Results 1 - 10 of 16
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[en] A general theory of thermo field dynamics in the renormalized interaction representation is presented in such a manner that the theory includes both the equilibrium and non-equilibrium situations. The significant proposal made in this paper is the concept of the spontaneous creation of dissipation. The theory is based on 1. the tilde conjugation rule, 2. the Hamiltonian and 3. the thermal state conditions. It is shown that, in terminology of the theory of the interaction representation, different thermal situations correspond to different choices of the renormalized Hamiltonian Ht in the interaction representation (and therefore, to different choices of the interaction representation) associated with the basic Hamiltonian H - H of thermo field dynamics. Any thermal situation (both in equilibrium and in non-equilibrium states) is controlled by the thermal state condition which may depend on time. The renormalized Hamiltonian Ht, contains several c-number quantities, which are to be determined by the self-consistent renormalization equations and which may depend on time. This time-dependent renormalization is a new situation which was not formulated in the Schwinger-Keldysh path-ordering formalism. The perturbative renormalization method in thermo field dynamics is reformulated from the most general viewpoint. (orig.)
[en] A new aspect of the Feynman path-integral method for nonequilibrium quantum field theory is discussed. It concerns the inclusion of the initial state conditions in the formulation of the Lagrangian formalism. It is demonstrated that, in certain cases, inhomogeneous thermal distribution is interpreted as a geometrical metric. (author). 13 refs
[en] The research paper is addressed to develop and validate an aircraft seat cushion to be used for the passenger seat directly integrated in the fuselage. For very light aircraft, these systems result to be a good choice in terms of weight reduction and space optimization, but can represent a challenging problem for crashworthiness design and a key energy-absorbing function for human protection from injuries so to improve the level of the safety. The first issue was dedicated to investigate the mechanical properties of four commercial foams, diffused in different industrial applications, which present nonlinear and time-dependent viscoelastic behavior, and finally to determine whether typical seat cushion materials are rate sensitive or not. Then, numerical simulations were validated with measurements to simulate the mechanical properties of foams and to evaluate the contact pressures, stress distribution, and the dependence of stress on the strain rate in order to provide adequate levels of both comfort and energy absorption.
[en] This paper proposes the family of non-stationary inverse Gamma processes for modeling state-dependent deterioration processes with nonlinear trend. The proposed family of processes, which is based on the assumption that the “inverse” time process is Gamma, is mathematically more tractable than previously proposed state-dependent processes, because, unlike the previous models, the inverse Gamma process is a time-continuous and state-continuous model and does not require discretization of time and state. The conditional distribution of the deterioration growth over a generic time interval, the conditional distribution of the residual life and the residual reliability of the unit, given the current state, are provided. Point and interval estimation of the parameters which index the proposed process, as well as of several quantities of interest, are also discussed. Finally, the proposed model is applied to the wear process of the liners of some Diesel engines which was previously analyzed and proved to be a purely state-dependent process. The comparison of the inferential results obtained under the competitor models shows the ability of the Inverse Gamma process to adequately model the observed state-dependent wear process
[en] In this paper, a competing risk model is proposed to describe the reliability of the cylinder liners of a marine Diesel engine. Cylinder liners presents two dominant failure modes: wear degradation and thermal cracking. The wear process is described through a stochastic process, whereas the failure time due to the thermal cracking is described by the Weibull distribution. The use of the proposed model allows performing goodness-of-fit test and parameters estimation on the basis of both wear and failure data. Moreover, it enables reliability estimates of the state of the liners to be obtained and the hierarchy of the failure mechanisms to be determined for any given age and wear level of the liner. The model has been applied to a real data set: 33 cylinder liners of Sulzer RTA 58 engines, which equip twin ships of the Grimaldi Group. Estimates of the liner reliability and of other quantities of interest under the competing risk model are obtained, as well as the conditional failure probability and mean residual lifetime, given the survival age and the accumulated wear. Furthermore, the model has been used to estimate the probability that a liner fails due to one of the failure modes when both of these modes act.
