195 research outputs found
Performance of Optically Readout GEM-based TPC with a 55Fe source
Optical readout of large Time Projection Chambers (TPCs) with multiple Gas
Electron Multipliers (GEMs) amplification stages has shown to provide very
interesting performances for high energy particle tracking. Proposed
applications for low-energy and rare event studies, such as Dark Matter search,
ask for demanding performance in the keV energy range. The performance of such
a readout was studied in details as a function of the electric field
configuration and GEM gain by using a Fe source within a 7 litre
sensitive volume detector developed as a part of the R\&D for the CYGNUS
project. Results reported in this paper show that the low noise level of the
sensor allows to operate with a 2~keV threshold while keeping a rate of
fake-events lesser than 10 per year. In this configuration, a detection
efficiency well above 95\% along with an energy resolution () of 18\%
is obtained for the 5.9 keV photons, demonstrating the very promising
capabilities of this technique
Italian carbonatite system: From mantle to ore-deposit
A new discovery of carbonatites at Pianciano, Ficoreto and Forcinelle in the Roman Region demonstrates that Italian carbonatites are not just isolated, mantle xenoliths-bearing, primitive diatremic rocks but also evolved subtype fluor-calciocarbonatite (F ~ 10 wt%) associated with fluor ore (F ~ 30 wt%). New data constrain a multi-stage petrogenetic process, 1-orthomagmatic, 2-carbothermal, 3-hydrothermal. Petrography and geochemistry are conducive to processes of immiscibility and decarbonation, rather than assimilation and crystal fractionation. A CO2-rich, ultra-alkaline magma is inferred to produce immiscible melilite leucitite and carbonatite melts, at lithospheric mantle depths. At the crustal level and in the presence of massive CO2 exsolution, decarbonation reactions may be the dominant processes. Decarbonation consumes dolomite and produces calcite and periclase, which, in turn, react with silica to produce forsterite and Ca silicates (monticellite, melilite, andradite). Under carbothermal conditions, carbonate breakdown releases Sr, Ba and LREE; F and S become concentrated in residual fluids, allowing precipitation of fluorite and barite, as well as celestine and anhydrite. Fluor-calciocarbonatite is the best candidate to exsolve fluids able to deposit fluor ore, which has a smaller volume. At the hydrothermal stage, REE concentration and temperature dropping allow the formation of LREEF2+ and LREECO3+ ligands, which control the precipitation of interstitial LREE fluorcarbonate and silicates: (bastnĂ€site-(Ce), Ce(CO3)F and britholite-(Ce), (Ce,Ca)5(SiO4,PO4)3(OH,F). Vanadates such as wakefieldite-(Ce), CeVO4, vanadinite, Pb5(VO4)3Cl and coronadite Pb(Mn4+ 6 Mn3+ 2)O16 characterise the matrix. At temperatures of â€100 °C analcime, halloysite, quartz, barren calcite, and zeolites (K-Ca) precipitate in expansion fractures, veins and dyke aureoles. © 2019 The Authors689909IGM SD RAS 0330-2016-0005The HiTech AlkCarb European Union Horizon 2020 project grant-agreement number 689909 supported this research. Mineralogical studies was also partly supported by the Russian State assignment project IGM SD RAS 0330-2016-0005
First evidence of luminescence in a He/CF gas mixture induced by non-ionizing electrons
Optical readout of Gas Electron Multipliers (GEM) provides very interesting
performances and has been proposed for different applications in particle
physics. In particular, thanks to its good efficiency in the keV energy range,
it is being developed for low-energy and rare event studies, such as Dark
Matter search. So far, the optical approach exploits the light produced during
the avalanche processes in GEM channels. Further luminescence in the gas can be
induced by electrons accelerated by a suitable electric field. The CYGNO
collaboration studied this process with a combined use of a triple-GEM
structure and a grid in an He/CF (60/40) gas mixture at atmospheric
pressure. Results reported in this paper allow to conclude that with an
electric field of about 11~kV/cm a photon production mean free path of about
1.0~cm was found
