bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of second‐generation MODIS aerosol retrieval (Collection 005) at Kanpur, India
Authors: Jethva Hiren , Satheesh S. K. , Srinivasan J.
Published: October 2007

The second‐generation MODIS aerosol retrieval (Collection 005) from EOS‐ Aqua (2002–2005) was evaluated using ground‐based AERONET measurements at Kanpur (26.45°N, 80.35°E) northern India. We found that the aerosol optical depth (AOD) retrievals are more accurate compared to that of previous retrieval (Collection 004). About 70% of the total retrievals at 0.47 μm and 0.55 μm and 60% of the retrievals at 0.66 μm wavelength in the new version fall within the pre‐launch uncertainty (Δτ = ±0.05 ± 0.15τ, where τ is AOD) with better correlation (R2 ∼ 0.83) at all three wavelengths. However, MODIS still tends to over‐estimate AOD for a few retrievals in the presence of dust aerosols. The error in the fine‐dominated AOD was large for most retrievals in the C005. However, the fine‐dominated AOD of Collection 004 was better correlated with the equivalent AERONET data. This suggests that the fine‐dominated AOD retrievals need to be re‐examined further.
Quasi‐Lagrangian superpressure balloon measurements of gravity‐wave momentum fluxes in the polar stratosphere of both hemispheres
Authors: Vincent R. A. , Hertzog A. , Boccara G. , Vial F.
Published: October 2007

Superpressure balloons were flown in 2002 and 2005 in the winter polar vortices of both hemispheres. The balloons can drift for months in the stratosphere acting as quasi‐Lagrangian tracers of air‐parcel motions. The meteorological datasets acquired are used to retrieve small‐scale internal atmospheric gravity wave parameters using wavelet techniques. For the first time, gravity wave momentum fluxes are estimated over wide geographical areas and the results will help constrain gravity wave parameterization schemes used in general circulation climate models. The importance of mountain waves is confirmed, with largest fluxes observed in the lee of Greenland and the Antarctic Peninsula. However, significant momentum fluxes are also observed over the oceans, showing the importance of other wave generation mechanisms.
Involvement of cannabinoid receptor CB2 in dectin‐1‐mediated macrophage phagocytosis
Authors: Shiratsuchi Akiko , Watanabe Ikuko , Yoshida Hiroko , Nakanishi Yoshinobu
Published: October 2007

Cannabinoid receptors are expressed in macrophages, but little is known of their roles. We here examined their involvement in phagocytosis. The presence of 2‐arachidonylglycerol, an endocannabinoid, augmented the phagocytosis of zymosan by mouse macrophages, while the phagocytosis of Escherichia coli, Staphylococcus aureus, apoptotic cells or latex beads remained unaffected. An agonist of the cannabinoid receptors CB1 and CB2 also stimulated the phagocytosis of zymosan. The stimulatory effect of 2‐arachidonylglycerol was abolished when phagocytosis reactions were carried out in the presence of an antagonist of CB2 but not of CB1. Furthermore, the phagocytosis of zymosan in the presence of 2‐arachidonylglycerol was severely inhibited by the addition of a β‐glucan‐containing carbohydrate or antibody neutralizing dectin‐1, a β‐glucan‐recognizing phagocytosis receptor. These results suggested that the activation of CB2 in macrophages leads to the stimulation of dectin‐1‐mediated phagocytosis.
Comparison of double-ended transition state search methods
Authors: Koslover Elena F. , Wales David J.
Published: October 2007

While a variety of double-ended transition state search methods have been developed, their relative performance in characterizing complex multistep pathways between structurally disparate molecular conformations remains unclear. Three such methods (doubly-nudged elastic band, a string method, and a growing string method) are compared for a series of benchmarks ranging from permutational isomerizations of the seven-atom Lennard-Jones cluster (LJ7) to highly cooperative LJ38 and LJ75 rearrangements, and the folding pathways of two peptides. A database of short paths between LJ13 local minima is used to explore the effects of parameters and suggest reasonable default values. Each double-ended method was employed within the framework of a missing connection network flow algorithm to construct more complicated multistep pathways. We find that in our implementation none of the three methods definitively outperforms the others, and that their relative effectiveness is strongly system and parameter dependent.
Photoabsorption and photofragmentation of isolated cationic silver cluster–tryptophan hybrid systems
Authors: Mitrić Roland , Petersen Jens , Kulesza Alexander , Bonačić-Koutecký Vlasta , Tabarin Thibault , Compagnon Isabelle , Antoine Rodolphe , Broyer Michel , Dugourd Philippe
Published: October 2007

We present a theoretical study of the size and structure selective absorption properties of cationic silver cluster–tryptophan Trp–Agn+ (n=2–5,9) hybrid systems supported by photofragmentation experiments. Our time-dependent density functional theory calculations provide insight into the nature of excitations in interacting nanoparticle-biomolecule subunits and allow to determine characteristic spectral features as fingerprints of two different classes of structures: charge solvated and zwitterionic. Moreover, different types of charge transfer transitions have been identified. Charge transfer from π system of tryptophan to silver cluster occurs for charge solvated structures while charge transfer from silver to the NH3+ group takes place for zwitterionic structures. This has been confirmed by experimentally measured photofragmentation channels and molecular dynamics simulations. Our findings provide fundamental insight into the structure- and size-dependent mechanism responsible for the enhanced absorption and emission in nanoparticle-biomolecular hybrid systems.
Deflection, drift, and advective growth in variable-density, laminar mixing layers
Authors: Bretonnet L. , Cazalbou J.-B. , Chassaing P. , Braza M.
Published: October 2007

