Thick to Thin: The Evolutionary Connection Between PG 1159 Stars and the Thin Helium-Enveloped Pulsating White Dwarf GD 358

Seismological observations with the Whole Earth Telescope (WET) allow the determination of the subsurface compositional structure of white dwarf stars. The hot DO PG 1159 has a helium surface layer with a mass of 0.001 Msun, while the cooler DB white dwarf GD 358 has a much thinner surface helium layer of 10^-6 Msun. These results imply that either there is no evolutionary relation between these two stars, or that there is an unknown mass loss mechanism. To investigate possible evolutionary links between these objects, we computed evolutionary sequences of white dwarf models including time-dependent diffusion. Our initial model is based on the PG~1159 pulsational data, and has a surface composition of 30% helium, 35% carbon, and 35% oxygen. Below this is a thin transition zone where the helium fraction falls to zero. As expected, diffusion caused a separation of the elements; a thickening surface layer of nearly pure helium overlays a deepening transition zone where the composition returns to the original surface composition. When the model reached the temperature range of GD~358 and the pulsating DB white dwarfs, this pure helium surface layer was 3x10^-6 stellar masses deep. The resulting evolved model is very similar to the model used by Bradley and Winget (1994) to match the pulsation observations of GD 358. The pulsation periods of this model also show a good fit to the WET observations. These results demonstrate the plausibility of a direct evolutionary path from PG 1159 stars to the much cooler DB white dwarfs by inclusion of time-dependent diffusion. A problem still remains in that our models have no hydrogen, and thus must retain their DB nature while their surface tempeture drops from 45,000K to 30,000K. Since there are no known DB stars in this range, we plan to address this problem in future calculations.Comment: LaTeX, 10 pages, using AAS Macros. 2 PostScript figures. Accepted for publication in The Astrophysical Journal Letters

Development of a preprototype times wastewater recovery subsystem

A three-man wastewater recovery preprototype subsystem using a hollow fiber membrane evaporator with a thermoelectric heat pump to provide efficient potable water recovery from wastewater on extended duration space flights was designed, fabricated, and tested at one-gravity. Low power, compactness and gravity insensitive operation are featured in this vacuum distillation subsystem. The tubular hollow fiber elements provide positive liquid/gas phase control with no moving parts, and provide structural integrity, improving on previous flat sheet membrane designs. A thermoelectric heat pump provides latent energy recovery. Application and integration of these key elements solved problems inherent in all previous reclamation subsystem designs

Development of a preprototype times wastewater recovery subsystem: Appendices

This Master Test Plan outlines the test program to be performed by Hamilton Standard during the Urine Water Recovery Subsystem Program. Testing is divided into three phases: (1) design support testing; development component testing; and acceptance testing. The completion of this test program verifies the subsystem operation

Infantile hemangioma presenting as colocolic intussusception in an infant case report with review of pathologic lead points

Infantile hemangioma (IH) is one of the most common vascular anomalies of early childhood and is usually recognized in the first few weeks to months of life as a solitary cutaneous lesion. This report documents our experience with a GLUT-1 positive IH presenting as the pathologic lead point in a colocolic intussusception in a 10-week-old infant who had no skin lesions. Literature suggests approximately 2% of all children presenting with an intussusception require surgical intervention; however, an IH as the pathologic lead point is unique

Exploring Arts Integration in Language Arts Instruction for Elementary Education

The purpose of this thesis is to provide insight on how arts integration in English language arts education increases engagement and achievement in students and teachers alike. Throughout my analysis of literature, local field research in two Central Florida public elementary schools, and my creation of a five-day arts-integrated writing unit, I found that arts integration, especially when utilizing Leonard Bernstein’s Artful Learning Method was observed to show a positive impact on students. Arts integration allowed for a child’s natural curiosity and instinct to create to take over, which created authentic learning experiences for the students. The research also demonstrated that arts integration enabled teachers to utilize their creativity, which in turn positively changed their perspectives on their career and teaching experience. Observations and the research literature examined in this thesis showed that arts integration can be a valuable outlet for both students and teachers, yet not always utilized due to high stakes testing, budgetary concerns, and time constraints in the elementary classroom

