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Search Results: 1 - 10 of 73243 matches for " Lei Yu "
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Liver Transplantation in the Elderly: An Evidence Based Review on Patient Outcome, Selection and Management Strategies  [PDF]
Lei Yu, Robert Carithers
Journal of Biomedical Science and Engineering (JBiSE) , 2014, DOI: 10.4236/jbise.2014.79065
Abstract: There has been a steady increase in the age of potential recipients for liver transplantation over the past two decades. While patients older than age 60, on average, did not do as well as younger patients after transplantation, optimizing patient selection could minimize this discrepancy. It is appropriate to evaluate functional elderly patients without significant medical comorbidities for liver transplantation for the same indications as younger patients. For elderly patients with hepa-tocellular carcinoma and otherwise compensated liver disease, however, it is important to consider alternative treatment modalities that could provide similar survival. Elderly candidates who became too ill should be compassionately counseled away from transplantation based on existing prognostic models that can accurately predict post-transplant mortality. Finally, elderly transplant candidates and recipients may benefit from a more tailored management strategy in terms of donor risk matching and less immunosuppression.
Approximate Continuous Aggregation via Time Window Based Compression and Sampling in WSNs  [PDF]
Lei Yu, Jianzhong Li, Siyao Cheng
Wireless Sensor Network (WSN) , 2010, DOI: 10.4236/wsn.2010.29081
Abstract: In many applications continuous aggregation of sensed data is usually required. The existing aggregation schemes usually compute every aggregation result in a continuous aggregation either by a complete aggregation procedure or by partial data update at each epoch. To further reduce the energy cost, we propose a sampling-based approach with time window based linear regression for approximate continuous aggregation. We analyze the approximation error of the aggregation results and discuss the determinations of parameters in our approach. Simulation results verify the effectiveness of our approach.
Calibration of Car-Following Models Considering the Impacts of Warning Messages from Tablet/Smartphone Application  [PDF]
Qing Li, Fengxiang Qiao, Lei Yu
Journal of Transportation Technologies (JTTs) , 2016, DOI: 10.4236/jtts.2016.62006
Abstract: The phenomenon of car-following is special in traffic operations. Traditional car-following models can well describe the reactions of the movements between two concessive vehicles in the same lane within a certain distance. With the invention of connected vehicle technologies, more and more advisory messages are in development and applied in our daily lives, some of which are related to the measures and warnings of speed and headway distance between the two concessive vehicles. Such warnings may change the conventional car-following mechanisms. This paper intends to consider the possible impacts of in-vehicle warning messages to improve the traditional car-following models, including the General Motor (GM) Model and the Linear (Helly) Model, by calibrating model parameters using field data from an arterial road in Houston, Texas, U.S.A. The safety messages were provided by a tablet/smartphone application. One exponent was applied to the GM model, while another one applied to the Linear (Helly) model, both were on the stimuli term “difference in velocity between two concessive vehicles”. The calibration and validation were separately conducted for deceleration and acceleration conditions. Results showed that, the parameters of the traditional GM model failed to be properly calibrated with the interference of in-vehicle safety messages, and the parameters calibrated from the traditional Linear (Helly) Model with no in-vehicle messages could not be directly used in the case with such messages. However, both updated models can be well calibrated even if those messages were provided. The entire research process, as well as the calibrated models and parameters could be a reference in the on-going connected vehicle program and micro/macroscopic traffic simulations.
Drivers’ Reaction of Warning Messages in Work Zone Termination Areas with Left Turn  [PDF]
Boya You, Fengxiang Qiao, Lei Yu
Journal of Transportation Technologies (JTTs) , 2016, DOI: 10.4236/jtts.2016.63013
Abstract: Work-zone crashes have always drawn public attention. A number of fatalities are recorded every year nationwide within work zone areas. Most existing countermeasures have been dedicated more to the advance warning areas, transition areas, and activity areas of work zone, than the termination areas, where drivers might play less attention to safety threats. In this study, the vehicle-to-vehicle communication based left turn warning system was applied at a work zone termination area, which is immediately followed by a T-intersection. The work-zone is located on the minor road side, while left turn vehicles will be appearing from the major street through the said T-intersection. A smart phone application was designed using Android coding system to provide several types of warning messages to drivers. Corresponding scenarios were designed in a driving simulator, and 20 subjects were recruited to participate in the simulation test followed by a questionnaire survey. The subjects received a warning message when driving to the termination area of a work zone on the coming left turn vehicles. Twenty test drivers’ driving speed, acceleration rates, and break reaction distance to the warning messages were studied in four different scenarios. Results show that the smartphone application has a great impact on driving behaviors, especially the female voice and the beep tone warning, which are recommended for possible field tests. Besides, the developed smartphone applications can be further updated for practical applications of similar needs.
