汇率目标区理论在我国的应用前景

本文从扩大人民币汇率浮动范围的角度出发,考察了汇率目标区理论以及Edwards的基本因素模型对确定目标区中心汇率的贡献,并结合我国1986-2003年间宏观经济基本因素和人民币实际汇率走势,用基本因素模型建立了与我国实情相应的均衡汇率模型。得出的结论是:影响人民币均衡汇率的主要基本因素有全要素生产率、对外偿债能力和政府支出,这与我国区域广阔、国内资本市场不发达以及政府在经济发展中占主导地位的特点是一致的;因此,在人民币汇率改革中可以考虑汇率目标区,并使用类似的基本因素模型来确定基准汇率和目标区边界;在目前条件下,±5%的变动幅度是可以接受的。     

三峡坝区花岗岩风化分带的化学风化特征指标研究

以前人应用物理性指标划分风化壳垂直分带为基础,对长江三峡坝区各地貌部位的采样,用X射线荧光光谱仪对样品进行化学成分分析,用显微镜对矿物组成进行鉴定,选取了12个具有代表性的、能反映化学风化特征的风化系数,进行了化学风化特征值的详细计算,对风化壳垂直分带的元素迁移规律和化学特征值做了系统描述,希能为三峡坝区风化壳的垂直分带提供化学特性指标,以完善风化壳垂直分带指标体系。     

Numerical simulation of mass transfer to micropolar fluid flow past a stenosed artery

A mathematical model of unsteady non‐Newtonian blood flow together with the mass transfer through constricted arteries has been developed. The mass transport refers to the movement of atherogenic molecules, i.e. blood‐borne components, such as low‐density lipoproteins from flowing blood into the arterial walls or vice versa. The flowing blood is represented as the suspension of all erythrocytes assumed to be Eringen's micropolar fluid and the arterial wall is considered to be rigid having cosine‐shaped stenosis in its lumen. The mass transfer to blood is controlled by the convection–diffusion equation. The governing equations of motion accompanied by the appropriate choice of the boundary conditions are solved numerically by Marker and Cell method and the results obtained are checked for numerical stability with the desired degree of accuracy. The quantitative analysis carried out finally includes the respective profiles of the flow‐field and the mass concentration along with their distributions over the entire arterial segment as well. The key factors, such as the wall shear stress and Sherwood number, are also examined for further quantitative insight into the flow and the mass transport phenomena through arterial stenosis. The present results show consistency with several existing results in the literature which substantiate sufficiently to validate the applicability of the model under consideration. Copyright © 2010 John Wiley & Sons, Ltd.     

Axial annular flow of plastic fluids: dead zones and plug-free flow

In axial annular flow, the shear stress decreases from its value τ(κR) at the inner cylinder to 0 at r = λR and increases from then on to τ(R) at the outer cylinder. For plastic fluids with a yield stress τ _c, λ will be such that flow commences when τ(κR) = τ(R) = τ _c. For fluids with position-dependent yield stresses (electro- and magnetorheological fluids are examples), the situation is more complex. While it is possible that yielding and flow occur everywhere, it is also possible that flow occurs only in parts of the fluid-filled space, and a dead zone (region in which the fluid is at rest) close to one of the walls exists. In that case, the fluid will flow no matter how small the applied pressure difference is. If P is large enough, the dead zone ceases to exist and flow without any plug is possible. The fluid flows as if no yield stress exists.

Distinctive features of the transonic flow past a cone-cylinder body at small angles of the bend in the body generator at the leading corner edge

The distinctive features of the transonic flow past cone-cylinder bodies with small angles of the bend in the body generator at the leading corner edge are considered. The mechanism of transonic flow restructuring downstream of the edge and the associated variation of the gasdynamic parameters are studied, the reasons for the formation of aerodynamic hysteresis are established, and the effect of the length of the cylindrical part of the body is determined.     

