bluuebunny/crossref_metadata_2025 huggingface dataset:
D and E region incoherent scatter radar density measurements over Jicamarca
Authors: Chau Jorge L. , Woodman Ronald F.
Published: December 2005

We present the first daytime E and D region incoherent scatter radar (ISR) measurements of electron densities at equatorial latitudes, using the Jicamarca ISR. Both measurements have been obtained using a high‐resolution ISR mode with a relatively short interpulse period. Usually, E region ISR measurements are not feasible due to the clutter caused by strong echoes from equatorial electrojet irregularities (EEJ). Our E region ISR measurements were possible during an event when EEJ echoes were absent and show an excellent agreement with an empirical model based on rockets measurements (FIRI). In addition, we show that the employed high resolution mode also works to get densities between 130 and 200 km even during strong EEJ events, a region that is poorly known. In the case of D region densities, normally they are difficult to obtain due to the presence of strong coherent echoes caused by mesospheric turbulent layers. Fortunately, these layers are usually organized in narrow regions; therefore using a high range resolution, we have been able to get weak signals from the regions in between the layers causing coherent echoes. Our preliminary results show that our D region density estimates are in reasonable agreement with empirical models, in some cases providing slightly larger values. These new D region estimates contain important geophysical information that we plan to explore in the future.
Simulation of the probability of midair interparticle collisions in an aeolian saltating cloud
Authors: Dong Zhibao , Huang Ning , Liu Xiaoping
Published: December 2005

Midair interparticle collisions in aeolian saltation are generally neglected because they are considered to be rare. A theoretical simulation model was developed to calculate the probability of these collisions for uniform‐sized sand. The collision probabilities during the ascending and descending stages and during the whole saltation process are calculated for saltating particles with different liftoff velocities and at different free‐stream wind velocities on the basis of data for particle concentrations in the saltating cloud. The collision probability is also calculated on the basis of the probability distribution for liftoff velocities. The calculated probabilities reveal that midair collisions should not be neglected. They increase in frequency with increasing free‐stream wind velocity and liftoff velocity and are nearly inevitable at high wind velocity. The collision probability is greater during the descending stage than during the ascending stage. Steady state saltation is maintained by feedback between the air stream and the saltating particles and between surface impacts and midair collisions. Increased surface impacts increase sand transport and the probability of midair collisions, but increased midair collisions may reduce surface impacts and sand transport. The feedback between surface impacts and midair collisions becomes more significant as wind velocity and sand transport increase.
Catastrophic flooding from an orographic thunderstorm in the central Appalachians
Authors: Hicks Naomi S. , Smith James A. , Miller Andrew J. , Nelson Peter A.
Published: December 2005

An orographic thunderstorm system in Pendleton County, West Virginia, produced 125–150 mm of rainfall in less than 1 hour on 9 August 2003. Rainfall and fluvial impacts were concentrated in the ungauged 2.1 km2 Saul's Run watershed. Despite the short duration of the event the flood produced significant fluvial impacts and abrupt changes in the extent of incision and channel widening. Hydrometeorological analyses of the storm are based on WSR‐88D radar reflectivity observations and rain gauge observations. The small multicell thunderstorms that produced the Saul's Run flood were not markedly different from other storms in the central Appalachian region on 9 August 2003. Detailed surveys of high watermarks and channel/floodplain geometry are used for hydraulic analyses of the Saul's Run flood, including estimation of peak discharge at four locations. Peak discharge estimates at the 1 km2 scale cluster around 18 m3 s−1, placing this event on the flood envelope curve for the mid‐Atlantic region. Observed rainfall, estimated peak discharge, and observer notes on timing of peak discharge are used along with a distributed hydrologic model to reconstruct hydrographs at multiple locations. Hydrologic modeling indicates that land use effects may have significantly influenced extreme flood response in Saul's Run. The wide range of fluvial impacts is consistent with patterns of boundary shear stress and unit stream power derived from a simulation of the Saul's Run flood using a 2‐D depth‐averaged hydraulic model.
Ensemble predictions of runoff in ungauged catchments
Authors: McIntyre Neil , Lee Hyosang , Wheater Howard , Young Andy , Wagener Thorsten
Published: December 2005

A new approach to regionalization of conceptual rainfall‐runoff models is presented on the basis of ensemble modeling and model averaging. It is argued that in principle, this approach represents an improvement on the established procedure of regressing parameter values against numeric catchment descriptors. Using daily data from 127 catchments in the United Kingdom, alternative schemes for defining prior and posterior likelihoods of candidate models are tested in terms of accuracy of ungauged catchment predictions. A probability distributed model structure is used, and alternative parameter sets are identified using data from each of a number of gauged catchments. Using the models of the 10 gauged catchments most similar to the ungauged catchment provides generally the best results and performs significantly better than the regression method, especially for predicting low flows. The ensemble of candidate models provides an indication of uncertainty in ungauged catchment predictions, although this is not a robust estimate of possible flow ranges, and frequently fails to encompass flow peaks. Options for developing the new method to resolve these problems are discussed.
Identification of preferred protein interactions by phage‐display of the human Src homology‐3 proteome
Authors: Kärkkäinen Satu , Hiipakka Marita , Wang Jing‐Huan , Kleino Iivari , Vähä‐Jaakkola Marika , Renkema G Herma , Liss Michael , Wagner Ralf , Saksela Kalle
Published: December 2005

