bluuebunny/crossref_metadata_2025 huggingface dataset:
Robust estimation with dynamic integral quadratic constraints: the discrete‐time case
Authors: Kao Chung‐Yao , Chen Min‐Chieh
Published: August 2013

The authors consider the problem of robust output estimation in the discrete‐time setting. The uncertainty in the system is characterised by integral quadratic constraints with dynamic multipliers. The main technical contribution of this study is to derive two different synthesis conditions in terms of linear matrix inequalities (LMI) by two different approaches. The LMI condition derived by the first approach allows one to find the robust estimator and the performance certificate simultaneously, whereas the condition by the second approach has a smaller size but requires an additional step for recovering the estimator. The synthesis conditions are validated by numerical examples. The results verify the equivalence of the two approaches and show that the two‐step approach is in fact computationally favourable when the system has large number of state variables.
Global stabilisation of high‐order non‐linear systems with time‐varying delays
Authors: Gao Fangzheng , Yuan Fushun , Wu Yuqiang
Published: August 2013

Under the weaker condition on the system non‐linearities, this study investigates the problem of global stabilisation by state feedback for a class of high‐order non‐linear systems with time‐varying delays. By using the method of adding a power integrator, a continuous state‐feedback controller is successfully designed, and the global asymptotic stability of the resulting closed‐loop system is proven with the help of an appropriate Lyapunov–Krasovskii functional. Two simulation examples are given to illustrate the effectiveness of the proposed approach.
Platform enabling intelligent safety applications for vulnerable road users
Authors: Dozza Marco , Idegren Martin , Andersson Tomas , Fernandez Andre
Published: August 2013

In 2009, 9108 vulnerable road users (VRUs; pedestrians and bicyclists) died in the EU and 4722 in the US. Active safety systems, that is intelligent systems able to predict and prevent crashes, may significantly help to reduce VRU fatalities and injuries; however, current active safety systems for VRUs are only found on high‐end vehicles, only support the host vehicle driver, and do not make use of wireless communication. The scope of this study is to describe the set‐up and real‐world verification of a platform to enable active safety systems for VRU. This platform is carried by VRUs and may support multiple road users using wireless communication. A simple conceptual application, addressing pedestrian safety at crossings, was developed to test the platform. This application was not cooperative (i.e. did not support multiple road users with wireless communication). The results presented in this study suggest that such a platform can be employed (i) as a logger for naturalistic studies on VRUs, (ii) to better understand VRU behaviour and accident causation and (iii) as a basis for the development of novel active safety applications, running on portable devices, such as future generation smart phones, and possibly enabled by wireless communication.
Operating compressed‐air energy storage as dynamic reactive compensator for stabilising wind farms under grid fault conditions
Authors: Le Ha Thu , Santoso Surya
Published: August 2013

Compressed‐air energy storage (CAES) is considered a promising energy storage system for many grid applications, including managing renewable variability and grid capacity concerns. However, compared with conventional generation such as coal or hydro, the cost of storage power of CAES is still high, which impedes its deployment. Therefore a standing question is how to operate CAES in the most efficient and economical fashion, that is, to exploit the system functions for maximum‐possible benefit. This study investigates the CAES dynamic reactive capability used to stabilise wind farms under grid fault conditions. Two considered operation modes are motor mode with leading power factor and synchronous condenser mode. Analysis with a 60‐MW wind farm and two types of popular wind turbines, namely stall‐regulated and doubly fed induction‐generator‐based WTs, shows that the CAES performance is comparable or better than that of an static var compensator in most situations investigated. Therefore the reactive‐power‐supply function should be considered in CAES design and operation to increase the system efficiency and value.
Optimal control of state‐of‐charge of superconducting magnetic energy storage for wind power system
Authors: Zhang Kun , Mao Chengxiong , Lu Jiming , Wang Dan , Chen Xun , Zhang Junfeng
Published: August 2013

The optimal control of state‐of‐charge (SOC) for superconducting magnetic energy storage (SMES), which is used to smooth power fluctuations from wind turbine, is essential to improve its technical and economical performance. Without an efficient control strategy, the SMES may go to the state of over‐charge or deep‐discharge, which will pose a significant effect on its service life and its technical performance. In this study, combined with wind forecasting technology and real‐time monitoring of SOC for the SMES, a double fuzzy logic control strategy is proposed that is applied to regulate SOC of SMES with the purpose of not only effectively smoothing the power fluctuations of wind turbine, but also preventing the SMES from occurring of the state of over‐charge/deep‐discharge and adjusting it to the appropriate SOC. The effectiveness of the proposed control strategy is verified by the simulation results.
Controlled reactive ion etching and plasma regrowth of titanium oxides of known thickness for production of metal‐oxide‐metal diodes
Authors: Dodd Linzi E. , Gallant Andrew J. , Wood David
Published: August 2013

The successful production, via two different oxidation processes, of metal‐oxide‐metal (MOM) diodes is presented. An innovative reactive ion etching and plasma assisted regrowth process has been used to provide oxides, which are in the thickness range 4.0–5.1 nm. These are thinner and physically more uniform than oxides grown in a furnace, resulting in diodes which should conduct via electron tunnelling across the MOM junction. Transmission electron microscopy analysis has been used in conjunction with time of flight secondary ion mass spectrometry analysis to verify oxide thickness and uniformity.
Nonadiabatic electron response in the Hasegawa-Wakatani equations
Authors: Stoltzfus-Dueck T. , Scott B. D. , Krommes J. A.
Published: August 2013

