Showing papers on "Deposition (chemistry) published in 2009"

Shifts in Lake N:P Stoichiometry and Nutrient Limitation Driven by Atmospheric Nitrogen Deposition

Abstract: Human activities have more than doubled the amount of nitrogen (N) circulating in the biosphere. One major pathway of this anthropogenic N input into ecosystems has been increased regional deposition from the atmosphere. Here we show that atmospheric N deposition increased the stoichiometric ratio of N and phosphorus (P) in lakes in Norway, Sweden, and Colorado, United States, and, as a result, patterns of ecological nutrient limitation were shifted. Under low N deposition, phytoplankton growth is generally N-limited; however, in high-N deposition lakes, phytoplankton growth is consistently P-limited. Continued anthropogenic amplification of the global N cycle will further alter ecological processes, such as biogeochemical cycling, trophic dynamics, and biological diversity, in the world's lakes, even in lakes far from direct human disturbance.

Atomic layer deposition apparatus

Abstract: A method and apparatus for atomic layer deposition (ALD) is described. The apparatus comprises a deposition chamber and a wafer support. The deposition chamber is divided into two or more deposition regions that are integrally connected one to another. The wafer support is movable between the two or more interconnected deposition regions within the deposition chamber.

Remote plasma source seasoning

Abstract: Methods of seasoning a remote plasma system are described. The methods include the steps of flowing a silicon-containing precursor into a remote plasma region to deposit a silicon containing film on an interior surface of the remote plasma system. The methods reduce reactions with the seasoned walls during deposition processes, resulting in improved deposition rate, improved deposition uniformity and reduced defectivity during subsequent deposition.

Two-Dimensional Modeling of Lithium Deposition during Cell Charging

Abstract: Empirical observations have shown that lithium deposition occurs preferentially at electrode edges and that extending the negative electrode beyond the edge of the positive by approximately 1 mm can prevent deposition from occurring. In this work, we use a simplified COMSOL Multiphysics model to explain this behavior and to investigate the conditions under which deposition occurs, paying particular attention to the magnitude of edge effects. Model results show that geometric effects generate overpotential at the edge of the electrode and create conditions which favor plating, despite unused capacity in the center of the electrode. Extending the negative electrode beyond the edge of the positive provides excess capacity where it is needed and prevents deposition from occurring before the cutoff potential is reached. Under the assumptions of this model, an extension of 0.4 mm is sufficient to prevent the onset of lithium deposition until after the cutoff potential is reached.

Nutrient availability and phytoplankton nutrient limitation across a gradient of atmospheric nitrogen deposition.

Abstract: Atmospheric nitrogen (N) deposition to lakes and watersheds has been increasing steadily due to various anthropogenic activities. Because such anthropogenic N is widely distributed, even lakes relatively removed from direct human disturbance are potentially impacted. However, the effects of increased atmospheric N deposition on lakes are not well documented. We examined phytoplankton biomass, the absolute and relative abundance of limiting nutrients (N and phosphorus (P)), and phytoplankton nutrient limitation in alpine lakes of the Rocky Mountains of Colorado (USA) receiving elevated (>6 kg N-ha-1-yr-1) or low (<2 kg N-ha-1-yr-1) levels of atmospheric N deposition. High deposition lakes had higher NO3-N and total N concentrations and higher total N : total P ratios. Concentrations of chlorophyll and seston carbon (C) were 2-2.5 times higher in high deposition relative to low-deposition lakes, while high-deposition lakes also had higher seston C:N and C:P (but not N:P) ratios. Short-term enrichment bioassays indicated a qualitative shift in the nature of phytoplankton nutrient limitation due to N deposition, as high deposition lakes had an increased frequency of primary P limitation and a decreased frequency and magnitude of response to N and to combined N and P enrichment. Thus elevated atmospheric N deposition appears to have shifted nutrient supply from a relatively balanced but predominantly N-deficient regime to a more consistently P-limited regime in Colorado alpine lakes. This adds to accumulating evidence that sustained N deposition may have important effects on lake phytoplankton communities and plankton-based food webs by shifting the quantitative and qualitative nature of nutrient limitation.

