bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsed field ionization-photoelectron bands for CS2+ in the energy range of 13.2–17.6 eV: An experimental and theoretical study
Authors: Liu Jianbo , Hochlaf M. , Ng C. Y.
Published: February 2003

Vacuum ultraviolet pulsed field ionization-photoelectron (PFI-PE) spectra for CS2 have been obtained in the energy range of 13.2–17.6 eV, revealing complex vibronic structures for the CS2+(B̃ 2Σu+ and C̃ 2Σg+) states. The PFI-PE spectra for CS2+(B̃ 2Σu+ and C̃ 2Σg+) are dominated by the ν1+ (symmetric stretching) mode. However, PFI-PE bands due to the ν2+ (bending) and ν3+ (antisymmetric stretching) modes with both even and odd quanta are clearly resolved. The simulation of rotational contours resolved in the origin PFI-PE bands yields accurate ionization energies of 14.4742±0.0005 eV (116 742±4 cm−1) and 16.1883±0.0005 eV (130 567±4 cm−1) for the formation of CS2+(B̃ 2Σu+ and C̃ 2Σg+) states from CS2(X̃ 1Σg+), respectively. The PFI-PE bands for Σu+2(302) and Σg+2(303) at 14.805 and 14.965 eV, which are in near energy resonance with the 0 K dissociation thresholds for the formation of S+(4S)+CS(X 1Σ+; ν″=0 and 1) from CS2, respectively, are found to be enhanced. These enhancements are rationalized by the prompt dissociation of excited CS2 in high-n (n⩾100) Rydberg states prior to PFI. Three-dimensional potential energy functions (PEFs) for CS2+(2 2Πu, B̃ 2Σu+, and C̃ 2Σg+) states have been generated theoretically using the complete active space self-consistent field and internally contracted multireference configuration interaction methods. On the basis of these PEFs, the harmonic frequencies for CS2+(2 2Πu, B̃ 2Σu+, and C̃ 2Σg+) and vibronic energy levels for CS2+(B̃ 2Σu+) have been calculated variationally. These theoretical predictions have made possible a satisfactory assignment of the vibronic bands resolved in the PFI-PE spectra for CS2+(B̃ 2Σu+ and C̃ 2Σg+). Using the theoretical predictions obtained here, we have also assigned vibronic bands for CS2+(2 2Πu) observed in the HeI photoelectron spectrum [Baltzer et al., Chem. Phys. 202, 185 (1996)].
Modified Bell–Plesset effect with compressibility: Application to double-shell ignition target designs
Authors: Amendt Peter , Colvin J. D. , Ramshaw J. D. , Robey H. F. , Landen O. L.
Published: February 2003

The effect of spherical convergence on the fluid stability of collapsing and expanding bubbles was originally treated by Bell [Los Alamos Scientific Laboratory Report No. LA-1321 (1951)] and Plesset [J. Appl. Phys. 25, 96 (1954)]. The additional effect of fluid compressibility was also considered by Bell but was limited to the case of nonzero density on only one side of a fluid interface. A more general extension is developed which considers distinct time-dependent uniform densities on both sides of an interface in a spherically converging geometry. A modified form of the velocity potential is used that avoids an unphysical divergence at the origin [Goncharov et al., Phys. Plasmas 7, 5118 (2000); Lin et al., Phys. Fluids 14, 2925 (2002)]. Two consequences of this approach are that an instability proposed by Plesset for an expanding bubble in the limit of large interior density is now absent and application to inertial confinement fusion studies of stability becomes feasible. The model is applied to a proposed ignition double-shell target design [Amendt et al., Phys. Plasmas 9, 2221 (2002)] for the National Ignition Facility [Paisner et al., Laser Focus World 30, 75 (1994)] for studying the stability of the inner surface of an imploding high-Z inner shell. Application of the Haan [Phys. Rev. A 39, 5812 (1989)] saturation criterion suggests that ignition is possible.
Diffusion and reaction for a spherical source and sink
Authors: McDonald Nyrée , Strieder William
Published: February 2003

Two chemically active spheres in an infinite medium, one a zeroth-order reactant source and the other a first-order sink, are considered for various sphere size ratios, center-to-center distances, and sink strengths from chemical to diffusion controlled conditions. This source–sink model simulates some aspects of biological mutualism interactions between different cells. Infinite series expansions in a single index n are obtained for the sink reaction rate and reactant concentration profiles using the bispherical expansion. Each of the coefficients, generated exactly by a matrix elimination method, is expressed in terms of nested, continued fractions easily evaluated for the given n. At intermediate and larger sink–source separation distances the sink reaction rate decays harmonically. For smaller sink–source separations with a highly reactive small sink, a local maximum in the sink reaction rate is found.
The effect of topological constraint on the theta temperature of a knotted polymer
Authors: Sheng Yu-Jane , Liao Chen-Shin
Published: February 2003

