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31.
采用荧光光谱和荧光寿命技术研究了温度对奶粉荧光特征的影响.通过比较奶粉与酪蛋白、乳糖及维生素的荧光光谱,确定了奶粉的荧光主要来自酪蛋白的贡献.随着温度的升高,奶粉和酪蛋白的荧光强度减小,其中幼儿配方奶粉和成人普通奶粉的荧光强度随温度升高减小的趋势基本相同,而婴儿配方奶粉的荧光强度随温度的升高出现了一个相对变化缓慢的平台区,酪蛋白的荧光强度随温度升高呈缓慢下降的趋势,下降的速度比奶粉的要缓.酪蛋白加热到90℃然后冷却至25℃,荧光强度部分恢复,说明一部分蛋白质的结构变化或者荧光基团的活性变化是可逆的.测量了不同温度下奶粉和酪蛋白的荧光寿命.奶粉和酪蛋白的荧光寿命曲线在双指数拟合之后,都有两个寿命,这两个寿命可能来自于色氨酸和苯丙氨酸.随着温度的升高,奶粉和酪蛋白的两个荧光寿命都减小. 相似文献
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33.
Trivalent osmium ions are substitutionally incorporated into aqueous precipitates and melt-grown single crystals of AgBr and AgC1. The ions are distributed between three structurally inequivalent lattice sites in both salts. From epr studies, we have inferred that these sites are distinguished by the arrangement of charge-compensating silver ion vacancies in the two closest cation subshells. The most reasonable dopant-vacancy configurations have been deduced from the epr data. These configurations persist up to at least 300 K, and are compared with those observed in other trivalent metal ion doped systems. 相似文献
34.
《International Journal of Polymer Analysis and Characterization》2012,17(5):437-453
Abstract A polystyrene-grafted polypropylene sample was prepared by solid-state grafting polymerization in the presence of 2,2,6,6-tetramethyl-piperidinyloxy. Temperature rising elution fractionation of the grafted PP was performed and the fractions were characterized by 1H- and 13C-NMR, FT-IR, GPC, DSC, and WAXD. Results show that the grafted PP fraction eluted at 114°C accounts for 42% of the graft copolymer and has the highest grafting degree, high melting temperature and crystallinity, and high molecular weight. All the phenomena suggest that the grafted polymer contains a major component that has low branch density and long branch chain and a minor component with high branch density and short branches. 相似文献
35.
Ben LI;Jingfeng ZHOU;Yi WANG;Yang BAI 《光子学报》2022,51(2):127-138
A space-transmission high-power near-infrared semiconductor laser beam with a rectangular laser spot is one of the key tools to improve the efficiency and quality of laser surface heat treatment. However, this kind of laser is difficult to apply to the surface heat treatment of flexible lasers inside workpieces. This is because the volume of the lasers increases greatly with increasing laser power and is affected by the space transmission of the laser beam. The spot of the ultrahigh-power laser beam from a commercial high-power fiber laser or a fiber-transmitted semiconductor laser is circular, which makes it difficult to control the spot overlap rate during the laser surface heat treatment process. It is difficult to change the ultrahigh-power circular laser spot into a rectangular spot through beam shaping technology. Laser incoherent spatial combining based on multifiber transmission is an effective method to reduce the risk of high-power laser transmission in a single fiber and realize the flexible transmission of high-power lasers. It has quickly become a research hotspot in the field of ultrahigh power laser systems. To solve the spot overlap rate control problem of ultrahigh power lasers transmitted by fibers in flexible laser surface heat treatment, a design scheme of arranging 18 semiconductor laser beams at 972 nm transmitted by fibers according to a “staggered rectangle” and implementing space incoherent beam combination was proposed in this paper. Based on this, a set of 10 kW rectangular spot laser beam combiners was developed. The optical elements in the combiner are all optical lenses made of fused silica glass. It is widely known that the accumulation of heat generated by long-term ultrahigh-power laser beam irradiation will produce serious thermal effects inside the optical lens, resulting in reduced beam quality and even irreversible damage inside the optical lens, which will seriously affect the safety and reliability of the combiner for long-term operation. However, the structural shielding of the combiner often makes the thermodynamic properties of the optical lenses difficult to directly detect and evaluate with experimental methods. With the rapid development of computer technology and calculation methods, the establishment of temperature field models based on finite