Modelling of start-up time for high temperature polymer electrolyte fuel cells

Start-up time is one of the important factors that limit the application of high temperature polymer electrolyte fuel cells in several areas. Present work involves the analysis of different warm-up methodologies to analyse the start-up time for phosphoric acid doped PBI membrane based fuel cells. With this objective a number of three dimensional thermal models have been developed. Different heating methodologies such as reactant heating, coolant heating and combined heating (reactant and ohmic) are simulated. The ohmic heating is implemented for generating heat in the membrane itself at high current densities. Hence, combining it with other heating techniques is found effective in reducing start-up times significantly.     

Structure of Polymeric PbTiO3 Gels

The structural features of PbTiO₃ gels were found to be highly dependent on hydrolysis conditions. Gels formed from acid-catalyzed solutions were clear and rubbery, whereas base-catalyzed gels were translucent or cloudy with phase separation. Direct TEM observations determined that acid-catalyzed gels were fibrous in character and physically homogeneous, whereas base-catalyzed gels had a coarse texture. Analyses by EDX and SAD indicated that acidic gels were chemically homogeneous and microcrystalline, whereas basic gels were heterogeneous and amorphous.     

Effect of SiC Content on Mechanical and Tribological Properties of Al2024-SiC Composites

Silicon - Aluminium matrix composites are scientifically engineered materials possessing higher potential in automotive, aerospace and defence applications. Therefore this study focuses on the...     

Optimization of bead geometry in electron beam welding using a Genetic Algorithm

Bead-on-plate welds were carried out on austenitic stainless steel plates using an electron beam welding machine. Experimental data were collected as per central composite design and regression analysis was conducted to establish input–output relationships of the process. An attempt was made to minimize the weldment area, after satisfying the condition of maximum bead penetration. Thus, it was posed as a constrained optimization problem and solved utilizing a Genetic Algorithm with a penalty function approach. The Genetic Algorithm was able to determine optimal weld-bead geometry and recommend the necessary process parameters for the same.     

Evolution of crystallographic texture and microstructure in the orthorhombic phase of a two-phase alloy Ti–22Al–25Nb

Evolution of crystallographic texture in the orthorhombic phase of a two-phase alloy Ti–22Al–25Nb (at%), consisting of orthorhombic (O) and bcc (β/B2) phases, was studied. The material was subjected to deformation in two-phase field as well as in the single β phase field. The resulting evolution of microstructure and crystallographic texture were recorded using scanning electron microscopy and X-ray diffraction. The orthorhombic phase underwent change in morphology (from platelets to equiaxed) on rolling in the two-phase field with the texture getting sharper with the amount of deformation. Rolling above β transus temperature led to hot deformation of single β phase microstructure and its subsequent cooling produced transformed coarse platelets of orthorhombic phase with texture in orientation relation with the high temperature deformed β phase.     

Quality of service provisioning in 802.11e networks: challenges, approaches, and future directions

In order to support diverse application requirements, a new standard called IEEE 802.11e is being proposed to improve quality of service in wireless LAN networks. There are, however, a few remaining challenges that need to be addressed in order to enable comprehensive QoS support using 802.11e. In this article we provide an overview of a few of these challenges, describe their possible impact on QoS, and provide a survey of techniques that potentially could be used to address the identified challenges. Specifically, we focus on three challenges: handling time-varying network conditions, adapting to varying application profiles, and managing link layer resources. Additionally, we present several potential future directions toward improved QoS in wireless networks.     

Rough-granular Approach for Impulse Fault Classification of Transformers using Cross-wavelet Transform

A novel approach based on information granulation using Rough sets for impulse fault identification of transformers has been proposed. It is found that the location and type of fault within a transformer winding can be classified efficiently by the features extracted from cross-wavelet spectra of current waveforms, obtained from impulse test. Results show that the proposed methodology can localize the fault within 5% of the winding length with a high degree of accuracy. The basic concepts of feature extraction using cross-wavelet transform and the method of classification of those features by rough-granular method are also explained.