bluuebunny/crossref_metadata_2025 huggingface dataset:
Quaternion symmetry in relativistic molecular calculations: The Dirac–Hartree–Fock method
Authors: Saue T. , Jensen H. J. Aa
Published: July 2002

A symmetry scheme based on the irreducible corepresentations of the full symmetry group of a molecular system is presented for use in relativistic calculations. Consideration of time-reversal symmetry leads to a reformulation of the Dirac–Hartree–Fock equations in terms of quaternion algebra. Further symmetry reductions due to molecular point group symmetry are then manifested by a descent to complex or real algebra. Spatial symmetry will be restricted to D2h and subgroups, and it will be demonstrated that the Frobenius–Schur test can be used to characterize these groups as a whole. The resulting symmetry scheme automatically provides maximum point group and time-reversal symmetry reduction of the computational effort, also when the Fock matrix is constructed in a scalar basis, that is, from the same type of electron repulsion integrals over symmetry-adapted scalar basis functions as in nonrelativistic theory. An illustrative numerical example is given showing symmetry reductions comparable to the nonrelativistic case.
Rovibrational Hamiltonians for general polyatomic molecules in spherical polar parametrization. I. Orthogonal representations
Authors: Mladenović Mirjana
Published: July 2002

The interdependence of the description of the internal geometry and the corresponding kinetic energy operator T̂ is investigated in detail for a general n-atomic molecule. For both space-fixed and body-fixed reference frames compact expressions of T̂ are derived which are applicable to any set of n−1 translationally and rotationally invariant internal vectors in a spherical polar parametrization. Simple analytical forms are given for reduced masses and kinetic coupling constants, which are the only vector specific parameters in the final rovibrational kinetic energy expression. The kinetic energy assumes the most separable form for an entirely orthogonal set of internal vectors. A highly efficient computer program for the calculation of rovibrational spectra of tetratomic molecules has been developed on the basis of this formulation. Calculations on the HF dimer and the metastable molecule HOCO illustrate the accuracy and flexibility of this approach.
Ab initio potential-energy surface for the He(S1)+NO(X2 Π) interaction and bound rovibrational states
Authors: Kl/os Jacek , Chal/asiński Grzegorz , Berry Mary T. , Bukowski Robert , Cybulski Sl/awomir M.
Published: July 2002

Adiabatic potential-energy surfaces for the A′2 and A″2 states of the He(1S)–NO(X 2Π) complex have been calculated at the restricted coupled cluster level of theory including single, double, and noniterated triple excitations [RCCSD(T)]. The potential-energy surface (PES) of the A′ state has three minima: for the T-shaped geometry, barely skewed toward oxygen (R=6.07 a0, Θ=96.7°, and De≈29.2 cm−1), and for two collinear forms. In contrast, PES of the A″ state has two minima, both related to T-shaped forms: (i) A global minimum, with He shifted toward nitrogen (R=6.27 a0, Θ=76.1°, and De≈25.3 cm−1), and a shoulderlike minimum, with He shifted toward oxygen (R=6.34 a0, Θ=117.6°, and De≈24.5 cm−1). The collinear forms of the A″ state correspond to saddle points. The A′ surface lies above the A″ surface, except in the vicinity of perpendicular arrangement. The interaction energies have been analyzed via perturbation theory of intermolecular forces. The shape and location of the minima is determined primarily by the anisotropy of the exchange component, and stronger repulsion of A′ is due to repulsion between the singly occupied anti-bonding π* orbital and He. A variational calculation of the bound rovibrational states supported by the potential suggests that the HeNO complex is bound by about 7 cm−1. The bound levels correlate with NO rotational levels with j=1/2 and j=3/2, and are well described as nearly free-rotor states in which j (NO rotation) and L (end-over-end rotation of R) are nearly good quantum numbers. Excited intermolecular stretching vibrations are not predicted to be bound.
A study of the relative importance of one and two-electron contributions to spin–orbit coupling
Authors: Fedorov Dmitri G. , Gordon Mark S.
Published: July 2002

The existing methods to estimate the magnitude of spin–orbit coupling for arbitrary molecules and multiconfigurational wave functions are reviewed. The form-factor method is extended from the original singlet–triplet formulation into arbitrary multiplicities. A simplified version of the mean-field method (the partial two-electron method, P2E) is formulated and tested versus the full two-electron operator on a set of representative molecules. The change of the one and two-electron spin–orbit coupling down the Periodic Table is investigated, and it is shown that the computationally much less demanding P2E method has an accuracy comparable to that of the full two-electron method.
Divergence in Møller–Plesset theory: A simple explanation based on a two-state model
Authors: Olsen Jeppe , Jørgensen Poul , Helgaker Trygve , Christiansen Ove
Published: July 2002

The convergence of the Møller–Plesset expansion is examined for Ne, F−, CH2, and HF and analyzed by means of a simple two-state model. For all systems, increasing diffuseness of the basis introduces highly excited diffuse back-door intruder states, resulting in an an alternating, ultimately divergent expansion. For F−, the divergence begins already at third order; for the remaining systems, it begins later. For CH2, the low-lying doubly excited state leads to a monotonic, slowly decreasing series at lower orders; for the stretched HF molecule, the low-lying doubly excited states lead to a slowly undulating series at lower orders. Although the divergence of the Møller–Plesset series does not invalidate the use of the second-order expansion, it questions the use of higher-order Møller–Plesset expansions in quantum-chemical studies.
Variational processes and stochastic versions of mechanics
Authors: Zambrini J. C.
Published: July 2002

