bluuebunny/crossref_metadata_2025 huggingface dataset:
A correlated basis set for nonadiabatic energy calculations on diatomic molecules
Authors: Kinghorn Donald B. , Adamowicz Ludwik
Published: July 2002

A new explicitly correlated basis set suitable for nonadiabatic energy calculation on small diatomic molecules is presented. The basis functions consist of correlated Gaussians multiplied by powers of the internuclear distance. N-body formulas for Hamiltonian matrix elements and energy gradient components are derived and presented along with a discussion of the nonadiabatic Hamiltonian and symmetry considerations. A sample calculation is presented for the ground state energy of the benchmark system H2+ in which rapid convergence to near exact results was observed.
Anion photoelectron spectroscopy of PdCO− and PdCN: Reactivity of Pd−
Authors: Klopcic Stephan A. , Moravec Vicki D. , Jarrold Caroline Chick
Published: July 2002

The ground electronic states of PdCO−/PdCO and PdCN−/PdCN are investigated using anion photoelectron spectroscopy (PES). The electron affinity of PdCO− is determined to be 0.604±0.010 eV. The anion PES of PdCO− exhibits a single, vibrationally resolved electronic band assigned to the Σ+1+e−←2Σ+ anion to neutral transition. The neutral carbonyl stretch is resolved and measured to be 2140±60 cm−1. There is an additional, partially resolved 350±40 cm−1 vibrational progression that is attributed to Pd–CO relative motion. The PES of PdCN− exhibits a single peak at 2.543±0.007 eV, which is the electron affinity of PdCN. This vertical electronic band is tentatively assigned to the Σ+2+e−←1Σ+ transition. The highest occupied molecular orbital of both the anion and neutral is described as a nonbonding spd hybrid orbital on Pd that does not affect the ionic bond of the neutral Pd+⋅CN− core. The various reactions of Pd and Pd− with methanol and acetonitrile along with other reactants that may be present in the ion source are considered.
Theory of single-molecule fluorescence spectroscopy of two-state systems
Authors: Berezhkovskii A. M. , Szabo Attila , Weiss G. H.
Published: July 2002

We derive an explicit expression for the probability density of the amplitudes of the biexponential fluorescence decay of a two-state system observed in single-molecule experiments of finite duration T. The shape of the probability density of the amplitudes depends on (k1+k2)T, where the ki are the interconversion rate constants. It approaches a delta function in the limit T→∞. When the interconversion rates in the ground and excited states differ, the single-molecule and bulk experiments will give different results even in the limit of infinite duration of the experiment.
The semirigid vibrating rotor target model for quantum polyatomic reaction dynamics
Authors: Zhang J. Z. H.
Published: July 2002

In this paper, we present detailed quantum treatment of the semirigid vibrating rotor target (SVRT) model for reaction dynamics involving polyatomic molecules. In the SVRT model, the reacting (target) molecule is treated as a semirigid vibrating rotor which can be considered as a three-dimensional generalization of the diatomic molecule. This model provides a realistic framework to treat reaction dynamics of polyatomic systems. Using the SVRT model, it becomes computationally practical to carry out quantitatively accurate quantum dynamics calculation for a variety of dynamics problems in which the reacting molecule is a polyatomic or complex molecule. In this work, specific theoretical treatment and mathematical formulation of the SVRT model are presented for three general classes of reaction systems: (1) reaction of an atom with a polyatomic molecule (atom–polyatom reaction), (2) reaction between two polyatomic molecules (polyatom–polyatom reaction), and (3) polyatomic reaction with a rigid surface (polyatom–surface reaction). Since the number of dynamical degrees of freedom in the SVRT model for the above three classes of dynamical problems is limited, accurate quantum (both ab initio and dynamical) calculations are possible for many reactions of practical chemical interest. In this paper, a time-dependent wave packet approach is employed to implement the SVRT model for dynamics calculation of polyatomic reactions.
Simulation and density functional study of a simple membrane separating two restricted primitive model electrolytes
Authors: Boda Dezső , Henderson Douglas , Rowley Richard , Sokołowski Stefan
Published: July 2002

A simple membrane, supporting charge densities σ1 and σ2=−σ1 on its inner and outer surfaces, is considered. In addition to the electrostatic potential, the membrane interacts with the surrounding fluid by a short range van der Waals-like potential. The fluid beyond the outer surface is a three-component restricted primitive electrolyte consisting of two cations and one anion. The membrane is impermeable to one of the cations so that the fluid in the membrane and beyond the inner surface is a two-component restricted primitive electrolyte. We use Monte Carlo simulations and density functional theory to study the density profiles of the electrolyte and the charge-electrostatic potential relationship for the membrane surfaces. Even though σ2=−σ1, the potentials on the membrane surfaces are not equal and opposite. We also study a membrane consisting of a single charged plane. For both models, the density functional results are in good agreement with the simulations.
The projection of a mechanical system onto the irreversible generalized Langevin equation
Authors: Hernandez Rigoberto
Published: July 2002

