National Educators' Workshop: Update 1988. Standard Experiments in Engineering Materials Science and Technology

Presented here is a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 88, held May 10 to 12, 1988 at the National Institute of Standards and Technology (NIST), Gaithersberg, Maryland. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community

National Educators' Workshop: Update 1989 Standard Experiments in Engineering Materials Science and Technology

Presented here is a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 89, held October 17 to 19, 1989 at the National Aeronautics and Space Administration, Hampton, Virginia. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community

National Educators' Workshop: Update 1991. Standard Experiments in Engineering Materials Science and Technology

Given here is a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 91, held at the Oak Ridge National Laboratory on November 12-14, 1991. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community

Faculty Perceptions of Teacher Professionalism in Christian Schools

Able school administrators understand that teachers are their most valuable asset. If Christian schools are to effectively serve the families who entrust their children to their care, teachers must demonstrate both professional competency and godly character. This study was an investigation of faculty perceptions of teacher professionalism at ten Christian schools in the mid-Atlantic region of the United States. An online survey of 24 items was completed by 230 teachers (males=30; females=200). The survey instrument was a modified version of Tichenor and Tichenor’s (2009) four dimensions of teacher professionalism. Data were analyzed using a multivariate analysis-of-variance (MANOVA) with gender as the independent variable. Results demonstrated statistically significant variance in totals on 18 of 24 individual items, three of the four dimensions, and on the total score

Corrigenda to and validation of Ozophora woodruffi Slater 2005 (Hemiptera: Lygaeidae)

Important missing specimen data are provided for the original description of Ozophora woodruffi Slater (2005: 245) (Hemiptera: Lygaeidae), along with additional comparative relationships. Because of the missing type information, according to ICZN rules (1999), the species became a nomen nudum. This paper now serves to validate the name, and authorship becomes Slater (2012)

Stochastic Ratcheting on a Funneled Energy Landscape is Necessary for Highly Efficient Contractility of Actomyosin Force Dipoles

Current understanding of how contractility emerges in disordered actomyosin networks of non-muscle cells is still largely based on the intuition derived from earlier works on muscle contractility. This view, however, largely overlooks the free energy gain following passive cross-linker binding, which, even in the absence of active fluctuations, provides a thermodynamic drive towards highly overlapping filamentous states. In this work, we shed light on this phenomenon, showing that passive cross-linkers, when considered in the context of two anti-parallel filaments, generate noticeable contractile forces. However, as binding free energy of cross-linkers is increased, a sharp onset of kinetic arrest follows, greatly diminishing effectiveness of this contractility mechanism, allowing the network to contract only with weakly resisting tensions at its boundary. We have carried out stochastic simulations elucidating this mechanism, followed by a mean-field treatment that predicts how contractile forces asymptotically scale at small and large binding energies, respectively. Furthermore, when considering an active contractile filament pair, based on non-muscle myosin II, we found that the non-processive nature of these motors leads to highly inefficient force generation, due to recoil slippage of the overlap during periods when the motor is dissociated. However, we discovered that passive cross-linkers can serve as a structural ratchet during these unbound motor time spans, resulting in vast force amplification. Our results shed light on the non-equilibrium effects of transiently binding proteins in biological active matter, as observed in the non-muscle actin cytoskeleton, showing that highly efficient contractile force dipoles result from synergy of passive cross-linker and active motor dynamics, via a ratcheting mechanism on a funneled energy landscape.Comment: 13 pages, 6 figure

A quantum dynamical comparison of the electronic couplings derived from quantum electrodynamics and Förster theory:Application to 2D molecular aggregates

The objective of this study is to investigate under what circumstances Förster theory of electronic (resonance) energy transfer breaks down in molecular aggregates. This is achieved by simulating the dynamics of exciton diffusion, on the femtosecond timescale, in molecular aggregates using the Liouville–von Neumann equation of motion. Specifically the focus of this work is the investigation of both spatial and temporal deviations between exciton dynamics driven by electronic couplings calculated from Förster theory and those calculated from quantum electrodynamics. The quantum electrodynamics (QED) derived couplings contain medium- and far-zone terms that do not exist in Förster theory. The results of the simulations indicate that Förster coupling is valid when the dipole centres are within a few nanometres of one another. However, as the distance between the dipole centres increases from 2 nm to 10 nm, the intermediate- and far-zone coupling terms play non-negligible roles and Förster theory begins to break down. Interestingly, the simulations illustrate how contributions to the exciton dynamics from the intermediate- and far-zone coupling terms of QED are quickly washed-out by the near-zone mechanism of Förster theory for lattices comprising closely packed molecules. On the other hand, in the case of sparsely packed arrays, the exciton dynamics resulting from the different theories diverge within the 100 fs lifetime of the trajectories. These results could have implications for the application of spectroscopic ruler techniques as well as design principles relating to energy harvesting materials

UV driven evaporation of close-in planets: energy-limited; recombination-limited and photon-limited flows

We have investigated the evaporation of close-in exoplanets irradiated by ionizing photons. We find that the properties of the flow are controlled by the ratio of the recombination time to the flow time-scale. When the recombination time-scale is short compared to the flow time-scale the the flow is in approximate local ionization equilibrium with a thin ionization front, where the photon mean free path is short compared to flow scale. In this "recombination limited" flow the mass-loss scales roughly with the square root of the incident flux. When the recombination time is long compared to the flow time-scale the ionization front becomes thick and encompasses the entire flow, with the mass-loss rate scaling linearly with flux. If the planet's potential is deep the flow is approximately "energy-limited"; however, if the planet's potential is shallow we identify a new limiting mass-loss regime, which we term "photon-limited". In this scenario the mass-loss rate is purely limited by the incoming flux of ionizing photons. We have developed a new numerical approach that takes into account the frequency dependence of the incoming ionizing spectrum and performed a large suite of 1D simulations to characterise UV driven mass-loss around low mass planets. We find the flow is "recombination-limited" at high fluxes but becomes "energy-limited" at low fluxes; however, the transition is broad occurring over several order of magnitude in flux. Finally, we point out the transitions between the different flow types does not occur at a single flux value, but depends on the planet's properties, with higher mass planets becoming "energy-limited" at lower fluxes.Comment: Published in Ap