bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser-induced fluorescence spectroscopy of the C4H and C4D radicals in a supersonic jet
Authors: Hoshina Kennosuke , Kohguchi Hiroshi , Ohshima Yasuhiro , Endo Yasuki
Published: July 2002

Laser-induced fluorescence (LIF) spectra of the C4H radical and its isotopomer C4D have been observed in a supersonic free jet expansion for the first time. The jet cooled free radicals have been generated in an electric discharge of 0.5% C2H2 or C2D2 in Ar using a pulsed discharge nozzle (PDN). Twenty and eighteen vibronic bands of C4H and C4D, respectively, have been observed in the 24 000–25 000 cm−1 region. Most of the observed bands have been assigned as either 2Π − 2Σ or two types of 2Σ − 2Σ Effective spin–orbit interaction constants were determined by analyses of the 2Π − 2Σ bands to be −14.7644(80) and −10.9926(35) cm−1 for C4H and C4D, respectively, leading to conclusion that the upper electronic state of the observed band system is B̃ 2Πi, in agreement with a recent ab initio calculation by Sobolewski and Adamowicz [J. Chem. Phys. 102, 394 (1995)]. Observation of two types of 2Σ − 2Σ bands, 2Σ+ − 2Σ+ and 2Σ(±) − 2Σ+ is explained by the difference of the magnitudes of Renner–Teller interactions for the bending vibrational modes involved. We were able to assign the ν5 (CCH bending) and ν6 (CCC bending) progressions of the B̃ 2Πi state, where the Renner–Teller interaction is large for ν5, and small for ν6. The vibrational frequencies and the Renner parameters were determined to be ω5=344 cm−1, ε5=−0.657, ω6=189.3 cm−1, and ε6=−0.0158 for C4H, and ω5=295 cm−1, ε5=−0.692, ω6=183.4 cm−1, and ε6=−0.0188 for C4D, respectively. Intensities of the symmetry forbidden 2Σ − 2Σ bands were larger than those of the symmetry allowed 2Π − 2Σ bands, suggesting a very small energy gap and strong vibronic mixing between the Ã 2Πi and X̃ 2Σ+ states. Fluorescence lifetime profiles exhibited fast decay (10–20 ns) followed by a very weak and slow decay (3–4 μs) component with complicated beat structures. The implication is that C4H in the B̃ 2Πi state has a fast relaxation path to nonradiative states through internal conversion, and therefore does not dissociate under near uv radiation at 400–417 nm.
Polyatomic molecular potential energy surfaces by interpolation in local internal coordinates
Authors: Thompson Keiran C. , Jordan Meredith J. T. , Collins Michael A.
Published: July 2002

We present a method for expressing a potential energy surface (PES) for polyatomic molecules as an interpolation of local Taylor expansions in internal coordinates. This approach extends and replaces an earlier method which was only directly applicable to molecules of no more than four atoms. In general, the local Taylor expansions are derived from ab initio quantum calculations. Here, the methodology is evaluated by comparison with an analytic surface for the reactions H+CH4⇌H2+CH3. Approximately 1000–1300 data points are required for an accurate 12-dimensional surface which describes both forward and backward reactions, at the energy studied.
Photoluminescence from nanosize gold clusters
Authors: Wilcoxon J. P. , Martin J. E. , Parsapour F. , Wiedenman B. , Kelley D. F.
Published: July 2002

We have observed visible light emission from nanosize gold clusters. Liquid chromatographic analysis of the metal clusters shows that relatively intense photoluminescence occurs only when the size of the metal nanocluster is sufficiently small (<5 nm). The emission is strongly Stokes shifted and is assigned to radiative recombination of Fermi level electrons and sp- or d-band holes. The electron and/or hole states are perturbed by surface states, as indicated by the dependence of the emission spectrum on the nature of the cluster surface. Finally, we found that large, nonemitting gold clusters can also be made luminescent by partial dissolution using KCN.
The calculation of free-energy differences by constrained molecular-dynamics simulations
Authors: den Otter W. K. , Briels W. J.
Published: July 2002

In this paper we set out to derive a relation between the constraint force and the derivative of the free energy for a system in which only the reaction coordinate is constrained. Our result differs from the expression by Mülders et al. [J. Chem. Phys. 104, 4869 (1996)] because we take into account the effect of the constraint on the sampled phase-space distribution. The method is illustrated with two prototypical numerical examples.
On the local and nonlocal components of solvation thermodynamics and their relation to solvation shell models
Authors: Matubayasi Nobuyuki , Gallicchio Emilio , Levy Ronald M.
Published: July 2002

A procedure for identifying the local and nonlocal components of excess partial molar quantities is presented. This procedure is based on an analysis of the excess thermodynamic quantities expressed as integrals of local estimators over the system volume. The local components can be described in terms of the solvation shell model and are independent of the condition of solute insertion. The nonlocal components are related to the asymptotic behavior of distribution functions at large distances from the solute and they give rise to the ensemble dependence of the thermodynamic quantities of solvation. It is shown that in the constant pressure process, by using natural choices for the local estimators, the nonlocal components of the excess partial molar energy, enthalpy, entropy, and volume are absent. The relationship between our analysis and a phenomenological model which expresses excess thermodynamic quantities in terms of the solute volume, surface area, and diameter is also considered and the validity of the local interpretation is discussed.
A molecular dynamics study of sub- and supercritical water using a polarizable potential model
Authors: Yoshii Noriyuki , Yoshie Hiromi , Miura Shinichi , Okazaki Susumu
Published: July 2002

