bluuebunny/crossref_metadata_2025 huggingface dataset:
A simple diffusion model showing anomalous scaling
Authors: Rowlands G. , Sprott J. C.
Published: August 2008

A number of iterated maps and one flow, which show chaotic behavior, have been studied numerically and their time evolution expressed in terms of higher-order moments Mm(t). All the cases show anomalous behavior with Mm(t)∼tg(m), with g(m)≠αm. A simple analytic treatment is given based on an effective diffusion that is dependent on both space and time. This leads to a form for g(m)∕m=a−b∕m, which is in good agreement with numerical results. This behavior is attributed to the presence of convective motion superimposed on the background diffusion, and hence this behavior is expected in a wide variety of maps and flows.
Shear flows induced by nonlinear evolution of double tearing modes
Authors: Wang Zheng-Xiong , Wang Xiaogang , Dong J. Q. , Kishimoto Y. , Li J. Q.
Published: August 2008

Shear flows induced by nonlinear evolution of double tearing modes are investigated in a resistive magnetohydrodynamic model with slab geometry. It is found that intensive and thin poloidal shear flow layers are generated in the magnetic island region driven by coupled reconnection process at both rational surfaces. The structure of the flow layers keeps evolving after the merging of magnetic separatrices and forms a few narrow vortices along the open field lines in the final stage of magnetic reconnection. The effects of the distance between both rational surfaces and the initial magnetic shear on the nonlinear evolution of the plasma flows are also taken into consideration and the relevant mechanism is discussed.
Influence of prepulse plasma formation on neutron production from the laser–target interaction
Authors: Davis J. , Petrov G. M.
Published: August 2008

The interaction of an intense ultrashort pulse laser with a planar uniform target was studied with a two-dimensional relativistic electromagnetic particle-in-cell method to determine the acceleration of deuterons and production of neutrons. A Au-CD2 double-layer planar target with thickness of ∼1μm and a preplasma of variable length was used to generate high-energy deuterons as a precursor for neutron production. The deuteron energy and angular distributions and the neutron production from D(d,n)–He3 nuclear fusion reactions were studied as a function of the preplasma scale length and target thickness. For very thin (submicron) targets the preplasma increases the neutron yield only marginally, but for realistic targets with thickness of a few microns the preplasma enhances the neutron yield by two orders of magnitude. Both the average deuteron energy and neutron yield peak at an optimum preplasma scale length Lpopt≈1∕k0 (k0 laser wave vector), which is of the order of one inverse laser wave vector.
Poloidal velocity of impurity ions in neoclassical theory
Authors: Wong S. K. , Chan V. S. , Solomon W. M.
Published: August 2008

A formula for the poloidal velocity of impurity ions in a two-species plasma is derived from neoclassical theory in the banana regime, with corrections from the boundary layer separating the trapped and transiting ions. The formula is applicable to plasmas with toroidal rotations that can approach the thermal speeds of the ions. Using the formula to determine the poloidal velocity of C+6 ions in a recently reported experiment [W. M. Solomon et al., Phys. Plasmas 13, 056116 (2006)] leads to agreement in the direction of the central region when it is otherwise from theories without strong toroidal rotations. Comparisons among these theories are made, demonstrating the degree of uncertainty of theoretical predictions.
A water bag model of driven phase space holes in non-neutral plasmas
Authors: Barth I. , Friedland L. , Shagalov A. G.
Published: August 2008

The formation and control of stable multiphase space hole structures and the associated Bernstein–Greene–Kruskal modes in trapped pure ion plasmas driven by an oscillating, chirped frequency perturbation are considered. The holes are formed by passing kinetic bounce resonances ωd=nπu∕L in the system, u and L are the longitudinal velocity of the plasma species and the length of the trap, and n is the multiplicity of the resonance (the number of the phase space holes). An adiabatic, quasi-one-dimensional water bag model of this excitation for an initially flat-top distribution of the ions in the trap is suggested, based on the isomorphism with a related problem in infinite quasineutral plasmas. A multiwater bag approach allows us to generalize the theory to other initial distributions. Numerical simulations yield a very good agreement with the theory until the coherent phase space structure is destroyed due to the resonance overlap when the decreasing driving frequency passes a critical value estimated within the water bag theory.
Splashing on elastic membranes: The importance of early-time dynamics
Authors: Pepper Rachel E. , Courbin Laurent , Stone Howard A.
Published: August 2008

We study systematically the effect of substrate compliance on the threshold for splashing of a liquid drop using an elastic membrane under variable tension. We find that the splashing behavior is strongly affected by the tension in the membrane and splashing can be suppressed by reducing this tension. The deflection of the membrane upon droplet impact is measured using a laser sheet, and the results allow us to estimate the energy absorbed by the film upon drop impact. Measurements of the velocity and acceleration of the spreading drop after impact indicate that the splashing behavior is set at very early times after, or possibly just before, impact, far before the actual splash occurs. We also provide a model for the tension dependence of the splashing threshold based on the pressure in the drop upon impact that takes into account the interplay between membrane tension and drop parameters.
Computer simulation and high level virial theory of Saturn-ring or UFO colloids
Authors: Bates Martin A. , Dennison Matthew , Masters Andrew
Published: August 2008

