bluuebunny/crossref_metadata_2025 huggingface dataset:
Gilbert ferromagnetic damping theory and the fluctuation-dissipation theorem
Authors: Widom A. , Vittoria C. , Yoon S. D.
Published: October 2010

The phenomenological Gilbert–Landau–Lifshitz theory of magnetic damping in ordered magnetic materials has long served as the central model employed in the analysis of considerable experimental magnetic resonance data. The problem undertaken here is to formulate the microscopic basis of the model in terms of usual theory of irreversible transport embodied in the fluctuation-dissipation-response theorems. As an application of the general method we establish a rigorous relationship between magnetic damping and acoustic damping implicit in magnetoelastic models.
Two-dimensional carbon nanostructures: Fundamental properties, synthesis, characterization, and potential applications
Authors: Wu Y. H. , Yu T. , Shen Z. X.
Published: October 2010

Since its discovery in less than five years ago, graphene has become one of the hottest frontiers in materials science and condensed matter physics, as evidenced by the exponential increase in number of publications in this field. Several reviews have already been published on this topic, focusing on single and multilayer graphene sheets. Here, we review the recent progresses in this field by extending the scope to various types of two-dimensional carbon nanostructures including graphene and free-standing carbon nanowalls/nanosheets. After a brief overview of the electronic properties of graphene, we focus on the synthesis, characterization and potential applications of these carbon nanostructures.
The interface and surface effects of the bicrystal nanowires on their mechanical behaviors under uniaxial stretching
Authors: Wang Fenying , Liu Yunhong , Yin Xing , Wang Nan , Wang Dongxu , Gao Yajun , Zhao Jianwei
Published: October 2010

Using molecular dynamics simulations, we have investigated systematically the mechanical deformation of bicrystalline metallic nanowires with [110]∥[100], [111]∥[100], and [111]∥[110] interfaces. When the size of the nanowire is larger than 20×20×60 (units: cell), the effect from the grain boundary is dominant in breaking as compared with the nanowire surface effect. For [110]∥[100] bicrystal, breaking occurred easily at the interface with no clear structural deformation of the grain interior. When the [111] direction was addressed, the sliding most likely took place in [100] region for [111]∥[100] but in both regions for [111]∥[110], causing obvious elongation of the nanowire. By exploring the stress-strain property and the stress concentration along the tensile direction, we elucidated how the interfacial microstructure affected the mechanical behavior. Reducing the wire size, the effect from the nanowire surface gradually becomes more pronounced, showing a new breaking position from the grain boundary in the [110]∥[100] sample.
Characterizing high energy spectra of NIF ignition Hohlraums using a differentially filtered high energy multipinhole x-ray imager
Authors: Park Hye-Sook , Dewald E. D. , Glenzer S. , Kalantar D. H. , Kilkenny J. D. , MacGowan B. J. , Maddox B. R. , Milovich J. L. , Prasad R. R. , Remington B. A. , Robey H. F. , Thomas C. A.
Published: October 2010

Understanding hot electron distributions generated inside Hohlraums is important to the national ignition campaign for controlling implosion symmetry and sources of preheat. While direct imaging of hot electrons is difficult, their spatial distribution and spectrum can be deduced by detecting high energy x-rays generated as they interact with target materials. We used an array of 18 pinholes with four independent filter combinations to image entire Hohlraums with a magnification of 0.87× during the Hohlraum energetics campaign on NIF. Comparing our results with Hohlraum simulations indicates that the characteristic 10–40 keV hot electrons are mainly generated from backscattered laser-plasma interactions rather than from Hohlraum hydrodynamics.
Broadband notch filter design for millimeter-wave plasma diagnostics
Authors: Furtula V. , Michelsen P. K. , Leipold F. , Salewski M. , Korsholm S. B. , Meo F. , Nielsen S. K. , Stejner M. , Moseev D. , Johansen T.
Published: October 2010

Notch filters are integrated in plasma diagnostic systems to protect millimeter-wave receivers from intensive stray radiation. Here we present a design of a notch filter with a center frequency of 140 GHz, a rejection bandwidth of ∼900 MHz, and a typical insertion loss below 2 dB in the passband of ±9 GHz. The design is based on a fundamental rectangular waveguide with eight cylindrical cavities coupled by T-junction apertures formed as thin slits. Parameters that affect the notch performance such as physical lengths and conductor materials are discussed. The excited resonance mode in the cylindrical cavities is the fundamental TE11. The performance of the constructed filter is measured using a vector network analyzer monitoring a total bandwidth of 30 GHz. We compare the measurements with numerical simulations.
Mechanism of heat-modification inside a glass after irradiation with high-repetition rate femtosecond laser pulses
Authors: Shimizu Masahiro , Sakakura Masaaki , Ohnishi Masatoshi , Shimotsuma Yasuhiko , Nakaya Takayuki , Miura Kiyotaka , Hirao Kazuyuki
Published: October 2010

