bluuebunny/crossref_metadata_2025 huggingface dataset:
XUV laser-plasma source based on solid Ar filament
Authors: Peth Christian , Kalinin Anton , Barkusky Frank , Mann Klaus , Toennies J. Peter , Rusin Lev Yu
Published: November 2007

We present a laser driven soft x-ray source based on a novel solid argon filament. The continuously flowing micron-sized filament (diameter ∼56μm, flow speed ∼5mm∕s) was used as a laser target in order to generate a plasma source of high brightness in the “water window” (2.2–4.4nm) spectral range. The emission properties of the source were characterized in detail with respect to crucial parameters such as positional and energy stability using an extreme ultraviolet (XUV) sensitive pinhole camera and an XUV spectrometer. The results are compared with an argon plasma based on a gas puff target operated under the same experimental conditions showing an increase of the brilliance by a factor of 84. By changing the capillary geometry from a constant diameter to a convergent shape the flow speed of the filament was significantly increased up to 250mm∕s, facilitating the operation at higher repetition rates.
Two-parameter generalization of the logarithm and exponential functions and Boltzmann-Gibbs-Shannon entropy
Authors: Schwämmle Veit , Tsallis Constantino
Published: November 2007

The q-sum x⊕qy≡x+y+(1−q)xy (x⊕1y=x+y) and the q-product x⊗qy≡[x1−q+y1−q−1]1∕(1−q) (x⊗1y=xy) emerge naturally within nonextensive statistical mechanics. We show here how they lead to two-parameter (namely, q and q′) generalizations of the logarithmic and exponential functions (noted, respectively, lnq,q′x and eq,q′x), as well as of the Boltzmann-Gibbs-Shannon entropy SBGS≡−k∑i=1Wpilnpi (noted Sq,q′). The remarkable properties of the (q,q′)-generalized logarithmic function make the entropic form Sq,q′≡k∑i=1Wpilnq,q′(1∕pi) satisfy, for large regions of (q,q′), important properties such as expansibility, concavity, and Lesche stability, but not necessarily composability.
Wave breaking and particle jets in intense inhomogeneous charged beams
Authors: Rizzato Felipe B. , Pakter Renato , Levin Yan
Published: November 2007

This work analyzes the dynamics of inhomogeneous, magnetically focused high-intensity beams of charged particles. While for homogeneous beams the whole system oscillates with a single frequency, any inhomogeneity leads to propagating transverse density waves which eventually result in a singular density build up, causing wave breaking and jet formation. The theory presented in this paper allows us to analytically calculate the time at which the wave breaking takes place. It also gives a good estimate of the time necessary for the beam to relax into the final stationary state consisting of a cold core surrounded by a halo of highly energetic particles.
Experimental study on the influence of foam porosity and pore size on the melting of phase change materials
Authors: Lafdi K. , Mesalhy O. , Shaikh S.
Published: November 2007

Experimental study was carried out to study the phase change heat transfer within a composite of phase change material (PCM) infiltrated high thermal conductivity foam. An experimental setup was built to measure the temperature profiles and capture the melting evolution of the PCM inside aluminum foams. Aluminum foams were used as the porous material, and low melting temperature paraffin wax was used as the PCM. It was observed from the results that the system parameters of the wax/foam composite had a significant influence on its heat transfer behavior. By using higher porosity aluminum foam, the steady-state temperature was reached faster as compared to the foams with lower porosity. Similarly for the bigger pore size foams the steady state was attained faster as compared to the smaller pore size foams. This was due to the greater effect of convection in both the higher porosity and bigger pore size foams. However, for the lower porosity foams the heater temperature was comparatively lower than the higher porosity foams due to greater heat conduction through the foam material. Therefore, an optimal value should be selected for the foam porosity and pore size such that the effects of both conduction and convection heat transfers can be completely utilized to have a greater and improved thermal performance for the wax/aluminum foam composite.
Recombination centers in as-grown and electron-irradiated ZnO substrates
Authors: Son N. T. , Ivanov I. G. , Kuznetsov A. , Svensson B. G. , Zhao Q. X. , Willander M. , Morishita N. , Ohshima T. , Itoh H. , Isoya J. , Janzén E. , Yakimova R.
Published: November 2007

Optical detection of magnetic resonance (ODMR) was used to study defects in ZnO substrates irradiated with 3MeV electrons at room temperature. The Zn vacancy and some other ODMR centers were detected. Among these, the Zn vacancy and two other centers, labeled as LU3 and LU4, were also commonly observed in different types of as-grown ZnO substrates. The LU3 and LU4 are related to intrinsic defects and act as dominating recombination centers in irradiated and as-grown ZnO.
Influence of Zeeman splitting and thermally excited polaron states on magnetoelectrical and magnetothermal properties of magnetoresistive polycrystalline manganite
La
0.8
Sr
0.2
MnO
3
Authors: Sergeenkov S. , Mucha J. , Pekala M. , Drozd V. , Ausloos M.
Published: November 2007

