bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonance-enhanced multiphoton-ionization photoelectron spectroscopy of even-parity autoionizing Rydberg states of atomic sulphur
Authors: Woutersen S. , Milan J. B. , Buma W. J. , de Lange C. A.
Published: July 2002

Several previously unobserved Rydberg states of the sulphur atom above the lowest ionization threshold are identified and assigned using (2+1) resonance-enhanced multiphoton-ionization photoelectron spectroscopy. All states were accessed by two-photon transitions from either the 3P ground or the 1D excited state, prepared by in situ photodissociation of H2S. The observed states derive from the (2Do)5p and (2Po)4p configurations. For the (2Do)5p 3F and (2Po)4p 3D triplets, extensive photoelectron spectroscopic studies enable a detailed comparison of the autoionization and photoionization rates of these states.
Molecular reactions in condensed carbon monoxide studied by ion photodesorption
Authors: Philippe L. , Hirayama T. , Ramage M. J. , Comtet G. , Rose M. , Hellner L. , Dujardin G.
Published: July 2002

Ion photodesorption processes from carbon monoxide condensed in multilayers have been studied for photon energies between 12 and 60 eV. In the low energy range (12–25 eV), only the CO+ ion desorbs and the desorption is induced by the formation of excited neutral states. In the high energy range (25–60 eV), a large variety of ions desorb: C+, O+, CO+, C2O+, (CO)2+, C3O2+, and C3O+. The desorption threshold for these ions is around 30 eV and is assigned to the formation of satellite states. The ion desorption is related to fragmentation processes and ion-molecule reactions on the surface. Comparison with gas phase results show that the dissociative ionization of CO can be modified in the condensed phase by charge-transfer processes. Kinetic energy measurements of the desorbed ions support the proposed mechanisms.
A binary mixture of monodisperse polymers of fixed architectures, and the critical and the theta states
Authors: Gujrati P. D.
Published: July 2002

We study the complete phase diagram for a model of a binary mixture of two interacting polymer species A and A′, each of fixed architecture (dendrimer, star, linear, or regularly branched polymer, brush, etc.) and size given by the number M (or M′) of monomers in it, on a lattice of coordination number q. For M′=1, the model describes a solution. Branchings, if any, are regular in these architectures. This feature alone makes these polymers different from polymers with random branchings studied in the preceding paper [J. Chem. Phys. 108, 5089 (1998)]. There exists a theta point regardless of the fixed architecture, which is not the case for random branchings. We identify this point as a tricritical point T at which one of the two sizes M and M′ diverges. Two critical lines C and C′ meet at T. The criticality along C corresponds to the criticality of an infinitely large polymer of any fixed architecture, not necessarily linear. This polymer is a fractal object. We identify the relevant order parameter and calculate all the exponents along C. The criticality along C′ is that of the Ising model. Connected to T is a line t of triple points. The above results are well-known for a solution of linear polymers which we have now extended to a binary mixture of polymers of any arbitrary but fixed architecture. Our results show that regular branchings have no effects on the topology of the phase diagram and, in particular, on the existence of a theta state. The critical properties are also unaffected which is a surprising result. We point out the same subtle difference between polymers at the theta point and random walks as was found for a very special class of randomly branched polymers in the preceding paper (see the text). The behavior of a blend of a fixed aspect ratio a=M/M′, M→∞, is singular, as discussed in the text.
Electron-hole pair contributions to scattering, sticking, and surface diffusion: CO on Cu(100)
Authors: Kindt James T. , Tully John C. , Head-Gordon Martin , Gomez Maria A.
Published: July 2002

To assess the importance of coupling to electron-hole pair (ehp) excitations for molecular sticking, scattering, and diffusion dynamics at metal surfaces, simulations of the CO/Cu(100) system were performed using the “molecular dynamics with electronic frictions” method. Over a range of incident translational energies, energy losses to ehp excitations produce a moderate increase in sticking probability and account for 5%–10% of initial translational energy in scattered molecules, significantly less than phonon losses. Vibrational excitation and deexcitation of scattered molecules, while remaining a minor pathway for energy flow, is strongly affected by the inclusion of ehp excitations. Finally, although equilibrium diffusion constants are unaffected by the inclusion of coupling to ehp, it causes a significant quenching of transient mobility following adsorption of translationally hot molecules.
Variational reaction path algorithm
Authors: Fast Patton L. , Truhlar Donald G.
Published: July 2002

In this paper we propose a new algorithm for calculating a reaction path and a set of local vibrational frequencies along a reaction path for dynamics calculations. The new method yields reasonable vibrational frequencies even when using a large step size. The algorithm is tested by carrying out variational transition state theory calculations including multidimensional semiclassical tunneling contributions, for the reaction OH+H2→H2O+H, and the results are very promising.
Photodissociation dynamics of the singlet and triplet states of the NCN radical
Authors: Bise Ryan T. , Choi Hyeon , Neumark Daniel M.
Published: July 2002