CYGNO: a gaseous TPC with optical readout for dark matter directional search
The CYGNO project has the goal to use a gaseous TPC with optical readout to
detect dark matter and solar neutrinos with low energy threshold and
directionality. The CYGNO demonstrator will consist of 1 m 3 volume filled with
He:CF 4 gas mixture at atmospheric pressure. Optical readout with high
granularity CMOS sensors, combined with fast light detectors, will provide a
detailed reconstruction of the event topology. This will allow to discriminate
the nuclear recoil signal from the background, mainly represented by low energy
electron recoils induced by radioactivity. Thanks to the high reconstruction
efficiency, CYGNO will be sensitive to low mass dark matter, and will have the
potential to overcome the neutrino floor, that ultimately limits
non-directional dark matter searches
Vitamin D responsive elements within the HLA-DRB1 promoter region in Sardinian multiple sclerosis associated alleles
Vitamin D response elements (VDREs) have been found in the promoter region of the MS-associated allele HLA-DRB1*15:01, suggesting that with low vitamin D availability VDREs are incapable of inducing *15:01 expression allowing in early life autoreactive T-cells to escape central thymic deletion. The Italian island of Sardinia exhibits a very high frequency of MS and high solar radiation exposure. We test the contribution of VDREs analysing the promoter region of the MS-associated DRB1 *04:05, *03:01, *13:01 and *15:01 and non-MS-associated *16:01, *01, *11, *07:01 alleles in a cohort of Sardinians (44 MS patients and 112 healthy subjects). Sequencing of the DRB1 promoter region revealed a homozygous canonical VDRE in all *15:01, *16:01, *11 and in 45/73 *03:01 and in heterozygous state in 28/73 *03:01 and all *01 alleles. A new mutated homozygous VDRE was found in all *13:03, *04:05 and *07:01 alleles. Functionality of mutated and canonical VDREs was assessed for its potential to modulate levels of DRB1 gene expression using an in vitro transactivation assay after stimulation with active vitamin D metabolite. Vitamin D failed to increase promoter activity of the *04:05 and *03:01 alleles carrying the new mutated VDRE, while the *16:01 and *03:01 alleles carrying the canonical VDRE sequence showed significantly increased transcriptional activity. The ability of VDR to bind the mutant VDRE in the DRB1 promoter was evaluated by EMSA. Efficient binding of VDR to the VDRE sequence found in the *16:01 and in the *15:01 allele reduced electrophoretic mobility when either an anti-VDR or an anti-RXR monoclonal antibody was added. Conversely, the Sardinian mutated VDRE sample showed very low affinity for the RXR/VDR heterodimer. These data seem to exclude a role of VDREs in the promoter region of the DRB1 gene in susceptibility to MS carried by DRB1* alleles in Sardinian patients
Performance of an Optically Read-Out Time Projection Chamber with ultra-relativistic electrons
The Time Projection Chamber (TPC) is an ideal candidate to finely study the charged particle ionization in a gaseous medium. Large volumes TPCs can be readout with a suitable number of channels offering a complete 3D reconstruction of an ultra-relativistic charged particle track, that is the sequence of its energy releases in the TPC gas volume. Moreover, He-based TPCs are very promising to study keV energy particles as nuclear recoils, opening the possibility for directional searches of Dark Matter (DM) and the study of Solar Neutrinos (SN). In this paper we report the analysis of the data acquired with a small TPC prototype (named LEMOn) built by the CYGNO collaboration that was exposed to a beam of 450 MeV electrons at the Beam Test Facility of National Laboratories of Frascati. LEMOn is operated with a He-CF4 mixture at atmospheric pressure and is based on a Gas Electron Multipliers amplification stage that produces visible light collected by a sub-millimeter position resolution scientific CMOS camera. This type of readout - in conjunction with a fast light detection - allows a 3D reconstruction of the electrons tracks. The electrons are leaving a trail of segments of ionizations corresponding to a few keV energy release each. Their study leads to predict a keV energy threshold and 1-10 mm longitudinal and 0.1-0.3 mm transverse position resolution for nuclear recoils, very promising for the application of optically readout TPC to DM searches and SN measurements
