bluuebunny/crossref_metadata_2025 huggingface dataset:
A new table-direct configuration interaction method for the evaluation of Hamiltonian matrix elements in a basis of linear combinations of spin-adapted functions
Authors: Krebs Stefan , Buenker Robert J.
Published: July 2002

A new table-direct CI (TDCI) scheme based on the table CI method for the direct computation of Hamiltonian matrix elements whose basis functions are linear combinations of spin-adapted functions ψα is presented, in which the explicit calculation and storage of the Hamiltonian matrix H in the basis {ψα} is avoided. Two algorithms are provided for the matrix element evaluation; (i) within the iterative Davidson diagonalization procedure of H and (ii) within the individualized configuration selection scheme of Buenker and Peyerimhoff, as included in the MRD-CI program of these authors. The new algorithm is employed to compute the equilibrium structural parameters of the lowest X 2A1 and A 2B2 states of NO2, solving secular equations of dimension 190 000 spin-adapted functions (384 000 determinants, 32 000 configurations), as well as the Te value for the corresponding transition.
Dynamic structure factor of semiflexible macromolecules in dilute solution
Authors: Harnau Ludger , Winkler Roland G. , Reineker Peter
Published: July 2002

The dynamic structure factor for molecular chains with variable stiffness in a dilute solution is investigated. In the limit of small scattering vectors q only the overall translational motion of the macromolecules contributes to the dynamic structure factor. The translational diffusion coefficient D exhibits a chain length dependence D∼1/√L for flexible chains and D∼ln L/L+const/L for rodlike chains. For flexible chains there is an intermediate scattering vector regime in which the decay rate or spectral linewidth of the dynamic structure factor is proportional to q3 indicating that stretching modes are dominant. Such an intermediate scattering vector regime cannot be observed for semiflexible or rodlike chains. At large scattering vectors q/2p≳1.5, where 1/2p is the persistence length of the macromolecules, the chain stiffness becomes important for any kind of molecules, i.e., even for very flexible ones. The dynamic structure factor and the decay rate are compared with experimental results of quasielastic neutron and light scattering experiments on different natural and synthetic macromolecules. These experimental results are in good agreement with the theoretical predictions. Furthermore, we determine the persistence length of F-actin from a dynamic light scattering experiment.
On the origin of matrix elements for electronic excitation (energy) transfer
Authors: Harcourt Richard D. , Ghiggino Kenneth P. , Scholes Gregory D. , Speiser Shammai
Published: July 2002

The origin of electronic energy transfer (EET) between two chromophores (D and A) is explored further for several molecular situations that may be encountered in experiment—namely, nonoverlapping active-space orbitals of the D and A chromophores, forbidden electronic excitations for both chromophores, and an allowed and a forbidden electronic excitation for the D and A chromophores, respectively. The theory is illustrated via the results of calculations of the EET matrix elements for model systems with both four–eight active-space electrons and all of the electrons included explicitly. In each case, it is found that any overlap contribution to these matrix elements is associated much more with charge-transfer and penetration terms rather than it is with the Dexter exchange integral. The calculated magnitude of the latter integral is always smaller than that of the Coulomb integral.
Bond energy oscillation in the cluster ion NO+(NO)n
Authors: Hiraoka Kenzo , Nasu Masayuki , Oomori Daisuke , Minamitsu Akihito
Published: July 2002

The gas-phase equilibria of the clustering reaction of NO+ with NO and F− with NO were measured with a pulsed electron-beam high-pressure mass spectrometer. Van’t Hoff plots of equilibrium constants lead to the determination of the thermochemical stabilities for NO+(NO)n with n=1–10 and F−(NO)n with n=1–3. The equilibrium constants Kn−1,n for the former reaction with n=4, 6, 8, and 10 were found to be larger than Kn−2,n−1 with (n−1)=3, 5, 7, and 9, respectively. That is, the cluster ions NO+(NO)n with even n are thermochemically more stable than the smaller ones, NO+(NO)n−1, under the present experimental conditions. The measured enthalpy (−ΔH 0n−1,n) and entropy changes (−ΔS0n−1,n) show odd–even oscillation. This is due to the electron-spin pairing effect, i.e., dimer pair formation in the cluster ions. The sudden decrease in the bond energies for the cluster NO+(NO)n between n=2 and 3 suggests that the core in the cluster NO+(NO)n is NO+(NO)2. The bond energy oscillation is also likely for the negative cluster ion F−(NO)n.
Molecular dynamics study of tracer diffusion of argon adsorbed on amorphous surfaces
Authors: Riccardo J. L. , Steele W. A.
Published: July 2002

An isokinetic molecular dynamics simulation of argon adsorbed on several model amorphous surfaces of titanium dioxide is carried out. The solid is represented by the Bernal Model in which the surface is taken to be the exposed face of a dense random packing of oxide ions. This surface is roughened by deleting varying numbers of oxides at random from the outer layer of the solid. Surface diffusion in the limit of very low coverage (tracer diffusion) is evaluated by following the dynamics of noninteracting single adatoms. The diffusion coefficient in the zero-density limit is calculated from velocity autocorrelation functions for adatoms at several temperatures ranging from 85 to 300 K. The temperature dependence of the diffusion constants obtained in this way shows nearly Arrhenius behavior in this temperature range. It is shown that surface roughening at the atomic scale give rise to a higher apparent activation energy for diffusion. A statistical characterization of the adsorptive field through distributions of local maxima and minima in the adsorption energy surface along the diffusion paths was performed in order to relate the surface diffusion of monatomic species on amorphous surfaces to the recently proposed Dual Site-Bond Description of Heterogeneous Surfaces (DSBD). Independent evidence supporting the theoretical hypothesis of the DSBD is also obtained.
Proton-ordered models of ordinary ice for quantum-mechanical studies
Authors: Casassa Silvia , Ugliengo Piero , Pisani Cesare
Published: July 2002

