from the magnetohydrodynamic equations in cylindrical geometry. Numerical solution of a case constrained solely by energy balance leads to a reasonable bound and nonlinear eigenfunctions that share intriguing features with experimental data: The dominant mode numbers appear to be correct, and field reversal is predicted at reasonable values of the pinch parameter. Although open questions remain, upon considering all bounding calculations to date it can be concluded, remarkably, that global energy balance constrains transport sufficiently so that bounds derived therefrom are not unreasonable and that bounding calculations are feasible even for involved practical problems. The potential of the method has hardly been tapped; it provides a fertile area for future research.
Effect of zeroth-order density inhomogeneity on ion acoustic soliton reflection in a finite ion temperature plasma
Authors: Singh Sanjay , Dahiya R. P.
Published: July 2002

Fourier transformation with respect to time is used to solve the differential equation for the amplitude of reflected waves generated as a result of an ion acoustic soliton incident on a density gradient. A general equation giving dependence of the reflected wave amplitude on the zeroth-order plasma density n0 is obtained. Reflection occurs for n0≤0.38, and the amplitude of the reflected wave increases with the increasing plasma density. The reflection coefficient for the reflected wave is defined, and it is shown that the tendency of reflection becomes weaker as the ion temperature is raised.
Solitary waves in a warm plasma with negative ions and drifting effect of electrons
Authors: Kalita B. C. , Devi N.
Published: July 2002

Propagation of ion-acoustic solitary waves in a warm plasma with negative ions under the drifting effect of electrons is considered. Compressive and rarefactive solitons are shown to exist depending on the drift velocity v′e of electrons for different values of Q′ (mj/mi—negative to positive ion mass ratio) ≥1 or ≤1. The amplitude of the compressive soliton for Q′≥1 and rarefactive soliton for Q′≤1 but small, is found to be greatest near v′e = 0 when r (=nj0/ni0, negative to positive ion number density ratio) ≤0.5, showing thereby the characteristic change in solitons for the inclusion of v′e.
Multiple equilibria of divertor plasmas
Authors: Vu H. X. , Prinja A. K.
Published: July 2002

A one-dimensional, two-fluid transport model with a temperature-dependent neutral recycling coefficient is shown to give rise to multiple equilibria of divertor plasmas (bifurcation). Numerical techniques for obtaining these multiple equilibria and for examining their stability are presented. Although these numerical techniques have been well known to the scientific community, this is the first time they have been applied to divertor plasma modeling to show the existence of multiple equilibria as well as the stability of these solutions. Numerical and approximate analytical solutions of the present one-dimensional transport model both indicate that there exists three steady-state solutions corresponding to (1) a high-temperature, low-density equilibrium, (2) a low-temperature, high-density equilibrium, and (3) an intermediate-temperature equilibrium. While both the low-temperature and the high-temperature equilibria are stable, with respect to small perturbations in the plasma conditions, the intermediate-temperature equilibrium is physically unstable, i.e., any small perturbation about this equilibrium will cause a transition toward either the high-temperature or low-temperature equilibrium.
Absorption of electron cyclotron radiation in tokamak plasmas with a superthermal tail in the electron velocity distribution
Authors: Montes A. , Dendy R. O.
Published: July 2002

A fully three-dimensional ray tracing code that includes a realistic antenna pattern, toroidal effects, and refraction is used to calculate the absorption by non-Maxwellian distributions of the extraordinary mode in the nonrelativistic limit away from normal incidence. The ray tracing approach extends results obtained by previous authors who used a relativistic treatment in slab geometry to a more realistic configuration and a broader range of parameters. A monotonically decreasing superthermal tail in the distribution of electron velocities parallel to the tokamak magnetic field is represented by adding a drifted Maxwellian distribution to a bulk Maxwellian distribution. This combines a high degree of flexibility in the set of tail parameters available with the possibility of obtaining exact analytic expressions for the dielectric tensor elements. At low densities, small tails (tail fraction ≂0.5%) can significantly alter the wave absorption characteristics, including the integrated absorption, spatial deposition profile, and velocity space deposition profile. Because of the presence of tail electrons, significant heating is found for high field side launching in a high-density plasma where the fundamental cyclotron resonance is cut off.
Evaluation of the slowing down tail enhanced, neoclassical alpha particle energy flux
Authors: Catto Peter J.
Published: July 2002

The non-Maxwellian slowing down tail formed by the energetic alpha particles produced in a fusing tokamak is shown to substantially enhance the neoclassical radial energy loss of alphas. The retention of the pitch angle scattering of the energetic tail alphas by the background ions leads to a neoclassical energy flux that can easily become larger than that of the alpha ash. The enhanced flux can also act to prevent the fusion alpha power from being deposited in the background plasma unless the banana width is sufficiently small.
Pressure surface distortion by applied ion cyclotron waves and magnetic field asymmetries
Authors: Myra J. R. , D’Ippolito D. A.
Published: July 2002

