bluuebunny/crossref_metadata_2025 huggingface dataset:
Amino-acid and water molecules adsorbed on water clusters in a beam
Authors: Moro Ramiro , Rabinovitch Roman , Kresin Vitaly V.
Published: August 2005

Water clusters (H2O)n and (D2O)n (n⩽15) are produced by supersonic expansion and then pick up an additional heavy or light water molecule, respectively, or an amino-acid molecule (glycine or tryptophan). The products are analyzed by electron bombardment ionization mass spectrometry. Ionization proceeds via the well-known loss of an OH or OD group, but these turn out to have a strong predilection to come from the guest, rather than the host, molecule: between 30% and 60% of the time the loss originates in the picked-up molecule, even for large n. In fact, the magnitude of this fraction depends on the guest, but is largely insensitive to the cluster size. The observations suggest that the host clusters are frozen into compact annealed shapes, and the adducts reside on the surface and form an inhomogeneity where dissociative ionization tends to localize. It is also notable that no significant amino-acid fragmentation is observed beyond the hydroxyl group loss, in contrast to other measurements employing electron-impact ionization.
Anomalous grazing incidence small-angle x-ray scattering studies of platinum nanoparticles formed by cluster deposition
Authors: Lee Byeongdu , Seifert Sönke , Riley Stephen J. , Tikhonov George , Tomczyk Nancy A. , Vajda Stefan , Winans Randall E.
Published: August 2005

The size evolution of platinum nanoparticles formed on a SiO2∕Si(111) substrate as a function of the level of surface coverage with deposited clusters has been investigated. The anisotropic shapes of sub-nanometer-size nanoparticles are changed to isotropic on the amorphous substrate as their sizes increased. Using anomalous grazing incidence small-angle x-ray scattering (AGISAXS), the scattering from nanoparticles on the surface of a substrate is well separated from that of surface roughness and fluorescence. We show that AGISAXS is a very effective method to subtract the background and can provide unbiased information about particle sizes of less than 1nm.
Isotropic-nematic interfacial tension of hard and soft rods: Application of advanced grand canonical biased-sampling techniques
Authors: Vink R. L. C. , Wolfsheimer S. , Schilling T.
Published: August 2005

Coexistence between the isotropic and the nematic phase in suspensions of rods is studied using grand canonical Monte Carlo simulations with a bias on the nematic order parameter. The biasing scheme makes it possible to estimate the interfacial tension γIN in systems of hard and soft rods. For hard rods with L∕D=15, we obtain γIN≈1.4kBT∕L2, with L the rod length, D the rod diameter, T the temperature, and kB the Boltzmann constant. This estimate is in good agreement with theoretical predictions, and the order of magnitude is consistent with experiments.
Anomalous temperature dependence of nuclear quadrupole interactions in strongly hydrogen-bonded systems from first principles
Authors: Schmidt J. , Sebastiani D.
Published: August 2005

We present an analysis of the effect of finite temperatures on the deuteron nuclear quadrupole coupling constants in a strongly hydrogen-bonded molecular crystal by means of first-principles Car-Parrinello molecular-dynamics simulations. Our findings agree well with experiments and provide a microscopic explanation of the anomalous increase of the quadrupole coupling in this class of systems. We show that a simple model based on the anharmonicity of the hydrogen bond potential fails to describe the temperature dependence of the couplings even qualitatively. Instead, the inclusion of fluctuations and disorder in terms of atomic motion of the surrounding molecules turns out to be important to obtain the correct magnitude of the temperature effect.
Semilattice graded weak Hopf algebra and its related quantum G-double
Authors: Li Fang , Cao Haijun
Published: August 2005

The major purpose of this paper is to construct a weak Hopf algebra with grading from a family of Hopf algebras, and then to gain a related quantum G-double with regular R-matrix. First, over a field k, we introduce a so-called semilattice graded weak Hopf algebra H=⊕α∈YHα. Then the quantum G-double D′(H) of H is obtained in case that H is commutative. Moreover, it is shown that D′(H) is semisimple (respectively, von Neumann regular) if and only if H is a semisimple (respectively, von Neumann regular) Hopf algebra. At last, a nontrivial example of semilattice graded weak Hopf algebras is obtained.
The photodissociation of ozone in the Hartley band: A theoretical analysis
Authors: Qu Z.-W. , Zhu H. , Grebenshchikov S. Yu. , Schinke R.
Published: August 2005

Three-dimensional diabatic potential energy surfaces for the lowest four electronic states of ozone with A′1 symmetry—termed X, A, B, and R—are constructed from electronic structure calculations. The diabatization is performed by reassigning corresponding energy points. Although approximate, these diabatic potential energy surfaces allow one to study the uv photodissociation of ozone on a level of theory not possible before. In the present work photoexcitation in the Hartley band and subsequent dissociation into the singlet channel, O3(X̃)+hν→O(D1)+O2(aΔg1), are investigated by means of quantum mechanical and classical trajectory calculations using the diabatic potential energy surface of the B state. The calculated low-resolution absorption spectrum as well as the vibrational and rotational state distributions of O2(aΔg1) are in good agreement with available experimental results.
Valence-band structures of layered oxychalcogenides, LaCuOCh (Ch=S, Se, and Te), studied by ultraviolet photoemission spectroscopy and energy-band calculations
Authors: Ueda Kazushige , Hosono Hideo , Hamada Noriaki
Published: August 2005

