3,870 research outputs found
Heat transfer and fluid flow in a partially or fully penetrated weld pool in gas tungsten arc welding
No full textIn this study, fluid flow driven by a combination of electromagnetic force, buoyancy force, are drag force, and surface tension gradient is numerically analyzed for a partially or fully penetrated weld pool in stationary gas tungsten are welding (GTAW). Irregular shape of the weld pool and the moving liquid-solid interface is handled by a boundary-fitted-coordinates technique. Surface tension on the top and the bottom free surfaces of the weld pool is found to play a critical role in determining the flow pattern in the weld pool. The calculated GTA weld bead geometry compares favorably with experimental results. (C) 2000 Elsevier Science Ltd. All rights reserved.This work was supported by the U.S. Army Research Office under grant number DAAH-95-1-0136 which is gratefully acknowledged
Mangarara Formation: exhumed remnants of a middle Miocene, temperate carbonate, submarine channel-fan system on the eastern margin of Taranaki Basin, New Zealand
No full textThe middle Miocene Mangarara Formation is a thin (1–60 m), laterally discontinuous unit of moderately to highly calcareous (40–90%) facies of sandy to pure limestone, bioclastic sandstone, and conglomerate that crops out in a few valleys in North Taranaki across the transition from King Country Basin into offshore Taranaki Basin. The unit occurs within hemipelagic (slope) mudstone of Manganui Formation, is stratigraphically associated with redeposited sandstone of Moki Formation, and is overlain by redeposited volcaniclastic sandstone of Mohakatino Formation. The calcareous facies of the Mangarara Formation are interpreted to be mainly mass-emplaced deposits having channelised and sheet-like geometries, sedimentary structures supportive of redeposition, mixed environment fossil associations, and stratigraphic enclosure within bathyal mudrocks and flysch. The carbonate component of the deposits consists mainly of bivalves, larger benthic foraminifers (especially Amphistegina), coralline red algae including rhodoliths (Lithothamnion and Mesophyllum), and bryozoans, a warm-temperate, shallow marine skeletal association. While sediment derivation was partly from an eastern contemporary shelf, the bulk of the skeletal carbonate is inferred to have been sourced from shoal carbonate factories around and upon isolated basement highs (Patea-Tongaporutu High) to the south. The Mangarara sediments were redeposited within slope gullies and broad open submarine channels and lobes in the vicinity of the channel-lobe transition zone of a submarine fan system. Different phases of sediment transport and deposition (lateral-accretion and aggradation stages) are identified in the channel infilling. Dual fan systems likely co-existed, one dominating and predominantly siliciclastic in nature (Moki Formation), and the other infrequent and involving the temperate calcareous deposits of Mangarara Formation. The Mangarara Formation is an outcrop analogue for middle Miocene-age carbonate slope-fan deposits elsewhere in subsurface Taranaki Basin, New Zealand
A Trend-Change Extension of the Cairns-Blake-Dowd Model
No full textThis paper builds on the two-factor mortality model known as the Cairns-Blake-Dowd (CBD) model, which is used to project future mortality. It is shown that these two factors do not follow a random walk, as proposed in the original model, but that each should instead be modelled as a random fluctuation around a trend, the trend changing periodically. The paper uses statistical techniques to determine the points at which there are statistically significant changes in each trend. The frequency of change in each trend is then used to project the frequency of future changes, and the sizes of historical changes are used to project the sizes of future changes. The results are then presented as fan charts, and used to estimate the range of possible future outcomes for period life expectancies. These projections show that modelling mortality rates in this way leaves much greater uncertainty over future life expectancy in the long term
Experimental studies of Hg(II)-Hg(0) transformations and their effects on Hg isotope fractionation
