bluuebunny/crossref_metadata_2025 huggingface dataset:
Long-term hyperglucagonaemia induces early metabolic and renal phenotypes of Type 2 diabetes in mice
Authors: Li Xiao C. , Liao Tang-dong , Zhuo Jia L.
Published: April 2008

Clinical studies have shown that patients with early Type 2 diabetes often have elevated serum glucagon rather than insulin deficiency. Imbalance of insulin and glucagon in favouring the latter may contribute to impaired glucose tolerance, persistent hyperglycaemia, microalbuminuria and glomerular injury. In the present study, we tested the hypothesis that long-term glucagon infusion induces early metabolic and renal phenotypes of Type 2 diabetes in mice by activating glucagon receptors. Five groups of adult male C57BL/6J mice were treated with vehicle, glucagon alone (1 μg/h via an osmotic minipump, intraperitoneally), glucagon plus the glucagon receptor antagonist [Des-His1-Glu9]glucagon (5 μg/h via an osmotic minipump), [Des-His1-Glu9]glucagon alone or a high glucose load alone (2% glucose in the drinking water) for 4 weeks. Glucagon infusion increased serum glucagon by 129% (P<0.05), raised systolic BP (blood pressure) by 21 mmHg (P<0.01), elevated fasting blood glucose by 42% (P<0.01), impaired glucose tolerance (P<0.01), increased the kidney weight/body weight ratio (P<0.05) and 24 h urinary albumin excretion by 108% (P<0.01) and induced glomerular mesangial expansion and extracellular matrix deposition. These responses were associated with marked increases in phosphorylated ERK1/2 (extracellular-signal-regulated kinase 1/2) and Akt signalling proteins in the liver and kidney (P<0.01). Serum insulin did not increase proportionally. Concurrent administration of [Des-His1-Glu9]glucagon with glucagon significantly attenuated glucagon-increased BP, fasting blood glucose, kidney weight/body weight ratio and 24 h urinary albumin excretion. [Des-His1-Glu9]glucagon also improved glucagon-inpaired glucose tolerance, increased serum insulin by 56% (P<0.05) and attenuated glomerular injury. However, [Des-His1-Glu9]glucagon or high glucose administration alone did not elevate fasting blood glucose levels, impair glucose tolerance or induce renal injury. These results demonstrate for the first time that long-term hyperglucagonaemia in mice induces early metabolic and renal phenotypes of Type 2 diabetes by activating glucagon receptors. This supports the idea that glucagon receptor blockade may be beneficial in treating insulin resistance and Type 2 diabetic renal complications.
Initiation factors for translation of proteins in the rectus abdominis muscle from patients on overnight standard parenteral nutrition before surgery
Authors: Iresjö Britt-Marie , Körner Ulla , Hyltander Anders , Ljungman David , Lundholm Kent
Published: April 2008

Previous studies have provided conflicting conclusions concerning the efficacy of improving protein balance in patients by standard intravenous nutrition [TPN (total parenteral nutrition)], which is either explained by suboptimal nutritional regimens or insensitive clinical methods. The aim of the present study was therefore to evaluate the effects on the initiation of translation of skeletal muscle proteins by standard overnight TPN. A total of 12 patients who underwent standard surgery were included. TPN was provided as an all-in-one treatment by constant infusion [0.16 gN·kg−1 of body weight·day−1 (30 kcal·kg−1 of body weight·day−1)]. Saline-infused patients served as controls. Rectus abdominis muscle biopsies were taken at the time of the operation. The phosphorylation state of the proteins for initiation of translation was quantified. Plasma glucose, and serum insulin, glycerol, triacylglycerols (triglycerides) and NEFAs (non-esterified fatty acids; ‘free fatty acids’) were not significantly altered during TPN infusion, whereas total plasma amino acids increased, as shown by increases in methionine, phenylalanine, threonine, alanine, arginine, aspartic acid, glycine and histidine (P<0.05). Overnight TPN increased the formation of active eIF4G–eIF4E (where eIF is eukaryotic-initiation factor) complexes (P<0.05), whereas the inhibitory complex 4E-BP1 (eIF4E-binding protein)–eIF4E was moderately decreased (P<0.06). TPN increased the amount of the most phosphorylated form of 4E-BP1 (P<0.05), and increased the amount (P<0.04) and phosphorylation (P<0.01) of p70S6K (70 kDa ribosomal protein S6 kinase). In conclusion, an overnight pre-operative constant infusion of standard TPN altered initiation factor complexes, indicating activation of the initiation of protein translation in rectus abdominis muscle in the presence of increased plasma amino acid levels, but without a concomitant increase in energy substrates and insulin. In contrast with our results from previous studies, the methodology used in the present study appears to be more sensitive in reflecting directional changes in human muscle protein synthesis compared with traditional methods, particularly based on measurements of amino acid flux.
Magnetic properties and microstructure of Fe∕Pt multilayer films capped with SiO2 amorphous layer for magnetic recording use
Authors: Ding Y. , Wei D. H. , Yao Y. D.
Published: April 2008

