bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of laser ablation: Contribution of ionization energy to the plasma and shock wave properties
Authors: Wen Sy-Bor , Mao Xianglei , Greif Ralph , Russo Richard E.
Published: August 2007

By fitting simulation results with experimentally measured trajectories of the shock wave and the vapor∕background gas contact surface, we found that inclusion of ionization energy in the analysis leads to a change in the evolution of the pressure, mass density, electron number density, and temperature of the vapor plume. The contribution of ionization energy to both the plasma and shock wave has been neglected in most studies of laser ablation. Compared to previous simulations, the densities, pressures, and temperatures are lower shortly after the laser pulse (<5ns), but become larger (by a factor of 2) as the time after the laser pulse increases (>50ns). The predicted laser energy conversion ratio also showed about a 20% increase (from 35% to 45%) when the ionization energy is considered. The changes in the evolution of the physical quantities result from the retention of the ionization energy in the vapor plume, which is then gradually transformed to kinetic and thermal energies. When ionization energy is included in the simulation, the vapor plume attains higher expansion speeds and temperatures for a longer time after the laser pulse. The better determination of the temperature history of the vapor plume not only improves the understanding of the expansion process of the laser induced vapor plume but also is important for chemical analysis. The accurate temperature history provides supplementary information which enhances the accuracy of chemical analysis based on spectral emission measurements (e.g., laser induced breakdown spectroscopy).
Dynamics of the Lorenz system having an invariant algebraic surface
Authors: Cao Jinlong , Zhang Xiang
Published: August 2007

In this paper, we characterize all dynamics of the Lorenz system ẋ=s(y−x), ẏ=rx−xz−y, ż=xy−bz having an invariant algebraic surface.
Spinodally synthesized magnetoelectric
Authors: Ren Shenqiang , Wuttig Manfred
Published: August 2007

Lead zirconium titanate/nickel ferrite (PZT/NFO) composites have been produced by crystallizing and spinodally decomposing a gel in a magnetic field below the Curie temperature of NFO. The gel had been formed by spinning a sol onto a silicon substrate. The ensuing microstructure, characterized by atomic force microscopy, magnetic force microscopy, (Lorentz) transmission electron microscopy, and scanning electron microscopy, is nanoscopically periodic and, determined by the direction of magnetic annealing field, anisotropic. The wavelength of the PZT/NFO alternation, 25nm, agrees within a factor of 2 with the theoretically estimated value. The macroscopic ferromagnetic and magnetoelectric responses correspond qualitatively and semiquantitatively to the features of the nanostructure. The maximum of the field dependent magnetoelectric susceptibility equals 1.8V∕cmOe.
Midinfrared photoluminescence and compositional modulation in pentanary GaInAsPSb alloys grown by liquid phase epitaxy
Authors: Krier A. , Smirnov V. M. , Batty P. J. , Yin M. , Lai K. T. , Rybchenko S. , Haywood S. K. , Vasil’ev V. I. , Gagis G. S. , Kuchinskii V. I.
Published: August 2007

Room temperature photoluminescence is reported from GaInAsSbP pentanary alloys grown by liquid phase epitaxy on GaSb. The epitaxial layers exhibited emission in the midinfrared between 3 and 4μm. Investigation of the structural and photoluminescence properties revealed localization effects associated with potential fluctuations in the pentanary alloy arising from compositional modulation.
Acoustic intensity measurement in a narrow duct by a two-sensor method
Authors: Biwa Tetsushi , Tashiro Yusuke , Nomura Hiroshi , Ueda Yuki , Yazaki Taichi
Published: August 2007

The use of two pressure sensors [Fusco et al., J. Acoust. Soc. Am. 91, 2229 (1992)] makes it possible to determine the acoustic intensity of a gas column in a duct, but the application of this method was limited to wide ducts. In this letter, the formulation of the method is modified to include narrow ducts where the duct radius is as small as the viscous boundary layer thickness of the gas. The validity of this method is shown by comparison with the direct measurements of the pressure and velocity.
Time resolved measurements by the pulse height analysis soft x-ray diagnostic on TCV
Authors: Madeira T. I. , Amorim P. , Duval B. P. , Varandas C. A. F.
Published: August 2007

A single chord, single processing chain, hybrid (analog/digital) pulse height analysis diagnostic has been developed for the TCV tokamak, aiming to provide the evolution of the plasma electron temperature with a software selectable minimum temporal resolution of 100ms. The high count rate (∼65kHz) together with an energy resolution of 190eV (at 5.9keV) were achieved by encoding the data stream with an on-site developed interface amplifier and time generator. The diagnostic was also used to investigate the non-Maxwellian behavior of the electron energy distribution function with strong electron cyclotron resonance heating and to monitor the presence of intrinsic and injected impurities in the 700eV–20keV energy range. The conversion of this diagnostic into a real-time control tool is under development.
Large deformation analysis of gellan gels
Authors: Kawai Shinnosuke , Nitta Yoko , Nishinari Katsuyoshi
Published: August 2007

