20,634 research outputs found

    Poisson transition rates from time-domain measurements with finite bandwidth

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    In time-domain measurements of a Poisson two-level system, the observed transition rates are always smaller than those of the actual system, a general consequence of finite measurement bandwidth in an experiment. This underestimation of the rates is significant even when the measurement and detection apparatus is ten times faster than the process under study. We derive here a quantitative form for this correction using a straightforward state-transition model that includes the detection apparatus, and provide a method for determining a system's actual transition rates from bandwidth-limited measurements. We support our results with computer simulations and experimental data from time-domain measurements of quasiparticle tunneling in a single-Cooper-pair transistor.Comment: 4 pages, 5 figure

    Operator Relations for SU(3) Breaking Contributions to K and K* Distribution Amplitudes

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    We derive constraints on the asymmetry a1 of the momentum fractions carried by quark and antiquark in K and K* mesons in leading twist. These constraints follow from exact operator identities and relate a1 to SU(3) breaking quark-antiquark-gluon matrix elements which we determine from QCD sum rules. Comparing our results to determinations of a1 from QCD sum rules based on correlation functions of quark currents, we find that, for a1^\parallel(K*) the central values agree well and come with moderate errors, whereas for a1(K) and a1^\perp(K*) the results from operator relations are consistent with those from quark current sum rules, but come with larger uncertainties. The consistency of results confirms that the QCD sum rule method is indeed suitable for the calculation of a1. We conclude that the presently most accurate predictions for a1 come from the direct determination from QCD sum rules based on correlation functions of quark currents and are given by: a1(K) = 0.06\pm 0.03, a1^\parallel(K*) = 0.03\pm 0.02, a1^\perp(K*) = 0.04\pm 0.03.Comment: 21 page

    Phased array-fed antenna configuration study

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    The scope of this contract entails a configuration study for a phased array fed transmit antenna operating in the frequency band of 17.7 to 20.2 GHz. This initial contract provides a basis for understanding the design limitations and advantages of advanced phased array and cluster feeds (both utilizing intergral MMIC modules) illuminating folded reflector optics (both near field and focused types). Design parametric analyses are performed utilizing as constraints the objective secondary performance requirements of the Advanced Communications Technology Satellite (Table 1.0). The output of the study provides design information which serves as a data base for future active phased array fed antenna studies such as detailed designs required to support the development of a ground tested breadboard. In general, this study is significant because it provides the antenna community with an understanding of the basic principles which govern near field phased scanned feed effects on secondary reflector system performance. Although several articles have been written on analysis procedures and results for these systems, the authors of this report have observed phenomenon of near field antenna systems not previously documented. Because the physical justification for the exhibited performance is provided herein, the findings of this study add a new dimension to the available knowledge of the subject matter

    Phased array-fed antenna configuration study: Technology assessment

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    Spacecraft array fed reflector antenna systems were assessed for particular application to a multiple fixed spot beam/multiple scanning spot beam system. Reflector optics systems are reviewed in addition to an investigation of the feasibility of the use of monolithic microwave integrated circuit power amplifiers and phase shifters in each element of the array feed

    TM digital image products for applications

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    Computer compatible tapes (CCTs) of LANDSAT 4 thematic mapper (TM) digital image products are compared and reviewed. The following tape formats are discussed: (1) raw band-sequential data (CCT-BT); (2) calibrated data (CCT-AT); and (3) geometrically resampled data (CCT-PT). Each format represents different steps in the process of producing fully corrected TM data. The CCT-BT images are uncorrected radiometrically or geometrically, CCT-AT data are radiometrically calibrated, and CCT-PT images are both radiometrically and geometrically corrected

    TM digital image products for applications

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    The image characteristics of digital data generated by LANDSAT 4 thematic mapper (TM) are discussed. Digital data from the TM resides in tape files at various stages of image processing. Within each image data file, the image lines are blocked by a factor of either 5 for a computer compatible tape CCT-BT, or 4 for a CCT-AT and CCT-PT; in each format, the image file has a different format. Nominal geometric corrections which provide proper geodetic relationships between different parts of the image are available only for the CCT-PT. It is concluded that detector 3 of band 5 on the TM does not respond; this channel of data needs replacement. The empty bin phenomenon in CCT-AT images results from integer truncations of mixed-mode arithmetric operations