Tokamak edge turbulence is strongly influenced by parallel electron physics, which relaxes density and potential fluctuations towards electron adiabatic response. Beginning with the paradigmatic Hasegawa-Wakatani equations (HWEs) for resistive tokamak edge turbulence, a unique decomposition of the electric potential (φ) into adiabatic (a) and nonadiabatic (b) portions is derived, based on the requirement that a neither drive nor respond to the parallel current j∥. The form of the decomposition clarifies that, at perpendicular scales large relative to the sound radius, the electron adiabatic response controls the nonzonal φ, not the fluctuating density n. Simple energy balance arguments allow one to rigorously bound the ratio of rms nonzonal nonadiabatic fluctuations (b̃) relative to adiabatic ones (ã). The role of the vorticity nonlinearity in transferring energy between adiabatic and nonadiabatic fluctuations aids intuitive understanding of self-sustained turbulence in the HWEs. When the normalized parallel resistivity is weak, b̃ becomes effectively slaved, allowing the reduction to an approximate one-field model that remains valid for strong turbulence. In addition to guiding physical intuition, the one-field reduction should greatly ease further analytical manipulations. Direct numerical simulation of the 2D HWEs confirms the convergence of the asymptotic formula for b̃.
An improved model for nanosecond pulsed laser ablation of metals
Authors: Lutey Adrian H. A.
Published: August 2013

A model is presented for the ablation of metals by nanosecond laser pulses, based on one-dimensional heat flow with temperature dependent material properties. A numerical optical calculation is introduced to account for laser beam absorption in the target, utilizing established matrix methods for electromagnetic plane wave propagation in multi-layered media. By including the effects of reflection from the dielectric-metal interface, the fall in reflectivity of aluminum during nanosecond laser pulses above the phase explosion threshold is found to be approximately twice that calculated in previous works. A simulated shielding coefficient is introduced to account for reflection and absorption of the incident laser beam by the ablation products. With these additions to foregoing models, good agreement between calculated and published experimental ablation data is attained for aluminum, both in terms of ablation threshold and depth. An investigation is subsequently carried out into the effects of laser wavelength, pulse duration and target thickness on the phase explosion threshold of aluminum.
Self-assembly of 50 bp poly(dA)·poly(dT) DNA on highly oriented pyrolytic graphite via atomic force microscopy observation and molecular dynamics simulation
Authors: Doi Kentaro , Takeuchi Hiroshi , Nii Ryosuke , Akamatsu Shingo , Kakizaki Toshiya , Kawano Satoyuki
Published: August 2013

This study has investigated the formation patterns resulting from the self-assembly of deoxyribonucleic acid (DNA) on highly oriented pyrolytic graphite (HOPG), using both experimental and molecular dynamics approaches. Under optimized conditions based on pretreatment of HOPG surface and specific solution concentrations, DNA is found to self-assemble to form various patterned networks. The associated self-assembly mechanism is elucidated using coarse-grained molecular dynamics simulations and fractal dimension analysis. The results of this work demonstrate an effective technique allowing the formation of arrays of negatively charged biomacromolecules on negatively charged HOPG surfaces.
Suppression of superconductivity by strong magnetic fields in PbTe/PbS heterostructures with a superconducting interface
Authors: Bengus S. V. , Sipatov A. Yu. , Yuzephovich S. I.
Published: August 2013

This is a comprehensive study of the effect of strong magnetic fields on superconductivity in PbTe/PbS heterostructures with semiconducting layers of different thicknesses. Metallic conductivity and superconductivity (critical temperature Tc ≤ 6.5 K) in PbTe/PbS heterostructures are caused by inversion of bands along a continuous network of misfit dislocations that develops at the interfaces between semiconductor layers of sufficient thickness (d > 80 nm). With decreasing d the continuity of the superconducting interface is disrupted, Tc decreases, and the metallic conductivity changes to a semiconducting type. Disruption of the continuity of the superconducting interface is found to be a necessary condition for observing a magnetic-field induced superconductor-insulator transition (SIT) and has a significant influence on its features: a fan-like set of resistance curves R(T); intersection of the R(B) curves for fields perpendicular, as well as parallel, to the interface; and, negative magnetoresistance. A scaling analysis based on Fisher's theoretical model is carried out for these samples. No evidence of a SIT was observed in heterostructures with a perfect interface. It appears that the SIT effect is related to percolation phenomena characteristic of granular superconductors.
Electronic mechanism of spontaneous magnetostriction in the layered system Mn2−xFexAs0.5P0.5
Authors: Val'kov V. I. , Golovchan A. V.
Published: August 2013

