bluuebunny/crossref_metadata_2025 huggingface dataset:
Kuhn on architectural style
Authors: Wang David
Published: August 2009

By any measure Thomas Kuhn's The Structure of Scientific Revolutions is a landmark in recent influential ideas. The very term ‘paradigm shift’, now common parlance, derives from this 1962 work. Structure redirected its own domain, the philosophy of science, from a logical positivist orientation in its evaluation of scientific progress to one that accommodates a complex mix of sociological, linguistic and psychological factors. Perhaps because of this interdisciplinary inclusiveness, Kuhn's insights have informed theory in many disciplines. A survey of the recent literature includes works in anthropology, comparative literature, criminal justice, art history, education and feminist studies.
Overlapping Institutions in the Realm of International Security: The Case of NATO and ESDP
Authors: Hofmann Stephanie C.
Published: August 2009

The North Atlantic Treaty Organization (NATO) and the European Union's (EU) European Security and Defense Policy (ESDP) both occupy the policy space of crisis management. This overlap has two effects. First, overlap has generated “chessboard politics” shaping member state strategies. Second, institutional overlap has generated a number of feedback effects. The prior existence of NATO shaped the conceptualization and organization of ESDP at its creation, and the existence of two alternative security institutions continues to influence the ways that the institutions evolve—how each institution defines security interests and how member states adjust the mandate of each institution to address changes in the security environment. Because both institutions are intergovernmentally organized and consensus-based, the actions and decisions of both institutions reflect the agreements of members. Chessboard politics and feedback effects are consequently interrelated—states strategize to affect outcomes in one venue or another, and decisions in one institution can affect decisions and behaviors in the other institution.
Transverse‐scale size of Pc3 ULF waves near the exterior cusp
Authors: Liu Y. H. , Fraser B. J. , Ables S. T. , Zhang B. C. , Liu R. Y. , Dunlop M. W. , Waterman J.
Published: August 2009

The concept of a geomagnetic field line has been widely used in the study of magnetospheric physical phenomena. For example, the mode in which ULF waves propagate relates to the direction of the field, with the Alfven wave mode propagating along the field direction. Very little is known about the perpendicular extent of the propagating wave. In this paper, wave coherency methods are utilized to analyze ULF waves in the Pc3 band that were simultaneously observed by the Cluster satellites near the exterior cusp and by ground stations at local magnetic noon near the footprint of the cusp. The results show that the coherency of waves observed at the ground on the H component is much larger than that on the D component, which is opposite to that seen by Cluster in space. The coherency between the H component on the ground and the y component in space was higher than the other combination of pairs, with the coherency between the satellite and the Daneborg (DNB) station having the maximum value. These results suggest that the polarization of the waves are rotated by 90° after propagating through the ionosphere, and the magnetic footprint of Cluster is closest to the DNB station at this time. The coherency of the Pc3 waves between the satellites is highly related to the alignment of satellite pairs with respect to the geomagnetic field direction. This alignment may provide a transverse‐scale size of the geomagnetic Pc3 ULF waves near the exterior cusp at ∼900 km with a coherency of 0.65.
Space Technology 5 multipoint observations of temporal and spatial variability of field‐aligned currents
Authors: Le G. , Wang Y. , Slavin J. A. , Strangeway R. J.
Published: August 2009

Space Technology 5 (ST5) is a constellation mission consisting of three microsatellites. It provides the first multipoint magnetic field measurements in low Earth orbit, which enables us to separate spatial and temporal variations. In this paper, we present a study of the temporal variability of field‐aligned currents using the ST5 data. We examine the field‐aligned current observations during and after a geomagnetic storm and compare the magnetic field profiles at the three spacecraft. The multipoint data demonstrate that mesoscale current structures, commonly embedded within large‐scale current sheets, are very dynamic with highly variable current density and/or polarity in ∼10 min time scales. On the other hand, the data also show that the time scales for the currents to be relatively stable are ∼1 min for mesoscale currents and ∼10 min for large‐scale currents. These temporal features are very likely associated with dynamic variations of their charge carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of mesoscale field‐aligned currents are found to be consistent with those of auroral parallel electric field.
Numerical simulation of a cascaded arc source with different Ar–H2 mixtures of nonlocal thermal equilibrium plasmas
Authors: Ahmad Zahoor
Published: August 2009

Cascaded arc of Pilot-PSI is modeled using numerical simulation code PLASIMO [G. M. Janssen, Ph.D. thesis, Eindhoven University of Technology (2000), http://plasimo.phys.tue.nl]. Pilot-PSI is a linear device used to produce a high density plasma column for the study of plasma surface interaction processes. In this modeling effort nonlocal thermal equilibrium plasma of Ar–H2 mixture is used. The purpose of these simulations is to optimize the cascaded arc for a higher yield of H+ ions and to investigate the role of Ar–H2 mixture ratios. The associative charge exchange reaction followed by dissociative recombination plays a very important role in the dissociation of H2 molecules and as a consequence the yield of H+ increases and of Ar+ decreases. The Ar+ density also decreases in the arc when H2 concentration is increased beyond certain value. With a mixture of 2.5 standard liters per minute Ar and 0.5 SLM H2 the H+ ion flux exceeds the flux obtained in pure H2 gas, at a reduced expenditure of energy per ion.
Influence of electron velocity distribution on the plasma expansion features
Authors: Shokoohi R. , Abbasi H.
Published: August 2009

