We performed the statistical analysis of acoustic emission time series in the ultrasonic frequency range, obtained experimentally from laboratory samples subjected to external uniaxial elastic stress. We found a power law scaling behavior in both the acoustic emission amplitude distribution and time correlation function, with exponents very close to those found in fracturing processes occurring at different time and space scales. These facts strongly suggest the existence of a critical dynamics underlying the process, which might be related to the idea of a self-organized critical state based on the energy dissipation through all the length scales.PACS numbers: 62.20.Mk, 05.40.+j, 91.60.Lj Power law behavior in physical phenomena is usually the fingerprint of temporal and spatial critical fluctuations of which well known examples are Ising-like systems, fractal growth phenomena, turbulence, etc. Unlike the usual second order phase transitions, some of the previous examples exhibit a critical behavior without the need to fine tune any control parameter; i.e., the critical state is an attractor of the dynamics. A few years ago Bak, Tang, and Wiesenfeld [1] termed this kind of situation "self-organized criticality" (SOC) and introduced a simple model of a dynamically driven system, inspired by the dynamics of sandpiles, that evolves spontaneously to a stationary critical state. This model is an example of SOC phenomenon in which a system with short range coupling self-stabilizes in a stationary state characterized by avalanches (activity) with power law distribution functions. Hence, the system has no characteristic length (and is therefore self-similar) and is in this sense critical. The SOC concept has been proposed also as a possible mechanism for the generation of the so-called 1/ f noise; however, it has been shown successively [2,3] that the spatialtemporal scaling in the SOC state does not necessarily manifest itself in nontrivial exponents for the power spectrum.Because of the importance of the SOC concept as a possible unifying framework for a wide range of physical phenomena, a lot of work has been devoted to studying these systems through computer simulations, theoretical approaches, and experimental findings [4]. In particular, the SOC framework has been proposed as a possible interpretation for the empirical observation of the energy release in earthquakes [5]. In fact, existence of statistical self-similarity in seismic processes is a well established fact, which has its strongest evidence in the power law behavior of the well known Gutenberg'S [6] and Omori's [7] empirical laws. Power law behavior was observed by Mogi [8] in the distribution of the maximum trace amplitude of audio signals emitted from samples subjected to various forms of stress, in analogy with the Ishimoto Iida 0031-9007/94/73(25)/3423(4)$06.00 empirical relation [9]. Hirata [10] observed self-similarity in the time frequency distribution of aftershock signals due to fracturation of basalt under constant stress. More recently, ...

Let Uε(g) be the simply connected quantized enveloping algebra at roots of one associated to a finite dimensional complex simple Lie algebra g. The De ConciniKac-Procesi conjecture on the dimension of the irreducible representations of Uε(g) is proved for the representations corresponding to the spherical conjugacy classes of the simply connected algebraic group G with Lie algebra g. We achieve this result by means of a new characterization of the spherical conjugacy classes of G in terms of elements of the Weyl group.

The usefulness of a predictor evaluation framework which combines a blocked cross-validation scheme with directional accuracy measures is investigated. The advantage of using a blocked cross-validation scheme with respect to the standard out-of-sample procedure is that cross-validation yields more precise error estimates of the prediction error since it makes full use of the data. In order to quantify the gain in precision when directional accuracy measures are considered, a Monte Carlo analysis using univariate and multivariate models is provided. The experiments indicate that more precise estimates are obtained with the blocked cross-validation procedure. An application is carried out on forecasting UK interest rate for illustration purposes. The results show that in such a situation with small samples the crossvalidation scheme may have considerable advantages over the standard out-of-sample evaluation procedure as it may help to overcome problems induced by the limited information the directional accuracy measures contain due to their binary nature.

A newborn baby boy presented with a full thickness defect of the scalp, skull, and dura measuring 6 x 7 cm caused by aplasia cutis congenita. Full thickness loss is extremely rare and to our knowledge this case is the twenty-first reported. It has an established mortality of up to 55%. An encephalocele forced us to do an emergency operation with a single large scalp flap based on the supratrochlear and superficial temporal arteries. After revision the child is now 9 months old and progressing well. There are several ways to treat these rare and delicate cases.

In the light of the recent financial crisis, we take a panel cointegration approach that allows for structural breaks to the analysis of the determinants of sovereign bond yield spreads in nine economies of the European Monetary Union. While we find evidence for a level break in the cointegrating relationship, we do not find empirical support for a regime shift and hence for a change in the pricing of the determinants of sovereign spreads. Moreover, resultsshow that (i) fiscal imbalances -namely expected government debt-to-GDP differentials -are the main long-run drivers of sovereign spreads; (ii) liquidity risks and cumulated inflation differentials have non-negligible weights; but (iii) all conclusions are ultimately connected to whether or not the sample of countries is composed of members of an Optimal Currency Area (OCA). In particular, we establish (i) that results are overall driven by those countries not passing the OCA test; and (ii) that investors closely monitor and severely punish the deterioration of expected debt positions of those economies exhibiting significant gaps in competitiveness.

Let G be a simple algebraic group over an algebraically closed field k of bad characteristic. We classify the spherical unipotent conjugacy classes of G. We also show that if the characteristic of k is 2, then the fixed point subgroup of every involutorial automorphism (involution) of G is a spherical subgroup of G.

Most econometric methods for testing the proposition of long-run monetary neutrality rely on the assumption that money and real output do not cointegrate. This paper argues that these results can be attributed in part to the low power of univariate tests, and that a violation of the noncointegration assumption is likely to result in a nonrejection of the neutrality proposition. To alleviate this problem, two new and more powerful panel cointegration tests are proposed. The tests are applied to a panel covering 10 countries between 1870 and 1986 and findings show that the neutrality proposition do not hold.JEL Classification: E50; C22; C23.

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