bluuebunny/crossref_metadata_2025 huggingface dataset:
Motor performance and magnetic properties of rotors with directly injected bonded magnets in laminated Fe-Si sheets
Authors: Komuro Matahiro , Kawamata Shouichi , Tajima Fumio , Koharagi H.
Published: May 2005

Directly injected bonded magnets in rotors have attracted attention because the injection process has various advantages compared to the application of sintered magnets. Anisotropic Nd2Fe14B, Sm2Fe17N3, and Sm2Co17 compounds were directly injected in rotors with laminated Fe-Si sheets. All bonded magnets had easy magnetization direction in the radial direction. The value of the coercive force for injected Nd2Fe14B was 17.9kOe at 298K and was smaller than that for Sm2Co17 at 398K. Demagnetization was found for all the bonded magnets in a magnetic field of −1kOe at 398K. The induced voltage wave forms for the three rotors showed sine waves. The value of induced voltage for Nd2Fe14B bonded magnet rotor reduced with increasing temperature by −0.16%∕K, which is in agreement with the temperature coefficient of Br.
Self-consistent model of field gradient driven particle aggregation in magnetic fluids
Authors: Hovorka O. , Yellen B. , Dan N. , Friedman G.
Published: May 2005

Particle aggregation in magnetic colloids driven by strong magnetic field gradients is studied using self-consistent field calculations. The model takes into account field screening due to average fluid magnetization and demagnetizing field arising from spatially varying magnetic particle concentration. Solutions for the problem of particle aggregation due to a single magnetic pole demonstrate that, in high particle concentration, the magnetic field must be calculated self-consistently.
Magnetization characteristics and inductance of transformer
Authors: Yamamoto T. , Sonoda T.
Published: May 2005

To produce the necessary secondary ac voltage using a transformer it is sufficient to control the current in the excitation winding so that the secondary voltage matches its desired value. The precision of the resulting secondary voltage, however, is affected by the stability of the voltage control circuit, and there have been practical limits to the achievable precision. Any discussion of the stability of voltage control circuits must begin with a clarification of the relationship between transformer excitation parameters and transformer constants. This paper verifies change in transformer constants to excitation parameters in an effort to develop design guidelines for the voltage control circuit. The B-H loop was found to differ widely for cores using voltage source excitation method, current source excitation method, and flux-controlling type excitation method.
Surface tension measurement techniques of magnetic fluids at an interface between different fluids using perpendicular field instability
Authors: Amin M. Shahrooz , Elborai Shihab , Lee Se-Hee , He Xiaowei , Zahn Markus
Published: May 2005

Two measurement techniques to determine the surface tension of ferrofluids using the perpendicular field instability are described. Four ferrofluid layers were examined with magnetic field applied perpendicularly to the surface of (1) oil-based ferrofluid in air; (2) water-based ferrofluid in air, (3) oil-based ferrofluid, and (4) fluorocarbon-based ferrofluid, both below a blend of 50% n-Propyl alcohol and 50% deionized water (propanol). Surface tension was accurately calculated by utilizing the measured Taylor wavelength from measurements of incipient fluid instability peaks and the measured densities of fluids. For cases (1) and (2), the calculated surface tension values were in good agreement with a tensiometer measurement. No accurate tensiometer measurements were conducted for the superposed liquids (3) and (4) since accurate tensiometer measurements are difficult for a two fluid layer system. The second less accurate method used the ferrofluid’s nonlinear Langevin magnetization characteristics to compute the surface tension from incipience of interfacial instability conditions. Discrepancies between the surface tensions measured by the two methods were probably due to the ferrofluid particle size distributions and the strong dependence of the ferrofluid magnetization on particle size.
Effect of rapid thermal annealing on the structure and magnetic properties of chemical vapor deposition cobalt layers
Authors: Deo N. , Bain M. F. , Montgomery J. H. , Gamble H. S.
Published: May 2005

This paper presents the results obtained on cobalt layers after rapid thermal annealing in N2 ambient at temperatures between 525 and 800°C. The cobalt layers were deposited by chemical vapor deposition from Co(CO)3NO on to oxidized-Si substrates at 450°C. As the anneal temperature increases from 525to800°C the percentage layer resistivity decrease goes from 35% to 55%. The lowest resistivity achieved was ∼11μΩcm for 300-nm-thick layers and ∼14μΩcm for 180-nm layer annealed in the range of 650–800°C. XRD analysis shows that a mixture of fcc and hcp cobalt grains is present in the as-deposited material. As the annealing temperature increases the fcc Co peaks increase due to crystallization of the material. This was confirmed by surface and microstructure analysis using SEM and AFM. The grain size had significantly increased to 200–300nm ranges for both 180- and 300-nm layers. From the hysteresis loops it was found that the coercivity values are significantly reduced to 25Oe from 350 and 140Oe due to high-temperature annealing to give soft magnetic property.
Universal method for computation of electrostatic potentials
Authors: Sundholm D.
Published: May 2005