Some possible connection between spin and charge degrees of freedom in magnetoresistive manganites is investigated through a thorough experimental study of the magnetic [alternating current susceptibility and direct current (dc) magnetization] and transport (resistivity and thermal conductivity) properties. Measurements are reported in the case of well characterized polycrystalline La0.8Sr0.2MnO3 samples. The experimental results suggest rather strong field-induced polarization effects in our material, clearly indicating the presence of ordered ferromagnetic regions inside the semiconducting phase. Using an analytical expression which fits the spontaneous dc magnetization, the temperature and magnetic field dependences of both electrical resistivity and thermal conductivity data are found to be well reproduced through a universal scenario based on two mechanisms: (i) a magnetization dependent spin polaron hopping influenced by a Zeeman splitting effect and (ii) properly defined thermally excited polaron states which have to be taken into account in order to correctly describe the behavior of the less conducting region. Using the experimentally found values of the magnetic and electron localization temperatures, we obtain L=0.5 nm and mp=3.2me for estimates of the localization length (size of the spin polaron) and effective polaron mass, respectively.
Electrocoloration and oxygen vacancy mobility of BaTiO3
Authors: Yoo H.-I. , Chang M.-W. , Oh T.-S. , Lee C.-E. , Becker K. D.
Published: November 2007

The electrical-insulation degradation of BaTiO3 is now of growing interest as the BaTiO3-based dielectric layers of multilayer ceramic capacitors are getting thinner to submicron thicknesses. The degradation is understood to be due to the electrotransport of oxygen vacancies and may be monitored by the colors emanating from the cathode and/or anode. In the case of single crystal BaTiO3, a brown color emanates from the anode and a blue color from the cathode. We will experimentally review the generation of the colors in BaTiO3 in electric fields, and discuss their origins and kinetics of color front migration. From the latter the oxygen vacancy mobility against temperature in the range of 150–500°C is subsequently determined and compared with all the literature data that have normally been estimated by other means at elevated temperatures.
Correlating exciton localization with compositional fluctuations in InGaN∕GaN quantum wells grown on GaN planar surfaces and facets of GaN triangular prisms
Authors: Khatsevich S. , Rich D. H. , Zhang X. , Dapkus P. D.
Published: November 2007

We have used spatially and temporally resolved cathodoluminescence (CL) to study the carrier recombination dynamics of InGaN quantum wells (QWs) grown on (0001)-oriented planar GaN and {11¯01}-oriented facets of GaN triangular prisms prepared by lateral epitaxial overgrowth in a metal-organic chemical vapor deposition system. The effects of In migration during growth on the resulting QW thickness and composition were examined. We employed a variable temperature time-resolved CL imaging approach that enables a spatial correlation between regions of enhanced exciton localization, luminescence efficiency, and radiative lifetime with the aim of distinguishing between excitons localized in In-rich quantum dots and those in the surrounding Ga-rich QW regions.
Anisotropic Zeeman splitting and Stark shift of In1−yMnyAs1−xNx oblate quantum dots
Authors: Zhang X. W. , Fan W. J. , Li S. S. , Xia J. B.
Published: November 2007

The electronic structure, Zeeman splitting, and Stark shift of In1−yMnyAs1−xNx oblate quantum dots are studied using the ten-band k⋅p model including the sp-d exchange interaction between the carriers and the magnetic ion. The Zeeman splitting of the electron ground states is almost isotropic. The Zeeman splitting of the hole ground states is highly anisotropic, with an anisotropy factor of 918 at B=0.1 T. The Zeeman splittings of some of the electron and hole excited states are also highly anisotropic. It is because of the spin-orbit coupling which couples the spin states with the anisotropic space-wave functions due to the anisotropic shape. It is found that when the magnetic quantum number of total orbital angular momentum is nearly zero, the spin states couple with the space-wave functions very little, and the Zeeman splitting is isotropic. Conversely, if the magnetic quantum number of total orbital angular momentum is not zero, the space-wave functions in the degenerate states are different, and the Zeeman splitting is highly anisotropic. The electron and hole Stark shifts of oblate quantum dots are also highly anisotropic. The decrease of band gap with increasing nitrogen composition is much more obvious in the smaller radius case because the lowest conduction level is increased by the quantum confinement effect and is closer to the nitrogen level.
Effect of liquid properties on electrosprays from externally wetted ionic liquid ion sources
Authors: Castro S. , Larriba C. , Fernandez de la Mora J. , Lozano P. , Sümer S. , Yoshida Y. , Saito G.
Published: November 2007

Ionic liquid ion sources (ILISs) are externally wetted and electrochemically etched and sharpened tungsten tips used as electrospraying sources for ionic liquids in a vacuum. They have recently shown an ability to operate as emitters of pure ion beams (no drops), even with ionic liquids of moderate surface tension (γ<40dyn∕cm) and electrical conductivity (K<1S∕m) that had in all prior reports (all based on conventional internally fed capillary tips) always operated in the mixed ion-drop regime. The present study uses time of flight mass spectrometry to analyze full ion beams emitted from ILISs for a diversity of ionic liquids with properties in the wide range 0.26<K(S∕m)<2.8, 39.3<γ(dyn∕cm)<48.6. Remarkably, all liquids tested achieve the purely ionic regime. The main effect of reducing electrical conductivity is a reduction of the emission current from 180to10nA.
Characterization of recompressed spall in copper gas gun targets
Authors: Becker R. , LeBlanc M. M. , Cazamias J. U.
Published: November 2007

