Vertical ground movements in the Campi Flegrei caldera as a chaotic dynamic phenomenon

The ground level in the Campi Flegrei caldera has never been stationary in the last 2,000 years. Historical data, and a nearly continuous tide-gauge record 20 years long, show that uplift and sinking have taken place on a variety of different time scales. In addition, the Campi Flegrei volcanic system appears to be sensitive to weak external forces such as tidal forces. We infer from these elements that the Campi Flegrei system is far from thermodynamic equilibrium, and suggest that its dynamics may be chaotic. We analyze the short-term variations of the ground level, and find that they can be described in a low-dimensional phase space. The dynamics of the Campi Flegrei system seems to have been phase-locked with tidal forces in the period following the 1970–1972 climax, and to have undergone a transition to chaos in some moment that preceded the presently continuing sinking phase.     

Meridional circulation from differential rotation in an adiabatically stratified solar/stellar convection zone

Meridional circulation in stellar convection zones is not generally well observed, but may be critical for the workings of MHD dynamos operating in these domains. Coriolis forces from differential rotation play a large role in determining what the meridional circulation is. Here, we consider the question of whether a stellar differential rotation that is constant on cylinders concentric with the rotation axis can drive a meridional circulation. Conventional wisdom says that it can not. Using two related forms of the governing equations that respectively estimate the longitudinal components of the curl of the meridional mass flux and the vorticity, we show that such differential rotation will drive a meridional flow. This is because to satisfy anelastic mass conservation, non-spherically symmetric pressure contours must be present for all differential rotations, not just ones that depart from constancy on cylinders concentric with the rotation axis. Therefore, the fluid is always baroclinic if differential rotation is present. This is because, in anelastic systems, the perturbation pressure must satisfy a Poisson type equation, as well as an equation of state and a thermodynamic equation. We support our qualitative reasoning with numerical examples, and show that meridional circulation is sensitive to the magnitude and form of departures from rotation constant on cylinders. The effect should be present in 3D global anelastic convection simulations, particularly those for which the differential rotation driven by global convection is nearly cylindrical in profile. For solar-like differential rotation, Coriolis forces generally drive a two-celled circulation in each hemisphere, with a second, reversed flow at high latitudes. For solar like turbulent viscosities, the meridional circulation produced by Coriolis forces is much larger than observed on the Sun. Therefore, there must be at least one additional force, probably a buoyancy force, which opposes the meridional flow to bring its amplitude down to observed values.     

湍流输送的非线性热力学性质

湍流输送是一种热力学不可逆过程,本文利用非线性热力学研究了湍流输送的特征. 将热力学流对热力学力以平衡态作为参考态进行Taylor展开,可以得到湍流输送系数是系统宏观参量梯度的Taylor级数. 线性湍流输送系数是Reynolds湍流闭合方案的K闭合湍流输送系数;而湍流输送系数非线性项则是系统偏离热力学平衡态所造成的热力学非线性效应. 湍流输送系数这一热力学性质提供了一种热力学湍流闭合方案. 线性湍流输送系数是正定的,湍流输送只能使系统宏观参量均匀化;而在远离平衡态的热力学非线性区,可能导致湍流输送系数负黏性现象. 在最小熵产生态的条件下,热力学流对热力学力Taylor展开的各级系数间存在一种递推关系. 利用这种递推关系大大减少了由实验确定的Taylor级数的系数个数.     

Equations of thermal convection for a viscous compressible mantle of the earth including phase transitions

A system of equations for the calculation of thermal convection in a compressible mantle with variable parameters and phase transitions is derived from the general laws of mass, momentum, and energy conservation and thermodynamic relations. Mantle convection is successively calculated in the anelastic liquid, truncated anelastic liquid, mean density, expanded Boussinesq, and Boussinesq approximations. Phase transitions are automatically taken into account with the help of effective thermodynamic parameters determined from general thermodynamic relations.     

