bluuebunny/crossref_metadata_2025 huggingface dataset:
Mixing enhancement behind a backward-facing step using tabs
Authors: Park Hyungmin , Jeon Woo-Pyung , Choi Haecheon , Yoo Jung Yul
Published: October 2007

Mixing enhancement behind a backward-facing step is experimentally investigated using multiple tabs located at the edge of the backward-facing step. The Reynolds number is 24000 based on the free-stream velocity and step height with a turbulent boundary layer flow at the inlet. A parametric study is performed to find the optimal tab configuration of minimizing the reattachment length. The parameters of the tab are its height and spanwise width, and the spanwise spacing between two adjacent tabs. For each tab configuration, we measure the reattachment length and wall pressure, and for the optimal configuration the streamwise velocity behind the step. For most tab configurations considered, the reattachment length decreases and turbulence intensity increases at almost all spanwise locations. The reattachment length and wall pressure show significant variations along the spanwise direction. It is found that the tabs introduce strong three-dimensional disturbances to the separating shear layer by producing a pair of counter-rotating streamwise vortices and entrain high momentum fluids into the recirculation region, which greatly enhances mixing behind the backward-facing step.
Measurement of the ion drag force in a collisionless plasma with strong ion-grain coupling
Authors: Nosenko V. , Fisher R. , Merlino R. , Khrapak S. , Morfill G. , Avinash K.
Published: October 2007

The ion drag force acting on dust grains was measured experimentally in a low-pressure Ar plasma in the regime of strong ion-grain coupling. Argon ions were drifting in the axial ambipolar electric field naturally present in a hot-filament dc discharge plasma. Following the method of Hirt et al. [Phys. Plasmas 11, 5690 (2004)], hollow glass microspheres were dropped into the plasma and allowed to fall due to gravity. The ion drag force was derived from the particle trajectory deflection from the vertical direction. The result is in reasonable agreement with a theoretical model that takes strong ion-grain coupling into account.
Dielectric relaxation and polar phonon softening in relaxor ferroelectric PbMg1/3Ta2/3O3
Authors: Kamba S. , Nuzhnyy D. , Veljko S. , Bovtun V. , Petzelt J. , Wang Y. L. , Setter N. , Levoska J. , Tyunina M. , Macutkevic J. , Banys J.
Published: October 2007

Relaxor ferroelectric PbMg1/3Ta2/3O3 ceramics and thin films were investigated by means of broad-band dielectric, time-domain terahertz (THz), and Fourier-transform infrared (IR) spectroscopy in the frequency range 100 Hz–90 THz at temperatures 100–490 K; the THz and IR spectra were studied from 20 to 900 K. A diffused and strongly temperature dependent peak in the complex permittivity is caused by a dielectric relaxation due to the dynamics of polar clusters. The relaxation appears below the Burns temperature Td in the THz range; it slows down on cooling through the microwave and MHz range and anomalously broadens. The shortest and longest relaxation times of the distribution of relaxation times follow Arrhenius and Vogel–Fulcher laws, respectively. The degree of the B-site order has only a small influence on the parameters of the dielectric relaxation and almost no influence on the phonon parameters. Below Tm≅180 K the distribution of relaxation frequencies becomes broader than our experimental spectral range, and frequency independent dielectric losses develop below 100 GHz in the spectra. Although the macroscopic crystal structure is cubic, IR spectra give evidence about the lower local symmetry, which can be assigned to the presence of the polar clusters below Td. Infrared spectra above Td still reveal more modes than predicted by selection rules in the paraelectric phase of the Fm3¯m space group so that we suggest selection rules which take into account chemical inhomogeneity in the β″-perovskite sublattice.
Synthesis of epitaxial BiFeO3 films by chemical solution deposition on Pt(100)
Authors: Tyholdt Frode , Fjellvåg Helmer , Gunnæs Anette Eleonora , Olsen Arne
Published: October 2007

Thin (012) oriented epitaxial films of rhombohedral (R3c) BiFeO3, ∼120 nm thickness, were obtained by means of chemical solution deposition on MgO(100)/Pt(100) substrates using an alkoxide based precursor system. X-ray diffraction and transmission electron microscopy (TEM) analysis confirmed good epitaxial matching to the substrate. The results show that careful control of the bismuth excess used for counterbalancing evaporation during crystallization is required. In contrast to lead-containing systems such as PZT, where Pb is pushed to the surface by the crystallization front where it evaporates, the Bi excess forms a Bi-rich phase at the BiFeO3/Pt interface. This phase is believed to represent a Fe substituted version of the high temperature phase δ-Bi2O3. TEM analysis shows that this phase grows on the substrate with (111) and (001) orientation. It is further found that BiFeO3 grows with (012) orientation on this phase as well, making an overall epitaxial film of BiFeO3 possible. Crystallization theory was applied to explain the presence of a Bi-rich secondary phase.
Influence of light on the Debye screening length in III–V, ternary, and quaternary materials
Authors: Ghatak K. P. , Bhattacharya S.
Published: October 2007