Complementary experiments and simulations are conducted to characterize the microstructure and mechanisms involved in recompression of spalled ductile metals. Soft capture experiments performed on copper targets in a gas gun include a dense secondary plate spaced behind the customary flyer to recompress the voids in the wake of the spall induced by the flyer. Control experiments are run without the secondary plate to obtain spall damage without recompression. The simulations feature explicit representation of void nucleating particles in a narrow strip of material spanning the flyer package and target. Analysis of the spall closure in the simulations reveals the void collapse mechanisms and the origin of features observed experimentally. The experiments and simulations show little trace of the prior voids, and a thin ribbon of highly strained material is the only readily observable remnant of the spall surface.
Optimization of magnetic properties of Co∕Pd multilayers by applying a large persistent biaxial stress
Authors: Mohanan Senthilnathan , Herr Ulrich
Published: November 2007

We report about optimization of the effective perpendicular magnetic anisotropy (Keff) of [Pd(0.98nm)∕Co(tnm)]30 multilayers by applying an in-plane biaxial tensile stress by loading the Ta substrate with hydrogen. The stress induced anisotropy enhances the Keff, which in turn increases the coercive field and the squareness of the perpendicular magnetization curves. A quantitative analysis of the data using a simple model yields magnetostriction constants for the [Pd(0.98nm)∕Co(tnm)]30 multilayers which are in good agreement with the literature values. We conclude that the Keff can be significantly enhanced by applying persistent in-plane biaxial tensile stress.
High performance thin film transistor with low temperature atomic layer deposition nitrogen-doped ZnO
Authors: Lim S. J. , Kwon Soon-ju , Kim Hyungjun , Park Jin-Seong
Published: November 2007

High performance thin film transistor (TFT) with atomic layer deposition (ALD) nitrogen doped ZnO (ZnO:N) as an active layer is demonstrated. The electrical properties of ZnO thin films were effectively controlled by in situ nitrogen doping using NH4OH as a source for reactants. Especially, the electron concentration in ZnO was lowered to below 1015cm−3. Good device characteristics were obtained from the inverted staggered type TFTs with ZnO:N channel and ALD Al2O3 gate insulator; μsat=6.7cm2∕Vs, Ioff=2.03×10−12A, Ion∕off=9.46×107, and subthreshold swing=0.67V∕decade. The entire TFT fabrication processes were carried out at below 150°C, which is a favorable process for plastic based flexible display.
Acoustic cloaking in three dimensions using acoustic metamaterials
Authors: Chen Huanyang , Chan C. T.
Published: November 2007

A scheme to achieve two dimensional (2D) acoustic cloaking is proposed by Cummer and Schurig [New J. Phys. 9, 45 (2007)] by mapping the acoustic equations to Maxwell’s equations of one polarization in the 2D geometry. We find that the acoustic equation can be mapped to the direct current conductivity equation in three dimensions, which then allows the design of three-dimensional acoustic cloaking using the coordinate transformation scheme. The perfect cloaking effect is confirmed by solving for the scattering problem using the spherical-Bessel function series expansion method.
Effects of shapes and orientations of reversed domains on the conversion efficiency of second harmonic wave in two-dimensional nonlinear photonic crystals
Authors: Li Jingjuan , Li Zhiyuan , Zhang Daozhong
Published: November 2007

The conversion efficiency of second harmonic wave in two-dimensional nonlinear photonic crystals consisting of square lattice and reversed domains of various shapes and orientations is studied numerically. Different shapes of reversed domains (circle, ellipse, rectangle, and square) are considered. We present numerical results and theoretical validations. The results indicate that for a given lattice symmetry and a fixed filling factor, the conversion efficiency of different order quasiphase matched process can be maximized by adjusting the shape and orientation of the reversed domains.
Crystal structure and thermoelectric properties of type-III clathrate compounds in the Ba–In–Ge system
Authors: Kim Jung-Hwan , Okamoto Norihiko L. , Kishida Kyosuke , Tanaka Katsushi , Inui Haruyuki
Published: November 2007

The crystal structure and thermoelectric properties of type-III clathrate compounds in the Ba–In–Ge system have been investigated as a function of In content. The solid solubility of In in the type-III clathrate compounds is determined to be about X=15 when expressed with the formula of Ba24InXGe100−X. Similar to our recent results obtained for type-III clathrate compounds in Ba–Al–Ge and Ba–Ga–Ge systems, values of electrical resistivity, Seebeck coefficient, and electronic thermal conductivity of those in the Ba–In–Ge system generally increase with the increase in the In content because of the decrease in the number of excess electrons as described with the simple Zintl concept. The changes in their lattice thermal conductivity with the In content are explained in terms not only of the low rattling frequency of the guest atom but also of the low Debye temperature of the cage framework.
Low frequency lumped element-based negative index metamaterial
Authors: Erentok Aycan , Ziolkowski Richard W. , Nielsen J. A. , Greegor R. B. , Parazzoli C. G. , Tanielian M. H. , Cummer Steven A. , Popa Bogdan-Ioan , Hand Thomas , Vier D. C. , Schultz S.
Published: November 2007

A lumped element-based negative index metamaterial (NIM) was designed, fabricated, and tested for operation at 400MHz in the ultrahigh frequency (UHF) band. At 400MHz the measured real part of the index of refraction of this NIM was nreal=−3.11 with a loss that was less than 1dB∕cm using unit cells whose overall size d was λ∕d∼75. The NIM bandwidth was >10% in the neighborhood of 400MHz.
Influence of the reactor wall composition on radicals’ densities and total pressure in Cl2 inductively coupled plasmas: II. During silicon etching
Authors: Cunge G. , Sadeghi N. , Ramos R.
Published: November 2007

