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Zhu Y.,Shanghai JiaoTong University | Liu Y.,Third Security | Ni L.M.,Hong Kong University of Science and Technology
Wireless Networks | Year: 2012

Duty cycling is a fundamental approach to conserving energy in sensor networks; however, it brings challenges to event detection in the sense that an event may be undetected or undergo a certain delay before it is detected, in particular when sensors are low duty-cycled. We investigate the fundamental relationship between event detection and energy efficiency. We quantify event detection performance by deriving the closed forms of detection delay and detectability with a relatively simple model. We also characterize the intrinsic tradeoff that exists between detection performance and system lifetime, which helps flexible design decisions for sensor networks. In addition, we propose a fully localized algorithm called CAS to cooperatively determine sensor wakeups. Without relying on location information, the distributed algorithm is easy to implement and scalable to network density and scale. Theoretical bounds of event detection are also studied to facilitate comparative study. Comprehensive experiments are conducted and results demonstrate that the proposed algorithm significantly improves event detection performance in terms of detection latency and detection probability. It reduces as high as 31% of detection delay and increases as much as 25% of detectability compared with the random independent scheme. Source

Liu Y.,Third Security | Ni L.,Hong Kong University of Science and Technology | Hu C.,Third Security
IEEE Journal on Selected Areas in Communications | Year: 2012

Topology control is an effective method to improve the energy-efficiency and increase the communication capacity of Wireless Sensor Networks (WSNs). Traditional topology control algorithms are based on deterministic model that fails to consider lossy links which provide only probabilistic connectivity. Noticing this fact, we propose a novel probabilistic network model. We meter the network connectivity using network reachability. It is defined as the minimal of the upper limit of the end-to-end delivery ratio between any pair of nodes in the network. We attempt to find a minimal transmission power for each node while the network reachability is above a given application-specified threshold. The whole procedure is called probabilistic topology control (PTC). We prove that PTC is NP-hard and propose a fully distributed algorithm called BRASP. We prove that BRASP has the guaranteed performance and the communication overhead is O(\vert E \vert + \vert V \vert). The experimental results show that the network energy-efficiency can be improved by up to 250% and the average node degree is reduced by 50%. © 2012 IEEE. Source

The public security industry standard “General technical requirements for micro-dose X-ray transmission body scanner” (GA 926-2011) was released in March 25, 2011 and was formally implemented in July 1, 2011.The X-ray radiation performance index of micro-dose X-ray transmission body scanner includes Dose Per Inspection and Leakage Radiation Rate. The standard requires that Dose Per Inspection should be tested by ionization dosimeter. However, it doesn't specify which kind of equipment should be used to test Leakage Radiation Rate, and only requires a high sensitivity dosimeter. Therefore it is necessary to synthetically consider numerical features and test accuracy requirements, select appropriate test methods and test equipments. Radiograph Method, Ionization Detection Method, Scintillation Detection Method and Semiconductor Detection Method are analysed and compared from the detection principle, the advantages and disadvantages, Ionization Chamber Dosimeter was selected to test Dose Per Inspection, Scintillation Detection Method was selected to test Leakage Radiation Rate. © (2014) Trans Tech Publications, Switzerland. Source

Qian C.,University of Texas at Austin | Liu Y.,Third Security | Ngan R.H.,Hong Kong University of Science and Technology | Ni L.M.,Hong Kong University of Science and Technology
IEEE Transactions on Parallel and Distributed Systems | Year: 2013

The growing importance of operations such as identification, location sensing, and object tracking has led to increasing interests in contactless Radio Frequency Identification (RFID) systems. Enjoying the low cost of RFID tags, modern RFID systems tend to be deployed for large-scale mobile objects. Both the theoretical and experimental results suggest that when tags are in large numbers, most existing collision arbitration protocols do not satisfy the scalability and time-efficiency requirements of many applications. To address this problem, we propose Adaptively Splitting-based Arbitration Protocol (ASAP), a scheme that provides efficient RFID identification for both small and large deployment of RFID tags, in terms of time and energy cost. Theoretical analysis and simulation evaluation show that the performance of ASAP is better than most existing collision-arbitration solutions and the time efficiency is close to the theoretically optimal values. © 1990-2012 IEEE. Source

Liu W.,Shanghai JiaoTong University | Liu W.,Philips | Shang Y.,Third Security | Yang X.,Shanghai JiaoTong University
Pattern Recognition Letters | Year: 2013

A nonparametric local region-based active contour driven by a local histogram fitting energy is presented. The energy is defined in terms of an evolving curve and two fitting histograms that approximate the distribution of object and background locally through a truncated Gaussian kernel. The kernel width for computing the fitting histograms should be different on different pixels, since the same kernel width applied may cause local minima of the energy. Three inequalities are introduced to determine whether larger kernel width should be considered. We do not assume any distributions in the presented method. The method therefore belongs to a nonparametric local region based active contour, and it can segment the regions whose distribution is hard to be predefined. Experimental results show desirable performances of our method. © 2013 Elsevier B.V. All rights reserved. Source

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