Near-field angular distributions of high velocity ions for low-power hall thrusters

Experimental angular distributions of high-energy primary ions in the near-field region of a small Hall thruster between 50-200 mm downstream of the thruster exit plane at a range of centerline angles have been determined using a highly-collimated, energy-selective diagnostic probe. The measurements reveal a wide angular distribution of ions exiting the thruster channel and the formation of a strong, axially-directed jet of ions along the thruster centerline. Comparisons are made to other experimental determinations as applicable

Development of wind tunnel techniques for the solution of problems in planetary Aeolian processes

Kutzbach reports wind profiles over a series of roughness elements on a frozen lake and how the wind profile changed as the surface roughness was varied. The approach of the current study was to duplicate Kutzbach's roughness arrays in the wind tunnel at 1/20 and 1/40 scales, and to compare the wind profiles over these scale models to those derived by Kutzbach at full scale in the field. The effects of scale differences and data reduction techniques are discussed. Although the study suggests that wind tunnel scale models can predict parameters measured in the field, the development of more definitive guidelines requires a field experiment designed specifically for comparison with wind tunnel results

“Only girls play with those”: An Analysis of Preschoolers’ Gender Schema Development through Gender Stereotype Knowledge and Recognition of Gendered Information

Since Sandra Bem’s introduction of Gender Schema Theory (GST), researchers have analyzed how gender schemas influence children’s information processing (Signorella, Bigler, & Liben, 1993; Welch-Ross & Schmidt, 1996). These studies, however, tested schema processing using familiar gender-atypical information (e.g., “only boys play with dolls”) instead of novel gender-atypical information (e.g., “only girls play with xylophones”). The present study seeks to fill this gap in the research by using novel gender-atypical information in order to test the extent to which children’s schemas influence their information processing. First, I tested children’s memory and preference for two picture books, one with a female main character and one with a male main character. These books included the character playing with novel gender-atypical and familiar gender-typical items. Second, I tested if boys and girls had dissimilar levels of gender stereotype knowledge (measured by a card sorting task based on Leinbach, Hort & Fagot, 1997). My first hypothesis was that children would have better memory for gender-typical than gender-atypical information. My second hypothesis was that children’s memory would be correlated with their scores on the sorting task. Finally, I hypothesized that children would prefer stories starring a protagonist of their own gender. My results did not support the idea that gender schemas are biasing children’s information processing. Limitations of my study include small sample size, more female than male participants, and the possible influences of children’s environment on their card sorting. Finally, I consider future research on the influences media has on children’s gender stereotypes

Building spelling power: word analysis lessons for grade 2.

Thesis (Ed.M.)--Boston Universit

Long-Term and Seasonal Drivers of Phytoplankton Assembly in a Subtropical Monomictic Lake

Seasonal phytoplankton dynamics in lakes are highly sensitive physicochemical changes in the water column. As climate-driven frequency and variability of precipitation increases, lakes may experience increased inputs of allochthonous organic matter and nutrients through pulsed rain events. The resultant effects of lake physicochemistry on phytoplankton seasonal succession and assemblage are poorly understood. In the current study, the phytoplankton assemblage of a subtropical monomictic lake was examined in the context of natural interannual oscillations in allochthonous dissolved organic carbon and nutrient inputs resulting in prolonged clear-water and dark-water phases over a 14-year period. Differences in water clarity and nutrient concentrations among phases caused pronounced assemblage and morphology-based functional grouping shifts largely associated with hydrologic effects of the Pacific Decadal Oscillation. Determining how phytoplankton assemblages respond to changes in allochthonous supplies is critical to understanding and predicting the cascading effects of climate on lake ecosystems at all latitudes

Patterns of Sexual Dimorphism in North American Indian Groups

This study examines patterns of sexual dimorphism in 26 North American Indian and Siberian groups. Past research on sexual dimorphism has looked into possible causative factors such as nutritional status, settlement type, marriage systems, sexual division of labor, and climate. No one explanation can be universally applied to all populations. Three measurements of height; standing height, sitting height, and sub-ischial height were examined for variation in sexual dimorphism. Univariate and multivariate statistical tests were performed to determine which component of stature contributes more to the variability in sexual dimorphism. Results of this study indicate that the groups of the Northwest coast and Siberia both exhibited a pattern of low sexual dimorphism relative to the inland North American groups. It is suggested that a more recent ancestry between the Northwest coast and Siberian groups is partly responsible for a similar pattern of dimorphism. Further, it is suggested that a long-standing adaptation to a cold climate in Siberia is evidenced in the low dimorphism of the Northwest coast and Siberian groups. Leg length contributed more to group variability, but it is known that leg length is more susceptible to environmental changes. This study suggests that the differences in sexual dimorphism patterns in North America and the similarities in patterning of the Northwest Coast groups and Siberian groups are a reflection of the involvement of a combination of genetic and environmental factors

Cool White Polymer Coatings based on Glass Bubbles for Buildings.

While most selective emitter materials are inadequate or inappropriate for building applications, here we present a techno-economically viable optical coating by integrating glass bubbles within a polymer film. A controlled glass bubble volume concentration from 0 to 70% leads to a selective solar reflectivity increase from 0.06 to 0.92 while the mid-infrared emissivity remains above 0.85. Outdoor measurements show the polymer coating on a concrete surface can provide a temperature reduction up to 25 °C during the day when conduction and convection are limited and a net cooling power greater than 78 W/m2 at a cost less than $0.005/W. The impact of polymer coating on common buildings is estimated as potential annual energy savings of 2-12 MJ/m2 and CO2 emission savings of 0.3-1.5 kg/m2. More savings are expected for higher surface-area-to-volume-ratio buildings, and the polymer coating is also expected to resolve cooling issues for old buildings with no air conditioning

Educating Lawyers: Preparation for the Profession of Law

Examines the unique aspects and limitations of legal education, as part of a series of reports from the foundation's Preparation for the Professions Program