Showing papers on "Deposition (chemistry) published in 1994"

Steep declines in atmospheric base cations in regions of Europe and North America

Abstract: HUMAN activities have caused marked changes in atmospheric chemistry over large regions of Europe and North America. Although considerable attention has been paid to the effects of changes in the deposition of acid anions (such as sulphate and nitrate) on terrestrial and aquatic ecosystems1–7, little is known about whether the concentrations of basic components of the atmosphere have changed over time8,9 and what the biogeochemical consequences of such potential changes might be. In particular, there has been some controversy8–12 as to whether declines in base-cation deposition have countered effects of recent reductions in SO2emission. Here we report evidence for steep declines in the atmospheric concentrations of base cations (sum of non-sea-salt Ca2+, Mg2+, K+ and Na+) over the past 10 to 26 years from high-quality precipitation chemistry records in Europe and North America. To varying but generally significant degrees, these base-cation trends have offset recent reductions in sulphate deposition in the regions examined. The observed trends seem to be ecologically important on decadal timescales, and support earlier contentions8–10 that declines in the deposition of base cations may have contributed to increased sensitivity of poorly buffered ecosystems.

Shape Deposition Manufacturing

Abstract: One challenge for solid freeform fabrication has been to develop the capability to directly create functional metal shapes which are dense, metallurgically bonded, geometrically accurate and with good surface appearance. Shape Deposition is a manufacturing paradigm which attempts to address these issues. It incorporates the advantages of several processes including solid freeform fabrication (complex geometries, rapidly planned), 5-axis CNC machining (accuracy, smooth surfaces), shot-peening (for stress relief) and 'microcasting' (a high-performance, weldbased material deposition process). These processes are integrated within a CAD/CAM system using robotic automation. This paper will present the current research in this effort.

Year 2020: Consequences of population growth and development on deposition of oxidized nitrogen

Abstract: With a current world population of 53 billion, fossil fuel and biomass burning have already greatly increased the emission of fixed nitrogen to the global atmosphere In 2020, with a projected population of 85 billion and an assumed 100% increase in per capita energy consumption relative to 1980 by the lesser developed countries, we predict an approximate 25% increase in total nitrogen deposition in the more developed country source regions such as North America In addition, reactive nitrogen deposition will at least double in less developed regions, such as SE Asia and Latin America, and will increase by more than 50% over the oceans of the Northern Hemisphere Although we also predict significant increases in the deposition of nitrogen from fossil-fuel sources over most of the Southern Hemisphere, particularly Africa, the tropical eastern Pacific, and the southern Atlantic and Indian Oceans, biomass burning and the natural sources of nitrogen oxides (lightning and biogenic soil emissions) are also important in these regions This increased deposition has the potential to fertilize both terrestrial and marine ecosystems, resulting in the sequestering of carbon Increases in nitrogen deposition have also been shown not only to acidify ecosystems but also to increase emissions of nitric oxide (NO), nitrous oxide (N[sub 2]O), carbonyl sulfide (COS), and carbon+sulfur (CS[sub 2]) to the atmosphere and decrease methane (CH[sub 4]) consumption in forest soils We also find that the atmospheric levels of nitrogen oxides increase significantly throughout much of the Northern Hemisphere and populated regions of the Southern Hemisphere This increase may lead to larger ozone concentrations with resulting increases in the oxidative capacity of the remote atmosphere and its ability to absorb IR radiation 31 refs, 3 figs, 1 tab

Laccase and the Deposition of Lignin in Vascular Plants

Abstract: Laccase (p-diphenolrOi oxidoreductase, EC 1.10.3.2) was the first enzyme used to polymerize a synthetic lignin (DHP) in vitro. Based on that work, laccase was proposed to perform the same function in vivo. However, various biochemical and histological studies eventually led most researchers to believe that peroxidases, not laccases, were principally responsible for monolignol polymerization in vascular plants. Recent evidence from several laboratories necessitates a re-evaluation of the relative roles played by oxidases and peroxidases in lignin deposition. In this paper, we review the current literature regarding plant laccases, äs well äs selected fungal laccases. From this body of evidence, we have developed a model for the evolution of lignin äs a structural polymer, and we describe how this model may be used to develop new questions regarding the origins of lignin and vascular plants.

Fluorocarbon high‐density plasmas. I. Fluorocarbon film deposition and etching using CF4 and CHF3

Abstract: Fluorocarbon film deposition in discharges used for oxide etching plays a key role in determining the profile shape of contact holes and the etch selectivity with respect to the mask and the underlayer. For low‐density capacitatively coupled rf discharges this deposition is due to neutral radicals. We report a study of fluorocarbon film deposition and etching phenomena in electron cyclotron resonance (ECR) discharges of CF4 and CHF3. Plasma operation without rf sample bias in the pressure range below 10 mTorr results in the deposition of fluorocarbon films for both gases, with the highest deposition rate in each case at 2 mTorr (≂120 nm/min for a 1000 W CF4 plasma and ≂180 nm/min for CHF3 using the same conditions). For CF4 this behavior differs dramatically from that seen for conventional rf diode plasmas where no deposition occurs. The deposition is due to the more efficient breakdown and ionization of CF4 and CHF3 in the ECR discharge and the lack of energetic ion bombardment of the substrate as compar...

