bluuebunny/crossref_metadata_2025 huggingface dataset:
Arctic sea ice response to wind stress variations
Authors: Watanabe Eiji , Hasumi Hiroyasu
Published: November 2005

Timescale of sea ice response to wind stress variations and the mechanisms controlling the timescale are investigated by a coupled sea ice–ocean model. Wind stress variations account for a significant part of the changes of sea ice volume in the Arctic Ocean over the last several decades. The changes of sea ice volume associated with wind stress are mainly induced by changes of sea ice outflow from the Arctic Ocean. While outflow immediately responds to wind stress variations, responses of sea ice volume lag behind the changes of the outflow by several years. For example, when the model is driven by interannually varying wind stress with the other atmospheric forcing components given by climatology, sea ice outflow abruptly decreases in 1996 and remains almost constant for the following several years. However, the responding increase of sea ice volume is gradual and continues for several years. In order to clarify the timescale of sea ice response to an abrupt change of wind stress and the mechanisms controlling the timescale, the model is forced by two typical wind stress fields, which cause small and large outflow. Equilibrium annual mean ice thickness averaged over the Arctic Ocean is different by about 50 cm between these two wind‐forcing fields. Starting from the equilibrium state obtained under one of these two fields, wind‐forcing is switched to the other. Adjustment time of ice thickness is then defined as the year when annual mean ice thickness is adjusted to new equilibrium by 90% of the difference between the two equilibria. The timescale of the sea ice response and the mechanisms controlling the timescale are found to be different depending on whether the outflow increases or decreases. When the outflow increases, the timescale depends on the advection time of the sea ice flowing toward the exits. When the outflow decreases, the timescale depends on the thermodynamic growth rate of sea ice. The change in the late 1990s corresponds to the latter case.
Nonlinear vorticity balance of the Antarctic Circumpolar Current
Authors: Hughes Chris W.
Published: November 2005

Using a recently published global ocean mean surface dynamic topography, based predominantly on drifter data, the near‐surface vorticity balance of the Antarctic Circumpolar Current (ACC) is calculated. With a little smoothing, the dynamic topography is found to produce good estimates of even such highly differentiated quantities as the relative vorticity advection. Two clear modes of flow are found in the ACC: meanders of wavelength 300–500 km, in which the nonlinear term is important, resulting in a balance between advection of relative and planetary vorticity, as in a stationary equivalent‐barotropic Rossby wave (this implies a surface divergence which is at least partly balanced by an opposite divergence at depth); and a flow with divergence associated with topographic features. It is tentatively concluded that the divergence of this latter flow is a scaled measure of bottom pressure torque. The inferred bottom pressure torque shows large‐scale topographic interactions, as well as a strong influence of some sharp topographic features such as the fracture zones and Macquarie ridge system south of the Tasman Sea, and the narrow ridges in Drake Passage.
Laboratory observations of the morphodynamic evolution of tidal channels and tidal inlets
Authors: Tambroni N. , Bolla Pittaluga M. , Seminara G.
Published: November 2005

This paper tackles the problem of morphodynamic equilibrium of tidal channels and tidal inlets. We report a laboratory investigation of the process whereby an equilibrium morphology is established in a tidal system consisting of an erodible channel connected through an inlet to a tidal sea. Observations suggest that a morphodynamic equilibrium is eventually established both in the inlet region and in the channel. The latter exhibits a weakly concave bed profile seaward, a weakly convex profile landward, and the formation of a “beach” close to the landward end of the channel. A second set of observations concerns the formation and development of both small‐ and large‐scale bed forms. In particular, small‐scale forms are found to develop in the channel and in the basin, while larger‐scale forms, i.e., tidal bars, develop in the channel. A last observation concerns the formation of an outer delta in the “sea” basin. Results concerning the long‐term equilibrium of the bed profile in the channel compare fairly satisfactorily with recent theoretical results. The nature and characteristics of the observed small‐scale forms appear to be consistent with theoretical predictions and field observations concerning “fluvial” ripples and tidal dunes; bars show features in general accordance with recent results of a stability theory developed for tidal bars. The hydrodynamics of the inlet region exhibits a strongly asymmetric character, as observed in the field and predicted in early theoretical works, while the overall characteristics of the outer delta conform to available empirical relationships.
Shear‐wave splitting: A diagnostic tool to monitor fluid pressure in geothermal fields
Authors: Tang Chuanhai , Rial Jose A. , Lees Jonathan M.
Published: November 2005

An experiment on the uses of shear‐wave splitting as an imaging tool in fracture‐controlled geothermal reservoirs was conducted at Krafla, Iceland. Fifteen days after the beginning of the seismic recording the injection was stopped for eleven days and then restarted, a sequence designed to determine whether shear‐wave splitting measurements can detect the transient response of the subsurface crack system to changes in fluid pressure. It was observed that time delays between the fast and slow split shear waves changed significantly and promptly with the stoppage and resumption of injection. Large time delays occurred only during injection, decreased substantially during the stoppage phase, and increased again as injection restarted. Comparisons of these results with similar observations at the Coso geothermal field in California strongly suggest that the time delay of split shear waves can be a useful proxy to monitor fluid pressure in the cracks and changes in crack density.
Diurnal warming in the tropical Pacific and its interannual variability
Authors: Clayson Carol Anne , Weitlich Derrick
Published: November 2005

