Finite element analysis of fault bend influence on stick-slip instability along an intra-plate fault

Earthquakes have been recognized as resulting from stick-slip frictional instabilities along the faults between deformable rocks. A three-dimensional finite-element code for modeling the nonlinear frictional contact behaviors between deformable bodies with the node-to-point contact element strategy has been developed and applied here to investigate the fault geometry influence on the nucleation and development process of the stick-slip instability along an intra-plate fault through a typical fault bend model, which has a pre-cut fault that is artificially bent by an angle of 5.6degrees at the fault center. The numerical results demonstrate that the geometry of the fault significantly affects nucleation, termination and restart of the stick-slip instability along the intra-plate fault, and all these instability phenomena can be well simulated using the current finite-element algorithm.

Influence of charge size distribution on net-power draw of tumbling mill based on DEM modelling

Modelling and optimization of the power draw of large SAG/AG mills is important due to the large power draw which modern mills require (5-10 MW). The cost of grinding is the single biggest cost within the entire process of mineral extraction. Traditionally, modelling of the mill power draw has been done using empirical models. Although these models are reliable, they cannot model mills and operating conditions which are not within the model database boundaries. Also, due to its static nature, the impact of the changing conditions within the mill on the power draw cannot be determined using such models. Despite advances in computing power, discrete element method (DEM) modelling of large mills with many thousands of particles could be a time consuming task. The speed of computation is determined principally by two parameters: number of particles involved and material properties. The computational time step is determined by the size of the smallest particle present in the model and material properties (stiffness). In the case of small particles, the computational time step will be short, whilst in the case of large particles; the computation time step will be larger. Hence, from the point of view of time required for modelling (which usually corresponds to time required for 3-4 mill revolutions), it will be advantageous that the smallest particles in the model are not unnecessarily too small. The objective of this work is to compare the net power draw of the mill whose charge is characterised by different size distributions, while preserving the constant mass of the charge and mill speed. (C) 2004 Elsevier Ltd. All rights reserved.

Clinical supervision: Its influence on client-rated working alliance and client symptom reduction in the brief treatment of major depression

Supervision of psychotherapists and counselors, especially in the early years of practice, is widely accepted as being important for professional development and to ensure optimal client outcomes. Although the process of clinical supervision has been extensively studied, less is known about the impact of supervision on psychotherapy practice and client symptom outcome. This study evaluated the impact of clinical supervision on client working alliance and symptom reduction in the brief treatment of major depression. The authors randomly assigned 127 clients with a diagnosis of major depression to 127 supervised or unsupervised therapists to receive eight sessions of problems-solving treatment. Supervised therapists were randomly assigned to either alliance skill- or alliance process-focused supervision and received eight supervision sessions. Before beginning treatment, therapists received one supervision session for brief training in the working alliance supervision approach and in specific characteristics of each case. Standard measures of therapeutic alliance and symptom change were used as dependent variables. The results showed a significant effect for both supervision conditions on working alliance from the first session of therapy, symptom reduction, and treatment retention and evaluation but no effect differences between supervision conditions. It was not possible to separate the effects of supervision from the single pretreatment session and is possible that allegiance effects might have inflated results. The scientific and clinical relevance of these findings is discussed.