Homogeneous DNA Detection Based on Fluorescence Quenching by Nanoparticles in Single-step Format :Target-Induced Configuration Transform

A new strategy for homogeneous detection of DNA hybridization in single-step format was developed based on fluorescence quenching by gold nanoparticles. The gold nanoparticle is functionalized with 5’-thiolated 48-base oligonucleotide (probe sequence), whose 3’-terminus is labeled with fluorescein (FAM), a negatively charged fluorescence dye. The oligonucleotide adopts an extended configuration due to the electrostatic repulsion between negatively charged gold nanoparticle and the FAM-attached probe sequence. After addition of the complementary target sequence, specific DNA hybridization induces a conformation change of the probe from an extended structure to an arch-like configuration, which brings the fluorophore and the gold nanoparticle in close proximity. The fluorescence is efficiently quenched by gold nanoparticles. The fluorescence quenching efficiency is related to the target concentration, which allows the quantitative detection for target sequence in a sample. A linear detection range from 1.6 to 209.4 nmol/L was obtained under the optimized experimental conditions with a detection limit of 0.1 nmol/L. In the assay system, the gold nanoparticles act as both nanoscaffolds and nanoquenchers. Furthermore, the proposed strategy, in which only two DNA sequences are involved, is not only different from the traditional molecular beacons or reverse molecular beacons but also different from the commonly used sandwich hybridization methods. In addition, the DNA hybridization detection was achieved in homogenous solution in a single-step format, which allows real-time detection and quantification with other advantages such as easy operation and elimination of washing steps.     

振动圆二色谱: 一种确定手性分子绝对构型的新方法

手性分子绝对构型的确定是一个极其重要且长期存在的问题. 振动圆二色谱是在红外波长区域测定分子圆二色性的一种新方法, 极大地扩展了圆二色谱的应用范围. 振动圆二色谱法通过构象搜索、量子化学计算等手段准确预测手性分子的振动圆二色谱图, 进而与实测谱图进行比较确定其绝对构型. 该方法已经得到了越来越广泛的应用, 必将成为一种有效测定手性分子绝对构型的常规方法.     

Synthesis and structural determination of the C33-C42 fragment of symbiodinolide

Symbiodinolide (1) is a polyol macrolide with a molecular weight of 2859 mu. As one of the degradation reactions, cross-metathesis of 2, which is a methyl ester of 1, with ethylene was performed to give the C33-C42 degraded fragment 4. The absolute configuration of 4 was estimated to be (36S,40S) by Mosher method. Stereoselective synthesis of 4 was achieved in 14 steps from l-aspartic acid. Synthetic bis-(S)- and (R)-MTPA esters exhibited the spectroscopic data identical with those of bis-(S)- and (R)-MTPA esters derived from the degraded fragment 4. Thus, the absolute stereochemistry of 4 was elucidated to be (36S,40S).     

The configuration polytope of ℓ-line configurations in Steiner triple systems

It has been shown that the number of occurrences of any ℓ-line configuration in a Steiner triple system can be written as a linear combination of the numbers of full m-line configurations for 1 ≤ m ≤ ℓ; full means that every point has degree at least two. More precisely, the coefficients of the linear combination are ratios of polynomials in v, the order of the Steiner triple system. Moreover, the counts of full configurations, together with v, form a linear basis for all of the configuration counts when ℓ ≤ 7. By relaxing the linear integer equalities to fractional inequalities, a configuration polytope is defined that captures all feasible assignments of counts to the full configurations. An effective procedure for determining this polytope is developed and applied when ℓ = 6. Using this, minimum and maximum counts of each configuration are examined, and consequences for the simultaneous avoidance of sets of configurations explored. To Alex Rosa on the Occasion of his Seventieth Birthday     

Stability of steady multi-wave configurations for the full Euler equations of compressible fluid flow

We are concerned with the stability of steady multi-wave configurations for the full Euler equations of compressible fluid flow. In this paper, we focus on the stability of steady four-wave configurations that are the solutions of the Riemann problem in the flow direction, consisting of two shocks, one vortex sheet, and one entropy wave, which is one of the core multi-wave configurations for the two-dimensional Euler equations. It is proved that such steady four-wave configurations in supersonic flow are stable in structure globally, even under the BV perturbation of the incoming flow in the flow direction. In order to achieve this, we first formulate the problem as the Cauchy problem (initial value problem) in the flow direction, and then develop a modified Glimm difference scheme and identify a Glimm-type functional to obtain the required BV estimates by tracing the interactions not only between the strong shocks and weak waves, but also between the strong vortex sheet/entropy wave and weak waves. The key feature of the Euler equations is that the reflection coefficient is always less than $1$, when a weak wave of different family interacts with the strong vortex sheet/entropy wave or the shock wave, which is crucial to guarantee that the Glimm functional is decreasing. Then these estimates are employed to establish the convergence of the approximate solutions to a global entropy solution, close to the background solution of steady four-wave configuration.     

Asymptotic normality in random graphs with given vertex degrees

We consider random graphs with a given degree sequence and show, under weak technical conditions, asymptotic normality of the number of components isomorphic to a given tree, first for the random multigraph given by the configuration model and then, by a conditioning argument, for the simple uniform random graph with the given degree sequence. Such conditioning is standard for convergence in probability, but much less straightforward for convergence in distribution as here. The proof uses the method of moments, and is based on a new estimate of mixed cumulants in a case of weakly dependent variables. The result on small components is applied to give a new proof of a recent result by Barbour and Röllin on asymptotic normality of the size of the giant component in the random multigraph; moreover, we extend this to the random simple graph.     

Random graphs with given vertex degrees and switchings

Random graphs with a given degree sequence are often constructed using the configuration model, which yields a random multigraph. We may adjust this multigraph by a sequence of switchings, eventually yielding a simple graph. We show that, assuming essentially a bounded second moment of the degree distribution, this construction with the simplest types of switchings yields a simple random graph with an almost uniform distribution, in the sense that the total variation distance is o(1). This construction can be used to transfer results on distributional convergence from the configuration model multigraph to the uniform random simple graph with the given vertex degrees. As examples, we give a few applications to asymptotic normality. We show also a weaker result yielding contiguity when the maximum degree is too large for the main theorem to hold.     

相对论效应在化学中的作用--纪念相对论发表100周年

讨论了相对论效应及其对第6周期元素的电子组态和性质的影响,阐述了在相对论效应作用下金的化学性质并将它和汞与银的化学性质进行对比．     

如何用光波激发金属表面等离体子振荡

通过求解金属表面的麦克斯韦方程,证明了光波不能直接激发表面等离体子波．介绍了Otto装置和Kretschmann装置,这两种装置可利用光波全反射时产生的倏逝波激发表面等离体子波,给出了这两种装置中棱镜和介质的相对电容率关系以及对中间层厚度的要求．     

Tokamak residual zonal flow level in near-separatrix region

Residual zonal flow level is calculated for tokamak plasmas in the near-separatrix region of a diverted tokamak. A recently developed method is used to construct an analytic divertor tokamak configuration. It is shown that the residual zonal flow level becomes smaller but still keeps finite near the separatrix because the neoclassical polarisation mostly due to the trapped particles goes larger in this region.