bluuebunny/crossref_metadata_2025 huggingface dataset:
Absorption, excitation, and emission spectroscopy of terrylene in p-terphenyl: Bulk measurements and single molecule studies
Authors: Kummer S. , Kulzer F. , Kettner R. , Basché Th. , Tietz C. , Glowatz C. , Kryschi C.
Published: July 2002

This paper reports spectroscopic investigations of the chromophore terrylene embedded in a matrix of crystalline p-terphenyl. While this system is particularly well suited for single molecule spectroscopy, little is known about the guest site configuration of terrylene. To shed some light on this issue, we employed absorption and fluorescence spectroscopy and compared the experimental data to the results of theoretical calculations. Based on this comparison we suggest a substitution scheme which is in agreement with all the spectroscopic evidence. The dispersed fluorescence spectra of single molecules in the wings of the inhomogeneous distribution deviate significantly from the bulk spectra. This observation is discussed in terms of a host-induced change of the structure and a possible C13 isotopic substitution of the chromophores. Finally we investigated the dynamic host–guest interactions via the temperature-dependent shift and broadening of single molecule excitation lines and found these processes dominated by coupling to characteristic pseudolocal phonon modes of the host, although chromophores in the wings of the inhomogeneous distribution exhibit additional contributions which we attribute to thermal matrix expansion.
Effective polarizabilities and local field corrections for nonlinear optical experiments in condensed media
Authors: Wortmann Rüdiger , Bishop David M.
Published: July 2002

A consistent extension of Onsager’s reaction field model to nonlinear-optical experiments in condensed media is presented. This model is used to derive effective (nonresonant) linear and nonlinear molecular polarizabilities involved in refractive index measurements, electric-field induced second-harmonic generation, hyper-Rayleigh scattering, third-harmonic generation and degenerate four-wave mixing. The commonly applied Lorentz correction, while being a useful approximation in linear optics, is demonstrated to lead to systematic errors of typically 20% in nonlinear optical experiments. This is due to an inherent inconsistency that originates from the implicit assumption of a cavity field factor for the nonlinear molecular response.
Molecular dynamics simulation of the diffusion of n-butane and i-butane in silicalite
Authors: Bouyermaouen A. , Bellemans A.
Published: July 2002

Diffusion of the two isomers of butane in silicalite is simulated by molecular dynamics at 300 K and low loading; it appears that n-butane diffuses much more rapidly, due to its elongated trans conformation, and that the vibrations of the silicalite lattice significantly contribute to increase the diffusion coefficient.
Photodissociation of triplet and singlet states of the CCO radical
Authors: Choi Hyeon , Mordaunt David H. , Bise Ryan T. , Taylor Travis R. , Neumark Daniel M.
Published: July 2002

The triplet and singlet states of the ketenylidene (CCO) radical are investigated using fast radical beam photofragment translational spectroscopy, in which CCO is generated by laser photodetachment of CCO− and subsequently photodissociated, and anion photoelectron spectroscopy. In the photodissociation experiment, two bands in which the upper state of CCO predissociates are studied. Photodissociation from excitation of the Ã 3Π–X̃ 3Σ− band in CCO is observed from 16 666–23 529 cm−1; resonances are observed and assigned to excited vibrational levels involving all three vibrational modes. We also report the first observation of the c̃ 1Π–ã 1Δ band in CCO. Here, the ã 1Δ state of CCO is generated by laser photodetachment at higher photon energy than was used to generate the X̃ 3Σ state. The c̃ 1Π state is approximately located by photoelectron spectroscopy of CCO−, and the photodissociation experiment shows that the origin of the c̃ 1Π–ã 1Δ band occurs around 17 170 cm−1. Kinetic-energy release spectra from both bands yield accurate values for the C–CO bond dissociation energy and heat of formation of CCO: D0(C–CO)=2.24±0.02 eV (51.7±0.5 kcal/mol) and ΔHf,2980(CCO)=4.04±0.02 eV (91.1±0.5 kcal/mol). Although the translational-energy distributions resulting from excitation to the Ã 3Π and c̃ 1Π states are clearly nonstatistical, consideration of the potential-energy surfaces indicates that dissociation from both states occurs via radiationless transitions to the X̃ 3Σ− state.
Magnetic field control of an electron tunnel current through a molecular wire
Authors: Petrov E. G. , Tolokh I. S. , May V.
Published: July 2002

The influence of an external magnetic field on the elastic interelectrode tunneling mediated by a molecular wire is studied theoretically for the case in which the wire contains paramagnetic ions. A spin-filtration effect for incoming electrons and a spin-polarization effect for outgoing electrons can be demonstrated for a wire including a single paramagnetic ion as well as a pair of identical antiferromagnetically coupled ions. It is assumed that each paramagnetic ion reduces its spin in the electronic ground-state from S to S−1/2 if the transferred electron forms an intermediate bound state with the ion. Just such a spin reduction results in a transfer which is spin forbidden for spin-down electrons along the predominant tunneling channels. These channels are characterized by the lowest possible spin-projections of the paramagnetic ions. The spin reduction also determines the magnetic field dependence of the transfer rate in a specific manner. In the case of two paramagnetic ions the combined action of the magnetic field and the exchange interaction between the ions is responsible for a step-like dependence of the tunnel current on the magnetic field. The exact dependence of the interelectrode current on the magnetic field-strength at a low temperature is derived in using Wigner’s 6j-symbols methods. The specific spin-polarization effect observed earlier in metal–ferromagnetic insulator–vacuum experiments on electron tunneling is explained in the framework of a spin-filtration effect at which the predominant tunneling channels are responsible for a tunnel interelectrode current.
On the chemical mechanism of surface enhanced Raman scattering: Experiment and theory
Authors: Kambhampati Patanjali , Child C. M. , Foster Michelle C. , Campion Alan
Published: July 2002

