Efficient interface conditions based on a 5-point finite difference operator

A new 5-point finite difference operator is developed for integrated optics simulations. Interfaces are taken into account accurately. The eigenvalues of the discretization matrix converge rapidly, according to O(x4). Implementation of the operator in a beam propagator leads to a highly efficient computation scheme.     

On the characterization of grid density in grid refinement studies for discretization error estimation

This paper discusses the estimation of discretization errors on the basis of power series expansions for grid sets that are not geometrically similar, that is, grids not exhibiting a constant grid refinement ratio for the entire computational domain. Simple test cases with structured and unstructured grids are used to demonstrate that reliable error estimates on the basis of power series expansions can be made if the grids are refined systematically. However, if the grid refinement ratio is not constant in the complete domain, the definition of the typical cell size is not obvious, and the observed order of accuracy may not be equal to the expected theoretical order of the discretization. Some alternatives for the definition of the typical cell size are tested. In these tests, the error estimation does not show a significant effect of the definition of the typical cell size even for some cases with data sets clearly outside the ‘asymptotic range’. For non‐geometrically similar grids, the best estimates of the observed order of accuracy are obtained with the typical cell size on the basis of the mode of the cell size (the cell size that occurs more often in a given grid). Copyright © 2012 John Wiley & Sons, Ltd.     

Length effects in VUV photofragmentation of protonated peptides

We have studied photoionization of protonated synthetic peptides YG(n)F (n = 0, 1, 3, 5, 10). Photon energies ranging from 8 to 30 eV were used. For YG(n)F peptides up to n = 5 small fragment ions related to the sidechains of the aromatic terminal amino acids Y and F dominate the fragmentation patterns. The associated yields scale with total photoabsorption cross section, demonstrating efficient hole migration towards the terminal amino acids upon photoionization of the peptide backbone. For n = 10 the side-chain loss channel is quenched and a series of large dications appear.     

Plasmid DNA damage by heavy ions at spread-out Bragg peak energies

Interaction of ionizing radiation with plasmid DNA can lead to formation of single strand breaks, double strand breaks and clustered lesions. We have investigated the response of the synthetic plasmid pBR322 in aqueous solution upon irradiation with ¹²C ions under spread-out Bragg peak conditions (densely ionizing) and with ¹³⁷Cs γ-photons (sparsely ionizing) as a function of dose. To evaluate the relevance of indirect effects, i.e. influences of diffusion limited radical induced DNA damage triggered by water radiolysis, the experiments were performed at various concentrations of the radical scavenger mannitol. Agarose gel electrophoresis was employed to quantify the DNA damage. At low scavenger concentration for a given dose DNA damage is higher for γ-photons than for ¹²C. For the latter, the microscopic dose distribution is inhomogeneous, with very high dose deposited along the few tracks through the solution. This is in agreement with the concept that scavengers efficiently reduce damage for γ-photons, implying that the underlying damage mechanism is single strand break induction by OH radicals. For ¹²C induced damage, the fraction of SSB and DSB that is unaffected by radical scavengers and thus due to direct effect is quantified.     

New true fourth-order accurate scalar beam propagation methods for both TE and TM polarization

New 2D scalar beam propagation methods for both TE and TM polarization are presented. Both second- and fourth-order accurate schemes, in the lateral stepsize, are shown. The methods use uniform discretization and can handle arbitrary positions of interfaces between materials with different refractive indices. Either Transparent Boundary Conditions or Perfectly Matched Layers are used at the boundary of the computational window.     

Determination of volume, shape and refractive index of individual blood platelets

Light scattering patterns (LSP) of blood platelets were theoretically and experimentally analyzed. We used spicular spheroids as a model for the platelets with pseudopodia. The discrete dipole approximation was employed to simulate light scattering from an individual spicular spheroid constructed from a homogeneous oblate spheroid and 14 rectilinear parallelepipeds rising from the cell centre. These parallelepipeds have a weak effect on the LSP over the measured angular range. Therefore, a homogeneous oblate spheroid was taken as a simplified optical model for platelets. Using the T-matrix method, we computed the LSP over a range of volumes, aspect ratios and refractive indices. Measured LSPs of individual platelets were compared one by one with the theoretical set and the best fit was taken to characterize the measured platelets, resulting in distributions of volume, aspect ratio and refractive index.     

改性纳米TiO2固相光催化降解废弃聚氯乙烯

用偶联剂改性的纳米TiO2作催化剂，采用包埋法制备了一种新型的可光催化降解的纳米PVC-M-TiO2复合薄膜．在空气中紫外光照的条件下进行了该薄膜的光催化降解实验，并与以末改性的TiO2为催化剂的PVC-Un-TiO3复合薄膜的降解效率进行了比较，利用光照失重、傅立叶红外（FT-IR）光谱和扫描电子显微镜（SEM）等方法对光照前后复合薄膜进行厂分析表征．实验结果表明PVC-M-TiO2复合薄（TiO2质量百分含量为2％）膜在空气中能被有效的降解，连续光照480h后降解效率达到36．9％，明屁高于纯膜及未改性的PVC-Un-TiO2复合膜。     

Multiple ionization and fragmentation of the DNA base thymine by interaction with C q+ ions

Ionization and fragmentation of the DNA base thymine upon interaction with keV C^q+ ions (q = 1 - 6) has been studied. By means of time-of-flight spectrometry of two or more thymine fragments in coincidence with an ejected electron we could investigate particular dissociation channels by means of their associated kinetic-energy-release. The fragmentation dynamics are strongly influenced by the C^q+ charge state: for low q values mainly fragmentation due to direct collisions is observed. With increasing q, electron capture becomes more important. For larger q we could identify several Coulomb explosion channels, leading to very energetic fragments.     

光学耗散系统的准热力学模型及其在光学双稳性相变问题上的应用

本文以光学耗散系统为范例,论证在满足细致平衡原理的条件下,可以与传统热力学相平行地发展一种“准热力学”模型。然后运用此模型系统而普遍地讨论了光学双稳系统的临界现象与相变。又借助Ginzburg-Landau模型处理了光学双稳性(第二类)临界点附近的涨落与关联。将平衡热力学的Landau相变理论推广到具有双稳性并远离热平衡的耗散系统。