bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial analysis of trends in extreme precipitation events in high‐resolution climate model results and observations for Germany
Authors: Tomassini L. , Jacob D.
Published: June 2009

A statistical extreme value analysis is applied to very high‐resolution climate model results and observations encompassing the area of Germany. Two control runs representing the current climate, as well as three scenario simulations of the regional climate model REMO, are investigated. The control runs were compared against high‐resolution observations. The analysis is divided into two main parts: first trends in extreme quantiles of daily precipitation totals are estimated in a station‐by‐station analysis. In the second part, the spatial characteristics of the estimated trends in heavy rainfall are investigated over the area of Germany by fitting a parametric geostatistical model to these trends. The rule of thumb of estimating trends in extreme quantiles of heavy precipitation based on the Clausius‐Clapeyron relation, about 6.5% per 1°C temperature increase, has been roughly confirmed for Germany by our study with respect to the observations, but the climate model computes weaker trends. In the control simulations, the climate model tends to underestimate trends in heavy rainfall compared to observations. In the scenario simulations, positive trends prevail (as in the observations). They are, however, relatively small when set in relation to the uncertainties. The trends become significantly positive to a larger spatial extent only in the A2 scenario simulation. The estimated shape of the extreme value distributions does not change significantly in the scenario simulations compared to the climate model control runs. The parameter estimates for the geostatistical model for the trends in extreme quantiles of daily precipitation sums are rather uncertain. The most striking feature of the analysis is a reduction of the spatial variance of the trends over the considered area of Germany in the scenario simulations compared to observations and, in particular, the climate model control runs.
Impact of geoengineered aerosols on the troposphere and stratosphere
Authors: Tilmes Simone , Garcia Rolando R. , Kinnison Douglas E. , Gettelman Andrew , Rasch Philip J.
Published: June 2009

A coupled chemistry climate model, the Whole Atmosphere Community Climate Model was used to perform a transient climate simulation to quantify the impact of geoengineered aerosols on atmospheric processes. In contrast to previous model studies, the impact on stratospheric chemistry, including heterogeneous chemistry in the polar regions, is considered in this simulation. In the geoengineering simulation, a constant stratospheric distribution of volcanic‐sized, liquid sulfate aerosols is imposed in the period 2020–2050, corresponding to an injection of 2 Tg S/a. The aerosol cools the troposphere compared to a baseline simulation. Assuming an Intergovernmental Panel on Climate Change A1B emission scenario, global warming is delayed by about 40 years in the troposphere with respect to the baseline scenario. Large local changes of precipitation and temperatures may occur as a result of geoengineering. Comparison with simulations carried out with the Community Atmosphere Model indicates the importance of stratospheric processes for estimating the impact of stratospheric aerosols on the Earth's climate. Changes in stratospheric dynamics and chemistry, especially faster heterogeneous reactions, reduce the recovery of the ozone layer in middle and high latitudes for the Southern Hemisphere. In the geoengineering case, the recovery of the Antarctic ozone hole is delayed by about 30 years on the basis of this model simulation. For the Northern Hemisphere, a onefold to twofold increase of the chemical ozone depletion occurs owing to a simulated stronger polar vortex and colder temperatures compared to the baseline simulation, in agreement with observational estimates.
Global dimming and brightening: A review
Authors: Wild Martin
Published: June 2009

There is increasing evidence that the amount of solar radiation incident at the Earth's surface is not stable over the years but undergoes significant decadal variations. Here I review the evidence for these changes, their magnitude, their possible causes, their representation in climate models, and their potential implications for climate change. The various studies analyzing long‐term records of surface radiation measurements suggest a widespread decrease in surface solar radiation between the 1950s and 1980s (“global dimming”), with a partial recovery more recently at many locations (“brightening”). There are also some indications for an “early brightening” in the first part of the 20th century. These variations are in line with independent long‐term observations of sunshine duration, diurnal temperature range, pan evaporation, and, more recently, satellite‐derived estimates, which add credibility to the existence of these changes and their larger‐scale significance. Current climate models, in general, tend to simulate these decadal variations to a much lesser degree. The origins of these variations are internal to the Earth's atmosphere and not externally forced by the Sun. Variations are not only found under cloudy but also under cloud‐free atmospheres, indicative of an anthropogenic contribution through changes in aerosol emissions governed by economic developments and air pollution regulations. The relative importance of aerosols, clouds, and aerosol‐cloud interactions may differ depending on region and pollution level. Highlighted are further potential implications of dimming and brightening for climate change, which may affect global warming, the components and intensity of the hydrological cycle, the carbon cycle, and the cryosphere among other climate elements.
Patterns of spatial and temporal variability of UV transparency in Lake Tahoe, California‐Nevada
Authors: Rose Kevin C. , Williamson Craig E. , Schladow S. Geoff , Winder Monika , Oris James T.
Published: June 2009

