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971.
大气臭氧层的破坏和温室效应的加剧,是当前世界面临的主要环境问题。文中通过对R600a制冷剂物理化学特性的介绍以及与R12制冷剂的对比,得出在冰箱领域,R600a是一种可以永久替代CFCs的环保型制冷剂,分析了R600a替代R12的制冷系统设计的一些要点,最后基于提高工作效率以及保障操作安全的考虑,阐述了R600a冰箱的维修工艺。 相似文献
972.
根据目标上实际最大光强与理想合成效果下最大光强的比值定义了合成效果因子,用以评价相干合成效果.在此基础上研究了影响相干合成效果的主要因素,并对合成效果因子的传输特性进行了研究.结果表明:阵列紧密程度对合成效果影响不大,在较小的空间占空比下有可能得到较好的合成效果.影响合成效果的主要因素是随机相位差,当随机相位差增大到一定程度时,光束合成其实已经由相干合成过渡到了非相干合成,得不到预期的相干合成效果;随着传输距离的增大,空间占空比对合成效果因子的影响将进一步减小,影响合成效果的主要因素之一是随机相位差. 相似文献
973.
The structure of the Si3Ox (x=2, 3) cluster is investigated; we find that the geometry of Si3O2 is similar to that of Si3O3 except for the oxygen-deficient defect structure (Si-Si band) which exists only in the Si3O2 cluster. It is known that oxygen-deficient defects are used to explain visible luminescence (especially blue, purple and ultraviolet light) from silicon-based materials, which are directly bound up with the excited states of the molecules. Therefore the excitation properties of the two clusters are also studied. Our results show that the absorption spectrum of Si3O2 is concentrated in the visible light region. In contrast, the absorption spectrum of Si3O3 is mainly located in the ultraviolet light region. The calculations are perfectly consistent with experimental data and also support the theory of oxygen-deficient defects. 相似文献
974.
The leakage current behaviours of polycrystalline BiFeO3 thin films are investigated by using both conductive atomic force microscopy and current-voltage characteristic measurements. The local charge transport pathways are found to be located mainly at the grain boundaries of the films. The leakage current density can be tuned by changing the post-annealing temperature, the annealing time, the bias voltage and the light illumination, which can be used to improve the performances of the ferroelectric devices based on the BiFeO3 films. A possible leakage mechanism is proposed to interpret the charge transports in the polycrystalline BiFeO3 films. 相似文献
975.
976.
977.
Effect of substrate temperature on microstructure and optical properties of single-phased Ag20 film deposited by using radio-frequency reactive magnetron sputtering method
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Using a radio-frequency reactive magnetron sputtering technique, a series of the single-phased Ag20 films are deposited in a mixture of oxygen and argon gas with a flow ratio of 2:3 by changing substrate temperature (Ts). Effects of the Ts on the microstructure and optical properties of the films are investigated by using X-ray diffractometry, scanning electron microscopy and spectrophotometry. The single-phased Ag20 films deposited at values of Ts below 200℃ are (111) preferentially oriented, which may be due to the smallest free energy of the (111) crystalline face. The film crystallization becomes poor as the value of Ts increases from 100℃ to 225℃. In particular, the Ag20 film deposited at Ts=225℃ loses the (111) preferential orientation. Correspondingly, the film surface morphology obviously evolves from a uniform and compact surface structure to a loose and gullied surface structure. With the increase of Ts value, the transmissivity and the reflectivity of the films in the transparent region are gradually reduced, while the absorptivity gradually increases, which may be attributed to an evolution of the crystalline structure and the surface morphology of the films. 相似文献
978.
Two-photon absorption(2PA) in zinc sulphide(ZnS) and Mn2+-doped ZnS quantum dots is reported by the z-scan technique,with nanosecond pulsed laser radiation at 355 nm.The observed values of the 2PA cross section of all the samples are 105 times larger than that of bulk ZnS. 相似文献
979.
Terahertz (THz) spectra of bentazon are determined within the range of 0.3 2.4 THz at room temperature.Density functional methods are used to compute the THz spectra using three different programs:Gaussian03 for isolated-molecule form,DMol 3 and CRYSTAL09 for solid-state forms.Among the three,the computed THz spectrum of CRYSTAL09 shows better bond length and angle agreements with Xray experimental results,and corresponds with observed THz experiment spectral characteristics.The isolated-molecule vibrational mode values are less by half than those derived from solid-state calculations.The last five peak positions of the two solid-state computations coincide with each other.Moreover,all the experimental THz absorption peaks are assigned by utilizing CRYSTAL09. 相似文献
980.
Morphology evolution of prior β grains of laser solid forming (LSF) Ti-xAl-yV (x 11,y 20) alloys from blended elemental powders is investigated. The formation mechanism of grain morphology is revealed by incorporating columnar to equiaxed transition (CET) mechanism during solidification. The morphology of prior β grains of LSF Ti-6Al-yV changes from columnar to equiaxed grains with increasing element V content from 4 to 20 wt.-%. This agrees well with CET theoretical prediction. Likewise, the grain morphology of LSF Ti-xAl-2V from blended elemental powders changes from large columnar to small equiaxed with increasing Al content from 2 to 11 wt.-%. The macro-morphologies of LSF Ti-8Al-2V and Ti-11Al-2V from blended elemental powders do not agree with CET predictions. This is caused by the increased disturbance effects of mixing enthalpy with increasing Al content, generated in the alloying process of Ti, Al, and V in the molten pool. 相似文献