Study of ballistic mode comet Encke mission opportunities

An analysis was conducted of the space mission to intercept the comet Encke. The two basic types of flight geometry considered for the mission are described. The primary interactions between time-of-flight and performance characteristics are displayed. The representative spacecraft characteristics for the Titan 3/Centaur launch vehicle are tabulated. The navigation analyses for the two missions are developed to show: (1) assessment of the navigation feasibility of the missions, (2) determination of the total velocity budget for the trim maneuvers, and (3) evaluation of dispersions at comet encounter

A Parametric Study of Water Vapor Condensation in Supersonic Nozzle Flow Fields

Combustion driven hypersonic and supersonic wind tunnels are impaired in their flight simulation abilities by the condensation of water vapor introduced into the test stream by the burning byproducts of air and hydrocarbon fuels. The purpose of this study is to evaluate the abilities of a condensation model to predict the beginning axial locations of vapor changing into liquid droplets and study the correlations with initial combustion chamber conditions. A test matrix with different fuels, chamber pressure, and equivalence ratio was applied to the FIRACON model written by Erickson, et al. [7] using the dimensions of the NASA Langley eight-foot-high heated wind tunnel nozzle. The results indicate higher chamber pressure and fuel-air equivalence ratio cause water vapor molecules to nucleate and condense further upstream of the nozzle, where as higher temperature delayed the condensation event in the expanding nozzle flow. At this time, FIRACON’s results can be considered qualitative in nature. General trends in the changes of the expanding flows due to varying initial chamber conditions can be seen, but the accuracy is unknown. A more thorough experimental and theoretical investigation of a condensing flow in a nozzle is needed to improve existing models before attaining results that could be considered relatively accurate or quantitative in nature

Quantifying loopy network architectures

Biology presents many examples of planar distribution and structural networks having dense sets of closed loops. An archetype of this form of network organization is the vasculature of dicotyledonous leaves, which showcases a hierarchically-nested architecture containing closed loops at many different levels. Although a number of methods have been proposed to measure aspects of the structure of such networks, a robust metric to quantify their hierarchical organization is still lacking. We present an algorithmic framework, the hierarchical loop decomposition, that allows mapping loopy networks to binary trees, preserving in the connectivity of the trees the architecture of the original graph. We apply this framework to investigate computer generated graphs, such as artificial models and optimal distribution networks, as well as natural graphs extracted from digitized images of dicotyledonous leaves and vasculature of rat cerebral neocortex. We calculate various metrics based on the Asymmetry, the cumulative size distribution and the Strahler bifurcation ratios of the corresponding trees and discuss the relationship of these quantities to the architectural organization of the original graphs. This algorithmic framework decouples the geometric information (exact location of edges and nodes) from the metric topology (connectivity and edge weight) and it ultimately allows us to perform a quantitative statistical comparison between predictions of theoretical models and naturally occurring loopy graphs.Comment: 17 pages, 8 figures. During preparation of this manuscript the authors became aware of the work of Mileyko at al., concurrently submitted for publicatio

The impact of the coronavirus disease 2019 pandemic on physical activity in U.S. children

This article examines the impact of the pandemic on the physical activity and play behavior of U.S. children and to provide evidence based recommendations to improve their physical activity

Repair or destruction: an intimate liaison between ubiquitin ligases and molecular chaperones in proteostasis

Cellular differentiation, developmental processes, and environmental factors challenge the integrity of the proteome in every eukaryotic cell. The maintenance of protein homeostasis, or proteostasis, involves folding and degradation of damaged proteins, and is essential for cellular function, organismal growth, and viability [1, 2]. Misfolded proteins that cannot be refolded by chaperone machineries are degraded by specialized proteolytic systems. A major degradation pathway regulating cellular proteostasis is the ubiquitin/proteasome-system (UPS), which regulates turnover of damaged proteins that accumulate upon stress and during aging. Despite the large number of structurally unrelated substrates, ubiquitin conjugation is remarkably selective. Substrate selectivity is mainly provided by the group of E3 enzymes. Several observations indicate that numerous E3 ubiquitin ligases intimately collaborate with molecular chaperones to maintain the cellular proteome. In this Review, we provide an overview of specialized quality control E3 ligases playing a critical role in the degradation of damaged proteins. The process of substrate recognition and turnover, the type of chaperones they team up with, and the potential pathogeneses associated with their malfunction will be further discusse

Assessing impacts of dropping water table in Casa Grande Ruins National Monument

A water resources assessment of the Casa Grande Ruins National Monument (CAGR) was conducted using historical and recent data. The data were sorted and analyzed to determine whether the monument grounds have the potential for subsidence, and in particular, differential subsidence. Further research was conducted to ascertain the cause of the loss of the mesquite woodland on the monument grounds in the 1940's. To determine the potential for subsidence at the monument, a subsidence model was constructed based on geology developed from well logs of local wells. The model allowed the water table to fall from the predevelopment level to the present, and to possible future levels. The region of the Casa Grande Ruins National Monument has the potential for subsidence and differential subsidence on a geological basis, should the water table drop sufficiently. The majority of the mesquites on the monument grounds died in the 1940's. This has been attributed to groundwater pumping that lowered the groundwater table, but may also have been caused by drought, loss of a perched aquifer, disruption of overland flow by construction around monument grounds, and construction of the contour dykes at CAGR.hydrology collectio

TNX/HLW Long Shaft Pumps 1995-2000

Problems with long shaft pumps are becoming clearer due to increased use, better instrumentation, more analysis, and increased testing activity. The problems are with reliability and not with hydraulic performance. The root cause of reliability problems is usually excessive vibration caused by design. The outlook for satisfactory pumps is improved as understanding of problems increases. Promising developments are emerging such as the tilt pad bearing. Alternative configurations, such as gas filled columns and submerged motor pumps, will require development. Continued development, in general, should be expected due to changing technology and industry changes. This report describes thirteen distinct pump programs starting with leakage of original mixer pumps in the 1980s and ending with the testing of tilt pad bearings now in progress. Eight of the programs occurred from 1996 to 2000. All involve long shaft pumps; all involve testing at TNX; and all involve a problem of some kind. The common technical issue among the activities is vibration and shaft (or rotor) instability due to journal bearings. In every case, excessive shaft vibration is a reasonable and probable explanation for some or all of the problems

Relation between muscle form and character of locomotion

TypescriptThesis (B.S.)--Purdue University, 1892School of ScienceB.S