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91.
以云南省滇中引水工程某段软岩引水隧洞建立实体模型,应用三维显式有限差分法程序FLAC3D对其施工开挖过程进行三维数值模拟。计算结果表明,软岩隧洞受到开挖面的空间约束效应,围岩应力逐步释放,相应围岩位移也逐渐增加;在横断面上,拱顶围岩沉降位移沿竖直径向的空间效应主要影响范围在3倍洞径(3D)左右,而拱腰围岩水平位移和拱底隆起位移在1.5D左右;掌子面向前推进过程中,掌子面的空间效应逐渐消失,拱顶、拱底位移在施工开挖面后方约2.5D~3D处趋于稳定,拱腰位移在约2D左右趋于稳定,围岩变形收敛:软岩隧洞需要及时施作初期支护,以提高围岩自承能力,限制位移的增长速度。 相似文献
92.
Juan Pedro Muñoz-Gea Josemaria Malgosa-Sanahuja Pilar Manzanares-Lopez 《Peer-to-Peer Networking and Applications》2013,6(3):340-360
Recently, a new peer-assisted architecture to build content delivery systems has been presented. This architecture is based on the use of the storage capacity of end-users’ set-top boxes (STBs), connected in a peer-to-peer (P2P) manner in order to help the content servers in the delivery process. In these systems, the contents are usually split into a set of smaller pieces, called sub-streams, which are randomly injected at the STBs. The present paper is focused on Video on Demand (VoD) streaming and it is assumed that the STB-based content delivery system is deployed over the global Internet, where the clients are distributed over different ISP networks. In this scenario, three different strategies are studied for increasing the percentage of data uploaded by peers, in order to offload the content servers as much as possible. First of all, a new mechanism is presented which determines which sub-stream has to be placed at which STB by a Non-Linear Programming (NLP) formulation. A different strategy for reducing the content server load is to take advantage of the available bandwidth in the different ISP networks. In this sense, two new mechanisms for forwarding the VoD requests to different ISP networks are presented. Finally, the present paper also shows that in some situations the available uplink bandwidth is associated with STBs that do not have the required sub-streams. Regarding this concern, a new mechanism has been designed that dynamically re-allocates some streams, which are being transmitted from specific STBs, to different STBs, in order to find the necessary resources to start new streaming sessions. 相似文献
93.
Muñoz CM 《Journal of microscopy》2011,243(3):257-266
For the validation of a cleaning method in conservation, the examination of the object's surface after the cleaning and the quantification of the cleaning efficiency are significant steps. In this study, several cleaning solutions were tested on a plasticized poly(vinyl chloride) object whose surface was characterized before and after cleaning by optical microscopy and noncontact profilometry. In addition, different methods to quantify the cleaning efficiency based on spectrocolorimetric and microscopic techniques were provided. The results showed that noncontact profilometry supported by optical microscopy and spectrocolorimetry was very useful for the characterization of the plasticized poly(vinyl chloride) surface before and after the cleaning and also for the determination of the cleaners' efficiency. 相似文献
94.
The pixel labeling problems in computer vision are often formulated as energy minimization tasks. Algorithms such as graph cuts and belief propagation are prominent; however, they are only applicable for specific energy forms. For general optimization, Markov Chain Monte Carlo (MCMC) based simulated annealing can estimate the minima states very slowly.This paper presents a sampling paradigm for faster optimization. First, in contrast to previous MCMCs, the role of detailed balance constraint is eliminated. The reversible Markov chain jumps are essential for sampling an arbitrary posterior distribution, but they are not essential for optimization tasks. This allows a computationally simple window cluster sample. Second, the proposal states are generated from combined sets of local minima which achieve a substantial increase in speed compared to uniformly labeled cluster proposals. Third, under the coarse-to-fine strategy, the maximum window size variable is incorporated along with the temperature variable during simulated annealing. The proposed window annealing is experimentally shown to be many times faster and capable of finding lower energy compared to the previous Gibbs and Swendsen-Wang cut (SW-cut) sampler. In addition, the proposed method is compared with other deterministic algorithms like graph cut, belief propagation, and spectral method in their own specific energy forms. Window annealing displays competitive performance in all domains. 相似文献
95.
