bluuebunny/crossref_metadata_2025 huggingface dataset:
Calcium Supplementation Does Not Alter Lipid Oxidation or Lipolysis in Overweight/Obese Women
Authors: Sampath Vanitha , Havel Peter J. , King Janet C.
Published: August 2008

Based on cell culture and studies in mice, increased dietary calcium appears to stimulate lipolysis and could possibly reduce body adiposity through hormonal influences on adipocyte calcium uptake. In this study, we investigated the effects of 1,500 mg supplemental calcium daily for 3 months on hormones regulating calcium and energy metabolism and rates of lipid oxidation and lipolysis in overweight women. Fifteen overweight (BMI > 25 kg/m2) premenopausal women were supplemented with 1,500 mg of calcium, as CaCO3, per day for 3 months while maintaining their usual diets and activity levels. Baseline and endpoint measurements were obtained after the subjects consumed a standardized 25% fat diet for 4 days. Lipid oxidation was measured by indirect calorimetry, lipolysis by infusion of deuterated glycerol, and body fat by dual‐energy X‐ray absorptiometry. Urinary calcium, circulating levels of hormones involved in energy and lipid metabolism (insulin, leptin, and adiponectin) or calcium metabolism (25(OH)D, 1,25(OH)2D), and parathyroid hormone (PTH)) were also measured. Urinary levels of calcium (P = 0.005) increased and 1,25(OH)2D declined (P = 0.03). However other parameters, including body weight, body fat, PTH, insulin, leptin, adiponectin, 25(OH)D, as well as rates of lipid oxidation and lipolysis were not altered by calcium supplementation. Calcium supplementation for 3 months increased urinary calcium excretion, decreased circulating levels of 1,25(OH)2‐D, but had no effect on rates of lipid oxidation or lipolysis, in these overweight women.
Weight Loss Expectations and Goals in a Population Sample of Overweight and Obese US Adults
Authors: Fabricatore Anthony N. , Wadden Thomas A. , Rohay Jeffrey M. , Pillitteri Janine L. , Shiffman Saul , Harkins Andrea M. , Burton Steven L.
Published: August 2008

The purpose of this study was to investigate weight loss expectations and goals in a population sample of US adults who planned to make a weight loss attempt, and to examine predictors of those expectations and goals. Participants were 658 overweight and obese adults (55% women, mean age = 47.9 years, BMI = 31.8 kg/m2) who responded to a telephone survey about weight loss. Respondents reported weight loss expectations (i.e., reductions they realistically expected) and goals (i.e., reductions they ideally desired) for an upcoming “serious and deliberate” weight loss attempt. They also reported the expectations they had, and the reductions they actually achieved, in a previous attempt. Respondents' weight loss expectations for their upcoming attempt (8.0% reduction in initial weight) were significantly more modest than their goals for that attempt (16.8%), and smaller than the losses that they expected (12.0%), and achieved (8.9%) in their most recent past attempt (Ps ≤ 0.003). Women and participants with higher BMIs had greater weight loss expectations and goals. After controlling for BMI, age, and gender, previous weight loss was unrelated to expectations (but was inversely related to goals) for the upcoming weight loss attempt. Results suggest that overweight and obese individuals can select realistic weight loss expectations that are more modest than their ideal goals. BMI and gender appear to be more important than previous weight loss experiences in determining expectations among persons planning a weight loss attempt.
A computational study of metastable states of CO2+
Authors: Mrugała Felicja
Published: August 2008

Extensive calculations of energies and lifetimes of vibronic and rovibronic states of the CO2+ dication are performed using the electronic energy potentials and spin-orbit couplings published recently by Šedivcová et al. [J. Chem. Phys. 124, 214303 (2006)] and by Eland et al. [J. Phys. B 37, 3197 (2004)]. Siegert quantization, bound-continuum configuration mixing, two-potential, and semiclassical methods are exploited in the calculations. Lifetimes for predissociation and tunneling, varying over a wide range, are determined, demonstrating a very good agreement between results yielded by the different methods. Dependence of the calculated predissociation characteristics (level widths and shifts) on the individual potentials and couplings is analyzed. The potentials of Šedivcová et al., especially the repulsive potential of the Σ3− state, are found insufficiently accurate in the medium range of the internuclear distance to be useful in simulations of the decay of the lowest vibronic states of the ion, X Π3(v=0,1) and a Σ1+(v=0,1). Combining the potentials of Eland et al. with the SO couplings of Šedivcová et al. is demonstrated to provide the best description of metastability of the ion so far. Purely vibronic models constructed in this way give lifetimes in a reasonable agreement with all existing experimental values and estimates. The largest deviations, τexpt/τcalc≃20, occur in the X Π3(v=1,2) cases. Strong evidence is provided that accounting for rotational motion of nuclei, spin-uncoupling perturbations, and diagonal spin-orbit couplings can reduce these deviations substantially, approximately ten times. The predissociation lifetimes of the rovibronic states A Σ30,1+(Jv) are predicted to be, with no exception, more than 100 times shorter than radiative lifetimes of these states.
Polymer infrared proximity sensor
Authors: Chen En-Chen , Tseng Shin-Rong , Ju Jia-Hong , Yang Chia-Ming , Meng Hsin-Fei , Horng Sheng-Fu , Shu Ching-Fong
Published: August 2008

