Average Oxidation Rate Research Articles

Physical and chemical performances of high Al steels

The effects of acid-soluble Al content on the physical and chemical performances of high Al steels were investigated. The results show that the distribution of acid-soluble Al in steel substrate is uniform. With increasing Al content, the strength and toughness of steels decrease a little but the hardness increases. The average yield strength and tensile strength are 425 MPa and 570 MPa, respectively, and the Rockwell hardness is 89. 7. For non-Al steels the average oxidation rate is up to 0.421 mg/(cm2 · h) at 1373 K. For high Al steels, when the mass fraction of Al is less than 5%, there is a thinner gray oxidized layer on surface and the oxidation rate is high; when the mass fraction of Al is more than 8.0%, the thin, close and yellow glossing film still exists, and the average oxidation rate is only 0.016 mg/(cm2 · h).

Oxidation of Combined Ingestion of Maltodextrins and Fructose during Exercise

To determine whether combined ingestion of maltodextrin and fructose during 150 min of cycling exercise would lead to exogenous carbohydrate oxidation rates higher than 1.1 g.min. Eight trained cyclists VO2max: 64.1 +/- 3.1 mL.kg.min) performed three exercise trials in a random order. Each trial consisted of 150 min cycling at 55% maximum power output (64.2+/-3.5% VO2max) while subjects received a solution providing either 1.8 g.min of maltodextrin (MD), 1.2 g.min of maltodextrin + 0.6 g.min of fructose (MD+F), or plain water. To quantify exogenous carbohydrate oxidation, corn-derived MD and F were used, which have a high natural abundance of C. Peak exogenous carbohydrate oxidation (last 30 min of exercise) rates were approximately 40% higher with combined MD+F ingestion compared with MD only ingestion (1.50+/-0.07 and 1.06+/-0.08 g.min, respectively, P<0.05). Furthermore, the average exogenous carbohydrate oxidation rate during the last 90 min of exercise was higher with combined MD+F ingestion compared with MD alone (1.38+/-0.06 and 0.96+/-0.07 g.min, respectively, P<0.05). The present study demonstrates that with ingestion of large amounts of maltodextrin and fructose during cycling exercise, exogenous carbohydrate oxidation can reach peak values of approximately 1.5 g.min, and this is markedly higher than oxidation rates from ingesting maltodextrin alone.

Nonlinearities in Source Receptor Relationships for Sulfur and Nitrogen Compounds

The relationship between emissions and deposition of air pollutants, both spatially and in time forms an important focus for science and for policy makers. In practice, this relationship may become nonlinear if the underlying processes change with time, or in space. Nonlinearities may also appear due to errors in emission or deposition data, and careful scrutiny of both data sources and their relationship provides a means of picking up such deficiencies. Nonlinearities in source receptor relationships for sulfur and nitrogen compounds in Europe have been identified in measurement data for the UK. In the case of sulfur, the dry deposition process has been shown to be strongly influenced by ambient concentrations of NH3, leading to substantial increases in deposition rate as SO2 concentrations decline and the ratio SO2/NH3 decreases. The field evidence extends to measurements over three different surfaces in three countries across Europe. A mechanistic understanding of the cause of this nonlinearity has been provided. Apparent nonlinearities also exist in the sulfur deposition field through the influence of shipping emissions. The effect is clear at west coast locations, where during a period in which land-based sulfur emissions declined by 50%, no significant decline in concentrations of SO(2-) in precipitation were observed. The sites affected are primarily the coastal regions of southwestern UK, where shipping sources contribute a substantial fraction of the deposited sulfur, but the effect is not detectable elsewhere. Full quantification of the spatially disaggregated emission and their changes in time will eliminate this apparent nonlinearity in the source-receptor data. For oxidized nitrogen emission and deposition in the UK, there is strong evidence of nonlinearity in the source-receptor relationship. The concentrations and deposition of NO(3-) in precipitation have declined little following a reduction in emissions of 45% during the period 1987 to 2001. The data imply a significant decrease in the average transport distance for oxidized nitrogen and most probably an increase in the average oxidation rate. However, the net effect of changes in aerosol chemistry due to changes in sulfur emissions and less competition for the main oxidants as a consequence of reductions in sulfur emission have not been separated. A quantitative explanation of the cause of this nonlinearity is lacking and the effects are therefore identified as an important uncertainty for the development of further protocols to control acidification, eutrophication and photochemical oxidants in Europe.

