Showing papers on "Deposition (chemistry) published in 2007"

Long-Term Increase in Dissolved Organic Carbon in Streamwaters in Norway Is Response to Reduced Acid Deposition

Abstract: Concentrations of dissolved organic carbon (DOC) in freshwaters have increased significantly in Europe and North America, but the driving mechanisms are poorly understood. Here, we test if the significant increase in TOC (total organic carbon, 90−95% DOC) in three acid-sensitive catchments in Norway of 14 to 36% between 1985 and 2003 is related to climate, hydrology, and/or acid deposition. Catchment TOC export increased between 10 and 53%, which was significant at one site only. The seasonal variation in TOC was primarily climatically controlled, while the deposition of SO4 and NO3negatively related to TOCexplained the long-term increase in TOC. We propose increased humic charge and reduced ionic strengthboth of which increase organic matter solubilityas mechanistic explanations for the statistical relation between reduced acid deposition and increased TOC. Between 1985 and 2003, ionic strength decreased significantly at all sites, while the charge density of TOC increased at two of the sites from 1−2 me...

Growth of ectomycorrhizal mycelia and composition of soil microbial communities in oak forest soils along a nitrogen deposition gradient

Abstract: Deciduous forests may respond differently from coniferous forests to the anthropogenic deposition of nitrogen (N). Since fungi, especially ectomycorrhizal (EM) fungi, are known to be negatively affected by N deposition, the effects of N deposition on the soil microbial community, total fungal biomass and mycelial growth of EM fungi were studied in oak-dominated deciduous forests along a nitrogen deposition gradient in southern Sweden. In-growth mesh bags were used to estimate the production of mycelia by EM fungi in 19 oak stands in the N deposition gradient, and the results were compared with nitrate leaching data obtained previously. Soil samples from 154 oak forest sites were analysed regarding the content of phospholipid fatty acids (PLFAs). Thirty PLFAs associated with microbes were analysed and the PLFA 18:2ω6,9 was used as an indicator to estimate the total fungal biomass. Higher N deposition (20 kg N ha−1 y−1 compared with 10 kg N ha−1 y−1) tended to reduce EM mycelial growth. The total soil fungal biomass was not affected by N deposition or soil pH, while the PLFA 16:1ω5, a biomarker for arbuscular mycorrhizal (AM) fungi, was negatively affected by N deposition, but also positively correlated to soil pH. Other PLFAs positively affected by soil pH were, e.g., i14:0, a15:0, 16:1ω9, a17:0 and 18:1ω7, while some were negatively affected by pH, such as i15:0, 16:1ω7t, 10Me17:0 and cy19:0. In addition, N deposition had an effect on the PLFAs 16:1ω7c and 16:1ω9 (negatively) and cy19:0 (positively). The production of EM mycelia is probably more sensitive to N deposition than total fungal biomass according to the fungal biomarker PLFA 18:2ω6,9. Low amounts of EM mycelia covaried with increased nitrate leaching, suggesting that EM mycelia possibly play an important role in forest soil N retention at increased N input.

Heavy minerals in use

Abstract: Foreword Part I: Heavy Minerals in the Study of Siliciclastic Sediments: Principles, Processes, and Products. Part II: Academic Research: Provenance, Transport, Deposition, Exhumation. Part III: Integrated and Interdisciplinary Heavy Mineral Applications. Part IV: Industrial Applications Concluding remarks

Interannual variation and trends in air pollution over Europe due to climate variability during 1958–2001 simulated with a regional CTM coupled to the ERA40 reanalysis

Abstract: A three-dimensional Chemistry Transport Model was used to study the meteorologically induced interannual variability and trends in deposition of sulphur and nitrogen as well as concentrations of su ...