We study the electron energy spectrum and the Debye screening length (DSL) for III–V, ternary, and quaternary materials in the presence of light waves, whose unperturbed energy band structures are defined by the three-band model of Kane. The solution of the Boltzmann transport equation on the basis of this newly formulated electron dispersion law will introduce new physical ideas and experimental findings in the presence of external photoexcitation. It has been found taking n-InAs, n-InSb, n-Hg1−xCdxTe, and n-In1−xGaxAsyP1−y lattice matched to InP, as examples that the DSL decreases with the increase in electron concentration, intensity, and wavelength, respectively in various manners. The strong dependence of the DSL on both light intensity and wavelength reflects the direct signature of light waves which is in contrast as compared with the corresponding bulk specimens of the said materials in the absence of external photoexcitation. The rate of change is totally band structure dependent and is significantly influenced by the presence of the different energy band constants. The classical DSL equation in the absence of light waves has been obtained as a special case of the present analysis under certain limiting conditions and this compatibility is the indirect test of our generalized formalism. We have also suggested an experimental method of determining the DSL in degenerate materials having arbitrary dispersion laws.
Thermal conductivity of YbB44Si2
Authors: Mori Takao , Martin Joshua , Nolas George
Published: October 2007

The low temperature thermal conductivity of YbB44Si2 is investigated. The rare earth boron icosahedra compounds are of interest as potential high temperature thermoelectric materials. The thermal conductivity of YbB44Si2 is relatively large below room temperature, showing crystalline behavior and having a peak exceeding 10 W/m/K at ∼35 K. This departs markedly from the low amorphouslike behavior observed in another rare-earth-containing boron cluster compound: RB66 (R=rare earth). From a comparison and consideration of the various models, we conclude that disorder is the important factor in the generally observed low thermal conductivities of these compounds, with RB66 being exceptionally disordered as compared to YbB44Si2.
Magnetic-electric properties of epitaxial multiferroic NiFe2O4–BaTiO3 heterostructure
Authors: Deng Chaoyong , Zhang Yi , Ma Jing , Lin Yuanhua , Nan Ce-Wen
Published: October 2007

A simple epitaxial heterostructure of NiFe2O4–BaTiO3 grown on (001)-SrTiO3 substrate was prepared via pulsed laser deposition. Structural characterization by x-ray diffraction and electron microscopy showed good horizontal heterostructure of (001)-NiFe2O4‖(001)-BaTiO3 epitaxially grown on the substrate, which presents simultaneously strong ferroelectric and ferromagnetic responses at room temperature. In particular, an obvious direct magnetoelectric coupling was observed in the heterostructured film, which provides a convincing measurement of the direct magnetoelectric effect in the multiferroic nanostructures.
Current-induced wave propagation on surfaces of voids in metallic thin films with high symmetry of surface diffusional anisotropy
Authors: Koronaki Eleni D. , Gungor M. Rauf , Siettos Constantinos I. , Maroudas Dimitrios
Published: October 2007

We report results of a systematic theoretical analysis of the electromigration driven morphological evolution of voids in metallic thin films based on self-consistent numerical simulations according to a fully nonlinear surface transport model that accounts for surface diffusional anisotropy. The analysis focuses on film planes with high symmetry of surface diffusional anisotropy. The simulations indicate that under very low anisotropy strengths, there is indeed the possibility of current driven wave propagation on the void surface. Specifically, surface waves appear prior to film failure over a broad range of electric field strengths: from very weak to quite strong. These interesting phenomena appear only at negative misorientation angles between the electric field direction and fast directions of surface diffusion for very low anisotropy strengths. However, for a slight increase in the anisotropy strength, current-induced wave propagation is observed also in the case of positive misorientation angles.
Pentacene and ZnO hybrid channels for complementary thin-film transistor inverters operating at 2V
Authors: Oh Min Suk , Hwang D. K. , Lee Kimoon , Choi Won Jun , Kim Jae Hoon , Im Seongil , Lee Seungjun
Published: October 2007

We report on the fabrication of complementary thin-film transistor (TFT) inverter with organic-inorganic hybrid channels. By adopting organic-pentacene p channel and inorganic-ZnO n channel, we have fabricated a model device of hybrid complementary TFT inverters at a low channel deposition temperature below 100°C. Although those p and n channels were deposited on high-temperature-processed thin gate oxide/p-Si here, our complementary device demonstrated good potentials toward air-stable logic applications, operating with an excellent voltage gain of ∼26 at 2V as well as with a dynamic response of ∼10ms.
Formation of self-organized platinum nanoparticles and their microphotoluminescence enhancement in the visible light region
Authors: Kang Chieh-Yu , Chao Cha-Hsin , Shiu Shu-Chia , Chou Li-Jen , Chang Mu-Tung , Lin Gong-Ru , Lin Ching-Fuh
Published: October 2007

Formation of Pt nanoparticles or nanoisland films as a function of annealing temperature, initial thickness, underlying substrates, and annealing process is investigated. Using microphotoluminescence (PL) measurement, we find great enhancement of self-emission in visible spectrum from Pt nanoparticles. The integral intensity of the micro-PL of the 49.38nm Pt nanoparticles is 38 times of that of the Pt thin film. In addition, the peak wavelength varies from 554to615nm as the surface morphology of Pt changes due to different annealing parameters. Spectral analyses suggest that this enhancement of micro-PL from Pt is due to the local field enhancement mechanism analogous to that of PL from noble metals.
Features of self-organization in ion modified nanocrystalline plasma vapor deposited AlTiN coatings under severe tribological conditions
Authors: Fox-Rabinovich G. , Veldhuis S. C. , Kovalev A. I. , Wainstein D. L. , Gershman I. S. , Korshunov S. , Shuster L. S. , Endrino J. L.
Published: October 2007

