bluuebunny/crossref_metadata_2025 huggingface dataset:
Masks and Selves in Contemporary Java: The Dances of Didik Nini Thowok
Authors: Mrázek Jan
Published: July 2005

This essay reflects on the plays of masks and selves in the dances and the life of Didik Nini Thowok, and the resonances between dance and life. An Indonesian of Chinese descent and a female impersonator whose comic dances combine different regional styles, Didik upsets notions of ethnic and gender stereotypes and identities, the notion of identity itself.
Semi-pullbacks for stochastic relations over analytic spaces
Authors: DOBERKAT ERNST-ERICH
Published: July 2005

The existence of semi-pullbacks for stochastic relations over analytic spaces is addressed. It is shown by means of a measure extension that the theory of measurable selectors for measurable relations may be employed for its solution. The category of stochastic relations is shown not to have (weak) pullbacks.
Modelling general recursion in type theory
Authors: BOVE ANA , CAPRETTA VENANZIO
Published: July 2005

Constructive type theory is an expressive programming language in which both algorithms and proofs can be represented. A limitation of constructive type theory as a programming language is that only terminating programs can be defined in it. Hence, general recursive algorithms have no direct formalisation in type theory since they contain recursive calls that satisfy no syntactic condition guaranteeing termination. In this work, we present a method to formalise general recursive algorithms in type theory. Given a general recursive algorithm, our method is to define an inductive special-purpose accessibility predicate that characterises the inputs on which the algorithm terminates. The type-theoretic version of the algorithm is then defined by structural recursion on the proof that the input values satisfy this predicate. The method separates the computational and logical parts of the definitions and thus the resulting type-theoretic algorithms are clear, compact and easy to understand. They are as simple as their equivalents in a functional programming language, where there is no restriction on recursive calls. Here, we give a formal definition of the method and discuss its power and its limitations.
Categorical models for Abadi and Plotkin's logic for parametricity
Authors: BIRKEDAL LARS , MØGELBERG RASMUS E.
Published: July 2005

We propose a new category-theoretic formulation of relational parametricity based on a logic for reasoning about parametricity given by Abadi and Plotkin. The logic can be used to reason about parametric models, such that we may prove consequences of parametricity that to our knowledge have not been proved before for existing category-theoretic notions of relational parametricity. We provide examples of parametric models and describe a way of constructing parametric models from given models of the second-order lambda calculus.
Inter-regional innovation in Brazilian agriculture and deforestation in the Amazon: income and environment in the balance
Authors: CATTANEO ANDREA
Published: July 2005

The paper examines how recent trends in agricultural productivity in Brazil, occurring both inside and outside the Amazon, affected deforestation and agricultural incomes. The analysis uses a computable general equilibrium model adapted to capture regional economic structures, and accounts for uncertainty concerning productivity improvements. Due to countervailing effects on deforestation of innovation inside and outside the Amazon – respectively, increasing and decreasing it – innovation in Brazilian agriculture in the period from 1985 to 1995 has not altered substantially deforestation rates. However, innovation inside the Amazon has to be reckoned as a driving force behind the continuing high levels of deforestation rates.

Innovation rates for livestock activities, inside and outside the Amazon, prove crucial in determining deforestation and agricultural income. Technological improvements outside the Amazon for small farm production systems and for farms in general in the North-East increase agricultural income, improve income distribution, and limit deforestation rates.
Deforestation in Cameroon: immediate causes and consequences
Authors: GBETNKOM DANIEL
Published: July 2005

The effects of deforestation in Cameroon such as the erosion of agricultural lands, drying up water bodies during dry seasons, desertification, disappearance of plant and animal species, modifications of both local and regional climatic conditions and global warming through its effect on the global carbon cycle are likely to affect agricultural activities and economic growth. This paper investigates the immediate causes and consequences of deforestation in Cameroon between 1970 and 2000. Quantitative estimates show that coffee, and cocoa producer prices, food crop prices, and the timber export price index, on the one hand, and the oil boom, the structural adjustment policies, and the devaluation of the CFA franc, on the other hand, are quite important in stimulating the clearing of forests. Equally, the agricultural value added per hectare increases the profitability of maintaining forests. The implication of these results is that the importance of non-forest policies is underappreciated in Cameroon.
Geochemical mapping of the Mariana arc‐basin system: Implications for the nature and distribution of subduction components
Authors: Pearce Julian A. , Stern Robert J. , Bloomer Sherman H. , Fryer Patty
Published: July 2005

