Selective maintenance optimisation for series-parallel systems alternating missions and scheduled breaks with stochastic durations

This paper deals with the selective maintenance problem for a multi-component system performing consecutive missions separated by scheduled breaks. To increase the probability of successfully completing its next mission, the system components are maintained during the break. A list of potential imperfect maintenance actions on each component, ranging from minimal repair to replacement is available. The general hybrid hazard rate approach is used to model the reliability improvement of the system components. Durations of the maintenance actions, the mission and the breaks are stochastic with known probability distributions. The resulting optimisation problem is modelled as a non-linear stochastic programme. Its objective is to determine a cost-optimal subset of maintenance actions to be performed on the components given the limited stochastic duration of the break and the minimum system reliability level required to complete the next mission. The fundamental concepts and relevant parameters of this decision-making problem are developed and discussed. Numerical experiments are provided to demonstrate the added value of solving this selective maintenance problem as a stochastic optimisation programme.     

Adaptive state observers for sensorless control of switched reluctance motors

In this paper, we address the problem of state observation for sensorless control of switched reluctance motors (SRMs), that is, the regulation of the motor measuring only the voltage and the current of the electrical supply. Instrumental for the construction of the observer is the derivation of algebraic relations, which define regression models, between the unknown rotor flux and the measured quantities. With the knowledge of the flux, it is shown that the mechanical coordinates can be estimated with suitably tailored adaptive nonlinear observers. Replacing the observed states, in a certainty equivalent manner, with a full information stabilizing law completes the sensorless controller design. In contrast with other motors, there is no universally accepted mathematical model to describe the dynamics of SRMs. To widen our target audience, we present the results for four different mathematical models reported in the literature. Simulation results with a precise (finite element) model of the SRM are used to illustrate the performance of the proposed observer and sensorless control.     

Geophysical wavelet library: Applications of the continuous wavelet transform to the polarization and dispersion analysis of signals

In the present paper, we consider and summarize applications of the continuous wavelet transform to 2C and 3C polarization analysis and filtering, modeling the dispersed and attenuated wave propagation in the time–frequency domain, and estimation of the phase and group velocity and the attenuation from a seismogram. Along with a mathematical overview of each of the presented methods, we show that all these algorithms are logically combined into one software package “Geophysical Wavelet Library” developed by the authors. The novelty of this package is that we incorporate the continuous wavelet transform into the library, where the kernel is the time–frequency polarization and dispersion analysis. This library has a wide range of potential applications in the field of signal analysis and may be particularly suitable in geophysical problems that we illustrate by analyzing synthetic, geomagnetic and real seismic data.     

Modelling the bleed port of a thermostatic expansion valve

This article presents a model to predict refrigerant flow rate through the bleed port of a thermostatic expansion valve using a separated flow model. Four types of inlet/outlet conditions: liquid/liquid; liquid/two-phase; two-phase/two-phase; and vapour/vapour are studied. Refrigerant flow rate predictions of the model are compared to measured data. The results of this comparison show that the model is within ±20% for 95% of the experimental data corresponding to either an inlet fluid in a sub-cooled or a two-phase state. When the inlet fluid is in a vapour state, the model is able to predict 96% of the experimental data within ±16%.     

Khaya gum – a natural and eco-friendly biopolymer dielectric for low-cost organic field-effect transistors (OFETs)

Journal of Materials Science: Materials in Electronics - Nature provides a wide range of dielectric biopolymers that can be used in electronic devices. In this work, organic field-effect...     

Characterization of Critical Determinants of ACE2–SARS CoV-2 RBD Interaction

Despite sequence similarity to SARS-CoV-1, SARS-CoV-2 has demonstrated greater widespread virulence and unique challenges to researchers aiming to study its pathogenicity in humans. The interaction of the viral receptor binding domain (RBD) with its main host cell receptor, angiotensin-converting enzyme 2 (ACE2), has emerged as a critical focal point for the development of anti-viral therapeutics and vaccines. In this study, we selectively identify and characterize the impact of mutating certain amino acid residues in the RBD of SARS-CoV-2 and in ACE2, by utilizing our recently developed NanoBiT technology-based biosensor as well as pseudotyped-virus infectivity assays. Specifically, we examine the mutational effects on RBD-ACE2 binding ability, efficacy of competitive inhibitors, as well as neutralizing antibody activity. We also look at the implications the mutations may have on virus transmissibility, host susceptibility, and the virus transmission path to humans. These critical determinants of virus–host interactions may provide more effective targets for ongoing vaccines, drug development, and potentially pave the way for determining the genetic variation underlying disease severity.     

