bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of the ring nitrogen and the amino group in the solvent dependence of the excited-state dynamics of 3-aminoquinoline
Authors: Panda Debashis , Datta Anindya
Published: August 2006

The nonradiative rate in 3-aminoquinoline is found to exhibit anomalous solvent dependence, being rather fast in nonpolar solvents and remarkably slower in more polar and especially, more protic ones. The cause of such behavior is investigated by studying the dependence of fluorescence spectral and temporal parameters on the solvent properties such as polarity and hydrogen bonding ability. Complementary quantum mechanical calculations have been performed and the picture that emerges from these studies is that of an excited state with a short radiative lifetime due to the flipping of the amino group. This state is selectively populated in nonpolar, nonhydrogen bonding solvents, but is destabilized with respect to the more polar intramolecular charge transfer (ICT) state in polar solvents and even more so in protic solvents and dimethylsulfoxide. The slower nonradiative rates in the ICT state is attributed to the more restricted motion of the amino group in this state. The role of hydrogen bonding of the amino group and the ring nitrogen in stabilization/destabilization of the ICT state and therefore on the nonradiative rate is also explored.
Application of a variational iteration method to linear and nonlinear viscoelastic models with fractional derivatives
Authors: Drăgănescu G. E.
Published: August 2006

Two nonlinear anelastic models with fractional derivatives, describing the properties of a series of materials as polymers, and polycrystalline materials are presented in this paper. These models are studied analytically, using a variational iteration method. The paper clarifies the different ways in which the fractional differentiation operator can be defined. A Volterra series method of model parameters identification from the experimental data is also presented.
Evidence of unquenched Re orbital magnetic moment in AA′FeReO6 double perovskites
Authors: Sikora M. , Kapusta Cz. , Borowiec M. , Oates C. J , Prochazka V. , Rybicki D. , Zajac D. , De Teresa J. M , Marquina C. , Ibarra M. R
Published: August 2006

Spin and orbital magnetic moments of rhenium in AA′FeReO6 double perovskites (A,A′=Ba, Sr, and Ca) have been directly probed employing x-ray magnetic circular dichroism at the Re L2,3 edges. A considerable orbital magnetic moment is observed in all the compounds studied, which confirm theoretical predictions of unquenched Re orbital moment despite its octahedral coordination. Relative orbital-to-spin moment ratio alters with lattice distortion from mL∕mS=−0.285to−0.337 from Ba2FeReO6 to Ca2FeReO6, respectively. Moreover, the spin moment of Re ion scales with Curie temperature, the most relevant property in spin electronics application of the compounds studied.
Multiplexing radiography using a carbon nanotube based x-ray source
Authors: Zhang J. , Yang G. , Lee Y. Z. , Chang S. , Lu J. P. , Zhou O.
Published: August 2006

Speed and temporal resolution are critical for tomographic imaging of objects in rapid motion. Current x-ray scanners record images sequentially in the time domain. The serial approach limits their performance and demands increasingly high x-ray peak power and gantry speed. We have developed a multipixel carbon nanotube based field emission x-ray source that produces spatially and temporally modulated radiations. Using this device we show the feasibility of multiplexing radiography that enables simultaneous collection of multiple projection images using frequency multiplexing. A drastic increase of the speed and reduction of the x-ray peak power are achieved without compromising the imaging quality.
Hybrid atomistic-coarse-grained treatment of multiscale processes in heterogeneous materials: A self-consistent-field approach
Authors: Diestler D. J. , Zhou H. , Feng R. , Zeng X. C.
Published: August 2006

A treatment of multiscale quasistatic processes that combines an atomistic description of microscopic heterogeneous (“near”) regions of a material with a coarse-grained (quasicontinuum) description of macroscopic homogeneous (“far”) regions is presented. The hybrid description yields a reduced system consisting of the original atoms of the near regions plus pseudoatoms (nodes of the coarse-graining mesh) of the far regions, which interact through an effective many-body potential energy Veff that depends on the thermodynamic state. The approximate nature of Veff gives rise to “ghost forces,” which are reflected in spurious heterogeneities close to interfaces between near and far regions. The impact of ghost forces, which afflict all previous hybrid schemes, is greatly diminished by a self-consistent-field hybrid atomistic-coarse-grained (SCF-HACG) methodology. Tests of the SCF-HACG technique on a fully three-dimensional prototypal model [Lennard-Jones (12,6) crystal] yield thermomechanical properties (e.g., local stress) in good agreement with “exact” properties computed in the fully atomistic limit. The SCF-HACG method is also successfully used to characterize the grain boundary in a Lennard-Jones bicrystal.
Tunable ultraviolet output from an intracavity frequency-doubled red vertical-external-cavity surface-emitting laser
Authors: Hastie Jennifer E. , Morton Lynne G. , Kemp Alan J. , Dawson Martin D. , Krysa Andrey B. , Roberts John S.
Published: August 2006

An optically pumped red vertical-external-cavity surface-emitting laser with an AlInGaP gain region produced more than 1W of continuous-wave output power at a wavelength of 675nm. Frequency doubling in a beta-barium borate crystal placed at an intracavity beam waist generated 120mW of total output power at 338nm. Using an intracavity birefringent filter a second harmonic tuning range of ∼5nm was achieved.
Quantitative analysis of compositional changes in InGaAs∕InGaAsP quantum wells on GaAs induced by intermixing with a low temperature grown InGaP cap layer
Authors: Hulko O. , Thompson D. A. , Czaban J. A. , Simmons J. G.
Published: August 2006

