bluuebunny/crossref_metadata_2025 huggingface dataset:
Physical and computational aspects of shock waves over power-law leading edges
Authors: Santos Wilson F. N.
Published: January 2008

Computations using the direct simulation Monte Carlo (DSMC) method are presented for hypersonic flow on power-law shaped leading edges. The primary aim of this paper is to examine the geometry effect of such leading edges on the shock-wave structure. The sensitivity of the shock-wave shape, shock-wave thickness, and shock-wave standoff distance to shape variations of such leading edges is investigated by using a model that classifies the molecules in three distinct classes: (1) undisturbed freestream, (2) reflected from the boundary, and (3) scattered, i.e., molecules that had been indirectly affected by the presence of the leading edge. The analysis showed that, for power-law shaped leading edge with exponent between 2∕3 and 1, the shock wave follows the body shape. It was found that, at the vicinity of the nose, the shock-wave power-law exponent is 1∕2. Far from the nose, calculations showed that the shock-wave shape is in surprising qualitative agreement with that predicted by the hypersonic small disturbance theory for the flow conditions considered.
Hardening by bubbles in He-implanted Ni
Authors: Knapp J. A. , Follstaedt D. M. , Myers S. M.
Published: January 2008

Detailed finite-element modeling of nanoindentation data is used to obtain the mechanical properties of Ni implanted with 1–10at.% He. The mechanical properties of this material elucidate the fundamental materials science of dislocation pinning by nanometer-size gas bubbles and also have implications for radiation damage of materials. Cross-section transmission electron microscopy showed that implantation of 1–5at.% He at room temperature or at 200°C produced a highly damaged layer extending to a depth of 700–800nm and containing a fine dispersion of He bubbles with diameters of 1.1±0.2nm. Implantation at 500°C enlarged the bubble sizes. By fitting the nanoindentation data with a finite-element model that includes the responses of both the implanted layer and the unimplanted substrate in the deformation, the Ni(He) layers are shown to have hardnesses as much as approximately seven times that of untreated Ni, up to 8.3±0.6GPa. Examination of the dependence of yield strength on He concentration, bubble size, and bubble density reveals that an Orowan hardening mechanism is likely to be in operation, indicating that the bubbles pin dislocation motion as strongly as hard second-phase precipitates do. This strong pinning of dislocations by bubbles is also supported by our numerical simulations, which show that substantial applied shear stress is required to move a dislocation through an empty cavity.
Electron dynamics and acceleration study in a magnetized plasma-filled cylindrical waveguide
Authors: Kumar Sandeep , Yoon Moohyun
Published: January 2008

In this article, EH01 field components are evaluated in a cylindrical waveguide filled with plasma in the presence of external static magnetic field applied along the direction of the mode propagation. The electron acceleration inside the plasma-filled cylindrical waveguide is investigated numerically for a single-electron model. It is found that the electron acceleration is very sensitive to the initial phase of mode-field components, external static magnetic field, plasma density, point of injection of the electron, and microwave power density. The maximum amplitude of the EH01 mode’s field components is approximately 100 times greater than the vacuum-waveguide case for operating microwave frequency f=7.64GHz, plasma density n0=1.08×1017m−3, initial phase angle ϕ0=60°, and microwave power ∼14MW in a cylindrical waveguide with a radius of 2.1cm. An electron with 100keV gets 27MeV energy gain in 2.5cm along the waveguide length in the presence of external power ∼14MW with a microwave frequency of 7.64GHz. The electron trajectory is also analyzed under the effects of magnetic field when the electron is injected in the waveguide at r=R∕2.
Engineering the electronic, magnetic, and gap-related properties of the quinternary half-metallic Heusler alloys
Authors: Özdoğan K. , Şaşıoğlu E. , Galanakis I.
Published: January 2008

We study the electronic and magnetic properties of the quinternary full Heusler alloys of the type Co2[Cr1−xMnx][Al1−ySiy] employing three different approaches: (i) the coherent potential approximation; (ii) the virtual crystal approximation; and (iii) supercell calculations. All three methods give similar results, and the local environment manifests itself only for small details of the density of states. All alloys under study are shown to be half-metals, and their total spin moments follow the so-called Slater–Pauling behavior of the ideal half-metallic systems. We especially concentrate on the properties related to the minority-spin band gap. We present the possibility to engineer the properties of these alloys by changing the relative concentrations of the low-valent transition metal and sp atoms in a continuous way. Our results show that for realistic applications, compounds rich in Si and Cr are ideal since they combine large energy gaps (around 0.6 eV), robust half-metallicity with respect to defects (the Fermi level is located near the middle of the gap), and high values of the majority-spin density of states around the Fermi level, which are needed for large values of the perfectly spin-polarized current in spintronic devices like spin valves or magnetic tunnel junctions.
Determination of solid phase chemical diffusion coefficient and density of states by electrochemical methods: Application to iridium oxide-based thin films
Authors: Backholm Jonas , Georén Peter , Niklasson Gunnar A.
Published: January 2008