Fe ∕ Pt multilayer films capped with an amorphous SiO2 layer have been fabricated in order to study the microstructure and magnetic properties via a molecular beam epitaxy technique at 400°C. The formation of granularlike FePt films was obtained with this process due to the interpenetration of SiO2 which has a lower surface energy. Studies of angular dependent coercivity show a tendency of a domain-wall motion weaken toward rotation of reverse-domain type upon thickness of SiO2 capping layer atop the Fe∕Pt multilayer films. The intergrain interaction was confirmed from the Kelly–Henkel plot that indicated the exchange coupling between neighboring grains in the uncapped FePt films. On the other hand, negative δM value was obtained when the FePt films capped with SiO2 layer, indicating that the SiO2 capping layer can lead to the reduction of intergrain exchange coupling in SiO2/FePt films.
State-selected imaging of HCCO radical photodissociation dynamics
Authors: Huang Cunshun , Estillore Armando D. , Suits Arthur G.
Published: April 2008

We present a dc sliced ion imaging study of HCCO radical photodissociation to CH and CO at 230nm. The measurements were made using a two-color reduced Doppler probe strategy. The CO rotational distribution was consistent with a Boltzmann distribution at 3500K. Using the dc slice ion imaging approach, we obtained CO images for various rotational levels of CO (v=0). The results are largely consistent with earlier work, albeit with a significant 0.9eV peak seen previously in the translational energy distributions absent in our state-selected imaging study.
Residual stresses in the elastoplastic multilayer thin film structures: The cases of Si/Al bilayer and Si/Al/SiO2 trilayer structures
Authors: Zhang X. C. , Xu B. S. , Xuan F. Z.
Published: April 2008

A theoretical model was developed to predict the thermal residual stresses within the elastoplastic multilayer thin film structures. The plastic deformation of one of the films was considered. Special analyses were made on the bilayer structures, i.e., a film overlaid on a substrate, as they are more of practical interest. Closed-form solutions were derived to estimate the residual stresses in the films and curvature of the multilayer film structure, and the relationship between the temperature difference and the thickness of the plastic zone. The cases of Si/Al bilayer and Si/Al/SiO2 multilayer structures were studied to illustrate the implementation of this model. In these structures, Al film was assumed to be plastically deformed. Results showed that, for both structures, there was a linear relationship existing between the thickness of the plastic zone in Al film and the temperature difference. SiO2 layer deposited on the aluminum film had an obvious influence on the critical temperature at which Al film started to be plastically deformed.
Including anharmonicity in the calculation of rate constants. II. The OH+H2→H2O+H reaction
Authors: Isaacson Alan D.
Published: April 2008

A recently developed method for calculating anharmonic vibrational energy levels at nonstationary points along a reaction path that is based on second-order perturbation theory in curvilinear coordinates is combined with variational transition state theory with semiclassical multidimensional tunneling approximations to calculate thermal rate constants for the title reaction. Two different potential energy surfaces were employed for these calculations, an improved version of the author’s surface 5 and the WSLFH surface of Wu et al. [J. Chem. Phys. 113, 3150 (2000)]. We present detailed comparisons of rate constants computed for the two surfaces with and without anharmonicity and with various approximations for incorporating tunneling along the reaction path. The results for this system are quite sensitive to the surface employed, the choice of coordinates (curvilinear versus rectilinear), and the inclusion of anharmonicity. A comparison with experiment provides information on the accuracy of these surfaces.
Magnetic properties and stability of L21 and B2 phases in the Co2MnAl Heusler alloy
Authors: Umetsu R. Y. , Kobayashi K. , Fujita A. , Kainuma R. , Ishida K.
Published: April 2008

Magnetic properties and stability of L21 and B2 phases in the Co2MnAl Heusler alloy were investigated. It was confirmed that the order-disorder transition from the B2 to L21 phase is located at about 950K and that the Curie temperature TC of the L21 phase is 726K which is about 50K higher than that (TC=677K) of the B2 phase. The difference in TC between the L21 and B2 phases is smaller than a theoretical prediction. On the other hand, the saturation magnetic moments Ms at 4.2K for the L21 and B2 phases were estimated to be 4.07μB∕f.u. and 4.16μB∕f.u., respectively, comparable to the value Mt=4 expected from the generalized Slater–Pauling relation.
Effect of vortex handedness on spin momentum torque dynamics in dual-vortex ferromagnetic nanopillar structures
Authors: Deak J. G.
Published: April 2008

An investigation of the dynamics of vortices driven by spin-momentum transfer in magnetic tunnel junction nanopillars containing a vortex in the hard ferromagnetic pinned layer (PL) and a vortex in the soft ferromagnetic free layer (FL) is presented. This dual vortex configuration is interesting because the handedness of the vortex in the PL can be set so that the SMT is either assisted or opposed by the torque due to the Amperean magnetic field produced by the current passing through the nanopillar. It is shown that the handedness of the vortex in the PL controls the dynamics of the nanopillar device. Micromagnetic simulations of the three-dimensional nanopillar structures were performed as a function of PL vortex handedness, spin polarization (η), and nanopillar dimensions. Generally, for positive η, it is found that when the PL vortex is set counter-clockwise (CCW), the FL vortex shows a well-defined switching behavior, where the handedness of the final vortex state in the FL is dependent on the current direction through the nanopillar, and the switching current is decreased as η is increased. In devices where the PL is magnetized clockwise (CW), the FL magnetization dynamics show a more complicated dependence on η. The CW magnetized PL nanopillars show high-current Amperean field-induced vortex switching at low η, chaotic oscillation at intermediate η, and well-defined low-current switching at high η. For negative η, the CCW and CW PL results invert.
Synthesis and characterization of smooth ultrananocrystalline diamond films via low pressure bias-enhanced nucleation and growth
Authors: Chen Y. C. , Zhong X. Y. , Konicek A. R. , Grierson D. S. , Tai N. H. , Lin I. N. , Kabius B. , Hiller J. M. , Sumant A. V. , Carpick R. W. , Auciello O.
Published: April 2008

