bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of HIV‐1 Nef on Retrograde Transport from the Plasma Membrane to the Endoplasmic Reticulum
Authors: Johannes Ludger , Pezo Valérie , Mallard Frédéric , Tenza Danièle , Wiltz Aimée , Saint‐Pol Agnès , Helft Julie , Antony Claude , Benaroch Philippe
Published: September 2009

HIV‐1 Nef protein down‐regulates several important immunoreceptors through interactions with components of the intracellular sorting machinery. Nef expression is also known to induce modifications of the endocytic pathway. Here, we analyzed the effects of Nef on retrograde transport, from the plasma membrane to the endoplasmic reticulum using Shiga toxin B‐subunit (STxB). Nef expression inhibited access of STxB to the endoplasmic reticulum, but did not modify the surface expression level of STxB receptor, Gb3, nor its internalization rate as measured with a newly developed assay. Mutation of the myristoylation site or of a di‐leucine motif of Nef involved in the interaction with the clathrin adaptor complexes AP1 and AP2 abolished the inhibition of retrograde transport. In contrast, mutations of Nef motifs known to interact with PACS‐1, βCOP or a subunit of the v‐ATPase did not modify the inhibitory activity of Nef on retrograde transport. Ultrastructural analysis revealed that Nef was present in clusters located on endosomal or Golgi membranes together with internalized STxB. Furthermore, in strongly Nef‐expressing cells, STxB accumulated in endosomal structures that labeled with AP1. Our observations show that Nef perturbs retrograde transport between the early endosome and the endoplasmic reticulum. The potential transport steps targeted by Nef are discussed.
Biochemical Sub‐Fractionation of the Mammalian Golgi Apparatus
Authors: Taguchi Tomohiko , Pypaert Marc , Warren Graham
Published: September 2009

We have exploited the breakdown of the Golgi apparatus that occurs during mitosis to isolate subfractions using immuno‐affinity methods. Rat liver Golgi stacks were treated with mitotic cytosol from HeLa cells, and the fragments were then incubated with antibodies immobilized on magnetic beads. Antibodies against the cis‐Golgi marker, GM130, bound membranes that were depleted in the trans‐Golgi network marker, TGN38, whereas antibodies against the cytoplasmic tail of TGN38 did the reverse. A range of other Golgi enzymes, SNAREs and tethers were also tested and were found to bind to anti‐GM130 antibodies to an extent that reflected their proximity to cis‐cisternae as determined by other techniques. This method should provide a useful complement to the immuno‐EM methods presently used to map the Golgi apparatus.
dup(19)(q12q13.2): Array‐based Genotype–Phenotype Correlation of a New Possibly Obesity‐related Syndrome
Authors: Davidsson Josef , Jahnke Karen , Forsgren Maria , Collin Anna , Soller Maria
Published: September 2009

Small supernumerary marker chromosomes (sSMCs) derived from the near‐centromeric area of chromosome 2 are very rare. In addition, duplications of the 2p11.2→q11.2 region have displayed considerable variability between patients harboring and lacking clinical findings. Moreover, constitutional duplication of the 19q12→q13.2 region has previously only been described in two cases and was associated with delay of developmental milestones, corpus callosum anomalies, and obesity. Herein, we present a genotype–phenotype correlation in a patient harboring two sSMCs derived from chromosomes 2 and 14 or 22, respectively. The DNA was studied using G‐banding, fluorescence in situ hybridization techniques, and array‐based comparative genomic hybridization. A 48,XX,+der(2)del(2)(p11)del(2)(q11.2),+der(14)t(14;19)(q11;q12)del(19)(q13.31) or 48,XX,+der(2)del(2)(p11)del(2)(q11.2),+der(22)t(22;19)(q11;q12)del(19)(q13.31) was detected in the patient. The sSMC 14;19 or 22;19, with its centromere originating from either chromosome 14 or 22, encompassed a 13.56 megabase (Mb) 19q derived region, harboring 263 genes, and the sSMC 2 a 2.71 Mb region including 29 genes. The patient had symptoms including a ventral septal defect, bilateral grade IV urinary reflux, corpus callosum agenesis, microphthalmia, and obesity. The 19q segment contained the genes AKT2, CEACAM1, CEBPA, LIPE, and TGFB1 which are involved in adipose tissue homeostasis and insulin resistance, and could potentially contribute to the obese phenotype observed. Array‐based genetic characterization and long‐term clinical evaluation with attention toward weight gain in patients with chromosome 19q duplications might in the future lead to the description of a obesity‐associated genetic syndrome, something that could have implications in management and treatment of patients carrying a dup(19)(q12q13.2). Whether the der(2)(p11q11.2) contributes to the phenotype remains inconclusive.
Experimental investigation of the Boltzmann relation for a bi-Maxwellian distribution in inductively coupled plasmas
Authors: Bang Jin Young , Chung Chin Wook
Published: September 2009