Specific features of the variable-density mixing layers without gravity effects are studied using self-similar solutions to the laminar and time-evolving variant of this flow. Density variations come from either mass or temperature mixing, accounting for, in the latter case, the effect of the Mach number. The transverse profiles of the flow quantities, as well as the time evolutions of the global characteristic scales of the mixing layer, are given for a wide range of density ratio and Mach-number values. When compared to the constant-density case, it appears that most of the specificity of these flows comes from the emergence of a nonzero transverse component of the velocity. First, it produces a deflection of the flow that can be either confined in the core of the layer or global, the whole layer being tilted at an angle from the initial flow direction. In most cases, this deflection is such that some part of the higher-density fluid is “entrained” in the direction of the lower-density fluid, leaving no possibility to define a dividing streamline. Second, it leads to a shift between the density profile and the profiles of the other flow quantities. This shift scales on the (time-increasing) mixing-layer thickness and therefore appears as a time drift. When global deflection is present, the tilting of the layer can be shown to be equivalent to a global drift of the mixing/shear layer toward the light-fluid side of the flow. Third, transport by the transverse velocity component affects the spreading of the mixing layer, giving rise to an additional effect referred to as advective growth. Examination of the density-ratio and Mach-number effects leads to surprising results: While the momentum thickness is always observed to decrease when increasing these parameters, conventional thicknesses (based on the profiles of the different variables) can show opposite behaviors depending on the form of the diffusion model for the considered variable.
Effective interaction energy of water dimer at room temperature: An experimental and theoretical study
Authors: Nakayama T. , Fukuda H. , Kamikawa T. , Sakamoto Y. , Sugita A. , Kawasaki M. , Amano T. , Sato H. , Sakaki S. , Morino I. , Inoue G.
Published: October 2007

Buffer-gas pressure broadening for the ν1+ν3 band of H2O at 1.34–1.44μm for a variety of buffer gases was investigated at room temperature using continuous-wave cavity ring-down spectroscopy. The effective interaction energy of water dimer under room temperature conditions was evaluated from the pressure broadening coefficients for rare gases using Permenter-Seaver’s relation. Monte Carlo simulations were performed using ab initio molecular orbital calculations to evaluate the interaction energies for the water dimer at 300K. In this theoretical calculation, the orientations of the two water molecules were statistically treated.
Spectrally narrowed edge emission from organic light-emitting diodes
Authors: Tian Yun , Gan Zhengqing , Zhou Zhaoqun , Lynch David W. , Shinar Joseph , Kang Ji-hun , Park Q-Han
Published: October 2007

A dramatic spectrally narrowed edge emission (SNEE) from small molecular organic light-emitting diodes at room temperature, with a full width at half maximum of 5–10nm, is described. The results show that this emission is due to irregular waveguide modes that leak from the indium tin oxide anode to the glass substrate at a grazing angle. Measurements of variable stripe length devices exhibit an apparent weak optical gain, but there is no observable threshold bias associated with this SNEE. Hence this apparent “optical gain” is suspected to result from misalignment of the propagating leaky waveguide mode and the collecting optics.
Simulated thermal decomposition and detonation of nitrogen cubane by molecular dynamics
Authors: Shi Yunfeng , Brenner Donald W.
Published: October 2007

We present simulations of a model molecular solid of nitrogen cubane subject to thermal agitation and mechanical shock. A new approach, a reactive state summation potential, has been used to model nitrogen cubane dissociation. At elevated temperatures, the system decomposes to N2 mixed with a small amount of oligomeric nitrogen. When subject to shock loading the system detonates above some critical threshold after which a shock front is self-sustained by the energy release from chemical reactions at a constant intrinsic speed. This is the first example of a fully three-dimensional atomic simulation of a chemically-sustained detonation. The spatial confinement of the shock front results in longer chain intermediates than in the case of thermal decomposition, suggesting that shock intermediates can be structurally very different from the same material subject to comparable temperatures and pressures.
In-plane structure and ordering at liquid sodium surfaces and interfaces from ab initio molecular dynamics
Authors: Walker Brent G. , Marzari Nicola , Molteni Carla
Published: October 2007

Atoms at liquid metal surfaces are known to form layers parallel to the surface. We analyze the two-dimensional arrangement of atoms within such layers at the surface of liquid sodium using ab initio molecular dynamics (MD) simulations based on a full version of density functional theory. Nearest neighbor distributions at the surface indicate mostly fivefold coordination, though there are noticeable fractions of fourfold and sixfold coordinated atoms. Bond angle distributions suggest a movement toward the angles corresponding to a sixfold coordinated hexagonal arrangement of the atoms as the temperature is decreased towards the solidification point. We rationalize these results with a distorted hexagonal model at the surface, showing a mixture of regions of five- and sixfold coordination. The liquid surface results are compared with classical MD simulations of the liquid surface, with similar effects appearing, and with ab initio MD simulations for a model solid-liquid interface, where a pronounced shift towards hexagonal ordering is observed as the temperature is lowered.
Adsorption and charge transfer dynamics of bi-isonicotinic acid on Au(111)
Authors: Ben Taylor J. , Mayor Louise C. , Swarbrick Janine C. , O’Shea James N. , Isvoranu Cristina , Schnadt Joachim
Published: October 2007

