共查询到20条相似文献，搜索用时 375 毫秒
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Traditional 802.11 power saving mechanism （PSM） treats multicast and broadcast traffic equally, and suffers significant performance degradation with multicast background traffic. This paper proposes an enhanced PSM that effectively differentiates multicast streams. It re-arranges the virtual bitmap of the traffic indication map （TIM） to carry traffic status for multicast groups and introduces a concept of sequential transmission of multi-addressed data to facilitate differentiation among multicast groups. Our analysis shows that the enhanced PSM can effectively save power in mixed traffic environments. 相似文献
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To ensure that limited resources are allocated more effectively to reduce marine risks, formal safety assessment (FSA), a proactive method, is introduced in planning a vessel traffic system (VTS). Based on the data of Wuhan port, some new solutions based on risk-indices are put forward. The weighted number of traffic accidents is predicted after the future weighted vessel traffic volume is estimated by analyzing the trend of trade development. To analyze risk acceptability, the as-low-as-reasonably-practicable (ALARP) matrix is transformed into a new model containing two parameters: the future weighted vessel traffic volume and the future weighted number of traffic accidents. The new risk control options (RCOs)can be identified by a revised Domino model with several feedback loops from all system levels to close a limited window of accident opportunity. The results indicate that the four most beneficial RCOs are a wider sub-area 1 channel, a VTS bridges area, a dredging sub-area 2 main route, and a VTS QSX anchorage to the 3rd bridge. The FSA is a method that is effective in evaluating the rationality, necessity and cost-effectiveness of VTS projects. 相似文献
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Traffic monitoring is of major importance for enforcing traffic management policies. To accomplish this task, the detection of vehicle can be achieved by exploiting image analysis techniques. In this paper, a solution is presented to obtain various traffic parameters through vehicular video detection system( VVDS). VVDS exploits the algorithm based on virtual loops to detect moving vehicle in real time. This algorithm uses the background differencing method, and vehicles can be detected through luminance difference of pixels between background image and current image. Furthermore a novel technology named as spatio-temporal image sequences analysis is applied to background differencing to improve detection accuracy. Then a hardware implementation of a digital signal processing (DSP) based board is described in detail and the board can simultaneously process fourchannel video from different cameras. The benefit of usage of DSP is that images of a roadway can be processed at frame rate due to DSP‘s high performance. In the end, VVDS is tested on realworld scenes and experiment results show that the system is both fast and robust to the surveillance of transportation. 相似文献
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Randomness plays a major role in the interpretation of many interesting traffic flow phenomena, such as hysteresis, capacity drop and spontaneous breakdown. The analysis of the uncertainty and reliability of traffic systems is directly associated with their random characteristics. Therefore, it is beneficial to understand the distributional properties of traffic variables. This paper focuses on the dependence relation between traffic flow density and traffic speed, which constitute the fundamental diagram （FD）. The traditional model of the FD is obtained essentially through curve fitting. We use the copula function as the basic toolkit and provide a novel approach for identifying the distributional patterns associated with the FD. In particular, we construct a rule-of-thumb nonparametric copula function, which in general avoids the mis-specification risk of parametric approaches and is more efficient in practice. By applying our construction to loop detector data on a freeway, we identify the dependence patterns existing in traffic data. We find that similar modes exist among traffic states of low, moderate or high traffic densities. Our findings also suggest that highway traffic speed and traffic flow density as a bivariate distribution is skewed and highly heterogeneous. 相似文献
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冯苏苇 《上海大学学报(英文版)》2005,9(1):1-5
Based on two main hypotheses of traffic economical equilibrium and the relationship between traffic density and the demand, an evolution equation of traffic cost was proposed to describe the change of cost under decreasing toll. Economical explanation of the model and a numerical case were given to demonstrate the constraint between the marginal traffic demand and the flow velocity. 相似文献
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In this paper, we propose a simply TCP-friendly source adaptation framework to provide a proportional bandwidth sharing service. Our scheme is based on the framework of Monotonic Response Function (MRF), can be used to bound the sending rate of a source within a predefined interval and provide very smooth traffic, and is suitable for multimedia applications over the Internet. As our scheme is also very simple and TCP-friendly, it is easy to be deployed over the current Internet. We verify our scheme with experimental studies. 相似文献
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A DYNAMIC MODEL OF MULTIPLE PATH TRAFFIC ASSIGNMENT 总被引：1，自引：0，他引：1
A “Random Shortest Path”traffic assignment model and its algorithm arepresented by simulating the trip-makers'route-choice characters,and the dynamic meth-od is introduced in the assignment model.It is a ideal multiple path assignment modelwhich can be carried out by the dynamic method and static method,can better reflect boththe shortest path factor and the random factor in the route-choice,and is of reasonableassignment volumes.Besides,both dynamic and static softwares particularly suited to thetraffic assignment of large and medium-sized transportation networks arc developed. 相似文献
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《英语辅导》2003,(20)
For many people in the U.K. owning a car is as essential as owning a house. Indeed many households now have at least two cars. Add to this the fact that most haulage in the U.K. is carried on the roads and you can begin to imagine the volume of traffic and the problems which this causes, not only in the big cities but 相似文献