In plasma, the Boltzmann relation is often used to connect the electron density to the plasma potential because it is not easy to calculate electric potentials on the basis of the Poisson equation due to the quasineutrality. From the Boltzmann relation, the electric potential can be simply obtained from the electron density or vice versa. However, the Boltzmann relation assumes that electrons are in thermal equilibrium and have a Maxwellian distribution, so it cannot be applied to non-Maxwellian distributions. In this paper, the Boltzmann relation for bi-Maxwellian distributions was newly derived from fluid equations and the comparison with the experimental results was given by measuring electron energy probability functions in an inductively coupled plasma. It was found that the spatial distribution of the electron density in bulk plasma is governed by the effective electron temperature, while that of the cold and hot electrons are governed by each electron temperature.
A study on stability and thermophysical properties (density and viscosity) of Al2O3 in water nanofluid
Authors: Pastoriza-Gallego M. J. , Casanova C. , Páramo R. , Barbés B. , Legido J. L. , Piñeiro M. M.
Published: September 2009

The dispersion and stability of nanofluids obtained by dispersing Al2O3 nanoparticles (obtained from different sources) in water have been analyzed. The differences arising from different dispersion techniques, the resulting particle size distribution, and time stability among the different samples are evaluated. Then the volumetric behavior up to high pressures (25 MPa) and atmospheric pressure viscosity were experimentally determined. It has been found that the influence of particle size in density is subtle but not negligible, but the differences in viscosity are very large and must be taken into account for any practical application. These viscosity differences can be rationalized by considering a theory describing the aggregation state of the nanofluid.
The image performance of a negative index slab and a layered slab using coupled surface modes
Authors: Ahmadi Akram , Mosallaei Hossein
Published: September 2009

This paper reviews the concept of high-resolution imaging of a negative index material (NIM) slab and compares its performance with the structure made based on the idea of coupled surface-modes layers. Fourier spectrum theoretical model and finite difference time domain numerical approach are applied to comprehensively characterize the structures and demonstrate the characteristics. It is highlighted that if the loss is small, a NIM slab can provide a better performance at a farther distance than the layered structure with the same thickness. However, considering a realistic design with relatively large loss, the later will offer a more promising performance to the loss and the image can be reconstructed in a farther distance from the object cascading more number of thin layers.
Nanosecond-pulse fiber lasers mode-locked with nanotubes
Authors: Kelleher E. J. R. , Travers J. C. , Sun Z. , Rozhin A. G. , Ferrari A. C. , Popov S. V. , Taylor J. R.
Published: September 2009

We demonstrate that mode-locking of ytterbium fiber lasers with a carbon nanotube saturable absorber can produce pulses ranging from 20 ps to 2 ns at repetition rates between 21 MHz and 177 kHz, respectively, depending on cavity length. Nonlinear polarization evolution is not responsible for mode-locking. Even in the nanosecond regime, clean single pulses are observed and the pulse train exhibits low jitter. Combined with extremely large chirp, these properties are suited for chirped-pulse amplification systems.
What zeroth-order Hamiltonian for CASPT2 adiabatic energetics of Fe(II)N6 architectures?
Authors: Kepenekian Mikaël , Robert Vincent , Le Guennic Boris
Published: September 2009

Complete active space self-consistent field (CASSCF) calculations and subsequent second-order perturbative treatment (CASPT2) have been carried out on a series of metallic complexes based on a Fe(II)N6 core. These compounds play a determinant role in the elaboration of potential bistable architectures such as spin-crossover materials. The adiabatic energies between the high-spin (HS) (S=2) and low-spin (LS) (S=0) states are evaluated with respect to the value of the shift ionization potential–electronic affinity (IPEA shift) recently introduced in the zeroth-order Hamiltonian [Ghigo et al., Chem. Phys. Lett. 396, 142 (2004)]. Based upon a series of experimental data, it is concluded that the commonly applied IPEA shift value (0.25 a.u.) is not satisfactory to properly discriminate the open-shell HS and closed-shell LS states. We suggest that a 0.50–0.70 a.u. value would be preferable for these specific adiabatic gap calculations.
Thermodiffusion in multicomponent hydrocarbon mixtures: Experimental investigations and computational analysis
Authors: VanVaerenbergh Stefan , Srinivasan Seshasai , Saghir M. Ziad
Published: September 2009

In an unprecedented experimental investigation, a ternary and a four component hydrocarbon mixture at high pressure have been studied in a nearly convection free environment to understand the thermodiffusion process. A binary mixture has also been investigated in this environment. Experimental investigations of the three mixtures have been conducted in space onboard the spacecraft FOTON-M3 thereby isolating the gravity-induced convection that otherwise interferes with thermodiffusion experiments on Earth. The experimental results have also been used to test a thermodiffusion model that has been calibrated based on the results of previous experimental investigations. It was found that with an increase in the number of components in the mixtures, the performance of the thermodiffusion model deteriorated. Computational analysis was also made to estimate the possible sources of errors. Simulations showed that the vibrations of the spacecraft could influence the estimates of thermodiffusion factors. It was also found that they are sensitive to slight variations in the temperature of the mixture.
Asymmetric recovery effect of exchange bias in polycrystalline NiFe/FeMn bilayers
Authors: Qiu X. P. , Shi Z. , Zhou S. M. , Du J. , Bai X. J. , Chantrell R. , Sun L.
Published: September 2009

