3,503 research outputs found

    Review of high-contrast imaging systems for current and future ground- and space-based telescopes I: coronagraph design methods and optical performance metrics

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    The Optimal Optical Coronagraph (OOC) Workshop at the Lorentz Center in September 2017 in Leiden, the Netherlands gathered a diverse group of 25 researchers working on exoplanet instrumentation to stimulate the emergence and sharing of new ideas. In this first installment of a series of three papers summarizing the outcomes of the OOC workshop, we present an overview of design methods and optical performance metrics developed for coronagraph instruments. The design and optimization of coronagraphs for future telescopes has progressed rapidly over the past several years in the context of space mission studies for Exo-C, WFIRST, HabEx, and LUVOIR as well as ground-based telescopes. Design tools have been developed at several institutions to optimize a variety of coronagraph mask types. We aim to give a broad overview of the approaches used, examples of their utility, and provide the optimization tools to the community. Though it is clear that the basic function of coronagraphs is to suppress starlight while maintaining light from off-axis sources, our community lacks a general set of standard performance metrics that apply to both detecting and characterizing exoplanets. The attendees of the OOC workshop agreed that it would benefit our community to clearly define quantities for comparing the performance of coronagraph designs and systems. Therefore, we also present a set of metrics that may be applied to theoretical designs, testbeds, and deployed instruments. We show how these quantities may be used to easily relate the basic properties of the optical instrument to the detection significance of the given point source in the presence of realistic noise

    Nanosecond-timescale spin transfer using individual electrons in a quadruple-quantum-dot device

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    The ability to coherently transport electron-spin states between different sites of gate-defined semiconductor quantum dots is an essential ingredient for a quantum-dot-based quantum computer. Previous shuttles using electrostatic gating were too slow to move an electron within the spin dephasing time across an array. Here we report a nanosecond-timescale spin transfer of individual electrons across a quadruple-quantum-dot device. Utilizing enhanced relaxation rates at a so-called `hot spot', we can upper bound the shuttle time to at most 150 ns. While actual shuttle times are likely shorter, 150 ns is already fast enough to preserve spin coherence in e.g. silicon based quantum dots. This work therefore realizes an important prerequisite for coherent spin transfer in quantum dot arrays.Comment: 7 pages including 2 pages of supplementary materia

    A Multicomponent Lattice Boltzmann Model for Multiphase Convection, Diffusion, and Reaction in Two Dimensions

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    The lattice Boltzmann method is a promising technique for modeling of multiphase fluids. In this paper, a multicomponent multiple-relaxation-time (MRT) model is developed for mass and momentum transport. In this model, diffusion of mass is defined in a fundamentally correct manner – gradients of chemical potential are the driving force for this movement. As a result, distinct fluid phases form or disappear as a result of diffusion toward a local chemical equilibrium. Numerical analysis of the model proves that the desired mass and momentum transport is being achieved and the multiphase performance of the model is tested numerically

    Development of Cortical GABAergic Innervation

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    The mature neocortex contains many different classes of GABAergic inhibitory interneurons, distributed, with some degree of selectivity, through six layers, and through many different regions. Some of the events in the early lives of these neurones that may determine their ultimate destination, their maturation and their selective innervation of targets appropriate for each subtype, are discussed. Both time and place of birth influence the class of interneuron that an early post-mitotic interneuronal precursor will become, driven by the selective expression of different combinations of transcription factors in different regions of their birth places in the ganglionic eminence and ventricular zone. The long distance migration of these precursors along tangential routes in marginal, subventricular, and intermediate zones and their final radial movement, into the developing cortex, is regulated by chemical cues, both attractant and repellent. Once they arrive at their final destination, they must integrate into the developing circuitry. As they mature within the cortex, their axons grow and branch in highly specific patterns that may be partially determined by the genetic blueprint for each interneuronal class and partly by the environment in which they find themselves. Finally, as each interneuron class begins to form synapses with only certain postsynaptic targets, cell–cell recognition, most probably via protein–protein interactions across the synaptic cleft, facilitate the formation of appropriate synapses

    GABA(A) receptor phospho-dependent modulation is regulated by phospholipase C-related inactive protein type 1, a novel protein phosphatase 1 anchoring protein

