- 曹毅宁;Hao Buchta;Erwin Patzak;郑小平;张汉一;
The benefit of a two-layer hybrid IP/MPLS (multi-protocol label switching) over a wavelength division multiplexing network has been analyzed considering both the cost and different grooming policies. A detailed cost and performance analysis of hybrid networks is done for three different grooming policies. The hybrid network cost is compared with that of an opaque network for equal traffic demand and equal blocking probability of dynamic requests of label switched paths. An algorithm is given to design optimum hybrid nodes for different grooming policies to provide the desired blocking probability for a given number of dynamic connection requests. The results show that all three applied grooming policies (IP layer first, optical layer first, and one hop first) result in lower costs of the hybrid network architecture than for the opaque network. In addition, an adaptive one hop first method is given to improve the best of the applied grooming policies, which limits grooming in heavily loaded hybrid nodes to achieve load balancing. The simulation results show that the new policy significantly reduces the overall blocking probability.
2009年06期 v.14 677-684页 [查看摘要][在线阅读][下载 632K] [下载次数：33 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：116 ] <正>Berkeley Lab and Tsinghua University forged ties on Aug.12,2009 to promote the development and implementation of building energy efficiency,a move intended to reduce energy consumption and greenhouse gas emissions in the U.S and China.
2009年06期 v.14 684页 [查看摘要][在线阅读][下载 213K] [下载次数：45 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：26 ] - 王丽婷;丁晓青;方驰;
In recent years,face recognition has often been proposed for personal identification.However,there are many difficulties with face recognition systems.For example,an imposter could login the face recognition system by stealing the facial photograph of a person registered on the facial recognition system.The security of the face recognition system requires a live detection system to prevent system login using photographs of a human face.This paper describes an effective,efficient face live detection method which uses physiological motion detected by estimating the eye blinks from a captured video sequence and an eye contour extraction algorithm.This technique uses the conventional active shape model with a random forest classifier trained to recognize the local appearance around each landmark.This local match provides more robustness for optimizing the fitting procedure.Tests show that this face live detection approach successfully discriminates a live human face from a photograph of the registered person's face to increase the face recognition system reliability.
2009年06期 v.14 685-690页 [查看摘要][在线阅读][下载 1037K] [下载次数：86 ] |[网刊下载次数：0 ] |[引用频次：5 ] |[阅读次数：80 ] - 张阳;崔慧娟;唐昆;
Packet losses usually result in frame losses in low bit rate video streaming over error prone net-works.The whole frame error concealment(EC) algorithm is then necessary for the decoder to improve the video quality.A refined bidirectional motion vector extrapolation was developed to improve the motion vector estimation precision by alleviating the effect of overlapped and hole regions with an adaptive overlapped block motion compensation to reduce block artifacts.A prescription-based framework was then developed to improve the error concealment at the encoder side.Simulations show that the EC algorithm at the decoder side outperforms the existing methods by 2-8 dB.Moreover,the prescription-based framework at the encoder side provides further peak signal to noise ratio improvement.
2009年06期 v.14 691-697页 [查看摘要][在线阅读][下载 795K] [下载次数：64 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：31 ] - 孔耀晖;刘爱荣;杨华中;
A complementary metal oxide semiconductor(CMOS) transconductor based on a high performance unity-gain buffer driving the degeneration resistor was used to obtain a highly linear voltage-to-current conversion with considerable reduction of the supply voltage.Simulations show that the transconductor using an 0.18-μm standard CMOS process with a 1.2-V supply voltage has less than -80 dB total harmonic distortion(THD) for a 1-MHz 0.4-Vp-p differential input signal.The third-order intermodulation is less than -63 dB for 0.25 Vp-p differential inputs at 1 MHz.The DC power consumption in the transconductor core is 240 μW.This topology is a feasible solution for low voltage and low power applications.
2009年06期 v.14 698-702页 [查看摘要][在线阅读][下载 522K] [下载次数：54 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：114 ] - 郑有志;覃征;
Objective evaluations of fused images are important in comparing the performance of different image fusion algorithms.This paper describes a structural similarity metric that does not use a reference image for image fusion evaluations.The metric is based on the universal image quality index and addresses not only the similarities between the input images and the fused image,but also the similarities among the input images.The evaluation process distinguishes between complementary information and redundant information using similarities among the input images.The metric uses the information classification to estimate how much structural similarity is preserved in the fused image.Tests demonstrate that the metric correlates well with subjective evaluations of the fused images.
2009年06期 v.14 703-709页 [查看摘要][在线阅读][下载 908K] [下载次数：118 ] |[网刊下载次数：0 ] |[引用频次：20 ] |[阅读次数：21 ] - 白铂;曹志刚;陈巍;易芝玲;
Wireless communication and broadcasting convergence networks provide a potential solution to greater traffic throughput in the future.In this paper,the throughput of a convergence network is analyzed based on the standardization project for specific requirements for local and metropolitan area networks in China,referred to as broadband wireless multimedia systems.The convergence network is modeled as a combination of a broadcasting channel and a multi-access channel with interference.The throughput is then given as a function of the time resource allocation by calculating the channel capacity with interference.The maximum throughput and the optimal time resource allocation are then determined for a given delay constraint and traffic requirements.The results give guidelines for time resource allocation and system design for convergence networks.