element analysis has become a simulation method widely used in the reliability analysis of laser irradiation optical components. At present, most thermodynamic finite element analysis studies on laser irradiation optical elements simplify the laser beam to an area heat source while ignoring the volume absorption of the laser beam by the optical element. However, the volume absorption of the laser beam by the optical lens itself is already one of the main factors affecting its thermodynamic properties with the continuous increase in laser incoherent space combining power. There is no report on the thermodynamic finite element analysis of multiple ultrahigh power laser beams transmitted through optical lenses under the premise that the laser beam is used as a volume heat source. To solve the above problems, the finite element thermodynamic model of the optical lens was established based on the mathematical model of the whole heat source of the 18 laser beams. The thermodynamic properties of all optical lenses under the condition of being irradiated by 18 laser beams participating in the combination for 1 000 s are simulated and analyzed using this model. The research results show that the maximum temperature, maximum thermal deformation and maximum equivalent thermal stress of the optical lens in the combiner stabilized after the 800 s time node. The simulated values of the maximum core temperature and the maximum equivalent thermal stress were 427.27 K and 12.68 MPa, respectively, which were significantly lower than the softening point temperature and thermal damage threshold of fused silica glass used to manufacture optical lenses. The maximum aperture of 0.1 corresponding to the simulated maximum thermal deformation of 4.53 μm was much smaller than the conventional machining tolerance of 2.0. The highest temperature on the exit surface of the window lens was measured during the laser beam combining time of 1 000 s. Both the experimental value and the simulated value of the highest temperature showed good consistency with the laser beam combining time. This shows that the established finite element thermal analysis model has good accuracy. The maximum combined power of 10.64 kW for the combined laser with a rectangular spot was measured when it was continuously operated for 1 000 s. The power instability of less than ±1.2% further experimentally verified the safety and reliability of the combiner under long-term operation. 相似文献
36.
37.
Pt-Sn/MgAl2O4催化剂的TPR和H2-TPD研究 总被引：3，自引：0，他引：3
Pt Sn/MgAl 2O 4 catalysts prepared by co impregnation with nominal 0 35% platinum and varying content of tin (0～2 5%) were characterized by temperature programmed reduction (TPR) and temperature programmed desorption of hydrogen (H 2 TPD). TPR results showed that platinum catalyzed the reduction of tin. However, the average oxidation state of tin after reduction depended upon the concentration of tin on the catalysts. H 2 TPD data indicated that tin addition inhibited the inactivated adsorption of hydrogen but promoted the activated adsorption, implying that tin modified both the ensembles of platinum and metal support interface, thus increasing hydrogen mobility and promoting hydrogen spillover. 相似文献
38.
爱因斯坦坚持场纲领的原因 总被引：5，自引：0，他引：5
探讨了爱因斯坦坚持场纲领的物理学认识基础和思想发展过程,分析了其坚持场纲领的目的及未获成功的原因。 相似文献
39.
界面缓蚀剂的吸附稳定性 总被引：9，自引：0，他引：9
研究表明：在一定条件下,阳极脱附电位可作为评价缓蚀剂吸附稳定性的一个经验参数：缓蚀剂吸脱附诱导的电化学振荡是缓蚀体系的一种特殊失稳状态,即缓蚀剂吸附过程与电极反应中间吸附态产物耦合的结果;卤素离子的协同作用不仅可以提高某些有机缓蚀剂的吸附复盖度,而且可以增强其吸附稳定性;微分极化曲线是研究吸附稳定性的有效方法。 相似文献
40.
A series of different commercial membranes were characterized by their moisture absorption and desorption properties under controlled humidity and temperature conditions. This work was made possible by combining the features of a constant humidity conditioning chamber with those of a thermogravimetric (TG) apparatus. These two modules were interconnected by tubing, rotameters, an atmosphere-recycling microbellows pump and switching valves. Under programmed heating and isothermal conditions reproducible data were obtained in terms of weight-gain or weight-lossvs. time and pore size. Evaluation of the resulting TG curves allowed us to report reasonable differences in the materials, some of which had been previously surface-modified by the manufacturer. 相似文献