Monte Carlo simulations are used to map out the complete phase diagram of hard body UFO systems, in which the particles are composed of a concentric sphere and thin disk. The equation of state and phase behavior are determined for a range of relative sizes of the sphere and disk. We show that for relatively large disks, nematic and solid phases are observed in addition to the isotropic fluid. For small disks, two different solid phases exist. For intermediate sizes, only a disordered fluid phase is observed. The positional and orientational structure of the various phases are examined. We also compare the equations of state and the nematic-isotropic coexistence densities with those predicted by an extended Onsager theory using virial coefficients up to B8.
Persistent current in coils made out of second generation high temperature superconductor wire.
Authors: Levin George A. , Barnes Paul N. , Murphy John , Brunke Lyle , Long J. David , Horwath John , Turgut Zafer
Published: August 2008

We report the results of an experimental study of a persistent coil made out of YBa2Cu3O7−δ coated conductors. The magnitude of the persistent current and the rate of decay were investigated. Two distinct modes of relaxation are evident—one is flux creep and the other, which is much faster, is of less obvious origin. Our conclusion is that the persistent current in such a coil can be large enough and decay slowly enough so that coated conductors can be used to make persistent coils for variety of applications.
Comment on “Ring-breaking electron attachment to uracil: Following bond dissociations via evolving resonances” [J. Chem. Phys. 128, 174302 (2008)]
Authors: Winstead Carl , McKoy Vincent
Published: August 2008

We point out that the assignment of π* resonances to calculated features in a recent paper by Gianturco et al. [J. Chem. Phys.128, 174302 (2008)] cannot be correct.
Controllable resistance and temperature dependency of carbon nanotube bundles
Authors: Mahanandia P. , Nanda K. K.
Published: August 2008

We report the controllable resistance of multiwalled carbon nanotube bundles for the possible application in nanoscale electronics. The resistance as well as the variation of resistance with temperature depends on the bundle diameter. The larger the diameter, smaller is the resistance and weaker is the variation of resistance with temperature that make the bundles advantageous in nanoscale electronics and in some other applications. As the resistance and the variation can be controlled by monitoring the bundle diameter, the temperature dependency of resistance can be employed in temperature thermometry.
Multiferroic BiMnO3 thin films with double SrTiO3 buffer layers
Authors: Son J. Y. , Shin Y.-H.
Published: August 2008

High quality BiMnO3 thin films with double SrTiO3 buffer layers were fabricated on Pt∕Ti∕SiO2∕Si and SrTiO3 substrates, in which SrTiO3 buffer layers were used to reduce leakage current in BiMnO3 thin films. The SrTiO3 buffer layers had a thickness of about 5nm obtained from the fitting of ellipsometer data, which gave the remarkable enhancement in leakage current. BiMnO3 thin films exhibited the ferromagnetic transition with the Curie temperature of about 105K. The Pt∕SrTiO3∕BiMnO3∕SrTiO3∕Pt and SrRuO3∕SrTiO3∕BiMnO3∕SrTiO3∕SrRuO3 capacitors showed good ferroelectric properties with the remanent polarization of about 9 and 16μC∕cm2, respectively.
Separation of bulk and surface electron transport in metamorphic InAs layers using quantitative mobility spectrum analysis
Authors: Lin Y. , Arehart A. R. , Carlin A. M. , Ringel S. A.
Published: August 2008

Electron transport in low dislocation density, strain-relaxed InAs layers grown on metamorphic InAsyP1−y∕InP substrates by molecular beam epitaxy was characterized using quantitative mobility spectrum analysis (QMSA) of Hall effect measurements. QMSA applied to systematically varied metamorphic InAs samples reveals high bulk electron mobilities of ∼20000cm2∕Vs at 300K at a Si doping concentration of 1×1017cm−3, simultaneously with a separate population of much slower electrons having an average mobility of ∼2400cm2∕Vs due to parallel conduction within the InAs surface electron accumulation layer. Measurements made on higher doped samples reveal only a single electron population participating in transport due to lowered surface band bending that reduces surface accumulation of electrons in conjunction with the high conductivity of the high mobility metamorphic InAs bulk that overwhelms any remaining surface conductivity in the Hall effect measurements.
Open optoelectrowetting droplet actuation
Authors: Chuang Han-Sheng , Kumar Aloke , Wereley Steven T.
Published: August 2008

We present experimental realization of an open optoelectrowetting (o-OEW) device for liquid droplet manipulations. The o-OEW device is realized by coplanar electrodes and a photoconductor. The local switching effect for electrowetting resulting from illumination is based on the tunable impedance of the photoconductor. Dynamic virtual electrodes are created using projected images, leading to free planar movements of droplets. Basic operations such as transporting and merging were demonstrated. Translational speed up to 3.6mm∕s was measured. Equivalent circuit analysis shows that the operational frequency for the current setup ranges from 100to800Hz.
High thermoelectric efficiency in lanthanum doped Yb14MnSb11
Authors: Toberer Eric S. , Brown Shawna R. , Ikeda Teruyuki , Kauzlarich Susan M. , Jeffrey Snyder G.
Published: August 2008

Lanthanum doping of the high-temperature p-type thermoelectric material Yb14MnSb11 enhances the figure of merit (zT) through carrier concentration tuning. This is achieved by substituting La3+ on the Yb2+ site to reduce the free hole concentration as expected from the change in valence. The high-temperature transport properties (Seebeck coefficient, electrical resistivity, Hall mobility, and thermal conductivity) of Yb13.6La0.4MnSb11 are explained by the change in carrier concentration using a simple rigid parabolic band model, similar to that found in Yb14Mn1−xAlxSb11. Together, use of these two dopant sites enables the partial decoupling of electronic and structural properties in Yb14MnSb11-based materials.
Wake field generation and nonlinear evolution in a magnetized electron-positron-ion plasma
Authors: Shukla P. K. , Brodin G. , Marklund M. , Stenflo L.
Published: August 2008

