bluuebunny/crossref_metadata_2025 huggingface dataset:
Inputs, storage, and transport of total and methyl mercury in two temperate forest wetlands
Authors: Selvendiran Pranesh , Driscoll Charles T. , Montesdeoca Mario R. , Bushey Joseph T.
Published: November 2008

The fluxes and pools of total mercury (THg) and methyl mercury (MeHg) were evaluated for two northern temperate forest wetlands: an abandoned beaver meadow and a riparian wetland. Mass balance calculations reveal that the wetlands are net sources of THg and MeHg, although, the magnitude of the source is a function of wetland connectivity to stream water. The volatilization rate of elemental mercury (Hgo) in the beaver meadow wetland is of similar magnitude compared to total atmospheric Hg deposition and constitutes an important component of the overall annual Hg budget. In contrast, annual Hgo fluxes exhibited net transfer from the atmosphere to soil at the riparian wetland possibly because volatilization rates were retarded by slower diffusion of Hgo through soil to the air‐water interface in water‐saturated soil. The storage of THg and MeHg in wetland soil is a large pool which appears coupled with carbon and sulfur accumulation. In the current scenario of decreasing Hg emissions and atmospheric deposition, the large “active” soil pool in wetlands is a potential short‐term and long‐term source of Hg and MeHg to downstream aquatic ecosystems.
Statistical Modeling of Epistasis and Linkage Decay using Logic Regression
Authors: Parker Thomas , Szucs Peter , Mahaffee Walt , Jannink Jean-Luc , Henning John
Published: November 2008

Logic regression has been recognized as a tool that can identify and model non-additive genetic interactions using Boolean logic groups. Logic regression, TASSEL-GLM and SAS-GLM were compared for analytical precision using a previously characterized model system to identify the best genetic model explaining epistatic interaction of vernalization-sensitivity in barley. A genetic model containing two molecular markers identified in vernalization response in barley was selected using logic regression while both TASSEL-GLM and SAS-GLM included spurious associations in their models. The results also suggest the logic regression can be used to identify dominant/recessive relationships between epistatic alleles through its use of conjugateoperators.
Erythrocyte Membrane Phosphatidylserine Exposure in Obesity
Authors: Solá Eva , Vayá Amparo , Martínez Marcial , Moscardó Antonio , Corella Dolores , Santaolaria Maria‐Luisa , España Francisco , Hernández‐Mijares Antonio
Published: November 2008

It has been suggested that increased erythrocyte membrane phosphatidylserine (PS) exposure could contribute to hypercoagulability and hemorheological disturbances in obesity. The aim of our study was to evaluate PS exposure in obese patients and in a control group and to correlate this with hemorheological properties, i.e., erythrocyte aggregability (EA) and deformability, and to evaluate the effect of weight loss on these parameters. An anthropometric and analytical evaluation was performed at baseline and after 3 months on a diet (very low‐calorie diet for 4 weeks and low‐calorie diet for 2 months) on 49 severe or morbid obese patients (37 women, 12 men) and 55 healthy volunteers (39 women, 16 men). PS exposure on erythrocyte membrane was performed by flow cytometry. Erythrocyte aggregation was measured using the Myrenne MA1 and the Sefam aggregometer. Erythrocyte deformability was determined in a stress diffractometer. Prothrombin fragment F1+2 (F1+2) was determined as a marker of the hypercoagulable state, and plasma malondialdehyde (MDA) as an indicator of oxidative stress. Obese patients had a higher EA index, higher PS exposure on erythrocyte membranes and higher levels of MDA and F1+2. The differences in erythrocyte aggregation and F1+2 between obese patients and the control group were maintained after adjusting for PS exposure. After 3 months of diet, a significant reduction in PS exposure on erythrocyte membrane was observed. Obese patients show increased PS exposure on erythrocyte membrane, with no effect on rheological properties. Increased PS exposure could contribute to hypercoagulability in these patients. Weight loss obtained with diet treatment reduces PS exposure on erythrocyte membrane.
The Impact of Obesity and Arthritis on Active Life Expectancy in Older Americans
Authors: Reynolds Sandra L. , McIlvane Jessica M.
Published: November 2008

This article examines the relationship of obesity and arthritis to length of life and length of disabled life in older American men and women. Secondary data analysis is conducted on three waves of the Asset and Health Dynamics Among the Oldest Old (AHEAD) survey (n = 7,381). Using integrated Markov chains, total, active, and disabled life expectancy in Americans aged ≥70 is estimated, with and without obesity and arthritis. Results indicate that neither obesity nor arthritis is related to the length of life for older men and women, alone or in combination. However, both conditions are significantly individually associated with increased length of disabled life in older men (1.4 years attributable to obesity; 1.2 years to arthritis at age 70; P < 0.05) and women (1.7 years attributable to obesity; 2.1 years to arthritis at age 70; P < 0.05). In addition, the combination of the two is significantly related to decreased active life, with nearly 50 and 60% of remaining life for 70‐year‐old men and women lived with disability, respectively (P < 0.05). Coupled with the fact that both obesity and arthritis are growing in prevalence, these findings represent one of the few clearly negative health trends in older adults today. These results should provide incentives for health‐care professionals to make concerted efforts to address both conditions in clinical settings.
Simulated morphological landscape of polymer single crystals by phase field model
Authors: Wang Dong , Shi Tongfei , Chen Jizhong , An Lijia , Jia Yuxi
Published: November 2008

