bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and anisotropy of three-dimensional turbulence in a current sheet
Authors: Onofri M. , Veltri P. , Malara F.
Published: June 2007

The nonlinear evolution of three-dimensional reconnection instabilities are studied in a current sheet where many resonant surfaces are simultaneously present at different locations of the simulation domain. The nonlinear evolution produces the development of anisotropic magnetohydrodynamic turbulence. The development of the energy spectrum is followed until the energy is transported to the dissipative length scale and the anisotropy of the spectrum is analyzed. The energy cascade is affected by the Alfvén effect and it takes place mainly in the direction perpendicular to the local average magnetic field. Anisotropy is also affected by propagation of perturbations across the main magnetic field, due to the growth of a transverse component related to reconnection. The direction of anisotropy varies with the position in space. The spectral index is different both from what is found in homogeneous isotropic turbulence and from the values predicted for magnetohydrodynamic turbulence with a uniform large-scale magnetic field.
Content-based networks: A pedagogical overview
Authors: Balcan Duygu , Erzan Ayşe
Published: June 2007

Complex interactions call for the sharing of information between different entities. In a recent paper, we introduced a combinatoric model which concretizes this idea via a string-matching rule. The model was shown to lend itself to analysis regarding certain topological features of the network. In this paper, we will introduce a statistical physics description of this network in terms of a Potts model. We will give an explicit mean-field treatment of a special case that has been proposed as a model for gene regulatory networks, and derive closed-form expressions for the topological coefficients. Simulations of the hidden variable network are then compared with numerically integrated results.
Electronic optical response of molecules in intense fields: Comparison of TD-HF, TD-CIS, and TD-CIS(D) approaches
Authors: Schlegel H. Bernhard , Smith Stanley M. , Li Xiaosong
Published: June 2007

Time-dependent Hartree-Fock (TD-HF) and time-dependent configuration interaction (TD-CI) methods with Gaussian basis sets have been compared in modeling the response of hydrogen molecule, butadiene, and hexatriene exposed to very short, intense laser pulses (760nm, 3cycles). After the electric field of the pulse returns to zero, the molecular dipole continues to oscillate due to the coherent superposition of excited states resulting from the nonadiabatic excitation caused by the pulse. The Fourier transform of this residual dipole gives a measure of the nonadiabatic excitation. For low fields, only the lowest excited states are populated, and TD-CI simulations using singly excited states with and without perturbative corrections for double excitations [TD-CIS(D) and TD-CIS, respectively] are generally in good agreement with the TD-HF simulations. At higher field strengths, higher states are populated and the methods begin to differ significantly if the coefficients of the excited states become larger than ∼0.1. The response of individual excited states does not grow linearly with intensity because of excited state to excited state transitions. Beyond a threshold in the field strength, there is a rapid increase in the population of many higher excited states, possibly signaling an approach to ionization. However, without continuum functions, the present TD-HF and TD-CI calculations cannot model ionization directly. The TD-HF and TD-CIS simulations are in good accord because the excitation energies obtained by linear response TD-HF [also known as random phase approximation (RPA)] agree very well with those obtained from singly excited configuration interaction (CIS) calculations. Because CIS excitation energies with the perturbative doubles corrections [CIS(D)] are on average lower than the CIS excitation energies, the TD-CIS(D) response is generally stronger than TD-CIS.
An upper bound for passive scalar diffusion in shear flows
Authors: Tran Chuong V.
Published: June 2007

This study is concerned with the diffusion of a passive scalar Θ(r,t) advected by general n-dimensional shear flows u=u(y,z,…,t)x̂ having finite mean-square velocity gradients. The unidirectionality of the incompressible flows conserves the streamwise scalar gradient, ∂xΘ, allowing only the cross-stream components to be amplified by shearing effects. This amplification is relatively weak because an important contributing factor, ∂xΘ, is conserved, effectively rendering a slow diffusion process. It is found that the decay of the scalar variance ⟨Θ2⟩ satisfies d⟨Θ2⟩∕dt≥−Cκ1∕3, where C>0 is a constant, depending on the fluid velocity gradients and initial distribution of Θ, and κ is the molecular diffusivity. This result generalizes to axisymmetric flows on both the plane and sphere having finite mean-square angular velocity gradients.
Nondestructive multispectral reflectoscopy between 800 and 1900nm: An instrument for the investigation of the stratigraphy in paintings
Authors: Karagiannis G. , Salpistis Chr. , Sergiadis G. , Chryssoulakis Y.
Published: June 2007

In the present work, a powerful tool for the investigation of paintings is presented. This permits the tuneable multispectral real time imaging between 200 and 5000nm and the simultaneous multispectral acquisition of spectroscopic data from the same region. We propose the term infrared reflectoscopy for tuneable infrared imaging in paintings (Chryssonlakis and Chassery, The Application of Physicochemical Methods of Analysis and Image Processing Techniques to Painted Works of Art, Erasmus Project ICP-88-006-6, Athens, June, 1989) for a technique that is effective especially when the spectroscopic data acquisition is performed between 800 and 1900nm. Elements such as underdrawings, old damage that is not visible to the naked eye, later interventions or overpaintings, hidden signatures, nonvisible inscriptions, and authenticity features can thus be detected with the overlying paint layers becoming successively “transparent” due to the deep infrared penetration. The spectroscopic data are collected from each point of the studied area with a 5nm step through grey level measurement, after adequate infrared reflectance (%R) and curve calibration. The detection limits of the infrared detector as well as the power distribution of the radiation coming out through the micrometer slit assembly of the monochromator in use are also taken into account. Inorganic pigments can thus be identified and their physicochemical properties directly compared to the corresponding infrared images at each wavelength within the optimum region. In order to check its effectiveness, this method was applied on an experimental portable icon of a known stratigraphy.
Dynamics of the ballooning mode and the relation to edge-localized modes in a spherical tokamak
Authors: Khan R. , Mizuguchi N. , Nakajima N. , Hayashi T.
Published: June 2007