We have determined the human genome to contain 296 different Src homology‐3 (SH3) domains and cloned them into a phage‐display vector. This provided a powerful and unbiased system for simultaneous assaying of the complete human SH3 proteome for the strongest binding to target proteins of interest, without the limitations posed by short linear peptide ligands or confounding variables of more indirect methods for protein interaction screening. Studies involving three ligand proteins, human immunodeficiency virus‐1 Nef, p21‐activated kinase (PAK)2 and ADAM15, showed previously reported as well as novel SH3 partners with nanomolar affinities specific for them. This argues that SH3 domains may have a more dominant role in directing cellular protein interactions than has been assumed. Besides showing potentially important new SH3‐directed interactions, these studies also led to the discovery of novel signalling proteins, such as the PAK2‐binding adaptor protein POSH2 and the ADAM15‐binding sorting nexin family member SNX30.
Yeast Trf5p is a nuclear poly(A) polymerase
Authors: Houseley Jonathan , Tollervey David
Published: December 2005

Recent analyses have shown that the activity of the yeast nuclear exosome is stimulated by the Trf4p–Air1/2p–Mtr4p polyadenylation (TRAMP) complex. Here, we report that strains lacking the Rrp6p component of the nuclear exosome accumulate polyadenylated forms of many different ribosomal RNA precursors (pre‐rRNAs). This polyadenylation is reduced in strains lacking either the poly(A) polymerase Trf4p or its close homologue Trf5p. In contrast, polyadenylation is enhanced by overexpression of Trf5p. Polyadenylation is also markedly increased in strains lacking the RNA helicase Mtr4p, indicating that it is required to couple poly(A) polymerase activity to degradation. Tandem affinity purification‐tagged purified Trf5p showed polyadenylation activity in vitro, which was abolished by a double point mutation in the predicted catalytic site. Trf5p co‐purified with Mtr4p and Air1p, indicating that it forms a complex, designated TRAMP5, that has functions that partially overlap with the TRAMP complex.
Tumour necrosis factor‐α depletes histone deacetylase 1 protein through IKK2
Authors: Vashisht Gopal Y N , Arora Tarandeep S , Van Dyke Michael W
Published: December 2005

Class I histone deacetylases (HDACs) are ubiquitous enzymes that repress gene expression by deacetylating histone tails and promoting chromatin compaction. Pro‐inflammatory agents activate programmes of gene expression through transcription factors such as nuclear factor‐κB (NF‐κB), even in the context of ubiquitous HDAC activity. How this is accomplished remains unknown. We found that cells treated with the pro‐inflammatory cytokine tumour necrosis factor‐α rapidly and substantially reduced HDAC1 protein levels without affecting other class I HDACs. In addition, HDAC1 depletion occurred through protein degradation, required IKK2 activity and resulted in increased transcription from both NF‐κB‐associated and unassociated gene promoters. Our study suggests that the activation of programmes of gene expression by pro‐inflammatory agents requires global changes in specific critical epigenetic regulators such as HDAC1.
Analysis of binary adsorption of polar and nonpolar molecules in narrow slit-pores by mean-field perturbation theory
Authors: Kotdawala R. R. , Kazantzis Nikolaos , Thompson Robert W.
Published: December 2005

In the present research study, we present the development of a model for predicting the adsorption of binary mixtures of nonpolar molecules, as well as polar molecules, based on density functional theory with mean-field approximation in narrow slit-pores. The first system under consideration is comprised of a binary mixture of nonpolar molecules, modeled by considering intermolecular dispersion forces, whereas the second system comprised of a binary mixture of polar molecules is modeled by considering orientation averaged electrostatic interactions, namely dipole-dipole and dipole-induced dipole interactions as well as dispersion interactions. An explicit equation for the Helmholtz free energy of the pore phase binary fluid mixture is derived. The proposed model is used to simulate the selective sorption of ethane from an ethane-methane mixture and water from a methanol-water mixture in the slit-pore. The simulated results are interpreted by studying the relative contributions of fluid-wall and fluid-fluid interactions. Finally, simulation results obtained are compared with the results of existing models and molecular simulations in the literature.
Generalized coherent states and the control of quantum systems
Authors: Teismann Holger
Published: December 2005

The control problem for linear and nonlinear Schrödinger equations is considered. The controls are given by applying a spatially homogeneous field or varying the frequency of a quadratic trapping potential. It is demonstrated that the existence of (exact or approximate) coherent-state-type solutions may severely limit the degree to which the system can be controlled.
Scattering model for understanding the optical behavior of powders embedded in a plastic matrix
Authors: Beluze L. , Varona C. , Viana B. , Tarascon J. M. , Morcrette M.
Published: December 2005

Powders embedded in a plastic matrix could exhibit attractive optical properties as flexible emissivity modulator. The choice of the materials to obtain significant contrasts in reflectivity and consequently in emissivity is discussed using a two-flux model to simulate qualitatively the performance of high- and low-absorptive materials. For high-absorptive compounds, such as metallic powders, high reflectivity values can be obtained with a large particle size of a highly conductive metal. The reflectivity value for spherical copper particles at about 2μm (about 70%) could be enhanced by 20% in the case of platelet-shaped particles. For low-absorptive compounds, reflection increases with decreasing absorption. For these compounds, larger particles do not lead to higher reflectivity values. An optimum size of the particles has to be found in order to obtain a maximum reflectivity value. Additional considerations on the electronic delocalization are also presented.
A calculation of the rovibronic energies and spectrum of the B̃A11 electronic state of SiH2
Authors: Guérout R. , Bunker P. R. , Jensen Per , Kraemer W. P.
Published: December 2005

