Increase In Surface Concentration Research Articles

Perturbations to tropospheric oxidants, 1985–2035: 2. Calculations of hydrogen peroxide in chemically coherent regions

Increasing global emissions of trace gases NO, CH 4, and CO, along with perturbations initiated by changes in stratospheric O 3 and H 2O, may cause tropospheric hydrogen peroxide (H 2O 2) levels to change. Specific scenarios of CH 4CONO emissions and global climate changes are used to predict HO 2 and H 2O 2 changes from 1985 to 2035 in a one-dimensional model that simulates different chemically coherent regions (e.g. urban, non-urban continental and marine mid-latitudes; marine and continental low latitudes). If CH 4 and CO emissions continue to increase throughout the troposphere at current rates (1% yr −), there will be large increases in H 2O 2, for example, more than 100% in the urban boundary layer from 1985 to 2035. Globally, H 2O 2 will increase 22% with HO 2 increasing 8% and O 3 increasing 13%. When CH 4, CO and NO emissions are specified on a regionally varying basis and are parameterized for high and low potential growth rates, globally averaged increases in surface concentrations are 12% for H 2O 2 and 18% for O 3. A global warming (with increased H 2O vapor) or stratospheric O 3 depletion superimposed on CH 4, CO and NO emissions changes will cut O 3 increases but add to peroxide, increasing levels as much as 150% above present day in some regions. Both globally uniform and region-specific scenarios predict a 10–15% loss in global OH from 1985 to 2035. Thus, conversion of OH to HO 2 and H 2O 2 in the atmosphere may signify a loss of gaseous oxidizing capacity in the atmosphere and an increase in aqueous-phase oxidizing capacity.

Cycling of nutrient elements in the North Sea

The cycling of elements of inorganic and organic nutrients (carbon, nitrogen, phosphorus and silicate) in the North Sea is described. The regional effects on nutrient cycling such as thermal and haline stratification, coastal interaction, river discharges, upwelling and frontal zones are discussed. The horizontal and vertical distribution of the inorganic nutrients (nitrate, phosphate, ammonia and silicate) at the surface is given for the whole North Sea during two situations: spring (1986) and winter (1987). In winter, highest nutrient concentrations were found at the northern boundary in the Atlantic inflow, and in the continental coastal waters. During the winter cruise, nutrient minima were detected in the Dogger Bank area. This is an indication that primary production continues during winter. Generally, the surface concentrations during winter were similar to the bottom concentrations. Except for phosphate, highest concentrations were measured just above the bottom. During late spring 1986 the concentrations of nutrients at the surface and below the densicline were generally significantly lower than during winter. Only at the Atlantic boundary in the north and near the estuaries higher concentrations were detected. In stratified parts of the North Sea, the decomposition of sedimented biomass caused the ammonia concentrations in the bottom layer to be significantly higher in spring than in winter. Incidents of frontal upwelling in the central North Sea introduce nutrient-rich bottom water into the euphotic zone, enhancing phytoplankton growth in the central North Sea during summer. The ratios of nitrogen nutrients to phosphate show that in the central North Sea nitrogen is a limiting factor rather than phosphorus, whereas in the continental coastal water and off England the opposite is true. Riverine input and trapping mechanisms in the estuaries and tidal flats cause the concentrations of organic matter (dissolved and particulate) to be highest in the coastal zones and to decrease seaward. During summer the concentration of dissolved organic carbon increases throughout the North Sea. It is calculated that about 60% of the biomass formed by primary production is converted into dissolved organic carbon, 40% directly goes into the foodweb. The biological impact of the plankton is readily apparent from increased surface concentrations of different dissolved organic substances during spring blooms. Examples of eutrophication and effects of nutrient limitation are given, together with other biological repercussions such as coupling of phytoplankton and nutrient succession. Budget calculations for the different nutrient elements show that in the North Sea the biological turnover greatly exceeds the estimated annual inflow and outflow of nutrient elements. Finally, recommendations are given for future research. They include analysing dissolved organic compounds and micronutrients and following multidisciplinary measurements strategies at one location in order to obtain more information for balancing budgets and for the detailed analysis of nutrient cycling in the North Sea.