User-Based Discrete-Time Queuing Analysis for Opportunistic Spectrum Access in Cognitive Radio Networks  [PDF]
Lei Zhang, Shanzhi Mou, Yu Wang
Advances in Pure Mathematics (APM) , 2019, DOI: 10.4236/apm.2019.91001
Abstract: In cognitive radio networks, the spectrum utilization can be improved by cognitive users opportunistically using the idle channels licensed to the primary users. However, the new arrived cognitive users may not be able to use the channel immediately since the channel usage state is random. This will impose additional time delay for the cognitive users. Excessive waiting delay can make cognitive users miss the spectrum access chances. In this paper, a discrete-time Markov queuing model from a macro point of view is provided. Through the matrix-geometric solution theory, the average sojourn time for cognitive users in the steady state before accessing the spectrum is obtained. Given the tolerant delay of cognitive users, the macro-based throughput is derived and an access control mechanism is proposed. The numerical results show the effects of service completion probability on average sojourn time and throughput. It is confirmed that the throughput can be obviously improved by using the proposed access control mechanism. Finally, the performance evaluations based on users are compared to that based on data packets.
A Method of Improving the Stability of Liao's Higher-Order Absorbing Boundary Condition
Lei Zhang;Tongbin Yu
PIER M , 2012, DOI: 10.2528/PIERM12092815
Abstract: Liao's absorbing boundary condition (ABC) is a classic ABC algorithm. It has the advantages of better absorption effect, easy programming and needless to split field. However its numerical stability is poor, especially for the higher-order ones, which greatly limits the scope of its application. To solve this problem, a weighting method for improving the stability of Liao's higher-order ABC is presented in this paper. This method is simple and effective, and it can be implemented easily compared with other improvement methods before. It improves the stability of Liao's higher-order ABC remarkably, and extends its application range.
Study on Optimization of Phase Offset at Adjacent Intersections
Yuanli GU,Lei Yu
International Journal of Intelligent Systems and Applications , 2010,
Abstract: Optimization of the phase offset at adjacent intersections is the key parameter regarding coordinated control of traffic signal for adjacent intersections, which decides the effect of the coordinated control for adjacent intersections. According to characters of saturated traffic flow of Chinese urban road, this thesis establishes a model for optimization of phase offset for adjacent interactions and finds a solution from such model by adopting genetic algorithm. The model is verified by actual traffic flow datum of two adjacent signal intersections on Changan Avenue. Then a comparison is made between the optimization result of such model and that of the existing mathematical method and SYNCHRO model, which indicates that the model established by this thesis can reduce the delay suffered by vehicles at the intersections and increase the traffic efficiency of the intersections.
Operational Mechanism and Evaluation System for Emergency Logistics Risks
Qi Cheng,Lei Yu
International Journal of Intelligent Systems and Applications , 2010,
Abstract: Lots of risks existed in the operating process of emergency logistics especially when natural disasters happened. Both operating mechanism and evaluation system research on Emergency Logistics Risks (ELR) are the basis of effective recognizing, preventing and responding to risks, so it’s of great theoretical and practical significance to study the formation and influence mechanism and to establish an evaluating index system for ELR. Firstly, some foundation research about ELR was carried out, including definition, characteristics and classification of ELR. The formation and influence mechanism of ELR were discussed. The research of questionnaire survey offered an objective support for theoretical mechanism and index system establishment. Then, the evaluating index system for ELR was established. This system was a multi-level index system, and mainly evaluated by the decision-making risk, dispatching and commanding risk, organizing and coordinating risk, executing and controlling risk, resources supporting risk and their sub index. The establishment principles and significance of the index system were discussed. Then, the fuzzy comprehensive evaluation and Delphi method were used to confirm the index weight and value. Finally, a case analysis on ELR of Yushu earthquake was conducted to demonstrate the evaluating index system and to evaluate the actual risk level.
Subpixel Edge Detection Based on Morphological Theory
Yu Lei,Nie Jiafa
Lecture Notes in Engineering and Computer Science , 2008,
Abstract:
The Root Analysis and the Impact on China of Sub-loan Crisis
Lei Zhang,Yuanyuan Yu
International Journal of Business and Management , 2009, DOI: 10.5539/ijbm.v4n4p183
Abstract: From 2007, a subprime storm began to blows from the US, and sweep across the whole world with a rapid speed. It makes the world economic growth slow -down, even Iceland and a fraction of the world’s countries fall into bankrupt. Behind this, the dollar hegemony of which the United States has been proud is exactly the main reason. Actually, the appreciation of RMB and the interest rates raised by the U.S. Federal Reserve have triggered the subprime mortgage crisis. Although the direct impact on China is not extremely great, the indirect influence can’t be underestimated. Face to the crisis, China should learn this lesson from it, control the real estate bubble, expand domestic demand and reduce the gap between rich and poor in order to realize the economy transformation.
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