We have investigated the chemical mechanism of surface enhanced Raman scattering (SERS) on an atomically smooth metal surface using electron energy loss spectroscopy (EELS) and molecular spectroscopy simulations. The EEL spectra of pyromellitic dianhydride (PMDA) adsorbed on Cu(100) and Cu(111) are reported. Simulations of the surface-enhanced Raman spectra and electron energy loss spectra (EELS) of pyromellitic dianhydride adsorbed on Cu(100) and Cu(111) are reported. The surface enhanced Raman spectra [J. Chem. Soc. Faraday Trans. 92, 4775 (1996)] and the EEL spectra are shown to be sensitive to crystal face. The relevant excited state observed in the EEL spectrum is not intrinsic to molecular PMDA, but results from chemisorption. The Raman spectra are sensitive to the incident laser polarization on both the (100) and (111) surfaces but in different ways. These observations are shown to be a result of the excited state potential energy surface having different shape, and the respective transition dipole moment having a different orientation on the two crystal faces. The nuclear coordinate dependence of the electronic transition dipole moment produces mode selective, polarization dependent Raman scattering cross sections. Based upon this observation we conclude that the transition dipole moment function that couples the ground electronic state to the resonant excited electronic state is also sensitive to the structure of the metal surface.
An in situ Raman spectroscopy study of subcritical and supercritical water: The peculiarity of hydrogen bonding near the critical point
Authors: Ikushima Yutaka , Hatakeda Kiyotaka , Saito Norio , Arai Masahiko
Published: July 2002

The Raman spectra of water are measured at temperatures up to 510 °C and at pressures up to 40 MPa. The peak frequency increases with temperature, indicating the break of hydrogen bonding, and it changes only slightly at higher temperatures above the critical point. The peak frequency has a maximum near the critical pressure, and the extent of hydrogen bonding significantly changes with pressure in this near-critical region. The deviation of the maximum frequency Δf relative to that of the monomer is in good agreement with the chemical shifts with the literature NMR data. The extent of the hydrogen bonding can be estimated from the Δf values. The Δf values at the near-critical points are significantly lower compared with those in super- or sub-critical conditions, and the strength of the hydrogen bonding weakens uniquely in the near-critical region.
A comparative study of dynamics in the nematic and reentrant-nematic phases of 60CB and 60CB/80CB mixture by deuteron nuclear magnetic resonance relaxation
Authors: Shen Xiaodong , Dong Ronald Y.
Published: July 2002

Deuteron longitudinal (T1Z) and quadrupolar (T1Q) spin-lattice relaxation times and quadrupolar splittings were measured over all the stable mesophases in a mixture of perdeuterated 4-n-hexyloxy-4′-cyanobiphenyl (6OCB) and 4-n-octyloxy-4′-cyanobiphenyl (8OCB) at 15.1 and 46 MHz, and compared with those reported previously for a pure 6OCB sample. The 6OCB/8OCB mixture has 28 wt. % of 6OCB and shows a nematic, smectic A and reentrant-nematic (RN) phases. We have carried out data analyses for both samples in order to achieve a consistent physical picture. The additive potential method is employed to construct the potential of mean torque using the quadrupolar splittings in these samples. A decouple model is used to describe correlated internal motions of the end chain, which are independent of the molecular reorientation. The latter motion is treated using the small-step rotational diffusion model of Tarroni and Zannoni, while the former motion is described using a master rate equation. In comparing the NMR results of the pure 6OCB sample and of the 6OCB/8OCB mixture, both the dynamic and static behaviors appear to be similar, and there are no dramatic changes upon entering the RN phase of 6OCB/8OCB, supporting the belief that the effects driving the reentrancy in this mixture are very subtle. The tumbling motion of 6OCB molecules, however, shows quite different behaviors in the two studied samples. Both 6OCB and 8OCB possess a strong terminal dipole and tend to form “loose” dimers. The degree of dimerization can be inferred from the tumbling motion of 6OCB molecules and their internal chain dynamics.
The ground state spectroscopic parameters and molecular geometry of SbH3
Authors: Fusina L. , Di Lonardo G. , De Natale P.
Published: July 2002

The rotation spectrum of stibine, SbH3, in the ground vibrational state was recorded in the region between 30 and 100 cm−1 at an unapodized resolution of about 0.0015 cm−1. ΔJ=+1, ΔK=0 transitions were measured and assigned up to J″=15 and K=12 for both Sb121 and Sb123 isotopomers. The data of each molecule were analyzed together with the J=0, 1 rotational transitions reported in the literature, a few A1–A2, K=3 splitting transitions and K=1←2, ΔK=3 “perturbation allowed” transitions measured recently with Fourier transform microwave spectroscopy, and ground state combination differences from the analysis of the high resolution spectra of the stretching and bending fundamental bands. The theoretical models adopted for the analysis included Δk=±3 or Δk=±6 interaction terms and correspond to two different reductions of the rotational Hamiltonian. From the obtained parameters, the r0 and the equilibrium structure were also determined for this molecule.
Effect of electrostatic interactions on the structure and dynamics of a model polyelectrolyte. II. Intermolecular correlations
Authors: Skibinska Lidia , Gapinski Jacek , Liu Hui , Patkowski Adam , Fischer Erhard W. , Pecora R.
Published: July 2002

