Inlet spillage drag tests and numerical flow-field analysis at subsonic and transonic speeds of a 1/8-scale, two-dimensional, external-compression, variable-geometry, supersonic inlet configuration

Accurate spillage drag and pressure data are presented for a realistic supersonic inlet configuration. Results are compared with predictions from a finite-differencing, inviscid analysis computer procedure. The analytical technique shows good promise for the evaluation of inlet drag, but necessary refinements were identified. A detailed description of the analytical procedure is contained in the Appendix

Bounds on the subdominant eigenvalue involving group inverses with applications to graphs

summary:Let $A$ be an $n\times n$ symmetric, irreducible, and nonnegative matrix whose eigenvalues are $\lambda _1 > \lambda _2 \ge \ldots \ge \lambda _n$. In this paper we derive several lower and upper bounds, in particular on $\lambda _2$ and $\lambda _n$, but also, indirectly, on $\mu = \max _{2\le i \le n} |\lambda _i|$. The bounds are in terms of the diagonal entries of the group generalized inverse, $Q^{\#}$, of the singular and irreducible M-matrix $Q=\lambda _1 I-A$. Our starting point is a spectral resolution for $Q^{\#}$. We consider the case of equality in some of these inequalities and we apply our results to the algebraic connectivity of undirected graphs, where now $Q$ becomes $L$, the Laplacian of the graph. In case the graph is a tree we find a graph-theoretic interpretation for the entries of $L^{\#}$ and we also sharpen an upper bound on the algebraic connectivity of a tree, which is due to Fiedler and which involves only the diagonal entries of $L$, by exploiting the diagonal entries of $L^{\#}$

Large igneous provinces track fluctuations in subaerial exposure of continents across the Archean–Proterozoic transition

Geological observations and numerical models imply that Archean continents were mostly submarine. In contrast, approximately one third of modern earth's surface area consists of subaerial continental crust. To temporally constrain changes in the subaerial exposure of continents, we evaluate the eruptive environment (submarine vs subaerial) of 3.4–2.0 Ga continental large igneous provinces (LIPs). Our results indicate that up until 2.4 Ga LIPs predominantly erupted onto submerged continents. This period of low freeboard was punctuated by local subaerial eruptions at 2.8–2.7 Ga and 2.5 Ga. From 2.4 Ga–2.2 Ga, extensive subaerial continental volcanism is recorded in six different cratons, supporting widespread subaerial continents at this time. An increase in exposed continental crust significantly impacts atmospheric and oceanic geochemical cycles and the supply of nutrients for marine bioproductivity. Thus, the 2.4–2.2 Ga high-freeboard conditions may have triggered the earliest global glaciation event and the first significant rise of atmospheric oxygen

Mesoarchean partial melting of mafic crust and tonalite production during high-T–low-P stagnant tectonism, Akia Terrane, West Greenland

The Ministry of Mineral Resources and Labour, Greenland Government supported field and analytical work. NJG acknowledges support from Australian Research Council grant FL160100168.Different geodynamic models exist for the growth and differentiation of Archean continental crust, ranging from horizontal tectonics with subduction zones to vertical tectonics with foundering of greenstone sequences. U–Pb zircon geochronology, field relationships, and pressure–temperature constraints from granulite-facies metabasite of the Akia Terrane of the North Atlantic Craton in West Greenland show that this terrane grew through two major magmatic growth episodes: an earlier one at c. 3.2 Ga, and a later one at c. 3.05–2.97 Ga. Phase equilibrium modelling for assemblages related to the latter indicates temperatures of >800 °C at 0.8 GPa in the stability field of garnet. U–Pb zircon geochronology and existing Hf isotope data are also consistent with a model involving protracted Mesoarchean magmatic growth with limited mantle addition during a prolonged period of high temperatures in a relatively stagnant tectonic regime prior to Neoarchean compressional tectonism in the Akia Terrane.Publisher PDFPeer reviewe

A Large, First-Year, Introductory, Multi-Sectional Biological Concepts of Health Course Designed to Develop Skills and Enhance Deeper Learning