Analyses of satellite‐derived diurnal sea surface warming of the equatorial Pacific basin from 1996 through 2000 indicate that there is, in addition to seasonal changes, an east‐west dipole. For roughly half the year, the western (eastern) Pacific experiences enhanced (decreased) diurnal warming: the opposite is true for the other six months. La Niña conditions in 1998 through 1999 affected the strength (but not the overall sign) of the dipole. Simple analyses using a comprehensive turbulent model indicate it is important to account for diurnal warming since the SST change over a day depends on the upper ocean changes due to diurnal warming. Since the tropical Pacific SST and east‐west SST gradient is of interest to ENSO processes, ocean models that do not incorporate diurnal warming may overestimate mixing‐induced cooling and the east‐west SST gradient.
Predominance of industrial Pb in recent snow (1994–2004) and ice (1842–1996) from Devon Island, Arctic Canada
Authors: Shotyk William , Zheng Jiancheng , Krachler Michael , Zdanowicz Christian , Koerner Roy , Fisher David
Published: November 2005

Atmospheric Pb contamination was studied using snow and ice from the Canadian arctic. Forty‐five samples representing the past ten years of snow accumulation on Devon Island contain an average of 45.2 pg/g of Pb but only 0.43 pg/g of Sc. The average ratio of Pb to Sc (105) is far greater than that of soil‐derived dust particles (in the range 1 to 5) which indicates that ca. 95 to 99% of recent Pb is anthropogenic. Isotopic analyses (206Pb, 207Pb, 208Pb) confirm that anthropogenic sources continue to dominate atmospheric Pb inputs. Unlike snow from Greenland which receives Pb predominantly from the U.S. (206Pb/207Pb ≈ 1.2), snow from Devon Island is less radiogenic (206Pb/207Pb ≈ 1.15). There are pronounced seasonal variations, and the snow samples containing the greatest Pb enrichments are from winter when the Arctic is dominated by air masses originating in Eurasia. While the elimination of gasoline lead additives in Europe, North America and Japan has helped to reduce Pb emissions during the past two to three decades, aerosols in the Arctic today are still highly contaminated by industrial Pb.
El Niño–related offshore phytoplankton bloom events around the Spratley Islands in the South China Sea
Authors: Isoguchi Osamu , Kawamura Hiroshi , Ku‐Kassim Ku‐Yaacob
Published: November 2005

Satellite chlorophyll‐a (Chl‐a) observations reveal offshore phytoplankton bloom events with high Chl‐a (>1 mg m−3) spreading over 300 km off the coasts around the Spratley Islands in the South China Sea (SCS) during the spring of 1998. The bloom entails anomalous wind jet and sea surface temperature (SST) cooling, suggesting that the wind jet‐induced mixing and/or offshore upwelling bring about the cooling and the bloom through the supply of nutrient‐rich waters into the euphotic zone. The strong wind jet is orographically formed responding to shifts in wind direction over the eastern SCS. The wind shift is connected with the Philippine Sea anomalous anticyclone that is established during El Niño, indicating the El Niño‐related offshore bloom. The long‐term reanalysis winds over the eastern SCS demonstrates that wind jet formation and associated offshore cooling/bloom are expected to occur in most cases of the subsequent El Niño years.
Should light wind and windy nights have the same temperature trends at individual levels even if the boundary layer averaged heat content change is the same?
Authors: Pielke Roger A. , Matsui Toshihisa
Published: November 2005

Long‐term climate trends of surface air temperature should not be expected to have the same trends for light wind and stronger wind nights, even if the trends in the boundary layer heat fluxes were the same. Parker (2004) segmented observed surface temperature data into lighter and stronger wind terciles in order to assess whether the reported large‐scale global‐averaged temperature increases are attributable to urban warming. We conclude, however, that trends at an individual height depend on wind speed, thermodynamic stability, aerodynamic roughness, and the vertical gradient of absolute humidity. We present an analysis to illustrate why temperature values at specific levels will depend on wind speed, and with the same boundary layer heat content change, trends in temperature should be expected to be different at every height near the surface when the winds are light, as well as different between light wind and stronger wind nights. This introduces a complexity into the assessment of long‐term surface temperature trends that has not been previously recognized.
Multistability and hysteresis in the climate‐cryosphere system under orbital forcing
Authors: Calov Reinhard , Ganopolski Andrey
Published: November 2005

Using the Earth system model of intermediate complexity CLIMBER‐2 we studied the stability diagram of the climate‐cryosphere system in the phase space of Milankovitch forcing (maximum summer insolation at 65°N, abbreviated as MF). We have shown that the equilibrium response of the climate‐cyrosphere system to MF reveals pronounced hysteresis behavior within the range of Earth's orbital parameters. Depending on MF, the climate‐cryosphere system has either one (glacial or interglacial) or two different equilibrium states. The MF thresholds of the transitions between the two states depend on parameterizations of ice‐sheet dynamics, but are rather insensitive to the choice of the orbital parameters used to obtain the same value of MF. A change of atmospheric CO2 concentration from its interglacial to the glacial value, shifts the hysteresis curve by about 15 W/m2. These results provide an important support to the conceptual models of glacial cycles based on multistability and hysteresis behavior.
Modeling ice algal growth and decline in a seasonally ice‐covered region of the Arctic (Resolute Passage, Canadian Archipelago)
Authors: Lavoie Diane , Denman Kenneth , Michel Christine
Published: November 2005

