bluuebunny/crossref_metadata_2025 huggingface dataset:
The prediction of molecular equilibrium structures by the standard electronic wave functions
Authors: Helgaker Trygve , Gauss Jürgen , Jo/rgensen Poul , Olsen Jeppe
Published: July 2002

A systematic investigation has been carried out of the accuracy of molecular equilibrium structures of 19 small closed-shell molecules containing first-row atoms as predicted by the following standard electronic ab initio models: Hartree–Fock (HF) theory, Mo/ller–Plesset theory to second, third, and fourth orders (MP2, MP3, and MP4), coupled-cluster singles and doubles (CCSD) theory; CCSD theory with perturbational triples corrections [CCSD(T)], and the configuration-interaction singles and doubles (CISD) model. For all models, calculations were carried out using the correlation-consistent polarized valence double-zeta (cc-pVDZ) basis, the correlation-consistent polarized valence triple-zeta (cc-pVTZ) basis, and the correlation-consistent polarized valence quadruple-zeta (cc-pVQZ) basis. Improvements in the basis sets shorten the bond distances at all levels. Going from cc-pVDZ to cc-pVTZ, bond distances are on the average reduced by 0.8 pm at the Hartree–Fock level and by 1.6 pm at the correlated levels. From cc-pVTZ to cc-pVQZ, the contractions are about ten times smaller and the cc-pVTZ basis set appears to yield bond distances close to the basis-set limit for all models. The models HF, MP2, and CCSD(T) give improved accuracy at increased computational cost. The accuracy of the Mo/ller–Plesset series oscillates, with MP3 being considerably less accurate than MP2 and MP4. The MP2 geometries are remarkably accurate, being only very slightly improved upon at the MP4 level for the cc-pVQZ basis. The CCSD equilibrium structures are only moderately accurate, being intermediate between MP2 and MP3. The accuracy of the CCSD(T) model, in contrast, is high and comparable to that observed in most experimental studies and it has been used to challenge the experimentally determined equilibrium structure of HNO. The CISD wave function provides structures of low quality.
Quantum dissipative dynamics of adsorbates near metal surfaces: A surrogate Hamiltonian theory applied to hydrogen on nickel
Authors: Baer Roi , Kosloff Ronnie
Published: July 2002

Dissipative dynamics of an adsorbate near a metal surface is formulated consistently by replacing the infinite system-bath Hamiltonian by a finite surrogate Hamiltonian. This finite representation is designed to generate the true short time dynamics of a primary system coupled to a bath. A detailed wave packet description is employed for the primary system while the bath is represented by an array of two-level systems. The number of bath modes determines the period the surrogate Hamiltonian reproduces the dynamics of the primary system. The convergence of this construction is studied for the dissipating Harmonic oscillator and the double-well tunneling problem. Converged results are obtained for a finite duration by a bath consisting of 4–11 modes. The formalism is extended to dissipation caused by electron-hole-pair excitations. The stopping power for a slow moving proton is studied showing deviations from the frictional limit at low velocities. Vibrational line shapes of hydrogen and deuterium on nickel were studied. In the bulk the line shape is mostly influenced by nonadiabatic effects. The interplay between two baths is studied for low temperature tunneling between two surface sites of hydrogen on nickel. A distinction between lattice modes that enhance the tunneling and ones that suppress it was found.
Ionization potentials and electron affinities from the extended Koopmans’ theorem applied to energy-derivative density matrices: The EKTMPn and EKTQCISD methods
Authors: Cioslowski Jerzy , Piskorz Pawel , Liu Guanghua
Published: July 2002

The extended Koopmans’ theorem (EKT) is combined with the energy-derivative formalism for the one- and two-particle reduced density matrices. Such a combination produces a versatile methodology for calculations of ionization potentials and electron affinities that, being applicable to any level of electron correlation treatment, is more general than the equation-of-motion (EOM) formalism. General expressions for the Feynman–Dyson amplitude, the pole strength, and the one-particle reduced density matrix of the hole state are derived. Like the electron propagator theory (EPT), the present approach provides a one-electron description of the electron attachment–detachment processes that is advantageous from the interpretive point of view. Numerical tests show that EKT calculations are capable of affording ionization potentials with accuracy comparable to that of the EPT methods but at a substantially lower computational cost.
Dynamics of sodium ions in NaClO4 complexed in poly(propylene-oxide): A 23Na nuclear magnetic resonance study
Authors: Chung S. H. , Jeffrey K. R. , Stevens J. R.
Published: July 2002

