Fracture criteria for discontinuously reinforced metal matrix composites

Summarized is the progress achieved during the period September 16, 1987 to August 15, l988 on NASA Grant NAG1-724, Fracture Criteria for Discontinuously Reinforced Metal Matrix Composites. Appended are copies of three manuscripts prepared under NASA funding during the performance period

Trends in source gases

Source gases are defined as those gases that, by their breakdown, introduce into the stratosphere halogen, hydrogen, and nitrogen compounds that are important in stratospheric ozone destruction. Given here is an update of the existing concentration time series for chlorocarbons, nitrous oxide, and methane. Also reviewed is information on halogen containing species and the use of these data for establishing trends. Also reviewed is evidence on trends in trace gases that influence tropospheric chemistry and thus the tropospheric lifetimes of source gases, such as carbon dioxide, carbon monoxide, or nitrogen oxides. Much of the information is given in tabular form

The roles of charge exchange and dissociation in spreading Saturn's neutral clouds

Neutrals sourced directly from Enceladus's plumes are initially confined to a dense neutral torus in Enceladus's orbit around Saturn. This neutral torus is redistributed by charge exchange, impact/photodissociation, and neutral-neutral collisions to produce Saturn's neutral clouds. Here we consider the former processes in greater detail than in previous studies. In the case of dissociation, models have assumed that OH is produced with a single speed of 1 km/s, whereas laboratory measurements suggest a range of speeds between 1 and 1.6 km/s. We show that the high-speed case increases dissociation's range of influence from 9 to 15 Rs. For charge exchange, we present a new modeling approach, where the ions are followed within a neutral background, whereas neutral cloud models are conventionally constructed from the neutrals' point of view. This approach allows us to comment on the significance of the ions' gyrophase at the moment charge exchange occurs. Accounting for gyrophase: (1) has no consequence on the H2O cloud; (2) doubles the local density of OH at the orbit of Enceladus; and (3) decreases the oxygen densities at Enceladus's orbit by less than 10%. Finally, we consider velocity-dependent, as well as species-dependent cross sections and find that the oxygen cloud produced from charge exchange is spread out more than H2O, whereas the OH cloud is the most confined.Comment: Accepted to the Journal of Geophysical Research, 49 pages, 10 figure

16. Relationship among Sleep, Food Security Status, Financial Factors During the Early COVID-19 Experience

Background Many factors affect college students’ health and wellness, including sleep habits, nutrition and financial stress. The COVID-19 experience can be considered an unprecedented experience influencing these factors. Purpose The purpose of this study was to explore the relationship among length of sleep, food security status, financial factors and risk of negative health outcomes during the early COVID-19 experience. Method Network sampling was used to conduct a cross-sectional online survey of college students as part of a research course experience. A subset of items related to food security status, sleep changes, family financial support and employment were analyzed for this study. Result Of the 282 respondents, 19.4% reported decreased sleep time, 40.3% reported increased sleep. Prior to the pandemic, 24.5% reported getting at least 8 hours of sleep, this decreased to 17% during May 2020. Thirty-four percent met the criteria for being food insecure as measured by the six-item USFSSM, which is consistent with current literature. Independent sample t-tests showed no statistical differences in change in sleep hours when comparing family financial support to no support, eligibility for stimulus check or higher risk for negative outcomes with COVID-19. No clear relationship was found with food security status. When comparing sleep time, those lacking family financial support, and those with higher health risks, averaged less than six hours of sleep compared to almost seven hours for others. Conclusions Additional research further characterizing changes in college students’ financial needs, food security status, and wellness indicators is needed to determine effective intervention strategies

Fracture criteria for discontinuously reinforced metal matrix composites

The effect of sample configuration on the details of initial crack propagation in discontinuously whisker reinforced aluminum metal matrix composites was investigated. Care was taken to allow direct comparison of fracture toughness values utilizing differing sample configurations and orientations, holding all materials variables constant, e.g., extrusion ration, heat treatment, and chemistry

WACCM-D Whole Atmosphere Community Climate Model with D-region ion chemistry

Energetic particle precipitation (EPP) and ion chemistry affect the neutral composition of the polar middle atmosphere. For example, production of odd nitrogen and odd hydrogen during strong events can decrease ozone by tens of percent. However, the standard ion chemistry parameterization used in atmospheric models neglects the effects on some important species, such as nitric acid. We present WACCM-D, a variant of the Whole Atmosphere Community Climate Model, which includes a set of lower ionosphere (D-region) chemistry: 307 reactions of 20 positive ions and 21 negative ions. We consider realistic ionization scenarios and compare the WACCM-D results to those from the Sodankylä Ion and Neutral Chemistry (SIC), a state-of-the-art 1-D model of the D-region chemistry. We show that WACCM-D produces well the main characteristics of the D-region ionosphere, as well as the overall proportion of important ion groups, in agreement with SIC. Comparison of ion concentrations shows that the WACCM-D bias is typically within ±10% or less below 70 km. At 70–90 km, when strong altitude gradients in ionization rates and/or ion concentrations exist, the bias can be larger for some groups but is still within tens of percent. Based on the good agreement overall and the fact that part of the differences are caused by different model setups, WACCM-D provides a state-of-the-art global representation of D-region ion chemistry and is therefore expected to improve EPP modeling considerably. These improvements are demonstrated in a companion paper by Andersson et al

Patterns of fatigue in adolescents receiving chemotherapy

Abstract: Purpose/Objectives: To describe patterns of fatigue in adolescents and the impact of fatigue during one month of chemotherapy, to explore variables that affect fatigue, and to explore the feasibility of collecting daily selfreport data in this population. Design: Longitudinal, descriptive. Setting: Two pediatric oncology centers in central Virginia. Sample: 20 adolescents with a variety of cancer diagnoses receiving chemotherapy. Methods: Adolescents described daily fatigue for one month using rating scales and qualitative diaries Main Research Variables: Fatigue severity. Finding: Adolescents commonly reported a peak in fatigue in the days immediately following chemotherapy administration. The most common pattern for adolescents who received chemotherapy on a schedule every three to four weeks was a "declining rollercoaster" pattern, with fatigue severity alternating on a daily basis but gradually declining until chemotherapy was scheduled again. Adolescents who received chemotherapy weekly showed more frequent peaks and troughs (the "yo-yo" pattern) that did not diminish in severity over the weeks of the study. Adolescents associated fatigue with other symptoms, particularly sleep-wake disturbances, pain, and nausea, and frequently reported that fatigue interfered with daily activities. Conclusions: Fatigue commonly bothers adolescents receiving chemotherapy, particularly in the days following chemotherapy administration and when other symptoms are present. Although fatigue interfered with the adolescents' abilities to maintain their usual lifestyles, many still participated in the typical activities of adolescence. Implications for Nursing: Fatigue is a complex and dynamic symptom. Oncology clinicians and researchers should frequently assess fatigue in adolescents receiving chemotherapy and apply timely and tailored interventions to match the factors that contribute to fatigue and influence fatigue severity. Management of fatigue during treatment will help adolescents stay involved in age-related activities and meet developmental milestones. Article: Adolescents diagnosed with cancer represent a group of patients with a unique cancer epidemiology, development profile, and research needs. The population's most common cancers include lymphoma, leukemia, central nervous system cancers, endocrine and germ cell tumors, and sarcomas--a spectrum of cancers different than that seen in adults or in younger childre

Lawson Criterion for Ignition Exceeded in an Inertial Fusion Experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin burn propagation into surrounding cold fuel, enabling the possibility of high energy gain. While scientific breakeven (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion