Analysis of three-component soil structures

Impregnated soil blocks were collected from a tillage trial at Condobolin, New South Wales. The object of the trial was to examine the consequences of performing the first tillage operation of the season on different dates. It was apparent that the soil broke up on tillage into the usual range of aggregate sizes plus a dust which was presumably composed of micro-aggregates. This was apparent on sections through the blocks which showed three components: voids, aggregates and dust.A statistical method for quantifying soil structure, developed earlier, is extended to include three components. Since this involves a large number of transition probabilities, two approximate simplified methods were tested. One of these, here called the ‘grey-state method’, could be widely applied in structure studies using automatic scanning devices where features brighter or darker than some adjustable threshold level are detected.The results show that the most recently tilled plot had the coarsest structure, but that the earlier two treatments were not significantly different from each other. The usual trend of decreasing aggregate size and decreasing porosity with increasing depth was not observed. Instead, there appeared to be some inversion of the usual layering of tilled soil which is attributed to the use of a motor-driven rod-weeder.     

Some algebraic structures for diffusion in social networks

Restrictions on influence structures discussed by Buskens and Yamaguchi (1999) and others lead the states of possible distributions of information to form an algebraic structure of a lattice that is closed under union. From an examination of such a lattice of distribution, it is possible to recreate an influence network that is not observed directly. Finally, it is noted that these structures are different from those examined via Galois lattices; therefore, if these diffusion processes occur, Galois lattices do not recreate the actual social structure underlying this diffusion.     

Time response of structure with interval and random parameters using a new hybrid uncertain analysis method

Practical structures often operate with some degree of uncertainties, and the uncertainties are often modelled as random parameters or interval parameters. For realistic predictions of the structures behaviour and performance, structure models should account for these uncertainties. This paper deals with time responses of engineering structures in the presence of random and/or interval uncertainties. Three uncertain structure models are introduced. The first one is random uncertain structure model with only random variables. The generalized polynomial chaos (PC) theory is applied to solve the random uncertain structure model. The second one is interval uncertain structure model with only interval variables. The Legendre metamodel (LM) method is presented to solve the interval uncertain structure model. The LM is based on Legendre polynomial expansion. The third one is hybrid uncertain structure model with both random and interval variables. The polynomial-chaos-Legendre-metamodel (PCLM) method is presented to solve the hybrid uncertain structure model. The PCLM is a combination of PC and LM. Three engineering examples are employed to demonstrate the effectiveness of the proposed methods. The uncertainties resulting from geometrical size, material properties or external loads are studied.     

Measurement and comparison of soil structures.

A model is established to describe the structures of tilled soils using Markov chain theory. The effectiveness of the model in describing soil structures, and its accuracy when the model parameters are determined from limited field data is investigated by a consideration of variances of the transition probabilities and Markov chain state occurances in finite length chains. Criteria for correlation of soil structures at small horizontal and vertical displacements are derived, in order to establish distances at which soil structures become effectively independent. In this, a mathematical analysis is made of limiting covariances, generally applicable to the type of Markov chain used in describing these structures, in order to drastically reduce computing time in processing field data. Similarity coefficients are defined from the theory to measure similarity in different soil structures, and are compared in practice.     

On some regularities in dynamic response of cyclic periodic structures

The paper deals with cyclic periodic structures modelling bladed disk assemblies of blades with friction elements for vibration damping. These elements placed between adjacent blades reduce the vibration amplitudes by means of dry friction resulting from centrifugal forces acting on the elements and relative displacements of the blades. However, the application of these friction elements results in an additional dynamical coupling which together with mistuning of some system parameters (e.g., blade eigenfrequency or contact parameters) may cause localization of vibration. In the present paper a linear approximation of such a system is investigated. The structure composed of cyclic periodic cells modelled each as a clamped-free beam interacting with each other by means of viscoelastic elements of complex stiffness is applied for dynamic system analysis. In case of free vibrations as well as in case of steady-state dynamic response to a harmonic pressure field, a perfect periodic structure and the structures with periodically mistuned parameters (blade eigenfrequencies and contact parameters) are studied. Some regularities in the dynamic response of the systems with mistuning have been noticed. Despite the fact that only a linear approximation has been used, the results and conclusions can be applied for models which describe the blade interaction in a nonlinear way.     

