Complete solution of the columbus problem for large-disturbance cases

The Columbus problem has been rigorously solved by Lyapunov's direct approach to the continuous system in gencral cases of large disturbance and the theory has proved to be in strict consistency with Kelvin's experiments.

Analysis of estrogens in environmental waters using polymer monolith in-polyether ether ketone tube solid-phase microextraction combined with high-performance liquid chromatography

A simple, rapid and sensitive on-line method for simultaneous determination of four endocrine disruptors (17 beta-estradiol, estriol, bisphenol A and 17 alpha-ethinylestradiol) in environmental waters was developed by coupling in-tube solid-phase microextraction (SPME) to high-performance liquid chromatography (HPLC) with fluorescence detection (FLD). A poly(acrylamide-vinylpyridine-NAP-methylene bisacrylamide) monolith, synthesized inside a polyether ether ketone (PEEK) tube, was selected as the extraction medium. To achieve optimum extraction performance, several parameters were investigated, including extraction flow-rate, extraction time, and pH value, inorganic salt and organic solvent content of the sample matrix. By simply filtered with nylon membrane filter and adjusting the pH of samples to 6.0 with phosphoric acid, the sample solution then could be directly injected into the device for extraction. Low detection limits (S/N = 3) and quantification limits (S/N = 10) of the proposed method were achieved in the range of 0.006-0.10 ng/mL and 0.02-0.35 ng/mL from spiked lake waters, respectively. The calibration curves of four endocrine disruptors showed good linearity ranging from quantification limits to 50 ng/mL with a linear coefficient R-2 value above 0.9913. Good method reproducibility was also found by intra- and inter-day precisions, yielding the RSDs less than 12 and 9.8%, respectively. Finally, the proposed method was successfully applied to the determination of these compounds in several environmental waters. (c) 2006 Elsevier B.V. All rights reserved.

Determination of mercury with a flow injection quartz tube atomic absorption spectrometry

A method was developed for the determination of micro mercury in the soil, plants and the traditional Chinese medicine using flow injection quartz tube-atomic absorption spectrometry. The effect of the factors such as acidity,. the carrier solution, the flow rate of reductive solution and argon gas, etc. on the determination was studied. When vanadic oxide, nitric acid and sulfuric acid were used to decompose the sample reliable result could be obtained. The characteristic mass of the method is 59 pg, the detection limit is 0.028 mug/L, RSD is < 3.9% and the recovery is in the range of 94% &SIM; 102%.

Peierls-Nabarro model of interfacial misfit dislocation: An analytic solution

We propose a method to treat the interfacial misfit dislocation array following the original Peierls-Nabarro's ideas. A simple and exact analytic solution is derived in the extended Peierls-Nabarro's model, and this solution reflects the core structure and the energy of misfit dislocation, which depend on misfit and bond strength. We also find that only with beta < 0.2 the structure of interface can be represented by an array of singular Volterra dislocations, which conforms to those of atomic simulation. Interfacial energy and adhesive work can be estimated by inputting ab initio calculation data into the model, and this shows the method can provide a correlation between the ab initio calculations and elastic continuum theory.

An exact solution for the three-phase piezoelectric cylinder model under antiplane shear and its applications to piezoelectric composites

A three-phase piezoelectric cylinder model is proposed and an exact solution is obtained for the model under a farfield antiplane mechanical load and a far-field inplane electrical load. The three-phase model can serve as a fiber/interphase layer/matrix model, in terms of which a lot of interesting mechanical and electrical coupling phenomena induced by the interphase layer are revealed. It is found that much more serious stress and electrical field concentrations occur in the model with the interphase layer than those without any interphase layer. The three-phase model can also serve as a fiber/matrix/composite model, in terms of which a generalized self-consistent approach is developed for predicting the effective electroelastic moduli of piezoelectric composites. Numerical examples are given and discussed in detail.