Y-Chromosome Based Evidence for Pre-Neolithic Origin of the Genetically Homogeneous but Diverse Sardinian Population: Inference for Association Scans
The island of Sardinia shows a unique high incidence of several autoimmune diseases with multifactorial inheritance, particularly type 1 diabetes and multiple sclerosis. The prior knowledge of the genetic structure of this population is fundamental to establish the optimal design for association studies in these diseases. Previous work suggested that the Sardinians are a relatively homogenous population, but some reports were contradictory and data were largely based on variants subject to selection. For an unbiased assessment of genetic structure, we studied a combination of neutral Y-chromosome variants, 21 biallelic and 8 short tandem repeats (STRs) in 930 Sardinian males. We found a high degree of interindividual variation but a homogenous distribution of the detected variability in samples from three separate regions of the island. One haplogroup, I-M26, is rare or absent outside Sardinia and is very common (0.37 frequency) throughout the island, consistent with a founder effect. A Bayesian full likelihood analysis (BATWING) indicated that the time from the most recent common ancestor (TMRCA) of I-M26, was 21.0 (16.0â25.5) thousand years ago (KYA) and that the population began to expand 14.0 (7.8â22.0) KYA. These results suggest a largely pre-Neolithic settlement of the island with little subsequent gene flow from outside populations. Consequently, Sardinia is an especially attractive venue for case-control genome wide association scans in common multifactorial diseases. Concomitantly, the high degree of interindividual variation in the current population facilitates fine mapping efforts to pinpoint the aetiologic polymorphisms
A role of BRCA1 and BRCA2 germline mutations in breast cancer susceptibility within Sardinian population
<p>Abstract</p> <p>Background</p> <p>In recent years, numerous studies have assessed the prevalence of germline mutations in <it>BRCA1 </it>and <it>BRCA2 </it>genes in various cohorts. We here extensively investigated the prevalence and geographical distribution of <it>BRCA1-2 </it>mutations in the entire genetically-homogeneous Sardinian population. The occurrence of phenotypic characteristics which may be predictive for the presence of <it>BRCA1-2 </it>germline mutations was also evaluated.</p> <p>Methods</p> <p>Three hundred and forty-eight breast cancer patients presenting a familial recurrence of invasive breast or ovarian carcinoma with at least two affected family members were screened for <it>BRCA1-2 </it>mutations by DHPLC analysis and DNA sequencing. Association of <it>BRCA1 </it>and <it>BRCA2 </it>mutational status with clinical and pathological parameters was evaluated by Pearson's Chi-Squared test.</p> <p>Results and Conclusion</p> <p>Overall, 8 <it>BRCA1 </it>and 5 <it>BRCA2 </it>deleterious mutations were detected in 35/348 (10%) families; majority (23/35;66%) of mutations was found in <it>BRCA2 </it>gene. The geographical distribution of <it>BRCA1-2 </it>mutations was related to three specific large areas of Sardinia, reflecting its ancient history: <it>a</it>) the Northern area, linguistically different from the rest of the island (where a <it>BRCA2 c.8764_8765delAG </it>mutation with founder effect was predominant); <it>b</it>) the Middle area, land of the ancient Sardinian population (where <it>BRCA2 </it>mutations are still more common than <it>BRCA1 </it>mutations); and <it>c</it>) the South-Western area, with many Phoenician and Carthaginian locations (where <it>BRCA1 </it>mutations are prevalent). We also found that phenotypic features such as high tumor grading and lack of expression of estrogen/progesterone receptors together with age at diagnosis and presence of ovarian cancer in the family may be predictive for the presence of <it>BRCA1-2 </it>germline mutations.</p
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