187 research outputs found
Taxonomic revision and phylogeny of the sharpshooter genus Dasmeusa Melichar, 1926, with a scanning electron microscopy study of D. pauperata (Fabricius, 1803) (Hemiptera: Cicadellidae: Cicadellini)
The genus Dasmeusa is distributed in Northern and Northeastern Brazil and the Guianas. Until the present study, six species were recognized within Dasmeusa. The species of this genus are very similar in terms of color and external morphology, being distinguished mainly by the male terminalia. Here, we review and redescribe Dasmeusa and its species, describe four new species, and present the first phylogenetic analysis of the genus, including 40 morphological characters and 15 terminal taxa. Dasmeusa flavescens Metcalf and Erythrogonia bicolor Metcalf are considered junior synonyms of the type-species, Dasmeusa pauperata (Fabricius). Scanning electron microscopy was employed for a detailed study of the integument of the type-species, including sensilla, surface sculpturing, brochosomes, organ of Evans, and other structures. The phylogenetic analysis with equal weights resulted in nine most parsimonious trees. The implied weighting method resulted in two trees, both with the same ingroup topology as observed in one of the nine equal-weights trees. This preferred topology is as follows: ((D. basseti (D. mendica (D. rafaeli sp. nov., D. falcifera sp. nov.))) (D. isabellina (D. oriximina sp. nov. (D. pauperata (D. imperialis, D. dinizi sp. nov.))))). Dasmeusa was recovered as monophyletic in all trees, being supported by five apomorphic characters
Search for two-neutrino double electron capture on Xe with the XMASS-I detector
Double electron capture is a rare nuclear decay process in which two orbital
electrons are captured simultaneously in the same nucleus. Measurement of its
two-neutrino mode would provide a new reference for the calculation of nuclear
matrix elements whereas observation of its neutrinoless mode would demonstrate
lepton number violation. A search for two-neutrino double electron capture on
Xe is performed using 165.9 days of data collected with the XMASS-I
liquid xenon detector. No significant excess above background was observed and
we set a lower limit on the half-life as years at 90%
confidence level. The obtained limit has ruled out parts of some theoretical
expectations. We obtain a lower limit on the Xe two-neutrino double
electron capture half-life of years at 90% confidence
level as well.Comment: 6 pages, 3 figures, accepted for publication in Physics Letters
Search for solar axions in XMASS, a large liquid-xenon detector
XMASS, a low-background, large liquid-xenon detector, was used to search for
solar axions that would be produced by bremsstrahlung and Compton effects in
the Sun. With an exposure of 5.6ton days of liquid xenon, the model-independent
limit on the coupling for mass 1keV is
(90% C.L.), which is a factor of two stronger than the existing experimental
limit. The bounds on the axion masses for the DFSZ and KSVZ axion models are
1.9 and 250eV, respectively. In the mass range of 10-40keV, this study produced
the most stringent limit, which is better than that previously derived from
astrophysical arguments regarding the Sun to date
Direct dark matter search by annual modulation in XMASS-I
A search for dark matter was conducted by looking for an annual modulation
signal due to the Earth's rotation around the Sun using XMASS, a single phase
liquid xenon detector. The data used for this analysis was 359.2 live days
times 832 kg of exposure accumulated between November 2013 and March 2015. When
we assume Weakly Interacting Massive Particle (WIMP) dark matter elastically
scattering on the target nuclei, the exclusion upper limit of the WIMP-nucleon
cross section 4.310cm at 8 GeV/c was obtained and we
exclude almost all the DAMA/LIBRA allowed region in the 6 to 16 GeV/c range
at 10cm. The result of a simple modulation analysis, without
assuming any specific dark matter model but including electron/ events,
showed a slight negative amplitude. The -values obtained with two
independent analyses are 0.014 and 0.068 for null hypothesis, respectively. we
obtained 90\% C.L. upper bounds that can be used to test various models. This
is the first extensive annual modulation search probing this region with an
exposure comparable to DAMA/LIBRA.Comment: 5 pages, 4 figure
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