10,629 research outputs found
Chemical characteristics of air from different source regions during the second Pacific Exploratory Mission in the Tropics (PEM-Tropics B)
Ten-day backward trajectories are used to determine the origins of air parcels arriving at locations of airborne DC-8 chemical measurements during NASA's second Pacific Exploratory Mission in the Tropics B that was conducted during February-April 1999. Chemical data at sites where the trajectories had a common geographical origin and transport history are grouped together, and statistical measures of chemical characteristics are computed. Temporal changes in potential temperature are used to determine whether trajectories experienced a significant convective influence during the 10-day period. Trajectories describing the aged marine Southern Hemispheric category remain over the South Pacific Ocean during the 10-day period, and their corresponding chemical signature indicates very clean air. The category aged marine air in the Northern Hemisphere is found to be somewhat dirtier. Subdividing its trajectories based on the direction from which the air had traveled is found to be important in explaining the various chemical signatures. Similarly, long-range northern hemispheric trajectories passing over Asia are subdivided depending on whether they had followed a mostly zonal path, had originated near the Indian Ocean, or had originated near Central or South America and subsequently experienced a stratospheric influence. Results show that the chemical signatures of these subcategories are different from each other. The chemical signature of the southern hemispheric long-range transport category apparently exhibits the effects of pollution from Australia, southern Africa, and South America. Parcels originating over Central and northern South America are found to contain the strongest pollution signature of all categories, due to biomass burning and other sources. The convective category exhibits enhanced values of nitrogen species, probably due to emissions from lightning associated with the convection. Values of various species, including peroxides and acids, confirm that parcels were influenced by the removal of soluble gas and particle species due to precipitation. Finally, current results are compared with those from the first PEM-Tropics mission that was conducted in the same region during the southern hemispheric dry season (August-October 1996) when extensive biomass burning occurred. Results show that air samples during PEM-Tropics B are considerably cleaner than those of its dry season counterpart. Copyright 2001 by the American Geophysical Union
Investigation of the phase behaviour of the 1: 1 adduct of mesitylene and hexafluorobenzene
Variable temperature X-ray diffraction has been used to probe the structure and dynamics of the solid adducts of 1,3,5-trimethylbenzene (mesitylene) and hexafluorobenzene. PXRD patterns and DSC traces of near equimolar mixtures reveal two solid-state phase-transitions at 179.2 K and 111.0 K. The crystal structures of all three solid phases of this material have been solved by SXD. In contrast to previous studies on the adduct benzene–hexafluorobenzene, there is pairing of the mesitylene and hexafluorobenzene molecules in all three phases, each consisting of close-packed parallel columns of alternating C6H3(CH3)3 and C6F6 molecules packed face to face in a staggered conformation. Differences in structure between the phases illustrate the subtle interplay of quadrupole versus bond-dipole electrostatic interactions
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Analysis of the atmospheric distribution, sources, and sinks of oxygenated volatile organic chemicals based on measurements over the Pacific during TRACE-P
Airborne measurements of a large number of oxygenated volatile organic chemicals (OVOC) were carried out in the Pacific troposphere (0.1 - 12 km) in winter/spring of 2001 (24 February to 10 April). Specifically, these measurements included acetone (CH3COCHA3), methylethyl ketone (CH3COC2H5, MEK), methanol (CH3OH), ethanol (C2H5OH), acetaldehyde (CH3CHO), propionaldehyde C2H 5CHO), peroxyacylnitrates (PANs) (CnH 2n+1COO2NO2), and organic nitrates (CnH2n+1ONO2). Complementary measurements of formaldehyde (HCHO), methyl hydroperoxide (CH 3OOH), and selected tracers were also available. OVOC were abundant in the clean troposphere and were greatly enhanced in the outflow regions from Asia. Background mixing ratios were typically highest in the lower troposphere and declined toward the upper troposphere and the lowermost stratosphere. Their total abundance (ΣOVOC) was nearly twice that of nonmethane hydrocarbons (Σ C2-C8 NMHC. Throughout the troposphere, the OH reactivity of OVOC is comparable to that of methane and far exceeds that of NMHC. A comparison of these data with western Pacific observations collected some 7 years earlier (February-March 1994) did not reveal significant differences. Mixing ratios of OVOC were strongly correlated with each other as well as with tracers of fossil and biomass/biofuel combustion. Analysis of the relative enhancement of selected OVOC with respect to CH 3Cl and CO in 12 plumes originating from fires and sampled in the free troposphere (3-11 km) is used to assess their primary and secondary emissions from biomass combustion. The composition of these plumes also indicates a large shift of reactive nitrogen into the PAN reservoir thereby limiting ozone formation. A three-dimensional global model that uses state of the art chemistry and source information is used to compare measured and simulated mixing ratios of selected OVOC. While there is reasonable agreement in many cases, measured aldehyde concentrations are significantly larger than predicted. At their observed levels, acetaldehyde mixing ratios are shown to be an important source of HCHO (and HOx) and PAN in the troposphere. On the basis of presently known chemistry, measured mixing ratios of aldehydes and PANs are mutually incompatible. We provide rough estimates of the global sources of several OVOC and conclude that collectively these are extremely large (150-500 Tg C yr-1) but remain poorly quantified. Copyright 2004 by the American Geophysical Union