Collisionless plasma expansion into vacuum is addressed emphasizing on the kinetic effects associated with the plasma electrons. It is an important issue since there are situations in which the plasmas are in nonequilibrium state. Thus, the electron distribution function (DF) that is generally non-Maxwellian has to be modeled. For this purpose, the generalized Lorentzian (kappa) DF is used to simulate the electron DF. The Maxwellian and kappa distributions differ substantially in a high-energy tail. Thus, the electron dynamics is studied by the Vlasov equation. Neglecting the ion temperatures, fluid equations are used for them. It is shown that by increasing the population of energetic electrons, the expansion takes place faster, the resulting electric field is stronger, and the ions are accelerated to higher energy.
Magnetic pressure and shape of ferrofluid seals in cylindrical structures
Authors: Ravaud R. , Lemarquand G. , Lemarquand V.
Published: August 2009

This paper presents a three-dimensional analytical model for studying the shape and the pressure of ferrofluid seals in totally ironless structures. This three-dimensional analytical approach is based on the exact calculation of the magnetic field components created by ring permanent magnets whose polarizations are either radial or axial. We assume that the ferromagnetic particles of the ferrofluid are saturated. Moreover, the permanent magnets (neodymium iron boron) used in the considered applications create a magnetic field which is much higher than the magnetic field created by the magnetic particles in the ferrofluid so the latter is neglected. Nevertheless, the static behavior of the ferrofluid seal depends on both the magnetic field produced by the permanent magnets and the saturation magnetization of the ferrofluid particles. Furthermore, the accurate knowledge of the ferrofluid seal shape as well as the magnetic pressure inside the ferrofluid seal is very useful for the design of devices using both permanent magnets and ferrofluid seals. It is emphasized here that our structures are completely ironless and thus, there are no iron-base piston for these structures. Then, this paper makes a review of the main structures using ring permanent magnets and ferrofluid seals. For each ironless structure, the shape and the pressure of the ferrofluid seals are determined.
A remark on the dimension of the attractor for the Dirichlet problem of the complex Ginzburg–Landau equation
Authors: Karachalios Nikos I.
Published: August 2009

Using the improved lower bound on the sum of the eigenvalues of the Dirichlet Laplacian proven by Melas [Proc. Am. Math. Soc. 131, 631 (2003)], we remark on a modified estimate of the dimension of the global attractor associated with the complex Ginzburg–Landau (CGL) equation ∂tu−(λ+iα)Δu+(κ+iβ)|u|2u−γu=0, supplemented with Dirichlet boundary conditions. This modified estimate could be of significance depending on β∊R being a small parameter, an important case for the CGL system.
Observation of strain in pseudomorphic Si1−xGex by tracking phonon participation in Si∕SiGe resonant interband tunnel diodes via electron tunneling spectroscopy
Authors: Yu Ronghua , Anisha R. , Jin Niu , Chung Sung-Yong , Berger Paul R. , Gramila Thomas J. , Thompson Phillip E.
Published: August 2009

High-sensitivity and low-noise electron tunneling spectroscopy was used to measure the phonon spectra via band-to-band tunneling in Si∕SiGe resonant interband tunneling diodes (RITD), tracking the effects of the weighted average Ge percentage in the central tunneling spacer. With a composite RITD tunneling barrier consisting of 4nm of intrinsic Si0.60Ge0.40 and n nm of intrinsic Si (n=4,6,8,10) all grown on Si substrates, the transverse acoustic (TA) phonon of Si0.60Ge0.40 was identified and the energy was measured to be 16±1meV. This is higher than the ∼14meV energy of the TA phonon in Si0.60Ge0.40 reported from measurements of Esaki tunnel diodes fabricated from bulk single crystals. The increase is attributed to the compressive strain in the Si0.60Ge0.40 layer grown on Si substrates. The observation of the upshift of phonon energy with strain by electron tunneling spectroscopy demonstrates the capability of electron tunneling spectroscopy to characterize residual strain.
Determination of thickness and dielectric constant of thin films by dual-wavelength light beaming effect of a metal nanoslit
Authors: Zhang Jian , Wang Guo Ping
Published: August 2009

We report simultaneous determination of the thickness and dielectric constant of thin films by dual-wavelength (488 and 645 nm) light beaming effect of a metal nanoslit in an optically thick metal film flanked by periodic corrugations. The feasibility of the method is confirmed by the finite-difference time-domain simulations, and sensitivities of 72°/RIU (RIU, Refractive Index Unit) at 488 nm and 32°/RIU at 645 nm are obtained, respectively. The unambiguous determination of the thickness and dielectric constant of the samples by just one-step measurement as well as the compact optical geometry of the structures suggests a highly portable and robust novel sensing technology.
Contamination-free imaging by electron induced carbon volatilization in environmental scanning electron microscopy
Authors: Toth Milos , Lobo Charlene J. , Lysaght Michael J. , Vladár András E. , Postek Michael T.
Published: August 2009