Energy-dispersive x-ray spectroscopy was used to analyze quantum well intermixing between an InGaAs quantum well (QW) and InGaAsP barriers grown on GaAs induced by a low temperature, molecular beam epitaxy grown, InGaP cap. This cap layer produces an enhanced blueshift of the photoluminescence (PL) wavelength following postgrowth annealing, and degradation of the PL signal. Cross-sectional transmission electron microscopy reveals modification of the whole structure, with formation of arsenic precipitates, broadening, and subsequent disappearance of the QWs in the capped structure. Uncapped samples are relatively unchanged. Increased phosphorus observed in the QW for capped structures confirms the diffusion of phosphorus from the P-rich cap.
Thermodynamic study of alkyl-cyclohexanes in liquid, glassy, and crystalline states
Authors: Mandanici Andrea , Cutroni Maria , Triolo Alessandro , Rodriguez-Mora Virginia , Ramos Miguel A.
Published: August 2006

The specific heat of some alkyl-cyclohexanes in their liquid, supercooled liquid, crystalline, and (for the first time) glassy states has been measured by quasiadiabatic calorimetry. Thermodynamic properties as well as the glass forming ability have been studied as a function of systematic changes of the molecular structure. Only one stable crystalline phase is observed experimentally for ethylcyclohexane, propylcyclohexane, and butylcyclohexane. In the case of methylcyclohexane, experimental evidence is provided of a crystal-to-crystal transition at temperatures just below the melting.
Electrostatic surface interactions in mixtures of symmetric and asymmetric electrolytes: A Monte Carlo study
Authors: Taboada-Serrano Patricia , Yiacoumi Sotira , Tsouris Costas
Published: August 2006

Canonical Monte Carlo simulations of the interaction between a uniformly charged spherical particle and a discretely charged planar surface in solutions of symmetric and asymmetric electrolytes were performed. To assess the nature of the interactions, the force exerted on the colloidal particle perpendicular to the planar surface was calculated. Attractive minima in the interaction force between the similarly charged surfaces reveal the occurrence of two phenomena: long-range attraction of electrostatic origin and short-range attraction due to depletion effects. The degree of electrostatic coupling determines the magnitude and range of like-charge attraction between the two surfaces.
Experimental verification of the temperature effects on Sader’s model for multilayered cantilevers immersed in an aqueous medium
Authors: Kim S. , Kihm K. D.
Published: August 2006

Recently, Sader [J. Appl. Phys. 84, 64 (1998)] and Green and Sader [J. Appl. Phys. 92, 6262 (2002)] developed a theory predicting thermally driven frequency responses of a microcantilever immersed in a fluid. This letter presents an experimental investigation of the temperature effects on Sader’s model using three cantilevers, with aspect ratios (AR=cantilever length/cantilever width) <4, for temperatures ranging from 10to70°C. It is shown that liquid viscosity is primarily responsible for variations in the frequency response to liquid temperature. Two cantilevers, with AR∼3.0, verify Sader’s predictions for the tested temperature range, while the third cantilever with AR∼2.0 shows gradual deviations with increasing temperature.
Finite-size effects in microrheology
Authors: Santamaría-Holek I. , Rubi J. M.
Published: August 2006

We propose a model to explain finite-size effects in intracellular microrheology observed in experiments. The constrained dynamics of the particles in the intracellular medium, treated as a viscoelastic medium, is described by means of a diffusion equation in which interactions of the particles with the cytoskeleton are modeled by a harmonic force. The model reproduces the observed power law behavior of the mean square displacement in which the exponent depends on the ratio between particle-to-cytoskeleton-network sizes.
A new approximation for atom-diatom rotational-relaxation cross sections
Authors: Dickinson Alan S.
Published: August 2006

A semiclassical approximation to the S matrix of the infinite-order-sudden approximation is introduced. This is employed to yield for the energy-transfer effective cross section a purely classical approximation, analogous to the Mason-Monchick approximation [J. Chem. Phys. 36, 1622 (1962)] for traditional collision integrals. Constraints on energy and on angular momentum transfer are included. Numerical evaluation of this new approximation can readily be performed alongside that for traditional collision integrals. The new result is tested against full classical trajectory calculations for six potential energy surfaces for the collision systems H–N2, He–N2, He–CO, and Ar–CO2. Differences of no more than 15% from the classical trajectory calculations have been obtained.
Mean field linear response within the elimination of the small component formalism to evaluate relativistic effects on magnetic properties
Authors: Roura P. G. , Melo J. I. , Ruiz de Azúa M. C. , Giribet C. G.
Published: August 2006

The linear response within the elimination of the small component formalism is aimed at obtaining the leading order relativistic corrections to magnetic molecular properties in the context of the elimination of the small component approximation. In the present work we extend the method in order to include two-body effects in the form of a mean field one-body operator. To this end we consider the four-component Dirac-Hartree-Fock operator as the starting point in the evaluation of the second order relativistic expression of magnetic properties. The approach thus obtained is the fully consistent leading order approximation of the random phase approximation four-component formalism. The mean field effect on the relativistic corrections to both the diamagnetic and paramagnetic terms of magnetic properties taking into account both the Coulomb and Breit two-body interactions is considered.
Excitation of fluorescence decay using a 265nm pulsed light-emitting diode: Evidence for aqueous phenylalanine rotamers
Authors: McGuinness Colin D. , Macmillan Alexander M. , Sagoo Kulwinder , McLoskey David , Birch David J. S.
Published: August 2006