The peak in the small angle x-ray scattering and the dynamic light-scattering slow mode for a 20 base-pair duplex oligonucleotide (“B-DNA”) are studied as functions of oligonucleotide and added-salt (NaCl) concentrations. Both the x-ray peak intensity and the relative intensity of the slow mode decrease as the added-salt concentration is increased. The hydrodynamic radius of the slow mode increases as the added-salt concentration is decreased. The x-ray peak gradually disappears with increasing salt while the slow mode decreases in intensity, but still has some residual intensity at the highest added-salt concentration studied. There is no abrupt change in either the peak or the slow mode with increasing salt. The existence and behavior of both the x-ray peak and the slow mode indicate local ordering in the solution due to electrostatic forces. The x-ray peak position for the oligonucleotide is correlated with the static light-scattering peak seen by other workers for dilute solutions of larger polyions. A simple model shows that the reduced electrostatic potential at the average distance between neighboring polyions is approximately the same for these polyelectrolytes. The slow mode has a hydrodynamic radius that increases with decreasing q at low added-salt concentrations, indicating a large correlation volume. The x-ray peak is a more local indicator of nearest-neighbor correlations among the polyions.
Structures and stabilities of doubly charged (MgO)nMg2+ (n=1–29) cluster ions
Authors: Aguado Andrés , López-Gejo Francisco , López José M.
Published: July 2002

Ab initio perturbed ion plus polarization calculations are reported for doubly charged nonstoichiometric (MgO)nMg2+ (n=1–29) cluster ions. We consider a large number of isomers with full relaxations of the geometries, and add the correlation correction to the Hartree–Fock energies for all cluster sizes. The polarization contribution is included at a semiempirical level also for all cluster sizes. Comparison is made with theoretical results for neutral (MgO)n clusters and singly charged alkali–halide cluster ions. Our method is also compared to phenomenological pair potential models in order to assess their reliability for calculations on small ionic systems. The large coordination-dependent polarizabilities of oxide anions favor the formation of surface sites, and thus bulk-like structures begin to dominate only after n=24. The relative stabilities of the cluster ions against evaporation of an MgO molecule show variations that are in excellent agreement with the experimental abundance spectra.
Imaging the alignment angular distribution: State symmetries, coherence effects, and nonadiabatic interactions in photodissociation
Authors: Bracker Allan S. , Wouters Eloy R. , Suits Arthur G. , Vasyutinskii Oleg S.
Published: July 2002

We establish a rigorous theoretical connection between measurements of the angular distribution of atomic photofragment alignment and the underlying dynamics of molecular photodissociation. We derive laboratory and molecular-frame angular momentum state multipoles as a function of photofragment recoil angles. These state multipoles are expressed in terms of alignment anisotropy parameters, which provide information on state symmetries, coherence effects, and nonadiabatic interactions. The method is intended for analysis of experimental data obtained with two-photon spectroscopy and ion imaging techniques, although it is readily modified for treating Doppler or time-of-flight mass spectrometer peak profiles. We have applied this method to the photodissociation of Cl2 at 355 nm, where we observe strong alignment in the ground state chlorine atom photofragments. Our analysis demonstrates that there are important contributions to the alignment from both incoherent and coherent perpendicular excitation. We also show that the existence of atomic alignment due to coherence requires that nonadiabatic transitions occur at long range.
Exciton-scaling and optical excitations of self-similar phenylacetylene dendrimers
Authors: Poliakov Evgeni Y. , Chernyak Vladimir , Tretiak Sergei , Mukamel Shaul
Published: July 2002

The collective electronic oscillators method is used to construct an effective Frenkel exciton Hamiltonian for conjugated dendrimers with fractal geometry. Self-similarity and the high degree of symmetry utilized by decomposing the space of optical excitations into irreducible representations make it possible to compute the one-exciton states and the linear optical response with reduced numerical effort that scales linearly rather than exponentially with the number of generations. The linear optical response is dominated by localized excitons belonging to the periphery.
The sorption induced glass transition in amorphous glassy polymers
Authors: van der Vegt N. F. A. , Briels W. J. , Wessling M. , Strathmann H.
Published: July 2002

Sorption of CO2 in both the glassy and the rubbery state of an amorphous polyethylenelike polymer was investigated using molecular dynamics simulations. The temperature was chosen such that the system was in its glassy state at low solute concentrations and its rubbery state at large solute concentrations. Both the pressure and the volume isotherms changed character at the transition concentration. The physical origin of these changes was clarified by investigation of the excess thermodynamic properties of the solute both below and above the transition concentration. Dynamical changes occuring at the glass transition were studied through the self-intermediate scattering function of the polymer atoms. This function was found to excellently reveal the difference between the dynamics of the glassy and rubbery state and therefore served as an independent tool monitoring the glass transition.
Liquid vapor equilibria for an ab initio model for water
Authors: Mackie A. D. , Hernández-Cobos J. , Vega L. F.
Published: July 2002