Potentiostatic intermittent titration technique (PITT) and electrochemical impedance spectroscopy (EIS) were investigated as methods to determine solid phase chemical diffusion coefficient (D) and electronic density of states (DOS). These techniques were then applied to iridium oxide (IrOx) and iridium-tantalum oxide (IrTaOx) thin films prepared by sputter deposition. The experiments, performed in 1M propionic acid between −0.2 and 0.8V vs Ag∕AgCl, showed effects of interfacial side reactions, whose contribution to the electrochemical response could be identified and corrected for in the case of PITT as well as EIS. It was found that D is strongly underestimated when using PITT with the common Cottrell formalism, which follows from non-negligible interfacial charge transfer and Ohmic resistances. EIS indicated an anomalous diffusion mechanism, and D was determined to be in the 10−11–10−10cm2∕s range for IrOx and IrTaOx. Both PITT and EIS showed that the intercalated charge as a function of potential exhibits a shape that resembles the theoretical DOS of crystalline iridium oxide, especially for IrTaOx.
Transient analysis of coaxial magnetic gears using finite element comodeling
Authors: Chau K. T. , Zhang Dong , Jiang J. Z. , Jian Linni
Published: January 2008

In this paper, the transient performance of coaxial magnetic gears is firstly analyzed and discussed in literature. The key is to employ finite element comodeling in such a way that both the finite element model of the driving motor and the finite element model of the magnetic gear are coupled together to perform time-stepping finite element analysis. Hence, the dynamic interactions between the motor rotor and the gear inner rotor as well as the gear outer rotor and the external load can be taken into account. The proposed transient analysis verifies that the magnetic gear takes the definite advantage of overload self-protection, whereas reveals that it suffers from speed oscillations with significant time delays between the two rotors which are unacceptable for servomechanism.
Tailored Taylor vortices
Authors: Sprague M. A. , Weidman P. D. , Macumber S. , Fischer P. F.
Published: January 2008

The stability of circular Couette flow in discontinuous axisymmetric geometries is investigated using numerical simulations and physical experiments. By contouring the geometry of the inner cylinder, Taylor vortices can be made to appear in discrete sections along the length of the cylinder while adjoining sections remain stable. The disparate flows are connected by transition regions that arise from the stability of the axially nonuniform base flow state. The geometry of the inner cylinder can be tailored to produce the simultaneous onset of Taylor vortices of different wavelength in neighboring sections. In another variant, a stack of inner cylinders of common radius are made to rotate independently to produce adjacent regions of stable and unstable flow.
Measuring the microwave frequency relative permittivity of polyetherimide/BaTi4O9 composites by using a rectangular cavity resonator
Authors: Yang Cheng-Fu , Wu Chia-Ching , Lee Yi-Zhi , Chen Ying-Chung
Published: January 2008

In this paper, high glass transition temperature (Tg) of polyetherimide (PEI) is used to mix with different weight percent (0–80wt%) of BaTi4O9 (BT4) ceramic powder to form a flexible PEI/BT4 composite. The relative permittivity of PEI/BT4 composites is developed from 1to16GHz using the “rectangular cavity resonator” method. The relative permittivity of PEI/BT4 composites is calculated by observing the frequencies of resonant cavity modes. From the results of dielectric properties, the relative permittivity of PEI/BT4 composites is almost unchanged as the measured frequency is changed. It conjectures that the polarization mode does not exist in BT4 ceramic powder.
Energy barrier and reversal mechanism in Co∕Pt multilayer nanodot
Authors: Okamoto S. , Kato T. , Kikuchi N. , Kitakami O. , Tezuka N. , Sugimoto S.
Published: January 2008

We have studied the reversal behavior in a single nanomagnet of Co∕Pt by using anomalous Hall effect measurement technique. [Co(0.6–1.4nm)∕Pt(2nm)]3 multilayer films were lithographically patterned into single dots with the diameter of 200nm. The magnetic anisotropy Ku of the dots was varied from 1.3×107 to 2.6×107erg∕cc by decreasing the Co thickness. From the rectangular magnetization curve and the Stoner–Wohlfarth–type angular dependence of reversal field, the magnetization reversal of the dot was concluded to proceed by the nucleation of a reversed embryo and its immediate expansion. The energy barrier Eb(0) for the magnetization reversal evaluated by the reversal probability experiment increased monotonically with Ku and showed the almost same dependence on Ku both at 300 and 100K. These results suggest that the reversal mechanism is simply dominated by the magnetic anisotropy Ku and is invariable in this temperature range. This behavior of Eb(0) can be qualitatively explained by considering the nucleation of an embryo having the size of domain wall width.
High photoexcited carrier multiplication by charged InAs dots in AlAs∕GaAs∕AlAs resonant tunneling diode
Authors: Wang Wangping , Hou Ying , Xiong Dayuan , Li Ning , Lu Wei , Wang Wenxing , Chen Hong , Zhou Junming , Wu E. , Zeng Heping
Published: January 2008

We present an approach for the highly sensitive photon detection based on the quantum dots (QDs) operating at temperature of 77K. The detection structure is based on an AlAs∕GaAs∕AlAs double barrier resonant tunneling diode combined with a layer of self-assembled InAs QDs (QD-RTD). A photon rate of 115 photons per second had induced 10nA photocurrent in this structure, corresponding to the photoexcited carrier multiplication factor of 107. This high multiplication factor is achieved by the quantum dot induced memory effect and the resonant tunneling tuning effect of QD-RTD structure.
Magnetocaloric properties of nanocrystalline Pr0.65(Ca0.6Sr0.4)0.35MnO3
Authors: Biswas Anis , Samanta Tapas , Banerjee S. , Das I.
Published: January 2008

