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近年来,深水探测中水下通讯节点的小型化、低功耗成为设计的难点。在水声通信中,普遍使用正弦脉宽调制(Sinusoidal Pulse Width Modulation, SPWM)信号驱动功率放大器进行工作。传统SPWM产生系统电路复杂度高,针对SPWM生成原理和电路实现,提出基于脉冲采样的SPWM生成方法,并进行性能分析;基于数字处理器设计了高能效SPWM发生系统,在保证SPWM信息损失较小的同时,减小硬件电路面积。实验结果表明,提出的高能效脉冲采样法与SPWM发生系统可以满足工程应用。 相似文献
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水下声信标信号检测是搜寻黑匣子的重要技术之一。针对水下声信标信号声源级低、脉冲宽度窄所带来的检测难题,充分利用声信标信号周期短、相邻脉冲信号相关性强等特点,提出了一种基于多脉冲积分的改进匹配滤波方法,通过前后脉冲匹配方法克服标准信号匹配处理中因信号畸变带来的匹配处理增益下降,通过多脉冲累积提高积分增益。通过仿真实验验证,当取多脉冲累积数为6时,在理想白噪声环境下,所提改进方法比传统单脉冲匹配滤波检测性能提高约4 dB,特别是在存在明显多普勒影响下,传统方法适应性下降,所提改进方法有9 dB的性能提高。通过对湖上实验数据的处理也验证了所提方法的有效性。 相似文献
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水声脉冲信号是由一个运动平台上的发射器发射的。信号的调制方式、载频、幅度、脉宽以及周期均为未知。该文介绍了一种水声脉冲信号检测的新方法。水声脉冲信号接收机输出的短时谱重心是不断起伏的。起伏在高信噪比时会变得很小,而在低信噪比(或无信号)时会变得很大。由于,起伏的绝对偏差移动平均可用来度量起伏的大小,因此,它可以被用来检测水声脉冲信号。还介绍了新检测方法的原理、算法以及仿真结果。在海洋噪声、运动载体的辐射噪声以及小的多途干扰背景中,该方法能可靠地检测水声脉冲信号,并能同时对信号的一些参数作出估计。 相似文献
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远距离水下声通信可以利用的频带很窄,因此,高速水声通信系统中通常采用相干数字通信技术。由于水下声通信信道具有时变多径严重、相位起伏快等特点,成功实现高速水声通信系统的关键是研究高效、强壮的锁相环与均衡器算法。本文介绍北京邮电大学信息学院研究设计的高速数字水声通信系统方案和实现算法,并给出对实测数据的处理结果。 相似文献
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研究了一种用多个不同频率的CW窄脉冲与帧同步脉冲的时延差携带信息的水声通信技术。该技术利用多个不同频率的CW矩形窄脉冲与帧同步CW矩形窄脉冲之间的时延值进行信息编码,在接收端采用时延估计和频率检测技术进行解码,从而使码元间距成为可携带信息的有用资源,将码元间距扩展到足够宽,既可有效地克服水声信号的多途影响、提高频带利用率,又可大大减少码元脉冲数量,达到节省能量并提高通信可靠性的目的。仿真结果表明,该水声通信编码体制数据传输速率适中,编码和解码简易,系统稳健。 相似文献
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为了满足水下航行体的大范围水下定位跟踪测试要求,针对基于座底式水声网络节点的跟踪测试技术进行深入研究。设计了一种紧凑型水声网络节点,该节点采用卧式安装结构,可通过水声或光电信号进行回收控制,具有结构轻便、布放效率高、回收可靠等特点。利用该水声网络节点,串行布放在某水域组成座底式长基线跟踪测试系统,该系统具备定位跟踪、航行参数遥测等功能。针对其定位跟踪及航行参数遥测功能进行湖上跑船试验,试验结果证明,该系统定位跟踪精度高,航行参数遥测功能可靠,遥测误码率低,总体覆盖范围大,可广泛应用于水下航行体的定位跟踪、导航测试等,具有较高的工程实用价值。 相似文献
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A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils. 相似文献
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The end of over unit products of more than Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits beer wine yellow wine fruit syrup wine others cover over % of the national top-branded liquor products.…… 《中国标准化(英文版)》2008,25(1):30
The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.…… 相似文献
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Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster. 相似文献
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N.A. Odintsova N.V. Ageenko K.V. Kiselev N.M. Sanina E.Y. Kostetsky 《International Journal of Refrigeration》2006,29(3):387
We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes. 相似文献
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David R. Smith F. R. Fickett 《Journal of research of the National Institute of Standards and Technology》1995,100(2):119-171
Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability. 相似文献
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Fco. Javier Franco Pérez Marc Gener Moret 《Materials and Manufacturing Processes》2017,32(7-8):876-884
ABSTRACTThe production of iron in Biscay (Basque Country, Spain) has been a hallmark of this territory of the North of the Iberian Peninsula throughout its history. The Archaeology team of the Basque Country Mining Museum has spent 13 years, so far, studying the origins of this activity through the evidences left at the old pre-hydraulic iron production workshops known as mountainside ironworks (ferrerías de monte) or haizeolak. It has catalogued 170 archaeometallurgical sites of this type in Biscay, and the archeological excavation of some of them has led to the knowledge of the different stages of the production process that took place in these workshops. The team has also experimentally reproduced the work carried out in a mountainside ironworks from the High Middle Ages, and it has currently started the characterization process of this type of activity through the study of the collected materials. 相似文献
