单位圆周上正交多项式渐近分析的Riemann-Hilbert方法

在单位圆周上考虑带特定权函数的正交多项式,利用Deift P.和Zhou X.所引进的关于振荡型Riemann-Hilbert问题的最速下降法,建立了这类正交多项式在整个复平面上的强渐近公式,发展和改进了一些经典结果.     

High-order soliton generation in dispersion flattened fiber

By using the amplified 10-GHz, 5.5-ps sech2 pulses with high quality and chirp-free from regeneratively mode-locked fiber laser (RMLFL) as the soliton source, 2-5 order optical soliton phenomena are observed successfully in a 4.28-km dispersion flattened fiber. The experimental results agree well with the theoretical calculation.     

Femtosecond laser ablation of Au film around single pulse threshold

Ablation process of 1-kHz femtosecond lasers (pulse duration of 148 fs, wavelength of 775 nm) of Au film on silica substrates is studied. The thresholds for single and multi pulses can be obtained directly from the relation between the squared diameter D2 of the ablated craters and the laser fluence φo. From the plot of the accumulated laser fluence Nφth(N) and the number of laser pulses N, incubation coefficient of Au film is obtained to be 0.765. Some experimental data obtained around the single pulse threshold are in good agreement with the theoretical calculation.     

基于二元光学设计的高能激光窗口的初步探讨

对非均匀近场强度分布影响强激光远场聚焦效果的原因进行了分析。对高能激光窗口进行了二元光学设计。提高了光束强度分布的均匀性,改善了光束质量。介绍了二元光学设计的基本原理,采用随机并行扰动爬山法对窗口的位相分布、变换后的光束强度分布、衍射效率和光束均匀性进行了计算。计算结果表明,基于二元光学设计的激光窗口能有效地改善光束强度分布的均匀性,提高了发射光束的质量。     

星形低分子量块状化合物的合成

近来对由不相容部分构成的块状共聚物的研究表明,通过改变各块的对比度(刚性与柔性,亲水性与亲油性,极性与非极性等)或改变各块的相对体积比, 均可改变这类物质的自组装行为获得新的液晶相态[1a].     

Design, Synthesis and Characterization of a Novel Schiff Base Bis(iminoantipyrine) and Its Modified Electrode

ThedevelopmentandaPplicationofchemicallymodifiedelectrodescontinuetobeareasofvigorousresearchactivityl-2.Recently,complexatioswithorganicreagentsasmodifiersincarbonpasteelectrodeshavebeenemployedforanalyticaldeterminations3.Schiffbaseligands,however,havebeenscarcelyreportedasmodifierstodeterminemetalions'.Theprincipalcharacteristicrequiredforthesuccessfulconstr[lctionofamodifiedcarbonpasteelectrodeisthatthesolubilityofthemodifiermustbesoslightinthesolventsemployedthatitremainstablyincorporated…     

A Novel Synthesis of Isoxazole Derivatives

Thenitronesareveryimportantinorganicsynthesis.TheyhavebeenwidelyutilizedasintermediatesfromwhichcomPlexheterocyclicornaturalcompoundsanddrugs"'weresynthesisedsuchasisoxazoline3andoxazine4.However,theconversionofnitronetoisoxazolebythermaldecompositionhasnotbeenreported.Inthispaper,wedevelopanewsyntheticmethodofisoxazolesfromheterocyclicnitronesasfollows:wi.-"'rtXfa.H;b.3,4-O-CH2-o-;c.4-CH3O,d.4-Cl;e.2-Brf.2-Cl,g.3,4-coCH3;h.3-ro2;i.4-so2;j.4-CH3Experiment8lAdriedroundbottomflaskundernit…     

1.54 μm Light emission from Er/O and Er/F doped Si p–i–n diodes grown by molecular beam epitaxy

Various light emitting devices (LED) have been processed using Er/O- and Er/F-doped Si layered structures grown by molecular beam epitaxy (MBE) at low temperature. A comparative study has been carried out in order to provide more understanding of the electroluminescence (EL) excitation and de-excitation mechanisms in particular at a high injection current regime. Comparing the experimental results with model calculations the values of excitation cross section, σ_ex, and effective Auger coefficient, C_A, have been determined for various devices operated at different biases. Time-resolved EL measurements of these Er/O- and Er/F-doped MBE Si structures, using an experimental set-up with a time response of 200 ns, have been performed with different excitation conditions. Besides the spontaneous Er emission (700 μs), some fast EL decay processes associated with the Auger energy transfer via free carriers (4 μs), and the hot carrier effects (200 ns) have been identified.     

基于粗糙集理论的胸部X线数字图象增强方法的研究

采用一种基于粗糙集理论实现胸部X线数字图象增强的新方法,该方法根据粗糙集的条件属性,将一幅采用双能量算法获得的肺部软组织X线数字图象划分为不同的子图象,然后对各个子图象分别作衬比增强从结果中可看出,采用种方法处理后得到的图象效果较为理想,能给临床上的医学工作者提供清晰的图象,同时也为后续的计算机辅助诊断提供有效的依据.     

Free-space Fresnel diffraction for the approximation of fractional Fourier transform

Fractional Fourier transformation of an object can be approximated by the object's free-space Fresnel diffraction pattern under some restricted conditions and plane wave illumination according to Hua's method. A better approximation is achieved under least-squared conditions developed in this paper. Simulation results verify that our theoretical development works for any fractional order a compared with the previous approach.