The B̃A11 electronic state of silylene (SiH2) is the second excited singlet state of the molecule and, like the analogous c̃ state of methylene (CH2), it is quasilinear with symmetry Σg+1 at linearity. This state dissociates to Si(D1)+H2(Σg+1). At equilibrium, the B̃ state of SiH2 has an energy that we calculate to be 0.71 eV above that of the dissociation products. However, there is a barrier to dissociation that allows quasibound rovibrational levels to occur, and some have been observed recently [Y. Muramoto et al., J. Chem. Phys. 122, 154302 (2005)]. Starting with our analytical ab initio potential-energy surface, we adjusted it in a fitting to the experimental term values in order to determine the optimum potential-energy function in the bound region. This potential has a C2v equilibrium structure with a SiH bond length of 1.459 Å and a bond angle of 165.4°; the barrier to linearity is only 129cm−1. Using the optimized potential-energy surface we calculate B̃-state term values, and using our calculated y and z dipole moment surfaces, we simulate the rotation-vibration spectrum of the state in order to assist in the detection of the matrix isolation spectrum.
A cryogenic voltage amplifier with 36MHz bandwidth using discrete GaAs metal-semiconductor field-effect transistors
Authors: Hu B. H. , Yang C. H.
Published: December 2005

We report a design procedure and performance of a voltage amplifier using commercially available GaAs metal-semiconductor field-effect transistors. There are two stages: a common-source amplifier that provides a moderate gain, followed by a common-drain stage for driving the 50Ω coaxial cable. The overall voltage gain measured at 4.2K with a 50Ω load is 3.3, with a bandwidth of 36MHz. The input-referred voltage noise is measured to be approximately 3.2nV∕√Hz in a wide frequency range.
Mixed quantum-classical Redfield master equation
Authors: Toutounji Mohamad
Published: December 2005

Redfield master equation is derived from mixed quantum-classical Liouville equation using product initial conditions. Simple two-level system example is given and comparison with Fermi golden rule is made.
A model for transits in dynamic response theory
Authors: De Lorenzi-Venneri Giulia , Wallace Duane C.
Published: December 2005

The first goal of vibration-transit (V-T) theory was to construct a tractable approximate Hamiltonian from which the equilibrium thermodynamic properties of monatomic liquids can be calculated. The Hamiltonian for vibrations in an infinitely extended harmonic random valley, together with the universal multiplicity of such valleys, gives an accurate first-principles account of the measured thermodynamic properties of the elemental liquids at melt. In the present paper, V-T theory is extended to nonequilibrium properties, through an application to the dynamic structure factor S(q,ω). It was previously shown that the vibrational contribution alone accurately accounts for the Brillouin peak dispersion curve for liquid sodium, as compared both with molecular-dynamics (MD) calculations and inelastic x-ray scattering data. Here it is argued that the major effects of transits will be to disrupt correlations within the normal-mode vibrational motion and to provide an additional source of inelastic scattering. We construct a parametrized model for these effects and show that it is capable of fitting MD results for S(q,ω) in liquid sodium. A small discrepancy between model and MD at large q is attributed to multimode vibrational scattering. In comparison, mode coupling theory formulates S(q,ω) in terms of processes through which density fluctuations decay. While mode coupling theory is also capable of modeling S(q,ω) very well, V-T theory is the more universal since it expresses all statistical averages, thermodynamic functions, and time correlation functions alike, in terms of the same motional constituents, vibrations and transits.
Automatic procedure for the correction of thermoelastic stress analysis data acquired in nonadiabatic conditions
Authors: Gallotti A. , Salerno A.
Published: December 2005

Thermoelastic stress analysis (TSA), performed on metallic components with a high diffusivity coefficient, seldom reaches adiabatic conditions. As a consequence, TSA results are affected by an attenuation whose entity varies locally, preventing the use of TSA as a reliable quantitative investigation means. The recovery of the adiabatic temperature and of the correct value of the first stress invariant, directly linked to it, can only be performed making an assumption on the local stress distribution. This article presents a method for automatically choosing, among a number of stress distribution functions, the one that performs the best correction of the raw TSA data. The implementation of this automatic correction procedure in a computer program allowed the point-by-point correction of whole TSA images.
Machine vision for high-precision volume measurement applied to levitated containerless material processing
Authors: Bradshaw R. C. , Schmidt D. P. , Rogers J. R. , Kelton K. F. , Hyers R. W.
Published: December 2005

By combining the best practices in optical dilatometry with numerical methods, a high-speed and high-precision technique has been developed to measure the volume of levitated, containerlessly processed samples with subpixel resolution. Containerless processing provides the ability to study highly reactive materials without the possibility of contamination affecting thermophysical properties. Levitation is a common technique used to isolate a sample as it is being processed. Noncontact optical measurement of thermophysical properties is very important as traditional measuring methods cannot be used. Modern, digitally recorded images require advanced numerical routines to recover the subpixel locations of sample edges and, in turn, produce high-precision measurements.
A method for determining the absorption ellipsoid of single conjugated polymer molecules and single luminescent nanoparticles
Authors: Ebihara Yohei , Vacha Martin
Published: December 2005