A new ICP‐MS database for glasses from the Mariana Trough, together with published and new ICP‐MS data from the Mariana arc, provides the basis for geochemical mapping of the Mariana arc‐basin system. The geochemical maps presented here are based on the graphic representation of spatial variations in geochemical proxies for the principal mantle and subduction components. The focus is on three elements with high and similar partition coefficients but different behavior in subduction systems, namely, Ba, Th, and Nb. Two elements with different partition coefficients, Ta and Yb, are used as normalizing factors. Ratio maps (Ta/Yb, Nb/Ta, Th/Ta, Ba/Ta, Ba/Th) provide the simplest petrogenetic insights, subduction zone addition maps based on deviations from a MORB array provide more quantitative insights, and component maps represent an attempt to isolate the different subduction components. The maps shown here indicate the presence of a variably depleted asthenosphere and three added components: a Nb‐Th‐Ba component, a Th‐Ba deep‐subduction component, and a Ba‐only shallow‐subduction component. The asthenosphere entering the system is enriched relative to N‐MORB and appears to be focused at three sites within the Mariana Trough. The Nb‐Th‐Ba component is present mainly in the north of the arc (the Northern Seamount province and northern Central Island Province), the northern edge of the Mariana Trough, and two locations within the Southern Seamount Province. It has a distinctively high Nb/Ta ratio and a moderate enrichment in Th and Ba relative to Nb. Its composition and distribution indicate that it may not be part of the present subduction system but instead originates in mantle lithosphere previously enriched above the subduction zone by addition of small‐degree, subduction‐modified mantle melts. The Th‐Ba component is present throughout the arc and, in minor amounts, in parts of the back‐arc basin. The Ba‐only component is mainly present in the central part of the arc and at the edges of the back‐arc basin. Overall, the geochemical maps provide a new perspective on the geochemical processes that accompany the evolution of an arc basin system from prerifting lithospheric enrichment, through arc‐rifting to arc volcanism and back‐arc spreading.
Independence and interdependencies among global ocean color properties: Reassessing the bio‐optical assumption
Authors: Siegel David A. , Maritorena Stéphane , Nelson Norman B. , Behrenfeld Michael J.
Published: July 2005

The bio‐optical assumption states that ocean optical properties should covary with the chlorophyll concentration. However, chlorophyll is not the only constituent capable of absorbing and scattering light as phytoplankton, detrital particles, colored dissolved organic material (CDOM), and suspended solids all contribute independently to ocean color. Here we employ a semi‐analytical ocean color algorithm, the Garver‐Siegel‐Maritorena model (GSM01), to decompose ocean color imagery from the Sea‐viewing Wide Field of view Sensor (SeaWiFS) into optically relevant components for phytoplankton absorption (related to the chlorophyll concentration, Chl), colored non‐algal absorption and particulate backscatter. Semi‐analytical Chl retrievals are consistent with available open ocean observations but show important differences compared with the standard SeaWiFS algorithm (OC4v4). These differences may be accounted for by the absorption due to colored detrital materials (CDM; the sum of colored dissolved organic material and detrital particulates). Values of CDM are a large and variable fraction of the total non‐water absorption at 440 nm varying from 30 to 40% in the subtropical gyres to more than 60% at high latitudes. Retrievals of particulate backscatter (BBP) vary comparatively little. In the tropical and subtropical oceans, changes in BBP are largely unrelated to Chl, while at higher latitudes, BBP increases mirror changes in Chl. For much of the ocean, alterations in the relationship between BBP and Chl are consistent with a physiological response by phytoplankton to changes in mixed layer light, nutrients, and temperature. Regional scale correspondences among the three ocean color properties illustrate both independent and interdependent variations which can be explained by assessing the regional scale forcing mechanisms driving changes in ocean color properties.
Production regimes in the northeast Atlantic: A study based on Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) chlorophyll and ocean general circulation model mixed layer depth
Authors: Lévy Marina , Lehahn Yoav , André Jean‐Michel , Mémery Laurent , Loisel Hubert , Heifetz Eyal
Published: July 2005

A 5 year time series of Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) ocean color images (SCHL) is compared with mixed layer depths (MLD) and atmospheric forcings from the Clipper model of the North Atlantic (1998–2002). This comparison is done over the region 16°–22°W, 30°–50°N, where subpolar mode waters are formed and which overlaps the region of the 2001 Programme Océan Multidisciplinaire Méso Echelle (POMME) experiment at sea. Three production regimes are identified on the basis of the seasonal cycling of SCHL and MLD: the well‐known subpolar and subtropical regimes and a midlatitude regime. The midlatitude regime is characterized by a single broad bloom weaker than the subpolar spring bloom and stronger than the subtropical fall bloom, which starts in fall as an entrainment bloom and peaks in spring as a restratification bloom. This specific regime is found between 35°N and 40°N (±2°) in the northeast Atlantic. It corresponds to winter MLDs between Ze (the depth of the euphotic layer) and 2Ze, i.e., it lays between the region where the winter MLD is greater than Sverdrup's critical depth (subpolar regime) and the region where the mixing is never deeper than the well‐lit layer (subtropical regime). The very specific characteristics of the midlatitude regime strengthen the biological carbon pump since production is active in winter within the waters to be subducted. The midlatitude regime also may provide an explanation for the unexpectedly low f ratios sometimes observed during the bloom in the region (North Atlantic Bloom Experiment, POMME). A large interannual variability is observed for the three regimes in terms of the timing and the intensity of the blooms and of the geographical boundaries of the regimes. These variabilities appear to be mainly driven by the synoptic and the low‐frequency atmospheric variabilities. It is also shown that in addition to the northward propagation of the subpolar spring bloom from 41°N (±1.3°) to 50°N, the (fall) entrainment bloom propagates southward over the whole latitudinal range (35°–50°N).
An observational study of ecohydrology of a sparse grassland at the edge of the Eurasian cryosphere in Mongolia
Authors: Zhang Yinsheng , Munkhtsetseg E. , Kadota T. , Ohata T.
Published: July 2005