The spectroscopy and photodissociation dynamics of the NCN radical have been investigated by fast beam photofragment translational spectroscopy. The B̃ 3Σu−←X̃ 3Σg−, c̃ 1Πu←ã 1Δg, and d̃ 1Δu←ã 1Δg transitions were examined. The major dissociation products for the B̃ 3Σu− and c̃ 1Πu states are N2(X̃ 1Σg+)+C(3P), while the d̃ 1Δu state dissociates to N2(X̃ 1Σg+)+C(1D). The dissociation channel, N(4S)+CN(X̃ 2Σ+) is observed for the B̃ 3Σu− state at photon energies greater than 4.9 eV, where it comprises ≈25±10% of the total signal. At all photon energies, the photofragment translational energy distributions show a resolved progression corresponding to the vibrational excitation of the N2 photofragment. The rotational distributions of the molecular fragments suggest that the dissociation pathway for the N2 loss channel involves a bent transition state while the N+CN photofragments are produced via a linear dissociation mechanism. The P(ET) distributions provide bond dissociation energies of 2.54±0.030 and 4.56±0.040 eV for the N2 and CN loss channels, respectively, yielding ΔHf,0 K(NCN)=4.83±0.030 eV.
Residual dipolar couplings between quadrupolar nuclei in high resolution solid state NMR: Description and observations in the high-field limit
Authors: Wi Sungsool , Frydman Lucio
Published: July 2002

Nonsecular dipolar couplings between spin-12 nuclei that are in close proximity to quadrupolar spins have been extensively documented in solid state nuclear magnetic resonance (NMR), particularly when involving directly bonded S=13C, I=14N spin pairs. These couplings arise due to the quadrupole-induced tilting of I’s nuclear spin quantization axes, and their most notable characteristic is that they cannot be entirely averaged away by conventional magic-angle-spinning (MAS). Nonsecular dipolar couplings can also be expected to arise when both I and S are quadrupolar nuclei, even if these have hitherto not been analyzed in detail due to the interfering effects brought about by first- and second-order quadrupolar anisotropies. Yet, the advent of new high resolution techniques for studying half-integer quadrupole nuclei in solids such as multiple-quantum MAS or dynamic-angle-spinning can change this state of affairs. The present study presents a theoretical and numerical analysis on the results that can be expected from these techniques when applied to the observation of homonuclear or heteronuclear quadrupolar spin pairs in the high field limit. Variable field multiple-quantum MAS NMR results are then presented for a variety of compounds possessing 11B–14N, 11B–11B and 55Mn–55Mn spin pairs, that validate these theoretical predictions and illustrate the valuable information that can be extracted from analyzing these residual MAS couplings. The research potential as well as resolution limitations that according to theoretical calculations these effects will impart on MQMAS spectra recorded at low or moderate magnetic fields are thus evidenced.
Hamiltonian approach to the existence of magnetic surfaces
Authors: Bernardin M. P. , Tataronis J. A.
Published: July 2002

A method is devised to investigate the existence of magnetic surfaces and magnetohydrodynamic (MHD) plasma equilibria in 3-D toroidal geometry. The key feature of this method is the utilization of a Hamiltonian formulation of the lines of force. Expanding the contravariant components of the magnetic field and scalar pressure in distance ρ from the magnetic axis, the 1-D Hamiltonian for the lines of force is written out explicitly. The Hamiltonian is then transformed to action-angle variables. It is shown that the action J corresponds to pressure in the equilibrium problem. Specifically, it is shown that if J is an invariant, then constant pressure and hence magnetic surfaces exist. A procedure of repeated canonical transformations is formulated and carried out to displace the coordinate dependence in the Hamiltonian to successively higher order in the expansion parameter, and thus make J an increasingly better adiabatic invariant. Arising in each successive canonical transformation is a series of potentially resonant denominators, i.e., denominators that may vanish. These potential resonances are identified, their significance explicated, and methods of handling them suggested.
Chebyshev polynomials and quadratic path integrals
Authors: Nash Patrick L.
Published: July 2002

A simple method for the evaluation of path integrals associated with quadratic Lagrangians is discussed. This approach makes use of a relationship between the Van Vleck–Morette determinant and a limit that involves the Chebyshev polynomials of the second kind.
Scalar and spinor solutions in the space-time of a domain wall
Authors: Bezerra Valdir B. , dos Santos Ivonete B.
Published: July 2002

The Klein–Gordon and Weyl equations are solved in the space-time of a plane vacuum domain wall. The solutions depend on global features of this space-time. In the spinor case the current is computed, showing its dependence on global features as well.
Triple products and Yang–Baxter equation. II. Orthogonal and symplectic ternary systems
Authors: Okubo Susumu
Published: July 2002

The result of Paper I in this set is generalized and the Yang–Baxter equation is solved in terms of triple systems called orthogonal and symplectic ternary systems. In this way, several other new solutions are found.
Multicentered solution for maximally charged dilaton black holes in arbitrary dimensions
Authors: Shiraishi Kiyoshi
Published: July 2002

A family of static multicentered solutions to modified Einstein–Maxwell equations coupled with a dilaton is constructed in (1+N) dimensional space–time (N≥2). For N≥3, the solutions are generalizations of the Majumdar–Papapetrou solution. We also find the solution in (1+2) dimensions, where the scalar and vector forces cancel each other in the static case. The interaction between two extreme charged dilaton black holes in the low-energy limit is investigated in (1+N) dimensions (N≥3). We find that there remains the residual velocity-dependent force in general cases, except for the case with N=a2.
Kerr–Schild gravitational fields in matter and the Kerr-interior problem in general relativity
Authors: Magli Giulio
Published: July 2002