The novel phase field model with the “polymer characteristic” was established based on a nonconserved spatiotemporal Ginzburg–Landau equation (TDGL model A). Especially, we relate the diffusion equation with the crystal growth faces of polymer single crystals. Namely, the diffusion equations are discretized according to the diffusion coefficient of every lattice site in various crystal growth faces and the shape of lattice is selected based on the real proportion of the unit cell dimensions. Spatiotemporal growth of syndiotactic polypropylene single crystals during isothermal crystallization has been investigated theoretically based on this phase field model. Two dimensional numerical calculations are performed to elucidate the faceted single crystal growth including square, rectangular, lozenge-shaped, and hexagonal single crystals. Our simulated patterns are in good agreement with the experimental morphologies, and the physical origin of polymer single crystal growth is discussed.
Magnetoresistance studies on Co∕AlOX∕Au and Co∕AlOX∕Ni∕Au tunnel structures
Authors: Liu R. S. , Canali C. M. , Samuelson L. , Pettersson H.
Published: November 2008

We report on magnetoresistance (MR) studies on Co∕AlOX∕Au and Co∕AlOX∕Ni∕Au magnetic tunnel junctions. In spite of the fact that the difference between the two samples is merely a 3nm thick Ni layer, there is a sharp contrast in MR behavior indicating that the electronic structure at the interface between the ferromagnetic electrodes and the insulating barrier dominates the MR signal. The former sample exhibits a clear tunneling anisotropic MR (TAMR), with the characteristic correlation between resistance and current direction, in contrast to the latter sample which displays a conventional tunneling MR (TMR) dominated by the relative orientation between the magnetization directions of the two electrodes. In addition, the TAMR has a much stronger temperature dependence than the TMR, indicating a much faster drop-off of the tunneling density of states anisotropy than the tunneling electron spin polarization with increasing temperature. Finally, we propose a possible simple way to distinguish TAMR from normal TMR by measuring the resistance of the device at different angles of the external magnetic field.
Invited Article: Physical and chemical analyses of impregnated cathodes operated in a plasma environment
Authors: Sengupta Anita , Kulleck James , Hill Norm , Ohlinger Wayne
Published: November 2008

Destructive analyses of impregnated-cathode assemblies from an ion thruster life test were performed to characterize erosion and degradation after 30 472 h of operation. Post-test inspection of each cathode included examination of the emitter (insert), orifice plate, cathode tube, heater, anode assembly, insulator, and propellant isolator. The discharge-cathode assembly experienced significant erosion due to ion sputtering from the discharge plasma. The keeper electrode plate was removed and the heater and orifice plate were heavily eroded at the conclusion of the test. Had the test continued, these processes would likely have led to cathode failure. The discharge cathode insert experienced significant tungsten transport and temperature dependent barium oxide depletion within the matrix. Using barium depletion semiempirical relations developed by Palluel and Shroff, it is estimated that 25 000 h of operation remained in the discharge insert at the conclusion of the test. In contrast, the neutralizer insert exhibited significantly less tungsten transport and barium oxide depletion consistent with its lower current operation. The neutralizer was estimated to have 140 000 h of insert life remaining at the conclusion of the test. Neither insert had evidence of tungstate or oxide layer formation, previously known to have impeded cathode ignition and operation in similar long duration hollow-cathode tests. The neutralizer cathode was in excellent condition at the conclusion of the test with the exception of keeper tube erosion from direct plume-ion impingement, a previously underappreciated life-limiting mechanism. The most critical finding from the test was a power dependent deposition process within the neutralizer-cathode orifice. The process manifested at low-power operation and led to the production of energetic ions in the neutralizer plume, a potential life-limiting process for the neutralizer. Subsequent return of the engine and neutralizer operation to full-power removed the deposits and energetic ion production ceased.
Monte Carlo simulations of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB): Pressure and temperature effects for the solid phase and vapor-liquid phase equilibria
Authors: Rai Neeraj , Bhatt Divesh , Siepmann J. Ilja , Fried Laurence E.
Published: November 2008

The transferable potentials for phase equilibria (TraPPE) force field was extended to nitro and amino substituents for aromatic rings via parametrization to the vapor-liquid coexistence curves of nitrobenzene and aniline, respectively. These groups were then transferred to model 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Without any further parametrization to solid state data, the TraPPE force field is able to predict TATB’s unit cell lengths and angles at 295K with mean unsigned percentage errors of 0.3% and 1.8% and the specific density within 0.5%. These predictions are comparable in accuracy to the GRBF model [Gee et al., J. Chem. Phys. 120, 7059 (2004)] that was parametrized directly to TATB’s solid state properties. Both force fields are able to reproduce the pressure dependence of TATB’s unit cell volume, but they underestimate its thermal expansion. Due to its energetic nature and unusually large cohesive energy, TATB is not chemically stable at temperature in its liquid range. Gibbs ensemble simulations allow one to determine TATB’s vapor-liquid coexistence curve at elevated temperatures and the predicted critical temperature and density for the TraPPE and GRBF model are 937±8 and 1034±8K, and 0.52±0.02 and 0.50±0.02g∕cm3, respectively.
Controlled transport of magnetic particles using soft magnetic patterns
Authors: Conroy Richard S. , Zabow Gary , Moreland John , Koretsky Alan P.
Published: November 2008

