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Stable isotopes of oxygen, nitrogen, and boron were used to identify the sources of nitrate (NO3–) in submarine groundwater discharge (SGD) into a large tidal estuary (Long Island Sound, NY, United States). Potential contaminants such as manure, septic waste and fertilizer overlap in δ15N and δ18O but have been shown to have distinctive δ11B in non-coastal settings. Two distinct subterranean estuaries were studied with different land-use up gradient, representative of (1) mixed medium-density residential housing and (2) agriculture. These sites have overlapping δ15N and δ18O measurements in NO3– and are unable to discriminate between different N sources. Boron isotopes and concentrations are measurably different between the two sites, with little overlap. The subterranean estuary impacted by mixed medium-density residential housing shows little correlation between δ11B and [B] or between δ11B and salinity, demonstrating that direct mixing relationships between fresh groundwater and seawater were unlikely to account for the variability. No two sources could adequately characterize the δ11B of this subterranean estuary. Groundwater N at this location should be derived from individual homeowner cesspools, although measured septic waste has much lower δ11B compared to the coastal groundwaters. This observation, with no trend in δ11B with [B] indicates multiple sources supply B to the coastal groundwaters. The agricultural subterranean estuary displayed a positive correlation between δ11B and [B] without any relationship with salinity. Binary mixing between sea spray and fertilizer can reasonably explain the distribution of B in the agricultural subterranean estuary. Results from this study demonstrate that δ11B can be used in combination with δ15N to trace sources of NO3– to the subterranean estuary if source endmember isotopic signatures are well-constrained, and if the influence of seawater on δ11B signatures can be minimized or easily quantified.

Bottom-waters in Smithtown Bay (Long Island Sound, NY) are subject to hypoxic conditions every summer despite limited nutrient inputs from waste-water and riverine sources, while modeling estimates of groundwater inputs are thought to be insignificant. Terrestrial and marine fluxes of submarine groundwater discharge (SGD) were quantified to Smithtown Bay using mass balances of 222 Rn, 224 Ra, 226 Ra and 228 Ra during the spring and summer of 2014/2015, in order to track this seasonal transition period. Intertidal pore waters from a coastal bluff (terrestrial SGD) and from a barrier beach (marine SGD) displayed substantial differences in N concentrations and sources, traced using a multi-isotope approach ( 222 Rn, Ra, δ 15 N-NO 3 − , δ 18 O-NO 3 − ). NO 3 − in terrestrial SGD did not display any seasonality and was derived from residential septic systems and fertilizer. Marine SGD N concentrations varied month-to-month because of mixing between oxic seawater and hypoxic saline pore waters; N concentrations were greatest during the summer, when NO 3 − was derived from the remineralization of organic matter. Short-lived 222 Rn and 224 Ra SGD fluxes were used to determine remineralized N loads along tidal recirculation flow paths, while long-lived 228 Ra was used to trace inputs of anthropogenic N in terrestrial SGD. 228 Ra-derived terrestrial N load estimates were between 20 and 55% lower than 224 Ra-derived estimates (excluding spring 2014); 228 Ra may be a more appropriate tracer of terrestrial SGD N loads. Terrestrial SGD NO 3 − (derived from 228 Ra) to Smithtown Bay varied from (1.40–12.8) ∗ 10 6 mol N y −1 , with comparable marine SGD NO 3 − fluxes of (1.70–6.79) ∗ 10 6 mol N y −1 derived from 222 Rn and 224 Ra. Remineralized N loads were greater during the summer compared with spring, and these may be an important driver toward the onset of seasonal hypoxic conditions in Smithtown Bay and western Long Island Sound. Seawater recirculation through the coastal aquifer can rival the N load from terrestrial SGD from a heavily polluted aquifer.

Burial of biogenic silica (bSitotal) in high sedimentation rate continental margins remains highly uncertain. Cosmogenic 32Si (t1/2~140 years) can be used to trace the fates of bSitotal postdeposition, including as opal (bSiopal) and diagenetically altered opal (bSialtered), the latter dominantly authigenic clay (bSiclay). To determine the magnitude and form of bSitotal storage in coastal sediments, conventional operational leaches targeting bSiopal and bSialtered (including bSiclay) were modified for large-scale samples necessary for measurement of 32Si. The 32Si activity was used to estimate total biogenic silica burial (bSitotal = bSiopal + bSialtered) in several depositional settings: Gulf of Papua, Gulf of Mexico, Long Island Sound, and in the previously studied Amazon-Guianas deltaic system. In subtropical and temperate regions, 32Si was detected in both traditional biogenic silica leaches (bSiopal) and residual authigenic clays. Traditional bSiopal and modified operational leaches designed to target the most reactive authigenic silicates (~bSialtered) consistently underestimate authigenic clay formation (bSiclay) and thus the magnitude of bSitotal burial in temperate coastal zones and subtropical deltas by 2–4-fold. In tropical deltas, 32Si activities in the residual fraction after removal of bSiopal demonstrate rapid and almost complete alteration of initial bSiopal to new forms, most likely bSiclay. Globally, 4.5–4.9 Tmol/yr Si may be trapped in marine nearshore deposits as rapidly formed clay (bSiclay), 100% of the “missing silica sink” in the marine silica budget.