To examine the electronic structure of the valence band, ultraviolet photoemission spectra of a series of layered oxychalcogenides, LaCuOCh (Ch=S, Se, and Te), were measured. The measurements were conducted using HeII, HeI, and NeI excitation lines to observe the excitation energy dependence of the spectral shape. Energy-band calculations based on a full-potential linearized augmented plain-wave method were performed. The calculated density of states and partial density of states were compared to the observed photoemission spectra. Five bands were observed in the valence band of LaCuOCh, and NeI radiation remarkably enhanced two of them. The energy dependence of the photoionization cross section of atomic orbitals indicated that the two enhanced bands were due to the Ch p states. Energy calculations were used to assign the remaining bands. The electronic structure of LaCuOCh was further discussed using molecular-orbital diagrams to visualize the (La2O2)2+ and (Cu2Ch2)2− layers as large donor-acceptor pairs. The energy-band calculation and molecular-orbital diagram analyses suggested that the main difference among the valence-band structures of LaCuOCh (Ch=S, Se, and Te) originates from the variations in the energy position of the Ch p bands. The observed spectra are consistent with the results of the band calculations and clearly show the energy variations in the Ch p bands with respect to spectral shape and excitation energy dependence.
Electric-dipole spin-resonance signals related to extended interstitial agglomerates in silicon
Authors: Mchedlidze T. , Binetti S. , Le Donne A. , Pizzini S. , Suezawa M.
Published: August 2005

Three electric-dipole spin-resonance signals, labeled TU7, TU8, and TU9, were detected after subjecting oxygen-rich silicon samples to two-step annealing procedures at 450 and 650°C for prolonged times. The formation and structural evolution of large interstitial agglomerates, known as rodlike defects, occur in oxygen-rich silicon material during similar annealing procedures. Comparison of parameters and formation peculiarities of the defects, inferred from the investigation of the detected signals, with those previously reported for rodlike defects, allowed the assigning of the TU7, TU8, and TU9 spectra to the line-interstitial defects, the planar defects, and the dislocation dipoles, respectively. Correlations of the spin-resonance signals and peculiarities in the photoluminescence spectra for the samples are reported and analyzed.
Time-dependent all-optical logic gates based on two coupled waves in bacteriorhodopsin film
Authors: Chen Guiying , Zhang Chunping , Guo Zongxia , Wang Xinyu , Tian Jianguo , Song Q. W.
Published: August 2005

When two coherent green beams offset from each other by a small angle are coupled in bacteriorhodopsin film, the diffraction intensity rises from zero to a maximum, and then decreases along with the writing time. Based on the change of the diffraction intensity with the writing time, we proposed and demonstrated a time-dependent all-optical exclusive not or (XNOR) operation and a time-dependent all-optical logical inverter (NOT) operation. Based on the relation between the self-diffraction intensity and the polarization states of the input beams, the time-dependent all-optical XNOR logic gate was achieved, and based on the relation between the polarization states of the diffraction beams and that of the recording beams, the time-dependent all-optical NOT logic gate was obtained.
High-efficiency photovoltaic devices based on annealed poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1- phenyl-(6,6)C61 blends
Authors: Reyes-Reyes Marisol , Kim Kyungkon , Carroll David L.
Published: August 2005

The effects of annealing and fullerene loading in regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) based bulk heterojunction photovoltaics have been investigated. Under specific loading and annealing conditions, a combination of morphological and electronic factors can be brought to play to achieve optimal filling factors, open-circuit voltage (Voc), and short-circuit current density (Jsc). We demonstrate that this occurs at surprisingly low loadings of PCBM and annealing temperatures nearing the melting point of the polymer. Further, we report power conversion efficiencies approaching 5% in the P3HT:PCBM system.
The mechanism of striation formation in plasma display panels
Authors: Iza F. , Yang S. S. , Kim H. C. , Lee J. K.
Published: August 2005

Despite the high pressure employed in plasma display panels, the energy balance of low-energy electrons is found to be dominated by inelastic collisions, and the resulting nonlocal electron kinetics plays a key role in the striation formation. Surface charge accumulation on the anode dielectric, however, is also needed for striations to form. It is the combined effect of surface charges and nonlocal electron kinetics that results in the striation formation in plasma display panel cells. Two-dimensional fluid simulations, which assume local electron kinetics, and two-dimensional particle-in-cell Monte Carlo collision simulations with a bare conducting anode show that striations do not form if either the nonlocal electron kinetics or the surface charge accumulation is not considered.
Analytical stress modeling of high-energy laser windows: Application to fusion-cast calcium fluoride windows
Authors: Klein Claude A.
Published: August 2005