Stationary Kerr–Schild gravitational fields in the interior of elastic–solid bodies are considered. It turns out that the Einstein field equations for such systems split into two parts: a ‘‘differential’’ part which may be written as a linear partial differential equation of the Maxwell type for a suitably defined, three-dimensional Euclidean vector and an ‘‘algebraic’’ (generally nonlinear) part which allows the calculation of the stresses supporting the bodies. These results are applied to the problem of finding the sources of the Kerr space–time, and a new class of solutions of the Einstein field equations is found. Such solutions describe sources of the Kerr metric composed by an elastic body and a shell distribution of elastic stress energy located on the matching surface. Some explicit examples of ‘‘half local’’ (singular) Kerr–Schild sources of the Kerr space–time are also given.
The KZ equation and the quantum-group difference equation in quantum self-dual Yang–Mills theory
Authors: Chau Ling-Lie , Yamanaka Itaru
Published: July 2002

From the time-independent current 𝒯̃(ȳ,k̄) in the quantum self-dual Yang–Mills (SDYM) theory, we construct new group-valued quantum fields Ũ(ȳ,k̄) and Ũ−1(ȳ,k̄) which satisfy a set of exchange algebras such that fields of 𝒯̃(ȳ,k̄)∼Ũ(ȳ,k̄)∂ȳŨ−1(ȳ,k̄) satisfy the original time-independent current algebra. For the correlation functions of the products of the Ũ(ȳ,k̄) and Ũ−1(ȳ,k̄) fields defined in the invariant state constructed through the current 𝒯̃(ȳ,k̄) we can derive the Knizhnik–Zamolodchikov (KZ) equations with an additional spatial dependence on k̄. From the Ũ(ȳ,k̄) and Ũ−1(ȳ,k̄) fields we construct the quantum-group generators, local, global and semi-local, and their algebraic relations. For the correlation functions of the products of the Ũ and Ũ−1 fields defined in the invariant state constructed through the semi-local quantum-group generators we obtain the quantum-group difference equations. We give the explicit solution to the two point function.
A natural extension of coherent state path integrals
Authors: Matsumoto Masao
Published: July 2002

We develop the formulation of the path integrals via the coherent states based on general starting vectors. In this paper we treat the case of the ordinary canonical (Heisenberg-Weyl) coherent state. We find that an additional term appears in the action in the path integral expression. Geometric phases associated with the path integrals, including the possibilities of the experimental detection, are also discussed.
Conditions on the stability of the external space solutions in a higher-dimensional quadratic theory of gravity
Authors: Kleidis K. , Varvoglis H. , Papadopoulos D. B.
Published: July 2002

By using Lyapounov’s direct method we examine the conditions under which stable solutions to the field equations for the scale function of the external space may be derived in the context of a five-dimensional quadratic theory of gravity. We show that the time evolution of the distance, in a diagram t–R, between our solution to the field equations and a neighbouring one is determined, in the linear approximation, in terms of a second-order linear differential equation. Asking for bounded solutions of this equation we arrive at a stability criterion for the external scale function solutions, indicating that there exist three types of cosmological evolution of the visible universe which are linearly stable at all times. These are (i) the Milne model, (ii) the spatially flat Friedmann radiation solution, and (iii) the De Sitter inflationary solution.
A q-deformed e(4) and continuous q-Jacobi polynomials
Authors: Floreanini Roberto , LeTourneux Jean , Vinet Luc
Published: July 2002

We present an algebraic interpretation of the continuous q-Jacobi polynomials. They are shown to realize a basis for a representation space of a q deformation of the four-dimensional Euclidean algebra e(4). A q analog of the expansion of an exponential in Jacobi polynomials is naturally obtained from this model.
Curvature-free asymmetric metric connections and Lanczos potentials in Kerr–Schild spacetimes
Authors: Andersson F. , Edgar S. Brian
Published: July 2002

The set of spinor equations linking the curvature spinors of a Riemann–Cartan space with the curvature spinors of the corresponding Riemann space is derived, and these are used to establish a simple relationship between Ψ-flat connections of the Riemann–Cartan space and Lanczos potentials of the Riemann space. This not only yields, very easily, a recent result of Bergqvist for the Kerr metric, but also enables Bergqvist’s result to be generalized; specifically we show that a curvature-free connection, associated with a class of Kerr–Schild metrics, can be identified as a Lanczos potential for the Weyl conformal curvature spinor of these spaces.
Symmetries, separability and volume forms
Authors: Sarlet W. , Sahadevan R. , Cantrijn F.
Published: July 2002

In order to clarify certain misconceptions in the literature, we discuss the details of the way determining equations for general symmetries of a Lagrangian system differ from determining equations for Noether symmetries, and establish the minimal set of extra conditions which have to be imposed in practical situations for the former to reduce to the latter. We further derive properties by which, in situations where the system is integrable through quadratic integrals in involution, the components of the corresponding Noether symmetries themselves can be used to compute the separation variables, if they exist, for the Hamilton–Jacobi equation.
Absence of singular spectrum for Schrödinger operators with anisotropic potentials and magnetic fields
Authors: Măntoiu Marius , Richard Serge
Published: July 2002

