bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultra-low temperature kinetics of neutral–neutral reactions: The reaction CN+O2 down to 26 K
Authors: Sims I. R. , Queffelec J. L. , Defrance A. , Rebrion-Rowe C. , Travers D. , Rowe B. R. , Smith I. W. M.
Published: July 2002

A new method is described which enables the measurement for the first time of the rates of neutral–neutral gas-phase reactions at temperatures down to 26 K (and in the future, below). Results for the reaction of CN radicals with O2 are presented and discussed in terms of current theoretical treatments.
Small angle neutron scattering study on poly(N-isopropyl acrylamide) gels near their volume-phase transition temperature
Authors: Shibayama Mitsuhiro , Tanaka Toyoichi , Han Charles C.
Published: July 2002

The small angle neutron scattering experiments were conducted on N-isopropyl acrylamide (NIPA) gels in D2O and on the corresponding NIPA solutions. The NIPA gels underwent a sharp, but a continuous volume phase transition at 34.6 °C from a swollen state to a shrunken state with increasing temperature. In the case of the gels, an excess scattering due to the presence of crosslinks was observed at low q region (q≤0.02 Å−1), where q is the magnitude of the scattering vector. The scattered intensity function for the gel was well described with a combination of Gauss and Lorentz-type functions, i.e., I(q)=IG(0)exp[−Ξ2q2]+[IL(0)/(1+ξ2q2)] as proposed by Geissler et al. IG(0) and IL(0) are the intensities at q=0 for the contributions of Gaussian and Lorentzian functions, respectively. The Gaussian part results from solidlike inhomogeneity, having a characteristic size of Ξ, which is due to the introduction of crosslinks into the system. The Lorentzian part is originated from the liquid nature of the local concentration fluctuations of the gel characterized with a thermal blob of dimension ξ. Ξ decreases systematically with polymer volume fraction, φ, indicating the nature of Ξ being the solidlike inhomogeneity. On the other hand, the intensity function for solutions was well fitted with the so-called Ornstein–Zernike (OZ) equation (a Lorentzian function), i.e., I(q)=[IL(0)/(1+ξ2q2)].

It was found that both ξ and IL(0) diverged at the spinodal temperature, Ts. The critical exponents, ν and γ, for the temperature dependence of ξ and IL(0), were estimated to be ∼0.60 and 1.2 for the gel, respectively, which were larger than the values for the solution of the same polymers (ν=0.45 and γ=0.8). These critical exponents for the gels support that the volume-phase transition of gels is classified to the three dimensional Ising model reported by Li and Tanaka. The concentration dependence of ξ and IL(0) was also well described with a power law relationship, i.e., ξ∼φνφ and IL(0)∼φγ;φ. The values of νφ and γφ at 23 °C are −3/4 and ∼−1/4, respectively, for the NIPA solutions, which are in good agreement with the theoretical prediction for polymer solutions in a good solvent. In the case of the NIPA gels, however, both νφ and γφ are ∼−1. These exponents were interpreted by taking account of the effects of crosslinking on the Flory’s interaction parameter.
Photochemistry of adsorbed molecules. XII. Photoinduced ion–molecule reactions at a metal surface for CH3X/RCl/Ag(111) (X=Br, I)
Authors: Dixon-Warren St. J. , Heyd D. V. , Jensen E. T. , Polanyi J. C.
Published: July 2002

A photoinduced ion–molecule reaction is reported between superimposed molecular layers of alkyl halides on a metal substrate CH3X/RCl/Ag(111) (where X=Br or I and R=CCl3, CHCl2, or CH2Cl) to form CH3Cl(ad) (wavelengths 193, 248, and 350 nm). The reaction is mediated by charge-transfer (CT) photodissociation, in which photoelectrons from the metal surface transfer to the lower layer of adsorbate RCl to form RCl−. These negative ions then react with the upper layer CH3X in an ion–molecule reaction to form CH3Cl+X−. The yield of product CH3Cl is found to be enhanced at ∼1 ML of adsorbed CH3X (upper layer) due to a decrease in the local potential in the region of the adsorbate–adsorbate interface that enhances the probability of CT to the lower layer. In addition to lowering the local potential at the interface, the adsorbed CH3X also lowers the surface work function; as a result changes in the microscopic local potential correlate (via the CT reaction rate) with changes in the observed macroscopic work function. The yield of CH3Cl decreases at still higher CH3X coverage in the upper layer as the work function increases. The ion–molecule reaction gives evidence of being a concerted process in which the Cl− reacts as it separates from RCl− rather than following separation. The reagent RCl−, as in the surface reaction discussed in the previous paper, is formed by CT from ‘‘hot’’ electrons rather than free photoelectrons.
Quantum mechanical calculation of the rate constant for the reaction H+O2→OH+O
Authors: Leforestier Claude , Miller William H.
Published: July 2002

Rigorous three-dimensional quantum mechanical calculations have been carried out for the cumulative reaction probability of the titled reaction for total angular momentum, J=0. Higher values of J are included approximately, and the resulting thermal rate constant agrees well with experimental values for 800≤T≤3000 K.
Potential curve of NaK a 3Σ+ state near dissociation limit
Authors: Ishikawa Kiyoshi , Mukai Norihito , Tanimura Mari
Published: July 2002