Oxidation of combined ingestion of glucose and fructose during exercise.

The purpose of the present study was to examine whether combined ingestion of a large amount of fructose and glucose during cycling exercise would lead to exogenous carbohydrate oxidation rates >1 g/min. Eight trained cyclists (maximal O(2) consumption: 62 +/- 3 ml x kg(-1) x min(-1)) performed four exercise trials in random order. Each trial consisted of 120 min of cycling at 50% maximum power output (63 +/- 2% maximal O(2) consumption), while subjects received a solution providing either 1.2 g/min of glucose (Med-Glu), 1.8 g/min of glucose (High-Glu), 0.6 g/min of fructose + 1.2 g/min of glucose (Fruc+Glu), or water. The ingested fructose was labeled with [U-(13)C]fructose, and the ingested glucose was labeled with [U-(14)C]glucose. Peak exogenous carbohydrate oxidation rates were approximately 55% higher (P < 0.001) in Fruc+Glu (1.26 +/- 0.07 g/min) compared with Med-Glu and High-Glu (0.80 +/- 0.04 and 0.83 +/- 0.05 g/min, respectively). Furthermore, the average exogenous carbohydrate oxidation rates over the 60- to 120-min exercise period were higher (P < 0.001) in Fruc+Glu compared with Med-Glu and High-Glu (1.16 +/- 0.06, 0.75 +/- 0.04, and 0.75 +/- 0.04 g/min, respectively). There was a trend toward a lower endogenous carbohydrate oxidation in Fruc+Glu compared with the other two carbohydrate trials, but this failed to reach statistical significance (P = 0.075). The present results demonstrate that, when fructose and glucose are ingested simultaneously at high rates during cycling exercise, exogenous carbohydrate oxidation rates can reach peak values of approximately 1.3 g/min.

Visualizing Superoxide Production in Normal and Diabetic Rat Islets of Langerhans

Oxygen free radicals have been implicated in beta-cell dysfunction and apoptosis associated with type 1 and type 2 diabetes mellitus. The roles of free radicals in diabetes have thus far been defined indirectly by monitoring oxidative tissue damage and the effects of antioxidants, free radical scavengers, and overexpression of superoxide dismutase. We employed the superoxide-mediated oxidation of hydroethidine to ethidium to dynamically and directly assess the relative rates of mitochondrial superoxide anion generation in isolated islets in response to glucose stimulation. Superoxide content of isolated islets increased in response to glucose stimulation. We next compared the oxyradical levels in Zucker lean control and Zucker diabetic fatty rat islets by digital imaging microfluorometry. The superoxide content of Zucker diabetic fatty islets was significantly higher than Zucker lean control islets under resting conditions, relatively insensitive to elevated glucose concentrations, and correlated temporally with a decrease in glucose-induced hyperpolarization of the mitochondrial membrane. Importantly, superoxide levels were elevated in islets from young, pre-diabetic Zucker diabetic fatty animals. Overproduction of superoxide was associated with perturbed mitochondrial morphology and may contribute to abnormal glucose signaling found in the Zucker diabetic fatty model of type 2 diabetes mellitus.

Ammonia oxidation at low temperature in a high concentration powdered activated carbon membrane bioreactor

In this study, a membrane bioreactor (MBR) with high concentration of powdered activated carbon was investigated to enhance the oxidation of ammonia at a water temperature lower than 4°C. A semi-pilot scale submersed suction type MBR was operated with a hollow fiber membrane module having a nominal pore size of 0.1μm and an effective filtration area of 0.05 m2. A powder activated carbon (PAC) concentration of 40 g/L was maintained in the reactor and the PAC was not replaced during the experiment. A control reactor without PAC was also operated for comparison. Water temperature of both reactors was controlled at 25, 10, 4 and 2°C. At a water temperature of 4°C, the influent ammonia nitrogen of 10 mg/L was removed completely in the reactor with PAC. On the other hand, the effluent concentration of the control reactor was fluctuated in a range of 3-6 mg/L. In addition, nitrite nitrogen was detected in the control reactor up to a maximum concentration of 6 mg/L at the same temperature. Still high removal efficiency was obtained in the reactor with PAC even at 2°C, but almost no ammonia oxidation was observed in the control reactor. The average ammonia oxidation rate of the powdered activated carbon reactor was 1.3-3.2 mg/L.h, which is 4.5 times higher than that of the control (0.51-0.63 mg/L.h). Filtration resistance was 2.45 × 1012m-1 for the reactor with PAC, which is one order lower than that of the control reactor (1.64 × 1013m-1). The microbial cake layer on the membrane surface caused the larger filtration resistance for the control reactor. Only one chemical cleaning was conducted for the membrane in the PAC reactor at the flux of 0.4-0.7 m/d while 3 times cleaning was required for that of the control.