Monte Carlo simulations were used to study the effect of topological constraints of knotted polymers on their theta temperatures. The theta temperatures were determined through two different definitions—the vanishing of the second virial coefficient A2=0, and the quasi-ideal behavior of the radius of gyration, 〈Rg2〉∼N. Prime knots with chain lengths from N=60 to 300 and with crossings from 31 to 91 were considered. For chains with finite lengths, it was found that the theta temperature determined from quasi-ideal condition of the knot increases, as the complexity of the knot increases. On the other hand, the topological complexity seemed to have no effect on the theta temperatures determined from the vanishing of the second virial coefficient. Also, our simulation results suggest that for chains with finite crossing numbers, as N→∞, theta temperatures for all knots obtained from two different approaches coincide and are equivalent to that of a linear polymer chain.
Monte Carlo simulation of homopolymer chains. I. Second virial coefficient
Authors: Withers Ian M. , Dobrynin Andrey V. , Berkowitz Max L. , Rubinstein Michael
Published: February 2003

The second virial coefficient, A2, is evaluated between pairs of short chain molecules by direct simulations using a parallel tempering Monte Carlo method where the centers of mass of the two molecules are coupled by a harmonic spring. Three off-lattice polymer models are considered, one with rigid bonds and two with flexible bonds, represented by the finitely extensible nonlinear elastic potential with different stiffness. All the models considered account for excluded volume interactions via the Lennard-Jones potential. In order to obtain the second virial coefficient we calculate the effective intermolecular interaction between the two polymer chains. As expected this intermolecular interaction is found to be strongly dependent upon chain length and temperature. For all three models the θ temperature (θn), defined as the temperature at which the second virial coefficient vanishes for chains of finite length, varies as θn−θ∞∝n−1/2, where n is the number of bonds in the polymer chains and θ∞ is the θ point for an infinitely long chain. Introducing flexibility into the model has two effects upon θn; the θ temperature is reduced with increasing flexibility, and the n dependence of θn is suppressed. For a particular choice of spring constant an n-independent θ temperature is found. We also compare our results with those obtained from experimental studies of polystyrene in decalin and cyclohexane, and for poly(methyl methacrylate) in a water and tert-butyl alcohol mixture, and show that all the data can be collapsed onto a single universal curve without any adjustable parameters. We are thus able to relate both A2 and the excluded volume parameter v, to the chain interaction parameter z, in a way relating not only the data for different molecular weights and temperatures, but also for different polymers in different solvents.
The bending rigidity of an amphiphilic bilayer from equilibrium and nonequilibrium molecular dynamics
Authors: den Otter W. K. , Briels W. J.
Published: February 2003

Helfrich’s theory predicts that the bending free energy of a tensionless amphiphilic bilayer is proportional to the square of the Fourier coefficients of the undulation modes. Equilibrium molecular dynamics simulations with coarse-grained amphiphiles confirm the correctness of this prediction for thermally excited undulations. The proportionality constant then provides the bending rigidity of the layer. Non-equilibrium methods, in particular umbrella sampling, potential of mean constraint force, and thermodynamic integration in Cartesian coordinates, have been used to extend the range of sampled amplitudes. For small amplitudes there is a good agreement with the equilibrium simulations, while beyond the thermally accessible amplitudes a clear deviation from theory is observed. Calculations of the elastic modulus showed a pronounced system size dependence.
Effective force between confined colloids clothed by end-grafted polymer chains in solution
Authors: Benhamou M. , Himmi M. , Benzouine F.
Published: February 2003

We consider colloidal particles clothed each by f end-grafted polymer chains, and immersed in a good solvent. The clothed particles are small enough to be regarded as star polymers. The purpose is a quantitative study of the influence of the confinement on the expression of the effective force between a pair of particles. Such a force originates from the swelling of grafted chains due to the presence of solvent. To simplify, we chose as confining geometry a thin space of thickness D delimited by two parallel plates. The problem depends on two natural lengths, which are the gyration radius, R3∼af1/5N3/5, of an isolated star polymer and the thickness D. Thus, there exist two regimes depending on whether R3 is smaller or greater than D. The system is confined only when D is below R3. We first present a detailed study of conformations of a confined star polymer (R3≫D). The confinement imposes to the star polymer to adopt a configuration parallel to the plates, which is characterized by a parallel radius, denoted by R∥. We show that the latter increases when D is decreased according to R∥∼af1/4D−1/4N3/4. The main result is that the star polymer becomes two dimensional, and where the grafted chains have blobs of size D as new units. The second purpose is a quantitative investigation of the effective force between two confined star polymers. For the unconfined regime (R3≪D), it is found that the force, F3(r), decays with interparticle distance r as F3(r)/kBT≃θ3(f )/r, with the amplitude θ3(f )≃(5/18)f3/2. Hence, for this regime, the force is similar to that relative to a three-dimensional colloidal solution of infinite extent. For the confined regime (R3≫D), however, a drastic change of the force expression occurs. For this regime, we show that the force is similar to the one governing the interaction between two-dimensional star polymers, and is given by F2(r)/kBT≃θ2(f )/r, with the exact amplitude θ2(f )=(2+9f2)/24. The two forces then decrease with distance according to the same decay, but with different amplitudes. As a conclusion, the effective force between two confined star polymers is θ2(f )/θ3(f )≃(3/20)(2+9f2)/f3/2 times more intense than that between unconfined ones. Finally, we say that the confinement may be a mechanism that reinforces the colloidal stabilization.
Experimental and theoretical determination of rotational-translational state-to-state rate constants for N2:He collisions at low temperature (3<T<20 K)
Authors: Maté B. , Thibault F. , Ramos A. , Tejeda G. , Fernández J. M. , Montero S.
Published: February 2003

