bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite area vortex motion on a sphere with impenetrable boundaries
Authors: Nelson Rhodri B. , McDonald N. Robb
Published: January 2009

Techniques based on conformal mapping and the numerical method of contour dynamics are presented for computing the motion of a finite area patch of constant vorticity on a sphere with impenetrable boundaries. Several examples of impenetrable boundaries are considered including a spherical cap, longitudinal wedge, half-longitudinal wedge, and a thin barrier. Finite area patch motion is compared to exact point vortex trajectories and good agreement is found between the point vortex trajectories and the centroid motion of finite area patches when the patch remains close to circular. More exotic motion of the finite area patches, particularly in the thin barrier case, is then examined. In the case when background flow owing to a dipole located on the barrier is present, the vortex path is pushed close to one of the barrier edges, leading to vortex shedding and possible splitting and, in certain cases, to a quasisteady trapped vortex. A family of vortex equilibria bounded between the gap in the thin barrier is also computed.
Discriminating the molecular pathways during uptake and release on nanoporous host systems
Authors: Heinke L. , Kärger J.
Published: January 2009

The use of optical techniques, such as interference microscopy, has enabled the observation of transient concentration profiles generated by intracrystalline transport diffusion in nanoporous host materials. In this way, the relevant transport parameters become directly accessible by experiment. We demonstrate that this novel type of information allows one to determine the fraction of molecules which, during molecular uptake (or release), are entering (or leaving) the host crystal through its different faces. By means of numerical calculations of a large amount of different uptake processes, the fraction of the respective fluxes is found to be reasonably calculated by means of the analytical solution for constant (i.e., mean) transport parameters. A more straightforward procedure, based on the assumption that the fraction of the flux is inversely proportional to the time constant calculated with the mean transport parameters, also yields reasonable results. It is shown that even for anisotropic mass transfer with strong concentration dependencies, the divergence from the actual results is generally less than 8%. In most cases such deviations would be below the limits of the accuracy of the determined transport parameters.
Couette and Poiseuille microflows: Analytical solutions for regularized 13-moment equations
Authors: Taheri Peyman , Torrilhon Manuel , Struchtrup Henning
Published: January 2009

The regularized 13-moment equations for rarefied gas flows are considered for planar microchannel flows. The governing equations and corresponding kinetic boundary conditions are partly linearized, such that analytical solutions become feasible. The nonlinear terms include contributions of the shear stress and shear rate, which describe the coupling between velocity and temperature fields. Solutions for Couette and force-driven Poiseuille flows show good agreement with direct simulation Monte Carlo data. Typical rarefaction effects, e.g., heat flux parallel to the wall and the characteristic dip in the temperature profile in Poiseuille flow, are reproduced accurately. Furthermore, boundary effects such as velocity slip, temperature jump, and Knudsen boundary layers are predicted correctly.
Thermal conductivity of (Zr,W)N/ScN metal/semiconductor multilayers and superlattices
Authors: Rawat Vijay , Koh Yee Kan , Cahill David G. , Sands Timothy D.
Published: January 2009

The cross-plane thermal conductivities of metal/semiconductor multilayers and epitaxial superlattices have been measured as a function of period by time-domain thermoreflectance at room temperature. (001)-oriented ZrN (metal)/ScN (semiconductor) multilayers and (Zr,W)N/ScN epitaxial superlattices with the rocksalt crystal structure were grown on (001)MgO substrates by reactive magnetron sputtering. A distinct minimum in thermal conductivity at a period of ∼6 nm is observed for ZrN/ScN multilayers. The minimum thermal conductivity of 5.25 W/m K is a factor of ∼2.7 smaller than the mean of the thermal conductivities (including only the lattice contributions) of the values measured for films of the constituent materials, and approximately equal to the lattice component of the thermal conductivity of a Zr0.65Sc0.35N alloy film (∼5 W/m K). Alloying the ZrN layers with WNx reduces the lattice mismatch, yielding epitaxial (Zr,W)N/ScN superlattices. The addition of WNx also reduces the thermal conductivity to ∼2 W/m K, a value that is sufficiently low to suggest promise for these materials as solid-state thermionic generators.
NMR shielding constants in BF3 and magnetic dipole moments of B11 and B10 nuclei
Authors: Jackowski Karol , Makulski Włodzimierz , Szyprowska Anna , Antušek Andrej , Jaszuński Michał , Jusélius Jonas
Published: January 2009

Gas-phase NMR spectra of B11, B10, and F19 in BF3 are reported, and high-level ab initio calculations of the corresponding NMR shielding constants are described. Extrapolation of the measured resonance frequencies to the zero-density limit ensures that the results correspond to the ab initio values for an isolated molecule. Simultaneous measurements of H3e resonance frequencies and application of the calculated shielding constants allow us to determine improved values of the nuclear magnetic dipole moments of B11 and B10. The magnetic moments of both isotopes are also determined independently by comparing with the F19 spectral parameters (frequencies and shielding constants). The separately derived nuclear magnetic moments are in good agreement, whereas the literature moments of both B11 and B10 are noticeably less accurate.
Computational electrodynamic simulation of direct current discharge
Authors: Shang J. S. , Huang P. G. , Yan H. , Surzhikov S. T.
Published: January 2009