The nonlinear propagation of a circularly polarized electromagnetic (CPEM) wave in a strongly magnetized electron-positron-ion plasma is investigated. Two coupled equations describing the interaction between a high-frequency CPEM wave and the low-frequency electrostatic wake field are derived. It is found that the generation of the wake fields partly depends on the presence of the ion species and the external magnetic field. The wake field generation in turn leads to deceleration and frequency down conversion of the electromagnetic pulse.
A molecular approach to the intermediate band solar cell: The symmetric case
Authors: Ekins-Daukes N. J. , Schmidt T. W.
Published: August 2008

Molecular materials may overcome some of the difficulties for making an intermediate band solar cell by storing energy in long-lived triplet states. Both the problems of fast nonradiative interband relaxation and selective photon absorption can be solved by this approach. A practical implementation of the molecular intermediate band solar cell is considered with a symmetric band alignment, resting on a proven triplet-triplet annihilation process. The limiting power conversion efficiency for this system exceeds that of a single bandgap device over a broad range, peaking at 40.6% for 1.9eV under 1 sun illumination.
Near-field analysis of surface electromagnetic waves in the bandgap region of a polymeric grating written on a one-dimensional photonic crystal
Authors: Sfez Tristan , Descrovi Emiliano , Dominici Lorenzo , Nakagawa Wataru , Michelotti Francesco , Giorgis Fabrizio , Herzig Hans-Peter
Published: August 2008

The spatial distribution of surface electromagnetic waves on a one-dimensional photonic crystal with a polymeric grating on top is mapped using a multiheterodyne scanning near-field optical microscope. The grating opens a bandgap. At the band edges, a stationary field formed by two surface waves with opposite propagation constants and almost identical amplitudes is produced. Field intensity maxima are localized to the grating peaks or grooves, depending on the wavelength. Far from the bandgap, we identify surface waves coupled via either the 0 or the −1 order of the grating. The corresponding phase profiles indicate that these waves propagate in opposite directions.
Strong nanopore pinning enhances Jc in YBa2Cu3O7−δ films
Authors: Wu J. Z. , Emergo R. L. S. , Wang X. , Xu G. , Haugan T. J. , Barnes P. N.
Published: August 2008

Transport critical current density (Jc) has been studied in YBa2Cu3O7−δ (YBCO) thin films doped with nanopores as pins on magnetic vortices. The density of the nanopores in the range of 5±3 pores/μm2 corresponds to an accommodation field Hm∼4.1–16.6 mT. High Jc up to 8.3 MA/cm2 has been observed on these porous YBCO films at 77 K and self-field. A close correlation between Jc and the magnetic pinning potential of the nanopores has been demonstrated below Hm, suggesting that nanopores are strong pins on the magnetic vortices.
Correlation between charge trap distribution and memory characteristics in metal/oxide/nitride/oxide/silicon devices with two different blocking oxides, Al2O3 and SiO2
Authors: Seo Y. J. , Kim K. C. , Kim H. D. , Joo M. S. , An H. M. , Kim T. G.
Published: August 2008

We examined the origin of the charge traps in bothSiO2/Si3N4/SiO2 (ONO) and Al2O3/Si3N4/SiO2 (ANO) structures and their effect on the memory characteristics by capacitance-voltage (C-V) measurements and deep level transient spectroscopy (DLTS). A larger memory window was observed by C-V for ANO, due to its higher trap density. The DLTS showed that nitride traps are dominant in ANO, while more Si/SiO2 interface-related traps are observed in ONO. The ANO capacitor outperforms the ONO one in terms of both the program efficiency and retention, which is attributed to the reduced number of interface traps in ANO.
Dynamics of ultraviolet emissions in Tm-doped AlN using above band gap excitation
Authors: Nepal N. , Zavada J. M. , Lee D. S. , Steckl A. J.
Published: August 2008

We report on dynamics of ultraviolet (UV) emissions using above band gap excitation in Tm-doped AlN epilayers grown by solid-source molecular beam epitaxy. The UV and visible photoluminescence (PL) spectra were measured using the frequency quadrupled output from a Ti:sapphire laser. In the UV region, dominant emissions at 298 and 358 nm were observed under 197 nm excitation. Temperature dependence of the PL intensities of these emission lines reveals a binding energy of ∼150 meV. The quenching of the UV emissions in AlN:Tm appears related to the thermal activation of the excitons bound to the rare-earth structured isovalent charge trap at 1.50 eV below the conduction band.
A three-dimensional ultrasonic cage for characterization of individual cells
Authors: Manneberg Otto , Vanherberghen Bruno , Svennebring Jessica , Hertz Hans M. , Önfelt Björn , Wiklund Martin
Published: August 2008

We demonstrate enrichment, controlled aggregation, and manipulation of microparticles and cells by an ultrasonic cage integrated in a microfluidic chip compatible with high-resolution optical microscopy. The cage is designed as a dual-frequency resonant filleted square box integrated in the fluid channel. Individual particles may be trapped three dimensionally, and the dimensionality of one-dimensional to three-dimensional aggregates can be controlled. We investigate the dependence of the shape and position of a microparticle aggregate on the actuation voltages and aggregate size, and demonstrate optical monitoring of individually trapped live cells with submicrometer resolution.
Spontaneous nanoclustering of ZrO2 in atomic layer deposited LayZr1−yOx thin films
Authors: Jinesh K. B. , Besling W. F. A. , Tois E. , Klootwijk J. H. , Wolters R. , Dekkers W. , Kaiser M. , Bakker F. , Tuominen M. , Roozeboom F.
Published: August 2008

