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排序方式: 共有284条查询结果,搜索用时 15 毫秒
1.
介绍了开发的全数字交流伺服系统的组成、基本原理及软、硬件结构。通过与模拟交流伺服系统的比较,说明了全数字交流伺服系统可编程能力强、系统稳定性好、系统性能提高等特点。 相似文献
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The preparation of a SiC coating on a carbon fiber surface using a sol-gel mixture of tetraethyl orthosilicat (TEOS) and phenolic resin was studied. FTIR and SEM investigations indicated that the SiC coating can be formed by carbothermal reduction of the sol-gel mixture at 1420°C for 15–20 min in an argon atmosphere. TGA of the coated fiber was also performed, showing that the SiC coating improves the thermooxidative stability of the carbon fiber. With the thickness of the obtained coating of 0.47 μm using a C/Si ratio of 4, this treatment does not affect the carbon fiber strength. 相似文献
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The effect of different organoclays and mixing methods on the cure kinetics and properties of epoxy nanocomposites based on Epon828 and Epicure3046 was studied. The two kinds of organoclay used in this study, both based on natural montmorillonite but differing in intercalant chemistry, were I.30E (Nanomer I.30E—treated with a long‐chain primary amine intercalant) and C.30B (Cloisite 30B—treated with a quaternary ammonium intercalant, less reactive with epoxy than the primary amine). The two mixing processes used to prepare the nanocomposites were (i) a room‐temperature process, in which the clay and epoxy are mixed at room temperature, and (ii) a high‐temperature process, in which the clay and epoxy are mixed at 120°C for 1 h by means of mechanical mixing. The nanocomposites were cured at room temperature and at high temperature. The quality of dispersion and intercalation/exfoliation were analyzed by scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction. The heat evolution of the epoxy resin formulation and its nanocomposite systems was measured using differential scanning calorimetry at different heating rates of 2.5, 5, 10, 15, and 20°C min?1. The cure kinetics of these systems was modeled by means of different approaches. Kissinger and isoconversional models were used to calculate the kinetics parameters while the Avrami model was utilized to compare the cure behavior of the epoxy systems. The cure kinetics and mechanical properties were found to be influenced by the presence of nanoclay, by the type of intercalant, and by the mixing method. POLYM. ENG. SCI., 47:649–661, 2007. © 2007 Society of Plastics Engineers. 相似文献
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Dan Chen Roland Ewald Georgios K. Theodoropoulos Ton Oguara Brian Logan 《Journal of Systems and Software》2008,81(12):2345-2360
Distributed simulation has emerged as an important instrument for studying large-scale complex systems. Such systems inherently consist of a large number of components, which operate in a large shared state space interacting with it in highly dynamic and unpredictable ways. Optimising access to the shared state space is crucial for achieving efficient simulation executions. Data accesses may take two forms: locating data according to a set of attribute value ranges (range query) or locating a particular state variable from the given identifier (ID query and update). This paper proposes two alternative routing approaches, namely the address-based approach, which locates data according to their address information, and the range-based approach, whose operation is based on looking up attribute value range information along the paths to the destinations. The two algorithms are discussed and analysed in the context of PDES-MAS, a framework for the distributed simulation of multi-agent systems, which uses a hierarchical infrastructure to manage the shared state space. The paper introduces a generic meta-simulation framework which is used to perform a quantitative comparative analysis of the proposed algorithms under various circumstances. 相似文献
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Ton HellingsJohan S.H. van Leeuwaarden Sem C. Borst Dee Denteneer 《Performance Evaluation》2011,68(8):728-746
CSMA is the predominant distributed access protocol for wireless mesh networks. Originally designed for single-hop settings, CSMA can exhibit severe performance problems in multi-hop networks in terms of stability and end-to-end throughput. To ensure a smoother flow of packets, we examine an enhancement referred to as Extra Back-off (EB) flow control. In this enhanced scheme a node remains silent for a certain extra back-off time (imposed on top of the usual back-off time that is part of CSMA) after it has transmitted a packet, to give both the downstream and upstream neighbors the opportunity to transmit. EB flow control entails only a small modification to CSMA, preserving its distributed character. In order to examine the performance of EB flow control, we analyze a novel class of Markov models at the interface between classical tandem queues and interacting particle systems. The results demonstrate that EB flow control provides an effective mechanism for improving the end-to-end throughput performance. 相似文献
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Varghese B Rajan V Van Leeuwen TG Steenbergen W 《The Review of scientific instruments》2007,78(12):126103
The performance of a graded index multimode fiber optic low coherence Mach-Zehnder interferometer with phase modulation is analyzed. Investigated aspects were its ability to measure path length distributions and to perform path length resolved Doppler measurements of multiple scattered photons in a turbid suspension of particles undergoing Brownian and translational motion. The path length resolution of this instrument is compared with a system using single mode fibers for illumination and detection. The optical path lengths are determined from the zero order moment of the phase modulation peak in the power spectrum. The weighted first moment, which is equal to the average Doppler shift, shows a linear response for different mean flow velocities within the physiological range. 相似文献
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Solvatochromic merocyanine dyes were immobilized onto polymer surfaces and copolymerized with acrylic resins, yielding novel reversibly solvatochromic polymers, which were used as solvent polarity indicators that exhibited different colors in water and alcohols. To generate solvatochromic polymer for solvent polarity indication, two solvatochromic merocyanine dyes containing moieties, which allow their immobilization onto polymer surfaces, or copolymerization with acrylic and vinyl monomers, were sequentially synthesized in four and six steps. Merocyanine dye (E)‐2‐(2‐(1‐(6‐aminohexyl)pyridinium‐4‐yl)vinyl)‐4,6‐dichlorophenolate (AHPVD) was prepared with a terminal aminohexyl group which allowed covalent bonding to activated carboxylated or sulfonated polymeric materials. The dyes were covalently bonded to the polymer surfaces, such as, nylon, polycarbonate, polyethylene terephthalate, and silicone. Solvatochromic merocyanine dye (E)‐2‐(2‐(1‐(6‐acrylamidohexyl)pyridinium‐4‐yl)vinyl)‐4,6‐dichlorophenolate (AAPVD) was synthesized for radical copolymerization with acrylate and vinyl monomers and oligomers. Side‐chain solvatochromic merocyanine‐containing hydrophilic polymers with differential water and alcohol absorption were obtained upon photoinitiated radical copolymerization with specially formulated acrylated resins. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44451. 相似文献
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The use of PET bottles for packaging soft drinks and mineral waters is still growing world wide. The production process for these bottles is improving constantly. These improvements are focussed on bottles with better barrier properties, higher inertness and higher heat stability. One of the factors determining the quality of PET bottles is the release of acetaldehyde into the product during storage. A literature survey was conducted on the odour and taste detection threshold of acetaldehyde in water. A method is described to rapidly determine the concentration of acetaldehyde in water up to a level of 1 μg/l. This method was used to determine the concentration of acetaldehyde in mineral water during storage in PET bottles. In still water no acetaldehyde could be found, whereas the concentration of acetaldehyde in carbonated mineral water increased steadily upon storage. Model experiments were performed to find an explanation. 相似文献