A drift-diffusion model for simulating direct current discharge including the externally applied magnetic field is analyzed by a high-resolution, diagonally dominant numerical procedure. Three different configurations of direct current discharge were studied numerically—the electrodynamic structures of the classic parallel electrodes of infinite and finite dimension, as well as the side-by-side electrode configurations. In the final configuration, an externally applied transverse magnetic field has also been applied in computational simulation to study the Lorentz force effect to the discharge structure. The solutions were compared to classic results, similar numerical simulations, and experimental observations of the discharge physics. Overall, the agreement is very good and the model can be used as a basis for the design of flow control experiments.
Propagation and stability of quantum dust-ion-acoustic shock waves in planar and nonplanar geometry
Authors: Masood W. , Siddiq M. , Nargis Shahida , Mirza Arshad M.
Published: January 2009

Dust-ion-acoustic (DIA) shock waves are studied in an unmagnetized quantum plasma consisting of electrons, ions, and dust by employing the quantum hydrodynamic (QHD) model. In this context, a Korteweg–deVries–Burger (KdVB) equation is derived by employing the small amplitude perturbation expansion method. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. It is found that the strength of the quantum DIA shock wave is maximum for spherical, intermediate for cylindrical, and minimum for the planar geometry. The effects of quantum Bohm potential, dust concentration, and kinematic viscosity on the quantum DIA shock structure are also investigated. The temporal evolution of DIA KdV solitons and Burger shocks are also studied by putting the dissipative and dispersive coefficients equal to zero, respectively. The effects of the quantum Bohm potential on the stability of the DIA shock is also investigated. The present investigation may be beneficial to understand the dissipative and dispersive processes that may occur in the quantum dusty plasmas found in microelectronic devices as well as in astrophysical plasmas.
Weakly nonlinear analysis of short-wave elliptical instability
Authors: Rodrigues Savio B. , De Luca Jayme
Published: January 2009

Two-dimensional inviscid flows with elliptical streamlines have linearly unstable three-dimensional modes close to the center of the ellipse. The linear instability equilibrates in the presence of enough viscosity, yielding a continuous set of neutrally stable plane waves known as Craik–Criminale waves (CCWs). For initial disturbance in a discrete superposition of plane waves our weakly nonlinear analysis yields a cubic ordinary differential equation for the slow-time evolution of the neutrally stable plane-wave amplitudes. In the subcritical region we find that all solutions eventually vanish, while in the supercritical region the amplitudes either saturate or have exponential growth; the existence of a finite-time blowup at cubic order being unlikely. The saturation to a steady state is possible only for special initial conditions, and for generic initial conditions the amplitudes saturate to a chaotic state. In contrast, a single CCW with exponential growth is still unstable, but it loses stability to cycles of growth and decay among the plane waves.
In situ measurements of stress evolution for nanotwin formation during pulse electrodeposition of copper
Authors: Xu Di , Sriram Vinay , Ozolins Vidvuds , Yang Jenn-Ming , Tu K. N. , Stafford Gery R. , Beauchamp Carlos
Published: January 2009

In situ stress measurements were performed during high frequency pulse electrodeposition of nanotwinned Cu thin films. Periodic stress changes during pulse-on and pulse-off periods were observed. The stress profile showed an abrupt increase in tensile stress to about 400 MPa during the pulse-on period and a stress relaxation during the pulse-off period. First-principles calculations predict that a complete relaxation of the tensile stress allows the formation of nanotwins separated by 28 nm or more. This is in good agreement with the results obtained from microstructural analysis of the Cu films fabricated during in situ stress measurements.
Capillary rise of a liquid into a deformable porous material
Authors: Siddique J. I. , Anderson D. M. , Bondarev Andrei
Published: January 2009

We examine the effects of capillarity and gravity in a model of one-dimensional imbibition of an incompressible liquid into a deformable porous material. We focus primarily on a capillary rise problem but also discuss a capillary/gravitational drainage configuration in which capillary and gravity forces act in the same direction. Models in both cases can be formulated as nonlinear free-boundary problems. In the capillary rise problem, we identify time-dependent solutions numerically and compare them in the long time limit to analytically obtain equilibrium or steady state solutions. A basic feature of the capillary rise model is that, after an early time regime governed by zero gravity dynamics, the liquid rises to a finite, equilibrium height and the porous material deforms into an equilibrium configuration. We explore the details of these solutions and their dependence on system parameters such as the capillary pressure and the solid to liquid density ratio. We quantify both net, or global, deformation of the material and local deformation that may occur even in the case of zero net deformation. In the model for the draining problem, we identify numerical solutions that quantify the effects of gravity, capillarity, and solid to liquid density ratio on the time required for a finite volume of fluid to drain into the deformable porous material. In the Appendix, experiments on capillary rise of water into a deformable sponge are described and the measured capillary rise height and sponge deformation are compared with the theoretical predictions. For early times, the experimental data and theoretical predictions for these interface dynamics are in general agreement. On the other hand, the long time equilibrium predicted theoretically is not observed in our experimental data.
Direct imaging of anisotropic minority-carrier diffusion in ordered GaInP
Authors: Haegel N. M. , Mills T. J. , Talmadge M. , Scandrett C. , Frenzen C. L. , Yoon H. , Fetzer C. M. , King R. R.
Published: January 2009