Nonlinear simulations based on the magnetohydrodynamic model have been executed to reveal the dynamics of the ballooning mode in the spherical tokamak plasma. The simulation results have reproduced the characteristic features of the edge-localized mode crash phase, where the filamentary structures are formed along the magnetic field in the edge region, and separated from the core plasma. Moreover, the finite Larmor radius effect is addressed.
Turbulence generator using a precessing sphere
Authors: Goto Susumu , Ishii Nobukazu , Kida Shigeo , Nishioka Michio
Published: June 2007

We propose a precessing sphere as a tabletop turbulence generator, which has less uncertainty in the setting of control parameters and the resulting high flow-reproducibility. The precession is realized by rotating the spin axis of a sphere around another axis (the precession axis). In our experiments, the two axes are fixed at right angles. The flow inside the sphere is governed only by two nondimensional parameters, one being Re (the Reynolds number defined by the maximum peripheral velocity around the spin axis) and the other being Γ (the rate of precession). The range of parameters for sustaining turbulence is revealed by the time-series analysis of velocity fields measured by particle image velocimetry. Well-developed turbulence can be sustained even for Γ of the order of a few percent when Re is beyond a few thousands.
General mechanism for inchworm nanoscale track walkers: Analytical theory and realistic simulation
Authors: Li Dan , Fan Dagong , Wang Zhisong
Published: June 2007

Nanomotors capable of directed transportation along an unlimited linear track are being vigorously pursued both theoretically and experimentally. This study generalizes a previously proposed mechanism for nanoscale track walkers by explicitly treating key molecular details of the walker-track systems. An energy-diagram analysis identifies pathways of energy flow through the walker’s movement cycle, and thereby enables us to develop an analytical theory for the track-walking mechanism. Realistic simulations of the walker’s movement cycles are also conducted. The results show that the walker’s directionality, run length, and speed depend critically on several key dimensional parameters of the walker-track systems. Most notably, the walker’s performance as a function of the binding site interval of the track exhibits an oscillating pattern, which is accurately reproduced by the analytical theory. The wealth of nanocontrol mechanisms identified in the proposed track-walker systems not only provides a framework for optimizing performance of the walker, but also clarifies major requirements for future experimental implementation.
Infrared microthermography of microfabricated devices
Authors: Furstenberg Robert , Kendziora C. A. , Stepnowski Stanley V. , McGill R. Andrew
Published: June 2007

We report a new experimental apparatus for infrared microthermography applicable to a wide class of samples including semitransparent ones and perforated devices. This setup is particularly well suited for the thermography of microfabricated devices. Traditionally, temperature calibration is performed using calibration hot plates, but this is not applicable to transmissive samples. In this work a custom designed miniature calibration oven in conjunction with spatial filtering is used to obtain accurate static and transient temperature maps of actively heated devices. The procedure does not require prior knowledge of the emissivity. Calibration and image processing algorithms are discussed and analyzed. We show that relatively inexpensive uncooled bolometer arrays can be a suitable detector choice in certain radiometric applications. As an example, we apply this method in the analysis of temperature profiles of an actively heated microfabricated preconcentrator device that incorporates a perforated membrane and is used in trace detection of illicit substances.
Monte Carlo simulation and molecular theory of tethered polyelectrolytes
Authors: Hehmeyer Owen J. , Arya Gaurav , Panagiotopoulos Athanassios Z. , Szleifer Igal
Published: June 2007

We investigate the structure of end-tethered polyelectrolytes using Monte Carlo simulations and molecular theory. In the Monte Carlo calculations we explicitly take into account counterions and polymer configurations and calculate electrostatic interaction using Ewald summation. Rosenbluth biasing, distance biasing, and the use of a lattice are all used to speed up Monte Carlo calculation, enabling the efficient simulation of the polyelectrolyte layer. The molecular theory explicitly incorporates the chain conformations and the possibility of counterion condensation. Using both Monte Carlo simulation and theory, we examine the effect of grafting density, surface charge density, charge strength, and polymer chain length on the distribution of the polyelectrolyte monomers and counterions. For all grafting densities examined, a sharp decrease in brush height is observed in the strongly charged regime using both Monte Carlo simulation and theory. The decrease in layer thickness is due to counterion condensation within the layer. The height of the polymer layer increases slightly upon charging the grafting surface. The molecular theory describes the structure of the polyelectrolyte layer well in all the different regimes that we have studied.
Determination of the critical Shields number for particle erosion in laminar flow
Authors: Ouriemi Malika , Aussillous Pascale , Medale Marc , Peysson Yannick , Guazzelli Élisabeth
Published: June 2007