The interaction of bi-isonicotinic acid (4,4′-dicarboxy-2,2′-bipyridine) with the Au(111) surface has been investigated using electron spectroscopic techniques. Near edge x-ray absorption fine structure (NEXAFS) spectra show that monolayers of the molecule lie flat to the surface and also reveal that the monolayer is sensitive to the preparation conditions employed. Core level x-ray photoelectron spectroscopy (XPS) shows that the adsorbed molecule does not undergo deprotonation upon adsorption. The “core-hole clock” implementation of resonant photoemission has been used to probe the coupling between molecule and substrate. This technique has revealed the possibility of ultrafast backtransfer from the substrate into the molecule upon resonant excitation of a N 1s core level electron. This is supported by a NEXAFS and XPS investigation of energy level alignments in the system.
Anisotropic morphology of nonpolar a-plane GaN quantum dots and quantum wells
Authors: Founta S. , Bougerol C. , Mariette H. , Daudin B. , Vennéguès P.
Published: October 2007

The growth of (11–20) or a-plane quantum dots and quantum wells by plasma-assisted molecular-beam epitaxy has been studied. It is shown that Ga-rich conditions lead to the formation of quantum dots, whereas quantum wells are obtained in N-rich conditions. Combining various experimental techniques, it is furthermore demonstrated that quantum dot nucleation along [1–100] and quantum well morphology in the (1–100) plane are influenced by anisotropic growth of AlN buffer layer. Moreover, it is established that peculiar morphological features of quantum dots and quantum wells, in particular the asymmetric shape of quantum dots, are related to the polar character of the [0001] direction in wurtzite nitride material.
Tensile strength and fracture toughness of brittle materials
Authors: Emmerich Francisco G.
Published: October 2007

The fracture properties of brittle materials under tension have been explained by many authors; however, questions such as the dependence of the tensile strength on the crack tip radius of curvature and the scatter of fracture toughness are still not well explained from fundamental principles. This work aims to address this question by using a force-atomistic approach: we analyze the forces that act in the solid down to the smallest dimensions in an atomistic context, verifying the satisfaction of the static equilibrium condition given by Newton’s second law up to the beginning of the rupture. We take into account the forces due to the applied stress, which may be very large at crack tips, and the material cohesion forces, particularly at the point of largest local strain and stress concentration, where the local hyperelasticity of the material plays a governing role. By considering and connecting microstructure and atomicity, and using an experimentally proved maximum tensile-stress criterion for fracture, here we obtain an expression for the tensile strength of the brittle materials, where an effective local cohesive stress is defined. Thus, we explain in a unified framework from fundamental principles a set of established experimental results of brittle fracture of materials under tension, including the dependence of the tensile strength on the crack tip radius of curvature and some scatter in reported values of fracture toughness and cleavage surface energy. This work can be useful to make more realistic predictions of fracture properties of brittle materials taking into account microstructure and atomicity.
Scaling of amplitude-frequency-dependence nonlinearities in electrostatically transduced microresonators
Authors: Agarwal Manu , Mehta Harsh , Candler Robert N. , Chandorkar Saurabh A. , Kim Bongsang , Hopcroft Matthew A. , Melamud Renata , Bahl Gaurav , Yama Gary , Kenny Thomas W. , Murmann Boris
Published: October 2007

This paper studies the scaling of nonlinearities in double-ended-tuning-fork microresonators. We find that the increase in resonant frequency associated with beam length reduction strongly improves current handling. For example, shortening the beams by a factor of 5 results in 20- and 100-fold increases in resonant frequency and sustainable signal current, respectively. Using the nonlinear models and scaling rules outlined in this work, we present considerations for optimization of the resonant structure and its electrostatic gap size.
Origin of macrostrains and microstrains in diamond-SiC nanocomposites based on the core-shell model
Authors: Palosz B. , Stelmakh S. , Grzanka E. , Gierlotka S. , Nauyoks S. , Zerda T. W. , Palosz W.
Published: October 2007

SiC-diamond nanocomposites were synthesized from nanodiamond and nanosilicon powders. A core-shell model of the composite nanocrystals was examined assuming that interatomic distances in the grain interior, the core, and at the surface shell (grain boundaries in nanocrystalline solids) are different. The samples were investigated by x-ray diffraction using synchrotron source. The powder diffractograms were elaborated based on the apparent lattice parameter methodology. The structure of the composites and its dependence on the sintering conditions is discussed. It is shown that as the sintering temperature increases the interatomic distances in the grain cores decrease, while the opposite occurs in the grain shells (forming the grain boundaries). Under some sintering temperature the interatomic distances in the core and in the shell get equal. However, for diamond this happens under different temperature than for SiC, thus internal strains in the composites are unavoidable.
Influence of some design parameters on the efficiency of solar cells with down-conversion and down shifting of high-energy photons
Authors: Badescu Viorel , De Vos Alexis
Published: October 2007

