bluuebunny/crossref_metadata_2025 huggingface dataset:
Present‐day strain accumulation and slip rates associated with southern San Andreas and eastern California shear zone faults
Authors: Spinler Joshua C. , Bennett Richard A. , Anderson Megan L. , McGill Sally F. , Hreinsdóttir Sigrún , McCallister Andrew
Published: November 2010

We present the first results from a dense network of 36 campaign and 46 continuous GPS stations located in the Eastern Transverse Ranges Province (ETR), a transition zone between the southernmost San Andreas fault (SSAF) and eastern California shear zone (ECSZ). We analyzed the campaign data together with available data from continuous GPS stations for the period 1994–2009. We used the GPS velocity estimates to constrain elastic block models to investigate fault‐loading rates representing four hypotheses characterized by different fault‐block geometries. Fault‐block scenarios include blocks bounded by the east‐striking left‐lateral Pinto Mountain, Blue Cut, and Chiriaco faults of the ETR; blocks bounded by a right‐lateral north‐northwest striking structure (the “Landers‐Mojave earthquake line”) that cuts obliquely across the ETR and mapped Mojave Desert faults; and combinations of these end‐member hypotheses. Each model implies significantly different active fault geometries, block rotation rates, and slip rates for ETR and ECSZ structures. All models suggest that SSAF slip rate varies appreciably along strike, generally consistent with rates derived from tectonic geomorphology and paleoseismology, with a maximum of ∼23 mm/yr right‐lateral along the southernmost Coachella Valley strand, decreasing systematically to <10 mm/yr right‐lateral through the San Gorgonio Pass region. Slip rate estimates for the San Jacinto fault are ∼12 mm/yr for all models tested. All four models fit the data equally well in a statistical sense. Qualitative comparison among models and consideration of geologic slip rates and other independent data reveals strengths and weaknesses of each model.
Quantitative earthquake forecasts resulting from static stress triggering
Authors: Hainzl S. , Brietzke G. B. , Zöller G.
Published: November 2010

In recent years, the triggering of earthquakes has been discussed controversially with respect to the underlying mechanisms and the capability to evaluate the resulting seismic hazard. Apart from static stress interactions, other mechanisms including dynamic stress transfer have been proposed to be part of a complex triggering process. Exploiting the theoretical relation between long‐term earthquake rates and stressing rate, we demonstrate that static stress changes resulting from an earthquake rupture allow us to predict quantitatively the aftershock activity without tuning specific model parameters. These forecasts are found to be in excellent agreement with all first‐order characteristics of aftershocks, in particular, (1) the total number, (2) the power law distance decay, (3) the scaling of the productivity with the main shock magnitude, (4) the foreshock probability, and (5) the empirical Båth law providing the maximum aftershock magnitude, which supports the conclusion that static stress transfer is the major mechanism of earthquake triggering.
A study of acoustic propagation from a large bolide in the atmosphere with a dense seismic network
Authors: Hedlin Michael A. H. , Drob Doug , Walker Kris , de Groot‐Hedlin Catherine
Published: November 2010

A large meteor entered the atmosphere above northeastern Oregon on 19 February 2008 at 530 PST. Several hundreds of broadband seismic stations in the U.S. Pacific Northwest recorded acoustic‐to‐seismic coupled signals from this event. The travel times of the first arriving energy are consistent with a terminal explosion source model, suggesting that the large size of the explosion masked any signals associated with a continuous line source along its supersonic trajectory. Several infrasound arrays in North America also recorded this event. Both the seismic and infrasound data have been used to locate the explosion in 3‐D space and time. Climatological atmospheric velocity models predict that infrasound signals from sources that occur at mid‐northern latitudes in winter are usually ducted to the east due to eastward zonal winds. In this paper, we analyze travel time picks and use 3‐D ray tracing to generate synthetic travel times based on various atmospheric models to show that the seismic network data instead reveal a predominant westward propagation direction. A sudden stratospheric warming event that reversed the zonal wind flow explains this westward propagation. The seismic data illuminate in unprecedented spatial detail the range and azimuthal definition of shadow zones out to a range of 500 km, suggesting that dense seismic networks can be used to study infrasound propagation at spatial resolutions that exceed that which can be done with only a handful of globally distributed infrasound arrays.
Analysis of the origin of the distribution of CO in the subtropical southern Indian Ocean in 2007
Authors: Duflot V. , Dils B. , Baray J. L. , De Mazière M. , Attié J. L. , Vanhaelewyn G. , Senten C. , Vigouroux C. , Clain G. , Delmas R.
Published: November 2010

