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Using the NA49 main TPC, the central production of hyperons has been measured in CERN SPS Pb - Pb collisions at 158 GeV c-1. The preliminary ratio, studied at 2.0 < y < 2.6 and 1 < pT < 3 GeV c-1, equals ~ (13 ± 4)% (systematic error only). It is compatible, within errors, with the previously obtained ratios for central S + S [1], S + W [2], and S + Au [3] collisions. The fit to the transverse momentum distribution resulted in an inverse slope parameter T of 297 MeV. At this level of statistics we do not see any noticeable enhancement of hyperon production with the increased volume (and, possibly, degree of equilibration) of the system from S + S to Pb + Pb. This result is unexpected and counterintuitive, and should be further investigated. If confirmed, it will have a significant impact on our understanding of mechanisms leading to the enhanced strangeness production in heavy-ion collisions.
We report measurements of Xi and Xi-bar hyperon absolute yields as a function of rapidity in 158 GeV/c Pb+Pb collisions. At midrapidity, dN/dy = 2.29 +/- 0.12 for Xi, and 0.52 +/- 0.05 for Xi-bar, leading to the ratio of Xi-bar/Xi = 0.23 +/- 0.03. Inverse slope parameters fitted to the measured transverse mass spectra are of the order of 300 MeV near mid-rapidity. The estimated total yield of Xi particles in Pb+Pb central interactions amounts to 7.4 +/- 1.0 per collision. Comparison to Xi production in properly scaled p+p reactions at the same energy reveals a dramatic enhancement (about one order of magnitude) of Xi production in Pb+Pb central collisions over elementary hadron interactions.
About half of present-day cloud condensation nuclei originate from atmospheric nucleation, frequently appearing as a burst of new particles near midday1. Atmospheric observations show that the growth rate of new particles often accelerates when the diameter of the particles is between one and ten nanometres2,3. In this critical size range, new particles are most likely to be lost by coagulation with pre-existing particles4, thereby failing to form new cloud condensation nuclei that are typically 50 to 100 nanometres across. Sulfuric acid vapour is often involved in nucleation but is too scarce to explain most subsequent growth5,6, leaving organic vapours as the most plausible alternative, at least in the planetary boundary layer7,8,9,10. Although recent studies11,12,13 predict that low-volatility organic vapours contribute during initial growth, direct evidence has been lacking. The accelerating growth may result from increased photolytic production of condensable organic species in the afternoon2, and the presence of a possible Kelvin (curvature) effect, which inhibits organic vapour condensation on the smallest particles (the nano-Köhler theory)2,14, has so far remained ambiguous. Here we present experiments performed in a large chamber under atmospheric conditions that investigate the role of organic vapours in the initial growth of nucleated organic particles in the absence of inorganic acids and bases such as sulfuric acid or ammonia and amines, respectively. Using data from the same set of experiments, it has been shown15 that organic vapours alone can drive nucleation. We focus on the growth of nucleated particles and find that the organic vapours that drive initial growth have extremely low volatilities (saturation concentration less than 10−4.5 micrograms per cubic metre). As the particles increase in size and the Kelvin barrier falls, subsequent growth is primarily due to more abundant organic vapours of slightly higher volatility (saturation concentrations of 10−4.5 to 10−0.5 micrograms per cubic metre). We present a particle growth model that quantitatively reproduces our measurements. Furthermore, we implement a parameterization of the first steps of growth in a global aerosol model and find that concentrations of atmospheric cloud concentration nuclei can change substantially in response, that is, by up to 50 per cent in comparison with previously assumed growth rate parameterizations.
The formation of secondary particles in the atmosphere accounts for more than half of global cloud condensation nuclei. Experiments at the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber have underlined the importance of ions for new particle formation, but quantifying their effect in the atmosphere remains challenging. By using a novel instrument setup consisting of two nano-particle counters, one of them equipped with an ion filter, we were able to further investigate the ion-related mechanisms of new particle formation. In autumn 2015, we carried out experiments at CLOUD on four systems of different chemical compositions involving monoterpenes, sulfuric acid, nitrogen oxides, and ammonia. We measured the influence of ions on the nucleation rates under precisely controlled and atmospherically relevant conditions. Our results indicate that ions enhance the nucleation process when the charge is necessary to stabilize newly formed clusters, i.e. in conditions where neutral clusters are unstable. For charged clusters that were formed by ion-induced nucleation, we were able to measure, for the first time, their progressive neutralization due to recombination with oppositely charged ions. A large fraction of the clusters carried a charge at 1.2 nm diameter. However, depending on particle growth rates and ion concentrations, charged clusters were largely neutralized by ion–ion recombination before they grew to 2.2 nm. At this size, more than 90 % of particles were neutral. In other words, particles may originate from ion-induced nucleation, although they are neutral upon detection at diameters larger than 2.2 nm. Observations at Hyytiälä, Finland, showed lower ion concentrations and a lower contribution of ion-induced nucleation than measured at CLOUD under similar conditions. Although this can be partly explained by the observation that ion-induced fractions decrease towards lower ion concentrations, further investigations are needed to resolve the origin of the discrepancy.