We present an experimental determination of state-to-state rotational–translational (RT) rate constants of N2:He collisions in the vibrational ground state as a function of temperature in the range 3<T<20 K. Raman spectroscopy in supersonic expansions of N2/He mixtures is used to determine the primary data that, together with the N2:N2 state-to-state RT rates previously determined [Ramos et al., Phys. Rev. A 66, 022702 (2002)], are needed to solve the master equation according to a procedure that does not impose any particular scaling law. We also report first principle calculations of the N2:He state-to-state RT rate constants performed using the full three-dimensional potential energy surface of Reid et al. [J. Chem. Phys. 107, 2329 (1997)], in the 3<T<300 K temperature range. The coupled-channel method, and the coupled-states approximation, were applied in the low (0–610 cm−1) and in the high (610–1500 cm−1) energy limits, respectively. A good agreement between theoretical and experimental results is found in the temperature range where comparison is possible.
Sub-Doppler spectroscopy of the PH radical: Hyperfine structure in the A 3Π state
Authors: Fitzpatrick James A. J. , Chekhlov Oleg V. , Western Colin M. , Ashworth Stephen H.
Published: February 2003

Sub-Doppler spectra of the A 3Π–X 3Σ−(0,0) and (1,0) bands of the PH radical have been recorded using an injection seeded single mode optical parametric oscillator in a supersonic jet expansion. Most of the rotational lines in these laser-induced fluorescence spectra exhibit clear splittings or asymmetry due to hyperfine structure. An analysis of this structure is presented in terms of the electronic structure and bonding of the molecule. Comparisons are drawn with the corresponding A 3Π state of the NH radical, and some shortcomings in the accepted methods for interpretation are highlighted and discussed.
Thickness dependent crystallization kinetics of sub-micron amorphous solid water films
Authors: Safarik D. J. , Meyer R. J. , Mullins C. B.
Published: February 2003

The kinetics of isothermal crystallization at the free surface of dense, 150–1050 bilayer (BL) (∼55–385 nm) thick amorphous solid water (ASW) films is investigated experimentally, and a model accounting for the observed thickness dependence is proposed. We find that as the ASW film thickness is increased above 150 BL, surface crystallization accelerates, rapidly at first and then more slowly until essentially size-independent kinetics are attained by 1050 BL. The potential origin of this thickness dependence is elucidated by a geometrical model of surface crystallization that we formulated using mechanistic information deduced from available experimental data. This simple mean-field model predicts that as film thickness is reduced below some critical value, the number of grains contributing to surface transformation progressively decreases, forcing each grain to convert a larger surface area and thus slowing crystallization. Good agreement between experimental data and the theory is realized using only two thickness-independent kinetic parameters (per temperature), suggesting that the model describes the basic physics of crystallization in these ASW films. Nucleation and growth rates determined via model fits range from ∼5.5×109 cm−3 s−1 and ∼0.3 Å/s at 136 K to ∼6.5×1010 cm−3 s−1 and ∼1.5 Å/s at 140 K, corresponding to activation energies of 100 and 68 kJ/mol, respectively.
Theory of polyelectrolyte adsorption on heterogeneously charged surfaces applied to soluble protein–polyelectrolyte complexes
Authors: de Vries R. , Weinbreck F. , de Kruif C. G.
Published: February 2003

Existing theoretical approaches to polymer adsorption on heterogeneous surfaces are applied to the problems of polyelectrolyte and polyampholyte adsorption on randomly charged surfaces. Also, analytical estimates are developed for the critical pH at which weakly charged polyelectrolytes and globular proteins start forming soluble complexes. Below a critical salt concentration, soluble complexes form “on the wrong side” of the protein isoelectric point due to the heterogeneity of the protein surface charge distribution. The analytical estimates are consistent with experimental data on soluble complexes in mixtures of gum arabic and whey protein isolate.
Molecular dynamics simulations of granular compaction: The single granule case
Authors: Sanchez-Castillo Francisco X. , Anwar Jamshed , Heyes David M.
Published: February 2003

We have carried out nonequilibrium molecular dynamics simulations of the compaction of a single three-dimensional granule composed of over 1000 Lennard-Jones (LJ) particles. The granule was contained within an orthorhombic box with repulsive walls and deformed by a vertically moving top wall. The compaction cycle adopted was intended to mimic the procedure employed in industrial tabletting processes, by compressing the granule during the downward movement of the top wall (compaction) followed by an upward movement of the top wall (decompaction). We have explored the effects of different compression rates on the deformation, microstructure, and the final integrity of the granule. Although the simulations are formally atomistic, we believe a mesoscopic significance can be attached to the results that makes them relevant to the larger scale compaction involved in industrially relevant processes. The cluster representation of the granule allows for significant deformation during the process, and the simulations reproduce a number of well-known effects found in the pharmaceutical tabletting and other literature. Rapid compaction resulted in an essentially elastic response and even break up of the formed tablet during the decompaction stage, an effect known as lamination. Slower compaction speeds, which enabled greater internal rearrangement of the LJ particles through plastic deformation, produced a more structurally uniform tablet at the end of the cycle. For the faster compaction speed the top wall moved away faster than the compacted material could recover, giving rise to misleadingly low values of the apparent elastic response of the material as measured by the force from the material on the top wall. We believe this could be an important issue when interpreting experimental data. These simulations were able to capture the transition between the fast and slow compaction rate regimes and reveal some rudiments of the lamination problem that plagues the industrial process of tabletting.
Multilayer water adsorption on rutile TiO2(110): A first-principles study
Authors: Zhang Changjun , Lindan Philip J. D.
Published: February 2003

