1,720,988 research outputs found
On the interplay between boundary conditions and the Lorentzian Wetterich equation
No full textIn the framework of the functional renormalization group and of the perturbative, algebraic approach to quantum field theory (pAQFT), in D'Angelo et al. [Ann. Henri Poinc. 25 (2024) 2295-2352] it has been derived a Lorentzian version of a flow equation à la Wetterich, which can be used to study nonlinear, quantum scalar field theories on a globally hyperbolic spacetime. In this work, we show that the realm of validity of this result can be extended to study interacting scalar field theories on globally hyperbolic manifolds with a timelike boundary. By considering the specific examples of half-Minkowski spacetime and of the Poincaré patch of Anti-de Sitter, we show that the form of the Lorentzian Wetterich equation is strongly dependent on the boundary conditions assigned to the underlying field theory. In addition, using a numerical approach, we are able to provide strong evidences that there is a qualitative and not only a quantitative difference in the associated flow and we highlight this feature by considering Dirichlet and Neumann boundary conditions on half-Minkowski spacetime
Electrical transport properties of V3Si, V5Si3 and VSi2 thin films
No full textResistivity measurements in a wide temperature range (2–1100 K) have been performed on thin films of V3Si, V5Si3, and VSi2 formed on an inert substrate. An anomalous resistivity behavior has been observed in these metallic compounds: The resistivity deviates from linearity and approaches a saturation value at the higher temperatures. The resistivity data can be fitted quite well to a phenomenological expression based on the idea that a limiting resistivity is reached when the electron mean free path is of the order of the interatomic spacing. The electron mean free paths, which have been computed from the experimental data, lend support to the above idea. The saturation phenomenon in V3Si and V5Si3 compounds is characterized by a limiting resistivity of the same magnitude as observed in several A15 materials and in the Mooij correlation, yet in VSi2 the resistivity saturates to a much higher value. The V3Si is a superconductor with a transition temperature around 15 K and a residual resistivity ratio of 10.6. On the other hand, V5Si3 and VSi2 thin compound films do not show superconductivity state down to 2 K. The temperature dependence of the Hall coefficient gives evidence of a complex and different electronic structure of the three compounds
Investigation on the charge collection properties of a 4H-SiC Schottky diode detector
No full textWe present experimental and theoretical data on the charge collection properties of a 4H-SiC epitaxial Schottky diode exposed to 5.48- and 2.00-MeV alpha particles. Hundred percent Charge Collection Efficiency (CCE) is, in particular, demonstrated for the 2.00-MeV alpha particles at reverse voltages higher than 40 V. By comparing measured CCE values with the outcomes of drift-diffusion simulations, a value of 500 ns is inferred for the hole lifetime within the lowly doped, active layer of virgin samples. The contributions of diffusion and funneling-assisted drift to CCE at low reverse voltages are pointed out
Characterisation of silicon carbide detectors response to electron and photon irradiation
No full textA preliminary study of the response of SiC devices to 22 MeV electrons and 6 MV photon beams from a linear accelerator is presented in view to assess the feasibility of SiC-based dosimeters. The devices used are 4H-SiC epitaxial n-type layers deposited onto a 4H-SiC n(+)-type substrate wafer doped with nitrogen. Schottky contacts have been formed by gold deposition on the epitaxial layer. The released charge has been observed to increase linearly with the electron dose up to 10 Gy. A linear dependence of the current response of the devices has been also observed as a function of the photon dose-rate in the 2-7 Gy/min range. A preliminary study of the photoconductive response to UV irradiation of semi-insulating 6H-SiC substrates is also reported on samples, with a bulk resistivity of approximate to 10(11) Omega cm, produced with a modified Lely technique
Electric field distribution in irradiated silicon detectors
No full textParticle irradiation causes dramatic changes in bulk properties of p (+)-n-n(+) silicon structures operating as particle detectors. Several attempts to model and justify such variations have been proposed in the last few years. The main unsolved problem remains in the determination of the electric field and depletion layer distributions as key-parameters to estimate the collection efficiency of the detector. By using optical beam induced current (OBIC) and surface potential (SP) measurements we determined the behavior of the electric field and confirmed the existence of a double-junction structure appearing after irradiation. (C) 2002 Elsevier Science B.V. All rights reserved
OPTICAL STUDY OF NIOBIUM DISILICIDE POLYCRYSTALLINE FILMS
No full textNbSi2 polycrystalline films, coevaporated and thermally annealed, were subjected to chemical and structural characterization, and then studied by reflectance from 0.06 to 6 eV and ellipsometry from 1.4 to 5 eV. The dielectric functions, obtained from Kramers-Kronig analysis and directly from ellipsometry, are also presented. Low-frequency free-carrier response is discussed in terms of the Drude model; the high-frequency interband structures are interpreted on the basis of the calculated density of states and photoemission results. A comparison is made with the optical properties of isoelectronic VSi2 and TaSi2 Polycrystalline films
Epitaxial silicon carbide charge particle detectors
No full textThe radiation detection properties of Schottky detectors made on epitaxial layers of 4H silicon carbide were evaluated. Exposure to 5.48 MeV alpha particles from a Am-241 source in vacumn led to robust signals from the detectors. The collection of the charge carriers was found to increase linearly with the square root of the applied reverse bias. (C) 1999 Elsevier Science B.V. All rights reserved
Double-junction effect in proton-irradiated silicon diodes
No full textThis article concerns the existence of a double-junction effect in proton-irradiated silicon p(+)-nu-n(+) (pin) diodes demonstrated by surface potential and optical-beam-induced current (OBIC) investigations. By increasing the diode biasing, the junctions existing at both ends in the irradiated devices move towards each other up to join, hence, causing a full depletion of the diodes. Due to the inhomogeneity of the electric field, however, the charge-carrier collection is strongly dependent on the position. The extent of the diode depletion layers at both ends and the shape of the electric field within the p(+)-nu-n(+) diodes are determined as a function of the bias applied. Three-dimensional photocurrent maps obtained by OBIC profiles allow for imaging the double junction. The deep level analysis evidences the presence of irradiation-induced defects, which are responsible for the double-junction effect
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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