The performance of a laser-window material must be assessed not only in terms of its ability to transmit high-power beams without generating undue optical distortion but also in terms of the constraints imposed by stress-related failure modes. In operational use, the stress field images the superposition of stresses originating from the mechanical load created by the pressure differential and the thermal load created by the laser beam. Here, we provide the tools to carry out an analysis of both pressure- and beam-induced stresses, and illustrate the procedure in the context of assessing the performance of a “model” window made of fusion-cast CaF2. The analysis assumes (a) operation on a time scale such that lateral heat diffusion can be ignored, and (b) cylindrically symmetric Gaussian beam shapes, which permit straightforward calculations of stress distributions that should be representative of worst case situations. Pressure-induced stresses strongly depend on the window’s aspect ratio, which suggests increasing the thickness to minimize the stress, but considerations relating to the optical performance require minimum allowable thicknesses based on a Weibull statistical analysis of the fracture probability. Beam-induced stresses are best evaluated in terms of (a) thickness-averaged radial and azimuthal stresses, which increase linearly with exposure time and depend on radial distances through the truncation parameter, and (b) across-the-thickness stress deviations relative to the average stress, which are caused by surface absorption and reach steady-state configurations on a time scale much shorter than the characteristic time for lateral heat transport. The average stress is always compressive and equibiaxial in the central region of the window, but its azimuthal component turns tensile in the rim region, thus threatening the structural integrity through brittle fracture. In addition, the coating-induced stress results in on-axis surface compressions that may exceed the yield strength of the windowpane material. In this light we formulate a figure of merit for stress, which demonstrates that promising laser-window materials must combine a small stress factor (expansion coefficient times elastic modulus) with superior thermal properties in terms of the product of heat capacity and thermal conductivity; CaF2 and SrF2 are the only known candidates that exhibit outstanding optical features at chemical laser wavelengths together with acceptable thermomechanical properties.
Experiments on the effects of aging on compliant coating drag reduction
Authors: Bandyopadhyay P. R. , Henoch C. , Hrubes J. D. , Semenov B. N. , Amirov A. I. , Kulik V. M. , Malyuga A. G. , Choi K.-S. , Escudier M. P.
Published: August 2005

We report the experimental results from a collaborative effort between USA, Russia, and UK on the development of compliant coatings for undersea application of reduction of drag. The focus is on “shelf-life” of coatings. The coatings are based on a linear interference theory of interaction between turbulence pressure fluctuation and the viscoelastic coating. The phase shift between boundary displacement and pressure fluctuation embodies the interference effect. The natural frequency of the coating is matched to the turbulent boundary layer region of maximum Reynolds stress production. Low-molecular weight rubber-like silicone coatings have been manufactured whose properties include slow and fast damping, slow and fast aging, and varying magnitudes of elasticity, density, and thickness as well as transparency. The dynamic modulus and loss tangent vary weakly over a range of frequencies and temperature allowing compatibility with broad spectrum of turbulence. Drag measurements have been carried out over a year by the three teams in their water tunnels independently of identical coated models. We show that, with some exceptions, drag reduction generally deteriorates with the age of the coatings.
Existence of receding and advancing contact lines
Authors: Eggers Jens
Published: August 2005

We study a solid plate plunging into or being withdrawn from a liquid bath to highlight the fundamental difference between the local behavior of an advancing or a receding contact line, respectively. It is assumed that the liquid partially wets the solid, making a finite contact angle in equilibrium. In our hydrodynamic description, which neglects the presence of the outer gas atmosphere, an advancing dynamic wetting line persists to arbitrarily high speeds. The receding wetting line, on the other hand, vanishes at a critical speed set by the competition between viscous and surface tension forces. In the advancing case, we apply existing matching techniques to the plunging plate geometry to significantly improve on existing theories. For the receding contact line, we demonstrate for the first time how the local contact line solution can be matched to the far-field meniscus. In doing so, we confirm our very recent criterion for the vanishing of the receding contact line, leading to the formation of a film covering the solid. The results of both the advancing and the receding cases are tested against simulations of the full model equations.
Three-dimensional computation of convection of water at the center of a superconducting magnet
Authors: Maki Syou , Ataka Mitsuo
Published: August 2005

Magnetothermal convection of water (diamagnetic) contained in a shallow, cylindrical vessel heated from below and cooled from above at the center of a superconducting magnet was numerically studied. Various flow patterns appeared under the influence of the magnetic body force. The flows induced by the magnetic force whose radial component at the vessel side wall was 5.0 times gravity became axisymmetric, and the direction of the flow was opposite to that of the buoyancy-driven thermal convection. When the radial component was as large as gravity, the breaking and recovery of the axisymmetric flow pattern were aperiodically repeated. When it was 0.1 or 0.5 times gravity, the flow showed a three-spoke pattern, breaking axisymmetry. It is discussed that the conditions to obtain such a spoke pattern experimentally are application of a relatively small magnetic field, use of a shallow vessel, and observation for sufficiently long time.
Subterranean silicon photonics: Demonstration of buried waveguide-coupled microresonators
Authors: Indukuri Tejaswi , Koonath Prakash , Jalali Bahram
Published: August 2005

Laterally-coupled silicon microresonators are fabricated beneath the surface of a silicon-on-insulator substrate using a modified separation by implantation of an oxygen technique. Implantation of oxygen ions into a substrate with patterned thermal oxide mask was utilized to realize buried waveguiding structures. Microdisk resonators in the buried silicon layer show loaded quality factors of 2000, with extinction ratios in excess of 20dB. The process also results in the formation of a silicon layer on the surface of the wafer that is suitable for the fabrication of electronic devices, thereby paving the way for three-dimensional monolithic integration of electronics and photonics in silicon.
Magnetic-field dependence of spin waves in ordered permalloy nanowire arrays in two dimensions
Authors: Liu H. Y. , Wang Z. K. , Lim H. S. , Ng S. C. , Kuok M. H. , Lockwood D. J. , Cottam M. G. , Nielsch K. , Gösele U.
Published: August 2005