The carbon and oxygen isotope compositions of calcium carbonate shells are widely accepted and applied proxies for tracking changes in paleoenvironmental conditions such as temperature, salinity and productivity. In order to accurately interpret isotopic measurements, diagenetic alteration must first be assessed. The occurrence of aragonitic shells is often taken as a first order sign of unaltered material because aragonite at the Earth9s surface is metastable and converts to calcite. However, even specimens that retain an aragonitic composition and are macroscopically well preserved often exhibit subtle to considerable signs of alteration when shell microstructure is examined using scanning electron microscopy (SEM). To determine the textural and isotopic effects of progressive alteration on differing types of shell microstructure, we undertook a comparative study of aragonitic shells from two regions frequently used in paleoenvironmental reconstructions and diagenetic studies – the Upper Cretaceous of the Gulf Coastal Plain (GCP) and the Western Interior Seaway (WIS). Because the GCP is within a passive margin setting and the WIS has experienced tectonic processes, we also evaluate how diagenetic history affects isotopic composition. Visually well-preserved ammonite, bivalve, and gastropod shells were collected from one locality in the GCP and examined using SEM. To evaluate microstructural preservation, we used a previously published scale based on WIS specimens for nacreous shell material and a complementary scale we developed for crossed lamellar microstructure. The stable carbon and oxygen isotope compositions of specimens across the preservational scale from both regions were analyzed. Isotopic composition does not change systematically with degrading preservation in the GCP specimens, a result that contrasts strongly with patterns in WIS specimens where isotopic composition systematically decreases with decreasing microstructural preservation. Dissimilar tectonic regimes that led to unique post-depositional conditions for each region are invoked to explain this difference. The WIS was a foreland basin subjected to significant meteoritic groundwater flow driven by active uplift, while the GCP was a passive margin that has remained close to sea level, with low hydraulic potential, since the time of deposition. Thus, during diagenesis the WIS shells were exposed to fluids that differed greatly from the seawater in which the organisms grew, whereas diagenetic fluids in GCP settings likely were similar to marine waters. As expected, shells with the best-preserved microstructure provide the most consistently reliable isotopic data for paleoenvironmental reconstructions, but our comparisons show that similar degrees of microstructural alteration can express very different diagenetic shifts in isotopic values.

Altres ajuts: the government of Spain and the Fulbright Commission for a post-doctoral fellowship to J.G-O. (ref 2007-0516) The approach to quantify submarine groundwater discharge using Ra isotopes generally involves developing a Ra mass balance in an estuary, bay or lagoon. In this work we present a 224Ra mass balance used to evaluate the importance of the submarine groundwater discharge (SGD) in Long Island Sound (NY, US), the third most important estuary in US, located between Long Island and Connecticut that is usually affected by summertime hypoxia in the western basin. Three surveys were conducted between April 2009 and August 2010 where 25 water stations were sampled for Ra isotopes, oxygen and Mn. Stations were oriented along 4 transects: one axial extending from the western to the eastern Sound and three longitudinal transects in the western, central and eastern Sound. The inventory of 224Ra in the water column in summer was circa 2 times greater than in winter, suggesting an increased 224Ra flux to the Sound in summer. A mass balance for 224Ra was constructed considering tidal exchange, inputs from rivers, desorption from resuspended particles, diffusive fluxes (including bioirrigation) from bottom sediments and radioactive decay in the water column. Fluxes of 224Ra from bottom sediments were measured by incubating cores under oxic conditions in a continuous flow mode such that the overlying water was circulated through a Mn-oxide fiber to maintain a constant activity of 224Ra. Fluxes from muddy sediments (comprising ~67% of the Sound bottom) ranged from 127 to 312dpmm-2d-1 and were ~60dpmm-2d-1 in sandy sediments (33% of the Sound). Incubations under hypoxic conditions showed variable fluxes depending on reduction and mobilization of Mn. The 224Ra mass balance shows a net input of Ra to the Sound of 106±50×1012dpmy-1 in spring and 244±112×1012dpmy-1 in the summer that is attributed to SGD. Elevated 224Ra values were observed near shore and in the pore fluids of the coarse beach sands along the Long Island and Connecticut coasts, suggesting that SGD driven by tidal recirculation through the beach face is a major source of 224Ra to the Sound. Seasonal variation in this source seems unlikely, and the calculated 224Ra SGD fluxes for spring and summer overlap within the uncertainties. Nevertheless we conclude that variations in the 224Ra water column inventories could be produced by seasonal changes in bioirrigation and/or redox cycling of Mn as well as sediment resuspension and desorption of 224Ra from resuspended particles, and that our mass balance underestimates these terms, particularly in the summer. 224Ra fluxes from sediments in estuaries, especially those with significant areas of muddy sediments and seasonal hypoxia, are important and should be well constrained in future uses of this isotope as a tracer for SGD.