Combined Effects of Nanoroughness and Ions Produced by Electrodeposition of Mesoporous Bioglass Nanoparticle for Bone Regeneration
Providing appropriate biophysical and biochemical cues to the interface is a facile strategy to enhance the osteogenic ability of metallic implants. Here we exploited this through the incorporation of mesoporous bioactive glass nanoparticles (MBGN) at a high content (1:1 by weight) to a biopolymer chitosan in the electrodeposition process of titanium. The MGBN/chitosan layer thickness, tunable by electrodeposition parameters, exhibited an accelerated ability of apatite mineral induction in a body simulating medium. Of note, the involvement of MBGN could generate nanoscale roughness in a unique range of 10-25 nm. Moreover, the layer showed a slowly releasing profile of ions (calcium and silicate) over weeks at therapeutically relevant doses. The ion-releasing nanotopological surface was demonstrated to alter the preosteoblasts responses in a way favorable for osteogenic differentiation. The combinatory cues of nanotopology (25 nm roughness) and ion release enabled highly accelerated cellular anchorage with somewhat limited spreading area at initial periods. The subsequent osteoblastic differentiation behaviors on the engineered surface, as examined up to 21 days, showed significantly enhanced alkaline phosphate activity and up-regulated expression of bone-associated genes (ALP, Col I, OPN, and OCN). These results indicate that the combinatory cues provided by nanotopology (25 nm roughness) and ions released from MBGN are highly effective in stimulating osteoblastic differentiation and suggest that the MBGN/chitosan may serve as a potential composition for bone implant coatings
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OH and HO2 chemistry in the North Atlantic free troposphere
Interactions between atmospheric hydrogen oxides and aircraft nitrogen oxides determine the impact of aircraft exhaust on atmospheric chemistry. To study these interactions, the Subsonic Assessment: Ozone and Nitrogen Oxide Experiment (SONEX) assembled the most complete measurement complement to date for studying HO(x) (OH and HO2) chemistry in the free troposphere. Observed and modeled HO(x) agree on average to within experimental uncertainties (±40%). However, significant discrepancies occur as a function of NO and at solar zenith angles >70°. Some discrepancies appear to be removed by model adjustments to HO(x)-NO(x) chemistry, particularly by reducing HO2NO2 (PNA) and by including heterogeneous reactions on aerosols and cirrus clouds
Seasonal differences in the photochemistry of the South Pacific: A comparison of observations and model results from PEM-Tropics A and B
A time-dependent photochemical box model is used to examine the photochemistry of the equatorial and southern subtropical Pacific troposphere with aircraft data obtained during two distinct seasons: the Pacific Exploratory Mission-Tropics A (PEM-Tropics A) field campaign in September and October of 1996 and the Pacific Exploratory Mission-Tropics B (PEM-Tropics B) campaign in March and April of 1999. Model-predicted values were compared to observations for selected species (e.g., NO2, OH, HO2) with generally good agreement. Predicted values of HO2 were larger than those observed in the upper troposphere, in contrast to previous studies which show a general underprediction of HO2 at upper altitudes. Some characteristics of the budgets of HOx, NOx, and peroxides are discussed. The integrated net tendency for O3 is negative over the remote Pacific during both seasons, with gross formation equal to no more than half of the gross destruction. This suggests that a continual supply of O3 into the Pacific region throughout the year must exist in order to maintain O3 levels. Integrated net tendencies for equatorial O3 showed a seasonality, with a net loss of 1.06×1011 molecules cm-2 s-1 during PEM-Tropics B (March) increasing by 50% to 1.60×1011 molecules cm-2 s-1 during PEM-Tropics A (September). The seasonality over the southern subtropical Pacific was somewhat lower, with losses of 1.21×1011 molecules cm-2 s-1 during PEM-Tropics B (March) increasing by 25% to 1.51×1011 molecules cm-2 s-1 during PEM-Tropics A (September). While the larger net losses during PEM-Tropics A were primarily driven by higher concentrations of O3, the ability of the subtropical atmosphere to destroy O3 was ∼30% less effective during the PEM-Tropics A (September) campaign due to a drier atmosphere and higher overhead O3 column amounts. Copyright 2001 by the American Geophysical Union
Activation of SGK1 in endometrial epithelial cells in response to PI3K/AKT inhibition impairs embryo implantation
Background: Serum & Glucocorticoid Regulated Kinase 1 (SGK1) plays a fundamental role in ion and solute transport processes in epithelia. In the endometrium, down-regulation of SGK1 during the window of receptivity facilitates embryo implantation whereas expression of a constitutively active mutant in the murine uterus blocks implantation. Methods/Results: Here, we report that treatment of endometrial epithelial cells with specific inhibitors of the phosphoinositide 3-kinase (PI3K)/AKT activity pathway results in reciprocal activation of SGK1. Flushing of the uterine lumen of mice with a cell permeable, substrate competitive phosphatidylinositol analogue that inhibits AKT activation (AKT inhibitor III) resulted in Sgk1 phosphorylation, down-regulation of the E3 ubiquitin-protein ligase Nedd4-2, and increased expression of epithelial Na+ channels (ENaC). Furthermore, exposure of the uterine lumen to AKT inhibitor III prior to embryo transfer induced a spectrum of early pregnancy defects, ranging from implantation failure to aberrant spacing of implantation sites. Conclusion: Taken together, our data indicate that the balanced activities of two related serine/threonine kinases, AKT and SGK1, critically govern the implantation process
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