The so-called irreversible generalized Langevin equation [R. Hernandez and F. L. Somer, J. Phys. Chem. B 103, 1064 (1999)], which extends the generalized Langevin equation (stochastic dynamics) to include irreversible changes—nonstationarity—in the solvent response, is shown to be the projection of an explicit time-dependent Hamiltonian system.
Atomic and molecular hydrogen interacting with Pt(111)
Authors: Olsen R. A. , Kroes G. J. , Baerends E. J.
Published: July 2002

This computational study is motivated by the apparent conflict between an experiment on dissociation of H2 and D2 on Pt(111), which suggests a rather corrugated potential energy surface (PES) for the H2/Pt(111) system, and an experiment showing only weak nonzero-order diffraction of HD scattering from Pt(111). In the calculations we have used density functional theory (DFT) within the generalized gradient approximation (GGA), including scalar relativistic effects and modelling the Pt(111) surface as a slab. We have found that the H2/Pt(111) PES is both energetically and geometrically corrugated. We have also found that there are reaction paths without or with very low barriers leading to dissociation of H2 on the Pt(111) surface, but that there are other reaction paths with substantial barriers. By performing extensive calculations on H interacting with a Pt(111) surface we have shown that a DFT/GGA approach that includes scalar relativistic effects is capable of describing the interaction between a hydrogen atom and a Pt(111) surface in a way that is, for the most part, consistent with experiments.
The electronic structure of PdC2H and PdC2HN determined by anion photoelectron spectroscopy
Authors: Moravec Vicki D. , Jarrold Caroline C.
Published: July 2002

The photoelectron spectra of PdC2H− and PdC2HN− are presented and analyzed. The electron affinity of the PdC2H complex is 1.98±0.03 eV, and the electron affinity of the PdC2HN complex is 2.17±0.03 eV. Both spectra are broadened by unresolved progressions in low-frequency vibrational modes of the neutral. Both also show activation of a higher-frequency mode (1720±170 cm−1 for PdC2H and 1800±200 cm−1 for PdC2HN) which suggests that back donation from the Pd dπ orbitals into the π* orbitals of the ligands is involved in the bonding in these species. The spectrum of PdC2H− also shows a transition to a dissociative excited neutral state with an excitation energy of 0.35±0.15 eV. The electronic structures of PdC2H and PdC2H− are explored by comparison with the isoelectronic PdCN and PdCN− species along with supporting density functional theory calculations. Σ+1, Σ+2, and Π2 terms are proposed for the ground anion, ground neutral, and dissociative neutral states, respectively. A chainlike (nonlinear) Pd–C–C–NH structure is proposed as being consistent with the spectrum of PdC2HN−.
Host–guest interactions in an organic crystal: β-hydroquinone clathrate with Ne and HF guests
Authors: Hermansson Kersti
Published: July 2002

Host–guest, guest–guest, and host–host interactions in the β-hydroquinone clathrate crystal have been calculated from periodic and cluster-type ab initio calculations. The potential energy surfaces for the positions of the enclosed guest molecules in the cage have also been studied. The host framework remains virtually unchanged upon guest enclosure. The inclusion energy for the polar HF molecule is about −7 to −9 kcal/mol, in good agreement with our extrapolation from existing calorimetric data for HBr and HCl, and about −1 to −2 kcal/mol for Ne. The guest–guest interaction is small.
Formation mechanism for polycyclic aromatic hydrocarbons in methane flames
Authors: Siegmann K. , Sattler K.
Published: July 2002

A laminar diffusion flame of methane was investigated using time-of-flight mass spectroscopy with two-photon UV laser ionization. Benzenoid polycyclic aromatic hydrocarbons (PAHs) up to 788 amu (C64H20) were detected in the combustion gases. Only the most compact PAHs are formed in the flame. The observed groups of PAH peaks with 24 amu spacings belong to PAHs with constant hydrogen content and are separated by 26 amu gaps. The sequences of PAH peaks with 24 amu spacing are explained by a repetitive bay closure mechanism. The first PAH of a constant H-sequence is proposed to form by a dimerization process. The PAHs observed can be arranged in a repetitive pattern in Dias’s formula periodic system.
Scaling theory for end-functionalized polymers confined between two surfaces: Predictions for fabricating polymer/clay nanocomposites
Authors: Kuznetsov Dmitri V. , Balazs Anna C.
Published: July 2002

Using scaling theory, we investigate the equilibrium behavior of a melt of functionalized chains, nonfunctionalized polymers, and two infinite, planar surfaces, which model clay sheets. The functionalized chains contain two end groups (one at each chain end) that are highly attracted to the surfaces. We calculate the free energy of the system as a function of the separation between the surfaces for various values of the following parameters: the end-group adsorption energy, the length and volume fraction of the end-functionalized chains, and the interaction energy between the different chains. For polymers confined between the surfaces, we also determine the fraction of loops, tails, bridges, and free chains within this gap. Finally, we isolate conditions for the formation of “exfoliated,” “intercalated,” and immiscible polymer/clay mixtures.
Proton transfer in the [phenol-NH3]+ system: An experimental and ab initio study
Authors: Kim Ho-Tae , Green Richard J. , Qian Jun , Anderson Scott L.
Published: July 2002

