高耐久性的聚合物纤维混凝土的性能及应用

纤维混凝土（FRC）对混凝土结构的耐久性有明显加强的作用,可以通过延长建筑物的使用寿命,节约建筑物维护和维修的费用．探讨一种新型的聚合物合成纤维水泥基复合材料ECC的工作性能和应用现状．大量研究表明PVA纤维混凝土可以通过牺牲部分抗压强度来提高材料抗裂性能．因此,如果在工程施工中,梁、板等受拉构件或者混凝土钢筋保护层等需要进行耐久性设计的构件使用ECC材料,会取得显著的抗裂性能,提高混凝土构件的耐久性,而以抗压强度起主要作用的抗压构件则建议谨慎使用．     

辊面氧化膜局部保留及其对粗轧板形的影响探讨

为改善粗轧R₂新辊上机1万t以内的板形游动和打滑问题,研究了3种不同形式辊面氧化膜局部保留的工作辊对粗轧板形的影响规律。通过分段函数的方法,磨削出3种不同形式的局部氧化膜保留的粗轧工作辊,分别为:上下辊均为半磨削,保留中间氧化膜;上辊为半磨削,下辊为全磨削,上辊保留中间氧化膜;上下辊均保留两肋氧化膜。对比了3种不同形式局部氧化膜保留的工作辊与全磨削工作辊轧制对应的带钢镰刀弯精度。试验结果表明:这3种粗轧工作辊氧化膜局部保留的方式,均可有效控制新工作辊上机初期的板形游动问题,与全磨削工作辊相比,这3种氧化膜局部保留方法可使粗轧板坯镰刀弯控制精度从33%提升至45%。通过对每次下线的工作辊上下对调,再仅将上辊保留中间氧化膜,下辊为全磨削,或者将上下辊均为半磨削和上下辊均保留肋氧化膜的工作辊交替使用,均可实现每套工作辊都有局部氧化膜保留,同时确保轧辊使用安全,有效控制粗轧工作辊上机初期带钢的板形游动问题并提高镰刀弯精度。     

The Seat Reservation Problem

We investigate the problem of giving seat reservations on-line. We assume that a train travels from a start station to an end station, stopping at k stations, including the first and last. Reservations can be made for any trip going from any station to any later station. The train has a fixed number of seats. The seat reservation system attempts to maximize income. We consider the case in which all tickets have the same price and the case in which the price of a ticket is proportional to the length of the trip. For both cases we prove upper and lower bounds of Θ(1/k) on the competitive ratio of any ``fair' deterministic algorithm. We also define the accommodating ratio which is similar to the competitive ratio except that the only sequences of requests allowed are sequences for which the optimal off-line algorithm could accommodate all requests. We prove upper and lower bounds of Θ(1) on the accommodating ratio of any ``fair' deterministic algorithm, in the case in which all tickets have the same price, but Θ(1/k) in the case in which the ticket price is proportional to the length of the trip. The most surprising of these results is that all ``fair' algorithms are at least 1/2 -accommodating when all tickets have the same price. We prove similar results bounding the performance of any ``fair' randomized algorithm against an adaptive on-line adversary. We also consider concrete algorithms; more specifically, First-Fit and Best-Fit. Received February 6, 1997; revised November 6, 1997.     

支持资源预定的多目通信的路由算法及其性能分析

目前Ｉｎｔｅｒｎｅｔ上的路由协议仅支持“尽力传送服务”。新型的应用问题如视屏会议,分布式模拟等需要有保障的服务质量,资源预定协议和ＲＳＶＰ等可以用来提供有保障的服务质量,但是它需要有新的路由协议。文中研究了支持资源预定的多目通信的路由问题,提出了两个路由算法。     

多媒体信息网络QoS的控制*

文章综述了多媒体信息网络在服务质量(QoS)研究方面的一些最近的工作,着重论述了接纳控制和信源整形、QoS选路和资源预留、基于QoS的传输调度、综合服务网的QoS控制等问题.文章还描述了多媒体信息网络QoS控制的技术以及所面临的问题和进一步的研究方向.     

拥塞控制卫星PRMA-AC协议及性能分析

卫星通信中PRMA协议在负荷较重时由于终端竞争加剧会引起信道拥塞,而较长的传播时延更进一步加剧了拥塞引起的丢包。该文提出一种利用话音终端在通话的不同阶段对信道资源的不同需求对终端进行区分的方案PRMA-AC,据此引入一种接入控制机制,以减少信道竞争,提高系统服务质量。文中给出了系统模型,对协议性能进行了理论分析,获得了新协议下的接入阻塞率、丢包率等性能指标,最后通过仿真与几种卫星通信中常用的PRMA协议进行了对比,证明了协议的性能。     

Subsidy strategy for reserving flexible capacity of emergency supply production

This paper investigates a government's subsidy strategy for motivating a manufacturer to set up a flexible production line for emergency supplies. Four subsidy strategies are proposed to ensure a desired service level in case of an emergency: zero subsidy, a fixed subsidy, a marginal subsidy, and a hybrid subsidy. We develop a game theoretical model to examine how the government can induce a manufacturer to set up a flexible production line that can respond promptly to an emergency, based on the manufacturer's cost structure (fixed and marginal costs). We find that when the marginal profit of an emergency product is higher than that of the manufacturer's regular product, a fixed (marginal) subsidy is the dominant strategy if the manufacturer's fixed (marginal) cost is high, while a hybrid subsidy strategy is dominant if both costs are high. When the marginal profit of an emergency product is lower than that of the manufacturer's regular product, neither a fixed subsidy nor a zero subsidy will be the dominant strategy. We also find that a marginal subsidy can ensure the effectiveness of the strategy, while a fixed subsidy helps improve strategy efficiency. We use government subsidy strategies implemented for Chinese COVID-19 emergency supplies as examples to demonstrate the effectiveness and efficiency of the subsidy strategies under the proposed framework. We also extend the discussion by considering the manufacturer's social consciousness.     

Using statistical data for reliable mobile communications

We examine the extent to which statistical mobility information can increase the reliability of the service experienced by users in mobile networks. Interrupted or dropped calls are an aspect of reliability that stems from the mobility of users. An existing user can move to a cell where there are no resources available to support their call. A natural solution is the reservation of resources in multiple cells that the user is likely to move to. This scheme is called selective reservations and it relies on predicting the next move of the user. Recently, there has been some work on estimating the movement probabilities (also known as the mobility profile) of the user. In this paper, we quantify the usefulness of the mobility profile to improve the reliability of the service perceived by the mobile users. We identify two parameters which characterize the profile: Accuracy and Focus. Accuracy expresses the probability that the host will move as we expect it to. Focus describes how well we can identify patterns in the movement of the users. In our simulations, we examine the effect of the quality of the predictions on the performance of the system. We show that Accuracy and Focus have great impact on the performance of selective reservations. We also show how flexibility in hand‐offs can help in decreasing the dropping probability, and how this can be facilitated by letting the users make a second try at moving in case it fails the first time. Copyright © 2001 John Wiley & Sons, Ltd.