The coexistence of the charge-ordered phase and the ferromagnetic phase has a strong effect on the magnetocaloric property of the nanocrystalline Pr0.65(Ca0.6Sr0.4)0.35MnO3 of average particle size 36 and 78 nm. The temperature dependence of the magnetic entropy change shows a tablelike behavior for the sample with a lower average particle size, for which the refrigerant capacity is significantly enhanced in comparison with the other.
Plasma interactions in ion beam assisted pulsed laser deposition of Al-O-N films
Authors: Voevodin A. A. , Jones J. G. , Zabinski J. S. , Waite A. R.
Published: January 2008

Interactions between plasmas produced by a nitrogen ion beam source and the pulsed laser ablation of an Al2O3 target were studied for the growth of Al-O-N films. Plasma fluxes from both sources were intersected on the substrate surface in a typical arrangement for ion beam assisted pulsed laser deposition (IBPLD). Plasma emission imaging and spectroscopic analyses were performed in real time, using laser pulses for analysis synchronization while varying the N2 background pressure in the range from 0.08 to 4 Pa. This study was focused on the detection of temporal and spatial plasma distributions, excitation states, and chemical reactions during the IBPLD process which were not present when operating each of the plasma sources separately. Two significant plasma interaction effects were discovered. One was the production of atomic N and O in the near-substrate region, resulting in the formation of NO molecules which then reacted with Al to form Al-O-N. Another was the formation of short-lived plasma channels connecting ion beam and laser-ablated plasmas, which was observed in the 2–4 Pa pressure regime. These channels resulted in plasma bending and shifting from the substrate surface and affected film composition. These findings suggest that the interaction of ion beam and laser ablation plumes in IBPLD might considerably affect plasma chemistry, excitation states, and spatial distribution, thus providing opportunities for the control of deposited film properties.
ac electro-osmotic micropump by asymmetric electrode polarization
Authors: Wu Jie (Jayne)
Published: January 2008

ac electro-osmosis (ACEO) has emerged recently as a promising strategy for fluid transport at microscale. With an array of planar interdigital electrodes immersed in an electrolyte, different charging mechanisms at electrode∕electrolyte interface and electrokinetic surface flows can be induced by nonuniform electrical fields. To implement ACEO micropump, asymmetry in an electrode pair is essential to generate net flow, which has been typically achieved through asymmetric electrode geometries. This work proposes asymmetric electrode polarization processes to break the electrode symmetry. A dc bias is superimposed onto ac potentials, so that the two electrodes in a pair undergo capacitive charging or Faradaic charging separately. Applying such signals, pumping action has been demonstrated with only a few volts of applied voltage and a power consumption in the range of milliwatts. Pumping velocity by asymmetric electrode polarization exhibits an exponential dependency on voltage.
Evidence for band structure effects in the magnetoresistance of Co-based Heusler compounds
Authors: Thomas A. , Weddemann A. , Ebke D. , Liu N.-N. , Hütten A. , Schmalhorst J. , Reiss G.
Published: January 2008

Magnetic tunnel junctions are prepared with Co-based Heusler compounds as one magnetic electrode and alumina as the tunnel barrier. The investigated compounds are Co2MnSi and Co2FeSi. An inversion of the tunnel magnetoresistance in the Co2FeSi as well as in the Co2MnSi case was found with alumina barriers at certain bias voltages at room and low temperatures. We present calculations of the density of states of these compounds based on fully relativistic spin-polarized KKR methods in order to elucidate the inversion.
Dynamic adhesive force measurements under vertical and horizontal motions of interacting rough surfaces
Authors: Yeo Chang-Dong , Lee Sung-Chang , Polycarpou Andreas A.
Published: January 2008

An instrument to measure dynamic adhesive forces between interacting rough surfaces has been developed. It consists of four parts, namely, main instrument body, vertical positioning system with both micrometer and nanometer positioning accuracies, horizontal positioning system with nanometer positioning accuracy, and custom-built high-resolution, and high dynamic bandwidth capacitive force transducer. The vertical piezoelectric actuator (PZT) controls the vertical (approaching and retracting) motion of the upper specimen, while the horizontal PZT controls the horizontal (reciprocal) motion of the lower specimen. The force transducer is placed in line with the upper specimen and vertical PZT, and directly measures the adhesive forces with a root-mean-square load resolution of 1.7μN and a dynamic bandwidth of 1.7kHz. The newly developed instrument enables reliable measurements of near-contact and contact adhesive forces for microscale devices under different dynamic conditions. Using the developed instrument, dynamic pull-in and pull-off force measurements were performed between an aluminum-titanium-carbide sphere and a 10nm thick carbon film disk sample. Three different levels of contact force were investigated; where for each contact force level the vertical velocity of the upper sample was varied from 0.074to5.922μm∕s, while the lower sample was stationary. It was found that slower approaching and retracting velocities result in higher pull-in and pull-off forces. The noncontact attractive force was also measured during horizontal movement of the lower sample, and it was found that the periodic movements of the lower disk sample also affect the noncontact surface interactions.
Group delay characteristics in coplanar waveguide left-handed media
Authors: Ibraheem Ibraheem A. , Schoebel Joerg , Koch Martin
Published: January 2008

