直管束流固耦合振动的数值模拟

为了研究反应堆结构中的诸如燃料棒、蒸汽发生器和其它换热器传热管束等的流体-结构交互作用问题,利用有限体积法离散大涡模拟(large eddy simulation, LES)的流体控制方程,用有限元方法求解结构动力学方程,并结合动网格技术,建立三维流体诱发振动的数值模型,模拟直管束中流体的流动及结构振动,实现计算结构动力学(computational structure dynamics, CSD)与计算流体力学(computational fluid dynamics, CFD)之间的联合仿真．首先,基于流固耦合方法对单管的流致振动特性进行了详细分析,得到了其动力学响应与流场特性;其次基于建立的传热管束流致振动计算模型,研究了两并列管、两串列管以及3×3正方形排列管束的流致振动行为．     

一种基于空间一致性降元的高光谱图像非监督分类

为了提高分类精度和边缘辨识性,该文引入图像空间一致性降元(pixels reduction with spatial coherence property, PRSCP)及线性回归分析,提出了一种基于空间一致性降元的非监督分类。该方法从像元光谱相似性出发,利用像元最小关联窗口合并相邻相似像元为像块完成降元。使用线性关系建模像块内像元的光谱向量,并利用F检验判断像块数据的线性显著性。利用一元线性回归(one dimensional linear regression, ODLR)估计出像块的基准向量,根据基准向量合并相似(同类)像块完成分类。利用AVIRIS数据评估了该方法性能,实验结果表明：与K-MEANS和ISODATA方法相比,该方法精度高、边缘辨识度好及鲁棒性强。     

Ka波段宽带谐波抑制定向耦合器

为解决传统分支线定向耦合器带宽较窄,且应用到线性化器等微波元件中时受谐波信号影响较大的问题,提出了一个宽带且带有谐波抑制功能的定向耦合器。该定向耦合器在双支节定向耦合器的基础上增加一个支节,可有效地提高定向耦合器的带宽,同时将其传输线支节替换为低通滤波结构,以实现对高次谐波抑制的作用。仿真结果表明,该定向耦合器的反射系数和隔离度均小于-15 dB,传输损耗小于3.8 dB,波动范围0.5 dB,相位差为90°且与双支节耦合器相比增加1 GHz带宽。满足耦合器的设计指标,可应用到微波元件中,提高微波元件的性能。     

Noether Symmetry and Conserved Quantities of Fractional Birkhoffian System in Terms of Herglotz Variational Problem

The aim of this paper is to study the Herglotz variational principle of the fractional Birkhoffian system and its Noether symmetry and conserved quantities. First, the fractional Pfaff-Herglotz action and the fractional PfaffHerglotz principle are presented. Second, based on different definitions of fractional derivatives, four kinds of fractional Birkhoff’s equations in terms of the Herglotz variational principle are established. Further, the definition and criterion of Noether symmetry of the fractional Birkhoffian system in terms of the Herglotz variational problem are given. According to the relationship between the symmetry and the conserved quantities, the Noether’s theorems within four different fractional derivatives are derived, which can reduce to the Noether’s theorem of the Birkhoffian system in terms of the Herglotz variational principle under the classical conditions. As applications of the Noether’s t heorems of the fractional Birkhoffian system in terms of the Herglotz variational principle, an example is given at the end of this paper.     

Noether symmetry and conserved quantity for dynamical system with non-standard Lagrangians on time scales

This paper focuses on studying the Noether symmetry and the conserved quantity with non-standard Lagrangians,namely exponential Lagrangians and power-law Lagrangians on time scales. Firstly, for each case, the Hamilton principle based on the action with non-standard Lagrangians on time scales is established, with which the corresponding Euler–Lagrange equation is given. Secondly, according to the invariance of the Hamilton action under the infinitesimal transformation, the Noether theorem for the dynamical system with non-standard Lagrangians on time scales is established.The proof of the theorem consists of two steps. First, it is proved under the infinitesimal transformations of a special one-parameter group without transforming time. Second, utilizing the technique of time-re-parameterization, the Noether theorem in a general form is obtained. The Noether-type conserved quantities with non-standard Lagrangians in both classical and discrete cases are given. Finally, an example in Friedmann–Robertson–Walker spacetime and an example about second order Duffing equation are given to illustrate the application of the results.     

