bluuebunny/crossref_metadata_2025 huggingface dataset:
Excited-state energies and distortions of d transition metal tetraoxo complexes: A density functional study
Authors: Stückl A. C. , Daul C. A. , Güdel H. U.
Published: July 2002

Excitation energies and excited-state distortions of 9 tetrahedral transition metal tetraoxo complexes with a formal d0 electron configuration have been investigated using density functional theory. A symmetry based calculation scheme was applied for the 3T2, 3T1, 1T2, and 1T1 states deriving from the first excited electron configurations. The multiplet method was combined with a transition state approach for the calculation of the excitation energies. The results are compared with those from experiments, and with other calculations. The experimental ground-state properties are very well reproduced. The calculated absorption energies are slightly overestimated, but with an overall very good agreement. Potential-energy curves are calculated for both the ground and first excited states. The experimentally determined expansion of the excited state as well as the reduction in the vibrational frequencies are reproduced by the calculation. The bonding in this series of complexes is characterized by their strong capability of electron redistribution. As a consequence, the formal charge at the metal center of 7+ in MnO4− is reduced to about 2+. The negative charge effectively transferred from the oxygens to the metal in the formal LMCT ligand-to-metal charge transfer excitation process is 0.06 for MnO4−. Thus there is not much physical meaning in the label LMCT.
A nondiagonal, renormalized extension of partial third-order quasiparticle theory: Comparisons for closed-shell ionization energies
Authors: Ortiz J. V.
Published: July 2002

Valence ionization energies of a set closed-shell molecules calculated in a nondiagonal, renormalized approximation of the electron propagator have an average absolute error of 0.17 eV. This procedure extends the partial third order, quasiparticle approximation of J. Chem. Phys. 104, 7599 (1996) that has proven successful in many applications. Elements of the self-energy matrix include all second-order and many higher-order terms. Because of its fifth power dependence on basis set size and its independence from electron repulsion integrals with four virtual orbital indices, this method has considerable promise for large molecules. Formal and computational comparisons with renormalized electron propagator techniques that are complete through third-order illustrate the advantages of this procedure.
Magnetic circular dichroism study of CdSe quantum dots
Authors: Kuno M. , Nirmal M. , Bawendi M. G. , Efros Alexander , Rosen Mervine
Published: July 2002

We study the magnetic circular dichroism (MCD) of exciton states near the band edge of CdSe nanocrystallites (quantum dots). The experiment probes the difference between left and right circularly polarized transitions in the presence of an external magnetic field. Analysis of the MCD signal determines the sign and magnitude of the exciton g-factor which is shown to be highly sensitive to the energy band parameters used in the effective mass approximation. The observation of theoretically predicted changes in the sign of the exciton g-factor between the first two transitions is in agreement with recent theory describing the presence of fine structure underlying the optical transitions of CdSe nanocrystallites.
Two-stage capillary condensation in pores with structured walls: A nonlocal density functional study
Authors: Röcken Petra , Somoza Andres , Tarazona Pedro , Findenegg Gerhard
Published: July 2002

We present phase diagrams for capillary condensation in chemically structured slit pores characterized by two first-order transitions from the confined “gas” over “liquid bridges” to “liquid.” The split adsorption is produced by a complex periodic wall potential in one of the lateral directions that mimics inhomogeneities in real materials. After the previous condensation of liquid drops at the most attractive adsorption sites these may combine to form liquid bridges between opposite walls, separated between them by “gas gaps.” Nonlocal density functional theory is employed to investigate this stepwise mechanism and the stability of the liquid bridges phase in function of the thermodynamic conditions and the pore structure, especially the ratio of the two typical lengths, the corrugation period λ and the pore width H. Macroscopic predictions for the subcritical phase equilibria and the critical limit complete the study. The calculations confirm our previous results [P. Röcken and P. Tarazona, J. Chem. Phys. 105, 2034 (1996)] for an Ising lattice-gas model solved in the mean-field approximation.
Vapor–liquid equilibria of linear and branched alkanes from perturbation theory
Authors: MacDowell L. G. , Vega C.
Published: July 2002

The vapor–liquid equilibrium properties of linear and branched alkanes with up to eight carbon atoms have been determined by means of a simple perturbation theory. An accurate equation of state for the reference system is combined with a mean field treatment of the perturbation term, along with a reasonable set of potential parameters. Experimental trends of the critical properties of alkanes are described qualitatively by the theory. In particular, the maximum in the critical pressure and density of linear alkanes as a function of the number of carbon atoms is reproduced and explained on a simple basis. The effect of branching on the critical properties is considered and it is found that the decrease in the critical temperature with branching is correctly predicted. With a few exceptions for some substances, other general trends in critical pressure and density are predicted and explained. The effect of branching on the principle of corresponding states is also studied, in particular on the coexistence densities and vapor pressures. It is found that branching reduces the slope of the vapor pressure curve and makes the coexistence curve narrower when these magnitudes are represented in a corresponding states plot. It is shown that a simple mean field theory is able to describe qualitatively the variation in the critical properties of linear and branched alkanes.
The fitting of potential energy surfaces using neural networks: Application to the study of vibrational levels of H3+
Authors: Prudente Frederico V. , Acioli Paulo H. , Neto J. J. Soares
Published: July 2002

