bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal stability of nitrogen in nitrided HfSiO2/SiO2/Si(001) ultrathin films
Authors: Herrera-Gomez A. , Aguirre-Tostado F. S. , Quevedo-Lopez M. A. , Kirsch P. D. , Kim M. J. , Wallace R. M.
Published: November 2008

We report on the stability under rapid thermal annealing (RTA) of the nitrogen depth profile in nitrided HfO2/SiO2/Si[001] and Hf0.8Si0.2O2/SiO2/Si[001] dielectric stacks. High resolution x-ray photoelectron spectroscopy (XPS) data indicate that the chemical component of nitrogen associated with the hafnium layer (binding energy of 396.7 eV) decreases considerably upon RTA. This was accompanied by a corresponding increase in the nitrogen component associated with silicon oxynitride (binding energy of 397.5 eV). A self-consistent analysis of the angle resolved XPS data indicated that the total amount of nitrogen in the film remains constant, suggesting that RTA causes an exchange of nitrogen between the hafnium and silicon layers. Transmission electron microscopy images show crystallization of the hafnium layer upon RTA, which is consistent with the loss of nitrogen. Data from time of flight secondary ion mass spectroscopy were consistent with the change in the nitrogen profile caused by RTA.
Direct assessment of vorticity alignment with local and nonlocal strain rates in turbulent flows
Authors: Hamlington Peter E. , Schumacher Jörg , Dahm Werner J. A.
Published: November 2008

A direct Biot-Savart integration is used to decompose the strain rate into its local and nonlocal constituents, allowing the vorticity alignment with the local and nonlocal strain rate eigenvectors to be investigated. These strain rate tensor constituents are evaluated in a turbulent flow using data from highly resolved direct numerical simulations. While the vorticity aligns preferentially with the intermediate eigenvector of the combined strain rate, as has been observed previously, the present results, for the first time, clearly show that the vorticity aligns with the most extensional eigenvector of the nonlocal strain rate. This, in turn, reveals a significant linear contribution to the vortex stretching dynamics in turbulent flows.
Phase transformation sequence and magnetic properties of melt-spun SmCo-based alloy after isochronal heat treatment
Authors: Xiong X. Y. , Finlayson T. R.
Published: November 2008

The phase transformation sequence, microstructure and compositions, and magnetic properties for a melt-spun Sm(Co0.68Fe0.2Cu0.1Zr0.02)7.5 alloy after isochronal heat treatments have been studied by using x-ray diffraction, transmission electron microscopy, three-dimensional atom probe (3DAP), and magnetometry. The as-spun ribbons had a single phase with the Cu7Tb structure. After being aged at 720°C, the single phase decomposed into two major phases: 2:17R and 1:5H, and one minor CoFeZr-rich phase. The formation of the Z-phase happened after the cellular structure, requiring a higher temperature than that for the cellular structure. The 3DAP analysis showed that Zr was depleted from the 2:17R and 1:5H phases by a half while the other elements remained almost unchanged when the aging temperature increased from 720to840°C. In contrast to the sintered permanent magnets, Cu was enriched in the 1:5H phase with a much higher concentration (>40at.%). The Cu enrichment also occurred at the boundary of the Z-phase. The coercivity achieved was Hc=4.34kOe following aging at 720°C. The highest maximum energy product, (BH)max, was 6.48MGOe after aging at 800°C and the remanence to saturation magnetization ratio, Mr∕Ms, was 0.69. This relatively low Hc and high Mr∕Ms ratio may be a consequence of the formation of a significant volume fraction of the CoFeZr-rich nanocrystalline phase.
Numerical simulation of deformation/motion of a drop suspended in viscous liquids under influence of steady electric fields
Authors: Hua Jinsong , Lim Liang Kuang , Wang Chi-Hwa
Published: November 2008

The deformation/motion of a droplet suspended in a viscous liquid under the influence of an applied external electric field is investigated through numerical simulations in an axisymmetric system. The two-phase flow field of the drop suspension system is simulated using a front tracking/finite volume method by solving the full Navier–Stokes equations. Three different electric field models are applied in order to take into account the effects of the electric field, electric charge, and electrical properties of liquids. Drops without net charges but finite electrical conductivity are simulated using a leaky dielectric model. Perfect dielectric model is used for the drops of electrically isolating fluid. To take into account the presence of net charges on drop surface, we proposed a simplified constant surface charge model. In addition, the simulation code using the leaky dielectric model and perfect dielectric model is validated systematically against the results of theoretical analysis, the available experimental data, and the simulations by other researchers. It shows that the proposed numerical method (front tracking/finite volume method coupled with various electric field models) can make reasonable prediction on droplet deformation/motion under an externally applied electric field. Under different combinations of liquid properties, the droplets may deform into either prolate or oblate shape and induce different inner and outer circulating flow patterns. When net charges are present on the droplet surface and an electric field is applied, both droplet deformation and motion can be reasonably predicted by the constant charge model. The simulation results demonstrate that the current numerical method may provide an effective approach to quantitatively analyze complex electrohydrodynamic problems.
Probing the plasma chemistry in a microwave reactor used for diamond chemical vapor deposition by cavity ring down spectroscopy
Authors: Ma Jie , Richley James C. , Ashfold Michael N. R. , Mankelevich Yuri A.
Published: November 2008