Accumulation of thermal energies by highly repeated irradiation of femtosecond laser pulses inside a glass induces the heat-modification whose volume is much larger than that of the photoexcited region. It has been proposed that the heat-modification occurs in the region in which the temperature had overcome a threshold temperature during exposure of laser pulses. In order to understand the mechanism of the heat-modification, we investigated the temperature distribution during laser exposure and the threshold temperature by analyzing the volume of the modification based on a thermal diffusion model. We found that the threshold temperature becomes lower with increasing laser exposure time. The dependence of the threshold temperature on the laser exposure time was explained by the deformation mechanism based on the temperature-dependent viscosity and viscoelastic behavior of a glass under a stress loading by thermal expansion. The deformation mechanism also could simulate a tear-drop shape of a heat-modification by simultaneous double-beams’ irradiation and the distribution of birefringence in a heat-modification. The mechanism proposed in this study means that the temperature-dependence of the viscosity of a glass should be essential for predicting and controlling the heat-modification.
Magnetic diagnostics for equilibrium reconstructions in the presence of nonaxisymmetric eddy current distributions in tokamaks (invited)
Authors: Berzak L. , Jones A. D. , Kaita R. , Kozub T. , Logan N. , Majeski R. , Menard J. , Zakharov L.
Published: October 2010

The lithium tokamak experiment (LTX) is a modest-sized spherical tokamak (R0=0.4 m and a=0.26 m) designed to investigate the low-recycling lithium wall operating regime for magnetically confined plasmas. LTX will reach this regime through a lithium-coated shell internal to the vacuum vessel, conformal to the plasma last-closed-flux surface, and heated to 300–400 °C. This structure is highly conductive and not axisymmetric. The three-dimensional nature of the shell causes the eddy currents and magnetic fields to be three-dimensional as well. In order to analyze the plasma equilibrium in the presence of three-dimensional eddy currents, an extensive array of unique magnetic diagnostics has been implemented. Sensors are designed to survive high temperatures and incidental contact with lithium and provide data on toroidal asymmetries as well as full coverage of the poloidal cross-section. The magnetic array has been utilized to determine the effects of nonaxisymmetric eddy currents and to model the start-up phase of LTX. Measurements from the magnetic array, coupled with two-dimensional field component modeling, have allowed a suitable field null and initial plasma current to be produced. For full magnetic reconstructions, a three-dimensional electromagnetic model of the vacuum vessel and shell is under development.
Origin of the giant negative photoresistance of ZnO single crystals
Authors: Barzola-Quiquia J. , Esquinazi P. , Villafuerte M. , Heluani S. P. , Pöppl A. , Eisinger K.
Published: October 2010

We have measured the temperature dependence (30 K≤T≤300 K) of the electrical resistance of ZnO single crystals prepared by hydrothermal method in darkness and under the influence of light in the ultraviolet range. The resistance decreases several orders of magnitude at temperatures T<200 K after illumination. Electron paramagnetic resonance studies under illumination reveal that the excitation of Li acceptor impurities is the origin for the giant negative photoresistance effect. Permanent photoresistance effect is also observed, which remains many hours after leaving the crystal in darkness.
Vibration characteristics of circular nanoplates
Authors: Assadi Abbas , Farshi Behrooz
Published: October 2010

This article deals with free vibration of circular nanoplates with consideration of surface properties due to high surface to volume ratio. Classical laminated plate is employed with inclusion of surface elasticity and surface residual stress effects. Solution of the resulting differential equation leads to size dependent behavior of natural frequencies and mode shapes of vibration to be demonstrated. Deviation of the results from conventional theories is shown to be due to changes in the arguments of Bessel functions in the corresponding characteristic equations.
Canonical surfaces associated with projectors in Grassmannian sigma models
Authors: Hussin V. , Yurduşen İ. , Zakrzewski W. J.
Published: October 2010

We discuss the construction of higher-dimensional surfaces based on the harmonic maps of S2 into CPN−1 and other Grassmannians. We show that there are two ways of implementing this procedure—both based on the use of the relevant projectors. We study various properties of such projectors and show that the Gaussian curvature of these surfaces, in general, is not constant. We look in detail at the surfaces corresponding to the Veronese sequence of such maps and show that for all of them this curvature is constant but its value depends on which mapping is used in the construction of the surface.
Thermoelectric properties of ternary diamondlike semiconductors Cu2Ge1+xSe3
Authors: Cho Jung Young , Shi Xun , Salvador J. R. , Yang J. , Wang H.
Published: October 2010

Ternary diamondlike semiconductors Cu2Ge1+xSe3 have been synthesized by direct-melting the constituent elements under several different synthetic conditions. The Hall effect and thermoelectric properties of Cu2Ge1+xSe3 were measured. All samples show positive Hall coefficients (RH) for the whole temperature range studied, and a positive Seebeck coefficient of 360 μV K−1 was observed at 300 K for Cu2GeSe3. Low thermal conductivities were also observed for all samples; the lowest value reaches 1.0 Wm−1 K−1 at 745 K.
Improvement in the accuracy of estimating the time-of-flight in an ultrasonic ranging system using multiple square-root unscented Kalman filters
Authors: Yao Zhen-Jing , Meng Qing-Hao , Zeng Ming
Published: October 2010

