bluuebunny/crossref_metadata_2025 huggingface dataset:
Cyclic mechanical strain promotes transforming‐growth‐factor‐β1‐mediated cardiomyogenic marker expression in bone‐marrow‐derived mesenchymal stem cells in vitro
Authors: Bhang Suk Ho , Gwak So‐Jung , Lee Tae‐Jin , Kim Sang‐Soo , Park Ho Hyun , Park Moon Hyang , Lee Dae‐Hee , Lee Soo‐Hong , Kim Byung‐Soo
Published: March 2010

Cardiomyocytes in the heart reside in mechanically dynamic environments, such as those subject to cyclic mechanical strain. TGF‐β1 (transforming growth factor‐β1) stimulates cardiomyogenic marker expression of BMMSCs (bone‐marrow‐derived mesenchymal stem cells). In the present study, we tested the hypothesis that cyclic mechanical strain promotes TGF‐β1‐mediated cardiomyogenic marker expression in BMMSCs in vitro. The mRNA expression of cardiac‐specific genes was more up‐regulated in BMMSCs cultured with a TGF‐β1 supplement and subjected to cyclic strain for 1 week than in BMMSCs cultured statically with a TGF‐β1 supplement. Immunocytochemical analyses and flow cytometric analysis showed that the proportions of cardiac troponin‐I‐positive cells and cardiac MHC (myosin heavy chain)‐positive cells and the proportions of cells expressing tropomyosin respectively were increased to a greater extent by TGF‐β1with cyclic strain than by TGF‐β1 alone. These results showed that cyclic strain promotes TGF‐β1mediated cardiomyogenic marker expression in BMMSCs in vitro.
Role of nitric oxide-mediated glutathionylation in neuronal function: potential regulation of energy utilization
Authors: Yap Li-Peng , Garcia Jerome V. , Han Derick S. , Cadenas Enrique
Published: March 2010

Excessive generation of nitric oxide radical (NO•) in neuroinflammation, excitotoxicity and during age-related neurodegenerative disorders entails the localized and concerted increase in nitric oxide synthase(s) expression in glial cells and neurons. The aim of the present study was to assess the biological significance of the impact of NO• on the cell's thiol status with emphasis on S-glutathionylation of targeted proteins. Exposure of primary cortical neurons or astrocytes to increasing flow rates of NO• (0.061–0.25 μM/s) resulted in the following. (i) A decrease in GSH (glutathione) in neurons accompanied by formation of GSNO (S-nitrosoglutathione) and GSSG (glutathione disulfide); neurons were far more sensitive to NO• exposure than astrocytes. (ii) A dose-dependent oxidation of the cellular redox status: the neuron's redox potential increased ~42 mV and that of astrocytes ~23 mV. A good correlation was observed between cell viability and the cellular redox potential. The higher susceptibility of neurons to NO• can be partly explained by a reduced capacity to recover GSH through lower activities of GSNO and GSSG reductases. (iii) S-glutathionylation of a small subset of proteins, among them GAPDH (glyceraldehyde-3-phosphate dehydrogenase), the S-glutathionylation of which resulted in inhibition of enzyme activity. The quantitative analyses of changes in the cell's thiol potential upon NO• exposure and their consequences for S-glutathionylation are discussed in terms of the distinct redox environment of astrocytes and neurons.
Global stability analysis of birhythmicity in a self-sustained oscillator
Authors: Yamapi R. , Filatrella G. , Aziz-Alaoui M. A.
Published: March 2010

We analyze the global stability properties of birhythmicity in a self-sustained system with random excitations. The model is a multi-limit-cycle variation in the van der Pol oscillator introduced to analyze enzymatic substrate reactions in brain waves. We show that the two frequencies are strongly influenced by the nonlinear coefficients α and β. With a random excitation, such as a Gaussian white noise, the attractor’s global stability is measured by the mean escape time τ from one limit cycle. An effective activation energy barrier is obtained by the slope of the linear part of the variation in the escape time τ versus the inverse noise intensity 1/D. We find that the trapping barriers of the two frequencies can be very different, thus leaving the system on the same attractor for an overwhelming time. However, we also find that the system is nearly symmetric in a narrow range of the parameters.
Function projective synchronization in chaotic and hyperchaotic systems through open-plus-closed-loop coupling
Authors: Sudheer K. Sebastian , Sabir M.
Published: March 2010

Recently introduced function projective synchronization in which chaotic systems synchronize up to a scaling function has important applications in secure communications. We design coupling function for unidirectional coupling in identical and mismatched oscillators to realize function projective synchronization through open-plus-closed-loop coupling method. Numerical simulations on Lorenz system, Rössler system, hyperchaotic Lorenz, and hyperchaotic Chen system are presented to verify the effectiveness of the proposed scheme.
Temperature dependent carrier lifetime studies of Mo in crystalline silicon
Authors: Paudyal Bijaya B. , McIntosh Keith R. , Macdonald Daniel H. , Coletti Gianluca
Published: March 2010

