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961.
962.
963.
Hongjun Zheng Shanliang Liu Chongqing Wu Huishan Yu Xin Li Weitao Wang Zhen Tian 《Optics & Laser Technology》2012,44(4):763-766
Pulse propagation characteristics at normal-dispersion region in dispersion-flatted-fibers are experimentally investigated by employing the second-harmonic generation frequency-resolved optical gating (SHG-FROG) method. It is found that the experimental results are consistent with the theoretical prediction. The initial optical pulse with negative chirp is compressed for nonlinear effect in the normal-dispersion fiber, and it evolves into near Gaussian pulse. Temporal width of the optical pulse decreases with the increase of the input power and propagation distance. The output pulse width for small dispersion is less than that for great dispersion at the same input power. The spectrum of the output pulse is still symmetrical about the central wavelength, and is broadened with the increase of input power. The spectral width of the output pulse is much wider than the input spectral width. 相似文献
964.
We present a review of photoexcited quasiparticle dynamics of cuprate and pnictide high‐temperature superconductors in regimes (temperature, doping) where different phases such as superconductivity, spin‐density‐wave (SDW) and pseudogap phases coexist or compete with one another. We start with the overdoped cuprate superconductor Y1–xCax Ba2Cu3O7–δ, where the superconducting gap and pseudogap coexist in the superconducting state. In another cuprate Tl2Ba2Ca2Cu3Oy, we ob‐ serve a competition between SDW and superconducting orders deep in the superconducting state. Finally, in the underdoped iron pnictide superconductor (Ba,K)Fe2As2, SDW order forms at 85 K, followed by superconductivity at 28 K. We also find the emergence of a normal‐state order that suppresses SDW at a temperature T * ~ 60 K and argue that this normal‐state order is a precursor to superconductivity. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
965.
This paper studies eigenvalues of the drifting Laplacian on compact Riemannian manifolds with boundary (possibly empty) and provides a general inequality for them. Using the general inequality, we obtain universal inequalities for eigenvalues of the drifting Laplacian of Payne-Pólya-Weinberger-Yang type for manifolds supporting some special functions. We also obtain a lower bound for the first eigenvalue of the square of the drifting Laplacian on compact manifolds with boundary under some condition on the Bakry-Ricci curvature. 相似文献
966.
Weimin Xia Zhuo Xu Qiuping Zhang Zhicheng Zhang Yuanqing Chen 《Journal of Polymer Science.Polymer Physics》2012,50(18):1271-1276
Thermal processing at various temperatures has been used to fabricate poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐co‐TrFE)] films with varied crystalline properties in an attempt to improve their piezoelectric properties. Although the dielectric constant of the films annealed at higher temperature is smaller than that of cooled and quenched ones, it has been shown that the annealed films possess larger crystallinity and stacked lamellar crystal grain size. The ferroelectric domains deriving from crystal region in all the samples are effectively improved by hot polarization. As a result, the remnant polarizations (Pr) and coercive electric field (Ec) of the corresponding films are improved at a low frequency due to the response of dipoles in crystal phase, and the largest piezoelectric constant in the longitudinal thickness mode (d33=?25 pC/N) is obtained in an annealed copolymer film. The results illustrate improving the crystal structure of P(VDF‐co‐TrFE) is an effective way to realize high electromechanical properties, which provides broadly applied scenery for this kind of copolymer in piezoelectric components. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 相似文献
967.
Sheng Xia Shan Yin Shimin Tao Yanhui Shi Liangce Rong Xianyong Wei Zhimin Zong 《Research on Chemical Intermediates》2012,38(9):2435-2442
One-pot, multicomponent reaction for the synthesis of novel substituted pyrimidine derivatives: 4-amino-5-carbonitrile-2-nitroaminopyrimidine from aromatic aldehydes, 1-nitroguanidine, and malononitrile under ethanol is described. Because of containing many active functional groups, such as amino, cyan and nitro, these products are important intermediate of organic synthesis. The advantages of this procedure include the short reaction time, mild reaction conditions, and excellent yields. 相似文献
968.
Low-temperature combustion synthesis of CuCr2O4 spinel powder for spectrally selective paints 总被引:1,自引:0,他引:1
Geng Qingfen Zhao Xin Gao Xianghu Yang Shengrong Liu Gang 《Journal of Sol-Gel Science and Technology》2012,61(1):281-288
CuCr2O4 spinel powder with high quality black hue, investigated as solar-absorbing pigment for spectrally selective paint, was synthesized
by an environmental friendly sol–gel combustion process using citric acid as the fuel and metal nitrates as oxidizers. Single-phase
CuCr2O4 spinel crystals were obtained after heat treatment of the as-burnt powder at a low temperature (600 °C) and the average crystallite
size of the CuCr2O4 powders increased with the calcining temperature. Morphological analysis of powders calcined at various temperatures was
done by field emission scanning electron microscopy. CuCr2O4 powder calcined at 700 °C was chosen as pigment to fabricate thickness sensitive spectrally selective paint coatings by simple
spray-coating technique. For the sake of comparison, the as-burnt powder composed of mixed metal oxides (i.e., CuO and Cr2O3) was also used as pigment. The results reveal that the spinel CuCr2O4 based paint coatings exhibit much higher spectral selectivity (α
s = 0.88–0.91, ε
100 = 0.27–0.35) which is depending on the coating thicknesses than that of coatings using as-burnt powder as pigment (α
s = 0.83–0.88, ε
100 = 0.60–0.66). The CuCr2O4-based paint coatings showed no visible degradation after 600 h of condensation test and the performance criterion value is
0.04, indicating that the coatings have excellent long term stability. 相似文献
969.