We show carbon monoxide (CO) distributions at different vertical levels over the subtropical southern Indian Ocean, analyzing an observation campaign using Fourier transform infrared (FTIR) solar absorption spectrometry performed in 2007 at Reunion Island (21°S, 55°E). The CO pollution levels detected by the FTIR measurements during the campaign show a doubling of the CO total columns during the Southern Hemisphere biomass burning season. Using correlative data from the Measurement of Pollution in the Troposphere instrument and back trajectories analyses, we show that the potential primary sources for CO throughout the troposphere in 2007 are southern Africa (June–August) and South America (September–October). A secondary potential contribution from Southeast Asia and Indonesia‐Malaysia was identified in the upper troposphere, especially in July and September. We examine the relation between the Asian monsoon anticyclone seasonal cycle and this result. We also investigate the relative contribution of different areas across the globe to the CO concentration in the subtropical southern Indian Ocean in 2007 using backward simulations combining the Lagrangian model FLEXPART 6.2, the Global Fire Emissions Database (GFEDv2.1) and the Emission Database for Global Atmospheric Research (EDGARv3.2‐FT2000). We confirm the predominance of the African and South American contributions in the CO concentration in the southern subtropical Indian Ocean below 11 km. We show that CO transported from Australia makes only a small contribution to the total CO concentration observed over Reunion Island, and that the long‐range transport of CO coming from Southeast Asia and Indonesia‐Malaysia is important, especially from June until September in the upper troposphere.
A piecewise linear model for detecting climatic trends and their structural changes with application to mesosphere/lower thermosphere winds over Collm, Germany
Authors: Liu R. Q. , Jacobi Ch. , Hoffmann P. , Stober G. , Merzlyakov E. G.
Published: November 2010

A piecewise linear model is developed to detect climatic trends and their structural changes in time series with a priori unknown number and positions of breakpoints (BPs). The departure (i.e., the initial noise term) of trends from time series is allowed to be interpreted by the first‐ and second‐order autoregressive models. The goodness of fit of candidate models, if the residuals are accepted as normally distributed white noise, is evaluated using the Schwarz Bayesian Information Criterion (BIC). The uncertainties of all trend parameters are estimated using the Monte‐Carlo method. The model is applied to the mesosphere and lower thermosphere (MLT) winds obtained at Collm, Germany, during 1960–2007. A persistent increase after ∼1980 of the zonal prevailing wind is observed in all seasons and hence in the zonal annual mean based on the primary models. Trends of the meridional prevailing wind are different for different seasons. Several major trend BPs are identified in the annual mean zonal and meridional winds according to BIC. However, in view of the large wind variability before the late 1970s, alternative models are considered. This provides four additional minor breaks. In some cases, the initial noise must be further interpreted by autoregressive models, suggesting that other unidentified factors may also play a role.
Comparison of modeling approaches for carbon partitioning: Impact on estimates of global net primary production and equilibrium biomass of woody vegetation from MODIS GPP
Authors: Ise Takeshi , Litton Creighton M. , Giardina Christian P. , Ito Akihiko
Published: November 2010

Partitioning of gross primary production (GPP) to aboveground versus belowground, to growth versus respiration, and to short versus long‐lived tissues exerts a strong influence on ecosystem structure and function, with potentially large implications for the global carbon budget. A recent meta‐analysis of forest ecosystems suggests that carbon partitioning to leaves, stems, and roots varies consistently with GPP and that the ratio of net primary production (NPP) to GPP is conservative across environmental gradients. To examine influences of carbon partitioning schemes employed by global ecosystem models, we used this meta‐analysis‐based model and a satellite‐based (MODIS) terrestrial GPP data set to estimate global woody NPP and equilibrium biomass, and then compared it to two process‐based ecosystem models (Biome‐BGC and VISIT) using the same GPP data set. We hypothesized that different carbon partitioning schemes would result in large differences in global estimates of woody NPP and equilibrium biomass. Woody NPP estimated by Biome‐BGC and VISIT was 25% and 29% higher than the meta‐analysis‐based model for boreal forests, with smaller differences in temperate and tropics. Global equilibrium woody biomass, calculated from model‐specific NPP estimates and a single set of tissue turnover rates, was 48 and 226 Pg C higher for Biome‐BGC and VISIT compared to the meta‐analysis‐based model, reflecting differences in carbon partitioning to structural versus metabolically active tissues. In summary, we found that different carbon partitioning schemes resulted in large variations in estimates of global woody carbon flux and storage, indicating that stand‐level controls on carbon partitioning are not yet accurately represented in ecosystem models.
Shaping the T‐cell repertoire in the periphery
Authors: Allen Stacey , Turner Stephen J , Bourges Dorothée , Gleeson Paul A , van Driel Ian R
Published: November 2010

Selection of T cells does not end with events in the thymus, but continues in extrathymic tissues and for the life of the organism. In this review, we examine how self‐reactive T cells are rendered harmless and the processes that select for T cells that are most efficient at combating pathogens. The implications of peripheral T‐cell selection for the immune response as animals age are discussed as is the critical role of dendritic cells in directing T‐cell differentiation.
Quantitative analysis of the transcription control mechanism
Authors: Mao Changhui , Brown Christopher R , Falkovskaia Elena , Dong Shawfeng , Hrabeta‐Robinson Eva , Wenger Lauren , Boeger Hinrich
Published: November 2010

Gene transcription requires a sequence of promoter state transitions, including chromatin remodeling, assembly of the transcription machinery, and clearance of the promoter by RNA polymerase. The rate‐limiting steps in this sequence are regulated by transcriptional activators that bind at specific promoter elements. As the transition kinetics of individual promoters cannot be observed, the identity of the activator‐controlled steps has remained a matter of speculation. In this study, we investigated promoter chromatin structure, and the intrinsic noise of expression over a wide range of expression values for the PHO5 gene of yeast. Interpretation of our results with regard to a stochastic model of promoter chromatin remodeling and gene expression suggests that the regulatory architecture of the gene expression process is measurably reflected in its intrinsic noise profile. Our chromatin structure and noise analyses indicate that the activator of PHO5 transcription stimulates the rates of promoter nucleosome disassembly, and assembly of the transcription machinery after nucleosome removal, but no other rates of the expression process.
Effect of antisense oligodeoxynudeotide targeted against NF-κB/P65 on cell proliferation and tumorgenesis of gastric cancer
Authors: Li Qi , Yu Yingyan , Gao Yong , jiang Hong , Zhu Zhenggang
Published: November 2010