A periodic Hartree-Fock ab initio study is presented concerning two proton-ordered structures of ordinary ice: one ferro-electric (C-ice), the other anti-ferro-electric (P-ice). The calculated energies are practically coincident, and in good agrement with the experimental stability of disordered ice Ih. Slabs are cut out from these crystals in order to formulate a model for studying the surface properties of ordinary ice. The stability of these two-dimensional periodic systems is discussed, and the relaxation of the P-ice slab formed by two bilayers parallel to the (001) face is considered. Finally, an embedded cluster method is adopted to calculate geometric and energetic properties of KOH and NaOH dissolved in C- and P-ice at low concentration. This study permits us to discuss the role of KOH in promoting the transition from disordered Ih to ordered C-ice, which has been observed to occur at 72 K [Leadbetter et al., J. Chem. Phys. 82, 424 (1985)].
Harmonic and anharmonic rate constants and transmission coefficients obtained from ab initio data
Authors: Isaacson Alan D.
Published: July 2002

Recent ab initio information of Kraka and Dunning on the reaction OH+H2→H2O+H is used to construct a potential energy surface in the vicinity of the reaction path. The resultant energy surface reproduces the ab initio reactant and product properties and provides a good fit to the ab initio data in the interaction region. Anharmonic vibrational energy levels involving the bound degrees of freedom orthogonal to the reaction coordinate are obtained using perturbation theory through second order for cubic terms and first order for quartic terms, with resonance effects removed. These energy levels are used in the calculation of transmission coefficients and thermal rate constants over the temperature range from 200 to 2400 K. The results are compared with those obtained from harmonic vibrational energy levels.
Reduced multireference couple cluster method. II. Application to potential energy surfaces of HF, F2, and H2O
Authors: Li Xiangzhu , Paldus Josef
Published: July 2002

The so-called reduced multireference (RMR) coupled cluster method restricted to singly and doubly excited clusters (CCSD) [see X. Li and J. Paldus, J. Chem. Phys. 107, 6257 (1997)] is employed to compute potential energy surfaces for the HF, F2 and H2O molecules over a wide range of geometries using basis sets of a double zeta (DZ) and DZ plus polarization (DZP) quality. The RMR-CCSD method belongs to a class of externally corrected CCSD approaches, which rely on a suitable non-CC wave function that is flexible enough to describe the dissociation process at hand and is used as a source of 3- and 4-body cluster amplitudes. These amplitudes are in turn used to achieve a more appropriate decoupling of the full CC chain of equations than that leading to the standard CCSD equations. The RMR-CCSD method employs for this purpose a MR-CISD wave function obtained with a relatively small active or model space. To illustrate the capabilities of this approach, the computed potential energy curves for the HF, F2 and H2O molecules are compared with the exact full CI or highly accurate large scale CI results, as well as with the MR-CISD results that are used as a source of 3- and 4-body amplitudes in the RMR-CCSD method. In all cases, the RMR-CCSD energies are far better than the standard CCSD energies or MR-CISD energies obtained with the same active space. The paper clearly demonstrates that the RMR-CCSD method provides very accurate data, while requiring only a modest increase in the computational effort over that of the standard CCSD method.
Constructing ab initio force fields for molecular dynamics simulations
Authors: Liu Yi-Ping , Kim Kyungsun , Berne B. J. , Friesner Richard A. , Rick Steven W.
Published: July 2002

We explore and discuss several important issues concerning the derivation of many-body force fields from ab initio quantum chemical data. In particular, we seek a general methodology for constructing ab initio force fields that are “chemically accurate” and are computationally efficient for large-scale molecular dynamics simulations. We investigate two approaches for modeling many-body interactions in extended molecular systems. The interactions are adjusted to reproduce the many-body energy in small molecular clusters. Subsequently, the potential parameters affecting only pair interactions are then varied to reproduce the ab initio binding energy of dimers. This simple procedure is demonstrated in the design of a new polarizable force field of water. In particular, this new model incorporates the usual many-body interactions due to electrostatic polarization and a type of nonelectrostatic many-body interactions exhibited in bifurcated hydrogen-bonded systems. The static and dynamical properties predicted by the new ab initio water potential are in good agreement with the successful empirical fluctuating-charge potential of Rick et al. and with experiment. The aforementioned “cluster” approach is compared with an alternative method, which regards many-body interactions as manifestations of the electrostatic polarization properties of individual molecules. The effort required to build ab initio databases for force field parametrization is substantially reduced in this alternative method since only the monomer properties are of interest. We found intriguing differences between these two approaches. Finally our results point to the importance of discriminating ab initio data for force field parametrization. This is essentially a consequence of the simple functional forms employed to model molecular interactions, and is inevitable for large-scale molecular dynamics simulations.
Collision cross section of rotational transition caused by the dipole–quadrupole interaction between CHF3 and nonpolar molecules
Authors: Gierszal S. , Galica J. , Miś-Kuźmińska E.
Published: July 2002