We present a combined theoretical and experimental study on the group delay behavior of four coplanar waveguide structures loaded with pairs of split-ring resonators (SRRs) and strip lines (SLs). These structures are effective left-handed media, which are designed to operate at S-band frequencies. For one and three pairs of SRRs/SLs full-wave simulations predict a maximum negative group delay of −3.9 and −7.9 ns, and a bandwidth of 160 and 150 MHz, respectively. Experimentally we find a group delay of −4.7 and −8.5 ns and a bandwidth of 190 and 290 MHz, respectively. Surprisingly, we do not observe a negative group delay if the structure contains an even number of SRRs/SLs pairs. Yet, the structures with an odd number of pairs may be used to control the dispersive effects for a variety of systems. Further, we discuss the group delay in the pass band as these structures may also be used as filters.
Heat transfer in vacuum packaged microelectromechanical system devices
Authors: Cai Chunpei
Published: January 2008

This study analyzes heat transfer effects inside vacuum packaged microelectromechanical system (MEMS) devices. A packaged device is simplified as four plates forming a square cavity, the bottom plate represents a hot chip, while the other three plates are maintained at room temperature. For a highly rarefied free molecular internal gas flow scenario, the corresponding detailed density and temperature fields are analytically determined with a proposed speculation. This speculation indicates that for a steady free molecular gas flow inside a convex closure domain formed by walls maintained at different temperatures: (1) the velocity distribution functions for those molecules diffusely reflected at different walls and traveling away from them are Maxwellian with different number densities; (2) for each distribution, niTi is a constant, where ni is the number density for the group of reflected molecules, and Ti is the temperature for the ith plate. For a near continuum flow scenario, the governing energy equation degenerates to Laplace’s equation with several temperature-jump wall boundary conditions. This study also includes discussions and comparisons among analytical results, simulation results from the direct simulation Monte Carlo method, and results by solving the Navier–Stokes equations with proper wall boundary conditions. The approach used in this study is generally applicable to study internal flows and heat transfer effects in other vacuum packaged MEMS devices with different shapes.
A microwave-induced plasma source: Characterization and application for the fast deposition of crystalline silicon films
Authors: Jia Haijun , Kuraseko Hiroshi , Kondo Michio
Published: January 2008

A microwave-induced plasma source is developed and is applied for the fast deposition of crystalline silicon films. In this paper, the plasma source is diagnosed first. Electron density, electron temperature, and discharge gas temperature of the plasmas generated in ambient air are studied using the optical emission spectroscopy method. The electron density is estimated by analyzing the Stark broadening of the hydrogen Hβ emission profile and is found to be as high as >1015 cm−3 over wide conditions. The Boltzmann plot method is used to calculate the electron temperature, which shows a value smaller than 1 eV. Analysis of the rotational structure of OH molecular emission reveals a discharge gas temperature in a range of ∼400–800 °C. Preliminary efforts of using the plasma source for Si film fast deposition are performed at a reduced pressure by using SiCl4 as the source gas. A fast deposition rate of 150 nm/s has been achieved for Si film with a high Raman crystallinity of Ic/Ia>10 even without using substrate heating and under a low H2 dilution condition. Mechanisms for these results are discussed in detail.
Kinetic arrest of martensitic transformation in the NiCoMnIn metamagnetic shape memory alloy
Authors: Ito Wataru , Ito Kouhei , Umetsu Rie Y. , Kainuma Ryosuke , Koyama Keiichi , Watanabe Kazuo , Fujita Asaya , Oikawa Katsunari , Ishida Kiyohito , Kanomata Takeshi
Published: January 2008

Magnetic and electrical resistivity changes due to a martensitic transformation in large magnetic fields were investigated in a NiCoMnIn alloy. The transformation is interrupted at about 150K during field cooling and does not proceed with further cooling. The obtained two-phase condition is frozen at low temperatures and zero field heating releases this condition, inducing a “forward” transformation. These unusual phenomena can be explained by an abnormal behavior in the transformation entropy change and an extremely low mobility of the phase interfaces detected at low temperatures.
A 9keV electron-impact liquid-gallium-jet x-ray source
Authors: Otendal M. , Tuohimaa T. , Vogt U. , Hertz H. M.
Published: January 2008

We demonstrate a high-brightness compact 9keV electron-impact microfocus x-ray source based on a liquid-gallium-jet anode. A ∼30W, 50kV electron gun is focused onto the ∼20m∕s, 30μm diameter liquid-gallium-jet anode to produce an ∼10μm full width at half maximum x-ray spot. The peak spectral brightness is >2×1010photons∕(smm2mrad2×0.1%BW). Calculation and experiments show potential for increasing this brightness by approximately three orders of magnitude, making the source suitable for laboratory-scale x-ray crystallography and hard x-ray microscopy.
X-ray stability and response of polymeric photodiodes for imaging applications
Authors: Keivanidis Panagiotis E. , Greenham Neil C. , Sirringhaus Henning , Friend Richard H. , Blakesley James C. , Speller Robert , Campoy–Quiles Mariano , Agostinelli Tiziano , Bradley Donal D. C. , Nelson Jenny
Published: January 2008

The x-ray stability of photodiodes made of poly(9,9-di-n-octylfluorene-co-benzothiadiazole):perylene diimide, poly[2,7-(9,9-di-n-octylfluorene)-co-(1,4-phenylene-[(4-sec-butylphenyl)imino]-1,4-phenylene)]:perylene diimide and poly(3-hexylthiophene):([6,6]-phenylC61-butyric acid methyl ester) (P3HT:PCBM) blends has been examined up to lifetime doses equivalent to those used in medical x-ray digital imaging applications. Dark currents and external quantum efficiencies (EQEs) are not significantly affected after exposure to 500Gy. Only in the case of P3HT:PCBM is a significant loss in EQE (17% of the initial value) observed. Possible reasons for the observed changes are proposed. When a scintillation layer is attached to the devices, a linear dependence of the photocurrent on the x-ray dose rate is observed for the three material systems.
Near-zero IR transmission in the metal-insulator transition of VO2 thin films
Authors: Balu R. , Ashrit P. V.
Published: January 2008

