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标准化概念定义的评论 总被引:2,自引:2,他引:0
本文阐述了标准概念定义的状况,总结了国际标准化组织和中国对标准化概念定义的历程,重点分析了国际标准化组织的标准化定义存在的问题,对国际标准化组织的标准化定义进行了分析和检验,对标准化的概念和定义的特性进行了理论性比较,对如何定义标准化概念进行了理性的讨论。 相似文献
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王淑霞 《现代测量与实验室管理》2015,(2):48+31
本文从认可准则对实验室监督工作的要求入手,对监督的意义和作用进行了阐述,同时对实验室监督工作现状进行了分析,并对监督工作的内容、方式和要求进行了论述。 相似文献
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《中国新技术新产品》2020,(10)
该文通过有限元分析及其理论计算2个方向对双柱立车工件偏载现象,对加工精度和使用寿命的影响进行了分析,对采用有限元分析方法解决实际问题的思路进行了剖析,对主轴系统受力状态进行了分析,指出了影响加工精度和机床使用寿命的关键参数,并从设计人员和使用人员的角度对偏载情况的注意事项进行了阐述,对于机床设计与维护具有一定的参考意义。 相似文献
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对某油田2002-2004年钻具失效情况进行了系统调查,查清了不同钻具的失效形式和失效次数。通过统计分析发现钻铤断裂次数最多,占钻具失效总数的比例最大。对钻铤断裂机理和受力状态进行了分析,认为钻铤断裂性质主要属于早期疲劳失效。对钻铤标准和实际使用状况进行了分析,找出了钻铤标准中存在的问题。对钻铤断裂原因从螺纹接头结构应力、残余应力和材料韧性等方面进行了分析,指出了导致钻铤断裂的产品质量问题。通过使用工况和钻井参数对钻铤的受力状态进行了分析,指出了使用操作对钻铤断裂的影响。最后对该油田依据上述结论采取措施后2009-2011年钻具失效情况进行了统计分析,发现钻具失效事故大幅度减少。 相似文献
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对自行研制的冰蓄冷系统专用风机盘管进行了阐述。对送风口附近存在的结雾和滴水现象进行了分析,提出了新的冰蓄冷系统专用风机盘管的设计方案,进而针对第一种方案进行了理论分析和设计计算。对相关工作进行了初步的展望。 相似文献
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Abstract A deterministic service model assisted by a sufficiently large playback buffer space can provide bounded delay guarantees for video packets and simplify network resource management. However, many popular mobile terminals do not have sufficient memory capacity for deterministic video services since the embedded memory is limited and needs to be shared by numerous software programs and masses of personal data. This paper improves the traditional deterministic modeling approach for delivering pre‐stored videos to mobile clients with QoS guarantees. The limitation of playback buffer space, the network delay jitter, the processing load of resource management, and the QoS guarantee are considered in the proposed mechanism. Some traffic smoothing operations are integrated into the proposed mechanism for reducing the playback buffer demand and data rate variation. This paper further proposes a smart video frame skip algorithm, originating at the sender for preventing possible overflow problems due to insufficient playback buffer space. The algorithm can determine the most suitable temporal range for skipping frames and prevent arbitrary discarding from inappropriate video frames such as I‐frames on the client side. Simulation results reveal that the proposed mechanism can effectively remedy situations of insufficient playback buffer space while still maintaining the advantages of deterministic services. 相似文献
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Zhibin Yang Nong Ye Ying‐Cheng Lai 《Quality and Reliability Engineering International》2006,22(4):429-444
The Internet has evolved into a shared, integrated platform of a broad range of applications with different Quality‐of‐Service (QoS) requirements. Routers are an important part of the Internet and play a critical role in assuring QoS. A router is usually placed between two networks to receive data packets from one network and then transmit those data packets to another network if necessary. Data packets are the actual units of data traveling on computer networks. A data packet has two parts: header and data. The data carries messages, such as e‐mail text, from computer applications. The header carries information that is required to control and manage the transmission of the data packet on computer networks. Existing approaches for providing QoS involve prediction or estimation for traffic characterization to determine parameters required of static traffic admission control. However, prediction or estimation inaccuracy in traffic characterization can result in inappropriate parameter settings for static admission control and, in turn, compromise QoS or resource utilization. This study presents a QoS model of a router with feedback control that monitors the state of resource usage and adaptively adjusts parameters of traffic admission control to overcome prediction or estimation inaccuracy and achieve a balance between QoS and resource utilization. The QoS model of a router with feedback control is simulated to test its performance on QoS and resource utilization in both heavy and light traffic conditions. The performance of the QoS model of a router with feedback control is also compared with that of two basic QoS models of a router with static admission control using admission control parameters resulting from over‐ and under‐characterization of traffic, respectively. The simulation results show that the QoS model of a router with feedback control achieves a better balance between QoS and resource utilization than the basic QoS models with over‐ and under‐characterizations of traffic in the heavy traffic condition. This study also shows that the three models of routers demonstrate similar QoS performances and resource utilization in the light traffic condition. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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The author evaluates the performance of bufferless optical packet switches equipped with shared tuneable optical wavelength converters (TOWC) and supporting the quality of service (QoS). The TOWCs are shared per output fibre and, hence each output fibre has a dedicated pool of TOWCs. The TOWCs are not completely shared within the node. The QoS, expressed in terms of the packet loss probability, is differentiated by giving the packets different priorities in accessing both the output wavelengths and the TOWCs. A scheduling algorithm is proposed and its complexity is evaluated. The QoS technique?s effectiveness is studied by means of an analytical model based on a probabilistic approach and validated by simulation results. The results show that the proposed technique to support the QoS facilitates a good differentiation of the QoS offered to packets. 相似文献
