bluuebunny/crossref_metadata_2025 huggingface dataset:
Fully atomistic modeling of an electric field poled guest-host nonlinear optical polymer
Authors: Kim Won-Kook , Hayden L. Michael
Published: July 2002

Fully atomistic molecular modeling is performed on an electric field poled guest-host nonlinear optical polymer system at two different densities. The higher density (HD) represents a sub-Tg system, while the lower density (LD) corresponds to a system above Tg. The electric field alignment of dopants was studied by calculating 〈cos θ〉 and 〈cos3 θ〉 and comparing with the theoretically predicted order parameters. For the LD system, the dipole orientational order achieved during 1.5 ns of NVT dynamics at 500 K was similar to the theoretical prediction. The applied field was also found to constrain the side group of the host, poly(methyl methacrylate) (PMMA). The shape of the volume swept by the dopants was found to be less cylindrical as the field was increased. The partial radial distribution functions indicated that the dopants were likely to be located near the host side group. No significant differences in the static conformational properties of the host were observed between poled and unpoled structures. In the HD system, the COOCH3 side group motion was found to be more correlated with dopant orientation than the atoms in the backbone units. In the LD system, nearly equal side group and backbone contributions were involved in dopant orientation.
The accurate calculation and prediction of the bond dissociation energies in a series of hydrocarbons using the IMOMO (integrated molecular orbital+molecular orbital) methods
Authors: Vreven Thom , Morokuma Keiji
Published: July 2002

The IMOMO (integrated molecular orbital+molecular orbital) method was used to accurately calculate and compare with the experiment for the single-bond C–H and C–C bond dissociation energies of a series of hydrocarbons, R1−R2→R1+R2, where R1 is H or CH3, while the largest R2 considered is 1,1-diphenylethyl, C(C6H5)2(CH3). While the geometries and zero point vibrational energies were obtained at the hybrid density function (B3LYP/6-31G) level for the real system, a small system, H–CH3 or CH3–CH3, was used as the “model” in the IMOMO energy calculation, for which a high level method is used. Of a large number of IMOMO combinations tested, the combination of the modified Gaussian-2 method (G2MSr) with the restricted open-shell second-order Møller–Plesset perturbation method (ROMP2), the IMOMO(G2MSr:ROMP2/6-31G(d)) method, yields the best results, and can be used for bond dissociation energy predictions of very large molecules. Finally, the IMOMO(G2MSr:ROMP2/6-31G(d)) method was used to predict the C–H bond dissociation energy in H–C(C6H5)3 and the C–C bond dissociation energy in CH3–C(C6H5)3, neither of which is available experimentally. These predicted values are 75.9 and 64.1 kcal/mol, respectively, which are smaller than any other C–H and C–CH3 BDE studied in this paper.
Quantum Monte Carlo simulation of intermolecular excited vibrational states in the cage water hexamer
Authors: Severson Mark W. , Buch Victoria
Published: July 2002

Rigid-body diffusion Monte Carlo simulations of the ground state and ten low-lying intermolecular excited vibrational states for the cage form of (H2O)6 are reported. The excited states are found by a nodal optimization procedure in which the fundamental excited-state nodes are constructed from the harmonic normal coordinates. The anharmonic effects in the excited states are found to be large. One of the states with relatively large transition intensity involves primarily flipping motions of the free OH bonds on the doubly bound monomers, and is assigned to the vibration–rotation–tunnelling band observed experimentally by Liu et al. [Nature 301, 501–503 (1996)].
Efficient adiabatic population transfer by two-photon excitation assisted by a laser-induced Stark shift
Authors: Rickes T. , Yatsenko L. P. , Steuerwald S. , Halfmann T. , Shore B. W. , Vitanov N. V. , Bergmann K.
Published: July 2002

We demonstrate and analyze a novel scheme for complete transfer of atomic or molecular population between two bound states, by means of Stark-chirped rapid adiabatic passage (SCRAP). In this two-laser technique a delayed-pulse laser-induced Stark shift sweeps the transition frequency between two coupled states twice through resonance with the frequency of the population-transferring coupling laser. The delay of the Stark-shifting pulse with respect to the pulse of the coupling-laser Rabi frequency guarantees adiabatic passage of population at one of the two resonances while the evolution is diabatic at the other. The SCRAP method can give a population-transfer efficiency approaching unity. We discuss the general requirements on the intensity and timing of the pulses that produce the Rabi frequency and, independently, the Stark shift. We particularly stress extension to a double-SCRAP technique, a coherent variant of stimulated emission pumping in the limit of strong saturation. We demonstrate the success of the SCRAP method with experiments in metastable helium, where a two-photon transition provides the Rabi frequency.
Covalent bond force profile and cleavage in a single polymer chain
Authors: Garnier Lionel , Gauthier-Manuel Bernard , van der Vegte Eric W. , Snijders Jaap , Hadziioannou Georges
Published: July 2002