The four naturally-occurring radium isotopes (223Ra, 224Ra, 226Ra and 228Ra) were used to estimate the submarine groundwater discharge (SGD) in the Isola La Cura marsh area in the northern Venice Lagoon (Italy). By determining the radium contributors to the study area (river, coastal ocean and sediments) the radium excess in the lagoon water was quantified through a mass balance model. This radium excess is attributed to a submarine groundwater discharge source and represents the most important input of radium. Possible endmembers were considered from analysis of groundwater samples (subtidal and marsh piezometers, marsh wells and seepage meters) that were enriched in Ra by one to two orders of magnitude relative to surface waters. In particular, a permeable layer at 80 cm depth in the surrounding marsh is considered to be representative of the most likely SGD source, although similar radium activities were measured in other subtidal porewater samples collected in the Isola La Cura area. The estimated SGD flux to the study area ranged from 1 · 109 to 6 · 109 L·d− 1, the same order of magnitude as the overall riverine input to the lagoon (3 · 109 L·d− 1). A major fraction of this SGD flux is likely recirculated seawater, as evidenced by the endmember salinity. The water residence time of 2 days was estimated by both using the shortest-lived radium isotope and estimating the volume of water exchanged between the lagoon and the open sea during a tidal cycle (tidal prism approach). This SGD flux could be used to estimate the input of other chemical species (metals, nutrients, etc.) via SGD which might affect the Venice Lagoon ecosystem.

Natural radioactivity in the environment originates from two sources. First, primordial radionuclides which were incorporated into the Earth at the time of its formation are still present in it because of their long half-lives. 238 U, 235 U, 232 Th and their decay series (Fig. 1), 40 K, 87 Rb and 187 Re are examples of this category. Second, cosmic ray-produced isotopes which are generated continuously in the atmosphere and earth's crust through interactions of cosmic rays with their constituents. 3 H, 14 C and 10 Be are some of the isotopes belonging to this group. The distribution of all these isotopes in the oceans is governed by their supply, radioactive decay, water mixing and their biogeochemical reactivity (the tendency to participate in biological and chemical processes) in sea water. Water circulation plays a dominant role in the dispersion of isotopes which are biogeochemically ‘passive’ (eg, 3 H, Rn), whereas biological uptake and release, solute–particle interactions and chemical scavenging exert major control in the distribution of biogeochemically ‘active’ elements (eg, C, Si, Th, Pb, Po). Systematic study of the isotopes of these two groups in the sea can yield important information on the physical and biogeochemical processes occurring in sea water.

Thorium-234 is increasingly used as a tracer of ocean particle flux, primarily as a means to estimate particulate organic carbon export from the surface ocean. This requires determination of both the 234 Th activity distribution (in order to calculate 234 Th fluxes) and an estimate of the C / 234 Th ratio on sinking particles, to empirically derive C fluxes. In reviewing C / 234 Th variability, results obtained using a single sampling method show the most predictable behavior. For example, in most studies that employ in situ pumps to collect size fractionated particles, C / 234 Th either increases or is relatively invariant with increasing particle size (size classes > 1 to 100s μm). Observations also suggest that C / 234 Th decreases with depth and can vary significantly between regions (highest in blooms of large diatoms and highly productive coastal settings). Comparisons of C fluxes derived from 234 Th show good agreement with independent estimates of C flux, including mass balances of C and nutrients over appropriate space and time scales (within factors of 2–3). We recommend sampling for C / 234 Th from a standard depth of 100 m, or at least one depth below the mixed layer using either large volume size fractionated filtration to capture the rarer large particles, or a sediment trap or other device to collect sinking particles. We also recommend collection of multiple 234 Th profiles and C / 234 Th samples during the course of longer observation periods to better sample temporal variations in both 234 Th flux and the characteristic of sinking particles. We are encouraged by new technologies which are optimized to more reliably sample truly settling particles, and expect the utility of this tracer to increase, not just for upper ocean C fluxes but for other elements and processes deeper in the water column.

The uranium and thorium decay series have numerous radionuclides with half-lives ranging from fractions of a second to a few years. The former include many of the isotopes of radon, polonium, bismuth, lead and thallium and these are generally too short to show appreciable disequilibrium with respect to their precursors in the decay series. Others, however, have half-lives that make them useful in tracing a variety of oceanic processes that occur on short time scales. This group includes isotopes of thorium: 234Th (half-life = 24.1 d), 227Th (18.6 d), 228Th (1.9 y), radium: 224Ra (3.64 d), 223Ra (11.1 d), radon: 222Rn (3.8 d) and polonium: 210Po (138 d). Of these, the Th isotopes and 210Po are particle-reactive, while the radium isotopes and radon tend to remain in solution. As a consequence, Th and Po are useful in quantifying the rate of scavenging from solution onto particles and the processes governing the dynamics of particles in the ocean, while Ra and Rn are appropriate tracers for fluid processes such as advection and diffusion (Cochran 1992). Other chapters in this volume highlight recent developments in the use of short-lived Ra isotopes and Rn as tracers of estuarine mixing and submarine groundwater discharge (Swarzenski et al. 2003; Porcelli and Swarzenski 2003). Likewise, the oceanic chemistries of the longer-lived particle reactive radionuclides in the U/Th series, such as 230Th, 231Pa and 210Pb are treated elsewhere in this volume (Henderson and Anderson 2003). Accordingly our emphasis here is with recent developments in the application of the short-lived Th isotopes (234Th, 227Th, 228Th) and 210Po as tracers for particle-associated processes. These radionuclides have in common the fact that each is produced by a longer lived parent which is stably dissolved …

Since heavy metal deposition records are scarced in urbanized areas, we used saltmarsh and marine sediments as proxies to reconstruct heavy metal fluxes during the last century in the Camargue (South France). 2l"Pb, l31 Cs and stable lead were analyzed in order to determine their inventories and to reconstruct temporal trends in concentrations and fluxes in two zones of the coastal environment. Two cores were collected in a saltmarsh environment and another one in the Gulf of Lions continental slope. Regarding the radionuclide profiles, one core from the saltmarsh appears to be influenced by Rhone flooding deposits. The other cores seem to reflect the atmospheric supply. Werner they were collected in different environment (saltmarsh and slope sediments), their pollutant lead inventories are in good agreement. The 210 Pb excess inventories determinate in the same core are also very concomitant, and confirm the level of anthropogenic accumulation.

