bluuebunny/crossref_metadata_2025 huggingface dataset:
A pseudopotential hole-particle treatment of neutral rare gas excimer systems. II. The Rydberg states of the Ar*2 dimer
Authors: Duplàa P. , Spiegelmann F.
Published: July 2002

A pseudopotential hole-particle model (corresponding to the formalism introduced in paper I) is applied to the determination of the Rydberg states of the Ar2* excimer with and without spin–orbit coupling. All the Λ–Σ Rydberg states (without spin–orbit coupling) adiabatically dissociating into Ar+Ar* (4s,4p,3d,5s,5p,4d), are investigated and all Ω states adiabatically dissociating into Ar+Ar*(4s,4p) have been determined including spin–orbit coupling. The calculation also includes at short distance attractive molecular configurations diabatically correlated with higher atomic asymptotes. The nature of the Λ–Σ states is analyzed and assigned with reference to the Rydberg orbitals of the Kr* united atom limit. Extensive comparison with previous calculations and experiments is carried on. For the lowest ungerade states (1)1u, 0−u, (1)0+u, and (2)0+u, good quantitative agreement is found with experimental high resolution studies. Several members of Rydberg series are calculated and assigned, yielding intra-Rydberg transition energies (1)3Σ+u((1)1u,0−u)→m 3Πg or m 3Σ+g in good correspondence with recent intra-Rydberg spectroscopy experiments. In particular the present calculation provides a likely interpretation of the infrared spectra of Ar2* as due to (1)3Σ+u→(1)3Σ+g transitions with an upper corresponding Ω state (1)1g,0−g containing quasi-bound vibrational levels.
High resolution infrared spectroscopy of cyanogen N-oxide, NCCNO
Authors: Guo Bujin , Pasinszki Tibor , Westwood Nicholas P. C. , Zhang Keqing , Bernath Peter F.
Published: July 2002

We report here on the first high resolution infrared absorption spectra of the semistable nitrile oxide, NCCNO. All of the fundamental modes of vibration (except for the lowest-frequency bending mode) and several combination bands have been measured with a Fourier transform spectrometer at a resolution of 0.005 cm−1. In this paper, we present analyses of υ4, the C–C stretching mode at 714.753 94(6) cm−1, υ6, the NCC bending mode at 403.925 97(6) cm−1, υ6+υ7 at 490.123 62(6) cm−1, and the tentatively assigned υ5+υ6 combination band at 826.291 86(8) cm−1. A simultaneous least squares fit of these four bands gives ground state rotational constants of B0=0.077 085 54(34) cm−1 and D0=4.570(30)×10−9 cm−1.
A density functional study of the global potential energy surfaces of the [H,C,N,O] system in singlet and triplet states
Authors: Mebel A. M. , Luna A. , Lin M. C. , Morokuma K.
Published: July 2002

Global potential energy surfaces (PESs) of the [H,C,N,O] system in singlet and triplet states have been investigated using the hybrid density functional B3LYP/6−311G(d,p) method. Isocyanic acid, HNCO 1, has been found to be the most stable isomer for both multiplicities. The adiabatic singlet–triplet splitting for 1 is 82.6 kcal/mol. In the singlet state, HNCO is energetically followed by cyanic acid, HOCN 2, 28.7 kcal/mol higher than 1, fulminic acid, HCNO 3 (67.9 kcal/mol), and isofulminic acid, HONC 4 (87.1 kcal/mol). In the triplet state, the branched NC(H)O isomer 37 is 0.3 kcal/mol higher than 31, followed by HOCN 32 (27.9 kcal/mol relative to triplet HNCO) and HCNO 33 (40.6 kcal/mol). The barriers for intramolecular rearrangements within singlet and triplet [H,C,N,O] system have been calculated to be high, and the isomerization processes in most cases are not expected to compete with fragmentations. Several minima on the singlet–triplet seam of crossing, relevant to the singlet [H,C,N,O] decomposition reactions, have also been found. The global features of the singlet and triplet PES have been applied to several important reactions, such as NH(3Σ−)+CO, thermal decomposition of HNCO, O(3P)+HCN, O(3P)+HNC, and CH(2Π)+NO(2Π). For these reactions, major product channels have been speculated and their activation energies have been reported. Adiabatic ionization potentials for singlet and triplet [H,C,N,O] have been found to be high, in the range of 180–270 kcal/mol.
Jahn–Teller effect in the ground and excited states of MnO2−4 doped into Cs2SO4
Authors: Brunold Thomas C. , Güdel Hans U. , Riley Mark J.
Published: July 2002

