bluuebunny/crossref_metadata_2025 huggingface dataset:
Exact solutions with noncommutative symmetries in Einstein and gauge gravity
Authors: Vacaru Sergiu I.
Published: March 2005

We present new classes of exact solutions with noncommutative symmetries constructed in vacuum Einstein gravity (in general, with nonzero cosmological constant), five-dimensional (5D) gravity and (anti) de Sitter gauge gravity. Such solutions are generated by anholonomic frame transforms and parametrized by generic off-diagonal metrics. For certain particular cases, the new classes of metrics have explicit limits with Killing symmetries but, in general, they may be characterized by certain anholonomic noncommutative matrix geometries. We argue that different classes of noncommutative symmetries can be induced by exact solutions of the field equations in commutative gravity modeled by a corresponding moving real and complex frame geometry. We analyze two classes of black ellipsoid solutions (in the vacuum case and with cosmological constant) in four-dimensional gravity and construct the analytic extensions of metrics for certain classes of associated frames with complex valued coefficients. The third class of solutions describes 5D wormholes which can be extended to complex metrics in complex gravity models defined by noncommutative geometric structures. The anholonomic noncommutative symmetries of such objects are analyzed. We also present a descriptive account how the Einstein gravity can be related to gauge models of gravity and their noncommutative extensions and discuss such constructions in relation to the Seiberg–Witten map for the gauge gravity. Finally, we consider a formalism of vielbeins deformations subjected to noncommutative symmetries in order to generate solutions for noncommutative gravity models with Moyal (star) product.
Ab initio molecular dynamics of liquid hydrogen chloride
Authors: Dubois Vincent , Pasquarello Alfredo
Published: March 2005

We carried out an ab initio molecular dynamics simulation of liquid hydrogen chloride (ℓ-HCl) at a temperature of 313 K. Comparison with inelastic neutron scattering data shows that the simulation achieves an overall good description of the structural correlations, improving significantly upon a description based on classical interaction potentials. Despite some minor differences between theory and experiment in the H–H partial structure factor, the simulation gives a description of the hydrogen bonding in impressive agreement with experiment, for both the amount and the bond-length distribution of the bonds. In the simulation, 40% of the molecules are nonbonded, while the hydrogen-bonded chains are short, principally consisting of dimers (25%) and trimers (15%). Neighboring molecules in the simulation are found to form L-shaped arrangements, like in the isolated (HCl)2 dimer and in crystalline phases of HCl. The time correlation of the molecular-axis orientation is found to be characterized by a very short decay time (0.13 ps), consistent with the short length of the hydrogen-bonded chains. Other dynamical properties investigated in this work include the diffusion coefficient and the vibrational density of states. We evaluated the molecular dipole of the HCl molecule in the liquid using a definition based on the coupling of rotational modes to an external electric field. The average dipole moment (1.53 D) derived in this way is found to be considerably larger than for the isolated molecule (1.11 D). Our results show that the dipole moment in ℓ-HCl undergoes large fluctuations, both in orientation and in modulus. Upon the onset of an external field, such dipole fluctuations concur to reduce the fluctuations of the dielectric response.
Integral equations for heat kernel in compound media
Authors: Pirozhenko I. G. , Nesterenko V. V. , Bordag M.
Published: March 2005

By making use of the potentials of the heat conduction equation the integral equations are derived which determine the heat kernel for the Laplace operator −a2Δ in the case of compound media. In each of the media the parameter a2 acquires a certain constant value. At the interface of the media the conditions are imposed which demand the continuity of the temperature and the heat flows. The integration in the equations is spread out only over the interface of the media. As a result the dimension of the initial problem is reduced by 1. The perturbation series for the integral equations derived are nothing else as the multiple scattering expansions for the relevant heat kernels. Thus a rigorous derivation of these expansions is given. In the one dimensional case the integral equations at hand are solved explicitly (Abel equations) and the exact expressions for the regarding heat kernels are obtained for diverse matching conditions. Derivation of the asymptotic expansion of the integrated heat kernel for a compound media is considered by making use of the perturbation series for the integral equations obtained. The method proposed is also applicable to the configurations when the same medium is divided, by a smooth compact surface, into internal and external regions, or when only the region inside (or outside) this surface is considered with appropriate boundary conditions.
Dissipating the Langevin equation in the presence of an external stochastic potential
Authors: Moix Jeremy M. , Hernandez Rigoberto
Published: March 2005

In the Langevin formalism, the delicate balance maintained between the fluctuations in the system and their corresponding dissipation may be upset by the presence of a secondary, space-dependent stochastic force, particularly in the low-friction regime. In prior work, the latter was dissipated self-consistently through an additional uniform (mean-field) friction [T. Shepherd and R. Hernandez, J. Chem. Phys. 115, 2430 (2001).] An alternative approach to ensure that equipartition is satisfied relies on the use of a space-dependent friction while ignoring nonlocal correlations. The approach is evaluated with respect to its ability to maintain constant temperature for two simple one-dimensional, stochastic potentials of mean force wherein the friction can be evaluated explicitly when there is no memory in the barriers. The use of a space-dependent friction is capable of providing qualitatively similar results to those obtained previously, but in extreme cases deviations from equipartition may be observed due to the neglect of the memory effects present in the stochastic potentials.
Validation of the density-functional based tight-binding approximation method for the calculation of reaction energies and other data
Authors: Krüger Thomas , Elstner Marcus , Schiffels Peter , Frauenheim Thomas
Published: March 2005