We have developed a coupled snow‐ice–ice algae model to investigate the importance of different ice algal growth limitation terms, as well as different loss terms, in regulating the ice algal biomass accumulation at the bottom of landfast ice in the Canadian Archipelago. The model results are compared with data collected from May to July 2002 at a station near Resolute in Barrow Strait. Our results show that ice algae are light limited at the beginning of the bloom, then fluctuate between light and nutrient limitation, finally remaining nutrient limited toward the end of the bloom. The fortnightly tide modulates the ice algal biomass through the supply of nutrient to the ice algal layer but mainly through modulation of the bottom ice melt rate. We also demonstrate that the bottom ice melt rate regulates the maximum biomass attained in the region and that a rapid increase in ice temperature can lead to a significant decline in ice algal biomass. The eventual termination of the bloom is triggered by melting of the snow cover and results from (1) increased ice algal losses due to high bottom ice melt rate and (2) decreased ice algal growth due to nutrient limitation caused by the formation of a meltwater lens below the ice. Finally, our results show that the snow cover controls the length of the bloom, such that earlier snowmelt that is expected to accompany climate warming may lead to a reduction in ice algal production.
Retrieval of biomass combustion rates and totals from fire radiative power observations: Application to southern Africa using geostationary SEVIRI imagery
Authors: Roberts G. , Wooster M. J. , Perry G. L. W. , Drake N. , Rebelo L.‐M. , Dipotso F.
Published: November 2005

Southern African wildfires are a globally significant source of trace gases and aerosols. Estimates of southern African wildfire fuel consumption have varied from hundreds to thousands of teragrams (Tg), and better‐constrained estimates are required to properly assess the effects of the pollutant emissions. A new approach for providing such estimates is via remote sensing observations of fire radiative power (FRP), a variable proportional to the rate of fuel consumption. The launch of the SEVIRI radiometer onboard the geostationary Meteosat‐8 platform presents a unique opportunity to monitor FRP at 15‐min intervals, allowing analysis of the complete diurnal cycle of biomass burning and calculation of the total fire radiative energy. Here we present the first FRP retrievals from SEVIRI and compare them to those derived from near‐coincident MODIS overpasses. Strong agreement is achieved on a per‐fire basis (r2 = 0.83, n = 139, p < 0.0001), although at the regional scale SEVIRI typically underestimates FRP with respect to MODIS due primarily to its inability to confidently detect fire pixels with FRP < ∼100 MW. Using relationships developed during ground‐based experiments, SEVIRI‐derived FRP measures are converted into estimates of the rate and total quantity of biomass combusted in southern Africa. During a 4.5 day monitoring period, and based on only the observed FRP recorded by SEVIRI, we infer that as a minimum estimate, peak combustion rates reached 50 tons/s and a total of 3.2 Tg of fuel was burnt in southern Africa. While provisional, we calculate that these figures maybe potentially increased upward by a factor of ∼3 to account for atmospheric absorption of the upwelling radiation and for fires that were potentially cloud covered or too weakly emitting to be detected by the geostationary imager. The new tool of SEVIRI‐derived FRP provides an insight into biomass burning on the African continent at a hitherto unobtainable temporal frequency, highly suited to the linking of pollutant emissions estimates to models of atmospheric transport.
Water vapor variability in the tropics and its links to dynamics and precipitation
Authors: Zveryaev Igor I. , Allan Richard P.
Published: November 2005

The distribution and variability of water vapor and its links with radiative cooling and latent heating via precipitation are crucial to understanding feedbacks and processes operating within the climate system. Column‐integrated water vapor (CWV) and additional variables from the European Centre for Medium‐Range Weather Forecasts (ECMWF) 40‐year reanalysis (ERA40) are utilized to quantify the spatial and temporal variability in tropical water vapor over the period 1979–2001. The moisture variability is partitioned between dynamical and thermodynamic influences and compared with variations in precipitation provided by the Climate Prediction Center Merged Analysis of Precipitation (CMAP) and the Global Precipitation Climatology Project (GPCP). The spatial distribution of CWV is strongly determined by thermodynamic constraints. Spatial variability in CWV is dominated by changes in the large‐scale dynamics, in particular associated with the El Niño–Southern Oscillation (ENSO). Trends in CWV are also dominated by dynamics rather than thermodynamics over the period considered. However, increases in CWV associated with changes in temperature are significant over the equatorial east Pacific when analyzing interannual variability and over the north and northwest Pacific when analyzing trends. Significant positive trends in CWV tend to predominate over the oceans while negative trends in CWV are found over equatorial Africa and Brazil. Links between changes in CWV and vertical motion fields are identified over these regions and also the equatorial Atlantic. However, trends in precipitation are generally incoherent and show little association with the CWV trends. This may in part reflect the inadequacies of the precipitation data sets and reanalysis products when analyzing decadal variability. Though the dynamic component of CWV is a major factor in determining precipitation variability in the tropics, in some regions/seasons the thermodynamic component cancels its effect on precipitation variability.
Trends in upper‐level cloud cover and surface divergence over the tropical Indo‐Pacific Ocean between 1952 and 1997
Authors: Norris Joel R.
Published: November 2005