The vapor–liquid coexistence densities for water near the critical point were determined using a polarizable ab initio based model and grand canonical Monte Carlo simulations combined with the histogram reweighting technique. The predictions of the model used, which is found to give good agreement with experimental data at ambient conditions, are far below the experimental critical temperature and density. The saturation pressure is also overestimated. The source of this discrepancy may be related to the high pressure that the model exhibits even for liquid water. Since there is no fitting to experimental data, it is possible to refine the potential in a systematic way. In particular, an improvement in the sampling of the ab initio calculation for the repulsive part of the intermolecular potential is suggested in order to obtain better agreement with experiment at high temperatures and pressures.
Simulation of a free energy upper bound, based on the anticorrelation between an approximate free energy functional and its fluctuation
Authors: Meirovitch Hagai
Published: July 2002

The local states and hypothetical scanning methods enable one to define a series of lower bound approximations for the free energy, FA from a sample of configurations simulated by any exact method. FA is expected to anticorrelate with its fluctuation σA, i.e., the better (i.e., larger) is FA the smaller is σA, where σA becomes zero for the exact F. Relying on ideas proposed by Meirovitch and Alexandrowicz [J. Stat. Phys. 15, 123 (1976)] we best-fit such results to the function FA=Fextp+C[σA]α where C, and α are parameters to be optimized, and Fextp is the extrapolated value of the free energy. If this function is also convex (concave down), one can obtain an upper bound denoted Fup. This is the intersection of the tangent to the function at the lowest σA measured with the vertical axis at σA=0. We analyze such simulation data for the square Ising lattice and four polymer chain models for which the correct F values have been calculated with high precision by exact methods. For all models we have found that the expected concavity always exists and that the results for Fextp and Fup are stable. In particular, extremely accurate results for the free energy and the entropy have been obtained for the Ising model.
Dynamical heterogeneity in nanoconfined poly(styrene) chains
Authors: Zax D. B. , Yang D.-K. , Santos R. A. , Hegemann H. , Giannelis E. P. , Manias E.
Published: July 2002

Fluids in nanoscopic confinements possess a variety of unusual properties, and in particular, remarkable dynamical heterogeneities which vary on length scales as short as a fraction of a nanometer. While the surface forces apparatus provides an experimental probe of macroscopic properties of fluids in contact with atomically smooth solid surfaces, few experimental probes are available which test the microscopic origins of these heterogeneities. In this article we describe our recent efforts to apply nuclear magnetic resonance spectroscopy to nanoscopically confined poly(styrene) (PS) created by intercalation into a surface-modified fluorohectorite. A comparison between surface-sensitive cross polarization experiments with spin–echo experiments which probe the entire organic layer suggests that PS in the center of the nanopores is more mobile than the bulk at comparable temperatures, while chain segments which interact with the surface are dynamically inhibited.
Density functional theory of simple polymers in a slit pore. I. Theory and efficient algorithm
Authors: Hooper Justin B. , McCoy John D. , Curro John G.
Published: July 2002

Previous applications of density functional (DF) theory required a single chain Monte Carlo simulation to be performed within a self-consistent loop. In the current work, a methodology is developed which permits the simulation to be taken out of the iterative loop. Consequently, the calculation of the self-consistent, medium-induced potential, or field, is decoupled from the simulation. This approach permits different densities, different forms of UM(r), and different wall–polymer interactions to be investigated from a single Monte Carlo simulation. The increase in computational efficiency is immense.
The c 3Σ+, b 3Π, and a 3Σ+ states of NaK revisited
Authors: Ferber R. , Pazyuk E. A. , Stolyarov A. V. , Zaitsevskii A. , Kowalczyk P. , Chen Hongmin , Wang He , Stwalley William C.
Published: July 2002

We present new c 3Σ+→a 3Σ+ laser induced fluorescence spectra of the NaK molecule, which clearly indicate that v0=20 is the first vibrational level of the c 3Σ+ state lying above v=0 of B 1Π state. These spectra are used in a multistep deperturbation (B 1Π∼c 3Σ+∼b 3Π) procedure to obtain improved a 3Σ+, b 3Π and c 3Σ+ potential energy curves. The deperturbation analysis is confirmed by the calculated electronic B 1Π∼c 3Σ+ and c 3Σ+∼b 3Π spin–orbit matrix elements obtained from many-body multipartitioning perturbation theory employing the relativistic effective potential method.
Molecular dynamics study of the intercalation of diblock copolymers into layered silicates
Authors: Lee Jae Youn , Baljon Arlette R. C. , Sogah Dotsevi Y. , Loring Roger F.
Published: July 2002

Polymer-layered silicate nanocomposites may be formed by annealing layered silicate particles with a polymer melt. Polymer molecules flow from a bulk melt into the galleries between silicate sheets, swelling the silicate structure. The use of an amphiphilic intercalant raises possibilities of forming novel structures and enhancing the intercalation kinetics relative to the case of homopolymer intercalants. We perform molecular dynamics simulations of the flow of a symmetric diblock copolymer from a bulk melt into a slit whose surfaces are modified by grafted surfactant chains, and whose walls are maintained at a constant pressure to permit the slit to open as polymer intercalates. Intercalation kinetics are examined for a variety of polymer–surface and interblock interactions and for thermodynamic states in which the bulk polymer occupies either a lamellar or disordered phase. Comparison to previous simulations of homopolymer intercalation demonstrates that diblock copolymers may be used to intercalate a block that would not spontaneously intercalate as a homopolymer.
Structure of spin groups associated with degenerate Clifford algebras
Authors: Ablamowicz Rafal
Published: July 2002

