bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared spectra of (NO)2+, (NO)2−, and (NO)3− trapped in solid neon
Authors: Lugez Catherine L. , Thompson Warren E. , Jacox Marilyn E. , Snis Anders , Panas Itai
Published: July 2002

New studies of the infrared spectra of the products which result on codeposition at approximately 5 K of a Ne:NO sample with Ne atoms that have been excited in a microwave discharge have led to new and revised assignments for several ionic species. The appearance of the ν1 absorption of ONNO+ for several new species with asymmetric isotopic substitution, but for no symmetrically substituted species, confirms the trans ground-state configuration for ONNO+. The behavior of a neon-matrix product absorption at 1227.5 cm−1 parallels that of an argon-matrix absorption at 1221.0 cm−1 which has recently been assigned to trans-ONNO−. The identity of the carrier of a product absorption at 1424.1 cm−1, contributed by a vibration of two symmetrically equivalent NO groups, has not been definitively established. This absorption exhibits complex photodestruction behavior. Three absorptions are assigned to cis,cis-(NO)3−, which has C2v symmetry, with the aid of density functional calculations of the isotopic substitution pattern for the vibrational fundamentals of this species. Similar calculations of the isotopic substitution patterns for other structures result in poor agreement with the experiments. Photodestruction of cis,cis-(NO)3− trapped in solid neon yields the N2O⋯NO2− complex.
Static polarizabilities of Nan (n⩽9) clusters: An all-electron density functional study
Authors: Calaminici Patrizia , Jug Karl , Köster Andreas M.
Published: July 2002

This paper presents static polarizabilities and polarizability anisotropies of sodium clusters up to nine atoms calculated in the framework of density functional theory. The calculations of the static polarizabilities and polarizability anisotropies have been performed using a finite field approach implemented in the density functional program ALLCHEM. The calculations were of the all-electron type. Local and gradient-corrected exchange-correlation functionals have been used. All molecular geometries were fully optimized at both levels of theory. A vibrational analysis was performed in order to discriminate between minima and transition state structures on the potential energy surfaces. Equilibrium geometries, bond distances, harmonic frequencies, static polarizabilities, and polarizability anisotropies for sodium clusters up to the nonamer are presented. The obtained results are compared with experimental data as well as with other theoretical results. The calculated and experimental polarizabilities are in good agreement. For the trimer and the hexamer, the effect of different isomers in the calculation of the polarizability was investigated. This work demonstrates that the used approach allows the prediction of reliable electro-optical properties of metallic systems.
Synergy of entropy and intermolecular coupling in supercooling liquids
Authors: Ngai K. L.
Published: July 2002

We show the Tg-scaled temperature dependence of the minimum number of molecules capable of undergoing a rearrangement, z*, in the Adam and Gibbs model of relaxation of glass-formers is strikingly similar to that of n and m=[d log τα/d(Tg/T)]. Here (1−n) and τα are, respectively, the exponent and the effective relaxation time in the Kohlrausch correlation function, exp[−(t/τα)1−n], of the primary α-relaxation, z* is obtained from the excess (configurational) entropy, Sc, of the Kauzmann paradox and Tg is the glass temperature. As functions of Tg/T, z*, n and m all assume their minimal values at high temperatures. On decreasing temperature they all increase monotonically with a more rapid change in the vicinity of some temperature TB above Tg. Moreover, from the data of a number of small molecule glass-formers in which the high temperature limit of Sc can be determined accurately, we find that at the glass temperature, Tg, z*(Tg) obtained from thermodynamic data correlates with the steepness index m=[d log τα/d(Tg/T)]T=Tg and the Kohlrausch exponents (1−n(Tg)). The similarity of the temperature dependencies of n, m, and z* makes plausible the explanation that the temperature dependences of the kinetic quantities, n and m, originate from that of z*, which is a pure thermodynamics quantity.
Effect of subphase Ca++ ions on the viscoelastic properties of Langmuir monolayers
Authors: Ghaskadvi R. S. , Carr Sharon , Dennin Michael
Published: July 2002

It is known that the presence of cations like Ca++ or Pb++ in the water subphase alters the pressure-area isotherms for fatty acid monolayers. The corresponding lattice constant changes have been studied using x-ray diffraction. Reflection-absorption spectroscopy has been used to probe the chemical composition of the film. We report on the first measurements of the time evolution of the shear viscosity of arachidic acid monolayers in the presence of Ca++ ions in the subphase. We find that the introduction of Ca++ ions to the water subphase results in an increase of the film’s viscosity by at least three orders of magnitude. This increase occurs in three distinct stages. First, there is a rapid change in the viscosity of up to one order of magnitude. This is followed by two periods, with very different time constants, of a relatively slow increase in the viscosity over the next 10 or more hours. The corresponding time constants for this rise decrease as either the subphase pH or Ca++ concentration is increased.
Nonequilibrium molecular dynamics simulation of transport and separation of gases in carbon nanopores. I. Basic results
Authors: Xu Lifang , Tsotsis Theodore T. , Sahimi Muhammad
Published: July 2002

