bluuebunny/crossref_metadata_2025 huggingface dataset:
A Risk‐Amplification Model of Victimization and Depressive Symptoms Among Runaway and Homeless Adolescents
Authors: Whitbeck Les B. , Hoyt Dan R. , Yoder Kevin A.
Published: April 2003

This report is an examination of a theoretical model of risk amplification within a sample of 255 homeless and runaway adolescents. The young people were interviewed on the streets and in shelters in urban centers of four Midwestern states. Separate models were examined for males (n = 102) and females (n = 153). Results indicated that street experiences such as affiliation with deviant peers, deviant subsistence strategies, risky sexual behaviors, and drug and/or alcohol use amplified the effects of early family abuse on victimization and depressive symptoms for young women. These street adaptations significantly increased the likelihood of serious victimization over and above the effects of early family history for both young men and women. Similarly, street behaviors and experiences increased the likelihood of depressive symptoms for young women over the effects of early family abuse, but not for young men. The risk‐amplification model from the life course theoretical perspective is discussed as an example of the cumulative continuity of maladaptive behaviors.
Moment problems and the causal set approach to quantum gravity
Authors: Ash Avner , McDonald Patrick
Published: March 2003

We study a collection of discrete Markov chains related to the causal set approach to modeling discrete theories of quantum gravity. The transition probabilities of these chains satisfy a general covariance principle, a causality principle, and a renormalizability condition. The corresponding dynamics are completely determined by a sequence of non-negative real coupling constants. Using techniques related to the classical moment problem, we give a complete description of any such sequence of coupling constants. We prove a representation theorem: every discrete theory of quantum gravity arising from causal set dynamics satisfying covariance, causality, and renormalizability corresponds to a unique probability distribution function on the non-negative real numbers, with the coupling constants defining the theory given by the moments of the distribution.
On the boson spectrum of the N particle Schrödinger operator with periodic binary potential (dense matter)
Authors: Arellano-Balderas Salvador , Kucherenko Valeri V.
Published: March 2003

A new asymptotic method is proposed for calculation of spectral series and corresponding asymptotic eigenfunctions for the spinless N particle Schrödinger equation when N tends to infinitum but the physical parameters and the volume are fixed (dense matter case).
Upper and lower limits for the number of S-wave bound states in an attractive potential
Authors: Brau Fabian , Calogero Francesco
Published: March 2003

New upper and lower limits are given for the number of S-wave bound states yielded by an attractive (monotonic) potential in the context of the Schrödinger or Klein–Gordon equation.
Effective mass of atom and the excitation spectrum in liquid helium-4 at T=0 K
Authors: Rovenchak A. A.
Published: March 2003

A self-consistent approach is applied for calculations within the two-time temperature Green function formalism in the random phase approximation for superfluid He4. The effective mass of the He4 atom is computed as m*=1.58m. The excitation spectrum is found to be in satisfactory agreement with experiment. The sound velocity is calculated as 230 m/s. The Bose-condensation temperature with the effective mass taken into consideration is estimated as 1.99 K.
ab-plane tunneling and Andreev spectroscopy of the superconducting gap and pseudogap in (Bi,Pb)2Sr2Ca2Cu3O10+δ and Bi2Sr2CaCu2O8+δ
Authors: D’yachenko A. I. , Tarenkov V. Yu. , Szymczak R. , Szymczak H. , Abal’oshev A. V. , Lewandowski S. J. , Leonyuk L.
Published: March 2003

We have measured the temperature dependence of gap features revealed by Andreev reflection (Δs) and by tunneling (Δ) in the ab plane of optimally and slightly overdoped microcrystals of (BiPb)2Sr2Ca2Cu3O10+δ (Bi2223) with critical temperature Tc=110–115 K, and Bi2Sr2CaCu2O8+δ (Bi2212) with Tc=80–84 K. The tunneling conductance of a Bi2223-insulator-Bi2223 junction shows peaks at the 2Δ gap voltage, as well as dips and broad humps at other voltages. In Bi2223, similarly to the well-known Bi2212 spectra, the energies corresponding to 2Δ, to the dip, and to the hump structure are in the ratio 2:3:4. This confirms that the dip and hump features are generic to the high-temperature superconductors, irrespective of the number of CuO2 layers or the BiO superstructure. On the other hand, in both compounds the Δ(T) and Δs(T) dependences are completely different, and we conclude that the two entities are of different natures.
One-dimensional model of a vortex in an easy-plane ferromagnet
Authors: Kovalev A. S. , Prilepsky J. E.
Published: March 2003

A simple one-dimensional model of a ferromagnet in a vortex configuration is proposed for qualitative description of the structure and dynamics of a vortex in a two-dimensional magnetic system. The model describes a system of four parallel spin chains with single-ion anisotropy of the easy-plane type and includes elements of both the continuum (along the chains) and discrete (perpendicular to the chains) descriptions. An analytical study is made of the static vortices and moving vortex solutions of stationary profile. The analytical results of a calculation of the static structure of the vortices are supplemented by a numerical analysis for the analogous discrete systems and are in good agreement with the numerical data. The approach is generalized to the case of the description of gyrotropic motion of vortices of stationary profile in the framework of the collective variables method for the combined continuum–discrete description. The results are analyzed and compared with the data for two-dimensional magnets.
High-Tc rf SQUID for magnetic microscopy
Authors: Khvostov S. S. , Timofeev V. P. , Garbuz A. S. , Shnyrkov V. I.
Published: March 2003