Gellan gel, a typical polysaccharide gel, is ruptured with different deformation behaviors from gelatin gel or rubber. It exhibits both strain hardening and softening; hardening is observed for moderate strain and softening occurs for larger strain. From the analyses of stress–strain curves of gellan gels, we propose forms of strain energy function. The fit with the proposed equation was excellent, while the existing models fail because they consider only one of hardening or softening effect. Furthermore, these equations are shown to be capable of extracting the hardening and softening effects separately from the observed stress–strain curves. By using these fitting equations, the concentration dependences of hardening and softening are investigated. It is shown that the degrees of hardening and softening both increase with increasing gellan concentration.
Multichannel filters with shape designing in two-dimensional photonic crystal slabs
Authors: Liu Ya-Zhao , Feng Shuai , Tian Jie , Ren Cheng , Tao Haihua , Li Zhi-Yuan , Cheng Bing-Ying , Zhang Dao-Zhong , Luo Qiang
Published: August 2007

We investigated the influence of the irregular shape of air holes on the optical characteristics of channel-drop filters built in a two-dimensional photonic crystal slab. Three differently shaped structures are tested by experiments and simulations to demonstrate the shape-tuning capability of the optical devices. A four-channel filter based on this shape design is presented. The photonic crystal consists of a triangular array of air holes fabricated by focused ion beam lithographic technology on a silicon slab with thickness of 260 nm. The filter contains a heterostructure with different lattice constants of 420 and 430 nm. In each channel, the filtering functionality is guaranteed by the indirect resonant coupling between waveguide and cavity. The elliptical air holes that surround the cavity have different parameters, and this leads to a fine tuning of the cavity’s resonant frequencies. The performance of the multichannel filter is found to be very encouraging.
Efficiency measurement and uncertainty discussion of an electric engine powered by a “self-breathing” and “self-humidified” proton exchange membrane fuel cell
Authors: Schiavetti Pierluigi , Del Prete Zaccaria
Published: August 2007

The efficiency of an automotive engine based on a “self-breathing” and “self-humidified” proton exchange membrane fuel cell stack (PEM FC) connected to a dc brushless electrical motor was measured under variable power load conditions. Experiments have been carried out on a small scale 150W engine model. After determining the fuel cell static polarization curve and the time response to power steps, the system was driven to copy on the test bench a “standard urban load cycle” and its instantaneous efficiencies were measured at an acquisition rate of 5Hz. The integral system efficiency over the entire urban load cycle, comprising the losses of the unavoidable auxiliary components of the engine, was then calculated. The fuel cell stack was operated mainly in “partial” dead-end mode, with a periodic anode flow channel purging, and one test was carried out in “pure” dead-end mode, with no anode channel purging. An uncertainty analysis of the efficiencies was carried out, taking into account either type A and type B evaluation methods, strengthening the discussion about the outcomes obtained for a system based on this novel simplified FC type. For our small scale engine we measured over the standard urban cycle, on the basis of the H2 high heating value (HHV), a tank-to-wheel integral efficiency of (18.2±0.8)%, when the fuel cell was operated with periodic flow channel purging, and of (21.5±1.3)% in complete dead-end operation mode.
Ab initio studies of structural, elastic, and electronic properties of RRh3BX (R=Sc, Y, La, and Ce)
Authors: Kojima Hidenobu , Sahara Ryoji , Shishido Toestu , Nomura Akiko , Kudou Kunio , Okada Shigeru , Kumar Vijay , Nakajima Kazuo , Kawazoe Yoshiyuki
Published: August 2007

The variations in the atomic and electronic structures as well as the elastic properties of perovskite-type RRh3BX (R=Sc, Y, La, and Ce) compounds are understood as a function of X in terms of the changes in the cohesive energy and the covalent and ionic bonding using ab initio calculations. A strong covalent bonding is obtained between B 2p and Rh 4d orbitals in all cases. For R=Ce, f-d hybridization is significant and the Fermi level lies in a pseudogap similar to the case where B is replaced by C, leading to further possibilities of designing such compounds.
Electromigration effect of Ni electrodes on the resistive switching characteristics of NiO thin films
Authors: Lee C. B. , Kang B. S. , Lee M. J. , Ahn S. E. , Stefanovich G. , Xianyu W. X. , Kim K. H. , Hur J. H. , Yin H. X. , Park Y. , Yoo I. K. , Park J.-B. , Park B. H.
Published: August 2007

The effects of Ni and Ni0.83Pt0.17 alloy electrodes on the resistance switching of the dc-sputtered polycrystalline NiO thin films were investigated. The initial off-state resistances of the films were similar to that of Pt∕NiO∕Pt film. However, after the first cycle of switching, the off-state resistance significantly decreased in the films with Ni in the electrode. It can be attributed to the migration of Ni from electrodes to the NiO films. The improvement in data dispersion of switching parameters is explained in terms of the decrease of the effective thickness of the films resulting from the migration of Ni.
Common reversal mechanisms and correlation between transient domain states and field sweep rate in patterned Permalloy structures
Authors: Lau J. W. , Beleggia M. , Zhu Y.
Published: August 2007

Complicated domain configurations generated during the magnetization reversal of Permalloy elements patterned in various shapes are the results of a surprisingly few switching mechanisms. By comparing the results from micromagnetic simulations with the experimentally observed switching events imaged by Lorentz microscopy, we found that nucleation and annihilation of vortices and vortex/antivortex pairs, and the propagation of Néel and cross-tie walls are common mechanisms for magnetization reversal in Permalloy elements with dimensions favorable to domain formation. In addition, for a given element, different mechanism combination(s) may transpire, depending on the sweep rate in the externally applied field. This is because energy maxima and minima are generally field dependent and that different field sweep rate alters the time allotted for thermally assisted transition between states.
Thermodynamics of flame impingement heat transfer
Authors: Som S. K. , Agrawal G. K. , Chakraborty Suman
Published: August 2007

