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Utilizing OnLine Short Text (OLST) in social networking tools such as microblogs, instant messaging platforms, and short message service via smart phones has become a routine in daily life. OLST is appealing for personal covert communication because it can hide information in a very short carrier text, and this concealment is hard to detect due to the diversity of normal traffic. However, designing appropriate schemes confronts several challenges: they need to be provably secure, and their performance needs to maintain high efficiency and handy usability due to the short length of OLST messages. In this paper, we propose a family of customized schemes known as HiMix, HiCod, HiOpt, and HiPhs for text steganography in OLST. These schemes are evaluated in terms of their security and their performance with regard to two metrics that address the particular characteristics of OLST: hiding rate and hiding ease. All proposed schemes are proved to be at least computationally secure, and their performance in terms of hiding rate and hiding ease justifies their applicability in social networking tools that utilize OLST.
2012年03期 v.17 225-231页 [查看摘要][在线阅读][下载 366K] [下载次数：52 ] |[网刊下载次数：0 ] |[引用频次：9 ] |[阅读次数：0 ] Information Technology (IT) investments, especially Enterprise Resource Planning (ERP) systems, are critical for the survival and development of companies. Therefore, understanding the impact of ERP investment is of great importance to managers and researchers. As a corporate performance indicator, Tobin's Q has some inherent advantages compared to other accounting indicators, and it can better reflect the contribution of ERP investment to company performance. This study employs multiple regression models to examine the impact of ERP investment on Tobin's Q. The sample consists of 126 manufacturing companies listed on the Shanghai and Shenzhen Stock Exchanges from 1999 to 2007. Empirical results show that in the first three years after ERP implementation, there is no significant change in Tobin's Q; however, in the fourth year, Tobin's Q increases significantly. The results indicate that, as a strategic long-term investment accompanied by large-scale business process reengineering and organizational learning, ERP implementation has time-lagged effects; nonetheless, it eventually produces significant benefits.
2012年03期 v.17 232-240页 [查看摘要][在线阅读][下载 370K] [下载次数：233 ] |[网刊下载次数：0 ] |[引用频次：11 ] |[阅读次数：0 ] -
Multi-source information can be utilized collaboratively to improve the performance of information retrieval. To make full use of the document and collection information, this paper introduces a new information retrieval model that relies on the Dempster-Shafer theory of evidence. Each query-document pair is taken as a piece of evidence for the relevance between a document and a query. The evidence is combined using Dempster's rule of combination, and the belief committed to the relevance is obtained. Retrieved documents are then ranked according to the belief committed to the relevance. Several basic probability assignments are also proposed. Extensive experiments over the Text REtrieval Conference (TREC) test collection ClueWeb09 show that the proposed model provides performance similar to that of the Vector Space Model (VSM). Under certain probability assignments, the proposed model outperforms the VSM by 63% in terms of mean average precision.
2012年03期 v.17 241-247页 [查看摘要][在线阅读][下载 311K] [下载次数：33 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] Many difficulties remain in identifying the sentence skeleton of Chinese sentences. The purpose of this paper is to automatically identify the sentence skeleton of Chinese sentences on the event level. Based on the event model, this paper discusses the relationship between events and concepts, and presents an event conceptualization method. It analyzes the event composition of Chinese sentences, classifies the relationships among events, and proposes a recursive description of the event composition of Chinese sentences. Based on these analyses, an algorithm for automatically identifying the sentence skeleton of Chinese sentences based on the event model is presented. The results of the final experiment show an 89% success rate, which demonstrates that the proposed algorithm is feasible and effective.
2012年03期 v.17 248-255页 [查看摘要][在线阅读][下载 320K] [下载次数：40 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] -
Density-based approaches in content extraction, whose task is to extract contents from Web pages, are commonly used to obtain page contents that are critical to many Web mining applications. However, traditional density-based approaches cannot effectively manage pages that contain short contents and long noises. To overcome this problem, in this paper, we propose a content extraction approach for obtaining content from news pages that combines a segmentation-like approach and a density-based approach. A tool called BlockExtractor was developed based on this approach. BlockExtractor identifies contents in three steps. First, it looks for all Block-Level Elements (BLE) & Inline Elements (IE) blocks, which are designed to roughly segment pages into blocks. Second, it computes the densities of each BLE&IE block and its element to eliminate noises. Third, it removes all redundant BLE&IE blocks that have emerged in other pages from the same site. Compared with three other density-based approaches, our approach shows significant advantages in both precision and recall.