Vibrational levels near the dissociation limit of NaK a  3Σ+ state are observed with an optical–optical double resonance technique. High resolution spectra are sensitively detected with the combination of perturbation facilitated polarization spectroscopy with frequency modulation spectroscopy. An electronically excited state, the B 1Π state, is mixed with the c 3Σ+ state through spin–orbit interaction. The transition from the X 1Σ+ state to the a 3Σ+ state through the B 1Π state is facilitated by the perturbation by the c 3Σ+ state. Hyperfine structures of the a 3Σ+(v=3−16,N=4−25) state are resolved with this spectroscopic technique and found to be independent of vibrational and rotational quantum number. The a 3Σ+ state can only be perturbed by the X 1Σ+ state through the hyperfine interaction. The vibrational levels (v≤16) of the a 3Σ+ state are demonstrably not perturbed by the X 1Σ+ state. The potential curve of the a 3Σ+ state is determined by the near-dissociation expansion fitting of molecular constants and the inverse perturbation analysis method. The coefficients C6, C8, and C10 of the potential function are determined to be (12.75±0.15)×106 cm−1 Å6, (2.22±0.19)×108 cm−1 Å8, and (1.100±0.061)×1010 cm−1 Å10, respectively. The dissociation energy, De, is obtained to be 207.858 ± 0.019 cm−1, which is 2.8 cm−1 above the highest observed vibrational level (v=16).
Phase transitions among the rotator phases of the normal alkanes
Authors: Sirota E. B. , Singer D. M.
Published: July 2002

We present the first calorimetric study of the normal alkanes CH3–(CH2)n−2–CH3 (21≤n≤30) covering the temperature range of the five rotator phases (whose structures were previously identified using x-ray scattering) with sufficient resolution to observe the various rotator to rotator transitions. We find first-order hexagonal–orthorhombic distortion transitions; second-order azimuthal tilt-angle rotation transitions, and two types of second-order tilting transitions, one of which has the higher symmetry phase at low temperature. These transitions appear to be mean field in character, in that they are without significant pretransitional fluctuations. We discuss the calorimetric signatures for the transitions in terms of the order parameters obtained from x-ray scattering data. In addition to the transitions, we find strong temperature variation of the heat capacity in the rotator phases not associated with the transitions.
Measuring the structure of etched silicon surfaces with Raman spectroscopy
Authors: Hines Melissa A. , Chabal Yves J. , Harris Timothy D. , Harris Alexander L.
Published: July 2002

We have measured the unenhanced, nonresonant surface Raman spectra of one monolayer of hydrogen bound to flat and stepped Si(111) surfaces prepared using a novel, aqueous fluorine etch. The orientation and normal mode composition of adsorbate vibrations are obtained from polarized, angle-resolved Raman spectra using a 3-layer dielectric model. This approach requires the experimental determination of both the anisotropy in the dynamic polarizability of the adsorbate bond and the effective dielectric constant in the vicinity of the adsorbate. The measured Si–H bond anisotropy is 0.263±0.028 in good agreement with gas phase measurements. The adsorbate dielectric constant is measured to be 3.78±0.20; this response is clearly nonlocal and predominantly due to polarization of the underlying silicon lattice. Using this technique, we find that the step dihydride on a Si[6(111)-(1̄1̄2)] surface is rotated 37°±4° from the surface normal in good agreement with the 31° predicted by ab initio cluster techniques, but significantly larger than the 12.5° predicted by pseudopotential slab calculations. In contrast to both theoretical predictions, the normal modes of this step dihydride display little concerted motion indicating that subsurface relaxation near the step edge reduces steric interactions much further than predicted. The observed anisotropic etch rates, evidenced by the production of atomically straight steps, are explained in terms of the measured distortion at the step edge.
A spectroscopically determined potential energy surface for the ground state of H216O: A new level of accuracy
Authors: Polyansky Oleg L. , Jensen Per , Tennyson Jonathan
Published: July 2002

The potential energy function for the electronic ground state of the water molecule has been obtained by fitting rotation-vibration term values involving J≤14 for 24 vibrational states of H216O together with 25 additional vibrational term values belonging to higher excited states. The fitting was carried out by means of an exact kinetic energy Hamiltonian. It was found that the differences between the exact kinetic energy calculations and calculations with the morbid program (i.e., calculations with an approximate kinetic energy operator) depend only very slightly on the parameters of the potential. This fact allowed us to make an inexpensive fitting using the morbid approach and still get the accuracy obtainable with the exact kinetic energy Hamiltonian. The standard deviation for 1600 term values was 0.36 cm−1. For 220 ground state energy levels the standard deviation was 0.03 cm−1. With the fitted potential, calculations of term values with J≤35 were carried out. This showed the excellent predictive power of the new potential. For the J=20 term values in the vibrational ground state, the deviations from experiment are typically below 0.2 cm−1. The discrepancy for the observed level with the highest Ka value, JKaKc = 20200, is only 0.008 cm−1. The calculated term value for the observed level with the highest J, 35035, deviates 0.1 cm−1 from experiment. Because of the level of accuracy achieved in these calculations, we can for the first time demonstrate the breakdown of the Born–Oppenheimer approximation for the water molecule. The high Ka level calculations allow us to show that the rotational energy level structure in water is at least of a very different nature than the fourfold cluster structures observed for H2Se and calculated for H2S, H2Se, and H2Te.
An ab initio molecular orbital study on adsorption at the MgO surface. III. Cooperativity of ionic adsorbates
Authors: Sawabe Kyoichi , Morokuma Keiji , Iwasawa Yasuhiro
Published: July 2002