Clifford algebras over finite-dimensional vector spaces endowed with degenerate quadratic form contain a nontrivial two-sided nilpotent ideal (the Jacobson radical) generated by the orthogonal complement of such spaces. Thus, they cannot be faithfully represented by matrix algebras. Following the theory of spin representations of classical Clifford algebras, the left regular (spin) representations of these degenerate algebras can be studied in suitably constructed left ideals. First, structure of the group of units of such algebras is examined for a quadratic form of arbitrary rank. It is shown to be a semidirect product of a group generated by the radical and the group of units of a maximal nondegenerate Clifford subalgebra. Next, in the special case of corank 1, Clifford, pin, and spin groups are defined an their structures are described. As an example, a Galilei–Clifford algebra over the Galilei space-time is considered. A covering theorem is then proved analogous to the one well known in the theory of spin and orthogonal groups.
Soliton and antisoliton interactions in the ‘‘good’’ Boussinesq equation
Authors: Manoranjan V. S. , Ortega T. , Sanz-Serna J. M.
Published: July 2002

The solitary-wave interaction mechanism for the good Boussinesq equation is investigated and found to be far more complicated than was previously thought. Three salient features are that solitary waves only exist for a finite range of velocities, that large solitons can turn into so-called antisolitons, and that it is possible for solitons to merge and split. Small solitons, however, appear to be stable. The existence of a potential well is linked to the different behaviors observed between small and large initial conditions.
Driven three-state model and its analytic solutions
Authors: Carroll C. E. , Hioe F. T.
Published: July 2002

For an atom or molecule in which two transitions are driven by laser beams, a three-state model is used. Transitions among the three states are caused only by the oscillating electric fields of the laser beams. The amplitudes and detunings of the two laser beams, which are various functions of the time, appear in the Schrödinger equation for the atom or molecule. In certain cases, the Schrödinger equation can be solved analytically, to find transition probabilities and the probability of no transition. This is done by using Clausen’s special function, or by assuming that the sum of the two detunings is zero at all times. Conditions for complete transfer of the population from the ground state to an excited state are obtained from the analytic solutions.
Quantum mechanics on p-adic fields
Authors: Ruelle Ph. , Thiran E. , Verstegen D. , Weyers J.
Published: July 2002

A formulation of quantum mechanics on p-adic number fields is presented. Quantum amplitudes are taken as complex functions of p-adic variables and it is shown how the Weyl approach to quantum mechanics can be generalized to the p-adic case. The p-adic analogs of simple one-dimensional systems (free particle, compact and noncompact oscillators) are defined by a ‘‘group of motion,’’ which is an Abelian subgroup of SL (2,Qp). In each case the evolution operator is a unitary representation of the appropriate group. Its spectrum is given by characters and its eigenstates are calculated.
Special conformal Killing vector space-times and symmetry inheritance
Authors: Coley A. A. , Tupper B. O. J.
Published: July 2002

Viscous heat-conducting fluid and anisotropic fluid space-times admitting a special conformal Killing vector (SCKV) are studied and some general theorems concerning the inheritance of the symmetry associated with the SCKV are proved. In particular, for viscous fluid space-times it is shown that (i) if the SCKV maps fluid flow lines into fluid flow lines, then all physical components of the energy-momentum tensor inherit the SCKV symmetry; or (ii) if the Lie derivative along a SCKV of the shear viscosity term ησab is zero then, again, we have symmetry inheritance. All space-times admitting a SCKV and satisfying the dominant energy condition are found. Apart from the vacuum pp-wave solutions, which are the only vacuum solutions that can admit a SCKV, the energy-momentum tensor associated with these space-times is shown to admit at least one null eigenvector and can represent either a viscous fluid with heat conduction or an anisotropic fluid. No perfect fluid space-times can admit a SCKV. These SCKV space-times and, also, space-times admitting a homothetic vector are used to illustrate the symmetry inheritance theorems.
Exact and steady-state solutions to sinusoidally excited, half-infinite chains of harmonic oscillators with one isotopic defect
Authors: Mokole E. L. , Mullikin A. L. , Sledd M. B.
Published: July 2002

A half-infinite chain of spring-mass oscillators with nearest-neighbor coupling is excited by a sinusoidal force applied to the mass at the accessible end of the chain. The identical linear springs are massless. Each mass has measure m(m>0) except one, which has measure μm(μ>0). An exact solution is given for the initial-value problem in which all initial velocities and displacements are zero. Behavior of the solution for large t (time) is examined. When the concept of average power supplied by the source to the chain in steady state is meaningful, expressions for average power are deduced.
Beltrami algebra and symmetry of the Beltrami equation on Riemann surfaces
Authors: Guo Han-Ying , Shen Jian-Min , Wang Shi-Kun , Xu Kai-Wen
Published: July 2002