We present here the measurement of the single-polymer entropic elasticity and the single covalent bond force profile, probed with two types of atomic force microscopes (AFM) on a synthetic polymer molecule: polymethacrylic acid in water. The conventional AFM allowed us to distinguish two types of interactions present in this system when doing force spectroscopic measurements: the first interaction is associated with adsorption sites of the polymer chains onto a bare gold surface, the second interaction is directly correlated to the rupture process of a single covalent bond. All these bridging interactions allowed us to stretch the single polymer chain and to determine the various factors playing a role in the elasticity of these molecules. To obtain a closer insight into the bond rupture process, we moved to a force sensor stable in position when measuring attractive forces. By optimizing the polymer length so as to fulfill the elastic stability conditions, we were able for the first time to map out the entire force profile associated with the cleavage of a single covalent bond. Experimental data coupled with molecular quantum mechanical calculations strongly suggest that the breaking bond is located at one end of the polymer chain.
The fractional diffusion equation
Authors: Wyss Walter
Published: July 2002

In one space—and in one time—dimension a diffusion equation is solved, where the first time derivative is replaced by the λ-fractional time derivative, 0<λ≤1. The solution is given in closed form in terms of Fox functions.
Static spherically symmetric space-times with six Killing vectors
Authors: Qadir Asghar , Ziad M.
Published: July 2002

It had been proved earlier that spherically symmetric, static space-times have ten, seven, six, or four independent Killing vectors (KV’s), but there are no cases in between. The case of six KV’s is investigated here. It is shown that the space-time corresponds to a hyperboloid cross a sphere, reminiscent of Kaluza–Klein theory, with a compactification from four down to two dimensions. In effect, there is a unique metric for this space-time corresponding to a uniform mass distribution over all space.
Generalized Burgers equations and Euler–Painlevé transcendents. III
Authors: Sachdev P. L. , Nair K. R. C. , Tikekar V. G.
Published: July 2002

It was proposed earlier [P. L. Sachdev, K. R. C. Nair, and V. G. Tikekar, J. Math. Phys. 27, 1506 (1986); P. L. Sachdev and K. R. C. Nair, ibid. 28, 977 (1987)] that the Euler–Painlevé equations  y(d2y/dη2)+a(dy/dη)2 +f(η)y(dy/dη)+g(η)y2+b(dy/dη) +c=0 represent generalized Burgers equations (GBE’s) in the same way as Painlevé equations represent the Korteweg–de Vries type of equations. The earlier studies were carried out in the context of GBE’s with damping and those with spherical and cylindrical symmetry. In the present paper, GBE’s with variable coefficients of viscosity and those with inhomogeneous terms are considered for their possible connection to Euler–Painlevé equations. It is found that the Euler–Painlevé equation, which represents the GBE ut+uβux=(δ/2)g(t)uxx, g(t)=(1+t)n, β>0, has solutions, which either decay or oscillate at η=±∞, only when −1<n<1. The solutions are shocklike when n=1. On the other hand, they oscillate over the whole real line when n=−1. Furthermore, the solutions monotonically decay both at η=+∞ and η=−∞, that is, they have a single hump form if β≥βn=(1−n)/(1+n). For β<βn, the solutions have an oscillatory behavior either at η=+∞ or at η=−∞, or at η=+∞ and η=−∞. For β=βn, there exists a single parameter family of exact single hump solutions, similar to those found for the nonplanar Burgers equations in Paper II. Thus the parametric value β=βn seems to bifurcate the families of solutions, which remain bounded at η=±∞. Other GBE’s considered here are also found to be reducible to Euler–Painlevé equations.

The scope of these equations is broadened by relating them to a large number of nonlinear DE’s selected from the compendia of Kamke [Differential Gleichungen : Lösungsmethoden und Lösungen (Akademische Verlagsgesellschaft, Leipzig, 1943)] and Murphy [Ordinary Differential Equations and their Solutions (Van Nostrand, Princeton, NJ, 1960)]. These latter equations arise from a wide range of physical applications and are of some historical interest as well. They are all special cases of a slightly generalized form of the Euler–Painlevé equation.
Recurrence relations for two-center harmonic oscillator integrals and their solutions using generating functions
Authors: Rashid Muneer A.
Published: July 2002

Using the algebraic second quantization formalism, the general recurrence relations for some two-center harmonic oscillator integrals are obtained. The various known special cases for one-center integrals are evident in the formalism. Generating functions for these integrals are obtained and most of them are solved to find explicit expressions for polynomial, exponential, and Gaussian operator integrals. For these cases, all the generating integrals needed for utilizing the recurrence relations are also calculated in their simplest forms.
Recursion relation of character expansion coefficient in SU(3) lattice gauge theory
Authors: Tanimura N. , Tanimura O.
Published: July 2002

In the SU(3) lattice gauge theory the recursion relations of coefficients of the character expansion are derived through the Schwinger–Dyson equation for the ensemble average containing multilink variables. The variables form two kinds of recursion relations which correspond to two independent integers λ and μ of the SU(3) (λμ) representation of the Young tableau. The property of the recursion relations in comparison with those of the U(1) and SU(2) groups is discussed.
The Goursat problem for the homogeneous wave equation
Authors: Hillion Pierre
Published: July 2002

The Goursat problem for the 3-D homogeneous wave equation is presented and some methods to solve it are discussed.
Adiabatic and post-adiabatic representations for multichannel Schrödinger equations
Authors: Aquilanti Vincenzo , Cavalli Simonetta , Sevryuk Mikhail B.
Published: July 2002