We present reproducible experimental measurements for the onset of grain motion in laminar flow and find a constant critical Shields number for particle erosion, i.e., θc=0.12±0.03, over a large range of small particle Reynolds number: 1.5×10−5⩽Rep⩽0.76. Comparison with previous studies found in the literature is provided.
Does confining the hard-sphere fluid between hard walls change its average properties?
Authors: Mittal Jeetain , Errington Jeffrey R. , Truskett Thomas M.
Published: June 2007

We use grand canonical transition-matrix Monte Carlo and discontinuous molecular dynamics simulations to generate precise thermodynamic and kinetic data for the equilibrium hard-sphere fluid confined between smooth hard walls. These simulations show that the pronounced inhomogeneous structuring of the fluid normal to the confining walls, often the primary focus of density functional theory studies, has a negligible effect on many of its average properties over a surprisingly broad range of conditions. We present one consequence of this insensitivity to confinement: a simple analytical equation relating the average density of the confined fluid to that of the bulk fluid with equal activity. Nontrivial implications of confinement for average fluid properties do emerge in this system, but only when the fluid is both (i) dense and (ii) confined to a gap smaller than approximately three particle diameters. For this limited set of conditions, we find that “in-phase” oscillatory deviations in excess entropy and self-diffusivity (relative to the behavior of the bulk fluid at the same average density) occur as a function of gap size. These paired thermodynamic/kinetic deviations from bulk behavior appear to reflect the geometric packing frustration that arises when the confined space cannot naturally accommodate an integer number of particle layers.
Efficient green emission from (112¯2) InGaN∕GaN quantum wells on GaN microfacets probed by scanning near field optical microscopy
Authors: Kawakami Y. , Nishizuka K. , Yamada D. , Kaneta A. , Funato M. , Narukawa Y. , Mukai T.
Published: June 2007

Nanoscopic optical characterization using scanning near field optical microscopy was performed on a (112¯2) microfacet quantum well (QW). It was revealed that the carrier diffusion length in the (112¯2) QW is less than the probing fiber aperture of 160nm, which is shorter than that of the (0001) QWs and is attributed to much faster radiative recombination processes in the (112¯2) QW due to a reduced internal electric field. Owing to this short diffusion length, the correlation between the internal quantum efficiency (IQE) and emission wavelength is elucidated. The highest IQE is ∼50% at 520nm, which is about 50nm longer than in (0001) QWs, suggesting that the (112¯2) QW is a suitable green emitter.
Microfabricated silicon leak for sampling planetary atmospheres with a mass spectrometer
Authors: Jamieson B. G. , Lynch B. A. , Harpold D. N. , Niemann H. B. , Shappirio M. D. , Mahaffy P. R.
Published: June 2007

A microfabricated silicon mass spectrometer inlet leak has been designed, fabricated, and tested. This leak achieves a much lower conductance in a smaller volume than is possible with commonly available metal or glass capillary tubing. It will also be shown that it is possible to integrate significant additional functionality, such as inlet heaters and valves, into a silicon microleak with very little additional mass. The fabricated leak is compatible with high temperature (up to 500°C) and high pressure (up to 100bars) conditions, as would be encountered on a Venus atmospheric probe. These leaks behave in reasonable agreement with their theoretically calculated conductance, although this differs between devices and from the predicted value by as much as a factor of 2. This variation is believed to be the result of nonuniformity in the silicon etching process which is characterized in this work. Future versions of this device can compensate for characterized process variations in order to produce devices in closer agreement with designed conductance values. The integration of an inlet heater into the leak device has also been demonstrated in this work.
Surface force apparatus for nanorheology under large shear strain
Authors: Bureau Lionel
Published: June 2007

We describe a surface force apparatus designed to probe the rheology of a nanoconfined medium under large shear amplitudes (up to 500μm). The instrument can be operated in closed loop, controlling either the applied normal load or the thickness of the medium during shear experiments. Feedback control allows us to greatly extend the range of confinement/shear strain attainable with the surface force apparatus. The performances of the instrument are illustrated using hexadecane as the confined medium.
Quantitative extraction of spectral line intensities and widths from x-ray spectra recorded with gated microchannel plate detectors
Authors: Dunham Greg , Bailey J. E. , Rochau G. A. , Lake P. W. , Nielsen-Weber L. B.
Published: June 2007

Plasma spectroscopy requires determination of spectral line intensities and widths. At Sandia National Laboratories Z facility we use elliptical crystal spectrometers equipped with gated microchannel plate detectors to record time and space resolved spectra. We collect a large volume of data typically consisting of five to six snapshots in time and five to ten spectral lines with 30 spatial elements per frame, totaling to more than 900 measurements per experiment. This large volume of data requires efficiency in processing. We have addressed this challenge by using a line fitting routine to automatically fit each spectrum using assumed line profiles and taking into account photoelectron statistics to efficiently extract line intensities and widths with uncertainties. We verified that the random data noise obeys Poisson statistics. Rescale factors for converting film exposure to effective counts required for understanding the photoelectron statistics are presented. An example of the application of these results to the analysis of spectra recorded in Z experiments is presented.
Universal characteristics of resonant-tunneling field emission from nanostructured surfaces
Authors: Johnson S. , Zülicke U. , Markwitz A.
Published: June 2007