The polarized low-temperature absorption spectra of the 3d1 ion MnO2−4 in the Cs2SO4 host consist of a very weak, highly-structured band in the near-infrared (NIR) region corresponding to the 2E→2T2(d→d) transition and a series of intense ligand-to-metal charge transfer (LMCT) excitations above 16 000 cm−1. As a result of the low-symmetry crystal-field (CF) potential in Cs2SO4 the 2T2 ligand-field (LF) state of MnO2−4 is split into its three orbital components at 10 557, 10 848, and 10 858 cm−1 above the ground state. The lowest-energy component serves as initial state for broadband luminescence to the 2E ground state, exhibiting unusually well-resolved fine structure at 15 K. The orbital splitting of 2E is 969 cm−1 and thus larger by more than 1 order of magnitude and of opposite sign compared to the result of a ligand-field calculation within the angular-overlap model (AOM). This discrepancy is explained with the large contribution of the second-nearest neighbor Cs+ ions to the CF potential of MnO2−4 in the Cs2SO4 host lattice. The vibrational progressions in the 2E↔2T2 absorption and luminescence spectra are dominated by O-Mn-O bending modes. This is the result of a weak E⊗e and a stronger T2⊗e Jahn–Teller (JT) effect in the ground and excited LF states, respectively. The observed vibronic levels in the luminescence spectrum are fitted with a single-mode E⊗e JT Hamiltonian with an additional term representing the noncubic CF potential in Cs2SO4. The JT effect in the 2T2 LF state causes a large displacement of the emitting level along the two coordinates of the e mode and thus substantially affects the intensity distribution in the luminescence spectrum. The fitted linear and quadratic vibronic constants for the 2E ground state are 91 and 12 cm−1, respectively, and for the 2T2 excited state the linear coupling constant is −790 cm−1. The corresponding JT stabilization energies are 14 and 925 cm−1 for 2E and 2T2, respectively.
Adsorption kinetics of chemisorption by surface abstraction and dissociative adsorption
Authors: Sholl David S.
Published: July 2002

The kinetics of diatomic molecules adsorbing onto single-crystal surfaces is considered when this process can occur by a combination of dissociative adsorption and surface abstraction. The latter process adsorbs one atom on the surface and scatters the other from the surface. This combination of adsorption mechanisms controls the adsorption of fluorine on silicon surfaces [Y. L. Li et al., Phys. Rev. Lett. 74, 2603 (1995); J. A. Jensen et al., Science 267, 493 (1995)]. The effects of a variety of phenomena on the adsorption kinetics are explored, including surface diffusion, adlayer ordering due to adsorbate–lateral interactions, and the existence of weakly bound physiosorbed precursor states. When possible, exact expressions characterizing the adsorption kinetics are derived. Otherwise, approximate expressions are derived and compared with Monte Carlo simulations.
How the structure of a confined fluid depends on the ensemble: Hard spheres in a spherical cavity
Authors: González A. , White J. A. , Román F. L. , Evans R.
Published: July 2002

The equilibrium structure of a hard-sphere fluid confined in a small spherical cavity is investigated. In such systems the statistical mechanical ensembles are no longer equivalent and we consider both open (grand canonical) and closed (canonical) cavities in order to analyze the effects of size and packing constraints on the density profile of the confined fluid. For systems in the grand canonical ensemble the profiles are obtained from grand canonical ensemble Monte Carlo simulations and from density functional theory. The profiles of the closed (canonical) systems are obtained by means of canonical ensemble Monte Carlo simulations. A scheme is proposed which expands the canonical ensemble density profiles in terms of grand canonical averages; this is formally a series in powers of the inverse average number of particles. By comparing canonical ensemble Monte Carlo data with the results of the expansion applied to grand canonical ensemble Monte Carlo data and to the results of density functional theory the series expansion is shown to converge very quickly in most situations, even when the cavity contains only a few particles. However, as a consequence of packing constraints, in certain situations the density profile develops a pronounced peak in the center of the cavity. Then significant differences arise between the canonical and grand canonical profiles and the convergence of the series is much slower in the central zone where the peak develops. Describing accurately the various terms in the expansion and, hence, the detailed shapes of the profiles provides a searching test of density functional approximations. We find that recent modifications of Rosenfeld’s fundamental measure theory, which are designed to describe situations of low effective dimensionality, perform better than his original theory and yield accurate results for all cases except those near maximum packing.
Recoil growth: An efficient simulation method for multi-polymer systems
Authors: Consta S. , Wilding N. B. , Frenkel D. , Alexandrowicz Z.
Published: July 2002

We present a new Monte Carlo scheme for the efficient simulation of multi-polymer systems. The method permits chains to be inserted into the system using a biased growth technique. The growth proceeds via the use of a retractable feeler, which probes possible pathways ahead of the growing chain. By recoiling from traps and excessively dense regions, the growth process yields high success rates for both chain construction and acceptance. Extensive tests of the method using self-avoiding walks on a cubic lattice show that for long chains and at high densities it is considerably more efficient than configurational bias Monte Carlo, of which it may be considered a generalization.
Effects of molecular association on mutual diffusion: A study of hydrogen bonding in dilute solutions
Authors: Lu J. G. , Kong Rita , Chan T. C.
Published: July 2002

Diffusivities of pseudoplanar molecules at trace concentration in methanol have been measured at 298.2 K using Taylor’s dispersion method. The data of the polar and nonpolar aromatic solutes are compared, and the effects due to solute–solvent interactions on diffusion, together with the solvation numbers, are determined. In this study, the effects are combined with the recently developed solute hydrogen-bond scales to unravel hydrogen bonding between solute and solvent. It is found that the degrees of association of the solutes with methanol decrease in the sequence hydroquinone>aromatic acids>phenols>aromatic amines>aprotic aromatic compounds. Except for o-nitrophenol, which is capable of intramolecular hydrogen bonding, all aromatic acids, phenols, and amines studied behave more as hydrogen-bond donor than acceptor in methanol. The present work also indicates that motions of associated molecules can be understood in terms of the molecular behavior of nonassociated solutes and the hydrogen-bond acidity/basicity of polar solutes.
Nematic contact lines and the Neumann and Young equations for liquid crystals
Authors: Rey Alejandro D.
Published: July 2002