A back-propagation neural network is utilized to fit the potential energy surfaces of the H3+ ion, using the ab initio data points of Dykstra and Swope, and the Meyer, Botschwina, and Burton ab initio data points. We used the standard back-propagation formulation and have also proposed a symmetric formulation to account for the symmetry of the H3+ molecule. To test the quality of the fits we computed the vibrational levels using the correlation function quantum Monte Carlo method. We have compared our results with the available experimental results and with results obtained using other potential energy surfaces. The vibrational levels are in very good agreement with the experiment and the back-propagation fitting is of the same quality of the available potential energy surfaces.
Rotation–vibration interactions in (HF)2. II. Rotation–vibration interactions in low-lying vibrational states
Authors: Wu Xudong T. , Hayes Edward F. , McCoy Anne B.
Published: July 2002

Results of a six-dimensional treatment of the rotation–vibration Hamiltonian for (HF)2 are presented. Energies of 40(J+1) states for J⩽4 are reported. These energies and the corresponding wave functions are used to analyze rotation–vibration interactions in (HF)2. Over the range of energies probed in this study, Coriolis couplings are found to be relatively unimportant and for 94% of the states the wave functions and energies can be approximated by the solutions to a Hamiltonian in which the Coriolis coupling terms are neglected. Rotation–vibration interactions are investigated in greater detail for the ground state and for states with one and two quanta of excitation in the intermolecular stretching vibration ν4. Specifically, we study the K and n4 dependencies of the tunneling splitting and the effective rotational constant that corresponds to rotation about the intermolecular axis. Based on an analysis of the wave functions and the potential, we find that the observed trends can be attributed to the fact that (HF)2 behaves like a quasilinear molecule whose large amplitude bending motions lead to significant wave amplitude in linear configurations, even in the vibrational ground state.
Molecular dynamics study of Sn-1 and Sn-2 chain conformations in dipalmitoylphosphatidylcholine membranes
Authors: Smondyrev A. M. , Berkowitz M. L.
Published: July 2002

We have used SCC order parameter to characterize conformations of the dipalmitoylphospatidylcholine (DPPC) hydrocarbon chains. A marked difference between the structures of Sn-1 and Sn-2 chains become evident by examining the SCC order parameter profile. For Sn-1 chain we observed “odd–even” effect which was recently found in experimental studies of DPPC membrane. We argue that different behavior of two chains might be due to a different positioning of ester groups in Sn-1 and Sn-2 chains relative to the surface of the membrane. We also tested the recursion relation between the SCD and SCC order parameters. Knowledge of SCC order parameter leads to the determination of the hydrocarbon chain lengths as was recently shown by Douliez et al. [J. Phys. Chem. 100, 18450 (1996)]. Our simulation allows us to compare hydrocarbon chain lengths determined from the SCC order parameter profile and measured directly. We also tested an alternative method to determine hydrocarbon chain length as a function of the average order parameter 〈|SCD|〉. Our results are in good agreement with experimentally observed values for the chain lengths. They are also complimentary to the experimental information and are helpful in validating assumptions and models used to extract data in experiments. At the same time new experimental data can help to refine force fields used in computer simulations and serve as a further test of their quality.
Solvation of clyclopentadienyl and substituted clyclopentadienyl radicals in small clusters. III. Pre-reactive clusters
Authors: Fernandez J. A. , Yao J. , Bernstein E. R.
Published: July 2002

The hydrogen abstraction reaction between cyclopentadienyl radicals [Xcpd, X=H, CH3(m), F, CN] and substituted methanes (CH4, C2H6, CH3CH2OH, CH3Cl, CH2F2, CHF3, and CH3OH) is studied for the isolated one-to-one van der Waals clusters created in a supersonic expansion. Three different types of fluorescence excitation spectra are characterized for these cluster systems: (1) sharp spectra are observed for some clusters, suggesting no cluster chemistry for either the ground or excited electronic states of Xcpd—CNcpd/CH3Cl, CH2F2, CHF3, CH3OH; (2) broad spectra are observed suggesting initiation of cluster chemistry on the excited state cluster potential energy surface—CNcpd–CH4, Fcpd–CHF2Cl, CHF3; and (3) only a greatly reduced bare radical signal is observed, but no cluster emission can be detected—cpd, mcpd/all substituted methanes, Fcpd–CH2F2, CH3Cl, CH3CH2OH, CH3OH, C2H6, and CNcpd/C2H6, CH3CH2OH. These results, taken together, suggest that the Xcpd radicals undergo an excited electronic state electrophilic hydrogen abstraction reaction with substituted methanes. The radical reactivities are in the order mcpd∼cpd>Fcpd>CNcpd and the substituted methane reactivities are in the order C2H6>C2H5OH>CH4>CH3Cl∼CH3OH>CH2F2>CHF2Cl>CHF3. All Xcpd radicals show intense, sharp spectra with CF4. This indication of an excited state Xcpd radical hydrogen abstraction reaction with substituted methanes is further explored by ab initio quantum chemistry techniques at the (7×7) CASSCF/6-31G (complete active space self-consistent field) and cc-pVDZ levels for cpd–CH4. Calculations confirm the idea that the ground state cluster has a reaction barrier (approximately +170 kJ/mol) and a positive free energy of reaction (∼80 kJ/mol). The excited cpd radical, however, can react with CH4 along a barrierless path to generate substantial hot ground product states (C5H6 and CH3). Experimental data are consistent with an Xcpd–C2H4 addition reaction, as well.
Structural effects of the solvent composition in colloidal liquids
Authors: Quesada-Pérez M. , Callejas-Fernández J. , Hidalgo-Álvarez R.
Published: July 2002