Many ultraviolet, x-ray and charged particle beam techniques are inhibited by the growth of carbonaceous films caused by cross linking of hydrocarbon contaminant adsorbates. In electron microscopy, such films obscure surface features and reduce resolution. We demonstrate how resolution degradation can be alleviated using a H2O environment via gas mediated, electron beam induced carbon volatilization, a process that competes with film growth. Net behavior is a function of electron flux, which provides control over growth kinetics during imaging. Under optimized conditions, film growth can be eliminated, removing contamination as a factor limiting image information content and resolution.
Buckling and elastic stability of vertical ZnO nanotubes and nanorods
Authors: Riaz M. , Fulati A. , Amin G. , Alvi N. H. , Nur O. , Willander M.
Published: August 2009

Buckling and elastic stability study of vertical well aligned ZnO nanorods grown on Si substrate and ZnO nanotubes etched from the same nanorods was done quantitatively by nanoindentation technique. The critical load, modulus of elasticity, and flexibility of the ZnO nanorods and nanotubes were observed and we compared these properties for the two nanostructures. It was observed that critical load of nanorods (2890 μN) was approximately five times larger than the critical load of the nanotubes (687 μN). It was also observed that ZnO nanotubes were approximately five times more flexible (0.32 nm/μN) than the nanorods (0.064 nm/μN). We also calculated the buckling energies of the ZnO nanotubes and nanorods from the force displacement curves. The ratio of the buckling energies was also close to unity due to the increase/decrease of five times for one parameter (critical load) and increase/decrease of five times for the other parameter (displacement) of the two samples. We calculated critical load, critical stress, strain, and Young modulus of elasticity of single ZnO nanorod and nanotube. The high flexibility of the nanotubes and high elasticity of the ZnO nanorods can be used to enhance the efficiency of piezoelectric nanodevices. We used the Euler buckling model and shell cylindrical model for the analysis of the mechanical properties of ZnO nanotubes and nanorods.
Thermoelastic damping in micromechanical resonators
Authors: Metcalf Thomas H. , Pate Bradford B. , Photiadis Douglas M. , Houston Brian H.
Published: August 2009

We show that the dominant energy loss mechanism in plate modes of a 1.5 μm thick silicon micromechanical resonator is thermoelastic damping. In situ ultra-high vacuum annealing lowers the dissipation of two neighboring resonance modes (460 and 510 kHz) at 120 K to Q−1≤5×10−7. From 120 to 400 K, the Q−1 of these modes increase at different rates, in quantitative agreement with a modification (that accounts for mode shape) of Zener’s theory of thermoelastic damping.
The interfacial thermal conductance between a vertical single-wall carbon nanotube and a silicon substrate
Authors: Fan Hai-Bo , Zhang Kai , Yuen Matthew M. F.
Published: August 2009

Molecular dynamics simulations were conducted to investigate the interfacial thermal conductance between a functionalized single-wall carbon nanotube and a silicon substrate. Based on Fourier’s law, interfacial thermal conductance of the system with different numbers of chemical bonds was calculated. The results showed that the interfacial thermal conductance increased with the increase in the number of chemical bonds formed between the carbon nanotube and the substrate, indicating that carbon nanotube patterned on the silicon substrate by chemical functionalization can improve not only interfacial adhesion but also interfacial thermal conductance. The results also showed that a shorter chain length of the functional groups between the carbon nanotube and the substrate gave a higher interfacial thermal conductance.
Flexible active-matrix cells with selectively poled bifunctional polymer-ceramic nanocomposite for pressure and temperature sensing skin
Authors: Graz Ingrid , Krause Markus , Bauer-Gogonea Simona , Bauer Siegfried , Lacour Stephanie P. , Ploss Bernd , Zirkl Martin , Stadlober Barbara , Wagner Sigurd
Published: August 2009

A monolithically integrated bifunctional frontplane is introduced to large area electronics. The bifunctional frontplane element is based on a composite foil of piezoelectric ceramic lead titanate nanoparticles embedded in a ferroelectric poly(vinylidene fluoride trifluoroethylene) polymer matrix. Bifunctionality to pressure and temperature changes is achieved by a sequential, area selective two-step poling process, where the polarization directions in the nanoparticles and the ferroelectric polymer are adjusted independently. Thereby, sensor elements that are only piezoelectric or only pyroelectric are achieved. The frontplane foil is overlaid on a thin-film transistor backplane. Our work constitutes a step toward multifunctional frontplanes for large area electronic surfaces.
On the Ehrenfest theorem of quantum mechanics
Authors: Friesecke Gero , Koppen Mario
Published: August 2009

We give a mathematically rigorous derivation of Ehrenfest’s equations for the evolution of position and momentum expectation values under general and natural assumptions which include atomic and molecular Hamiltonians with Coulomb interactions.
Dependence of the low to high confinement mode transition power threshold and turbulence flow shear on injected torque
Authors: Schlossberg D. J. , McKee G. R. , Fonck R. J. , Burrell K. H. , Gohil P. , Groebner R. J. , Shafer M. W. , Solomon W. M. , Wang G.
Published: August 2009

The power required to induce a bifurcation from a low-confinement mode to a high-confinement mode in DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] plasmas is found to depend sensitively on the injected neutral beam torque and consequent toroidal rotation. Plasmas exhibit a factor of 2–4 reduction in this power threshold, dependent on ion ∇B drift direction. Correlated with this change, turbulence velocity measurements near 0.9<r/a<1.0 for balanced injection demonstrate significantly larger poloidal flow shear at a given injection power, relative to cocurrent injection, facilitating the confinement transition.
Gaussian wave packet states of scalar fields in a universe of de Sitter
Authors: Lopes C. E. F. , Pedrosa I. A. , Furtado C. , de M. Carvalho A. M.
Published: August 2009