Finding lower bounds on the complexity of secret sharing schemes by linear programming

Optimizing the maximum, or average, length of the shares in relation to the length of the secret for every given access structure is a difficult and long-standing open problem in cryptology. Most of the known lower bounds on these parameters have been obtained by implicitly or explicitly using that every secret sharing scheme defines a polymatroid related to the access structure. The best bounds that can be obtained by this combinatorial method can be determined by using linear programming, and this can be effectively done for access structures on a small number of participants.By applying this linear programming approach, we improve some of the known lower bounds for the access structures on five participants and the graph access structures on six participants for which these parameters were still undetermined. Nevertheless, the lower bounds that are obtained by this combinatorial method are not tight in general. For some access structures, they can be improved by adding to the linear program non-Shannon information inequalities as new constraints. We obtain in this way new separation results for some graph access structures on eight participants and for some ports of non-representable matroids. Finally, we prove that, for two access structures on five participants, the combinatorial lower bound cannot be attained by any linear secret sharing scheme.     

土壤分层结构下传输线感应雷电压算法研究

针对架空传输线感应雷过电压求解时理想地表假设与真实情况之间的矛盾,提出了一种基于Rusck模型,利用等效线高取代实际线高的方法,实现了土壤电导率分层结构下传输线感应雷电压的快速求解.与FDTD模拟结果对比验证了该方法的有效性和优越性.研究结果表明:对于电导率小于0.1 S/m的单质土壤类型,求解感应电压时应考虑电导率的影响,且电压峰值随电导率减小而增大.对于分层土壤结构,当上层土壤导电性较小时,感应电压随上层土壤增厚而变大;反之,随上层厚度增加而减小,当厚度超过5 m时,可忽略分层结构的影响.     

Analysis of fluid storage tanks including foundation-superstructure interaction

An analytical formulation is developed to predict the flexural behavior of a cylindrical liquid storage tank resting on an isotropic elastic soil medium, which is modelled as a half space. The interface between the plate foundation and the soil medium is considered to be smooth and continuous. The plate deflection function is assumed in the form of a power series expansion in terms of the radial coordinate. The procedure accounts for the interactions between the tank wall and the plate foundation, and between the plate foundation and the soil medium. The principle of minimum potential energy is used to evaluate the unknown coefficients appearing in the assumed power series expansion and also the unknown interacting forces at the tank wall-plate foundation junction. Any number of terms can be considered in the assumed deflection function. Analytical expressions are obtained for the plate foundation deflections and radial moment, the contact stress distribution, the tank wall displacements, and the tank wall stress resultants. The results obtained compare well with the finite element analysis of a similar problem. Results of a parametric study are also presented to demonstrate the effect of the various geometric and material parameters on the flexural behavior of the system.     

电磁波在三相土介质中的传播

研究电磁波(EM波)在土中的传播特性,必须获得如介电常数和磁导率等基本电磁参数.在麦克斯韦方程组的基础上,提出了等效模型来计算土体介电常数.利用该模型的计算结果与实测数据符号很好,可以为利用电磁波法测量土体含水量,土体的CT分析以及土工环境监测奠定理论基础.     

Comprehensive approach to student sectioning

Student sectioning is the problem of assigning students to particular sections of courses they request while respecting constraints such as course structures, section limits, and reserved spaces. Students may also provide preferences on class times and course alternatives. In this paper, three approaches to this problem are examined and combined in order to tackle it on a practical level: student sectioning during course timetabling, batch sectioning after a complete timetable is developed, and online sectioning for making additional changes to student schedules. An application and some practical results of the proposed solutions based on actual data are also included.     

Software reliability assessment models based on cumulative bernoulli trial processes

The binomial software reliability growth model (SRGM) contains most existing SRGMs proposed in earlier work as special cases, and can describe every software failure-occurrence pattern in continuous time. In this paper, we propose generalized binomial SRGMs in both continuous and discrete time, based on the idea of cumulative Bernoulli trials. It is shown that the proposed models give some new unusual discrete models as well as the well-known continuous SRGMs. Through numerical examples with actual software failure data, two estimation methods for model parameters with grouped data are provided, and the predictive model performance is examined quantitatively.     

Determination of the mechanical indices of composite materials by testing multilayered samples

The mechanical indices of materials such as composites reinforced by braids and ribbons are difficult to determine by standard methods. Moreover, the indices of such materials may be greatly altered when they are converted into various structures. It has been suggested that these indices be determined by analyzing the structure testing data. The determination of linear and nonlinear elastic, plastic, and viscoelastic parameters of reinforced materials is discussed. A very simple structure, namely, cylindrical shells made by symmetric winding, is studied as an example. Equilibrium conditions are used to obtain resolving equations relative to the mechanical indices. Convergence of iteration methods is examined. The effect of the scatter of experimental data on the calculated results is analyzed.Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 5, pp. 607–615, September–October, 1995.     