Gastric cancer is still a major health problem worldwide due to its frequency, poor prognosis and limited treatment options. To study the inhibitory effect of nuclear transcription factor kappa B(NF-κB) antisense oligodeoxynucleotide(ASODN) on the growth and tumorgenesis of human gastric cancer, we synthesis and transfect ASODN of NF-κB/P65 to gastric cancer cell line. The effect of ASODN of NF-κB/P65 on the proliferation of gastric cancer cells was measured by MTT method. The subcutaneous xenograft model of human gastric cancer was established in nude mice and the tumor growth curve was observed. The cell proliferation was significantly inhibited in P65 ASODN transfected group in vitro (P<0.05). In vivo, tumor formation test showed that the tumor volume in nude mice in ASODN group was obviously smaller than in other groups (P<0.05), the apoptosis index (AI) was significantly higher (P<0.001). Stimultaneously, MVD in ASODN group was markedly lower than in other groups (P<0.01). Our findings suggest that P65 ASODN can inhibit gastric cancer cells proliferation and tumorgenesis by inducing cell apoptosis and inhibiting tumor angiogenesis. NF-κB can be used as a new biological therapeutic target of gastric cancer.
Charting the NF-kB pathway interactome map
Authors: Tieri Paolo , Termanini Alberto , Bellavista Elena , Salvioli Stefano , Franceschi Claudio
Published: November 2010

One of the phenomena observed in human aging is the progressive increase of a systemic inflammatory state, a condition referred to as “inflammaging”, negatively correlated with longevity. The five components of the Nuclear Factor kB (NF-kB) family are prominent mediators of inflammation. Several different signaling pathways activated by very diverse stimuli converge on NF-kB, resulting in a regulatory system characterized by high complexity. It is increasingly recognized that the number of components that impinges upon phenotypic outcomes of signal transduction pathways may be higher than those taken into consideration from canonical pathway representations. Scope of this analysis is to provide a wider, systemic picture of such intricate signaling system.
Non‐coding RNAs and their epigenetic regulatory mechanisms
Authors: Zhou Huihui , Hu Hu , Lai Maode
Published: November 2010

It is widely accepted that ncRNAs (non‐coding RNAs), as opposed to protein‐coding RNAs, represent the majority of human transcripts; and the regulatory roles of many of these ncRNAs have been elucidated over the past decade. One important role so far recognized for ncRNAs is their participation in the epigenetic regulation of genes. Indeed, it is becoming increasingly apparent that most epigenetic mechanisms of gene expression are controlled by ncRNAs. In this review, the different types of ncRNA that are strongly linked to epigenetic regulation are characterized and their possible mechanisms discussed.
Centroid molecular dynamics: Comparison with exact results for model systems
Authors: Polyakov E. A. , Lyubartsev A. P. , Vorontsov-Velyaminov P. N.
Published: November 2010

The relation between the accuracy of centroid molecular dynamics correlation functions, and the geometry of the centroid potential is investigated. It is shown that, depending on the temperature, there exist several regimes, and in each of them certain features of the exact Kubo correlation functions are reproduced. The change of regimes is related to the emergence of barriers in the centroid potential. In order to clarify how the above described picture of regimes is modified in real systems when dissipation is important, a methodology is developed to test the accuracy of centroid correlation functions for the model of a particle coupled to a harmonic heat bath. A modification of the centroid molecular dynamics method to include the influence of the heat bath is introduced. Preliminary results of comparison of centroid molecular dynamics with the numerically exact results of filtered propagator functional method are presented.
Stability analysis of unbounded uniform dense granular shear flow based on a viscoplastic constitutive law
Authors: Chen Wen-Yau , Lai Jeng-You , Young D. L.
Published: November 2010

Asymptotic and transient stability analyses of unbounded uniform granular shear flow at high solids volume fractions were carried out in the paper, based on a model composed of the viscoplastic constitutive law [P. Jop, Y. Forterre, and O. Pouliquen, Nature (London) 441, 727 (2006)] and the dilatancy law [O. Pouliquen et al., J. Stat. Mech.: Theory Exp. (2006) P07020]. We refer to this model as the VPDL (meaning of the “viscoplastic and dilatancy laws”) thereinafter. In this model, dense granular flows were treated as a viscoplastic fluid with a Drucker–Prager-like yielding criterion. We compared our results to those obtained using the frictional-kinetic model (FKM) [M. Alam and P. R. Nott, J. Fluid Mech. 343, 267 (1997)]. Our main result is that unbounded uniform dense granular shear flows are always asymptotically stable at large time based on the VPDL model, at least for two-dimensional perturbations. This is valid for disturbances of layering modes (i.e., the perturbations whose wavenumber vectors are aligned along the transverse coordinate) as well as for nonlayering modes (the streamwise component of the wavenumber vector is nonzero). By contrast, layering modes can be unstable based on the FKM constitutive laws. Interestingly, in the framework of the VPDL, the analysis shows that significant transient growth may occur owing to the non-normality of the linear system, although disturbances eventually decay at large time.
Poloidal rotation and its relation to the potential vorticity flux
Authors: McDevitt C. J. , Diamond P. H. , Gürcan Ö. D. , Hahm T. S.
Published: November 2010