A computational approach to determine electrostatic interaction and gravitational potentials by performing direct numerical integration is presented. The potential is expanded using finite-element functions of arbitrary order. The method does not involve any solutions of systems of linear equations. The potential is instead obtained as a sum of differential contributions. Thus, no boundary conditions for the potential are needed. It is computationally efficient and well suited for parallel computers, since the innermost loops constitute matrix multiplications and the outer ones can be used as parallel indices. Without using prescreening or other computational tricks to speed up the calculation, the algorithm scales as N4∕3 where N denotes the grid size.
Iterative CI general singles and doubles (ICIGSD) method for calculating the exact wave functions of the ground and excited states of molecules
Authors: Nakatsuji Hiroshi , Ehara Masahiro
Published: May 2005

The iterative configuration-interaction general singles and doubles (ICIGSD) method was applied to various closed- and open-shell electronic states of molecules within finite basis sets and was shown to give the exact results that are identical to the full CI ones. The structure of the ICIGSD is unique among the ICI formalisms, that is, the singularity problem intrinsic to atomic and molecular Hamiltonians can be avoided. The convergence of the ICIGSD method was fairly good regardless of the characters of the electronic states and the qualities of the basis sets; only several iterations were enough for obtaining microhartree accuracy. These favorable properties are attributed to the unique GSD structure. The present method was shown to be applicable to various spin states and to quasidegenerate states appearing in bond dissociation process. We have also applied the ICIGSD-CI method to calculate the excited states simultaneously. We have confirmed that the ICIGSD-CI method is accurate for calculating the excited states the symmetries of which are not only similar to but also different from that of the ground state.
Interactions of Li, Ca, and Al with aromatic carbon materials: An ab initio study
Authors: Zhao Y. L. , Lin C. S. , Zhang R. Q. , Wang R. S.
Published: May 2005

The interactions of benzene (C6H6), naphthalene (C10H8), and perinaphthene (C13H9) with metal atoms (Li, Ca, and Al) were studied using second-order Møller–Plesset perturbation theory. By analyzing the frontier molecular orbitals, geometric structures, binding energies, and charge transfers, it was found that these metal atoms can bond strongly with C13H9, but can only bond weakly with C6H6 and C10H8. The bonding nature between a metal atom and C13H9 at their ground state depends significantly on the valence orbital of the metal atom and the π-bonding distribution of the aromatic hydrocarbons. The spindly shaped 3p valence orbital of an Al atom results in the deviation of the adsorption site to the edge of C13H9, whereas the ball-shaped 2s∕4s valence orbitals of a Li and a Ca atom facilitate their overlap with the second lowest unoccupied molecular orbital of C13H9. Further, Hartree–Fock and density-functional theory methods were demonstrated generally to be unreliable in describing the interactions of metal atoms with these π systems.
Through-space contributions to two-dimensional double-quantum J correlation NMR spectra of magic-angle-spinning solids
Authors: Fayon Franck , Massiot Dominique , Levitt Malcolm H. , Titman Jeremy J. , Gregory Duncan H. , Duma Luminita , Emsley Lyndon , Brown Steven P.
Published: May 2005

A routinely used assumption when interpreting two-dimensional NMR spectra obtained with a commonly used double-quantum (DQ) magic-angle-spining (MAS) pulse sequence referred to as the refocused incredible natural abundance double-quantum transfer experiment (INADEQUATE) [A. Lesage, M. Bardet, and L. Emsley, J. Am. Chem. Soc. 121, 10987 (1999)] has been that correlation peaks are only observed for pairs of nuclei with a through-bond connectivity. The validity of this assumption is addressed here by theory, experiment, and computer simulations. If the isotropic chemical shifts of the two nuclei are different and the MAS frequency is far from rotational resonance, the theoretical description demonstrates that DQ correlation peaks are indeed indicative of a J coupling. However, if the isotropic chemical shifts are the same, it is shown that DQ peaks can appear for pairs of nuclei even in the absence of a through-bond J coupling. These peaks appear in the specific case of a pair of nuclei with a nonzero through-space dipole-dipole coupling and chemical shift anisotropy tensors having different principal magnitudes or orientations, provided that the MAS frequency is comparable to or smaller than the chemical shift anisotropies. Experimental P31 spectra recorded on a sample of TiP2O7 and computer simulations show that the magnitude of these anomalous peaks increases with increasing B0 magnetic field and that they decrease with increasing MAS frequency. This behavior is explained theoretically.
Anion of the formic acid dimer as a model for intermolecular proton transfer induced by a π* excess electron
Authors: Bachorz Rafał A. , Harańczyk Maciej , Dąbkowska Iwona , Rak Janusz , Gutowski Maciej
Published: May 2005

The neutral and anionic formic acid dimers have been studied at the second-order Møller–Plesset and coupled-cluster level of theory with single, double, and perturbative triple excitations with augmented, correlation-consistent basis sets of double- and triple-zeta quality. Scans of the potential-energy surface for the anion were performed at the density-functional level of theory with a hybrid B3LYP functional and a high-quality basis set. Our main finding is that the formic acid dimer is susceptible to intermolecular proton transfer upon an excess electron attachment. The unpaired electron occupies a π* orbital, the molecular moiety that accommodates an excess electron “buckles,” and a proton is transferred to the unit where the excess electron is localized. As a consequence of these geometrical transformations, the electron vertical detachment energy becomes substantial, 2.35 eV. The anion is barely adiabatically unstable with respect to the neutral at 0 K. However, at standard conditions and in terms of Gibbs free energy, the anion is more stable than the neutral by +37meV. The neutral and anionic dimers display different IR characteristics. In summary, the formic acid dimer can exist in two quasidegenerate states (neutral and anionic), which can be viewed as “zero” and “one” in the binary system. These two states are switchable and distinguishable.
High-order discretization schemes for biochemical applications of boundary element solvation and variational electrostatic projection methods
Authors: Gregersen Brent A. , York Darrin M.
Published: May 2005