The properties of the adiabatic representation of a multichannel Schrödinger equation are analyzed by exploiting the Hamiltonian and symplectic nature of the coefficient and transformation matrices, respectively. Use of this algebraic structure of the problem is shown to be in line with an approach developed by Fano and Klar [Klar and Fano, Phys. Rev. Lett. 37, 1132 (1976); Klar, Phys. Rev. A 15, 1452 (1977)] in their introduction of the postadiabatic potentials. The formal calculations due to Klar and Fano which halve the order of the matrices involved are given a rigorous mathematical background and described in a more general setup from the viewpoint of the theory of Hamiltonian and symplectic linear operators. An infinite sequence of postadiabatic representations is constructed and an algorithm for the choice of a symplectic transformation matrix for each representation is proposed. The interaction of fluorine atoms with hydrogen halides is considered as an example: In these cases, it is found that the first-postadiabatic representation shows lower coupling than the adiabatic one, and this provides a proper choice for a decoupling approximation. The present results, and in particular the recipes for obtaining the eigenvalues and eigenvectors of relevant matrices manipulating matrices of half the size, offer interesting perspectives for the numerical integration of multichannel Schrödinger equations.
An explicit description of the symplectic structure of moduli spaces of flat connections
Authors: King Christopher , Sengupta Ambar
Published: July 2002

The moduli space of flat connections on a principal G-bundle over a compact oriented surface of genus g≥1 is considered herein. Using the holonomies around noncontractible loops, the moduli space is described as a quotient of a submanifold of G2g. An explicit expression is obtained for the symplectic form on the smooth part of moduli space, and several properties of this form are established.
Black holes cannot support conformal scalar hair
Authors: Zannias T.
Published: July 2002

It is shown that the only static asymptotically flat nonextrema black hole solution of the Einstein-conformally invariant scalar field equations having the scalar field bounded on the horizon is the Schwarzschild solution.
Finite-dimensional representations of the quantum superalgebra Uq[gl(2/2)]. II. Nontypical representations at generic q
Authors: Ky Nguyen Anh , Stoilova Nedialka I.
Published: July 2002

The construction approach proposed in the previous paper [N. A. Ky, J. Math. Phys. 35, 2583 (1994)] allows us there and in the present paper to construct at generic deformation parameter q all finite-dimensional representations of the quantum Lie superalgebra Uq[gl(2/2)]. The finite-dimensional Uq[gl(2/2)]-modules Wq constructed in the previous paper are either irreducible or indecomposable. If a module Wq is indecomposable, i.e., when the condition (4.41) in the previous paper does not hold, there exists an invariant maximal submodule of Wq, say, Iqk, such that the factor representation in the factor module Wq/Iqk is irreducible and called nontypical. Here, in this paper, indecomposable representations and nontypical finite-dimensional representations of the quantum Lie superalgebra Uq[gl(2/2)] are considered and classified as their module structures are analyzed and the matrix elements of all nontypical representations are written down explicitly.
A new relation among Catalan numbers
Authors: Nilsson Bengt E. W. , Sundell Per
Published: July 2002

We derive a new highly nonlinear relation among binary Catalan numbers. The proof presented here utilizes techniques and results from two-dimensional conformal quantum field theory and string theory.
Variational representation of the projection dynamics and random motion of highly dissipative systems
Authors: Gafiychuk V. V. , Lubashevskii I. A.
Published: July 2002

We propose the method of investigation of highly dissipative systems, which are based on the approximation of the attractor by some manifold. The projection dynamic equations for the general form of such manifold of the dissipative dynamic system are obtained. Variational principles for the projection dynamics are considered. On the basis of the projection dynamic equations we investigate the influence of the random forces on the behaviour of the system.
The classification of static plane symmetric space–times according to their Ricci collineations
Authors: Farid Taha Bin , Qadir Asghar , Ziad M.
Published: July 2002

Static plane symmetric space–times are classified according to their Ricci collineations (RCs). Their relation with isometries of the space–times is established. Unlike the spherically symmetric space–times, some metrics are found for a nondegenerate Ricci tensor which have more RCs than isometries.
Linear connections on extended space-time
Authors: Kehagias A. , Madore J. , Mourad J. , Zoupanos G.
Published: July 2002

A modification of Kaluza–Klein theory is proposed which is general enough to admit an arbitrary finite noncommutative internal geometry. It is shown that the existence of a nontrivial extension to the total geometry of a linear connection on space–time places severe restrictions on the structure of the noncommutative factor. A counter-example is given.
Infinite-dimensional Estabrook–Wahlquist prolongations for the sine-Gordon equation
Authors: Finley J. D. , McIver John K.
Published: July 2002

We are looking for the universal covering algebra for all symmetries of a given partial differential equation (PDE), using the sine-Gordon equation as a typical example for a nonevolution equation. For nonevolution equations, Estabrook–Wahlquist prolongation structures for nonlocal symmetries depend on the choice of a specific subideal of the contact module to define the PDE. For each inequivalent such choice we determine the most general solution of the prolongation equations, as subalgebras of the (infinite-dimensional) algebra of all vector fields over the space of nonlocal variables associated with the PDE, in the style of Vinogradov covering spaces. We show explicitly how previously known prolongation structures, known to lie within the Kac–Moody algebra, A(1)1, are special cases of these general solutions, although we are unable to identify the most general solutions with previously studied algebras. We show the existence of gauge transformations between prolongation structures, viewed as determining connections over the solution space, and use these to relate (otherwise) distinct algebras. Faithful realizations of the universal algebra allow integral representations of the prolongation structure, opening up interesting connections with algebras of Toeplitz operators over Banach spaces, an area that has only begun to be explored.
Theory and predictions for finite-amplitude waves in two-dimensional plane Poiseuille flow
Authors: Barkley Dwight
Published: July 2002