We have performed theoretical and experimental studies of field emission from nanostructured semiconductor cathodes. Resonant tunneling through electric-field-induced interface bound states is found to strongly affect the field-emission characteristics. Our analytical theory predicts power-law and Lorentzian-shaped current–voltage curves for resonant-tunneling field emission from three-dimensional substrates and two-dimensional accumulation layers, respectively. These predicted line shapes are observed in field emission characteristics from self-assembled silicon nanostructures. A simple model describes formation of an accumulation layer and of the resonant level in these systems.
Growth and spectroscopic characterization of Er3+:CaWO4
Authors: Cornacchia Francesco , Toncelli Alessandra , Tonelli Mauro , Favilla Elena , Subbotin Kirill A. , Smirnov Valerii A. , Lis Denis A. , Zharikov Evgenii V.
Published: June 2007

In this work we present the growth and spectroscopic investigation of Er3+ in CaWO4 single crystals. Er3+ polarized absorption has been measured at room temperature from UV to 1700nm, and the fluorescence from the most important emitting states from the visible to the infrared has been recorded at 10 and 300K in the two possible polarizations. The lifetimes of the lower lying excited states have been measured as a function of the temperature to evaluate the contribution of nonradiative decay processes. The absorption spectra enabled us to determine radiative lifetimes of the emitting states by means of the the Judd-Ofelt approach. The stimulated emission cross section has been estimated for the 1.5μm transition. A comparison of the theoretical and experimental results permitted to obtain an estimate of the actual Er3+ doping level. A calculation of the effective gain cross section for the 1.5μm transition is also presented. These experimental results are discussed in order to evaluate the potentialities of Er3+ in this material as active medium in solid state laser devices.
A universal formulation for the transport V(I) curve of a superconducting cylinder with a power law E(J)
Authors: Chen D.-X. , Gu C.
Published: June 2007

A simple and universal formulation for the transport V(I) curve is given for a superconducting cylinder of radius a with a power law E(J), E=(Ec∕Jc)∣J∕Jc∣n−1J. This formulation is a function of Ec, Jc, n, a, and the current sweeping rate R. Concepts of the full penetration and the relevant voltage as well as several influencing factors in using this formulation are discussed.
Anisotropy of crystalline ferromagnets with defects
Authors: Cullen J. , Zhao P. , Wuttig M.
Published: June 2007

This letter describes a model of the anisotropy of crystalline ferromagnetic alloys containing defect clusters. The focus is on ⟨100⟩-type pairs in bcc lattices each of which is assigned a uniaxial anisotropy of fixed magnitude. The lattice is also characterized by a coherent anisotropy energy due to the transition element host lattice as well as an isotropic exchange and magnetic dipole energy. This model is applied to a study of the concentration dependence of the fourfold magnetic anisotropy Keff(C) of quenched bcc Fe1−CGaC alloys. It yields Keff(C)∝1−κC4 which gives a good account of the dependence of Keff on C. In particular, it accounts for the collapse of Keff at C≈0.2, provided the magnitude of the local anisotropy energy is three orders of magnitude larger than that of the coherent fourfold anisotropy energy.
Structural, electrical, and optical characterizations of epitaxial Zn1−xGaxO films grown on sapphire (0001) substrate
Authors: Snure Michael , Tiwari Ashutosh
Published: June 2007

In this paper we report the structural, electrical, and optical properties of epitaxial Zn1−xGaxO films (x=0–0.05) grown on single crystal sapphire (0001) substrate by pulsed laser deposition technique. Structural and elemental analysis was performed using high-resolution x-ray diffraction (θ-2θ and Φ scan) and energy dispersive x-ray spectroscopy. Temperature dependent electrical resistivity and thermoelectric power measurements were performed over the temperature range of 77–300K and 296–373K, respectively. Hall effect and optical transmission measurements were preformed at room temperature. All these studies showed that the structural, electrical as well as the optical characteristics of Zn1−xGaxO films depend very sensitively on the Ga contents. As the Ga doping concentration is increased, initially an increase in carrier concentration and optical band gap is observed (until x=0.04), which is followed by a decrease at higher concentrations. These features were attributed to the combined effect of band filling (Burstein-Moss effect), electronic correlation, and epitaxial strain present in the system. Above parameters also affected the electrical properties of the films quite significantly. Zn1−xGaxO films with 1% of Ga doping (x=0.01) showed metal-like electrical resistivity. However, for higher doping levels, enhanced scattering potential, arising from randomly distributed impurity atoms, resulted in the Anderson localization of electronic states.
Study on the quantum confinement effect on ultraviolet photoluminescence of crystalline ZnO nanoparticles with nearly uniform size
Authors: Fu Z. D. , Cui Y. S. , Zhang S. Y. , Chen J. , Yu D. P. , Zhang S. L. , Niu L. , Jiang J. Z.
Published: June 2007

Crystalline ZnO nanoparticles with nearly uniform size were studied using photoluminescence and Raman spectroscopy. The main spectral feature of ultraviolet photoluminescence is attributed to the recombination of free exciton (FX) and the first surface phonon replica of FX emission. The energy of FX emission shows a clear blueshift as the size of nanoparticles decreases, indicating that the quantum confinement effect exists in the electronic structure of nano-ZnO, although no confinement effect on the vibrational modes has been found in the same series of samples.
Probing the ferroelectric phase transition through Raman spectroscopy in Pb(Fe2∕3W1∕3)1∕2Ti1∕2O3 thin films
Authors: Kumar Ashok , Murari N. M. , Katiyar R. S. , Scott James F.
Published: June 2007