We present the results of extensive nonequilibrium Molecular Dynamics simulations of transport of a binary gas mixture of CO2 and CH4 through a carbon nanopore, in the presence of an external chemical potential or concentration gradient. The CH4 molecules are represented as Lennard-Jones (LJ) hard spheres, while the CO2 molecules are modeled both as LJ hard spheres, as well as three-site linear structures to account for their quadrupole moments. The effect of the various factors, including the structure of the pore walls, temperature, feed composition, and the molecular models and their parameters, on the transport, adsorption, and separation of the gases is investigated in detail. While the structure of the pore walls has virtually no effect on the separation factor, the temperature of the system, the pore size, and the molecular models and their parameters strongly influence it.
Isotopic effects on vibrational energy transfer in CO
Authors: Coletti Cecilia , Billing Gert D.
Published: July 2002

Rate constants for vibrational energy exchange in CO collisions have been calculated for normal CO and two isomers. The calculations have been carried out using a semiclassical collision model in which translational and rotational motions are treated classically. The vibrational degrees of freedom are quantized. The theoretical predicted rates agree well with recent experimental data.
Improved hydrodynamic interaction in macromolecular bead models
Authors: Carrasco B. , Garcı́a de la Torre J.
Published: July 2002

The calculation of hydrodynamic properties of macromolecules in terms of bead models requires an adequate description of the hydrodynamic interaction between the spherical elements. For this purpose, the original or modified Oseen tensor are customarily used, although it has been shown that this simple description may lead to erroneous results, particularly for rotational coefficients. In this paper we study several more elaborate theories for multisphere systems. We apply those treatments to our problem of rigid bead models, implementing them in computer programs, and making calculations for various test structures. The comparison of the results from the various theories, and from other, presumably very accurate procedures, allow us to give some guidelines to improve the treatment of hydrodynamic interactions in macromolecular bead models. These advances are introduced in new versions of our public-domain computer software.
Relaxation dynamics and their spatial distribution in a two-dimensional glass-forming mixture
Authors: Perera Donna N. , Harrowell Peter
Published: July 2002

Molecular dynamics simulations are used to explore the spatial fluctuations associated with structural relaxation and particle transport in a supercooled binary mixture in two dimensions. The study includes (i) the characterization of heterogeneities in the local particle dynamics in terms of their length scale and lifetime, (ii) the relationship between local kinetics and local structure/composition, and (iii) preliminary identification of the principal collective motions involved in the long-time relaxation of the supercooled liquid.
A failing of coupled-states calculations for inelastic and pressure-broadening cross sections: Calculations on CO2–Ar
Authors: Roche Christine F. , Dickinson Alan S. , Hutson Jeremy M.
Published: July 2002

Fully quantal benchmark calculations of pressure-broadening cross sections for infrared and Raman lines of CO2 perturbed by Ar are carried out using both close-coupling (CC) and coupled-states (CS) calculations. CS calculations are found to underestimate the cross sections by up to 15%. The effect occurs even for isotropic Raman cross sections, which are not affected by reorientation contributions. The discrepancy arises mostly for collisions with large orbital angular momenta l, occurring on the long-range part of the potential. It may be attributed to collisions that are adiabatic rather than sudden in nature. A hybrid computational method, employing CS calculations for low l and decoupled l-dominant (DLD) calculations for high l, offers a promising solution.
First principles calculations of Si doped fullerenes: Structural and electronic localization properties in C59Si and C58Si2
Authors: Billas I. M. L. , Massobrio C. , Boero M. , Parrinello M. , Branz W. , Tast F. , Malinowski N. , Heinebrodt M. , Martin T. P.
Published: July 2002

Si-doped heterofullerenes C59Si and C58Si2, obtained from C60 by replacing one and two C atoms with Si atoms, are investigated via first principles calculations. Static geometry optimizations show that structural deformations occur in the vicinity of the dopant atoms and give rise to Si–C bonds significantly larger than the ordinary C–C bonds of the fullerene cage. In the case of C58Si2, the lowest energy isomer has two Si atoms located at distances corresponding to third nearest neighbors. The electronic structure of these heterofullerenes, although globally close to that of C60, is characterized by a strong localization of both the HOMO’s and the LUMO’s on the Si sites. Charge transfer occurs from the dopant atoms to the nearest neighbor C atoms, contributing to the formation of polar Si–C bonds. A detailed analysis of the charge localization, based on the electron localization function and maximally localized Wannier function approaches, reveals that the bonding of Si in the fullerene cage consists of two single and one weak double bond, thus preserving the conjugation pattern of the undoped C60. Beside the charge localization along the bonds, we observe a peculiar region of charge localization outside the cage above each Si atom. These features are discussed in comparison with the corresponding patterns exhibited by the C60 system.
Hexapole state-selection and orientation of asymmetric top molecules: CH2F2
Authors: Hain Toby D. , Moision Robert M. , Curtiss Thomas J.
Published: July 2002