The longitudinal magnetic-field dependence of quantized spin waves in ordered permalloy nanowire arrays in two dimensions (2D) has been studied by Brillouin spectroscopy. The results were analyzed on the basis of collective spin waves in a hexagonal 2D nanowire array and compared with the results obtained from an analysis of spin waves in an isolated wire. It is found that only the lowest-frequency spin-wave mode of an isolated nanowire is marginally influenced by the presence of neighboring nanowires. These findings are significant for the theoretical understanding and the future technological utilization of magnetic nanowires.
High-fluence Si-implanted diamond: Optimum implantation temperature for SiC formation
Authors: Weishart H. , Eichhorn F. , Heera V. , Pécz B. , Barna Á. , Skorupa W.
Published: August 2005

In this paper the authors investigate the effect of implantation temperature on the structural properties of diamond implanted with high fluences of Si between 5.3×1017Sicm−2 and 1×1018Sicm−2. In order to reduce radiation-induced damage and to enhance SiC formation the implantations were performed at elevated temperatures in the range from 900to1200°C. Subsequently, all samples were annealed for 10min at 1500°C in a rf-heated furnace. X-ray diffraction revealed the formation of cubic SiC nanocrystallites in a buried layer inside the implanted diamond. The implantation-induced damage was assessed by analyzing graphitization of the surface-near layer using Raman spectroscopy. With increasing Si fluence the implantation-induced damage rises and the nearly perfect alignment of the formed SiC crystallites within the host diamond lattice deteriorates. However, raising the implantation temperature from 900to1000°C reduces the damage in the diamond and increases the amount, size, and epitaxial alignment of the crystalline SiC precipitates. Further increase of the implantation temperature gives no improvement in the quality of the SiC-rich layer. Instead, the damaged diamond converts into graphite and the formation of SiC crystallites is obstructed.
Homogeneous cosmologies from the quasi-Maxwell formalism
Authors: Costa João , Natário José
Published: August 2005

We show how to use the quasi-Maxwell formalism to obtain solutions of Einstein’s field equations corresponding to homogeneous cosmologies—namely Einstein’s universe, Gödel’s universe, and the Ozsvath-Farnsworth-Kerr class I solutions—written in frames for which the associated observers are stationary.
A simple parametrization for G2
Authors: Cacciatori Sergio L.
Published: August 2005

We give a simple parametrization of the G2 group, which is consistent with the structure of G2 as a SU(3) fibration. We also explicitly compute the (bi)invariant measure, which turns out to have a simple expression.
Defects introduced into electroplated Cu films during room-temperature recrystallization probed by a monoenergetic positron beam
Authors: Uedono A. , Suzuki T. , Nakamura T. , Ohdaira T. , Suzuki R.
Published: August 2005

Positron annihilation was used to probe vacancy-type defects in electroplated Cu films deposited on Ta∕SiO2∕Si. Doppler broadening spectra of the annihilation radiation were measured for the Cu films during grain growth at room temperature (i.e., self-annealing). The line-shape parameter S increased during self-annealing, and the observed time dependence of S was well described by the Johnson-Mehl-Avrami-Kolmogorov kinetics. After self-annealing, the values of S were found to be larger than the S value for annealed pure Cu, suggesting that the positrons annihilated from the trapped state by vacancy-type defects in grains. From a comparison with the results of previous isochronal annealing experiments, the major species of defects introduced during self-annealing was found to be vacancy clusters. The size of these defects increased, but their concentration decreased, with increasing film thickness. In thicker Cu films, an enhanced flow of atoms and subsequent rapid grain growth cause such defect behavior.
Three-dimensional simulation of atom and ion dynamics in a stationary plasma thruster
Authors: Lazurenko A. , Kim V. , Bishaev A. , Auweter-Kurtz M.
Published: August 2005

A three-dimensional model of atom and ion dynamics in the accelerating channel of a stationary plasma thruster (SPT) is based on the model kinetic equations. Electron dynamics is described based on available experimental data. The expression for the electric field was obtained from the equation of electron impulse conservation law with the use of “thermalized potential” assumption. The simulation was performed for a particular SPT with a thrust vector deviation. A quantitative agreement with the experimental results was obtained on thrust and thrust vector deviation angles for two different SPT operation modes. Calculated distributions of macroparameters demonstrate azimuthally asymmetrical ionization and acceleration processes in this particular SPT.
Superlattice in an interminiband resonance ac field
Authors: Litvinov V. I. , Manasson A.
Published: August 2005

We discuss the properties of miniband electrons in a superlattice illuminated by a strong electromagnetic field. If the ac field is in resonance with a two-miniband superlattice, gaps in the quasienergy spectrum appear. The gap is proportional to the Bessel function and oscillates with the ac electric field. The resonant ac driving force makes the quasienergy spectrum tunable and may decrease the critical dc field for electrical domains to form.
Nanometric deformations of thin Nb layers under a strong electric field using soft x-ray laser interferometry
Authors: Jamelot G. , Ros D. , Carillon A. , Rus B. , Mocek T. , Kozlová M. , Präg A. R. , Joyeux D. , Phalippou D. , Boussoukaya M. , Kalmykow M. , Ballester F. , Jacques E.
Published: August 2005

