排序方式: 共有14条查询结果,搜索用时 15 毫秒
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The performance requirements of a RF receiver for a packet division multiple access technology (PDMA) terminal and the corresponding calculations under the true PDMA signal excitations are presented in the paper. The output signal-to-noise power ratio, the reference receiving sensitivity, the maximum input RF power and the dynamic range, the out-of-channel selectivity and the third-order inter-modulation/cross-modulation characteristics are all analyzed for the PDMA terminal RF receiver in detail. And a feasible indirect method for obtaining the output noise power-spectrum-density of the terminal transmitter by measuring transceiver noise figure is also presented. 相似文献
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对聚酰亚胺的性能及应用领域作了简要介绍,并着重对四种重要的聚酰亚胺单体二酐(均苯四甲酸二酐,联苯四甲酸二酐,单醚四甲酸二酐,三苯双醚四甲酸二酐)的合成方法进行了综述。 相似文献
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Haiqing Li Johnson V. John Seong Jin Byeon Min Seon Heo Jun Hak Sung Kwang-Ho Kim Il Kim 《Progress in Polymer Science》2014
Controlled accommodation of metal nanostructures (MNSs) into the matrix of a well-defined polymer architecture offers an effective approach to achieve hierarchically structured nanocomposites with tunable synergistic properties to broaden application potentials in the emerging fields of energy, environmental science, and medicine. This review focuses on the recently developed zero-dimensional and one-dimensional MNSs@polymer hybrid nanostructures obtained by solution-based synthetic strategies. Progress in the controlled synthesis of those hybrid nanostructures in terms of the number (e.g., monomer, dimer and trimer), organization manner (e.g., linear alignment or confined assembly in certain domains), and spatial arrangement (e.g., in the core and shell) of the MNSs within the distinct polymer matrices are detailed. The synergistic properties and potential applications of those MNSs@polymer hybrids associated with their compositions and morphologies are also reviewed. 相似文献
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在认知无线网络中,主用户与认知用户要求在频率选择性衰落信道下与它们各自相应的接收机进行同时通信.主用户与认知用户之间的干扰必须尽可能消除以实现两者的频谱共享.本文提出了认知正交频分复用(OFDM)中采用Vandermonde预编码的预编码多址接入(PDMA)策略,它有效利用认知信道的频率选择性构成频率波束成型器.在主用户干扰受限和最优功率分配策略下,采用Vandermonde预编码可使认知用户达到高比特传输率.理论推导过程均采用数值计算与仿真得到证明.数值计算与仿真结果表明,最优输入功率分配策略可使认知用户对主用户不产生干扰的前提下获得可达比特传输率(ABR).同时,数值仿真验证了理论推导过程.在认知无线网络中,采用Vandermonde预编码器构成PDMA,认知用户接收机信噪比与主用户目标速率均可以显著影响认知用户的可达比特率. 相似文献
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Mehmet Atilla TasdelenMuhammet U. Kahveci Yusuf Yagci 《Progress in Polymer Science》2011,36(4):455-567
Telechelic polymers, defined as macromolecules that contain two reactive end groups, are used as cross-linkers, chain extenders, and important building blocks for various macromolecular structures, including block and graft copolymers, star, hyperbranched or dendritic polymers. This review article describes the general techniques for the preparation of telechelic polymers by living and controlled/living polymerization methods; namely atom transfer radical polymerization, nitroxide mediated radical polymerization, reversible addition-fragmentation chain transfer polymerization, iniferters, iodine transfer polymerization, cobalt mediated radical polymerization, organotellurium-, organostibine-, organobismuthine-mediated living radical polymerization, living anionic polymerization, living cationic polymerization, and ring opening metathesis polymerization. The efficient click reactions for the synthesis of telechelic polymers are also presented. 相似文献
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对二维对流扩散问题,应用延迟修正-TDMA和ADI-PDMA方法,求解对流项采用QUICK,CD格式的离散方程。通过SIMPLER算法求解二维移动顶盖驱动方腔内不可压缩流体流动和方腔内自然对流换热。比较了采用延迟修正-TDMA和ADI-PDMA两种求解代数方程组的性能,分析了影响上述两种方法求解速度、收敛的因素。在相同的条件下,通过计算证明了延迟修正-TDMA的健壮性强、精度较高、收敛速度较快。 相似文献
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Andrew GregoryMartina H. Stenzel 《Progress in Polymer Science》2012,37(1):38-105
Reversible addition fragmentation chain transfer (RAFT) polymerization has made a huge impact in macromolecular design. The first block copolymers were described early on, followed by star polymers and then graft polymers. In the last five years, the types of architectures available have become more and more complex. Star and graft polymers now have block structures within their branches, or a range of different branches can be found growing from one core or backbone. Even the synthesis of hyperbranched polymers can be positively influenced by RAFT polymerization, allowing end group control or control over the branching density. The creative combination of RAFT polymerization with other polymerization techniques, such as ATRP or ring-opening polymerization, has extended the array of available architectures. In addition, dendrimers were incorporated either as star core or endfunctionalities. A range of synthetic chemistry pathways have been utilized and combined with polymer chemistry, pathways such as ‘click chemistry’. These combinations have allowed the creation of novel structures. RAFT processes have been combined with natural polymers and other naturally occurring building blocks, including carbohydrates, polysaccharides, cyclodextrins, proteins and peptides. The result from the intertwining of natural and synthetic materials has resulted in the formation of hybrid biopolymers. Following these developments over the last few years, it is remarkable to see that RAFT polymerization has grown from a lab curiosity to a polymerization tool that is now been used with confidence in material design. Most of the described synthetic procedures in the literature in recent years, which incorporate RAFT polymerization, have been undertaken in order to design advanced materials. 相似文献
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设计了一种用于测试SDRAM的可编程直接存储器存取控制模块(PDMA),把设计的PDMA作为IP软核,在基于PCI环境的RTL仿真平台上进行功能仿真、综合并将结果下载到PFGA上,建立基于FPGA的测试平台进行硬件测试验证。结果表明,板上PDMA工作频率66MHz,达到快速访问的设计要求。PDMA仿真了多个IP与SDRAM的数据交换,并且建立在通用的PCI环境下。因此本设计方法和建立的仿真测试环境可用于不同的IP,是解决不同IP开发中十分重要的仿真测试方案,大大缩短了IP开发的测试和验证的时间,对于发展IP软核有重要意义。 相似文献