In an industrial inductively coupled plasma reactor dedicated to silicon etching in chlorine-based chemistry, the density of Cl2 molecules and the gas temperature are measured by means of laser absorption techniques, the density of SiClx (x⩽2) radicals by broadband absorption spectroscopy, the density of SiCl4 and ions by mass spectrometry, and the total gas pressure with a capacitance gauge. These measurements permit us to estimate the mole fractions of Cl, SiCl4, and etch product radicals when etching a 200mm diameter silicon wafer. The pure Cl2 plasma is operated in well prepared chamber wall coating with a thin film of SiOCl, AlF, CCl, or TiOCl. The impact of the chemical nature of the reactor wall’s coatings on these mole fractions is studied systematically. We show that the reactor wall coatings have a huge influence on the radicals densities, but this is not only from the difference on Cl–Cl recombination coefficient on different surfaces. During silicon etching, SiClx radicals sticking on the reactor walls are etched by Cl atoms and recycled into the plasma by forming volatile SiCl4. Hence, the loss of Cl atoms in etching the wall deposited silicon is at least as important as their wall recombination in controlling the Cl atoms density. Furthermore, because SiCl4 is produced at high rate by both the wafer and reactor walls, it is the predominant etching product in the gas phase. However, the percentage of redeposited silicon that can be recycled into the plasma depends on the amount of oxygen present in the plasma: O atoms produced by etching the quartz roof window fix Si on the reactor walls by forming a SiOCl deposit. Hence, the higher the O density is, the lower the SiCl4 density will be, because silicon is pumped by the reactor walls and the SiOCl layer formed is not isotropically etched by chlorine. As a result, in the same pure Cl2 plasma at 20mTorr, the SiClx mole fraction can vary from 18% in a SiOCl-coated reactor, where the O density is the highest, to 62% in a carbon-coated reactor, where there is no O. In the latter case, most of the Cl mass injected in the reactor is stored in SiCl4 molecules, which results in a low silicon etch rate. In this condition, the Cl mass balance is verified within 10%, and from the silicon mass balance we concluded that SiClx radicals have a high surface loss probability. The impact of the reactor wall coating on the etching process is thus important, but the mechanisms by which the walls control the plasma chemistry is much more complicated than a simple control through recombination reaction of halogen atoms on these surfaces.
Hexagonal structures on metal-coated two-dimensional microlens arrays
Authors: Pikulin A. , Bityurin N. , Langer G. , Brodoceanu D. , Bäuerle D.
Published: November 2007

Hexagonally shaped apertures on metal-coated colloidal lattices of microspheres have been observed within certain parameter regimes of femtosecond Ti:sapphire-laser irradiation. The occurrence of such structures is explained by electromagnetic field interferences caused by the array of microspheres. The calculations are based on the splitting of the incident laser field into narrow paraxial Gaussian beams and their subsequent tracing and summation.
Mass and position determination of attached particles on cantilever based mass sensors
Authors: Dohn S. , Svendsen W. , Boisen A. , Hansen O.
Published: November 2007

An analytical expression relating mass and position of a particle attached on a cantilever to the resulting change in cantilever resonant frequency is derived. Theoretically, the position and mass of the attached particle can be deduced by combining measured resonant frequencies of several bending modes. This finding is verified experimentally using a microscale cantilever with and without an attached gold bead. The resonant frequencies of several bending modes are measured as a function of the bead position. The bead mass and position calculated from the measured resonant frequencies are in good agreement with the expected mass and the position measured.
Shear force control for a terahertz near field microscope
Authors: Buersgens F. , Acuna G. , Lang C. H. , Potrebic S. I. , Manus S. , Kersting R.
Published: November 2007

We report on the advancement of apertureless terahertz microscopy by active shear force control of the scanning probe. Extreme subwavelength spatial resolution and a maximized image contrast are achieved by maintaining a tip-surface distance of about 20nm. The constant distance between scanning tip and surface results in terahertz images that mirror the dielectric permittivity of the surface.
Common-path optical coherence tomography with side-viewing bare fiber probe for endoscopic optical coherence tomography
Authors: Sharma Utkarsh , Kang Jin U.
Published: November 2007

All-fiber-optic common-path optical coherence tomography (OCT) using a side-viewing bare fiber probe has been demonstrated and analyzed. A bare single mode fiber tip is angle cleaved at ∼49° to enable side illumination due to total internal reflection. The bare fiber probe was inserted in an arterial tissue and a circumferential OCT scan was obtained. The research is aimed at realizing highly miniaturized monolithic probes for possible applications in miniature endoscopic OCT or intravascular OCT. The effects of the angle of the cleaved fiber on reference reflection and the sensitivity of the common-path OCT system have been studied theoretically. The angle cleaved fiber probe is also used in series with a microlens to analyze and optimize its performance in a common-path OCT system. Our research aims to explore the combined advantages of common-path OCT and extremely simplified miniature probe design and to discuss how it may greatly simplify the endoscopic OCT instrumentation eventually.
Negative reflections of electromagnetic waves in a strong chiral medium
Authors: Zhang Chao , Cui Tie Jun
Published: November 2007