In this paper we analyze the system proposed by Trupke et al. [J. Appl. Phys. 92, 1668 (2002)] to increase solar cell efficiency. The system consists of adding to the solar cell a so-called down-converter, which is a device able to convert the high-energy incident photons into photons of lower energy. The contribution consists of taking account (i) the nonradiative recombination in both solar cell and converter, (ii) the refractive index of solar cell and converter materials, and (iii) the solar radiation concentration. Two configurations are studied: the cell and rear converter (C-RC) and front converter and cell (FC-C). The main conclusions of this work are as follow. (1) For ideal down-converters, with radiative recombination only, the solar energy conversion efficiency may be, or may not be, increased by adding a front (or a rear) down-converter to the cell, depending on the value of the solar cell refractive index. (2) More realistic systems, where nonradiative recombinations exist inside the converter, are also considered. The efficiency of the FC-C system is generally less than the efficiency of a single cell. C-RC systems perform better than the cell operating alone for some values of the refractive indices. (3) C-RC systems perform generally better than FC-C systems whatever the values of the refractive indices and the concentration ratio.
Multiplexed operation of a micromachined ultrasonic droplet ejector array
Authors: Forbes Thomas P. , Degertekin F. Levent , Fedorov Andrei G.
Published: October 2007

A dual-sample ultrasonic droplet ejector array is developed for use as a soft-ionization ion source for multiplexed mass spectrometry (MS). Such a multiplexed ion source aims to reduce MS analysis time for multiple analyte streams, as well as allow for the synchronized ejection of the sample(s) and an internal standard for quantitative results and mass calibration. Multiplexing is achieved at the device level by division of the fluid reservoir and separating the active electrodes of the piezoelectric transducer for isolated application of ultrasonic wave energy to each domain. The transducer is mechanically shaped to further reduce the acoustical crosstalk between the domains. Device design is performed using finite-element analysis simulations and supported by experimental characterization. Isolated ejection of ∼5 μm diameter water droplets from individual domains in the micromachined droplet ejector array at around 1 MHz frequency is demonstrated by experiments. The proof-of-concept demonstration using a dual-sample device also shows potential for multiplexing with larger numbers of analytes.
Asymptotic behavior of condensate solutions in the Chern-Simons-Higgs theory
Authors: Choe Kwangseok
Published: October 2007

We study the asymptotic behavior of condensate solutions in the Chern-Simons-Higgs model as the Chern-Simons coupling parameter tends to zero. Using the variational method, we prove that there exist condensate solutions which show concentration phenomena.
The effect of Mg substitution for Ti on transport and thermoelectric properties of TiS2
Authors: Qin X. Y. , Zhang J. , Li D. , Dong H. Z. , Wang L.
Published: October 2007

Magnesium substituted compounds MgxTi1−xS2 (0⩽x⩽0.15) were prepared by solid-state reaction, and their transport and thermoelectric properties were investigated from 5to310K. The results indicate that at low temperatures (T<∼175K), a transition from metallike to semiconductorlike behavior occurred after the substitution of Mg for Ti, which implies that intrinsically TiS2 is a semiconductor and this transition can be ascribed to de-degeneration through the reduction in electron concentration due to Mg2+ substitution for Ti4+. Furthermore, it was found that dc conductivity σ for MgxTi1−xS2 (x>0) obeyed Mott’s two-dimensional (2D) variable range hopping law lnσ∝T−1∕3 at T<∼50K, indicating that TiS2 possess 2D transport characteristics. The appearance of Mott’s 2D law could originate from a potential disorder introduced by Mg substitution for Ti in S–Ti–S slabs. Meanwhile, the significant enhancement of absolute thermopower of MgxTi1−xS2 (x>0) in the whole temperature range investigated could also be attributed to the reduction of electronic concentration after doping. The thermoelectric figure of merit ZT of heavily substituted compounds (x=0.10 and 0.15) was smaller than that of TiS2, owing to the large increase of both their electrical resistivity and (lattice) thermal conductivity presumably caused by the reduced electron concentration and increased acoustic velocity, respectively. Nevertheless, ZT of the lightly substituted compound Mg0.04Ti0.96S2 enhanced substantially due to the remarkable increase in its thermopower, and specifically it is ∼1.6 times as great as that of TiS2 at 300K, indicating that doping (substitution) is an effective approach to enhance thermoelectric performance of TiS2.
Photoemission from metals and cesiated surfaces
Authors: Jensen Kevin L. , Moody N. A. , Feldman D. W. , Montgomery E. J. , O’Shea P. G.
Published: October 2007

A model of photoemission from coated surfaces is significantly modified by first providing a better account of the electron scattering relaxation time that is used throughout the theory, and second by implementing a distribution function based approach (“Moments”) to the emission probability. The latter allows for the evaluation of the emittance and brightness of the electron beam at the photocathode surface. Differences with the Fowler-Dubridge model are discussed. The impact of the scattering model and the Moments approach on the estimation of quantum efficiency from metal surfaces, either bare or partially covered with cesium, are compared to experiment. The estimation of emittance and brightness is made for typical conditions, and the derivation of their asymptotic limits is given. The adaptation of the models for beam simulation codes is briefly discussed.
Grand canonical Monte Carlo simulation study of capillary condensation between nanoparticles
Authors: Kim Seonmin , Ehrman Sheryl H.
Published: October 2007

