Statistical analysis of iron geochemical data suggests limited late Proterozoic oxygenation.

Sedimentary rocks deposited across the Proterozoic-Phanerozoic transition record extreme climate fluctuations, a potential rise in atmospheric oxygen or re-organization of the seafloor redox landscape, and the initial diversification of animals. It is widely assumed that the inferred redox change facilitated the observed trends in biodiversity. Establishing this palaeoenvironmental context, however, requires that changes in marine redox structure be tracked by means of geochemical proxies and translated into estimates of atmospheric oxygen. Iron-based proxies are among the most effective tools for tracking the redox chemistry of ancient oceans. These proxies are inherently local, but have global implications when analysed collectively and statistically. Here we analyse about 4,700 iron-speciation measurements from shales 2,300 to 360 million years old. Our statistical analyses suggest that subsurface water masses in mid-Proterozoic oceans were predominantly anoxic and ferruginous (depleted in dissolved oxygen and iron-bearing), but with a tendency towards euxinia (sulfide-bearing) that is not observed in the Neoproterozoic era. Analyses further indicate that early animals did not experience appreciable benthic sulfide stress. Finally, unlike proxies based on redox-sensitive trace-metal abundances, iron geochemical data do not show a statistically significant change in oxygen content through the Ediacaran and Cambrian periods, sharply constraining the magnitude of the end-Proterozoic oxygen increase. Indeed, this re-analysis of trace-metal data is consistent with oxygenation continuing well into the Palaeozoic era. Therefore, if changing redox conditions facilitated animal diversification, it did so through a limited rise in oxygen past critical functional and ecological thresholds, as is seen in modern oxygen minimum zone benthic animal communities.

Natural Language Processing and Assessment of Resident Feedback Quality.

OBJECTIVE: To validate the performance of a natural language processing (NLP) model in characterizing the quality of feedback provided to surgical trainees. DESIGN: Narrative surgical resident feedback transcripts were collected from a large academic institution and classified for quality by trained coders. 75% of classified transcripts were used to train a logistic regression NLP model and 25% were used for testing the model. The NLP model was trained by uploading classified transcripts and tested using unclassified transcripts. The model then classified those transcripts into dichotomized high- and low- quality ratings. Model performance was primarily assessed in terms of accuracy and secondary performance measures including sensitivity, specificity, and area under the receiver operating characteristic curve (AUROC). SETTING: A surgical residency program based in a large academic medical center. PARTICIPANTS: All surgical residents who received feedback via the Society for Improving Medical Professional Learning smartphone application (SIMPL, Boston, MA) in August 2019. RESULTS: The model classified the quality (high vs. low) of 2,416 narrative feedback transcripts with an accuracy of 0.83 (95% confidence interval: 0.80, 0.86), sensitivity of 0.37 (0.33, 0.45), specificity of 0.97 (0.96, 0.98), and an area under the receiver operating characteristic curve of 0.86 (0.83, 0.87). CONCLUSIONS: The NLP model classified the quality of operative performance feedback with high accuracy and specificity. NLP offers residency programs the opportunity to efficiently measure feedback quality. This information can be used for feedback improvement efforts and ultimately, the education of surgical trainees.

Spontaneous restoration of functional ß-cell mass in obese SM/J mice.

Maintenance of functional ß-cell mass is critical to preventing diabetes, but the physiological mechanisms that cause ß-cell populations to thrive or fail in the context of obesity are unknown. High fat-fed SM/J mice spontaneously transition from hyperglycemic-obese to normoglycemic-obese with age, providing a unique opportunity to study ß-cell adaptation. Here, we characterize insulin homeostasis, islet morphology, and ß-cell function during SM/J's diabetic remission. As they resolve hyperglycemia, obese SM/J mice dramatically increase circulating and pancreatic insulin levels while improving insulin sensitivity. Immunostaining of pancreatic sections reveals that obese SM/J mice selectively increase ß-cell mass but not α-cell mass. Obese SM/J mice do not show elevated ß-cell mitotic index, but rather elevated α-cell mitotic index. Functional assessment of isolated islets reveals that obese SM/J mice increase glucose-stimulated insulin secretion, decrease basal insulin secretion, and increase islet insulin content. These results establish that ß-cell mass expansion and improved ß-cell function underlie the resolution of hyperglycemia, indicating that obese SM/J mice are a valuable tool for exploring how functional ß-cell mass can be recovered in the context of obesity.