Sumitra Mukhopadhyay

Abstract: Mullite and spinel forming sols were prepared from hybrid precursors having both organic and inorganic origins. Refractory grade graphite flakes were coated by these sols and their performances were compared in terms of oxidation resistance and water-wettability. Particle size distribution, structural evolution and related characteristics of both mullite and spinel gels have been investigated by dynamic light scattering (DLS), differential thermal analysis (DTA), X-ray diffraction (XRD) and infrared spectra (IR) studies. Coated graphites have also been studied by IR and XRD tests along with scanning electron microscopy (SEM) with energy dispersive spectral (EDS) analysis. The better performance of spinel coated graphite was confirmed. The mechanism of spinel formation on graphite was suggested to take place via intermediate gamma alumina phase formation from boehmite sol. It was clarified by DLS, XRD and microstructural analysis of dried and calcined gels.

Abstract: An intimate mixture of common hydrated magnesium salt and cheaper boehmite sol had been used as a cost-effective precursor of reactive nanometric spinel (1:1) powder. It was gelled at controlled pH, temperature and time, and calcined at significantly lower temperature after soft mechanochemical treatment. X-ray diffraction (XRD), infrared spectra, differential thermal analysis (with thermogravimetry), proton-nuclear magnetic resonance (NMR) and transmission electron microscope studies were carried out to investigate the incipient formation of low crystalline nanosized domains in the still-hydrated spinel. Spinel nanoparticles are protected by a thin chemisorbed layer of (OH) groups held around the active surface of the aggregates. Selected properties of conventional Al 2 O 3 –spinel and Al 2 O 3 MgO castables were compared with the same formulated by the chemical-route spinel fines. Cold and hot strengths of the refractory castable containing commercial spinel with excess alumina powder were the best, while the same bonded by reactive magnesia and coprecipitated spinel fines were not satisfactory. Performance of sol–gel spinel is comparable to the preformed spinel with 78% alumina.

Abstract: A nanostructured sol gel coating of calcium aluminate (CaAl2O4) over flaky graphite has been prepared by a hybrid set of precursors. X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), differential thermal analysis (DTA), particle size distribution and microstructural studies have been performed to understand the phase evolution of calcium aluminate and its related characteristics. The topography and microstructural aspects of coated and uncoated graphites have been differentiated by atomic force microscopy (AFM) and scanning electron microscopy (SEM) with energy dispersive spectral (EDS) analysis. FTIR and XRD patterns of both graphites have also been investigated to substantiate the evolution of a thin extended hydrophilic film of calcium aluminate over coated ones. The better oxidation resistance of coated graphite has been confirmed by thermogravimetric analysis (TGA). Improved water-wettability of coated graphites has been examined by the ‘ball-in-hand’ test for moisture requirement during installation of a high alumina based refractory castable composite containing that graphite. Green bulk density of castable cubes has been determined to corroborate the better performance of the graphite coated with calcium aluminate.

Abstract: The performance of alumina-carbon castables containing graphite flakes coated by nanosized Ca-doped γ-Al2O3 phases has been investigated in terms of refractoriness under load (RUL) and oxidation resistance tests. The coating characteristics and its beneficial effects in castable matrix have been conceived by water-wettability test, differential scanning calorimetry and some physical characteristics. In this regard, a schematic representation of coated graphite has been proposed to elucidate its sustainability in the refractory mass. The comparative gain in performance of the refractory has also been ascertained by scanning electron microscope (SEM) and X-ray diffraction (XRD) studies of the castable matrix. The sol–gel coating overcomes the pitfalls of including uncoated graphites in castables and should be explored for commercial utilization.

