203 research outputs found
Discrete Abelian Gauge Theories for Quantum Simulations of QED
We study a lattice gauge theory in Wilson's Hamiltonian formalism. In view of
the realization of a quantum simulator for QED in one dimension, we introduce
an Abelian model with a discrete gauge symmetry , approximating
the theory for large . We analyze the role of the finiteness of the
gauge fields and the properties of physical states, that satisfy a generalized
Gauss's law. We finally discuss a possible implementation strategy, that
involves an effective dynamics in physical space.Comment: 13 pages, 3 figure
A Computational Strategy for Eurocode 8-Compliant Analyses of Reinforced Concrete Structures by Seismic Envelopes
A procedure is presented for performing Eurocode 8-compliant spectral analyses of reinforced concrete structures by means of seismic response envelopes. To account for global torsion effects in the computation of the supreme envelope an algorithmic rotational response spectrum is defined. The presented strategy turns out to be particularly appropriate for finite element models including accidental eccentricity due to mass shifting since seismic envelopes can be computed by making reference to a single structural model rather than to separate models characterized by different signs of the accidental eccentricity. The proposed procedure is theoretically formulated and numerically tested by analyzing a rotationally stiff and a rotationally flexible building as well as two irregular structures. Moreover, it is compared with an alternative formulation derived from a recently proposed strategy concerning accidental torsion. The results show that the proposed procedure is coherent with the analysis procedures provided by standard codes and computationally more efficient
An Accurate and Computationally Efficient Uniaxial Phenomenological Model for Steel and Fiber Reinforced Elastomeric Bearings
We present a uniaxial phenomenological model to accurately predict the complex hysteretic behavior of bolted steel reinforced
elastomeric bearings and unbonded fiber reinforced elastomeric bearings. The proposed model is based on a set of only five
parameters, directly associated with the graphical properties of the hysteresis loop, leads to the solution of an algebraic equation
for the evaluation of the isolator restoring force, requires only one history variable, and can be easily implemented in a computer
program. The proposed model is validated by means of experimental tests and numerical simulations. In particular, the results
predicted analytically are compared with some experimental results selected from the literature. Furthermore, numerical accuracy
and computational efficiency of the model are assessed by performing nonlinear time history analyses on a single degree of freedom
mechanical system and comparing the results with those associated with a modified version of the celebrated Bouc-Wen model
A class of uniaxial phenomenological models for simulating hysteretic phenomena in rate-independent mechanical systems and materials
We present a general formulation of a class of uniaxial phenomenological models, able to accurately simulate hysteretic phenomena in rate-independent mechanical systems and materials, which requires only one history variable and leads to the solution of a scalar equation for the evaluation of the generalized force. Two specific instances of the class, denominated Bilinear and Exponential Models, are developed as an example to illustrate the peculiar features of the formulation. The Bilinear Model, that is one of the simplest hysteretic models which can be emanated from the proposed class, is first described to clarify the physical meaning of the quantities adopted in the formulation. Specifically, the potentiality of the proposed class is witnessed by the Exponential Model, able to simulate more complex hysteretic behaviors of rate-independent mechanical systems and materials exhibiting either kinematic hardening or softening. The accuracy and the computational efficiency of this last model are assessed by carrying out nonlinear time history analyses, for a single degree of freedom mechanical system having a rate-independent kinematic hardening behavior, subjected either to a harmonic or to a random force. The relevant results are compared with those obtained by exploiting the widely used Bouc–Wen Model
Nonlinear Dynamic Analysis of Seismically Base-Isolated Structures by a Novel OpenSees Hysteretic Material Model