We investigate the reflection properties of electromagnetic/optical waves in isotropic lossless and lossy chiral media. When the chiral parameter is strong enough, we show that an unusual negative reflection occurs at the interface between a chiral medium and a perfectly conducting plane, where the incident wave and one of the reflected eigenwaves lie in the same side of the interface normal. Using such a property, we further demonstrate the focusing ability of such a conducting plane in the strong chiral medium.
Doping poly(p-phenylene vinylene) with phosphomolybdate through layer-by-layer fabrication for optoelectronic applications
Authors: Nelson Christopher B. , Vyas Ritesh N. , Mou Yongyan , Li Ku’yen , Rabalais J. Wayne , Irwin George M. , Wang Bin
Published: November 2007

Poly(p-phenylene vinylene) mulilayers have been prepared from its cationic precursor via the layer-by-layer deposition. The photoluminescence (PL) and film thickness of the multilayers have been examined via fluorimetry and atomic force microscopy. The PL of the multilayers has been observed that is consistent with the literature results. When phosphomolybdate PMo12 is incorporated into the multilayer structure, PL quenching is detected that is proportional to the amount of PMo12 used. The quenching is interpreted as exciton diffusion through the polymer multilayers, followed by exciton dissociation at the polymer/PMo12 interface. We show that the modeling used for calculating the PL intensities derived from inorganic semiconductors is also applicable to conjugated polymers. According to the model, an exciton diffusion length is found to be 11.5±0.4nm.
Effects of molecular orientation on surface-plasmon-coupled emission patterns
Authors: Hiep Hoang Minh , Fujii Minoru , Hayashi Shinji
Published: November 2007

We observed azimuthal distributions of surface-plasmon-coupled emission from thin layers of randomly oriented and oriented sexithiophene molecules deposited on 50-nm-thick Ag films. For the randomly oriented layer, we observed a uniform and isotropic cone of emission, showing that the surface plasmons are excited isotropically in all directions on the Ag surface. The emission pattern for the oriented layer exhibited a much stronger intensity along the direction of molecular orientation, showing that surface plasmons propagating parallel to the molecular orientation are excited most effectively. These results demonstrate that surface-plasmon-coupled emission provides a new simple approach to the determination of molecular orientation in thin films.
Direct measurement of topography-dependent charging of patterned oxide/semiconductor structures
Authors: Upadhyaya G. S. , Shohet J. L. , Kruger J. B.
Published: November 2007

Electron shading, or topography-dependent charging, occurs during plasma exposure of wafers with high-aspect-ratio features due to an imbalance between the electron and ion currents that reach the feature bottoms. High-aspect-ratio pit structures were exposed to an electron cyclotron resonance plasma. The surface potential of the structures after plasma exposure was measured with scanning surface-potential microscopy (SSPM). The results show that SSPM can be used to measure the differential charging in a high-aspect-ratio pit. In situ depletion of the plasma-induced charge with ultraviolet radiation was time resolved using SSPM. A circuit model is used to explain the experimental results.
Self-organized nanostructures on atmospheric microplasma exposed surfaces
Authors: Mariotti Davide , Švrček Vladimir , Kim Dae-Gun
Published: November 2007

We present here the observation of self-organized nanostructures on atmospheric microplasma exposed surfaces. In particular, we present the formation of self-aligned Mo-oxide nanoparticles, as well as the production of self-organized carbon-based connections between silicon nanocrystal micrograins and between Ag nanoparticles. The strong electromagnetic fields that are present at the processing surface play an important role in the self-organization process. This result represents an interesting phenomenon and suggests possible routes to promote and exploit self-organization for the production of nanostructured materials.
X-ray diamond detectors with energy resolution
Authors: Conte G. , Girolami M. , Salvatori S. , Ralchenko V.
Published: November 2007

Polycrystalline diamond detectors with energy resolving capability of the impinging beam were realized and tested by using a miniature pyroelectric x-ray pulse generator. Microstrip structures were defined by photolithography aimed to reduce parasitic capacitances and to perform characterization measurements in a sandwich configuration. Leakage currents as low as 20pA at 500V were measured on a 270μm thick device. Pulse height distributions were carried out around TaLα (8.14keV) and CuKα (8.05keV) characteristic lines of the source. Energy resolution at 200V was found equal to 9% with an increase to 11% at 500 V. When the bias was increased to the maximum voltage the sample shows an Ohmic behavior.
Large and opposite changes of the third-order optical nonlinearities of chalcogenide glasses by femtosecond and continuous-wave laser irradiation
Authors: Zhang Qiming , Liu Wei , Liu Liying , Xu Lei , Xu Yinsheng , Chen Guorong
Published: November 2007

We report that the nonlinear refractive index (n2) of As2S3 glass can be enhanced after irradiation by a femtosecond laser but suppressed after irradiation by a continuous-wave (cw) laser, although both the femtosecond laser and cw laser induce photodarkening in the glass. Photodarkening by the femtosecond laser increases n2 by as much as 50%, while irradiation by a subbandgap cw laser decreases n2 by as much as 60% of its original value. The results provide a way to manipulate the third-order optical nonlinearity of this photonic glass. Mechanisms of the optical nonlinearity changes are discussed.
Low efficiency roll off at high current densities in Ir-complex based electrophosphorescence diode with exciton diffusing and fluorescence compensating layers
Authors: Zhang Dongyu , Li Wenlian , Chu Bei , Zhu Jianzhuo , Li Tianle , Han Lianglaing , Bi Defeng , Li Xiao , Yang Dongfang , Yan Fei , Liu Huihui , Wang Dan , Tsuboi Taiju
Published: November 2007