Driving mechanisms of nitrogen transport and transformation in lacustrine wetlands

As an essential component of proteins and genetic material for all organisms, nitrogen (N) is one of the major limiting factors that control the dynamics, biodiversity and functioning of lacustrine wetlands, in which intensified N biogeochemical activities take place. Reactive N loaded into wetland ecosystems has been doubled due to various human activities, including industrial, agricultural activities and urbanization. The main driving mechanisms of N transport and transformation in lacustrine wetlands are categorized to pushing forces and pulling forces in this study. Geomorphology, wetland age, N concentrations, and temperature are the main pushing forces (passive forces); whereas water table variation, oxygen concentration, other elements availability, oxidation-reduction potential (Eh) and pH, and microorganisms are the predominant pulling forces (active forces). The direction and kinetic energy of reactions are determined by pulling forces and then are stimulated by pushing forces. These two types of forces are analyzed and discussed separately. Based on the analysis of driving mechanisms, possible solutions to wetland N pollutions are proposed at individual, regional and global scales, respectively. Additional research needs are addressed to obtain a thorough understanding of N transport and transformations in wetlands and to reduce detrimental impacts of excessive N on such fragile ecosystems.     

Thermodynamic properties of calcium ferrite-type MgAl2O4: A first principles study

The diamond anvil cell experiments have revealed that the calcium ferrite(CF)-type aluminous phase is probably an important component of subducted mid-oceanic ridge basalt(MORB) in the lower mantle. In this study, we have performed first principles lattice dynamics calculations for the Mg Al_2O_4 end-member of the aluminous phase based on density functional perturbation theory using two functionals within the local density approximation(LDA) and generalized gradient approximation(GGA) for bracketing the calculated properties at their lower and upper limits, respectively. A simple empirical pressure correction at zero temperature has been applied to both LDA and GGA. The results of room-temperature equation of state(EOS) and zero-pressure thermal expansion calculated by GGA with pressure correction have shown the best agreement with available experimental data. The high-pressure and temperature thermodynamic properties have been obtained using the GGA with correction method. The pressure-volume relations are fitted with a third-order high-temperature Birch-Murnaghan EOS. The isobaric heat capacity, the coefficient of thermal expansion and isothermal bulk modulus are fitted with polynomials and their coefficients are reported in the range of 0–40 GPa and 300–2000 K. The density profile of MORB estimated using the computational thermo-elastic constants supports the hypothesis that the subducted oceanic slabs could gain enough downwelling forces into the lower mantle.     

相空间广义拟余能原理用于弹性结构扭振分析

在大跨度桥梁设计中,抗风是工程师们最关心的问题之一,也是桥梁动力稳定问题的重要研究领域。本文按照广义力和广义位移之间的对应关系,将相空间的弹性动力学的基本方程乘上相应的虚量,然后积分,代数相加,并考虑到体积力和面积力均为伴生力,建立了适用于研究大跨度桥梁流固耦合初值问题相空间的两类变量的广义拟余能原理。应用该原理,解决了一个非保守桥梁流固耦合问题的具体算例。并且讨论了如何应用非保守系统的广义拟变分原理进行大跨度桥梁近似计算的问题。     

Origin of tectonic stresses in the Chinese continent and adjacent areas

Based on data of principal stress orientation from focal mechanism and of geological features in China, we made pseudo-3D genetic algorithm finite element (GA-FEM) inversion to investigate the main forces acting on the Chinese continent and adjacent areas which form the Chinese tectonic stress field. The results confirm that plate boundary forces play the dominant role in forming the stress field in China, as noticed by many previous researchers. However, we also find that topographic spreading forces, as well as basal drag forces of the lower crust to the upper crust, make significant contribution to stresses in regional scale. Forces acting on the Chinese continent can be outlined as follows: the collision of the India plate to the NNE is the most important action, whereby forces oriented to the NW by the Philippine plate and forces oriented to the SWW by the Pacific plate are also important. Topographic spreading forces are not negligible at high topographic gradient zones, these forces are perpendicular to edges of the Tibetan Plateau and a topographic gradient belt running in the NNE direction across Eastern China. Basal drag forces applied by the ductile flow of the lower crust to the base of upper crust affect the regional stress field in the Tibetan Plateau remarkably, producing the clockwise rotation around the eastern Himalaya syntax.     