Transport and diagenesis of trace metals and organic matter in Palos Verdes shelf sediments affected by a wastewater outfall

Abstract Particles from the Whites Point/JWPCP outfalls operated by the Los Angeles County Sanitation District (LACSD) have been discharged onto the Palos Verdes (PV) shelf, Southern California, since the late 1930s. Since the early 1950s, they have made a significant contribution to the sedimentary deposits on the shelf. In order to study the transport and diagenesis of organic carbon (OC) and associated trace metals, replicate sediment cores were collected during 1996 and 1997 at four different sites at the ∼60 m isobath on the PV shelf, and analyzed for OC, Ag, Al, Cd, Cr, Cu, Mn, Ni, Pb, and Zn. We conclude from these results that a significant fraction of OC and associated heavy metals were transported laterally on silt particles from shallower environments. Cross-shelf transport of sediments caused multiple peaks in measured profiles of OC and trace metals at site 6C, 2 km away from the outfall. The same mechanism is likely to contribute to a concentration decrease that is smaller than that expected from decreases from the Whites Point outfall emissions. Based on Pb/OC ratios in sediments, deposited in 1971, and comparisons to the outfall from the same year, we estimate that 50±10% of the OC deposited in the early 1970s, now buried at 30–50 cm depth, had oxidized since that time, implying a half-life of about 26 years for the outfall-OC, as an upper limit. The average OC oxidation rate at peak depth (about 2 mg C cm −2 year −1 ) is, however, only about 10% of the present-day OC accumulation rate (20 mg C cm −2 year −1 ), which itself is adding not much more than 1% per year to the post-1950s OC inventory (∼1500 mg cm −2 ). We furthermore estimate that the OC inventory in PV shelf sediments in 1971 was equivalent to about 35% of that emitted by the outfall. OC and trace metal inventories did not decrease in the period 1981 to 1997, contrary to those of other contaminants such as DDTs and PCBs.

The effect of termite biomass and anthropogenic disturbance on the CH4 budgets of tropical forests in Cameroon and Borneo

SummaryThe exchange of CH4 between tropical forests and the atmosphere was determined by simultaneously measuring the net CH4 flux at the soil surface and assessing the flux contribution from soil‐feeding termite biomass, both within the soil profile and in mounds. In Cameroon the flux of CH4 ranged from a net emission of 40.7 ng m–2 s–1 to a net CH4 oxidation of –53.0 ng m–2 s–1. Soil‐inhabiting termite biomass was significantly correlated with CH4 flux. Termite mounds emitted up to 2000 ng s–1 mound–1. Termite‐derived CH4 emission reduced the soil sink strength by up to 28%. Disturbance also had a strong effect on the soil sink strength, with the average rate of CH4 oxidation, at – 17.5 ng m–2 s–1, being significantly smaller (≈ 36%) at the secondary forest site than the –27.2 ng m–2 s–1, observed at the primary forest site. CH4 budgets calculated for each site indicated that both forests were net sinks for CH4 at – 6.1 kg ha–1 y–1 in the near‐primary forest and – 3.1 kg ha–1 y–1 in the secondary forest.In Borneo, three forest sites representing a disturbance gradient were examined. CH4 oxidation rates ranged from 0 to – 32.1 ng m–2s–1 and a significant correlation between the net flux and termite biomass was observed only in an undisturbed primary forest, although the biomass was insufficient to cause net emission of CH4. Rates of CH4 oxidation were not significantly different across the disturbance gradient but were, however, larger in the primary forest (averaging – 15.4 ng m–2 s–1) than in an old‐growth secondary forest (–13.9 ng m–2s–1) and a young secondary re‐growth (– 10.8 ng m–2s–1). CH4 flux from termite mounds ranged from net oxidation in an abandoned mound to a maximum emission of 468 ng s–1 mound–1. CH4 budgets calculated for each site indicated that CH4 flux from termite mounds had an insignificant effect on the budget of CH4 at the regional scale at all three forest sites. Annual oxidation rates were – 4.8, – 4.2 and – 3.4 kg ha–1 y–1 in the primary, secondary and young secondary forests, respectively.