Based on the spin-fluctuation approach and the first-principles calculations of electronic structure, the mechanism of spontaneous magnetostriction accompanying the first order ferromagnetism–paramagnetism transitions in the Mn2−xFexAs0.5P0.5 magnetocaloric system is analyzed. When simulating the electronic structure of the paramagnetic phase by the state with disordered local moments, it was shown that the main contribution to the emergence of a giant anisotropic magnetostriction was associated with the destruction of local magnetic moments of iron in the layers with tetrahedral anion environment. Relying on the analysis of numerical experiments it was established that the destruction of the local magnetic moments of Fe in the paramagnetic phase with the local Mn magnetic moments conserved was a consequence of disappearance of the long-range ferromagnetic order in the d-electron subsystem of manganese.
Discrimination between the human prostate normal cell and cancer cell by using a novel electrical impedance spectroscopy controlling the cross-sectional area of a microfluidic channel
Authors: Kang Giseok , Kim Young-jae , Moon Hong-sang , Lee Jeong-Woo , Yoo Tag-Keun , Park Kwangsung , Lee Jong-Hyun
Published: August 2013

The prostate biopsy method shows a high false negative result because the suspicious tissue considered as cancer is not confirmed during tissue sampling. Thus, repeated biopsy procedures and diagnostic errors in relation to prostate cancer frequently occur. The purpose of this research is to enhance the prostate cancer detection rate by using microfluidic electrical impedance spectroscopy (μEIS), which allows real-time measurement of the electrical impedance of a single human prostate normal cell and cancer cell. The μEIS was equipped with a movable flexible membrane, which is operated by pneumatic pressure to capture the single cell on the surface of sensing electrodes. The forced tight contact between the cell and electrodes makes it possible to measure the electrical characteristics of the cell with a high sensitivity. The μEIS discriminates well between normal human prostate cells (RWPE-1) and cancer cells (PC-3) at 8.7 kHz based on the electrical signal responses of the cells. The average difference rates of admittance magnitude and susceptance are 54.55% and 54.59%, respectively. The developed μEIS also shows high repeatability, which was verified by a deionized water test conducted before and after each cell assay; the maximum variance of both the impedance and admittance at 8.7 kHz was as small as 9.48%.
A model for turbulent mixing based on shadow-position conditioning
Authors: Pope Stephen B.
Published: August 2013

In the modeling and simulation of mixing and reaction in turbulent flows using probability density function (PDF) methods, a key component is the mixing model, which represents the mixing effected by molecular diffusion. A new model, called the shadow-position mixing model (SPMM), is introduced and its performance is illustrated for two test cases. The model involves a new variable—the shadow position—and mixing is modeled as a relaxation of the composition to its mean conditional on the shadow position. The model is constructed to be consistent with turbulent dispersion theory, and to be local in the composition space, both to adequate approximations. The connections between the SPMM and previous mixing models are discussed. The first test case of a scalar mixing layer shows that the SPMM yields scalar statistics in broad agreement with experimental data. The second test case of a reactive scalar mixing layer with idealized non-premixed combustion shows that the SPMM correctly yields stable combustion, whereas simpler models incorrectly lead to extinction. The model satisfies all required realizability and transformation properties and correctly yields Gaussian distributions in appropriate circumstances. The SPMM is generally applicable to turbulent reactive flows using different PDF approaches in the contexts of both Reynolds-averaged Navier-Stokes modeling and large-eddy simulation.
Hot electron production and diffuse excited states in C70, C82, and Sc3N@C80 characterized by angular-resolved photoelectron spectroscopy
Authors: Olof Johansson J. , Bohl Elvira , Henderson Gordon G. , Mignolet Benoit , Dennis T. John S. , Remacle Francoise , Campbell Eleanor E. B.
Published: August 2013

Angular-resolved photoelectron spectroscopy using wavelength-tuneable femtosecond laser pulses is presented for a series of fullerenes, namely, C70, C82, and Sc3N@C80. The photoelectron kinetic energy distributions for the three molecules show typical thermal electron spectra with a superimposed peak structure that is the result of one-photon ionization of diffuse low-angular momenta states with electron density close to the carbon cage and that are related to so-called super atom molecular orbitals. Photoelectron angular distributions confirm this assignment. The observed structure is less prominent compared to the thermal electron background than what was observed in C60. It can be concluded that hot electron emission is the main ionization channel for the larger and more complex molecules for these excitation conditions.
Radio-frequency sheath-plasma interactions with magnetic field tangency points along the sheath surface
Authors: Kohno H. , Myra J. R. , D'Ippolito D. A.
Published: August 2013

Computer simulations of radio-frequency (RF) waves propagating across a two-dimensional (2D) magnetic field into a conducting boundary are described. The boundary condition for the RF fields at the metal surface leads to the formation of an RF sheath, which has previously been studied in one-dimensional models. In this 2D study, it is found that rapid variation of conditions along the sheath surface promote coupling of the incident RF branch (either fast or slow wave) to a short-scale-length sheath-plasma wave (SPW). The SPW propagates along the sheath surface in a particular direction dictated by the orientation of the magnetic field with respect to the surface, and the wave energy in the SPW accumulates near places where the background magnetic field is tangent to the surface.
A portable quartz micro balance for physical vapor deposition techniques
Authors: Stuckenholz S. , Büchner C. , Thielsch G. , Heyde M. , Freund H.-J.
Published: August 2013