On the Asymptotics of Trimmed Best k-Nets

Trimmed best k-nets were introduced in J. A. Cuesta-Albertos, A. Gordaliza and C. Matrán (1998, Statist. Probab. Lett.36, 401–413) as a robustified L_∞-based quantization procedure. This paper focuses on the asymptotics of this procedure. Also, some possible applications are briefly sketched to motivate the interest of this technique. Consistency and weak limit law are obtained in the multivariate setting. Consistency holds for absolutely continuous distributions without the (artificial) requirement of a trimming level varying with the sample size as in J. A. Cuesta-Albertos, A. Gordaliza and C. Matrán (1998, Statist. Probab. Lett.36, 401–413). The weak convergence will be stated toward a non-normal limit law at a O_P(n^−1/3) rate of convergence. An algorithm for computing trimmed best k-nets is proposed. Also a procedure is given in order to choose an appropriate number of centers, k, for a given data set.     

Radon anomalies along faults in North of Jordan

Radon emanation was sampled in five locations in a limestone quarry area using SSNTDs CR-39. Radon levels in the soil air at four different well-known traceable fault planes were measured along a traverse line perpendicular to each of these faults. Radon levels at the fault were higher by a factor of 3–10 than away from the faults. However, some sites have broader shoulders than the others. The method was applied along a fifth inferred fault zone. The results show anomalous radon level in the sampled station near the fault zone, which gave a radon value higher by three times than background. This study draws its importance from the fact that in Jordan many cities and villages have been established over an intensive faulted land. Also, our study has considerable implications for the future radon mapping. Moreover, radon gas is proved to be a good tool for fault zones detection.     

On the width of hybrid zones

Hybrid zones occur when two species are found in close proximity and interbreeding occurs, but the species’ characteristics remain distinct. These systems have been treated in the biology literature using partial differential equations models. Here we investigate a stochastic spatial model and prove the existence of a stationary distribution that represents the hybrid zone in equilibrium. We calculate the width of the hybrid zone, which agrees with the PDE formula only in dimensions d≥3$d\ge 3$. Our results also give insight into properties of hybrid zones in patchy environments.     

Evaluation of models for flame stretch due to curvature in the thin reaction zones regime

Direct numerical simulation (DNS) was used to study modelling assumptions for the curvature-propagation component of flame stretch in the thin reaction zones regime of turbulent premixed combustion, a regime in which small eddies can penetrate the preheat zone but not the thinner fuel breakdown zone. Simulations of lean hydrogen–air and methane–air flames were conducted, and statistics of flame stretch due to curvature, henceforth referred to simply as stretch, were extracted from a species mass fraction iso-surface taken to represent the flame. The study focussed on investigating the modelling assumptions of Peters [J. Fluid Mech. 384 (1999) 107]. It was found that the mean stretch is dominated by stretch due to correlations of flame speed with curvature, and specifically the effects of tangential diffusion. The modelling suggestions of Peters were found to provide an improvement over the assumptions of a constant flame speed or a flame speed governed by the linear relationship with stretch at small and steady stretch. However for the conditions considered here, diffusive-thermal effects remain well into the thin reaction zones regime, and the suggestions of Peters generally over-predict the mean compressive stretch. An effective diffusivity for flame stretch was suggested and evaluated for the methane simulations. It was found that the effective diffusivity was comparable to the mass diffusivity for flames with a high ratio of flame time to eddy turnover time. The length scales contributing to stretch were investigated, and it was found that while most flame area has a radius of curvature greater than the laminar flame thickness, most stretch occurs in more tightly curved flame elements.     

Angular criterion to distinguish between Fraunhofer and Fresnel diffraction

The distinction between Fresnel and Fraunhofer diffraction is an essential condition for the accurate analysis of diffracting structures. In this paper we propose a criterion based on the angle subtended by the first minimum of the diffraction pattern from the centre of the diffracting aperture. The determination of the minimum of the diffraction pattern is the crucial point to assure the accuracy of the criterion. Therefore, the applicability of adequate thresholds for detection is discussed. The criterion is also generalized by expressing it in terms of the number of Fresnel zones delimited by the aperture. Simulations are reported to illustrate the feasibility of the criterion.