The Neumann and Young equations for three-phase contact lines, when one of the phases is a nematic liquid crystal, have been derived using momentum balances and liquid-crystal surface physics models. The Neumann equation for nematic contact lines is a balance of three tension and two bending forces, the latter arising from the characteristic anisotropic surface anchoring of nematic liquid crystal surfaces. For a given interface the bending forces are always orthogonal to the tension forces, and in the presence of a nematic phase the Neumann triangle of isotropic phases becomes the Neumann pentagon. The Young equation for solid–fluid–nematic contact lines differs from the classical equation by a bending force term, which influences the wetting regimes’ transitions, the contact angles, and allows for a novel orientation-induced wetting transition cascade. For a nematic contact line, the partial wetting–spreading transition occurs for positive values of the spreading parameter, and the partial wetting–dewetting transition sets in at values smaller than the classical result. The interval of static contact angles is less than π radians. For a given solid–nematic–isotropic fluid at a fixed temperature, the spreading → partial wetting → spreading → partial wetting → spreading transition cascade may occur when the director at the contact line rotates from the planar to the homeotropic orientation state.
On the algebra of Dirac bispinor densities: Factorization and inversion theorems
Authors: Crawford J. P.
Published: July 2002

The algebraic system formed by Dirac bispinor densities ρi≡ψ̄Γiψ is discussed. The inverse problem—given a set of 16 real functions ρi, which satisfy the bispinor algebra, find the spinor ψ to which they correspond—is solved. An expedient solution to this problem is obtained by introducing a general representation of Dirac spinors. It is shown that this form factorizes into the product of two noncommuting projection operators acting on an arbitrary constant spinor.
Canonical structures for dispersive waves in shallow water
Authors: Neyzi Fahrünisa , Nutku Yavuz
Published: July 2002

The canonical Hamiltonian structure of the equations of fluid dynamics obtained in the Boussinesq approximation are considered. New variational formulations of these equations are proposed and it is found that, as in the case of the KdV equation and the equations governing long waves in shallow water, they are degenerate Lagrangian systems. Therefore, in order to cast these equations into canonical form it is again necessary to use Dirac’s theory of constraints. It is found that there are primary and secondary constraints which are second class and it is possible to construct the Hamiltonian in terms of canonical variables. Among the examples of Boussinesq equations that are discussed are the equations of Whitham–Broer–Kaup which Kupershmidt has recently expressed in symmetric form and shown to admit tri-Hamiltonian structure.
Casorati determinant solution for the relativistic Toda lattice equation
Authors: Ohta Yasuhiro , Kajiwara Kenji , Matsukidaira Junta , Satsuma Junkichi
Published: July 2002

The relativistic Toda lattice equation is decomposed into three Toda systems, the Toda lattice itself, Bäcklund transformation of Toda lattice, and discrete time Toda lattice. It is shown that the solutions of the equation are given in terms of the Casorati determinant. By using the Casoratian technique, the bilinear equations of Toda systems are reduced to the Laplace expansion form for determinants. The N-soliton solution is explicitly constructed in the form of the Casorati determinant.
Superintegrability on the two-dimensional hyperboloid
Authors: Kalnins E. G. , Miller W. , Pogosyan G. S.
Published: July 2002

In this work we examine the basis functions for classical and quantum mechanical systems on the two-dimensional hyperboloid that admit separation of variables in at least two coordinate systems. We present all of these cases from a unified point of view. In particular, all of the special functions that arise via variable separation have their essential features expressed in terms of their zeros. The principal new results are the details of the polynomial bases for each of the nonsubgroup bases, not just the subgroup spherical coordinate cases, and the details of the structure of the quadratic symmetry algebras.
Elliptic Ruijsenaars–Schneider model from the cotangent bundle over the two-dimensional current group
Authors: Arutyunov G. E. , Frolov S. A. , Medvedev P. B.
Published: July 2002

It is shown that the elliptic Ruijsenaars–Schneider model can be obtained from the cotangent bundle over the two-dimensional current group by means of the Hamiltonian reduction procedure.
Aharonov–Bohm effect with δ-type interaction
Authors: Da̧browski L. , Šťovı́ček P.
Published: July 2002

A quantum particle interacting with a thin solenoid and a magnetic flux is described by a five-parameter family of Hamilton operators, obtained via the method of self-adjoint extensions. One of the parameters, the value of the flux, corresponds to the Aharonov–Bohm effect; the other four parameters correspond to the strength of a singular potential barrier. The spectrum and eigenstates are computed and the scattering problem is solved.
Algebro-geometric solutions of (2+1)-dimensional coupled modified Kadomtsev–Petviashvili equations
Authors: Geng Xianguo , Dai H. H.
Published: July 2002

New (2+1)-dimensional integrable coupled modified Kadomtsev–Petviashvili (mKP) equations are proposed with the help of known (1+1)-dimensional soliton equations. The (2+1)-dimensional coupled mKP equations are decomposed into systems of solvable ordinary differential equations. The Abel–Jacobi coordinates are introduced to straighten the flows, from which new algebro-geometric solutions of the (2+1)-dimensional mKP equation and algebro-geometric solutions of the (2+1)-dimensional coupled mKP equations are obtained in terms of the Riemann theta functions.
Improved bounds for sampling colorings
Authors: Vigoda Eric
Published: July 2002