A theoretical model for entropy generation and utilization of work potential (exergy) in flame impingement (both premixed and diffusion) heat transfer has been developed in this article, to offer physical insights on the optimal operational regimes, depicting high values of the surface heat flux with minimal exergy destruction, within the practical constraints. The irreversibility components due to different physical processes have been evaluated from a general entropy transport equation. The velocity, temperature, and species concentration fields required for the solution of entropy transport equation have been determined from the numerical computation of flow-field in the flame. Global two-step chemical kinetics has been considered with methane (CH4) and air as fuel and oxidizer, respectively. The results have been predicted in terms of average nondimensional heat flux, expressed as Nusselt number at the target plate, the irreversibility components, and second law efficiency, as functions of the pertinent input parameters such as the jet Reynolds number and the ratio of plate separation distance to nozzle diameter (H∕d). The average Nusselt number has been found to increase with an increase in jet Reynolds number and a decrease in H∕d ratio, up to a value of 8. The dominant source of thermodynamic irreversibility in a premixed flame has been attributed to the thermal energy exchange whereas, in a diffusion flame, the same has been attributed to an uncontrolled exchange of electrons accompanying the reactive kinetics. The second law efficiency has been found to increase with an increase in jet Reynolds number and an increase in the H∕d ratio, up to a value of 20. Values of the jet Reynolds number greater than 10 000 and H∕d ratio in the tune of 15 have been observed to pertain to the regime of optimum flame impingement heat transfer, consistent with the energy and exergy balance constraints.
Production of neutrals and their effects on the ion charge states in cathodic vacuum arc plasmas
Authors: Anders André , Oks Efim M. , Yushkov Georgy Yu.
Published: August 2007

Cathodic arc plasmas are considered fully ionized and they contain multiply charged ions, yet gaseous and metal neutrals can be present. It is shown that they can cause a significant reduction of the ion charge states as measured far from the cathode spots. Several cathode materials were used to study the evolution of the mean ion charge state as a function of time after arc ignition. The type of cathode material, arc current amplitude, intentionally increased background gas, additional surfaces placed near the plasma flow, and other factors influence the degree of charge state reduction because all of these factors influence the density of neutrals. In all cases, it was found that the mean ion charge state follows an exponential decay of first order, Q¯(t)=A exp(−t∕τ)+Q¯ss, where A is a parameter describing the importance of the decay, τ is the characteristic decay time, and Q¯ss is a steady-state value approached for continuous arc operation. The extrapolated values Q¯(t→0) indicate surprisingly high mean charge states as produced at cathode spots and not “skewed” by charge exchange collisions with neutrals.
Effect of the bias current on the magnetic field switching in micrometer AlOx-based tunnel junctions
Authors: Martínez-Boubeta C.
Published: August 2007

We have examined the relationship between switching characteristics and the tunnel magnetoresistance under finite bias in microscopic low resistance (RA<30Ωμm2) tunnel junctions with AlOx barriers. By switching the free layer with a magnetic field applied in plane along the magnetically easy axis, it is observed that the coercive field depends strongly on the bias current. Steps on the R-H curve due to nonuniform magnetization reversal can be attributed to the in-plane domain wall pinning effect, and it is thought to account for the diminished junction resistance changes upon the application of perpendicular-to-plane spin-polarized currents.
Spatial confinement effects in laser-induced breakdown spectroscopy
Authors: Shen X. K. , Sun J. , Ling H. , Lu Y. F.
Published: August 2007

The spatial confinement effects in laser-induced breakdown of aluminum (Al) targets in air have been investigated both by optical emission spectroscopy and fast photography. A KrF excimer laser was used to produce plasmas from Al targets in air. Al atomic emission lines show an obvious enhancement in the emission intensity when a pair of Al-plate walls were placed to spatially confine the plasma plumes. Images of the Al plasma plumes showed that the plasma plumes evolved into a torus shape and were compressed in the Al walls. The mechanism for the confinement effects was discussed using shock wave theory.
Design of negative-refractive-index materials on the basis of rods with a gradient of the dielectric constant
Authors: Sergentu V. V. , Ursaki V. V. , Tiginyanu I. M. , Foca F. , Föll H. , Boyd Robert W.
Published: August 2007

The authors propose an approach to the design of negative-refractive-index materials based on the use of dielectric rods with a gradient of the dielectric constant. A triangular-lattice photonic crystal assembled from multilayer dielectric rods with a refractive index approximating a fish-eye profile is shown to exhibit a negative refractive index in the wavelength range defined by the inequality 0.67<a∕λ<0.83, where a is the lattice constant of the photonic crystal. A lens consisting of a plane-parallel slab of such a photonic crystal slab is shown to be able to form an image of a point source in this wavelength range. According to the calculations, particularly high-quality images can be obtained at the wavelength λ=(3∕2)a, where the fish-eye dielectric rods scatter the light like a medium with the refractive index equal to −0.85.
New delay-integration method for resolving individual components of a pair of composite signals
Authors: Petrek Derek J. , Bhushan Bharat
Published: August 2007