Features of self-organization in the hard AlTiN plasma vapor deposited (PVD) coatings have been investigated under severe frictional conditions associated with high temperatures and stresses, which are typical for high-speed cutting. Aluminum-rich (around 67at.%) (Al67Ti33)N hard PVD coating has been modified by means of the “duplex” post-treatment, including annealing in vacuum at 700°C with subsequent ion implantation by Ar+. Structure modification of the surface layer has been studied using x-ray photoelectron spectroscopy, electron energy loss fine structure, and high resolution electron energy loss spectroscopy methods. Micromechanical characteristics of the coating have been studied using the nanoindentation method. Coefficient of friction was measured in relation to temperature. Wear behavior of the coating has been investigated under severe conditions of HSC of 1040 steel. Results show that the enhancement of nonequilibrium processes during friction due to ion implantation of AlTiN coating by Ar+ leads to a dominating formation of protective triboceramics on the surface with sapphire-like structure that critically improves wear performance. Analytical modeling of the mass transfer within initial stage of wear was performed based on the concept of irreversible thermodynamics and self-organization in order to formulate the principles of friction control.
Shock structure in low density gas mixture flows over cylinders and plates
Authors: Maltsev R. V. , Plotnikov M. Yu. , Rebrov A. K.
Published: October 2007

This paper presents the results of direct Monte Carlo simulation of transverse hypersonic flow of gas mixtures around a cylinder and a plate. The main objective of the current analysis was the deceleration of heavy atoms in the shock layer in front of the cylinder and the plate. Data are presented for the structure of the disturbed flow, density, velocity, temperature distribution, and energy distribution function of the heavy atoms colliding with the body. Parametric analysis is provided for a wide range of Knudsen numbers, surface temperatures, adsorption probabilities, and gas mixture compositions.
Detection of Cs2Ge+ clusters for the quantification of germanium atoms by secondary ion mass spectrometry: Application to the characterization of Si1−xGex layers (⩽x⩽1) and germanium diffusion in silicon
Authors: Gavelle Mathieu , Scheid Emmanuel , Cristiano Fuccio , Armand Claude , Hartmann Jean-Michel , Campidelli Yves , Halimaoui Aomar , Fazzini Pier-Francesco , Marcelot Olivier
Published: October 2007

We have studied the matrix effects in Si1−xGex structures under O2+ and Cs+ bombardments. Matrix effects are practically suppressed with Cs2Ge+ secondary ions, for Ge concentrations between 0 and 100at.%. A procedure for the accurate quantification of the Ge concentration in Si1−xGex alloys using Cs2Ge+ and CsGe+ clusters has been proposed. For structures in which the Ge content is constant over several hundreds of nanometers, both methods provide very similar results, with an excellent agreement between the Ge concentrations measured by secondary ions mass spectrometry and x-ray diffraction. However, for continuously varying Ge concentration profiles, the nonlinear response of the CsGe+ normalized intensity and the persistence of strong matrix effects for CsSi+ ions lead to differences between the Ge concentration profiles measured with the CsGe+ method compared to the Cs2Ge+ one. The latter is therefore the only reliable method for the study of Ge indiffusion into Si from a pure Ge layer grown by chemical vapor deposition. An application of this method to the analysis of Ge indiffusion in Si at 900°C is also reported.
Gallium nitride metal-semiconductor-metal photodetectors prepared on silicon substrates
Authors: Chuang R. W. , Chang S. P. , Chang S. J. , Chiou Y. Z. , Lu C. Y. , Lin T. K. , Lin Y. C. , Kuo C. F. , Chang H. M.
Published: October 2007

Gallium nitride (GaN) ultraviolet metal-semiconductor-metal photodetectors (PDs) grown on Si substrates were demonstrated. The dark current of PDs fabricated on Si substrates was substantially smaller in magnitude compared to identical devices prepared on sapphire substrates. With an incident wavelength of 359nm, the maximum responsivities of the n−-GaN MSM photodetectors with TiW and Ni∕Au contact electrodes were 0.187 and 0.0792A∕W, corresponding to quantum efficiencies of 64.7% and 27.4%, respectively. For a given bandwidth of 1kHz and a given bias of 5V, the corresponding noise equivalent powers of our n−-GaN MSM photodetectors with TiW and Ni∕Au electrodes were 1.525×10−12 and 5.119×10−12W, respectively. Consequently, the values of detectivity (D*) determined for devices with TiW and Ni∕Au electrodes were then calculated to be 1.313×1012 and 3.914×1011cmHz0.5W−1, respectively.
Quantitative modeling of the annealing-induced changes of the magnetotransport in Ga1−xMnxAs alloys
Authors: Michel C. , Baranovskii S. D. , Thomas P. , Heimbrodt W. , Elm M. T. , Klar P. J. , Goldlücke B. , Wurstbauer U. , Reinwald M. , Wegscheider W.
Published: October 2007

We study the changes of magnetoresistance induced by controlled thermal annealing at temperatures ranging from 300to600°C of a Ga0.98Mn0.02As alloy grown by low-temperature molecular beam epitaxy. We use a resistor-network model for describing the electrical transport as a function of temperature and external magnetic field. The model is founded on classical semiconductor band transport and neglects many-body interactions. The peculiarities of dilute magnetic semiconductors, in particular, the magnetic-field induced changes of the density of states and the potential fluctuations due to the giant Zeeman splitting in the paramagnetic phase as well as spontaneous magnetization effects in the ferromagnetic phase, are accounted for in a mean-field fashion. This empirical transport model based on reasonable assumptions and realistic material parameters yields a satisfactory quantitative description of the experimentally obtained temperature and magnetic-field dependence of the resistivity of the entire series of annealed Ga0.98Mn0.02As samples, which exhibit metallic, semiconducting, and almost insulating transport behavior with increasing annealing temperature. Our analysis provides further understanding of the annealing-induced changes of the transport properties in dilute magnetic III-Mn-V semiconductors.
Double-junction three-terminal photovoltaic devices: A modeling approach
Authors: Emziane M. , Nicholas R. J.
Published: October 2007

