4,172,057 research outputs found

    Uncovering missing links with cold ends

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    To evaluate the performance of prediction of missing links, the known data are randomly divided into two parts, the training set and the probe set. We argue that this straightforward and standard method may lead to terrible bias, since in real biological and information networks, missing links are more likely to be links connecting low-degree nodes. We therefore study how to uncover missing links with low-degree nodes, namely links in the probe set are of lower degree products than a random sampling. Experimental analysis on ten local similarity indices and four disparate real networks reveals a surprising result that the Leicht-Holme-Newman index [E. A. Leicht, P. Holme, and M. E. J. Newman, Phys. Rev. E 73, 026120 (2006)] performs the best, although it was known to be one of the worst indices if the probe set is a random sampling of all links. We further propose an parameter-dependent index, which considerably improves the prediction accuracy. Finally, we show the relevance of the proposed index on three real sampling methods.Comment: 16 pages, 5 figures, 6 table

    Hymn to the heroes of Malta

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    Ġabra ta’ poeżiji u proża li tinkludi: Alla fil-ħolqien ta’ Ġużè Agius Bonello – Is-sena u l-bniedem ta’ Ġużè Ellul-Mercer – Li tiżra’ taħsad ta’ Vic. Apap – Huwa ta’ Gino Muscat-Azzopardi – Żewġ friefet ta’ Vincent Caruana – Iċ-ċagħka ta’ Ġużè Borg – Warda midbiela ta’ C. Gauci – It-tfajla tas-sulfarini ta’ Albert M. Cassola – L-aħħar traduzzjoni ta’ May Butcher qabel ma mietet – Hymn to the heroes of Malta.N/

    Three-Valued Modal Logic for Qualitative Comparative Policy Analysis with Crisp-Set QCA

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    Contradictory and missing outcomes are problems common to many qualitative comparative studies, based on the methodology of crisp-set QCA. They also occur in public policy analyses, e.g. if important background variables are omitted or outcomes of new policies are technically censored. As a new solution to these problems, this article proposes the use of three-valued modal logic, originally introduced by the Polish philosopher Jan Lukasiewicz (1970). In addition to true and false, indeterminate is the third truth-value in this alternative approach, which serves to code missing or contradictory data. Moreover, modal operators allow a differentiation between strict and possible triggers and inhibitors of policy outcomes. The advantages of three-valued modal logic in crisp-set QCA are illustrated by an empirical example from comparative welfare policy analysis. Its conclusions allow comparisons with the corresponding results from a conventional crisp-set QCA of the same data-set

    LETS get real: constraints on the development of Local Exchange Trading Schemes

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    Local Exchange Trading Schemes (LETS) are widely promoted as a new tool for local economic development, but until recently the focus has been on their alleged ‘potential’ rather than the realities of their operation. This paper assesses the practical economic role of LETS by examining the amount of trading conducted, and demonstrates that both the volume of trading and the value of the trades are very low. Drawing on an intensive case study of the first UK LETS created explicitly as part of a local authority’s anti-poverty strategy, explanations for the low levels of participation are suggested, and significant structural constraints on the development of LETS are identified

    Buffer influence on magnetic dead layer, critical current and thermal stability in magnetic tunnel junctions with perpendicular magnetic anisotropy

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    We present a thorough research on Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of MTJs, such as critical switching current and thermal stability. We investigate devices consisting of buffer/FeCoB/MgO/FeCoB/Ta/Ru multilayers for three different buffers: Ta 5 / Ru 10 / Ta 3, Ta 5 / Ru 10 / Ta 10 and Ta 5 / Ru 20 / Ta 5 (all thicknesses in nm). In addition, we study systems with a single FeCoB layer deposited above as well as below the MgO barrier. The crystallographic texture and the roughness of the buffers are determined by means of XRD and atomic force microscopy measurements. Furthermore, we examine the magnetic domain pattern, the magnetic dead layer thickness and the perpendicular magnetic anisotropy fields for each sample. Finally, we investigate the effect of the current induced magnetization switching for nanopillar junctions with lateral dimensions ranging from 1 {\mu}m down to 140 nm. Buffer Ta 5 / Ru 10 / Ta 3, which has the thickest dead layer, exhibits a large increase in the thermal stability factor while featuring a slightly lower critical current density value when compared to the buffer with the thinnest dead layer Ta 5 / Ru 20 / Ta 5

    Controlling the near-surface superfluid density in underdoped YBa₂Cu₃O<sub>6+<i>x</i></sub> by photo-illumination

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    The interaction with light weakens the superconducting ground state in classical superconductors. The situation in cuprate superconductors is more complicated: illumination increases the charge carrier density, a photo-induced effect that persists below room temperature. Furthermore, systematic investigations in underdoped YBa₂Cu₃O6+x (YBCO) have shown an enhanced critical temperature Tc. Until now, studies of photo-persistent conductivity (PPC) have been limited to investigations of structural and transport properties, as well as the onset of superconductivity. Here we show how changes in the magnetic screening profile of YBCO in the Meissner state due to PPC can be determined on a nanometer scale utilizing low-energy muons. The data obtained reveal a strongly increased superfluid density within the first few tens of nanometers from the sample surface. Our findings suggest a non-trivial modification of the near-surface band structure and give direct evidence that the superfluid density of YBCO can be controlled by light illumination

    Ya got ta know when ta hold ‘em: Maori women and gambling

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    Gambling among Maori women is under-researched. In this study, I interviewed thirty Maori women to investigate how they got involved in gambling, what maintained their gambling and what they thought might help to moderate their gambling. I found that the whanau was central to understanding these issues. As children, my participants were exposed to gambling within their whanau. As adults, whanau and other social support relationships were an integral part of their gambling, which most commonly occurred in the context of card schools and housie. A sense of reciprocity was important in both forms of gambling. Card schools were reported to be close-knit groups within which the money circulated, giving all a chance to win. By playing housie, the women felt that they were contributing to the welfare of their marae. Through the social bonds of gambling and the acquisition of skills, gambling contributed to these women’s sense of identity. On the other hand, financial and relationship difficulties were identified as negative consequences of gambling. The women felt there was a need for Maori-focused services for problem gambling