A series of molecular dynamics calculations for water has been carried out along an isochore at 1 g/cm3 and an isotherm at 600 K in order to examine microscopic properties of water in the sub- and supercritical states. A polarizable potential model proposed by Dang (RPOL model) was employed to take into account the state dependence of intermolecular interaction. Along the isochore, fluid structure changes from tetrahedral icelike structure at room temperature to simple-liquidlike one at high temperatures. Orientational correlation between a tagged molecule and its neighbors is reduced substantially with increasing temperature, though hydrogen bonds between two molecules persist even at 600 K. As temperature increases, the number of the hydrogen bonds per molecule decreases monotonically from 3.2 at 280 K to 1.9 at 600 K. The activation barrier for diffusion at 600 K is about half as large as that at room temperature. A collective polarization relaxation loses collective character above the temperature where the structural change occurs. Along the isotherm, on the other hand, the long-ranged tail of radial distribution functions was observed near the critical density ρc. Ornstein-Zernike behavior, however, was not found owing to the present small system. The number of hydrogen bonds decreases almost linearly as a function of the density from 1.9 at 1 g/cm3 to 0 in the gas limit. However, the hydrogen bonds were still found near the critical density. At densities below ρc, density dependence of the diffusion coefficients are qualitatively described by the simple kinetic theory for gases. At higher densities, the diffusion coefficients deviate from the prediction by the kinetic theory. Rotational correlation function at low density has the form similar to free rotors, while at high densities, the rotational relaxation may be described by rotational diffusion. It indicates that the rotational dynamics changes continuously around the critical density from a gaslike one to a liquidlike one.
Zero electron kinetic energy spectroscopy of the KrBr−, XeBr−, and KrCl− anions
Authors: Yourshaw Ivan , Lenzer Thomas , Reiser Georg , Neumark Daniel M.
Published: July 2002

Three rare-gas halide (RgX−) anions, KrBr−, XeBr−, and KrCl−, and the corresponding neutral, open-shell van der Waals complexes are studied with anion zero electron kinetic energy spectroscopy. The spectra for each system reveal well-resolved progressions in the low frequency vibrations of the anion and one or more of the three neutral electronic states accessed by photodetachment, providing a detailed spectroscopic probe of the Rg–X− and Rg–X interaction potentials. In the case of KrBr−, transitions to all three of the “covalent” neutral electronic states (the X1/2, I3/2, and II1/2 states) were observed. For XeBr−, transitions to the X1/2 and II1/2 neutral states were observed. For KrCl−, only the X1/2 state could be studied. From our data, we construct model potentials for the anion and each observed neutral state, and these are compared with other experimental and theoretical potentials.
Influence of restricted environment and ionic interactions on water solvation dynamics
Authors: Pant Debi , Riter Ruth E. , Levinger Nancy E.
Published: July 2002

Polar solvation dynamics of water sequestered inside Aerosol OT (AOT) reverse micelles have been investigated as a function of the surfactant countercation, specifically replacing Na+ for K+ and Ca2+. For Ca-AOT reverse micelles, the solvation dynamics for the smallest micelles probed occurs on a subnanosecond time scale. The K-AOT reverse micelles display an additional ultrafast component that is attributable to bulklike water motion. As previously reported for Na-AOT reverse micelles [Riter, Willard, and Levinger, J. Phys. Chem. B 102, 2705 (1998)], solvent mobility increases with increasing micellar size for both Ca-AOT and K-AOT reverse micelles. The solvation dynamics in strongly ionic aqueous solutions of Ca2+ and K+ have also been investigated. The 10 M electrolyte solutions display water motion on significantly shorter time scales with substantial ultrafast components. These results show that the micellar interfacial structure plays a significant role in immobilizing intramicellar water and that solvent immobilization in the reverse micelles is not merely a result of solvent–ion interactions.
Zero electron kinetic energy and photoelectron spectroscopy of the XeI− anion
Authors: Lenzer Thomas , Furlanetto Michael R. , Asmis Knut R. , Neumark Daniel M.
Published: July 2002

The XeI− anion and the corresponding neutral X1/2, I3/2, and II1/2 electronic states have been studied by means of zero electron kinetic energy (ZEKE) and photoelectron spectroscopy. The ZEKE spectra show rich and well-resolved progressions in the low-frequency vibrations of the anion and the neutral van der Waals complexes. From our spectroscopic data we construct model potentials for the anion and three neutral states, which are compared to previously obtained potential functions for this system. The intensity of the I3/2←anion transitions relative to the X1/2←anion transitions in the XeI− ZEKE spectrum is considerably lower than expected from a Franck-Condon simulation based on the model potentials. Comparison with the photoelectron spectrum of XeI− indicates this is due to a small s-wave partial cross section for photodetachment to the I3/2 state.
Torsional potential of biphenyl: Ab initio calculations with the Dunning correlation consisted basis sets
Authors: Tsuzuki Seiji , Uchimaru Tadafumi , Matsumura Kazunari , Mikami Masuhiro , Tanabe Kazutoshi
Published: July 2002