We study magnetic Schrödinger operators of the form H=(P−a)2+V in L2(Rm+p), with m⩾2. We get a limiting absorption principle and the absence of singular spectrum under rather mild and especially anisotropic hypothesis. The magnetic field B and the potential V will be connected by some Rm-conditions, but in the Rp-variable there will be almost no constraints. If m=2 and p=0, our results contrast with the known fact that P2+V always has bound states if V is negative.
Fields and currents of Abrikosov–Josephson vortices in a thin film
Authors: Malishevskiı̆ A. S.
Published: July 2002

Fields and currents induced by vortex structures in a Josephson junction in a thin superconducting film are considered. Simple asymptotic regularities describing fields and currents induced by solitary Abrikosov–Josephson vortices and periodic chains of such vortices are obtained. These regularities are applied to some nonlinear small-scale states.
Electron density of states and spin fluctuations in weak itinerant magnets
Authors: Povzner A. A. , Volkov A. G. , Bayankin P. V.
Published: July 2002

The influence of zero-point and thermal spin fluctuations on the electronic structure and magnetic properties of weak itinerant magnets is considered. The possibility of considerable complex reconstruction of electron state density in fluctuating exchange and charge fields is demonstrated for Fe1−xCoxSi. The temperature dependence of paramagnetic susceptibility is in agreement with experimental data obtained for Fe1−xCoxSi.
Effect of pressure on phase transitions in fluosilicate hexahydrates of bivalent metals
Authors: Asadov S. K. , Zavadskii È. A. , Kamenev V. I. , Todris B. M.
Published: July 2002

The results of experiments on hydrostatic pressure effect on the stability of crystalline phase states in fluosilicate hexahydrates of bivalent metals MSiF66(H2O), where M = Mg, Mn, Fe, Co, Ni, and Zn, are considered in a wide temperature range. The results of measurements are presented on the P–T diagram of crystalline states. A generalized P–T diagram permitting the classification of the properties of individual compounds and identification of high-pressure phases is constructed. The obtained results are compared with theoretical models.
Dipole magnet model for CsDy(MoO4)2
Authors: Anders A. I. , Bondarenko V. S. , Bordovsky S. B. , Feger A. , Orendacheva A.
Published: July 2002

The energy of the ordered state of the rare-earth subsystem of CsDy(MoO4)2 is calculated in the pure dipole approximation, and the magnetic configuration corresponding to the ground state is determined. The temperature dependence of the magnetic heat capacity is calculated in the temperature range T>TN, and a good agreement with the experiment is observed.
Resistive studies of creep controlled by plastic deformation of a vortex lattice
Authors: Obolenskii M. A. , Bondarenko A. V. , Shklovskii V. A. , Vovk R. V. , Prodan A. A.
Published: July 2002

Current–voltage characteristics (IVC) are measured for YBaCuO single crystals in a magnetic field applied at 45° to twinning planes. The current- and field dependences of the pinning potential are derived from the IVC curves. The obtained dependences indicate that the flux creep in the range of relatively strong magnetic fields is controlled by the plastic deformation of the vortex lattice.
Helicons and magnetoimpurity waves in layered conductors
Authors: Gvozdikov V. M. , Ermolaev A. M. , Vega-Monroy R.
Published: July 2002

It is shown that local electron states, caused by impurities in a layered conductor placed in an external magnetic field, give rise to resonant corrections δσαβ(ω) to the high-frequency conductivity tensor δσαβ(ω) of the layers. These corrections appear due to the resonant transitions of electrons between the Landau levels and the local states and change dramatically the spectrum of collective electromagnetic oscillations in the system because of the “branch crossing” nearby the frequency ω0 (ℏω0 is the local state energy). As a result, a new magnetoimpurity wave, ω−(k), appears in the spectrum in addition to the helicon mode, ω+(k), which is known to exist in a pure layered conductor in a perpendicular magnetic field (k is the wave vector along the magnetic field). In the long wavelength limit, ka≪1, the helicon-like mode ω+(k) has a gap of the order of ω0, whereas the magnetoimpurity mode in this limit goes to zero ω−(k)∼(ka)2 (a is the distance between adjacent layers). The small damping of these modes due to the broadening of the Landau levels and the magnetoimpurity levels are also calculated.
De Haas–van Alphen oscillation in both the normal and superconducting mixed states of NbSe2, CeRu2, URu2Si2, and UPd2Al3 (Review Article)
Authors: Inada Y. , Ōnuki Y.
Published: July 2002

The de Haas–van Alphen (dHvA) oscillation was observed clearly in both the normal and superconducting mixed states in NbSe2, CeRu2, URu2Si2, and UPd2Al3. The dHvA frequency, which is proportional to the extremal cross-sectional area of the Fermi surface, does not change in magnitude between the normal and mixed states. For the f-electron superconductors, the cyclotron effective mass is found to be reduced and the corresponding Dingle temperature or scattering rate of the conduction electron increases in the mixed state. An anisotropic energy gap with a line node for URu2Si2 and UPd2Al3 is discussed from the angular dependence of the dHvA amplitude in the mixed state.
Low-temperature magnetic properties and stress effects in glassy Fe-B alloys: the eutectic region
Authors: Beznosov A. B. , Fertman E. L. , Eremenko V. V. , Desnenko V. A. , Bengus V. Z.
Published: July 2002