It is shown that the Beltrami equation has an infinite-dimensional symmetry, namely the Beltrami algebra, on its solution spaces. The Beltrami algebra with central extension and its supersymmetric version are explicitly found.
A Schrödinger-type equation over the field of p-adic numbers
Authors: Kochubei Anatoly N.
Published: July 2002

A Schrödinger-type pseudo-differential equation related to p-adic quantum mechanics is considered. Formulas for the solution of the Cauchy problem and the uniqueness result are given.
Boundary values as Hamiltonian variables. I. New Poisson brackets
Authors: Soloviev Vladimir O.
Published: July 2002

The ordinary Poisson brackets in field theory do not fulfill the Jacobi identity if boundary values are not reasonably fixed by special boundary conditions. It is shown that these brackets can be modified by adding some surface terms to lift this restriction. The new brackets generalize a canonical bracket considered by Lewis, Marsden, Montgomery, and Ratiu for the free boundary problem in hydrodynamics. The definition of Poisson brackets used herein permits the treating of to treat boundary values of a field on equal footing with its internal values and the direct estimation of estimate the brackets between both surface and volume integrals. This construction is applied to any local form of Poisson brackets.
Master equation based formulation of nonequilibrium statistical mechanics
Authors: Gaveau Bernard , Schulman L. S.
Published: July 2002

For a nonequilibrium system characterized by its state space, by a dynamics defined by a transfer matrix and by a reference equilibrium dynamics given by a detailed-balance transfer matrix, we define various nonequilibrium concepts: relative entropy, dissipation during the relaxation to the stationary state, path entropy, cost for maintaining the system in a nonequilibrium state, fluctuation-dissipation theory, and finally a tree integral formula for the stationary state.
On the structure of symmetric self-dual Lie algebras
Authors: Figueroa-O’Farrill José M. , Stanciu Sonia
Published: July 2002

A finite-dimensional Lie algebra is called (symmetric) self-dual, if it possesses an invariant nondegenerate (symmetric) bilinear form. Symmetric self-dual Lie algebras have been studied by Medina and Revoy, who have proven a very useful theorem about their structure. In this paper we prove a refinement of their theorem that has wide applicability in conformal field theory, where symmetric self-dual Lie algebras start to play an important role due to the fact that they are precisely the Lie algebras that admit a Sugawara construction. We also prove a few corollaries that are important in conformal field theory.
A group analysis approach for a nonlinear differential system arising in diffusion phenomena
Authors: Torrisi M. , Tracinà R. , Valenti A.
Published: July 2002

We consider a class of second-order partial differential equations which arises in diffusion phenomena and, following a new approach, we look for a Lie invariance classification via equivalence transformations. A class of exact invariant solutions containing an arbitrary function is obtained.
Explicit solutions of supersymmetric KP hierarchies: Supersolitons and solitinos
Authors: Ibort A. , Martínez Alonso L. , Medina Reus E.
Published: July 2002

Wide classes of explicit solutions of the Manin-Radul and Jacobian supersymmetric KP hierarchies are constructed by using line bundles over complex supercurves based on the Riemann sphere. Their construction extends several ideas of the standard KP theory, such as wave functions, ∂̄-equations and τ-functions. Thus, supersymmetric generalizations of N-soliton solutions, including a new purely odd ‘‘solitino’’ solution, as well as rational solutions, are found and characterized.
Nonholonomic constraints in time-dependent mechanics
Authors: Giachetta G. , Mangiarotti L. , Sardanashvily G.
Published: July 2002

The constraint reaction force of ideal nonholonomic constraints in time-dependent mechanics on a configuration bundle Q→R is obtained. Using the vertical extension of Hamiltonian formalism to the vertical tangent bundle VQ of Q→R, the Hamiltonian of a nonholonomic constrained system is constructed. The present setting is more general than the one usually considered in the literature on nonholonomic mechanics.
Simple spin networks as Feynman graphs
Authors: Freidel L. , Krasnov K.
Published: July 2002

We show how spin networks can be described and evaluated as Feynman integrals over an internal space. This description can, in particular, be applied to the so-called simple SO(D) spin networks that are of importance for higher-dimensional generalizations of loop quantum gravity. As an illustration of the power of the new formalism, we use it to obtain the asymptotics of an amplitude for the D simplex and show that its oscillatory part is given by the Regge action.
Superconductors with charge- and spin-density waves: theory and experiment (Review)
Authors: Gabovich A. M. , Voitenko A. I.
Published: July 2002

The properties of existing superconductors with ejectron spectrum instabilities, namely charge-density waves (CDWs) and spin-density waves (SDWs), are reviewed. In such substances the superconducting gap exists over the whole Fermi surface, whereas the dielectric gap emerges only on its nested sections. In particular, CDW superconductors include layered dichalcogenides, NbSe3, compounds with the A15 and C15 structures, etc. There is a lot of evidence that high-Tc oxides also belong to this group of materials. SDW superconductors include, e.g., URu2Si2 and related heavy-fermion compounds, Cr–Re alloys and organic superconductors. The theoretical description given in this review is based mostly on the Bilbro-McMillan model of the partially dielectrized metal. Various thermodynamic and electrodynamic properties are calculated in the framework of this model. The main subject of the review is the nonstationary Josephson effect in tunnel junctions involving CDW or SDW superconductors. A new effect of symmetry breaking in symmetrical tunnel junctions is predicted by the authors. A comparison with experiment is given.
Self-dilating viscous fingers in wedge-shaped Hele-Shaw cells
Authors: Ben Amar Martine , Hakim Vincent , Mashaal Maurice , Couder Yves
Published: July 2002