The authors describe the characteristics and application of a 265nm AlGaN light-emitting diode (LED) operated at 1MHz repetition rate, 1.2ns pulse duration, 1.32μW average power, 2.3mW peak power, and ∼12nm bandwidth. The LED enables the fluorescence decay of weakly emitting phenylalanine to be measured routinely, even in dilute solution. For pH of 6–9.2, the authors find evidence for a biexponential rather than monoexponential decay, providing direct evidence for the presence of phenylalanine rotamers with a photophysics closer to the other two fluorescent amino acids tryrosine and tryptophan than has previously been reported.
Dispersive electromagnetic drift modes in nonuniform quantum magnetoplasmas
Authors: Shukla P. K. , Ali S.
Published: August 2006

The existence of new electromagnetic drift modes in nonuniform quantum magnetoplasmas is predicted. For this purpose, new dispersion relations are derived by employing the quantum magnetohydrodynamic equation for plasmas without and with ion motions. The effects of electron corrections due to quantum fluctuations, density gradients, and external magnetic field strengths on the angular wave frequencies and growth/damping rates are examined. The present analytical and numerical investigations are relevant to dense astrophysical objects.
Segregation of lead in Cu–Zn alloy under electric current pulses
Authors: Wang X. L. , Guo J. D. , Wang Y. M. , Wu X. Y. , Wang B. Q.
Published: August 2006

In this letter, it is found that when the critical electric current pulse (ECP) passes through a Cu–Zn alloy with lead inclusions, those inclusions will disappear and transfer into grain boundaries or defects, forming many dispersed small particles of lead. Such kind of lead transfer can be produced by no other heat treatments than ECP. The theoretical analysis points out that this phenomenon is attributed to its specific effect on reducing considerably the diffusion activation energy of lead in the alloy. Therefore, the ECP treatment would provide a promising method to refine materials and to improve their physical properties.
On the origin of increased open circuit voltage of dye-sensitized solar cells using 4-tert-butyl pyridine as additive to the electrolyte
Authors: Dürr M. , Yasuda A. , Nelles G.
Published: August 2006

A combination of electrical measurements and surface analysis techniques was used to investigate the electronic structure of the TiO2/electrolyte interface and its change upon addition of 4-tert-butyl pyridine to the electrolyte. A reduced interface defect density and a resulting reduction of charge carrier recombination were found to be the main mechanism for an increased open circuit voltage of dye-sensitized solar cells with 4-tert-butyl pyridine in the electrolyte. The reduction of interface defect states was traced back to specific binding of 4-tert-butyl pyridine at defect sites on the TiO2 surface.
Statistical analysis of the electrical breakdown time delay distributions in krypton
Authors: Maluckov Čedomir A. , Karamarković Jugoslav P. , Radović Miodrag K. , Pejović Momčilo M.
Published: August 2006

The statistical analysis of the experimentally observed electrical breakdown time delay distributions in the krypton-filled diode tube at 2.6mbar is presented. The experimental distributions are obtained on the basis of 1000 successive and independent measurements. The theoretical electrical breakdown time delay distribution is evaluated as the convolution of the statistical time delay with exponential, and discharge formative time with Gaussian distribution. The distribution parameters are estimated by the stochastic modelling of the time delay distributions, and by comparing them with the experimental distributions for different relaxation times, voltages, and intensities of UV radiation. The transition of distribution shapes, from Gaussian-type to the exponential-like, is investigated by calculating the corresponding skewness and excess kurtosis parameters. It is shown that the mathematical model based on the convolution of two random variable distributions describes experimentally obtained time delay distributions and the separation of the total breakdown time delay to the statistical and formative time delay.
Ultrastable and efficient red organic light emitting diodes with doped transport layers
Authors: Meerheim Rico , Walzer Karsten , Pfeiffer Martin , Leo Karl
Published: August 2006

We demonstrate extremely stable and highly efficient red p-i-n-type organic light emitting diodes (OLEDs) based on an iridium-based electrophosphorescent dye in suitable host materials. The OLEDs reach lifetimes well above 1×107h at 100cd∕m2 initial luminance and reach at the same time a performance of 12.4% external quantum efficiency. This high lifetime is attributed to a combination of the low current density needed to reach a certain luminance and to the high stability of the materials against both charge carriers and excitons.
23
GHz
operation of a room temperature photovoltaic quantum cascade detector at 5.35μm
Authors: Hofstetter Daniel , Graf Marcel , Aellen Thierry , Faist Jérôme , Hvozdara Lubos , Blaser Stéphane
Published: August 2006

We present a room temperature operated 5.35μm quantum cascade detector which was tested at high frequencies using an optical heterodyne experiment. Two slightly detuned continuous wave distributed feedback single mode quantum cascade lasers were used to generate a beating signal. The maximum frequency at which the resulting microwave signal could be detected was 23GHz. The cutoff behavior of our device was modeled with a simple RLC circuit and showed excellent agreement with the experimental data.
Correlation of hydrogen bond lengths and angles in liquid water based on Compton scattering
Authors: Hakala M. , Nygård K. , Manninen S. , Huotari S. , Buslaps T. , Nilsson A. , Pettersson L. G. M. , Hämäläinen K.
Published: August 2006

