Design considerations and experimental studies on semi-active smart pin joint

Hostile dynamic loadings such as severe wind storms, earthquakes, and sudden impacts can cause severe damage to many civil engineering structures. An intelligent structural system equipped with smart structural members that are controllable in real-time is an effective solution to structural damage and failure during such situations. Civil intelligent structures with controllable properties to adapt to any changes due to dynamic loadings can lead to effective protection of structures and their occupants. In this paper, design and testing of a semi-active magnetorheological (MR) pin joint, in which the moment resistance can be controlled in real-time by altering the magnetic field, is reported with the view of using it as a potential candidate for smart members in the development of intelligent structures. Design of prototype smart pin joints includes theoretical analysis related to the radius of the rotary plate, the property of MR fluids and the gap between the rotary plate and the casing based on the requirements of the dynamics of MR pin joints. FEM analysis was deployed to study the distribution of the magnetic field along the gap. It is found, from the theoretical analysis and experimental verification, that the MR pin joint with a diameter of 180 mm can produce a torque of up to 30 Nm, which meets requirements for semi-active members in a multi-storey prototype building model in the next stage of research and development.     

Thermal and crystallization behavior of SiO2-PbF2 glass system in the presence of ErF3 and Al2O3

Oxyfluoride glass-ceramics have been introduced as one of the best bulk hosts for upconversion process of rare-earth ions. However, less attention to the technological topics in the process of glass crystallization has hindered the development of them in industrial scale applications. In this research, SiO₂–PbF₂ glasses were investigated to clarify the ambiguous role of rare-earth ions and alumina content in the microstructure and crystallization behavior. Results indicated that Er³⁺ addition caused a liquid-liquid phase separation via nucleation and growth mechanism, which led to single phase crystallization of β-PbF₂:Er³⁺ solid solution. Moreover, Er³⁺ had a significant effect on the crystallite size, size distribution, and PbF₂ crystallization temperature. On the other hand, increasing Al₂O₃ content enhanced the transparency and thermal stability of glass samples, whereas it reduced the amount of fluorine loss and increased the dissolution of Er³⁺ in fluoride crystalline structure. These results address some of the most controversial issues about crystallization behavior of rare-earth-doped oxyfluoride glasses.     

Development of a high precision flexure-based microgripper

This paper presents the design and development of a high precision microgripper for micromanipulation. The design is based on a hybrid flexure-based compliant mechanism and a bias spring structure which render high fidelity and inherent mechanical advantages. Finite element analysis (FEA) was conducted to evaluate responses of the model under specified load and displacement to investigate optimum design of the model. The prototype of the proposed microgripper was fabricated using electro-discharge machining (EDM) process. An experimental study of the performance was carried out and the results are presented. The experimental results are also compared with the computational analysis results. The results show that a high level of displacement amplification and a maximum stroke of 100 μm can be achieved.     

Using ozone to reduce recalcitrant compounds and to enhance biodegradability of pulp and paper effluents.

The effect of ozone based oxidation on removing recalcitrant organic matter (ROM) and enhancing the biodegradability of alkaline bleach plant effluent was investigated. A bubble column ozonation tower was used in the study. The experiments were carried out at different temperatures (20 degrees C and 60 degrees C) and pH (9 and 11), with a number of biological and chemical parameters being monitored including BOD5, COD, TC, pH, color, and molecular weight distribution of organics (nominal cut off of 1,000 Da). Biodegradability of the effluent was determined based on BOD5/COD of the wastewater throughout the process. For all the experiments, ozonation enhanced the biodegradability of the effluent by 30-40%, which was associated with noticeable removal of ROM including high molecular weight (HMW) and color-causing organics by about 30% and 60%, respectively. While the biodegradability of HMW fraction increased by about 50%, there was no biodegradability improvement for low molecular weight (LMW) portion, which was originally readily biodegradable (with BOD5/COD of about 0.5). Statistical analysis of variance (ANOVA) revealed neither pH nor temperature played significant role on the ozonation process at 95% confidence level.     

Characterization of low range GaAs

We present the results of a study of GaAs material grown at substrate temperatures below 250°C (low range GaAs) by molecular beam epitaxy. This material is amorphous and highly resistive and can be converted to single crystal through annealing process. The crystallization process is investigated by transmission electron microscopy, reflection high-energy electron diffraction, and double-crystal x-ray diffraction techniques.     

Local and global instabilities associated with continuing crack extension in dissipative solids

The model developed here links microstructural and continuum mechanics aspects of the early stages of the fracture process occurring in dissipative solids. A variable size damage zone, endowed with a structure of its own determined by the microstructural parameters related to the material ductility and grain size, is incorporated into a moving dominant crack. Prior to and during the course of crack extension, the energy dissipation mechanisms of diverse nature are activated within the volume of the localized damage zone, providing a substantial contribution to the effective material toughness. A criterion for quasi-static crack based on self-similarity of the crack-tip region is used to set up a governing equation of motion. The stress-transferring ability of the damage zone depends on the separation distance created between the two opposite boundaries of the fractures zone, and it determines the history of a quasi-static crack development including the attainment of the terminal instability point. Although detailed information regarding the distribution of stress prevailing within the nonlinear zone is lacking, it is shown that certain plausible governing equations may be constructed and employed to define material resistance curve in sufficiently large specimens (within the so-called ssy range), which is then used to predict the onset of catastrophic fracture. Six different specimen configurations are considered and the pertinent macro-mechanical stability analysis is presented in detail. The class of materials susceptible to this type of analysis is not restricted by the usual LEFM or EPFM constraint. This revised version was published online in August 2006 with corrections to the Cover Date.     

Characterizations of regular ordered semigroups in terms of (α, β)-fuzzy generalized bi-ideals

In this paper, the concept of an (α, β)-fuzzy generalized bi-ideal in an ordered semigroup is introduced, which is a generalization of the concept of a fuzzy generalized bi-ideal in an ordered semigroup. Using this concept, some characterization theorems are provided. The upper/lower parts of an (∈, ∈ ∨ q)-fuzzy generalized bi-ideal are introduced and some characterizations of regular ordered semigroups are given. Also, we consider the concept of implication-based fuzzy generalized bi-ideals in an ordered semigroup. In particular, the implication operators in Lukasiewicz system of continuous-valued logic are discussed.     

Intuitionistic (<Emphasis Type="Italic">S</Emphasis>, <Emphasis Type="Italic">T</Emphasis>)-fuzzy hyperquasigroups

The concept of intuitionistic fuzzy subhyperquasigroups in a hyperquasigroup with respect to an s-norm and a t-norm on intuitionistic fuzzy sets is introduced and their properties of such hyperquasigroups are studied. Intuitionistic (S, T)-fuzzy relations on a hyperquasigroup G are discussed. In particular, we investigate connections hyperquasigroups with binary quasigroups.