The magnetic properties of glassy Fe100−xBx (x=14,16,17,20) alloys under a low mechanical stress (up to 68 MPa) at temperatures 10–300 K, in magnetic fields up to 40 Oe, have been studied. Low temperature anomalies of magnetic susceptibility, as well as substantial differences in the effects of stresses on the low field magnetic characteristics of alloys with various boron contents, have been revealed. The eutectic alloy Fe83B17 was found to be the least sensitive to applied stresses, magnetic fields, and temperature changes: it possesses the lowest magnetic induction in the reversibility fields region and the highest local anisotropy fluctuations. The hypoeutectic Fe84B16 alloy is the most sensitive to applied stresses at room temperature, but its sensitivity substantially reduces with increasing load, as well as with decreasing temperature. The results obtained reflect the special character of the alloys electronic structure at the eutectic point.
Low-temperature softening of β-tin single crystals on doping with substitutional impurities
Authors: Soldatov V. P. , Natsik V. D. , Diulin A. N. , Kirichenko G. I.
Published: July 2002

The yield stresses of single crystals of solid solutions of β-tin with substitutional impurities of indium, cadmium, and zinc are measured over a wide interval of low temperatures (1.6–150 K). The low-temperature impurity softening effect is observed, which is manifested in a decrease in the yield stresses of the alloys in comparison with that of pure tin. The temperature and concentration boundaries of the existence region of this effect are established, and the dependence on the combined size and modulus misfit parameter between the atoms of tin and the impurities, which characterizes the strength of the impurity barriers for the motion of dislocations in the alloy, is determined. Analysis of the data obtained indicates a qualitative agreement of the observed regularities of the impurity softening effect and the behavior that follows from the model of Sato and Meshii, which takes into account the role of impurity atoms both as centers of nucleation of kinks on screw dislocations and as centers of opposition to the lateral dispersal of the kinks along the dislocation line.
Thermodynamics of an atomic monolayer with diatomic substitutional impurities
Authors: Poltavskaya M. I. , Chishko K. A.
Published: July 2002

The low-temperature thermodynamics of a two-dimensional monatomic crystalline matrix containing a diatomic molecular impurity is investigated theoretically. Typical examples of this type of system are monatomic layers of rare gases (Ne, Ar, Kr, Xe) with included molecules of the type N2 and O2. Another example is a hydrogen film, which is a mixture of ortho and para components. Expressions are obtained which describe the crystalline field for a diatomic impurity with allowance for both the contribution of the atoms of the 2D matrix and the field created by the atoms of the substrate. Thus the effective crystalline field is a complicated function of the orientation of the diatomic rotator. In particular, the equilibrium orientation of the rotator depends substantially on the relative amplitudes of the crystalline fields of the matrix and substrate. For example, if the attraction exerted by the substrate is dominant, then the rotator in the equilibrium state will be oriented perpendicular to the layer, and in the opposite case the equilibrium orientation of the rotator will correspond to one of its positions in the plane of the layer. In these two cases the spectra of rotational states of the diatomic impurities and, hence, the thermodynamic characteristics of the system are substantially different. The temperature dependence of the impurity specific heat of the system exhibits a low-temperature peak, the position of which corresponds to temperatures T∼B/2 (B is the rotational constant of the impurity) for rotators lying in the plane of the layer, and T∼KB (K is the amplitude of the crystalline field) for rotators perpendicular to the layer. Such behavior of the system is in principle amenable to experimental observation.
Direct and large-eddy simulations of three-dimensional compressible Navier–Stokes turbulence
Authors: Zang T. A. , Dahlburg R. B. , Dahlburg J. P.
Published: July 2002

This paper reports results from the numerical implementation and testing of the compressible large-eddy simulation (LES) model described by Speziale et al. [Phys. Fluids 31, 940 (1988)] and Erlebacher et al. (to appear in J. Fluid Mech.). Relevant quantities from 323 ‘‘coarse grid’’ LES solutions are compared with results generated from 963 direct numerical simulations (DNS) of three-dimensional compressible turbulence. It is found that the 323 LES results overall agree well with their 963 DNS counterparts. Moreover, the new DNS results confirm several recent conclusions about compressible turbulence that have been based primarily on two-dimensional simulations.
Upstream-advancing nonlinear waves excited in an axisymmetric transcritical flow of rotating fluid
Authors: Hanazaki Hideshi
Published: July 2002

A numerical study of the inertial waves in an axisymmetric transcritical flow of rotating fluid passing through a long circular tube is described. The waves are excited either by an obstacle on the axis of the tube or by a local undulation of the tube wall. In all the calculations, the flow has a circulation of the Burgers-vortex type. The solutions of the Navier–Stokes equations are compared with the solutions of the forced KdV (Korteweg–de Vries) equation and it is found that the waves that appear in the solutions of the Navier–Stokes equations are described, at least qualitatively, by the solutions of the forced KdV equation. In this study, the forced KdV equation that has also a cubic nonlinear term is derived. However, the effect of the cubic nonlinearity is found to be small, at least for the upstream circulation distribution used in this study.
Temporally and spatially pulsating solitons in a nonlinear stage of the long-wave Buneman instability
Authors: Kono Mitsuo , Kawakita Masahiro
Published: July 2002

