Development of TPS flight test and operational instrumentation

Thermal and flow sensor instrumentation was developed for use as an integral part of the space shuttle orbiter reusable thermal protection system. The effort was performed in three tasks: a study to determine the optimum instruments and instrument installations for the space shuttle orbiter RSI and RCC TPS; tests and/or analysis to determine the instrument installations to minimize measurement errors; and analysis using data from the test program for comparison to analytical methods. A detailed review of existing state of the art instrumentation in industry was performed to determine the baseline for the departure of the research effort. From this information, detailed criteria for thermal protection system instrumentation were developed

Transient terahertz spectroscopy of excitons and unbound carriers in quasi two-dimensional electron-hole gases

We report a comprehensive experimental study and detailed model analysis of the terahertz dielectric response and density kinetics of excitons and unbound electron-hole pairs in GaAs quantum wells. A compact expression is given, in absolute units, for the complex-valued terahertz dielectric function of intra-excitonic transitions between the 1s and higher-energy exciton and continuum levels. It closely describes the terahertz spectra of resonantly generated excitons. Exciton ionization and formation are further explored, where the terahertz response exhibits both intra-excitonic and Drude features. Utilizing a two-component dielectric function, we derive the underlying exciton and unbound pair densities. In the ionized state, excellent agreement is found with the Saha thermodynamic equilibrium, which provides experimental verification of the two-component analysis and density scaling. During exciton formation, in turn, the pair kinetics is quantitatively described by a Saha equilibrium that follows the carrier cooling dynamics. The terahertz-derived kinetics is, moreover, consistent with time-resolved luminescence measured for comparison. Our study establishes a basis for tracking pair densities via transient terahertz spectroscopy of photoexcited quasi-two-dimensional electron-hole gases.Comment: 14 pages, 8 figures, final versio

Elimination of TFA-Mediated Cleavage in Distributed Drug Discovery

Distributed Drug Discovery (D3) is a multi-disciplinary approach to the discovery of new drugs, which target neglected diseases or conditions common to developing-world countries. As part of a continuing effort to improve D3 methodology, two approaches for eliminating the final step TFA-mediated resin cleavage are proposed for investigation. Cleavage under basic conditions (saponification) and mild acid conditions (dilute HCl/hexafluoroisopropanol or dilute HCl/trifluoroethanol) represent improvements in safety and convenience to the undergraduate student researcher. Previous studies have shown that saponification provides yields comparable to the traditional TFA cleavage but recovery is not as convenient. Further improvements in the saponification workup will be evaluated by analyzing the effectiveness of simple trituration with acetone compared to use of a strong anion-exchange resin or drying reagents to isolate the free acid from the salt. Different trituration procedural modifications have been made and are being tested. Results have shown that in the presence of methanol, esterification will occur when the acid is liberated from the salt using HCl. To counter this problem, the samples are first evaporated to remove methanol and then the pH is adjusted with HCl. It was shown that using acetic acid did not result in pH levels low enough to guarantee complete protonation of the carboxylate. Through the use of a Bill-Board, an apparatus that holds six reaction vessels, several procedural modifications can be carried out simultaneously. Analysis is conducted by liquid chromatography coupled with a mass spectrometer and with nuclear magnetic resonance spectroscopy. Further studies will be carried out to assess the efficiency and practicality of using mild acidic conditions for cleavage using HCl/hexafluoroisopropanol or dilute HCl/trifluoroethanol. Both saponification and mild acid cleavage would represent improvements in safety and convenience to the undergraduate student researcher

New combinations for Sonoran Desert plants

We provide new nomenclatural combinations for three Sonoran Desert plants: Opuntia engelmannii var. laevis (J.M. Coulter) Felger, Verrier, & Carnahan, comb. nov.; Parkinsonia florida subsp. peninsulare (Rose) Hawkins & Felger, comb. nov.; and Parkinsonia ×sonorae (Rose & I.M. Johnston ex I.M. Johnston) Hawkins & Felger, comb. nov

Antibody Markers Identify a Common Progenitor to Sympathetic Neurons and Chromaffin Cells in vivo and Reveal the Timing of Commitment to Neuronal Differentiation in the Sympathoadrenal Lineage

Using specific antibody markers and double-label immunofluorescence microscopy, we have followed the fate of progenitor cells in the sympathoadrenal (SA) sublineage of the neural crest in developing rat embryos. Such progenitors are first recognizable in the primordial sympathetic ganglia at embryonic day 11.5 (E11.5), when they express tyrosine hydroxylase. At this stage, the progenitors also coexpress neuronal markers such as SCG 10 and neurofilament, together with a series of chromaffin cell markers called SA 1–5 (Carnhan and Patterson, 1991 a). The observation of such doubly labeled cells is consistent with the hypothesis that these cells represent a common progenitor to sympathetic neurons and adrenal chromaffin cells. Subsequent to E 11.5, expression of the chromaffin markers is extinguished in the sympathetic ganglia but retained by cells within the adrenal gland. Concomitant with the loss of the SA 1-5 immunoreactivity in sympathetic ganglia, a later sympathetic neuron-specific marker, B2, appears. In dissociated cell suspensions, some B2+ cells that coexpress SA 1 are seen. This implies a switch in the antigenic phenotype of developing sympathetic neurons, rather than a replacement of one cell population by another. The SA 1--B2 transition does not occur for the majority of cells within the adrenal primordium. In vitro, most B2+ cells fail to differentiate into chromaffin cells in response to glucocorticoid. Instead, they continue to extend neurites and then die. Taken together, these data imply that the SA 1--B2 transition correlates with a loss of competence to respond to an inducer of chromaffin differentiation. Thus, the development of SA derivatives is controlled both by environmental signals and by changes in the ability of differentiating cells to respond to such signals

Fractionation effects in phase equilibria of polydisperse hard sphere colloids

The equilibrium phase behaviour of hard spheres with size polydispersity is studied theoretically. We solve numerically the exact phase equilibrium equations that result from accurate free energy expressions for the fluid and solid phases, while accounting fully for size fractionation between coexisting phases. Fluids up to the largest polydispersities that we can study (around 14%) can phase separate by splitting off a solid with a much narrower size distribution. This shows that experimentally observed terminal polydispersities above which phase separation no longer occurs must be due to non-equilibrium effects. We find no evidence of re-entrant melting; instead, sufficiently compressed solids phase separate into two or more solid phases. Under appropriate conditions, coexistence of multiple solids with a fluid phase is also predicted. The solids have smaller polydispersities than the parent phase as expected, while the reverse is true for the fluid phase, which contains predominantly smaller particles but also residual amounts of the larger ones. The properties of the coexisting phases are studied in detail; mean diameter, polydispersity and volume fraction of the phases all reveal marked fractionation. We also propose a method for constructing quantities that optimally distinguish between the coexisting phases, using Principal Component Analysis in the space of density distributions. We conclude by comparing our predictions to perturbative theories for near-monodisperse systems and to Monte Carlo simulations at imposed chemical potential distribution, and find excellent agreement.Comment: 21 pages, 23 figures, 2 table