A proximity sensor that combines a polymer light-emitting diode and a polymer photodiode is presented. The operation wavelength is in the near infrared from 700to850nm. The infrared emission is obtained by adding a color conversion film of polyvinylpyrrolidone polymer matrix blended with infrared dye 1,1-diethyl-2,2-dicarbocyanine iodide to a red polymer light-emitting diode. The photodetector relies on the direct charge-transfer exciton generation in a donor-acceptor polymer blend of poly(3-hexylthiophene) and (6,6)-phenyl-C61-butyric acid methyl ester. The detection distance is up to 19cm for objects with various colors and roughness under ambient indoor lighting.
Lateral organic bilayer heterojunction photoconductors
Authors: Ho John C. , Arango Alexi , Bulović Vladimir
Published: August 2008

We demonstrate a two-terminal, lateral organic bilayer photoconductor that generates an external quantum efficiency of (12±1)%, with an internal quantum efficiency of (140±2)% indicative of photon-to-electron conversion gain. The photoconductor incorporates a heterojunction between N,N′-bis(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (TPD) and 3,4,9,10-perylenetetracarboxylic bisbenzimidazole (PTCBI). Excitons generated with photoexcitation of PTCBI dissociate at the PTCBI/TPD interface and raise the charge carrier concentration in TPD, increasing device conductance. The exposed top surface enables interaction with chemical analytes in the environment, motivating the use of the photoconductor as a chemical sensor that transduces chemical signals into amplified changes in the electrical response.
Effect of annealing on the spectral and nonlinear optical characteristics of thin films of nano-ZnO
Authors: Irimpan Litty , Ambika D. , Kumar V. , Nampoori V. P. N. , Radhakrishnan P.
Published: August 2008

The annealing effect on the spectral and nonlinear optical (NLO) characteristics of ZnO thin films deposited on quartz substrates by sol-gel process is investigated. As the annealing temperature increases from 300–1050 °C, there is a decrease in the band gap, which indicates the changes of the interface of ZnO. ZnO is reported to show two emission bands, an ultraviolet (UV) emission band and another in the green region. The intensity of the UV peak remains the same while the intensity of the visible peak increases with increase in annealing temperature. The role of oxygen in ZnO thin films during the annealing process is important to the change in optical properties. The mechanism of the luminescence suggests that UV luminescence of ZnO thin films is related to the transition from conduction band edge to valence band, and green luminescence is caused by the transition from deep donor level to valence band due to oxygen vacancies. The NLO response of these samples is studied using nanosecond laser pulses at off-resonance wavelengths. The nonlinear absorption coefficient increases from 2.9×10−6 to 1.0×10−4 m/W when the annealing temperature is increased from 300 to 1050 °C, mainly due to the enhancement of interfacial state and exciton oscillator strength. The third order optical susceptibility χ(3) increases with increase in annealing temperature (T) within the range of our investigations. In the weak confinement regime, T2.4 dependence of χ(3) is obtained for ZnO thin films. The role of annealing temperature on the optical limiting response is also studied.
Kinetic and collisional effects on the linear evolution of fast ignition relevant beam instabilities
Authors: Cottrill L. A. , Langdon A. B. , Lasinski B. F. , Lund S. M. , Molvig K. , Tabak M. , Town R. P. J. , Williams E. A.
Published: August 2008

The fast ignition scheme will involve the generation and transport of a relativistic electron beam, which may be subject to a number of instabilities that act to inhibit energy transport. This study will address the effects of collisions and the initial electron beam distribution on the linear evolution of these instabilities for theoretical distributions including the relativistic waterbag, the relativistic Maxwellian (Jüttner), and the saddle point (low temperature) approximation of the relativistic Maxwellian. It will then be shown that a more physical distribution obtained from a 2D explicit particle-in-cell simulation of the laser-plasma interaction can be best modeled with a Jüttner distribution, but well-approximated with a relativistic waterbag distribution. In sum, for all distributions of interest, collisions were found to have the ability to both suppress and enhance growth for the filamentary instability, while they only suppress growth for the two-stream instability.
On alpha stable distribution of wind driven water surface wave slope
Authors: Joelson M. , Néel M. C.
Published: August 2008

We propose a new formulation of the probability distribution function of wind driven water surface slope with an α-stable distribution probability. The mathematical formulation of the probability distribution function is given under an integral formulation. Application to represent the probability of time slope data from laboratory experiments is carried out with satisfactory results. We compare also the α-stable model of the water surface slopes with the Gram–Charlier development and the non-Gaussian model of Liu et al. [J. Phys. Oceanogr. 27, 782 (1997)]. Discussions and conclusions are conducted on the basis of the data fit results and the model analysis comparison.
Effects of grain, grain boundary, and dc electric field on giant dielectric response in high purity CuO ceramics
Authors: Thongbai Prasit , Maensiri Santi , Yamwong Teerapon
Published: August 2008

Giant dielectric constant ε′ of ∼(2.8–3.7)×104 was observed in high purity CuO (99.999%) ceramics with grain sizes of 4.57±1.71 and 9.57±3.01 μm. The ε′ and Ea increase with an increase in grain size due to the different electrical properties in the grains. The high dielectric response observed in the CuO ceramics can be described by the internal barrier layer capacitance model. The resistance of grain boundaries (Rgb) and the dielectric constant of the CuO samples decrease with increasing dc bias due to the decrease in grain boundaries capacitance, whereas the resistance of grains (Rg) remains constant.
Self-organized metallic nanoparticle and nanowire arrays from ion-sputtered silicon templates
Authors: Oates T. W. H. , Keller A. , Noda S. , Facsko S.
Published: August 2008

