Angular diameter distances reconsidered in the Newman and Penrose formalism

Using the Newman and Penrose spin coefficient (NP) formalism, we provide a derivation of the Dyer-Roeder equation for the angular diameter distance in cosmological space-times. We show that the geodesic deviation equation written in NP formalism is precisely the Dyer-Roeder equation for a general Friedman-Robertson-Walker (FRW) space-time, and then we examine the angular diameter distance to redshift relation in the case that a flat FRW metric is perturbed by a gravitational potential. We examine the perturbation in the case that the gravitational potential exhibits the properties of a thin gravitational lens, demonstrating how the weak lensing shear and convergence act as source terms for the perturbed Dyer-Roeder equation.Comment: 21 pages, 6 figures, accepted to GR

The Internet as Ideological Battleground

Recent global events that have brought to light the use of new technologies by terrorist groups have focused attention on the role of the internet in the radicalisation of vulnerable individuals and groups towards a violent extremism. In 2007, the case of Abdul Basheer, a law graduate in Singapore arrested for attempting to join the Taliban in Afghanistan drew attention to the use of the Internet as a source of inspiration and information for would be terrorists. More recently Sydney man Belal Khazaal became the first person to be convicted on the charge of making a document connected with assisting in a terrorist act after using material already available on the internet to develop his own publication The Rules of Jihad - Short Judicial Rulings and Organisational Instructions For Fighters And Mujahideen Against Infidels . Both cases point to the developing role of the Internet in the process of radicalisation and suggest that the Internet has become an important tactical tool in the terrorists’ repertoire. The role of the Internet in radicalisation and the extent to which it contributes to the process through which latent beliefs translate into violent actions is not fully understood. However, with the developing strand of terrorism studies that deals with the diffusion of intent as an integral component of counter terrorism efforts has come an understanding of terrorism as a battle of words and ideas. Nowhere is this more evident than on the internet

Facing the growing problem of the electric power consumption in Egyptian residential building using building performance simulation program

Egypt has been experiencing recurrent power cuts especially at the summer, with the problem being made worse by the extra demands placed on the electrical grid by the advent of the holy month of Ramadan. Electricity shortages are now a problem in Cairo, Alexandria, Sohag, Qena, Luxor, Aswan, and Nubia, as well as in the Nile Delta governorates of Beheira and Qalioubiya. The aim of this study is to develop a model for the Egyptian residential building using Building Performance Simulation Program and make sensitivity analysis on some variables effecting the electric power consumption in order to help faceting the growing problem in Egypt. The model was created using the IES-VE 2012 (Integrated Environmental Solution ). The simulation model was verified against the survey data for the Egyptian apartment and same model simulated using energy Plus simulation tool. The results of the program describing different situations for energy using profile for the air conditions, lighting and equipments in respect to building layout and construction climate and pattern of use. This model can be used in the future to help in reducing the electric power consumption in the residential building

Solving reaction-diffusion equations 10 times faster

The most popular numerical method for solving systems of reaction-diffusion equations continues to be a low order finite-difference scheme coupled with low order Euler time stepping. This paper extends previous 1D work and reports experiments that show that with high--order methods one can speed up such simulations for 2D and 3D problems by factors of 10--100. A short MATLAB code (2/3D) that can serve as a template is included.\ud \ud This work was supported by the Engineering and Physical Sciences Research Council (UK) and by the MathWorks, Inc