This letter describes the fundamental process underlying the synthesis of ultrananocrystalline diamond (UNCD) films, using a new low-pressure, heat-assisted bias-enhanced nucleation (BEN)/bias enhanced growth (BEG) technique, involving H2∕CH4 gas chemistry. This growth process yields UNCD films similar to those produced by the Ar-rich/CH4 chemistries, with pure diamond nanograins (3–5nm), but smoother surfaces (∼6nm rms) and higher growth rate (∼1μm∕h). Synchrotron-based x-Ray absorption spectroscopy, atomic force microscopy, and transmission electron microscopy studies on the BEN-BEG UNCD films provided information critical to understanding the nucleation and growth mechanisms, and growth condition-nanostructure-property relationships.
Depletion potential in the infinite dilution limit
Authors: Yuste Santos Bravo , Santos Andrés , López de Haro Mariano
Published: April 2008

The depletion force and depletion potential between two in principle unequal “big” hard spheres embedded in a multicomponent mixture of “small” hard spheres are computed using the rational function approximation method for the structural properties of hard-sphere mixtures [S. B. Yuste, A. Santos, and M. López de Haro, J. Chem. Phys. 108, 3683 (1998)]. The cases of equal solute particles and of one big particle and a hard planar wall in a background monodisperse hard-sphere fluid are explicitly analyzed. An improvement over the performance of the Percus–Yevick theory and good agreement with available simulation results are found.
Analytical solution for restricted diffusion in circular and spherical layers under inhomogeneous magnetic fields
Authors: Grebenkov Denis S.
Published: April 2008

We propose an analytical solution for restricted diffusion of spin-bearing particles in circular and spherical layers in inhomogeneous magnetic fields. More precisely, we derive exact and explicit formulas for the matrix representing an applied magnetic field in the Laplacian eigenbasis and governing the magnetization evolution. For thin layers, a significant difference between two geometrical length scales (thickness and overall size) allows for accurate perturbative calculations. In these two-scale geometries, apparent diffusion coefficient (ADC) as a function of diffusion time exhibits a new region with a reduced but constant value. The emergence of this intermediate diffusion regime, which is analogous to the tortuosity regime in porous media, is explained in terms of the underlying Laplace operator eigenvalues. In general, regions with constant ADCs would be reminiscent of multiscale geometries, and their observation can potentially be used in experiments to detect the length scales by varying diffusion time.
Screening of hydrodynamic interactions in Brownian rod suspensions
Authors: Pryamitsyn Victor , Ganesan Venkat
Published: April 2008

We present the details and results of a simulation study addressing the dynamics and rheology of rod suspensions over a wide regime of concentrations ranging from dilute to concentrated systems. Our study compares the results of two complementary simulation methods. The first method adapts a recently proposed explicit solvent simulation strategy and incorporates both hydrodynamical effects and steric interactions between the rod units. We compare the results of such a method with those obtained from a Brownian dynamics simulation approach which retains the steric interactions but neglects the effects of hydrodynamic interactions. Overall, our results in the context of the translational and rotational diffusivities are in agreement with the hydrodynamical predictions in the dilute regime and the corresponding results of the tube model and its extensions thereof in the semidilute regimes. The latter results suggest that effects of hydrodynamic interactions on the translational and rotational diffusivities are secondary relative to the steric interactions and at best lead only to a small correction to the results of the classical tube model. Our results in the context of linear viscoelasticity also broadly confirms the predictions of the tube model for the storage and loss moduli and allows us to extract for the first time the independent hydrodynamic and Brownian contributions to the zero shear viscosity. While the relative magnitudes of these contributions are consistent with the theoretical predictions, the quantitative magnitudes are quite different from the theoretical predictions. Overall, these results confirm the validity of the hydrodynamic “screening” hypothesis and ratify the neglect of hydrodynamical stresses in quantifying the linear rheology of Brownian rod suspensions.
The initial single yeast cell adhesion on glass via optical trapping and Derjaguin–Landau–Verwey–Overbeek predictions
Authors: Castelain Mickaël , Pignon Frédéric , Piau Jean-Michel , Magnin Albert
Published: April 2008