The temperature-dependent hydrogen-bond geometry in liquid water is studied by x-ray Compton scattering using synchrotron radiation combined with density functional theory analysis. Systematic changes, related to the weakening of hydrogen bonding, are observed in the shape of the Compton profile upon increasing the temperature. Using model calculations and published distribution functions of hydrogen-bond geometries obtained from a NMR study we find a significant correlation between the hydrogen-bond length and angle. This imposes a new constraint on the possible local structure distributions in liquid water. In particular, the angular distortions of the short hydrogen bonds are significantly restricted.
Effect of self-organization in polymer/fullerene bulk heterojunctions on solar cell performance
Authors: Shrotriya Vishal , Yao Yan , Li Gang , Yang Yang
Published: August 2006

The authors investigate the effect of self-organization by controlling the growth rate on the performance of polymer/fullerene bulk-heterojunction solar cells. The effect of growth rate on the morphology of the active layer is studied by atomic force microscopy technique. The electrical characterization by dark current and photocurrent measurements is performed. The hole mobility in the polymer increases by about two orders in magnitude and the carrier transport becomes highly balanced. Increased exciton generation rate, more efficient electron-hole pair dissociation, higher carrier mobility, and balanced carrier transport in the active layer explain the enhancement in the short-circuit current and fill factor.
High electron mobility lattice-matched AlInN∕GaN field-effect transistor heterostructures
Authors: Gonschorek M. , Carlin J.-F. , Feltin E. , Py M. A. , Grandjean N.
Published: August 2006

Room temperature electron mobility of 1170cm2∕Vs is obtained in an undoped, lattice-matched, Al0.82In0.18N∕GaN field-effect transistor heterostructure, while keeping a high (2.6±0.3)×1013cm−2 electron gas density intrinsic to the Al0.82In0.18N∕GaN material system. This results in a two-dimensional sheet resistance of 210Ω∕◻. The high mobility of these layers, grown by metal-organic vapor phase epitaxy on sapphire substrate, is obtained thanks to the insertion of an optimized AlN interlayer, reducing the alloy related interface roughness scattering.
Knight shift detection using gate-induced decoupling of the hyperfine interaction in quantum Hall edge channels
Authors: Masubuchi S. , Hamaya K. , Machida T.
Published: August 2006

A method for the observation of the Knight shift in nanometer-scale region in semiconductors is developed using resistively detected nuclear magnetic resonance (RDNMR) technique in quantum Hall edge channels. Using a gate-induced decoupling of the hyperfine interaction between electron and nuclear spins, the authors obtain the RDNMR spectra with or without the electron-nuclear spin coupling. By a comparison of these two spectra, the values of the Knight shift can be given for the nuclear spins polarized dynamically in the region between the relevant edge channels in a single two-dimensional electron system, indicating that this method has a very high sensitivity compared to a conventional NMR technique.
Spatial coherence properties of electroluminescence from Alq3-based organic light emitting diodes
Authors: Saxena Kanchan , Mehta Dalip Singh , Srivastava Ritu , Kamalasanan M. N.
Published: August 2006

We report the measurement of spatial coherence properties of light emitted by organic electroluminescent devices based on tris-(8-hydroxyquinoline) aluminum. Coherence measurements were performed using Young’s double slit experiment. Fourier-transform technique was used for the measurement of visibility of the interference fringes from which the modulus of the degree of spatial coherence was determined. Experimental results were compared with the theoretical values and it is shown that the coherence properties of the light emitted by a simple organic light emitting device match with those of practical Lambertian sources.
Electron trap density distribution of Si-rich silicon nitride extracted using the modified negative charge decay model of silicon-oxide-nitride-oxide-silicon structure at elevated temperatures
Authors: Kim Tae Hun , Park Il Han , Lee Jong Duk , Shin Hyung Cheol , Park Byung-Gook
Published: August 2006

The authors modified the charge decay model of silicon-oxide-nitride-oxide-silicon-type memory at the temperatures above 150°C. The modified model includes the effect of the internal electric field induced by the charges trapped in silicon nitride layer. The authors extracted the trap density distributions in energy level of the Si-rich silicon nitride using the model and compared them with those of stoichiometric silicon nitride. It has been revealed that the Si-rich silicon nitride has larger trap density in shallow energy level than the stoichiometric silicon nitride and this relation is reversed as the energy level goes deeper.
Elastic behavior of polycrystalline thin films inferred from in situ micromechanical testing and modeling
Authors: Faurie D. , Renault P.-O. , Le Bourhis E. , Goudeau Ph. , Castelnau O. , Brenner R. , Patriarche G.
Published: August 2006

Synchrotron x-ray diffraction combined with in situ tensile testing is used to investigate the anisotropic elastic behavior of gold thin films exhibiting a fiber texture and columnar grains. Micromechanical modeling based on the self-consistent model and accounting for both crystallographic and morphological textures is applied. Flat-disk shaped inclusions must be used in the model to reproduce accurately experimental data, owing to the surface effects.
High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser
Authors: Hübers H.-W. , Pavlov S. G. , Richter H. , Semenov A. D. , Mahler L. , Tredicucci A. , Beere H. E. , Ritchie D. A.
Published: August 2006

The quantum cascade laser is a powerful, narrow linewidth, and continuous wave source of terahertz radiation. The authors have implemented a distributed feedback device in a spectrometer for high-resolution gas phase spectroscopy. Amplitude as well as frequency modulation schemes have been realized. The absolute frequency was determined by mixing the radiation from the quantum cascade laser with that from a gas laser. The pressure broadening and the pressure shift of a rotational transition of methanol at 2.519THz were measured in order to demonstrate the performance of the spectrometer.
7
dB
quadrature squeezing at 860nm with periodically poled KTiOPO4
Authors: Suzuki Shigenari , Yonezawa Hidehiro , Kannari Fumihiko , Sasaki Masahide , Furusawa Akira
Published: August 2006

