39 research outputs found
General features of Bianchi-I cosmological models in Lovelock gravity
We derived equations of motion corresponding to Bianchi-I cosmological models
in the Lovelock gravity. Equations derived in the general case, without any
specific ansatz for any number of spatial dimensions and any order of the
Lovelock correction. We also analyzed the equations of motion solely taking
into account the highest-order correction and described the drastic difference
between the cases with odd and even numbers of spatial dimensions. For
power-law ansatz we derived conditions for Kasner and generalized Milne regimes
for the model considered. Finally, we discuss the possible influence of matter
in the form of perfect fluid on the solutions obtained.Comment: extended version of published Brief Repor
Cosmology in three dimensions: steps towards the general solution
We use covariant and first-order formalism techniques to study the properties
of general relativistic cosmology in three dimensions. The covariant approach
provides an irreducible decomposition of the relativistic equations, which
allows for a mathematically compact and physically transparent description of
the 3-dimensional spacetimes. Using this information we review the features of
homogeneous and isotropic 3-d cosmologies, provide a number of new solutions
and study gauge invariant perturbations around them. The first-order formalism
is then used to provide a detailed study of the most general 3-d spacetimes
containing perfect-fluid matter. Assuming the material content to be dust with
comoving spatial 2-velocities, we find the general solution of the Einstein
equations with non-zero (and zero) cosmological constant and generalise known
solutions of Kriele and the 3-d counterparts of the Szekeres solutions. In the
case of a non-comoving dust fluid we find the general solution in the case of
one non-zero fluid velocity component. We consider the asymptotic behaviour of
the families of 3-d cosmologies with rotation and shear and analyse their
singular structure. We also provide the general solution for cosmologies with
one spacelike Killing vector, find solutions for cosmologies containing scalar
fields and identify all the PP-wave 2+1 spacetimes.Comment: 35 pages, 2 figure
Culex pipiens, an Experimental Efficient Vector of West Nile and Rift Valley Fever Viruses in the Maghreb Region
West Nile fever (WNF) and Rift Valley fever (RVF) are emerging diseases causing epidemics outside their natural range of distribution. West Nile virus (WNV) circulates widely and harmlessly in the old world among birds as amplifying hosts, and horses and humans as accidental dead-end hosts. Rift Valley fever virus (RVFV) re-emerges periodically in Africa causing massive outbreaks. In the Maghreb, eco-climatic and entomologic conditions are favourable for WNV and RVFV emergence. Both viruses are transmitted by mosquitoes belonging to the Culex pipiens complex. We evaluated the ability of different populations of Cx. pipiens from North Africa to transmit WNV and the avirulent RVFV Clone 13 strain. Mosquitoes collected in Algeria, Morocco, and Tunisia during the summer 2010 were experimentally infected with WNV and RVFV Clone 13 strain at titers of 107.8 and 108.5 plaque forming units/mL, respectively. Disseminated infection and transmission rates were estimated 14–21 days following the exposure to the infectious blood-meal. We show that 14 days after exposure to WNV, all mosquito st developed a high disseminated infection and were able to excrete infectious saliva. However, only 69.2% of mosquito strains developed a disseminated infection with RVFV Clone 13 strain, and among them, 77.8% were able to deliver virus through saliva. Thus, Cx. pipiens from the Maghreb are efficient experimental vectors to transmit WNV and to a lesser extent, RVFV Clone 13 strain. The epidemiologic importance of our findings should be considered in the light of other parameters related to mosquito ecology and biology