Active control and parameter updating techniques for nonlinear thermal network models

 The present article reports on active control and parameter updating techniques for thermal models based on the network approach. Emphasis is placed on applications where radiation plays a dominant role. Examples of such applications are the thermal design and modeling of spacecrafts and space-based science instruments. Active thermal control of a system aims to approximate a desired temperature distribution or to minimize a suitably defined temperature-dependent functional. Similarly, parameter updating aims to update the values of certain parameters of the thermal model so that the output approximates a distribution obtained through direct measurements. Both problems are formulated as nonlinear, least-square optimization problems. The proposed strategies for their solution are explained in detail and their efficiency is demonstrated through numerical tests. Finally, certain theoretical results pertaining to the characterization of solutions of the problems of interest are also presented. Received 27 July 2000     

Bi-objective optimisation for integrated scheduling of single machine with setup times and preventive maintenance planning

This paper deals with an integrated bi-objective optimisation problem for production scheduling and preventive maintenance in a single-machine context with sequence-dependent setup times. To model its increasing failure rate, the time to failure of the machine is subject to Weibull distribution. The two objectives are to minimise the total expected completion time of jobs and to minimise the maximum of expected times of failure of the machine at the same time. During the setup times, preventive maintenance activities are supposed to be performed simultaneously. Due to the assumption of non-preemptive job processing, three resolution policies are adapted to deal with the conflicts arising between job processing and maintenance activities. Two decisions are to be taken at the same time: find the permutation of jobs and determine when to perform the preventive maintenance. To solve this integrated problem, two well-known evolutionary genetic algorithms are compared to find an approximation of the Pareto-optimal front, in terms of standard multi-objective metrics. The results of extensive computational experiments show the promising performance of the adapted algorithms.     

Hydroxyapatite coatings: a comparative study between plasma-spray and pulsed laser deposition techniques

A comparative study between hydroxyapatite coatings produced by two different techniques, plasma spray (PS) and pulsed-laser deposition (PLD) was carried out. Plasma spray is currently commercially used for coating dental and orthopaedical implant devices, and pulsed-laser deposition (or laser-ablation deposition) gave good results in the field of high critical temperature superconductive thin films, and is being applied to produce calcium phosphate coatings for biomedical purposes. X-ray diffraction was used to control the crystallinity of the coatings, scanning electron microscopy for the surface and cross-sectional morphology, and the pull test to determine the tensile strength of the coatings. This study reveals that the pulsed-laser deposition technique appears to be a very good candidate to replace the plasma spray in many biomedical applications, because it overcomes most of the drawbacks of the plasma spray.     

Mechanical characteristics of optical coatings prepared by various techniques: a comparative study

Good performance of optical coatings depends on the appropriate combination of optical and mechanical properties. Therefore, successful applications require good understanding of the relationship between optical microstructural and mechanical characteristics and film stability. In addition, there is a lack of standard mechanical tests that allow one to compare film properties measured in different laboratories. We give an overview of the methodology of mechanical measurements suitable for optical coatings; this includes depth-sensing indentation, scratch resistance, friction, abrasion and wear testing, and stress and adhesion evaluation. We used the techniques mentioned above in the same laboratory to systematically compare the mechanical behavior of frequently used high- and low-index materials, namely, TiO2, Ta2O5, and SiO2, prepared by different complementary techniques. They include ion-beam-assisted deposition by electron-beam evaporation, magnetron sputtering, dual-ion-beam sputtering, plasma-enhanced chemical-vapor deposition, and filtered cathodic arc deposition. The mechanical properties are correlated with the film microstructure that is inherently related to energetic conditions during film growth.     

Solvent and melting induced microspheres sintering techniques: a comparative study of morphology and mechanical properties

In this work we propose a bottom up approach founded on the assembly of building blocks by solvent induced microparticle sintering to realize multifunctional polymer scaffolds with predefined pore dimension and fully percolative pathway, able to include interspersing microdepot for the release of bioactive molecules. The aim of this study was to develop a versatile method of microspheres sintering based on the partial dissolution of the surface of adjacent microparticles and to compare it with melting induced microspheres sintering, just developed in a previous work. The two techniques were compared in terms of morphology, porosity and mechanical properties. The high potential of customizing the sintering process by the proper selection of the sintering techniques as well as microparticles with different features (e.g., material, size, shape, inner porosity) allows obtaining a wide pattern of micro/nanostructures with bio-inspired mechanical response so satisfying all basic requirements of a “smart” scaffold for bone tissue engineering.     