It has been found by Pugh and Saffman [J. Fluid Mech. 194, 295 (1988)] that in a two-dimensional channel, the stability of finite-amplitude steady waves to modulated waves can depend on the boundary conditions imposed on the flow. In particular, near the limit point in Reynolds number, stability can depend on whether the flux or the mean pressure gradient is prescribed for the flow. Here a continuous range of intermediate boundary conditions is defined and studied using bifurcation theory. Based only on previous numerical solutions to the Navier–Stokes equations at constant mean flux and constant mean pressure gradient, it is shown that the finite-amplitude steady waves must have a double-zero eigenvalue at some intermediate boundary condition. From this a unifying picture emerges for the dynamics near the limit point in Reynolds number and specific predictions are made for finite-amplitude solutions to the Navier–Stokes equations. These predictions include the existence of a homoclinic orbit and a degenerate Hopf bifurcation.
Results of counterneutral beam injection on the DIII-D tokamak
Authors: Schissel D. P. , Allen S. L. , Burrell K. H. , DeBoo J. C. , Groebner R. J. , Kellman A. G. , Ohyabu N. , Petersen P. I. , Sager G. T. , Snider R. T. , Wood R. D. ,   the DIII-D Research Team
Published: July 2002

Limiter, single-null, and double-null divertor plasmas have been heated by hydrogen neutral beam injection in the direction opposite to that of the plasma current. The H-mode power threshold is reduced by approximately 25% for counterinjection. Sawtooth suppression was possible only for high neutral beam power and for high values of the safety factor. No confinement improvement over similar coinjection discharges was observed in H-mode, L-mode, or limiter discharges. In plasmas without sawteeth, metallic impurity buildup in the central region of the plasma eventually leads to a reduction in confinement. The parametric dependence of energy confinement for both L-and H-mode plasmas was found to behave in the same manner during similar coinjection experiments. H-mode confinement increased linearly with increasing plasma current (65 msec/MA at 9 MW). Both L-mode and H-mode energy confinement decreased with increasing neutral beam power. At 1.25 MA, the L-mode plasmas had a confinement time that was less than that predicted by Kaye–Goldston scaling.
Transition from neoclassical to turbulent electron diffusion
Authors: Kim D. E. , Choi Duk-In , Horton W. , Yushmanov P. N. , Parail V. V.
Published: July 2002

Electron diffusion in tokamak geometry is calculated including both the Coulomb collisional pitch angle scattering and the electromagnetic drift wave fluctuation spectrum. In the weak fluctuation limit the neoclassical banana-plateau diffusion coefficient is recovered. At higher fluctuation levels typical of the mixing length amplitude the anomalous transport formulas of drift wave turbulence are recovered using test particle simulations.
Enhanced confinement in tokamaks
Authors: Stambaugh R. D. , Wolfe S. M. , Hawryluk R. J. , Harris J. H. , Biglari H. , Prager S. C. , Goldston R. J. , Fonck R. J. , Ohkawa T. , Logan B. G. , Oktay E.
Published: July 2002

The physics of enhanced confinement regimes in tokamaks is reviewed and some directions for further enhancements are assessed. The H-mode confinement regime is examined. A number of other observations of enhanced confinement, having in common peaked density profiles, are compared to the theory of ion temperature gradient modes. Two schemes of promise in enhancing confinement, second stability and control of electric fields, are discussed. The contributions of alternate concepts to understanding tokamak transport are described.
Reduced magnetofluid dynamics in the lower-hybrid frequency range
Authors: Seyler C. E.
Published: July 2002

The electromagnetic two-fluid dynamics for plasmas in a strong applied magnetic field is investigated using a model for phenomena having frequencies in the range Ωi ≪ ω ≪ Ωe and long parallel wavelengths ε≡L⊥/L∥ ≪ 1. The model retains the essential nonlinear physics of the magnetosonic, lower-hybrid, and oblique whistler waves. At least two unstable modes can exist for equilibria with magnetic shear; a local magnetic interchange whistler mode and a collisionless tearing mode. These modes are studied using a quadratic energy relation for linear stability and by three-dimensional time-dependent numerical computations.
Dynamics of Ne-like populations in the germanium x-ray laser
Authors: Nantel M. , Kieffer J. C. , La Fontaine B. , Pépin H. , Enright G. D. , Villeneuve D. M. , Dunn J. , Baldis H. A. , Peyrusse O.
Published: July 2002

Time- and two-dimensional (2-D) space-resolved monochromatic imaging is used to study the dynamics of Ne-like populations in the electron collisionally excited germanium x-ray laser. Large-scale variations in the n=3 level population, specifically the upper level of the 2s2p63d-2s2p63p laser transition, are observed in plasmas created in uniform and nonuniform irradiation conditions, and the degree of homogeneity along the amplification axis is related to the x-ray gain. The influence of inhomogeneities on the core-excited 3d-3p x-ray lasers is discussed.
Longitudinal friction and intermediate Mach number collisionless transverse magnetosonic shocks
Authors: Manheimer Wallace M. , Spicer Daniel S.
Published: July 2002

