Polymers from renewable resources. VIII. Thermal properties of the interpenetrating polymer networks derived from castor oil–isophorone diisocyanate–polyacrylamides

Castor oil was reacted with isophorone diisocyanate varying the isocyanate/hydroxyl ratio to produce a number of polyurethanes (PUs). All the PUs were reacted with acrylamide and methacrylamide using ethylene glycol dimethacrylate as the crosslinker and benzoyl peroxide as the initiator. Thermogravimetric analysis of the polymers was conducted using a computer analysis method for assigning the kinetic mechanism. The degradation steps have been discussed in the light of the kinetic parameters. © 1995 John Wiley & Sons, Inc.     

Motif patterns in 2D

Motif patterns consisting of sequences of intermixed solid and don’t-care characters have been introduced and studied in connection with pattern discovery problems of computational biology and other domains. In order to alleviate the exponential growth of such motifs, notions of maximal saturation and irredundancy have been formulated, whereby more or less compact subsets of the set of all motifs can be extracted, that are capable of expressing all others by suitable combinations. In this paper, we introduce the notion of maximal irredundant motifs in a two-dimensional array and develop initial properties and a combinatorial argument that poses a linear bound on the total number of such motifs. The remainder of the paper presents approaches to the discovery of irredundant motifs both by offline and incremental algorithms.     

Optimization of friction stir welding process using NSGA-II and DEMO

In welding processes, the selection of optimal process parameter settings is very important to achieve best weld qualities. In this work, neuro-multi-objective evolutionary algorithms (EAs) are proposed to optimize the process parameters in friction stir welding process. Artificial neural network (ANN) models are developed for the simulation of the correlation between process parameters and mechanical properties of the weld using back-propagation algorithm. The weld qualities of the weld joint, such as ultimate tensile strength, yield stress, elongation, bending angle and hardness of the nugget zone, are considered. In order to optimize those quality characteristics, two multi-objective EAs that are non-dominated sorting genetic algorithm II and differential evolution for multi-objective are coupled with the developed ANN models. In the end, multi-criteria decision-making method which is technique for order preference by similarity to the ideal solution is applied on the Pareto front to extract the best solutions. Comparisons are conducted between results obtained from the proposed techniques, and confirmation experiments are performed to verify the simulated results.

     

Determination of deuterium site occupancy in ZrCoD3 and its role in improved durability of Zr–Co–Ni deuterides against disproportionation

In the present study, we have for the first time reported the occupancy of deuterium in a new interstitial site of ZrCoD₃ which explain the hydrogen induced disproportionation behavior of ZrCo alloy. We have also reported the effect of Ni substitution on interstitial site occupancy of deuterium in ZrCo_1−xNi_xD₃, which in turn explains the improved durability of these Ni substituted deuterides against disproportionation. The crystal structure of the ZrCo_1−xNi_x (x = 0.0, 0.1, 0.2, 0.3) deuterides was investigated by X-ray powder diffraction and neutron diffraction methods. The XRD data reveals a single phase formation for all deuterides with varying Ni content (x). The neutron diffraction study shows that deuterium occupies a new site 8e in addition to 4c₂ and 8f₁. Additionally, the Zr–D distance in 8e site is shorter than that in ZrD₂. Therefore, increase in 8e site occupancy will in turn decreases the durability against disproportionation and vice-versa. Furthermore, the neutron diffraction reveals that occupancy of new 8e site decreases and its Zr–D distance increases with increase in Ni content, which explicate the higher durability against disproportionation for Ni rich compound.     

