664 research outputs found

    Magnetic Properties of the low dimensional spin system (VO)2_2P2_2O7_{7}: ESR and susceptibility

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    Experimental results on magnetic resonance (ESR) and magnetic susceptibility are given for single crystalline (VO)2_2P2_2O7_{7}. The crystal growth procedure is briefly discussed. The susceptibility is interpreted numerically using a model with alternating spin chains. We determine JJ=51 K and δ\delta=0.2. Furthermore we find a spin gap of 6\approx 6meV from our ESR measurements. Using elastic constants no indication of a phase transition forcing the dimerization is seen below 300 K.Comment: 7 pages, REVTEX, 7 figure

    Empirical behavior of a world stock index from intra-day to monthly time scales

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    Most of the papers that study the distributional and fractal properties of financial instruments focus on stock prices or foreign exchange rates. This typically leads to mixed results concerning the distributions of log-returns and some multi-fractal properties of exchange rates, stock prices, and regional indices. This paper uses a well diversified world stock index as the central object of analysis. Such index approximates the growth optimal portfolio, which is demonstrated under the benchmark approach, it is the ideal reference unit for studying basic securities. When denominating this world index in units of a given currency, one measures the movements of the currency against the entire market. This provides a least disturbed observation of the currency dynamics. In this manner, one can expect to disentangle, e.g., the superposition of the two currencies involved in an exchange rate. This benchmark approach to the empirical analysis of financial data allows us to establish remarkable stylized facts. Most important is the observation that the repeatedly documented multi-fractal appearance of financial time series is very weak and much less pronounced than the deviation of the mono-scaling properties from Brownian-motion type scaling. The generalized Hurst exponent H(2) assumes typical values between 0.55 and 0.6. Accordingly, autocorrelations of log-returns decay according to a power law, and the quadratic variation vanishes when going to vanishing observation time step size. Furthermore, one can identify the Studentt distribution as the log-return distribution of a well-diversified world stock index for long time horizons when a long enough data series is used for estimation. The study of dependence properties, finally, reveals that jumps at daily horizon originate primarily in the stock market while at 5min horizon they originate in the foreign exchange market. The principal message of the empirical analysis is that there is evidence that a diffusion model without multi-scaling could reasonably well model the dynamics of a broadly diversified world stock inde

    L'impossible musée. Notes sur l'architecture muséale dans le canton de Vaud

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    Histoire de l'architecture muséale vaudois

    European summer climate variability in a heterogeneous multi-model ensemble

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    Recent results from an enhanced greenhouse-gas scenario over Europe suggest that climate change might not only imply a general mean warming at the surface, but also a pronounced increase in interannual surface temperature variability during the summer season (Schär etal., Nature 427:332-336, 2004). It has been proposed that the underlying physical mechanism is related to land surface-atmosphere interactions. In this study we expand the previous analysis by including results from a heterogeneous ensemble of 11 high-resolution climate models from the PRUDENCE project. All simulations considered comprise 30-year control and enhanced greenhouse-gas scenario periods. While there is considerable spread in the models' ability to represent the observed summer variability, all models show some increase in variability for the scenario period, confirming the main result of the previous study. Averaged over a large-scale Central European domain, the models simulate an increase in the standard deviation of summer mean temperatures between 20 and 80%. The amplification occurs predominantly over land points and is particularly pronounced for surface temperature, but also evident for precipitation. It is also found that the simulated changes in Central European summer conditions are characterized by an emergence of dry and warm years, with early and intensified depletion of root-zone soil moisture. There is thus some evidence that the change in variability may be linked to the dynamics of soil-moisture storage and the associated feedbacks on the surface energy balance and precipitatio

    A New Method for Finishing Minicavities

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    Minicavities were prepared in 26 caries-free teeth. Cavity preparation and the finishing of the occlusal area and the gingival floor was done with diamond burs (diameter 1 mm, grain sizes 90 μm and 15 μm, respectively). For the finishing of the axial box margin and the proximo-cervicaI curved border, a new set was developed: It is composed of an EVA-system with the total amplitude reduced to 0.34 mm, and a highly flexible file (Cavishape, grain 15 μm). The shape of this file had to be modified in order to follow the proximo-cervical curvature. The efficiency of the new device was compared with the axial margin trimmer by means of scanning electron microscopy and a score system. The new device allowed a significantly better finishing of the proximo-cervical curvature and of the axial box margin

    Microscopic Theory for the Markovian Decay of Magnetization Fluctuations in Nanomagnets

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    We present a microscopic theory for the phonon-driven decay of the magnetization fluctuations in a wide class of nanomagnets where the dominant energy is set by isotropic exchange and/or uniaxial anisotropy. Based on the Zwanzig-Mori projection formalism, the theory reveals that the magnetization fluctuations are governed by a single decay rate ωc\omega_c, which we further identify with the zero-frequency portion of the associated self-energy. This dynamical decoupling from the remaining slow degrees of freedom is attributed to a conservation law and the discreteness of the energy spectrum, and explains the omnipresent mono-exponential decay of the magnetization over several decades in time, as observed experimentally. A physically transparent analytical expression for ωc\omega_c is derived which highlights the three specific mechanisms of the slowing down effect which are known so far in nanomagnets.Comment: 7 page

    Elevation gradients of European climate change in the regional climate model COSMO-CLM

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    A transient climate scenario experiment of the regional climate model COSMO-CLM is analyzed to assess the elevation dependency of 21st century European climate change. A focus is put on near-surface conditions. Model evaluation reveals that COSMO-CLM is able to approximately reproduce the observed altitudinal variation of 2m temperature and precipitation in most regions and most seasons. The analysis of climate change signals suggests that 21st century climate change might considerably depend on elevation. Over most parts of Europe and in most seasons, near-surface warming significantly increases with elevation. This is consistent with the simulated changes of the free-tropospheric air temperature, but can only be fully explained by taking into account regional-scale processes involving the land surface. In winter and spring, the anomalous high-elevation warming is typically connected to a decrease in the number of snow days and the snow-albedo feedback. Further factors are changes in cloud cover and soil moisture and the proximity of low-elevation regions to the sea. The amplified warming at high elevations becomes apparent during the first half of the 21st century and results in a general decrease of near-surface lapse rates. It does not imply an early detection potential of large-scale temperature changes. For precipitation, only few consistent signals arise. In many regions precipitation changes show a pronounced elevation dependency but the details strongly depend on the season and the region under consideration. There is a tendency towards a larger relative decrease of summer precipitation at low elevations, but there are exceptions to this as wel
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