Bifurcation and instability modelling by a multimechanism elasto‐plastic model

The bifurcation and instability conditions in geomechanics are closely related to the elasto‐plastic behaviour. In this paper the potential of a multimechanism elasto‐plastic model to predict various modes of failure is examined. First, a brief overview for the essential aspects of the constitutive model and the development of the elasto‐plastic constitutive matrix for this model are presented. Then, numerical simulations of different drained and undrained paths in the axisymmetric and plane‐strain conditions for the Hostun sand are illustrated. These examples confirm the capacity of the model to reproduce instability and strain localization phenomena. The obtained response is in agreement with experimental observations, theoretical developments and numerical analyses existing in the literature. Copyright © 2007 John Wiley & Sons, Ltd.     

A second note on Hori-Lie perturbation technique

In this second note we show how to avoid the introduction of Hori's pseudo-time in analytical planetary theory in the case of the eight principal planets of our solar system excluding Pluto.     

The elimination of the 1:2 critical terms of a first order theory of Uranus perturbed by Neptune through Von Zeipel method

In this paper we eliminate in a first order U-N theory the 1 : 2 critical terms up to the third degree with respect to eccentricity — inclination in both parts, main and indirect of the U-N planetary Hamiltonian. We operate the Von Zeipel technique. We adopt, in this theory, the Jacobi-Radau coordinates, and the Poincaré canonical variables. We neglect powers higher than the third in the eccentricity-inclination. This paper is related to the two previous articles (Kamel, 1982; 1983).     

Expansion of the inverse of mutual distance between two bodies raised to any power

We calculate the expression forΔ ^-s in terms of true anomalies and classical orbital elements, referring to a common fixed plane and working up to power four of eccentricities and tangents of inclinations. We obtained two final results: the first wheny ^′>y, the second wheny>y ^′.     

Deciphering the interaction between quaternary and continental Sabkhas aquifers in Central Tunisia using hydrochemical and isotopic tools

Climate aridity and intensive exploitation due to uncontrolled pumping for irrigation have caused a drastic decrease in the piezometric level of the shallow aquifer of Chougafiya plain, central Tunisia, and have seriously degraded groundwater quality. According to the hydrochemical data (Cl^?, SO₄ ^2?, NO₃ ^?, HCO₃ ^?, Br^?, Na⁺, Mg²⁺, K⁺, Ca²⁺, Sr²⁺) and the stable isotopes (¹⁸O and ²H content), groundwater salinization in the investigated aquifer is caused by four main processes: (1) evaporite dissolution (2) cation exchange reactions (3) evaporation processes and (4) mixing with Sabkhas salt water causing salinity to increase in the central and southern parts of the basin. The radiogenic (³H) isotope data provided insight into the presence of significant contemporaneous recharge waters in the western part of the shallow aquifer. The movement of the tritiated water may have occurred according to the general flow path (NW–SE). When tritium was used in conjunction with the stable isotopes and chloride, the mixing process could be clearly identified, especially in the central part of the study area.     

Dielectric screening in the nonextensive Thomas-Fermi model

The dielectric screening process is revisited within the theoretical framework of the nonextensive Thomas-Fermi model with thermal effects. The nonextensive counterpart of the Fermion distribution function is used. It is found that the nonextensive corrections (which vanish in the zero-temperature limit) are more noticeable as the nonextensive character of the electrons becomes important. Our results should assist in interpreting the screening in dense stellar medium.     

The actualization of neoliberal space and the loss of housing affordability in Santa Monica,California

This paper reveals the contingent aspect associated with the actualization of a neoliberal space. The paper examines the material, institutional, and economic conditions necessary for a neoliberal agenda to transform its urban policy objectives into a material reality. The study follows changes in housing conditions in Santa Monica, California from 1990 to 2008. During this period, the confluence of three sets of events led to the actualization of a neoliberal space. First, housing damage from the 1994 Northridge earthquake removed “dead capital” from the housing sector. Second, subsequent administrative actions at the local level and more importantly deregulation legislation at the state level eliminated rent control regulations and created market incentives that favored upscale development. Finally, the state’s economic recovery generated a substantial flow of private investments into the real estate market. These combined factors led not only to the dismantling of affordable housing in Santa Monica, but also to the erosion of residents’ and local authorities’ ability to manage housing choices and, consequently, to a historic restructuring of Santa Monica’s physical and social space. These changes had a disproportionately and negative effect on low-income and minority renters.     

Flow exchange between the deep and shallow groundwaters in the Sbeϊtla synclinal basin (Tunisia): an isotopic approach

Stable (¹⁸O, ² H) and radiogenic (³H, ¹⁴C) isotopes of water have been used to constrain the source, origin, age, migration pathway and mixing processes in the Sbeïtla (Tunisia) system. The system is composed of an upper unconfined Middle Miocene aquifer with a variable thickness from 10–300 m, an intermediate confined/unconfined Lower Miocene aquifer about 100 m thick and a deeper confined Lower Cretaceous aquifer about 150 m thick separated by a thin clay layer. A total of 53 groundwater samples from the three aquifers and spring samples were collected during February and March 2000 and isotopically analysed using conventional methods. The stable isotopes composition of waters establishes that the deep groundwater (depleted as compared to present corresponding local rainfall) is ancient water recharged probably during the late Pleistocene and the early Holocene periods. The relatively recent water in the superficial aquifer is composed of mixed waters resulting presumably from upward leakage from the deeper groundwater. The radiogenic (³H, ¹⁴C) isotopes data confirm that the recent water, with a tritium content between 6.5 and 19 TU, represents post-nuclear recharge and the ancient groundwater with low carbon-14 contents between 7 and 26 pmC infiltrated between 8,000 to 20,000 years ago. When used in conjunction with the stable isotopes data, the mixing process can be clearly identified, especially in the Sbeïtla sill area. Groundwater of the upper aquifer exhibits isotopic signatures of both the old and recent waters. By using isotopic mass balance, the computed contribution of the deep groundwater in recharging the upper aquifer is up to 94%.     

A second order Jupiter-Saturn planetary theory

We complete by this part II the establishment of a second order secular Jupiter-Saturn theory. This is achieved by taking into consideration the influence of the indirect part of the planetary disturbing function, and expressing the second order secular Hamiltonian in terms of Poincaré's canonical variables.     

Application of Hori's technique in general planetary theory

In this part we present the complete solution of the planetary canonical equations of motion by the method of G. Hori through successive changes of canonical variables using the Lie series. Thus, we can eliminate the long or critical terms of the planetary perturbing function, in our general planetary theory. In our formulas, we neglect perturbation terms of order higher than the third with respect to planetary masses.