We investigated the performance of the approximative density functional method DFTB versus BLYP and G2 with respect to zero-point corrected reaction energies, vibrational frequencies, and geometry parameters for a set of 28 reactions and 22 representative molecules containing C, H, N, and O (DFTB—density-functional based tight-binding approximation). The DFTB reaction energies show a mean absolute deviation versus the G2 reference of 4.3kcal∕mol only. The corresponding value for the vibrational frequencies amounts to 75cm−1 versus BLYP/cc-pVTZ. With very few exceptions bond lengths and angles are in excellent agreement with the results of higher-level methods.
Stretching a heteropolymer
Authors: Jarkova Elena , Vlugt Thijs J. H. , Lee Nam-Kyung
Published: March 2005

We study the elastic properties of single heteropolymers. By means of exact enumeration of conformations, Monte Carlo (MC) simulation, and variational principles, we calculate equilibrium force-extension curves of heterocopolymers for specific arrangements of the monomer types along the sequence. At a given extension z, the time averaged measured force is the weighted sum of restoring forces for various configurations. Using variational principles, we calculate force-extension (f-z) curves of heteropolymers with fixed extensions z. These results are compared with f-z curves obtained from MC simulations and exact enumeration of all conformations. Typical random sequences manifest several piecewise unfoldings of blocks of various size, which are overlapping due to thermal fluctuations. The shape of the elastic response of a heteropolymer reflects the disorder in the primary block structure and the binding energies of these blocks.
Homoclinic motions in the vibrational spectra of floppy systems: The LiCN molecule
Authors: Borondo F. , Vergini E. , Wisniacki D. A. , Zembekov A. A. , Benito R. M.
Published: March 2005

Recent experimental and theoretical methods allowed the efficient investigation of highly excited rovibrational states of molecular systems. At these levels of excitation the correspondence principle holds, and then classical mechanics can provide intuitive views of the involved processes. In this respect, we have recently shown that for completely hyperbolic systems, homoclinic motions, which are known to organize the classical chaotic region in Hamiltonian systems, imprint a clear signature in the corresponding highly excited quantum spectra. In this Communication we show that this result also holds in mixed systems, by considering an application to the floppy LiNC∕LiCN molecular system.
Two-spinor curvature structures for a class of conformally flat space–times
Authors: Cardoso J. G.
Published: March 2005

A well-known class of conformally flat space–times which admit decomposable Christoffel connexions is considered. It is shown that the corresponding spin-affine configurations can be constructed within the framework of Infeld–van-der-Waerden’s γ-formalism only if a specific constancy property is imposed on one of the densities borne by the expression for a typical metric function. Explicit expressions for the gravitational spinors of those space–times are then derived.
Transient complex oscillations in a closed chemical system with coupled autocatalysis
Authors: Zhao Jinpei , Chen Yu , Wang Jichang
Published: March 2005

In this study, hydroquinone was introduced to the classic Belousov–Zhabotinsky (BZ) reaction to build up coupled autocatalytic feedbacks. Various complex dynamical behaviors including successive period-adding bifurcations, irregular oscillations, and frequency modulations were observed in the coupled reaction system. Not only the complexity of oscillations but also the time period during which complex oscillations persist were found to depend greatly on the initial concentration of hydroquinone, which was expected to manifest the coupling strength in the studied system. Dependence of the observed transient complex oscillations on concentrations of ferroin, sulfuric acid, bromate, and malonic acid was also characterized systematically. Numerical simulations with a modified BZ model via incorporating reactions involving hydroquinone and products of hydroquinone qualitatively reproduced the influence of hydroquinone seen in experiments.
Dielectric properties of A- and B-site-doped BaTiO3(I):La- and Al-doped solid solutions
Authors: Bobade S. M. , Gulwade D. D. , Kulkarni A. R. , Gopalan P.
Published: March 2005

Extremely small amounts of La and Al doping on the A and B site of BaTiO3, respectively, resulting in a solid solution of the type Ba1–3xLa2xTi1–3xAl4xO3 have been investigated. The compositions have been prepared by the Pechini process. The x-ray diffraction (XRD) reveals the presence of tetragonal (P4∕mmm) phase. The XRD data has been analyzed using FULLPROF, a Rietveld refinement package. The compositions have been characterized by dielectric spectroscopy between room temperature and 200°C. The resulting compounds (0⩽x⩽0.008) exhibit a remarkable decrease in the Curie temperature as well as a significant enhancement of the dielectric constant.
Current noise spectra of Schottky barrier diodes with electron traps in the active layer
Authors: Pérez S. , González T.
Published: March 2005