Capillary condensation at the nanoscale differs from condensation in the bulk phase, because it is a strong function of surface geometry and gas-surface interactions. Here, the effects of geometry on the thermodynamics of capillary condensation at the neck region between nanoparticles are investigated via a grand canonical Monte Carlo simulation using a two-dimensional lattice gas model. The microscopic details of the meniscus formation on various surface geometries are examined and compared with results of classical macromolecular theory, the Kelvin equation. We assume that the system is composed of a lattice gas and the surfaces of two particles are approximated by various shapes. The system is modeled on the basis of the molecular properties of the particle surface and lattice gas in our system corresponding to titania nanoparticles and tetraethoxy orthosilicate molecules, respectively. This system was chosen in order to reasonably emulate our previous experimental results for capillary condensation on nanoparticle surfaces. Qualitatively, our simulation results show that the specific geometry in the capillary zone, the surface-surface distance, and the saturation ratio are important for determining the onset and broadening of the liquid meniscus. The meniscus height increases continuously as the saturation ratio increases and the meniscus broadens faster above the saturation ratio of 0.90. The change of the radius of curvature of the particle surface affects the dimensions of the capillary zone, which drives more condensation in narrow zones and less condensation in wide zones. The increase of surface-surface distance results in the decrease of the meniscus height or even the disappearance of the meniscus entirely at lower saturation ratios. These effects are significant at the nanoscale and must be carefully considered in order to develop predictive relationships for meniscus height as a function of saturation conditions.
Effects of the high-temperature-annealed self-buffer layer on the improved properties of ZnO epilayers grown by helicon-wave-excited-plasma sputtering epitaxy on a-plane sapphire substrates
Authors: Koyama T. , Fouda A. N. , Shibata N. , Chichibu S. F.
Published: October 2007

The use of the high-temperature-annealed self-buffer layer (HITAB) enabled to observe free A-and B-exciton emissions at 9K from ZnO heteroepitaxial films grown by the sputtering epitaxy method using a helicon-wave-excited plasma on uniaxially nearly lattice-matched (112¯0) Al2O3 substrates. The result was correlated with a twofold decrease in the densities of threading dislocations having both the screw and edge components, according to the dislocation concealing in ZnO HITAB due to lateral mass transport of low-temperature deposited ZnO nanocrystalline grains during high temperature annealing.
Electronic properties of adsorbates on GaAs(001)-c(2×8)∕(2×4)
Authors: Winn Darby L. , Hale Michael J. , Grassman Tyler J. , Sexton Jonathan Z. , Kummel Andrew C. , Passlack Matthias , Droopad Ravi
Published: October 2007

A systematic experimental and theoretical study was performed to determine the causes of oxide-induced Fermi level pinning and unpinning on GaAs(001)-c(2×8)∕(2×4). Scanning tunneling spectroscopy (STS) and density functional theory (DFT) were used to study four different adsorbates’ (O2, In2O, Ga2O, and SiO) bonding to the GaAs(001)-c(2×8)∕(2×4) surface. The STS results revealed that out of the four adsorbates studied, only one left the Fermi level unpinned, Ga2O. DFT calculations were used to elucidate the causes of the Fermi level pinning. Two distinct pinning mechanisms were identified: direct (adsorbate induced states in the band gap region) and indirect pinnings (generation of undimerized As atoms). For O2 dissociative chemisorption onto GaAs(001)-c(2×8)∕(2×4), the Fermi level pinning was only indirect, while direct Fermi level pinning was observed when In2O was deposited on GaAs(001)-c(2×8)∕(2×4). In the case of SiO on GaAs(001)-c(2×8)∕(2×4), the Fermi level pinning was a combination of the two mechanisms.
Stress-induced magnetization in polycrystalline Ni–Fe–Ga ferromagnetic shape memory alloy
Authors: Kustov Sergey , Corró Miquel , Cesari Eduard
Published: October 2007

Results are reported for simultaneous experimental studies of the stress-induced magnetic induction and of anelasticity in a polycrystalline Ni–Fe–Ga ferromagnetic shape memory alloy. The authors found in the martensitic state a linear relationship between mechanically induced induction and stress amplitude, in contrast to a strong nonlinearity of the anelastic strain. This difference between elastic and magnetic responses to applied stress points to inefficient coupling between the motion of elastic twins/domain boundaries and magnetic domain walls. They argue that, in acoustic experiments, magnetic domain walls in Ni–Fe–Ga polycrystals perform only linear displacements within local potential minima, characteristic for the microeddy current magnetomechanical damping.
Contrasting aging behavior of as-grown and annealed BaTiO3 single crystals grown by KF-flux technique
Authors: Bao Huixin , Zhang Lixue , Wang Yu , Liu WenFeng , Zhou Chao , Ren Xiaobing
Published: October 2007

Acceptor-doped ferroelectrics generally show a pronounced aging effect. However, the KF-flux-grown BaTiO3 single crystals, which are known to contain acceptor impurities K+, show no aging effect. This exception poses a potential challenge to the current understanding of ferroelectric aging and may provide a clue for reducing aging effect in acceptor-doped ferroelectrics. To solve this puzzle, we compared the ferroelectric and dielectric aging effects of the as-grown and annealed KF-flux-grown BaTiO3 single crystals. We found that although the as-grown BaTiO3 showed almost no aging effect, the annealed BaTiO3 showed clear aging effect. Chemical analysis revealed that the as-grown crystals contain not only acceptor impurity K+ but also higher concentration of anion donor F−; on the other hand, the annealed crystals contain mostly K+, as a result of F− evaporation. Based on defect chemistry analysis and the microscopic mechanism of the aging, the difference in the aging behavior of the two kinds of crystal is fully explained. Our result suggests that besides the thermodynamic driving force due to the symmetry-conforming short-range ordering of point defects, kinetic factors (the mobility of point defects) also play a crucial role in determining whether or not aging appears. Donor doping is an effective way to reduce the aging effect through eliminating mobile oxygen vacancies.
Frequency response of an atomic force microscope in liquids and air: Magnetic versus acoustic excitation
Authors: Herruzo Elena T. , Garcia Ricardo
Published: October 2007

