Microgravity manipulator demonstration

A test rig is being developed that will be used to demonstrate and evaluate approaches to limiting manipulator base reactions in microgravity environments. The demonstration will include a 4-degrees-of-freedom arm, control computing facilities, and a base reaction measurement system

Stability Testing and Analysis of a PMAD DC Test Bed for the Space Station Freedom

The Power Management and Distribution (PMAD) DC Test Bed at the NASA Lewis Research Center is introduced. Its usefulness to the Space Station Freedom Electrical Power (EPS) development and design are discussed in context of verifying system stability. Stability criteria developed by Middlebrook and Cuk are discussed as they apply to constant power DC to DC converters exhibiting negative input impedance at low frequencies. The utility-type Secondary Subsystem is presented and each component is described. The instrumentation used to measure input and output impedance under load is defined. Test results obtained from input and output impedance measurements of test bed components are presented. It is shown that the PMAD DC Test Bed Secondary Subsystem meets the Middlebrook stability criterion for certain loading conditions

Effects of Urbanization on Buff-bellied Hummingbirds in Subtropical South Texas

Urbanization and its associated processes affect wildlife in a variety of ways. Understanding how this increasing land use type affects biological communities is important for conservation efforts. Hummingbirds (family Trochilidae) are one taxon that has showed positive responses to varying intensities of urban development. We surveyed for Buff-bellied Hummingbird (Amazilia yucatanensis), a species on its northern range-limits, in urban woodlands, residential, natural, and revegetated habitats. We examined how urbanization is affecting Buff-bellied Hummingbird populations in South Texas with point-count surveys and GIS analysis. We found that Buff-bellied Hummingbirds had greater relative abundances in urban settings when compared with peri-urban habitats, and were more likely to be found with increasing impervious cover. Our results support the growing literature showing how, in some species, urbanization can have positive impacts

Avian communities in an urbanizing region: Abundance patterns and effects of local habitat features

The Lower Rio Grande Valley of Texas has experience rapid population growth and increase of urban area since the mid-20th century. The goal of this thesis were to: 1) explore patterns of avian communities in suburban and remnant urban woodlands, with particular interest in native forest species, and 2) to assess how local habitat variables, such as number of native trees, affect avian communities in suburban habitats, and 3) provide recommendations to municipalities and homeowners to enhance urban habitats for birds. Results indicated that remnant urban woodlands provided habitat for common native forest bird species that otherwise avoided suburban habitats, and therefore should be conserved. Increased vegetation cover had a positive effect on bird diversity and native forest bird species richness while increased impervious cover and grass cover decreased both avian community metrics. Local habitat features were correlated with bird species abundances and bird diversity metrics

Microgravity robotics technology program

A research program to develop technology for robots operating in the microgravity environment of the space station laboratory is described. These robots must be capable of manipulating payloads without causing them to experience harmful levels of acceleration, and the motion of these robots must not disturb adjacent experiments and operations by transmitting reactions that translate into damaging effects throughout the laboratory. Solutions to these problems, based on both mechanism technology and control strategies, are discussed. Methods are presented for reduction of robot base reactions through the use of redundant degrees of freedom, and the development of smoothly operating roller-driven robot joints for microgravity manipulators is discussed

Frequency domain model for analysis of paralleled, series-output-connected Mapham inverters

The Mapham resonant inverter is characterized as a two-port network driven by a selected periodic voltage. The two-port model is then used to model a pair of Mapham inverters connected in series and employing phasor voltage regulation. It is shown that the model is useful for predicting power output in paralleled inverter units, and for predicting harmonic current output of inverter pairs, using standard power flow techniques. Some examples are compared to data obtained from testing hardware inverters

Verschraenkung versus Stosszahlansatz: Disappearance of the Thermodynamic Arrow in a High-Correlation Environment

The crucial role of ambient correlations in determining thermodynamic behavior is established. A class of entangled states of two macroscopic systems is constructed such that each component is in a state of thermal equilibrium at a given temperature, and when the two are allowed to interact heat can flow from the colder to the hotter system. A dilute gas model exhibiting this behavior is presented. This reversal of the thermodynamic arrow is a consequence of the entanglement between the two systems, a condition that is opposite to molecular chaos and shown to be unlikely in a low-entropy environment. By contrast, the second law is established by proving Clausius' inequality in a low-entropy environment. These general results strongly support the expectation, first expressed by Boltzmann and subsequently elaborated by others, that the second law is an emergent phenomenon that requires a low-entropy cosmological environment, one that can effectively function as an ideal information sink.Comment: 4 pages, REVTeX

Entrepreneurial capital, social values and Islamic traditions: exploring the growth of women-owned enterprises in Pakistan

Main ArticleThis study seeks to explore the variables contributing to the growth of women-owned enterprises in the Islamic Republic of Pakistan. Based on a previously established multivariate model, it uses two econometric approaches: first classifying variables into predetermined blocks; and second, using the general to specific approach. Statistical analyses and in-depth interviews confirm that women entrepreneurs’ personal resources and social capital have a significant role in their business growth. Further, it reveals that the moral support of immediate family, independent mobility and being allowed to meet with men play a decisive role in the sales and employment growth of women-owned enterprises in an Islamic country such as Pakistan

Distortion and regulation characterization of a Mapham inverter

Output voltage Total Harmonic Distortion (THD) of a 20kHz, 6kVA Mapham resonant inverter is characterized as a function of its switching-to-resonant frequency ratio, f sub s/f sub r, using the EASY5 engineering analysis system. EASY5 circuit simulation results are compared with hardware test results to verify the accuracy of the simulations. The effects of load on the THD versus f sub s/f sub r ratio is investigated for resistive, leading, and lagging power factor load impedances. The effect of the series output capacitor on the Mapham inverter output voltage distortion and inherent load regulation is characterized under loads of various power factors and magnitudes. An optimum series capacitor value which improves the inherent load regulation to better than 3 percent is identified. The optimum series capacitor value is different than the value predicted from a modeled frequency domain analysis. An explanation is proposed which takes into account the conduction overlap in the inductor pairs during steady-state inverter operation, which decreases the effective inductance of a Mapham inverter. A fault protection and current limit method is discussed which allows the Mapham inverter to operate into a short circuit, even when the inverter resonant circuit becomes overdamped

Observations on Bog and Pollen Stratigraphy of the Des Moines Glacial Lobe, lowa

As part of an investigation into the effect of environmental changes of landscape and soils on the Des Moines lobe (Cary till), three deep bogs (Colo, Jewell, McCulloch) were examined in detail. The center profile of each has a surface peat underlain by deep, dark-colored, calcareous silts; these in turn are underlain by a second peat zone which passes into basal calcareous silts and eventually to till. Preliminary pollen data on the Colo bog shows six zones. The key zones are Zone 1 (0 to 75 inches), in which the pollen is of dominantly herbaceous genera indicating an open grassland environment, and Zones IV and V (102 to 155 to 212 inches) dominated by pollen of forest species. The changes in bog and pollen strata were probably related to a marked change from a cool climate in the early postglacial to a warmer climate in the latter part of the postglacial continuing to the present