The adoption of any binder system for structural concrete depends on the performance characteristics desired for addressing the long-term deformation and durability concerns. The major properties ...influencing the performance includes the shrinkage characteristics governing the long-term deformation, and durability characteristics related to various transport mechanisms, governing the performance in different service conditions. This paper describes the potential of Limestone Calcined Clay Cement (LC3) for use in structural concrete in comparison with Ordinary Portland Cement (OPC) and fly ash based blended cement (FA30). Three types of concrete mixtures were designed for the study, two based on achieving an equivalent strength grade (M30 and M50 concrete grade) with each binder, and the third with equal binder content and w/b ratio. Mechanical properties such as compressive strength and elastic modulus, and autogenous and drying shrinkage, along with various durability parameters of the different concretes were assessed. Oxygen permeability, rapid chloride penetration, chloride migration, resistivity development and water sorptivity were the various parameters considered for evaluation of durability performance. The results indicate the superiority of LC3 binder over other binders in producing durable concrete, especially in a chloride laden environment. The major reason for the better performance was attributed to the more compact and dense microstructure of the system with the LC3 binder against OPC and FA30. The drying shrinkage performance was seen to be similar for concrete with all three binders.
In this work, the thermodynamic performance of a single slope solar still with cotton cloth energy storage medium was compared with a simple solar still without energy storage. Two solar stills with ...similar dimensions (one with cotton cloth energy storage and another without energy storage) were fabricated and investigated its performance under the hot humid climatic conditions of Chennai in India during the summer months of 2017. The performance was evaluated in terms of energy and exergy analysis based on first and second law of thermodynamics, respectively, for 2 mm, 4 mm, 6 mm and 8 mm cotton cloth thickness. The results showed that the maximum energy and exergy efficiency of a solar still was observed to be 23.8% and 2.6%, respectively, for 6 mm cotton cloth thickness. The results confirmed that the cotton cloth regenerative medium has enhanced the still productivity by about 24.1% when compared to the solar still without heat storage.
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•PANI/PVA/GO and PANI/PVA nanofibers were prepared via electrospinning.•Specific capacitance of the nanofibers was calculated from Cyclic Voltammetry.•Nanofibrous morphology ...positively influences the specific capacitance value.•GO inclusion enhances the specific capacitance of PANI/PVA composite nanofibers.
High-performance energy-storage gadgets, including supercapacitors hold great capability for various applications, such as portable electronics, electric vehicles etc. Portable electronics industry necessitates the employment of energy storage devices with large energy and power densities. Supercapacitors require electrode materials having better morphology, surface area, and carrier mobility that provide high capacitance. In this work we concentrate on the synthesis and electrochemical characterization of a material suitable to be used as supercapacitor electrode. Graphene Oxide/Polyaniline/Polyvinyl alcohol nanofibers were obtained via electrospinning process. The crystalline structure and morphology of developed nanofibers have been illustrated using X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM). The electrochemical performance of the PANI-PVA-GO composite nanofibers was investigated as a supercapacitor electrode material through Cyclic Voltammetry (CV) studies. The nanofibers comprising Graphene Oxide exhibited better specific capacitance than polymer nanofibers thereby providing a novel way for fabrication of supercapacitor electrodes. This manuscript also gives a comparison of specific capacitance achieved by different compositions of Graphene Oxide, Polymers and transition metals reported in previous works.
Creep deformation and rupture behaviour of 9Cr–1.8W–0.5Mo–VNb steel have been investigated at 873K, 923K and 973K over a stress range of 80–220MPa. The absence of clear primary creep regime and ...prolonged secondary stage of creep deformation have been noticed under lower stress level at 973K. The variation of minimum creep rate with applied stress obeyed Norton's power law of creep. The apparent stress exponents of 15.2, 12.3 and 5.8, and apparent activation energy of 619kJ/mole have been estimated for creep deformation of the steel. The apparent stress exponents and activation energy have been rationalised on the basis of threshold stress. The threshold stress values of 137.5MPa, 83.3MPa and 29.7MPa were obtained at 873K, 923K and 973K respectively. The threshold stress compensated true stress exponent of 4 and true activation energy of 244kJ/mole, and threshold stress normalised by Orowan stress confirms that the lattice diffusion assisted localised climb of dislocation is the rate controlling of creep deformation in the steel. The steel obeyed Monkman and modified Monkman–Grant relationships. Damage tolerance factor of 6 in the steel demonstrates that the microstructural degradation such as coarsening of precipitates and subgrain structure is the dominant creep damaging mechanism in the steel.
The intermittent network connectivity and unawareness of global network knowledge are remarkable challenges when designing efficient Position-based Opportunistic Routing (POR) for Delay Tolerant ...Networks (DTNs). The best progress set selection of POR effectively handles the intermittent connectivity issue and improves the reliable performance of DTNs. Hence, the optimal progress set selection and catching capacity decide the routing reliability of DTN-POR. This paper proposes a context-aware DTN-POR protocol STAP to ensure reliable DTN routing with minimum overhead STAP design is divided into three folds: application diversity and network failures, context-aware best progress set selection, and enhanced caching management. The application diversity and network failure switch the nodes in harsh environments to DTN mode for transmitting the data packets successfully to the destination. Selecting context-aware relay nodes ensures highly successful data transmissions in the absence of end-to-end connectivity. The probability estimation maximizes the data reachability by considering unique node and application-level context attributes in the best progressive set. Finally, the enhanced catching management strategy limits the number of data copies with effective catch invalidation, resulting in minimum overhead. The proposed STAP accomplishes better results in different scenarios and improves the packet delivery ratio with a minimum duplication rate.