We propose a simple method for the measurement of the absorption ellipsoid of luminescent nanoparticles. The method is based on a combination of far-field and near-field polarized excitation in a wide-field fluorescence microscope and provides the orientation and axes ratio r of a rotationally symmetric ellipsoid. Potential applications of the method including the study of conjugated polymer conformations are discussed.
Near-edge electronic structure in NbS2
Authors: Kim Changki , Kelty Stephen P.
Published: December 2005

The near-edge electronic and structural properties of 2H-NbS2 were investigated using scanning tunneling microscopy (STM) and density-functional calculations. Geometry optimization of the near-edge structure using density-functional calculations was performed on [1¯010]- and [101¯0]-terminated layer edges. Ribbon model systems also included variation of the number of bound sulfur atoms at the edges. Atomic resolution STM data exhibit a pronounced electronic density of states at the outermost edge atomic sites but are otherwise bulklike in the near-edge region. Optimized NbS2 ribbon structures confirm the STM results indicating that minimal reconstruction occurs and that the edge electronic structure exhibits a significant increase in local density of states compared to bulk. Simulated STM images using extended Hückel tight-binding calculations based on optimized ribbon structures successfully modeled the experimental STM results. The results indicate that the [101¯0] “Nb” edges are preferentially observed compared to the [1¯010] “S” edge possibly due to differences in stability.
Theory of ultrafast optical manipulation of electron spins in quantum wells
Authors: Jin Jinshuang , Li Xin-Qi
Published: December 2005

Based on a multiparticle-state stimulated Raman adiabatic passage approach, a comprehensive theoretical study of the ultrafast optical manipulation of electron spins in quantum wells is presented. In addition to corroborating experimental findings [Gupta et al., Science 292, 2458 (2001)], we improve the expression for the optical-pulse-induced effective magnetic field, in comparison with the one obtained via the conventional single-particle ac Stark shift. Further study of the effect of hole-spin relaxation reveals that, while the coherent optical manipulation of electron spin in undoped quantum wells would deteriorate in the presence of relatively fast hole-spin relaxation, the coherent control in doped systems can be quite robust against decoherence. The implications of the present results on quantum dots will also be discussed.
Photoreflectance study of GaAsSb∕InP heterostructures
Authors: Chouaib H. , Bru-Chevallier C. , Guillot G. , Lahreche H. , Bove P.
Published: December 2005

Photoreflectance (PR) spectroscopy experiments are reported on GaAsSb∕InP heterostructures. The GaAsSb PR spectrum is studied as a function of temperature and the transition nature is shown to change from Franz-Keldysh oscillations (FKO) at room temperature to a third derivative functional form (TDFF) line shape at low temperatures. Combining both analysis (FKO and TDFF) in the same sample, we derive internal electric field and phase values of the PR transition, together with accurate values for alloy band gap energy on the whole temperature range. Type II interface recombination is shown to reduce photovoltage effects as a function of temperature. FKO are found to appear for a very weak electric field (8kV∕cm) in the GaAsSb∕InP heterostructure, contrary to usual observations. This point is discussed in relation with the broadening parameter of the transition.
Decomposition of time-covariant operations on quantum systems with continuous and∕or discrete energy spectrum
Authors: Janzing Dominik
Published: December 2005

Every completely positive map G that commutes with the Hamiltonian time evolution is an integral or sum over (densely defined) CP-maps Gσ where σ is the energy that is transferred to or taken from the environment. If the spectrum is non-degenerate each Gσ is a dephasing channel followed by an energy shift. The dephasing is given by the Hadamard product of the density operator with a (formally defined) positive operator. The Kraus operator of the energy shift is a partial isometry which defines a translation on R with respect to a non-translation-invariant measure. As an example, this decomposition is explicitly calculated for the rotation invariant Gaussian channel on a single mode. The question of under what conditions a covariant channel destroys superpositions between mutually orthogonal states on the same orbit is addressed. For channels which allow mutually orthogonal output states on the same orbit, a lower bound on the quantum capacity is derived using the Fourier transform of the CP-map-valued measure (Gσ).
Controlled introduction of flux pinning centers in YBa2Cu3O7−x films during pulsed-laser deposition
Authors: Varanasi C. , Barnes P. N. , Burke J. , Carpenter J. , Haugan T. J.
Published: December 2005

To introduce controlled random inclusion of nanometer-sized nonsuperconducting particulates in YBa2Cu3O7−x films for flux pinning enhancement, a special pulsed-laser-ablation YBa2Cu3O7−x target with a Y2BaCuO5 sector was made and the films were deposited on LaAlO3 substrates. Initial results showed that the films consist of 10–20 nm-sized precipitates. In a 0.5μm thick film, a transport critical current density (Jc)>3MA∕cm2 at 77 K in self-field was measured. Magnetization Jc at 77 and 65 K showed significant improvements in these films with fine precipitates as compared to regular YBa2Cu3O7−x films (>10 times increase at 9 T, 65 K).
Incorporating spatial dependence into a multicellular tumor spheroid growth model
Authors: Garner Allen L. , Lau Y. Y. , Jackson Trachette L. , Uhler Michael D. , Jordan David W. , Gilgenbach Ronald M.
Published: December 2005