Chameleon stars: diffusion and spectroscopic transformations in white dwarfs

White dwarfs stars are the end product of stellar evolution, generating no energy by nuclear fusion, slowly cooling over time. As they cool, their intense gravity causes the lightest element--either hydrogen or helium--to float to the surface. This gravitational settling is responsible for the observed nearly pure surface composition of white dwarfs. In this investigation, I model this settling process in these stars by constructing a sequence of models which represent the star at different stages as it cools;As white dwarfs cool, at certain temperatures they undergo nonradial pulsations. Most importantly, a change in the composition as a function of the depth within the star causes differences in the pulsations of the star. Pulsations are then a natural way of measuring the depth of surface layers of pure composition formed by gravitational settling;I calculated a sequence of models representing the evolution of white dwarfs. The initial model was of a young, hot white dwarf at a surface temperature of Teff~ 130,000K, representing the pulsating white dwarf PG 1159. The model has a surface layer of mixed He, C, and O containing about 10-3 of the stellar mass. This model was evolved until it cooled to 25,000K, where it again undergoes pulsations. By this temperature, settling causes the formation of a surface layer of helium containing about 10-6 of the stellar mass. Observations of GD 358, a pulsating helium-rich white dwarf at Teff~25,000K, show that it has a surface helium layer of roughly this thickness. This indicates that stars like PG 1159 may evolve to stars like GD 358, despite the incongruity in surface layer mass;Finally, there exists a range of temperature, from 45,000K to 30,000K, where all observed white dwarfs have hydrogen dominated surfaces. I added hydrogen to the PG 1159 models to investigate its effects. The calculations show that hydrogen diffuses very quickly to the surface, and would be present at the surface in detectable quantities. This contradiction with observations of PG 1159, which shows no detectable hydrogen, implies some other mechanism, such as mass loss, which alters the surface abundance of white dwarfs

FULL-TIME NON-TENURE TRACK FACULTY: IDENTITY AND DEPARTMENTAL PERSPECTIVES

This study examines perceptions of 12 full-time non-tenure track faculty members about their professional and academic selves in a research-intensive university. A phenomenological approach is used to gain insight into the complexities of the experience of being a full-time faculty member, off the tenure-track, whose primary responsibility is teaching within a research-intensive institution. The notion of tenurestream as the only desired path to being an academic is challenged by these faculty members’ understanding of their identities. This researcher considers how professional identities may be understood and suggests that the meanings and values these faculty members attach to their professional roles may be embedded in their perceptions of how their role fits within the department. Throughout this qualitative inquiry, the perspectives of these faculty members are positioned as a primary source of data about the experience of being a full-time non-tenure track faculty member. By using a phenomenological approach and taking a constructivist perspective this researcher finds that extant theories that view this population through a deficit model are inaccurate. Additionally, essentialist and homogenizing descriptions of this population are also found to be insufficient. A qualitative analysis suggests the viability of an alternative description of this population, one which reflects the nuanced view of professional identity these participants expressed. Based on structural categories adapted from Martin’s (2002) three perspective view of organizational culture, their perceptions are categorized according to the congruence expressed between their social identity and their professional role. Perceptions shared about their departmental culture are similarly categorized which provides insight about the influence of policies, practices, and collegial interactions on professional lives

Development of a preprototype times wastewater recovery subsystem, addendum

Six tasks are described reflecting subsystem hardware and software modifications and test evaluation of a TIMES wastewater recovery subsystem. The overall results are illustrated in a figure which shows the water production rate, the specific energy corrected to 26.5 VDC, and the product water conductivity at various points in the testing. Four tasks are described reflecting studies performed to develop a preliminary design concept for a next generation TIMES. The overall results of the study are the completion of major design analyses and preliminary configuration layout drawings

Addendum: Development of a preprototype times wastewater recovery subsystem

The results of the second generation operational improvements and the TIMES (Thermoelectric Integrated Membrane Evaporation Subsystem) 2 study are covered. Areas covered in the second generation operational improvements are improved temperature control, water quality improvements, subsytem operational improvements, solid handling improvements, wastewater pretreatment optimization, and membrane rejuvenation concepts. The task for the TIMES 2 study are thermoelectric regenerator improvement, recycle loop pH operational criteria, recycle loop component optimization, and hollow fiber membrane evaporator improvement. Results are presented and conclusions are drawn from both studies