Viscous fingering in a wedge-shaped Hele-Shaw cell is analyzed. The shape of a self-dilating viscous finger is shown to obey a time-independent nonlinear integrodifferential equation that is solved numerically. The results show that there is a continuum of zero-surface-tension solutions for any wedge angle between 0 and π/2. When surface tension is taken into account only a discrete set of solutions exist. In contrast to the classical case, different branches merge for finite values of the surface tension parameters.
Nonlinear optical guiding in the separable beam limit
Authors: Metzler N. , Antonsen T. , Levush B.
Published: July 2002

The nonlinear theory of optical guiding in a free electron laser amplifier is developed for the case in which the axial and radial dependence of the fluctuating current in the electron beam can be separated. Such a separation can be motivated if either the betatron wavelength is shorter than other lengths of interest (synchrotron wavelength, vacuum Rayleigh length) or if the radiation waist exceeds the beam radius. In such cases, assuming a Gaussian profile for the electron beam density enables the wave equation to be solved exactly and the radiation field experienced by the particles to be expressed as a one-dimensional convolution of the current source. Analytical and numerical calculations of the effect of diffraction on the gain and nonlinear saturation of a free electron laser amplifier are presented. The constraints imposed by diffraction on efficiency enhancement by tapering are examined.
Spectral characteristics of a free electron laser with time-dependent beam energy
Authors: Antonsen T. M. , Levush B.
Published: July 2002

The spectral characteristics of a continuous beam free electron laser are studied both numerically and analytically. The average spectral width and the probability distribution of mode amplitudes determined from nonlinear numerical simulations are found to agree with a simple theory based on the linear growth of each mode in the presence of a white noise source. Included in the numerical simulation model is the time dependence of the beam energy and its effect on the spontaneous emission rate. Based on this model predictions of the frequency of observing a single dominant mode in the recent University of California at Santa Barbara experiments [FEL ’89, 11th International Conference on Free Electron Lasers, Conference Digest (IEEE), New York, 1989), Paper p. 2.19] are made. The predicted frequency is somewhat lower than observed. However, other features of the simulations do agree with experimental results.
Electron flow in the pinch region of a relativistic electron-beam diode
Authors: Markovits M. , Nardi E. , Zinamon Z.
Published: July 2002

The flow of electrons produced in the pinch region of a relativistic electron beam (REB) diode is studied by means of the time-dependent Kα emission from a double-layered anode. The anode materials were Cu and Ni foils of various thicknesses. The experimental data were analyzed using detailed Monte-Carlo simulation. Results indicate that no anomalous deposition processes seem to occur, and that the angular distribution at the anode can be fairly well represented by an axially symmetric angular distribution with an angle of incidence of 60° to the normal.
A simplified Vlasov–Landau treatment of electron motion in the orbitron maser
Authors: Alexeff Igor
Published: July 2002

An electron ring trapped in a logarithmic potential well (orbitron) is studied. The electrons in the ring possess a spread in angular velocity. A forward traveling-wave line is used to simulate a cavity resonator. For a Maxwellian, or monotonically increasing electron distribution function with increasing orbital frequency, sinusoidal perturbations are damped. For an inverted energy distribution, they grow. The growth rate at harmonics of the orbital frequency increases linearly with harmonic number.
Long-time quasilinear evolution of the free-electron laser instability for a relativistic electron beam propagating through a helical magnetic wiggler
Authors: Davidson Ronald C. , Yin Y. Z.
Published: July 2002

The long-time quasilinear development of the free-electron laser instability is investigated for a tenuous electron beam propagating in the z direction through a helical wiggler field B0=−B̂ cos k0zêx−B̂ sin k0zêy. The analysis neglects longitudinal perturbations (δφ≂0) and is based on the nonlinear Vlasov–Maxwell equations for the class of beam distributions of the form fb(z,p,t) =n0δ(Px)δ(Py)G(z,pz,t), assuming ∂/∂x=0=∂/∂y. The long-time quasilinear evolution of the system is investigated within the context of a simple ‘‘water-bag’’ model in which the average distribution function G0( pz,t) =(2L)−1∫L−L dz G(z,pz,t) is assumed to have the rectangular form G0( pz,t) =[2Δ(t)]−1 for ‖pz−p0(t)‖ ≤Δ(t), and G0( pz,t) =0 for ‖pz−p0(t)‖ >Δ(t). Making use of the quasilinear kinetic equations, a coupled system of nonlinear equations is derived which describes the self-consistent evolution of the mean electron momentum p0(t), the momentum spread Δ(t), the amplifying wave spectrum ‖Hk(t)‖2, and the complex oscillation frequency ωk(t) +iγk(t).