Escherichia coli O157:H7 Transport in Saturated Porous Media: Role of Solution Chemistry and Surface Macromolecules

Abstract: The transport and deposition behavior of Escherichia coli O157:H7 was investigated in saturated packed-bed columns and micromodel systems over a range of ionic strength (IS) (1, 10, and 100 mM) and pH (5.8, 8.4, and 9.2) conditions. At a given IS, elevated solution pH resulted in decreased deposition as a result of the increase in the measured zeta potential of the quartz sand. This deposition trend was consistent with predictions from classic Derjaguin−Landau−Verwey−Overbeek (DLVO) theory. Conversely, the E. coli O157:H7 deposition was inversely proportional to IS (1−100 mM) at high pH conditions (8.4 and 9.2), whereas no effect of IS was observed at pH 5.8. This deposition trend was not consistent with DLVO theory, but could be explained by pH-associated electrosteric stabilization. This phenomenon is driven by the pH-dependent protonated state of functional groups on E. coli O157:H7 surface macromolecules and the corresponding conformational state of the bacterial polymers. Results from this study de...

Hierarchically Porous Gd3+-Doped CeO2 Nanostructures for the Remarkable Enhancement of Optical and Magnetic Properties

Abstract: Rare earth ion-doped CeO2 has attracted more and more attention because of its special electrical, optical, magnetic, or catalytic properties. In this paper, a facile electrochemical deposition rou...

Meridional transport and deposition of atmospheric 10 Be

Abstract: . 10Be concentrations measured in ice cores exhibit larger temporal variability than expected based on theoretical production calculations. To investigate whether this is due to atmospheric transport a general circulation model study is performed with the 10Be production divided into stratospheric, tropospheric tropical, tropospheric subtropical and tropospheric polar sources. A control run with present day 10Be production rate is compared with a run during a geomagnetic minimum. The present 10Be production rate is 4–5 times higher at high latitudes than in the tropics whereas during a period of no geomagnetic dipole field it is constant at all latitudes. The 10Be deposition fluxes, however, show a very similar latitudinal distribution in both the present day and the geomagnetic minimum run indicating that 10Be is well mixed in the atmosphere before its deposition. This is also confirmed by the fact that the contribution of 10Be produced in the stratosphere is dominant (55%–70%) and relatively constant at all latitudes. The contribution of stratospheric 10Be is approximately 70% in Greenland and 60% in Antarctica reflecting the weaker stratosphere-troposphere air exchange in the Southern Hemisphere.

Oil Recovery from Petroleum Sludge by Solvent Extraction

Abstract: Technical problems associated with sludge deposition in storage units of petroleum industries are enormous. The conventional methods of management are laborious and uneconomical; the hydrocarbon co...

Layer-by-layer deposition of polyelectrolytes. Dipping versus spraying.

Abstract: We studied the properties of polyelectrolyte multilayer films prepared using the technique of polyelectrolyte deposition from solution (dipping) or supplying the solutions to the surface by spraying. The quality of films obtained by those two techniques was compared to find out whether the well-established dipping procedure can be replaced with the spraying technique. Neutron and X-ray reflectometric studies were performed on the samples of interest. We found that multilayers prepared by dipping are thicker, denser and less rough than films having the same number of layers, i.e., having the same number of deposition cycles, obtained by spraying.

Influence of Solution Chemistry on the Deposition and Detachment Kinetics of a CdTe Quantum Dot Examined Using a Quartz Crystal Microbalance

Abstract: Recent reports underline the potential environmental and public health risks linked to the "nano" revolution, yet little is known regarding the environmental fate and impacts of most nanomaterials following release in natural soils and groundwaters. Quantum dots (QDs) are one example of engineered nanomaterials that have been demonstrated to exhibit cytotoxic effects; hence the fate of this material in aqueous environments is of particular interest. In this study, a quartz crystal microbalance (QCM) was used to examine the interaction of a commercially available carboxyl terminated CdTe QD with a model sand (i.e., silica) surface. The deposition kinetics of the QD onto clean silica coated QCM crystals were measured over a wide range of solution conditions, in the presence of either monovalent (K+) or divalent cations (Ca2+). QD deposition rates onto silica were significantly greater in the presence of calcium versus potassium. Solution pH also influenced QD deposition behavior, with increased deposition observed ata lower pH value. The rate of QD release from the silica surface was also monitored using QCM measurements and found to be comparable to the rate of particle deposition when the monovalent salt was used. In contrast, the rate of QD release was considerably lower than the rate of deposition when particles were deposited in the presence of Ca2+. Physicochemical characterization of the QD suspended in varying electrolytes provided insights into the role of solution chemistry on particle size and electrophoretic mobility(surface charge). Measurements of QD size using dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to interpret the QD deposition behavior in different solution chemistries. Lower particle deposition rates observed at high ionic strengths were attributed to aggregation of the QDs resulting in decreased convective-diffusive transport to the silica surface.

