911 research outputs found
The Nylon Scintillator Containment Vessels for the Borexino Solar Neutrino Experiment
Borexino is a solar neutrino experiment designed to observe the 0.86 MeV Be-7
neutrinos emitted in the pp cycle of the sun. Neutrinos will be detected by
their elastic scattering on electrons in 100 tons of liquid scintillator. The
neutrino event rate in the scintillator is expected to be low (~0.35 events per
day per ton), and the signals will be at energies below 1.5 MeV, where
background from natural radioactivity is prominent. Scintillation light
produced by the recoil electrons is observed by an array of 2240
photomultiplier tubes. Because of the intrinsic radioactive contaminants in
these PMTs, the liquid scintillator is shielded from them by a thick barrier of
buffer fluid. A spherical vessel made of thin nylon film contains the
scintillator, separating it from the surrounding buffer. The buffer region
itself is divided into two concentric shells by a second nylon vessel in order
to prevent inward diffusion of radon atoms. The radioactive background
requirements for Borexino are challenging to meet, especially for the
scintillator and these nylon vessels. Besides meeting requirements for low
radioactivity, the nylon vessels must also satisfy requirements for mechanical,
optical, and chemical properties. The present paper describes the research and
development, construction, and installation of the nylon vessels for the
Borexino experiment
Implications of miRNA expression pattern in bovine oocytes and follicular fluids for developmental competence
Developmental competence determines the oocyte capacity to support initial embryo growth, but the molecular mechanisms underlying this phenomenon are still ill-defined. Changes in microRNA (miRNA) expression pattern have been described during follicular growth in several species. Therefore, aim of this study was to investigate whether miRNA expression pattern in cow oocyte and follicular fluid (FF) is associated with the acquisition of developmental competence. Samples were collected from ovaries with more than, or fewer than, 10 mid-antral follicles (H- and L-ovaries) because previous studies demonstrated that this parameter is a reliable predictor of oocyte competence. After miRNA deep sequencing and bioinformatic data analysis, we identified 58 miRNAs in FF and 6 in the oocyte that were differentially expressed between H- and L-ovaries. Overall, our results indicate that miRNA levels both in FF and in the ooplasm must remain within specific thresholds and that changes in either direction compromising oocyte competence. Some of the miRNAs found in FF (miR-769, miR-1343, miR-450a, miR-204, miR-1271 and miR-451) where already known to regulate follicle growth and their expression pattern indicate that they are also involved in the acquisition of developmental competence. Some miRNAs were differentially expressed in both compartments but with opposite patterns, suggesting that miRNAs do not flow freely between FF and oocyte. Gene Ontology analysis showed that the predicted gene targets of most differentially expressed miRNAs are part of a few signalling pathways. Regulation of maternal mRNA storage and mitochondrial activity seem to be the processes more functionally relevant in determining oocyte quality. In conclusion, our data identified a few miRNAs in the follicular fluid and in the ooplasm that modulate the oocyte developmental competence. This provides new insights that could help with the management of cattle reproductive efficiency
Transcatheter CoreValve implantation for aortic regurgitation in a Jehovah's witness with prior aortic dissection
Indications for transcatheter valve implantation have been extended to treat native valve aortic regurgitation in case of disproportionate risk for open surgery. Transcatheter aortic valves are also an attractive alternative in patients who refuse blood transfusions. We report the successful off-label implantation of a self-expandable transcatheter valve in a Jehovah's Witness with prior replacement of the ascending aorta for Type A dissection, residual severe aortic regurgitation and refractory heart failure
In Vitro Acute Exposure to DEHP Affects Oocyte Meiotic Maturation, Energy and Oxidative Stress Parameters in a Large Animal Model
A microfabricated sensor for thin dielectric layers
We describe a sensor for the measurement of thin dielectric layers capable of
operation in a variety of environments. The sensor is obtained by
microfabricating a capacitor with interleaved aluminum fingers, exposed to the
dielectric to be measured. In particular, the device can measure thin layers of
solid frozen from a liquid or gaseous medium. Sensitivity to single atomic
layers is achievable in many configurations and, by utilizing fast, high
sensitivity capacitance read out in a feedback system onto environmental
parameters, coatings of few layers can be dynamically maintained. We discuss
the design, read out and calibration of several versions of the device
optimized in different ways. We specifically dwell on the case in which
atomically thin solid xenon layers are grown and stabilized, in cryogenic
conditions, from a liquid xenon bath
Cosmogenic 11C production and sensitivity of organic scintillator detectors to pep and CNO neutrinos
Several possible background sources determine the detectability of pep and
CNO solar neutrinos in organic liquid scintillator detectors. Among such
sources, the cosmogenic 11C nuclide plays a central role. 11C is produced
underground in reactions induced by the residual cosmic muon flux. Experimental
data available for the effective cross section for 11C by muons indicate that
11C will be the dominant source of background for the observation of pep and
CNO neutrinos. 11C decays are expected to total a rate 2.5 (20) times higher
than the combined rate of pep and CNO neutrinos in Borexino (KamLAND) in the
energy window preferred for the pep measurement, between 0.8 and 1.3 MeV.
This study examines the production mechanism of 11C by muon-induced showers
in organic liquid scintillators with a novel approach: for the first time, we
perform a detailed ab initio calculation of the production of a cosmogenic
nuclide, 11C, taking into consideration all relevant production channels.
Results of the calculation are compared with the effective cross sections
measured by target experiments in muon beams.
This paper also discusses a technique for reduction of background from 11C in
organic liquid scintillator detectors, which allows to identify on a one-by-one
basis and remove from the data set a large fraction of 11C decays. The
background reduction technique hinges on an idea proposed by Martin Deutsch,
who suggested that a neutron must be ejected in every interaction producing a
11C nuclide from 12C. 11C events are tagged by a three-fold coincidence with
the parent muon track and the subsequent neutron capture on protons.Comment: 11 pages, 6 figures; added one section detailing comparison with
previous estimates; added reference
Early surgical anteroseptal ventricular endocardial restoration after acute myocardial infarction : pathophysiology and surgical considerations
Background. The efficacy and safety of surgical anteroseptal ventricular endocardial restoration (a procedure that excludes non-contracting scarred segments) in the left ventricle with chronic dilation and remodeling secondary to an anterior myocardial infarction are well established. We present a small series and discuss the indication for early left ventricular restoration in the setting of complicated acute myocardial infarction. Methods. Early ventricular restoration was performed in 8 patients (4 males, 4 females, mean age 70 \ub1 8 years). A postinfarction ventricular septal defect was diagnosed in 3 cases. All patients were operated, on an urgent or emergent basis, between 1 and 16 days following the onset of infarction. Surgical coronary revascularization was associated in 7 patients. Results. There was one operative death. At discharge, echocardiographic morphofunctional assessment revealed: a reduction of the left ventricular end-diastolic and end-systolic volume indexes, an increase of the ejection fraction, and, most importantly, an improvement of remote myocardial shortening fraction. At a mean follow-up of 15.6 months (range 2-21 months), there were no late deaths and all survivors are in NYHA functional class I or II. Conclusions. Left ventricular restoration may represent an effective adjunct to the surgical management of patients with an acute extensive anterior myocardial infarction complicated by severe heart failure, with or without septal rupture
New Echocardiographic Parameters Predicting Successful Trans-Ventricular Beating-Heart Mitral Valve Repair with Neochordae at 3 Years: Monocentric Retrospective Study
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