基于琼斯矩阵的FIR晶体光滤波器设计方法

FIR晶体光滤波器由夹在两个偏振片之间的N个厚度相同的晶片构成,设计过程中需要根据要求的频率响应求出各个晶体波片的光轴方向和输出端偏振片的通光方向.提出了一种基于琼斯矩阵的反向递推设计方法.FIR晶体光滤波器的琼斯矩阵是各个晶片以及偏振片琼斯矩阵的乘积,利用这一关系可以建立简单的反向递推关系,并计算出与输出偏振分量对应的正交偏振分量,通过迭代运算确定所有元件的角度参数.实例设计的结果与使用其它方法得到的结果一致,设计过程简单.     

锁相检测式二维小角度测量装置

介绍了一种新型的二维小角度检测装置。由于该装置采用了光电自准直结构,以高灵敏度的四象限硅光电探测器作为检测元件,采用交流调制,锁相放大的方法对信号进行了处理,所以有效地消除了直流漂移的影响,提高了稳定性和测试精度。分析了光斑的形状和大小对测试结果的影响,研制了专门的标定装置。首先由高精度的光电自准直仪标定测量角度与输出信号的关系,并将相关数据存入单片机,然后由软件拟合出关系曲线。测量时,既可自动显示角度的大小,同时也可以与计算机相连。该测试系统结构小巧,具有较高的测量精度。     

小分子RNA家族中的新成员--microRNA

近来,人们在多种生物中发现了一类新的小分子RNA——microRNA(miRNA)．miRNA是20～24nt的单链RNA,在进化上具有高度的保守性,它通过与靶mRNA不完全互补配对,抑制蛋白翻译,调节内源基因表达,在基因调控中扮演了重要的角色．miRNA和siRNA(small interferenceRNA)在生成机制、作用途径等方面关系密切,它们既有区别又相互联系．小分子RNA的研究将是今后分子生物学的研究热点之一．     

Facile one-pot synthesis of α-bromoketones from olefins using bromide/bromate couple as a nonhazardous brominating agent

A new method for the preparation of α-bromoketones from olefins using bromide/bromate couple as a nonhazardous brominating agent has been developed. Several α-bromoketones were successfully prepared from a variety of olefins by this method. This procedure is an alternative to conventional molecular bromine.     

A photo-oxidation procedure using UV radiation/H2O2 for decomposition of wine samples — Determination of iron and manganese content by flame atomic absorption spectrometry

This paper proposes the use of photo-oxidation with UV radiation/H₂O₂ as sample pretreatment for the determination of iron and manganese in wines by flame atomic absorption spectrometry (FAAS). The optimization involved the study of the following variables: pH and concentration of buffer solution, concentrated hydrogen peroxide volume and irradiation time. The evaluation of sample degradation was monitored by measuring the absorbance at the maximum wavelength of red wine (530 nm). Using the experimental conditions established during the optimization (irradiation time of 30 min, oxidant volume of 2.5 mL, pH 10, and a buffer concentration of 0.15 mol L^− 1), this procedure allows the determination of iron and manganese with limits of detection of 30 and 22 μg L^− 1, respectively, for a 5 mL volume of digested sample. The precision levels, expressed as relative standard deviation (RSD), were 2.8% and 0.65% for iron and 2.7% and 0.54% for manganese for concentrations of 0.5 and 2.0 mg L^− 1, respectively. Addition/recovery tests for evaluation of the accuracy were in the ranges of 90%–111% and 95%–107% for iron and manganese, respectively. This digestion procedure has been applied for the determination of iron and manganese in six wine samples. The concentrations varied from 1.58 to 2.77 mg L^− 1 for iron and from 1.30 to 1.91 mg L^− 1 for manganese. The results were compared with those obtained by an acid digestion procedure and determination of the elements by FAAS. There was no significant difference between the results obtained by the two methods based on a paired t-test (at 95% confidence level).     