Recent models for organism and tumor growth yield simple scaling laws based on conservation of energy. Here, we extend such a model to include spatial dependence to model necrotic core formation. We adopt the allometric equation for tumor volume with a reaction-diffusion equation for nutrient concentration. In addition, we assume that the total metabolic energy and average cellular metabolic rate depend on nutrient concentration in a Michaelis-Menten-like manner. From experimental results, we relate the necrotic volume to nutrient consumption and estimate both the time and nutrient concentration at necrotic core formation. Based on experimental results, we demand that the necrotic core radius varies linearly with tumor radius after core formation and extend the equations for tumor volume and nutrient concentration to the postnecrotic core regime. In particular, we obtain excellent agreement with experimental data and the final steady-state viable rim thickness.
Characteristics of GaAsN∕GaAsSb type-II quantum wells grown by metalorganic vapor phase epitaxy on GaAs substrates
Authors: Khandekar A. A. , Hawkins B. E. , Kuech T. F. , Yeh J. Y. , Mawst L. J. , Meyer J. R. , Vurgaftman I. , Tansu N.
Published: December 2005

Pseudomorphic four-period GaAs0.978N0.022∕GaAs0.78Sb0.22 type-II multiquantum well structures were grown on (100) GaAs substrates by metalorganic vapor phase epitaxy at 530°C. The GaAs0.978N0.022 layers were grown at a V/III ratio of 685 and N∕V ratio of 0.96, whereas the GaAs0.78Sb0.22 was grown at a V/III ratio of 3.8 and Sb∕V ratio of 0.8. The superlattice peaks in the x-ray diffraction θ-2θ scans around the (400) GaAs peak were fitted using a dynamical simulation model to determine layer thickness and alloy compositions. The GaAsN and GaAsSb thicknesses were ∼8nm and ∼5nm, respectively. The photoluminescence (PL) spectra were obtained at 30K and the PL peak energy was found to match the type-II transition energy obtained from a 10-band k∙p model. Postgrowth annealing under arsine-H2 with a N2 cooldown was found to increase the low temperature PL intensity and result in the appearance of luminescence at room temperature.
Design and performance of sliced-aperture corrugated feed horn antennas
Authors: Singal J. , Wollack E. , Kogut A. , Limon M. , Mirel P. , Lubin P. , Seiffert M.
Published: December 2005

We report on the design of corrugated feed horn microwave antennas at 3.3, 5.6, 7.8, and 10.2 GHz for the absolute radiometer for cosmology, astrophysics, and diffuse emission experiment. These horns have low sidelobe symmetrical beams with 12° full width at half power, and three noteworthy features: a 30° slice at the aperture, a profiled rather than a linear taper, and a slowly varying groove depth along the length of the horn. The profiled taper and varying groove depth provided a narrow beam given the existing physical spatial constraints of the instrument in which the horns are used. The 30° slice was necessary for instrumental considerations and has a minimal effect on the symmetry of the beam. The slice reduces the effective aperture radius and overall length to that corresponding to an unsliced horn with an aperture at roughly the middle of the slice and does not introduce any undesirable effects.
High-temperature calcium vapor cell for spectroscopy on the 4s2S1–4s4pP13 intercombination line
Authors: Erickson Christopher J. , Neyenhuis Brian , Durfee Dallin S.
Published: December 2005

We have demonstrated a high-temperature vapor cell for absorption spectroscopy on the Ca intercombination line. The cell uses a dual-chamber design to achieve the high temperatures necessary for an optically dense vapor while avoiding the necessity of high-temperature vacuum valves and glass-to-metal seals. We have observed over 50% absorption in a single pass through the cell. Although pressure broadening in the cell prevented us from performing saturated-absorption spectroscopy, the broadening resulted in higher signal-to-noise ratios by allowing us to probe the atoms with intensities much greater than the 0.2μW∕cm2 saturation intensity of the unbroadened transition. The techniques presented in this article could easily be applied to study other transitions in a variety of atomic species.
Modification of photoionization mass spectrometer with synchrotron radiation as ionization source
Authors: Huang Chaoqun , Yang Bin , Yang Rui , Wang Jing , Wei Lixia , Shan Xiaobin , Sheng Liusi , Zhang Yunwu , Qi Fei
Published: December 2005

In this article we introduce a modification on ion optics of a reflectron time-of-flight mass spectrometer for the study of flame chemistry with synchrotron radiation as a continuous ionization source. A small bias voltage is used in the extraction region to simultaneously reduce the background ion signal, eliminate secondary ionization process caused by photoelectrons, increase the ion detection efficiency, and improve the mass resolution.
Development of liquid-metal-ion source low-energy ion gun/high-temperature ultrahigh vacuum scanning tunneling microscope combined system
Authors: Uchigasaki M. , Kamioka T. , Hirata T. , Shimizu T. , Lin F. , Shinada T. , Ohdomari I.
Published: December 2005

A liquid-metal-ion source low-energy ion gun/high-temperature ultrahigh vacuum scanning tunneling microscope combined system (LMIS-IG/STM) has been developed in order to investigate the ion beam modification process in situ based on our previous ion gun/STM combined system (IG/STM). Various kinds of metal ions can be irradiated with low acceleration energy of 0.01–5keV during STM observation at 400–600°C. As an example, real-time STM observation of Si(111)7×7 surface irradiated with Si2+ ions is demonstrated. The STM results have shown that the surface defects generated by Si2+ ion irradiation exhibit similar behavior of surface defects induced by Ar+ irradiation with IG/STM.
Frequency-modulation atomic force microscopy at high cantilever resonance frequencies using the heterodyne optical beam deflection method
Authors: Fukuma Takeshi , Kimura Kenjiro , Kobayashi Kei , Matsushige Kazumi , Yamada Hirofumi
Published: December 2005