This paper is concerned with the microstructure observed in colloidal dispersions of charged polymeric particles and their interaction potential at very low ionic strength. Both aspects are probed with the aid of new experimental data for nonaqueous media. The structure factor of ordered dispersions (with methanol–water and ethanol–water solvent mixtures) was determined using static light scattering. A different behavior (in the studied range of molar fraction) depending on the alcohol type is found. These results are analyzed assuming a Yukawa potential and applying integral equation theories (the Ornstein–Zernike equation and the HNC closure). The obtained effective charge is almost constant for methanol–water mixtures, whereas a decrease with the alcohol molar fraction is observed for ethanol–water. In order to account for these effects, a charge renormalization procedure is applied and discussed. The surface charge turns out to be an unsuitable input parameter for such an approach.
Transport coefficients of electrolyte solutions from Smart Brownian dynamics simulations
Authors: Jardat M. , Bernard O. , Turq P. , Kneller G. R.
Published: July 2002

We present results of Brownian dynamics simulations of aqueous 1-1 electrolyte solutions in the 1-molar concentration range. The electrical conductivity and the self-diffusion coefficients obtained from the simulations are compared to experimental data. The interaction potential between the ions is modeled by pairwise repulsive 1/rn soft-core interactions (n=9 or n=12) and Coulomb forces. We take into account hydrodynamic interactions and integrate the stochastic equations of motion with large time steps of about 100 femtoseconds, combined with an acceptance criterion known from the Smart Monte Carlo method. In this way, details of the dynamics of particles in close contact are not considered and the short-ranged repulsive forces act effectively as constraint forces preventing overlap configurations. The lengths of the performed simulations (about 10 nanoseconds) and the number of ions (216) allow to obtain single particle as well as collective transport coefficients with sufficient precision. For this purpose we use Kubo expressions which can be applied on the mesoscopic time scale of Brownian dynamics simulations. It is shown that hydrodynamic interactions must be taken into account to obtain agreement with the experimental data. They lower the electrical conductivity, as expected, but increase the self-diffusion coefficients, confirming a recent finding for colloids.
Arrhenius-type temperature dependence of the segmental relaxation below Tg
Authors: O’Connell Paul A. , McKenna Gregory B.
Published: July 2002

In a recent paper DiMarzio and Yang [J. Res. Natl. Inst. Stand. Technol. 102, 135 (1997)] predicted that transport properties such as viscosity and diffusion coefficient do not follow the typical Williams, Landel, and Ferry (WLF) [J. Am. Chem. Soc. 77, 3701 (1955)] or Vogel–Fulcher-type of temperature dependence as the glass transition is approached. Rather, a transition to an Arrhenius-type of temperature dependence is predicted. Here we describe long term aging experiments that explore the temperature dependence of the viscoelastic response of polycarbonate in the vicinity of the glass transition. Aging the material for long times below the nominal glass transition temperature, assures that equilibrium is attained and we can directly test the DiMarzio–Yang prediction. In tests in which glassy samples of polycarbonate were aged into equilibrium at temperatures up to 17 °C below the conventionally measured glass transition temperature, we find that the results are consistent with a transition from Vogel–Fulcher or WLF-type behavior to Arrhenius-type behavior. Our results are discussed within the context of other measurements on nonpolymeric glasses and other recent results on polymeric glass formers.
Interaction-site-model description of collective excitations in liquid water. I: Theoretical study
Authors: Chong Song-Ho , Hirata Fumio
Published: July 2002

Collective excitations in liquid water are investigated using the recently developed theory for dynamics of molecular liquids which is based on the interaction-site model for polyatomic fluids, the projection-operator formalism of Zwanzig and Mori, and the simple approximation scheme for memory functions. It is shown that all the essential features of collective excitations in water, reported previously by neutron-scattering experiments, molecular dynamics simulations and dielectric theories, are well reproduced by the present theory.
Relaxation phenomena and development of structure in a physically crosslinked nonionic microemulsion studied by photon correlation spectroscopy and small angle x-ray scattering
Authors: Schwab Mario , Stühn Bernd
Published: July 2002