An all-optical technique has been used to provide the first direct measurement of anisotropic minority-carrier diffusion in an ordered alloy of GaInP. Direct imaging of the minority-carrier diffusion distribution resulting from generation at a quasipoint source is obtained using an optical microscope coupled to a scanning electron microscope. Minority-carrier diffusion lengths ranging from 3 to 60 μm are measured by this technique in double heterostructures of GaInP, GaAs, and GaInAs, providing a key parameter of interest to the performance of state-of-the-art triple junction solar cells. Here we show a direct measurement of anisotropy in minority-carrier mobility in ordered GaInP, which is evident in the oval-shaped distribution of the recombination luminescence. A factor of 1.6 increase in minority electron mobility along the [110] major axis is reported.
Neutral gas heating in helium microplasmas
Authors: Jugroot M.
Published: January 2009

The present study details a self-consistent model of charged and neutral particle dynamics which is applied to atmospheric small-space (200 μm) discharges in helium. Hydrodynamic transport equations of the self-consistent and time-dependant model are described with an emphasis on the different terms involved in the close coupling among charged species, neutral species, and the electric field. Those equations are solved by two-dimensional numerical schemes for both species transport and electric field. The microplasmas are studied from an initial cloud until the stages of charged particle overamplification in small spaces, where transients are particularly important. Gas heating, neutral depletion initiation, and electric field reversal are observed, highlighting the close interaction between neutral gas and charged species in governing the evolution of the microplasma.
Production of vibrationally excited H2O from charge exchange of H3O+ with cesium
Authors: Mann Jennifer E. , Xie Zhen , Savee John D. , Bowman Joel M. , Continetti Robert E.
Published: January 2009

The center-of-mass kinetic energy release for the dissociation of H3O following charge exchange of H3O+ with cesium has been studied experimentally and modeled using quasiclassical trajectory calculations based on an ab initio potential energy surface for H3O+ and “direct dynamics” for H3O. Branching fractions for the H2O+H and OH+H2 dissociation channels have been measured and compared to the calculations. The dominant channel is found to be H2O+H and the experimental kinetic energy release spectrum reveals that H2O is formed with a vibrational inversion in stretching vibrations, coupled with low bending and rotational excitation.
Formation process of high-purity Ge-on-insulator layers by Ge-condensation technique
Authors: Nakaharai S. , Tezuka T. , Hirashita N. , Toyoda E. , Moriyama Y. , Sugiyama N. , Takagi S.
Published: January 2009

Formation process of Ge-on-insulator (GOI) layers by Ge condensation with very high purity of Ge is clarified in terms of diffusion behaviors of Si and Ge in a SiGe layer. It is shown that the diffusion behavior affects the Ge condensation process, and the purity of GOI layer can be determined by the relation between oxidation and diffusion of Si. Experimental results support a model of GOI formation that the selective oxidation of Si in SiGe continues until the formation of a GOI layer with the residual Si fraction of less than 0.01%. Based on this model, we quantitatively clarify the reason why GOI layers can reach very low residual Si fraction without oxidizing Ge by calculating the diffusion behavior of Si during the Ge condensation process. As a result, we have found that the thermal diffusion of Si is sufficiently fast so that the selective oxidation of Si can continue during the GOI formation process until the averaged residual Si fraction in the SGOI layer becomes lower than 0.03%, which is essentially consistent with the experimental results. In addition, we have found that, even if the GOI layer is thick, the Ge purity of GOI layer can approach 100% infinitely in principle by enhancing the Si diffusion in SGOI compared to the oxidation rate of SGOI.
Photoluminescence, optically stimulated luminescence, and thermoluminescence study of RbMgF3:Eu2+
Authors: Dotzler C. , Williams G. V. M. , Rieser U. , Robinson J.
Published: January 2009

Optically stimulated luminescence (OSL) and thermoluminescence are observed in polycrystalline RbMgF3:Eu2+ after x-ray, γ-ray, or β irradiation. The main electron traps are F-centers but there are other unidentified traps. The main hole traps at room temperature are probably Eu3+ and thermal or optical stimulation leads to electron-hole recombination at the Eu3+ site and Eu2+ emissions arising from P6J to S87/2 and 4f5d(Eg) to S87/2 transitions. We find that some of the electron traps can be emptied by infrared stimulation and all of the electron traps can be emptied by white light stimulation. The OSL dark decay is long and exceeds 5 days for traps that are emptied by white light stimulation after initial infrared bleaching. Our results show that this compound can be used as a radiation dosimeter for intermediate dose levels where the R87b self-dose does not significantly affect the dose reading.
Influence of erbium on the electronic structure of Fe(65−x)Mo14C15B6Erx (x=,1,2) bulk metallic glasses
Authors: Büttner M. , Shiflet G. J. , Gu X. J. , Poon S. J. , Reinke P.
Published: January 2009

Fe ( 65 − x ) Mo 14 C 15 B 6 Er x bulk metallic glasses have been investigated by means of photoelectron spectroscopy. In order to obtain a clean surface the samples were fractured and analyzed in vacuum. The impact of the incorporation of Er on the local atomic structure, the bonding, and the valence band density of states was examined. Our results show that Er addition modifies the B–C bonding environment, which is expressed in the appearance of an additional peak in the C 1s core level. It also affects the Fe 3s multiplet splitting, indicating changes in the valence band electronic configuration. The change in the electronic structure is corroborated by examination of x-ray photoelectron spectroscopy (XPS) valence band spectra.
Influence of La doping on structural and dielectric properties of SrBi2Nb2O9 ceramics
Authors: Verma Maya , Sreenivas K. , Gupta Vinay
Published: January 2009