Vanadium dioxide films have been prepared with different thicknesses using radio-frequency magnetron sputtering technique followed by postdeposition annealing in oxygen ambient. Films with a thickness of 300nm show a switching efficiency of ∼74% and most importantly with a near-zero infrared transmission in the switched state. As the film thickness decreases, the inherent transmission in the switched state increases along with reduced switching efficiencies.
Enhanced thermal conductivity by aggregation in heat transfer nanofluids containing metal oxide nanoparticles and carbon nanotubes
Authors: Wensel Jesse , Wright Brian , Thomas Dustin , Douglas Wayne , Mannhalter Bert , Cross William , Hong Haiping , Kellar Jon , Smith Pauline , Roy Walter
Published: January 2008

An approximately 10% increase in the thermal conductivity (TC) of heat transfer nanofluids containing metal oxide nanoparticles and carbon nanotubes has been determined with very low percentage loading (around 0.02wt%) of these two nanomaterials. These fluids are very stable and the viscosity remains approximately the same as water. A possible explanation for these interesting results is the aggregation of metal oxide particles on the surface of nanotubes by electrostatic attraction and form the aggregation chain along the nanotube. Time dependant magnetic results demonstrate that, under the influence of a strong outside magnetic field, the TC value decreases. Also, the TC value decreases when the pH is shifted from 7 to 11.45.
Diffraction microscopy using 20kV electron beam for multiwall carbon nanotubes
Authors: Kamimura Osamu , Kawahara Kota , Doi Takahisa , Dobashi Takashi , Abe Takashi , Gohara Kazutoshi
Published: January 2008

Diffraction microscopy with iterative phase retrieval using a 20kV electron beam was carried out to explore the possibility of high-resolution imaging for radiation-sensitive materials. Fine, homogeneous, and isolated multiwall carbon nanotubes (MWCNTs) were used as specimens. To avoid lens aberrations, the diffraction patterns were recorded without a postspecimen lens. One- and two-dimensional iterative phase retrievals were executed. Images reconstructed from the diffraction pattern alone showed a characteristic structure of MWCNTs with the finest feature corresponding to a carbon wall spacing of 0.34nm.
Contact resistance of dibenzotetrathiafulvalene-based organic transistors with metal and organic electrodes
Authors: Shibata Koji , Ishikawa Ken , Takezoe Hideo , Wada Hiroshi , Mori Takehiko
Published: January 2008

Thin-film transistors of dibenzotetrathiafulvalene (DBTTF) are investigated by changing the source and drain (S/D) electrode materials. Not only the mobility but also the contact resistance, estimated from the transfer line method, changes depending on the metal work functions. Nonetheless, S/D electrodes made of a metallic organic charge-transfer salt, (tetrathiafulvalene) (tetracyanoquinodimethane) [(TTF)(TCNQ)] exhibits much smaller contact resistance, which is attributed to small potential shift on the organic/organic interface compared with the organic/metal interface. A thin film of (DBTTF)(TCNQ) works as an active layer of air-stable n-channel organic transistors when (TTF)(TCNQ) is used as the S/D electrodes.
Ion irradiation in liquid of μm3 region for cell surgery
Authors: Iwai Yoshio , Ikeda Tokihiro , Kojima Takao M. , Yamazaki Yasunori , Maeshima Kazuhiro , Imamoto Naoko , Kobayashi Tomohiro , Nebiki Takuya , Narusawa Tadashi , Pokhil Grigory P.
Published: January 2008

We present here a cell surgery scheme involving selective inactivation or disruption of cellular structures. Energetic ions are injected into a cell through a tapered glass capillary like a microinjection method. A slight but essential difference from microinjection is that a thin window is prepared at the outlet so that no liquid material can flow in or back through the outlet while still allowing energetic ions to penetrate into the cell. An ∼MeV He ion beam from such a capillary having 10μm outlet diameter inactivated a selected volume (∼μm3) of fluorescent molecules located in a HeLa cell nucleus.
Violet luminescence in phosphorus-doped ZnO epitaxial films
Authors: Allenic A. , Pan X. Q. , Che Y. , Hu Z. D. , Liu B.
Published: January 2008

A violet luminescence band at 3.1099eV was observed at 12.5K in phosphorus-doped ZnO epitaxial films deposited by O2 plasma-assisted pulsed laser ablation. The band results from a transition between a shallow donor and a deep acceptor induced by phosphorus doping. The activation energy of the acceptor varies with the phosphorus concentration [P] and is 0.34eV when [P] is 1.7×1019cm−3. Under oxygen-rich conditions, the dominant acceptor in P2O5-doped ZnO may be the zinc vacancy, in agreement with recent first-principles calculations.
Characterization of AlN metal-semiconductor-metal diodes in the spectral range of 44–360nm: Photoemission assessments
Authors: BenMoussa A. , Hochedez J. F. , Dahal R. , Li J. , Lin J. Y. , Jiang H. X. , Soltani A. , De Jaeger J.-C. , Kroth U. , Richter M.
Published: January 2008