Amorphous poly(propylene oxide), PPO (molecular weights, 425 and ∼106), complexed with NaClO4 salt has ionic conductivities as high as 10−5 S/cm at room temperature. In an attempt to directly study the dynamics of the Na+ ions, (I=3/2) nuclear magnetic resonance (NMR) spin-lattice relaxation times, T1, and spin–spin relaxation times, T2, at a resonance frequency of 77.0 MHz have been measured over the temperature range from 150 to 390 K. A range of salt compositions [(PPO)nNaClO4; n=8–30] have been investigated. In addition, the glass transition temperature for each sample is reported. The recovery of equilibrium magnetization following a π/2 pulse is biexponential as expected for a spin I=3/2 system in the viscous liquid region. Below Tg a better fit to the magnetization recovery curve can be obtained if Kohlrausch–Williams–Watts (KWW) functions are used in place of the exponential functions. At low temperature the molecular motion has slowed to the point where a common spin temperature is not achieved by ionic diffusion. Two T2 values are observed over a limited temperature region near the T1 minimum. In the remaining low temperature region only the T2 associated with the central transition could be determined because the large 23Na quadrupole coupling constant made detection of the satellite transitions impossible. There is no evidence from the NMR relaxation time data for two Na+ populations. The experimental spin-lattice relaxation times can be analyzed to determine the correlation time for the ionic motion as a function of reciprocal temperature. The correlation time data display a distinct change in behavior at Tg which is interpreted as an indication of a crossover between two ionic transport mechanisms. Plots of T1 as a function of Tg/T indicate that dynamics for T>Tg are largely determined by the flexibility of the polymer host (the α process) whereas a different process dominates for T>Tg (presumably the β process). A comparison of correlation times derived from NMR relaxation times and ionic conductivities show a marked difference especially in the region of Tg. The conductivity decreases rapidly while the sodium ion motion continues with a correlation time ∼10−6 s through the glass transition.
Anisotropy of two-photon excited f–f transitions of Eu2+ in KMgF3
Authors: Francini R. , Grassano U. M. , Boiko S. , Tarasov G. G. , Scacco A.
Published: July 2002

Polarization dependence of sharp intraconfigurational 4f7 transitions of Eu2+ in KMgF3 have been studied by means of two-photon excitation spectroscopy. A new puzzle appears connected with the site-symmetry distortion at the Eu2+ ions and the weakness of third-order spin-orbit corrections, suggesting a mechanism for intraconfigurational interaction independent from crystal-field strength and from the site symmetry on the rare-earth ion. Intensity and polarization dependencies of the 8S7/2→6P7/2,6P5/2,6D9/2 transitions have been satisfactorily interpreted in terms of second-order perturbation theory.
Potential curves for several electronic states of the MgHe, Mg+He, and Mg+2He van der Waals complexes
Authors: Leung Allen W. K. , Julian Ryan R. , Breckenridge W. H.
Published: July 2002

We have estimated the potential curves of the Mg(3s3pπ)⋅He[3Π], Mg(3pπ3pπ)⋅He[3Σ−], Mg+(3s)⋅He[2Σ+], Mg+(3pπ)⋅He[2Π], and Mg+2(2p6)⋅He[1Σ+] van der Waals states by means of ab initio calculations. Similar to the analogous doubly excited states of MgNe, MgAr, and MgKr, the Mg(3pπ3pπ)⋅He[3Σ−] state is found to be unusually strongly bound, De=2386 cm−1, a bond strength which is an astounding 165 times that of the singly excited Mg(3s3pπ)⋅He[3Π] state and 35 times that of the Mg+(3s)⋅He ion. The strong bonding is attributed primarily to the lack of a Mg(3s) electron, so that all the attractive forces can extend to smaller internuclear distances because there is no Mg(3sσ)/He(1sσ) repulsion. In fact, the Mg(3pπ3pπ)⋅He[3Σ−], Mg+(3pπ)⋅He[2Π], and Mg+2(2p6)⋅He[1Σ+] states have quite similar bond energies and bond lengths, indicating that for RG=He, the primary attractive force in all these states is the ion/induced-dipole interaction of the “Mg+2/He” core. This is consistent with the fact that the bond energy of the Mg(3pπ3pπ)⋅He[3Σ−] state is more than four times greater than that of the Mg(3pπ3pπ)⋅Ne[3Σ−] state, where there is substantial Mg(3pπ)/Ne(2pπ) repulsion not present in the Mg(3pπ3pπ)⋅He[3Σ−] state.
Berry phases for Landau Hamiltonians on deformed tori
Authors: Lévay Péter
Published: July 2002

Parametrized families of Landau Hamiltonians are introduced, where the parameter space is the Teichmüller space (topologically the complex upper half plane) corresponding to deformations of tori. The underlying SO(2,1) symmetry of the families enables an explicit calculation of the Berry phases picked up by the eigenstates when the torus is slowly deformed. It is also shown that apart from these phases that are local in origin, there are global non-Abelian ones too, related to the hidden discrete symmetry group Γϑ (the theta group, which is a subgroup of the modular group) of the families. The induced Riemannian structure on the parameter space is the usual Poincare metric on the upper half plane of constant negative curvature. Due to the discrete symmetry Γϑ the geodesic motion restricted to the fundamental domain of this group is chaotic.
Bethe ansatz study for ground state of Fateev Zamolodchikov model
Authors: Ray Subhankar
Published: July 2002

A Bethe ansatz study of a self-dual ZN spin lattice model, originally proposed by V. A. Fateev and A. B. Zamolodchikov, is undertaken. The connection of this model to the Chiral Potts model is established. Transcendental equations connecting the zeros of Fateev–Zamolodchikov transfer matrix are derived. The free energies for the ferromagnetic and the anti-ferromagnetic ground states are found for both even and odd spins.
Symmetry requirement for a deformation operator related to density functional theory
Authors: Bokanowski Olivier
Published: July 2002