Many scientific measurements are actually a composite of two or more indirectly measured values. A distance measurement, for example, is actually a measurement of the true distance and some amount of error added together. A new method for decomposing a pair of such composite signals into their individual components in certain situations is described. The method utilizes a delay time difference between the components in each of the two composite signals to provide information necessary to reconstruct the individual components. This decomposition would allow for the possible removal of one of the components, such as in the case of unwanted noise. The method is able to distinguish between two signals with similar frequencies and amplitudes, making it a viable solution in situations where simple low- or high-pass filtering would remove needed signal information. Three successful applications of the method are described, including measurement of lateral tape motion (LTM) in a magnetic data storage tape drive and removal of additive noise from both an electrical and a mechanical system.
Effects of chemical fluctuations on microstructures and properties of multiferroic BiFeO3 thin films
Authors: Luo W. B. , Zhu J. , Li Y. R. , Wang X. P. , Zhao D. , Xiong J. , Zhang Y.
Published: August 2007

Bi Fe O 3 films have been grown on SrTiO3 (001) substrates by pulsed laser deposition. It was found that oxygen partial pressure is crucial to phase purity, surface morphology, and surface chemistry. Single-phase BFO films were obtained at 1Pa O2, while Bi2O3 appeared in the films deposited at 0.01Pa as confirmed by x-ray diffractions. It was revealed that Fe2+ and metallic Bi exist in the films fabricated at 0.01Pa by x-ray photoelectron spectroscopy investigation. Owing to Fe2+ in the samples deposited at 0.01Pa, the saturation magnetization is much larger than the ones fabricated at 1Pa. A well-saturated ferroelectric hysteresis loop with a polarization of 23.6μC∕cm2 was observed in the single-phase samples. In contrast, the films deposited at 0.01Pa exhibited poor ferroelectric properties.
Novel method for mechanical characterization of polymeric nanofibers
Authors: Naraghi Mohammad , Chasiotis Ioannis , Kahn Harold , Wen Yongkui , Dzenis Yuris
Published: August 2007

A novel method to perform nanoscale mechanical characterization of highly deformable nanofibers has been developed. A microelectromechanical system (MEMS) test platform with an on-chip leaf-spring load cell that was tuned with the aid of a focused ion beam was built for fiber gripping and force measurement and it was actuated with an external piezoelectric transducer. Submicron scale tensile tests were performed in ambient conditions under an optical microscope. Engineering stresses and strains were obtained directly from images of the MEMS platform, by extracting the relative rigid body displacements of the device components by digital image correlation. The accuracy in determining displacements by this optical method was shown to be better than 50nm. In the application of this method, the mechanical behavior of electrospun polyacrylonitrite nanofibers with diameters ranging from 300to600nm was investigated. The stress-strain curves demonstrated an apparent elastic-perfectly plastic behavior with elastic modulus of 7.6±1.5GPa and large irreversible strains that exceeded 220%. The large fiber stretch ratios were the result of a cascade of periodic necks that formed during cold drawing of the nanofibers.
Time-domain reconstruction using sensitivity coefficients for limited view ultrawide band tomography
Authors: Abdullah M. Z. , Yin W. , Bilal M. , Armitage D. W. , Mackin R. , Peyton A. J.
Published: August 2007

This article addresses time-domain ultrawide band (UWB) electromagnetic tomography for reconstructing the unknown spatial characteristic of an object from observations of the arrivals of short electromagnetic (EM) pulses. Here, the determination of the first peak arrival of the EM traces constitutes the forward problem, and the inverse problem aims to reconstruct the EM property distribution of the media. In this article, the finite-difference time-domain method implementing a perfectly matched layer is used to solve the forward problem from which the system sensitivity maps are determined. Image reconstruction is based on the combination of a linearized update and regularized Landweber minimization algorithm. Experimental data from a laboratory UWB system using targets of different contrasts, sizes, and shapes in an aqueous media are presented. The results show that this technique can accurately detect and locate unknown targets in spite of the presence of significant levels of noise in the data.
Production of high-current heavy ion jets at the short-wavelength subnanosecond laser-solid interaction
Authors: Badziak J. , Kasperczuk A. , Parys P. , Pisarczyk T. , Rosiński M. , Ryć L. , Wołowski J. , Jabłoński S. , Suchańska R. , Krousky E. , Láska L. , Mašek K. , Pfeifer M. , Ullschmied J. , Dareshwar L. J. , Földes I. , Torrisi L. , Pisarczyk P.
Published: August 2007

Generation of ion fluxes at the interaction of 70J, 0.438μm subnanosecond laser pulse with a massive planar target has been investigated. It is shown that after proper optimization of high-Z (Cu or Ta) target irradiation, a highly collimated heavy ion jet of the ion current >100A and the ion current density >1A∕cm2 at 1m from the target can be produced with an energy conversion efficiency nearly 10%.
High-efficiency particulate air filter test stand and aerosol generator for particle loading studies
Authors: Arunkumar R. , Hogancamp Kristina U. , Parsons Michael S. , Rogers Donna M. , Norton Olin P. , Nagel Brian A. , Alderman Steven L. , Waggoner Charles A.
Published: August 2007