A portable quartz crystal micro balance for physical vapor deposition techniques is presented. The device is used for the calibration of evaporators employed in the preparation of thin film systems that are studied in surface science. The design is based upon a portable sample setup, highly versatile and customizable. It can be transported within an ultrahigh vacuum system, stored in a sample garage and be used in front of different evaporators. Details of the setup are described. Finally, the performance of the device is demonstrated and compared to scanning tunneling microscopy measurements.
The numerical study of the adsorption of flexible polyelectrolytes with the annealed charge distribution onto an oppositely charged sphere by the self-consistent field theory
Authors: Tong Chaohui
Published: August 2013

The adsorption of flexible polyelectrolytes (PEs) with the annealed charge distribution onto an oppositely charged sphere immersed in a PE solution is studied numerically with the continuum self-consistent field theory. The numerical study reveals interesting scaling relationships between the boundary layer thickness and the surface charge density of the sphere as well as the degree of ionization of the monomers of the PE chains in the bulk solution. The dependences of the degree of charge compensation of the total amount of charges on adsorbed PE chains over the surface charges upon various system parameters are investigated. In particular, the effect of the radius of the charged sphere on the degree of charge compensation is carefully examined. The numerical study indicates that the curvature effect is closely related to the surface electric potential of the charged sphere. Moreover, in this study of the adsorption of PEs with the annealed charge distribution, a comparison with the corresponding case for PEs with the smeared charge distribution in terms of the boundary layer scaling law and the degree of charge compensation is also presented.
Quantum effects in the capture of charged particles by dipolar polarizable symmetric top molecules. I. General axially nonadiabatic channel treatment
Authors: Auzinsh M. , Dashevskaya E. I. , Litvin I. , Nikitin E. E. , Troe J.
Published: August 2013

The rate coefficients for capture of charged particles by dipolar polarizable symmetric top molecules in the quantum collision regime are calculated within an axially nonadiabatic channel approach. It uses the adiabatic approximation with respect to rotational transitions of the target within first-order charge–dipole interaction and takes into account the gyroscopic effect that decouples the intrinsic angular momentum from the collision axis. The results are valid for a wide range of collision energies (from single-wave capture to the classical limit) and dipole moments (from the Vogt–Wannier and fly-wheel to the adiabatic channel limit).
Particle-in-cell simulations of collisionless shock formation via head-on merging of two laboratory supersonic plasma jets
Authors: Thoma C. , Welch D. R. , Hsu S. C.
Published: August 2013

We describe numerical simulations, using the particle-in-cell (PIC) and hybrid-PIC code lsp [T. P. Hughes et al., Phys. Rev. ST Accel. Beams 2, 110401 (1999)], of the head-on merging of two laboratory supersonic plasma jets. The goals of these experiments are to form and study astrophysically relevant collisionless shocks in the laboratory. Using the plasma jet initial conditions (density ∼1014–1016 cm−3, temperature ∼ few eV, and propagation speed ∼20–150 km/s), large-scale simulations of jet propagation demonstrate that interactions between the two jets are essentially collisionless at the merge region. In highly resolved one- and two-dimensional simulations, we show that collisionless shocks are generated by the merging jets when immersed in applied magnetic fields (B∼0.1–1 T). At expected plasma jet speeds of up to 150 km/s, our simulations do not give rise to unmagnetized collisionless shocks, which require much higher velocities. The orientation of the magnetic field and the axial and transverse density gradients of the jets have a strong effect on the nature of the interaction. We compare some of our simulation results with those of previously published PIC simulation studies of collisionless shock formation.
Overcoming challenges to the formation of high-quality polycrystalline TiO2:Ta transparent conducting films by magnetron sputtering
Authors: Neubert M. , Cornelius S. , Fiedler J. , Gebel T. , Liepack H. , Kolitsch A. , Vinnichenko M.
Published: August 2013

The work is focused on understanding the physical processes responsible for the modification of the structure, electrical and optical properties of polycrystalline TiO2:Ta films formed by annealing of initially amorphous films grown by direct current magnetron sputtering of electrically conductive ceramic targets. It is shown that fine tuning of the oxygen content during deposition of amorphous TiO2:Ta films is critical to achieving low resistivity and high optical transmittance after annealing. Increasing the total pressure during magnetron sputter deposition is shown to decrease the sensitivity of the annealed films to the oxygen flow variation during deposition of the initially amorphous layers. Polycrystalline anatase TiO2:Ta films of low electrical resistivity (ρH = 1.5 × 10−3 Ω cm), high free electron mobility (μH = 8 cm2/Vs), and low extinction (k550nm = 0.006) are obtained in this way at a total pressure of 2 Pa. The dependence of the polycrystalline film electrical properties on the oxygen content is discussed in terms of Ta dopant electrical activation/deactivation taking into account the formation of compensating defects at different oxygen pressures. The temperature-dependent transport of the polycrystalline anatase TiO2:Ta films is investigated showing the dominant role of the optical phonon scattering in the case of films with an optimum Ti/O ratio.
X-rays from a microsecond X-pinch
Authors: Appartaim R. K.
Published: August 2013