Changes in soil pH across England and Wales in response to decreased acid deposition

Abstract: Analysis of data from the National Soil Inventory of England and Wales obtained between 1978 and 2003 shows widespread increases in soil pH - i.e., soils became less acid - across both countries during the survey period. In general, soil pH increased under all land uses. At least part of the increase and its regional variation could be explained by decreased sulphur deposition from the atmosphere. Changes in liming practices on arable land probably also contributed. The effect of decreased sulphur deposition was moderated by land use, soil properties - particularly soil pH and organic carbon content - and the level of past sulphur deposition.

Natural and engineered nano and colloidal transport: role of zeta potential in prediction of particle deposition.

Abstract: This study is designed to answer the question of whether the zeta-potential measurement of natural and engineered nano and colloidal particles can be used as a general predictor for their transport and deposition within porous medium. The transport and deposition of engineered zeolite particles and natural colloids (soil and sediment colloids) was studied and evaluated considering their zeta-potential measurement. The zeta-potential of Ca2+ or K+ saturated zeolite particles increased (i.e., became less negative) with increasing bulk ionic strength, independent of the cation species in the bulk solution, while the zeta-potential of Ca2+ or K+ saturated natural colloids was dependent on the cation species in the bulk solution, unexpectedly decreasing with the bulk K+ concentrations while increasing with bulk Ca2+ concentrations (10−5 to 10−2 M). The particle deposition rate coefficient (k) was sensitive to the cation species in the bulk solution and on the cation exchangeable sites of the particle surfaces....

Effects of N and P fertilization on the greenhouse gas exchange in two northern peatlands with contrasting N deposition rates

Abstract: . Peatlands are important ecosystems in the context of biospheric feedback to climate change, due to the large storage of organic C in peatland soils. Nitrogen deposition and increased nutrient availability in soils following climate warming may cause changes in these ecosystems affecting greenhouse gas exchange. We have conducted an N and P fertilization experiment in two Swedish bogs subjected to high and low background N deposition, and measured the exchange of CO2, CH4 and N2O using the closed chamber technique. During the second year of fertilization, both gross primary production and ecosystem respiration were significantly increased by N addition in the northernmost site where background N deposition is low, while gross primary production was stimulated by P addition in the southern high N deposition site. In addition, a short-term response in respiration was seen following fertilization in both sites, probably associated with rapid growth of nutrient-limited soil microorganisms. No treatment effect was seen on the CH4 exchange, while N2O emission peaks were detected in N fertilized plots indicating the importance of taking N2O into consideration under increased N availability. In a longer term, increased nutrient availability will cause changes in plant composition, which will further act to regulate the peatland greenhouse gas exchange.

A new twist on mud deposition; mud ripples in experiment and rock record

Abstract: 4 | June 2009 ABSTRACT Recent flume experiments with muddy suspensions have demonstrated that low-energy settings are not a prerequisite for the accumulation of muds and shales. Flocculation produces deposition-prone aggregates even in freshwater, and these floccules form bedload ripples at flow velocities that would also produce ripples in sandy sediments. Floccule ripples are crosslaminated but have a much higher water content (80-90 % by volume) than sand ripples and are thus subject to substantial compaction. Because of this, we must expect that original crosslaminae become severely flattened and are difficult to recognize in the rock record. Nonetheless, a survey of ancient shales has shown that certain intrinsic features of cross-lamination, such as basal downlap and top truncation of laminae, are still recognizable and allow identification of current-deposited muds. The example of the Cambrian Eau Claire Formation is used to illustrate how this approach can change our perception of the depositional setting of certain mudstone successions.