The dynamical structure of any reasonable stochastic version of classical mechanics is investigated, including the version created by Nelson [E. Nelson, Quantum Fluctuations (Princeton U.P., Princeton, NJ, 1985); Phys. Rev. 150, 1079 (1966)] for the description of quantum phenomena. Two different theories result from this common structure. One of them is the imaginary time version of Nelson’s theory, whose existence was unknown, and yields a radically new probabilistic interpretation of the heat equation. The existence and uniqueness of all the involved stochastic processes is shown under conditions suggested by the variational approach of Yasue [K. Yasue, J. Math. Phys. 22, 1010 (1981)].
On the motion of the first Lee–Yang zero
Authors: Tasaki Hal
Published: July 2002

In the d-dimensional ferromagnetic Ising and φ4 systems, the motion of the first Lee–Yang zero when the lattice size tends to infinity is studied. In particular, a power law behavior at the critical point, which is distinct from those in noncritical points, is elucidated.
Continuous Hahn polynomials and the Heisenberg algebra
Authors: Bender Carl M. , Mead Lawrence R. , Pinsky Stephen S.
Published: July 2002

Continuous Hahn polynomials have surfaced in a number of somewhat obscure physical applications. For example, they have emerged in the description of two-photon processes in hydrogen, hard-hexagon statistical mechanical models, and Clebsch–Gordan expansions for unitary representations of the Lorentz group SO(3,1). In this paper it is shown that there is a simple and elegant way to construct these polynomials using the Heisenberg algebra.
On Woltjer’s variational principle for force-free fields
Authors: Laurence Peter , Avellaneda Marco
Published: July 2002

The existence of minimizers for Woltjer’s variational principle is established and that the minimizers are force-free fields. This method has the nature of a constructive implicit function theorem and handles successfully the nonconvex constraint of constant total helicity. Domains of arbitrary connectivity are allowed as well as nonhomogeneous boundary conditions and periods.
Examples of braided groups and braided matrices
Authors: Majid Shahn
Published: July 2002

Matrix braided groups are developed as an analog of the ‘‘coordinate functions’’ on a group or supergroup. The ±1 in the super case is replaced by braid statistics. There are braided group analogs of all the classical simple Lie groups as well as braided matrix groups and braided matrices B(R) for every regular solution R of the quantum Yang–Baxter equations. A direct verification of B(R) is provided and some of the simplest examples are computed in detail.
Cosmic vacuum strings and domain walls in Brans–Dicke theory of gravity
Authors: Barros A. , Romero C.
Published: July 2002

The gravitational field of cosmic vacuum strings and domain walls in the context of Brans–Dicke theory of gravity are investigated. Using the weak field approximation, the solutions which describe the space–time and the scalar field generated by these topological structures are found, the results are compared with the ones obtained in General Relativity.
Interchannel resonances at a threshold
Authors: Baumgartner B.
Published: July 2002

Fermi’s Golden Rule, the perturbation theoretic formula for calculating the half-width of a resonance, is not applicable to the case of a transition from a bound state into an open channel, when the energy of the bound state is exactly at the threshold of the continuum. We study solvable models of this phenomenon. The exact results coincide in leading order with the formulas found by modifying Fermi’s Golden Rule.
Wavelet analysis of signals with gaps
Authors: Frick Peter , Grossmann Alex , Tchamitchian Philippe
Published: July 2002

A recently introduced algorithm [Frick et al., Astrophys. J. 483, 426 (1997)] of spectral analysis of data with gaps via a modified continuous wavelet transform is developed and studied. This algorithm is based on a family of functions called "gapped wavelets" which fulfill the admissibility condition on the gapped support. The wavelet family is characterized by an additional parameter which should be calculated for every scale and position. Three theorems concerning the properties of gapped wavelet transform are formulated and proved. They affirm the global stability of the algorithm as well as its stability in both limits of large and small scales. These results are illustrated by some numerical examples, which show that the algorithm really attenuates the artifacts coming from gaps (and/or boundaries), and is particularly efficient at small and large scales.
Wick’s theorem for nonsymmetric normal ordered products and contractions
Authors: Evans T. S. , Kibble T. W. B. , Steer D. A.
Published: July 2002

We consider arbitrary splits of field operators into two parts; ψ=ψ++ψ−, and use the corresponding definition of normal ordering introduced earlier [T. S. Evans and D. A. Steer, Nucl. Phys. B 474, 481 (1996)]. In this case the normal ordered products and contractions have none of the special symmetry properties assumed in existing proofs of Wick’s theorem. Despite this, we prove that Wick’s theorem still holds in its usual form as long as the contraction is a c-number. Wick’s theorem is thus shown to be much more general than existing derivations suggest, and we discuss possible simplifying applications of this result.
Bethe ansatz solution of a closed spin 1 XXZ Heisenberg chain with quantum algebra symmetry
Authors: Links Jon , Foerster Angela , Karowski Michael
Published: July 2002

