138,866 research outputs found

    A New Method of Calculating the Spin-Wave Velocity cc of Spin-1/2 Antiferromagnets With O(N)O(N) Symmetry in a Monte Carlo Simulation

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    Motivated by the so-called cubical regime in magnon chiral perturbation theory, we propose a new method to calculate the low-energy constant, namely the spin-wave velocity cc of spin-1/2 antiferromagnets with O(N)O(N) symmetry in a Monte Carlo simulation. Specifically we suggest that cc can be determined by c=L/βc = L/\beta when the squares of the spatial and temporal winding numbers are tuned to be the same in the Monte Carlo calculations. Here β\beta and LL are the inverse temperature and the box size used in the simulations when this condition is met. We verify the validity of this idea by simulating the quantum spin-1/2 XY model. The cc obtained by using the squares of winding numbers is given by c=1.1348(5)Jac = 1.1348(5)Ja which is consistent with the known values of cc in the literature. Unlike other conventional approaches, our new idea provides a direct method to measure cc. Further, by simultaneously fitting our Monte Carlo data of susceptibilities χ11\chi_{11} and spin susceptibilities χ\chi to their theoretical predictions from magnon chiral perturbation theory, we find cc is given by c=1.1347(2)Jac = 1.1347(2)Ja which agrees with the one we obtain by the new method of using the squares of winding numbers. The low-energy constants magnetization density M{\cal M} and spin stiffenss ρ\rho of quantum spin-1/2 XY model are determined as well and are given by M=0.43561(1)/a2{\cal M} = 0.43561(1)/a^2 and ρ=0.26974(5)J\rho = 0.26974(5)J, respectively. Thanks to the prediction power of magnon chiral perturbation theory which puts a very restricted constraint among the low-energy constants for the model considered here, the accuracy of M{\cal M} we present in this study is much precise than previous Monte Carlo result.Comment: 5 pages, 7 figure

    Shared-Control for a UAV Operating in the 3D Space

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    This paper presents a shared-control scheme for a UAV moving in a 3D space while its feasible Cartesian position set is defined by a group of linear inequalities. A hysteresis switch is used to combine the human input and the feedback control input based on the definitions of a safe set, a hysteresis set and a “dangerous” set. Case studies given in the paper show the effectiveness of the shared-control algorithm

    Very High Precision Determination of Low-Energy Parameters: The 2-d Heisenberg Quantum Antiferromagnet as a Test Case

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    The 2-d spin 1/2 Heisenberg antiferromagnet with exchange coupling JJ is investigated on a periodic square lattice of spacing aa at very small temperatures using the loop-cluster algorithm. Monte Carlo data for the staggered and uniform susceptibilities are compared with analytic results obtained in the systematic low-energy effective field theory for the staggered magnetization order parameter. The low-energy parameters of the effective theory, i.e.\ the staggered magnetization density Ms=0.30743(1)/a2{\cal M}_s = 0.30743(1)/a^2, the spin stiffness ρs=0.18081(11)J\rho_s = 0.18081(11) J, and the spin wave velocity c=1.6586(3)Jac = 1.6586(3) J a are determined with very high precision. Our study may serve as a test case for the comparison of lattice QCD Monte Carlo data with analytic predictions of the chiral effective theory for pions and nucleons, which is vital for the quantitative understanding of the strong interaction at low energies.Comment: 5 pages, 4 figures, 1 tabl

    The GLASS project: supporting secure shibboleth-based single sign-on to campus resources

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    Higher and Further education institutions in the UK are in the process of migrating their IT infrastructures to exploit Shibboleth technologies for federated access management. Ease of use and secure access are paramount to the successful uptake of these technologies, both from the end user and system administrator perspective. The JISC-funded GLASS project is a one-year project investigating the use of Shibboleth to support single sign-on to a variety of campus resources at the University of Glasgow including browser-based email access; the Moodle online virtual learning environment; the WebSURF online student records facility, and a network filestore browser. This paper describes the implementation issues and experiences gained in rolling out the Shibboleth technologies to support federated access management

