343 research outputs found
Positronium signature in organic liquid scintillators for neutrino experiments
Electron anti-neutrinos are commonly detected in liquid scintillator
experiments via inverse beta decay, by looking at the coincidence between the
reaction products, neutron and positron. Prior to positron annihilation, an
electron-positron pair may form an orthopositronium (o-Ps) state, with a mean
life of a few ns. Even if the o-Ps decay is speeded up by spin flip or pick off
effects, it may introduce distortions in the photon emission time distribution,
crucial for position reconstruction and pulse shape discrimination algorithms
in anti-neutrino experiments. Reversing the problem, the o-Ps induced time
distortion represents a new signature for tagging anti-neutrinos in liquid
scintillator.
In this paper, we report the results of measurements of the o-Ps formation
probability and lifetime, for the most used solvents for organic liquid
scintillators in neutrino physics (pseudocumene, linear alkyl benzene,
phenylxylylethane, and dodecane). We characterize also a mixture of
pseudocumene +1.5 g/l of 2,5-diphenyloxazole, a fluor acting as wavelength
shifter.
In the second part of the paper, we demonstrate that the o-Ps induced
distortion of the scintillation photon emission time distributions represent an
optimal signature for tagging positrons on an event by event basis, potentially
enhancing the anti-neutrino detection.Comment: 6 pages, 9 figure
Características de plantas em genótipos de feijão carioca relacionadas à habilidade competitiva com plantas daninhas.
Swelling of positronium confined in a small cavity
The electron density at the positron (contact density) in the ground state positronium (Ps) formed in condensed matter is generally found to be lower than in vacuum. This is usually attributed to microscopic electric fields which polarize Ps, by acting on the two particles of the atom. In this paper we quantitatively investigate an opposite effect. It is due to the confinement of Ps in small cavities existing in the host solid (e.g. free volume in polymers), which increases the contact density. Although this phenomenon is greater, the smaller is the size of the cavity, Ps polarization seems to play anyway a predominant role
Interferência de plantas daninhas em diferentes cultivares de feijão do grupo carioca.
O objetivo desse trabalho foi avaliar a habilidade competitiva de cultivares de feijão do grupo carioca com plantas daninhas. As perdas de produtividade de grãos em cultivares de feijão carioca, decorrentes da interferência exercida pelas plantas daninhas, variaram de 42,2 a 61,2 %, sendo que as cultivares que apresentaram as menores perdas de produtividade também suprimiram em maior grau o crescimento das plantas daninhas. Não foi possível identificar, de forma consistente, características de plantas associadas à redução de produtividade de grãos em função da interferência de plantas daninhas
Habilidade competitiva de genótipos de feijão comum do grupo "preto" com plantas daninhas.
A hipótese dessa pesquisa é de que há variabilidade entre genótipos de feijão do grupo Preto quanto à competitividade com plantas daninhas e é possível identificar características de plantas que explicam expressivamente a habilidade competitiva. O objetivo desse trabalho foi avaliar a habilidade competitiva de genótipos de feijão do grupo preto com plantas daninhas. As perdas de produtividade de grãos em genótipos de feijão preto, decorrentes da interferência exercida pelas plantas daninhas, variaram de 30,8 a 54,9 %, sendo que os genótipos que apresentaram as menores perdas de produtividade também suprimiram em maior grau o crescimento das plantas daninhas. Houve tendência de aumento das reduções de produtividade de grãos em razão da interferência de plantas daninhas com o aumento da produtividade verificada na ausência de interferência. Não foi possível identificar características de plantas que afetam significativamente a habilidade dos genótipos de feijão em competir com plantas daninhas
Tracing U mobility in deep groundwater using Ra isotopes
The mobility of natural U is compared among four boreholes in a fractured granite using Ra isotopes and geochemical modelling. Rn-222/Ra-226 activity ratios (ARs) spanning an order of magnitude underline differences in reactive surface area. (Ra-224/Ra-228)(ARs) up to 9 indicate recent changes in hydrogeochemistry, and (Ra-226/Ra-228)(ARs) 0.6-30 indicate variable deposition of U. Dissolved U is related to dissolution of a solid U(VI) phase by groundwater with HCO3- > 20 mg.L-1. U reduction is hindered by Ca2UO2(CO3)(3)(0)
22q11.2 Deletion Syndrome. Impact of Genetics in the Treatment of Conotruncal Heart Defects
Congenital heart diseases represent one of the hallmarks of 22q11.2 deletion syndrome. In particular, conotruncal heart defects are the most frequent cardiac malformations and are often associated with other specific additional cardiovascular anomalies. These findings, together with extracardiac manifestations, may affect perioperative management and influence clinical and surgical outcome. Over the past decades, advances in genetic and clinical diagnosis and surgical treatment have led to increased survival of these patients and to progressive improvements in postoperative outcome. Several studies have investigated long-term follow-up and results of cardiac surgery in this syndrome. The aim of our review is to examine the current literature data regarding cardiac outcome and surgical prognosis of patients with 22q11.2 deletion syndrome. We thoroughly evaluate the most frequent conotruncal heart defects associated with this syndrome, such as tetralogy of Fallot, pulmonary atresia with major aortopulmonary collateral arteries, aortic arch interruption, and truncus arteriosus, highlighting the impact of genetic aspects, comorbidities, and anatomical features on cardiac surgical treatment
Eletrolite leakage as a technique to diagnose euphorbia heterophylla biotypes resistant to ppo-inhibitors herbicides
22Ne and 23Na ejecta from intermediate-mass stars: The impact of the new LUNA rate for 22Ne(p,gamma)23Na
We investigate the impact of the new LUNA rate for the nuclear reaction NeNa on the chemical ejecta of intermediate-mass stars, with particular focus on the thermally-pulsing asymptotic giant branch (TP-AGB) stars that experience hot-bottom burning. To this aim we use the PARSEC and COLIBRI codes to compute the complete evolution, from the pre-main sequence up to the termination of the TP-AGB phase, of a set of stellar models with initial masses in the range , and metallicities , , and . We find that the new LUNA measures have much reduced the nuclear uncertainties of the Ne and Na AGB ejecta, which drop from factors of to only a factor of few for the lowest metallicity models. Relying on the most recent estimations for the destruction rate of Na, the uncertainties that still affect the Ne and Na AGB ejecta are mainly dominated by evolutionary aspects (efficiency of mass-loss, third dredge-up, convection). Finally, we discuss how the LUNA results impact on the hypothesis that invokes massive AGB stars as the main agents of the observed O-Na anti-correlation in Galactic globular clusters. We derive quantitative indications on the efficiencies of key physical processes (mass loss, third dredge-up, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anti-correlation, and the observational constraints on the CNO abundance. Results for the corresponding chemical ejecta are made publicly available
Experimental trials and theoretical background about foaming, slag refractory interaction and feasibility of crude magnesium carbonate injection as foaming agent and its use for EAF refractory protection
A theoretical overview about the slag structure, their compatibility with the refractories and their foaming behaviorhas been realized. Such a theoretical background is the basis for the performed experimental trials focused onthe use of crude MgCO3 injected within the slag. This raw material can develop the gaseous phases (CO2) neededfor the slag foaming and it can provide the MgO useful to make the slag compatible with the refractories. Theexperimentation has been performed through the injection of different specific quantities of MgCO3 and theobtained results pointed out a significant decrease of refractory wear, a saving of the specific electric energy, adecrease of the lime injection and of the anthracite powder needed to induce the foaming effect
- …