共查询到20条相似文献,搜索用时 421 毫秒
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针对激光晶体生长后期晶体生长炉温度上漂导致晶体不能维持等径生长的问题,采用一种基于自适应学习率优化算法改进BP神经网络与经典PID控制技术相结合的方法应用到晶体生长控制过程中,通过改进的BP神经网络的自学习以及调整加权系数,实现一种由BP神经网络整定的最佳PID控制.通过MATLAB/Simulink仿真对比表明,改进的BP神经网络PID控制算法较传统PID控制方法具有较好的控制性能和鲁棒性,能够有效克服晶体生长炉的温漂问题,更好地保持晶体等径生长,提高了控制精度. 相似文献
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大尺寸氟化物晶体的生长是基于对晶体炉热交换的实验研究和计算结果,在晶体生长过程的不同阶段解决了复杂结构生长容器的边界条件和温场的二维计算任务.我们在这里给出了晶体生长过程中温场设置和转变的具体数据.所有的计算都是根据晶体、熔体,容器材料的光学特性与光谱和温度的关系以及它们的热物理值与温度的关系做出的.这些结果包括了迄今有关氟化物晶体生长系统和过程的最精确的数据,可用于生长技术工艺的发展以及晶体生长炉和容器的设计. 相似文献
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本文建立了一个二维全局模型对120 KG单晶硅炉的热系统进行了数值模拟.通过对温场的单独模拟以及温场流场的耦合模拟得到了不同模型下晶体生长所需要的功率,并将两组模拟值与实验数据进行对比得到了加入流体流动后系统所产生的功率损耗.同时对晶体生长过程的分阶段模拟得到了晶体生长过程热系统温度分布的变化规律以及熔体流动的变化规律.结果显示,在整个晶体生长过程中流体流动所产生的功率损耗占实际功率的21.6;左右. 相似文献
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Crystallography Reports - A technique of temperature-controlled biocrystal nucleation, at which the growth onset of one crystal suppresses the development of other nuclei, is proposed. This is... 相似文献
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The thermal variant of the classical nucleation‐growth‐separation principle is shown, both theoretically and experimentally, to be a reliable tool for studying protein crystal nucleation. The classical nucleation theory is used to elucidate the temperature dependence of crystal nucleus size. A one‐to‐one ratio of the number density of nuclei formed to crystals grown to visible size is achieved using the nucleation‐growth‐separation method. The experiments conducted in such a way show that new nuclei are prevented from appearing while avoiding any crystal loss due to dissolution. The same method is used to study experimentally the interval of growth temperatures where the number density of (nucleated) crystals is relatively insensitive to the growth temperature. It is argued that this temperature interval corresponds to the width of the so‐called metastable zone. 相似文献
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在分析了单晶锗片低温抛光工艺的基础上,进行了四种不同参数的单晶锗片低温抛光实验.分析了不同温度条件下,单晶锗片去除速率的变化原因,提出了基于醚类辅助抛光液的自锐型低温抛光工艺,为冰冻固结磨料抛光单晶锗片的研究开辟了新途径.结果表明:环境温度对冰冻固结磨料抛光盘表层融化速率影响显著,10℃时即会导致融化过快;抛光区域摩擦产生的热量小于环境温度-10℃时的对流换热,会导致冰盘表面二次凝固;环境温度-10℃时加入醚类辅助抛光液可实现冰盘在低温下的自锐性. 相似文献
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为了研制低温高硬度熔块釉配方,确定了R2O-RO-Al2O3-SiO2-B2O3低温系熔块釉配方,在此基础上,做4因素3水平的正交试验.通过灰熔点测试仪、压力试验机、XRD、SEM、维氏硬度仪等测试手段,研究9个R2O-RO-Al2O3-SiO2-B2O3系熔块釉烧成过程、物相组成、微观结构和釉面硬度.结果表明:以抗折强度和维氏硬度两个指标为基准,通过综合评分法对釉配方进行比较评分,6号釉配方的综合性能最优,熔融温度为865 ℃,抗折强度为79 MPa,维氏硬度为6006 MPa.通过4号和6号釉配方制得的釉浆来包裹支撑剂填充多孔砖,透水砖试样性能远远超过所规定的标准,性能优异,抗压强度分别为57 MPa,54.5 MPa,耐磨性即磨坑长度分别为21 mm,24 mm. 相似文献
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We report the results of measurement and analysis of the electrical conductivity of two synthetic highly purified copolymers of the polyacene quinone radical (PAQR) type. The dc conductivity was examined as a function of temperature and pressure. The conductivity-pressure relation is observed to go as log σ versus . The conductivities under moderate pressure (400–5000 atm) show linear relationships on log σ versus plots in the temperature range 70 K < T < 300 K. The possible interpretations as variable range hopping or as nearest neighbour hopping with distributions of activation energies are discussed. 相似文献
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The temperature coefficient of refractive index dn/dT and that of volume expansion β have been measured by an interferometric procedure designed to determine the coefficients simultaneously, with one sample. The temperature coefficient of electronic polarizability φ have been calculated from dn/dT and β. φ is expressed as the sum of the contributions of each glass component, φi·φi is expressed as follows: φi = ßiγi, where ßi is the thermal change in cation-oxygen distance and γi is the change in electronic polarizability due to the inter-ionic distance change. φi decreases as the ionic field strength z/a2 of the cation increases, which is the same tendency as that of ßi. γi, calculated from φi and ßi, gradually increases as z/a2 increases. This means that φi is mainly determined by the elongation of the inter-ionic distance, and it also suggests that the deformation of the electron cloud of oxygen ion due to the inter-ionic distance change, γi becomes larger, as the electronic polarizing power of the cation increases. 相似文献
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J. Linhart 《Crystal Research and Technology》2002,37(8):849-867
This article is devoted theoretical and experimental researches of temperature fields which are formed in area semi‐transparent, diffusely transmitting and scattering boundary of two optical environments. It is revealed, that thus can arise non‐monotonic or at certain conditions completely an inverse temperature field. The phenomenon of inversion of a stationary temperature field is revealed theoretically and subsequently is experimentally confirmed. The specific conditions of occurrence of the phenomenon of inversion are determined. During the crystal growth process behind the front of crystallization there can be a congestion of impurities or micro‐bubbles which are grasped by the moving front of crystallization. It results in occurrence diffusely transmitting and scattering boundary on which the radiating thermal flux going from the melt is dissipated in a growing crystal. In turn under the certain conditions it could result in non‐monotonic of temperature field in area of phase boundary and even in full inversion. The experimental equipment was developed and results of experimental measurements which completely confirm theoretical conclusions are given. The described phenomenon could be meet in growing of such optical crystals as sapphire, ruby, fluorides etc. It is specified, that the similar conditions can arise as well on boundary of solid‐gas and liquid‐gas. 相似文献
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Crystallography Reports - A mathematical model has been developed and numerical calculations of lysozyme protein crystallization from a homogeneous aqueous solution under temperature field control... 相似文献