This manuscript describes the design, characterization, and operational range of a test stand and high-output aerosol generator developed to evaluate the performance of 30×30×29cm3 nuclear grade high-efficiency particulate air (HEPA) filters under variable, highly controlled conditions. The test stand system is operable at volumetric flow rates ranging from 1.5to12standardm3∕min. Relative humidity levels are controllable from 5%–90% and the temperature of the aerosol stream is variable from ambient to 150°C. Test aerosols are produced through spray drying source material solutions that are introduced into a heated stainless steel evaporation chamber through an air-atomizing nozzle. Regulation of the particle size distribution of the aerosol challenge is achieved by varying source solution concentrations and through the use of a postgeneration cyclone. The aerosol generation system is unique in that it facilitates the testing of standard HEPA filters at and beyond rated media velocities by consistently providing, into a nominal flow of 7standardm3∕min, high mass concentrations (∼25mg∕m3) of dry aerosol streams having count mean diameters centered near the most penetrating particle size for HEPA filters (120–160nm). Aerosol streams that have been generated and characterized include those derived from various concentrations of KCl, NaCl, and sucrose solutions. Additionally, a water insoluble aerosol stream in which the solid component is predominantly iron (III) has been produced. Multiple ports are available on the test stand for making simultaneous aerosol measurements upstream and downstream of the test filter. Types of filter performance related studies that can be performed using this test stand system include filter lifetime studies, filtering efficiency testing, media velocity testing, evaluations under high mass loading and high humidity conditions, and determination of the downstream particle size distributions.
Pentacene-based thin-film transistors with multiwalled carbon nanotube source and drain electrodes
Authors: Chang Chia-Hao , Chien Chao-Hsin , Yang Jung-Yen
Published: August 2007

In this letter, the authors propose a practical and reliable approach—using deposited multiwalled carbon nanotubes (MWCNTs) as source and drain electrodes—for reducing the contact resistance (Rc) in pentacene-based bottom-contact thin-film transistors. The value of Rc of the devices was closely linked to the resultant length of the deposited MWCNTs; the lowest value was 3×108Ωμm. The largest saturation mobility was 0.14cm2∕Vs; this value reached up to three times higher when the threshold voltage was determined using the maximum transconductance (Gm,max) extrapolation method, rather than the constant current method. The on/off ratio was more than 106.
Substantial reduction in the depinning field of vortex domain walls triggered by spin-transfer induced resonance
Authors: Nozaki T. , Maekawa H. , Mizuguchi M. , Shiraishi M. , Shinjo T. , Suzuki Y. , Maehara H. , Kasai S. , Ono T.
Published: August 2007

An influence of spin-transfer-induced resonant excitation of a vortex magnetic domain wall on magnetization reversal process was investigated in Permalloy nanowires. Sizable reduction of the depinning field was observed under an application of radio frequency current when the frequency coincided with resonance of the vortex core. The resonant frequency was found to increase by shrinking the wire width. These results lead the authors to conclude that the spin-transfer-induced resonant excitation assists the depinning of the vortex domain walls. This provides an important insight for the realization of novel magnetic memory and logic devices based on current-driven domain wall manipulation.
Beam shaping and effective guiding in the bulk of photorefractive crystals through linear beam dynamics
Authors: DelRe E. , Pierangelo A. , Palange E. , Ciattoni A. , Agranat A. J.
Published: August 2007

The authors demonstrate a technique to optically imprint through linear beam propagation an index pattern in the bulk of a photorefractive crystal capable of beam reshaping and waveguiding. The procedure is based on the separation into two distinct phases of the photosensitive and refractive response, so that light is in all cases undergoing only linear propagation. When saturation in the response becomes dominant, the scheme is able to achieve both one-dimensional and two-dimensional waveguiding. The result allows the straightforward writing of multiwaveguide circuits, where traditional schemes based on spatial solitons are in practice burdened by nonlinearity.
Narrow (≈4meV) inhomogeneous broadening and its correlation with confinement potential of pyramidal quantum dot arrays
Authors: Leifer K. , Pelucchi E. , Watanabe S. , Michelini F. , Dwir B. , Kapon E.
Published: August 2007

The inhomogeneous broadening in the luminescence spectra of ordered arrays of pyramidal GaAs∕AlGaAs semiconductor quantum dots (QDs) was studied as a function of the dot size. Dot arrays with inhomogeneous broadening as small as 4.1meV and a corresponding ground state to first excited state transition separation of 28meV were obtained. By evaluating the QD energy levels using a multiband k∙p model, the authors estimated that the observed inhomogeneous broadening corresponds to dot height fluctuations of about 1–2 ML across the array.
InGaAs single photon avalanche detector with ultralow excess noise
Authors: Zhao Kai , Zhang Arthur , Lo Yu-hwa , Farr William
Published: August 2007

An InGaAs single photon avalanche detector capable of sub-Geiger mode (Photomultiplier-tube-like) operation is reported. The device achieves a stable gain at around 106. The gain fluctuation is greatly suppressed through a self-quenching effect, thus an equivalent excess noise factor as low as 1.001 is achieved. In the photon counting experiment, the device is operated in the nongated mode under a dc bias. Because of its unique characteristics of self-quenching and self-recovery, no external quenching circuit is needed. The device shows a single photon response of around 30ns and a self-recovery time of about 300ns.
Unsaturated charge injection at high-frequency fatigue of Pt∕Pb(Zr,Ti)O3∕Pt thin-film capacitors
Authors: Jiang A. Q. , Lin Y. Y. , Tang T. A.
Published: August 2007