Absolute column densities of C2(a) and CH radicals and H(n=2) atoms have been measured in a diamond growing microwave reactor operating with hydrocarbon/Ar/H2 gas mixtures as functions of height (z) above the substrate surface and process conditions. The monitored species are each localized in the hot plasma region, where Tgas∼3000 K, and their respective column densities are each reproduced, quantitatively, by two-dimensional (r,z) modeling of the plasma chemistry. The H(n=2) distribution is seen to peak nearer the substrate, reflecting its sensitivity both to thermal chemistry (which drives the formation of ground state H atoms) and the distributions of electron density (ne) and temperature (Te). All three column densities are found to be sensitively dependent on the C/H ratio in the process gas mixture but insensitive to the particular choice of hydrocarbon (CH4 and C2H2). The excellent agreement between measured and predicted column densities for all three probed species, under all process conditions investigated, encourages confidence in the predicted number densities of other of the more abundant radical species adjacent to the growing diamond surface which, in turn, reinforces the view that CH3 radicals are the dominant growth species in microwave activated hydrocarbon/Ar/H2 gas mixtures used in the chemical vapor deposition of microcrystalline and single crystal diamond samples.
Parametric analysis for a miniature loudspeaker used in cellular phones
Authors: Shiah Y. C. , Her Hong-Ching , Huang Jin H. , Huang Brant
Published: November 2008

To play melodious sound, a miniature loudspeaker in a cellular phone needs to generate a wide smooth sound-pressure-level distribution over the midfrequency spectrum ranging from 600 Hz to 10 kHz. This paper reports on a parametric study on the effects of various design parameters on the sound-pressure-level distribution. The electromechanoacoustical analogous approach has been applied to simulate the sound-pressure level. Experiments have been conducted to verify the analysis. The role of each design parameter has been addressed to improve the overall sound-pressure-level performance over the midfrequency spectrum.
Observation of coherent acoustic and optical phonons in bismuth nanowires by a femtosecond pump-probe technique
Authors: Kolomenskii Alexandre A. , Jerebtsov Sergey N. , Liu Haidong , Zhang Hong , Ye Zuxin , Luo Zhiping , Wu Wenhao , Schuessler Hans A.
Published: November 2008

Coherent acoustic and optical phonon oscillations in Bi nanowire samples were studied with a femtosecond pump-probe technique. Laser pulses of 50 fs excited simultaneously acoustic oscillations at a frequency of about 9.5 GHz and optical phonons in the terahertz range. The transmission signal of nanowires on a glass substrate and the signal of light scattered from freestanding nanowires were measured. The acoustic velocity in nanowires was found to be close to that of bulk polycrystalline material. The changes in the optical phonon frequency at different laser fluences were simulated taking into account excitation inhomogeneity, lattice anharmonicity, diffusion, and recombination of the carriers and gave good agreement with experimental results.
Magnetic ordering anisotropy in epitaxial orthorhombic multiferroic YMnO3 films
Authors: Hsieh C. C. , Lin T. H. , Shih H. C. , Hsu C.-H. , Luo C. W. , Lin J.-Y. , Wu K. H. , Uen T. M. , Juang J. Y.
Published: November 2008

Orthorhombic YMnO3 thin films with (200), (020), and (001) orientations were, respectively, obtained by pulsed laser deposition on SrTiO3(110), LaAlO3(110), and SrTiO3(001) substrates. The results demonstrate that the strain between film and substrate can serve as an alternative in transforming the thermodynamically stable hexagonal YMnO3 into the orthorhombic phase, which previously could be obtained with high-pressure high temperature syntheses and epitaxy-stabilized thin film processes. More importantly, these films allow us, for the first time, to unambiguously disclose the intrinsic magnetic property along different crystallographic orientations. Our results show that, although the antiferromagnetic (AFM) ordering remains the same, there is an additional spin reordering transition which is very much dependent on the crystallographic orientation along which the measuring field was applied and on the in-plane crystallographic alignment of the films. Detailed analyses indicate that the origin of the observed second reordering may be due to some strain-induced canted AFM state instead of the incommensurate lock-in transitions conceived previously.
Spectroscopic determination of electron concentration in n-type GaSb
Authors: Maslar J. E. , Hurst W. S. , Wang C. A.
Published: November 2008

Phonon-plasmon coupled mode Raman spectra of n-type GaSb were measured at room temperature as a function of electron concentration. These spectra were obtained using an optical system based on 752.55 nm excitation. Utilization of this wavelength permits greater sensitivity to GaSb coupled mode Raman scattering over a wider doping range than is possible with visible wavelength excitation-based systems. A relatively simple spectral model for the electronic contribution to the dielectric function was evaluated for determination of electron concentration from the bulk coupled mode spectra. The electron concentrations were determined from the Raman spectra by minimizing the sum of the squared residuals between a measured and a simulated spectrum as a function of Fermi energy and a plasmon damping parameter. The electron concentrations determined from the fits to the Raman spectra were compared to the electron concentrations determined from single magnetic field Hall effect measurements that were corrected to account for carriers in two conduction band minima. The electron concentrations determined using the two methods differed from ≈−16% at low doping levels to ≈+24% at high doping levels. In general, compared to the electron concentrations determined from the corrected Hall effect measurements, the electron concentrations determined from the Raman spectra were lower for epilayers with lower Hall effect electron concentrations and higher for epilayers with higher Hall effect electron concentrations. The deviations between the results obtained with the two methods were attributed to the impact of uncertainties in GaSb material properties on the accuracy of the correction to the single field Hall effect measurements and to the limitations of the spectral model employed.
Influence of interfacial dislocations on hysteresis loops of ferroelectric films
Authors: Li Y. L. , Hu S. Y. , Choudhury S. , Baskes M. I. , Saxena A. , Lookman T. , Jia Q. X. , Schlom D. G. , Chen L. Q.
Published: November 2008

