考虑固结和流变耦合作用的基坑工程时间效应

软土地区深基坑工程具有时间效应。基坑的各项参数,比如墙体水平位移和支撑轴力等,其数值不会因开挖的停止而不再发生变化。其原因一般地是土体固结和流变等效应所引起的。本文采用MERCHANT模型来模拟土体的流变性,依据Biot固结有限元法编制了有限元分析程序。程序分别以渗透系数和粘滞系数来反映固结的快慢和流变性的强弱。通过计算温州地区饱和软粘土地基深基坑开挖工程实例,验证了程序的可信性。程序通过对参考算例的分析,分别得到了纯固结作用和流变与固结耦合作用对基坑性状影响的规律:固结有利,流变不利,耦合作用使得具体的各项参数表现复杂化。     

影响橄榄石集合体蠕变性质物化因素的研究进展

综述了高温高压条件下岩石和矿物流变性的实验研究结果 ,总结了影响橄榄石集合体流变性能的各种物理和化学因素 .岩石和矿物在高温高压条件下变形的微观机制主要有 2种 :扩散蠕变和位错蠕变 .橄榄石集合体在扩散蠕变机制作用下 ,应变率 ε和差应力之间的关系为线性 ;在位错蠕变机制作用下 ,差应力指数n约等于 3.在相同差应力作用下 ,温度、熔融组分与橄榄石集合体的应变率是正相关的 .含水条件下 ,橄榄石集合体的强度显著降低 .颗粒度对差应力和应变率的影响比较复杂 ,低应变率和小颗粒度对应的差应力指数约等于 1 ;高应变率和粗糙颗粒度时 ,n为 3左右 .     

A principal stress method of stress analysis

The equations of equilibrium in a stress field as given by Lamé are compared with those given by Cauchy. The (P ? Q and P ? R) terms of the Lamé equations identified by the new words detend and double detend are invariant for any point in a stress field. The principal stresses are defined as real stress components. The $\text{?Xx}\text{?x}$ terms of the Cauchy equations are considered as imaginary force components. Real and imaginary stress and force components are differentiated by the differences between ray vectors, as for example a force which has only one real value and direction, and diffuse vectors, as for example a gradient, which has a real value in any direction. Shear is differentiated from detend value by its variation with the direction in which it is taken. Shear is found to be an imaginary component of force parallel to a plane.The photoelastic equidetend (isochromatic) and isoclinic maps of a plane stress field define, for any point, a gradient triangle with the three maximum gradients, Δ(P ? Q) ΔP and Δ ? Q, for its sides. Five quantities, the detend (P ? Q), the ratio of the detend to its gradient (r₄), the ratio (r₃) of the isoclinic normal ds₃ to the stress axis direction change along its length dα, the direction of the equidetend normal (θ) and the orientation of an isoclinic line (ω) with reference to a principal stress direction, determine each gradient triangle. Five equations which define elements of the gradient triangle in terms of the five measurable quantities, are developed. Definition of the triangle can be complete with two of the five measurable quantities or two of the five equations omitted. Graphic integration of principal stress changes along any line in a stress field can be made by plotting the line straight and measuring the area swept out by the normal projections, along the line, of the sides of the gradient triangle, after it has been rotated through 90 degrees.Properties of the gradient triangle are used to solve several symmetrical stress problems and to integrate along two lines through a stress field.     

Velocity effect of a lightning charge wave moving along a single wire transmission line

A wave equation solution for a moving charge on a simple one-wire, lossless transmission line is presented using Laplace transforms. The effect of lightning charge velocity on line potential as the charge moves along the transmission line is shown mathematically to be discontinuous should the wave velocity become the speed of light.     