The capture cross sections of both electrons σn and holes σp were determined for interstitial molybdenum in crystalline silicon over the temperature range of −110 to 150 °C. Carrier lifetime measurements were performed on molybdenum-contaminated silicon using a temperature controlled photoconductance instrument. Injection dependent lifetime spectroscopy was applied at each temperature to calculate σp and σn. This analysis involved a novel approach that independently determined the capture cross sections at each temperature assuming a known defect density and thermal velocity. Since the energy state is in the lower half of the bandgap, the determination of σp is unaffected by the defect energy at all temperatures, and σp is found to decrease with temperature in a fashion consistent with excitonic Auger capture. At temperatures below 0 °C, the determination of σn is also unaffected by the defect energy due to the suppression of thermal emission, and σn decreases with temperature as well. It is shown that a projection of σn to higher temperature suggests the defect has an energy of 0.375 eV above the valance band edge of silicon.
Growth of linearly ordered arrays of InAs nanocrystals on scratched InP
Authors: Fonseca-Filho H. D. , Almeida C. M. , Prioli R. , Pires M. P. , Souza P. L. , Wu Z. H. , Wei Q. Y. , Ponce F. A.
Published: March 2010

Linear arrays of InAs nanocrystals have been produced by metalorganic vapor phase epitaxy on scratches performed with an atomic force microscope tip along specific crystallographic directions of an (100) InP wafer. Scratches along ⟨110⟩ generate highly mobile defects that extend far from the scratch region along easy-glide directions. On the other hand, ⟨100⟩ scratches result in highly-localized plastic deformation, hardening, and possibly frictional heating. In both cases, growth of nanocrystals was observed only on the scratched areas. Random nucleation of nanocrystals is observed along ⟨110⟩ scratches, while linearly ordered growth occur along ⟨100⟩ scratches. We attribute these observations to the delocalized nature of the dislocations in the ⟨110⟩ case, giving the appearance of random nucleation, while highly localized crystal defects along the ⟨100⟩ scratch lines act as nucleation sites for the growth of linear arrays of nanocrystals.
Native oxides and carbon contamination removal from InAs(100) surface by molecular hydrogen flow at moderate substrate temperatures: Stoichiometric and morphological studies
Authors: Lyadov Y. , Akhvlediani R. , Hoffman A. , Klin O. , Weiss E.
Published: March 2010

Native oxides and carbonaceous contamination removal from InAs(100) surfaces by thermal annealing at reduced temperatures under molecular hydrogen flow is reported and compared to vacuum annealing at similar temperatures. The thermal annealing experiments were carried out in the 250–360 °C range and at constant hydrogen pressure of 5×10−6 torr. The complete reduction of native oxides and carbon contamination was achieved at temperatures as low as 300 and 340 °C, respectively, under molecular hydrogen flux. Chemical and compositional monitoring of the surface was performed by x-ray photoelectron spectroscopy and x-ray induced Auger spectroscopy. The surface morphology, before and after annealing, was imaged by atomic force microscope at tapping noncontact mode.
A chip-level electrothermal-coupled design model for high-power light-emitting diodes
Authors: Huang Shanjin , Wu Hao , Fan Bingfeng , Zhang Baijun , Wang Gang
Published: March 2010

An advanced three-dimensional electrothermal-coupled simulation model basing on finite-element method numerical simulation is developed to study the electrical and thermal properties of chip-level high-power GaN-based light-emitting diodes (LEDs). The current spreading, heat generation, and transfer in the device are comprehensively considered in this model. The current-spreading effect of the transparent current-spreading layer and the thermal performance of LEDs with interdigitated-electrodes are investigated. The simulation results prove that the temperature distribution in the active layer is strongly affected by the electrode pattern. The obvious heat accumulation in LEDs with conventional interdigitated-electrode patterns can be seen both in the simulated results and the infrared measured results. The heat transfer efficiency can be improved by using a symmetry electrode pattern design. The thermal management of the bump configurations in flip-chip LEDs is also studied. A more reasonable and thermal effective bump configuration is presented, and the simulated results show that a lower average temperature and more uniform heat distribution in the chips can be obtained.
Evaluation of threading dislocation densities in In- and N-face InN
Authors: Gallinat C. S. , Koblmüller G. , Wu Feng , Speck J. S.
Published: March 2010

The threading dislocation (TD) structure and density has been studied in In- and N-face InN films grown on GaN by plasma-assisted molecular beam epitaxy. The TD densities were determined by nondestructive x-ray diffraction rocking curve measurements in on-axis symmetric and off-axis skew symmetric geometries and calibrated by transmission electron microscopy measurements. TD densities were dominated by edge-type TDs with screw-component TDs accounting for less than 10% of the total TD density. A significant decrease in edge-type TD density was observed for In-face InN films grown at increasingly higher substrate temperatures. In-face InN films grown with excess In exhibited lower TD densities compared to films grown under N-rich conditions. The edge-type TD density of N-face InN films was independent of substrate temperature due to the higher allowable growth temperatures for N-face InN compared to In-face InN. TD densities in In-face InN also showed a strong dependence on film thickness. Films grown at a thickness of less than 1 μm had higher TD densities compared with films grown thicker than 1 μm. The lowest measured TD density for an In-face InN film was ∼1.5×1010/cm2 for 1 μm thick films.
Stress and doping uniformity of laser crystallized amorphous silicon in thin film silicon solar cells
Authors: Agaiby R. M. B. , Becker M. , Thapa S. B. , Urmoneit U. , Berger A. , Gawlik A. , Sarau G. , Christiansen S. H.
Published: March 2010