The collision cross section of rotational transition J=0→1 in the CHF3 molecule caused by nonpolar perturbers has been measured. The observed cross sections depend linearly on (mQ22)1/3, where Q2 is the quadrupole moment of the perturber and m is the reduced mass of the colliding molecules. Calculations based on the Murphy-Boggs theory using the dipole-quadrupole and first order dispersion interactions for a description of CHF3+C2H2, C6H6, CO2, O2 collisions are in qualitative agreement with the experimental results. The theoretical values are in general lower than the experimental values, and especially in the case of O2 collisions, the first order dispersion interaction contributes largely to the collision cross section.
Dynamics of glass-forming liquids. V. On the link between molecular dynamics and configurational entropy
Authors: Richert R. , Angell C. A.
Published: July 2002

We compare dielectric relaxation τ(T) data of several low molecular weight glass-forming liquids with the predictions of the Adam–Gibbs theory using experimental data for the configurational entropy Sc(T). Combination of Adam–Gibbs and Vogel–Fulcher equations yields an expression for Sc(T) which can be compared with experimental data. Good agreement is found for a range of temperatures near Tg<T<TB which depends on the fragility of the liquid and on the presence of a β relaxation. For fragile liquids, TB coincides with a qualitative change in the temperature dependence of the relaxation time scale or viscosity, with the temperature Tβ, where Johari–Goldstein-type β processes tend to merge into the α process, and with other crossover temperatures. For nonfragile liquids, TB/Tg increases, and the deviations from the Adam–Gibbs equation weaken or disappear altogether. The significance of TB, and of the Sc(T) temperature dependence implied by the Vogel–Fulcher theory fitting, are discussed in terms of the landscape paradigm.
Theoretical analysis of electronic delocalization
Authors: Mo Yirong , Peyerimhoff Sigrid D.
Published: July 2002

A block-localized wave function method is introduced to evaluate the electronic delocalization effect in molecules. The wave function for the hypothetical and strictly localized structure is constructed based on the assumption that all electrons and primitive basis functions can be divided into several subgroups; each localized molecular orbital is expanded in terms of primitive orbitals belonging to only one subgroup. The molecular orbitals belonging to the same subgroup are constrained to be mutually orthogonal, while those belonging to different subgroups are free to overlap. The final block-localized wave function at the Hartree–Fock level is expressed by a Slater determinant. In this manner, the energy difference between the Hartree–Fock wave function and the block-localized wave function can be generally defined as the electronic delocalization energy. The method is applied to two cases. The first concerns the resonance stabilization in the allyl ions. We find that the vertical resonance energies for the planar cation and anion are −45.7 (or −44.7) and −46.7 (or −48.2) kcal/mol at the HF/6-31G* (or 6-31+G*) level, respectively. Their rotational barriers are decomposed in terms of conjugation, hyperconjugation, steric effect, and pyramidalization. The n→σ* negative hyperconjugation in the staggered allyl anion is very strong and stabilizes the system by as much as −13 kcal/mol. The second concerns the hyperconjugation effect in propene. Our calculations suggest that the theoretical hyperconjugation energy in propene is about −5 kcal/mol, which is close to the experimental estimate (−2.7 kcal/mol) derived from the hydrogenation heats of propene and ethylene. Comparisons between the results based on the present block-localized wave function method and those based on the natural bond orbital method are presented and discussed. The examples demonstrate that the block-localized wave function method can be employed as a useful model to analyze chemical bondings and intuitive concepts.
An ab initio analysis of medium perturbation on molecular polarizabilities
Authors: Morita Akihiro , Kato Shigeki
Published: July 2002

The effect of medium perturbation on the polarizabilities of solute molecules in condensed environment are evaluated and analyzed. Some solutes, including Ne, Ar, CH4, Cl−, and H2O, in liquid water and argon were treated employing a supermolecule approach with Monte Carlo simulations and ab initio molecular orbital calculations explicitly considering the solvent molecules. Dielectric solute–solvent interaction was calibrated to derive the intrinsic polarizabilities of solutes. The results revealed a general tendency of decrease in the polarizabilities in solutions from the vacuum values, as much as 13%–18% for neutral solute species and 37% for Cl− in water. The tendency was moderate in liquid argon, 1%–9% reduction for neutral species and 18% for Cl−. About a half of the reduction was attributed to the solute–solvent exchange interaction. Those results are not renormalized with the medium polarization, and thus suitable to model the intermolecular interactions in liquids.
Some fundamental statistical mechanical relations concerning physical clusters of interest to nucleation theory
Authors: Reiss Howard , Bowles Richard K.
Published: July 2002

A number of statistical mechanical formulas, important to the theory of nucleation, have been used, recently and in the past, in both molecular and phenomenological theories of nucleation without a full description (and possibly without a full understanding) of their fundamental meanings. These formulas have involved the numbers of physical clusters, the reversible work of formation of such clusters, and the distinct roles of translational and internal cluster degrees of freedom. In this paper we perform careful molecular level analyses of some of these formulas in an effort to establish their fundamental bases.
Ewald summation and reaction field methods for potentials with atomic charges, dipoles, and polarizabilities
Authors: Nymand Thomas M. , Linse Per
Published: July 2002

