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International audience; We extend previous results on the exponential off-diagonal decay of the entries of analytic functions of banded and sparse matrices to the case where the matrix entries are elements of a C⁎-algebra.

Material behaviour description frequently used in commercial codes may not be adequate to simulate real forming processes. One of the reasons is the fact that they rarely include the modeling of internal damage of material. This is a decisive feature in order to be able to predict defective parts in processes like forging or to describe processes in which fracture is a part of the process itself as in sheet blanking or metal cutting. In large deformation of metals, when plastic deformation reaches a threshold level, which may depend on the loading, the fatigue limit and the ultimate stress, a ductile damage process may occur concomitantly with the plastic deformation due to the nucleation, growth and coalescence of micro-voids. Although damage and plastic deformation are two distinct dissipative processes, they influence each other. In this paper a numerical benchmark of the uniaxial tensile tests, for aluminium alloy, has been performed using Ls-Dyna and Deform 2D without damage. Then, a numerical uniaxial tensile tests has been studied using a coupled model of elasto-plasticity and ductile damage implemented in LS-DYNA. Experimental material property present in literature has been used.

The evaluation of safety parameters for binary and ternary mixtures of hydrogen and light hydrocarbons is essential for the definition of the combustion characteristics of bio-derived fuel-gas mixtures. Furthermore, with specific reference to laminar burning velocity, there is a strong need to define simple correlations, which would allow a fast prediction of global burning velocity of the mixtures starting from molar compositions and laminar burning velocity of the pure components, in analogy with Le Chatelier's rule for flammability limits. In this paper, a preliminary experimental and numerical study is performed for the assessment of safety parameters for mixtures of methane, propane and hydrogen with air at initial ambient pressure. Explosion tests have been conducted in a reinforced 5 liters steel vessel. The PREMIX module of the CHEMKIN package, coupled to the Marinov detailed reaction scheme, has been used to compute the un-stretched laminar burning velocity. For model validation, results have been compared to experimental data. Copyright © 2012, AIDIC Servizi S.r.l.

Purpose – The purpose of this paper is to present the use of the compensation theorem (CT), well known in the analysis of linear electric networks, to compute sensitivity of the performance functions used in the robust design or tolerance analysis of electromagnetic devices. Design/methodology/approach – The CT is first illustrated in the case of a simple field analysis problem. Then, using numerical simulations, the effectiveness of compensation approach for assessing impact of the small modification of material properties is shown. The numerical simulations are performed with a finite elements code based on an integral formulation. Findings – The complexity of additional computations to assess the effect of small variations involved in sensitivity analysis can be reduced. Research limitations/implications – The method can be applied only to linear systems; in addition, although compensation applies to any variations, the reduction of computational complexity is achieved only for small variations, giving localized effects. Practical implications – The method proposed in the paper can speed up the computations of sensitivity arrays in the robust design and tolerance analysis of electromagnetic device, when numerical methods are applied. Originality/value – The use of CT in field computations is not new, but its adoption in the sensitivity computation is new to the best knowledge of authors.

The aim of this work is the evaluation of the radiation contribution to the steady-state heat transfer in metallic foams by means of the radiative conductivity model. Because of the complexity of the structure, reference is made to a simplified physical radiative model, where the elementary cell of the foams is treated as a cubic cell. The contribution of the radiation heat transfer is investigated on a local basis. The local radiative conductivity has been used to evaluate the influence of radiative heat transfer in a two dimensional conductive-convective-radiative problem involving a forced fluid flow within a heated channel filled with a metallic foam. The effect of the solid emissivity and the foam porosity is pointed out for different foams.

The evaluation of the heat loss from finite arrays of horizontal buried cylinders is very interesting for many practical applications. A considerable effort has been done in the field of the electrical engineering to develop methods for calculating the thermal flux from the cables system to the ground surface through the soil. Nevertheless, the modeling hypothesis currently assumed for the case of arrays of a finite number of pipes-cables introduces approximations that can involve inaccuracies in calculation. In this paper the extent of such inaccuracies is investigated by numerical techniques. Results show that the thermal resistance value of the worst refrigerated cylinder, obtained from numerical simulation, can result even 60% higher than the value calculated with standard IEC–IEEE method, while the thermal resistance of the whole array does not differ from the value obtained with the standard IEC–IEEE calculation method. Some correlating equations to obtain more accurate results in the thermal resistance calculation for the worst refrigerated cylinder are proposed.

We review how transport properties for chaotic dynamical systems may be studied through cycle expansions, and show how anomalies can be quantitatively described by hierarchical sequences of periodic orbits. © 2003 Elsevier B.V. All rights reserved.

We consider the parallel computation of the stationary probability distribution vector of ergodic Markov chains with large state spaces by preconditioned Krylov subspace methods. The parallel preconditioner is obtained as an explicit approximation, in factorized form, of a particular generalized inverse of the generator matrix of the Markov process. Graph partitioning is used to parallelize the whole algorithm, resulting in a two-level method. Conditions that guarantee the existence of the preconditioner are given, and the results of a parallel implementation are presented. Our results indicate that this method is well suited for problems in which the generator matrix can be explicitly formed and stored. © 2001 IMACS. Published by Elsevier Science B.V. All rights reserved.