We present measurements of in situ nanometric-resolution topographical modifications of thin niobium layers subjected to strong electric fields. The Nb layers, deposited on a fused silica substrate, are interferometrically flash probed using soft x-ray laser (XRL) at the wavelength of 21.2nm. Its pulses are reflected by the probed sample under grazing incidence angle, and the information about surface deformation is obtained by a Fresnel wave-front-division interferometer. It was experimentally established that the probing pulses at the soft x-ray wavelength do neither produce any measurable photoelectric-field emission, nor alter the topographical features of the probed surface. The examined Nb electrodes were periodically probed while the electric field was increased up to 80MV∕m, and alterations of their topographical characteristics with a resolution of ∼2nm in the relief elevation were obtained. It was found that behavior of the Nb layer strongly depends on the polarity of the applied voltage. Only small modifications are observed with the Nb surface at the positive potential, whereas the negative potential induces significant transient surface perturbations, with peak-to-valley elevation differences ∼50nm. The qualitative nature of these modifications was observed to be unrelated to intermittent parasitic breakdowns.
Thermodynamic efficiency of an intermediate band photovoltaic cell with low threshold Auger generation
Authors: Ley M. , Boudaden J. , Kuznicki Z. T.
Published: August 2005

The detailed balance method is used to study the thermodynamic efficiency of an intermediate band photovoltaic cell with low threshold Auger generation. Hot electrons generated by high-energy photons pump electrons from the intermediate band to the conduction band. The intermediate band is filled up after absorption of low-energy photons. A thermodynamic efficiency of about 70% is obtained, which is higher than the maximal efficiency of 63.2% for an intermediate band solar cell without Auger generation. The optimum band gap is shifted towards the silicon band gap. This result gives silicon its place in the new generation of solar cell materials using generation mechanism absent in single-band-gap solar cells.
Theory of shear-induced migration in dilute polymer solutions near solid boundaries
Authors: Ma Hongbo , Graham Michael D.
Published: August 2005

In this work, a continuum theory is developed for the behavior of flowing dilute polymer solutions near solid surfaces, using a bead-spring dumbbell model of the dissolved polymer chains. Hydrodynamic interactions between the chains and the wall lead to migration away from the wall in shear flow. At steady state, this hydrodynamic effect is balanced by molecular diffusion; an analytical expression for the resulting concentration profile is derived. It is shown that the depletion layer thickness is determined by the normal stresses that develop in flow and can be much larger than the size of the polymer molecule. The transient development of this depletion layer is also studied, as well as the spatial development downstream from an entrance. Numerical and similarity solutions in these cases show that the developing concentration profile generally displays a maximum at an intermediate distance from the wall.
The response of compliant coating to nonstationary disturbances
Authors: Kulik Victor M. , Rodyakin Sergey V. , Suh Sung-Bu , Lee Inwon , Chun H. H.
Published: August 2005

The amplitude and phase lag of surface deformation were determined for a compliant coating under the action of turbulent pressure fluctuations. For this purpose, pressure fluctuations were measured experimentally. The amplitude and duration of coherent wave train of pressure fluctuations were investigated using digital filtration. The transient response was calculated for stabilization of forced oscillations of the coating in approximation of local deformation. The response of coating was analyzed with considerations of its inertial properties and limited duration of coherent harmonics action of pressure fluctuations. It is shown that a compliant coating interacts only with a frequency range near the first resonance. According to the analysis, with increasing elasticity modulus of the coating material E, deformation amplitude decreases as 1∕E, and dimensionless velocity of the coating surface decreases as 1∕E. For sufficiently hard coatings, deformation amplitude becomes smaller than the thickness of the viscous sublayer, while the surface velocity remains comparable to the vertical velocity fluctuations of the flow.
Biexciton luminescence in InAs nanorods
Authors: Baskoutas Sotirios , Terzis Andreas F.
Published: August 2005

The binding energy of a biexciton confined in InAs nanorods is calculated using the potential morphing method. Once the system under investigation is in a crossover state, the spectral shapes of the exciton and biexciton photoluminescence were predicted. Our results indicate that for the decreasing length of the nanorod, the emission peaks of exciton and biexciton shift to higher energies. Moreover the energy separation between the exciton and biexciton emission peaks shows a maximum at a characteristic length around 24nm. Finally, we have confirmed that, as it is expected, the emission peaks shift to higher energies and the energy separation between them decreases for decreasing temperature.
Deep-level defects in n-type 6H silicon carbide induced by He implantation
Authors: Ling C. C. , Chen X. D. , Brauer G. , Anwand W. , Skorupa W. , Wang H. Y. , Weng H. M.
Published: August 2005

Defects in He-implanted n-type 6H–SiC samples have been studied with deep-level transient spectroscopy. A deep-level defect was identified by an intensity with a logarithmical dependence on the filling pulse width, which is characteristic of dislocation defects. Combined with information extracted from positron-annihilation spectroscopic measurements, this defect was associated with the defect vacancy bound to a dislocation. Defect levels at 0.38∕0.44eV (E1∕E2), 0.50, 0.53, and 0.64∕0.75eV (Z1∕Z2) were also induced by He implantation. Annealing studies on these samples were also performed and the results were compared with those obtained from e−-irradiated (0.3 and 1.7MeV) and neutron-irradiated n-type 6H–SiC samples. The E1∕E2 and the Z1∕Z2 signals found in the He-implanted sample are more thermally stable than those found in the electron-irradiated or the neutron-irradiated samples.
Exchange biasing of ferromagnetic Cr-doped GaN using a MnO overlayer
Authors: Liu H. X. , Wu Stephen Y. , Singh R. K. , Newman N.
Published: August 2005