During atomic layer deposition of homogeneous LayZr1−yOx thin films spontaneous segregation of ZrO2 nanocrystals that are embedded in an amorphous La2O3 matrix takes place. This occurs if the Zr content in the LayZr1−yOx film rises above 30%, i.e., if the pulse ratio between the lanthanum precursor and the zirconium precursor is larger than four. X-ray diffraction analysis shows that the ZrO2 nanocrystals are in the tetragonal phase, which is the most stable configuration of this material with the highest dielectric permittivity. These nanocrystal-embedded thin films exhibit higher dielectric constants as the Zr content increases.
Electrically controlled silicon-based photonic crystal chromatic dispersion compensator with ultralow power consumption
Authors: Png Ching Eng , Park Gi Ho , Lim Soon Thor , Li Er Ping , Danner Aaron J. , Ogawa Kensuke , Tan Yong Tsong
Published: August 2008

We show full three-dimensional electrical and optical simulation of a tunable silicon-based photonic crystal chromatic dispersion compensator with high power efficiency and ultralow power consumption (114 nW), operating at a speed of 40.5 MHz. The device exploits a structure where the optical field maximum is not in a photonic crystal waveguide, but rather in a hybrid Si3N4/Si/SiO2 structure that will allow greater ease of fiber coupling due to larger mode size and reduced loss. The chromatic dispersion compensation is broadband and produces constant second order chromatic dispersion over an optical communication band such as C-band.
Atomic control and characterization of surface defect states of TiO2 terminated SrTiO3 single crystals
Authors: Kareev M. , Prosandeev S. , Liu J. , Gan C. , Kareev A. , Freeland J. W. , Xiao Min , Chakhalian J.
Published: August 2008

By using an alternative wet-etch procedure, we have obtained high-quality atomically flat TiO2 terminated surfaces of SrTiO3 single crystals with the morphology equivalent to that of the conventional wet-etch methods. By applying a combined power of photoluminescence (PL) spectroscopy, reflection high-energy electron diffraction, atomic force microscopy imaging, and soft x-ray absorption (XAS), we were able to identify and monitor the complex evolution of oxygen defect states and Ti valency at the surface and near-surface layers. Our experiments revealed a high level of local defects resulting in the presence of the Ti3+ states at the surface. We have developed a method to control the defect states capable of a marked reduction of the defect concentration. We have demonstrated that the PL and XAS are able to distinguish the surface-related Ti3+ states from oxygen vacancies trapping charge transfer vibronic excitons that define the PL intensity. The experimental findings will have important implications for the growth of high-quality ultrathin complex oxide heterostructures.
Fano filters based on transferred silicon nanomembranes on plastic substrates
Authors: Qiang Zexuan , Yang Hongjun , Chen Li , Pang Huiqing , Ma Zhenqiang , Zhou Weidong
Published: August 2008

We report here the characteristics of surface-normal optical filters based on Fano resonances on patterned single crystalline silicon nanomembranes (SiNMs), which were fabricated and transferred onto transparent plastic substrates using a SiNM wet transfer process. Detailed experimental and theoretical analyses were carried out on the angular- and polarization-dependent transmission properties. The filter transmission is independent of the incident beam polarization under surface-normal conditions. Angle-independent transmission was observed for specific Fano resonances with certain polarizations. The measured angle-dependent transmission agrees well with the simulated transmission and dispersion properties based on the propagation wave-vector analysis.
Hydrogen storage in alkali-metal-decorated organic molecules
Authors: Huang Bing , Lee Hoonkyung , Duan Wenhui , Ihm Jisoon
Published: August 2008

We investigate the feasibility of alkali-metal (AM)-decorated organic molecules for hydrogen storage using first-principles density functional calculations. The present studies indicate that AMs bind strongly to some organic molecules, and Li-doped organic molecules exhibit a higher storage capacity (>10 wt %) than Na or K. The adsorption energies of dihydrogen on Li-decorated organic molecules are in the range of 10–30 kJ/mol, acceptable for reversible H2 adsorption/desorption near room temperature. Regarding the H2 adsorption mechanism, it is demonstrated that the dipole originating from the charge transfer within the AM-organic molecule complex induces a dipole in the H2 molecule.
Effects of atmospheric neutrons and natural contamination on advanced microelectronic memories
Authors: Wrobel F. , Gasiot J. , Saigné F. , Touboul A. D.
Published: August 2008

We have investigated material susceptibilities to atmospheric neutrons by calculating nuclear cross sections for every natural element from carbon to bismuth. The alpha emitters that can be present in microelectronic devices have also been identified. To improve the performance of microelectronic devices, the semiconductor industry has introduced a number of chemical elements in the device process. These elements experience a natural flux of neutrons and can also contain natural radioactive isotopes. In both cases, device reliability can be compromised. We show that, at ground level, the introduction of an element may be more important than the effect of neutrons.
GaNAsSb material for ultrafast microwave photoconductive switching application
Authors: Tan K. H. , Yoon S. F. , Tripon-Canseliet C. , Loke W. K. , Wicaksono S. , Faci S. , Saadsaoud N. , Lampin J. F. , Decoster D. , Chazelas J.
Published: August 2008