The spectral density of magnetic flux noise SΦ1/2(f ) is investigated for high-Tc rf SQUIDs with a pumping frequency of 390–457 MHz, placed inside three-layer Permalloy and superconducting shields. A superconducting interferometer with inner dimensions of the pickup loop of 100×100 μm is prepared by thin-film technology with a YBaCuO–PrBaCuO–YBaCuO Josephson junction of the ramp-edge type. It is shown that with the use of a cooled preamplifier, the energy sensitivity of SQUIDs in the “white” noise region (at frequencies above 1 kHz) is 4×10−30 J/Hz and is mainly determined by the intrinsic noise of the high-Tc superconducting interferometer and the shields. At low frequencies the predominant noise is from external fields penetrating directly into the shields. The addition of a ferromagnetic antenna to the SQUID microscope increases the intrinsic noise of the magnetometer to 8×10−30 J/Hz at frequencies above 1 kHz.
Detection of nuclear spin conversion of CD4 molecules in a solid solution of deuteromethane in krypton
Authors: Bagatskiı̆ M. I. , Manzheliı̆ V. G. , Mashchenko D. A. , Dudkin V. V.
Published: March 2003

The heat capacity of the solid solutions (CD4)0.05Kr0.95 and (CD4)0.05Kr0.948(O2)0.002 are investigated in the temperature interval 0.7–1.6 K. The contribution to the heat capacity of the solutions from the rotational subsystem is separated out. Conversion between the A and T nuclear spin species of CD4 is detected. It is shown that in unconcentrated solutions of methane isotopes in krypton the rate of conversion is larger for the deuteromethane molecules than for the methane molecules.
The character of transport caused by E×B drift turbulence
Authors: Scott B.
Published: March 2003

The basic character of diffusive transport in a magnetized plasma depends on what kind of transport is modeled. E×B turbulence under drift ordering has special characteristics: it is nearly incompressible, and it cannot lead to magnetic flux diffusion if it is electrostatic. The E×B velocity is also related to the Poynting energy flux. Under quasineutral dynamics, electric fields are not caused by transport of electric charge but by the requirement that the total current is divergence free. Consequences for well constructed computational transport models are discussed in the context of a general mean field analysis, which also yields several anomalous transfer mechanisms not normally considered by current models.
The analytical energy gradient scheme in the Gaussian based Hartree–Fock and density functional theory for two-dimensional systems using the fast multipole method
Authors: Tobita Motoi , Hirata So , Bartlett Rodney J.
Published: March 2003

The analytical total energy gradient scheme for the Hartree–Fock and density functional crystalline orbital theory is formulated for infinitely extended periodic systems of general dimensions and implemented for those of two dimensions. Two major differences between the analytical gradient scheme for extended systems and that for molecular systems are described in detail. The first is the treatment of the long-range Coulomb interactions, which arise due to the infinite nature of the system size. The long-range effect is efficiently included by the multipole expansion technique and its extension, the fast multipole method. The use of the fast multipole method enables us to include the long-range effect up to the order of micrometer to millimeter region around the reference unit cell by virtue of the logarithmic cost scaling of the algorithm achieved by regrouping distant multipoles together and reducing the number of pairwise interactions. The second is the formulation of analytical gradient expressions with respect to unit cell parameters. In HF theory they can be calculated by accumulating forces acting on atoms multiplied by some appropriate factors, while there is an extra term which requires a special numerical treatment in grid-based density functional theory. Specifically, it is shown that the quadrature weight derivatives do not vanish even in the limit of infinitely fine grid when calculating the gradients with respect to unit cell parameters, and are essential in evaluating those gradients. Combining the analytical gradient scheme and an efficient inclusion of the long-range interaction makes it feasible to perform a full geometry optimization of extended systems at ab initio levels. As an illustration, the long-range interaction energies are computed for a two-dimensional sheet of hydrogen-fluoride. The CPU time reduction on going from the explicit evaluation of the two-electron integrals to multipole expansion, and from the multipole expansion to fast multipole method is significant. Geometry optimizations are performed on an infinite two-dimensional hexagonal boron-nitride sheet and the dependence of the gradients on various parameters are investigated.
Response to “Comment on ‘One-dimensional model of the plasma flow in a Hall thruster’ ” [Phys. Plasmas 10, 1172 (2003)]
Authors: Ahedo E. , Martı́nez-Sánchez M.
Published: March 2003

There is no missing term in the reduced equation for the density. The controversy comes from an error on the original paper in the equation for the electron temperature, but the subsequent equations and calculations were based on the correct equation. A minor error in a figure is accepted.
Dust acoustic shock wave at high dust density
Authors: Ghosh Samiran , Sarkar Susmita , Khan Manoranjan , Avinash K. , Gupta M. R.
Published: March 2003

