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101.
根据衍射光学理论分析了红外系统后向反射光强的分布,反射区域可以分成近场传输区域、菲涅耳衍射区域和夫琅和费衍射区域。在菲涅耳衍射区域内,反射光斑中心光强是呈明暗变化的,反射光斑中心光强在0~1km内剧烈振荡,1~3km之间达到峰值,然后随传输距离的继续增加,反射光斑中心光强逐渐减小。在夫琅和费衍射区域内,光斑图像中央是亮光斑,周围环绕着明暗交替的圆环。  相似文献   
102.
Nile red bound to human serum albumin (HSA) shows an order of magnitude increase in the probe's fluorescence intensity. Here, we report on the fluorescence characteristics of the probe-protein complex in Trizma buffer (pH 7.1), urea, guanidine hydrochloride, and AOT/isooctane/buffer reverse micelles using both steady—state and time-resolved fluorescence techniques. With a view to illustrating the use of extrinsic probe fluorescence spectroscopy in protein research, we demonstrate that protein unfolding can be observed through measurements of the probe's time-resolved anisotropy and steady-state fluorescence spectrum. Moreover, this shows that thermal unfolding is fundamentally different from using denaturant, with respect to changes in both the nanosecond diffusional rotation of the probe at intermediate stages and in the denatured protein's structure. Also, the large Stokes shift of Nile red allows the changes in the environment of the probe-protein complex in reverse micelles of varying waterpool size to be easily identified in the steady-state fluorescence. This was not seen in earlier work exploiting the intrinsic tryptophan fluorescence of HSA and further demonstrates the complementary information that extrinsic fluorescence probe studies can offer protein science. We discuss the complex acrylamide quenching characteristics of Nile red bound to HSA in terms of the possibility of at least two binding sites for the probe and the effect of acrylamide on the probe-protein structure at very high quencher concentrations.  相似文献   
103.
Lead containing calcium zinc sodium fluoroborate (LCZSFB) glasses doped with different concentrations of trivalent dysprosium ions were prepared and investigated by the XRD, FTIR, optical absorption, photoluminescence and decay curve analysis. The experimentally determined oscillator strengths have been determined by measuring the areas under the absorption peaks and the Judd–Ofelt (J–O) intensity parameters were calculated using the least squares fit method. From the evaluated J–O parameters the radiative transition probability rates, radiative lifetimes and branching ratios were calculated for 4F9/2 excited level. Room temperature photoluminescence spectra for different concentrations of Dy3+-doped LCZSFB glasses were obtained by exciting the glass samples at 386 nm. The intensity of Dy3+ emission spectra increases with increasing concentration of 0.1, 0.25, 0.5 and 1.0 mol% and beyond 1.0 mol% the concentration quenching is observed. The measuring branching ratios are reasonably high for transitions 4F9/26H15/2 and 6H13/2, suggesting that the emission at 484 and 576 nm, respectively, can give rise to lasing action in the visible region. From the visible emission spectra, yellow–blue (Y/B) intensity ratios and chromaticity color coordinates were also estimated. The lifetimes of 4F9/2 metastable state for the samples with different concentrations were also measured and discussed.  相似文献   
104.
The complex orientation dependence in space of Raman active vibrations in the orthorhombic structure of polyethylene (PE) is discussed in terms of Raman tensor elements as intrinsic physical parameters of the lattice. Building upon the symmetry assignment of these vibrational modes, we systematically studied, from both theoretical and experimental viewpoints, the changes of polarized intensity for the Ag and the B2g + B3g vibrational modes with respect to PE molecular orientation. After explicitly expanding the Raman selection rules associated with the Ag and the B2g + B3g modes, introducing them into general expressions of the orientation distribution function, and validating them by means of a least‐square fitting procedure on experimental data, we compare here two mesostructural models for a highly crystallized and self‐aligned PE fiber structure. Stereological arguments are shown concerning the arrangement of orthorhombic fibrils in such a sample that unfold the correct values of five independent Raman tensor elements for orthorhombic PE. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   
105.
Experimental evidence for surface segregation of Pt at (1 1 1) surfaces of ternary (Pt, Ni)3Al alloys is presented, based upon Auger electron spectroscopy, low energy ion scattering, and angle-resolved X-ray photoelectron spectroscopy. Density functional calculations in the dilute limit confirm that Pt segregation is energetically favored.  相似文献   
106.