We report a photoconductive switch with GaNAsSb as active material for microwave switching application. The GaNAsSb layer was grown by molecular beam epitaxy in conjunction with a rf plasma-assisted nitrogen source and a valved antimony cracker source. The 0.5 μm thick GaNAsSb photoabsorption layer contains 3.5% of N and 9% of Sb. The switch exhibits pulsed response with full width at half maximum of 30 ps and photoresponse of up to 1.6 μm. In microwave switching application, the switch shows ON/OFF ratio of 11 dB at 1 GHz and response up to 15 GHz.
Contactless electroreflectance of GaN bulk crystals grown by ammonothermal method and GaN epilayers grown on these crystals
Authors: Kudrawiec R. , Misiewicz J. , Rudziński M. , Zając M.
Published: August 2008

Room temperature contactless electroreflectance (CER) spectroscopy has been applied to study the energy gap, optical quality, and band bending for n-type and semi-insulating GaN crystals grown by ammonothermal method. Broad CER resonances typical of band-to-band absorption with opposite phases, which indicates opposite band bendings, have been clearly observed for the two types of GaN crystals. In addition, GaN epilayers have been grown by metalorganic chemical vapor deposition on these crystals and characterized by CER spectroscopy. Very narrow CER resonances (∼15 meV), typical of high quality material, have been observed for these epilayers. It confirms the excellent usefulness of ammonothermal GaN substrates for GaN homoepitaxy.
Electron injection assisted phase transition in a nano-Au-VO2 junction
Authors: Xu Gang , Huang C.-M. , Tazawa Masato , Jin Ping , Chen D.-M. , Miao L.
Published: August 2008

The semiconductor-metal transition of vanadium dioxide (VO2) thin films epitaxially grown on C-plane sapphire is studied by depositing Au nanoparticles onto the thermochromic films forming a metal-semiconductor contact, namely, a nano-Au-VO2 junction. It reveals that Au nanoparticles have a marked effect on the reduction in the phase transition temperature of VO2. A process of electron injection in which electrons flow from Au to VO2 due to the lower work function of the metal is believed to be the mechanism. The result may support the Mott–Hubbard phase transition model for VO2.
A study of metal-oxide-semiconductor capacitors on GaAs, In0.53Ga0.47As, InAs, and InSb substrates using a germanium interfacial passivation layer
Authors: Kim Hyoung-Sub , Ok I. , Zhang M. , Zhu F. , Park S. , Yum J. , Zhao H. , Lee Jack C. , Majhi Prashant , Goel N. , Tsai W. , Gaspe C. K. , Santos M. B.
Published: August 2008

In this letter, we present electrical characteristics of HfO2-based metal-oxide-semiconductor capacitors (MOSCAPs) on n- and p-type GaAs, In0.53Ga0.47As, InAs, and InSb substrates, along with the effect of a thin germanium interfacial passivation layer. We found that MOSCAPs on all n-type substrates showed good C-V characteristics with small frequency dispersion (<10% and <200 mV). However, MOSCAPs on p-type GaAs and In0.53Ga0.47As substrates exhibited poor C-V characteristics implying severe Fermi level pinning, as has also been seen for p-type InP substrate. On the other hand, MOSCAPs on p-type InAs and InSb substrates, known as smaller bandgap materials, showed good C-V characteristics. We also present plausible mechanism for Fermi level pinning and interface characteristics.
Efficiency enhancement of polymer photovoltaic devices hybridized with ZnO nanorod arrays by the introduction of a vanadium oxide buffer layer
Authors: Takanezawa Kazuko , Tajima Keisuke , Hashimoto Kazuhito
Published: August 2008

The introduction of an electron-blocking layer of vanadium oxide between the organic layer and the Ag electrode was studied as a means of improving the performance of bulk heterojunction photovoltaic devices based on poly(3-hexylthiophene): (6,6)-phenyl C61 butyric acid methyl ester hybridized with vertically aligned ZnO nanorod arrays. The power conversion efficiency was further improved to 3.9% by applying a short circuit current density of 10.4 mA cm−2, an open circuit voltage of 0.58 V, and a fill factor of 65% under AM1.5 100 mW cm−2 irradiation, owing to the electron collection “antenna” effect of the ZnO nanorod arrays.
On the origin of ferromagnetism in CeO2 nanocubes
Authors: Ge M. Y. , Wang H. , Liu E. Z. , Liu J. F. , Jiang J. Z. , Li Y. K. , Xu Z. A. , Li H. Y.
Published: August 2008

Magnetic behaviors of pure CeO2 nanoparticles and nanocubes have been investigated both experimentally and theoretically. It is found that monodisperse CeO2 nanocubes with an average size of 5.3 nm do show ferromagnetic behavior at ambient temperature with a saturation magnetization of about 5.7 memu/g and coercive force of about 69 Oe. First-principles calculations reveal that oxygen vacancies in pure CeO2 cause spin polarization of f electrons for Ce ions surrounding oxygen vacancies, resulting in net magnetic moment for pure CeO2 samples. One oxygen vacancy at surface can induce more magnetic moments than those induced by one oxygen vacancy in bulk. The results obtained here provide evidence that pure CeO2 sample with oxygen vacancies can indeed have magnetic behavior. This study will stimulate more investigations for understanding the origin of ferromagnetic TM-doped CeO2 (TM=3d transition metals) in a particular case and TM-doped semiconductor oxides in general at ambient temperature.
Transition of ion-acoustic perturbations in multicomponent plasma with negative ions
Authors: Sharma Sumita Kumari , Devi Kavita , Adhikary Nirab Chandra , Bailung Heremba
Published: August 2008