Staffing across multiple time periods with uneven demand is a common problem in many organizations. There are many models for optimal cyclic personnel scheduling, but none of these incorporates the optimal number-of-workers problem or the optimal staff-skills-composition problem. In this paper, we introduce a variation on cyclic scheduling that incorporates discrete-event simulation and specialized data collection for a staffing plan as part of a general methodology. The result is a four-step approach based on a stochastic optimization model for scheduling and staffing an organization. We illustrate this approach with a semiconductor manufacturing case study.

[1] The natural cosmogenic radionuclide 7Be (T1/2 = 53.4 d) is supplied to the surface ocean from the atmosphere and, in the Arctic Ocean, can be used as a tracer of the efficiency with which sea ice intercepts the atmospheric fluxes of chemical species and of the importance of ice as a transport mechanism for particulate matter and chemical species. Analyses of 7Be in samples of surface water, surface sea ice, water beneath the ice, sea ice sediments, and precipitation from the Eurasian Basin of the Arctic Ocean show that the fraction of sea ice coverage determines the amount of 7Be in the surface water. When sea ice coverage is 80%, the water column inventory drops to 58 ± 20 Bq m−2. The 7Be inventory in sea ice is 39 ± 23 Bq m−2, and mass balance calculations show that sea ice can intercept 30 ± 18% of the atmospheric flux of 7Be during the studied period. We suggest that other atmospherically transported contaminants should be similarly intercepted. 7Be in the ice also can be used to estimate that the annual transport and release of sediment to the ablation area of the Fram Strait is ∼500 g m−2, a value comparable to previously measured fluxes in sediment traps deployed in the area.

Since the 1950s, nuclear weapon testing and releases from the nuclear industry have introduced anthropogenic radionuclides into the sea, and in many instances their ultimate fate are the bottom sediments. The Arctic Ocean is one of the most polluted in this respect, because, in addition to global fallout, it is impacted by regional fallout from nuclear weapon testing, and indirectly by releases from nuclear reprocessing facilities and nuclear accidents. Sea-ice formed in the shallow continental shelves incorporate sediments with variable concentrations of anthropogenic radionuclides that are transported through the Arctic Ocean and are finally released in the melting areas. In this work, we present the results of anthropogenic radionuclide analyses of sea-ice sediments (SIS) collected on five cruises from different Arctic regions and combine them with a database including prior measurements of these radionuclides in SIS. The distribution of 137Cs and 239,240Pu activities and the 240Pu/239Pu atom ratio in SIS showed geographical differences, in agreement with the two main sea ice drift patterns derived from the mean field of sea-ice motion, the Transpolar Drift and Beaufort Gyre, with the Fram Strait as the main ablation area. A direct comparison of data measured in SIS samples against those reported for the potential source regions permits identification of the regions from which sea ice incorporates sediments. The 240Pu/239Pu atom ratio in SIS may be used to discern the origin of sea ice from the Kara-Laptev Sea and the Alaskan shelf. However, if the 240Pu/239Pu atom ratio is similar to global fallout, it does not provide a unique diagnostic indicator of the source area, and in such cases, the source of SIS can be constrained with a combination of the 137Cs and 239,240Pu activities. Therefore, these anthropogenic radionuclides can be used in many instances to determine the geographical source area of sea-ice. © 2010 Elsevier B.V., This work was partially funded by the Ministerio de Eduación y Ciencia of Spain (POL2006-00449). The US National Science Foundation supported portions of this study. The first author expresses her gratitude to MEC through her scholarship AP2006-03071. Support for the research of PM was received through the prize ICREA Academia, funded by the Generalitat de Catalunya. Support from the government of Spain and the Fulbright Commission for a post-doctoral fellowship to J.G.-O. (ref 2007-0516) is gratefully acknowledged.

Ra isotopes are a powerful tool for quantifying the flux of submarine groundwater discharge (SGD) into the sea. Previous studies of 223Ra and 224Ra mass balances in coastal embayments have shown that the Ra balance is dominated by supply via SGD, exchange with the open ocean and radioactive decay. The current study shows that a single time series over a tidal cycle at the principal inlet to Great South Bay (NY, US) is sufficient to determine the net flux of Ra across the inlet, and also can be used to estimate the decay of short-lived Ra in the bay. Estimates of the net Ra flux obtained from a single tidal time-series by using three different approaches agree with those determined from a more time-consuming survey of Ra within the bay, and may represent a first step of estimating SGD in bays and coastal lagoons.