Dielectric and impedance spectroscopy of barium orthovanadate ceramics

Barium orthovanadate (Ba₃V₂O₈), a derivative of perovskite family has been prepared using a mixed-oxide technique. The room temperature X-ray diffraction analysis has confirmed the formation of a single phase compound in trigonal crystal structure. The study of microstructure by scanning electron microscopy shows that the compound has well defined grains, distributed uniformly throughout the surface. The studies of dielectric parameters (ε_r and tan δ) of the compound as a function of temperature at three different frequencies (100, 500, 1,000 kHz) exhibit that they are almost temperature independent at low and medium temperature ranges. Detailed studies of impedance and related parameters exhibit that the electrical properties of the material are strongly dependent on temperature, and bear a good correlation with its microstructures. The bulk resistance, evaluated from complex impedance spectra, is found to be decreasing with rise in temperature. It shows that the material has negative temperature co-efficient of resistance similar to that of semiconductors. The same behaviour has also been observed in the study of I–V characteristics of the material. The complex electric modulus analysis indicates the possibility of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The ac conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law.     

Thermodynamic investigations of ThO2-UO2 solid solutions

Heat capacities and enthalpy increments of solid solutions Th_1−yU_yO₂(s) (y = 0.0196, 0.0392, 0.0588, 0.098, 0.1964) and Simfuel (y = 0.0196) were measured by using a differential scanning calorimeter and a high temperature drop calorimeter. The heat capacities were measured in two temperature ranges: 127-305 K and 305-845 K and enthalpy increments were determined in the temperature range 891-1698 K. A heat capacity expression as a function of uranium content y and temperature and a set of self-consistent thermodynamic functions for Th_1−yU_yO₂(s) were computed from present work and the literature data. The oxygen potentials of Th_1−yU_yO_2+x(s) have been calculated and expressed as a polynomial functions of uranium content y, excess oxygen x and temperature T. The phase diagram, oxygen potential diagram of thorium-uranium-oxygen system and major vapour species over urania thoria mixed oxide have been computed using FactSage code.     

Land surface temperature variation in relation to vegetation type using MODIS satellite data in Gujarat state of India

The Moderate Resolution Imaging Spectroradiometer (MODIS) has provided an improved capability for moderate resolution land surface monitoring and for studying surface temperature variations. Surface temperature is a key variable in the surface energy balance. To investigate the temporal variation of surface temperature in relation to different vegetation types, MODIS data from 2000–04 were used, especially in the reproductive phase of crops (September–October). The vegetation types used for this study were agriculture in desert areas, rainfed agriculture, irrigated agriculture, and forest. We found that among the different vegetation types, the desert‐based agriculture showed the highest surface temperature followed by rainfed agriculture, irrigated agriculture, and forest. The variation in surface temperature indicates that the climatic variation is mostly determined by the different types of vegetation cover on the Earth's surface rather than rapid climate change attributable to climatic sources. The mean land surface temperature (LST) and air temperature (T _a) were plotted for each vegetation type from September to October during 2000 and 2004. Higher temperatures were observed for each vegetation type in 2000 as compared to 2004 and lower total rainfall was observed in 2000. The relationship between MODIS LST and T _a measurements from meteorological stations was established and illustrated that years 2000 and 2004 had a distinct climatic variability within the time‐frame in the study area. In all test sites, the study found that there was a high correlation (r = 0.80–0.98) between LST and T _a.     

Inclusion of CdSe quantum dots on the P-doped emitter of Si solar cells

We investigated Cadium Selenide quantum dots embedded in the Si solar cell in order to improve the efficiency of conventional Si solar cell. CdSe quantum dots with 3 to approximately 4 nm size were printed on the phospho-silicate glass layer grown over the emitter surface of p-n junction Si solar cells during the phosphorous diffusion process. Ohmic contact was formed by the contribution of nanoparticles at the Si emitter in spite of the existance of phospho-silicate glass layer. The enhanced light absorption due to the quantum dots was ranged from 500 to 600 nm where the CdSe nanodots have the corresponding emission wavelength of 560 nm. The efficiency of reference solar cell with the glass layer was measured to be 1.0% and it was increased to 12.72% for the reference sample without the glass layer. Furthermore, the efficiency of CdSe quantum dot sample was measured to be 13.6%. This indicates that the quantum dots play the roles of both the formation of tunneling channel and the enhancement of the light conversion efficiency in the visible spectral range.