Evolution of ion-acoustic compressive (positive) and rarefactive (negative) perturbations in a multicomponent plasma with negative ions has been investigated in a double plasma device. Transition of compressive solitons in electron-positive ion plasma, into a dispersing train of oscillations in a multicomponent plasma, when the negative ion concentration r exceeds a critical value rc, has been observed. On the other hand, an initial rarefactive perturbation initially evolves into a dispersing train of oscillations in electron-positive ion plasma and transforms into rarefactive solitons in a multicomponent plasma when the negative ion concentration is higher than the critical value. The Mach velocity and width of the compressive and rarefactive solitons are measured. The compressive solitons in the range 0<rrc have different characteristics than the Korteweg–de Vries (KdV) solitons at r=0 and modified KdV solitons at r=rc. A nonlinear differential equation having two terms to account for the lower and higher order nonlinearity has been used to explain the observed results.
The amorphous origin and the nucleation of intermetallic compounds formed at the interface during the soldering of Sn–3.0Ag–0.5Cu on a Cu substrate
Authors: Pan Chien-Cheng , Yu Chang-Ho , Lin Kwang-Lung
Published: August 2008

A short time reflow of 15s at 250°C, followed by a liquid nitrogen quench, of the Sn–3Ag–0.5Cu solder on a Cu substrate gave rise to a three-layer interfacial structure. In addition to the commonly known η-Cu6Sn5∕ε-Cu3Sn layers, an amorphous layer with a thickness of less than 50nm exists between the Cu substrate and the thin ε-Cu3Sn layer. Nanocrystalline ε-Cu3Sn cells, revealed by transmission electron microscopy (TEM), as fine as 10nm were detected within the amorphous region. The results of TEM analysis suggest that the nucleation of interfacial intermetallic compound ε-Cu3Sn occurs within the amorphous layer.
Thermal poling induced second-order nonlinearity in femtosecond-laser-modified fused silica
Authors: An Honglin , Fleming Simon , McMillen Benjamin W. , Chen Kevin P. , Snoke David
Published: August 2008

Thermal poling was utilized to induce second-order nonlinearity in regions of fused silica modified by 771 nm femtosecond laser pulses. With second-harmonic microscopy, it was found that the nonlinearity in the laser-modified region was much lower than that in nonmodified regions. This is attributed to a more rigid glass network after irradiation by the femtosecond laser pulses and/or lack of mobile alkali ions. Measurement of the distribution of chemical elements in the femtosecond-laser-modified region in a soda lime glass revealed a lower level of sodium ions.
Demographic indications of decline in the spectacled flying fox (Pteropus conspicillatus) on the Atherton Tablelands of northern Queensland
Authors: Fox Samantha , Luly Jon , Mitchell Catlin , Maclean Jenny , Westcott David A.
Published: August 2008

A lack of information about the spectacled flying fox (Pteropus conspicillatus) makes management and conservation of this vulnerable species difficult. The analysis of population dynamics using life-history traits and life tables is widely used in planning for the conservation and management of wildlife. In the present study, the first life table for any species of bat is provided and age estimates derived from counts of annual increments in tooth cementum rings are used to assess population trends and life-history traits in the spectacled flying fox on the Atherton Tablelands in north Queensland. As a result of high mortality, longevity was much shorter than expected from a theoretical basis. Life-table analyses suggest that the population experienced a 16% decrease during the 2 years of study. Absence of extended longevity to compensate for low reproductive output and delayed sexual maturity in ‘slow end’ mammal species such as P. conspicillatus reduces the window of opportunity for females to reproduce and adapt to changes in mortality rates. This study suggests that spectacled flying fox populations are sensitive to increased mortality and that reducing mortality rates should be the primary goal in conservation planning for P. conspicillatus.
How hot do nest boxes get in the tropics? A study of nest boxes for the endangered mahogany glider
Authors: Isaac J. L. , Parsons M. , Goodman B. A.
Published: August 2008

As hollow-bearing trees become scarcer due to habitat loss, the use of nest boxes as a management tool for hollow-dependent species is likely to increase. However, nest-box use can be variable among species and habitats, and one possible reason may be that nest boxes offer little protection against extreme temperatures compared with natural hollows; this may be particularly important in the tropics. Here, we measured the microclimate of 16 nest boxes, installed as part of a recovery program for an endangered arboreal marsupial, the mahogany glider, during the summer in tropical north Queensland. We also measured the microclimate of 14 naturally occurring refuges (hollows in standing and fallen trees) at the same study sites. Nest boxes were significantly hotter during the day than were natural refuges (either in fallen or standing live trees) and experienced a greater range of temperatures. The most important factors explaining variation in daytime temperature in boxes was box aspect and the amount of canopy cover directly above the box: boxes that faced north, and those with greater canopy cover, were up to 7°C cooler than those that faced south or had little cover. We discuss our results in relation to the use of nest boxes in management plans for arboreal marsupials in the tropics.
Dynamical reconstruction of the exciton in LiF with inelastic x-ray scattering
Authors: Abbamonte Peter , Graber Tim , Reed James P. , Smadici Serban , Yeh Chen-Lin , Shukla Abhay , Rueff Jean-Pascal , Ku Wei
Published: August 2008