We used an optical tweezer to investigate the adhesion of yeast Saccharomyces cerevisiae onto a glass substrate at the initial contact. Micromanipulation of free-living objects with single-beam gradient optical trap enabled to highlight mechanisms involved in this initial contact. As a function of the ionic strength and with a displacement parallel to the glass surface, the yeast adheres following different successive ways: (i) Slipping and rolling at 1.5mM NaCl, (ii) slipping, rolling, and sticking at 15mM NaCl, and (iii) only sticking at 150mM. These observations were numerous and reproducible. A kinetic evolution of these adhesion phenomena during yeast movement was clearly established. The nature, range, and relative intensity of forces involved in these different adhesion mechanisms have been worked out as a quantitative analysis from Derjaguin–Landau–Verwey–Overbeek (DLVO) and extended DLVO theories. Calculations show that the adhesion mechanisms observed and their affinity with ionic strength were mainly governed by the Lifshitz–van der Waals interaction forces and the electrical double-layer repulsion to which are added specific contact forces linked to “sticky” glycoprotein secretion, considered to be the main forces capable of overcoming the short-range Lewis acid-base repulsions.
Electron emission from laser-heated fullerene dianions: Probing the repulsive Coulomb barrier
Authors: Concina Bruno , Neumaier Marco , Hampe Oliver , Kappes Manfred M.
Published: April 2008

Electron detachment from fullerene dianions Cm2− (m=76,84) stored in a room temperature Penning trap was probed upon pulsed laser excitation at wavelengths of 355 and 532nm. The fraction of Cm2− surviving trapping times exceeding tens of milliseconds under UHV conditions, as well as the fraction of singly charged anions Cm− generated were recorded as a function of the laser fluence. Analysis by means of Poisson statistics yields absolute absorption cross sections and the number of photons necessary to induce the detachment. The cross sections obtained are in good agreement with the literature values. By describing the electron detachment as a statistical unimolecular process, we deduce effective activation energies from the number of photons required. These energies are compared to the sum of the second electron affinity and the Coulomb barrier height as calculated from an electrostatic charging model.
Nitrile and thiocyanate IR probes: Quantum chemistry calculation studies and multivariate least-square fitting analysis
Authors: Choi Jun-Ho , Oh Kwang-Im , Lee Hochan , Lee Chewook , Cho Minhaeng
Published: April 2008

Hydration effects on the CN stretching mode frequencies of MeCN and MeSCN are investigated by carrying out ab initio calculations for a number of MeCN-water and MeSCN-water complexes with varying number of water molecules. It is found that the CN frequency shift induced by the hydrogen-bonding interactions with water molecules originate from two different ways to form hydrogen bonds with the nitrogen atom of the CN group. Considering the MeCN- and MeSCN-water cluster calculation results as databases, we first examined the validity of vibrational Stark effect relationship between the CN frequency and the electric field component parallel to the CN bond and found no strong correlation between the two. However, taking into account of additional electric field vector components is a simple way to generalize the vibrational Stark theory for the nitrile chromophore. Also, the electrostatic potential calculation method has been proposed and examined in detail. It turned out that the interactions of water molecules with nitrogen atom’s lone pair orbital and with nitrile π orbitals can be well described by the electrostatic potential calculation method. The present computational results will be of use to quantitatively simulate various linear and nonlinear vibrational spectra of nitrile compounds in solutions.
Modeling of amorphous InGaZnO4 thin film transistors and their subgap density of states
Authors: Hsieh Hsing-Hung , Kamiya Toshio , Nomura Kenji , Hosono Hideo , Wu Chung-Chih
Published: April 2008

We report a model of the carrier transport and the subgap density of states in amorphous InGaZnO4 (a-IGZO) for device simulation of a-IGZO thin-film transistors (TFTs) operated in both the depletion mode and the enhancement mode. A simple model using a constant mobility and two-step subgap density of states reproduced well the characteristics of the a-IGZO TFTs. a-IGZO exhibits low densities of tail states and deep gap states, leading to small subthreshold swings and high mobilities.
On the computation and contribution of conductivity in molecular ionic liquids
Authors: Schröder C. , Haberler M. , Steinhauser O.
Published: April 2008

In this study we present the results of the molecular dynamics simulation of the ionic liquids: 1-butyl-3-methyl-imidazolium tetrafluoroborate and trifluoromethylacetate as well as 1-ethyl-3-methyl-imidazolium dicyanamide. Ionic liquids are characterized by both a molecular dipole moment and a net charge. Thus, in contrast to a solution of simple ions in a (non-) polar solvent, rotational and translational effects influence the very same molecule. This study works out the theoretical framework necessary to compute the conductivity spectrum and its low frequency limit of ionic liquids. Merging these computed conductivity spectra with previous simulation results on the dielectric spectra of ionic liquids yields the spectrum of the generalized dielectric constant, which may be compared to experiments. This spectrum was calculated for the three ionic liquids over six orders of magnitude in frequency ranging from 10MHz to 50THz. The role of rotation and translation and their coupling term on the generalized dielectric constant is discussed in detail with a special emphasis on the zero-frequency limit. Thereby, the frequency dependence of the cross correlation between the collective rotational dipole moment and the current is discussed.
Correlation holes for the helium dimer
Authors: Piris M. , Lopez X. , Ugalde J. M.
Published: April 2008