We report the observation of an exchange biasing of ferromagnetic Cr-doped GaN films by an antiferromagnetic MnO overlayer. The center of the magnetic hysteresis loop shifts to a negative magnetic field by ∼70Oe when measured after a positive field cooling. An enhancement of the coercive field of the Cr-doped GaN film is also found when the exchange-biasing MnO overlayer is present. The mechanism responsible for the exchange bias is attributed to the exchange coupling at the ferromagnetic Cr–GaN∕antiferromagnetic MnO interface.
Linear stability of ultrathin slipping films with insoluble surfactant
Authors: Hu Guo-Hui
Published: August 2005

To study the dewetting process of ultrathin slipping films, the stability characteristics of the surfactant-covered ultrathin films with slippage are analyzed with linear theory. A set of nonlinear equations for the film thickness and the concentration of surfactant is derived based on lubrication approximation for Newtonian viscous fluid. Results show slippage can always enhance the development of perturbations, and reduce the number density of holes when rupture occurs. A prominent characteristic of the stability is that two branches of solutions are found in the dispersion relation. This might lead to an inflexion in the growth rate curve of the most unstable modes, and a cusp point in the corresponding wave number curve for infinite slippage, which indicates that the slip has a profound effect on the linear stability of the films. The influences of the Marangoni number M, equilibrium distance lc, and the base concentration of surfactant Γ0 on the linear stability are also discussed for different slip lengths in the present study.
Deep-ultraviolet light-emitting diodes for frequency domain measurements of fluorescence lifetime in basic biofluorophores
Authors: Vita P. , Kurilčik N. , Juršėnas S. , Žukauskas A. , Lunev A. , Bilenko Y. , Zhang J. , Hu X. , Deng J. , Katona T. , Gaska R.
Published: August 2005

We report on the development of deep-ultraviolet light-emitting diodes with AlGaN multiple-quantum-well active region for real-time fluorescence lifetime sensing in natural biofluorophores. The peak wavelengths of the devices are 340 and 280 nm, linewidth at half maximum approximately 10 nm, wall-plug efficiency up to 0.9%, output power in the milliwatt range, peak-to-background ratio up to four orders of magnitude, and cutoff frequencies for electrical modulation in the range of 100 MHz. Devices with high-frequency modulated output were demonstrated for frequency domain fluorescence lifetime measurements in basic biological autofluorophores (nicotinamide adenine dinucliotide, riboflavin, tyrosine, and tryptophan) with subnanosecond resolution.
Generation of ultrahigh-frequency tunable acoustic waves
Authors: Choi J. D. , Feurer T. , Yamaguchi M. , Paxton B. , Nelson K. A.
Published: August 2005

We demonstrate versatile generation of ultrahigh-frequency, tunable acoustic waves. A novel retroreflection-based pulse shaper is used to generate optical pulse sequences whose frequency is tunable in the 2–2000 GHz range through movement of a single delay line. Multiple-cycle acoustic waves are detected interferometrically at the back of a 15 nm aluminum transducing film and the back of a film-sample-film assembly configured for narrowband acoustic spectroscopy.
Magnetization switching and tunneling magnetoresistance effects of synthetic antiferromagnet free layers consisting of amorphous NiFeSiB
Authors: Chun Byong Sun , Yoo Ilsang , Kim Young Keun , Hwang Jae Youn , Rhee Jang Roh , Kim Taewan , Park Wanjun
Published: August 2005

A synthetic antiferromagnet (SAF) structure comprising of ferromagnetic amorphous Ni16Fe62Si8B14 layers has been devised and employed as a free layer of magnetic tunnel junctions (MTJs) to enhance cell switching performance. We observed −0.03erg∕cm2 of exchange coupling energy (Jex) by inserting a 0.5 nm Ru layer in between NiFeSiB layers. In Si∕SiO2∕Ta 45∕Ru 9.5∕IrMn 10∕CoFe 7∕AlOx1.5∕(single NiFeSiB 7) or [NiFeSiB(t)∕Ru 0.5∕NiFeSiB(7−t)]∕Ru 60(nm) MTJ structures, we found size dependence of the switching field originating from the lower Jex both experimentally and by simulation. The NiFeSiB SAF structure showed lower switching field than traditional CoFe and CoFeB SAF structures. This is because NiFeSiB possesses low saturation magnetization (Ms=800emu∕cm3) and high anisotropy constant (Ku=2,700erg∕cm3). These properties were proven beneficial for the switching characteristics such as reducing the coercivity (Hc) and increasing the sensitivity in micrometer to submicrometer sized elements.
Optically controlled slow and fast light in optical fibers using stimulated Brillouin scattering
Authors: González-Herráez Miguel , Song Kwang-Yong , Thévenaz Luc
Published: August 2005

We demonstrate a method to achieve an extremely wide and flexible external control of the group velocity of signals as they propagate along an optical fiber. This control is achieved by means of the gain and loss mechanisms of stimulated Brillouin scattering in the fiber itself. Our experiments show that group velocities below 71000km∕s on one hand, well exceeding the speed of light in vacuum on the other hand and even negative group velocities can readily be obtained with a simple benchtop experimental setup. We believe that the fact that slow and fast light can be achieved in a standard single-mode fiber, in normal environmental conditions and using off-the-shelf instrumentation, is very promising for a future use in real applications.
Flow-limited field-injection electrostatic spraying for controlled formation of charged multiple jets of precursor solutions: Theory and application
Authors: Gu Wenhua , Singh Ravindra , Kim Kyekyoon
Published: August 2005