The absorption of light by materials proceeds through the formation of excitons, which are states in which an excited electron is bound to the valence hole it vacated. Understanding the structure and dynamics of excitons is important, for example, for developing technologies for light-emitting diodes or solar energy conversion. However, there has never been an experimental means to study the time-dependent structure of excitons directly. Here, we use causality-inverted inelastic x-ray scattering (IXS) to image the charge-transfer exciton in the prototype insulator LiF, with resolutions Δ
t
= 20.67 as (2.067 × 10
−17
s) in time and Δ
x
= 0.533 Å (5.33 × 10
−11
m) in space. Our results show that the exciton has a modulated internal structure and is coherently delocalized over two unit cells of the LiF crystal (≈8 Å). This structure changes only modestly during the course of its life, which establishes it unambiguously as a Frenkel exciton and thus amenable to a simplified theoretical description. Our results resolve an old controversy about excitons in the alkali halides and demonstrate the utility of IXS for imaging attosecond electron dynamics in condensed matter.
Modeling oncogene addiction using RNA interference
Authors: Rothenberg S. Michael , Engelman Jeffrey A. , Le Sheila , Riese David J. , Haber Daniel A. , Settleman Jeffrey
Published: August 2008

The clinical efficacy of selective kinase inhibitors suggests that some cancer cells may become dependent on a single oncogene for survival. RNAi has been increasingly used to understand such “oncogene addiction” and validate new therapeutic targets. However, RNAi approaches suffer from significant off-target effects that limit their utility. Here, we combine carefully titrated lentiviral-mediated short hairpin RNA knockdown of the epidermal growth factor receptor (EGFR) with heterologous reconstitution by EGFR mutants to rigorously analyze the structural features and signaling activities that determine addiction to the mutationally activated EGFR in human lung cancer cells. EGFR dependence is differentially rescued by distinct EGFR variants and oncogenic mutants, is critically dependent on its heterodimerization partner ErbB-3, and surprisingly, does not require autophosphorylation sites in the cytoplasmic domain. Quantitative “oncogene rescue” analysis allows mechanistic dissection of oncogene addiction, and, when broadly applied, may provide functional validation for potential therapeutic targets identified through large-scale RNAi screens.
B-vitamin deficiency causes hyperhomocysteinemia and vascular cognitive impairment in mice
Authors: Troen Aron M. , Shea-Budgell Melissa , Shukitt-Hale Barbara , Smith Donald E. , Selhub Jacob , Rosenberg Irwin H.
Published: August 2008

In older adults, mildly elevated plasma total homocysteine (hyperhomocysteinemia) is associated with increased risk of cognitive impairment, cerebrovascular disease, and Alzheimer's disease, but it is uncertain whether this is due to underlying metabolic, neurotoxic, or vascular processes. We report here that feeding male C57BL6/J mice a B-vitamin-deficient diet for 10 weeks induced hyperhomocysteinemia, significantly impaired spatial learning and memory, and caused a significant rarefaction of hippocampal microvasculature without concomitant gliosis and neurodegeneration. Total hippocampal capillary length was inversely correlated with Morris water maze escape latencies (
r
= −0.757,
P
< 0.001), and with plasma total homocysteine (
r
= −0.631,
P
= 0.007). Feeding mice a methionine-rich diet produced similar but less pronounced effects. Our findings suggest that cerebral microvascular rarefaction can cause cognitive dysfunction in the absence of or preceding neurodegeneration. Similar microvascular changes may mediate the association of hyperhomocysteinemia with human age-related cognitive decline.
Evaluating and optimizing computational protein design force fields using fixed composition-based negative design
Authors: Alvizo Oscar , Mayo Stephen L.
Published: August 2008

An accurate force field is essential to computational protein design and protein fold prediction studies. Proper force field tuning is problematic, however, due in part to the incomplete modeling of the unfolded state. Here, we evaluate and optimize a protein design force field by constraining the amino acid composition of the designed sequences to that of a well behaved model protein. According to the random energy model, unfolded state energies are dependent only on amino acid composition and not the specific arrangement of amino acids. Therefore, energy discrepancies between computational predictions and experimental results, for sequences of identical composition, can be directly attributed to flaws in the force field's ability to properly account for folded state sequence energies. This aspect of fixed composition design allows for force field optimization by focusing solely on the interactions in the folded state. Several rounds of fixed composition optimization of the 56-residue β1 domain of protein G yielded force field parameters with significantly greater predictive power: Optimized sequences exhibited higher wild-type sequence identity in critical regions of the structure, and the wild-type sequence showed an improved Z-score. Experimental studies revealed a designed 24-fold mutant to be stably folded with a melting temperature similar to that of the wild-type protein. Sequence designs using engrailed homeodomain as a scaffold produced similar results, suggesting the tuned force field parameters were not specific to protein G.
Replication termination mechanism as revealed by Tus-mediated polar arrest of a sliding helicase
Authors: Bastia Deepak , Zzaman Shamsu , Krings Gregor , Saxena Mukesh , Peng Xiaohua , Greenberg Marc M.
Published: August 2008