A kinetic generalization of a Taylor identity appropriate to a strongly magnetized plasma is derived. This relation provides an explicit link between the radial mixing of a four–dimensional (4D) gyrocenter fluid and the poloidal Reynolds stress. This kinetic analog of a Taylor identity is subsequently utilized to link the turbulent transport of poloidal momentum to the mixing of potential vorticity. A quasilinear calculation of the flux of potential vorticity is carried out, yielding diffusive, turbulent equipartition, and thermoelectric convective components. Self-consistency is enforced via the quasineutrality relation, revealing that for the case of a stationary small amplitude wave population, deviations from neoclassical predictions of poloidal rotation can be closely linked to the growth/damping profiles of the underlying drift wave microturbulence.
Femtosecond pump/supercontinuum-probe spectroscopy: Optimized setup and signal analysis for single-shot spectral referencing
Authors: Dobryakov A. L. , Kovalenko S. A. , Weigel A. , Pérez-Lustres J. L. , Lange J. , Müller A. , Ernsting N. P.
Published: November 2010

A setup for pump/supercontinuum-probe spectroscopy is described which (i) is optimized to cancel fluctuations of the probe light by single-shot referencing, and (ii) extends the probe range into the near-uv (1000–270 nm). Reflective optics allow 50 μm spot size in the sample and upon entry into two separate spectrographs. The correlation γsame between sample and reference readings of probe light level at every pixel exceeds 0.99, compared to γconsec<0.92 reported for consecutive referencing. Statistical analysis provides the confidence interval of the induced optical density, ΔOD. For demonstration we first examine a dye (Hoechst 33258) bound in the minor groove of double-stranded DNA. A weak 1.1 ps spectral oscillation in the fluorescence region, assigned to DNA breathing, is shown to be significant. A second example concerns the weak vibrational structure around t=0 which reflects stimulated Raman processes. With 1% fluctuations of probe power, baseline noise for a transient absorption spectrum becomes 25 μOD rms in 1 s at 1 kHz, allowing to record resonance Raman spectra of flavine adenine dinucleotide in the S0 and S1 state.
Bimetallic nanopetals for thousand-fold fluorescence enhancements
Authors: Fu Chi-Cheng , Ossato Giulia , Long Maureen , Digman Michelle A. , Gopinathan Ajay , Lee Luke P. , Gratton Enrico , Khine Michelle
Published: November 2010

We present a simple, ultra-rapid and robust method to create sharp nanostructures—nanopetals—in a shape memory polymer substrate demonstrating unprecedented enhancements for surface enhanced sensing over large surface areas. These bimetallic nanostructures demonstrate extremely strong surface plasmon resonance effects due to the high density multifaceted petal structures that increase the probability of forming nanogaps. We demonstrate that our nanopetals exhibit extremely strong surface plasmons, confining the emission and enhancing the fluorescence intensity of the nearby high-quantum yield fluorescein by >4000×. The enhancements are confined to the extremely small volumes at the nanopetal borders. This enables us to achieve single molecule detection at relatively high and physiological concentrations.
Influence of low atomic number plasma component on the formation of laser-produced plasma jets
Authors: Kasperczuk A. , Pisarczyk T. , Badziak J. , Borodziuk S. , Chodukowski T. , Gus’kov S. Yu. , Demchenko N. N. , Ullschmied J. , Krousky E. , Masek K. , Pfeifer M. , Rohlena K. , Skala J. , Pisarczyk P.
Published: November 2010

The results of investigations are presented that are connected with a very simple method of plasma jet formation, which consists in irradiating a massive planar target made of material with relatively high atomic number by a partly defocused laser beam. This brief communication is aimed at investigations of interaction of axially symmetrical light (plastic-CH) plasma with heavy (copper) plasma. It demonstrates that a relatively thin plastic plasma envelope can compress the Cu plasma and control the Cu-jet formation.
Rarefied gas flows through a curved channel: Application of a diffusion-type equation
Authors: Aoki Kazuo , Takata Shigeru , Tatsumi Eri , Yoshida Hiroaki
Published: November 2010

Rarefied gas flows through a curved two-dimensional channel, caused by a pressure or a temperature gradient, are investigated numerically by using a macroscopic equation of convection-diffusion type. The equation, which was derived systematically from the Bhatnagar–Gross–Krook model of the Boltzmann equation and diffuse-reflection boundary condition in a previous paper [K. Aoki et al., “A diffusion model for rarefied flows in curved channels,” Multiscale Model. Simul. 6, 1281 (2008)], is valid irrespective of the degree of gas rarefaction when the channel width is much shorter than the scale of variations of physical quantities and curvature along the channel. Attention is also paid to a variant of the Knudsen compressor that can produce a pressure raise by the effect of the change of channel curvature and periodic temperature distributions without any help of moving parts. In the process of analysis, the macroscopic equation is (partially) extended to the case of the ellipsoidal-statistical model of the Boltzmann equation.
Steady state performance test analysis of actively cooled extractor grids for SST-1 neutral beam injector
Authors: Jana M. R. , Mattoo S. K. , Khan M.
Published: November 2010