A nonlinear equation describing the development of the Buneman instability has been derived and solved with the aid of Hirota’s bilinear transform [J. Math. Phys. 14, 810 (1973)] to give a variety of stationary solutions, such as pulsating solitons, temporally localized and spatially periodic solutions, as well as ordinary solitons.
Frequency and angular distribution of electron cyclotron emission at high temperatures (100–500 keV)
Authors: Bornatici M. , Ruffina U. , Spada M.
Published: July 2002

The distribution of the electron cyclotron emission with respect to both the frequency and the viewing angle is analyzed for a loss-cone as well as an anti-loss-cone electron distribution function at temperatures between 100 and 500 keV. The accuracy of two approximate formulas for the continuous part of the emission spectrum is investigated by comparison with exact numerical values.
Finite bandwidth drive effect on the parametric decay instability near the lower hybrid frequency
Authors: Harper-Slaboszewicz V. J. , Mizuno K. , Idehara T. , De Groot J. S.
Published: July 2002

The effect of a finite bandwidth driver on hot electron production near the lower hybrid frequency is studied experimentally. The heating rate slowly decreases and the threshold for hot electron production slowly increases with the increasing driver bandwidth.
The effect of background temperature on the synchrotron maser process
Authors: Yoon Peter H.
Published: July 2002

The amplification process of a high-frequency transverse electromagnetic wave in a plasma by relativistic electrons whose momentum distribution function has an inverted population or a peak in the momentum pitch angle is known as the synchrotron maser process. In this paper, the effect of a finite temperature of the background plasma that supports the electromagnetic wave is incorporated in the analysis of the synchrotron maser mechanism. The analysis shows that the finite background temperature significantly enhances the amplification rate of the synchrotron maser process.
Natural elongation and triangularity of tokamak equilibria
Authors: Hakkarainen S. P. , Betti R. , Freidberg J. P. , Gormley R.
Published: July 2002

Quasianalytic formulas are calculated for the elongation κ and triangularity δ of the plasma surface of a free-boundary tokamak equilibrium. The final results give κ and δ as functions of five quantities: the inverse aspect ratio ε, the poloidal beta βp, the internal inductance li, and the quadrupole and hexapole moments of the externally applied field. The agreement with numerically computed equilibria is found to be quite good when A≥3, κ≤1.5, and δ≤0.2 and when the plasma is limited by the vacuum vessel wall and not diverted by the presence of a separatrix on the plasma surface.
Stability and compressional heating of large field-reversed configurations in the FRX-C/LSM device
Authors: Tuszewski M. , Barnes D. C. , Rej D. J. , Taggart D. P.
Published: July 2002

Recent data from the FRX-C/LSM device [Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1989), Vol. II, p. 517] concerning the stability, translation, and compression heating of field-reversed configurations (FRC’s) are reported. FRC tilt instabilities are clearly observed for the first time, a major step toward reconciling theory and experiments. Grossly stable FRC’s appear to be restricted to very kinetic and elongated plasmas. Internal probing of translated FRC’s reveals substantial toroidal field and nearly force-free magnetic field profiles in the central region of the compact toroid. High-power magnetic compression of translated FRC’s is demonstrated. Substantial heating is observed, while the FRC confinement properties remain mostly unchanged.
Kinetic stabilization of interchange modes in an axisymmetric mirror by large orbit radius thermal ions
Authors: Krall J. , Seyler C. E. , Sudan R. N.
Published: July 2002

A dispersion functional analysis that includes the full kinetic effects of large Larmor radius thermal ions is applied to the problem of stability of an axisymmetric mirror to finite azimuthal mode number (m) interchange modes. Vlasov theory is used to describe the ions, which are imbedded in a background of fluid electrons. The dispersion functional is solved numerically, both for a trial function displacement, where only the growth rate is determined, and the general case, where both the displacement and the growth rate are determined. In the trial function case, it is found that finite Larmor radius (FLR) effects are recovered, with a significant reduction in the growth rate when (ρi/L)2≳γMHD/Ωi. In a general case, the growth rate is reduced, but not so strongly as in the trial function case. It is shown heuristically that FLR effects may be recovered from the analysis and that these effects increase with the phase-space decorrelation time of the thermal ion distribution.
Total and partial radiative power loss at high impurity recycling studied in the Extrap-T1 reversed-field pinch experiment
Authors: Zastrow Klaus-Dieter , Brzozowski Jerzy H.
Published: July 2002

