Thermal stress relaxation in magnesium matrix composites controlled by dislocation breakaway

In metal matrix composites (MMCs) thermal stress relaxation can be achieved either by interface debonding, crack propagation or by dislocation motion. The present paper shows that in the case of magnesium matrix, interface thermal stresses are relaxed by dislocation motion. Moreover the results obtained by mechanical spectroscopy prove that this dislocation motion is controlled by a solid friction mechanism, which is not thermally activated. This point is very interesting for the development of MMCs, which exhibit a high damping capacity over a wide frequency range. Dislocation hysteretic motion in the magnesium matrix is evidenced by the dependence of the mechanical loss on the stress amplitude. The obtained relationship obeys perfectly to the Granato–Lücke model for dislocation breakaway.     

Autonomous bioremediation of a microbial protein (bioremediase) in Pozzolana cementitious composite

The self-bioremediation in cementitious composite material is one of the most interesting avenues relating to damage management and self-life of constructions, which needs to be cogitated. The self-bioremediation of a microbial protein-impregnated cementitious material has been explored in this work. The bioremediase protein was isolated from a hot spring bacterium (BKH1) and incorporated at three different concentrations into commercial Pozzolana cements that are widely used for mortar sample preparation. Artificial cracks were generated within the mortar samples by applying partial breaking load (50 %) and the samples were cured under water for different days. Image analysis by Crackscope and microstructure analysis by field emission scanning electron microscope ascertained the formation of irregular crystalline healing material within the cracks of the test samples. X-ray diffractometer and energy dispersive spectra analyses confirmed that the irregular crystalline structures were due to the deposition of new silicate phase (Gehlenite) within the cracks. Increase of ultrasonic pulse velocity and compressive strength, augmentation of sulphate resistance, decrease of chloride permeability and water absorption capacity revealed that there were overall improvement of mechanical properties and durability of the protein-incorporated mortar samples compared to the control (without protein incorporation) mortar samples. This cost effective and eco-friendly self-bioremediation phenomenon observed in mortar is evolved due to the biosilicification activity of bioremediase protein when amended in mortar samples. The exceptional potential of the microbial bioremediase protein for self-bioremediation attribute may add a new dimension in self-healing construction technology in near future.     

Integration of GIS and multicriteria decision analysis for urban aquaculture development in Bangladesh

Site selection is a key factor in any aquaculture operation, affecting both success and sustainability as well as solving land or water use conflicts. This study was conducted to identify suitable sites for carp farming development in urban water bodies (UWBs) of Chittagong, Bangladesh using Geographical Information Systems (GIS) based MultiCriteria Evaluation (MCE) of water, soil and infrastructure database. ASTER imagery and 14 thematic layers were analyzed with ENVI and GIS capabilities, and developed a series of GIS models to identify and prioritize the appropriate UWBs for carp farming. The study identified 487 UWBs occupying 362 ha and revealed 280 ha (77%) is the most suitable, 36 ha (10%) is moderately suitable and 46 ha (13%) is not suitable which was consistent with field verification. The results are encouraging for extension of carp culture and diversify the economic activities of the urban dwellers.     

Design and simulation of a novel GaN based resonant tunneling high electron mobility transistor on a silicon substrate

For the first time, we have introduced a novel GaN based resonant tunneling high electron mobility transistor (RTHEMT) on a silicon substrate. A monolithically integrated GaN based inverted high electron mobility transistor (HEMT) and a resonant tunneling diode (RTD) are designed and simulated using the ATLAS simulator and MATLAB in this study. The 10% Al composition in the barrier layer of the GaN based RTD structure provides a peak-to-valley current ratio of 2.66 which controls the GaN based HEMT performance. Thus the results indicate an improvement in the current-voltage characteristics of the RTHEMT by controlling the gate voltage in this structure. The introduction of silicon as a substrate is a unique step taken by us for this type of RTHEMT structure.     

Impact of source waters,disinfectants, seasons and treatment approaches on trihalomethanes in drinking water: a comparison based on the size of municipal systems

This study compares concentrations of trihalomethanes (THMs) in municipal water for 2001–2007 from the small and large systems in two provinces in Canada (Newfoundland and Quebec) based on source waters, disinfectants, seasons and treatment approaches. Approximately 71 and 94%, respectively, of the municipal systems in Quebec and Newfoundland are small systems (serving fewer than 3000 people). The small systems serve approximately 8.6% (0.57 million) and 44.1% (0.18 million) of the populations in Quebec and Newfoundland, respectively. Concentrations of THMs and its variability are much higher in the small systems (Quebec: 0–941 μg/L; Newfoundland: 0–875 μg/L) than in the systems with populations 10 000 or more (Quebec: 0–364 μg/L; Newfoundland: 2.3–205 μg/L). The study reveals that the differences in THMs between the small and medium/large systems are because of different types of source waters, treatments, disinfection strategies and seasons. The results emphasize that regulatory agencies must focus more on the occurrence of DBPs in small systems and identify strategies to reduce their levels in drinking water.     