    Evaluation of Seeding Rates of AU Triumph and Endophyte-Infected Kentucky 31 Tall Fescue

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    Increased difficulty in stand establishment of tall fescue (Festuca arundinacea Schreb.) has been reported by producers since the introduction of endophyte (Acremonium coenophialum Morgan Jones and Gams)-free tall fescue seed into the market place. This has encouraged the use of higher seeding rates for endophyte-free tall fescue without scientific basis. The objective of this study was to determine whether ‘AU Triumph’, and endophyte-free cultivar, and endophyte-infected ‘Kentucky 31’ differ in minimum seeding rates for successful establishment. Experiments were established at two locations in each of two years, using a randomized complete block with four replications. Soils at the two locations were Cahaba fine sandy loam (fine-loamy, siliceous, thermic Typic Hapludult) and Sumter clay (fine-silty, carbonatic, thermic Rendollic Eutrochreps). For a period of 17-19 mo after planting, dry matter yields were determined whenever forage reached approximately 6 in. in height. Each location x year combination was analyzed independently. Linear and quadratic effects of seeding rate were tested at each harvest date, and single degree of freedom comparisons were made for cultivar effects and their interactions with the linear and quadratic effects. At harvest dates when significant linear or quadratic effects were detected for seeding rate, response curves were fitted. In some juvenile stands (first or second post planting harvests), dry matter yields increased with increasing seeding rates, or increased with increasing seeding rates to approximately 20 Ib seed/acre and then leveled off. Seeding rates did not affect tall fescue yields at later harvests. Lack of cultivar interactions with seeding rate indicates there is no basis for recommending higher seeding rates of AU Triumph than for endophyte-infected Kentucky 31 under these conditions

    The Legacy of ERA, Privatization and the Policy Ratchet

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    This article explores the ways in which the neo-liberal impetus toward the privatization of state schooling signalled in the Education Reform Act 1988 (ERA) has become embedded in the English school system. Four main points are made. First, that ERA itself was of huge strategic rather than substantive importance as far as privatization is concerned. Second, by tracing the lineage of privatization from ERA onwards a 'ratchet' effect of small and incremental policy moves can be identified, which have disseminated, embedded and naturalized privatization within public sector provision. Third, that while privatization has been taken up and taken much further by New Labour than it had been by the Conservatives there are differences between the two sets of governments in the role of privatization in education policy and the role of the state. Fourth, the participation of private providers in the planning and delivery of state services has put the private sector at the very heart of policy. At points the article draws upon interviews conducted with private sector providers. © 2008 Sage Publications

    Harnessing Marine Renewable Energy from Poole Harbour: Case Study

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    Global warming and its impact on our environment, society, economies and security is one of the fundamental concerns of our time. In response, the United Kingdom government has put in place a legally binding target of an 80% reduction in greenhouse gas emissions on 1990 levels by 2050. The United Kingdom will need to achieve a tenfold expansion of energy supply from renewable sources by 2020 to meet its share of the European Union renewable energy target. The marine and coastal environment’s renewable energy potential in Britain is high. It is estimated that it has 50% of the tidal energy, 35% of wave and 40% of wind resources in the European Union. Use of geothermal resources using heat pump technology is the least evolved sector, but in 2010 contributed to 0.7 TWh of energy and it is believed that non domestic heat pumps could contribute up to 22 TWh by 2020. In the Southwest of England, Poole Harbour has been recognised as a potential, highly predictable source of tidal and heat energy. Local groups are embarking on a feasibility study for harnessing this energy for the benefit of the community. The purpose of this article is to examine the potential conflict of interest between the laudable aims of promoting the use of renewable energy and of safeguarding ecosystems and their biodiversity. Using Poole Harbour as a case study, it will consider the environmental and economic costs and benefits of a Community Renewable Energy project (the Poole Tidal Energy Partnership) in the context of an area subject to a number of statutory and non-statutory designations to protect nationally and internationally important habitats and species. The paper identifies key environmental legislation, including spatial planning law and policy, which will facilitate exploring whether there is potential for reconciling what may be perceived as competing objectives for sustainable development
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