Laboratory Studies of Heterogeneous Chemistry

A high vacuum Knudsen flow reactor was used to determine the reactive uptake coefficient, γ, of isoprene on sulfuric acid films as a function of sulfuric acid weight percent, temperature, and relative humidity. No discernible dependence was observed for γ over the range of temperatures (220 − 265 K) and pressures (10−7 Torr -10−4 Torr) studied. However, the uptake coefficient increased with increased sulfuric acid concentration between the range of 78 wt % (γi 10−4) and 93 wt % (γi 10−3). In addition to the Knudsen Cell, a bulk study was conducted between 60 and 85 wt % H2SO4 to quantify uptake at lower acid concentrations and to determine reaction products. After exposing sulfuric acid to gaseous isoprene the condensed phase products were extracted and analyzed using gas chromatography/mass spectrometry (GC/MS). Isoprene was observed to polymerize in the sulfuric acid and form yellow/red colored monoterpenes and cyclic sesquiterpenes. Finally, addition of water to the 85 wt % sulfuric acid/isoprene product mixture released these terpenes from the condensed phase into the gas phase. Together these experiments imply that direct isoprene uptake will not produce significant SOA; however, terpene production from the small uptake may be relevant for ultrafine particles and could affect growth and nucleation. Several laboratory and field studies have suggested that the simple aldehyde glyoxal could be a significant source of secondary organic aerosol (SOA) in the lower troposphere. However, recent studies have found that particles in the upper troposphere also contain significant amounts of organic material, with average organic mass fractions as high as 70%. We have examined whether glyoxal could be a source of SOA in the upper troposphere. The uptake of glyoxal to aerosols generally requires the presence of liquid water. Aerosols in the upper troposphere that could have supercooled liquid on the surface are cirrus ice and particles containing hygroscopic organic material. Several studies indicate cirrus ice may be coated with supercooled liquid HNO3/H2O. Thus we have utilized a high vacuum Knudsen Cell to measure the uptake of glyoxal on ice exposed to nitric acid at temperatures and pressures relevant to the upper troposphere. Here we present kinetic and spectroscopic data that indicates uptake of glyoxal is efficient on these films and irreversible. Spectroscopic data indicates the glyoxal is oxidized to glyoxylic acid, and the presence of glyoxylic acid has been confirmed via derivatization of the products followed by gas chromatography mass spectrometry. We have used the glyoxylic acid products from the ice experiments to test whether hygroscopic organic material exposed to water and nitric vapour would also uptake glyoxal. We have found that the uptake of glyoxal and oxidation to glyoxylic acid occurs in the presence of supercooled HNO3/H2O liquid on glyoxylic acid even at water pressures below the saturation pressure of ice. The critical saturation ratio required for heterogeneous nucleation of ice was studied on ammonium nitrate films in the presence of nitric acid. Under these conditions deliquescence of the particles was not observed; however, prior to deliquescence the uptake of H2O was observed. Fourier transform infrared reflectance absorbance spectroscopy (FTIR-RAS) indicates the water absorbed water is liquid like in nature, and the film exists as a mixed solid/liquid phase prior to ice nucleation. The films were observed to freeze prior to the predicted saturation ratio for homogeneous freezing. At temperatures lower than 200 K and nitric acid pressures greater than 10-7 Torr, nitric acid trihydrate (NAT) nucleation was observed if the saturation ratio was held below the critical saturation ratio for heterogeneous ice nucleation. The growth rate of the NAT and ice films was measured under similar conditions. NAT growth is considerably slower, and laboratory evidence indicates the growth is regulated by the pressure of nitric acid. The critical saturation ratio for ice nucleation on NAT was determined to be higher than the mixed phase films, and approached the ratio required to nucleate ice on the hydrophobic gold surface

DECISION SUPPORT TOOL FOR RETIREMENT PLANNING

In this research, a Microsoft Excel retirement planning decision support tool is developed to help Marine Corps Officers visualize their own time horizon to achieve retirement. Basic and advanced features allow individuals to adjust all of the variables within the tool to represent their unique financial retirement goals. The decision support tool will also help eligible Marine Corps Officers to choose between the Legacy Retirement System and Blended Retirement System, by understanding each retirement plan and calculating which plan would provide more financial benefit.http://hdl.handle.net/10945/60381Outstanding ThesisCaptain, United States Marine CorpsApproved for public release; distribution is unlimited

Identification of Residues that Specify Substrate Binding in the Aldo-Keto Reductase, YDL124w

This presentation was given at the ACS National Meeting

2012 Update to the 2005 Town of Middletown Comprehensive Plan

This document is an update to the 2005 Town of Middletown Comprehensive Plan and serves as a guide for Middletown’s land use decisions and annexation policy. It also serves as a consolidated reference containing demographic, housing, economic, environmental, and historical information about Middletown.Town of Middletow