Deposition of TiN and HfO{sub 2} in a commercial 200 mm remote plasma atomic layer deposition reactor

Abstract: The authors describe a remote plasma atomic layer deposition reactor (Oxford Instruments FlexAL™) that includes an inductively coupled plasma source and a load lock capable of handling substrates up to 200mm in diameter. The deposition of titanium nitride (TiN) and hafnium oxide (HfO2) is described for the combination of the metal-halide precursor TiCl4 and H2–N2 plasma and the combination of the metallorganic precursor Hf[N(CH3)(C2H5)]4 and O2 plasma, respectively. The influence of the plasma exposure time and substrate temperature has been studied and compositional, structural, and electrical properties are reported. TiN films with a low Cl impurity content were obtained at 350°C at a growth rate of 0.35A∕cycle with an electrical resistivity as low as 150μΩcm. Carbon-free (detection limit <2at.%) HfO2 films were obtained at a growth rate of 1.0A∕cycle at 290°C. The thickness and resisitivity nonuniformity was <5% for the TiN and the thickness uniformality was <2% for the HfO2 films as determined over 20...

The influence of spray properties on intranasal deposition.

Abstract: While numerous devices, formulations, and spray characteristics have been shown to influence nasal deposition efficiency, few studies have attempted to identify which of these interacting factors plays the greatest role in nasal spray deposition. The deposition patterns of solutions with a wide range of surface tensions and viscosities were measured using an MRI-derived nasal cavity replica. The resulting spray plumes had angles between 29 degrees and 80 degrees and contained droplet sizes (D(v50)) from 37-157 microm. Each formulation contained rhodamine 590 as a fluorescent marker for detection. Administration angles of 30 degrees , 40 degrees , or 50 degrees above horizontal were tested to investigate the role of user technique on nasal deposition. The amount of spray deposited within specific regions of the nasal cavity was determined by disassembling the replica and measuring the amount of rhodamine retained in each section. Most of the spray droplets were deposited onto the anterior region of the model, but sprays with small plume angles were capable of reaching the turbinate region with deposition efficiencies approaching 90%. Minimal dependence on droplet size, viscosity, or device was observed. Changes in inspiratory flow rate (0-60 L/min) had no significant effect on turbinate deposition efficiency. Both plume angle and administration angle were found to be important factors in determining deposition efficiency. For administration angles of 40 degrees or 50 degrees , maximal turbinate deposition efficiency (30-50%) occurred with plume angles of 55-65 degrees , whereas a 30 degrees administration angle gave an approximately 75% deposition efficiency for similar plume angles. Deposition efficiencies of approximately 90% could be achieved with plume angles <30 degrees using 30 degrees administration angles. Both the plume angle and administration angle are critical factors in determining deposition efficiency, while many other spray parameters, including particle size, have relatively minor influences on deposition within the nasal cavity.

Effects of atmospheric inorganic nitrogen deposition on ocean biogeochemistry

Abstract: We perform a sensitivity study with the Biogeochemical Elemental Cycling (BEC) ocean model to understand the impact of atmospheric inorganic nitrogen deposition on marine biogeochemistry and air-sea CO2 exchange. Simulations involved examining the response to three different atmospheric inorganic nitrogen deposition scenarios namely, Pre-industrial (22 Tg N/year), 1990s (39 Tg N/year), and an Intergovernmental Panel on Climate Change (IPCC) prediction for 2100, IPCC-A1FI (69 Tg N/year). Globally, the increasing N deposition had widespread, but modest effects on export production and air-sea CO2 exchange. The maximum increase in N deposition was 47 Tg N/year since Pre-industrial control for the IPCC-A1FI case, which had an increase in primary production (0.98 Gt C/year or 2%), export production (0.16 Gt C/year or 3%) and a decrease in atmospheric pCO2 of 1.66 ppm (0.6%) relative to the Pre-industrial control. In some regions, atmospheric N inputs supported >20% of the export production in the current era and >50% of the export production in the IPCC-A1FI case. As nitrogen deposition increased, N fixation decreased because the diazotrophs were outcompeted by diatoms and small phytoplankton under more N-replete conditions. This decrease in N fixation could partially counteract the ongoing increase in new nitrogen inputs via atmospheric N deposition.

