Surface discharge through an insulator in a vacuum

A model for the mechanism of stationary discharges over insulators in a vacuum was developed. Upon introduction of this discharge, the insulator charges as a result of secondary emissions, in such a way that electrons coming from the cathode strike with an average secondary electron yield of 1, and so that the secondary electrons return again to the insulator through the electric field near the insulator. When the secondary electrons strike, electrons with an average yield of 1 are released again. The electrons move in short faults toward the anode, which they strike with lesser energy

The structure of crystals of some aromatic polycyclic hydrocarbons: 2:13-benzfluoranthene and acenaphthene

This thesis records the work carried out on the crystal structures of 2:13-Benzfluoranthene and acenaphthene. The structure of the first of these had to be completely determined, whereas in the case of the second structure, only the z parameters had to be determined, the x and y coordinates needing only refinement. Both these structures were refined to quite high accuracy. In one case low temperature data was used, and in the other Geiger counter measurements at room temperature were employed for one zone of reflections, to increase the reliability of the results

Cross-Disciplinary Technical Problem: Delivery of a NASA Scientific Payload to the ISS

Program management directed the Engineering team to study how to fit Plant Habitat (PH) within a M03 cargo transfer bag (CTB) while packed with perimeter-protective foam for stowage during launch

Investigation of a Lagrangian-point Propellant Depot Rendezvous Approach for an Interplanetary Mission to Mars

This thesis investigates the feasibility of a refueling station for a beyond Earth orbit (BEO) mission. The propellant depot is located at the L2 -Lagrangian point within the Earth-Moon system. This investigation determines if a refueling mission will reduce propulsive energy requirements necessary for Earth departure of a BEO-vehicle to achieve an interplanetary transfer to Mars. Furthermore, this research presents a trade study which identifies approximate total requirements for a direct and rendezvous mission to Mars as well as the necessary fuel masses to complete each approach. This analysis provides conclusive information in determining the benefits in utilizing a rendezvous location for refueling a spacecraft en versus loading the required fuel masses into a launch vehicle to support a direct transfer to Mars

Longitudinal variations, the opposition effect and monochromatic albedos for Mars

Magnitude at zero phase, phase coefficient, and monochromatic albedo computed for Mars as function of wavelengt

Polytopic vector analysis in igneous petrology: Application to lunar petrogenesis

Lunar samples represent a heterogeneous assemblage of rocks with complex inter-relationships that are difficult to decipher using standard petrogenetic approaches. These inter-relationships reflect several distinct petrogenetic trends as well as thermomechanical mixing of distinct components. Additional complications arise from the unequal quality of chemical analyses and from the fact that many samples (e.g., breccia clasts) are too small to be representative of the system from which they derived. Polytopic vector analysis (PVA) is a multi-variate procedure used as a tool for exploratory data analysis. PVA allows the analyst to classify samples and clarifies relationships among heterogenous samples with complex petrogenetic histories. It differs from orthogonal factor analysis in that it uses non-orthogonal multivariate sample vectors to extract sample endmember compositions. The output from a Q-mode (sample based) factor analysis is the initial step in PVA. The Q-mode analysis, using criteria established by Miesch and Klovan and Miesch, is used to determine the number of endmembers in the data system. The second step involves determination of endmembers and mixing proportions with all output expressed in the same geochemical variable as the input. The composition of endmembers is derived by analysis of the variability of the data set. Endmembers need not be present in the data set, nor is it necessary for their composition to be known a priori. A set of any endmembers defines a 'polytope' or classification figure (triangle for a three component system, tetrahedron for a four component system, a 'five-tope' in four dimensions for five component system, et cetera)

Rate theory for correlated processes: Double-jumps in adatom diffusion

We study the rate of activated motion over multiple barriers, in particular the correlated double-jump of an adatom diffusing on a missing-row reconstructed Platinum (110) surface. We develop a Transition Path Theory, showing that the activation energy is given by the minimum-energy trajectory which succeeds in the double-jump. We explicitly calculate this trajectory within an effective-medium molecular dynamics simulation. A cusp in the acceptance region leads to a sqrt{T} prefactor for the activated rate of double-jumps. Theory and numerical results agree

Signaling Microdomains InsP3 Receptor Localization Takes on New Meaning

AbstractA fundamental question in cell biology is how different receptor-mediated signaling cascades, despite utilizing many of the same intracellular components, can generate specific cellular responses. Delmas and colleagues (in this issue of Neuron) address this question in relation to the muscarinic acetylcholine receptor (M1AchR) and the B2 bradykinin receptor (B2R). Using Trp channel isoforms as biosensors for PLC stimulation in response to agonist activation, they demonstrate a role for signaling microdomains in the induction of such selective responses