Chao Michael Zhang

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In this work we present a characterization of spam on Twitter. We find that 8% of 25 million URLs posted to the site point to phishing, malware, and scams listed on popular blacklists. We analyze the accounts that send spam and find evidence that it originates from previously legitimate accounts that have been compromised and are now being puppeteered by(More)
Based on the underlying graphene lattice symmetry and an itinerant magnetism model on a bipartite lattice, we propose a unifi ed geometric rule for designing graphene-based magnetic nanostructures: spins are parallel (ferromagnetic (FM)) on all zigzag edges which are at angles of 0° and 120° to each other, and antiparallel (antiferromagnetic (AF)) at angles(More)
Nonsmooth nonconvex regularization has remarkable advantages for the restoration of piecewise constant images. Constrained optimization can improve the image restoration using a priori information. In this paper, we study regularized nonsmooth nonconvex minimization with box constraints for image restoration. We present a computable positive constant θ for(More)
Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract A set S ⊆ V (G) in G is a [1,2]-set if it satisfies that 1 ≤ |N (v)∩S| ≤ 2 for every vertex v ∈ V \ S. The minimum cardinality of a [1,2]-set of G, denoted by γ [1,2] (G), is called the(More)
Beginning with several basic hypotheses of quantum mechanics, we give a new quantum model in econophysics. In this model, we define wave functions and operators of the stock market to establish the Schrödinger equation for the stock price. Based on this theoretical framework, an example of a driven infinite quantum well is considered, in which we use a(More)
Genuine multipartite nonlocality (GMN) has been recognized as the strongest form of multipartite quantum correlation. However, there exist states that cannot violate the Svetlichny inequality derived from the standard definition of GMN, even though they possess GMN properties. The reason is that the standard definition of GMN allows correlations that permit(More)
______________________________________________ Date iii Acknowledgements At first, it is my great pleasure to work with my thesis advisor, Professor Zoran Ninkov, for his valuable advice and guidance through my two-year experience at CIS. He is always encouraging and often tells me to start work from the most fundamental physics and then to more deep(More)
This article studies the necessary and sufficient conditions for asymptotic stability of the linear positive systems with bounded time-varying delays on time scales. Using Lyapunov functions, asymptotic stability conditions for positive systems with constant delays on time scales are established. The relations between the two types of systems have been(More)
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