We study symmetry properties of an operator that has been introduced in Quantum Chemistry under the name of “Local Scaling Method,” or “Local Scaling Transformation.” This operator is defined using deformations of the space R3. It has previously been used in order to obtain density-functional approximations of the N-electron problem, and new N-representability results. In order that the operator satisfies a natural symmetry requirement associated with the symmetry group of a molecule, we show that only the deformations that commute with all operations of the symmetry group may be used. These deformations are listed and practical consequences explained.
Kinetics of cluster growth in expanding rare-gas jet
Authors: Ratner M. A.
Published: July 2002

The growth of clusters in an overcooled atomic jet is calculated with the simultaneous allowance for two processes: the condensation of supersaturated gas and the cluster-cluster aggregation. These processes are consistently described within a quasi-equilibrium approach for large enough clusters, while their nucleation stage is allowed for phenomenologically by the use of a fitting parameter. The theory quantitatively describes the experimental dependence of the mean cluster size on the initial gas temperature within a broad range of sizes. The mean size of clusters, their distribution over sizes and the contribution of clusters to the total mass of the jet are calculated versus the distance from the gas ejection point (nozzle entry). It is shown that these characteristics are mainly determined by the initial gas entropy which is equivalent to the empirical law of corresponding jets. The size distribution function has a halfwidth exceeding the mean cluster size and is close (on a relative scale) to a universal curve. The broad size distribution of clusters should be taken into account when analyzing spectroscopic data on the size dependence of electronic processes in a cluster.
Particle orbits from the Lagrangian and the Eulerian Korteweg–de Vries equations
Authors: Provenzale A. , Osborne A. R. , Boffetta G. , Serio M.
Published: July 2002

The particle orbits obtained by integrating the velocity field of the Eulerian Korteweg–deVries (KdV) equation and the trajectories given by the Lagrangian KdV equation are contrasted. It is shown that the two classes of orbits, while apparently equivalent, may be quite different. In particular, a spurious wave drift is generated by integrating the Eulerian velocities. It is shown that these differences are due to a mixing of perturbation orders inherent in the integration of the Eulerian velocity field. It is believed that these results may have some implications on the calculation of particle orbits in Eulerian flow models obtained by a perturbation expansion of the primitive equations.
Spin detonation in reactive particles–oxidizing gas flow
Authors: Zhang F. , Grönig H.
Published: July 2002

Development of detonation waves in corn starch particles–oxidizing gas mixtures was studied in a horizontal circular tube having an inside diameter of 141 mm and a test section length of 17.4 m. The results show that a stable self-sustained detonation can be achieved in such a heterogeneous system. The sequence of the transition process was essentially recognized as follows: (1) initial particle ignition, (2) pressure wave amplification by coherent energy release, (3) unsteady reaction shock, and (4) spin detonation. Thus transverse waves play a dominant role in stable detonation propagation in this two-phase system. The spin structure exists both on the circumference and in the inner region of the cross section. For a stable single spin detonation there are two constant velocities at the wave front: axial propagation velocity and angular velocity.
The point explosion with heat conduction
Authors: Reinicke P. , Meyer-ter-Vehn J.
Published: July 2002

The influence of nonlinear heat conduction is investigated for strong point explosions in an ambient gas. An ideal gas equation of state and a heat conductivity depending on temperature and density in power-law form are assumed. It is shown that two spherical waves are obtained—a shock wave and a heat wave. They have sharp fronts which run at different speeds, in general, and in a relative order depending on parameters and time. Starting from the underlying Lie group symmetry, self-similar solutions of the problem are discussed in detail; they exist under the assumption that the ambient gas density decays with a given power of the radius. The non-self-similar situation, occurring for uniform density, is also considered. In this case, the shock front first runs behind the heat front, but then overtakes it at a certain time t1. For t≫t1, the well-known hydrodynamic solution of the problem without heat conduction becomes valid, except for a central, almost isobaric region where heat conduction modifies the classical result and keeps the temperature finite. It is shown that this central zone still has the form of a heat wave with a sharp front and evolves self-similarly, though with a smaller similarity exponent than the global hydrodynamic wave. Analytic results for the central temperature and the radial extension of the conduction dominated zone are given.
Chaotic behavior of particles in 2-D cavity flow
Authors: Liu Minye , Peskin Richard L.
Published: July 2002

A mathematical model for study of cavity flows is constructed using a deformed Hill’s vortex flow together with superposition of the basic flow and its image. By changing direction of the flow and its image, corotating and counter-rotating modes can be obtained. Unsteady flow is simulated by periodic activation of the basic flow and/or its image. The objective of the study is examination of the details of chaotic behavior of particles in the flow. Poincaré sections are used and the primary parameter varied is T, the period of the moving walls. For very small T the particle trajectories are quasiperiodic and there is no chaotic region for either co- or counter-rotating flows, regardless of initial particle positions. Chaotic regions appear when T is large. By following a single particle, it was determined that its trajectory becomes chaotic only within a specific range of T which depends on the initial condition; this implies a relationship between T and the period of the particle motion. Within the test range of T (1.0 – 40.0), for a given T the chaotic regions are larger for the counter-rotating case. When the velocity field was perturbed with a small unsteady component added to the basic flow, it was found that the regular (nonchaotic) trajectories in the counter-rotating flow were more easily perturbed than those in the corotating flow. It is expected that mixing in counter-rotating flows is more efficient than in corotating flow. Both continuous and discontinuous wall motions were used. Symmetric regular regions in the Poincaré section are found in both space and time. By following particle paths, it was found that the regular and quasiperiodic trajectories are symmetric in space. The conclusions obtained thus far are consistent with laboratory experiments.1 In addition to T, we are examining the effects of geometric aspect ratio, position of fixed points, etc. Future plans include study of particles with inertia, and study of three-dimensional cavities.
Chaotic advection in a complex annular geometry
Authors: Barkley Dwight , Karniadakis George Em , Kevrekidis Ioannis G. , Shen Zhen-Hua , Smits Alexander J.
Published: July 2002