    Shot boundary detection in MPEG videos using local and global indicators

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    Shot boundary detection (SBD) plays important roles in many video applications. In this letter, we describe a novel method on SBD operating directly in the compressed domain. First, several local indicators are extracted from MPEG macroblocks, and AdaBoost is employed for feature selection and fusion. The selected features are then used in classifying candidate cuts into five sub-spaces via pre-filtering and rule-based decision making. Following that, global indicators of frame similarity between boundary frames of cut candidates are examined using phase correlation of dc images. Gradual transitions like fade, dissolve, and combined shot cuts are also identified. Experimental results on the test data from TRECVID'07 have demonstrated the effectiveness and robustness of our proposed methodology. * INSPEC o Controlled Indexing decision making , image segmentation , knowledge based systems , video coding o Non Controlled Indexing AdaBoost , MPEG videos , feature selection , global indicator , local indicator , rule-based decision making , shot boundary detection , video segmentation * Author Keywords Decision making , TRECVID , shot boundary detection (SBD) , video segmentation , video signal processing References 1. J. Yuan , H. Wang , L. Xiao , W. Zheng , J. L. F. Lin and B. Zhang "A formal study of shot boundary detection", IEEE Trans. Circuits Syst. Video Technol., vol. 17, pp. 168 2007. Abstract |Full Text: PDF (2789KB) 2. C. Grana and R. Cucchiara "Linear transition detection as a unified shot detection approach", IEEE Trans. Circuits Syst. Video Technol., vol. 17, pp. 483 2007. Abstract |Full Text: PDF (505KB) 3. Q. Urhan , M. K. Gullu and S. Erturk "Modified phase-correlation based robust hard-cut detection with application to archive film", IEEE Trans. Circuits Syst. Video Technol., vol. 16, pp. 753 2006. Abstract |Full Text: PDF (3808KB) 4. C. Cotsaces , N. Nikolaidis and I. Pitas "Video shot detection and condensed representation: A review", Proc. IEEE Signal Mag., vol. 23, pp. 28 2006. 5. National Institute of Standards and Technology (NIST), pp. [online] Available: http://www-nlpir.nist.gov/projects/trecvid/ 6. J. Bescos "Real-time shot change detection over online MPEG-2 video", IEEE Trans. Circuits Syst. Video Technol., vol. 14, pp. 475 2004. Abstract |Full Text: PDF (1056KB) 7. H. Lu and Y. P. Tan "An effective post-refinement method for shot boundary detection", IEEE Trans. Circuits Syst. Video Technol., vol. 15, pp. 1407 2005. Abstract |Full Text: PDF (3128KB) 8. G. Boccignone , A. Chianese , V. Moscato and A. Picariello "Foveated shot detection for video segmentation", IEEE Trans. Circuits Syst. Video Technol., vol. 15, pp. 365 2005. Abstract |Full Text: PDF (2152KB) 9. Z. Cernekova , I. Pitas and C. Nikou "Information theory-based shot cut/fade detection and video summarization", IEEE Trans. Circuits Syst. Video Technol., vol. 16, pp. 82 2006. Abstract |Full Text: PDF (1184KB) 10. L.-Y. Duan , M. Xu , Q. Tian , C.-S. Xu and J. S. Jin "A unified framework for semantic shot classification in sports video", IEEE Trans. Multimedia, vol. 7, pp. 1066 2005. Abstract |Full Text: PDF (2872KB) 11. H. Fang , J. M. Jiang and Y. Feng "A fuzzy logic approach for detection of video shot boundaries", Pattern Recogn., vol. 39, pp. 2092 2006. [CrossRef] 12. R. A. Joyce and B. Liu "Temporal segmentation of video using frame and histogram space", IEEE Trans. Multimedia, vol. 8, pp. 130 2006. Abstract |Full Text: PDF (864KB) 13. A. Hanjalic "Shot boundary detection: Unraveled and resolved", IEEE Trans. Circuits Syst. Video Technol., vol. 12, pp. 90 2002. Abstract |Full Text: PDF (289KB) 14. S.-C. Pei and Y.-Z. Chou "Efficient MPEG compressed video analysis using macroblock type information", IEEE Trans. Multimedia, vol. 1, pp. 321 1999. Abstract |Full Text: PDF (612KB) 15. C.-L. Huang and B.-Y. Liao "A robust scene-change detection method for video segmentation", IEEE Trans. Circuits Syst. Video Technol., vol. 11, pp. 1281 2001. Abstract |Full Text: PDF (241KB) 16. Y. Freund and R. E. Schapire "A decision-theoretic generalization of online learning and an application to boosting", J. Comput. Syst. Sci., vol. 55, pp. 119 1997. [CrossRef] On this page * Abstract * Index Terms * References Brought to you by STRATHCLYDE UNIVERSITY LIBRARY * Your institute subscribes to: * IEEE-Wiley eBooks Library , IEEE/IET Electronic Library (IEL) * What can I access? Terms of Us