The absolute responsivity of a metal-semiconductor-metal (MSM) photodiode based on high quality AlN material has been tested from the vacuum ultraviolet (vuv) to the near UV wavelength range (44–360nm). The metal finger Schottky contacts have been processed to 2μm in width with spacing between the contacts of 4μm. In the vuv wavelength region, the measurement methodology is described in order to distinguish the contribution of the photoemission current from the internal diode signal. In the wavelength range of interest, AlN MSM is sensitive and stable under brief vuv irradiation. The MSM shows a 200∕360nm rejection ratio of more than four orders of magnitude and demonstrates the advantages of wide band gap material based detectors in terms of high rejection ratio and high output signal for vuv solar observation missions.
Tailoring hole spin splitting and polarization in nanowires
Authors: Csontos D. , Zülicke U.
Published: January 2008

Spin splitting in p-type semiconductor nanowires is strongly affected by the interplay between quantum confinement and spin-orbit coupling in the valence band. The latter’s particular importance is revealed in our systematic theoretical study presented here, which has mapped the range of spin-orbit coupling strengths realized in typical semiconductors. Large controllable variations of the g factor with associated characteristic spin polarization are shown to exist for nanowire subband edges, which therefore turn out to be a versatile laboratory for investigating the complex spin properties exhibited by quantum-confined holes.
Unipolar resistive switching characteristics of ZnO thin films for nonvolatile memory applications
Authors: Chang Wen-Yuan , Lai Yen-Chao , Wu Tai-Bor , Wang Sea-Fue , Chen Frederick , Tsai Ming-Jinn
Published: January 2008

Highly (002)-oriented and columnar-grained ZnO thin films were prepared by radio frequency magnetron sputtering at room temperature. The Pt∕ZnO∕Pt devices exhibit reversible and steady bistable resistance switching behaviors with a narrow dispersion of the resistance states and switching voltage. Only a low forming electric field was required to induce the resistive switching characteristics. The resistance ratios of high resistance state to low resistance state were in the range of 3–4 orders of magnitude within 100cycles of test. It was also found that the conduction mechanisms dominating the low and high resistance states are Ohmic behavior and Poole-Frenkel emission, respectively.
Colossal internal barrier layer capacitance effect in polycrystalline copper (II) oxide
Authors: Sarkar Sudipta , Jana Pradip Kumar , Chaudhuri B. K.
Published: January 2008

Dielectric spectroscopy analysis of the high permittivity (κ∼104) copper (II) oxide (CuO) ceramic shows that the grain contribution plays a major role for the giant-κ value at low temperature, whereas grain boundary (GB) contribution dominates around room temperature and above. Moreover, impedance spectroscopy analysis reveals electrically heterogeneous microstructure in CuO consisting of semiconducting grains and insulating GBs. Finally, the giant dielectric phenomenon exhibited by CuO is attributed to the internal barrier layer (due to GB) capacitance mechanism.
Reduction of nonspecific surface-particle interactions in optoelectronic tweezers
Authors: Hwang Hyundoo , Oh Youngjae , Kim Jae-Jun , Choi Wonjae , Park Je-Kyun , Kim Se-Hwan , Jang Jin
Published: January 2008

We demonstrate three-dimensional optoelectronic tweezers (3D OET) for the adsorption-free manipulation of microparticles. In typical OET, nonspecific interactions between the manipulated particles and the device surfaces, such as hydrophobic, Van der Waals, and electrostatic interactions, interfere with the effective microparticle manipulation. Here, by using the 3D OET device, which is composed of two photoconductive layers, we succeeded in three-dimensional focusing and manipulating polystyrene microbeads in a channel-less microenvironment without the particle adsorption. The 3D OET with the light-induced negative dielectrophoresis also shows a higher particle trapping efficiency and less particle adsorption rate than typical OET.
Transparent organic light-emitting diodes consisting of a metal oxide multilayer cathode
Authors: Ryu Seung Yoon , Noh Joo Hyon , Hwang Byoung Har , Kim Chang Su , Jo Sung Jin , Kim Jong Tae , Hwang Hyeon Seok , Baik Hong Koo , Jeong Hee Seong , Lee Chang Ho , Song Seung Yong , Choi Seung Ho , Park Si Young
Published: January 2008

The authors have developed a semitransparent, multilayered cathode of indium tin oxide (ITO)/Ag/tungsten oxide (WO3) for transparent organic light-emitting diodes. The device showed a weak negative differential resistance (NDR), until the operating voltage of 8V was reached. NDR was due to the resonant tunneling by both the quantum barrier and quantum well. The silver oxide (Ag2O) on the Ag metal was confirmed by x-ray photoelectron spectroscopy, and the energy levels of Ag2O were quantized due to the quantum size effect and this produced the resonant tunneling channels. The device using ITO∕Ag∕WO3 with a LiF∕Al bilayer was superior to those devices which only used ITO or WO3, mainly because the out coupling was enhanced by employing a WO3 material, which is much more transparent than ITO.
Submicron-scale manipulation of phase separation in organic solar cells
Authors: Chen Fang-Chung , Lin Yi-Kai , Ko Chu-Jung
Published: January 2008

This paper describes a method for controlling the submicron-scale phase separation of poly(3-hexylthiophene) and (6,6)-phenyl-C61-butyric acid methyl ester in organic solar cells. Using microcontact printing of self-assembled monolayers on the device buffer layer to divide the surface into two regimes having different surface energies, an interdigitated structure aligned vertical to the substrate surface is achieved after spontaneous surface-directed phase separation. The power conversion efficiency increases upon decreasing the grating spacing, reaching 2.47%. The hole mobility increased as a consequence of improved polymer chain ordering, resulting in higher device efficiency, while smaller pattern sizes were used.
Martensitic transformations in Ag–Au bimetallic core-shell nanoalloys
Authors: Chen Fuyi , Johnston Roy L.
Published: January 2008