In this work, we study quantum effects of a massive scalar field in the de Sitter spacetime. We reduce the problem to that of a time-dependent harmonic oscillator and use exact linear invariants and the dynamic invariant method to derive the corresponding Schrödinger states in terms of solutions of a second order ordinary differential equation. Afterwards, we construct Gaussian wave packet states and calculate the quantum dispersions as well as the quantum correlations for each mode of the quantized scalar field. It is further shown that the center of the Gaussian wave packet remains trapped in the origin.
Electrical transport in laser-crystallized polycrystalline silicon-germanium thin-films
Authors: Scheller L.-P. , Weizman M. , Nickel N. H. , Yan B.
Published: August 2009

We report on the electrical transport properties of intentionally undoped, laser-crystallized polycrystalline silicon-germanium thin-films. The electrical transport in this material strongly depends on the alloy composition and the crystallization procedure. At low temperatures the undoped germanium-rich samples show an unexpected high p-type conductivity with a weak temperature dependence. Posthydrogenation results in a pronounced decrease in the conductivity and a change in the dominating low temperature transport behavior. The results are discussed in terms of a grain-boundary dominated transport model.
Exploring Ce3+/Ce4+ cation ordering in reduced ceria nanoparticles using interionic-potential and density-functional calculations
Authors: Migani Annapaola , Neyman Konstantin M. , Illas Francesc , Bromley Stefan T.
Published: August 2009

The performance of atomistic calculations using interionic potentials has been examined in detail with respect to the structures and energetic stabilities of ten configurational isomers (i.e., distinct Ce3+/Ce4+ cationic orderings) of a low energy octahedral ceria nanoparticle Ce19O32. The outcome of these calculations is compared with the results of corresponding density-functional (DF) calculations employing local and gradient corrected functionals with an additional corrective onsite Coulombic interaction applied to the f-electrons (i.e., LDA+U and GGA+U, respectively). Strikingly similar relative energy ordering of the isomers and atomic scale structural trends (e.g., cation-cation distances) are obtained in both the DF and interionic-potential calculations. The surprisingly good agreement between the DF electronic structure calculations and the relatively simple classical potentials is not found to be due to a single dominant interaction type but is due to a sensitive balance between long range electrostatics and local bonding contributions to the energy. Considering the relatively high computational cost and technical difficulty involved in obtaining charge-localized electronic solutions for reduced ceria using DF calculations, the use of interionic potentials for rapid and reliable preselection of the most stable Ce3+/Ce4+ cationic orderings is of considerable benefit.
The effects of target mounts in direct-drive implosions on OMEGA
Authors: Igumenshchev I. V. , Marshall F. J. , Marozas J. A. , Smalyuk V. A. , Epstein R. , Goncharov V. N. , Collins T. J. B. , Sangster T. C. , Skupsky S.
Published: August 2009

The effects of two types of target mounts, stalks and spider silks, on the implosion of both room-temperature D2-gas-filled shells and cryogenic D2-ice-filled shells have been studied both experimentally and by means of two-dimensional simulations. The simulations indicate that the hydrodynamic effect of the expanding plasma created by the ablation of material from the target mounts and refraction of laser light by this plasma induce perturbations in the imploding shell that are damaging to the implosion. The spider silks are the more-damaging type of mount since the silks (typically four) are arrayed over the target surface, whereas the stalk (typically one) meets the target at a single point. Stalks are therefore preferred over silks as a target mount. The scale and magnitude of the perturbations induced by the spider silks have been verified by planar-target experiments performed on the OMEGA laser [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1995)]. The perturbations predicted by simulations to arise from stalks qualitatively agree with the results of implosion experiments using Ti-doped plastic shells.
Substrate Fermi level effects in photocatalysis on oxides: Properties of ultrathin TiO2/Si films
Authors: Kazazis D. , Guha S. , Bojarczuk N. A. , Zaslavsky A. , Kim H.-C.
Published: August 2009

Photocatalysis has widespread applications from solar cells to photolithography. We studied the photocatalytic properties of TiO2 films of thicknesses down to 2 nm, grown on n-type and p-type silicon wafers, using the oxidation of isopropanol as a model system. Direct in vacuo mass spectrometry measurements were performed under irradiation above the TiO2 bandgap. We present a model consistent with our experimental results, which indicate that only near-surface electron-hole pair generation is relevant and that the reaction rate can be controlled by varying the substrate Fermi level in going from n-type to p-type silicon, by approximately a factor of 2.
High dielectric permittivity in semiconducting Pr0.6Ca0.4MnO3 filled polyvinylidene fluoride nanocomposites with low percolation threshold
Authors: Devi Chandrasekhar K. , Venimadhav A. , Das A. K.
Published: August 2009