The cooperativity between coadsorbed molecules on the MgO surface was investigated with the ab initio molecular orbital (MO) method using (MgO)4 and (MgO)6 clusters as models of the catalytic surface. On the pair of three-coordinate sites, the H2, NH3, or H2O molecule is chemisorbed heterolytically, like H−–Mg–O–H+, H2N−–Mg–O–H+, or HO−–Mg–O–H+. When the two adsorbate molecules are cochemisorbed on the adjacent set of four three-coordinate sites, the total chemisorption energy is much larger than the sum of chemisorption energies of each molecule. The extra stability, i.e., the energy cooperativity, is almost the same, around 20 kcal/mol, regardless of the adsorbed species, as far as both of them are heterolytically chemisorbed. The H2–CO coadsorbed system, in which CO is adsorbed nondissociatively, shows no cooperativity. The cooperativity above is partly due to the electrostatic attraction between the coadsorbed ionic species and partly due to the enhanced charge transfer (CT) interaction. Based on these results, it is suggested that higher coordination sites, inactive for chemisorption by themselves, may be activated by preadsorption at the neighboring pair of three-coordinate sites and may actually be ‘‘the active catalytic site’’ on the MgO surface.
On the effects of molecular fluctuations on models of chemical chaos
Authors: Matías M. A. , Güémez J.
Published: July 2002

In this work the effects of molecular or intrinsic fluctuations on some models of coupled chemical reactions exhibiting low-dimensional deterministic chaos are investigated. The study is performed by considering the system at the mesoscopic level, namely by stochastically simulating the corresponding chemical master equation. Two specific models are studied: the isothermal three-variable autocatalator of Peng et al. and a chemical version of Rössler’s model of spiral chaos. The main conclusions are that the corresponding strange attractors obtained in these models are robust against fluctuations, although when the system is near the onset of chaos the presence of fluctuations may anticipate the appearance of chaos.
Four-center reactions: A quantal model for H4
Authors: Hernández Marta I. , Clary David C.
Published: July 2002

We develop a quantal model for studying four-center reactions, A2+B2→2AB, and collision induced dissociation A2+B2→A+B2+A. The method involves using hyperspherical coordinates to describe vibrations of the A2 and B2 bonds and a global vibration and rotation of the exchange products. Application to the H4 system is presented, using a realistic potential energy surface. The reaction goes through a four-center linear transition state located just above the dissociation threshold. In the energy range studied (5–5.5 eV), collision induced dissociation competes with the four-center reaction and is the dominant process. It is found that vibrational energy, originally deposited in one of the diatomic partners, is much more efficient than translational energy in promoting reaction. Vibrational and rotational final distributions show that the products are internally hot. This simple quantal model, yet very demanding computationally, illustrates in detail many features of the H4 dynamics above the dissociation threshold, and could serve to study other four center reactions with trapezoidal or linear transition states.
Structural relaxation in viscous glycerol: Coherent neutron scattering
Authors: Wuttke J. , Petry W. , Pouget S.
Published: July 2002

Structural relaxation in viscous glycerol has been followed from 5.9 ps to 3.7 ns by coherent neutron scattering around the structure factor maximum. In a 100 K interval, the line shape of the decay function shows no significant temperature dependence; the mean relaxation time scales accurately with viscosity. Interparticle correlations decay slower and with less stretching than self correlations at similar wave numbers.
The ultrafast intramolecular dynamics of phthalocyanine and porphyrin derivatives
Authors: Zhong Qinghua , Wang Zhaohui , Liu Yunqi , Zhu Qihe , Kong Fanao
Published: July 2002

The internal conversion and intramolecular vibrational relaxation processes of nitro-tri-tert-butylphthalocyanine, tetra-phenylporphyrin (TPP), and tetra-tert-butylphthalocyanine (BuPc) in chloroform solution were investigated with an ultrafast time-resolved fluorescence depletion method. A regular fluorescence depletion was observed, indicating that the vibrational relaxation in the S1 state takes a few hundred femtoseconds to several picoseconds. For TPP and BuPc, an additional sharp dip superposes on the regular depletion. It is explained by an ultrafast internal conversion process from the S2 state to the S1 state with a time of a few tens of femtoseconds.
Orientational phase transition in molecular monolayer on an air–water interface
Authors: Jiang M. , Zhong Fan , Xing D. Y. , Wang Z. D. , Dong Jinming
Published: July 2002

A theoretical model is presented to study the phase transition of molecular orientation in a Langmuir monolayer on air–water interface. The polar molecules are treated as rodlike dipoles with three types of interactions; short-range steric repulsive interaction among the molecules, polar interaction between the molecules and water surface, and dipolar interaction among the molecules. The orientational order parameters, 〈cos θ〉 and 〈(3 cos2 θ−1)/2〉, are calculated as functions of the molecular density and temperature. It is shown that compressing the molecular area will lead to a continuous phase transition of the molecular orientation.
Dynamic simulation of a platelike particle dispersed system
Authors: Yamamoto Satoru , Matsuoka Takaaki
Published: July 2002