Lake Tahoe is an ultra‐oligotrophic subalpine lake that is renowned for its clarity. The region experiences little cloud cover and is one of the most UV transparent lakes in the world. As such, it is an ideal environment to study the role of UV radiation in aquatic ecosystems. Long‐term trends in Secchi depths showed that water transparency to visible light has decreased in recent decades, but limited data are available on the UV transparency of the lake. Here we examine how ultraviolet radiation varies relative to longer‐wavelength photosynthetically active radiation (PAR, 400–700 nm, visible wavelengths) horizontally along inshore‐offshore transects in the lake and vertically within the water column as well as temporally throughout 2007. UV transparency was more variable than PAR transparency horizontally across the lake and throughout the year. Seasonal patterns of Secchi transparency differed from both UV and PAR, indicating that different substances may be responsible for controlling transparency to UV, PAR, and Secchi. In surface waters, UVA (380 nm) often attenuated more slowly than PAR, a pattern visible in only exceptionally transparent waters with very low dissolved organic carbon. On many sampling dates, UV transparency decreased progressively with depth suggesting surface photobleaching, reductions in particulate matter, increasing chlorophyll a, or some combination of these increased during summer months. Combining these patterns of UV transparency with data on visible light provides a more comprehensive understanding of ecosystem structure, function, and effects of environmental change in highly transparent alpine and subalpine lakes such as Tahoe.
On the secular change of spring onset at Stockholm
Authors: Qian Cheng , Fu Congbin , Wu Zhaohua , Yan Zhongwei
Published: June 2009

A newly developed method, the Ensemble Empirical Mode Decomposition, was applied to adaptively determine the timing of climatic spring onset from the daily temperature records at Stockholm during 1756–2000. Secular variations of spring onset and its relationships to the North Atlantic Oscillation (NAO) and to the temperature variability were analyzed. A clear turning point of secular trend in spring onset around 1884/1885, from delaying to advancing, was found. The delaying trend of spring onset (6.9 days/century) during 1757–1884 and the advancing one (−7 days/century) during 1885–1999 were both significant. The winter NAO indices were found to be correlated with the spring onset at Stockholm at an inter‐annual timescale only for some decades, but unable to explain the change of the long‐term trends. The secular change from cooling to warming around the 1880s, especially in terms of spring temperature, might have led to the secular change of spring onset.
ENSO Modoki impact on the Southern Hemisphere storm track activity during extended austral winter
Authors: Ashok Karumuri , Tam C.‐Y. , Lee W.‐J.
Published: June 2009

Impacts of the recently discovered ENSO Modoki phenomena on extended winter storm track activity in the Southern Hemisphere are examined using the observed rainfall, sea surface temperature, and reanalyzed upper air circulation data for the period 1979–2004. The partial correlation technique is utilized to distinguish the impact of ENSO Modoki events from those of the ENSO and Indian Ocean Dipole (IOD). El Niño Modoki events introduce an anomalous blocking over central eastern Australia, which suppresses the storm track activity from southwest till centraleast, reducing the storm‐associated rainfall in southeastern tip and portions of the southeast. On the other hand, the storm track activity in central Argentina is enhanced owing to the strengthened upper air westerlies in this region. The impacts from the ENSO Modoki events are apparently stronger than the individual impacts from the ENSO and IOD events.
Coiled‐coil interactions are required for post‐Golgi R‐SNARE trafficking
Authors: Gordon David E , Mirza Myriam , Sahlender Daniela A , Jakovleska Jovana , Peden Andrew A
Published: June 2009

The sorting of post‐Golgi R‐SNAREs (vesicle‐associated membrane protein (VAMP)1, 2, 3, 4, 7 and 8) is still poorly understood. To address this, we developed a system to investigate their localization, trafficking and cell‐surface levels. Here, we show that the distribution and internalization of VAMPs 3 and 8 are determined solely through a new conserved mechanism that uses coiled‐coil interactions, and that VAMP4 does not require these interactions for its trafficking. We propose that VAMPs 3 and 8 are trafficked while in a complex with Q‐SNAREs. We also show that the dileucine motif of VAMP4 is required for both its internalization and retrieval to the trans‐Golgi network. However, when the dileucine motif is mutated, the construct can still be internalized potentially through coiled‐coil interactions with Q‐SNAREs.
Ataxia telangiectasia mutated activation by transcription‐ and topoisomerase I‐induced DNA double‐strand breaks
Authors: Sordet Olivier , Redon Christophe E , Guirouilh‐Barbat Josée , Smith Susan , Solier Stéphanie , Douarre Céline , Conti Chiara , Nakamura Asako J , Das Benu B , Nicolas Estelle , Kohn Kurt W , Bonner William M , Pommier Yves
Published: June 2009

Ataxia telangiectasia mutated (ATM), the deficiency of which causes a severe neurodegenerative disease, is a crucial mediator for the DNA damage response (DDR). As neurons have high rates of transcription that require topoisomerase I (TOP1), we investigated whether TOP1 cleavage complexes (TOP1cc)—which are potent transcription‐blocking lesions—also produce transcription‐dependent DNA double‐strand breaks (DSBs) with ATM activation. We show the induction of DSBs and DDR activation in post‐mitotic primary neurons and lymphocytes treated with camptothecin, with the induction of nuclear DDR foci containing activated ATM, γ‐H2AX (phosphorylated histone H2AX), activated CHK2 (checkpoint kinase 2), MDC1 (mediator of DNA damage checkpoint 1) and 53BP1 (p53 binding protein 1). The DSB–ATM–DDR pathway was suppressed by inhibiting transcription and γ‐H2AX signals were reduced by RNase H1 transfection, which removes transcription‐mediated R‐loops. Thus, we propose that Top1cc produce transcription arrests with R‐loop formation and generate DSBs that activate ATM in post‐mitotic cells.
The SOS response promotes qnrB quinolone‐resistance determinant expression
Authors: Da Re Sandra , Garnier Fabien , Guérin Emilie , Campoy Susana , Denis François , Ploy Marie‐Cécile
Published: June 2009

