Avalanches and clusters in planar crack front propagation

We study avalanches in a model for a planar crack propagating in a disordered medium. Due to long-range interactions, avalanches are formed by a set of spatially disconnected local clusters, the sizes of which are distributed according to a power law with an exponent $\tau_{a}=1.5$. We derive a scaling relation $\tau_a=2\tau-1$ between the local cluster exponent $\tau_a$ and the global avalanche exponent $\tau$. For length scales longer than a cross-over length proportional to the Larkin length, the aspect ratio of the local clusters scales with the roughness exponent of the line model. Our analysis provides an explanation for experimental results on planar crack avalanches in Plexiglas plates, but the results are applicable also to other systems with long-range interactions.Comment: 7 pages, 6 figures, accepted for publication in Physical Review

Comment on ``Self-organized criticality and absorbing states: Lessons from the Ising model"

According to Pruessner and Peters [Phys. Rev. E {\bf 73}, 025106(R) (2006)], the finite size scaling exponents of the order parameter in sandpile models depend on the tuning of driving and dissipation rates with system size. We point out that the same is not true for {\em avalanches} in the slow driving limit.Comment: 3 pages, 1 figure, to appear in Phys. Rev.

Tunability of the optical absorption in small silver cluster-polymer hybrid systems

We have calculated the absorption characteristics of different hybrid systems consisting of Ag, Ag2 or Ag3 atomic clusters and poly(methacrylic acid) (PMAA) using the time-dependent density-functional theory. The polymer is found to have an extensive structural-dependency on the spectral patterns of the hybrid systems relative to the bare clusters. The absorption spectrum can be `tuned' to the visible range for hybrid systems with an odd number of electrons per silver cluster, whereas for hybrid systems comprising an even number of electrons, the leading absorption edge can be shifted up to about 4.5 eV. The results give theoretical support to the experimental observations on the absorption in the visible range in metal cluster-polymer hybrid structures.Comment: Updated layout and minor changes in versions 2 and

What's the Matter with Relatedness?

A core proposition of the resource-based view of the firm is that related diversification is more efficient than unrelated diversification. Nevertheless, the empirical evidence is usually described as mixed or unstable. We empirically examine three possible explanations for the nature of these findings. One is that they reflect measurement problems. Another is that they reflect a failure to take the resource-based view far enough in terms of recognizing firm heterogeneity. The third is that the resource-based view is misspecified: relatedness is not a significant determinant of efficiency. We use a detailed line-of-business sample to examine these three explanations. Our findings clearly indicate that the main problem is measurement, and we describe an approach to overcoming these problems

Relatedness and Acquirer Performance

Includes bibliographical references.Uncorrected proofWhile the strategic management literature suggests that related diversification is superior to unrelated diversification, there is little evidence that acquirers benefit from pursuing related targets. We argue that the empirical literature is plagued by poor measures of relatedness. Moreover, many empirical studies do not control adequately for the characteristics of the market for corporate control. We argue that not only value creation, but also value appropriation, depend on the relatedness of acquirer and target. Using an improved measure of relatedness, we provide empirical evidence that acquirer returns are positively and significantly correlated with relatedness

A discrete solvent reaction field model for calculating frequency-dependent hyperpolarizabilities of molecules in solution

We present a discrete solvent reaction field (DRF) model for the calculation of frequency-dependent hyperpolarizabilities of molecules in solution. In this model the solute is described using density functional theory (DFT) and the discrete solvent molecules are described with a classical polarizable model. The first hyperpolarizability is obtained in an efficient way using time-dependent DFT and the (2n+1) rule. The method was tested for liquid water using a model in which a water molecule is embedded in a cluster of 127 classical water molecules. The frequency-dependent first and second hyperpolarizabilities related to the electric field induced second harmonic generation (EFISH) experiment, were calculated both in the gas phase and in the liquid phase. For water in the gas phase, results are obtained in good agreement with correlated wave function methods and experiments by using the so-called shape-corrected exchange correlation (xc)-potentials. In the liquid phase the effect of using asymptotically correct functionals is discussed. The model reproduced the experimentally observed sign change in the first hyperpolarizaibility when going from the gas phase to the liquid phase. Furthermore, it is shown that the first hyperpolarizability is more sensitive to damping of the solvent-solute interactions at short range than the second hyperpolarizability. (C) 2003 American Institute of Physics

Interleukin-1 Inhibition and Fatigue in Primary Sjögren's Syndrome – A Double Blind, Randomised Clinical Trial

Objectives: Fatigue is a major cause of disability in primary Sjögren’s syndrome (pSS). Fatigue has similarities with sickness behaviour in animals; the latter mediated by pro-inflammatory cytokines, in particular interleukin (IL)-1, acting on neuronal brain cells. We hypothesised that IL-1 inhibition might improve fatigue in pSS patients; thus, we examined the effects and safety of an IL-1 receptor antagonist (anakinra) on fatigue. Methods: Twenty-six pSS patients participated in a double-blind, placebo-controlled parallel group study. Patients were randomised to receive either anakinra or a placebo for four weeks. Fatigue was evaluated by a fatigue visual analogue scale and the Fatigue Severity Scale. The primary outcome measure was a group-wise comparison of the fatigue scores at week 4, adjusted for baseline values. Secondary outcome measures included evaluation of laboratory results and safety. The proportion of patients in each group who experienced a 50 % reduction in fatigue was regarded as a post-hoc outcome. All outcomes were measured at week 4. Results: There was no significant difference between the groups in fatigue scores at week 4 compared to baseline after treatment with anakinra. However, six out of 12 patients on anakinra versus one out of 13 patients on the placebo reported a 50 % reduction in fatigue VAS (p = 0.03). There were two serious adverse events in each group. Conclusions: This randomised, double-blind, placebo-controlled trial of IL-1 blockade did not find a significant reduction i

Power spectra of self-organized critical sandpiles

We analyze the power spectra of avalanches in two classes of self-organized critical sandpile models, the Bak-Tang-Wiesenfeld model and the Manna model. We show that these decay with a $1/f^\alpha$ power law, where the exponent value $\alpha$ is significantly smaller than 2 and equals the scaling exponent relating the avalanche size to its duration. We discuss the basic ingredients behind this result, such as the scaling of the average avalanche shape.Comment: 7 pages, 3 figures, submitted to JSTA