The dynamics of Lagrangian particles in a complex geometry is studied, both experimentally and through a full numerical simulation of the Navier–Stokes equations. The geometry is an annulus whose walls can be rotated independently. Stationary cylindrical rods can be positioned within the annulus in several arrangements. A variety of heteroclinic orbits are found at low Reynolds numbers, where the fluid flow is steady. As the flow becomes unsteady to a time-periodic (two-dimensional) state, it spontaneously gives rise to heteroclinic tangles that provide the organizing structure for the chaotic motion of fluid particles.
A new mechanism of period doubling in free shear flows
Authors: Tomboulides A. G. , Triantafyllou G. S. , Karniadakis G. E.
Published: July 2002

In this Letter numerical evidence for a new period-doubling mechanism in free shear flows is presented. As a case study, the three-dimensional flow in the wake of an infinitely long circular cylinder at Reynolds number 300 is considered. It is shown that the flow in the wake doubles its period of oscillation by alternating between oscillation modes, which are identical in every respect, except from their spanwise structure. There is no merging of vortices, and the flow preserves its basic vortex-street structure.
Nonparallel-flow stability of an axisymmetric buoyant plume in a coflowing uniform stream
Authors: Tveitereid M. , Riley D. S.
Published: July 2002

Nonparallel effects of the basic flow and disturbances are included in a linear stability study of an axisymmetric thermal plume in a coflowing uniform stream. On invoking a slowly varying approximation and undertaking a multiple scale analysis, a larger region of stability than that predicted by parallel-flow theory is obtained. The amplification rate of the perturbation depends on the flow quantity under consideration and so there is no unique boundary between stable and unstable perturbations. The calculated critical Reynolds numbers for the perturbation velocities are, however, of the same order of magnitude, the lowest being 32.9 for a pure plume, and they increase significantly as the strength of the external stream increases. There are two mechanisms for instability: one is shear driven, the other gravitational.
Multiple, two-dimensional solutions to the Dean problem in curved triangular ducts
Authors: Nandakumar K. , Mees P. A. J. , Masliyah J. H.
Published: July 2002

The two-dimensional, stationary form of the equations of motion governing the flow in loosely coiled ducts of equilateral, triangular cross section are solved using a finite volume discretization procedure. The primary solution branch consists of a flow with two large, symmetrical streamwise vortices which are generated by the centrifugal force. Earlier works have investigated the formation of additional Moffat vortices near the corner of such ducts, driven by the secondary flow. Such corner vortices tend to be extremely weak in strength. When the outer wall is flat and one corner of the triangle points inwards, centrifugal instability gives rise to the formation of an additional pair of vortices near the center of the outer wall. Such four-cell solutions appear as dual solutions at the same Dean number, Dn, and the additional vortices are much stronger than the Moffat vortices. This phenomenon is very similar to those observed in the Dean problem for square and circular cross section. The four-cell solutions are found to be unstable to asymmetric perturbations. When the orientation of the triangular duct is changed such that the inner wall is flat such additional vortices do not form near the outer region of the duct and a unique two-cell solution that remains stable is obtained for Dean numbers as high as 350.
Viscous and adiabatic heating effects in three-dimensional compressible convection at infinite Prandtl number
Authors: Balachandar S. , Yuen D. A. , Reuteler D.
Published: July 2002

A three-dimensional direct numerical simulation (using a fully spectral method) of compressible convection of an infinite Prandtl number fluid in a wide box with dimensions 5×5×1 was conducted. Depth-dependent viscosity, thermal expansivity, and thermal conductivity have been included in order to model deep-seated processes in the Earth’s mantle. Solutions have been obtained up to a surface Rayleigh number of 4×107. There is a remarkable contrast between the dynamics of the upper and lower boundary layers. Very few cylindrical plumes are developed at the bottom but they merge collectively to form a strong upwelling, which pulses chaotically. Viscous and adiabatic heating are found to become important at high Rayleigh numbers, larger than 107. These results have important implications on the thermal structure of early Earth, where there might have been dramatic effects from intense mechanical heating near the top boundary layer.
Self-consistent radial sheath
Authors: Hazeltine R. D.
Published: July 2002

The boundary layer arising in the radial vicinity of a tokamak limiter is examined, with special reference to the TEXT tokamak [Nucl. Fusion 27, 1125 (1987); Phys. Fluids 27, 2956 (1984)]. It is shown that sheath structure depends upon the self-consistent effects of ion guiding-center orbit modification as well as the radial variation of E×B-induced toroidal rotation. Reasonable agreement with experiment is obtained from an idealized model, which, however simplified, preserves such self-consistent effects. It is argued that the radial sheath, which occurs whenever confining magnetic field lines lie in the plasma boundary surface, is an object of some intrinsic interest. It differs from the more familiar axial sheath because magnetized charges respond very differently to parallel and perpendicular electric fields.
Effects of orbit squeezing on ion transport in the banana regime in tokamaks
Authors: Shaing K. C. , Hazeltine R. D.
Published: July 2002