The design and optimization of three-terminal photovoltaic devices based on two InGaAs(P) and/or InP single homojunction cells are reported. Four different band gap combinations were simulated for the top (1–1.34eV) and bottom (0.74–1eV) cells lattice matched to InP. The device structure comprises two single-junction cells connected back to back and separated by an InP layer serving as the middle common contact. The device active layers were optimized by modeling, and the predictions led to devices with a total thickness of 4.3μm or below, and showed that moderate doping concentrations in the range of 1–5×1017cm−3 are optimal. The device performance was simulated for various illumination conditions and operating temperatures. Due to the split of the incident spectrum, the bottom cell response is found to be different from that expected for a single-junction cell having the same band gap. It was found that the optimal band gap combination that delivers the best total efficiency is achieved with 1.2 and 0.74eV for the top and bottom cells, respectively. In light of our findings, the potential applications of such devices in conventional (thermo)photovoltaics and concentrator solar cells are also discussed.
Changes of optical properties of retroreflector installed in LHD
Authors: Akiyama T. , Kawahata K. , Ashikawa N. , Tokitani M. , Okajima S. , Nakayama K. , Yoshida N. , Ebihara A. , Tokunaga K. , Ohtawa Y. , Tsuji-Iio S.
Published: October 2007

This article describes changes of optical properties of retroreflectors installed on the inner wall of the vacuum vessel of the Large Helical Device. They were made of stainless steel and were used for a CO2 laser polarimeter. The reflectivity for a CO2 laser beam dropped up to 40% after the start of glow discharge cleanings and main plasma experiments. Then it decreased gradually. The reflectivity in a wavelength range shorter than 10μm decreased significantly through one experimental campaign (about 4months). On the other hand the reflectivity in a wavelength range longer than 50μm was larger than 70%. Decrease in the reflectivity in the central region of mirrors was more significant (the reflectivity for visible beams became almost zero) than that in the edge. The distribution of the reflectivity along the radial direction is expected to be related to the shape of the retroreflector. The parallelism of the reflected beam to an incident one also deteriorated. The changes in the polarization angle and in the ellipticity of reflected light polarization were not observed from the visible to the far infrared range.
Efficient initiation of photonuclear reactions using quasimonoenergetic electron beams from laser wakefield acceleration
Authors: Reed S. A. , Chvykov V. , Kalintchenko G. , Matsuoka T. , Yanovsky V. , Vane C. R. , Beene J. R. , Stracener D. , Schultz D. R. , Maksimchuk A.
Published: October 2007

Pulses of nearly monoenergetic relativistic electrons have been generated by laser wakefield acceleration and used to perform photonuclear activation of carbon, copper, and photofission in uranium. Using bremsstrahlung converter targets, the electron beams generated by this technique have been shown to be effective in producing high energy γ-rays (tens of MeV) that are necessary to efficiently induce photonuclear reactions. Quantitative γ-ray spectroscopy of the irradiated C, Cu, and U samples indicates that more than 105 reactions were produced per joule of laser energy. The activation yield measurements have been compared with Monte Carlo modeling of electromagnetic cascade and photonuclear processes occurring in the targets to infer the characteristics of the laser accelerated electron beams.
Structure, dielectric, and piezoelectric properties of CuO-doped K0.5Na0.5NbO3–BaTiO3 lead-free ceramics
Authors: Lin Dunmin , Kwok K. W. , Chan H. L. W.
Published: October 2007

Lead-free piezoelectric ceramics (1−x)K0.5Na0.5NbO3+xBaTiO3+ymol% CuO have been fabricated by an ordinary sintering technique. Our results show that the doping of CuO is effective in promoting the densification of the ceramics. With the doping of CuO, all the ceramics can be well sintered and exhibit a dense, pure perovskite structure. After the formation of a solid solution with BaTiO3, both the paraelectric cubic–ferroelectric tetragonal and ferroelectric tetragonal–ferroelectric orthorhombic phase transition temperatures decrease and a relax behavior is induced. Coexistence of the orthorhombic and tetragonal phases is formed in the ceramics with 0.04⩽x⩽0.06 and y=1.00 at room temperature. Because of the more possible polarization states arising from the coexistence of the two phases and the improved densification, the piezoelectric and dielectric properties of the ceramics are enhanced significantly. The ceramic with x=0.06 and y=1.00 exhibits the optimum properties: d33=193pC∕N, kp=0.43, kt=0.40, and TC=314°C. On the other hand, the ceramics with 0⩽x⩽0.01 and y=1.0 exhibit excellent “hard” piezoelectric characteristics: kp∼0.40, kt∼0.47, Qm∼1940, εr∼230, and tanδ∼0.5%.
Effects of high-temperature anneals and Co60 gamma-ray irradiation on strained silicon on insulator
Authors: Park K. , Canonico M. , Celler G. K. , Seacrist M. , Chan J. , Gelpey J. , Holbert K. E. , Nakagawa S. , Tajima M. , Schroder D. K.
Published: October 2007