We investigated the influence of dislocations, located at the interface of a ferroelectric film and its underlying substrate, on the ferroelectric hysteresis loop including the remanent polarization and coercive field using phase-field simulations. We considered epitaxial ferroelectric BaTiO3 films and found that the hysteresis loop is strongly dependent on the type and density of interfacial dislocations. The dislocations that stabilize multiple ferroelectric variants and domains reduce the coercive field, and consequently, the corresponding remanent polarization also decreases.
Extrusion formation mechanism on silicon surface under the silica cluster impact studied by molecular dynamics simulation
Authors: Chen Ruling , Luo Jianbin , Guo Dan , Lu Xinchun
Published: November 2008

Molecular dynamic simulation is applied in analyzing the deformation of silicon surface under the impact of large silica cluster. The mechanism of such a deformation is largely different from the cases of ion bombardment and indentation. With the impact of large silica cluster, the silicon surface is extruded due to the combinational effects of thermal spread, phase transformation, and crystallographic slip. It is found that thermal spread is the most significant one among these three effects. The extrusions on silicon surface will be in embryo during the impact unloading stage and will grow up during the cluster rebounding stage. Furthermore, the critical impact velocity to induce the formation of extrusions on silicon surface is associated with the incidence angle of the cluster, while it is independent from the size of the cluster. The findings are instructive in optimizing the process parameters for ultraprecision machining of silicon wafer.
Structural and electrical properties of Ge1Sb2Te4 face centered cubic phase
Authors: Prokhorov E. , Trapaga G. , González-Hernández J.
Published: November 2008

The aim of this article is to study the properties of the crystalline face centered cubic Ge1Sb2Te4 phase as a function of annealing and measuring temperature. This material is one of the stoichiometric members of the Ge:Sb:Te family, which is widely used in the phase change data storage and one candidate for multistate recording. The electrical properties of this material have been investigated using two independent methods, the four probe impedance and the Hall measurements, and the results are interpreted in terms of structural parameters obtained from x-ray diffraction and transmission electron microscopy results. Experimental results have shown the polycrystalline nature of the film and that the transport properties have a strong dependence on the annealing temperature. An increase in the annealing temperature leads to an increase in the grain size, carrier concentration, mobility, and to a decrease in the volume fraction of grain boundaries. The mobility is limited by scattering of charge carries at the grain boundaries and can be described by a conduction model based on thermionic emission over the potential barriers. The large changes in the room temperature resistivity (more than 25 times) and effective capacitance (about 30%) of the polycrystalline state upon annealing due to various structural configurations increase (in addition to the amorphous in the crystalline transition) the dynamical range for multistate recording applications.
Dynamic motion of red blood cells in simple shear flow
Authors: Sui Y. , Chew Y. T. , Roy P. , Cheng Y. P. , Low H. T.
Published: November 2008

A three-dimensional numerical model is proposed to simulate the dynamic motion of red blood cells (RBCs) in simple shear flow. The RBCs are approximated by ghost cells consisting of Newtonian liquid drops enclosed by Skalak membranes which take into account the membrane shear elasticity and the membrane area incompressibility. The RBCs have an initially biconcave discoid resting shape, and the internal liquid is assumed to have the same physical properties as the matrix fluid. The simulation is based on a hybrid method, in which the immersed boundary concept is introduced into the framework of the lattice Boltzmann method, and a finite element model is incorporated to obtain the forces acting on the nodes of the cell membrane which is discretized into flat triangular elements. The dynamic motion of RBCs is investigated in simple shear flow under a broad range of shear rates. At large shear rates, the cells are found to carry out a swinging motion, in which periodic inclination oscillation and shape deformation superimpose on the membrane tank treading motion. With the shear rate decreasing, the swinging amplitude of the cell increases, and finally triggers a transition to tumbling motion. This is the first direct numerical simulation that predicts both the swinging motion of the RBCs and the shear rate induced transition, which have been observed in a recent experiment. It is also found that as the mode changes from swinging to tumbling, the apparent viscosity of the suspension increases monotonically.
Luminescence study of Eu3+ doped GdVO4 nanoparticles: Concentration, particle size, and core/shell effects
Authors: Singh N. Shanta , Ningthoujam R. S. , Devi L. Romila , Yaiphaba N. , Sudarsan V. , Singh S. Dorendrajit , Vatsa R. K. , Tewari R.
Published: November 2008

Nanoparticles of GdVO4 doped with Eu3+ and core/shell of GdVO4:Eu3+/GdVO4 are prepared by urea hydrolysis method using ethylene glycol as capping agent as well as reaction medium at 130 °C. Unit cell volume increases when GdVO4 is doped with Eu3+ indicating the substitution of Gd3+ lattice sites by Eu3+. From luminescence study, it is confirmed that there is no particle size effect on emission positions of Eu3+. Optimum luminescence intensity is found to be in 5–10 at. % Eu3+. Above these concentrations, luminescence intensity decreases due to concentration quenching effect. There is an enhancement in luminescence intensity of core/shell nanoparticles. This has been attributed to the reduction in surface inhomogenities of Eu3+ surroundings by bonding to GdVO4 shell. The lifetime for D50 level increases with annealing and core/shell formation.
Dielectric tunability of graded barium strontium titanate multilayers: Effect of thermal strains
Authors: Okatan M. B. , Cole M. W. , Alpay S. P.
Published: November 2008