We performed small angle x-ray scattering (SAXS), photon correlation spectroscopy (PCS), and oscillatory frequency sweep experiments to investigate the static and dynamic properties of a transient network. The system under investigation is an oil in water microemulsion containing the nonionic surfactant C12E5 (penta ethylene glycol mono dodecyl ether). The microemulsion consists of micelles (spherical oil droplets covered by the surfactant) with radius Rm≈10 nm, which are dispersed in water. Adding a triblock copolymer with a hydrophilic midblock and hydrophobic end blocks (stearate-poly ethylene oxide-stearate) to the microemulsion leads to the interconnection of the micelles and thus to the formation of a transient network. We describe the structural behavior under addition of the triblock copolymer with a hard sphere model based on the Percus–Yevick pair correlation function. In the dynamic light scattering experiment we observe three relaxational processes. The fast and the slow relaxation time vary with scattering vector q as τi=(Diq2)−1 whereas the intermediate relaxation process is independent of the scattering vector q. The relaxation time of this local process compares well with the terminal relaxation time measured in an oscillatory shear experiment. The nature of this intermediate process is therefore attributed to the characteristic lifetime of a network junction point.
Temperature-dependent shear viscosity coefficient of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX): A molecular dynamics simulation study
Authors: Bedrov Dmitry , Smith Grant D. , Sewell Thomas D.
Published: July 2002

Equilibrium molecular dynamics methods were used in conjunction with linear response theory and a recently published potential-energy surface [J. Phys. Chem. B 103, 3570 (1999)] to compute the liquid shear viscosity and self-diffusion coefficient of the high explosive HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) over the temperature domain 550–800 K. Predicted values of the shear viscosity range from 0.0055 Pa *s at the highest temperature studied up to 0.45 Pa *s for temperatures near the melting point. The results, which represent the first publication of the shear viscosity of HMX, are found to be described by an Arrhenius rate law over the entire temperature domain studied. The apparent activation energy for the shear viscosity is found to scale with the heat of vaporization in a fashion consistent with those for a wide variety of simple nonmetallic liquids. The self-diffusion coefficient, which requires significantly shorter trajectories than the shear viscosity for accurate calculation, also exhibits an Arrhenius temperature dependence over the simulated temperature domain. This has potentially important implications for predictions of the shear viscosity at temperatures near the melting point.
The static, cylindrically symmetric strings in general relativity with cosmological constant
Authors: Linet B.
Published: July 2002

The static, cylindrically symmetric solutions to Einstein’s equations with a cosmological term describing cosmic strings are determined. The discussion depends on the sign of the cosmological constant.
Transition of a Kantowski–Sachs cosmological model into an inflationary era
Authors: Gro/n O/.
Published: July 2002

An empty Kantowski–Sachs universe model with a cosmological constant is found. It emerges from a pancake singularity at t=0. If the cosmological constant is of the same magnitude as that induced by a GUT vacuum phase transition, this universe enters an exponentially expanding era at the GUT time tG=1,0⋅10−35 sec. The universe then isotropizes rapidly, and the shear diminishes by a factor of 10−56 if this inflationary era lasts for t1=1,3⋅10−33 sec, as is the case in Guth’s inflationary universe model.
Existence and uniqueness properties for the one-dimensional magnetotellurics inversion problem
Authors: MacBain John A. , Bednar J. Bee
Published: July 2002

The one-dimensional magnetotelluric (MT) inversion problem is well known to be ill posed and nonlinear. This paper seeks an understanding of the mappings underlying the nonlinear relationships. These properties are used to study the validity of some exploration aspects of the problem that are essential for the practical use of MT as an exploration tool. This study has two major segments—results in response space and results in geologic space. In response space, the existence of optimal admittance curves has been proven. In the case of continuous data, uniqueness has been established. For discrete data, a relationship between alternative optimal solutions has been derived. In geologic space, the results are extremely significant to MT’s applicability to exploration. A class of conductivity functions Y, which contains all possible natural geological conditions, has been used as a framework for the study. Over this class Y, the one-dimensional magnetotellurics problem has been proven to be uniquely invertible from the admittance curves. This precludes the possibility of two different geologic models yielding the same complete data. As a result, the path is now clear to generate a description of a unimodal statistical distribution of feasible inversions to the real-world exploration problem with finitely sampled noisy data.
Power law singularities in the scale covariant theory
Authors: Beesham A.
Published: July 2002

Power asymptote singularities are discussed in the scale covariant theory of gravitation. Some general results are derived. Special attention is paid to the Friedmann [A. Friedmann, Z. Phys. 10, 377 (1922)] and Kasner [E. Kasner, Am. J. Math. 43, 217 (1921)] models. A wider class of behavior is exhibited and it is shown that the results obtained constitute a generalization of the corresponding general relativistic results.
Geometric Lagrangian approach to first-order systems and applications
Authors: Cariñena José F. , López Carlos , Rañada Manuel F.
Published: July 2002

The geometric theory of presymplectic systems is developed to study both the Lagrangian and Hamiltonian formulations of a system described by a Lagrangian linear in the velocities. The results are used to study some related problems for second-order differential equations and regular Lagrangians.
Gravitational analogs of the Aharonov–Bohm effect
Authors: Bezerra V. B.
Published: July 2002

