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91.
Zhijun Yuan Qihong Lou Jun Zhou Jingxing Dong Yunrong Wei Zhijiang Wang Hongming Zhao Guohua Wu 《Optics & Laser Technology》2009,41(4):380-383
The effect of laser fluence on the crystallization of amorphous silicon irradiated by a frequency-doubled Nd:YAG laser is studied both theoretically and experimentally. An effective numerical model is set up to predict the melting threshold and the optimized laser fluence for the crystallization of 200-nm-thick amorphous silicon. The variation of the temperature distribution with time and the melt depth is analyzed. Besides the model, the Raman spectra of thin films treated with different fluences are measured to confirm the phase transition and to determine the optimized fluence. The calculating results accord well with those obtained from the experimental data in this research. 相似文献
92.
Abstract
Nicotinamide crystallizes with 3-hydroxy-2-naphthoic acid and 4-aminobenzoic acid to give rise to cocrystal 1 and 2, respectively. Cocrystal 1, [C11H8O3][C6H6N2O], crystallizes in the monoclinic space group C2/c with a = 25.810(4), b = 4.8932(5), c = 23.869(4) ?, β = 107.078(8)o, V = 2881.6(7) ?3, Z = 8, C17H14N2O4, M r = 310.30, D c = 1.431 g/cm3. Cocrystal 2, [C7H7NO2][C6H6N2O]·H2O, crystallizes in the triclinic space group P-1 with a = 7.214(5), b = 7.326(5), c = 13.484(11) ?, α = 83.23(2), β = 77.189(18), γ = 80.35(2)o, V = 682.7(9) ?3, Z = 2, C13H15N3O4, M r = 277.28, D c = 1.349 g/cm3. Similar carboxylic acid···pyridine synthon R 22(7) can be observed in the two cocrystals. In 1, amide of nicotinamide forms a C(4) chain from the anti H to its carbonyl oxygen. In 2, the amide forms a R 22(8) homodimer which is linked into 2D layer by water molecule through different hydrogen-bonding interactions. The 3D hydrogen-bonded structure results from a synthon R 42(8) from amide, water and amino group of 4-aminobenzoic acid. 相似文献93.
Zi‐Jing Li Hong‐Xiang Lou Wen‐Tao Yu Pei‐Hong Fan Dong‐Mei Ren Bin Ma Mei Ji 《Helvetica chimica acta》2005,88(10):2637-2640
The known 7,8‐secolabdane type diterpenoids neopallavicinin ( 1 ), pallavicinin ( 2 ), and 18‐hydroxypallavicinin ( 3 ) were isolated from Pallavicinia ambigua, and their structures were determined. The X‐ray crystal structure of 1 was solved, and, in combination with CD and NMR studies, the absolute configurations of 1 – 3 were established. A possible biogenetic pathway for 1 and 2 from a single labdane precursor is proposed. 相似文献
94.
Lou van den Dries 《manuscripta mathematica》1999,98(2):133-137
We indicate a complete set of elementary invariants for the ring of Witt vectors over a perfect field of prime characteristic,
where this ring is equipped with its unique multiplicative set of representatives for the residue field.
Received: 31 March 1998 相似文献
95.
The multi-linear variable separation approach is reviewed in this article. The method has been recently established and successfully
solved a large number of nonlinear systems. One of the most exciting findings is that the basic multi-linear variable separation
solution can be expressed by a universal formula including two (1+1)-dimensional functions, and at least one is arbitrary
for integrable systems. Furthermore, the method has been extended in two different ways so as to enroll more low dimensional
functions in the solution.
相似文献
96.
97.
98.
α-Trifluoromethyl alkenes can be used as peptide isosteres, moreover, the pre-installed vinyl group make it possible that transformation to diverse fluorine-containing unities. However, the cross-coupling of benzyl group with α-trifluoromethyl alkenes has yet to be developed. In this report, we describe a general method for the cross-coupling of benzylzinc reagents with 2-bromo-3,3,3-trifluoropropene (BTP) to afford diverse α-trifluoromethylalkene derivatives by using Pd(TFA)2 as catalyst. This method takes advantage of cheap industrial available fluorine building blocks and easily prepared benzylzinc reagents to generate α-trifluoromethylalkene derivatives, which features with mild reaction conditions, wide substrate scope and feasibility of product transformations. 相似文献
99.
Sheng Chen Jun Qiu He‐Lou Xie Hai‐Liang Zhang 《Journal of polymer science. Part A, Polymer chemistry》2013,51(13):2804-2816
Based on 2, 5‐bis[(4‐alkoxyphenyl)oxycarbonyl]styrenes (M‐OCm, m is the number of the carbons of alkyl tails, m = 1, 4, and 18), three series of binary copolymers with high‐molecular weights, {poly(M‐OC1‐co‐M‐OC4), poly(M‐OC1‐co‐M‐OC18), and poly(M‐OC4‐co‐M‐OC18)} have been prepared via free‐radical polymerization. The random nature of the copolymers was expected on the basis of the assumed similar reactivities because of the analogous monomers. The phase behaviors of copolymers were studied by DSC, POM, and one‐dimensional wide‐angle X‐ray diffraction. The results showed that liquid crystalline (LC) phase structures of copolymers, containing smectic phase, reentrant isotropic phase, columnar phase. and isotropic phase, were strongly depended on the composition and the alkyl length due to the competing among the steric effect, the microphase separation and the driving force of the entropy. When one of them occupied a dominant position, the LC phase structure can be presented for the copolymers. Otherwise, the LC phase structure is lost despite the pair of corresponding homopolymers forming mesogenic structure. Therefore, through copolymerization, LC behavior of the mesogen‐jacketed liquid crystalline polymers can be greatly varied. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2804–2816 相似文献
100.
Liping Lou Yasuhiro Koike Yoshiyuki Okamoto 《Journal of polymer science. Part A, Polymer chemistry》2010,48(22):4938-4942
2,3,4,5,6‐Pentafluoro and 4‐trifluoromethyl 2,3,5,6‐tetrafluoro styrenes were readily copolymerized with methyl methacrylate (MMA) by a free radical initiator. The copolymers were soluble in tetrahydrofuran and acetone. The films obtained were transparent and flexible. The glass transition temperatures (Tgs) of the copolymers were found positively deviated from the Gordon–Taylor equation. The positive deviation could be accounted for by dipole–dipole intrachain interaction between the methyl ester group of MMA and the highly fluorinated aromatic moiety, which resulted in a decrease in the segmental mobility of the polymer chains and the enhanced Tg values of the copolymers. The water absorption of PMMA was greatly decreased by copolymerization of MMA with the highly fluorinated styrenes. With as little as 10 mol % of pentafluoro styrene content in the copolymer, the water absorption was decreased to one‐third of that for pure PMMA. The fluorinated styrenes‐MMA copolymers were thermally stable up to 420 °C under air and nitrogen atmospheres. With 50 mol % of MMA in the copolymer, the copolymer was still stable up to 350 °C. Since these copolymers contain a large number of fluorine atoms, the light absorption in the region of the visible to near infrared is decreased in comparison with nonfluorinated polymers. Thus, these copolymers may be suitable for application in optical devices, such as optical fibers and waveguides. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献