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71.
Absolute sphericity measurement: a comparative study of the use of interferometry and a Shack-Hartmann sensor 总被引:1,自引:0,他引:1
A comparison of absolute sphericity measurements with a ShackHartmann sensor and a TwymanGreen interferometer is presented. The absolute deviations of a test sphere from its ideal shape were calculated in both cases from the measured wave aberrations of three different positions. Very good qualitative and quantitative agreement of the results was achieved. The difference of the root-mean-square values of the two methods was 1/1000 of a wavelength. 相似文献
72.
Dynamic range expansion of a Shack-Hartmann sensor by use of a modified unwrapping algorithm 总被引:4,自引:0,他引:4
An algorithm for expanding the dynamic range of Shack--Hartmann sensors is proposed. The distribution of the spot dislocations is treated with a modified unwrapping algorithm that is widely used in interferometry. The algorithm unwraps the spot dislocations and assigns the spots to their original subapertures, leading to a huge expansion of the dynamic range. For the proposed algorithm there remains a limitation on the maximum wave-front curvature instead of on the maximum wave-front slope. Examples are given that show spot fields that were wrapped four times; the measured wave front had a peak-to-valley value of 116 lambda . 相似文献
73.
Dragan A. Marković Zoltan Djarmati Ratko M. Jankov Dragan M. Marković Ljubiša M. Ignjatović 《Mikrochimica acta》1996,124(3-4):219-226
The electrochemical behaviour and mechanism of the redox process of the natural antioxidant rosmanol 9-ethyl ether, isolated fromSaliva officinalis L., were studied. The cyclic voltammograms of rosmanol 9-ethyl ether (R9EE), at characteristic pH values, and the electrochemical parameters for all investigated pH values were measured. Three characteristic pH regions, each with different behaviour of R9EE, were identified. In regions of pH < 4 and pH > 5 only one anodic peak appeared, whereas in the solutions of pH 4–5 two anodic peaks could be noted. The overall oxidation mechanism at pH < 4 is an e.H.e.H. oxidation mechanism, which as a final product gives a quinonic molecule. The influence of pH on the second oxidation peak potential tends towards zero in accordance with the preceding dissociation of the one of phenolic groups, thus suggesting an e.e.H. mechanism at pH > 5. This means that at the pH values expected in plant cells, R9EE has an unexpected structure, making this substance a potent antioxidant. Electrochemical and spectrophotometric measurements enabled us to establish an extremely low pK
a value (4.35) for R9EE. 相似文献
74.
Luis M. De León-Rodríguez Zoltan Kovacs Ana Cristina Esqueda-Oliva 《Tetrahedron letters》2006,47(39):6937-6940
A high yielding N-trans diprotection procedure for cyclen has been developed by using succinimide carbamate derivates of Boc and Cbz and chloroformate protecting groups. 相似文献
75.
De-Cai Fang P. Fabian Zoltan Szekely Xiao-Yuan Fu Ting-Hua Tang Imre G. Csizmadia 《Journal of Molecular Structure》1998,430(1-3):161-170
Ab initio (HF/6-31G** and B3LYP/6-31 + + G**) methods have been used to study the stability and structure of complexes between CH3SO−3 and CH3NH+3 or C(NH2)+3. Results show that no hydrogen jump is involved in the complex formations, which is different from previous work studying complexes between CH3COO− and CH3NH+3. In addition, we have studied complexes between CH3SO−3 and HC(NH2)+3 or +H3NC(NH2)3, all of which have a cage structure. 相似文献
76.
Zeng H Schelly ZA Ueno-Noto K Marynick DS 《The journal of physical chemistry. A》2005,109(8):1616-1620
The structures of (PbS)n (n = 1-9) clusters are investigated with density functional theory at the B3LYP level. Various pseudopotential basis sets on lead and the 6-31+G basis set on sulfur were employed. Full geometry optimization and extensive searches of the potential energy surface were carried out for clusters with n = 1-6. We find that even small PbS clusters (n > 2) start to take on the characteristic features of the rock salt structure of solid-state PbS (galena). The origin of some of the structural aspects of these crystals is shown to be associated with the partial covalent nature of the Pb-S bond. The magnitude of the HOMO-LUMO gap oscillates with increasing size of the clusters, in agreement with the observed behavior of the corresponding UV absorption bands of ultrasmall PbS quantum dots. Direct conformation of this oscillation was found by CIS(D) calculations, for which the absorption with the largest oscillator strength oscillates as the clusters grow from PbS to (PbS)9. 相似文献
77.
78.
Tel T Karolyi G Pentek A Scheuring I Toroczkai Z Grebogi C Kadtke J 《Chaos (Woodbury, N.Y.)》2000,10(1):89-98
We review and generalize recent results on advection of particles in open time-periodic hydrodynamical flows. First, the problem of passive advection is considered, and its fractal and chaotic nature is pointed out. Next, we study the effect of weak molecular diffusion or randomness of the flow. Finally, we investigate the influence of passive advection on chemical or biological activity superimposed on open flows. The nondiffusive approach is shown to carry some features of a weak diffusion, due to the finiteness of the reaction range or reaction velocity. (c) 2000 American Institute of Physics. 相似文献
79.
80.
An interesting property of Gaussian 1/f noise was found experimentally a few years ago: The amplitude truncation does not change the power spectral density of the noise under rather general conditions. Here we present a brief theoretical derivation of this invariant property of band-limited Gaussian 1/f noise and include 1/f(alpha) noises also with 0=alpha<2. It is shown that when alpha=1, a transformation of keeping only the sign of the zero-mean 1/f(alpha) noise does not alter the shape of the spectral density. The theoretical results are extended to truncation levels differing significantly from the mean value. Numerical simulation results are also presented to draw attention to unsolved problems of amplitude truncation using asymmetric levels. (c) 2001 American Institute of Physics. 相似文献