Impact of Alginate Conditioning Film on Deposition Kinetics of Motile and Nonmotile Pseudomonas aeruginosa Strains

Abstract: The initial deposition of bacteria in most aquatic systems is affected by the presence of a conditioning film adsorbed at the liquid-solid interface. Due to the inherent complexity of such films, their impact on bacterial deposition remains poorly defined. The aim of this study was to gain a better understanding of the effect of a conditioning film on the deposition of motile and nonmotile Pseudomonas aeruginosa cells in a radial stagnation point flow system. A well-defined alginate film was used as a model conditioning film because of its polysaccharide and polyelectrolyte nature. Deposition experiments under favorable (nonrepulsive) conditions demonstrated the importance of swimming motility for cell transport towards the substrate. The impact of the flagella of motile cells on deposition is dependent on the presence of the conditioning film. We showed that on a clean substrate surface, electrostatic repulsion governs bacterial deposition and the presence of flagella increases cell deposition. However, our results suggest that steric interactions between flagella and extended polyelectrolytes of the conditioning film hinder cell deposition. At a high ionic strength (100 mM), active swimming motility and changes in alginate film structure suppressed the steric barrier and allowed conditions favorable for deposition. We demonstrated that bacterial deposition is highly influenced by cell motility and the structure of the conditioning film, which are both dependent on ionic strength.

On the Accumulation of Mud

Abstract: Mudstones can be deposited under more energetic conditions than widely assumed, requiring a reappraisal of many geologic records.

Patterned Deposition of a Mixed-Coordination Adenine−Silver Helicate, Containing a π-Stacked Metallacycle, on a Graphite Surface

Abstract: A novel mixed-valence silver complex with modified adenine and its adsorption behavior on different substrates was studied by atomic force microscopy, and selective patterning on a graphite surface is described in this report.

Deposition from Crude Oils in Heat Exchangers

Abstract: Deposition in flow lines and processing and heat transfer equipment arises from fouling species, which may either be present in the fluid or generated in the vicinity of the equipment surface. Recent research on deposition during heat transfer from petroleum feedstocks is reviewed. For low-sulfur light crude oils, deposition is largely due to particulates and gums. For medium-sulfur crude oils, the formation of iron sulfides plays a major role in deposition. In unstable heavy oil systems, suspended asphaltenes are the fouling species. Trace quantities of impurities such as dissolved oxygen or suspended corrosion products add markedly to deposit formation. The influences of flow velocity, bulk and surface temperatures, and particulate concentrations are demonstrated through experimental results and compared to expectations from simple models. Through an understanding of the key steps in the deposition processes, a rational mitigation strategy can be formulated.

Effect of agricultural land use on the chemistry of groundwater from basaltic aquifers, Jeju Island, South Korea

Abstract: Geochemical processes were identified as controlling factors of groundwater chemistry, including chemical weathering, salinization from seawater and dry sea-salt deposition, nitrate contamination, and rainfall recharge. These geochemical processes were identified using principal component analysis of major element chemistry of groundwater from basaltic aquifers in Jeju Island, South Korea, a volcanic island with intense agricultural activities. The contribution of the geochemical processes to groundwater chemistry was quantified by a simple mass-balance approach. The geochemical effects due to seawater were considered based on Cl contributions, whereas the effects due to natural chemical weathering were based on alkalinity. Nitrogenous fertilizers, and especially the associated nitrification processes, appear to significantly affect groundwater chemistry. A strong correlation was observed between Na, Mg, Ca, SO4 and Cl, and nitrate concentrations in groundwater. Correspondingly, the total major cations, Cl, and SO4 in groundwater were assessed to estimate relative effect of N-fertilizer use on groundwater chemistry. Cl originates more from nitrate sources than from seawater, whereas SO4 originates mostly from rainwater. N-fertilizer use has shown the greatest effect on groundwater chemistry, particularly when nitrate concentrations exceed 6–7 mg/L NO3–N. Nitrate contamination significantly affects groundwater quality and 18% of groundwater samples have contamination-dominated chemistry.