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    GABA(A) receptors are critical in controlling neuronal activity. Here, we examined the role for phospholipase C-related inactive protein type 1 (PRIP-1), which binds and inactivates protein phosphatase 1alpha (PP1alpha) in facilitating GABA(A) receptor phospho-dependent regulation using PRIP-1(-/-) mice. In wild-type animals, robust phosphorylation and functional modulation of GABA(A) receptors containing beta3 subunits by cAMP-dependent protein kinase was evident, which was diminished in PRIP-1(-/-) mice. PRIP-1(-/-) mice exhibited enhanced PP1alpha activity compared with controls. Furthermore, PRIP-1 was able to interact directly with GABA(A) receptor beta subunits, and moreover, these proteins were found to be PP1alpha substrates. Finally, phosphorylation of PRIP-1 on threonine 94 facilitated the dissociation of PP1alpha-PRIP-1 complexes, providing a local mechanism for the activation of PP1alpha. Together, these results suggest an essential role for PRIP-1 in controlling GABA(A) receptor activity via regulating subunit phosphorylation and thereby the efficacy of neuronal inhibition mediated by these receptors

    On the new very early table varieties obtained by crossing different varieties of grapevine

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    In order to obtain new table grape varieties which ripen before or at the same time as variety Pearl of Csaba, we performed many intervarietal crossings at our experimental station, using the following parents: Pearl of Csaba, Chasselas Bouvier, Muscat Ottonel, Queen of Vineyard, Cardinal, Dattier de Beyrouth, Ribier.The Government Commission acknowledged five very early varieties, three of which have also better agrobiological and technological characteristics than the variety Pearl of Csaba.The new variety Demir Door ripens on average 6 d, the new variety Early of Belgrade 3-5 d earlier, and the new variety Grochanka ripens at the same time or 1-3 d later as the control variety Pearl of Csaba.Due to multiple regression analysis, biological characteristics as yield, cluster and berry weights and sugar content strongly depend on meteorological conditions (temperature, rainfall and solar radiation); this is valid for all the new varieties and the variety Pearl of Csaba at all locations investigated.Analysis of variance (level of 0.05 and 0.01) shows that compared to the control variety we obtained with new varieties significantly greater yields, very significant large cluster and berry weights and very significantly better uvological characteristics of berry. The average yields for all investigated locations were increased in comparison to the control variety Pearl of Csaba: Demir Door +3.004 kg/ha, Early of Belgrade +6.259 kg/ha, Grochanka +7.065 kg/ha.Organoleptic characteristics are much improved with all new varieties which is illustrated by increased indexes.All investigated varieties are acknowledged genotypes of Vitis vinifera L, and all of these new varieties exhibited better biological and technological parameters than Pearl of Csaba

    A review of strategies, methods and technologies to reduce non-beneficial consumptive water use on farms considering the FAO56 methods

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    In the past few decades, research has developed a multitude of strategies, methods and technologies to reduce consumptive water use on farms for adaptation to the increasing incidence of water scarcity, agricultural droughts and multi-sectoral competition for water. The adoption of these water-saving practices implies accurate quantification of crop water requirements with the FAO56 crop coefficient approach, under diverse water availability and management practices. This paper critically reviews notions and means for maintaining high levels of water consumed through transpiration, land and water productivity, and for minimizing non-beneficial water consumption at farm level. Literature published on sound and quantified experimentation was used to evaluate water-saving practices related to irrigation methods, irrigation management and scheduling, crop management, remote sensing, plant conditioners, mulching, soil management and micro-climate regulation. Summary tables were developed on the benefits of these practices, their effects on non-beneficial water consumption, crop yields and crop water productivity, and the directions for adjustment of FAO56 crop coefficients when they are adopted. The main message is that on-farm application of these practices can result in water savings to a limited extent (usually<20%) compared to sound conventional practices, however this may translate into large volumes of water at catchment scale. The need to streamline data collection internationally was identified due to the insufficient number of sound field experiments and modelling work on the FAO56 crop water requirements that would allow an improved use of crop coefficients for different field conditions and practices. Optimization is required for the application of some practices that involve a large number of possible combinations (e.g. wetted area in micro-irrigation, row spacing and orientation, plant density, different types of mulching, in-field water harvesting) and for strategies such as deficit irrigation that aim at balancing water productivity, the economics of production, infrastructural and irrigation system requirements. Further research is required on promising technologies such as plant and soil conditioners, and remote sensing applicationsinfo:eu-repo/semantics/publishedVersio
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