The adsorption of water on the TiO2(110) surface has become the model process in efforts to understand metal oxide–aqueous solution interfaces. Considerable progress has been made in understanding low-coverage situations where first-principle calculations have been employed to good effect. However, current theory is less well developed for coverage above one monolayer. Here we present results of calculations on the adsorption process in forming the second water layer, that is, the adsorption of water on the fully hydrated surface. We show that there are many competitive adsorption sites owing to the numerous hydrogen-bonding possibilities. The presence of the second layer water molecules facilitates proton transfer among the adsorbates within chainlike configurations, and we present some illustration of these processes. We show how the adsorption energetics computed here along with recent calculations on defective surface and low-coverage adsorption may be used to provide a satisfactory interpretation of the temperature programmed desorption data for this system. Finally, we compute the vibrational spectrum for H and compare with the high-resolution electron-energy-loss spectroscopy measurements.
Controlling crystallization of Pb(Zr,Ti)O3 thin films on IrO2 electrodes at low temperature through interface engineering
Authors: Maki K. , Liu B. T. , Vu H. , Nagarajan V. , Ramesh R. , Fujimori Y. , Nakamura T. , Takasu H.
Published: February 2003

Pb ( Zr,Ti ) O 3 (PZT) capacitors were fabricated on IrO2–Si substrates with and without SrRuO3 (SRO) template layers using a modified sol-gel process. The crystallization temperature of PZT films was lowered significantly by interposing a thin SRO layer between the PZT and IrO2, which modifies the nucleation and growth of perovskite PZT by acting as a structural and chemical template. At 450 °C, the films deposited directly on IrO2 were not perovskite phase and therefore not ferroelectric; at 550 °C, they exhibited a mixed perovskite–pyrochlore microstructure. In contrast, the introduction of a thin (10–50 nm) SRO template layer yielded complete perovskite phase at temperatures down to 450 °C. Test capacitors exhibited desirable ferroelectric properties, including low saturation voltage, high resistivity, small pulse-width dependence, and good fatigue endurance, which provides a promising way to low-temperature integration of high-density ferroelectric random access memories with a stacked-type capacitor structure.
Absence of the rotator phase and evolution of dynamical motions in cluster monolayers
Authors: Mukhopadhyay R. , Mitra S. , Pradeep T. , Tsukushi I. , Ikeda S.
Published: February 2003

Alkyl chain dynamics in monolayer protected metal cluster systems has been studied by the quasielastic neutron scattering technique, using two different instruments having very different energy windows. Long chain thiolate protected clusters such as Au–ODT (Au–SC18H37) are rotationally frozen at room temperature (RT) in a wide time scale of 10−9 to 10−12 s. The rotator phase is absent at RT even in much smaller chain length systems, Au–OT (Au–SC8H17) and Au–HT (Au–SC6H13). Dynamics was found to evolve upon increase in temperature. Alkyl chains in a metal cluster superlattice such as Ag–ODT (Ag–SC18H37) are also dynamically frozen at RT in the whole time scale range. Evolution of dynamics with temperature is found to be different in the superlattice and isolated cluster systems. In the former, the chains participating in the inter-cluster interaction were found to be dynamically different from those without. On heating just above the chain melting temperature (Tcm), chains not involved in the inter-cluster interaction become dynamic first. Other chains start softening subsequently and, on increasing temperature near to the superlattice melting, all the chains eventually become dynamic. The uniaxial diffusion motion about the chain axis consistently described the dynamics of the monolayers, both in isolated cluster and in superlattice systems. Direct information on the dynamics of cluster monolayers is obtained for the first time.
Hamiltonian guiding center equations in toroidal magnetic configurations
Authors: White Roscoe , Zakharov Leonid E.
Published: February 2003

Guiding center equations for particle motion in a toroidal magnetic configuration are derived using general magnetic coordinates. For the case of axisymmetry, the explicit transformation to exact Hamiltonian canonical variables is presented for the first time. Approximate canonical coordinates are introduced also for three-dimensional configurations with strong toroidal magnetic field. Previous derivations made use of so-called Boozer equilibrium coordinates, which are highly nonuniform and are canonical only in the exceptional case of low beta, up–down symmetric configurations. The present formalism is valid for arbitrary, spatially well distributed magnetic coordinates, greatly increasing the accuracy of calculations. Magnetostatic equilibrium is not assumed in the present formalism, the analysis holds for any configuration with nested flux surfaces.
Collision effects on the saturated electrostatic potential along a magnetic field line
Authors: Katanuma I. , Tatematsu Y. , Ishii K. , Saito T. , Yatsu K.
Published: February 2003

