Short communication : Modeling competing effects of cooling rate, grain size, and radiation damage in low-temperature thermochronometers

Funding Information: Financial support. This research has been supported by the NSERC Discovery, and from the Geological Survey of Canada, Natural Resources Canada. Publisher Copyright: © Copyright:Low-temperature multi-thermochronometry, in which the (U-Th)ĝ€¯/ĝ€¯He and fission track methods are applied to minerals such as zircon and apatite, is a valuable approach for documenting rock cooling histories and relating them to geological processes. Here we explore the behaviors of two of the most commonly applied low-temperature thermochronometers, (U-Th)ĝ€¯/ĝ€¯He in zircon (ZHe) and apatite (AHe), and directly compare them against the apatite fission track (AFT) thermochronometer for different forward-modeled cooling scenarios. We consider the impacts that common variations in effective spherical radius (ESR) and effective uranium concentration (eU) may have on cooling ages and closure temperatures under a range of different cooling rates. This exercise highlights different scenarios under which typical age relationships between these thermochronometers (ZHe>AFT>AHe) are expected to collapse or invert (either partially or fully). We anticipate that these predictions and the associated software we provide will be a useful tool for teaching, planning low-temperature multi-thermochronometry studies, and for continued exploration of the relative behaviors of these thermochronometers in temperature-time space through forward models.Peer reviewe

The influence of upper-plate advance and erosion on overriding plate deformation in orogen syntaxes

Focused, rapid exhumation of rocks is observed at some orogen syntaxes, but the driving mechanisms remain poorly understood and contested. In this study, we use a fully coupled thermomechanical numerical model to investigate the effect of upper-plate advance and different erosion scenarios on overriding plate deformation. The subducting slab in the model is curved in 3-D, analogous to the indenter geometry observed in seismic studies. We find that the amount of upper-plate advance toward the trench dramatically changes the orientation of major shear zones in the upper plate and the location of rock uplift. Shear along the subduction interface facilitates the formation of a basal detachment situated above the indenter, causing localized rock uplift there. We conclude that the change in orientation and dip angle set by the indenter geometry creates a region of localized uplift as long as subduction of the down-going plate is active. Switching from flat (total) erosion to more realistic fluvial erosion using a landscape evolution model leads to variations in rock uplift at the scale of large catchments. In this case, deepest exhumation again occurs above the indenter apex, but tectonic uplift is modulated on even smaller scales by lithostatic pressure from the overburden of the growing orogen. Highest rock uplift can occur when a strong tectonic uplift field spatially coincides with large erosion potential. This implies that both the geometry of the subducting plate and the geomorphic and climatic conditions are important for the creation of focused, rapid exhumation.Peer reviewe

Evidence that there are only two tRNA<SUP>Phe</SUP> genes in Escherichia coli

pheV, one of the genes that code for tRNAPhe, was deleted from the chromosome of a strain of Escherichia coli K-12. As a consequence of this mutation, expression of pheA, the gene for chorismate mutase P-prephenate dehydratase, the first enzyme in the terminal pathway of phenylalanine biosynthesis, was derepressed. Similar derepression of pheA has been reported in pheR mutants of E. coli K-12 (J. Gowrishankar and J. Pittard, J. Bacteriol. 150:1130-1137, 1982). Attempts to introduce a pheR mutation into the &#916; pheV strain failed under circumstances suggesting that this combination of mutations is lethal. Southern blot analysis of pheV+ and &#916; pheV strains indicated that there are only two tRNAPhe genes in E. coli. It is recommended that the names pheU and pheV be retained for these genes

Response of a Rheologically Stratified Lithosphere to Subduction of an Indenter-Shaped Plate : Insights Into Localized Exhumation at Orogen Syntaxes

This study investigates the influence of the 3-D geometry of a down-going plate, the rheological structure of the upper plate, and the migration of the overriding plate toward the trench in relation to the overall subduction velocity on the exhumation pattern in orogen syntaxes. Using a thermomechanical numerical code (DOUAR), we analyze the strain localization, rock uplift, and exhumation response of a rheologically stratified continental lithosphere to subduction of a convex-upward-shaped indenter. The models consider three thermorheological lithospheric profiles that determine the degree of mechanical coupling between the upper crust and lithospheric mantle. These models include a strong, cratonic lithosphere; a weaker, younger (and hotter) continental plate; and an intermediate case. The strongly coupled case predicts a localization of high rock uplift rates along narrow linear bands crossing the entire model domain parallel to the trench. In contrast, in a weakly coupled lithosphere, rock uplift is concentrated within a curved ellipse region of anomalously high exhumation rates located above the indenter apex. The aspect ratio of the localized area of rapid rock uplift is controlled by the initial width of the rigid indenter and the relationship between boundary velocities. In particular, the combination of little or no upper plate migration with a narrow indenter causes a nearly circular region (similar to 100-km diameter) of rapid exhumation that resembles the pattern of thermochronometer ages observed in orogen syntaxes such as the Southeast Alaska and the Olympic Mountains of the Cascadia subduction zone (western USA).Peer reviewe