The characteristics of x-rays emitted by X-pinches driven by discharging a current of ∼320 kA with a quarter period of 1 μs in crossed 25 μm wires have been investigated. The x-ray emissions are studied using filtered silicon photodiodes, diamond radiation detectors, and pinhole cameras. The results show that predominantly x-rays from the microsecond X-pinch tend to be emitted in two distinct sets of bursts. The first is predominantly “soft,” i.e., with photon energy hν < 5 keV, followed by a second set of bursts beginning up to 100 ns following the initial bursts, and usually consisting of higher photon energies. Our results show, however, that the x-ray emissions do not contain a significant component with hν > 10 keV as might be expected from electron beam activity within the plasma or from the X-pinch diode. High-resolution images obtained with the observed x-rays suggest a well-defined small source of soft x-rays that demonstrates the potential of the microsecond X-pinch.
Thickness dependent electronic structure and morphology of rubrene thin films on metal, semiconductor, and dielectric substrates
Authors: Sinha Sumona , Mukherjee M.
Published: August 2013

The evolution of the electronic structure and morphology of rubrene thin films on noble-metal, semiconductor and dielectric substrates have been investigated as a function of thickness of deposited films by using photoelectron spectroscopy and atomic force microscopy. The clean polycrystalline Au and Ag were used as noble-metals, whereas, H passivated and SiO2 coated Si (100) were used as semiconductors and dielectric substrates. Discussion and comparison on interface dipole, energy level alignment, and surface morphology for the four cases are presented. The formation of dipole at metallic interfaces is found to occur due to push back effect. S parameter obtained from the variation of barrier height with the change of work function of the contacting metal indicates moderately weak interaction between rubrene and the metal substrates. The thickness dependent energy level alignment of the physisorbed rubrene films on different substrates is explained by a dielectric model in terms of electrostatic screening of photo-holes or photoemission final state relaxation energy. Films on all the substrates are found to grow following Stranski−Krastnov type growth mode and are more ordered at higher coverage.
pH sensing properties of graphene solution-gated field-effect transistors
Authors: Mailly-Giacchetti Benjamin , Hsu Allen , Wang Han , Vinciguerra Vincenzo , Pappalardo Francesco , Occhipinti Luigi , Guidetti Elio , Coffa Salvatore , Kong Jing , Palacios Tomás
Published: August 2013

The use of graphene grown by chemical vapor deposition to fabricate solution-gated field-effect transistors (SGFET) on different substrates is reported. SGFETs were fabricated using graphene transferred on poly(ethylene 2,6-naphthalenedicarboxylate) substrate in order to study the influence of using a flexible substrate for pH sensing. Furthermore, in order to understand the influence of fabrication-related residues on top of the graphene surface, a fabrication method was developed for graphene-on-SiO2 SGFETs that enables to keep a graphene surface completely clean of any residues at the end of the fabrication. We were then able to demonstrate that the electrical response of the SGFET devices to pH does not depend either on the specific substrate on which graphene is transferred or on the existence of a moderate amount of fabrication-related residues on top of the graphene surface. These considerations simplify and ease the design and fabrication of graphene pH sensors, paving the way for developing low cost, flexible, and transparent graphene sensors on plastic. We also show that the surface transfer doping mechanism does not have significant influence on the pH sensing response. This highlights that the adsorption of hydroxyl and hydronium ions on the graphene surface due to the charging of the electrical double layer capacitance is responsible for the pH sensing mechanism.
Transitions of bandgap and built-in stress for sputtered HfZnO thin films after thermal treatments
Authors: Li Chih-Hung , Chen Jian-Zhang , Cheng I-Chun
Published: August 2013

HfZnO thin films with various Hf contents are sputter-deposited on glass substrates from HfxZn1−xO (x = 0, 2.5, 5, 7.5, and 10 at. %) targets at room temperature. The incorporation of Hf in the ZnO film leads to the amorphorization of the materials. The amorphous structures of high-Hf-content films remain after annealing at 600 °C for 30 min. The built-in stresses of as-deposited films are compressive. As the annealing temperature increases, the stresses are relaxed and even become tensile. The films exhibit a high transmission of 80% in the visible region. The optical bandgap increases with the Hf content, but it decreases with the annealing temperature. This can be attributed to the alteration of strain (stress) status in the films and atomic substitution. The reduction of bandgap partly results from the grain growth, which is due to the quantum confinement effect of the small grains. Hf doping increases the resistivity of ZnO owing to the disorder of the material structure and the higher bandgap, which result in more carrier traps and less thermally excited carriers in the conduction bands.
Anisotropic Bruggeman effective medium approaches for slanted columnar thin films
Authors: Schmidt Daniel , Schubert Mathias
Published: August 2013

Two different formalisms for the homogenization of composite materials containing ellipsoidal inclusions based on Bruggeman's original formula for spherical inclusions can be found in the literature. Both approximations determine the effective macroscopic permittivity of such an idealized composite assuming randomly distributed dielectric particles of equal shape and differ only in the definition of the depolarization factors. The two approaches are applied to analyze ellipsometric Mueller matrix spectra acquired in the visible and near-infrared spectral region from metal and semiconductor slanted columnar thin films. Furthermore, the effective dielectric function tensor generated by the two Bruggeman formalisms is compared to effective major axes dielectric functions individually determined with a homogeneous biaxial layer approach. Best-match model parameters of all three model approaches are discussed and compared to estimates from scanning electron microscope images. The structural parameters obtained from all three optical modeling approaches agree well with the electron microscopy technique. A comparative discussion is given for the validity and applicability of the three model approaches for analysis of future devices structures that may require optical readout using generalized ellipsometry methods.
Positron scattering from hydrogen atom embedded in dense quantum plasma
Authors: Bhattacharya Arka , Kamali M. Z. M. , Ghoshal Arijit , Ratnavelu K.
Published: August 2013

