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Monitoring nearest neighbor queries with cache strategies
PAN Peng, LU Yan-sheng
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2007, 8(4): 529-537.
https://doi.org/10.1631/jzus.2007.A0529
The problem of continuously monitoring multiple K-nearest neighbor (K-NN) queries with dynamic object and query dataset is valuable for many location-based applications. A practical method is to partition the data space into grid cells, with both object and query table being indexed by this grid structure, while solving the problem by periodically joining cells of objects with queries having their influence regions intersecting the cells. In the worst case, all cells of objects will be accessed once. Object and query cache strategies are proposed to further reduce the I/O cost. With object cache strategy, queries remaining static in current processing cycle seldom need I/O cost, they can be returned quickly. The main I/O cost comes from moving queries, the query cache strategy is used to restrict their search-regions, which uses current results of queries in the main memory buffer. The queries can share not only the accessing of object pages, but also their influence regions. Theoretical analysis of the expected I/O cost is presented, with the I/O cost being about 40% that of the SEA-CNN method in the experiment results.
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A level set based segmentation approach for point-sampled surfaces
MIAO Yong-wei, FENG Jie-qing, ZHENG Guo-xian, PENG Qun-sheng
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2007, 8(4): 575-585.
https://doi.org/10.1631/jzus.2007.A0575
Segmenting a complex 3D surface model into some visually meaningful sub-parts is one of the fundamental problems in digital geometry processing. In this paper, a novel segmentation approach of point-sampled surfaces is proposed, which is based on the level set evolution scheme. To segment the model so as to align the patch boundaries with high curvature zones, the driven speed function for the zero level set inside narrow band is defined by the extended curvature field, which approaches zero speed as the propagating front approaches high curvature zone. The effectiveness of the proposed approach is demonstrated by our experimental results. Furthermore, two applications of model segmentation are illustrated, such as piecewise parameterization and local editing for point-sampled geometry.
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Adaptive foreground and shadow segmentation using hidden conditional random fields
CHU Yi-ping, YE Xiu-zi, QIAN Jiang, ZHANG Yin, ZHANG San-yuan
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2007, 8(4): 586-592.
https://doi.org/10.1631/jzus.2007.A0586
Video object segmentation is important for video surveillance, object tracking, video object recognition and video editing. An adaptive video segmentation algorithm based on hidden conditional random fields (HCRFs) is proposed, which models spatio-temporal constraints of video sequence. In order to improve the segmentation quality, the weights of spatio-temporal constraints are adaptively updated by on-line learning for HCRFs. Shadows are the factors affecting segmentation quality. To separate foreground objects from the shadows they cast, linear transform for Gaussian distribution of the background is adopted to model the shadow. The experimental results demonstrated that the error ratio of our algorithm is reduced by 23% and 19% respectively, compared with the Gaussian mixture model (GMM) and spatio-temporal Markov random fields (MRFs).
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SimWall: a practical user-friendly stereo tiled display wall system
XIE Li-jun, ZHENG Yao, YANG Ting-jun, GAO Wen-xuan, PAN Ning-he
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2007, 8(4): 596-604.
https://doi.org/10.1631/jzus.2007.A0596
SimWall is a user-friendly, stereo tiled display wall system composed of 18 commodity projectors operated by a Linux graphics cluster. Collaborating together, these projectors work as a single logical display capable of giving a high-resolution show, large-scale, and passive stereo scene. In order to avoid tedious system setup and maintenance, software-based automatic geometry and photometric calibration are used. The software calibration is integrated to the system seamlessly by an on-card transform method and is transparent to users. To end-users, SimWall works just as a common PC, but provides super computing, rendering and displaying ability. In addition, SimWall has stereoscopic function that gives users a semi-immersive experience in polarized passive way. This paper presents system architecture, implementation, and other technical issues such as hardware constraints, projectors alignment, geometry and photometric calibration, implementation of passive stereo, and development of overall software environment.
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A P2P streaming service architecture with distributed caching
GUO Pan-hong, YANG Yang, LI Xin-you
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2007, 8(4): 605-614.
https://doi.org/10.1631/jzus.2007.A0605
Multimedia streaming served through peer-to-peer (P2P) networks is booming nowadays. However, the end-to-end streaming quality is generally unstable due to the variability of the state of serve-peers. On the other hand, proxy caching is a bandwidth-efficient scheme for streaming over the Internet, whereas it is a substantially expensive method needing dedicated powerful proxy servers. In this paper, we present a P2P cooperative streaming architecture combined with the advantages of both P2P networks and multimedia proxy caching techniques to improve the streaming quality of participating clients. In this framework, a client will simultaneously retrieve contents from the server and other peers that have viewed and cached the same title before. In the meantime, the client will also selectively cache the aggregated video content so as to serve still future clients. The associate protocol to facilitate the multi-path streaming and a distributed utility-based partial caching scheme are detailedly discussed. We demonstrate the effectiveness of this proposed architecture through extensive simulation experiments on large, Internet-like topologies.