多变量、多分布随机边界元法结构可靠性计算

在对非正态变量正态化的基础上，利用对随机变量求偏导数的方法，了二维弹性随机边界元积分方程，提出了多变量、多分布的随机结构可靠性计算方法，文中主要考虑了材料的随机结构强度，随机材料性能参数以及随机载荷等，数值算例表明，本文的算法是可靠而有效的。     

Vibration avoidance method for flexible robotic arm manipulation

A new principle, run with flexible deformation, for avoiding vibration throughout trajectories of a flexible robot manipulator is proposed. It comprises the hysteretic and leading mechanisms to maintain a steady pace of flexible (neutral surface) evolution with rigid (joint axis) advance, with the surface staying on a single side of the axis for constant deformation. A simple proportional–derivative (PD) controller is presented to realize the mechanisms, capable of adapting deformation into an invariant set that the single-sided pace-keeping is dependable over a steady or transient period. Analytically this set is the dynamic equilibrium target, in which negativeness of the Lyapunov function’s derivative is uncertain, and is proven globally uniformly asymptotically stable via a generalized Lyapunov and LaSalle’s argument. Further, the desired deformation is same stable in the sense of Lyapunov theorem due to recursive slowdown by the controller. The theoretical work is validated by the numerical simulations, which shows that the desired performance is well achieved. Significant advantages such as vibration-free servo control of a flexible-axis-based trajectory are demonstrated.     

Simplified nonlinear analysis to compute neutral axis depth in prestressed concrete rectangular beams

Recent research in concrete analysis and design has revealed that the shear capacity contributed by concrete correlates well with the neutral axis depth. While nonlinear analysis calculation of the neutral axis depth is trivial for reinforced concrete beams, it is iterative for prestressed concrete beams and does not lend itself to straightforward hand calculations. In this study, a program is developed to simulate the response of prestressed concrete rectangular sections subjected to monotonic bending taking into account cracking, yielding and ultimate states. This program is used to benchmark a simplified analytical procedure devised to perform the same task by hand. Accordingly, critical observations made to a large pool of experimental and analytical results reveal that the moment-curvature and moment-extreme fiber strain can be accurately modeled as trilinear relationships. The four key points that define the trilinear functions (initial, cracking, yielding and ultimate) may be computed analytically from simple equations derived based on consistent assumptions with the true behavior. Once the simplified analysis is performed, the computation of the neutral axis depth becomes a simple hand calculation. A parametric study was performed to further simplify the analytical procedure by computing the four key points that define the trilinear functions through linear relationships that were derived based on regression analysis of a large number of beam solutions. The neutral axis depth was calculated using the analytical and the simplified procedures for three beams with different ratios of prestressing steel and concrete strength. The results compared well with the iterative numerical procedure.     

河道型水库蓄水诱发地震的数值模拟

利用二维弹性有限元模型,计算了河道型水库蓄水造成的地应力变化,进而计算了走向平行于水库长轴的不同倾角断层面上库仑应力变化,以此来评价水库蓄水对库区断层稳定性的影响.结果表明,蓄水增加的压应力非常有限;如果背景应力场有利于正断层活动,蓄水可能会导致一定深度和倾角的断层更加危险;如果背景应力场有利于浅表的逆断层活动,蓄水会抑制不同倾角的逆断层活动.     

Stresses and deformations in pipe flanges subjected to creep at high temperatures

Various solutions have been made for determining the stresses in pipe flanges using the theory of elasticity (I). There are many cases, however, of pipe flanges which are subjected to stresses and at the same time a high temperature such that creep occurs.This paper gives an analysis of the stresses and deformations produced in a circular ring of rectangular cross section subjected to twisting couples uniformly distributed along its center line. Such a solution will also give an approximate analysis of the pipe flange. This approximation is justified in view of the complexity of the problem and the uncertainties still present in the fundamental creep-stress relation for metals. In the solution of this problem a deflection theory is also developed for straight beams subjected to bending accompanied by creep.     

A study of cortisol and certain metabolites in some chronic stress-disorders

Present study, involved two groups of chronic stress disorders, e.g. bronchial asthma and rheumatoid arthritis. Clinical investigations were launched on the blood samples of human subjects in which the levels of plasma cortisol, blood glucose, total plasma protein and serum cholesterol were assayed in diseased and normal control subjects. Observations in-vitro exhibited a notable change in the levels of all the biochemical parameters in patients of chronic disorders with respect to those of normal controls. The biochemical changes in asthmatics were comparatively more pronounced than those of rheumatoid arthritis patients. It reveals that bronchial asthma is an acute and early onset disorder because with chronicity of stressful events, there is a decline in stress response since hypothalamo-pituitary-adrenal (HPA) axis is not so competent to undergo major remodelling of its circuitry necessary for homeostatic maintanence.     