Dust acoustic (DA) shock wave at high dust density, i.e., the dust electroacoustic (DEA) or dust Coulomb (DC) shock wave has been investigated incorporating the nonadiabatic dust charge variation. The nonlinear DEA (DC) shock wave is seen to be governed by the Korteweg–de Vries Burger equation, in which the Burger term is proportional to the nonadiabaticity generated dissipation. It is seen that the shock strength decreases but after reaching minimum, it increases as the dust space charge density |qdnd| increases and the shock strength of DA wave is greater than that of DEA (DC) wave. Moreover the DEA (DC) shock width increases appreciably with increase mass mi of the ion component of the dusty plasma but for DA shock wave the effect is weak.
Density profile control with current ramping in a transport simulation of IGNITOR
Authors: Hu B. , Horton W. , Zhu P. , Porcelli F.
Published: March 2003

Current ramping to achieve reversed shear confinement enhancement and peaked density profiles are important for achieving ignition conditions in the high-field tokamak IGNITOR [Coppi et al., Phys. Scri. 45, 112 (1992)]. Previous transport simulations used either fixed density profiles or obtained flat density profiles leading to a conclusion that a mechanism for peaking the density profile is required for ignition. In this paper an enhanced particle confinement regime that produces ignition before the sawtooth activity begins is explored. It is shown that fast current ramping is a general scheme leading to density profile peaking. In these simulations, peaked density profiles result from the formation of internal transport barrier due to reversed magnetic shear, which is produced by controlled plasma current and volume-averaged density ramping. Such a programmed Ohmic heating scheme is demonstrated to be an effective approach to achieve ignition of a deuterium-tritium plasma.
Hydrogen bonding in solid ammonia from ab initio calculations
Authors: Fortes A. D. , Brodholt J. P. , Wood I. G. , Vočadlo L.
Published: March 2003

We have carried out ab initio simulations on the ambient pressure phase I of solid ammonia, and on the high-pressure phase IV. Our plane-wave pseudopotential calculations yield very good agreement with existing structural data, lattice energies, and equations of state. We have also studied the tendency toward symmetrization of the hydrogen bonds at high pressures and find that, unlike pure ice, this process should not occur at experimentally achievable pressures, i.e., <300 GPa. Moreover, our results show that ammonia IV does not contain a bifurcated hydrogen bond, as has previously been suggested.
Legendre transformation and analytical mechanics: A geometric approach
Authors: Massa Enrico , Pagani Enrico , Vignolo Stefano
Published: March 2003

A revisitation of the Legendre transformation in the context of affine principal bundles is presented. The argument, merged with the gauge-theoretical considerations developed by Massa et al., provides a unified representation of Lagrangian and Hamiltonian mechanics, extending to arbitrary nonautonomous systems the symplectic approach of Tulczyjew.
Nitride-mediated epitaxy of CoSi2 on Si(001)
Authors: Chong R. K. K. , Yeadon M. , Choi W. K. , Stach E. A. , Boothroyd C. B.
Published: March 2003

Epitaxial layers of CoSi2 have been grown on Si(100) by the technique of nitride-mediated epitaxy. An ultrathin layer of silicon nitride was formed on the Si(001) surface by exposure to ammonia gas at 900 °C, followed by the deposition of a layer of Co ∼20 Å in thickness at room temperature. The sample was then annealed at 600 °C and the microstructure monitored by in situ transmission electron microscopy and diffraction. The formation of epitaxial islands of CoSi2 was observed directly, with no evidence of the formation of intermediate phases. The CoSi2 islands were found to be elongated along the in-plane Si〈110〉 directions, consistent with reports of the deposition of Co by molecular beam epitaxy on clean Si(100) at low deposition rates and elevated temperature. This technique of silicidation may be of particular interest in the fabrication of advanced devices incorporating multilayer oxide/nitride gate stacks.
Quantum soliton dynamics in vibrational chains: Comparison of fully correlated, mean field, and classical dynamics
Authors: Neuhauser Daniel , Baer Roi , Kosloff Ronnie
Published: March 2003

The dynamics of a chain of vibrational bonds which develop a classical solitary compression wave is simulated. A converged fully correlated quantum mechanical calculation is compared with a time dependent mean field approach (TDSCF) and with a classical simulation. The dynamics were all generated from the same Hamiltonian. The TDSCF and classical calculations show a fully developed solitary wave with the expected dependence of group velocity on amplitude. The full quantum calculations show a solitary-like wave which propagates for a while but then degrades. The robustness of the compression wave depends on the initial preparation. Evidence of partial recurrence of the wave has also been observed.
Critical behaviors of the sound attenuation in a spin-1 Ising model
Authors: Keskin Mustafa , Erdem Riza
Published: March 2003

Critical behaviors of the sound attenuation in a spin-1 Ising system with bilinear (J) and biquadratic (K) interactions are investigated within the framework of cluster variation method and Onsager theory of irreversible thermodynamics. The sound wave is assumed to couple mainly to the order parameter fluctuations which decay via order parameter relaxation processes. Two relaxation times are obtained and an expression is found for the sound attenuation coefficient (α) in terms of these relaxation times. The temperature behavior of the sound attenuation near the phase transition temperatures (Tc) is analyzed according to various values of Onsager coefficients (γij) and sound frequency (ω). For TTc the data give evidence that there is no relaxational contribution to sound attenuation coming from order parameter fluctuations. On the other hand, a convergence is found in attenuation just below the critical and the tricritical points as (Tc−T), while a jump-discontinuity is observed for the first-order behavior. The frequency variation of the sound attenuation is also investigated and in addition to ω2-attenuation dependence observed in the hydrodynamic regime it is observed that in the high frequency region the attenuation is independent of ω and the ratio of two interaction parameters (J/K).
Equilibrium free energies from path sampling of nonequilibrium trajectories
Authors: Sun Sean X.
Published: March 2003