We present a microscopic analysis of current fluctuations in a GaAs n+-n-metal Schottky barrier diode containing electron traps in the active layer. An ensemble Monte Carlo simulation is used for the calculations. We analyze the influence of generation-recombination mechanisms of electrons with traps on the current–voltage characteristics and noise spectra of the diode. The presence of traps reduces both the flatband voltage and the current level in the series-resistance regime. With respect to the noise, significant modifications are observed in the current noise spectra. In the barrier-limited regime, while at low-frequency shot noise is not found to change, the returning-carriers peak is strongly modulated by the influence of the traps. Beyond flatband conditions generation-recombination noise becomes evident at low frequency, exhibiting a quadratic dependence on the current.
Dirichlet series and the integrability of multilinear differential equations
Authors: Pickering A. , Prada J.
Published: March 2005

We explore the relationship between the integrability of nonsemilinear partial differential equations and formal Dirichlet series solutions. To this end we consider a variety of integrable and nonintegrable differential equations. We also demonstrate that such series solutions are a natural extension to the nonlinear case of those obtained by basic solution techniques for linear ordinary differential equations.
New analysis for determination of hemispherical total emissivity by feedback-controlled pulse-heating technique
Authors: Watanabe Hiromichi , Matsumoto Tsuyoshi
Published: March 2005

A new analysis for the determination of hemispherical total emissivity has been developed on electrically conductive materials under a brief steady-state established by a feedback-controlled pulse-heating technique. The new analysis is based on an equation describing a more realistic situation of the thermal balance of the sample during the “apparently” static period. The dependency of sample temperature on time and space during the apparently static period is necessary in carrying out the new analysis, and is semiempirically estimated using experimental results for the electrical resistivity of the sample as a function of time. The new analysis was applied to the determination of the emissivity of molybdenum at temperatures beyond 1500 K. Contrary to the general expectation, the emissivity derived by the new analysis, which takes conductive heat loss into account, is systematically larger than that derived by the previous analysis, which neglects the heat loss. The deviation between the new and previous analyses is explained in terms of five factors. The dominant factor is associated with the decrease in the average temperature of the sample during the apparent temperature plateau and cannot be neglected even at the beginning of the apparently static period. The emissivity determined on molybdenum by the new analysis is in good agreement with the literature data obtained by two different methods.
Liquid-nitrogen-jet laser-plasma source for compact soft x-ray microscopy
Authors: Jansson P. A. C. , Vogt U. , Hertz H. M.
Published: March 2005

We describe a liquid-nitrogen-jet laser-plasma source with sufficient brightness, uniformity, stability, and reliability to be suitable for compact water-window soft x-ray transmission microscopy. A cooled capillary nozzle arrangement allows long-term operation and avoids previously reported jet instabilities. The source is quantitatively characterized by calibrated slit-grating spectroscopy and zone-plate imaging. The absolute photon number in the major spectral lines (λ=2.48nm and λ=2.88nm) is 1.0×1012photons∕(pulse×sr×line). The source diameter is ∼20μm (full width at half maximum) and the spatial stability is better than ±2μm. Within an area with uniformity of 20%, the average source brightness is 4×108photons∕(pulse×sr×μm2×line), which allows operation of a compact soft x-ray transmission microscope with exposure times of a few minutes.
Applications of quartz tuning forks in spectroscopic gas sensing
Authors: Kosterev Anatoliy A. , Tittel Frank K. , Serebryakov Dmitry V. , Malinovsky Alexander L. , Morozov Igor V.
Published: March 2005

A recently introduced approach to photoacoustic detection of trace gases utilizing a quartz tuning fork (TF) as a resonant acoustic transducer is described in detail. Advantages of the technique called quartz-enhanced photoacoustic spectroscopy (QEPAS) compared to conventional resonant photoacoustic spectroscopy include QEPAS sensor immunity to environmental acoustic noise, a simple absorption detection module design, and its capability to analyze gas samples ∼1mm3 in volume. Noise sources and the TF properties as a function of the sampled gas pressure, temperature and chemical composition are analyzed. Previously published results for QEPAS based chemical gas sensing are summarized. The achieved sensitivity of 5.4×10−9cm−1W∕√Hz is compared to recent published results of photoacoustic gas sensing by other research groups. An experimental study of the long-term stability of a QEPAS-based ammonia sensor is presented. The results of this study indicate that the sensor exhibits very low drift, which allows data averaging over >3h of continuous concentration measurements. Architecture and practical implementation of autonomous QEPAS-sensor controller electronics is described. Future developments of QEPAS technique are outlined.
A simple transfer-optics system for an extreme-ultraviolet synchrotron beamline
Authors: Tarrio C. , Grantham S. , Vest R. E. , Liu K.
Published: March 2005

Radiometric experiments often require comparatively high intensities in the extreme ultraviolet, in the microwatt range. The monochromators that provide the high throughput needed for these experiments, though, do not always allow for end stations to be switched out easily. At the National Institute of Standards and Technology Synchrotron Ultraviolet Radiation Facility, the only beamline with sufficient extreme-ultraviolet power has a multi-ton endstation, which cannot be moved. We will describe a set of transfer optics that allow the photon beam to be collimated and deflected through a port on the downstream end of the large chamber. This allowed an absolute cryogenic radiometer to be attached, with the entrance cavity underfilled. We will describe ray-tracing results and offer preliminary results of the radiometer-based throughput of the system.
InN polarity determination by convergent-beam electron diffraction
Authors: Mitate Toshitsugu , Mizuno Seiichiro , Takahata Hiroko , Kakegawa Ryu , Matsuoka Takashi , Kuwano Noriyuki
Published: March 2005