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回顾了IP QoS的发展,总结了IP网中不同QoS技术的特征,提出了一种基于域的QoS分类方法,将各种QoS技术归结为时域、空域、逻辑域和层域。通过该方法可以更加深入地分析采用不同QoS技术对网络引入的代价,对构建一个合理的具有QoS保证的IP网具有一定的指导意义。 相似文献
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Cross-layer cooperation for accurate admission control decisions in mobile ad hoc networks 总被引:2,自引:0,他引:2
Mobile ad hoc networks (MANETs) are unpredictable by nature. Providing any kind of reliability for quality of service (QoS) in such networks is challenging. Quantifying available resources accurately, avoiding interference with ongoing QoS traffic and adapting to QoS violations caused by nodes' mobility are the main concerns for the design of an efficient admission control protocol in MANETs. Adaptive admission control (AAC), a novel admission control protocol which uses robust and accurate resource estimation and prediction techniques for relevant admission decisions has been proposed. Furthermore, AAC uses statistical QoS provision to counteract the QoS threatening mobility. Through simulations, we show that our proposed scheme outperforms existing approaches in terms of correctness and overall performance. 相似文献
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A mobile agent based on-demand quality of service (QoS) unicast routing scheme for supporting multimedia applications is proposed that considers bandwidth, delay and packet loss as QoS metrics for feasible path computation. A mobile agent is employed to find multiple QoS paths and select a best path among them to preserve resources so as to increase call success ratio and network bandwidth utilisation as well as adapt to network dynamics. The scheme is simulated in various network scenarios (sparse and dense networks) to verify performance and operation effectiveness, and compared with RSVP-based QoS routing by using an internet routing protocol. The results demonstrate significant improvements in call success ratio and network bandwidth utilisation compared with RSVP-based QoS routing, both in case of sparse and dense networks. Benefits of the agent-based scheme are adaptability, flexibility, and support for component-based software engineering features such as software reuse, customisation and maintainability 相似文献
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Yang Yang Zhang Wuxiong Hu Honglin Zhang Sihai Wang Xin Zhao Haitao Zhou Wuyang Wei Jibo 《中国工程科学》2011,13(1):24-29
During the last two decades, mobile communication systems (such as GSM, GPRS and 3G networks), wireless broadcasting networks, wireless local area networks (WLAN or WiFi), and wireless sensor networks have been successfully developed and widely deployed through different technological routes for providing a variety of communication services in different application scenarios. While making tremendous contributions to social progress and economic growth, these heterogeneous wireless networks consume a lot of energy in achieving overlapped service coverage, and at the same time, generate strong electromagnetic interference (EMI) and radiation pollution, especially in big cities with high building density and user population. In order to guarantee the overall return on investment (ROI), improve user experience and quality of service (QoS), save energy, reduce EMI and radiation pollution, and enable the sustainable deployment of new profitable applications and services, this paper proposes a cross-network cooperation mechanism to effectively share network resources and infrastructures, and then adaptively control and match multi-network energy distribution characteristics according to actual user/service requirements in different geographic areas. Some idle or lightly-loaded Base Stations (BS or BSs) will be temporally turned off for saving energy and reducing EMI. Initial simulation results show the proposed approach can significantly improve the overall energy efficiency and QoS performance across multiple cooperative wireless networks. 相似文献
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Nadia Tabassum Allah Ditta Tahir Alyas Sagheer Abbas Hani Alquhayz Natash Ali Mian Muhammad Adnan Khan 《计算机、材料和连续体(英文)》2021,67(3):3129-3141
Cloud computing is becoming popular technology due to its functional properties and variety of customer-oriented services over the Internet. The design of reliable and high-quality cloud applications requires a strong Quality of Service QoS parameter metric. In a hyperconverged cloud ecosystem environment, building high-reliability cloud applications is a challenging job. The selection of cloud services is based on the QoS parameters that play essential roles in optimizing and improving cloud rankings. The emergence of cloud computing is significantly reshaping the digital ecosystem, and the numerous services offered by cloud service providers are playing a vital role in this transformation. Hyperconverged software-based unified utilities combine storage virtualization, compute virtualization, and network virtualization. The availability of the latter has also raised the demand for QoS. Due to the diversity of services, the respective quality parameters are also in abundance and need a carefully designed mechanism to compare and identify the critical, common, and impactful parameters. It is also necessary to reconsider the market needs in terms of service requirements and the QoS provided by various CSPs. This research provides a machine learning-based mechanism to monitor the QoS in a hyperconverged environment with three core service parameters: service quality, downtime of servers, and outage of cloud services. 相似文献