The square-root unscented Kalman filter (SRUKF) is applied to identify the shape parameters of an ultrasonic echo envelope. The SRUKF has better stability than the normal unscented Kalman filter (UKF) because the square-root of the error covariance matrix used in the SRUKF guarantees positive semidefiniteness. Considering the effect of the initial state on the convergence speed of filters, the multi-SRUKF is used to estimate the time-of-flight (TOF). Each SRUKF has a different initial state. The result estimated in a limited time with minimum mean square error is finally adopted. Simulation experiments for various couples of shape parameters and signal-to-noise ratios validate the improvement in the TOF accuracy. Real experiments using the echo signals of a SensComp 600 ultrasonic transducer show that the relative means and standard deviations of the TOF error obtained using the multi-SRUKF method are less than 0.2% and 0.15%, respectively.
Note: Mechanical study of micromachined polydimethylsiloxane elastic microposts
Authors: Cheng Qi , Sun Zhe , Meininger Gerald A. , Almasri Mahmoud
Published: October 2010

This paper reports the detailed statistical measurement of Young’s modulus (E) and spring constant of micromachined three-dimensional polydimethylsiloxane microposts with various sizes using atomic force microscope. The paper also describes the design and fabrication of these microposts. The micropost array was fabricated with a height to diameter aspect ratio of up to 10. We have found that posts with different sizes have different E values, and posts that are cured at room temperature have smaller Young’s modulus than the ones that are cured at 65 °C for the same duration.
Investigation of methyl methacrylate-oligomer adsorbed on grooved substrate of different aspect ratios by coarse-grained configurational-bias Monte Carlo simulation
Authors: Chang Chun-Yi , Ju Shin-Pon
Published: October 2010

The coarse-grained configurational-bias Monte Carlo simulation was used to investigate structural behaviors of methyl methacrylate (MMA)-oligomers adsorbed on grooved substrates with different aspect ratios. In this study, three types of chains are classified according to their positions relative to the groove. Types 1, 2, and 3 represent the entire MMA-oligomer within the groove, the MMA-oligomer partially within the groove, and the oligomer outside the groove, respectively. The orientational order parameters of types 1 and 2 oligomers decrease with the increase of groove width, but the orientational order parameter of type 3 oligomers is approximately equal to 0.1. In addition, observation of the orientational order parameters of type 1 oligomers interacting with the grooved substrate at different interaction strengths decrease with increasing the groove width. Furthermore, the orientational order parameters of type 1 oligomers within the narrowest (20 Å) and the widest (35 Å) groove with different depths were determined. For the narrowest groove, the arrangement of type 1 oligomers will be influenced by the groove width. However, in the case of the widest groove, the orientational order parameter of type 1 oligomers is approximately equal to 0.2.
Linear gyrokinetic simulation of high-n toroidal Alfvén eigenmodes in a burning plasma
Authors: Chen Yang , Parker Scott E. , Lang J. , Fu G.-Y.
Published: October 2010

A hybrid gyrokinetic ions/massless fluid electron model is used to study the stability of high-n toroidal Alfvén eigenmodes (TAEs) in ITER [M. Shimada et al., Nucl. Fusion 47, S1 (2007)]. The hybrid model has been implemented in the particle-in-cell turbulence simulation code GEM [Y. Chen and S. E. Parker, J. Comput. Phys. 220, 839 (2007)]. The adequacy of the hybrid model for simulating TAEs has been previously demonstrated [J. Lang et al., Phys. Plasmas 16, 102101 (2009)] by comparing the simulated TAE mode frequency and structure with an eigenmode analysis, and the thermal ion kinetic damping effect with analytic theory. By using a global particle-in-cell code the effects of large orbit width and nonlocal mode structures can be accurately included. Damping rate due to numerical filtering is carefully monitored, and convergence with respect to particle number, grid resolution, etc., is thoroughly tested. The simulations show that the most unstable modes in ITER lie in the rage of 10<n<20. Thermal ion pressure effect and alpha particle nonperturbative effect are important in determining the mode radial location and stability threshold. The thermal ion Landau damping rate and radiative damping rate from the simulations are compared with analytical estimates. The thermal ion Landau damping is the dominant damping mechanism. Plasma elongation has a strong stabilizing effect on the alpha driven TAEs. The central alpha particle pressure threshold for the most unstable n=15 mode is about βα(0)=0.7% for the fully shaped ITER equilibrium.
Dissociative CdSe/ZnS quantum dot-molecule complex for luminescent sensing of metal ions in aqueous solutions
Authors: Baranov A. V. , Orlova A. O. , Maslov V. G. , Toporova Yu. A. , Ushakova E. V. , Fedorov A. V. , Cherevkov S. A. , Artemyev M. V. , Perova T. S. , Berwick K.
Published: October 2010

The optical properties of dissociative luminescent sensors based on a complex consisting of highly luminescent hydrophobic core/shell CdSe/ZnS quantum dots (QDs) and 1-(2-pyridilazo)-2-naphtol (PAN) molecules in organic solutions and a polymer film are reported. It is demonstrated, using Ni2+ and Co2+ ions as an illustrative example, that the QD/PAN sensor may have applications in the quantitative luminescent sensing of metal ions in aqueous solutions.
Scalar theory of electromagnetic wave in a spherically symmetric radially anisotropic and inhomogeneous medium: Photonic atoms
Authors: Zhu Guanghao
Published: October 2010