To establish an accurate determination technique for the polarity of InN by convergent-beam electron diffraction (CBED), we clarified the influence of the electron incidence direction, film thickness, and the temperature factor B on CBED patterns by simulation. The electron incidence direction of [11¯00] and a film thinner than 50nm were found to be preferable for easy and reliable polarity determination. Using an InN film grown on a (0001¯) GaN template on (0001) sapphire by metalorganic vapor-phase epitaxy, observation of the CBED pattern in the thin region of the film was confirmed from the simulation result. This InN film was clearly determined to have N polarity and the value of B was estimated to be less than 2.0Å2.
Direct observation of a pure focused evanescent field of a high numerical aperture objective lens by scanning near-field optical microscopy
Authors: Jia Baohua , Gan Xiaosong , Gu Min
Published: March 2005

Intensity distributions of a tightly focused evanescent field generated by a center blocked high numerical aperture (1.65) objective lens are investigated by a scanning near-field optical microscope. The pure focused evanescent field is mapped and a splitting phenomenon of the focal spot along the direction of polarization, caused by depolarization, is observed not only on the interface, where the evanescent field is generated, but also in the parallel planes away from the interface. The decaying nature of the focused evanescent field shows good agreement with the theoretical predication, indicating that the field is purely evanescent and does not contain a significant contribution from the propagating component. It is found in our experiment that the light coupling efficiencies of the longitudinal polarization component Ez and the transverse polarization component Ex to the fiber probe differ by a factor of 3.
Effect of the misalignment between the applied and internal magnetic fields on the critical currents of “tilted coated conductors”
Authors: Maiorov B. , Gibbons B. J. , Kreiskott S. , Matias V. , Holesinger T. G. , Civale L.
Published: March 2005

We present angular-dependent measurements of the critical current density (Jc) of a YBa2Cu3O7 film grown on tilted buffered Ion-Beam-Assisted-Deposition MgO metal tapes. We compare samples with the current parallel and perpendicular to the tape’s direction. In samples with the current parallel to the tape, we observe an asymmetric angular dependence of Jc and a shift of the ab-planes maxima position with the magnetic field strength. The shift is a result of the misalignment between the applied and internal magnetic fields. The misalignment effect takes place at fields lower than 3T at T=75.5K. For samples with the current perpendicular to the tape, we find an overall reduced value of Jc, the angular behavior is symmetrical, and no shift in the maxima position as a function of the magnetic field is observed. These results indicate that the effect of misalignment between the applied and internal magnetic fields must be taken into account when studying the angular dependence of Jc.
White-light emission from organics-capped ZnSe quantum dots and application in white-light-emitting diodes
Authors: Chen Hsueh Shih , Wang Shian Jy Jassy , Lo Chun Jeu , Chi Jim Yong
Published: March 2005

Organics-capped ZnSe quantum dots were synthesized by a colloidal chemical approach using ZnO and Se powder as precursors. The photoluminescence of the specimens showed strong white emission (∼200nm full width at half maximum) in the visible range under ambient conditions. The white emission was attributed to the mixing of blue emission of ZnSe nanocrystals exhibiting quantum confinement effect with green-red emission of radiative deep levels from ZnSe surface strained lattice. Based on organic-capped ZnSe quantum dots, the white-light-emitting diodes were fabricated using a near-UV InGaN chip as the excitation source. The diodes emitted white light with CIE chromaticity coordinates of (0.38 and 0.41) and show great potential for use in lighting applications.
Changes of magnetic domain structure induced by temperature-variation and electron-beam irradiation in Pr0.5Sr0.5CoO3
Authors: Uchida M. , Mahendiran R. , Tomioka Y. , Matsui Y. , Ishizuka K. , Tokura Y.
Published: March 2005

In situ observation of magnetic domain structures of Pr0.5Sr0.5CoO3 was made by Lorentz electron microscopy to reveal an unusual magnetic behavior around 120K below the Curie temperature (TC∼220K). The observations in a cooling run clearly showed that the magnetic domain structure changes below about 90K and that the transformed domain structure remains unchanged down to 20K. Furthermore, it was found that an electron-beam irradiation in an electron microscope induces a reversible transformation of the magnetic domain structure at 20K. Possible mechanisms of such magnetic-domain structural changes are discussed.
Electrical spin pumping of quantum dots at room temperature
Authors: Li C. H. , Kioseoglou G. , van ’t Erve O. M. J. , Ware M. E. , Gammon D. , Stroud R. M. , Jonker B. T. , Mallory R. , Yasar M. , Petrou A.
Published: March 2005