The point of maximum curvature as a marker for physiological time series

We present a geometric analysis of the model of Stirling. In particular we analyze the curvature of a heart rate time series in response to a step like increment in the exercise intensity. We present solutions for the point of maximum curvature which can be used as a marker of physiological interest. This marker defines the point after which the heart rate no longer continues to rapidly rise and instead follows either a steady state or slow rise. These methods are then applied to find analytic solutions for a mono exponential model which is commonly used in the literature to model the response to a moderate exercise intensity. Numerical solutions are then found for the full model and parameter values presented in Stirling

Ketone body 3-hydroxybutyrate as a biomarker of aggression

Human aggression is a complex behaviour, the biological underpinnings of which remain poorly known. To gain insights into aggression biology, we studied relationships with aggression of 11 low-molecular-weight metabolites (amino acids, ketone bodies), processed using H-1 nuclear magnetic resonance spectroscopy. We used a discovery sample of young adults and an independent adult replication sample. We studied 725 young adults from a population-based Finnish twin cohort born 1983-1987, with aggression levels rated in adolescence (ages 12, 14, 17) by multiple raters and blood plasma samples at age 22. Linear regression models specified metabolites as the response variable and aggression ratings as predictor variables, and included several potential confounders. All metabolites showed low correlations with aggression, with only one-3-hydroxybutyrate, a ketone body produced during fasting-showing significant (negative) associations with aggression. Effect sizes for different raters were generally similar in magnitude, while teacher-rated (age 12) and self-rated (age 14) aggression were both significant predictors of 3-hydroxybutyrate in multi-rater models. In an independent replication sample of 960 adults from the Netherlands Twin Register, higher aggression (self-rated) was also related to lower levels of 3-hydroxybutyrate. These exploratory epidemiologic results warrant further studies on the role of ketone metabolism in aggression.Peer reviewe

Megathrust Heterogeneity, Crustal Accretion, and a Topographic Embayment in the Western Nepal Himalaya : Insights From the Inversion of Thermochronological Data

Between 81 degrees 30MODIFIER LETTER PRIMEE and 83 degrees E, the Himalayan range's "perfect" arcuate shape is interrupted by an embayment. We hypothesize that thrust geometry and duplexing along the megathrust at midlower-crustal depths play a leading role in growth of the embayment as well the southern margin of the Tibetan plateau. To test this hypothesis, we conducted thermokinematic modeling of published thermochronologic data from the topographic and structural embayment in the western Nepal Himalaya to investigate the three-dimensional geometry and kinematics of the megathrust at midlower-crustal depths. Models that can best reproduce observed cooling ages suggest that the megathrust in the western Nepal Himalaya is best described as two ramps connected by a long flat that extends further north than in segments to the east and west. These models suggest that the high-slope zone along the embayment lies above the foreland limb of an antiformal crustal accretion zone on the megathrust with lateral and oblique ramps at midlower-crustal depths. The lateral and oblique ramps may have initiated by ca. 10 Ma. This process may have controlled along-strike variation in Himalayan-plateau growth and therefore development of the topographic embayment. Finally, we analyze geological and morphologic features and propose an evolution model in which landscape and drainage systems across the central-western Himalaya evolve in response to crustal accretion at depth and the three-dimensional geometry of the megathrust. Our work highlights the importance of crustal accretion at different depths in orogenic-wedge growth and that the midlower crustal accretion determines the location of plateau edge.Peer reviewe

Self-Regulation in a Web-Based Course: A Case Study

Little is known about how successful students in Web-based courses self-regulate their learning. This descriptive case study used a social cognitive model of self-regulated learning (SRL) to investigate how six graduate students used and adapted traditional SRL strategies to complete tasks and cope with challenges in a Web-based technology course; it also explored motivational and environmental influences on strategy use. Primary data sources were three transcribed interviews with each of the students over the course of the semester, a transcribed interview with the course instructor, and the students’ reflective journals. Archived course documents, including transcripts of threaded discussions and student Web pages, were secondary data sources. Content analysis of the data indicated that these students used many traditional SRL strategies, but they also adapted planning, organization, environmental structuring, help seeking, monitoring, record keeping, and self-reflection strategies in ways that were unique to the Web-based learning environment. The data also suggested that important motivational influences on SRL strategy use—self-efficacy, goal orientation, interest, and attributions—were shaped largely by student successes in managing the technical and social environment of the course. Important environmental influences on SRL strategy use included instructor support, peer support, and course design. Implications for online course instructors and designers, and suggestions for future research are offered

Sprint interval and sprint continuous training increases circulating CD34+ cells and cardio-respiratory fitness in young healthy women

The improvement of vascular health in the exercising limb can be attained by sprint interval training (SIT). However, the effects on systemic vascular function and on circulating angiogenic cells (CACs) which may contribute to endothelial repair have not been investigated. Additionally, a comparison between SIT and sprint continuous training (SCT) which is less time committing has not been made

Towards a ‘Long View’: Historical Perspectives on the Scaling and Replication of Social Ventures

Social ventures are now widely regarded as playing an essential role in addressing persistent and pervasive societal challenges. This insight has prompted an active search for readily-scaleable and replicable business models. However, relatively little consideration has been given to the longer-term growth and performance of these hybrid organizational forms. This paper examines how historically-informed research might enhance our understanding of growth processes. It considers the conceptualization of organizational growth in social ventures and the relevance of prevailing constructs. The explanatory potential of ‘long view’ approaches examined by applying three constructs, opportunity recognition, entrepreneurial adjustment, and institutional structure, in a comparative historical analysis of two British social ventures