The internal rotational barrier heights of biphenyl were calculated with the Dunning correlation consisted basis sets (up to cc-pVQZ, 960 basis functions) and the electron correlation correction by the second order Mo/ller-Plesset method (MP2). Although previous Hartree–Fock (HF) and MP2 calculations showed that the internal rotational barrier height at 0° (ΔE0) was substantially larger than that at 90° (ΔE90), our MP2/cc-pVQZ//MP2/6-31G* calculations showed that ΔE0 (2.28 kcal/mol) was close to ΔE90 (2.13 kcal/mol), which agreed with the estimation from experimental measurements. The calculations of benzene dimers suggested that the dispersion interaction increased the relative stability of the coplanar conformer. The basis sets employed in the previous calculations were not large enough to evaluate the attractive dispersion interaction. The underestimation of the stabilization of the coplanar conformer by the dispersion interaction would be one of the reasons for the overestimation of ΔE0 in the previous calculations.
A new analytic equation of state for liquid water
Authors: Jeffery C. A. , Austin P. H.
Published: July 2002

We develop a new analytical equation of state for water based on the Song, Mason, and Ihm equation of state and Poole et al.’s simple model of the free energy of strong tetrahedral hydrogen bonds. Repulsive and attractive forces are modeled using a modification of the Weeks–Chandler–Anderson decomposition of the pair potential, with closed tetrahedral hydrogen bonds contributing both internal energy and entropy to the free energy of water. Strong tetrahedral hydrogen bonds are modeled explicitly using a simplified partition function. The resulting equation of state is 20–30 times more accurate than equivalent simple cubic equations of state over a wide range of pressures (0.1→3000 bar) and temperatures (−34→1200 °C) including the supercooled region. The new equation of state predicts a second liquid–liquid critical point at pC′=0.954 kbar, ρC′=1.045 g cm−3 and TC′=228.3 K. The temperature of this second critical point is above the homogeneous freezing temperature at 1 kbar, thus this region of the phase diagram may be experimentally accessible. The phase diagram also suggests that the homogeneous nucleation temperature above 1.2 kbar may be determined by a phase transition from high-density water to low-density water.
Sum-frequency generation from thiophenol on silver in the mid and far-IR
Authors: Braun R. , Casson B. D. , Bain C. D. , van der Ham E. W. M. , Vrehen Q. H. F. , Eliel E. R. , Briggs A. M. , Davies P. B.
Published: July 2002

Sum-frequency (SF) spectra of a monolayer of thiophenol on silver are reported in the mid and far-IR (infrared). The free-electron laser FELIX was used to reach wavelengths up to 54 μm. Molecular vibrations of thiophenol are observed at wavelengths near 10 μm (three modes), 14 μm (1 mode), and 24 μm (1 mode). The appearance of the different vibrational modes in the spectra varies dramatically due to interference between the resonant sum-frequency signal and the nonresonant sum-frequency signal from silver. The standard model used to describe line shapes in SF spectra is shown to be insufficient to explain the different line shapes for the various vibrational modes of thiophenol on silver.
Geometric investigation of low-dimensional manifolds in systems approaching equilibrium
Authors: Davis Michael J. , Skodje Rex T.
Published: July 2002

Many systems approach equilibrium slowly along surfaces of dimension smaller than the original dimensionality. Such systems include coupled chemical kinetics and master equations. In the past the steady state approximation has been used to estimate these lower dimensional surfaces, commonly referred to as “manifolds,” and thus reduce the dimensionality of the system which needs to be studied. However, the steady state approximation is often inaccurate and sometimes difficult to define unambiguously. In recent years two methods have been proposed to go beyond the steady state approximation to improve the accuracy of dimension reduction. We investigate these methods and suggest significant modifications to one of them to allow it to be used for the generation of low-dimensional manifolds in large systems. Based on the geometric investigations, two other approaches are suggested which have some advantages over these two methods for the cases studied here. All four approaches are geometric and offer advantages over methods based on the evaluation of time-dependent behavior, where phenomenological rate laws are extracted from the time-dependent behavior.
Thermodynamic properties of sulfurhexafluoride in the critical region
Authors: Wyczalkowska A. Kostrowicka , Sengers J. V.
Published: July 2002

An equation, that incorporates a crossover from singular thermodynamic behavior asymptotically close to the critical point to regular thermodynamic behavior far away from the critical point, is presented for calculating the thermodynamic properties of sulfurhexafluoride in the critical region. The equation is constructed by applying a crossover transformation to a truncated classical Landau expansion. The equation is capable of representing the thermodynamic properties of sulfurhexafluoride at temperatures from 310 to 390 K in an appreciable range of densities around the critical density.
Dynamics of a wetting liquid in nanopores: An optical Kerr effect study of the dynamics of acetonitrile confined in sol-gel glasses
Authors: Loughnane Brian J. , Farrer Richard A. , Scodinu Alessandra , Fourkas John T.
Published: July 2002