We report on electrical control of the spin polarization of InAs∕GaAs self-assembled quantum dots (QDs) at room temperature. This is achieved by electrical injection of spin-polarized electrons from an Fe Schottky contact. The circular polarization of the QD electroluminescence shows that a 5% electron spin polarization is obtained in the InAs QDs at 300K, which is remarkably insensitive to temperature. This is attributed to suppression of the spin-relaxation mechanisms in the QDs due to reduced dimensionality. These results demonstrate that practical regimes of spin-based operation are clearly attainable in solid-state semiconductor devices.
Impact of interface structure on Schottky-barrier height for Ni∕ZrO2(001) interfaces
Authors: Dong Y. F. , Wang S. J. , Chai J. W. , Feng Y. P. , Huan A. C. H.
Published: March 2005

The Schottky-barrier heights for the Ni and ZrO2 interfaces have been determined using the x-ray photoemission method. Depending on the surface treatment of ZrO2, the variation of Schottky-barrier heights at Ni∕ZrO2 interfaces was found as large as 0.76±0.10eV. The p-type Schottky-barrier height for the oxygen-rich (oxygen-deficient) interface was measured to be 2.60eV (3.36eV). First-principles calculations provide a microscopic explanation of such variation, which was attributed to the different interface dipole formed by interfacial Ni–O, Ni–Zr bonds, or oxygen vacancies.
Low dose ionizing radiation detection using conjugated polymers
Authors: Silva E. A. B. , Borin J. F. , Nicolucci P. , Graeff C. F. O. , Netto T. Ghilardi , Bianchi R. F.
Published: March 2005

In this work, the effect of gamma radiation on the optical properties of poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) is studied. The samples were irradiated at room temperature with different doses from 0Gyto152Gy using a Co60 gamma ray source. For thin films, significant changes in the UV-visible spectra were only observed at high doses (>1kGy). In solution, shifts in absorption peaks are observed at low doses (<10Gy), linearly dependent on dose. The shifts are explained by conjugation reduction, and possible causes are discussed. Our results indicate that MEH-PPV solution can be used as a dosimeter adequate for medical applications.
Enhancement of hole injection using iridium-oxide-coated indium tin oxide anodes in organic light-emitting diodes
Authors: Kim Soo Young , Lee Jong-Lam , Kim Ki-Beom , Tak Yoon-Heung
Published: March 2005

We report the enhancement of hole injection using an IrOx layer between indium tin oxide anodes and 4,4’-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl in organic light-emitting diodes (OLEDs). The turn-on voltage of OLEDs decreased from 7V to 4V and the maximum luminescence value increased from 1200cd∕m2 to 1800cd∕m2 as the Ir layer changed to IrOx by surface treatment using O2 plasma. Synchrotron radiation photoelectron spectroscopy results showed that the work function increased by 0.6eV as the Ir layer transformed into IrOx. Thus, the hole injection energy barrier was lowered, reducing the turn-on voltage and increasing the quantum efficiency of OLEDs.
Spin on dopants for high-performance single-crystal silicon transistors on flexible plastic substrates
Authors: Zhu Z.-T. , Menard E. , Hurley K. , Nuzzo R. G. , Rogers J. A.
Published: March 2005

Free-standing micro/nanoelements of single-crystal silicon with integrated doped regions for contacts provide a type of material that can be printed onto low-temperature device substrates, such as plastic, for high-performance mechanically flexible thin-film transistors (TFTs). We present simple approaches for fabricating collections of these elements, which we refer to as microstructured silicon (μs-Si), and for using spin-on dopants to introduce doped regions in them. Electrical and mechanical measurements of TFTs formed on plastic substrates with this doped μs-Si indicate excellent performance. These and other characteristics make the material potentially useful for emerging large area, flexible ‘macroelectronic’ devices.
Photorefractivity of Hafnium-doped congruent lithium–niobate crystals
Authors: Razzari Luca , Minzioni Paolo , Cristiani Ilaria , Degiorgio Vittorio , Kokanyan Edvard P.
Published: March 2005

Transient and steady-state measurements of photoinduced birefringence in Hf-doped congruent lithium–niobate crystals are presented. Through a systematic investigation of crystals with different dopant concentrations, we find that Hf doping induces a progressive decrease of photorefraction up to a threshold concentration of about 4 mol %. Such a decrease is correlated to a corresponding increase in photoconductivity. The interpretation of measurements has to take into account heating effects that may be attributed to nonlinear absorption processes.
Optoacoustic imaging using thin polymer étalon
Authors: Ashkenazi Shai , Hou Yang , Buma Takashi , O’Donnell Matthew
Published: March 2005

Optical detection of ultrasound is a promising technique for high frequency imaging arrays. Detection resolution approaches the optical resolution, which can be on the order of the optical wavelength. We describe here an optical technique for ultrasound detection based on a thin (10μm) Fabry–Perot étalon optimized for high resolution imaging. The signal to noise ratio (SNR) approaches that of an ideal piezoelectric transducer over a 100MHz bandwidth. Array functionality is demonstrated by scanning a probe beam along a line. Thermoelastic excitation was applied to generate acoustic waves in a test phantom containing a single “pointlike” source. An image of the source was reconstructed using signals acquired from the étalon detector array.
Effect of triggered discharge using an excimer laser with high-repetition-rate of the order of kilohertz
Authors: Yamaura Michiteru , Watanabe Takashi , Hayashi Nobuya , Ihara Satoshi
Published: March 2005