Neutral beam injection (NBI) system is a workhorse to heat magnetically confined tokamak fusion plasma. The heart of any NBI system is an ion extractor system. Steady State Superconducting Tokamak-1 (SST-1) needs 0.5 MW of hydrogen beam power at 30 kV to raise the plasma ion temperature to ∼1 keV and 1.7 MW of hydrogen beam power at 55 kV for future upgradation. To meet this requirement, an ion extractor system consisting of three actively cooled grids has been designed, fabricated, and its performance test has been done at MARION test stand, IPP, Julich, Germany. During long pulse (14 s) operation, hydrogen ion beam of energy 31 MJ has been extracted at 41 kV. In this paper, we have presented detailed analysis of calorimetric data of actively cooled extractor grids and showed that by monitoring outlet water temperature, grid material temperature can be monitored for safe steady state operation of a NBI system. Steady state operation of NBI is the present day interest of fusion research. In the present experimental case, performance test analysis indicates that the actively cooled grids attain steady state heat removal condition and the grid material temperature rise is ∼18°C and saturates after 10 s of beam pulse.
A sensitive and versatile laser scanning confocal optical microscope for single-molecule fluorescence at 77 K
Authors: Hirschfeld V. , Hübner C. G.
Published: November 2010

We developed a cryostat suitable for a laser scanning confocal microscope which allows for a short working distance and thus the usage of an objective with a high numerical aperture ensuring high collection efficiency. The in situ preparation of a thin layer of amorphous water is realized in a part of the cryostat, a Dewar vessel, which is put onto a custom-made, liquid-nitrogen immersed spin-coater. First tests on the setup are performed on a perylenemonoimide/polymethyl methacrylate model system using a standard oil objective and a dry objective at ambient temperature as well as a dry objective at liquid nitrogen temperature (77 K). Fluorescence resonance energy transfer (FRET) measurements on doubly labeled, freeze-quenched polyproline chains show the applicability of the new method on biomolecules. The alternating laser excitation (ALEX) is modified to a line-scanning process (slow ALEX) to optimize the sorting of the labeled molecules. Photophysics and photochemistry at liquid nitrogen temperature are investigated.
Local response dispersion method. II. Generalized multicenter interactions
Authors: Sato Takeshi , Nakai Hiromi
Published: November 2010

Recently introduced local response dispersion method [T. Sato and H. Nakai, J. Chem. Phys. 131, 224104 (2009)], which is a first-principles alternative to empirical dispersion corrections in density functional theory, is implemented with generalized multicenter interactions involving both atomic and atomic pair polarizabilities. The generalization improves the asymptote of intermolecular interactions, reducing the mean absolute percentage error from about 30% to 6% in the molecular C6 coefficients of more than 1000 dimers, compared to experimental values. The method is also applied to calculations of potential energy curves of molecules in the S22 database [P. Jurečka et al., Phys. Chem. Chem. Phys. 8, 1985 (2006)]. The calculated potential energy curves are in a good agreement with reliable benchmarks recently published by Molnar et al. [J. Chem. Phys. 131, 065102 (2009)]. These improvements are achieved at the price of increasing complexity in the implementation, but without losing the computational efficiency of the previous two-center (atom-atom) formulation. A set of different truncations of two-center and three- or four-center interactions is shown to be optimal in the cost-performance balance.
The relativistic treatment of spin-0 particles under the rotating Morse oscillator
Authors: Bayrak O. , Soylu A. , Boztosun I.
Published: November 2010

We present the energy eigenvalues and corresponding normalized eigenfunctions of the relativistic spin-0 particles by solving the Klein–Gordon equation. Analytical forms for the energy eigenvalues and eigenfunctions have been derived by using Pekeris approximation to the centrifugal term within the framework of the asymptotic iteration method for the equal vector and scalar rotating Morse oscillator. The eigenvalue equation results in a transcendental form, in which the numerical values are presented in atomic units for arbitrary n and ℓ quantum states.
Femtosecond laser-ultrasonic investigation of plasmonic fields on the metal/gallium nitride interface
Authors: Chen Hung-Pin , Wen Yu-Chieh , Chen Yi-Hsin , Tsai Cheng-Hua , Lee Kuang-Li , Wei Pei-Kuen , Sheu Jinn-Kong , Sun Chi-Kuang
Published: November 2010

By using femtosecond laser-ultrasonic, we demonstrate an approach to study the surface plasmon field optically excited in the interface between metal and a semiconductor thin film. By femtosecond impulsive excitation on gallium–nitride (GaN), different optical probe signals were observed when the impulse-excited nanoacoustic pulse propagated through the metal film and metal nanoslits. By analyzing the shape and temporal response of thus induced acousto-optical signals, our femtosecond laser-ultrasonic study not only reveals the plasmonic field distribution optically excited in the metal/substrate interface but also confirms that the penetration depth of surface plasmon field into the substrate agrees well with a simulation result.
Generation of episodic magnetically driven plasma jets in a radial foil Z-pinch
Authors: Suzuki-Vidal Francisco , Lebedev Sergey V. , Bland Simon N. , Hall Gareth N. , Swadling George , Harvey-Thompson Adam J. , Chittenden Jeremy P. , Marocchino Alberto , Ciardi Andrea , Frank Adam , Blackman Eric G. , Bott Simon C.
Published: November 2010

