Mapping of periodically poled crystals via spontaneous parametric down-conversion

A new method for characterization of periodically poled crystals is developed based on spontaneous parametric down-conversion. The method is demonstrated on crystals of Y:LiNbO3, Mg:Y:LiNbO3 with non-uniform periodically poled structures, obtained directly under Czochralski growth procedure and designed for application of OPO in the mid infrared range. Infrared dispersion of refractive index, effective working periods and wavelengths of OPO were determined by special treatment of frequency-angular spectra of spontaneous parametric down-conversion in the visible range. Two-dimensional mapping via spontaneous parametric down-conversion is proposed for characterizing spatial distribution of bulk quasi-phase matching efficiency across the input window of a periodically poled sample.Comment: 19 pages, 6 figure

A Study of Strange Particles Produced in Neutrino Neutral Current Interactions in the NOMAD Experiment

Results of a detailed study of strange particle production in neutrino neutral current interactions are presented using the data from the NOMAD experiment. Integral yields of neutral strange particles (K0s, Lambda, Lambda-bar) have been measured. Decays of resonances and heavy hyperons with an identified K0s or Lambda in the final state have been analyzed. Clear signals corresponding to K* and Sigma(1385) have been observed. First results on the measurements of the Lambda polarization in neutral current interactions have been obtained.Comment: Accepted for publication in Nuclear Physics B as a rapid communicatio

Early land plant spore assemblages from the Late Silurian of Skane, Sweden

peer reviewedA palynological study based on sedimentary rocks (mainly calcareous siltstones and mudstones with minor carbonate beds) from the upper Silurian Öved-Ramsåsa Group in the Klinta 1 and Bjärsjölagård 2 drillcores, Skåne, Sweden, reveals a rich assemblage of well-preserved spores produced by early land plants. Thirty-four spore taxa belonging to 19 genera, including the new species Scylaspora klintaensis sp. nov., were identified. The palynoflora is characterized by cryptospores and trilete spores. The dominant spore species are the cryptospores Gneudnaspora plicata followed by Gneudnaspora divellomedia. Based on the presence of biostratigraphically important spore species such as Hispanaediscus lamontii, Artemopyra radiata, Emphanisporites neglectus, Synorisporites cf. libycus and Synorisporites tripapillatus, the age of the studied strata is interpreted to be of a Late Silurian age. Although the palynological assemblages are strongly dominated by miospores and other land plant fragments, marine microfossils are also present and the sedimentary succession is interpreted to have been deposited in a nearshore marine environment

Palynological evidence for the age of the Brewer Conglomerate, Amadeus Basin, central Australia

An assemblage of spores recovered from the Undandita Member of the Brewer Conglomerate, the uppermost unit of the Pertnjara Group in the Amadeus Basin of central Australia, establishes the age of that formation as Late Devonian. Comparison with spore assemblages from sedimentary basins in Western Australia indicates that the central Australian assemblage is dateable within the post-early Frasnian to pre-late Famennian interval. Fish remains and spores previously described from the Parke Siltstone at the base of the Pertnjara Group are of probable early Frasnian age, so it now appears that the entire group was deposited during the Late Devonian. The Brewer Conglomerate is of synorogenic origin, and was deposited during uplift associated with the Alice Springs Orogeny; the spore data thus indicate that this tectonic event began in the Late Devonian. Isotopic age determinations in the Arltunga Nappe Complex and the Strangways Range of the Arunta Block have yielded Early Carboniferous dates. These possibly reflect a later stage of deformation than that which was responsible for the deformation and folding of the Brewer Conglomerate