Decoding the History of the Early Solar System Using Comet Volatile Compositions

Understanding the evolution of the solar system, as well as its current volatile content, requires knowledge of the initial conditions present in the solar nebula. As some of the first objects to accrete in the solar nebula, cometary nuclei are among the most primitive remnants of solar system formation, and their present-day volatile composition likely reflects the composition and conditions where (and when) they formed. As such, the volatile compositions of cometary nuclei may serve as fossils of solar system formation. High-resolution near-infrared spectroscopy offers a valuable tool for sampling the primary volatile (i.e., ices subliming directly from the nucleus) composition of comets via analysis of fluorescence emission in cometary comae. Sampling fluorescence emission from a suite of primary volatiles has become possible from state-of-the-art ground-based observatories. An overarching goal of comet volatile composition studies is determining whether comets can be classified according to their volatile content and what this reveals about the history of the early solar system. Early work produced encouraging results, but recent work has left pressing questions regarding whether a compositional taxonomy based on near-infrared measurements is feasible, as well as how to place such measurements into a meaningful context. These include questions such as: Are observed systematic compositional differences between ecliptic comets and Oort cloud comets the result of evolutionary effects or reflective of formative conditions? Is temporal variability in coma composition a common phenomenon, and if so, how can present-day measurements be related to natal solar system conditions? This work examines these questions in the context of near-infrared measurements of an Oort cloud comet, a Jupiter-family comet, and an ecliptic comet. The interplay between evolutionary effects, formative conditions, and temporal variability is examined in the context of the evolving composition-based taxonomy and the interpretation of the results of comet composition studies

Analysis of response style differences on the Multidimensional Students’ Life Satisfaction Scale between Croatian and American youth

Measurement equivalence has been noted as particularly important in cross-cultural research to ensure that attributes, attitudes, and/or perceptions are accurately assessed across groups of interest. Although response style differences appear to be a phenomenon noted across a variety of nations, few such studies have focused on youth and no studies have investigated response style differences in life satisfaction measures. In this investigation, 308 American and 227 Croatian youth were administered the Multdimensional Students’ Life Satisfaction Scale (MSLSS: Huebner, 1994) to assess their global satisfaction, as well as their satisfaction with friends, family, living environment, school and self. Results found no response style differences across most MSLSS domains, with the exception of self satisfaction and school satisfaction. American youth reported a greater tendency to respond to self and school satisfaction items at the positive end of the response continuum, while Croatian youth responded more frequently to the mid-point on self satisfaction items. Some gender differences were noted on the friendship and school satisfaction domains. A discussion of these findings and their implications conclude the paper

Oxidation Through Coating Cracks of SiC-Protected Carbon/Carbon

The oxidation of SiC-protected carbon/carbon through machined slots and naturally occurring craze cracks in the SiC was studied. The slot and crack geometries were characterized, and the subsurface oxidation of the carbon/carbon substrate at temperatures of 1000 to 1300 C in air was assessed using weight change, x-ray computed tomography, and optical microscopy of sections. Rate constants were derived from these measurements and compared with a two-step diffusion control model of carbon oxidation. Oxidation kinetic measurements on both the specimens with machined slots and with naturally occurring craze cracks showed good agreement with the model

NDE for Characterizing Oxidation Damage in Reinforced Carbon-Carbon

In this study, coated reinforced carbon-carbon (RCC) samples of similar structure and composition as that from the NASA space shuttle orbiter s thermal protection system were fabricated with slots in their coating simulating craze cracks. These specimens were used to study oxidation damage detection and characterization using NDE methods. These specimens were heat treated in air at 1143 and 1200 C to create cavities in the carbon substrate underneath the coating as oxygen reacted with the carbon and resulted in its consumption. The cavities varied in diameter from approximately 1 to 3 mm. Single-sided NDE methods were used since they might be practical for on-wing inspection, while x-ray micro-computed tomography (CT) was used to measure cavity sizes in order to validate oxidation models under development for carbon-carbon materials. An RCC sample having a naturally-cracked coating and subsequent oxidation damage was also studied with x-ray micro-CT. This effort is a follow-on study to one that characterized NDE methods for assessing oxidation damage in an RCC sample with drilled holes in the coating. The results of that study are briefly reviewed in this article as well. Additionally, a short discussion on the future role of simulation to aid in these studies is provided

Oxidation Through Coating Cracks of SiC-Protected Carbon/Carbon

The oxidation of SiC-protected carbon/carbon through machined slots and naturally occurring craze cracks in the SiC was studied. The slot and crack geometries were characterized, and the subsurface oxidation of the carbon/carbon substrate at temperatures of 1000 to 1300 C in air was assessed using weight change, x-ray computed tomography, and optical microscopy of sections. Rate constants were derived from these measurements and compared with a two-step diffusion control model of carbon oxidation. Oxidation kinetic measurements on both the specimens with machined slots and with naturally occurring craze cracks showed good agreement with the model