Robust H∞ dynamic output-feedback control for four-wheel independently actuated electric ground vehicles through integrated AFS/DYC

This paper simultaneously addresses the parameter/state uncertainties, external disturbances, input saturations, and actuator faults in the handling and stability control for four-wheel independently actuated (FWIA) electric ground vehicles (EGVs). Considering the high cost of the available sensors for vehicle lateral velocity measurement, a robust H_∞ dynamic output-feedback controller is designed to control the vehicle motion without using the lateral velocity information. The investigated parameter/state uncertainties include the tire cornering stiffness, vehicle mass, and vehicle longitudinal velocity. The unmodeled terms in the vehicle lateral dynamics model are dealt as the external disturbances. Faults of the active steering system and in-wheel motors can cause dangerous consequences for driving, and are considered in the control design. Input saturation issues for the tire forces can deteriorate the control effects, and are handled by the proposed strategy. Integrated control with active front steering (AFS) and direct yaw moment (DYC) is adopted to control the vehicle yaw rate and sideslip angle simultaneously. Simulation results based on a high-fidelity and full-car model via CarSim-Simulink show the effectiveness of the proposed control approach.     

Optimizing between data transformation and parametric weighting for stable binary classification

In this paper, an optimization problem is formulated for stable binary classification. Essentially, the objective function seeks to optimize a full data transformation matrix along with the learning of a linear parametric model. The data transformation matrix and the weight parameter vector are alternatingly optimized based on the area above the receiver operating characteristic curve criterion. The proposed method improves the existing means via an optimal data transformation rather than that based on the diagonal, random and ad-hoc settings. This optimal transformation stretches beyond the fixed settings of known optimization methods. Extensive experiments using 34 binary classification data sets show that the proposed method can be more stable than competing classifiers. Specifically, the proposed method shows robustness to imbalanced and small training data sizes in terms of classification accuracy with statistical evidence.     

空间统计视角下的农村居民点分布变化及驱动因素分析——以鄞州区滨海平原为例

农村居民点分布变化研究是优化农地利用、村庄规划的基础,以空间自相关等为核心的空间统计方法能定量刻画居民点分布演变的态势,成为当前学界探索热点。本文采用空间自相关方法、标准距离与标准差椭圆空间统计方法、密度分析方法,分析了鄞州滨海平原咸祥镇、瞻岐镇2005年、2011年的农居点分布特征及变化和驱动因素,研究结果显示:1农村居民点分布由2005年的空间随机分布演变为2011年的集聚模式,农村居民点分布呈现向外扩张的态势,分布区域、尺度扩大;2农村居民点主要以西南-东北轴为布局方向,东北、南、东三个方向为2005-2011年重点发展方向,其中东北方向最为突出;比较2005年,2011年农村居民点分布出现了多个密集中心,新增农村居民点密集核心分布于滨海平原东北部与南部;3政策和规划因素,包括鄞州区滨海投资创业区块、象山港大桥、交通线路规划等工程项目,以及高程、河流等自然因素是其分布特征变化的主要驱动因素。     

Observer based sliding mode controller for vehicles with roll dynamics

In this work, considering the roll dynamics and actuator dynamics, an observer-based control scheme for a vehicle is proposed. The proposal considers a nonlinear higher order sliding mode observer to estimate unmeasurable lateral velocity, roll angle and roll velocity. Using the observer information, a controller based on block control with sliding mode technique is designed for the reference trajectory tracking of the lateral and yaw velocities of the vehicle. The stability of the complete closed-loop system including zero dynamics is analyzed. The effectiveness of the proposed scheme is demonstrated through CarSim simulations.     

液固两相槽道流中柱状粒子取向的数值研究

对柱状粒子在槽道流场内的运动进行数值模拟，然后用统计方法得出大量柱状粒子的取向分布；给出了粒子长径比、粒子密度和流场区域对粒子取向分布的影响．计算结果表明，柱状粒子长径比的变化对粒子取向分布的影响不明显，粒子密度对粒子取向分布有一定影响，而流场区域所造成的流场横向速度梯度对粒子取向分布有重要影响．随着流场横向速度梯度增大，粒子取向趋势愈加明显，且当流场横向速度梯度增大到一定程度时，粒子取向都趋向于流动方向．文中部分结果与相关实验进行了比较，两者定性吻合较好。     

Moments generating function of the harmonic mean of two non-identical gamma random variables and its applications in wireless communications

In this paper, a closed-form expression for the moments generating function of the half-harmonic mean of two independent, not necessarily identically distributed gamma random variables with arbitrary parameters is presented. This statistical result is useful to the performance analysis of dual-hop wireless communication systems with amplify-and-forward relays in a Nakagami-m fading environment. The proposed mathematical analysis is substantiated by various numerically evaluated and computer simulation results.     