Inspired by magnetic bubble memory technology, we demonstrate the temporal and spatial manipulation of superparamagnetic beads guided by soft magnetic patterns in a rotating magnetic field. Soft magnetic structures allow complex and repetitive tasks to be performed. As a demonstration, we show cyclic capture and release of antibodies from different microfluidic streams.
Pair correlation functions of simple solutes in a Lennard-Jones solvent
Authors: Ben-Naim Arieh , Shen Vincent K.
Published: November 2008

We have calculated the pair correlation functions for several binary mixtures composed of simple solutes in a Lennard-Jones solvent. In particular, we have studied the solute-solute pair correlation functions and their dependence on the total density, the solvent Lennard-Jones parameters, and on the solute-solute energy parameter. All the results were obtained from solving the Percus–Yevick equations, as well as from Monte Carlo simulations. The relevance of these results to the problem of hydrophobic interactions is also discussed.
Doping of Ge–SixGe1−x core-shell nanowires using low energy ion implantation
Authors: Nah Junghyo , Varahramyan K. , Liu E.-S. , Banerjee S. K. , Tutuc E.
Published: November 2008

We investigate the doping of germanium (Ge)–silicon germanium (SixGe1−x) core-shell nanowires (NWs) by low energy (3 keV) boron (B) ion implantation. Ge–SixGe1−x core-shell NWs were implanted with B atoms at different doses from 1×1014 to 1×1015 cm−2, and subsequently annealed for dopant activation. Using four-point, gate-dependent resistance measurements, we determine the resistivity, doping levels, and contacts resistance of the B-doped Ge–SixGe1−x NWs. Our findings show that depending on the implantation dose, the doping level of B-doped NWs ranges from 1×1018 to 2×1020 cm−3.
Nonlinear quantum time correlation functions from centroid molecular dynamics and the maximum entropy method
Authors: Paesani Francesco , Voth Gregory A.
Published: November 2008

A new approach for the calculation of nonlinear quantum time correlation functions within the path-integral centroid dynamics formalism is presented. This approach combines information on the real-time dynamics obtained from centroid molecular dynamics with classical operators with information on the corresponding imaginary-time dynamics obtained from path-integral molecular dynamics. Nonlinear quantum correlation functions in the high and low temperature regimes computed for model potentials are in remarkably good agreement with the corresponding exact results, suggesting that the method represents an effective and accurate approach for the investigation of general quantum time correlation functions in systems with many degrees of freedom.
Exact integral constraint requiring only the ground-state electron density as input on the exchange-correlation force −∂Vxc(r)/∂r for spherical atoms
Authors: March N. H. , Nagy Á.
Published: November 2008

Following some studies of ∫n(r)∇V(r)dr by earlier workers for the density functional theory (DFT) one-body potential V(r) generating the exact ground-state density, we consider here the special case of spherical atoms. The starting point is the differential virial theorem, which is used, as well as the Hiller–Sucher–Feinberg [Phys. Rev. A 18, 2399 (1978)] identity to show that the scalar quantity paralleling the above vector integral, namely, ∫n(r)∂V(r)/∂rdr, is determined solely by the electron density n(0) at the nucleus for the s-like atoms He and Be. The force −∂V/∂r is then related to the derivative of the exchange-correlation potential Vxc(r) by terms involving only the external potential in addition to n(r). The resulting integral constraint should allow some test of the quality of currently used forms of Vxc(r). The article concludes with results from the differential virial theorem and the Hiller–Sucher–Feinberg identity for the exact many-electron theory of spherical atoms, as well as for the DFT for atoms such as Ne with a closed p shell.
An efficient implementation for determining volume polarization in self-consistent reaction field theory
Authors: Vilkas Marius J. , Zhan Chang-Guo
Published: November 2008

An efficient algorithm of the surface and volume polarization for electrostatics (SVPE) method in self-consistent reaction field (SCRF) theory, denoted by SV(1)PE, has been proposed to simulate direct volume polarization potential with a single layer of point charges outside the solute cavity while the indirect effects of volume polarization on surface polarization are still simulated with multiple layers of point charges. The free energies of solvation calculated using the SV(1)PE algorithm (implemented in GAUSSIAN03) reproduce the corresponding values calculated using the standard SVPE implementation within an error of only ∼0.1% when the solute cavity is defined by the standard 0.001e/a03 solute charge isodensity contour. The SV(1)PE results are much less sensitive to the used cavity size in comparison with the well-established surface and simulated volume polarization for electrostatics [SS(V)PE] method which simulates volume polarization through an additional surface charge distribution on the cavity surface. The SCRF calculations using the SV(1)PE method are more efficient than those using the original SVPE method.
First-principles study of thermal and electron-activated dissociation of acetone on Si(001)
Authors: Lee Jun-Ho , Lee Ji Young , Cho Jun-Hyung
Published: November 2008

Using first-principles density-functional calculations, we investigate the reaction of acetone on the Si(001) surface, which exhibits the conversion from a kinetically controlled reaction to thermodynamically controlled one by means of thermal anneal or the highly confined electron beam of the scanning tunneling microscopy (STM) tip. We identified the four different reaction pathways forming not only two kinds of di-σ structures on top of a single Si dimer (termed as the [2+2] cycloaddition structure) and across the ends of two adjacent Si dimers but also two bridge-bonded dissociative structures (termed the “end-bridge” and “dimer-bridge” structures) involving two adjacent Si dimers. Our calculated energy profiles for the reaction pathways show not only that formation of the [2+2] cycloaddition structure is kinetically favored because of its low-energy barrier, but also that, as temperature increases, the kinetically favored [2+2] cycloaddition structure is converted to the more thermodynamically stable end-bridge and dimer-bridge structures via an intermediate state where the O atom forms a dative bond to the down Si atom of the buckled dimer. In addition, we find that the Si–C bonding (antibonding) states of the [2+2] cycloaddition structure appear at about 1–2 (2–3) eV below (above) the Fermi level, in which injected holes (electrons) through the STM tip can be created (trapped) to give rise to a Si–C bond breakage. These results manifest that the kinetically controlled reaction of acetone on Si(001) is associated with the [2+2] cycloaddition structure, rather than the α-H cleavage structure proposed by a recent STM experiment.
Dependence on chirp rate and spectral resolution of the terahertz field pulse waveform measured by electro-optic detection using a chirped optical pulse and a spectrometer and its effect on terahertz spectroscopy
Authors: Murakami H. , Shimizu K. , Katsurada M. , Nashima S.
Published: November 2008