Large first-year biology classes, with their heavy emphasis on factual content, contribute to low student engagement and misrepresent the dynamic, interdisciplinary nature of biological science. We sought to redesign a course to deliver fundamental biology curriculum through the study of health, promote skills development, and encourage a deeper level of learning for a large, multi-section first-year class. We describe the Biological Concepts of Health course designed to encourage higher-order learning and teach oral communication and independent learning skills to large numbers of first-year students. We used the Blooming Biology Tool to determine the cognitive skills level assessed in the newly developed course and the courses it replaced. This evidence-based approach demonstrated that our new course design achieved the goal of encouraging a deeper level of cognition, and further, successfully introduced both oral communication and independent learning skills in large first-year classes.  En mettant l’emphase sur un contenu factuel, les grandes classes de biologie de première année contribuent au faible engagement des élèves et donnent une représentation imprécise de la nature dynamique et interdisciplinaire des sciences de la biologie. Afin d’offrir un programme fondamental en biologie par l’étude de la santé, de promouvoir le perfectionnement des compétences et d’encourager un niveau d’apprentissage marqué, nous avons repensé un cours pour une grande classe de première année contenant plusieurs sous-groupes. Nous décrivons le cours « Biological Concepts of Health » conçu pour encourager l’apprentissage supérieur, ainsi que pour enseigner la communication orale et les habiletés d’apprentissage individualisé à un grand nombre d’étudiants de première année. Pour déterminer le niveau d’habiletés cognitives évalué dans ce cours nouvellement conçu et les cours qu’il remplace, nous avons utilisé le « Blooming Biology Tool ». Cette approche éprouvée démontre que ce nouveau cours a atteint son but d’encourager l’approfondissement des connaissances et, par ailleurs, a réussi à introduire la communication orale, de même que les habiletés d’apprentissage individualisé aux grandes classes de première année

North Atlantic Craton architecture revealed by kimberlite-hosted crustal zircons

The Maniitsoq project is supported by the Ministry of Mineral Resources, Government of Greenland. NJG and PAC thank Australian Research Council grant FL160100168 for financial support. ON is supported by Australian Research Council grant FT140101062 and the Melbourne TIE team.Archean cratons are composites of terranes formed at different times, juxtaposed during craton assembly. Cratons are underpinned by a deep lithospheric root, and models for the development of this cratonic lithosphere include both vertical and horizontal accretion. How different Archean terranes at the surface are reflected vertically within the lithosphere, which might inform on modes of formation, is poorly constrained. Kimberlites, which originate from significant depths within the upper mantle, sample cratonic interiors. The North Atlantic Craton, West Greenland, comprises Eoarchean and Mesoarchean gneiss terranes – the latter including the Akia Terrane – assembled during the late Archean. We report U–Pb and Hf isotopic, and trace element, data measured in zircon xenocrysts from a Neoproterozoic (557 Ma) kimberlite which intruded the Mesoarchean Akia Terrane. The zircon trace element profiles suggest they crystallized from evolved magmas, and their Eo- to Neoarchean U–Pb ages match the surrounding gneiss terranes, and highlight that magmatism was episodic. Zircon Hf isotope values lie within two crustal evolution trends: a Mesoarchean trend and an Eoarchean trend. The Eoarchean trend is anchored on 3.8 Ga orthogneiss, and includes 3.6–3.5 Ga, 2.7 and 2.5–2.4 Ga aged zircons. The Mesoarchean Akia Terrane may have been built upon mafic crust, in which case all zircons whose Hf isotopes lie within the Eoarchean trend were derived from the surrounding Eoarchean gneiss terranes, emplaced under the Akia Terrane after ca. 2.97 or 2.7 Ga, perhaps during late Archean terrane assembly. Kimberlite-hosted peridotite rhenium depletion model ages suggest a late Archean stabilization for the lithospheric mantle. The zircon data support a model of lithospheric growth via tectonic stacking for the North Atlantic Craton.Publisher PDFPeer reviewe

Stirred not shaken; critical evaluation of a proposed Archean meteorite impact in West Greenland

Funding Information: The Ministry of Mineral Resources and Labour, Greenland Government supported field and analytical work.Large meteorite impacts have a profound effect on the Earth's geosphere, atmosphere, hydrosphere and biosphere. It is widely accepted that the early Earth was subject to intense bombardment from 4.5 to 3.8 Ga, yet evidence for subsequent bolide impacts during the Archean Eon (4.0 to 2.5 Ga) is sparse. However, understanding the timing and magnitude of these early events is important, as they may have triggered significant change points to global geochemical cycles. The Maniitsoq region of southern West Greenland has been proposed to record a ∼3.0 Ga meteorite impact, which, if confirmed, would be the oldest and only known impact structure to have survived from the Archean. Such an ancient structure would provide the first insight into the style, setting, and possible environmental effects of impact bombardment continuing into the late Archean. Here, using field mapping, geochronology, isotope geochemistry, and electron backscatter diffraction mapping of 5,587 zircon grains from the Maniitsoq region (rock and fluvial sediment samples), we test the hypothesis that the Maniitsoq structure represents Earth's earliest known impact structure. Our comprehensive survey shows that previously proposed impact-related geological features, ranging from microscopic structures at the mineral scale to macroscopic structures at the terrane scale, as well as the age and geochemistry of the rocks in the Maniitsoq region, can be explained through endogenic (non-impact) processes. Despite the higher impact flux, intact craters from the Archean Eon remain elusive on Earth.Publisher PDFPeer reviewe