It is shown that for collisionless transverse magnetosonic shocks, there exists an intermediate range of Mach numbers between the maximum Mach number for transverse resistivity and the onset of significant ion reflection. In this intermediate range, the structure is dominated by a breakdown of the quasineutrality approximation, and longitudinal friction is a simple fluid model for the dissipation mechanism which forms the shock. Applications are discussed for laboratory shocks as well as the Earth’s bow shock.
On the generation of turbulent wall friction
Authors: Orlandi Paolo , Jiménez Javier
Published: July 2002

The formation of streaky velocity structures in the near wall region of turbulent boundary layers is studied through a simplified two-dimensional computational model in the plane normal to the average velocity. It is shown that the redistribution of the longitudinal velocity by streamwise vortices produces features very similar to those observed in the experiments, and that compact streamwise vortices form naturally from more general vorticity distributions. It is also shown, both numerically and analytically, that one effect of the formation of the streaks is to increase the average wall friction, and it is suggested that this effect is responsible for the higher friction in turbulent boundary layers, as opposed to laminar ones. An approximate quantitative analysis of the process supports this assumption.
Theory of drop formation
Authors: Eggers Jens
Published: July 2002

The motion of an axisymmetric column of Navier–Stokes fluid with a free surface is considered. Due to surface tension, the thickness of the fluid neck goes to zero in finite time. After the singularity, the fluid consists of two halves, which constitute a unique continuation of the Navier–Stokes equation through the singular point. The asymptotic solutions of the Navier–Stokes equation are calculated, both before and after the singularity. The solutions have scaling form, characterized by universal exponents as well as universal scaling functions, which are computed without adjustable parameters.
Large-scale flows and resonances in 2-D thermal convection
Authors: Prat J. , Massaguer J. M. , Mercader I.
Published: July 2002

Recent experiments of thermal convection in finite containers of intermediate and large aspect ratios have shown the presence of flows spanning the largest dimension of the container [R. Krishnamurti and L. N. Howard, Proc. Natl. Acad. Sci. 78, 1985 (1981); J. Fluid Mech. 170, 385 (1986)]. Large-scale flows of this kind computed from two-dimensional (2-D) numerical simulations are presented. The marginal stability curves for the bifurcations are computed in the range of aspect ratios L=1,...,6 and for Prandtl number σ =10. The nonlinear dynamics of the bifurcated solution is explored for containers with aspect ratios L=1,2,4. By increasing the Rayleigh number from criticality the system produces different sequences of symmetry breaking, Hopf-type bifurcations, which finally result in large scale flows, oscillatory net mass flux and chaos. The bifurcation involves different mode resonances with vertical and horizontal couplings, which are modeled using formal group theoretical techniques.
The nonaxisymmetric instability of the wide-gap spherical Couette flow
Authors: Araki Keisuke , Mizushima Jiro , Yanase Shinichiro
Published: July 2002

The nonaxisymmetric linear stability of spherical Couette flow is investigated numerically when the ratio of gap width to inner sphere radius (R2−R1)/R1=0.5. The basic flow becomes unstable at Rec=1245 and the associated azimuthal wave number is nc=5, which agrees remarkably well with the experimental results by Egbers and Rath [Acta Mech. 81, 3 (1990)]. The marginal mode is oscillatory and has a distinctive wavy structure around the equator and spirals extended in each hemisphere. Sufficiently large spatial resolution is found to be required in order to avoid serious underestimation of the critical Reynolds number.
Three-dimensional simulation of wavy Taylor vortex flow by direct simulation Monte Carlo method
Authors: Riechelmann Dirk , Nanbu Kenichi
Published: July 2002

Wavy Taylor vortex flow between two concentric cylinders is simulated on molecular level by the direct simulation Monte Carlo method. The number of cells in circumferential direction is greatly reduced by introducing the idea of locally axisymmetrical collision. As found in experiment, the wavy Taylor vortices are seen to move in azimuthal direction. The frequency of the azimuthal waves is in agreement with the experimental observation. It is the first time that wavy Taylor vortex flow is simulated by means of a molecular approach.
Toroidal vortices in resistive magnetohydrodynamic equilibria
Authors: Montgomery David , Bates Jason W. , Li Shuojun
Published: July 2002

When a time-independent electric current flows toroidally in a uniform ring of electrically conducting fluid, a Lorentz force results, j×B, where j is the local electric current density, and B is the magnetic field it generates. Because of purely geometric effects, the curl of j×B is nonvanishing, and so j×B cannot be balanced by the gradient of any scalar pressure. Taking the curl of the fluid’s equation of motion shows that the net effect of the j×B force is to generate toroidal vorticity. Allowed steady states necessarily contain toroidal vortices, with flows in the poloidal directions. The flow pattern is a characteristic “double smoke ring” configuration. The effect seems quite general, although it is analytically simple only in special limits. One limit described here is that of high viscosity (low Reynolds number), with stress-free wall boundary conditions on the velocity field, although it is apparent that similar mechanical motions will result for no-slip boundaries and higher Reynolds numbers. A rather ubiquitous connection between current-carrying toroids and vortex rings seems to be implied, one that disappears in the “straight cylinder” limit.
Double diffusive convection in a vertical rectangular cavity
Authors: Ghorayeb Kassem , Mojtabi Abdelkader
Published: July 2002