The Ewald summation technique and the reaction field method have been generalized to potentials with atomic charges, dipole moments, and anisotropic polarizabilities. These are two common methods to treat long-range interactions in molecular simulations. Expressions for the potential energy, the electrostatic potential, the electrostatic field, the electrostatic field gradient, the force, and the virial are given, allowing for the calculation of long-range contributions to these properties within the Ewald summation or reaction field methods. We have compared numerical results using the Ewald summation under vacuum conditions with those from direct summations for a number of simple systems and found a complete agreement within the numerical precision with the exception of trivial shifts of the potential. The expressions given will facilitate the use of polarizable models in molecular simulations and hence improving our understanding of condensed matter.
On some classes of unbounded commutants of unbounded operator families
Authors: Shabani J.
Published: July 2002

Some classes of unbounded commutants and bicommutants and their behavior with respect to the quasiweak*-topology which seems to play here the role of the weak topology for bounded operators, are investigated. In particular, some sufficient conditions are given in order that the bicommutants be the quasiweak*-closure of the original set of operators.
Algebra of operators for a system of composite and elementary particles
Authors: Zinoun A. , Cortois J.
Published: July 2002

In this paper, a system made up of two different fermion species with two algebraical structures, a bigraded-Lie structure and a Lie superalgebra structure, are shown. The Lie superalgebra structure gives the normal commutation relations, while the bigraded Lie structure gives the abnormal commutation relations. The Lie superalgebra structure seems to be the most convenient for studying systems of composite and elementary particles.
Lie groups as spin groups
Authors: Doran C. , Hestenes D. , Sommen F. , Van Acker N.
Published: July 2002

It is shown that every Lie algebra can be represented as a bivector algebra; hence every Lie group can be represented as a spin group. Thus, the computational power of geometric algebra is available to simplify the analysis and applications of Lie groups and Lie algebras. The spin version of the general linear group is thoroughly analyzed, and an invariant method for constructing real spin representations of other classical groups is developed. Moreover, it is demonstrated that every linear transformation can be represented as a monomial of vectors in geometric algebra.
Arbitrary powers of D’Alembertians and the Huygens’ principle
Authors: Bollini C. G. , Giambiagi J. J.
Published: July 2002

By means of some reasonable rules the operators that can represent arbitrary powers of the D’Alembertian and their corresponding Green’s functions are defined. It is found which powers lead to the validity of Huygens’ principle. The specially interesting case of powers that are half an odd integer in spaces of odd dimensionality, obey Huygens’ principle, and can be expressed as iterated D’Alembertians of the retarded potential are discussed. Arbitrary powers of the Laplacian operator as well as their corresponding Green’s functions are also discussed.
Quantization of generalized spinning particles: New derivation of Dirac’s equation
Authors: Rivas Martin
Published: July 2002

Quantization of generalized Lagrangian systems suggests that wave functions for elementary particles must be defined on the kinematical space rather than on configuration space. For spinning particles the center of mass and center of charge are different points. Their separation is of the order of the Compton wavelength. Spin-1/2 particles arise if the classical model rotates but no half integer spins are obtained for systems with spin of orbital nature. Dirac’s equation is obtained when quantizing the classical relativistic spinning particles whose center of charge is circling around its center of mass at the speed c. Internal orientation of the electron completely characterizes its Dirac’s algebra.
Perturbation theory for the Dirac equation in two-dimensional space
Authors: Kiselev O. M.
Published: July 2002

Basis functions associated with the two-component hyperbolic Dirac equation were obtained. The expansion via the basis functions separates time and spatial variables in a linearized Davey–Stewartson I equation. It is possible to solve this equation by the Fourier method.
A note on the vortex trail behind bluff bodies
Authors: Gai S. L.
Published: July 2002

In a recent paper Sirovich [Phys. Fluids 28, 2723 (1985)] has shown that the rotation number of the wake behind a bluff body is uniquely related to the Reynolds number. It is shown in this Brief Communication that it is also uniquely related to the drag variation when a vortex street from a bluff body is interfered with drag reducing devices such as splitter plates and base bleed.
Viscous cross-waves: An analytical treatment
Authors: Bernoff Andrew J. , Kwok L. P. , Lichter Seth
Published: July 2002

Viscous effects on the excitation of cross-waves in a semi-infinite box of finite depth and width are considered. A formalism using matched asymptotic expansions and an improved method of computing the solvability condition is used to derive the relative contributions of the free-surface, sidewall, bottom, and wavemaker viscous boundary layers. This analysis yields an expression for the damping coefficient previously incorporated on heuristic grounds. In addition, three new contributions are found: a viscous detuning of the resonant frequency, a slow spatial variation in the coupling to the progressive wave, and a viscous correction to the wavemaker boundary condition. The wavemaker boundary condition breaks the symmetry of the linear neutral stability curve at leading order for many geometries of experimental interest.
Induction zone structure for a high-speed deflagration with variable mole chemistry
Authors: Kirkköprü Kadir , Kassoy D. R.
Published: July 2002

