Search

Group services are highly important for a variety of computing application domains. In this paper, we study the fundamental problem of allocating a set of service patrons to a set of service groups in an attempt to maximize the total profit gained by the grouping platform. The problem under consideration is unique in that group service is not provided at all unless its lower bound requirement is satisfied. In addition, we allow each service patron to join multiple groups. In this paper, after proving the hardness property of the problem, we focus first on a special case of the problem. To this end, we propose two approaches. One aims at providing a suboptimal solution using a 1/2-approximation algorithm. The other approach turns to seeking an optimal solution using a branch and bound technique. For this purpose, we introduce a theorem that captures a useful property of an optimal allocation. Based on this theorem, we design an efficient branch and bound algorithm to find an optimal solution. We then extend these methods to solve the general problem. Extensive experiments show that our branch and bound algorithm is able to obtain an optimal solution with a small amount of computation time in many different settings. [ABSTRACT FROM PUBLISHER]

We investigate how to well utilize radio frequency identification techniques for real-time location systems (RTLS). A new control method, locate tracking tag through reader power control and candidate region intersection (LOCTREC), has been proposed to improve the RTLS estimation accuracy by eliminating trivial tag information from the estimation procedure. Multireaders were deployed and operated with multipower level to progressively refine the target tag region for accurate location estimation. To enhance the LOCTREC, visual tag interpolation algorithms were adopted to further refine the tag grid to enhance location estimation. Experiments showed that the estimation errors is 70% smaller than its counterpart of LANDMARC and SpotON which deploy regularly spaced reference tags to determine signal strength. For intuitive displaying the result, a video surveillance module was integrated with the RTLS to visually render the located objects, based on which context-aware services can be developed. One example is a smart wheelchair (SWC) with a friendly user-environment control interface that enables SWC users to interact with his living environment like a normal healthy person. [ABSTRACT FROM PUBLISHER]

Abstract: This paper proposes a vision-based indoor localization service system that adopts affine scale invariant features (ASIFT) in MapReduce framework. Compared to prior vision-based localization methods that use scale invariant features or bag-of-words to match database images, the proposed system with ASIFT achieves better localization hit rate, especially when the query image has a large viewing angle difference to the most similar database image. The heavy computation imposed by ASIFT feature detection and image registration is handled by processes designed in MapReduce framework to speed up the localization service. Experiments using a Hadoop computation cluster provide results that show the performance of the localization system. The better localization hit rate is demonstrated by comparing the proposed approach to previous work based on scale invariant feature matching and visual vocabulary. [Copyright &y& Elsevier]

This paper proposes an image sequence-based navigation method under the teaching-replay framework for robots in piecewise linear routes. Waypoints used by the robot contain either the positions with large heading changes or selected midway positions between junctions. The robot applies local visual homing to move between consecutive waypoints. The arrival at a waypoint is determined by minimizing the average vertical displacements of feature correspondences. The performance of the proposed approach is supported by extensive experiments in hallway and office environments. While the homing speed of robots using other approaches is constrained by the speed in the teaching phase, our robot is not bounded by such limit and can travel much faster without compromising the homing accuracy. [ABSTRACT FROM AUTHOR]

A two-phase flow model for an acceleration-driven compressible fluid mixing layer is applied to an initially planar/cylindrical/spherical fluid configuration. A conservative form of the one-dimensional compressible equations is derived under the assumption that the fluid concentration is continuous. With a hyperbolic conservation law for the concentration gradient, the model supports traveling discontinuities in this quantity. The primary examples of this wave type are the moving boundaries of a finite mixing layer, which determine the instability growth rate. Constitutive laws for interfacial averages, previously derived for planar incompressible mixing, are reinterpreted and shown to be applicable to other one-dimensional mixing problems of interest. The equations of motion for an incompressible mixing layer in planar, cylindrical, or spherical geometry are solved exactly, up to a history integral of a function of the edge trajectories, and without assuming incompressible flow outside the layer. Full solutions are obtained by numerically integrating a coupled system of ordinary differential equations for the volume fraction characteristics. Results for self-similar Rayleigh–Taylor mixing in planar geometry are compared to the work of others. This comparison suggests that the shape of the fluid concentration profile is primarily a consequence of mass conservation, parameterized by the expansion ratio of the mixing zone edges. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Charging schemes utilizing mobile wireless chargers can be applied to prolong the lifespan of a wireless sensor network. In considering charging schemes with mobile chargers, most current studies focus on charging each sensor from a single position, then optimizing the moving paths of the chargers. However, in reality, a wireless charger may charge the same sensor from several positions in its path. In this paper we consider this fact and seek to minimize both the number of charging locations and the total required charging time. Two charging plans are developed. The first plan considers the charging time required by each sensor and greedily selects the charging service positions. The second one is a two-phase plan, where the number of charging positions is first minimized, then minimum charging times are assigned to every position according to the charging requirements of the nearby sensors. This paper also corrects a problem neglected by some studies in minimizing the number of charging service positions and further provides a corresponding solution. Empirical studies show that compared with other minimal clique partition (MCP)-based methods, the proposed charging plan may save up to 60% in terms of both the number of charging positions and the total required charging time. [ABSTRACT FROM AUTHOR]