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«Strengthening the Nation through Diversity, Innovation & Leadership in STEM San Antonio,Texas · October 3-6, 2013 Get Connected! Connect with the ...»

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1 Over 100 years has passed since the development of one of the most fundamental tests in statistics: the Student t-test. Subjective Bayesian approaches for the Student t-test are common, while objective Bayesian procedures are still needed. In this research, we argue that the Bayesian t-test, based on conjugate priors, is inconsistent and strongly subjective. We propose objective procedures that are consistent: Bayesian information criterion (BIC), Zellner and Siow’s conventional approach, modified Jeffreys’ prior, intrinsic priors, and Berger robust priors (referred to here as robust priors). We test this procedure in the case of strongly unbalanced samples. Classifying two sets of Bayes factors, BIC and Zellner and Siow, depends on the t-statistics and the sample size n. Jeffreys’ prior, intrinsic, conjugate, and robust approaches depend on the t-statistics, n and the term nδ = n1 n2/(n1 + n2). We argue that the second set of Bayes factors are better suited for unbalanced problems, acknowledging that the conjugate Bayes factor has problems of its own. Jeffreys, intrinsic, and robust Bayes factors all have the same qualitative behavior and are close to each other for moderate to large sample sizes. For small sample sizes, the robust Bayes factor has the edge because it is the only one that is in closed form. Choosing the right version of objective Bayes factor is critical for scientists and will allow them to use them in a more efficient and frequent way.

Room 205

DEVELOPING AN ESTIMATOR FOR FISHERY WITHDRAWALS BY THE FOR-HIRE RECREATIONAL SECTOR IN

THE GULF OF MEXICO

Vianey Leos Barajas, Mark Kaiser.

Iowa State University, Ames, IA.

The Gulf of Mexico supports the largest recreational fisheries in the country in terms of economic value, total effort, and contributions to total fisheries removals. In 2006, the National Research Council recognized that, in the Gulf of Mexico, the magnitude of the for-hire sector and the potential scale for fishery removals warrant the use of mandatory logbooks as the source of catch and effort data. We developed an estimator τ = NκΨ, where N represents total trips taken, κ is the expected effort per trip, and Ψ is the expected catch per unit effort, for estimation of total catch during any given time period, as long as there is sufficient fishing activity. Effort is defined as the fishing hours multiplied by the number of anglers per trip, and catch is one of four types of fishery removals: harvest, release 120 ft, release 120 ft, and mortality. We take a Bayesian approach to the estimation of τ by obtaining a posterior distribution via a combination of direct sampling from known distributions and Markov chain Monte Carlo methods. Through this approach, uncertainty is automatically captured in the quantiles of the posterior distribution. Red snapper data is used to demonstrate the uses of the estimator τ and the usefulness of logbook report data when compared to data obtained through more expensive sampling methods.

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ATMOSPHERIC SCIENCES/METEOROLOGY

Room 213B

AEROSOL DISCRIMINATION THROUGH THE POLARIZATION OF SCATTERED LIGHT

Patricio Piedra, Patrick Hamill.

San Jose State University, San Jose, CA.

Despite considerable efforts by many atmospheric scientists, distinguishing between types of aerosols in Earth’s atmosphere is still a big issue. Current techniques for aerosol discrimination through light scattering are based on statistical clustering by optical characteristics. These methodologies often depend on the geographic location of the observations. For example, aerosols with optical characteristics similar to those of Mexico City are grouped into aerosols of type urban-industrial. In contrast, the degree of linear polarization (DLP) is extremely sensitive to the particular characteristics of the scattered particle and constitutes a more accurate method. Hansen, who used DLP to determine the characteristics of the particles of the atmosphere of Venus in 1973, demonstrated this fact. With this motivation, a similar theoretical analysis is being attempted to identify the physical characteristics of Earth’s aerosols.

The study focuses on inferring the DLP as a function of the angle of scattering for aerosols interacting with sunlight.

A computer program has been developed and performs Mie scattering calculations to determine the parallel and perpendicular components of the electric field of scattered light. In addition, the program allows for any continuous particle size distribution and outputs the DLP as a function of the angle of scattering. The relationship between the DLP and the angle of scattering is distinctive for each particle size distribution and effective size parameter. The implementation of linear polarization methods allows the identification of aerosol types. The DLP method establishes the particle size distribution and index of refraction as the main physical basis for discrimination between aerosols.