Single-shot measurement of a terahertz field pulse waveform by electro-optic sampling using a chirped optical pulse and a spectrometer was demonstrated by and Jiang and Zhang [Appl. Phys. Lett. 72, 1945 (1998)]. We have performed an experimental and theoretical investigation into the dependence of the waveform thus measured on the chirp rate and spectral resolution. It was found that the waveform exhibits multicyclic behavior at a chirp rate of −0.24 THz2, which corresponds to a chirped-pulse width of over 10 ps, for the monocyclic original terahertz field, while it approaches the monocyclic behavior with decreasing pulse width. Further, broadening of the spectral resolution of the spectrometer gives rise to a monocyclic waveform in the chirp rate range where the waveform is expected to be multicyclic. In addition, we have derived an analytical expression for the terahertz field pulse waveform thus measured without using the method of stationary phase. The theoretical results were found to be consistent with measured ones. Finally, we examined the spectral bandwidth and resolution of terahertz spectroscopy using this method.
Optical emission and energy disposal characterization of the laser ablation process of CaF2, BaF2, and NaCl at 1064 nm
Authors: Villagran-Muñiz M. , Sobral H. , Rinaldi C. A. , Cabanillas-Vidosa I. , Ferrero J. C.
Published: November 2008

A method to simultaneously measure the fraction of incident energy spent as absorbed, scattered, and consumed energy by the plasma generated in the ablation process is presented. The results obtained allowed to make an energy balance in the ablation process of halogenated earth alkaline metal crystals (NaCl, BaF2, and CaF2) and to relate the nature of the crystal structure to the absorbed energy. The latter could be determined by monitoring the magnitude of the breakdown induced by the discharge between the plates of a capacitor. Simultaneously, time resolved optical emission spectroscopy was used to analyze the ion emission intensity and as a function of the energy absorbed by the sample. This plot shows the usual sigmoid behavior for the ablation process with the three typical regions, corresponding to the vaporization, screening, and ablation regimes. A heuristic equation has been used to analyze this process in terms of the nature of the crystal structure. From this equation the critical absorbed energy for each of the studied samples could also be determined.
Magnetic cluster glass behavior and grain boundary effect in Nd0.7Ba0.3MnO3 nanoparticles
Authors: Roy B. , Das S.
Published: November 2008

The magnetic and transport properties of Nd0.7Ba0.3MnO3 nanoparticles were explored by transmission electron microscopy, x-ray powder diffraction, resistivity, magnetoresistance, thermopower (S), and magnetic measurements. The metal-insulator transition behavior of the temperature dependence of resistivity for the sample with the largest particle size changes to insulating nature with the decrease in the particle size due to the enhancement of the grain boundary effect. The magnetoresistance of the nanoparticles is analyzed in the light of a phenomenological model based on the spin polarized tunneling at the grain boundaries. The thermopower of the samples shows a crossover from negative to positive values and at high temperatures S follows adiabatic small polaron hopping theory. The zero field cooled and field cooled (FC) magnetizations display broad ferromagnetic transition. The Curie temperature (TC) and the irreversibility temperature (Tirr) decrease considerably with the decrease in the particle size. During cooling the ac susceptibility of the nanoparticles exhibits two magnetic phase transitions with paramagnetic, ferromagnetic, and glassy phases. The frequency dependent peak in the out of phase part (χ″) of the ac susceptibility is the signature of cluster glass behavior. Large thermomagnetic irreversibility, monotonic increase in the FC magnetization, nonsaturation of the magnetization, and the observation of two distinct magnetic transitions in ac susceptibility give evidence for the cluster glass nature of the nanoparticles.
Direct observation of changes to domain wall structures in magnetic nanowires of varying width
Authors: O’Shea K. J. , McVitie S. , Chapman J. N. , Weaver J. M. R.
Published: November 2008

Lorentz microscopy has been used to explore the structure variation of domain walls in thin Permalloy nanowires in the vicinity of symmetric triangular antinotches. The antinotches present a complex potential landscape to domain walls. Walls can be trapped in front of, partly enter, or be trapped inside the antinotches according to the geometry of the latter and, in the case of vortex domain walls, the chirality. In all cases, the magnetization distribution was determined. Of particular note was the structure the wall assumed during depinning from the antinotch, complex forms extending over distances several times the wire width being observed.
Directional properties of hard x-ray sources generated by tightly focused ultrafast laser pulses
Authors: Hou Bixue , Mordovanakis Aghapi , Easter James , Krushelnick Karl , Nees John A.
Published: November 2008

