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61.
先从介绍信息组织的方式与方法入手,提出了从网上一次信息、二次信息、三次信息的角度探讨网络信息组织方式的特点:一次信息组织方式有自由文本方式、数据库方式、超文本方式、主页方式:二次信息组织方式有搜索引擎方式、指示数据库方式、菜单方式、主题树方式;三次信息组织方式有元搜索引擎等方式。最后介绍了网络信息组织的新成果及其发展方向。 相似文献
62.
Muhammad Qadeer Sharif Pingzhi Fan 《中国电子科技》2007,5(2):97-101
This paper presents an efficient dynamic spectrum allocation (DSA) scheme in a flexible spectrum licensing environment where multiple networks coexist and interfere with each other. In particular, an extension of virtual boundary concept in DSA is proposed, which is spectrally efficient than the previous virtual boundary concept applied to donor systems only. Here, the same technique is applied to both donor and rental systems so as to further reduce the occurrences where the insertion of guard bands is obligatory and as a result provides better spectral efficiency. The proposed extension improves the spectrum utilization without any compromise on interference and fairness issues. 相似文献
63.
Yasushi Ishido Arihiro Kanazawa Shokyoku Kanaoka Sadahito Aoshima 《Journal of polymer science. Part A, Polymer chemistry》2013,51(21):4684-4693
Side group structures of aldehydes were demonstrated to have decisive effects on cationic copolymerizations with alkyl vinyl ether (VE). Alternating copolymerizations of isobutyl VE (IBVE) and plant‐derived aldehydes with acyclic side chains such as trans‐2,cis‐6‐nonadienal, trans‐2‐nonenal, and citral proceeded under appropriate reaction conditions with the EtSO3H/GaCl3 initiating system. In addition, some aldehydes copolymerized in a well‐controlled fashion to yield alternating copolymers with controlled molecular weights and narrow molecular weight distributions. Quantitative and selective acid hydrolysis of the resulting alternating copolymers, based on the acetal structures in the main chains, was also achieved to give other conjugated aldehydes as nearly sole degradation products. Copolymerization results of IBVE and various plant‐derived aldehydes with acyclic or cyclic side groups suggested that electron‐donating ability and bulkiness of the side groups were most likely responsible for the alternating and/or controlled copolymerization behaviors. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4684–4693 相似文献
64.
Jifu Wang Kejian Yao Andrew L. Korich Shigeng Li Shuguo Ma Harry J. Ploehn Peter M. Iovine Chunpeng Wang Fuxiang Chu Chuanbing Tang 《Journal of polymer science. Part A, Polymer chemistry》2011,49(17):3728-3738
Rosin polymer–grafted lignin composites were prepared via “grafting from” atom transfer radical polymerization (ATRP) with the aid of 2‐bromoisobutyryl ester‐modified lignin as macroinitiators. Three different monomers derived from dehydroabietic acid (DA) were used for execution of grafting from ATRP, while DA was separately attached onto lignin by a simple esterification reaction. Kinetic studies indicated controlled and “living” characteristics of all monomer polymerizations. Thermal studies indicated that rosin polymer–grafted lignin composites exhibited glass transition temperatures in a broad temperature range from ~20 to 100°C. The grafting of both DA and rosin polymers significantly enhanced hydrophobicity of lignin. Static contact angle measurement of water droplets showed ~90° for all these rosin modified lignin composites. X‐ray photoelectron spectroscopy demonstrated that the surface of rosin–lignin composites was dominated with chemical compositions originating from the hydrocarbon rich rosin moiety. The impartation of hydrophobicity of rosin into lignin provided excellent water resistance of this class of renewable polymers, as all rosin‐modified lignin composites showed water uptake below 1.0 wt %. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
65.