CHEMISTRY (EXCEPT BIOCHEMISTRY)

Room 206A

ARTIFICIAL PHOTOSYNTHESIS SYSTEM FOR WATER OXIDATION BASED ON ETS-SUPPORTED COBALT

CLUSTERS Joselyn Del Pilar-Albaladejo, Prabir Dutta.

Ohio State University, Columbus, OH.





Solar-driven, artificial photosynthetic systems promise to be a viable alternative for H2 production as fuel. Three elements are essential for artificial photosynthetic systems: membrane, photosensitizer, and catalyst. In our current work, we have successfully created zeolite-supported cobalt clusters of 200 nm for water oxidation, which is known to be the most challenging reaction in water splitting. Oxygen evolution was tested in the presence of photochemically generated Ru(bpy)33+ at pH 6. Organic photosensitizers for light harvesting, such as Ru(bpy)33+, are susceptible to degradation, and this presents a major drawback for artificial photosynthetic systems. ETS-10 is a microporous titanosilicate that contains O-Ti-O-Ti- chains surround by insulating SiO2 layers that allow quantum confinement of electrons and holes, which leads to interesting optical properties. As zeolites, they also have ion-exchanging properties and are thermally stable, which makes them ideal for catalyst deposition. ETS-10 has a band gap of 4.03 eV that can be moved to lower energies by partial substitution of oxygen by nitrogen. The tunable optical properties of ETS-10 make it an ideal material for solar light harvesting and charge transport. We propose to couple the cobalt clusters with nitrated ETS-10 and examine their water oxidation properties using silver ions as electron acceptors.

Eventually, the goal is to assemble a visible-light absorbing ETS-10 membrane that allows light harvesting and charge separation with the opposite sides of the membrane hosting water oxidation (cobalt based) and reduction (initially Pt) catalysts for water splitting.

358 ORAL ABSTRACTS

Room 217A

ELECTROCHEMICAL DNA-BASED SENSORS FOR ATP MONITORING IN THE BRAIN

Melissa E Davila Morris, Samiullah Wagan, James Taylor, Ryan White.

University of Maryland, College Park, MD.

Recent studies have demonstrated that nonneuronal cells in the brain, or glial cells, play a much more active role in central nervous system function than was previously thought. For example, recent reports demonstrate that dynamic interactions between astrocytes (a type of glia) and neurons play a crucial role in dendritic formation and the development of abnormalities in the developmental disorder known as fragile-X syndrome. Astrocytes achieve this through the release of specific chemical messengers known as gliotransmitters. In this study, we developed an electrochemical, aptamer-based (E-AB) sensor to monitor adenosine triphosphate (ATP), a known gliotransmitter.

E-AB sensors are specific, selective, and sensitive. They are capable of detecting target analytes even in the most challenging complex matrices (e.g., cerebral spinal fluid). The ATP E-AB sensor comprises an electrode-bound DNA aptamer that specifically binds ATP and is modified at the distal end with a redox marker for electrochemical interrogation. Here we demonstrate the fabrication and characterization of these sensors as microcylinder electrodes (50 μm diameter) suitable for monitoring in real time the release of ATP directly in the brain.

Room 206A

A NOVEL MODULAR SCAFFOLD FOR CYSTEINE-DERIVED LIPID ANALOGUES AS TISSUE TARGETING

LIGANDS IN LIPOSOME FORMULATIONS

Magaly Salinas1, Idaira Hueso-Falcon2, Adelphe Mfuh1, Shaunak Pandya1, C. Mauli Agrawal1, George R. Negrete1.

University of Texas at San Antonio, San Antonio, TX, 2Instituto Universitario de Bio-Orgánica Antonio González, 1 Universidad de La Laguna, Tenerife, ES.

Lipopeptides are biologically active compounds that constitute a promising family for future antibiotics and as anchored ligands for directing liposomes to target tissues. A novel class of lipid analogues was developed from L-cysteine via cyclocondensation with m-nitrobenzaldehyde and acylation with acryloyl chloride yielding a trifunctionalized thiazolidine core with carboxylic acid, aryl nitro, and acryloyl substituents. The core can be used to generate an array of compounds in a highly modular process with hydrophobic units, ligand units for binding to target tissues, and fluorophores for binding and localization studies. The fatty component of the cysteine-derived lipid analogue (CLA) is appended via conjugate addition of thiol analogues to the acrylamide functionality of the core. The amino terminus of a linker is connected at the carboxylate end of the thiazolidine via carbodiimide coupling chemistry. Subsequently, a peptide ligand is coupled to the carboxylate end of the attached linker. Reduction of the aryl nitro group to the corresponding amine allows the attachment of a fluorophore for diagnostic techniques. We will demonstrate the use of these novel targeting CLAs in various liposomal formulations to improve drug delivery and binding affinity for αvβ3 integrin receptors that are over-expressed on human cancer cells. (Partially funded by NIGMS MBRS-RISE GM060655.) Room 206A

