Bragg scattering induces Fano resonance in photonic crystals

We present a study of a Fano resonance between a narrow Bragg band and disorder-induced continuum in photonic crystals where the continuum is either of the broad band Fabry-Pérot scattering in an imperfect one-dimensional photonic crystal or Mie scattering in an imperfect three-dimensional photonic crystal. Our experimental studies of synthetic opals have demonstrated how the Fano resonance may lead to a transmission spectrum exhibiting a Bragg dip with an asymmetric profile or a Bragg rise.     

Subtree Transfer Operations and Their Induced Metrics on Evolutionary Trees

. Leaf-labelled trees are widely used to describe evolutionary relationships, particularly in biology. In this setting, extant species label the leaves of the tree, while the internal vertices correspond to ancestral species. Various techniques exist for reconstructing these evolutionary trees from data, and an important problem is to determine how "far apart" two such reconstructed trees are from each other, or indeed from the true historical tree. To investigate this question requires tree metrics, and these can be induced by operations that rearrange trees locally. Here we investigate three such operations: nearest neighbour interchange (NNI), subtree prune and regraft (SPR), and tree bisection and reconnection (TBR). The SPR operation is of particular interest as it can be used to model biological processes such as horizontal gene transfer and recombination. We count the number of unrooted binary trees one SPR from any given unrooted binary tree, as well as providing new upper and lower bounds for the diameter of the adjacency graph of trees under SPR and TBR. We also show that the problem of computing the minimum number of TBR operations required to transform one tree to another can be reduced to a problem whose size is a function just of the distance between the trees (and not of the size of the two trees), and thereby establish that the problem is fixed-parameter tractable.     

大孔聚丙烯醛-呋喃-2-硫代酰腙螯合树脂的合成及其性能的初步研究

合成了一新型高分子骨架，大孔内烯醛－苯乙烯－二乙烯苯三元共聚物树脂骨架，通过其含有的活泼醛基与呋喃－2－硫代酰肼螯合剂进行高分子反应，制备了一种含氮、硫配位原子的螯合树脂，聚丙烯醛－呋喃－2－硫代酰腙。对其与贵金属离子的吸附性能进行了初步研究，结果表明，该树脂对金、钯及铂具有选择性吸附作用，吸附容量分别为1.20mmol/g干树脂，0.37mmol/g干树脂及0.28mmol/g干树脂。     

Nitrogen heterocycles as building blocks for new metallosupramolecular architectures

The syntheses of representative examples of five classes of new heterocyclic ligands are described. These include N,N'-chelating bis-heterocycles, binucleating ligands, cyclometallated compounds, chiral ligands and a family of polyheteroaryl-linked arenes.     

Estimation of two normal means which may be common

Consider the problem of estimating the mean of a normal population when independent samples from this as well as a second normal population are available. Pre-test estimators which combine the two sample means if a test of the hypothesis of equal population means accepts but otherwise use only the first sample mean, are compared to limited translation estimators which are derived in the spirit of Bickel (1984, Ann. Statist., 12, 864–879) (we also cover the cases of unknown variances). Our conclusion is that if the accuracy with which the second population mean can be estimated is of the same or better order of magnitude as teh accuracy with which the first can be estimated, then the limited translation estimators largely dominate the pre-test estimators in terms of mean square error loss.This research was supported by grants from the FRD of the CSIR of South Africa.     

应用分析电子显微镜考察铂锡催化剂上的积炭

在高分散铂锡催化剂上分别以正丁烷,正己烷及长链烷烃为反应物经催化剂脱氢表面积炭。从电子显微镜图像观察到积炭有多种结构,最小的炭粒呈条纹排列,炭粒集聚形成球状炭黑及不同形状的石墨结晶。选区电子衍射分析炭(002)晶面间距有3.35～4.13A变化表明石墨化程度不同。三种积炭样品的电子能量损失谱相应地亦展示明显的差别。     

Fluorosulfonic acid induced ring opening of pinanones: pinane chirality in synthesis1

The acid-catalysed ring opening of a number of substituted nopinones to give 4-(2-propyl)cyclohex-2-enones is described. In an application of this reaction use has been made of pinane chirality in the synthesis of R-o-mentha-2,4-diene (13) by fluorosulfonic acid-catalysed rupture of cis-verbanone (8) to (4S,5R)- and (4R,5R)-5-methyl-4(2-propyl)cyclohex-2-enone (9 and 10) followed by reduction-elimination.