A series of high-order surface element discretization schemes for variational boundary element methods are introduced. The surface elements are chosen in accord with angular quadrature rules for integration of spherical harmonics. Surface element interactions are modeled by Coulomb integrals between spherical Gaussian functions with exponents chosen to reproduce the exact variational energy and Gauss’s law for a point charge in a spherical cavity. The present work allows high-order surface element expansions to be made for variational methods such as the conductorlike screening model for solvation and the variational electrostatic projection method for generalized solvent boundary potentials in molecular simulations.
Ions in water: The microscopic structure of concentrated hydroxide solutions
Authors: Imberti S. , Botti A. , Bruni F. , Cappa G. , Ricci M. A. , Soper A. K.
Published: May 2005

Neutron-diffraction data on aqueous solutions of hydroxides, at solute concentrations ranging from 1 solute per 12 water molecules to 1 solute per 3 water molecules, are analyzed by means of a Monte Carlo simulation (empirical potential structure refinement), in order to determine the hydration shell of the OH− in the presence of the smaller alkali metal ions. It is demonstrated that the symmetry argument between H+ and OH− cannot be used, at least in the liquid phase at such high concentrations, for determining the hydroxide hydration shell. Water molecules in the hydration shell of K+ orient their dipole moment at about 45° from the K+-water oxygen director, instead of radially as in the case of the Li+ and Na+ hydration shells. The K+-water oxygen radial distribution function shows a shallower first minimum compared to the other cation-water oxygen functions. The influence of the solutes on the water-water radial distribution functions is shown to have an effect on the water structure equivalent to an increase in the pressure of the water, depending on both ion concentration and ionic radius. The changes of the water structure in the presence of charged solutes and the differences among the hydration shells of the different cations are used to present a qualitative explanation of the observed cation mobility.
Energy landscape paving simulations of the trp-cage protein
Authors: Schug Alexander , Wenzel Wolfgang , Hansmann Ulrich H. E.
Published: May 2005

We evaluate the efficiency of multiple variants of energy landscape paving in all-atom simulations of the trp-cage protein using a recently developed new force field. Especially, we introduce a temperature-free variant of the method and demonstrate that it allows a fast scanning of the energy landscape. Nativelike structures are found in less time than by other techniques. The sampled low-energy configurations indicate a funnel-like energy landscape.
Switching in organic devices caused by nanoscale Schottky barrier patches
Authors: Kunardi Linda , Troadec Cedric , Chandrasekhar N.
Published: May 2005

We have identified a possible electronic origin of metal filaments, invoked to explain the switching behavior of organic devices. Interfaces of two representative organics polyparaphenylene (PPP) and poly(2-methoxy-5-2-ethyl-hexyloxy-1,4-phenylenevinylene) with Ag are investigated using ballistic emission microscopy. Nanometer scale spatial nonuniformity of carrier injection is observed in ballistic electron emission microscopy images of both interfaces. The measured Schottky barrier (SB) appears to be consistent with metal states tailing into the gap of the PPP. We find that the SB values exhibit a distribution, even for the diodes with low ideality factors. The implications of this distribution on the measured physical properties of the diode are discussed, in light of work on devices of similar geometry, published in the literature. We also demonstrate that patches of low SB are likely to nucleate current filaments which can cause local ionization and are reported to be responsible for the switching behavior observed in metal-organic, metal-CuS and Ag–AgSe structures.
Electronic spectroscopy of toluene–rare-gas clusters: The external heavy atom effect and vibrational predissociation
Authors: Doyle Richard J. , Love Emily S. J. , Da Campo Raffaello , Mackenzie Stuart R.
Published: May 2005

Toluene–X van der Waals clusters (where X=Ne, Ne2, Ar, Ar2, Kr, Xe) have been investigated by fluorescence excitation spectroscopy in the region of the S1-S0 transition. With the exception of Xe, for each rare-gas studied, we have assigned cluster transitions in the region of all the strong monomer vibrational bands up to 1000cm−1 above the origin band. We have further investigated the S1 relaxation dynamics for each vibrational level of each complex, via their fluorescence decay profiles. Clustering with neon has little appreciable effect on the vibrationless S1 lifetime. By contrast, the clusters with argon and krypton exhibit markedly shorter fluorescence lifetimes compared with the monomer. The effect is so severe in the case of toluene–Xe clusters that no fluorescence signals were observed. We interpret these results in terms of an external heavy atom effect in which the rate of intersystem crossing in toluene is influenced by the cluster partner. For clusters built upon excited S1 vibrational levels, the situation is potentially complicated by intramolecular vibrational redistribution and vibrational predissociation (VP). The majority of the fluorescence decay profiles were satisfactorily modeled using single exponential decays. The emission following pumping of the 371¯ level in the toluene–Kr cluster, however, is an exception. We have modeled the decay of this level with a simple kinetic scheme including VP and determined a predissociation rate of (1.04±0.54)×107s−1.
Response theory for vibrational wave functions
Authors: Christiansen Ove
Published: May 2005