Numerical solution of the incompressible Navier-Stokes equations with an upwind compact difference scheme

A new finite difference method for the discretization of the incompressible Navier-Stokes equations is presented. The scheme is constructed on a staggered-mesh grid system. The convection terms are discretized with a fifth-order-accurate upwind compact difference approximation, the viscous terms are discretized with a sixth-order symmetrical compact difference approximation, the continuity equation and the pressure gradient in the momentum equations are discretized with a fourth-order difference approximation on a cell-centered mesh. Time advancement uses a three-stage Runge-Kutta method. The Poisson equation for computing the pressure is solved with preconditioning. Accuracy analysis shows that the new method has high resolving efficiency. Validation of the method by computation of Taylor's vortex array is presented.

Shock Tube Studies on Recombination Kinetics of Sodium Ion with Electron

The ionization kinetics of sodium diluted in argon is studied in a shock tube, in which the test gas mixture is ionized by a reflected shock wave and subsequently quenched by a strong rarefaction wave. A Langmuir electrostatic probe is used to monitor the variation of the ion number density at the reflection shock wave region. The working state of the probe is in the near fi-ee fall region and a correction for reduction of the probe current due to elastic scattering in the probe sheath is introduced. At the temperature range of 800 to 2600 K and in the ambience of argon gas, the three-body recombination rate coefficient of the sodium ion with electron is determined: 3.43 x 10(-14)T(-3.77) cm(6).s(-1).

Flame Propagation of H_2-Air in a Semi-Open Obstructed Tube

针对氢／空气混合物,通过实验研究了其预混火焰在半开口管道中的火焰传播加速现象,结果表明,火焰传播状态随着氢气当量比的变化而发生改变。当氢／空气混合物被点燃后,由于障碍物的扰动,火焰在管道中不断加速传播,并最终到达一准稳态传播。在氢气当量比0.31附近时,火焰速度发生跃变。当氢气当量比足够大时,火焰传播由爆燃态转变为爆轰态。在本实验条件下,爆燃转准爆轰的临界条件是d/Lambda>=2.6（d是圆环形障碍物内径,人是爆轰格胞尺度）。障碍物阻塞比的变化对最大火焰速度和压力提升的影响不明显。

An Analytical Solution for Three-Dimensional Diffraction of Plane P-Waves by a Hemispherical Alluvial Valley with Saturated Soil Deposits

An analytical solution for the three-dimensional scattering and diffraction of plane P-waves by a hemispherical alluvial valley with saturated soil deposits is developed by employing Fourier-Bessel series expansion technique. Unlike previous studies, in which the saturated soil deposits were simulated with the single-phase elastic theory, in this paper, they are simulated with Biot's dynamic theory for saturated porous media, and the half space is assumed as a single-phase elastic medium. The effects of the dimensionless frequency, the incidence angle of P-wave and the porosity of soil deposits on the surface displacement magnifications of the hemispherical alluvial valley are investigated. Numerical results show that the existence of a saturated hemispherical alluvial valley has much influence on the surface displacement magnifications. It is more reasonable to simulate soil deposits with Biot's dynamic theory when evaluating the displacement responses of a hemispherical alluvial valley with an incidence of P-waves.

Effects of the orientation of microgravity on the concentration distribution in crystallization from solution

A quasi-steady state growth and dissolution in a 2-D rectangular enclosure is numerically investigated. This paper is an extension to indicate the effects of the orientation of gravity on the concentration field in crystallization from solution under microgravity, especially on the lateral non-uniformity of concentration distribution at the growth surface. The thermal and solute convection are included in this model.