The induction zone characteristics of a planar subsonic high-speed reactive flow downstream of a specific origin are investigated theoretically for the global irreversible reaction F+Ox→νP. The equation of state for the reacting gas mixture is more general than that for a constant molecular weight gas. Perturbation methods based on the limit of high activation energy are used to construct the general parameter-dependent analytical solutions. The dependence of the ignition delay distance on the kinetic, stoichiometric, and flow parameters is discussed in detail. Significantly, it is shown that the reaction with a mole decrement (ν=1) yields the minimum, and a mole increment (ν=3) yields the maximum ignition delay distance when the chemical heat addition and the origin values of parameters are fixed. The physics and length scales found from the perturbation analysis are used as a guide in generating supporting numerical solutions.
Hypersonic expansion of the Fokker–Planck equation
Authors: Fernández-Feria R.
Published: July 2002

A systematic study of the hypersonic limit of a heavy species diluted in a much lighter gas is made via the Fokker–Planck equation governing its velocity distribution function. In particular, two different hypersonic expansions of the Fokker–Planck equation are considered, differing from each other in the momentum equation of the heavy gas used as the basis of the expansion: in the first of them, the pressure tensor is neglected in that equation while, in the second expansion, the pressure tensor term is retained. The expansions are valid when the light gas Mach number is O(1) or larger and the difference between the mean velocities of light and heavy components is small compared to the light gas thermal speed. They can be applied away from regions where the spatial gradient of the distribution function is very large, but it is not restricted with respect to the temporal derivative of the distribution function. The hydrodynamic equations corresponding to the lowest order of both expansions constitute two different hypersonic closures of the moment equations. For the subsequent orders in the expansions, closed sets of moment equations (hydrodynamic equations) are given. Special emphasis is made on the order of magnitude of the errors of the lowest-order hydrodynamic quantities. It is shown that if the heat flux vanishes initially, these errors are smaller than one might have expected from the ordinary scaling of the hypersonic closure. Also it is found that the normal solution of both expansions is a Gaussian distribution at the lowest order. One of the expansions is applied to a simplified form of the shock wave problem where an exact solution of the Fokker–Planck equations is known.
Free and guided convection in evaporating layers of aqueous solutions of sucrose. Transport and sedimentation of solid particles
Authors: Simon Blaise , Pomeau Yves
Published: July 2002

In a thin layer of an aqueous solution of sucrose, convection due to evaporation takes place, after a chaotic regime, as a unique toroidal roll occupying the whole container. When a mask drilled with holes is placed just above the upper surface of the fluid layer, there is cellular convection imposed by the distribution of holes. Immersed solid particles preferentially settle at the bottom of the cell walls, where the fluid is rising. This is explained by the combined effects of diffusion and convection, when the latter is dominant (large Péclet number).
Beam profile studies for a phase-mixed ion beam focused with a one-eighth betatron wavelength focusing cell
Authors: Watrous J. , Ottinger P. F.
Published: July 2002

The focusing properties of a one-eighth betatron wavelength focusing cell are used to determine to what extent a modification of the initial phase-space distribution of an ion beam can alter the number density profile of the beam at the focal plane. It is shown that the main modification is to alter the natural 1/r profile to include an off-axis peak. The relative difficulty with which the ion beam can be concentrated into this off-axis peak is then considered. Estimates of the source brightness (extraction ion diode source current density divided by the square of the microdivergence) required to deliver a given amount of beam current into a given annular region at the focal plane are derived.
Stability properties of magnetohydrodynamic cylindrical flows
Authors: Pietrini P. , Torricelli-Ciamponi G.
Published: July 2002

A normal-mode stability analysis is performed on a set of stationary equilibrium configurations, originally introduced by Chiuderi, Pietrini, and Torricelli-Ciamponi (Astrophys. J., in press) to describe the structure of extragalactic jets. The examined equilibria are characterized by three parameters that allow the magnetic field configuration and the magnitude of the flow speed to be changed. Moreover, two different cases for the equilibrium velocity field are considered, namely v0∥B0, and a purely longitudinal v0. Thus the instability properties of a wide range of magnetic and flow structures are studied numerically and the growth rates as a function of the longitudinal wavenumber k are derived for the azimuthal mode numbers m=0,+1,−1. The aim is both to analyze the behavior of the instability growth rates as a function of the equilibrium parameters and the flow structure and to look for the existence of regions in the equilibrium parameter space corresponding to stable equilibria. A restricted ‘‘stable’’ region for the two considered flow patterns has been identified: configurations characterized by a predominantly longitudinal magnetic field and a velocity smaller or comparable to the Alfvén speed turn out to be stable.
Optically guided laser wake-field acceleration*
Authors: Esarey E. , Sprangle P. , Krall J. , Ting A. , Joyce G.
Published: July 2002

The laser wake-field acceleration concept is studied using a general axisymmetric formulation based on relativistic fluid equations. This formalism is valid for arbitrary laser intensities and allows the laser–plasma interaction to be simulated over long propagation distances (many Rayleigh lengths). Several methods for optically guiding the laser pulse are examined, including relativistic guiding, preformed plasma density channels and tailored pulse profiles. Self-modulation of the laser, which occurs when the pulse length is long compared to the plasma wavelength and the power exceeds the critical power, is also examined. Simulations of three possible laser wake-field accelerator (LWFA) configurations are performed and discussed: (i) a channel-guided LWFA, (ii) a tailored-pulse LWFA, and (iii) a self-modulated LWFA.
Nonlinear dispersive periodic waves in the presence of instability and damping
Authors: Kawahara Takuji , Toh Sadayoshi
Published: July 2002