Characterization of silica-titania mixed oxides

A series of coprecipitated silica-titanias containing between 0 and I00 mol% titania were characterized by various methods. These materials are often used as supports for catalysts in the reduction of NO x and are shown to be micro-, meso-, and macroporous. All textural quantities decrease with the addition of TiO 2 to SiO 2. The macroporosity, of vital importance in the highly diffusion-controlled NO x reduction, reaches a maximum value at 50 mol% TiO 2. X-ray diffraction, FT-IR, and XPS studies showed that the materials, calcined at 723 K, consisted of a SiO 2-TiO 2 glass phase, an amorphous silica phase, and an anatase phase. At I0 mol% TiO 2, rutile was observed, by XRD, in addition to anatase. XPS data indicate the presence of a TiO 2 phase in all Ti-containing samples, a SiO 2 phase at and below 50 mol% TiO 2, and a SiO 2-TiO 2 phase at and above 75 mol% TiO 2. The quantitative XPS analysis indicates a heterogeneous distribution of phases with an increased surface concentration of Si phases. Similar results were obtained by the FT-IR studies, which additionally indicate the presence of surface free silanol groups in all samples and detect tetrahedrally substituted Ti 4+ in the SiO 2 phase.

Lysozyme adsorption at the air/water interface

The adsorption of reductively methylated chicken egg white lysozyme (EC 3.2.1.17) to the air/water interface has been measured by the radiotracer technique. This method enables direct determination of surface excess concentration as well as relative rates of adsorption and desorption. Improvements in calibration and radiolabeling techniques led to differences between the present results and previous lysozyme isotherms reported in the literature. The isotherm indicates monolayer saturation at low concentrations of bulk protein (below 2 × 10 −5 wt%) and multilayer adsorption at high concentrations (above 10 −3 wt%). At intermediate concentrations, an abrupt increase in surface concentration with increasing bulk concentration indicates a change in orientation of the adsorbed protein molecules. Adsorption experiments performed by sequential addition of protein to the bulk solution provide evidence that lysozyme molecules adsorbed at concentrations below the multilayer region do not exchange significantly with lysozyme molecules in the bulk solution. A kinetic model which incorporates the monolayer plateau, the multilayer adsorption, and the change of orientation of adsorbed lysozyme is presented.

Composition profiles due to bombardment-induced segregation in Cu-Ni samples as deduced by auger spectroscopy

Concentration profiles in Cu0.57Ni0.43 samples have been studied as a function of ion fluence (ions/cm2). Samples were bombarded with 7 keV Ar+ to a fixed fluence and subsequently profiled by alternately etching with 0.7 keV Ar+ and measuring with Auger spectroscopy. The technique used is that of Pons et al., where the surface layer concentration is extracted from the signal difference before and after each etching. We stress that low energy and low current must be used during the etching in order to ensure the minimum perturbation of the profile. In addition, low-energy Auger signals are essential to achieve high surface sensitivity. The measurements indicate a bombardment-induced segregation of copper in agreement with the results obtained by other spectroscopies. Concerning the profiles versus fluence, an increase in surface concentration and in subsurface depletion can be observed as the initial ion fluence increases.

Photo-enhanced catalytic decomposition of isopropanol on V2O5

The effect of UV-visible photo irradiation has been investigated on the decomposition of isopropanol over V2O5. A ∼ 2.5-fold photo-enhancement in the rate of the dehydration (-H2O) reaction was observed under UV-visible photo irradiation compared to thermal heating of the catalyst. The increase in propene yield under photo irradiation is believed to be initiated from photo excitation (photo-reduction) of the V2O5 complex to [-V4+-O−] * thus, increasing surface concentration of V4+ species. The V4+ active surface species is assumed to serve as the center for adsorption of isopropanol. The observed increase in water formation along with the formation of propene suggests that the rate determining step for the dehydration reaction is desorption of water. Selectivity toward the dehydrogenation (-H2) reaction has also been measured to be ∼ 1% under UV-visible photo irradiation as compared to ∼ 15% under thermal heating of the catalyst.

Adsorption of Pb(II) by a marine bacterium: the effect of cell concentration and pH

Adsorption of Pb from synthetic seawater solution onto the marine bacterium Pseudomonas atlantica displayed many of the feature commonly encountered in studies of trace metal adsorption onto hydrous oxides. These included: (1) indication of multisite adsorption behaviour, and (2) ‘particle effects’ (indicated by decreased adsorption density with increasing surface concentration). For suspensions of P. atlantica this effect is attributed to the release of dissolved organic material which binds Pb in solution. Differences in Pb binding to P. atlantica relative to oxide surfaces includes: (1) relatively low fractional (%) adsorption over a wide range of solution pH, Pb, and cell concentrations, and (2) lack of a marked, pH-dependent, adsorption edge.