The Interaction Between Shock Waves and Foam in a Shock Tube

An experimental study and a numerical simulation were conducted to investigate the mechanical and thermodynamic processes involved in the interaction between shock waves and low density foam. The experiment was done in a stainless shock tube (80mm in inner diameter, 10mm in wall thickness and 5360mm in length). The velocities of the incident and reflected compression waves in the foam were measured by using piezo-ceramic pressure sensors. The end-wall peak pressure behind the reflected wave in the foam was measured by using a crystal piezoelectric sensor. It is suggested that the high end-wall pressure may be caused by a rapid contact between the foam and the end-wall surface. Both open-cell and closed-cell foams with different length and density were tested. Through comparing the numerical and experimental end-wall pressure, the permeability coefficients a and 0 are quantitatively determined.

Influence of the Configuration of Obstacles on Premixed Flame Acceleration in a Tube

在一端封闭、一端开口的火焰传播管中均匀布置障碍物,研究了障碍物结构对管道中预混火焰传播的影 响。结果表明,由于障碍物的扰动,火焰不断加速,在阻塞比相同的条件下,最终的火焰稳态速度与障碍物的形状 和间距基本无关,其中障碍物间距仅仅影响火焰的加速速率,在障碍物间距约等于火焰传播管内径( W/ D≈1. 0) 时,平均火焰速度达到最大值,火焰到达稳态传播的距离最短。同时,本文用一维简化模型模拟了火焰在障碍物管 道中的加速过程,计算结果与实验测试结果在定性上比较吻合,说明在管内火焰速度较低的情况下,用一维可压缩 流动近似处理能初步揭示管内火焰的加速机制。

Optical Diagnostic and Modeling Solution Growth Process of Sodium Chlorate Crystals

Both a real time optical interferometric experiment and a numerical simulation of two-dimension non-steady state model were employed to study the growth process of aqueous sodium chlorate crystals. The parameters such as solution concentration distribution, crystal dimensions, growth rate and velocity field were obtained by both experiment and numerical simulation. The influence of earth gravity during crystal growth process was analyzed. A reasonable theory model corresponding to the present experiment is advanced. The thickness of concentration boundary layer was investigated especially. The results from the experiment and numerical simulation match well.

Perturbational Finite Volume Method For The Solution of 2-D Navier-Stokes Equations on Unstructured and Structured Colocated Meshes

Based on the first-order upwind and second-order central type of finite volume( UFV and CFV) scheme, upwind and central type of perturbation finite volume ( UPFV and CPFV) schemes of the Navier-Stokes equations were developed. In PFV method, the mass fluxes of across the cell faces of the control volume (CV) were expanded into power series of the grid spacing and the coefficients of the power series were determined by means of the conservation equation itself. The UPFV and CPFV scheme respectively uses the same nodes and expressions as those of the normal first-order upwind and second-order central scheme, which is apt to programming. The results of numerical experiments about the flow in a lid-driven cavity and the problem of transport of a scalar quantity in a known velocity field show that compared to the first-order UFV and second-order CFV schemes, upwind PFV scheme is higher accuracy and resolution, especially better robustness. The numerical computation to flow in a lid-driven cavity shows that the under-relaxation factor can be arbitrarily selected ranging from 0.3 to 0. 8 and convergence perform excellent with Reynolds number variation from 102 to 104.

Oxyhydrogen combustion and detonation driven shock tube

The performance of combustion driver ignited by multi-spark plugs distributed along axial direction has been analysed and tested. An improved ignition method with three circumferential equidistributed ignitors at main diaphragm has been presented, by which the produced incident shock waves have higher repeatability, and better steadiness in the pressure, temperature and velocity fields of flow behind the incident shock, and thus meets the requirements of aerodynamic experiment. The attachment of a damping section at the end of the driver can eliminate the high reflection pressure produced by detonation wave, and the backward detonation driver can be employed to generate high enthalpy and high density test flow. The incident shock wave produced by this method is well repeated and with weak attenuation. The reflection wave caused by the contracted section at the main diaphragm will weaken the unfavorable effect of rarefaction wave behind the detonation wave, which indicates that the forward detonation driver can be applied in the practice. For incident shock wave of identical strength, the initial pressure of the forward detonation driver is about 1 order of magnitude lower than that of backward detonation.