The present work investigates the evolution of micro-Raman spectra of (1−x)Pb(Fe2∕3W1∕3)O3−xPbTiO3 (PFWT) (x=0.50) thin films in the temperature range from 80to600K. Raman and dielectric data indicate that the crystal structure changes from tetragonal to cubic, i.e., a ferroelectric phase transition at 575K. The dielectric properties of PFWT thin films were studied in the temperature range of 80–600K over a wide range of frequencies. The slope of the reciprocal of the dielectric constant is 2:1, matched well with the simplest Landau free energy model, and it indicates a continuous second order displacive ferroelectric phase transition.
Formation of magnetite in bismuth ferrrite under voltage stressing
Authors: Lou X. J. , Yang C. X. , Tang T. A. , Lin Y. Y. , Zhang M. , Scott J. F.
Published: June 2007

Micro-Raman studies show that under ∼700kV∕cm of dc voltage stressing for a few seconds, magnetite Fe3O4 forms in thin-film bismuth ferrite BiFeO3, probably due to phase separation. No evidence is found spectroscopically of hemite α-Fe2O3, maghemite γ-Fe2O3, or Bi2O3. This may relate to the controversy regarding the magnitude of magnetization in BiFeO3.
White light emitting diode by using α-Ca2P2O7:Eu2+, Mn2+ phosphor
Authors: Hao Zhendong , Zhang Jiahua , Zhang Xia , Sun Xiaoyuan , Luo Yongshi , Lu Shaozhe , Wang Xiao-jun
Published: June 2007

The α-Ca2P2O7:Eu2+, Mn2+ phosphors show two emission bands peaking at around 416 (blue) and 600nm (orange), originating from the allowed f-d transition of Eu2+ and the forbidden T14-A16 transition of Mn2+, respectively, under near ultraviolet (UV) excitation at 400nm. Spectroscopy and fluorescence lifetime measurements demonstrate that energy transfer from Eu2+ to Mn2+ performs with transfer efficiency as high as 65% for Mn2+ concentration of 12mol%. The authors have fabricated a white light emitting diode (LED) through the integration of GaN near-UV chip and two phosphor blends (α-Ca2P2O7:Eu2+, Mn2+ blue-orange phosphor and Ba2SiO4:Eu2+ green phosphor) into a single package. The white LED shows color rendering index of 78, luminescent efficiency of 9lm∕W, and low color point variation against forward-bias currents.
Radiation and polarization properties of free-exciton emission from AlN (0001) surface
Authors: Taniyasu Yoshitaka , Kasu Makoto , Makimoto Toshiki
Published: June 2007

Free-exciton emission from AlN (0001) surface was characterized by angle-dependent photoluminescence (PL) measurement. As the radiation direction was inclined from the surface normal (c-axis direction), the emission intensity increased. This is because the optical transition between the conduction band and the top valence band is mainly allowed for light with the electric field parallel to the c-axis direction of AlN (E‖c) and consequently the free-exciton emission is strongly polarized for E‖c. By analyzing the angle-dependent PL intensities, the polarization ratio was estimated to be 0.995. This high polarization ratio results from the large negative crystal-field splitting energy.
Observation of the negative differential capacitance in Schottky diodes with InAs quantum dots near room temperature
Authors: Lin S. D. , Ilchenko V. V. , Marin V. V. , Shkil N. V. , Buyanin A. A. , Panarin K. Y. , Tretyak O. V.
Published: June 2007

The negative differential capacitance (NDC) of Schottky diodes with the layers of InAs quantum dots (QDs) has been clearly observed near room temperature. A simple model involving two zero-dimensional quantum states is proposed to explain the NDC behavior. The simulation results show that the NDC is caused by the fast charging-discharging process in the second states of QDs.
Direct observation of relaxation dynamics of spin-polarized electrons excited at a higher-energy spin-split subband in a diluted magnetic semiconductor quantum well
Authors: Saito K. , Park J. H. , Souma I. , Oka Y. , Murayama A.
Published: June 2007

The authors observe relaxation dynamics of spin-polarized electrons excited at a higher-energy spin-split subband in a diluted magnetic semiconductor quantum well by means of pump-probe absorption spectroscopy. Time dependences of the circularly polarized saturated absorbance directly show the relaxation of spin-polarized electrons, which is inaccessible by photoluminescence. The probe-energy dependence of the relaxation time is obtained ranging from 2to100ps at 2.5T within the absorption band. This dependence is systematically explained by both the intraband energy relaxation of the spin-polarized electrons and the subsequent electron-spin relaxation that is modified by effects of the exciton localization.
Defect reduction in GaN epilayers grown by metal-organic chemical vapor deposition with in situ SiNx nanonetwork
Authors: Xie Jinqiao , Chevtchenko Serguei A. , Özgür Ümit , Morkoç Hadis
Published: June 2007

