Studies of retrogression and reaging behavior in a 1441 Al-Li-Cu-Mg-Zr alloy

A 1441 Al-Li-Cu-Mg-Zr alloy in the peak-aged T8 temper was subjected to retrogression treatment and immediately reaged to various tempers. Transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), hardness measurements, tensile testing, scanning electron microscopy (SEM) fractography, and electrochemical polarization studies have been made to characterize the retrogression and the retrogression and reaging (RRA) behavior of the alloy. Retrogression of the T8 temper causes dissolution of δ′ (Al₃Li) precipitates into solid solution, resulting in a decrease of hardness and tensile strength and an increase of ductility. Reaging the retrogressed state causes restoration of strength and ductility properties because of the reprecipitation of the δ′ phase in the matrix, confirmed by TEM, XRD, and DSC studies and image analysis. The SEM fractographs revealed predominantly intergranular fracture in all the tempers due to strain localization at the grain boundaries. The gross aging time of the RRA tempers approaches that of the over-aged T7 temper, which would contribute to an improvement of the stress-corrosion cracking (SCC) resistance while maintaining the T8 temper mechanical properties.     

Electrochemical behaviour of retrogressed and reaged (RRA) 8090 and 1441 Al–Li–Cu–Mg–Zr alloys

8090 and 1441 Al–Li–Cu–Mg–Zr alloys of peak aged T8 tempers were subjected to retrogression treatment followed by reageing to peak aged (RRA) T77 tempers. Electrochemical polarization studies were carried out on the alloys of T8, T77 and over aged T7 tempers, in 3.5% NaCl, 3.5% NaCl + 0.1M LiCl + 0.3% H₂O₂ and 3.5% NaCl + 0.1M LiCl + 0.7% H₂O₂ solutions. The shape of the polarization curves is similar for all the tempers of both alloys in all environments. The corrosion rates are more or less the same irrespective of the tempers. However, the open circuit potentials (OCP) shift towards more negative potential with the RRA treatment and ageing time. The OCP values of the T7 tempers were found to be the most negative; for the T77 tempers it lies between that of the T7 and T8. Further, the OCP values for all tempers of both alloys shifted anodically with addition of LiCl and H₂O₂ in 3.5% NaCl solution. TEM, XRD and DSC studies of microstructural features of the alloys in the T8, RRA and T7 tempers have been used to explain the observed electrochemical behaviour.     

Organic Dye Degradation Under Solar Irradiation by Hydrothermally Synthesized ZnS Nanospheres

The green synthesis of ZnS nanospheres using Citrus limetta (sweet lime) juice as a capping agent through a conventional hydrothermal method was studied. The particle size, morphology, chemical composition, band gap, and optical properties of the synthesized ZnS nanospheres were characterized using x-ray diffraction spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and ultraviolet–visible spectroscopy. The photocatalytic activity of the ZnS nanospheres was evaluated by degradation of rhodamine B (RhB) and methyl orange (MO) under solar irradiation. Upon 150 min of solar irradiation, the extent of degradation was 94% and 77% for RhB and MO, respectively.     

Evolutionary non‐cooperative spectrum sharing game: long‐term coexistence for collocated cognitive radio networks

Collocated cognitive radio networks (CRNs) employ coexistence protocols to share the spectrum when it is not being used by the licensed primary users. These protocols work under the assumption that all spectrum bands provide the same level of quality of service, which is somewhat simplistic because channel conditions as well as the licensee's usage of allocated channels can vary significantly with time and space. These circumstances dictate that some channels may be considered better than others; therefore, CRNs are expected to have a preference over the choice of available channels. Because all CRNs are assumed to be rational and select the best available channels, it can lead to an imbalance in contention for disparate channels, degraded quality of service, and an overall inefficient utilization of spectrum resource. In this paper, we analyze this situation from a game theoretic perspective and model the coexistence of CRNs with heterogeneous spectrum as an evolutionary anti‐coordination spectrum‐sharing game. We derive the evolutionarily stable strategy (ESS) of the game by proving that it cannot be invaded by a greedy strategy. We also derive the replicator dynamics of the proposed evolutionary game, a mechanism with which players can learn from their payoff outcomes of strategic interactions and modify their strategies at every stage of the game and subsequently converge to ESS. Because all CRNs approach ESS based solely upon the common knowledge payoff observations, the evolutionary game can be implemented in a distributed manner. Finally, we analyze the game from the perspective of fairness using Jain's fairness index under selfish behavior from CRNs. Copyright © 2016 John Wiley & Sons, Ltd.     