Scattering of positrons from the ground state of hydrogen atoms embedded in dense quantum plasma has been investigated by applying a formulation of the three-body collision problem in the form of coupled multi-channel two-body Lippmann-Schwinger equations. The interactions among the charged particles in dense quantum plasma have been represented by exponential cosine-screened Coulomb potentials. Variationally determined hydrogenic wave function has been employed to calculate the partial-wave scattering amplitude. Plasma screening effects on various possible mode of fragmentation of the system e++H(1s) during the collision, such as 1s→1s and 2s→2s elastic collisions, 1s→2s excitation, positronium formation, elastic proton-positronium collisions, have been reported in the energy range 13.6-350 eV. Furthermore, a comparison has been made on the plasma screening effect of a dense quantum plasma with that of a weakly coupled plasma for which the plasma screening effect has been represented by the Debye model. Our results for the unscreened case are in fair agreement with some of the most accurate results available in the literature.
Effect of volume and surface charges on discharge structure of glow dielectric barrier discharge
Authors: Xu Shao-Wei , He Feng , Wang Yu , Li Lulu , Ouyang Ji-Ting
Published: August 2013

The effect of volume and surface charges on the structure of glow dielectric barrier discharge (DBD) has been investigated numerically by using two-dimensional (2D) fluid modeling. The local increase of volume or surface charges induces a kind of activation-inhibition effect, which enhances the local volume discharge and inhibits the discharge in neighborhoods, resulting in non-uniform discharge. The activation-inhibition effect due to the non-uniform volume and/or surface charges depends on the non-uniformity itself and the applied voltage. The activation-inhibition of non-uniform charges has different effects on the volume charges and the accumulated surface charges. The distribution of remaining free charges (seed electrons) in volume at the beginning of voltage pulse plays a key role for the glow DBD structure, resulting in a patterned DBD, when the seed electrons are non-uniform at higher frequency and moderate voltage or uniform DBD, when the seed electrons are uniform at lower frequency or high voltage. The distribution of surface charges is not the determining factor but a result of the formed DBD structure.
Comprehensive efficiency analysis of organic light-emitting diodes featuring emitter orientation and triplet-to-singlet up-conversion
Authors: Schmidt Tobias D. , Setz Daniel S. , Flämmich Michael , Frischeisen Jörg , Michaelis Dirk , Mayr Christian , Rausch Andreas F. , Wehlus Thomas , Scholz Bert J. , Reusch Thilo C. G. , Danz Norbert , Brütting Wolfgang
Published: August 2013

We present a method to achieve a consistent, comprehensive efficiency analysis of fluorescent organic light-emitting diodes (OLEDs) showing non-isotropic emitter orientation and triplet-to-singlet up-conversion. Combining photoluminescence lifetime and external quantum efficiency measurements on OLEDs with varying cavity length allows for an independent determination of the radiative emitter efficiency under optical as well as electrical excitation. The difference clearly shows a significant enhancement of the singlet exciton fraction to more than 25% under electrical operation. Furthermore, the presented method does not require detailed information about the emitting system and is generally applicable for a comprehensive efficiency analysis of bottom-emitting OLEDs.
Communication: Analytic gradients in the random-phase approximation
Authors: Rekkedal Johannes , Coriani Sonia , Iozzi Maria Francesca , Teale Andrew M. , Helgaker Trygve , Pedersen Thomas Bondo
Published: August 2013

The relationship between the random-phase-approximation (RPA) correlation energy and the continuous algebraic Riccati equation is examined and the importance of a stabilizing solution is emphasized. The criterion to distinguish this from non-stabilizing solutions can be used to ensure that physical, smooth potential energy surfaces are obtained. An implementation of analytic RPA molecular gradients is presented using the Lagrangian technique. Illustrative calculations indicate that RPA with Hartree-Fock reference orbitals delivers an accuracy similar to that of second-order Møller–Plesset perturbation theory.
Capacitance-voltage characteristics of a 4,4′-bis[(N-carbazole)styryl]biphenyl based organic light-emitting diode: Implications for characteristic times and their distribution
Authors: Zhang Le , Nakanotani Hajime , Adachi Chihaya
Published: August 2013

The characteristic times and their distributions of a fluorescent 4,4′-bis[(N-carbazole)styryl]biphenyl-based organic light-emitting diode (OLED) were studied using impedance spectroscopy. The four defined characteristic times (transit time, recombination time, trapping time, and ac characteristic time) and their dc bias dependences were obtained from the frequency dependence of capacitance. The trapped carrier density distribution in the time domain was revealed from the voltage dependence of the OLED. The relative value of each characteristic time is suggested to play an important role in determining the profile of the frequency- and voltage-dependent capacitance of OLEDs.
Characterization of flow units in metallic glass through structural relaxations
Authors: Zhu Z. G. , Wen P. , Wang D. P. , Xue R. J. , Zhao D. Q. , Wang W. H.
Published: August 2013