SEISMIC RESPONSE OF SLIDING STRUCTURES TO BIDIRECTIONAL EARTHQUAKE EXCITATION

Seismic response of a one-storey structure with sliding support to bidirectional (i.e. two horizontal components) earthquake ground motion is investigated. Frictional forces, which are mobilized at the sliding support, are assumed to have ideal Coulomb-friction characteristics. Coupling effects due to circular interaction between the frictional forces are incorporated in the governing equations of motion. Effects of bidirectional interaction of frictional forces on the response are investigated by comparing the response to two-component excitation with the corresponding response produced by the application of single-component excitations in each direction independently. It is observed that the response of the sliding structure is influenced significantly by the bidirectional interaction of frictional forces. Further, it is shown that the design sliding displacement may be underestimated if the bidirectional interaction of frictional forces is neglected and the sliding structures are designed merely on the basis of single-component excitation.     

Earthquake interaction forces between two structures of different rigidities

A combined structure is assumed to be composed of a rigid part and a flexible part. Each component structure would have a different period of natural vibration if it were built independently. When they are combined in one structure and subjected to an earthquake, there must be generated some interaction forces so that the component structures will have a common vibration. In this paper is an analytical method described to evaluate such interaction forces The general principle is as follows. For each of the component structures, equations of motion taking account of the unknown interaction forces are derived first. Then by eliminating the interaction forces, equations of motion of the combined structure are obtained. After solving these equations and substituting the solution into the equations of motion of the component structures, the unknown interaction forces are obtained directly In the present paper, two structures corresponding to two-degree elastic systems are considered; numerical examples also are included.     

Damage evolution and fluid flow in poroelastic rock

We present a formulation for mechanical modeling of the interaction between fracture and fluid flow. Our model combines the classic Biot poroelastic theory and a damage rheology model. The model provides an internally consistent framework for simulating coupled evolution of fractures and fluid flow together with gradual transition from brittle fracture to cataclastic flow in high-porosity rocks. The theoretical analysis, based on thermodynamic principles, leads to a system of coupled kinetic equations for the evolution of damage and porosity. A significant advantage of the model is the ability to reproduce the entire yield curve, including positive and negative slopes, in high-porosity rocks by a unified formulation. A transition from positive to negative values in the yield curve, referred to as a yield cap, is determined by the competition between the two thermodynamic forces associated with damage and porosity evolution. Numerical simulations of triaxial compression tests reproduce the gradual transition from localized brittle failure to distributed cataclastic flow with increasing pressure in high-porosity rocks and fit well experimentally measured yield stress for Berea sandstone samples. We modified a widely used permeability porosity relation by accounting for the effect of damage intensity on the connectivity. The new damage-permeability relation, together with the coupled kinetics of damage and porosity evolution, reproduces a wide range of realistic features of rock behavior. We constrain the model variables by comparisons of the theoretical predictions with laboratory results reporting porosity and permeability variation in rock samples during isotropic and anisotropic loading. The new damage-porosity-permeability relation enables simulation of coupled evolution of fractures and fluid flow and provides a possible explanation for permeability measurements in high-porosity rocks, referred to as the “apparent permeability paradox.” The text was submitted by the authors in English.     

SOME IMPLICATIONS OF STATISTICAL MECHANICS IN GEOMORPHOLOGY

Abstract

The statistical content of a recent thermodynamic analogy introducing the concept of entropy into landscape evolution is investigated. It is shown that this thermodynamic analogy is indeed physically fully justified, provided the regression of the fluctuations is linear. Some consequences of this analogy on the evolution of mountain ranges and slopes are presented.     

A unifying framework for watershed thermodynamics: constitutive relationships

The balance equations for mass and momentum, averaged over the scale of a watershed entity, need to be supplemented with constitutive equations relating flow velocities, pressure potential differences, as well as mass and force exchanges within and across the boundaries of a watershed. In this paper, the procedure for the derivation of such constitutive relationships is described in detail. This procedure is based on the method pioneered by Coleman and Noll through exploitation of the second law of thermodynamics acting as a constraint-type relationship. The method is illustrated by its application to some common situations occurring in real world watersheds. Thermodynamically admissible and physically consistent constitutive relationships for mass exchange terms among the subregions constituting the watershed (subsurface zones, overland flow regions, channel) are proposed. These constitutive equations are subsequently combined with equations of mass balance for the subregions. In addition, constitutive relationships for forces exchanged amongst the subregions are also derived within the same thermodynamic framework. It is shown that, after linearisation of the latter constitutive relations in terms of the velocity, a watershed-scale Darcy's law governing flow in the unsaturated and saturated zones can be obtained. For the overland flow, a second order constitutive relationship with respect to velocity is proposed for the momentum exchange terms, leading to a watershed-scale Chezy formula. For the channel network REW-scale Saint–Venant equations are derived. Thus, within the framework of this approach new relationships governing exchange terms for mass and momentum are obtained and, moreover, some well-known experimental results are derived in a rigorous manner.     