Molecular beams of the b-type asymmetric top molecule methylenefluoride (CH2F2) were focused and rotationally state-selected with an electrostatic hexapole. The focusing behavior is mediated by the dependence of rotational energy on electric field strength, the Stark effect. The matrix quantum theory needed to calculate the rotational energies of asymmetric top molecules within an electric field are summarized. These Stark energies were calculated and parameterized for the lowest 165|JτM〉 rotational levels of CH2F2. Excellent agreement was found between classical trajectory simulations incorporating these calculated energies and experimentally measured hexapole focusing spectra. Based on this agreement, the rotational state distribution transmitted by the hexapole as a function of hexapole voltage has been ascertained. Comparisons are made with simulated focusing spectra of the a-type rotor, formaldehyde (H2CO). The theoretical formalism needed to describe the orientational probability distribution functions (opdf's) of hexapole-selected asymmetric top wave functions is developed and applied to the experimentally selected states of CH2F2. Calculated opdf's demonstrate the remarkable control we have over the orientation by varying the “orienting” field strength in the region following the hexapole selector.
Molecular electronic structure using auxiliary field Monte Carlo, plane-waves, and pseudopotentials
Authors: Baer Roi , Neuhauser Daniel
Published: July 2002

Shifted contour auxiliary field Monte Carlo is implemented for molecular electronic structure using a plane-waves basis and norm conserving pseudopotentials. The merits of the method are studied by computing atomization energies of H2, BeH2, and Be2. By comparing with high correlation methods, DFT-based norm conserving pseudopotentials are evaluated for performance in fully correlated molecular computations. Pseudopotentials based on generalized gradient approximation lead to consistently better atomization energies than those based on the local density approximation, and we find there is room for designing pseudopotentials better suited for full valence correlation.
Cahn–Hilliard theory with triple-parabolic free energy. I. Nucleation and growth of a stable crystalline phase
Authors: Gránásy László , Oxtoby David W.
Published: July 2002

Nucleation and growth of a stable crystalline phase are described in the framework of a single-order-parameter Cahn–Hilliard theory. A piecewise parabolic free energy-order parameter relationship composed of three parabolas is adopted with a negative curvature coefficient (λ1) for the central part. An analytical solution of the problem is presented. The work of formation of critical fluctuations, the temperature coefficient of their interfacial free energy, and the Tolman length are found to be sensitive to the value of λ1, whereas the steady-state growth rate is rather insensitive. It is demonstrated that for systems of known free-energy order parameter relationship, the triple-parabola approximation is useful in obtaining qualitative and semiquantitative results for nucleation and growth rates.
A density functional theory study of CH2 and H adsorption on Ni(111)
Authors: Michaelides A. , Hu P.
Published: July 2002

Ab initio total energy calculations within the density functional theory framework have been used to study the adsorption of CH2 and H as well as the coadsorption of CH2 and H on Ni(111). H binds strongly at threefold hollow sites with calculated adsorption energies of 2.60 and 2.54 eV at the face-centered-cubic (fcc) and hexagonal-close-packed (hcp) hollow sites, respectively. Adsorption energies and H-Ni distances are found to agree well with both experimental and theoretical results. CH2 adsorbs strongly at all high symmetry sites with calculated adsorption energies of 3.26, 3.22, 3.14 and 2.36 eV at the fcc, hcp, bridge and top sites, respectively. Optimized structures are reported at all sites, and, in the most stable hollow sites there is considerable internal reorganization of the CH2 fragment. The CH2 molecule is tilted, the hydrogens are inequivalent and the C-H bonds are lengthened relative to the gas phase. In the CH2-H coadsorption systems the adsorbates have a tendency to move toward bridge sites. The bonding of all adsorbates to the surface is analyzed in detail.
Efficient real-space approach to time-dependent density functional theory for the dielectric response of nonmetallic crystals
Authors: Kootstra F. , de Boeij P. L. , Snijders J. G.
Published: July 2002

Time-dependent density functional theory has been used to calculate the static and frequency-dependent dielectric function ε(ω) of nonmetallic crystals. We show that a real-space description becomes feasible for crystals by using a combination of a lattice-periodic (microscopic) scalar potential with a uniform (macroscopic) electric field as perturbation in a periodic structure calculation. The induced density and microscopic potential can be obtained self-consistently for fixed macroscopic field by using linear response theory in which Coulomb interactions and exchange-correlation effects are included. We use an iterative scheme, in which density and potential are updated in every cycle. The explicit evaluation of Kohn–Sham response kernels is avoided and their singular behavior as function of the frequency is treated analytically. Coulomb integrals are evaluated efficiently using auxiliary fitfunctions and we apply a screening technique for the lattice sums. The dielectric function can then be obtained from the induced current. We obtained ε(ω) for C, Si, and GaAs within the adiabatic local density approximation in good agreement with experiment. In particular in the low-frequency range no adjustment of the local density approximation (LDA) band gap seems to be necessary.
Construction of the second constant of motion for two-dimensional classical systems
Authors: Kaushal R. S. , Mishra S. C. , Tripathy K. C.
Published: July 2002

A general method for the construction of the second constant of motion of third and fourth orders is given for two-dimensional systems in terms of z=q1+iq2, and z̄=q1−iq2. Correspondingly, the third- and fourth-order potential equations are obtained whose solutions directly provide the integrable systems. Using the Holt ansatz, the potential equation corresponding to the third-order invariants has been reduced to a pair of potential equations whose solutions yield a large class of integrable systems.
Concepts of conditional expectations in quantum theory
Authors: Ozawa Masanao
Published: July 2002

