GPS／GLONASS组合接收机自备完善性监测和导航性能研究

本文应用近似径向误差保护判别准则，研究不同数量的卫星发生硬故障条件下，飞机非精密进场或终端航行时，ＧＰＳ／气压高度表组合系统、ＧＰＳ／ＧＬＯＮＡＳＳ／气压高度表组合系统接收机自备完善性监测可用性和导航解的可用性     

Elastostatic solutoins for semi-infinite orthotropic cantilevered strips

The elastostatic solutions of semi-infinite orthotropic cantilevered strips with traction free edges and loading at infinity are governed by the differential equation φ,_xyxy+(2+δ₀)φ,_xyzzz+φ,_zzzz with δ₀>-4. Based on the work of [10] for δ₀>0 case, this paper completes the case δ₀=0 for isotropic materials and the case 0>δ₀>-4 for orthotropic materials. The solutions of the above problems have important application in the properly formulated boundary conditions of plate theories for prescribed displacement edge data.     

Simulation du front d'écoulement dans les procédés de moulage des composites liquides

This work proposes a procedure of finite difference discretized in a system of curvilinear coordinates adapted to the shape of the saturated zone, to simulate a flow in the LCM (Liquid Composites Molding) process. Formulation and the numerical application of the procedure are described. We describe two configurations of injections. A good agreement is found between numerical, analytical and literature experimental results. To cite this article: M. Hattabi et al., C. R. Mecanique 333 (2005).     

脆性材料的扩展裂纹前缘形态与三维J积分

本文利用超声波断口图技术对不同类型的PMMA试件进行了测试。这些试件为承受均匀拉伸或三点弯曲变形的带单侧贯穿裂纹的PMMA板，其中拉伸试件又分为光面和带表面沟槽的两种。得到了这些试件断口上的超声波线。发现它们为平面线．其凸凹方向与试件的表面状态有关。基于有限元法，计算了试件的三维J积分，考察了杨氏模量和泊松比对其的影响．结果发现泊松比影响J积分曲线形状，而杨氏模量只影响其绝对数值，不影响其曲线形状。得到的试件在不同裂纹长度下的三维J积分与它们断口图上的超声波线的形状和凸凹方向相似。说明在脆性材料中，扩展裂纹前缘曲线形态是三维J积分的作用的结果。     

半无限空心截锥的特征值与端部效应

本文通过Birkhoff-Morgan关于单参数连续群不变性理论建立了空心半无限截锥的特征值方程,由此可以得到不同锥角下空心锥体的特征值,利用最小二乘法,本文得到了应力展开式中的各特征值系数,并由此得到问题的解。     

纤维段裂试验的界面端应力奇异性研究

纤维段裂试验是测定纤维复合材料界面剪切强度的细观实验方法之一，其试验结果与其他三种细观试验方法(纤维拔出、纤维压人和微珠脱粘)测得的结果各不相符，相差较大。针对该问题，仔细研究了纤维段裂试验过程，可发现如下两个问题，首先是试件中纤维断裂造成的界面端应力奇异性问题；其次是纤维断成临界长度时界面是否脱粘的问题。针对界面端应力奇异性问题，本文建立了界面端轴对称分析模型，运用渐近展开法，推导出求解界面端特征值的特征方程，并由此得到应力奇异性指数随Dundurs常数的变化规律；采用文献[5]所用试件的纤维／基体性能数据，计算出了界面端的应力奇异性指数，并与文献[7]得到的其他三种试验的界面端应力奇异性指数进行比较，发现纤维段裂试件也存在界面端应力奇异性，而且应力奇异性最强，也说明了与其他三种试验结果不具可比性。本文还对纤维断成临界长度时界面是否脱粘的问题，进行了讨论。     

Statistics of the deformation of the front of a tunnel-crack propagating in some inhomogeneous medium

We present a statistical analysis of some geometrical features of the front of a tensile tunnel-crack propagating quasistatically, according to some Paris-type law, in some elastic solid with spatially varying Paris constant. The work is based on an earlier formula of the authors, which provides the first-order change of the distribution of the mode I stress intensity factor along the front of a tunnel-crack, arising from some small but otherwise arbitrary in-plane perturbation of this front. The quantities studied include the power spectrum and the autocorrelation function of the deviation of the two parts of the front from reference straight lines, the autocorrelation function of the derivative of this deviation in the direction of the crack front, the mean squared fluctuation of the deviation, and its correlation distance. The various measures of the magnitude of the deviation of the front from straightness are all found to increase in time at a considerable rate, which means in some sense that the “wavyness” of the front continuously grows. However, the correlation distance of the deviation also increases, which mitigates the preceding conclusion, since it means in another sense that the crack front tends to “straighten back” in time. Also, comparisons are made with the cases of a semi-infinite crack propagating quasistatically or dynamically, using some results of Rice and coworkers for the latter case. The rate of growth of the various measures of the magnitude of the deviation from straightness is much larger for the tunnel-crack than for the semi-infinite one. This is because the finite width of the tunnel-crack induces a “destabilizing” effect of the straight configuration of the front for sinusoidal perturbations with large wavelengths, which is typical of such finite crack geometries.     

A FULLY ELECTRONICALLY TUNED 283–365 GHz LOCAL OSCILLATOR

A fully electronically tuned 283–365 GHz local oscillator developed for radio astronomical applications is presented. The source is constructed with a 15.7–20.3 GHz YIG oscillator followed by multipliers and amplifiers. It is shown that eliminating spurious harmonic products is essential in achieving low-noise operation of mixers pumped by this LO. This is done with suitable filters, the design of which is described.     

A generalization of the Keisler‐Morley theorem to recursively saturated ordered structures

We prove a model theoretic generalization of an extension of the Keisler‐Morley theorem for countable recursively saturated models of theories having a κ ‐like model, where κ is an inaccessible cardinal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Markovian receiver collision analysis of high‐speed multi‐channel networks

Two synchronous transmission multi‐channel multi‐access protocols for high‐speed network architecture are studied in this paper. Analytic discrete time Markovian models are developed for finite number of stations and finite number of channels for the symmetric and asymmetric access rights proposed protocols. The effect of receiver collision phenomenon is examined and analysed on the performance measures evaluation and estimated by the probability of packet rejection at destination. Also, numerical results are presented for comparison for various numbers of data channels and stations. Copyright © 2005 John Wiley & Sons, Ltd.