In the present work, we study the onset of double diffusive convection in vertical enclosures with equal and opposing buoyancy forces due to horizontal thermal and concentration gradients (in the case GrS/GrT=−1, where GrS and GrT are, respectively, the solutal and thermal Grashof numbers). We demonstrate that the equilibrium solution is linearly stable until the parameter RaT|Le−1| reaches a critical value, which depends on the aspect ratio of the cell, A. For the square cavity we find a critical value of Rac|Le−1|=17 174 while previous numerical results give a value close to 6000. When A increases, the stability parameter decreases regularly to reach the value 6509, and the wave number reaches a value kc=2.53, for A→∞. These theoretical results are in good agreement with our direct simulation. We numerically verify that the onset of double diffusive convection corresponds to a transcritical bifurcation point. The subcritical solutions are strong attractors, which explains that authors who have worked previously on this problem were not able to preserve the equilibrium solution beyond a particular value of the thermal Rayleigh number, Rao1. This value has been confused with the critical Rayleigh number, while it corresponds in fact to the location of the turning point.
Viscosity scaling in suspensions of non-Brownian rodlike particles
Authors: Ralambotiana T. , Blanc R. , Chaouche M.
Published: July 2002

A systematic experimental study of the settling of a spherical ball in a fiber suspension for different particle aspect ratios and a wide range of volume concentrations is presented. The situation where the ball size is much greater than the fiber length is considered. First, it has been observed that, even at very low concentration, the flow induced by the sphere drastically modifies the orientation distribution of the particles. It was found that, in the dilute and semidilute regime, the viscosity inferred from the sphere falling velocity scales with the excluded volume and compares well with existing shear measurements. Moreover, the viscosity was found to be almost independent of the initial orientation distribution of the fibers, indicating that the rheological response of the suspension was dominated by the configuration induced by the sphere displacement.
Multidimensional stability analysis of overdriven gaseous detonations
Authors: Clavin Paul , He Longting , Williams Forman A.
Published: July 2002

Multidimensional instabilities of planar detonations that lead to cellular structures are addressed by use of a distinguished limit in which the propagation Mach number is large and the difference between the specific heats at constant pressure and at constant volume is small. In this limit, the Neumann-state Mach number is small, and the fractional variations of the pressure change after the Neumann state also are small for the overdriven conditions that are considered, under which the heat release is comparable in magnitude with the thermal enthalpy at the Neumann state. The resulting post-shock flow is quasi-isobaric in the first approximation. For all linear modes the analysis provides a dispersion relation expressing the frequency and the linear growth rate in terms of the transverse wavelength. The analysis serves to demonstrate how the interactions among the entropy waves, the varying rate of heat release and the transverse flow induced by the large density change across the wrinkled shock result in the multidimensional instability. The instabilities have a large transverse length but oscillate and evolve on a short time, comparable with the transit time of a fluid particle through the detonation. The coupling with the acoustic waves is a stabilizing factor, dominant at short wavelengths for assuring a suitably large ratio of transverse wavelength to detonation thickness for instability. Even when the detonation is stable to planar disturbances, so that there is a range of stability at long wavelengths, it is shown that there always exists an intermediate range of wavelengths for which the detonation is unstable. This is true even when heat-release rates are entirely independent of temperature, corresponding to detonations that are very stable to planar disturbances. A sufficiently large temperature sensitivity modifies the multidimensional instability. The general chemical kinetics adopted, having different temperature sensitivities for induction and for heat release, the former possibly large, is of the same character as that previously developed by the first authors for describing the planar stability and nonlinear oscillations of galloping detonations but differs from one-step activation-energy asymptotics, which produces nonphysical, spurious instability under all conditions. From the present extension to multiple dimensions with moderate overdrive, inferences are drawn concerning differences that arise for strong overdrive and when Chapman–Jouguet conditions are approached.
On mass transport of progressive edge waves
Authors: Mok K. M. , Yeh Harry
Published: July 2002

The boundary-layer solutions for progressive edge waves on a uniformly sloping beach are derived. The Larangian mass transport in the cross-shore direction is found to be caused by the viscous effect and it changes direction within the boundary layer. For validation of the theoretical model, laboratory experiments are performed. The measured mass transports of mode 0 and 1 edge waves are in good agreement with the theory qualitatively but not quantitatively. The discrepancies appear to be caused by the failure of the theory near the shoreline, where the boundary layer is no longer thin. The inviscid Stokes drift caused by the nonlinear interactions of different edge-wave modes within the potential flow field is also investigated theoretically and verified by experiments. It is found that near-shore circulation cells can be formed by the nonlinear interactions between different progressive edge-wave modes.
Analytical scalings for flame interaction with sound waves
Authors: Bychkov Vitaliy
Published: July 2002