It is shown that ion transport in the banana regime in tokamaks is reduced in the presence of a strong shear in the radial electric field Er , as is often observed in the edge region. For simplicity, the ordering with ρpi‖d ln Er /dr‖ ≫ 1 but c‖Er‖/Bpvti < 1 is adopted. Here, ρpi is the ion poloidal gyroradius, Bp is the poloidal magnetic field strength, vti is the ion thermal speed, and c is the speed of light. A kinetic transport theory similar to those for bumpy tori and stellarators is developed to show that the ion thermal conductivity χi is reduced by a factor of roughly S−3/2, where S = 1 − (ρpi d ln Er /dr)(cEr Bpvti). The result reflects more than simple orbit squeezing: The fraction of trapped ions is also modified by S.
Magnetic reconnection in electron magnetohydrodynamics
Authors: Bulanov S. V. , Pegoraro F. , Sakharov A. S.
Published: July 2002

The magnetic field dynamics and reconnection processes in a highly conducting plasma are investigated in the regimes where Ohm’s law is dominated by the Hall term, using a single (electron) fluid description (electron magnetohydrodynamics). In these regimes, which correspond to the frequency range of the so-called whistler (helicon) mode, the electromagnetic field is nearly force free: (j×B)/c+eneE=0. The evolution of the magnetic field in the vicinity of an X line is discussed in the linear and nonlinear regimes. The propagation of whistler waves results in the steepening of their wave front and in the increase of the electric current density in the neighborhood of the magnetic separatrix surfaces. Small-scale magnetic reconnection occurs near surfaces where k⋅B=0, with k the mode wave number, and tearing-type modes can be unstable due to the effect of electron inertia. A class of exact self-similar solutions is obtained. These describe, within the scope of a local approximation, the nonlinear time development (magnetic collapse) of the singularities that occur in three-dimensional magnetic configurations. Flat electric current sheets are formed during this collapse. Finally, the rate of reconnection in the electron-magnetohydrodynamic frequency range is estimated in the framework of a steady-state approximation.
Mode conversion and electron heating near the upper-hybrid resonance frequency
Authors: Smith Bruce L. , Okuda H. , Abe H.
Published: July 2002

Mode conversion near the upper-hybrid resonance frequency and electron heating are studied using a one-dimensional electromagnetic relativistic particle code. It is found that for a sufficiently small pump field E0, E20/4πnTe ≲0.01, electron heating is localized in a region near the electron cyclotron layer where the pump frequency is equal to the local electron gyrofrequency. For stronger pump fields, electron heating takes place more or less uniformly across a region between the upper-hybrid resonance layer and the cyclotron layer. In addition, a significant fraction of electromagnetic energy associated with the pump is found to be reflected back into the vacuum from a region in the plasma near the upper-hybrid resonance layer for both strong (E20/4πnTe ≊1) and weak pumps (E20/4πnTe ≪1).
Multiple Raman up-conversion of radiation from pre-existing Langmuir turbulence
Authors: Russell D. , Goldman M. , Newman D. L.
Published: July 2002

The equilibrium states described by a damped and driven kinetic equation governing the evolution of the spectrum of radiation in a stationary Langmuir-turbulent plasma are studied. Both Langmuir and transverse spectra are assumed to be one-dimensional in wavenumber space. A source of radiation at the plasma frequency and a uniform rate of dissipation at the higher harmonics are assumed. The radiation is characterized by an effective temperature z, proportional to the Langmuir energy density and inversely proportional to the dissipation rate of the transverse waves. If z<1 the equilibrium photon spectrum decreases with increasing frequency as a power law in z. If z>1, photons scattered out of certain regions of phase space may return at a significant rate, and the spectrum is found to have a global maximum above the plasma frequency ωp. The location of this maximum is proportional to z1/3 ωp, which may be many times the plasma frequency. Applications to a laser-plasma experiment and to the solar wind environment are discussed.
q=2 sawteeth and major disruptions in tokamaks
Authors: Kleva Robert G. , Drake J. F. , Boyd D. A.
Published: July 2002

In numerical simulations of q=2 tearing modes, the maximum amplitude of the mode is found to increase rapidly as the safety factor on axis q(0) rises above 1.5. The associated magnetic islands grow to the center of the column, encompassing virtually the entire plasma cross section. As a result of the formation of these very large islands, the hot central plasma is rapidly convected out to the edge of the column, thereby destroying central confinement. Experimental evidence from several tokamaks linking the formation of these very large islands with major disruptions is presented. Typically, major disruptions are observed to occur in two (or more) stages. During the first stage(s) q rises on axis while the final stage, which terminates the discharge, is associated with the violent growth of an m=2 perturbation. Under some circumstances q=2 sawteeth are predicted to occur. Evidence for such sawteeth in a divertor tokamak is discussed.
The turbulent exponential jet
Authors: Breidenthal Robert
Published: July 2002

