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101.
This study tested competing predictions about the implications of Internet use for traditional inequities in social support availability. Using survey data collected as part of the Pew Internet and American Life Project, inequities in social support availability stemming from demographic and network-related factors were examined among non-users, Internet users, and Internet users who also participated in a social network site (SNS). The results offered evidence consistent with the social compensation perspective. Traditional inequities in support availability related to age, race, and total network size persisted among respondents who did not use the Internet, but were less evident or absent among Internet users and/or Internet users who participated in an SNS. Using the Internet to connect with others appeared to be an important mechanism through which inequality in support availability was mitigated. 相似文献
102.
103.
刘健 《湖州师范学院学报》2008,30(1):29-32
应用三角形不等式中重要的R-r-s方法,证明了锐角三角形的中线与内角平分线的两个不等式,提出了两个未解决的猜想不等式. 相似文献
104.
研究了Hausdorff拓扑向量空间中一类广义多值向量变分不等式问题(GMVVIP),把定义在凸集上的GMVVIP部分地推广到了非凸集并运用KKM定理得到了这类GMVVIP解的存在性定理. 相似文献
105.
The suboptimal reliable guaranteed cost control (RGCC) with multi-criterion constraints is investigated for a class of uncertain continuous-time systems with sensor faults. A fauk model in sensors, which considers outage or partial degradation of sensors, is adopted. The influence of the disturbance on the quadratic stability of the closed-loop systems is analyzed. The reliable state-feedback controller is developed by a linear matrix inequalities (LMIs) approach, to minimize the upper bound of a quadratic cost fimction under the conditions that all the closed-loop poles be placed in a specified disk, and that the prescribed level of H∞ disturbance attenuation and the upper bound constraints of control inputs' magnitudes be guaranteed. Thus, with the above muki-criterion constraints, the resulting closed-loop system can provide satisfactory stability, transient property, a disturbance rejection level and minimized quadratic cost performance despite possible sensor faults. 相似文献
106.
Delay-dependent robust control for uncertain discrete singular systems with time-varying delay 总被引:1,自引:0,他引:1
The design problem of delay-dependent robust control For uncertain discrete singular systems with time-varying delay is addressed in this paper. The uncertainty is assumed to be norm-bounded. By establishing a finite sum inequality based on quadratic terms, a new delay-dependent robust stability condition is derived and expressed in terms of linear matrix inequalities (LMIs). A suitable robust state feedback control law is presented, which guarantees that the resultant closed-loop system is regular, causal and stable for all admissible uncertainties. Numerical examples are given to demonstrate the applicability of the proposed method. 相似文献
107.
Input-output approach to robust stability and stabilization for uncertain singular systems with time-varying discrete and distributed delays 总被引:3,自引:0,他引:3
Based on input-output approach, the robust stability and stabilization problems for uncertain singular systemswith time-varying delays are investigated. The parameter uncertainties are assumed to be norm-bounded and the time-varying delays include both discrete delay and distributed delay. By introducing a new input-output model, the time-delay system is embedded in a family of systems with a forward system without time delay and a dynamical feedback uncertainty. A sufficient and necessary condition, which guarantees the system regular, impulse-free and stable for all admissible uncertainties, is obtained. Based on the strict linear matrix inequality, the desired robust state feedback controller is also obtained. Finally, a numerical example is provided to demonstrate the application of the proposed method. 相似文献
108.
中国城市人均GDP差异影响因素的分析 总被引:6,自引:0,他引:6
在阐明当前我国城市人均GDP水平差异现状的基础上,通过多元回归分析,揭示造成这种差异的原因。结论是目前我国城市人均GDP水平差异很大,资本投入是影响城市人均GDP的决定性因素,其次是城市的产业结构。外资只对东部和大中城市有明显影响。人口规模与城市人均GDP之间关系不大,在大城市组甚至呈负相关。分析表明转变我国粗放的经济增长方式已经非常迫切,片面“做大”城市规模对提高城市的经济发展水平于事无补。 相似文献
109.
不等式作为数学的基本内容,同时最值问题又是不等式问题中一大热门考点,它可以与函数,图像,解析几何等知识紧密结合在一起,将问题变得复杂化,成为大多数初学者的一大难点.本文以具体题目为例,探究一种关于不等式题型的一种模式解题方法,归纳并总结了以圆锥曲线,向量,函数为背景的不等式问题,并且对每一道问题进行点评,总结,让读者建立起基本的不等式思维. 相似文献
110.