Jarzynski’s relation between equilibrium free energy and nonequilibrium work is rewritten as an average of work with respect to a work weighted ensemble. The present form is more appropriate for computer application of Jarzynski’s relation where the dissipative work is frequently much greater than kBT. Monte Carlo sampling of very short nonequilibrium trajectories yields good estimates of the equilibrium free energy change. The procedure can be thought of as a generalization of thermodynamic integration in ordinary free energy calculations. Very short trajectories can be used to compute the free energy difference. In the infinitely short trajectory limit, we recover the thermodynamic integration scheme. We also show that free energy estimate can be obtained from moments of the work distribution. The last result is most useful for experimental measurements of the free energy.
Pair-correlated coupled cluster theory: An alternative multireference coupled cluster method
Authors: Li Shuhua , Ma Jing , Jiang Yuansheng
Published: March 2003

We describe an alternative multireference coupled cluster (MRCC) method, pair-correlated coupled cluster (PCCC) theory, for treating the ground state of closed-shell systems with degeneracy or quasidegeneracy. With the separated electron pair (SEP) wave function as a reference, the PCCC wave function is truncated according to how many electron pairs are explicitly correlated. The inclusion of only two-pair correlation defines the PCCC2 scheme, and the inclusion of up to three-pair correlation gives the PCCC3 scheme. The PCCC theory is well defined within the natural orbital (of the SEP reference) description and size extensive. We present the formalism of the PCCC theory by taking the PCCC2 scheme as an example, and implement the PCCC2 and PCCC3 schemes at the ab initio level with various basis sets. Then illustrative applications are presented for systems such as the perpendicular insertion reaction path of Be into H2, the simultaneous bond stretching in AlH3 and H2O. The results show that the overall performance of PCCC methods is competitive to that of the RCCSD(T) or UCCSD(T) method at stretched geometries, but slightly inferior to that of the CCSD(T) method at the equilibrium geometry.
Interionic potentials from ab initio molecular dynamics: The alkaline earth oxides CaO, SrO, and BaO
Authors: Aguado Andrés , Bernasconi Leonardo , Madden Paul A.
Published: March 2003

Transferable potential models of interatomic interactions in CaO, SrO, and BaO are obtained by fitting the forces and stress tensor given by the aspherical ion model (AIM) [J. Chem. Phys. 108, 10209 (1998)] to those obtained from the ab initio molecular dynamics code CASTEP on condensed phase ion configurations generated at different values of pressure, temperature, and coordination environment. The AIM allows for dipole and quadrupole polarization of the ions as well as for ion-shape deformation due to short-range interactions. The potentials produce thermal expansivities, elastic properties, and phonon dispersion curves of these materials in excellent agreement with experiment. The BaO potential is also found to reproduce the complicated pressure-driven phase transitions observed in experiments on this material, even though these structures were not represented in the fitting procedure. The fitting process shows the increasing significance of cation polarization and shape deformation for the interionic interactions on descending the alkaline earth group, and this becomes an essential feature to account for the stability of the observed high-pressure phases of BaO.
Density-functional theory studies of xanthate adsorption on the pyrite FeS2(110) and (111) surfaces
Authors: Hung Andrew , Yarovsky Irene , Russo Salvy P.
Published: March 2003

We have used the density functional theory (DFT) method with a plane wave-pseudopotential basis to compute the structure and properties of a model xanthate molecule (HOCS2−) and its adsorption characteristics on the pyrite FeS2(110) and (111) surfaces. Molecular calculations revealed that HOCS2− and CH3CH2OCS2− have similar head group electronic structure and, therefore, the use of the model xanthate is a justifiable approximation in simulations of xanthate head group attachment to FeS2 surfaces. Results from DFT calculations suggest that HOCS2− readily undergoes dissociation at the fourfold coordinated surface Fe on the (110) surface, and the bridging S of the (111) surface. These results suggest that xanthate may undergo chemisorption at defect sites on real FeS2 surfaces, which contain low-coordinate Fe sites and sites in proximity to cleaved S–S bonds.
Multiresolution analysis generated by a seed function
Authors: Bagarello F.
Published: March 2003

In this paper we use the equivalence result originally proved by the author, which relates a multiresolution analysis (MRA) of L2(R) and an orthonormal set of single electron wave functions in the lowest Landau level, to build up a procedure which produces, starting with a certain square-integrable function, a MRA of L2(R).
Positive measure spectrum for Schrödinger operators with periodic magnetic fields
Authors: Gruber Michael J.
Published: March 2003

We study Schrödinger operators with periodic magnetic field in R2, in the case of irrational magnetic flux. Positive measure Cantor spectrum is generically expected in the presence of an electric potential. We show that, even without electric potential, the spectrum has positive measure if the magnetic field is a perturbation of a constant one.
Absolute cross sections for electron-impact ionization of N2O, H2S, and CS2 from threshold to 1000 eV
Authors: Lindsay B. G. , Rejoub R. , Stebbings R. F.
Published: March 2003