Simultaneous and locally resolved determination of the mechanical stress variation and the free hole concentration using Raman spectroscopy is demonstrated in laser crystallized amorphous silicon layers. Such layers are often used for the fabrication of thin film solar cells, e.g., on borosilicate glass substrates. The combined effects of stress and doping on the Raman signal can be separated based on the use of three wavelengths in the visible. The results show that the free hole concentration in the samples investigated varies between 1×1018 and 1.3×1019 cm−3. Stress as well as the free hole concentration vary substantially within the sample. The stress level varies between 575 and 850 MPa (±12 MPa). Cross-sectional transmission electron microscopy images show the presence of extended lattice defects such as dislocations and grain boundaries in the crystallized Si layer which could account for the lateral stress variations detected by Raman spectroscopy. The impact of film inhomogeneity in terms of stress and doping on the performance of a solar cell will be discussed.
A proposed new energy source: The “mixing energy” of engine exhaust gas
Authors: Gellender Martin
Published: March 2010

One potential source of useful energy that seems to be unrecognized and overlooked is the “entropy of mixing” of engine exhaust gases with the atmosphere. In particular, exhaust gases from combustion engines typically contain carbon dioxide at concentrations 250 times greater than in the atmosphere and have an oxygen concentration that is typically less than one-tenth the oxygen concentration in the atmosphere. Fuel cell power sources can produce exhaust gases containing CO2 concentrations 1000 times greater than in the air. Currently, engine exhaust gases are simply ejected into the atmosphere where they spontaneously mix with the air, and the potential to do useful work is lost. Rather than discarding combustion gases into the atmosphere, it is possible—in principle—to exploit the entropy of mixing to produce useful work. However, the energy that could potentially be produced by mixing exhaust gases with air is at least an order of magnitude less than the energy released by combustion of the fuel. Exploiting this energy source is likely to prove difficult and expensive with current technology, but ultimately, this “mixing energy” could be an incremental energy source to be finessed from combustion engines, kilns, furnaces, and fuel cell power sources. This article proposes conceptual designs for “mixing engines” that could augment the power output of a diesel engine by as much as 3.0% or augment the power output of a fuel cell power plant by 3.5%.
Gold cluster beyond hollow cage: A double shell structure of Au58
Authors: Dong C. D. , Gong X. G.
Published: March 2010

It is well known that gold cluster can have planar or hollow cagelike structure due to the relativistic effect. In this study, by first principles calculation on the Au58 cluster, we propose that gold cluster of medium size can form a shell-like structure, which is demonstrated by the remarkable robustness of a double shell structure with a hollow inner shell of ten atoms.
Toward eliminating the electronic structure bottleneck in nonadiabatic dynamics on the fly: An algorithm to fit nonlocal, quasidiabatic, coupled electronic state Hamiltonians based on ab initio electronic structure data
Authors: Zhu Xiaolei , Yarkony David R.
Published: March 2010

An algorithm for constructing a quasidiabatic, coupled electronic state Hamiltonian, in a localized region of nuclear coordinate space, suitable for determining bound state spectra, is generalized to determine a nonlocal Hamiltonian capable of describing, for example, multichannel nonadiabatic photodissociation. For Nstate coupled electronic states, the Hamiltonian, Hd, is a symmetric Nstate×Nstate matrix whose elements are polynomials involving: decaying exponentials exp(−ari,jn) n=1,2, where ri,j=Ri−Rj, ri,j=|ri,j|, Rj locates the jth nucleus; and scaled dot-cross product coordinates, proportional to ri,j×ri,k•ri,l. The constructed Hamiltonian is constrained to reproduce, exactly, the ab initio data, energies, gradients, and derivative coupling at selected points, or nodes, in nuclear coordinate space. The remainder of the ab initio data is approximated in a least-squares sense using a normal equations approach. The fitting procedure includes a damping term that precludes oscillations due to the nodal constraints or local excesses of parameters. To illustrate the potential of the fitting procedure an Hd is constructed, with the full nuclear permutation-inversion symmetry, which describes portions of the 1,2 A1 potential energy surfaces of NH3, including the minimum energy point on the 1,2 A1 seam of conical intersection and the NH2+H asymptote. Ab initio data at 239 nuclear configurations was used in the construction which was tested at 48 additional nuclear configurations. While the energy range on the ground and excited potential energy surface is each individually ∼45 000 cm−1, the root mean square error for the energies at all points is only 93.6 cm−1. The location and local conical topography of the minimum energy conical intersection is exactly reproduced. The derivative couplings are shown to be well reproduced, justifying the attribute quasidiabatic.
Properties of TiO2-based transparent conducting oxide thin films on GaN(0001) surfaces
Authors: Kasai J. , Hitosugi T. , Moriyama M. , Goshonoo K. , Hoang N. L. H. , Nakao S. , Yamada N. , Hasegawa T.
Published: March 2010

Anatase Nb-doped TiO2 transparent conducting oxide has been formed on GaN(0001) surfaces using a sputtering method. Amorphous films deposited at room temperature were annealed at a substrate temperature of 500 °C in vacuum to form single-phase anatase films. Films with a thickness of 170 nm exhibited a resistivity of 8×10−4 Ω cm with absorptance less than 5% at a wavelength of 460 nm. Furthermore, the refractive index of the Nb-doped TiO2 was well matched to that of GaN. These findings indicate that Nb-doped TiO2 is a promising material for use as transparent electrodes in GaN-based light emitting diodes (LEDs), particularly since reflection at the electrode/GaN boundary can be suppressed, enhancing the external quantum efficiency of blue LEDs.
Z
eff
profile diagnostics using visible bremsstrahlung continuum for nonaxisymmetric plasmas with finite β in large helical device
Authors: Zhou H. Y. , Morita S. , Goto M. , Dong C. F.
Published: March 2010