We discuss the dynamics of an amplitude modulation atomic force microscope in different environments such as water and air. Experiments, analytical expressions, and numerical simulations show that the resonance curves depend on the excitation method used to drive the cantilever, either mechanical or magnetic. This dependence is magnified for small force constants and quality factors, i.e., below 1N∕m and 10, respectively. We show that the equation for the observable, the cantilever deflection, depends on the excitation method. Under mechanical excitation, the deflection involves the base and tip displacements, while in magnetic excitation, the cantilever deflection and tip displacement coincide.
Enhancement of the allowed gradient in a dielectric-loaded superconducting cavity
Authors: Abdo Baleegh , Schächter Levi
Published: October 2007

It is shown that by incorporating a nonisotropic conductive thin film in a dielectric loaded super-conductive structure, it is possible to design an accelerator cavity wherein the maximum magnetic field at the surface of the superconductive material is below the critical value, although the gradient on axis may exceed 50MV∕m.
Faithful qubit transmission against collective noise without ancillary qubits
Authors: Li Xi-Han , Deng Fu-Guo , Zhou Hong-Yu
Published: October 2007

We present a faithful qubit transmission scheme with linear optics against collective noise, not resorting to ancillary qubits. Its setup is composed of three unbalanced polarization interferometers, based on a polarizing beam splitter, a beam splitter, and a half wave plate, which makes this scheme more feasible than others with present technology. The fidelity of successful transmission is 1, independent of the parameters of the collective noise, and the success probability for obtaining an uncorrupted state can be improved to 100% with some time delayers. Moreover, this scheme has some good applications in one-way quantum communication for rejecting the errors caused by the collective noise in quantum channel.
Effects of the medium on synthesis of nanopowders by wire explosion process
Authors: Cho C. , Choi Y. W. , Kang C. , Lee G. W.
Published: October 2007

Silver nanopowder was produced in air and water media by wire explosion process. Size of the particles formed in water was smaller than that in air. In water medium, compared with air, the delay of plasma formation resulted in a higher energy deposition in the wire. As a consequence, there were no micrometer size particles in the powder, which is attributed to the complete vaporization of the wire. It is considered that the wire explosion in liquid medium meets three conditions to form smaller particles, namely, higher energy deposition in the wire, sufficient expansion volume, and quick cooling of the particles.
Protein detection using a radio frequency biosensor with amplified gold nanoparticles
Authors: Chien J. H. , Chen P. H. , Kuo L. S. , Lin C. S. , Wang H.
Published: October 2007

This study presents a device for protein detection using a low-pass radio frequency filter with gold nanoparticles (AuNPs). Self-assembled multilayer gold nanoparticles were immobilized on the sensing surface of the filter by sandwich immunoassay. The measured frequency of the filter ranges from 50MHzto30GHz. The multilayer gold nanoparticles result in a change of 3dB bandwidth of the low-pass filter. Results show that 1ng∕μl of RIgG solution can be detected after triple-layer AuNPs are completely formed. The change in 3dB bandwidth increases with the concentration of target protein. Therefore, this device has potential for protein quantification.
Kaposi's sarcoma herpesvirus-encoded latency-associated nuclear antigen stabilizes intracellular activated Notch by targeting the Sel10 protein
Authors: Lan Ke , Verma Subhash C. , Murakami Masanao , Bajaj Bharat , Kaul Rajeev , Robertson Erle S.
Published: October 2007

Deregulation of the evolutionarily conserved Notch signaling is highly correlated with oncogenesis. Intracellular activated Notch (ICN) is a protooncogene linked to the transcription activation of a number of cellular genes involved in cell cycle regulation, differentiation, and proliferation. Stability of ICN is tightly regulated by the Sel10-mediated ubiquitin–proteasome pathway. Sel10 can function as a negative regulator of Notch and exhibits activities of a tumor-suppressor protein. This article shows that the Kaposi's sarcoma-associated herpesvirus (KSHV) latency-associated nuclear antigen (LANA) directly interacts with Sel10 and forms a complex in KSHV-infected cells. This results in suppression of ICN ubiquitination and degradation. The carboxyl terminus of LANA interacts with the F-box and WD40 domains of Sel10 and competes with ICN for binding to Sel10. This elevated level of ICN is also critical for maintaining the enhanced proliferation of KSHV-infected tumor cells. These findings describe a mechanism by which the KSHV-encoded LANA protein regulates ubiquitination of ICN mediated by the F-box component of the E3 ligase Sel10, leading to proliferation of the virus-infected cells.
Chymotryptic specificity determinants in the 1.0 Å structure of the zinc-inhibited human tissue kallikrein 7
Authors: Debela Mekdes , Hess Petra , Magdolen Viktor , Schechter Norman M. , Steiner Thomas , Huber Robert , Bode Wolfram , Goettig Peter
Published: October 2007