Measurements of the radiative power loss are performed on the Extrap-T1 reversed-field pinch [Phys. Scr. 44, 358 (1991)] using an absolutely calibrated vacuum ultraviolet spectrometer in the wavelength range between 100 and 1700 Å. The contributions to the radiative power loss from deuterium, carbon, nitrogen, oxygen, and chlorine are measured. These partial radiative power losses are further divided into contributions from different ionization stages of these impurities. The additional contribution to the cooling rate due to ionization processes is estimated. Impurities are found to be a main contributor to the power loss in the initial phase of the discharge. Toward the end of the discharge, radiative power loss amounts to less than 10% of the input power, due to the decrease of the electron density. Because of the short particle confinement time and high recycling of impurities, specifically oxygen, the rate coefficient for radiative power loss per ion is only slightly reduced by the increase of the temperature beyond the temperature of maximum radiative power loss per ion.
On the control of the m=2 rotational instability in a high-field theta pinch
Authors: Campos D. O. , Kunze H.-J.
Published: July 2002

Investigations on the stabilization of the m=2 rotational instability in a high-field theta pinch with a normalized separatrix radius of χs=0.14 are reported. With multipole fields lower than a theoretical threshold by factors of 2.5 and 2.1 no stabilization was observed in contrast to successful stabilization of low-field configurations with χs=0.4–0.6 reported in the literature.
Nonlinear diffusive interpenetration of a plasma and a magnetic field
Authors: Levin Jacob , Meerson Baruch
Published: July 2002

Nonlinear diffusive interpenetration of a finite-β plasma and a magnetic field is considered in the framework of the one-fluid magnetohydrodynamics (MHD) in the slab geometry. If the characteristic interpenetration time is much longer than the magnetoacoustic time, the process proceeds under the force equilibrium. Then the problem can be reduced to a single second-order nonlinear diffusion equation in the Lagrangian coordinates. Two examples of the interpenetration are considered. The first presents the diffusion of a plasma into a plasma in a perpendicular magnetic field. The problem proves to be self-similar, and its solution is found. The second one concerns the diffusive expansion of an initially confined plasma slab across a perpendicular magnetic field. The problem is solved numerically and the results are compared with an asymptotic self-similar solution, found earlier in the low-β limit.
Space charge disruption of an intense ion beam and its suppression by a fully ionized plasma during the formation of a rotating ion beam
Authors: Nakagawa Yoshiro
Published: July 2002

The space charge disruption of an intense ion beam has been observed and studied in detail by injecting an intense annular ion beam into a half-cusp magnetic field in vacuum. Subsequently, a rotating intense ion beam was formed without space charge disruption by injecting the annular ion beam (∼70 keV, 5 kA, 400 nsec, radius; R=10 cm, ni≂5×1011/cc) into a half-cusp magnetic field in which space charge neutralization was obtained by a fully ionized plasma (ne≂5×1013/cc) produced by a plasma source of large caliber (220 mm diameter). The induced net current in the plasma was found to arise from the rotating ion beam itself.
Numerical simulation of the thermal turbulent mixing layer
Authors: MacInnes J. M.
Published: July 2002

Inappropriate initial conditions discovered in a recently reported model calculation of the thermal mixing layer are corrected. Good agreement with measurement is restored by a reoptimization of model coefficients.
Modified drag theory of permeability
Authors: Wilkinson David
Published: July 2002

A modified version of the drag theory of permeability for a granular porous medium is presented. The technique employs the Brinkman equation to interpolate between the microscopic (Stokes) equation and the macroscopic (Darcy) equation, but differs from previous treatments in that the medium is built up iteratively beginning with the smallest grains. A discussion of the geometry corresponding to this construction is presented. The result for the permeability takes the form of a nonlinear differential equation which may be integrated numerically for a given choice of porosity and grain size distribution. Numerical results for the case of spherical grains with a log-normal distribution of sizes are presented, and compared to the predictions of the Kozeny equation for the same geometry. It is found that for narrow distributions the present method gives a somewhat higher permeability than the Kozeny equation, but that for wide distributions it gives a lower permeability. It is shown that in the limits of narrow or wide distribution the differential equation for the permeability may be solved explicitly, and it is suggested that in the latter case the result may be exact.
Oscillations of a compound drop system undergoing rotation
Authors: Lyell M. J. , Wang T. G.
Published: July 2002

A compound liquid drop system is comprised of three immiscible concentric fluids: a core fluid of density ρ(i) surrounded by a shell of density ρ(s) which is embedded in a medium of density ρ(0). In this analysis, the fluids are incompressible and inviscid. The effect of rotation upon the modes of oscillation of a compound drop is investigated. Rotation rate is considered as a small perturbation of the normal modes of the compound drop, thus introducing the effects of a Coriolis force and a centrifugal distortion.
Instabilities excited by an energetic ion beam and electron temperature anisotropy in tandem mirrors
Authors: da Jornada E. H. , Gaffey J. D. , Winske D.
Published: July 2002

The theory of cross-field ion streaming instabilities is applied to the parameter regime of the end cells of the upgraded Tandem Mirror Experiment with neutral beam injection. The cross-field ion drift as well as the electron thermal anisotropy Te⊥>Te∥ provides the free-energy that drives various instabilities. Three instabilities, a nearly perpendicular propagating modified two-stream instability, an obliquely propagating ion–ion streaming instability, and an obliquely propagating electromagnetic lower-hybrid instability, have been identified. The first two waves are electrostatic and have the largest growth rate. For the actual operation conditions of the tandem mirror machines, it is found that the ion–ion streaming instability has the largest growth rate. When more energetic neutral beams become available, the two-stream instability may play the dominant role in the stability of these devices.
Diffusivities of transferable quantities in turbulent flow with mean velocity distribution
Authors: Yuu Shinichi
Published: July 2002

