On intuitionistic fuzzy sub-hyperquasigroups of hyperquasigroups

The notion of intuitionistic fuzzy sets was introduced by Atanassov as a generalization of the notion of fuzzy sets. In this paper, we consider the intuitionistic fuzzification of the concept of sub-hyperquasigroups in a hyperquasigroup and investigate some properties of such sub-hyperquasigroups. In particular, we investigate some natural equivalence relations on the set of all intuitionistic fuzzy sub-hyperquasigroups of a hyperquasigroup.     

Constitutive Relationships for Steel Fibre Reinforced Concrete at Elevated Temperatures

Steel fibre reinforced concrete (SFRC) is an advanced cementitious composite where fibres can act as a profitable replacement for diffused reinforcement, like welded steel mesh, especially for thin cross sections. In this case fire becomes a very important condition in the design. Previous experimental research has shown the benefits in fire resistance of steel fibres, when structural elements are bent. The proper understanding of the effects of elevated temperatures on the properties of SFRC is necessary. In this study, constitutive relationships are developed for high-strength FRSC subjected to fire, with the purpose of given that capable modelling and to specify the fire-performance criteria for concrete structures. They are developed for unconfined FRSC specimens that include compressive and tensile strengths, modulus of elasticity, modulus of rupture, strain at peak stress, and compressive stress–strain relationships at elevated temperatures. The proposed relationships at elevated temperature are compared with experimental results. These results are used to establish compressive stress–strain relationships. Further experimental results for tension and the other main parameters at elevated temperature are needed in order to establish well-founded models and to improve the proposed constitutive relationships, which are general, rational, and fit well with the experimental results.     

High Strength Polypropylene Fibre Reinforcement Concrete at High Temperature

Concrete is an inherently brittle material with a relatively low tensile strength compared to compressive strength. Reinforcement with randomly distributed short fibres presents an effective approach to the stabilization of the crack and improving the ductility and tensile strength of concrete. A variety of fibre types, including steel, synthetics, and natural fibres, have been applied to concrete. Polypropylene (PP) fibre reinforcement is considered to be an effective method for improving the shrinkage cracking characteristics, toughness, and impact resistance of concrete materials. Also, the use of PP fibre has been recommended by all of the researchers to reduce and eliminate the risk of the explosive spalling in high strength concrete at elevated temperatures. In this study, constitutive relationships are developed for normal and high-strength PP fibre reinforcement concrete (PPFRC) subjected to high temperatures to provide efficient modelling and specify the fire-performance criteria for concrete structures. They are developed for unconfined PPFRC specimens that include compressive and tensile strengths, elastic modulus, modulus of rupture, strain at peak stress as well as compressive stress–strain relationships at elevated temperatures. The proposed relationships at elevated temperature are compared with experimental results. These results are used to establish more accurate and general compressive stress–strain relationships prediction. Further experimental results for tension and the other main parameters at elevated temperature are needed in order to establish well-founded models and to improve the proposed constitutive relationships, which are general, rational, and fit well with the experimental results.     

Investigation in Mathematical Models of Chloride Diffusion Coefficient in Concrete Exposed to Marine Environment

Degradation of RC （reinforced concrete） in maritime structures has become a worldwide problem due to its excessive costs of maintenance, repair and replacement in addition to its environmental impacts and safety issues. Degradation of both concrete and steel which is the main reason of reduction in the service life of RC structures strongly depends on the diffusion process of moisture and aggressive species. In this paper, the major and popular mathematical models of diffusion process in concrete are surveyed and investigated. Predominantly in these models, the coefficient of chloride diffusion into the concrete is assumed to be constant. Whereas, experimental records indicate that diffusion coefficient is a function of time. Subsequently, data analysis and comparisons between the existing analytical models for predicting the diffusion coefficient with the existing experimental database are carried out in this study. Clearly, these comparisons reveal that there are gaps between the existing mathematical models and previously recorded experimental results. Perhaps, these gaps may be interpreted as influence of the other affecting parameters on the diffusion coefficient such as temperature, aggregate size and relative humidity in addition to the water cement ratio. Accordingly, the existing mathematical models are not adequate enough to predict the diffusion coefficient precisely and further studies need to be performed.     