The orientational dynamics of acetonitrile and acetonitrile-d3 confined in nanoporous glasses have been studied using optical Kerr effect spectroscopy. The decays can be fit to the sum of three exponentials, the fastest of which corresponds to relaxation of bulk-like liquid. We present evidence that the intermediate exponential arises from the exchange of molecules bound to the pore surfaces into the bulk liquid, whereas the slowest exponential corresponds to surface relaxation. A comparison to nuclear magnetic resonance data demonstrates that the liquid at the pore surfaces is more highly ordered than that in the bulk. Surface-modification studies demonstrate that hydrogen bonding is responsible for the extreme inhibition of dynamics at the pore surfaces.
Vibrational analysis of HOCl up to 98% of the dissociation energy with a Fermi resonance Hamiltonian
Authors: Jost Remy , Joyeux Marc , Skokov Sergei , Bowman Joel
Published: July 2002

We have analyzed the vibrational energies and wave functions of HOCl obtained from previous ab initio calculations [J. Chem. Phys. 109, 2662 (1998); 109, 10273 (1998)]. Up to approximately 13 000 cm−1, the normal modes are nearly decoupled, so that the analysis is straightforward with a Dunham model. In contrast, above 13 000 cm−1 the Dunham model is no longer valid for the levels with no quanta in the OH stretch (v1=0). In addition to v1, these levels can only be assigned a so-called polyad quantum number P=2v2+v3, where 2 and 3 denote, respectively, the bending and OCl stretching normal modes. In contrast, the levels with v1⩾2 remain assignable with three vi quantum numbers up to the dissociation (D0=19 290 cm−1). The interaction between the bending and the OCl stretch (ω2≅2ω3) is well described with a simple, fitted Fermi resonance Hamiltonian. The energies and wave functions of this model Hamiltonian are compared with those obtained from ab initio calculations, which in turn enables the assignment of many additional ab initio vibrational levels. Globally, among the 809 bound levels calculated below dissociation, 790 have been assigned, the lowest unassigned level, No. 736, being located at 18 885 cm−1 above the (0,0,0) ground level, that is, at about 98% of D0. In addition, 84 “resonances” located above D0 have also been assigned. Our best Fermi resonance Hamiltonian has 29 parameters fitted with 725 ab initio levels, the rms deviation being of 5.3 cm−1. This set of 725 fitted levels includes the full set of levels up to No. 702 at 18 650 cm−1. The ab initio levels, which are assigned but not included in the fit, are reasonably predicted by the model Hamiltonian, but with a typical error of the order of 20 cm−1. The classical analysis of the periodic orbits of this Hamiltonian shows that two bifurcations occur at 13 135 and 14 059 cm−1 for levels with v1=0. Above each of these bifurcations two new families of periodic orbits are created. The quantum counterpart of periodic orbits are wave functions with “pearls” aligned along the classical periodic orbits. The complicated sequence of ab initio wave functions observed within each polyad is nicely reproduced by the wave functions of the Fermi resonance Hamiltonian and by the corresponding shapes of periodic orbits. We also present a comparison between calculated and measured energies and rotational constants for 25 levels, leading to a secure vibrational assignment for these levels. The largest difference between experimental and calculated energies reaches 22 cm−1 close to D0.
A theoretical study of the vibrational energy spectrum of the HOCl/HClO system on an accurate ab initio potential energy surface
Authors: Peterson Kirk A. , Skokov Sergei , Bowman Joel M.
Published: July 2002

A new, global analytical potential energy surface is constructed for the X 1A′ electronic ground state of HOCl that accurately includes the HClO isomer. The potential is obtained by using accurate ab initio data from a previously published surface [Skokov et al., J. Chem. Phys. 109, 2662 (1998)], as well as a significant number of new data for the HClO region of the surface at the same multireference configuration interaction, complete basis set limit level of theory. Vibrational energy levels and intensities are computed for both HOCl and HClO up to the OH+Cl dissociation limit and above the isomerization barrier. After making only minor adjustments to the ab initio surface, the errors with respect to experiment for HOCl are generally within a few cm−1 for 22 vibrational levels with the largest error being 26 cm−1. A total of 813 bound vibrational states are calculated for HOCl. The HClO potential well supports 57 localized states, of which only the first 3 are bound. The strongest dipole transitions for HClO were computed for the fundamentals—33, 2.9, and 25 km/mol for ν1, ν2, and ν3, respectively. From exact J=1 ro-vibrational calculations, state dependent rotational constants have been calculated for HClO. Lastly, resonance calculations with the new potential demonstrate that the presence of the HClO minimum has a negligible effect on the resonance states of HOCl near the dissociation threshold due to the relatively high and wide isomerization barrier.
A consistent third-order propagator method for electronic excitation
Authors: Trofimov A. B. , Stelter G. , Schirmer J.
Published: July 2002

A propagator method referred to as third-order algebraic–diagrammatic construction [ADC(3)] for the direct computation of electronic excitation energies and transition moments is presented. This approach is based on a specific reformulation of the diagrammatic perturbation expansion for the polarization propagator, and extends the existing second-order [ADC(2)] scheme to the next level of perturbation theory. The computational scheme combines diagonalization of a Hermitian secular matrix and perturbation theory for the matrix elements. The characteristic properties of the method are compact configuration spaces, regular perturbation expansions, and size-consistent results. The configuration space is spanned by singly and doubly excited states, while the perturbation expansions in the secular matrix extend through third order in the p-h block, second order in the p-h/2p-2h coupling block, and first order in the 2p-2h block. While the simpler ADC(2) method, representing a counterpart to the MP2 (second-order Mo/ller–Plesset) ground-state method, recommends itself for application to larger molecules, the ADC(3) scheme is aimed at a more accurate description of molecular excitation spectra. The relationship of the ADC(3) scheme with coupled cluster methods is discussed, focusing here in particular on the treatment of transition moments.
Saddle-node bifurcations in the spectrum of HOCl
Authors: Weiß J. , Hauschildt J. , Grebenshchikov S. Yu. , Düren R. , Schinke R. , Koput J. , Stamatiadis S. , Farantos S. C.
Published: July 2002