Between July 2002 and June 2004 we recorded many ecohydrological observations at a sparse grassland site on the southern periphery of the Eurasian cryosphere in Mongolia. Grass growth at the study site shows significant difference of biomass between drier and moister years. Seasonal change of PAR albedo is a good indicator of temporal change of biomass. The stresses of atmosphere and soil water to grass have been evaluated at the study site using index of air temperature stress degree‐day (SDD) and soil water stress (SWS). SDD was small and prevailingly negative. Variations in the SWS tracked precipitation fluctuations. Variability of two indexes may imply that atmospheric heat stress for the growing grass was weak compared to soil water stress for such a semiarid region. The above conclusion is supported by irrigation experimental observation as well; clear differences of biomass were observed between watered and unwatered ground after irrigation commenced. Soil evaporation and transpiration were estimated using a soil moisture parameterization and verified with micro‐Lysimeter observations. Variability of evapotranspiration shows temporal decline processes' response to precipitation events or snow melting. During the observation period, evapotranspiration totaled 301.6 mm, and precipitation totaled 319.5 mm. The mean partition of transpiration in evapotranspiration was 22%, which was small during wetter grass‐growing periods but large in drier periods. The growing period is short along the periphery of the cryosphere, but water fluxes during the growing period contribute significantly to the annual water cycle.
Holocene climatic changes in Greenland: Different deuterium excess signals at Greenland Ice Core Project (GRIP) and NorthGRIP
Authors: Masson‐Delmotte V. , Landais A. , Stievenard M. , Cattani O. , Falourd S. , Jouzel J. , Johnsen S. J. , Dahl‐Jensen D. , Sveinsbjornsdottir A. , White J. W. C. , Popp T. , Fischer H.
Published: July 2005

Water stable isotope measurements (δD and δ18O) have been conducted on the Holocene part of two deep Greenland ice cores (Greenland Ice Core Project (GRIP) and NorthGRIP), located ∼320 km apart. These combined measurements provide the first two continuous Greenland Holocene deuterium excess profiles (d = δD − 8δ18O), a parameter strongly influenced by changes in moisture sources. We discuss here temporal and regional fluctuations of the deuterium excess within central to north Greenland, with a mean temporal resolution of ∼4 years. Although GRIP and NorthGRIP exhibit similar annual mean surface temperatures and δ18O levels, a significant offset of modern deuterium excess is observed between the two sites. We attribute this offset to a different mix of modern moisture sources, pointing to regional‐scale differences in moisture advection toward Greenland. The common long‐term deuterium excess Holocene increasing trend is probably related to the increased relative contribution of low‐latitude moisture to Greenland snowfall, in response to the change in the Earth obliquity, as symmetrically observed in Antarctica. Three abrupt declines punctuate the GRIP excess record (8.2, 4.5, and 0.35 ka BP), suggesting associated reorganizations of the northern high latitudes hydrological cycle. The 8.2 ka BP event is characterized by (1) a rapid cooling followed by a progressive warming and (2) a deuterium excess cooling restricted to GRIP, therefore totally different from rapid events during glacial times. By contrast, the NorthGRIP deuterium excess record is more stable. We propose that a slightly larger proportion of moisture supplied by local storm tracks to GRIP induces an isotopic compensation mechanism between simultaneous site and source temperature coolings, resulting in a rather temperature‐insensitive δ18O profile, together with well‐marked deuterium excess amplitudes. NorthGRIP δ18O seems less biased by isotopic processes and should provide a more reliable past temperature record.
Reference antenna techniques for canceling radio frequency interference due to moving sources
Authors: Mitchell D. A. , Robertson J. G.
Published: July 2005

We investigate characteristics of radio frequency interference (RFI) signals that can affect the excision potential of some interference mitigation algorithms. The techniques considered are those that modify signals from auxiliary reference antennas to model and cancel interference from an astronomical observation. These techniques can be applied in the time domain, where the RFI voltage is modeled and subtracted from the astronomy signal path (adaptive noise canceling), or they can be applied to the autocorrelated and cross‐correlated voltage spectra in the frequency domain (postcorrelation canceling). For ideal receivers and a single, statistically stationary interfering signal, both precorrelation and postcorrelation filters can result in complete cancellation of the interference from the observation. The postcorrelation method has the advantage of being applied on tens or hundreds of millisecond timescales rather than tens or hundreds of nanosecond timescales. However, this can be a disadvantage if the RFI transmitter location is changing, since the cross‐correlated power measurements which link the interference power in the astronomy and reference signal paths can decorrelate. If the decorrelation is not too severe, it can be allowed for, at the expense of a noise increase. The time domain adaptive cancelers are allowed to slightly vary their internal coefficients and adapt to changing phases during the integrations, which means that they avoid the decorrelation problem. However, the freedom to adapt also results in a noise increase. In this paper the ability of both types of cancelers to excise interference originating from a moving source is compared. The cancelers perform well on both observed and simulated data, giving complete cancellation.
Subglacial conditions during and after stoppage of an Antarctic Ice Stream: Is reactivation imminent?
Authors: Vogel S. W. , Tulaczyk S. , Kamb B. , Engelhardt H. , Carsey F. D. , Behar A. E. , Lane A. L. , Joughin I.
Published: July 2005