A quantum scalar particle is considered in the following background gravitational fields due to (a) a tubular matter source with axial interior magnetic field and vanishing exterior magnetic field; (b) slowly moving mass currents (weak approximation); and (c) a spinning cosmic string. It is shown that in the flat space-time around these sources, the energy spectrum and wave function of the particle depend on the amount of matter and magnetic field (tubular matter source case), on the velocity of the moving mass currents, and on the angular momentum in the spinning cosmic string case. These represent gravitational analogs of the Aharonov–Bohm effect in electrodynamics and are due to global (topological) features of the background space-times under consideration.
On the structure of quantum phase space
Authors: Aldrovandi R. , Galetti D.
Published: July 2002

The space of labels characterizing the elements of Schwinger’s basis for unitary quantum operators is endowed with a structure of symplectic type. This structure is embodied in a certain algebraic cocycle, whose main features are inherited by the symplectic form of classical phase space. In consequence, the label space may be taken as the quantum phase space: It plays, in the quantum case, the same role played by phase space in classical mechanics, some differences coming inevitably from its nonlinear character.
Nontrivial soliton scattering in an integrable chiral model in (2+1)-dimensions
Authors: Sutcliffe P. M.
Published: July 2002

Soliton solutions of an integrable chiral model in (2+1)-dimensions are studied. Through the solution of a ‘‘Riemann problem with zeros’’ solitons of this model have already been found [R. S. Ward, J. Math. Phys. 29, 386 (1988)] which scatter in a trivial manner. By exploiting a connection with the O(3) σ model, it is shown that the model also has solitons that are not contained in the above construction, and whose scattering properties are highly nontrivial. Soliton scattering is also discussed for a σ model which interpolates between this integrable model and the SU(2) chiral σ model.
Kantowski–Sachs metrics with source: A conformally invariant scalar field
Authors: Xanthopoulos Basilis C. , Zannias Thomas
Published: July 2002

Solutions of the coupled Einstein conformally invariant massless scalar field equations are derived under the assumption that the metric admits a four-parameter group of isometries with spacelike generators, where further, the three-parameter subgroup of isometries acts multiply transitive on two-dimensional surfaces. The general solution of the system is obtained and some properties concerning the singularity structure are briefly discussed. Results for all three cases are presented, i.e., for the case where the three-dimensional group of isometries acts on two-dimensional orbits of positive, negative, or zero curvature. The first two classes belong to the Kantowski–Sachs class of metrics, while the third one is of Bianchi type I with additional rotational symmetry.
The basis of nonlocal curvature invariants in quantum gravity theory. Third order
Authors: Barvinsky A. O. , Gusev Yu. V. , Vilkovisky G. A. , Zhytnikov V. V.
Published: July 2002

A complete basis of nonlocal invariants in quantum gravity theory is built to third order in space–time curvature and matter-field strengths. The nonlocal identities are obtained which reduce this basis for manifolds with dimensionality 2ω<6. The present results are used in heat-kernel theory, theory of gauge fields and serve as a basis for the model-independent approach to quantum gravity and, in particular, for the study of nonlocal vacuum effects in the gravitational collapse problem.
Quantum deformations of nonsemisimple algebras: The example of D=4 inhomogeneous rotations
Authors: Lukierski Jerzy , Ruegg Henri , Nowicki Anatol
Published: July 2002

A general class of deformations of the complexified D=4 Poincaré algebra O(3,1;C)⊇T4(C) is considered with a classical (undeformed) subalgebra O(3;C)⊇T4(C) and deformed relations preserving the O(3;C) tensor structure. We distinguish the class of quantum deformations—the complex noncocommutative Hopf algebras—which depend on one complex mass parameter κ. Further, we consider the real Hopf algebras, obtained by imposing the reality conditions. For any choice of real metric [O(4), O(3,1), or O(2,2)] the parameter κ becomes real. All (e.g., Minkowski as well as Euclidean) real quantum algebras with standard reality condition contain as nonlinearities the hyperbolic functions of the energy operator and can be interpreted as introducing an imaginary time lattice. The symmetries of the models with real time lattice are described by a real quantum algebra with nonstandard reality conditions and trigonometric nonlinearities.
Five-dimensional axisymmetric stationary solutions as harmonic maps
Authors: Matos Tonatiuh
Published: July 2002

The complete scheme of the application of one- and two-dimensional subspaces and the subgroups method to five-dimensional gravity with a G3 group of motion are presented here in space–time and in potential space formalisms. From this method one obtains the Kramer, Belinsky–Ruffini, Dobiasch–Maison, Clément, Gross–Perry–Sorkin solutions, etc., as special cases.
Geometry of canonical correlation on the state space of a quantum system
Authors: Petz Dénes
Published: July 2002