Directional properties of ultrafast laser-based hard x-ray sources are experimentally studied using tightly focused approximately millijoule laser pulses incident on a bulk Mo target. Energy distributions of Kα and total x rays, as well as source-size distributions are directionally resolved in vacuum and in flowing helium, respectively. Directional distributions of x-ray emission is more isotropic for p-polarized pump than for s-polarized. Based on source-size measurements, a simple two-location model, with expanded plasma and bulk material, is employed to represent the x-ray source profile.
High intensity x-ray line emission from aluminum plasmas generated by a 120TW, 30fs laser pulse
Authors: Yang Jiamin , Hu Zhimin , Zhang Jiyan , Zhu Tuo , Zhao Yang , Wen Tianshu , Wang Zhebin , Ding Yaonan , Wei Mingxi , Yang Guohong , Zhang Baohan
Published: November 2008

The K-shell x-ray spectra from the aluminum plasmas generated by the interaction of the 120TW, 30fs laser with aluminum targets have been measured by defocusing the laser beam. Laser energy-normalized intensity of the He-a line increases with the laser intensity approximately as a power law ε∝ILγ with the much smaller exponent of γ=0.062 compared to γ=0.2∼0.5 in the previous experiments, which is caused by the stronger radial thermal diffusivity in the target for the smaller laser spot. Laser-to-He-a line conversion efficiency of up to 1.9×10−3 and as high as about 3×1013 photons/2π Sr aluminum He-a line x-ray source have been achieved for a single shot due to the preplasma effect and relatively large laser spot and energy for the single shot. The x-ray spectra as a function of the laser intensity are also analyzed to get the electron temperature and density.
Physics of collisionless phase mixing
Authors: Tsiklauri D. , Haruki T.
Published: November 2008

Previous studies of phase mixing of ion cyclotron (IC), Alfvénic, waves in the collisionless regime have established the generation of parallel electric field and hence acceleration of electrons in the regions of transverse density inhomogeneity. However, outstanding issues were left open. Here we use the 2.5D, relativistic, fully electromagnetic particle-in-cell code and an analytic magnetohydrodynamic (MHD) formulation, to establish the following points: (i) Using the generalized Ohm’s law we find that the parallel electric field is supported mostly by the electron pressure tensor, with a smaller contribution from the electron inertia term. (ii) The generated parallel electric field and the fraction of accelerated electrons are independent of the IC wave frequency remaining at a level of six orders of magnitude larger than the Dreicer value and approximately 20%, respectively. The generated parallel electric field and the fraction of accelerated electrons increase with the increase of IC wave amplitude. The generated parallel electric field seems to be independent of plasma beta, while the fraction of accelerated electrons strongly increases with the decrease of plasma beta (for plasma beta of 0.0001 the fraction of accelerated electrons can be as large as 47%). (iii) In the collisionless regime IC wave dissipation length (that is defined as the distance over which the wave damps) variation with the driving frequency shows a deviation from the analytical MHD result, which we attribute to a possible frequency dependence of the effective resistivity. (iv) Effective anomalous resistivity, inferred from our numerical simulations, is at least four orders of magnitude larger than the classical Spitzer value.
A filtered-wall formulation for large-eddy simulation of wall-bounded turbulence
Authors: Bhattacharya Amitabh , Das Arup , Moser Robert D.
Published: November 2008

Simulating high Reynolds number wall-bounded turbulence using large-eddy simulation (LES) requires modeling the subgrid force in the bulk of the flow and instantaneous viscous and pressure stresses at the wall. Here, LES of turbulent channel flow is conducted at Reτ=590 using a filtered-wall formulation, in which a buffer region with u=0 is attached adjacent to the wall, and the underlying velocity field defined over the extended domain is filtered using a nonlocal filter (in this case, a Fourier cutoff filter) in all directions. The instantaneous wall stress is computed by first prescribing a target velocity field for the filtered velocity inside the buffer and then minimizing the error between the actual and target velocity at every time step. The optimal LES (OLES) approach is used to model the subgrid force in terms of the resolved velocity field via linear stochastic estimation. The correlations required to carry out this stochastic estimation are computed from direct numerical simulation (DNS). Results of the LES simulation show reasonable agreement with filtered DNS statistics. Also, simulations performed after introducing modifications to the linear OLES kernel show that the positive eigenvalues in the kernel and the skew-symmetric part of the kernel play important roles in LES of wall-bounded turbulence.
Ga
As
∕
Al
Ga
As
quantum dot laser fabricated on GaAs (311)A substrate by droplet epitaxy
Authors: Mano T. , Kuroda T. , Mitsuishi K. , Nakayama Y. , Noda T. , Sakoda K.
Published: November 2008

We have demonstrated photopumped laser action of self-assembled GaAs∕AlGaAs quantum dots (QDs) grown on GaAs (311)A substrate by droplet epitaxy. Due to the short migration distance of Ga adatoms across the (311)A surface, high-density QDs were created with high uniformity. The QDs exhibited a narrow spectral band of intense photoluminescence from the QD ensemble, reflecting their small size distribution and high quality. Using the QDs on the (311)A surface as an active laser medium, we observed multimodal stimulated emissions at temperatures of up to 300K.
Epitaxial growth of high mobility Cu2O thin films and application to p-channel thin film transistor
Authors: Matsuzaki Kosuke , Nomura Kenji , Yanagi Hiroshi , Kamiya Toshio , Hirano Masahiro , Hosono Hideo
Published: November 2008

