Wuzhou Zhang

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Nearest-neighbor search, which returns the nearest neighbor of a query point in a set of points, is an important and widely studied problem in many fields, and it has a wide range of applications. In many of them, such as sensor databases, location-based services, face recognition, and mobile data, the location of data is imprecise. We therefore study(More)
We study the convex-hull problem in a probabilistic setting, motivated by the need to handle data uncertainty inherent in many applications, including sensor databases, location-based services and computer vision. In our framework, the uncertainty of each input point is described by a probability distribution over a finite number of possible locations(More)
CAPTCHA is a test that can tell humans and computer programs apart automatically. The aim is to allow the server to identify the visitor is a human or a computer, and only provide services to human. It can improve the current server system and user information security. The static plane visual CAPTCHA based on OCR problems with the advantages of(More)
Nearest-neighbor queries, which ask for returning the nearest neighbor of a query point in a set of points, are important and widely studied in many fields because of a wide range of applications. In many of these applications, such as sensor databases, location based services, face recognition, and mobile data, the location of data is imprecise. We(More)
In order to avoid tremendous attack from malicious computer programs, CAPTCHA (Completely Automated Public Turing test to tell Computers and Human Apart) mechanism has been introduced to distinguish humans and computers. Due to the fast development of pattern recognition and artificial intelligence technology, there are increasing safety loopholes(More)
In this paper, we introduce the notion of τ -skyline as an alternative representation for uncertain skylines. Given a parameter τ ∈ [0,1] and a set P of n uncertain points in the plane, where each uncertain point Pi is described by a discrete probability distribution defined over k locations, the τ -skyline region of P is the set of points q in the plane(More)
In this paper, we present algorithms for the top-k nearest neighbor searching where the input points are exact and the query point is uncertain under the L1 metric in the plane. The uncertain query point is represented by a discrete probability distribution function, and the goal is to efficiently return the top-k expected nearest neighbors, which have the(More)