A Riemannian metric is defined on the state space of a finite quantum system by the canonical correlation (or Kubo–Mori/Bogoliubov scalar product). This metric is infinitesimally induced by the (nonsymmetric) relative entropy functional or the von Neumann entropy of density matrices. Hence its geometry expresses maximal uncertainty. It is proven that the metric is monotone under stochastic mappings, however, an example shows that it is not the only such Riemannian metric. This fact is remarkable because in the probabilistic case, the Markovian monotonicity property characterizes the Fisher information metric. The essential difference appears in the curvatures of a classical state space and a quantum one. A conjecture is made that the scalar curvature is monotone with respect to the ‘‘more mixed’’ (statistical) partial order of density matrices. Furthermore, an information inequality resembling the Cramér–Rao inequality of classical statistics is established. The inequality provides a lower bound for the canonical correlation matrix (of an unbiased observable) and it is saturated when a (partial) observation level and the corresponding family of coarse-grained states are considered.
Singularity analysis and localized coherent structures in (2+1)-dimensional generalized Korteweg–de Vries equations
Authors: Radha R. , Lakshmanan M.
Published: July 2002

In this article, a singularity structure analysis of a (2+1)-dimensional generalized Korteweg–de Vries equation studied originally by Boiti et al., admitting a weak Lax pair, is carried out and it is proven that the system satisfies the Painlevé property. Its bilinear form is constructed in a natural way from the P analysis and then it is used to generate ‘‘multidromion’’ solutions (exponentially decaying solutions in all directions). The same analysis can be extended to construct the multidromion solutions of the generalized Nizhnik–Novikov–Veselov (NNV) equation from which the NNV equation follows as a special case.
Asymptotics of radial wave equations
Authors: Morehead James J.
Published: July 2002

The Langer modification is an improvement in the WKB analysis of the radial Schrödinger equation. We derive a generalization of the Langer modification to any radial operator. For differential operators we write the modified classical symbols explicitly and show that the WKB wavefunctions with the modification have the exact limiting behavior for small radius. Unlike in the Schrödinger case, generally the modified radial analysis is not equivalent to the WKB analysis of the full problem before reduction by the spherical symmetry.
Flat wormholes from cosmic strings
Authors: Clément Gérard
Published: July 2002

We describe the analytical extension of certain cylindrical multi-cosmic string metrics to wormhole spacetimes with only one region at spatial infinity, and investigate in detail the geometry of asymptotically Minkowskian wormhole spacetimes generated by one or two cosmic strings. We find that such wormholes tend to lengthen rather than shorten space travel. Possible signatures of these wormholes are briefly discussed.
Relation between the Kadometsev–Petviashvili equation and the confocal involutive system
Authors: Cao Cewen , Wu Yongtang , Geng Xianguo
Published: July 2002

The special quasiperiodic solution of the (2+1)-dimensional Kadometsev–Petviashvili equation is separated into three systems of ordinary differential equations, which are the second, third, and fourth members in the well-known confocal involutive hierarchy associated with the nonlinearized Zakharov–Shabat eigenvalue problem. The explicit theta function solution of the Kadometsev–Petviashvili equation is obtained with the help of this separation technique. A generating function approach is introduced to prove the involutivity and the functional independence of the conserved integrals which are essential for the Liouville integrability.
Matrix representation of octonions and generalizations
Authors: Daboul Jamil , Delbourgo Robert
Published: July 2002

We define a special matrix multiplication among a special subset of 2N×2N matrices, and study the resulting (nonassociative) algebras and their subalgebras. We derive the conditions under which these algebras become alternative nonassociative, and when they become associative. In particular, these algebras yield special matrix representations of octonions and complex numbers; they naturally lead to the Cayley–Dickson doubling process. Our matrix representation of octonions also yields elegant insights into Dirac’s equation for a free particle. A few other results and remarks arise as byproducts.
Behavior of the layered crystals TlInS2 and TlGaSe2 near phase transitions in a static electric field
Authors: Allakhverdiev K. R. , Akhmed-zade N. D. , Mamedov T. G. , Mamedov T. S. , Seidov Mir-Gasan Yu.
Published: July 2002

The effect of an orienting electric field on the anomalies of the temperature dependence of the dielectric constant ε of the crystals TlInS2 and TlGaSe2 and of the pyroelectric current i in TlInS2 near phase transitions is investigated. It is found that the ε(T) profile of both crystals undergoes the same transformation at the point of the phase transition to the incommensurate phase under the influence of a static electric field applied in the plane of the layer. It is established that the maximum of ε(T) in TlGaSe2 and of i(T) in TlInS2 at the point of the phase transition to the commensurate polar phase is shifted in a certain range of orienting electric fields and that the sign of the temperature shift depends on the value of the external electric field. An interpretation is offered for the experimental results.
Temperature gradients and drag effects produced by convection of interfacial internal energy around bubbles
Authors: Torres Francisco E. , Herbolzheimer Eric
Published: July 2002

When a bubble translates, the resulting motion of the interface causes interfacial energy to be convected from the front to the back of the bubble. In the front regions, this convection causes the interface to cool until conduction from the bulk can balance the removal of interfacial energy, while analogous heating occurs at the rear locations; therefore, the motion induces a temperature gradient around the bubble. It is predicted that these microscale effects can add to yield macroscopic temperature gradients and energy fluxes in swarms of moving bubbles. The extent to which the temperature gradient across a single bubble changes the migration velocity by inducing interfacial tension gradients is also considered; the calculations reveal this effect to be significant for low viscosity liquids such as liquid CO2 and most liquids, including water, at elevated temperatures.
Experimental and numerical study of electromagnetic effects on resonance cones
Authors: Kortshagen U. , Piel A.
Published: July 2002