Volatile element evolution of chondrules through time

International audienceChondrites and their main components, chondrules, are our guides into the evolution of the Solar System. Investigating the history of chondrules, including their volatile element history and the prevailing conditions of their formation, has implications not only for the understanding of chondrule formation and evolution but for that of larger bodies such as the terrestrial planets. Here we have determined the bulk chemical composition-rare earth, refrac-tory, main group, and volatile element contents-of a suite of chon-drules previously dated using the Pb−Pb system. The volatile element contents of chondrules increase with time from ∼1 My after Solar System formation, likely the result of mixing with a volatile-enriched component during chondrule recycling. Variations in the Mn/Na ratios signify changes in redox conditions over time, suggestive of decoupled oxygen and volatile element fugacities, and indicating a decrease in oxygen fugacity and a relative increase in the fugacities of in-fluxing volatiles with time. Within the context of terrestrial planet formation via pebble accretion, these observations corroborate the early formation of Mars under relatively oxidizing conditions and the protracted growth of Earth under more reducing conditions, and further suggest that water and volatile elements in the inner Solar System may not have arrived pairwise

Parallel Discovery Strategies Provide a Basis for Riboswitch Ligand Design.

Riboswitches are mRNA domains that make gene-regulatory decisions upon binding their cognate ligands. Bacterial riboswitches that specifically recognize 5-aminoimidazole-4-carboxamide riboside 5'-monophosphate (ZMP) and 5'-triphosphate (ZTP) regulate genes involved in folate and purine metabolism. Now, we have developed synthetic ligands targeting ZTP riboswitches by replacing the sugar-phosphate moiety of ZMP with various functional groups, including simple heterocycles. Despite losing hydrogen bonds from ZMP, these analogs bind ZTP riboswitches with similar affinities as the natural ligand, and activate transcription more strongly than ZMP in vitro. The most active ligand stimulates gene expression ~3 times more than ZMP in a live Escherichia coli reporter. Co-crystal structures of the Fusobacterium ulcerans ZTP riboswitch bound to synthetic ligands suggest stacking of their pyridine moieties on a conserved RNA nucleobase primarily determines their higher activity. Altogether, these findings guide future design of improved riboswitch activators, and yield insights into how RNA-targeted ligand discovery may proceed

Differential regulation of synaptic and extrasynaptic α4 GABA(A) receptor populations by protein kinase A and protein kinase C in cultured cortical neurons

The GABA(A) α4 subunit exists in two distinct populations of GABA(A) receptors. Synaptic GABA(A) α4 receptors are localized at the synapse and mediate phasic inhibitory neurotransmission, while extrasynaptic GABA(A) receptors are located outside of the synapse and mediate tonic inhibitory transmission. These receptors have distinct pharmacological and biophysical properties that contribute to interest in how these different subtypes are regulated under physiological and pathological states. We utilized subcellular fractionation procedures to separate these populations of receptors in order to investigate their regulation by protein kinases in cortical cultured neurons. Protein kinase A (PKA) activation decreases synaptic α4 expression while protein kinase C (PKC) activation increases α4 subunit expression, and these effects are associated with increased β3 S408/409 or γ2 S327 phosphorylation respectively. In contrast, PKA activation increases extrasynaptic α4 and δ subunit expression, while PKC activation has no effect. Our findings suggest synaptic and extrasynaptic GABA(A) α4 subunit expression can be modulated by PKA to inform the development of more specific therapeutics for neurological diseases that involve deficits in GABAergic transmission

Pb evolution in the Martian mantle

The initial Pb compositions of one enriched shergottite, one intermediate shergottite, two depleted shergottites, and Nakhla have been measured by Secondary Ion Mass Spectrometry (SIMS). These values, in addition to data from previous studies using an identical analytical method performed on three enriched shergottites, ALH 84001, and Chassigny, are used to construct a unified and internally consistent model for the differentiation history of the Martian mantle and crystallization ages for Martian meteorites. The differentiation history of the shergottites and Nakhla/Chassigny are fundamentally different, which is in agreement with short-lived radiogenic isotope systematics. The initial Pb compositions of Nakhla/Chassigny are best explained by the late addition of a Pb-enriched component with a primitive, non-radiogenic composition. In contrast, the Pb isotopic compositions of the shergottite group indicate a relatively simple evolutionary history of the Martian mantle that can be modeled based on recent results from the Sm–Nd system. The shergottites have been linked to a single mantle differentiation event at 4504 Ma. Thus, the shergottite Pb isotopic model here reflects a two-stage history 1) pre-silicate differentiation (4504 Ma) and 2) post-silicate differentiation to the age of eruption (as determined by concordant radiogenic isochron ages). The μ-values (238U/204Pb) obtained for these two different stages of Pb growth are μ1 of 1.8 and a range of μ2 from 1.4–4.7, respectively. The μ1-value of 1.8 is in broad agreement with enstatite and ordinary chondrites and that proposed for proto Earth, suggesting this is the initial μ-value for inner Solar System bodies. When plotted against other source radiogenic isotopic variables (Sri, γ187Os, ε143Nd, and ε176Hf), the second stage mantle evolution range in observed mantle μ-values display excellent linear correlations (r2 > 0.85) and represent a spectrum of Martian mantle mixing-end members (depleted, intermediate, enriched)