An astigmatism-corrected Czerny–Turner-type visible spectrometer coupled with a charge-coupled device has been installed in large helical device (LHD) to measure visible bremsstrahlung continuum. A full vertical profile has been observed from the elliptical plasmas at horizontally elongated plasma cross section through a 44 fiber parallel array with vertical observation length of ∼1 m. Line emissions can be easily eliminated by use of the visible spectrometer instead of an interference filter. A nonmonotonic bremsstrahlung emission profile, which is originated in the thick ergodic layer surrounding the main plasma, has been observed for normal discharges in all the magnetic configurations of LHD. After analyzing the detailed structure, the lower half of the vertical bremsstrahlung emission profile is found to be free of the strong edge bremsstrahlung emission in inwardly shifted magnetic configurations (Rax≤3.60 m). The nonmonotonic bremsstrahlung emission disappeared in extremely high-density discharges (ne≥1014 cm−3) because of the reduction of the plasma outside boundary. When the local emissivity is calculated using Abel inversion, the solution is very sensitive to the distortion of the magnetic surface structure. The influence of the magnetic surface distortion based on the finite β effect is examined as error estimation in addition to unclear edge plasma boundary due to the presence of the ergodic layer. The result indicates that the determination of the normalized minor radius for each observation chord gives a larger influence on the Abel inversion rather than the determination of the chord length. When the observed chord-integrated bremsstrahlung intensity profile is flat, the resultant uncertainty seen in the bremsstrahlung emissivity profile becomes large, in particular, at the plasma center. The Zeff profile calculated with consideration of density and temperature profiles is verified in neutral-beam-heated discharges with H2 and C pellet injections, where the Zeff values should be close to 1 and 6, respectively. Analysis on the flat and hollow electron density profiles results in a fairly flat Zeff profile.
Terahertz and infrared photodetection using p-i-n multiple-graphene-layer structures
Authors: Ryzhii V. , Ryzhii M. , Mitin V. , Otsuji T.
Published: March 2010

We propose to utilize multiple-graphene-layer structures with lateral p-i-n junctions for terahertz and infrared (IR) photodetection and substantiate the operation of photodetectors based on these structures. Using the developed device model, we calculate the detector dc responsivity and detectivity as functions of the number of graphene layers and geometrical parameters and show that the dc responsivity and detectivity can be fairly large, particularly, at the lower end of the terahertz range at room temperatures. Due to relatively high quantum efficiency and low thermogeneration rate, the photodetectors under consideration can substantially surpass other terahertz and IR detectors. Calculations of the detector responsivity as a function of modulation frequency of THz and IR radiation demonstrate that the proposed photodetectors are very fast and can operate at the modulation frequency of several tens of gigahertz.
Chain packing in polycarbonate glasses
Authors: Stueber Dirk , Yu Tsyr-Yan , Hess Berk , Kremer Kurt , O’Connor Robert D. , Schaefer Jacob
Published: March 2010

Chain packing in homogeneous blends of carbonate C13-labeled bisphenol A polycarbonate with either (i) CF3-labeled bisphenol A polycarbonate or (ii) ring-F-labeled bisphenol A polycarbonate has been characterized using C13{F19} rotational-echo double-resonance (REDOR) nuclear magnetic resonance. In both blends, the C13 observed spin was at high concentration, and the F19 dephasing or probe spin was at low concentration. In this situation, an analysis in terms of a distribution of isolated heteronuclear pairs of spins is valid. Nearest-neighbor separation of C13 and F19 labels was determined by accurately mapping the initial dipolar evolution using a shifted-pulse version of REDOR. Based on the results of this experiment, the average distance from a ring-fluorine to the nearest C13O is more than 1.2 Å greater than the corresponding CF3C13O distance. Next-nearest and more-distant-neighbor separations of labels were measured in a 416-rotor-cycle constant-time version of REDOR for both blends. Statistically significant local order was established for the nearest-neighbor labels in the methyl-labeled blend. These interchain packing results are in qualitative agreement with predictions based on coarse-grained simulations of a specially adapted model for bisphenol A polycarbonate. The model itself has been previously used to determine static and dynamic properties of polycarbonate with results in good agreement with those from rheological and neutron scattering experiments.
Subquadratic wavenumber dependence of the structural relaxation of supercooled liquid in the crossover regime
Authors: Bhattacharyya Sarika Maitra , Bagchi Biman , Wolynes Peter G.
Published: March 2010

As a liquid is progressively supercooled toward its glass transition temperature, an intriguing weakening of the wavenumber (q) dependence of the structural relaxation time τ(q) in the intermediate-to-large q limit is observed both in experiments and simulation studies. Neither continuous Brownian diffusive dynamics nor discontinuous activated events can alone explain the anomalous wavenumber dependence. Here we use our recently developed theory that unifies the mode coupling theory for continuous dynamics, with the random first order transition theory treatment of activated discontinuous motion as a nucleationlike instanton process to understand the wavenumber dependence of density relaxation. The predicted smooth change in mechanism of relaxation from diffusive to activated, in the crossover regime, is wavevector dependent and appears to be responsible for the observed subquadratic, almost linear, q dependence of the relaxation time.
Geometrical statistics and vortex structures in helical and nonhelical turbulences
Authors: Li Yi
Published: March 2010