Limit analysis of flow through conical converging dies

A variety of mathematical models may be used to analyse plastic deformation during a metal-forming process. One of these methods—limit analysis—places the estimate of required power between an upper bound and a lower bound. The upper and lower bound analyses are designed so that the actual power or forming stress requirement is less than that predicted by the upper bound and greater than that predicted by the lower bound. Finding a lower upper bound and a higher lower bound reduces the uncertainty of the actual power requirement. Upper and lower bounds will permit the determination of such quantities as required forces, limitations on the process, optimal die design, flow patterns, and prediction and prevention of defects.Fundamental to the development of both upper bound and lower bound solutions is the division of the body into zones. For each of the zones there is written either a velocity field (upper bound) or a stress field (lower bound). A better choice of zones and fields brings the calculated values closer to actual values.In the present work, both upper and lower bound solutions are presented for axisymmetric flow through conical converging dies. For the upper bound triangular velocity fields have been solved and compared to previously published work on spherical velocity fields. It is found that each type provides a lower solution over a part of the range of process variables. A previously published lower bound solution for axisymmetric flow is refined.     

A microfluidic shear device that accommodates parallel high and low stress zones within the same culturing chamber

Fluid shear stress (FSS) plays a critical role in regulating endothelium function and maintaining vascular homeostasis. Current microfluidic devices for studying FSS effects on cells either separate high shear stress zone and low shear stress zone into different culturing chambers, or arranging the zones serially along the flow direction, which complicates subsequent data interpretation. In this paper, we report a diamond shaped microfluidic shear device where the high shear stress zone and the low shear stress zone are arranged in parallel within one culturing chamber. Since the zones with different shear stress magnitudes are aligned normal to the flow direction, the cells in one stress group are not substantially affected by the flow-induced cytokine/chemokine releases by cells in the other group. Cell loading experiments using human umbilical vein endothelial cells show that the device is able to reveal stress magnitude-dependent and loading duration-dependent cell responses. The co-existence of shear stress zones with varied magnitudes within the same culturing chamber not only ensures that all the cells are subject to the identical culturing conditions, but also allows the resemblance of the differential shear stress pattern in natural arterial conditions. The device is expected to provide a new solution for studying the effects of heterogeneous hemodynamic patterns in the onset and progression of various vascular diseases.     

Improved analytical solutions to a stagnation-point flow past a porous stretching sheet with heat generation

This paper investigates the steady laminar flow in a porous medium of an incompressible viscous fluid impinging on a permeable stretching surface with heat generation. The resulting system of coupled non-linear ordinary differential equations is solved analytically via homotopy analysis method (HAM). Analytical results are presented for the wall shear stress and the wall heat transfer coefficient as well as the velocity and temperature profiles for some values of governing parameters such as Prandtl number, stretching parameter, porosity parameter and the heat generation/absorption parameter. Appropriate auxiliary parameter, ?, is determined by minimizing Euclidean norm of residual. The convergence of the obtained series solutions is explicitly studied.     

The distribution of benefits from technical change among classes of consumers and producers: An ex anteanalysis of beans in Brazil

Because new agricultural technology in developing countries has sometimes bypassed small farmers who are an important social group in low income countries, design of technology specifically appropriate to small farmers has been advocated as a policy goal. This paper appraises the comparative returns to investment in small farm biased, scale neutral, and large farm biased technology for bean production in Brazil. A consumer surplus model is developed to estimate the distribution of benefits among producing sectors and classes of consumers. While previous studies have relied on geometrical approximations to measure economic benefits as the area under the supply shifts, here an exact analytic solution is obtained by integrating from the supply axis. Scale neutral technology leads to significant small farmer benefits while maximizing benefits to consumers. Large farm biased technology results in less benefits to small farmers and consumers and only minor gains to large farmers when compared to scale neutral technology. Small farm biased technology produces the greatest gains to small farmers, but the lowest level of benefits to consumers.