The Coulomb collision effects on a saturated electrostatic potential (plug potential) formation in the end-mirror cell of a tandem mirror were investigated by a Monte Carlo simulation of ion orbits. A non-Maxwellian electron distribution function, which leads to a modified Boltzmann law, is assumed to obtain the electrostatic potential. An ion velocity distribution is determined by the Monte Carlo simulation of ions. It was found that a saturated electrostatic potential is formed in a wide range of the Coulomb collisionality. Especially, fewer Coulomb collisions were found to create a higher saturated electrostatic potential along a magnetic field, although the Coulomb collisions are necessary for a saturated electrostatic potential formation.
Dynamics of Al thin foils irradiated by a subpicosecond high intensity laser pulse
Authors: Gallant P. , Kieffer J. C. , Dorchies F. , Peyrusse O.
Published: February 2003

The decompression time of very thin self-standing aluminum foils (500 Å<thickness<2500 Å) irradiated by a high intensity P-polarized ultrashort laser pulse (I∼1018 W/cm2, tFWHM∼400 fs) has been measured. Results, inferred from a quantitative analysis of time resolved x-ray spectroscopy (500 fs resolution), indicate that the target decompression, during the few picoseconds after the laser pulse, is faster with thinner foil and with higher intensity. However, the measured expansion is slower than the one calculated with one-dimensional hydrodynamic calculation. Limits of the experimental method and possible sources of discrepancies are discussed.
Dopants for independent control of precessional frequency and damping in Ni81Fe19 (50 nm) thin films
Authors: Reidy S. G. , Cheng L. , Bailey W. E.
Published: February 2003

Dilute impurities can be used to control the dynamical response of ferromagnetic thin film magnetization at frequencies >1 GHz. Central lanthanide dopants (Sm, Eu, Tb, Dy, and Ho) have been investigated for their effect on the magnetization dynamics of Ni81Fe19 (50 nm). We find that Sm, Dy, and Ho contribute an increase on damping α up to four times stronger per concentration than that provided by Tb, with minimal effect on precessional frequency. One dopant, Eu, leaves α unchanged but boosts the resonant frequency fp of the system by ∼500 MHz for 3% addition, equivalent to a dynamic anisotropy field of 9 Oe, “stiffening” the system. The results indicate that precessional frequency and damping may be controlled independently in magnetoelectronic device materials.
Influence of betatron oscillation on filamentation instability in self-pinched hollow electron beam
Authors: Uhm Han S. , Choi Eun H.
Published: February 2003

Influence of the betatron oscillation on stability properties of the filamentation instability in a self-pinched hollow electron beam is investigated within the framework of the Vlasov–Maxwell equations, assuming that an infinitely long hollow electron beam is propagating through an annular plasma channel where the collisions between plasma electrons and neutral gas molecules dominate on all physical processes. The dispersion relation of the body wave perturbations is obtained, including influence of the amplitude of the betatron oscillation and of a spread in the canonical angular momentum on stability properties. It is shown that growth rate of the high azimuthal-mode perturbations in body wave is substantially reduced by the amplitude of the betatron oscillation. The necessary and sufficient condition for instability of the surface perturbations originated from current neutralization f indicates that the finite beam thickness has strong stabilizing influence. Previous simulation data are in qualitative agreement with the analytical results. However, the theoretical analysis overestimates the growth rate in comparison with simulation data.
Long time scale electron beam penetration of blowoff plasma in multipulse x-ray radiography
Authors: Sgro A. G. , Kwan T. J. T.
Published: February 2003

In the context of multipulse x-ray radiography, the interaction of a relativistic electron beam pulse with the low density halo surrounding the blowoff plasma from a target due to previous pulses is calculated in two dimensions on time scales comparable to the pulse duration. In the halo, the density of the beam and plasma system is low enough that the interaction is collisionless. At the outer edge of the halo, the density is lower than the beam density. The electric field due to the impinging beam rapidly pushes the background electrons radially outward and the beam is not disrupted by the two stream instability because of the absence of the background electrons. As the beam propagates closer to the target where the background density is much higher than the beam density, some electrons are also pushed radially outward, but most remain. The beam propagates through about the first 5 cm of the background before a part of it is disrupted at early times by the two stream instability. At later times, the instability is extinguished when a channel deficient in background electrons forms through which the beam then propagates without further significant disruption. The beam spot size is restored and the remains comparable to the initial size.
Comparison between kinetic and fluid simulations of slab ion temperature gradient driven turbulence
Authors: Sugama H. , Watanabe T.-H. , Horton W.
Published: February 2003

A detailed comparison between kinetic and fluid simulations of collisionless slab ion temperature gradient driven turbulence is made. The nondissipative closure model (NCM) for linearly unstable modes, which is presented by Sugama, Watanabe, and Horton [Phys. Plasmas 8, 2617 (2001)], and the dissipative closure model by Hammett and Perkins (HP) [Phys. Rev. Lett. 64, 3019 (1990)] are used in separate fluid simulations. The validity of these closure models for quantitative prediction of the turbulent thermal transport is examined by comparing nonlinear results of the fluid simulations with those of the collisionless kinetic simulation of high accuracy. Simulation results show that, in the saturated turbulent state, the turbulent thermal diffusivity χ obtained from the HP model is significantly larger than the χ given by the NCM which is closer to χ measured in the kinetic simulation. Contrary to the dissipative form of the parallel heat flux closure relation assumed in the HP model, the NCM describes well the exact kinetic simulation, in which for some unstable wave numbers k, the imaginary part of the ratio of the parallel heat flux qk to the temperature fluctuation Tk is a oscillatory function of time and sometimes takes positive values. The positive values of Im(qk/Tk), imply the negative parallel heat diffusivity, correlate with the occasional inward heat flux occurring for the wave numbers k, and reduce the total χ.
Spatial distribution of ion energies in an inertial electrostatic confinement device
Authors: Khachan J. , Moore D. , Bosi S.
Published: February 2003