A concept of conditional expectations in quantum theory is established with interrelations to previously introduced concepts of the Cycon–Hellwig conditional expectations and a posteriori states, which are analogous to the existing interrelations in the classical probability theory among conditional expectations related to random variables, those related to σ subalgebras and conditional probability distributions. These three concepts are shown to have satisfactory statistical interpretation in the quantum measuring processes. For the above purpose, we introduce an integration with respect to functions with values in the states of operator algebras and positive operator valued measures such that the resulting indefinite integrals are completely positive map valued measures. Eventually, it is proved that in the von Neumann algebraic formulation, the Cycon–Hellwig conditional expectations always exist as completely positive map valued measures.
Spectral properties of an optical polaron in a magnetic field
Authors: Löwen H.
Published: July 2002

An optical polaron, which is exposed to a homogeneous magnetic field, is considered. Making use of functional analytical methods of Fröhlich [Fortschr. Phys. 22, 159 (1974)], it is proved that the ground-state energy, the magnetic polaron mass, and the number of virtual phonons in the ground state are analytical functions of the electron–phonon coupling parameter and the magnetic field strength. Consequently, a discontinuous stripping transition, which was claimed recently by several authors, does not exist. In fact, some authors have stated that the discontinuities they encounter might indeed be artifacts due to the approximation. The spectrum of the momentum-decomposed Fröhlich Hamiltonian is analyzed; bounds and smoothness properties of the ground state and the discrete excited states are derived. All results hold also for lower spatial dimensions.
Notes on a class of homogeneous space-times
Authors: Calvão M. O. , Rebouças M. J. , Teixeira A. F. F. , Silva W. M.
Published: July 2002

The breakdown of causality in homogeneous Gödel-type space-time manifolds is examined. An extension of Rebouças–Tiomno (RT) and Accioly–Gonçalves studies is made. The existence of noncausal curves is also investigated under two different conditions on the energy-momentum tensor. An integral representation of the infinitesimal generators of isometries is obtained, extending previous works on the RT geometry.
Duals and propagators: A canonical formalism for nonlinear equations
Authors: Cacuci D. G. , Perez R. B. , Protopopescu V.
Published: July 2002

A new formalism for solving general nonlinear equations is proposed. Given a nonlinear operator equation, a dual operator is constructed, canonically, similar to the adjoint operator in linear theory. By using this dual operator, advanced and retarded propagators (analogs of the Green’s functions in linear theory) are generated. These propagators satisfy the customary reciprocity and semigroup properties and yield the formal solution of the original nonlinear problem. It is further shown that these propagators can be obtained either by solving a linear equation that still contains an implicit dependence on the problem’s solution or by solving a closed-form nonlinear integral equation from which the problem’s solution itself is completely eliminated. The formalism is canonical in the sense that its applicability is not affected by the particularities of the nonlinear operator, boundary conditions, and underlying phase space. All aspects of applying this formalism to nonlinear problems are illustrated analytically on the Riccati equation.
Singular anharmonicities and the analytic continued fractions. II. The potentials V(r)=a
r2+b
r−4+c
r−6
Authors: Znojil M.
Published: July 2002

The c=0 results of Paper I [J. Math. Phys. 30, 23 (1989)] are extended. In spite of the presence of an additional coupling constant, the Laurent series solutions of the Schrödinger equation that are obtained remain similar to Mathieu functions. Indeed, the recurrences for coefficients preserve their three-term character, their analytic continued fraction solutions still converge, etc. The formulas become even slightly simpler for c≠0 due to a certain symmetry of the equations to be solved. An acceleration of convergence is better understood and a few numerical illustrations of efficiency are also delivered.
The free Dirac operator on compact and noncompact graphs
Authors: Bulla W. , Trenkler T.
Published: July 2002

The free Dirac operator defined on composite one-dimensional structures consisting of finitely many half-lines and intervals is investigated. The influence of the connection points between the constituents is modeled by transition conditions for the wave functions or equivalently by different self-adjoint extensions of the Dirac operator. General relations between the parameters of the extensions and the eigenvalues resp. the scattering coefficients are derived and then applied to the cases of a bundle of half-lines, a point defect, a branching line, and an eye-shaped structure.
Maxwell’s equations for nonsmooth media; fractal-shaped and pointlike objects
Authors: Dorren H. J. S. , Tip A.
Published: July 2002

Maxwell’s equations are considered for the case of nonsmooth media, such as fractal-shaped and pointlike objects. In the first case the standard method of fitting normal and tangential field components breaks down. This problem is solved by showing that a proper time evolution for this situation can be obtained as a limiting case of a family of smooth ones. Thus a nonsmooth case can always be approximated by a smooth one with arbitrary precision. It is, in general, not possible to modify Maxwell’s equations by a boundary condition in a single point. Here this problem is circumvented by using the recently developed theory of generalized point interactions [J. F. van Diejen and A. Tip, J. Math. Phys. 32, 630 (1991)]. This results in a Pontryagin space setting leading to a unitary scattering matrix in the Hilbert space associated with the field energy. The latter can be constructed in such a way that, asymptotically, for low frequencies, the scattering cross section for standard Mie scattering is recovered.
Special orthonormal frames
Authors: Nester James M.
Published: July 2002