Cu 2 O epitaxial films were grown for high mobility p-channel oxide thin-film transistors (TFTs). The use of a (110) MgO surface and fine tuning of a growth condition produced single phase epitaxial films with hole Hall mobilities ∼90 cm2 V−1 s−1 comparable to those of single crystals (∼100 cm2 V−1 s−1). TFTs using the epitaxial film channels exhibited p-channel operation although the field-effect mobilities and the on-to-off current ratio were not yet satisfactory (∼0.26 cm2 V−1 s−1 and ∼6, respectively).
Growth and field emission characteristics of diamond films on macroporous silicon substrate
Authors: Arora S. K. , Chhoker S. , Sharma N. K. , Singh V. N. , Vankar V. D.
Published: November 2008

The effect of substrate pretreatments such as ultrasonication or scratching by diamond powder on the microstructure and field emission characteristics of diamond grown over silicon and macroporous (anodized) silicon substrates was investigated. These films were grown in a hot filament chemical vapor deposition (CVD) system. Scanning electron microscope (SEM) studies revealed that ultrasonic pretreatment of the substrates increases nucleation density of CVD diamond by two orders of magnitude. Atomic force microscopy and energy dispersive x-ray analysis of the substrates showed that seeding is responsible for the enhanced nucleation density of diamond. SEM study showed that diamond powder scratching of porous silicon leads to uniform coverage of the substrate by the CVD diamond. Cross-sectional SEM showed growth of diamond inside the pores only after pretreating porous silicon with diamond powder. Raman spectroscopy of all the samples showed a scattering peak corresponding to diamond. Discontinuous diamond films also exhibited Raman bands corresponding to nanocrystalline diamond, diamondlike carbon, graphite, and silicon carbide. The presence of these phases of carbon was further confirmed by high resolution transmission electron microscopy studies. Field emission studies revealed that discontinuous diamond films grown on porous silicon (after diamond powder ultrasonic pretreatment) had the lowest threshold field (5.4 V/μm).
Thermal transport properties of nanocrystalline Bi–Sb–Te thin films prepared by sputter deposition
Authors: Liao Chien-Neng , Wang Yu-Chu , Chu Hsu-Shen
Published: November 2008

Grain-size dependent thermal conductivity of sputtered nanocrystalline Bi–Sb–Te thin films was measured by a 3ω method. By changing deposition temperature from 100 °C to room temperature, the mean grain size of the Bi–Sb–Te films decreased from 83 to 26 nm and the lattice thermal conductivity reduced from 0.79 to 0.45 W/mK proportionally. The effect of grain boundary on lattice thermal conductivity can be described by an effective thermal boundary resistance that was determined in the range of 0.56–1.8×10−8 m2K/W for the nanocrystalline Bi–Sb–Te thin films studied.
High shear rheology of shear banding fluids in microchannels
Authors: Nghe Philippe , Degré Guillaume , Tabeling Patrick , Ajdari Armand
Published: November 2008

We characterize heterogeneous flows of a wormlike micelles solution in microchannels. Combining a pressure resistant microfabrication technology and a performant particle image velocimetry setup, we succeed in determining the nonlinear rheology of this fluid over 4 decades in shear rate and in particular more than 1 decade beyond the end of the stress plateau. We performed an independent measurement of the slip length with 1 μm resolution.
Segregation of tungsten at γ′(L12)/γ(fcc) interfaces in a Ni-based superalloy: An atom-probe tomographic and first-principles study
Authors: Amouyal Yaron , Mao Zugang , Seidman David N.
Published: November 2008

γ ( fcc ) / γ ′ ( L 1 2 ) heterophase interfaces in a Ni-based superalloy are investigated using atom-probe tomography and first-principles calculations. Flat {100} interfaces exhibit a confined (nonmonotonic) Gibbsian interfacial excess of tungsten, ΓW=1.2±0.2 nm−2, corresponding to a 5 mJ m−2 decrease in interfacial free energy. Conversely, no measurable segregation of W is detected at curved interfaces. First-principles calculations for a Ni–Al–W system having a {100} interface indicate a decrease in the interfacial energy of 5 mJ m−2 due to W segregation. Similar calculations for {110} and {111} interfaces predict an increase of 1 and 9 mJ m−2 in their energies, respectively, and therefore no heterophase segregation.
Influence of strong electric fields on the growth, modification, and destruction of thin oxide films at the titanium surface
Authors: Kovalevskii S. A. , Dalidchik F. I. , Grishin M. V. , Gatin A. K.
Published: November 2008

The influence of strong electric fields (∼107 V/cm) on the growth, modification, and destruction of thin oxide films at the metal surfaces are studied for a titanium tip of a scanning tunneling microscope (STM) oxidized in oxygen at different tip potentials. The spectroscopic measurements show that, in sufficiently strong fields (V≤−7.5 V) preventing migration of oxygen ions from the surface to bulk, the dielectric oxide films can form even for exposures of ∼10 L. At voltages V>−7.5 V, i.e., at lower fields, as well as for the opposite polarity, the conducting oxide films containing predominantly Ti+2 and Ti+3 ions are formed at the tip for the same exposures. The possibility of structural modification in the electric field of STM is demonstrated for titanium nanooxides.
Electron spin resonance study of self-trapped holes in CdWO4 scintillator crystals
Authors: Laguta V. V. , Nikl M. , Rosa J. , Grinyov B. V. , Nagornaya L. L. , Tupitsina I. A.
Published: November 2008

