The study of dynamic singularities of seismic signals by the generalized Langevin equation

Analytically and quantitatively we reveal that the generalized Langevin equation (GLE), based on a memory function approach, in which memory functions and information measures of statistical memory play a fundamental role in determining the thin details of the stochastic behavior of seismic systems, naturally leads to a description of seismic phenomena in terms of strong and weak memory. Due to a discreteness of seismic signals we use a finite-discrete form of the GLE. Here we studied some cases of seismic activities of Earth ground motion in Turkey with consideration of the complexity, nonergodicity and fractality of seismic signals. © 2009 Elsevier B.V. All rights reserved

Jamming Model for the Extremal Optimization Heuristic

Extremal Optimization, a recently introduced meta-heuristic for hard optimization problems, is analyzed on a simple model of jamming. The model is motivated first by the problem of finding lowest energy configurations for a disordered spin system on a fixed-valence graph. The numerical results for the spin system exhibit the same phenomena found in all earlier studies of extremal optimization, and our analytical results for the model reproduce many of these features.Comment: 9 pages, RevTex4, 7 ps-figures included, as to appear in J. Phys. A, related papers available at http://www.physics.emory.edu/faculty/boettcher

Riemannian Sparse Coding for Positive Definite Matrices

International audienceInspired by the great success of sparse coding for vector valued data, our goal is to represent symmetric positive definite (SPD) data matrices as sparse linear combinations of atoms from a dictionary, where each atom itself is an SPD matrix. Since SPD matrices follow a non-Euclidean (in fact a Riemannian) geometry, existing sparse coding techniques for Euclidean data cannot be directly extended. Prior works have approached this problem by defining a sparse coding loss function using either extrinsic similarity measures (such as the log-Euclidean distance) or kernelized variants of statistical measures (such as the Stein divergence, Jeffrey's divergence, etc.). In contrast, we propose to use the intrinsic Riemannian distance on the manifold of SPD matrices. Our main contribution is a novel mathematical model for sparse coding of SPD matrices; we also present a computationally simple algorithm for optimizing our model. Experiments on several computer vision datasets showcase superior classification and retrieval performance compared with state-of-the-art approaches

Extremal Optimization for Graph Partitioning

Extremal optimization is a new general-purpose method for approximating solutions to hard optimization problems. We study the method in detail by way of the NP-hard graph partitioning problem. We discuss the scaling behavior of extremal optimization, focusing on the convergence of the average run as a function of runtime and system size. The method has a single free parameter, which we determine numerically and justify using a simple argument. Our numerical results demonstrate that on random graphs, extremal optimization maintains consistent accuracy for increasing system sizes, with an approximation error decreasing over runtime roughly as a power law t^(-0.4). On geometrically structured graphs, the scaling of results from the average run suggests that these are far from optimal, with large fluctuations between individual trials. But when only the best runs are considered, results consistent with theoretical arguments are recovered.Comment: 34 pages, RevTex4, 1 table and 20 ps-figures included, related papers available at http://www.physics.emory.edu/faculty/boettcher

The Impact of Brand Quality on Shareholder Wealth

This study examines the impact of brand quality on three components of shareholder wealth: stock returns, systematic risk, and idiosyncratic risk. The study finds that brand quality enhances shareholder wealth insofar as unanticipated changes in brand quality are positively associated with stock returns and negatively related to changes in idiosyncratic risk. However, unanticipated changes in brand quality can also erode shareholder wealth because they have a positive association with changes in systematic risk. The study introduces a contingency theory view to the marketing-finance interface by analyzing the moderating role of two factors that are widely followed by investors. The results show an unanticipated increase (decrease) in current-period earnings enhances (depletes) the positive impact of unanticipated changes in brand quality on stock returns and mitigates (enhances) their deleterious effects on changes in systematic risk. Similarly, brand quality is more valuable for firms facing increasing competition (i.e., unanticipated decreases in industry concentration). The results are robust to endogeneity concerns and across alternative models. The authors conclude by discussing the nuanced implications of their findings for shareholder wealth, reporting brand quality to investors, and its use in employee evaluation

Response of Grafted and Self-Rooted Tomato Plants to Saline Conditions in Closed Substrate System

5th Balkan Symposium on Vegetables and Potatoes -- OCT 09-12, 2011 -- Tirana, ALBANIAWOS: 000323606200061Grafting could be used as a means to alleviate salt stress in some greenhouse vegetables if appropriate rootstock is selected. In this research, the response of tomato rootstocks 'Beaufort' (L. esculentum x L. hirsutum) and 'Resistar' (L. esculentum) against to salinity was compared with self grafted ones (cv. Gokce F-1) in a PE covered greenhouse during the autumn and spring season of 2007-2008. Plants were grown in perlite (6 L plant(-1)) with the density of 3.5 plants m(-2). The electrical conductivity of the nutrient solution supplied to the plants, which had a standard composition for tomato, was adjusted to 2.0 (control), 6.0 or 10.0 dS m(-1) by adding 0, 42 or 84 mmol L-1 NaCl in order to determine rootstock-salt reaction. The experimental design was randomized parcels with 2 factors with 3 replicates. The results showed that rootstocks increased plant height, stem diameter, root and shoot fresh and dry weight, total and marketable yield. These parameters decreased dramatically with the increase of salinity. Salinity stress especially reduced mean fruit weight and increased amount of nonmarketable fruits. Although higher yield was obtained at 2 dS m(-1) in both growing seasons, the plants grafted onto Beaufort had the highest yields under saline conditions. It was concluded that grafting could increase plant vigor and yield resulting in better performance under saline conditions, however detrimental effect of salinity was more severe in spring season.Int Soc Hort Sci (ISHS