Crossover Behavior in Burst Avalanches of Fiber Bundles: Signature of Imminent Failure

Bundles of many fibers, with statistically distributed thresholds for breakdown of individual fibers and where the load carried by a bursting fiber is equally distributed among the surviving members, are considered. During the breakdown process, avalanches consisting of simultaneous rupture of several fibers occur, with a distribution D(Delta) of the magnitude Delta of such avalanches. We show that there is, for certain threshold distributions, a crossover behavior of D(Delta) between two power laws D(Delta) proportional to Delta^(-xi), with xi=3/2 or xi=5/2. The latter is known to be the generic behavior, and we give the condition for which the D(Delta) proportional to Delta^(-3/2) behavior is seen. This crossover is a signal of imminent catastrophic failure in the fiber bundle. We find the same crossover behavior in the fuse model.Comment: 4 pages, 4 figure

Regularization Algorithms Based on Total Least Squares

Discretizations of inverse problems lead to systems of linear equations with a highly ill-conditioned coefficient matrix, and in order to compute stable solutions to these systems it is necessary to apply regularization methods. Classical regularization methods, such as Tikhonov's method or truncated {\em SVD}, are not designed for problems in which both the coefficient matrix and the right-hand side are known only approximately. For this reason, we develop {\em TLS}\/-based regularization methods that take this situation into account. Here, we survey two different approaches to incorporation of regularization, or stabilization, into the {\em TLS} setting. The two methods are similar in spirit to Tikhonov regularization and truncated {\em SVD}, respectively. We analyze the regularizing properties of the methods and demonstrate by numerical examples that in certain cases with large perturbations, these new methods are able to yield more accurate regularized solutions than those produced by the standard methods. (Also cross-referenced as UMIACS-TR-96-65

Extension and approximation of mm-subharmonic functions

Let $\Omega\subset \mathbb C^n$ be a bounded domain, and let $f$ be a real-valued function defined on the whole topological boundary $\partial \Omega$. The aim of this paper is to find a characterization of the functions $f$ which can be extended to the inside to a $m$-subharmonic function under suitable assumptions on $\Omega$. We shall do so by using a function algebraic approach with focus on $m$-subharmonic functions defined on compact sets. We end this note with some remarks on approximation of $m$-subharmonic functions

Spin Glasses: Model systems for non-equilibrium dynamics

Spin glasses are frustrated magnetic systems due to a random distribution of ferro- and antiferromagnetic interactions. An experimental three dimensional (3d) spin glass exhibits a second order phase transition to a low temperature spin glass phase regardless of the spin dimensionality. In addition, the low temperature phase of Ising and Heisenberg spin glasses exhibits similar non-equilibrium dynamics and an infinitely slow approach towards a thermodynamic equilibrium state. There are however significant differences in the detailed character of the dynamics as to memory and rejuvenation phenomena and the influence of critical dynamics on the behaviour. In this article, some aspects of the non-equilibrium dynamics of an Ising and a Heisenberg spin glass are briefly reviewed and some comparisons are made to other glassy systems that exhibit magnetic non-equilibrium dynamics.Comment: To appear in J. Phys.: Condens. Matter, Proceedings from HFM2003, Grenobl

Workplace sexual harassment and depressive symptoms:A cross-sectional multilevel analysis comparing harassment from clients or customers to harassment from other employees amongst 7603 Danish employees from 1041 organizations

