进步观念确立的基本前提

进步观念是近代以来占据主导地位的历史观,很多思想家的历史理论都是在这一主导性的观念下建构的,这其中也包括马克思的唯物主义历史观。理性主体的形成、稳定法则的信念、线性时间的确立和世俗价值的取向,是历史进步观在近代得以确立的四个基本的理论前提。通过对它们的梳理和分析,不但可以加深对历史进步观念的理解,而且可以确证,只要这些前提性条件存在,进步观念就依然是人类历史的主题。

Slope stability analysis considering joined influences of nonlinearity and dilation

The soil masses of slopes were assumed to follow a nonlinear failure criterion and a nonassociated flow rule.The stability factors of slopes were calculated using vertical slice method based on limit analysis.The potential sliding mass was divided into a series of vertical slices as well as the traditional slice technique.Equating the external work rate to the internal energy dissipation,the optimum solutions to stability factors were determined by the nonlinear programming algorithm.From the numerical results,it is found that the present solutions agree well with previous results when the nonlinear criterion reduces to the linear criterion,and the nonassociated flow rule reduces to the associated flow rule.The stability factors decrease by 39.7%with nonlinear parameter varying from 1.0 to 3.0.Dilation and nonlinearity have significant effects on the slope stability factors.

Pseudo-dynamic analysis of seismic stability of reinforced slopes considering non-associated flow rule

The required reinforcement force to prevent instability and the yield acceleration of reinforced slopes are computed under seismic loading by applying the kinematic approach of limit analysis in conjunction with the pseudo-dynamic method for a wide range of soil cohesion, friction angle, dilation angle and horizontal and vertical seismic coefficients. Each parameter threatening the stability of the slope enhances the magnitude of the required reinforcement force and vice versa. Moreover, the yield acceleration increases with the increase in soil shear strength parameters but decreases with the increase in the slope angle. The comparison of the present work with some of the available solutions in the literatures shows a reasonable agreement.

Influences of nonassociated flow rules on three-dimensional seismic stability of loaded slopes

The influences of soil dilatancy angle on three-dimensional （3D） seismic stability of locally-loaded slopes in nonassociated flow rule materials were investigated using a new rotational collapse mechanism and quasi-static coefficient concept. Extended Bishop method and Boussinesq theorem were employed to establish the stress distribution along the rupture surfaces that are required to obtain the rate of internal energy dissipation for the nonassociated flow rule materials in rotational collapse mechanisms. Good agreement was observed by comparing the current results with those obtained using the translational or rotational mechanisms and numerical finite difference method. The results indicate that the seismic stability of slopes reduces by decreasing the dilatancy angle for nonassociated flow rule materials. The amount of the mentioned decrease is more significant in the case of mild slopes in frictional soils. A nearly infinite slope under local loading, whether its critical failure surface is 2D or 3D, not only depends on the magnitude of the external load, but also depends on the dilataney angle of soil and the coefficient of seismic load.

Energy analysis of stability on shallow tunnels based on non-associated flow rule and non-linear failure criterion

On the basis of upper bound theorem, non-associated flow rule and non-linear failure criterion were considered together.The modified shear strength parameters of materials were obtained with the help of the tangent method. Employing the virtual power principle and strength reduction technique, the effects of dilatancy of materials, non-linear failure criterion, pore water pressure,surface loads and buried depth, on the stability of shallow tunnel were studied. In order to validate the effectiveness of the proposed approach, the solutions in the present work agree well with the existing results when the non-associated flow rule is reduced to the associated flow rule and the non-linear failure criterion is degenerated to the linear failure criterion. Compared with dilatancy of materials, the non-linear failure criterion exerts greater impact on the stability of shallow tunnels. The safety factor of shallow tunnels decreases and the failure surface expands outward when the dilatancy coefficient decreases. While the increase of nonlinear coefficient, the pore water pressure coefficient, the surface load and the buried depth results in the small safety factor. Therefore, the dilatancy as well as non-linear failure criterion should be taken into account in the design of shallow tunnel supporting structure. The supporting structure must be reinforced promptly to prevent potential mud from gushing or collapse accident in the areas with abundant pore water, large surface load or buried depth.

