Numerically generated quasi-equilibrium orbits of black holes: Circular or eccentric?

We make a comparison between results from numerically generated, quasi-equilibrium configurations of compact binary systems of black holes in close orbits, and results from the post-Newtonian approximation. The post-Newtonian results are accurate through third PN order (O(v/c)^6 beyond Newtonian gravity), and include rotational and spin-orbit effects, but are generalized to permit orbits of non-zero eccentricity. Both treatments ignore gravitational radiation reaction. The energy E and angular momentum J of a given configuration are compared between the two methods as a function of the orbital angular frequency \Omega. For small \Omega, corresponding to orbital separations a factor of two larger than that of the innermost stable orbit, we find that, if the orbit is permitted to be slightly eccentric, with e ranging from \approx 0.03 to \approx 0.05, and with the two objects initially located at the orbital apocenter (maximum separation), our PN formulae give much better fits to the numerically generated data than do any circular-orbit PN methods, including various ``effective one-body'' resummation techniques. We speculate that the approximations made in solving the initial value equations of general relativity numerically may introduce a spurious eccentricity into the orbits.Comment: 6 pages, 4 figures, to be submitted to Phys. Rev.

Edaphic fauna in soil profile after three decades of different soil management and cover crops in a subtropical region

Abstract This research evaluated the effects of long-term (30 years) winter cover crops under conventional farming system and no-tillage system on edaphic fauna in a Rhodic Hapludox soil, from Paraná State, Brazil. We used three winter cover crops (black oat, hairy vetch and fallow), and as a reference a fragment of natural forest. Soil monoliths were collected at two times, one during the flowering of maize (April 2013) and the other during the flowering of soybean (January 2014). The extraction of the monoliths was carried out in three layers in the soil profile (0-10, 10-20 and 20-30 cm). Seventeen taxonomic groups were sampled. The density of the edaphic fauna is inversely related to soil depth. The winter crops associated with the no-tillage system in long-term resulted in fauna densities similar to the natural environment, with a higher density (density increase of 2.2x) at a depth of 10-20 cm in areas with black oat. At 0-10 cm depth, black oat and vetch under no-tillage systems resulted in an increase of 62% and 69% (April 2013) and 46 and 44% (January 2014), respectively, in the density of soil fauna, when compared to the same winter crops in conventional farming system

Dilatonic current-carrying cosmic strings

We investigate the nature of ordinary cosmic vortices in some scalar-tensor extensions of gravity. We find solutions for which the dilaton field condenses inside the vortex core. These solutions can be interpreted as raising the degeneracy between the eigenvalues of the effective stress-energy tensor, namely the energy per unit length U and the tension T, by picking a privileged spacelike or timelike coordinate direction; in the latter case, a phase frequency threshold occurs that is similar to what is found in ordinary neutral current-carrying cosmic strings. We find that the dilaton contribution for the equation of state, once averaged along the string worldsheet, vanishes, leading to an effective Nambu-Goto behavior of such a string network in cosmology, i.e. on very large scales. It is found also that on small scales, the energy per unit length and tension depend on the string internal coordinates in such a way as to permit the existence of centrifugally supported equilibrium configuration, also known as vortons, whose stability, depending on the very short distance (unknown) physics, can lead to catastrophic consequences on the evolution of the Universe.Comment: 10 pages, ReVTeX, 2 figures, minor typos corrected. This version to appear in Phys. Rev.