The resonance cone (rc) diagnostic is usually based on kinetic theory within the electrostatic approximation. Numerical and experimental results are presented, which reveal the influence of the neglected electromagnetic terms in the dispersion relation. In the near field a shift of the rc toward smaller angles occurs, which may be important at high electron densities and temperatures. In the far field the phase variation inside the cone turns out to be useful as a new electron density diagnostic in the regime of high densities, where the rc diagnostic was previously not applicable.
Saturation of a single mode driven by an energetic injected beam. I. Plasma wave problem
Authors: Berk H. L. , Breizman B. N.
Published: July 2002

A formalism is established for calculating the saturation level of a discrete mode that is destabilized by the distribution function formed by a high-energy injected beam. The electrostatic plasma wave interaction is studied here for two problems. In one the distribution function is formed by injection of a source with a velocity spread and a steady-state bump-on-tail instability is established with only particle annihilation taken into account. In the second problem particle drag as well as particle annihilation is accounted for. In both problems the self-consistent distribution function in the presence of a finite amplitude wave needs to be calculated. By calculating the power transfer between particles and a finite amplitude wave, the saturation level of the discrete mode can be predicted. The drag problem with annihilation has the interesting feature that in steady state holes in phase space are formed for a large enough amplitude wave and the power transferred from particles to waves can be greatly enhanced as a result of the drag force on the holes.
Electromagnetic effect on the toroidal electron temperature gradient mode
Authors: Kim J. Y. , Horton W.
Published: July 2002

The electromagnetic effect on the toroidal electron temperature gradient mode is investigated using local kinetic and fluid theories. It is found that the electromagnetic effect on the toroidal mode differs from that for the slab mode. For the slab mode, the electromagnetic effect gives a strong stabilization, while for the toroidal mode there is a destabilization. In particular, the modes with perpendicular wavelength comparable to the electron skin depth are destabilized by the finite electron inertia. It is shown that this contrasting result for the toroidal mode occurs mainly because the stabilizing effect of the parallel transit drift is significantly reduced by the finite electromagnetic term.
Collisional plasma sheath model
Authors: Sheridan T. E. , Goree J.
Published: July 2002

The effects of ion collisionality on the plasma sheath are revealed by a two-fluid model. In contrast to previous work, the ion–neutral collision cross section is modeled using a power law dependence on ion energy. Exact numerical solutions of the model are used to determine the collisional dependence of the sheath width and the ion impact energy at the wall. Approximate analytical solutions appropriate for the collisionless and collisionally dominated regimes are derived. These approximate solutions are used to find the amount of collisionality at the center of the transition regime separating the collisionless and collisional regimes. For the constant ion mean-free-path case, the center of the transition regime for the sheath width is at a sheath width of five mean-free paths. The center of the transition regime for the ion impact energy is at a sheath width of about one-half of a mean-free path.
Turbulent transport in the Madison Symmetric Torus reversed-field pinch
Authors: Rempel T. D. , Almagri A. F. , Assadi S. , Den Hartog D. J. , Hokin S. A. , Prager S. C. , Sarff J. S. , Shen W. , Sidikman K. L. , Spragins C. W. , Sprott J. C. , Stoneking M. R. , Zita E. J.
Published: July 2002

Measurements of edge turbulence and the associated transport are ongoing in the Madison Symmetric Torus (MST) reversed-field pinch [Fusion Technol. 19, 131 (1991)] using magnetic and electrostatic probes. Magnetic fluctuations are dominated by m=1 and n ∼2R/a, tearing modes. Particle losses induced by magnetic field fluctuations have been found to be ambipolar (〈J̃∥ B̃r〉/B0=0). Electrostatic fluctuations are broadband and turbulent, with mode widths Δm∼3–7 and Δn∼70–150. Particle, parallel current, and energy transport arising from coherent motion with the fluctuating Ẽ×B drift have been measured. Particle transport via this channel is comparable to the total particle loss from MST. Energy transport (from 〈P̃Ẽφ 〉/B0) due to electrostatic fluctuations is relatively small, and parallel current transport (from 〈J̃∥ Ẽφ〉/B0) may be small as well.
Unified fluid/kinetic description of plasma microinstabilities. Part I: Basic equations in a sheared slab geometry
Authors: Chang Zuoyang , Callen J. D.
Published: July 2002