For exchange bias in polycrystalline NiFe/FeMn bilayers, the hysteretic behavior of the angular dependence and the recovery effect has been studied. In particular, the pinning direction (PD) at the ending remanent state of each hysteresis loop is identified. In the hysteretic behavior, in addition to the coercivity, the PD also demonstrates different angular dependence between clockwise and counterclockwise rotations of the external magnetic field. Measurements of the recovery effect consist of two major steps. In the first step, the PD is deviated from the initial one by using its hysteretic effect and training effect. For polycrystalline NiFe/FeMn bilayers, the rotated PD is located at the maximal angle θPD0 of ±22° with respect to the initial ones. As for the second step, an external magnetic field is applied at a specific orientation θH−RE and then switched off at the same orientation. For the negative θPD0, the recovery effect only occurs for 0<θH−RE<180° with the maximal effect at θH−RE=90° and vanishes for 180°<θH−RE<360°, and vice versa for the positive θPD0. Therefore, the recovery effect shows an asymmetric angular dependence on θH−RE. The recovery effect of the PD also depends on the magnitude and the application time of the recovery magnetic field. For the exchange field and the coercivity, similar recovery behaviors are observed and attributed to the recovery effect of the PD. These phenomena clearly show that the motion of antiferromagnet spins not only obeys the thermally activated transition but also strongly depends on the magnetization reversal mechanism of the ferromagnet layer.
Percolating network of ultrafast transport channels in severely deformed nanocrystalline metals
Authors: Divinski Sergiy V. , Ribbe Jens , Reglitz Gerrit , Estrin Yuri , Wilde Gerhard
Published: September 2009

Severe plastic deformation is nowadays used to produce sizable amounts of bulk nanocrystalline materials, which render them suitable for innovative applications ranging from biomedical implants to off-shore or aerospace structures, owing to favorable combinations of high mechanical strength and enhanced ductility they offer. Enhanced atom diffusion along internal interfaces is largely responsible for the resulting property combinations. Severe plastic deformation processing of metals is demonstrated to create bulk nanostructured materials with a hierarchy of internal interfaces. On top of that, specific diffusion channels providing pathways for ultrafast transport of atoms have been identified. The defects that represent the constituents of the fast diffusion network were visualized by means of the focused ion beam technique. Nonequilibrium grain boundaries, nonequilibrium triple junctions, and microvoids/microcracks compose the percolating network of ultrafast diffusion channels, which represent an important and newly recognized feature of severely deformed materials.
Compact modeling of charge carrier mobility in organic thin-film transistors
Authors: Marinov O. , Deen M. J. , Datars R.
Published: September 2009

Finding the common points in theoretical models for mobility in thin-film transistors (TFTs), we demonstrate that there exists a generic analytical model for the mobility in organic TFTs (OTFTs), and the generic model is then converted into a TFT Compact Mobility Model, which is physically derivable from one perspective, and properly arranged to be suitable for compact modeling of OTFTs from another perspective, by separation and proper interfacing of temperature and bias dependence of the mobility, both significant for OTFTs, with the compact models for electrical current in OTFT. The proposed TFT Compact Mobility Model is verified theoretically and against experimental data, and the model is applicable even for high temperatures T>To, above the characteristic temperature To of the distribution of states in the organic material, a condition at which other models diverge in principle. The improvement is achieved by the identification of a temperature “shaping” function, which contains a diverging function when derived theoretically elsewhere at idealized assumptions, and we suggest an approach to remedy the problem, since divergence in characteristic equations of compact models is not allowed. However, an open question remains for the bias enhancement in mobility at high temperatures, for which case no physical model is available at present. Another essential practical feature of the TFT Compact Mobility Model is that the model is both upgradable and reducible, allowing for easier implementation, modifications and independence of characterization techniques, enabling a systematic fitting of experimental data with large scattering in the values, which is the case for OTFT nowadays.
Simulation of electron transport in (0001) and (112¯0) 4H-SiC inversion layers
Authors: Pennington G. , Goldsman N.
Published: September 2009

Monte Carlo simulations are used to investigate electron transport in the inversion layer of a 4H silicon carbide metal-oxide-semiconductor field-effect transistor (MOSFET). The electronic subband structure is solved self-consistently along with the perpendicular field at the semiconductor-oxide interface. Inversion channel scattering rates due to acoustic and polar optical phonons, ionized dopants, trapped charge, and interface roughness are considered. Transport within (0001) and (112¯0) oriented inversion layers are compared. Simulations of the MOSFET low-field mobility, incorporating previously published experimental results for threshold voltages and charge densities, are found to agree well with experimental results. The mobility of the (112¯0) channel is much larger (90 cm2/V s) than that of the (0001) channel (<40 cm2/V s) due to a reduction in interface states. Furthermore, the mobility has a temperature coefficient of approximately −3/2 for (112¯0) layers due to dominant phonon scattering and +1 for (0001) layers, where interface trap scattering dominates. Since the band structure is very similar, transport variations among the two crystal orientations are found to result largely from the enhanced interface trap density in the (0001)-oriented interfaces.
Dynamic field and current distributions in multifilamentary YBa2Cu3O7−δ thin films with magnetic coupling
Authors: Lucarelli Andrea , Yang Ran , Grilli Francesco , Haugan Timothy , Barnes Paul , Lüpke Gunter
Published: September 2009

We report on the effects of different multifilamentary geometries on the dynamic current and field distributions in YBa2Cu3O7−δ thin films. Finite-element model simulations are presented that allow a direct comparison of the calculated magnetic flux and current profiles with experimental data obtained by time-resolved magneto-optical imaging. We find that increasing the distance between filaments reduces the magnetic coupling and decreases the ac losses. Screening and transport currents also redistribute more evenly between all filaments. The measured transport current density profiles are in good agreement with the modified critical state model.
Piezoelectric properties of domain engineered barium titanate single crystals with different volume fractions of domain walls
Authors: Xiang Yang , Zhang Rui , Cao Wenwu
Published: September 2009