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A network model is proposed to support service differentiation for mobile Ad Hoc networks by combining a fully distributed admission control approach and the DIFS based differentiation mechanism of IEEE802.11. It can provide different kinds of QoS (Quality of Service) for various applications. Admission controllers determine a committed bandwidth based on the reserved bandwidth of flows and the source utilization of networks. Packets are marked when entering into networks by markers according to the committed rate. By the mark in the packet header, intermediate nodes handle the received packets in different manners to provide applications with the QoS corresponding to the pre-negotiated profile. Extensive simulation experiments showed that the proposed mechanism can provide QoS guarantee to assured service traffic and increase the channel utilization of networks. 相似文献
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陈盈 《英语大王(小学)》2005,(7)
I live in Nanjing.on my way to school. I can see a lot of air pollution. Look at the smoke from traffic. It's quite dirty. The workers are burning rubbish near a construction site. And smoke and dust come from fire and construction site. 相似文献
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A weighted time-based global hierarchical path planning method is proposed to obtain the global optimal path from the starting point to the destination with time optimal control. First, the grid- or graph-based modeling is performed and the environment is divided into a set of grids or nodes. Then two time-based features of time interval and time cost are presented. The time intervals for each grid are built, during each interval the condition of the grid remains stable, and a time cost of passing through the grid is defined and assigned to each interval. Furthermore, the weight is introduced for taking both time and distance into consideration, and thus a sequence ofmultiscale paths with total time cost can be achieved. Experimental results show that the proposed method can handle the complex dynamic environment, obtain the global time optimal path and has the potential to be applied to the autonomous robot naviga- tion and traffic environment. 相似文献
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A main shortcoming of mobile Ad-hoc network‘s reactive routing protocols is the large volume of far-reaching control traffic required to support the route discovery (RD) and route repair (RR) mechanism.Using a random mobility model,this paper derives the probability equation of the relative distance (RDIS) between any two mobile hosts in an ad-hoc network.Consequently,combining with average equivalent hop distance (AEHD) ,a host can estimate the routing hops between itself and any destnation host each time the RD/RR procedure is triggered,and reduce the flooding area of RD/RR messages. Simulation results show that this optimized route repair (ORR) algorithm can significantly decreace the communication overhead of RR process by about 35％. 相似文献
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Optimal velocity functions for car-following models 总被引：1，自引：0，他引：1
The integral part of the optimal velocity car-following models is the optimal velocity function （OVF）, which can be derived from measured velocity-spacing data. This paper discusses several characteristics of the OVF and presents regression analysis on two classical datasets, the Lincoln and Holland tunnels, with different possible OVFs. The numerical simulation of the formation of traffic congestion is conducted with three different heuristic OVFs, demonstrating that these functions give results similar to those of the famous Bando OVF （Bando et al., 1995）. Also an alternative method is present for determining the sensitivity and model parameters based on a single car driving to a fixed barrier. 相似文献
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《海外英语》2014,(11):21-21
When was the last time you felt stressed？ What did you do about it？ Here are a few ways of dealing with stress. Stress is the feeling you get when you＇ re under pressure. All sorts of situations can cause stress： moving home, financial difficulties, work overload, driving in heavy traffic, noisy neighbours, pollution, uncertainty... 相似文献
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Design patterns are micro architectures that have proved to be reliable,robust and easy to implement.Detecting design pattern from source code of object-oriented system can help a designer,a developer or a maintainer to understand the software system.In this paper,a new method is provided which can detect design patterns from source code combining both static and dynamic analysis.To acquire the run-time dynamic information of software systems,a code instrumentation method is adopted.At the same time,all static and dynamic information is presented in UML diagrams format.The pattern detection process and its detection results are visual and interactive.This method is tested on a call center and a traffic simulation system.Experimental results prove that the method is effective in design patterns detection. 相似文献
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WANG Yang ZHAN Yi-chun YU Shao-hua 《重庆大学学报(英文版)》2007,6(4):265-272
This paper investigates the routing among autonomous systems (ASs) with quality of service (QoS) requirements. To avoid the intractability of the problem, abstract QoS capability must be informed among ASs, because the routhing which constrained QoS has been proved to be nondeterministic polynomial-time (NP) hard even inside an AS. This paper employs the modified Dijkstra algorithm to compute the maximum bottleneck bandwidth inside an AS. This approach lays a basis for the AS-level switching capability on which interdomain advertisement can be performed. Furthermore, the paper models the aggregated traffic in backbone network with fractional Brownian motion (FBM), and by integrating along the time axis in short intervals, a good estimation of the distribution of queue length in the next short intervals can be obtained. The proposed advertisement mechanism can be easily implemented with the current interdomain routing protocols. Numerical study indicates that the presented scheme is effective and feasible. 相似文献
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丁楠 《中学英语之友(教育研究与实践)》2008,(1):4-6
(A) Our town is a new town.Here,the buildings are tall;the streets arebusy;the traffic(交通)is heavy,but the pollution is not serious.In ourtown,most of the buildings have fifteen to twenty floors.Most of thepeople 相似文献
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One-dimensional traffic model was studied with the consideration of stochastic deceleration by using the lattice Boltzmannmethod.The evolution equation for vehicle density was derived,which has the form of the Burgers equation exhibiting the effect of viscosity corresponding to the deceleration.The simulation with the model shows that the variation of vehicle density in space tends to a periodic one,which implies the existence of kinematic waves in the 1D traffic flow and coincides with theoretical prediction. 相似文献