64,158 research outputs found

    On the existence of asymptotically good linear codes in minor-closed classes

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    Let C=(C1,C2,…)\mathcal{C} = (C_1, C_2, \ldots) be a sequence of codes such that each CiC_i is a linear [ni,ki,di][n_i,k_i,d_i]-code over some fixed finite field F\mathbb{F}, where nin_i is the length of the codewords, kik_i is the dimension, and did_i is the minimum distance. We say that C\mathcal{C} is asymptotically good if, for some ε>0\varepsilon > 0 and for all ii, ni≥in_i \geq i, ki/ni≥εk_i/n_i \geq \varepsilon, and di/ni≥εd_i/n_i \geq \varepsilon. Sequences of asymptotically good codes exist. We prove that if C\mathcal{C} is a class of GF(pn)(p^n)-linear codes (where pp is prime and n≥1n \geq 1), closed under puncturing and shortening, and if C\mathcal{C} contains an asymptotically good sequence, then C\mathcal{C} must contain all GF(p)(p)-linear codes. Our proof relies on a powerful new result from matroid structure theory

    Agenda for Change: views and experiences from estates and facilities staff

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    Purpose – Agenda for Change is the biggest reform of staff pay in the UK National Health Service NHS) since it began in 1948. As well as introducing a standardised pay structure; it also aims to improve recruitment, retention and staff morale. The aim of this study is to look in-depth at the experiences and opinions of a range of estates and facilities staff surrounding Agenda for Change during the implementation period. Design/methodology/approach – Focus groups were used as the primary method of data collection in an attempt to tap into the views and opinions of staff working at operational positions in a wide range of trusts. Findings – One of the most important and common themes, which reoccurred throughout the focus groups, was the view that the Agenda for Change framework was designed around the needs of nursing staff. Therefore, the framework did not adequately cater for the needs of estates and facilities staff. Specific concerns related to this included; the role or contribution of estates and facilities staff during patient care was not fairly reflected; trade qualifications were not recognised, particularly in comparison to academic qualifications; members of the job matching panels did not have the appropriate knowledge to make decisions surrounding estates and facilities jobs; nurses were more likely to make progress through the bands than estates and facilities staff.</p

    Development of Heterogeneous Photosensitized Transition Metal Oxide Water-Splitting Catalysts on Silica Support

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    The research presented in this manuscript describes the development of photosensitized inexpensive catalysts based on readily available materials. The investigation covers synthesis and characterization of photosensitizers based on porphyrins, mechanical and thermal coating of solid support with semiconducting transition metal oxides, photosensitization of the semiconducting layer, and characterization of the photoelectrochemical properties displayed by the new materials. The process of water oxidation is of primary interest here, with little emphasis put on reduction of protons to gaseous hydrogen. Photoelectrochemically produced protons serve as a probe of effectiveness of the catalysts. Several systems are described, and two catalysts are identified as the most efficient

    DETERMINANTS OF THE VALUE OF SITE-SPECIFIC INFORMATION (SSI) IN AGRICULTURE: A UNIFYING THEORY TO ANALYZE ITS RELATIVE IMPACTS

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    This paper develops a theoretically consistent behavioral model of farmer decision-making that allows for analysis of the relative impacts of the determinants of SSI value. The model departs from previous literature by assuming that SSI reduces uncertainty, but not eliminate it. Results show that increasing the accuracy (or the "level of informativeness") of SSI, increasing initial wealth, improving management ability to reduce uncertainty in the posterior, and increasing the uncertainty in the prior, increases the value of SSI. Furthermore, mean input use is found to decrease, as SSI becomes more "informative." On the other hand, the value of SSI is found to be decreasing as relative risk aversion increases. These results have policy implications for controlling non-point source pollution from fertilizer inputs and SSI-adoption behavior.Farm Management, Research Methods/ Statistical Methods,

    Dust obscuration studies along quasar sight lines using simulated galaxies

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    We use the results of a set of three-dimensional SPH-Treecode simulations which model the formation and early evolution of disk galaxies, including the generation of heavy elements by star formation, to investigate the effects of dust absorption in quasar absorption line systems. Using a simple prescription for the production of dust, we have compared the column density, zinc abundance and optical depth properties of our models to the known properties of Damped Lyman alpha systems. We find that a significant fraction of our model galaxy disks have a higher column density than any observed DLA system. We are also able to show that such parts of the disk tend to be optically thick, implying that any background quasar would be obscured through much of the disk. This would produce the selection effect against the denser absorption systems thought to be present in observations.Comment: 7 pages, 8 figures, to be published in MNRA

    Localization transitions in non-Hermitian quantum mechanics

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    We study the localization transitions which arise in both one and two dimensions when quantum mechanical particles described by a random Schr\"odinger equation are subjected to a constant imaginary vector potential. A path-integral formulation relates the transition to flux lines depinned from columnar defects by a transverse magnetic field in superconductors. The theory predicts that the transverse Meissner effect is accompanied by stretched exponential relaxation of the field into the bulk and a diverging penetration depth at the transition.Comment: 4 pages (latex) with 3 figures (epsf) embedded in the text using the style file epsf.st

    Jointly Optimal Channel Pairing and Power Allocation for Multichannel Multihop Relaying

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    We study the problem of channel pairing and power allocation in a multichannel multihop relay network to enhance the end-to-end data rate. Both amplify-and-forward (AF) and decode-and-forward (DF) relaying strategies are considered. Given fixed power allocation to the channels, we show that channel pairing over multiple hops can be decomposed into independent pairing problems at each relay, and a sorted-SNR channel pairing strategy is sum-rate optimal, where each relay pairs its incoming and outgoing channels by their SNR order. For the joint optimization of channel pairing and power allocation under both total and individual power constraints, we show that the problem can be decoupled into two subproblems solved separately. This separation principle is established by observing the equivalence between sorting SNRs and sorting channel gains in the jointly optimal solution. It significantly reduces the computational complexity in finding the jointly optimal solution. It follows that the channel pairing problem in joint optimization can be again decomposed into independent pairing problems at each relay based on sorted channel gains. The solution for optimizing power allocation for DF relaying is also provided, as well as an asymptotically optimal solution for AF relaying. Numerical results are provided to demonstrate substantial performance gain of the jointly optimal solution over some suboptimal alternatives. It is also observed that more gain is obtained from optimal channel pairing than optimal power allocation through judiciously exploiting the variation among multiple channels. Impact of the variation of channel gain, the number of channels, and the number of hops on the performance gain is also studied through numerical examples.Comment: 15 pages. IEEE Transactions on Signal Processin
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