A systematic redefinition of the species belonging to the genus Geomyphilus Gordon and Skelley, 2007 (Coleoptera: Scarabaeidae: Aphodiinae) of Mexico and neighboring countries is presented. The new species G. tuzincola of Mexico is described and figured. The new combination Coelotrachelus macgregori (Islas, 1955) is proposed.
Besides the two species at present known belonging to the genus Trichonotuloides Balthasar (T. glyptus (Bates) and T. latecrenatus (Bates)), two new Mexican species, T. alfonsinae and T. hansferyi, are herein described (Coleoptera: Scarabaeidae: Aphodiinae). The complete set of fi gures is supplied for all taxa herein dealt with.
Systematic revision of the genus Orodaliscoides Schmidt, 1913 (Coleoptera: Scarabaeidae: Aphodiinae)
(2012)
The species belonging to the genus Orodaliscoides Schmidt (Coleoptera: Scarabaeidae: Aphodiinae) are redescribed and figured. The following new combinations are proposed: Orodaliscoides fimbripes (Brown, 1928) and Orodaliscoides giulianii (Gordon, 1977).
The American species belonging to the genera Alloblackburneus Bordat and Blackburneus Schmidt (Coleoptera: Scarabaeidae: Aphodiinae) are redescribed and figured. Seven new species are described: Alloblackburneus guadalajarae, A. ibanezbernali; Blackburneus amazonicus, B. sanfilippoi, B. surinamensis, B. teposcolulaensis, B. thomasi. The neotype of Scarabaeus rubeolus Palisot de Beauvois, 1809 is designated. The lectotype of Blackburneus argentinensis (Schmidt, 1909) and of Blackburneus laxepunctatus (Schmidt, 1910) are
designated. The following new combinations are proposed: Alloblackburneus aegrotus (Horn, 1870); Alloblackburneus cavidomus (Brown, 1927); Alloblackburneus cynomysi (Brown, 1927); Alloblackburneus fordi (Gordon, 1974); Alloblackburneus geomysi (Cartwright, 1939); Alloblackburneus lentus (Horn, 1870); Alloblackburneus rubeolus (Palisot de Beauvois, 1805); Alloblackburneus saylori (Hinton, 1934); Alloblackburneus tenuistriatus (Horn, 1887); Alloblackburneus troglodytes (Hubbard, 1894).
The American species belonging to the genus Gonaphodiellus Schmidt (Coleoptera: Scarabaeidae: Aphodiinae) are redescribed and figured. Two new genera are described: Gonaphodioides and Gonaphodiopsis. Fourteen new species are described: Gonaphodiellus arcanus, G. cerropuntanus, G. manantlanicus, G. martinpierai, G. omiltemicus, G. sacatepequezis, Gonaphodioides newtoni, G. ratcliffei, G. skelleyi, Gonaphodiopsis deloyai, G. hypogea, G. montesdeocai, G. pachecoi, G. teopiscaensis. The lectotype of Aphodius columbicus (Harold, 1880) is designated. The following new combinations are proposed: Gonaphodiellus nigrinus (Schmidt, 1916), Gonaphodioides acutecernans (Balthasar, 1960), Gonaphodioides chapini (Hinton, 1934), Gonaphodioides columbicus (Harold, 1880), Gonaphodioides sincerus (Petrovitz, 1973). Aphodius (Gonaphodiellus) xalapensis Galante, Stebnicka and Verdú, 2003 is placed as a junior synonym of Gonaphodiellus bimaculosus (Schmidt, 1909), new synonymy. Aphodius ataenioides Hinton, 1938 and Aphodius (Blackburneus) castanescens Petrovitz, 1973 are placed as junior synonyms of Gonaphodioides chapini (Hinton, 1934), new synonymies.