A new, self-similar, turbulent jet flow is postulated in which the global vorticity Ω is a constant following any vortex. In contrast, conventional self-similar flows all exhibit Ω inversely proportional to the vortex age. In order for the new, postulated flow to exist, the nozzle exit speed must increase exponentially with time. It is shown that this circumstance may strongly inhibit the entrainment of ambient fluid into the jet.
Growth of phase space holes near linear instability
Authors: Dupree Thomas H.
Published: July 2002

Previous calculations of hole growth in a one-dimensional electron–ion plasma are extended to a greater range of parameter space including the region around linear instability. The effect of the ion-acoustic resonance on hole growth is analyzed and the relationship to linear instability is discussed. Agreement with computer simulations is much improved. Energy and momentum conservation are discussed and proved for both holes and waves.
Particle simulations of current-driven drift waves in shearless and sheared magnetic fields
Authors: Leboeuf J. N. , Thayer D. R. , Sydora R. D. , Diamond P. H.
Published: July 2002

The nonlinear behavior of the collisionless current-driven drift instability in shearless and sheared magnetic fields is studied by means of particle simulation. Electrostatic models with guiding center electrons and full dynamic ions are used in both two-and-one-half and three dimensions. The electron current (J∥), in the direction parallel to the magnetic field but perpendicular to the density gradient in the x direction, is maintained throughout the simulation. Instability thresholds, growth rates, real frequency spectra, and mode structures observed in the simulation are in good agreement with theory. Saturation of the unstable modes occurs by a flattening of the electron distribution function in x-v∥ space. The measured potential saturation levels and final distribution functions are consistent with a quasilinear plateau theory for both shearless and sheared magnetic field configurations.
The single-particle and collective descriptions of the anomalous Doppler resonance and the role of ion dynamics
Authors: Dendy R. O. , Lashmore-Davies C. N. , Montes A.
Published: July 2002

The connection between three aspects—single-particle, beam, and continuous velocity distribution—of the anomalous Doppler effect are investigated. The key quantity is the power Re(j ⋅ E*) dissipated by electrostatic waves interacting with a non-Maxwellian electron velocity distribution. Its spatial components describe energy flows that are the counterparts in classical electrodynamics to the quantum properties of the single-particle anomalous Doppler effect. A complete plasma physics treatment requires the inclusion of ion dynamics. Examination of the large-k region of wavenumber space—in contrast to the well-known small-k region—shows that ion Landau damping is important in stabilizing plasmas for which the electron velocity distribution considered alone is destabilizing. Finally, by choosing simple models for the superthermal electron velocity distribution, general features of the instability, and those specific to particular tail models, are identified analytically and numerically.
Electrostatic beam instabilities in a positive/negative ion plasma
Authors: Galvez Miguel , Gary S. Peter
Published: July 2002

This paper examines the linear theory of electrostatic waves and instabilities in an unmagnetized, homogeneous Vlasov plasma. The first configuration considered is that of a stable plasma with three Maxwellian components: electrons, positive ions, and negative ions. The dispersion properties of the lightly damped ion modes are studied as a function of relative electron density and relative component temperatures. The second configuration considered is that of a tenuous electron–ion beam with drift speed v0b streaming through a negative/positive ion plasma. If the beam is very tenuous, an electron beam instability satisfying ωr≂kv0b is excited; if the beam is more dense, the instability becomes Buneman-like with parabolic dispersion. The thresholds and maximum growth rates of these instabilities are described as functions of the beam density and drift speed.
Finite temperature effects on the space-time evolution of two-stream instabilities
Authors: Francis G. , Ram A. K. , Bers A.
Published: July 2002

Pinch-point instability analysis is used to study the effects of finite temperature on the time-asymptotic pulse shapes of electrostatic and electromagnetic two-stream instabilities. Their absolute or convective instability nature is established over the entire regime from instability threshold at finite temperatures to the cold-plasma hydrodynamic limit. The analysis is based upon nonrelativistic Vlasov theory dispersion relations for streams and plasmas with Maxwellian thermal distributions.
Relativistic particle acceleration by obliquely propagating electromagnetic fields
Authors: Villalón Elena , Burke William J.
Published: July 2002

The relativistic equations of motion are analyzed for charged particles in a magnetized plasma and externally imposed electromagnetic fields (ω, k), which have wave vectors k that are at arbitrary angles. The particle energy is obtained from a set of nonlinear differential equations, as a function of time, initial conditions, and cyclotron harmonic numbers. For a given cyclotron resonance, the energy oscillates in time within the limits of a potential well; stochastic acceleration occurs if the widths of different Hamiltonian potentials overlap. The net energy gain for a given harmonic increase with the angle of propagation, and decreases as the magnitude of the wave magnetic field increases. Potential applications of these results to the acceleration of ionsopheric electrons are presented.
Resonant generation of internal waves on the soft sea bed by a surface water wave
Authors: Wen Feng
Published: July 2002

The nonlinear response of an initially flat sea bed to a monochromatic surface progressive wave was studied using the multiple scale perturbation method. Two opposite-traveling subliminal internal ‘‘mud’’ waves are selectively excited and form a resonant triad with the surface wave. The amplitudes of the internal waves grow on a time scale much longer than the period of the surface wave. It was found that the sea bed response is critically dependent on the density ratio of water and soil, depth of water, and depth and viscosity of the saturated soil. The result of instability analysis is in qualitative agreement with the result of a wave flume experiment.
Evolution of the fingering pattern of an impacting drop
Authors: Thoroddsen S. T. , Sakakibara J.
Published: July 2002