A piezoelectric domain wall model has been developed to analyze the effective piezoelectric properties of domain engineered BaTiO3 (BT) single crystals with different volume fractions of 90° domain walls. The model takes into account the nonuniform deformation in the domain wall region, which can create additional anisotropy to enhanced functional properties of multidomain single crystals. Our theoretical results indicate that a larger volume fraction of domain walls will produce larger effective piezoelectric coefficients. In addition, with the increase in domain wall volume fraction, [011]c poled BT single crystals will have a much larger piezoelectric property enhancement than [111]c poled BT single crystals.
Stimulated Brillouin scattering of the beat wave of two lasers in a plasma
Authors: Panwar Anuraj , Sharma A. K.
Published: September 2009

Stimulated Brillouin scattering of two collinear lasers in a plasma is investigated. Lasers exert a longitudinal ponderomotive force on electrons, imparting them oscillatory axial velocity at the beat frequency. This velocity acts as a driver for parametric excitation of an ion acoustic wave (ω,k⃗) and a noncollinear sideband electromagnetic wave (ω′,k⃗′). The driver velocity v⃗0− couples to the sideband wave to exert a ponderomotive force at (ω,k⃗) on the electrons, driving the ion acoustic wave. The density perturbation of ion acoustic wave beats with v⃗0− to produce a nonlinear current at (ω′,k⃗′), driving the sideband. In the case of finite spot size Gaussian laser beams, the beat wave has a Gaussian profile and excites an ion acoustic wave (ω,k⃗) and a backscattered TM mode (ω′,k⃗z′). The growth rate scales as the product of amplitudes of the lasers and maximizes at optimum values of scattering angles. The parametric instability of difference frequency driver is stronger than the sum frequency driver.
Laser-induced electron dynamics including photoionization: A heuristic model within time-dependent configuration interaction theory
Authors: Klinkusch Stefan , Saalfrank Peter , Klamroth Tillmann
Published: September 2009

We report simulations of laser-pulse driven many-electron dynamics by means of a simple, heuristic extension of the time-dependent configuration interaction singles (TD-CIS) approach. The extension allows for the treatment of ionizing states as nonstationary states with a finite, energy-dependent lifetime to account for above-threshold ionization losses in laser-driven many-electron dynamics. The extended TD-CIS method is applied to the following specific examples: (i) state-to-state transitions in the LiCN molecule which correspond to intramolecular charge transfer, (ii) creation of electronic wave packets in LiCN including wave packet analysis by pump-probe spectroscopy, and, finally, (iii) the effect of ionization on the dynamic polarizability of H2 when calculated nonperturbatively by TD-CIS.
Must Kohn–Sham oscillator strengths be accurate at threshold?
Authors: Yang Zeng-hui , van Faassen Meta , Burke Kieron
Published: September 2009

The exact ground-state Kohn–Sham (KS) potential for the helium atom is known from accurate wave function calculations of the ground-state density. The threshold for photoabsorption from this potential matches the physical system exactly. By carefully studying its absorption spectrum, we show the answer to the title question is no. To address this problem in detail, we generate a highly accurate simple fit of a two-electron spectrum near the threshold, and apply the method to both the experimental spectrum and that of the exact ground-state Kohn–Sham potential.
Fast phase transition process of Ge2Sb2Te5 film induced by picosecond laser pulses with identical fluences
Authors: Huang Huan , Zuo Fangyuan , Zhai Fengxiao , Wang Yang , Lai Tianshu , Wu Yiqun , Gan Fuxi
Published: September 2009

Fast phase transition processes on Ge2Sb2Te5 film induced by picosecond laser pulses were studied using time-resolved reflectivity measurements. It was found that after picosecond laser pulse priming, reversible switching could be occurred upon picosecond laser pulse irradiation with the same well-chosen fluence. This is very different from general knowledge that reversible phase change process will be induced by laser pulses with different powers; that is, amorphization process needs much higher fluence than crystallization process. The possible mechanism was discussed qualitatively by a melting-cooling model.
On the use of stabilizing transformations for detecting unstable periodic orbits in high-dimensional flows
Authors: Crofts Jonathan J. , Davidchack Ruslan L.
Published: September 2009

We explore the possibility of extending the stabilizing transformations approach [J. J. Crofts and R. L. Davidchack, SIAM J. Sci. Comput. (USA) 28, 1275 (2006)]. to the problem of locating large numbers of unstable periodic orbits in high-dimensional flows, in particular those that result from spatial discretization of partial differential equations. The approach has been shown to be highly efficient when detecting large sets of periodic orbits in low-dimensional maps. Extension to low-dimensional flows has been achieved by the use of an appropriate Poincaré surface of section [D. Pingel, P. Schmelcher, and F. K. Diakonos, Phys. Rep. 400, 67 (2004)]. For the case of high-dimensional flows, we show that it is more efficient to apply stabilizing transformations directly to the flows without the use of the Poincaré surface of section. We use the proposed approach to find many unstable periodic orbits in the model example of a chaotic spatially extended system—the Kuramoto–Sivashinsky equation. The performance of the proposed method is compared against other methods such as Newton–Armijo and Levenberg–Marquardt algorithms. In the latter case, we also argue that the Levenberg–Marquardt algorithm, or any other optimization-based approach, is more efficient and simpler in implementation when applied directly to the detection of periodic orbits in high-dimensional flows without the use of the Poincaré surface of section or other additional constraints.
Assessment of thermoelectric performance of Cu2ZnSnX4, X=S, Se, and Te
Authors: Sevik C. , Çağın T.
Published: September 2009

