Explore the vast range of titles available.

We present a 4-body calculation of scattering between an antihydrogen atom (H¯) and a positronium (Ps) aiming at the prediction of cross sections for the production of antihydrogen positive ions H¯+. The antihydrogen positive ions are expected to be a useful source of ultra-cold anti-atoms for the test of matter-antimatter gravity. We convert the Schrödinger equation to a set of coupled integro-differential equations that involve intermediate states which facilitate the internal region description of the scattering wavefunction. They are solved using a compact finite difference method. Our framework is extended to scattering between an excited Ps and H. Cross sections of the reactions, Ps (1s/2s/3s) H¯→e−+H¯+, in s-wave collisions, are calculated. It is found that the reactions originating from Ps (1s/2s) + H¯ produce H¯+ with a constant cross section within 0.05 eV above the threshold while the reaction cross section from Ps (3s) decreases as the collision energy increases in the same energy interval. Just above the threshold, the cross section of H¯+ production from Ps (3s) + H¯ in s-wave collision is 7.8 times larger than that from Ps (1s) + H¯ in s-wave and 2.3 times larger than that from Ps (2s) + H¯ in s-wave. The near-threshold de-excitation reaction from Ps (3s) + H¯ occurs more rapidly than the H¯+ production.

Synopsis We present the 4-body calculation of the antihydrogen-positronium scattering aiming at the prediction of cross sections for the production of antihydrogen positive ions. The latter are expected to be a useful source of ultra-cold atoms for the test of matter-antimatter gravity. We convert the Schrödinger equation to a set of coupled integro-differential equations that involve intermediate states and are solved using the compact finite difference method. We will present the investigation of the rearrangement reaction between the ground-state antihydrogen atom and the excited positronium.

A range of complementary radionuclide proxies in sediments of the southernmost Atlantic Ocean over the past 140,000 years indicate that glacial periods were characterized by greatly increased fluxes of biogenic detritus out of surface waters. This increase in export production, which may have contributed to lower concentrations of carbon dioxide in the glacial atmosphere, was accompanied by more than a fivefold increase in accumulation of lithogenic iron transported by winds from Patagonian deserts. These observations support the hypothesis that the iron limitation of today's Southern Ocean productivity was relieved in glacial periods by a greater supply of iron from wind-blown dust.

The primary mode of interaction of dissolved phosphate with fluvial inorganic suspended particles is via a reversible two-step sorption process. The first step, adsorption/desorption on surfaces, has fast kinetics (minutes-hours). The second step, solid-state diffusion of adsorbed phosphate from the surface into the interior of particles, has slow kinetics (days-months) and is dependent on the time history of the previous surface sorption and the chemistry of the solid diffusional layer. Natural clay particles with a surficial armoring of reactive iron and aluminum hydroxyoxides resulting from chemical weathering of rocks and soils have a high capacity for absorbing phosphate in the second step and for maintaining low \"equilibrium phosphate concentrations\" in solution. Extrapolation of laboratory sorption and extraction experiments with natural soils and suspended sediments to the environment suggests that the phosphate concentrations of unperturbed turbid rivers $(SPM>50 mg liter^-1)$ are controlled near the dynamic equilibrium phosphate concentration of their particles $(EPC_0=0.2-1.5\\mu M)$ and that fluvial suspended particles \"at equilibrium\" contain up to $10\\mu mol-P g^-1$ that is desorbable. Release of this phosphate from particles entering the sea produces the characteristic shape and magnitude of input profiles of dissolved phosphate observed in unperturbed estuaries. On a global scale, fluvial particulates could transport from 1.4 to $14\\times 10^10 mol yr^-1$ of reactive phosphate to the sea, some 2-5 times more than that in the dissolved load alone.