Analytical scalings for the problem of flame interaction with acoustic waves of controlled intensity are obtained on the basis of the linear equation for a perturbed flame front. Both stabilization of the hydrodynamic flame instability by sound waves of small amplitudes and excitation of the parametric instability at the flame front by sound waves of sufficiently large amplitudes are considered. The stability limits obtained analytically agree well with the previous numerical calculations. Besides, the analytical results for the minimum amplitude of sound waves needed to induce the parametric instability and for the typical wavelength of the instability are in excellent agreement with the experimental results on propane flames.
Damping of toroidal Alfvén modes in DIII-D
Authors: Mett R. R. , Strait E. J. , Mahajan S. M.
Published: July 2002

The previously developed single-gap kinetic theory for toroidicity-induced Alfvén eigenmodes (TAE) is extended and applied to Doublet III-D [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] experimental data. It is found that the theory gives reasonable agreement with the data when an appropriate magnetohydrodynamic boundary condition is accounted for. As is shown, this boundary condition is equivalent to an appropriate real frequency shift relative to the continuum gap. The correct eigenfunction near the gap, and thus the correct damping, is obtained by using the gap structure calculated from an equilibrium reconstruction that includes low aspect ratio, noncircularity, and finite beta effects, combined with an experimentally measured frequency. In the considered experimental cases, the damping is well into the nonideal regime.
High performance and current drive experiments in the JAERI Tokamak-60 Upgrade*
Authors: Kondoh T. ,   the JT-60 Team
Published: July 2002

Recent high-fusion-triple-product and current drive experiments in the JAERI Tokamak-60 Upgrade (JT-60U) [Plasma Devices Oper. 1, 43 (1990)] are reported. The fusion triple product of 1.1×1021 m−3 s keV has been achieved in a more improved confinement mode (high-βp H-mode) in which the confinement is improved in the edge region as well as the core region. The most remarkable feature in the improved confinement mode is the multistage formation of transport barriers. The transport barrier was formed in the plasma interior first. After that, the transport barrier was formed in the edge region. For steady-state operation and current profile control, lower hybrid current drive (LHCD) and neutral beam current drive (NBCD) experiments with bootstrap current contribution are also in progress. Full current drive of 3.6 MA has been achieved at a density of 1.1×1019 m−3 with a current drive efficiency of ne⋅Rp⋅ICD/PLH=2.5×1019 m−2 A W−1 with a 5.7 MW LH wave injection. Current profile control with various LH wave spectra and with NBCD were also demonstrated.
Thickness of the layer of high shear radial electric field in JFT-2M H-mode plasmas
Authors: Ida K. , Itoh K. , Itoh S.-I. , Miura Y. , Fukuyama A. ,   JFT-2M Group
Published: July 2002

The poloidal rotation velocity profiles both in low-confinement (L) and high-confinement (H) mode measured in JAERI Fusion Torus 2 Modified (JFT-2M) [Phys. Rev. Lett. 65, 1364 (1990)] are compared with H-mode models based on ion orbit loss. The profiles of poloidal rotation velocity measured in L and H modes are consistent with the calculation which consists of ion orbit loss model. The observed dependence of the thickness of the layer of high shear Er on poloidal gyroradius is explained by the radial transport of poloidal rotation velocity.
Stabilization of resistive wall modes by slow plasma rotation
Authors: Boozer Allen H.
Published: July 2002

External kinks that drive magnetic islands inside a plasma can be stabilized by a resistive wall for even a slow plasma rotation. It is shown that only a subclass of ideal kinks avoid driving islands and stabilization by slow rotation. In addition, the separatrix of a tokamak divertor causes external kink instabilities to have resonant surfaces within the plasma and drive islands. Consequently, tokamaks with a hot divertor scrape-off layer may be more stable to resistive wall modes than tokamaks with limiters. It is shown that the calculation and description of the stability of wall modes is greatly simplified by the use of the inductance, resistance, and torque associated with a surface current.
Stimulated Brillouin backscatter of a short-pulse laser
Authors: Hinkel D. E. , Williams E. A. , Berger R. L.
Published: July 2002

Stimulated Brillouin backscattering (SBBS) from a short-pulse laser, where the pulse length is short compared to the plasma length, is found to be qualitatively different than in the long pulse regime, where the pulse length is long compared to the plasma length. After an initial transient of order the laser pulse length transit time, the instability reaches a steady state in the variables x′=x−Vgt, t′=t, where Vg is the pulse group velocity. In contrast, SBBS in a long pulse can be absolutely unstable and grows indefinitely, or until nonlinearities intervene. The motion of the laser pulse induces Doppler related effects that substantially modify the backscattered spectrum at higher intensities, where the instability is strongly coupled (i.e., has a growth rate large compared to the ion acoustic frequency).
Computer simulations of the chaotic dynamics of the Pierce beam–plasma system
Authors: Matsumoto Hiroshi , Yokoyama Hiroyuki , Summers Danny
Published: July 2002

