On delay adjustment for dynamic load balancing in distributed virtual environments

Distributed virtual environments (DVEs) are becoming very popular in recent years, due to the rapid growing of applications, such as massive multiplayer online games (MMOGs). As the number of concurrent users increases, scalability becomes one of the major challenges in designing an interactive DVE system. One solution to address this scalability problem is to adopt a multi-server architecture. While some methods focus on the quality of partitioning the load among the servers, others focus on the efficiency of the partitioning process itself. However, all these methods neglect the effect of network delay among the servers on the accuracy of the load balancing solutions. As we show in this paper, the change in the load of the servers due to network delay would affect the performance of the load balancing algorithm. In this work, we conduct a formal analysis of this problem and discuss two efficient delay adjustment schemes to address the problem. Our experimental results show that our proposed schemes can significantly improve the performance of the load balancing algorithm with neglectable computation overhead.     

A new model of job design: Initial evidence and implications for future research

Clegg and Spencer's (2007) model of job design synthesizes and extends recent conceptions of the job design process by incorporating variables such as knowledge, motivation, and trust into a cyclical and dynamic system. The objective of this study was to examine the sequential organization of variables that comprise the model, as a basis from which to justify further investigations of the model's dynamic properties. Data were collected via questionnaires from 432 participants in two work organizations. Results obtained from structural equation modeling are broadly supportive of the proposed relationships between the variables. Implications of this initial study for future research and practice are discussed. © 2011 Wiley Periodicals, Inc.     

A review on improving the autonomy of unmanned surface vehicles through intelligent collision avoidance manoeuvres

In recent years unmanned vehicles have grown in popularity, with an ever increasing number of applications in industry, the military and research within air, ground and marine domains. In particular, the challenges posed by unmanned marine vehicles in order to increase the level of autonomy include automatic obstacle avoidance and conformance with the Rules of the Road when navigating in the presence of other maritime traffic. The USV Master Plan which has been established for the US Navy outlines a list of objectives for improving autonomy in order to increase mission diversity and reduce the amount of supervisory intervention. This paper addresses the specific development needs based on notable research carried out to date, primarily with regard to navigation, guidance, control and motion planning. The integration of the International Regulations for Avoiding Collisions at Sea within the obstacle avoidance protocols seeks to prevent maritime accidents attributed to human error. The addition of these critical safety measures may be key to a future growth in demand for USVs, as they serve to pave the way for establishing legal policies for unmanned vessels.     

Controlled teleportation via photonic Faraday rotations in low-Q cavities

This paper presents feasible experimental schemes to realize controlled teleportation protocols via photonic Faraday rotations in low-Q cavities. The schemes deal with controlled teleportation of superposition states and two-particle entanglement of atomic states. The information is encoded in lambda configured three-level atoms trapped inside coupled cavities by optical fibers. Also, we estimate the success probability and the current feasibility of the schemes.     

Computer simulations of time-dependent suppression of EOF by polymer coatings

We use molecular dynamics simulations in order to investigate the time evolution of the effect of adsorbed polymer coatings on the electro-osmotic flow (EOF) in a capillary. Weakly adsorbed coatings show no time-dependent performance, but they do not strongly reduce the EOF. On the other hand, strongly adsorbed coatings made of longer polymer chains are often quenched in non-equilibrium conformations that can strongly reduce the EOF over extremely long periods of time. For intermediate adsorption strengths, we observe that the EOF increases as a function of time due to the relaxation of the coating layer. The concentration of polymers in solution and the length of the polymer chains also affect the time-dependence of the EOF. These results show that the quality of electrophoretic separations can depend on the waiting time between the formation of the coating and the beginning of the separation. We conclude by suggesting experimental tests of our predictions.     

Numerical modeling of multiphase flows in microfluidics and micro process engineering: a review of methods and applications

This article presents a comprehensive review of numerical methods and models for interface resolving simulations of multiphase flows in microfluidics and micro process engineering. The focus of the paper is on continuum methods where it covers the three common approaches in the sharp interface limit, namely the volume-of-fluid method with interface reconstruction, the level set method and the front tracking method, as well as methods with finite interface thickness such as color-function based methods and the phase-field method. Variants of the mesoscopic lattice Boltzmann method for two-fluid flows are also discussed, as well as various hybrid approaches. The mathematical foundation of each method is given and its specific advantages and limitations are highlighted. For continuum methods, the coupling of the interface evolution equation with the single-field Navier–Stokes equations and related issues are discussed. Methods and models for surface tension forces, contact lines, heat and mass transfer and phase change are presented. In the second part of this article applications of the methods in microfluidics and micro process engineering are reviewed, including flow hydrodynamics (separated and segmented flow, bubble and drop formation, breakup and coalescence), heat and mass transfer (with and without chemical reactions), mixing and dispersion, Marangoni flows and surfactants, and boiling.     

Microstructural changes during ageing of Cu-2.5 wt% Ti

Microstructural changes in Cu-2.5wt % Ti during ageing at 573 and 773 K have been studied by transmission electron microscopy. Ageing times ranged from 60 sec to 200 h. Ordering of the precipitates was observed after very short ageing treatments at 773 K, and coarsening according tot ^1/3 was also observed from very early times. The particles were observed to become increasingly aligned into rod-like groups along 10 0 as ageing progressed. These results permit a new interpretation of the strengthening mechanisms in this alloy.     