A numerical method for computing the dynamics of a platelike particle dispersed system is presented. The particle simulation method (PSM) for fiber suspensions is extended to handle a platelike particle, which is modeled with an array of spheres. Each pair of adjacent spheres is connected and deformed by three types of springs; stretch, bend, and twist. The motion of the platelike particles in flow is followed by solving the translational and rotational equations of motion for each constituent sphere. The mobility matrix for each particle is calculated to obtain the hydrodynamic force and torque exerted on each sphere. For the hydrodynamic interaction among particles, the near-field lubrication force is considered when the separation between spheres belonging to different particles is close, but the far-field part is neglected. The method was applied to the dilute and concentrated system. For the dilute system, the motion of isolated square and rectangular platelike particles was calculated in a simple shear flow. The computed rotation orbits of a rigid square platelike particle were in good agreement with those calculated by Jeffery’s equation for an oblate spheroid (disk). The characteristic behavior, which is unknown from the classical theory, of the rigid rectangular particle and the soft square particle was revealed. For the concentrated system, transient behavior of the platelike particles in a simple shear flow was calculated by dispersing them into a unit cell with periodic boundaries. The planar orientation of particles was observed in the microstructure of the concentrated system, and furthermore the orientation of the major axis of particles in the shear direction appeared in the rectangular platelike particle dispersed system.
The excitation scheme: A new method for calculation of vibrational circular dichroism spectra
Authors: Bouř P. , McCann J. , Wieser H.
Published: July 2002

An alternate procedure for calculating vibrational circular dichroism is proposed. The method eliminates the need to solve the magnetically perturbed SCF equations which leads to an overall decrease in computer time. Instead, an expansion over electronic excited states is partially used to estimate the molecular response to the magnetic field and nuclear displacements. A rigid orbital approximation is used for the electronic states. The rotational strengths obtained in this manner are compared to original experimental data for camphor and α-pinene, and previous calculations on propylene oxide and oxirane. In all cases good agreement of simulated spectral intensities with experiment is observed. Although extensive approximations had to be adopted in the current implementation, the excitation scheme yields results superior to those obtained by the classical MFP or VCT formulations of VCD for camphor and α-pinene, whereas MFP/GIAO theory performs better in the case of oxirane.
Calculation of the rotation–vibration states of water up to dissociation
Authors: Mussa Hamse Y. , Tennyson Jonathan
Published: July 2002

We present rotation–vibrational levels of water up to the dissociation limit using two recent, global potential energy surfaces. These calculations are performed using our recently developed discrete variable representation (DVR) based parallel code (PDVR3D), which runs on computers with massively parallel processors. Variational tests on the convergence of these results show convergence within 0.5 cm−1. Analysis of the highest wave functions for the vibrational energy levels are also shown. Tests on previous calculations performed using conventional computers suggest that convergence for high-lying rotationally excited states is not as good as claimed.
Photoelectron spectroscopy of As−, As2−, As3−, As4−, and As5−
Authors: Lippa T. P. , Xu S.-J. , Lyapustina S. A. , Nilles J. M. , Bowen K. H.
Published: July 2002

The negative ion photoelectron spectra of As−, As2−, As3−, As4−, and As5− have been measured. From these, the electron affinities of As, As2, As3, As4, and As5 have been determined to be 0.814, 0.739, 1.45, <0.8, and ∼1.7 eV, respectively. In the case of As2−, the following molecular constants were also determined: re(As2−)=2.239 Å, ωe(As2−)=293 cm−1, ωeχe(As2−)=4.9 cm−1, D0(As2−)=3.89 eV, and ΔE[2Πg(3/2)−2Πg(1/2)]=0.256 eV. In the case of As3−, vertical detachment energy (VDE) was measured to be 1.62 eV, and for As3, ΔE(2A2−2B1) was determined to be 0.36 eV. For As4−, VDE was found to be 1.52 eV. The relatively high stability of As5− suggests that it, like P5−, may be a candidate for forming cluster-assembled, ionic crystals of stoichiometry, MAs5, where M is an alkali metal atom. Similiarities with other small cluster anions of Group V elements are also discussed.
Folding dynamics with nonadditive forces: A simulation study of a designed helical protein and a random heteropolymer
Authors: Takada Shoji , Luthey-Schulten Zaida , Wolynes Peter G.
Published: July 2002

We propose a reduced model of proteins and simulate folding of a designed three helix bundle protein with 54 residues, the dynamics of a random heteropolymer, and the helix formation of a short peptide, up to ∼1 μs, near the estimated lower bound of folding time. The model has explicit backbone atoms, while solvent effects are taken into account via effective potentials. Interactions include two multibody terms; (1) the hydrogen bond strength reflecting the local dielectric constant that is dependent on protein configuration and (2) the hydrophobic force which depends on the local density of peptide atoms imitating the solvent accessible surface area model of hydrophobic force. With this model, all trajectories of a designed protein reach a native like conformation within 0.5 μs although they exhibit some remaining residual fluctuations. On the other hand, a random polymer collapses to several nonspecific compact forms and continues to change its global shape. A 16 residue segment forming a helix in the designed protein does not stably form a helix when it is cleaved, illustrating the effect of nonadditivity.
The vibrational spectra of CO2+, (CO2)2+, CO2−, and (CO2)2− trapped in solid neon
Authors: Thompson Warren E. , Jacox Marilyn E.
Published: July 2002