Absolute partial and total cross sections for electron-impact ionization of N2O, H2S, and CS2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of N2O+, N2+, NO+, N+, and O+ from N2O; for production of (H2S++HS++S+) and H+ from H2S; and for production of CS2+, S2+, CS+, S+, C+, and CS22+ from CS2. The total cross sections are obtained as the sum of these partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly-charged ions is ±6–8%. For all three targets the cross sections for production of lighter fragment ions are found to be greater than previously reported which is consistent with the presumption of incomplete collection of energetic ions in the earlier studies. Agreement with recent theoretical calculations is satisfactory for N2O but not for H2S or CS2.
Semiclassical estimation of Franck–Condon factors and transition rates for vertical and nonvertical transitions
Authors: Sergeev A. V. , Segev Bilha
Published: March 2003

We develop a systematic way for estimating multidimensional Franck–Condon factors and transition rates for vertical and nonvertical transitions. By analyzing the phase-space overlap integral, we find the most probable positions and momenta of the nuclei immediately after the electronic transition. We find the transition rate by treating the dominant region in phase space as a funnel for the transition and by calculating the flow of probability through this funnel. We use the Wigner representation and its semiclassical limit and find that the transition occurs through a point(s) on the final surface of constant energy where the initial Wigner function is maximal. This dominant contribution is estimated analytically. Results are illustrated for Harmonic, Morse and Poeschl–Teller oscillators.
Diffusive relaxation processes and low-frequency dynamical properties in bulk and confined ethylene glycol by neutron spectroscopy
Authors: Crupi V. , Majolino D. , Migliardo P. , Venuti V.
Published: March 2003

In this work, we report on a detailed study of the diffusional and vibrational dynamics of liquid ethylene glycol (EG: HO–CH2CH2–OH) in the bulk state and confined in a matrix of sol-gel porous glass with 26 Å interconnected cylindrical pores. The investigation is performed, by incoherent quasielastic and inelastic neutron scattering (IQENS and IINS), as a function of temperature. IQENS data have been definitively interpreted in terms of the α-relaxation dynamics predicted by mode coupling theory for supercooled liquids. We verified that a description by means of an Havriliak–Negami profile is consistent with the measured spectral line shape. Furthermore, IINS spectra show a clear different evolution versus T of the vibrational density of states, Z(ω), passing from the bulk samples to the confined ones, revealing, in particular, a thermal stabilization of the disordered longitudinal acoustic mode induced by interaction of EG molecules with the active silanol (Si–OH) groups of the surface.
A new technique to optimize the coil winding path for the arbitrarily distributed magnetic field and application to a helical confinement system
Authors: Abe Mitsushi , Nakayama Takeshi , Okamura Shoichi , Matsuoka Keisuke
Published: March 2003

A new technique to calculate the optimum modular coil winding path for a helical plasma confinement system has been developed. The technique is based on current potential on an arbitrary surface with finite elements and singular value decomposition (SVD). No function is assumed for the current potential distribution, and then, little error occurs from modeling. The SVD is applied to the response matrix from the current potential to the magnetic field on the plasma surface. The current distribution is constructed from an eigen distribution obtained through SVD so that the normal field component is small. The coil winding path is determined along the flow lines or equi-contour lines of current potential. The current on the obtained coil winding path was confirmed able to generate good magnetic surfaces.
Structure effects on the energetic, electronic, and magnetic properties of palladium nanoparticles
Authors: Zhang Wenqin , Ge Qingfeng , Wang Lichang
Published: March 2003

A systematic investigation of palladium nanoparticles of up to 55 atoms (1.4 nm) has been conducted using density functional theory with a plane wave basis set. The stability of these nanoparticles increases with cluster size and dimensionality. It also depends strongly on the cluster structures through two factors, the coordination numbers of atoms and the strength of the single bonds. Both the energy gap between the highest occupied and the lowest unoccupied molecular orbitals and the magnetic moment change oscillatorily with cluster size. Furthermore, highly magnetic clusters tend to have large energy gaps. Analysis of the atom-resolved magnetic moment reveals that the local magnetism of a cluster depends mainly on the atomic bonding environments. A simple approach is proposed to predict relative stabilities of various structures for larger clusters. In addition, a structure factor is defined to correlate quantitatively various properties of the Pd clusters with their structures.
On the asymptotic distribution of the commutator and anticommutator of random matrices
Authors: Vasilchuk V.
Published: March 2003

We study in the limit of infinite matrix order the normalized eigenvalue counting measures of the commutator and anticommutator of two Hermitian (or real symmetric) matrices rotated independently one respect to another by the random unitary (or orthogonal) Haar distributed matrix. We establish the convergence with probability 1 to a limiting nonrandom measure. We obtain and analyze the functional equations for the Stieltjes transforms of the limiting measures.
Boundary behavior of quantum Green’s functions
Authors: Šamaj L. , Percus J. K. , Kalinay P.
Published: March 2003