In this paper we conduct an analysis of the geometrical and vortical statistics in the small scales of helical and nonhelical turbulences generated with direct numerical simulations. Using a filtering approach, the helicity flux from large scales to small scales is represented by the subgrid-scale (SGS) helicity dissipation. The SGS helicity dissipation is proportional to the product between the SGS stress tensor and the symmetric part of the filtered vorticity gradient, a tensor we refer to as the vorticity strain rate. We document the statistics of the vorticity strain rate, the vorticity gradient, and the dual vector corresponding to the antisymmetric part of the vorticity gradient. These results provide new insights into the local structures of the vorticity field. We also study the relations between these quantities and vorticity, SGS helicity dissipation, SGS stress tensor, and other quantities. We observe the following in both helical and nonhelical turbulences: (1) there is a high probability to find the dual vector aligned with the intermediate eigenvector of the vorticity strain rate tensor; (2) vorticity tends to make an angle of 45° with both the most contractive and the most extensive eigendirections of the vorticity strain rate tensor; (3) the vorticity strain rate shows a preferred alignment configuration with the SGS stress tensor; (4) in regions with strong straining of the vortex lines, there is a negative correlation between the third order invariant of the vorticity gradient tensor and SGS helicity dissipation fluctuations. The correlation is qualitatively explained in terms of the self-induced motions of local vortex structures, which tend to wind up the vortex lines and generate SGS helicity dissipation. In helical turbulence, we observe that the joint probability density function of the second and third tensor invariants of the vorticity gradient displays skewed distributions, with the direction of skewness depending on the sign of helicity input. We also observe that the intermediate eigenvalue of the vorticity strain rate tensor is more probable to take negative values. These interesting observations, reported for the first time, call for further studies into their dynamical origins and implications.
Analytical and molecular simulation study of water condensation behavior in mesopores with closed ends
Authors: Jang Changsoo , Han Bongtae
Published: March 2010

Mesopores present in inorganic barrier films have a unique structure since the bottom sides are blocked by underlying polymer substrates. Characterization of pore blockage by water condensation is important in understanding gas transport mechanisms because the pore blockage changes the transmission behavior of water vapor itself as well as other gases. In this study a water condensation behavior inside mesopores is investigated analytically and numerically. Appropriate modifications from the classical Kelvin equation-based solution are suggested to account for local and discrete molecular interactions and submolecular meniscus tip geometry. Grand canonical Monte Carlo simulations are also conducted to simulate the present problem and the result is compared with the analytical solutions.
A theoretical insight into the catalytic effect of a mixed-metal oxide at the nanometer level: The case of the highly active metal/CeOx/TiO2(110) catalysts
Authors: Graciani Jesús , Plata José J. , Sanz Javier Fdez. , Liu Ping , Rodriguez José A.
Published: March 2010

The structural and electronic properties of CeOx species supported on the rutile TiO2(110) surface have been examined by means of periodic density-functional calculations that use a generalized gradient approximation functional including a Hubbard-like type correction. Deposition of Ce atoms leads in a first step to Ce3+ ions bound to the surface through bridge and in-plane oxygen atoms, the released electrons occupying the Ti 3d empty orbitals. Further addition of Ce and molecular oxygen gives place to Ce2O3 dimers diagonally arranged on the surface, in agreement with the spots observed in the scanning tunnel microscope images. The formation process of CeOx nanoparticles (NPs) on the TiO2 surface is highly exothermic and our calculations show that the redox properties of the Ce(III)-Ce(IV) couple are significantly altered when it is supported on TiO2. In particular the reactivity against CO/O2 indicates that on the surface the presence of Ce(III) is favored over Ce(IV) species. Our results also indicate that the CeOx/TiO2 interface should be seen like a real mixed-metal oxide rather than a supported NP of ceria. Finally, in the context of the high catalytic activity of the M/CeOx/TiO2 (M=Au,Cu,Pt) systems in the water-gas shift reaction, we have examined the dissociation of water on the CeOx/TiO2 surface and estimated a barrier as small as 0.04 eV, i.e. ∼8 times smaller than that computed for a TiO2 oxygen vacancy. This result agrees with the experimental superior catalytic activity of the M/CeOx/TiO2 systems over M/TiO2.
Vibrational relaxation of NO−(v=1) in icosahedral (Ar)12NO− clusters
Authors: Shin H. K.
Published: March 2010

Relaxation dynamics of NO−(v=1) in icosahedral (Ar)12NO− clusters are studied using classical dynamics and semiclassical procedures over the temperature range of 100–300 K. The minimum energy of the equilibrium configuration (−9875 cm−1) needed in the study is determined by varying the cluster size z in (Ar)zNO−. NO−(v=1) is embedded in the cluster, which is filled with low frequency motions: 39 cm−1 for the argon modes, 77 cm−1 for the Ar⋯NO− substructure vibration, 109 cm−1 for the librational frequency of restricted rotation, and 128 cm−1 for oscillatory local translation. Dynamics calculations show that in the early time period (<20 ps), part of the vibrational energy rapidly transfers to rotation, but most energy transfers to Ar atoms on a long time scale (∼1 ns). The long time scale leads to the relaxation rates of 0.403 ns−1 at 100 K and 0.453 ns−1 at 300 K. The rates calculated using analytical formulations vary nearly linearly from 0.288 ns−1 at 100 K to 0.832 ns−1 at 300 K. Although the temperature dependence is stronger in the latter, both approaches give the rates on a nanosecond time scale. The principal energy transfer pathway is from NO− vibration to Ar vibrations via oscillatory local translation, while the NO− rotation is in a librational state. The energy transfer probabilities are two orders of magnitude larger than the vibration-to-translation probabilities in the gas phase collision Ar–NO−(v=1).
Density functional study of CO and NO adsorption on Ni-doped MgO(100)
Authors: Valero Rosendo , Gomes José R. B. , Truhlar Donald G. , Illas Francesc
Published: March 2010