A formalism for deriving and implementing response functions for vibrational wave functions is described. The formalism utilizes a recently developed second-quantization formulation of many-mode dynamics to define nonredundant parameterizations for different types of approximate vibrational wave functions. The derived response functions cover the cases of an exact state, a vibrational self-consistent field state, and a vibrational configuration interaction state. Sample calculations are presented for the linear-response function and response excitation energies for a two-mode model system and for formaldehyde employing a quartic force field. The advantages and disadvantages of the response theoretical approach for describing excitation energies using different parameterizations are discussed.
Overtone spectroscopy of H2O clusters in the vOH=2 manifold: Infrared-ultraviolet vibrationally mediated dissociation studies
Authors: Nizkorodov Sergey A. , Ziemkiewicz Michael , Nesbitt David J. , Knight Alan E. W.
Published: May 2005

Spectroscopy and predissociation dynamics of (H2O)2 and Ar–H2O are investigated with vibrationally mediated dissociation (VMD) techniques, wherein vOH=2 overtones of the complexes are selectively prepared with direct infrared pumping, followed by 193nm photolysis of the excited H2O molecules. As a function of relative laser timing, the photolysis breaks H2O into OH and H fragments either (i) directly inside the complex or (ii) after the complex undergoes vibrational predissociation, with the nascent quantum state distribution of the OH photofragment probed via laser-induced fluorescence. This capability provides the first rotationally resolved spectroscopic analysis of (H2O)2 in the first overtone region and vibrational predissociation dynamics of water dimer and Ar–water clusters. The sensitivity of the VMD approach permits several vOH=2 overtone bands to be observed, the spectroscopic assignment of which is discussed in the context of recent anharmonic theoretical calculations.
Guided ion-beam studies of the kinetic-energy-dependent reactions of Con+(n=2–16) with D2: Cobalt cluster-deuteride bond energies
Authors: Liu Fuyi , Armentrout P. B.
Published: May 2005

The kinetic-energy-dependent cross sections for the reactions of Con+(n=2–16) with D2 are measured as a function of kinetic energy over a range of 0–8 eV in a guided ion-beam tandem mass spectrometer. The observed products are ConD+ for all clusters and ConD2+ for n=4,5,9–16. Reactions for the formation of ConD+(n=2–16) and Co9D2+ are observed to exhibit thresholds, whereas cross sections for the formation of ConD2+ (n=4,5,10–16) exhibit exothermic reaction behavior. The Con+–D bond energies as a function of cluster size are derived from the threshold analysis of the kinetic-energy dependence of the endothermic reactions and are compared to previously determined metal–metal bond energies, D0(Con+–Co). The bond energies of Con+–D generally increase as the cluster size increases, and roughly parallel those for Con+–Co for clusters n⩾4. These trends are explained in terms of electronic and geometric structures for the Con+ clusters. The bond energies of Con+–D for larger clusters (n⩾10) are found to be very close to the value for chemisorption of atomic hydrogen on bulk-phase cobalt. The rate constants for D2 chemisorption on the cationic clusters are compared with the results from previous work on cationic and neutral cobalt clusters.
The (4,0) mode of HF dimer at 14700cm−1
Authors: Yu Zhenhong , Hammam Essam , Klemperer William
Published: May 2005

The ΔK=0 and 1 subbands of the (4,0)←(0,0) transition of (HF)2, near 14700cm−1, have been measured by molecular-beam intracavity laser-induced fluorescence. The hydrogen interchange tunneling is basically quenched in (4, 0) for both K=0 and 1 levels, consistent with the early suggestion from a phenomenological model [H.-C. Chang and W. Klemperer, J. Chem. Phys. 104, 7830 (1996)]. The band origin ν0=14700.458(7)cm−1 and rotational constant (B+C)∕2=0.222 78(31)cm−1 are determined for K=0 of the (4, 0) mode. From the observed ΔK=1←0 spectrum, we determined that A=24.3cm−1,(B+C)∕2=0.22296(20)cm−1, and (B−C)=4.5(2)×10−3cm−1. The predissociation linewidths of both K=0 and 1 levels are 470(30) MHz with no apparent rotational dependence.
Molecular dynamics simulation of the polymer electrolyte poly(ethyleneoxide)∕LiClO4. I. Structural properties
Authors: Siqueira Leonardo J. A. , Ribeiro Mauro C. C.
Published: May 2005

Molecular dynamics (MD) simulations of poly(ethylene oxide) (PEO)∕LiClO4 polymer electrolyte have been performed for three different salt concentrations (oxygen atoms of polymer to Li+ cations ratio of 31:1, 16:1, and 8:1) and two temperatures (373 and 500K). A united atom model, in which hydrogen atoms are not considered, has been used for PEO. The PEO model has been validated by comparing the static structure factor S(k) calculated by MD simulations of pure PEO at 363K (32 PEO chains with a molecular weight of 1174) with previous experimental data obtained by neutron scattering spectroscopy. A low wave-vector peak develops in the calculated S(k) when LiClO4 is added in the polymeric matrix, which indicates an extended-range order in PEO∕LiClO4 melts. Contact ionic pairs are observed, which are favored as temperature increases. PEO chain as a whole becomes less extended (smaller radius of gyration) upon addition of LiClO4. Radius of gyration increases with temperature at low salt concentration, but it is only marginally affected by temperature at high concentration.
Nucleation on cylindrical plates: Sharp transitions and double barriers
Authors: Husowitz B. , Talanquer V.
Published: May 2005

