A new age‐ and state‐dependent degradation process with possibly negative increments

A new age‐ and state‐dependent degradation process is proposed, which can be used in the case the degradation phenomenon under study is not necessarily monotonic increasing. In particular, the degradation increments of the proposed model are assumed to be possibly dependent on each other and negative. The model is obtained by generalizing the well‐known and largely applied Wiener process and partially preserves the mathematically tractability of the Wiener process. In the paper, the main features and properties of the proposed model are first discussed and the maximum likelihood estimators of its parameters are derived. An applicative example is finally developed, which shows the feasibility and the effectiveness of the proposed approach.     

AHP‐IFM Target: An Innovative Method to Define Reliability Target in an Aerospace Prototype Based on Analytic Hierarchy Process

Reliability target definition is a crucial aspect of any reliability analysis. In literature, there are two types of analysis. The first one, called ‘bottom‐up’, goes back to the system's target using data of units through a fault tree analysis. Reliability data of components could be only partially available, particularly in the case of innovative systems. In the second type of analysis, called ‘top‐down’, starting from similar systems, the target of each unit is defined, by applying allocation techniques. Also, in this case, reliability data of similar systems might not be available, and the choice of the most appropriate technique could be tricky. The purpose of the present research is to combine the advantages of both usual approaches. The newly developed approach is based on the integrated factors method, whose values are adjusted trough a multicriteria method, the analytic hierarchy process, depending on the importance of each factor and each unit. The innovation of the proposed model consists in its dynamism, as most of the literature methods use constant weights for the factors involved in reliability allocation. No method takes into account the assignment of a different level of significance (weight) to different units of the system, simultaneously with the considered factors. The developed approach has been applied on an aerospace prototype system. The results show the goodness of the new method and its ability to overcome the problems noted in literature. Copyright © 2017 John Wiley & Sons, Ltd.     

A multi-failure additive dependability model for transit system effectiveness analysis

Dependability has been recognized in the transportation reliability literature as an effective measure of transit system service quality. Dependability models link system dependability with reliability and maintainability characteristics of subsystems, incorporating special operating characteristics and recovery policy from failure of each particular transit system. In this paper a new transit system dependability model is proposed, which considers the possibility that a passenger may be delayed by the occurrence of more than one failure in a trip. The mathematical difficulties associated with the algebra of random variables are overcome by using the Monte Carlo method. The results of the proposed model are compared with those relative to different modelling approaches in the literature, by applying the model to a common test scenario.     

Low latency complex event processing on parallel hardware

Most complex information systems are event driven: each part of the system reacts to the events happening in the other parts, potentially generating new events. Complex event processing (CEP) engines in charge of interpreting, filtering, and combining primitive events to identify higher level composite events according to a set of rules are the new breed of message-oriented middleware, which is being proposed today to better support event-driven interactions.     

A Statistical Method for SVBRDF Approximation from Video Sequences in General Lighting Conditions

We present a statistical method for the estimation of the Spatially Varying Bidirectional Reflectance Distribution Function (SVBRDF) of an object with complex geometry, starting from video sequences acquired with fixed but general lighting conditions. The aim of this work is to define a method that simplifies the acquisition phase of the object surface appearance and allows to reconstruct an approximated SVBRDF. The final output is suitable to be used with a 3D model of the object to obtain accurate and photo‐realistic renderings. The method is composed by three steps: the approximation of the environment map of the acquisition scene, using the same object as a probe; the estimation of the diffuse color of the object; the estimation of the specular components of the main materials of the object, by using a Phong model. All the steps are based on statistical analysis of the color samples projected by the video sequences on the surface of the object. Although the method presents some limitations, the trade‐off between the easiness of acquisition and the obtained results makes it useful for practical applications.     