When a Ne:CO2 mixture is subjected to Penning ionization and/or photoionization by neon atoms in their first excited states, between 16.6 and 16.85 eV, and the products are rapidly frozen at approximately 5 K, the infrared spectrum of the resulting deposit includes absorptions assigned to CO2+, (CO2)2+, CO2−, and (CO2)2−. The lowest (μ 2∑u+) Renner component of the bending fundamental of CO2+ trapped in a neon matrix appears near the gas-phase band center, but other Renner components are undetectable. Absorptions of a photolabile product correspond to the recently identified CO-stretching fundamentals of (CO2)2+. Weak infrared absorptions at 1253.8 and 714.2 cm−1 are assigned to ν1 and ν2 of CO2−, respectively, and a moderately intense absorption at 2894.7 cm−1 is assigned to the ν1+ν3 combination band of that product. As in other recent argon- and neon-matrix studies, two weak infrared absorptions can be assigned to the two infrared-active OCO-stretching fundamentals of the D2d structure of (CO2)2−. Detailed isotopic substitution studies support all of these assignments. A weak absorption near the CO2 bending fundamental, for which isotopic substitution data are incomplete, may be contributed either by a second fundamental of (CO2)2− (D2d) with b2 symmetry or by a weakly interacting (CO2)n⋅⋅CO2− complex. Such ion–molecule complexes contribute other absorptions near ν3 of CO2 and of CO2−.
Constant surface tension simulations of lipid bilayers: The sensitivity of surface areas and compressibilities
Authors: Feller Scott E. , Pastor Richard W.
Published: July 2002

Eight molecular dynamics simulations of a hydrated lipid bilayer have been carried out differing only in the applied surface tension, γ, defining the boundary conditions of the periodic cell. The calculated surface area per molecule and deuterium order parameter profile are found to depend strongly on γ. We present several methods to calculate the area compressibility modulus, KA, from the simulations. Equivalence between the constant area and constant surface tension ensembles is investigated by comparing the present simulations with earlier work from our laboratories and we find simulation results to depend much more strongly on the specified surface area or surface tension than on the ensemble employed.
Ab initio study of hydrogen dissociation at a surface divacancy on the (001) MgO surface
Authors: D’Ercole Annalisa , Pisani Cesare
Published: July 2002

An embedded-cluster Hartree–Fock approximation is adopted for simulating the heterolytic dissociation of hydrogen at a “tub” divacancy of MgO corresponding to the removal of two nearest neighbor ions at the (001) surface. Two stable dissociated configurations are identified, where the hydroxyl is formed either at a surface four-coordinated oxygen (Tα) or at the five-coordinated oxygen at the bottom of the tub (Tβ). In both configurations, the other atom of the molecule forms a hydride-vacancy complex (HV) near the site of the missing oxygen. The results are discussed with reference to a previous investigation concerning the isolated anion vacancy, where the dissociated configuration (Fα) was similar to Tα. The dissociation process in the three cases is shown to critically depend on the electrostatic field at the defect and on steric hindrance constraints. Tα and Tβ are stable with respect to the undissociated molecule by a few kcal/mol, but only the latter can be reached with low activation energy; Fα is thermodynamically unstable. The dissociation of the HV complex in the presence of ultraviolet radiation is next studied, resulting in the removal of a neutral H atom, while a lone electron remains trapped at the vacancy. This paramagnetic state is characterized, and its features compared with those obtained from recent experiments concerning the Fs(H) color center. On the whole, only the Tβ model is in fair agreement with experimental evidence concerning that center, although definite discrepancies are left.
Fluid transport properties by equilibrium molecular dynamics. III. Evaluation of united atom interaction potential models for pure alkanes
Authors: Dysthe D. K. , Fuchs A. H. , Rousseau B.
Published: July 2002

Results of new simulations for n-butane, n-decane, n-hexadecane, and 2-methylbutane at different state points for seven different united atom interaction potential models are presented. The different models are evaluated with respect to the criteria simplicity, transferability, property independence, and state independence. Viscosities are increasingly underestimated (up to 80%) and diffusion coefficients are overestimated (up to 250%) as the density increases and temperature decreases. Clear evidence was found that the torsion potential is more important at high packing fractions and for longer chains. The comparison of transport coefficients is argued to be a measure of “goodness” of the interaction potential models resulting in a ranking of the models.
Path integral molecular dynamics for Bose–Einstein and Fermi–Dirac statistics
Authors: Miura Shinichi , Okazaki Susumu
Published: July 2002

In this paper, we propose a promising extension of the path integral molecular dynamics method to Bose–Einstein and Fermi–Dirac statistics. The partition function for the quantum statistics was rewritten in a form amenable to the molecular dynamics method with the aid of an idea of pseudopotential for the permutation of particles. Our pseudopotential, here, is a rigorous one describing the whole effect of Bose–Einstein and Fermi–Dirac statistics. For a model calculation, we chose a system consisting of three independent particles in a one-dimensional harmonic well. The calculation has been performed for the particles obeying Bose–Einstein and Fermi–Dirac statistics. The calculated kinetic and potential energies were in excellent agreement with the analytical results even near the ground state. It was found that the pseudopotential shows attractive and repulsive characters for the static properties of Bose–Einstein and Fermi–Dirac particles, respectively. For interacting model particle systems, we studied a bosonic triatomic cluster. The calculated thermodynamic quantities were in qualitative agreement with those obtained by Fourier path integral Monte Carlo calculation.
Nuclear magnetic resonance quantum computing exploiting the pure spin state of para hydrogen
Authors: Hübler Patrick , Bargon Joachim , Glaser Steffen J.
Published: July 2002