Lie symmetries of soliton equations with self-consistent sources via source generation procedure

In this paper, the ‘source generation’ procedure (SGP) proposed by Hu and Wang [X.B. Hu, H.Y. Wang, Construction of dKP and BKP equation with self-consistent sources, Inverse Problems 22 (2006) 1903-1920] is utilized to derive Lie symmetries of bilinear soliton equations with self-consistent sources (SESCS) such as KPESCS, BKPESCS, and differential-difference KPESCS. Furthermore, it is shown that these Lie symmetries constitute generators of the corresponding Lie symmetry algebras.     

An oriented coloring of planar graphs with girth at least five

An oriented k-coloring of an oriented graph G is a homomorphism from G to an oriented graph H of order k. We prove that every oriented graph with a maximum average degree less than and girth at least 5 has an oriented chromatic number at most 16. This implies that every oriented planar graph with girth at least 5 has an oriented chromatic number at most 16, that improves the previous known bound of 19 due to Borodin et al. [O.V. Borodin, A.V. Kostochka, J. Nešet?il, A. Raspaud, É. Sopena, On the maximum average degree and the oriented chromatic number of a graph, Discrete Math. 206 (1999) 77-89].     

团队中枢节点的效率模型

集团性是社会网络的显著特征.团队作为一个小规模的社会网络,也存在网络结构的非均匀性以及中枢节点.在阐述团队网络的集团性和中枢节点导致网络的两面性等结构特征的基础上,运用小世界模型的局部效率和集聚系数等指标,建立了团队中枢节点的效率模型,并通过网络结构的调整(如加键和断键重连)研究了网络结构对中枢节点的效率的影响.     

Determination of metals, metalloids and non-volatile ions in airborne particulate matter by a new two-step sequential leaching procedure Part B: Validation on equivalent real samples

Due to the lack of proper standard materials for airborne particulate matter collected on filters, a validation scheme was developed, which is here described, to the aim of testing the application of leaching procedures performing both ions and elemental determinations on real samples of airborne particulate matter collected on filters. The scheme has been developed on a two-step leaching method (extraction in acetate buffer and acid dissolution of residue) previously developed by authors and consists of two series of tests to be run on n pairs of equivalent parallel samples filter-collected. The first series of tests aims to assess on real samples the equivalence between results obtained by the tested procedure with those obtained by the EMEP ions extraction and the EN 12341 standard methods, whereas the second aims to evaluate the reproducibility of analytical results of elemental determination in the leached and dissolved fractions; in the latter case data reliability is also evaluated as a function of the environment-intrinsic variability of real samples.To avoid errors due to sampling differences data from filter pairs were standardized both by gravimetric determination of loaded filters, according to the EN 12341 standard and by the rate [SO₄²⁻]_A/[SO₄²⁻]_B, where [SO₄²⁻] indicate the soluble sulphate concentration in the extract; in the latter case values improved for all elements and in both fractions. Results of equivalence with standard methods and reproducibility tests are evaluated as mean relative percentage differences (Δ%) and percentage elements recoveries (R%). The application of the validation scheme to the two-step leaching method is here discussed for non-volatile ions and for 17 elements detected on 22 pairs of low-volume collected PM₁₀ samples on Teflon filters.     

On the efficient evaluation of Fourier patterns for nanoparticles and clusters

Samples made of an isotropically oriented ensemble of atomic clusters or structures that are not large crystals (i.e. extended less than 10 periods in each direction) are at the frontier of today's material science and chemistry. Examples are nanoparticles, nanotubes, amorphous matter, polymers, and macromolecules in suspension. For such systems the computation of powder diffraction patterns (which may provide an efficient characterization) is to be performed the hard way, by summing contributions from each atom pair. This work deals with performing such computation in the most practical and efficient way. Three main points are developed: how to encode the enormous array of interatomic distances (which increase as the square or higher powers of the cluster diameter) to a much smaller array of equispaced values on a coarse grid (whose size increases linearly with the diameter); how to perform a fast computation of the diffraction pattern from this equispaced grid; how to optimize the grid step to obtain an arbitrarily small error on the computed diffraction pattern. Theory and examples are jointly developed and presented.