Line and point defect reductions in thin GaN epilayers with single and double in situ SiNx nanonetworks on sapphire substrates grown by metal-organic chemical vapor deposition were studied by deep-level transient spectroscopy (DLTS), augmented by x-ray diffraction (XRD), and low temperature photoluminescence (PL). All samples measured by DLTS in the temperature range from 80to400K exhibited trap A (peak at ∼325K) with an activation energy of 0.55–0.58eV, and trap B (peak at ∼155K) with an activation energy of 0.21–0.28eV. The concentrations of both traps were much lower for layers with SiNx nanonetwork compared to the reference sample. The lowest concentration was achieved for the sample with 6min deposition SiNx nanonetwork, which was also lower than that for a sample prepared by conventional epitaxial lateral overgrowth. In concert with the DLTS results, PL and XRD linewidths were reduced for the samples with SiNx network indicating improved material quality. Consistent trend among optical, structural, and DLTS results suggests that SiNx network can effectively reduce both point and line defects.
Undoped homojunction chalcogen thin-film transistors on glass
Authors: Song Ki-Bong , Lee Sang-Su , Kim Kyung-Am , Suh Jeong-Dae , Kim Jun-Ho , Lee Taek-Sung , Cheong Byung-ki , Kim Won-Mock
Published: June 2007

A technique to develop an undoped homojunction chalcogen thin-film transistor (UHJ-c-TFT) on glass is described. The UHJ-c-TFT is based on ternary chalcogenide alloy amorphous (α) Ge2Sb2Te5 (GST) and the positively cooled crystalline (χ) GST. The α-GST and the positively cooled χ-GST are used as a channel layer and ohmic contact layer, respectively. In the UHJ-c-TFT, the authors realize electric rectification by the energy difference from the Fermi level of the α-GST and the Fermi level of the positively cooled χ-GST. The UHJ-c-TFT shows the clear gate characteristics of a typical p-channel enhancement mode.
Age validation of canary rockfish (Sebastes pinniger) using two independent otolith techniques: lead-radium and bomb radiocarbon dating
Authors: Andrews Allen H. , Kerr Lisa A. , Cailliet Gregor M. , Brown Thomas A. , Lundstrom Craig C. , Stanley Richard D.
Published: June 2007

Canary rockfish (Sebastes pinniger) have long been an important part of recreational and commercial rockfish fishing from south-east Alaska to southern California, but localised stock abundances have declined considerably. Based on age estimates from otoliths and other structures, lifespan estimates vary from ~20 years to over 80 years. For the purpose of monitoring stocks, age composition is routinely estimated by counting growth zones in otoliths; however, age estimation procedures and lifespan estimates remain largely unvalidated. Typical age validation techniques have limited application for canary rockfish because they are deep-dwelling and may be long-lived. In this study, the unaged otolith of the pair from fish aged at the Department of Fisheries and Oceans Canada was used in one of two age validation techniques: (1) lead-radium dating and (2) bomb radiocarbon (14C) dating. Age estimate accuracy and the validity of age estimation procedures were validated based on the results from each technique. Lead-radium dating proved successful in determining that a minimum estimate of lifespan was 53 years and provided support for age estimation procedures up to ~50–60 years. These findings were further supported by Δ14C data, which indicated that a minimum estimate of lifespan was 44 ± 3 years. Both techniques validate, to differing degrees, age estimation procedures and provide support for inferring that canary rockfish can live more than 80 years.
Relationship between phosphorus fractions and properties of highly calcareous soils
Authors: Adhami Ebrahim , Memarian Hamid Reza , Rassaei Farzad , Mahdavi Ehsan , Maftoun Manouchehr , Ronaghi Abdol-Majid , Fasaei Reza Ghasemi
Published: June 2007

Inorganic phosphorus (P) sequential fractionation schemes are applicable techniques to interpret soil P status. The present study was initiated to determine the origin of various P fractions in highly calcareous soils. Inorganic P forms were determined by a sequential fractionation procedure extracting with NaOH (NaOH-P), Na citrate-bicarbonate (CB-P), Na citrate 2 times (C1-P and C2-P), Na citrate-ascorbate (CAs-P), Na citrate-bicarbonate-dithionite (CBD-P), Na acetate (NaAc-P), and HCl (HCl-P). Results showed that NaOH-P was negatively correlated with active iron oxides. CB-P was positively correlated with silt content and negatively related to citrate-bicarbonate-dithionite extractable Fe (Fed). This result illustrates the weathering effect on Ca-P, with Ca-P content declining as a consequence of weathering. A negative correlation was observed between C1-P and citrate ascorbate extractable Fe (FeCAs). Second citrate extractable P (C2-P) was negatively related to calcium carbonate equivalent and positively related to hydroxylamine-hydrochloride and neutral ammonium acetate-hydroquinone extractable Mn (Mnh and Mnq). Fine silt (Fsilt) was the most influential factor affecting CAs-P. It seemed citrate-dithionite-bicarbonate extractable Al (Ald), Mnh, and Mnq have been sinks for CBD-P, while free iron oxide compounds (Feo, Fec, and FeCAs) were a major contributing factor for the formation of NaAc-P. Stable P compounds (HCl-P) of highly calcareous soils originated from coarse silt (Csilt) and hydroxylamine-hydrochloride extractable Mn (Mnh).
The spatial differences in arylsulfatase enzyme activity on hillslopes along a climatic transect
Authors: Zwikel Shai , Lavee Hanoch , Sarah Pariente
Published: June 2007