We consider the problem of sampling uniformly at random from the set of proper k-colorings of a graph with maximum degree Δ. Our main result is the design of a simple Markov chain that converges in O(nk log n) time to the desired distribution when k>116Δ.
Measurements and stability calculations of the disturbance growth in an unstable three-dimensional boundary layer
Authors: Bippes H. , Müller B. , Wagner M.
Published: July 2002

The amplification of disturbances developing under conditions of natural transition in the unstable three-dimensional boundary-layer flow on a swept-back flat plate is measured with the aid of hot-wire anemometry. A detailed analysis of the experimental data allows identification of the most amplified instability modes and determination of their growth rates. The results are compared with linear stability theory. Although the amplification process is affected by nonlinearities starting a short distance downstream of the positions where the disturbances become of measurable size, in some essential respects the applicability of linear theory can be examined. It turns out that the initial amplification rates of the stationary instability modes are fairly well predicted whereas the amplification rates of the nonstationary modes are overestimated. A remarkable feature is that the disturbances with the largest amplitudes are not, in every case, the most amplified ones in theory as well as in experiment.
Axial dynamics in field-reversed theta pinches. II: Stability
Authors: Tuszewski M. , Taggart D. P. , Chrien R. E. , Rej D. J. , Siemon R. E. , Wright B. L.
Published: July 2002

Detailed stability studies are made with new diagnostics in the FRX-C/LSM field-reversed theta pinch [Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1989), Vol. II, p. 517]. These studies seek the origin of a degradation of the confinement properties of field-reversed configurations (FRC’s) that appears associated with strong axial dynamics during plasma formation. Several instabilities are observed, including rotational modes, interchanges, and tilt instabilities. Only the latter are strongly correlated with FRC confinement. Tilt instabilities are observed for FRC’s with larger average number of ion gyroradii (s∼3–5) and smaller separatrix elongations (e∼3–4). Coincidently, strong axial dynamics occurs for cases with larger s and smaller e values, through increases in either reversed bias field or fill pressure. These data provide some understanding of FRC stability. In agreement with finite Larmor radius theory, there is a regime of gross stability for the very kinetic and elongated FRC’s with s/e<0.2–0.3. This is the regime that has been studied in most FRC experiments. However, tilt and other instabilities are observed for FRC’s with s/e∼1. Additional stabilization techniques will be required for future large-size FRC’s.
Influence of trapped thermal particles on internal kink modes in high temperature tokamaks
Authors: Antonsen T. M. , Bondeson Anders
Published: July 2002

The effects of thermal trapped particles on the n=1 internal kink mode are studied using drift kinetic theory. Strong modifications of the magnetohydrodynamic (MHD) results are found, and marginal stability generally occurs at nonzero rotation frequency. For equal electron and ion temperatures, the trapped particles increase the marginal poloidal beta at q=1 substantially above the MHD value. For unequal electron and ion temperatures, the drift resonance with the hotter species becomes increasingly destabilizing and for sufficiently unequal temperatures, this leads to instability below the ideal-MHD threshold. Treatment of trapped thermal particles requires consideration of the effects of an electrostatic potential. The potential is weakly stabilizing for the internal kink mode. Furthermore, finite beta couples unstable, nearly electrostatic, trapped particle modes to the internal kink mode. At high beta, thermal fluctuations of the trapped particle modes can lead to significant internal kink displacements.
Kinetic tilting stability of field-reversed configurations
Authors: Barnes Daniel C. , Schwarzmeier James L. , Lewis H. Ralph , Seyler Charles E.
Published: July 2002

Stability of the internal tilting mode in an elongated prolate field-reversed configuration (FRC) is investigated numerically. Eigenfrequencies are calculated from a Vlasov-fluid dispersion functional that is separated into fluid and kinetic portions. The latter are evaluated by a Monte Carlo method following a sample of the equilibrium orbits. An innovative Fourier transform technique is developed to reduce the operation count of the algorithm. Kinetic growth rates obtained for an experimentally relevant equilibrium indicate essential stabilization of internal tilting in an FRC with s̄≲2, where s̄ measures the number of thermal gyroradii in the configuration. For s̄→∞ the kinetic growth rates approach previous magnetohydrodynamic (MHD) values.
Traveling waves on fluid interfaces: Normal form analysis of the Kuramoto–Sivashinsky equation
Authors: Chang Hsueh-Chia
Published: July 2002

Traveling wave solutions of the Kuramoto–Sivashinsky equation, hθ+4hhη+hηη+shηηηη=0, are investigated using the normal form analysis of nonlinear dynamic theory. Theoretical correlations between wavelength and amplitude and between wave velocity and amplitude are obtained for periodic and solitary propagating patterns. Since the equation describes several interfacial instabilities, these correlations are relevant to many physical phenomena. They are favorably compared to experimental data of finite waves on vertically falling films.
Instability and transition of a three-dimensional boundary layer on a swept flat plate
Authors: Nitschke-Kowsky P. , Bippes H.
Published: July 2002

Stability features are studied experimentally for the unstable three dimensional boundary layer flow on a swept-back flat plate. A pressure gradient on the flat plate is induced by a displacement body. Infinite sweep conditions are approximated by means of contoured endplates. For the measurements, hot-wire and surface hot-film anemometry as well as flow visualization techniques are used. In addition to stationary waves, traveling waves are also traced. The cross-flow Reynolds numbers for the first appearance of either instability mode are of approximately the same magnitude. Wavelength and the direction of stationary vortices, as well as the frequencies of the most amplified traveling waves, are measured for different Reynolds numbers. The data obtained by the measurements are compared with the results of linear stability theory. The location of the final transition on the swept flat plate has proved to be fairly well predicted by the empirical transition criterion of Coustols (Thèse de Docteur Ingénieur, Ecole Nationale Supérieur de l’Aéronautique et de l’Espace, Toulouse, 1983).
On the permeability of unidirectional fibrous media: A parallel computational approach
Authors: Ghaddar Chahid K.
Published: July 2002

