Fabrication of Wear-Resistant Ti3AlC2/Al3Ti Hybrid Aluminum Composites by Friction Stir Processing

Metallurgical and Materials Transactions A - Hybrid nanocomposites have potential as wear-resistant materials. However, synthesizing these nanocomposites by conventional molten state methods result...     

Mechanical,electrical, and thermal expansion properties of carbon nanotube-based silver and silver-palladium alloy composites

The mechanical, electrical, and thermal expansion properties of carbon nanotube（CNT）-based silver and silver–palladium（10：1, w/w） alloy nanocomposites are reported. To tailor the properties of silver, CNTs were incorporated into a silver matrix by a modified molecular level-mixing process. CNTs interact weakly with silver because of their non-reactive nature and lack of mutual solubility. Therefore, palladium was utilized as an alloying element to improve interfacial adhesion. Comparative microstructural characterizations and property evaluations of the nanocomposites were performed. The structural characterizations revealed that decorated type-CNTs were dispersed, embedded, and anchored into the silver matrix. The experimental results indicated that the modification of the silver and silver–palladium nanocomposite with CNT resulted in increases in the hardness and Young＇s modulus along with concomitant decreases in the electrical conductivity and the coefficient of thermal expansion（CTE）. The hardness and Young＇s modulus of the nanocomposites were increased by 30%？40% whereas the CTE was decreased to 50%-60% of the CTE of silver. The significantly improved CTE and the mechanical properties of the CNT-reinforced silver and silver–palladium nanocomposites are correlated with the intriguing properties of CNTs and with good interfacial adhesion between the CNTs and silver as a result of the fabrication process and the contact action of palladium as an alloying element.     

Stability analysis of a class of digital filters utilizing single saturation nonlinearity

A novel criterion for the global asymptotic stability of a class of digital filters utilizing single saturation nonlinearity is presented. An example showing the effectiveness of the present criterion is given.     

Modified criterion for global asymptotic stability of fixed-point state-space digital filters using two’s complement arithmetic

A criterion for the global asymptotic stability of fixed-point state-space digital filters using two’s complement arithmetic is presented. The criterion is a modified form of a well-known criterion due to Mills, Mullis, and Roberts. The criterion is in the form of linear matrix inequality and, hence, computationally tractable. An example shows the effectiveness of the modified criterion.     

Securing communication using function extraction technology for malicious code behavior analysis

Since computer hardware and Internet is growing so fast today, security threats of malicious executable code are getting more serious. Basically, malicious executable codes are categorized into three kinds – virus, Trojan Horse, and worm. Current anti-virus products cannot detect all the malicious codes, especially for those unseen, polymorphism malicious executable codes. The newly developed virus will create the damages before it has been found and updated in database. The basic idea of the proposed system is, it will analyze the behavior of the malicious codes and based on the behavior signature of the malicious code content filtering mechanism will be used to filter out contents, so that, the system will be secured from the future communication processes. The behavior of the code is analyzed using the function extraction technology. The function extraction technology will replace the function codes into algebraic expressions. Based on the behavior of the malicious codes, it will be categorized into different kinds of malicious codes. The detected malicious code will be prevented from execution. Based on the type of malicious code, appropriate security mechanism will be used for further communication.     

Novel organic–inorganic hybrid coatings prepared by the sol–gel process: corrosion and mechanical properties

(Hyperbranched polyurethane‐urea)/[(3‐aminopropyl)triethoxysilane]‐ZnO (HBPUU‐APTES‐ZnO) hybrid coatings were synthesized using an inexpensive mixing technique by varying the APTES‐modified ZnO concentration. The mechanical and surface properties of the hybrid coating films were studied and compared with unmodified and modified ZnO. The corrosion, solvent and abrasion resistance show significant enhancement in HBPUU‐APTES‐ZnO hybrids and their properties are increased with increasing APTES‐ZnO concentration. This hybrid coating has opened up an opportunity for automotive topcoat application. Copyright © 2012 Society of Chemical Industry     

Investigation of the effect of ZnO nanoparticles on the thermomechanical and microbial properties of hyperbranched polyurethane‐urea hybrid composites

Hybrid coatings of hyperbranched polyurethane‐urea (HBPUU) containing ZnO nanoparticles were prepared by mixing the hyperbranched polyurethane with the nanoparticles. The films were stored at room temperature and laboratory humidity conditions for one week to yield completely cured hybrid films. The ZnO nanoparticles were found to be well dispersed in the polymer up to 3 wt%. The structure–property relationship of various HBPUU–ZnO hybrid coatings was analysed using a Fourier transform infrared peak deconvolution technique with a Gaussian curve‐fitting procedure, while their viscoelastic, thermomechanical and surface morphology were studied using X‐ray diffraction, dynamic mechanical thermal analysis, thermogravimetric analysis, a universal testing machine, scanning electron microscopy, atomic force microscopy and contact angle instruments. The thermal stability and mechanical properties of the hybrid composite films improved with increasing ZnO content, which was believed to be due to thermal insulation in the presence of nanoparticles. Water contact angle data suggested that the hydrophobic character of the hybrid composites increased with increasing nanoparticle concentration. The antimicrobial property of the HBPUU–ZnO hybrid coatings was studied using the disc diffusion method. HBPUU–ZnO hybrid coatings showed good antimicrobial properties compared to HBPUU. Copyright © 2012 Society of Chemical Industry     

Comparative Study on Thermodynamic Analysis of CO2 Utilization Reactions

Thermodynamic analysis of dimethyl ether (DME) and methane synthesis from CO₂ hydrogenation, and dry reforming of methane was performed using Gibbs free energy minimization. The effects of temperature, pressure, and feed composition on conversion, selectivity, and yield were investigated for each process. High pressure, high H₂/CO₂ ratio, and low temperature favored DME production. The yield of methane during CO₂ methanation increased at lower temperature, higher pressure, and H₂/CO₂ ratio. The yield of synthesis gas improved at higher temperature. Comparison of the three processes demonstrated that the CO₂ conversion was highest during CO₂ methanation reaction if the fraction of CO₂ mol in the feed was less than 0.3. Above this value in the feed, dry reforming allowed the highest CO₂ conversion.     

Optimization of a plate-fin heat exchanger design through an improved multi-objective teaching-learning based optimization (MO-ITLBO) algorithm

Teaching-learning-based optimization (TLBO) is a recently developed heuristic algorithm based on the natural phenomenon of teaching-learning process. In the present work, multi-objective improved teaching-learning-based optimization (MO-ITLBO) algorithm is introduced and applied for the multi-objective optimization of plate-fin heat exchangers. The basic TLBO algorithm is improved to enhance its exploration and exploitation capacities by introducing the concept of number of teachers, adaptive teaching factor, tutorial training and self-motivated learning. The MO-ITLBO algorithm uses a grid-based approach to adaptively assess the non-dominated solutions maintained in an external archive. Minimizing total annual cost and the total weight of heat exchanger as well as minimization of total pressure drop and maximization of heat exchanger effectiveness for specific heat duty requirement are considered as objective functions. Two application examples are presented to demonstrate the effectiveness and accuracy of the proposed algorithm.