We have investigated the radial electron pair probability distributions (REPPDs) of the helium dimer within the Piris natural orbital functional (PNOF) theory. The analytical formulas to evaluate intracule densities, Fermi, Coulomb, and total correlation holes using our reconstruction functional PNOF-2 [J. Chem. Phys. 126, 214103 (2007)] are derived. The Löwdin’s Coulomb holes from PNOF-2 and full configuration interaction calculations are analyzed showing a very similar behavior. New definitions of the Coulomb and Fermi holes based on the cumulant expansion of the two-particle reduced density matrix are presented. The holes are defined in terms of the exact one-particle reduced density matrix and the two-particle cumulant without any reference to the Hartree–Fock state. Through these definitions, we analyze separately the contribution of each component to the total REPPD at several values of the internuclear distance. A straight connection between the Coulomb hole and dispersion interactions is observed.
Spin-orbit effects in the photoabsorption of WAu12 and MoAu12: A relativistic time dependent density functional study
Authors: Stener M. , Nardelli A. , Fronzoni G.
Published: April 2008

The electronic structure of both WAu12 and MoAu12 has been calculated at the density functional theory (DFT) level, employing the zero order regular approximation at the scalar relativistic level and including a spin-orbit coupling. The effect of the inclusion of the spin-orbit coupling is discussed, and the differences assigned to the nature of the encaged atom (W or Mo) are identified. Then, the excitation spectra of both clusters are calculated at the time-dependent DFT level, also in this case at both scalar relativistic and spin-orbit levels. The inclusion of spin-orbit coupling is mandatory for an accurate description in the low energy region. At higher energy, where the density of states is higher, the convoluted intensity can be properly described already at the scalar relativistic level. The consequences of the spin-orbit coupling on the excitation spectrum of the clusters indicate that while in WAu12 the lowest excitations are essentially shifted in energy with respect to the scalar relativistic results, in MoAu12, a dramatic splitting in many lines is actually predicted, revealing a quite different behavior of the two clusters.
Ice nucleation on hydrophilic silicon
Authors: Ochshorn Eli , Cantrell Will
Published: April 2008

We have used Fourier transform infrared spectroscopy to study thin water films on a hydrophilic silicon surface in the temperature range from 20to−20°C. Throughout that range, the spectra of the water adjacent to the silicon surface are consistent with that of bulk water near 25°C. Thicker films (>1μm) freeze at −11±1°C. We reconcile the apparent paradox of a thin film of water which is quite liquidlike at a temperature where freezing of thicker films occurs by hypothesizing that the nucleation event in the thicker film is triggered by a critical ice embryo which forms at some small distance from the silicon surface, as opposed to in direct contact with it.
Monte Carlo simulations of fluids whose particles interact with a logarithmic potential
Authors: Heyes D. M. , Rickayzen G. , Powles J. G.
Published: April 2008

Monte Carlo simulations of a model fluid in which the particles interact via a continuous potential that has a logarithmic divergence at a pair separation of σ, which we introduced in J. G. Powles et al., Proc. R. Soc. London, Ser. A 455, 3725 (1999), have been carried out. The potential has the form, ϕ(r)=−ϵln(f(r)), where ϵ sets the energy scale and f(r)=1−(σ∕r)m. The value of m chosen was 12 but the qualitative trends depend only weakly on the value of m, providing it is greater than 3. The potential is entirely repulsive and has a logarithmic divergence as ∼−ln(r∕σ−1) in the r→σ limit. Predictions of the previous paper that the internal energy can be computed at all temperatures using the standard statistical mechanics formula for continuous potentials are verified here. The pressure can be calculated using the usual virial expression for continuous potentials, although there are practical limitations in resolving the increasingly important contribution from the r→σ limit at reduced temperatures greater than ∼5. The mean square force ⟨F2⟩ and infinite frequency shear G∞ and bulk K∞ moduli are only finite for T*=kBT∕ϵ<1. The logarithmic fluid’s physical properties become increasingly more like that of the hard sphere fluid with increasing temperature, showing a sharp transition in the behavior of the mean square force and infinite frequency elastic constants at T*=1. The logarithmic fluid is shown to exhibit a solid-fluid phase transition.
Linear-scaling fixed-node diffusion quantum Monte Carlo: Accounting for the nodal information in a density matrix-based scheme
Authors: Kussmann Jörg , Ochsenfeld Christian
Published: April 2008

A reformulation of the fixed-node diffusion quantum Monte Carlo method (FN-DQMC) in terms of the N-particle density matrix is presented, which allows us to reduce the computational effort to linear for the evaluation of the local energy. The reformulation is based on our recently introduced density matrix-based approach for a linear-scaling variational QMC method [J. Kussmann et al., Phys. Rev. B. 75, 165107 (2007)]. However, within the latter approach of using the positive semi-definite N-particle trial density (ρNT(R)=∣ΨT(R)∣2), the nodal information of the trial function is lost. Therefore, a straightforward application to the FN-DQMC method is not possible, in which the sign of the trial function is usually traced in order to confine the random walkers to their nodal pockets. As a solution, we reformulate the FN-DQMC approach in terms of off-diagonal elements of the N-particle density matrix ρNT(R;R′), so that the nodal information of the trial density matrix is obtained. Besides all-electron moves, a scheme to perform single-electron moves within N-PDM QMC is described in detail. The efficiency of our method is illustrated for exemplary calculations.
Determination of the orientation distribution function in aligned single wall nanotube polymer nanocomposites by polarized Raman spectroscopy
Authors: Pérez Ricardo , Banda Sumanth , Ounaies Zoubeida
Published: April 2008