State of the art review of quality,reliability and maintenance issues in closed-loop supply chains with remanufacturing

The design of reverse logistics and remanufacturing processes and the recovery of end-of-life products have been well-studied in the literature. Quality, reliability, maintenance and warranty for recovered products and the remanufacturing activities that extend their life are integral issues in reverse logistics. This paper reviews recent and relevant literature on these issues in closed-loop supply chains, with a focus on remanufactured or second-hand products. The published literature is first classified into domain areas of research and practice. The wide array of mathematical tools and techniques used in the literature are then identified and mapped. Finally, the findings are summarised and the main research gaps are highlighted.     

Model-based approaches for interoperability of next generation enterprise information systems: state of the art and future challenges

Enterprise businesses are more than ever challenged by competitors that frequently refine and tailor their offers to clients. In this context, enterprise information systems (EIS) are especially important because: (1) they remain one of the last levers to increase the performance and competitiveness of the enterprise, (2) we operate in a business world where the product itself has reached a limit of performance and quality due to uniform capacity of industrial tools in a globalized economy and (3) the EIS can increase the product value thanks to additional digital services (built on data associated to the product) in order to meet and fit better client’s needs. However, the use of EISs reaches a limit in collaborative environments because enterprises management methods diverge and EISs are mainly inflexible resource packages that are not built with an interoperability objective. Consequently, we need to make EISs interoperable in order to achieve the needed gains competitiveness and performance. This paper contribution can be summarized as follows: (1) it relates existing work and it examines barriers that, at the moment, are preventing further improvements due to current methodological and technological limits, and (2) it proposes a conceptual framework and five challenges that model based approaches must overcome to achieve interoperability between EIS in the near and long term.     

Intestinal parasites in the vendors and consumers of street food. A study conducted in the Dakar area

To determine the origin and nature of mucinlike material in fine-needle aspiration (FNA) smears of the breast in noncancerous breast lesions, we studied breast FNA smears from four patients. All smears contained epithelial cells floating in a mucinlike background, which raised suspicion for mucinous (colloid) carcinoma. Mucicarmine stain was performed on one smear from each case. Subsequent tissue biopsy specimens were studied using mucicarmine, periodic acid-Schiff with and without diastase, and alcian blue stains at pH 2.7 and 0.9 on selected tissue sections. Correlation of the cytologic and histologic findings of each lesion was performed. The mucinlike background in all four FNA smears stained strongly with mucicarmine. Corresponding biopsy specimens revealed pseudoangiomatous hyperplasia in the first case, fibroadenoma and atypical ductal hyperplasia in the second, benign phyllodes tumor in the third, and fibroadenoma in the fourth. Each lesion in cases 1 to 3 was associated closely with fibrocystic changes. In case 4, cystic changes were located within the fibroadenoma. On tissue sections of all four cases, the cyst contents and 10% to 50% of normal lobule and duct contents stained with mucicarmine, indicating that the cyst contents were the most probable source of mucin in the FNA smears. The presence of pools of mucicarmine-positive material in FNA smears of the breast is not an exclusive feature of mucinous carcinoma; mucicarmine-positive mucin can arise from benign cystic changes as well as from normal lobules and ducts.     

Plasmodium falciparum- and merozoite surface protein 1-specific antibody isotype balance in immune Senegalese adults

This study shows markedly different isotype distributions of antibodies to asexual blood stages of Plasmodium falciparum and to merozoite surface protein 1 in clinically immune Senegalese adults depending on the study site. The relationships between immunoglobulin M (IgM) and IgG and between IgG3 and IgG1 antibodies differed in settings where transmission is perennial compared to settings where it is seasonal. This suggests a role for antibody class and/or subclass production and utilization in the regulation of protective immunity to such antigens.