24,541 research outputs found

    Random and aperiodic quantum spin chains: A comparative study

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    According to the Harris-Luck criterion the relevance of a fluctuating interaction at the critical point is connected to the value of the fluctuation exponent omega. Here we consider different types of relevant fluctuations in the quantum Ising chain and investigate the universality class of the models. At the critical point the random and aperiodic systems behave similarly, due to the same type of extreme broad distribution of the energy scales at low energies. The critical exponents of some averaged quantities are found to be a universal function of omega, but some others do depend on other parameters of the distribution of the couplings. In the off-critical region there is an important difference between the two systems: there are no Griffiths singularities in aperiodic models.Comment: 4 pages RevTeX, 2 eps-figures include

    Thermocycling experiments with the three-dimensional Ising spin glass model

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    A characteristic feature of the non--equilibrium dynamics of real spin glasses at low temperatures are strong aging effects. These phenomena can be manipulated by changing the external parameters in various ways: a thermo-cycling experiment consists for instance of a short heat pulse during the waiting time, by which the relaxation might be strongly affected. Results of numerical experiments of this kind, performed via Monte Carlo simulations of the three dimensional Ising spin glass model, are presented. The theoretical implications are discussed and the scenario found is compared with the experimental situation.Comment: LaTeX 13 pages (+6 figures upon request), THP11-9

    Notice and Intervention in ICWA CINA Cases 1992

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    This study is a preliminary investigation of the relationship between the notice requirement and intervention in a sample of Indian Child Welfare Act (ICWA) Child in Need of Aid (CINA) cases in Alaska in 1992. A randomized sample by geographic district of all active Alaska Native children cases drawn from the "Prober" computerized database of the Alaska Division of Family and Youth Services (DFYS) constituted the study population. Data collection occurred through review of social workers' case files in Juneau, Fairbanks, Bethel, and Anchorage

    Felony Definition: A White Paper

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    As part of a larger project to improve the quality and timeliness of Alaska criminal history records, the Alaska Department of Public Safety intends to upgrade the Alaska Public Safety Information Network (APSIN) to provide an indicator to show whether a conviction is for a felony or a misdemeanor. This white paper presents an operational definition of felony which accommodates the limits of APSIN by referring to data fields currently available and makes recommendations to alleviate ambiguity about the category of offense for convictions which can be either felony or misdemeanor.Alaska Department of Public Safet

    Defending a simple theory of conditionals

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    This paper extends the defense of a simple theory of indicative conditionals previously proposed by the author, in which the truth conditions are material, and Grice-style assertability conditions are given to explain the paradoxes of material implication. The paper discusses various apparent counter-examples to the material account in which conditionals are not asserted, and so the original theory cannot be applied; it is argued that, nevertheless, the material theory can be defended
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