A recent experiment on In-doped Cu2ZnSnSe4 [X. Y. Shi et al., Appl. Phys. Lett. 94, 122103 (2009)] has shown promising thermoelectric performance characteristics. In this letter, we analyze relevant electronic and transport properties of Cu2ZnSnSe4 and similar compounds, Cu2ZnSnS4 and Cu2ZnSnTe4, to assess their potential as thermoelectric materials. Using density functional theory and Boltzmann transport equations, we determine Seebeck coefficients, conductivities, and power factors of closely related polymorphs with space groups, I4¯, I4¯2m, and P4¯2m for each compound. Based on their electronic structure and transport properties, we conclude that other two compounds could have similar potential as thermoelectric materials.
The impact of contact formation on the light emission from ambipolar transistors
Authors: Schidleja Martin , Melzer Christian , Roth Michael , Schwalm Thorsten , Gawrisch Christian , Rehahn Matthias , von Seggern Heinz
Published: September 2009

In this letter the effect of the charge carrier injection on the performance of ambipolar light-emitting organic field-effect transistors will be investigated. For the analysis, the light output and spatial information of the recombination zone from different devices will be compared. The three investigated devices provide either Ohmic contacts for one or both charge carrier types or hindered injection for both. It will be demonstrated that the light emission in the different operation regimes of the transistor can be used to characterize the contact properties at source and drain.
Orientation of nematic liquid crystal in open glass microstructures
Authors: Azarinia H. , Beeckman J. , Neyts K. , Schacht E. , Gironès J. , James R. , Fernandez F. A.
Published: September 2009

Liquid crystal materials can have bulk reorientation due to surface interaction and are therefore of interest for biosensing applications. We present a setup, with holes etched in a substrate, filled with liquid crystal and covered by a sample fluid. The influence of the depth of the microcavities and the type of liquid on the liquid crystal orientation is investigated by experiments and simulations.
Analysis of linewidth enhancement factor for quantum well structures based on InGaAsN/GaAs material system
Authors: Miloszewski Jacek M. , Wartak M. S. , Weetman P. , Hess O.
Published: September 2009

We performed an extensive numerical study of the linewidth enhancement factor (α-parameter) in single and multiple-quantum-well structures built from In0.38Ga0.62 As1−yNy/GaAs material systems. A ten-band kp Hamiltonian matrix was used in the calculations and solved self-consistently with Poisson’s equation. The linewidth enhancement factor was evaluated as a function of wavelength, nitrogen composition, well width, and carrier density and shows significant dependence on those parameters. The simulated results are in good agreement with published experimental data for a single quantum well. We demonstrate that engineering the desired linewidth enhancement factor is possible by varying the aforementioned parameters.
Influence of Li content on electrical properties of highly piezoelectric (Li,K,Na)NbO3 thin films prepared by sol-gel processing
Authors: Lai Fengping , Li Jing-Feng , Zhu Zhi-Xiang , Xu Ying
Published: September 2009

Lead-free piezoelectric xLiNbO3–(1−x)(K0.52Na0.58)NbO3 (LKNN) (x=0, 0.04, 0.06, and 0.08) thin films on Pt/Ti/SiO2/Si(100) substrates were prepared by a sol-gel method. The effects of the Li substitution content on the crystal structure, microstructure, and electrical properties of LKNN films were investigated. The Li substitution leads to a remarkable improvement in the piezoelectric properties of the films. The LKNN film with an optimized Li substitution of x=0.06 showed a high local effective piezoelectric coefficient d33∗ of 192 pm/V, which is comparable to the piezoelectric performance of Pb(Zr,Ti)O3 films. An enhanced ferroelectricity was also obtained in the x=0.06 LKNN film, with a remnant polarization of 9.7 μC/cm2 and a coercive field of 36.5 kV/cm. Furthermore, an in-depth analysis of the leakage current characteristics of the LKNN films was also conducted in this study.
Energy losing rate and open-circuit voltage analysis of organic solar cells based on detailed photocurrent simulation
Authors: Yu Junsheng , Huang Jiang , Zhang Lei , Jiang Yadong
Published: September 2009

The J-V characteristics and photovoltaic response of indium tin oxide/pentacene (dnm)∕C60 (40nm)∕BCP (10nm)∕Ag (100nm) devices have been systematically analyzed. By fitting the J-V characteristics of the fabricated devices, photocurrent densities Jph were obtained. Meanwhile, we proposed a modified optical transfer matrix theory to satisfy the reasonable trend between P0R0 and film thickness of pentacene layers. Then, we revealed that an accurate rate of energy loss can be defined as Eloss=1−βJe∕P0R0. Also, the relationship between open-circuit voltage VOC, compensation voltage V0 and initial polaron-pair bounding energy EB was determined based on the detailed study and simulation of device photocurrent.
Exact solution of the Poisson–Nernst–Planck equations in the linear regime
Authors: Golovnev A. , Trimper S.
Published: September 2009