The triggering ability of the laser-triggered lightning method is improved by using a KrF excimer laser with a high-repetition-rate of the order of kHz order. It is clarified that the effect of a triggered discharge is considerably enhanced when the plasma density is greater than 1013cm−3. Thus far, the laser-triggered lightning method has not been expected to display a triggering ability since one pulse of an excimer laser possesses energy of less than 1J, and the produced plasma has a low density of 1012cm−3, its plasma density is one order lower than that required for its application in the triggering and guiding of lightning discharge. The enhancement of plasma density achieved by utilizing the accumulation effect of charged particles generated by the high-repetition-rate laser was 1013cm−3. This led to an effective a 50% reduction in the self-breakdown voltage.
GaInAs∕AlGaAsSb quantum-cascade lasers
Authors: Yang Q. , Manz C. , Bronner W. , Kirste L. , Köhler K. , Wagner J.
Published: March 2005

Quaternary-barrier-containing GaInAs∕AlGaAsSb quantum-cascade lasers, motivated by reducing the barrier height compared to that in GaInAs∕AlAsSb quantum-cascade lasers, have been demonstrated. The design of these quaternary-barrier-containing lasers is based on triple-quantum-well vertical-transition active regions, and their fabrication relies on molecular-beam-epitaxial growth of Ga0.47In0.53As∕AlGaAs1−xSbx (x close to 0.45) heterostructures on n-InP substrates. Including twenty-five periods of active regions and injection regions, the quantum-cascade lasers operate up to T⩾400K in pulsed mode, with an emission wavelength of about 4.9 μm at room temperature. The characteristic temperature T0 of the threshold current density is 169 K in the temperature range between 280 and 400 K.
Rethinking Change in Old Industrial Regions: Reflecting on the Experiences of North East England
Authors: Hudson Ray
Published: March 2005

The author reflects upon regional economic change and the ways in which this is conceptualised and understood, drawing heavily but not exclusively on some thirty years of research on economy, politics and society in the North East of England. The principal question that this paper addresses is: how are the long periods of continuity, punctuated by occasional major shifts in developmental trajectory and the region's place in the global economy, to be understood? The author seeks to answer this question by exploring the extent to which continuity and change in the region's developmental trajectory can be understood in terms of evolutionary and institutional concepts and the varying engagement of the state with issues of socioeconomic development and change. The value of theoretical plurality in seeking to understand uneven development in capitalism is demonstrated and the limits to public policies that seek to address regional problems indicated.
Rethinking Innovation: Context and Gender
Authors: Blake Megan K , Hanson Susan
Published: March 2005

Geographers have a keen interest in innovation because of its connection to regional economic advantage. We argue that, to date, understandings of innovation are predominantly technological and product driven and defined in universal terms such that the nature of innovation is stripped of its contextual influence and is overly masculinist. Through combined analysis of interview material from two complementary studies on the gendering of entrepreneurship based in the United States, this paper challenges current conceptualisations of innovation within geography. We show how the context, both social and geographical, of an innovation is elementary to its identification as innovative. Moreover, we reveal some of the many instances of innovation that occur in economic sectors and by agents that are typically ignored or undervalued by current research and by policy. Our analysis challenges researchers and policymakers to expand their concepts of regional and urban development beyond those processes associated with technologically defined and growth-oriented originality, such that notions of local development may enhance the social well-being of places and be more gender inclusive.
Global influences on rangelands of Australia
Authors: Robertson G. A.
Published: March 2005

Globalisation is a key pressure affecting the current and future use of the rangelands of Australia. While primary producers often perceive an insatiable demand for food as a guarantee of business success, declining population growth rates and high levels of productivity improvement in world food production are reducing the importance of food and fibre from the rangelands. This, combined with significant changes in consumer demands, is driving rangeland producers to meet market specifications for quality, safety, animal welfare and sustainability.
Sustainability is a particular challenge with the rangelands certain to be affected by global warming and the politics and strategies required to reduce greenhouse gas emissions. Currently the rangelands produce a higher proportion of greenhouse gases compared with their contribution to the economy. However, they also provide an opportunity for carbon sequestration.
While international trade liberalisation has been of advantage to the grazing industries in the rangelands, increased global awareness of the Australian rangelands, facilitated by the communications revolution, is encouraging alternative uses including tourism, existence value and other conservation and biodiversity management uses. The growing concept of multi-functionality will also impact on the rangelands as international government programmes continue to encourage non-commercial, surplus production of food.
These influences are forcing major changes in the way land is used and what it produces.
Are miners the bunnies or the bilbies of the rangelands?
Authors: Read J. L.
Published: March 2005