The problems of viscous and inertial flows through unidirectional fibrous porous media are addressed using an entirely parallel computational approach. The pertinent partial differential equations, derived from homogenization theory, are solved by a parallel finite element method in conjunction with Monte Carlo techniques to predict the statistical permeability coefficient. A nip-element method, which mitigates the frequent geometry-induced numerical difficulties, while providing both accurate approximations for the permeability coefficient, and rigorous error estimates, is also presented. The seepage permeability coefficient is determined for a wide range of fiber concentration. It is shown to deviate markedly at low porosities from the behavior predicted by earlier cell models, while exhibiting generally good agreement at high, and moderate porosities with the cell models, and with the limited available experimental and analytical results. Limited but illustrative inertial flow results at moderate Reynolds numbers are also presented for both regular and random arrays. For regular arrays, the flow is found to be unsteady for Reynolds numbers greater than approximately 150 at which traveling waves characterized by distinct periods and amplitudes are observed. Some modest discrepancy is found in comparison with available data which is attributed to the unsteady effects and other numerical issues. For random arrays, several configuration permeability values are calculated and compared satisfactorily against the Ergun correlation.
Coherent structures and dynamics in a neutrally stratified planetary boundary layer flow
Authors: Lin Ching-Long , McWilliams James C. , Moeng Chin-Hoh , Sullivan Peter P.
Published: July 2002

Coherent structures and the dynamics of a neutrally stratified planetary boundary layer flow are studied through a large eddy simulation, which includes surface roughness, Coriolis force, and a capping inversion. Quadrant analysis and flow visualization show that low-speed negative momentum flux (ejection) is the dominant feature throughout most of the boundary layer. The initiation of vortical structures is observed to be associated with vorticity sheets and pressure maxima, which are formed dynamically when low-speed negative momentum flux collides with either high-speed negative momentum flux (sweep) or the mean flow. Four dimensional conditional averages are used to study the statistical behavior of ejections and sweeps. The shape, strength, lifetime, and origin of the conditionally sampled structures at three different heights are discussed. Near the surface, sweeps are observed to induce ejections when colliding with the surface. The evolution of sweep-induced ejections near the wall is discussed.
The structure of an infinitely strong shock wave
Authors: Cercignani Carlo , Frezzotti Aldo , Grosfils Patrick
Published: July 2002

The structure of a shock wave propagating through a hard-sphere gas is obtained by the Direct Simulation Monte Carlo method (DSMC), in the limit of infinitely large Mach number. The shock profiles and the distribution function of molecular velocities f are compared with Grad’s and Mott–Smith approximations. It is shown that the “regular” part of f, exhibits a singularity in the velocity space at the location of the upstream bulk speed.
The influence of magnetic fluctuations on collisional drift-wave turbulence
Authors: Camargo Suzana J. , Scott Bruce D. , Biskamp Dieter
Published: July 2002

A two-dimensional isothermal collisional drift-wave turbulence model including magnetic fluctuations is studied numerically. The model has as limits the electrostatic collisional drift-wave and two-dimensional magnetohydrodynamic systems. The electromagnetic and electrostatic regimes for thermal gradient-driven (drift-wave) turbulence are decided by the parameter β̂=(4πnT/B2)(L2s/L2n), where Ls and Ln are the parallel and background profile scale lengths, respectively. Significant electromagnetic effects were found only for β̂∼10 for most parameters, and were most pronounced in the strongly adiabatic regime for drift waves. The principal effect of the magnetic fluctuations is magnetic induction in the parallel force balance for electrons, which is linear. This diminishes the adiabaticity of the system by reducing the immediacy of the dissipative coupling between the density and electrostatic potential fluctuations. The transport was still found to be dominantly electrostatic even for β̂=10, although its level decreased with β̂ due to reduced coherency in the coupling between E×B velocity and density fluctuations.
Ion–neutral collision effects on Alfvén surface waves
Authors: Uberoi C. , Datta Ajanta
Published: July 2002

It is well established that in magnetized partially ionized plasmas, the dispersion of the shear Alfvén waves is strongly influenced by the ion–neutral collisions. In the case of inhomogeneous plasmas, the study of these collisions on Alfvén surface waves can become important, especially in understanding resonant absorption of Alfvén waves. In this paper, the dispersion equation for the surface waves in partially ionized plasma along a plasma–plasma interface is derived and it is shown that ion–neutral collisions can cause a drastic change in the Alfvén surface waves’ propagation characteristics. For the case when ion–neutral coupling is weak, the wave propagates along the interface with the natural frequency of Alfvén surface waves in the charged medium without friction. When coupling is strong, this frequency is determined by the mass densities of both ions and neutrals in both media. When the ionization fraction is low, these two frequencies can differ by several orders of magnitude. There also exists a range of frequencies, depending on the collisions, in which the surface waves do not propagate. The damping of surface waves due to ion–neutral collisions can be very small in the case of strong coupling. For weak coupling, this damping can become large due to large collision frequencies. The effect of this on the resonant absorption of surface waves is discussed briefly. The possibility of propagation of surface waves along thin plasma–plasma interfaces is also considered in the context of some astrophysical systems.
Linear stability theory and bypass transition in shear flows
Authors: Schmid Peter J.
Published: July 2002