Based on quantum mechanical angular momentum operators, we establish a scalar potential theory for describing electromagnetic wave in a spherically symmetric radially anisotropic and inhomogeneous dielectric medium. The developed scalar theory is validated by rederiving the prescription for spherical invisible cloaking against electromagnetic wave. As an application of the scalar potential theory, it is shown that under appropriate radial anisotropy conditions photons can be localized, in a manner that is analogous to the bounded electrons in atoms. We refer to such localized states as the photonic atoms in order to reflect their conceptual significance as an extension to the analogies between photons and electrons. The developed scalar potential theory is expected to be helpful in practice.
Excited states and electronic spectra of extended tetraazaporphyrins
Authors: Fukuda Ryoichi , Ehara Masahiro , Nakatsuji Hiroshi
Published: October 2010

Electronic excited states, electronic absorption, and magnetic circular dichroism (MCD) spectra of free-base tetraazaporphyrin (TAP), phthalocyanine (Pc), naphthalocyanine (Nc), and anthracocyanine (Ac) were studied by quantum chemical calculations using the symmetry-adapted cluster-configuration interaction (SAC-CI) method. Not only optically allowed states including the Q- and B-bands but also optically forbidden states were calculated for transitions whose excitation energies were lower than 4.5 eV. The present SAC-CI calculations consistently assigned the absorption and MCD peaks as optically allowed π→π∗ excitations, although these calculations using double-zeta basis limit quantitative agreement and discussion. For Nc and Ac, excited states beyond the four-orbital model appeared in the low-energy region. The low-energy shifts of the Q-bands with the extension of molecular size were explained by the orbital energies. The splitting of the Q-bands decreases with extension of the molecular size. This feature was reproduced by the SAC-CI calculations but the configuration interaction with single excitations and time-dependent density functional theory calculations failed to reproduce this trend. Electron correlation in the excited states is important in reproducing this splitting of the Q-bands and in describing the energy difference between the B2u and B3u states of free-base porphyrins.
Analytic energy gradient in combined time-dependent density functional theory and polarizable force field calculation
Authors: Si Dejun , Li Hui
Published: October 2010

Formulas for evaluating analytic energy gradient are derived for combined time-dependent density functional theory (TDDFT) and polarizable force field methods that incorporate dipole polarizability tensors and linearly induced point dipoles. The Z-vector method for determining relaxed one-particle difference density matrix in regular TDDFT methods is extended to include induced dipoles. The analytic gradient of the mutual polarization energy of the force field and the TDDFT excited state can be formulated by using the TDDFT difference density-induced dipoles and the transition state density-induced dipoles. All the forces and torques involving induced dipoles can be efficiently evaluated using standard electrostatic formulas as if the induced dipoles were permanent dipoles. The formulas are given in the most general form and are applicable to various flavors of polarizable force fields. Implementation and tests with a polarizable five-point water model show that the formulas are rigorous. The carbonyl vibration modes and infrared spectrum intensities of a cluster formed by acetone and two water molecules are studied.
Trigonometric Sutherland systems and their Ruijsenaars duals from symplectic reduction
Authors: Fehér L. , Ayadi V.
Published: October 2010

Beside its usual interpretation as a system of n indistinguishable particles moving on the circle, the trigonometric Sutherland system can be viewed alternatively as a system of distinguishable particles on the circle or on the line, and these three physically distinct systems are in duality with corresponding variants of the rational Ruijsenaars–Schneider system. We explain that the three duality relations, first obtained by Ruijsenaars in 1995, arise naturally from the Kazhdan–Kostant–Sternberg symplectic reductions of the cotangent bundles of the group U(n) and its covering groups U(1)×SU(n) and R×SU(n), respectively. This geometric interpretation enhances our understanding of the duality relations and simplifies Ruijsenaars’ original direct arguments that led to their discovery.
Two-dimensional acoustic metamaterial with negative modulus
Authors: Ding Changlin , Hao Limei , Zhao Xiaopeng
Published: October 2010

We designed a two-dimensional acoustic metamaterial with periodical array of split hollow sphere (SHS) and investigated its transmission behaviors in the impedance tube system. The results showed that the acoustic metamaterial exhibited a transmission dip and inverse phase close to 5 kHz, which indicated the local resonance of SHS. Based on the homogeneous-media theory, the effective modulus of the acoustic metamaterial was calculated to be negative. The finite element method and resonant model simulation results also confirmed the local resonance and negative response in acoustic metamaterial, which agreed well with experiment results. This metamaterial is able to achieve the double negative acoustic metamaterial conveniently by arraying acoustic “atoms” with negative mass density in the matrix.
Tunneling-barrier controlled excitation transfer in hybrid quantum dot-quantum well nanostructures
Authors: Mazur Yu. I. , Dorogan V. G. , Marega E. , Zhuchenko Z. Ya. , Ware M. E. , Benamara M. , Tarasov G. G. , Vasa P. , Lienau C. , Salamo G. J.
Published: October 2010