The spatial distribution of ion energies was measured in an inertial electrostatic confinement device, which can be used as a small nuclear fusion source for the generation of neutrons. Using Doppler shift spectroscopy and a single ended Langmuir probe it was found that a virtual anode was established at the center of the electrostatic potential well resulting in much reduced ion energies at this point. Moreover, there was direct correlation between the ion energies and the spatial plasma potential showing the validity of the probe measurements. It was shown that the ion energy is a maximum at the point where the potential is the deepest, which occurs about halfway between the center and the cathode radius.
Relativistic electromagnetic solitons in a warm quasineutral electron–ion plasma
Authors: Lontano Maurizio , Passoni Matteo , Bulanov Sergei V.
Published: February 2003

The one-dimensional model for the interaction of electromagnetic (EM) waves of relativistic amplitude with a multicomponent hot plasma developed in a previous paper [M. Lontano et al., Phys. Plasmas 9, 2562 (2002)] is applied to the case of an electron–ion plasma. It is assumed that the plasma responds to the presence of large amplitude EM fields by retaining its quasineutrality, that is |Ne−ZNi|/Ne≪1, where Ne and Ni are the electron and ion density, respectively, and Z is the ion charge state. Contrary to what happens with drifting solitons, it is found that standing solitons admit relativistic and ultrarelativistic amplitudes, depending on the plasma temperature. Moreover, it is shown that even in “cold” plasmas the finite temperature directly determines the intensity and the shape of the localized solutions. Large amplitude solitons are found also in the case of different electron and ion temperatures. In addition, the “penetration depth” of an EM wave in a relativistic plasma is discussed, and scalings with the temperature and frequency are obtained. The validity limits of the quasineutral approximation is discussed in the light of the results of the available multidimensional numerical simulations and of the first experimental observations of soliton-like EM structures in high density plasmas.
Suppression of magnetic instabilities in accelerating plasma surfaces by sheared electron flow
Authors: Chakrabarti Nikhil
Published: February 2003

The effect of sheared poloidal electron flow on interchange instability associated with electron inertia in a magnetized plasma is studied. By a nonmodal calculation, it is shown that due to the sheared transverse electron flow, the growth rate of the magnetic interchange instability may suppress when certain critical conditions are met. That transient growth rate of the mode is arrested and has been demonstrated from the analytic solutions. For the complete stabilization the importance of dissipative effects are shown in an approximate analysis.
Endohedral motions inside capped single-walled carbon nanotubes
Authors: Cioslowski Jerzy , Rao Niny , Pernal Katarzyna , Moncrieff David
Published: February 2003

B3LYP/6-311G* electronic structure calculations reveal that the dependence of the complexation energy Ecmpl(z) on the longitudinal displacement z of the guest in endohedral complexes of the Na+ cation with capped [5,5] armchair single-walled carbon nanotubes stems from an interplay between the polarization of the host by the electric field of the guest and the guest–host steric repulsion. Overall, Ecmpl(z) is characterized by the presence of a periodic pattern of local minima and maxima that reflect the discrete nature of the tube and of a pair of global minima located at fixed distances from the tube termini. Because of the large barrier height/zero-point energy ratio, the endohedral motion of the Na+ cation at T=0 [K] is largely confined to a surface that internally follows the contour of the tube. Vibrations perpendicular to the surface give rise to transitions in the vicinity of 100 [cm−1], whereas the unimpeded motions within the surface result in a plethora of transitions with onsets as low as 0.1 [cm−1].
Resistance proof, folding-inhibitor drugs
Authors: Broglia R. A. , Tiana G. , Berera R.
Published: February 2003

Conventional drugs work, as a rule, by inhibiting the enzymatic activity of specific proteins, capping their active site. In this paper we present a model of nonconventional drug design based on the inhibiting effects small peptides obtained from segments of the protein itself have on the folding ability of the system. Such peptides attach to the newly expressed (unfolded) protein and inhibit its folding, inhibition which cannot be avoided but through mutations which in any case denaturate the enzyme. These peptides, or their mimetic molecules, can be used as effective alternative drugs to those already available, displaying the advantage of not suffering from the upraise of resistance.
Self-affine roughness effects on the double-layer charge density and capacitance in the nonlinear regime
Authors: Palasantzas G. , Backx G. M. E. A.
Published: February 2003

In this paper we investigate the influence of self-affine roughness on the charge density and capacitance of electrical double layers within the nonlinear regime. The roughness influence is significant for small roughness exponents (H<0.5) and/or large long wavelength roughness ratios w/ξ, as well as small Debye lengths λD (<ξ). With increasing electrode voltage, the apparent charge density increases fast in an exponential manner for relatively high voltages. On the other hand, the charge capacitance increases up to a maximum after which it approaches an asymptotic value, which is determined by the roughness ratio of the actual to apparent flat interface area. The roughness influence is amplified within the nonlinear regime if the interface becomes rougher at any lateral roughness wavelength (smaller exponent H and/or larger ratio w/ξ). Finally, the total charge capacitance, which is obtained by considering the contribution from the thin Helmholtz layer, is also shown to be highly sensitive to interface roughness details within the nonlinear regime.
Energy landscapes of model glasses. II. Results for constant pressure
Authors: Middleton Thomas F. , Wales David J.
Published: February 2003