A detailed analysis of the bound-state spectrum of HOCl (hypoclorous acid) in the ground electronic state is presented. Exact quantum mechanical calculations (filter diagonalization) are performed employing an ab initio potential energy surface, which has been constructed using the multireference configuration-interaction method and a quintuple-zeta one-particle basis set. The wave functions of all bound states up to the HO+Cl dissociation threshold are visually inspected in order to assign the spectrum in a rigorous way and to elucidate how the spectrum develops with energy. The dominant features are (1) a 2:1 anharmonic resonance between the bending mode and the OCl stretching mode, which is gradually tuned in as the energy increases, and (2) a saddle-node bifurcation, i.e., the sudden birth of a new family of states. The bifurcation is further investigated in terms of the structure of the classical phase space (periodic orbits, continuation/bifurcation diagram). It is also discussed how the spectrum of bound states persists into the continuum and how the various types of quantum mechanical continuum wave functions affect the state-specific dissociation rates.
The structure of saturated lithium– and potassium–ammonia solutions as studied by using neutron diffraction
Authors: Wasse Jonathan C. , Hayama Shusaku , Skipper Neal T. , Benmore Chris J. , Soper Alan K.
Published: July 2002

The technique of isotopic substitution in neutron diffraction has been used to measure the structure of saturated solutions of lithium and potassium in ammonia. Isotopic substitution of *N by N15, combined with difference analysis, shows that K+ acts as a “structure breaking” ion while Li+ acts as a “structure making” ion. As a consequence, it is only for the latter that we observe intermediate range order, in the form of a pre-peak at ∼1 Å−1 in the k-space data. From our analysis, we also find that lithium is tetrahedrally coordinated by ammonia molecules, at both 230 and 100 K. Potassium, on the other hand, is octahedrally coordinated at 160 K.
A method for molecular dynamics simulation of confined fluids
Authors: Wang Jee-Ching , Fichthorn Kristen A.
Published: July 2002

We report the development of a simulation method, with advantages for simulating fluids confined between solid substrates and in equilibrium with bulk fluids. For molecular-dynamics simulations, the isothermal–isobaric constraint method is modified to implement this method. Long-range corrections to the pressure tensor for simple confined systems are also derived and included. Consistent with previous studies employing the grand-canonical ensemble, confined Lennard-Jones and model n-decane fluids investigated with this method show layering induced by the confining surfaces, oscillatory surface-force profiles, and step-like dependencies of the number of confined molecules on surface separation. For a confined Lennard-Jones fluid, increasing the bulk pressure at a fixed temperature enhances layering, increases the effect of surface structure on the surface-force profile, and causes the surface forces to be more repulsive.
Accurate ab initio near-equilibrium potential energy and dipole moment functions of the ground electronic state of ozone
Authors: Xie Daiqian , Guo Hua , Peterson Kirk A.
Published: July 2002

We report a highly correlated multireference configuration interaction calculation of the near-equilibrium potential energy surface of ozone using a large correlation consistent basis set. Three-dimensional analytical expressions are obtained for the potential energy and dipole moment functions using least-squares fits to ab initio points near the C2v equilibrium geometry. Low-lying vibrational band origins of O316 and some of its isotopic variants are calculated using the ab initio potential energy function. The calculated fundamental frequencies for the symmetric stretching and bending vibrations are within about 3 cm−1 of the observed values, while that for the antisymmetric stretch deviates from experiment by about 13 cm−1. The agreement with experiment can be significantly improved if the ab initio potential energy function is scaled in the antisymmetric stretching coordinate. Absolute infrared absorption intensities are also calculated using ab initio electric dipole moment functions and in good agreement with the available experimental data.
An equation of state à la Carnahan–Starling for a five-dimensional fluid of hard hyperspheres
Authors: Santos Andrés
Published: July 2002

The equation of state for five-dimensional hard hyperspheres arising as a weighted average of the Percus–Yevick compressibility (35) and virial (25) equations of state is considered. This Carnahan–Starling-type equation turns out to be extremely accurate, despite the fact that both Percus–Yevick equations of state are rather poor.
On the viscous fluid interpretation of some exact solutions
Authors: Carot J. , Ibanez J.
Published: July 2002

An example of the equivalence between a perfect fluid and a viscous fluid is presented, showing that the Schwarzschild interior solution obtained from a perfect fluid can also be derived from a viscous fluid with heat conduction. The equivalence between a scalar field and a viscous fluid is investigated, showing that under certain circumstances, both can generate, from Einstein’s equations, the same space-time geometry. Some examples are presented and, in particular, it is shown that every plane-symmetric solution deduced from a scalar field can also be derived from a viscous fluid.
A brief study on the transformation of Maxwell equations in Euclidean four-space
Authors: Zampino E.
Published: July 2002