The qnr genes are plasmid‐borne fluoroquinolone‐resistance determinants widespread in Enterobacteriaceae. Three families of qnr determinants (qnrA, B and S) have been described, but little is known about their expression and regulation. Two new determinants, qnrC and qnrD, have been found recently. Here, we describe the characterization of the qnrB2 promoter and the identification of a LexA‐binding site in the promoter region of all qnrB alleles. LexA is the central regulator of the SOS response to DNA damage. We show that qnrB2 expression is regulated through the SOS response in a LexA/RecA‐dependent manner, and that it can be induced by the quinolone ciprofloxacin, a known inducer of the SOS system. This is the first description of direct SOS‐dependent regulation of an antibiotic‐resistance mechanism in response to the antibiotic itself.
Biostratigraphy of the Ruteh Formation at Harijan section (Central Alborz) northern Iran using foraminifera and conodont
Authors: Hamdi Bahaoddin , Sadeghi Abbas , Kohansa Ebrahim , Shafiee Ardestani Meysam , Balmak Behnaz
Published: June 2009

In order to study the fossil contents of the Ruteh Formation for biostratigraphical purposes, the 200 meters thick section was sampled at Harijan section, Central Alborz. The sequence is mainly made up of limestone and shale's. The lower contact of the formation with Dorud Formation is disconform while the upper contact with under learing Dorud Formation is disconformable with overling Nesen Formation is as well as disconformable. Fifty four species belonging to 27 genera (foraminifera and conodonts) were identified and three biozones were differentiated. These are formation: 1- Schubertella giraudi- Codonofusiella distincta Assemblage Zone, 2- Cribrigenerina sumatruna- Langella ocarina Assemblage Zone, 3- Sweetognathus whitei Biozone. Based on, these an age of Yackhtaschian - Murghabian is quoted to the formation.
Molecular dynamics simulation of the energetic reaction between Ni and Al nanoparticles
Authors: Henz Brian J. , Hawa Takumi , Zachariah Michael
Published: June 2009

Molecular dynamics simulations are used to simulate the energetic reaction of Ni and Al particles at the nanometer scale. The effect of particle size on reaction time and temperature for separate nanoparticles has been considered as a model system for a powder metallurgy system. Coated nanoparticles in the form of Ni-coated Al nanoparticles and Al-coated Ni nanoparticles are also analyzed as a model for nanoparticles embedded within a matrix. The differences in melting temperature and phase change behavior, e.g., the volumetric expansion of Al between Al and Ni, are expected to produce differing results for the coated nanoparticle systems. For instance, the volumetric expansion of Al upon melting is expected to produce large tensile stresses and possibly rupture in the Ni shell for Ni-coated Al. Simulation results show that the sintering time for separate and coated nanoparticles is nearly linearly dependent on the number of atoms or volume of the sintering nanoparticles. We have also found that nanoparticle size and surface energy are important factors in determining the adiabatic reaction temperature for both systems at nanoparticle sizes of less than 10 nm in diameter.
Bulk asymptotics of skew-orthogonal polynomials for quartic double well potential and universality in the matrix model
Authors: Ghosh Saugata
Published: June 2009

We derive bulk asymptotics of skew-orthogonal polynomials πm(β), β=1, 4, defined with respect to the weight exp(−2NV(x)), V(x)=gx4/4+tx2/2, g>0 and t<0. We assume that as m,N→∞, there exists an ϵ>0 such that ϵ≤(m/N)≤λcr−ϵ, where λcr is the critical value that separates skew-orthogonal polynomials with two cuts from those with one cut. Simultaneously we derive asymptotics for the recursive coefficients of skew-orthogonal polynomials. The proof is based on obtaining a finite term recursion relation between skew-orthogonal polynomials and orthogonal polynomials and using asymptotic results of orthogonal polynomials derived by Bleher and Its [“Semiclassical asymptotics of orthogonal polynomials, Riemann-Hilbert problems, and universality in the matrix model,” Ann. Math. 150, 185 (1999)]. Finally, we apply these asymptotic results of skew-orthogonal polynomials and their recursion coefficients in the generalized Christoffel–Darboux formula [Ghosh, S., “Generalized Christoffel-Darboux formula for skew-orthogonal polynomials and random matrix theory,” J. Phys. A 39, 8775 (2006)] to obtain level densities and sine kernels in the bulk of the spectrum for orthogonal and symplectic ensembles of random matrices.
Gain stabilization control system of the upgraded magnetic proton recoil neutron spectrometer at JET
Authors: Sjöstrand Henrik , Sundén E. Andersson , Conroy S. , Ericsson G. , Johnson M. Gatu , Giacomelli L. , Gorini G. , Hellesen C. , Hjalmarsson A. , Popovichev S. , Ronchi E. , Tardocchi M. , Weiszflog M. ,   JET EFDA Contributors
Published: June 2009

Burning plasma experiments such as ITER and DEMO require diagnostics capable of withstanding the harsh environment generated by the intense neutron flux and to maintain stable operating conditions for times longer than present day systems. For these reasons, advanced control and monitoring (CM) systems will be necessary for the reliable operation of diagnostics. This paper describes the CM system of the upgraded magnetic proton recoil neutron spectrometer installed at the Joint European Torus focusing in particular on a technique for the stabilization of the gain of the photomultipliers coupled to the neutron detectors. The results presented here show that this technique provides good results over long time scales. The technique is of general interest for all diagnostics that employ scintillators coupled to photomultiplier tubes.
Pyrazine luminogens with “free” and “locked” phenyl rings: Understanding of restriction of intramolecular rotation as a cause for aggregation-induced emission
Authors: Qin Anjun , Lam Jacky W. Y. , Mahtab Faisal , Jim Cathy K. W. , Tang Li , Sun Jingzhi , Sung Herman H. Y. , Williams Ian D. , Tang Ben Zhong
Published: June 2009