We demonstrate a production method for self-organized arrays of metal nanoparticles and aligned nanowires. Ion beam-sputtered Si∕SiO2 substrates are used as templates for metallic vapor deposition, forming aligned arrays of 5–20nm silver and cobalt nanoparticles with a period of 35nm. The 20nm diameter cobalt nanowires with lengths in excess of a micrometer are produced under appropriate conditions. All processing steps can be integrated into a single vacuum chamber and performed in a matter of minutes at mild temperatures. This inherently scalable technique can be extended to a range of substrate materials, array patterns, and nanoparticle materials.
S passivation of GaAs and band bending reduction upon atomic layer deposition of HfO2/Al2O3 nanolaminates
Authors: Aguirre-Tostado F. S. , Milojevic M. , Choi K. J. , Kim H. C. , Hinkle C. L. , Vogel E. M. , Kim J. , Yang T. , Xuan Y. , Ye P. D. , Wallace R. M.
Published: August 2008

A systematic study of the interface engineering and dielectric properties of nanolaminated hafnium aluminate on GaAs is presented. The dielectrics were deposited using atomic layer deposition of alternating cycles of HfO2 and Al2O3 on GaAs substrates. High resolution x-ray photoelectron spectroscopy (XPS) showed differences in space charge amounts at the interface for the two surface treatments [NH4OH or (NH4)2S]. In-situ XPS analysis shows that chemical bonding to oxygen across the nanolaminate film is independent of the interface formation conditions. In addition, the GaAs surface treated with (NH4)2S shows a decreased band bending and slightly thinner films with respect to NH4OH.
Optimal design of nanoplasmonic materials using genetic algorithms as a multiparameter optimization tool
Authors: Yelk Joseph , Sukharev Maxim , Seideman Tamar
Published: August 2008

An optimal control approach based on multiple parameter genetic algorithms is applied to the design of plasmonic nanoconstructs with predetermined optical properties and functionalities. We first develop nanoscale metallic lenses that focus an incident plane wave onto a prespecified, spatially confined spot. Our results illustrate the mechanism of energy flow through wires and cavities. Next we design a periodic array of silver particles to modify the polarization of an incident, linearly polarized plane wave in a desired fashion while localizing the light in space. The results provide insight into the structural features that determine the birefringence properties of metal nanoparticles and their arrays. Of the variety of potential applications that may be envisioned, we note the design of nanoscale light sources with controllable coherence and polarization properties that could serve for coherent control of molecular, electronic, or electromechanical dynamics in the nanoscale.
Charge transfer in the TCNQ-sexithiophene complex
Authors: Braun K.-F. , Hla S. W.
Published: August 2008

Molecular crystals from thiophene molecules can be doped with TCNQ-F4 molecules for use in all-organic optoelectronic and semiconductor devices. The charge transfer and the molecular orbital energy level formation in between these two organic molecules are investigated here by density functional theory calculations. The isolated molecules are calculated nonbonded and bonded together, forming a charge transfer complex (CTC). The relaxed structure of the complex shows essentially coplanar and centered molecules with the α-sexithiophene rings tilted alternatingly by 4.8°. The bond formation of these molecules results in a charge transfer of ∼0.4e from the α-sexithiophene to the TCNQ-F4 molecule. The highest occupied molecular orbital–lowest unoccupied molecular orbital gap width is reduced as compared to the isolated molecules due to the newly formed orbitals in the CTC. Upon adsorption on a Au(111) surface, electrons are transferred onto the molecule complex, thereby causing the molecular levels to align asymmetric with respect to the charge neutrality level. The theoretical results for the single molecule and CTC layer are compared to experimental photoemission and scanning tunneling spectroscopy results.
Interband absorption of vanadium studied by probing the size-dependent change in energy bands of vanadium particles
Authors: Anno Eiji
Published: August 2008

For interband absorption with peak at about 2.5–3.0 eV of vanadium, the contribution of the transition from the Fermi level in the region near state Σ1 to state Σ4 has been investigated experimentally. The contribution was proposed by Romaniello et al. [Phys. Rev. B 73, 075115 (2006)]. When the size of vanadium particles was decreased, the interband absorption weakened remarkably. Considering the raising of the position of state Σ1 with energy-band broadening due to lattice contraction, the remarkable weakening can qualitatively be ascribed to the ceasing of the transition mentioned above. This confirms the contribution.
Measurement of driving force of catalytic nanomotors in dilute hydrogen peroxide by torsion balance
Authors: Gibbs J. G. , Zhao Y.-P.
Published: August 2008

A simple torsion balance is designed to directly determine the force generated by catalytic nanomotor nanorods. A 1 cm1 silicon substrate coated with ∼3.1×108 nanomotors was attached to a balancing weight and submerged into different concentrations of hydrogen peroxide. The force generated through the catalytic reaction leads to a measurable torque applied to the torsion balance. The force is on the order of 10−14−10−13 N per individual nanomotor and has a linear concentration dependence with a slope of 4.82×10−14 N per percentage of hydrogen peroxide in agreement with previous studies.
Resonant forcing of nonlinear systems of differential equations
Authors: Gintautas Vadas , Hübler Alfred W.
Published: August 2008

