529 research outputs found
A new approach for the ortho-positronium lifetime determination in a vacuum cavity
Currently, the experimental uncertainty for the determination of the
ortho-positronium (o-Ps) decay rate is at 150 ppm precision; this is two orders
of magnitude lower than the theoretical one, at 1 ppm level. Here we propose a
new proof of concept experiment aiming for an accuracy of 100 ppm to be able to
test the second-order correction in the calculations, which is ppm. The improvement relies on
a new technique to confine the o-Ps in a vacuum cavity. Moreover, a new method
was developed to subtract the time dependent pick-off annihilation rate of the
fast backscattered positronium from the o-Ps decay rate prior to fitting the
distribution. Therefore, this measurement will be free from the systematic
errors present in the previous experiments. The same experimental setup
developed for our recent search for invisible decay of ortho-positronium is
being used. The precision will be limited by the statistical uncertainty, thus,
if the expectations are fulfilled, this experiment could pave the way to reach
the ultimate accuracy of a few ppm level to confirm or confront directly the
higher order QED corrections. This will provide a sensitive test for new
physics, e.g. a discrepancy between theoretical prediction and measurements
could hint the existence of an hidden sector which is a possible dark matter
candidate.Comment: 12 pages, 8 Figures, prepared for the proceedings of the PSAS2018
conference, Vienna (Austria
Intense beam of metastable Muonium
Precision spectroscopy of the Muonium Lamb shift and fine structure requires
a robust source of 2S Muonium. To date, the beam-foil technique is the only
demonstrated method for creating such a beam in vacuum. Previous experiments
using this technique were statistics limited, and new measurements would
benefit tremendously from the efficient 2S production at a low energy muon
( keV) facility. Such a source of abundant low energy has
only become available in recent years, e.g. at the Low-Energy Muon beamline at
the Paul Scherrer Institute. Using this source, we report on the successful
creation of an intense, directed beam of metastable Muonium. We find that even
though the theoretical Muonium fraction is maximal in the low energy range of
keV, scattering by the foil and transport characteristics of the beamline
favor slightly higher energies of keV. We estimate that
an event detection rate of a few events per second for a future Lamb shift
measurement is feasible, enabling an increase in precision by two orders of
magnitude over previous determinations
Long-term monitoring on the occurrence of a myxosporean parasite <i>Kudoa camarguensis</i> (Myxosporean) on the common goby (Teleostei, Pisces) <i>Pomatoschistus microps</i>
The evolution of a host-parasite system composed of Pomatoschistus microps-Kudoa camarguensis was investigated in the Vaccares lagoon (Rhone river Delta, France) from 1993 to 1997. During this long-term monitoring, centennial flooding of the Rhone river occurred, leading to an inrush of about 110 million m3 of freshwater in the Vaccares lagoon. The salinity drastically dropped from 14 to 5 g l-1 in 1 Wk. We observed that the annual prevalence and abundance of the myxosporean parasite decreased from 12.18 in 1993 to 3.7% in 1997 and from 1.10 in 1993 to 0.27 in 1997, respectively. Here, we discuss the possible reasons for the rapid decline of this host-parasite system following the flood
Positron annihilation in latex templated macroporous silica films: pore size and ortho-positronium escape
International audienceDepth profling of positron annihilation characteristics has been used to investigate the pore size distribution in macroporous PMMA latex templated SiO2 films deposited on glass or Si and prepared with 11-70% porosity. The correlation between the annihilation characteristics shows that o-Ps escape (re-emission) into vacuum occurs in all films with a porosity threshold that is pore size dependent. For 60 ± 2% porosity, the o-Ps reemission yield decreases from ~ 0:25 to ~ 0:11 as the pore size increases from 32 to 75 nm. The o-Ps reemission yield is shown to vary linearly with the specific surface area per mass unit and the slope is independent of pore size, 9:1±0:4 g cm-1. For 32 nm pores, the o-Ps annihilation lifetimes in the films, 17(2)ns and 106(5) ns, show that o-Ps annihilates from micropores with small effective size (1:4 ± 4 nm) and from macropores with large effective size (~ 32 nm). Above the porosity threshold, the o-Ps-escape model predicts the annihilation lifetime in the films to be 19±2 ns. Our results imply that o-Ps effciently detects the microporosity present in the silica walls. At low porosity, its capture into the micropores competes with its capture into the macropores. At higher porosity (when the distance between micropores and macropores become small), this capture into the micropores assists the capture into the macropores
Successful pregnancy in a patient with short bowel syndrome after surgical rehabilitation and sGLP-2 treatment: novel report on endogenous GLP-2 levels at delivery and during breastfeeding
Pregnant patients with short bowel syndrome (SBS) and chronic intestinal failure (CIF) can successfully reach to term their pregnancies while on parenteral nutrition (PN) but with high rates of complications. The combination of rehabilitation surgery, combined with the use of novel treatment with enterohormones, especially semisynthetic glucagon-like peptide 2 (sGLP-2), has increased the chances to achieve intestinal sufficiency. Here, we report the case of a 33-year-old female with SBS/CIF (anatomy type 2), weaned off PN using sGLP-2 for 3.7 years, discontinued when she became pregnant. She was able to carry the pregnancy to term without any additional PN support. Considering that, we queried if the endogenous GLP-2 (eGLP-2) levels in this SBS patient, during the pregnancy and breastfeeding period, could be like those presented in healthy pregnant women and in non-pregnant SBS patients. Also, we inquired if there was any passage or increase in the plasmatic eGLP-2 from the fetus to the mother. Thus, we determined eGLP-2 levels in paired neonatal (cord blood) and maternal plasma samples from the SBS pregnant patient (n = 1), healthy pregnant women (controls, n = 2), and non-pregnant SBS patients (n = 12). The results indicated that the SBS pregnant patient showed higher eGLP-2 levels than non-SBS pregnant patients and healthy pregnant women along all the period studied. Furthermore, we found that the maternal sample had higher eGLP-2 levels than the neonatal sample, suggesting that fetal contribution to maternal eGLP2 levels would be minor. In conclusion, this study not only reports for the first time a case of a patient with SBS that was able to achieve intestinal adaptation after combining the use of autologous reconstructive surgery and sGLP-2, but also enlightens the possibility of carrying out an uneventful pregnancy and lactation without any nutritional support and remaining independent of sGLP-2.Fil: Gentilini, Maria Virginia. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Medicina Traslacional, Trasplante y BioingenierÃa. Fundación Favaloro. Instituto de Medicina Traslacional, Trasplante y BioingenierÃa; ArgentinaFil: Doeyo, M.. Fundación Favaloro; ArgentinaFil: Ortega, M.. Fundación Favaloro; ArgentinaFil: Illidge Perez, L.. Fundación Favaloro; ArgentinaFil: Rumbo, C.. Fundación Favaloro; ArgentinaFil: Arriola Benitez, Paula Constanza. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Medicina Traslacional, Trasplante y BioingenierÃa. Fundación Favaloro. Instituto de Medicina Traslacional, Trasplante y BioingenierÃa; ArgentinaFil: Crivelli, A.. Fundación Favaloro; ArgentinaFil: Rumbo, MartÃn. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto de Estudios Inmunológicos y Fisiopatológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Estudios Inmunológicos y Fisiopatológicos; ArgentinaFil: Solar, H.. Fundación Favaloro; ArgentinaFil: Gondolesi, Gabriel Eduardo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Medicina Traslacional, Trasplante y BioingenierÃa. Fundación Favaloro. Instituto de Medicina Traslacional, Trasplante y BioingenierÃa; Argentin
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