Hybrid approach for localization in anisotropic sensor networks

In many real-world applications including agricultural, meterological, military applications, etc, localization techniques are widely used to estimate the geographic locations of sensor nodes based on the precision positions of a few anchors equipped with special hardware. Existing localization algorithms mainly try to improve their accuracy in position estimation by using various heuristic-based or mathematical techniques. Every node in the network follows the same technique to find its physical location. However, each individual method with its own strength can only outperform the others in some but not all nodes. Based on this observation, we develop a hybrid approach for the localization problem. Each node collects the same kind of information. By analysing the information, a node can decide what is the best localization algorithm to use. Different nodes can make their own decisions. Our simulation results reveal that the hybrid approach is effective that it outpeforms existing algorithms. To the best of our knowledge, our work presents the first effort in solving the absolute localization problem by adopting a hybrid approach. © 2006 IEEE.published_or_final_versio

BlueGame - A bluetooth enabled multi-player and multi-platform game: An experience report

Computer games on mobile devices including cellular phones or handheld computers have become a fast expanding industry due to the recent advance in hardware and software supports. Most large mobile game and handheld vendors mainly focus on improving the interactivity and visual effects of, commonly single-user, mobile games. In this project, we carefully designed and then implemented an interactive multi-player action game, namely the BlueGame, transferrable between different computing platforms supported by the Bluetooth wireless technology. In addition to individual user's convenience to continue the multi-player game, our BlueGame prototype highlighted certain shortcomings of the existing Bluetooth technology, and more importantly our valuable experience gained for future wireless game development. ©2006 IEEE.published_or_final_versio

Optical afterglows from cylindrical jets of short gamma-ray bursts

Observations of extragalactic radio jets and young stellar jets show that the jets are cylindrical; i.e., they maintain a nearly constant cross section on large scales. It has been suggested that the afterglow behaviors of some long-duration gamma-ray bursts (GRBs) are consistent with the cylindrical jet model of GRBs. Here we study the afterglow emission of cylindrical jets from short-duration GRBs. For the usual conical jet geometry, it is argued that, because of the low fluence of short GRBs, the prospects of detecting the optical afterglow 10 hr after the burst are not promising. However, in the present work we find that if the jets are cylindrical, the chance for detecting the optical afterglow will be increased, even if the burst occurs in a low-density (n ∼ 10-3 cm-3) medium. Since the jets are expected to not be well collimated initially and the time when they change from conical to cylindrical is not exactly known, we discuss two cases for the afterglow of cylindrical jets: the jets becoming cylindrical (1) after the gamma-ray - emitting phase and (2) before the gamma-ray - emitting phase. In both cases, the light-curve behaviors, especially the peak time, are sensitive to the cross section radius of the cylindrical jet. In the former case we find that for viewing angles less than ∼0.03 rad relative to the jet axis, typical short GRBs have a late-time R-band afterglow with a maximum apparent magnitude of mR ≲ 23, given that the efficiency for producing gamma rays and the shock microphysical parameters of the afterglow are the same in short and long bursts. For the latter case the optical afterglows can always be readily detected with mR < 23 at 10 hr after the burst. Comparison between model light curves and observational upper limits of the optical afterglow flux of a few short GRBs are also made. © 2005. The American Astronomical Society. All rights reserved.published_or_final_versio

Improving localization in wireless sensor networks with an evolutionary algorithm

Wireless sensor networks are highly useful for many location-sensitive applications including environmental monitoring, military applications, disaster management, etc. Localization in wireless sensor networks concerns about the precise estimation of node positions given a relatively small portion as anchor nodes with their absolute positions predetermined. Intrinsically, localization is an unconstrained optimization problem based on various distance/path measures. Most of the existing work focus on increasing the accuracy in position estimation typically by using different heuristic-based or mathematical techniques. On the other hand, there were many complex optimization problems successfully tackled by the nature inspired search algorithms including the ant-based or genetic algorithms. In this paper, we propose to adapt an evolutionary approach, namely a microgenetic algorithm, and integrate as a post-optimizer into some existing localization techniques such as the Ad-hoc Positioning System (APS) to further improve their position estimation. Clearly, our proposed MGA is so adaptable that it can easily be integrated into other localization methods. More importantly, the remarkable improvements obtained by the prototype of our proposed evolutionary optimizer on certain anisotropic topologies of our simulation tests prompt for further investigation. © 2006 IEEE.published_or_final_versio