Lanthanum doped SrBi2Nb2O9 ceramics with the chemical formula SrBi2−xLaxNb2O9 (SBLN) (x=0–0.5) have been prepared through conventional solid state route. X-ray diffraction reveals the shrinkage of unit cell of strontium bismuth niobate with incorporation of La3+ dopant, having no lone pair electrons. Shifting of Raman phonon modes indicates the reduced rattling space of NbO6 octahedra with increase in La doping concentration. Further, the softening of lowest frequency phonon mode with increasing x in SBLN shows the transition from ferroelectric to paraelectric at room temperature. The dielectric properties for all the compositions are studied as a function of temperature (25 to 500 °C) over the frequency range of 10 kHz–1 MHz. With increase in lanthanum doping concentration the phase transition becomes diffused and transition temperature gets shifted toward lower temperature. A phase transition from normal ferroelectric to paraelectric has been observed via relaxor-type ferroelectrics with increase in x. The frequency dependence of transition temperature was studied in terms of Vogel–Fulcher relation for SBLN (x=0.4).
Thermoelectric power and structural properties in two-phase Sn/SnTe alloys
Authors: Gelbstein Yaniv
Published: January 2009

The influence of the metallurgical states of solid solutions on the thermoelectric power (TEP) measurements, due to electron scattering by crystalline defect, has been well studied. Yet, second phase formation influence on TEP has been neglected and was mainly discussed theoretically. Here we show a correlation between measured TEP and the microstructure of two-phase Sn/Te alloys. The TEP values were fitted to a coupled model based on the Bergman–Levy and the general effective medium equations and shown to conform to the lower bound region, corresponds to a parallel addition configuration.
Two-fluid regimes of the resistive and collisionless tearing instability
Authors: Hosseinpour M. , Bian N. , Vekstein G.
Published: January 2009

The two-fluid (electrons and ions) plasma description is used to investigate spontaneous magnetic reconnection (tearing instability) in a sheared force-free magnetic configuration. The study includes both collisional (resistive) and collisionless (electron inertia) reconnection mechanisms. Together with the Hall effect, this yields various instability regimes, which can be identified by the magnitude of the four nondimensional parameters: Lundquist number S⪢1, electron/ion mass ratio μ≡me∕mi⪡1, plasma β, and the scaled ion inertial skin-depth di=c∕(ωpil), with l being the shear length of the magnetic field. The role of the electron gyroviscosity in the collisionless case is also clarified.
Quantum electron-acoustic double layers in two electron species quantum plasma
Authors: Sah Om Prakash
Published: January 2009

The existence and the characteristic properties of electron-acoustic double layers are investigated in three component unmagnetized dense quantum plasmas consisting of stationary background ions and two electron populations: one “cold” and the other “hot.” Using the one-dimensional quantum hydrodynamic model and the reductive perturbation technique, a generalized form of nonlinear quantum Korteweg–de Vries equation governing the dynamics of weak electron acoustic double layers is derived. A stationary solution of this equation is obtained to discuss the existence criteria of different types of double layers and their characteristic properties. It is shown that two types of compressive double layers: one in the lower δ-parameter region and the other at the higher δ-parameter region, along with rarefactive double layers in the intermediate region, may exist, where δ=nec0∕neh0 is the ratio of unperturbed cold to hot electron densities. The width, the amplitude, and the velocity of these double layers are significantly affected by the δ-parameter. The relevance of the present investigation is also discussed.
Dynamics of femtosecond laser induced voidlike structures in fused silica
Authors: Mermillod-Blondin A. , Bonse J. , Rosenfeld A. , Hertel I. V. , Meshcheryakov Yu. P. , Bulgakova N. M. , Audouard E. , Stoian R.
Published: January 2009

Focused ultrafast laser irradiation of fused silica usually induces a spatially modulated refractive index variation in the bulk material. Strong energy concentration leads to the localized formation of a lower-density cavitylike depressed structure surrounded by compacted matter. We report on applying time-resolved phase contrast microscopy to investigate the timescale of the void formation. We indicate a temporal behavior consistent with shock wave generation and subsequent rarefaction.
Spatially modulated fluorescence emission from moving particles
Authors: Kiesel Peter , Bassler Michael , Beck Markus , Johnson Noble
Published: January 2009

An optical detection technique for a flow cytometer is described, which delivers high signal-to-noise discrimination without precision optics to enable a flow cytometer that can combine high performance, robustness, compactness, low cost, and ease of use. The enabling technique is termed “spatially modulated emission” and generates a time-dependent signal as a continuously fluorescing bioparticle traverses a predefined pattern for optical transmission. Correlating the detected signal with the known pattern achieves high discrimination of the particle signal from background noise. The technique is demonstrated with measurements of fluorescent beads flowing through a microfluidic chip.
An algorithm to sculpt photon dispersion in a subwavelength nanostructure
Authors: Zhang Feng , Holliday Kito S. , Lammert Paul E. , Crespi Vincent H.
Published: January 2009

We introduce a method of gradient-based optimization that continuously deforms a periodic dielectric distribution to generate photonic structures that possess any desired figure of merit expressible in terms of the electromagnetic eigenmodes. As an example, we generate forbidden regions between specified bands at extremely low dielectric contrast.
A thermodynamic model and estimation of the experimental value of spontaneous polarization in a wurtzite GaN
Authors: Yan W. S. , Zhang R. , Xie Z. L. , Xiu X. Q. , Han P. , Lu H. , Chen P. , Gu S. L. , Shi Y. , Zheng Y. D. , Liu Z. G.
Published: January 2009