In magnetic confinement devices the pressure surfaces must obey the parallel current constraint. In a tandem mirror, nonquadrupole magnetic field components or ion cyclotron range of frequencies (ICRF) ponderomotive effects enter the parallel current equation in a nontrivial way. The extra terms cause a shift of the plasma column and/or distortion of the pressure surface shape. These effects are examined for three cases of interest: magnetic error fields due to misaligned coils, axial asymmetries in the quadrupole or solenoidal fields, and azimuthally asymmetric ponderomotive effects associated with applied ICRF waves. The ambipolar potential can compensate for asymmetries and permit lowest order isorrhopic equilibria in some cases, but if the passing density between cells is too small (np/na<rTa/eΦRc) this cannot occur and the flux surfaces of the cells disconnect.
Electron flow in a relativistic electron beam pinched diode collective acceleration system
Authors: Nardi E. , Markovitz M. , Zinamon Z.
Published: July 2002

Investigations of the electron component of the composite collectively accelerated ion and electron beam produced in a relativistic electron beam pinch diode are reported. The experiments consisted of examining the Kα x-ray signal induced by the propagating electron beam and comparing this with the Kα signal produced in the anode. The measurements dealt with propagation velocity, beam front current density as a function of distance from the anode, and the temporal structure of the beam front as a function of distance. Time dependent structure consisting of several peaks was observed. The velocity of the beam front was seen to increase with the addition of CH2 to the anode.
Plasma transport by relaxation of localized perturbations
Authors: Hossain Murshed , Hu Pung Nien , Kress Michael , Blank Albert A. , Grad Harold
Published: July 2002

Localized perturbations in temperature and density are introduced on a background (approximate) steady-state plasma. A simulation of the evolving plasma was carried out on a transport time scale. In all these simulations, the mass diffusion rate λξ is significantly less than that, λ1, based on resistivity alone. Braginskii transport has mainly been used and it has been found that λξ∼0.1λ1. Cases were also tested in which thermal conductivity is much larger than resistivity and it was found in the most extreme cases λξ=0.5λ1. The results are explained in terms of the linearized diffusion eigenvalues and their (approximate) eigenmodes. The eigenvalues reflect the coupled effect of plasma diffusion and heat flow. Since this coupling is intrinsic to the magnetohydrodynamic system of equations itself, the coupling should generally be taken into consideration. In particular, it is concluded that theories neglecting coupling may inevitably interpret transport as ‘‘anomalous.’’ These results are an initial step toward understanding the unresolved confinement issues for tokamaks including pellet induced increased particle confinement.
Nonlinear wave propagation in collisionless finite-beta inhomogeneous plasmas
Authors: Katou K. , Weiland J.
Published: July 2002

Four coupled nonlinear evolution equations for the electrostatic potential, the density fluctuation, and the two vector potentials are derived from the two-fluid and Maxwell’s equations that describe low-frequency collisionless finite-beta inhomogeneous plasmas. Under the assumption of weak turbulence, the above equations reduce to the nonlinear Schrödinger equation. The technique adopted here is considered as an extension of the formal Karpman–Krushkal [Sov. Phys. JETP 28, 277 (1969)] method to a system of nonlinear partial differential equations. The general exact traveling wave solution to the nonlinear Schrödinger equation is obtained with the help of the Hamilton–Jacobi theory. This general solution may be regarded as describing a final nonlinear stage of the modulational instability. It is also shown that a solitary wave solution to the nonlinear Schrödinger equation, which corresponds to the limiting case of the general solution, is given by means of the simple iterative method.
The nonlinear counterstreaming-beam wakefield accelerator
Authors: Yan Yiton T.
Published: July 2002

Using a counterstreaming electron beam to support a nonlinear wakefield for particle acceleration is investigated theoretically. This scheme has the following advantages over the plasma wakefield accelerator (PWFA): (1) easier beam loading; (2) higher transformer ratio; and (3) easier beam-pulse shaping. Additionally, the achievable accelerating gradient (GeV/m) is as large as that which can be obtained with a PWFA. A numerical comparison between this scheme and the PWFA is given.
Energy confinement in turbulent fluid plasmas
Authors: Bhattacharjee A. , Hameiri Eliezer
Published: July 2002

Scaling laws for energy confinement in a turbulent plasma dominated by resistive pressure-driven modes are revisited. New scaling laws are obtained under a consistent low-beta approximation, and differ from earlier theories primarily in their dependence on the plasma pressure.
Tearing mode growth in a regime of weak magnetic shear
Authors: Riyopoulos S. , Hazeltine R. D.
Published: July 2002