Carlos Gañán Jose L. Muñoz Oscar Esparza Jorge Mata-Díaz Juan Hernández-Serrano Juanjo Alins 《Journal of Network and Computer Applications》2013,36(5):1337-1351
Vehicular Ad Hoc Networks (VANETs) require mechanisms to authenticate messages, identify valid vehicles, and remove misbehaving vehicles. A public key infrastructure (PKI) can be used to provide these functionalities using digital certificates. However, if a vehicle is no longer trusted, its certificates have to be revoked and this status information has to be made available to other vehicles as soon as possible. In this paper, we propose a collaborative certificate status checking mechanism called COACH to efficiently distribute certificate revocation information in VANETs. In COACH, we embed a hash tree in each standard Certificate Revocation List (CRL). This dual structure is called extended-CRL. A node possessing an extended-CRL can respond to certificate status requests without having to send the complete CRL. Instead, the node can send a short response (less than 1 kB) that fits in a single UDP message. Obviously, the substructures included in the short responses are authenticated. This means that any node possessing an extended-CRL can produce short responses that can be authenticated (including Road Side Units or intermediate vehicles). We also propose an extension to the COACH mechanism called EvCOACH that is more efficient than COACH in scenarios with relatively low revocation rates per CRL validity period. To build EvCOACH, we embed an additional hash chain in the extended-CRL. Finally, by conducting a detailed performance evaluation, COACH and EvCOACH are proved to be reliable, efficient, and scalable. 相似文献
96.
Shams Qazi Raad Raad Yi Mu Willy Susilo 《Journal of Network and Computer Applications》2013,36(2):582-592
A wormhole attack is one of the hardest problems to detect whereas it can be easily implanted in any type of wireless ad hoc network. A wormhole attack can easily be launched by the attacker without having knowledge of the network or compromising any legitimate nodes. Most existing solutions either require special hardware devices or make strong assumptions in order to detect wormhole attacks which limit the usability of these solutions. In this paper, we present a security enhancement to dynamic source routing (DSR) protocol against wormhole attacks for ad hoc networks which relies on calculation of round trip time (RTT). Our protocol secures DSR against a wormhole attack in ad hoc networks for multirate transmissions. We also consider the processing and queuing delays of each participating node in the calculation of RTTs between neighbors which to date has not been addressed in the existing literature. This work provides two test cases that show that not taking multirate transmission into consideration results in miss identifying a wormhole attack. 相似文献
97.
Esteban J. Palomo Enrique Domínguez Rafael M. Luque-Baena José Muñoz 《Neural Processing Letters》2013,37(1):69-87
Both image compression based on color quantization and image segmentation are two typical tasks in the field of image processing. Several techniques based on splitting algorithms or cluster analyses have been proposed in the literature. Self-organizing maps have been also applied to these problems, although with some limitations due to the fixed network architecture and the lack of representation in hierarchical relations among data. In this paper, both problems are addressed using growing hierarchical self-organizing models. An advantage of these models is due to the hierarchical architecture, which is more flexible in the adaptation process to input data, reflecting inherent hierarchical relations among data. Comparative results are provided for image compression and image segmentation. Experimental results show that the proposed approach is promising for image processing, and the powerful of the hierarchical information provided by the proposed model. 相似文献
98.
软件体系结构是软件工程中的一个新兴的领域,它与软件工程技术的发展有着相当密切的关系,本文从软件工程技术的发展谈到了软件体系构建的必然性,并且在文章的最后对软件工程的发展现状和未来前景做出了总结. 相似文献
99.
100.
本文对经典SUSAN算法进行了改进,提出了WSUSAN,即加权SUSAN的概念,与经典算法相比,WSUSAN角点的检出精度大幅提高,而运算复杂度和运算量仍保持在原数量级。作为WSUSAN的应用,本文进行了基于WSUSAN角点的遥感图像矢量化的研究,主要研究的内容包括过检出角点的筛选、角点排序和矢量化等。经过仿真测试,证明该算法有很好的鲁棒性。 相似文献