This paper gives a brief introduction and review of linear stability theory with emphasis on nonmodal effects. The temporal and spatial framework is discussed and the response to periodic and stochastic forcing is addressed. An extension to nonautonomous evolution problems is presented. Bypass transition due to the secondary instability of streaks is used as an example to illustrate the role of a nonmodal linear mechanism in the breakdown to turbulence.
D
–
3
He
proton spectra for diagnosing shell ρR and fuel Ti of imploded capsules at OMEGA
Authors: Li C. K. , Hicks D. G. , Séguin F. H. , Frenje J. A. , Petrasso R. D. , Soures J. M. , Radha P. B. , Glebov V. Yu. , Stoeckl C. , Harding D. R. , Knauer J. P. , Kremens R. , Marshall F. J. , Meyerhofer D. D. , Skupsky S. , Roberts S. , Sorce C. , Sangster T. C. , Phillips T. W. , Cable M. D. , Leeper R. J.
Published: July 2002

Recent work has resulted in the first high-resolution, spectroscopic measurements of energetic charged particles on OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 496 (1997)]. Energy spectra of charged fusion products have been obtained from two spectrometers, and have been used to deduce various physical quantities in imploded capsules. In this paper the first use of 14.7 MeV deuterium–helium3 (D–3He) proton spectra for diagnosing shell areal density (ρR) and fuel ion temperature (Ti) is discussed. For thick-plastic shell capsules, shell areal densities between 20 and 70 mg/cm2 and ion temperatures between 3 and 5 keV have been determined. The spectral linewidths associated with such capsules are found to be wider than the doppler widths. This effect, the focus of future study, is the result of ρR evolution during the burn; or is the result of an extended burn region; or results from nonuniformities in the shell. For thin-glass shell capsules, the spectral linewidths are dominated by the doppler width, and ion temperatures between 10 and 15 keV were determined. These measurements have been also compared and contrasted with the results from neutron measurements and from one-dimension hydrodynamic simulations.
Depletion and enhancement mode In0.53Ga0.47As/InP junction field-effect transistor with a p+-InGaAs confinement layer
Authors: Cheng Julian , Forrest S. R. , Stall R. , Guth G. , Wunder R.
Published: July 2002

A self-aligned all-In0.53Ga0.47 As junction field-effect transistor structure grown by molecular beam epitaxy is described, using p+-InGaAs as the confinement layer for the n channel. Devices have been made to operate in either the depletion mode or the enhancement mode. Transconductances of 90 mS/mm have been observed, with low capacitance (0.7 pF/mm) and low gate leakage.
High efficiency homojunction InP solar cells
Authors: Yamamoto Akio , Yamaguchi Masafumi , Uemura Chikao
Published: July 2002

Homojunction InP solar cells with a high conversion efficiency of 18.0% have been fabricated using thermal diffusion of sulphur into p-type InP. An open-circuit voltage Voc as high as 0.837 V which resulted from a reduction in leakage current was attained by employing mesa etching as a method for sectioning cells on a diffused wafer. Fill factor was also increased to 82.9% owing to both a small diode ideality factor (≲1.3) and a low cell series resistance (≲0.5 Ω cm2). As a result of the improvement in these factors, a conversion efficiency as high as 18.0% (an active-area conversion efficiency of 20.1%) under AM1.5 illumination was obtained. A phenomenon whereby shunt resistance in a mesa-etched cell is reduced by illumination is discussed. This is due to the additional current flowing from the peripheral p-InP region bared by the mesa etching.
Dependence of resonant tunneling current on well widths in AlAs/GaAs/AlAs double barrier diode structures
Authors: Tsuchiya Masahiro , Sakaki Hiroyuki
Published: July 2002

The dependence of current components on GaAs well widths is studied in AlAs/GaAs/AlAs double barrier diode structures having AlAs barriers of 8 atomic layers. It is shown for the first time that the density JRT of resonant current varies from 8×102 to 1.6×104 A cm−2 by the choice of the well width from 9 to 5 nm in accordance with theoretical calculations. Furthermore, one of these diodes shows excellent current-voltage characteristics at room temperature with a peak to valley ratio of 3, the highest value ever reported.
Growth of GaAs by metalorganic chemical vapor deposition using thermally decomposed trimethylarsenic
Authors: Vook D. W. , Reynolds S. , Gibbons J. F.
Published: July 2002

We have developed a novel thermal precracking technique which has improved the electrical quality of GaAs grown using trimethylarsenic, while maintaining excellent surface morphology. Background doping is reduced by a factor of 5, and carbon incorporation is reduced by a factor of 10 or more. This method may prove useful for reducing carbon incorporation from other organometallic arsenic sources as well. Net background doping below 1016 cm−3 and room-temperature electron mobilities of 4000–4500 cm2/V s have been obtained. These are the best values reported for GaAs grown using trimethylarsenic.
Near-band-gap luminescence from a GaAs-AlGaAs interface
Authors: ’t Hooft G. W. , van der Poel W. A. J. A. , Molenkamp L. W. , Foxon C. T.
Published: July 2002