A comparative study of EVA with and without thermal history for different lamination process parameters

In more than 80% of the worldwide photovoltaic (PV) modules, mostly very fragile and 200 μm thick, crystalline silicon solar cells are encapsulated into ethylene-vinyl acetate (EVA) foils, which bond the module components together, provide physical protection, electrical insulation and a barrier for moisture ingress. The understanding of what can happen with EVA during its transport, storage and lamination process is necessary to optimize the quality of the PV module for its long exposure to outdoor weather conditions. Achieving a proper cross-link density of over 70%, it is essential to overcome the cold flow of EVA and to make the module durable. In this work, the feasibility of the use of differential scanning calorimetry (DSC) compared with the solvent extraction (SE) method by toluene were evaluated in order to provide structural information on the EVA curing kinetics and the cross-link density. DSC tests were performed on a DTA DuPont1600 tester. The temperature range for the test was from −50 °C to 200 °C, with the heating rate of 10 °C/min, and the endothermic and exothermic peaks were evaluated. Toluene solvent extractions were performed on the same set of samples that were analyzed by DSC. The measured cross-link density shows a direct dependence on the pre-lamination conditions of EVA, which is in good agreement with the data obtained with the DSC method.     

Reduction techniques for the PNS problems: a novel technique and a review

Process Network Synthesis (PNS) has an enormous practical impact. The problem is very difficult to solve, determining the cost optimal network of operating units with fixed charge belongs to the complexity class of NP-hard problems. Therefore, it is important to develop reduction algorithms to minimize the size of the problem. In the present work the available reduction techniques for PNS problems are reviewed as well as a further reduction algorithm is presented. The performance of the new algorithm is examined by empirical analysis.     

Comparison and analysis of Acoustography with other NDE techniques for foreign object inclusion detection in graphite epoxy composites

This paper presents the use of a novel through-transmission ultrasonic (TTU) Acoustography non-destructive evaluation (NDE) method to detect foreign object inclusion (FOI) defects in graphite epoxy composite laminates. The study employed three different composite test standards with varied size FOI defects embedded at varying depth within the composite laminates. For validation, Acoustography results were directly compared with conventional immersion TTU testing and infrared thermography (IRT) methods. From results obtained, it was demonstrated that the Signal-to-Noise Ratio (SNR) measurements for Acoustography were more than 6:1 and were in good correlation with immersion TTU and IRT results. The defect sizing ability of TTU Acoustography for FOI defects in graphite epoxy composite laminates were also in strong correlation with immersion TTU and IRT techniques. Finally, for the three laboratory systems employed in this study, typical panel TTU Acoustography inspection time was just about three minutes to scan a 300 mm × 300 mm (11.8″ × 11.8″) area, which was more than three times faster compared to IRT and sixty times faster to conventional immersion TTU C-Scan techniques. This is a very significant finding for the reason that Acoustography is being developed as a faster, more efficient, and affordable alternative to traditional ultrasonic inspection systems for composite manufacturing quality control and quality assurance (QC/QA) and field maintenance of composite structure applications.     

A comparative study of linear and non-linear regression analysis for ammonium exchange by clinoptilolite zeolite

Ammonium ion exchange from aqueous solution using clinoptilolite zeolite was investigated at laboratory scale. Batch experimental studies were conducted to evaluate the effect of various parameters such as pH, zeolite dosage, contact time, initial ammonium concentration and temperature. Freundlich and Langmuir isotherm models and pseudo-second-order model were fitted to experimental data. Linear and non-linear regression methods were compared to determine the best fitting of isotherm and kinetic model to experimental data. The rate limiting mechanism of ammonium uptake by zeolite was determined as chemical exchange. Non-linear regression has better performance for analyzing experimental data and Freundlich model was better than Langmuir to represent equilibrium data.     

Data analysis from a multi-centre, comparative study of angiographic examinations leading to practical guidelines for the optimisation of patient doses

In this study, patient doses were analysed against exposure parameters and procedure protocol. Patient doses were measured in seven hospitals for a standard diagnostic vascular examination. Image quality was assessed using the contrast-detail phantom from Nijmegen (CD-DISC 2.0). A link between dose and image quality was investigated. Image quality strongly depends on the preset dose level. The higher the dose level, the better the image quality, but also the higher the patient dose. However, no clear correlation was found between total dose-area product (DAP) or effective dose and image quality. A large range in patient dose was found: DAP (22-130 Gy cm2) and effective dose (3.9-16.8 mSv). A difference in number of frames was also found in the different centres, owing to different frame rates (3-2-1 frames per second) and use of oblique projections. Differences in doses and exposure settings offer the possibility of optimising patient doses in angiography and interventional radiology.     

