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61.
Due to the fact that human activities and most sustainability issues are closely related to energy use, the energy system is a sound framework for providing lead indicators for sustainable development. Common energy-economic models enable the estimation of future states of the energy system. An energy system-based lead indicator set can be used to develop consistent and coherent future indicator estimates and to track sustainability, a clear advantage over existing sets. 相似文献
62.
63.
Xiaoming Zhou Martin Jacobsson Henk Uijterwaal Piet Van Mieghem 《International Journal of Communication Systems》2008,21(6):643-663
Although packet delay and loss are two important parameters of the Internet performance, to the best of our knowledge, the evolution of large‐scale IPv6 delay and loss performance has previously not been studied. In this paper, we analyze more than 600 end‐to‐end IPv6 paths between about 26 testboxes of RIPE Network Coordination Centre over two years, and compare the delay and loss performance over time with their IPv4 counterparts. We present and discuss the measurement methodologies and show that IPv6 paths have a higher delay and loss than their IPv4 counterparts. The main reason for the worse performance stems from IPv6‐in‐IPv4 tunnels rather than from native IPv6 paths and such tunnels are still widely used today. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
64.
采用传递比较法对二厘米微波衰减标准装置不确定度进行了验证。测量标准装置的重复性以组内实验标准偏差sn(A)定量表征,测量标准装置的稳定性用组间实验标准偏差sm定量表征。 相似文献
65.
本文通过对中州分公司正在考虑建设的信息网建设实际情况,结合山东分公司、广西分公司取得的经验,对计量管理信息网的应用进行了探讨。 相似文献
66.
Bayazit Mahmut; Hammer Tove Helland; Wazeter David L. 《Canadian Metallurgical Quarterly》2004,89(4):738
Methodological problems in studies of union commitment were identified and illustrated with data from 4,641 members and 479 stewards in 297 local teachers' unions. Using a 20-item union commitment scale, results confirmed the existence of 3 substantive factors and 1 method factor at the individual level of analysis: loyalty to the union, responsibility to the union, willingness to work for the union, and a factor of negatively worded items. Tests of measurement invariance showed that the scale captured commitment for rank-and-file members but not for union stewards. The authors also found partial measurement invariance between long-time and newer members and full measurement invariance between men and women. Finally, the authors found that violation of the statistical assumption of independence reduced model fit when individual commitment scores were analyzed without attention to the hierarchical nature of the data. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
67.
Predictions of the discharge and the associated sediment concentration are very useful ingredients in any water resources reservoir design, planning, maintenance, and operation. Although there are many empirical relationships between the discharge and sediment concentration amounts, they need estimation of model parameters. Generally, parameter estimations are achieved through the regression method (RM), which has several restrictive assumptions. Such models are locally valid and their structures and parameter values are questionable from region to others. This paper proposes a new approach for sediment concentration prediction provided that there are measurements of discharge and sediment concentration. The basis of the methodology is a dynamic transitional model between successive time instances based on two variables, namely, discharge and sediment concentration measurements. The transition matrix elements are estimated from the measurements through a special form of the artificial neural networks as perceptrons. The sediment concentration predictions from discharge measurements are achieved through a perceptron Kalman filtering (PKF) technique. In the meantime, this technique also provides temporal predictions. A certain portion of the measurement sequence is employed for the model parameter estimations through training and the remaining part is used for the model verification. Detailed comparisons between RM and PKF approaches are presented and, finally, it is shown that the latter model works dynamically by simulating the observation scatter diagram in the best possible manner with smaller prediction errors. The application of the methodology is performed for the discharge and sediment concentration measurements obtained from the Mississippi River basin at St. Louis, Missouri. It is found that the PKF methodology has smaller average relative, root-mean-square, and absolute errors than RM. Furthermore, graphical representation, such as the scatter and frequency diagrams, indicated that the PKF approach has superiority over the RM. 相似文献
68.
A Novel Segmentation and Feedback Model for Resolving Contention in Optical Burst Switching 总被引:2,自引:0,他引:2
A novel segmentation and feedback model (SFM) applied to resolve contention is proposed. Simulation and performance analyses show that the SFM effectively avoids contentions in optical burst switching (OBS). The long delay time of deflection routing and the immature technology of wavelength converters and optical buffers are not deployed in the SFM. The SFM does not only realize fast switching but also allows preemption by higher priority bursts. 相似文献
69.
70.
J. Gegner Priv.‐Doz. Dr. W. Nierlich M. Brückner 《Materialwissenschaft und Werkstofftechnik》2007,38(8):613-623
Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology. 相似文献