Use of modified standard 20-node isoparametric brick elements for representing stress/strain fields at a crack tip for elastic and perfectly plastic material

The analysis of defects in engineering structures and components has to take into account the singular strain field at the crack tip. The problems encountered in such analyses have unique geometries, have some non-linear elastic plastic behaviour and are three-dimensional in nature. Their solution calls for the use of the finite element method. Two-dimensional fracture mechanics analysis methods have been developed and proved by other researchers to show that 8-noded collapsed finite elements have the required singular strain fields for both the elastic and perfectly plastic material conditions. This paper proves the conditions under which three-dimensional collapsed elements represent the stress/strain fields at a crack tip required for elastic and perfectly plastic material, including crack tip blunting in the latter case. The collapsed elements presented can be used with confidence and give large savings in computing time, which is an essential point in three-dimensional finite element calculations.

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Résumé L'analyse des défauts dans les constructions et dans les composants doit prendre en considération le champ singulier de déformation à l'extrémité d'une fissure. Les problèmes rencontrés dans une telle analyse présentent des géométries uniques, un comportement élasto-plastique sensiblement non linéaire et sont tri-dimensionnelles par nature. Leur solution fait appel à l'utilisation de la méthode par éléments finis. Des méthodes d'analyse en mécanique de rupture bi-dimensionnelles ont été développées, et d'autres chercheurs ont établi qu'elles montrent que les éléments finis à 8 noeuds présentent les champs de déformation singuliers, requis à la fois pour les conditions de matériaux élastiques et parfaitement plastiques. La présente étude établit les conditions sous lesquelles des éléments tri-dimensionnels représentent les champs contrainte/déformation à l'extrémité d'une fissure, requis dans le cas de matériaux élastiques et parfaitement plastiques, y compris l'arrondissement de l'extrémité de la fissure pour ce dernier cas. Les éléments présentés peuvent être utilisés avec confiance et procurent de grandes économies de temps dans les calculs, ce qui est essentiel dans le cas des éléments finis à 3 dimensions.

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List of symbols x, y, z coordinates in the real space - g, h, s coordinates in the normalized cubic space - , , coordinates in modified normalized cubic space - u, v, w vectors of displacements inx, y andz direction, respectively - vectors of coordinatesx, y andz - vectors of displacementsu, v andw - N vector of shape functions - M vector of reduced shape functions - vector of stress components - vector of strain components - D matrix containing material properties - J determinant of the Jacobian matrix - J Jacobian matrix - r distance from the crack tip     

A central crack of mode III in a rectangular sheet with fixed edges

This paper discusses the general solution, by use of the Fourier transform and Fourier series, of the stress intensity factor in a rectangular sheet containing a central crack of mode III, where its boundary is constrained, but its crack surface is subjected to an arbitrary anti-plane load. As examples of numerical computing, consider three circumstances: (1) the boundary parallel to a central crack is fixed; (2) the boundary perpendicular to a central crack is fixed; (3) all of the boundaries around a central crack are fixed but the crack surface is subjected to a constant load.En faisant appel à une transformation de Fourier et aux séries de Fourier, on discute dans cet article de la solution générale au facteur d'intensité de contraintes existant dans une tôle rectangulaire comportant une fissure centrale de mode III, lorsque les bords sont fixés mais que la surface de la fissure est soumise à une charge antiplanaire arbitraire. Comme exemple de calcul numérique, on envisage trois cas distincts:

Fatigue crack growth by crack tip cyclie plastic deformation: the unzipping model

A fatigue crack may propagate by the mechanism of crack tip cyclic plastic deformation, by the mechanism of fracture of brittle particles and embrittled grain boundaries,or, often, by a combination of both. Neutnann and Vehoff have made in situ observations of alternate shear decohhesions on two intersecting conjugate slip bands at a crack tip as the basic mechanism of fatigue crack growth. It is a mechanism by plastic deformation. A micro-mechanism based finite element model is made to simulate the unzipping process of the crack tip shear decohesion mechanism. The calculated crack growth rates by the finite element model agree very well with the measured rates in the intermediate K region of a number of materials

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Résumé La propagation d'une fissure de fatigue peut être due au mécanisme de déformation plastique cyclique de l'extrémité de la fissure, au mécanisme de rupture de portions fragiles et de frontières de grains fragilisées ou, souvent, à une combinaison de ces deux mécanismes.Neumann et Vehoff ont procédé à des observations in situ des décohésions par cisaillement alterné dans deux bandes de glissement s'intersectant à l'extrémité d'une fissure, et ont décrit ce mécanisme par déformation plastique comme un mécanisme de base de la propagation d'une fissure de fatigue.En vue de simuler le processus d'ouverture qui régit le mécanisme de décohésion par cisaillement à l'extrémité dame fissure, on élabore un modèle par éléments finis basé sur un mécanisme à échelle microscopique. On trouve que les vitesses de propagation d'une fissure calculées grâce à ce modèle par éléments finis sont en très bon accord lvee les vitesses mesurées dans la zone des K intermédiaries et pour plusieurs matériaux.