These coupled equations are solved numerically for a wide range of system parameters, assuming that the input power spectrum Pk(t=0) is flat and nonzero for a finite range of wavenumber k that overlaps with the region of k space where the initial growth rate satisfies γk(t=0) >0. To summarize the qualitative features of the quasilinear evolution, as the wave spectrum amplifies it is found that there is a concomitant decrease in the mean electron energy γ0(t)mc2=[m2c4+e2B̂2/k20 +p20(t)c2]1/2, an increase in the momentum spread Δ(t), and a downshift of the growth rate γk(t) to lower k values. After sufficient time has elapsed, the growth rate γk has downshifted sufficiently far in k space so that the region where γk >0 no longer overlaps the region where the initial power spectrum Pk(t=0) is nonzero. Therefore, the wave spectrum saturates, and γ0(t) and Δ(t) approach their asymptotic values.
Excitation of ion-acoustic rarefactive solitons in a two-electron-temperature plasma
Authors: Nishida Yasushi , Nagasawa Takeshi
Published: July 2002

Rarefactive ion-acoustic solitons have been observed in a two-electron-temperature plasma. Some of the characteristics can be interpreted by the solution of the Kortweg–de Vries (K–dV) equation. The Mach number of the solitons is a function of the temperature ratio of hot and cold components.
Rapid shear flow of a dry magnetic powder in an externally applied magnetic field: An experimental study
Authors: Craig Kevin , Buckholz R. H. , Domoto G.
Published: July 2002

In this paper, the rapid simple shearing flow of a dry cohesionless soft-ferromagnetic metal powder is studied in an externally applied magnetic field. An annular shear-cell apparatus was used to test the powder. Dry metal powder is contained in the annular channel. The powder is rapidly sheared by rotating one of the shear transmission surfaces while the other shear transmission surface remains fixed. Various magnetic fields are applied to the metal powder during the shearing motion. At present this field effect on the flow is not well understood. The shear stress and normal stress on the stationary surface are measured as a function of the following parameters: fractional solids content, shear rate, shear-cell gap thickness, and the magnitude and direction of the magnetic field strength. Both the fractional solids content and the shear-cell gap thickness are kept at prescribed values during stress measurements. The shear stress and normal stress are observed to increase with the application of a magnetic field. A framework is developed that explains the magnetic field effect in shear flow applications.
The nonlinear eikonal relation of a weakly inhomogeneous magnetized plasma upon the action of arbitrarily polarized finite wavelength electromagnetic waves
Authors: Stefan V. , Krall N. A. , McBride J. B.
Published: July 2002

Based on a hydrodynamic Maxwell formalism of a weakly inhomogeneous magnetized plasma, a mode–mode coupling eikonal relation is derived. Finite wavelength and arbitrary polarization of a monochromatic driver pump have been taken into account as well as longitudinal and transverse components of the self-consistent plasma electric field. A weak turbulence theory method is used to solve the resulting inhomogeneous Volterra-type integral equation in tensorial form, i.e., an expansion of hydrodynamic quantities over the resultant electric field (driver pump and self-consistent field) up to the third order. The eikonal coupling relation thus obtained is discussed for the case of longitudinal and transverse interactions.
Scaling laws for a self-generated axial magnetic field in laser-produced plasma
Authors: Chakraborty B. , Khan Manoranjan , Bhattacharyya B. , Deb Sukanta , Pant H. C.
Published: July 2002

The generation of an axial magnetic field caused by the interaction of standing waves formed by two counterpropagating, elliptically polarized electromagnetic waves with a laser-produced plasma has been investigated. Study of the variation of magnetization with different powers and wavelengths available from Nd–glass and CO2 lasers shows that induced axial magnetization increases linearly with an increase in power for all wavelengths and increases exponentially with the wavelengths for different laser powers at a particular plasma density. The variation of magnetization with plasma density reveals that the peak value of magnetization occurs below the critical density (nc) for a particular wavelength and power. Scaling laws for the induced axial magnetic field have been given. The poloidal fields arising from such mechanisms are important in the lateral energy and axial energy transport mechanisms. Such a field inhibits lateral energy transport, but axial energy propagation may be increased.
Electron diamagnetism and toroidal coupling of tearing modes
Authors: Cowley S. C. , Hastie R. J.
Published: July 2002

Using a simple model for the layer of the tearing mode, it is demonstrated that toroidally coupled tearing modes with two rational surfaces are most unstable when the ω*’s of the electrons at the rational surfaces are equal. The onset of instability may then occur because of the tuning of ω* rather than the passage of Δ′-like quantities through zero. This mechanism for the onset of instability is sharp since the resonance is narrow. The effect of toroidal rotation is also discussed.
On the two-way interaction between homogeneous turbulence and dispersed solid particles. II. Particle dispersion
Authors: Truesdell G. C. , Elghobashi S.
Published: July 2002

Part I of this paper [Elghobashi and Truesdell, Phys. Fluids A 5, 1790 (1993)] examined the modulation of turbulence by the particles. Here the effects of the two-way interaction on particle dispersion are discussed. In zero gravity, the two-way coupling enhances the alignment of the surrounding fluid velocity vector with the direction of the solid particle trajectory. This alignment reduces the mean-square relative velocity and increases the Lagrangian velocity autocorrelation coefficient of the solid particle, the fluid point and the surrounding fluid, and the mean-square displacement of the solid particles. However, the fluid point mean-square displacement decreases because the larger inertia of the solid particles increases the decay rate of turbulence energy. In gravity environment, the particles augment the component of turbulence energy in the gravity direction, and thus increase the mean-square displacement of the solid particles and fluid points in that direction. However, their dispersion in the lateral directions is reduced due to the crossing trajectories effect [Yudine, Adv. Geophys. 6, 185 (1959)].