The authors observed −7.2±0.2dB quadrature squeezing at 860nm by using a subthreshold continuous-wave pumped optical parametric oscillator with a periodically poled KTiOPO4 crystal as a nonlinear optical medium. The squeezing level was measured with the phase of homodyne detection locked at the quadrature. The blue light induced infrared absorption was not observed in the experiment.
High sensitivity autocorrelator based on a fluorescent liquid core fiber
Authors: Lelek Mickaël , Louradour Frédéric , Couderc Vincent , Viale Pierre , Février Sébastien , Auguste Jean Louis , Blondy Jean Marc , Barthélémy Alain
Published: August 2006

The hollow core of an air-silica microstructured fiber was selectively filled with an alcoholic solution containing a laser dye (coumarin 515). This innovative liquid core fiber was used to build an efficient intensity autocorrelator operating by transverse imaging of the nonlinear fluorescence. Accurate measurement of pulse duration in the picosecond regime with submilliwatt average power has been demonstrated in the near infrared.
Mechanomagnetic spectroscopy of phase transitions in ferromagnetic shape memory alloys
Authors: Kustov Sergey , Masdeu Francesc , Cesari Eduard
Published: August 2006

A technique for direct experimental investigations of coupling between applied elastic stress and magnetic response in ferromagnetic shape memory alloys over the temperature ranges of paramagnetic to ferromagnetic and martensitic transformations has been developed, based on the inverse magnetostriction (Villary) effect. Primary characteristics available from the experiment are elastic and anelastic properties and, the most important, signal related to stress-induced magnetization.
Study of geometrical and operational parameters controlling the low frequency microjet atmospheric pressure plasma characteristics
Authors: Kim Dan Bee , Rhee J. K. , Moon S. Y. , Choe W.
Published: August 2006

Controllability of small size atmospheric pressure plasma generated at low frequency in a pin to dielectric plane electrode configuration was studied. It was shown that the plasma characteristics could be controlled by geometrical and operational parameters of the experiment. Under most circumstances, continuous glow discharges were observed, but both the corona and/or the dielectric barrier discharge characteristics were observed depending on the position of the pin electrode. The plasma size and the rotational temperature were also varied by the parameters. The rotational temperature was between 300 and 490K, being low enough to treat thermally sensitive materials.
Distributed mode coupling in microring channel drop filters
Authors: Chen Qin , Yang Yue-De , Huang Yong-Zhen
Published: August 2006

The authors present the observation of wide transmission dips in a microring channel drop filter by two-dimensional finite-difference time-domain simulation. The authors show that distributed mode coupling between the input waveguide and the resonator results in the oscillations of the coupling efficiency and the envelope of transmission spectra with wavelength. The critical coupling as the light just passing through the coupling region is important for optimizing related devices. If the width of the input waveguide is different from that of the ring resonator, the phenomenon can be greatly reduced.
Effect of size-asymmetric electrolyte on single-file osmosis
Authors: Raghunathan A. V. , Aluru N. R.
Published: August 2006

Single-file osmosis through a 0.9nm diameter semipermeable carbon membrane using various size-asymmetric electrolyte solutions is investigated using molecular dynamics simulations. In an uncharged pore, the osmotic flux with a KCl solution is found to be higher than that of in a NaCl solution, i.e., JKCl>JNaCl, for the same concentration gradient of solute. Mean force and hydration analysis indicate that distinct ion-water and ion-pore molecular interactions cause a differential cation and anion affinity to the pore, leading to the observed size-asymmetric electrolyte dependence on osmotic flux. The water orientation in the pore during osmosis is also related to the ion affinity and exhibits a size-asymmetric electrolyte dependence.
Effects of linewidth enhancement factor on period-one oscillations of optically injected semiconductor lasers
Authors: Hwang S. K. , Liang D. H.
Published: August 2006

The behavior of period-one oscillations in optically injected semiconductor lasers as a function of linewidth enhancement factor is investigated. The occurrence of the dynamics is favored by large values of the factor. The dependence of the spectral features of the dynamics on the factor suggests a strong relation between the emergence of the dynamics and the preferred cavity resonance under external perturbation.
Probing nanoscale local lattice strains in advanced Si complementary metal-oxide-semiconductor devices
Authors: Huang J. , Kim M. J. , Chidambaram P. R. , Irwin R. B. , Jones P. J. , Weijtmans J. W. , Koontz E. M. , Wang Y. G. , Tang S. , Wise R.
Published: August 2006

Local lattice strains in nanoscale Si complementary metal-oxide-semiconductor (MOS) transistors are directly measured by convergent beam electron diffraction (CBED). Through both high spatial resolution and high strain sensitivity of the CBED technique, compressive strains on the order of 10−3 from a p-type MOS transistor with a sub-100nm gate length are detected. One-dimensional quantitative strain mapping is demonstrated. The tensile strains from a ⟨100⟩ channel n-type MOS transistor are observed at the ⟨910⟩ zone axis. It is found that the strain increases with the thickness of the silicon nitride-capping layer, which is consistent with the device’s electrical behavior.
Optical amplification in Nd3+ doped electro-optic lanthanum lead zirconate titanate ceramics
Authors: Zhang Jingwen W. , Zou Yingyin K. , Chen Qiushui , Zhang Run , Li Kewen K. , Jiang Hua , Huang Pi-Ling , Chen Xuesheng
Published: August 2006