The replication terminator protein Tus of
Escherichia coli
promotes polar fork arrest at sequence-specific replication termini (
Ter
) by antagonizing DNA unwinding by the replicative helicase DnaB. Here, we report that Tus is also a polar antitranslocase. We have used this activity as a tool to uncouple helicase arrest at a Tus–
Ter
complex from DNA unwinding and have shown that helicase arrest occurred without the generation of a DNA fork or a bubble of unpaired bases at the Tus–
Ter
complex. A mutant form of Tus, which reduces DnaB–Tus interaction but not the binding affinity of Tus for
Ter
DNA, was also defective in arresting a sliding DnaB. A model of polar fork arrest that proposes melting of the Tus–
Ter
complex and flipping of a conserved C residue of
Ter
at the blocking but not the nonblocking face has been reported. The model suggests that enhanced stability of Tus–
Ter
interaction caused by DNA melting and capture of a flipped base by Tus generates polarity strictly by enhanced protein–DNA interaction. In contrast, the observations presented here show that polarity of helicase and fork arrest
in vitro
is generated by a mechanism that not only involves interaction between the terminator protein and the arrested enzyme but also of Tus with
Ter
DNA, without any melting and base flipping in the termination complex.
Clients’ experiences of relational depth in person‐centred counselling
Authors: Knox Rosanne
Published: August 2008

This study explored clients’ experiences of relational depth using a qualitative methodology. Semi‐structured interviews were conducted with 14 participants who had been clients of predominately person‐centred counselling. Participants were asked to focus on specific moments which they had experienced as relational depth. The clients’ descriptions of those experiences showed some similarity to therapists’ descriptions, including feelings of aliveness, realness, and openness, although there were also some significant differences described. Participants experienced their therapists as being holding, accepting, and ‘really real’, and as offering something over and above what they had expected from a professional therapeutic relationship. Such moments were often seen by participants as being highly significant moments in the therapy with an enduring positive effect. The implications of these findings are discussed and areas for further research highlighted.
Self-construal priming modulates the scope of visual attention
Authors: Lin Zhicheng , Han Shihui
Published: August 2008

Although it is well documented that cultures influence basic cognitive processes such as attention, the underlying mechanisms remain unclear. We tested the hypothesis that self-concepts that characterize people from different cultures mediate the variation of visual attention. After being primed with self-construals that emphasize the Eastern interdependent self or the Western independent self, Chinese participants were asked to discriminate a central target letter flanked by compatible or incompatible stimuli (Experiment 1) or global/local letters in a compound stimulus (Experiment 2). Experiment 1 showed that, while responses were slower to the incompatible than to the compatible stimuli, this flanker compatibility effect was increased by the interdependent relative to the independent self-construal priming. Experiment 2 showed that the interdependent-self priming resulted in faster responses to the global than to the local targets in compound letters whereas a reverse pattern was observed in the independent-self priming condition. The results provide evidence for dynamics of the scope of visual attention as a function of self-construal priming that switches self-concept toward the interdependent or independent styles in Chinese.
E2-25K/Hip-2 regulates caspase-12 in ER stress–mediated Aβ neurotoxicity
Authors: Song Sungmin , Lee Huikyong , Kam Tae-In , Tai Mei Ling , Lee Joo-Yong , Noh Jee-Yeon , Shim Sang Mi , Seo Soo Jung , Kong Young-Yun , Nakagawa Toshiyuki , Chung Chul-Woong , Choi Deog-Young , Oubrahim Hammou , Jung Yong-Keun
Published: August 2008

Amyloid-β (Aβ) neurotoxicity is believed to contribute to the pathogenesis of Alzheimer's disease (AD). Previously we found that E2-25K/Hip-2, an E2 ubiquitin-conjugating enzyme, mediates Aβ neurotoxicity. Here, we report that E2-25K/Hip-2 modulates caspase-12 activity via the ubiquitin/proteasome system. Levels of endoplasmic reticulum (ER)–resident caspase-12 are strongly up-regulated in the brains of AD model mice, where the enzyme colocalizes with E2-25K/Hip-2. Aβ increases expression of E2-25K/Hip-2, which then stabilizes caspase-12 protein by inhibiting proteasome activity. This increase in E2-25K/Hip-2 also induces proteolytic activation of caspase-12 through its ability to induce calpainlike activity. Knockdown of E2-25K/Hip-2 expression suppresses neuronal cell death triggered by ER stress, and thus caspase-12 is required for the E2-25K/Hip-2–mediated cell death. Finally, we find that E2-25K/Hip-2–deficient cortical neurons are resistant to Aβ toxicity and to the induction of ER stress and caspase-12 expression by Aβ. E2-25K/Hip-2 is thus an essential upstream regulator of the expression and activation of caspase-12 in ER stress–mediated Aβ neurotoxicity.
Poleward transport of Eg5 by dynein–dynactin in Xenopus laevis egg extract spindles
Authors: Uteng Marianne , Hentrich Christian , Miura Kota , Bieling Peter , Surrey Thomas
Published: August 2008

Molecular motors are required for spindle assembly and maintenance during cell division. How motors move and interact inside spindles is unknown. Using photoactivation and photobleaching, we measure mitotic motor movement inside a dynamic spindle. We find that dynein–dynactin transports the essential motor Eg5 toward the spindle poles in Xenopus laevis egg extract spindles, revealing a direct interplay between two motors of opposite directionality. This transport occurs throughout the spindle except at the very spindle center and at the spindle poles, where Eg5 remains stationary. The variation of Eg5 dynamics with its position in the spindle is indicative of position-dependent functions of this motor protein. Our results suggest that Eg5 drives microtubule flux by antiparallel microtubule sliding in the spindle center, whereas the dynein-dependent concentration of Eg5 outside the spindle center could contribute to parallel microtubule cross-linking. These results emphasize the importance of spatially differentiated functions of motor proteins and contribute to our understanding of spindle organization.