Pulsed and Continuous Wave Acrylic Acid Radio Frequency Plasma Deposits: Plasma and Surface Chemistry

Abstract: Plasma polymers have been formed from acrylic acid using a pulsed power source. An on-pulse duration of 100 μs was used with a range of discharge off-times between 0 (continuous wave) and 20 000 μs. X-ray photoelectron spectroscopy (XPS) has been used in combination with trifluoroethanol (TFE) derivatization to quantify the surface concentration of the carboxylic acid functionality in the deposit. Retention of this functionality from the monomer varied from 2% to 65%. When input power was expressed as the time-averaged energy per monomer molecule, Emean, the deposit chemistry achieved could be described using a single relationship for all deposition conditions. Deposition rates were monitored using a quartz crystal microbalance, which revealed a range from 20 to 200 μg m-2 s-1, and these fell as COOH functional retention increased. The flow rate was found to be the major determinant of the deposition rate, rather than being uniquely defined by Emean, connected to the rate at which fresh monomer enters the...

Self-assembled epitaxial nanocomposite BaTiO3-NiFe2O4 films prepared by polymer-assisted deposition.

Abstract: We present a new approach, cost-effective polymer-assisted deposition, to prepare self-assembled epitaxial BaTiO3−NiFe2O4 nanocomposite films on LaAlO3 substrates. Ferroelectric BaTiO3 is embedded ...

Chronic Nitrogen Deposition Enhances Nitrogen Mineralization Potential of Semiarid Shrubland Soils

Abstract: Semiarid chaparral and coastal sage shrublands of southern California have been exposed to high levels of atmospheric N for decades, which has the capacity to increase both N and C storage and cycling in these N-limited systems. Thus we hypothesize that soil C and N mineralization will be higher in areas that have been exposed to high atmospheric N deposition. This hypothesis was tested in a 50-wk laboratory incubation experiment where the inorganic N (NH 4 + NO 3 ) and CO 2 production of chaparral and coastal sage soils were repeatedly measured. Soil was incubated in the dark at a constant temperature of 25°C and a soil moisture of 0.25 kg H 2 O kg -1 dry soil (65% water-filled pore space). Relative differences in N deposition exposure between the study sites were quantified by repeatedly rinsing and collecting the N accumulated on branch surfaces during 1 yr. Temporal trends in cumulative C and N mineralization were best described by single-pool first-order and zero-order models, respectively. Total N mineralization, but not C mineralization, increased linearly with relative N deposition, and NO 3 accounted for 95% of the total inorganic N accumulated during the 50-wk incubation. The soil δ 15 N natural abundance increased with relative N deposition (r = 0.85, P < 0.05) and the soil C/N ratio declined with relative N deposition (r = -0.74, P < 0.05), suggesting that N deposition exposure enhanced N mineralization in part because of increases in the soil organic matter quality (i.e., lower C/N ratio). Furthermore, soil C storage declined as a function of relative N deposition exposure, indicating that high atmospheric N inputs are not likely to stimulate soil C storage in these semiarid ecosystems.

Preparation of highly dispersed PEM fuel cell catalysts using electroless deposition methods

Abstract: A methodology for the electroless deposition (ED) of PtCl6 2� using dimethylamine borane (DMAB) on a Rh-seeded carbon support has been developed for electrochemical and fuel cell applications. This procedure required seeding the carbon with a Rh-precursor catalyst via wet impregnation prior to the exposure of an aqueous ED bath containing PtCl6 2� , DMAB, and sodium citrate (complexing/stabilizing agent). Kinetic parameters that affect the extent and rate of PtCl6 2� deposition include concentrations of PtCl6 2� , DMAB, and sodium citrate as well as pH and concentrations of Rh seed sites. A linear relationship between rate and extent of PtCl6 2� deposition and DMAB and Rh concentrations was found while the citrate concentration had little effect on rate and a modest effect on extent. Lastly, extent of PtCl6 2� deposition showed a maximum with respect to pH. Characterization of the Rh-seeded, carbon support by transmission electron microscopy (TEM) shows that the Rh particle diameters remain constant at 33–43 A u as the Rh weight loading increases from 0.4% to 2.2% to 4.4%. Further, after deposition of similar loadings of Pt, TEM

The effect of deposition rate on the intrinsic stress in copper and silver thin films