This study investigates the spatial pattern of linear trends in surface‐observed upper‐level (combined midlevel and high‐level) cloud cover, precipitation, and surface divergence over the tropical Indo‐Pacific Ocean during 1952–1997. Cloud values were obtained from the Extended Edited Cloud Report Archive (EECRA), precipitation values were obtained from the Hulme/Climate Research Unit data set, and surface divergence was alternatively calculated from wind reported by Comprehensive Ocean‐Atmosphere Data Set and from wind derived from Smith and Reynolds Extended Reconstructed sea level pressure data. Between 1952 and 1997, upper‐level cloud cover increased by about 4%‐sky‐cover over the central equatorial South Pacific and decreased by about 4–6%‐sky‐cover over the adjacent subtropics, the western Pacific, and the equatorial Indian Ocean. Trends in precipitation and surface convergence are usually positive where upper‐level cover trends are positive and negative where they are negative. Consistency between time series of upper‐level cloud cover reported by EECRA and the International Satellite Cloud Climatology Project (ISCCP) during 1984–1997 for various subregions provides further confirmation that the surface‐observed upper cloud trends are real. Estimated radiative effects of surface‐observed cloud cover anomalies are also well correlated with all‐sky radiation flux anomalies reported by the Earth Radiation Budget Satellite in most areas. Contrastingly, EECRA and ISCCP low‐level cloud cover regional time series exhibit little correspondence, and EECRA low‐level cloud cover trends are uniformly positive across the tropical Indo‐Pacific with no apparent relationship to changes in surface divergence. Although the spatial pattern of upper‐level cloud trends resembles that associated with El Niño, the trends are approximately three times larger than those predicted by a linear relationship to sea surface temperature in the Niño3.4 region.
Live‐cell imaging of endogenous Ras‐GTP illustrates predominant Ras activation at the plasma membrane
Authors: Augsten Martin , Pusch Rico , Biskup Christoph , Rennert Knut , Wittig Ute , Beyer Katja , Blume Alfred , Wetzker Reinhard , Friedrich Karlheinz , Rubio Ignacio
Published: November 2005

Ras‐GTP imaging studies using the Ras‐binding domain (RBD) of the Ras effector c‐Raf as a reporter for overexpressed Ras have produced discrepant results about the possible activation of Ras at the Golgi apparatus. We report that RBD oligomerization provides probes for visualization of endogenous Ras‐GTP, obviating Ras overexpression and the side effects derived thereof. RBD oligomerization results in tenacious binding to Ras‐GTP and interruption of Ras signalling. Trimeric RBD probes fused to green fluorescent protein report agonist‐induced endogenous Ras activation at the plasma membrane (PM) of COS‐7, PC12 and Jurkat cells, but do not accumulate at the Golgi. PM illumination is exacerbated by Ras overexpression and its sensitivity to dominant‐negative RasS17N and pharmacological manipulations matches Ras‐GTP formation assessed biochemically. Our data illustrate that endogenous Golgi‐located Ras is not under the control of growth factors and argue for the PM as the predominant site of agonist‐induced Ras activation.
Approach for maximizing chaotic mixing in microfluidic devices
Authors: Balasuriya Sanjeeva
Published: November 2005

This paper uses recent theoretical work to determine the best configurations for cross-channel micromixers in optimizing mixing between two fluids. Insight into the positioning, widths, and flow protocols within the lateral channels is provided.
Evanescent high pressure during hypersonic cluster-surface impact characterized by the virial theorem
Authors: Gross A. , Levine R. D.
Published: November 2005

Matter under extreme conditions can be generated by a collision of a hypersonic cluster with a surface. The ultra-high-pressure interlude lasts only briefly from the impact until the cluster shatters. We discuss the theoretical characterization of the pressure using the virial theorem and develop a constrained molecular-dynamics procedure to compute it. The simulations show that for rare-gas clusters the pressures reach the megabar range. The contribution to the pressure from momentum transfer is comparable in magnitude and is of the same sign as that (“the internal pressure”) due to repulsive interatomic forces. The scaling of the pressure with the reduced mechanical variables is derived and validated with reference to the simulations.
Development of a cooled He*(2S3) beam source for measurements of state-resolved collision energy dependence of Penning ionization cross sections: Evidence for a stereospecific attractive well around methyl group in CH3CN
Authors: Horio Takuya , Yamazaki Masakazu , Maeda Satoshi , Hatamoto Takuro , Kishimoto Naoki , Ohno Koichi
Published: November 2005

A low-temperature discharge nozzle source with a liquid-N2 circulator for He*(2S3) metastable atoms has been developed in order to obtain the state-resolved collision energy dependence of Penning ionization cross sections in a low collision energy range from 20 to 80 meV. By controlling the discharge condition, we have made it possible to measure the collision energy dependence of partial ionization cross sections (CEDPICS) for a well-studied system of CH3CN+He*(2S3) in a wide energy range from 20 to 350 meV. The anisotropic interaction potential energy surface for the present system was obtained starting from an ab initio model potential via an optimization procedure based on classical trajectory calculations for the observed CEDPICS. A dominant attractive well depth was found to be 423 meV (ca. 10kcal∕mol) at a distance of 3.20 Å from the center of mass of CH3CN in the N-atom side along the CCN axis. In addition, a weak attractive well (ca. 0.9kcal∕mol) surrounding the methyl group (−CH3) has been found and ascribed to the interaction between an unoccupied molecular orbital of CH3CN and 2s atomic orbital of He*(2S3).
Variational calculation for the doubly excited state (2p2)3Pe of BeIII
Authors: Bhattacharyya S. , Sil A. N. , Mukherjee T. K. , Mukherjee P. K.
Published: November 2005