Mass-analyzed threshold ionization (MATI) has been used to prepare phenol cations in selected vibrational states, including the ground state. Reactions of ground state C6H5OH+ with ND3, studied in a guided ion-beam apparatus, are reported, along with related ab initio calculations. This paper focuses on the energetics and product branching in the proton transfer (PT) channel. Based on thermochemistry in the literature, combined with calculations of the intracomplex PT barrier, PT was expected to make up a large fraction of the total reactive scattering. Experimentally, it is found that PT has a small cross section with clear threshold behavior, and the conclusion is that the PT reaction is endoergic by 4.5±1 kcal/mole. Assuming that NH3 has a proton affinity of 204.0 kcal/mole, this results in a proton affinity for phenoxy radical of 208.7 kcal/mole, and a neutral PhO–H bond energy of 91.1 kcal/mole. The results are used to reinterpret previous dissociative photoionization studies of phenol-ammonia complexes.
Direct observation of charge-transfer-to-solvent (CTTS) reactions: Ultrafast dynamics of the photoexcited alkali metal anion sodide (Na−)
Authors: Barthel Erik R. , Martini Ignacio B. , Schwartz Benjamin J.
Published: July 2002

Charge-transfer-to-solvent (CTTS) transitions have been the subject of a great deal of interest recently because they represent the simplest possible charge transfer reaction: The CTTS electron transfer from an atomic ion to a cavity in the surrounding solvent involves only electronic degrees of freedom. Most of the work in this area, both experimental and theoretical, has focused on aqueous halides. Experimentally, however, halides make a challenging choice for studying the CTTS phenomenon because the relevant spectroscopic transitions are deep in the UV and because the charge-transfer dynamics can be monitored only indirectly through the appearance of the solvated electron. In this paper, we show that these difficulties can be overcome by taking advantage of the CTTS transitions in solutions of alkali metal anions, in particular, the near-IR CTTS band of sodide (Na−) in tetrahydrofuran (THF). Using femtosecond pump–probe techniques, we have been able to spectroscopically separate and identify transient absorption contributions not only from the solvated electron, but also from the bleaching dynamics of the Na− ground state and from the absorption of the neutral sodium atom. Perhaps most importantly, we also have been able to directly observe the decay of the Na−* excited CTTS state, providing the first direct measure of the electron transfer rate for any CTTS system. Taken together, the data at a variety of pump and probe wavelengths provide a direct test for several kinetic models of the CTTS process. The model which best fits the data assumes a delayed ejection of the electron from the CTTS excited state in ∼700 fs. Once ejected, a fraction of the electrons, which remain localized in the vicinity of the neutral sodium parent atom, recombine on a ∼1.5-ps time scale. The fraction of electrons that recombine depends sensitively on the choice of excitation wavelength, suggesting multiple pathways for charge transfer. The spectrum of the neutral sodium atom, which appears on the ∼700-fs charge-transfer time scale, matches well with a species of stochiometry (Na+, e−) that has been identified in the radiation chemistry literature. All the results are compared to previous studies of both CTTS dynamics and alkali metal solutions, and the implications for charge transfer are discussed.
Geminal functional theory: A synthesis of density and density matrix methods
Authors: Mazziotti David A.
Published: July 2002

The energy of any atom or molecule with an even number N of electrons is shown to be an exact functional of a single geminal where the functionals for both the kinetic energy and the external potential are explicitly known. We derive the foundations for geminal functional theory (GFT) through a generalized constrained search and the use of two theorems which demonstrate that all one-particle properties of atoms and molecules with even N may be parametrized by a single geminal [A. J. Coleman, Int. J. Quantum Chem. 63, 23 (1997); D. W. Smith, Phys. Rev. 147, 896 (1966)]. By generalizing constrained search to optimize the universal functionals with respect to the 2-RDM (two particle reduced density matrix) rather than the wave function, we closely connect the one-density, the 1-RDM (one-particle reduced density matrix), and the geminal functional theories with 2-RDM minimization of the energy. Constrained search with the 2-RDM emphasizes that all energy functional methods must implicitly account for the N-representability of the 2-RDM within their universal functionals. An approximate universal functional for GFT, equivalent to a variational ansatz using the antisymmetrized geminal power wave function, yields energies that are significantly better than those from Hartree–Fock and yet rigorously above the exact energy.
Billiard systems on quadric surfaces and the Poncelet theorem
Authors: Chang Shau-Jin , Shi Kang-Jie
Published: July 2002

Billiard systems constrained to move on a quadric surface with confocal quadric boundaries were studied. The trajectory of a billiard is described as a collection of geodesic segments joining on the boundary. At the joining points, the trajectory obeys the law of reflection. It was found that the geodesic segments are all tangent to a common confocal quadric curve (a caustic) on this quadric surface. If a trajectory is closed, then all trajectories sharing the same caustic quadric are all closed and have the same period and length. Thus a generalization of Poncelet’s theorem on a quadric surface is achieved. The elliptical billiard systems on spheres and pseudospheres were studied and results were obtained that are similar to those on a plane. The results can be extended to n dimensions.
Classification of unitary highest weight representations for noncompact real forms
Authors: Garcia-Escudero Juan , Lorente Miguel
Published: July 2002