Mechanisms of the laser plume expansion during the ablation of LiMn2O4

Abstract: Films of LiMn2O4 prepared by pulsed laser ablation deposition are typically lithium deficient when grown at background pressures ranging between 10−4 and 20 Pa The deficiency of light atomic species such as lithium in LiMn2O4 thin films occurs as a result of the different behavior of the species during plume expansion and the deposition of the film at elevated deposition temperatures The plasma plume evolution in vacuum and 20 Pa oxygen pressure are studied using two spectroscopic techniques: emission spectroscopy and plume imaging Higher velocities and a wider spatial distribution of lithium atoms are observed in vacuum when compared with manganese and oxygen species Plume species are slowed down due to collisions with gas molecules when ablating LiMn2O4 in an oxygen atmosphere As a result, a strong deceleration of the plasma front occurs, and the effect is more pronounced for the light species, eg, Li Comparing the spatial manganese and lithium distribution within the plasma, the lithium species

Sulfuric acid deposition from stratospheric geoengineering with sulfate aerosols

Abstract: [1] We used a general circulation model of Earth's climate to conduct geoengineering experiments involving stratospheric injection of sulfur dioxide and analyzed the resulting deposition of sulfate. When sulfur dioxide is injected into the tropical or Arctic stratosphere, the main additional surface deposition of sulfate occurs in midlatitude bands, because of strong cross-tropopause flux in the jet stream regions. We used critical load studies to determine the effects of this increase in sulfate deposition on terrestrial ecosystems by assuming the upper limit of hydration of all sulfate aerosols into sulfuric acid. For annual injection of 5 Tg of SO2 into the tropical stratosphere or 3 Tg of SO2 into the Arctic stratosphere, neither the maximum point value of sulfate deposition of approximately 1.5 mEq m−2 a−1 nor the largest additional deposition that would result from geoengineering of approximately 0.05 mEq m−2 a−1 is enough to negatively impact most ecosystems.

Fog deposition to a Tillandsia carpet in the Atacama Desert

Abstract: . In the Atacama Desert, one of the driest places on earth, fog deposition plays an important role for the water balance and for the survival of vulnerable ecosystems. The eddy covariance method, previously applied for the quantification of fog deposition to forests in various parts of the world, was used for the first time to measure deposition of fog water to a desert. In this exploratory study we estimate the amount of water available for the ecosystem by deposition and determine the relevant processes driving fog deposition. This is especially important for the species Tillandsia landbecki living in coastal Atacama at the limit of plant existence with fog and dew being the only sources of water. Between 31 July and 19 August 2008 approximately 2.5 L m−2 of water were made available through deposition. Whole-year deposition was estimated as 25 L m−2. Turbulent upward fluxes occurred several times during the evenings and are explained by the formation of radiation fog. In connection with that, underestimates of the deposition are assumed. More detailed studies covering various seasons and all parameters and fluxes contributing to the local energy balance are suggested. This will help to further develop understanding about the processes of (i) deposition of water to the desert, and (ii) intensification of advection fog through additional formation of radiation fog.

Methods and apparatus for deposition reactors

Abstract: The invention relates to a method and an apparatus in which precursor vapor (101) is guided along at least one in-feed line (141,142) into a reaction chamber (110) of a deposition reactor, and material is deposited on surfaces of a batch of vertically placed substrates (170) by establishing a vertical flow of precursor vapor in the reaction chamber and having it enter in a vertical direction in between said vertically placed substrates (170).

Inhibition of γ-Secretase Activity by Helical β-Peptide Foldamers

Abstract: Alzheimer’s disease (AD) is a neurodegenerative disorder pathologically characterized by extensive extracellular deposition of amyloid-β (Aβ) peptides as senile plaques, and inhibition of “amyloido...

Room temperature ozone sensing properties of p-type CuCrO2 nanocrystals

Abstract: Delafossite-type oxide CuCrO 2 nanocrystals and microcrystals were synthesized by hydrothermal and sol–gel method, respectively, and ozone sensors were prepared by deposition of the solution containing CuCrO 2 samples. At room temperature, the sensors resistance decreased upon exposure to 50–200 ppm ozone. This can be explained by the gas sensing characteristics of p-type oxide semiconductor. We also compared the response features of CuCrO 2 nanocrystals with CuCrO 2 microcrystals, and CuCrO 2 nanocrystals gave rise to better response features than CuCrO 2 microcrystals.