Based on the Poisson–Nernst–Planck equations (PNP), the spatiotemporal charge, concentration profile, and the electric field in polyelectrolytes are analyzed. The system is subjected to a dc applied voltage. Different to recent papers we obtain an exact analytical solution of the PNP in the linear regime, which is characterized by an inevitable coupling between the spatial and the temporal behavior. In the long time limit the systems tends in a nonexponential manner to the steady state predicted by the Debye–Hueckel theory, where the time scale for the crossover into the steady state is determined by the Debye screening length and the initial concentration. The higher the initial concentration is the faster the system evolves into the stationary state. The Debye screening length characterizes not only the asymptotic behavior but also the spatiotemporal evolution of the system at finite times. Using experimental data the concentration profile and the electric field is shown to be on a master curve parametrized by the screening length.
Coupling of InGaN/GaN multiquantum-wells photoluminescence to surface plasmons in platinum nanocluster
Authors: Oh Tae Su , Jeong Hyun , Lee Yong Seok , Kim Jan Di , Seo Tae Hoon , Kim Hun , Park Ah Hyun , Lee Kang Jea , Suh Eun-Kyung
Published: September 2009

We present the coupling of InGaN/GaN multiquantum-wells (MQWs) photoluminescence (PL) to surface plasmons (SPs) in platinum (Pt) nanoclusters (PNCs). To tune the extinction spectrum of Pt thin film through surface modification such as PNC, the thermal annealing method was employed. From conventional PL and time-resolved PL measurements, enhanced emission and faster luminescence decay time of the PNC-formed InGaN/GaN MQWs was observed with blueshifted emission behavior near the plasmon absorption band of PNC. A Purcell enhancement factor, which was calculated to describe the increase in spontaneous emission rate (Rse), revealed an approximate 2.2 times enhancement of Rse at 425 nm. We believe that these phenomena result from efficient energy transfer in PNC-formed InGaN/GaN MQWs by SPs coupling.
Erbium-doped GaN optical amplifiers operating at 1.54 μm
Authors: Dahal R. , Ugolini C. , Lin J. Y. , Jiang H. X. , Zavada J. M.
Published: September 2009

Strip optical waveguides based on erbium (Er)-doped AlGaN/GaN:Er/AlGaN heterostructures have been fabricated and characterized in the optical communication wavelength window near 1.54 μm. The propagation loss of these waveguide amplifiers have been measured at 1.54 μm and found to be 3.5 cm−1. Moreover, the optical amplification properties of the waveguides were measured using a signal input at 1.54 μm and a broadband GaN light-emitting diode at 365 nm as pump source. A relative signal enhancement of ∼8 cm−1 was observed. The implications of such devices in photonic integrated circuits for optical communications are discussed.
Tailoring near-field patterns with concentrically corrugated plates
Authors: Imani Mohammadreza F. , Grbic Anthony
Published: September 2009

We present a device that can form a two-dimensional subwavelength focus along a specified near-field focal plane. The device, referred to as a corrugated near-field plate, consists of a coaxially fed aperture in a concentrically corrugated metallic surface. A procedure for designing such devices is outlined. In addition, simulation results are reported for a design that operates at around 1 GHz and forms a focus with a null-to-null beamwidth of λ/20 at a focal plane λ/15 from its surface. The effect of losses is also studied. Such devices will find use in near-field microscopy and probing systems.
Improved electrical stability in cyclically bent organic thin film transistors with nanocomposite gate dielectrics and surface passivation
Authors: Noh H. Y. , Seol Y. G. , Lee N.-E.
Published: September 2009

This paper investigates reliability improvements in cyclically bent bottom-gated pentacene organic thin film transistors by employing surface passivation as well as nanocomposite gate dielectrics. The variation in the hysteresis of the cyclically bent nanocomposite devices with increased Al2O3 nanoparticle fractions without surface passivation decreased. This was primarily attributed to the absence of change in charge trapping sites such as hydroxyl (OH) groups in the gate dielectrics due to reduced susceptibility of the nanocomposite dielectrics to penetration of water molecules. Furthermore, surface passivation of the devices by depositing organic thin films effectively improved their stability in the off-state current due to protection of the pentacene, which prevented penetration of ambient water.
Excitation, detection, and passive cooling of a micromechanical cantilever using near-field of a microwave resonator
Authors: Hao L. , Gallop J. C. , Cox D.
Published: September 2009

Micro/nanomechanical resonators are important for nanoscale and quantum physics. We show that a microwave near-field coaxial resonator system allows mechanical cantilever excitation on a scale much shorter than the microwave wavelength. Thermal noise is observed in the unexcited system, enabling room temperature displacement sensitivity of ∼70 fm/Hz1/2. The measured force between near-field probe and cantilever varies with separation, in excellent agreement with theory. Uniquely, optical excitation and read-out lasers are also included. We demonstrate passive cantilever mode cooling from 300 to 100 K by frequency detuning the microwave resonator and propose pulsed cooling operation to enable several high-sensitivity applications.
Electron beam induced deposition of residual hydrocarbons in the presence of a multiwall carbon nanotube
Authors: Rykaczewski K. , Henry M. R. , Fedorov A. G.
Published: September 2009