Generic phenomenon of polarization fatigue for Pt∕Pb(Zr,Ti)O3∕Pt thin-film capacitors, sensitive to the fatigue number but regardless of fatigue frequency below 1MHz, is interpreted in terms of charge injection during polarization reversal. The present results clearly demonstrate the enhanced fatigue endurance with reduced pulse width below 175ns as well as the fatigue-free nature of the film with downscaling of the pulse width close to time of polarization reversal. The fitting on the basis of an interfacial passive-layer model yields a characteristic time of 120ns for by-electrode charge injection responsible for the fatigue during electrical-field overstressing.
Fabrication of organic bulk heterojunction solar cells by a spray deposition method for low-cost power generation
Authors: Vak Doojin , Kim Seok-Soon , Jo Jang , Oh Seung-Hwan , Na Seok-In , Kim Juhwan , Kim Dong-Yu
Published: August 2007

The authors report on a spray deposition method as a cost-efficient technique for the fabrication of organic solar cells (OSCs). Active layers of OSCs were fabricated using conventional handheld airbrushes. Although the spray deposited film showed a relatively rougher surface than spin coated ones, pinhole-free and constant thickness films could be obtained. An optimized OSC showed 2.83% of power conversion efficiency and 52% of incident photon to current conversion efficiency even though the device was fabricated in air. The performance of sprayed OSCs was comparable to that of the spin coated devices fabricated in air.
Traditional and ecological fires and effects of bushfire laws in north Australian savannas
Authors: Preece Noel
Published: August 2007

Landscape fires are common and frequent across the north Australian savannas, and are arguably an essential component of regional ecosystem dynamics. Seasonal biases in fire regimes and the high frequency of late dry season fires in a large proportion of the region have been presented as an impediment to appropriate land management. Legislation regulating the lighting of fires applies to the whole of the savannas. The legislation seeks to control the lighting of fires, provides for permit systems to operate in each jurisdiction, and is supported by policies and guidance manuals. The present paper argues that the legislation fails to address prescribed burning, the biophysical and social realities of contemporary regimes, and management needs. The policies and legislation are in need of some fundamental changes, including recognition of the concept of prescribed burning, mechanisms to promote regional fire management strategies and plans, and recognition of indigenous traditional practices.
Combustion characteristics of north-eastern USA vegetation tested in the cone calorimeter: invasive versus non-invasive plants
Authors: Dibble Alison C. , White Robert H. , Lebow Patricia K.
Published: August 2007

In the north-eastern United States, invasive plants alter forest fuels, but their combustion characteristics are largely unknown. We assessed unground samples of foliage and twigs in the cone calorimeter for 21 non-invasive, native species, paired with 21 invasive species (18 non-native). Variables included sustained ignition, peak heat release rate, total heat release, and especially average effective heat of combustion, which is independent of initial sample mass. Heat of combustion was overall slightly lower for invasive species than for counterpart non-invasive species, and was significantly lower for Norway maple, black locust, and glossy buckthorn than for three non-invasive trees. It was low for invasive Japanese stiltgrass, sheep sorrel, and glossy buckthorn, and for non-invasive whitegrass, interrupted fern, grape, sphagnum moss, and three-lobed bazzania. Heat of combustion was high for invasive roundleaf greenbrier (native), scotchbroom, tree-of-heaven, Japanese honeysuckle, Japanese barberry, swallow-wort, and garlic mustard, and for non-invasive plants of fire-prone ecosystems: black huckleberry, pitch pine, bear oak, northern bayberry, and reindeer lichen. Heat content of twigs and foliage interrelates with other factors that affect fire behaviour, yet the cone calorimeter results enabled comparison of combustion properties among many species. These data have potential application as improved inputs for fire behaviour modelling.
Human and biophysical factors influencing modern fire disturbance in northern Wisconsin
Authors: Sturtevant Brian R. , Cleland David T.
Published: August 2007

Humans cause most wildfires in northern Wisconsin, but interactions between human and biophysical variables affecting fire starts and size are not well understood. We applied classification tree analyses to a 16-year fire database from northern Wisconsin to evaluate the relative importance of human v. biophysical variables affecting fire occurrence within (1) all cover types, and (2) within forest types in each of four different fire size groupings (all fires; fires ≥0.4 ha (1 acre); fires ≥4 ha (10 acres); fires ≥16 ha (40 acres)). Housing density was the most important indicator of fire observations. Increasing minimum fire size increased the relative importance of biophysical variables. Key biophysical variables included land cover type, soil moisture indicators, and an index of presettlement fire rotation associated with glacial landforms. Our results indicate the likelihood of fire starts is primarily influenced by human activity in northern Wisconsin, whereas biophysical factors determine whether those fire starts become large fires. Important interactions between human and biophysical variables were observed for nearly all fire types and size thresholds examined. Our results have implications for both ecological restoration and the management of fire risk within historically fire-prone systems currently experiencing rapid rural development.
Separating combustion from pyrolysis in HIGRAD/FIRETEC
Authors: Colman Jonah J. , Linn Rodman R.
Published: August 2007