We present experimental results of the formation of magnetically driven plasma jets, showing for the first time a way of producing episodic jet/ouflows in the laboratory. The jets are produced using a 6.5 μm thick aluminum disk (a radial foil), which is subjected to the 1 MA, 250 ns current pulse from the MAGPIE generator [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1533 (1996)]. The early time motion of the foil is characterized by the bulk motion of the mass due to the magnetic pressure, together with the formation of a surface plasma following the direction of the J×B force. A low density plasma fills the region above the foil preceding the formation of subsequent magnetically driven jets on the axis of expanding magnetic bubbles. The outflows emerge in timescales of ∼30–40 ns and their episodic nature is the result of current reconnection in the foil, aided by the formation of current-driven instabilities in the jet and the distribution of mass available from the foil. The additional inductance due to the new current path inside the cavities was measured using an inductive probe, allowing to estimate the energy balance associated with the episodes. The measured temperature of the compressed jet resulted in Te∼300 eV and a magnetic Reynolds number of ReM∼200–1000, allowing the experiments to be in the regime relevant for scaled representations of astrophysical outflows.
Investigation of magnetic anisotropy of (Ge,Mn) nanocolumns
Authors: Jain A. , Jamet M. , Barski A. , Devillers T. , Porret C. , Bayle-Guillemaud P. , Gambarelli S. , Maurel V. , Desfonds G.
Published: November 2010

Thin films of Ge1−xMnx containing Mn-rich nanostructures, so called nanocolumns, are grown by molecular-beam-epitaxy at low growth temperature (Tg) on Ge(001) substrate. Depending on the growth temperature, these nanocolumns can be either crystalline or amorphous. A quantitative study of magnetic anisotropy of these nanocolumns is performed by superconducting quantum interference device and electron paramagnetic resonance. We present a correlation between the structural morphology (diamond lattice) and the magnetic properties in these nanocolumns. Crystalline (Ge,Mn) nanocolumns (Tg=100 °C) exhibit fourth-order magnetic anisotropy due to the coupling between their magnetization and the cubic lattice whereas amorphous columns (Tg=150 °C) only exhibit second-order shape anisotropy.
Shear-flow excitation mechanisms of recessed localized arc-filament plasma actuators
Authors: Kleinman R. R. , Bodony D. J. , Freund J. B.
Published: November 2010

Localized arc-filament plasma actuators, placed near the nozzle lip of a laboratory jet, have recently been demonstrated to have sufficient control authority to significantly excite the jet downstream [M. Samimy et al., J. Fluid Mech. 578, 305 (2007)]. This class of plasma actuator, which in this application is recessed in a small cavity near the nozzle lip, causes intense local heating. This heating is thought to be the root mechanism of its influence on the flow, but how this principally entropic thermal source couples with the vortical jet shear layer turbulence downstream is unclear. We investigate this using direct numerical simulations, which match the flow conditions of the corresponding experiment, including Reynolds number, but are two-dimensional to ease computational expense. Despite this obvious modeling approximation, the simulations include the key features of the laboratory system: a thin boundary layer, a plasma-like thermal source in a small recessed cavity, a nozzle lip, and a downstream free shear layer. Results are shown to match the temperature and near-field pressure measured in the laboratory actuators. It is found that the cavity, which was initially included to shield the actuator plasma from the flow, is essential for its action. Thermal expansion within the cavity leads to an ejection of fluid from it, which perturbs the boundary layer and the downstream mixing layer. There is a finite baroclinic torque, but its effects are relatively minor. An alternate actuator designed to mimic the pressure effects of the full actuator, without its concomitant thermal heating, is nearly as effective at exciting the shear layer. An actuator model without the cavity recess does not provide effective actuation. These results suggest that there is significant potential to optimize the actuation authority through design of cavity recesses that augment its effect.
Bulk heterojunction solar cells based on a low-bandgap carbazole-diketopyrrolopyrrole copolymer
Authors: Jo Jang , Gendron David , Najari Ahmed , Moon Ji Sun , Cho Shinuk , Leclerc Mario , Heeger Alan J.
Published: November 2010

Bulk heterojunction (BHJ) solar cells fabricated with a phase separated nanomaterial comprising a carbazole-diketopyrrolopyrrole copolymer (PCBTDPP) and [6,6]-phenyl C70-butyric acid methyl ester (PC70BM) are demonstrated with power conversion efficiency>3.5%. The PCBTDPP:PC70BM BHJ nanomorphology was controlled by changing the length of the alkyl side-chain of the polymer and by utilizing processing additives.
Influences of the biaxial strain and c-screw dislocation on the clustering in InGaN alloys
Authors: Lei Huaping , Chen Jun , Ruterana Pierre
Published: November 2010

Using the molecular dynamics simulation based on Stillinger–Weber potentials, the roles of lattice mismatch and threading dislocations (c-screw type) on phase segregation in InGaN alloys have been explored. The thermodynamic stability and structural deformation of the InGaN alloys with In-rich clusters are analyzed when biaxial stress and c-screw dislocations act on the systems. The results show that the formation of In-rich clusters is suppressed in the case of lattice mismatch, whereas it takes place in the presence of c-screw dislocations independent of the strain condition of InGaN alloys.
Synthesis and optical properties modulation of ZnO/Eu2O3 nanocable arrays
Authors: Yang Lei , She Yajuan , Zhao Shihua , Yue Shihai , Wang Qian , Hu Aiping , Zhang Wei
Published: November 2010