We apply methods of density-functional theory in statistical mechanics to study the properties of droplets and bubbles formed on a single cylindrical plate or between two such disks immersed in a metastable fluid. Our approach allows us to analyze the properties of different types of aggregates and investigate the effect of disk size, disk separation, and solid-fluid interactions on the dynamics of a liquid-vapor phase transition. The finite size of disks induces nucleation phenomena that are not observed in the cases of either a planar wall or a slit pore. Heterogeneous nucleation on a single disk is characterized by the existence of two distinct types of critical nuclei that control the phase-transition dynamics at different supersaturations. Asymmetric droplets or bubbles formed on one side of the disk are the preferred nucleation path at high supersaturations. However, these types of aggregates become unstable close to the binodal, where they abruptly collapse into nuclei that engulf the cylindrical plates. Droplet or bubble nucleation in between two disks may occur through a free-energy barrier with one or two maxima depending on the value of the system parameters and the supersaturation. Metastable droplets or bubbles corresponding to local minima of the free energy are observed forming between two plates only after density fluctuations in the system achieve a critical size. These types of aggregates only exist for cylindrical plates larger than a minimum size given a fixed distance between the disks. The stability of these droplets and bubbles decreases when the plates are separated.
Mechanisms of H2 dissociative adsorption on the Pt(211) stepped surface
Authors: McCormack Drew A. , Olsen Roar A. , Baerends Evert Jan
Published: May 2005

We utilize classical trajectory calculations to study the reaction dynamics of the dissociative adsorption of H2 on the stepped Pt(211) surface. The potential-energy surface has been obtained through an accurate interpolation of density-functional theory data at the generalized gradient approximation level, using the corrugation reduction procedure. New techniques for visualizing the collective dynamics of trajectories are introduced to elucidate the reaction mechanisms involved. Reaction exhibits a nonmonotonic dependence on collision energy, first decreasing with energy, and then increasing. A strong component of direct nonactivated reaction exists at the top edge of the step over the entire range of energies. The inverse relationship between reaction and collision energy at low energies is attributed to trapping in weak chemisorption wells. These wells also influence the direct reaction at the step, leading to a strong asymmetric dependence on incidence angle. Reaction on the terrace is activated, and only contributes significantly at high energies. Agreement with experiments on Pt(533) [A. T. Gee, B. E. Hayden, C. Mormiche, and T. S. Nunney, J. Chem. Phys. 112, 7660 (2000); Surf. Sci. 512, 165 (2002)] is good, and we are able to suggest new interpretations of the experimental data.
New observations regarding deterministic, time-reversible thermostats and Gauss’s principle of least constraint
Authors: Bright Joanne N. , Evans Denis J. , Searles Debra J.
Published: May 2005

Deterministic thermostats are frequently employed in nonequilibrium molecular dynamics simulations in order to remove the heat produced irreversibly over the course of such simulations. The simplest thermostat is the Gaussian thermostat, which satisfies Gauss’s principle of least constraint and fixes the peculiar kinetic energy. There are of course infinitely many ways to thermostat systems, e.g., by fixing ∑i∣pi∣μ+1. In the present paper we provide, for the first time, convincing arguments as to why the conventional Gaussian isokinetic thermostat (μ=1) is unique in this class. We show that this thermostat minimizes the phase space compression and is the only thermostat for which the conjugate pairing rule holds. Moreover, it is shown that for finite sized systems in the absence of an applied dissipative field, all other thermostats (μ≠1) perform work on the system in the same manner as a dissipative field while simultaneously removing the dissipative heat so generated. All other thermostats (μ≠1) are thus autodissipative. Among all μ thermostats, only the μ=1 Gaussian thermostat permits an equilibrium state.
Artifacts in dynamical simulations of coarse-grained model lipid bilayers
Authors: Jakobsen Ask F. , Mouritsen Ole G. , Besold Gerhard
Published: May 2005

With special focus on dissipative particle dynamics simulations of anisotropic and complex soft matter, such as lipid bilayers in water, we have investigated the occurrence of artifacts in the results obtained from dynamical simulations of coarse-grained particle-based models. The particles are modeled by beads that interact via soft repulsive conservative forces (as defined in dissipative particle dynamics simulations), harmonic bond potentials, as well as bending potentials imparting stiffness to the lipid tails. Two different update schemes are investigated: dissipative particle dynamics with a velocity-Verlet-like integration scheme [G. Besold, I. Vattulainen, M. Karttunen, and J. M. Polson, Phys. Rev. E 63, R7611 (2000)] and Lowe–Andersen thermostatting [C. P. Lowe, Europhys. Lett. 47, 145 (1999)] with the standard velocity-Verlet integration algorithm. By varying the integration time step, we examine various physical quantities, in particular pressure profiles and kinetic bead temperatures, for their sensitivity to artifacts caused by the specific combination of integration technique and the thermostat. We then propose a simple fingerprint method that allows monitoring the presence of simulation artifacts.
Shell-confined hydrogen atom
Authors: Sen K. D.
Published: May 2005