Semiconducting Pr0.6Ca0.4MnO3 nanoparticles with width of ∼50nm and length ∼80–150nm were prepared by sol-gel method. The dielectric behavior of Pr0.6Ca0.4MnO3, polyvinylidene fluoride composites was investigated by varying the Pr0.6Ca0.4MnO3 volume fraction and frequency. The percolation threshold of the composites was found to be 0.1 and an enhanced effective dielectric permittivity of ∼700 with low dielectric loss of ∼0.3 at 103Hz near the percolation threshold was observed. The low percolation threshold was attributed to the nanosize and nonspherical shape of the filler particles, and the enhanced dielectric properties have been explained by using boundary layer capacitance effect and percolation theory.
A finite excluded volume bond-fluctuation model: Static properties of dense polymer melts revisited
Authors: Wittmer J. P. , Cavallo A. , Kreer T. , Baschnagel J. , Johner A.
Published: August 2009

The classical bond-fluctuation model (BFM) is an efficient lattice Monte Carlo algorithm for coarse-grained polymer chains where each monomer occupies exclusively a certain number of lattice sites. In this paper we propose a generalization of the BFM where we relax this constraint and allow the overlap of monomers subject to a finite energy penalty ε. This is done to vary systematically the dimensionless compressibility g of the solution in order to investigate the influence of density fluctuations in dense polymer melts on various static properties at constant overall monomer density. The compressibility is obtained directly from the low-wave vector limit of the static structure factor. We consider, e.g., the intrachain bond-bond correlation function P(s) of two bonds separated by s monomers along the chain. It is shown that the excluded volume interactions are never fully screened for very long chains. If distances smaller than the thermal blob size are probed (s⪡g) the chains are swollen according to the classical Fixman expansion where, e.g., P(s)∼g−1s−1/2. More importantly, the polymers behave on larger distances (s⪢g) like swollen chains of incompressible blobs with P(s)∼g0s−3/2.
Speed determination of single Sr adatoms moving within Si(111)-7×7 half unit cells
Authors: Zhachuk R. , Teys S. , Olshanetsky B. , Pereira S.
Published: August 2009

In this paper we report on the motion of individual Sr adatoms within the limits of Si(111)-7×7 half unit cells (HUCs). The fast movement of the atom at the Si surface produces sharp signal fluctuations in scanning tunneling microscopy (STM) images resulting into noiselike patches. It is found that the length of the observed image streaks is a function of the scanning tip velocity. A Monte Carlo simulation implementing a model of independently moving Sr adatom and scanning tip, accounts for the observed STM image features quantitatively. Thus, by colleting STM images at various scanning speeds and matching simulated image features to the experimental observations, allows the average speed of Sr adatom within the limits of Si(111)-7×7 HUC to be estimated: 300 nm/s.
Three-dimensional flow driven by iso- and counter-rotation of a shallow pool and a disk on the free surface
Authors: Li You-Rong , Wu Chun-Mei , Wu Shuang-Ying , Peng Lan
Published: August 2009

In order to understand the fundamental characteristics of the forced flow driven by iso- and counter-rotation of a shallow pool and a disk on the free surface, we conducted a series of unsteady three-dimensional numerical simulations in a shallow pool. The ratio of the disk to pool radius is Rs=0.3 and the aspect ratio of pool is H=0.06. The results indicated that the forced flow driven by disk and pool rotation is axisymmetric and steady at the small rotation Reynolds number. However, when Reynolds number exceeds a critical value, the flow will undergo a transition to three-dimensional oscillatory flow, which is characterized by the velocity fluctuation waves traveling in the azimuthal direction. The propagating direction and the velocity of the waves depend on the rotation rates and directions of the disk and pool. Besides, the critical conditions for the onset of the oscillatory flow were determined. The details of the flow fields were discussed and the mechanism of the flow pattern transition was also exhibited.
Planar S-(S/F)-S Josephson junctions induced by the inverse proximity effect
Authors: Vávra O. , Pfaff W. , Strunk Ch.
Published: August 2009

We present a utilization of the inverse proximity effect in superconductor-ferromagnet (S-F) bilayer to generate lateral Josephson junctions. The weak link is created by a Pd0.95Fe0.05 strip across a Nb bridge. Close to TC and in perpendicular magnetic field the junctions exhibit a modulation of the critical current IC(B) similar to a Fraunhofer interference pattern which proves the dc Josephson effect. The structure contains three weak links (two different areas) in series which result in the observation of two periods scalable with the areas penetrated by magnetic flux. Measurements of Shapiro steps prove the presence of the ac Josephson effect.
Observation of electron tunneling induced photon emission in gallium (Ga) doped (1%) zinc oxide (ZnO) sample using scanning tunneling microscopy
Authors: Dey Shirshendu , Shinde S. D. , Adhi K. P. , Dharmadhikari C. V.
Published: August 2009

Electron tunneling induced photon emission in gallium doped (1%) zinc oxide was detected by scanning tunneling microscope in ambient condition. Simultaneously acquired topography and photon maps reveal interesting correlation. Photon maps depict few intense emission spots. Existence of a threshold tunneling current (6 nA) and applied bias (1.8 V), for detectable photon emission was observed. Further analysis of the results suggests Fowler-type photon emission which is ascribed to radiative electron-hole recombination. Localized photon emission spectroscopy exhibits prominent peaks at hν=2.96, 3.43, and 3.80 eV, which match well with the results obtained from photoluminescence studies.
Dielectric response of high permittivity polymer ceramic composite with low loss tangent
Authors: Subodh G. , Deepu V. , Mohanan P. , Sebastian M. T.
Published: August 2009