White-light-emitting materials have attracted considerable attention because of their applications, such as large-surface emitting devices and displays. However, simply mixing nanoparticles would result in uneven color. Nanocables are expected to improve the chemical stability and color uniformity. Herein we demonstrate the synthesis of Eu2O3/ZnO nanocable arrays embedded in anodic alumina template via a versatile, simple, and cheap method. In order to control the composition of the cable with low cost, a two-step synthesis including an electric field deposition and a sol-gel template approach is used to fabricate the nanocable. The product is investigated by x-ray powder diffraction, transmission electron microscopy, selected area electron diffraction, and photoluminescence (PL) spectrum. The results show that ordered Eu2O3/ZnO nanocable arrays with an average inside diameter of 20–40 nm and wall thickness of 20–40 nm were prepared. By adjusting the excitation wavelength, change of the emitting color of the cables from blue to white could be obtained. Energy and charge transfer were found by investigating the electronic transition and recombination in the PL process. These arrays are promising for applications in display, white phosphors, and ultraviolet detectors owing to the special optical properties. And this method may be of much significance in the synthesis of nanocables with the controllable composition.
Axisymmetric oscillation modes of a double droplet system
Authors: Ramalingam Santhosh K. , Basaran Osman A.
Published: November 2010

A double droplet system (DDS) consists of a sessile and a pendant drop that are coupled through a liquid filled cylindrical hole in a plate of thickness d. For a small hole radius R, equilibrium shapes of both drops are sections of spheres. While DDSs have a number of applications in microfluidics, a DDS oscillating about its equilibrium state can be used as a fast focusing liquid lens. Here, a DDS consisting of an isothermal, incompressible Newtonian fluid of constant density ρ and constant viscosity μ that is surrounded by a gas is excited by oscillating in time (a) the pressure in the gas surrounding either drop (pressure excitation), (b) the plate perpendicular to its plane (axial excitation), and (c) the hole radius (radial excitation). In contrast with previous works that assumed transient drop shapes are spherical, they are determined here by simulation and used to identify the natural modes of axisymmetric oscillations from resonances observed during frequency sweeps with DDSs for which the combined volume V of the two drops is less than (4/3)πR3. Pressure and axial excitations are found to have identical responses but axial and radial excitations are shown to excite different modes. These modes are compared to those exhibited by single pendant (sessile) drop systems. In particular, while a single pendant (sessile) drop has one additional oscillation mode compared to a free drop, a DDS is found to exhibit roughly twice as many oscillation modes as a pendant (sessile) drop. The effects of dimensionless volume V/R3, dimensionless plate thickness d/R, and Ohnesorge number Oh=μ/ρRσ, where σ is the surface tension of the DDS-gas interface, on the resonance frequencies are also investigated.
High intensity x-ray diffraction in transmission mode employing an analog of Poisson’s spot
Authors: Evans Paul , Rogers Keith , Chan Jer , Rogers Joseph , Dicken Anthony
Published: November 2010

Poisson’s spot is a diffraction phenomenon producing an intensity maximum at the center of the geometric shadow of circular opaque objects. In an analog of the Poisson spot experiment, we show that a tubular cone of x-rays incident upon a crystalline sample produces diffraction spots or foci, corresponding to Bragg maxima within a transmission shadow. We discuss the beam geometry and the intensity gain recorded at the foci in transmission mode. We describe the geometric growth and decay of the foci over a linear axis with the aid of a movie sequence synchronized with the plotting of a diffractogram. The mean signal of a small central area in each successive camera image provides the intensity data for the diffractogram.
Compositional evolution of SiGe islands on patterned Si (001) substrates
Authors: Zhang Jianjun , Rastelli Armando , Schmidt Oliver G. , Bauer Günther
Published: November 2010

The authors investigate, by atomic-force-microscopy-based nanotomography, the composition evolution of ordered SiGe islands grown on pit-patterned Si (001) substrates as their size and aspect ratio increase with increasing Ge deposition. Compared to islands grown on flat substrates, the ordered island arrays show improved size, shape, and compositional homogeneity. The three-dimensional composition profiles of individual pyramids, domes, and barns reveal that the Ge fraction at the base and in subsurface regions of the islands decreases with increasing amount of deposited Ge.
Attofarad capacitance measurement corresponding to single-molecular level structural variations of self-assembled monolayers using scanning microwave microscopy
Authors: Wu Shijie , Yu Jing-Jiang
Published: November 2010

Scanning microwave microscopy (SMM) proves to be capable of quantitatively measuring the minute capacitance difference between self-assembled monolayers (SAMs) with subnanometer variation in layer thickness. Using decanethiol and octadecanthiol as an example, the coexistence of two different SAMs on the same substrate with a well-known height difference of 0.88 nm is achieved via an atomic force microscopy-based nanolithography method known as nanografting. SMM was first calibrated against a capacitance standard developed by NIST. The measured capacitance difference is about 24 aF under the condition that the effective tip/sample contact area was estimated to be ∼60 nm in diameter.
Room temperature gate modulation of electron spin relaxation time in (110)-oriented GaAs/AlGaAs quantum wells
Authors: Iba Satoshi , Koh Shinji , Kawaguchi Hitoshi
Published: November 2010

A (110)-oriented p-i-n structure with GaAs/AlGaAs quantum wells (QWs) was fabricated, and the effect of an applied electric field on the electron spin relaxation time was investigated by utilizing polarization- and time-resolved photoluminescence measurements. We demonstrated a tenfold modulation of the electron spin relaxation time from 4.0 to 0.3 ns in the QWs through the Rashba spin-orbit coupling induced by applying an external electric field at room temperature.
Electrostatic soliton and double layer structures in unmagnetized degenerate pair plasmas
Authors: Mahmood S. , Khan S. A. , Ur-Rehman H.
Published: November 2010

