1,606 research outputs found
Beta decays with momentum space Majorana spinors
We construct and apply to beta decays a truly neutral local quantum field
that is entirely based upon momentum space Majorana spinors. We make the
observation that theory with momentum space Majorana spinors of real C parities
is equivalent to Dirac's theory. For imaginary C parities, the neutrino mass
can drop from the single beta decay trace and reappear in 0\nu \beta \beta, a
curious and in principle experimentally testable signature for a non-trivial
impact of Majorana framework in experiments with polarized sources.Comment: 7 pages, 1 figure; needs svjour.cls, svepj.cl
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
Finite strains fully coupled analysis of a horizontal wellbore drilled through a porous rock formation
Wellbore instability, in particular in deep perforations, continues to be one of the major problem in the oil and gas industry, that can dramatically increase production costs. Eventual instabilities may be prevented supporting temporarily the wellbore with mud circulation. If instability may occur, the value of the mud pressure needs to be sufficiently high to prevent compressional failure, but it should also be lower than a critical value that would cause tensile failure and unintentional hydraulic fracturing. Predicting faithfully the stress distribution around a borehole, and moreover the yielding and failure zones, is a challenging but fundamental task, essential to estimate the correct mud pressure and hence to prevent instabilities and sand production. This study focuses on quantifying the pressure distribution, stress field and plastic zones around a horizontal borehole drilled at great depth through a highly porous rock formation. The perforation of a wellbore in a saturated porous material is a coupled problem, which involves deformations of the solid phase and simultaneous diffusion of the fluid phase. A fully coupled finite element method is adopted, considering both material non linearity (elastoplasticity) and geometric nonlinearity (finite deformations) in the solid matrix, resulting in a so called u−p formulation. The variation of porosity and permeability, as consequence of the finite deformations of the solid matrix, is taken into account. The model adopts an elastoplastic constitutive law characterized by two yield surfaces, that is able to capture the dilatant and compactant plastic mechanism. The simulations investigate the quasi-static transient phenomenon associated with the perforation, until the steady state condition is reached. The model describes the evolution of the stress and pressure distribution, and moreover the propagation of the plastic zones around the borehole. The work demonstrates the capability of the finite deformations coupled approach to simulate the whole process, giving an instrument to determine the stability and sand production of the wellbore
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
Nonadiabatic effects in the dynamics of atoms confined in a cylindric time-orbiting-potential magnetic trap
In a time-orbiting-potential magnetic trap the neutral atoms are confined by
means of an inhomogeneous magnetic field superimposed to an uniform rotating
one. We perform an analytic study of the atomic motion by taking into account
the nonadiabatic effects arising from the spin dynamics about the local
magnetic field. Geometric-like magnetic-fields determined by the Berry's phase
appear within the quantum description. The application of a variational
procedure on the original quantum equation leads to a set of dynamical
evolution equations for the quantum average value of the position operator and
of the spin variables. Within this approximation we derive the
quantum-mechanical ground state configuration matching the classical adiabatic
solution and perform some numerical simulations.Comment: 12 pages, 4 figure
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
Landau-Zener problem in a three-level neutrino system with non-linear time dependence
We consider the level-crossing problem in a three-level system with
non-linearly time-varying Hamiltonian (time-dependence ). We study the
validity of the so-called independent crossing approximation in the
Landau-Zener model by making comparison with results obtained numerically in
density matrix approach. We also demonstrate the failure of the so-called
"nearest zero" approximation of the Landau-Zener level-crossing probability
integral.Comment: 11 pages, 3 figures. To be published in Physical Review
On the hyperbolicity and causality of the relativistic Euler system under the kinetic equation of state
We show that a pair of conjectures raised in [11] concerning the construction
of normal solutions to the relativistic Boltzmann equation are valid. This
ensures that the results in [11] hold for any range of positive temperatures
and that the relativistic Euler system under the kinetic equation of state is
hyperbolic and the speed of sound cannot overcome .Comment: 6 pages. Abridged version; full version to appear in Commun. Pure
Appl. Ana
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
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