We study resonances of nonlinear systems of differential equations, including but not limited to the equations of motion of a particle moving in a potential. We use the calculus of variations to determine the minimal additive forcing function that induces a desired terminal response, such as an energy in the case of a physical system. We include the additional constraint that only select degrees of freedom be forced, corresponding to a very general class of problems in which not all of the degrees of freedom in an experimental system are accessible to forcing. We find that certain Lagrange multipliers take on a fundamental physical role as the effective forcing experienced by the degrees of freedom which are not forced directly. Furthermore, we find that the product of the displacement of nearby trajectories and the effective total forcing function is a conserved quantity. We demonstrate the efficacy of this methodology with several examples.
Scaling of sensitivity and efficiency in planar microresonators for electron spin resonance
Authors: Narkowicz R. , Suter D. , Niemeyer I.
Published: August 2008

Electron spin resonance (ESR) of volume-limited samples or nanostructured materials can be made significantly more efficient by using microresonators whose size matches that of the structures under investigation. We describe a series of planar microresonators that show large improvements over conventional ESR resonators in terms of microwave conversion efficiency (microwave field strength for a given input power) and sensitivity (minimum number of detectable spins). We explore the dependence of these parameters on the size of the resonator and find that both scale almost linearly with the inverse of the resonator size. Scaling down the loops of the planar microresonators from 500 down to 20 μm improves the microwave efficiency and the sensitivity of these structures by more than an order of magnitude and reduces the microwave power requirements by more than two orders of magnitude.
Stability of B–H and B–D complexes in diamond under electron beam excitation
Authors: Barjon J. , Mehdaoui A. , Jomard F. , Chevallier J. , Mer C. , Nesladek M. , Bergonzo P. , Pernot J. , Omnès F. , Deneuville A.
Published: August 2008

The substitution of hydrogen by deuterium is generally known to increase the stability of the defect passivation in semiconductors, occasionally giving rise to giant isotope effects. In this work, the stability under an electron beam irradiation of boron-hydrogen and boron-deuterium pairs in diamond are compared. The dissociation kinetics was followed in situ by cathodoluminescence spectroscopy. Surprisingly, B–H complexes are more stable than B–D complexes under electron beam at low temperature (∼100K), with a dissociation rate about twice smaller. These experimental results are coherent with a dissociation mechanism involving a cumulative vibrational excitation of the complexes.
Anisotropic pressure, transport, and shielding of magnetic perturbations
Authors: Mynick H. E. , Boozer A. H.
Published: August 2008

The effect on a tokamak of applying a nonaxisymmetric magnetic perturbation δB is computed. An equilibrium with scalar pressure p yields zero net radial current, and therefore zero torque. Thus, the usual approach, which assumes scalar pressure, is not self-consistent, and masks the close connection that exists between that radial current and the in-surface currents, which provide shielding or amplification of δB. Here, the pressure anisotropy, p∥,p⊥≠p, and from this, both the radial and in-surface currents, are analytically computed. The surface average of the radial current recovers earlier expressions for ripple transport, while the in-surface currents provide an expression for the amount of self-consistent shielding the plasma provides.
Surface and interface phonon-polaritons in bilayer systems of polar ternary mixed crystals
Authors: Bao J. , Liang X. X.
Published: August 2008

The surface and interface phonon-polaritons in bilayer systems consisting of polar ternary mixed crystals are investigated in the modified random-element-isodisplacement model and the Born–Huang approximation, based on the Maxwell’s equations with the boundary conditions. The numerical results of the surface and interface phonon-polariton frequencies as functions of the wave vector and the composition of the ternary mixed crystals in GaAs/AlxGa1−xAs, ZnS/ZnSxSe1−x, and ZnSe/ZnxCd1−xSe bilayer systems are obtained and discussed. It is shown that there are six branches of surface and interface phonon-polaritons in binary/ternary systems. The effects of the “two-mode” and “one-mode” behaviors of the ternary mixed crystals on the surface and interface phonon-polariton modes are shown in the dispersion curves. The electric fields of surface and interface phonon-polaritons are also presented for various cases.
Composition control of Cu(InGa)(SeS)2 deposited by elemental coevaporation
Authors: Nishiwaki Shiro , Shafarman William N.
Published: August 2008

Cu ( InGa ) ( SeS ) 2 films were deposited by thermal coevaporation of the elements at a substrate temperature of 550 °C with various [S]/[S+Se] and [Cu]/[In+Ga] ratios to investigate the preferred incorporation of S and Se under off-stoichiometric conditions. Deposition with a uniform flux-time profile under Cu-poor conditions, i.e., [Cu]/[In+Ga]<1, leads to preferential incorporation of Se relative to the vapor flux. With [Cu]/[In+Ga]>1, S is preferentially incorporated and, in this case, the resulting [S]/[Se+S] ratio in the film depends on the relative In and Ga concentrations. These results are compared to thermodynamic and kinetic models which both provide a functional form that can be used to predict the film composition from knowledge of the fluxes. Deposition processes, which use sequential layers of Cu-excess and Cu-poor growth, result in nonhomogeneous chalcogen composition. For Cu-poor followed by Cu-excess deposition, preferential incorporation of S occurs when the film reaches Cu-excess composition. For Cu-excess followed by Cu-free deposition, growth of Se-rich material is initiated while the film still contains excess Cu. Finally, a model of the film microstructure based on the incorporation of S and Se is discussed.
EOS calculations for hydrothermal diamond anvil cell operation
Authors: Presser Volker , Heiß Martin , Nickel Klaus G.
Published: August 2008