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A vague-set-based fuzzy multi-objective decision making model for bidding purchase
WANG Zhou-jing, QIAN Edward Y.
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2007, 8(4): 644-650.
https://doi.org/10.1631/jzus.2007.A0644
A vague-set-based fuzzy multi-objective decision making model is developed for evaluating bidding plans in a bidding purchase process. A group of decision-makers (DMs) first independently assess bidding plans according to their experience and preferences, and these assessments may be expressed as linguistic terms, which are then converted to fuzzy numbers. The resulting decision matrices are then transformed to objective membership grade matrices. The lower bound of satisfaction and upper bound of dissatisfaction are used to determine each bidding plan’s supporting, opposing, and neutral objective sets, which together determine the vague value of a bidding plan. Finally, a score function is employed to rank all bidding plans. A new score function based on vague sets is introduced in the model and a novel method is presented for calculating the lower bound of satisfaction and upper bound of dissatisfaction. In a vague-set-based fuzzy multi-objective decision making model, different valuations for upper and lower bounds of satisfaction usually lead to distinct ranking results. Therefore, it is crucial to effectively contain DMs’ arbitrariness and subjectivity when these values are determined.
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Precise asymptotics in the law of the logarithm for random fields in Hilbert space
FU Ke-ang, ZHANG Li-xin
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2007, 8(4): 651-659.
https://doi.org/10.1631/jzus.2007.A0651
Consider the positive d-dimensional lattice Z+d (d≥2) with partial ordering ≤, let {XK; K∈Z+d be i.i.d. random variables taking values in a real separable Hilbert space (H, ||∙||) with mean zero and covariance operator ∑, and set partial sums SN =∑K≤NXK, N∈Z+d. Under some moment conditions, we obtain the precise asymptotics of a kind of weighted infinite series for partial sums SN as ε↘0 by using the truncation and approximation methods. The results are related to the convergence rates of the law of the logarithm in Hilbert space, and they also extend the results of (Gut and Spǎtaru, 2003).
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Conservation laws for energy and momentum in curved spaces
LÓPEZ-BONILLA J., MORALES J., OVANDO G.
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2007, 8(4): 665-668.
https://doi.org/10.1631/jzus.2007.A0665
In arbitrary Riemannian 4-spaces, continuity equations are constructed which could be interpreted as conservation laws for the energy and momentum of the gravitational field. Special attention is given to general relativity to obtain, of natural manner, the pseudotensors of Einstein, Landau-Lifshitz, Möller, Goldberg and Stachel, and also the conservation equations of Komar, Trautman, DuPlessis and Moss.
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New solutions of shear waves in piezoelectric cubic crystals
ZAKHARENKO A.A.
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2007, 8(4): 669-674.
https://doi.org/10.1631/jzus.2007.A0669
Acoustic wave propagation in piezoelectric crystals of classes 4̄3m and 23 is studied. The crystals Tl3VS4 and Tl3TaSe4 (4̄3m) of the Chalcogenide family and the crystal Bi12TiO20 (23) possess strong piezoelectric effect. Because the surface Bleustein-Gulyaev waves cannot exist in piezoelectric cubic crystals, it was concluded that new solutions for shear-horizontal surface acoustic waves (SH-SAWs) are found in the monocrystals using different electrical boundary conditions such as electrically “short” and “open” free-surfaces for the unique [101] direction of wave propagation. For the crystal Tl3TaSe4 with coefficient of electromechanical coupling (CEMC) Ke2=e2/(C×g)~1/3, the phase velocity Vph for the new SH-SAWs can be calculated with the following formula: Vph=(Va+Vt)/2, where Vt is the speed of bulk SH-wave, Vt=Vt4(1+Ke2)1/2, Va=aKVt4, aK=2[Ke(1+Ke2)1/2−Ke2]1/2, and Vt4=(C44/ρ)1/2. It was found that the CEMC K2 evaluation for Tl3TaSe4 gave the value of K2=2(Vf–Vm)/Vf~0.047 (~4.7%), where Vf~848 m/s and Vm~828 m/s are the new-SAW velocities for the free and metallized surfaces, respectively. This high value of K2(Tl3TaSe4) is significantly greater than K2(Tl3VS4)~3% and about five times that of K2(Bi12TiO20).
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23 articles
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