Strained silicon on insulator was exposed to high-temperature annealing and high-dose Co60 gamma (γ)-ray irradiation to study the tenacity of the bond between the strained Si film and the underlying buried oxide. During the high-temperature anneals, the samples were ramped at a rate of 150°C/s to 850°C then ramped to 1200, 1250, and 1300°C at a rate of approximately 5×105°C∕s for millisecond duration anneals. For the irradiation experiments, the samples were irradiated with Co60 γ rays to a dose of 51.5kGy. All samples were characterized by ultraviolet (UV) Raman, pseudo metal-oxide-semiconductor field-effect transistor (Ψ-MOSFET) current voltage, Hall mobility, and photoluminescence (PL) to verify changes in strain. UV Raman, PL, and Ψ-MOSFET measurements show no strain relaxation for the high-temperature annealed samples and only very slight relaxation for the γ-ray irradiated samples.
Flow around a confined rotating cylinder at small Reynolds number
Authors: Champmartin Stéphane , Ambari Abdelhak , Roussel Nicolas
Published: October 2007

A numerical finite-volume technique to solve the two-dimensional Navier-Stokes equations is applied to the rotation of a rigid circular cylinder between parallel plane walls. In this confined situation, the torque exerted on the cylinder is a function of both the distance between the two walls and the position between them. In the absence of experimental results for this problem, we propose here new data of the torque in a wide range of confinements and we study the influence of the eccentricity of the cylinder. When the cylinder rotates close to a wall, there is also a fall of pressure that is likely to create cavitation in the fluid, in accordance with experimental results. Finally, a force parallel to the plane parallel boundaries is numerically obtained, whereas it is theoretically found to be equal to zero in the presence of a single wall. This phenomenon is studied in detail and an explanation is proposed here. The same results could be obtained for the torque experienced by a cylinder translating parallel to the parallel walls.
Stationary stochastic processes in a group system
Authors: Heo Jaeseong
Published: October 2007

In this paper, we discuss positive definite functions of locally compact groups into the predual of von Neumann algebras or C*-algebras. For a predual-valued or a C*-algebra valued weakly continuous covariant positive definite function, the corresponding covariant representation in a covariant group system is constructed. We consider some generalization of the time domain of stochastic processes to a locally compact group, and we use covariant representations in a group system to obtain invariant stationary stochastic processes induced from predual-valued covariant positive definite functions and covariant stationary stochastic processes induced from C*-algebra valued covariant positive definite functions.
Highly directional radiation pattern of microdisk cavities
Authors: Peter E. , Dousse A. , Voisin P. , Lemaître A. , Martrou D. , Cavanna A. , Bloch J. , Senellart P.
Published: October 2007

The far field radiation pattern of microdisk cavities embedding a quantum well is measured through angle resolved microphotoluminescence. The radiation pattern presents two narrow lobes slightly off the disk plane, in apparent contradiction with previous theoretical predictions. The observed radiation pattern is shown to result from interferences with light reflected by the sample substrate. It can be fully reproduced given the microdisk precise geometry as well as the whispering gallery mode azimuthal number.
Digitally balanced detection for optical tomography
Authors: Hafiz Rehan , Ozanyan Krikor B.
Published: October 2007

Analog balanced Photodetection has found extensive usage for sensing of a weak absorption signal buried in laser intensity noise. This paper proposes schemes for compact, affordable, and flexible digital implementation of the already established analog balanced detection, as part of a multichannel digital tomography system. Variants of digitally balanced detection (DBD) schemes, suitable for weak signals on a largely varying background or weakly varying envelopes of high frequency carrier waves, are introduced analytically and elaborated in terms of algorithmic and hardware flow. The DBD algorithms are implemented on a low-cost general purpose reconfigurable hardware (field-programmable gate array), utilizing less than half of its resources. The performance of the DBD schemes compare favorably with their analog counterpart: A common mode rejection ratio of 50dB was observed over a bandwidth of 300kHz, limited mainly by the host digital hardware. The close relationship between the DBD outputs and those of known analog balancing circuits is discussed in principle and shown experimentally in the example case of propane gas detection.
A magnetron sputtering system for the preparation of patterned thin films and in situ thin film electrical resistance measurements
Authors: Arnalds U. B. , Agustsson J. S. , Ingason A. S. , Eriksson A. K. , Gylfason K. B. , Gudmundsson J. T. , Olafsson S.
Published: October 2007

We describe a versatile three gun magnetron sputtering system with a custom made sample holder for in situ electrical resistance measurements, both during film growth and ambient changes on film electrical properties. The sample holder allows for the preparation of patterned thin film structures, using up to five different shadow masks without breaking vacuum. We show how the system is used to monitor the electrical resistance of thin metallic films during growth and to study the thermodynamics of hydrogen uptake in metallic thin films. Furthermore, we demonstrate the growth of thin film capacitors, where patterned films are created using shadow masks.
Embedding of the Lie superalgebra D(2,1;α) into the Lie superalgebra of pseudodifferential symbols on S1∣2
Authors: Poletaeva Elena
Published: October 2007

We obtain an embedding of the one-parameter family of exceptional simple Lie superalgebras D(2,1;α) into the Lie superalgebra of pseudodifferential symbols on the supercircle S1∣2. Correspondingly, there is an embedding of D(2,1;α) into a nontrivial central extension of the derived contact superconformal algebra K′(4) realized in terms of 4×4 matrices over a Weyl algebra.
Energy pathways in nanoscale thermal radiation
Authors: Lee B. J. , Park K. , Zhang Z. M.
Published: October 2007