Charged multijets of precursor solutions were produced by flow-limited field-injection electrostatic spraying. The number of jets was precisely controlled by adjusting the flow rate of the solution and the current field-injected into it. Field injection was effected by inserting a high-voltage tungsten needle inside an insulating nozzle containing the solution. A theory, based on instability analysis, was formulated to describe the multijet formation and enable calculation of the number of jets and the size of the drops resulting from jet breakup. The theory is in good agreement with the experiment.
Realization of highly uniform self-assembled InAs quantum wires by the strain compensating technique
Authors: Huang X. Q. , Wang Y. L. , Li L. , Liang L. , Liu F. Q.
Published: August 2005

Self-assembled InAs quantum wires (QWRs) on InP(001) substrate have been grown by molecular-beam epitaxy, using a strain compensating technique. Atom force microscope, Transmission electron microscopy, and high-resolution x-ray diffraction are used to characterize their structural properties. We proposed that, by carefully adjusting composition of InAlGaAs buffer layer and strain compensating spacer layers, stacked QWRs with high uniformity could be achieved. In addition, the formation mechanism and vertical anti-correlation of QWRs are also discussed.
Thermal depoling of high Curie point Aurivillius phase ferroelectric ceramics
Authors: Yan Haixue , Zhang Hongtao , Reece Michael J. , Dong Xianlin
Published: August 2005

The thermal depoling behavior of several different Aurivillius phase ferroelectric ceramics has been studied. This includes two-layer (CaBi2Nb2O9,Ca0.9Ba0.1Bi2Nb2O9,Bi3NbTiO9,Bi3Nb1.2Ti0.8O9), three-layer (Bi4Ti3O12), and four-layer [CaBi4Ti4O15,Ca0.94(Na,Ce)0.03Bi4Ti4O15] compounds. All of them have a high Curie point (Tc⩾675°C). The orthorhombic structured materials show good resistance to thermal depoling up to temperatures close to their Curie points. However, Bi4Ti3O12, which has a monoclinic structure, shows a significant reduction in d33 well before its Curie point. The monoclinic distortion produces more non-180° ferroelectric domain structures, and it is the thermal instability of these that accounts for their thermal depoling behaviour. Excess Nb doping of Bi3NbTiO9 produces a significant reduction in its resistance to thermal depoling, suggesting that the doping produces a lowering of the crystallographic symmetry.
Molecular basis of listeriolysin O pH dependence
Authors: Schuerch Daniel W. , Wilson-Kubalek Elizabeth M. , Tweten Rodney K.
Published: August 2005

Listeriolysin O (LLO) is a cholesterol-dependent cytolysin that is an essential virulence factor ofListeria monocytogenes. LLO pore-forming activity is pH-dependent; it is active at acidic pH (<6), but not at neutral pH. In contrast to other pH-dependent toxins, we have determined that LLO pore-forming activity is controlled by a rapid and irreversible denaturation of its structure at neutral pH at temperatures >30°C. Rapid denaturation is triggered at neutral pH by the premature unfolding of the domain 3 transmembrane β-hairpins; structures that normally form the transmembrane β-barrel. A triad of acidic residues within domain 3 function as the pH sensor and initiate the denaturation of LLO by destabilizing the structure of domain 3. These studies provide a view of a molecular mechanism by which the activity of a bacterial toxin is regulated by pH.
Geologic constraints on the macroevolutionary history of marine animals
Authors: Peters Shanan E.
Published: August 2005

The causes of mass extinctions and the nature of taxonomic radiations are central questions in paleobiology. Several episodes of taxonomic turnover in the fossil record, particularly the major mass extinctions, are generally thought to transcend known biases in the geologic record and are widely interpreted as distinct macroevolutionary phenomena that require unique forcing mechanisms. Here, by using a previously undescribed compilation of the durations of sedimentary rock sequences, I compare the rates of expansion and truncation of preserved marine sedimentary basins to rates of origination and extinction among Phanerozoic marine animal genera. Many features of the highly variable record of taxonomic first and last occurrences in the marine animal fossil record, including the major mass extinctions, the frequency distribution of genus longevities, and short- and long-term patterns of genus diversity, can be predicted on the basis of the temporal continuity and quantity of preserved sedimentary rock. Although these results suggest that geologically mediated sampling biases have distorted macroevolutionary patterns in the fossil record, preservation biases alone cannot easily explain the extent to which the sedimentary record duplicates paleobiological patterns. Instead, these results suggest that the processes responsible for producing variability in the sedimentary rock record, such as plate tectonics and sea-level change, may have been dominant and consistent macroevolutionary forces throughout the Phanerozoic.
Enhancing the anticancer properties of cardiac glycosides by neoglycorandomization
Authors: Langenhan Joseph M. , Peters Noël R. , Guzei Ilia A. , Hoffmann F. Michael , Thorson Jon S.
Published: August 2005