Electromagnetic-type fields in Euclidean four-space are studied by changing the sign of the time differential term in Faraday’s law of induction. Although a covariant set of field equations can be derived, difficulties arise in the case of time-dependent fields.
Exact model for a relativistic star
Authors: Tikekar Ramesh
Published: July 2002

Assuming that the physical three-space in a relativistic superdense star has the geometry of a three-spheroid, a static spherically symmetric model based on an analytic closed-form solution of Einstein’s field equations is presented. Assuming the density of the order of 2×1014 g cm−3, estimates of the total mass and size of the stars of the model are obtained for various values of a density-variation parameter that is suitably defined. The total mass and the boundary radius of each of these models are of the order of the mass and size of a neutron star.
Isotropic geometry and twistors in higher dimensions. I. The generalized Klein correspondence and spinor flags in even dimensions
Authors: Harnad J. , Shnider S.
Published: July 2002

An equivariant diffeomorphism is given between flag varieties of totally isotropic subspaces of a complex inner product space and certain orbits under the complex spin group within flag varieties of the associated spinor modules. This allows a generalization of the Klein correspondence underlying twistor theory, applicable to arbitrary (even) dimensional conformally compactified Minkowski space and its isotropic subspaces.
A factorization of the scattering matrix for the Schrödinger equation and for the wave equation in one dimension
Authors: Aktosun Tuncay
Published: July 2002

For the one-dimensional Schrödinger equation with a potential decaying at both ends of the real axis, the scattering matrix of the potential is given explicitly in terms of the scattering matrices corresponding to the fragments of this potential. A similar result also holds for the wave equation in a nonhomogeneous, nondispersive medium, where the wave speed has the same asymptotics at both ends of the real line.
Spectral theory and x-ray diffraction
Authors: Dworkin Steven
Published: July 2002

Crystallographers use x-ray spectra to understand the structure of solids and ergodic theorists use spectra of abstract dynamical systems for structural studies; the relation of the two is shown here.
The unified approach to integrable relativistic equations: Soliton solutions over nonvanishing backgrounds. I
Authors: Barashenkov I. V. , Getmanov B. S. , Kovtun V. E.
Published: July 2002

The scheme for unified description of integrable relativistic massive systems provides an inverse scattering formalism that encompasses universally all (1+1)-dimensional systems of this kind. In this work the N-soliton solution (over an arbitrary background) is constructed for some generic system which is associated with the sl(2,C) case of the scheme and whose reductions include the complex sine-Gordon equation, the massive Thirring model and other equations, both in the Euclidean and Minkowski spaces. Thus the N-soliton solutions for all these systems emerge in a unified form differing only in the type of constraints imposed on their parameters. In an earlier paper the case of the zero background was considered, while here, we concentrate on the case of the nonvanishing constant background, i.e., on the N-kink solutions.
Three-dimensional formulation of the Maxwell equations for stationary space–times
Authors: Torres del Castillo G. F. , Mercado-Pérez J.
Published: July 2002

Using the correspondence between a stationary space–time and a curved three-dimensional space with a static magnetic field and a conservative field of force, the Maxwell equations in a stationary space–time are expressed in terms of fields associated with the corresponding three-dimensional geometry. The Maxwell equations take a form analogous to the one they have in flat space–time. The Ricci tensor of the space–time is also written in terms of the three-dimensional fields.
Primary and secondary stability analysis of a three-dimensional boundary-layer flow
Authors: Fischer T. M. , Dallmann U.
Published: July 2002

A three-dimensional, incompressible boundary-layer flow is investigated theoretically with respect to primary and secondary instability. These investigations accompany a basic transition experiment, which is being performed at the DLR in Göttingen [B. Müller, in Laminar-Turbulent Transition, edited by D. Arnal and R. Michel (Springer-Verlag, Berlin, 1990), p. 489]. Primary stationary and secondary nonstationary disturbances are used to model the mean flow and the fluctuations of a measured (quasi-) saturation state. The analysis is based on a Falkner–Skan–Cooke approximation of the undisturbed flow. Good agreement of the secondary stability model with this experiment is obtained, especially concerning the spatial distribution of the rms fluctuation. A striking change of the vortex pattern due to secondary instability has not been observed.
The effect of gravity modulation on thermosolutal convection in an infinite layer of fluid
Authors: Saunders B. V. , Murray B. T. , McFadden G. B. , Coriell S. R. , Wheeler A. A.
Published: July 2002

The effect of time-periodic vertical gravity modulation on the onset of thermosolutal convection in an infinite horizontal layer with stress-free boundaries is investigated using Floquet theory for the linear stability analysis. Situations for which the fluid layer is stably stratified in either the fingering or diffusive regimes of double-diffusive convection are considered. Results are presented both with and without steady background acceleration. Modulation may stabilize an unstable base solution or destabilize a stable base solution. In addition to synchronous and subharmonic response to the modulation frequency, instability in the double-diffusive system can occur via a complex conjugate mode. In the diffusive regime, where oscillatory onset occurs in the unmodulated system, regions of resonant instability occur and exhibit strong coupling with the unmodulated oscillatory frequency. The response to modulation of the fundamental instability of the unmodulated system is described both analytically and numerically; in the double-diffusive system this mode persists under subcritical conditions as a high-frequency lobe.
Nonaxisymmetric thermal equilibria of a cylindrically bounded guiding-center plasma or discrete vortex system
Authors: Smith Ralph A. , O’Neil Thomas M.
Published: July 2002