We show in this letter that when nanoscale radiation between two parallel plates is considered, the Poynting vector is decoupled for each parallel wavevector component (β) due to the nature of thermal emission, as manifested by the fluctuation-dissipation theorem. The streamlines calculated by tracing the Poynting vector vividly demonstrate that the spectral radiative energy travels in infinite directions along curved lines. Depending on the β value, the energy pathway may exhibit considerable lateral shift. This letter elucidates the fundamental characteristics of nanoscale thermal radiation that is important for applications, such as near-field optical sensors and energy conversion devices.
Detailed interpretation of the 5f-6d absorption spectrum of U3+ in Cs2NaYCl6 and high pressure effects based on an ab initio simulation
Authors: Ruipérez Fernando , Barandiarán Zoila , Seijo Luis
Published: October 2007

The 5f→6d(t2g) absorption spectrum of U3+-doped Cs2NaYCl6 is simulated with a quantum chemical ab initio embedded-cluster approach applied to U3+ substitutional defects of Oh local symmetry. The first-principles results help to provide a detailed interpretation of the very rich experimental absorption spectrum of this material between 14 000 and 25000cm−1. Also, the effects of high pressures up to 26kbars on the absorption spectrum are predicted, the most relevant feature being a redshift of around 21cm−1∕kbar, which is the fingerprint of a bond length shortening upon 5f→6d(t2g) excitation.
Substrate heating influence on plume propagation during pulsed laser deposition of complex oxides
Authors: Sambri A. , Amoruso S. , Wang X. , Radovic’ M. , Miletto Granozio F. , Bruzzese R.
Published: October 2007

We investigate the effects of the substrate-heater temperature on the expansion dynamics of laser plumes of complex oxides in oxygen atmosphere. We observed a considerable reduction of the background gas resistance to plume propagation as the substrate temperature was increased, leading to a remarkable change in the velocity of the species impacting the substrate during film growth. The deposition temperature thus influences film growth not only through its direct thermal effect on surface kinetics of adatoms, but also by affecting the energetic properties of the precursors in the gas phase. We interpret the results with a simplified model of plume front propagation, accounting for the change in the background gas density induced by the substrate temperature.
Mechanical deformation and failure of electrospun polyacrylonitrile nanofibers as a function of strain rate
Authors: Naraghi Mohammad , Chasiotis Ioannis , Kahn Harold , Wen Yongkui , Dzenis Yuris
Published: October 2007

The mechanical deformation of 12μm long electrospun polyacrylonitrile (PAN) nanofibers with diameters of 300–600nm was investigated. The nanofibers were subjected to cold drawing in atmospheric conditions and at strain rates between 10−2 and 10−4s−1. The ultimate strain of the PAN nanofibers was 60%–130% varying monotonically with the strain rate. On the contrary, the fiber tensile strength, ranging between 30 and 130MPa, varied nonmonotonically with the slowest drawing rate resulting in the largest ductilities and fiber strengths. At the two faster rates, the large fiber ductilities originated in the formation of a cascade of ripples (necks), while at the slowest strain rate, the nanofibers deformed homogeneously allowing for the largest engineering strengths and extension ratios.
N–O related shallow donors in silicon: Stoichiometry investigations
Authors: Wagner H. E. , Alt H. Ch. , von Ammon W. , Bittersberger F. , Huber A. , Koester L.
Published: October 2007

For clarification of the unknown chemical composition of the electrically active N–O defects in silicon, an ingot with variable oxygen content and fixed nitrogen concentration was investigated by infrared spectroscopy. Shallow donor spectra taken at different sample positions, i.e., oxygen concentrations, show a strong oxygen influence on the absorption of the different N–O species, allowing determination of the number of oxygen atoms for each species via the corresponding mass-action law. From that, the energetically deepest defect N–O-5 is associated with a NO configuration, whereas the strongest complex N–O-3 has NO2 composition. Further members of the shallow donor family contain three oxygen atoms.
Polarity-dependent reversible resistance switching in Ge–Sb–Te phase-change thin films
Authors: Pandian Ramanathaswamy , Kooi Bart J. , Palasantzas George , De Hosson Jeff T. M. , Pauza Andrew
Published: October 2007

In this paper, we demonstrate reversible resistance switching in a capacitorlike cell using a Ge–Sb–Te film that does not rely on amorphous-crystalline phase change. The polarity of the applied electric field switches the cell resistance between lower- and higher-resistance states, as was observed in current-voltage characteristics. Moreover, voltage pulses less than 1.25V showed this switching within time scales of microseconds with more than 40% contrast between the resistance states. The latter are found to be nonvolatile for months. The switching could also be achieved at nanoscales with atomic force microscopy with a better resistance contrast of three orders of magnitude.
Thermally induced capacitive effect of a nanoporous monel
Authors: Qiao Yu , Punyamurtula Venkata K. , Han Aijie
Published: October 2007

As temperature changes, the equilibrium condition at a solid-liquid interface would be disrupted and the ion density varies, which, in turn, affects the interface potential. In the current study, this phenomenon is analyzed by using nanoporous monel electrodes. The experimental data show that, as the ion density is thermally adjusted, the capacitive effect leads to a significant thermal-to-electric energy conversion.
Chemical composition changes across the interface of amorphous LaScO3 on Si (001)
Authors: Liu F. , Duscher G.
Published: October 2007