Nitrogen, carbon, and sulfur metabolism in natural thioploca samples

Filamentous sulfur bacteria of the genus Thioploca occur as dense mats on the continental shelf off the coast of Chile and Peru. Since little is known about their nitrogen, sulfur, and carbon metabolism, this study was undertaken to investigate their (eco)physiology. Thioploca is able to store internally high concentrations of sulfur globules and nitrate. It has been previously hypothesized that these large vacuolated bacteria can oxidize sulfide by reducing their internally stored nitrate. We examined this nitrate reduction by incubation experiments of washed Thioploca sheaths with trichomes in combination with 15N compounds and mass spectrometry and found that these Thioploca samples produce ammonium at a rate of 1 nmol min-1 mg of protein-1. Controls showed no significant activity. Sulfate was shown to be the end product of sulfide oxidation and was observed at a rate of 2 to 3 nmol min-1 mg of protein-1. The ammonium and sulfate production rates were not influenced by the addition of sulfide, suggesting that sulfide is first oxidized to elemental sulfur, and in a second independent step elemental sulfur is oxidized to sulfate. The average sulfide oxidation rate measured was 5 nmol min-1 mg of protein-1 and could be increased to 10.7 nmol min-1 mg of protein-1 after the trichomes were starved for 45 h. Incorporation of 14CO2 was at a rate of 0.4 to 0.8 nmol min-1 mg of protein-1, which is half the rate calculated from sulfide oxidation. [2-14C]acetate incorporation was 0.4 nmol min-1 mg of protein-1, which is equal to the CO2 fixation rate, and no 14CO2 production was detected. These results suggest that Thioploca species are facultative chemolithoautotrophs capable of mixotrophic growth. Microautoradiography confirmed that Thioploca cells assimilated the majority of the radiocarbon from [2-14C]acetate, with only a minor contribution by epibiontic bacteria present in the samples.

In-situ HIP synthesis of TiB2/SiC ceramic composites

Dense TiB 2 /SiC ceramic composites were fabricated by means of in-situ HIP synthesis processing from TiH 2 , Si, C and B 4 C powder blends. The microstructure and mechanical properties of the ceramic matrix composites were investigated using X-ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy and microhardness. The grains of TiB 2 and SiC in the ceramic matrix composites are fine, the TiB 2 grains being regular-platelet, and the SiC grains being are irregular polygon. The mechanical properties of the composite are mainly affected by their densities. As the density increases, the properties of the composites improve. The microhardness, fracture toughness K IC and flexural strength are, respectively, 14.80 GPa, 4.75 MPa m 1/2 and 408.62 MPa in the 96% density TiB 2 /SiC composites. The crack propagation path is deflected in these composites. TiB 2 /SiC composites also have an excellent oxidation resistance. The average oxidation rate of TiB 2 /SiC is about 10 −10 m s −1 from 1073 to 1473 K.

The effect of chironomid larvae on production, oxidation and fluxes of methane in a flooded rice soil

Tube-dwelling invertebrates affect microbial processes by feeding on sediment bacteria, by creating structures with properties different from that of the bulk sediment, by disturbing the benthic boundary layer, and by pumping water through their tubes. We studied the effects of Chironomidae in a flooded soil. Tubes were at least 1.5 cm long and ca. 2 mm in diameter, and extended through the anoxic subsurface soil over most of their length. Larvae had no effect on CH4 flux across the sediment surface either by diffusion or by ebullition. In vitro, CH4 oxidation rates in tubes were significantly (P<0.05) higher than those in surface and subsurface soil. At a mixing ratio of 20 000 ppmv, average CH4 oxidation rates of tubes, surface soil, and bulk soil were 2, 0.4, and 1 μmol g dry wt.−1 h−1, respectively. The number of CH4 oxidizing bacteria determined by the most probable number (MPN) technique was higher in chironomid tubes than in the other soil compartments. CH4 production in tubes was significantly (P<0.05) higher than in the anoxic bulk soil, while no CH4 was produced in the surface soil during 240 h of incubation. We conclude that chironomid tubes are microsites with an intensified microbial activity, where CH4 production and oxidation may be tightly coupled.