Periodic solutions of a nonlinear dispersive equation involving both growth and damping mechanisms are investigated numerically and theoretically. General features of equilibrium periodic states for a strongly dispersive case are found to be well explained by means of a perturbation analysis of the cnoidal wave solutions.
Neutral transport in plasmas with velocity dependent charge exchange collision frequency
Authors: Prinja Anil K.
Published: July 2002

It is shown that conventional, ad hoc approximations to the charge exchange kernel employed in rapid neutral transport calculations in plasmas violate important symmetry properties of the original kernel and yield an incorrect asymptotic spectral distribution. An alternative systematic scheme of approximation and modeling is proposed that even to zeroth order yields a more accurate representation of the kernel. The approximation retains important features of the original kernel and is computationally appealing. A variational principle is developed for the particle albedo and average emergent neutral energy from a half-space plasma, which allows extensive numerical comparisons of the various charge exchange models. Exact Monte Carlo results are also presented for a special case to assess the relative accuracy of the models. The results indicate that the proposed new model is twice as accurate as the conventional model for the albedo, although the magnitude is probably acceptably accurate for all models. However, the proposed model can be significantly more accurate than the ad hoc models in predictions for the average emergent energy. The origin of this discrepancy is traced to the original inconsistency in the approximation to the kernel.
Onset of spatial oscillations in a deep rotating fluid differentially heated from below
Authors: Quon Charles
Published: July 2002

In this paper, the onset of spatial oscillations is studied in a deep rotating fluid differentially heated from below for two sets of dimensionless parameters, σβ=0.20 and 10, where σ is the Prandtl number and β the thermal Rossby number. The time dependent solutions have been used to identify accurately the onset of instabilities, and to obtain effective (virtual) length scales for the computation of critical Rayleigh numbers. It is found that the critical Rayleigh numbers for instabilities for both sets of parameters are O(103), which suggests that the governing mechanism for the initial stages of instabilities is similar to that of Bénard instability for a thin layer of fluid.
Quasilinear energy balance of resistive modes
Authors: Pegoraro F. , Schep T. J.
Published: July 2002

The global energy balance of collisional and semicollisional resistive modes is related term by term to the quadratic form derived from the linear dispersion equation. The partition of the released magnetic and electron pressure energy into dissipation, electron compression along field lines, and ion energy is explicitly discussed for internal kink modes, tearing modes, and resistive Alfvén modes.
Three-dimensional vortical structures of transition in plane channel flow
Authors: Biringen S.
Published: July 2002

Three-dimensional visualization of flow field structures in transitional plane channel flow obtained from a numerical simulation is presented at two Reynolds numbers. At the one-spike stage, independent of Reynolds number, it is seen that the flow is characterized by a multilayer vortex system. In the upper layer, total vorticity vector plots indicate a high-shear layer dominated by spanwise vorticity, whereas the middle layer (corresponding approximately to the critical layer) forms a vortex loop (λ vortex) consisting of strong streamwise and spanwise vorticity components. At the three-spike stage prior to breakdown, the vortical structure becomes concave in the flow direction. This process is accompanied by intense vortex liftup activity near the wall, which seems to originate at the legs of the vortex loop trailing the high-shear layer. Finally, at the five-spike stage, it is suggested that high-vorticity regions (vortical structures) develop into horseshoe eddies in planes inclined to the main flow direction.
Laser Doppler measurement of turbulence parameters in a two-dimensional plane wall jet
Authors: Schneider M. E. , Goldstein R. J.
Published: July 2002

A computer-controlled data acquisition system has been designed and constructed to automate measurement of turbulent velocity correlations in a two-dimensional turbulent wall jet. Measurements are made with a single component laser Doppler velocimeter system in a flow of air on a flat plate with stagnant surroundings. Measurements of a number of turbulence parameters have been completed and compared with existing hot-wire data. The measurements are made at two downstream locations at a Reynolds number, based on slot width, of 14 000. Earlier hot-wire data for a two-dimensional turbulent wall jet in stagnant surroundings show much scatter in the outer region where local turbulence intensities range from 40% to 70%. The laser Doppler velocimeter gives repeatable values and eliminates the bias in hot-wire measurements due to reversing flow and errors in corrections for high turbulence effects. The measured turbulent normal stresses are somewhat higher than those previously reported throughout the flow field. The turbulent shear stress is in good agreement with previous hot-wire results near the wall. Hot wires are shown to indicate low values of the Reynolds stress in the turbulent outer regions where they are affected by strong flow reversals. The new measurements agree well with predictions based on momentum integral methods.
A low-dimensional Galerkin method for the three-dimensional flow around a circular cylinder
Authors: Noack Bernd R. , Eckelmann Helmut
Published: July 2002