Determining the spontaneous polarization is a fundamental problem in the III-nitride field. However the experimental value of the spontaneous polarization has not yet been reported. In this study, a thermodynamic model is proposed to investigate the spontaneous polarization of GaN from the GaN high-pressure phase transition. Total macroscopic polarization is directly expressed as coefficients in expansion, and these coefficients are found to be conducted in experiments. The experimental value of the spontaneous polarization of GaN is estimated to be around −0.022 C/m2.
Proton effects on low noise and high responsivity silicon-based photodiodes for space environment
Authors: Pedroza Guillaume , Gilard Olivier , Bourqui Marie-Lise , Bechou Laurent , Deshayes Yannick , How Lip Sun , Rosala François
Published: January 2009

A series of proton irradiations has been carried out on p-n silicon photodiodes for the purpose of assessing the suitability of these devices for the European Galileo space mission. The irradiations were performed at energies of 60, 100, and 150 MeV with proton fluences ranging from 1.7×1010 to 1×1011 protons/cm2. Dark current, spectral responsivity, and dark current noise were measured before and after each irradiation step. We observed an increase in both dark current, dark current noise, and noise equivalent power and a drop of the spectral responsivity with increasing displacement damage dose. An analytical model has been developed to investigate proton damage effects through the modeling of the electro-optical characteristics of the photodiode. Experimental degradations were successfully explained taking into account the degradation of the minority carrier diffusion length in the N-region of the photodiode. The degradation model was then applied to assess the end-of-life performance of these devices in the framework of the Galileo mission.
Oscillating holograms recorded in photorefractive crystals by a frequency detuned feedback loop
Authors: Freschi A. A. , Telles A. C. C. , Frejlich J. , Donatti D. A.
Published: January 2009

We report an optoelectronic feedback loop suitable for generating noise-free interference patterns oscillating at arbitrary waveforms. The technique allows controlling the frequency detuning between the interfering beams through a phase modulator in a closed-loop interferometer. We use the dither signal method and propose a quasisynchronous demodulation scheme to create a phase modulated error signal for driving the loop. The dynamics of the interference fringes is easily controlled by a voltage waveform from a function generator, which is used in association with a time delay circuit for shifting the frequency of the reference signal used for lock-in demodulation. The technique is specially suited for applications involving low-frequency phase oscillations, such as those frequently encountered in the generation of space-charge waves in highly resistive photorefractive materials. The processing scheme allows real time monitoring of the hologram strength, and absolute values for the diffraction efficiency and the holographic phase shift can be obtained. Photorefractive wave oscillations ranging from approximately 100 mHz to 10 Hz were produced in a nominally undoped Bi12TiO20 sample. The technique can be readily applied to other fields of optical interferometry, such as for testing optical surfaces, optimizing adaptive holographic devices, measuring physical quantities, among other applications.
Robust organic lasers comprising glassy-cholesteric pentafluorene doped with a red-emitting oligofluorene
Authors: Wei Simon K. H. , Chen Shaw H. , Dolgaleva Ksenia , Lukishova Svetlana G. , Boyd Robert W.
Published: January 2009

Doped with a red-emitting oligofluorene, fluid and glassy cholesteric liquid crystal (CLC) films are characterized by similar lasing thresholds and efficiencies. With picosecond excitations the output from a glassy CLC laser is temporally stable, but that from a fluid CLC laser decays with time. The difference in stability is attributable to external perturbations on supramolecular structure in the fluid but not the solid state, such as heating through optical pumping, light-induced pitch dilation, and laser-induced flow.
Role of carrier reservoirs on the slow phase recovery of quantum dot semiconductor optical amplifiers
Authors: Kim J. , Meuer C. , Bimberg D. , Eisenstein G.
Published: January 2009

The gain and phase recovery dynamics of quantum-dot (QD) semiconductor optical amplifiers are calculated, including all the optical transitions involved in successive carrier recovery processes. The carrier recovery dynamics of inhomogeneously broadened QDs is simulated by solving 1088 coupled rate equations. The respective contributions of QD states and quantum-well carrier reservoirs to the gain and phase changes are identified both temporally and spectrally. We show that the slow phase recovery component of the QD ground state is induced by the slow carrier dynamics of the carrier reservoir due to a slowly varying line shape function of the refractive index change.
Second harmonic atomic force microscopy of living Staphylococcus aureus bacteria
Authors: Turner Robert D. , Kirkham Jennifer , Devine Deirdre , Thomson Neil H.
Published: January 2009

Monitoring higher harmonics of the drive frequency in amplitude-modulation atomic force microscopy can give extra information on local surface properties. The first to fourth harmonics inclusive were monitored on the surface of individual Staphylococcus aureus bacteria and on the polycarbonate filter in which they were trapped. The second harmonic response was sufficient to create the first higher harmonic images of the surfaces of living bacterial cells under aqueous buffer. Mapping the second harmonic signal onto the height (Z piezo-signal) shows that they are largely uncorrelated, suggesting that it measures local surface properties related to mechanics and/or chemical interactions.
Electrowetting retroreflectors: Scalable and wide-spectrum modulation between corner cube and scattering reflection
Authors: Kilaru M. K. , Cumby B. , Heikenfeld J.
Published: January 2009