Sediment and heavy metal accumulation were studied in a canal of Venice (Rio di S.Angelo) that has typical characteristics of medium-to-small canals with respect to dimensions, boat traffic and pollution sources. The tidal dynamics are particularly weak in this approximately 5-m wide canal. Four cores were collected across a section and five additional cores were collected from the longitudinal axis. The canal was dredged in the late 1950s, and therefore the collected cores represent approximately 40 years of deposition. Excess Pb-210 and Cs-137 are present throughout the sediment cores and inventories of both radionuclides are greater toward the canal margins than in the center, indicating enhanced deposition along the margins. The margin cores show a Cs-137 peak at 30 to 45 cm depth that we attribute to input from the 1986 Chernobyl accident. Two of the cores are sufficiently long to show increases of Cs-137 at depth, probably related to the 1963 global fallout input. The Cs-137 profiles are consistent with accumulation rates of approximately 2 to 3 cm y-1. Excess Pb-210 activities show little variability in the upper 25 to 45 cm of the margin cores, and decrease by a factor of approximately 2 over the next roughly 30 cm of the cores. As the canal shoaled with sediment deposition, resuspension of sediment by boat traffic along the canal center likely produced increased deposition along the margins. Concentrations of heavy metals fall within the average of values determined for the whole canal network. Arsenic, cadmium, copper lead and zinc show clear decreases toward the sediment-water interface, suggesting recent reductions of contaminant inputs.

The age and habitat of the giant squid, Architeuthis sanctipauli Velain, 1877, were determined based on isotopic analyses of the statoliths of three female specimens captured off Tasmania, Australia, between January and March 1996. Assuming that the aragonite of the statoliths formed in equilibrium with seawater, δ18O analyses indicated that the squid lived at temperatures of 10.5–12.9°C, corresponding to average depths of 125–250 m and maximum depths of 500 m. The capture records indicated that these squid may have occasionally ranged still deeper, to as much as 1000 m. All the statoliths were labeled with bomb 14C (Δ14C=+22.9‰ to +44.6‰), consistent with the depths inferred from δ18O. A thin section through one of the statoliths revealed 351 growth increments grouped into check-ring structures every 10–16 increments. A model for statolith growth and the pattern of temporal change in Δ14C in the water column was used to estimate the ages of the three specimens. These estimates were very sensitive to the choice of depth range over which Δ14C values were integrated. Assuming that the capture depths represented the maximum habitat depths of these individuals, the calculations suggested an age of 14 years or less. More refined age estimates require a better understanding of the variation of Δ14C and temperature with depth in the areas in which the squids live.

A new open‐atmosphere chemical vapor deposition (CVD) technique has been developed that we term combustion chemical vapor deposition (CCVD). During CCVD a flame provides the necessary environment for the deposition of a dense film whose elemental constituents are derived from solution, vapor, or gas sources. Ag, YSZ, BaTiO3, YIG, YBa2Cu3Ox, and Y2BaCuO5 have been deposited via CCVD with the combustion of a sprayed, cation‐containing, organic solution as the sole heat source. CCVD could, for some applications, be less expensive and more flexible than conventional CVD.

The authors derived a set of analytical models for serial production lines with multiple operation stations and multiple inspection/repair stations. Multiple defect types may be acquired by the production units from the raw stock as well as during processing at operation stations. The analytical models are steady-state equations for outgoing quality level, throughput rate and scrap rates. The analytical models are based on (1) traffic rate equations of the flow through a production line when represented as a directed flow network and (2) probabilistic models of changes in defect attributes of the production units as they flow. The formulas may be used for evaluating inspection configuration designs including the formulation of optimal cost models.

Lightweight stainless steel foams approaching 10% theoretical density are being fabricated via direct reduction. These foams are formed using a coaxial nozzle process that generates hollow ceramic spheres at high rates from an acetone-based slurry. The Fe2O3/Cr2O3 hollow spheres are reduced in a hydrogen/argon atmosphere at high temperature resulting in individual hollow metal spheres. Using more viscous slurry of similar composition, the spheres are bonded at points of contact into a quasi-closed cell structure and further heat treated to reduce the bond phase. The result is a Fe-12Cr alloy hollow sphere foam with a density on the order of 1 g/cc. Addition of carbon and further heat treatments allow the control of strength and ductility through micro structure. Mechanical testing is being conducted to determine attainable properties that can be compared to existing foam models.

The objective of this paper is to report on the fabrication process and document the microstructure of metal-metal syntactic foams. The composite microstructure consists of thin-wall, hollow Fe-Cr stainless steel spheres cast in various metal matrices including aluminum alloys 6061, 7075, 413, magnesium alloy AZ31B, and unalloyed aluminum and magnesium. Hollow spheres were formed from slurries of fine particle size iron and chromium oxides via the coaxial nozzle process. The oxides were reduced and sintered in hydrogen to the corresponding Fe-Cr alloy. Spheres were sufficiently uniform to allow arrangement into random or periodic arrays. These arrays were infiltrated by an aspiration casting process, resulting in a structure less dense than the matrix metal.