An amorphous, high-dielectric-constant LaScO3 film was deposited directly on Si (001) by molecular-beam deposition at ∼100°C. Various transmission electron microscopy techniques were applied to study the interface at atomic resolution. We observed an ∼3.5-nm-thick interfacial layer that was not previously detected with other techniques. The interfacial layer contained defects and its density changes gradually. The interface was not only structurally sharp but also chemically sharp within the detection limit of the experimental methods. The chemical composition of the bulk oxide film was stoichiometric, but the interfacial layer was oxygen poor.
Midinfrared lead-chalcogenide vertical external cavity surface emitting laser with 5μm wavelength
Authors: Rahim M. , Arnold M. , Felder F. , Behfar K. , Zogg H.
Published: October 2007

Midinfrared vertical external cavity surface emitting lasers for 5μm wavelength have been realized. The active parts consist either of a 2μm thick PbTe gain layer or of two 150nm PbTe layers embedded in Pb1−xEuxTe barriers, and an epitaxial two pair Pb1−yEuyTe∕BaF2 Bragg mirror. They are optically pumped with a 1.5μm laser. No precautions for efficient heat removal were implemented. The two-layer structure emits 1–2mW continuous wave at 95K with threshold pump power as low as ∼300mW. In pulsed mode, peak powers are >50mW, and lasing occurs up to ∼140K.
Charge-retraction time-of-flight measurement for organic charge transport materials
Authors: Wallace Jason U. , Young Ralph H. , Tang Ching W. , Chen Shaw H.
Published: October 2007

This letter describes an all-electrical technique, charge-retraction time-of-flight (CR-TOF), to measure charge carrier mobility through an organic layer. Carriers are injected and accumulated at a blocking interface, then retracted. The retraction current transient is nearly indistinguishable from a traditional time-of-flight photocurrent. The CR-TOF technique is validated by measurement of the hole mobility of two well-known compounds, 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine and 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl, utilizing 1,3,5-tris(N-phenylbenzimidazol-2-yl)-benzene as a hole-blocking layer. A sample layer thickness of less than 300nm can be used for the measurement.
Strong dependence of transport properties of metal-semiconductor-metal graphene ribbons on their geometrical features
Authors: Andriotis Antonis N. , Richter Ernst , Menon Madhu
Published: October 2007

The conducting properties of various finite graphene ribbons and their junctions are investigated. These were found to depend strongly on their size and geometric features. Small arm-chair ribbons, when connected through tapered geometries, are found to exhibit very narrow conducting windows. No conductance is found through small armchair zigzag armchair ribbon junctions when connected via pentagon-heptagon defect lines. However, the conducting windows become broader as the size of the ribbons increases.
The Use of Novel F-RAFT Agents in High Temperature and High Pressure Ethene Polymerization: Can Control be Achieved?
Authors: Busch Markus , Roth Marion , Stenzel Martina H. , Davis Thomas P. , Barner-Kowollik Christopher
Published: October 2007

Simulations are employed to establish the feasibility of achieving controlled/living ethene polymerizations. Such simulations indicate that reversible addition–fragmentation chain transfer (RAFT) agents carrying a fluorine Z group may be suitable to establish control in high-pressure high-temperature ethene polymerizations. Based on these simulations, specific fluorine (F-RAFT) agents have been designed and tested. The initial results are promising and indicate that it may indeed be possible to achieve molecular weight distributions with a polydispersity being significantly lower than that observed in the conventional free radical process. In our initial trials presented here (using the F-RAFT agent isopropylfluorodithioformate), a correlation between the degree of polymerization and conversion can indeed be observed. Both the lowered polydispersity and the linear correlation between molecular weight and conversion indicate that control may in principle be possible.
Increased survival of muscle stem cells lacking the
MyoD
gene after transplantation into regenerating skeletal muscle
Authors: Asakura Atsushi , Hirai Hiroyuki , Kablar Boris , Morita Shigeru , Ishibashi Jeff , Piras Bryan A. , Christ Amanda J. , Verma Mayank , Vineretsky Karin A. , Rudnicki Michael A.
Published: October 2007

MyoD is a myogenic master transcription factor that plays an essential role in muscle satellite cell (muscle stem cell) differentiation. To further investigate the function of MyoD in satellite cells, we examined the transplantation of satellite cell-derived myoblasts lacking the
MyoD
gene into regenerating skeletal muscle. After injection into injured muscle,
MyoD
−/−
myoblasts engrafted with significantly higher efficiency compared with wild-type myoblasts. In addition,
MyoD
−/−
myoblast-derived satellite cells were detected underneath the basal lamina of muscle fibers, indicating the self-renewal property of
MyoD
−/−
myoblasts. To gain insights into
MyoD
gene deficiency in muscle stem cells, we investigated the pathways regulated by MyoD by GeneChip microarray analysis of gene expression in wild-type and
MyoD
−/−
myoblasts.
MyoD
deficiency led to down-regulation of many muscle-specific genes and up-regulation of some stem cell markers. Importantly, in
MyoD
−/−
myoblasts, many antiapoptotic genes were up-regulated, whereas genes known to execute apoptosis were down-regulated. Consistent with these gene expression profiles,
MyoD
−/−
myoblasts were revealed to possess remarkable resistance to apoptosis and increased survival compared with wild-type myoblasts. Forced expression of MyoD or the proapoptotic protein Puma increased cell death in
MyoD
−/−
myoblasts. Therefore,
MyoD
−/−
myoblasts may preserve stem cell characteristics, including their resistance to apoptosis, expression of stem cell markers, and efficient engraftment and contribution to satellite cells after transplantation. Furthermore, our data offer evidence for improved therapeutic stem cell transplantation for muscular dystrophy, in which suppression of MyoD in myogenic progenitors would be beneficial to therapy by providing a selective advantage for the expansion of stem cells.
Next Generation of Self-Management Education: Web-based Bipolar Disorder Program
Authors: Proudfoot Judith , Parker Gordon , Hyett Matthew , Manicavasagar Vijaya , Smith Meg , Grdovic Sue , Greenfield Leah
Published: October 2007