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As demands about environment protection are growing up, dry cutting technology is getting more and more concerns from all over the world. Main works performed here are study on dry cutting performances and wear mechanisms of M2high-speed steel (HSS) twist drills with CrAlTiN multicomponent coatings, which was deposited using magnetron sputter ion plating system, in drilling 45 and 30CrMnSiA steel, and their comparisons to those in drilling the same steel but using monolayer CrN and commercial TiN coated drills. Drilling performances of drills are evaluated mainly through the measurements of width on outer corner flank land and the cutting forces. Results show that performances of CrAlTiN coated drills are better than those of monolayer CrN and TiN coated drills. In drilling 45 and 30CrMnSiA steel, the average tool life of the CrAlTiN coated drills are 17.2 and 11.8 times higher than those of the uncoated drills. Observing wear of the drill with scanning electronic microscope, results show that there is no crack or spallation of the CrAlTiN coatings in wear zones. Main mechanism of the wear here is adhesion. 相似文献
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Arc spraying coatings are widely used in various applications, but uncommon in cast iron substrate. Different surface pretreatment technology is tested on substrates of gray cast iron. Surface roughness and residual stress were measured by TR200 and X-ray diffraction analyzer. Influence of different surface pretreatment methods ( dry blasting and fusebond) on roughness and residual stress was analyzed. The arc-sprayed coatings of wire 3Cr13 (φ2mm) on gray cast iron substrate is studied. The microstructure and interface of bonding layer were observed by SEM. The bond strength was taken by tensile test. Results show that bond strength with grit blasting is higher than fuse-bond; it is feasible to make wire 3Cr13 coating with arc spraying on cast iron substrate roughened by grit blasting. 相似文献
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TiO2 ceramic coatings with thickness of 20 μm were formed on the surface of pure titanium by micro-plasma oxidation. Their micro-structures were investigated by by using X-ray diffraction and their surface images were detected by using scan electronic microscope. There were three kinds of TiO2 coatings, pure anatase type TiO2 phase, mixed phases consisted of rutile type TiO2 phase and anatase type TiO2 phase, pure rutile type TiO2 phase. The coating surface with the pure anatase type TiO2 phase is rough, while the coating surface with the pure rutile type TiO2phase is smooth. The upper coating surface with the mixed type TiO2 phases is anatase type TiO2 structure and the subsurface of the TiO2 coating is rutile type TiO2structure. 相似文献
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R. Owsiński S. Kamiński M. Szymaniec A. Niesłony T. Łagoda 《Materialwissenschaft und Werkstofftechnik》2015,46(10):1059-1067
The insightful discussion of the relationship between the construction of metallographic and fatigue life and proposition of mathematical relationships describing this relationship was conducted in the paper. This paper presents a method for estimating the fatigue life, based on the construction of the microstructural material taking into account the grain size and the participation of ferrite and pearlite phase. 相似文献