The nonlinear growth for the m/n≥2 resistive tearing mode is studied in the case when the rational surface q(r0)=m/n falls in a regime of weak magnetic shear, q′(r0)≂0. The island width is determined self-consistently from the nonlinear, zero-helicity component of the perturbed magnetic flux that provides the local shear. It is found that the magnetic perturbation keeps growing exponentially in the nonlinear regime on a hybrid resistive-Alfvénic time scale, while the island width and the vorticity grow on a much slower time scale. Accordingly, much faster release of magnetic energy results for modes growing near minima of hollow q profiles.
Stability of the thermodynamic equilibrium: A test of the validity of dynamic models as applied to gyroviscous perpendicular magnetohydrodynamics
Authors: Faghihi Mustafa , Scheffel Jan , Spies Günther O.
Published: July 2002

Stability of the thermodynamic equilibrium is put forward as a simple test of the validity of dynamic equations, and is applied to perpendicular gyroviscous magnetohydrodynamics (i.e., perpendicular magnetohydrodynamics with gyroviscosity added). This model turns out to be invalid because it predicts exponentially growing Alfvén waves in a spatially homogeneous static equilibrium with scalar pressure.
Structure of shock waves in relativistic simple gases
Authors: Cercignani C. , Majorana A.
Published: July 2002

The method proposed by Mott-Smith [Phys. Rev. 82, 885 (1951)] to compute the structure of shock waves according to classical kinetic theory is extended to relativistic shocks. The results for the shock thickness are in remarkably good agreement with the results obtained from Eckart’s continuum theory.
The propagation of spherical and cylindrical shock waves in real gases
Authors: Steiner H. , Gretler W.
Published: July 2002

Real gas and heat transfer effects are included in the solution of the blast wave resulting from a point or line explosion. Due to the extremely high temperatures, particularly at the beginning of shock propagation, the assumption of perfect gas is not valid. The equation of state takes into account the high temperature effects of vibration, dissociation, electronic excitation, and ionization, as well as the intermolecular forces at high pressures. The computation of the flow problem is carried out using the method of characteristics which has been modified to the effects of radiative and conductive heat transfer. The results show considerable deviation in the initial stages of the explosion from the perfect gas solution, in particular the temperature profiles and the thermodynamic state immediately behind the front.
Linear stability analysis of plane Couette flow with viscous heating
Authors: Yueh Chao-Sheng , Weng Cheng-I
Published: July 2002

The linear stability of a plane Couette flow of Newtonian fluids with exponential dependence of viscosity on temperature according to the Arrhenius law and Nahme law is investigated. The modified Chebyshev polynomials of the second kind are used in Galerkin’s method to solve the eigenvalue problem. The combinations of Chebyshev polynomials to form the modified ones for satisfying the required boundary conditions, and their orthogonality conditions, are derived. It is found that an analysis that does not include enough terms of the trial functions may lead to erroneous results. The results show that instability occurs for fluids with highly temperature-sensitive viscosity in a range of the Brinkman numbers; when the temperature-sensitive viscosity is small enough, instability is not observed. Furthermore, only two kinds of modes, the viscous and inviscid ones, are found for the instability of the flow system. Also, the results indicate that the fluids obeying the Arrhenius-type model are more stable than those of the Nahme-type model if both are based on the same temperature-sensitive viscosity, reference viscosity, and temperature.
Quasi-steady dissipative nonlinear critical layer in a stratified shear flow
Authors: Troitskaya Yu. I. , Reznik S. N.
Published: July 2002

When a wave with small but finite amplitude ε propagates towards the CL, where the effects of nonlinearity and dissipation are essential, the jump of mean vorticity over the CL appears. For the dynamically stable stratified shear flow with the gradient Richardson number Ri≳1/4 the jump of vorticity has the same order as the undisturbed one [J. Fluid Mech. 233, 25 (1991)]. The process of formation of the flow with this substantial jump of vorticity (or ‘‘break’’ of the velocity profile) in the CL is studied at large time after beginning of the process. The transition region between the CL and the undisturbed flow, the dissipation boundary layer (DBL), is shown to be formed. Its thickness grows in time proportional to √t (t being time), and the CL moves towards the incident wave. When the jump of the wave momentum flux over the CL is constant in time, the flow characteristics can be found in the most simple way. The velocity profile in the DBL appears to be self-similar, the displacement of the CL is proportional to √t and the values of vorticity at the both sides of the CL do not depend on time and they are determined only by the constant wave momentum flux. It is shown that, to provide the constant jump of the wave momentum flux the amplitude of the wave radiated by the source in the undisturbed flow region should vary in a certain complicated manner, because it reflects from the time-dependent (broadening) velocity profile in the DBL. On the other hand, the wave momentum flux from the steady source (for example, the corrugated wall) depends on time. When the coefficients of reflection from the CL (R) and from the DBL (r) are small, this dependence is weak and the wave and flow parameters depending on time are found as series in R and r. The wave–flow interaction for this case is studied.