This work focuses on the derivation of the orientation distribution function (ODF) for a uniaxial-axially symmetric system using polarized Raman spectroscopy. A numerical methodology is proposed to determine the ODF that is formulated in terms of Legendre polynomials and the principle of maximum information entropy. The ultimate goal is to quantify the alignment of single wall nanotubes (SWNTs) in a polymer matrix using the experimental information from the Raman intensity. Some of the mathematical and numerical steps in the determination of ODF, not clarified in the current literature, are shown in this work. The proposed numerical methodology to obtain the ODF is illustrated using an experimental case. Electric field–aligned SWNT-urethane dimethacrylate/1,6-hexanediol dimethacrylate nanocomposites are investigated at different processing conditions to bring forward factors that may enhance the alignment of SWNT inclusions in the polymer. ODF results indicate that the higher electric field frequencies produce a good alignment of the SWNT inclusions; a result also corroborated by optical microscopy imaging and electrical conductivity measurements.
Magnetic domain wall propagation in nanowires under transverse magnetic fields
Authors: Bryan Matthew T. , Schrefl Thomas , Atkinson Del , Allwood Dan A.
Published: April 2008

We have investigated the propagation of transverse domain walls in magnetic nanowires under axial and transverse magnetic fields using three-dimensional micromagnetic modeling. Transverse magnetic fields change the domain wall width and, below the Walker field, either increase or decrease the domain wall velocity depending when the field and wall magnetization are parallel or antiparallel, respectively. Furthermore, differences in the Walker field also appear for opposite transverse fields, and a surprising result is that under relatively high axial and transverse fields, Walker breakdown can be completely suppressed and the domain wall velocity returns to several hundreds of ms−1.
Surface charge algebra in gauge theories and thermodynamic integrability
Authors: Barnich Glenn , Compère Geoffrey
Published: April 2008

Surface charges and their algebra in interacting Lagrangian gauge field theories are constructed out of the underlying linearized theory using techniques from the variational calculus. In the case of exact solutions and symmetries, the surface charges are interpreted as a Pfaff system. Integrability is governed by Frobenius’ theorem and the charges associated with the derived symmetry algebra are shown to vanish. In the asymptotic context, we provide a generalized covariant derivation of the result that the representation of the asymptotic symmetry algebra through charges may be centrally extended. Comparison with Hamiltonian and covariant phase space methods is made. All approaches are shown to agree for exact solutions and symmetries while there are differences in the asymptotic context.
Energetics of multiple-ion species hohlraum plasmas
Authors: Neumayer P. , Berger R. L. , Callahan D. , Divol L. , Froula D. H. , London R. A. , MacGowan B. J. , Meezan N. B. , Michel P. A. , Ross J. S. , Sorce C. , Widmann K. , Suter L. J. , Glenzer S. H.
Published: April 2008

A study of the laser-plasma interaction processes has been performed in multiple-ion species hohlraum plasmas at conditions similar to those expected in indirect drive inertial confinement fusion targets. Gas-filled hohlraums with electron densities of 5.5×1020 and 9×1020cm−3 are heated by 14.3kJ of laser energy (wavelength 351nm) to electron temperatures of 3keV and backscattered laser light is measured. Landau damping of the ion acoustic waves is increased by adding hydrogen to a CO2 or CF4 gas. Stimulated Brillouin backscattering of a 351nm probe beam is found to decrease monotonically with increasing Landau damping, accompanied by a comparable increase in the transmission. More efficient energy coupling into the hohlraum by suppression of backscatter from the heater beams results in an increased hohlraum radiation temperature, showing that multiple-ion species plasmas improve the overall hohlraum energetics. The reduction in backscatter is reproduced by linear gain calculations as well as detailed full-scale three-dimensional laser-plasma interaction simulations, demonstrating that Landau damping is the controlling damping mechanism in inertial confinement fusion relevant high-electron temperature plasmas. These findings have led to the inclusion of multiple-ion species plasmas in the hohlraum point design for upcoming ignition campaigns at the National Ignition Facility.
Line length dependence of threshold current density and driving force in eutectic SnPb and SnAgCu solder electromigration
Authors: Yoon Min-Seung , Ko Min-Ku , Kim Bit-Na , Kim Byung-Joon , Park Yong-Bae , Joo Young-Chang
Published: April 2008

The relationship between the threshold current density and the critical line length in eutectic SnPb and SnAgCu electromigrations were examined using solder lines with the various lengths ranging from 100to1000μm. When the electron wind-force was balanced by the back-stress gradient force, the net flux of electromigration is zero, at which the current density and line length are defined as the threshold current density and the critical length, respectively. It was found that in SnAgCu electromigration, the 1∕L dependence on the threshold current density showed good agreement, whereas the threshold current densities of the eutectic SnPb deviated from the 1∕L dependence. The balance between the electron wind-force and the back-stress gradient force was the main factor determining the threshold product of SnAgCu electromigration. On the other hand, in the case of eutectic SnPb, the chemical driving force is contributed as a back-flux force in addition to the back-stress gradient force. The existence of the chemical driving force was caused by the nonequilibrium Pb concentration inside the Pb-rich phases between the cathode and anode during the electromigration procedure.
The correspondence between Tracy–Widom and Adler–Shiota–van Moerbeke approaches in random matrix theory: The Gaussian case
Authors: Rumanov Igor
Published: April 2008

