排序方式: 共有12条查询结果,搜索用时 156 毫秒
1.
ZHAO Xue CHEN De-Zhan WANG Zhen HAO Zhao-Ling 《结构化学》2007,26(8):980-987
5,8-Hihydroxyl-1,4-naphthazarin was taken as a model compound to explore the effect of halogen substitution on intramolecular proton transfer process. Calculations indicate that the substitution in the R2- and R4-positions far away from the active region has much weaker influence on the IPT process than that in the R1-and R3-positions. IPT barriers for substitution in the R1-position are higher than that of parent molecule. However, it is quite reverse for substitution in the R3-position. The IPT process is a proton transfer process coupled with charge separation and coulombic interaction would be dominant during this process. As for naphthazarin, halogen substitution would decrease the quantum yields of O2 but increase those of 1O2. 相似文献
2.
The novel coordination polymer [Pr(BYBA)3(H2O)2]·[Pr(BYBA)3(H2O)] (BYBAH = 2-benzoylbenzoic acid) was yielded by hydrothermal synthesis, determined by single-crystal X-ray diffraction, and characterized by FT-IR and UV-Vis spectra. The crystal crystallizes in the triclinic system, space group P with a = 9.112(3), b = 14.644(5), c = 27.076(11) (A), α = 84.223(3), β = 87.816(4), γ = 88.902(4)o, V = 3592(2) (A)3, C84H60O21Pr2, Mr = 1687.14, Z = 2, F(000) = 1700, Dc = 1.560 g/cm3, μ = 1.419 mm-1, the final R = 0.0485 and wR = 0.1258 for 13035 observed reflections with I>2((I). The compound contains two different building units, [Pr2(BYBA)6(H2O)4] and [Pr2(BYBA)6(H2O)2]. It is noticeable that [Pr2(BYBA)6(H2O)4] is an isolated binuclear building block, in which the Pr3 ion centers are both located in an eight-coordinated environment. However, in [Pr2(BYBA)6(H2O)2] the Pr3 ion centers are located in a nine-coordinated environment and connected by BYBA ligands to form 1D chains. 相似文献
3.
Dong-shanZhou Xiao-liangWang BoChe LiangLi Jin-luChen GiXue 《高分子科学》2005,(2):159-163
Entropic contribution to the interaction parameter xeff in the model incompressible polymer/oligomer system is calculated by the lattice cluster theory (LCT). It is found that in the oligomer solvent, there exists a wide concentration range that the non-combinatorial “entropic interaction” term xeff φ1φ2 perceptibly counteracts the mean field combinary entropy ΔSMF. With the increase of the solvent size, both xeff and the ratio xefc φ1φ2/ΔSMF first reach their maximum and finally become trivially to zero. It is worth noting that no any demixing was found in the current calculation. This makes the controversial idea “entropically driven demixing” even elusive. However, we propose that further work on compressible polymer solution with structured monomer will witness the demixing owning to an increased configurational correlation. 相似文献
4.
This paper investigates the exact and approximate spectrum assignment properties associated with realizable output-feedback pole-placement type controllers for single-input single-output linear time-invariant time-delay systems with commensurate point delays. The controller synthesis problem is discussed through the solvability of a set of coupled diophantine equations of polynomials. An extra complexity is incorporated to the above design to cancel extra unsuitable dynamics being generated when solving the above diophantine equations. Thus, the complete controller tracks any arbitrary prefixed (either finite or delaydependent) closed-loop spectrum. However, if the controller is simplified by deleting the above mentioned extra complexity, then the robust stability and approximated spectrum assignment are still achievable for a certain sufficiently small amount of delayed dynamics. Finally, the approximate spectrum assignment and robust stability problems are revisited under plant disturbances if the nominal controller is maintained. In the current approach, the finite spectrum assignment is only considered as a particular case to the designer‘s choice of a (delay-dependent) arbitrary spectrum assignment objective. 相似文献
5.