Using Jakobsen theorems, unitarizability in Hermitian symmetric spaces is discussed. The set of all missing highest weights is explicitly calculated and the construction of their corresponding highest weights vectors is studied.
Moyal quantization with compact symmetry groups and noncommutative harmonic analysis
Authors: Figueroa Héctor , Gracia-Bondía José M. , Várilly Joseph C.
Published: July 2002

The phase-space approach to quantization of systems whose symmetry group is compact and semisimple is developed from two basic principles: covariance and traciality. This generalizes results and methods already implemented for spin systems [J. C. Várilly and J. M. Gracia-Bondía, Ann. Phys. 190, 107 (1989)]. The twisted product of phase-space functions is shown to be the image of group convolution in the context of a novel Fourier theory on the coadjoint orbits.
On the characterization of probabilities: A generalization of Bell’s inequalities
Authors: Beltrametti Enrico G. , Maczynski Maciej J.
Published: July 2002

A partial solution to the problem of generalizing Bell’s inequalities to arbitrary numbers of physical properties is proposed. It is first assumed that the considered sets of probabilities correspond to events which satisfy a postulate ensuring that they form an orthomodular partially ordered set admitting a full set of states. In this framework a theorem generalizing Bell’s inequalities to an arbitrary finite number of events is proven. An interpretation of these results in Hilbert space is indicated. Conditions characterizing the classicality of so-called correlation probabilities are then found, and a method for verifying inequalities involving measurable correlations is discussed.
Quantum symmetries of q-difference equations
Authors: Floreanini Roberto , Vinet Luc
Published: July 2002

A general method is presented to determine the symmetry operators of linear q-difference equations. It is applied to q-difference analogs of the Helmoltz, heat, and wave equations in diverse dimensions. The symmetries are found to generate q-deformations of classical Lie algebras. The method of separation of variables is used to obtain solutions which are seen to involve many basic special functions. This allows the derivation of various identities and formulas for these q-functions.
Wavelet frames and admissibility in higher dimensions
Authors: Führ Hartmut
Published: July 2002

This paper is concerned with the relations between discrete and continuous wavelet transforms on k-dimensional Euclidean space. We start with the construction of continuous wavelet transforms with the help of square-integrable representations of certain semidirect products, thereby generalizing results of Bernier and Taylor. We then turn to frames of L2(Rk) and to the question, when the functions occurring in a given frame are admissible for a given continuous wavelet transform. For certain frames we give a characterization which generalizes a result of Daubechies to higher dimensions.
Probing quantum gravity through exactly soluble midi-superspaces I
Authors: Ashtekar A. , Pierri M.
Published: July 2002

It is well-known that the Einstein-Rosen solutions to the 3+1- dimensional vacuum Einstein’s equations are in one to one correspondence with solutions of 2+1-dimensional general relativity coupled to axi-symmetric, zero rest mass scalar fields. We first re-examine the quantization of this midi-superspace paying special attention to the asymptotically flat boundary conditions and to certain functional analytic subtleties associated with regularization. We then use the resulting quantum theory to analyze several conceptual and technical issues of quantum gravity.
The instability of a liquid jet in a compressible airstream
Authors: Li H.-S. , Kelly R. E.
Published: July 2002

The instability of a liquid jet immersed in a coflowing compressible airstream has been investigated on the basis of a linear, inviscid stability analysis, assuming uniform velocity profiles within the liquid and gas. Both two-dimensional and circular jets are investigated. Pronounced peaks in the temporal and spatial growth rates occur for values of the free-stream Mach number close to unity. A change from convective to absolute instability also occurs in this transonic flow regime of the gas.
Backflow effect in model sedimentation experiments
Authors: Ambari A. , Gauthier-Manuel B. , Guyon E.
Published: July 2002

Sedimentation involves a complex interplay between suspended particles which interact via the long range backflow induced by any individual particle on all the other ones. The measurement of the drag force on a sphere falling in a viscous liquid parallel to vertical walls in different geometries offers a simpler geometry to study the effect of the ‘‘backflow.’’ Our experiments show that in a cylindrical tube the minimum of the drag force is obtained for a position of the sphere away from the axis while it is in the vertical plane of symmetry for two parallel walls. The difference is attributed to the different nature of the backflow in the two cases. An additional and practical result is a word of warning concerning the use of falling ball viscosimeters.
The plane wake of a cylinder: Measurements and inferences on turbulence modeling
Authors: Aronson D. , Löfdahl L.
Published: July 2002

Hot wire measurements in the far field region of the plane wake of a cylinder have been carried out. The data obtained indicated that transverse distributions of mean-velocity and Reynolds stresses were self-preserving for a downstream distance greater than 400 momentum thicknesses. Dissipation rate and triple velocity correlations were measured at a downstream position of 880 momentum thicknesses, these measured profiles were compared with the profiles obtained from closure models for the Reynolds stress equations. It was found that the dissipation rate anisotropy could essentially be accounted for by the employed model, larger deviations were observed between the measured and modeled profiles for the triple velocity correlations.
Chaotic transport by Rossby waves in shear flow
Authors: del-Castillo-Negrete Diego , Morrison P. J.
Published: July 2002