A comparative study of hyperelastic and hypoelastic material models with constant elastic moduli for large deformation problems

Many finite element programs including commercial codes for large deformation analysis employ incremental formulations of rate-type constitutive equations which are based on hyperelastic or hypoelastic material models with constant elastic moduli. In this paper, a comparative study is carried out for hyperelastic and hypoelastic material models with constant elastic moduli of a face-centered cubic single crystal of copper. A strain energy function from the inter-atomic potential for single-crystal copper is also considered for the hyperelastic material model to obtain physically based elastic deformations. Numerical results show that constant elastic moduli of hypoelastic material models can cause considerable errors in stress and strain increments when the changes in volume and cross-sectional area of a material are not negligible.     

Molecular dynamics simulation of the thermal conductivity of shorts strips of graphene and silicene: a comparative study

Classical non-equilibrium molecular dynamics is employed to model short-strips of single-layered materials consisting of either carbon (graphene) or silicon (silicene) atoms. Both materials are modeled using their respective parameterizations of the Tersoff potential, and their thermal conductivities are then determined through non-equilibrium molecular dynamics. The present results indicate that both materials experienced increasing thermal conductivities as length increased, and graphene had far more rapid increases than silicene. Both armchair and zigzag chiralities in silicene has significant differences in thermal conductivities but not in graphene. Graphene possesses significantly higher thermal conductivities than silicene at every length scale and chirality, and this is found to be attributed to the fewer excitable phonon frequencies, as shown through the vibrational density of states.     

A study of magneto-thermoelastic problems with thermal relaxation and heat sources in a three-dimensional infinite rotating elastic medium

This paper is concerned with a study of magneto-thermoelastic problems with thermal relaxation and heat sources in a three-dimensional infinite rotating elastic medium. The medium under consideration is assumed to be homogeneous, orthotropic, electrically as well as thermally conducting. The fundamental equations of the three-dimensional problem of generalized thermoelasticity with one relaxation parameter including heat source in an infinite rotating elastic medium under the influence of magnetic field are obtained as a vector-matrix differential equation form in the Laplace–Fourier transform domain which is then solved by the eigenvalue approach. A closed form solution of the problem is derived in the Laplace–Fourier domain. Finally, the inversion of the transform solution is obtained numerically in the space–time domain. Results of this paper presented graphically and then compared with previous results available in the literature. Two short appendices are included in this paper in order to make the work self-contained.     

Tearing behaviour of two types of leather: A comparative study carried out at the local scale using the full kinematic and thermal field measurement techniques

Leather materials undergo various strain and stress states during their elaboration process and their application in numerous different functions. Among the key properties required for such materials, tearing resistance appears as one of the most important. In this paper, the tearing behaviour of two types of leather, a grain pigskin leather and a grain calf leather, was investigated at the local scale using the full‐field techniques. During the tests, thermal fields were measured at the surface of the two leathers by means of an infrared camera. Measurements of the displacement and deformation fields were also performed at the surface of the pigskin sample using the digital image correlation technique, which was not possible for the calf sample due to surface wrinkling. The results obtained enable us to discuss and compare the tearing resistance of both leathers in terms of the thermal activity in the zone of influence of the crack. The best tearing resistance was obtained for the grain calf leather that has undergone a retanning operation and whose matrix contained a plasticiser.     

Infrared thermography for void mapping of a graphene/epoxy composite and its full‐field thermal simulation

Important challenges are faced during the manufacturing of graphene nanoplatelet (GNP)/polymer composites, associated with material quality and how to eliminate or reduce fabrication‐induced defects in the effort to improve performance. In the present work, infrared thermography (IRT) is used to measure void content and map void distribution, formed during fabrication of GNP/epoxy nanocomposites. Taking into consideration the size of each pixel (~100 μm), this method enables the non‐destructive detection of flaws with a size of approximately 200 μm. Their effect on thermal conductivity of the nanocomposite is studied by a 3D multiscale finite element analysis. Generic and full‐field comparisons demonstrate a good agreement between measurements and numerical predictions, validating assumptions and simplifications made in the proposed model.     

Synthesis of MCM-48 with a high thermal and hydro-thermal stability

High thermal and hydro-thermal stable MCM-48 was synthesized by a mixed nonionic-cationic surfactant templating pathway. The sample retains its cubic structure when at 1000 °C for 2 h and when calcined in air with 100% water vapor at 600 °C for 2 h.