A low-dimensional Galerkin method for the three-dimensional flow around a circular cylinder is constructed. The investigation of the wake solutions for a variety of basic modes, Hilbert spaces, and expansion modes reveals general mathematical and physical aspects which may strongly effect the success of low-dimensional simulations. Besides the cylinder wake, detailed information about the construction of similar low-dimensional Galerkin methods for the sphere wake, the boundary-layer, the flow in a channel or pipe, the Taylor–Couette problem, and a variety of other flows is given.
On the dependence on the formulation of some nonparallel stability approaches applied to the Taylor flow
Authors: Griffond Jérôme , Casalis Grégoire
Published: July 2002

In a study of the stability of the nonparallel Taylor flow in a channel with wall injection, see Taylor [Proc. R. Soc. London, Ser. A 234, 456 (1956)], Lee and Beddini [The 35th AIAA/ASME/ASEE Joint Propulsion Conference and Exhibit, AIAA-99-2508, 20–24 June 1999, Los Angeles, California, 1999] recently reported some discrepancies between their results and those of Casalis et al. [Phys. Fluids 10, 2558 (1998)], whereas they seem to agree perfectly with those of Varapaev and Yagodkin [Izv. Akad. Nauk SSSR Mekh. Zhidk. Gaza 4, 91 (1969)]. In Casalis et al. [Phys. Fluids 10, 2558 (1998)], the difference with Varapaev and Yagodkin [Izv. Akad. Nauk SSSR Mekh. Zhidk. Gaza 4, 91 (1969)] has not been clarified, so that it seems important to explain that the discrepancies do not come from a mistake but from a different choice of formulation. In addition, it will be shown that these discrepancies are related to the inconsistent nature of the stability approach which is used in the three papers.
One-dimensional solitary kinetic Alfvén waves in low-beta plasma
Authors: Wang Xu-yu , Wang Xue-yi , Liu Zhen-xing , Li Zhong-yuan
Published: July 2002

A two-dimensional homogeneous magnetohydrodynamic (MHD) model is applied to investigate one-dimensional solitary kinetic Alfvén waves (SKAWs) and their degenerated ion-acoustic solitons in a low-beta plasma, in which electron pressure and electron inertial effects are all taken into account. In contrast to the results of the one-dimensional SKAWs model obtained by Hasegawa and Mima [Phys. Rev. Lett. 37, 690 (1976)], Shukla et al. [J. Plasma Phys. 28, 125 (1982)], and Wu et al. [Phys. Plasmas 3, 2879 (1996)], both density hump and dip Alfvénic solitons are found to exist in the kinetic limit (2me/mi≪β≪1) and in the inertial limit (β≪2me/mi) (β=8πnTe/B02 denotes the ratio of the plasma thermal pressure to the magnetic pressure), while in the transition region (β−2me/mi), both super-Alfvénic and sub-Alfvénic solitons with a density hump or a dip are found to exist. Due to the finite-β effect, the Alfvénic solitons may degenerate into super-acoustic density hump solitons over all the range of plasma β. This result provides a one-dimensional SKAWs model to account for the observations from the Freja satellite, in which not only SKAWs accompanied by dip density solitons, but also SKAWs accompanied by hump density solitons, are found in the Earth’s ionospheric altitude.
Recrystallization solvent effects on second-order nonlinear optical organic materials
Authors: Tabei Hisao , Kurihara Takashi , Kaino Toshikuni
Published: July 2002

Recrystallization solvent effects on second harmonic generation (SHG) of acetylene derivatives are reported. SHG intensities of substituted diphenylacetylene recrystallized from strong polar solvents are enhanced in crystalline states.
Residual stress effects on refractive indices in undoped silica-core single-mode fibers
Authors: Hibino Yoshinori , Hanawa Fumiaki , Abe Tetuju , Shibata Shuichi
Published: July 2002

It is reported for the first time that refractive indices are reduced remarkably by residual stress in undoped silica-core/fluorine-doped silica-clad single-mode fibers. The very high residual stress concentrated at the small diameter core is induced by drawing tension because of the difference in viscosity between the core and cladding. The decrease in refractive indices results from photoelastic effects due to residual stress in the core.
Tellurium thin-film transistor deposited on polyester film having plasma polymerized films on double-layered gate insulators
Authors: Hirai H. , Sekiguchi H. , Miyata S. , Kobayashi S.
Published: July 2002

A tellurium thin-film transistor deposited on polyester film having plasma polymerized films as double-layered gate insulators has been successfully fabricated. Films of plasma polymerized acetonitrile and benzene were used for the insulator and passivation films of the thin-film transistor, respectively. The attained drain current on-off ratio was about 1×103 at a current density of 0.8 mA/mm2. These values qualify the device to drive the pixels of a twisted nematic liquid crystal display panel.
Experimental realization of a resonant tunneling transistor
Authors: Woodward T. K. , McGill T. C. , Burnham R. D.
Published: July 2002

We report experimental realization of a three-terminal negative differential resistance (NDR) device. As proposed by A. R. Bonnefoi, T. C. McGill, and R. D. Burnham [IEEE Electron. Dev. Lett. EDL-6, 636 (1985)], the structure consists of a GaAs-AlxGa1−xAs double-barrier tunneling heterostructure, the current through which is controlled by an integrated vertical field-effect transistor. We present results for two samples grown by metalorganic chemical vapor deposition. Both samples exhibit NDR in their source-drain current-voltage characteristics at 77 K, with peak-to-valley current ratios ranging between 3 and 5.3. One sample exhibits NDR at room temperature. The position and peak-to-valley current ratio of the NDR can be modulated by gate voltage. Due to asymmetry in the doping levels of the two GaAs cladding layers, resonant tunneling peaks occur at much larger voltages in reverse bias than in forward bias.
Efficient side lobe suppression of laser diode arrays
Authors: Leger James R. , Swanson Gary J. , Holz Michael
Published: July 2002

