The vacuum Friedmann-type solutions in Barber's theory of gravitation

Vacuumk=0 Friedmann-type solutions in the continuous creation theory of gravitation proposed by Barber have recently been found by Reddy (1987). Here we obtain thek=±1 Friedmann solutions in Barber's theory. Also, we show that these models are, in fact, vacuum Brans-Dicke solutions that have been studied earlier by Lorenz-Petzold (1984).     

Compact models with regular charge distributions

We model a compact relativistic body with anisotropic pressures in the presence of an electric field. The equation of state is barotropic, with a linear relationship between the radial pressure and the energy density. Simple exact models of the Einstein–Maxwell equations are generated. A graphical analysis indicates that the matter and electromagnetic variables are well behaved. In particular, the proper charge density is regular for certain parameter values at the stellar center unlike earlier anisotropic models in the presence of charge. We show that the electric field affects the mass of stellar objects and the observed mass for a particular binary pulsar is regained. Our models contain previous results of anisotropic charged matter with a linear equation of state for special parameter values.     

Social networks and undocumented Mozambican migration to South Africa

This paper analyses the social networks which facilitate and sustain undocumented migration from Mozambique to South Africa. A key contention is that the migrant social networks are not limited to a spatially bounded area; transcend geography, location and territory; can be considered as spatial conveyors of social capital; and operate transnationally at three different locations: in the sending communities, on borders and in the destination areas. In the sending communities, interpersonal relationships are based on bonds of kinship, and friendship through which the migrants get moral and material support for the movement. At the borders migrants establish connections with border agents, guides, and conveyors who support them in entering South Africa and provide transportation to their preferred destinations. At the destination areas the newcomers have also counted on the bonds of kinship and friendship among former immigrants, who assist them on their arrival with accommodation and food as well as in the process of getting jobs and documentation. In South Africa undocumented migrants were subjected to high levels of xenophobia, exploitation and deportation, structural, sociopolitical forces against which social networks are largely ineffective. However, through the social networks the undocumented Mozambican labour migration to South Africa has become a self-sustained circular process that is difficult to control.     

Stochastic characterization of earthquakes through their response spectrum

If earthquakes are modelled by a stochastic process, it is possible to interpret the associated response spectrum in terms of the statistics of extreme values of oscillator response to the process. For a stationary earthquake model this interpretation leads to a relationship between the power spectral density function of the process and the response spectrum. This relationship is examined in this paper and forms the basis for two methods presented to obtain the power spectrum of the earthquake process from its response spectrum. One of these methods is approximate but leads to an explicit representation of the power spectral density function in terms of the response spectrum. The other method is exact wherein an iterative scheme for the solution of the problem is established. An example problem is solved to illustrate the use of the two methods and it is shown that for small values of damping, the approximate derivation yields a fairly accurate solution.