We characterize the evolution of flow units associated with the flow “defects” in metallic glass by monitoring the fictive temperature change of a typical metallic glass upon isothermal annealing below its glass transition temperature. The correlations between the fictive temperature Tf, enthalpy change, and the concentration of flow units have been obtained. Such correlations help in understanding the evolution process of flow units, structural feature, and structural relaxation behaviors in metallic glasses, and can rationalize effects of the cooling rate, aging, and annealing on properties and structure of metallic glasses.
Semiconductor optical parametric generators in isotropic semiconductor diode lasers
Authors: Bijlani Bhavin J. , Abolghasem Payam , Helmy Amr S.
Published: August 2013

We report on the characteristics of an intracavity semiconductor optical parametric generator in multiple-quantum well AlGaAs/InGaAs Bragg reflection waveguide lasers emitting between 986 and 995 nm. The cavity of the laser is phase-matched for down-conversion of pump photons to a signal between 1739 and 1767 nm and an idler between 2235 and 2328 nm. The normalized conversion efficiency is calculated to be 1.23×103 %W−1cm−2 above laser threshold and 1.25×104 %W−1cm−2 below threshold. The demonstrated device is potential for the realization of integrated parametric devices such as electrically pumped entangled photon-pair sources and optical parametric oscillation, where quantum optical effects can unfold.
Circulating but not immobilized N-deglycosylated von Willebrand factor increases platelet adhesion under flow conditions
Authors: Fallah M. A. , Huck V. , Niemeyer V. , Desch A. , Angerer J. I. , McKinnon T. A. J. , Wixforth A. , Schneider S. W. , Schneider M. F.
Published: August 2013

The role of von Willebrand factor (VWF) as a shear stress activated platelet adhesive has been related to a coiled-elongated shape conformation. The forces dominating this transition have been suggested to be controlled by the proteins polymeric architecture. However, the fact that 20% of VWF molecular weight originates from glycan moieties has so far been neglected in these calculations. In this study, we present a systematic experimental investigation on the role of N-glycosylation for VWF mediated platelet adhesion under flow. A microfluidic flow chamber with a stenotic compartment that allows one to mimic various physiological flow conditions was designed for the efficient analysis of the adhesion spectrum. Surprisingly, we found an increase in platelet adhesion with elevated shear rate, both qualitatively and quantitatively fully conserved when N-deglycosylated VWF (N-deg-VWF) instead of VWF was immobilized in the microfluidic channel. This has been demonstrated consistently over four orders of magnitude in shear rate. In contrast, when N-deg-VWF was added to the supernatant, an increase in adhesion rate by a factor of two was detected compared to the addition of wild-type VWF. It appears that once immobilized, the role of glycans is at least modified if not—as found here for the case of adhesion—negated. These findings strengthen the physical impact of the circulating polymer on shear dependent platelet adhesion events. At present, there is no theoretical explanation for an increase in platelet adhesion to VWF in the absence of its N-glycans. However, our data indicate that the effective solubility of the protein and hence its shape or conformation may be altered by the degree of glycosylation and is therefore a good candidate for modifying the forces required to uncoil this biopolymer.
GaN polarity determination by photoelectron diffraction
Authors: Romanyuk O. , Jiříček P. , Paskova T. , Bieloshapka I. , Bartoš I.
Published: August 2013

A nondestructive approach to determine the wurtzite GaN crystal polarity based on X-ray photoelectron diffraction is proposed. The approach, utilizing the ratio of photoemitted electron currents excited by a standard laboratory X-ray source from the N 1s level in the (101¯0) plane at polar angles of 20° and 25°, is tested on GaN crystals. The photoelectron intensity ratio I20/I25 is larger or smaller than unity for GaN(0001) or GaN(0001¯), respectively. The approach can be used for polarity determination of other binary wurtzite crystals. The atom with the smaller electron scattering cross-section should be used as the emitter.
Magneto-optical studies of Gd-implanted GaN: No spin alignment of conduction band electrons
Authors: Buß J. H. , Rudolph J. , Shvarkov S. , Semond F. , Reuter D. , Wieck A. D. , Hägele D.
Published: August 2013

Gd-implanted wurtzite GaN as a candidate for a ferromagnetic dilute magnetic semiconductor is investigated by time-resolved magneto-optical spectroscopy. We observe a strong increase of the electron spin lifetimes for increasing Gd doses, while the electron spin Larmor precession frequency is independent of the Gd concentration. These findings are well explained by carrier localization at defects and a negligible interaction with Gd ions. The data show that Gd-implanted GaN cannot be used for an electron spin aligner.
Early history and rationale for outdoor chamber work at the University of North Carolina
Authors: Jeffries Harvey E. , Kamens Richard M. , Sexton Kenneth
Published: August 2013

