Arrested Cracks in Nonlinear Lattice Models of Brittle Fracture

We generalize lattice models of brittle fracture to arbitrary nonlinear force laws and study the existence of arrested semi-infinite cracks. Unlike what is seen in the discontinuous case studied to date, the range in driving displacement for which these arrested cracks exist is very small. Also, our results indicate that small changes in the vicinity of the crack tip can have an extremely large effect on arrested cracks. Finally, we briefly discuss the possible relevance of our findings to recent experiments.Comment: submitted to PRE, Rapid Communication

Adjunctive quetiapine for serotonin reuptake inhibitor-resistant obsessive-compulsive disorder: A meta-analysis of randomised controlled treatment trials

Small studies have shown positive effects from adding a variety of antipsychotic agents in patients with obsessive–compulsive disorder who are unresponsive to treatment with serotonin reuptake inhibitors. The evidence, however, is contradictory. This paper reports a meta-analysis of existing double-blind randomized placebo-controlled studies looking at the addition of the second-generation antipsychotic quetiapine in such cases. Three studies fulfilled the inclusion criteria. Altogether 102 individuals were subjected to analysis using Review Manager (4.2.7). The results showed evidence of efficacy for adjunctive quetiapine (< 400 mg/day) on the primary efficacy criterion, measured as changes from baseline in total Yale–Brown Obsessive Compulsive Scale scores (P = 0.008), the clinical significance of which was limited by between-study heterogeneity. The mechanism underlying the effect may involve serotonin and/or dopamine neurotransmission

Crack Front Waves and the dynamics of a rapidly moving crack

Crack front waves are localized waves that propagate along the leading edge of a crack. They are generated by the interaction of a crack with a localized material inhomogeneity. We show that front waves are nonlinear entities that transport energy, generate surface structure and lead to localized velocity fluctuations. Their existence locally imparts inertia, which is not incorporated in current theories of fracture, to initially "massless" cracks. This, coupled to crack instabilities, yields both inhomogeneity and scaling behavior within fracture surface structure.Comment: Embedded Latex file including 4 figure

Dynamical stability of the crack front line

Dynamical stability of the crack front line that propagates between two plates is studied numerically using the simple two-dimensional mass-spring model. It is demonstrated that the straight front line is unstable for low speed while it becomes stable for high speed. For the uniform model, the roughness exponent in the slower speed region is fairly constant around 0.4 and there seems to be a rough-smooth transition at a certain speed. For the inhomogeneous case with quenched randomness, the transition is gradual.Comment: 14 pages, 7 figure

Experimental Benchmarks and Initial Evaluation of the Performance of the PASM System Prototype

The work reported here represents experiences with the PASM parallel processing system prototype during its first operational year. Most of the experiments were performed by students in the Fall semester of 1987. The first programming, and the first timing measurements, were made during the summer of 1987 by Sam Fineberg. The goal of the collection of experiments presented here was to undertake an Application-driven Architecture Study of the PASM system as a paradigm for parallel architecture evaluation in general. PASM was an excellent vehicle for experimenting with this evaluation technique due to its unique architectural features. Among these are: 1. A reconfigurable, partitionable multistage circuit-switched network. 2. Support for both SIMD and MIMD programs. 3. Ability to execute hybrid SIMD/MIMD programs. 4. An instruction queue which allows overlap of control-flow and data manipulation between micro-control (MC) units and processing elements (PE). It had been hypothesized that superlinear speed-up over the number of PEs could be attained with this feature, and experimental results verified this. 5. Support for barrier synchronization of MIMD tasks. This feature was exploited in some non-standard ways to show the ability to decouple variant length SIMD instructions into multiple MIMD streams for an overall performance benefit. This type of study is expected to continue in the future on PASM and other parallel machines at Purdue. This report should serve as a guide for this future work as well

The Classification of Obsessive–Compulsive and Related Disorders in the ICD-11

Background To present the rationale for the new Obsessive–Compulsive and Related Disorders (OCRD) grouping in the Mental and Behavioural Disorders chapter of the Eleventh Revision of the World Health Organization’s International Classification of Diseases and Related Health Problems (ICD-11), including the conceptualization and essential features of disorders in this grouping. Methods Review of the recommendations of the ICD-11 Working Group on the Classification for OCRD. These sought to maximize clinical utility, global applicability, and scientific validity. Results The rationale for the grouping is based on common clinical features of included disorders including repetitive unwanted thoughts and associated behaviours, and is supported by emerging evidence from imaging, neurochemical, and genetic studies. The proposed grouping includes obsessive–compulsive disorder, body dysmorphic disorder, hypochondriasis, olfactory reference disorder, and hoarding disorder. Body-focused repetitive behaviour disorders, including trichotillomania and excoriation disorder are also included. Tourette disorder, a neurological disorder in ICD-11, and personality disorder with anankastic features, a personality disorder in ICD-11, are recommended for cross-referencing. Limitations Alternative nosological conceptualizations have been described in the literature and have some merit and empirical basis. Further work is needed to determine whether the proposed ICD-11 OCRD grouping and diagnostic guidelines are mostly likely to achieve the goals of maximizing clinical utility and global applicability. Conclusion It is anticipated that creation of an OCRD grouping will contribute to accurate identification and appropriate treatment of affected patients as well as research efforts aimed at improving our understanding of the prevalence, assessment, and management of its constituent disorders

Fracture precursors in disordered systems

A two-dimensional lattice model with bond disorder is used to investigate the fracture behaviour under stress-controlled conditions. Although the cumulative energy of precursors does not diverge at the critical point, its derivative with respect to the control parameter (reduced stress) exhibits a singular behaviour. Our results are nevertheless compatible with previous experimental findings, if one restricts the comparison to the (limited) range accessible in the experiment. A power-law avalanche distribution is also found with an exponent close to the experimental values.Comment: 4 pages, 5 figures. Submitted to Europhysics Letter

Phase-Field Model of Mode III Dynamic Fracture

We introduce a phenomenological continuum model for mode III dynamic fracture that is based on the phase-field methodology used extensively to model interfacial pattern formation. We couple a scalar field, which distinguishes between ``broken'' and ``unbroken'' states of the system, to the displacement field in a way that consistently includes both macroscopic elasticity and a simple rotationally invariant short scale description of breaking. We report two-dimensional simulations that yield steady-state crack motion in a strip geometry above the Griffith threshold.Comment: submitted to PR

Quasi-Static Fractures in Disordered Media and Iterated Conformal Maps

We study the geometrical characteristic of quasi-static fractures in disordered media, using iterated conformal maps to determine the evolution of the fracture pattern. This method allows an efficient and accurate solution of the Lam\'e equations without resorting to lattice models. Typical fracture patterns exhibit increased ramification due to the increase of the stress at the tips. We find the roughness exponent of the experimentally relevant backbone of the fracture pattern; it crosses over from about 0.5 for small scales to about 0.75 for large scales, in excellent agreement with experiments. We propose that this cross-over reflects the increased ramification of the fracture pattern.Comment: submitted to Physical Review Letter