A thermodynamic model was developed to analyze the effect of the difference in the thermal expansion coefficient (TEC) of a multilayered barium strontium titanate Ba1−ySryTiO3 (BST) ferroelectric heterostructure and a passive substrate on the dielectric properties by taking into account electrostatic and electromechanical interactions between the ferroelectric layers. Results show that the dielectric constant and tunability can be maximized by minimizing the TEC mismatch. Furthermore, lower processing temperatures lead to lower thermal strains and thus to better dielectric properties. We also provide a numerical analysis describing the effect of thermal strains on dielectric properties of a compositionally graded trilayer consisting of BST 60/40, BST 75/25, and BST 90/10 on a variety of substrates including Si, sapphire (α-Al2O3), SrTiO3, MgO, and LaAlO3. The multilayer BST heterostructure on Si is expected to experience high in-plane tensile strains due to the large TEC mismatch, resulting in dielectric permittivities and tunabilities lower compared to the same multilayer on SrTiO3 or LaAlO3 for which there is a better TEC match. For BST multilayers on MgO, SrTiO3, Si, and sapphire, higher processing temperatures lead to lower dielectric response and tunability.
Characteristics of amorphous Ag0.1(Ge2Sb2Te5)0.9 thin film and its ultrafast crystallization
Authors: Song Ki-Ho , Kim Sung-Won , Seo Jae-Hee , Lee Hyun-Yong
Published: November 2008

An amorphous chalcogenide Ge2Sb2Te5 film is most commonly used for phase-change data storage, in which its small volume is switched between amorphous and crystalline states by local heating with short laser or current pulses. A speed of amorphous-to-crystalline phase transformation in Ge2Sb2Te5 and Ag0.1(Ge2Sb2Te5)0.9 films has been evaluated on a nanosecond time scale using a 658-nm laser beam. The focused laser beam with a diameter <10 μm was illuminated in the power (P) and pulse duration (t) ranges of 1–17 mW and 10–460 ns, respectively, with subsequent detection of the response signals reflected from the film surface. We also evaluated the material characteristics, such as optical absorption and energy gap, crystalline phases, and sheet resistance of as-deposited and annealed films. The experiments showed that the crystallization speed of the Ge2Sb2Te5 film is largely improved by adding Ag. For example, the threshold pulse durations (tT) for Ge2Sb2Te5 and Ag0.1(Ge2Sb2Te5)0.9 films are approximately 70 and 30 ns for P=7 mW. In addition, the sheet resistance in the amorphous state of the Ag0.1(Ge2Sb2Te5)0.9 film is approximately ten times that of the Ge2Sb2Te5 film. This improvement can lead to a low programming current in electronic operation. To understand the ultrafast crystallization in the amorphous Ag0.1(Ge2Sb2Te5)0.9 film, we suggest heat confinement by electron hopping.
Ion transport in polyacetylene ionomers
Authors: Lin Fuding , Wang Yongjun , Lonergan Mark
Published: November 2008

Ion transport in cationically and anionically functionalized polyacetylene ionomers, PAC and PAA, respectively, was investigated by analyzing the impedance responses of thin film Au∣ionomer∣Au sandwich configurations. Samples were measured over a frequency range of 10−2–106 Hz and a temperature range of 298–398 K. Electrode polarization at low frequencies and dispersion due to ion hopping at higher frequencies were observed. The impedance data were analyzed first without the reliance on a specific model, then through equivalent circuit modeling, to estimate the dc (bulk) ion conductivity σ0, ion hopping rate ωh, and dielectric constant of the polymer matrix. The dispersive ion hopping conduction was best modeled by a distributed process involving the Kohlrausch–Williams–Watts stretched exponential decay function. The ionic conductivity of both ionomers exhibited an Arrhenius dependence on temperature with similar activation energies: 0.94 eV for PAC and 0.97 eV for PAA. At 308 K, the ionic conductivity of PAC was measured to be 1.1×10−11 S/cm while that of PAA was measured to be 1.3×10−12 S/cm. The dielectric constant for the polymer matrix in the absence of ionic polarization was found to be ϵD=4.5 for PAC and ϵD=4.2 for PAA at 308 K. The assignment of the conductivity to ionic processes implies an extremely small intrinsic electronic conductivity in these polymeric semiconductors.
Achieving a low interfacial density of states in atomic layer deposited Al2O3 on In0.53Ga0.47As
Authors: Chiu H. C. , Tung L. T. , Chang Y. H. , Lee Y. J. , Chang C. C. , Kwo J. , Hong M.
Published: November 2008

Atomic-layer-deposited Al2O3 on In0.53Ga0.47As with short air exposure between the oxide and semiconductor deposition has enabled the demonstration of nearly ideal frequency-dependent and quasistatic capacitance-voltage (C-V) characteristics. The excellent quasistatic C-V characteristics indicate a high efficiency of 63% for the Fermi-level movement near the midgap. A low mean interfacial density of states (D¯it)∼2.5×1011 cm−2 eV−1 was determined under 1 MHz using a charge pumping method, which was also employed to probe the depth profile of bulk traps (Nbt) and the energy dependence of Dit at 50 kHz: a low Nbt∼7×1018 cm−3 and a Dit of (2–4)×1011 cm−2 eV−1 in the lower half of the band gap and a higher Dit of ∼1012 cm−2 eV−1 in the upper half of the band gap. The employment of charge pumping method has given a more accurate determination of Dit, which is usually overestimated using other commonly methods such as the Terman, conductance, and high-low frequencies due to the influence of weak inversion at room temperature.
Magnetoresistance of a multilayered film in a current-perpendicular- to-plane geometry
Authors: Anisimov A. V. , Popov A. P.
Published: November 2008