The thermal equilibria of a two-dimensional guiding-center model for a single-species plasma bounded by a cylindrical conductor are considered in the microcanonical ensemble. The same description applies to identical point vortices in a two-dimensional, ideal fluid surrounded by a circular streamline. The statistically dominant configurations are displaced asymmetrically from the axis, for sufficiently large energies at specified canonical angular momentum. The transition between symmetric and asymmetric states resembles a second-order phase transition, and occurs at negative temperatures. It is related to a bifurcation in the mean-field (Vlasov) description. The theory is compared with Monte Carlo simulations of microcanonical ensembles of guiding centers.
High-beta discharges in the DIII-D tokamak
Authors: Ferron J. R. , Chu M. S. , Helton F. J. , Howl W. , Kellman A. G. , Lao L. L. , Lazarus E. A. , Lee J. K. , Osborne T. H. , Strait E. J. , Taylor T. S. , Turnbull A. D.
Published: July 2002

Low-q (q95<3) double-null divertor discharges with values of the volume-average toroidal beta as high as 9.3% have been operated in the DIII-D tokamak [Fusion Technol. 8, 441 (1985)]. In discharges with q95≊5, values of βT/(I/aB) as high as 5 have been obtained. These discharges are shown to be at or below the stability limit to the value of beta for infinite-n, ideal ballooning modes. The discharges are significantly below the beta limit for ideal,low toroidal mode number kink modes. The kink mode beta limit is shown to be strongly dependent on the radial profiles of plasma pressure and current. The theoretical beta limit in DIII-D is shown to be in the range βT/(I/aB)=4 –5 depending on the value of I/aB, and this is consistent with the experiment. High-beta discharges have been operated with ion temperature up to 17 keV. Steady-state, high-beta, low-q operation is demonstrated by a discharge with I/aB=2.6, q95=2.7, in which βT>7% is maintained for 1.5 sec.
Plasma spectroscopy in inertial confinement fusion and soft x-ray laser research
Authors: Griem Hans R.
Published: July 2002

After a review of the basic theory of quantitative spectroscopy of atoms and incompletely stripped ions immersed in plasmas, applications to diagnostics and modeling of dense plasmas are discussed. Density and temperature measurements are emphasized, together with magnetic and electric-field measurements and determination of anisotropy in the electron distribution function. The important role of spectral line broadening in soft x-ray laser research is pointed out. There is a possibility of collisional narrowing of the usual thermal Doppler line profile, although this narrowing may be compensated or over-compensated by the broadening effects of elastic ion–ion collisions. At very high power levels, the laser line may also be broadened by the laser field via resonant dynamical Stark effects.
Internal magnetic and electrostatic fluctuation measurements of magnetohydrodynamic modes in the Texas Experimental Tokamak (TEXT)
Authors: Simcic V. J. , Crowley T. P. , Schoch P. M. , Aydemir A. Y. , Yang X. Z. , Connor K. A. , Hickok R. L. , Wootton A. J. , McCool S. C.
Published: July 2002

A heavy ion-beam probe has been used to make the first internal measurements of magnetic fluctuations in a hot tokamak. The magnetic vector potential fluctuation, Ãφs, is measured during magnetohydrodynamic (MHD) activity and is in reasonable agreement with the prediction of a three-dimensional, resistive, compressible, nonlinear MHD code. Associated density and potential fluctuation measurements and magnetic island widths are also presented.
Analytic studies of hot electron transport
Authors: Lindman E. L. , Swartz K.
Published: July 2002

An analytic model of thermal transport is applied to the problems of thermal smoothing and heat transport. The diffusion approximation is taken and collision rates are used that are functions of the particle energy. The distribution function at low velocities is found to be strongly dependent on the assumed velocity dependence of the particle energy-loss rate. The often assumed velocity dependence of v−3 leads to qualitatively incorrect results. Smoothing of transverse perturbations is examined in three dimensions; these are found to decay as exp(−kpx) for kp large, where kp is the wavenumber of the transverse perturbation, and x is the inward radial coordinate. Finally, an alternate formulation of the ‘‘delocalized heat flux,’’ which is in the form of a convolution over the local free-streaming heat flux, is obtained. The weighting is determined by a solution of the Fokker–Planck equation.
The effect of a perturbation on the flow over a bluff cylinder
Authors: Armstrong B. J. , Barnes F. H. , Grant I.
Published: July 2002

Measurements are presented of the frequency of vortex shedding from, in turn, a circular, a D-section cylinder, and a flat plate for a flow that has a single-frequency perturbation superimposed on its mean velocity component. It is found that over a range of velocities the vortex shedding locks-in to the frequency of the perturbation such that the shedding frequency is half the perturbation frequency. Also, the range of velocities for which lock-in occurs increases as the perturbation amplitude is increased. With lock-in, the mean base pressure is found to decrease, and measurements of the vortex shedding from the circular cylinder show that the correlation of vortex shedding increases. The changes associated with lock-in are found to be greatest for the circular cylinder.
Numerical simulations of turbulent trapping in the weak beam–plasma instability
Authors: Theilhaber K. , Laval G. , Pesme D.
Published: July 2002