2012年03期 v.17 256-264页 [查看摘要][在线阅读][下载 3798K] [下载次数：47 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] Heterogeneous systems with both Central Processing Units (CPUs) and Graphics Processing Units (GPUs) are frequently used to accelerate short-ranged Molecular Dynamics (MD) simulations. The most time-consuming task in short-ranged MD simulations is the computation of particle-to-particle interactions. Beyond a certain distance, these interactions decrease to zero. To minimize the operations to investigate distance, previous works have tiled interactions by employing the spatial attribute, which increases the memory access and GPU computations, hence decreasing performance. Other studies ignore the spatial attribute and construct an all-versus-all interaction matrix, which has poor scalability. This paper presents an improved algorithm. The algorithm first bins particles into voxels according to the spatial attributes, and then tiles the all-versus-all matrix into voxel-versus-voxel sub-matrixes. Only the sub-matrixes between neighboring voxels are computed on the GPU. Therefore, the algorithm reduces the distance examine operations and limits additional memory access and GPU computations. This paper also adopts a multi-level programming model to implement the algorithm on multi-nodes of Tianhe-lA. By employing (1) a patch design to exploit parallelism across the simulation domain, (2) a communication overlapping method to overlap the communications between CPUs and GPUs, and (3) a dynamic workload balancing method to adjust the workloads among compute nodes, the implementation achieves a speedup of 4.16x on one NVIDIA Tesla M2050 GPU compared to a 2.93 GHz six-core Intel Xeon X5670 CPU. In addition, it runs 2.41x faster on 256 compute nodes of Tianhe-lA (with two CPUs and one GPU inside a node) than on 256 GPU-excluded nodes.
2012年03期 v.17 265-277页 [查看摘要][在线阅读][下载 801K] [下载次数：20 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] -
To enhance the energy efficiency and performance of algorithms with Graphics Processing Unit (GPU) accelerators in source-code development, we consider the power efficiency based on data transfer bandwidth and power consumption in key situations. First, a set of primitives is abstracted from program statements. Then, data transfer bandwidth and power consumption in different granularity sizes are considered and mapped into proper primitives. With these mappings, a programmer can intuitively determine the power efficiency and performance in different running states of a thread. Finally, this intuition enables the programmer to tune the algorithm in order to achieve the best energy efficiency and performance. Using these power-aware principles, two Fast Fourier Transform (FFT) methods are compared. The mapping between power consumption and primitives is helpful for algorithm tuning in source-code levels.
2012年03期 v.17 278-286页 [查看摘要][在线阅读][下载 681K] [下载次数：32 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] Face detect application has a real time need in nature. Although Viola-Jones algorithm can handle it elegantly, today's bigger and bigger high quality images and videos still bring in the new challenge of real time needs. It is a good idea to parallel the Viola-Jones algorithm with OpenCL to achieve high performance across both AMD and NVidia GPU platforms without bringing up new algorithms. This paper presents the bottleneck of this application and discusses how to optimize the face detection step by step from a very nave implementation. Some brilliant tricks and methods like CPU execution time hidden, stubbles usage of local memory as high speed scratchpad and manual cache, and variable granularity were used to improve the performance. Those technologies result in 4-13 times speedup varying with the image size. Furthermore, those ideas may throw on some light on the way to parallel applications efficiently with OpenCL. Taking face detection as an example, this paper also summarizes some universal advice on how to optimize OpenCL program, trying to help other applications do better on GPU.
2012年03期 v.17 287-295页 [查看摘要][在线阅读][下载 1787K] [下载次数：111 ] |[网刊下载次数：0 ] |[引用频次：4 ] |[阅读次数：0 ] -
This paper describes how to derive quantitative information about the effect of traffic incidents on urban traffic flow from the raw measurements detected by sectional loop sensors. The two critical parameters of the travel delay and queue length, which reflect the temporal and spatial properties of incident-induced congestion, cannot be directly determined from commonly used loop sensors. The modified queuing diagram is used here to quantify incident-induced queues and travel delays on signalized arteries using sensor data from the targeted and upstream links. The method is tested using data generated by the VISSIM simulation model, with results indicating its efficiency and accuracy with an average relative travel delay error of 18.67% for all samples which falls to 8.07% for high volume and very high volume conditions.