The method to calculate the electrical resistance of a multilayered film consisting of any finite number of ferromagnetic and nonmagnetic layers for a given collinear magnetic configuration is proposed. The problem is solved for the geometry when the current flows perpendicular to the film plane. The method is based on the description of the resistance of a multilayered film by the differential equation for the current polarization which satisfies two boundary conditions at the interface between adjacent ferromagnetic layers. It is demonstrated that the description of the stack resistance depending on the mutual collinear orientation of ferromagnetic layers can be reduced to the routine mathematical calculations. Also it is shown that in the case of tunneling barriers between ferromagnetic layers one has to determine the barrier resistance asymmetry coefficient in order to calculate magnetoresistance of a multilayer film as a function of ferromagnetic layer collinear magnetic configuration. It is essential that these asymmetry parameters cannot be obtained directly from experiment. In the present work, the expressions for these parameters are derived within Slonczewski model from similar parameters in a ferromagnetic-tunneling barrier-nonmagnetic stack which can be measured experimentally. The obtained results allow one to evaluate the magnetoresistance values in a multilayered film consisting of any finite number of ferromagnetic layers.
Universal scaling in wildfire fractal propagation
Authors: Porterie Bernard , Kaiss Ahmed , Clerc Jean-Pierre , Zekri Lotfi , Zekri Nouredine
Published: November 2008

A small-world network model is proposed to predict wildfire behavior near critical propagation conditions. It includes long-range connections due to flame radiation and a weighting procedure based on times of degradation and combustion of vegetation. Scaling laws are found universal near the propagation transition. For isotropic propagation, the critical behavior of the usual percolation theory is recovered, whereas, for anisotropic conditions due to wind and/or topography, propagation is fractal with a dimension of 1.3 and a critical exponent of the correlation length of 1.7, following the extrapolation for Euclidian systems. The exponent value agrees well with that of directed percolation.
Diffusion of atmospheric gases into barrier-layer sealed organic light emitting diodes
Authors: Mandlik Prashant , Han Lin , Wagner Sigurd , Silvernail Jeff A. , Ma Rui-Qing , Hack Michael , Brown Julie J.
Published: November 2008

Organic light emitting diodes (OLEDs) are protected from the atmosphere with a barrier layer. Even when this permeation barrier is hermetic, dark spots still may grow and dark sheets may extend into the OLED. These grow by diffusion from the atmosphere along the interfaces between the barrier layer with embedded particles or with the substrate. Observed growth rates of dark spots and sheets are modeled by a single diffusion mechanism. Similar normalized flux densities along the two pathways and a diffusion coefficient of ∼10−8 cm2/s suggest a similar polymeric structure of the barrier/particle and barrier/substrate interfaces.
Directional enhanced acoustic radiation caused by a point cavity in a finite-size two-dimensional phononic crystal
Authors: Hsu Feng-Chia , Wu Tsung-Tsong , Hsu Jin-Chen , Sun Jia-Hong
Published: November 2008

In this letter, we present results of a study on the directional enhanced radiation generated by a point resonant cavity operating at the band-gap frequency of a two-dimensional finite-size phononic crystal. We find that the directive radiation for operating frequency within the band gap comes from the direction-dependent transmittance property of the square-lattice phononic crystal. The directive-radiation characteristic can be capitalized on enhancing the emission from the phononic crystals by coupling the source with point-defect modes, and the enhanced directive radiation patterns with main lobe width less than 12.9° are demonstrated.
Half-cycle atomic layer deposition reaction studies of Al2O3 on In0.2Ga0.8As (100) surfaces
Authors: Milojevic M. , Aguirre-Tostado F. S. , Hinkle C. L. , Kim H. C. , Vogel E. M. , Kim J. , Wallace R. M.
Published: November 2008

The reduction in III–V interfacial oxides by atomic layer deposition of Al2O3 on InGaAs is studied by interrupting the deposition following individual trimethyl aluminum (TMA) and water steps (half cycles) and interrogation of the resultant surface reactions using in situ monochromatic x-ray photoelectron spectroscopy (XPS). TMA is found to reduce the interfacial oxides during the initial exposure. Concentrations of Ga oxide on the surface processed at 300 °C are reduced to a concentration on the order of a monolayer, while AsOx species are below the level of detection of XPS.
Dynamic-gate operation in nanoelectronic amplifiers due to reduced screening
Authors: Worschech L. , Hartmann D. , Forchel A.
Published: November 2008

Semiconductor nanostructures in shape of a Y were patterned lithographically in a two-dimensional electron gas. One of the branches was pinched off, so it can act as a gate for the other branch. Such nanoelectronic amplifiers show switching voltages smaller than the thermal limit and tunable bistability. The authors related their observations to a reduced-screening induced dynamic capacitance, which can exceed the contribution from the geometric capacitance.
Robert Henry Symons 1934 - 2006
Authors: Rogers George E. , Elliott William H.
Published: November 2008