2009年06期 v.14 710-717页 [查看摘要][在线阅读][下载 616K] [下载次数：100 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：28 ] - 常冬霞;张贤达;
A genetic clustering algorithm was developed based on dynamic niching with data attraction.The algorithm uses the concept of Coulomb attraction to model the attraction between data points.Then,the niches with data attraction are dynamically identified in each generation to automatically evolve the optimal number of clusters as well as the cluster centers of the data set without using cluster validity functions or a variance-covariance matrix.Therefore,this clustering scheme does not need to prespecify the number of clusters as in existing methods.Several data sets with widely varying characteristics are used to demonstrate the superiority of this algorithm.Experimental results show that the performance of this clustering algorithm is high,effective,and flexible.
2009年06期 v.14 718-724页 [查看摘要][在线阅读][下载 508K] [下载次数：35 ] |[网刊下载次数：0 ] |[引用频次：8 ] |[阅读次数：38 ] - 苏泳涛;张贤达;
In multi-user multiple-input single-output orthogonal frequency-division multiplexing(MISO-OFDM) downlinks with limited feedback,both linear precoders(LP) and Tomlinson-Harashima precoders(THP) experience performance degradation due to inaccurate channel state information at the transmitter(CSIT).This analysis treats the downlink channels as random quantities and exploits their second order statistics in robust precoding schemes to correct the errors introduced in the feedback procedure.The time-domain channel vectors are found to reduce the feedback overhead more than the frequency-domain vectors.A compression and restoration method and a codebook design are also given to obtain compact feedback quantities.Simulations show that the robust LP and THP are superior to the previous methods with tradeoffs possible between performance and feedback overhead.
2009年06期 v.14 725-731页 [查看摘要][在线阅读][下载 2708K] [下载次数：44 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：43 ] <正>The President of the California Institute of Technology Professor Jean-Lou Chameau and the Chancellor of the University of California at Santa Barbara Professor Henry Yang both delivered speeches in the Tsinghua Global Vision Lecture Series
2009年06期 v.14 731页 [查看摘要][在线阅读][下载 214K] [下载次数：15 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：25 ] - 李志恒;尹胜超;张毅;李力;
The four-parameter lag-lead compensator design has received much attention in the last two decades.However,most approaches have been either trial-and-error or only for special cases.This paper presents a non-trial-and-error design method for four-parameter lag-lead compensators.Here,the compensator design problem is formulated into a polynomial function optimization problem and solved by using the recently developed sum-of-squares(SOS) techniques.This result not only provides a useful design method but also shows the power of the SOS techniques.
2009年06期 v.14 732-734页 [查看摘要][在线阅读][下载 271K] [下载次数：76 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：31 ] - 姜敏;张曾科;李向旭;李慧;
In most probabilistic teleportation schemes,if the teleportation fails,the unknown quantum state will be completely ruined.In addition,the frequently proposed high-dimensional unitary operations are very difficult to realize experimentally.To maintain the integrity of the unknown quantum state to be teleported,this analysis does not focus attention on the original multi-particle state but seeks to construct a faithful channel with an ancillary particle and a unified high-dimensional unitary operation.The result shows that if the construction of the multi-group Einstein-Podolsky-Rosen pair succeeds,the original multi-particle state can be used to deterministically teleport the unknown quantum state of the entangled multiple particles which avoids undermining the integrity of the unknown state brought about by failure.This unified high-dimensional operation is appealing due to the obvious experimental convenience.
2009年06期 v.14 735-738页 [查看摘要][在线阅读][下载 333K] [下载次数：25 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：99 ] - 潘鸿飞;梁栋;唐俊;王年;李薇;
An important aim in pattern recognition is to cluster the given shapes.This paper presents a shape recognition and retrieval algorithm.The algorithm first extracts the skeletal features using the medial axis transform.Then,the features are transformed into a string of symbols with the similarity among those symbols computed based on the edit distance.Finally,the shapes are identified using dynamic programming.Two public datasets are analyzed to demonstrate that the present approach is better than previous approaches.
2009年06期 v.14 739-745页 [查看摘要][在线阅读][下载 1148K] [下载次数：54 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：29 ] - 方东平;席海峰;王晓明;张传敏;赵挺生;
High-rise reinforced concrete buildings are in great demand in developing countries with rapid urbanization.Construction engineers are facing more and more safety control challenges.One major issue is the understanding of the load distributions,especially the maximum slab load,of structures under construction,which is time dependent.Previous methods were mainly targeted to specific examples,providing specific solutions without addressing the fundamental issues of finding general solutions for load distributions in reinforced concrete buildings with different geometrical and material characteristics during construction.The concept of a structural characteristic parameter is used here to parameterize the main geometrical and material characteristics of concrete structures for generalized assessments of load distributions during construction.The maximum slab load for 20 different construction shoring/reshoring schemes is presented.The results indicate that the traditional simplified method may underestimate or overestimate the maximum slab load,depending mainly on the shoring/reshoring schemes.The structural characteristic parameter approach was specifically developed to assist construction engineers to estimate load distributions to assure safe construction procedures.