Interdisciplinary design optimization: A search method

The design of architectural structures frequently involves interdisciplinary aspects and aesthetic considerations which, being of subjective nature, are difficult to quantify. The computer-aided design optimization model presented here, therefore, is an attempt to optimize, in an interdisciplinary context, quantifiable parameters only. The objective function is graphically illustrated to give the designer a means to evaluate the impact of esoteric design decisions on performance variables, such as costs. A search method is used, i.e., evaluation of a discrete number of designs and nonlinear interpolation. The model's system of computer programs is demonstrated on the sample of an anticlastic cable roof structure.This paper contains excerpts from Refs. 1–2.     

STOPPING RULES AND THE CONTROL OF STOCK POLLUTANTS

A stock pollutant is defined as a residual waste that might accumulate over time. This paper examines some of the important distinctions between degradable and nondegradable stock pollutants and between nondegradable stock pollutants with known versus uncertain environmental cost. The latter case is examined using the more recent literature on stochastic control with Brownian motion. The presence of irreversibility and uncertainty is known to lead to more conservative investment rules and places a value on the preservation of options. In the case of a nondegradable stock pollutant with Brownian environmental cost, options are preserved by stopping accumulation at a lower level than in the corresponding certainty-equivalent problem. The model presented in this paper permits the derivation of closed-form stopping rules. For a simple numerical problem, the optimal nondegradable stock with Brownian environmental cost was 20 to 45 percent lower than the optimal level with known environmental cost. The empirical study of an actual nondegradable stock pollutant will require time series data on private and social cost in order to estimate drift and variance parameters which will influence the actual extent to which the optimal stock is less than the certainty-equivalent stock.     

Linear Elastic Wave Propagation in Unsaturated,Unconsolidated Soils

By means of a macroscopic linear model for a poroelastic medium with three deformable components the acoustic behavior of four unconsolidated soil types, filled by water and air, is studied. Necessary material parameters are mainly gathered from the German standard DIN 4220. It provides some useful parameters, as for example, van Genuchten parameters, for thirty-one different soil types including sands, silts and clays. There appear four body waves: three longitudinal waves and one shear wave. The slowest compressional wave does only exist if at least two pore fluids appear and is driven by the capillary pressure between the pore fluids. The wave analysis yields the dependence of velocities and attenuations of these waves on the saturation and on the frequency. This is compared to the so far most frequently studied case of partially saturated sandstones. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Weighted estimating equation: modified GEE in longitudinal data analysis

The method of generalized estimating equations （GEE） introduced by K. Y. Liang and S. L. Zeger has been widely used to analyze longitudinal data. Recently, this method has been criticized for a failure to protect against misspecification of working correlation models, which in some cases leads to loss of efficiency or infeasibility of solutions. In this paper, we present a new method named as ＇weighted estimating equations （WEE）＇ for estimating the correlation parameters. The new estimates of correlation parameters are obtained as the solutions of these weighted estimating equations. For some commonly assumed correlation structures, we show that there exists a unique feasible solution to these weighted estimating equations regardless the correlation structure is correctly specified or not. The new feasible estimates of correlation parameters are consistent when the working correlation structure is correctly specified. Simulation results suggest that the new method works well in finite samples.     

Joint Bayesian Analysis of Factor Scores and Structural Parameters in the Factor Analysis Model

A Bayesian approach is developed to assess the factor analysis model. Joint Bayesian estimates of the factor scores and the structural parameters in the covariance structure are obtained simultaneously. The basic idea is to treat the latent factor scores as missing data and augment them with the observed data in generating a sequence of random observations from the posterior distributions by the Gibbs sampler. Then, the Bayesian estimates are taken as the sample means of these random observations. Expressions for implementing the algorithm are derived and some statistical properties of the estimates are presented. Some aspects of the algorithm are illustrated by a real example and the performance of the Bayesian procedure is studied using simulation.     

过抽样信号的恢复

本文根据傅立叶分析和重抽样理论讨论了关于过抽样信号恢复的处理方法 ,所提出的重抽样信号恢复平均法对于强噪音背景下弱信号的提取 ,其效果是比较明显的     

介质与结构三维动力相互作用分析的半解析边界元—半解析有限元结合法

本文将半解析边界元一半解析有限无结合法用于介质与结构的动力相互作用研究:用半解析边界元法分析具有复杂地表面的半无限介质,用半解析有限元法分析具有任意截面形状的柱体结构,利用介质与结构交界面上的位移相容条件和力平衡条件,将介质与结构联系起来。联立京解上述半解析边界元方程和半解析有限元方程,对应每一时间步进,可同时求出介质与结构交界面上的位移、速度、加速度和相互作用力以及地表面的运动情况.与目前广泛研究的边界元—有限元结合法相比,本方法在介质与结构二个个区域各降低了一维空间,因而离散单元数和计算工作量大幅度减少,人工输入数据非常简单.文中还考虑了地下结构的长跨比效应、厚度效应和介质效应.