The adsorption of small molecules such as NO or CO on surfaces of magnetic oxides containing transition metals is difficult to model by current density functional approximations. Two such oxides are NiO(100) and Ni-doped MgO(100). Here we compare the results of a theoretical model of the Ni-doped MgO(100) surface with experimental results on NiO(100), which introduces some uncertainty into a quantitative theory-experiment comparison. In the present work, we tested seven meta-GGA and hybrid metafunctionals, in particular, three developed by the Minnesota group (M05, M06-L, and M06), and TPSS, TPSSh, TPSSKCIS, and B1B95; six GGA functionals, including BP86, PBE, and four other functionals that are modifications of PBE (PBEsol, SOGGA, revPBE, and RPBE); five hybrid GGA functionals (B3LYP, PBE0, B97–2, B97–3, and MPWLYP1M); and one unconventional functional of the generalized gradient type with scaled correlation called MOHLYP. The Minnesota meta-GGA functionals were found in the past to be very good choices when transition metal atoms were present; the other functionals chosen are a selection from the most currently used and most promising sets of functionals for bulk solids and surfaces and for transition metals. The difficulty is due to the charge transfer between open shells in the case of NO and to the weak character of the interaction in the case of CO. It is shown that the M06 hybrid meta functional applied to NO or CO on a model of the Ni-doped MgO(100) surface is able to provide a good description of both adsorbate geometries and binding energies. The M06 vibrational frequency shifts are more accurate than for other functionals, but there is still room for improvement.
Growth modes of ZnO nanostructures from laser ablation
Authors: Amarilio-Burshtein I. , Tamir S. , Lifshitz Y.
Published: March 2010

ZnO nanowires (NWs) and other nanostructures were grown by laser ablation of a ZnO containing target onto different substrates with and without the presence of an Au catalyst. The morphology and structure of the NWs were studied using high resolution scanning and transmission electron microscopes [including imaging, selected area electron diffraction (SAED), and energy dispersive x-ray spectroscopy (EDS)]. The different growth modes obtainable could be tuned by varying the Zn concentration in the vapor phase keeping other growth parameters intact. Possible growth mechanisms of these nanowires are suggested and discussed.
Effects of barrier layers on device performance of high mobility In0.7Ga0.3As metal-oxide-semiconductor field-effect-transistors
Authors: Zhao Han , Chen Yen-Ting , Yum Jung Hwan , Wang Yanzhen , Zhou Fei , Xue Fei , Lee Jack C.
Published: March 2010

We have applied single InP barrier layer with different thicknesses and InP/In0.52Al0.48As double-barrier layer to In0.7Ga0.3As Al2O3 metal-oxide-semiconductor field-effect-transistors (MOSFETs) and investigated their effects on device performance. In0.7Ga0.3As MOSFETs with 3 nm InP single-barrier attain 22% higher peak effective mobility while devices with 5 nm InP attain 58% higher peak mobility than the ones without barrier. Devices using InP/In0.52Al0.48As double-barrier achieve mobility enhancement at both low-field (68% at peak mobility) and high-field (55%) compared to ones without barrier. High channel mobility of 4729 cm2/V s has been obtained using InP/In0.52Al0.48As barrier and atomic-layer-deposited Al2O3 gate oxide.
Photoelectron spectroscopy of cold aluminum cluster anions: Comparison with density functional theory results
Authors: Ma Lei , v. Issendorff Bernd , Aguado Andrés
Published: March 2010

Photoelectron spectra of cold aluminum cluster anions Aln− have been measured in the size range n=13–75 and are compared to the results of density functional theory calculations. Good agreement between the measured spectra and the calculated density of states is obtained for most sizes, which gives strong evidence that the correct structures have been found. In particular the results confirm the occurrence of rather different structural motifs in this size range, from fcc-like stacks over fragments of decahedrons to disordered structures. An analysis of the density of states of representatives of the different structural motifs shows that the electronic structure is strongly influenced by the cluster geometry, and that a clear jelliumlike electron shell structure is present only in some exceptional cases.
Small volume laboratory on a chip measurements incorporating the quartz crystal microbalance to measure the viscosity-density product of room temperature ionic liquids
Authors: Doy N. , McHale G. , Newton M. I. , Hardacre C. , Ge R. , MacInnes J. M. , Kuvshinov D. , Allen R. W.
Published: March 2010

A microfluidic glass chip system incorporating a quartz crystal microbalance (QCM) to measure the square root of the viscosity-density product of room temperature ionic liquids (RTILs) is presented. The QCM covers a central recess on a glass chip, with a seal formed by tightly clamping from above outside the sensing region. The change in resonant frequency of the QCM allows for the determination of the square root viscosity-density product of RTILs to a limit of ∼10 kg m−2 s−0.5. This method has reduced the sample size needed for characterization from 1.5 ml to only 30 μl and allows the measurement to be made in an enclosed system.
Interfacial oxygen and nitrogen induced dipole formation and vacancy passivation for increased effective work functions in TiN/HfO2 gate stacks
Authors: Hinkle C. L. , Galatage R. V. , Chapman R. A. , Vogel E. M. , Alshareef H. N. , Freeman C. , Wimmer E. , Niimi H. , Li-Fatou A. , Shaw J. B. , Chambers J. J.
Published: March 2010