Transport and mixing properties of Rossby waves in shear flow are studied using tools from Hamiltonian chaos theory. The destruction of barriers to transport is studied analytically, by using the resonance overlap criterion and the concept of separatrix reconnection, and numerically by using Poincaré sections. Attention is restricted to the case of symmetric velocity profiles with a single maximum; the Bickley jet with velocity profile sech2 is considered in detail. Motivated by linear stability analysis and experimental results, a simple Hamiltonian model is proposed to study transport by waves in these shear flows. Chaotic transport, both for the general case and for the sech2 profile, is investigated. The resonance overlap criterion and the concept of separatrix reconnection are used to obtain an estimate for the destruction of barriers to transport and the notion of banded chaos is introduced to characterize the transport that typically occurs in symmetric shear flows. Comparison between the analytical estimates for barrier destruction and the numerical results is given. The role of potential vorticity conservation in chaotic transport is discussed. An area preserving map, termed standard nontwist map, is obtained from the Hamiltonian model. It is shown that the map reproduces the transport properties and the separatrix reconnection observed in the Hamiltonian model. The conclusions reached are used to explain experimental results on transport and mixing by Rossby waves in rotating fluids.
Propagation velocity of perturbations in turbulent channel flow
Authors: Kim John , Hussain Fazle
Published: July 2002

A database obtained from direct numerical simulation of a turbulent channel flow is analyzed to extract the streamwise component of the propagation velocity V of velocity, vorticity, and pressure fluctuations from their space-time correlations. A surprising result is that V is approximately the same as the local mean velocity for most of the channel, except for the near-wall region. For y+≤15, V is virtually constant, implying that perturbations of all flow variables propagate like waves near the wall. In this region, V is 55% of the centerline velocity Uc for velocity and vorticity perturbations and 75% of Uc for pressure perturbations. This is equal to U at y+=15 for velocity and vorticity perturbations, and equal to U at y+=20 for pressure perturbations, indicating that the dynamics of the near-wall turbulence is controlled by turbulence structures present near y+≂15–20. Scale dependence of V is also examined by analyzing the bandpass-filtered flow fields. This paper contains comprehensive documentation on the propagation velocities, which should prove useful in the evaluation of Taylor’s hypothesis. An attempt has been made to explain some of the data in terms of the current understanding of organized structures.
Filtration at large pressures for strongly flocculated suspensions
Authors: Landman K. A. , Russel W. B.
Published: July 2002

Filtration using large pressures is an effective method for removing liquids from a flocculated suspension and creating a high volume fraction filtercake. Recent experimental work exhibits phenomena that are unexplained by previous calculations with nonlinear models. These models are modified and now predict the region of clear liquid and the high concentration of the filtercake observed in filtration at large pressure. The governing equations are based on the assumption that, at sufficiently high volume fractions, a network forms through the aggregation of flocs and possesses a compressive yield stress Py(φ) that depends only on the local volume fraction φ.
Waves in plasmas: Highlights from the past and present
Authors: Stix Thomas H.
Published: July 2002

To illustrate the development of some fundamental concepts in plasma waves, a number of experimental observations, going back over half a century, are reviewed. Particular attention is paid to the phenomena of dispersion, collision-free damping, ray trajectories, amplitude transport, plasma wave echoes, finite-Larmor-radius and cyclotron and cyclotron-harmonic effects, nonlocal response, and mode conversion; to the straight-trajectory approximation and two-level phase mixing; and to quasilinear diffusion and its relation to radio-frequency heating, current drive, and induced neoclassical transport, and to stochasticity and superadiabaticity. Not only is the constructive interplay between experiment and theory noted, but also that major advances have come from each of the many disciplines that invoke plasma physics as a tool, including radio communication, astrophysics, controlled fusion, space physics, and basic research.
Density limit disruptions in tokamaks
Authors: Kleva Robert G. , Drake J. F.
Published: July 2002

Magnetohydrodynamic simulations are presented which reproduce the rapid drop in the central temperature observed during density limit disruptions in tokamaks. The loss of central confinement is triggered by edge radiation which destabilizes a q=1 kink mode. A bubble of cold plasma is injected from the edge into the center by the q=1 kink. This bubble bears a striking resemblance to the cold plasma that is observed to move from the edge into the center during density limit disruptions on the JET tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. 1, p. 433], initiating the loss of central confinement. The bubble profile produced by the q=1 kink is unstable to a broad spectrum of modes which progressively reduce the magnetic shear between the q=2 surface and the center. The q=2 mode then grows across the center, broadening the current and throwing the hot plasma to the wall.
Three-wave interactions and type II irregularities in the equatorial electrojet
Authors: Albert Jay M. , Sudan R. N.
Published: July 2002

A spectral description of a model of convective turbulence in the E region of the equatorial ionosphere is considered. It is demonstrated that three complex modes are sufficient to generate a stochastic steady state, in a manner analogous to similar models of the Euler equation and of drift waves. Complex terms in the nonlinear coupling coefficient are retained that are usually dropped on the basis of large kL, where L is the density gradient scale length. In addition, some parallel damping is included. Parameters that lead to a stochastic steady state are then found by explicitly solving for the wave vectors that reproduce growth rates and nonlinear coupling terms from a known stochastic case of a drift wave model.
Quasilinear evolution of Alfvén-ion-cyclotron and mirror instabilities driven by ion temperature anisotropy
Authors: Yoon Peter H.
Published: July 2002