hK7 or human stratum corneum chymotryptic enzyme belongs to the human tissue kallikrein (hKs) serine proteinase family and is strongly expressed in the upper layers of the epidermis. It participates in skin desquamation but is also implicated in diverse skin diseases and is a potential biomarker of ovarian cancer. We have solved x-ray structures of recombinant active hK7 at medium and atomic resolution in the presence of the inhibitors succinyl-Ala-Ala-Pro-Phe-chloromethyl ketone and Ala-Ala-Phe-chloromethyl ketone. The most distinguishing features of hK7 are the short 70–80 loop and the unique S1 pocket, which prefers P1 Tyr residues, as shown by kinetic data. Similar to several other kallikreins, the enzyme activity is inhibited by Zn
2+
and Cu
2+
at low micromolar concentrations. Biochemical analyses of the mutants H99A and H41F confirm that only the metal-binding site at His
99
close to the catalytic triad accounts for the noncompetitive Zn
2+
inhibition type. Additionally, hK7 exhibits large positively charged surface patches, representing putative exosites for prime side substrate recognition.
A chloroplast cyclophilin functions in the assembly and maintenance of photosystem II in
Arabidopsis thaliana
Authors: Fu Aigen , He Zengyong , Cho Hye Sun , Lima Amparo , Buchanan Bob B. , Luan Sheng
Published: October 2007

Photosynthetic light reactions rely on the proper function of large protein complexes (including photosystems I and II) that reside in the thylakoid membrane. Although their composition, structure, and function are known, the repertoire of assembly and maintenance factors is still being determined. Here we show that an immunophilin of the cyclophilin type, CYP38, plays a critical role in the assembly and maintenance of photosystem II (PSII) supercomplexes (SCs) in
Arabidopsis
. Mutant plants with the
CYP38
gene interrupted by T-DNA insertion showed stunted growth and were hypersensitive to high light. Leaf chlorophyll fluorescence analysis and thylakoid membrane composition indicated that
cyp38
mutant plants had defects in PSII SCs. Sucrose supplementation enabled the rescue of the mutant phenotype under low-light conditions, but failed to mitigate hypersensitivity to high-light stress. Protein radiolabeling assays showed that, although individual thylakoid proteins were synthesized equally in mutant and wild type, the assembly of the PSII SC was impaired in the mutant. In addition, the D1 and D2 components of the mutant PSII had a short half-life under high-light stress. The results provide evidence that CYP38 is necessary for the assembly and stabilization of PSII.
Proliferative arrest and rapid turnover of thymic epithelial cells expressing Aire
Authors: Gray Daniel , Abramson Jakub , Benoist Christophe , Mathis Diane
Published: October 2007

Expression of autoimmune regulator (Aire) by thymic medullary epithelial cells (MECs) is critical for central tolerance of self. To explore the mechanism by which such a rare cell population imposes tolerance on the large repertoire of differentiating thymocytes, we examined the proliferation and turnover of Aire+ and Aire− MEC subsets through flow cytometric analysis of 5-bromo-2′deoxyuridine (BrdU) incorporation. The Aire+ MEC subset was almost entirely postmitotic and derived from cycling Aire− precursors. Experiments using reaggregate thymic organ cultures revealed the presence of such precursors among Aire− MECs expressing low levels of major histocompatibility complex class II and CD80. The kinetics of BrdU decay showed the Aire+ population to have a high turnover. Aire did not have a direct impact on the division of MECs in vitro or in vivo but, rather, induced their apoptosis. We argue that these properties strongly favor a “terminal differentiation” model for Aire function in MECs, placing strict temporal limits on the operation of any individual Aire+ MEC in central tolerance induction. We further speculate that the speedy apoptosis of Aire-expressing MECs may be a mechanism to promote cross-presentation of the array of peripheral-tissue antigens they produce.
Dethiosulfatibacter aminovorans gen. nov., sp. nov., a novel thiosulfate-reducing bacterium isolated from coastal marine sediment via sulfate-reducing enrichment with Casamino acids
Authors: Takii Susumu , Hanada Satoshi , Tamaki Hideyuki , Ueno Yutaka , Sekiguchi Yuji , Ibe Akihiro , Matsuura Katsumi
Published: October 2007

A sulfate-reducing enrichment culture originating from coastal marine sediment of the eutrophic Tokyo Bay, Japan, was successfully established with Casamino acids as a substrate. A thiosulfate reducer, strain C/G2T, was isolated from the enrichment culture after further enrichment with glutamate. Cells of strain C/G2Twere non-motile rods (0.6–0.8 μm×2.2–4.8 μm) and were found singly or in pairs and sometimes in short chains. Spores were not formed. Cells of strain C/G2Tstained Gram-negatively, despite possessing Gram-positive cell walls. The optimum temperature for growth was 28–30 °C, the optimum pH was around 7.8 and the optimum salt concentration was 20–30 g l−1. Lactate, pyruvate, serine, cysteine, threonine, glutamate, histidine, lysine, arginine, Casamino acids, peptone and yeast extract were fermented as single substrates and no sugar was used as a fermentative substrate. A Stickland reaction was observed with some pairs of amino acids. Fumarate, alanine, proline, phenylalanine, tryptophan, glutamine and aspartate were utilized only in the presence of thiosulfate. Strain C/G2Tfermented glutamate to H2, CO2, acetate and propionate. Thiosulfate and elemental sulfur were reduced to sulfide. Sulfate, sulfite and nitrate were not utilized as electron acceptors. The growth of strain C/G2Ton Casamino acids or glutamate was enhanced by co-culturing withDesulfovibriosp. isolated from the original mixed culture enriched with Casamino acids. The DNA G+C content of strain C/G2Twas 41.0 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain C/G2Tformed a distinct cluster with species of the genusSedimentibacter. The closest relative wasSedimentibacter hydroxybenzoicus(with a gene sequence similarity of 91 %). On the basis of its phylogenetic and phenotypic properties, strain C/G2T(=JCM 13356T=NBRC 101112T=DSM 17477T) is proposed as representing a new genus and novel species,Dethiosulfatibacter aminovoransgen. nov., sp. nov.
EzTaxon: a web-based tool for the identification of prokaryotes based on 16S ribosomal RNA gene sequences
Authors: Chun Jongsik , Lee Jae-Hak , Jung Yoonyoung , Kim Myungjin , Kim Seil , Kim Byung Kwon , Lim Young-Woon
Published: October 2007