High-temperature scanning tunnelling microscopy, scanning tunnelling spectroscopy and current imaging tunnelling spectroscopy (HT-STM/STS/CITS) were used to study the topographic and electronic structures changes due to surface modifications of the TiO2(1 1 0) surface caused by the STM tip. In situ high-temperature STM results showed that the created modifications were stable even at elevated temperatures. The STS/CITS results showed the presence of energy gap below the Fermi level on the untreated regions. The disappearance of energy gap below the Fermi level on the modifications created by the tip was observed. It is assumed that the presence of the tip can change the chemical stoichiometry of the surface from TiO2−x towards Ti2O3.  相似文献   
107.
基于近红外光谱技术的石油组分定量分析新方法   总被引:12,自引:1,他引:12  
针对石油化工产品生产控制和质量检查的需要,为提高测定产品组成的效率,将近红外光谱法作为基础测定方法,以直馏柴油、加氢精制柴油和催化裂化柴油为校正模型的训练样本,测定其中饱和烃、胶质、单环芳烃、双环芳烃、三环芳烃和环烷烃的组成,论述了采用模糊神经网络建立校正模型测定石油化工产品组成的可行性。基于dSPACE硬件平台,用验证样本对模糊神经网络校正模型进行了检验,实验结果表明,该方法响应快、误差小、鲁棒性强,在近红外长波区内,校正样品和验证样品的均方误差小于10-6。该方法可用于石油化工产品的生产工艺研究中。  相似文献   
108.
We report on the free diffusion of single molecule near an interface studied using fluorescence correlation spectroscopy. In particular, we show that the chemical nature of the substrate may modify the free diffusion of a widely used molecule (rhodamine 6G), thus inducing unexpected effects in fluorescence correlation spectroscopy measurements. Our results show a strong influence, up to a few micrometer from the interface, of the surface polarity. This effect is assessed through the relative weight of the two dimensions diffusion process observed close to the surface. Our results are discussed in terms of competition between surface-solvent, solvent-molecule and molecule-surface specific interactions.  相似文献   
109.
Since 1997 we systematically perform direct angle resolved photoemission spectroscopy (ARPES) on in-situ grown thin (<30 nm) cuprate films. Specifically, we probe low-energy electronic structure and properties of high-T c superconductors (HTSC) under different degrees of epitaxial (compressive vs. tensile) strain. In overdoped and underdoped in-plane compressed (the strain is induced by the choice of substrate) ≈15 nm thin La2 − x Sr x CuO4 (LSCO) films we almost double T c to 40 K, from 20 K and 24 K, respectively. Yet the Fermi surface (FS) remains essentially two-dimensional. In contrast, ARPES data under tensile strain exhibit the dispersion that is three-dimensional, yet T c drastically decreases. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the two-dimensional character of the dispersion and increases T c, while the tensile strain acts in the opposite direction and the resulting dispersion is three-dimensional. We have established the shape of the FS for both cases, and all our data are consistent with other ongoing studies, like EXAFS. As the actual lattice of cuprates is like a ‘Napoleon-cake’, i.e. rigid CuO2 planes alternating with softer ‘reservoir’, that distort differently under strain, our data rule out all oversimplified two-dimensional (rigid lattice) mean field models. The work is still in progress on optimized La-doped Bi-2201 films with enhanced T c.   相似文献   
110.
Si/SiNx/SiO2多层膜的光致发光   总被引:1,自引:0,他引:1  
采用射频磁控溅射法,制备了具有强光致可见发光的纳米Si/SiNx/SiO2多层膜,利用傅立叶红外吸收(FTIR)谱,光致发光(PL)谱对其进行了研究。用260nm光激发得到的PL谱中观察到高强度的392nm(3.2eV)和670nm(1.9eV)光致发光峰,分析认为它们分别来自于缺陷态≡Si-到价带顶和从导带底到缺陷态≡Si-的辐射跃迁而产生的光致激发辐射复合发光。PL谱中只有370nm(3.4eV)处发光峰的峰位会受退火温度的影响,结合FTIR谱认为370nm发光与低价氧化物—SiOx(x<2.0)结合体有密不可分的关系。当SiO2层的厚度增大时,发光强度有所增强,800℃退火后出现最强发光,认为具有较大SiO2层厚度的Si/SiNx/SiO2结构多层膜更有利于退火后形成Si—N网络,能够得到更高效的光致发光。用量子限制-发光中心(QCLC)模型解释了可能的发光机制,并建立了发光的能隙态(EGS)模型。  相似文献   
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