We have developed a frequency-modulation atomic force microscope (FM-AFM) with a wideband cantilever deflection sensor using the heterodyne optical beam deflection method. The method enhances the bandwidth of the deflection measurement up to the maximum frequency for the laser power modulation, which can be as high as gigahertz order. The phase and frequency of the cantilever vibration at 5.24MHz are detected with a deflection noise density of 100fm∕Hz. FM-AFM imaging is performed on a Au(111) surface with a high-frequency cantilever.
Strong terahertz emission from (100) p-type InAs
Authors: Mendis R. , Smith M. L. , Bignell L. J. , Vickers R. E. M. , Lewis R. A.
Published: December 2005

Terahertz emission has been observed from (100) Zn-acceptor-doped InAs under illumination by fs pulses of near-infrared radiation. Turning the crystal about the surface normal produces two maxima per rotation, whether the angle of incidence is 45° or 75°, in contrast to (111) p-InAs, where three maxima per rotation have been reported. The emitted terahertz power has a quadratic variation with the pump power and decreases with increasing temperature in the range 20–300K. This behavior is consistent with a photocurrent surge being the dominant terahertz generating mechanism at low excitation fluences. The p-type InAs generates about two orders of magnitude more power than the standard unbiased terahertz emitter, 1mm thick ZnTe.
Superprism phenomena in polymeric woodpile structures
Authors: Serbin Jesper , Gu Min
Published: December 2005

An analysis of the optical properties of photonic woodpile structures is presented. We demonstrate large superprism phenomena inside polymeric woodpile structures having a refractive index of less than n=1.6. Due to the low contrast in refractive indices the structures investigated do not possess a complete photonic band gap. Nevertheless, their photonic band structures show strong anisotropy at frequencies slightly above the band gap in the (Γ-X) direction, leading to an extreme sensitivity to the angle and the frequency of the incident light in the propagation direction inside the crystal. Furthermore, if the woodpile structure is arranged in a prism-like shape, the transmitted beam outside the crystal shows a strong sensitivity to the frequency and angle of the incident light.
Thermal conduction in ultrathin pure and doped single-crystal silicon layers at high temperatures
Authors: Liu Wenjun , Asheghi Mehdi
Published: December 2005

This work presents the in-plane thermal-conductivity data for pure as well as boron-doped (1.6×1021∕cm3), arsenic-doped (2.3×1020∕cm3), and phosphorus-doped (2.3×1020∕cm3) silicon layers of thickness 30nm in the temperature range of 300–450K. The steady-state Joule heating and electrical resistance thermometry are used to measure the lateral thermal conductivity of suspended silicon layers. Thermal-conductivity data for pure and doped single-crystalline thin silicon layers can be interpreted using thermal-conductivity integral in relaxation-time approximation that accounts for phonon-boundary and phonon-impurity scatterings. No additional fitting parameters are used in this work in contrast with previous studies that required an unusually large phonon-impurity scattering coefficient to fit the thermal-conductivity data for bulk doped silicon to the predictions of the thermal-conductivity integral in relaxation-time approximation.
Printing of organic and inorganic nanomaterials using electrospray ionization and Coulomb-force-directed assembly
Authors: Welle Aaron M. , Jacobs Heiko O.
Published: December 2005

This letter reports on an additive printing process to deposit organic and inorganic nanomaterials onto desired areas on a surface. The process combines electrospray ionization with Coulomb-force-directed assembly. Electrospray ionization is used to bring the desired nanomaterial into the gas phase while carrier gas, global, and localized electric fields are used to deposit the material onto desired locations on a substrate. Albumin fluorescein isothiocyanate bovine, avidin sulforhodamine, and gold colloids were sprayed from an aqueous solution and patterned with a resolution as high as 100nm.
Dielectric barrier hollow cathode discharge and its enhanced performance for light source
Authors: Lee Tae Il , Park Ki Wan , Baik Hong Koo , Lee Seong-Min
Published: December 2005

We invented the dielectric barrier hollow cathode discharge (DBHCD) configuration as a novel light source and studied on the physical properties of discharge and the possibility of the parallel operation of many holes of the DBHCD without additional impedances such as inductance or capacitance. The electrical characteristics and the photo images of discharges sustained in cavity were investigated. The experimental result showed that the surface discharge mode was transformed into a hollow cathode mode according to a decrease of the pD (operating pressure times hole diameter). The parallel operation of the 13 arrays of DBHCD was also possible without additional impedances for limiting current. We measured the relative IR emission efficiency of the coplanar dielectric barrier discharge (CDBD) and DBHCD to evaluate the enhanced performance as light sources. According to the experiment, the 25 arrays of DBHCD result in 30%-enhanced performance in IR emission efficiency compared with CDBD.
Approach for investigating lateral conduction in self-assembled monolayers
Authors: Gowda Srivardhan , Mathur Guru , Li Qiliang , Surthi Shyam , Misra Veena
Published: December 2005