Nuclear magnetic resonance (NMR) is well-suited to implement quantum algorithms experimentally. However, there are serious problems associated with the noisy mixed initial state that is described by the thermal equilibrium density operator of NMR spectroscopy. Here we present a new strategy to dramatically increase the sensitivity of a NMR quantum computing experiment. Para hydrogen can be used to prepare a density operator in a suitable molecule that is very close to a pure state, an improvement on the order of 104 compared to “conventional” NMR quantum computing. Our strategy is demonstrated experimentally solving the Deutsch–Jozsa problem based on para hydrogen and Vaska’s complex.
The anomaly structure of theories with external gravity
Authors: Bonora L. , Pasti P. , Tonin M.
Published: July 2002

The cohomology problem of the overall local symmetry group of theories with external gravity, including diffeomorphisms, local Lorentz, and gauge transformations, is studied, in order to determine all possible anomalies. To this end the nontrivial cohomology classes of the coupled system of two coboundary operators are classified in the abstract. Using this result and a technical assumption the nontrivial cohomology classes of the coboundary operator associated with diffeomorphisms are determined. These possible anomalies split in any dimension into two distinct families. Both are calculated (the second only in four dimensions). Using known results about gauge and local Lorentz anomalies, the possible anomalies of the overall local symmetry group are determined.
Construction of hyperbolic monopoles
Authors: Chakrabarti A.
Published: July 2002

Methods are presented for explicit construction of hyperbolic monopoles as defined by Atiyah [M. F. Atiyah, Commun. Math. Phys. 93, 437 (1984); and ‘‘Magnetic monopoles in hyperbolic space, ’’ unpublished lecture notes, 1984]. The techniques permit the extraction of flat-space self-dual monopoles trivially through a simple rescaling. Relationships to previous works of the present author are indicated.
Bianchi VI0 viscous fluid cosmology with magnetic field
Authors: Ribeiro Marcelo Byrro , Sanyal Abhik Kumar
Published: July 2002

A spatially homogeneous Bianchi type VI0 model containing a viscous fluid in the presence of an axial magnetic field has been studied. A barotropic equation of state together with a pair of linear relations among the square root of matter density, shear scalar, and expansion scalar have been assumed. Solutions are obtained in the presence of a magnetic field, only in two special cases, which are comparatively easy. The complete solutions for this model in the absence of a magnetic field are also obtained. The presence of a magnetic field in the former case, however, does not in effect cause any major modification in the fundamental nature of the initial singularity of the expanding model.
Conserved quantities and symmetries of KP hierarchy
Authors: Matsukidaira J. , Satsuma J. , Strampp W.
Published: July 2002

Conserved quantities and symmetries of the KP equation from the point of view of the Sato theory that provides a unifying approach to soliton equations is studied. Conserved quantities are derived from the generalized Lax equations. Some reductions of the KP hierarchy such as KdV, Boussinesq, a coupled KdV, and Sawada–Kotera equation are also considered. By expansion of the squared eigenfunctions of the Lax equations in terms of the τ function, symmetries of the KP equations are obtained. The relationship of this procedure to the two-dimensional recursion operator newly found by Fokas and Santini is discussed.
Painlevé analysis and reducibility to the canonical form for the generalized Kadomtsev–Petviashvili equation
Authors: Brugarino Tommaso , Greco Antonio M.
Published: July 2002

The most general Kadomtsev–Petviashvili (KP) type equation, [ut+â(t,x,y)u+b(t,x,y) ux+c(t,x,y)uux+d(t, x,y)uxxx]x+k(t,x,y) uyy=e(t,x,y), is studied and the conditions for the coefficients, in order that it owns complete integrability, are determined via a Painlevé test. Finally, it is proved that the above conditions are the same as those requested for reducing the equation to the canonical form via suitable transformations.
The summation of the ordinary and renormalized perturbation series for the ground state energy of the quartic, sextic, and octic anharmonic oscillators using nonlinear sequence transformations
Authors: Weniger Ernst Joachim , Čížek Jiří , Vinette Francine
Published: July 2002

The strongly divergent Rayleigh–Schrödinger perturbation expansion for the ground state energy of the quartic, sextic, and octic anharmonic oscillator and a corresponding renormalized perturbation expansion [F. Vinette and J. Čížek, J. Math. Phys. 32, 3392 (1991)] are summed by Padé approximants, by Levin’s sequence transformation [D. Levin, Int. J. Comput. Math. B 3, 371 (1973)], and by a closely related sequence transformation which was suggested recently [E. J. Weniger, Comput. Phys. Rep. 10, 189 (1989)]. It is shown that the renormalized perturbation expansion can be summed much more easily than the original perturbation expansion from which it was derived, and that Levin’s sequence transformation diverges and is not able to sum the perturbation expansions. The Padé summation of the renormalized perturbation expansions gives relatively good results in the quartic and sextic case. In the case of the octic anharmonic oscillator, even the renormalized perturbation expansion is not Padé summable. The best results are clearly obtained by the new sequence transformation which, for instance, is able to sum the renormalized perturbation expansions for the infinite coupling limits of the quartic, sextic, and octic anharmonic oscillator, and which produces at least in the quartic and sextic case extremely accurate results.
Quantum temporal logic and decoherence functionals in the histories approach to generalized quantum theory
Authors: Isham C. J. , Linden N.
Published: July 2002