Nitrogen-containing heterocyclic pyrazine luminogens with “free” (1) and “locked” (2) phenyl rings were readily prepared in high yields. The propeller-shaped luminogen 1 shows aggregation-induced emission feature, whereas the disk-shaped chromophore 2 shows conventional aggregation-caused quenching effect, offering a direct evidence to support our hypothesis that restriction of intramolecular rotation is the main cause for the AIE phenomenon.
Modified shape of the Eiffel Tower determined for an atmospheric boundary-layer wind profile
Authors: Weidman P. D.
Published: June 2009

The design and construction of the Eiffel Tower was based, in part, on a uniform horizontal wind model giving 300 kg m−2 kinematic pressure acting on the surface of the tower. Eiffel received a patent for his method of construction that eliminates the need for diagonal trellis bars used to resist the moment of an oncoming wind. At the end of the 19th century boundary-layer theory, laminar or turbulent, was nonexistent. Now, however, models for atmospheric flow over rough landscapes are available, the simplest being a power-law distribution of velocity with height. In this paper we deduce the shape of the tower had Eiffel incorporated this information into the design and construction of his world famous tower. Moreover, we prove Eiffel’s observation that the tower profile conforms to the moment distribution wrought by the wind.
Sensitivity and optimal forcing response in separated boundary layer flows
Authors: Alizard Frédéric , Cherubini Stefania , Robinet Jean-Christophe
Published: June 2009

The optimal asymptotic response to time harmonic forcing of a convectively unstable two-dimensional separated boundary layer on a flat plate is numerically revisited from a global point of view. By expanding the flow disturbance variables and the forcing term as a summation of temporal modes, the linear convective instability mechanism associated with the response leading to the maximum gain in energy is theoretically investigated. Such a response is driven by a pseudoresonance of temporal modes due to the non-normality of the underlying linearized evolution operator. In particular, the considered expansion on a limited number of modes is found able to accurately simulate the linear instability mechanism, as suggested by a comparison between the global linear stability analysis and a linearized direct numerical simulation. Furthermore, the dependence of such a mechanism on the Reynolds number and the adverse pressure gradient is investigated, outlining a physical description of the destabilization of the flow induced by the rolling up of the shear layer. Therefore, the convective character of the problem suggests that the considered flat plate separated flows may act as a selective noise amplifier. In order to verify such a possibility, the responses of the flow to the optimal forcing and to a small level of noise are compared, and their connection to the onset of self-excited vortices observed in literature is investigated. For that purpose, a nonlinear direct numerical simulation is performed, which is initialized by a random noise superposed to the base flow at the inflow boundary points. The band of excited frequencies as well as the associated peak match with the ones computed by the asymptotic global analysis. Finally, the connection between the onset of unsteadiness and the optimal response is further supported by a comparison between the optimal circular frequency and a typical Strouhal number predicted by numerical simulations of previous authors in similar cases.
Role of initial conditions on noise from underexpanded pipe jets
Authors: Jothi T. J. S. , Srinivasan K.
Published: June 2009

An experimental investigation of acoustic radiation from underexpanded air jets of different shear layer thicknesses has been performed. The initial shear layer thickness variation is achieved by allowing the jet to exit through pipes of various lengths. The lengths of the pipes considered for the present study are in the range 1≤L/D≤6. The pressure ratio of the pipe jets is varied from 3 to 7 corresponding to fully expanded jet Mach numbers of 1.35≤Mj≤1.92. Acoustic radiation is characterized in terms of overall sound pressure level, directivity, tonal, and broadband shock associated noise. Increase in initial shear layer thickness in pipe jets results in the decrease of screech tone amplitude (by up to 20 dB), and increase in broadband shock associated noise level. Turbulent mixing noise levels are higher for shorter (L/D) pipe jets compared to longer ones. Longer pipe jets exhibit more number of screech modes while the shorter pipe jets show only one or two screech modes. The screech frequency and the peak frequency of broadband shock associated noise do not show much variation with increase in initial shear layer thickness. The screech frequency of a jet with negligible shear layer thickness (orifice jet) is found to be higher compared to those of finite shear layer thickness from pipe jets.
Direct enumeration studies of band-gap properties of AlxGayIn1−x−yP alloys
Authors: Jungthawan Sirichok , Limpijumnong Sukit , Collins Reuben , Kim Kwiseon , Graf Peter A. , Turner John A.
Published: June 2009

A band-gap database of a large number of configurations (∼5000 configurations) is produced for AlGaInP semiconductor alloys using an empirical pseudopotential method. Our results show that the band gap of this alloy system depends strongly on the cation arrangement in addition to the alloy composition. This indicates that one can effectively control the band gap of alloys by controlling the cation arrangement. For each given alloy composition, the range of possible band gaps is calculated and the complete database of the results is made available online. Our results show that a majority of alloy configurations have band gaps smaller than those predicted by Vegard’s law. Our results also show several systematic trends in the band gaps depending on the superlattice directions.
End-compensated magnetostatic cavity for polarized H3e neutron spin filters
Authors: McIver J. W. , Erwin R. , Chen W. C. , Gentile T. R.
Published: June 2009