Borehole observations from the base of the West‐Antarctic Ice Sheet (WAIS) reveal the presence of a 10 to 15 m thick accretionary basal ice layer in the upstream area of Kamb Ice Stream (KIS). This ice layer has formed over a time of several thousand years by freeze‐on of subglacial water to the ice base and has recorded during this time basal conditions upstream of its current location. Analysis of samples and videos sequences from boreholes drilled to the bottom of KIS confirms that KIS‐stoppage was due to basal freeze‐on and that relubrication of the ice stream is well underway. These results further suggest that ice stream cyclicity may be shorter than expected (1000s of years) and that a restart of KIS may be imminent within decades to centuries.
Cirrus induced polarization in 122 GHz aura Microwave Limb Sounder radiances
Authors: Davis C. P. , Wu D. L. , Emde C. , Jiang J. H. , Cofield R. E. , Harwood R. S.
Published: July 2005

Previous simulation studies have outlined the possibility of significant polarization signals in microwave limb sounding due to horizontally aligned ice crystals in cirrus clouds. From the recently launched Aura MLS instrument, we present the first polarized microwave limb sounding observations of cirrus clouds. We also present polarized radiative transfer simulations, which show qualitative agreement with these observations, and indicate the limits to which aligned non‐spherical particles are influencing bulk optical properties of cirrus clouds at microwave wavelengths. Although 122 GHz is not ideal for cloud measurements due to strong O2 absorption, data and simulations suggest that preferential crystal orientation is causing small, but noticeable, partial vertical polarization, which can be replicated in simulations by considering all particles as horizontally aligned oblate spheroids with aspect ratios of around 1.2 ± 0.15.
A high‐resolution time series of oxygen isotopes from the Kolyma River: Implications for the seasonal dynamics of discharge and basin‐scale water use
Authors: Welp L. R. , Randerson J. T. , Finlay J. C. , Davydov S. P. , Zimova G. M. , Davydova A. I. , Zimov S. A.
Published: July 2005

Intensification of the Arctic hydrologic cycle and permafrost melt is expected as concentrations of atmospheric greenhouse gases increase. Quantifying hydrologic cycle change is difficult in remote northern regions; however, monitoring the stable isotopic composition of water runoff from Arctic rivers provides a means to investigate integrated basin‐scale changes. We measured river water and precipitation δ18O and δD to partition the river flow into snow and rain components in the Kolyma River basin. On an annual basis, we found water leaving the basin through the river consisted of 60% snow and 40% rain. This is compared with annual precipitation inputs to the watershed of 47% snow and 53% rain. Despite the presence of continuous permafrost, and fully frozen soils in the spring, our analysis showed not all spring snowmelt runs off into the river immediately. Instead, a substantial portion is retained and leaves the basin as growing season evapotranspiration.
Correction of atmospheric dynamical seasonal forecasts using the leading ocean‐forced spatial patterns
Authors: Lin Hai , Derome Jacques , Brunet Gilbert
Published: July 2005

A statistical approach to correct ensemble seasonal forecasts is formulated based on the regression of the forecast model's leading forced singular value decomposition (SVD) patterns and the observed 500 hPa geopotential height. This technique is applied to the winter forecasts from two general circulation models (GCMs). The performance of the corrected forecasts is assessed by comparing their cross‐validated skill with that of the original GCM ensemble mean forecasts. We are particularly interested in the forecast skill of the Pacific/North American (PNA) and the North Atlantic Oscillation (NAO). In the case of the PNA, the technique significantly improves the skill of the less skillful of the two models, and does not modify significantly that of the other model, which produces very good PNA forecasts even before the correction. For the NAO, the correction significantly improves the forecast skill of both models.
Extreme CO concentrations in the upper troposphere over northeast Asia in June 2003 from the in situ MOZAIC aircraft data
Authors: Nedelec Philippe , Thouret Valérie , Brioude Jérôme , Sauvage Bastien , Cammas Jean‐Pierre , Stohl Andreas
Published: July 2005

This paper analyses 320 MOZAIC (Measurements of Ozone aboard Airbus in‐service airCraft) flights between Europe and East Asia in the year 2003. Carbon monoxide (CO) measurements in the upper troposphere (UT) clearly show the influence of plumes from boreal forest fires burning around Lake Baikal between April and July. On many flights, CO concentrations were above 300 ppbv over several hundred kilometers, with values above 500 ppbv over 50 kilometers and peaks up to 800 ppbv. To our knowledge, such high UT CO concentrations have never been reported before. A case study reveals that biomass burning plumes were rapidly transported by a warm conveyor belt. On the regional and seasonal scale, MOZAIC monthly‐mean concentrations were above 150 ppbv on average, i.e. 30% above the northern hemisphere background as determined over Europe.
Climate anomalies generate an exceptional dinoflagellate bloom in San Francisco Bay
Authors: Cloern James E. , Schraga Tara S. , Lopez Cary B. , Knowles Noah , Grover Labiosa Rochelle , Dugdale Richard
Published: July 2005

