16343531
3D video segmentation using point distance histograms
Similar to 2D video segmentation, 3D video segmentation is to divide the 3D video in temporal domain into a set of meaningful and manageable segments (shots) that are used as basic elements for indexing. This paper proposes a temporal segmentation method for 3D video for the first time as far as we know. Point distance histograms are used considering the tradeoff between computational cost and effectiveness. In order to reflect the real motion of 3D object, three fixed points are selected, which can avoid what we call "the same sphere problem." And simulation results on total 285 frames, which are composed of four different sequences, show our method is very effective.
38590214
Motion Composition of 3D Video
3D video, which is composed of a sequence of mesh models and can provide the user with interactivity, is attracting increasing attention in many research groups. However, it is time-consuming and expensive to generate 3D video sequences. In this paper, a motion composition method is proposed to edit 3D video based on the user’s requirements so that 3D video can be re-used. By analyzing the feature vectors, the hierarchical motion structure is parsed and then a motion database is set up by selecting the representative motions. A motion graph is constructed to organize the motion database by finding the possible motion transitions. Then, the best path is searched based on a proposed cost function by a modified Dijkstra algorithm after the user selects the desired motions in the motion database, which are called key motions in this paper. Our experimental results show the edited 3D video sequence looks natural and realistic.
10511708
Automatic diagnosis and response to memory corruption vulnerabilities
Cyber attacks against networked computers have become relentless in recent years. The most common attack method is to exploit memory corruption vulnerabilities such as buffer overflow and format string bugs. This paper presents a technique to automatically identify both known and unknown memory corruption vulnerabilities. Based on the observation that a randomized program usually crashes upon a memory corruption attack, this technique uses the crash as a trigger to initiate an automatic diagnosis algorithm. The output of the diagnosis includes the instruction that is tricked to corrupt data, the call stack at the time of corruption, and the propagation history of corrupted data. These results provide useful information in fixing the vulnerabilities. Moreover, the diagnosis process also generates a signature of the attack using data/address values embedded in the malicious input message, and is used to block future attacks. Such a signature is further associated with the program execution state to reduce false positives without decreasing the detection rate. The proposed techniques enable the development of a decentralized self-diagnosing and self-protecting defense mechanism for networked computers. We report the implementation experience and experimental evaluation of a prototype system on Linux.
2254306
An efficient direct approach for computing shortest rectilinear paths among obstacles in a two-layer interconnection model
In this paper, we present a direct approach for routing a shortest rectilinear path between two points among a set of rectilinear obstacles in a two-layer interconnection model that is used for VLSI routing applications. The previously best known direct approach for this problem takes O(nlog^2n) time and O(nlogn) space, where n is the total number of obstacle edges. By using integer data structures and an implicit graph representation scheme (i.e., a generalization of the distance table method), we improve the time bound to O(nlog^3^/^2n) while still maintaining the O(nlogn) space bound. Comparing with the indirect approach for this problem, our algorithm is simpler to implement and is probably faster for a quite large range of input sizes.
15045053
A monotone finite element scheme for convection-diffusion equations
A simple technique is given in this paper for the construction and analysis of a class of finite element discretizations for convection-diffusion problems in any spatial dimension by properly averaging the PDE coefficients on element edges. The resulting finite element stiffness matrix is an M-matrix under some mild assumption for the underlying (generally unstructured) finite element grids. As a consequence the proposed edge-averaged finite element scheme is particularly interesting for the discretization of convection dominated problems. This scheme admits a simple variational formulation, it is easy to analyze, and it is also suitable for problems with a relatively smooth flux variable. Some simple numerical examples are given to demonstrate its effectiveness for convection dominated problems.
8946964
Extending Network Lifetime for Precision-Constrained Data Aggregation in Wireless Sensor Networks
This paper exploits the tradeoff between data quality and energy consumption to extend the lifetime of wireless sensor networks. We consider the applications that require some aggregate form of sensed data with precision guarantees. Our key idea is to differentiate the precisions of data collected from different sensor nodes to balance their energy consumption. This is achieved by partitioning the precision constraint of data aggregation and allocating error bounds to individual sensor nodes in a coordinated fashion. Three factors affecting the lifetime of sensor nodes are identified: (1) the changing pattern of sensor readings; (2) the residual energy of sensor nodes; and (3) the communication cost between the sensor nodes and the base station. We analyze the optimal precision allocation in terms of network lifetime and propose an adaptive precision allocation scheme that dynamically adjusts the error bounds of sensor nodes. Experimental results using real data traces show that the proposed scheme significantly improves network lifetime compared to existing methods.
11486473
Circumference of Graphs with Bounded Degree
Karger, Motwani, and Ramkumar Algorithmica, 18 (1997), pp. 82--98] have shown that there is no constant approximation algorithm to find a longest cycle in a Hamiltonian graph, and they conjectured that this is the case even for graphs with bounded degree. On the other hand, Feder, Motwani, and Subi [SIAM J. Comput., 31 (2002), pp. 1596--1607] have shown that there is a polynomial time algorithm for finding a cycle of length $n^{\log_32}$ in a 3-connected cubic n-vertex graph. In this paper, we show that if G is a 3-connected n-vertex graph with maximum degree at most d, then one can find, in O(n3) time, a cycle in G of length at least $\Omega(n^{\log_b2})$, where $b=2(d-1)^2+1$.