Time-resolved evolution of fly ash during pulverized coal combustion

The time resolved evolution of ash during the combustion of individual char particles has been studied using a Montana lignite, a North Dakota Beulah lignite, and a synthetic char prepared from doped sucrose. The three chars were selected to illustrate the effects of macroporosity and mineral matter content on the ash evolution. The synthetic char is distinguished from the lignites by being macropore-free. The ash content was varied from 17%(Montana) to 37%(Beulah). When the chars are reacted under external-diffusion-controlled conditions, the mineral matter is released as the carbon surface recedes. The ash particles on the surface of the char aggregate and grow in size with increasing char burnout. The rate of growth of particle size increases markedly as the extent of burnout increases because of the increase in surface concentration of released ash. The ash sizes are larger for the char with the higher mineral content. As complete burnout is approached, however, the macroporous lignite chars fragment yielding smaller final ash particles than the macropore-free sucrose char. A percolation model applied to the ash formation processes was used to demonstrate the major features of the dependence of the time resolved evolution of ash on macroporosity.

Fixation of molecular nitrogen on a rhodium/titanium dioxide SMSI (strong metal–support interaction) catalyst

The presence of Ti3+ and its increase in surface concentration during high temperature reduction are responsible for the large amounts of nitrogen chemisorption on a titania-supported Rh system at room temperature.

XPS and ISS analysis of Fischer-Tropsch catalysts

The surface compositions of K and Cu containing Fe/Mn oxide catalysts for Fischer-Tropsch synthesis were investigated by XPS and ISS. The surface species after calcination are identified as Fe2O3, Mn2O3, MnO2, CuO and most likely KO2, and after in situ reduction at 723 K Fe0, Cu0, Fe2+ and Fe3+ oxides, MnO and KOH. Mn and K are enriched on the surfaces after calcination and reduction; the Cu surface content is approximately equal to the bulk concentration. The K enrichment is especially strong and ISS indicates that potassium is mainly confined to the uppermost layers. The degree of reduction of Fe is strongly dependent on the amount of Cu or K. The change in surface composition during Fischer-Tropsch reaction in the XPS equipment can be correlated to the activity of the catalysts. The pure and Cu containing samples show a constant activity and only a small increase in carbon surface concentration. The K containing catalysts deactivate after a short time and are then totally covered by carbon. On all catalyst surfaces a small amount of carbonate is formed.

Mechanism of K562-induced human natural killer cell inactivation using highly enriched effector cells isolated via a new single-step sheep erythrocyte rosette assay

In this study, we used preparations highly enriched in human natural killer (NK) cells to further characterize the mechanism of taget-cell-induced NK inactivation. Highly enriched populations of NK cells were obtained by a newly developed, single-step sheep red blood cell rosette assay. This method, which did not require any incubation steps to facilitate cell contact, permitted a rapid and efficient isolation if NK cells from adherent-cell-depleted peripheral blood lymphocytes. The non-rosetted cells had high NK activity, possessed large granular lymphocyte (LGL) morphology and expressed the NK-associated antigens Leu-11a, Leu-7, OKM1 and NKH-1. In contrast, the rosetted cells had significantly lower NK activity, possessed typical lymphocyte morphology and expressed the T-cell-associated marker OKT3. Next, we examined the ability of these NK-enriched effector cells (EC c) to become inactivated by K562. Functional studies revealed that EC c lost ≥95% of their lytic capacity following incubation with K562 at a ratio of 2/1 for 6 h. However, to achieve this level of inactivation, it was essential that the cell suspension be gently mixed every 90–120 min. Inactivation was not due to cell death and did not reflect changes in the percentages of cells bearing the Leu-11a, Leu-7, OKM1 and NKH-1 antigens, but was associated with an increase in cell surface concentration of OKM1. As judged by gross morphology, the percentages of LGL in EC c before and after treatment with K562 were essentially the same. Finally, K562-treated EC c also lost their ability to mediate antibody-dependent cellular cytotoxicity (ADCC), suggesting that both NK-cell-mediated cytotoxicity and ADCC may involve a common lytic pathway.

Effects of Concentration and Application Method on Decay and Residual Activity of Foliar Chlorpyrifos

The decay of chlorpyrifos applied as emulsifiable concentrate to foliage of commercially grown oranges, greenhouse tomato, and outdoor potted cotton was measured under different application conditions. Foliar residue decay was found to be dependent on concentration of active ingredient, amount, and method by which chlorpyrifos was applied to the crop; increase in tank or surface concentrations resulted in a marked decrease in initial rate of loss of the residue. Depending on concentration and application technique, time required for the initial deposit to lose half its quantity ranged from 15 to 139 h on greenhouse tomato leaves, from 1.4 to 96 h on orange leaves, and from 5.5 to 57 h on cotton leaves. The effect of the concentration on decay of foliar chlorpyrifos was observed for both low-volume and high-volume spray conditions; relative changes in decay rate were larger for low-volume residues than for high-volume residues in most cases. Bioassay of a constant dose of chlorpyrifos applied to cotton leaves at different concentrations and at various drop densities revealed a longer residual activity of the more concentrated treatment against both Spodoptera littoralis (Boisduval) and Bemisia tabaci (Gennadius).

