Implicit and Implicit–Explicit Strong Stability Preserving Runge–Kutta Methods with High Linear Order

Strong stability preserving (SSP) time discretizations preserve the monotonicity properties satisfied by the spatial discretization when coupled with the first order forward Euler, under a certain time-step restriction. The search for high order strong stability preserving time-stepping methods with high order and large allowable time-step has been an active area of research. It is known that implicit SSP Runge–Kutta methods exist only up to sixth order; however, if we restrict ourselves to solving only linear autonomous problems, the order conditions simplify and we can find implicit SSP Runge–Kutta methods of any linear order. In the current work we find implicit SSP Runge–Kutta methods with high linear order \(p_{lin} \le 9\) and nonlinear orders \(p=2,3,4\), that are optimal in terms of allowable SSP time-step. Next, we formulate a novel optimization problem for implicit–explicit (IMEX) SSP Runge–Kutta methods and find optimized IMEX SSP Runge–Kutta pairs that have high linear order \(p_{lin} \le 7\) and nonlinear orders up to \(p=4\). We also find implicit methods with large linear stability regions that pair with known explicit SSP Runge–Kutta methods. These methods are then tested on sample problems to demonstrate the sharpness of the SSP coefficient and the typical behavior of these methods on test problems.     

Cognitive engineering of a new telephone operator workstation using COGNET

Many cognitive engineering methodologies for user-centered design involve modeling procedural knowledge; others deal with domain semantics or conceptual models. COGnitive NEwork of Tasks (COGNET) is a framework for modeling human cognition and decision-making which provides an integrated representation of the knowledge, behavioral actions, strategies and problem solving skills used in a domain or task situation, yielding a powerful cognitive engineering tool. A case study of the design of the user interface for a new telephone operator workstation is presented to illustrate the derivation of the design from the components of the COGNET model. The model does not directly convey any specific feature of the interface design, but rather a formal representation of what the user must do with the resulting interface. This information is then evolved through a set of transformations which systematically move toward design features, in a fully traceable manner.

Relevance to industry

With the increasing prevalence of technical systems in complex work domains, cognitive engineering is necessary in designing the user interface for those systems to promote efficient integration of person and machine. The cognitive engineering methodology presented here addresses that need.     

Application of the principles of linear fracture mechanics to the composite materials

Application of the principles of linear fracture mechanics to the orthotropic composite materials is examined. It is shown that fracture toughness of unidirectional composites is independent of crack length but dependent on crack-fiber orientation. For experimental verification of the above principles, uni-directional glass epoxy material (Scotchply 1002) was used. The fracture toughness of Scotchply 1002 for different crack-fiber orientations is obtained by utilizing Solid Sap finite element program and compact tension specimens. An empirical formula relating the fracture toughness of the material for different crack-fiber orientation is found.

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Résumé On examine l'application du principe de la mécanique linéaire de rupture aux matériaux composites orthotropes. On montre que la ténacité à la rupture de composites unidirectionnels est indépendante de la longueur de la fissure mais dépend de l'orientation des fibres par rapport à cette fissure. Pour vérifier de manière expérimentale les principes ci-dessus, on a utilisé un matériau en verre epoxy unidirectionnel (Scotchply 1002). La ténacité à la rupture du Scotchply 1002 pour différentes orientations fibre/fissure a été obtenue en utilisant un programme à élément fini Solid Sap et des éprouvettes de traction compactes. On a trouvé une formule empirique mettant en relation la ténacité à la rupture du matériau pour différentes orientations fibre/fissure.

     

Quantitative use of Rayleigh waves to locate and size subsurface holes

An ultrasonic inspection method is used to obtain the circumference of a subsurface hole and the depth of the hole below the surface. A pitch-catch Rayleigh wave transducer set-up was used to launch a Rayleigh surface wave at the flaw and to capture and record the scattered waves. The frequency spectrum of the scattered waves can be used to obtain the depth of the hole. The ligament of material between the hole and the surface is sent into resonance, and this feature can be extracted from the scattered waves' frequency spectrum. The frequency is a function of the ligament length; thus the hole depth can be obtained. The circumference of the hole is found from a time of flight measurement. A Rayleigh wave is formed that travels around the hole's surface. The length of time required for the wave to travel around the hole is a measure of the circumference.     

Parallel path consistency

Filtering algorithms are well accepted as a means of speeding up the solution of the consistent labeling problem (CLP). Despite the fact that path consistency does a better job of filtering than arc consistency, AC is still the preferred technique because it has a much lower time complexity. We are implementing parallel path consistency algorithms on multiprocessors and comparing their performance to the best sequential and parallel arc consistency algorithms.^(1,2) (See also work by Kerethoet al. ⁽³⁾ and Kasif⁽⁴⁾) Preliminary work has shown linear performance increases for parallelized path consistency and also shown that in many cases performance is significantly better than the theoretical worst case. These two results lead us to believe that parallel path consistency may be a superior filtering technique. Finally, we have implemented path consistency as an outer product computation and have obtained good results (e.g., linear speedup on a 64K-node Connection Machine 2).     

Threshold energies in the light emission characteristics of silicon MOS tunnel diodes

Hot electron luminescence of MOS tunnel structures with sub-3 nm oxide layer on p-Si is experimentally studied. Radiation spectra are shown to exhibit thresholds whose positions depend on the initial energy E of injected electrons. Simultaneously, a threshold-like increase of the light intensity at a selected wavelength as a function of E is revealed, and attributed to the onset of different luminescence mechanisms.     

ALGAMES: a fast augmented Lagrangian solver for constrained dynamic games

Autonomous Robots - Dynamic games are an effective paradigm for dealing with the control of multiple interacting actors. This paper introduces augmented Lagrangian GAME-theoretic solver (ALGAMES),...     

Nurse and patient reactions to social displays of depression.

Examined the interpersonal responses of 27 nurses and 27 hospitalized patients with chronic medical conditions to a target who appeared either to have a chronic physical impairment or to be able-bodied, and who enacted either a depressed or nondepressed role. It was predicted that while nurses and patients would have negative reactions to the depressed targets, patient reactions to the depressed target with a physical impairment would be less negative than nurse reactions on the basis of perceived similarity. Results indicated that both groups had negative perceptions of the depressed targets. The similarity hypothesis, however, was not explicitly supported. The reactions of health-care staff to depressed medical patients may reinforce the patients' depressive behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)