The impact of a drop on a solid surface generates a rapidly expanding thin jet traveling along the surface. We study the evolution of the fingering pattern at the edge of this jet during the impact of a water drop on a glass plate. Multiple-flash photography shows that systematic changes in frontal shapes take place during the expansion. The initial fingers widen and split in two. This splitting is in many cases limited to the development of a double peak on each finger. The subsequent interaction of two such adjacent undulations often results in merging which produces three pronounced fingers. Despite the significant changes in the frontal shapes, the number of fundamental undulations remains approximately constant during the expansion. The progenitors of these azimuthal disturbances are observed right at first contact. Some heuristic arguments based on capillary waves are put forth to explain the splitting and merging. The main focus of this study is on impacts having Reynolds numbers of about 15 000, based on the drop diameter. The corresponding Weber numbers are about 1000.
Resistive wall stabilization of kink and tearing modes
Authors: Finn John M.
Published: July 2002

A study is made of the effect of a resistive wall and rigid plasma rotation on kink modes. It is shown that modes with mode rational surfaces in the plasma, for example, β-driven external kinks in a torus, are stabilized just below the ideal threshold by becoming resistive (tearing-like) modes, which can be stabilized in the presence of a resistive wall and rotation. Explicit calculations are shown for reduced magnetohydrodynamics (MHD) in a cylinder, and arguments are made regarding the applicability to the finite β toroidal case.
Quantitative predictions of tokamak energy confinement from first-principles simulations with kinetic effects
Authors: Kotschenreuther M. , Dorland W. , Beer M. A. , Hammett G. W.
Published: July 2002

A first-principles model of anomalous thermal transport based on numerical simulations is presented, with stringent comparisons to experimental data from the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. This model is based on nonlinear gyrofluid simulations, which predict the fluctuation and thermal transport characteristics of toroidal ion-temperature-gradient-driven (ITG) turbulence, and on comprehensive linear gyrokinetic ballooning calculations, which provide very accurate growth rates, critical temperature gradients, and a quasilinear estimate of χe/χi. The model is derived solely from the simulation results. More than 70 TFTR low confinement (L-mode) discharges have been simulated with quantitative success. Typically, the ion and electron temperature profiles are predicted within the error bars, and the global energy confinement time within ±10%. The measured temperatures at r/a≂0.8 are used as a boundary condition to predict the temperature profiles in the main confinement zone. The dramatic transition to the improved confinement in the supershot regime is also qualitatively explained. Further work is needed to extend this model of core heat transport to include particle and momentum transport, the edge region, and other operating regimes besides the ITG-dominated L mode. Nevertheless, the present model is very successful in predicting thermal transport in the main plasma over a wide range of parameters.
Bounce averaged trapped electron fluid equations for plasma turbulence
Authors: Beer M. A. , Hammett G. W.
Published: July 2002

A novel set of nonlinear fluid equations for mirror-trapped electrons is developed which differs from conventional fluid equations in two main respects: (1) the trapped-fluid moments average over only two of three velocity space dimensions, retaining the full pitch angle dependence of the trapped electron dynamics, and (2) closure approximations include the effects of collisionless wave-particle resonances with the toroidal precession drift. Collisional pitch angle scattering is also included. By speeding up calculations by at least √mi/me, these bounce averaged fluid equations make possible realistic nonlinear simulations of turbulent particle transport and electron heat transport in tokamaks and other magnetically confined plasmas.
Toroidal coupling of ideal magnetohydrodynamic instabilities in tokamak plasmas
Authors: Hegna C. C. , Connor J. W. , Hastie R. J. , Wilson H. R.
Published: July 2002

A theoretical framework is developed to describe the ideal magnetohydrodynamic (MHD) stability properties of axisymmetric toroidal plasmas. The mode structure is described by a set of poloidal harmonics in configuration space. The energy functional, δW, is then determined by a set of matrix elements that are computed from the interaction integrals between these harmonics. In particular, the formalism may be used to study the stability of finite-n ballooning modes. Using for illustration the s-α equilibrium, salient features of the n■∞ stability boundary can be deduced from an appropriate choice of test function for these harmonics. The analysis can be extended to include the toroidal coupling of a free-boundary kink eigenfunction to the finite-n ideal ballooning mode. A unified stability condition is derived that describes the external kink mode, a finite-n ballooning mode, and their interaction. The interaction term plays a destabilizing role that lowers the instability threshold of the toroidally coupled mode. These modes may play a role in understanding plasma edge phenomena, L–H physics and edge localized modes (ELMs).
Two-fluid theory of collisionless magnetic reconnection
Authors: Biskamp D. , Schwarz E. , Drake J. F.
Published: July 2002

Theoretical studies of collisionless reconnection in the framework of two-fluid theory are presented. In the high-β case (β≳1) reconnection is controlled by the whistler mode, leading to decoupling of ions from electrons on scales <c/ωpi. Though reconnection requires electron inertia, the reconnection rate is independent thereof, controlled only by ion inertia. Reconnection is hence much faster than in the absence of the Hall term. In the opposite limit of small β the strong axial field suppresses the whistler mode. Hence ions have to follow the electrons in the narrow reconnection layer δ∼c/ωpe, forming a macroscopic current sheet which strongly reduces the reconnection rate. Theoretical scaling laws are confirmed by numerical simulations.
Ionization instability in dusty plasmas
Authors: D’Angelo N.
Published: July 2002