Amorphous carbon deposited via electron beam induced deposition (EBID) is frequently used to make a low-temperature Ohmic contact with low electrical resistance and improved mechanical characteristics of the multiwall nanotube (MWNT) substrate or MWNT-MWNT interface. However, influence of the MWNT on the EBID process has not been quantified. In this work, we experimentally and theoretically investigate the growth dynamics of EBID of residual hydrocarbons in presence of a MWNT. We demonstrate that the properties of MWNT do not impact amorphous carbon deposition process.
A neutron imaging device for sample alignment in a pulsed neutron scattering instrument
Authors: Grazzi F. , Scherillo A. , Zoppi M.
Published: September 2009

A neutron-imaging device for alignment purposes has been tested on the INES beamline at ISIS, the pulsed neutron source of Rutherford Appleton Laboratory (U.K.). Its use, in conjunction with a set of movable jaws, turns out extremely useful for scattering application to complex samples where a precise and well-defined determination of the scattering volume is needed.
Single-shot ultrafast electron diffraction with a laser-accelerated sub-MeV electron pulse
Authors: Tokita Shigeki , Inoue Shunsuke , Masuno Shinichiro , Hashida Masaki , Sakabe Shuji
Published: September 2009

We have demonstrated single-shot measurement of electron diffraction patterns for a single-crystal gold foil using 340 keV electron pulses accelerated by intense femtosecond laser pulses with an intensity of 2×1018 W/cm2. The measured electron beam profile is faithfully reproduced by the numerical simulation of the electron trajectory, providing evidence that the electron pulse spontaneously expands in time owing to the velocity spread produced in the acceleration process, but is not distorted in an irreversible nonlinear manner. This study shows that the laser acceleration is promising for the development of pulse compression methods for single-shot femtosecond electron diffraction.
Contaminant gas removal using thin-film Ti electrode microdischarges
Authors: Wright Scott A. , Gianchandani Yogesh B.
Published: September 2009

We report a method for the selective chemisorption of oxygen and nitrogen in sealed cavities utilizing microdischarges between thin-film Ti electrodes. The method is used to remove contaminating air from both inert and organic gas environments, reducing the nitrogen and oxygen concentrations by factors of 50 and 16, respectively. A microchip-based optical emission spectroscopic sensor is used to monitor the purification. The purification improves the ability of the optical emission sensor to detect carbon by a factor of 8. The method has been tested at temperatures between 23 and 200 °C.
How hydrophobic hydration responds to solute size and attractions: Theory and simulations
Authors: Athawale Manoj V. , Jamadagni Sumanth N. , Garde Shekhar
Published: September 2009

We focus on the hydration of a methane and spherical single and multisite C60 and C180 solutes over a range of solute-water attractions to quantify the vicinal water structure and their hydration thermodynamics using extensive molecular dynamics simulations and theory. We show that water structure near larger solutes is more sensitive to solute-water attractions compared to that near smaller ones. To understand the sensitivity, we separate the solute-water potential of mean force into a direct solute-water interaction and an indirect or solvent contribution [ω(r)]. In the absence of ω(r), water density in the solute vicinity would increase exponentially with solute-water interactions. Instead, ω(r) becomes increasingly repulsive with strengthening of solute-water attractions thereby opposing those direct interactions. We term this phenomenon “competitive expulsion,” which characterizes the repulsion of a test water molecule by the hydration shell solvent waters. We develop a physically motivated theoretical approach to predict changes in ω(r) with attractions. We call this approach the modified-EXP (M-EXP) approximation owing to the similarity of ideas and especially our final expression with that of the EXP approximation of Chandler and Andersen [J. Chem. Phys. 57, 1930 (1972)]. Solute-water radial distribution functions and chemical potentials calculated using the M-EXP approach are in good agreement with simulation data. These calculations highlight the sensitivity of hydration structure and thermodynamics of bucky ball like solutes to solute-water interactions. We find that excess chemical potentials of bucky balls with standard alkane-like carbon-water interactions parameters are negative, suggesting the need for a careful calibration of those parameters for predictions of solubility, wetting, and water-mediated interactions using molecular simulations.
Characterization of fiber texture by ω-scan x-ray diffraction
Authors: Fei W. D. , Liu C. Q. , Ding M. H. , Li W. L. , Wang L. D.
Published: September 2009

On the basis of ω-scan x-ray diffraction (XRD), quantitative and qualitative characterization methods for fiber texture are proposed. The physical meaning of ω-scan curve is discussed in detail, and it is shown that the relative intensity curve of ω-scan XRD for a certain crystal plane is proportional to the pole density of the plane. Then qualitative and quantitative characterization methods for fiber texture are proposed from the concept of pole density. The proposed methods can be used in any crystal system. As an example for experimental verification, an orientation distribution function (ODF) experiment and a series of ω-scan XRD experiments are performed on a sputtered platinum film. From the comparison between the result of the ODF experiment and that of the analyses on the ω-scan XRD experiments, it is proved that the proposed qualitative and quantitative methods are effective and simple.
Degradation of organic light emitting diodes by nucleated telephone cord blisters
Authors: Akande Wali O. , Soboyejo Wole
Published: September 2009

This letter presents the results of a study into adhesion-related degradation mechanisms in single layer polymer light emitting diodes with poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] as the active layer. These studies reveal spiral-shaped blister patterns that are associated with rapid degradation of the device. Scanning electron microscopy and atomic force microscopy images of these defects reveal that these patterns are spiral telephone cord failures that form as a result of compressive stresses in the device.
Complex network from time series based on phase space reconstruction
Authors: Gao Zhongke , Jin Ningde
Published: September 2009