This report describes results of field and laboratory studies focusing on the Ob River system. Analyses of suspended particles collected in 1994 and 1995 show that the 240Pu/239Pu atom ratio is lower than global fallout throughout the system (except in the Taz River). Low values of the ratio in the Ob River before it joins the Irtysh suggest that Tomsk-7 is an important source of reprocessing Pu to the system. As much as 39% of the Pu in this part of the river could be derived from reprocessing. 239,240Pu/137Cs activity ratios are depressed relative to global fallout in the Irtysh and Tobal Rivers suggesting that releases from Mayak are also occurring and labelling particles in the system. Mayak is also the apparent source of elevated 12% to the Ob. Decreases in 129I from the Tobal to the Ob at confluence points of the Tobal with the Irtysh and Irtysh with the Ob are evident, probably due to dilution. Laboratory mixing experiments of filtered Ob River water and sea water were performed to determine radionuclide removal in the estuary of the Ob. Removal varied in the order Am>>>Co=I>Cs. Am displayed significant removal (tilde 38%) at 5 ppt salinity, with most of the uptake onto particles in the 0.2 - 1 micrometer size range. Cs and I were most reactive at 0 ppt salinity and uptake decreased with increasing salinity. Irradiation of Ob River water with UV to photooxidize dissolved organic matter caused an increase in uptake of Am onto particles.

The distribution of dissolved and particulate 234Th in the upper 200 m of the water column was obtained for three stations in the Ross Sea off Victoria Land and Terra Nova Bay. At site 24a, close to the retreating ice margin, all the sampled depths showed deficiencies in 234Th relative to the equilibrium with 238U. These are related to uptake of 234Th onto sinking particles. Residence times of 234Th in solution and of particulate 234Th were 130-247 days and 8.1-6.6 days, respectively. A high particle flux (1.23-5.03 g m-2 d-1) was calculated at this station. At the other two sites (11c and 15c), 234Th depth profiles are irregular, probably due to the release of dissolved 234Th by decomposing particles at certain depths, or to the contribution from lateral advection. Bulk mass fluxes measured by floating traps at stations 11c and 15c are very low (66-138 mg m-2 d-1). Also fluxes of organic carbon and nitrogen, and biogenic silica are reported for these two sites. The calculated fluxes are discussed with respect to methodologies and to the dynamics of the ice margin retreat.

Several thorium isotopes (Th-234, Th-228, Th-230) are produced from decay of dissolved parents in sea water and associated strongly with particles. We have used measurements of these isotopes in solution and on suspended (>0.5 μm) and sinking particles, coupled with the known rates of their production and decay, to determine radionuclide (and by extension carbon) fluxes in the surface ocean. The short half-life of Th-234 (24 days) makes it a particularly appropriate tracer for variations in particle fluxes over time scales of weeks to months, and shipboard measurements of The-234 were made by gamma spectrometry during the JGOFS North Atlantic Bloom Experiment (April-May, 1989). The results show increasing association of Th-234 with particles and consequent removal from surface water as the spring phytoplankton bloom progressed. Depth profiles of Th-234 determined four times during the course of the bloom permit calculations of the net export of Th-234 at several depths in the water column. These Th-234 fluxes may be converted to carbon fluxes if the C/Th-234 ratio of material sinking out of the euphotic zone is known. Using the C/Th-234 ratio measured in suspended particles and sediment trag material gives a range of euphotic zone carbon export of 15–42 mmol C/m2/d and 6–20 mmol C/m2/d, respectively, over the course of the bloom.

A model consisting of three phases — solution, small suspended particles (Ps) and large, sinking particles (PL) has been used to determine particle cycling rate constants as a function of depth in the NW Atlantic (Nares Abyssal Plain). The rate constants were determined by inverting the model using available data on dissolved phosphate, dissolved (Ad) and particulate thorium isotopes (As and AL), suspended particle concentrations, and mass and thorium activity fluxes. The model envisions small particle formation (at a rate β1) in its upper two layers (see figure below). At all depths, small particles decompose (at a rate β-1) and aggregate into large particles (at a rate β2), and large particles disaggregate into small particles (at a rate β-2) and sink with a velocity ω. Thorium adsorbed onto particles behaves in a similar manner. Thorium in solution is adsorbed onto small particles at a rate that is a function of the particle concentration (k1Ps) and desorbed (at a rate k-1). Thorium is produced by a dissolved parent and decays (λ) in each phase. Particles and thorium can be advected, diffused, and change with time. Initial estimates for the rate constants were made based on prior work and the available data. Measured values and initial estimates were weighted for the inversion by the variance associated with each term. The sum of the time dependence and transport terms for each phase are included in the inversion, but assumed equal to zero with a large variance. The rate constants obtained with the inversion (k1=5.1•104 L g-1 y-1; k-1=2 y-1; and 0.1< β-1

Near surface (

We provide least squares estimates of particle-cycling rate constants and their errors at 13 depths in the Northwest Atlantic Ocean using a compilation of published results and conservation equations for thorium and particle cycling. The predicted rates of particle aggregation and disaggregation vary through the water column. The means and standard deviations, based on lognormal probability distributions, for the lowest and highest rates of aggregation (β2) and disaggregation (β−2) in the water column are 8±27 y−1 < β2 < 18±90 y−1, and 580±2000 y−1 < β−2 < 3×103±104y−1. Median values for these rates are 2.1 y−1 < β2 < 3.2y−1, and 149 y−1 < β−2 < 156 y−1. Predicted rate constants for thorium adsorption (k1 = 5.0 ± 1.0 × 104 m3 kg−1 y−1) and desorption (k−1 = 3.1±1.5 y−1) are consistent with previous estimates. Least squares estimates of the sum of the time dependence and transport terms from the particle and thorium conservation equations are on the same order as other terms in the conservation equations. Forcing this sum to equal zero would change the predicted rates. Better estimates of the time dependence of thorium activities and particle concentrations and of the concentration and flux of paniculate organic matter would help to constrain estimates of β2 and β−2.