The cold fluid theory of the Pierce beam–plasma system is modified by the incorporation of warm plasma effects. The controlling parameter α in the cold theory, where α=Lωp/V0, L=diode width, ωp=plasma frequency, and V0=beam velocity at injection, is replaced in the warm theory by an effective value of α involving the thermal velocity. The theory is verified by means of a fluid simulation code; the phase states for a cold plasma, including the chaotic state, are recovered for a warm plasma, but with a shift in values of the bifurcation parameter. Furthermore, in order to include plasma kinetic effects, an extensive electrostatic particle simulation code is developed to model the Pierce system. Among the new physical effects arising in this particle model are the local and global thermalization of electrons by electrostatic waves, and blocking oscillations due to particle reflection and trapping. As the parameter α is decreased, the electric field at the injection point typically changes state as follows: blocking oscillation→small fluctuations→quasisteady oscillation→prechaotic oscillation→chaos→blocking oscillation→dc electric field. The mechanics of chaotic oscillations in the Pierce system are examined with particular regard to kinetic effects.
Feedback stabilization of the resistive shell mode in a tokamak fusion reactor
Authors: Fitzpatrick Richard
Published: July 2002

Stabilization of the “resistive shell mode” is vital to the success of the “advanced tokamak” concept. The most promising reactor relevant approach is to apply external feedback using, for instance, the previously proposed “fake rotating shell” scheme [R. Fitzpatrick and T. H. Jensen, Phys. Plasmas 3, 2641 (1996)]. This scheme, like other simple feedback schemes, only works if the feedback controlled conductors are located inside the “critical radius” at which a perfectly conducting shell is just able to stabilize the ideal external kink mode. In general, this is not possible in a reactor, since engineering constraints demand that any feedback controlled conductors be placed outside the neutron shielding blanket (i.e., relatively far from the edge of the plasma). It is demonstrated that the fake rotating shell feedback scheme can be modified so that it works even when the feedback controlled conductors are located well beyond the critical radius. The gain, bandwidth, current, and total power requirements of such a feedback system for a reactor sized plasma are estimated to be less than 100, a few Hz, a fews tens of kA, and a few MW, respectively. These requirements could easily be met using existing technology. It is concluded that feedback stabilization of the resistive shell mode is possible in a tokamak fusion reactor.
A study of the efficiency of “intelligent shells”
Authors: Jensen T. H.
Published: July 2002

An “Intelligent Shell” [C. M. Bishop, Plasma Phys. Controlled Fusion 31, 1179 (1985)] is a resistive wall equipped with feedback loops intended to make it appear ideally conducting to the plasma. Two problems associated with intelligent shells are addressed, using a simple model solved numerically, namely, the influence on the stabilization efficiency of the number of feedback loops employed and of gaps between loops of the feedback system. Without gaps between the sensor loops it is found that a modest number of loops per period (such as eight) is almost as stabilizing as infinitely many loops. It is also found that the stabilizing effect is decreasing rapidly by increasing gaps between loops.
Equations for studies of feedback stabilization
Authors: Boozer Allen H.
Published: July 2002

Important ideal magnetohydrodynamic (MHD) instabilities grow slowly when a conducting wall surrounds a toroidal plasma. Feedback stabilization of these instabilities may be required for tokamaks and other magnetic confinement concepts to achieve adequate plasma pressure and self-driven current for practical fusion power. Equations are derived for simulating feedback stabilization, which require the minimum information about an ideal plasma for an exact analysis. The equations are solved in the approximation of one unstable mode, one wall circuit, one feedback circuit, and one sensor circuit. The analysis based on a single unstable mode is shown to be mathematically equivalent to the standard analysis of feedback of the axisymmetric vertical instability of tokamaks. Unlike that analysis, the method presented here applies to multiple modes that are coupled by the wall and to arbitrary toroidal mode numbers.
Dust acoustic drift waves in a dusty plasma
Authors: Prasad P. V. Siva Rama
Published: July 2002

Dust acoustic drift waves (in which the dust particles provide the inertia for the wave, and electrons and ions follow a linearized Boltzmann distribution) are studied in a magnetized inhomogeneous dusty plasma, considering the coupling of the perturbation of charge on the dust particles to the waves self-consistently. It is found that, when the dust particle density is homogeneous but the electron and ion densities are inhomogeneous, the dust drift wave branch is unstable; while, when the dust particle density is inhomogeneous, the modified dust acoustic wave branch is unstable. Furthermore, the coupling of the perturbation of charge on the dust particles to the waves tends to suppress these instabilities.
The role of radial particle flow on power balance in DIII-D
Authors: Porter G. D. ,   DIII-D team
Published: July 2002

The importance of radial particle flow on the power flowing across the last closed flux surface (separatrix) in DIII-D [Luxon et al., International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1986), Vol. I, p. 159] is considered. The perpendicular thermal diffusivity at the separatrix is near 1 m2/s in low confinement operation (L-mode), and 0.1 m2/s in high confinement (H-mode). The particle diffusivity is about one-fourth of the thermal diffusivity producing radial particle fluxes of the order of kilo-amperes. The particle flux is 10 to 100 times the particle input from neutral beam sources, consistent with core fueling being dominated by neutral recycling. The radial particle flux scales with the neutral pressure in the private flux region, suggesting the core is fueled predominantly from neutrals which recycle from the divertor, through the private flux, and into the core near the singular point where the poloidal field is zero (X-point). There is significant core power loss associated with the large particle flux across the separatrix. The electron temperature measured at the top of the edge pedestal in H-mode operation scales inversely with the particle flux. In turn, the core energy confinement scales with the pedestal temperature, and hence inversely with the particle flux. The results presented here indicate the global particle confinement time is between 0.5 and 2 times the global energy confinement time.