A quantum algebra invariant integrable closed spin 1 chain is introduced and analyzed in detail. The Bethe ansatz equations as well as the energy eigenvalues of the model are obtained. The highest weight property of the Bethe vectors with respect to Uq(sl(2)) is proved.
Phase transitions on nonamenable graphs
Authors: Lyons Russell
Published: July 2002

We survey known results about phase transitions in various models of statistical physics when the underlying space is a nonamenable graph. Most attention is devoted to transitive graphs and trees.
Surface and quasi-surface phonons and transformation waves in a hexagonal crystal
Authors: Kosevich A. M. , Savotchenko S. E. , Matsokin D. V.
Published: July 2002

A simple model of the dynamics of a layered crystal having a hexagonal lattice with weak interaction of atoms in neighboring basal planes is formulated. Vibrations propagating in the basal plane with displacement vectors lying in the same plane are investigated. Energy–momentum relations are obtained for low-frequency (Rayleigh type) as well as high-frequency (gap-mode) vibrations localized at the free surface. The region of existence of quasi-surface phonons, whose boundaries are determined to a considerable extent by the shape of constant-frequency surfaces for two branches of bulk vibrations is determined. It is shown that peculiarities in the interaction of elastic waves with the crystal surface appear in the bulk spectrum at certain frequencies. The dispersion curves for surface vibrations separated from the continuous spectrum have a continuation in this spectrum in the form of dependences corresponding to transformation of a transverse wave into a longitudinal one. The effect of a surface monolayer of impurity atom on localized and pseudolocalized vibrations is investigated.
Transport asymmetry in skewed turbulence
Authors: Wyngaard John C. , Weil Jeffrey C.
Published: July 2002

Large-eddy simulations have shown that passive, conservative scalars emitted into the convective boundary layer (CBL) of the atmosphere have unusual diffusion properties. A species introduced through an area source at the layer top and having zero flux through the bottom (i.e., one undergoing ‘‘top-down’’ diffusion) has a well-behaved eddy diffusivity, but one introduced at the bottom, with zero flux at the top (‘‘bottom-up’’ diffusion) has a much different diffusivity profile in the same turbulence field. It is suggested that the roots of this transport asymmetry lie in the interaction between skewness of the transporting turbulence and the gradient of the flux of the transported scalar. A kinematic model is used to show that this interaction can indeed induce transport asymmetry in small-time-scale, homogeneous turbulence. The present simulations with a Lagrangian particle model confirm that this asymmetry extends to large-time-scale, inhomogeneous turbulence. A heuristic model of convective turbulence suggests that its asymmetric transport is also described by the kinematic model but with the small-time-scale restriction removed. In all cases the transport asymmetry effects scale with the parameter SσwTL/h, where S, σw, and TL are the skewness, standard deviation, and Lagrangian integral time scale of the transporting turbulence, and h is the layer depth; a scalar flux gradient is required as well.
Effect of heat transfer on the subharmonic instability of compressible boundary layers
Authors: Masad J. A. , Nayfeh A. H.
Published: July 2002

The effect of heat transfer on the subharmonic instability of a two-dimensional compressible boundary layer over a flat plate is analyzed using the Floquet model. The resulting problem is solved numerically by using both finite differences and the computer code suport. Results are presented for different Mach numbers. For supersonic flows, results for the first and second modes are presented. The results for an adiabatic flat plate are in good agreement with the results of the numerical simulations of Thumm et al. [in Laminar-Turbulent Transition, edited by D. Arnal and R. Michel (Springer-Verlag, Berlin, 1990), p. 271; (private communication)]. When the wall temperature is decreased and the primary wave is a second-mode wave, it is found that the subharmonic instability is shifted to higher frequencies and downstream locations. When the primary wave is a first-mode wave, the effect of cooling might be stabilizing or destabilizing depending on the frequency. When the primary wave is a first mode, cooling stabilizes the subharmonic wave at low spanwise wave numbers and destabilizes it at higher spanwise wave numbers. When the primary wave is either a first- or a second-mode wave, the most amplified subharmonic mode shifts toward a higher spanwise wave number as the cooling level increases.
Diffusion and geometric effects in passive advection by random arrays of vortices
Authors: Avellaneda M. , Torquato S. , Kim I. C.
Published: July 2002

The Lagrangian transport of a passive scalar in a class of incompressible, random stationary velocity fields, termed ‘‘random-vortex’’ models, is studied. These fields generally consist of random distributions of finite-sized elementary vortices in space with zero mean velocity in the presence of molecular diffusion D. The effects of vortex density, vortex strength, and sign of the vorticity on the Lagrangian history of a fluid particle [i.e., mean-square displacement σ2(t) and velocity autocorrelation function ℛ(t)] on the specific random-vortex models which possess identical energy spectra but different higher-order statistics for a Péclet number of 100 are investigated. This is done by a combination of Monte Carlo simulations of the Langevin equations and analysis. It is found that the Lagrangian autocorrelation ℛ(t) and the mean-square displacement σ2(t) can be significantly different as the density of the vortices increases and when there are long-range correlations in the sign of the vorticity. A simple theory based on a model for ℛ(t) agrees strikingly well with the present simulations. It is found that D* increases with vortex density, suggesting that Gaussian fields are maximally dissipative among a wide class of vortex flows with given energy spectra.
Real gas effects on hypersonic boundary-layer stability
Authors: Malik M. R. , Anderson E. C.
Published: July 2002

