Improvements in Carrier-to-Noise-Ratio (CNR) of Lightwave Amplitude Modulated Vestigial-Sideband (AM-VSB) Transmission Systems by the Use of Optical Isolators

In lightwave community antena television (CATV) systems as well as other optical fiber communication networks, a transmitted optical signal is known to be degraded by an intensity noise produced within the fiber due to the interference between the signal and doubly reflected light. We report on the improvements to the signal degradation due to the double Rayleigh backscattering by inserting optical isolators in the trunk lines of the systems. A carrier-to-noise ratio (CNR) has been calculated as a function of the number and the insertion loss of the isolators. The calculated results indicate that there is an optimum number of isolators, and if the insertion loss is less than 0.3 dB, the CNR degradation can be restored by more than 60%. To test the calculated results, we conducted experiments for the specific case of employing one isolator, and obtained good agreements between the two.     

A thickness independent radiochromic film dosimetry system

A new radiochromic thin film dosimeter has been developed for use in radiation processing. The dosimeter's properties are similar to those of the commercially available FWT-60-00 Radiochromic Detectors with three key differences: 1) a lower sensitivity allows reading the optical density at the peak of the absorbtion spectrum (ca. 600 nm) for absorbed doses to over 50 kGy, 2) a radiation-insensitive dye additive allows for automatic thickness correction, and 3) another additive extends to higher doses the agreement between gamma and E-beam calibrations. The dosimeter is analyzed for its sensitivity, temperature and humidity dependencies, stability, reproducibility, and agreement of gamma and E-beam calibrations.     

90°束转动环形非稳腔模场数值分析

用矩阵方法导出了ＵＲ９０（ｕｎｓｔａｂｌｅｒｉｎｇｒｅｓｏｎａｔｏｒｗｉｔｈ９００１６７ｂｅａｍｒｏｔａｔｉｏｎ）环形非稳腔的衍射积分方程，获得了腔的等价菲涅耳数Ｎｅｑ的关系公式，分析了反向模的抑制方法并给出反向模抑制镜的曲率半径，通过数值计算的方法阐明了腔模本征值与放大因子Ｍ的变化关系，当腔的放大因子Ｍ＝１．２时，得到了腔的模场分布曲线。     

非傍轴光束的光束质量因子．I特性分析

使用傅里叶变换和施瓦兹不等式证明：非傍轴标量光束的Ｍ２因子存在有一个只能无限趋近、却永远都不可能达到的下限１；并对一些与此相关的问题进行了讨论     

高密度聚乙烯粉末的电子束辐射接枝

高密度聚乙烯粉末的电子束辐射接枝王勇，黄劲，李瑞海（成都科技大学纺织工学院，成都６１００６５）（成都科技大学高分子材料系６１００６５）关键词：ＨＤＰＥ粉末，电子束辐射，接枝聚合本文采用电子束予辐射法使聚乙烯粉末表面产生活性中心，然后通过液－固相接枝共...     

Overall values of conventional discrepancy indices for related and unrelated models of a non-centrosymmetric crystal with a centrosymmetric group

Theoretical expressions for the overall values of the conventional discrepancy indicesR(F) andR(I) are derived for a non-centrosymmetric crystal with a centrosymmetric group by taking the centrosymmetric group and a part of the other atoms in the unit cell as the trial structure. These results are used to obtain tables of values of these indices in terms of the parameter σ _1c ² and σ ₁ ² which define the fractional contribution to the local mean intensity from the centrosymmetric group and all the known atoms respectively. Contribution No. 561     

亚乙基硫脲分子键伸缩模式与全耦合模式键极化率的对比及其拉曼激发虚态的相关研究

从拉曼峰强着手,得到了键伸缩模式与全耦合模式两种不同计算条件下,亚乙基硫脲(ethylene thiourea,ETU)分子的键极化率,并比较分析了两种计算结果的异同.研究表明:在键伸缩模式的算法中,仅考虑势能分布中键对称伸缩比重相对较大的部分拉曼峰参与极化率计算,显然忽略了键伸缩与键弯曲间的相互耦合,造成了与弯曲振动耦合较强的部分键伸缩极化率值存在一定误差.因此,此方法虽能使问题简化,但却丢失了一些信息.而全耦合模式算法考虑了所有振动模式(键伸缩与键弯曲)相互影响的情况,能更全面的反映键电荷的分布情况,但却会使问题的求解过程变得复杂.同时,在拉曼激发虚态的相关研究中,两种计算方法却得到几乎一致的键极化率弛豫方式(呈单指数规律衰减)及相同的衰减特征时间.     

基于随机并行梯度下降算法的多波长激光相干合成

由于受到受激布里渊散射(SBS)等非线性效应的限制,单频激光放大器的功率在百瓦量级,以非单频激光多波长激光作为种子源能够有效地抑制SBS并提高放大器功率.与单频激光相干合成相比,非单频率、多波长激光的相干合成有望将输出激光功率成量级地提高.基于随机并行梯度下降(stochastic parallel gradient descent,SPGD)算法,实现了四波长激光的相干合成.在系统闭环时,四路多波长激光合成后的主瓣能量能够提高3倍,达到理想值的75%.验证了多波长、非单频激光相干合成的可行性,为高功率相干合成的发展提供了新的途径.     

对于具有大范围运动和非线性变形的柔性梁的有限元动力学建模

研究具有大范围运动和非线性变形的柔性梁的有限元动力学建模.采用有限元方法对梁结构进行离散,利用Lagrange方程建立系统的精确动力学方程.该方程不仅增加了新的表征纵向、横向、侧向弯曲变形,以及扭转变形的耦合项,同时包含了变形运动与大范围运动之间的相互耦合项.