A systematic spectroscopic study of the carrier transfer between quantum dot (QD) and quantum well (QW) layers is carried out in a hybrid dot-well system based on InAs QDs and InGaAs QWs. We observe a strong dependence of the QD and QW photoluminescence (PL) both on the dot-well barrier thickness and height. For thick (or high) barriers QD and QW systems accumulate independently sufficient photogenerated carrier densities to be seen in PL even at low nonresonant excitation power. For thin (or low) barriers it is impossible to detect the PL signal from QW at low excitation densities due to effective carrier transfer from QW to QDs. Strong state-filling effects of the excited QD states influence the carrier transfer efficiencies. By investigating the carrier dynamics using time-resolved spectroscopy and the state-filling effects in the continuous wave excitation regime the basic characteristics of interlevel, intersublevel, and dot-well relaxation are determined. The mechanisms of the dot-well coupling are discussed.
Structure and photoluminescence of Ge nanoclusters embedded in GeOx films deposited using laser assistance at low temperature
Authors: Tsai Tai-Cheng , Liu Day-Shan , Lou Li-Ren , Lee Ching-Ting
Published: October 2010

Crystalline Ge nanocluster-embedded GeOx films were deposited at low temperature using a laser-assisted plasma enhanced chemical-vapor deposition system. The structural and optical properties of the films deposited under various power densities of the assisting CO2 laser beam were investigated. The size of the Ge nanoclusters decreased and the number density of the Ge nanoclusters increased with an increase in the laser power used in the film deposition. The Ge nanoclusters crystallization was improved with an increase in the assisting laser power. The observed photoluminescence (PL) characteristics, including the spectral position, decay curve, and intensity of the emission bands, can be attributed to the quantum confinement effect. These experimental results verified that the PL emission originated from the recombination of electron-hole pairs in the Ge nanoclusters. Furthermore, the growth process of the Ge nanoclusters was qualitatively studied.
Simultaneous measurement of ultrasonic longitudinal wave velocities and thicknesses of a two layered media in the absence of an interface echo
Authors: Kannajosyula Surya Prakash , Chillara Vamshi Krishna , Balasubramaniam Krishnan , Krishnamurthy C. V.
Published: October 2010

A measurement technique has been developed to extract the phase information of successive echoes for the simultaneous estimation of thicknesses and ultrasonic velocities of individual layers in a two layered media. The proposed method works in the absence of an interface echo and requires the total thickness of the sample to be known. Experiments have been carried out on two layered samples of white cast iron and gray cast iron with layer thickness variation in the range of 2–8 mm for total thickness variation in the range of 12–13 mm. Comparison with micrographs of a few samples confirmed the model predictions. The model is found to be sensitive to the total sample thickness but fairly insensitive to noise in the data.
Homoepitaxial growth of catalyst-free GaN wires on N-polar substrates
Authors: Chen X. J. , Perillat-Merceroz G. , Sam-Giao D. , Durand C. , Eymery J.
Published: October 2010

The shape of c-oriented GaN nanostructures is found to be directly related to the crystal polarity. As evidenced by convergent beam electron diffraction applied to GaN nanostructures grown by metal-organic vapor phase epitaxy on c-sapphire substrates: wires grown on nitridated sapphire have the N-polarity ([0001¯]) whereas pyramidal crystals have Ga-polarity ([0001]). In the case of homoepitaxy, the GaN wires can be directly selected using N-polar GaN freestanding substrates and exhibit good optical properties. A schematic representation of the kinetic Wulff’s plot points out the effect of surface polarity.
Direct communication between magnetic tunnel junctions for nonvolatile logic fan-out architecture
Authors: Lyle Andrew , Harms Jonathan , Patil Shruti , Yao Xiaofeng , Lilja David J. , Wang Jian-Ping
Published: October 2010

We experimentally demonstrated a magnetic tunnel junction (MTJ) based circuit that allows direct communication between elements without intermediate sensing amplifiers. The input of the circuit consists of three MTJs connected in parallel. The direct communication is realized by connecting the output in series with the input and applying voltage across the series connections. Combining the circuit with complementary metal oxide semiconductor current mirrors allows for fan-out to multiple outputs. The change in resistance at the input resulted in a voltage swing across the output of 150–200 mV for the closest input states which is sufficient to realize all of the Boolean primitives.
Direct observation of Si(111) √7×√7-Co structure and its local electronic structure
Authors: Odagiri Mayu , Mochizuki Izumi , Shigeta Yukichi , Tosaka Aki
Published: October 2010

The structure of Si(111) √7×√7 R19.1°-Co reconstructed surface have been investigated by scanning tunneling microscopy (STM). Three proposed sites on the reconstructed surface, the Co atom site, the cap-adatom site and the bridge-adatom site have been all visualized by STM. The electric structure at each adatom site was measured by scanning tunneling spectroscopy, exactly. The reason why the bridge site can be visualized under the restricted condition is also explained by the local electric state above the Fermi level.
Use of an autonomous sensor to evaluate the biological performance of the advanced turbine at Wanapum Dam
Authors: Deng Zhiqun , Carlson Thomas J. , Duncan Joanne P. , Richmond Marshall C. , Dauble Dennis D.
Published: October 2010