Training-induced alterations in fat and carbohydrate metabolism during exercise in elderly subjects.

Compared with young adults, fat oxidation is lower in elderly persons during endurance exercise performed at either the same absolute or relative intensity. We evaluated the effect of 16 wk of endurance training on fat and glucose metabolism during 60 min of moderate intensity exercise [50% of pretraining peak oxygen consumption (VO2peak)] in six elderly men and women (74 +/- 2 yr). Training caused a 21% increase in mean VO2peak. The average rate of fat oxidation during exercise was greater after (221 +/- 28 mumol/min) than before (166 +/- 17 mumol/min) training (P = 0.002), and the average rate of carbohydrate oxidation during exercise was lower after (3,180 +/- 461 mumol/min) than before (3,937 +/- 483 mumol/min) training (P = 0.003). Training did not cause a significant change in glycerol rate of appearance (Ra), free fatty acid (FFA) Ra, and FFA rate of disappearance during exercise. However, glucose Ra during exercise was lower after (1,027 +/- 95 mumol/min) than before (1,157 +/- 69 mumol/min) training (P = 0.01). These results demonstrate that a 16-wk period of endurance training increases fat oxidation without a significant change in lipolysis (glycerol Ra) or FFA availability (FFA Ra) during exercise in elderly subjects. Therefore, the training-induced increase in fat oxidation during exercise is likely related to alterations in skeletal muscle fatty acid metabolism.

98/01275 Specifying fly ash for durable concrete: Keck, R. H. and Riggs, E. H. Concr. Int., 1997, 19, (4), 35–38

The impact of microbiological metal sulfide oxidation on acid mine drainage generation was studied for two different mine tailings. Microorganisms were quantified using different methods: (1) SYBR Green II direct counting, (2) TaqMan quantitative, real-time PCR (Q-PCR), (3) catalyzed reporter deposition–fluorescence in situ hybridization (CARD-FISH) and (4) most probable number (MPN) cultivation of acidophilic Fe(II) oxidizers. Potential pyrite or pyrrhotite oxidation rates were measured by microcalorimetry.In the uncovered, pyrrhotite-containing tailings near Selebi-Phikwe, Botswana, acidophilic Fe(II)-oxidizing microorganisms were present in high numbers (MPN) of up to 107 cells g− 1 dw (mean value 3 × 106 cells g− 1 dw) throughout the entire water unsaturated, oxidized zone of about 25 m (at the tailings dam periphery) with a paste pH in the range of 3–4. Mean numbers of living Bacteria (CARD-FISH) and total microorganisms (SYBR Green II) were 1 × 107 cells g− 1 dw and 8 × 107 cells g− 1 dw, respectively. Cell numbers obtained by Q-PCR analysis were in the same range. The average potential pyrrhotite oxidation rate measured by microcalorimetry was 3.4 × 10−4 mol pyrrhotite m− 3 tailings s− 1 at 25 °C. About half of the pyrrhotite oxidation activity was biologically catalyzed.By contrast, in the covered pyrite-containing tailings in Impoundment 1 in Kristineberg, northern Sweden, acidophilic Fe(II)-oxidizing microorganisms (mean value 5 × 105 cells g− 1 dw) were only detected in a distinct zone of oxidized tailings between the cover and the unoxidized tailings where low pH values down to 3 prevailed. Bacterial numbers obtained by Q-PCR analysis were much higher (mean value 3 × 108 cells g− 1 dw). The proportion of biological pyrite oxidation was up to 100% for the oxidized zone. The average potential pyrite oxidation rate was 1.6 × 10−5 mol pyrite m− 3 tailings s− 1 at 10 °C, an order of magnitude lower than that for the pyrrhotite-containing tailings.

