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排序方式: 共有347条查询结果,搜索用时 62 毫秒
1.
水下光通信充分利用了海水对激光的衰减窗口效应,具有隐蔽、安全、非接触和快速机动等特性,兼具无线通信和光纤通信的优点,其关键技术在于光收发端机的研制;PPM(Pulse Position Modulation)数字脉冲位置调制具有低平均功率和高峰值功率等特性,特别适合用于无线数字光通信。两者性能的融合需要高灵敏度数字光接收机的实现。利用阵列光电检测接收、高速A/D转换和信号处理等相关技术,采用DSP处理器,高灵敏度的数字光PPM接收机得以实现,实验和测试表明它大大降低了接收机对于整个系统信噪比的要求,获得了较好的性能。 相似文献
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AO Sheng-Mei YAN Jia-Ren 《理论物理通讯》2007,47(1):15-18
Three types of expression in the dark-soliton perturbation theory based on squared Jost solutions are invesgigaged in ghis paper. It is shown that there are three formally different results about the effects of perturbagion on a dark soliton, and it is proved by means of a transformation between two integral variables that they are essentially equivalent. 相似文献
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The examination of 19F chemical shifts for ca. 650 F-alkylated compounds of general formula CF3(CF2)nCF2X led to the following conclusions: the CF2 groups α to X are very sensitive to the nature of X, and are spread over a range of 85 ppm. The effect of the length of the F-alkyl chain decreases rapidly, so that δCF2(α) can already be considered as characteristic of X for n = 1 or 2 for most practical purposes. Solvent effects (in 9 different solvents having ε = 1.8 to 52.1) were found to be rather small except for the F-alkyl iodides. A chart which indicates the domain in which the CF2(α) resonance signal is to be expected is given for 42 different series of F-alkylated compounds; it is expected to provide the synthetic chemist with a useful tool for the identification and characterization of such compounds. 相似文献
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Santini Jr Richards AC Scheidt R Cima MJ Langer R 《Angewandte Chemie (International ed. in English)》2000,39(14):2396-2407
Controlled-release systems are common in a number of product areas, including foods, cosmetics, pesticides, and paper. Microencapsulated systems, for example, are used for the release of flavors and vitamins in foods, fragrances in perfumes, and inks in carbonless copy paper. Controlled-release systems for drug delivery first appeared in the 1960s and 1970s. In the past three decades, the number and variety of controlled release systems for drug-delivery applications has increased dramatically. Many of these use polymers having particular physical or chemical characteristics such as biodegradability, biocompatibility, or responsiveness to pH or temperature changes. However, recent advances in the field of microfabrication have created the possibility of a new class of controlled-release systems for drug delivery, namely, that of small, programmable devices. Their small size, potential for integration with microelectronics, and ability to store and release chemicals on demand could make controlled-release microchips useful in a number of areas, including medical diagnostics, analytical chemistry, chemical detection, industrial process monitoring and control, combinatorial chemistry, microbiology, and fragrance delivery. More importantly, drug-delivery microchips resulting from this convergence of controlled release and microfabrication technologies may provide new treatment options to clinicians in their fight against disease. 相似文献
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A series of new polyfluorinated dienes 3, containing the novel -CFCHCHCF-, pattern has been synthesized (50–70% yields) by reacting perfluoroalkyl iodides with perfluoroalkyl-ethylenes in the presence of copper. The monoalkenes RfCFCHCH2CF2R′f and the saturated compounds RfCF2CH2CH2CF2R′f were obtained by varying the experimental conditions. The 1H and 19F NMR spectra are analysed and the reaction mechanism is discussed. 相似文献