The hydrothermal diamond anvil cell (HDAC) is an excellent tool for high-temperature, high-pressure (hydrothermal) experiments. For an accurate determination of pressure induced by a certain temperature in an isochoric sample chamber volume, an equation of state (EOS) of water can be used instead of direct measurement. This paper reviews the theoretic background and provides all needed equations for the application of EOS of water to HDAC experiments summarizing state-of-the-art knowledge and incorporating up-to-date thermodynamic data. The p-T conditions determined using the IAPWS-95 formulation for the thermodynamic properties of ordinary water are in agreement with values obtained from direct methods or other established EOS formulations. In particular, (1) the calculation of density through the (a) melting point or (b) homogenization method along with determining (2) pressure as a function of density and temperature or (3) density as a function of pressure and temperature is explained. As a new aspect in the context of HDAC operations, the critical influence of nucleation and a strategy to overcome this problem are discussed. Furthermore, we have derived new polynomial equations, which allow the direct calculation of the fluid phase’s density from the melting temperature. These are implemented in a spreadsheet program, which is freely available for interested users.
The measurement of mechanical properties of glycerol, m-toluidine, and sucrose benzoate under consideration of corrected rheometer compliance: An in-depth study and review
Authors: Hutcheson S. A. , McKenna G. B.
Published: August 2008

Determination of the mechanical response of materials can be fraught with error if rheometer compliance is not properly taken into account. The resulting inaccuracies in the determined mechanical properties of the materials of interest can result in mistakes in material modeling, design, and theory. In the present work, we build on our previous report [K. Schröter, S. A. Hutcheson, X. Shi, A. Mandanici, and G. B. McKenna, J. Chem. Phys. 125, 214507 (2006)] and investigate the effects of instrument compliance that result from use of a commercial rotary rheometer and its fixtures on the determination of the dynamic shear and stress relaxation responses of glycerol, m-toluidine, and sucrose benzoate near to the glass transition regime. We revisit the procedure for compliance corrections presented in earlier work and correct dynamic shear data for these materials. We also present a new correction procedure to obtain shear stress relaxation curves from data that was obtained using this instrument. In addition, we broaden our consideration of compliance effects to materials, such as polymer melts, that have lower moduli than the simple glass formers previously considered. We discuss the possible errors for the viscoelastic response of glass-forming liquids and polymer melts or rubber networks that have been reported in the literature. A major purpose of the present work is to alert the community to possible problems in modulus values and relaxation functions obtained for a large number of materials for which rotary rheometers were used in a range where material stiffness (modulus and geometry effects) was comparable to the rheometer stiffness. Finally, we include recommendations for both experimental protocol and instrument design to avoid, minimize, or correct for compliance effects.
Molecular-orbital-free algorithm for excited states in time-dependent perturbation theory
Authors: Lucero Melissa J. , Niklasson Anders M. N. , Tretiak Sergei , Challacombe Matt
Published: August 2008

A nonlinear conjugate gradient optimization scheme is used to obtain excitation energies within the random phase approximation (RPA). The solutions to the RPA eigenvalue equation are located through a variational characterization using a modified Thouless functional, which is based upon an asymmetric Rayleigh quotient, in an orthogonalized atomic orbital representation. In this way, the computational bottleneck of calculating molecular orbitals is avoided. The variational space is reduced to the physically-relevant transitions by projections. The feasibility of an RPA implementation scaling linearly with system size N is investigated by monitoring convergence behavior with respect to the quality of initial guess and sensitivity to noise under thresholding, both for well- and ill-conditioned problems. The molecular-orbital-free algorithm is found to be robust and computationally efficient, providing a first step toward large-scale, reduced complexity calculations of time-dependent optical properties and linear response. The algorithm is extensible to other forms of time-dependent perturbation theory including, but not limited to, time-dependent density functional theory.
Ion-pair dissociation of N2O in the 16.25–16.41eV: Dynamics and electronic structure
Authors: Zhou Chang , Mo Yuxiang
Published: August 2008

The ion-pair dissociation dynamics of N2O→XUVN2+(XΣg+2,υ)+O−(Pj2) at 16.248, 16.271, 16.389, and 16.411eV have been studied using the velocity map imaging method and tunable XUV laser. The electronic structures of the ion-pair states have been studied by employing the ab initio quantum chemical calculation. The translational energy distributions and the angular distributions of the photofragments have been measured. The results show that about 40% of available energies are transformed into the translational energies, and the first excited vibrational states are populated most strongly for all four excitation energies. The anisotropy parameters β are ∼1. The ab initio calculations at the level of CASSCF∕6-311++g(3df) show that the equilibrium geometries of the ion-pair states are nonlinear with bond lengths R(N–N)=1.10Å, R(N–O)=2.15Å, and bond angle N–N–O=103°, respectively. The ion-pair states are formed by electron migration from the bonding σ orbital of NN to the antibonding σ orbital localized primarily on the O atom. Combining the experimental and theoretical results, it is concluded that the ion-pair dissociation occurs via predissociation of Rydberg states with Σ+1 symmetry, which converges to the ion-core N2O+(AΣ+2).
Femtosecond spectroscopy of solvated electrons from sodium-ammonia-d3 solutions: Temperature jump versus local density jump
Authors: Lindner Jörg , Unterreiner Andreas-N. , Vöhringer Peter
Published: August 2008