We consider the time-independent Green’s function for the Schrödinger operator with a one-particle potential, defined in a d-dimensional domain. Recently, in one dimension (1D), the Green’s function problem was solved explicitly in inverse form, with diagonal elements of the Green’s function as prescribed variables. In this article, the 1D inverse solution is used to derive leading behavior of the Green’s function close to the domain boundary. The emphasis is put onto “universal” expansion terms which are dominated by the boundary and do not depend on the particular shape of the applied potential. The inverse formalism is extended to higher dimensions, especially to 3D, and subsequently the boundary form of the Green’s function is predicted for an arbitrarily shaped domain boundary.
The internal kink mode in an anisotropic flowing plasma with application to modeling neutral beam injected sawtoothing discharges
Authors: Graves J. P. , Sauter O. , Gorelenkov N. N.
Published: March 2003

For some time it has not been clear to what extent neutral injected beam ions have a stabilizing influence on sawteeth. To investigate this, the well known toroidal internal kink instability is generalized to account for weakly anisotropic and flowing equilibria. An analytical approach is proposed, which upon employing an appropriate model distribution function, accurately accounts for the hot ion response of neutral beam injection (NBI) to the internal kink mode. Large fluid contributions, which are expected to arise as a consequence of the anisotropic velocity deposition of NBI, are identified and shown to be stabilizing to the internal kink mode for populations with large passing fractions. In particular for tangential injection, such as that employed in the Joint European Torus [J. Wesson, Tokamaks, 2nd ed. (Oxford Science, Oxford, 1997), p. 581], it is found that fast ion stabilization can be dominated by anisotropic fluid effects rather than kinetic effects. In contrast, for predominantly trapped populations, the anisotropic fluid effects are destabilizing and thus reduce the stabilizing role of fast ions. This is especially evident for cases where the subsonic sheared toroidal plasma rotation induced by unbalanced NBI reduces kinetic stabilization. Sheared plasma rotation orientated either co or counter to the plasma current can reduce fast ion stabilization, but counter-rotation has the greatest effect by impeding the conservation of the third adiabatic invariant.
General relations between radial integrals in nonrelativistic and relativistic calculation schemes
Authors: Jonauskas V. , Karazija R.
Published: March 2003

Using the equivalent relativistic operator and the correspondence of its terms to the operators in the Breit–Pauli approximation the relativistic analogs for the integrals of Coulomb, spin–contact, spin–orbit, spin–spin and other interactions are obtained. They give the possibility to take into account not only direct but also indirect relativistic effects by performing the calculations of atomic structure with existing general programs in a nonrelativistic scheme with relativistic Breit–Pauli corrections.
Multiple algebraisations of an elliptic Calogero–Sutherland model
Authors: Brihaye Yves , Hartmann Betti
Published: March 2003

Recently, Gómez-Ullate et al. [Phys. Lett. B 511, 112 (2001)] have studied an N-particle quantum problem with elliptic-function potentials. They have shown that the Hamiltonian operator preserves a finite dimensional space of functions and as such is quasi-exactly solvable (QES). In this article we show that other types of invariant function spaces exist, which are in close relation to the algebraic properties of the elliptic functions. Accordingly, series of new algebraic eigenfunctions can be constructed.
The dynamics of electron–ion coupling in the shock transition region
Authors: Shimada Nobue , Hoshino Masahiro
Published: March 2003

In the shock transition region the process of electron–ion coupling under Buneman instability between inflow electrons and reflected ions is investigated. Buneman instability often evolves into a highly nonlinear state with strong wave–particle interaction like velocity phase hole (vortex) dynamics. Previous studies have shown that these electron holes contribute to the strong electron heating and acceleration. In this study, how electron holes affect the ions and interact with them is examined. Under the condition of Buneman instability dominant, the electron holes preserve their coherent large-amplitude structure for a sufficiently long period of time to modify the ion population electrostatically. Electron holes resonate with the ion population through the ion-acoustic branch, and then some of the inflow ions are rapidly decelerated and reflected by the electric field at the electron holes. As a result of gaining additional energy from the inflow ion population, the amplitude of the electric field of the hole becomes 40% larger than what was estimated in some previous studies, which did not take the coupling ions into account. Although the electron hole–ion coupling state is seen in such a small scale as electron inertia length (c/ωpe), this large electric field of the electron hole leads to a strong disturbance and heating of the plasma. This study may provide a first indication of what regulates strong electron heating in the shock transition region through the coupling process between the electrons and ions .
𝒩-point and higher-genus osp(1|2) fusion
Authors: Rasmussen Jørgen
Published: March 2003

We study affine osp(1|2) fusion, the fusion in osp(1|2) conformal field theory, for example. Higher-point and higher-genus fusion is discussed. The fusion multiplicities are characterized as discretized volumes of certain convex polytopes, and are written explicitly as multiple sums measuring those volumes. We extend recent methods developed to treat affine su(2) fusion. They are based on the concept of generalized Berenstein–Zelevinsky triangles and virtual couplings. Higher-point tensor products of finite-dimensional irreducible osp(1|2) representations are also considered. The associated multiplicities are computed and written as multiple sums.
Integrability of Kersten–Krasil’shchik coupled KdV–mKdV equations: singularity analysis and Lax pair
Authors: Kalkanli Ayşe Karasu , Sakovich Sergei Yu. , Yurduşen Ísmet
Published: March 2003

