5,635 research outputs found

    Challenges in Double Beta Decay

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    After nearly 80 years since the first guess on its existence, neutrino still escapes our insight: the mass and the true nature (Majorana or Dirac) of this particle is still unknown. In the past ten years, neutrino oscillation experiments have finally provided the incontrovertible evidence that neutrinos mix and have finite masses. These results represent the strongest demonstration that the Standard Model of electroweak interactions is incomplete and that new Physics beyond it must exist. None of these experimental efforts could however shade light on some of the basic features of neutrinos. Indeed, absolute scale and ordering of the masses of the three generations as well as charge conjugation and lepton number conservation properties are still unknown. In this scenario, a unique role is played by the Neutrinoless Double Beta Decay searches: these experiments can probe lepton number conservation, investigate the Dirac/Majorana nature of the neutrinos and their absolute mass scale (hierarchy problem) with unprecedented sensitivity. Today Neutrinoless Double Beta Decay faces a new era where large scale experiments with a sensitivity approaching the so-called degenerate-hierarchy region are nearly ready to start and where the challenge for the next future is the construction of detectors characterized by a tonne-scale size and an incredibly low background, to fully probe the inverted-hierarchy region. A number of new proposed projects took up this challenge. These are based either on large expansions of the present experiments or on new ideas to improve the technical performance and/or reduce the background contributions. n this paper, a review of the most relevant ongoing experiments is given. The most relevant parameters contributing to the experimental sensitivity are discussed and a critical comparison of the future projects is proposed.Comment: 70 pages, 16 figures, 6 tables. arXiv admin note: text overlap with arXiv:1109.5515, arXiv:hep-ex/0501010, arXiv:0910.2994 by other author

    A Lagrangian finite element method for the simulation of 3D compressible flows

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    The numerical solution of compressible fluid flows is of paramount importance in many industrial and engineering applications. Compared to the classical fluid dynamics, the introduction of the fluid compressibility changes the formulation of the problem and consequently its computational treatment. Among the possible numerical solutions of compressible flow problems, the finite element method has always been privileged. However, the standard Eulerian approaches with fixed domain are not particularly suited to represent the strong shock waves and the significant movement of the external boundaries. On the contrary, in problems characterized by evolving surfaces, Lagrangian approaches can be very effective. The governing equations of compressible flow problems are mass, momentum and energy conservation. These equations are discretized in the spirit of the Lagrangian Particle Finite Element Method (PFEM). The strong distortions of the mesh, typical of the Lagrangian approaches, are managed with a continuous remeshing of the computational domain. The nodal unknowns are velocities, density and internal energy. To fully exploit the potential of continuous remeshing, only nodal variables are stored and consequently only linear interpolation are used. In addition, an artificial viscosity has been introduced to stabilize the formation and propagation of shock waves. Finally, explicit time integration of the governing equations enables a highly efficient solution of the discretized problem. The proposed approach has been validated against typical benchmarks of gas dynamics in the presence of strong shock waves. A very good agreement has been shown in all the tests proving the excellent accuracy and versatility of the proposed method

    Green's functions for the evaluation of anchor losses in mems

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    The issue of dissipation has a peculiar importance in micro-electro-mechanical-structures (MEMS). Among the sources of damping that affect their performance, the most relevant are [1]: thermoelastic coupling, air damping, intrinsic material losses, electrical loading due to electrode routing, anchor losses. Moreover, recent experimental results indicate the presence of additional temperature dependent dissipation mechanisms which are not yet fully understood (see e.g. [2, 12]). In a resonating structure the quality factor Q is defined as: Q = 2πW/ΔW (1) where ΔW and W are the energy lost per cycle and the maximum value of energy stored in the resonator, respectively. According to eq. (1), the magnitude of Q ultimately depends on the level of energy loss (or damping) in a resonator. The focus of the present contribution is set on anchor losses and the impact they have in the presence of axial loads. Anchor losses are due to the scattering of elastic waves from the resonator into the substrate. Since the latter is typically much larger than the resonator itself, it is assumed that all the elastic energy entering the substrate through the anchors is eventually dissipated. The semi-analytical evaluation of anchor losses has been addressed in several papers with different levels of accuracy [3, 6]. These contributions consider a resonator resting on elastic half-spaces and assume a weak coupling, in the sense that the mechanical mode, as well as the mechanical actions transmitted to the substrate, are those of a rigidly clamped resonator. The displacements and rotations induced in the half-space are provided by suitable Green's functions. Photiadis, Judge et al. [7] studied analytically the case of a 3D cantilever beam attached either to a semi-infinite space or to a semi-infinite plate of finite thickness. Their results are based on the semi-exact Green's functions established in [4]. More recently Wilson-Rae et al. [9, 10] generalized all these approaches using the involved framework of radiation tunnelling in photonics. Unfortunately, these contributions provide estimates of quality factors that differ quantitatively. In this paper we revisit the procedure of [7], which rests on simple mechanical principles, but starting from the exact Green's functions for the half space studied by Pak [14]. Through a careful analysis utilizing the theory of residues and inspired by the work of Achenbach [15], we show that the results obtained coincide exactly with those of [9], but for the case of torsion

    Numerical simulation of landslide-reservoir interaction using a PFEM approach

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    A Particle Finite Element Method is here applied to the simulation of landslide-water interaction. An elastic-visco-plastic non-Newtonian, Bingham-like constitutive model has been used to describe the landslide material. Two examples are presented to show the potential of the approach

    Generation of Noise Time Series with arbitrary Power Spectrum

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    Noise simulation is a very powerful tool in signal analysis helping to foresee the system performance in real experimental situations. Time series generation is however a hard challenge when a robust model of the noise sources is missing. We present here a simple computational technique which allows the generation of noise samples of fixed length, given a desired power spectrum. A few applications of the method are also discussed.Comment: 4 pages, 7 figure

    A Lagrangian PFEM approach tothe numerical simulation of 3D large scale landslides impinging in water reservoirs

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    Landslides are exceptional natural hazards that can generate extensive damage to structures and infrastructures causing a large number of casualties. A particularly critical condition occurs when the landslide impinges in water reservoirs generating high waves. This work proposes a numerical tool to simulate the macroscopic behavior of a propagating landslide. The Particle Finite Element Method (PFEM) is here used and adapted to the specific case of landslide runout. The Lagrangian Navier-Stokes equations of incompressible fluids are used to describe the macroscopic landslide behavior. A rigid-visco-plastic law with a pressure dependent threshold, typical of a non-Newtonian, Bingham-like fluid, is used to characterize the constitutive behavior of the flowing material. Special attention is devoted to the definition of ad-hoc pressure-dependent slip boundary conditions at the interface between the flowing mass and the basal surface to better represent the real landslide-slope interaction. The proposed approach has been validated against numerical benchmarks and small scale experimental tests, showing a good agreement with the physical measurements. Real case scenarios have also been considered. 3D geometries of critical sites, where landslides have occurred, have been reconstructed allowing for the simulation of large scale real landslide runouts. Results are compared with post-event images and measurements, showing the accuracy and the capability of the method
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