Mixmaster chaos

The significant discussion about the possible chaotic behavior of the mixmaster cosmological model due to Cornish and Levin [J.N. Cornish and J.J. Levin, Phys. Rev. Lett. 78 (1997) 998; Phys. Rev. D 55 (1997) 7489] is revisited. We improve their method by correcting nontrivial oversights that make their work inconclusive to precisely confirm their result: ``The mixmaster universe is indeed chaotic''.Comment: 9 pages, 4 figure

Fractal escapes in Newtonian and relativistic multipole gravitational fields

We study the planar motion of test particles in gravitational fields produced by an external material halo, of the type found in many astrophysical systems, such as elliptical galaxies and globular clusters. Both the Newtonian and the general-relativistic dynamics are examined, and in the relativistic case the dynamics of both massive and massless particles are investigated. The halo field is given in general by a multipole expansion; we restrict ourselves to multipole fields of pure order, whose Newtonian potentials are homogeneous polynomials in cartesian coordinates. A pure (n)-pole field has (n) different escapes, one of which is chosen by the particle according to its initial conditions. We find that the escape has a fractal dependency on the initial conditions for (n>2) both in the Newtonian and the relativistic cases for massive test particles, but with important differences between them. The relativistic motion of massless particles, however, was found to be regular for all the fields we could study. The box-counting dimension was used in each case to quantify the sensitivity to initial conditions which arises from the fractality of the escape route.Comment: 17 pages, 7 figures, uses REVTE

Formation of a molecular Bose-Einstein condensate and an entangled atomic gas by Feshbach resonance

Processes of association in an atomic Bose-Einstein condensate, and dissociation of the resulting molecular condensate, due to Feshbach resonance in a time-dependent magnetic field, are analyzed incorporating non-mean-field quantum corrections and inelastic collisions. Calculations for the Na atomic condensate demonstrate that there exist optimal conditions under which about 80% of the atomic population can be converted to a relatively long-lived molecular condensate (with lifetimes of 10 ms and more). Entangled atoms in two-mode squeezed states (with noise reduction of about 30 dB) may also be formed by molecular dissociation. A gas of atoms in squeezed or entangled states can have applications in quantum computing, communications, and measurements.Comment: LaTeX, 5 pages with 4 figures, uses REVTeX

Insufficient potassium and sulfur supply threaten the productivity of perennial forage grasses in smallholder farms on tropical sandy soils

Aims Perennial forage grass production has the potential to improve smallholder livelihoods in the tropics. However, nutrient management is often challenging, especially on infertile sandy soils. This study tested whether typical nutrient management limits the productivity and sustainability of perennial forage grass systems on sandy soils. Methods Nutrient balances were estimated for four fields of either Megathyrsus maximus cv. Tanzania or Urochloa hybrid Mulato II. Nutrient limitations were then evaluated in a nutrient omission experiment. Results All soils were sandy (< 10% clay), neutral to acidic (pH (CaCl2) 4.6 to 6.7) and had plant-limiting concentrations of total nitrogen, extractable potassium and extractable sulfur. Nitrogen inputs were typically higher than outputs, with balances ranging from −16 kg ha−1 yr−1 to 293 kg ha−1 yr−1, yet concentrations in forage shoots were low at all sites. Phosphorus balances ranged from −5 kg ha−1 yr−1 to 77 kg ha−1 yr−1 and concentrations in forage shoots were adequate. Potassium inputs were low, resulting in balances from −79 kg ha−1 yr−1 to −138 kg ha−1 yr−1 at locations that did not apply inorganic potassium fertilizer. Potassium concentrations in forage shoots were low and omission of potassium resulted in severely depressed biomass production. Inorganic sulfur fertilizers were not applied to forages and the sulfur balance varied from −1 kg ha−1 yr−1 to −24 kg ha−1 yr−1. Sulfur concentrations in shoots were correspondingly low and production was depressed when sulfur was omitted in the experiment. Conclusion Balanced nutrition was not achieved, despite substantial fertilizer inputs, resulting in deficiencies of potassium and sulfur, inefficient use of nitrogen and excesses of phosphorus. If current practices continue, potassium and sulfur depletion, phosphorus accumulation and soil acidification can be expected. Recommendations for balanced nutrient management that accounts for high rates of removal in biomass, variable concentrations in organic fertilizers, and leaching potential, are needed to sustain the productivity of perennial forages on tropical sandy soils

Feshbach spectroscopy of an ultracold mixture of Rb-85 and Cs-133

We report the observation of interspecies Feshbach resonances in an optically trapped mixture of 85Rb and 133Cs. We measure nine resonances in the lowest spin channel for a magnetic field range from 0 to 700 G and show that they are in good agreement with coupled-channel calculations. The interspecies background scattering length is close to zero over a large range of magnetic fields, permitting the sensitive detection of Feshbach resonances through interspecies thermalization. Our results confirm the quality of the Rb-Cs potential curves [ Phys. Rev. A 85 032506 (2012)] and offer promising starting points for the production of ultracold polar molecules