We have expanded upon the “Magic Box” concept, a coil driven magnetic parallel plate capacitor constructed out of mu-metal, by introducing compensation sections at the ends of the box that are tuned to limit end-effects similar to those of short solenoids. This ability has reduced the length of the magic box design without sacrificing any loss in field homogeneity, making the device far more applicable to the often space limited neutron beam line. The appeal of the design beyond affording longer polarized H3e lifetimes is that it provides a vertical guide field, which facilitates neutron spin transport for typical polarized beam experiments. We have constructed two end-compensated magic boxes of dimensions 28.4×40×15 cm3 (length×width×height) with measured, normalized volume-averaged transverse field gradients ranging from 3.3×10−4 to 6.3×10−4 cm−1 for cell sizes ranging from 8.1×6.0 to 12.0×7.9 cm2 (diameter×length), respectively.
Validation of the paraxial beam-tracing method in critical cases
Authors: Maj Omar , Pereverzev Grigory V. , Poli Emanuele
Published: June 2009

Paraxial Wentzel–Kramers–Brillouin (WKB) (beam-tracing) solutions of a scalar wave equation are compared to the exact solutions for the two important cases of reflection from a plasma with linearly increasing density and of oblique propagation in the presence of an absorbing half plane. In these situations, the beam-tracing technique is close to its limits of validity, yet these conditions are often met in practical applications. More specifically, the first case is relevant to reflectometry diagnostics, whereas the second case models the absorption of electron-cyclotron beams obliquely launched onto the resonance layer, as envisaged, for instance, for the ITER upper launcher [M. A. Henderson et al., Nucl. Fusion 48, 054013 (2008)]. In both cases, the beam-tracing approach is found to reproduce well the exact behavior of the wave for experimentally relevant parameters, confirming the robustness of WKB-based techniques close to or even beyond their range of applicability. For the latter case, moreover, the analysis presented here allows an evaluation of the reflection of part of the beam by the steep gradients of the absorption coefficient at the resonance layer, our results yielding an upper bound on the amount of reflected power.
Quantum error correction on infinite-dimensional Hilbert spaces
Authors: Bény Cédric , Kempf Achim , Kribs David W.
Published: June 2009

We present a generalization of quantum error correction to infinite-dimensional Hilbert spaces. We find that, under relatively mild conditions, much of the structure known from systems in finite-dimensional Hilbert spaces carries straightforwardly over to infinite dimensions. We also find that, at least in principle, there exist qualitatively new classes of quantum error correcting codes that have no finite-dimensional counterparts. We begin with a shift of focus from states to algebras of observables. Standard subspace codes and subsystem codes are seen as the special case of algebras of observables given by finite-dimensional von Neumann factors of type I. The new classes of codes that arise in infinite dimensions are shown to be characterized by von Neumann algebras of types II and III, for which we give in-principle physical examples.
On the extraction of interface trap density in the Pt/La2O3/Ge gate stack and the determination of the charge neutrality level in Ge
Authors: Bozyigit D. , Rossel C.
Published: June 2009

The study of trap densities at the oxide-semiconductor interface of the new generation of field-effect transistors is essential for the optimization of their electrical performance. The conventional conductance method, which was efficiently applied to Si, turns out to be less appropriate on alternative substrates, such as the lower band gap germanium (Ge), because of the strong influence of minority carrier processes. Recent investigations show that these restrictions might be severe and lead to incorrect conclusions. We identify here the appearance of such processes, compare the conventional conductance method with the full conductance method of Martens et al., IEEE Electron Device Lett. 27, 405 (2006), and propose an extension of the latter. By applying a reverse bias to source and drain with respect to the substrate, it becomes possible to separate, on the same device, the contribution of electron and hole trap distributions. Our approach allows us to determine the position of the charge neutrality level at the surface of the semiconductor, which is found to be at 0.14 eV above the valence band.
Dipolar gyres generated by continuous forcing on a polar β-plane
Authors: Afanasyev Y. D. , Jewtoukoff V.
Published: June 2009

Dipolar vortices generated by a force applied to an area of finite size are investigated in a rotating, polar β-plane fluid. The laboratory polar β-plane is dynamically equivalent to the polar regions of the ocean or the atmosphere where the Coriolis parameter varies quadratically with latitude. Both forced and unforced evolution of the flow is observed. The altimetric imaging velocimetry method is employed for imaging the rotating flows and measuring the velocity and surface elevation fields. The forced dipoles were observed to rotate in the anticyclonic direction from their initial orientation where the axis of the dipole is aligned with the direction of the force toward some steady state where the axis of the dipole is at an angle to the direction of the force. The theoretical prediction of the rotation angle is found to be in good agreement with the experimental results. Asymptotic solutions for limiting cases when forced dipoles are affected either by the Ekman-type bottom friction or by the γ-effect are found. The experiments also demonstrate that the unforced free dipoles rotate anticyclonically with almost steady rate and emit basin-scale Rossby waves.
First-principles investigation of mechanical and electronic properties of MNNi3 (M=Zn, Mg, or Cd)
Authors: Li Chong , Chen W. G. , Wang Fei , Li S. F. , Sun Q. , Wang Songyou , Jia Yu
Published: June 2009