Effective work function (EWF) changes of TiN/HfO2 annealed at low temperatures in different ambient environments are correlated with the atomic concentration of oxygen in the TiN near the metal/dielectric interface. EWF increases of 550 meV are achieved with anneals that incorporate oxygen throughout the TiN with [O]=2.8×1021 cm−3 near the TiN/HfO2 interface. However, further increasing the oxygen concentration via more aggressive anneals results in a relative decrease of the EWF and increase in electrical thickness. First-principles calculations indicate the exchange of O and N atoms near the TiN/HfO2 interface cause the formation of dipoles that increase the EWF.
Acoustic stabilization of electric arc instabilities in nontransferred plasma torches
Authors: Rat V. , Coudert J. F.
Published: March 2010

Electric arc instabilities in dc plasma torches lead to nonhomogeneous treatments of nanosized solid particles or liquids injected within thermal plasma jets. This paper shows that an additional acoustic resonator mounted on the cathode cavity allows reaching a significant damping of these instabilities, particularly the Helmholtz mode of arc oscillations. The acoustic resonator is coupled with the Helmholtz resonator of the plasma torch limiting the amplitude of arc voltage variations. It is also highlighted that this damping is dependent on friction effects in the acoustic resonator.
AlGaN-based ultraviolet photodetector with micropillar structures
Authors: Lai Wei-Chih , Peng Li-Chi , Chen Chien-Chun , Sheu Jinn-Kong , Shei Shih-Chang
Published: March 2010

We demonstrated a single AlGaN layer with two different Al contents on the GaN μ-pillars template. It was found by the selective wavelength spatial cathodoluminescence images that the emission wavelengths of the AlGaN layer were at 345 and 325 nm on the side of the cone and on the top and valley surface of pillars, respectively. The Schottky-type photodetectors were also demonstrated on double Al contents of deposited AlGaN on GaN micropillar templates. The three steps of responses occurred at about 326, 346, and 356 nm with responsivities of 1.1×10−2, 5.9×10−3, and 4.04×10−3 A/W, respectively.
Heat assisted spin torque switching of quasistable nanomagnets across a vacuum gap
Authors: Herzog G. , Krause S. , Wiesendanger R.
Published: March 2010

Current-induced magnetization switching of thermally quasistable magnetic nanoislands is demonstrated using a spin-polarized scanning tunneling microscope. The magnetization of an individual Fe nanoisland consisting of about 40 atoms on a W(110) surface is reversibly switched between two quasistable states by the application of spin-polarized tunnel current pulses without an applied magnetic field. The pulse length is shown to be crucial for a high switching efficiency. Sweeping the tunnel current from the nanoampere to the microampere regime allows for the determination of critical switching currents.
An electrically injected quantum dot spin polarized single photon source
Authors: Bhattacharya Pallab , Das Ayan , Basu Debashish , Guo Wei , Heo Junseok
Published: March 2010

The characteristics of an electrically injected spin polarized single photon source have been investigated. The GaAs-based microcavity diode consists of a single InAs/GaAs self-organized quantum dot as the single photon source and a MnAs/Al0.1Ga0.9As Schottky tunnel barrier for the ferromagnetic contact to inject spin polarized electrons. The measured output circular polarization of the biexciton emission at λ∼1130 nm exhibits a switching behavior as a function of magnetic field, in the Faraday geometry, the value remaining near-zero for B<1 T and ∼6%–8% for B≥1 T. The linear polarization shows a complementary trend. The results are explained in the framework of the exciton fine structure in the quantum dot and the effects of electron-hole exchange splitting, due to in-plane quantum dot anisotropy, and Zeeman splitting on the spin eigenstates and their coupling to the photon field.
All-silicon sub-Gb/s telecom detector with low dark current and high quantum efficiency on chip
Authors: Tanabe Takasumi , Sumikura Hisashi , Taniyama Hideaki , Shinya Akihiko , Notomi Masaya
Published: March 2010

We demonstrate channel selective 0.1-Gb/s photoreceiver operation at telecom wavelength using a silicon high-Q photonic crystal nanocavity with a laterally integrated p-i-n diode. Due to the good crystal property of silicon the measured dark current is only 15 pA. The linear and nonlinear characteristics are investigated in detail, in which we found that the photocurrent is enhanced of more than 105 due to the ultrahigh-Q (Q≃105). With the help of two-photon absorption, which is visible at a surprisingly low input power of 10−8 W, the quantum efficiency of this device reaches ∼10%.
Molecular diversity and genetic structure of modern and traditional landrace cultivars of wheat (Triticum aestivum L.)
Authors: Raman Harsh , Stodart B. J. , Cavanagh Colin , Mackay M. , Morell Matthew , Milgate Andrew , Martin Peter
Published: March 2010