As high as 13.0dB single-pass gain was obtained at 1064.4nm in a thin electro-optic ceramic plate of neodymium doped lanthanum-modified lead zirconate titanate (Nd:PLZT). Pumping with a diode laser, gains were achieved in 1.0 and 0.5mol% Nd ion doped samples over a broad seed laser power ranging from tens of nanowatts to tens of milliwatts at room temperature. The broad absorption spectra of Nd:PLZT made it insensitive to the pump wavelength. The Nd:PLZT had a total scattering loss coefficient of less than 0.06cm−1 and exhibited a considerable quadratic electro-optic coefficient greater than 0.30×10−16m2∕V2.
Observation of a quasimonoenergetic electron beam from a femtosecond prepulse-exploded foil
Authors: Wang X. , Nishikawa K. , Nemoto K.
Published: August 2006

We report the first observation of a quasimonoenergetic electron beam emitted from a femtosecond prepulse-exploded foil. At 5ns earlier, a 7.5-μm-thick plastic foil is irradiated by a copropagating femtosecond prepulse of modest intensity (1.5×1017W∕cm2), which then explodes to become an underdense foil plasma. When a 70-fs high-intensity (2.5×1018W∕cm2) pulse arrives and interacts with it, a collimated electron beam of divergence angle ≲4° is emitted in the forward direction. The energy spectrum of the electron beam shows a quasimonoenergetic peak at 0.63MeV of energy spread ∼21%, within which about 50 pC of charge is contained.
Embrittlement in a bulk nanocrystalline alloy induced by room-temperature aging
Authors: Fan G. J. , Choo H. , Liaw P. K.
Published: August 2006

The effect of room-temperature aging on the mechanical behaviors of an electrodeposited bulk nanocrystalline (nc) Ni–Fe alloy has been investigated. The tensile elongation to failure, εf, of the bulk nc Ni–Fe alloy decreased from approximately 7.2% in the as-deposited state to 5.0%, after aging at room temperature for one year. Moreover, the fatigue-endurance limit decreased from about 260to190MPa. This aging-induced embrittlement may be mainly due to the enhanced atomic diffusivity in the nc materials, leading to the segregation of the impurity atoms at the grain boundaries.
Modified Sagnac interferometer for high-sensitivity magneto-optic measurements at cryogenic temperatures
Authors: Xia Jing , Beyersdorf Peter T. , Fejer M. M. , Kapitulnik Aharon
Published: August 2006

The authors describe a geometry for a Sagnac interferometer with a zero-area Sagnac loop for measuring the magneto-optic Kerr effect at cryogenic temperatures. The apparatus is capable of measuring absolute Kerr rotation without any modulation of the magnetic state of the sample and is intrinsically immune to reciprocal effects such as linear birefringence and thermal fluctuations. A single strand of polarization-maintaining fiber is fed into a He-3 cryostat, eliminating the need for optical viewports. With an optical power of only 10μW, they demonstrate static Kerr measurements with a shot-noise-limited sensitivity of 1×10−7rad∕Hz down to 0.5K.
Switchable nanometer contacts: Ultrathin Ag nanostructures on Si(100)
Authors: Gardinowski G. , Schmeidel J. , Pfnür H. , Block T. , Tegenkamp C.
Published: August 2006

The fabrication and characterization of metallic nanometer-sized gaps suitable for conductivity measurements of single molecules were studied. Controlled gap formation by electromigration (EM) is demonstrated in contiguous and ultrathin Ag structures wetting the Si(100) substrate. The gaps obtained are in the range of nanometers or even subnanometers, as revealed by lateral conductivity measurements and scanning tunneling microscopy carried out under ultrahigh vacuum conditions. Annealing to 300K closes the gap by enabling surface diffusion of Ag, and another cycle of opening by EM at 80K can be performed. The functionality of the contacts is demonstrated by insertion of ferrocenedithiol molecules into the gap.
Location of lanthanide impurity levels in the III-V semiconductor GaN
Authors: Dorenbos P. , van der Kolk E.
Published: August 2006

Knowledge from lanthanide spectroscopy on wide band gap (6–10eV) inorganic compounds is used to understand and predict optical and electronic properties of the lanthanides in the III-V semiconductor GaN. For the first time the location of the 4fn ground state energy of each divalent and trivalent lanthanide ion relative to the valence and conduction bands in GaN is presented. The authors will demonstrate that the quantum efficiency of luminescence from Pr3+, Eu3+, Tb3+, and Yb3+ depends on the location of the lanthanide levels. Level location also controls electron acceptor and electron donor properties of lanthanide ions.
Thermal conductivity of tubular and core/shell nanowires
Authors: Prasher Ravi
Published: August 2006

Analytical solution of the Boltzmann transport equation (BTE) for phonon transport in tubular and core-shell nanowire is obtained. Thermal conductivity calculated from the analytical solution of BTE is in excellent agreement with a recently reported numerical model [R. Yang et al., Nano Lett. 5, 1111 (2005)]. Results show that thermal conductivity of tubular and core-shell nanowire can be significantly smaller than the bulk thermal conductivity.
Charge-dipole model to compute the polarization of fullerenes
Authors: Mayer A. , Lambin Ph. , Langlet R.
Published: August 2006