We describe a large dinoflagellate bloom, unprecedented in nearly three decades of observation, that developed in San Francisco Bay (SFB) during September 2004. SFB is highly enriched in nutrients but has low summer‐autumn algal biomass because wind stress and tidally induced bottom stress produce a well mixed and light‐limited pelagic habitat. The bloom coincided with calm winds and record high air temperatures that stratified the water column and suppressed mixing long enough for motile dinoflagellates to grow and accumulate in surface waters. This event‐scale climate pattern, produced by an upper‐atmosphere high‐pressure anomaly off the U.S. west coast, followed a summer of weak coastal upwelling and high dinoflagellate biomass in coastal waters that apparently seeded the SFB bloom. This event suggests that some red tides are responses to changes in local physical dynamics that are driven by large‐scale atmospheric processes and operate over both the event scale of biomass growth and the antecedent seasonal scale that shapes the bloom community.
The tu8 Mutation of Arabidopsis thaliana Encoding a Heterochromatin Protein 1 Homolog Causes Defects in the Induction of Secondary Metabolite Biosynthesis
Authors: Bennett R. N. , Wenke T. , Freudenberg B. , Mellon F. A. , Ludwig‐Müller J.
Published: July 2005

Abstract: The tu8 mutant of Arabidopsis thaliana (L.) Heynh. was previously described as deficient in pathogen‐induced auxin and glucosinolate (GSL) accumulation, as well as in heat‐induced accumulation of cytosolic Hsp90, the latter feature was accompanied by reduced thermotolerance at higher temperatures. The mutated gene was shown to be a novel allele ofTERMINAL FLOWER2, encoding the only Arabidopsis homolog for heterochromatin protein 1 (Kim et al., 2004). In this report, we investigated the influence of heat stress on auxin and GSL content, as well as the accumulation of several secondary metabolites derived from the phenylpropanoid pathway, including anthocyanins and sinapine derivatives, in the mutant tu8. tu8 had less sinapine and sinapoyl esters compared to the wild type. In addition, the induction of sinapine by heat shock in Columbia was not found in tu8. Anthocyanins were also induced by heat stress in wild type plants, whereas tu8 showed only slight induction of these compounds and only at higher temperatures. GSLs were induced at higher temperatures in the wild type, but induction was absent in tu8. Transcript levels known to be involved in IAA/glucosinolate synthesis and metabolism (nitrilase and myrosinase) were examined and both showed developmental regulation, while only nitrilase mRNA levels differed between wild type and mutant seedlings. Treatment of Columbia and tu8 with jasmonic acid (JA), a known inducer of glucosinolates, showed differences between wild type and tu8 with respect to induction of individual GSLs and anthocyanins. However, the transcript level of the TU8/TFL2 gene after heat shock and jasmonate treatment did not change. Loss of function or altered function in the heterochromatin protein most likely lead to the pleiotropic phenotype observed for the tu8 mutant.
Feature of electron energy distribution in a low-pressure capacitive discharge
Authors: You S. J. , Chung C. W. , Chang H. Y.
Published: July 2005

The evolution of the electron energy distribution function is investigated in the low-pressure capacitive discharge under the collisionless electron heating regime, where the electron mean-free path is comparable to or larger than the system length. As the gas pressure decreases from 50 to 10 mTorr, a different feature of electron energy distribution with a plateau in the low-energy electron range, indicating the strong electron heating in that energy range, is found. This observed result can be explained in terms of collisionless heating from the interaction between the electron bouncing motion and the oscillating sheath [Y. M. Aliev, I. D. Kaganovich, and H. Schuter, Phys. Plasmas 4, 2413 (1997)]. A simple calculation of the electron energy distribution with the energy diffusion coefficient, including the electron bounce effect, is in good agreement with the experiment.
Microdamage in polycrystalline ceramics under dynamic compression and tension
Authors: Zhang K. S. , Zhang D. , Feng R. , Wu M. S.
Published: July 2005

In-grain microplasticity and intergranular microdamage in polycrystalline hexagonal-structure ceramics subjected to a sequence of dynamic compression and tension are studied computationally using the Voronoi polycrystal model, by which the topological heterogeneity and material anisotropy of the crystals are simulated explicitly. The constitutive modeling considers crystal plasticity by basal slip, intergranular shear damage during compression, and intergranular mode-I cracking during tension. The model parameters are calibrated with the available shock compression and spall strength data on polycrystalline α-6H silicon carbide. The numerical results show that microplasticity is a more plausible micromechanism for the inelastic response of the material under shock compression. On the other hand, the spallation behavior of the shocked material can be well predicted by intergranular mode-I microcracking during load reversal from dynamic compression to tension. The failure process and the resulting spall strength are, however, affected strongly by the intensity of local release heterogeneity induced by heterogeneous microplasticity, and by the grain-boundary shear damage during compression.
Residual stress measurement in carbon coatings of optical fibers from the fiber bending curvature and coating thickness difference
Authors: Shiue Sham-Tsong , Lin Hung-Chien , Shen Ting-Ying , Ouyang Hao
Published: July 2005

The residual stress measurement in carbon coatings of optical fibers is theoretically and experimentally investigated. A simple formula used to measure the residual stresses in the thin film deposited on a cylindrical substrate with the bending curvature is proposed. During a temperature drop, the carbon-coated optical fiber is bent due to the nonuniform deposition of coating materials. The axial residual stresses in carbon coatings of optical fibers can be measured from the fiber bending curvature and coating thickness difference. Furthermore, if Young’s modulus of carbon coatings is known, the thermal expansion coefficient of carbon coatings can be determined.
Iterated stretching and multiple beads-on-a-string phenomena in dilute solutions of highly extensible flexible polymers
Authors: Oliveira Mónica S. N. , McKinley Gareth H.
Published: July 2005