In this paper the simultaneous nonlinear evolution of the Alfvén-ion-cyclotron and mirror instabilities driven by an anisotropic ion distribution function are studied. The ions are modeled by a bi-Maxwellian distribution function. For the sake of generality, two ion components are considered; the initially isotropic component and a population possessing a large temperature anisotropy with perpendicular temperature greater than parallel temperature. Here, perpendicular and parallel are defined with respect to the ambient magnetic field. The analysis is based on quasilinear kinetic theory. It is shown that initially, the mirror mode grows at a slightly faster rate when compared with the ion-cyclotron mode, but the subsequent evolution shows that the ion-cyclotron mode saturates at a much larger intensity. Simultaneously, large perpendicular temperature associated with the anisotropic ions is substantially reduced as the free energy is taken away by the unstable waves, while the parallel temperature increases so as to reduce the anisotropy. The initially isotropic ions, on the other hand, are also heated in the direction perpendicular to the ambient magnetic field vector.
Nonlinear evolution of electron-beam–plasma interactions
Authors: Cheung P. Y. , Wong Alfred Y.
Published: July 2002

The nonlinear evolution of the electron-beam–plasma instability is investigated experimentally in two stages in a large, uniform, and unmagnetized plasma. In the initial stage, the beam-driven, linearly unstable wave saturates due to changes in the beam distribution. At sufficiently intense wave amplitude, the instability evolves into a second stage where nonlinear effects due to the ponderomotive force dominate and the wave rapidly undergoes spatial collapse and contracts to very small scale lengths in the coexisting density cavity. The transverse contraction of the wave agrees with theories on three-dimensional Langmuir collapse. This second stage can further be classified according to the beam strength. At low beam density, a single collapsing wave packet is formed and the electron beam decouples from the collapsing wave and propagates relatively unperturbed through the plasma. At higher beam density, multiple field spikes are formed both along and across the beam path and the beam distribution is broadened through successive scattering by the multiple intense field spikes.
Nonlinear growth of Kelvin–Helmholtz instability: Effect of surface tension and density ratio
Authors: Rangel R. H. , Sirignano W. A.
Published: July 2002

The nonlinear evolution of initially small disturbances at an interface separating two fluids of different density and velocity, including surface tension effects, is investigated with the use of the vortex-sheet discretization approach. The location of the interface is tracked in time by following the motion of each vortex under the combined influence of all other vortices. The influence of surface tension and density discontinuity is incorporated in an equation governing the evolution of the circulation of each vortex. Increasing the surface tension or the density ratio is shown to reduce the growth of the disturbance. For density ratios larger than 0.2 a critical wavenumber exists that divides the unstable part of the spectrum into a region where a vorticity singularity can develop (with interface rollup) and a region where two finite vortical centers are formed (with partial or no rollup). For lower density ratios this bifurcation phenomenon is not observed.
Stability of a planar flame front in a compressible flow
Authors: Travnikov O. Yu. , Liberman M. A. , Bychkov V. V.
Published: July 2002

The effect of flow compressibility on the hydrodynamic stability of a planar flame front of finite thickness is investigated. It is shown that a flame front becomes more unstable with the increase of the Mach number of the flame generated flow. Particularly, even for a flow with relatively small Mach numbers ∼0.1–0.2 the maximal growth rate of the flame instability becomes 2–3 times larger than the growth rates for a flame in the incompressible flow.
Linear stability of viscous supersonic plane Couette flow
Authors: Hu Sean , Zhong Xiaolin
Published: July 2002

The linear stability of viscous compressible plane Couette flow is not well understood even though the stability of incompressible Couette flow has been studied extensively and has been shown to be stable to linear disturbances. In this paper, the viscous linear stability of supersonic Couette flow for a perfect gas governed by Sutherland viscosity law was studied using two global methods to solve the linear stability equations. The two methods are a fourth-order finite-difference method and a spectral collocation method. Two families of wave modes, modes I and II, were found to be unstable at finite Reynolds numbers, where mode II is the dominant instability among the unstable modes. These two families of wave modes are acoustic modes created by sustained acoustic reflections between a wall and a relative sonic line when the mean flow in the local region is supersonic with respect to the wave velocities. The effects of viscosity on the stability of the two families of acoustic modes were studied by comparing the viscous results at finite Reynolds numbers with the inviscid results published by Duck, Erlebacher, and Hussaini [J. Fluid Mech. 258 (1994)]. It was shown that viscosity plays a destabilizing role in both mode I and mode II stability for supersonic Couette flow in a range of Reynolds numbers and wavenumbers. The effects of compressibility, three-dimensionality, and wall cooling on the two wave families were also studied. The stability of supersonic Couette flow was found to be different from that of the unbounded boundary layers in many aspects because of the effects of additional boundary conditions at the upper wall.
Fluid models for kinetic effects on coherent nonlinear Alfvén waves. I. Fundamental theory
Authors: Medvedev M. V. , Diamond P. H.
Published: July 2002