High-temperature effects alter the physical and transport properties of a gas, air in particular, due to vibrational excitation and gas dissociation, and thus the chemical reactions have to be considered in order to compute the flow field. Linear stability of high-temperature boundary layers is investigated under the assumption of chemical equilibrium and this gas model is labeled here as ‘‘real gas model.’’ In this model, the system of stability equations remains of the same order as for the perfect gas and the effect of chemical reactions is introduced only through mean flow and gas property variations. Calculations are performed for Mach 10 and 15 boundary layers and the results indicate that real gas effects cause the first mode instability to stabilize while the second mode is made more unstable. It is also found that the second mode instability shifts to lower frequencies. There is a slight destabilizing influence of real gas on the Goertler instability as compared to the perfect gas results.
Wave propagation in the ion cyclotron range of frequencies through the turbulent edge
Authors: Thayer David R.
Published: July 2002

It is pointed out that the turbulent tokamak edge can significantly affect the transmission of a wave in the ion cyclotron range of frequencies during auxiliary heating at the resonant layer. Because of the large edge density fluctuations, it is necessary to consider an order unity expansion parameter for the general propagator theory of wave propagation. Consequently, a renormalized theory for the scattering process is developed and utilized to determine the backscattering (one dimensional) and spectral wavenumber spread (two dimensional) of incident energy.
Small Larmor radius limit for a warm relativistic electron fluid
Authors: Anile A. M. , Muscato O.
Published: July 2002

A fluid model is considered for a relativistic warm plasma, obtained with a closure approach that allows for a nonvanishing heat tensor. A small Larmor radius limit is assumed and a simplified magneto-fluid model that generalizes the relativistic Chew–Goldberg–Low model [Proc. R. Soc. London Ser. A 236, 112 (1956)] is obtained.
Electron beam transport in gas-loaded free-electron lasers
Authors: Yariv Shalom , Friedland Lazar
Published: July 2002

The effects of the presence of helical wiggler and axial guide magnetic fields on the quality of the electron beam in a gas-loaded free-electron laser are investigated. The electron velocity space diffusion theory in the free-electron laser is developed and tested in Monte Carlo simulations. The theory is applied in estimating the collisional limitations on the interaction length of the laser. It is shown that two competing effects related to collisions cause the gain loss in gas-loaded free-electron lasers, i.e., (a) the growing phase mismatch between the electrons and the wave and (b) the destruction of the coherent transverse helical beam motion. The second effect dominates in the absence of the guide field, provided the wiggler field strength is sufficiently small.
Toroidal semicollisional microinstabilities and anomalous electron and ion transport
Authors: Romanelli F. , Briguglio S.
Published: July 2002

The toroidal semicollisional microinstabilties driven by trapped electron dynamics and ion temperature gradients are analyzed using kinetic theory. Analytic dispersion relations are derived and discussed, with particular attention to the modeling of anomalous electron and ion thermal conductivity. Relations with previously derived models of anomalous transport and experimentally observed trends of the global energy confinement time are also discussed.
Temperature distribution of a tokamak with a constant heat conductivity
Authors: Yoshikawa S.
Published: July 2002

An analytical expression of the detached plasma radius in an Ohmically heated tokamak plasma was obtained. The assumption was made that the (anomalous) heat conductivity is constant and independent of minor radius r. The resultant nonlinear differential equation has a universal solution for the plasma temperature as a function of r. The shape is very similar to the so-called profile consistency model. As the average plasma density increases, the tokamak plasma, which is first attached to either the limiter or divertor, detaches itself from the limiter and forms a toroidal plasma whose boundary is clearly marked by a radiative boundary layer where the power input to the plasma is radiated away. As the plasma density increases, the radius of the plasma shrinks until the surface safety factor becomes less than ∼2, whereupon the plasma disruption starts. The density limit calculated by this model agrees with the experimental observation.
Root-mean-square emittance of multiple beam systems
Authors: Rhee M. J. , Boulais K. A.
Published: July 2002

A general expression for the rms emittance of a multiple beam system is unambiguously derived. The emittances for rectangular and circular arrays of identical beamlets are analyzed and expressed in terms of quantities associated with the beamlet distribution and the array geometry. A few examples relevant to actual experiments are included.
Fast wave damping on non-Maxwellian electrons
Authors: Moroz P. E. , Hershkowitz N. , Majeski R. P. , Tataronis J. A.
Published: July 2002

Theoretical studies of fast wave damping on electrons are presented. Different regimes of importance for fast wave plasma heating and current drive in tokamaks are considered. Various cases of Maxwellian and multi-Maxwellian, isotropic and anisotropic electron distribution functions are investigated. In all cases, fast wave damping on electrons is due to three terms: Landau damping, transit-time magnetic pumping (TTMP), and the cross-term effect. Expressions for all these terms are derived for all regimes considered. Although in most cases Landau damping, TTMP, and the cross-term effect are the same order of magnitude, regimes are found that can be referred to as the pure Landau damping regimes, or pure TTMP regimes. A key parameter that defines the character of fast wave damping is found: δα=ε2/γαεε3. In simplified form, and far from resonances, it can be written as δα≊−2ω2/ΩiΩeβα, where α specifies the appropriate regime.
The evolution of slightly nonideal, non-neutral plasma
Authors: Avinash K.
Published: July 2002