The dynamics of elastocapillary thinning in high molecular weight polymer solutions are reexamined using high-speed digital video microscopy. At long times, the evolution of the viscoelastic thread deviates from self-similar exponential decay and the competition of elastic, capillary, and inertial forces leads to the formation of a periodic array of beads connected by axially uniform ligaments. This configuration is itself unstable and successive instabilities propagate from the necks connecting the beads and the ligaments. This iterated process results in the development of multiple generations of beads in agreement with the predictions of Chang, Demekin, and Kalaidin [“Iterated stretching of viscoelastic jets,” Phys. Fluids 11, 1717 (1999)] although experiments yield a different recursion relation between successive generations. At long times, finite molecular extensibility truncates the iterated instability and axial translation of the bead arrays along the interconnecting threads leads to a progressive coalescence before the rupture of the filament.
Stoichiometric amorphous MoO3 films: A route to high performance electrochromic devices
Authors: Sian Tarsame S. , Reddy G. B.
Published: July 2005

The effect of stoichiometry on the coloration efficiency (η) and cycling life of MoO3 films has been investigated and underlying reasons discussed in the paper. Optical studies reveal that as-deposited and 150 °C annealed films are nonstoichiometric while films deposited by activated reactive evaporation are stoichiometric. Nonstoichiometry in unintercalated MoO3 is associated with lower valence states of Mo is responsible for absorption in the 400–1000-nm spectral region. It is found that this nonstoichiometry affects η and the cycling life of the films adversely.
Thermodynamic anomalies in a lattice model of water: Solvation properties
Authors: Pretti M. , Buzano C.
Published: July 2005

We investigate a lattice-fluid model of water, defined on a three-dimensional body-centered-cubic lattice. Model molecules possess a tetrahedral symmetry, with four equivalent bonding arms. The model is similar to the one proposed by Roberts and Debenedetti [J. Chem. Phys. 105, 658 (1996)], simplified by removing distinction between “donors” and “acceptors.” We focus on the solvation properties, mainly as far as an ideally inert (hydrophobic) solute is concerned. As in our previous analysis, devoted to neat water [J. Chem. Phys. 121, 11856 (2004)], we make use of a generalized first-order approximation on a tetrahedral cluster. We show that the model exhibits quite a coherent picture of water thermodynamics, reproducing qualitatively several anomalous properties observed both in pure water and in solutions of hydrophobic solutes. As far as supercooled liquid water is concerned, the model is consistent with the second critical-point scenario.
On the evaluation of the Kirkwood-Buff integrals of aqueous acetone mixtures
Authors: Perera A. , Sokolić F. , Almásy L. , Westh P. , Koga Y.
Published: July 2005

The Kirkwood-Buff integrals of acetone-water mixtures are determined using two experimental techniques: small-angle neutron scattering and vapor pressure measurements, in order to test the precision and reliability that can be achieved. The data are then compared with those previously reported by different authors, which tend to show considerable variation between them. The various possible sources of inaccuracies are pointed out, both from experimental origins and from the numerical treatment of the data. Comparison with recent simulation results allows to critically compare different models and provide some information about the microstructure of the aqueous mixture.
Molecular-dynamics study of structure II hydrogen clathrates
Authors: Alavi Saman , Ripmeester J. A. , Klug D. D.
Published: July 2005

Molecular-dynamics simulations are used to study the stability of structure II hydrogen clathrates with different H2 guest occupancies. Simulations are done at pressures of 2.5kbars and 1.013bars and for temperatures ranging from 100to250K. For a structure II unit cell with 136 water molecules, H2 guest molecule occupancies of 0–64 are studied with uniform occupancies among each type of cage. The simulations show that at 100K and 2.5kbars, the most stable configurations have single occupancy in the small cages and quadruple occupancy in the large cages. The optimum occupancy for the large cages decreases as the temperature is raised. Double occupancy in the small cages increases the energy of the structures and causes tetragonal distortion in the unit cell. The spatial distribution of the hydrogen guest molecules in the cages is determined by studying the guest-water and guest-guest radial distribution functions at various temperatures.
Ab initio dynamics study of poly-para-phenylene vinylene
Authors: Zheng Guang , Clark S. J. , Tulip P. R. , Brand S. , Abram R. A.
Published: July 2005

We present an ab initio dynamics investigation within a density-functional perturbation theory framework of the properties of the conjugated polymer poly-para-phenylene vinylene (PPV) in both the isolated chain and crystalline states. The calculated results show that for an isolated chain, most of the vibrational modes correspond to experimentally observed modes in crystalline PPV. However, additional hitherto unidentified modes have been observed in experiment and our calculations on crystalline material have allowed us to assign these. We also present the results of calculations of the polarizability and permittivity tensors of the material, which are in reasonable agreement with the typical values for conjugated polymers. Dynamical Born effective charges [S. Baroni, S. de Gironcoli, A. Dal Corso, and P. Giannozzi, Rev. Mod. Phys. 73, 515 (2001)] are calculated and compared with atomic charges obtained from Mulliken population analysis [M. D. Segall, C. J. Pickard, R. Shah, and M. C. Payne, Mol. Phys. 89, 571 (1996)] and we conclude that effective charges are more appropriate for use in the study of the dynamics of the system. Notable differences are found in the infrared-absorption spectra obtained for the isolated chain and crystalline states, which can be attributed to the differences in the crystalline packing effects, which clearly play a key role in influencing the lattice dynamics of PPV.
Calculation of two-dimensional plasma sheath with application to radial dust oscillations
Authors: Sheridan T. E.
Published: July 2005