We report on low-temperature photoluminescence from an ultrapure GaAs-Al0.33Ga0.67As heterostructure grown with molecular beam epitaxy. A luminescence band centered at 1.509–1.510 eV is observed. In spectral shape and polarization this band distinguishes itself from the defect related lines of H. Kuenzel and K. Ploog [Appl. Phys. Lett. 37, 416 (1980)]. Furthermore, this band disappears when the top cladding Al0.33Ga0.67As layer is removed. The emission band is further characterized by measuring its dependence on excitation density and temperature as well as its temporal behavior. We discuss possible recombination mechanisms for this band. The most likely candidate is luminescence related to a defect pair situated at or near the interface of the heterojunction.
Indium phosphide solar cells made by ion implantation
Authors: Keavney C. J. , Spitzer M. B.
Published: July 2002

High-efficiency indium phosphide solar cells of the shallow homojunction type have been made using ion implantation to form the emitter layer. An anneal in phosphine was used to recover the implant damage. The cells show a 5% higher short-circuit current than cells with a similar base but with an epitaxial emitter. The open-circuit voltage is slightly higher than that of the epitaxial cells, and the fill factor slightly lower. Conversion efficiency of 18.8% (air mass zero, total area) has been achieved; this is the highest thus far reported for an InP cell.
Deep level transient spectroscopy on single, isolated interface traps in field-effect transistors
Authors: Karwath A. , Schulz M.
Published: July 2002

Electron emission from single, isolated traps is observed in stepped current transients of micrometer-size metal oxide semiconductor field-effect transistors. Deep level transient spectroscopy evaluation is performed by counting traps to estimate the average state density Dit ≊6 ×1010 eV−1 cm−2 close to the conduction-band edge (Ec−Eit =20–250 meV). The capture coefficient (prefactor for activated emission) is determined to Bn =10−21 cm3 s−1 for these slow traps.
Role of strain and growth conditions on the growth front profile of InxGa1−xAs on GaAs during the pseudomorphic growth regime
Authors: Berger Paul R. , Chang Kevin , Bhattacharya Pallab , Singh Jasprit , Bajaj K. K.
Published: July 2002

Theoretical and experimental studies are presented to understand the initial stages of growth of InGaAs on GaAs. Thermodynamic considerations show that, as strain increases, the free-energy minimum surface of the epilayer is not atomically flat, but three-dimensional in form. Since by altering growth conditions the strained epilayer can be grown near equilibrium or far from equilibrium, the effect of strain on growth modes can be studied. In situ reflection high-energy electron diffraction studies are carried out to study the growth modes and surface lattice spacing before the onset of dislocations. The surface lattice constant does not change abruptly from that of the substrate to that of the epilayer at the critical thickness, but changes monotonically. These observations are consistent with the simple thermodynamic considerations presented.
A functional genetic screen identifies regions at the C-terminal tail and death-domain of death-associated protein kinase that are critical for its proapoptotic activity
Authors: Raveh Tal , Berissi Hanna , Eisenstein Miriam , Spivak Taly , Kimchi Adi
Published: July 2002

Death-associated protein kinase (DAP-kinase) is a Ca
+2
/calmodulin-regulated serine/threonine kinase with a multidomain structure that participates in apoptosis induced by a variety of signals. To identify regions in this protein that are critical for its proapoptotic activity, we performed a genetic screen on the basis of functional selection of short DAP-kinase-derived fragments that could protect cells from apoptosis by acting in a dominant-negative manner. We expressed a library of randomly fragmented DAP-kinase cDNA in HeLa cells and treated these cells with IFN-γ to induce apoptosis. Functional cDNA fragments were recovered from cells that survived the selection, and those in the sense orientation were examined further in a secondary screen for their ability to protect cells from DAP-kinase-dependent tumor necrosis factor-α-induced apoptosis. We isolated four biologically active peptides that mapped to the ankyrin repeats, the “linker” region, the death domain, and the C-terminal tail of DAP-kinase. Molecular modeling of the complete death domain provided a structural basis for the function of the death-domain-derived fragment by suggesting that the protective fragment constitutes a distinct substructure. The last fragment, spanning the C-terminal serine-rich tail, defined a new regulatory region. Ectopic expression of the tail peptide (17 amino acids) inhibited the function of DAP-kinase, whereas removal of this region from the complete protein caused enhancement of the killing activity, indicating that the C-terminal tail normally plays a negative regulatory role. Altogether, this unbiased screen highlighted functionally important regions in the protein and revealed an additional level of regulation of DAP-kinase apoptotic function that does not affect the catalytic activity.
Predator-induced stress makes the pesticide carbaryl more deadly to gray treefrog tadpoles (
Hyla versicolor
)
Authors: Relyea Rick A. , Mills Nathan
Published: July 2002

Global declines in amphibians likely have multiple causes,
including widespread pesticide use. Our knowledge of pesticide effects
on amphibians is largely limited to short-term (4-d) toxicity tests
conducted under highly artificial conditions to determine lethal
concentrations (LC50). We found that if we used slightly longer
exposure times (10–16 d), low concentrations of the pesticide carbaryl
(3–4% of LC50
4-d
) killed 10–60% of gray treefrog
(
Hyla versicolor
) tadpoles. If predatory cues also were
present, the pesticide became 2–4 times more lethal, killing 60–98%
of tadpoles. Thus, under more realistic conditions of increased
exposure times and predatory stress, current application rates for
carbaryl can potentially devastate gray treefrog populations. Further,
because predator-induced stress is ubiquitous in animals and
carbaryl's mode of action is common to many pesticides, these negative
impacts may be widespread in nature.
Murine cytomegalovirus M78 protein, a G protein-coupled receptor homologue, is a constituent of the virion and facilitates accumulation of immediate-early viral mRNA
Authors: Oliveira Sofia A. , Shenk Thomas E.
Published: July 2002