The composite‐based low voltage field emitter cathode offers distinct advantages for high‐frequency applications. It is based on a directionally solidified ZrO2⋅Y2O3–W eutectic composite containing aligned, single‐crystal tungsten fibers, ≊500 nm in diameter, with spatial densities of 2–50×106/cm2. The composite can be etched to form fibers of virtually any length with tip radii of 5–10 nm. A gridded structure can be formed around the fibers using a line‐of‐sight vapor deposition process. Because of the thickness of the composite chips used as the substrate (0.5 mm) and the high resistivity of the oxide matrix, the insulator film can be made extremely thin, thereby reducing the extractor aperture radius. Emission tests have verified this configuration results in measurably higher field enhancement values for the arrays.

Determination of radium, thorium, uranium isotopes, and /sup 210/Pb in sediments and sediment pore waters from North Equatorial Pacific deep-sea clay-silicous oozes shows that the radium and uranium isotopes are mobile in the pore water. The concentration-depth profiles of radium can be understood in terms of a diagenetic model which takes into account mixing of sediment particles by bioturbation, molecular diffusion in the pore water, adsorption onto particle surfaces, as well as radioactive production and decay. The /sup 234/U//sup 238/U activity ratios in several samples are higher than the seawater value, indicating some enrichment of /sup 234/U in the pore water. However, the absolute concentrations of /sup 238/U and /sup 234/U are 25% lower than those in seawater, suggesting that the sediments form a sink for uranium isotopes. /sup 210/Pb is present in the pore water at concentrations approx. 20% that of /sup 226/Ra. The origin of /sup 210/Pb in the pore water is uncertain and could be due either to its in situ mobilization in the sediments or subsequent production in the laboratory from the decay of /sup 222/Rn. /sup 230/Th is present in measurable concentrations in the pore waters, but its distribution does not show any systematic trendmore » with depth or other parameters. The most likely source of /sup 230/Th appears to be minute amounts of sediment particles collected in the pore waters during the squeezing operation.« less

Shell deposition rates of specimens of Arctica islandica (Mollusca: Bivalvia) from the New York Bight were determined using natural /sup 228/Ra and /sup 228/Th and bomb /sup 14/C. The specimens from deep (>55 m) offshore waters show annual growth banding. A shell obtained from the inner bight at

Growth rates of four Nautilus scrobiculatus Lightfoot and three N. pompilius Linnaeus captured in Papua New Guinea in 1985 were measured using a chronology based on the naturally occurring radionuclides 210Pb and 210Po. The age of the las septum in mature specimens of both species was more than one year, whereas the time of septal formation in a submature specimen of N. pompilius was ca 180 d. The 210Po/210Pb method was also used to determine the growth rates of four immature N. pompilius captured in the Philippines in 1983 before and after introduction into an aquarium. Introduction into the aquarium was marked by a dramatic decrease in the activity of 210Pb of the septa, the formation of a black line on the exterior of the shell, and a reduction in the spacing of adjacent septa in two specimens. Based on the number of septa formed in the aquarium, the average time of septal formation ranged from 50 to 80 d. These estimates were consistent with those calculated from the 210Po/210Pb activity ratios of the septa that formed in the aquarium, thus providing a check on the radiometric method. The average time of septal formation just prior to introduction into the aquarium appears, within the uncertainty of the radioactive measurements, to have been similar to that in the aquarium, indicating no dramatic alteration in the growth rate of these specimens.

Lipid class compounds have been used to determine the sources of organic material in atmospheric aerosols from remote marine areas1–6. Recently, it has been shown that the temporal variability of terrestrial source marker organic compounds in aerosols from the tropical North Pacific is directly related to the seasonality of dust storm activity in China3,4. However, little is known about the detailed emission and transport mechanisms of these compound classes from the continents. We report here, as part of the Sea/Air Exchange Program (SEAREX), the particle size distributions of aliphatic hydrocarbons and 210Pb in aerosols in the upwelling zone off the coast of Peru to elucidate these mechanisms.

A sensitive technique for the measurement of dissolved and particulate actinide concentrations and water column distributions is described. Pu, Am, and Th isotopes are collected using large-volume, wire-mounted electrical pumping systems. Particles were removed by filtration, and actinides by absorption on MnO2-coated filters. The very large volumes processed (up to 4000 liters) result in very sensitive and precise concentration measurements after analyses of the samples by standard radiochemical and alpha spectrometric techniques.

Cubic ZrO2 stabilized with 9.8 m/o yttria was implanted with 50 keV nitrogen ions at dose levels 1015 to 3 × 10-2 cm. Microhardness measurements indicated hardness increases up to 3 × 10 N cm at low indenter loads for unannealed crystals but no hardness change occurred for annealed samples. At f=3 × 1016 N+ cm-2, a critical dose was exceeded resulting in softening of both annealed and unannealed films. Exceeding this critical dose resulted in shearing of the implanted film due to compressive strain, as evidenced by blistering and chipping at indentation edges. The sheared film thickness was 1300 A. Sputter Auger profiles indicated constant N concentration from 150 to 1300 A rather than the expected Gaussian distribution. Stress induced diffusion was thought responsible for the square profile.