Nonrelativistic energy of the (2p2)3Pe state of Be2+ has been calculated using Ritz-variational method. The trial wave function is of Hylleraas type. The upper-bound energy E=−3.38271242077a.u. calculated by us is the lowest yet obtained.
Characterization of the plasma on dielectric fiber (velvet) cathodes
Authors: Krasik Ya. E. , Gleizer J. Z. , Yarmolich D. , Krokhmal A. , Gurovich V. Ts. , Efimov S. , Felsteiner J. , Bernshtam V. , Saveliev Yu. M.
Published: November 2005

An investigation of the properties of the plasma and the electron beam produced by velvet cathodes in a diode powered by a ∼200kV, ∼300ns pulse is presented. Spectroscopic measurements demonstrated that the source of the electrons is surface plasma with electron density and temperature of ∼4×1014cm−3 and ∼7eV, respectively, for an electron current density of ∼50A∕cm2. At the beginning of the accelerating pulse, the plasma expands at a velocity of ∼106cm∕s towards the anode for a few millimeters, where its stoppage occurs. It was shown by optical and x-ray diagnostics that in spite of the individual character and nonuniform cross-sectional distribution of the cathode plasma sources, the uniformity of the extracted electron beam is satisfactory. A mechanism controlling the electron current-density cross-sectional uniformity is suggested. This mechanism is based on a fast radial plasma expansion towards the center due to a magnetic-field radial gradient. Finally, it was shown that the interaction of the electron beam with the stainless-steel anode does not lead to the formation of an anode plasma.
The effect of dopants on the microwave dielectric properties of Ba(Mg0.33Ta0.67)O3 ceramics
Authors: Surendran Kuzhichalil P. , Sebastian Mailadil T. , Mohanan Pezholil , Jacob Mohan V.
Published: November 2005

The effect of dopants with different valencies and ionic radii on the densification, structural ordering, and microwave dielectric properties of Ba(Mg1∕3Ta2∕3)O3 (BMT) is investigated. It is found that dopants such as Sb2O5, MnO, ZrO2, WO3, and ZnO improve the microwave dielectric properties of BMT. Addition of trivalent dopants is detrimental to the cation ordering and dielectric properties of BMT. A correlation between the microwave dielectric properties of BMT and ionic radii of the dopant has been established. The variation of the dielectric properties of pure and doped BMT at cryogenic temperatures is also discussed.
Composition and carrier-concentration dependence of the electronic structure of InyGa1−yAs1−xNx films with nitrogen mole fraction of less than 0.012
Authors: Kang Youn-Seon , Robins Lawrence H. , Birdwell Anthony G. , Shapiro Alexander J. , Thurber W. Robert , Vaudin Mark D. , Fahmi M. M. E. , Bryson Damian , Mohammad S. Noor
Published: November 2005

The electronic structure of Si-doped InyGa1−yAs1−xNx films on GaAs substrates, grown by nitrogen-plasma-assisted molecular-beam epitaxy, was examined by photoreflectance (PR) spectroscopy at temperatures between 20 and 300K. The films were approximately 0.5μm thick and had nitrogen mole fraction between x=0.0014 and x=0.012, measured indirectly by a secondary-ion-mass spectrometry calibration; indium mole fraction between y=0.052 and y=0.075, measured by electron-dispersive x-ray spectroscopy; and carrier concentration between 2×1016 and 1.1×1018cm−3, measured by Hall effect. Three critical-point transitions were identified by PR: the fundamental band gap (highest valence band to the lowest conduction band); the spin-orbit split valence band to the lowest conduction band; and the highest valence band to a nitrogen impurity band (above the lowest conduction band). The measured critical-point energies were described by a band anticrossing (BAC) model with the addition of a Burstein-Moss band-filling term. The fitted BAC parameters were similar to previously reported values. The N impurity level was located 0.3004±0.0101eV above the conduction-band edge at 20K and 0.3286±0.0089eV above the conduction-band edge at 295K. The BAC interaction parameter was 2.588±0.071eV. From the small magnitude of the Burstein-Moss energy shift with increasing carrier concentration, it was inferred that the carrier concentration probed by PR is reduced from the bulk (Hall-effect) carrier concentration by a reduction factor of 0.266±0.145. The PR lines broadened with increasing carrier concentration; the line broadening tracked the predicted Burstein-Moss energy shift for the bulk carrier concentration. The surface-normal lattice constants of the films were measured by x-ray diffraction. Comparison of the measured lattice constants with Vegard’s law showed the presence of tensile strain (in the surface-normal direction) with magnitude between 1.5×10−3 and 3.0×10−3. The effect of strain on the PR energies was too small to observe.
Elasticity of high coupling relaxor-ferroelectric lead zinc niobate-lead titanate crystals
Authors: Amin Ahmed , Cross Leslie E.
Published: November 2005