Mechanical and electronic properties of an antiperovskite-type superconductor ZnNNi3 as well as its isostructural and isovalent counterparts MgNNi3 and CdNNi3 have been studied by using the first-principles calculations. Lattice constant a, bulk modulus B, elastic constants of cubic lattice (C11, C12, and C44), compressibility K, shear modulus G, tetragonal shear modulus G′, effective charges, as well as electronic structures of the three compounds have been calculated. The results show that the lattice constants of the three compounds have a relationship a(ZnNNi3)<a(MgNNi3)<a(CdNNi3), while on the contrary, the order of the bulk modulus is B(CdNNi3)<B(MgNNi3)<B(ZnNNi3), consisting with the tetragonal shear modulus G′. The neighboring Ni and N atoms are prone to form covalent bonds, while the M-Ni/N (M=Zn, Mg, or Cd) favor ionic nature. For the electronic structures, Ni 3d and the hybridization between Ni 3d and N 2p have the most contributions to the total density of states at the Fermi level [N(EF)] for all the three compounds. Although the component of M in the compounds has very small contributions to the N(EF), it may lead to a small shift in the bands near the Fermi level and therefore influence the values of N(EF), which probably results in the ZnNNi3 superconductivity at TC≈3 K while the other two compounds show no indication of superconducting transition down to the temperature.
On the dynamics of chaotic spiking-bursting transition in the Hindmarsh–Rose neuron
Authors: Innocenti G. , Genesio R.
Published: June 2009

The paper considers the neuron model of Hindmarsh–Rose and studies in detail the system dynamics which controls the transition between the spiking and bursting regimes. In particular, such a passage occurs in a chaotic region and different explanations have been given in the literature to represent the process, generally based on a slow-fast decomposition of the neuron model. This paper proposes a novel view of the chaotic spiking-bursting transition exploiting the whole system dynamics and putting in evidence the essential role played in the phenomenon by the manifolds of the equilibrium point. An analytical approximation is developed for the related crucial elements and a subsequent numerical analysis signifies the properness of the suggested conjecture.
Dielectric behavior and phase transition in perovskite oxide Pb(Fe1/2Nb1/2)1−xTixO3 single crystal
Authors: Jia Yanmin , Luo Haosu , Or Siu Wing , Wang Yu , Chan Helen Lai Wa
Published: June 2009

Perovskite oxide Pb(Fe1/2Nb1/2)0.52Ti0.48O3 crystals, which were grown using a modified Bridgman method, show a high low-frequency dielectric constant response at room temperature. The Curie phase transition occurs at 523 K. The characteristic frequency of the dielectric dispersion versus the inverse of temperature obeys an Arrhenius relation, which shows a thermally activated behavior. The thermal activation energy for relaxation was found to be ∼0.14 eV. The high dielectric permittivity was attributed to oxygen vacancies and conduction via hopping carriers.
Ferroelectric phase transition and low-temperature structure fluctuations in Ba4Nd2Ti4Nb6O30 tungsten bronze ceramics
Authors: Zhu X. L. , Chen X. M. , Liu X. Q. , Li X. G.
Published: June 2009

Dielectric characteristics of Ba4Nd2Ti4Nb6O30 tungsten bronze ceramics have been investigated over a broad range of temperature and frequency. The real part of the dielectric constant (ε′) shows a sharp peak at 417 K indicating the ferroelectric phase transition. Two dielectric relaxations are observed in the lower temperature range, which are very obvious in the dielectric loss (tan δ) and the imaginary part of the dielectric constant (ε″). The differential scanning calorimetry (DSC), Raman scattering, and ultrasonic studies of the present ceramics have also been conducted in a broad temperature range covering the ferroelectric transition and/or the dielectric relaxation temperatures. The endothermal peak in the DSC curve around the ferroelectric transition temperature confirms the first-order structural transition with the transition enthalpy of 5.72 kJ/mol. Steplike anomalies in the wave number of the Raman vibrations and abnormal drop of the intensity of the Raman spectra are observed accompanying the ferroelectric phase transition. The dielectric relaxations in the temperature range below Tc are attributed to the structure fluctuations associated with the coupling between the polarizability in the ab plane and the c axis displacement, as well as the remaining random field effects, which are suggested as the possible origin of the anomalous reduction of the Raman intensity below Tc as well as the anomalies in the ultrasonic velocity and attenuation measurements. Freezing of these structure fluctuations are detected by the ultrasonic anomaly at about 120 K and the increasing Raman intensity below 150 K.
An exchange-Coulomb model potential energy surface for the Ne–CO interaction. I. Calculation of Ne–CO van der Waals spectra
Authors: Dham Ashok K. , McCourt Frederick R. W. , Meath William J.
Published: June 2009