2012年03期 v.17 296-303页 [查看摘要][在线阅读][下载 2390K] [下载次数：32 ] |[网刊下载次数：0 ] |[引用频次：6 ] |[阅读次数：0 ] Complete and reliable field traffic data is vital for the planning, design, and operation of urban traffic management systems. However, traffic data is often very incomplete in many traffic information systems, which hinders effective use of the data. Methods are needed for imputing missing traffic data to minimize the effect of incomplete data on the utilization. This paper presents an improved Local Least Squares (LLS) approach to impute the incomplete data. The LLS is an improved version of the K Nearest Neighbor (KNN) method. First, the missing traffic data is replaced by a row average of the known values. Then, the vector angle and Euclidean distance are used to select the nearest neighbors. Finally, a regression step is used to get weights of the nearest neighbors and the imputation results. Traffic flow volume collected in Beijing was analyzed to compare this approach with the Bayesian Principle Component Analysis (BPCA) imputation approach. Tests show that this approach provides slightly better performance than BPCA imputation to impute missing traffic data.
2012年03期 v.17 304-309页 [查看摘要][在线阅读][下载 532K] [下载次数：116 ] |[网刊下载次数：0 ] |[引用频次：26 ] |[阅读次数：0 ] -
Complex networks are now the focus of many branches of research. Particularly, the scale-free property of some networks is of great interest, due to their importance and pervasiveness. Recent studies have shown that in some complex networks, e.g., transportation networks and social collaboration networks, the degree distribution follows the so-called "shifted power law" (or Mandelbrot law) P ( k ) ∝ ( k + c )-γ. This study analyzes some evolving networks that grow with linear preferential attachments. Recent results for the quotient Gamma function are used to prove the asymptotic Mandelbrot law for the degree distribution in certain conditions. The best fit values for the scaling exponent, γ , and the shifting coefficient, c , can be directly calculated using Bernoulli polynomial functions. The study proves that the degree distribution of some complex networks follows an asymptotic Mandelbrot law with linear preferential attachment depicted by P k ∝ ( k +(b+a+1)/2~(-b-a).
2012年03期 v.17 310-312页 [查看摘要][在线阅读][下载 293K] [下载次数：23 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] This paper presents an approach to deterministically teleport an arbitrary two-qubit state through a one-dimensional four-qubit cluster state serving as a probabilistic quantum channel. The channel is modulated in advance to avoid damage to the original states in this scheme, which is caused by the inevitable failure of constructing a channel between the sender and the receiver. The scheme is flexible because the channel can be modulated either by the sender or by the receiver, with the option of deciding whether the sender or the receiver modulates the channel, according to the distribution of the available particle resources. The efficiency can be improved by reusing previously discarded results that may lead to a faithful channel. The scheme can be uniformly performed, so the design process can be greatly simplified to realize a reliable deterministic teleportation. Finally, the scheme is extended to deterministic teleportation of an arbitrary n-qubit state in a generalized form.
2012年03期 v.17 313-318页 [查看摘要][在线阅读][下载 273K] [下载次数：25 ] |[网刊下载次数：0 ] |[引用频次：3 ] |[阅读次数：0 ] -
Sensor bias estimation is an inherent problem in multi-sensor data fusion systems. Classical methods such as the Generalized Least Squares (GLS) method can have numerical problems with ill-conditioned sets which are common in practical applications. This paper describes an azimuth-GLS method that provides a solution to the ill-conditioning problem while maintaining reasonable accuracy compared with the classical GLS method. The mean square error is given for both methods as a criterion to determine when to use this azimuth-GLS method. Furthermore, the separation boundary between the azimuth-GLS favorable region and that of the GLS method is explicitly plotted. Extensive simulations show that the azimuth-GLS approach is preferable in most scenarios.
2012年03期 v.17 319-323页 [查看摘要][在线阅读][下载 498K] [下载次数：29 ] |[网刊下载次数：0 ] |[引用频次：9 ] |[阅读次数：0 ] The Rao-Blackwellized Particle Filter (RBPF) is widely used for high dimensional nonlinear systems, often with a linear Gaussian substructure. However, the RBPF is just a specific method in the class of Rao-Blackwellized Filtering (RBF). This paper analyzes the recursive structure of the RBF from a more general perspective. The research starts from a general system model and studies the interconnected relationships between the two subspaces during the iterations. The results illustrate the working mechanisms of the RBF with an extensible framework for easily building Rao-Blackwellized algorithms with common nonlinear filters. Several examples are given to illustrate how to build new filters using this framework.