Prediction of hardness for sintered HSS components using response surface method

Sintered high speed steel (HSS) components have been formed using powder metallurgy (PM) process. Water-atomized and vacuum—annealed powders of T-15 grade HSS along with other ingredients like Zn-stearate (2%) and alumina (Al₂O₃) were used to produce the components. The percentage of alumina, sintering temperature and sintering time were considered as the controllable process parameters while the hardness of the sintered components was considered as the response variable. A 2³ full factorial design of experiments (DOE) was used to collect experimental data to statistically analyze the effect of process parameters on the hardness of sintered HSS components. It has been observed that the percentage of alumina, sintering temperature and also their interaction affects the hardness very significantly while duration of sintering temperature does not affects the hardness significantly. A second order response surface model (RSM) has been used to develop a predicting equation of hardness based on the data collected by a statistical design of experiments known as central composite design (CCD). The analysis of variance (ANOVA) shows that the observed data fits well into the assumed second order RSM model.     

The amphiphilic block copolymers of 2-(dimethylamino)ethyl methacrylate and methyl methacrylate: Synthesis by atom transfer radical polymerization and solution properties

Amphiphilic di- and tri-block copolymers of poly(methyl methacrylate) (PMMA) and poly(2-dimethylamino)ethyl methacrylate (PDMAEMA) have been synthesized by atom transfer radical polymerization (ATRP) at ambient temperature (35 °C) in the environment-friendly solvent, aqueous ethanol (water 16 vol%) using CuCl/o-phenanthroline as the catalyst. The PDMAEMA blocks are contaminated with ethyl methacrylate (EMA) residues to the extent of 1-2 mol% of DMAEMA depending on the length of the PDMAEMA block. The EMA forms through the autocatalyzed ethanolysis of the DMAEMA monomer and undergoes random copolymerization with the latter. The rate of ethanolysis is unexpectedly greater in the aqueous ethanol than in neat ethanol, which has been attributed to the higher polarity of the former than of the latter. In contrast to the ethanolysis no hydrolysis of DMAEMA in the aqueous ethanol medium could be detected for 133 h. The block copolymers form micelles in water. Their solubility and CMC in neutral water have been studied. Dynamic light scattering (DLS) studies reveal that for a fixed degree of polymerization (DP) of the PMMA block the hydrodynamic diameter of the micelles in methanolic water (water 95 vol%) increases at a faster rate with the DP of the PDMAEMA block when it is much greater than that of the PMMA block compared to when it is less than or close to that of the latter.     

A framework for ICT standards creation: The case of ITU-T standard H.350

This paper addresses a fundamental question: Is there a standard way of creating standards? Based on our first-hand experience of creating a technical ICT standard called H.350, we pondered over the process and reflected on what really happened. H.350 is a Directory Services for Multimedia standard ratified by the International Telecommunications Union in September 2003. Resulting from an Internet2 Video Middleware working group the new H.350 standard provides a uniform way to store and locate information related to video and voice over IP (VoIP) in directories that are linked seamlessly to enterprise directories. There were many socio-economic-technical factors that led to the creation of H.350 and we were able to organize the process into a framework, which we present here. We have combined the “public policy good” model and the “stakeholder analysis model” in standards creation into a comprehensive framework that can help the research community to better understand what goes on in standards creation. We conducted in-depth interviews with the core H.350 team to learn more about the entire process and their experience. The findings from these interviews further validate our framework. We apply the case of H.350 to our framework and help understand the forces that affect development of ICT standards.