Qiang Peng Xiangju Liu Yuancheng Qin Dan Zhou Jun Xu 《Journal of polymer science. Part A, Polymer chemistry》2011,49(20):4458-4467
A new series of low‐bandgap copolymers based on electron‐accepting thieno[3,4‐b]pyrazine (TPZ) and different electron‐donating aza‐heteroaromatic units, such as carbazole (CZ), dithieno[3,2‐b:2′,3′‐d]pyrrole (TPR) and dithieno[3,2‐b:2′,3′‐e]pyridine (TPY), have been synthesized by Suzuki or Stille coupling polymerization. The resulting copolymers were characterized by NMR, elemental analysis, gel permeation chromatography, thermogravimetric analysis, and differential scanning calorimetry. UV–vis absorption and cyclic voltammetry measurements show that TPZ‐based copolymer with TPR has the best absorption due to the strongest intramolecular charge transfer effect and smallest bandgap. The basic electronic structure of D‐A model compounds of these copolymers were also studied by density functional theory (DFT) calculations. The conclusion of calculation agreed also well with the experimental results. The polymer solar cells (PSCs) based on these copolymers were fabricated with a typical structure of ITO/PEDOT:PSS/copolymer:PC71BM/Ca/Al under the illumination of AM 1.5G, 100 mW cm?2. The performance results showed that TPZ‐based copolymer with TPR donor segments showed highest efficiency of 1.55% due to enhanced short‐circuit current density. The present results indicate that good electronic, optical, and photovoltaic properties of TPZ‐based copolymers can be achieved by just fine‐tuning the structures of aza‐heteroaromatic donor segments for their application in PSCs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
66.
Robert Quintana Antxon martínez de Ilarduya Abdelilah Alla Sebastián Muñoz‐Guerra 《Journal of polymer science. Part A, Polymer chemistry》2011,49(10):2252-2260
Three series of terephthalate polyesters (copolyesters and terpolyesters) containing 70, 80, and 90 mol % of ethylene glycol respectively, 1,4‐cyclohexanedimethanol (CHDM) and isosorbide in varying ratios, were synthesized by melt polycondensation. It was found that only ~75 mol % of the feeding isosorbide was incorporated in the resulting polyesters and that their content in diethylene glycol oscillated between 2 and 4 mol %. The polyesters had weight‐average molecular weights in the 25,000–33,000 g mol?1 range and polydispersities between 2 and 2.5. The combined 1H and 13C NMR analysis revealed that the microstructure of all these polyesters was at random. They showed good thermal stability with decomposition temperatures above 400 °C. Their glass‐transition temperatures were observed to increase with the content in cyclic diols, this effect being more pronounced when isosorbide was the replacing comonomer. Only the series containing 90 mol % of ethylene terephthalate units was able to crystallize upon cooling from the melt. Compared isothermal crystallizations revealed that isosorbide was more effective than CHDM in repressing the crystallizability of PET. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
67.
Andreia F. Sousa Alessandro Gandini Armando J. D. Silvestre Carlos Pascoal Neto José J. C. Cruz Pinto Christer Eckerman Bjarne Holmbom 《Journal of polymer science. Part A, Polymer chemistry》2011,49(10):2281-2291
This article reports the successful synthesis and characterization of two types of completely biobased polymers prepared by the polycondensation or polytransesterification of suberin fragments, isolated by different procedures and from two different vegetable sources. These polymerizations were conducted with different experimental conditions in terms of the type of catalyst, the reaction medium and temperature, as well as the molar ratio between the reactive moieties. The ensuing linear or partly crosslinked polyesters were characterized by conventional spectroscopic techniques, SEC, DSC, XRD, DMA, and TGA. These hydrophobic materials represent an original contribution to the growing field of polymers from renewable resources. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
68.
高校人力资源管理中的模糊综合评判 总被引:6,自引:0,他引:6
人力资源管理是高校管理的重要组成部分。本简要介绍了高校人力资源的状况,讨论了模糊综合评判理论在人力资源管理中的应用。 相似文献
69.
An effective ant colony optimization algorithm (ACO) for multi-objective resource allocation problem (MORAP) 总被引:3,自引:0,他引:3
The multi-objective resource allocation problem (MORAP) addresses the important issue which seeks to find the expected objectives by allocating the limited amount of resource to various activates. Resources may be manpower, assets, raw material or anything else in limited supply which can be used to accomplish the goals. The goals may be objectives (i.e., minimizing costs, or maximizing efficiency) usually driven by specific future needs. In this paper, in order to obtain a set of Pareto solution efficiently, we proposed a modified version of ant colony optimization (ACO), in this algorithm we try to increase the efficiency of algorithm by increasing the learning of ants. Effectiveness and efficiency of proposed algorithm was validated by comparing the result of ACO with hybrid genetic algorithm (hGA) which was applied to MORAP later. 相似文献
70.
针对Ad Hoc网络特点,提出基于发布订阅机制实现信息高效分发的方案和架构,并结合网络资源受限等因素,提出了高效利用网络资源的QoS控制和多点递送等关键技术解决方案。通过仿真分析,该方案可以大幅提升Ad Hoc网络资源利用率。 相似文献