The research was conducted in Israel at 4 sites located along a south-north transect, along which climatic conditions range from arid in the south, through semi-arid, and Mediterranean, to humid Mediterranean in the north. At each site soil samples were collected in summer, winter, and spring over a 2-year period, from 3 microenvironments, from depths of 0–20 and 50–100 mm. The selected microenvironments at the arid, semi-arid, and Mediterranean sites were ‘under shrub’, ‘between shrubs’, and ‘under rock fragments’; those at the humid Mediterranean site were ‘under shrub’, ‘between shrubs’, and ‘under tree’. Intracellular and extracellular arylsulfatase enzyme activities, and some soil properties, were examined. The research aims were: (1) to analyse the relationship between arylsulfatase enzyme activity and some soil properties; (2) to analyse the effects of soil components (local factor) and climatic conditions (regional factor) on arylsulfatase enzyme activity. At both arid sites the organic carbon content, which had a positive effect on arylsulfatase activity, was much higher under shrubs and somewhat higher under rock fragments than between shrubs. At the semi-arid site this was also true of the moisture content. However, at the arid site high soil salinity and dryness limited the enzyme activity, especially the intracellular activity, under shrubs and rock fragments, respectively. In contrast, at the semi-arid site the organic matter was the main limiting factor of enzyme activity. Thus, the intracellular and extracellular activities of the enzyme were considerably higher under shrubs, and somewhat higher under rock fragments, than between shrubs. With increasing rainfall amount towards the Mediterranean sites the enzyme activity increased sharply and the differences between the under shrub, under rock fragment, and between shrubs microenvironments decreased sharply, mainly as a result of the reduction in the spatial variations in organic carbon. At the humid Mediterranean site enzyme activity under trees was considerably higher than that in other microenvironments, and this was expressed in the more suitable environmental conditions under trees, i.e. higher content of organic carbon, moisture, and aggregates.
Relationship between dielectric permittivity and water content for vadose zone materials of volcanic origin
Authors: Stenger R. , Wöhling T. , Barkle G. F. , Wall A.
Published: June 2007

Seven materials, encompassing a young volcanic soil, its parent material, two older buried soils (Palaeosols), and an underlying older volcanic deposit were investigated in a laboratory study to determine the relationship between dielectric permittivity (ϵc) and water content (θ). Empirical 3rd-order polynomial models generally fitted the data better than semi-physical 3-phase mixing models and normalised conversion functions. Based on their different dielectric response, which presumably is mainly due to their different bulk density (and thus porosity), the materials could be grouped into Ignimbrite materials and Palaeosol materials. Relative to the Ignimbrites, Palaeosols showed a particularly muted response at the low end of dielectric permittivity measurements, which could be due to a particularly high amount of bound water in these allophane-rich materials and/or to greater microstructural and phase configuration effects. Applying the Topp equation resulted in substantial underestimations of the water contents of both groups. A relationship previously developed on New Zealand sandy volcanic soils fitted our Ignimbrite materials well, but still underestimated the water contents of the Palaeosols substantially. Normalised conversion functions described both material groupings reasonably well, demonstrating that bulk density differences can explain a substantial part of the variation of ϵc–θ relationships between different materials.
Pyrophosphate and orthophosphate addition to soils: sorption, cation concentrations, and dissolved organic carbon
Authors: McBeath T. M. , Lombi E. , McLaughlin M. J. , Bünemann E. K.
Published: June 2007

Liquid polyphosphate fertilisers contain both orthophosphate and pyrophosphate, and have shown significant yield increases compared to granular orthophosphate fertiliser on highly phosphorus (P) fixing soils. The P sorption chemistry of the dominant P species in a polyphosphate fertiliser (pyrophosphate and orthophosphate) was compared on a range of Australian soils, and the effect of these P species on equilibrium solution chemistry was also examined.
Phosphorus supplied as pyrophosphate had a stronger sorption affinity than orthophosphate in all soils. The greater efficiency of pyrophosphate-based fertiliser on some soil types is therefore not due to reduced sorption of this P supplied as pyrophosphate compared to P supplied as orthophosphate fertiliser.
In general, the addition of pyrophosphate to soil resulted in a larger decrease in calcium concentration in solution compared to orthophosphate. In contrast, there was an increase in iron concentration in solution with pyrophosphate addition, indicating sequestration reactions associated with the dissolution of dissolved organic carbon into soil solution. The pyrophosphate ion generally mobilised more Fe into solution than orthophosphate in several soils, likely through complexation reactions leading to Fe desorption/dissolution from the soil solid phase.
These findings highlight the differences in soil chemical reactions that occur with the addition of polyphosphate fertilisers, which may contribute to their yield advantage in some soil types.
Variation in ectoparasite infestation on the brown antechinus, Antechinus stuartii, with regard to host, habitat and environmental parameters
Authors: Lorch Dagmar , Fisher Diana O. , Spratt David M.
Published: June 2007