The authors present a charge-dipole model for the calculation of the polarization of fullerenes and carbon nanotubes. By expressing the electrostatic interactions in terms of normalized propagators, the technique achieves a better consistency and an improved stability. In its most elementary form, the model depends on a single parameter and provides an excellent agreement with reference data. The technique is illustrated with a C720 fullerene and enables one to quantify the role of free charges in the polarization of these structures. The positioning of these charges suggests that field-induced adsorption of small molecules should be enhanced at pentagonal rings and defects.
Energy Transfer in Monolayer Assemblies of Surfactant Ruthenium Complexes
Authors: Johansen O , Kowala C , Mau AWH , Sasse WHF
Published: August 2006

Energy transfer in
monolayer assemblies has been studied with bis(2,2'-bipyridyl)(dioctadecyl
2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) perchlorate (1) as acceptor and bis(2,2'-bipyridyl)-
(4,4'-dieicosyl-2,2'-bipyridyl)ruthenium(II) perchlorate (2), bis(2,2'-bipyridyl)(4-eicosyl-4'-methyl-
2,2'-bipyridyl)ruthenium(II) perchlorate (3), or bis(o-phenanthroline)(4,4'-dioctadecyl-2,2'-bipyridyl)-
ruthenium(II) (4) as donor. Forster theory was used to analyse
transfer rate constants, obtained by measuring the reduction in intensity of
the donor luminescence in the presence of acceptors. This luminescence
quenching involves energy transfer and not electron transfer because of the
sensitized luminescence intensity of the acceptor. The efficiency of energy transfer
depends on the relative orientations of the alkyl chains. The observed rates of
transfer greatly exceed the efficiency predicted from the Forster theory for
the distance between the chromophores; it is
suggested that the alkyl chains take part in the transfer of excitation energy.
This effect can be largely suppressed by the insertion of a 'spacer' monolayer
of cadmium arachidate between donor and acceptor
layers.
Ecological and evolutionary significance of sizes of giant extinct kangaroos
Authors: Helgen Kristofer M. , Wells Rod T. , Kear Benjamin P. , Gerdtz Wayne R. , Flannery Timothy F.
Published: August 2006

A method, based on femoral circumference, allowed us to develop body mass estimates for 11 extinct Pleistocene megafaunal species of macropodids (Protemnodon anak, P. brehus, P. hopei, P. roechus, Procoptodon goliah, ‘P.’ gilli, Simosthenurus maddocki, S. occidentalis, Sthenurus andersoni, S. stirlingi and S. tindalei) and three fossil populations of the extant eastern grey kangaroo (Macropus giganteus). With the possible exception of P. goliah, the extinct taxa were browsers, among which sympatric, congeneric species sort into size classes separated by body mass increments of 20–75%. None show evidence of size variation through time, and only the smallest (‘P.’ gilli) exhibits evidence suggestive of marked sexual dimorphism. The largest surviving macropodids (five species of Macropus) are grazers which, although sympatric, do not differ greatly in body mass today, but at least one species (M. giganteus) fluctuated markedly in body size over the course of the Pleistocene. Sexual dimorphism in these species is marked, and may have varied through time. There is some mass overlap between the extinct and surviving macropodid taxa. With a mean estimated body mass of 232 kg, Procoptodon goliah was the largest hopping mammal ever to exist.
Structural ultraviolet ornamentation in the butterfly Hypolimnas bolina L. (Nymphalidae): visual, morphological and ecological properties
Authors: Kemp Darrell J. , Macedonia Joseph M.
Published: August 2006

Many butterflies exhibit structurally coloured wing patches that are stunningly bright and iridescent in their appearance, yet functionally obscure. These colours are often exaggerated in males, which suggests a sexually selected origin. We studied the visual properties, morphological basis, and interindividual variation of structural wing colouration in the common eggfly, Hypolimnas bolina L. (Nymphalidae). Males of this territorial species possess highly directional UV/violet colouration that fully overlaps smaller white patches on their dorsal wing surfaces. We sampled 56 males, including territorial residents and non-resident ‘floaters’ and assessed the properties of their structural colour using reflectance spectrometry and scanning electron microscopy. The patches reflect strongly in the UV range (300–400 nm), with a peak of ~360 nm, and the wing scales in these regions exhibit a ridge-lamellar surface architecture that has known function in other species as a multiple thin-film interference mirror. Peak UV brightness was variable, and both brightness and peak hue varied systematically across age classes. UV brightness was also related to hue independently of the age-related variation. Territorial residents possessed duller UV markings than their non-resident contemporaries, which is not consistent with exaggeration due to male–male competition. The high phenotypic variance is, however, consistent with a putative role for this male-limited trait as a sexual ornament.
Social aggregation by thick-tailed geckos (Nephrurus milii, Gekkonidae): does scat piling play a role?
Authors: Shah Bansi , Hudson Simon , Shine Richard
Published: August 2006