The present communication investigates the dielectric response of the Sr9Ce2Ti12O36 ceramics loaded high density polyethylene and epoxy resin. Sr9Ce2Ti12O36 ceramic filled polyethylene and epoxy composites were prepared using hot blending and mechanical mixing, respectively. 40 vol % ceramic loaded polyethylene has relative permittivity of 12.1 and loss tangent of 0.004 at 8 GHz, whereas the corresponding composite using epoxy as matrix has permittivity and loss tangent of 14.1 and 0.022, respectively. The effective medium theory fits relatively well for the observed permittivity of these composites.
Quasi-single-crystal (001) SrTiO3 templates on Si
Authors: Park J. W. , Baek S. H. , Bark C. W. , Biegalski M. D. , Eom C. B.
Published: August 2009

The integration of multifunctional oxides on semiconductor devices requires the formation of single-crystal-like oxide templates directly on silicon. We report the fabrication of quasi-single-crystal (001) SrTiO3 templates on (001) Si by annealing 100 nm thick molecular beam epitaxy-grown epitaxial SrTiO3 films at 900 °C. The full width at half maximum of the (002) rocking curve is 0.006°, which is much narrower than SrTiO3 bulk single crystals. An atomically smooth TiO2-terminated surface is obtained by buffered-HF etching, which allows us to create functional oxide heterointerfaces on Si. Epitaxial SrRuO3 thin films grown on the quasi-single-crystal SrTiO3 template exhibit a superior crystalline quality and surface morphology.
Stress-induced anomalous shift of optical band gap in ZnO:Al thin films
Authors: Mohanty Bhaskar Chandra , Jo Yeon Hwa , Yeon Deuk Ho , Choi Ik Jin , Cho Yong Soo
Published: August 2009

Thickness-dependent stress relaxation and its unreported effect on optical band gap of Al-doped ZnO thin films have been investigated. The thinnest film (∼84 nm) had a stress of −8.39×109 Nm−2, carrier concentration of 1.73×1019 cm−3 and optical band gap of 3.69 eV, a value significantly higher than the reported ones. With increase in thickness, magnitude of the stress decreased, and correspondingly a redshift of fundamental absorption band edge was observed. A linear dependence of optical band gap on stress in the films with a coefficient of 54.6 meV/GPa has been observed.
Efficiency of dye sensitized solar cells based on TiO2 nanotubes filled with nanoparticles
Authors: Alivov Yahya , Fan Z. Y.
Published: August 2009

From comparative studies of dye sensitized solar cell (DSSCs) fabricated using nanotubes (NTs) filled with nanoparticles (NPs) and empty NTs it is shown that filling of TiO2 NTs with NPs significantly increase efficiency of DSSCs. This increase depended on NT diameter and was found to be 17.4%, 55.6%, and 131% for solar cells with 40 nm, 80 nm, and 160 nm diameter NTs. The highest efficiency was observed for samples with 80 nm diameter NTs, which was 5.94% for ∼5 μm NT thickness DSSCs.
Negative differential resistance based on electron injection/extraction in conducting organic films
Authors: Xie Xian Ning , Gao Xingyu , Wang Yuzhan , Wang Junzhong , Loh Kian Ping , Wee Andrew Thye Shen
Published: August 2009

This work reports a mechanism of negative differential resistance (NDR) observed for perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) films. The NDR is based on electron injection and extraction at the metal/PTCDA interface, and is governed by the joint effect of electronic and ionic components. Consequently, the NDR behavior exhibits a monotonous dependence on the voltage scan rate, and the number of NDR peaks is also sensitive to the work function of metal electrodes. The results provide further understanding on the diverse manifestation of NDR, and would be useful in organic electronic applications.
Defect reduction in epitaxial GaSb grown on nanopatterned GaAs substrates using full wafer block copolymer lithography
Authors: Jha Smita , Liu C.-C. , Kuan T. S. , Babcock S. E. , Nealey P. F. , Park J. H. , Mawst L. J. , Kuech T. F.
Published: August 2009

Defect reduction in the large lattice mismatched system of GaSb on GaAs, ∼7%, was accomplished using full wafer block copolymer (BCP) lithography. A self-assembled BCP mask layer was used to generate a hexagonal pattern of ∼20 nm holes on ∼40 nm centers in a 20 nm SiO2 layer. GaSb growth initially takes place selectively within these holes leading to a dense array of small, strain-relaxed epitaxial GaSb islands. The GaSb grown on the patterned SiO2 layer exhibits a reduction in the x-ray linewidth attributed to a decrease in the threading dislocation density when compared to blanket pseudomorphic film growth.
Density functional study on ferromagnetism in nitrogen-doped anatase TiO2
Authors: Tao J. G. , Guan L. X. , Pan J. S. , Huan C. H. A. , Wang L. , Kuo J. L. , Zhang Z. , Chai J. W. , Wang S. J.
Published: August 2009

We report first principles calculations on the magnetism and electronic structures for nitrogen-doped anatase TiO2 (N:TiO2). Our calculations indicate that magnetic state is the ground state for N:TiO2 systems. An isolated N atom produces a total magnetic moment of 1.00μB and introduces spin-polarized 2p states in the band gap. The origin of the magnetic moments is the holes in N 2p π band of the N dopant. Several doping configurations studied suggest the existence of ferromagnetic coupling between N dopants. The ferromagnetism in N:TiO2 can be attributed to the hole-mediated double exchange through the strong p-p interaction between N and O.
Fluctuation theory of single-file diffusion
Authors: Felderhof B. U.
Published: August 2009