Abstract: The effect of changing the deposition rate on the development of stress in evaporated copper and silver thin films deposited on oxidized silicon was examined. In situ stress measurements were made during deposition in ultrahigh vacuum using a scanning laser curvature system. In some experiments, the deposition rate was alternated without interruption of deposition. For copper thin films, a change in deposition rate has no effect on the development of the tensile stress, while the magnitude of the postcoalescence compressive stress decreases with increasing deposition rate. In silver films, the film thickness at the tensile maximum increases slightly with increasing deposition rate, while the magnitude of the postcoalescence compressive stress again decreases with increasing deposition rate. Analysis of the heat flow during deposition shows that the radiative heating and condensation contribute roughly equally to the temperature rise of the sample.

Contributions of nitrogen deposition and forest regrowth to terrestrial carbon uptake

Abstract: The amount of reactive nitrogen deposited on land has doubled globally and become at least five-times higher in Europe, Eastern United States, and South East Asia since 1860 mostly because of increases in fertilizer production and fossil fuel burning. Because vegetation growth in the Northern Hemisphere is typically nitrogen-limited, increased nitrogen deposition could have an attenuating effect on rising atmospheric CO2 by stimulating the vegetation productivity and accumulation of carbon in biomass. This study shows that elevated nitrogen deposition would not significantly enhance land carbon uptake unless we consider its effects on re-growing forests. Our results suggest that nitrogen enriched land ecosystems sequestered 0.62–2.33 PgC in the 1980s and 0.75–2.21 PgC in the 1990s depending on the proportion and age of re-growing forests. During these two decades land ecosystems are estimated to have absorbed 13–41% of carbon emitted by fossil fuel burning. Although land ecosystems and especially forests with lifted nitrogen limitations have the potential to decelerate the rise of CO2 concentrations in the atmosphere, the effect is only significant over a limited period of time. The carbon uptake associated with forest re-growth and amplified by high nitrogen deposition will decrease as soon as the forests reach maturity. Therefore, assessments relying on carbon stored on land from enhanced atmospheric nitrogen deposition to balance fossil fuel emissions may be inaccurate.

Influence of growth rate on microstructure and optoelectronic behaviour of ZnS films

Abstract: Nanocrystalline ZnS films have been grown on glass substrates by close spaced evaporation at various deposition rates, with a constant substrate temperature of 300 °C. The x-ray photoelectron spectroscopy studies revealed that nearly stoichiometric ZnS layers were grown at deposition rates in the range 20–30 A s−1. The x-ray diffraction data confirmed the cubic structure of ZnS films for all the deposition rates. The surface morphological studies were made using an atomic force microscope, which indicated a rough surface and that the roughness increases with the deposition rate. The optical analysis showed that the layers grown at a deposition rate of 30 A s−1 exhibited the highest optical transmittance of 82%. The optical band gap of the films varied in the range 3.63–3.54 eV with the change in the deposition rate. The effect of the rate of deposition on the photoluminescence characteristics was also studied, which showed an increase in luminescence intensity with the decrease in the particle size. The electrical properties of the layers were highly influenced by the deposition rate. The temperature dependence of electrical conductivity was measured and the activation energies were also evaluated.

Simultaneous assessment of deposition effects of base cations, sulfur, and nitrogen using an extended critical load function for acidification.

Abstract: Base cations (BC) play an important role to prevent soil acidification. In certain acid sensitive areas, such as China, BC deposition is high and a considerable fraction is of anthropogenic origin. BC deposition might decrease in the future with the implementation of air pollution control measures. The effect of changes in BC deposition, however, has seldom been considered in critical load calculations based on the steady-state mass balance (SSMB) method. In order to better quantify the importance of the BC deposition for acid deposition mitigation policy, an extension of the SSMB method for critical load calculation for soil acidification is presented. The BC deposition is taken into account as a variable along with sulfur (S) and nitrogen (N) deposition, creating an S−N−BC critical load function. As a case study, critical loads of S and N for the Tie Shan Ping catchment in Chongqing in southwest China under variable BC deposition were calculated. Results indicate that abatement of BC deposition has sign...