Lateral conductivity within a monolayer is a key factor in the implementation of emerging dense molecular memory devices since it determines the degree of cross talk between cells. Lateral interactions within a monolayer could also lead to loss of charge through defective sites. Existing characterization techniques are limited to probing the electrical communication between molecules and attached electrodes. In this paper we demonstrate a test structure consisting of n type and p type doped silicon islands to isolate vertical conduction from lateral conduction. This structure is a useful characterization tool for tailoring the intrinsic properties of the molecules for information storage.
Structural transitions in NaBH4 under pressure
Authors: Kumar Ravhi S. , Cornelius Andrew L.
Published: December 2005

The structure of the technologically important hydrogen storage compound NaBH4 has been investigated under pressures up to 30 GPa by in situ angle dispersive high pressure x-ray diffraction using synchrotron x rays and a diamond anvil cell. Our experimental results show pressure-induced structural transitions of α-NaBH4 (cubic - Fm3m) to β-NaBH4 (tetragonal - P421c) at 6.3 GPa and further to an orthorhombic phase (Pnma) at 8.9 GPa. The high pressure orthorhombic phase is found to be stable up to 30 GPa. The cubic phase is completely recovered on releasing the pressure back to ambient.
Low-threshold amplified spontaneous emission in thin films of poly(tetraarylindenofluorene)
Authors: Laquai Frédéric , Keivanidis Panagiotis E. , Baluschev Stanislav , Jacob Josemon , Müllen Klaus , Wegner Gerhard
Published: December 2005

We report on amplification of blue light (469 nm) via amplified spontaneous emission in asymmetric planar waveguides of a fully arylated polyindenofluorene derivative. A very low threshold value of about 3μJ∕cm2(∼375W∕cm2) for amplification of light has been demonstrated by pumping the waveguides at 3.0 eV (410 nm) with a stripe shape excitation beam. Moderate gain coefficients up to 21cm−1 and loss coefficients around 6cm−1 have been measured. All measurements were performed under ambient conditions. No sample degradation could be observed which testifies to the excellent stability of the material against photodegradation.
Impact of N-induced potential fluctuations on the electron transport in Ga(As,N)
Authors: Ishikawa F. , Mussler G. , Friedland K.-J. , Kostial H. , Hagenstein K. , Däweritz L. , Ploog K. H.
Published: December 2005

We investigate the electron transport in Ga(As,N) layers focusing on the influence of potential fluctuations. With increasing electron concentration, a metal-insulator transition is observed in the temperature dependence of the resistivity for a series of samples containing 0.8% of N. The observed behavior is discussed in the frame of Anderson transition. By increasing the N concentration up to 2.2%, we observe an increase of the potential fluctuations’ amplitude. Mean-square values for the intrinsic N-induced fluctuation γN are obtained from percolation theory to be larger than 30 meV. Rapid thermal annealing reduces γN significantly for samples with higher N concentration. These large potential fluctuations lead to electron localization and induce thermally activated conductivity which is observable up to 300 K.
Onset of percolation and the temperature dependence of the persistent critical current in YBa2Cu3O7−δ films
Authors: Jung J. , Chow K. H. , Egilmez M. , Welsh A.
Published: December 2005

We investigated the effects of oxygen redistribution on the temperature dependence of the critical current Ic(T) in YBa2Cu3O7−δ thin films. In order to induce a very slow “motion” of oxygen in the sample, we performed careful annealing of the films in argon at 175 °C. A gradual transformation of Ic(T) into a Ginzburg–Landau-like dependence of the form Ic(T)=Ico(1−T∕Tc)3∕2 is observed, implying that the superconducting film is being transformed into a percolative (filamentary) state upon annealing.
Resistance steps and large magnetoresistive effect in La0.67Sr0.33MnO3 nanoconstriction array
Authors: Liu H. J. , Ong C. K.
Published: December 2005

The transport properties of La0.67Sr0.33MnO3 (LSMO) nanoconstriction array under large applied current with current density in the order of 105A∕cm2 have been investigated. A series of resistance steps were observed at 78 K with applied current up to 1.0 mA. The critical current value at which resistance jump occurs varied with temperatures and the applied magnetic fields. The observation was attributed to the local heating induced phase transition at the section of nanoconstrictions where phase separation is dominant. A large low field magnetoresistive ratio of 52.2% was achieved at 78 K with the magnetic field up to 3000 Gauss when the biased current was set to 0.34 mA. This LSMO nanoconstriction array shows promise in the application of magnetic field sensors.
Efficiency of water and nutrient use in containerised plants irrigated by overhead, drip or capillary irrigation
Authors: Goodwin P. B. , Murphy M. , Melville P. , Yiasoumi W.
Published: December 2005