No full textUnderstanding the redox transformations of inorganic forms of mercury (Hg) is necessary for understanding the fate of mercury in environmental systems. In this study, the interactions of Hg(0) and Hg(II) with organic and inorganic substances were characterized using mercury stable isotopes. Interactions of a mixed Hg(0)-Hg(II) solution with thiol and humic substances were observed, with no net changes to redox speciation. In the presence of mercaptoacetic acid (MCA), an equilibrium isotope enrichment factor (ε202Hg = δ202HgHg(II) - δ202HgHg(0)) of 1.34‰ between the Hg(II) and Hg(0) fractions was observed, similar with previously published values for Hg(0) oxidation by thiols. The equilibrium ε202Hg values similarly determined for 2-mercaptopropionic acid (MPA) and Suwannee River humic acids were 2.03‰ and 1.50‰, respectively. Reduction of mercury by siderite (FeCO3) was also characterized with respect to isotope fractionation over the course of the reaction. This reaction resulted in an 87% reduction of Hg(II) over 30 minutes, with change in mercury isotope ratios of the reactant. Kinetic ε202Hg values for the reduction of Hg(II) by siderite (ε202Hg = δ202HgHg(0) - δ202HgHg(II)) were determined by closed-system model (-1.59‰) and Rayleigh distillation model (-1.07‰; product enrichment in light isotopes). The final equilibrium state exhibited an equilibrium ε202Hg of -0.67‰. The results from the experiments conducted suggest that there is equilibrium isotope exchange between thiol-bound Hg(II) and dissolved Hg(0), and that the reduction by siderite is rapid and may involve multiple processes through the reaction.M.S.Includes bibliographical reference
Enduring legacy of a toxic fan via episodic redistribution of California gold mining debris
No full textThis work was supported by National Science Foundation Grants BCS-0521663 and EAR-1226741 (to M.B.S.), Grant BCS-0520933 (to L.A.J.), and Grant BCS-0521774 (to R.A.). M.B.S. also received support from The Carnegie Trust for Scottish Universities and The Royal Society of Edinburgh. J.L.H. was supported by a Natural Environment Research Council Fellowship (United Kingdom).The interrelationships between hydrologically driven evolution of legacy landscapes downstream of major mining districts and the contamination of lowland ecosystems are poorly understood over centennial time scales. Here, we demonstrate within piedmont valleys of California’s Sierra Nevada, through new and historical data supported by modeling, that anthropogenic fans produced by 19th century gold mining comprise an episodically persistent source of sediment-adsorbed Hg to lowlands. Within the enormous, iconic Yuba Fan, we highlight (i) an apparent shift in the relative processes of fan evolution from gradual vertical channel entrenchment to punctuated lateral erosion of fan terraces, thus enabling entrainment of large volumes of Hg-laden sediment during individual floods, and (ii) systematic intrafan redistribution and downstream progradation of fan sediment into the Central Valley, triggered by terrace erosion during increasingly long, 10-y flood events. Each major flood apparently erodes stored sediment and delivers to sensitive lowlands the equivalent of ∼10–30% of the entire postmining Sierran Hg mass so far conveyed to the San Francisco Bay-Delta (SFBD). This process of protracted but episodic erosion of legacy sediment and associated Hg is likely to persist for >104 y. It creates, within an immense swath of river corridor well upstream of the SFBD, new contaminated floodplain surfaces primed for Hg methylation and augments/replenishes potential Hg sources to the SFBD. Anticipation, prediction, and management of toxic sediment delivery, and corresponding risks to lowland ecology and human society globally, depend on the morphodynamic stage of anthropogenic fan evolution, synergistically coupled to changing frequency of and duration extreme floods.Peer reviewe
Liquid structure of Rb-Hg alloys studied by neutron diffraction
No full textThe structures of liquid Rb–Hg alloys were studied as a function of composition by neutron diffraction. In the intermediate Rb concentration range, the obtained structure factors show a small prepeak, which may be an evidence of the formation of Hg polyanion units in liquids. The Reverse Monte Carlo (RMC) analysis was applied to separate the total radial distribution function into the corresponding partial radial distribution functions. Up to 10 at.% Rb, no obvious changes are found for the first peak position of the partial radial distribution functions of the Hg–Hg pair and that of the Hg–Rb pair. The first peak position between the Hg–Rb pairs increases above 20 at.% Rb. In addition to the first peak, a subpeak between Hg–Hg pairs can be seen in the large distance. At 60 at.% Rb, the nearest neighbor distance between Hg atoms shows the closest value in the concentration range studied. These results indicate that with the progress of charge transfer the solvation structure in the dilute Rb concentration range changes into the structure containing polyanions composed of Hg species