We report on the first production of an antihydrogen beam by charge exchange of 6.1 keV antiprotons with a cloud of positronium in the GBAR experiment at CERN. The 100 keV antiproton beam delivered by the AD/ELENA facility was further decelerated with a pulsed drift tube. A 9 MeV electron beam from a linear accelerator produced a low energy positron beam. The positrons were accumulated in a set of two Penning–Malmberg traps. The positronium target cloud resulted from the conversion of the positrons extracted from the traps. The antiproton beam was steered onto this positronium cloud to produce the antiatoms. We observe an excess over background indicating antihydrogen production with a significance of 3–4 standard deviations.

Although alternative interpretations are possible, research results support previous studies that indicate lower glacial productivity in the Southern Ocean and raise new questions about the role of ocean productivity in models of the causes (or remedies) for changes in atmospheric concentrations of carbon dioxide.

We report on the first production of an antihydrogen beam by charge exchange of 6.1 keV antiprotons with a cloud of positronium in the GBAR experiment at CERN. The 100 keV antiproton beam delivered by the AD/ELENA facility was further decelerated with a pulsed drift tube. A 9 MeV electron beam from a linear accelerator produced a low energy positron beam. The positrons were accumulated in a set of two Penning–Malmberg traps. The positronium target cloud resulted from the conversion of the positrons extracted from the traps. The antiproton beam was steered onto this positronium cloud to produce the antiatoms. We observe an excess over background indicating antihydrogen production with a significance of 3–4 standard deviations.

A Russian-American fieldwork effort on Lake Baikal, its tributaries, and surrounding hot springs was undertaken in June-July 1991. Here we report on aspects of major ion (Ca2+ , Mg2+ , Na+, K+, Alk, Cl-, SO4 2- ) and several minor and trace element (Li isotopes, Sr isotopes, Ba, Al, V, Cr, Ni, Cu, Ge, Cd, Hg, U) cycles. Our riverine data for major ions generally concur with the more extensive, time-averaged Russian database; for the most part the homogeneously distributed major ions appear to be at steady state and dominated by riverine throughputs in the lake. Exceptions include Mg2+, which may be removed to a small extent (≤ 15% of its riverine flux) by hydrothermal activity, and Na+and Cl-, which seem to be impacted by pollution. Of the minor and trace elements, V also seems subject to anthropogenic disturbance. Other elements for which reliable data are available show concervative steady-state distributions (Li, Cr, Sr) or are subject to redistribution and removal within the lake (Ge, Al, Cu, Ni, Ba, U) as a result of involvement in a variety of particle cycling processes that tend to obscure non-natural influences. Chemical geothermometers for the four hot springs sampled (Smeyney, Khakuci, Kotelnikovski, Davsha) indicate subsurface reaction temperatures ranging from 70 to 150⚬C and converging to smaller ranges (± 15⚬C) for a given spring. Both depletions (Mg, Ba, Cu, Ni, Sr, U) and enrichments (Na, K, Cl, Li, Al, Ge, Sr, U) with respect to lake water were observed. Ge levels in spring waters are sufficiently enriched over lake waters tha Ge could serve as a useful tracer of subaquatic hydrothermal waters.

We investigate two methods to include the strong nuclear force in hydrogen–antihydrogen scattering calculations. First, we construct a model optical potential with parameters determined by the measured shift and width of the protonium ground state. Although this potential is a very crude model for the strong nuclear force, its parameters may be adjusted to reproduce both bound states and low-energy annihilation cross sections to within the experimental accuracy. It is then shown that this potential may be reduced to a short-distance boundary condition in terms of the proton–antiproton strong-interaction scattering length. Elastic and annihilation cross sections for ground-state hydrogen–antihydrogen scattering are calculated for s- and p-waves, and collision energies up to 1 atomic unit. The two methods are found to agree to within about 1%. The main source of discrepancy is that the scattering-length approach does not account for vacuum polarization, relativistic, and finite-size corrections. We verify that the range of the strong interaction potential does not affect the hydrogen–antihydrogen s-wave scattering properties, and that the strong interaction has negligible influence on p-wave scattering. PACS Nos.: 36.10.-k, 34.90.+q