The relaxation dynamics of solvated electrons from sodium-ammonia-d3 solutions was studied by femtosecond time-resolved near-infrared spectroscopy. The experimental pump-probe data reveal a pulse-width limited pump-induced redshift of the absorption spectrum of the ammoniated electron and a subsequent slower blueshift on a time scale of roughly 200 fs. The spectrotemporal response is interpreted using the nonadiabatic relaxation mechanism for cavity-bound solvated electrons in condensed phases. In particular, we develop a local density-jump model, which traces the dynamic spectrum back to a sequence of a pump-induced cavity expansion due to Pauli repulsion and a succeeding cavity contraction upon nonadiabatic return of the electron back to its ground state. Using the existing thermodynamic data of the solvent and experimental temperature and density-dependent absorption spectra of metal-ammonia solutions, an overall increase in the interparticle distance within the solvent cavity of 25% is crudely estimated. The density-jump model is compared to the temperature-jump model we proposed previously for the femtosecond relaxation dynamics of metal-NH3 solutions.
Quasibinary amorphous phase in a three-dimensional system of particles with repulsive-shoulder interactions
Authors: Fomin Yu. D. , Gribova N. V. , Ryzhov V. N. , Stishov S. M. , Frenkel Daan
Published: August 2008

We report a computer-simulation study of the equilibrium phase diagram of a three-dimensional system of particles with a repulsive-step potential. Using free-energy calculations, we have determined the equilibrium phase diagram of this system. At low temperatures, we observe a number of distinct crystal phases. However, under certain conditions the system undergoes a glass transition in a regime where the liquid appears thermodynamically stable. We argue that the appearance of this amorphous low-temperature phase can be understood by viewing this one-component system as a quasibinary mixture.
Semiclassical initial value series representation in the continuum limit: Application to vibrational relaxation
Authors: Moix Jeremy M. , Pollak Eli
Published: August 2008

A recently formulated continuum limit semiclassical initial value series representation (SCIVR) of the quantum dynamics of dissipative systems is applied to the study of vibrational relaxation of model harmonic and anharmonic oscillator systems. As is well known, the classical dynamics of dissipative systems may be described in terms of a generalized Langevin equation. The continuum limit SCIVR uses the Langevin trajectories as input, albeit with a quantum noise rather than a classical noise. Combining this development with the forward-backward form of the prefactor-free propagator leads to a tractable scheme for computing quantum thermal correlation functions. Here we present the first implementation of this continuum limit SCIVR series method to study two model problems of vibrational relaxation. Simulations of the dissipative harmonic oscillator system over a wide range of parameters demonstrate that at most only the first two terms in the SCIVR series are needed for convergence of the correlation function. The methodology is then applied to the vibrational relaxation of a dissipative Morse oscillator. Here, too, the SCIVR series converges rapidly as the first two terms are sufficient to provide the quantum mechanical relaxation with an estimated accuracy on the order of a few percent. The results in this case are compared with computations obtained using the classical Wigner approximation for the relaxation dynamics.
Revisiting the real space density functional theory of hard sphere freezing in the Percus–Yevick approximation
Authors: Verma Anurag , Ford David M.
Published: August 2008

Dong and Evans (DE) recently studied the freezing transition of a hard sphere fluid using classical density functional theory [J. Chem. Phys.125, 204506(2006)]. They calculated the solid-liquid coexistence densities and Lindemann parameter using a free energy perturbation truncated at second order, with the liquid-state direct correlation function (dcf) evaluated in the Percus–Yevick (PY) approximation. The density of the solid was represented in real space as a sum of Gaussian functions centered at the lattice sites; only nearest neighbor interactions were included when calculating the perturbation integrals due to the sharpness of the Gaussians and the short range of the PY dcf. We present an alternative derivation that evaluates the real space integrals in a different manner, focusing on an intermediate function that is analogous to the indirect correlation function of the Ornstein–Zernike theory. Our approach provides a basis for extending the ideas of DE to systems with longer-ranged interactions and perhaps more insight on the consequences of various assumptions. We also report an updated set of numerical values for the coexistence densities and Lindemann parameter of the hard sphere system that are consistent with our equations and those of DE; the updated coexistence densities are in better agreement with Monte Carlo values than those originally reported by DE.
Experimental and theoretical characterization of MSi16−, MGe16−,MSn16−, and MPb16− (M=Ti, Zr, and Hf): The role of cage aromaticity
Authors: Furuse Shunsuke , Koyasu Kiichirou , Atobe Junko , Nakajima Atsushi
Published: August 2008

Silicon (Si), germanium (Ge), tin (Sn), and lead (Pb) clusters mixed with a group-4 transition metal atom [M=titanium (Ti), zirconium (Zr), and hafnium (Hf)] were generated by a dual-laser vaporization method, and their properties were analyzed by means of time-of-flight mass spectroscopy and anion photoelectron spectroscopy together with theoretical calculations. In the mass spectra, mixed neutral clusters of MSi16, MGe16, and MSn16 were produced specifically, but the yield of MPb16 was low. The anion photoelectron spectra revealed that MSi16, MGe16, and MSn16 neutrals have large highest occupied molecular orbital–lowest unoccupied molecular orbital gaps of 1.5–1.9eV compared to those of MPb16 (0.8–0.9eV), implying that MSi16, MGe16, and MSn16 are evidently electronically stable clusters. Cage aromaticity appears to be an important determinant of the electronic stability of these clusters: Calculations of nucleus-independent chemical shifts (NICSs) show that Si164−, Ge164−, and Sn164− have aromatic characters with negative NICS values, while Pb164− has an antiaromatic character with a positive NICS value.
Dihydrogen bond cooperativity in (HCCBeH)n clusters
Authors: Alkorta Ibon , Elguero José , Solimannejad Mohammad
Published: August 2008