Early re-brightenings in GRB afterglows as signatures of low-to-high density boundary

The association of long gamma-ray bursts (GRBs) with star forming regions and the idea of massive stars as progenitors of GRBs are widely accepted. Because of their short lifetimes, it is very likely that massive stars are still embedded in dense molecular clouds when they give birth to GRBs. Stellar winds from GRB progenitors can create low-density bubbles with sizes and densities strongly depending on the initial ambient density. A boundary between the bubble and the dense molecular cloud must exist with the density at the boundary increasing from that of the bubble to that of the outer cloud. We have calculated the lightcurves of the afterglows in such environments with three regions: the stellar wind region, the boundary, and the molecular cloud. We show that the interaction between the cylindrical jet and the density boundary can result in a re-brightening of the afterglow occurring as early as ∼1 day after the GRB. We compare our models with the optical afterglows of GRB 970508, GRB 000301C, and GRB 030226. We find that the values of our model parameters, including the radius of the wind bubble, the densities in the bubble and in the outer molecular cloud are within typical ranges. © 2005 Elsevier B.V. All rights reserved.postprin

CHANDRA DETECTION OF A NEW DIFFUSE X-RAY COMPONENT FROM THE GLOBULAR CLUSTER 47 TUCANAE

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Building smart cameras on mobile tablets for hand gesture recognition

Mobile tablets have become very popular due to their portability and the wide diversity of the applications available. The touch screens and built-in accelerometers facilitate different forms of input instead of keyboards and mice. Nowadays, high-resolution cameras become a standard feature in a mobile device. Nevertheless, this camera is seldom considered to serve as a form of user inputs to the application, although similar technology is realized in some home entertainment systems. This paper describes our experience on making a smart camera on an iPad that can recognize pre-defined hand gestures. We study the time performance of performing image processing on an iPad. We find that due to the limited computational power of the mobile device, recognition results may not be available fast enough for a real-time application. We explore applying cloud computing to solve the problem. To the best of our knowledge, this is the first study on recognizing hand gestures on an iPad. Our results facilitate the development of a brand new type of applications that require smart cameras. © 2012 ACM.published_or_final_versio

Turning mobile phones into a mobile quiz platform to challenge players' knowledge: An experience report

In the past few years, many new mobile technologies including the 3G, WiFi or mobileTV have created unprecedented learning opportunities on mobile devices. Furthermore, such technologies continuously fuel the rapid growth of new fields of research like the edutainment for educational entertainment. In a recent project awarded by the Hong Kong Wireless Development Center, we have developed a mobile quiz game system on 3G mobile phone networks in China, Hong Kong or other countries to facilitate learning anytime and anywhere. Our developed mobile quiz system is so generic that it can be readily extended to any wireless network. In this paper, we discuss about the design and possible uses of our quiz system in mobile learning, and also share the relevant experience in system development with the evaluation strategies carefully examined. After all, our work shed light on many interesting directions for future exploration. © 2008 IEEE.published_or_final_versionThe 8th IEEE International Conference on Advanced Learning Technologies (ICALT 2008), Santander, Cantabria, Spain, 1-5 July 2008. In Proceedings of the 8th ICALT, 2008, p. 943-94

Gamma-Ray Emission of the Kes 73/1E 1841-045 Region Observed with the Fermi Large Area Telescope

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HIGH-ENERGY EMISSIONS FROM THE GAMMA-RAY BINARY LS 5039

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