An optical technique is described which converts multilobed far-field patterns from in-phase laser arrays into a single-lobed pattern. The technique redistributes the output light from the laser array to produce a uniformly illuminated aperture. This filled aperture produces negligible side lobes, and efficiently channels the array power into the main lobe. Experiments performed on a ten-element Y-guide laser array show an increase in main lobe power from 51 to 90% of the total array power.
Cellular and dendritic morphologies on stationary and moving liquid-solid interfaces in zone-melting recrystallization
Authors: Im J. S. , Tomita H. , Thompson C. V.
Published: July 2002

It is well known that when Si films are radiatively heated there exists a range of incident intensities for which liquid and solid regions coexist at near uniform temperature. Based on in situ microscopic observation of solidification interface morphologies, we argue that this phenomenon is responsible, at least in part, for the morphology of the liquid-solid interface in zone-melting recrystallization. We demonstrate this effect through stationary interface experiments. It is observed that even a stationary interface exposed to a gradient in radiation intensity develops interface morphologies similar to those of moving interfaces.
Ultimate limit in low threshold quantum well GaAlAs semiconductor lasers
Authors: Lau K. Y. , Derry P. L. , Yariv A.
Published: July 2002

Gain measurements were performed on buried heterostructure single quantum well lasers to ascertain the transparency current density, which represents a basic limit in the threshold current. By using the optimal design approach, a lowest threshold of 0.55 mA in a 120-μm-long device was achieved. Modulation of the low threshold laser by a pseudorandom digital stream at 1.3 Gbit/s without current bias is demonstrated.
Atom probe analysis of a ceramic oxide superconductor
Authors: Cerezo A. , Grovenor C. R. M. , Hoyle R. M. , Smith G. D. W.
Published: July 2002

Field-ion specimens have been produced from a bulk ceramic yttrium barium cuprate superconductor, allowing quantitative atom probe analysis from this new class of materials. This technique offers the potential for high-resolution quantitative analysis for oxygen concentrations in the near-surface regions and the study of microchemistry of contact/superconductor interfaces. Preliminary results are presented on bulk compositions and the surface modifications following vacuum annealing.
X-ray laser gain from Bragg reflection coupling in channeled relativistic beam systems
Authors: Strauss M. , Amendt P. , Rostoker N. , Ron A.
Published: July 2002

The application of distributed feedback by Bragg reflections in electron beam channeling x-ray lasers is investigated. Expressions for low threshold gain are derived for this cavity mirror structure in single crystals and are shown to have possible application in reducing beam high current requirements by many orders of magnitude.
High T
c superconductor/noble-metal contacts with surface resistivities in the 10−10 Ω cm2 range
Authors: Ekin J. W. , Larson T. M. , Bergren N. F. , Nelson A. J. , Swartzlander A. B. , Kazmerski L. L. , Panson A. J. , Blankenship B. A.
Published: July 2002

Contact surface resistivities (product of contact resistance and area) in the 10−10 Ω cm2 range have been obtained for both silver and gold contacts to high Tc superconductors. This is a reduction by about eight orders of magnitude from the contact resistivity of indium solder connections. The contact resistivity is low enough to be considered for both on-chip and package interconnect applications. The contacts were formed by sputter depositing either silver or gold at low temperatures (<100 °C) on a clean surface of Y1 Ba2 Cu3 O7−δ (YBCO) and later annealing the contacts in oxygen. Annealing temperature characteristics show that for bulk-sintered YBCO samples there is a sharp decrease in contact resistivity after annealing silver/YBCO contacts in oxygen for 1 h at temperatures above ∼500 °C and gold/YBCO contacts for 1 h above ∼600 °C. Oxygen annealing for longer times (8 h) did not reduce the contact resistivity of silver contacts as much as annealing for 1 h. Auger microprobe analysis shows that indium/YBCO contacts contain a significant concentration of oxygen in the indium layer adjacent to the YBCO interface. Silver and gold contacts, on the other hand, contain almost no oxygen and have favorable interfacial chemistry with low oxygen affinity. Silver also acts as a ‘‘switchable’’ passivation buffer, allowing oxygen to penetrate to the YBCO interface at elevated temperatures, but protecting the YBCO surface at room temperature.
Substrate and capping layer effects on the phonon spectrum of ultrathin superlattices
Authors: Lockwood D. J. , Dharma-wardana M. W. C. , Aers G. C. , Baribeau J.-M.
Published: July 2002

GemSin ultrathin superlattices have been grown on (001) Si substrates and partly capped with Si. Raman scattering from acoustic phonons in the long-wavelength region shows unexpectedly intense broad peaks that develop into an increased number of sharper intense peaks on capping. We identify these peaks with resonant phonon modes and use a linear chain model to expose the importance of substrate-superlattice-capping layer interactions in these multilayer structures.