New geometry optimization techniques are introduced for characterizing local minima, transition states, and pathways corresponding to enthalpy surfaces at constant pressure. Results are obtained for comparison with the potential energy surfaces of model glass formers studied in previous work. The constant pressure condition, where the the box lengths of the simulation cell vary, makes the enthalpy surface less rugged than the potential energy surface corresponding to the same mean density. Analysis of barrier heights as a function of pressure provides insight into transport and relaxation processes. Elementary rearrangements can be separated into “diffusive” and “nondiffusive” processes, where the former involve changes in the nearest-neighbor coordination of at least one atom, and the latter do not. With increasing pressure the barrier heights for cage-breaking rearrangements rise, while those for cage-preserving rearrangements appear relatively unchanged. The “strong” or “fragile” character of the system can therefore change with pressure because the barriers encountered vary in a systematic fashion. The geometric mean normal mode frequencies of a binary Lennard-Jones system decrease with increasing potential energy for constant pressure, rather than increase as they do at constant volume, in agreement with a simple model.
Molecular dynamics study of aqueous solvation dynamics following OClO photoexcitation
Authors: Brooksby Craig , Prezhdo Oleg V. , Reid Philip J.
Published: February 2003

The solvation dynamics following photoexcitation of aqueous chlorine dioxide (OClO) are investigated by classical molecular dynamics. A total of four OClO/water models are employed, including standard and customized OClO models together with SPC/F and TIP3P water. The simulation results are used to predict the time scale of solvent-induced optical dephasing, and excellent agreement with experiment is observed. The simulations demonstrate that the solvation dynamics of aqueous OClO are dominated by the short-ranged mechanical solute–solvent interactions. When compared to the aqueous solvation of spherical solutes, the solvation dynamics of OClO exhibit a novel effect. The role of the faster translational and librational water motions is suppressed in the dielectric component of the response, but is emphasized in the mechanical response, in stark contrast to the results for other spherical systems. The faster translational motions appear in the mechanical response due to the noncentrosymmetric nature of the OClO–water interaction, enhanced by OClO–water hydrogen bonding.
Study of the energy transfer processes in polyfluorene doped with tetraphenyl porphyrin
Authors: Lyons Benjamin P. , Wong Kam Sing , Monkman Andrew P.
Published: February 2003

The energy transfer processes between polyfluorene and tetraphenyl porphyrin have been investigated through steady state and time resolved measurements. Radiative transfer is found to be negligible and so the results are analyzed in terms of Förster resonance energy transfer. Rate equations are fitted to the experimental data to obtain values for the concentration dependent energy transfer rate. From this, we calculate a value of 38 Å for the energy transfer distance. This compares well with the value for the Förster radius we calculate from the spectral overlap, even though Förster theory is not strictly valid for this system.
Estimation of the degree of hydrogen bonding between quinoline and water by ultraviolet–visible absorbance spectroscopy in sub- and supercritical water
Authors: Osada Mitsumasa , Toyoshima Katsunori , Mizutani Takakazu , Minami Kimitaka , Watanabe Masaru , Adschiri Tadafumi , Arai Kunio
Published: February 2003

UV–visible spectra of quinoline was measured in sub- and supercritical water (25 °C<T<430 °C and 0.1 MPa<P<40 MPa), and the degree of hydrogen bonding between quinoline and water was estimated from solvatochromic shifts in the π–π* absorbance band. Hydrogen bonding decreased with increasing temperature from 25 to 360 °C. At supercritical conditions (380 °C<T<400 °C), hydrogen bonding abruptly decreased where the isothermal compressibility of water was large (0.5<ρr<1.5). In this condition, local density around quinoline was lower than bulk density, namely negative solvation, and it led to the cleavage of hydrogen bonding between quinoline and water.
Effective interaction range in the spin crossover phenomenon: Wajnflasz and domain models
Authors: Nishino Masamichi , Miyashita Seiji , Boukheddaden Kamel
Published: February 2003

The importance of cooperative interaction has been pointed out in the spin crossover phenomena. Sorai and co-workers have proposed a so-called domain model, in which the degree of correlation is expressed by a phenomenological parameter characterizing the sharpness of the transition. Wajnflasz has introduced a pioneering statistical model, in which the microscopic interaction and the entropy effect are considered. In the present work, we study the relation between these two models. In particular, we derive the analytical relation between the effective interaction range of the domain model and the microscopic parameters of the Wajnflasz model.
Theoretical study of stereodynamics for the reactions Cl+H2/HD/D2
Authors: Chen Mao-Du , Han Ke-Li , Lou Nan-Quan
Published: February 2003