The recent suggestion that a temporal form of quantum logic provides the natural mathematical framework within which to discuss the proposal by Gell-Mann and Hartle for a generalized form of quantum theory based on the ideas of histories and decoherence functionals is analyzed and developed herein. Particular stress is placed on properties of the space of decoherence functionals, including one way in which certain global and topological properties of a classical system are reflected in a quantum history theory.
Classification of six-vertex-type solutions of the colored Yang–Baxter equation
Authors: Sun Xiao-dong , Wang Shi-kun , Wu Ke
Published: July 2002

In this paper, symmetries and spectral-dependent six-vertex-type solutions of the colored Yang–Baxter equation are discussed. It is shown that each nondegenerate six-vertex-type solution of the colored Yang–Baxter equation is equivalent to one of the six basic solutions up to five solution transformations and all solutions can be classified into two types called the Baxter type and the free-Fermion type.
On realizations of solutions of the KdV equation by determinants on operator ideals
Authors: Aden H. , Carl B.
Published: July 2002

Using new developments in the theory of traces, determinants, and elementary operators on quasi-Banach operator ideals we clarify and extend Marchenko’s method for realizing solutions of the KdV equation. Moreover, we point out why abstract traces and determinants on quasi-Banach operator ideals are appropriate tools for obtaining solutions of the KdV equation. The method we present can also be applied to other nonlinear equations in soliton physics.
Drinfeld constructions of the quantum affine superalgebra Uq(gl(m/n̂))
Authors: Fan Heng , Hou Bo-yu , Shi Kang-jie
Published: July 2002

We apply the method of the central extensions introduced by Reshetikhin and Semenov–Tian–Shansky to the case of the Perk–Shultz model. By using the method proposed by Frenkel–Ding, we establish the Drinfeld constructions of the quantum affine superalgebra Uq(gl(m̂/n)).
Toroidal and level 0 Uq′(sln+1∧) actions on Uq(gln+1∧) modules
Authors: Miki Kei
Published: July 2002

(1) Utilizing a braid group action on a completion of Uq(sln+1∧), an algebra homomorphism from the toroidal algebra Uq(sln+1,tor) (n⩾2) to a completion of Uq(gln+1∧) is obtained. (2) The toroidal actions by Saito induces a level 0 Uq′(sln+1∧) action on level 1 integrable highest weight modules of Uq(sln+1∧). Another level 0 Uq′(sln+1∧) action was defined by Jimbo et al., in the case n=1. Using the fact that the intertwiners of Uq(sln+1∧) modules are intertwiners of toroidal modules for an appropriate comultiplication, the relation between these two level 0 Uq′(sln+1∧) actions is clarified.
Wave packet revivals and quasirevivals in one-dimensional power law potentials
Authors: Robinett R. W.
Published: July 2002

The harmonic oscillator and the infinite square well are two of the simplest one-dimensional quantum systems which exhibit wave packet revivals (trivially so in the case of the oscillator.) These two potentials can be thought of as special cases of the general one-dimensional power-law potential given by V(k)(x)=V0|x/a|k (with k=2 and k→∞ for the oscillator and square well, respectively.) Using an autocorrelation function approach and the WKB approximation for the quantized energy levels in such potentials, we exhibit numerical evidence for wave packet revivals in the case of arbitrary k>0 which agree well with more analytic results. We derive expressions for the revival and collapse time scales in terms of the physical quantities of the system as well as the wave packet parameters. We find that both times scale with the power-law exponent k as |(k+2)/(k−2)|. In this way, we can explicitly exhibit the approach to the two familiar limiting cases. We also briefly consider the case of a “half” well where an infinite wall in added at the origin.
Steady thermocapillary flows of thin liquid layers. I. Theory
Authors: Tan M. J. , Bankoff S. G. , Davis S. H.
Published: July 2002

A thin liquid layer rests on a horizontal plane that is subject to a two-dimensional spatially periodic temperature distribution. Thermocapillary forces on the free surface result in a dimpling interface and a steady viscous flow. Long-wave theory is used to study this system and to determine whether or not there is film dryout locally, and how such dimpling and/or dryout is affected by London–van der Waals forces, surface tension, and hydrostatic effects.
Shear dispersion
Authors: Young W. R. , Jones Scott
Published: July 2002

This review of shear dispersion emphasizes that the usual one-dimensional diffusion equation, derived by Taylor [Proc. R. Soc. London Ser. A 219, 186 (1953)], is an asymptotic result that is valid only at large time. One route to earlier validity is a systematic wave-number expansion based on the center manifold theorem. This procedure captures much of the early behavior but it does discard exponentially decaying transients. However, in some cases of practical importance, such as tracer release experiments in rivers, the observation of ‘‘anomalous diffusion’’ (i.e., tracer variance growing nonlinearly with time) is at odds with this asymptotic reduction. Alternative approximations and models, which account for exponential transients using a description that is nonlocal in time are reviewed. A secondary theme of this review is the application of shear dispersion to mixing of passive and active scalars in rivers and estuaries. An example is shear dispersion of salt in which the shear flow is created by salinity gradients. Other examples include fixed flux convection.
The boundary layers due to shear flow over a still fluid
Authors: Wang C. Y.
Published: July 2002