A theoretical study has been carried out on the clusters formed by the association of ethynylhydroberyllium (HC≡CBeH) monomers. The monomer presents a linear disposition with a dipole moment of 0.94 D. Clusters from two to six monomers have been calculated for three different configurations (linear, cyclic with dihydrogen bonds, and cyclic with hydrogen bonds to the π-cloud), the third one being the most stable. The electronic properties of the clusters have been analyzed by means of the atoms in molecules and natural bond orbitals methodologies. Cooperative effects, similar to the ones described for standard hydrogen bonded clusters, are observed in those configurations where dihydrogen bonds are the main interacting force.
Asymptotic theory of the linear transport equation in anisotropic media
Authors: Sanchez Richard , Ragusa Jean , Masiello Emiliano
Published: August 2008

We consider linear transport in an anisotropic medium with velocity dependent cross sections σ(r,v,t) and scattering kernel P(r,v′→v,t). We introduce a scaling in terms of a small parameter ϵ, where the leading-order term describes an equilibrium in velocity space between collisions with a cross section that is an even function of v and scattering modes even-even and odd-odd in v and v′. We show that the asymptotic solution of the transport equation leads to a diffusion equation with a drift term with an error in ϵ2 and derive consistent initial and boundary conditions from the analysis of the initial and boundary layers. The analysis of the drift terms shows that they result from anisotropic interactions with the medium and also from streaming between neighboring but different equilibria. The restriction of our results to isotropic media yields back the Larsen–Keller diffusion equation, while the one-speed form reduces to the result obtained by Pomraning and Prinja [Ann. Nucl. Energy 22, 159 (1995)] for the particular case of isotropic cross sections with an “output” scattering kernel P(r,Ω,t).
Evolving functional network properties and synchronizability during human epileptic seizures
Authors: Schindler Kaspar A. , Bialonski Stephan , Horstmann Marie-Therese , Elger Christian E. , Lehnertz Klaus
Published: August 2008

We assess electrical brain dynamics before, during, and after 100 human epileptic seizures with different anatomical onset locations by statistical and spectral properties of functionally defined networks. We observe a concave-like temporal evolution of characteristic path length and cluster coefficient indicative of a movement from a more random toward a more regular and then back toward a more random functional topology. Surprisingly, synchronizability was significantly decreased during the seizure state but increased already prior to seizure end. Our findings underline the high relevance of studying complex systems from the viewpoint of complex networks, which may help to gain deeper insights into the complicated dynamics underlying epileptic seizures.
Novel angular encoder for a quick-extended x-ray absorption fine structure monochromator
Authors: Stötzel J. , Lützenkirchen-Hecht D. , Fonda E. , De Oliveira N. , Briois V. , Frahm R.
Published: August 2008

New concepts for time-resolved x-ray absorption spectroscopy using the quick-extended x-ray absorption fine structure (QEXAFS) method are presented. QEXAFS is a powerful tool to gain structural information about, e.g., fast chemical reactions or phase transitions on a subsecond scale. This can be achieved with a monochromator design that employs a channel-cut crystal on a cam driven tilt table for rapid angular oscillations of the Bragg angle. A new angular encoder system and a new data acquisition were described and characterized that were applied to a QEXAFS monochromator to get spectra with a directly measured accurate energy scale. New electronics were designed to allow a fast acquisition of the Bragg angle values and the absorption data during the measurements simultaneously.
Resonant Raman of O–H/O–D vibrations and photoluminescence studies in LiTaO3 thin film
Authors: Satapathy S. , Kumar Shailendra , Raja Sekhar B. N. , Sathe V. G. , Gupta P. K.
Published: August 2008

Resonant Raman spectra (RRS) of O–H and O–D vibration and libration modes, their combinations, and higher harmonics have been observed in LiTaO3 polycrystalline thin films. RRS peaks are superimposed on photoluminescence (PL) spectrum. Monochromatic light from a xenon lamp is used as excitation source. PL spectrum shows two broad peaks: first near the band gap in UV (4.4–4.8 eV) and another in the sub-band-gap region (<4.0 eV). Band gap PL along with RRS peaks are reported for the first time. PL excitation spectrum shows a peak at 4.8 eV. Peak positions and full width at half maximum of RRS peaks depend on the excitation energy. Dispersions of the fundamental and the third harmonic of the stretching mode of O–H with excitation energy are about 800 and 2000 cm−1/eV, respectively. This dispersion is much higher than reported in any other material.
Perturbative calculation of Franck–Condon integrals: New hints for a rational implementation
Authors: Borrelli Raffaele , Peluso Andrea
Published: August 2008