Environmental context Imagine in 1968 having to tell the largest cities in the US that they would have to spend billions of dollars to reduce human exposure to a gas in their air that no one emitted and that no one knew for sure how it came to be there. This history recalls how scientists and policy makers met this challenge so that by 1985 effective programs were in place. Abstract The University of North Carolina (UNC) outdoor chamber facility was established in 1972. The chamber produces reliable and interpretable results using ambient sunlight, temperature and weather, providing an effective physical model system for learning about atmospheric chemistry. This article recounts the 40-year history of the chamber facility, from the early days in understanding ozone–precursor relationship to the latest in studying gas and particulate toxicities on human lung cells.
Triphenyltin chloride induces spindle microtubule depolymerisation and inhibits meiotic maturation in mouse oocytes
Authors: Shen Yu-Ting , Song Yue-Qiang , He Xiao-Qin , Zhang Fei , Huang Xin , Liu Yu , Ding Lu , Xu Lin , Zhu Mao-Bi , Hu Wen-Feng , Qi Zhong-Quan , Wang Hai-Long , Yang Xiang-Jun
Published: August 2013

Meiosis produces haploid gametes for sexual reproduction. Triphenyltin chloride (TPTCL) is a highly bioaccumulated and toxic environmental oestrogen; however, its effect on oocyte meiosis remains unknown. We examined the effect of TPTCL on mouse oocyte meiotic maturation in vitro and in vivo. In vitro, TPTCL inhibited germinal vesicle breakdown (GVBD) and first polar body extrusion (PBE) in a dose-dependent manner. The spindle microtubules completely disassembled and the chromosomes condensed after oocytes were exposed to 5 or 10 μg mL–1 TPTCL. γ-Tubulin protein was abnormally localised near chromosomes rather than on the spindle poles. In vivo, mice received TPTCL by oral gavage for 10 days. The general condition of the mice deteriorated and the ovary coefficient was reduced (P < 0.05). The number of secondary and mature ovarian follicles was significantly reduced by 10 mg kg–1 TPTCL (P < 0.05). GVBD decreased in a non-significant, dose-dependent manner (P > 0.05). PBE was inhibited with 10 mg kg–1 TPTCL (P < 0.05). The spindles of in vitro and in vivo metaphase II oocytes were disassembled with 10 mg kg–1 TPTCL. These results suggest that TPTCL seriously affects meiotic maturation by disturbing cell-cycle progression, disturbing the microtubule cytoskeleton and inhibiting follicle development in mouse oocytes.
SIRT1 regulates adaptive response of the growth hormone--insulin-like growth factor-I axis under fasting conditions in liver
Authors: Yamamoto Masaaki , Iguchi Genzo , Fukuoka Hidenori , Suda Kentaro , Bando Hironori , Takahashi Michiko , Nishizawa Hitoshi , Seino Susumu , Takahashi Yutaka
Published: August 2013

Adaptation under fasting conditions is critical for survival in animals. Sirtuin 1 (SIRT1), a protein deacetylase, plays an essential role in adaptive metabolic and endocrine responses under fasting conditions by modifying the acetylation status of various proteins. Fasting induces growth hormone (GH) resistance in the liver, leading to decreased serum insulin-like growth factor-I (IGF-I) levels as an endocrine adaptation for malnutrition; however, the underlying mechanisms of this action remain to be fully elucidated. Here we report that in vivo knockdown of SIRT1 in the liver restored the fasting-induced decrease in serum IGF-I levels and enhanced the GH-dependent increase in IGF-I levels, indicating that SIRT1 negatively regulates GH-dependent IGF-I production in the liver. In vitro analysis using hepatocytes demonstrated that SIRT1 suppresses GH-dependent IGF-I expression, accompanied by decreased tyrosine phosphorylation on signal transducer and activator of transcription (STAT) 5. GST pull-down assays revealed that SIRT1 interacts directly with STAT5. When the lysine residues adjacent to the SH2 domain of STAT5 were mutated, STAT5 acetylation decreased concomitant with a decrease in its transcriptional activity. Knockdown of SIRT1 enhanced the acetylation and GH-induced tyrosine phosphorylation of STAT5, as well as the GH-induced interaction of the GH receptor with STAT5. These data indicate that SIRT1 negatively regulates GH-induced STAT5 phosphorylation and IGF-I production via deacetylation of STAT5 in the liver. In addition, our findings explain the underlying mechanisms of GH resistance under fasting conditions, which is a known element of endocrine adaptation during fasting.
Role of activity-dependent BDNF expression in hippocampal–prefrontal cortical regulation of behavioral perseverance
Authors: Sakata Kazuko , Martinowich Keri , Woo Newton H. , Schloesser Robert J. , Jimenez Dennisse V. , Ji Yuanyuan , Shen Liya , Lu Bai
Published: August 2013

Significance

The brain-derived neurotrophic factor (
Bdnf
) gene is expressed either constitutively or in an activity-dependent manner. Selective disruption of activity-dependent brain-derived neurotrophic factor protein expression (BDNF-KIV mice) results in specific deficits in GABAergic transmission in the prefrontal cortex (PFC) and a form of long-term synaptic plasticity in the hippocampus. Surprisingly, PFC-dependent working memory and hippocampus-dependent spatial and fear memory are normal. In contrast, BDNF-KIV mice exhibit pronounced behavioral perseverance, as reflected by impairments in spatial memory reversal and fear memory extinction. Thus, activity-dependent BDNF expression in hippocampal–PFC circuits may play an important role in cognitive behavior in vivo. Our study also may shed light on the pathogenesis of several cognitive disorders in which perseverance is prominent, including schizophrenia and posttraumatic stress disorder.