A natural gauge condition is used to select special orthonormal frames and thereby a preferred teleparallel geometry on a Riemannian manifold of any dimension. The condition is equivalent to a nonlinear elliptic system for a rotation. Existence and uniqueness of solutions are discussed. Certain special cases and applications are noted.
Arnold’s singularity theory and gravitational lensing
Authors: Petters A. O.
Published: July 2002

Caustics in gravitational lensing are formulated from a symplectic geometric viewpoint. Arnold’s singularity theory is then used to give a rigorous local classification of generic gravitational lensing caustics and their evolutions. A local classification is also presented of generic image surfaces, time-delay image surfaces, big caustics, and bicaustics. The results of each classification are discussed and graphically illustrated.
Some remarks on the essential spectrum of transport operators with abstract boundary conditions
Authors: Latrach Khalid
Published: July 2002

This article deals with the analysis of the essential spectrum of the one-dimensional transport operator with general boundary conditions where an abstract boundary operator relates the incoming and the outgoing fluxes. After a complete description of the spectrum of the transport equation with vacuum boundary conditions, sufficient conditions are given in terms of boundary and collision operators assuring the stability of the essential spectrum. The article ends with an analysis of the essential spectrum of the neutron transport operator in arbitrary dimension. Finally, some open problems are indicated.
Hamiltonian formulation of the teleparallel description of general relativity
Authors: Maluf José W.
Published: July 2002

The Hamiltonian formulation of the teleparallel description of Einstein’s general relativity is established. Under a particular gauge fixing the Hamiltonian of the theory is written in terms of first class constraints. The algebra of the Hamiltonian and vector constraints resembles that of the standard Arnowitt–Deser–Misner formulation. This geometrical framework might be relevant as it is known that in manifolds with vanishing curvature tensor but with nonzero torsion tensor it is possible to carry out a simple construction of Becchi–Rouet–Stora–Tyutin-like operators.
Maximum entropy in the Hamburger moments problem
Authors: Tagliani Aldo
Published: July 2002

The maximum-entropy approach to the solution of the Hamburger inverse problem of moments, in which one seeks to recover a positive density function p(x) [where x∈(−∞,+∞)] from the values of a finite N+1 of its moments, is considered. The obtained results show that unexpected upper bounds for the moments do not exist in the general Hamburger finite moment problem, unlike in the symmetric case previously considered. Some physical examples, illustrating the use of partial information to determine the approximate function, are presented.
On informational completeness of covariant localization observables and Wigner coefficients
Authors: Healy D. M. , Schroeck F. E.
Published: July 2002

An orthogonality theorem is obtained for square integrable representations on homogeneous spaces of a locally compact group. From this, a series of lemmas is derived showing the informational completeness of natural covariant localization operators, as well as of the generalized Wigner distributions (matrix elements of the group). Some of these results give explicit reconstruction formulas for the quantum state from its expectation values against these families of operators. The results are applied to special (phase space) representations of the Heisenberg, affine, and Galilei groups.
The Dirac gamma matrices as ‘‘relics’’ of a hidden symmetry?: As fundamental representations of the algebra sp(4,R)
Authors: Lee Dae-Gyu
Published: July 2002

The relationship between the Dirac gamma (γ) matrices and the fundamental representations of the algebra sp(4,R) are clarified, which is locally isomorphic to the de Sitter algebra o(3,2). There are six sets of ten γ-matrices among the fifteen traceless γ-matrices, which satisfy the algebra sp(4,R). The representations can be identified with, and transformed into, one another through the permutation group of three objects S3. While each element of the invariant subgroup of S3 transforms an o(3,2)-like sp(4,R) representation into another o(3,2)-like sp(4,R), any other element of S3 transforms an o(3,2)-like sp(4,R) into an o(2,3)-like sp(4,R), and vice versa. We discuss physical implications of this group-theoretical analysis.
Curvature collineations of some static spherically symmetric space–times
Authors: Bokhari Ashfaque H. , Kashif A. R.
Published: July 2002

Curvature collineations of some static spherically symmetric space–times are derived and compared with isometries and Ricci collineations for corresponding space–times.
Renormalized contact potential in two dimensions
Authors: Henderson R. J. , Rajeev S. G.
Published: July 2002

We obtain for the attractive Dirac δ-function potential in two-dimensional quantum mechanics a renormalized formulation that avoids reference to a cutoff and running coupling constant. Dimensional transmutation is carried out before attempting to solve the system, and leads to an interesting eigenvalue problem in N−2 degrees of freedom (in the center of momentum frame) when there are N particles. The effective Hamiltonian for N−2 particles has a nonlocal attractive interaction, and the Schrodinger equation becomes an eigenvalue problem for the logarithm of this Hamiltonian. The three-body case is examined in detail, and in this case a variational estimate of the ground-state energy is given.
Theory of nonequilibrium first-order phase transitions for stochastic dynamics
Authors: Gaveau Bernard , Schulman L. S.
Published: July 2002