Hydropower is the largest renewable energy resource in the United States and the world. However, hydropower dams have adverse ecological impacts because migrating fish may be injured or killed when they pass through hydroturbines. In the Columbia and Snake River basins, dam operators and engineers are required to make those hydroelectric facilities more fish-friendly through changes in hydroturbine design and operation after fish population declines and the subsequent listing of several species of Pacific salmon under the Endangered Species Act of 1973. Public Utility District No. 2 of Grant County, Washington, requested authorization from the Federal Energy Regulatory Commission to replace the ten turbines at Wanapum Dam with advanced hydropower turbines designed to improve survival for fish passing through the turbines while improving operation efficiency and increasing power generation. As an additional measure to the primary metric of direct injury and mortality rates of juvenile Chinook salmon using balloon tag-recapture methodology, this study used an autonomous sensor device—the Sensor Fish—to provide insight into the specific hydraulic conditions and physical stresses experienced by the fish as well as the specific causes of fish biological response. We found that the new hydroturbine blade shape and the corresponding reduction of turbulence in the advanced hydropower turbine were effective in meeting the objectives of improving fish survival while enhancing operational efficiency of the dam. The frequency of severe events based on Sensor Fish pressure and acceleration measurements showed trends similar to those of fish survival determined by the balloon tag-recapture methodology. In addition, the new turbine provided a better pressure and rate of pressure change environment for fish passage. Overall, the Sensor Fish data indicated that the advanced hydroturbine design improved passage of juvenile salmon at Wanapum Dam.
Pigtailed CdS nanoribbon ring laser
Authors: Ma Yaoguang , Li Xiyuan , Yang Zongyin , Yu Huakang , Wang Pan , Tong Limin
Published: October 2010

We demonstrated a pigtailed nanoribbon ring laser constructed with a 600 nm wide and 330 nm thick CdS nanoribbon. When the 20-μm-diameter ring was irradiated by light from a supercontinuum source, multi longitudinal mode laser emission was observed around 523.5 nm with full widths at half maximum of 0.27 nm. The laser output from the pigtail showed strong orientation-dependent polarization, with a maximum polarization ratio of 5 and power up to 3.7 nW.
Nuclear motion in carbonyl sulfide induced by resonant core electron excitation
Authors: Laksman J. , Céolin D. , Gisselbrecht M. , Sorensen S. L.
Published: October 2010

The angular anisotropy for selected dissociation channels is measured at resonantly excited states of Σ and Π symmetries at the C and O K-shell ionization edges of carbonyl sulfide. While the kinetic energy released in the reaction is mainly independent of the excitation energy, the angular anisotropy and momentum correlation clearly show deformation of the OCS molecule in the C 1s−1π∗1 state. The discovery of a two-body fragmentation channel SO+/C+ with a well defined angular anisotropy indicates the rapid formation of the CSO isomeric species.
Effect of concentration on low-frequency noise of multiwall carbon nanotubes in high-density polyethylene matrix
Authors: Barone C. , Pagano S. , Neitzert H. C.
Published: October 2010

Transport and noise measurements of multiwall carbon nanotubes in high-density polyethylene matrix are reported. In these composites current transport occurs through a random tunnel junctions network, formed by adjacent carbon nanotubes. Low-frequency noise investigations reveal a 1/f behavior induced by resistance fluctuations. An unusual temperature dependence in samples with different nanotube concentration is found. This can be explained by a transition from a fluctuation-induced tunneling mechanism to a thermally activated regime, occurring at increasing nanotube concentration and resulting in a decrease in the overall noise.
A simple method to evaluate the optimal size of nanoparticles for endocytosis based on kinetic diffusion of receptors
Authors: Li Xinlei , Xing Da
Published: October 2010

We have presented an analytic thermodynamic model to elucidate the mechanism of receptor-mediated endocytosis of nanoparticles (NPs) and provided a simple method to evaluate the optimal size of NPs by minimizing the kinetic diffusion time of the free receptors around the bound region toward the contact surface with NPs. It is found that the average density of receptors and chemical energy release upon the binding of a ligand-receptor pair determine the optimal size of NPs if the bending modulus of membranes and the cross-sectional area of the receptor are constants. The optimal radius of NPs can be calculated based on our model.
Carbon nanotube stabilized conductive polymers
Authors: Li Yi-Fan , Wong I-Sing , Lai Tao-Cheng , Chin Wei , Hsu Wen-Kuang
Published: October 2010

Carbon nanotubes act as radical scavengers in UV-irradiated conductive polymer (poly3,4-ethylenedioxythiophene:polystyrene sulfonate) and effect is verified by conductivity, electron paramagnetic resonance, and infrared absorption data.
Mapping of localized spin-wave excitations by near-field Brillouin light scattering
Authors: Jersch J. , Demidov V. E. , Fuchs H. , Rott K. , Krzysteczko P. , Münchenberger J. , Reiss G. , Demokritov S. O.
Published: October 2010

We report on the experimental study of the spatial characteristics of high-frequency spin-wave modes localized at the edges of micrometer-size in-plane magnetized permalloy ellipses. Using a near-field Brillouin light scattering technique, we have mapped the modes with the spatial resolution of few tens of nanometers. We show that the width of the localization area strongly depends on the applied magnetic field and reduces to about 85 nm for high fields. We also demonstrate that the existing theoretical models do not appropriately describe spatial characteristics of the modes.
Effect of GaN interlayer on polarity control of epitaxial ZnO thin films grown by molecular beam epitaxy
Authors: Wang X. Q. , Sun H. P. , Pan X. Q.
Published: October 2010