2012年03期 v.17 324-328页 [查看摘要][在线阅读][下载 462K] [下载次数：26 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] -
In this paper, a real-time system that utilizes hand gestures to interactively control the presentation is proposed. The system employs a thermal camera for robust human body segmentation to handle the complex background and varying illumination posed by the projector. A fast and robust hand localization algorithm is proposed, with which the head, torso, and arm are sequentially localized. Hand trajectories are segmented and recognized as gestures for interactions. A dual-step calibration algorithm is utilized to map the interaction regions between the thermal camera and the projected contents by integrating a Web camera. Experiments show that the system has a high recognition rate for hand gestures, and corresponding interactions can be performed correctly.
2012年03期 v.17 329-336页 [查看摘要][在线阅读][下载 2263K] [下载次数：33 ] |[网刊下载次数：0 ] |[引用频次：5 ] |[阅读次数：0 ] A satellite image adaptive restoration method was developed that avoids ringing artifacts at the image boundary and retains oriented features. The method combines periodic plus smooth image decomposition with complex wavelet packet transforms. The framework first decomposes a degraded satellite image into the sum of a "periodic component" and a "smooth component". The Bayesian method is then used to estimate the modulation transfer function degradation parameters and the noise. The periodic component is deconvoluted using complex wavelet packet transforms with the deconvolution result of the periodic component then combined with the smooth component to get the final recovered result. Tests show that this strategy effectively avoids ringing artifacts while preserving local image details (especially directional textures) without amplifying the noise. Quantitative comparisons illustrate that the results are comparable with previous methods. Another benefit is that this approach can process large satellite images with parallel processing, which is important for practical use.
2012年03期 v.17 337-343页 [查看摘要][在线阅读][下载 936K] [下载次数：41 ] |[网刊下载次数：0 ] |[引用频次：6 ] |[阅读次数：0 ] -
Traffic classification is critical to effective network management. However, more and more proprietary, encrypted, and dynamic protocols make traditional traffic classification methods less effective. A Message and Command Correlation (MCC) method was developed to identify interactive protocols (such as P2P file sharing protocols and Instant Messaging (IM) protocols) by session analyses. Unlike traditional packet-based classification approaches, this method exploits application session information by clustering packets into application messages which are used for further classification. The efficacy and accuracy of the MCC method was evaluated with real world traffic,including P2P file sharing protocols Thunder and BitTorrent, and IM protocols QQ and GTalk. The tests show that the false positive rate is less than 3% and the false negative rate is below 8%, and that MCC only needs to check 8.7% of the packets or 0.9% of the traffic. Therefore, this approach has great potential for accurately and quickly discovering new types of interactive application protocols.
2012年03期 v.17 344-353页 [查看摘要][在线阅读][下载 1039K] [下载次数：17 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] Driver drowsiness is one of the major causes of traffic accidents. This paper presents a nonintrusive drowsiness recognition method using eye-tracking and image processing. A robust eye detection algorithm is introduced to address the problems caused by changes in illumination and driver posture. Six measures are calculated with percentage of eyelid closure, maximum closure duration, blink frequency, average opening level of the eyes, opening velocity of the eyes, and closing velocity of the eyes. These measures are combined using Fisher's linear discriminant functions using a stepwise method to reduce the correlations and extract an independent index. Results with six participants in driving simulator experiments demonstrate the feasibility of this video-based drowsiness recognition method that provided 86% accuracy.
2012年03期 v.17 354-362页 [查看摘要][在线阅读][下载 1698K] [下载次数：114 ] |[网刊下载次数：0 ] |[引用频次：8 ] |[阅读次数：0 ] -
<正>Tsinghua Science and Technology (Tsinghua Sci Technol), an academic journal sponsored by Tsinghua University, is published bimonthly. This journal aims at presenting the up-to-date scientific achievements with high creativity and great significance in computer and electronic engineering. Contributions all over the world are welcome.
2012年03期 v.17 363页 [查看摘要][在线阅读][下载 826K] [下载次数：7 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] 下载本期数据