4,249 research outputs found

    New results from an extensive aging test on bakelite Resistive Plate Chambers

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    We present recent results of an extensive aging test, performed at the CERN Gamma Irradiation Facility on two single--gap RPC prototypes, developed for the LHCb Muon System. With a method based on a model describing the behaviour of an RPC under high particle flux conditions, we have periodically measured the electrode resistance R of the two RPC prototypes over three years: we observe a large spontaneous increase of R with time, from the initial value of about 2 MOhm to more than 250 MOhm. A corresponding degradation of the RPC rate capabilities, from more than 3 kHz/cm2 to less than 0.15 kHz/cm2 is also found.Comment: 6 pages, 7 figures, presented at Siena 2002, 8th Topical Seminar on Innovative Particle and Radiation Detectors 21-24 October 2002, Siena, Ital

    Extracellular vesicle-induced differentiation of neural stem progenitor cells

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    Neural stem progenitor cells (NSPCs) from E13.5 mouse embryos can be maintained in culture under proliferating conditions. Upon growth-factor removal, they may differentiate toward either neuronal or glial phenotypes or both. Exosomes are small extracellular vesicles that are part of the cell secretome; they may contain and deliver both proteins and genetic material and thus play a role in cell–cell communication, guide axonal growth, modulate synaptic activity and regulate peripheral nerve regeneration. In this work, we were interested in determining whether NSPCs and their progeny can produce and secrete extracellular vesicles (EVs) and if their content can affect cell differentiation. Our results indicate that cultured NSPCs produce and secrete EVs both under proliferating conditions and after differentiation. Treatment of proliferating NSPCs with EVs derived from differentiated NSPCs triggers cell differentiation in a dose-dependent manner, as demonstrated by glial-and neuronal-marker expression

    Gaucher Disease and Myelofibrosis: A Combined Disease or a Misdiagnosis?

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    Background: Gaucher disease (GD) and primary myelofibrosis (PMF) share similar clinical and laboratory features, such as cytopenia, hepatosplenomegaly, and marrow fibrosis, often resulting in a misdiagnosis. Case Report: We report here the case of a young woman with hepatosplenomegaly, leukopenia, and thrombocytopenia. Based on bone marrow (BM) findings and on liver biopsy showing extramedullary hematopoiesis, an initial diagnosis of PMF was formulated. The patient refused stem cell transplantation from an HLA-identical sibling. Low-dose melphalan was given, without any improvement. Two years later, a BM evaluation showed Gaucher cells. Low glucocerebrosidase and high chitotriosidase levels were indicative for GD. Molecular analysis revealed N370S/complex I mutations. Enzyme replacement therapy with imiglucerase was commenced, resulting in clinical and hematological improvements. Due to an unexpected and persistent organomegaly, PMF combined with GD were suspected. JAK2V617F, JAK2 exon 12, MPL, calreticulin, and exon 9 mutations were negative, and BM examination showed no marrow fibrosis. PMF was excluded. Twenty years after starting treatment, the peripheral cell count and liver size were normal, whereas splenomegaly persisted. Conclusion: In order to avoid a misdiagnosis, a diagnostic algorithm for patients with hepatosplenomegaly combined with cytopenia is suggested

    Nucleon generalized polarizabilities within a relativistic Constituent Quark Model

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    Nucleon generalized polarizabilities are investigated within a relativistic framework, defining such quantities through a Lorentz covariant multipole expansion of the amplitude for virtual Compton scattering. The key physical ingredients in the calculation of the nucleon polarizabilities are the Lorentz invariant reduced matrix elements of the electromagnetic transition current, which can be evaluated from off-energy-shell helicity amplitudes. The evolution of the proton paramagnetic polarizability, ÎČpara(q)\beta_{para}(q), as a function of the virtual-photon three-momentum transfer q, q, is explicitly evaluated within a relativistic constituent quark model by adopting transition form factors obtained in the light-front formalism. The discussion is focussed on the role played by the effects due to the relativistic approach and to the transition form factors, derived within different models.Comment: 14 pages and three figures (included), to appear in Phys. Rev. C (May 1998

    Dystonia: sparse synapses for D2 receptors in striatum of a DYT1 knock-out mouse model

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    Dystonia pathophysiology has been partly linked to downregulation and dysfunction of dopamine D2 receptors in striatum. We aimed to investigate the possible morpho-structural correlates of D2 receptor downregulation in the striatum of a DYT1 Tor1a mouse model. Adult control Tor1a+/+ and mutant Tor1a+/− mice were used. The brains were perfused and free-floating sections of basal ganglia were incubated with polyclonal anti-D2 antibody, followed by secondary immune-fluorescent antibody. Confocal microscopy was used to detect immune-fluorescent signals. The same primary antibody was used to evaluate D2 receptor expression by western blot. The D2 receptor immune-fluorescence appeared circumscribed in small disks (~0.3–0.5 ÎŒm diameter), likely representing D2 synapse aggregates, densely distributed in the striatum of Tor1a+/+ mice. In the Tor1a+/− mice the D2 aggregates were significantly smaller (ÎŒm2 2.4 ± SE 0.16, compared to ÎŒm2 6.73 ± SE 3.41 in Tor1a+/+) and sparse, with ~30% less number per microscopic field, value correspondent to the amount of reduced D2 expression in western blotting analysis. In DYT1 mutant mice the sparse and small D2 synapses in the striatum may be insufficient to “gate” the amount of presynaptic dopamine release diffusing in peri-synaptic space, and this consequently may result in a timing and spatially larger nonselective sphere of influence of dopamine action