The evolution of cold and slightly nonideal, non-neutral plasma is discussed. It is argued that small deviations due to viscosity or inertia break the topological constraints associated with the streamlines of the E×B flow. The fluctuations then shuffle charges at the cost of electrostatic energy. As a result the energy decreases, keeping the helicity of the two-dimensional flow (equal to the total charge) constant. The final state is calculated in a rotating frame in terms of average properties of the initial state.
X-ray spectroscopy of high-energy density inertial confinement fusion plasmas
Authors: Keane C. J. , Hammel B. A. , Kania D. R. , Kilkenny J. D. , Lee R. W. , Osterheld A. L. , Suter L. J. , Mancini R. C. , Hooper C. F. , Delamater N. D.
Published: July 2002

Analysis is presented of K- and L-shell spectra obtained from Ar and Xe dopants seeded into the fuel region of plastic capsules indirectly imploded using the Nova laser. Stark broadening measurements of the n=3-1 lines in H- and He-like Ar (Ar Ly-β and He-β, respectively) are used to infer fuel electron density, while spatially averaged fuel electron temperature is deduced from the ratio of the intensities of these lines. Systematic variations in Ar spectral features are observed as a function of drive conditions. A spectral postprocessing code has been developed to simulate experimental spectra by taking into account spatial gradients and line transfer effects, and shows good agreement with experimental data. It is shown that correct modeling of the x-ray emission requires a proper treatment of the coupled radiative transfer and kinetics problem. Continuum lowering effects are shown not to affect diagnostic line ratios, within the confines of a simple model. A recently developed diagnostic based on fitting measured line profiles of Ar He-β and its associated dielectronic satellites to theory is shown to provide a simultaneous measure of electron temperature and electron density. L-shell Xe spectroscopy is under development as an electron temperature and electron-density diagnostic. Density and temperature sensitive ratios of spectral features each consisting of many lines have been identified. Observed Xe spectra from imploded cores show the same qualitative behavior with temperature, as predicted by model calculations of Xe emission spectra. Stark broadening of Ne-like Xe 4-2 lines appears viable as an electron density diagnostic for Ne∼1025 cm−3 and is under continuing investigation. (Based on the invited paper 8I3 at the 1992 APS/DPP annual meeting [Bull. Am. Phys. Soc. 37, 1553 (1992)].)
The near field of a fully turbulent circular jet
Authors: Hayakawa M. , Iida S. , Takezawa S.
Published: July 2002

The near-field measurement of fully turbulent jets discharged from a straight circular pipe indicates the presence of quasiperiodic velocity perturbations. The Strouhal number based on the predominant frequency falls in the range of the preferred mode for the jet with a potential core and has an asymptotic value of 0.38 in the high Reynolds number regime. Regular perturbations are not observed in the mixing region immediately downstream from the pipe exit.
Effect of intake flow on ambient turbulence
Authors: Uberoi Mahinder S. , Nishiyama Randall T.
Published: July 2002

A small streamlined axisymmetric intake is placed at various locations on the axis of a large axisymmetric turbulent jet. The ratio of the mean velocity in the intake to that of the ambient fluid is varied from zero to thirteen. The effective diameter d* of the intake is determined by its physical size and the range of influence of the intake flow on the ambient jet fluid. Intensities of the components of turbulent velocity are measured in the ambient fluid and in and around the intake. In most cases the intake faced the jet. The ambient turbulence may be idealized as three mutually orthogonal linear vortex filaments of circular cross section and diameter S which is indicative of the scale of energy containing eddies. The vortex filaments deform as the flow is drawn into the intake. In the case d*<S, only parts of vortex filaments of size d* enter the intake. The two effects are used to calculate the intensities of the components of turbulent velocity as a function of d*/S and ratios of mean velocity and density in the intake to their respective values in the ambient fluid. The results agree with experiments within wide ranges of the parameters.
Compact form for the relativistic ponderomotive Hamiltonian
Authors: Cary John R. , Newberger Barry S.
Published: July 2002

The infinite series of functions present in the ponderomotive Hamiltonian are explicitly summed using Newberger’s sum rule. The result is a compact and easily evaluated expression for the ponderomotive Hamiltonian. Application of the K-χ theorem yields the linear susceptibility of relativistic magnetized plasma in agreement with, but generalizing, the previous result of Weiss and Weitzner.
Modulational instabilities of upper-hybrid laser radiation in a strongly magnetized plasma
Authors: Salimullah Md. , Liu Y. G. , Haines M. G.
Published: July 2002

A theoretical investigation is made of the modulational and filamentation instabilities of laser radiation at the upper-hybrid frequency in the presence of the self-generated magnetic field of the order of a few megagauss in a laser-produced plasma. The nonlinear Vlasov equation is solved to obtain the low-frequency response of magnetized electrons in the plasma. The present theory is valid for short-wavelength perturbations and arbitrary values of the wavenumber. It is observed that the growth rates of the instabilities are very sensitive to the plasma parameters near the critical density layer. The growth rate of the modulational instability is always larger than that of the filamentation instability for the same power density of the incident laser radiation. It is further noticed that the modulational instability decreases slowly with the magnetic field, while the filamentation instability remains almost insensitive to the magnetic field.
Comment on ‘‘Bubbles rising in a tube and jets falling from a nozzle’’ [Phys. Fluids 2
7, 1090 (1984)]
Authors: Modi Vijay
Published: July 2002