FLOCCULENCE OF BREWERY YEASTS AND THEIR SURFACE PROPERTIES: CHEMICAL COMPOSITION, ELECTROSTATIC CHARGE AND HYDROPHOBICITY

The flocculence of a top and a bottom fermentation brewery yeast was studied through the cell surface properties: surface composition (X-ray photoelectron spectroscopy), surface charge (microelectrophoresis) and hydrophobicity (adhesion tests). Aerobic Cultures and fermentation simulating industrial conditions were performed. The flocculence (tendency to flocculate in favourable conditions) has been determined by a test which separated the occurrence of flocculation and the measurement of its manifestation (suspension clearing); the flocculating agents were ethanol and calcium. The top fermentation strain does not flocculate with calcium alone but is very sensitive to ethanol (0.01% (v/v)). The lower flocculence observed for cells cultured on malt extract as compared with cells cultured on yeast extract is accompanied by a more negative zeta potential. The bottom fermentation strain which has a more negative surface flocculates only in the presence of calcium but ethanol enhances the process. The variation of flocculence according to the culture medium and harvesting time is correlated to the variation of the phosphate surface concentration. This is not paralleled by a variation of the zeta potential which does not decrease below a value of about-35 mV as the phosphate surface concentration increases. The increase of flocculence as a function of culture time correlates also with an increase of the cell hydrophobicity; this is more obvious for the cultures than for the fermentations.

Exchange and correlation effects on screening in a two-dimensional electron gas.

A simple expression for the screening constant in a two-dimensional electron gas (2D EG) of finite thickness is obtained within the framework of a 2D version of the linearized Thomas-Fermi-Dirac equation, which includes effects of the exchange-correlation energy. For the case of 2D EG in an ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As/GaAs system the role of the correlation energy is shown to be small compared to that of exchange. Effect of the exchange energy on the screening constant decreases with the increasing surface concentration n of electrons. For n\ensuremath{\approxeq}${10}^{11}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ the screening constant increases by 50% compared to its value calculated for noninteracting particles.

Adsorption of low density lipoproteins onto selected biomedical polymers.

This study examines the interaction of human low density lipoprotein (LDL) with a select group of biomedical polymers. The adsorption characteristics of LDL on cured filler-free poly(dimethyl Siloxane) (C-PDMS), Biomer, Cardiomat 610, Kraton 1650, poly(hydroxyethyl methacrylate) (PHEMA) and glass are presented. Adsorption of LDL to charged hydrophilic glass control surfaces occurred rapidly, reaching plateau concentrations within one minute (0.19 +/- 0.01 ug/cm2). Adsorption of LDL to polymer surfaces appeared to be dependent upon both the polymer hydrophobicity (or apolar nature), and flexibility (or dynamic nature) at the interface. Increased surface concentrations were observed for Biomer (0.32 +/- 0.01 ug/cm2) as well as other polymers which exhibited both hydrophobic and elastomeric properties. Temperature changes between 25 degrees C and 37 degrees C were found to significantly influence the surface concentration of LDL on Biomer (0.16 +/- 0.01 ug/cm2 at 25 degrees C versus 0.32 +/- 0.01 ug/cm2 at 37 degrees C). A lipid core phase transition at 36 degrees C was believed to be responsible for the temperature influence. Preliminary competitive adsorption studies of LDL with albumin (HSA) and serum on silicone surfaces suggests that LDL adsorption occurred rapidly and preferentially (0.25 +/- 0.01 ug/cm2 for LDL alone; 0.33 +/- 0.01 ug/cm2 for LDL + HSA; 0.15 +/- 0.01 ug/cm2 LDL + serum). Preliminary studies on the role of LDL in calcification were not conclusive. It can be concluded that LDL adsorption is dependent upon polymer hydrophobicity, flexibility and temperature. Competitive adsorption experiments suggests that LDL may have a substantial influence on protein adsorption.

Influence of L-ascorbic acid, blood cells and components on protein adsorption/desorption on polycarbonate.