A dynamic definition of a first-order phase transition is given. It is based on a master equation description of the time evolution of a system. When the operator generating that time evolution has an isolated near degeneracy there is a first-order phase transition. Conversely, when phenomena describable as first-order phase transitions occur in a system, the corresponding operator has near degeneracy. Estimates relating degree of degeneracy and degree of phase separation are given. This approach harks back to early ideas on phase transitions and degeneracy, but now enjoys greater generality because it involves an operator present in a wide variety of systems. Our definition is applicable to what have intuitively been considered phase transitions in nonequilibrium systems and to problematic near equilibrium cases, such as metastability.
Classification of low-dimensional Lie super-bialgebras
Authors: Juszczak C. , Sobczyk J. T.
Published: July 2002

A thorough analysis of Lie super-bialgebra structures on Lie super-algebras osp(1;2) and super e(2) is presented. A combined technique of computer algebraic computations and subsequent identification of equivalent structures is applied. In all the cases, Poisson–Lie brackets on supergroups are found. The possibility of quantizing them in order to obtain quantum groups is discussed. It turns out to be straightforward for all but one structure for the super-E(2) group.
Extended supersymmetries for the Schrödinger–Pauli equation
Authors: Niederle J. , Nikitin A. G.
Published: July 2002

It is argued that extended, reducible, and generalized supersymmetry (SUSY) are common in many systems of standard nonrelativistic quantum mechanics. For example, it is proved that a well-studied quantum mechanical system of a spin-12 particle interacting with constant and homogeneous magnetic field admits the N=4 SUSY and has the internal symmetry so(3,3). Then an approach of energy spectra of a SUSY nature is presented and developed. It is applied to a wide class of systems described by the Schrödinger–Pauli equation admitting N=3, N=4, and N=5 SUSY. Some of these supersymmetries have a very peculiar property—their supercharges are realized without usual fermionic variables. It is shown that for them, the usual extension N=3 to N=4 SUSY is no longer guaranteed.
On the time evolution of the mean-field polaron
Authors: Bechouche P. , Nieto J. , Arriola E. Ruiz , Soler J.
Published: July 2002

In this paper a mean-field theory for the evolution of an electron in a crystal is proposed in the framework of the Schrödinger formalism. The well-posedness of the problem as well as the conservation laws associated to the invariances of the Action Functional of the problem and the stability of the minimal energy solution are studied.
Distortion of homogeneous turbulence by axisymmetric strain and dilatation
Authors: Lee Moon Joo
Published: July 2002

Rapid distortion theory is applied to study distortion of homogeneous turbulence subject to two different axisymmetric strain modes: contraction and expansion. Exact expressions for turbulence structural quantities are obtained in closed form by assuming initially isotropic turbulence and the asymptotic behavior at large total strains is also presented. Comparison with numerical simulations at high strain rate shows remarkably good agreement for all the quantities considered. Differences in effects of the two axisymmetric strain modes on evolution of the turbulence statistics are investigated in detail. It is found that (i) both velocity and vorticity fluctuations are enhanced more efficiently by contraction than by expansion; (ii) contraction produces much higher anisotropy in velocity and vorticity than expansion; (iii) root-mean-square pressure is slightly reduced during contraction, whereas it increases rapidly during expansion; and (iv) vortical structures of rodlike shape develop in a contraction flow, while disklike structures develop in an expansion flow. For flows of uniform, time-dependent density ρ(t) at low turbulence Mach number, it is shown that, by a decomposition of mean strain-rate tensor, statistical correlations are related to those in the equivalent incompressible flow, e.g., Rij(e) =(ρ/ρ0)2/3R⋆ij (e⋆), where e is the total strain and e⋆ is the corresponding incompressible total strain (ρ0 is the initial density). The decomposition is applied to isotropic, one-dimensional, and two-dimensional dilatation cases to explore the effect of compressibility on turbulence. Terms in the transport equation of the Reynolds-stress tensor are evaluated for axisymmetric strain flows. A simple model for the pressure–strain-rate term is proposed by incorporating structural parameters and history effects based on the rapid distortion analysis. Prediction of the improved model agrees well with the numerical simulation results, even in cases at low strain rate.
A contribution toward rational modeling of the pressure–strain-rate correlation
Authors: Lee Moon Joo
Published: July 2002

A novel method of obtaining an analytical expression of the ‘‘linear part’’ of the pressure–strain-rate tensor in terms of the anisotropy tensor of the Reynolds stresses has been developed, where the coefficients of the seven independent tensor terms are functions of the invariants of the Reynolds-stress anisotropy. The coefficients are evaluated up to fourth order in the anisotropy of the Reynolds stresses to provide a guidance for development of a turbulence model.
Lord Rayleigh and hydrodynamic similarity
Authors: Rott N.
Published: July 2002

The history of two domains in fluid mechanics, in which Lord Rayleigh made explicit use of hydrodynamic similarity, are investigated: the theory of aerodynamic drag and the treatment of the aeolian tones. The great impact of Rayleigh’s ideas on the development of hydrodynamic similarity theory and applications is described, during his lifetime and beyond. Many historical details involving Lord Rayleigh’s contemporaries are also presented in an attempt to give a vivid description of a crucial epoch in the history of fluid mechanics. A brief description of certain modern developments is appended.
Lagrangian motion of fluid particles induced by three-dimensional standing surface waves
Authors: Umeki Makoto
Published: July 2002