SYNTHESIS OF AG PD/PT CORE-SHELL MULTIPLY TWINNED NANOPARTICLES AND THEIR ATOMIC

RESOLUTION IMAGING BY USING CS-CORRECTED SCANNING TRANSMISSION ELECTRON MICROSCOPY

Subarna Khanal, Nabraj Bhattarai, J.Jesus Velazquez-Salazar, Daniel Bahena, Arturo Ponce, Miguel Yacaman.

University of Texas at San Antonio, San Antonio, TX.

The synthesis of noble metal (e.g., Pd, Pt, Au, and Ag) nanoparticles with controlled atomic distributions has attracted significant interest due to their size-tunable properties, which depend on the variation of composition and structure.

Recently, multimetallic nanoparticles have attracted extensive research attention because of their diverse potential applications as compared to monometallic nanoparticles. Controlling the morphology of nanostructures can provide a great opportunity to stimulate their possible applications by tuning their catalytic, electronic, and optical properties and enhancing their reactivity, selectivity, and stability. AgPd/Pt core-shell trimetallic nanocrystals with multiply twinned Graduate

–  –  –

atoms on the (111) surfaces are expected to be the most active catalysts with many applications in fuel cells. In this work, we have successfully synthesized AgPd/Pt core-shell multiply twinned particles with icosahedral morphology.

Cs-corrected scanning transmission electron microscopy in combination with high angle annular dark field (HAADF), bright field (BF) and energy dispersive X-ray spectroscopy (EDS) detectors allowed us to probe the structure of these nanoparticles at the atomic level revealing the core and the shell regions. The core is AgPd alloy, and the shell is Pt.

–  –  –

Moreover, the line profile of the EDS analysis reveals the elemental composition of these nanostructures and confirms the structures are core-shell, which is expected to be the most active catalysts.

Room 214B

ISOMERASE ACTIVITY OF CANDIDA RUGOSA LIPASE IN CONVERSION OF RACEMIC PROFENS TO (S)PROFENS

Saideh Mortazavi, James Salvador.

University of Texas at El Paso, El Paso, TX.

Profens are sold as racemic mixtures where the (S)-enantiomer has the desired effect and the (R)-enantiomer may have harmful side effects. Thus the efficacy of profens can be improved and side effects reduced by isolating (S)profen as opposed to consuming its racemic mixture. We propose a new method to convert racemic profens to (S)profens using inexpensive chemicals and enzymatic methods, whereas previous methods wasted the undesired (R)-profens. The Candida rugosa lipase (CRL)-catalyzed dynamic kinetic resolution (DKR) of ibuprofen methyl ester (IME) was optimized to convert racemic ibuprofen to (S)-ibuprofen in 3 days. The best concentration of various buffers for these reactions was found to be 0.5 M at pH 7.6. The commercial lipase mixture was found to be acidic due to the lowered pH on the enzyme addition to the reaction flask. Dimethylformamide (DMF) was determined to be a better cosolvent than dimethylsulfoxide (DMSO) as it maintained the reaction pH, with evidence of the latter functioning as an oxidizing agent because of the lowered reaction pH. Lower concentrations of IME and higher stirring rates both led to faster conversions. The minimal amount of lipase needed was determined to be 20 mg/ml buffer, facilitating a much easier workup. Attempts to racemize the (R)-ibuprofen methyl ester with the same reaction conditions as DKR, excluding CRL, led to no racemization, which indicates that enolization and racemization of (R)-IME is catalyzed by CRL enzyme. To our knowledge, no one has reported that the enolization is enzymatic and not purely chemical.

Room 206A

PROFILING ENOXAPARIN SEC FRACTIONS BY PROBING FOR 3-O-SULFO OLIGOSACCHARIDES USING [1H,

15N] HSQC NMR Consuelo N. Beecher, Derek J. Langeslay, Kemal Solakyildirim, Cynthia K. Larive.

University of California, Riverside, Riverside, CA.



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