In order to be preferred land-users of the Australian rangelands, mining operations should legacy net environmental, social and economic benefits in the regions that they operate. The positive and negative environmental implications of the Olympic Dam mine in arid South Australia are compared in this study. Criteria assessed include the relative area of affected v. improved landscape, environmental research, pest control and the facilitation of proactive conservation and sustainable diversification outcomes. A call is made for consistent treatment of potential environmental impacts across all rangeland users and the adoption of biodiversity trading to improve regional conservation outcomes. A challenge is issued to miners and other rangeland land-users to demonstrate that, like bilbies, their net environmental effects are beneficial.
Opportunities for the future in Australia's grazed rangelands
Authors: Hunt L. P.
Published: March 2005

The importance, use and management of Australia's grazed rangelands are being questioned. Financial returns from pastoralism have declined for some and there is increasing interest in alternative land uses. There are also concerns for the protection of natural resources and the conservation of biodiversity. As a result many rangeland users and residents consider that the pastoral rangelands are at a point when substantial and radical change in the way they are used, administered and managed must be implemented. One perspective on the future values the rangelands for all natural resource values that provide sustainable incomes for its residents, strives for more integrated natural resource management, involves the development of more tightly integrated regional economies, and facilitates an increased influence of local communities in guiding land use in their regions. These changes offer many opportunities for individual sectors and for cross-sectoral benefits, cooperation and integration. They offer truly complementary options for future use, although there are still likely to be conflicts over land use. To realise these opportunities will require legislative reform, improved knowledge and skills in pastoralists, legislators and advisers, and better planning processes that engage all stakeholders, set appropriate targets, have land capability as a basis for land use decisions and provide for satisfactory conflict resolution. An understanding of the ecological and economic implications of a new mix of land uses is also required.
The germinable soil seedbank of Eucalyptus victrix grassy woodlands at Roy Hill station, Pilbara district, Western Australia
Authors: Graham R. A. , Florentine S. K. , Fox J. E. D. , Luong T. M.
Published: March 2005

The paper reports soil seedbank species composition, of Eucalyptus victrix grassy woodlands, of the upper Fortescue River in the Pilbara District, Western Australia. In this study, our objectives were to investigate germinable soil seedbanks and species composition in response to three simulated seasons, using emergence.
Variation in seed density from three depths was tested. Four field sites were sampled. Thirty samples were collected in late spring, after seed rain and before summer rainfall. From each sample spot, three soil depths (surface, 1–5, and 6–10 cm) were segregated from beneath surface areas of 100 cm2. Samples were later incubated in a glasshouse to simulate three different seasonal conditions (autumn, winter and spring). Germinating seedlings were recorded on emergence and grown until identified.
Forty-one species germinated, comprising 11 grasses (7 annuals and 4 perennials), 25 annual herbs and 5 perennial herbs. Distribution patterns of germinable seed in both the important annual grass Eragrostis japonica and the perennial Eragrostis setifolia (a preferred cattle fodder species), suggest that seedbank accumulation differs among species and between sites. In part, this may be associated with the absence of grazing. Species with most total germinable seed were E. japonica (Poaceae; 603/m2), and the annual herbs Calotis multicaulis (Asteraceae; 346/m2), and Mimulus gracilis (Scrophulariaceae; 168/m2). Perennial grass seed was sparse. Spring simulation gave most germination (1059), followed by autumn (892) and winter (376) sets. Greatest species diversity was produced from the spring simulation (33 species), followed by autumn (26), and winter (22). Of the total germination, 92% came from 17 species that were represented in all three simulations. Of the 1227 grass seedlings counted, most were recruited from the surface soil (735), followed by the 5 (310) and 10 (182) cm depths. Marginally more grass seedlings germinated from the spring simulation (558) than the autumn set (523). Only 11.9% of grass germinants came from the winter simulation. All grass species recruited from the soil seedbanks had a C4 photosynthetic pathway. Except for Cenchrus ciliaris all grass species are native to Australia. Of the four sites sampled, one fenced to exclude cattle five years earlier had significantly more germination than the three unfenced sites. Seedbank sampling produced several new records for plants in the areas sampled.
An economic assessment of the impact of grazing land condition on livestock performance in tropical woodlands
Authors: MacLeod N. D. , Ash A. J. , McIvor J. G.
Published: March 2005

Beef cattle grazing is the dominant economic use of the tropical woodlands of northern Australia. Land condition has declined over a large part of the region as a result of over-utilisation of pastures through poor management of grazing, fire and vegetation. While often assumed to be the case, there is little empirical evidence to support a link between deteriorating land condition and reduced economic outcomes for livestock production. A model of a representative livestock enterprise near Charters Towers in northern Queensland is used in conjunction with a simulation of 100 trials that is consistent with long-term rainfall in the region to examine the relationship between stocking rates, animal production and economic outcomes.
The present study supports a view that ecological and economic outcomes of grazing management do have some general linkages. However, the linkages are less direct than suggested by common definitions of resource degradation and simple stocking rate models. Key economic parameters include the reproductive performance of breeding herds, the level and duration of supplementary feeding required to meet seasonal feed shortages under different land condition and stocking rate regimes, and additional capital invested in larger herds when stocking rates are increased. An overgrazing spiral is hypothesised whereby there is a short-term economic incentive to exploit the natural capital of land in good condition by grazing at relatively high stocking rates. Should land condition deteriorate, a much lower stocking rate is warranted. In an extreme case of a shift to very poor land condition, there is limited scope for profitable production.
The 100 year mean values of many production variables for good and moderate condition land for the range of stocking rates trialled are similar. The inherent variation in climatic conditions in the woodlands region and the ability and skills of managers may lead to the actual differences in these measures passing un-noticed before major land resource problems become apparent.
Native couch grasses for revegetating severely salinised sites on the inland slopes of NSW
Authors: Semple W. S. , Cole I. A. , Koen T. B.
Published: March 2005