The elastic response of a [001]-oriented and -poled ferroelectric rhombohedral lead zinc niobate-lead titanate single crystal close to the morphotropic phase region is examined under thermal, electrical, and mechanical boundaries similar to those used in sound projectors. Resonance measurements yielded a monotonically decreasing Young’s modulus as a function of temperature in the ferroelectric rhombohedral state with a sudden stiffening near the ferroelectric rhombohedral (FR)-ferroelectric tetragonal (FT) transition. The quasistatic, zero-field stress-strain response revealed a FR instability under uniaxial compression. A dc bias field stabilized the FR state under compressive stress. Young’s modulus derived from the linear elastic response below instability agrees well with resonance data for FR. A larger modulus than expected for FT was observed above instabilities. The elastic response is analyzed in terms of ferroelectric-ferroelectric transitions as predicted by a high-order Devonshire theory. Implications for sound projectors are discussed.
Fabrication of cerium-doped LaNiO3 thin films on LaAlO3 (100) substrate by pulsed laser deposition
Authors: Lekshmi I. Chaitanya , Gayen Arup , Sarma D. D. , Hegde M. S. , Chockalingam S. P. , Chandrasekhar N.
Published: November 2005

In this study we report the fabrication of La1−xCexNiO3(0⩽x⩽0.4) thin films on a LaAlO3 (100) substrate by pulsed laser deposition where the cerium ions are believed to be in the Ce (IV) oxidation state. At low Ce concentrations, the films grow in the (100) direction with a pseudocubic structure and above x∼0.3, they exhibit a change in the crystal symmetry. Core-level photoelectron spectroscopic studies of the thin films deposited have shown that the cerium exists in the +4 oxidation state. Correspondingly, the nickel exhibits mixed valency in these thin films. Conductivity of this highly metallic system progressively decreases as more and more Ce is doped. In the range 0.3<x<0.4, the system undergoes a transition from metallic to semiconducting behavior. The electrical nature of La1−xCexNiO3 thin films gives clear indications of significant electron-lattice interactions present for compositions close to the transition.
Monte Carlo simulation on the resistivity and magnetization in anisotropic layered structure
Authors: Yao X. Y. , Dong Sh. , Zhu H. , Yu H. , Liu J.-M.
Published: November 2005

An anisotropic layered mode structure composed of line groups as an approach to anisotropic bilayered manganites is constructed based on the elementary interactions existing in the bilayered manganites. The anisotropic electronic transport and magnetic behaviors of the mode structure are investigated using Monte Carlo simulation and the microscopic resistor network scheme in Ising model. The simulation reproduces qualitatively the main characteristic transport behaviors of bilayered manganites. The significant anisotropy in resistivity and ferromagnetic orderings along different orientations is observed, and the underlying physics is discussed in the framework of spatial correlation of the microscopic metallic resistor network. The simulated results are believed to cast some light on the understanding of the anomaly in the transport behaviors of bilayered manganites, which are gaining more and more importance.
Effect of cerium ions in an arc peripheral plasma on the growth of radial single-walled carbon nanotubes
Authors: Sato Y. , Motomiya K. , Jeyadevan B. , Tohji K. , Sato G. , Ishida H. , Hirata T. , Hatakeyama R.
Published: November 2005

Radial single-walled carbon nanotubes (radial SWCNTs) are formed by using a direct current (dc) arc discharge when carbon and metal atoms are mixed in a gas phase after the vaporization and cooled together in a liquid droplet. Since SWCNTs sprout through the precipitation of saturated carbon atoms from liquid droplets during cooling, a mass synthesis of radial SWCNTs can be achieved when a large number of liquid droplets are generated. In order to understand the effects of arc peripheral plasma parameters (electrons, ions, radical atoms, and molecules) on the growth of radial SWCNTs, the optimum production efficiency of radial SWCNTs is investigated by superimposing a radio-frequency (rf) plasma on the thermal arc plasma and controlling the arc peripheral plasma density. Two parameters—the rf power and the dc potential—of the rf electrode, which is equipped above 20 mm from the center of an arc-discharge point, are changed with the constant He pressure (200 Torr), dc arc current (75 A), and power (2000 W). The production yield of radial SWCNTs is found to be enhanced under the condition of the rf power of 100 W and the dc component of the rf electrode voltage of −22V, revealing that the optimum ion flux and ion bombardment energy are important key parameters for the formation of radial SWCNTs.
Transverse and longitudinal space-charge-induced broadenings of ultrafast electron packets
Authors: Collin S. , Merano M. , Gatri M. , Sonderegger S. , Renucci P. , Ganière J.-D. , Deveaud B.
Published: November 2005

High brightness ultrafast electron sources are limited by space-charge effects. In the high-electron-density regime, Coulomb repulsion induces both transverse and longitudinal broadenings of electron packets. We describe a three-dimensional mean-field model, which takes into account Coulomb repulsion in all directions. Measurements of spatial electron pulse widths are carried out after extraction from a photoemission electron gun. Experiments and simulation results are in very good agreement. Coulomb repulsion effects are found to occur close to the photocathode in the extraction region. The correlation between transverse and temporal broadenings of electron packets is discussed and gives the limits for the generation of high-electron-density ultrafast electron pulses. Pulses of temporal length of about 2ps and a diameter of about 30μm should be obtained.
Current conduction mechanisms in post-nitridation rapid-thermal-annealed gate oxides on 4H silicon carbide
Authors: Cheong Kuan Yew , Bahng Wook , Kim Nam-Kyun
Published: November 2005