98/01267 Preparation of activated carbons from bituminous coals with CO 2 activation influence of coal oxidation : Teng, H. et al. Carbon, 1997, 35, (2), 275–283

The impact of microbiological metal sulfide oxidation on acid mine drainage generation was studied for two different mine tailings. Microorganisms were quantified using different methods: (1) SYBR Green II direct counting, (2) TaqMan quantitative, real-time PCR (Q-PCR), (3) catalyzed reporter deposition–fluorescence in situ hybridization (CARD-FISH) and (4) most probable number (MPN) cultivation of acidophilic Fe(II) oxidizers. Potential pyrite or pyrrhotite oxidation rates were measured by microcalorimetry.In the uncovered, pyrrhotite-containing tailings near Selebi-Phikwe, Botswana, acidophilic Fe(II)-oxidizing microorganisms were present in high numbers (MPN) of up to 107 cells g− 1 dw (mean value 3 × 106 cells g− 1 dw) throughout the entire water unsaturated, oxidized zone of about 25 m (at the tailings dam periphery) with a paste pH in the range of 3–4. Mean numbers of living Bacteria (CARD-FISH) and total microorganisms (SYBR Green II) were 1 × 107 cells g− 1 dw and 8 × 107 cells g− 1 dw, respectively. Cell numbers obtained by Q-PCR analysis were in the same range. The average potential pyrrhotite oxidation rate measured by microcalorimetry was 3.4 × 10−4 mol pyrrhotite m− 3 tailings s− 1 at 25 °C. About half of the pyrrhotite oxidation activity was biologically catalyzed.By contrast, in the covered pyrite-containing tailings in Impoundment 1 in Kristineberg, northern Sweden, acidophilic Fe(II)-oxidizing microorganisms (mean value 5 × 105 cells g− 1 dw) were only detected in a distinct zone of oxidized tailings between the cover and the unoxidized tailings where low pH values down to 3 prevailed. Bacterial numbers obtained by Q-PCR analysis were much higher (mean value 3 × 108 cells g− 1 dw). The proportion of biological pyrite oxidation was up to 100% for the oxidized zone. The average potential pyrite oxidation rate was 1.6 × 10−5 mol pyrite m− 3 tailings s− 1 at 10 °C, an order of magnitude lower than that for the pyrrhotite-containing tailings.

The sulfidation and oxidation behavior of sputter-deposited Cr-refractory metal alloys at high temperatures

Cr-Nb and Cr-Mo alloys have been sputter-deposited on to quartz substrate, and their sulfidation and oxidation behavior has been studied as a function of temperature and alloy composition in He-S 2 and Ar-O 2 atmospheres. The sulfidation of these alloys follows a parabolic rate law, being diffusion controlled. The sulfidation rates of Cr-Nb alloys decrease with increasing niobium content in the alloy, and the sulfidation resistance of the high niobium alloys is comparable with that of niobium. The sulfidation resistance of Cr-Mo alloys is independent of alloy composition, being comprable with that of molybdenum. The sulfide scales formed on these alloys consist of two layers, comprising an outer chromium sulfide layer and an inner layer composed mainly of refractory metal sulfides. The formation of the refractory metal sulfide scales is responsible for the high sulfidation resistance to sulfide corrosion. Under the oxidation condition the Cr-Mo alloys are rapidly oxidized due to the formation of volatile molybdenum oxide. The oxidation of Cr-Nb alloys proceeds accompanying partial breakdown and the restoration of the scales, but the average oxidation rates are almost the same as their sulfidation rates. Consequently, the Cr-Nb alloys possess high resistance to both sulfidation and oxidation at high temperatures.

Does cholesterol discriminate between sphingomyelin and phosphatidylcholine in mixed monolayers containing both phospholipids?

