EPON动态带宽分配的QOS特性分析

在动态带宽分配(dynamic bandwidth allocation,DBA)的研究中,往往对带宽利用率关注较多,但现实是能够支持多业务网络的服务质量(Qos)越来越重要.基于上述情况通过研究提出了新的基于业务的带宽分配方式,和现有的基于节点(ONU based)方式进行对比,分析了两种带宽分配方式的Qos特性.仿真试验表明:两种方式在带宽利用率上差别不大,但ServiceBased方式对主要利润业务的Qos有显著提高.     

Super SBI Dynamic Network DEA approach to measuring efficiency in the provision of public services

The current financial crisis has had a significant impact on European governments’ finances and has led to a series of government interventions to control the public debt and deficit. Therefore, the aim of this paper is to identify inefficiencies in the management of public finance, such as overspending, unreasonable debt, and excessive taxes, while maintaining the same level of social welfare. Thus, we propose a two‐stage network data envelopment analysis (DEA) structure that accounts for both allocation of the public budget and transformation of government expenditures into services to the people and the economy. Financial assets, debt, and employment have been included as carryover activities over successive periods of time. Finally, a super‐efficiency approach allows discriminating between the efficient European governments. We have applied the proposed approach to the period from fiscal years 2008 to 2012. Results show that not only high‐deficit countries, but also major countries such as Germany and France have performed poorly. The slack‐based measure of inefficiency (SBI) metrics, whose directional vector components are defined as the yearly national GDP, point out the feasible reductions in taxes and debt issuances, along with feasible targets for government expenditure.     

利用发送和接收时隙分配策略改善无线传感器网络MAC协议能效

摘　要 针对无线传感器网络中存在数据冲突和串音而影响MAC协议能量效率的问题,提出了基于接收和基于发送的TDMA-MAC协议时隙分配策略。通过考虑各种无线收发器模式(即发送、接收、休眠和空闲)花费的不同时间段来计算WSN能耗,假设聚类中WN数据包时间间隔为指数分布,采用两级TDMA方法实现对多步聚类的评估。利用OPNET Modeler软件执行仿真实验验证了本文模型的有效性,仿真结果表明,基于接收的SAS的能效是基于发送的SAS的5倍,相比基于分簇的TDMA/CDMA混合HCT-MAC协议,本文协议可节省4.3%的能量,减少了0.35ms的端到端延迟,相比倍增超周期多信道MAC协议,可节省10.8%的能量,减少了1ms的端到端延迟。     

Shear localization sensitivity analysis for Johnson–Cook constitutive parameters on serrated chips in high speed machining of Ti6Al4V

This research aims to investigate the influence of material constitutive parameters on the serrated chip formation during high speed machining (HSM) of Ti6Al4V alloys with finite element simulations and cutting experiments. The Johnson–Cook (JC) constitutive model and JC fracture model with an energy-based ductile failure criterion are adopted to simulate the HSM process. Five JC constitutive model parameters such as initial yield stress, hardening modulus, strain hardening coefficient, strain rate dependency coefficient, and thermal softening coefficient are included in this research. Shear localization sensitivity is novelly proposed to describe variations of serrated chips under different JC constitutive model parameters. Shear localization sensitivity is subdivided into chip serration sensitivity and chip bending sensitivity. The research finds that the influences of initial yield stress and thermal softening coefficient parameters on the chip serration and bending are much more prominent than those of the rest three JC constitutive model parameters. With initial yield stress or hardening modulus in JC constitutive model increasing, the chip serration sensitivity increases and the chip bending sensitivity decreases. However, the influences of the rest three parameters on chip serration sensitivity are opposite. High speed orthogonal cutting experiments of Ti6Al4V are carried out to validate the simulation results under different cutting speeds ranging from 50 m/min to 3000 m/min and fixed uncut chip thickness with 0.1 mm. The results show that the serrated degree of chips increases with the cutting speed increasing until the chips become completely fragmented. The cutting speed break point of chip morphology from serrated to fragmented ones for Ti6Al4V is about 2500 m/min. The average cutting force decreases with the cutting speed increasing, which is a prominent advantage for HSM. This paper can help to get deeper insights into the serrated chip formation mechanism in HSM.