Communal deposition of faeces into scat piles plays a role in pheromonal communication among group members in many ‘social’ vertebrates, including the scincid lizard Egernia stokesii. How general is this apparent link between scat piling and sociality? Thick-tailed geckos (Nephrurus milii, Gekkonidae) are large nocturnally active lizards that are widely distributed across southern Australia. They spend the daylight hours inactive inside retreat sites, typically rock crevices or burrows. Unusually among geckos, these animals often form groups of several individuals at these times. Our observations of captive N. milii showed that they also form discrete scat piles. However, habitat-selection experiments suggested that adding scats to a crevice did not modify the lizards’ probability of using that crevice. Thus, although Nephrurus milii scat pile (at least in captivity), communal faeces deposits do not appear to serve a social role in this taxon.
Faecal steroid analysis and urinary cytology of the squirrel glider (Petaurus norfolcensis)
Authors: Woodd Carly , Czarny Natasha A. , Gunn Ian M. G. , Sturrock Wayne
Published: August 2006

Non-invasive techniques were used to investigate the reproductive biology of captive squirrel gliders (Petaurus norfolcensis) for 3 months during the breeding season. The squirrel glider is a medium-sized marsupial glider of eastern Australia and is currently listed as a threatened species as a result of habitat destruction and fragmentation. Urinary cytology was used to determine the timing of oestrus, and the presence of sperm confirmed mating. Progesterone and oestradiol-17β were identified in faecal samples via thin-layer chromatography, and were used to characterise the reproductive cycle. Reproductive activity was observed in three of four females, with births occurring during June and July. A preoestrus increase in faecal oestradiol-17β was detected in a single female, whilst significant increases occurred post partum (±2 days) in two of four females, suggesting that the squirrel glider may undergo a postpartum oestrus. Faecal progesterone profiles showed low concentrations before oestrus and significantly elevated concentrations after oestrus, which were maintained throughout pregnancy. Parturition coincided with a decrease in progesterone concentrations (±1 day). This study successfully used non-invasive monitoring of urinary cytology and faecal steroids to define luteal and gestational length as 16–17 days, a previously unpublished detail.
Den-use and home-range characteristics of bobucks, Trichosurus cunninghami, resident in a forest patch
Authors: Martin Jennifer K.
Published: August 2006

Detailed knowledge of how individuals use space when active and while sheltering is crucial to understanding the habitat requirements of a species. I present the first home-range estimates for bobucks, Trichosurus cunninghami, that are based on both nocturnal and diurnal radio-tracking fixes. I tracked 37 individuals (14 adult females, 14 adult males, three subadult females and six subadult males) between mid-1999 and late 2003 in a forest patch in the Strathbogie Ranges, south-eastern Australia. I collected a total of 9562 diurnal fixes (mean 309 fixes per adult) and 5211 nocturnal fixes (mean 169 fixes per adult). All individuals used multiple den-trees; adults used a mean of 7.2 den-trees per individual. Adult bobucks of both sexes had a mean home-range size of 6.0 ha. There were no significant differences in the mean number of den-trees used or in the mean home-range size of adult males and females. Subadults used significantly fewer den-trees and had significantly smaller home ranges than adults. This study demonstrates the importance of large and long-term datasets in accurately determining the habitat requirements of a population.
Larvae of two signal fly species (Diptera:Platystomatidae), Duomyia foliata McAlpine and Plagiostenopterina enderleini Hendel, are scavengers of sea turtle eggs
Authors: Hall Sabrina C. B. , Parmenter C. John
Published: August 2006

Dipteran larvae are known to infest turtle eggs. However, the few studies conducted on this topic have presented conflicting conclusions as to whether the larvae function as scavengers of necrotic nest material or as egg and hatchling predators. These two very different roles in the nest will have equally different effects on the subsequent hatch and emergence success of affected sea turtle nests. The association between dipteran larvae and sea turtle nest invasion was investigated by measuring rates of infestation in excavated green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtle nests at field sites in central Queensland, Australia. Excavations were performed within 24 h of hatchling emergence, and necrotic embryos and dead hatchlings were found to be infested with two larval species of the Platystomatidae: Plagiostenopterina enderleini and Duomyia foliata. This work represents the first description of the association between these dipteran species and sea turtle nests, and a new geographic collection record for D. foliata. High rookery infestation rates versus low prevalence of propagule infestation suggest that the larvae preferentially infest dead embryos. The fact that some pipped hatchlings were devoured in-shell presents the possibility that the larvae may act opportunistically as predators. However, the two dipteran species appear to be primarily scavengers of necrotic material within the nests, which means that the threat to sea turtle populations from these flies is probably minimal.
Condition and fate of logged forests in the Brazilian Amazon
Authors: Asner Gregory P. , Broadbent Eben N. , Oliveira Paulo J. C. , Keller Michael , Knapp David E. , Silva José N. M.
Published: August 2006

The long-term viability of a forest industry in the Amazon region of Brazil depends on the maintenance of adequate timber volume and growth in healthy forests. Using extensive high-resolution satellite analyses, we studied the forest damage caused by recent logging operations and the likelihood that logged forests would be cleared within 4 years after timber harvest. Across 2,030,637 km
2
of the Brazilian Amazon from 1999 to 2004, at least 76% of all harvest practices resulted in high levels of canopy damage sufficient to leave forests susceptible to drought and fire. We found that 16 ± 1% of selectively logged areas were deforested within 1 year of logging, with a subsequent annual deforestation rate of 5.4% for 4 years after timber harvests. Nearly all logging occurred within 25 km of main roads, and within that area, the probability of deforestation for a logged forest was up to four times greater than for unlogged forests. In combination, our results show that logging in the Brazilian Amazon is dominated by highly damaging operations, often followed rapidly by deforestation decades before forests can recover sufficiently to produce timber for a second harvest. Under the management regimes in effect at the time of our study in the Brazilian Amazon, selective logging would not be sustained.