The self-trapping of holes at oxygen anions was studied by electron spin resonance in UV irradiated CdWO4 crystals. Analysis of superhyperfine interaction of the holes with W183 and C111,113d isotopes shows that the self-trapped hole is either delocalized in the space between two energetically equivalent nearest neighbor oxygen ions or tunnels between them. When the temperature increases above 40–50 K the self-trapped holes are thermally liberated and can be retrapped by oxygen ions perturbed by impurity ions. In case of the Nb5+ or Li+ stabilizing impurities the O− centers are thermally stable up to 160–170 K. The study of kinetic characteristics of the self-trapped holes suggests that holes leave oxygen ions by thermally assisted tunneling mechanism via two slightly different channels. Corresponding ionization probabilities are defined by the Arrhenius law with an average thermal ionization energy E=90(5) meV. Calculated pre-exponential factors, about 105 s−1, are small, which is consistent with the tunneling mechanism. Thermal stability and kinetic characteristics of the trapped holes are discussed in light of the scintillation and thermoluminescence characteristics of CdWO4.
Melting/collapse of charge orbital ordering and spread of relaxation time with frequency in La0.50Ca0.50MnO3+δ by impedance spectroscopy
Authors: Nadeem M. , Akhtar M. J.
Published: November 2008

Impedance spectroscopy has been employed to investigate the microscopic nature of the charge/orbital ordering (COO) in polycrystalline La0.50Ca0.50MnO3+δ sample at different temperatures. The modulations of relaxation time with temperatures show different behaviors of Z′ and Z″. An equivalent circuit model (R1C)(R2Q) has been employed to investigate the electrical parameters of La0.50Ca0.50MnO3+δ at different temperatures. The resistance of grain and grain boundaries shows maxima at metal-insulator (MI) transition temperature (≈153 K). Three temperature zones have been identified. In the first temperature zone which has been from 85 to 140 K, below MI transition temperature, melting of COO with strong Jahn–Teller (JT) distortions has been reported. In the second zone, around MI transition temperature, melting and collapse of COO with weak JT distortion result in colossal drop in Z′. In the third temperature zone, above MI transition temperature, charge ordering (CO) around 203 K and onset of short range CO at 253 K have been determined.
Phonon-assisted ultraviolet anti-Stokes photoluminescence from GaN film grown on Si (111) substrate
Authors: Tripathy Suvranta K. , Xu Guibao , Mu Xiaodong , Ding Yujie J. , Jamil Muhammad , Arif Ronald A. , Tansu Nelson , Khurgin Jacob B.
Published: November 2008

Phonon-assisted anti-Stokes photoluminescence (ASPL) in the ultraviolet region has been observed in the GaN film grown on a Si (111) substrate. The ASPL peaks are observable only at sufficiently low temperatures. In addition, even if the photon energy is ≈318meV below the transition energy for bound excitons, the ASPL peaks can be still observed. Based on our analysis, the donor-acceptor pairs and bound excitons have played primary roles in the generation of ASPL. Upon the absorption of photons, the ionizations of the neutral donors and neutral acceptors are assisted by longitudinal-optical phonons.
Coherent manipulation of magnetization precession in ferromagnetic semiconductor (Ga,Mn)As with successive optical pumping
Authors: Hashimoto Y. , Munekata H.
Published: November 2008

We report the dynamic control of magnetization precession by light alone. A ferromagnetic (Ga,Mn)As epilayer was used for experiments. Amplitude of precession was modulated to a large extent by tuning the time interval between two successive optical pump pulses, which induced torques on magnetization through a nonthermal process. Nonlinear effect in precession motion was also discussed.
Valence band offset of the ZnO/AlN heterojunction determined by x-ray photoemission spectroscopy
Authors: Veal T. D. , King P. D. C. , Hatfield S. A. , Bailey L. R. , McConville C. F. , Martel B. , Moreno J. C. , Frayssinet E. , Semond F. , Zúñiga-Pérez J.
Published: November 2008

The valence band offset of ZnO/AlN heterojunctions is determined by high resolution x-ray photoemission spectroscopy. The valence band of ZnO is found to be 0.43±0.17 eV below that of AlN. Together with the resulting conduction band offset of 3.29±0.20 eV, this indicates that a type-II (staggered) band line up exists at the ZnO/AlN heterojunction. Using the III-nitride band offsets and the transitivity rule, the valence band offsets for ZnO/GaN and ZnO/InN heterojunctions are derived as 1.37 and 1.95 eV, respectively, significantly higher than the previously determined values.
Tuning the electrical switching of polymer/fullerene nanocomposite thin film devices by control of morphology
Authors: Laiho Ari , Majumdar Himadri S. , Baral Jayanta K. , Jansson Fredrik , Österbacka Ronald , Ikkala Olli
Published: November 2008

The working principles of thin film organic memory devices remain debated and tunability has been less presented. We show that the nanostructure of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and polystyrene (PS) allows facile tuning of switching behavior for low PCBM concentrations upon annealing above the glass transition temperature of PS. By increasing the PCBM concentration from 2 to 6 wt %, the switching voltage from off to on state during the first voltage sweep systematically decreases. In subsequent voltage sweeps negative differential resistance effect is observed. Above ca. 7 wt %, chains of PCBM clusters couple the electrodes, which leads to Ohmic behavior.
Nanomechanical thermal analysis of electrospun polymer fibers
Authors: Wang Wei , Bushby Andrew J. , Barber Asa H.
Published: November 2008

