5,294 research outputs found

    Limb Darkening and Planetary Transits II: Intensity profile correction factors for a grid of model stellar atmospheres

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    The ability to observe extrasolar planets transiting their stars has profoundly changed our understanding of these planetary systems. However, these measurements depend on how well we understand the properties of the host star, such as radius, luminosity and limb darkening. Traditionally, limb darkening is treated as a parameterization in the analysis, but these simple parameterizations are not accurate representations of actual center-to-limb intensity variations (CLIV) to the precision needed for interpreting these transit observations. This effect leads to systematic errors for the measured planetary radii and corresponding measured spectral features. We compute synthetic planetary transits using model stellar atmosphere CLIV and corresponding best-fit limb-darkening laws for a grid spherically symmetric model stellar atmospheres. From these light curves we measure the differences in flux as a function of the star's effective temperature, gravity, mass, and the inclination of the planet's orbit.Comment: 10 pages, 8 figures, submitted to AAS journals. Comments welcom

    Carnival, dialogue, and drama, in the study and presentation of a literary and a liturgical text

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    The thesis considers three pieces of dialogue.1. Ivan and Alyosha in The Brothers Karamazov by Fyodor Dostoievski. 2 Dorothy Heathcote and some sixth form students in a classroom in Stockton on Tees. 3 A priest and congregation in a church in Carlisle. In each of these dialogues one factor can be isolated. It is the factor of "jolly relativity". It is a relativizing quality. It diminishes the absolute character of any speech. Mikhail Bakhtin's theory of dialogicality is applied to the classroom drama of Dorothy Heathcote and to the Eucharistic prayer said in a church. The thesis claims that what happens in the dialogue of Alyosha and Ivan in the first extract also happens in the other two dialogues

    Simulating Electronic Commerce:A Game Environment Utilizing Software and Human Agents

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    Electronic Commerce [EC] is still in the developmental stages. Neither the technological nor the cultural constructs have solidified. The result is that there is no way of predicting what applications of EC will prosper [Kala-96]. We propose a simulation environment, that incorporates software agents and human agents in a game format to create a quasi-natural setting, for evaluating aspects of electronic commerce

    Charge-voltage curves of Shaker potassium channel are not hysteretic at steady state

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    Charge-voltage curves of many voltage-gated ion channels exhibit hysteresis but such curves are also a direct measure of free energy of channel gating and, hence, should be path-independent. Here, we identify conditions to measure steady-state charge-voltage curves and show that these are curves are not hysteretic. Charged residues in transmembrane segments of voltage-gated ion channels (VGICs) sense and respond to changes in the electric field. The movement of these gating charges underpins voltage-dependent activation and is also a direct metric of the net free-energy of channel activation. However, for most voltage-gated ion channels, the charge-voltage (Q-V) curves appear to be dependent on initial conditions. For instance, Q-V curves of Shaker potassium channel obtained by hyperpolarizing from 0 mV is left-shifted compared to those obtained by depolarizing from a holding potential of -80 mV. This hysteresis in Q-V curves is a common feature of channels in the VGIC superfamily and raises profound questions about channel energetics because the net free-energy of channel gating is a state function and should be path independent. Due to technical limitations, conventional gating current protocols are limited to test pulse durations of \u3c500 ms, which raises the possibility that the dependence of Q-V on initial conditions reflects a lack of equilibration. Others have suggested that the hysteresis is fundamental thermodynamic property of voltage-gated ion channels and reflects energy dissipation due to measurements under non-equilibrium conditions inherent to rapid voltage jumps (Villalba-Galea. 2017. Channels. https://doi.org/10.1080/19336950.2016.1243190). Using an improved gating current and voltage-clamp fluorometry protocols, we show that the gating hysteresis arising from different initial conditions in Shaker potassium channel is eliminated with ultra-long (18-25 s) test pulses. Our study identifies a modified gating current recording protocol to obtain steady-state Q-V curves of a voltage-gated ion channel. Above all, these findings demonstrate that the gating hysteresis in Shaker channel is a kinetic phenomenon rather than a true thermodynamic property of the channel and the charge-voltage curve is a true measure of the net-free energy of channel gating

    Control interface concepts for CHARA 6-telescope fringe tracking with CHAMP+MIRC

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    Cophasing six telescopes from the CHARA array, the CHARA-Michigan Phasetracker (CHAMP) and Michigan Infrared Combiner (MIRC) are pushing the frontiers of infrared long-baseline interferometric imaging in key scientific areas such as star- and planet-formation. Here we review our concepts and recent improvements on the CHAMP and MIRC control interfaces, which establish the communication to the real-time data recording & fringe tracking code, provide essential performance diagnostics, and assist the observer in the alignment and flux optimization procedure. For fringe detection and tracking with MIRC, we have developed a novel matrix approach, which provides predictions for the fringe positions based on cross-fringe information.Comment: 6 pages, 4 figures, published in SPIE conference proceedings (http://dx.doi.org/10.1117/12.926559
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