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A laser ablation/ionization mass spectrometer system is described for the direct chemical analysis of solids. An Nd:YAG laser is used for ablation and ionization of the sample in a quadrupole ion trap operated in an ion-storage (IS) mode that is coupled with a reflectron time-of-flight mass spectrometer (TOF-MS). Single pulse experiments have demonstrated simultaneous detection of up to 14 elements present in glasses in the ppm range. However, detection of the components has produced non-stoichiometric results due to difference in ionization potentials and fractionation effects. Time-of-flight secondary ionization mass spectrometry (TOF-SIMS) was used to spatially map elemental species on the surface and provide further evidence of fractionation effects. Resolution (m/Δm) of 1500 and detection limits of approximately 10 pg have been achieved with a single laser pulse. The system configuration and related operating principles for accurately measuring low concentrations of isotopes are described.

The purpose of this project includes an experimental and modeling investigation into water and hydrated ion structure and transport at nanomaterials interfaces. This is a topic relevant to understanding the function of many biological systems such as aquaporins that efficiently shuttle water and ion channels that permit selective transport of specific ions across cell membranes. Carbon nanotubes (CNT) are model nanoscale, hydrophobic channels that can be functionalized, making them artificial analogs for these biological channels. This project investigates the microscopic properties of water such as water density distributions and dynamics within CNTs using Nuclear Magnetic Resonance (NMR) and the structure of hydrated ions at CNT interfaces via X-ray Absorption Spectroscopy (XAS). Another component of this work is molecular simulation, which can predict experimental measurables such as the proton relaxation times, chemical shifts, and can compute the electronic structure of CNTs. Some of the fundamental questions this work is addressing are: (1) what is the length scale below which nanoscale effects such as molecular ordering become important, (2) is there a relationship between molecular ordering and transport?, and (3) how do ions interact with CNT interfaces? These are questions of interest to the scientific community, but they also impact the futuremore » generation of sensors, filters, and other devices that operate on the nanometer length scale. To enable some of the proposed applications of CNTs as ion filtration media and electrolytic supercapacitors, a detailed knowledge of water and ion structure at CNT interfaces is critical.« less

To examine the role of Drosophila optomotor blind (omb)-related T-box genes in development of human and mouse retina.Mouse Tbx2, Tbx3, and Tbx5 and human TBX2 cDNAs were isolated from retinal cDNA libraries by hybridization to the Drosophila omb gene. Gene expression patterns in developing retina were analyzed by in situ hybridization.TBX2/Tbx2, TBX3/Tbx3, and TBX5/Tbx5 were expressed asymmetrically across the embryonic neural retina with highest levels of mRNA within dorsal and peripheral retina. The dorsoventral gradient of TBX2 expression disappeared before the ganglion cell layer (GCL) formed. Its expression then became restricted to the inner neuroblastic retina and later to the GCL and inner nuclear layer (INL). The dorsal expression domains of TBX5/Tbx5 and TBX3/Tbx3 were maintained during formation of the GCL. As the retina matured, TBX3/Tbx3 expression was restricted to the INL, and TBX5/Tbx5 was expressed within the GCL.The expression pattern of TBX2, TBX3, and TBX5 within the developing retina supports the idea that the encoded transcription factors play a role in providing positional information important for topographic mapping and in differentiation of distinct cell types across the laminar axis of the retina.

The near inevitable transfer of explosive particulate matter through fingerprints makes it possible to detect concealed explosives through surface sampling. Repeatable and well-characterized fingerprint simulation facilitates quantitative comparison between particulate sampling methods for subsequent detection of trace explosive residues. This study employs a simple, but reproducible sampling system to determine the accuracy of a fingerprint simulation. The sampling system uses a gas jet to entrain particles from a substrate and the resulting airborne particles are then aspirated onto a Teflon filter. A calibrated Barringer IonScan 400 ion mobility spectrometer was used to determine the mass of explosive material collected on the filter. The IonScan 400 was calibrated with known masses of 2,4,6-trinitrotoluene (TNT). The resulting calibration curve is in good agreement with that obtained by Garofolo et al. (1994) for an earlier model of the instrument. The collection efficiency of the sampling system was measured for three particle sizes (8.0. 10.0, and 13.0 microm) using spherical polystyrene particles laced with known quantities of TNT. Collection efficiency ranged from less than 1% for the larger particles to 5% for the smaller particles. Particle entrainment from the surface was monitored with dark field imaging of the remaining particles. The sampling system was then applied to two C4 test samples--a fingerprint transfer and a dry Teflon transfer. Over 100 ng of RDX was collected from the dry transfer sample, while less than 1 ng was collected from the fingerprint transfer. Possible explanations for this large difference are presented based on the system calibration.

Synopsis The origins and general characteristics of a very soft, sensitive, normally consolidated marine clay are described. The clay was formed in a sheltered location from restricted types of source material and could be expected to be more uniform than most shallow marine deposits, yet its properties show fairly large variations about a mean trend. Standard sampling methods provided satisfactory samples for compressibility tests but not for strength test. In situ vane tests and laboratory tests on samples obtained with a Swedish foil sampler gave equivalent undrained shear strength results. The clay has a small finite surface strength and strength incrcascs linearly with depth. The overall ratio of undrained shear strength to effective over-burden pressure is rather smaller than would be expected from the Atterberg limits. Une description est faite dcs origincs et des caractéristiques d'une argile marine normalement consolidée, très molle et sensible. L'argile a été formée dans un emplacement abrité à partir de types limités d'un matériau de base et l'on pouvait s'attendre à la trouver plus uniforme que la plupart des dépôts marins à peu de profondeur. mais ses propriétés présentent cependant des variations assez importantes par rapport à un type moyen. Les méthodes d'échantillonnage standard ont fourni des échantillons satisfaisants pour des épreuves de compressibilité mais pas pour des épreuves de résistance. Des essais sur place avec palettes et des essais de laboratoire sur des échantillons obtenus à l'aide d'un échantillonneur enfeuilles suédois ont donné des résultats équivalents de résistance au cisaillement à teneur en eau constante. L'argile possède une petite résistance superficielle finie et sa résistance augmente linéairement avec la profondeur. Le rapport total de la résistance au cisaillement à teneur en eau constante à la pression de surcharge effective est plutôt plus petit que l'on pourrait s'y attendre d'après les limites d'Atterberg.