Stress intensity factor analysis of friction sliding at discontinuity interfaces and junctions

A stress intensity factor (SIF) analysis for two-dimensional fractures with frictional contact (crack friction) is presented. This analysis is carried out using the symmetric-Galerkin boundary element method, and a modified quarter-point crack tip element. As in case of non-contact fracture, it is shown that highly accurate SIFs can be obtained, even with the simple Displacement Correlation SIF technique. Moreover, with the modified crack tip element, the mesh on the crack does not need to be excessively refined in order to achieve high accuracy. This meshing advantage is especially important in the context of the nonlinear frictional contact problem, as the computing time for the iterative process strongly depends on the number of elements used. Several numerical examples are presented and the SIF results are compared with available analytical or reference solutions. This research was supported in part by the University of South Alabama Research Council, and by the Applied Mathematical Sciences Research Program of the Office of Mathematical, Information, and Computational Sciences, U.S. Department of Energy under contract DE-AC05-00OR22725 with UT-Battelle, LLC.     

Uniplanar-axial orientation in hot-rolled polymers

The orientations produced by high temperature rolling of polyoxymethylene (126 C) and polytetrafluoroethylene (150 C) and nylon 66 are examined by pole figures. No evidence is found to support the theory of Akahane and Mochizuki that it is the plane of the zig-zag chains that orientates into the rolling plane in nylon 66. The classical rolling texture of Bunn and Garner describes the pole figures except for the (100) pole, which is observed at 28 to the transverse direction; in the texture of Bunn and Garner it should occur at 24 . In hot-rolled polyoxymethylene the texture observed corresponds to a unique orientation of the hexagonal unit cell: (10¯10) planes parallel to the rolling plane and c-axis parallel to rolling direction. The polyoxymethylene texture differs significantly from the pseudo-fibre textures observed in the cold-rolled polymer. The rolling texture of hot-rolled polytetrafluoroethylene is similar to that of hot-rolled polyoxymethylene. These results show the plastic slip system in polyoxymethylene and polytetrafluoroethylene to be (10¯10) [0001].     

Use of optimization methods to solve heat convection problems with unknown wall boundary conditions

In convection heat transfer problems, it is convenient to solve the governing differential equations by using straightforward marching techniques for numerical integration. However, the boundary layer equations in these heat transfer problems are not of the initial value type even though they are parabolic equations. Consequently marching techniques are not successful until correct initial values are known. A means of determining these initial values is presented herein. Selected optimization methods are utilized in conjunction with marching integration techniques to solve third- and fourth-order ordinary differential equations which have three unknown initial boundary conditions. Two optimization methods, one deterministic and the other non-deterministic in nature, are used both independently and in combination as determined by the particular circumstances. Two applications are used to demonstrate the technique and comparison is made with existing solutions.     

Hydrologic Response of Streams Restored with Check Dams in the Chiricahua Mountains,Arizona

In this study, hydrological processes are evaluated to determine impacts of stream restoration in the West Turkey Creek, Chiricahua Mountains, southeast Arizona, during a summer‐monsoon season (June–October of 2013). A paired‐watershed approach was used to analyze the effectiveness of check dams to mitigate high flows and impact long‐term maintenance of hydrologic function. One watershed had been extensively altered by the installation of numerous small check dams over the past 30 years, and the other was untreated (control). We modified and installed a new stream‐gauging mechanism developed for remote areas, to compare the water balance and calculate rainfall–runoff ratios. Results show that even 30 years after installation, most of the check dams were still functional. The watershed treated with check dams has a lower runoff response to precipitation compared with the untreated, most notably in measurements of peak flow. Concerns that downstream flows would be reduced in the treated watershed, due to storage of water behind upstream check dams, were not realized; instead, flow volumes were actually higher overall in the treated stream, even though peak flows were dampened. We surmise that check dams are a useful management tool for reducing flow velocities associated with erosion and degradation and posit they can increase baseflow in aridlands. © 2015 The Authors. River Research and Applications published by John Wiley & Sons, Ltd.     

Using vector quantization for image processing

A review is presented of vector quantization, the mapping of pixel intensity vectors into binary vectors indexing a limited number of possible reproductions, which is a popular image compression algorithm. Compression has traditionally been done with little regard for image processing operations that may precede or follow the compression step. Recent work has used vector quantization both to simplify image processing tasks, such as enhancement classification, halftoning, and edge detection, and to reduce the computational complexity by performing the tasks simultaneously with the compression. The fundamental ideas of vector quantization are explained, and vector quantization algorithms that perform image processing are surveyed     

Decolorization of an azo dye by unacclimated activated sludge under anaerobic conditions

Studies on the reductive decolorization of a complex azo dye, Reactive Red 3.1, were made as part of the development of a practical approach to better exploit the metabolic potential of biomass in wastewater treatment. Decolorization was achieved at low and variable rates by mixed microbial cultures under various environmental conditions, including low pH and high salt concentration. It was caused by reductive cleavage of the azo bond to yield two aromatic amines. More reliable and effective decolorization rates, of up to 20–30 mg l⁻¹ h⁻¹, were given by unadapted activated sludge, (6 g l⁻¹) incubated with 400 mg l⁻¹ of Reactive Red 3.1 under anaerobic conditions. Decolorization also occurred best in static conditions.     

Development and use of modelling techniques for real‐time bathing water quality predictions

Real‐time prediction of bathing water quality is suggested as an appropriate regulatory approach in recent WHO Guidelines and new European Union (EU) standards for bathing water quality. The Scottish Environment Protection Agency (SEPA) has developed the first EU real‐time bathing water quality predictions at 10 sites throughout Scotland since 2004. This paper covers two stages in the evolution of modelling tools which inform these predictions based on antecedent rainfall and river flow, using four sites as examples. These tools, together with associated advisory systems, demonstrate the potential to minimise public exposure to adverse water quality where this occurs in discrete episodes after rainfall events. In addition, they allow an effective prediction and communication system to provide significant compliance benefits as samples taken during periods when bathing is not advised are disregarded for classification purposes.     

Stability,performance and sensitivity analysis of I.I.D. jump linear systems

This paper presents a symmetric Kronecker product analysis of independent and identically distributed jump linear systems to develop new, lower dimensional equations for the stability and performance analysis of this type of systems than what is currently available. In addition, new closed form expressions characterising multi-parameter relative sensitivity functions for performance metrics are introduced. The analysis technique is illustrated with a distributed fault-tolerant flight control example where the communication links are allowed to fail randomly.