We demonstrate a fac-tris(2-phenylpyridine) iridium-based electrophosphorescent organic green-light emitting diode with a considerably reduced current-efficiency roll off at high current density. Such a low roll off of efficiency was achieved by inserting nondoped 4,4′-N,N′-dicarbazole-biphenyl (CBP) layer and a tris-(8-hydroxy-quinoline) aluminum (Alq3) layer between the emitting and electron-transporting layers to diffuse excitons from the emitting layer. The Alq3 layer is found to contribute as a complementary green fluorescent emitter at high current density. Thus, only a small decrease from 20.7to16.7cd∕A was detected in current efficiency when the current density increases from 3.9to100mA∕cm2. A high current efficiency of 12.6cd∕A was achieved even at 350mA∕cm2, indicating that the efficiency roll off was drastically reduced when compared with the device without CBP and Alq3 layers.
Solid state reaction at the interface between Heusler alloys and Al cap accelerated by elevated temperature and rough surface
Authors: Kallmayer M. , Hild K. , Eichhorn T. , Schneider H. , Jakob G. , Conca A. , Jourdan M. , Elmers H. J. , Gloskovskii A. , Schuppler S. , Nagel P.
Published: November 2007

We have investigated the solid state reaction at the interface of Co2Cr0.6Fe0.4Al, Co2FeSi, and Ni2MnGa Heusler alloy films and Al cap layers using x-ray absorption spectroscopy in transmission and total electron yield mode. At elevated temperatures and at rough surfaces the deposited Al severely reacts with the surface of a Heusler alloy indicated by changes of the absorption spectra. Microspectroscopy using photoemission electron microscopy reveals that the reaction proceeds inhomogeneously with reaction nuclei separated on a micron length scale.
The influence of visible light on transparent zinc tin oxide thin film transistors
Authors: Görrn P. , Lehnhardt M. , Riedl T. , Kowalsky W.
Published: November 2007

The characteristics of transparent zinc tin oxide thin film transistors (TTFTs) upon illumination with visible light are reported. Generally, a reversible decrease of threshold voltage Vth, saturation field effect mobility μsat, and an increase of the off current are found. The time scale of the recovery in the dark is governed by the persistent photoconductivity in the semiconductor. Devices with tuned [Zn]:[Sn] ratio show a shift of Vth of less 2V upon illumination at 5mW∕cm2 (brightness >30000cd∕m2) throughout the visible spectrum. These results demonstrate TTFTs which are candidates as pixel drivers in transparent active-matrix organic light emitting diode displays.
Sources of Somatosensory Input to the Caudal Belt Areas of Auditory Cortex
Authors: Hackett Troy A , Smiley John F , Ulbert Istvan , Karmos George , Lakatos Peter , de la Mothe Lisa A , Schroeder Charles E
Published: November 2007

The auditory cortex of nonhuman primates is comprised of a constellation of at least twelve interconnected areas distributed across three major regions on the superior temporal gyrus: core, belt, and parabelt. Individual areas are distinguished on the basis of unique profiles comprising architectonic features, thalamic and cortical connections, and neuron response properties. Recent demonstrations of convergent auditory – somatosensory interactions in the caudomedial (CM) and caudolateral (CL) belt areas prompted us to pursue anatomical studies to identify the source(s) of somatic input to auditory cortex. Corticocortical and thalamocortical connections were revealed by injecting neuroanatomical tracers into CM, CL, and adjoining fields of marmoset ( Callithrix jacchus jacchus) and macaque ( Macaca mulatta) monkeys. In addition to auditory cortex, the cortical connections of CM and CL included somatosensory (retroinsular, Ri; granular insula, Ig) and multisensory areas (temporal parietal occipital, temporal parietal temporal). Thalamic inputs included the medial geniculate complex and several multisensory nuclei (supra- geniculate, posterior, limitans, medial pulvinar), but not the ventroposterior complex. Injections of the core (A1, R) and rostromedial areas of auditory cortex revealed sparse multisensory connections. The results suggest that areas Ri and Ig are the principle sources of somatosensory input to the caudal belt, while multisensory regions of cortex and thalamus may also contribute. The present data add to growing evidence of multisensory convergence in cortical areas previously considered to be ‘unimodal’, and also indicate that auditory cortical areas differ in this respect.
Multimodal Ternus: Visual, Tactile, and Visuo — Tactile Grouping in Apparent Motion
Authors: Harrar Vanessa , Harris Laurence R
Published: November 2007

Gestalt rules that describe how visual stimuli are grouped also apply to sounds, but it is unknown if the Gestalt rules also apply to tactile or uniquely multimodal stimuli. To investigate these rules, we used lights, touches, and a combination of lights and touches, arranged in a classic Ternus configuration. Three stimuli (A, B, C) were arranged in a row across three fingers. A and B were presented for 50 ms and, after a delay, B and C were presented for 50 ms. Subjects were asked whether they perceived AB moving to BC (group motion) or A moving to C (element motion). For all three types of stimuli, at short delays, A to C dominated, while at longer delays AB to BC dominated. The critical delay, where perception changed from group to element motion, was significantly different for the visual Ternus (3 lights, 162 ms) and the tactile Ternus (3 touches, 195 ms). The critical delay for the multimodal Ternus (3 light – touch pairs, 161 ms) was not different from the visual or tactile Ternus effects. In a second experiment, subjects were exposed to 2.5 min of visual group motion (stimulus onset asynchrony = 300 ms). The exposure caused a shift in the critical delay of the visual Ternus, a trend in the same direction for the multimodal Ternus, but no shift in the tactile Ternus. These results suggest separate but similar grouping rules for visual, tactile, and multimodal stimuli.
Enhanced Optic Flow Speed Discrimination While Walking: Contextual Tuning of Visual Coding
Authors: Durgin Frank H , Gigone Krista
Published: November 2007