The objective of this work was to examine the interaction of cholesterol with both phosphatidylcholines, 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC) or 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC), and sphingomyelins, N- oleoyl- d - sphingomyelin (O-SPM) or N- palmitoyl- d - sphingomyelin (P-SPM), in monolayers at an air/water interface. We used cholesterol oxidase to probe for the relative strength of sterol-phospholipid interaction, and fluorescence microscopy to visualize lateral domain formation in the mixed monolayers. The ternary mixed monolayers, which contained cholesterol, POPC, and O-SPM had a twofold higher average oxidation rate than the corresponding system containing DPPC and P-SPM. This difference in oxidation rate between saturated and unsaturated systems was observed irrespective of the ratio between phosphatidylcholine and sphingomyelin in the monolayer. With either the saturated or the unsaturated systems, however, the rate of oxidation was influenced by the ratio of phosphatidylcholine to sphingomyelin. As the monolayer content of phosphatidylcholine increased and the sphingomyelin content decreased correspondingly (to maintain a constant cholesterol-to-phospholipid molar ratio), an increase in the average oxidation rate was seen in both saturated and mono-unsaturated monolayer systems. The relationship between the rate of cholesterol oxidation and the phosphatidylcholine/sphingomyelin ratio was not linear, suggesting a preferential interaction of cholesterol with sphingomyelin even when phosphatidylcholine was present in the monolayer. The formation and stability of cholesterol-rich lateral (liquid-condensed) domains in the monolayers, as determined by monolayer fluorescence microscopy, was found to be highly influenced by the phospholipid class, the degree of acyl chain saturation, and by the ratio of phosphatidylcholine to sphingomyelin in the monolayer. The differences in cholesterol oxidation rates and lateral domain formation, as a function of the ratio of two phospholipids in the monolayers, apparently derived from differences in the hydrophobic interactions between the lipids.

ＳＯ２を含有する火力発電所排ガスからのＣＯ２の除去技術

For CO2 removal from flue gases containing SO2 at thermal power plants, secondary alkanolamine with high molecular weight (abb. HIA) was selected as an absorbent because of low utility consumption. SO2 forms sulfite salt in absorbent and it is oxidized with O2 to form the sulfate. These salts called Heat Stable Salts (HSS) reduce CO2 removal ratio. On the other hand, the sulfite consumes O2 in the absorbent and the resistance to oxidation of HIA can be expected. We estimated the relationship between concentration of HSS and CO2 removal ratio, and the resistance to oxidation of HIA absorbent by the presence of SO2 in treated gas. Based on these results, pilot testing (flue gas capacity: 1, 000 Nm3/h, CO2 removal ratio: 90%) was carried using coal oil mixture-fired power plant flue gas for continuous 2, 000 hours (accumulating time of 2, 441 h) to evaluate the resistance to oxidation and regeneration heat of HIA.Oxalic acid by oxidative degradation was accumulated 0.0095% after completion of pilot testing, and its amount was 0.1 times as low as that of LNG-fired flue gas. Furthermore, four kinds of cyclic amines were detected by GC-MS analyses and three of them were compounds by oxidative degradation. Their amounts of the mixture were spectrophotometrically determined to be 0.19% based on a reasonable assumption of the average molar absorptivity of the mixture. Average oxidation rate of the mixture was estimated 8.8x10-5%/h. This was 0.4% of the total loss of HIA.Regeneration heat of HIA was 20% as low as that of the conventional absorbent even in the case of accumulation of HSS up to 2% as the reduced concentration of H2SO4.

Potential aerobic methane oxidation in a Sphagnum-dominated peatland—Controlling factors and relation to methane emission

The potential aerobic methane oxidation (an estimate of the viable biomass of methane-oxidizing microorganisms) was assessed in various plant communities of a boreal, Sphagnum-dominated, mixed mire in Sweden. The relationships between potential oxidation and probable controlling environmental factors, such as water table depth, soil temperature and pore-water methane concentrations were also examined. Finally, the relationship between potential methane oxidation and the rate of net methane emission was evaluated. Potential methane oxidation ranged between 0.0 and 4.7 μg CH 4 g −1 wet peat h −1, and the areal estimates for the 0–40 cm depth interval ranged between 0.04 and 16 g CH 4 m −2 d −1. The depth of maximal potential oxidation was correlated with the depth of the water table ( r 2 = 0.64). Most communities showed a positive relationship between average rate of potential methane oxidation and water table depth ( r 2 = 0.66), i.e. the greater the vertical extension of aerated surface peat, the higher the methane oxidation capacity. In non-waterlogged communities (water table more than 5 cm below the vegetation surface), a positive correlation was found between the potential oxidation and methane concentration in peat pore-water ( r 2 = 0.44). These results suggest that the supplies of methane and oxygen largely control the biomass of methanotrophs across plant communities. Overall, net methane emission rates were negatively, but only weakly, correlated with the potential oxidation, suggesting that aerobic oxidation often controls emission rates from comparatively dry communities of Sphagnum peatlands, but that other factors also influence the emission.

