Learning About Teaching Science: Improving Teachers\u27 Practice Through Collaborative Professional Learning

This single, descriptive qualitative case study provides a snapshot of elementary teachers and their school principal’s multiple and competing views about personal and contextual factors affecting teacher engagement in collaborative professional learning (CPL) related to science education within the school environment. This study was viewed through the lens of Situated Learning Theory primarily by Lave and Wenger (1991) because viewing knowledge as situated has implications for understanding teacher learning and the design of instructional activities. Data were collected from three female elementary teachers and their school principal in Ontario for a period of six months. The data included: five principal interviews; two teacher focus groups; three surveys (Science Teaching Efficacy Beliefs Instrument, Science Teachers’ Pedagogical Discontentment scale, Beliefs about Reform Science Teaching and Learning); two questionnaires (demographics questionnaire, Professional Development Continuum Rubric) and; monthly professional development logs. The process of thematic coding was employed to analyze the data, and the findings were written with thick descriptions based on the narratives from the participants and descriptive data. Three interpretive insights and implications into the synthesis of the findings included: (a) the lack of emphasis on science in Ontario’s elementary education, (b) the limited time available for CPL about science, and (c) the limited number of teaching partners to collaborate about science. The interconnectedness of the three concepts highlights the multiple and complex domains that influence teacher engagement in collaborative professional learning related to elementary science education in Ontario, Canada. The overarching implication put forward in this research is the provision of ongoing professional learning with in-situ instructional science coaches working alongside the teachers to further develop their science teaching strategies related to inquiry-based approaches. To implement such concept, it is suggested that science is included in the School Effectiveness Framework so that when individual schools include science in their School Improvement Plan. Secondly, time for CPL needs to be included in teachers’ Collective Agreement. The benefits of these changes may include more teachers across the school engaging in CPL related to inquiry-based science, and expanding the network of teachers who collaborate with one another regarding science within the school setting

Two-Player Envy-Free Multi-Cake Division

We introduce a generalized cake-cutting problem in which we seek to divide multiple cakes so that two players may get their most-preferred piece selections: a choice of one piece from each cake, allowing for the possibility of linked preferences over the cakes. For two players, we show that disjoint envy-free piece selections may not exist for two cakes cut into two pieces each, and they may not exist for three cakes cut into three pieces each. However, there do exist such divisions for two cakes cut into three pieces each, and for three cakes cut into four pieces each. The resulting allocations of pieces to players are Pareto-optimal with respect to the division. We use a generalization of Sperner’s lemma on the polytope of divisions to locate solutions to our generalized cake-cutting problem

Fluctuating semiflexible polymer ribbon constrained to a ring

Twist stiffness and an asymmetric bending stiffness of a polymer or a polymer bundle is captured by the elastic ribbon model. We investigate the effects a ring geometry induces to a thermally fluctuating ribbon, finding bend-bend coupling in addition to twist-bend coupling. Furthermore, due to the geometric constraint the polymer's effective bending stiffness increases. A new parameter for experimental investigations of polymer bundles is proposed: the mean square diameter of a ribbonlike ring, which is determined analytically in the semiflexible limit. Monte Carlo simulations are performed which affirm the model's prediction up to high flexibility.Comment: 6 pages, 3 figures, Version as published in Eur. Phys. J.

A generalized theory of semiflexible polymers

DNA bending on length scales shorter than a persistence length plays an integral role in the translation of genetic information from DNA to cellular function. Quantitative experimental studies of these biological systems have led to a renewed interest in the polymer mechanics relevant for describing the conformational free energy of DNA bending induced by protein-DNA complexes. Recent experimental results from DNA cyclization studies have cast doubt on the applicability of the canonical semiflexible polymer theory, the wormlike chain (WLC) model, to DNA bending on biological length scales. This paper develops a theory of the chain statistics of a class of generalized semiflexible polymer models. Our focus is on the theoretical development of these models and the calculation of experimental observables. To illustrate our methods, we focus on a specific toy model of DNA bending. We show that the WLC model generically describes the long-length-scale chain statistics of semiflexible polymers, as predicted by the Renormalization Group. In particular, we show that either the WLC or our new model adequate describes force-extension, solution scattering, and long-contour-length cyclization experiments, regardless of the details of DNA bend elasticity. In contrast, experiments sensitive to short-length-scale chain behavior can in principle reveal dramatic departures from the linear elastic behavior assumed in the WLC model. We demonstrate this explicitly by showing that our toy model can reproduce the anomalously large short-contour-length cyclization J factors observed by Cloutier and Widom. Finally, we discuss the applicability of these models to DNA chain statistics in the context of future experiments

Heat rejection sublimator

A sublimator includes a sublimation plate having a thermal element disposed adjacent to a feed water channel and a control point disposed between at least a portion of the thermal element and a large pore substrate. The control point includes a sintered metal material. A method of dissipating heat using a sublimator includes a sublimation plate having a thermal element and a control point. The thermal element is disposed adjacent to a feed water channel and the control point is disposed between at least a portion of the thermal element and a large pore substrate. The method includes controlling a flow rate of feed water to the large pore substrate at the control point and supplying heated coolant to the thermal element. Sublimation occurs in the large pore substrate and the controlling of the flow rate of feed water is independent of time. A sublimator includes a sublimation plate having a thermal element disposed adjacent to a feed water channel and a control point disposed between at least a portion of the thermal element and a large pore substrate. The control point restricts a flow rate of feed water from the feed water channel to the large pore substrate independent of time