Numerical simulations of the weak beam–plasma instability were done in the turbulent regime where small-scale trapping is a dominant feature of the instability, a regime with behavior not predicted by quasilinear theory. It occurs when the trapping frequency ν=(k2D)1/3 is larger than the growth rate γk of the instability. The results of the simulations were compared with those of a specific model of the turbulence, the so-called ‘‘turbulent trapping’’ model, which gives precise formulas for the particle correlation functions, and predicts a growth rate well enhanced over the quasilinear value. It was found that the model gives accurate predictions for the correlation functions, and thus provides a good description of the turbulent structure of phase space. On the other hand, while growth rates were enhanced over the quasilinear values, the enhancements observed are smaller than expected from the quantitative predictions of the model.
Laboratory-generated, shallow-water surface waves: Analysis using the periodic, inverse scattering transform
Authors: Osborne A. R. , Petti M.
Published: July 2002

The space-time evolution of laboratory-generated, shallow-water wave trains is considered in one-space and one-time dimensions. An electronic control-and-feedback system is used to generate periodic/quasiperiodic wave trains in a laboratory flume (0.76×0.8×46 m3) in which five spatially distributed, resistance wave gauges simultaneously record time series of the surface wave field. A concrete ramp with a slope of 0.02 minimizes reflections, and thus ensures near-unidirectional wave motion. The data are analyzed using both (1) linear Fourier analysis and (2) a relatively new kind of nonlinear Fourier analysis based upon the inverse scattering transform (IST) for the periodic Korteweg–de Vries (KdV) equation. The periodic IST formalism consists of a linear superposition of the ‘‘hyperelliptic-function oscillation modes,’’ which are intrinsically nonlinear, while simultaneously undergoing nonlinear interactions with each other. The KdV oscillation modes may be viewed as the ‘‘sine waves’’ of the periodic scattering transform, although they are generally nonsinusoidal in shape. The amplitudes of the oscillation modes are constants of the motion for wave motion governed purely by KdV. For a series of experiments in the Ursell number range 0.30<U<0.99, it is found that the linear Fourier modes have amplitudes that vary substantially in space and time, while the inverse scattering modes are found to be nearly constant. It is therefore suggested that the inverse scattering formulation may be more appropriate than linear Fourier analysis for describing the nonlinear dynamical motions studied experimentally herein. Introducing the concept of ‘‘phase locking’’ among the IST modes, features in the data that are referred to as ‘‘coherent structures’’ are identified. Such structures are found not to be strictly solitons (they constitute multiple cnoidal wave interactions), although they have many of the properties normally identified with solitons, including preservation of their amplitudes after collisions with other waves.
On the interpretation of vortex breakdown
Authors: Keller Jakob J.
Published: July 2002

Studying the numerous papers that have appeared in the recent past that address ‘‘vortex breakdown,’’ it may be difficult for a reader to avoid getting rather confused. It appears that various authors or even schools have conflicting views on the correct interpretation of the physics of vortex breakdown. Following the investigation by Keller et al. [Z. Angew. Math. Phys. 36, 854 (1985)], in this paper, axisymmetric forms of vortex breakdown, as originally defined by Benjamin [J. Fluid Mech. 14, 593 (1962)] are addressed. It is argued that at least some of the previous investigations have been concerned with different aspects of the same phenomena and may, in fact, not disagree. One of the most fundamental questions in this context concerns the properties of the distributions of total head and circulation on the downstream side of vortex breakdown transitions. Some previous investigators have suggested that the downstream flow would exhibit properties that are similar to those of a wake. For this reason the phenomenon of vortex breakdown is investigated for a class of distributions of total head and circulation in the domain of flow reversal that is substantially more general than in previous investigations. Finally, a variety of problems are discussed that are crucial for a more complete theory of vortex breakdown, but have not yet been solved. It is shown that for the typically small flow speeds in a domain of flow reversal produced by a vortex breakdown wave, the departures of both vortex core size and swirl number, with respect to the case of uniform total pressure in the zone of flow reversal, as discussed by Keller et al. [Z. Angew. Math. Phys. 36, 854 (1985)], remain surprisingly small. As a consequence, the possible appearance of large departures from a Kirchhoff-type wake must be due to viscous diffusion at low and due to shear-layer instabilities at high Reynolds numbers.
Rheology of dilute suspensions of charged fibers
Authors: Chen Shing Bor , Koch Donald L.
Published: July 2002

The rheology of a dilute suspension of charged fibers with a large ratio of length L to diameter d is examined. The fibers may possess both a net charge and a charge dipole and it is assumed that the Hartmann number is small. The double layer thickness λ is large compared with the rod diameter and may be comparable with the fiber length. Although the shear rate is sufficiently small so that the deformation of the double layer is small, no restriction is placed on the rotary Péclet number of the rods. The velocity disturbance caused by the rods is neglected when calculating the double layer deformation. This approximation is accurate when λ/L=O(1) and L/d is very large, but leads to an overestimate of the ion cloud distortion for small values of λ/L or moderate values of L/d. The counterion cloud affects the stress both directly through a primary electroviscous stress and indirectly by exerting an electric torque that changes the fiber orientation distribution. The additional stress caused by electrostatics shear thins for a fiber with a net charge. However, when the fiber has a charge dipole, the electrical stress may increase with increasing shear rate at sufficiently high Péclet numbers. At very high Péclet numbers, the electrical torque can lead to a fixed orientation of the fibers near the flow direction of the simple shear flow.