The acoustic solitons and double layers are studied in unmagnetized quantum electron-positron plasmas in the presence of stationary ions. The quantum hydrodynamic model is employed and reductive perturbation method is used to derive the Korteweg–de Vries (KdV) and extended KdV equations for solitons and double layers, respectively. It is found that in the linear limit both slow acoustic and fast Langmuir waves can propagate in such type of quantum plasmas like in classical pair-ion or pair plasmas. The amplitude and width of the electrostatic solitons are found to be decreasing with the increase in concentration of positrons (or decrease in the concentration of ions) in degenerate electron-positron-ion plasmas. It is found that only rarefactive double layer can exist in such plasmas which depend on various parameters. The dependence of double layer structure on ion concentration and quantum diffraction effects of electrons and positrons are also discussed. The results are also elaborated graphically by considering dense plasma parameters in the outer layers of astrophysical objects such as white dwarfs and neutron stars.
Decay properties of artificial two-domain structures in LiNbO3 crystals studied by scanning probe microscope
Authors: Kan Yi , Bo Huifeng , Lu Xiaomei , Xu Tingting , Jin Yaming , Wu Xiaobo , Huang Fengzhen , Zhu Jinsong
Published: November 2010

Decay processes of artificial two-domain structures with various distances in LiNbO3 crystals were carefully investigated using scanning probe microscope. The decay behavior of the composite domains is found closely related to the set domain distance. Detailed analysis indicates that the tip field mostly affects the lateral domain wall motion of the domains in two-domain structures, while the repulsive force of bound charges mainly influences vertical domain wall motion. Thin sample thickness and large domain distance are inferred beneficial for manufacturing small scaled stable domain structures.
Competitive emission process in mixed single layer top-emission organic light emitting device with reduced efficiency roll-off
Authors: Wang Zhaokui , Lou Yanhui , Naka Shigeki , Okada Hiroyuki
Published: November 2010

The authors investigate efficiency roll-off in 5,6,11,12-tetraphenylnaphthacene (rubrene)-based mixed single layer top-emission organic light emitting devices by codoping with special additive dopants. The efficiency roll-off is suppressed after codoping rubrene with phenoxazone (Nile red). Due to dual nature of rubrene acting as electron hopping site and hole trap, it not only captures carrier producing light but also transfers energy to Nile red and then produces light. Meanwhile, Nile red molecules can also get energy from host directly. There exists a competitive process between three emission mechanisms, which depress self-quenching of dye molecules during emission, resulting in improved efficiency and lowered driving voltage.
The effect of periodically moving boundaries on thermomagnetic convection in ferrofluids
Authors: Bajaj Renu
Published: November 2010

The thermomagnetic instability in a horizontal layer of ferrofluids heated from below, with the boundaries oscillating periodically about zero or nonzero mean velocity, in the presence of vertical magnetic field is investigated numerically. The two boundaries are considered rigid, kept at fixed values of temperature, and are magnetically permeable. Chebyshev tau method and Floquet theory are used to discuss the stability of the flow. Oscillatory shear flow is observed to affect the onset of instability as convective patterns in the form of rolls in the direction transverse to the shear flow. Oscillatory solutions synchronous to the frequency of modulation are observed. Subharmonic solutions have not been detected in the considered range of parameters. The amplitude and the frequency of oscillation of the velocity of the rigid boundaries affect the flow field of vertical velocity, temperature field, and the magnetic potential significantly.
Polarization-engineered GaN/InGaN/GaN tunnel diodes
Authors: Krishnamoorthy Sriram , Nath Digbijoy N. , Akyol Fatih , Park Pil Sung , Esposto Michele , Rajan Siddharth
Published: November 2010

We report on the design and demonstration of polarization-engineered GaN/InGaN/GaN tunnel junction diodes with high current density and low tunneling turn-on voltage. Wentzel–Kramers–Brillouin calculations were used to model and design tunnel junctions with narrow band gap InGaN-based barrier layers. N-polar p-GaN/In0.33Ga0.67N/n-GaN heterostructure tunnel diodes were grown using molecular beam epitaxy. Efficient interband tunneling was achieved close to zero bias with a high current density of 118 A/cm2 at a reverse bias of 1 V, reaching a maximum current density up to 9.2 kA/cm2. These results represent the highest current density reported in III-nitride tunnel junctions and demonstrate the potential of III-nitride tunnel devices for a broad range of optoelectronic and electronic applications.
Generation of compact radially polarized beam at 850 nm in vertical-cavity surface-emitting laser via plasmonic modulation
Authors: Cai Likang , Zhang Jing , Bai Wenli , Wang Qing , Wei Xin , Song Guofeng
Published: November 2010

We propose a convenient approach for generating compact radially polarized laser beam by integrating concentric gold rings on the surface of a vertical-cavity surface-emitting laser. Due to the polarization selection of the surface plasmon polariton mode excited by the gold rings, a radially polarized beam at 850 nm is experimentally demonstrated. The physical mechanisms of the generation are numerically and analytically analyzed by employing finite-difference time-domain method and metal-insulator-metal plasmonic waveguide theory.