Combining the Gupta potential and bond order analysis in a molecular dynamics simulation, a martensitic transformation is observed in the 147-atom AucoreAgshell nanostructure at 328K. The response time for this transformation is about 7ps at 350K. In pure gold clusters, it was previously thought that a similar solid-to-solid transformation is a prelude to melting transitions. In the present case, atomic pathway snapshots show that the heating energy is used to overcome the energy barrier for initiating the spontaneous process. The subsequent twist-deformation propagation and termination are clearly observed.
Synthesis of Carbon Nanotubes, and the Effect on Thermal Stability in High-Impact Polystyrene
Authors: Kong Qinghong , Zhang Junhao
Published: January 2008

Carbon nanotubes (CNTs) with diameters ranging from 40 to 100 nm have been synthesized by the solvothermal process using ethanol as a carbon source and LaNiO3 as catalyst. The synthesized CNTs can be used for filaments in high-impact polystyrene (HIPS). HIPS/CNT nanocomposites have been prepared by the melt–intercalation process. Thermogravimetric analysis and differential scanning calorimetry indicate that the thermal stability of HIPS/CNT nanocomposites is better than that of HIPS. The thermal degradation mechanism was investigated by pyrolysis gas chromatography mass spectrometry.
Aminimides as Potential CNS Acting Agents. II Design, Synthesis, and Receptor Binding of 4′-Arylalkyl Aminimide Analogues of Clozapine as Prospective Novel Antipsychotics
Authors: Capuano Ben , Crosby Ian T. , Lloyd Edward J. , Neve Juliette E. , Taylor David A.
Published: January 2008

We report the synthesis of a series of second generation aminimide-based analogues of clozapine, investigating the length of the linker between the aminimide functional group and the introduced aryl moiety. The chemistry and structural characterization of this series of 4′-arylalkyl aminimide analogues of clozapine are described. Preliminary findings on the biochemical effects of linker length and type of aryl moiety on affinity for dopamine D4 and serotonin 5-HT2A receptors are discussed. All of the compounds showed a marked reduction in binding at the two receptors when compared with clozapine, thus showing a reduced potential for atypical antipsychotic activity.
Microwave-Assisted Direct Amination: Rapid Access to Multi-Functionalized N6-Substituted Adenosines
Authors: Ashton Trent D. , Scammells Peter J.
Published: January 2008

Analogues of adenosine have a range of interesting biological activities and potential therapeutic applications. A method for the efficient preparation of highly functionalized N6-substituted adenosines has been developed from the corresponding tert-butyldimethylsilyl-protected inosine. The key step in this procedure is a microwave-assisted amination reaction between an appropriately substituted inosine and an amine in the presence of PyBroP. High yields of desired N6-substituted adenosines were achieved with hindered amines and the reaction was also found to accommodate a range of substituents on the inosine precursor.
Unique elastic properties of the spectrin tetramer as revealed by multiscale coarse-grained modeling
Authors: Mirijanian Dina T. , Voth Gregory A.
Published: January 2008

The force-extension profile of tetrameric spectrin is determined by using multiscale computer simulation. Fluctuation results of atomistic simulations of double spectrin repeat units (DSRU) are used to systematically build a coarse-grained (CG) model for the tetrameric form of spectrin. It is found that the spectrin tetramer can be modeled as a soft polymer with a unique flat force-extension profile over the range of biologically important lengths. It is also concluded that in the cytoskeletal network of the red blood cell the tetramer is in an “overcompressed” state. These findings are in contrast to the commonly used models of spectrin tetramer elasticity, namely the “entropic spring” polymer models. From these results, it is concluded that stable intact helical linker regions are needed to maintain the soft elasticity of the spectrin tetramer.
Mechanism of selectivity in aquaporins and aquaglyceroporins
Authors: Hub Jochen S. , de Groot Bert L.
Published: January 2008

Aquaporins and aquaglyceroporins form a family of pore proteins that facilitate the efficient and selective flux of small solutes across biological membranes. We studied the selectivity of aquaporin-1 (AQP1) and the bacterial glycerol facilitator, GlpF, for O
2
, CO
2
, NH
3
, glycerol, urea, and water. Using molecular dynamics simulations, we calculated potentials of mean force for solute permeation along the aquaporin channels and compared them with the alternative pathway across the lipid bilayer. For small solutes permeating through AQP1, a remarkable anticorrelation between permeability and solute hydrophobicity was observed, whereas the opposite trend was observed for permeation through the membrane. This finding renders AQP1 a selective filter for small polar solutes, whereas GlpF was found to be highly permeable for small solutes and permeable for larger solutes. Surprisingly, not solute-channel but water-channel interactions were found to be the key determinant underlying the selectivity mechanism of aquaporins. Hence, a hydrophobic effect, together with steric restraints, determines the selectivity of aquaporins.
Nilpotent orbits in classical Lie algebras over F

2
n

and the Springer correspondence
Authors: Xue Ting
Published: January 2008

We give the number of nilpotent orbits in the Lie algebras of orthogonal groups under the adjoint action of the groups over F