In this letter we report current-conduction mechanisms in nitrided gate oxides on n-type 4H SiC subjected to various rapid-thermal-annealing temperatures. The experimental results show that by increasing SiC-SiO2 interface trap density, current conduction in the oxide is increased. Fowler-Nordheim (FN) tunneling which is assisted by SiC-SiO2 interface trap is responsible to the current conduction. In contrast, the current conduction through the oxide is significantly reduced when the oxide is having a multiple discrete energy level of electron trap center. This center enables trapping of electrons that are injected from SiC substrate via FN tunneling, causing a reduction in leakage current and an improvement in oxide breakdown strength. Based on the results, a model has been hypothesized and reasons for these observations have been presented.
Photoluminescence linewidths from multiple layers of laterally self-ordered InGaAs quantum dots
Authors: Wang Zh. M. , Mazur Y. I. , Seydmohamadi Sh. , Salamo G. J. , Kissel H.
Published: November 2005

Laterally ordered multilayered arrays of InGaAs quantum dots are investigated by photoluminescence as a function of high index GaAs substrates. Different laser wavelengths are used to investigate the photoluminescence from quantum dots layer-by-layer. High optical quality is demonstrated for laterally ordered quantum dot arrays. GaAs(511)B is identified as the optimum high index substrate for growth of InGaAs∕GaAs multilayered quantum dots, demonstrating strong photoluminescence with a narrow full width at half maximum linewidth of 23meV in spite of the potential for misfit dislocations.
Functionalization of carbon nanotubes by argon plasma-assisted ultraviolet grafting
Authors: Yan Y. H. , Chan-Park M. B. , Zhou Q. , Li C. M. , Yue C. Y.
Published: November 2005

We have demonstrated the functionalization of single-wall carbon nanotubes (SWNTs) by argon (Ar) plasma-assisted ultraviolet (UV) grafting of 1-vinylimidazole (VZ). The Ar plasma treatment generates defect sites at the tube ends and sidewalls, which act as the active sites for the subsequent UV grafting of VZ monomer. Atomic force microscopy analyses indicate that the original nanotube bundles exfoliate to individual tubes after the VZ grafting. By control of the deposited energy of Ar plasma treatment (200W) and treatment time (5min), no visible chopping of the functionalized SWNT was observed. This method may be extended to other vinyl monomers and offers another diverse way of sidewall functionalization of SWNT.
Dynamic readout of subdiffraction-limited pit arrays with a silver superlens
Authors: Wei Jingsong , Gan Fuxi
Published: November 2005

Recent theoretical and experimental results suggested that the silver superlens could be constructed through controlling silver thin film thickness and preparation conditions, and applied in subdiffraction-limited optical imaging and optical lithography. In this work, we report another significant application of silver superlens—ultrahigh density optical data storage. With the silver superlens the subdiffraction-limited pit arrays on an optical disk are dynamically read out and the carrier-to-noise ratio can reach 25dB for the thin film thickness of 46nm. The readout laser power and readout velocity have little effect on the carrier-to-noise ratio. Additionally, in our experiment the silver thin film thickness needs to be controlled in the range from 20to80nm.
Ultralow loss successive divisions using silicon-on-insulator microwaveguides
Authors: Marris D. , Vivien L. , Pascal D. , Rouvière M. , Cassan E. , Lupu A. , Laval S. , Fédéli J. M. , El Melhaoui L.
Published: November 2005

The low excess loss experimental demonstration of ten successive light divisions is presented. This distribution is realized by using shallow-etched rib silicon-on-insulator waveguides with compact beam splitters and 90° turns based on total internal reflection corner mirrors. The measured excess optical loss is only 0.7dB per division. This result is an important step in a 1 to 1024 optical distribution demonstration.
Cavitation dynamics on the nanoscale
Authors: Kotaidis Vassilios , Plech Anton
Published: November 2005

The ultrafast excitation of gold nanoparticle sols causes a strong nonequilibrium heating of the particle lattice and subsequently of the water shell close to the particle surface. Above a threshold in laser fluence, which is defined by the onset of homogeneous nucleation, nanoscale vapor bubbles develop around the particles, expand and collapse again within the first nanosecond after excitation. We show the existence of cavitation on the nanometer and subnanosecond time scale, described within the framework of continuum thermodynamics.
Strong changes in the dielectric functions of cytosine upon molecular modification
Authors: Suzuki Yu , Gordan Ovidiu D. , Silaghi Simona D. , Zahn Dietrich R. T. , Schubert Anett , Thiel Werner R. , Cobet Christoph , Esser Nobert , Braun Walter
Published: November 2005

The DNA base cytosine and its variant 1-allylcytosine were deposited as thick layers onto silicon substrates using organic molecular beam deposition. The dielectric functions of these materials were measured in the vacuum ultraviolet range from 4.0to9.5eV using synchrotron radiation. In the experiments, the slight modification of the molecules results in very pronounced differences in the optical response. This was unexpected in the light of time dependent density functional theory calculation predicting a very similar optical response for both molecules. We attribute the substantial change in the optical response to stronger intermolecular interaction upon the molecular modification.
Preparation of intrinsic and N-doped p-type ZnO thin films by metalorganic vapor phase epitaxy
Authors: Du Guotong , Ma Yan , Zhang Yuantao , Yang Tianpeng
Published: November 2005

The intrinsic p-type ZnO thin films were prepared by controlling the oxygen partial pressure during growth. The E2 (high) mode at 432.2cm−1 appeared in the Raman spectrum of the film. The photoluminescence spectra taken at 77 K showed the emission band C in the violet region, which originated from zinc vacancy and varied in intensity in accordance with the quantity of the carrier concentration in the films. The N-doped p-type ZnO films were realized by N2 plasma. The Raman spectrum showed the dominant A1 (LO) mode at 580cm−1, that was the result of the host-lattice defects generated by N dopant rather than the N-related local vibration modes.
Polarized photovoltage spectroscopy study of InAs∕GaAs(001) quantum dot ensembles
Authors: Bhattacharyya Jayeeta , Ghosh Sandip , Malzer Stefan , Döhler G. H. , Arora B. M.
Published: November 2005