Concentrations of lead, ^(210)Pb, and ^(210)Po were measured in rain selected for least influence by local sources of contamination at several tropical and subtropical islands (Enewetak; Pigeon Key, Florida; and American Samoa) and shipboard stations (near Bermuda and Tahiti). Ratios expressed as ng Pb/dpm ^(210)Pb in rain were 250–900 for Pigeon Key (assuming 12% adsorption for ^(210)Pb and no adsorption for lead), depending on whether the air masses containing the analyzed rain came from the Caribbean or from the continent, respectively; about 390 for the northern Sargasso Sea downwind from emissions of industrial lead in North America; 65 for Enewetak, remote from continental emissions of industrial lead in the northern hemisphere; and 14 near Tahiti, a remote location in the southern hemisphere where industrial lead emissions to the atmosphere are much less than in the northern hemisphere. (The American Samoa sample yielded a higher ratio than Tahiti; the reason for this is not clear but may be due to local Pb sources.) The corresponding fluxes of lead to the oceans, based on measured or modeled ^(210)Pb precipitation fluxes, are about 4 ng Pb/cm^2y for Tahiti, 10 for Enewetak, and 270 for the Sargasso Sea site, and between 110 to 390 at Pigeon Key.

The (228)Ra/(226)Ra ratios in a previously dated vesicomyid clam shell were used to determine that seawater was in contact with mid-oceanic-ridge basalt glass for 22-45 years prior to arrival to the surface at 350 degrees C at the Galapagos Rise Spreading Center. The minimum rate of reaction for the 45-year sojourn time, based on a water/rock ratio of 2.8 derived from (226)Ra concentrations, is 8 g of basalt altered per kg of seawater per year.

Publisher Summary This chapter provides an overview of the sources and sinks of nuclides in Long Island Sound (LIS). The LIS has the properties of a large protected settling basin. In such a system, many of the processes affecting the behavior of material injected into the coastal zone can be followed more directly than in some other systems more responsive to large-scale and seasonal variables. The Connecticut River is the most important river draining into LIS. This river is least important in the transport of metals to LIS. The distribution of trace metals in LIS sediments is discussed in the chapter. Trace-metal distributions in mussels and oysters are studied. The cause of the observed trace-metal distributions is analyzed, and the processes affecting the deposition and accumulation of trace metals in LIS are outlined. Processes that affect the vertical distribution of nuclides in the sediment pile are also described.

The age of a deep-sea clam, Tindaria callistiformis, from 3803 m depth has been determined by 228Ra (6.7 year half-life) chronology of separated size fractions of a captured population. A length of 8.4 mm is attained in about 100 years. Shells of this size fraction show about 100 regularly spaced bands, indicating that the growth feature may be an annual one.

The characteristics of cordierite type compositions and the relationship between thermal expansion and raw materials, processing, and gross composition are examined. Other possible support materials are reviewed briefly. These included mullite, zircon, beryl, spodumene, aluminum titanate, silicon nitride, and other low expansion compositions. Raw material cost, processing, and reactivity with the catalysis are discussed for these materials.

In order to test the assumption that accretion rates of intertidal salt marshes are approximately equal to rates of sea-level rise along the Rhode Island coast,210Pb analyses were carried out and accretion rates calculated using constant flux and constant activity models applied to sediment cores collected from lowSpartina alterniflora marshes at four sites from the head to the mouth of Narragansett Bay. A core was also collected from a highSpartina patens marsh at one site. Additional low marsh cores from a tidal river entering the bay and a coastal lagoon on Block Island Sound were also analyzed. Accretion rates for all cores were also calculated from copper concentration data assuming that anthropogenic copper increases began at all sites between 1865 and 1885. Bulk density and weight-loss-on-ignition of the sediments were measured in order to assess the relative importance of inorganic and organic accumulation. During the past 60 yr, accretion rates at the eight low marsh sites averaged 0.43±0.13 cm yr−1 (0.25 to 0.60 cm yr−1) based on the constant flux model, 0.40±0.15 cm yr−1 (0.15 to 0.58 cm yr−1) based on the constant activity model, and 0.44±0.11 cm yr−1 (0.30 to 0.59 cm yr−1) based on copper concentration data, with no apparent trend down-bay. High marsh rates were 0.24±0.02 (constant flux), 0.25±0.01 (constant activity), and 0.47±0.04 (copper concentration data). The cores showing closest agreement between the three methods are those for which the excess210Pb inventories are consistent with atmospheric inputs. These rates compare to a tide gauge record from the mouth of the bay that shows an average sea-level rise of 0.26±0.02 cm yr−1 from 1931 to 1986. Low marshes in this area appear to accrete at rates 1.5–1.7 times greater than local relative sea-level rise, while the high marsh accretion rate is equal to the rise in sea level. The variability among the low marsh sites suggests that marshes may not be poised at mean water level to within better than ±several cm on time scales of decades. Inorganic and organic dry solids each contributed about 9% by volume to low marsh accretion, while organic dry solids contributed 11% and inorganic 4% to high marsh accretion. Water/pore space accounted for the majority of accretion in both low and high marshes. If water associated with the organic component is considered, organic matter accounts for an average of 91% of low marsh and 96% of high marsh accretion. A dramatic increase in the organic content at a depth of 60 to 90 cm in the cores from Narragansett Bay appears to mark the start of marsh development on prograding sand flats.