2
n

. Let
G
be an adjoint algebraic group of type
B, C
, or
D
defined over an algebraically closed field of characteristic 2. We construct the Springer correspondence for the nilpotent variety in the Lie algebra of
G
.
Energy of Tycho's Supernova Remnant is increasing with time
Authors: Barenblatt Grigory Isaakovich
Published: January 2008

It is shown, using the Zeldovich integral relations, that the energy of Tycho's Supernova Remnant is strongly growing with time, approximately as
t
1/3
. This growth can be attributed to the exothermic reactions going inside the remnant. The use of the assumption of the adiabaticity of the motion inside of the shock front, and no losses or gain of energy at the front, seems therefore unjustified.
Resurrection of the flagellar rotary motor near zero load
Authors: Yuan Junhua , Berg Howard C.
Published: January 2008

Flagellated bacteria, such as
Escherichia coli
, are propelled by helical flagellar filaments, each driven at its base by a reversible rotary motor, powered by a transmembrane proton flux. Torque is generated by the interaction of stator proteins, MotA and MotB, with a rotor protein FliG. The physiology of the motor has been studied extensively in the regime of relatively high load and low speed, where it appears to operate close to thermodynamic equilibrium. Here, we describe an assay that allows systematic study of the motor near zero load, where proton translocation and movement of mechanical components are rate limiting. Sixty-nanometer-diameter gold spheres were attached to hooks of cells lacking flagellar filaments, and light scattered from a sphere was monitored at the image plane of a microscope through a small pinhole. Paralyzed motors of cells carrying a motA point mutation were resurrected at 23°C by expression of wild-type MotA, and speeds jumped from zero to a maximum value (≈300 Hz) in one step. Thus, near zero load, the speed of the motor is independent of the number of torque-generating units. Evidently, the units act independently (they do not interfere with one another), and there are no intervals during which a second unit can add to the speed generated by the first (the duty ratio is close to 1).
Outcome of Planned Discharge from Case Management: A 3 Year Retrospective Study
Authors: Backus Linda , Weinkove John , Lucas Marilyn , Jespersen Sean
Published: January 2008

Objective: To investigate the rates of relapse of mental illness in adults requiring acute intervention at a mental health service following a planned discharge process from community case management.

Method: A planned approach to identifying and facilitating patient discharge was identified and incorporated into clinical team reviews. Data regarding service contacts of all discharged patients were collected at 1 year and then 3 years following planned discharge and reviewed in detail. Demographic factors and clinical variables were collected in anticipation that useful predictors for successful discharge might be identified.

Results: Using a planned approach, a greater number of patients were discharged from case management to the care of a primary treating practitioner. Discharges increased from 11 in 2000 to 46 in 2001. Of the 46 patients discharged from case management, 22 patients (47.8%) had no contact with the service during the first 12 months. Twenty-four patients accessed the Service requiring no further action, but at some point nine (19.6%) required acute intervention. The remaining 15 patients (32.6%) were managed successfully either by the triage service or non-urgent referral for psychiatric consultation. During the 3 year period 10 patients (21.7%) continued to have no contact with the service. Nineteen patients (41.3%) required acute intervention; the remaining 17 (36.9%) were successfully managed through triage or via non-urgent psychiatric review requiring no further action by the Service. Of the seven patients who had been on a community treatment order during their treatment, only one had further contact with the Service.

Conclusions: A planned approach to the discharge of patients from case management to the community resulted in an increased number of patient discharges. While most patients did not rapidly relapse, a number of patients did have contact with the Service and 19 (41.3%) required at least one acute intervention during the 3 year follow-up period. The findings reflect the importance of relapse prevention and management and service re-entry planning with triage services, patients, carers and other key workers. The frequency of service use and the variation of services required by patients highlight the importance of availability of a variety of adequately resourced levels of service response.
Follow up of Post-Traumatic Stress Disorder Symptoms in Australian Servicemen Hospitalized in 1942–1952
Authors: Watson Paddy Burges , Daniels Brett
Published: January 2008

Objective: To follow up survivors of Australian services hospitalized in 1942–1952 and compare their reported symptoms of post-traumatic stress disorder (PTSD) with symptoms in their hospital files.

Method: Twelve survivors were interviewed and combatants completed the revised Impact of Event Scale.

Results: Eight survivors had symptoms satisfying a diagnosis of PTSD at the time of the study. There was underreporting of most relevant symptoms in their hospital files.

Conclusions: PTSD symptoms were probably common during and after World War II. The findings have implications for the management of PTSD generally and the treatment of ageing WWII veterans in particular.
Post-Traumatic Stress Disorder Symptoms in the Files of Australian Servicemen Hospitalized in 1942–1952
Authors: Watson Paddy Burges , Daniels Brett
Published: January 2008

Objective: To investigate post-traumatic stress disorder (PTSD) symptomatology in servicemen hospitalized 1942–1952.

Method: Hospital files of servicemen (n = 590) were studied and PTSD symptoms in groups, based on service experience, were compared.

Results: Based on their hospital files, 19% of servicemen were classified as having partial PTSD. No full cases of PTSD were identified, due primarily to the small number of recorded avoidance symptoms and the limited information in relation to the stressor criterion. Prisoners of war had the highest reported avoidance and lowest intrusive symptoms compared with other combatants.

Conclusions: PTSD symptoms may have been common during and after World War II. At that time avoidance was not considered a symptom of disorder. Intrusive and arousal symptoms may be the core symptoms of PTSD and avoidance symptoms need to be reconsidered.