Self-assembled monolayer coating for micro-mechanical devices

Abstract: A method of forming of a monomolecular coating (19) for surfaces of contacting elements (11, 17) of micro-mechanical devices (10), specifically, devices that have moving elements that contact other elements and that tend to stick as a result of the contact. The method uses liquid deposition, with the device being placed in a solution that contains a precursor to the formation of the coating. The precursor is chosen based on coordination chemistry between the precursor and the surface to be coated.

Surface-water acidification and extinction at the Cretaceous-Tertiary boundary

Abstract: If published estimates of SO2 volatilization and NOx generation by the Cretaceous-Tertiary (K-T) impact were atmospherically converted to sulfuric and nitric acid, globally dispersed, and rapidly rained out, the resulting acid concentrations would bracket a critical threshold in surface-ocean chemistry. Rapid and globally uniform deposition of masses corresponding to the lowest estimates would have had no major effect on sea-surface chemistry. However, similar deposition of masses corresponding to the highest estimates would have provided enough acid to destroy the carbonate-buffering capacity of the upper 100 m of the world ocean and catastrophically reduce surface-ocean pH. Despite the possible effect of the highest estimated acid yields, scenarios that rely on acid rain as the primary explanation of global K-T extinctions are not readily compatible with K-T records of terrestrial and marine survival or culturing studies of modern marine plankton. The possibility that acid rain was a primary cause of K-T extinctions can be tested further by analysis of geographic variation in extinction intensity, because such variation was a likely consequence if the impact resulted in global dispersal and rapid globally uniform deposition of more than ∼6 x 1016 mol of H2SO4 or 1.2 x 1017 mol of HNO3.

Anomalous boundary scavenging in the Middle Atlantic Bight: evidence from 230Th, 231Pa, 10Be and 210Pb

Abstract: Boundary scavenging processes result in the deposition of particle-reactive chemical substances in ocean margin sediments at rates much greater than their average rate of deposition over the entire ocean. Sediments and samples collected by time-series sediments traps were studied to examine the nature and extent of boundary scavenging in the Middle Atlantic Bight (MAB) region of the NW Atlantic. Here, new results are presented for 230Th, 231Pa and 10Be and compared to older findings, based on studies of 210Pb, where it appeared that the normal enhancement of particle-reactive trace-metal deposition at ocean margins was absent. In contrast to the behavior of 210Pb, deposition rates of 230Th, 231Pa and 10Be exceed their local rates of supply, in some cases by more than an order of magnitude. Enhanced deposition of these tracers is clearly occurring in the MAB. An unusual feature of boundary scavenging, however, is that the pattern of enhanced deposition follows the order Be > Th > Pa > Pb, whereas the expected order be Be > Pb ≥ Pa > Th. Furthermore, unsupported 231Pa/230Th activity ratios are consistently less than their production ratio of 0.093, in contrast to ratios typically found at other ocean margins in the range of 0.2–0.3. Export from the region of fine-grained manganese-rich particles is postulated to explain the low fluxes of 210Pb and the low 231Pa/230Th ratios. Other trace elements which have high affinities for adsorption to Mn oxides may, like Pb and Pa, have much lower rates of deposition in the MAB than in other, more typical, ocean-margin environments.

Assessment of soil acidification effects on forest growth in Sweden

Abstract: The results of mapping critical loads, areas where they have been exceeded and steady state (Ca+Mg+K)/Al ratios of soils in Sweden, has been used to assess the order of magnitude of the ecological and economic risks involved with acid deposition for Swedish forests. The results of the calculations indicate that 81% of the Swedish forested area receive acid deposition in excess of the critical load at present. Under continued deposition at 1990 level, forest die-back is predicted to occur on approximately 1% of the forested area, and significant growth rate reductions are predicted for 80% of the Swedish forested area. For Sweden, growth losses in the order of 17.5 million m−3 yr−1 is predicted, equivalent to approximately 19% of current growth. Comparable losses can be predicted for other Nordic countries. The soil acidification situation is predicted to deteriorate significantly during the next 5–15 years, unless rapid emission reductions can be achieved. A minimum deposition reduction over Sweden of 85% on sulphur deposition and 30% on the N deposition in relation to 1990 level is required in order to protect 95% of the Swedish forest ecosystems from adverse effects of acidification. A minimum reduction of 60% on sulphur deposition and 30% on the N deposition is required to keep forest harvest at planned levels.

The effect of body weight and energy intake on the composition of deposited tissue in pigs.