Calculations of electronic energy and static dipole polarizability are reported for the hydrogen atom in the ns states (n=1–6) confined between two impenetrable concentric spheres of inner and outer radii placed at the locations of the radial nodes corresponding to the free hydrogen ns (n=2–7) orbitals. Interesting new conditions of degeneracy arising due to the shell confinement are discussed. Shell-confined states of unusually high polarizability are predicted for hydrogen atom as the inner sphere radius is shifted towards the outer nodal points of the free atom corresponding to the higher principal quantum numbers.
Vibrational density of states and Lindemann melting law
Authors: Luo Sheng-Nian , Strachan Alejandro , Swift Damian C.
Published: May 2005

We examine the Lindemann melting law at different pressures using the vibrational density of states (DOS), equilibrium melting curve, and Lindemann parameter δL (fractional root-mean-squared displacement, rmsd, at equilibrium melting) calculated independently from molecular dynamics simulations of the Lennard-Jones system. The DOS is obtained using spectra analysis of atomic velocities and accounts for anharmonicity. The increase of δL with pressure is non-negligible: δL is about 0.116 and 0.145 at ambient and extreme pressures, respectively. If the component of rmsd normal to a reflecting plane as in the Debye–Waller-factor-type measurements using x rays is adopted for δL, these values are about 0.067(±0.002) and 0.084(±0.003), and are comparable with experimental and calculated values for face-centered-cubic elements. We find that the Lindemann relation holds accurately at ambient and high pressures. The non-negligible pressure dependence of δL suggests that caution should be exerted in applying the Lindemann law to obtaining the high pressure melting curve anchored at ambient pressure.
Feynman integrals for nonsmooth and rapidly growing potentials
Authors: de Faria Margarida , Oliveira Maria João , Streit Ludwig
Published: May 2005

The Feynman integral for the Schrödinger propagator is constructed as a generalized function of white noise, for a linear space of potentials spanned by finite (signed) measures of bounded support and Laplace transforms of such measures, i.e., locally singular as well as rapidly growing at infinity. Remarkably, all these propagators admit a perturbation expansion.
High-intensity positive beams extracted from a compact double-chamber ion source
Authors: Huck H. , Somacal H. , DiGregorio D. E. , Fernández Niello J. O. , Igarzábal M. , DiPaolo H. , Reinoso M.
Published: May 2005

This work presents the design and development of a simple ion source, the associated ion extraction optics, and the beam transport of a low-energy and high-current proton accelerator. In its actual version, the ion source can deliver positive proton currents up to 100mA. This rather high beam current is achieved by adding a small ionization chamber between the discharge chamber containing the filament and the extraction electrode of the ion source. Different parameters of the ion source and the injection beam line are evaluated by means of computer simulations to optimize the beam production and transmission.
Investigation of machine compliance uniformity for nanoindentation screening of wafer-supported libraries
Authors: Warren Oden L. , Dwivedi Arpit , Wyrobek Thomas J. , Famodu Olugbenga O. , Takeuchi Ichiro
Published: May 2005

The reliability of nanoindentation results can depend critically on an accurate assessment of the machine compliance term. The common practice is to determine the machine compliance from a small reference specimen, then apply its value to a much larger wafer-supported library. The present study investigates the validity of this approach by thoroughly testing bare 76.2 mm diameter, 410μm thick Si(100) wafers mounted on two vacuum chucks of different design. We find that the small-sample value of the machine compliance is adequate for the majority of the wafer, including areas directly over vacuum rings and a circular center port of ordinary dimensions. However, vacuum chucks with a tweezer slot should be avoided in combinatorial materials science applications. But even in the absence of a tweezer slot, it may be necessary to generate an accurate machine compliance map for the wafer perimeter if the thin-film library extends beyond the outermost vacuum ring to the wafer edge. The Young’s modulus and the hardness of silicon are found to be 169±3GPa and 12.2±0.2GPa, respectively, over well-mounted regions of the wafer; both values are in good agreement with the literature.
High-throughput synthesis equipment applied to polymer research
Authors: Hoogenboom Richard , Schubert Ulrich S.
Published: May 2005

To speed up synthetic polymer research, a workflow dedicated to automated polymer synthesis and characterization was developed. The workflow consists of several synthesis robots with online and offline analytical equipment. For screening of reaction parameters and for library synthesis, robots equipped with glass reactors and vortex agitation are applied that match very well the classical (small-scale) laboratory experiments. For the screening and library preparation also a microwave synthesizer can be used. For upscaling purposes and process development, a robot containing 100mL tank reactors with mechanical stirring is utilized. This robot also offers the possibility to continuously feed reagents to the reactor and to operate in batch, semibatch or continuous mode.
Use of fluorescence for the high-throughput evaluation of synergistic thermal and photo stabilizer interactions in poly (vinyl chloride)
Authors: Wu Chunyong , Wicks Douglas A.
Published: May 2005