HIGRAD/FIRETEC is a coupled atmosphere/wildfire behavior model based on conservation of mass, momentum, species, and energy. It combines a three-dimensional transport model that uses a compressible-gas fluid dynamics formulation with a physics-based wildfire model, to represent the coupled behavior of the local atmosphere and wildfire. In its current formulation, combustion and pyrolysis are treated as a single process, which depends on the local densities of wood and oxygen, the levels of turbulent mixing, and a probability distribution function (PDF) for temperature in the solid. The PDF is employed to estimate the volume fraction that is hot enough to burn. This burning model is now being extended to deal with pyrolysis and combustion as separate processes. Some fire behaviors, such as flash events, crowning, and fire ‘whirls’, may depend on the ability of combustion to take place in a separate spatial location from the pyrolysis. We refer to this burning model as ‘non-local’. In the non-local burning model, pyrolysis is dealt with in roughly the same way as formerly, but now as an endothermic process. Instead of producing solely inert gasses, it now produces a mixture of inert and combustible gasses. Combustion is handled as a separate gas–gas reaction, which is highly exothermic. The basic premise of the HIGRAD/FIRETEC burning model is retained, i.e. that the rate of a reaction is limited by the rate at which the reactants can be brought together (mixing limited). In the non-local burning model, the reactants for pyrolysis can be thought of as heat and wood, for combustion: the reactive gas and oxygen. A few simple test cases that used idealised geometries were simulated with both burning models, and the results were compared. The non-local burning model was found to give results comparable to the local burning model in terms of the fire-line shape and the spread rate for these simple test cases.
Stand-specific litter moisture content calibrations for the Canadian Fine Fuel Moisture Code
Authors: Wotton B. Mike , Beverly Jennifer L.
Published: August 2007

A large dataset of litter moisture measurements collected at several sites across Canada by the Canadian Forest Service over the period from 1939 to 1961 is analysed. The stands in which sampling was carried out were described by three main variables: forest type (pine, spruce, Douglas fir, mixedwood and deciduous), season (spring, summer and fall), and stand density (light, moderate and dense). All three variables were found to have a significant influence on the relationship between the Canadian Forest Fire Weather Index System’s Fine Fuel Moisture Code (FFMC) and surface litter moisture. Moisture in the upper duff layer was also found to have a significant influence on the relationship between FFMC and litter moisture content, with a wetter duff layer leading to moister surface conditions than would be indicated by the FFMC value. A model for litter moisture is developed, which provides a method of adjusting the standard FFMC value for the influences of forest type, stand density, season and duff moisture content.
Post-fire recolonisation of a montado area by the endangered Cabrera vole (Microtus cabrerae)
Authors: do Rosário Inês T. , Mathias Maria da Luz
Published: August 2007

The Cabrera vole is an endangered species frequently found in the montado, a savannah-like ecosystem well adapted to fire. Although it is assumed that regular burning is not very prejudicial to this vole, the impact of fire is unknown. This research studied, for the first time, recolonisation by the Cabrera vole after wildfire. Colonies were monitored over one year after a wildfire and the most relevant ecological features in their reestablishment were identified. During the first eight months, all the 18 surveyed colonies remained unoccupied. However, after one year, 11 were recolonised. Vegetation structure and composition in the colonies (vegetation height, plant families diversity, percentage of bare ground and cover of shrubs before the fire), which are important features in offering protection and nutrition, were closely related to reoccupation of the colonies. Surprisingly, fire intensity did not influence recolonisation. Distance from unburned areas proved to be a factor that delayed recolonisation. The importance of the montado for this species was reinforced by the evidence that recolonisation occurred preferentially in colonies surrounded by this habitat type.
Development of an index for quick comparison of helicopter costs and benefits
Authors: Trethewey Diane
Published: August 2007

A helicopter comparison index was developed to incorporate cost and benefit information for individual helicopters for large wildland fire suppression operations. The costs and benefits for individual helicopters are unique. Costs consist of daily availability and hourly flight rates. Benefits depend on the payload, which depends on the altitude and temperature of operation, weight of the helicopter, equipment on board, crew, and fuel. Because of the complexity of calculating payload, previous methods for deploying helicopters classified helicopters into three types according to their typical payload. The least expensive helicopter of the desired type was deployed. Because this classification system produces a broad range of benefits within each helicopter type, this method may not deploy the most efficient helicopter.
The helicopter comparison index can be calculated at representative altitudes and temperatures before it is needed. As the work is done beforehand, the helicopters can be compared quickly when they are needed. The helicopter comparison index allows helicopters to be compared based on the efficiency of the individual helicopters rather than just their cost of operation. Evaluation of Type I helicopters shows that using the helicopter comparison index instead cost of operation has savings potential of 20 to 45 percent.
Estimation of dead fuel moisture content from meteorological data in Mediterranean areas. Applications in fire danger assessment
Authors: Aguado I. , Chuvieco E. , Borén R. , Nieto H.
Published: August 2007