We tested the hypothesis that long-term adaptation to the normal contingencies between walking and its multisensory consequences (including optic flow) leads to enhanced discrimination of appropriate visual speeds during self-motion. In experiments 1 (task 1) and 2 a two-interval forced-choice procedure was used to compare the perceived speed of a simulated visual flow field viewed while walking with the perceived speed of a flow field viewed while standing. Both experiments demonstrated subtractive reductions in apparent speed. In experiments 1 and 3 discrimination thresholds were measured for optic flow speed while walking and while standing. Consistent with the optimal-coding hypothesis, speed discrimination for visual speeds near walking speed was enhanced during walking. Reduced sensitivity was found for slower visual speeds. The multisensory context of walking alters the coding of optic flow in a way that enhances speed discrimination in the expected range of flow speeds.
Multisensory-Mediated Auditory Localization
Authors: Bolognini Nadia , Leor Fabrizio , Passamonti Claudia , Stein Barry E , Làdavas Elisabetta
Published: November 2007

Multisensory integration is a powerful mechanism for maximizing sensitivity to sensory events. We examined its effects on auditory localization in healthy human subjects. The specific objective was to test whether the relative intensity and location of a seemingly irrelevant visual stimulus would influence auditory localization in accordance with the inverse effectiveness and spatial rules of multisensory integration that have been developed from neurophysiological studies with animals [Stein and Meredith, 1993 The Merging of the Senses (Cambridge, MA: MIT Press)]. Subjects were asked to localize a sound in one condition in which a neutral visual stimulus was either above threshold (supra-threshold) or at threshold. In both cases the spatial disparity of the visual and auditory stimuli was systematically varied. The results reveal that stimulus salience is a critical factor in determining the effect of a neutral visual cue on auditory localization. Visual bias and, hence, perceptual translocation of the auditory stimulus appeared when the visual stimulus was supra-threshold, regardless of its location. However, this was not the case when the visual stimulus was at threshold. In this case, the influence of the visual cue was apparent only when the two cues were spatially coincident and resulted in an enhancement of stimulus localization. These data suggest that the brain uses multiple strategies to integrate multisensory information.
Vision and Touch: Multiple or Multisensory Representations of Objects?
Authors: Lacey Simon , Campbell Christine , Sathian K
Published: November 2007

The relationship between visually and haptically derived representations of objects is an important question in multisensory processing and, increasingly, in mental representation. We review evidence for the format and properties of these representations, and address possible theoretical models. We explore the relevance of visual imagery processes and highlight areas for further research, including the neglected question of asymmetric performance in the visuo – haptic cross-modal memory paradigm. We conclude that the weight of evidence suggests the existence of a multisensory representation, spatial in format, and flexibly accessible by both bottom — up and top — down inputs, although efficient comparison between modality-specific representations cannot entirely be ruled out.
Knowledge about a Common Source Can Promote Visual — Haptic Integration
Authors: Helbig Hannah B , Ernst Marc O
Published: November 2007

The brain integrates object information from multiple sensory systems to form a unique representation of our environment. Temporal synchrony and spatial coincidence are important factors for multisensory integration, indicating that the multisensory signals come from a common source. Spatial separations can lead to a decline of visual – haptic integration (Gepshtein et al, 2005 Journal of Vision5 1013–1023). Here we tested whether prior knowledge that two signals arise from the same object can promote integration even when the signals are spatially discrepant. In one condition, participants had direct view of the object they touched. In a second condition, mirrors were used to create a spatial separation between the seen and the felt object. Participants saw the mirror and their hand in the mirror exploring the object and thus knew that they were seeing and touching the same object. To determine the visual — haptic interaction we created a conflict between the seen and the felt shape using an optically distorting lens that made a rectangle look like a square. Participants judged the shape of the probe by selecting a comparison object matching in shape. We found a mutual biasing effect of shape information from vision and touch, independent of whether participants directly looked at the object they touched or whether the seen and the felt object information was spatially separated with the aid of a mirror. This finding suggests that prior knowledge about object identity can promote integration, even when information from vision and touch is provided at spatially discrepant locations.
The Role of Hand Size in the Fake-Hand Illusion Paradigm
Authors: Pavani Francesco , Zampini Massimiliano
Published: November 2007