Abstract: Many pig growth models assume that there is no effect of energy intake and of body weight on the ratio of lipid to protein deposition rate in pigs below their maximal protein deposition rate. An experiment was performed to check whether an effect of body weight and of amount of energy intake on this partitioning of energy is indeed absent when protein deposition is limited by energy intake. Two constant amounts of energy were given above maintenance requirement (12·6 and 16·3 MJ digestible energy (DE) per day for production, treatment L and H, respectively). A total of 52 entire male pigs were slaughtered at 25,45, 65, 85 or 105 kg live weight. Results showed that, for both levels of intake, the ratio of lipid to protein deposition rate increased with increasing body weight. At the L energy intake, the ratio of lipid to protein deposition rate increased from 0·74 at 25 kg to 0·99 at 105 kg body weight. In animals receiving the H treatment, the ratio of lipid to protein deposition rate increased from 0·82 to 1·35 in that weight range. This change in nutrient partition was also reflected in daily gain. Daily gain declined with increasing live weight, a decrease of 150 g/day over the weight range 25 to 105 kg. The 3·7 MJ DE difference in energy intake between treatment H and L resulted in an average overall difference of 105 g daily gain. A control group fed ad libitum showed that protein deposition capacity was above 200 g/day, thus the pigs at the L and H treatment were below their protein deposition capacity. It was concluded that both live weight and energy intake influence the ratio of lipid to protein deposition rate. The mechanism of partitioning between lipid and protein deposition below maximal protein deposition capacity needs further specification in order to improve the predictions of growth models which use the linear-plateau concept.

Constructing PbI2 nanoparticles into a multilayer structure using the molecular deposition (MD) method

Abstract: MD films are adopted as matrices for the assembly of Pbl2 nanoparticles into a layer structure; UV–VIS and X-ray diffraction results prove that the multilayers formed have a well-defined layer structure.

Electrodeposition of Ni1 − x Al x in a Chloroaluminate Melt

Abstract: The formation of Ni[sub 1[minus]x]Al[sub x] from a molten 2 AlCl[sub 3]-NaCl electrolyte containing up to 0.17 mol/liter Ni(II) has been investigated using a variety of electrochemical techniques. The standard reversible potential for Ni/Ni(II) is found to be in the range of 0.86 to 0.93 V (vs. Al). In a nickel-free electrolyte aluminum deposition on tungsten occurs via instantaneous nucleation upon an underpotential deposition aluminum layer. In contrast, bulk nickel deposition occurs by progressive formation and diffusion-limited growth of three-dimensional nuclei. The number of nickel atoms forming a critical nuclei, n[sub c], is dependent on overpotential. At potentials below 0.750 V, n[sub c] = 0 with the active sites on the electrode playing the role of critical nuclei. These sites are occupied according to first-order kinetics. At potentials above 0.7 V compact nickel deposits are obtained. As the potential is decreased below 0.6 V Ni[sub 1[minus]x]-Al[sub x] formation occurs. Between 0.6 and 0.0 V alloy composition is a function of potential. The rate of the aluminum partial reaction is first order in the Ni(II) concentration which makes alloy composition independent of Ni(II) concentration over the range investigated. Separate experiments demonstrate that aluminum underpotential deposition on nickel occurs in this potentialmore » regime. Thus, alloy formation may be envisioned as aluminum underpotential deposition proceeding simultaneously with diffusion-limited nickel deposition. The underpotential deposition reaction occurs rapidly such that the alloy composition is determined by the free energy of alloy formation. When the potential is decreased below the reversible potential of aluminum, 0.0 V, phase formation is complicated by a competition between alloy formation and overpotential driven kinetics of aluminum deposition.« less

Temperature effect on settling velocity and deposition of cohesive sediments

Abstract: Results from deposition experiments in an annular flume are presented. Tests were carried out using kaolinite clay in distilled water and salt water as well as natural river water and sediment. Identical experiments carried out at different temperatures show that as temperature decreases, a larger proportion of the material initially suspended will settle out. The effective settling velocity is also higher when temperature decreases, in direct contrast to published results from settling tube experiments.

Multiple layer tungsten deposition process

Abstract: Tungsten plugs are formed in a manner which avoids the formation of unwanted tungsten volcanoes by depositing at least three and preferably five to seven layers of tungsten within a contact hole to form a layered plug. In particularly useful embodiments, the layers are deposited at alternating fast and slow rates of deposition.

Determination of the 241Pu Deposition in Finland after the Chernobyl Accident

Abstract: Transuranium nuclides, including a considerable amount of Pu, were released in the Chernobyl explosion. Plutonium was separated from lichen and peat samples by coprecipitation and anion exchange. A portion of the separated Pu fraction was taken for measurement of Pu with a low-background liquid scintillation counter, Quantulus 1220, equipped with a pulse shape analyser. The detection limit for Pu was 0.007 Bq with a counting time of 600 minutes. The plutonium-241 concentrations of the peat samples varied between < 3 and 430 Bq m~ in Southern Finland. The radioactivity ratio of 241 Pu to 239.240^ i n t h e fallout from Chernobyl was 94.8. The fallout pattern of Pu resembles the patterns of other refractory nuclides, Zr and Ce. The concentrations in lichen samples collected from regions of heaviest deposition were comparable to those of the heaviest weapons test fallout in the early 1960's.