The selection of thermal and photo stabilizers for poly (vinyl chloride) (PVC) using conventional methods is a time-consuming process. The high-throughput screening method developed in this research demonstrates rapid and efficient ways to quantify the effectiveness of PVC stabilizers with respect to raw plastic materials, stabilizers, levels of use, and testing conditions. An experimental protocol using liquid sampling and fluorescence measurement was developed to determine the effectiveness of formulations. This was used to evaluate the performance of stabilizers based on the change of fluorescence emission at 440nm after thermal aging or ultraviolet (UV) radiation. The performance of PVC formulations using six different types of stabilizers was successfully mapped for both PVC resin and flexible PVC.
UV photodissociation of the van der Waals dimer (CH3I)2 revisited: Pathways giving rise to ionic features
Authors: Vidma Konstantin V. , Baklanov Alexey V. , Khvorostov Evgeny B. , Ishchenko Valerii N. , Kochubei Sergei A. , Eppink André T. J. B. , Chestakov Dmitri A. , Parker David H.
Published: May 2005

The CH3I A-state-assisted photofragmentation of the (CH3I)2 van der Waals dimer at 248nm and nearby wavelengths has been revisited experimentally using the time-of-flight mass spectrometry with supersonic and effusive molecular beams and the “velocity map imaging” technique. The processes underlying the appearance of two main (CH3I)2 cluster-specific features in the mass spectra, namely, I2+ and translationally “hot” I+ ions, have been studied. Translationally hot I+ ions with an average kinetic energy of 0.94±0.02eV appear in the one-quantum photodissociation of vibrationally excited I2+(Π3∕2,g2) ions (⟨E⟩vib=0.45±0.11eV) via a “parallel” photodissociation process with an anisotropy parameter β=1.55±0.03. Comparison of the images of I+ arising from the photoexcitation of CH3I clusters versus those from neutral I2 shows that “concerted” photodissociation of the ionized (CH3I)2+ dimer appears to be the most likely mechanism for the formation of molecular iodine ion I2+, instead of photoionization of neutral molecular iodine.
Continuous limit of discrete sawtooth maps and its algebraic framework
Authors: Benatti Fabio , Cappellini Valerio
Published: May 2005

We study the presence of a logarithmic time scale in discrete approximations of sawtooth maps on the 2-torus. The techniques used are suggested by quantum mechanical similarities, and are based on a particular class of states on the torus, that fulfill dynamical localization properties typical of quantum coherent states.
Darboux points and integrability of Hamiltonian systems with homogeneous polynomial potential
Authors: Maciejewski Andrzej J. , Przybylska Maria
Published: May 2005

In this paper we study the integrability of natural Hamiltonian systems with a homogeneous polynomial potential. The strongest necessary conditions for their integrability in the Liouville sense have been obtained by a study of the differential Galois group of variational equations along straight line solutions. These particular solutions can be viewed as points of a projective space of dimension smaller by one than the number of degrees of freedom. We call them Darboux points. We analyze in detail the case of two degrees of freedom. We show that, except for a radial potential, the number of Darboux points is finite and it is not greater than the degree of the potential. Moreover, we analyze cases when the number of Darboux points is smaller than maximal. For two degrees of freedom the above-mentioned necessary condition for integrability can be expressed in terms of one nontrivial eigenvalue of the Hessian of potential calculated at a Darboux point. We prove that for a given potential these nontrivial eigenvalues calculated for all Darboux points cannot be arbitrary because they satisfy a certain relation which we give in an explicit form. We use this fact to strengthen maximally the necessary conditions for integrability and we show that in a generic case, for a given degree of the potential, there is only a finite number of potentials which satisfy these conditions. We also describe the nongeneric cases. As an example we give a full list of potentials of degree four satisfying these conditions. Then, investigating the differential Galois group of higher order variational equations, we prove that, except for one discrete family, among these potentials only those which are already known to be integrable are integrable. We check that a finite number of potentials from the exceptional discrete family are not integrable, and we conjecture that all of them are not integrable.
An elliptical Talbot interferometer for fiber Bragg grating fabrication
Authors: Pissadakis Stavros , Reekie Laurence
Published: May 2005

A simple and easily aligned two-mirror interferometer for fabricating Bragg gratings in optical bulk materials, waveguides, and fibers is presented. The interferometer consists of a simple phase mask splitting element and two dielectric mirrors optimized for maximum reflectance at an incident angle of 45 deg. By choosing a suitable optical configuration the half-period of the phase mask is patterned on the interference plane, while a wide range of periodicities can be inscribed by adjusting the relative angles between the interferometer folding mirros. The operation of the interferometer is demonstrated for grating inscription in Ge-doped optical fibers, using 213 nm, 150 ps Nd:YAG radiation.
Controlled line shaped electron beam for silicon zone melting recrystallization on float glass substrates
Authors: Gromball F. , Groth C. , Müller J.
Published: May 2005