A mixed method of approximation is discussed starting from a suitably modified expression of the Hu-Washizu variational principle in which the independent fields are displacements, stresses and strain gaps defined as the difference between compatible strains and strain fields. The well-posedness of the discrete problem is discussed and necessary and sufficient conditions are provided. The analysis of the mixed method reveals that the discrete problem can be split into a reduced problem and in a stress recovery. Accordingly, the discrete stress solution is univocally determined once an interpolating stress subspace is chosen. The enhanced assumed strain method by Simo and Rifai is based on an orthogonality condition between stresses and enhanced strains and coincides with the reduced problem. It is shown that the mixed method is stable and converges. Computational issues in the context of the finite element method are discussed in detail and numerical performances and comparisons are carried out. Copyright © 2001 John Wiley & Sons, Ltd.

This paper presents results related to the shuttle imaging radar C and X-band synthetic aperture radar (SIR-C/X-SAR) Italian experiments carried out at the calibration backup supersite CB1 (Matera, in southern Italy). C-, L- and X-band active radar calibrations (ARC) were deployed for radiometric analysis of the microwave instrument on board the NASA space shuttle. The main objectives of this investigation—namely, ground instrumentation validation, image quality assessment, and radiometric calibration—are accomplished by making measurements from the signatures of the ARCs, whose radar cross section (RCS) was known from laboratory measurements. The expected RCS of each deployed target, as seen by the sensor, is reconstructed on the radiometrically calibrated images, taking into account the uncertainties in the measurements made on the impulse response function and the accuracy of the laboratory tests. Numerical results derived from the standard single-look complex (SLC) products provided by the Jet Propulsion Laboratory and by the German and Italian processing and archiving facilities show good performance of the ARCs and of the SAR processors, also indicating acceptable stability of the calibration parameters of SIR-C and X-SAR. A simple self-organizing clustering algorithm is applied to the areas centered on the ARCs to obtain histograms of scattering properties of bare and ploughed soil. The comparison with backscattering statistics databases gives good agreement with the backscatter data derived from the calibrated SAR imagery.

At the interface between two fluids of different density and in the presence of gravity, there are well known periodic surface waves which can propagate for long distances with little attenuation, as it is for instance the case at the surface of the sea. If wind is present, these waves progressively accumulate energy as they propagate and grow to large sizes—this is the Kelvin–Helmholtz instability. On the other hand, we show in this paper that for a given wind strength, there is potential for the growth of a localized nonlinear wave. This wave can reach a size such that the hydrostatic pressure drop from top to bottom equals the stagnation pressure of the wind. This process for the disruption of the flat interface is localized and nonlinear. We study the properties of this wave using numerical simulations of the Navier–Stokes equations.

1.SNTRODUCTSON Composite materials are used in many fields of aerospace engineering and the investigation of their thermal performances is required during both their manufacturing and their employment [1]. In aerospace field composite materials are used to furnish a better protection from high temperatures in the critical zones of engines than the traditional materials. In fact, the high temperatures could cause irreversible damages. Therefore the thermal analysis of composite materials, employed to realise any part of engine, is very challenging. In this case, the anisotropic behavior of the thermal conductivity should be considered to optimize the use of composite materials and a great deal of studies are focused on thermophysica l measurements [2-6]. These kinds of investigation s are very difficult for both the geometry and the complexity of the equations which describe the phenomenon. The thermal distribution can be determined by means of the numerical methods [7-10]. For this reason the thermal designer develops home-made procedure to solve the specific problem. On the other hand it is possible to use commercial software. It is important to observe that, even if a home-made procedure is used, it is useful to have a reference standard given by commercial software to validate the implemented numerical code.

The hazard function is a key component in the inferential process in survival analysis and relevant for describing the pattern of failures. However, it is rarely shown in research papers due to the difficulties in nonparametric estimation. We developed the bshazard package to facilitate the computation of a nonparametric estimate of the hazard function, with data-driven smoothing. The method accounts for left truncation, right censoring and possible covariates. B-splines are used to estimate the shape of the hazard within the generalized linear mixed models framework. Smoothness is controlled by imposing an autoregressive structure on the baseline hazard coefficients. This perspective allows an ‘automatic’ smoothing by avoiding the need to choose the smoothing parameter, which is estimated from the data as a dispersion parameter. A simulation study demonstrates the capability of our software and an application to estimate the hazard of Non-Hodgkin’s lymphoma in Swedish population data shows its potential.

In this paper we study numerically the motion of the follower near a characteristic point of a cam. An analytical formulation of the cam profile has been proposed, in terms of a function depending on a given angular parameter. Therefore we investigate the smoothness of the relative trajectory by applying the wavelet analysis. Our proposed procedure proves that the wavelet analysis can be utilized for studying the dynamic response of a mechanical system, which depends on the regularity of the profile of the cam.

Bounds for entries of matrix functions based on Gauss-type quadrature rules are applied to adjacency matrices associated with graphs. This technique allows to develop inexpensive and accurate upper and lower bounds for certain quantities (Estrada index, subgraph centrality, communicability) that describe properties of networks. © 2010 Elsevier Inc. All rights reserved.

Small autonomous embedded systems powered by means of energy harvesting techniques, have gained momentum in industry and research. This paper presents a simple, yet effective and complete energy harvesting solution which permits the exploitation of an arbitrary number of ambient energy sources. The proposed modular architecture collects energy from each of the connected harvesting subsystems in a concurrent and independent way. The possibility of connecting a lithium-ion or nickel-metal hydride rechargeable battery protects the system against long periods of ambient energy shortage and improves its overall dependability. The simple, fully analogue design of the power management and battery monitoring circuits minimizes the component count and the parasitic consumption of the harvester. The numerical simulation of the system behavior allows an in-depth analysis of its operation under different environmental conditions and validates the effectiveness of the design.