Bob Symons died in Adelaide on 4 October 2006 after a long illness. He was distinguished through his contributions to our knowledge of the structure, function and replication of plant viruses, viroids and virusoids. His research culminated in the discovery of the hammerhead folding of the RNA chain and its role as a ribozyme in self-cleavage of the RNA in some of these plant pathogens. He was a leader in his field and was responsible for commercial applications of his research and the establishment in Adelaide of the first Australian company to produce and market molecular biologicals for research.
R. W. E. MacIvor: Late-nineteenth-century Advocate for Scientific Agriculture in South-eastern Australia
Authors: Collins David J. , Rae Ian D.
Published: November 2008

Ralph Waldo Emerson MacIvor, a Scottish chemist, was brought to Victoria in 1876 by the prominent landowner W. J. Clarke to lecture to farmers on scientific agriculture. MacIvor lectured frequently over the next few years, joining in agricultural politics and supporting the establishment of agricultural colleges. He also lectured in South Australia and New Zealand. His lectures were fully reported in the press and in 1879 he incorporated their content in a book, The Chemistry of Agriculture. He was one of the unsuccessful applicants for the University of Melbourne's chair of chemistry to which David Orme Masson was appointed in 1886. In 1884, MacIvor was appointed by the new Sydney Technical College to lecture in country districts on scientific agriculture, but served for less than a year. He returned to Britain where he practised in London as a consulting analytical chemist. MacIvor came with experience in original chemical research, but he was not brought to Australia to conduct research in agricultural chemistry. His role was to act as instructor and advocate for scientific agriculture.
A Poissonian explanation for heavy tails in e-mail communication
Authors: Malmgren R. Dean , Stouffer Daniel B. , Motter Adilson E. , Amaral Luís A. N.
Published: November 2008

Patterns of deliberate human activity and behavior are of utmost importance in areas as diverse as disease spread, resource allocation, and emergency response. Because of its widespread availability and use, e-mail correspondence provides an attractive proxy for studying human activity. Recently, it was reported that the probability density for the inter-event time τ between consecutively sent e-mails decays asymptotically as τ−α, with α ≈ 1. The slower-than-exponential decay of the inter-event time distribution suggests that deliberate human activity is inherently non-Poissonian. Here, we demonstrate that the approximate power-law scaling of the inter-event time distribution is a consequence of circadian and weekly cycles of human activity. We propose a cascading nonhomogeneous Poisson process that explicitly integrates these periodic patterns in activity with an individual's tendency to continue participating in an activity. Using standard statistical techniques, we show that our model is consistent with the empirical data. Our findings may also provide insight into the origins of heavy-tailed distributions in other complex systems.
Ocean methane hydrates as a slow tipping point in the global carbon cycle
Authors: Archer David , Buffett Bruce , Brovkin Victor
Published: November 2008

We present a model of the global methane inventory as hydrate and bubbles below the sea floor. The model predicts the inventory of CH4in the ocean today to be ≈1600–2,000 Pg of C. Most of the hydrate in the model is in the Pacific, in large part because lower oxygen levels enhance the preservation of organic carbon. Because the oxygen concentration today may be different from the long-term average, the sensitivity of the model to O2is a source of uncertainty in predicting hydrate inventories. Cold water column temperatures in the high latitudes lead to buildup of hydrates in the Arctic and Antarctic at shallower depths than is possible in low latitudes. A critical bubble volume fraction threshold has been proposed as a critical threshold at which gas migrates all through the sediment column. Our model lacks many factors that lead to heterogeneity in the real hydrate reservoir in the ocean, such as preferential hydrate formation in sandy sediments and subsurface gas migration, and is therefore conservative in its prediction of releasable methane, finding only 35 Pg of C released after 3 °C of uniform warming by using a 10% critical bubble volume. If 2.5% bubble volume is taken as critical, then 940 Pg of C might escape in response to 3 °C warming. This hydrate model embedded into a global climate model predicts ≈0.4–0.5 °C additional warming from the hydrate response to fossil fuel CO2release, initially because of methane, but persisting through the 10-kyr duration of the simulations because of the CO2oxidation product of methane.
The Wnt modulator sFRP2 enhances mesenchymal stem cell engraftment, granulation tissue formation and myocardial repair
Authors: Alfaro Maria P. , Pagni Matthew , Vincent Alicia , Atkinson James , Hill Michael F. , Cates Justin , Davidson Jeffrey M. , Rottman Jeffrey , Lee Ethan , Young Pampee P.
Published: November 2008

Cell-based therapies, using multipotent mesenchymal stem cells (MSCs) for organ regeneration, are being pursued for cardiac disease, orthopedic injuries and biomaterial fabrication. The molecular pathways that regulate MSC-mediated regeneration or enhance their therapeutic efficacy are, however, poorly understood. We compared MSCs isolated from MRL/MpJ mice, known to demonstrate enhanced regenerative capacity, to those from C57BL/6 (WT) mice. Compared with WT-MSCs, MRL-MSCs demonstrated increased proliferation, in vivo engraftment, experimental granulation tissue reconstitution, and tissue vascularity in a murine model of repair stimulation. The MRL-MSCs also reduced infarct size and improved function in a murine myocardial infarct model compared with WT-MSCs. Genomic and functional analysis indicated a downregulation of the canonical Wnt pathway in MRL-MSCs characterized by significant up-regulation of specific secreted frizzled-related proteins (sFRPs). Specific knockdown of sFRP2 by shRNA in MRL-MSCs decreased their proliferation and their engraftment in and the vascular density of MRL-MSC-generated experimental granulation tissue. These results led us to generate WT-MSCs overexpressing sFRP2 (sFRP2-MSCs) by retroviral transduction. sFRP2-MSCs maintained their ability for multilineage differentiation in vitro and, when implanted in vivo, recapitulated the MRL phenotype. Peri-infarct intramyocardial injection of sFRP2-MSCs resulted in enhanced engraftment, vascular density, reduced infarct size, and increased cardiac function after myocardial injury in mice. These findings implicate sFRP2 as a key molecule for the biogenesis of a superior regenerative phenotype in MSCs.
Evidence for a human-specific mechanism for diet and antibody-mediated inflammation in carcinoma progression
Authors: Hedlund Maria , Padler-Karavani Vered , Varki Nissi M. , Varki Ajit
Published: November 2008