Two approaches to the derivation of integrable differential equations for random matrix probabilities are compared. Both methods are rewritten in such a form that simple and explicit relations between all TW dependent variables and τ-functions of ASvM are found, for the example of finite size Gaussian matrices. Orthogonal function systems and Toda lattice are seen as the core structure of both approaches and their relationship.
Structural and electrical characterization of AuPtAlTi Ohmic contacts to AlGaN∕GaN with varying annealing temperature and Al content
Authors: Fay M. W. , Han Y. , Brown P. D. , Harrison I. , Hilton K. P. , Munday A. , Wallis D. , Balmer R. S. , Uren M. J. , Martin T.
Published: April 2008

The effect of varying annealing temperature and Al layer thickness on the structural and electrical characteristics of AuPtAlTi∕AlGaN∕GaN Ohmic contact structures has been systematically investigated. The relationship between annealing temperature, Al content, interfacial microstructure, surface planarity, and contact resistance is examined. In particular, the presence of a detrimental low temperature Pt–Al reaction is identified. This is implicated in both the requirement for a higher Al:Ti ratio than is required for related AuPdAlTi contact schemes and through the degraded temperature dependent resistance behaviour of the annealed AuPtAlTi contacts.
Ultrafast exciton transfers in DNA and its nonlinear optical spectroscopy
Authors: Hyeon-Deuk Kim , Tanimura Yoshitaka , Cho Minhaeng
Published: April 2008

We have calculated the nonlinear response function of a DNA duplex helix including the contributions from the exciton population and coherence transfers by developing an appropriate exciton theory as well as by utilizing a projector operator technique. As a representative example of DNA double helices, the B-form (dA)10-(dT)10 is considered in detail. The Green functions of the exciton population and coherence transfer processes were obtained by developing the DNA exciton Hamiltonian. This enables us to study the dynamic properties of the solvent relaxation and exciton transfers. The spectral density describing the DNA base-solvent interactions was obtained by adjusting the solvent reorganization energy to reproduce the absorption and steady-state fluorescence spectra. The time-dependent fluorescence shift of the model DNA system is found to be ultrafast and it is largely determined by the exciton population transfer processes. It is further shown that the nonlinear optical spectroscopic techniques such as photon echo peak shift and two-dimensional photon echo can provide important information on the exciton dynamics of the DNA double helix. We have found that the exciton-exciton coherence transfer plays critical roles in the peculiar energy transfer and ultrafast memory loss of the initially created excitonic state in the DNA duplex helix.
Enhancement of upconversion luminescence of Er doped Al2O3 films by Ag island films
Authors: Aisaka Takeho , Fujii Minoru , Hayashi Shinji
Published: April 2008

Strong enhancement of upconversion photoluminescence (PL) of Er3+ in the visible range was achieved by placing it near rough Ag island films. In order to understand the mechanism of the enhancement, PL was excited by 978 and 488nm light and the enhancement factors were obtained in a wide spectral range (520nmto1.6μm). The emission and excitation wavelength dependence of the enhancement factors revealed that both the incident electric fields and the radiative decay rate of Er3+ are enhanced due to the excitation of surface plasmons supported by Ag islands. It was found that the upconversion PL is more sensitive to the enhancement of the incident electric field than the downconversion PL because of the multiphoton absorption process. The present result indicates that the upconversion PL obtains more benefit from the metal-enhanced fluorescence technique than the downconversion PL.
Differential sputter yields in Si1−xGex
Authors: Hossain M. Zubaer , Freund Jonathan B. , Johnson H. T.
Published: April 2008

Sputter yields for ion bombardment of Si1−xGex alloys are computed using molecular dynamics simulations with the target material modeled using the Stillinger–Weber empirical potential. The results show that Si atoms are preferentially sputtered relative to Ge atoms for all x. The parameters of the Stillinger–Weber potential are altered to investigate the relative importance of atomic mass, bonding energy, atomic number, and atomic density leading to the observed differential sputter yields. The results explain an experimentally observed nonlinear dependence of total sputter yields on composition in Si1−xGex [Tuboltsev et al., Phys. Rev. B 72, 205434 (2005)].
Supersymmetric version of a hydrodynamic system in Riemann invariants and its solutions
Authors: Grundland A. M. , Hariton A. J.
Published: April 2008

In this paper, a supersymmetric extension of a system of hydrodynamic-type equations involving Riemann invariants is formulated in terms of a superspace and superfield formalism. The symmetry properties of both the classical and supersymmetric versions of this hydrodynamical model are analyzed through the use of group-theoretical methods applied to partial differential equations involving both bosonic and fermionic variables. More specifically, we compute the Lie superalgebras of both models and perform classifications of their respective subalgebras. A systematic use of the subalgebra structures allows us to construct several classes of invariant solutions, including traveling waves, centered waves, and solutions involving monomials, exponentials, and radicals.
On the question of percolation threshold in polyvinylidene fluoride/nanocrystalline nickel composites
Authors: Panda Maheswar , Srinivas V. , Thakur A. K.
Published: April 2008