Collisionless regime kinetic models for coherent nonlinear Alfvén wave dynamics are studied using fluid moment equations with an approximate closure anzatz. Resonant particle effects are modeled by incorporating an additional term representing dissipation akin to parallel heat conduction. Unlike collisional dissipation, parallel heat conduction is presented by an integral operator. The modified derivative nonlinear Schrödinger equation thus has a spatially nonlocal nonlinear term describing the long-time evolution of the envelope of parallel-propagating Alfvén waves, as well. Coefficients in the nonlinear terms are free of the (1−β)−1 singularity usually encountered in previous analyses, and have a very simple form that clarifies the physical processes governing the large-amplitude Alfvénic nonlinear dynamics. The nonlinearity appears via coupling of an Alfvénic mode to a kinetic ion-acoustic mode. Damping of the nonlinear Alfvén wave appears via strong Landau damping of the ion-acoustic wave when the electron-to-ion temperature ratio is close to unity. For a (slightly) obliquely propagating wave, there are finite Larmor radius corrections in the dynamical equation. This effect depends on the angle of wave propagation relative to B0 and vanishes for the limit of strictly parallel propagation. Explicit magnetic perturbation envelope equations amenable to further analysis and numerical solution are obtained. Implications of these models for collisionless shock dynamics are discussed.
Obliquely propagating electrostatic solitary structures in a magnetized hot dusty plasma with trapped ions
Authors: Mamun A. A. , Alam M. N. , Azad A. K.
Published: July 2002

A theoretical investigation has been made of obliquely propagating electrostatic solitary structures in a hot magnetized three-component dusty plasma, which consists of a negatively charged hot dust fluid, Blotzmann distributed electrons, and free and trapped ions. It has been found that owing to the departure from the Boltzmann ion distribution to a trapped ion one, the dynamics of small but finite-amplitude electrostatic waves in a magnetized hot dusty plasma is governed by the modified Korteweg–de Vries (KdV) equation. The latter admits a stationary solitary wave solution that has a larger amplitude, a smaller width, and higher propagation velocity, than that involving Boltzmann distributed ions. It has been shown that the effects of obliqueness, external magnetic field, trapped ions, and free electrons change the behavior of these electrostatic solitary structures that have been found to exist with only negative potential in this dusty plasma model.
Weakly nonlinear dynamics of electrostatic perturbations in marginally stable plasmas
Authors: del-Castillo-Negrete D.
Published: July 2002

A single-wave model equation describing the weakly nonlinear evolution and saturation of localized electrostatic perturbations in marginally stable plasmas, with or without collisions, is derived using matched asymptotic expansions. The equation is universal in the sense that it is independent of the equilibrium, and it contains as special cases the beam-plasma and the bump-on-tail instability problems among others. In particular, the present work offers a systematic justification of the single-wave, beam-plasma model originally proposed by O’Neil, Winfrey, and Malmberg. The linear theory of the single-wave model is studied using the Nyquist method, and solutions of the linear initial value problem of stable perturbations which exhibit transient growth and do not Landau damp are presented. Families of exact nonlinear solutions are constructed, and numerical results showing the growth and saturation of instabilities, transient growth of stable perturbations, and marginal stability relaxation are presented. The single-wave model equation is analogous to the equation describing vorticity dynamics in marginally stable shear flows and thus, all the results presented are directly applicable to fluid dynamics.
Solitary Alfvén wave in an electron positron ion plasma
Authors: Kakati H. , Goswami K. S.
Published: July 2002

Solitary Alfvén waves in electron positron ion plasmas are investigated. The Alfvén wave is shown to have an exact solitary wave solution for a small but finite value of β. It is shown that the existence regions are different if the value of β is changed; however, the change in Kx simply changes the soliton width.
Theory of laser wakes in plasma channels
Authors: Shvets G. , Li X.
Published: July 2002

Excitation of accelerating modes in transversely inhomogeneous plasma channels is considered as an initial value problem. Discrete eigenmodes are supported by plasma channels with sharp density gradients. These eigenmodes are collisionlessly damped as the gradients are smoothed. Using collisionless Landau damping as the analogy, the existence and damping of these “quasi-modes” is studied by constructing and analytically continuing the causal Green’s function of wake excitation into the lower half of the complex frequency plane. Electromagnetic nature of the plasma wakes in the channel makes their excitation nonlocal. This results in the algebraic decay of the fields with time due to phase-mixing of plasma oscillations with spatially-varying frequencies. Characteristic decay rate is given by the mixing time τm, which corresponds to the dephasing of two plasma fluid elements separated by the collisionless skin depth. For wide channels analytic expressions for the field evolution are derived. Implications for electron acceleration in plasma channels are discussed.
Plasma jet formation and magnetic-field generation in the intense laser plasma under oblique incidence
Authors: Sentoku Y. , Ruhl H. , Mima K. , Kodama R. , Tanaka K. A. , Kishimoto Y.
Published: July 2002