We propose in this paper a reliable method for constructing complex networks from a time series with each vector point of the reconstructed phase space represented by a single node and edge determined by the phase space distance. Through investigating an extensive range of network topology statistics, we find that the constructed network inherits the main properties of the time series in its structure. Specifically, periodic series and noisy series convert into regular networks and random networks, respectively, and networks generated from chaotic series typically exhibit small-world and scale-free features. Furthermore, we associate different aspects of the dynamics of the time series with the topological indices of the network and demonstrate how such statistics can be used to distinguish different dynamical regimes. Through analyzing the chaotic time series corrupted by measurement noise, we also indicate the good antinoise ability of our method.
Pumping properties of the hybrid single-electron transistor in dissipative environment
Authors: Lotkhov S. V. , Kemppinen A. , Kafanov S. , Pekola J. P. , Zorin A. B.
Published: September 2009

Pumping characteristics were studied of a hybrid normal-metal/superconductor single-electron transistor embedded in high-Ohmic environment. Two 3 μm long microstrip resistors of CrOx with a sum resistance R≈80 kΩ were placed adjacent to the transistor. Substantial improvement of pumping and a reduction of the subgap leakage were observed in the low-megahertz range. At higher frequencies (0.1–1 GHz), pumping performance deteriorated compared to reference devices without resistors by the slowdown of tunneling and by electronic heating.
Smallest artificial molecular neural-net for collective and emergent information processing
Authors: Bandyopadhyay Anirban , Sahu Satyajit , Fujita Daisuke
Published: September 2009

While exploring the random diffusion of 2 bit molecular switches (we define as molecular neuron) on an atomic flat Au (111) substrate, we have found that at least four molecules are required to construct a functional neural net. Surface electron density wave enables communication of one to many molecules at a time—a prerequisite for the parallel processing. Here we have shown that in a neural net of several molecules, some of them could dynamically store information as memory and consistently replicate the fundamental relationship that is found only in a collective and emergent computing system like our brain.
Variation of leakage current mechanisms by ion substitution in BiFeO3 thin films
Authors: Zhong Zhiyong , Ishiwara Hiroshi
Published: September 2009

Pure BiFeO3 (BFO) and 3, 5, and 7 at. % Mn-substituted BFO (BFMO) films were formed by chemical solution deposition with a crystallization temperature of ∼550 °C. The leakage current density in a BFO film was found to be subject to space-charge-limited conduction, instead of Poole–Frenkel emission. Moreover, the serious transient effect from the traps was observed, indicating the density of trap states is relatively high in the BFO film. On the contrary, the leakage currents in BFMO films were found to be subject to trap-free Ohmic conduction.
Enhancement of the magnetotransport and magnetoresistive anisotropy in Sm0.55Sr0.45MnO3/Nd0.55Sr0.45MnO3 bilayers
Authors: Egilmez M. , Abdelhadi M. , Salman Z. , Chow K. H. , Jung J.
Published: September 2009

In a sharp contrast to bulk Sm0.55Sr0.45MnO3 (SSMO) the SSMO films grown on LaAlO3 and SrTiO3 substrates exhibit insulating behavior with a negligible magnetoresistive effect. However, when these films are buffered by a thin layer of Nd0.55Sr0.45MnO3 a large low field magnetoresistance along with the bulklike properties are observed. These results are reproducible and suggest that the low field magnetoresistance and magnetoresistive anisotropy could be enhanced dramatically in multilayered manganite films. These changes are attributed to the differences in the strain states of these films.
Phosphonic acid self-assembled monolayer and amorphous hafnium oxide hybrid dielectric for high performance polymer thin film transistors on plastic substrates
Authors: Acton Orb , Osaka Itaru , Ting Guy , Hutchins Daniel , Ma Hong , McCullough Richard D. , Jen Alex K.-Y.
Published: September 2009

A vacuum-free solution processed hybrid dielectric composed of an n-octadecyl-phosphonic acid self-assembled monolayer on amorphous sol-gel processed hafnium oxide (HfOx) is demonstrated for low-voltage polymer semiconductor-based thin film transistors (TFTs). The phosphonic acid/HfOx hybrid dielectric provides high capacitance (0.41 μF/cm2), low leakage current (5×10−8 A/cm2), and is compatible with plastic substrates. The utility of this dielectric is demonstrated by fabricating high performance polymer TFTs based on a spin coated thiophene-thiazolothiazole copolymer with operating voltages under −2 V, negligible hysteresis, subthreshold slopes as low as 100 mV/dec, and hole mobilities up to 0.11 cm2 V s.
Improvement of SiO2/4H-SiC interface properties by oxidation using hydrogen peroxide
Authors: Palmieri R. , Radtke C. , Boudinov H. , da Silva E. F.
Published: September 2009

The effect of using H2O2 in the thermal growth process of dielectric films on n-type 4H-SiC substrates has been investigated. In comparison to conventional oxide growth using H2O, we found that the interface trap density is reduced close to the conduction band edge of 4H-SiC. This electrical improvement is correlated with the decrease in SiCxOy compounds at the SiO2/4H-SiC interface region as confirmed by two independent methods. These results point to the use of H2O2 as an alternative passivating agent of SiO2/4H-SiC interface electrically active defects.