The dielectric behavior of polyvinylidene fluoride (PVDF), nanocrystalline nickel (nc-Ni) composites has been investigated over a broad frequency range of 40Hz–10MHz. High effective dielectric constant (εeff=2050) and low loss (tanδ=10) at 100Hz have been observed near the percolation threshold. To the best of our knowledge, this is the highest εeff value reported to date among the PVDF based metal-polymer composites. The dielectric properties have been explained by using boundary layer capacitor effect and percolation theory while the dielectric anomalies are attributed to process of fabrication leading to thick insulating layer between the filler particles forming a gap in effective tunneling range of two filler particles and also making a difficulty in probability of higher order tunneling.
An entropy-based approach to the freezing of the generalized exponential model
Authors: Saija Franz
Published: April 2008

Recently, it has been shown that particles interacting through ultrasoft bounded pair potentials exhibit clustering phenomena both in the fluid and solid regimes. In this note we apply a phenomenological criterion for the localization of the freezing against the “exact” phase diagram of the generalized exponential model obtained from advanced numerical simulation techniques.
Operating regimes of corona and silent discharges in coaxial cylindrical reactors
Authors: Yehia Ashraf
Published: April 2008

The physical mechanisms of the electrical discharges formed in coaxial cylindrical reactors have been investigated in this paper under different operating conditions for the reactors. The reactors were fed by natural air flowing with a constant rate at atmospheric conditions and stressed by an ac voltage. The wave form of the ac voltage applied to the reactors has been studied corresponding to the discharge current, over the whole range of the operating conditions. The results have shown that the operating conditions for the reactor modify the physical mechanism inside it in the form of either corona or silent discharges or spark over. The onset voltage of the different electrical discharges formed inside the reactors has agreed with Peek’s equation, whatever the operating conditions. Subsequently, empirical equations concerning the operating conditions for the reactors have been derived by using Peek’s and Townsend’s equations. The derived equations represent suitable criterions to predict the different types of the electrical discharges that will form inside the reactors under any operating conditions. The results have been illustrated by recorded oscillograms showing the wave form of the ac voltage applied to the reactors and the corresponding current pulses.
Standoff detection of explosive residues using photothermal microcantilevers
Authors: Van Neste C. W. , Senesac L. R. , Yi D. , Thundat T.
Published: April 2008

Standoff detection of trace explosives is gaining attention due to its immediate relevance in countering terrorist threats based on explosive devices. However, most currently available standoff techniques rely on expensive, complex, and bulky equipment. We have demonstrated highly selective and sensitive standoff detection of explosive residues on surfaces by using photothermal spectroscopy carried out with bimaterial microcantilever sensors. The demonstrated sensitivity of the technique, 100ng∕cm2, is sufficient to detect the explosive contamination generally found on explosive devices. The sensitivity of the technique can be further improved by optimizing the bimaterial cantilever and by using higher intensity infrared sources.
Effects of interfacial sulfidization and thermal annealing on the electrical properties of an atomic-layer-deposited Al2O3 gate dielectric on GaAs substrate
Authors: Cheng Chao-Ching , Chien Chao-Hsin , Luo Guang-Li , Yang Chun-Hui , Chang Ching-Chih , Chang Chun-Yen , Kei Chi-Chung , Hsiao Chien-Nan , Perng Tsong-Pyng
Published: April 2008

In this study we investigated the interfacial chemistry occurring between an atomic-layer-deposited Al2O3 high-k film and a GaAs substrate and the impact of sulfidization and thermal annealing on the properties of the resultant capacitor. We observed that sulfide passivation of the Al2O3∕GaAs structure improved the effect of Fermi level pinning on the electrical characteristics, thereby providing a higher oxide capacitance, smaller frequency dispersion, and reduced surface states, as well as decreased interfacial charge trapping and gate leakage currents. Photoemission analysis indicated that the (NH4)2S-treated GaAs improved the quality of the as-deposited Al2O3 thin film and preserved the stoichiometry of the dielectric during subsequent high-temperature annealing. This behavior was closely correlated to the diminution of GaAs native oxides and elemental arsenic defects and their unwanted diffusion. In addition, thermal processing under an O2 atmosphere, relative to that under N2, decreased the thickness of the Al2O3 gate dielectric and relieved the gate leakage degradation induced by metallic arsenic; as a result, superior dielectric reliability was attained. We discuss the underlying thermochemical reactions that account for these experimental observations.
DC-biased ferroelectrets with large piezoelectric d33-coefficients
Authors: Hillenbrand J. , Sessler G. M.
Published: April 2008

The application of external dc voltages significantly increases the piezoelectric d33-coefficients of ferroelectret films and also enhances their thermal stability. In this paper, interferometric measurements and model calculations with such dc-biased ferroelectret films are reported. It is shown experimentally and theoretically that the d33-coefficient of the inverse piezoelectric effect of these films actually consists of a part depending on internal electret charges and a part linearly depending on the external dc voltage. Very high d33-coefficients of up to 1200pC∕N at a frequency of 5kHz are determined interferometrically. These are explained quite well by the model calculations. The model departs from an existing theoretical description by assuming that the forces generated by the electric field act on the entire cellular structure and not only on the gas voids.