Global stress pattern constrained on deep mantle flow and tectonic features

Global stress patterns in the lithosphere which are constrained on the deep mantle flow and global tectonic features are investigated. The drag forces acting on the bottom of the lithosphere and the boundary-generating forces are used in our computing models. Comparing them with the stress map constructed by in situ stress measurements in boreholes, focal mechanisms, geological structures and other geophysical and geological observations, we find that these forces are the main control of the global lithospheric stress pattern.     

与高岭石固相平衡的酸性天然地表水中铝的缓冲作用的计算机模拟

基于质量守恒以及电中性条件,采用化学平衡计算法,计算模拟研究了高岭石固相平衡的酸性天然地表水中铝的缓冲作用对ｐＨ值,酸中和容量ＡＮＣ和缓冲强度β的影响,讨论了影响酸性地表水ｐＨ估算的各种因素,如溶解硅酸的浓度,溶解总无机碳的浓度,溶解总氟和总有机碳的浓度及温度等。模型被用于实际水样的分析,所得结果与实验值符合较好,用ＭｏｎｔｅＣａｒｌｏ模拟考察了由于平衡常数的选择以及水化学参数测量误差而带来的不确     

非保守弹性动力系统两类变量的广义拟变分原理及其应用

按照广义力和广义位移之间的对应关系,将弹性动力学的各基本方程分别乘上相应的虚量,然后在相应的体积域和面积域上积分,将积分式代数相加,再将代数和在时间域上积分,代入本构关系,并考虑到体积力和面积力均为伴生力,进而建立了非保守弹性动力系统的第1类两类变量的广义拟变分原理;再应用类似的方法,通过代入另一类本构关系,建立了非保守弹性动力系统的第2类两类变量广义拟变分原理.应用第1类两类变量广义拟余能原理给出同时求解1个典型的非保守弹性动力系统的固有频率、变形和内力的计算方法.最后,讨论了有关问题.     

不同距离力源作用下脆性破裂的稳定性和止裂

根据断裂力学的原理, 提出了脆性破裂的止裂准则, 给出了最小止裂方程. 利用Erdogan的集中力的零频Green函数解, 分析了点力和简单分布力的位置对脆性破裂的稳定性和止裂的作用, 给出了若干典型条件下临界载荷、 失稳边界线、 止裂点的计算结果. 近距离力源引起的稳定性破裂, 对于解释一些蠕裂和构造的形成是有意义的; 不同距离力源引起的失稳破裂, 对于解释不同震级地震的发生和停止是有意义的. 强地震的发生有可能是远场力与近场力各种复合作用的结果. 本文的结果对于认识诱发地震的力学机制也有重要意义.      

Steadiness and stop of brittle fracture driven by the forces in different distances

Introduction The problem of crack stop of fault is of special importance in geosciences. This is because the risk of rupture of large scale fault is taken as the object of investigation in the geosciences. In some meaning, the stop of earthquake rupture is more important than initial because of its influ-ence on the prediction of energy releasing during the earthquake. There are quite a few of factors that cause stop of the fault. For example, the effect of barriers, the rapid healing of shea…     

ON THE DYNAMIC MECHANISM OFEROSION PROCESS

Erosion process is controlled and affected by various forces of different nature. Erosion processes induced or affected by these forces can be classified into three cate- gories: erosion process induced by endogenic agent, by exogenic agent and associated with human activities. In this article, various dynamic mechanisms are systematically reviewed. Effects of tectonic stress and gravitational stress fields on erosion, effects of human activity on erosion, effect of exogenic forces such as water and wind erosion are discussed respectively.