The relation between turbulent diffusivities for transferable quantities and the Lagrangian displacement of fluid particles in a flow field with a mean velocity distribution is derived on the assumption of a gradient transport. The turbulent diffusivities in a plane jet and in two interacting plane parallel jets are calculated by using Lagrangian trajectories that have been computed based on a simple model. The results indicate that the mean velocity distribution affects the turbulent transport, and that neglect of this factor can give a fivefold overestimation of the diffusivity in interacting jets.
Neutral particle density transients in gaseous discharges
Authors: Metze A. , Ernie D. W. , Oskam H. J. , Chanin L. M.
Published: July 2002

A model is presented which describes the neutral density transients in gaseous discharges. It is shown that the duration of the initial density transient is governed by the speed of sound in the gas in which the discharge is produced. The development of the gas-flow velocity pattern in the discharge tube is a consequence of the interplay between three competing volume forces: (a) the driving volume force, which is generated by the interaction of the charged particles with the neutral particles, (b) the viscosity force, and (c) the neutral pressure gradient force. The influence of the geometry of the discharge tube on the neutral particle density transients is also discussed. The initial neutral particle density transient is believed to be the origin of acoustic resonances observed in rf-excited gaseous discharges.
Vortex pair annihilation in Taylor wavy-vortex flow
Authors: Crawford Gerald L. , Park Kwangjai , Donnelly Russell J.
Published: July 2002

We have made precision measurements of the vortex pair size and wavy mode amplitude of vortices in wavy Taylor–Couette vortex flow. These results are compared to a model advanced by Park and Crawford to account for expulsion of vortex pairs as the Reynolds number is increased in the wavy-vortex regime.
Physical mechanisms for hot-electron stabilization of low-frequency interchange modes
Authors: Sanuki Heiji , Chen Francis F.
Published: July 2002

The stabilization of low-frequency background and hot-electron interchange modes is studied by using a relatively simple multi-fluid model. Physical pictures for the stabilization mechanisms such as the ‘‘charge-uncovering’’ effect are given and compared with the stabilization of interchange modes by the finite Larmor radius (FLR) effect.
Temperature (Tonks–Dattner) resonances theoretically revisited: New temperature and density diagnostics
Authors: Gaigneaux M. , Vandenplas P. E.
Published: July 2002

A theoretical revision, motivated by experiments performed in a wide range of frequencies (0.4 GHz<f<4 GHz), leads to the accurate prediction in a greatly extended domain of the densities at which temperature (Tonks–Dattner) resonances occur in a plasma column. It is shown that a two-fluid scalar perturbed pressure plasma description using the radial density profile determined from positive column plasma discharge theory perfectly explains the experiments at low densities, a domain within which Parker, Nickel, and Gould [Phys. Rev. Lett. 11, 183 (1963); Phys. Fluids 7, 1489 (1964)] have computed the corresponding theoretical curves for the first two resonances. Introducing new dimensionless parameters, a new representation of these curves is developed, which results in a general linear law permitting a direct comparison with experimental results over a much wider density domain than was previously the case. Moreover this new law permits the direct measurement of the electron temperature and of the average density independently of each other using the plot of a single resonance.
Particle-in-cell simulations of azimuthal instabilities in relativistic electron layers
Authors: Gisler Galen R.
Published: July 2002

Negative-mass and cyclotron-maser instabilities in electron rings or layers lead to breaking of the azimuthal symmetry. The short-wavelength modes are generally thought to be harmless since they saturate by increasing the thickness and energy spread of the original layer. The long-wavelength (or low-order) modes, on the other hand, can be devastating to the integrity of the layer. Linear theory has predicted that the growth rates for negative-mass instability modes are proportional to the azimuthal mode number, so that the low-order modes would not be important until quite late in time. In contrast, the simulations presented here show that low-order modes can arise quite early in time, out of nonlinear states of the high-order modes. At low currents, azimuthal instabilities can be effectively suppressed (as predicted by linear theory) by starting out with a thicker layer, with the particle energy varying with radius. The dispersion in circulation frequency so introduced effectively damps all growing waves. Unfortunately, at high currents (field reversal factors ζ≳2%), making the layer thicker does not help. All growth rates are faster at the higher densities, and the high mode numbers grow to substantial amplitudes before damping is effective. Beating of nearby high-order modes gives rise to global modes that destroy the layer within a few rotations.
The stability of a planar layer of insulating liquid subjected to charge injection and rotation
Authors: Oliveri S. , Atten P. , Castellanos A.
Published: July 2002

The problem of the hydrodynamic stability of a plane dielectric liquid layer subjected to unipolar injection and rotation examined here is in many ways analogous to that of rotating horizontal fluid layer heated from below. In both situations instability is likely to arise as steady or oscillatory convection depending on the values of only two parameters. The critical conditions for which instability sets in as a steady convection are determined as functions of both the Taylor number and the level of injection. Because of the mathematical complexity of the problem, the onset of convection as overstability is determined only for the particular case of weak injection. In this case, an analytical treatment is carried out that allows discrimination of regions of steady and oscillatory convective instability.