Dust particles are often confined radially in a plasma potential well above a cylindrical depression in an otherwise flat electrode. The structure of the two-dimensional, time-independent sheath is computed for this geometry using cold, collisionless ions and Boltzmann electrons. A depression with a radius of 16 Debye lengths and a depth of 2 Debye lengths is modeled for negative electrode biases from 6 to 32 times the electron temperature. The normalized radial oscillation frequency for a dust particle in the well is computed from the sheath potential structure. The model results agree qualitatively with the experimental measurements.
An aluminum-gate metal-oxide-silicon capacitor with a tunnel-thin oxide under the bidirectional electric stress
Authors: El Hdiy A. , Khlil R. , Jin Y. , Tyaginov S. E. , Shulekin A. F. , Vexler M. I.
Published: July 2005

Bidirectional electric stresses are performed in metal—oxide—silicon capacitors with ultrathin (2.5 nm) oxides and with highly doped substrates. The observed effects are compared to those occurring under the conventional unidirectional constant-current overload. The effects observed after stress of ultrathin oxides bring into play defects of comparable nature to those noted for thick oxides, namely, neutral traps. Furthermore, soft breakdown events are scrutinized based on defect creation throughout the oxide and modulation of charge state trapping at the interfaces.
Annealing properties of open volumes in HfSiOx and HfAlOx gate dielectrics studied using monoenergetic positron beams
Authors: Uedono A. , Ikeuchi K. , Yamabe K. , Ohdaira T. , Muramatsu M. , Suzuki R. , Hamid A. S. , Chikyow T. , Torii K. , Yamada K.
Published: July 2005

Thin Hf0.6Si0.4Ox and Hf0.3Al0.7Ox films fabricated by metal-organic chemical-vapor deposition and atomic-layer-deposition techniques were characterized using monoenergetic positron beams. Measurements of the Doppler broadening spectra of annihilation radiation and the lifetime spectra of positions indicated that positrons annihilated from the trapped state by open volumes that exist intrinsically in amorphous structures of the films. For HfSiOx, the mean size of the open volumes and their size distribution decreased with increasing postdeposition annealing (PDA) temperature. For HfAlOx, although the overall behavior of the open volumes in response to annealing was similar to that for HfSiOx, PDA caused a separation of the mean size of the open volumes. When this separation occurred, the value of the line-shape parameter S increased, suggesting an oxygen deficiency in the amorphous matrix. This fragmentation of the amorphous matrix can be suppressed by decreasing the annealing time.
The influence of defects and postdeposition treatments on the free carrier density in lightly phosphorus-doped large-grained polycrystalline silicon films
Authors: Straub Axel , Inns Daniel , Terry Mason L. , Gebs Raphael , Aberle Armin G.
Published: July 2005

The influence of postdeposition treatments (rapid thermal annealing and hydrogenation) on the doping of large-grained polycrystalline silicon p+nn+ thin-film diodes on glass substrates is investigated using resistivity and impedance analysis measurements. Whereas in the lightly phosphorus-doped base region both treatments are found to cause an increase in the active doping concentration, hydrogenation decreases the active doping concentration of both heavily doped layers (Al and P). The different behavior is attributed to acceptorlike defects which are present in the nonhydrogenated base region in a similar concentration as the atomic phosphorus concentration and which are well passivated by hydrogenation. From posthydrogenation annealing experiments and temperature-dependent impedance analysis measurements, different temperature dependences and activation energies (depending on the posthydrogenation annealing temperature) are found for the lightly doped base region. The temperature dependences are quantitatively described using a simple model comprising three energy levels within the silicon band gap: the phosphorus doping level, a shallow donorlike defect level about 0.2 eV below the conduction-band edge, and a midgap acceptorlike defect level. From this model it can be concluded that (i) the density of the acceptorlike defect in our n-type base region is at least 1×1017cm−3 after the rapid thermal anneal, and (ii) that hydrogenation reduces this defect density by more than a factor of 10. The results of this work demonstrate that accurate control of the doping in large-grained polycrystalline Si films is possible, provided the effects of defects and the necessary postdeposition treatments (such as rapid thermal annealing and hydrogenation) are carefully accounted for.
Photoreflectance and surface photovoltage spectroscopy of beryllium-doped GaAs∕AlAs multiple quantum wells
Authors: Čechavičius B. , Kavaliauskas J. , Krivaitė G. , Seliuta D. , Valušis G. , Halsall M. P. , Steer M. J. , Harrison P.
Published: July 2005