The integrability of a coupled KdV–mKdV system is tested by means of singularity analysis. The true Lax pair associated with this system is obtained by the use of prolongation technique.
Enhanced electron–ion energy exchange due to a super-Gaussian electron velocity distribution function
Authors: Bibi F. Alouani , Matte J.-P.
Published: March 2003

An analytical description of electron–ion energy exchange in plasmas in which the electron velocity distribution is super-Gaussian due to heating by a strong laser field is presented. The ion to electron temperature ratio at which collisional electron–ion energy exchange cancels increases from 1 in a Maxwellian plasma to 1.98 in a strongly super-Gaussian plasma. Numerical examples illustrating this dependence in nonequilibrium laser heated plasmas are presented.
Comment on “Parallel electric fields in the upward current region of the aurora: Numerical solutions” [Phys. Plasmas 9, 3695 (2002)]
Authors: Lennartsson O. W.
Published: March 2003

In a recent paper Ergun et al. [Phys. Plasmas 9, 3695 (2002)] endeavor to obtain realistic one-dimensional numerical solutions of the Vlasov–Poisson equations for an oblique strong double layer in the space environment, given a set of data based constraints. Here it is argued that their numerical methods are overly simplified and that a fully dynamic, multidimensional analysis is needed even for the lowest-order solution.
Total variation in Hamiltonian formalism and symplectic-energy integrators
Authors: Chen Jing-Bo , Guo Han-Ying , Wu Ke
Published: March 2003

We present a discrete total variation calculus in Hamiltonian formalism in this paper. Using this discrete variation calculus and generating functions for the flows of Hamiltonian systems, we derive symplectic-energy integrators of any finite order for Hamiltonian systems from a variational perspective. The relationship between the symplectic integrators derived directly from the Hamiltonian systems and the variationally derived symplectic-energy integrators is explored.
An investigation of entanglement and quasiprobability distribution in a generalized Jaynes-Cummings model
Authors: Abdel-Aty Mahmoud
Published: March 2003

In this paper, we consider a unified approach to study the degree of entanglement of two-level systems interacting with a quantized electromagnetic field. We investigate a range of parameters in a generalized Jaynes–Cummings model (JC-model) with intensity-dependent, field nonlinearity and nonresonant coupling. In terms of the density matrix and without the diagonal approximation we derive an explicit expression for the entanglement degree using a function analogous to mutual entropy. This notion is inspired by the fact that the quantum state may be interpreted as a measure of information. With the aid of the quasiprobability distribution function, the statistical properties of the field are analyzed. It is shown that when the atom is initially in its upper-level and the one-photon at resonance, the Q-function splits into two peaks and counter rotate in phase space.
The effect of plasma shielding on dust particle interaction in low pressure plasmas
Authors: Markes M. E. , Williams P. F.
Published: March 2003

The interaction of charged dust particles in plasma is often modeled assuming a constant charge on each particle with the particle charge determined by requiring zero net current to the particles when they are far apart. In this paper the variation in particle charge is calculated for two-body encounters of dust particles taking into consideration mutual electrostatic shielding and a finite Debye length λD. Results are reported for particle radii between 0.0105λD and 0.349λD. Work is also calculated as a function of particle separation, and it is shown that dust particle energies greater than 50 eV are required before the variation in charge becomes significant. It is also demonstrated that for particles with radii greater than λD/10 the plasma can act to increase the force at separations less than 3λD, and it is shown that the Debye–Hückel factor (1+a/λD) may overestimate particle charge by as much as ten percent for larger particles.
Modes in a non-neutral plasma of finite length, m=0,1
Authors: Rasband S. Neil , Spencer Ross L.
Published: March 2003

For realistic, cold equilibria of finite length representing a pure electron plasma confined in a cylindrical Malmberg–Penning trap, the mode spectrum for Trivelpiece–Gould, m=0, and for diocotron, m=1, modes is calculated numerically. A novel method involving finite elements is used to successfully compute eigenfrequencies and eigenfunctions for plasma equilibria shaped like pancakes, cigars, long cylinders, and all things in between. Mostly sharp-boundary density configurations are considered but also included in this study are diffuse density profiles including ones with peaks off axis leading to instabilities. In all cases the focus has been on elucidating the role of finite length in determining mode frequencies and shapes. For m=0 accurate eigenfrequencies are tabulated and their dependence on mode number and aspect ratio is computed. For m=1 it is found that the eigenfrequencies are 2% to 3% higher than given by the Fine–Driscoll formula [Phys. Plasmas 5, 601 (1998)]. The “new modes” of Hilsabeck and O’Neil [Phys. Plasmas 8, 407 (2001)] are identified as Dubin modes. For hollow profiles finite length in cold-fluid can account for up to ∼70% of the theoretical instability growth rate.
Stimulated scattering and harmonic generation from relativistically intense laser light in plasma
Authors: Barr H. C. , Hill L. J.
Published: March 2003