Glycosylated natural products are reliable platforms for the development of many front-line drugs, yet our understanding of the relationship between attached sugars and biological activity is limited by the availability of convenient glycosylation methods. When a universal chemical glycosylation method that employs reducing sugars and requires no protection or activation is used, the glycorandomization of digitoxin leads to analogs that display significantly enhanced potency and tumor specificity and suggests a divergent mechanistic relationship between cardiac glycoside-induced cytotoxicity and Na
+
/K
+
-ATPase inhibition. This report highlights the remarkable advantages of glycorandomization as a powerful tool in glycobiology and drug discovery.
Structure of dimeric mitochondrial ATP synthase: Novel F
0
bridging features and the structural basis of mitochondrial cristae biogenesis
Authors: Minauro-Sanmiguel Fernando , Wilkens Stephan , García José J.
Published: August 2005

The F
1
F
0
–ATP synthase exists as a dimer in mitochondria, where it is essential for the biogenesis of the inner membrane cristae. How two ATP synthase complexes dimerize to promote cristae formation is unknown. Here we resolved the structure of the dimeric F
1
F
0
ATP synthase complex isolated from bovine heart mitochondria by transmission electron microscopy. The structure of the ATP synthase dimer has an overall conic appearance that is consistent with the proposed role of the dimeric enzyme in mitochondrial cristae biogenesis. The ATP synthase dimer interface is formed by contacts on both the F
0
and F
1
domains. A cross-bridging protein density was resolved which connects the two F
0
domains on the intermembrane space side of the membrane. On the matrix side of the complex, the two F
1
moieties are connected by a protein bridge, which is attributable to the IF
1
inhibitor protein.
Tuning in to musical rhythms: Infants learn more readily than adults
Authors: Hannon Erin E. , Trehub Sandra E.
Published: August 2005

Domain-general tuning processes may guide the acquisition of perceptual knowledge in infancy. Here, we demonstrate that 12-month-old infants show an adult-like, culture-specific pattern of responding to musical rhythms, in contrast to the culture-general responding that is evident at 6 months of age. Nevertheless, brief exposure to foreign music enables 12-month-olds, but not adults, to perceive rhythmic distinctions in foreign musical contexts. These findings may indicate a sensitive period early in life for acquiring rhythm in particular or socially and biologically important structures more generally.
Synergistic induction of tissue factor by coagulation factor Xa and TNF: Evidence for involvement of negative regulatory signaling cascades
Authors: Hezi-Yamit Ayala , Wong Paul W. , Bien-Ly Nga , Komuves Laszlo G. , Prasad K. S. Srinivasa , Phillips David R. , Sinha Uma
Published: August 2005

Enzymes of the blood coagulation pathway enhance the inflammatory response leading to endothelial dysfunction, accounting, in part, for the vascular complications occurring in sepsis and cardiovascular disease. The responses of endothelial cell activation include induction of the expression of tissue factor (TF), a membrane glycoprotein that promotes thrombosis, and of E-selectin, a cell adhesion molecule that promotes inflammation. In this report, we demonstrate synergistic interactions between the coagulation factor Xa (fXa) and the proinflammatory cytokines TNF, IL-1β, and CD40L, leading to enhanced expression of TF and E-selectin in endothelial cells. A detailed analysis of the molecular pathways that could account for this activity of fXa showed that fXa inhibited the cytokine-induced expression of dual specificity phosphatases, MAP kinase phosphatase-L, -4, -5, and -7, blocking a negative regulatory effect on c-Jun N-terminal kinase. The synergistic interaction between fXa and TNF was also involved in the inhibition of A20 and IκBα expression in the IκB kinase-NF-κB pathway. The data indicate that inhibition of negative regulatory signaling accounts for the amplification of cytokine-induced endothelial cell activation by fXa.
Reelin and glutamic acid decarboxylase
67
promoter remodeling in an epigenetic methionine-induced mouse model of schizophrenia
Authors: Dong E. , Agis-Balboa R. C. , Simonini M. V. , Grayson D. R. , Costa E. , Guidotti A.
Published: August 2005

Reduction of prefrontal cortex glutamic acid decarboxylase (GAD
67
) and reelin (mRNAs and proteins) expression is the most consistent finding reported by several studies of postmortem schizophrenia (SZ) brains. Converging evidence suggests that the reduced GAD
67
and reelin expression in cortical GABAergic interneurons of SZ brains is the consequence of an epigenetic hypermethylation of
RELN
and

GAD
67

promoters very likely mediated by the overexpression of DNA methyltransferase 1 in cortical GABAergic interneurons. Studies of the molecular mechanisms (DNA methylation plus related chromatin remodeling factors) that cause the down-regulation of reelin and GAD
67
in SZ brains have important implications not only to understand the disease pathogenesis but also to improve present pharmacological interventions to treat SZ. The mouse treated with
l
-methionine models some of the molecular neuropathologies detected in SZ, including the hypermethylation of
RELN
promoter CpG islands and the down-regulation of reelin and GAD
67
expression. We now report that in these mice,
RELN
and

GAD
67

promoters express an increased recruitment of methyl-CpG binding domain proteins. In these mice the histone deacetylase inhibitor valproate, which increases acetylated histone content in cortical GABAergic interneurons, also prevents MET-induced
RELN
promoter hypermethylation and reduces the methyl-CpG binding domain protein binding to
RELN
and

GAD
67

promoters. These findings suggest that DNA hypermethylation and the associated chromatin remodeling may be critically important in mediating the epigenetic down-regulation of reelin and GAD
67
expression detected in cortical GABAergic interneurons of SZ patients.