Corner cube and spherical retroreflectors are ubiquitous in conspicuity and range-finding applications since they reflect light back to the illumination source with unmatched efficiency. We report here a switchable electrowetting retroreflector platform that provides multiple novel features, including (a) using <0.5 μJ/cm2 electrical energy to switch from a light scattering state, (b) low loss and wide spectrum as limited only by the absorption spectrum of water, (c) use of ultrasimple self-assembly of 103–105 liquid lenslets/in.2 on a polymer/Al corner-cube substrate, and (d) change in retroreflected irradiance of >10:1 over a ±30° field of view.
Advanced intensity correlation method for evaluating Poisson’s ratio of fiberlike material
Authors: Hu Zhenxing , Xie Huimin , Hua Tao , Wang Zhaoyang
Published: January 2009

An advanced intensity correlation method for evaluating Poisson’s ratio of fiberlike materials is presented. The method is based on wave diffraction theory and digital image correlation (DIC) analysis. With the new method, the transverse strain of the fiberlike specimen under stretch can be conveniently and accurately determined by fitting the DIC-measured deformation distributions as a straight line following the theoretical diffraction model. The validity and flexibility of the method have been verified by numerical simulations and an experiment. The method can be readily extended to the characterizations of many fiberlike materials.
Soft ytterbium-based bulk metallic glasses with strong liquid characteristic by design
Authors: Wang J. Q. , Wang W. H. , Bai H. Y.
Published: January 2009

A family of Yb-based bulk metallic glasses with excellent glass-forming ability has been fabricated based on the elastic moduli correlations. The YbZnMg(Cu) glasses exhibit very strong liquid characteristic in fragility (m=26±5), while soft mechanical characteristics, such as low bulk elastic modulus (e.g., Young’s modulus is about 26.5 GPa), small Poisson’s ratio (0.276), low Vickers hardness (1.52 GPa) and Debye temperature, and exceptionally low glass transition temperature (Tg∼347 K). The soft bulk metallic glasses with exceptional values of Tg, fragility, Debye temperature, and elastic moduli confirm some found correlations in metallic glasses.
Electric pressure-induced ferromagnetism mediated by Prussian blue junction
Authors: Moritomo Y. , Shibata T.
Published: January 2009

We investigated the cation transport through a physically made junction between Prussian blue analogs, Na0.72−δNi[Fe(CN)6]0.685.1H2O and Na1.60−δCo[Fe(CN)6]0.902.9H2O. Difference between the cation affinities of the respective compounds causes an electromobile force in the open state and induces spontaneous cation transfer through the junction in the short state. In addition, the doping levels (δ) of the respective compounds are reversibly controlled by an external electric pressure V (=0.6 V). We demonstrated that the Prussian blue junction realizes an electric pressure-induced ferromagnetism.
Modeling and measuring transient discharge current of microelectromechanical switches after dielectric charging by voltage stress
Authors: Molinero D. , Castañer L.
Published: January 2009

Dielectric charging effect in microelectromechanical systems has been studied using transient discharge current measurements after applying both positive and negative voltage stresses. An analytical model considering a single trap in the dielectric has been developed after the derivation of an equivalent circuit of the switch. The total amount of charge trapped can be measured and also the main parameters of the trap and dielectric layer. It is shown that the sign of the stress voltage is important in terms of the amount of charge trapped and of the trap properties
Lateral heterojunction photodetector consisting of molecular organic and colloidal quantum dot thin films
Authors: Osedach Tim P. , Geyer Scott M. , Ho John C. , Arango Alexi C. , Bawendi Moungi G. , Bulović Vladimir
Published: January 2009

We demonstrate a heterojunction photodetector of lateral geometry that utilizes an evaporated film of the hole-transporting molecular material N,N′-bis(3-methylphenyl)-N,N′-bis(phenyl)-9,9-spirobifluorene (spiro-TPD) as a charge transport layer and that is sensitized across visible wavelengths by a thin film of colloidal CdSe nanocrystal quantum dots (QDs). High photon-to-electron quantum conversion efficiencies are obtained at room temperature as a result of photoconductive gain. With an electric field of 3.0×105 V/cm applied across the electrodes, we measure the external quantum efficiency at the first QD absorption peak (at wavelength λ=590 nm) to be 13%, corresponding to an internal quantum efficiency of approximately 80%. The operating mechanism of these devices is discussed, noting that the optical response is dominated by the QD absorption spectrum while the charge transport nearly exclusively takes place in the spiro-TPD.
Oxygen vacancy effect on room-temperature ferromagnetism of rutile Co:TiO2 thin films
Authors: Yan Wensheng , Sun Zhihu , Pan Zhiyun , Liu Qinghua , Yao Tao , Wu Ziyu , Song Cheng , Zeng Fei , Xie Yaning , Hu Tiandou , Wei Shiqiang
Published: January 2009

The x-ray absorption near edge structure spectroscopy and first-principles calculations were combined to study the local and electronic structures of rutile Co:TiO2 thin film with room-temperature ferromagnetism. It was revealed that the CoTi2+ substituting the Ti site forms CoTi2+-VO complex with the O vacancy generated in the annealing process. The O vacancy induces a spin-split donor impurity band with a t2g character within the gap region. We proposed that the strong exchange interaction between the localized carriers captured by O vacancy and the substitutional Co ions leads to the ferromagnetism of the Co:TiO2 thin film.
Polarization loss and leakage current reduction in Au/Bi3.15Nd0.85Ti3O12/Pt capacitors induced by electron radiation
Authors: Li Yushu , Ma Ying , Zhou Yichun
Published: January 2009