A concise general dispersion relation is found to describe electron parametric instabilities driven by relativistically intense circularly polarized laser light in plasma. It is valid for densities from rarefied plasma up to overdense regions accessible by self-induced transparency due to the relativistic electron mass increase. In the form of a fourth order scalar difference equation, it describes stimulated harmonic generation as well as stimulated Raman scattering, the relativistic modulational and filamentation instabilities, and the two-plasmon decay. It is also related to analytic results for stimulated harmonic generation from rarefied plasma and to synchrotron radiation from single electrons.
Asymptotic expansion of the quasiconfluent hypergeometric function
Authors: Abad J. , Sesma J.
Published: March 2003

The asymptotic expansion of the hypergeometric function F12(a,b;c;z/b) in the case of quasiconfluence, i.e., for |b|→∞, is revised. A very simple expansion, in terms of a semiasymptotic sequence of polynomials, is presented. Some properties of those polynomials are discussed.
Spatially-resolved nonlinearity measurements of YBa2Cu3O7−δ bicrystal grain boundaries
Authors: Lee Sheng-Chiang , Anlage Steven M.
Published: March 2003

We have developed a near-field microwave microscope to locally excite a superconducting film and measure second- and third-order harmonic responses at microwave frequencies. We study the local nonlinear response of a YBa2Cu3O7−δ thin film grown on a bicrystal SrTiO3 substrate. The location of the bicrystal grain boundary is clearly identified by the microscope through higher harmonic response, and the spatial resolution is on the order of the magnetic loop diameter, about 500μm. The harmonic power and spatial resolution are modeled with a one-dimensional extended Josephson junction simulation. From the model, the second-order harmonic response is dominated by Josephson vortex generation and flow. A geometry-free nonlinear scaling current density JNL≅104∼105 A/cm2 is also extracted from the data, indicating that the grain boundary weak link is the dominant nonlinear source in this case.
Confinement-enhanced biexciton binding energy in ZnO/ZnMgO multiple quantum wells
Authors: Chia C. H. , Makino T. , Tamura K. , Segawa Y. , Kawasaki M. , Ohtomo A. , Koinuma H.
Published: March 2003

By employing a nanosecond pump-probe method, biexciton formation process was investigated in ZnO/Zn1−xMgxO (x=0.26) multiple quantum wells (MQWs) grown on ScAlMgO4 substrate by laser molecular-beam epitaxy. Bleaching of absorption due to the saturation of excitonic states, and induced absorption related to the exciton–biexciton transition were observed in their spectra. It is demonstrated that the pump-probe method allows us to precisely determine binding energies of exciton complexes even applied to the semiconductor quantum structures where the localization effect are not negligible. This is because a transition from free-excitonic states to free-biexcitonic states is involved in the induced absorption process. The biexciton binding energy is a monotonically decreasing function of well width (Lw). For the MQWs with Lw smaller than 2.5 nm, the biexciton binding energy is larger than 25 meV, comparable to the thermal energy of room temperature.
Surface segregation of boron in BxGa1−xAs/GaAs epilayers studied by x-ray photoelectron spectroscopy and atomic force microscopy
Authors: Dumont H. , Rutzinger D. , Vincent C. , Dazord J. , Monteil Y. , Alexandre F. , Gentner J. L.
Published: March 2003

The behavior of boron incorporation into GaAs has been studied by x-ray photoelectron spectroscopy, x-ray diffraction, and atomic force microscopy. As the boron content of the film was increased, both the characteristic peak for the B 1s core level at 188 eV and As Auger transition (260 eV) could be detected by XPS. At 550–600 °C, single crystalline films could only be grown for x⩽0.06. Upon increasing the diborane flux in the gas phase, the film stoichiometry and the boron surface composition evolved rapidly towards a boron-rich subarsenide compound. This trend is followed by a clear degradation of the surface morphology and an increase in the surface roughness. A surface segregation of boron is suggested due to the high diborane vapor supersaturation needed during growth.
Radiation hardness of InGaAs/GaAs quantum dots
Authors: Guffarth F. , Heitz R. , Geller M. , Kapteyn C. , Born H. , Sellin R. , Hoffmann A. , Bimberg D. , Sobolev N. A. , Carmo M. C.
Published: March 2003

The interaction between point defects in the matrix and excitons localized in self-organized InGaAs/GaAs quantum dots is investigated for structures irradiated by protons. The exciton ground state is demonstrated to be unaffected by radiation doses up to 1014 p/cm2. The close proximity of radiation-induced defects leads to a strong nonmonotonous temperature dependence of the luminescence yield: Carriers are lost via tunneling from excited quantum dot states to irradiation-induced defects below ∼100 K, whereas at higher temperatures, carriers escape to the barrier and are captured by defects.
Annealing of isolated amorphous zones in silicon
Authors: Donnelly S. E. , Birtcher R. C. , Vishnyakov V. M. , Carter G.
Published: March 2003

In situ transmission electron microscopy has been used to observe the production and annealing of individual amorphous zones in silicon resulting from impacts of 200-keV Xe ions at room temperature. As has been observed previously, the total amorphous volume fraction decreases over a temperature range from room temperature to approximately 500 °C. When individual amorphous zones were monitored, however, there appeared to be no correlation of the annealing temperature with initial size: zones with similar starting sizes disappeared (crystallized) at temperatures anywhere from 70 °C to more than 400 °C. Frame-by-frame analysis of video recordings revealed that the recovery of individual zones is a two-step process that occurred in a stepwise manner with changes taking place over seconds, separated by longer periods of stability.