Abstract Background Previous research has reported that sexual harassment can lead to reduced mental health. Few studies have focused on sexual harassment conducted by clients or customers, which might occur in person-related occupations such as eldercare work, social work or customer service work. This study examined the cross-sectional association between sexual harassment by clients or customers and depressive symptoms. We also examined if this association was different compared to sexual harassment conducted by a colleague, supervisor or subordinate. Further, we investigated if psychosocial workplace initiatives modified the association between sexual harassment by clients or customers and level of depressive symptoms. Methods We used data from the Work Environment and Health in Denmark cohort study (WEHD) and the Work Environment Activities in Danish Workplaces Study (WEADW) collected in 2012. WEHD is based on a random sample of employed individuals aged 18–64. In WEADW, organizational supervisors or employee representatives provided information on workplace characteristics. By combining WEHD and WEADW we included self-reported information on working conditions and health from 7603 employees and supervisors in 1041 organizations within 5 occupations. Data were analyzed using multilevel regression and analyses adjusted for gender, age, occupation and socioeconomic position. Results Exposure to workplace sexual harassment from clients or customers was statistically significantly associated with a higher level of depressive symptoms (2.05; 95% CI: 0.98–3.12) compared to no exposure. Employees harassed by colleagues, supervisors or subordinates had a higher mean level of depressive symptoms (2.45; 95% CI: 0.57–4.34) than employees harassed by clients or customers. We observed no statistically significant interactions between harassment from clients and customers and any of the examined psychosocial workplace initiatives (all p > 0.05). Conclusions The association between sexual harassment and depressive symptoms differed for employees harassed by clients or customers and those harassed by colleagues, supervisors or subordinates. The results underline the importance of investigating sexual harassment from clients or customers and sexual harassment by colleagues, supervisors or subordinates as distinct types of harassment. We found no modification of the association between sexual harassment by clients or customers and depressive symptoms by any of the examined psychosocial workplace initiatives

Understanding adhesion at as-deposited interfaces from ab initio thermodynamics of deposition growth: thin-film alumina on titanium carbide

We investigate the chemical composition and adhesion of chemical vapour deposited thin-film alumina on TiC using and extending a recently proposed nonequilibrium method of ab initio thermodynamics of deposition growth (AIT-DG) [Rohrer J and Hyldgaard P 2010 Phys. Rev. B 82 045415]. A previous study of this system [Rohrer J, Ruberto C and Hyldgaard P 2010 J. Phys.: Condens. Matter 22 015004] found that use of equilibrium thermodynamics leads to predictions of a non-binding TiC/alumina interface, despite the industrial use as a wear-resistant coating. This discrepancy between equilibrium theory and experiment is resolved by the AIT-DG method which predicts interfaces with strong adhesion. The AIT-DG method combines density functional theory calculations, rate-equation modelling of the pressure evolution of the deposition environment and thermochemical data. The AIT-DG method was previously used to predict prevalent terminations of growing or as-deposited surfaces of binary materials. Here we extent the method to predict surface and interface compositions of growing or as-deposited thin films on a substrate and find that inclusion of the nonequilibrium deposition environment has important implications for the nature of buried interfaces.Comment: 8 pages, 6 figures, submitted to J. Phys.: Condens. Matte

Magnetic Brane Solutions in AdS

We construct asymptotically AdS_5 solutions of Einstein-Maxwell theory dual to N=4 SYM theory on R^{3,1} in the presence of a background magnetic field. The solutions interpolate between AdS_5 and a near horizon AdS_3\times T^2. The central charge of the near horizon region, and hence low temperature entropy of the solution, is found to be \sqrt{4\over 3} times that of free N=4 SYM theory. The entropy vanishes at zero temperature. We also present the generalization of these solutions to arbitrary spacetime dimensionality.Comment: 17 page

Two-dimensional electron transport in the presence of magnetic flux vortices

We have considered the conductivity properties of a two dimensional electron gas (2DEG) in two different kinds of inhomogeneous magnetic fields, i.e. a disordered distribution of magnetic flux vortices, and a periodic array of magnetic flux vortices. The work falls in two parts. In the first part we show how the phase shifts for an electron scattering on an isolated vortex, can be calculated analytically, and related to the transport properties through a force balance equation. In the second part we present numerical results for the Hall conductivity of the 2DEG in a periodic array of flux vortices. We find characteristic peaks in the Hall conductance, when plotted against the filling fraction. It is argued that the peaks can be interpreted in terms of ``topological charge'' piling up across local and global gaps in the energy spectrum.Comment: 47 pages, Revtex 3.0, 18 postscript figures can be obtained from our WWW-server: http://roemer.fys.ku.dk/vortices.htm , or on request from the Authors. Note that this paper is a thoroughly revised version of cond-mat/940405