Majorana and the quasi-stationary states in Nuclear Physics

A complete theoretical model describing artificial disintegration of nuclei by bombardment with alpha-particles, developed by Majorana as early as in 1930, is discussed in detail alongside the basic experimental evidences that motivated it. By following the quantum dynamics of a state resulting from the superposition of a discrete state with a continuum one, whose interaction is described by a given potential term, Majorana obtained (among the other predictions) the explicit expression for the integrated cross section of the nuclear process, which is the direct measurable quantity of interest in the experiments. Though this is the first application of the concept of quasi-stationary states to a Nuclear Physics problem, it seems also that the unpublished Majorana's work anticipates by several years the related seminal paper by Fano on Atomic Physics.Comment: latex, amsart, 13 page

Charge transport and mobility in monolayer graphene

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Contact-damage coupled modelling of FRP reinforcements under variable loading times

In the last years FRP (Fiber Reinforced Polymer) technology has been developed to repair damaged concrete structures. In this work it is proposed to investigate the complex mechanism of stress-strain evolution at the FRP interface, during different loading programs (short or long-time loadings), until complete debonding. This study has been performed by means of a fully threedimensional approach within the context of damage mechanics, to appropriately catch transversal effects as well as normal stresses, developing a realistic and comprehensive study of the delamination process. The adhesion properties have been reconstructed through a contact model incorporating an elastic-damage constitutive law, relating inter-laminar stresses acting in the sliding direction. A F.E. research code (FRPCON) has been developed, including a numerical procedure accounting for Mazars’s damage law inside the contact algorithm. The code is able to describe the delamination process considering the different surface preparation of the concrete part as well. The long-time behaviour of these composite structures has been studied by means of two visco-elastic formulations: i) Bazant’s B3 law has been considered for the concrete component, where creep effect is composed by three different terms, i.e. the elastic part, basic creep and drying creep; ii) for FRP’s fibres and matrix a micromechanical approach has been implemented. The experimental results of long-time bending tests have been used to calibrate and validate the numerical models

Aggregate behaviour in concrete materials under high temperature conditions

Concrete under high temperature conditions is a topic of wide interest for applications in several engineering fields, from nuclear to civil as well as building engineering

A search for double beta decays of tin isotopes with enhanced sensitivity

A search for the various double beta decay modes of 124Sn and 112Sn has been performed on 75 kg.days of data. New half-life limits for excited states in 124Sn have been obtained including a lower limit for the decay into the first excited 2+ state of 124Te of T_half > 0.87e20 yrs (90% CL) and into the first excited 0+ state of T_half > 1.08e20 yrs (90% CL). Ground state and excited state transitions of 112Sn have also been experimentally explored. A limit for the 2 neutrino double electron capture of T_half > 1.8e19 yrs (90% CL) is obtained. The non-observation of de-excitation gammas from the 0+ at 1888.5keV results in a lower half-life limit on the 0 neutrino double electron capture decay of 112Sn of T_half > 0.8e19 yrs (90% CL), despite a possible resonant enhancement of the decay rate due to degenerated states.Comment: 6 pages, 7 figures, updated analysis and tex

The Turin Shroud face: the evidence of maxillo-facial trauma

The Turin Shroud (TS) is a linen cloth commonly associated with Jesus Christ, his crucifixion and burial. Several medical specialists have debated the injuries of the TS Man, nevertheless there are no detailed and quantitative data about the anatomy of the TS face. The purpose of this study was to analyse the cephalometric measurements of the face image of the TS. The TS face image was acquired by a picture and processed using a cephalometric software, Oris Ceph® (Up to date 2012). The image of the soft tissues was processed in order to obtain skeletal points and a cephalometric analysis of the soft and skeletal tissues was performed. Image processing of the TS face shows that the Man represented in it has undergone a maxillo-facial trauma, especially a left displacement of the mandible, probably due to temporo-mandibular joint lesions. This condition has not been described before, despite several studies on the subject

The Turin Shroud face: the evidence of maxillo-facial trauma

The Turin Shroud (TS) is a linen cloth commonly associated with Jesus Christ, his crucifixion and burial. Several medical specialists have debated the injuries of the TS Man, nevertheless there are no detailed and quantitative data about the anatomy of the TS face. The purpose of this study was to analyse the cephalometric measurements of the face image of the TS. The TS face image was acquired by a picture and processed using a cephalometric software, Oris Ceph® (Up to date 2012). The image of the soft tissues was processed in order to obtain skeletal points and a cephalometric analysis of the soft and skeletal tissues was performed. Image processing of the TS face shows that the Man represented in it has undergone a maxillo-facial trauma, especially a left displacement of the mandible, probably due to temporo-mandibular joint lesions. This condition has not been described before, despite several studies on the subject

An Euler-Bernoulli beam element with lumped plasticity applied on RC framed structures