In a one-dimensional suspension of Brownian particles, which cannot pass each other, the mean square displacement of a selected particle grows at long times with the square root of time, rather than linearly. It is shown that the coefficient of the square root, the so-called single-file mobility, can be derived from fluctuation theory, involving the velocity time scale and the fluctuation-dissipation theorem. The single-file mobility is expressed in terms of the collective diffusion coefficient and the isothermal osmotic compressibility, in agreement with the result derived earlier by Kollmann on the basis of the generalized Smoluchowski equation [M. Kollmann, Phys. Rev. Lett. 90, 180602 (2003)].
Probing the structural, crystalline, and electrical properties of carbon nanotubes grown on nickel filled carbon nanofibers
Authors: Zhang Hongxin , Feng Peter X. , Jin Peng , Makarov Vladimir I. , Fonseca Luis , Morell Gerardo , Weiner Brad R.
Published: August 2009

Carbon nanotubes (CNTs) were produced on nickel filled carbon nanofiber substrates. The carbon source was provided by irradiation of pyrolytic graphite. The mean outer diameter of the CNTs, which was identified as multiwalled carbon nanotubes, varies in the range of 5–15 nm. The crystallographic structures, chemical compositions, and bond structures of the carbon materials were investigated. The modified crystal structure was attributed to better lattice arrangement resulting from increased lattice vibration at high substrate temperature. The improved electron field emission behavior of the obtained sample at higher temperature could be caused by the increasing effective emission sites.
On structural correlations in the percolation of hard-core particles
Authors: Miller Mark A.
Published: August 2009

Percolation in colloidal suspensions is sometimes simulated by the random insertion of impenetrable particles into a box. However, configurations generated in this way are not representative of an equilibrated suspension. Here, we quantify the effect of the insertion method on the percolation threshold for systems of spherical particles.
Analysis of charge loss in nonvolatile memory with multi-layered SiC nanocrystals
Authors: Lee Dong Uk , Lee Tae Hee , Kim Eun Kyu , Shin Jin-Wook , Cho Won-Ju
Published: August 2009

A nonvolatile memory device with multilayered SiC nanocrystals for long-term data storage was fabricated, and its electrical properties were analyzed. The average size and density of the SiC nanocrystals, which were formed between the tunnel and control oxide layers, were approximately 5 nm and 2×1012 cm−2, respectively. The memory window of nonvolatile memory with the multilayer of SiC nanocrystals was about 2.5 V after program and erase voltages of ±12 V were applied for 500 ms, and then it was maintained at about 1.1 V for 105 s at 75 °C. The activation energy estimated from charge losses of 25% to 50% increased from 0.03 to 0.30 eV, respectively. The charge loss could be caused by a Pool–Frenkel current of holes and electrons between the SiC quantum dots and the carrier charge traps around the SiC nanocrystals embedded in SiO2 or the degradation effect of the tunnel oxide by stress induced leakage current.
Social bonds between unrelated females increase reproductive success in feral horses
Authors: Cameron Elissa Z. , Setsaas Trine H. , Linklater Wayne L.
Published: August 2009

In many mammals, females form close social bonds with members of their group, usually between kin. Studies of social bonds and their fitness benefits have not been investigated outside primates, and are confounded by the relatedness between individuals in primate groups. Bonds may arise from kin selection and inclusive fitness rather than through direct benefits of association. However, female equids live in long-term social groups with unrelated members. We present 4 years of behavioral data, which demonstrate that social integration between unrelated females increases both foal birth rates and survival, independent of maternal habitat quality, social group type, dominance status, and age. Also, we show that such social integration reduces harassment by males. Consequently, social integration has strong direct fitness consequences between nonrelatives, suggesting that social bonds can evolve based on these direct benefits alone. Our results support recent studies highlighting the importance of direct benefits in maintaining cooperative behavior, while controlling for the confounding influence of kinship.
Independent evolution of knuckle-walking in African apes shows that humans did not evolve from a knuckle-walking ancestor
Authors: Kivell Tracy L. , Schmitt Daniel
Published: August 2009

Despite decades of debate, it remains unclear whether human bipedalism evolved from a terrestrial knuckle-walking ancestor or from a more generalized, arboreal ape ancestor. Proponents of the knuckle-walking hypothesis focused on the wrist and hand to find morphological evidence of this behavior in the human fossil record. These studies, however, have not examined variation or development of purported knuckle-walking features in apes or other primates, data that are critical to resolution of this long-standing debate. Here we present novel data on the frequency and development of putative knuckle-walking features of the wrist in apes and monkeys. We use these data to test the hypothesis that all knuckle-walking apes share similar anatomical features and that these features can be used to reliably infer locomotor behavior in our extinct ancestors. Contrary to previous expectations, features long-assumed to indicate knuckle-walking behavior are not found in all African apes, show different developmental patterns across species, and are found in nonknuckle-walking primates as well. However, variation among African ape wrist morphology can be clearly explained if we accept the likely independent evolution of 2 fundamentally different biomechanical modes of knuckle-walking: an extended wrist posture in an arboreal environment (
Pan
) versus a neutral, columnar hand posture in a terrestrial environment (
Gorilla
). The presence of purported knuckle-walking features in the hominin wrist can thus be viewed as evidence of arboreality, not terrestriality, and provide evidence that human bipedalism evolved from a more arboreal ancestor occupying the ecological niche common to all living apes.
Structural basis of yeast Tim40/Mia40 as an oxidative translocator in the mitochondrial intermembrane space
Authors: Kawano Shin , Yamano Koji , Naoé Mari , Momose Takaki , Terao Kayoko , Nishikawa Shuh-ichi , Watanabe Nobuhisa , Endo Toshiya
Published: August 2009