相空间中非保守系统的Herglotz广义变分原理及其Noether定理

与经典变分原理相比,基于由微分方程定义的作用量的Herglotz广义变分原理给出了非保守动力学系统的一个变分描述,它不仅能够描述所有采用经典变分原理能够描述的动力学过程,而且能够应用于经典变分原理不能适用的非保守或耗散系统.将Herglotz广义变分原理拓展到相空间,研究相空间中非保守力学系统的Herglotz广义变分原理与Noether定理及其逆定理.首先,提出相空间中Herglotz广义变分原理,给出相空间中非保守系统的变分描述,导出相应的Hamilton正则方程;其次,基于非等时变分与等时变分之间的关系,导出相空间中Hamilton-Herglotz作用量变分的两个基本公式;再次,给出Noether对称变换的定义和判据,提出并证明相空间中非保守系统基于Herglotz变分问题的Noether定理及其逆定理,揭示了相空间中力学系统的Noether对称性与守恒量之间的内在联系.在经典条件下,Herglotz广义变分原理退化为经典变分原理,与之相应的相空间中的Noether定理退化为经典Hamilton系统的Noether定理.文末以著名的Emden方程和平方阻尼振子为例说明上述方法和结果的有效性.     

关于Mei对称性与Noether对称性的关系——以Lagrange系统为例

文章以Lagrange系统为例研究Mei对称性与Noether对称性之间的关系.基于无限小生成元向量作用下Lagrange函数的变分问题,建立了其Euler--Lagrange方程,研究了该变分问题的Noether对称性与守恒量.研究表明:该变分问题的Euler--Lagrange方程,Noether等式和Noether守恒量分别与Lagrange系统Mei对称性的判据方程,结构方程和Mei守恒量完全一致.文末以著名的Emden方程为例说明结果的应用.     

Evidence of polymorphic transformations of Sn under high pressure

The high-pressure polymorphs and structural transformation of Sn were experimentally investigated using angledispersive synchrotron x-ray diffraction up to 108.9 GPa. The results show that at least at 12.8 GPa β-Sn→bct structure transformation was completed and no two-phase coexistence was found. By using a long-wavelength x-ray, we resolved the diffraction peaks splitting and discovered the formation of a new distorted orthorhombic structure bco from the bct structure at 31.8 GPa. The variation of the lattice parameters and their ratios with pressure further validate the observation of the bco polymorph. The bcc structure appears at 40.9 GPa and coexists with the bco phase throughout a wide pressure range of40.9 GPa–73.1 GPa. Above 73.1 GPa, only the bcc polymorph is observed. The systematically experimental investigation confirms the phase transition sequence of Sn as β-Sn→bct→bco→ bco + bcc→bcc upon compression to 108.9 GPa at room temperature.     

荧光光谱结合支持向量机测定食用色素纯度

采用一种由原点矩法改造所得的特征压缩算法对荧光光谱数据进行预处理,将处理后的数据与加权最小二乘支持向量机(WLS-SVM)算法结合,建立鲁棒回归模型,用以预测实际食用色素粉末的纯度。以亮蓝和胭脂红这2种色素为例论述该方法对实际食用色素粉末纯度的预测效果。首先,利用FLS920荧光光谱仪测量获得两种色素的标准样本和实际样本在最佳激发波长下的荧光发射光谱数据,利用由原点矩法改造所得的特征压缩算法对获取的荧光光谱数据进行压缩和变换,一方面缩短了算法的运算时间,另一方面也提高了模型的预测精度。将预处理后的荧光光谱数据输入加权最小二乘支持向量机中建立浓度预测模型,该模型对亮蓝、胭脂红实际样本溶液给出的预测光谱与它们的实测光谱吻合程度好,半高峰宽区间内的平均决定系数分别为0.662和0.931。所有亮蓝、胭脂红溶液的预测浓度和标称浓度之间具有良好的线性关系,相关系数分别为0.997和0.992。由此通过多项式拟合得到的亮蓝、胭脂红粉末的预测纯度分别为61.0%和72.3%。