In a recent paper, Vanden-Broeck computed the shape of a two-dimensional jet emerging from a vertical nozzle [Phys. Fluids 27, 1090 (1984)]. He showed that the slope of the free surface at the separation points is either horizontal or vertical. Here the local behavior of the flow in the neighborhood of the separation point is investigated. It is shown that an additional solution with a 120 degree angle is also possible.
The production of highly unidirectional lower-hybrid waves
Authors: McWilliams R. , Okubo M. , Platt R. C. , Sheehan D. P.
Published: July 2002

The development of a highly unidirectional lower-hybrid wave source would improve the electron current drive efficiency in tokamaks. Lower-hybrid waves launched from a phased wave array are shown to be reflected from a grid placed in a cold, low-density plasma. The antenna–grid combination results in highly unidirectional lower-hybrid waves.
Modeling two-dimensional large bubbles in a rectangular channel of finite width
Authors: Couët B. , Strumolo G. S. , Dukler A. E.
Published: July 2002

Using a Green’s function approach with a dipole formulation, it is possible to find the shape of a two-dimensional steady Taylor bubble satisfying Bernoulli’s equation. This is done for the case of bubbles rising in a vertical channel. Our inviscid treatment leads to an infinite set of shapes. Using experimental evidence, however, it is possible to obtain one shape and a comparison with experiments is presented. The potential bubble so chosen has the distinction that it is the only one in the family of potential curves with a circular nose. An integral mass and momentum balance analysis in the liquid region between the free surface and the walls is also conducted, which takes fluid viscosity into account. By requiring a match between the two techniques at the nose, a viscous bubble is obtained that agrees well with both the potential bubble and experiments.
Linear stability of obliquely propagating electromagnetic waves in magnetically insulated gaps
Authors: Chang C. L. , Ott E. , Antonsen T. M.
Published: July 2002

A linear stability analysis for obliquely propagating electromagnetic waves in a magnetically insulated planar anode–cathode gap is presented. Previously published work [Phys. Fluids 24, 1821 (1981)] considered propagation perpendicular and parallel to the insulating magnetic field. Here the effect of propagation at oblique angles to the insulating field is considered. In general, growth rates decrease monotonically when the propagation angle becomes more parallel to B, and this effect is more pronounced for shorter-wavelength waves for which analytic asymptotic results are obtained.
Applicability of the geometrical optics at the high electron cyclotron harmonics
Authors: Imre Kaya
Published: July 2002

Nearly perpendicular wave propagation across the Nth electron cyclotron harmonic layer in a weakly inhomogeneous plasma is investigated. It is shown that, when N>2, unlike the case for N≤2, the relativistic corrections and the mode conversion to Bernstein waves do not alter the current density to the lowest significant order in the expansion parameter, which is the ratio of the electron thermal speed to the speed of light. Thus, when N>2, the geometrical optics method should be applicable in this case, and hence at all angles of incidence.
Instability near the lower-hybrid frequency in an ion beam–plasma system
Authors: Idehara Toshitaka , Tomita Naoyoshi
Published: July 2002

An ion beam is generated by extracting ions from a dc discharge plasma and injecting them into a plasma produced independently of the beam source. Thus, an ion beam–plasma system is produced in which the beam parameters vary independently from those of the plasma. It is confirmed by using this system that a test wave becomes unstable near the lower-hybrid frequency  flh, and the unstable wave is observed only in the region where the beam is present.
Local and ballooning instabilities in configurations with a helical magnetic axis
Authors: Mond Michael
Published: July 2002

The stability of a sheared configuration with high beta is studied by investigating the normal modes of the linearized magnetohydrodynamic equations. First, a single ordinary differential equation is obtained that governs the behavior of modes that are localized around rational surfaces. In addition, the equation that describes the properties of ballooning modes is derived.
Convection in rotating binary mixtures. I. Thresholds
Authors: Bhattacharjee Jayanta K.
Published: July 2002

Onset of convection in rotating binary mixtures is considered with both idealized and realistic boundary conditions. Stationary and oscillatory convection are possible. The threshold Rayleigh numbers, critical wavenumbers, and frequency are determined analytically.
Alternative analysis of CO2-laser-produced plasma waves
Authors: Simon Albert , Short Robert W.
Published: July 2002

McIntosh et al. [Phys. Rev. Lett. 57, 337 (1986); Phys. Fluids 29, 3451 (1986)] have carried out experiments in which electron plasma waves produced in a gas jet target by a CO2-laser pulse were studied by picosecond-resolution Thomson scattering of a ruby-laser pulse. In addition, spectra of the scattered laser light and of the fast electrons were obtained. Their analysis of the data was based on the assumption that the plasma waves are created by the onset of the stimulated Raman scattering instability. This led to a number of difficulties in the interpretation of the data. It is shown here that an alternative model of the origin of these plasma waves [Phys. Rev. Lett. 53, 1912 (1984)], used previously in analyzing Raman data in several other experiments, removes all these difficulties and is in agreement with the data. In this model, the plasma waves are produced by pulses of fast electrons arising at the quarter-critical surface.
Parametric decay of a fast wave to two electromagnetic slow waves at half the pump frequency
Authors: Chiu S. C.
Published: July 2002