[en] The non-stationary Gamma process is a widely used mathematical model to describe degradation phenomena whose growth rate at time t depends only on the current age of the item and not on the accumulated damage up to t. Nevertheless, the Gamma process is not a proper choice when there is empirical evidence that the variance-to-mean ratio of the process varies with time, because the Gamma process implies a constant variance-to-mean ratio. This paper proposes a generalization of the non-stationary Gamma process, which can be viewed as a time discretization of the extended Gamma process and allows one to describe time-dependent degradation phenomena whose variance varies with time t, not necessarily in proportion to the mean. A way to approximate the exact distribution of the degradation growth over a given time interval is given and a test for assessing whether the assumption of the Gamma process can be rejected or not is discussed. Finally, the proposed model is applied to a real dataset consisting of the sliding wear data of four metal alloy specimens.
[en] This paper aims to model the failure pattern of repairable systems in presence of explained and unexplained heterogeneity. The failure pattern of each system is described by a Power Law Process. Part of the heterogeneity among the patterns is explained through the use of a covariate, and the residual unexplained heterogeneity (random effects) is modeled via a joint probability distribution on the PLP parameters. The proposed approach is applied to a real set of failure time data of powertrain systems mounted on 33 buses employed in urban and suburban routes. Moreover, the joint probability distribution on the PLP parameters estimated from the data is used as an informative prior to make Bayesian inference on the future failure process of a generic system belonging to the same population and employed in an urban or suburban route under randomly chosen working conditions. - Highlights: • We describe the failure process of buses powertrain system subject to heterogeneity. • Heterogeneity due to different service types is explained by a covariate. • Random effect is modeled through a joint pdf on failure process parameters. • The powertrain reliability under new future operating conditions is estimated
[en] The main purpose of the work described in this paper has been to establish the protocol for a new non-disruptive technique of intervention, based on microwave treatment, for cleaning operations on monumental historical buildings, to eliminate biodeteriogens infesting stones. Non-destructive methods in the cleaning operations, should not only preserve the physical integrity, the chemical-mineralogical and structural identity of materials, but, when the exhalation of pollutant agents (like for example Radon gas) from building materials is considered, also, make the indoor air quality (IAQ) levels healthy. Therefore, one of the main steps of the protocol proposed in this paper is concerned with the assessment of the Radon exhalation rate in order to verify that microwave treatments do not increase the Radon naturally exhalated by building materials. In this paper, the preliminary results of the Radon measurements performed on two different type of tuff samples (grey tuff and yellow tuff), typical of the Italian traditional construction heritage, with the E-PERM passive technique at the Environmental Radioactivity Laboratory (Amb.Ra.), University of Salerno, Italy, ISO 9001:2008 certified, are summarized. (paper)
[en] The selected device for the ALICE Time-of-Flight array is the Multigap Resistive Plate Chamber (MRPC). We have tested this device at the Gamma Irradiation Facility at CERN to evaluate the rate dependence. We find that the rate capability of the MRPC easily exceeds the 50 Hz/cm2 maximum expected rate at the ALICE experiment. In addition, we have measured the power dissipated for an equivalent flux of 1.6 kHz/cm2 of through-going muons to be 650 mW/m2
[en] The possibility of performing neutrino astronomy by means of a detector above the ground depends critically on the feasibility of a rejection power on the order of 1011 required to discriminate the enormous background of cosmic downward going muons form the signal of upward going muons produced by neutrinos. In order to check whether and how this rejection is obtainable, we have built in the Physics Department of the University of Bari a horizontal cosmic muon telescope (MINI) instrumented with resistive plate counters. By performing time-of-flight measurements, we have estimated the rejection power of our telescope for left and right coming cosmic muons. The rejection dependence on a few fundamental parameters like minimum number of points per track, telescope length, RPC time resolution and on trigger configuration has been investigated. (orig.)