The estimation of moisture content of dead fuels is a critical variable in fire danger assessment since it is strongly related to fire ignition and fire spread potential. This study evaluates the accuracy of two well-known meteorological moisture codes, the Canadian Fine Fuels Moisture Content and the US 10-h, to estimate fuel moisture content of dead fuels in Mediterranean areas. Cured grasses and litter have been used for this study. The study was conducted in two phases. The former aimed to select the most efficient code, and the latter to produce a spatial representation of that index for operational assessment of fire danger conditions. The first phase required calibration and validation of an estimation model based on regression analysis. Field samples were collected in the Cabañeros National Park (Central Spain) for a six-year period (1998–2003). The estimations were more accurate for litter (r2 between 0.52) than for cured grasslands (r2 0.11). In addition, grasslands showed higher variability in the trends among the study years. The two moisture codes evaluated in this paper offered similar trends, therefore, the 10-h code was selected since it is simpler to compute. The second phase was based on interpolating the required meteorological variables (temperature and relative humidity) to compute the 10-h moisture code. The interpolation was based on European Centre for Medium Range Weather Forecasting (ECMWF) predictions. Finally, a simple method to combine the estimations of dead fuel moisture content with other variables associated to fire danger is presented in this paper. This method estimates the probability of ignition based on the moisture of extinction of each fuel type.
Ionotropic glutamate-like receptor δ2 binds
d
-serine and glycine
Authors: Naur Peter , Hansen Kasper B. , Kristensen Anders S. , Dravid Shashank M. , Pickering Darryl S. , Olsen Lars , Vestergaard Bente , Egebjerg Jan , Gajhede Michael , Traynelis Stephen F. , Kastrup Jette S.
Published: August 2007

The orphan glutamate-like receptor GluRδ2 is predominantly expressed in Purkinje cells of the central nervous system. The classification of GluRδ2 to the ionotropic glutamate receptor family is based on sequence similarities, because GluRδ2 does not form functional homomeric glutamate-gated ion channels in transfected cells. Studies in GluRδ2
−/−
knockout mice as well as in mice with naturally occurring mutations in the GluRδ2 gene have demonstrated an essential role of GluRδ2 in cerebellar long-term depression, motor learning, motor coordination, and synaptogenesis. However, the lack of a known agonist has hampered investigations on the function of GluRδ2. In this study, the ligand-binding core of GluRδ2 (GluRδ2–S1S2) was found to bind neutral amino acids such as
d
-serine and glycine, as demonstrated by isothermal titration calorimetry. Direct evidence for binding of
d
-serine and structural rearrangements in the binding cleft of GluRδ2–S1S2 is provided by x-ray structures of GluRδ2–S1S2 in its
apo
form and in complex with
d
-serine. Functionally,
d
-serine and glycine were shown to inactivate spontaneous ion-channel conductance in GluRδ2 containing the lurcher mutation (EC
50
values, 182 and 507 μM, respectively). These data demonstrate that the GluRδ2 ligand-binding core is capable of binding ligands and that cleft closure of the ligand-binding core can induce conformational changes that alter ion permeation.
Patterns of damage in genomic DNA sequences from a Neandertal
Authors: Briggs Adrian W. , Stenzel Udo , Johnson Philip L. F. , Green Richard E. , Kelso Janet , Prüfer Kay , Meyer Matthias , Krause Johannes , Ronan Michael T. , Lachmann Michael , Pääbo Svante
Published: August 2007

High-throughput direct sequencing techniques have recently opened the possibility to sequence genomes from Pleistocene organisms. Here we analyze DNA sequences determined from a Neandertal, a mammoth, and a cave bear. We show that purines are overrepresented at positions adjacent to the breaks in the ancient DNA, suggesting that depurination has contributed to its degradation. We furthermore show that substitutions resulting from miscoding cytosine residues are vastly overrepresented in the DNA sequences and drastically clustered in the ends of the molecules, whereas other substitutions are rare. We present a model where the observed substitution patterns are used to estimate the rate of deamination of cytosine residues in single- and double-stranded portions of the DNA, the length of single-stranded ends, and the frequency of nicks. The results suggest that reliable genome sequences can be obtained from Pleistocene organisms.
‘See and treat’ regime by LEEP conisation is a safe and time saving procedure among women with cytological high‐grade squamous intraepithelial lesion
Authors: KJELLBERG LENNART , TAVELIN BJÖRN
Published: August 2007

Background. Assess the value of colposcopic evaluation preceding loop electrosurgical excision procedure (LEEP) conisation of cytological high grade squamous intraepithelial lesion (HSIL), and study risk factors for recurrence. Methods. Consecutive follow‐up among women undergoing LEEP conisation from January 2001 to December 2004. Results. Some 528 LEEP conisations were performed because of suspected or verified cervical dysplasia. On classified samples, cytology, punch biopsy and histopathology of the cone specimen showed cervical intraepithelial neoplasia (CIN)2 or a higher degree in 48.5, 36.2 and 58.6%, respectively. Sensitivity for HSIL out of cytology and colposcopically directed punch biopsy was 74.4 and 73.3%, respectively. Likewise, among 286 women with all 3 samples, positive and negative predictive value for HSIL in Papanicolaou (Pap) smear and punch biopsy was 78.5, 73.2% and 60.3, 63.6%, respectively. Positive cone margins were found in 16.8%. Residual/recurrent disease, defined as any grade of dysplasia at cytological follow‐up, was found among 9.4%. Significant risk for recurrent/residual disease was found among those with positive marginal status. Median time from colposcopy to conisation was 2 months. Conclusions. An immediate colposcopically‐guided LEEP conisation after HSIL Pap smear may be a safe and time saving strategy. Positive cone margins are a risk factor for residual/recurrent disease.