A line shaped electron beam system for the zone melting recrystallization (ZMR) of thick silicon films on float glass substrates is described. The low thermal stability of the glass requires a rapid regulated zone heating. The electron beam system allows the ZMR in a continuous scan without pulsing. The setup consists of the tungsten wire with a Pierce reflector as line cathode and the moving substrate as anode. A negative voltage applied on the reflectors limits the electron emission and provides the necessary control. The melt energy for optimized processing decreases with an increase of the velocity. The beam profiles and penetration depth of the electrons is discussed. Homogenous polycrystalline silicon areas of several 10cm2 are achieved on a tungsten coated borosilicate float glass for the intended use as solar cell absorber.
Multidetection (e,2e) electron spectrometer
Authors: van Boeyen R. W. , Williams J. F.
Published: May 2005

An electron-pair coincidence spectrometer, using only a single electrostatic toroidal analyzer, has been developed for the study of final-state electron pairs following ionization by electron impact. The system allows the angular and energy distribution of electron pairs emitted in a selected plane to be detected by a single planar microchannel plate stack followed by two position-sensitive semicircular wedge-and-strip anodes. The output signals are decoded into energy, angle and nanosecond coincidence timing information from which relative energy and angular triple differential ionization cross sections are determined. The performance of the instrument is indicated by He I photoionization of krypton and the first measurements of differential cross sections for electron-impact ionization of the P3∕22 and P1∕22 states of krypton. For perpendicular-plane scattering and an excess energy of 10 eV for the P3∕22 state and 0.67 eV less for the P1∕22 state, these cross sections are significantly different for the two states and indicate the importance of the final state of the ion in the scattering process.
Tracking frequency laser distance gauge
Authors: Phillips J. D. , Reasenberg R. D.
Published: May 2005

Advanced astronomical missions with greatly enhanced resolution and physics missions of unprecedented accuracy will require laser distance gauges of substantially improved performance. We describe a laser gauge, based on Pound–Drever–Hall locking, in which the optical frequency is adjusted to maintain an interferometer’s null condition. This technique has been demonstrated with pm performance. Automatic fringe hopping allows it to track arbitrary distance changes. The instrument is intrinsically free of the nm-scale cyclic bias present in traditional (heterodyne) high-precision laser gauges. The output is a radio frequency, readily measured to sufficient accuracy. The laser gauge has operated in a resonant cavity, which improves precision, can suppress the effects of misalignments, and makes possible precise automatic alignment. The measurement of absolute distance requires little or no additional hardware, and has also been demonstrated. The proof-of-concept version, based on a stabilized HeNe laser and operating on a 0.5 m path, has achieved 10 pm precision with 0.1 s integration time, and 0.1 mm absolute distance accuracy. This version has also followed substantial distance changes as fast as 16mm∕s. We show that, if the precision in optical frequency is a fixed fraction of the linewidth, both incremental and absolute distance precision are independent of the distance measured. We discuss systematic error sources, and present plans for a new version of the gauge based on semiconductor lasers and fiber-coupled components.
Optimal operating conditions and characteristics of acetone∕CaF2 detector for inverse photoemission spectroscopy
Authors: Banik S. , Shukla A. K. , Barman S. R.
Published: May 2005

Performance and characteristics of a band-pass photon detector using acetone gas and CaF2 window (acetone∕CaF2) have been studied and compared with an ethanol∕MgF2 detector. The optimal operating conditions are found to be 4mbar acetone pressure and 745±20V anode voltage. The count rate obtained by us is about a factor of 3 higher than what has been reported earlier for the acetone detector. Unlike other gas filled detectors, this detector works in the proportional region with very small dead time (4μs). A detector bandpass of 0.48±0.01eV full width at half maximum is obtained.
Quantitative ellipsometric microscopy at the silicon–air interface
Authors: Linke F. , Merkel R.
Published: May 2005

Ellipsometric microscopy is a technique that combines the merits of ellipsometry and light microscopy, i.e., it allows noninvasive, label-free measurements of thin film thickness and refractive index at high lateral resolution. Here we give a detailed description of the technique including a complete calibration scheme and a model to correct for the instrumental polarization of the imaging optics. The performance of the instrument was studied experimentally. We found a lateral resolution of 1μm and an absolute height accuracy of 3nm. The measured refractive indices were accurate to 2.3% and the height sensitivity of the instrument was smaller than 5Å. Another virtue of the instrument design besides its good performance is that it is in essence an extension of standard light microscopy and could be integrated into commercial microscopes.
Sensitive power compensated scanning calorimeter for analysis of phase transformations in small samples
Authors: Lopeandía A. F. , Cerdó L l. , Clavaguera-Mora M. T. , Arana Leonel R. , Jensen K. F. , Muñoz F. J. , Rodríguez-Viejo J.
Published: May 2005

We have designed and developed a sensitive scanning calorimeter for use with microgram or submicrogram, thin film, or powder samples. Semiconductor processing techniques are used to fabricate membrane based microreactors with a small heat capacity of the addenda, 120nJ∕K at room temperature. At heating rates below 10K∕s the heat released or absorbed by the sample during a given transformation is compensated through a resistive Pt heater by a digital controller so that the calorimeter works as a power compensated device. Its use and dynamic sensitivity is demonstrated by analyzing the melting behavior of thin films of indium and high density polyethylene. Melting enthalpies in the range of 40–250μJ for sample masses on the order of 1.5μg have been measured with accuracy better than 5% at heating rates ∼0.2K∕s. The signal-to-noise ratio, limited by the electronic setup, is 200nW.