SiO2-rich condrules in ordinary chondrites

The solar system abundances of Mg, Fe, and Si dictate that chondritic meteorites are silica-deficient compared to most terrestrial or lunar igneous rocks; thus olivine-orthopyroxene assemblages are commonly observed in ordinary chondrites. However, in the unequilibrated H-chondrites Sharps, Bremervorde, and Dhajala, we have observed chondrules and fragments which contain either tridymite or cristobalite as a major phase

Isotopic Heterogeneity in Calcium-Aluminum-Rich Meteoritic Inclusions

Calcium-Aluminum-rich inclusions (CAI), found in meteorites, are among the oldest known solids identified in the solar system. Analyses of CAI have provided constraints on physical and chemical conditions that existed just prior to, and during planetary formation. A few rare inclusions, called FUN (for Fractionation and Unknown Nuclear effects), exhibit large isotopic anomalies and have provided insight into nucleosynthetic and nebular processes. In this thesis, data obtained on the petrography, chemistry and isotopic compositions of CAI, identified in the carbonaceous chondrite Allende, are used as tracers to address several specific questions: 1) What are the relationships between fine and coarse-grained CAI? 2) What are the differences, in composition and origin, between FUN inclusions and isotopically normal CAI? 3) What was the role of volatility-controlled processes, such as distillation and condensation, in the evolution of CAI? 4) What was the role of chemical alteration and isotopic reequilibration in the evolution of CAI? Isotopic data were obtained by thermal ionization and ion microprobe mass spectrometry for individual grains within both fine and coarse-grained CAI, and correlated with petrographic and chemical observations. Evidence is presented for the enrichment of fine-grained inclusions in the lighter isotopes of Mg, in contrast to coarse-grained CAI, which are enriched in the heavier isotopes. Isotopic heterogeneity was observed within both fine and coarse-grained inclusions. Heterogeneity is discussed in the context of primary and secondary phases, mineral alteration processes, and isotopic reequilibration. A new class of coarse-grained inclusion, characterized by a distinct purple color and high spinel contents (≥50%), were identified and found to exhibit a high frequency (20%) of FUN isotopic anomalies. Four new FUN inclusions were identified and studied in detail. The correlated isotopic fractionation for Mg, Si, and Cr in these inclusions, suggests the importance of volatility-controlled formation processes. A model is presented for the evolution of FUN inclusions, involving distillation of ordinary chondritic material, with a mass loss of around 70%, followed by exchange with isotopically normal reservoirs. The high spinel contents and large isotopic fractionation of these inclusions, may indicate that they formed at higher temperatures than isotopically normal CAI.</p

Health-status outcomes with invasive or conservative care in coronary disease

BACKGROUND In the ISCHEMIA trial, an invasive strategy with angiographic assessment and revascularization did not reduce clinical events among patients with stable ischemic heart disease and moderate or severe ischemia. A secondary objective of the trial was to assess angina-related health status among these patients. METHODS We assessed angina-related symptoms, function, and quality of life with the Seattle Angina Questionnaire (SAQ) at randomization, at months 1.5, 3, and 6, and every 6 months thereafter in participants who had been randomly assigned to an invasive treatment strategy (2295 participants) or a conservative strategy (2322). Mixed-effects cumulative probability models within a Bayesian framework were used to estimate differences between the treatment groups. The primary outcome of this health-status analysis was the SAQ summary score (scores range from 0 to 100, with higher scores indicating better health status). All analyses were performed in the overall population and according to baseline angina frequency. RESULTS At baseline, 35% of patients reported having no angina in the previous month. SAQ summary scores increased in both treatment groups, with increases at 3, 12, and 36 months that were 4.1 points (95% credible interval, 3.2 to 5.0), 4.2 points (95% credible interval, 3.3 to 5.1), and 2.9 points (95% credible interval, 2.2 to 3.7) higher with the invasive strategy than with the conservative strategy. Differences were larger among participants who had more frequent angina at baseline (8.5 vs. 0.1 points at 3 months and 5.3 vs. 1.2 points at 36 months among participants with daily or weekly angina as compared with no angina). CONCLUSIONS In the overall trial population with moderate or severe ischemia, which included 35% of participants without angina at baseline, patients randomly assigned to the invasive strategy had greater improvement in angina-related health status than those assigned to the conservative strategy. The modest mean differences favoring the invasive strategy in the overall group reflected minimal differences among asymptomatic patients and larger differences among patients who had had angina at baseline

Initial invasive or conservative strategy for stable coronary disease

BACKGROUND Among patients with stable coronary disease and moderate or severe ischemia, whether clinical outcomes are better in those who receive an invasive intervention plus medical therapy than in those who receive medical therapy alone is uncertain. METHODS We randomly assigned 5179 patients with moderate or severe ischemia to an initial invasive strategy (angiography and revascularization when feasible) and medical therapy or to an initial conservative strategy of medical therapy alone and angiography if medical therapy failed. The primary outcome was a composite of death from cardiovascular causes, myocardial infarction, or hospitalization for unstable angina, heart failure, or resuscitated cardiac arrest. A key secondary outcome was death from cardiovascular causes or myocardial infarction. RESULTS Over a median of 3.2 years, 318 primary outcome events occurred in the invasive-strategy group and 352 occurred in the conservative-strategy group. At 6 months, the cumulative event rate was 5.3% in the invasive-strategy group and 3.4% in the conservative-strategy group (difference, 1.9 percentage points; 95% confidence interval [CI], 0.8 to 3.0); at 5 years, the cumulative event rate was 16.4% and 18.2%, respectively (difference, 121.8 percentage points; 95% CI, 124.7 to 1.0). Results were similar with respect to the key secondary outcome. The incidence of the primary outcome was sensitive to the definition of myocardial infarction; a secondary analysis yielded more procedural myocardial infarctions of uncertain clinical importance. There were 145 deaths in the invasive-strategy group and 144 deaths in the conservative-strategy group (hazard ratio, 1.05; 95% CI, 0.83 to 1.32). CONCLUSIONS Among patients with stable coronary disease and moderate or severe ischemia, we did not find evidence that an initial invasive strategy, as compared with an initial conservative strategy, reduced the risk of ischemic cardiovascular events or death from any cause over a median of 3.2 years. The trial findings were sensitive to the definition of myocardial infarction that was used