Bi 3.15 Nd 0.85 Ti 3 O 12 (BNT) thin films have been deposited on Pt/Ti/SiO2/Si substrates by a sol-gel method. Au top electrodes were formed by sputtering to fabricate capacitors with Au/BNT/Pt structure. The prepared capacitors were then subjected to 10 Mrad(Si) electron radiation. Loss in the remanent polarization and reduction in the leakage current were observed after radiation. Possible mechanisms concerning the radiation-induced changes were discussed. The polarization loss was attributed to the screening effects of trapped charge carriers, while the observed leakage currents showed a grain boundary limited conduction behavior.
C
70
close-packed surfaces and single molecule void-formation by local electric field through a scanning tunneling microscope tip
Authors: Ohta Yohei , Mitsuhashi Ryoji , Nouchi Ryo , Fujiwara Akihiko , Hino Shojun , Kubozono Yoshihiro
Published: January 2009

A C70 close-packed surface was formed by a heating of the Si surface, which is covered with C70 molecules. The close-packed surface is assigned to high-temperature hexagonal close-packed phase. The stability of C70 close-packed surface and formation of nanometer scale structures are studied by the application of local electric field to the close-packed surface. An application of local electric field from scanning tunneling microscope tip to the C70 close-packed surface caused molecular scale evaporation. The application of local electric field near strain in the surface produced a very large void by an evaporation of more than 20 of C70 molecules.
Electric polarization enhancement in multiferroic CoCr2O4 crystals with Cr-site mixing
Authors: Kim Ingyu , Oh Yoon Seok , Liu Yong , Chun Sae Hwan , Lee Jun-Sik , Ko Kyung-Tae , Park Jae-Hoon , Chung Jae-Ho , Kim Kee Hoon
Published: January 2009

Single crystals of multiferroic cobalt chromite Co(Cr2−xCox)O4 have been grown via several methods to have different Co3+ doping levels (x=0.0, 0.14, and 0.18). Under magnetic fields, all the crystals display electric polarization reversal below their spiral spin ordering temperatures. We find that both saturated electric polarization and magnetization under magnetic fields increase significantly with the increase in x. This result can be qualitatively explained by a broken balance between at least two electric polarization contributions existing in CoCr2O4 and is expected to be useful in tailoring electric polarization in similar kinds of multiferroics.
Direct synthesis of nanocrystalline NaAlH4 complex hydride for hydrogen storage
Authors: Xiao X. Z. , Chen L. X. , Fan X. L. , Wang X. H. , Chen C. P. , Lei Y. Q. , Wang Q. D.
Published: January 2009

Nanocrystalline NaAlH4 was directly synthesized by ball milling NaH/Al with TiF3 catalyst under hydrogen pressure of 15–25 bar within 50 h. It is found that the synthesized NaAlH4 exhibits a high reversible hydrogen capacity of 4.7 wt % with fast reaction kinetics. It can absorb about 3.5 wt % hydrogen even at ambient temperature. The Ti–Al–H active species formed during reactive ball milling may act as catalyzing agent for hydrogen dissociation/recombination during in situ hydrogenation process and subsequent hydriding/dehydriding cycle.
Optical spectroscopy of Eu3+ and Tb3+ doped glass ceramics containing LiYbF4 nanocrystals
Authors: Chen Daqin , Yu Yunlong , Huang Ping , Weng Fangyi , Lin Hang , Wang Yuansheng
Published: January 2009

The Eu3+ and Tb3+ doped glass ceramics containing tetragonal LiYbF4 nanocrystals were prepared. The Stark splitting emission, the low electric dipole D50→F72 transition, and the long lifetime of Eu3+ evidenced the partition of rare earth into LiYbF4. For Tb3+ doped glass ceramic, intense ultraviolet emission of Tb3+: G56, D53→F76 transition via cooperative sensitization of Yb3+ and bright blue cooperative luminescence originated from the coupled state of Yb3+–Yb3+ ionic pairs were achieved under 976 nm excitation, ascribing to the low-phonon-energy environment of rare earth ions enriched in nanocrystals and the efficient Yb3+–Tb3+ or Yb3+–Yb3+ interionic interactions.
Passivation of oxygen vacancy states and suppression of Fermi pinning in HfO2 by La addition
Authors: Liu D. , Robertson J.
Published: January 2009

We show that group III elements such as La, Y, Sc, and Al can passivate adjacent oxygen vacancies in HfO2 and ZrO2 by shifting the vacancy gap state up into the conduction band. The shift arises from the outward relaxation of the cations around the vacancy due to its positive charge, becoming a closed shell configuration. La substitution at Hf sites in HfO2 suppresses Fermi level pinning because its holes offer a deeper sink for electrons generated by the vacancy than transfer to the metal gate.
The effects of sediment quality on benthic macroinvertebrates in the River Murray, Australia
Authors: Townsend K. R. , Pettigrove V. J. , Carew M. E. , Hoffmann A. A.
Published: January 2009

Aquatic sediments act as a sink for pollutants that potentially impact on aquatic communities. However, spatial correlations between pollution, hydrology, catchment disturbance and other factors make it difficult to determine the impact of sediment pollution. Field-based microcosm experiments utilising aquatic macroinvertebrates are one approach to isolating the biological effects of sediment pollution on aquatic biota. A field-based microcosm experiment was used to assess the effects of sediment from 14 sites along the River Murray system, Australia. Aquatic ecosystem declines have been observed in this river, but few studies have investigated the quality of its sediments or their biological impact. Chironomidae (midge larvae) dominated the microcosm experiment and were useful as bioindicators of sediment quality. Community composition, high incidences of larval mouthpart deformities in Procladius paludicola and skewed sex ratios in Tanytarsus fuscithorax indicated sediments from irrigation districts were having a toxic effect, but only nutrients were detected at biologically relevant concentrations and these did not correlate with species responses. The present study showed that the biological endpoints used in the microcosm approach can elucidate sediment toxicity even in the absence of supporting sediment chemistry and could successfully be applied to examine changes in sediment quality along a river system.
Igf1r as a therapeutic target in a mouse model of basal-like breast cancer
Authors: Klinakis Apostolos , Szabolcs Matthias , Chen Guoying , Xuan Shouhong , Hibshoosh Hanina , Efstratiadis Argiris
Published: January 2009

Considering the strong association between dysregulated insulin-like growth factor (IGF) signaling and various human cancers, we have used an expedient combination of genetic analysis and pharmacological treatment to evaluate the potential of the type 1 IGF receptor (Igf1r) for targeted anticancer therapy in a mouse model of mammary tumorigenesis. In this particular strain of genetically modified animals, histopathologically heterogeneous invasive carcinomas exhibiting up-regulation of the
Igf1r
gene developed extremely rapidly by mammary gland-specific overexpression of constitutively active oncogenic Kras* (mutant Kras
G12D
). Immunophenotyping data and expression profiling analyses showed that, except for a minor luminal component, these mouse tumors resembled basal-like human breast cancers. This is a group of aggressive tumors of poor prognosis for which there is no targeted therapy currently available, and it includes a subtype correlating with
KRAS
locus amplification. Conditional ablation of
Igf1r
in the mouse mammary epithelium increased the latency of Kras*-induced tumors very significantly (≈11-fold in comparison with the intact model), whereas treatment of tumor-bearing animals by administration of picropodophyllin (PPP), a specific Igf1r inhibitor, resulted in a dramatic decrease in tumor mass of the main forms of basal-like carcinomas. PPP also was effective against xenografts of the human basal-like cancer cell line MDA-MB-231, which carries a
KRAS
G13D
mutation.
Global analysis of the yeast lipidome by quantitative shotgun mass spectrometry
Authors: Ejsing Christer S. , Sampaio Julio L. , Surendranath Vineeth , Duchoslav Eva , Ekroos Kim , Klemm Robin W. , Simons Kai , Shevchenko Andrej
Published: January 2009

Although the transcriptome, proteome, and interactome of several eukaryotic model organisms have been described in detail, lipidomes remain relatively uncharacterized. Using
Saccharomyces cerevisiae
as an example, we demonstrate that automated shotgun lipidomics analysis enabled lipidome-wide absolute quantification of individual molecular lipid species by streamlined processing of a single sample of only 2 million yeast cells. By comparative lipidomics, we achieved the absolute quantification of 250 molecular lipid species covering 21 major lipid classes. This analysis provided ≈95% coverage of the yeast lipidome achieved with 125-fold improvement in sensitivity compared with previous approaches. Comparative lipidomics demonstrated that growth temperature and defects in lipid biosynthesis induce ripple effects throughout the molecular composition of the yeast lipidome. This work serves as a resource for molecular characterization of eukaryotic lipidomes, and establishes shotgun lipidomics as a powerful platform for complementing biochemical studies and other systems-level approaches.
Chromosomal location targets different MYC family gene members for oncogenic translocations
Authors: Gostissa Monica , Ranganath Sheila , Bianco Julia M. , Alt Frederick W.
Published: January 2009

The MYC family of cellular oncogenes includes
c-Myc
,
N-myc
, and
L-myc
, which encode transcriptional regulators involved in the control of cell proliferation and death. Accordingly, these genes become aberrantly activated and expressed in specific types of cancers. For example,
c-Myc
translocations occur frequently in human B lymphoid tumors, while
N-myc
gene amplification is frequent in human neuroblastomas. The observed association between aberrations in particular MYC family genes and specific subsets of malignancies might reflect, at least in part, tissue-specific differences in expression or function of a given MYC gene. Since c-Myc and N-myc share substantial functional redundancy, another factor that could influence tumor-specific gene activation would be mechanisms that target aberrations (e.g., translocations) in a given MYC gene in a particular tumor progenitor cell type. We have previously shown that mice deficient for the DNA Ligase4 (Lig4) nonhomologous DNA end-joining factor and the p53 tumor suppressor routinely develop progenitor (pro)-B cell lymphomas that harbor translocations leading to
c-Myc
amplification. Here, we report that a modified allele in which the
c-Myc
coding sequence is replaced by
N-myc
coding sequence (
NCR
allele) competes well with the wild-type
c-Myc
allele as a target for oncogenic translocations and amplifications in the Lig4/p53-deficient pro-B cell lymphoma model. Tumor onset, type, and cytological aberrations are similar in tumors harboring either the wild-type
c-Myc
gene or the
NCR
allele. Our results support the notion that particular features of the
c-Myc
locus select it as a preferential translocation/amplification target, compared to the endogenous
N-myc
locus, in Lig4/p53-deficient pro-B cell lymphomas.