Perturbative approaches to the mode mixing effects in the calculation of Franck–Condon integrals are analyzed and discussed. The zero order multidimensional Franck–Condon integrals are factorized into products of one-dimensional ones, so that recurrence relations can be used without need of storing a huge number of data. Calculations on model systems show that at the second order of perturbation, the method gives results in very good agreement with the exact ones, even in the case of significantly large Duschinsky effect. The accuracy of the results can be substantially improved by grouping together all those modes which are strongly mixed with each other, usually a few ones, for which Franck–Condon integrals can be computed exactly, and using the perturbative approach for treating the smaller mixing between all the other modes.
Time dependent density functional theory study of the near-edge x-ray absorption fine structure of benzene in gas phase and on metal surfaces
Authors: Asmuruf Frans A. , Besley Nicholas A.
Published: August 2008

The near-edge x-ray absorption fine structure of benzene in the gas phase and adsorbed on the Au(111) and Pt(111) surfaces is studied with time dependent density functional theory. Excitation energies computed with hybrid exchange-correlation functionals are too low compared to experiment. However, after applying a constant shift the spectra are in good agreement with experiment. For benzene on the Au(111) surface, two bands arising from excitation to the e2u(π*) and b2g(π*) orbitals of benzene are observed for photon incidence parallel to the surface. On Pt(111) surface, a broader band arises from excitation to benzene orbitals that are mixed with the surface and have both σ*(Pt–C) and π* characters.
A statistical approach to optimization of alumina etching in a high density plasma
Authors: Li Xiao , Highsmith Alton , Gupta Subhadra , Paranjpe Ajit , Rook Katrina
Published: August 2008

Inductively coupled plasma (ICP) reactive ion etching of Al2O3 with fluorine-based gas chemistry in a high density plasma reactor was carried out in an initial investigation aimed at data storage applications. A statistical design of experiments was implemented to optimize etch performance with respect to process variables such as ICP power, platen power, direct current (dc) bias, and pressure. Both soft photoresist masks and hard metal masks were investigated in terms of etch selectivity and surface properties. The reverse power dependence of dc bias on the ratio of ICP to platen power was elucidated. Etch mechanisms in terms of physical and ion enhanced chemical etchings were discussed. The F-based chemistry greatly enhances the etch rate of alumina compared to purely physical processes such as ion milling. Etch rates as high as 150 nm/min were achieved using this process. A practical process window was developed for high etch rates, with reasonable selectivity to hard masks, with the desired profile, and with low substrate bias for minimal damage.
Fast crystallization of chalcogenide glass for rewritable memories
Authors: Sun Zhimei , Zhou Jian , Blomqvist Andreas , Johansson Börje , Ahuja Rajeev
Published: August 2008

By ab initio molecular dynamics simulations, we unraveled the unique network structure of amorphous Ge1Sb2Te4, which shows high rank of ordering and mostly consists of distorted defective octahedrons with a small portion of distorted tetrahedrons. The phase transition from amorphous to cubic Ge1Sb2Te4 would be mainly a process of angle rearrangements of tetrahedrons to octahedrons and vice versa.
Enhanced power factor of epitaxial layered cobaltite NaxCoO2 thin film induced by strain: x=0.5,0.7
Authors: Son J. Y. , Shin Y. H. , Park C. S.
Published: August 2008

Epitaxial Na0.5CoO2 thin films were fabricated by the sodium deintercalation of the epitaxial Na0.7CoO2 thin films in the solution of iodine-dissolved acetonitrile, in which the epitaxial Na0.7CoO2 thin films were deposited on (001) sapphire substrates by pulsed laser deposition. The Na0.7CoO2 thin films show small resistivity, which is probably due to the high crystallinity as well as the compressive strain of 1.1% along the a-axis. From the spectroscopic ellipsometry analysis, we obtained the optical constants as well as the optical conductivities for the Na0.5CoO2 and Na0.7CoO2 thin films and the increased energy splitting between eg and a1g results from the structural strain of the Na0.7CoO2 thin film. We suggest that the structural strain should be the source of the lower resistivity and the preservation of the strongly correlated system up to 200 K for the Na0.7CoO2 thin film. At 300 K, the Na0.7CoO2 thin film exhibits the enhanced power factor (S2/ρ) of 94 μW/K2 cm with the low electrical resistivity of 177 μΩ cm and the high thermoelectric power of 128.9 μV/K.
Light emission and enhanced nonlinearity in nanophotonic waveguide circuits by III–V/silicon-on-insulator heterogeneous integration
Authors: Roelkens G. , Liu L. , Van Thourhout D. , Baets R. , Nötzel R. , Raineri F. , Sagnes I. , Beaudoin G. , Raj R.
Published: August 2008

The heterogeneous integration of a III–V thin film on top of a silicon-on-insulator (SOI) optical waveguide circuit by means of adhesive divinylsiloxane-benzocyclobutene (DVS-BCB) die-to-wafer bonding is demonstrated, thereby achieving light emission and enhanced nonlinearity in ultracompact SOI cavities. This approach requires ultrathin DVS-BCB bonding layers to allow the highly confined optical mode to overlap with the bonded III–V film. The transfer of sub-100-nm III–V layers using a 65 nm DVS-BCB bonding layer onto SOI racetrack resonator structures is demonstrated. Spontaneous emission coupled to a SOI bus waveguide, spectrally centered around the resonator resonances, is observed by optically pumping the III–V layer. Strong carrier-induced nonlinearities are observed in the transmission characteristics of the III–V/SOI resonator structure. The all-optical control of an optical signal in these III–V/SOI resonators is demonstrated.