Abstract: This paper entails an extended investigation on sol–gel thin film of calcium aluminate (CaAl 2 O 4 ) over graphite flakes that improved their oxidation resistance and water wettability. The commercial preparation of calcium aluminate has been compared with the sol–gel synthesis by differential thermal analysis (DTA) and X-ray diffraction (XRD) to assess the feasibility of the latter for coating preparation. Poorly crystalline nanostructured Ca-doped γ-Al 2 O 3 is considered to be an important intermediate for this preparation. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) of the calcined gel have been carried out to ascertain its composition. Quantitative chemical analysis of sol gel derived calcium aluminate was also estimated. Atomic force microscopy (AFM) has been conducted to ensure the evolution of hydrophilic nanosized cementitious phases on graphite. Zeta potential values of coated and uncoated graphites with increasing pH have also been determined to distinguish between their compatibility in a refractory castable matrix. Improved physical properties of that high alumina castable containing coated graphite, e.g. apparent porosity (AP), bulk density (BD), cold crushing strength (CCS) have been measured to evaluate the refractory quality. The reasons for its better performance are explored by taking further insight on the microstructural analyses of the fired castable (1500 °C) soaked for an extended period.

Abstract: Thank you very much for reading swarm intelligence from natural to artificial systems. As you may know, people have search hundreds times for their chosen books like this swarm intelligence from natural to artificial systems, but end up in malicious downloads. Rather than reading a good book with a cup of coffee in the afternoon, instead they juggled with some infectious bugs inside their computer.

Abstract: To overcome the shortcoming of poor diversity of Artificial Bee Colony(ABC)algorithm,this paper presents a modified Artificial Bee Colony algorithm.Unlike ABC in which onlooker bees choose employed bees from the colony according to proportional fitness choosing strategy,in MABC,in order to decrease the selection pressure and further improve the diversity,it does not set onlooker bees,as a result of no selection pressure on employed bees(solutions).The simulation results show that the presented algorithm can ensure the colony diversity and improve the performances of ABC.

Abstract: Particle swarm optimization (PSO) is a population based meta-heuristic search algorithm that has been widely applied to a variety of problems since its advent. In PSO, the inertial weight not only has a crucial effect on its convergence, but also plays an important role in balancing exploration and exploitation during the evolution. However, PSO is easily trapped into the local optima and premature convergence appears when applied to complex multimodal problems. To address these issues, we present a modified particle swarm optimization with chaos-based initialization and robust update mechanisms. On the one side, the Logistic map is utilized to generate uniformly distributed particles to improve the quality of the initial population. On the other side, the sigmoid-like inertia weight is formulated to make the PSO adaptively adopt the inertia weight between linearly decreasing and nonlinearly decreasing strategies in order to achieve better tradeoff between the exploration and exploitation. During this process, a maximal focus distance is formulated to measure the particle's aggregation degree. At the same time, the wavelet mutation is applied for the particles whose fitness value is less than that of the average so as to enhance the swarm diversity. In addition, an auxiliary velocity-position update mechanism is exclusively applied to the global best particle that can effectively guarantee the convergence of MPSO. Extensive experiments on CEC′13/15 test suites and in the task of standard image segmentation validate the effectiveness and efficiency of the MPSO algorithm proposed in this paper.

Abstract: Nanographite oxide prepared by a chemical oxidation method was characterized by SEM, XRD, FT-IR, zeta potential and BET surface area. The use of nanographite oxide as an adsorbent to remove p-nitrophenol from aqueous solutions was investigated. Adsorption experiments were carried out as a function of the contact time, initial p-nitrophenol concentration, pH, adsorbent dosage, and temperature. It was found that the nanographite oxide possessed a large surface area and was particularly effective for the removal of p-nitrophenol. The removal efficiency of p-nitrophenol decreased with an increase of the solution pH from 4.0 to 7.0 and an increase in the temperature. The adsorption of p-nitrophenol onto nanographite oxide reached equilibrium within 2 h. The maximum adsorption capacity of nanographite oxide for p-nitrophenol was 268.5 mg/g at 283 K and a natural pH. The Freundlich isotherm was the best choice to describe the adsorption behavior. The kinetic data were presented by the pseudo-second-order kinetic model. The parameters suggested that the adsorption process of p-nitrophenol onto nanographite oxide occurred via physisorption process and was exothermic in nature. Hydrogen-bonding, electron donor–acceptor and Lewis acid/base interactions were the main mechanisms affecting the adsorption capacity, while dispersive interactions were also found to influence the adsorption of p-nitrophenol through the influence of its deactivating functional groups on the aromatic ring. The results showed that nanographite oxide can be used as a new adsorbent which has higher adsorption capacity and faster adsorption rate for the removal of p-nitrophenol.