Lagrangian motion of fluid particles on three-dimensional weakly nonlinear standing surface waves is studied by inviscid irrotational theory. The three-dimensional flow inside the fluid in a square cylinder is derived when two internally resonant modes (m,n) and (n,m) are excited. Using the property that particles initially located on the surface continue to float on it, the three-dimensional flow can be reduced to two dimensional. It is found that a second-order drift velocity emerges on the surface, which is proportional to the angular momentum associated with the surface displacement. The drift velocity is vortical and consists of derivatives of modes interacting with the two first-order modes. Streamline patterns of drift motion show a large-scale structure for m≂n and a small-cell flow for m≫n. The surface flow is a superposition of this drift velocity and the first- and second-order oscillatory velocity with zero time average. When the expansion parameter ε remains small, the numerical Poincaré plot of particle paths for the two-dimensional surface flow shows sets of tori and heteroclinic orbits. Breakdown of tori by resonance of the wave oscillation and drift flow and the period-doubling bifurcations create chaotic layers as ε becomes large. For sufficiently large ε, a single particle moves randomly over a distance of the size of a container. Numerically computed Lyapunov exponents and fractal dimension show that the random particle motion is chaotic and weakly dissipative.
A note on the force on an accelerating spherical drop at low-Reynolds number
Authors: Galindo V. , Gerbeth G.
Published: July 2002

The time-dependent drag force on a spherical drop is analyzed for the linear limit of small Reynolds numbers. There is an error in literature on the generalization of the known Basset memory kernel of a rigid sphere to the case of a drop. Correct results are presented here. A new overshooting effect is found if thermocapillarity is driving the drop motion rather than gravity.
Diagnostic applications of transient synchrotron radiation in tokamak plasmas
Authors: Fisch N. J. , Kritz A. H.
Published: July 2002

Transient radiation, resulting from a brief, deliberate perturbation of the velocity distribution of superthermal tokamak electrons, can be more informative than the steady background radiation that is present in the absence of the perturbation. It is possible to define a number of interesting inverse problems that exploit the two-dimensional frequency-time data of the transient radiation signal.
Radiation-dependent ionization model for laser-created plasmas
Authors: Busquet M.
Published: July 2002

For the simulation of laser-created plasmas, hydrodynamic codes need an atomic physics package, for both the equation of state and the optical properties, which does not use the hypothesis of local thermodynamical equilibrium (LTE). However, in x-ray laser studies, as well as in indirect drive inertial confinement fusion studies, high-Z materials can be found where radiation trapping can induce a significant departure from the optically thin description. A method is presented in which an existing LTE code can be changed into a non-LTE code with radiation-dependent ionization. This method is numerically simple and its cost, in terms of computing time, is low enough to be used in two-dimensional simulations.
Drift wave model for inward energy transport in tokamak plasmas
Authors: Weiland J. , Nordman H.
Published: July 2002

Stationary inward flows of electron energy have been obtained in transport code simulations of reactive drift wave systems. The recent experimental results with off-axis electron cyclotron heating in the DIII-D tokamak [Phys. Rev. Lett. 68, 52 (1992)] have been recovered with peaked electron temperature profiles and strong profile consistency.
Natural convection in a differentially heated corner region
Authors: Kimura Shigeo , Bejan Adrian
Published: July 2002

This is a fundamental study of the phenomenon of natural convection in the region formed by a vertical warm wall rising above a cold horizontal wall, or in the region between a cold vertical wall extending downward from a warm horizontal surface. The study consists of scale analysis, numerical simulations, and an asymptotic solution of the low Rayleigh number limit. The scale analysis predicts the persistence of a single cell in the corner region, regardless of Rayleigh number. The cell migrates toward the corner as the Rayleigh number RaH increases: the flow rate and the net heat transfer rate vary as Ra1/7H. The scale analysis is verified qualitatively and quantitatively by means of numerical experiments in the range RaH =103–107, Pr=0.7–7, H/L=1–4, where Pr is the Prandtl number and H/L is the height/length ratio of the corner region. Additional numerical simulations are presented for cases where one or both walls have uniform heat flux; in these cases, the heat transfer rate shows nearly the same behavior as when the corner walls are both isothermal. The asymptotic solution for the RaH→0 limit shows that the flow field is relatively insensitive to whether the wall temperature varies continuously or discontinuously through the corner point.
Particle loss rates from electrostatic wells of arbitrary mirror ratios
Authors: Catto Peter J. , Li Xing Zhong
Published: July 2002

Single integral expressions for the particle loss rate from an electrostatic trap with ZeΦ0/T≫1 are derived that span all possible mirror ratios R, where Φ0, Z, and T are the potential well depth, charge number, and species temperature. The two expressions are shown to be identical for a range of intermediate R so that one expression is valid for small to intermediate R (R≲1), while the other is appropriate from intermediate to large R (R≫T/ZeΦ0). Three particularly simple analytic limits are found to exist: (i) R≪T/ZeΦ0, (ii) T/ZeΦ0≪R≲1, and (iii) R≫1.
Space-charge wave propagation in inhomogeneous waveguides
Authors: Anselmo A. , Kerslick G. , Nation J. A. , Providakes G.
Published: July 2002