Unified fluid/kinetic equations for the plasma perturbed density (ñ), parallel flow velocity (ũ∥) and temperature (T̃) are developed in a sheared slab geometry by calculating the fluid moment closure relations kinetically. At first, a set of (unclosed) nonlinear perturbed fluid equations for ñ, ũ∥ and T̃ is developed using a drift ordering analysis and a new gyroviscous force (△⋅Πg). Thereafter, to develop linear closure relations for b⋅∇⋅Π̃∥ and q̃∥, a drift-kinetic version of a new Chapman–Enskog-like (CEL) equation is developed and solved by using a moment approach and a physically realistic collision operator (Lorentz scattering operator plus the momentum restoring terms). The resultant closure relations for b⋅△⋅Π̃∥ and q̃∥ unify the fluid and kinetic approaches. In the collisional fluid limit the equations reduce to the well-known Braginskii equations. In the adiabatic limit they reproduce the usual kinetic results, including Landau damping. It is shown that this new CEL approach is more compatible with a fluidlike description of plasmas than the usual drift/gyrokinetic approach. Remarkably simplified forms of the closure relations are presented. The results are compared with other Landau damping models and shown to be more accurate, complete, and physically realistic. Applications of this set of equations to various microinstabilities in tokamak plasmas are presented in a separate paper (Part II) [Phys. Fluids B 4, 1182 (1992)].
Nonlinear gyrofluid description of turbulent magnetized plasmas
Authors: Brizard Alain
Published: July 2002

Nonlinear gyrofluid equations are obtained from the gyrocenter-fluid moments of the nonlinear gyrokinetic Vlasov equation, which describes an equilibrium magnetized nonuniform plasma perturbed by electromagnetic field fluctuations (δφ,δA∥,δB∥), whose space-time scales satisfy the gyrokinetic ordering: ω≪Ωi, ‖k∥‖/k⊥≪1, and ε⊥≡(k⊥ρi)2≂𝒪(1). These low-frequency (reduced) fluid equations contain terms of arbitrary order in ε⊥ and take into account the nonuniformity in the equilibrium density and temperature of the ion and electron species, as well as the nonuniformity in the equilibrium magnetic field. From the gyrofluid equations, one can systematically derive nonlinear reduced fluid equations with finite-Larmor-radius (FLR) corrections, which contain linear and nonlinear terms of 𝒪(ε⊥), by expressing the gyrocenter-fluid moments appearing in the gyrofluid equations in terms of the particle-fluid moments, and then keeping terms up to 𝒪(ε⊥) in the ε⊥ expansion of the gyrofluid equations. By using gyrocenter-fluid moments, this new gyrofluid approach effectively bypasses the issue of the gyroviscous cancellations, while retaining all the important diamagnetic effects and the gyroviscous corrections. From the present FLR-corrected reduced fluid equations, the reduced Braginskii equations are recoverd for the ion and electron species (without collisional dissipation) and the ideal reduced magnetohydrodynamic (MHD) equations (in the absence of FLR effects).
Simple theory of a nonlinear diocotron mode
Authors: Fine K. S.
Published: July 2002

A simple perturbation theory of the frequencies and density distortions of the l=1 diocotron mode on pure electron plasma columns is presented. This mode is the dynamical state of an off-axis electron column which is orbiting around the containment axis at the E×B drift velocity. The theory predicts shifts in the orbit frequency and quadrupole distortions of the plasma surface, both varying as the offset squared, in good agreement with experiments. The results also apply to a two-dimensional vortex patch in an inviscid fluid with circular boundaries.
Kinetic theory of toroidicity-induced Alfvén eigenmodes
Authors: Mett R. R. , Mahajan S. M.
Published: July 2002

An analytic kinetic description of the toroidicity-induced Alfvén eigenmode (TAE) is presented. The theory includes electron parallel dynamics nonperturbatively, an effect that is found to strongly influence the character, and damping of the TAE−contrary to previous theoretical predictions. A parallel conductivity model that includes collisionless (Landau) damping on the passing electrons and collisional damping on both trapped and passing electrons is used. Together, these mechanisms damp the TAE more strongly than previously expected. This is because the TAE couples (or merges) with the kinetic Alfvén wave (KAW) within the gap region under conditions that depend on the gap size, the shear, the magnitude of the conductivity, and the mode numbers. The high damping could be relevant to recent experimental measurements of the TAE damping coefficient. In addition, the theory predicts a ‘‘kinetic’’ TAE, whose eigenfreqeuency lies just above the gap, whose existence depends on finite conductivity, and that is formed by the coupling of two KAW’s
Turbulence structures associated with the bursting event
Authors: Kim John
Published: July 2002

Turbulence structures in a wall-bounded shear layer during the bursting event detected by a conditional sampling technique are investigated using data obtained from large-eddy simulation of turbulent channel flow. Streamlines are constructed from the ensemble-averaged velocity field to illustrate the flow patterns associated with the bursting event. They exhibit the ‘‘splatting’’ motions during the sweep event and the existence of a pair of counterrotating streamwise vortices during the ejection process.
Electromagnetic hot plasma modes in a dense plasma near the second harmonic electron-cyclotron frequency
Authors: Matsuda Kyoko
Published: July 2002

Obliquely propagating electromagnetic hot plasma modes near the second harmonic electron-cyclotron frequency have been studied for a plasma of density around the cutoff density of the ordinary mode using the nonrelativistic dispersion equation. There are several branches of new electromagnetic hot plasma modes in the frequency region of 5% to 20% less than the second harmonic frequency. They are quite similar to the new modes near the fundamental frequency reported recently. There are two branches of the extraordinary mode. At the limit of small perpendicular wavenumber, one of the branches becomes a right wave of the hot plasma dispersion, and the other becomes either a left wave or a plasma wave.