城市人多添堵?--人口与通勤的实证研究和中美比较

虽然国家确立了以城市群为主体的城镇发展模式,但是人们依然对大城市有所恐惧,一个重要的原因便是担心人口增长会造成通勤时间的大幅增加,并引发严重的交通拥堵。本文首先从理论上阐述了城市更大的人口规模造成通勤时间增加或减少的机制,然后利用2010年全国城镇住户基本情况抽样调查和人口普查的数据进行计量分析,发现人口规模增加一倍仅带来通勤时间的小幅上升,实证结果与基于美国数据发现的"通勤时间稳定法则"结果非常相似。我们同时也发现,城市人口规模增加一倍,交通拥堵只有非常小的增加,这是因为大城市通勤方式的改变可以缓解"人口—通勤"的紧张关系。

控制人口能缓解城市通勤问题吗——基于人群异质性通勤模式的比较分析

本文利用“2011年全国流动人口动态监测调查数据”和“2010年全国城镇住户基本情况抽样调查数据”,对比分析了中国城市流动人口和常住人口的通勤特征。研究发现,流动人口的平均通勤时间远低于常住人口;并且随着城市人口规模增加,其通勤时间增加的速度慢于常住人口。因此,平均来看流动人口对城市平均通勤时间没有显著的影响。进一步的分析发现,在从事职业方面,有较高比例的流动人口从事经商、商贩、餐饮等商业服务业,这些职业从业人员通勤时间短,且通勤时间对城市人口规模变化并不敏感;在居住类型方面,流动人口中有很高比例的人通过租房或者雇主提供的住房解决居住问题,他们通勤时间较短,并且通勤时间不随城市人口规模增加而发生较大变化。因此流动人口呈现出短距离通勤比例较高的特征。根据本文的研究结果,治理城市拥堵时,须慎重采取简单控制人口规模的方式。

CONVERGENCE OF THE LAX-FRIEDRICHS SCHEME AND STABILITY FOR CONSERVATION LAWS WITH A DISCONTINUOUS SPACE-TIME DEPENDENT FLUX

The authors give the first convergence proof for the Lax-Friedrichs finite differencescheme for non-convex genuinely nonlinear scalar conservation laws of the formu_t + f(k(x, t), u)_x = 0,where the coefficient k(x, t) is allowed to be discontinuous along curves in the (x, t)plane. In contrast to most of the existing literature on problems with discontinuouscoefficients, here the convergence proof is not based on the singular mapping approach,but rather on the div-curl lemma (but not the Young measure) and a Lax type en-tropy estimate that is robust with respect to the regularity of k(x, t). Following [14],the authors propose a definition of entropy solution that extends the classical Kruzkovdefinition to the situation where k(x, t) is piecewise Lipschitz continuous in the (x, t)plane, and prove the stability (uniqueness) of such entropy solutions, provided that theflux function satisfies a so-called crossng condition, and that strong traces of the solu-tion exist along the curves where k(x, t) is discontinuous. It is shown that a convergentsubsequence of approximations produced by the Lax-Friedrichs scheme converges tosuch an entropy solution, implying that the entire computed sequence converges.

PARALLEL STABILIZATION

A new algorithm for the stabilization or (possibly turbulent, chaotic) distributed systems,governed by linear or non linear systems of equations is presented.The SPA (Stabilization Parallel Algorithm) is based on a systematic parallel decompositionof the problem (related to arbitrarily overlapping decomposition of domains) and on a penaltyargument.SPA is presented here for the case of linear parabolic equations, with distributed or boundarycontrol. It extends to practically all linear and non linear evolution equations, as it will bepresented in several other publications.