Age replacement policy in a random environment using systemability

Preventive maintenance is a group of maintenance policies based on preventive actions in order to predate the failure of a component or a system. Usually, these policies are designed using a series of data related to the studied units. All policies do not consider the effect of the environment where the components or systems operate. In this article, one of the most used policies, the age replacement policy, is also discussed taking into consideration the environmental effects using an innovative concept, introduced by Pham, called systemability. Several numerical examples are carried out in order to illustrate the aim of this work. The importance of environmental factors is also demonstrated thanks to the application to a real case.     

Beam tests of composite steel-concrete members: A three-dimensional finite element model

Modern construction makes frequent use of composite steel-concrete beams for bridge and building applications. This paper describes a three-dimensional finite element model in which all components forming the composite member are modelled by means of solid elements. The proposed approach is developed using the commercial software Abaqus and is able to model the composite response without requiring information from push-out tests commonly performed to define the constitutive relationship for the shear connectors. All materials are assumed to behave in a nonlinear fashion. Contact between the elements is simulated using surface-to-surface and embedment techniques. The adequacy and accuracy of the proposed modelling approach are validated against experimental results available in the literature on simply-supported and continuous beam tests with both solid and composite slabs.     

An LMI approach for H ∞ analysis and control of discrete-time piecewise affine systems

In this paper we investigate some analysis and control problems for discrete-time hybrid systems in the piece-wise affine form. By using arguments from the dissipativity theory for non-linear systems, we show that H X analysis and synthesis problems can be formulated and solved via linear matrix inequalities by taking into account the switching structure of the considered system. In this paper we address the generalized problem of controlling hybrid systems whose switching structure does not depend only on the state but also on the control input.     

Effect of sugar, citric acid and egg white type on the microstructural and mechanical properties of meringues

Meringues are characterized by a predominant air phase and their overall quality is intimately related with microstructure. The formation of meringues microstructure relies on the capacity of egg white (EW) proteins to form voluminous and stable foams and it is ultimately related with the chemical properties of proteins and with the addition of ingredients such as sugars, salts, acids and surfactants.The study aimed at assessing the influence of sugar/EW ratio, citric acid and EW type on the microstructural and mechanical properties of meringues. Meringues prepared with different sugar/EW, citric acid level and different EW type were subjected to microstructural analysis by X-ray microtomography and to mechanical assessment by compression tests.Results demonstrate the ability of X-ray microtomography to reconstruct the 3D microstructure of meringues allowing the measurement of porosity, size, shape and distribution of pores. Citric acid, sugar concentration and EW type play a fundamental role on meringues microstructural parameters and mechanical properties. Low sugar/EW ratios as well as increasing citric acid levels increase the air phase and result in a softer texture of meringues. Moreover, low sugar/EW ratios and increasing citric acid in the meringue result in a reduction of pore size and also influence the shape of pores. Meringues microstructural and mechanical properties are affected by the EW quality: fresh and pasteurized EWs and EWs stored at refrigerated temperatures scored the highest structural and mechanical performances, while powdered and frozen EWs and albumens from old eggs showed the worst results. Not only the balance among ingredients but also the choice of raw materials can strongly affect the final quality of meringues.     

Shelf life of ready‐to‐cook cauliflower mixtures as affected by packaging film mass transport properties

In this work, the influence of packaging mass transport properties on quality loss of fresh‐cut cauliflower mixtures was addressed. The study was organised in two subsequent experimental steps; first, the selection of micro‐perforated packaging films was carried out by monitoring the package headspace gas concentrations of fresh‐cut white, green cauliflower and roman cabbage. Then, the effects of the barrier properties of the selected micro‐perforated film on shelf life of two different fresh‐cut cauliflower mixtures, stored at 4 ± 1 °C, were addressed. Results suggested that, among the investigated films, the micro‐perforated polymeric matrix with the lowest oxygen transmission rate value showed the best performance as it created the optimum headspace gas composition for each cauliflower variety, as well as, for the product mixtures. The appearance of visible moulds was the factor limiting product shelf life that accounted for about 18 days for both the investigated cauliflower mixtures.     

Process and terminations variations aware stability criteria for microwave amplifiers

Two novel process variations aware, necessary and sufficient conditions suitable for implementation in CAD optimizers are proposed to check amplifiers stability. Case studies are presented, showing that the new criteria allow robust amplifier design, under variation of active device immittance parameters in pre‐specified rectangular regions, due to manufacturing tolerances. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 23: 619–626, 2013.     

Contribution of the fill to the static behaviour of arched masonry structures: theoretical formulation

In the paper, one presents the theoretical set-up of an original formulation aimed at accounting for the contribution of the fill to the structural strength of masonry vaults and arches and at providing an evaluation about its skill of cooperating to stress absorption with the main vaulted resisting structure. Usually the action of components ordinarily regarded as non-structural members is often neglected in static analyses. Actually, it is a common practice to assume a number of elements of vaulted or arched constructions, such as the fill and the buttress, as completely unable to exert any structural action, rather than trying to evaluate their contribution; therefore, those are usually assumed to be a dead weight, unable to contribute to the bearing capacity of the vault. Starting from the consideration that the fill is somehow subject to some pre-compression because of the permanent load, an approach is proposed where the fill is considered to be able to provide a partial absorption of the variable loads with a reduced load transmission onto the main structural members. The procedure leads to more realistic evaluations about the safety assessment of vaulted structures, which are in major agreement with their real behaviour.     

A variational integrators approach to second order modeling and identification of linear mechanical systems

The theory of variational integration provides a systematic procedure to discretize the equations of motion of a mechanical system, preserving key properties of the continuous time flow. The discrete-time model obtained by variational integration theory inherits structural conditions which in general are not guaranteed under general discretization procedures. We discuss a simple class of variational integrators for linear second order mechanical systems and propose a constrained identification technique which employs simple linear transformation formulas to recover the continuous time parameters of the system from the discrete-time identified model. We test this approach on a simulated eight degrees of freedom system and show that the new procedure leads to an accurate identification of the continuous-time parameters of second-order mechanical systems starting from discrete measured data.     

Characterization of laser energy consumption in sintering of polymer based powders

This paper presents an analysis of Laser Sintering (LS) process from an energy standpoint. LS has a potential as an environmental benign alternative to traditional processes but only few authors deal with the process optimization including the energy aspects. This work evaluates the effect of the energy density in processing of two polymeric materials: polyamide powder and a phenolic resin coated sand. The different behaviour of the two materials is studied by analysing the geometrical features (depth and width) of linear sintered structures. In particular the volumetric productivity and the energy intensity of the process are calculated to characterize the sintering process.It is shown how an upper limit to the energy consumption can be remarked. Measurements reveal that within the energy density range of 0.02-0.1 J/mm² the whole energy input is useful for the agglomeration process. The use of higher energy density produces different results for both the cases analysed. A proper selection of energy density maintains the energy requirement below the level of 10⁶ J/kg which is considered a lower limit for manufacturing process.