When a hand (either real or fake) is stimulated in synchrony with our own hand concealed from view, the felt position of our own hand can be biased toward the location of the seen hand. This intriguing phenomenon relies on the brain's ability to detect statistical correlations in the multisensory inputs (ie visual, tactile, and proprioceptive), but it is also modulated by the pre-existing representation of one's own body. Nonetheless, researchers appear to have accepted the assumption that the size of the seen hand does not matter for this illusion to occur. Here we used a real-time video image of the participant's own hand to elicit the illusion, but we varied the hand size in the video image so that the seen hand was either reduced, veridical, or enlarged in comparison to the participant's own hand. The results showed that visible-hand size modulated the illusion, which was present for veridical and enlarged images of the hand, but absent when the visible hand was reduced. These findings indicate that very specific aspects of our own body image (ie hand size) can constrain the multisensory modulation of the body schema highlighted by the fake-hand illusion paradigm. In addition, they suggest an asymmetric tendency to acknowledge enlarged (but not reduced) images of body parts within our body representation.
Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism
Authors: Caspi Avshalom , Williams Benjamin , Kim-Cohen Julia , Craig Ian W. , Milne Barry J. , Poulton Richie , Schalkwyk Leonard C. , Taylor Alan , Werts Helen , Moffitt Terrie E.
Published: November 2007

Children's intellectual development is influenced by both genetic inheritance and environmental experiences. Breastfeeding is one of the earliest such postnatal experiences. Breastfed children attain higher IQ scores than children not fed breast milk, presumably because of the fatty acids uniquely available in breast milk. Here we show that the association between breastfeeding and IQ is moderated by a genetic variant in
FADS2
, a gene involved in the genetic control of fatty acid pathways. We confirmed this gene–environment interaction in two birth cohorts, and we ruled out alternative explanations of the finding involving gene–exposure correlation, intrauterine growth, social class, and maternal cognitive ability, as well as maternal genotype effects on breastfeeding and breast milk. The finding shows that environmental exposures can be used to uncover novel candidate genes in complex phenotypes. It also shows that genes may work via the environment to shape the IQ, helping to close the nature versus nurture debate.
Socialization between toddlers and robots at an early childhood education center
Authors: Tanaka Fumihide , Cicourel Aaron , Movellan Javier R.
Published: November 2007

A state-of-the-art social robot was immersed in a classroom of toddlers for >5 months. The quality of the interaction between children and robots improved steadily for 27 sessions, quickly deteriorated for 15 sessions when the robot was reprogrammed to behave in a predictable manner, and improved in the last three sessions when the robot displayed again its full behavioral repertoire. Initially, the children treated the robot very differently than the way they treated each other. By the last sessions, 5 months later, they treated the robot as a peer rather than as a toy. Results indicate that current robot technology is surprisingly close to achieving autonomous bonding and socialization with human toddlers for sustained periods of time and that it could have great potential in educational settings assisting teachers and enriching the classroom environment.
Developmental pathway of CD4+CD8−medullary thymocytes during mouse ontogeny and its defect inAire−/−mice
Authors: Li Juan , Li Yan , Yao Jin-Yan , Jin Rong , Zhu Ming-Zhao , Qian Xiao-Ping , Zhang Jun , Fu Yang-Xin , Wu Li , Zhang Yu , Chen Wei-Feng
Published: November 2007

The newly generated single-positive (SP) thymocytes undergo further maturation in the thymic medulla before their emigration to the periphery. The present study was undertaken to validate a developmental program we proposed for CD4SP medullary thymocytes and to explore the mechanisms regulating this process. During mouse ontogeny, the emergence of different subsets of CD4SP thymocytes followed a strict temporal order from SP1 to SP4. Parallel to the transition in surface phenotype, a steady increase in function was observed. As further evidence, purified SP1 cells were able to sequentially give rise to SP2, SP3, and SP4 cells in intrathymic adoptive transfer and in culture. Notably, the development of CD4SP cells in the medulla seemed to be critically dependent on a functionally intact medullary epithelial cell compartment becauseRelbandAiredeficiency were found to cause severe blockage at the transition from SP3 to SP4. Taken together, this work establishes an ontogenetically and functionally relevant maturation program for CD4SP thymocytes. Precise dissection of this program should facilitate further inquiry into the molecular mechanisms governing normal thymocyte development and its disturbance in pathological conditions.
An ITAM-signaling pathway controls cross-presentation of particulate but not soluble antigens in dendritic cells
Authors: Graham Daniel B. , Stephenson Linda M. , Lam Siu Kit , Brim Karry , Lee Hyang Mi , Bautista Jhoanne , Gilfillan Susan , Akilesh Shreeram , Fujikawa Keiko , Swat Wojciech
Published: November 2007

Dendritic cells (DC) possess a unique capacity for presenting exogenous antigen on major histocompatibility class I, a process that is referred to as cross-presentation, which serves a critical role in microbial and tumor immunity. During cross-presentation, antigens derived from pathogen-infected or tumor cells are internalized and processed by DCs for presentation to cytotoxic T lymphocytes (CTLs). We demonstrate that a signaling pathway initiated by the immunoreceptor tyrosine–based activation motif (ITAM)–containing adaptors DAP12 and FcRγ utilizes the Vav family of Rho guanine nucleotide exchange factors (GEFs) for processing and cross-presentation of particulate, but not soluble, antigens by DCs. Notably, this novel pathway is crucial for processing and presentation of particulate antigens, such as those associated with Listeria monocytogenes bacteria, yet it is not required for antigen uptake. Mechanistically, we provide evidence that in DCs, Vav GEFs are essential to link ITAM-dependent receptors with the activation of the NOX2 complex and production of reactive oxygen species (ROS), which regulate phagosomal pH and processing of particulate antigens for cross-presentation. Importantly, we show that genetic disruption of the DAP12/FcRγ–Vav pathway leads to antigen presentation defects that are more profound than in DCs lacking NOX2, suggesting that ITAM signaling also controls cross-presentation in a ROS-independent manner.