Exchange-Coulomb model potential energy surfaces have been developed for the Ne–CO interaction. The initial model is a three-dimensional potential energy surface based upon computed Heitler–London interaction energies and literature results for the long-range induction and dispersion energies, all as functions of interspecies distance, the orientation of CO relative to the interspecies axis, and the bond length of the CO molecule. Both a rigid-rotor model potential energy surface, obtained by setting the CO bond length equal to its experimental spectroscopic equilibrium value, and a vibrationally averaged model potential energy surface, obtained by averaging the stretching dependence over the ground vibrational motion of the CO molecule, have been constructed from the full data set. Adjustable parameters in each model potential energy surface have been determined through fitting a selected subset of pure rotational transition frequencies calculated for the N20e–C12O12 isotopolog to precisely known experimental values. Both potential energy surfaces provide calculated results for a wide range of available experimental microwave, millimeter-wave, and midinfrared Ne–CO transition frequencies that are generally far superior to those obtained using the best current literature potential energy surfaces. The vibrationally averaged CO ground state potential energy surface, employed together with a potential energy surface obtained from it by replacing the ground vibrational state average of the CO stretching dependence of the potential energy surface by an average over the first excited CO vibrational state, has been found to be particularly useful for computing and/or interpreting mid-IR transition frequencies in the Ne–CO dimer.
Fokker–Planck simulations for core heating in subignition cone-guiding fast ignition targets
Authors: Johzaki Tomoyuki , Nakao Yasuyuki , Mima Kunioki
Published: June 2009

On the basis of two-dimensional coupled relativistic Fokker–Planck and fluid simulations, the core heating by fast electron beam in subignition cone-guiding fast ignition targets is investigated. It was found that the magnetic field due to the thermoelectric current reduces the beam pinching due to the resistive magnetic field. Compared with the carbon-deuterium fuel used in the early phase of Fast Ignition Realization Experiment, phase-I, the core heating of deuterium-tritium (DT) fuel used in the later phase is less effective. One reason is the slower temperature relaxation between bulk electron and ion for the DT case, which is previously reported by Johzaki et al. [Phys. Plasmas 15, 062702 (2008)]. In addition, in the lower-Z DT case, the pinching effects by the resistive magnetic field are weaker due to smaller resistivity; the optical thickness for fast electron beam is smaller, which leads to further reduction in core heating efficiency. It was also found that the fast electron beam quality deteriorates during the transport in the only 10 μm thickness high-Z (e.g., Au and Cu) cone tip because of the collisional scattering and drag. As the result, the core heating efficiency considerably goes down compared to the case neglecting the transport in the cone tip.
Theoretical investigation of the Ωg,u(+/−) states of K2 dissociating adiabatically up to K(4p P23/2)+K(4p P23/2)
Authors: Jraij A. , Allouche A. R. , Magnier S. , Aubert-Frécon M.
Published: June 2009

A theoretical investigation of the electronic structure of the K2 molecule, including spin-orbit effects, has been performed. Potential energies have been calculated over a large range of R up to 75a0 for the 88 Ωg,u(+/−) states dissociating adiabatically into the limits up to K(4p P23/2)+K(4p P23/2). Equilibrium distances, transition energies, harmonic frequencies, as well as depths for wells and heights for barriers are reported for all of the bound Ωg,u(+/−) states. Present ab initio calculations are shown to be able to reproduce quite accurately the small structures (wells and barrier) displayed at very long-range (R>50a0) by the (2,3)1u and (2)0g− purely long-range states. As the present data could help experimentalists, we make available extensive tables of energy values versus internuclear distances in our database at the web address http://www-lasim.univ-lyon1.fr/spip.php?rubrique99.
Rotation velocities in the plasma edge driven viscously by scrape-off layer flows
Authors: Stacey W. M.
Published: June 2009

Scrape-off layer parallel flows and the viscous fluxes in the plasma edge driven thereby are calculated from neoclassical theory for a model problem representative of a present experiment, using an analytical model for elongated flux surface geometry with a Shafranov shift to provide a realistic evaluation of important poloidal dependences. The estimated effects of the viscous torques of toroidal and poloidal momentum driven by these scrape-off layer flows on rotation velocities in the edge plasma are substantial, suggesting possible explanations for various experimental observations.
Anomalous, hysteretic, transverse magnetoresistance in superconducting thin films with magnetic vortex arrays
Authors: Villegas J. E. , Sharoni A. , Li C.-P. , Schuller Ivan K.
Published: June 2009

We have studied a superconducting/ferromagnetic hybrid system in which the normal to superconducting phase transition is controlled by the magnetic history. An anomalous transverse resistance appears at the phase transition, which shows magnetic hysteresis and a strong current dependence. We show that the anomaly originates from current redistributions due to the inhomogeneous superconductivity of this system.
Effects of nitrogen incorporation on the interfacial layer between thermally grown dielectric films and SiC
Authors: Corrêa S. A. , Radtke C. , Soares G. V. , Miotti L. , Baumvol I. J. R. , Dimitrijev S. , Han J. , Hold L. , Kong F. , Stedile F. C.
Published: June 2009

C-containing interlayers formed between the SiC substrate and dielectric films thermally grown in O2, NO, and in O2 followed by annealing in NO were investigated. X-ray reflectometry and x-ray photoelectron spectroscopy were used to determine N and C incorporation in dielectric films and interlayers, as well to determine their mass densities and thicknesses. The thickest C-containing interlayer was observed for films thermally grown in O2, whereas the thinnest one was observed for films directly grown in NO, evidencing that the presence of N decreases the amount of carbonaceous compounds in the dielectric/SiC interface region.
Model for electron mobility as a function of carrier concentration and strain in heavily doped strained silicon
Authors: Bennett N. S. , Cowern N. E. B. , Sealy B. J.
Published: June 2009