Epitaxial ZnO thin films were grown on nitrided (0001) sapphire substrates with an intervening GaN layer by rf-plasma-assisted molecular beam epitaxy. It was found that polarity of the ZnO epilayer could be controlled by modifying the GaN interlayer. ZnO grown on a distorted 3-nm-thick GaN interlayer has Zn-polarity while ZnO on a 20-nm-thick GaN interlayer with a high structural quality has O-polarity. High resolution transmission electron microscopy analysis indicates that the polarity of ZnO epilayer is controlled by the atomic structure of the interface between the ZnO buffer layer and the intervening GaN layer.
Communication: ROHF theory made simple
Authors: Tsuchimochi Takashi , Scuseria Gustavo E.
Published: October 2010

Restricted open-shell Hartree–Fock (ROHF) theory is formulated as a projected self-consistent unrestricted HF (UHF) model by mathematically constraining spin density eigenvalues. This constrained UHF (CUHF) wave function is identical to that obtained from Roothaan’s effective Fock operator. The α and β CUHF Fock operators are parameter-free and have eigenvalues (orbital energies) that are physically meaningful as in UHF, except for eliminating spin contamination. This new way of solving ROHF leads to orbitals that turn out to be identical to semicanonical orbitals. The present approach removes ambiguities in ROHF orbital energies.
Is Centaurus A Special? A Neutral-Hydrogen Perspective
Authors: Struve Christian , Morganti Raffaella , Oosterloo Tom A. , Emonts Bjorn H. C.
Published: October 2010

Due to its proximity, the neutral hydrogen belonging to Cen A can be observed at high resolution with good sensitivity. This allows us to study the morphology and kinematics in detail, in order to understand the evolution of this radio-loud source (e.g. merger history, AGN activity). At the same time, it is important to compare results to other sources of the same class (i.e. early-type galaxies in general and radio galaxies in particular) to see how Cen A fits into the global picture of early-type/radio galaxy evolution. The amount of Hi, the morphology of a warped disk with Hi clouds surrounding the disk and the regular kinematics of the inner part of the Hi disk are not unusual for early-type galaxies. The growing evidence that mergers are not necessarily responsible for AGN activity fits with the observational result that the recent merger event in Cen A is not directly connected to the current phase of activity. Based on these results, we conclude that Cen A has typical neutral hydrogen properties for an early-type and radio galaxy and it can therefore — from the perspective of Hi — be seen as a typical example of its class.
Centaurus A at Hard X-Rays and Soft Gamma-Rays
Authors: Steinle H.
Published: October 2010

Cen A, at a distance of less than 4 Mpc, is the nearest radio-loud AGN. Its emission is detected from radio to very-high energy gamma-rays. Despite the fact that Cen A is one of the best studied extragalactic objects the origin of its hard X-ray and soft gamma-ray emission (100 keV <E< 50 MeV) is still uncertain. Observations with high spatial resolution in the adjacent soft X-ray and hard gamma-ray regimes suggest that several distinct components such as a Seyfert-like nucleus, relativistic jets, and even luminous X-ray binaries within Cen A may contribute to the total emission in the MeV regime that has been detected with low spatial resolution. As the Spectral Energy Distribution of Cen A has its second maximum around 1 MeV, this energy range plays an important role in modeling the emission of (this) AGN. As there will be no satellite mission in the near future that will cover this energies with higher spatial resolution and better sensitivity, an overview of all existing hard X-ray and soft gamma-ray measurements of Cen A is presented here defining the present knowledge on Cen A in the MeV energy range.
The Many Faces of the Gas in Centaurus A (NGC 5128)
Authors: Morganti Raffaella
Published: October 2010

Centaurus A (NGC 5128) is ideal for investigating the characteristics and role of gas in an earlytype galaxy in the presence of a radio-loud active nucleus. The different phases of the gas—hot (X-ray), warm (ionized), and cold (H i and molecular)—are all detected in this object and can be studied at very high spatial resolution, due to its proximity. This richness makes Centaurus A truly unique. Spatially, these gas structures span from the pc to the tens of kpc scale. Thus, they allow us to trace very different phenomena, from the formation and evolution of the host galaxy, to the interplay between nuclear activity and interstellar medium and the feeding mechanism of the central black hole. A lot of work has been done to study and understand the characteristics of the gas in this complex object, and the present paper summarizes what has been achieved so far.
Habitat use and feeding habits of juvenile fishes in an infrequently flooded Atlantic saltmarsh
Authors: Valiñas Macarena , Acha Eduardo M. , Iribarne Oscar
Published: October 2010

In saltmarshes, marsh creeks provide an important corridor between the marsh and the subtidal habitat for fishes. We compare fish and prey in a Spartina densiflora marsh creek with a tidal flat in the SW Atlantic (Argentina) to evaluate the hypotheses that: (1) benthic prey abundance is higher in the marsh creek, and therefore the abundance of benthivorous fishes and predation pressure on benthos is higher in this area; and (2) marsh creeks act as refuge areas for fishes. Fish abundance and benthic prey availability were sampled over four seasons, and dietary composition of Odontesthes argentinensis and Micropogonias furnieri was assessed. Brevoortia aurea was more abundant in the marsh creek, Micropogonias furnieri showed the opposite pattern, and Odontesthes argentinensis and Ramnogaster arcuata did not dominate either habitat. As expected, smaller fishes were more abundant in the marsh creek. Food abundance was higher in the marsh creek but only M. furnieri consumed more prey in this area, while O. argentinensis consumed more in the tidal flat. Differences in prey accessibility and sediment features between areas could explain these results. This work highlights the importance of marsh creeks as refuge and/or feeding grounds for fishes in infrequently flooded saltmarshes.
Properties of natural microlayers on Australian freshwater storages and their potential to interact with artificial monolayers
Authors: Pittaway Pamela A. , van den Ancker Tania R.
Published: October 2010