The mitochondrial intermembrane space (IMS) contains many small cysteine-bearing proteins, and their passage across the outer membrane and subsequent folding require recognition and disulfide bond transfer by an oxidative translocator Tim40/Mia40 in the inner membrane facing the IMS. Here we determined the crystal structure of the core domain of yeast Mia40 (Mia40C4) as a fusion protein with maltose-binding protein at a resolution of 3 Å. The overall structure of Mia40C4 is a fruit-dish-like shape with a hydrophobic concave region, which accommodates a linker segment of the fusion protein in a helical conformation, likely mimicking a bound substrate. Replacement of the hydrophobic residues in this region resulted in growth defects and impaired assembly of a substrate protein. The Cys296-Cys298 disulfide bond is close to the hydrophobic concave region or possible substrate-binding site, so that it can mediate disulfide bond transfer to substrate proteins. These results are consistent with the growth phenotypes of Mia40 mutant cells containing Ser replacement of the conserved cysteine residues.
Engineering of bio-hybrid materials by electrospinning polymer-microbe fibers
Authors: Liu Ying , Rafailovich Miriam H. , Malal Ram , Cohn Daniel , Chidambaram Dev
Published: August 2009

Although microbes have been used in industrial and niche applications for several decades, successful immobilization of microbes while maintaining their usefulness for any desired application has been elusive. Such a functionally bioactive system has distinct advantages over conventional batch and continuous-flow microbial reactor systems that are used in various biotechnological processes. This article describes the use of polyethylene oxide
99
-polypropylene oxide
67
-polyethylene oxide
99
triblock polymer fibers, created via electrospinning, to encapsulate microbes of 3 industrially relevant genera, namely,
Pseudomonas
,
Zymomonas
, and
Escherichia
. The presence of bacteria inside the fibers was confirmed by fluorescence microscopy and SEM. Although the electrospinning process typically uses harsh organic solvents and extreme conditions that generally are harmful to bacteria, we describe techniques that overcome these limitations. The encapsulated microbes were viable for several months, and their metabolic activity was not affected by immobilization; thus they could be used in various applications. Furthermore, we have engineered a microbe-encapsulated cross-linked fibrous polymeric material that is insoluble. Also, the microbe-encapsulated active matrix permits efficient exchange of nutrients and metabolic products between the microorganism and the environment. The present results demonstrate the potential of the electrospinning technique for the encapsulation and immobilization of bacteria in the form of a synthetic biofilm, while retaining their metabolic activity. This study has wide-ranging implications in the engineering and use of novel bio-hybrid materials or biological thin-film catalysts.
Mitochondrial bioenergetic deficit precedes Alzheimer's pathology in female mouse model of Alzheimer's disease
Authors: Yao Jia , Irwin Ronald W. , Zhao Liqin , Nilsen Jon , Hamilton Ryan T. , Brinton Roberta Diaz
Published: August 2009

Mitochondrial dysfunction has been proposed to play a pivotal role in neurodegenerative diseases, including Alzheimer's disease (AD). To address whether mitochondrial dysfunction precedes the development of AD pathology, we conducted mitochondrial functional analyses in female triple transgenic Alzheimer's mice (3xTg-AD) and age-matched nontransgenic (nonTg). Mitochondrial dysfunction in the 3xTg-AD brain was evidenced by decreased mitochondrial respiration and decreased pyruvate dehydrogenase (PDH) protein level and activity as early as 3 months of age. 3xTg-AD mice also exhibited increased oxidative stress as manifested by increased hydrogen peroxide production and lipid peroxidation. Mitochondrial amyloid beta (Aβ) level in the 3xTg-AD mice was significantly increased at 9 months and temporally correlated with increased level of Aβ binding to alcohol dehydrogenase (ABAD). Embryonic neurons derived from 3xTg-AD mouse hippocampus exhibited significantly decreased mitochondrial respiration and increased glycolysis. Results of these analyses indicate that compromised mitochondrial function is evident in embryonic hippocampal neurons, continues unabated in females throughout the reproductive period, and is exacerbated during reproductive senescence. In nontransgenic control mice, oxidative stress was coincident with reproductive senescence and accompanied by a significant decline in mitochondrial function. Reproductive senescence in the 3xTg-AD mouse brain markedly exacerbated mitochondrial dysfunction. Collectively, the data indicate significant mitochondrial dysfunction occurs early in AD pathogenesis in a female AD mouse model. Mitochondrial dysfunction provides a plausible mechanistic rationale for the hypometabolism in brain that precedes AD diagnosis and suggests therapeutic targets for prevention of AD.