The M78 protein of murine cytomegalovirus exhibits sequence
features of a G protein-coupled receptor. It is synthesized with early
kinetics, it becomes partially colocalized with Golgi markers, and it
is incorporated into viral particles. We have constructed a viral
substitution mutant, SM
sub
M78, which lacks most of the
M78 ORF. The mutant produces a reduced yield in cultured 10.1
fibroblast and IC21 macrophage cell lines. The defect is multiplicity
dependent and greater in the macrophage cell line. Consistent with its
growth defect in cultured cells, the mutant exhibits reduced
pathogenicity in mice, generating less infectious progeny than
wild-type virus in all organs assayed. SM
sub
M78 fails to
efficiently activate accumulation of the viral m123 immediate-early
mRNA in infected macrophages. M78 facilitates the accumulation of the
immediate-early mRNA in cycloheximide-treated cells, arguing that it
acts in the absence of
de novo
protein synthesis. We
conclude that the M78 G protein-coupled receptor homologue is delivered
to cells as a constituent of the virion, and it acts to facilitate the
accumulation of immediate-early mRNA.
Prions in skeletal muscle
Authors: Bosque Patrick J. , Ryou Chongsuk , Telling Glenn , Peretz David , Legname Giuseppe , DeArmond Stephen J. , Prusiner Stanley B.
Published: July 2002

Considerable evidence argues that consumption of beef products from cattle infected with bovine spongiform encephalopathy (BSE) prions causes new variant Creutzfeldt–Jakob disease. In an effort to prevent new variant Creutzfeldt–Jakob disease, certain “specified offals,” including neural and lymphatic tissues, thought to contain high titers of prions have been excluded from foods destined for human consumption [Phillips, N. A., Bridgeman, J. & Ferguson-Smith, M. (2000) in
The BSE Inquiry
(Stationery Office, London), Vol. 6, pp. 413–451]. Here we report that mouse skeletal muscle can propagate prions and accumulate substantial titers of these pathogens. We found both high prion titers and the disease-causing isoform of the prion protein (PrP
Sc
) in the skeletal muscle of wild-type mice inoculated with either the Me7 or Rocky Mountain Laboratory strain of murine prions. Particular muscles accumulated distinct levels of PrP
Sc
, with the highest levels observed in muscle from the hind limb. To determine whether prions are produced or merely accumulate intramuscularly, we established transgenic mice expressing either mouse or Syrian hamster PrP exclusively in muscle. Inoculating these mice intramuscularly with prions resulted in the formation of high titers of nascent prions in muscle. In contrast, inoculating mice in which PrP expression was targeted to hepatocytes resulted in low prion titers. Our data demonstrate that factors in addition to the amount of PrP expressed determine the tropism of prions for certain tissues. That some muscles are intrinsically capable of accumulating substantial titers of prions is of particular concern. Because significant dietary exposure to prions might occur through the consumption of meat, even if it is largely free of neural and lymphatic tissue, a comprehensive effort to map the distribution of prions in the muscle of infected livestock is needed. Furthermore, muscle may provide a readily biopsied tissue from which to diagnose prion disease in asymptomatic animals and even humans.
Acceleration of atherogenesis by COX-1-dependent prostanoid formation in low density lipoprotein receptor knockout mice
Authors: Praticò Domenico , Tillmann Cyrus , Zhang Zhi-Bing , Li Hongwei , FitzGerald Garret A.
Published: July 2002

The cyclooxygenase (COX) product, prostacyclin (PGI
2
),
inhibits platelet activation and vascular smooth-muscle cell migration
and proliferation. Biochemically selective inhibition of COX-2 reduces
PGI
2
biosynthesis substantially in humans. Because deletion
of the PGI
2
receptor accelerates atherogenesis in the
fat-fed low density lipoprotein receptor knockout mouse, we wished to
determine whether selective inhibition of COX-2 would accelerate
atherogenesis in this model. To address this hypothesis, we used dosing
with nimesulide, which inhibited COX-2
ex vivo
,
depressed urinary 2,3 dinor 6-keto PGF
1α
by approximately
60% but had no effect on thromboxane formation by platelets, which
only express COX-1. By contrast, the isoform nonspecific inhibitor,
indomethacin, suppressed platelet function and thromboxane formation
ex vivo
and
in vivo
, coincident with
effects on PGI
2
biosynthesis indistinguishable from
nimesulide. Indomethacin reduced the extent of atherosclerosis by
55 ± 4%, whereas nimesulide failed to increase the rate of
atherogenesis. Despite their divergent effects on atherogenesis, both
drugs depressed two indices of systemic inflammation, soluble
intracellular adhesion molecule-1, and monocyte chemoattractant
protein-1 to a similar but incomplete degree. Neither drug altered
serum lipids and the marked increase in vascular expression of COX-2
during atherogenesis. Accelerated progression of atherosclerosis is
unlikely during chronic intake of specific COX-2 inhibitors.
Furthermore, evidence that COX-1-derived prostanoids contribute to
atherogenesis suggests that controlled evaluation of the effects of
nonsteroidal anti-inflammatory drugs and/or aspirin on plaque
progression in humans is timely.