The ionization instability in a dusty plasma in which the neutral gas is ionized by a constant flux of energetic electrons with energy slightly above the ionization energy is examined by using fluid equations for the three charged components, namely positive ions, electrons, and negatively charged dust grains. The presence of negatively charged dust increases both the frequency and the growth rate of the IA (ion-acoustic) wave excited through the ionization instability. The DA (dust-acoustic) mode, even in the absence of ion–neutral collisions, ion viscosity, and neutral gas drag on the dust grains, is always damped within the parameter ranges explored here and relevant to laboratory plasmas. The present results on the DA wave excitation are at variance with results obtained by Shukla and Morfill [Phys. Lett. A 216, 153 (1996)].
Transition from resistive ballooning to ηi driven turbulence in tokamaks
Authors: Zeiler A. , Biskamp D. , Drake J. F. , Rogers B. N.
Published: July 2002

The mechanisms of turbulent transport in the collisional tokamak edge plasma are investigated linearly and nonlinearly, focusing specifically on the transition from resistive modes to ion temperature gradient driven (ηi) modes. Linear eigenvalue calculations demonstrate that resistive ballooning and toroidal ηi modes can exist as separate roots with similar growth rates but with differing structure along the magnetic field. While the typical transverse scale length of the resistive modes depends strongly on collisionality, the transverse scales of the ηi mode are essentially independent of the collisionality, even in the absence of any assumption on the adiabaticity of the electrons. Three-dimensional nonlinear simulations quantitatively describe the transition between the resistivity dominated outermost edge and regions with moderately higher temperature where resistive modes are stabilized and the collisionless ηi mode dominates. A significant result is that the ηi modes continue to drive significant particle transport even in regimes where the linear stability analysis indicates the electrons are dominantly adiabatic. The particle transport is driven by the nonadiabatic, long-parallel-wavelength component of the wave spectrum. As in earlier calculations of ηi turbulence, the self-generated poloidal flows are relatively strong, much stronger than in cold ion simulations, and strongly influence the saturation levels and associated transport rates. The implications of the results for understanding edge transport and density and temperature profiles are discussed.
Plasma simulation studies using multilevel physics models
Authors: Park W. , Belova E. V. , Fu G. Y. , Tang X. Z. , Strauss H. R. , Sugiyama L. E.
Published: July 2002

The question of how to proceed toward ever more realistic plasma simulation studies using ever increasing computing power is addressed. The answer presented here is the M3D (Multilevel 3D) project, which has developed a code package with a hierarchy of physics levels that resolve increasingly complete subsets of phase-spaces and are thus increasingly more realistic. The rationale for the multilevel physics models is given. Each physics level is described and examples of its application are given. The existing physics levels are fluid models (3D configuration space), namely magnetohydrodynamic (MHD) and two-fluids; and hybrid models, namely gyrokinetic-energetic-particle/MHD (5D energetic particle phase-space), gyrokinetic-particle-ion/fluid-electron (5D ion phase-space), and full-kinetic-particle-ion/fluid-electron level (6D ion phase-space). Resolving electron phase-space (5D or 6D) remains a future project. Phase-space-fluid models are not used in favor of δf particle models. A practical and accurate nonlinear fluid closure for noncollisional plasmas seems not likely in the near future.
Antiphase-domain-free growth of cubic SiC on Si(100)
Authors: Shibahara K. , Nishino S. , Matsunami H.
Published: July 2002

Single crystals of cubic SiC that are free of antiphase domains were successfully grown by chemical vapor deposition on Si substrates inclined at 2° from (100) towards (011). The relationship between the generation of antiphase domains and the inclination of a surface was investigated by using spherically polished Si substrates. Inclination, except towards (011), resulted in the generation of antiphase domains. Elimination of antiphase domains was confirmed by molten KOH etching of the grown layer.
Pivotal role of cyclic nucleoside phosphodiesterase 4 in Tat-mediated CD4+T cell hyperactivation and HIV type 1 replication
Authors: Secchiero Paola , Zella Davide , Curreli Sabrina , Mirandola Prisco , Capitani Silvano , Gallo Robert C. , Zauli Giorgio
Published: July 2002

We show here that HIV type 1 (HIV-1) Tat protein, in combination with anti-CD3/CD28 mAbs, promotes IL-2 production and proliferation of primary CD4+T lymphocytes, obtained from HIV-1-seronegative donors. This effect was observed when Tat was immobilized on a solid support, but it was not observed with soluble Tat. Such hyperactivation was accomplished by recruiting the rolipram-sensitive cyclic nucleoside phosphodiesterase 4 and resulted in increased susceptibility to HIV-1 infection. Accordingly, rolipram potently inhibited HIV-1 replication in cultures stimulated by anti-CD3/CD28 ± Tat. These results add to the concept that decreasing Tat activity is an important addition to anti-HIV-1 therapy, and they suggest a target for anti-HIV-1 chemotherapy, phosphodiesterase 4.