Thermomechanical properties of individual electrospun semicrystalline polyethylene oxide (PEO) fibers were measured using atomic force microscopy based indentation. Fibers showed a higher elastic modulus than corresponding films despite a lower crystallinity, indicating significant molecular alignment along the principle fiber axis. Heating of the fibers gave a progressive loss in elastic modulus highlighting a dominant amorphous thermomechanical response. This is in contrast to softening of an amorphous phase and melting of a crystalline phase in semicrystalline bulk PEO films.
Experimental demonstration of tunable negative phase velocity and negative refraction in a ferromagnetic/ferroelectric composite metamaterial
Authors: Zhao Hongjie , Kang Lei , Zhou Ji , Zhao Qian , Li Longtu , Peng Liang , Bai Yang
Published: November 2008

A tunable left-handed transmission is demonstrated experimentally in a ferromagnetic/ferroelectric composite metamaterial (CMM) consisting of an array of yttrium iron garnet (YIG) rods combined with barium strontium titanate (BST) rods. We observed a passband in the CMM within the overlap of the stop bands of YIG rods alone and BST rods alone. Both measured phase velocity and refractive index of the CMM are shown to be negative at the relevant frequency range. The frequency showing left handedness can be adjusted continuously, dynamically, and reversibly by an applied magnetic field with a sensitive response of 3.5 GHz/kOe.
Interface control and leakage current conduction mechanism in HfO2 film prepared by pulsed laser deposition
Authors: Wang Hao , Wang Y. , Zhang J. , Ye C. , Wang H. B. , Feng J. , Wang B. Y. , Li Q. , Jiang Y.
Published: November 2008

The N2 atmosphere postannealing is introduced to improve the interfacial quality and the dielectric properties of HfO2 films prepared by pulsed laser deposition. The disappearance of interface layer between HfO2 film and Si substrate and the decrease of leakage current densities after annealing are further confirmed by high-resolution cross-sectional transmission electron microscopy investigation and electrical measurement. Electric conduction analysis results show that the dominant leakage current conduction mechanisms of the annealed HfO2 film are the Schottky emission at low electric field, the trap-assisted tunneling, and space-charge-limited current at high electric field for the gate and substrate injections, respectively.
Reconfiguration of microring resonators by liquid adhesion
Authors: Barrios C. A. , Holgado M. , Guarneros O. , Gylfason K. B. , Sánchez B. , Casquel R. , Sohlström H.
Published: November 2008

We present a procedure to reconfigure microring resonators based on liquid surface adhesion. Droplets of organic solvents were deposited over Si3N4/SiO2 strip- and slot-waveguide ring resonators, and the transmission spectra were measured several hours after the evaporation of the droplets at room temperature. Our measurements show that the optical properties of the microrings are significantly modified by liquid adhered to the waveguides, persisting even 96 h after bulk evaporation. Liquid-solid interfacial forces slow down liquid evaporation at the nanoscale, enabling permanent photonic configurations. Rewriteability is achieved by removing the adhered liquid with heat.
Quantitative scanning thermal microscopy using double scan technique
Authors: Kim Kyeongtae , Chung Jaehoon , Won Jongbo , Kwon Ohmyoung , Lee Joon Sik , Park Seung Ho , Choi Young Ki
Published: November 2008

Although scanning thermal microscope has shown the highest spatial resolution in local temperature and thermophysical property measurement, its usefulness has been severely limited due to difficulties in quantitative measurement. We propose a double scan technique that measures temperature only from the heat transfer through the tip-sample contact by the subtraction of the signal due to the heat transfer through the air. A rigorous theoretical model for this technique is derived. The effectiveness of the double scan technique in quantitative temperature measurement is demonstrated experimentally.
Selective-hydrogen sensing at room temperature with Pt-coated InN nanobelts
Authors: Lim Wantae , Wright J. S. , Gila B. P. , Pearton S. J. , Ren F. , Lai Wei-Ta , Chen Li-Chyong , Hu Ming-Shien , Chen Kuei-Hsien
Published: November 2008

The hydrogen sensing characteristics of multiple InN nanobelts grown by metalorganic chemical vapor deposition were investigated. Pt-coated InN sensors could selectively detect hydrogen at the tens of ppm level at 25 °C, while uncoated InN showed no detectable change in current when exposed to hydrogen under the same conditions. Upon exposure to various concentrations of hydrogen (20–300 ppm) in N2 ambient, the relative resistance change increased from 1.2% at 20 ppm H2 to 4% at 300 ppm H2. Approximately 90% of the initial InN resistance was recovered within 2 min by exposing the nanobelts to air. Temperature-dependent measurements showed larger resistance change and faster response at high temperature compared to those at room temperature due to increase in catalytic dissociation rate of H2 as well as diffusion rate of atomic hydrogen into the Pt/InN interface. The Pt-coated InN nanobelt sensors were operated at low power levels (∼0.5 mW).
Polarity driven formation of InAs/GaAs hierarchical nanowire heterostructures
Authors: Paladugu Mohanchand , Zou Jin , Guo Ya-Nan , Zhang Xin , Joyce Hannah J. , Gao Qiang , Tan H. Hoe , Jagadish C. , Kim Yong
Published: November 2008

The structural and morphological characteristics of InAs/GaAs radial nanowire heterostructures were investigated using transmission electron microscopy. It has been found that the radial growth of InAs was preferentially initiated on the {112}A sidewalls of GaAs nanowires. This preferential deposition leads to extraordinarily asymmetric InAs/GaAs radial nanowire heterostructures. Such formation of radial nanowire heterostructures provides an opportunity to engineer hierarchical nanostructures, which further widens the potential applications of semiconductor nanostructures.