The parametric decay process of a fast wave at the ion-cyclotron range of frequencies (ICRF) into two electromagnetic slow (or ordinary) waves is considered. It is shown that in the dipole approximation of the pump wave, the decay process is possible at around half the frequency of the pump. Plasmas of interest that are susceptible to this decay process include deuterium–hydrogen (D–H), deuterium–helium 3 (D–He3), and deuterium–tritium (D–T) plasmas. It is shown that the growth rate may approach a few percent of the pump frequency at the edge, and may thus lead to edge electron heating.
Scaling and dissipation in the GOY shell model
Authors: Kadanoff Leo , Lohse Detlef , Wang Jane , Benzi Roberto
Published: July 2002

This is a paper about multifractal scaling and dissipation in a shell model of turbulence, called the Gledzer–Ohkitani–Yamada (GOY) model. This set of equations describes a one-dimensional cascade of energy towards higher wave vectors. When the model is chaotic, the high-wave-vector velocity is a product of roughly independent multipliers, one for each logarithmic momentum shell. The appropriate tool for studying the multifractal properties of this model is shown to be the energy flux on each shell rather than the velocity on each shell. Using this quantity, one can obtain better measurements of the deviations from Kolmogorov scaling (in the GOY dynamics) than were available up to now. These deviations are seen to depend upon the details of inertial-range structure of the model and hence are not universal. However, once the conserved quantities of the model are fixed to have the same scaling structure as energy and helicity, these deviations seem to depend only weakly upon the scale parameter of the model. The connection between multifractality in the velocity distribution and multifractality in the dissipation is analyzed. Arguments suggest that the connection is universal for models of this character, but the model has a different behavior from that of real turbulence. Also, the scaling behavior of time correlations of shell velocities, of the dissipation, and of Lyapunov indices are predicted. These scaling arguments can be carried over, with little change, to multifractal models of real turbulence.
Effects of inertia on the hydrodynamics near moving contact lines
Authors: Stoev K. , Ramé E. , Garoff S.
Published: July 2002

We investigate the effects of inertia on the hydrodynamics in the microscopic vicinity of moving contact lines. These hydrodynamics control the macroscopic shape and spreading of fluid bodies across solid surfaces. We perform experiments at low capillary number (Ca<0.1) and negligible (10−4) to moderate (Re∼1) Reynolds number. On a microscopic scale, inertia decreases the dynamic curvature of the free surface near the contact line compared to the case with Re=0 at the same Ca. On a macroscopic scale, inertia lowers the apparent contact angle of the static-like macroscopic interface compared to the situations with the same Ca but negligible Re.
Parametric decay of an electromagnetic wave near electron cyclotron harmonics
Authors: Istomin Ya. N. , Leyser T. B.
Published: July 2002

A system of equations describing the nonlinear coupling of high frequency electron Bernstein (EB) and upper hybrid (UH) waves near harmonics of the electron cyclotron frequency with low frequency lower hybrid (LH) waves in a homogeneous, weakly magnetized, and weakly collisional plasma is derived. The EB and UH modes are described by a single second order equation, taking into account the interaction with low frequency density fluctuations. The ponderomotive force of the high frequency oscillations increases near the cyclotron harmonics due to the resonance with the electron motion. The obtained equations are used to study the parametric decay of an infinite wavelength electromagnetic pump wave into EB or UH waves and LH waves. The threshold electric fields are sufficiently low to be exceeded in high frequency ionospheric modification experiments. However, the instability cannot be excited for pump frequencies near the cyclotron harmonics. For the decay into EB waves, the resulting forbidden frequency range depends on the harmonic number in a power law manner, consistent with observations of stimulated electromagnetic emissions in ionospheric modification experiments. Further, for sufficiently high pump electric fields the instability is also suppressed, when the frequency mismatch around the eigenfrequencies at which the interaction can occur is of the order of the frequency separation between the EB and UH modes near the cyclotron harmonics.
Observation of Stark shifts in quantum well intersubband transitions
Authors: Harwit Alex , Harris J. S.
Published: July 2002

We have observed Stark shifts of quantum well intersubband transitions in a perpendicular electric field. Two samples consisting of 100 and 120 Å GaAs quantum wells separated by 350 Å AlGaAs barriers showed optical absorption peaks at 11.1 and 13.9 μm, respectively. In an electric field of 36 kV/cm, the 13.9 μm peak shifted to 13.7 μm and the 11.1 μm shifted to 11.0 μm, in good agreement with theoretical calculations. These tunable transitions can be applied to high-speed infrared light modulators.
Band structure of metallic pyrochlore ruthenates Bi2Ru2O7 and Pb2Ru2O6.5
Authors: Hsu William Y. , Kasowski Robert V. , Miller Thomas , Chiang Tai-Chang
Published: July 2002