2009年06期 v.14 746-755页 [查看摘要][在线阅读][下载 699K] [下载次数：225 ] |[网刊下载次数：0 ] |[引用频次：3 ] |[阅读次数：23 ] - 方东平;席海峰;王晓明;张传敏;
Site measurements have shown that slab loads re-distribute,between the slabs during the concrete curing,while the external loadings and structural geometry remain the same.Some have assumed that this is caused by concrete shrinkage and creep,but there have been no studies on how these factors exactly influence the load distributions and to what degree these influences exist.This paper analyzes the influences of concrete shrinkage,creep,and temperature on the load re-distributions among slabs.Although these factors may all lead to load re-distribution,the results show that the influence of concrete shrinkage can be neglected.Simulations indicate that shrinkage only reduces slab loads by a maximum of 1.1%.Creep,however,may reduce the maximum slab load by from 3% to 16% for common construction schemes.More importantly,temperature variations between day and night can cause load fluctuation as large as 31.6%.This analysis can,therefore,assist site engineers to more accurately estimate slab loads for construction planning.
2009年06期 v.14 756-764页 [查看摘要][在线阅读][下载 686K] [下载次数：191 ] |[网刊下载次数：0 ] |[引用频次：3 ] |[阅读次数：25 ] - 程琳;许项东;邱松林;
A set of constrained Newton methods were developed for static traffic assignment problems.The Newton formula uses the gradient of the objective function to determine an improved feasible direction scaled by the second-order derivatives of the objective function.The column generation produces the active paths necessary for each origin-destination pair.These methods then select an optimal step size or make an orthogonal projection to achieve fast,accurate convergence.These Newton methods based on the constrained Newton formula utilize path information to explicitly implement Wardrop's principle in the transport network modelling and complement the traffic assignment algorithms.Numerical examples are presented to compare the performance with all possible Newton methods.The computational results show that the optimal-step Newton methods have much better convergence than the fixed-step ones,while the Newton method with the unit step size is not always efficient for traffic assignment problems.Furthermore,the optimal-step Newton methods are relatively robust for all three of the tested benchmark networks of traffic assignment problems.
2009年06期 v.14 765-775页 [查看摘要][在线阅读][下载 580K] [下载次数：116 ] |[网刊下载次数：0 ] |[引用频次：5 ] |[阅读次数：27 ] -
<正>Tsinghua University's School of Economics and Management (SEM) announced the appointment on August 18,2009 of former Senior Associate Dean of the Harvard Business School Professor F. Warren McFarlan as Co-Director of SEM's
2009年06期 v.14 775页 [查看摘要][在线阅读][下载 234K] [下载次数：38 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：20 ] - 金盛;王殿海;王立明;
Off-ramp area congestion and off-ramp queue spill over are wide-spread reasons for expressway traffic jams in China.A control strategy was developed to reduce the number of collisions between expressway and surface street vehicles and to reduce spill over by controlling the surface street vehicles to improve the traffic conditions near expressway off-ramps.This control algorithm monitors the traffic conditions at the off-ramp using occupancy rates and a performance index for the surface street vehicles,and then optimizes the control signal split and cycle length for the surface street vehicles assuming that the off-ramp queue is shorter than the minimum allowable length.Simulations indicate improvements in the traffic flow with the average vehicle travel time nearly 10% less and the off-ramp queue reduced significantly.
2009年06期 v.14 776-781页 [查看摘要][在线阅读][下载 618K] [下载次数：80 ] |[网刊下载次数：0 ] |[引用频次：5 ] |[阅读次数：27 ] - 龙瀛;毛其智;党安荣;
Urban growth analysis and simulation have been recently conducted by cellular automata(CA) models based on self-organizing theory which differs from system dynamics models.This paper describes the Beijing urban development model(BUDEM) which adopts the CA approach to support urban planning and policy evaluation.BUDEM,as a spatio-temporal dynamic model for simulating urban growth in the Beijing metropolitan area,is based on the urban growth theory and integrates logistic regression and MonoLoop to obtain the weights for the transition rule with multi-criteria evaluation configuration.Local sensitivity analysis for all the parameters of BUDEM is also carried out to assess the model's performances.The model is used to identify urban growth mechanisms in the various historical phases since 1986,to retrieve urban growth policies needed to implement the desired(planned) urban form in 2020,and to simulate urban growth scenarios until 2049 based on the urban form and parameter set in 2020.The model has been proved to be capable of analyzing historical urban growth mechanisms and predicting future urban growth for metropolitan areas in China.
2009年06期 v.14 782-794页 [查看摘要][在线阅读][下载 728K] [下载次数：635 ] |[网刊下载次数：0 ] |[引用频次：29 ] |[阅读次数：294 ] <正>~~
2009年06期 v.14 795-799页 [查看摘要][在线阅读][下载 220K] [下载次数：17 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：16 ]