Dynamic modelling of a flexure-based mechanism for ultra-precision grinding operation

This paper presents the dynamic modelling and performance evaluation methodologies of a flexure-base mechanism for ultra-precision grinding operation. The mechanical design of the mechanism is briefly described. A piezoelectric actuator is utilized to drive the moving platform. A flexure-based structure is utilized to guide the moving platform and to provide preload for the piezoelectric actuator. By simplifying the Hertzian contact as a linear spring and damping component, a bilinear dynamic model is developed to investigate the dynamic characteristics of the flexure-based mechanism. Based on the established model, the separation phenomenon between the moving platform and the piezoelectric actuator is analyzed. The influences of the control voltage and the preload stiffness on the maximum overshoot are extensively investigated. The slope and cycloidal command signals are utilized to reduce and/or avoid the overshoot of such flexure-based mechanism for rapid positioning. The effects of the rising time of the command signals on the maximum overshoot and the settling time are also explored. Experiments are performed to verify the established dynamic model and the performance of the developed flexure-based mechanism.     

Optimization of autothermal reactor for maximum hydrogen production

Efficient generation of hydrogen is an important enabling technology for commercialization of fuel cells for homes and cars of the future. A methodology for optimization of an autothermal reactor with respect to system parameters is described. Furthermore, a framework for theoretical interpretation of reforming reactions is developed using an atomic balance approach, which is utilized to determine the reforming reaction space and maximum monolith temperature for a methane reformer.     

In Vitro-In Vivo Correlation of Indomethacin Release from Prolonged Release W/O/W Multiple Emulsion System

A prolonged release oral w/o/w multiple emulsion was formulated using hydroxypropyl methyl cellulose as thickening agent. The polymer when used in different proportions, controlled indomethacin release from the biphasic emulsion system. Double emulsification technique was used for formulation of the biphasic emulsion system. The stability of the emulsion was found to be inversely proportional to the drug release characteristics. The in vitro release of indomethacin followed diffusional path through the oil layer and through the polymeric oil. The in vivo release studies were carried out using rabbits as animal models. A good linear correlation was obtained between in vivo-in vitro drug release from such multiple emulsion system.     

A method of computing numerically integrated stiffness matrices

A method of formulating and computing numerically integrated stiffness matrices is presented. Through a better organization of the formulation which is easily achieved by the use of index notation, the computations for integrating and evaluating the element stiffness matrix are substantially reduced. For cases in which the terms of the material property tensor are not functions of position co-ordinates (elastic isotropic and anisotropic materials), a further reduction in computation is achieved by multiplying the material property-tensor after the numerical integration has been carried out.     

Structural,morphological, and optical properties of W-doped VO2 thin films prepared by sol-gel spin coating method

Thermochromic VO₂ thin films were deposited on soda-lime glass via sol-gel method. Doping was done through adding tungstic acid solution to the vanadium solution precursor. Grazing incidence x-ray diffractometer (GIXRD) results showed that VO₂ and V₆O₁₃ phases were formed together in the heat-treated sample. According to the GIXRD result of the W-doped sample, only VO₂ remained. Field-emission scanning electron microscopy (FESEM) micrographs showed that the VO₂ grain size decreased from about 70 to about 25 nm for undoped film and 2 wt% W-doped films, respectively. Atomic force microscopy (AFM) results showed that the root mean square roughness for the film with 180 nm thickness was about 18 nm, and 2 wt% W-doped film had a smoother surface. Diffuse reflectance spectroscopy (DRS) results showed that the band gap energy for undoped, 1 wt% W- doped, and 2 wt% W-doped VO₂ thin films was 1.7, 1.3, and 0 eV, respectively. Four-point probe resistivity measurements showed a significant decrement, from approximately 1 MΩ at 15°C to <100 Ω at 80°C. Regarding Vis-NIR spectroscopy results, maximum optical transmission for undoped and W-doped films was approximately 75% and 35%, respectively.     

Synergistic effect of micro- and nano-TiO2 on hydrophobic,mechanical, and electrical properties of hybrid polyurethane composites

Journal of Materials Science: Materials in Electronics - One of the ways to improve the performance of ceramic insulators in polluted climates is to use polymer coatings reinforced with ceramic...