Wheat is one of the most important cereal crops of the world. In order to achieve continued genetic gain in wheat improvement programs, an assessment and utilisation of genetic diversity in a wide range of germplasm are required. The Australian Winter Cereal Collection (AWCC, Tamworth) holds over 33 000 accessions of wheat. In this study, we scanned the genome of 1057 accessions of hexaploid common wheat (Triticum aestivum L.) originating from different geographic regions of the world, with 178 polymorphic DArT™ markers. These accessions comprised modern cultivars (MCs), advanced breeding lines (BLs), and landrace cultivars (LCs). Our results indicate that the LCs had higher polymorphic information content (PIC values) than the MCs and BLs. Cluster and principal coordinate analysis based on genetic distance matrices enabled classification of the 1057 accessions into 12 subgroups. The structure of subgroups appeared to be geographically determined and was generally consistent with pedigrees. Molecular analyses revealed that LCs have unique alleles compared with MCs and BLs, which may be useful for the genetic improvement of wheat.
Determinants of the proportion of break crops on Western Australian broadacre farms
Authors: Robertson M. J. , Lawes R. A. , Bathgate A. , Byrne F. , White P. , Sands R.
Published: March 2010

Break crops (e.g. pulses, lupins, canola, oats) underpin the continued profitability of cereal (wheat or barley) based cropping sequences. The area sown on farms to break crops varies widely across geographical regions according to climate, soil type mix, enterprise mix (crop v. livestock), and other constraints such as the prevalence of soil-borne disease. Given recent fluctuations in the area of established break crops in Western Australia, there are concerns about their long-term prospects in the farming system. A survey of the area and grain yield of break crops on-farm was combined with whole-farm bio-economic modelling to determine the upper limit to the area of break crops on representative farms in 4 agro-climatic regions. Sensitivity analysis was conducted to ascertain the potential effects of varying commodity prices (sheep and grain), costs of production, and assumptions on the yield of break crops and the boost to the yield of following cereals. The survey revealed that the two dominant break crops, lupins and canola, occupied 8–12% and 8–9%, respectively, of farm area on those farms that grew them in the medium-rainfall zone and this declined to 6–8% and 7–10% in the drier region. Nevertheless, the modelling results show that break crops are an important component of the farming system, even where the area is small, and the response of whole-farm profit to percent of the farm allocated to break crops is relatively flat near the optimum of 23–38%. The modelled area of break crops at maximum profit is higher than that found in farm surveys. The discrepancy could possibly be explained by the lower break crop yields realised by farmers and a reduced boost to cereal yields following break crops than assumed in models. Also, deterministic models do not account for risk, which is an important consideration in the decision to grow break crops. However, the yield difference does not explain the discrepancy entirely and raises questions about farmer motivations for adoption of break crops. The scope for increased area of break crops beyond 23–38% of the farm is limited, even with increases in the yield enhancements in subsequent cereal crops, higher break crop prices, and higher fertiliser costs. Further research is required to better quantify costs and benefits of break crops in Western Australian farming systems.
Does grazing of infected wheat by sheep result in salivary transmission of Wheat streak mosaic virus?
Authors: Fahim M. , Dove H. , Kelman W. M. , Ayala-Navarrete L. , Larkin P. J.
Published: March 2010

Research is reported probing the concern of some wheat producers that grazing of early sown, dual-purpose wheat for winter forage may accentuate the spread of Wheat streak mosaic virus (WSMV). In experiments with housed sheep, we investigated whether there were any grounds for this concern. In the first experiment, sheep were allowed to graze heavily virus-infected wheat in trays, followed over a period of 24 h by a series of test trays of healthy wheat. The grazed plants were allowed to recover and new leaves were tested for symptoms and the presence of virus. In total, 2352 test plants were negative for WSMV, assessed through symptoms, ELISA, and RT-PCR. In the second experiment, no WSMV particles (assayed with ELISA) or RNA (assayed by RT-PCR) were detected in any saliva samples collected from sheep 0.5, 7.5, and 24.5 h after being fed heavily virus-infected wheat. Furthermore, these saliva samples, when inoculated onto test wheat seedlings under optimal conditions, failed to transmit the virus. In a third experiment we showed that the urea concentration in sheep saliva is at least two orders of magnitude lower than that required to render WSMV non-infective, and therefore is not responsible for the failure of sheep to transmit the virus. Our data provide no support for the suggestion that grazing sheep spread the WSMV between plants in a grazed wheat crop as a consequence of the grazing process itself.
Optimized low-level liquid scintillation spectroscopy of
35
S for atmospheric and biogeochemical chemistry applications
Authors: Brothers Lauren A. , Dominguez Gerardo , Abramian Anna , Corbin Antoinette , Bluen Ben , Thiemens Mark H.
Published: March 2010

Anthropogenic activities, dominated by emissions of sulfur dioxide (SO
2
), have perturbed the global sulfur (S) cycle. Uncertainties in timescales of S transport and chemistry in the atmosphere lead to uncertainties in the predicted impact of S emissions. Measurements of cosmogenic
35
S may potentially be used to resolve existing uncertainties in the photochemical and chemical transformation of S in the environment. The lack of a simple, effective, and highly sensitive technique to measure
35
S activity in samples with low activities may explain the scarcity of published measurements. We present a set of new sample handling and measurement procedures optimized for the measurement of
35
S in natural samples with activities as low as 0.20 dpm above background (2
σ
, integration time = 2 hr). We also report simultaneous measurements of aerosol (

) and gas phase (

) collected at inland and coastal locations; the range of observed activities corresponds to SO
2
residence lifetimes of 0.2 ± 0.04 (coastal) - 22.3 d ± 0.04 (inland). These optimized techniques offer the potential for resolving atmospheric processes that occur on 6–12-hour timescales as well as resolving transport phenomena such as stratospheric mixing into the troposphere.