Patients with cancer have circulating heterophile antibodies that agglutinate animal red cells via recognition of the mammalian cell surface sialic acidN-glycolylneuraminic acid (Neu5Gc), which was long considered an oncofetal antigen in humans. However, humans are genetically deficient in Neu5Gc production and instead metabolically accumulate Neu5Gc from dietary sources, particularly red meats and milk products. Moreover, mice with a human-like defect showed no alternate pathway for Neu5Gc synthesis and even normal humans express anti-Neu5Gc antibodies. We show here that human tumors accumulate Neu5Gc that is covalently attached to multiple classes of glycans. The paradox of human tumor Neu5Gc accumulation in the face of circulating anti-Neu5Gc antibodies was hypothesized to be due to facilitation of tumor progression by the resulting low-grade chronic inflammation. Indeed, murine tumors expressing human-like levels of Neu5Gc show accelerated growth in syngeneic mice with a human-like Neu5Gc deficiency, coincident with the induction of anti-Neu5Gc antibodies and increased infiltration of inflammatory cells. Transfer of polyclonal monospecific syngeneic mouse anti-Neu5Gc serum also enhanced growth of transplanted syngeneic tumors bearing human-like levels of Neu5Gc, with tumors showing evidence for antibody deposition, enhanced angiogenesis and chronic inflammation. These effects were suppressed by a cyclooxygenase-2 inhibitor, a drug type known to reduce human carcinoma risk. Finally, affinity-purified human anti-Neu5Gc antibodies also accelerate growth of Neu5Gc-containing tumors in Neu5Gc-deficient mice. Taken together, the data suggest that the human propensity to develop diet-related carcinomas is contributed to by local chronic inflammation, resulting from interaction of metabolically-accumulated dietary Neu5Gc with circulating anti-Neu5Gc antibodies.
Eosinophil granules function extracellularly as receptor-mediated secretory organelles
Authors: Neves Josiane S. , Perez Sandra A. C. , Spencer Lisa A. , Melo Rossana C. N. , Reynolds Lauren , Ghiran Ionita , Mahmudi-Azer Salahaddin , Odemuyiwa Solomon O. , Dvorak Ann M. , Moqbel Redwan , Weller Peter F.
Published: November 2008

Intracellular granules in several types of leukocytes contain preformed proteins whose secretions contribute to immune and inflammatory functions of leukocytes, including eosinophils, cells notably associated with asthma, allergic inflammation, and helminthic infections. Cytokines and chemokines typically elicit extracellular secretion of granule proteins by engaging receptors expressed externally on the plasma membranes of cells, including eosinophils. Eosinophil granules, in addition to being intracellular organelles, are found as intact membrane-bound structures extracellularly in tissue sites of eosinophil-associated diseases. Neither the secretory capacities of cell-free eosinophil granules nor the presence of functional cytokine and chemokine receptors on membranes of leukocyte granules have been recognized. Here, we show that granules of human eosinophils express membrane receptors for a cytokine, IFN-γ, and G protein–coupled membrane receptors for a chemokine, eotaxin, and that these receptors function by activating signal-transducing pathways within granules to elicit secretion from within granules. Capacities of intracellular granule organelles to function autonomously outside of eosinophils as independent, ligand-responsive, secretion-competent structures constitute a novel postcytolytic mechanism for regulated secretion of eosinophil granule proteins that may contribute to eosinophil-mediated inflammation and immunomodulation.
Functional assessment of allelic variants in the
SLC26A4
gene involved in Pendred syndrome and nonsyndromic EVA
Authors: Pera Alejandra , Dossena Silvia , Rodighiero Simona , Gandía Marta , Bottà Guido , Meyer Giuliano , Moreno Felipe , Nofziger Charity , Hernández-Chico Concepción , Paulmichl Markus
Published: November 2008

Pendred syndrome is an autosomal recessive disorder characterized by sensorineural hearing loss, with malformations of the inner ear, ranging from enlarged vestibular aqueduct (EVA) to Mondini malformation, and deficient iodide organification in the thyroid gland. Nonsyndromic EVA (ns-EVA) is a separate type of sensorineural hearing loss showing normal thyroid function. Both Pendred syndrome and ns-EVA seem to be linked to the malfunction of pendrin (SLC26A4), a membrane transporter able to exchange anions between the cytosol and extracellular fluid. In the past, the pathogenicity of
SLC26A4
missense mutations were assumed if the mutations fulfilled two criteria: low incidence of the mutation in the control population and substitution of evolutionary conserved amino acids. Here we show that these criteria are insufficient to make meaningful predictions about the effect of these
SLC26A4
variants on the pendrin-induced ion transport. Furthermore, we functionally characterized 10 missense mutations within the
SLC26A4
ORF, and consistently found that on the protein level, an addition or omission of a proline or a charged amino acid in the SLC26A4 sequence is detrimental to its function. These types of changes may be adequate for predicting SLC26A4 functionality in the absence of direct functional tests.
Striatal dysregulation of Cdk5 alters locomotor responses to cocaine, motor learning, and dendritic morphology
Authors: Meyer Douglas A. , Richer Edmond , Benkovic Stanley A. , Hayashi Kanehiro , Kansy Janice W. , Hale Carly F. , Moy Lily Y. , Kim Yong , O'Callaghan James P. , Tsai Li-Huei , Greengard Paul , Nairn Angus C. , Cowan Christopher W. , Miller Diane B. , Antich Pietro , Bibb James A.
Published: November 2008