We studied ectoparasite infestation patterns in a wild population of brown antechinuses, Antechinus stuartii (Dasyuridae) at three sites in south-eastern New South Wales, over a period of seven months. Ectoparasite diversity on brown antechinuses was particularly high for a small mammal: 18 species of ectoparasites were recorded, including one undescribed species of mite. Ectoparasite infestation varied between study sites and changed seasonally. Variation between sites was related to habitat and environmental parameters, and the highest ectoparasite infestations were encountered in the coolest habitat with greatest depth of leaf litter. Host population densities varied only slightly between sites, and host density was not considered to be a primary factor influencing ectoparasite infestation. This is the first study to provide a host record of ectoparasites of Antechinus stuartii sensu stricto.
Hippocampus queenslandicus Horne, 2001 - a new seahorse species or yet another synonym?
Authors: Teske Peter R. , Lourie Sara A. , Matthee Conrad A. , Green David M.
Published: June 2007

During the past six years, 15 new seahorse species (Syngnathidae: Hippocampus) have been described on the basis of morphological characters. This approach is known to be problematic, and most species names in Hippocampus are now considered to be synonyms. Genetic methods have great potential to resolve the confused taxonomy of the genus, but none have yet been incorporated into species descriptions. In the present study, mitochondrial control region and cytochrome b DNA sequences, as well as morphological data from the recently described Queensland seahorse, Hippocampus queenslandicus Horne, 2001, were compared with corresponding data from closely related seahorse species to determine whether there is strong support for distinction of this taxon. The haplotypes of H. queenslandicus were nested among haplotypes belonging to two of the three major Southeast Asian lineages of H. spinosissimus Weber, 1913. Although incomplete lineage sorting characteristic of very recently diverged species cannot be ruled out, the genetic results suggest that H. queenslandicus is paraphyletic. Morphometric analysis further fails to provide strong support for the species status of H. queenslandicus. We conclude that support for the distinctness of H. queenslandicus is weak, and indicate that it is a synonym of H. spinosissimus. The taxonomic validity of other recently described seahorse species should be similarly scrutinised using combined genetic and detailed morphological methods.
Monogamy in an Australian arboreal marsupial, the yellow-bellied glider (Petaurus australis)
Authors: Brown Meredeth , Carthew Susan M. , Cooper Steven J. B.
Published: June 2007

Several Australian arboreal marsupials have been reported to show variation in mating system across populations, but most previous studies have not included genetic analyses to confirm the observations. Our aim was to test the hypothesis that monogamy was the predominant mating system in a population of yellow-bellied gliders (Petaurus australis) in south-western Victoria, using a combination of behavioural observations and molecular genetic analyses. Home-range overlap, cohesiveness of pairs, rates of den site co-occupancy and location of den trees within the home ranges of 13 adult gliders were determined via radio-tracking. A monogamous social system predominated, demonstrated by extensive home-range overlap between cohabiting adult males and females (40–100%) and little home-range overlap between adjacent territories (<14%). Males spent ~55% of their active time within 25 m of their female partners and 55–85% of their sleeping time in dens with their female partner. The parentage of all juveniles spotlighted within the 400-ha study area was analysed using five microsatellite DNA markers. Of 37 individuals genotyped, eight of 13 juveniles were assigned both social parents as true parents with ≥80% confidence. These results suggest that social and genetic monogamy predominated in this population of yellow-bellied gliders.
Nilpotent orbits of linear and cyclic quivers and Kazhdan-Lusztig polynomials of type A
Authors: Henderson Anthony
Published: June 2007

The intersection cohomologies of closures of nilpotent orbits of linear (respectively, cyclic) quivers are known to be described by Kazhdan-Lusztig polynomials for the symmetric group (respectively, the affine symmetric group). We explain how to simplify this description using a combinatorial cancellation procedure, and we derive some consequences for representation theory.
Multiple 40-kDa Heat-Shock Protein Chaperones Function in Tom70-dependent Mitochondrial Import
Authors: Bhangoo Melanie K. , Tzankov Stefan , Fan Anna C.Y. , Dejgaard Kurt , Thomas David Y. , Young Jason C.
Published: June 2007

Mitochondrial preproteins that are imported via the translocase of the mitochondrial outer membrane (Tom)70 receptor are complexed with cytosolic chaperones before targeting to the mitochondrial outer membrane. The adenine nucleotide transporter (ANT) follows this pathway, and its purified mature form is identical to the preprotein. Purified ANT was reconstituted with chaperones in reticulocyte lysate, and bound proteins were identified by mass spectrometry. In addition to 70-kDa heat-shock cognate protein (Hsc70) and 90-kDa heat-shock protein (Hsp90), a specific subset of cochaperones were found, but no mitochondria-specific targeting factors were found. Interestingly, three different Hsp40-related J-domain proteins were identified: DJA1, DJA2, and DJA4. The DJAs bound preproteins to different extents through their C-terminal regions. DJA dominant-negative mutants lacking the N-terminal J-domains impaired mitochondrial import. The mutants blocked the binding of Hsc70 to preprotein, but with varying efficiency. The DJAs also showed significant differences in activation of the Hsc70 ATPase and Hsc70-dependent protein refolding. In HeLa cells, the DJAs increased new protein folding and mitochondrial import, although to different extents. No single DJA was superior to the others in all aspects, but each had a profile of partial specialization. The Hsp90 cochaperones p23 and Aha1 also regulated Hsp90–preprotein interactions. We suggest that multiple cochaperones with similar yet partially specialized properties cooperate in optimal chaperone–preprotein complexes.