Objective: Education and self-management training assist patients with bipolar disorder to take control of their condition and to reduce disability, but the timeliness and availability of the education are important. A free Web-based bipolar education program has been recently developed to provide accessible evidence-based information for patients, carers and health professionals. The present paper describes the nine-module program, reports usage data and user profiles, and overviews the aims and methodology of a randomized controlled trial to measure its impact.

Methods: Customized Web reports were developed to measure usage of the Web-based program, and to profile its users on a month-by-month basis. Data on the percentage of completers of each module were also collected. A randomized controlled trial evaluating the program in people with newly diagnosed bipolar disorder was also commenced.

Results: More than 8000 visitors used the online program in its first 6 months. Users were predominantly female, of a broad cross-section of ages, 43.5% with bipolar disorder, and with the remainder describing themselves as health professionals, carers/family/friends of a person with bipolar disorder or members of the general public. The majority (76%) completed the sessions they commenced.

Conclusions: The Web-based education program is attracting a steady stream of users and is exhibiting good completion rates. This preliminary support for the program's utility requires validation from our randomized controlled trial before definite conclusions can be drawn.
Maternal Mental Health and Child Behaviour Problems at 2 Years: Findings from the Pacific Islands Families Study
Authors: Gao Wanzhen , Paterson Janis , Abbott Max , Carter Sarnia , Iusitini Leon
Published: October 2007

Objective: The present study investigated associations between the timing and persistence of maternal psychological disorder and child behaviour problems in a cohort of Pacific 2-year-old children in New Zealand.

Method: Mothers of a cohort of 1398 Pacific infants born in South Auckland, New Zealand were interviewed when their children were 6 weeks, 12 and 24 months of age. Within the context of a wider interview, data regarding maternal mental health were obtained at these times and maternal reports of child behaviour were gathered when the children were 2 years old.

Results: Prevalence rates for internalizing problems were significantly higher in children of mothers who had self-reported symptoms of psychological disorder (11.9% in no symptoms, 27.8% in early symptoms of postnatal depression, 21.1% in late symptoms of psychological disorder and 42.9% in persistent or recurrent symptoms). The adjusted odds ratio (OR) of a child having internalizing problems was 1.38 (95% confidence interval (CI): 0.79–2.43) in those of mothers reporting early symptoms of postnatal depression, 1.45 (95%CI: 0.85–2.49) in late symptoms of psychological disorder, and 2.93 (95%CI: 1.54–5.57) in persistent or recurrent symptoms relative to the no symptoms group. For externalizing problems, the effects of maternal psychological disorder were not significant.

Conclusions: Maternal persistent or recurrent symptoms of psychological disorder may contribute to the behaviour problems of children as young as 2 years old. However, the timing of disorder, whether it is infant or toddler exposure, does not appear to be as crucial. Improved understanding of the associations between maternal psychological disorder and early child behaviour problems may help maternal and child health professionals design appropriate and effective screening and intervention programs to help Pacific mothers and children.
Theories of Autism
Authors: Levy Florence
Published: October 2007

The purpose of the present paper was to review psychological theories of autism, and to integrate these theories with neurobiological findings. Cognitive, theory of mind, language and coherence theories were identified, and briefly reviewed. Psychological theories were found not to account for the rigid/repetitive behaviours universally described in autistic subjects, and underlying neurobiological systems were identified. When the developing brain encounters constrained connectivity, it evolves an abnormal organization, the features of which may be best explained by a developmental failure of neural connectivity, where high local connectivity develops in tandem with low long-range connectivity, resulting in constricted repetitive behaviours.
Trial of Interpersonal Counselling after Major Physical Trauma
Authors: Holmes Alex , Hodgins Gene , Adey Sarah , Menzel Shelly , Danne Peter , Kossmann Thomas , Judd Fiona
Published: October 2007

Objective: The purpose of the present study was to determine if interpersonal counselling (IPC) was effective in reducing psychological morbidity after major physical trauma.

Methods: One hundred and seventeen subjects were recruited from two major trauma centres and randomized to treatment as usual or IPC in the first 3 months following trauma. Measures of depressive, anxiety and post-traumatic symptoms were taken at baseline, 3 months and 6 months. The Structured Clinical Interview for DSM IV diagnoses was conducted at baseline and at 6 months to assess for psychiatric disorder.

Results: Fifty-eight patients completed the study. Only half the patients randomized to IPC completed the therapy. At 6 months the level of depressive, anxiety and post-traumatic symptoms and the prevalence of psychiatric disorder did not differ significantly between the intervention and treatment-as-usual groups. Subjects with a past history of major depression who received IPC had significantly higher levels of depressive symptoms at 6 months.

Conclusion: IPC was not effective as a universal intervention to reduce psychiatric morbidity after major physical trauma and may increase morbidity in vulnerable individuals. Patient dropout is likely to be a major problem in universal multi-session preventative interventions.