Motor learning and neuro-adaptations to drugs of abuse rely upon neuronal signaling in the striatum. Cyclin-dependent kinase 5 (Cdk5) regulates striatal dopamine neurotransmission and behavioral responses to cocaine. Although the role for Cdk5 in neurodegeneration in the cortex and hippocampus and in hippocampal-dependent learning has been demonstrated, its dysregulation in the striatum has not been examined. Here we show that strong activation of striatal NMDA receptors produced p25, the truncated form of the Cdk5 co-activator p35. Furthermore, inducible overexpression of p25 in the striatum prevented locomotor sensitization to cocaine and attenuated motor coordination and learning. This corresponded with reduced dendritic spine density, increased neuro-inflammation, altered dopamine signaling, and shifted Cdk5 specificity with regard to physiological and aberrant substrates, but no apparent loss of striatal neurons. Thus, dysregulation of Cdk5 dramatically affects striatal-dependent brain function and may be relevant to non-neurodegenerative disorders involving dopamine neurotransmission.
Stochasticity and traffic jams in the transcription of ribosomal RNA: Intriguing role of termination and antitermination
Authors: Klumpp Stefan , Hwa Terence
Published: November 2008

In fast-growing bacteria, ribosomal RNA (rRNA) is required to be transcribed at very high rates to sustain the high cellular demand on ribosome synthesis. This results in dense traffic of RNA polymerases (RNAP). We developed a stochastic model, integrating results of single-molecule and quantitative in vivo studies of
Escherichia coli
, to evaluate the quantitative effect of pausing, termination, and antitermination (AT) on rRNA transcription. Our calculations reveal that in dense RNAP traffic, spontaneous pausing of RNAP can lead to severe “traffic jams,” as manifested in the broad distribution of inter-RNAP distances and can be a major factor limiting transcription and hence growth. Our results suggest the suppression of these pauses by the ribosomal AT complex to be essential at fast growth. Moreover, unsuppressed pausing by even a few nonantiterminated RNAPs can already reduce transcription drastically under dense traffic. However, the termination factor Rho can remove the nonantiterminated RNAPs and restore fast transcription. The results thus suggest an intriguing role by Rho to enhance rather than attenuate rRNA transcription.
Inducible and reversible gene silencing by stable integration of an shRNA-encoding lentivirus in transgenic rats
Authors: Herold Marco J. , van den Brandt Jens , Seibler Jost , Reichardt Holger M.
Published: November 2008

Currently, tools to generate loss-of-function mutations in rats are limited. Therefore, we have developed a lentiviral single-vector system for the temporal control of ubiquitous shRNA expression. Here, we report transgenic rats carrying an insulin receptor-specific shRNA transcribed from a regulatable promoter and identified by concomitant EGFP expression. In the absence of the inducer doxycycline (Dox), we observed no siRNA expression. However, Dox treatment at very low concentrations led to a rapid induction of the siRNA and ablation of INSR protein expression. As anticipated, blood glucose levels increased, whereas insulin signaling and glucose regulation were impaired. Importantly, this phenotype was reversible (i.e., discontinuation of Dox treatment led to INSR re-expression and remission of diabetes symptoms). The lentiviral system offers a simple tool for reversible gene ablation in the rat and can be used for other species that cannot be manipulated by conventional recombination techniques.
α-Catenin mediates initial E-cadherin-dependent cell–cell recognition and subsequent bond strengthening
Authors: Bajpai Saumendra , Correia Joana , Feng Yunfeng , Figueiredo Joana , Sun Sean X. , Longmore Gregory D. , Suriano Gianpaolo , Wirtz Denis
Published: November 2008

α-Catenin is essential in cadherin-mediated epithelium development and maintenance of tissues and in cancer progression and metastasis. However, recent studies question the conventional wisdom that α-catenin directly bridges the cadherin adhesion complex to the actin cytoskeleton. Therefore, whether α-catenin plays a direct role in cadherin-dependent cell adhesion is unknown. Here, single-molecule force spectroscopy measurements in cells depleted of α-catenin or expressing the hereditary diffuse gastric cancer associated V832M E-cadherin germ-line missense mutation show that α-catenin plays a critical role in cadherin-mediated intercellular recognition and subsequent multibond formation within the first 300 ms of cell contact. At short contact times, α-catenin mediates a 30% stronger interaction between apposing E-cadherin molecules than when it cannot bind the E-cadherin–β-catenin complex. As contact time between cells increases, α-catenin is essential for the strengthening of the first intercellular cadherin bond and for the ensuing formation of additional bonds between the cells, all without the intervention of actin. These results suggest that a critical decision to form an adhesion complex between 2 cells occurs within an extremely short time span and at a single-molecule level and identify a previously unappreciated role for α-catenin in these processes.