Creep rupture behavior of 9Cr–1.8W–0.5Mo–VNb (ASME grade 92) ferritic steel weld joint fabricated by activated TIG (A-TIG) welding process have been investigated at 923K over a stress range of ...80–150MPa. The weld joint was comprise of fusion zone, heat affected zone (HAZ) and base metal. The HAZ consisted of coarse prior-austenite grain (CGHAZ), fine prior-austenite grain (FGHAZ) and intercritical (ICHAZ) regions in an order away from the fusion zone to base metal. A hardness trough was observed at the outer edge of HAZ of the weld joint. TEM investigation revealed the presence of coarse M23C6 precipitates and recovery of martensite lath structure into subgrain in the ICHAZ of the weld joint, leading to the hardness trough. The weld joint exhibited lower creep rupture lives than the base metal at relatively lower stresses. Creep rupture failure location of the weld joint was found to shift with applied stress. At high stresses fracture occurred in the base metal, whereas failure location shifted to FGHAZ at lower stresses with significant decrease in rupture ductility. SEM investigation of the creep ruptured specimens revealed precipitation of Laves phase across the joint, more extensively in the FGHAZ. On creep exposure, the hardness trough was found to shift from the ICHAZ to FGHAZ. Extensive creep cavitation was observed in the FGHAZ and was accompanied with the Laves phase, leading to the premature type IV failure of the steel weld joint at the FGHAZ.
Nitrogen‐rich carbon nitride is obtained as ultrasmall, discrete, mesoporous nanoparticles (see picture) by reaction of ethylenediamine with CCl4 in the nanochannels of a mesoporous silica template. ...Its high nitrogen content, large surface area, and large pore volume make it a highly active catalyst for transesterification of β‐keto esters of aryl, aliphatic, and cyclic primary alcohols.
The object of the present investigations is to evaluate the mechanical properties across the SMAW, SAW, FCAW and A-GTAW weld joints of micro alloyed HSLA steel. The correlation between ...microstructure, micro-hardness and tensile properties obtained using automated ball indent (ABI) has been undertaken. The variation of yield strength (YS), ultimate tensile strength (UTS) and strain hardening component (n) values across base metal, heat affected zone and weld metal were obtained from the ABI results and validated with the standard conventional tensile test results. The cross-weld joints were found to have minor increase in yield strength with corresponding decrease ductility as compared to the base steel. The high strength of weld metals was attributed to the presence of high percentage of bainitic and acicular ferritic microphases. The transformation of base metal to bainitic structure was found to be the significant factor contributing to the strength of HAZ in the weld joints. The tensile strength was observed to vary significantly across the weld joints. The strength values (YS and UTS) decreased systematically across the weld joint from weld metal to base metal. The strain hardening exponent was found to be comparable across the weld joints with marginal higher values for HAZ. The comparable values of strain hardening exponent for weld metal and base metal showed the balanced strength and ductility of the welds. The FCAW and SAW were found to be better welding techniques that provide sufficient strength and least variation in mechanical properties across the weld joints.
Wireless networks have emerged as a key enabling technology, expanding rapidly and offers numerous potential applications. The security issues have to be adequately addressed to realize the potential ...of multi-hop cooperative wireless network scenarios. The open nature of the wireless network is the opportunity for invaders launching various attacks with minimum effort owing to the multi-hop scenario of routing protocols. Routing protocols work based on the assumption that intermediate nodes are cooperating and well-behaving. Even in the presence of strong authentication mechanisms, detecting the continuous and selective packet dropping attack is a challenging process. This paper focuses on the design of a secure routing framework, and extend it to the routing protocols of various multi-hop wireless networks vulnerable to such attacks. The proposed hybrid security framework combats the routing misbehavior attacks in the presence of a wide range of malicious nodes. The proposed framework extends the hybrid security model adaptable to various multi-hop wireless networks with flexible routing overhead. The framework introduces a dummy packet based acknowledgment scheme that inserts dummy packets in the real payload traffic and masks the dummy traffic sequence through the dynamic traffic pattern. It optimizes the dummy packet generation based on the packet drop experienced and minimized the dummy traffic to balance the routing security and overhead. It confirms the presence of malicious nodes based on the dummy packet dropping and relies on the trust mechanism to eliminate the misbehaving nodes in the critical path. The use of subjective and fuzzy trust model validates the accuracy of uncertain evidence and contextual factors in the trust. The effectiveness of the framework is realized by applying it on various routing protocols in wireless networks. The performance evaluation confirms excellent packet delivery of the proposed hybrid framework over various networks in a highly vulnerable environment.
In the recent years, there has been increased in concern on shrinkage response of concrete systems as abundant cases of premature deterioration were reported. The major factors affecting the ...deterioration of a concrete system are quality, composition and the surrounding environment. In connection with this, the work concentrates on the study of long-term effects on materials used in the concrete (supplementary cementitious materials SCMs) such as fly ash, slag and silica fume as a blended concrete system. To carry out the experimental work, nine concrete mixes were designed for varying proportions of SCMs and w/b. Evolution of compressive strength, elastic modulus, shrinkage and selected durability parameters were tested under a controlled laboratory condition. Based on the work, it was found that the inclusion of fly ash, slag and silica fume on the concrete systems enhance the compressive strength in long-term, also the shrinkage response of the ternary systems shows a substantial reduction in the measured strain. Durability performance like chloride penetration and sorptivity had a better performance in comparison with the conventional concrete systems.