Holocene peat Hg anomalies
No full textThis project examines the major explosive volcanic eruptions recorded in peat. Hg data from three peat profiles, the Hongyuan and Dangxiong peat from the Tibetan Plateau and the Pinet peat record from France, were synthesized here to support our conclusions. All the Hg data and the MATLAB script are prepared for the manuscript entitled "Tibetan peat saw Holocene global major explosive volcanic eruptions".Corresponding author: Haijun PENG, [email protected].</p
MATRIX ISOLATION ESR STUDIES OF Hg RADICALS: , , , and
No full textAuthor Institution: Furman University; University of Western AustraliaAtomic mercury vapor was passed through various rare gas plasma discharges and condensed in neon, argon, and krypton rare gas matrices at cryogenic temperatures for electron spin resonance (ESR) investigations. The first ESR spectrum of , observed in Ne, Ar, and Kr matrices is presented, with determination of its magnetic parameters, which exhibited excellent agreement with gas phase values. The ratio of the values for and is shown to vary slightly from to HgH/HgD. This variation can be attributed to electronic structure differences surrounding the mercury nucleus. Observation of in a Kr lattice also provides information on the required energy gap between the electron affinity of an isolated species and the ionization potential of the matrix host atom. HgH and HgD were observed in experiments where the plasma discharge was doped with a small percentage of gas. The HgH/HgD radicals were observed for the firs t time in a neon matrix, providing a comparison of the various magnetic parameters to earlier argon matrix results. The electronic structure and magnetic parameters of will be analyzed based upon these new matrix results for and HgH
Freedom of choice or force of circumstance? : Eastern European sex-workers in the Republic of Cyprus ; paper for the conference 'Alltag der Globalisierung. Perspektiven einer transnationalen Anthropologie', January 16-18, 2003, Institute of Cultural Anthropology and European Ethnology, Johann Wolfgang Goethe University, Frankfurt am Main
No full textThis paper focuses on Eastern European migrants who, since the beginning of the 1990s, are entering the Republic Cyprus as “artistes”. This is a visa permit status as well as an euphemism for short-term work permits in the local sex industry. In addition to exploring the migrational experiences of these women and their living and working conditions in the Republic of Cyprus, the paper reconstructs, empirically and analyt ically, the connection between immigration and the local sex industry. Here, several categories of social actors and institutions in Cyprus are actively involved. The rhetoric of government representatives, entrepreneurs and clients in the sex business on the one hand is contrasted with the discourse of local NGO representatives concerned with immigrants’ rights on the other hand. The paper comes to the conclusion that all of these discursive positions ultimately do not do justice to the complex process of decisionmaking that women undergo who migrate into the sex industry. Either, freedom of choice is emphasized – such as by entrepreneurs and the government – or the domination of women – as in the public statements of the NGO. In order to analyze the ambivalent tension between freedom of choice and submission to force by which the women’s decision is characterized, the author employs Michel Foucault’s concept of governmentality, which describes forms of political regulation that use the individual’s freedom of action as an instrument to exercise power
Comparison of system architecture and converter topology for a solar powered electric vehicle charging station
No full textAccepted Author ManuscriptOld - EWI-ESE-DC&S DC systems & StoragePhotovoltaic Materials and Device
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