The production and transportation of fluorescent light produced in wavelength-shifting fibers (WSFs) coupled to YAP scintillation crystal is simulated using the GEANT4 codes.An advantage of the wavelength-shifting fiber readout technique over a direct readout with a position-sensitive photo-sensor is the reduced requirement for position sensitive photomultiplier tube photocathode area.With this gamma-ray detector,the gamma camera is small and flexible and has larger effective field of view and low cost.Simulation results show that a) a mean 12 of photons per 59.5 keV gamma ray interaction is produced in the WSF located nearest to the incident gamma ray,and a spatial resolution of 3.6 mm FWHM is obtained,b)a mean 27 of photons per 140 keV gamma ray interaction is produced and a spatial resolution of 3.1 mm FWHM is obtained.Results demonstrate the feasibility of this concept of a compact gamma-ray detector based on wavelength-shifting fibers readout.However,since the very low photoelectron levels,it is very important to use a photon counting device with good single photo-electron response to readout the WSFs. 相似文献
6.
Jian-bin Song Qing-yong Chen Min-qiao Ren Xiao-hong Sun Hui-liang Zhang Hong-fang Zhang Shu-yun Wang Zhi-shen Mo 《高分子科学》2006,(2):187-193
The wide-angle X-ray diffraction (WAXD) patterns of isothermally crystallized Nylon 1212 show that γ-form crystals form below 90℃ and the α-form crystals can exist above 140℃. In the temperature range of 90-140℃, the α-form and γ-form crystals coexist. Variable-temperature WAXD exhibits that the nylon 1212 γ-form does not show crystal transition on heating, while α-form isothermally crystallized at 160℃ exhibits Brill transition at a little higher than 180℃ on heating. The multiple melting behaviors of Nylon 1212 isothermally crystallized from melt come from a complex mechanism of different crystal structures, dual lamellar population and melting-recrystallization. In polarized optical microscope (POM) observations, Nylon 1212 isothermally crystallized at 175℃ shows the ringed banded spherulites. However, at temperatures below 160℃ the ringed banded image disappears, and cross-extinct spherulites are formed. 相似文献
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8.
YING Xiaoa DENG Qina LIAO Shi-Junb HU Xi-Mingb LIU Hai-Yangb② CHANG Chi-Kwongc② a 《结构化学》2007,26(8):955-961
The second-order nonlinear optical (NLO) properties of 5,10,15-triphenylcorrole (TPC), 5,10,15,20-tetraphenylporphyrin (TPP) and L-amino acid bridged bis-corroles 1, 2, 3 and 4 have been calculated by using TDHF/PM3 method based on the RHF/6-31G (TPC and TPP) or semiempirical PM3 (1, 2, 3, 4) optimized geometries. Calculation results showed TPC and TPP have C1 and D2h symmetry, respectively when N-H protons are localized on the nitrogen atoms. TPC is the second-order NLO active chromophore due to the cancellation of centrosymmetrical structure and its first hyperpolarizability β increases to 11.524×10-30 esu. Under electrical dipole approximation, β values of bis-corroles 1, 2, 3 and 4 vary from 9.831×10-30 to 14.221×10-30 esu, and no much improvement in the first hyperpolarizability was observed as compared to TPC monomer. However, β values of bis-corroles 1, 2, 3 and 4 are improved by about 4 times as compared to their bis-porphyrin counterparts. The analysis of β components indicates that β of this kind of bis-corroles is mainly contributed from its radial component βr. With the variation of amino acid side chains, βHRS, β, βxyz, βr and βa of bis-corroles change remarkably. Chiral L-amino acid bridged bis-corroles 2, 3 and 4 have a right-handed helix structure, and their chiral component βxyz matches βxyz ∝ r2ζ/L4 (helix parameters), showing the second-order chiral NLO response of these bis-corroles could be described by one-electron helical model theory. It was found that the radial component βr of chiral helix bis-corroles also matches β r ∝ r2ζ/L4. 相似文献
9.
Zhenhui Chen Bo Lu Zhixue Xu Wei Zhuang Chuang Yu Deshui Yu Kaikai Huang Xuzong Chen Jinbiao Chen 《中国光学快报(英文版)》2008,6(5)
Calcium is one prospective element for the modern optical frequency standard.The 423-nm transition line of calcium atoms has been widely used in laser slowing and laser cooling, the precise spectrum measurement, and the magnetic optical trapping (MOT).However, there is no any available commercial diode laser working at this wavelength.We built a 423-nm laser based on extra bow-tie cavity and by using a Brewster cut uncoated BIBO (BiB3O6) crystal, which worked at room temperature, with conversion efficiency of 3.75%, and a potential up to 20%. 相似文献
10.
本文对函数 y=f ( x)与 y=|f ( x) |的部分性质进行了比较和分析 ,指出了它们性质上的区别与联系 . 相似文献