We present an optical study of beryllium δ-doped GaAs∕AlAs multiple quantum well (QW) structures designed for sensing terahertz (THz) radiation. Photoreflectance (PR), surface photovoltage (SPV), and wavelength-modulated differential surface photovoltage (DSPV) spectra were measured in the structures with QW widths ranging from 3to20nm and doping densities from 2×1010to5×1012cm−2 at room temperature. The PR spectra displayed Franz-Keldysh oscillations which enabled an estimation of the electric-field strength of ∼20kV∕cm at the sample surface. By analyzing the SPV spectra we have determined that a buried interface rather than the sample surface mainly governs the SPV effect. The DSPV spectra revealed sharp features associated with excitonic interband transitions which energies were found to be in a good agreement with those calculated including the nonparabolicity of the energy bands. The dependence of the exciton linewidth broadening on the well width and the quantum index has shown that an average half monolayer well width fluctuations is mostly predominant broadening mechanism for QWs thinner than 10nm. The line broadening in lightly doped QWs, thicker than 10nm, was found to arise from thermal broadening with the contribution from Stark broadening due to random electric fields of the ionized impurities in the structures. We finally consider the possible influence of strong internal electric fields, QW imperfections, and doping level on the operation of THz sensors fabricated using the studied structures.
Optimization of ultraviolet emission and chemical species generation from a pulsed dielectric barrier discharge at atmospheric pressure
Authors: Lu Xinpei , Laroussi Mounir
Published: July 2005

One of the attractive features of nonthermal atmospheric pressure plasmas is the ability to achieve enhanced gas phase chemistry without the need for elevated gas temperatures. This attractive characteristic recently led to their extensive use in applications that require low temperatures, such as material processing and biomedical applications. The agents responsible for the efficient plasma reactivity are the ultraviolet (UV) photons and the chemically reactive species. In this paper, in order to optimize the UV radiation and reactive species generation efficiency, the plasma was generated by a dielectric barrier discharge driven by unipolar submicrosecond square pulses. To keep the discharge diffuse and to maintain low operating temperatures, helium (He) was used as a carrier gas. Mixed with helium, varying amounts of nitrogen (N2) with the presence of trace amounts of air were used. The gas temperature was determined to be about 350K at a 1-kHz pulse frequency for all cases and only slightly increased with frequency. The UV emission power density, PUV, reached its highest level when 5% to 10% of N2 is mixed to a balance of He. A maximum PUV of about 0.8mW∕cm2 at 10-kHz pulse frequency for a He(90%)+N2(10%) mixture was measured. This was more than four times higher than that when He or N2 alone was used. Furthermore, the emission spectra showed that most of the UV was emitted by excited NO radicals, where the oxygen atoms came from residual trace amounts of air. In addition to NO, NO2, and excited N2, N2+, OH, and He were also present in the plasma.
Local density of states mapping of a field-induced quantum dot by near-field photoluminescence microscopy
Authors: Matsuda K. , Saiki T. , Nomura S. , Aoyagi Y.
Published: July 2005

We have described near-field photoluminescence microscopy of a field-induced quantum-dot structure based on a Be–δ-doped GaAs–Al1−xGaxAs single heterojunction with a surface square mesh gate. The local density of states in the field-induced quantum dot was mapped by measuring the spatial distribution of the near-field photoluminescence intensity, because the photoluminescence spectrum owing to the recombination of holes bound to Be accepters with electrons in an electron gas contains information on the electronic density of states. Experimentally, we observed that the electrons confined in lower energy states spatially localize in a field-induced quantum dot.
Modeling of anomalous hysteresis behavior of compositionally graded ferroelectric films at low fields
Authors: Wong C. K. , Shin F. G.
Published: July 2005

We study the hysteresis behavior of compositionally graded ferroelectric films by theoretical simulations. Anomalous vertical (polarization) shift behavior of hysteresis loops measured by a Sawyer-Tower circuit at low/medium applied fields is investigated. The anomalous ferroelectric response is discussed by the use of a multilayer model to account for the variation of properties across the film thickness. Electrical conductivities of the ferroelectric layers have been taken into account and time-dependent space-charge-limited conduction has been adopted. The effects of charge mobility and the amplitude of applied field on the D-E loop shift were examined. Theoretical calculations are discussed in relation to the experimental data from previous works.
A novel apparatus for solidification of polymer samples under simultaneous high pressures and high cooling rates
Authors: Sorrentino Andrea , Pantani Roberto , Picarella Diego , Titomanlio Giuseppe
Published: July 2005

The crystallization of polymers under pressure has recently attracted particular interest for being a powerful method of obtaining different crystal structures and morphologies. A specific molecular conformation may indeed induce remarkable changes in polymer solvent resistance and mechanical performance. In this work an experimental apparatus was designed and developed to investigate the effects of pressure and cooling rate on polymer samples. The apparatus, based on the confining fluid technique, is able to impose constant external pressures and different cooling rates during the solidification of polymer samples. In its current configuration, the device can reach 1250bars and a maximum cooling rate of 40°C∕s (measured at 200°C) with water at 5°C as a cooling medium. Preliminary results obtained with Syndiotactic Polystyrene confirm that, in addition to thermal history, external pressure is indeed a significant factor for inducing changes in crystalline polymeric structures. The stable orthorhombic β form is favored for specimens solidified under pressure, whereas the overall final crystallinity degree (α and β forms) gradually decreases with both cooling rate and pressure.