This paper reports an assessment of the potential of an irrigation system based on capillary matting in comparison to the industry standard, overhead irrigation, and to drip irrigation, for plants growing in pots. The systems were evaluated on the basis of the dry weights of the plants grown, water-use efficiency (volume of runoff) and the environmental impact of the systems. The environmental impact was assessed by the volumes of runoff and the amounts of nitrate nitrogen and phosphate phosphorus in the runoff. Rose and tomato grew on capillary mat as large as or larger than (dry weight) with drip or overhead irrigation when controlled-release fertiliser (Osmocote Plus, 5–6 month release) was mixed through the medium. Lavender and pansy showed no significant difference between the irrigation systems. However, when the fertiliser was applied to the surface or in the dibble hole, pansy, dianthus and anisodontea grew larger with overhead than with capillary irrigation.The volumes of water used by the drip and capillary systems were about equal at 2.6 and 3.3 L/pot.week, respectively, as were the volumes of runoff produced, 0.43 and 0.39 L/pot.week, but both were far lower than the corresponding values for the overhead system, where water use was 7.13 L/pot.week, and the runoff 3.00�L/pot.week. At the end of the trial, plants grown with capillary irrigation had a high electrical conductivity in the surface layers of the pots when controlled-release fertiliser was either mixed evenly through (1997, EC 2.04 dS/m) or was applied to the top of the mix (1998, EC 0.87 dS/m). On the other hand, with overhead watering the EC was more evenly distributed (1997, EC range 0.30–0.36 dS/m) or highest at the bottom of the pot (1998, EC 0.97 dS/m). The concentrations of nutrients in the runoff from the capillary mat system, nitrate nitrogen 6.2 mg/L and phosphate phosphorus 0.12 mg/L, were lower than those for either of the other systems, overhead giving 9.7 and 0.49 mg/L and drip 11.5 and 0.49 mg/L of nitrogen and phosphorus, respectively. Total nutrient leaching per week for nitrate and phosphate, respectively, was 320 and 16.2 mg/m2 for overhead, 53.9 and 3.1 mg/m2 for drip and 26.4 and 0.50 mg/m2 for capillary irrigation. Thus, capillary irrigation gave more efficient water and nutrient use and reduced nutrient contamination of the environment compared with the drip or overhead irrigation systems.
The Sustainable Grazing Systems National Experiment. 1. Introduction and methods
Authors: Andrew M. H. , Lodge G. M.
Published: December 2005

This paper outlines the development and design of the Sustainable Grazing Systems (SGS) National Experiment from the initial call for expressions of interest, through several workshop processes to the final selection and implementation of its 6 component sites, and the general methodology used at each. Sites were located in Western Australia, western Victoria, north-east Victoria, and on the Central Tablelands, North West Slopes, and the eastern Riverina of New South Wales. Sites in Western Australia, north-east Victoria, the North West Slopes, and the eastern Riverina also had subsites. Methods for the sites and subsites (data collection for pastures, livestock, weather, soils and site characterisation) are presented to provide a central reference, and to save duplication in subsequent papers. Descriptions are provided of the location, average annual rainfall, major pasture, soil and stock types, design and number of treatments, and initial soil levels (0–10 cm) of phosphorus, electrical conductivity, and pH for sites and subsites. Also outlined is the major focus of the research undertaken at each site. While sites studied regionally relevant issues, they operated under a common protocol for data collection with a minimum data set being specified for each of 5 unifying themes: pastures, animal production, water, nutrients, and biodiversity. Economic analyses were also undertaken at the macro- and micro-level, and a procedural tool developed for appraising the on- and off-farm impacts of different systems. To give effect to the themes, common database and modelling tools were developed specifically for the national experiment, so that collectively sites comprised a single experiment.
SGS Pasture Theme: effect of climate, soil factors and management onpasture production and stability across the high rainfall zone of southern Australia
Authors: Sanford P. , Cullen B. R. , Dowling P. M. , Chapman D. F. , Garden D. L. , Lodge G. M. , Andrew M.H. , Quigley P. E. , Murphy S. R. , King W. McG. , Johnston W. H. , Kemp D. R.
Published: December 2005

The Sustainable Grazing Systems (SGS) National Experiment (NE) Pasture Theme explored factors that influenced annual herbage accumulation and perennial grass and legume content across the NE sites, in the high rainfall zone (HRZ, >600 mm/year annual rainfall) of southern Australia using multi-variate analysis and the SGS Pasture Model. Annual rainfall was a poor predictor of annual herbage accumulation. The length of growing season accounted for 30% of the variation in annual herbage accumulation. Much of the remaining 70% of variation in annual herbage accumulation was explained by soil Olsen P, the proportion of native species in the pasture and stocking rate, together with interactions among other factors including legume content. Simulated effects of set stocking and rotational grazing on herbage accumulation using the SGS Pasture Model, predicted that rotational grazing was unlikely to result in large increases in herbage accumulation. In contrast, it was predicted that the adoption of deep-rooted C3 and C4 perennial grasses could provide useful increases in herbage accumulation. Perennial grass content and basal cover were both significantly influenced by growing season length (P<0.001), grazing method (P<0.001) and an interaction between stocking rate and soil pH (P = 0.002). These analyses suggested that to maintain or improve the perennial grass component of a pasture at medium–high stocking rates, it was crucial to adopt grazing strategies that included rotation or resting. Perennial grass percent also significantly (P<0.001) increased in response to ameliorating the soil pH. Legume content of pastures significantly (P<0.001) increased in response to set stocking and increased stocking rate.To be botanically stable and productive, sown pastures based on perennial grasses in the HRZ of southern Australia will need to be grazed at high stocking rates (15–23 DSE/ha) in combination with rotational grazing or resting, and with adequate soil P. Additional gains in production and stability could be obtained by ensuring an adequate legume component, including a C4 perennial grass and ameliorating soil acidity. Pastures based on native perennial grasses may require lower soil P and more conservative stocking rates, depending on species.