Most of existing reinforced concrete structures suffer due to corrosion of steel and concrete degradation. In many cases existing structures reveal to be inadequate to absorb the expected seismic load and need to be rehabilitated according to the in force code. In the worst case some structures have not been designed to absorb horizontal actions. The rehabilitation process begins with the complete knowledge of its geometrical configuration and the evaluation of the vulnerability of the structure to seismic loads. This analysis permits to identify critical zones and to establish focused strengthening actions. A comparison between the behavior of the structure in the current and in the future configurations determines the goodness of adopted intervention techniques. The evaluation of the vulnerability of an RC structure to seismic loads can be done by performing nonlinear finite element analyses. In literature, three different approaches have been tuned to simulate the elastoplastic behavior of a beam/column element: lumped elastoplasticity models, distributed nonlinearity models, fiber models. Lumped models consider the constitutive nonlinearity concentrated at a section level of a frame element, usually employing nonlinear springs at the ends of beam/column elements. Distributed nonlinearity models average the nonlinearity over a finite element by considering the possibility to form plastic hinges at different evaluation points of the element and calculating weighted integrals of the section responses. Fiber models subdivide a section with a large number of finite elements and nonlinearity is related to the stress-strain relationship of a single finite element. Within lumped models, commercial finite element programs contemplate the possibility to develop plasticity at the two ends of the beam only. In the particular cases where plasticity concentrates in points different than the ends of the beam, it computationally comes in the need to proceed with a re-meshing of the model or in the definition of multiple elements before running the analysis. In the first case, it results in an increased computational cost of the analysis. In the second case, a less precision of the response is obtained especially when the exact position of the plastic hinge is not a-priori known. The present work is devoted to the implementation of a new elastoplastic 3D Euler-Bernoulli beam element including slope discontinuities, in the framework of lumped elastoplasticity models. In the new finite element, plastic hinges can appear at any position of the beam, theoretically in a priori not-established number. Multiple slope discontinuities are included in the analysis through a non uniform bending stiffness of the beam, making use of the Dirac-delta function. Fictitious springs, with a stiffness variable according to the level of plasticity in the section, transfer the correct bending moment in correspondence of plastic hinges.The nonlinear behavior of the hinge is defined in the framework of a thermo-dynamically consistent elastoplastic theory. Associated flow rules are derived in the classical manner adopting a convex activation domain known in literature and experimentally calibrated for reinforced concrete sections. The activation domain is similar to the one suggested by the Italian seismic code. It is given in a My-Mz bending moment reference system for a fixed axial force. An elastoplastic behavior is assumed for section curvatures, while deformations in the axial and shear directions are assumed elastic. The elastoplastic frame element is introduced in a finite element analysis program to run nonlinear simulations on 2D and 3D framed structures. To this end, state equations and flow rules are rewritten in a discrete manner to solve the single iteration of the Newton-Raphson procedure. A classic elastic predictor phase is followed by a plastic corrector phase in the case of activation of the inelastic phenomena. The corrector phase is based on the evaluation of return bending moments by employing the closest point projection method, in order to satisfy the loading-unloading conditions (Kuhn-Tucker relations). The formation of one or more hinges inside a finite element modifies the distribution of internal forces and its stiffness matrix. As a consequence, the global stiffness matrix is continuously modified at each plastic load step until it becomes singular. Numerical examples are furnished as validation tests of the program. The efficiency of the proposed model is demonstrated comparing the results with those available in literature

Investigation of stress-strain behaviour in concrete materials through the aid of 3D advanced measurement techniques

This work deals with the investigation of the mechanical behaviour of cementitious materials, following a mesoscopic approach where aggregates, grains and cement paste are explicitly represented, and the strict comparison between the numerical results and the experimental results from uniaxial tests is carried out. For this purpose, solid models are created with the support of advanced techniques of measurement and detection, such as laser scanners or computer tomography (CT). The 3D laser- scanning technique in fact allows to acquire the exact shape of the grains added to the concrete mix design while, through the adoption of an ad-hoc random distribution algorithm, a realistic disposition of the inclusions is guaranteed. The industrial CT instead, is able to reproduce exactly the tested specimens; the geometry of the inclusions and their placement. Once reconstructed realistic geometries for the models, the mechanical behaviour of concrete under uniaxial compression tests is numerically studied. A specific constitutive behaviour is assigned to each component; an elasto-plastic law with damage is assumed for the cement matrix while the aggregates are conceived to behave elastically. The implemented damage-plasticity model consists in the combination of the non-associated plasticity model by Men\ue9trey-Willam, where the yield surface is described in function of the second and the third invariant of the deviatoric stress tensor and the scalar isotropic damage model by Mazars. Comparisons between numerical and experimental results fairly prove the correctness of the suggested approach

Numerical modelling of ellipsoidal inclusions

Within the framework of numerical algorithms for the threedimensional random packing of granular materials this work presents an innovative formulation for polydispersed ellipsoidal particles, including an overlapping detection algorithm for an optimized simulation of the mesostructure of geomaterials, particularly concrete. Granular composite cement-based materials can be so reconstructed with adequate precision in terms of grain size distribution. Specifically, the algorithm performance towards the assumed inclusion shape (ellipsoidal or spheric) and degree of regularity (round or irregular) is here discussed. Examples on real grading curves prove that this approach is effective. The advantages of the proposed method for computational mechanics purposes are also disclosed when properly interfaced with visualization CAD (Computer Aided Design) tools