Studies on the dynamical stereochemistry of the Cl+H2 reaction and its isotopic variants, especially the isotope effect on the product polarization, have been performed at a collision energy of 6.0 kcal/mol on two potential energy surfaces, i.e., G3 surface [T. C. Allison et al., J. Phys. Chem. 100, 13575 (1996)] and BW2 surface [W. Bian and H.-J. Werner, J. Chem. Phys. 112, 220 (2000)]. Quantum mechanical and quasiclassical trajectories calculations of the polarization-dependent differential cross sections for the Cl+H2 reaction have been carried out on the BW2 potential energy surface, and the results indicate that the quasiclassical approximation in general does as good as exact quantum mechanics. Calculations also show that the rotational alignment of the HCl product obtained on the BW2 surface for Cl+H2 reaction is stronger than that calculated on the G3 surface, which implies that the effect of van der Waals force on product polarization is quite weak. The distributions of P(θr) and P(φr) derived from the Cl+H2 and its isotopic reactions indicate that the isotope effect on the product polarization calculated on the G3 potential energy surface is distinct, whereas the isotope effect on the product polarization computed on the BW2 surface is indistinct.
The relative contributions of temperature and volume to structural relaxation of van der Waals molecular liquids
Authors: Paluch M. , Roland C. M. , Casalini R. , Meier G. , Patkowski A.
Published: February 2003

Pressure-volume-temperature measurements were carried out on two van der Waals liquids, 1,1′-bis(p-methoxyphenyl)cyclohexane (BMPC) and 1,1′-di(4-methoxy-5methylphenyl)cyclohexane (BMMPC). In combination with dielectric spectroscopy results, the relative contribution of temperature and density to the structural relaxation times were quantified. We find that the ratio of the isobaric expansion coefficient [−ρ−1 (∂ρ/∂T)P, where ρ is mass density and T is temperature, evaluated at P=0.1 MPa] to the coefficient of isochronal expansivity [−ρ−1 (∂ρ/∂T)τ, evaluated at τ=1 s] equals 0.58 and 0.72 for BMPC and BMMPC, respectively. This indicates that density exerts more influence on the structural relaxation times than does thermal energy. Corroborating this finding, the ratio of the isochoric activation energy to the activation energy at constant pressure is determined to be ca. 0.4 at ambient pressure for both glass formers. The prevalence of density over thermal energy is contrary to prevailing ideas concerning the dynamics of supercooled liquids, and must be taken into account in developing models of the glass transition.
Polyaniline nanotube composites: A high-resolution printable conductor
Authors: Blanchet Graciela B. , Fincher C. R. , Gao F.
Published: February 2003

Polyaniline/single wall carbon nanotube composites were prepared to be used as printable conductors for organic electronics devices. We show here that the high aspect ratio of single wall carbon nanotubes enables percolation into a conducting network at extremely low nanotube concentration. The nature of the transport mechanism is revealed by the temperature dependence of the conductivity of these percolating composites. We demonstrate here that these thin composite films are printable via laser ablation with high resolution while retaining appropriate conductivity. The utility of these findings is illustrated by printing structures, which could serve as a source and drain with 7 μm channel and 2 S/cm conductivity for use in plastic transistors.
Physicochemical properties of HfO2 in response to rapid thermal anneal
Authors: Lysaght Patrick S. , Foran Brendan , Bersuker Gennadi , Chen Peijun J. , Murto Robert W. , Huff Howard R.
Published: February 2003

Changes in the composition of atomic layer deposited, uncapped hafnium dioxide films, as a function of anneal temperature, have been evaluated by several advanced analytical techniques including; x-ray reflectivity, high-resolution transmission electron microscopy, and medium energy ion scattering. It is shown that such measurements of the high-k/Si interface layer are inconclusive and may be misinterpreted to suggest the presence of an HfxSi1−xO2 (x∼0.5) transition layer. It is also demonstrated that high-temperature anneal of uncapped films may result in the formation of voids which propagate through the dielectric layer into the silicon substrate. Trends associated with defect generation, interfacial oxide growth, and the low probability of material intermixing during anneal processing are discussed.
Nanopore sequencing of polynucleotides assisted by a rotating electric field
Authors: Chen C.-M. , Peng E.-H.
Published: February 2003

The translocation kinetics of a polynucleotide chain through a nanopore is studied using Monte-Carlo simulations for both lattice and off-lattice models, by which we demonstrate a method in sequencing polynucleotides assisted by a rotating electric field. At low frequencies of the rotating field, the translocation time of the chain is inversely proportional to the rotating field frequency. More specifically, in these cases, the translocation time of each nucleotide is nearly quantized, and thus it greatly improves the resolution of blockade-current time series obtained from nanopore sequencing experiments. The polynucleotide sequences can be accurately determined from analyzing several time series of current variation through the nanopore.
Effect of additional nonmagnetic acceptor doping on the resistivity peak and the Curie temperature of Ga1−xMnxAs epitaxial layers
Authors: Yuldashev Sh. U. , Im Hyunsik , Yalishev V. Sh. , Park C. S. , Kang T. W. , Lee Sanghoon , Sasaki Y. , Liu X. , Furdyna J. K.
Published: February 2003

We have investigated the effect of additional doping by Be on the properties of Ga1−xMnxAs (x=0.03). For this relatively low value of x, the Curie temperature is observed to increase with increasing Be concentration. We show that the temperature dependence of the resistivity at zero magnetic field, including the resistivity maximum near the Curie temperature, can be successfully described by the magnetoimpurity scattering model proposed by Nagaev [Phys. Rep. 346, 387 (2001)] in both the paramagnetic and the ferromagnetic temperature regions. Quantitative analysis of the data in terms of this model yields the value of the p–d exchange energy |N0β|≈1.6 eV for Ga0.97Mn0.03As.