In this paper, an account is presented of an investigation into the propagation of large amplitude space-charge waves in an inhomogeneous waveguide. The study is motivated by the possibility of using these waves for the collective acceleration of ions. Measurements are reported that show an increase in the wave phase velocity as the guide diameter, and hence the effective plasma frequency is decreased. Results are also presented which show that the wave phase velocity is a function of its amplitude, and that large amplitude, nonlinear waves propagate more slowly than those described by linear theory. The results demonstrate that it is possible to control the wave propagation characteristics, and therefore indicate the electron-beam-supported slow space-charge waves provide a suitable medium for collective ion acceleration. Finally, a summary is given of possible advantages of an electron beam-wave accelerator over those using externally generated rf fields.
Viscous effects in a collisional tokamak plasma with strong rotation
Authors: Stacey W. M. , Sigmar D. J.
Published: July 2002

The full viscosity tensor for an axisymmetric toroidal plasma in the collisional regime (with strong rotation) is calculated, including gyroviscosity and O(ε) poloidal variations over the flux surface. It is shown that the resulting viscous force is of sufficient magnitude to account for the radial transfer of toroidal momentum that must be inferred in order to explain the rotation measurements in tokamak experiments. The consequences of a viscous force of this form and magnitude on particle transport and on the evolution of toroidal and poloidal rotation velocities are discussed.
Weibel instability in the spherical corona of a laser fusion target
Authors: True M. A.
Published: July 2002

The Weibel instability is caused by anisotropy in the velocity distribution. In the collisionless spherical corona of a laser fusion target, anisotropy in electron velocity space is naturally produced by a localized source because angular momentum, l=mv⊥r, is conserved and the perpendicular energy, E⊥=l2/2mr2, decreases at radii large compared to the source radius. This occurs even if the source is locally isotropic (e.g., inverse bremsstrahlung around the critical density). Linear growth rates are computed for the Weibel instability with a model distribution that includes the aforementioned effects as well as diffusion in angular momentum and energy loss by hydrodynamic expansion.
Equilibrium properties of short field-reversed configurations
Authors: Tuszewski M. , Spencer R. L.
Published: July 2002

Some features of short field-reversed configuration (FRC) equilibria relevant to transport and stability are studied numerically and analytically. It is shown that magnetic field curvature effects significantly increase the FRC magnetization for plasma elongations ε≤4.
Null-collision technique in the direct-simulation Monte Carlo method
Authors: Koura Katsuhisa
Published: July 2002

The null-collision concept is introduced into the direct-simulation Monte Carlo method in the rarefied gas dynamics. The null-collision technique overcomes the principle fault in the time-counter technique and the difficulties in the collision-frequency technique. The computation time required for the null-collision technique is comparable to that for the time-counter technique. Therefore, it is concluded that the null-collision technique is superior to any other existing techniques in the direct-simulation Monte Carlo method.
Investigations of the magnetic field structure of high-power, short-duration rotamak discharges
Authors: Durance G. , Jones I. R.
Published: July 2002

In this paper, the application of the rotating magnetic field method of driving plasma current to the generation of a compact torus configuration known as the rotamak is described. The results obtained in a high-power (few MW), short-duration (∼80 μsec) rotamak experiment are presented [Phys. Rev. Lett. 44, 1676 (1980)]. In particular, the magnetic structure of the stable, oblate, compact torus configuration that is produced in the experiment is described in detail.
The organized motion outside a turbulent wake
Authors: Antonia R. A. , Shah D. A. , Browne L. W. B.
Published: July 2002

Velocity fluctuations are measured in both the intermittent and irrotational regions outside the turbulent/nonturbulent interface of a self-preserving wake. In the outer part of the intermittent region, there is a tendency for all the predictions of the theory of Phillips [Proc. Cambridge Philos. Soc. 51, 220 (1955)] to be satisfied by the nonturbulent data. At larger distances from the interface, the level of the velocity fluctuations becomes comparable with the background turbulence but the organized motion induced by coherent structures within the wake can still be identified. The contribution of this motion to the normal stresses satisfies irrotationality and homogeneity and the amplitude of this motion decays in a manner consistent with Phillips’ theory.
Ion rotational velocity of a field-reversed configuration plasma measured by neutral beam probe spectroscopy
Authors: Ito Yoshifumi , Tanjyo Masayasu , Ohi Shoichi , Goto Seiichi , Ishimura Tsutomu
Published: July 2002

The ion rotational angular velocity Ω and the ion temperature Ti of a translated field-reversed configuration (FRC) plasma are measured using neutral beam probe spectroscopy. The value of Ω is ∼(1.0∼1.2)×Ω* at the onset time of the n=2 rotational instability, where Ω* is the ion diamagnetic frequency for a rigid-rotor equilibrium. The ion rotational direction is the same as the ion diamagnetic direction. The value of Ω is smaller than the angular frequency ωre of the n=2 instability, which can yield experimental evidence of the ion kinetic effects on the n=2 instability in the FRC plasma. When the octupole field is applied to the plasma in order to suppress the n=2 deformation, Ω is slightly reduced. The ion temperature Ti is ∼70 eV at the onset time of the n=2 instability.