A constant shear flow passes on top of a heavier, still fluid. Similarity solutions are found for the boundary layers on both sides of the interface.
Temperature fluctuations and transport in a tokamak edge plasma
Authors: Lin H. , Bengtson Roger D. , Ritz Ch. P.
Published: July 2002

Using the technique first described by Robinson and Rusbridge [Plasma Phys. 11, 73 (1969)] electron temperature fluctuations have been measured in the scrape-off layer of the TEXT tokamak [Nucl. Technol. Fusion 1, 479 (1981)] to be T̃e/Te ≂0.4ñe/ne. Particle and energy transport were estimated from 〈ñe Ẽθ〉 and 〈T̃e Ẽθ〉 correlations. The fluctuation-driven particle transport was consistent with earlier measurements and with measurements of global particle confinement. A high correlation of temperature and electric field fluctuations and a low but positive correlation between density and temperature fluctuations were observed.
Soliton propagation, collision, and reflection at a sheath in a positive ion–negative ion plasma
Authors: Cooney Jamie L. , Gavin Matthew T. , Williams James E. , Aossey David W. , Lonngren Karl E.
Published: July 2002

Experiments on the propagation and collision of a Korteweg–deVries soliton in a positive ion–negative ion plasma are described. Both a one-dimensional overtaking collision and a two-dimensional resonant collision are examined. Soliton propagation into a steady-state plasma sheath created by an additional biased metal plate in such a plasma is large enough that the detailed soliton motion in the locally inhomogeneous plasma can be easily studied. A partial reflection and partial transmission of the soliton at a critical density within the sheath is observed and interpreted.
Statistical approach to cubic Langmuir turbulence
Authors: Sun Guo-Zheng , Nicholson D. R. , Rose Harvey A.
Published: July 2002

Previous work on the cubic direct interaction approximation applied to the truncated (in Fourier space) cubically nonlinear Schrödinger equation model of Langmuir turbulence is extended to more modes. In the undriven, undamped case, excellent agreement between the statistical theory and a numerical ensemble of solutions of the dynamic equations is obtained. In the driven, damped case, satisfactory agreement is obtained provided the dynamic ensemble is limited to initial conditions in the basin of attraction.
Experimental investigation of turbulence generated by breaking waves in water of intermediate depth
Authors: Chang Kuang-An , Liu Philip L.-F.
Published: July 2002

This paper reports a set of laboratory data for breaking waves in the water of intermediate depth. A monochromatic wave train with a wave height of 14.5 cm and a wavelength of 121 cm was generated in a water depth, h, of 20 cm. The wave train breaks consistently at a distance of about 2h from the wave generator. The instantaneous velocity fields under the breaking waves on a two-dimensional vertical plane were measured by using the particle image velocimetry (PIV) technique. By repeating the same experiments twenty times and performing the ensemble average, mean velocity, mean vorticity, turbulence intensity, and other flow properties such as the Reynolds stress and the mean strain rate were calculated. Outside the aerated region, where the density of air bubbles is high, the experimental data show that the mean vorticity was of the same order of magnitude as (C/h) (≈6 s−1) with C being the phase speed. The maximum turbulence intensity outside the aerated region was in the order of magnitude of 0.1 C (≈11 cm/s). The time-averaged (over one wave period) turbulence intensity under the wave trough level was one order of magnitude smaller, i.e., it was about 0.04 C (≈4.8 cm/s). Based the experimental data, the transport equation for turbulent kinetic energy was further examined. The turbulence dissipation rate and its time scale were also estimated. Under the trough level at the measurement section, which was about 3h downstream from the breaking point, the turbulence production, and dissipation were of the same order of magnitude, but not identical. The turbulence advection, production, and dissipation were equally important, while the turbulence diffusion was almost negligible.
First results from Alcator-C-MOD*
Authors: Hutchinson I. H. , Boivin R. , Bombarda F. , Bonoli P. , Fairfax S. , Fiore C. , Goetz J. , Golovato S. , Granetz R. , Greenwald M. , Horne S. , Hubbard A. , Irby J. , LaBombard B. , Lipschultz B. , Marmar E. , McCracken G. , Porkolab M. , Rice J. , Snipes J. , Takase Y. , Terry J. , Wolfe S. , Christensen C. , Garnier D. , Graf M. , Hsu T. , Luke T. , May M. , Niemczewski A. , Tinios G. , Schachter J. , Urbahn J.
Published: July 2002

Early operation of the Alcator-C-MOD tokamak [I.H. Hutchinson, Proceedings of IEEE 13th Symposium on Fusion Engineering, Knoxville, TN, edited by M. Lubell, M. Nestor, and S. Vaughan (Institute of Electrical and Electronic Engineers, New York, 1990), Vol. 1, p. 13] is surveyed. Reliable operation, with plasma current up to 1 MA, has been obtained, despite the massive conducting superstructure and the associated error fields. However, vertical disruptions are not slowed by the long vessel time constant. With pellet fueling, peak densities up to 9×1020 m−3 have been attained and ‘‘snakes’’ are often seen. Initial characterization of divertor and scrape-off layer is presented and indicates approximately Bohm diffusion. The edge plasma shows a wealth of marfe-like phenomena, including a transition to detachment from the divertor plates with accompanying radiative divertor regions. Energy confinement generally appears to exceed the expectations of neo-Alcator scaling. A transition to Ohmic H mode has been observed. Ion cyclotron heating experiments have demonstrated good power coupling, in agreement with theory.