We have studied self-assembled InAs quantum dot (QD) ensembles on GaAs(001) substrate using polarized photovoltage spectroscopy. The photovoltage spectrum shows four prominent QD related features whose nature differs for probe light incident along [001] and polarized parallel to [110] and [11¯0] directions. The polarization anisotropy suggests that for the lowest energy transition there is only a change in the oscillator strength with change in polarization, while for the higher energy transitions there is also an apparent shift in the transition energy. By comparison with simulations of the absorption spectrum, we show that the main features of the observed polarization anisotropy can be understood on the basis of a model where an anisotropic two dimensional harmonic oscillator potential represents the lateral confinement of the carriers within the QD in the (001) plane.
Effect of Cu3Sn coatings on electromigration lifetime improvement of Cu dual-damascene interconnects
Authors: Yan M. Y. , Suh J. O. , Ren F. , Tu K. N. , Vairagar A. V. , Mhaisalkar S. G. , Krishnamoorthy Ahila
Published: November 2005

A 20 nm thick Cu3Sn intermetallic compound overlayer on Cu interconnect surfaces was found to effectively block dominant surface diffusion paths, thus resulting in close to one order of magnitude improvement in electromigration lifetimes. This improvement may be explained on the basis of the terrace-ledge-kink model in which the supply of Cu adatoms by the dissociation of atoms from the kinks on the Cu surface steps is hindered by a stronger chemical binding of Sn atoms to the kink sites. The mode of electromigration failures seem to have changed from surface diffusion-induced void formation at the cathode via corner to interfacial and grain-boundary diffusion-induced void formation in the interconnect line.
Transmission electron microscopic observation of nanoindentations made on ductile-machined silicon wafers
Authors: Yan Jiwang , Takahashi Hirokazu , Tamaki Jun’ichi , Gai Xiaohui , Kuriyagawa Tsunemoto
Published: November 2005

Nanoindentation tests were performed on a ductile-machined silicon wafer with a Berkovich diamond indenter, and the resulting indents were examined with a transmission electron microscope. It was found that the machining-induced subsurface amorphous layer undergoes significant plastic flow, and the microstructure of the indent depends on the indentation load. At a small load (∼20mN), most of the indented region remains to be amorphous with minor crystalline nuclei; while under a large load (∼50mN), the amorphous phase undergoes intensive recrystallization. The understanding and utilization of this phenomenon might be useful for improving the microscopic surface properties of silicon parts produced by a ductile machining process.
Formation of a reacted layer at the barrierless Cu(WN)∕Si interface
Authors: Chu J. P. , Lin C. H.
Published: November 2005

This letter reports the formation of a reacted layer between Cu film and barrierless Si substrate during annealing. The Cu films with a minor WN phase are deposited by reactive cosputtering of Cu and W in an Ar∕N2 mixture gas. After annealing at 530 °C for 1 h, a ∼200-nm-thick reacted layer formed at the Cu(WN)∕Si interface acts as a barrier to protect the film from extensive interactions with Si. X-ray diffraction, focused ion beam, and transmission electron microscopy results confirm the presence of this layer and show this layer is mainly composed of Cu2WO4, Cu3Si, and Si2N2O. Leakage current and resistivity evaluations reveal the superior thermal reliability of Cu with a dilute amount of WN at the temperatures up to 530 °C, suggesting its potential application in the advanced barrierless metallization.
Mercury cadmium telluride resonant-cavity-enhanced photoconductive infrared detectors
Authors: Wehner J. G. A. , Musca C. A. , Sewell R. H. , Dell J. M. , Faraone L.
Published: November 2005

Resonant-cavity-enhanced Hg1−xCdxTe photoconductive detectors for midwave infrared wavelengths are investigated for use in multi- and hyper-spectral sensor systems. Resonant-cavity-enhanced performance is modeled, and compared with measured performance of fabricated devices. The responsivity of fabricated devices shows resonant cavity enhancement, with performance limited by surface recombination.
Band alignment in ultrathin Hf–Al–O∕Si interfaces
Authors: Jin H. , Oh S. K. , Kang H. J. , Lee S. W. , Lee Y. S. , Cho M.-H.
Published: November 2005

Band alignment in Hf–Al–O thin films, grown on Si(100) by atomic layer deposition, was determined via x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The changes in conduction band offset, valence band offset, and bandgap were obtained as a function of annealing temperature. The bandgap Eg was found to be 5.7±0.05eV for as-deposited Hf–Al–O. After annealing at 600 °C, the increase in Eg was 0.2 eV, and then nearly unchanged up to 850 °C. The conduction band offset ΔEc increased slowly from 0.82±0.05eV at room temperature to 1.28±0.05eV at 850 °C. Even though the band profile of Hf–Al–O is still asymmetric with respect to HfO2, it satisfies the minimum requirement for the determination of the carrier barrier height. The band profiles, obtained via reflection electron energy loss spectroscopy, provided us some insight, which is both convenient and at the same time important, into the way to identify high-k dielectric materials, and we also found that the Hf–Al–O is a promising dielectric material for practical applications.