Poly dimethylsiloxane/carbon nanofiber nanocomposites: fabrication and characterization of electrical and thermal properties

This article presents the fabrication and characterization of poly dimethylsiloxane/carbon nanofiber (CNF)-based nanocomposites. Although silica and carbon nanoparticles have been traditionally used to reinforce mechanical properties in PDMS matrix nanocomposites, this article focuses on understanding their impacts on electrical and thermal properties. By adjusting both the silica and CNF concentrations, 12 different nanocomposite formulations were studied, and the thermal and electrical properties of these materials were experimentally characterized. The developed nanocomposites were prepared using a solvent-assisted method providing uniform dispersion of the CNFs in the polymer matrix. Scanning electron microscopy was employed to determine the dispersion of the CNFs at different length scales. The thermal properties, such as thermal stability and thermal diffusivity, of the developed nanocomposites were studied using thermogravimetirc and laser flash techniques. Furthermore, the electrical volume conductivity of each type of nanocomposite was tested using the four-probe method to eliminate the effects of contact electrical resistance during measurement. Experimental results showed that both CNFs and silica were able to impact on the overall properties of the synthesized PDMS/CNF nanocomposites. The developed nanocomposites have the potential to be applied to the development of new load sensors in the future.     

Robust fault detection of turbofan engines subject to adaptive controllers via a Total Measurable Fault Information Residual (ToMFIR) technique

This paper provides a new design of robust fault detection for turbofan engines with adaptive controllers. The critical issue is that the adaptive controllers can depress the faulty effects such that the actual system outputs remain the pre-specified values, making it difficult to detect faults/failures. To solve this problem, a Total Measurable Fault Information Residual (ToMFIR) technique with the aid of system transformation is adopted to detect faults in turbofan engines with adaptive controllers. This design is a ToMFIR-redundancy-based robust fault detection. The ToMFIR is first introduced and existing results are also summarized. The Detailed design process of the ToMFIRs is presented and a turbofan engine model is simulated to verify the effectiveness of the proposed ToMFIR-based fault-detection strategy.     

Physical properties of ethylene vinyl acetate copolymer (EVA)/natural rubber (NR) blend based foam

In this study an attempt was made to improve the rebound resilience and to decrease the density of ethylene‐vinyl acetate copolymer (EVA) foam. For this purpose, EVA was blended with natural rubber (NR), and EVA/NR blends were foamed at 155°C, 160°C, and 165°C. To investigate the correlation between crosslinking behavior and physical properties of foams, crosslinking behavior of EVA/NR blends was monitored. The physical properties of the foams were then measured as a function of foaming temperatures and blend compositions: 165°C was found to be the optimal temperature for a crosslinking of EVA/NR foam. As a result, the density of EVA/NR blend foamed at 165°C was found to be the lowest. EVA/NR (90/10) blend, foamed at 165°C, showed lower density, better rebound resilience, and greater tear strength than EVA foam. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2212–2216, 2004     

Surface modification of henequen (Agave fourcroydes) fibers by ultraviolet curing with 2‐hydroxyethylacrylate and ethylacrylate: Effect of additives on degradable properties

Henequen fibers were grafted with a double impregnating monomer 2‐hydroxyethylacrylate (HEA) and ethylacrylate (EA) to improve the physicomechanical properties. The fibers soaked in different concentration (1–10%) of monomer + MeOH solution along with photoinitiator Irgacure 907 [2%] were cured under ultraviolet (UV) lamp at different UV radiation intensities (2–14 passes). Concentration of monomer at different radiation intensities was optimized with extent of mechanical properties such as polymer loading, tensile strength, and elongation at break. Enhanced tensile strength (268%) and elongation at break (110%) were achieved by the polymer treated fibers than untreated virgin fibers. We observed that, henequen fibers treated by 3% EA showed better physico‐mechanical properties than those treated by 5% HEA. The tensile properties of henequen fibers treated by 3% EA can be enhanced by adding aloxysilane; 3‐(trimethoxysilyl) propylmethacrylate additives with bulk monomer EA (3%). The degradability of the treated and untreated fibers due to accelerated weathering were also studied and it has been found that surface modified henequen fibers produced more resistivity towards different weathering conditions than untreated fibers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4000–4006, 2006