Flow tagging velocimetry in a superorbital expansion tube

Abstract. A non-intrusive laser-based method for direct velocity measurements has been demonstrated in a superorbital flow facility. The method is based upon laser enhanced ionisation velocimetry in which a tagged region is created by two step excitation of sodium and subsequent collisional ionisation. The achieved depletion of neutral atoms is then interrogated by planar laser induced fluorescence. The velocities were measured in the freestream at a superorbital condition yielding km/s. These results compare favourably with the measured shock speeds in the facility. Received 15 March 1999 / Accepted 2 March 2000     

A strongly polynomial algorithm for the minimum maximum flow degree problem

Let us consider a network flow respecting arc capacities and flow conservation constraints. The flow degree of a node is sum of the flow entering and leaving it. We study the problem of determining a flow that minimizes the maximum flow degree of a node. We show how to solve it in strongly polynomial time with linear programming.     

基于球形颗粒几何排列的离散元试样高效生成方法

在球体离散元数值模拟中,颗粒的初始排列状态是影响计算效率和计算结果的重要环节。本文采用前进面几何构造算法,提出了一种基于网格搜索的球形颗粒随机排列高效算法。通过求解空间三边方程,满足了粒径设置的任意大小的颗粒依次置入前进面的外侧,并与构成前进面的三个颗粒相互接触。为获得高体积分数的颗粒簇,该算法允许颗粒改变其粒径大小。采用颗粒网格化方法可以简化前进面的搜索,并由此提高排列效率。通过计算平均配位数、体积分数和二阶结构张量的特征值,对不同粒径比下得到的立方体试样进行了分析,得到试样配位数及体积分数均随着粒径比的增大而增大,且得到的试样为各向同性。此外,空间网格的大小和初始颗粒的生成点对随机排列的效率均会产生显著的影响。最后,对非规则铁路道砟进行了精细构造及压碎模拟,发现DEM模拟得到的应力-应变曲线与试验结果基本吻合,验证了该算法得到的颗粒试样在模拟道砟裂纹起裂、扩展等过程的有效性。     

Chromium(III) determination without sample treatment by batch and flow injection potentiometry

A new and easy device for direct detection of chromium(III) in batch and flow analysis without previous oxidation/reduction or preconcentration steps of samples is designed and evaluated. For this purpose a potentiometric sensor with solid state membrane based on carbon paste matrix is developed. The sensor is modified with di(2-hydroxyphenylimino)ethane and the principal analytical parameters of the potentiometric response in batch and flow analysis are optimized and calculated. Optimal detection limits (1.4 × 10⁻⁷ M in static mode and 5.4 × 10⁻⁷ M in on-line analysis) and selectivity to trivalent chromium are obtained in both analysis modes. The use of this device to direct detection of chromium(III) in real samples is tested using a sediment Certified Reference Material. Chromium(III) determination is also carried out with successful results in environmental samples such as extracts from soils used as barriers in landfills and industrial samples such as waste waters from electroplating industries.     

Existence of traveling wavefronts in a cooperative systems with discrete delays

In this paper, we consider an important Lotka-Volterra model describing a two-species cooperative system with diffusive and discrete delays, and investigate the existence of traveling wavefronts by some mathematics tools including the monotone iteration technique as well as the upper and lower solution method. The results obtained can be seen as a generalization of previous results.     

High-performance liquid chromatographic determination of phenolic compounds in natural water coupled with on-line flow injection membrane extraction-preconcentration

A liquid chromatographic method for determination of trace phenolic compounds has been established, coupled with an on-line supported liquid membrane extraction-preconcentration flow-injection system. Tributyl-phosphate dissolved in kerosene was used as the carrier of the supported liquid membrane. Four phenolic compounds (phenol, catechol, resorcinol and hydroquinone) were chosen as the model compounds and the experiment conditions were optimized. Under the optimum conditions, calibrations were linear in the range of 1-500 microg/L, with good correlation coefficients (r > 0.999). The total analysis time of the system was 22 min, including the membrane extraction, liquid chromatographic separation and equilibration times.     

Flow-injection enhanced chemiluminescence method for determination of ciprofloxacin in pharmaceutical preparations and biological fluids

A novel rapid and sensitive analytical method, enhanced chemiluminescence with flow-injection sampling, is described for determination of ciprofloxacin. The method is based on the chemiluminescence reaction of the potassium permanganate–sodium thiosulfate–ciprofloxacin system. An enhanced chemiluminescence reaction was developed, and optimum conditions for CL emission were investigated. The chemiluminescence intensity was linearly dependent on ciprofloxacin concentration in the range 1.0×10⁻⁸–1.0×10⁻⁵ g mL⁻¹. The detection limit was 4×10⁻⁹ g mL⁻¹. The relative standard deviation was 1.8% for eleven measurements of 2.0×10⁻⁷ g mL⁻¹ ciprofloxacin standard solution. The new method enables simple, sensitive, and rapid determination of ciprofloxacin and has been successfully used for determination of ciprofloxacin in biological fluids and in ciprofloxacin hydrochloride tablet and injection.     

Assessment of camera models for use in planar velocimetry calibration

The performance of three implementations of pinhole-based camera models for use in common light-sheet imaging arrangements is investigated on the background of application to particle image velocimetry (PIV) and Doppler global velocimetry (DGV). Calibration data obtained from translated planar calibration targets was found to yield camera attitude within 0.1° on four different test cases with object distance varying as little as 2% depending on the choice of camera model. Camera calibration using data from a single image of coplanar points is considered a viable alternative to manual triangulation of camera positions but is restricted to off-normal viewing directions.

Potentiometric and voltammetric polymer lab chip sensors for determination of nitrate, pH and Cd(II) in water

Microparticles are phospholipid vesicles shed mostly in biological fluids, such as blood or urine, by various types of cells, such as red blood cells (RBCs), platelets, lymphocytes, endothelial cells. These microparticles contain a subset of the proteome of their parent cell, and their ready availability in biological fluid has raised strong interest in their study, as they might be markers of cell damage. However, their small size as well as their particular physico-chemical properties makes them hard to detect, size, count and study by proteome analysis. In this review, we report the pre-analytical and methodological caveats that we have faced in our own research about red blood cell microparticles in the context of transfusion science, as well as examples from the literature on the proteomics of various kinds of microparticles.     

Notes on pedal and contrapedal curves of fronts in the Euclidean plane

A pedal curve (a contrapedal curve) of a regular plane curve is the locus of the feet of the perpendiculars from a point to the tangents (normals) to the curve. These curves can be parametrized by using the Frenet frame of the curve. Yet provided that the curve has some singular points, the Frenet frame at these singular points is not well‐defined. Thus, we cannot use the Frenet frame to examine pedal or contrapedal curves. In this paper, pedal and contrapedal curves of plane curves, which have singular points, are investigated. By using the Legendrian Frenet frame along a front, the pedal and contrapedal curves of a front are introduced and properties of these curves are given. Then, the condition for a pedal (and a contrapedal) curve of a front to be a frontal is obtained. Furthermore, by considering the definitions of the evolute, the involute, and the offset of a front, some relationships are given. Finally, some illustrated examples are presented.