The band structure of Bi2Ru2O7 and Pb2Ru2O6.5 has been computed self-consistently from first principles for the first time by the pseudofunction method. We discover that the 6s bands of Bi and Pb are very deep and unlikely to contribute to the metallic behavior as previously believed. The unoccupied 6p bands, however, are only several eV above the Fermi energy and are mixed with the Ru 4d band at the Fermi surface via the framework O atoms, leading to band conduction and delocalized magnetic moments. The predicted location of the 6s bands and the location and width of the O 2p band are confirmed by synchrotron radiation and ultraviolet electron spectroscopy of single crystals.
Reactive oxygen generated by Nox1 triggers the angiogenic switch
Authors: Arbiser Jack L. , Petros John , Klafter Robert , Govindajaran Baskaran , McLaughlin Elizabeth R. , Brown Lawrence F. , Cohen Cynthia , Moses Marsha , Kilroy Susan , Arnold Rebecca S. , Lambeth J. David
Published: July 2002

The reactive oxygen-generating enzyme Nox1 transforms NIH 3T3 cells, rendering them highly tumorigenic and, as shown herein, also increases tumorigenicity of DU-145 prostate epithelial cells. Although Nox1 modestly stimulates cell division in both fibroblasts and epithelial cells, an increased mitogenic rate alone did not account fully for the marked tumorigenicity. Herein, we show that Nox1 is a potent trigger of the angiogenic switch, increasing the vascularity of tumors and inducing molecular markers of angiogenesis. Vascular endothelial growth factor (VEGF) mRNA becomes markedly up-regulated by Nox1 both in cultured cells and in tumors, and VEGF receptors (VEGFR1 and VEGFR2) are highly induced in vascular cells in Nox1-expressing tumors. Matrix metalloproteinase activity, another marker of the angiogenic switch, also is induced by Nox1. Nox1 induction of VEGF is eliminated by coexpression of catalase, indicating that hydrogen peroxide signals part of the switch to the angiogenic phenotype.
Adenovirus-mediated gene delivery and
in vitro
microinsemination produce offspring from infertile male mice
Authors: Kanatsu-Shinohara Mito , Ogura Atsuo , Ikegawa Masaya , Inoue Kimiko , Ogonuki Narumi , Tashiro Kei , Toyokuni Shinya , Honjo Tasuku , Shinohara Takashi
Published: July 2002

Sertoli cells play a pivotal role in spermatogenesis through their interactions with germ cells. To set up a strategy for treating male infertility caused by Sertoli cell dysfunction, we developed a Sertoli cell gene transfer system by using an adenovirus vector, which maintained long-term transgene expression in the testes of infertile mice. Introduction of an adenovirus carrying the mouse Steel (
Sl
) gene into Sertoli cells restored partial spermatogenesis in infertile Steel/Steel
dickie
(

Sl/Sl
d

) mutant mouse testes. Although these males remained infertile, round spermatids and spermatozoa from the testes produced normal fertile offspring after intracytoplasmic injection into oocytes. None of the offspring showed evidence of germ line transmission of adenoviral DNA. Thus, we demonstrate a successful treatment for infertility by using a gene therapy vector. Therefore, adenovirus-mediated gene delivery into Sertoli cells not only provides an efficient and convenient means for studying germ cell–Sertoli cell interactions through manipulation of the germ cell microenvironment
in vivo
, but also is a useful method to treat male infertility resulting from a Sertoli cell defect.
Erectile dysfunction in cyclic GMP-dependent kinase I-deficient mice
Authors: Hedlund Petter , Aszódi Attila , Pfeifer Alexander , Alm Per , Hofmann Franz , Ahmad Marianne , Fässler Reinhard , Andersson Karl-Erik
Published: July 2002

The generation of nitric oxide (NO) in penile erectile tissue and the subsequent elevation of cyclic GMP (cGMP) levels are important for normal penile erection. Current treatments of erectile dysfunction elevate either cGMP levels by blocking cGMP degrading phosphodiesterase 5 or cyclic AMP (cAMP) levels by intrapenile injection of prostaglandin E1. The molecular target or targets of cGMP in erectile tissue and the role of cAMP for normal penile erection are not known. Herein, we report that mice lacking cGMP-dependent kinase I (cGKI) have a very low ability to reproduce and that their corpora cavernosa fail to relax on activation of the NO/cGMP signaling cascade. Elevation of cAMP by forskolin, however, induces similar relaxation in normal and cGKI-null corpus cavernosum. In addition, sperm derived from cGKI-null mice is normal, can undergo acrosomal reactions, and can efficiently fertilize eggs. Altogether, these data identify cGKI as the downstream target of cGMP in erectile tissue and provide evidence that cAMP signaling cannot compensate for the absence of the cGMP/cGKI signaling cascade
in vivo
.
Computational adaptive optics for live three-dimensional biological imaging
Authors: Kam Z. , Hanser B. , Gustafsson M. G. L. , Agard D. A. , Sedat J. W.
Published: July 2002

Light microscopy of thick biological samples, such as tissues, is
often limited by aberrations caused by refractive index variations
within the sample itself. This problem is particularly severe for live
imaging, a field of great current excitement due to the development of
inherently fluorescent proteins. We describe a method of removing such
aberrations computationally by mapping the refractive index of the
sample using differential interference contrast microscopy, modeling
the aberrations by ray tracing through this index map, and using
space-variant deconvolution to remove aberrations. This approach will
open possibilities to study weakly labeled molecules in
difficult-to-image live specimens.