    Splitting of the pi - rho spectrum in a renormalized light-cone QCD-inspired model

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    We show that the splitting between the light pseudo-scalar and vector meson states is due to the strong short-range attraction in the ^1S_0 sector which makes the pion and the kaon light particles. We use a light-cone QCD-inspired model of the mass squared operator with harmonic confinement and a Dirac-delta interaction. We apply a renormalization method to define the model, in which the pseudo-scalar ground state mass fixes the renormalized strength of the Dirac-delta interaction.Comment: 9 pages, 2 figures, revtex, accepted by Phys. Rev. D; Corrected typo

    Extended van Royen-Weisskopf formalism for lepton-antilepton meson decay widths within non-relativistic quark models

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    The classical van Royen-Weisskopf formula for the decay width of a meson into a lepton-antilepton pair is modified in order to include non-zero quark momentum contributions within the meson as well as relativistic effects. Besides, a phenomenological electromagnetic density for quarks is introduced. The meson wave functions are obtained from two different models: a chiral constituent quark model and a quark potential model including instanton effects. The modified van Royen-Weisskopf formula is found to improve systematically the results for the widths, giving an overall good description of all known decays.Comment: 22 pages, 3 figures, RevTex, epsfig. To be published in Nucl. Phys.

    Electromagnetic form factors in the light-front formalism and the Feynman triangle diagram: spin-0 and spin-1 two-fermion systems

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    The connection between the Feynman triangle diagram and the light-front formalism for spin-0 and spin-1 two-fermion systems is analyzed. It is shown that in the limit q+ = 0 the form factors for both spin-0 and spin-1 systems can be uniquely determined using only the good amplitudes, which are not affected by spurious effects related to the loss of rotational covariance present in the light-front formalism. At the same time, the unique feature of the suppression of the pair creation process is maintained. Therefore, a physically meaningful one-body approximation, in which all the constituents are on their mass-shells, can be consistently formulated in the limit q+ = 0. Moreover, it is shown that the effects of the contact term arising from the instantaneous propagation of the active constituent can be canceled out from the triangle diagram by means of an appropriate choice of the off-shell behavior of the bound state vertexes; this implies that in case of good amplitudes the Feynman triangle diagram and the one-body light-front result match exactly. The application of our covariant light-front approach to the evaluation of the rho-meson elastic form factors is presented.Comment: corrected typos in the reference

    Neutron spectrometer for fast nuclear reactors

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    In this paper we describe the development and first tests of a neutron spectrometer designed for high flux environments, such as the ones found in fast nuclear reactors. The spectrometer is based on the conversion of neutrons impinging on 6^6Li into α\alpha and tt whose total energy comprises the initial neutron energy and the reaction QQ-value. The 6^6LiF layer is sandwiched between two CVD diamond detectors, which measure the two reaction products in coincidence. The spectrometer was calibrated at two neutron energies in well known thermal and 3 MeV neutron fluxes. The measured neutron detection efficiency varies from 4.2×10−4\times 10^{-4} to 3.5×10−8\times 10^{-8} for thermal and 3 MeV neutrons, respectively. These values are in agreement with Geant4 simulations and close to simple estimates based on the knowledge of the 6^6Li(n,α\alpha)tt cross section. The energy resolution of the spectrometer was found to be better than 100 keV when using 5 m cables between the detector and the preamplifiers.Comment: submitted to NI

    Neutron diffraction study of Bronze Age tools from second millennium BC dwellings in Italy

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    Neutron diffraction was utilized to characterise XX to XIII century BC bronze axes (Ancient to Late Bronze Age) from "Terramare" and other Bronze Age settlements near Modena, Italy. Archaeometric metallurgy issues have been addressed by means of phase and texture analysis from measurements carried out at the ROTAX and GEM beam lines of the neutron spallation source ISIS of the Rutherford Appleton Laboratory (UK), Neutron data provide accurate composition and structural information from the bulk of the alloy, with good grain statistics, without limitations due to surface alterations and with few limitations as to sample size. Bronze composition results are in good agreement with data obtained by micro-sampling and traditional analytical techniques thus confirming the validity of the method used for a totally non-destructive determination of the alloy composition from precise lattice parameter measurements. Phase analysis from diffraction profiles provides identification and quantification of surface alteration and corrosion products, free of interference with the analysis of the bulk alloy. Furthermore, texture analysis techniques may yield information on the ancient production methods of the artefacts. © Società Italians di Fisica
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