In a previous study we have shown that vitamin C has some effect on the polymer surface by adsorption to it, which would probably affect the protein adsorption and platelet adhesion. The present work has been extended to demonstrate the influence of vitamin C on the kinetics of protein-polymer interaction, using labeled proteins, in the presence and absence of red blood cells, platelets and white blood cells. It appears that vitamin C causes an increase in albumin surface concentration compared to bare substrate which seems to decrease slightly in the presence of blood cells. On the other hand, the infusion of vitamin C to the fibrinogen blood cells system dramatically inhibits the fibrinogen surface binding. The role of L-ascorbic acid to reduce the protein adsorption in the presence of blood cells is discussed by taking into account the interaction of vitamin C with the polymer surface, the interaction of vitamin C with the proteins and cellular membrane, and the interaction of proteins and cells with the polymer itself. The effect of various blood components also seems to be important, and slight differences in the adsorption pattern of proteins are observed in the presence of urea, creatinine, bilirubin, Fe ion and zinc at normal blood levels.

Surface compositional changes of TiC, B 4C and SiC at high temperatures

Changes in the surface composition of TiC, B 4C and SiC single-crystals and coatings have been studied by using Auger electron spectroscopy. The analysis of the surface composition was performed under a heat treatment up to 1500°C and/or an argon-ion bombardment (3 keV. 7 μA/cm 2). In both the TiC single-crystal and coating, an increase in the surface composition of carbon atoms was observed as the temperature was raised, regardless of the bombardment. Carbon atoms diffused to the surface of the coating to form graphite-type carbon above 1000°C. In case of the B 4C single-crystal, a remarkable increase in surface concentration of carbon atoms was observed at 1000°C and 1250°C, while such a drastic change was not observed during the bombardment. On B 4C coating, graphite-type carbon atoms existed in the near-surface region at 1500°C. On the SiC single-crystal, the surface composition of carbon atoms increased on raising the temperature regardless of the bombardment. At 1500°C the surface was completely covered with graphite-type carbon atoms.

Internal oxidation of nickel alloys with an increasing surface concentration of oxygen

Internal oxidation of nickel alloys with an increasing surface concentration of oxygen

Surface pressure from block copolymers with one block forming a monolayer and the other block dangling in solution

Surface pressure has been measured as a function of surface concentration for monolayers of poly(dimethylsi1oxane)-polystyrene (PDMS-PS) diblock copolymers, PDMS-poly(wmethy1styrene) (PDMS-PaMS) multiblock copolymers, and the respective homopolymers, spread on the surface against air of tricresyl phosphate at 26 C. A sparingly soluble monolayer was formed by PDMS homopolymer. No surface pressure was associated with either PS or PaMS homopolymer; these appeared to pass into bulk solution. For the block copolymers, at low surface concentrations the surface pressure was indistinguishable from that for PDMS homopolymer at the same concentration of PDMS. At higher concentrations the surface pressure exceeded this value, to an extent which increased with increasing surface concentration of PS or PaMS. The supplemental surface pressure from dangling chains was calculated by subtraction. The findings are in qualitative agreement with theoretical predictions by de Gennes, Alexander, and Cantor that osmotic interactions between polymer chains dangling into a liquid from an interface contribute substantially to the reduction of surface tension. Idealizations in the theoretical models are noted.

Reliability/design assessment by internal-node timing-margin analysis using laser photocurrent-injection : Daniel J. Burns, Mark T. Pronobis, Charles A. Eldering and Robert J. Hillman. Proc. IEEE Reliab. Phys. Conf. 76 (1984)

Perovskite type catalysts La0.7Sr0.3Cr1−xRuxO3 (0.025 ≤ x ≤ 0.100) were synthesized by annealing a mixture of metal oxides and carbonates gradually up to 1000 °C in air, and characterized by XRPD, XPS, TPD, SEM-EDS and the van der Pauw method. The CO oxidation activity was investigated in a differential recycle reactor. According to the XRPD results, all samples achieved a perovskite structure, with a small presence of SrCrO4 phase. The XPS results revealed that the surface composition of all samples differed considerably from the stoichiometric value with an important segregation of strontium and mainly ruthenium with regard to chromium at the surface of the catalysts. The sharp decrease of resistivity with increasing surface concentration of ruthenium and the independence of the resistivity on temperature for the sample with x = 0.100 imply the possible presence of SrRuO3, La–Ru–O and highly dispersed RuO2 (invisible by XRPD), known as good electric conductors, at the surface. The CO oxidation activity increases with increasing the degree of substitution (x). The surface concentrations of ruthenium are almost the same in the samples with x = 0.075 and 0.100. Those samples showed the similar values of resistivity in whole investigated temperature range and very close CO oxidation activity, which indicates that the concentration of Ru4+ in the surface region and its stability are determining factors for the CO oxidation activity. The main results of this study are that ruthenium perovskites have a high thermal stability and CO oxidation activity.