Ion measurements during Pioneer Venus reentry: Implications for solar cycle variation of ion composition and dynamics

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95616/1/grl7044.pd

Geochemical fingerprints of seawater in the Late Mesoproterozoic Midcontinent Rift, North America : life at the marine-land divide

The 1.1 Ga Midcontinent Rift (MCR) is a thick volcanic-sedimentary succession that forms a curvilinear belt through central North America and crops out along its northern apex around Lake Superior. Sedimentary units of the MCR have been long interpreted as fluvial-lacustrine and invited a number of studies on the early evolution of life in non-marine habitats. One of the key units is the siliciclastic Nonesuch Formation, thought to record deposition in a large lake. However, recent sedimentological observations indicate the presence of marine incursions. To further test this interpretation, we analysed trace element abundances in a broad suite of samples from multiple drill cores through the Nonesuch Formation. We aimed to differentiate geochemical influences of sediment provenance from post-depositional hydrothermal overprint and thereby identify authigenic enrichments in fluid-mobile elements that are indicators of primary environmental conditions. Our results reveal discrete enrichments in Mo and U in organic- and sulphide-rich horizons, which are most parsimoniously interpreted as marine signatures. This conclusion is supported by Sr/Ba ratios, which suggest mixing between freshwater and saltwater, and by rare cm-thick gypsum in the upper Copper Harbor Formation immediately below the Nonesuch rocks. The gypsum displays δ34S values of +25.9 ± 0.6‰, consistent with input of marine sulphate at least during parts of the basin's history. Collectively, our geochemical data support the sedimentological interpretation that this portion of the MCR archives a marine-influenced estuarine system. Although this conclusion rules out that microbial life documented from the MCR was living in exclusively freshwater habitats, the Nonesuch Fm and associated rocks still hold important clues about organisms that were capable of withstanding salinity gradients and bridging the gap between the marine and non-marine environments of the mid-Proterozoic.PostprintPeer reviewe

Implementing Primordial Binaries in Simulations of Star Cluster Formation with a Hybrid MHD and Direct N-Body Method

The fraction of stars in binary systems within star clusters is important for their evolution, but what proportion of binaries form by dynamical processes after initial stellar accretion remains unknown. In previous work, we showed that dynamical interactions alone produced too few low-mass binaries compared to observations. We therefore implement an initial population of binaries in the coupled MHD and direct N-body star cluster formation code Torch. We compare simulations with, and without, initial binary populations and follow the dynamical evolution of the binary population in both sets of simulations, finding that both dynamical formation and destruction of binaries take place. Even in the first few million years of star formation, we find that an initial population of binaries is needed at all masses to reproduce observed binary fractions for binaries with mass ratios above the $q \geq 0.1$ detection limit. Our simulations also indicate that dynamical interactions in the presence of gas during cluster formation modify the initial distributions towards binaries with smaller primary masses, larger mass ratios, smaller semi-major axes and larger eccentricities. Systems formed dynamically do not have the same properties as the initial systems, and systems formed dynamically in the presence of an initial population of binaries differ from those formed in simulations with single stars only. Dynamical interactions during the earliest stages of star cluster formation are important for determining the properties of binary star systems.Comment: 15 pages, 14 figures, submitted to MNRAS and edited to address positive referee's repor

Quantifying the Bayesian Evidence for a Planet in Radial Velocity Data

We present results from a data challenge posed to the radial velocity (RV) community: Namely, to quantify the Bayesian "evidence"for n = {0, 1, 2, 3} planets in a set of synthetically generated RV data sets containing a range of planet signals. Participating teams were provided the same likelihood function and set of priors to use in their analysis. They applied a variety of methods to estimate the marginal likelihood for each n-planet model, including cross-validation, the Laplace approximation, importance sampling, and nested sampling. We found the dispersion in across different methods grew with increasing n-planet models: ∼3 for zero planets, ∼10 for one planet, ∼102-103 for two planets, and >104 for three planets. Most internal estimates of uncertainty in for individual methods significantly underestimated the observed dispersion across all methods. Methods that adopted a Monte Carlo approach by comparing estimates from multiple runs yielded plausible uncertainties. Finally, two classes of numerical algorithms (those based on importance and nested samplers) arrived at similar conclusions regarding the ratio of for n- A nd (n + 1)-planet models. One analytic method (the Laplace approximation) demonstrated comparable performance. We express both optimism and caution: We demonstrate that it is practical to perform rigorous Bayesian model comparison for models of ≤3 planets, yet robust planet discoveries require researchers to better understand the uncertainty in and its connections to model selection.Fil: Nelson, Benjamin E.. Northwestern University; Estados UnidosFil: Ford, Eric B.. Pennsylvania State University; Estados UnidosFil: Buchner, Johannes. Pontificia Universidad Católica de Chile; Chile. Universidad Católica de Chile; ChileFil: Cloutier, Ryan. University of Toronto; CanadáFil: Díaz, Rodrigo Fernando. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Faria, Joaõ P.. Universidad de Porto; PortugalFil: Hara, Nathan C.. Universite Ifm Geneve (ifm); SuizaFil: Rajpaul, Vinesh M.. University of Cambridge; Estados UnidosFil: Rukdee, Surangkhana. Pontificia Universidad Católica de Chile; Chile. Universidad Católica de Chile; Chil