Long range intermolecular forces in triatomic systems: connecting the atom-diatom and atom-atom-atom representations

The long-range forces that act between three atoms are analysed in both atom-diatom and atom-atom-atom representations. Expressions for atom-diatom dispersion coefficients are obtained in terms of 3-body nonadditive coefficients. The anisotropy of atom-diatom C_6 dispersion coefficients arises primarily from nonadditive triple-dipole and quadruple-dipole forces, while pairwise-additive forces and nonadditive triple-dipole and dipole-dipole-quadrupole forces contribute significantly to atom-diatom C_8 coefficients. The resulting expressions are applied to dispersion coefficients for Li + Li_2 (triplet) and recommendations are made for the best way to obtain global triatomic potentials that dissociate correctly both to three separated atoms and to an atom and a diatomic molecule.Comment: To be published in a special issue of Molecular Physics in honour of Mark Chil

Electrostatic Langmuir and SEAWs in spin polarized plasma double layer

The quantum hydrodynamic model of the electrostatic waves in the two parallel layers of two dimensional electron gases (2DEGs) is developed. It is considered for two regimes: classic regime and quantum regime with the separate spin evolution. Two Langmuir-like waves are found in classic case which have an interference-like pattern in the frequency dependence on concentration $\omega^{2}\sim(n_{01}+n_{02}\pm2\sqrt{n_{01}n_{02}})$. They appear instead of two 2D Langmuir waves in noninteracting 2DEGs. The spectrum of four waves is found in the quantum regime. Two extra waves are related to the separate spin evolution and associated to the spin-electron acoustic waves. The influence of the quantum Bohm potential is considered either.Comment: 9 pages, 14 figure

Hidden Symmetries of Higher Dimensional Black Holes and Uniqueness of the Kerr-NUT-(A)dS spacetime

We prove that the most general solution of the Einstein equations with the cosmological constant which admits a principal conformal Killing-Yano tensor is the Kerr-NUT-(A)dS metric. Even when the Einstein equations are not imposed, any spacetime admitting such hidden symmetry can be written in a canonical form which guarantees the following properties: it is of the Petrov type D, it allows the separation of variables for the Hamilton-Jacobi, Klein-Gordon, and Dirac equations, the geodesic motion in such a spacetime is completely integrable. These results naturally generalize the results obtained earlier in four dimensions.Comment: 5 pages, no figure

Broadband Spectrum Survey Measurements for Cognitive Radio Applications

It is well known that the existing spectrum licensing system results in a gross under-utilization of the frequency spectrum. Spectrum background measurements – spectrum surveys – provide useful data for spectrum regulation, planning or finding frequency niches for spectrum sharing. Dynamic spectrum sharing as a main goal of cognitive radio (CR) is the modern option on how to optimize usage of the frequency spectrum. A spectrum survey measurement system is introduced with results obtained from a variety of markedly different scenarios allowing us, unlike other studies, to focus on wideband and fast spectrum scans. The sensitivity of the receiver is no worse than -113 dBm in the whole band. The utilization of the frequency spectrum is analyzed to prove its under-utilization and to show spectrum sharing opportunities. This was shown to be true in the frequency band higher than 2.5 GHz. A comparison with other spectrum survey campaigns is provided

An Adaptive Threshold in Mammalian Neocortical Evolution

Expansion of the neocortex is a hallmark of human evolution. However, it remains an open question what adaptive mechanisms facilitated its expansion. Here we show, using gyrencephaly index (GI) and other physiological and life-history data for 102 mammalian species, that gyrencephaly is an ancestral mammalian trait. We provide evidence that the evolution of a highly folded neocortex, as observed in humans, requires the traversal of a threshold of 10^9 neurons, and that species above and below the threshold exhibit a bimodal distribution of physiological and life-history traits, establishing two phenotypic groups. We identify, using discrete mathematical models, proliferative divisions of progenitors in the basal compartment of the developing neocortex as evolutionarily necessary and sufficient for generating a fourteen-fold increase in daily prenatal neuron production and thus traversal of the neuronal threshold. We demonstrate that length of neurogenic period, rather than any novel progenitor-type, is sufficient to distinguish cortical neuron number between species within the same phenotypic group.Comment: Currently under review; 38 pages, 5 Figures, 13 Supplementary Figures, 2 Table

Accelerated black holes in an anti-de Sitter universe

The C-metric is one of few known exact solutions of Einstein's field equations which describes the gravitational field of moving sources. For a vanishing or positive cosmological constant, the C-metric represents two accelerated black holes in asymptotically flat or de Sitter spacetime. For a negative cosmological constant the structure of the spacetime is more complicated. Depending on the value of the acceleration, it can represent one black hole or a sequence of pairs of accelerated black holes in the spacetime with an anti-de Sitter-like infinity. The global structure of this spacetime is analyzed and compared with an empty anti-de Sitter universe. It is illustrated by 3D conformal-like diagrams.Comment: 14 pages, 17 figures [see http://utf.mff.cuni.cz/~krtous/physics/CADS/ for the version with the high quality figures and for related animations and interactive 3D diagrams

Ultracold collisions involving heteronuclear alkali metal dimers

We have carried out the first quantum dynamics calculations on ultracold atom-diatom collisions in isotopic mixtures. The systems studied are spin-polarized 7Li + 6Li7Li, 7Li + 6Li2, 6Li + 6Li7Li and 6Li + 7Li2. Reactive scattering can occur for the first two systems even when the molecules are in their ground rovibrational states, but is slower than vibrational relaxation in homonuclear systems. Implications for sympathetic cooling of heteronuclear molecules are discussed.Comment: 4 pages, 3 figure