Chromium electrodeposition from Cr(III) aqueous solutions

The aim of this work is to study an alternative plating process to obtain chromium coatings through electrodeposition from baths containing trivalent chromium, as aqueous solutions of Cr (III) are significantly less dangerous, in terms of human health and environmental impact, as compared to the traditional Cr (VI) baths employed for this purpose. In order to overcome problems regarding the reduction of Cr (III) in aqueous solution, two approaches were followed: i) the possibility of co-depositing chromium along with a second metal, which could help the process of discharge of Cr³⁺ on the substrate; ii) the use of a specific ligand for the Cr³⁺ ion, which can generate easily reducible complexes at the metal-solution interphase. Both approaches led to interesting results: in particular, the co-deposition enabled us to obtain NiCr alloy with a high percentage of chromium, and the deposition using specific complexing agents allowed optimal bath compositions to be developed both for decorative and hard chromium plating.     

Shear tests of carbon fiber plates bonded to concrete with control of snap-back

In the present paper the problem of brittle debonding between carbon-fiber plates (FRP) and concrete was studied by means of single lap shear tests. Driving the test by controlling the displacement of the free edge of the plate made it possible to describe the pull-out curve up to complete debonding, including the snap-back branch. This permitted to observe that, in the present tests, failure mode and brittleness strongly depend upon the bond length. In particular, specimens with long bond length display a snap-back in the pull-out curve, whereas specimens with short bond length display a softening. Besides, debonding occurs with a transition from mode II to a mixed mode fracture as the bond length decreases, showing different failure mechanisms and a remarkable reduction of the dissipated fracture energy. Moreover, the measured bond-slip relationships show a reduction of the bond strength close to the free edge of the plate that is caused by peeling stresses. Finally, results of the experimental tests are compared with finite element simulations with standard bond-slip laws.     

A prototype of a fuel cell PEM emulator based on a buck converter

After a brief introduction about fuel cell systems, and their modelling, this paper proposes a possible solution to emulate a proton exchange membrane fuel cell (PEM-FC) system by using a DC–DC buck converter. The fuel cell system, including all its auxiliaries and related control systems, is emulated by a buck converter realized experimentally and controlled in the DSPACE environment. The realization of the buck converter allows the behaviour of any fuel cells to be easily emulated since only the modification of the control law of the switch is necessary. The proposed emulator can be applied easily to other fuel cell systems if the polarization curve has the same current rate and maximum power. In this way it is possible to utilize the converter and perform the necessary tests to optimize a fuel cell system by avoiding the waste of hydrogen and the purchase of cells as well as any cell damage. With regard to current other types of emulators, the one presented here has the following characteristics: (1) all the auxiliaries of the system have been considered, each including its own control system, as in a real FCS, (2) the converter is a classical buck converter with a free-wheeling diode and is designed to have a high bandwidth and to be practically always in conduction mode (discontinuous mode appears only at very low currents) (3) the voltage control is made by a space-state controller, able to fix properly the closed loop poles of the system, thus guaranteeing the desired bandwidth of the control system and (4) it can be used in laboratory as a stand-alone low-cost system for design and experimental purposes.     

Experimental investigation of the heat exchange to a compartmentalized plug flow

A two-phase (air–water), tubular counterflow heat exchanger was developed for industrial unitary process applications to realize an active heat transfer control. A controlled train of air plugs was injected in a stratified smooth water flow to yield a compartmentalized, continuous two-phase flow whose stability was carefully monitored. Related Nusselt numbers were evaluated for single- and two-phase flows, at the same flow regimes. This comparison shows how the traveling, controlled air plug “turbulators” allowed for a large heat transfer rate increase, for all observed heating rates and phase velocity ratios. The analysis includes a comparison with the available literature correlations, and the efficiency of the adopted heat transfer control is finally inferred while a range of flow regimes is identified which optimizes the heat exchange.     

Rolling-horizon and fix-and-relax heuristics for the parallel machine lot-sizing and scheduling problem with sequence-dependent set-up costs

In this paper we develop new rolling-horizon and fix-and-relax heuristics for the identical parallel machine lot-sizing and scheduling problem with sequence-dependent set-up costs. Unlike previous papers, our procedures are based on a compact formulation relying on the hypotheses of identical machines. This feature makes our approach suitable for large-scale applications (with hundreds of machines) arising in the textile and fiberglass industries. Moreover, our procedures are shown to provide a feasible solution for any feasible instance. Comparisons with lower bounds provided by a truncated branch-and-bound show that the gap between the best heuristic solution and the lower bound never exceeds 3%.