Localization effects and measure source terms in numerical schemes for balance laws

This paper investigates the behavior of numerical schemes for nonlinear conservation laws with source terms. We concentrate on two significant examples: relaxation approximations and genuinely nonhomogeneous scalar laws. The main tool in our analysis is the extensive use of weak limits and nonconservative products which allow us to describe accurately the operations achieved in practice when using Riemann-based numerical schemes. Some illustrative and relevant computational results are provided.

     

差分吸收光谱法测量大气污染的测量误差分析

差分吸收光谱技术被广泛地应用于测量大气中微量元素的浓度，尽管该技术利用最小二乘法来反演待测气体的浓度，能够得到很高的测量精度。但是，由于仪器本身的噪声以及测量波段其它气体的干扰等，使得仪器的测量有一定的误差，而且上述因素还决定着仪器的测量下限。对差分吸收光谱方法的测量误差以及引起误差的原因作了详细的分析。     

In situ neutron diffraction study (300-1273 K) of non-stoichiometric strontium ferrite SrFeOx

The high-temperature cubic phase of non-stoichiometric strontium ferrite SrFeO_x (2.5≤x≤3.0) has been studied by in situ neutron powder diffraction in air over the temperature range 300-1273 K. The composition of SrFeO_x changes within the range 2.56≤x≤2.81 from 1273 to 673 K, respectively.Rietveld refinements of the diffraction patterns show that the high-temperature cubic phase of SrFeO_x is consistent with a face-centred Fm3c structure. This structure leads to agreement with previous density measurements. This cell allows the high-temperature structure of SrFeO_x to be described in terms of a solid solution of the composition end members. Cubic SrFeO_x at high temperature is found to closely obey Vegard's law. The density of cubic SrFeO_x is also found to exhibit a linear relationship with composition.     

一维光学格子孤子的传输特性及控制研究

利用解析和数值方法研究了在具有横向折射率周期性调制的克尔型非线性介质中光学格子孤子的传输，得到了孤子参数的演化方程以及格子孤子的形成和稳定传输的条件.结果表明：当光束的入射角小于某临界角度时，光束可被类似波导形式的路径俘获而稳定传输，该临界角随折射率调制周期、调制深度的增加而增大，且光束越窄临界值越大.此外，线性空间啁啾虽然对光束传输的中心位置没有任何影响，但会导致光束发散从而破坏格子孤子的形成和稳定传输，对此提出了采用特定功率取值来补偿啁啾作用从而形成格子孤子的方案. 关键词： 光孤子 光学格子 光传输 矩方法     

微振动光电检测与数据采集系统的设计

提出了一种新的光学非接触式测量方法测量了物体的微振动振幅。用激光作为光源,以四象限硅光电池[1]作为光电探测器,借助三角测量原理,投射在振动源表面的激光反射光束在光电探测器上产生平面位移,将位移信号放大,通过A/D模块采集电压数值,并通过串口通信机制在PC终端实时显示。实验结果表明,该方法原理正确,灵敏度高,便于实现连续、快速、自动化检测,在工业在线检测方面具有良好的应用前景。     

宽带膜厚实时监控过程中膜层折射率的确定方法

为了准确计算出镀膜过程中每层膜的折射率，介绍了实时监控过程中确定膜层折射率的2种方法：一种是由实测的透射比光谱直接反算出膜层的折射率；另一种是用最小二乘法的优化算法实时拟合折射率。试验结果表明：在线反算适合单点监控，所得折射率误差小于2%。然而在实际镀膜过程中,由于宽带内膜层参数误差较大,一般大于25%。为此，采用最小二乘法拟合，即在整个宽光谱范围内采集每个波长点的信息，所得结果误差很小，一般都在2％～5%之间,有时可达到10%,在很大程度上提高了实际镀膜时膜厚监控的精度。     

掺钕聚甲基丙烯酸甲酯的光学特性

研究了制备的掺钕螯合物Nd(DBM)3Phen材料的吸收光谱、激发光谱、荧光光谱,应用Judd-Ofelt理论计算了该材料的强度参量．分析了钕离子激发态4F3／2的辐射寿命(631 μs)和4F3／2→4IJ′跃迁的受激发射截面和荧光分支比．     

A Modified Quasi-Newton Method for Structured Optimization with Partial Information on the Hessian

This paper develops a modified quasi-Newton method for structured unconstrained optimization with partial information on the Hessian, based on a better approximation to the Hessian in current search direction. The new approximation is decided by both function values and gradients at the last two iterations unlike the original one which only uses the gradients at the last two iterations. The modified method owns local and superlinear convergence. Numerical experiments show that the proposed method is encouraging comparing with the methods proposed in [4] for structured unconstrained optimization Presented at the 6th International Conference on Optimization: Techniques and Applications, Ballarat, Australia, December 9–11, 2004     

Simulation of the nonlinear vibration of a string using the Cellular Automata based on the reflection rule

In this study, the nonlinear dynamic responses of a string are simulated using the Cellular Automata method based on the reflection rule. In the case of nonlinear systems, the velocity of wave propagation is not constant and depends on the amplitude. A new treatment of the dynamic time step is proposed for the Cellular Automata method considering the effect of the propagation velocity. As numerical examples, first, the dynamic responses of a string with linear characteristic are simulated using the Cellular Automata method. A typical resonance curve can be obtained. Second, the dynamic responses of a string with nonlinear characteristic are simulated using the proposed method. Some characteristic types of vibration can be obtained. It is concluded that the linear and nonlinear dynamic responses of a string may be obtained by simulation using the Cellular Automata method.     

TOF-SIMS imaging of chlorhexidine-digluconate transport in frozen hydrated biofilms of the fungus Candida albicans

The diffusion of the anti-microbial chlorhexidine digluconate (CHG) has been studied in C. albicans biofilms by time-of-flight secondary-ion mass spectrometry (TOF-SIMS). C. albicans has been shown to become resistant to common anti-microbial agents, including CHG, when growing as a biofilm. Mass transport resistance within biofilms has commonly been suggested as a resistance mechanism, but measurement of transport for most anti-microbial agents in biofilms has proven extremely difficult because of the heterogeneity of the biofilms and the difficulty in detecting these agents within an intact biofilm. In this study, TOF-SIMS has been used to study the transport of CHG and glucose in a frozen hydrated biofilm. The TOF-SIMS images reveal a progression of CHG from the top of the biofilm to its base with time. Images suggest that there are channels within the biofilm and show preferential binding of CHG to cellular components of the biofilm. Additionally, both living and dead cells can be identified in the TOF-SIMS images by the sequestration of K⁺ and the presence of cell markers. This study demonstrates that TOF-SIMS has the unique potential to simultaneously observe the presence of an antimicrobial agent, concentration of nutrients, and the viability of the cell population.