Strain engineering plays a pivotal role in modern devices due to the advantages it offers in enhancing carrier mobility, μ. In addition to strain, ε, carrier concentration, N, also determines mobility and an understanding of the functional dependence μ(N,ε) at various levels of strain is vital. Although well established for low and moderate doping, currently little is known about μ(N) for high carrier concentrations (>1019 cm−3) in strained Si. We present experimental data to fill this void, allowing an extension of the current model for μ(N) [Masetti et al., IEEE Trans. Electron DevicesIETDAI0018-9383 30, 764 (1983)] to account for strain. We also consider the influence of strain induced from dopant atoms. Experiments show the effects of tensile strain as a mobility enhancer are reduced but still significant at high doping concentrations. The model reproduces this effect and accounts for μ(N,ε) across the full range of doping concentrations.
p
-type doping efficiency of MoO3 in organic hole transport materials
Authors: Hamwi S. , Meyer J. , Winkler T. , Riedl T. , Kowalsky W.
Published: June 2009

We report on the p-type doping efficiency of molybdenum trioxide (MoO3) in the ambipolar organic charge transport material 4,4′-Bis(carbazol-9-yl)-biphenyl (CBP). Kelvin probe analysis is used to study the work function with increasing thickness of doped CBP layers with varied MoO3 concentration deposited on indium tin oxide (ITO). Based on the model of a one-sided abrupt (n+p) junction between ITO and the MoO3 doped CBP layer, the density of free holes has been determined. A surprisingly low p-type doping efficiency of less than 2% has been derived. Segregation and clustering of the MoO3 dopant could explain these results.
Charge conduction mechanisms of atomic-layer-deposited Er2O3 thin films
Authors: Jinesh K. B. , Lamy Y. , Tois E. , Besling W. F. A.
Published: June 2009

The charge transport mechanism through atomic-layer-deposited erbium oxide thin films has been analyzed with current-voltage (I-V) measurements. At low electric field, i.e., below 3 MV/cm, the charge conduction through 10 nm thick Er2O3 films is dominated by Poole–Frenkel electron injection. However, Fowler–Nordheim tunneling of holes also occurs at higher electric fields through the oxide. Various electronic and material parameters such as the trap density, activation energy of the traps, and interface defect density are extracted from the I-V and parallel conductance (GP) measurements as a function of frequency.
Recent Science from Australian Large-Scale Millimetre Mapping Projects: Proceedings from a Swinburne University Workshop
Authors: Bains I. , Breen S. L. , Burton M. G. , Cunningham M. R. , Jones P. A. , Kawamura A. , Lo N. , Rowell G. P. , Walsh A.
Published: June 2009

Since the recent upgrades to the Australia Telescope National Facility (ATNF) Mopra telescope back-end and receiver system, it has risen from an under-subscribed facility to a sought-after instrument with heavy international competition to gain time. Furthermore, the introduction of the on-the-fly mapping capability in 2004 has made this technique one of Mopra's most popular observing modes. In addition, the recent upgrade of the NANTEN millimetre-wavelength telescope to the sub-millimetre NANTEN2 instrument, has provided a complementary, higher-frequency facility to Mopra. A two-day workshop was held at Swinburne University in June 2008 to disseminate the current state of ongoing large-scale mapping projects and associated spin-offs that the telescopes' upgrades have facilitated, and to decide upon future research directions. Here, we provide a summary of the result-oriented talks as a record of the state of Australian-access single-dish millimetre science in 2008.
Velocity-Curve Analysis of the Spectroscopic Binary Stars V373 Cas, V2388 Oph, V401 Cyg, GM Dra, V523 Cas, AB And and HD 141929 by Artificial Neural Networks
Authors: Karami K. , Ghaderi K. , Mohebi R. , Sadeghi R. , Soltanzadeh M. M.
Published: June 2009

We used an Artificial Neural Network (ANN) to derive the orbital parameters of spectroscopic binary stars. Using measured radial velocity data of seven double-lined spectroscopic binary systems V373 Cas, V2388 Oph, V401 Cyg, GM Dra, V523 Cas, AB And and HD 141929, we found corresponding orbital and spectroscopic elements. Our numerical results are in good agreement with those obtained by others using more traditional methods.
Trim24 targets endogenous p53 for degradation
Authors: Allton Kendra , Jain Abhinav K. , Herz Hans-Martin , Tsai Wen-Wei , Jung Sung Yun , Qin Jun , Bergmann Andreas , Johnson Randy L. , Barton Michelle Craig
Published: June 2009

Numerous studies focus on the tumor suppressor p53 as a protector of genomic stability, mediator of cell cycle arrest and apoptosis, and target of mutation in 50% of all human cancers. The vast majority of information on p53, its protein-interaction partners and regulation, comes from studies of tumor-derived, cultured cells where p53 and its regulatory controls may be mutated or dysfunctional. To address regulation of endogenous p53 in normal cells, we created a mouse and stem cell model by knock-in (KI) of a tandem-affinity-purification (TAP) epitope at the endogenous
Trp-53
locus. Mass spectrometry of TAP-purified p53-complexes from embryonic stem cells revealed Tripartite-motif protein 24 (Trim24), a previously unknown partner of p53. Mutation of
TRIM24
homolog,
bonus
, in
Drosophila
led to apoptosis, which could be rescued by p53-depletion. These in vivo analyses establish
TRIM24/bonus
as a pathway that negatively regulates p53 in
Drosophila
. The Trim24-p53 link is evolutionarily conserved, as
TRIM24
depletion in human breast cancer cells caused p53-dependent, spontaneous apoptosis. We found that Trim24 ubiquitylates and negatively regulates p53 levels, suggesting Trim24 as a therapeutic target to restore tumor suppression by p53.