16S rRNA gene sequences have been widely used for the identification of prokaryotes. However, the flood of sequences of non-type strains and the lack of a peer-reviewed database for 16S rRNA gene sequences of type strains have made routine identification of isolates difficult and labour-intensive. In the present study, we generated a database containing 16S rRNA gene sequences of all prokaryotic type strains. In addition, a web-based tool, named EzTaxon, for analysis of 16S rRNA gene sequences was constructed to achieve identification of isolates based on pairwise nucleotide similarity values and phylogenetic inference methods. The system developed provides users with a similarity-based search, multiple sequence alignment and various phylogenetic analyses. All of these functions together with the 16S rRNA gene sequence database of type strains can be successfully used for automated and reliable identification of prokaryotic isolates. The EzTaxon server is freely accessible over the Internet at http://www.eztaxon.org/
Rheinheimera texasensis sp. nov., a halointolerant freshwater oligotroph
Authors: Merchant Mubina M. , Welsh Allana K. , McLean Robert J. C.
Published: October 2007

A Gram-negative, rod-shaped, motile, non-spore-forming bacterium, designated strain A62-14BT, was isolated from a constant-temperature, spring-fed, freshwater lake. On the basis of the complete 16S rRNA gene sequence, strain A62-14BTwas shown to belong to the classGammaproteobacteria, being most closely related toRheinheimerasp. HTB082 (96.2 % sequence similarity),Rheinheimera baltica(95.01 %),Rheinheimera pacifica(96.35 %),Rheinheimera perlucidaandAlishewanella fetalis(95.9 %). The major fatty acids (C16 : 1ω7c, 38.56 %; C16 : 0, 19.04 %; C12 : 03-OH, 12.83 %; C18 : 1ω7c, 7.70 %) and the motility of strain A62-14BTsupport its affiliation to the genusRheinheimera. The salt intolerance of strain A62-14BT, together with the results of other physiological and biochemical tests, allowed the differentiation of this strain from the three species of the genusRheinheimerawith validly published names. Therefore strain A62-14BTrepresents a novel species of the genusRheinheimera, for which the nameRheinheimera texasensissp. nov. is proposed. The type strain is A62-14BT(=ATCC BAA-1235T=DSM 17496T). The description of the genusRheinheimerais emended to reflect the halointolerance and freshwater origin of strain A62-14BT.
Reinekea blandensis sp. nov., a marine, genome-sequenced gammaproteobacterium
Authors: Pinhassi Jarone , Pujalte María J. , Macián M. Carmen , Lekunberri Itziar , González José M. , Pedrós-Alió Carlos , Arahal David R.
Published: October 2007

A novel heterotrophic, moderately halophilic, strictly aerobic, motile bacterium was isolated from a seawater sample collected at the Blanes Bay Microbial Observatory in the north-western Mediterranean Sea. Analysis of its 16S rRNA gene sequence, retrieved from the whole-genome sequence, showed that this bacterium was most closely related to the single-species genera Reinekea and Saccharospirillum (95 and 94 % sequence similarity, respectively) within the class Gammaproteobacteria. The data from phenotypic, genotypic, chemotaxonomic and phylogenetic analyses supported the creation of a novel species of the genus Reinekea to accommodate this bacterium, for which the name Reinekea blandensis sp. nov. is proposed. The type strain is MED297T (=CECT 7120T =CCUG 52066T).
Chryseobacterium haifense sp. nov., a psychrotolerant bacterium isolated from raw milk
Authors: Hantsis-Zacharov Elionora , Halpern Malka
Published: October 2007

Strain H38T was isolated during a study on the diversity of culturable psychrotolerant bacteria in raw milk. Comparative 16S rRNA gene sequence analysis showed that strain H38T belongs to the genus Chryseobacterium (family Flavobacteriaceae, phylum Bacteroidetes), with the highest similarity (96.7 %) to Chryseobacterium hispanicum VP48T. Strain H38T grows aerobically, at 4–41 °C, with 0–2.5 % NaCl and at pH 6.5–10.5. Light induces the formation of yellow carotenoid pigments. The dominant cellular fatty acids are 15 : 0 iso (41.6 %), 15 : 0 anteiso (16.6 %) and 17 : 0 iso 3-OH (10.3 %). The G+C content of the DNA is 37.8 mol%. On the basis of its phenotypic properties and phylogenetic distinctiveness, strain H38T (=LMG 24029T =DSM 19056T) is classified in the genus Chryseobacterium as the type strain of a novel species, for which the name Chryseobacterium haifense sp. nov. is proposed.