Availability for enzyme-catalyzed oxidation of cholesterol in mixed monolayers containing both phosphatidylcholine and sphingomyelin

In this study we have examined the interaction between cholesterol and phospholipids in monolayers using cholesterol oxidase ( Streptomyces cinnamomeus) as a probe. Monolayers containing cholesterol and phospholipids in different molar ratios were exposed to cholesterol oxidase at a lateral surface pressure of 20 mN/m (at 30°C). The rate of cholesterol oxidation by cholesterol oxidase was faster in a monolayer consisting of a mono-unsaturated phospholipid (either 1-stearoyl-2-oleoyl- sn-glycero-3-phosphocholine (SOPC) or N-oleoyl-sphingomyelin (O-SPM)) and cholesterol than it was in a monolayer of a saturated phospholipid (either 1,2-distearoyl- sn-glycero-3-phosphocholine (DSPC) or N-stearoyl- sphingomyelin (S-SPM)) and cholesterol. This suggests that the susceptibility of cholesterol to oxidation by cholesterol oxidase was markedly affected by the phospholipid acyl chain composition. In addition, cholesterol was oxidized more readily in a phosphatidylcholine-containing monolayer as compared with a sphingomyelin monolayer (at a similar degree of acyl chain saturation). The average rate of oxidation, as a function of the cholesterol/phospholipid (C/PL) molar ratio in a binary monolayer (with cholesterol and one phospholipid class), was linear except for one discontinuity, at 1:1 for phosphatidylcholine monolayers (either SOPC or DSPC) and at 2:1 for sphingomyelin monolayers (O-SPM or S-SPM). We interpret these discontinuities as indicating the stoichiometry at which cholesterol can exist dispersed in the monolayer without lateral segregation into cholesterol-rich clusters. Next, ternary monolayers were examined (with cholesterol and one phosphatidylcholine and one sphingomyelin species). In ternary monolayers where sphingomyelin dominated (67 mol% sphingomyelin and 33 mol% phosphatidylcholine plus cholesterol) the stoichiometry was 2:1 irrespective of the acyl chain composition of the phospholipid species. In ternary monolayers where phosphatidylcholine dominated (67 mol% phosphatidylcholine and 33 mol⨿ sphingomyelin) the stoichiometry was 1:1 for monolayers containing SOPC/S-SPM, SOPC/O-SPM and DSPC/S-SPM but 2:1 for the system DSPC/O-SPM. A further titration of the DSPC/O-SPM system showed that the 2:1 stoichiometry changed to a 1:1 stoichiometry only when the O-SPM content decreased below 5 mol%. The observation that such a small amount

Pulsed‐Potential Oxidation of Methanol: I . Smooth Platinum Electrode with and without Tin Surface Modification

During the electrooxidation of methanol on platinum, an adsorbate poison forms which results in the rapid decay of the initially high current. The poison may be oxidatively removed to regenerate an active Pt surface, but only at a high anodic polarization at which a methanol fuel cell may not produce power. In this paper, an alternative strategy to steady‐state (DC) operation is studied as a means of improving the average methanol oxidation rate on a smooth Pt electrode. A periodic, rectangular waveform is potentiostatically applied alternating from a high anodic polarization of duration to a low anodic polarization of duration for a cycle time equal to . The potential is sufficiently anodic to oxidize the poison to form carbon dioxide; during the remainder of the cycle, the polarization is lowered to at which methanol oxidation occurs. A fixed value of was used (1.18 V), and the effects of , , and were studied. In addition, surface modification of the electrode with Sn in conjunction with the periodic control was examined. For both the unmodified and Sn‐modified Pt electrode, the current density exhibited a maximum with frequency at each . The time‐averaged methanol oxidation current density at was three orders‐of‐magnitude above the DC current of 9 μA/cm2 at the same voltage; at , a five orders‐of‐magnitude increase was found above a DC current of 0.03 μA/cm2. From conventional current‐voltage‐time and coulomb measurements, the most likely poison composition is . In the presence of Sn, the time‐averaged methanol oxidation current at was at best approximately a factor of 2 above that obtained in its absence using the same potential waveform.