Microlayers are natural surface films derived from hydrophobic organic compounds that form on most lakes and streams. Holarctic brown-water lakes have been most commonly studied, with Australian research limited to marine microlayers. Artificial monolayers based on long-chain fatty alcohols have been applied to freshwater storages to reduce evaporative loss. As a water conservation strategy, monolayer technology was not widely adopted because of variable field performance. However, the role of natural microlayers in reducing monolayer performance has not previously been investigated. In the present study, microlayer and subsurface samples from six water storages in Queensland were characterised for water-quality indices, including biochemical oxygen demand, permanganate index and ultraviolet light absorbance. Microlayer enrichment in south-eastern Queensland is comparable to or higher than that in holarctic lakes. The results indicated that microlayer compounds have the potential to disrupt monolayers in at least the following three ways: as substrates for microbes capable of degrading monolayer compounds, as chromophores accelerating photodegradation, and as impurities disrupting the molecular packing required to reduce evaporative loss. The knowledge gained from studying natural microlayers can also be used to benchmark novel monolayer compounds, to minimise their environmental impact on freshwater ecosystems.
Spatial and fishing effects on sampling gear biases in a tropical reef line fishery
Authors: Welch David J. , Mapstone Bruce D. , Davies Campbell R. , Russ Garry R.
Published: October 2010

Biased estimates of population parameters for harvested stocks can have severe implications for fishery management strategy choices. Hook-and-line fishing gear is size-selective and therefore collects biased samples from wild populations. Such biases may also vary in space and time. To assess this assertion, we compared line- and spear-caught samples of the main target species of an Australian hook-and-line fishery to quantify relative bias in size and age structure estimates. We also assessed the consistency of biases among four fishery regions and between two management zones – areas open and closed to fishing. Fish less than 310 mm and younger than 4 years comprised a larger proportion of the speared than the line samples regardless of region or management zone. Conversely, hook-and-line sampled more fish in larger size classes (>370 mm) and older age classes (≥6 years) relative to spear fishing. These biases were qualitatively, but not quantitatively, consistent in all regions and management zones. This variation in sampling resulted in different inferences about regional and zone-related patterns in population size and age structure. We recommend careful consideration of sampling bias when drawing conclusions about regional and management zone effects on fish populations.
Changes in organic-matter dynamics and physicochemistry, associated with riparian vegetation loss and river regulation in floodplain wetlands of the Murray River, Australia
Authors: Watkins Susanne C. , Quinn G. P. , Gawne Ben
Published: October 2010

Extensive clearing of floodplain forests potentially reduces organic matter available to floodplain wetlands. Furthermore, on rivers regulated to provide irrigation water in summer, floodplain wetlands that were previously inundated in spring, now flood in summer/autumn. In the Murray–Darling Basin, Australia, this has changed the timing of organic matter entering the aquatic phase, since leaf fall peaks in summer. Field surveys and mesocosm experiments on floodplain wetlands on the River Murray revealed faster processing rates of leaves in summer/autumn than spring, and no difference between cleared and forested wetlands. Temperature and leaf carbon : nitrogen ratio could not explain these differences, and instead, changes to leaf chemistry associated with ‘terrestrial ageing’ between peak leaf fall in summer and inundation in spring is more likely. The results indicated that the reduction of input of organic matter through riparian tree clearing and changing the timing of inundation interact to alter organic-matter standing stocks and rates of decomposition in floodplain wetlands. Restoring both natural timing of high flows and riparian vegetation might be required for recovery of these wetlands.
Weak effects of plant diversity on leaf-litter breakdown in a tropical stream
Authors: Dudgeon David , Gao Becky W.
Published: October 2010

The relationship between biodiversity and ecosystem functioning is incompletely understood, particularly the relative influence of species richness and composition on functioning. We investigated the effects of plant species diversity on litter breakdown rate (a measure of functioning) and the associated detritivorous macroinvertebrates in a tropical stream in Hong Kong by using single-species and three- and four-species mixtures of leaves with contrasting breakdown rates. We hypothesised that the scarcity of shredding detritivores in Hong Kong streams would limit the scope for diversity effects attributable to differences in leaf composition. Nonetheless, breakdown rates were affected by differences in composition (constituent species within a mixture) rather than richness (number of species in a mixture). Ficus fistulosa (Moraceae) was a key species in mixtures, producing non-additive effects through acceleration of breakdown of other constituent species. There were no other positive (or any negative) non-additive effects of mixing. Leaf diversity did not affect macroinvertebrate functional organisation or taxonomic composition. Assemblages on all litter types were dominated by collector-gatherers (mainly chironomids, >70% of total abundance), and shredders were scarce (<5%). Although diversity had no obvious bottom-up influence on detritivores, non-additive effects of mixing may arise from the influence of litter quality on microbially mediated breakdown in this tropical stream.