9,924 research outputs found

    Fixed points of quantum gravity in higher dimensions

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    We study quantum gravity in more than four dimensions by means of an exact functional flow. A non-trivial ultraviolet fixed point is found in the Einstein-Hilbert theory. It is shown that our results for the fixed point and universal scaling exponents are stable. If the fixed point persists in extended truncations, quantum gravity in the metric field is asymptotically safe. We indicate physical consequences of this scenario in phenomenological models with low-scale quantum gravity and large extra dimensions.Comment: Talk presented at Einstein Century Meeting, Paris, 15-22 July 200

    A reappraisal of the evidence on PPP: a systematic investigation into MA roots in panel unit root tests and their implications

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    Panel unit root tests of real exchange rates – as opposed to univariate tests – usually reject non-stationarity. These tests, however, could be biased if the real exchange rate contained MA roots. Indeed, two independent arguments claim that the real exchange rate, being a sum of a stationary and a non-stationary component, is possibly an ARIMA (1, 1, 1) process. Monte Carlo simulations show, how systematic changes in the parameters of the components, of the test equation and of the correlation matrix affect the size of first and second generation panel unit root tests. Two components of the real exchange rate, the real exchange rate of a single good and a weighted sum of relative prices, are constructed from the data for a panel of countries. Computation of the relevant parameters reveals that panel unit root tests of the real exchange rate are severely oversized, usually much more so than simple ADF tests. Thus, the evidence for PPP from panel unit root tests may be merely due to extreme size biases. --panel unit root test,purchasing power parity,real exchange rate,Monte Carlo simulation

    Modeling Spatial Autocorrelation in Spatial Interaction Data: A Comparison of Spatial Econometric and Spatial Filtering Specifications

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    The need to account for spatial autocorrelation is well known in spatial analysis. Many spatial statistics and spatial econometric texts detail the way spatial autocorrelation can be identified and modelled in the case of object and field data. The literature on spatial autocorrelation is much less developed in the case of spatial interaction data. The focus of interest in this paper is on the problem of spatial autocorrelation in a spatial interaction context. The paper aims to illustrate that eigenfunction-based spatial filtering offers a powerful methodology that can efficiently account for spatial autocorrelation effects within a Poisson spatial interaction model context that serves the purpose to identify and measure spatial separation effects to interregional knowledge spillovers as captured by patent citations among high-technology-firms in Europe.

    Stress Testing German Industry Sectors: Results from a Vine Copula Based Quantile Regression

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    Measuring interdependence between probabilities of default (PDs) in different industry sectors of an economy plays a crucial role in financial stress testing. Thereby, regression approaches may be employed to model the impact of stressed industry sectors as covariates on other response sectors. We identify vine copula based quantile regression as an eligible tool for conducting such stress tests as this method has good robustness properties, takes into account potential nonlinearities of conditional quantile functions and ensures that no quantile crossing effects occur. We illustrate its performance by a data set of sector specific PDs for the German economy. Empirical results are provided for a rough and a fine-grained industry sector classification scheme. Amongst others, we confirm that a stressed automobile industry has a severe impact on the German economy as a whole at different quantile levels whereas e.g., for a stressed financial sector the impact is rather moderate. Moreover, the vine copula based quantile regression approach is benchmarked against both classical linear quantile regression and expectile regression in order to illustrate its methodological effectiveness in the scenarios evaluated.Comment: 12 page

    Hybridization and spin decoherence in heavy-hole quantum dots

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    We theoretically investigate the spin dynamics of a heavy hole confined to an unstrained III-V semiconductor quantum dot and interacting with a narrowed nuclear-spin bath. We show that band hybridization leads to an exponential decay of hole-spin superpositions due to hyperfine-mediated nuclear pair flips, and that the accordant single-hole-spin decoherence time T2 can be tuned over many orders of magnitude by changing external parameters. In particular, we show that, under experimentally accessible conditions, it is possible to suppress hyperfine-mediated nuclear-pair-flip processes so strongly that hole-spin quantum dots may be operated beyond the `ultimate limitation' set by the hyperfine interaction which is present in other spin-qubit candidate systems.Comment: 7 pages, 3 figure

    A Mobility Model for the Realistic Simulation of Social Context

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    Simulation is a fundamental means for evaluating mobile applications based on ad-hoc networks. In recent years, the new breed of social mobility models (SMMs) has risen. Contrary to most classical mobility models, SMMs model the social aspects of human mobility, i.e. which users meet, when and how often. Such information is indispensable for the simulation of a wide range of socially-aware communication protocols mostly based on delay-tolerant networks, including opportunistic ad-hoc routing and data dissemination systems. Each SMM needs a model of the relations between a set of relevant people (called social network model -- SNM) in order to simulate their mobility. Existing SMMs lack flexibility since each of them is implicitly restricted to a specific, simplifying SNM. We present GeSoMo (General Social Mobility Model), a new SMM that separates the core mobility model from the structural description of the social network underlying the simulation. This simple and elegant design principle gives GeSoMo generalizing power: Arbitrary existing and future SNMs can be used without changing GeSoMo itself. Our evaluation results show that GeSoMo produces simulations that are coherent with a broad range of empirical data describing real-world human social behavior and mobility

    Clinician empathic speech and client change language : is there an association between empathic speech and change talk in motivational interviewing sessions?

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    Empathy is the state of knowing or being aware of another persons perspective and the ability to express empathy is acknowledged as an important component within effective psychotherapy. Motivational interviewing (MI) is a specific method of psychotherapy in which clinician expressions of empathy are held to be an active ingredient and a central component of effective practice. Although empathy has long been a part of the theoretical explanation of effective MI, there is little known about the function of empathy as expressed by the clinician and the association between such in-session speech and client change language. This study identified the empathic speech of clinicians and explored the association of such speech with client change language. The study found that frequencies of empathic speech shared a significant positive correlation with client change talk as well as client sustain talk. This correlation between empathic speech and change talk was mediated by several clinician variables, such as MI-consistent behaviors and clinician reflections of client change talk. Similarly, the relationship between empathic speech and client sustain talk was mediated by reflections of client sustain talk

    Motivational Interviewing Treatment Integrity and Client Change: Using ROC Analysis to Explore the Relationship Between MI Fidelity Level and Drinking Outcome.

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    Those engaged in the research and practice of MI have shown interest in treatment adherence as an indicator of effective MI and have expressed curiosity in the threshold at which MI practice could be viewed as good enough\u27. The most widely used and often cited of MI integrity measures are the Motivational Interviewing Skills Code (MISC) and the Motivational Interviewing Treatment Integrity code (MITI). These adherence tools share similar descriptive coding systems for therapist in-session behavior. MI fidelity standards are often used as reference points for therapist performance, yet practitioners rarely meet full criteria. Further, substandard ratings have been associated with positive client change. These findings have elicited questions about the necessary levels of therapist treatment adherence to promote client change and suggested the need for empirically-derived fidelity standards. This study analyzed existing data from a sample of Motivational Enhancement Therapy (MET) sessions from Project MATCH (Matching Alcohol Treatments to Client Heterogeneity) that were audio recorded and previously coded with the MISC. MI adherence variables were analyzed along with client drinking outcomes to test the relationship between therapist fidelity and client change. Therapist adherence was determined using behavioral codes common to the MITI and MISC. Client change thresholds were determined using clinically significant change standards developed by Jacobson and Truax. The relationships between therapist adherence level and client change thresholds were examined using Receiver Operating Characteristic (ROC) analysis. Findings showed mixed support for the relationship between therapist adherence level and client drinking outcomes, but yielded levels of therapist MI adherence associated with client changes in drinking outcomes
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