Long-scale jet-like x-ray emission was observed in the experiments on the interactions of 100 TW laser light with plasmas. The jet formation is investigated by simulations with a two-dimensional particle code. When an S-polarized intense laser is irradiated obliquely on an overdense plasma, collimated MeV electrons are observed from the critical surface in the specular reflection direction. These electrons are found to be accelerated through the coronal plasma by the reflected laser light, which was modulated at the reflection point. The quasisteady magnetic channel occurs simultaneously and collimates the energetic electrons along the specular direction. In the case of P-polarized laser, it is found that an outgoing electron stream is induced at the critical surface due to Brunel mechanism. Megagauss quasistatic magnetic fields are generated and pinch the electron stream. The angle of ejected electron depends on the electron’s energy. The emission direction of the jet generated by the P-polarized light is determined by the canonical momentum conservation along the target surface.
The physics issues that determine inertial confinement fusion target gain and driver requirements: A tutorial
Authors: Rosen Mordecai D.
Published: July 2002

This paper presents a simplified, tutorial approach to determining the gains of inertial confinement fusion (ICF) targets, via a basic, zero-dimensional (“0-D”), energy “bookkeeping” of input (parametrized by ICF drivers’ coupling efficiencies to the target, and subsequent hydrodynamic efficiencies of implosion) versus output (thermonuclear burn efficiency and target fuel mass). Physics issues/constraints such as hydrodynamic instabilities, symmetry and implosion velocity requirements will be discussed for both the direct drive (driver impinging directly on the target) and indirect drive (x-ray implosion within a driver heated hohlraum) approaches to ICF. Supplementing the 0-D model with simple models for hohlraum wall energy loss (to predict coupling efficiencies) and a simple one-dimensional (1-D) model of the implosion as a spherical rocket (to predict hydrodynamic implosion efficiencies) allows gains to be predicted that compare well with the results of complex two-dimensional (2-D) radiation hydrodynamic simulations.
Electron equilibrium and confinement in a modified Penning trap and its application to Penning fusion
Authors: Barnes D. C. , Schauer M. M. , Umstadter K. R. , Chacon L. , Miley G.
Published: July 2002

The Penning fusion concept is described. Recent theoretical work on eliminating limitations on thermonuclear gain (Q) associated with ion–ion collisions is reviewed. A critical issue identified is the demonstration of the desired spherical electron configuration. Constraints on the electron distribution function are derived. A small combined trap (majority electrons), PFX-I (Penning Fusion eXperiment-Ions) has been constructed to study these issues. PFX-I is described. Two diagnostics described for electrons are destructive dumping of trapped electrons and noninvasive optical detection of impact induced fluorescence. Initial results of PFX-I operation at applied voltages V0 up to 2 kV and magnetic fields B up to 1.14 T are described. Electron equilibrium is found to be consistent with trap filling to the space charge limit, with inventory proportional to V0 and independent of B. Electron confinement times range from 1 to 10 ms and are determined by neutral pressure. These results are interpreted and future directions sketched.
Magnetic field lines, Hamiltonian dynamics, and nontwist systems
Authors: Morrison P. J.
Published: July 2002

Magnetic field lines typically do not behave as described in the symmetrical situations treated in conventional physics textbooks. Instead, they behave in a chaotic manner; in fact, magnetic field lines are trajectories of Hamiltonian systems. Consequently the quest for fusion energy has interwoven, for 50 years, the study of magnetic field configurations and Hamiltonian systems theory. The manner in which invariant tori breakup in symplectic twist maps, maps that embody one and a half degree-of-freedom Hamiltonian systems in general and describe magnetic field lines in tokamaks in particular, will be reviewed, including symmetry methods for finding periodic orbits and Greene’s residue criterion. In nontwist maps, which describe, e.g., reverse shear tokamaks and zonal flows in geophysical fluid dynamics, a new theory is required for describing tori breakup. The new theory is discussed and comments about renormalization are made.
Laser induced electron acceleration in the presence of static electric and magnetic fields in a plasma
Authors: Tsakiris G. D. , Gahn C. , Tripathi V. K.
Published: July 2002

Results of a fully relativistic three-dimensional (3-D) single particle code, supported by a theoretical model, on direct laser acceleration of electrons in radial electric and azimuthal magnetic static fields are presented. The ponderomotive force and the longitudinal components of the laser field are taken into account in the code. The electron motion in the static fields is similar to the motion in a magnetic wiggler. At resonance, when the bounce frequency of the wiggling motion is within a few percent of the Doppler shifted laser frequency, the amplitude of transverse oscillation shows a rapid increase accompanied by a fast rise in energy and parallel momentum. For this situation, a theoretical model of energy exchange between the electrons and the laser provides reasonable estimate of energy gain. The single particle code is used in Monte Carlo simulations to study the energy distribution and angular spread of the accelerated electrons in a self-focused high intensity laser pulse interaction.
Intensity-dependent cyclotron resonance in a GaAs/GaAlAs two-dimensional electron gas
Authors: Rodríguez G. A. , Hart R. M. , Sievers A. J. , Keilmann F. , Schlesinger Z. , Wright S. L. , Wang W. I.
Published: July 2002

Cyclotron resonance of a two-dimensional electron gas at a GaAs/GaAlAs interface is measured in the far infrared at intensities of up to 10 kW/cm2. Both the cyclotron mass and the carrier density are independent of intensity but the relaxation time changes with a dependence which is similar to that observed earlier in high dc field mobility studies.