Two scalded saline sites on the inland slopes of NSW were selected for an evaluation of ten accessions of warm-season stoloniferous/rhizomatous grass species: common couch (Cynodon dactylon), marine couch (Sporobolus virginicus), rats-tail couch (S. mitchellii), salt-water couch (Paspalum vaginatum), water couch (P. distichum) and one exotic, kikuyu (Pennisetum clandestinum). Most species performed well at Wagga Wagga but only common couch, marine couch and salt-water couch did at Manildra, where they consistently outperformed the other native species in terms of survival, groundcover and vigour. Salt-water couch had the highest mean vegetative cover at both sites. Differences in salinity, pH (acid cf. alkaline) and particularly topsoil moisture probably accounted for differing plant performances at the two sites. In a follow-up production study of the most successful accessions under relatively dry conditions at Manildra, the 'Yamba' accession of marine couch consistently produced more leaf/seedhead dry matter (1057 � 172 kg/ha) during the growing season than the others. However, salt-water couch consistently produced more ex-plot stolon/rhizome dry matter (974 � 127 kg/ha) than the other two species. This probably explained its ability, unlike marine couch, to maintain groundcover during a regime of regular cutting. Further evaluation under grazing and recreational uses is recommended. The genetic material evaluated was only a small sample of salt-tolerant native grasses. The variable performance of the four accessions of rats-tail couch, for example, suggested that more salt-tolerant types are likely to be found.
Persistence of dead trees and fallen timber in the arid zone: 76 years of data from the T.G.B. Osborn Vegetation Reserve, Koonamore, South Australia
Authors: Sinclair R.
Published: March 2005

Very little information is available about how long dead trees remain standing, or fallen logs persist, in the Australian arid zone. Data on dead timber longevity were extracted from records of both permanent quadrats and photopoints on the T.G.B. Osborn Vegetation Reserve on Koonamore Station, South Australia. Two species were examined, Acacia aneura (mulga) and Myoporum platycarpum (false sandalwood, sugarwood). Some individuals of mulga are capable of standing dead for over 75 years, while dead M. platycarpum may stand for over 60 years. Dead Myoporum trees remained standing for an average of 31.2 � 5.7 years, fallen trunks persisted for 38.4 � 3.7 years. Standing dead A. aneura persisted on average for 40.0 � 3.7 years, fallen trunks for 22.4� 6.3 years. These figures are almost certainly underestimates. The reasons why are discussed and some comparisons made with temperate forests and tropical mangroves.
Observations on survival and early growth of natural regeneration in floodplain coolibah Eucalyptus victrix (Myrtaceae) in the Pilbara, Western Australia
Authors: Fox J. E. D. , Florentine S. K. , Westbrooke M. E. , Hurst C.
Published: March 2005

Observations are presented on the natural regeneration of Eucalyptus victrix L. Johnson and K. Hill (coolibah), the dominant tree species of grassy woodlands on the floodplain of the Fortescue River, north of Newman in the Pilbara district of Western Australia. The main objectives of this study were to examine: (i) survival of newly recruited E. victrix seedlings on flooded and burnt sites, and (ii) growth and survival of established plants in a gilgaied landscape. Populations of newly-recruited seedlings following flooding or fire were monitored opportunistically at 'Marillana' and 'Ethel Creek' stations, for up to two years from tagging. A population of saplings at 'Roy Hill' station was observed over eight years.
Seedling densities of E. victrix in flooded sites were 0.32 and 1.03 plants/m2 in 1995 and 1997 respectively. Locally high densities reached from 1.2 to 17.7 plants/m2 on areas of 28 and 6 m2 respectively. At the burnt site at 'Ethel Creek', 1.30 plants/m2 were observed where 58 seedlings were recorded on an area of 445 m2 a year after a natural fire. Many of these persisted well into their second year, whereas seedlings recruited in the flooded sites generally lasted less than a year (250-376 days). In contrast, persistence of a cohort of 100 established saplings < 2 m tall in a gilgaied landscape at 'Roy Hill' was high. During 8 years of observations, only one sapling was lost. Those found at the edges of gilgais had attained greater heights (3.91 � 1.14 m) than saplings located inside (3.16 � 0.95 m) or on top (3.12 � 0.93 m) of the gilgais.
This study demonstrates that the seedling stage in E. victrix is critical, in that once newly recruited individuals reach the sapling stage (0.611 m), mortality rates are much reduced. Unfortunately, it was not possible during the course of this study to locate a cohort of young seedlings that did survive and so any consideration of the conditions necessary for their survival is purely speculative.