The complex response characterizing elastomeric isolation bearings is reproduced by employing a novel uniaxial hysteretic model that has been recently formulated and successfully implemented in OpenSees. Such a novel OpenSees material model offers several advantages with respect to differential models typically available in commercial software products for structural analysis, such as 3D-BASIS and CSi programs. Firstly, it is based on a set of only five model parameters that have a clear mechanical significance; such a property not only allows one to drastically simplify the parameters identification process, but it also allows the model to be used in practice. In addition, the model does not require numerical methods for the evaluation of the restoring force since the latter is computed by solving an algebraic equation. To encourage researchers and designers to adopt the proposed model for research and practical purposes, we demonstrate its accuracy by performing some numerical tests in OpenSees. In particular, we first employ the recently implemented model to compute the nonlinear dynamic response of a seismically base-isolated structure with elastomeric bearings and, subsequently, we compare the results with those obtained by modeling the seismic isolators with the OpenSees BoucWen uniaxial material model, that is one of the most popular and accurate hysteretic models currently available in OpenSees
Strength hierarchy provisions for transverse confinement systems of shell structural elements
Through-the-thickness (TT) confinement of masonry and concrete panels by composite
or steel reinforcements, aiming at seismic retrofit of existing structures, has recently
growth in popularity. However, structural design of transversal reinforcements, modeled
as an homogeneized material, is often performed by neglecting the cyclic nature
of seismic actions and by using static approaches. For this reason, a proper strength
hierarchy between the confined core material and the confining devices should be accounted
for in order to ensure that the retrofit system remains effective until the crisis
of the core material is attained. This research introduces strength hierarchy conditions
for TT-confinement systems, made of materials exhibiting a nonlinear behavior, aiming
at determining the minimum strength required for uniaxial confining devices. The
relevant relationships, theoretically derived by assuming a Drucker Prager constitutive
model for the confined material and by enforcing equilibrium and compatibility
conditions between the core and the confining devices, are characterized by simple
mechanical parameters, usually available in common practice applications, familiar to
most of the designers. Numerical examples confirm the effectiveness of the proposed
provisions
Endoscopic Submucosal Dissection of Gastric Neoplastic Lesions. An Italian, Multicenter Study
Endoscopic submucosal dissection (ESD) allows removing neoplastic lesions on gastric
mucosa, including early gastric cancer (EGC) and dysplasia. Data on ESD from Western countries
are still scanty. We report results of ESD procedures performed in Italy. Data of consecutive patients
who underwent ESD for gastric neoplastic removal were analyzed. The en bloc resection rate and
the R0 resection rates for all neoplastic lesions were calculated, as well as the curative rate (i.e., no
need for surgical treatment) for EGC. The incidence of complications, the one‐month mortality, and
the recurrence rate at one‐year follow‐up were computed. A total of 296 patients with 299 gastric
lesions (80 EGC) were treated. The en bloc resection was successful for 292 (97.6%) and the R0 was
achieved in 266 (89%) out of all lesions. In the EGC group, the ESD was eventually curative in 72.5%
(58/80) following procedure. A complication occurred in 30 (10.1%) patients. Endoscopic treatment
was successful in all 3 perforations, whereas it failed in 2 out of 27 bleeding patients who were
treated with radiological embolization (1 case) or surgery (1 case). No procedure‐related deaths at
one‐month follow‐up were observed. Lesion recurrence occurred in 16 (6.2%) patients (6 EGC and
10 dysplasia). In conclusion, the rate of both en bloc and R0 gastric lesions removal was very high in
Italy. However, the curative rate for EGC needs to be improved. Complications were acceptably low
and amenable at endoscopy
Analytical solution of elastic fields induced by a 2D inclusion of arbitrary polygonal shape
Abstract We generalize a recent application of the equivalent inclusion method, Jin et al. (2011), to derive the elastic field induced by a constant eigenstrain applied to an elliptic inclusion whose boundary is approximated by a polygon, the number of sides being assigned so as to recover the analytical values of the entries of the Eshelby tensor. The generalization consists in the fact that displacements, strains, stresses and the Eshelby tensor can be given a unique expression, holding inside and outside the inclusion, thus avoiding the recourse to the derivation of distinct expressions, based upon different approaches, for the elastic fields. The proposed approach has been successfully applied to evaluate the elastic fields induced by an elliptical cavity in a linear isotropic infinite plate subjected to a remote loading by recovering the classical solutions by Inglis (1913) and Maugis (1992). Furthermore it can easily be applied to elliptical holes arbitrarily oriented with respect to the loading direction
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