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81.
Context-aware computing is an exciting paradigm in which applications perceive and react to changing environments in an unattended manner. To enable behavioral adaptation, a context-aware application must dynamically acquire context data from different operating spaces in the real world, such as homes, shops and persons. Motivated by the sheer number and diversity of operating spaces, we propose a scalable context data management system in this paper to facilitate data acquisition from these spaces. In our system, we design a gateway framework for all operating spaces and develop matching algorithms to integrate the local context schemas of operating spaces into a global set of domain schemas upon which SQL-based context queries can be issued from applications. The system organizes the operating space gateways as peers in semantic overlay networks and employs distributed query processing techniques over these overlays. Evaluation results on a prototype implementation demonstrate the effectiveness of our system design. 相似文献
82.
Previous studies of call admission control (CAC) in mobile communication networks focused on call blocking and call dropping mechanisms. However, achieving global optimization of the system benefit is a complicated process. In this paper, we propose a benefit optimization model that accommodates as many users as possible, while simultaneously maintaining system-wide quality of service (QoS) in terms of admission control. To clarify the CAC concept, we construct a framework of CAC policies, derive associated interference models based on the framework, and then investigate the effects of the policies on the system benefit. In addition, to solve the complicated integer programming problem, we adopt the Lagrangean relaxation approach, and employ Lagrangean multipliers to perform sensitivity analysis of several parameters. The contribution of this study is twofold: the novel problem formulation and the improvement in the system benefit. The computational results demonstrate that the system accrues more benefit as new traffic is loaded and the number of users increases. Meanwhile, the sensitivity analysis shows that proper assignment of the strength of power-controlled signals is a key factor in the global optimization of the system benefit. 相似文献
83.
Jui-Pin Hung Ching-Yuan Lin Tzuo-Liang Luo 《Journal of Failure Analysis and Prevention》2011,11(6):684-692
The vibration analysis method has been widely used to detect faults in the components of a machine. For a linear positioning stage, its vibration characteristics are closely related to and affected by the preload of linear guides. To clarify the meaning of the vibration signals coming out from an abnormal machine, in this study we aimed to investigate the influence of a faulty linear guide on the vibration and acoustic characteristics of a positioning stage through experimental and finite element modeling approaches. Experimental measurements indicate that stages equipped with abnormal or damaged linear guides indeed exhibit different vibration behavior compared to stages with intact guides. According to finite element analysis, the variation in vibration characteristics can be attributed to the changes in the structural stiffness of linear guides because of rolling ball defects. This phenomenon was also found in the acoustic characteristics measured for stages under various preloaded conditions, providing further correlations between the variations in acoustic characteristics and changes in structural stiffness. The present results clearly show that faulty conditions of linear guides can be effectively detected by means of monitoring the vibration and acoustic characteristics of the stage. 相似文献
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A carbon-containing CoCrFeNi high entropy alloy (HEA) with heterogeneous structures was obtained through thermome-chanical treatments,which induced concurrent recrystallization and carbide precipitation in the alloy.A combination of high yield strength (556 MPa) and large uniform elongation (45%) was achieved in the investigated alloy.The enhancement of the strength is attributed to the combined effects of grain refinement,precipitation strengthening and microstructural het-erogeneity.Our work demonstrated that the heterogeneity design could be realized by thermomechanical processes,which provided a practical strategy for producing HEAs with high performance. 相似文献
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Self‐Crack‐Filled Graphene Films by Metallic Nanoparticles for High‐Performance Graphene Heterojunction Solar Cells 下载免费PDF全文
89.
A Thieno[3,2‐b][1]benzothiophene Isoindigo Building Block for Additive‐ and Annealing‐Free High‐Performance Polymer Solar Cells 下载免费PDF全文
90.
Fiber‐reinforced composite structures can be tailored to desire mechanical properties and to embed microstrip antenna in aerospace applications. The electromagnetic characteristics of a microstrip antenna on isotropic and uniaxial substrates have been known, but that embedded in composite laminated substrates remain unavailable to date. This work aims at analyzing the performance of microstrip antenna embedded in composite laminated substrates by spectral domain analysis. Parameter studies are conducted to investigate the effects of the substrate's dielectric constants, the fiber directions (the orientation between the antenna and the laminate layers), and the stacking sequence on antenna's resonant frequency and radiation pattern. The antenna size when embedded in composite laminated substrates is larger than that when attached on isotropic substrates, or conversely, the resonant frequency will deviate lower if assuming the substrate as isotropic. The far‐field pattern in composite laminated substrates is more ‘directional’ than that in isotropic substrates. The antenna gain in the substrates of symmetric stacking with ±45° fiber direction is 20 dB better than that in isotropic substrates in some elevations. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献