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31.
32.
通过数值求解一维瞬态受激布里渊散射(SBS)声光耦合波方程,从理论上分析了泵浦激光参数及光学材料参数对SBS过程发生阈值的影响。以SBS过程中建立起来的应力场抗拉(压)强度和散射场的反射率为判据,分析了激光脉宽及作用区域长度对激光超声破坏材料效果的影响,探讨了短脉冲激光(约ns)引起的激光超声对材料的破坏机理;讨论了通过参数配置有效遏制SBS过程激光超声对光学材料的破坏问题。 相似文献
33.
A facile, rapid and regioselective method for the 1-O-deacylation of peracylated glycopyranoses is described which occurs under mild conditions by absorption onto alumina using microwave irradiation. 相似文献
34.
Z. J. Yu L. J. Liu R. X. Zhuo 《Journal of polymer science. Part A, Polymer chemistry》2003,41(1):13-21
The ring‐opening polymerization of ε‐caprolactone (ε‐CL), initiated by carboxylic acids such as benzoic acid and chlorinated acetic acids under microwave irradiation, was investigated; with this method, no metal catalyst was necessary. The product was characterized as poly(ε‐caprolactone) (PCL) by 1H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, and gel permeation chromatography. The polymerization was significantly improved under microwave irradiation. The weight‐average molecular weight (Mw) of PCL reached 44,800 g/mol, with a polydispersity index [weight‐average molecular weight/number‐average molecular weight (Mw/Mn)] of 1.6, when a mixture of ε‐CL and benzoic acid (25/1 molar ratio) was irradiated at 680 W for 240 min, whereas PCL with Mw = 12,100 and Mw/Mn = 4.2 was obtained from the same mixture by a conventional heating method at 210 °C for 240 min. A degradation of the resultant PCL was observed during microwave polymerization with chlorinated acetic acids as initiators, and this induced a decrease in Mw of PCL. However, the degradation was hindered by benzoic acid at low concentrations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 13–21, 2003 相似文献
35.
In this article we use classical formulas involving the K–Bessel function in two variables to express the Poisson kernel on a Riemannian manifold in terms of the heat kernel. We then use the small time asymptotics of the heat kernel on certain Riemannian manifolds to obtain a meromorphic continuation of the associated Poisson kernel to all values of complex time with identifiable singularities. This result reproves in a different setting by different means a well–known theorem due to Duistermaat and Guillemin [DG 75]. Also, we develop analytic expressions for the heat kernel beyond asymptotic expansions. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
36.
37.
The mucosal upheaval (MU), where the mucosal wave starts and propagates upward, appears only when the vocal fold vibrates. The location of the MU histologically and the effect of changes in mean air flow rate (MFR) and vocal fold length on occurrence of the MU were studied in twelve excised canine larynges. The lower surface of the vocal fold was marked to serve as a landmark for subsequent study. Cricothyroid approximation was performed to lengthen the vocal fold. After taking high-speed pictures or recording stroboscopic images from the tracheal side, a small cut wound was made at the mark. This wound served to compare the position of the MU with the histologically identified location of the mark. The larynx was then sectioned in the frontal plane. Before lengthening the vocal fold, the MU occurred on the area where the lamina propria became thinner and where the muscular layer neared the epithelial layer. After lengthening the vocal fold, the MU actually shifted medially compared with its original position. The subglottic area surrounded by the bilateral MUs became longer and thinner. Whether or not complete glottal closure during a vibratory cycle was achieved did not alter these findings. In contrast, with a fixed vocal fold length the MU appeared more laterally as MFR increased, but, based on the relation with the mark, its location on the vocal fold did not change from its original position before increase of MFR. 相似文献
38.
We analyze the critical length for design purposes of six-dimensional spaces invariant under translations and reflections
containing the functions 1, cos t and sin t. These spaces also contain the first degree polynomials as well as trigonometric and/or hyperbolic functions. We identify
the spaces whose critical length for design purposes is greater than 2π and find its maximum 4π. By a change of variables,
two biparametric families of spaces arise. We call shape preservation region to the set of admissible parameters in order
that the space has shape preserving representations for curves. We describe the shape preserving regions for both families.
To our friend Mariano Gasca on occasion of his 60th birthday
Research partially supported by the Spanish Research Grant MTM2006-03388, by Gobierno de Aragón and Fondo Social Europeo. 相似文献
39.
We propose objectives consisting of two mirrors with central holes for passage of a light beam. The optical layout ensures
multiple reflection of rays from both mirrors. We consider several approaches to calculating the design parameters for which
three and four aberrations do not occur. The objectives can be used in optical devices operating in the UV and IR regions
of the spectrum.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 267–270, March–April, 2007. 相似文献
40.
Gap length (GL) of reading head is one of the most critical parameters for high-density magnetic recording systems. A novel method is proposed for quantitative evaluation of the GL fluctuation among a batch of magneto-resistive/giant magneto-resistive heads with same structure design. The method works at head-gimbal assembly level and the evaluation can be done with any read/write analysis equipment. The testing process is based on harmonic analysis of the readback signal. The testing system consists of a selected reference head and sample heads for evaluation. A GL variation function is introduced for the evaluation of GL deviation between the reference head and sample head. This method proved to be easy for implementation and results suggest that variation of GL is considerable and has obvious effect on recording performance in high recording density systems. 相似文献